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A SHORT HISTORY 
OF BIOLOGY 


A General Introduction to the 
Study oj Living Things 

By 

CHARLES SINGER 


Pnsca luvcnt alios : ego me nunc denique natum 
gratulor. Haec aetas monbus apta mcis. 

o\ii), Ars amatorta^ lii. 12 1 


Let others tcujcl m the past, but as for me I rejoice 
tn my o%un age. These are the times for me. 


OXFORD 

THE CLARENP'^N PRESS 



PKINTED IN GREAT BRIIaIa AT-'THE UNIVERSITY PRESS, OXFORD 
BY JOHN JOHNSON, l^INTER TO TH?: UNIVERSITY 



TO 

DR. AGNES ARBER 




PREFACE 


T his work attempts to give, in simple language, a 
critical survey of the historical development of bio¬ 
logical problems. The bypaths and blind alleys of the 
subject are left unexplored. The immense extensions of 
detailed knowledge in many departments are discussed 
only in so far as they influence our thought about living 
things. Biographical detail is not included unless it can 
be seen to have a direct influence upon the course of 
science. The mechanism of transmission of the biological 
tradition is but lightly touched upon. The exposition 
of the origin and development of the main problems 
of biology is the objective on which we shall concentrate. 

The author has striven to write in such a way as to 
demand only a minimum scientific training for the com¬ 
prehension of his matter. Technical terms have been used 
as seldom as possible, and never without explanation. 
Overlapping has been largely avoided by cross references. 
The reader is advised to refer constantly to the table of 
contents. This will enable him to appreciate better his 
position at any point in the narrative as a whole. The 
‘Introduction’ is perhaps more suitably read after and not 
before the book itself. 

It has been possible to curtail considerably the length 
of the book since the author has already treated such topics 
as the influence of Galileo on science generally, Galenic 
anatomy and physiology, the circulation of the blood, the 
philosophical implications of scientific specialization and 
their relation to utilitarian thought, the discovery of the 
nature of the air, advances in knowledge of bacteriology, 
immunity, and epidemics, in his Short History of Medicine 
which is, in some degree, a companion volume to this. 

The book is written by one who finds mechanist inter- 



viii Preface 

pretations of life unsatisfying. His attitude is prompted 
largely by the ‘relativity of functions’, that is by the con¬ 
ditioning of any one form of vital activity by innumerable 
concurrent forms, and this not only in the organism as a 
whole, but in each part susceptible of independent investi¬ 
gation. He recognizes, however, that the mechanist out¬ 
look has been responsible for countless far-reaching and 
important biological investigations, and he is aware that 
it remains indispensable for advances in many biological 
departments. He is, moreover, acutely conscious of the 
danger of confounding physical with metaphysical issues. 
He would, however, urge that there are many scientific pro¬ 
positions that are acceptable on one level of investigation 
but not on another. Thus the meteorologist finds that 
winds tend to move along the lines of equal barometric pres- 
tion, but this does not deflect the physicist from his convic- 
sure that the gases with which he deals take the line of least 
resistance from high to low pressure. But the victories of 
the experimental method are too numerous, too complete, 
too general, for us to lose faith in its value because it fails 
to reveal a universe completely consistent with itself. We 
must accept with resignation the ineluctable fact that there 
are an increasing number of antitheses in the world of our 
experience which science exhibits no sign of resolving. 
If there were no such antitheses there would be no place 
for philosophy, or rather philosophy would become a 
department of science. 

During the progress of the work a great deal of help 
has been received. Mrs. Singer has read and re-read it 
repeatedly. Much of its form as a whole and a large part 
of the matter of the last two chapters is due to her. Dr. 
Agnes Arber has read the work both in manuscript and in 
proof. She has prevented the appearance of many errors 
and the book owes a great deal to her penetrating and 
critical mind. 



Preface ix 

Help has also been given by Dr. W. T. Caiman, F.R.S., 
Keeper of Zoology, British Museum, Professor F. J. Cole, F.R.S., 
of the University of Reading, Dr. Paul Delaunay of Le Mans, 
Mr. Clifford Dobell, F.R.S., Protistologist to the Medical Research 
Institute, Professor Herbert M. Evans of the University of Cali¬ 
fornia, Mrs. T. H. Montgomery of the Woods Hole Marine 
Biological Institute, Massachusetts, Professor F. W. Oliver, F.R.S., 
of Cairo and lately of University College, London, Dr. M. C. 
Rainer, Professor Donald S. Robertson of the University of Cam¬ 
bridge, Professor G. Senn of the University of Basel, and Professor 
D. M. S. Watson, F.R.S., of University College, London. To 
all of these the author would tender his hearty thanks. 

Professor T. H. Morgan of the California Institute of Techno¬ 
logy has made many suggestions for the last two chapters. The 
intimate association of this distinguished worker with the theory 
of the gene, of which he is the foremost architect, has made his 
assistance peculiarly gracious and acceptable. 

On special points the author has had help from four of his pupils, 
Dr. J. S. Prendergast of University College, London, and Wor¬ 
cester College, Oxford, Dr. F. Prescott of the Western Polytechnic, 
London, Dr. S. D. Wingate of University College, London, and 
his niece Miss Eleanor Singer, B.Sc., of the University of Cali¬ 
fornia. To the last he is indebted for drawing or redrawing a 
number of figures. The sources of these and of the other figures 
are acknowledged in the List of Illustrations. 

Among its predecessors along similar tracks the book owes 
most to Dr. E. S. Russell’s admirable Form and Function^ a con- 
trihution to the History of Animal Morphology (London, 1916). 
The author must also express his indebtedness to Professor E. B. 
Wilson’s great treatise. The Cell (Third edition, Macmillan 
Company, New York, 1925}. 

The substance of the work was delivered as lectures during the 
summer of 1930 to students of biology at the University of Cali¬ 
fornia at Berkeley. The author renders his thanks to the President 
and Regents of that body for the opportunity thus given him. 

C. S. 

UNIVERSITY COLLEGE, LONDON 

January 1931 



TABLE OF CONTENTS 


INTRODUCTION , 


PART L THE OLDER BIOLOGY 

I . The Rise of Ancient Science. 

SECT. PAGE 

1. Hippocrates (c. 460-r. 370 b.c.) . . . . i 

2. Doctrine of the Four Humours .... 7 

3. Aristotle (384-322 b.c.) ..... 9 

4. Aristotle’s Biological Works . . . .14 

5. Aristotle on the Habits of Fish . . . .18 

6. Handicaps of Early Naturalists . . ... 22 

7. Aristotle on Octopuses and their Allies ... 26 

8. Aristotle on Whales, Porpoises, and Dolphins . . 31 

9. Aristotle on the Placental Dog-fish (‘Galeos’) . . 32 

10. The Aristotelian Bee-master . . . *35 

II. Aristotle on the Nature of Life .... 37 

12. Classification of Animals derived from Aristotle . 41 

13. Theophrastus (r. 380—287 b.c.) and his Botanical Works 44 

11. Decline and Fall of Ancient Science. 

1. Foundation of the Alexandrian School (r. 300 b.c.) . 53 

2. Beginnings of Scientific Plant Illustration (r. 50 b.c.) 55 

3. Dioscorides and Pliny (ji//J.D.) . • • 57 

4. Galen (a.D. 130-200) ..... 59 

5. The Dark Ages (a.d. 200-1200) .... 62 

6. Thirteenth-century Revival of Learning and Art . 67 

7. Roger Bacon (1214—94) and Scholasticism . . 70 

8. Albertus Magnus (120^80) .... 72 

9. Medieval Anatomy ...... 75 

III. Rebirth of Inquiry. 

1. Naturalism in Art ...... 78 

2. Humanism . . . . . . .83 

3. The German Fathers of Botany .... 86 








Table of Contents xi 

4. I'he Naturalist Commentators .... 88 

5. The Encyclopedic Naturalists . . . .92 

6. The Revival of Anatomy ..... 96 

7. Renaissance Art versus Modern Science . . .98 

8. Vesalius on the ‘Fabric of the Human Body’ . . loi 

9. Successors of Vesalius . . . . .104 

10. Harvey (1578-1657) and the Circulation of the Blood 108 

11. Influence of the Discovery of the Circulation . . 114 


PART II. THE HISTORICAL FOUNDATIONS 
OF MODERN BIOLOGY 


IV. On the Inductive Philosophy and some of its Instru¬ 
ments. 


I. The Change from Medieval to Modern Thought 

. 119 

2. Francis Bacon (1561-1639) 


120 

3. Rene Descartes (1596-1650) 


. 125 

4. Early Collections of Plants and Animals . 


. 130 

5. Early Patrons of Science 


• 133 

6. The First Scientific Societies 


• 135 

7. The Advent of Scientific Journals . 


■ 138 

8, Early Museums .... 


142 

9. Introduction of the Microscope 


• 145 

10. Malpighi (1628-94) .... 


• 151 

II. Grew (1641-1712) .... 


. 156 

12. Swammerdam (1637—80) 


. 158 

13. Leeuwenhoek (1632-1723) 


164 

14. Hooke (1635-1703) . . . . 


. 168 

15. Influence of the Classical Microscopists . 


170 

V. Rise of Classificatory Systems. 



I. Absence of System in Early Naturalists . 


172 

2. First Attempts at Formal Classification . 


• 173 

3. What is a Genus ? What is a Species 1 


• 175 

4. The Binomial Nomenclature 


. 178 

5. Jung (1587-1657) .... 


• 179 

6. Ray (1627-1705) .... 


181 












xii Table of Contents 

7. Tournefort (1656-1708) ..... 184 

8. Linnaeus (1707-78) . . . . . .185 

g,/The ^Systema Naturae^ • • • .187 

10. The Successors of Linnaeus . . . .192 

11. Modern Systems of Classification . . . .197 

VI. Rise of Comparative Method. 

1. Comparative Studies in the Seventeenth Century . 201 

2. Some Eighteenth-century Conceptions of Nature . 206 

3. Hunter (1728-93) ...... 208 

4. The Naturphilosophen: Kant (1724-1804)5 Goethe 

(1749-1832)5 and Oken (1779-1851) . . 212 

5. The Eclipse of Naturphilosophie . . . .219 

6. Cuvier (1769-1832) and the Principle of Correlation 

of Parts ....... 223 

7. 'Le R^gne jfnimaP (iSij) ..... 227 

8. The Doctrine of Catastrophes . . . *231 

9. Owen (1804-92) and Palaeontology . . . 233 

VII. Distribution in Space and Time. 

1. Early Biological Exploration. Joseph Banks (1743- 

1820) and Robert Brown (1773-1858) . . 236 

2. Pre-evolutionary Geological Theory . . .241 

3. Darwin (1809-82)5 the1831-5)5and Island Life 244 

4. Oceanic Exploration from the ^Beagle to the '"Challenger 251 

5. The ^Challenger Expedition (1872—6) and the Rise of 


Oceanography ...... 254 

6. Distribution of Life in the Sea , . . .257 

7. Distribution of Life on Land .... 266 

8. Geological Succession . . . . .272 

9. Interrelations of Species ..... 278 

10. Migration ....... 282 


VIII. Evolution. 

I. BufFon (1707-88) and Erasmus Darwin (1731-1802) 288 

'-2. Lamarck (1744-1829) and his Successors . . 292 

3. The ^Origin of Species* and the Validity of its Argument 296 

4. The Reception of the Doctrine of Evolution , . 303 










XV 


Table oj Contents 

5. TJbc Biogenetic Law ...... 467 

6. The Earlier Morphological Embryologists . . 470 

7. First Reaction of Evolutionary 'Eheory on Embryology 473 


8. The Systemic Evolutionary Embryologists . . 480 

9. Digression on Metamorphosis .... 486 

10. Developmental Mechanics ..... 489 

11. The Science of E^xperimental Embryology . . 492 

XIV. Sex. 

1. First Attempts to Analyse the Nature of Generation . 497 

2. Early Writers on Pollination . . . . 500 

3. The Modern Study of Pollination .... 506 

4. Sexual Dimorphism . . . . . . ^11 

5. Alternation of Generations . . . , . 5^5 

6. Early Observations on Cellular Phenomena of Sexual 

Union ....... 522 

7. Nuclear Phenomena of Sex ..... 524 

8. Factors Determining Sex and Sex Character . . 532 

9. Nuclear Phenomena of Parthenogenesis . . . .535 


XV. Mechanism of Heredity. 

1. Earlier Conceptions of Heredity .... 539 

2. Galton (1822-1911) and the Statistical Study of the 

Phenomena of Heredity . . . . .541 

3. Weismann (1834-1914) and the Germ Plasm . . 543 

4. I'he Study of Discontinuous Variation, 1859-1900 . 548 

5. De Vries (1848- ) and the Doctrine of Mutations . 551 

6. The Work of Mendel (1822-84) and its Rediscovery 

(1900) . . . . • . • -553 

7. Nuclear Phenomena in Relation to Mendelian Charac¬ 

ters ........ 559 

8. Theory of the Gene ...... 562 

INDEX.569 




LIST OF ILLUSTRATIONS 

[C. PAGE 

1. Head of bronze bust of Aristotle from Herculaneum. Copy of 

an original that was probably of fourth century b.c. Frontispiece 

2. Faience models from Crete of about 1700 b.c. Flying fish, 

paper nautilus, bivalve molluscs, and rocks are shown. 

From Sir Arthur Evans, Palace of Minos^ 1921, by per¬ 
mission of Macmillan & Co., Ltd. .... 3 

3. Clay plate from Louvre showing marine forms. Fourth 

century b.c. From Morin-Jean, Le dessin des animaux en 
Grhe d^apres les vasespeintes, (Henri Laurens, Paris, 1911) 5 

4. Diagram of four elements, qualities, and humours . 8 

5. The States of ancient Greece . . . . .11 

6. Expansion of Macedon . . . . .13 

7. Aristotle’s cat-fish from Theodore Gill in Annual Report of 

Regents of the Smithsonian Institute for 1905 . . . 19 

8. Male American cat-fish from Gill, as above . . .19 

9. Diagram of torpedo-fish . . . . *23 

10. Torpedo ocellata from Guillaume Rondelet, De piscibus 

marinis, Paris, 1554 . . . . . 23 

11. Angler-fish from Rondelet, as above . . 23 

12. Restoration of Aristotelian diagram of genito-urinary system 

of mammal. Author . . . . . .25 

13 and 14. Diagrams of stages in development of Sepia from 
Prof. D’Arcy W. Thompson’s translation of Aristotle’s 
Historia animalium, Oxford, 1910 . . . 28 

15. The Paper Nautilus from Pierre Belon, Vhistoire naturelle des 

estranges poissons marins, Paris, 1551. . . . 29 

16. Female of Paper Nautilus from H. de Lacaze-Duthiers, 

Archives de zoologie expdrimentale. 1892 . . . 30 

17. Development of Aristotle’s placental dogfish, d:c., redrawn 

by author from Johannes Muller, Ueber den glatten Hai 
des Aristoteles. Berlin, 1842 . . . . *33 

18. Diagram of Aristotle’s‘Ladder of Life’ .... 40 

19. Germination of bean from Marcello Malpighi, Anatome 

plantarum. London, 1679 ..... 48 

20. Germination of wheat from Malpighi, as above . . 49 

21. Assyrian bas-relief redrawn from Sir Arthur Henry Layard’s 

Nineveh and its Remains. London, 1849 . . *51 



List of Illustrations xvii 

22. A ’ totle’s lantern from Edward Forbes, History of British 

Starfishes, London, 1841 . . . . . 52 

23. Break up of the Empire of Alexander .... 54 

24. Aristolochia pallida traced in outline by author from the 

facsimile of the Codex Dioscuridei Aniciae Julianiae. 
Leyden, 1906 ....... 56 

25. Adonis aestivalis, 2is ohovc . . . . . .56 

26. Erodium malachoides, as above . . . . .58 

27. Geranium/nolle, dis ohovc . . . . . .58 

28. Roman Empire about A.D. 100 ..... 61 

29. Strawberry from a MS. of Apuleius of sixth century at 

Leyden (Voss Q 9) . . . . . .64 

30. Strawberry from a Cassel MS. of the eleventh century . 65 

31. Distribution of power at end of the eighth century . . 68 

32. ‘Basilisca’ from a MS. herbal of about a.d. 1200 in the 

Bodleian Library (Ashmole 1462) . . . .69 

33. Stone carving of about a.d. 1260 at Chartres cathedral. 

Photograph by Levy et Ncurdein rcunis . . . 69 

34. M edieval centres of learning . . . . -71 

3 5. Diagrams of developing bird and fish. Author . . . 74 

36. Diagram of orange leaf. Author . . . . *75 

37. Dissection scene of early fourteenth century from MS. in 

Bodleian Library (Ashmole 399) .... 76 

38. Head of‘Flora’from Botticelli’s . . .81 

39. Drawing by Leonardo of marsh marigold and wood anemone 

now at Windsor Castle, from facsimile by Rouveyre. 

Paris, 1901 . . . . . . . .81 

40. Birds in flight by Leonardo from the facsimile Codice sul volo 

degli uccelli by G. Piumati and C. Ravaisson-Mollien. 

Paris, 1893 ........ 82 

41. Drawings of movements of heart by Leonardo from the 

facsimile Quaderni d'anatomia I, by C. L. Vangensten, 

A. Fonahn, and H. Hopstock. Christiania, 19ii . . 82 

42. Cavities of the skull by Leonardo from M. Holl, Archiv fur 

Anatomie und Entzaickelungsgeschichte, redrawn from 
facsimile, DelE anatomia, Fogli B, by T. SabatchnikofF 
and G. Piumati. Turin, 1901 . .... 82 

43. Drawing of brain with ventricles injected with wax from 

facsimile Quademi d'anatomia V. Christiania, 1906 . 82 

44. Skeleton of man and bird compared from Pierre Belon, 

Vhistoire de la nature des Oyseaux, Paris, 1555 . . 87 

2613-3 \y 




xviii List of Illustrations 

45. A female killer-whale and her young from Pierre Belon, 

Vhistoire naturelle des estranges poissons marins. Paris, 1551 90 

46. A whale and her young attacked by a killer-whale from 

Gesner, De ptsctum et aquatilium animantium natura, 
Zurich, 1558, after Olaus Magnus, Historia de gentibus 
septentrionalibus ....... 90 

47. Placental dogfish of Aristotle from Guillaume Rondelet, De 

piscibus marinis. Paris, 15 54 . . . . .92 

48. Eggs of Sepia from Rondelet, as above .... 93 

49. Sepia from Rondelet, as above . . . . .93 

50. Octopus from Gesner, De piscium natura, Zurich, 1558, 

from a drawing sent him by Rondelet, . . .93 

51. Sea urchin from Rondelet, as above . . . *95 

52. Snails from Gesner, . . . .95 

53. Hornets from MS. by Thomas Moufet in British Museum 

(Sloane 4014) ....... 96 

54. Arm and arm bones by Leonardo from the facsimile Quaderni 

d^anatomia ........ 99 

55. Muscles of arm from A. Vesalius, De fabric a corporis kumani, 

Basel, 1543..99 

56. Skulls from Vesalius, De fabric a corporis humaniy 1543 . 102 

57. Skeleton prepared by Vesalius at Basel from photograph 

kindly supplied by Prof. Gustav Senn of Basel . .103 

58. Diagram of action of heart according to Galen and Servetus 

by Miss Eleanor Singer . . . . . *105 

59. Valves in veins of arm from Fabricius, De venarum ostio/is. 

Venice, 1603. Photograph kindly supplied by Dr. K. J. 
Franklin of Oriel College, Oxford . . . .106 

60. Diagram of circulation of blood. Author . . .109 

61. Thoracic duct and receptaculum chyli of dog from Jean 

Ttequet, Experimenta nozfa anato/nica, Hardewyck, 1651 109 

62. Autograph lines of William Harvey (1615) from the Pre- 

lectiones anatomiae universalis MS. in British Museum . 113 

63. Embryonic membranes and circulation of a bird by Miss 

Eleanor Singer , . . . . . .116 

64. Embryonic membranes and circulation of a mammal by 

Miss Elinor Singer . . . . . .116 

65. Deep sea fishes obtained by the Challengery redrawn and 

grouped by Miss Eleanor Singer from the Challenger Reports 117 

66. Portrait of Descartes by Franz Hals . . . .118 

67. The University of Padua about 1600 from a contemporary 

engraving.130 




List oj Illustrations xix 

68. Rhinoceros from a drawing by Diirer in the British Museum 131 

69. Meeting of the Academic des Sciences in 1671, from a con¬ 

temporary copper plate by Sebastien Le Clerc . . 137 

70. Montague house at the end of the eighteenth century, from 

R. J. Thornton’s Illustrations of the Sexual System of 


Linnaeus. London, 1799 . . . . ,143 

71-4. Enlarged figures of bee and weevil from Francesco Stelluti, 

Persio tradotto. Rome, 1630 . . . . *147 

75. Microscope from R. Hooke’s London, 1665 . 149 

76. Structure of feather from Hooke’s . .149 


77-9. Microscopic structures of plants from M. Malpighi, 

Anatomes pi ant arum idea. London, 1675 • * • ^53 

80-2. Gall and gall fly from Malpighi, Degallis. London, 1679 155 

83-5. Section of pine and thistle and fibres of fir from N. Grew, 

Anatomy of Plants. London, 1682 . . . .157 

86. Dissected bean from Grew, as above . . . -159 

87. Development of dragon-fly from Swammerdam, Histoire 

generale des insectes. Utrecht, 1685 . . . .160 

88. Mouth parts of bee from Swammerdam, Biblia naturae. 

Leyden, 1737 ....... 161 

89. Dissected May fly from Swammerdam, as above . . 161 

90-2. Development of gnat from Swammerdam, as above . 163 

93. Cardiac muscle-fibres from ‘Epistola 82’, written 1694, in 

Arcana naturae. Delft, 1695 . .167 

94. Development of flea from ‘Epistola 76’, written 1693, in 

Leeuwenhoek’s Arcana naturae. Delft, 1695 . . 167 

95. Flea magnified from R. Hooke’s Micrograpkia. London, 1665 169 

96. Heads of bees from Stelluti, Persio tradotto. Rome, 1630 171 

97. Linnaeus from R. J. Thornton, Illustrations of the Sexual 

System of Linnaeus. London, 1799 . . . .185 

98. Euphorbia apios from P. Belon, Les observations de plusiers 

singulariteT:. Paris, 1553 . . . . .185 

99. Swedish warship pursuing British vessel. From Thornton, 

as for Fig. 97 . . . . . . .191 

100. The anatomical theatre at Padua about the middle of the 
eighteenth century. From a contemporary stipple en¬ 
graving ........ 203 

I o I. Crop of male pigeon from John Hunter, Observations on certain 

parts of the Animal Economy. London, 1762 . . 209 

102. Drawings by W. Clift of aural apparatus in Hunter’s collection 
from Everard Home, Lectures on Comparative Anatomy. 
London, 6 vols., 1814-28 ..... 209 

b2 


2613*3 



XX 


List oj Illustrations 

103. Skull of Ichthyosaurus drawn by Clift from Home, as above 211 

104. ‘Archetype’ of vertebrate skeleton from E. S. Russell, Form 

and Function {]ohn Murray), after R.Owen, ‘On the funda¬ 
mental type or homologies of the vertebrate skeleton’, 


Association Reports, 1846. . . . . .219 

105. Wing of Pterodactyl, Bat, and Bird, from G. J. Romanes, 

Darzvin and after Darzvin (Longmans Green & Co., I.td., 

1897), after drawings in the British Museum (Natural 
History) . . . . . . . .221 

106. Homology of bones and muscles iii leg of horse and man as 

shown in drawing at Windsor Castle from Leonardo’s 

Quaderni \. Christiania, 1916 . . .221 

107. Archaeopteryx Lithographic a as restored by R. Ow^en, Anatomy 

of Vei'te hr ate s (Longmans Green & Co., Ltd., 1866) . 225 

108. Archaeopteryx as restored by W. H. Flower from G. J. 

Romanes, Darzvin and after Darzvin (Longmans Green 
&c Co., Ltd., 1897) . . . . . .225 

109. Mylodon rohustus from R. Ow'en, Description of the Skeleton 

of an Extinct Gigantic Sloth. London, 1842 . . 2 34 

no. Skeleton of Megatherium from S. Cuvier, Recherches sur les 

ossemens fossiles. Paris, 1812 . . . . *235 

111. Map of Australia with inset of coast as known to Captain 

Cook. The latter traced from his Account of the royages 
for making Discoveries in the Southern Hemisphere. London, 

1773.. • : • *239 

112. Mean surface currents of the Atlantic Ocean after Science of 

the Sea, 2nd edition by E. J. Allen. Oxford, 1928 . . 249 

113. Land and water hemispheres from 'V. H. Huxley, Physio¬ 

graphy, 1877, by permission of Macmillan & Co,, Ltd. . 249 

114. H.M.S. Challenger from Science of the Sea, 2nd edition, by 

E. J. Allen . . . . . . . .250 

115. Section through Wyville I'homson Ridge from data by 

W. Herdman, Founder of Oceanography. Miss Eleanor 
Singer . . . . . . . .252 

116. Map of part of North Sea show^ing Wyville Thomson Ridge 253 

117. Rhabdosphaera ixom Challenger Reports, vo\.\ . . .258 

118. Coccosphaera ixom Challenger Reports, vo\.\ . . .258 

119. Peridinium from Dr. Marie Lebour in Science of the Sea, 

2nd edition, by E. J. Allen . . . . .258 

120. DisL^xSLTn okCoscinodiscus . . . . . .258 

121. Map of oceanic sea-bottom by Miss Eleanor Singer from data 

in Challenger Reports, vol. i, and elsewhere . . .259 



List of Illustrations xxi 

122. Globigerina after Science of the Sea, 2nd edition, by 

E. J. Allen . , . . . .261 

123. Hexanastra Challenger Reports, . . 261 

124. Map of ocean depths by Miss Eleanor Singer from data in 

Challenger Reports, . . *265 

125. Zoogeographical regions adapted from A. R. Wallace, Geo¬ 

graphic Distribution of Animals, . .266 

126. Distribution of land and sea in Cretaceous period from Science 

of the Sea, 2nd edition, by E. J. Allen . . . 269 

127. Geological succession of higher organisms. Author . . 273 

128. Lyginodendron Oldhamium from D. H. Scott, Studies in Fossil 

Botany (A. k C. Black, Ltd., 1900). Inset drawing by 
Prof. F. W. Oliver . . . . . *275 

129. Idealized Carboniferous scene. Slightly modified from 

F. H. Knowlton, Plants of the Past (Princeton University 

Press) ........ 277 

130. Map of migration of American Golden Plover modified by 

Miss Eleanor Singer from Sir Arthur Shipley’s Life 
(Cambridge University Press, 1925) .... 283 

131. Map of part of South America to show distribution of species 

of Chinchona tree modified from Clements R. Markham, 
Peruvian Bark. London, 1880. . . . . 283 

132. Distribution of European and American eels modified from 

diagrams on exhibition in the British Museum (Natural 
History) ........ 286 

133. Fossil skeleton of Pterodactyl from Cuvier, Recherches sur les 

ossemensfossiles. Paris, 1812 . . . . .287 

134. Peripatus capensis from H. N. Moseley, Notes by a Naturalist 

on the ^Challenged. London, 1879 . . . *307 

135. Evolution of foot of modern horse from T. H. Huxley, 

American Addresses. London, 1877 . . . *308 

136. Skulls of Helladotherium, Okapi, and Giraffe from E. Ray 

Lankester, Transactions of Zoological Society, vol. xvi . 309 

137. Heteronotus trinodosus illustrating mimicry from D. Sharp, 

Cambridge Natural History, vol. vi, by permission of 
Macmillan Co., Ltd. . . . . . .316 

138-9. Mistletoe from Malpighi, Anatome Plantarum. London, 

1679.320 

140. Lemna gibba and Spirodela polyrhixa from A. Arber, fVater 
Plants (Cambridge University Press, 1920) after Hegel- 
maier . . . . . . . . .321 



xxii List of Illustrations 

141. Portrait of Darwin by W. W. Ouless. By permission, from the 
portrait at Christ’s College, Cambridge. (Photograph by 
J. Palmer Clarke) . . . . *324 

142-3. Plant-cells from R. Hooke’s Micrographia, 1665 . . 326 

144. Cells from Schwann’s Mikroskopische Vntersuchungen. Berlin, 

1839 . . . . . . • . • 3.33 

145. Mitosis modified from E. B. Wilson, The Cell^ 3rd edition 

(Macmillan Company, New York, 1925) . . . 343 

146. Epidermal cell of earthworm from O. Biitschli, Ueher mikro¬ 

skopische Schaume, i%<)2 ...... 347 

147. Hair-cells of potato showing protoplasmic streaming from 

Schleiden, Ueher Phytogenesis . . . . -353 

148. From Hales, Vegetable Staticks. London, 1727 . . 365 

149. Diagram of Nitrogen Cycle . . . . 379 

150. Diagrams to illustrate ‘phases’ of colloidal system . . 385 

151-3. Drawings by Goethe to illustrate morphology of leaves 

from the atlas of A. Hansen’s Goethes Metamorphose der 
PJlanxen, Giessen, 1907 . . . . .387 

154. Diagrams of upper part of human thigh bone to illustrate 

stresses and strains . . . . . .402 

155. Diagram of reflex arc . . . , . .416 

156. r^igufe to illustrate action of muscles and ligaments moving 

foot. From Vesalius, De fabric a corporis humani. Basel, 

1543 - • . ; • • • . . 429 

157. Diagram of Pasteur’s experiment to prove that putrefactive 

organisms are air-borne . . . . -441 

158. Drawings made in 1876 by Koch and Cohn to illustrate 

development of Anthrax bacillus . . . -457 

159. Series from Fabricius ab Aquapendente, De formatione ovi et 

pulli, Venice, 1621, illustrating development of chick . 459 

160. Part of title-page of William Harvey, De generatione ani- 

malium. London, 1651. . . . .461 

161. Diagrams redrawn from C. F. Wolff, Theoria generationis, 

Halle, 1759 • * -463 

162. Diagrams of arteries of gill-slits in fish, bird, and mammal after 

Rathke and Le Conte from G. J. Romanes, Darwin and 
after Darwin (Longmans Green & Co., Ltd., 1897) . 471 

163. Sections of three early stages in development of hen’s egg 

modified from A. M. Marshall, Vertebrate Embryology 
(John Murray, 1893), after M. Duval (1885) . . 472 

164. Early development of Amphioxus modified from Marshall 

after B. Hatschek (1881) , . . , , 475 



List oj Illustrations xxiii 

165. Sections of Amphioxus modified from Marshall after B. 

Hatschek (1881) . . . . . . 476 

166. Late embryo of Amphioxus after Hatschek (1881) and young 

Amphioxus after Kowalewsky (1867). Both modified from 
Marshall ........ 477 

167. Development of Phallusia mammillata modified from A. 

Kowalewsky, ‘Weitere Studien iiber die Entwickelung der 
einfachen Ascidien’, Archiv fur mikroskopische Anatomic^ 

1871 • •..477 

168. Haeckel’s five primary stages of ontogeny from E. S. Russell, 

Form and Function (John Murray, 1916) . . . 484 

169. Types of insect metamorphosis from Jan Goedart, Meta¬ 

morphosis naturaiis. Middelburg, 1662 . . .487 

170. Developing forms of Crustacea from John Vaughan Thomp¬ 

son, Cork, 1828-30 . . . 488 

171. Development of normal and mutilated egg of the mollusc 

Dentalium from the Journal of Experimental Zoologyy 
vol. i (Wistar Institute of Anatomy and Biology), after 
E. B. Wilson ....... 495 

172. Seventeenth-century figures of spermatozoa: a-c, from 

Leeuwenhoek in the Philosophical Transactions for 1679; 
e-f from the same author’s Arcana naturae \ dy after 
Hartsoeker from P. E. Launois, Les peres de biologie. 

Paris, 1904 ........ 499 

173. Figures of pollination from F. Buonanni, Micrographia^ 1691 501 

174. Pollination of Nigella from C. G. Sprengel, Das entdekte 

Geheimniss der Natur, Berlin, 1793 . . -504 

175. Fertilization of Asclepias from Collected Works of Robert 

Brown, London, 1866-8 ..... 505 

176. The process of fertilization in plants: A, from Amici in the 

Memorie di Societa Italiana, Modena, 1823; jB-C, from 
Schleiden in Ratisbon, 1845 .... 507 

177. Types of cowslip modified by Miss Eleanor Singer from 

Darwin, Effects of Cross and Self Fertilization, London, 

1876.509 

178. Map of distribution of Aconitum and Bom bus from Knuth, 

Handbook of Flower Pollination, Oxford, 1898 . . 510 

179-80. Sexual dimorphism in Cirripedia. All save 180 a and 
c from Darwin, Monograph of the Cirripedia, London, 

1846-51 . 512-13 

181. Edrioiychnus Schmidtii illustrating sexual dimorphism from 

C. Tate Regan, Philosophical Transactions^ 1927 , • SH 



XXIV 


List oj Illustrations 

182. Spore-bearing apparatus of Polypodium, from Swammerdam, 

Biblta naturae . . . . . . .518 

183. Spermatozoids of various plants from various sources redrawn 

and arranged by Miss Eleanor Singer . . . *519 

184. Development of Archegonium of moss from English transla¬ 

tion of Hofmeister’s London, 1862 . . 521 

185. Archegonia of liver-wort and fern from Strasburger . . 521 

186. Sexual process of Vaucherta sessilis from N. Pringsheim. 

Journal of Royal Microscopical Society, 1855 . . 523 

187. Fertilization of Asterias glacialis from Balfour, after Fol, 

Reckerches sur la flcondation. Geneva, 1879 . . 525 

188. Oogenesis and Spermatogenesis according to teaching of 

Boveri (1892) . . . . . . .526 

189. Diagram of Mciosis and Fertilization modified from J. B. S. 

Haldane and J. Huxley, Animal Biology. Oxford, 1927 528 

190. Diagram of three types of alternation of generations modified 

from E. B. Wilson, The Cell, 3rd edition (Macmillan Com¬ 


pany, New York, 1925) . ..... 531 

191. Diagram of continuity of germ-plasm from E. S. Goodrich, 

Living Organisms. Oxford, 1924 . . . -545 

192. Diagram of spermatozoon, modified from E. B. Wilson, Tbe 

C^//(Macmillan Company, New York) . . . 546 

193. Diagram illustrating Mcndelian inheritance, after T. H. 

Morgan, Tbe Theory of the Gene (Yale University Press) 559 

194. Combs of domesticated races of fowls, from 1 \ H. Morgan, 

The Theory of the Gene (Yale University Press, 1928) . 564 




INTRODUCTION 

§ I. Some implications of scientific specialization 

S CIENTIFIC specialists commonly insist that the 
nature of their current investigations are too abstruse, 
intricate, obscure, to be understood save by the specially 
trained. The reiteration of this statement, true in itself, 
has engendered a widespread and dangerous fallacy. 
Great scientific advances are not now, nor have they ever 
been, of their own nature specially difficult of comprehen¬ 
sion. On the contrary, a test of the significance of a 
scientific doctrine is the degree to which it can be reduced 
to a simple formula. It is not the positive conquests of 
science that are peculiarly obscure, but rather the confused 
yet active battle-front along which science is advancing at 
any given moment. 

Nevertheless many scientific workers remain convinced 
that their results can never penetrate the mind of that 
singularly obtuse being, the ‘general reader’. The very 
attempt to make their studies intelligible is still suspected 
by the scientifically initiated. It is, however, a corollary 
to the subdivision of the sciences that the exponent of one 
science becomes a ‘general reader’ for his colleague in 
another science. If those men of science be right who 
assume as inevitable their own unintelligibility to a public 
all too ready to accept this assumption, then is the outlook 
of our age gloomy indeed. As knowledge advances it 
must become more divided. As it becomes more divided, 
it will be appreciated by fewer and fewer. In the limit, 
the body of science will be so fragmented that each in¬ 
vestigator will be intelligible only to himself. He can thus 
leave no scientific heir. The system must collapse. 
Science must perish from off the goodly land into which 
its specialist leaders have brought it from out the wilderness 



xxvi Introduction 

of medieval ratiocination. The experimental method must 
spontaneously disintegrate! 

Let us glance at some of the elements in this cheerless 
prospect. 

The increasing subdivision of the sciences is a product 
of the last hundred years, and has been made necessary 
by the vast and rapid increase of knowledge. Only through 
the conviction of its value held by its exponents could this 
subdivision have become possible. It is doubtless psy¬ 
chologically necessary to most members of our fallible 
species that, for the doing of good scientific work, the 
worker should estimate the value of his method very highly. 
Every department of science is of the highest impor¬ 
tance—to those who work at it. And is not the historian of 
science even as other men ? 

Yet in fact the justification for splitting off a particular 
department from its parent stock is merely that certain 
specific problems may be solved or at least defined. Once 
those problems are solved—or exactly defined, which is 
nearly the same thing—the speciality has in part fulfilled 
its function, and that which its exponents have to purvey 
becomes incorporated into the general organon of know¬ 
ledge. 

Many illustrations might be given of this thesis. One, 
taken from the field of biology, will suffice. In the first 
half of the nineteenth century, with the advent of the cell 
theory and the improvement of the microscope, the study 
of microscopic organisms assumed a peculiar importance. 
Specialists of various kinds devoted themselves to the 
investigation of these organisms and at last succeeded in 
defining certain of them as beings, either plants or animals, 
consisting of but one cell. The knowledge of the structure 
and habits of microscopic animal forms, ‘Protozoa’ as they 
came to be called, now became part of the current body of 
biological knowledge. General zoologists included the 



Introduction xxvii 

group in their survey. Then in the later nineteenth 
century it was found that certain diseases that afflict 
man are of protozoal origin. Intensive investigation of the 
disease-producing Protozoa became urgent, and ‘Proto¬ 
zoology’ gained a name (i 904) and became again a separate 
science. Much knowledge acquired by the new specialist, 
the protozoologist, has since been placed at the disposal 
of the general zoologist, while other products of his activity 
have j oined the main stream of ‘ Cytology’. Since the number 
of diseases of protozoal origin is relatively limited, it is 
probable that a time will come when the protozoologist 
will cease to exist in fact, if not in name, and that we shall 
find him devoting himself to general problems of the cell. 

Science as it exists to-day is made up of such more or 
less temporary special departments—‘scientific outposts’ 
as we may perhaps name {hem. No man can hope to 
grasp the nature of current progress in all of these. But 
that is no reason why the picture of nature that science 
reveals should be any less clear and sharp in our day than 
in previous ages. It would be a poor sort of science that 
made the world less and not more intelligible. The 
author of this work is convinced that it is possible to give 
a picture of the state of scientific knowledge as a whole. 
What is unfortunately lacking is a supply of writers with 
adequate scientific and literary experience who would 
apply themselves to the task of exposition. 

How shall science be expounded ? The mechanism has 
been fairly established for those who deal with any one of 
the numerous departments. The technique of the special¬ 
ized text-book has reached a high stage of development. 
But when an attempt is made to cover simultaneously a 
number of the sciences, we are still in the experimental 
stage. Attempts at a ‘general survey’ of the combined 
sciences are legion, but they create a very unsatisfactory 
impression on the trained and critical reader. They are 



xxviii Introduction 

often one-sided and always disjointed. This method of 
presentation has been repeatedly tried and found wanting, 
for continuity, the cardinal element of scientific thought, 
is lacking in these over-simplified schemes. 

Must we then accept the dismal claim of the specialist 
as to his essential isolation.? The author of this work 
believes that such a view is wrong, both in fact and in prin¬ 
ciple. He believes that it is due to a basic error as to the 
true nature of specialization. He believes that the error 
is philosophically baneful and scientifically injurious. He 
believes that the natural antidote to these evils is the proper 
use of the historical method in science. He believes that the 
way to cover any very wide scientific area is by the frank 
introduction of history. He believes that the proper crown 
of a scientific education is a general survey of the processes 
by which the most important current scientific ideas have 
reached their present state of development. 

Moreover, even men of science who express little re¬ 
gard for history are not as neglectful of it as they some¬ 
times think. Oft they entertain an angel unawares. In the 
actual teaching of science, an historical method is almost 
invariably adopted, though its historical character may be 
unperceived by the teacher himself since the history with 
which he deals is very recent. Indeed, he cannot discuss 
scientific conclusions without discussing how they have 
been reached. And is not this history.? Moreover, the 
wider he spreads his scientific net, the more varied the 
scientific conclusions that he discusses, the farther must 
he go back in history to obtain his viewpoint. 

§ 2 . History in relation to scientific exposition 

The working man of science is accustomed to dis¬ 
tinguish in his mind between the historical development 
of his subject and the active process by which he is himself 
developing it. This distinction is among the fruits of 



Introduction xxix 

specialization. We hear little of it from the less specialized, 
but no less wise, scientific men of the seventeenth and 
eighteenth centuries. Reflection will bring conviction 
that the distinction cannot be maintained in the twentieth 
century, even on the ‘common-sense’ basis. The extension 
of knowledge must be based upon that already achieved. 
Now the limits of knowledge are by no means clearly de¬ 
marcated. Between the unknown and the known is no 
well-surveyed frontier, but rather a ragged and ill-defined 
borderland. Before he reaches the firm ground on which 
alone foundations can be safely laid, the man of science 
must perforce work back a little till he is behind that 
disturbed and shifting area. As we widen the sphere of 
our scientific purview, so shall we need—if we would make 
our vision clear and free from distortion—to penetrate 
ever farther back in history. Unless we adopt a wide 
historical outlook, we shall find ourselves unable to grasp 
the nature of the great problems which we are discussing. 

The trouble with the ‘general surveys’ is that, in aban¬ 
doning the historical method, they have lost the con¬ 
necting links between the departments of knowledge. It 
is as though one would seek to gain a complete picture of 
the form of a plant from cross sections of its numerous 
branches. The way in which the parts of the plant are 
related to each other can only be made apparent by 
tracing them from the stem from which they all spring. 
This is the task of history. 

It is an essential element of the scientific method of 
investigation that the investigator separate a part of the 
universe and consider it in and for itself. In this sense 
specialism is certainly implicit in the scientific method. 
But the separation of part of the universe, for purposes of 
investigation^ is a very different thing from the belief that 
that part of the universe is in fact separate from other parts. 
Yet a survey of science that does not introduce the 



XXX Introduction 

historical method must assume this absurd and untenable 
position. Surely the natural and proper way to survey the 
sciences is to treat them as arising seriatim in the course 
of the ages from that desire which is innate in every human 
being to know what Nature has to reveal. Thus ex¬ 
pounded, the sciences become records of the process of 
human inquiry, and science itself coextensive with the 
history of science. Uhistoire de la science^ c’est la science 
meme. 

§ 3. Methods of presenting the history of science 

Having discussed the error of him who neglects or seeks 
to neglect the historical method, we turn to consider the 
position of him who devotes himself to the history of the 
sciences. The first question that arises is as to what area 
of the sciences shall be covered in a single survey.^ 
Specialization has its dangers for the historian as for the 
scientist. 

Many writers have devoted themselves to the histories 
of one or other of the special sciences. But the sciences 
have developed and are developing not in watertight 
compartments but in intimate relation to each other. The 
limits of the separate sciences, as they are recognized in 
our time, are largely artificial and related to pressing 
practical needs. A more intellectually satisfying considera¬ 
tion than the history of a science is surely the history of a 
problem. The great problems of science demand for their 
solution many different sciences in turn. Problems are 
definite entities. Sciences—which at best are but special 
methods of research and at worst mere technical exper¬ 
tises —have no separate and permanent existence. To 
take a single example, the attempt to elucidate the 
mechanism of heredity, the problem which is foremost in 
the minds of contemporary biological thinkers, has drawn 



Introduction xxxi 

upon the whole gamut of the biological sciences. It 
would be impossible to restrict either the efforts or the 
conclusions of workers on heredity to the department of 
the zoologist or the botanist or the biochemist or the 
cytologist or the statistician or the experimental embryo¬ 
logist. It has seemed well, therefore, to construct this 
book so as to lead up to the study of biological problems. 

At the outset of his effort, the historian of science finds 
himself in face of a dilemma which can be resolved only 
by an omniscience to which he seldom lays claim. There 
are two courses open to him. To both fundamental 
objections may be urged. 

On the one hand, he can decide that his history shall 
terminate at some definite point of time in the past. He 
can then write a truncated account of the development of 
science which will avoid dangerous discussion of current 
problems, or at least partisanship in regard to them. The 
feat when accomplished—^and it has often been performed 
—fails to arouse even momentary consideration from the 
working man of science, or to deflect him from his view 
that history is the child’s play of antiquarians, suitable, 
perhaps, to be dallied with in extreme old age when the 
grasshopper becomes a burden and laboratory work is 
perforce abandoned. Man goeth forth to his work and to 
his labour until the evening. In the plenitude of his power 
he must pass old-time records without regard, and must 
concentrate on the contemplation of the living issues with 
which he is faced, for ancient history cannot solve modern 
problems. 

On the other hand, the historian may decide to bring 
his story ‘up to date’. To accomplish this he must per¬ 
force assume an unjustified position of authority. He 
must give much the same definiteness of tone to his 
interpretation of current and recent scientific advances as 
he has bestowed on those of the more remote past. Thus 



xxxii Introduction 

he must take sides in some matters, at least, in which he is 
ill-qualified to act as judge. His temerarious intervention 
in domestic differences will not fail to call down upon him 
the imprecations of those from whom he differs, while his 
ignorance may draw upon him the derision of those with 
whom he agrees. In any event he cannot cover, of his 
own knowledge, the whole area of the subject of which he 
treats. Thus his emphases and elisions will alike be sub¬ 
ject to the criticism of working men of science. 

With this choice of evils before him, the author of the 
present work has elected for the second, the less easy and 
the more dangerous course. He would ask the patient 
reader and he would implore the impatient to consider 
the reasons for his choice. Unless those reasons be in the 
reader’s mind, he can neither understand the purpose of 
this volume nor appreciate any value that it may have. 

§ 4. Arrangement of the work 

The arrangement of the book is conditioned by the 
attempt to lead up to the consideration of current bio¬ 
logical problems. Now in the history of problems—as in 
other forms of history—it soon appears that ‘periods’ are 
artificial though handy abstractions. It is difficult to establish 
their limits and impossible to make them exact. As abstrac¬ 
tions they are a convenient framework for setting forth 
our knowledge. But the framework must not be turned 
into a bed of Procrustes. Useful as aide memoire, it is 
dangerous as doctrine and wholly destructive as dogma. 
In what follows the periods will, in fact, be found con¬ 
stantly to overlap. 

Bearing this qualification in mind, the subjects with 
which we have to deal arrange themselves, with com¬ 
parative facility, under three main headings, corresponding 
to the three Parts of the book. 

We begin by treating of the ‘Older Biology’ (Part I). The 



Introduction xxxiii 

knowledge of living things, elevated into a great system 
by Aristotle (Chapter I) and developed by Theophrastus, 
Galen, and others among the Ancients, dwindled during 
the Middle Ages (Chapter II), to be revived again in the 
sixteenth and early seventeenth centuries by such great 
investigators as Leonardo da Vinci, Vesalius, and Harvey 
(Chapter III). 

At the dawn of the seventeenth century the inductive 
method makes a formal entry into the biological field 
(Part II). Francis Bacon and Descartes are its first philo¬ 
sophers. The assumption that the phenomena presented 
by living things can be brought under general laws, even 
as can the phenomena of the inorganic world, leads us 
to a position in which a new incentive is provided for the 
accumulation of biological data. The investigation of 
nature becomes organized. Scientific academies and jour¬ 
nals appear. The microscope appears. It is the special 
instrument of the biological sciences around which a com¬ 
plex technique progressively gathers (Chapter IV). The 
recognition of the amazing multiplicity of living things 
calls for special classificatory treatment of which Idnnaeus 
is the leading exponent (Chapter V). The details of organic 
structure, revealed by Cuvier and his predecessors and 
successors, prove themselves no less susceptible of orderly 
arrangement (Chapter VI). The distribution of plants 
and animals in space becomes gradually correlated with 
their distribution in time. This is the work of a host of 
explorers, travellers, geologists, and systematists among 
whom Alexander von Humboldt, Charles Lyell, A. R. 
Wallace, and J. D. Hooker deserve especially to be com¬ 
memorated (Chapter VII). Finally, classificatory schemes, 
the data derived from comparative anatomy and the facts 
of distribution, are brought together under a grand 
generalization frequently adumbrated in earlier times but 
more significantly formulated by Charles Darwin. With 



xxxiv Introduction 

Evolution as its keystone, the basal arch of classical biology 
is completed (Chapter VIII). 

The foundations of a scientific biology being now 
truly laid, there emerge into clearer light those problems 
that have constituted the main themes of biological thought 
for the last seventy years. We now enter on the third and 
longest section of our narrative. Here we must entirely 
neglect what are called the ‘separate biological sciences’, 
since the discussion of their individual history and develop¬ 
ment would obscure the issue that we seek. It is problems 
that must now claim our undivided attention. In attempt¬ 
ing their solution, men of science have frequently sought 
aid in the researches of a remoter past. For the most part, 
however, the attempted solution and, what is no less 
important, the definite formulation of these problems is 
the product of the last seventy years. 

Among the numerous biological problems we distin¬ 
guish seven for specially detailed discussion, since these 
seven seem to us to include most of the minor biological 
questions. To each of these seven problems we devote 
a chapter (IX—XV). Historically the earliest to emerge 
into modernity was that marvellous relation between the 
organism as a whole and the cells of which it is composed. 
What is the mysterious power that makes these living units 
subserve a common end ? (Chapter IX). As we attack the 
question we find ourselves involved in a discussion of the 
essential nature of the process which we call Life, a subject of 
debate from the time when philosophy came first into being 
(Chapter X). How are the countless internal activities of 
the organism related to each other ? (Chapter XI). And 
when and how was the beginning of that relationship that 
varies infinitely in detail, but is ever directed to the same 
ends—the preservation of the internal environment of the 
organism concurrently with the multiplication and ex¬ 
tension of the organism with reference to its external 



Introduction xxxv 

environment? (Chapter XII). How may these activities 
be traced in the development of the individual organism ? 
(Chapter XIII). As time has gone on, such problems have 
been referred to two main themes which have come to 
occupy the centre of the biological scene. These are the 
essential nature of sex with the marvel of generation 
(Chapter XIV) and the apparatus by which, in the sexual 
process, the nature of the parent organism is conveyed to 
or altered in the offspring (Chapter XV). ‘Heredity’ 
is the note on which we close our story. It is the 
outstanding topic of current biology. 




PARTI. THE OLDER BIOLOGY 

I 

THE RISE OF ANCIENT SCIENCE 

§ I. Hippocrates {c. 4()0-c. 370 s.c-) 

S CIENTIFIC knowledge begins with the people who 
came to call themselves the Hellenes, but whom we know 
as the Greeks. These were a collection of tribes of mixed 
origin that invaded the coasts and lands of the eastern part 
of the Mediterranean. They came from the north and 
settled in their new home toward the end of the second 
millennium before Christ. 

At the time of the coming of the Greeks the shores of 
the eastern Mediterranean were inhabited by highly 
civilized people whose rich and brilliant culture had been 
slowly built up during thousands of years of contact with 
Egypt and other empires of the ancient East (Fig. 2). The 
invaders partly displaced and partly mingled with the 
older inhabitants. With the resulting disturbances the 
ancient civilization fell in ruins about 1000 b . c . 

From the ashes there gradually emerged the distinctive 
Greek civilization. The first Greek tribes to become 
highly civilized were the lonians and the Dorians. The 
lonians were especially fond of philosophy and were 
interested too in mathematics and astronomy. Less civi¬ 
lized but perhaps more practical were the Dorians. Just 
on the frontier between the two tribes, but within Dorian 
territory, was the island of Cos. There a medical school 
arose about 600 b. c. It is the earliest scientific institution 
the works of which have come down to us. 

We have no clear idea of the way in which this medical 
school was organized. A very considerable number of 
books written by members of the school have, however, sur- 

26r3.3 


B 



Rise of Ancient Science 

vived. The earliest of them was composed about 500 b. c. 
The greatest member of the school was one Hippocrates, 
often spoken of as ‘the father of medicine’. We must 
remember that all the biological sciences were first studied 
because of their bearing on medicine. Hippocrates, there¬ 
fore, might well be called also ‘the father of biology’. 

Hippocrates was born on the island of Cos about the 
year 460 b. c., and he lived to be about a hundred years 
old. He learnt medicine on his native island, and he 
practised and taught it in various other islands and on 
the mainland of Greece. Such accounts as we have of him 
describe him as a man of very noble character, dignified 
bearing, and humane feeling. 

A great many books bear the name of Hippocrates, 
but very few of these can be really his work. Some of the 
best and most interesting of them are, however, of about 
his date. By studying them we can get a good idea of 
what he knew and of how he worked. 

If we were to examine these early medical works, we 
should find that whole departments of knowledge which 
are now considered necessary for a doctor are entirely 
absent from them. Thus, for instance, they betray little 
or no anatomical, physiological, or chemical knowledge. 
The doctor of those times had no instruments for 
examining patients, such as listening tubes, thermometers, 
or magnifying glasses. He had only his own senses to 
guide him and he had very little record of what those who 
had gone before had seen of disease. On the other hand, 
his senses were well trained and he observed carefully and 
well, and put down what he saw with a wonderful eye 
for what was essential. 

The real scientific value of these Hippocratic works 
lies in the careful record of what was seen. There were, 
of course, observations of scientific matters by peoples 
earlier than the Greeks. Thus we have, for example, notes 



Hippocrates 3 

on the positions and movements of stars by Assyrian 
scribes, written on clay tablets in the curious arrow- 
shaped writing known as cuneiform. Many of these notes 
are centuries earlier than Hippocrates. Moreover, from 
the writings of the Greeks themselves, we have information 
concerning men of science who were earlier than Hippo- 



Fig. 2 . Faience models from Crete of pre-Hellenic origin. Flying fish, paper 
nautilus, and other marine objects are shown. 

crates. Among them was the Ionian Thales of Miletus 
who predicted and observed the eclipse of the 28th of May 
585 B.c. But the great interest of the Hippocratic writings 
is that we have the works complete, while those of Thales 
and of the other predecessors of Hippocrates are either 
lost or survive only in fragments. The Hippocratic works 
not only record things seen, but they sometimes even tell 
us how these observations were made. Thus we can follow 
the physician into the sick-room and watch him at work. 

Among the most striking of the Hippocratic works is a 
collection of short sayings or Aphorisms as they are called. 



4 Rise of Ancient Science 

They show that many well-known proverbs in use to¬ 
day, especially such as concern food and diet, come to 
us from remote antiquity. Among the Hippocratic Apho¬ 
risms which have passed into common speech are: 

Art is long and life is short. 

Desperate diseases need desperate remedies. 

Sleeping too much is as bad as waking too much. 

One man’s meat is another man’s poison. 

Phrases such as these, however, are not science in the 
ordinary sense of the word. Their importance for us lies 
in the spirit in which they were made rather than in the 
observations themselves. To understand that spirit better 
we must compare it to that of the less scientific doctor of 
the time. Now in the days of Hippocrates a great many 
diseases were generally ascribed to the action of gods 
or demons or supernatural beings. One quite common 
disease was in fact actually called the sacred or divine 
disease on this account, and the popular opinion about it 
was shared by many physicians. One of the Hippocratic 
physicians studied the sacred disease and came to the con¬ 
clusion that he had found out its actual cause. He says: 
‘It seems to me that the disease called sacred is no more divine than 
any other. It has a natural cause, just as other diseases have. Men 
think it divine merely because they do not understand it. But if 
they called everything divine which they did not understand, why 
there would be no end of divine things! 

‘Those who make a to-do about such things as being due to the gods 
appear to me, therefore, like certain magicians who pretend to be 
very religious and to know what is hidden from others. If you 
watch these fellows treating the disease, you will see them use all 
kinds of incantations and magic, but they are also very careful in 
regulating diet. Now if food makes the disease better or worse, how 
can they say it is the gods who do this? Nay, even in saying such a 
thing, they show impiety and suggest that there are no gods. 

‘The fact is that this invoking of the gods to explain diseases and 
other natural events is all nonsense. It doesn’t really matter whether 



Hippocrates 5 

you call such things divine or not. In Nature all things are alike in 
this, that they can all be traced to preceding causes. Shall we say 
then that they are divine or not divine? Since they are all alike in 
this respect, it is really only a matter of words.’ [Somewhat para- 
phrased.^ 


The fine book On the sacred disease from which this 
passage is taken was written about 400 b.c. It might 



Fig. 3. Rectangular plate of baked clay from Louvre decorated with the 
figures of four marine fish and two shells. The work of a Greek artist of South 
Italy of the fourth century B. c. 

justly be called the‘Charter of Science’, for it sets forth 
the scientific method of assuming natural explanations 
for all observable events. While it is still ringing in our 
ears let us see how far men had got in those days in biolo¬ 
gical knowledge. 

First of all, the artists had long been at work represent¬ 
ing animal forms. Often they had made very exact 
studies, some of which disclose observation that might 
well be called scientific. The Greeks were essentially a 
maritime people. They nearly all lived within sight of 












6 Rise of Ancient Science 

the sea and a great many of them were employed as fisher¬ 
men or sailors. It was natural therefore that they should 
take an especial interest in marine creatures, and many 
remarkably good representations of fishes have come down 
to us from the fourth and fifth and even from the sixth 
century b.c. (Fig. 3). 

But the Greeks were not content to examine only the 
external forms of animals. A beginning had actually been 
made with dissection of the internal parts. Thus about 
500 B.c. Alcmaeon, a Greek of Croton in Southern Italy, 
had described the nerves of the eye and the tube that 
connects the mouth with the ear. If you pinch your nose, 
and, keeping your mouth closed, distend your cheeks by 
blowing gently, you feel something move in your ear. This 
is the membrane of the ear-drum (Fig. 102). The cavity 
of this drum is connected with the mouth by a pipe, the 
so-called Eustachian tube. In this action you have driven 
air from the mouth through the Eustachian tube into 
the ear. Fmstachi (p. 105), after whom this structure is 
named, was a writer of the sixteenth century. Yet these 
tubes were described by Alcmaeon two thousand years 
earlier. This is one of many instances in which modern 
discoveries were anticipated by the Greeks. 

Alcmaeon made many other researches but only a most 
fragmentary record of them has survived. He began the 
study of the development of the young animal. Embryology 
as it is now called, and he worked at it in much the same 
way that we do nowadays. He examined incubated eggs 
and watched the body of the chick developing. 

Other Greek scientific men in the earlier part of the 
fourth century were following this same line of research. 
The work of one of these gives an intelligible account of 
the parts of the developing chick. 

There is another department of biology which is very 
ancient indeed and was more widely though less satis- 



Hippocrates 7 

factorily pursued. This department is botany. Plants 
were studied by Hippocrates and his contemporaries 
and predecessors, though solely for their medical applica¬ 
tion. We have several works of the time of Hippocrates 
which tell us a good deal about how the physicians of the 
day used plants as drugs. These works show that a great 
number of different kinds of herbs were distinguished. 
Such writings are, however, of very little scientific value 
because they tell us hardly anything about the plants 
themselves. 

§2. Doctrine of the Four Humours 

Before we part with the Hippocratic writings we must 
refer to one topic which is of great importance for 
the effect that it had on the beliefs of the following ages. 
This was a very peculiar view of the constitution of the 
body. 

The ancients supposed that all matter was made up of 
the four essential earth, air, fire, and water. 

These, it was thought, were either in opposition or in 
alliance with each other. Thus, water was opposed to fire 
but allied to earth. These oppositions and affinities were 
associated with the view that each element was com¬ 
pounded of a pair of ‘primary qualities’, heat and cold, 
moisture and dryness (Fig. 4). 

This strange conception was further developed by the 
Greek medical writers. The Hippocratic works suppose 
that all living bodies are made up of four humours, Blood 
(sanguis), Yellow Bile (cholera). Black Bile (melancholia), 
and Phlegm (pituita). These four Humours had a special 
relationship with the four Elements (Fig. 4). Health 
depended upon the Humours being mixed, or to use the 
old word tempered or complexioned, in the right proportion. 
If one or other was in excess the patient suffered accord¬ 
ingly. This theory was thought to explain the nature of all 



8 Rise of Ancient Science 

disease. Diseases were classified according to the humour 
in excess as sanguine, choleric, melancholic, or phlegmatic. 
Moreover every individual, it was supposed, had a nature 
tending to one of the four types of disease. 

Men of science have, of course, long ago abandoned 
this belief, yet it still finds a place in many expressions in 



Fig. 4. The four Elements in association with the four Humours 
and the four Qualities. 


current use. We still speak of a man’s temperament or a 
lady’s complexion^ and we are all of us at times more or 
less sanguine^ choleric^ melancholy^ or phlegmatic. The use 
of these words dates back to the time when they had 
a definite physiological meaning. Each humour became 
associated with a special organ, the blood with the liver, 
melancholy or black bile with the spleen, phlegm 
with the lungs, and choler with the gall bladder. 
To show how firmly impressed and lasting this theory 
was we may quote from an English poem by John Gower 
(1340-1408), a contemporary of Chaucer (1340-1400). 




9 


Doctrine oj the Four Humours 

The poem was dedicated to King Richard II: 

The spleen is to Melancholy 
Assigned for herbergery [lodging]. 

The moist Phlegm with the cold 
Hath in the lungs for his hold 
Ordained him a proper stede [place] 

To dwell there as he is bede [bid]. 

To the Sanguine complexion 
Nature of his inspection 
A proper house hath in the liver 
For his dwelling made deliver [ready]. 

The drier Choler with his heat 
By way of kinde [nature] his proper seat 
Hath in the gall where he dwelleth 
So as the philosopher tclleth.’' 

The philosopher mentioned in the last line is the greatest 
of all Greek men of science, and perhaps the greatest of 
all men of science, the philosopher par excellence. He was 
often spoken of in the Middle Ages simply as ‘the philo¬ 
sopher’. That man is Aristotle, and to him we now turn. 

§3. Aristotle (384-322 b-C-') 

Aristotle was born in 384 b.c. at Stagira, a small town 
of the Chalcidice. Stagira was a Greek settlement, but it 
lay far from such centres as Athens of the Ionian cities 
where there had dwelt for centuries a population in¬ 
terested in intellectual matters. Moreover, Stagira lay on 
the frontiers of the state of Macedon into which it was 
soon to be absorbed. Athenians or lonians looked upon 
the inhabitants of Macedon much as well-bred and well- 
educated people were accustomed to regard the inhabitants 
of the ‘back woods’ a hundred years ago. 

In the fourth century, however, this attitude was be¬ 
ginning to change. On the one hand, the older Greek 

^ The spelling is partially modernized. 



lo Rise of Ancient Science 

world was split up into very small states (Fig. 5) which 
were constantly quarrelling. These minute states were 
the poorer because individual liberty in some of them was 
carried to an excess that prevented the adequate develop¬ 
ment of trade. The population in many of them had 
become very dense but consisted largely of slaves. Most 
people dwelt in or near the towns. The denseness of the 
population necessitated an intensive form of agriculture so 
that there was little wild or uncultivated land left. 

On the other hand, the Macedonians were on the rise 
in most of the matters in which the older Greek states 
were on the decline. Macedon was, for one thing, by far 
the largest of the Greek states (Fig. 6). It was a kingdom 
governed by an absolute monarch to whom the ‘liberty 
of the subject’ seemed less important than the unity and 
power of his kingdom. The Macedonian lands were but 
half developed, large tracts of wild and forest country 
still remaining. But most important of all, Macedon 
came under a series of very able rulers. One of these 
was Philip, father of Alexander. 

Philip was a statesman of the first rank, a man of high 
intellectual attainments, an admirer of the culture and 
civilization of the more settled parts of the Greek world. 
He tried to attract learned and cultured Greeks to Mace¬ 
don, and he prided himself on being a Greek and not a 
semi-civilized barbarian. 

The father of Aristotle was physician to Amyntas II, 
king of Macedon, who was himself the father of Philip. It 
was probably from his father, the physician, that Aristotle 
early acquired his taste for biological investigation. Galen 
(p. 59) tells us that the members of the guild to which Aris¬ 
totle’s father had belonged practised the art of dissection. 

Aristotle at seventeen was sent to what was the equi¬ 
valent of a university. He went to Athens where he 
became a pupil of the great philosopher Plato. The insti- 



Aristotle 11 

tution where Plato taught was known as the Academy. 
The word was simply the name of a grove of trees where 
Plato and his pupils were wont to assemble. From that 
grove the school of Plato took its name, and from the 
school of Plato we have the modern meaning of the word 
‘Academy ’ as a place of learning. 



There can be no doubt that Plato influenced his pupil 
Aristotle a great deal, but in certain philosophical matters 
there were profound differences between the two men. 
So far as science was concerned, we note that Plato had 
a strong bias towards mathematics while Aristotle was 
essentially a biologist. Aristotle, however, remained closely 
attached to his master and continued to be a member of 
his school till Plato’s death in 347 b. c. Aristotle perhaps 






















12 Rise of Ancient Science 

expected to become head of the Academy. In this, how¬ 
ever, he was disappointed, and he left Athens to reside 
at the court of the sovereign of a small Greek state on the 
coast of Asia Minor opposite to the island of Lesbos. 

Aristotle’s bias towards natural history now had full 
play. He had ample leisure and he was in a good position 
for investigating marine animals. The results of his 
investigations at Lesbos come out in his biological treatises. 
These are, at least in outline, the earliest of his works. 

In the year 342 b.c., when Aristotle was 42 years of 
age, he received an invitation from King Philip of Mace- 
don to become tutor to his son Alexander. He accepted 
and settled in Macedon, where he remained for seven 
years. 

Alexander must have owed much to his training by 
the greatest of biologists. It seems probable, however, 
that Alexander early passed out of Aristotle’s hands. 
Thus, in the year 339 b.c., when Alexander was only 
only 16 or 17, we hear of him taking charge of the king¬ 
dom during his father’s absence. In the year 336 Philip 
was assassinated, Alexander succeeded to the throne, and 
Aristotle left Macedon to return again to Athens. There 
is evidence that tutor and pupil were not on good terms, 
though Alexander retained through life an interest in 
science. Aristotle and Alexander never met again. 

Aristotle on returning to Athens in 336 was forty- 
eight years old. He began again to teach, but he did not 
return to the Academy. He set up his own school or 
university, which became known as the Lyceum^ and he 
very soon gathered around him a large band of able 
pupils. It was during this second Athenian period that 
most of his philosophical work was done. His life remained 
uneventful, though marked by great mental activity, until 
the year 323 b.c. 

It is pleasant to remember that, just as Plato taught in a 



Aristotle 13 

grove, the Academy^ so Aristotle taught in a garden. The 
word Lyceum is derived from an epithet of Apollo and was 
a familiar name for a temple to that god which stood hard 
by Aristotle’s garden. The epithet Lykeios happens to be 
peculiarly appropriate to Aristotle, for its meaning is 
‘luminous’ or ‘light-bearing’. In the Lyceum Aristotle 



Fig. 6 . Expansion of Macedon during the reign of Philip, father of Alexander 
the Great. The vertically shaded area shows the extent of Macedon at Philip’s 
accession, the black outline its extent at his death. 


had his own favourite walk or peripatos, where he used to 
teach while walking. Hence his followers of later genera¬ 
tions are often called Peripatetics. 

During the thirteen years, from 336 to 323 B.c., while 
Aristotle was teaching in his garden, the power of Alexan¬ 
der was rapidly growing. By overthrowing the vast and 
immeasurably wealthy Persian Empire, which for two 
centuries had ruled nearly all the civilized Near East, 
including Egypt, he succeeded to the position of the 








































14 Rise of Ancient Science 

Persian kings. He even crossed the Indus and fought 
successful battles in the Punjab (Fig. 23, p. 54). In spite of 
this the small Greek states still held jealously aloof from 
the upstart Macedonian power. Feeling ran high as these 
Greek states saw that they were inevitably to be engulfed 
into the huge Alexandrian realm. 

Suddenly in 323 b. c. came the unexpected news of the 
death of the conqueror Alexander at Babylon at the age 
of thirty-three. The excitement was intense. The party 
most opposed to Macedon seized power in Athens. 
Aristotle, who had spent a long time in Macedon 
as tutor to Alexander, was under suspicion' of having 
Macedonian sympathies. He thought it prudent to 
withdraw from Athens. He died in the following year, 
aged sixty-two. In his will he named his favourite pupil 
Theophrastus as head of the Lyceum, the school that he 
had founded (see pp. 44-56). 

The surviving works of Aristotle place him as among 
the very greatest biologists of all time. He set himself 
to cover all human knowledge, and succeeded in this 
vast task in a way in which no one has succeeded before 
or since. He was a deeply original thinker, and he had 
an unrivalled capacity for arranging his own and other 
people’s material. To these qualities he added first-class 
powers of observation and great shrewdness of judgement. 
No succeeding thinker has exercised so great an influence. 

§4. Aristotle's Biological Works 

Of Aristotle’s biological works a number have sur¬ 
vived, and these fortunately in a fairly complete state. 
Four are major treatises, and there are a number of less 
importance. The major works are most frequently referred 
to by their titles translated into Latin. They are: 

(a) On psyche (De anima). 

(b) Histories about animals (Historia animalium). 



Aristotle's Biological Works 15 

(c) On the generation of animals (De generatione 

animalium). 

(d) On the parts of animals (De partibus animalium). 

The very names of some of these are of interest and 
have themselves a history. Thus the first On psyche deals 
with what we may call the living principle, the quality or 
nature or essence, or whatever we may call it, that dis¬ 
tinguishes living substance. This quality or nature or 
essence departs or ceases to exist or to act when living 
substance dies. Now various interpretations have been 
put on Aristotle’s views in this matter. Gradually the 
vtoxdi. psyche that he uses for living principle has been trans¬ 
ferred to other subjects. It has nowadays come to be 
used for a particular property of living things, namely 
mind, or even the power to think. In this way we have 
the science of Psychology which deals with the properties 
of mind. Of this science Aristotle may fairly be said to 
be the founder, and he devoted a large number of books 
to it. 

Now the word psyche had a long and adventurous 
history before Aristotle came to use it. The oldest Greek 
work we have is the poem known as the Iliad of Homer, 
which deals with the siege of the city of Troy by the 
Greeks. Parts of this poem date from about 1050 b. c. and 
therefore nearly 700 years before Aristotle. These parts 
were thus written about as long before him as the signing 
of Magna Charta is before us! This gives an idea of the 
time that Greek civilization had been growing. In the 
Iliad of Homer we find the word psyche often used in the 
sense of breath. 

Breathing is the most obvious sign of life, and when a 
man ceases to breathe we know that he is dead. So from 
breath the word psyche came to mean life, then the principle 
of life, and then the soul or again the mind. It is interesting 



16 Rise of Ancient Science 

to observe that in other ancient languages, as for instance 
Hebrew and Latin, the word for soul or life has gone 
through exactly the same history, being gradually changed 
from its original meaning of breath. A part of the story 
of this word is told for us in the Bible where we read in 
the book of Genesis ‘And the Lord God formed man of the 
dust of the ground, and breathed into his nostrils the 
breath of life, and man became a living souV, 

The name of the second of the great biological works 
of Aristotle has also had a very peculiar and interesting 
history. We have translated the title Histories about 
animals, and the Greek title reads Historiai peri ta zoa. 
Now our English word history is derived from the Greek 
word historia, but its meaning has altered somewhat in the 
passage. At first the Greek word really meant the process 
of learning by inquiry, and this is the sense in which 
Aristotle uses it. It next came to mean the knowledge 
that was obtained by inquiry, and finally it was taken to 
mean the setting forth of this knowledge. The title of the 
work of Aristotle should, therefore, perhaps be translated 
Inquiries about animals. To give it a modern ring we 
might well render it Zoological researches, for that is 
what the book really contains. And what are researches 
but inquiries about things.? When the word ‘history’ 
first entered the English language, it had the original 
Greek meaning of either inquiry or the results of inquiry. 
The word History in the ordinary sense, unqualified, 
has now come to mean the story of the past. It still 
retains its old meaning, however, in our term Natura 
History. The word story is only a shortened form of the 
word history. 

The actual contents of Aristotle’s biological works may 
be divided into two parts {a) Observations, and (f) De¬ 
ductions or Theories. These two elements are closely 
interwoven in all important biological works. There can 



Aristotle's Biological Works 17 

be no important series of observations unless the observer 
is prompted by some theory. Conversely, there can be 
no valuable theory that is not based on a careful accumu¬ 
lation of observations. The two elements cannot be 
separated in the mind of the man of science. There are 
those who pride themselves on collecting facts without 
any reference to theory. In making this claim, the collec¬ 
tor is exhibiting his ignorance both of the history of 
science and of the object of science. It can easily be 
shown that some theory is, and must be, at the back of 
all effective collecting. If no theory is there, then the 
collecting is aimless and unscientific. Science has neither 
need nor place for human jackdaws. 

It is interesting to recall that Darwin, the greatest 
biological successor of Aristotle, laid great stress on the 
value of the formation of a theory to justify and stimulate 
the collection of observations. The condition of success is, 
of course, that the theory must be abandoned or changed 
freely to fit the observations. 

Darwin in his Autobiography has some thoughts on 
this point which suggest the value of hypothesis in scien¬ 
tific discovery. ‘From my youth’, he says, ‘I have had the 
strongest desire to understand or explain whatever I 
observed, that is, to group all facts under some general 
laws.’ But he adds, ‘I have steadily endeavoured to keep 
my mind free so as to give up any hypothesis, however 
much beloved (and I cannot resist forming one on every 
subject), as soon as facts are shown to be opposed to it.’ 
Although observations and theory are thus inseparable, 
we must nevertheless distinguish them for the purpose 
of our narrative. In what follows, we shall first discuss 
some of the more interesting or important of Aristotle’s 
actual observations and then deal with his theories. 


2613.3 



18 Rise oj Ancient Science 

§5. Aristotle on the Habits of Fish. 

Aristotle was fond of watching animals and their ways. 
It is evident, too, that he was careful in keeping notes of 
what he saw. We shall first glance at his remaj’kable 
account of the breeding habits of the cat-fish (Figs. 7 and 8): 

‘The cat-fish deposits its eggs in shallow water, generally close to 
roots or close to reeds. The eggs are sticky and adhere to the roots. 
‘The female cat-fish having laid her eggs, goes away. The male 
stays on and watches over the eggs, keeping off all other little fishes 
that might steal the eggs or fry. He thus continues for forty or fifty 
days, till the young are sufficiently grown to escape from the other 
fishes for themselves. Fishermen can tell where he is on guard for, 
in warding off the little fishes, he sometimes makes a rush in the 
water and gives utterance to a kind of muttering noise. Knowing 
his earnestness in parental duty the fishermen drag into a shallow 
place the roots of water plants to which the eggs are attached, and 
there the male fish, still keeping by the young, is caught by the hook 
when snapping at the little fish that come by. Even if he perceive 
the hook, he will still keep by his charge, and will even bite the 
hook in pieces with his teeth.’ [Abbreviated.'\ 

Aristotle draws attention also to another peculiarity of 
this fish, namely its power of giving forth sound. ‘Fishes 
can produce no voice for they have no lungs or windpipe, 
but certain of them, as the cat-fish in the river Achelous, 
emit inarticulate sounds and squeaks by a rubbing motion 
of their gill covers.’ 

The Achelous is a river of continental Greece which 
runs into the sea opposite the island of Ithaca and just at the 
mouth of the gulf of Corinth (Fig. 5). For many centuries 
the only notice taken of this account of the cat-fish of the 
Achelous river was to laugh at it. The passages in which 
there are references to it were thought to be spurious 
or to be simply erroneous. The cat-fish that are known 
in Europe do not look after their young in this fashion, 
though some can make a noise with their gill covers. 



Aristotle on Habits oj Fish 19 

This was the state of knowledge of the habits of cat-fish 
until the middle of the nineteenth century. About that 
time the matter was taken up by the distinguished Swiss 



Fig. 7. Aristotle’s cat-fish, Parasi/urus Aristotelis. 

Fig. 8. Male American cat-fish (Ameiurus) on guard over nest. 


naturalist, Louis Agassiz (1807-73, PP- 304 > 4^2) of 
Harvard. Now in America there are cat-fish, though of 
different species to those known in Europe. Agassiz ob¬ 
served that the male American cat-fish look after their 
young just as described by Aristotle (Fig. 8). This made 















20 Rise of Ancient Science 

him suspect that the story of Aristotle might be true also 
for Greek cat-fish. It happened that he had cat-fish 
sent to him from the river Achelous (1856). These, he 
found, were a peculiar species, different from the other 
European cat-fish and from the American form in which 
he had observed the male guarding the young. Working 
twenty-two centuries after Aristotle, and in a continent 
unknown to that great naturalist, Agassiz therefore called 
his newly discovered cat-fish after Aristotle. Unfortu¬ 
nately his description was overlooked by naturalists. It 
was not until twenty years ago (1906) that Parasi/urus 
Aristotelis (Fig. 7) became properly known to men of 
science. That we are, even now, without information 
more modern than Aristotle as to the breeding habits of 
this creature gives some indication of the value of his 
work. 

Probably most people have heard of the electric fish 
known as the Torpedo from which the instrument of 
destruction has been given its name. A great deal of 
research has been devoted to this animal, and we now 
know how it produces its electric discharge. It is charac¬ 
teristic of all muscle substance that, at the moment of 
contraction, it gives rise to an electric disturbance. In 
ordinary muscle this discharge can only be detected by 
means of delicate instruments. In the Torpedo fish the 
anterior part of the body is expanded and flattened (Figs. 
9 and 10). This flat expanded body contains two special 
and peculiar kidney-shaped tracts of muscular substance 
(Fig. 9) in which the contractile power is reduced to a 
minimum but the power of producing an electrical dis¬ 
turbance is greatly increased. The electric shock from one 
of these creatures can easily numb and kill a smaller 
animal. The commonest Mediterranean species of this 
fish is Torpedo ocellata in which there are five large eye-like 
pigment spots on the dorsal surface (Fig. 10). This form 



Aristotle on Habits oj Fish 21 

was well known to the early Greeks and excellent figures 
of it are encountered on pottery from the sixth century 
B.c. onward. 

Another peculiar form of fish common in the Medi¬ 
terranean is the so-called Angler fish. This animal has, 
like the Torpedo, a somewhat flattened body. Some of 
the rays of the dorsal fins of the Angler are long and 
movable and terminate in a fleshy flap. These flaps are 
used by the fish as baits to attract smaller creatures. The 
animal is ‘protectively’ coloured, that is to say it is of 
the colour of the ground on which it lives, and is therefore 
almost completely invisible. It has an enormous head and 
huge mouth. The Angler lies still at the bottom. When 
small fishes are attracted by the baits, the great mouth 
opens and the little victims are engulfed. Owing to the 
enormous extension of the head of the Angler fish, the 
anterior, or so-called ‘pectoral’ fins, which are attached to 
the bony skeleton of the head, are carried backward right 
behind the posterior, or so-called ‘pelvic’ fins. 

Here is Aristotle’s description of the habits of these 
two animals, the Torpedo and the Angler (Figs. 9-11): 

‘In marine creatures one may observe many ingenious devices 
adapted to the circumstances of their lives. The accounts commonly 
given of the Torpedo and Angler are perfectly true. 

‘In both these fishes the breadth of the anterior part of the body is 
much increased. In the Torpedo the two lower fins (i.e. the so- 
called “pelvic” fins) are placed in the tail. This fish uses the broad 
expansion of its body to serve the office of a fin. In the Angler the 
upper fins (i.e. the “pectoral” fins) are placed behind the under fins 
(i. e. the pelvic fins). The latter are placed in this fish close to the 
head. 

‘The Torpedo stuns the creatures that it wants to catch, overpower¬ 
ing them by the force of shock in its body and feeding upon them. 
It hides in the sand and mud, and catches all the creatures that swim 
within reach of its stunning power. The Torpedo is known to cause 
a numbness even to human beings. 



22 Rise of Ancient Science 

‘The Angler stirs himself up a place where there is plenty of mud 
and sand and hides himself there. He has a filament projecting in 
front of his eyes. This filament is long, thin and hair-like and 
rounded at the tip. It is used as a bait. The little creatures on 
which this fish feeds swim up to the filament taking it for a bit 
of the seaweed that they eat. Then the Angler raises the filament, 
and when the little fishes strike against it he sucks them down 
into his mouth. 

‘That these creatures get their living thus is evident from the fact 
that while sluggish themselves they are yet often found with mullets 
in their stomachs and mullets are very swift fish. Moreover the 
Angler is usually thin when taken after having lost the tips of his 
filaments.’ ^Abbreviated from several passages.^ 

In these and in many other passages in his biological 
works we see Aristotle, the first and in many ways the 
greatest of all naturalists, actually watching the creatures 
he loves. He is leaning out of a boat in the great gulf that 
indents the island of Lesbos, intent on what is going on at 
the bottom of the shallow water. In the bright sun and in 
the still, clear water of the Mediterranean every detail, 
every movement, can be discerned. Hour after hour he 
lies there, motionless, watching, absorbed, and he has left 
for us his imperishable account of some of the things that 
he has seen with his own eyes. 

§ 6. Handicaps of Early Naturalists 

Still, clear water and bright sun are advantages that 
Aristotle enjoyed over the naturalists of our own time and 
country. But if he had these advantages he had also 
many handicaps from which we have been freed, and 

Description of Figs, 9, 10, and ii. 

Fig. 9. Diagram of the electric organs of the Torpedo-fish. 

Fig. 10. Torpedo ocellata from Rondelet (1554, see p. 91). 

Fig. II. Angler-fish from Rondelet (1554)* Note the wide gaping mouth 
and the fishing filaments above it. Only the large pectoral fins are seen. 
The pelvic fins are in front of the pectorals, concealed by the anterior expan¬ 
sion of the body. 




Lfl*]*] 




24 Rise oj Ancient Science 

freed partly by him. Only by keeping in mind these dis¬ 
advantages under which Aristotle worked can we judge 
such mistakes as he made. Remember that his study was 
new. He had no books to consult, no training for such 
work, no instruments, to help him, no learned societies, 
and only such learned companions as he had himself 
trained, to encourage and support him. He was as yet 
without a library—indeed the very idea of a great library 
was his own. 

Moreover, Aristotle suffered from a drawback from 
which the Greeks never wholly freed themselves but from 
which their work has delivered us. He was without a special 
scientific nomenclature. The special words that we use in 
the sciences, ugly and difficult as they are, save an immense 
amount of labour and, in the end, make the subject easier 
to understand. Thus, if we had been writing the descrip¬ 
tion of the fishes of which we have read Aristotle’s ac¬ 
count, we should have spoken of their pectoral and pelvic 
fins. Any naturalist accustomed to deal with fish would 
know at once exactly what was meant. The words pec¬ 
toral and pelvic applied to a fish’s fins have a definite 
anatomical meaning that would be quite unmistakable to a 
modern naturalist because he has traced these fins through 
a whole series of fishes and has seen how they vary. 

But the Greeks were beginning their subject. They 
had had no time to trace these fins through whole series 
of fishes. They could only describe them by their position, 
‘upper’ and ‘lower’. We who come after the Greeks, when 
in need of a new scientific term, turn to their language 
or to that of their heirs, the Latins. The Greeks had no 
literature that was classical to them upon which to draw. 
Nevertheless we shall see them making a beginning of a 
scientific nomenclature (p. 47). It is a process, however, 
which did not go nearly so far in Antiquity as it has gone 
with us. 



Ducts from Ducts from 

aorta {Renat vein (Renal 



Fig. 12, The generative and urinary systems of a mammal as described by 
Aristotle. The part framed in a dotted rectangle is a restoration of a lost diagram 
prepared by Aristotle and described in his Historia animalium. The legends in 
brackets are the modern scientific terms. The others are either transliterations of 
the terms used by Aristotle or literal translations of such terms. 









26 Rise of Ancient Science 

There is yet another matter in which we have the 
advantage of Aristotle, but in which our advantage is 
based and founded on his work. In reading or listening 
to any account of biological matters we are greatly helped 
by drawings or diagrams. In fact, without such drawings 
or diagrams biological investigation would be impossible. 
Aristotle appears to have been the first to illustrate a 
biological treatise. In his works such diagrams are often 
referred to. Unfortunately the figures have long since 
disappeared, but his descriptions are not infrequently of a 
character that enables us to reconstruct them. 

There are several places in Aristotle’s great Histories 
about animals in which the lost diagram can be restored with 
confidence. An admirable example is his description of the 
general structure of the urinary and reproductive organs in 
the mammalian group, the animals, that is, that suckle 
their young. The ducts and vessels in connexion with these 
organs have a very complicated relationship. Aristotle 
describes them well and in a way that shows that he had 
dissected them. He actually refers to ‘the accompanying 
diagram’. It is therefore a great satisfaction, in reading his 
text, to be able to reconstruct this diagram from the objects 
themselves and to find that the facts fit his description 
(Fig. 12). We shall come across other cases where we can 
supply the figures missing from his text. 

§ 7. Aristotle on Octopuses and their Allies 

Aristotle was extremely interested in the problem of 
how creatures come into existence. If he had lived now¬ 
adays we should, perhaps, have called him an embryologist. 
Embryo is a Greek word, and means, in that language, 
the young animal or plant before it has left the body 
of the mother or before it has come out of its egg or 
seed, and while still incapable of independent life. In 
connexion with embryology Aristotle refers to his dia- 



Aristotle on Octopuses and their Allies 27 

grams several times. There is in his works a delightful 
description of the development of the Octopus and of the 
Sepia or cuttlefish, forms of marine molluscs that are 
provided respectively with eight and ten arms. These 
creatures, now described by men of science as belonging to 
the group of Cephalopoda (see p. 230, Figs. 48-50, p. 93), 
specially interested Aristotle. We shall quote his descrip¬ 
tion and associate with it some suitable drawings: 

‘The octopus breeds in spring, lying hid for about two months. 
The female, after laying her eggs, broods over them. She thus gets 
out of condition since she does not go in quest of food during this 
time. The eggs are discharged into a hole and are so numerous that 
they would fill a vessel much larger than the animal’s body. After 
about fifty days, the eggs burst. The little creatures creep out, and 
are like little spiders, in great numbers. The characteristic form of 
their limbs is not yet visible in detail, but their general outline is 
clear. They are so small and helpless that the greater number perish. 
They have been seen so extremely minute as to be absolutely with¬ 
out organization [remember Aristotle had no lens or microscope] but 
nevertheless when touched they moved. The eggs of the septa look 
like a bunch of grapes (Fig .48, p, 93), and are not easily separated 
from one another. They are stuck together by some moist sticky 
substance exuded by the female. They are white at first but larger 
and black after this sticky substance has been exuded. 

The sixteenth-century naturalist, Guillaume Rondelet 
(p. 91), based his great work on Mediterranean marine 
creatures upon Aristotle. Rondelet’s drawings of the 
octopus and of the sepia are excellent, and his figure of the 
grape-like egg-clusters of the sepia is especially appro¬ 
priate here since he used it to illustrate this identical passage 
of Aristotle (p. 93). To this day Mediterranean fishermen 
call the eggs ‘grapes of the sea’. Aristotle savs that 

‘The young sepia is first distinctly formed inside the egg out of the 
white substance. When the egg bursts it comes out. The inner 
part is formed as soon as the egg is laid and is something like a hail¬ 
stone. Out of this substance the young sepia grows, being, however, 



2 8 Rise of Ancient Science 

attached by the head in the same way as a developing bird is attached 
by the belly, ["I'his refers to observations which Aristotle had made on 
the chick developing within the egg, see Figs. 13-14, and cp. Figs. 34 
and 63.] As the young sepia grows the white substance dwindles 
and, moreover, as with the yolk in birds’ eggs, it finally disappears. In 
the young sepia^ as in most animals, the eyes are at first relatively 




Figs. 13 and 14. Diagrams of a younger and an older stage in the develop¬ 
ment of the Sepia or cuttlefish as described by Aristotle. 

very large. To illustrate all this by means of a figure let j 1 repre¬ 
sent the egg, B and C the eyes, and D the body of the little sepia. 

If, when the young ones are fully formed, you cut the outer 
covering a moment too soon, the young creatures eject pigment, 
and their colour changes from white to red in their alarm.’ 

The habit of the Cephalopoda of ejecting their ‘ink’ to 
cover their retreat is well known. A certain type of 
painter’s pigment is called ‘sepia’ and is still, in fact, often 
derived from that animal. Moreover, the colour-changes 
which flit across the skin of the creatures appear to be 
expressive of their emotions. These changes are, how- 


Aristotle on Octopuses and their Allies 29 

ever, in large part protective and enable the animals to 
resemble their surroundings, and thus deceive their 
enemies or their prey. 

The study of the Cephalopods affords us also a good 
example of how the Aristotelian works sometimes err. 
One of the most beautiful and interesting of the Cephalo- 



Fig. 15. The Paper Nautilus, Argonauta Argo, from Belon (i 551, see pp. 89-91). 
The animal is drawn using its arms as oars and its membrane as a sail. 


pods is the so-called Paper Nautilus (to be clearly dis¬ 
tinguished from the Pearly Nautilus^. This exquisite 
creature has long been studied by naturalists, but we have 
acquired an accurate idea of its habits only in very modern 
times. The Aristotelian work tells us that 

‘it is an octopus, but one peculiar both in its nature and habits. It 
often lives near the shore, and is apt to be thrown up on the beach 
where it is found with its shell detached. 

‘The Paper Nautilus rises from deep water and swims on the sur¬ 
face. Between its feelers is a web, like that between the toes of web¬ 
footed birds, but much thinner. When there is a breeze it uses this 
for a sail and lets down some of its feelers alongside as oars (Fig. 15). 
If startled it can fill its shell with water and sink. As regards the 




30 Rise of Ancient Science 

formation of the shell, knowledge is not yet satisfactory. The shell 
does not appear to be there from the beginning but to grow as in 
other shell-fish. Nor is it ascertained whether the creature can live 
without its shell.’ 

The use by the Paper Nautilus of the membrane as a 
sail and of the arms as oars is now known to be a myth, 





Fig. 1 6 . Female of the Paper Nautilus, Argonauta Argo, swimming just 
below the surface of the water. The arrow shows the direction of movement. 
B is the parrot-like beak. Tr is the shell. Br. p is the base of one of the two 
special shell-carrying posterior arms. The other end of the arm is expanded 
into a wide membrane F. This membrane embraces the shell which can be seen 
extending beyond it both at Tr and at C, I'he membrane was supposed to 
form the ‘sail’ (see fig. 15). En is the funnel which projects between the two 
anterior arms Br, a. The animal moves by the force of a jet of water driven 
forth from the funnel. From Lacaze-Duthiers, 1892. 

though many excellent modern naturalists have believed 
it. The legend has earned for the creature its scientific 
name of ‘Argonaut’ (Argonauta argo\ the word meaning 
‘sailor of the Argo’, the ship on which Jason embarked in 
quest of the golden fleece. Belon (p. 89), a contemporary 
of Rondelet, gives a fine figure of the Argonauta with its 
membrane set as a sail and using its arms as oars 1 (Fig. 15.) 









Aristotle on Octopuses and their Allies 31 

Some of the questions asked by Aristotle about the 
Argonaut can now, after the fullness of time, be answered. 
It progresses neither by sailing nor rowing, but by ejecting 
a jet of water from its ‘funnel’ (Fig. 16). The shell is in no 
organic connexion with the body of the creature but is 
used as a sort of perambulator to support and aerate the 
developing young. Moreover, the animal does not will¬ 
ingly sink below the surface, and if forced to do so will 
rise again: it is indeed doubtful if it is able to sink at all 
by its own efforts. 

§ 8. Aristotle on Whales^ Porpoises, and Dolphins 

Aristotle had a clear idea of the nature of the great 
classes of animals, and he knew the important anatomical, 
physiological, and embryological differences between, for 
instance, the mammals, the class of animals to which man 
belongs, and the fishes. Thus he knew that mammals 
have lungs, breathe air, and have warm blood. He knew 
that they bring forth their young alive—that is to say, 
that they are viviparous —that they suckle their young, 
and that their young, while within their mother’s body, 
are attached to the womb by means of a navel-string and 
a structure now known as the placenta. He knew that 
none of these features are encountered in fishes. 

Knowing these things he separated the Cetaceans, that 
is to say the group of animals that contains the whales, 
dolphins, and porpoises, from the true fishes. He placed 
the Cetaceans near or with the mammals, but he was 
almost the only writer that did this for nearly two 
thousand years. In discussing the general nature of 
mammals Aristotle says 

‘Among viviparous ariimals are man, the horse, the seal, and other 
animals that are hair-coated and also, of marine animals, the ceta¬ 
ceans. These latter creatures have a blow-hole and are provided 
with lungs and breathe. Thus the dolphin has been seen asleep with 



32 The Rise of Ancient Science 

his nose above water, and snoring. The dolphin takes in water and 
discharges it through his blow-hole but he also inhales air into his 
lungs, so that if caught in a net he is quickly suffocated for lack of 
air. He can, however, live for some time out of water, but keeps 
up, all the while, a dull moaning sound. The cetaceans take in water 
only as incidental to their mode of feeding for, as they get their food 
from the water, they cannot but take it in. 

‘The dolphin and porpoise bear one at a time but sometimes two. 
The whale two at a time but sometimes one. These animals 
are provided with milk and suckle their young (Fig. 46, p. 90). The 
young of the dolphin grow rapidly, being full-grown at ten years 
of age. They bring forth their young in summer and never at any 
other season. The young accompany them for a considerable time 
and these creatures are in fact remarkable for the strength of their 
parental affection.’ [ythbreviated.] 

§ 9. On the Placental Dog-fish (^Galeos') 

Now in view of the difference in the normal mode of 
development of mammals (including Cetaceans) on the 
one hand and of fishes on the other, there is a certain 
observation by Aristotle that is most significant and 
worthy of further attention. Aristotle knew quite well 
that fishes usually differ from the mammals in being 
oviparous^ that is to say in bringing forth their young as 
eggs and not as independent moving creatures. But he 
knew that there is a group of fishes in a few of which the 
young are sometimes brought forth actively alive. This 
group he called the Selache^ and he tells us that it includes 
the sharks and rays. But among his Selache he knew of 
one form in which the resemblance to the mammals goes 
even farther than the mere production of lively young. 

Description of Fig. 17. 

J. Young free-swimming Mustelus ^vulgaris. B. Embryo of Mustelus laenjis 
with placental yolk-sac. C. Embryo of Mustelus lae^is with yolk-sac attached 
to uterus. D. Egg of Mustelus n^ulgaris viewed as a transparent object. E. 
Dissection of the lower end of uterus of Mustelus laevis showing relations of 
two placentae to uterine wall. 




*33 


unopened- 
yolk sac 
with umbilical 
cord attach* 


vesicular 
fbldinqsoP— 
wallor Ljolk 
sac 

cut wall oP— 
uterus 

lower end oF- 
uterus 



cut edge oF 
golksac 

main vessels 
oF yol k sac 

uolic sac 
^laidopeg 

branches oF 
vessels of yolk sac 
DR surface of 
Foetal placenta 



albuminous 

coat 


ryolk sac 
attached 
to embryo 


Fig. 17. Development of Aristotle’s placental dogfish (‘Galeos’) compared to that of 
an allied species. From Johannes Miiller, 1842. See note opposite. 


2613.3 




34 of Ancient Science 

In mammals the embryo before birth is connected with 
the mother’s womb by a cord. The point of attachment 
to the embryo can still be seen in the grown creature and 
is the navel. At the other end the cord is attached to the 
womb by a large flat organ, which is detached after the 
young is born and is therefore called the afterbirth^ other¬ 
wise known as the ‘placenta’. There are just a few ‘Sela- 
chia’—as scientific men now call Aristotle’s Selache —in 
which something similar takes place. 

Aristotle tells us that there is a shark-like fish called 
‘Galeos’ which, ‘as it were, lays eg^s within itself. These 
eggs being deposited in the womb acquire an attachment 
to it much like the placenta of a mammal. In the Galeos 
he tells us that 

‘the eggs shift into the womb and descend, and the young develop 
with the navel-string attached to the womb. As the egg substance 
gets used up the young is sustained, to all appearances, just as in 
mammals. The navel-string is long and adheres to the under part 
of the womb, each navel-string being attached to the womb by a 
sucker [i.e. placenta] and to the young in the place where the liver 
is. Each embryo, as in the case of mammals, is provided with separate 
embryonic membranes.’ 

Now this is a very extraordinary statement and one 
which seems at first sight most unlikely to be true. 
Naturalists for centuries passed it over or regarded it as a 
forgery. It attracted, indeed, very little attention until, 
in the middle of the nineteenth century, the great German 
naturalist Johannes Mtiller (p. 388) proved that Aristotle 
had been perfectly correct in his description. Mtiller 
showed that there are, in fact, a very few Selachia which 
in this respect resemble mammals. This was an amazing 
confirmation of an observation that had been made by 
Aristotle twenty-two hundred years before (Fig. lyj.i 

To prevent misunderstanding it should, however, be 

* Rondelet (Fig. 46, p. 92) in the sixteenth and Stensen in the seventeenth 
century made imperfect observations on similar lines. 



The Placental Dog-fish 35 

added that, though the placenta of Galeos bears a con¬ 
siderable resemblance to that of a mammal in both form 
and function, it is yet, in fact, derived from a different 
structure. The placenta of the mammal is derived from 
an embryonic structure known as the ‘allantois’, that of 
the Galeos from the yolk sac itself. The distinction will be 
made clearer if the reader will glance at Figs. 34, 63—4. 

§10. The Aristotelian Bee-master 

Other Greek naturalists besides Aristotle were occupied 
in observing and recording the habits of animals. Such 
a one was the author of a fine treatise on bees which is 
usually printed as part of Aristotle’s Historia animalium. 
It was evidently written by a practical bee-master. 

The author of this account does not understand the nature 
of the queen bee. He is uncertain whether that creature 
should be regarded as a male or as a female. We know 
now that the animals he calls the ‘ruler bees’ are females 
or queens, that the drones are males, and that the worker 
bees, though unable under ordinary circumstances to pro¬ 
duce any young are, in fact, females whose development 
has been arrested. This bee-master writes:— 

‘Very remarkable diversity is observed in the methods of working 
and general habits of bees. When the hive has been delivered to 
them clean and empty, they build their waxen cells, constructing 
the combs downwards from the top of the hive, and go down and 
down, linking the cells together until they reach the bottom. 

‘The cells, both those for honey and for the grubs, are double-doored, 
two cells being upon a single base, one pointing one way and one the 
other, after the manner of a double goblet. The two or three con¬ 
centric rows of cells at the commencement of the comb and at¬ 
tached to the hives, are small and empty of honey. The cells that 
are well filled with honey are most thoroughly luted with wax. 
The ordinary bee is generated in the cells of the comb, but the ruler 
bees in cells apart from the rest. There are six or seven ruler bees 
which grow in a way quite different from the ordinary brood. 



36 Rise oj Ancient Science 

‘The drones, as a rule, keep inside the hive. When they go out, 
they soar up in the air in a stream, whirling round and round in a 
kind of gymnastic exercise. This over, they come inside the hive 
and feed ravenously. The ruler bees never go outside the hive 
except with a “swarm” in flight, and during such a “swarming” all 
the other bees cluster around them. These rulers have the abdomen 
or part below the waist half as large again. They arc called by some 
“mothers” from an idea that they generate the [worker] bees. As 
proof, they declare that drones appear even when there is no ruler 
bee in the hive, but that the [worker] bees do not appear in his 
absence. Others, again, assert that the drones are male and the 
[worker] bees female. 

‘Bees gather the beeswax with their front legs, wipe it off on to the 
middle legs, and pass it on to the hollow curves of the hind legs. 
Thus laden, they fly home, and by their manner of flight one may see 
plainly that their load is heavy. On a trip the bee does not fly from 
a flower of one kind to a flower of another, but from one violet, say, 
to another violet, and never meddles with another flower until it has 
got back to the hive. 

‘Whenever the working-bees kill an enemy they try to do so out of 
doors. Bees that die are removed from the hive, and in every way 
the creature is remarkable for its cleanly habits. Away from the 
hive they attack neither their own species nor any other creature, 
but in the close proximity of the hive they kill whatever they get 
hold of. Bees that sting die from their inability to extract the sting 
without at the same time extracting their intestines. The bee may 
recover, if the person stung presses the sting out ; but once the bee 
loses its sting it must die.’ 

‘When the flight of a swarm is imminent, a monotonous and quite 
peculiar sound made by all the bees is heard for several days. For two 
or three days in advance a few bees are seen flying round the hive. 
When they have swarmed, they fly away and separate off to each of 
the rulers. If a small swarm happens to settle near a large one, it will 
shift to join this large one, and if the ruler whom they have aban¬ 
doned follows them, they put him to death. [Jhhreviated.] 

Save for the vagueness as to the sex of the rulers and of 
other kinds of bees, this account is admirable. 



( 37 ) 

§11. Aristotle on the Nature of Life 

We have so far considered Aristotle as a practical 
working naturalist. When, however, we come to consider 
the inferences and theories that he deduces from his obser¬ 
vations, we must feel that we are in the presence not only 
of an eminent naturalist but of a supremely great intellect. 

The most fundamental division among biologists is 
between the schools known as the Vitalists and the Mecha¬ 
nists. The diiference between the thinkers of these two 
groups turns on the nature of life (Latin, vita') itself. As 
Biology is the science or rather the group of sciences con¬ 
cerned with living forms, this question is of fundamental 
character. Nevertheless, it must be admitted that no 
great progress in this matter has been made since the 
time of Aristotle. The question as to the nature of life 
divides naturalists now as it did then. 

What is a vitalist ? The answer, so far as it can be 
given at this stage, is that a vitalist thinks that living 
things contain some principle of a quite peculiar nature 
and quite different from anything that is found in matter 
that is not living. A vitalist must further believe that 
this principle not only exists but has some manner in 
which it shows itself to us. A mechanist denies the truth 
of both these beliefs of the vitalist, and claims that all the 
actions and movements and activities of living things can 
be expressed as the outcome of forces which can be inves¬ 
tigated in matter that is not living. In this sense of the 
word there can be no doubt that Aristotle was a vitalist. 

Looking round for some word for the principle that 
differentiated living from not living substance, Aristotle 
hit, as we have seen, upon the word -psyche (p. 15). Now 
when he began to examine different living things he 
reached the conclusion that there were different kinds or 
orders of psyche or soul. He thus came to differentiate 
between a vegetative, an animal, and a rational soul. 



38 Kise oj Ancient Science 

The first or lowest was the vegetative soul. Aristotle 
regarded plants as the lowest living forms, and the qualities 
of life that he distinguished in plants he regarded as alone 
essential for this lowest form of soul. These qualities 
seemed to him to be nutrition, growth, and the power of 
reproduction. 

He considered that while animals had these qualities, 
they had also the power of movement, and the movements 
that they made seemed to correspond to what they felt. 
Animals then possessed, he thought, a second order of 
soul, to which he ascribed the sensitive and motive powers. 

Lastly, man had all these qualities exhibited by the 
lower creation, both plants and animals, but he had certain 
others. He could reason and his movements and actions 
were dictated by his thoughts. He was therefore equipped, 
in Aristotle’s view, not only with a vegetative and an 
animal soul but also with a rational or intellectual soul. 

This distinction between the vegetable or nutritive, 
the animal or sensitive, and the human or rational soul is 
to be found over and over again in the literature of all 
subsequent ages. It still lingers in popular speech, much 
in the same way as does the doctrine of the humours 
(p. 8). Thus, to give an instance, perhaps the most 
widely read scientific work of the Middle Ages was the 
treatise On the Properties of Things by a Franciscan monk, 
one Bartholomew of England, who wrote it about 1230. 
This work contains many references to the three kinds of 
soul of Aristotle. It was translated into English by a 
Cornishman, John of Trevisa (1326—1412), whose works 
are particularly interesting as specimens of early English 
prose. This translation was among the first books printed 
in London. It was produced by Wynkyn de Worde in 
1495 and is certainly one of the finest volumes published 
in England in the fifteenth century. In it we read: 

‘In divers bodies be three manner souls; Vegetahilis^ that giveth life 



Aristotle on Nature of Life 39 

and no feeling as in plants and roots; Sensibtlis, that giveth life and 
feeling and not reason in unskilfull beasts; Rationaiis, that giveth 
life, feeling and reason in men.’' 

Similarly, to this day, we speak of vegetative existence, 
of sensual feelings, of rational behaviour, all reminiscences 
of Aristotle’s point of view. 

vi But to return to Aristotle himself. Early in the course of 
his thinking he completely separated man from lower 
creatures. As his knowledge increased he seems to have 
become less inclined to make this distinction absolute. 
Indeed he came to admit that animals share to some 
extent with man in the possession of a rational soul. 
His final position demanded no fundamental distinction 
between life or soul, and mind. This is the position of 
an important school of modern biologists (pp. 426—9). 

It is probable that in ascribing to animals certain 
human qualities, Aristotle was influenced by his advance 
towards what would nowadays be called a belief in 
Evolution^ a topic that we shall have to discuss more fully 
later (ch. viii). It cannot be said that he ever definitely 
attained to the ‘evolutionary’ point of view. But it is evi¬ 
dent that he was moving in that direction, and perhaps if he 
had lived another ten years he might have reached it. But, 
whether we call him an Evolutionist or whether we deny 
him that title, it is yet quite easy to read an evolutionary 
meaning into some of his biological writing. To do so is 
to develop but not to force his meaning. 

In Aristotle’s biological works nothing is more remark¬ 
able than his efforts to get some sort of way of exhibiting 
the relationships of living things. The method that he 
actually adopts for doing this is to arrange them in a sort of 
scale, a scala naturae or ‘ladder of nature’, as the naturalists 
of a generation or two ago would have called it. This scala 


* Spelling partially modernized. 



40 Rise of Ancient Science 

naturae of Aristotle, as the earliest of its kind, is a subject of 
great interest and is worthy of all possible respect (Fig. 18). 
This is how he describes it: 

‘Nature’, he says, ‘proceeds little by little from things lifeless to 
animal life in such a way that it is impossible to determine the exact 
line of demarcation, nor on which side thereof an intermediate 


MAN 

VIVIPAROUS QUADRUPEDS 
CETE 
OVIPARA 
MALACIA 
MALACOSTRACA 
ENTOMA 
OSTRACODERMA 



* Mammals 
= CiTtaccanr 

= Reptiles; Dlrds.Ampihlhans’ 

- CephaU^pedS’ 
s Crustaceans 
= Other Arthropods' 
s Other Molluscs' 

* Asadiansetw'. 

» Hololhunans’retc. 
s Sponges 


TETHYA 

HOLOTHURIA 

SPONGIAE 


''' 

Fig. i8. The ^cala Naturae or ‘ Ladder of Life ’ according to the descriptions 

of Aristotle. 



form should lie. Thus, next after lifeless things in the upward scale 
comes the plant. Of plants one will differ from another as to its 
amount of apparent vitality. In fact the whole of plant-kind, 
whilst devoid of life as compared with animal-kind, is endowed with 
life as compared with other forms of matter. Indeed there is in 
plants a continuous scale of ascent towards the animal. Thus one 
is at a loss to say of certain beings in the sea whether they be 
animal or vegetable.’ 

‘A sponge completely resembles a plant, in that it is attached to a 
rock, and that when separated from this it dies. Slightly different 
from the sponges are certain other sea creatures, the Holothurians 
which, though free and unattached, yet have no feeling, so that their 



Aristotle on Nature of Life 41 

life is but that of a plant separated from the ground. For even 
among land-plants there are some that are independent of the soil— 
or even entirely free. Such, for example, is the plant which is 
found on Parnassus, and which some call the Epipetrum [i.e. the 
common house-leekj. This you may hang up and it will yet live for 
a considerable time. It is therefore sometimes a matter of doubt 
whether a given organism should be classed with plants or with 
animals. Thus there are the Tethya^ marine organisms that so far 
resemble plants as that they never live free and unattached, but, on 
the other hand, inasmuch as they have a certain fleshlike substance, 
they must be supposed to possess some degree of sensibility.’ 

‘The Acalephae or “Sea-nettles” lie outside the recognized groups. 
Their constitution, like that of the Tethya^ approximates them on 
the one side to plants, on the other to animals. Some can detach 
themselves and can fasten on their food, and they are sensible of 
objects which come in contact with them, and in this sense they 
have an animal nature. Yet they are closely allied to plants, firstly 
by the imperfection of their structures, secondly by being able to 
attach themselves to the rocks, and thirdly by having no visible 
residuum (after drying) notwithstanding that they possess a mouth.’ 
‘Thus Nature passes from lifeless objects to animals in such un¬ 
broken sequence, interposing between them beings which live and 
yet are not animals, so that scarcely any difference seems to exist 
between two neighbouring groups owing to their close proximity.’ 
[Abbreviated from several passages,^ 


§ 12. Classification of Animals derivedfrom Aristotle 

Aristotle does not make any formal classification of 
animals. But scattered through his works are many 
terms employed in a way which suggests that they might 
be developed for classificatory purposes. By examining 
his definitions of these terms we are enabled to draw up 
the arrangement of animal forms which we may reason¬ 
ably regard as the Aristotelian classificatory scheme. With 
his great interest in reproduction, this must be based 
primarily on the process of generation. 



42 

ENAIMA == VERTEBRATES 

(Having red blood and either viviparous or oviparous) 

1. Man. 

2. Cetaceans. 

3. Viviparous quadrupeds. 

(^7) Ruminants with cutting teeth in 

lower jaw only, and with cloven 
hoofs = Sheep, Oxen, &c. 

(^b) Solid-hoofed animals = Horses, 
Asses, &c. 

(c) Other viviparous quadrupeds. 

4. Birds. 

(a) Birds of prey with talons. 
(i)"Swimmers with webbed feet. 

(r) Pigeons, doves, &c. 

(d) Swifts, martins, &c. 

(e) Other birds. 

5. Oviparous quadrupeds Amphibians 
and most Reptiles. 

6. Serpents. 

7. Fishes— 

[a) Selachians = Cartilaginous fishes 
(‘Galeos’ an exception.) 

(^) Other fishes. 

ANAIMA = INVERTEBRATES 

(Without red blood and viviparousy vermiparous, budding or 
spontaneous) 

With perfect eggs . /8. Cephalopods. 

1^9. Crustaceans. 

With eggs of special 10. Insects, spiders, scorpions, &c. 
type. 

With generative ii. Molluscs (except Cephalopods), 

slime, buds, or spon- Echinoderms, &c. 

taneous generation. 

With spontaneous 12. Sponges, Coelenterates, &c. 
generation. 




Classification derived from Aristotle 43 

Some of the elements in this classification are funda¬ 
mentally unsatisfactory in that they are based on negative 
characters. Such is the group of Anaima which is 
paralleled by our own equally convenient yet negative 
and biologically meaningless equivalent Invertebrata. It 
is but fair to remember that even this term Invertebrata 
held a meanihg to naturalists up to about fifty years ago 
(p. 293). Other Aristotelian groupings, such as the sub¬ 
divisions of the viviparous quadrupeds, can only be some¬ 
what forcibly extracted out of Aristotle’s text. But there 
are yet others, such as the separation of the cartilaginous 
from the bony fishes, that exhibit true genius and betray a 
knowledge that can only have been reached by careful 
investigation. Remarkably brilliant, too, is his treatment 
of Molluscs. 

In our modern systems of classification we employ 
certain technical terms which are of Greek or Latin 
origin. The most important of these are the words genus 
and species, two words which are simply Latin translations 
of Greek words used by Aristotle. We owe our idea of 
the species in modern biology directly to Aristotle. Our 
use of the word genus differs considerably from his, but 
there can be no doubt that it also is rooted in his works. 
We shall consider the conceptions of genus and species 
later (pp. i75fF.). 

Aristotle was not content with investigations of the 
structure and habits of animals in the field which we nowa¬ 
days call ‘Zoology’. He wrote also works on the functions 
of the organs and parts of the body, that is on Physiology, 
and also, perhaps, on Botany. In the former subject, 
Physiology, it must be confessed that his efforts were less 
successful than in Zoology. He was not, in fact, an 
experimenter but rather an observer, and he had no exact 
body of knowledge of experimental physics and chemistry 



44 -Rw oj Ancient Science 

on which to build. Some of his successors among the 
Greeks, for example Galen (p. 59), far excelled him 
here. We shall therefore pass over Aristotle’s physiological 
views. His theory of the nature of generation, however, 
is of great importance and is considered in detail else¬ 
where (p. 497). 

No botanical treatise by Aristotle has come down to us. 
We have, however, very full botanical works by his pupil 
and successor as head of the Lyceum, Theophrastus, to 
whose work we now turn. 

§ 13. Theophrastus{c. 2,^0—B.c.)iindhis Botanical Works 

Theophrastus was born about 380 on the island of 
Lesbos, where perhaps Aristotle first met him. Leaving 
his native land he went, like his master, to Athens and 
there, like him, he attended first the school of Plato. 
Later he transferred to the Lyceum. He became devoted 
to Aristotle and carried on his teacher’s work after Aris¬ 
totle had left Athens for the last time. This affection for 
Aristotle expresses itself in his will, in which he inserted 
special clauses for the preservation of the busts of his 
master. It is not improbable that it is to this clause that 
we owe the survival of a portrait bust of Aristotle 
(Frontispiece). 

The whole active life of Theophrastus may be said to be 
a commentary on Aristotle. He had not his master’s 
vast attainments, but his abilities were good, his industry 
very great, and his interests wide. He lived to a very 
advanced age, dying in the year 287 b. c. not far from a 
hundred years old. His writings covered a wide range of 
subjects, but we are concerned only with the biological 
works. These are devoted to Botany, which is the more for¬ 
tunate in that no botanical work of Aristotle has survived. 

Theophrastus has left what are usually called two 
treatises on Botany. One of them, however, which is by 



Theophrastus 45 

far the more interesting of the two, the so-called History 
of Plants^ is in fact not one work, but a collection of works. 
One part of this collection is really a scrap-book made up 
of such folk-lore about plants as was going about in the 
time of Theophrastus. It is a very entertaining book and 
it is important too, for our purpose, as showing the in¬ 
ferior kind of material on which scientific men of the day 
had to build. We have seen how, in the Hippocratic 
works, plants are onlyconsideredfor their uses in medicine. 
In this Theophrastian scrap-book we are told a little more 
about them but in a most superstitious and gossiping 
vein. A few anecdotes from the book are worth relation. 

We learn a good deal about the gathering of drugs 
from the botanical collections of Theophrastus, for they are 
essentially practical works. Thus we hear how frankin¬ 
cense and myrrh are collected. The story tells how certain 
travellers landed to look for water while on a coasting 
voyage from the ‘Bay of Heroes’ on the coast of Arabia. 
They saw the gums being collected. 

‘They reported that incisions were made on the stems and branches 
to extract gum. Palm leaf mats were sometimes put underneath, to 
collect the resin. The whole mountain range in that region, they 
said, is under the sway of the Sabaeans. These people are honest 
in dealing with one another. Myrrh and frankincense arc collected 
from all parts into the Temple of the Sun which is very sacred and 
guarded by armed Sabaeans. Here each man piles up his store. On 
his pile he puts a tablet stating the measure and the price. When 
the merchants come they look at the tablets and, whichever pile 
pleases them, they put down the price on the spot. Then the priest 
takes a third part of the price for the god and leaves the rest. This 
remains safe for the owners till they claim it. The sailors, however, 
greedily took some of the frankincense and myrrh when no one was 
about and sailed away.’ \Ahhrevtated,'\ 

There are many such travellers’ tales. A number of 
the accounts of plants, morever, are the merest superstition. 



46 Rise of Ancient Science 

These yarns Theophrastus had evidently collected not 
because he believed in them but because he thought that 
these idle notions might themselves have some interest 
—as indeed they have to the student of folk-lore. Here 
is such a story : 

‘Druggists and herb diggers enjoin that in cutting certain roots one 
should stand to windward. Thus if you cut thapsia, feeing other than 
windward, your body will swell up. Again, some roots should be 
gathered at night, others by day, and yet others, as for instance 
the honeysuckle, before the sun strikes them. Hellebore makes the 
head heavy, and men therefore cannot dig it up for long unless 
they first eat garlic and take a draught of wine. The peony should 
be gathered by night, for, if a man is seen by a woodpecker while 
collecting the fruit, he is in danger of going blind. While cutting 
fever-wort beware of the buzzard-hawk.’ \Ahhreviated.'\ 

There is much nonsense of this sort. Students of folk¬ 
lore have found superstitions of a like kind among 
English and continental peasants. It is a debated question 
to what extent such beliefs are really native and to what 
extent they are merely further degraded forms of classi¬ 
cal material of this type. 

But we must turn from such gossip to the serious 
work of Theophrastus. He had not the inspiration of 
Aristotle. Being mainly an observer and collector of facts, 
rather than a great theorizer, he suffered especially from the 
lack of technical scientific terms. To describe accurately a 
plant or even a leaf in the language in ordinary use would 
often take pages and tax the powers of a first-class descrip¬ 
tive writer. Modern botanists have invented an elaborate . 
terminology that took its origin with Jung (p. 180), the 
use of which saves a vast amount of mental and clerical 
labour. This question of scientific nomenclature among 
the Greeks has already been touched upon (p. 24). 

There are cases in which Theophrastus seeks to give 
a special technical meaning to words in more or less 



Theophrastus 47 

current use. Among such words are carpos = fruit, peri- 
carpion = seed vessel ==^pericarp^ and metra^ the word used 
by him for the central core of any stem whether formed of 
wood, pith, or other substance. It is from the usage of 
Theophrastus that the botanical definitions of fruit and 
pericarp have come down to us. 

We may easily discern also the purpose for which he 
introduced into botany the term metra —a word meaning 
primarily the womb —and the vacancy in the Greek lan¬ 
guage which it was made to fill. 

‘Metra’, he says, ‘is that which is in the middle of the wood, 
being third in order from the bark and thus like to the marrow 
in bones. Some call it the hearty others the inside^ yet others call 
only the innermost part of the metra itself the hearty while others 
again call this marrow 

He is thus inventing a word to cover all the different 
kinds of core and importing it from another study. This 
is the method of modern scientific nomenclature which 
hardly existed for botanists even as late as the sixteenth 
century of our era. 

Theophrastus understood the value of developmental 
study, a conception derived from his master. 

‘A plant’, he says, ‘has power of germination in all its parts, for it 
has life in them all, wherefore we should regard them not for what 
they are hut for what they are becoming,'* 

The various modes of plant reproduction are dis¬ 
tinguished by Theophrastus thus: 

‘The manner of generation of trees and plants are these: (1) spon¬ 
taneous, (2) from a seed, (3) from a root, (4) from a piece torn off, 
(5) from a branch or twig, (6) from the trunk itself, or (7) from 
pieces of the wood cut up small.’ 

The marvel of generation, of how plants and animals 
come into being, must have awakened admiration from 



48 Rise of Ancient Science 

an early date. We have seen it occupying the attention 
of Aristotle. He, like Theophrastus and like all naturalists 



Fig. 19. Development of Dicotyledon. The germination of the bean from 
Malpighi (1679). ^ ^he root is just appearing, c shows the seedling in 

section, e is cf in section with the cotyledons removed. On the rootlets of i 
are seen the root nodules, and on its stem the first axillary buds. Root hairs are 
shown in d, f, and /. For the nature of the root nodules see p. 380. 


until the seventeenth century, believed in the existence of 
spontaneous generation in plants and in lower animal 
forms. That is to say, they believed that plants and 
animals could arise without the intervention of parents. 



Theophrastus 49 

anew, out of matter that could not be regarded as living. 
How could they believe otherwise ? These men were 
without microscopes and without the means of minute 



Fig. 20. Development of Monocotyledon. 7 'he germination of a grain of 
wheat from Malpighi (1679). e is the last of the series. Inf-h the monocotyle- 
donous character is apparent. In e branches are appearing. *The multiple 
character of the rootlets’, on which in cereals Theophrastus lays stress, is 
apparent throughout from b to f. Root hairs are seen throughout. 

investigation to which the advances of modern times 
have accustomed us. All antiquity believed in sponta¬ 
neous generation, and the destruction of that belief is 
one of the most important advances made by modern 
biology. It is a subject to which we shall have presently 
to return (chap. xii). 

In his description of the process of germination, Theo- 


50 Rise of Ancient Science 

phrastus has left us his views on the formation of the 
plant in the seed. It is the first account of the subject on 
record and the best that was made until the seventeenth 
century of the Christian era. 

‘In some plants [Dicotyledons] root and leaves germinate from the 
same point and in some [Monocotyledons] from opposite ends of 
the seeds. 7 'hus in the bean and other leguminous plants [Dicoty¬ 
ledons] the root and stem arise from the same point, namely their 
place of attachment to the pod. Wheat and barley and such cereals 
[Monocotyledons], however, germinate from opposite ends corre¬ 
sponding to the position of the seed in the ear, the root from the 
stout lower part, the shoot from the upper. 

‘In all leguminous plants the seeds have plainly two lobes and are 
double. As the bud germinates within the seed and increases in size, 
the seeds split. All such seeds arc in two halves [Dicotyledons]. 
I n cereals, however, the seeds being in one piece, this does not happen, 
but the root grows a little before the shoot [Monocotyledons]. 
‘Barley and wheat [Monocotyledons] come up with one leaf, but 
peas, beans, and chick peas with more leaves [Dicotyledons]. All 
leguminous plants have a single woody root, from which grow 
slender side roots [Dicotyledons]. Wheat, barley, and other 
cereals, however, have numerous slender roots which are matted 
together [Monocotyledons]. There is thus a contrast between 
these two kinds, for the leguminous plants have a single root and 
many side growths above from the single stem [Dicotyledons], while 
the cereals have many roots and send up many shoots, but these have 
no side shoots [Monocotyledons].’ 

Can there be any doubt that we have here an excellent 
piece of first-hand observation on the behaviour of ger¬ 
minating seeds ? The distinction between the dicotyle¬ 
dons and the monocotyledons (which we have indicated 
by the words in brackets) is quite clearly set forth, though 
the emphasis on various points is not quite what we 
should make to-day. The observations are, however, 
accurate and clear and might be used in company with 



Theophrastus 51 

the plates of a modern text-book. In fact the figures of the 
seventeenth-century naturalist Marcello Malpighi, whom 
we shall presently discuss (p. 151), illustrate this passage 
from Theophrastus admirably. The reader is advised to 
keep his eye on the beautiful figures of Malpighi (Figs. 



Fig. 21. Assyrian bas-relief from the walls of the palace of Assur-nasir-paJ 
(885-860 B.C.), discovered at Calah (Nimrud) by Sir Henry Layard and now 
in the British Museum. 

Supernatural figures hold in the right hand the male inflorescence of the 
date palm. They shake these inflorescences over a conventionalized repre¬ 
sentation of the female palm, the form of which can be realized if the ornamenta¬ 
tion around it be disregarded. This ornamentation perhaps itself represents 
a series of palm trees. In that case we may interpret the central structure 
as a male tree standing in a grove of female trees. 


19 and 20) while re-reading this account by Theophrastus 
of the manner of germination of Monocotyledons and 
Dicotyledons. 

There is one very peculiar aspect of the question of 
generation of plants to which we shall now call attention. 
In ancient writings, plants are frequently described as male 






52 Rise of Ancient Science 

and female, and one writer, Pliny (a.d, 23—79, pp. 57—9), 
went so far as to say that some considered that all plants 
had sex. This sounds very modern, but examination of 
passages in ancient writings that refer to sex in plants 
shows that the so-called ‘males’ and ‘females’ are usually 
different species. In a few cases a sterile variety is de¬ 
scribed as the male and a fertile as the female. The real 
distinction between male and female parts of plants was 
not understood till modern times (pp. 500-11). 

In the case of date palms, however, in which the male 
and female organs are found on different trees, instead 
of being on the same tree or combined in the same flower, 
the nature of the difference between the two types of 
flower, male and female, was really grasped by Theophras¬ 
tus and by other ancient writers. 

‘With dates,’ says Theophrastus, ‘the males should be brought to the 
females, for the male makes them ripen and persist. When the male 
is in flower it is the custom to cut off the spathe with the flower and 
shake the dust over the fruit of the female. If treated thus the fruit 
is not shed.’ 

This is a description of the artificial fertilization of the 
palm tree which was known to the ancient Babylonians 
and Egyptians as well as to the Greeks, and is still em¬ 
ployed in the E-ast. It was in fact practised centuries 
before Theophrastus (Fig. 22). 

Fig. 22. ‘Aristotle’s Lantern’, the five-rayed 
mouth-parts of the sea-urchin. 



II 


DECLINE AND FALL OF ANCIENT SCIENCE 

§1. Foundation of the Alexandrian School {about 300 b.c.) 

T he Athenian scientific school virtually came to an 
end in the generation after the death of Alexander 
in 323 B.c. His Empire broke up (Fig. 23), and Athens 
ceased to be an important centre. The different parts of 
the Empire of Alexander were seized by his generals. 
Egypt fell to Ptolemy. He founded a dynasty which 
reigned for nearly three hundred years. The last of the 
Ptolemaic sovereigns was Queen Cleopatra, who died in 
the year 30 b.c. These Ptolemaic sovereigns took much 
interest in science. The first established the learned tradi¬ 
tion. The second instituted a library and museum at 
Alexandria, a city that had been founded and named after 
the great pupil of Aristotle. This city now became the 
centre of the scientific world. Learned men flocked to it 
and were supported by funds specially provided by the 
Ptolemaic rulers. 

It was at Alexandria that Anatomy first became a 
recognized discipline. We may distinguish a definite 
‘Alexandrian period’ in the history of science. It covers 
the last 300 years before the Christian era. Unfortunately 
the biological works of the Alexandrian school during 
the Ptolemaic period have perished. We have, however, 
fragments of the writings of two biologists of the time, 
Herophilus and Erasistratus. 

The first important biological teacher of the school of 
Alexandria was a Greek, Herophilus {c. 280 b. c.). It was 
he who began to dissect the human body and to com¬ 
pare its structure with that of animals. He recognized 
the brain as the centre of the nervous system, and he 



54 Decline and Fall of Ancient Science 

regarded it as the seat of the intelligence. There are 
several parts of the brain which still bear the names which 
Herophilus gave them. One part, which he called the 
wine-press, in Latin torcular, is spoken of by anatomists to 
this day as the torcular of Herophilus. It is the meeting-place 
of four great veins at the back of the head, which gave 
rise, as was thought, to a circular or whirling movement 
of the blood. 



Herophilus made the first clear distinction between 
arteries and veins. He observed that the arteries pulsate 
vigorously while the veins do so little if at all. Hero¬ 
philus did not, however, ascribe this movement of 
the arteries to the action of the heart, but considered it to 
be a natural movement of the vessels themselves. 

About contemporary with the anatomist Herophilus 
was the physiologist Erasistratus, who was also a Greek 
and also taught at Alexandria. The physiology of Erasis¬ 
tratus was based on the idea that every organ is made 
up of a three-fold system of vessels—^veins, arteries, and 
nerves. In those days, and for long after, the nerves were 
wrongly regarded as hollow. It was thought that their 
cavities convey something material, the hypothetical 








Alexandrian School 55 

nervous fluid, in much the same way as the arteries and 
veins convey blood (see p. 355). 

Erasistratus, like Herophilus, paid particular attention 
to the brain. He distinguished between the main brain, 
the so-called cerebrum, and the lesser brain, the so-called 
cerebellum. He observed the convolutions in the brain of 
both men and animals, and associated their greater com¬ 
plexity in man with his higher intelligence. He made a 
number of experiments on animals. By their means he 
distinguished between the anterior nerve-roots of the 
spinal cord, which convey the impulse of motion to the 
muscles, and the posterior roots, which convey the im¬ 
pressions from the surface of the body, some of which 
are felt as sensations (Fig. 155, p. 416). 

§ 2. Beginnings of Scientific Plant Illustration (50 b.c.) 

After the death of Cleopatra, in 30 b.c., Egypt passed 
completely under the power of Rome, and became a 
Roman province. The school of Medicine in Alexandria 
continued for some hundreds of years but steadily lost 
its vitality. Indeed, with the advent of Roman rule 
almost all departments of science languished. 

Apart from anatomy and physiology, there was only 
one aspect of biology in which any advance was made 
under the Roman Empire. This was Botany. With the 
cessation of scientific curiosity, medical men remained 
the only class who took any interest in Nature. For the 
purposes of their work they needed many drugs which 
they obtained from plants. Now one of the difficulties 
in dealing with these plants was that of identification of 
the different kinds. Since there was as yet hardly any 
special scientific terminology, plants were most easily 
identified by means of pictures. 

The art of botanical drawing began to be practised to¬ 
wards the end of the first century b.c. Copies of figures of 



56 Decline and Fall of Ancient Science 

that period have come down to us with the name of the 
artist,Crateuas,attached to them. This Crateuas was a herb- 
gatherer as well as an artist, and his drawings are peculiarly 



Fig. 24. ‘Round Aristolochia’, Fic. 25. ‘Argemone’, 

Aristolochiapallida. Adonis aesti'valis. 

Plants drawn by Crateuas about 100 B.c. and copied about a.d. 500. 


interesting as introducing a new art that was combined 
with real study of Nature (Figs. 24-5). The effect of this 
combination is to be discerned also in the decorative art of 
the early Roman Empire, and especially in those works 
which were executed under the first and greatest of the 
Roman Emperors. In this so-called ‘Augustan’ art we 




Plant Illustration 57 

often see peculiarly close and accurate studies of animal and 
plant forms of a kind quite different from that encountered 
in the earlier and better known Greek art. 

§3. Dioscorides and Pliny {1st century j.d.). 

Along with the development of the Roman Empire 
(Fig. 28) came greatly improved means of communication 
and an increase in the complexity of life. Medical services 
became organized, especially in connexion with the army, 
and the traffic in drugs became regulated. The old 
difficulty of identification of plants repeatedly cropped up. 
Special works were prepared to aid in identification. The 
best-known of these was by Dioscorides, an Asiatic Greek 
military surgeon in the army of the Emperor Nero. 

The work of Dioscorides exercised great influence on 
the ages which followed, and is to be traced into modern 
botany. Many names which he used are still employed 
by botanists. His descriptions though always short are 
occasionally good and often include the habit and locality 
of the plant. Dioscorides is recognized as one of the 
founders of botany. 

Despite the descriptions of Dioscorides, there was still 
difficulty in identifying some of the plants in his drug 
list. At a very early date, therefore, and probably 
during his lifetime, copies of the herbal of Dioscorides 
were prepared with pictures of the plants described. 
Thus the work of Crateuas, begun in the previous century, 
was extended (Figs. 26-7). 

In the same century as Dioscorides, the Greek natu¬ 
ralist, there lived and worked the Roman naturalist, Pliny, 
a man of an entirely different character and outlook. 
Pliny was a well-born gentleman, and an able and efficient 
civil servant. He was a man of immense industry with 
an enthusiasm for collection. He did not, however, collect 
natural history objects, but only information or rather 



58 Decline and Fall of Ancient Science 

misinformation about them. He put together a vast number 
of extracts from works concerning every aspect of Nature. 
These he embodied in his famous book on Natural History. 
Unfortunately, Pliny’s judgement was in no way compar- 



Fig. 26, Erodium malachoides, Fic. 27. Geranium molle. 

Figures from the so'called ‘Juliana Anicia Manuscript’ of Dioscorides written 
in Byzantium a. D. 512. These figures are from originals probably contem¬ 
porary with or not much later than Dioscorides himself. 

able to his industry. He was excessively credulous. Thus his 
work became a repository of tales of wonder, of travellers’ 
and sailors’ yarns, and of superstitions of farmers and 
labourers. As such it is a very important source of informa¬ 
tion for the customs of antiquity, though as science, judged 
by the standards of his great predecessors, such as Aristotle 
or Theophrastus or Erasistratus, it is simply laughable. 
Despite the low quality of his material, Pliny’s work was 



Dioscorides and Pliny 59 

widely read during the ages which followed. He was the 
main source of such little natural history as was studied for 
a thousand years after his time. Many common supersti¬ 
tions have thus passed into current belief from Pliny. 

One idea which comes down to us direct from Pliny 
is very commonly encountered among ignorant people. 
It is the belief that every animal, plant and mineral has 
some use\ that is to say, was formed for the benefit of 
man. Not infrequently one hears ignorant people ask 
‘What is the use of flies ‘What were stinging-nettles 
made for.?’ and so on. Such questions are based upon 
an obsolete and untenable view of the world. They ignore 
altogether the fact that flies and stinging-nettles have 
their own lives, which they live without regard to human 
beings; that they or their like existed before man appeared 
upon the earth and that they may continue to exist after he 
has ceased to be. They ignore the biological point of view, 
but express admirably the point of view of the gullible, 
foolish, and industrious Pliny of nineteen hundred years 
ago. 

§4. Galen 130-200) 

After Pliny there was only one important biological 
investigator in antiquity. This was the physician, Galen. 
He was born at Pergamum in Asia Minor. Pergamum 
and Alexandria were the two rival seats of learning in 
later antiquity. At fifteen Galen was attending philoso¬ 
phical lectures. At sixteen he began to study medicine in 
his native town. Long before he was twenty he appeared 
as an author, and he remained a very industrious writer 
throughout his life. The bulk of his works is enormous, 
and they cover every department of medicine. 

When Galen was twenty he went travelling for study, 
as was the custom in his day. Among the many places 
that he visited for this purpose was Alexandria, where 



6 o Decline and Fall of Ancient Science 

he learned anatomy at the medical school. When he was 
twenty-eight he returned to his native city, where for four 
years he acted as surgeon to the gladiators. In a. d. i6i, 
when the great philosopher-emperor, Marcus Aurelius, 
had recently come to the throne, Galen migrated to Rome 
to seek his fortune, as many of his countrymen were 
doing. He was soon called to be physician to the emperor 
himself. At the same time his eminence as an anatomist 
and physiologist became recognized. Crowds came to 
his lectures on these subjects, on which he composed 
several important works. 

Galen did not dissect the human body. He had, 
however, frequently dissected the bodies of animals. 
Thus he examined the structure of sheep, oxen, pigs, dogs, 
bears, and many other creatures. He perceived the re¬ 
semblance between the anatomy of the human body and 
that of monkeys. Many of his anatomical descriptions 
which are intended to refer to the human subject are, in 
fact, taken from an examination of the body of the 
so-called Barbary ape. This animal is the only ape still 
existing in a wild state in Europe. It is found now only 
on the rock of Gibraltar, where a very few still roam at 
large. In Galen’s time it was, however, commoner, and 
he had little difficulty in getting specimens. The animal 
is not unlike the little monkeys that are often carried 
by organ-grinders, Galen’s descriptions of the muscular 
system are almost entirely taken from the Barbary ape. 
In addition to the muscles, Galen gave good descriptions 
of the bones and joints, and some of the terms that he 
employed are still in use by anatomists. 

Besides describing the structure of animals, Galen did 
a good deal of work on the functions of their organs. In 
other words, he was a physiologist. Thus he investigated 
the functions of the spinal cord, and he sought to find out 
what were the purposes served by the act of breathing, 



Galen 61 

and by the movements of the heart. Among the curious 
errors that he made in the course of these inquiries, we 
may mention his belief that air enters the heart direct 
from the wind-pipe, and that blood passes from one side 
of the heart to the other through the septum between the 
ventricles (Fig. 58, p. 105). 



Fig. 28. The Roman Empire at its greatest extent, about a.d. ioo. The towns 
marked were the main centres of learning at the time. 


Galen so impressed the men of his time and of suc¬ 
ceeding ages that for centuries his works were regarded 
as almost infallible. No detail which he mentioned was 
allowed to be altered, and all the errors that he made 
were passed on to the men of the ages which followed him. 
On the other hand, his works were too long and too 
difficult for general study. Thus, whilst his errors were 
remembered, much of the excellent work which he did 
was forgotten. The anatomy and physiology of the ages 
which followed represent a progressive deterioration from 
the standard of Galen, whose best works were gradually 
lost or allowed to fall into oblivion. 

























































62 DecJme and Fall of Ancient Science 

Some explanation is necessary of the extraordinary re¬ 
spect in which the works of Galen were held during the 
Middle Ages. The reason is Galen’s religion. At the 
end of the second century of the Christian era, when 
Galen was at work, the influence of Christianity was 
making itself generally felt in the Empire. Now Galen, 
though he remained a pagan, developed on his own 
account a religion which was not unlike early Christianity 
or Judaism. He believed in one God and he had read 
some of the books of the Bible. Moreover, he speaks 
with some benevolence of Christianity, and he mentions 
certain biblical characters by name. He developed the 
idea that every organ in the human body was created by 
God in the most perfect possible form, with a view to the 
end that God had in mind for the use of that organ. This 
attitude fitted in well with that of the Christianity of his 
time and of the ages which immediately followed. It 
explains the immense respect in which the name and 
works of Galen were held for fifteen hundred years. In 
the Middle Ages it was even believed that Galen had 
been converted to Christianity. 

§ 5. The Dark Ages ( a . d . 200—1200) 

After Galen we encounter no biological activity for 
many centuries. There are some who expand the views of 
Galen, but they add nothing to him—except misunder¬ 
standing! The credulous Pliny, the most read of all the 
ancient writers, is constantly copied and his text as con¬ 
stantly corrupted. Ecclesiastical authors, with edification 
'klways in view, produce moralized and sometimes illus¬ 
trated animal stories which exhibit no intelligent observa¬ 
tion and are often childish to the verge of imbecility. The 
least fantastic of these productions are perhaps the so- 
called ‘manuscript herbals’. 

Dioscorides was now the favourite herbal author. He 



The Dark Ages 63 

wrote in the Greek language understood by every educated 
man in the earlier centuries of the Roman Empire. As 
time went on, Greek became neglected in the west of 
Europe. For learned purposes it was replaced by Latin. 
Greek herbals were therefore translated. The work was 
done slavishly and with no improvement on the original. 
The figures too were copied from hand to hand, getting 
worse and worse and more and more formal at each stage. 
Finally they became unrecognizable. Nevertheless this 
unintelligent process continued until the sixteenth century. 

The remarkable thing about all this copying was that 
neither the artist nor the scribe who wrote the text ever 
thought of looking for himself at the organisms he was 
describing. Thus, even the commonest plants, such as the 
strawberry (Figs. 29-30), are described and drawn in the 
most conventional way. This period of entire absence of 
observation we may rightly describe, so far as science is 
concerned, as the Dark Ages. The Dark Ages in Science 
last for at least a thousand years—from the death of Galen 
till the thirteenth century. 

The causes of the decline of ancient science have 
often been discussed. The beginning of the process goes 
back very far. We can notice a definite change for the 
worse between the writers of remoter antiquity such as 
Hippocrates, Aristotle, and Theophrastus, and those of 
the Alexandrian and Roman schools, such as Herophilus, 
Pliny, and Galen. 

What caused this deterioration } It was, perhaps, con¬ 
nected with the fact that, at about the time of the death of 
Aristotle, the Greek states lost their independence. The 
habit of seeking knowledge for its own sake—‘science’ as 
we now call it—^had been the peculiar creation of the 
inhabitants of certain small Greek states. Of these Attica, 
with its capital, Athens, was the chief. As these ceased to 
be independent, their citizens also lost their independence 



64 Decline and Fall oj Ancient Science 

of thought. The scientific habit was transported to foreign 
soil and deteriorated in the process. 

Nevertheless science lived on at Alexandria and at 
Rome. Not until the death of Galen did it cease to exhibit 



Fig. 29. Strawberry from a South French herbal, c. a.d. 550. The 
‘runners’ are represented in excessive numbers. The characteristic 
arrangement of leaves in threes is exaggerated to fours and fives as in 
the nearly allied cinquefoil. 

signs of activity. What was the cause of this cessation.? 
It is a question to which various answers have been given. 

It has often been said that the rise of Christianity was 
destructive of science. This view is untenable for two 
main reasons. On the one hand, science had begun its 
downward course long before the birth of Christianity. 
On the other hand, at the end of the second century of the 
Christian era, when ancient science was effectively dead. 



The Dark Ages 65 

the Christians formed still only a small and obscure sect, 
that had little or no influence in that class which might be 
expected to study science. It is true that the intense 
spiritual interest of Christianity in the early centuries did 



Fig. 30. The same plant as in Fig. 29 after many copyings as it appears 
in a Rhenish herbal c. lo^o. I'he ‘runners' have become thorns and the 
plant confused with a blackberry. 

nothing to promote science, and later discouraged any re¬ 
vival of science. It is, however, untrue to say that the rise of 
Christianity had any definite relation to the fall of science. 

A much more efficient factor in the destruction of 
ancient science was the habitual mental attitude of the 
ruling class in the Roman Empire. The Romans were 
essentially a practical people. Their best energies were 
devoted to ordering and governing their Empire. They 


66 Decline and Fall oj Ancient Science 

produced great military leaders, great lawyers, great en¬ 
gineers. Such practical men seldom appreciate theoretical 
investigations. Now, whereas Science can be applied to 
the practical matters of life, yet this application is not in 
itself Science. Science cannot flourish without purely 
theoretical investigations undertaken for their own sake. 

We may take an example in illustration of this point. 
The Roman military organization naturally required a 
medical service. The need for this service was clearly 
perceived by the military leaders. A service was instituted 
and was well and carefully organized. Thus far the Roman 
rulers showed their practical good sense: Yet these leaders 
never perceived the need of having their medical officers 
trained on scientific lines. They established no effective 
medical schools. No effective training in anatomy and 
physiology was to be found anywhere in the Roman Empire. 

Had a great Roman military leader been questioned on 
this point, he would probably have replied, ‘Of course they 
want anatomy, but isn’t Galen’s anatomy good enough.?’ 
But he would be wrong. It is not by reading that science 
is sustained; it is by contact with the object—by systematic 
observation and experiment. From these the Roman army 
doctor was shut off. One of the few Roman leaders who 
appreciated science was Julius Caesar. It was an ill day 
for science when he fell. 

When we consider this Roman ‘practical’ attitude to 
abstract knowledge, it can cause no surprise that other 
departments of science were in like case to medicine. Even 
such a study as geography was allowed to languish. The 
brilliant and steadfast defences of the Empire would have 
been far more effectively and economically conducted had 
the Roman leaders had a grip of the geography of Europe. 
But their geography was of a purely military kind. It took 
no account of areas thought to be devoid of military im¬ 
portance. If a fraction of the cost of defence had been 



The Dark Ages 67 

spent on exploration, the geographical results would have 
caused a fundamental alteration in the distribution of the 
Roman forces. But the frontiers remained unscientifically 
and extravagantly drawn (Fig. 27). They collapsed. The 
barbarian tribes shattered the barriers and wandered through 
Europe, wasting as they went and destroying, like chil¬ 
dren, all the beauty and order that had been stored from 
the past. The Empire is submerged, the civilization of 
antiquity is at an end, and the voice of science is silent for 
a thousand years. 

The contempt for and neglect of science by the Roman 
leaders is significant, because it teaches a lesson which is 
of value to-day, and of value in every department of 
science and not least in Biology. The importance to the 
practical affairs of life of abstract science, studied for its 
own sake, is often forgotten. The whole mechanism by 
which our civilization is held together is based on science. 
Our trains and our motor-cars, our medical service and our 
food-supplies, depend ultimately on discoveries made with¬ 
out thought for their practical application. Unfortunately, 
the general direction of scientific research is largely deter¬ 
mined by men who are mainly interested in its application. 
If a time should ever come when the importance of theo¬ 
retical knowledge and investigation are neglected, our 
science will go the way of that of Greece and Rome, and 
we shall plunge again into an age of darkness. 

§ 6. Thirteenth-century Revival of Learning and Art 

While the knowledge and intelligence of men in 
Western Europe steadily deteriorated, there was one part 
of the world where the old traditions lingered. After the 
fall of ancient science, the most civilized part of the world 
was the Near East. In Syria, in Asia Minor, in Con¬ 
stantinople, men still read Greek scientific woi ks. Then 
in the seventh century came the great movement of Islam 



68 Decline and Fall of Ancient Science 

(Fig. 31). It established Arabic as a literary language and 
the face of the world was changed. 

Intellectual leadership thus passed, by the ninth cen¬ 
tury, to people of Arabic speech. It remained with them 
till the thirteenth century. The science of these Arabic¬ 
speaking peoples was based on translations of the Greek 
works into Arabic. These were prepared in large numbers 
and ardently studied throughout Islamic countries. Islam 
was a rapidly conquering religion and soon extended not 



only through the Near East but also over the whole of North 
Africa, as well as Spain, Portugal, South Italy, Sicily, and 
many Mediterranean islands. The European peoples 
came to recognize their intellectual inferiority to these 
Eastern peoples. They made attempts to secure transla¬ 
tions of their scientific works. These were made from the 
Arabic into Latin and were achieved largely with the help 
of Jews. 

The movement for the translation of Arabic works into 
Latin began in the eleventh century. Such versions did 
not, however, become common until the beginning of the 
thirteenth century. 

So far as biology is concerned, the most important 
l^atin translations from the Arabic were the biological 



Thirteenth-century Revival 69 

works of Aristotle. They were turned into Latin early in the 
thirteenth century by Michael Scot (d. c, 1235), ^^e wizard, 
of whom we read in Scott’s Lay of the Last Minstrel. 
Michael had journeyed to Sicily where Arabic was spoken, 
and had obtained a Jewish assistant. His learning in all 
kinds of mysterious books, which few but he could read, 
earned him his reputation as magician. The superstitious 



Fic. 32. 'Basilisca , pcriiaps the Basil, representing the extreme formal degrada¬ 
tion of plant painting. From an Anglo-Normal herbal written about A.n. 1200. 
Contrast with Fig. 33. 

Fig. 33. Naturalistic stone carving of Columbine of about A.D. 1260. From 
a panel in the south porch of C'hartres Cathedral. 


people of the time attached a similar magical glamour to 
many others who had a smattering of Arabic or Hebrew. 
Men who had thus acquired some knowledge of Arabian 
science were commonly thought to have had commerce 
with the Devil. 

Besides the biological works of Aristotle, some of the 
most important works of Galen and of Hippocrates soon 
became available. Dioscorides had been transplanted much 
earlier, but manuscripts both of him and of Pliny now 



70 Decline and Fall oj Ancient Science 

began to be more common. The world was at last awaken¬ 
ing from its long sleep. 

There was another important movement in the thir¬ 
teenth century that had its effect on Science. This was the 
great religious and artistic revival of which the wonderful 
cathedrals in the so-called ‘Gothic’ style are the best-known 
memorials. In certain departments this revival certainly 
had an effect upon biology. If we examine the illustrated 
manuscripts of the age, we shall find that, for the first time 
for many centuries, the artists do something more than copy. 
They are at last endeavouring to represent things as they 
really are. The effort to make pictures like nature has begun. 

Now men cannot make their pictures like nature unless 
they study nature. This the illustrators of manuscripts at 
last began to do. Thus we meet with the interesting fact 
that the real revival of observation, the basic process of 
science, was the work not of men habitually occupied in 
scientific pursuits, but of artists. The process spread. It 
is to be found not only among the miniaturists, but also 
among the masons and minor craftsmen who decorated 
the cathedrals. These men loved to put their own ob¬ 
servations into their work, and we often find good repre¬ 
sentations of animals and especially of plants in the 
architectural ornaments of cathedrals (Fig. 32). 

§7. Roger Bacon (1214—94) and Scholasticism 

But if this was the effect of the revival of art, literature 
exercised a less favourable influence. Reading, it is true, 
became much wider. The Universities, which came into 
great prominence at this period (Fig. 34), drew attention 
to the existence of a vast literature, partly sacred but to a 
great extent also philosophical and largely of Arabic origin. 
Some medical men were awakened by the translations of 
works of Hippocrates, Aristotle, and Galen from Arabic 
into Latin. But it was the study of the texts of these that 



Roger Bacon and Scholasticism 71 

absorbed their energies. They took almost as little in¬ 
terest in nature outside their books as did the men of the 
Dark Ages. 

The system of thought that arose from the study and 
comment on these texts is known as ‘Scholasticism’. The 



Fig. 34, Medieval centres of learning. V = Republic of Venice. For 
universities, the century of foundation is given in Roman figures. 


scholastics were characterized by their interest in words as 
opposed to things. Very few exhibited any ability as 
observers. The literature which they produced is enor¬ 
mous in bulk though low in quality. Yet the Scholastic Age, 
even in scientific matters, had advanced greatly on the 
Dark Ages. Some few of the ablest thinkers of the time 
perceived the importance of going direct to the original 
Greek texts instead of to the Arabic from which their 
versions were derived. There was a yet smaller group 
that appreciated, if intermittently, the value of direct 
observation. 








72 Decline and Fall of Ancient Science 

Prominent among this select band were Roger Bacon 
and Albertus Magnus. Both were Friars. The great 
religious movement of the thirteenth century had led to 
the foundation of many new religious orders. Most in¬ 
fluential among these were the Franciscans and the 
Dominicans. Both orders included many learned and able 
men, and among their other activities, they undertook 
much of the teaching work at the Universities. They were 
specially active at the University of Paris, where both the 
English Franciscan Roger Bacon and the German Domi¬ 
nican Albertus Magnus were teachers. Paris was the great 
scholastic university and at that time the intellectual head 
of the world. Both Franciscans and Dominicans had 
houses there. 

Roger Bacon is rightly described as a ‘p^op^et of 
science’. I.ong before there had been in Latin Europe any 
systematic observation of Nature, he perceived the value 
and interest of the process and some of the results to which 
it was likely to lead. He studied especially the science of 
optics. He understood something of the action of lenses, 
and indeed proposed their use as spectacles and predicted 
the invention of the microscope and telescope. 

Interesting and fascinating as is the career of Roger 
Bacon, most of his scientific work was in departments 
other than biology. We note that the charge of practising 
magic, so freely made against Michael Scot, was no less 
freely made in after years against the memory of Roger 
Bacon, and even of Albertus Magnus. 

§ 8. Albertus Magnus (1206-80) 

The Dominican Albrecht of Cologne, usually called 
Albertus Magnus, though less original and forceful as a 
thinker than Roger, was far more influential on the age in 
which he lived. He exhibited amazing activity, alike as 
writer and teacher. He produced, in works of enormous 



Albertus Magnus 73 

bulk, a vast encyclopaedia of the science of his time based, 
however, entirely on the writings of Aristotle, 

In his biological works Albertus follows Aristotle al¬ 
most word for word, working always on Latin translations 
from Arabic. He gives a sentence or part of a sentence of 
Aristotle and then adds a few words of his own in com¬ 
mentary. From our point of view it is difficult to imagine 
a worse method of dealing with a scientific topic. Never¬ 
theless, investigation of the biological works of Albertus 
has shown that they contain a considerable amount of 
personal observation. There can be no doubt that he was 
a naturalist of some ability. It is remarkable that so busy a 
man could observe quietly and accurately amidst his 
countless preoccupations, for he had onerous teaching and 
ecclesiastical duties to perform. Considering his circum¬ 
stances, it is no less remarkable that he sometimes ventures 
to criticize Aristotle. 

His most extensive biological effort, which follows 
closely the works circulated in his day in the name of 
Aristotle, is his treatise On animals. In it he says that 

‘between the mode of development of the eggs of birds and of fishes 
there is this difference: during the development of the fish the 
second of the two great veins which extend from the heart [as 
described by Aristotle in birds] does not exist. In fish, the vein 
which extends to the outer covering in the eggs of birds—wrongly 
called by some the navel vein because it carries the blood to the 
exterior parts—is absent, but the vein that corresponds to the yolk- 
vein of birds—which carries to the embryo the nourishment by 
which its parts increase—is present. In fishes as in birds, channels 
extend from the heart first to the head and the eyes, and thus the 
upper parts develop first. As the growth of the young fish increases, 
the yolk decreases, being incorporated into the members of the 
young fish. It disappears entirely when development and formation 
are complete. The beating of the heart is conveyed to the lower 
part of the belly, carrying pulse and life to the inferior members. 
‘While the young fish are small and not yet fully developed, they 



74 Decline and Fall oj Ancient Science 

have veins of great length which take the place of the navel-string, 
but as they grow and develop, these shorten and contract into the 
body towards the heart, as we have said of birds.’ [Abbreviated,"] 

A glance at sketches of embryos of birds and of fishes 
will make Albertis meaning clear. In the embryos of birds, 
as of mammals but not of fishes, there develops a mem¬ 
branous sac, the allantois (Greek ‘sausage-shaped’). This 



Fig. 35. Diagrams of a developing bird {d), and of earlier {b) and later (c) 
embryos of a fish, to illustrate the text of Albertus Magnus. 


sac is provided with a special blood-supply separate from 
the yolk sac (Fig. 35). It is to this special blood-supply 
that Albert is referring. We may add that the allantois 
remains free in the embryos of birds, but in those of mam¬ 
mals it takes part in the formation of the placenta. In this 
respect the placenta of the placental dogfish of Aristotle 
also differs from the placenta of mammals (Figs. 63-4). 

The treatise of Albert On plants is one of his most 
learned works. It is, perhaps, the best work on natural 
history produced during the Middle Ages. The descrip¬ 
tions of the plants themselves are brief. When they are 
not first-hand, attention is always directed to the fact. 
Albert is, however, helpless in his attempt to draw up 
any general account of plants, since he reaches no satis¬ 
factory basis of classification and is equally ignorant both 



Albertus Magnus 75 

of their minute structure and of their true mode of repro¬ 
duction. 

A single example will illustrate the accuracy with which 
Albert observed plants. He describes the orange tree, 
which he had an opportunity of seeing on a visit to Italy. 
He says that 

‘the leaf is, as it were, in the form of two leaves, of which the 
greater is set upon the base of the lesser, and there is a definite mark 
at the place of junction of the two leaves. There are woody strands 



Fig. 36. Leaf of orange tree as described by Albertus Magnus. 


which run through the leaves. And it is characteristic of this tree 
that the strands, or veins, are so set that in the part near the stem 
they run towards the base and in the distal part they run towards 
the apex.’ 

In the leaf of the orange the petiole is winged, giving the 
appearance of a second leaf. The articulation between the 
blade and the winged petiole shows that it is really a com¬ 
pound leaf with a single terminal leaflet. The veins also 
run as Albert describes. Albert’s meaning will be under¬ 
stood on glancing at an orange leaf (Fig, 36). 

§9. Medieval Anatomy 

In the great awakening of the thirteenth century the 
Universities came to exercise a profound effect on social, 
political, and intellectual conditions. In most of them 
medical faculties grew up. In some, anatomy came to be 







76 Decline and Fall oj Ancient Science 

studied, at first simply from books. The atmosphere was 
still utterly scholastic, and the scholastic method devoted 
itself rather to sharpening wits than to training senses. 
There was no practical instruction. 



Fig. 37. I'he earliest known representation of dissection (early fourteenth 
century). The operator is being admonished by a physician and a monk. The 
body, that of a female, has been opened. Kidneys, heart, lungs, stomach, &c., 
are strewn around. The operator holds a knife in his left hand and the liver 

in his right. 

With the fourteenth century change set in. This first 
made itself felt at Bologna. The University there is the 
most ancient to which the term can be rightly attached. 
An organized medical faculty existed at Bologna as far 
back as the middle of the twelfth century. It was the law 
school, however, that was best known and most frequented 
by students. The medical faculty at Bologna was at first 
subject to the school of law. Dissection began there 





Medieval Anatomy 77 

naturally as part of the process of legal investigation. There 
were cases of murder or of supposed murder in which an 
examination of the dead body was desirable. Thus human 
dissection was revived, after being in abeyance for more 
than a thousand years (Fig. 37). 

The first practical anatomist of whom we hear was a 
teacher at Bologna. He bore the name Mondino (diminu¬ 
tive of Raymond; r. 1270—1326). He dissected a number 
of domestic animals, notably pigs and dogs, and a few 
human bodies. Although he observed first-hand, it can¬ 
not be said that he set out to make discoveries in the 
manner of a modern biologist. Like Albertus, he was still 
obsessed by the written word. Mondino possessed a 
number of Latin anatomical works translated from the 
Arabic. For these he had a very great regard, and his 
investigations were undertaken chiefly to verify them. He 
advised students to follow his example so that they might 
remember the better what the great anatomists had said. 
Yet it was something that he and his followers did really 
make an attempt to see things with their own eyes. It was, 
at least, an improvement on the mere book knowledge of 
the earlier scholastics. 

There was, moreover, another department on which 
Mondino had a deep influence. All students of biology 
find as a preliminary difficulty the large number of terms 
for organs, structures, or processes. It is impossible to 
define these on each occasion that they occur, and they are 
introduced as a convenient sort of shorthand. Terms in¬ 
vented from the dead languages, Greek and Latin, save 
much space. Now Mondino was engaged in introducing 
anew a study of the structure and functions of the body. 
He needed new words and took them, not as we do from 
Latin and Greek, but from Arabic. Thus arose a biological 
nomenclature of Arabic origin. 



REBIRTH OF INQUIRY 
§ I. Naturalism in Art 

W ITH the fourteenth century began a period of 
travel. Information concerning rare and strange 
creatures came in from overseas. Trade, especially with 
the East, was increasing, and drugs were brought from 
foreign countries. Along with commerce came also 
travellers’ tales, both true and false. Those of Marco Polo 
(1254-1324) are specimens of the true, those bearing the 
name of Sir John Mandeville {c. 1370) of the false. 
Later, regular expeditions went forth to explore the un¬ 
known world. The most famous are the great journeys of 
Vasco da Gama {c. 1460-1524) to the East Indies and of 
Christopher Columbus (1446—1506) to the West Indies. 

Curiosity was being aroused in other matters besides 
that of the greater and more distant world. Men were 
looking more keenly at the things immediately around 
them. In the thirteenth century attempts at naturalistic 
representations had been made (Fig. 33). These became 
more frequent and by the fifteenth century were much more 
successful. One cause of this was the ‘rediscovery of an¬ 
tiquity’. Scholars were now investigating the great literary 
masterpieces of Greece and Rome. These, in their turn, 
aroused curiosity as to the material remains of ancient 
civilization. Men sought out and examined specimens of 
Greek and Roman statuary. By studying these master¬ 
pieces the great Italian artists learned to represent nature 
more accurately. The study reacted on the typical art of 
the period, that of Painting. 

An examination of the works of the Italian masters of 
painting of the second half of the fifteenth century shows 
a very rapid improvement in the capacity for naturalistic 
interpretation. It affects alike the representation of 



Naturalism in Art 79 

scenery, the portrayal of the human and of the animal 
body, and the treatment of minute details of plants and 
flowers. A glance at the work of some of these great men 
will at once bring the process before the mind. We may 
select Botticelli and Leonardo da Vinci. 

The charm of the work of Sandro Botticelli (1444— 
1510) is universally recognized. But his greatness was 
based on the fact that he was much more than a painter. 
He was also a man of extraordinary originality of mind 
and remarkable attainments. 

Botticelli was born at Florence. From his earliest years 
he exhibited a desire to paint. He was apprenticed to 
Fra Lippo Lippi (1406-69), an exquisite artist whose 
work was but little touched by the naturalistic spirit. 
Botticelli’s first independent picture was the Adoration of 
the Magi (1467), now in the National Gallery in London. 
At that time he had not yet come under the full influence 
of naturalism. Very soon, however, he developed a pecu¬ 
liarly beautiful style of his own, which has earned him the 
affection of all who love painting. With the general 
character of his art we are not here concerned. What 
matters to us is that he was an admirable observer and a 
lover of plant life. Nearly all his later pictures contain 
very careful flower studies. 

Perhaps the best known of all Botticelli’s pictures is the 
famous Spring at Florence. This entrancing picture, 
painted in 1478, is typical of the spirit of the Renaissance. 
Venus, with Cupid hanging over her, stands in a grove of 
orange and myrtle. She welcomes the approach of Spring, 
who enters with Flora and Zephyr. From the mouth 
of Flora there flows a garland of flowers most accurately 
and beautifully rendered (Fig. 38). The picture is, in fact, 
largely a botanical study. It reveals Botticelli as the first 
painter of plants in modern times. Over thirty species can 
be detected in this one picture. 



8 o Rebirth of Inquiry 

The best representative of the Renaissance artist- 
naturalists is Leonardo da Vinci. Not only was he great in 
almost every department of art—Painting, Sculpture, 
Design—but he excelled as an engineer and inventor, as an 
anatomist, and as an observer of nature. He occupies a place 
alsoin the history of philosophy andof mathematics. There 
aremany other departmentsin whichhe added to knowledge. 
Here we are concerned only with his biological work. 

(rf) As human anatomist. Leonardo as an artist was 
particularly interested in the human form. Artists need 
some knowledge of anatomy, but they study for the most 
part the bones and the superficial muscles. Ixonardo’s 
insatiable desire for knowledge led him to much more 
searching investigations. His studies of human anatomy 
extended to all parts of the body and were most wonder¬ 
fully illustrated by his own pencil. They were by far the 
best work of the kind up to his time, and were at least a 
century in advance of his age (Figs. 42—3 and 54). 

{b) As investigator of animal bodies. Leonardo was led 
to compare the structure of man with that of animals, the 
bodies of which he also dissected. He reached many 
illuminating conclusions. Thus he brought out accurately 
the relation of the bones in the human leg with those of 
the horse’s hind leg. He showed that the so-called ‘hock’ 
really corresponds to the ankle of man, while the ‘stifle 
joint’ corresponds to the knee. These facts were not 
generally recognized till long after the time of Leonardo. 
Here is but one example among many of his acute obser¬ 
vation in comparative anatomy (Fig. 106, p. 220). 

(r) As physiologist. Leonardo made many experiments 
which, had they been widely known, would have enor¬ 
mously advanced the knowledge of the working of the 
animal body. Thus he gave an account, in some respects 
singularly accurate, of the movements of the heart (Fig. 
41). He described the action of the eye, particularly in 



Fig. 38. Hoad of Flora from Botticelli’s Prima^^era (i 





82 RebirtKoj Inquiry 

relation to lenses. He Investigated the mechanics of the 
various joints. He made striking embryological observa- 




42 


B 



Fig. 40. Drawings from Leonardo’s note-book On the flight of birds. They 
show the resistance of the air to the action of the wings at various angles and 
in various positions (1505). 

Fig. 41. Diagrams by Leonardo of experiment on heart. A needle through the 
chest wall of a pig penetrates the heart and shows its movement externally 

(c. 1500). 

Fig. 42. The human skull. To the right it is shown complete. To the left it is 
cut in a plane parallel to the paper. Above the orbit on this side is seen in the 
thickness of the bone a large cavity known as the frontal sinus. Below the orbit 
and in the upper jaw is an even larger cavity, sometimes spoken of as the antrum 
of Highmore. Both these cavities are recorded by Leonardo for the first time. 
Nathaniel Highmore, the ‘discoverer’ of the structure bearing his name, lived 
1613-85. His discovery was 150 years after Leonardo’s. 

Fig. 43. Outline of human brain with cavities indicated by shading (c. 1514). 
The outline of both brain and its cavities is more accurate than any drawing made 
by previous anatomists. Leonardo suggests that the cavities of the brain may 
be injected with wax, the first suggestion of injection with solid matter for the 
examination of the form of bodily cavities. The method is now widely practised. 


tions. His investigation of the flight of birds may be said 
to be the beginning of the scientific study of the mechanics 
of flight (Fig. 40). 


Naturalism in Art 83 

{d) As student of plants. He prepared many drawings 
of plants which show him to have been a close student of 
their habits and habitats (Fig. 39). In this department he 
had only two serious rivals among artists, his older friend, 
the Italian Botticelli, and his younger contemporary the 
German Albrecht Dilrer (1471—1528). 

§2. Humanism 

A very few of the scholastics—Roger Bacon among 
them—had attempted to reach the Greek originals behind 
the Arabic versions of their Latin scientific texts. Their 
efforts were half-hearted, and rarely successful. As the 
centuries wore on, the Near East, where men still spoke 
and read Greek, became more accessible. Greek manu¬ 
scripts came to Western Europe in increasing numbers. 

In the fifteenth century some of the acutest minds of the 
age—and indeed of any age—were busily occupied in 
seeking to retrieve the learning of antiquity. The libraries 
of old monasteries were ransacked; emissaries were sent 
to the East; Greeks were tempted to the West by princely 
payment; all with the hope of gleaning classical remains. 
The great energy and ability exerted in this task were at 
last rewarded. By the middle of the fifteenth century 
nearly all that was to be found of Greek learning had been 
brought to the West. 

It happened, too, that a new invention came soon to 
the aid of these students of the classics. The art of printing 
was introduced about the middle of the fifteenth century. 
Printing helped to establish the Classics in the position 
in education that they occupied from that time until the 
nineteenth century. A landmark in our subject is the 
appearance at Venice in 1476 of the beautiful editio 
princeps of the biological works of Aristotle. These were 
translated into Latin from Greek by Theodore Gaza 
(1400-76) of Salonika, who had long resided in Italy. 



84 Kebirth of Inquiry 

The men who made a special study of the new classical 
material were very different from the old scholastics. 

The schoolmen had been chiefly interested in theology 
and in a theological type of philosophy. They attached 
great importance to reasoning. The so-called ‘disputa¬ 
tions’, or arguments in public, were the main exercises in 
the medieval university. The scholastics, moreover, gave 
very little attention to literary form. Medieval writings 
are generally tedious in presentation and almost always 
hideous in form. 

All this was changed by the men of the new school. 
They studied the noble literary models of antiquity and 
they saw the beautiful ancient statuary which was being 
unearthed. They were conscious too of the creative spirit 
of the art of the age, which drew so largely on the past. 
Men under such influences felt themselves heirs to a great 
tradition. They were absorbed, like the great writers of 
old, in mankind, in humanity. ‘I am a man and deem 
nothing human remote from me’ was the dictum of one 
of their great models, Terence, the Latin poet. ‘Consider 
the sorrows of thy fellows to be thine own’, a yet greater, 
Menander, the Greek playwright, had said. The greatest 
and wisest of them all, Socrates, four hundred years before 
the birth of Christ, had lived a life and died a death that 
were to illustrate his own saying: ‘As for me, it is not the 
Athenians nor even the Greeks that are my brothers, but 
all Mankind.’ 

It was because they took to heart these sayings of the 
great writers of old, because they cared for men and not 
for argument, that those who studied antiquity became 
known as, and called themselves humanists. The term 
umanista was invented by one of themselves, the poet 
Ariosto (1474-1533). Their studies were ‘the humanities’. 
The humanists were informed by a lofty spirit which passed 
at times into ecstasy but not seldom into arrogance. 



Humanism 85 

The influence of the classical writings at their best has 
been summed up by a writer sufficiently removed from 
antiquity to feel its force as something outside his world, 
and yet sufficiently near to the Dark Ages to be instinct 
with a brooding fear that the days of spiritual freedom 
were gone for ever. Longinus, a philosopher of the third 
century of the Christian era, when active Greek thought 
was no more, had truly written that ‘from the sublime 
spirit of the ancients there flow into the minds of those who 
emulate them, emanations like those from certain holy 
shrines. These inspire even the most ungifted with the 
enthusiasm and greatness of others.’ 

The humanists, moved by the spirit of antiquity, turned 
to the great scientific works of Greece. With loving care 
and with superb skill they prepared editions and transla¬ 
tions of the classics. By the end of the first half of the 
sixteenth century Hippocrates, Aristotle, Theophrastus, 
Dioscorides, Galen, and scores of others were available 
in texts which could probably be compared favourably 
with any accessible to the ancients in the period of classical 
decline. 

But the humanist spirit was far from being all wisdom 
and love. Intoxicated by the beauty of the classics, the 
humanists developed a furious enmity against the scholas¬ 
tics. The Arabian texts, on which scholasticism had been 
nourished, aroused, in some of its enemies, an insensate 
anger which is very difficult for us now to understand and 
impossible for us to share. The texts were ‘castigated’ and 
the very language was ‘purified’ by the humanists from the 
technical terms which had been derived from the Arabic. 
Words of Arabic origin were remorselessly hunted down 
and Greek or Latin terms were substituted. 

Thus it has come about that our modern biological 
vocabulary is almost exclusively Greek or Latin. Never¬ 
theless, an Arabic biological term has survived here and 



86 Rebirth of Inquiry 

there, usually by accident. Sometimes such words have 
escaped suppression because they look like and were mis¬ 
taken for Greek. They were, so to speak, protectively 
coloured against the attacks of their enemies. Perhaps the 
commonest of these Greek-looking words that are really 
Arabic is nucha (French nuque\ Italian, Spanish, and Por¬ 
tuguese nuca) a term for ‘the back of the neck’. A few 
plant names, such as sesame^ are also of Arabic origin. In 
the mathematical, chemical, and astronomical vocabulary, 
a larger number of Arabic terms has survived. 

§3. The German Fathers of Botany 

The group of movements which had thus come to 
flower by the beginning of the sixteenth century placed 
the student of nature in a peculiarly favourable position. 
He had now the works of antiquity on which to draw. 
The craft of printing was at his disposal. Artists had 
learnt to represent details of nature effectively. And, 
finally, the wood-cutter had so perfected his craft, that the 
figures of the artist could be effectively transferred to the 
printed page. Thus it came about that the first adequately 
illustrated botanical books were produced. 

The new development began in Germany, the home of 
printing, where the practice had reached a very high 
standard. Otto Brunfels of Mainz (1489—1534) was the 
first to produce a work on plants, the figures of which rely 
wholly on observation (1530). The drawings are firm, 
sure, and faithful. It is very interesting to compare them 
with those of a good modern text-book. The text, how¬ 
ever, is befogged by an error from which botanists took 
long to free themselves. Brunfels identifies his plants— 
gathered in the neighbourhood of Strasbourg—^with those 
of Dioscorides, who worked on the shores of the Eastern 
Mediterranean. 

A younger German botanist was Jerome Bock of 



German Fathers oj Botany 87 

Heiderbach (1498—1554), who escaped some of the errors 
of Brunfels. Bock’s figures (i 539) are not as good as those 
of Brunfels. Of interest for us, however, are his careful 
descriptions of plants and of their mode of occurrence. 



Fig. 44. I'lie skeleton of a man and of a bird compared by Belon (1555). 
Corresponding^ letters point to parts which Belon regarded as homologous in the 
two cases. He is particularly successful in his treatment of the limb bones. 


the first of the kind since Greek times. Only by collating 
a large number of such descriptions did botanists outgrow 
the habit of comparing all their plants with those of the 
ancients. 

The most remarkable of the early German botanists was 
Leonard Fuchs (1501—66). His botanical work (1542), 
intended as a guide to the collection of medicinal plants, 



88 Rebirth oj Inquiry 

is a landmark in the history of natural knowledge. Fuchs 
had a good acquaintance with the (ireek and Latin classics, 
and was, withal, an excellent observer, so that his identi¬ 
fications of plants are supported by adequate knowledge. 
His woodcuts are of extraordinary beauty and truth. They 
established a tradition of plant illustration which is 
traceable to the present day. Fuchs enjoys a verdant 
immortality in the beautiful group of American plants 
known as ‘Fuchsias’. 

Fuchs arranged his plants in alphabetical order. He 
gives us nothing of classification, hardly anything that can 
be called plant geography, little concerning the essential 
nature of plants or of their relation to other living things. 
His book is, in fact, a herbal pure and simple. Yet by close 
observation of details and by their accurate record on the 
printed page, it may claim a place among the pioneer 
works or modern science. He includes in his work an 
admirable glossary of botanical terms. 

§ 4. The Naturalist Commentators 

The humanistic movement in its spread northward soon 
had further effects. Scholars, impressed by the new at¬ 
titude to nature, occupied themselves in identifying the 
plants and animals mentioned by ancient writers and 
especially by Aristotle, Dioscorides, and Pliny. This 
gradually led them farther afield, as strange new animals 
and plants were coming to Europe from America and the 
East Indies. 

One of the earliest and most typical of the scholar- 
naturalists was the Englishman, William Turner {c. 1510- 
68). While at Cambridge he published Libellus de re 
herbaria (1538). It treats of classical plant-names. He 
visited Conrad Gesner (pp. 92—4) at Ziirich, and corre¬ 
sponded with him for many years. He travelled about the 
Continent. At Cologne he published a work on birds (1544) 



Naturalist Commentators 89 

which attempts to determine those named by Aristotle and 
Pliny, adding notes from his own observations on many 
species. This is the first ornithological book in the modern 
scientific spirit. Turner was also a zealous botanist and 
showed sound judgement in botanical matters. His Herbal 
(best edition London 1568) marks the start of botany in 
England. Another service that he rendered to this country 
was the introduction of lucerne, which he called ‘horned 
clover’. 

Somewhat similar to the history of Turner is that of the 
German, Valerius Cordus (1515—44), who became a pro¬ 
fessor at Wittenberg. Cordus began by editing Dios- 
corides. Becoming wearied with the meticulous examina¬ 
tion of texts, he turned to investigate the plants themselves. 
He explored the forests and mountain glens round Witten¬ 
berg and found many hitherto undescribed kinds. His 
History of Plants has descriptions of between four and 
five hundred species. Dying at twenty-nine in 1544, 
his work was seen through the press by Gesner (1561). 
Cordus was the first to make a systematic and scientific 
examination of the structure of flowers. 

In France the humanist movement was particularly 
active. In the works of Rabelais (i 490-1553), some have 
discerned the new observational spirit. For our purpose, 
however, it is better displayed by two younger contem¬ 
poraries, Belon and Rondelet. 

Pierre Belon (1517-64) of Le Mans, after taking a 
medical degree, studied in Germany with Valerius Cordus. 
The years 1546—9 he spent in travel in the Near East, 
during which he kept careful notes on natural history. 
Later he produced a book on fishes (1551) and another 
on birds (1555), both well illustrated. These, though 
based on Aristotle, show much original observation. 
It is interesting to note the clearness with which he 
grasps the general principles of comparative anatomy. 



90 Rebirth of Inquiry 

Thus, for instance, he exhibits the skeleton of a bird 
placed by the side of a man, and compares them bone for 
bone (Fig. 44). 



46 


Fig. 45. A female killer-whale and her newdy-born young. The young whale is 
linked to the placenta, which is in process of extrusion. From Belon (1551). 
Fig. 46. A whale suckling her young and attacked by a ‘killer-whale' Orca 
gladiator^ the ‘Belua trurulenta dentibus' of Olaus Magnus. The breasts of the 
mother, the dorsal fin of the killer, and the blow-holes of all three animals are 
greatly emphasized. From Gesner after Olaus Magnus (1558). 

The whale is much better represented by Belon than by Gesner. But Gesner, 
living at Zurich, saw nothing of marine animals, while Belon was quite familiar 

with them. 

Belon was the first to figure the attachment of the 
embryo ‘cetacean’ to its mother(Fig. 45). This established 
the group as mammals in confirmation of Aristotle 
(p. 31). The word ‘mammal’ (Latin mamma^ an udder) 
was introduced by Linnaeus (p. 185) in the eighteenth 









Naturalist Commentators 91 

century and refers to the habit of suckling the young. The 
mammalian character of the cetaceans was, however, 
recognized by other sixteenth-century writers besides 
Belon. Thus Gesner and several others emphasized it 
by figuring whales as equipped with a whole series of 
mammae (Fig. 46). 

Belon wrote a systematic work on botany in the form 
of a short treatise on cone-bearing trees (1553), which is 
the first monograph of a plant group. He was a good 
draughtsman and in the course of his travels he sketched 
many interesting plants, several of which he was the first 
to figure (Fig. 98, p. 185). 

More accurate than Belon as an observer, though less 
imbued with comparative principles, was Guillaume Ron- 
delet of Montpellier (i 507—66). Rondelet was a friend of 
Rabelais, by whom he was infected with the humanist 
spirit. Rondelet’s great work is a painstaking and well- 
illustrated investigation of the fishes and other marine 
animals of the Mediterranean (i 554). Its motive is largely 
to verify the views of Aristotle, but Rondelet describes 
many forms for the first time. He deserves great credit for 
having discerned the relation of embryo to mother in the 
placental dogfish (Figs. 47 and 17). Rondelet’s illustra¬ 
tion of the structure of a sea urchin is the earliest figure 
we have (1554) of a dissected invertebrate (Fig. 51). It 
exhibits the complex oral apparatus which has since be¬ 
come known as Aristotle’s lantern (Fig. 22). 

Another able naturalist of the time was Pietro Andrea 
Mattioli of Siena (1500-77). He practised as a court 
physician and devoted his leisure to translating, annotat¬ 
ing and illustrating the text of Dioscorides. He was a 
most skilful botanist and in constant correspondence with 
Gesner and Aldrovandi. The first edition of his Com¬ 
mentaries on Dioscorides appeared in Italian at Venice in 
1544. It was translated into many languages, among 



92 Kebirth oj Inquiry 

them Latin, Bohemian, and French. Artistically some¬ 
what inferior to the work of the German fathers, it is, 
especially in its later editions, one of the best works of 
descriptive natural history of the century. By reason of 
the extensive, accurate, and discerning scholarship that it 
displays, it is still in current use for the study of Dio- 
scorides. Moreover, especially in the later editions, it con- 



Fig. 47. The placental dogfish of Aristotle (p. 32) with young still attached 
by navel-string. From Rondelet (1554). 

tains descriptions of many plants of which Dioscorides had 
certainly no knowledge. Mattioli had access to the great 
Juliana Anicia manuscript (Figs. 26-7, p. 58) in the 
preparation of his work. 

§ 5. The Encyclopedic Naturalists 

Even during the sixteenth century, acute need was felt 
for some arrangement of the available biological know¬ 
ledge. Thus arose the work of the ‘Encyclopedists’. 
They made it their business to collect all known facts 
about living things. Their works are often enormously 
bulky and usually finely illustrated. Most of their figures 
are borrowed. Their huge volumes, however, are not only 
beautiful in themselves, but are interesting to the historian 
as giving a summary view of the biological knowledge of 
the day. 

Conrad Gesner (1516-65), the great Swiss naturalist, is 
the best representative of this school. His learning was 
vast. The central position of Zurich, where he dwelt, 



49 


50 


Fig. 49. I'he ‘Sepia’, ^epia officinalis^ from Rondelct (1554). 

50. I'he ‘Polypus’ (French poulpe). Octopus <vulgaris, from Gesner 
(1558) from a drawing sent him by Rondelet. 



94 Rebirth of Inquiry 

enabled him to get news of scientific activities throughout 
Europe. The five folio volumes of his great Historiae 
animalium (1551—1621) are really separate works on 
rather arbitrarily arranged animal groups. A number of 
the figures are original, and, like the descriptions, give 
evidence of careful observation. The account of fishes is 
perhaps the most valuable. It contains figures and descrip¬ 
tions of a number of invertebrates. Some of his figures of 
the commonest animals have a freshness and vigour seldom 
equalled in works on natural history (Fig. 52). The work 
of Gesner is regarded as the starting-point of modern 
zoology. To his contemporaries he was best known as a 
patron of learning and as a botanist, but his own most 
important botanical works were not published till two 
hundred years after his death (1751—71). 

There is a special reason why Gesner should be re¬ 
membered by nature lovers. It is strange that neither in 
Antiquity nor in the Middle Ages nor at the Renaissance 
of Learning was there any real appreciation of mountain 
scenery. Mountains were regarded with dread or even 
disgust. Gesner was among the first to voice a feeling for 
mountains. In a letter to a friend he speaks of the wonders 
of mountain scenery, and declares his intention of climbing 
at least one each year, not only to collect plants, but also for 
air and exercise. He wrote a description of Mount Pilatus 
which is probably the earliest work on mountaineering. 

A writer worthy of mention was Ulissi Aldrovandi 
(1522—1605). Despite trouble with the Inquisition, he 
was appointed professor at the papal university of Bologna. 
The botanical garden founded there (1567) was among 
the earliest connected with a university, and of it he be¬ 
came the first director. He was a voluminous writer. In 
1599 he published three tomes on birds, and in 1602 
a treatise, finely illustrated, on insects. This last was his 
best work. Although he exhibits no formal system of 



Encyclopaedic Naturalists 95 

classification of animals, yet the arrangement of the figures 
displays an instinctive grasp of natural affinities. Others of 
Aldrovandi’s monographs appeared after his death. He 



Fig. 51. The Comnion Sea Urchin from Rondelet (1554). ITe animal has 
been opened by a section in the horizontal plane. The upper half, shown above, 
exhibits the intestine and the sexual gland. In the lower half can be seen the 
complex oral apparatus known as Aristotle's Lantern (see also Fig. 22). The 
arrangement on a 5-rayed basis is well seen. This is the earliest figure of a dis¬ 
sected invertebrate. Fig. 52. Snails from Gesner (1558). 


had designed the whole to form an enormous encyclo¬ 
pedia of living things. 

Among the encyclopedic naturalists is to be included 
the Londoner Thomas Moufet (1553—1604). Travelling 
extensively in Italy, Spain, France, Germany, Switzerland, 
and Denmark, he came to take much interest in insects. 
He kept copious notes of his observations and illustrated 


g 6 Rebirth of Inquiry 

them by figures, for he was an accomplished draughts¬ 
man. He had considerable literary power, his master¬ 
piece being his Theatre of Insects (Latin 1634, English 
1658). Both as regards text and figures it is the best work 
of its kind to its date, and it shows a new standard of 
exactness in the study of invertebrate animals. The manu¬ 
script still exists (Fig. 53). 

Gesner, Aldrovandi, and Moufet represent an important 
phase in the history of biology. They were still tied to 



Fig. 53. Drawing of hornets from a manuscript prepared by 1 homas Moufet 

about 1588. 

classical traditions. But the biological knowledge of an¬ 
tiquity had now been fairly mastered. The significance 
for science of classical scholarship was on the wane, and 
the work of the later schools is conducted in a new spirit. 

§ 6. The Revival of Anatomy 

The beginnings of effective plant study have been 
traced to a fortunate combination of Humanistic Learning, 
Renaissance Art, and the perfection of the Craft of Print¬ 
ing. The same is true of the study of the animal body. A 
beginning had been made by Leonardo, but his work 
remained hidden until our own time. The real father of 
modern Anatomy was Andreas Vesalius (1514—64). 

Even as a boy Vesalius was always observing nature and 





Revival of Anatomy 97 

dissecting the bodies of animals. He studied first at 
Louvain in his native Belgium and afterwards at Paris. 
Now the university of I^ouvain, and even more Paris, were 
extremely conservative centres. The instruction was still 
medieval and pinned to the texts of Galen. Vesalius was 
highly successful as student and teacher, and he became 
very learned in Galen. Fortunately for himself and for 
the world, Vesalius quarrelled with his superiors and de¬ 
cided to seek his fortune elsewhere. He determined on 
Italy, settled at Padua, and at the end of 1537, when 
twenty-three, was appointed professor there. Immediately 
he showed himself as a man of great energy and introduced 
sweeping reforms. 

It may cause surprise that a Belgian new-comer should 
be elected at an Italian University. But at that time there 
was only one language of learning—I^atin. The lectures 
were in Latin. The native language of a professor was, 
therefore, not of great importance provided that he spoke 
and wrote I.atin fluently. This essential accomplishment 
Vesalius had early acquired. His teaching powers appealed 
to the students at Padua who then chose the professors. 

In the old days of Mondino (p. 77) the professor had 
dissected on his own account. The successors of Mon¬ 
dino had abandoned this difficult and tiring process. They 
had been content to read their lectures from the text of Galen, 
while a demonstrator (Latin demonstro^ ‘I point out’) indicated 
the parts to the students. Hence our modern academic titles 
Reader and Demonstrator, The basic reform of Vesalius 
was to do away with demonstrators and other inter¬ 
mediaries between himself and the object, and to put his 
own hand to the business. 

Such a change he had already sought to make at Paris, 
where he was opposed by the conservative elements. At 
Padua he succeeded, and was soon lecturing to large 
audiences. His energy was irresistible. In five years he 



98 Rebirth oj Inquiry 

had completed and printed the great work on which his 
fame is based, and he was still only twenty-eight when 
that magnificent volume appeared. He did no further 
important work. His De fabrica corporis humani (Basel 
1543) is both the first great modern work of science and 
the foundation-stone of modern biology. 

§ 7. Renaissance Art versus Modern Science 

If a modern man of science turn to the masterpiece of 
Vesalius, he meets a difficulty at the very outset. A modern 
biological work is divided into sections, each devoted to 
some special organ or function or process. But Vesalius 
does not abstract in quite this way. Though he speaks of 
the parts separately, he is always thinking of the body as 
a whole. This is in the background of his mind, even 
when he is speaking of some minor structure. He is, in 
fact, dealing with living anatomy, and tries to fit the part 
he is discussing into a living whole. For this reason his 
figures are seldom diagrammatic, but usually represent 
the parts of the body as in a living model (Fig. 55). 

This habit of ever picturing the living figure, behind the 
organ or the structure, places Vesalius in a class quite 
apart from most modern biologists. His power of vision, 
in making him a great creative biologist, made him at the 
same time a great creative artist. To understand Vesalius 
we must try to rid ourselves of certain ideas which come to 
us from our education. We must think like Renaissance 
artists, and not like modern men of science. 

The modern biologist’s first task, like that of the ana¬ 
tomist of the time of Vesalius, is to describe carefully and 
accurately the structures with which he deals. So far, and 
so far only, the methods of the two resemble each other. 
In the further application of their knowledge they differ 
greatly. The modern biologist treats his material com¬ 
paratively, from the point of view of development and 



Renaissance Art versus Modern Science 99 

origins, and always with the idea of Evolution at the back 
of his mind. This was to some extent the case with a few 



54 55 

Fig. 54. Right arm and arm bones from Leonardo (about i^oo). The limb 
is drawn from the front. Fhe artist is portraying the effects of rotation of the 
radius about the ulna. The line of action of the muscles is indicated by cords 
attached to the bones. 

Fig. 55. Dissection of left arm from Vesalius (1543). The limb is drawn 
from the back. The muscles are well portrayed. I'he bones come to the surface 
at H where the head of the humerus is showm and at O where the upper end or 
olecranon of the ulna is seen. The movement suggested is identical with that in 
Leonardo’s drawings. 

Renaissance men of science, e.g. Belon (Fig. 44). But not 
so with Vesalius and his followers. As the title of his great 
work implies, for him the body is always a fabric, that is a 



loo Rebirth oj Inquiry 

■piece of workmanship, the artificer being the Great Crafts¬ 
man, the Almighty Himself. 

The Renaissance Latin fabrica is not, however, ade¬ 
quately translated by the English ‘fabric’. Fabrica is not 
merely a thing wrought, but one which, being wrought, is 
doing that for which it was wrought. So we speak to-day 
of ‘the workings’ of a machine or the ‘works’ of a clock 
(compare German Fabrik = factory). The parts of it are 
meaningless without the whole. So these figures of bones 
or muscles by Vesalius are not placed in the symmetrical 
and diagrammatic positions as in a modern text-book, but 
are represented as parts of a living man. 

Vesalius, a child of his age, could not help thinking of 
the end or object to which man is made. He considers 
the end, the modern biologist thinks of the origin. 
Though Vesalius had revolted against Galen, he was still 
looking with Galen’s eyes. For Vesalius, as for Galen, Man 
is a work of art, God an Artist, men’s bodies are the 
Artist’s ‘studies’ for His Great Design. 

There is another aspect of the vigorous mind of Vesalius. 
He was a very learned man. He was well acquainted with 
all the new-found wealth of antiquity which the humanists 
were making accessible to the reading public. He was, 
moreover, a somewhat boastful man and one given to dis¬ 
play. Thus, for example, he claimed more knowledge of 
Arabic and Hebrew than he possessed. But there is 
no doubt of the genuineness of his classical learning, and 
he took an active part in that battle of books, the war of 
the Humanists against the Scholastics (pp. 83-6). 

We must thus think of Vesalius as trebly equipped for 
his task. Firstly, by his native genius for dissection, 
developed at Paris, and stimulated by the freedom of 
teaching at Padua. Secondly, by the current attitude to¬ 
ward the human body, exalted by contact with Renaissance 
Art and sublimed by his own superb power of visual 



Renaissance Art versus Modern Science loi 

imagination. Thirdly, by an excellent education according 
to the standards of his time, directed along humanist lines 
by some of the ablest humanists of the day. 

§ 8. Fesalius on the 'Fabric of the Human Body' (1543) 

Since the work of Vesalius is so important for the his¬ 
tory of our subject, and since it set a standard for after 
ages, we must give some account of it. The book opens 
with a description of the bones and joints, the general 
classification of which is from Galen. The first bone con¬ 
sidered is the skull. It is astonishing to find here an 
examination in the modern manner of the different shapes 
of human skulls. Anthropologists attach great importance 
to these. Skulls are systematically measured and in¬ 
dividuals and races are classed as broad-headed, long¬ 
headed, and round-headed. This is exactly what Vesalius 
does (Fig. 56). He follows this matter up farther by 
comparing the skull of man with that of certain animals, 
notably the dog. 

Of all the anatomical subjects of which Vesalius treats, 
he is most successful with the muscles. His representa¬ 
tions of these are actually superior in certain respects to 
most modern anatomical figures. Vesalius, with an artist’s 
eye, has succeeded in representing these muscles with 
their normal degree of contraction.* In other words, he 
has represented living figures as if their skins were trans¬ 
parent. This is a much more difficult task, and one in¬ 
volving more real knowledge, than any mere presentation 
of dead anatomy. Therefore naturalists still return to 
these figures and have something to learn from them, al¬ 
though they were prepared four hundred years ago 
(Fig- 55)- 

Ihe account by Vesalius of the structure of the heart 

* In fact most of the drawings are not by Vesalius himself, but there can be 
no doubt that he supervised them in every detail and determined the poses. 



102 Rebirth of Inquiry 

has a special interest. The workings of the heart and 
blood system had always been a puzzle. The current 
solution was that of Galen (Fig. 58). 

Galen supposed that the basic principles of life were 
certain ‘spirits’ which dwelt in the blood. Blood was 
formed in the liver and then charged with natural spirits. 
It was distributed thence by the veins in which it ebbed 
and flowed. One main branch of the venous system was 



Fig. 56. From Vesalius (1543) illustrating types of skull. They correspond to 
the ‘round’ (left), the ‘long’ (middle), and the ‘short’ headed types of modern 
physical anthropology. 


the right ventricle of the heart. For the blood that entered 
this there were two possible fates. The greater part, having 
parted with its impurities, which were carried off to the 
lung, returned to the liver. But a fractional part of the 
venous blood trickled through minute channels in the 
septum between the ventricles to the left ventricle. There 
it met air brought from the lung and became a higher type 
of spirit, the vital spirits. These spirits were distributed by 
the arteries, some of which went to the brain. There the 
blood became changed into a third spirit, the animal 
spirits. These were distributed by the nerves which were 
thought to be hollow. The conception has given rise to 
our modern term ‘full of animal spirits’ which means full 
of nervous energy. 

It will be seen that Galen’s scheme depends on the sup- 


Ve salt US on 'Fabric oj the Human Body' {1543) 103 

posed existence of pores in the septum between the 
ventricles, 

Vesalius generally follows the physiological views of 
Galen. He gives a very good description of the structure 
of the heart. When, however, he comes to the septum 
between the ventricles he is puzzled. He tells us that: 

‘ The septum is formed from the very densest substance of the 
heart. It abounds on both sides with pits. Of these none, so far 



Fig. 57. Skeleton prepared by Vesalius. In 1546 Vesalius passed through 
Basel. He had with him a skeleton on which he w^as invited to demonstrate. 
On leaving the town he presented it to the University, in whose charge it remains 
to this day. It is the oldest biological preparation made with a scientific motive 
that is now in existence. 


as the senses can perceive, penetrate from the right to the left 
ventricle. We wonder at the art of the Creator which causes 
blood to pass from right to left ventricle through invisible pores.’ 

This exclamation shows that he was not quite satisfied 
with Galen’s view. Twelve years after the appearance of 
the first edition of his great work Vesalius brought out a 
second edition. He has again examined the pits on the 
septum. This time he says; 

‘ Although sometimes these pits are conspicuous, yet none, so 
far as the senses can perceive, passes from right to left ventricle.’ 

He goes on to say that; 

‘Not long ago I would not have dared to turn aside even a hair’s 
breadth from Galen. But it seems to me that the septum of the 
heart is as thick, dense and compact as the rest of the heart. I do 
not see, therefore, how even the smallest particle can be transferred 
from the right to the left ventricle through the septum.’ 



104 Rebirth oj Inquiry 

This attitude to Galen makes it evident that we are on 
the eve of a biological revolution. Men are no longer 
satisfied with the traditions of the ancients. 

§ 9. Successors of Vesalius 

In his doubts as to the physiological views of Galen 
Vesalius was not alone. A fellow student with him in 
Paris had been a Spaniard, Miguel Servet (1511—53). 
This Servetus was very fond of religious argument, and 
his writings were equally unwelcome to both Catholics and 
Protestants. Early in his career the Spanish Inquisition 
made efforts to secure his person. His religious views are 
not of interest to us, but a passage in his Restitution of 
Christianity (1553) shows that he had abandoned Galen’s 
view of the action of the heart. He was reaching out to¬ 
ward the idea of the blood moving in a circular manner, 
Servetus rightly considered that the arterial blood ‘is pro¬ 
duced by the mingling in the lungs of the inspired air with 
the blood which is communicated from the right ventricle’. 
He goes on to say that 

‘this communication does not take place, as is generally believed, 
through the septum of the heart, but by a remarkable device the 
blood is driven from the right ventricle through a long passage in the 
lungs. It is there rendered lighter in colour, and from the pul¬ 
monary artery is poured into the pulmonary vein. There it is mixed 
with the inspired air, and by expiration cleansed of impurities. At 
length, completely mingled with the air, it is drawn in by the left 
ventricle during its expansion, ready to become vital spirit’ 
(Fig. 58, inset). 

This is the first clear account of the lesser circulation. 
Similar views were expressed (1559) by Realdo Columbo- 
(1516-59) of Padua. Servetus was burned at the stake 
for his religious views by the Protestants at Geneva in 
1553. The Restitutio Christianismi was burned with him, 
and only three copies have survived. 



Successors oj Vesalius 105 

Foremost as an anatomist among the contemporaries and 
immediate successors of Vesalius was Bartolomeo Eustachi 
(1520-74). He takes a somewhat isolated place since he was 
not connected with the North Italian universities and was 



Fig. 58. Diagram of action of heart and blood-vessels according to Galen. 
Inset on right is a diagram of the circulation in the lung according to Servetus. 


moreover a great upholder of Galen. Eustachi practised in 
clerical circles at Rome. He is remembered for the ‘Eus¬ 
tachian tubes’ in the discovery of which he was anticipated 
by some two thousand years by Alcmaeon (p. 6). Among 
the other investigations of Eustachi was his attempt, the 
first in history, to study anatomical variations in indi¬ 
viduals, and his examination of the organ of voice. He 
also investigated the nerve-supply of muscles. 

The works of Eustachi remained for the most part un¬ 
published during his life and were not given to the world 





io6 Rebirth of Inquiry 

until the eighteenth century (1714). Thus they had very 
little influence on his contemporaries. 

In the second half of the sixteenth century, following 
on the stimulus of the work of Vesalius, there was much 
biological activity. Anatomy, Physiology, Botany, Zoo¬ 
logy, all made considerable progress. These subjects were 
taught especially in the Universities of North Italy. No- 





Fig. 5:9. From Fahricius ab Aquapendentc (1603) to show valves in veins. 
The * knots ’ (lettered 000 0 ) indicate the valves in the arm, which is bandaged 
above the elbow to bring them into greater prominence. Below are two 
veins that have been removed and turned inside out. On these the valves 

project. 


where were they prosecuted with such energy and ability 
as at Padua, the old school of Vesalius. 

Directly in the tradition of Vesalius was his pupil 
Gabriele Fallopio (1523-62), who succeeded him at 
Padua. Fallopio made some important investigations of 
the nervous system and of the generative organs, both of 
which have parts to which anatomists still attach his name. 
He gave its scientific title to the structure that we now call 
the ‘placenta’ (Fig. 64). 

Of the pupils of Fallopio the two ablest were the Hol¬ 
lander Volcher Goiter (1543-76.?) and the Italian 
Hieronymo Fabrizzi. Goiter studied also with Eustachi 




Successors oj Ve salt us 107 

and Rondelet (p. 91), and turned later to comparative 
anatomy. He was the first systematic exponent of this 
subject since Aristotle, but confined himself to the skele¬ 
ton. Among his figures we note one of the skeleton of a 
monkey which he compares with that of man. Coiter also 
gave an account of the development of the chick, opening 
eggs day by day to trace the progress of the young animal. 
His work influenced Fabrizzi. 

Of all Paduan teachers the most influential after Vesalius 
was Hieronymo Fabrizzi (1537-1619), known as Fab- 
ricius of Aquapendente, from his native Tuscan village. 
He taught at Padua for sixty-four years, and was deeply 
learned and an admirable observer. Most of his writings 
have physiological bearing. He was the effective founder 
of the modern science of Embryology (p. 458). He also 
did important work in applying the principles of mechanics 
to muscular movement. 

Late in the sixteenth century Fabricius made certain 
observations which he published in his book On the Valves 
oj the Veins (1603). He describes 

‘thin little membranes distributed at intervals on the inside of the 
veins. Their mouths are directed towards the root of the veins, 
that is, towards the heart. In the other direction, that is away from 
the heart, they are closed.’ 

We know now that these valves hinder the flow except 
to the heart. Indeed, Fabricius shows this by an actual 
experiment (Fig. 59). He demonstrates that if an arm be 
lightly bandaged so as to compress the veins and thus 
prevent the flow of blood, the veins swell up. This is be¬ 
cause blood can get into the veins from the arteries through 
the capillaries but cannot move farther on toward the 
heart, being stopped by the pressure of the bandage. The 
valves show up as swellings in the course of the veins. 
Fabricius draws attention to this. Yet his explanation is 
merely that the valves to a certain extent delay the blood 



io8 Rebirth of Inquiry 

and so prevent the whole of it flowing to the feet or the 
hands and collecting there. 

He thus failed to recognize the true function of these 
valves. He was thinking on the old Galenic lines of the 
ebb and flow of blood in the veins. For him veins convey 
blood back and forth, carrying nutrient blood from the 
liver to the tissues, and bringing the exhausted blood from 
the tissues back to the liver. 

§ lo. Harvey (1578—1657) and the Circulation of the Blood 

As the sixteenth century was closing there came to 
Padua a young Englishman, William Harvey. He had 
been educated at Gonville and Caius College, Cambridge, 
which had already a link with Padua. Gonville Hall, 
as it had previously been called, had been refounded in 
1557 by John Caius (1510—73) whose name it now bears. 
Caius studied in Padua under Vesalius as far back as 1539. 
Full of the stimulus of the great teacher, he returned to 
England and lectured on anatomy in London (1544—64) 
before he moved to Cambridge. 

Harvey reached Padua in 1597 when Fabricius was 
at the very height of his powers. There still stands the 
curious theatre lined with carved oak, where the great 
teacher used to lecture by candle light (Fig. 100, p. 203). 

In 1602 Harvey returned to England. In 1615 he was 
called to lecture on anatomy at the Royal College of 
Physicians in London. The manuscript notes of his first 
course show that he had already mastered the idea of the 
circular movement of the blood. 

In 1618 Harvey was appointed physician to King 
James I, and became very busy. He continued, however, 
to lecture regularly at the Royal College of Physicians. 
These lectures embodied the most revolutionary doctrine 
delivered by the most sober and conservative of teachers. 
Their full importance was not appreciated for some years. 



Harvey and Circulation oj Blood 109 

In 1628 there happened an event of primary importance 
for the progress of science, the publication at Frankfort of 
Harvey’s great work. It is a miserably printed little Latin 
quarto of 72 pages. In this Anatomical Dissertation con- 



60 61 


Fig. 60. Diagram of the circulation of the blood. Fig. 6i . From Pecquet (1651). 
A dog opened to show the main lymphatic channel or thoracic duct. This duct 
arises in the receptaculum chyli, a structure in the abdomen between the kidneys, 
into which chyle is brought from the intestines by the lacteah. From the rece¬ 
ptaculum chyli the thoracic duct passes up through the chest or thorax along the 
backbone. It terminates by branches which empty into the venous system, 
usually in the suhclanjian njeins. 

cerning the Motion of the Heart and Blood he refers to 
his examination of the heart’s action in some forty species, 
including worms, insects, Crustacea, and fish. It would 
to-day be regarded as a ‘comparative’ study. Since his 
time, physiologists have concentrated their attention almost 
exclusively on the workings of the body of man and of the 



no Kebirth of Inquiry 

higher animals which resemble him. During the last few 
years there has been a tendency to return again to the 
‘comparative’ method on which the science of physiology 
was started by Harvey. 

It is by no means difficult nowadays to understand the 
circulation of the blood (Fig. 6o). If a frog be opened, the 
heart can be seen beating and the blood being propelled 
through the arteries and returned through the veins. With a 
microscope the capillary vessels can be discerned in the 
web of the frog’s foot, and the blood can be watched as it 
courses through these minute vessels which connect arteries 
and veins. But Harvey had no microscope and he was 
brought up with a wrong view of the action of the heart. 

He observed that the heart, if grasped, can be felt to 
harden during its active or contracted period. Thus it may 
be compared to the biceps muscle of the arm which does the 
same. He therefore regarded the heart as a hollow muscle. 

Next he observed that the contraction of the heart is 
simultaneous with the expansion of the arteries. The 
expansion of the arteries can be felt at one’s own wrist and 
is, in fact, the pulse. The determination of the pulse as 
simultaneous with the contraction of the heart was very 
important, since the pulse had been thought to be the 
active expansion of the artery. But as the artery expands as 
the heart contracts^ it seemed to Harvey that the arteries must 
be expanding because blood is forced into them by the heart. 

Harvey watched the hearts of cold-blooded animals. 
These beat slowly, and their action can be the more easily 
followed. He saw that the auricles contract first and that 
their contraction is followed by that of the ventricles. 

Harvey now referred back to his knowledge of the 
structure of the heart. Blood, he observed, can enter the 
right auricle through the great vein, the vena cava, the 
opening of which is patent. When the right auricle con¬ 
tracts it drives the blood into the right ventricle, which is 



Harvey and Circulation oj Blood 111 

still dilated. The opening from right auricle into right 
ventricle, though guarded by valves, is then quite patent. 

Having reached the right ventricle, the blood cannot 
return whence it came even when the right ventricle con¬ 
tracts, because valves between the auricle and ventricle 
prevent this. When the right ventricle contracts, the blood 
must therefore pass into the only exit open to it, namely 
the pulmonary artery. Again, it is prevented from return¬ 
ing to the ventricle by valves at the root of the pulmonary 
artery. Of these valves Harvey made a special study. 

He then turned to examine the left side of the heart. 
He found there a state of things very similar to that in 
the right side. Blood can enter the left auricle from the 
pulmonary vein, and from the left auricle it can pass into 
the left ventricle. When the left ventricle contracts, the 
blood within it is stopped from returning into the left 
auricle by valves which lie between the left auricle and the 
left ventricle. It is thus forced into the only exit open to 
it, namely, the great artery or aorta. Return from there 
is also stopped, because the root of the aorta, like that of 
the pulmonary artery, is guarded by valves (Fig. 6o). 

Some of these observations had been made by Harvey’s 
predecessors, Galen among them, but none had put them 
altogether in logical order. At this stage, however, 
Harvey introduces an entirely new idea. He insists that 
the flow of blood is not only in one direction, but is 
continuously in one direction. This leads him to his crucial 
discussion. Consider, he says, the capacity of the heart. 
Suppose the ventricle holds but two ounces. If the pulse 
beats seventy-two times in a minute, then in one hour 
the left ventricle will force into the aorta no less than 
72 x6ox 2 = 8,640 of ounces = 540 pounds, i.e. three 
times the weight of a heavy man! Where can all this blood 
come from ? Where can it all go to ? The point is made with 
great force. There is no parallel to it in earlier literature. 



112 Rebirth of Inquiry 

Harvey reflected that blood sent out by the aorta can 
come only from the veins. This conclusion was reinforced 
by a very simple experiment. If an artery is cut, the 
animal bleeds to death. The bleeding gets slower and 
slower until finally it ceases as the blood is exhausted and 
death approaches. The reason must be that the blood 
that is lost does not reach the veins, and so cannot 
return to the arteries. 

The great discovery now dawned on him. 

‘I began to think whether there might not be a movementy as it 
werey in a circle, I saw that the blood, forced by the action of the 
left ventricle into the arteries, was sent out to the body at large. In 
like manner the blood forced by the action of the right ventricle 
into the pulmonary artery is sent out to the lungs.’ 

It was now manifest why in dead animals there is 
usually so much blood in the veins and so little in the 
arteries, so much in the right ventricle and so little in the left. 
‘T.'he true cause is that there is no passage to the arteries save 
through lungs and heart. When an animal ceases to breathe and the 
lungs to move, the blood in the pulmonary artery no longer passes 
therefrom into the pulmonary vein and thence to the left ventricle. 
But the heart, surviving for a while and contriving to pulsate, the 
left ventricle and the arteries continue to distribute their blood to 
the body at large, and to send it into the veins’ [where it accumu¬ 
lates but whence it does not return]. {Slightly abbreviated,'] 

In the light of the new idea, Harvey repeated the simple 
experiments on the arm of a living man from which his 
teacher Fabricius had drawn his erroneous conclusion 
(pp. 107-8). By placing the fingers of one or both hands 
along the veins at different points, he showed that the 
flow of blood was always toward the knots and not away 
from them. Harvey’s demonstration was now complete. 

‘All things, both argument and ocular demonstration, thus confirm 
that the blood passes through lungs and heart by the force of the 
ventricles and is driven thence and sent forth to all parts of the body. 




Fig. 62. Lines from autograph lecture notes of William Harvey, written in 
1615 and containing the first reference to the circulation. Transcription \ 


V\H constat per fabricam cordis sanguinem 
per pulmones in Aortam perpetuo 
transferri, as by two clacks of a 
water bellows to raysc water 
constat per ligaturam transitum sanguinis 
ab artcriis ad venas 
unde A perpetuum sanguinis motum 
in circulo fieri pulsu cordis. 

Translation’. —On account of the structure of the heart William Harvey holds 
that the blood is constantly passed through the lungs into the aorta, as by two 
clacks of a water bellows to raise water. Moreover, on account of the action of 
a bandage [on the vessels of the arm] he holds that there is a transit of blood from 
the arteries to the veins. It is thus demonstrated that a perpetual motion of the 
blood in a circle is caused by the heart beat. 

Explanation of Terms: A clack is a valve, and a <water hellov^s is a pump 
A is Harvey’s shorthand sign for it is demonstrated, and his abbreviated initial 
\\H is used to indicate his own views or observations. The clacks referred to are 
the valves in the aorta and pulmonary artery. 


2613.3 


I 



114 Rebirth of Inquiry 

There it makes its way into the veins and pores of the flesh. It 
flows by the veins everywhere from the circumference to the centre, 
from the lesser to the greater veins. By them it is discharged into 
the vena cava and finally into the right auricle of the heart. T he 
blood that is carried in one direction by the arteries, in the other 
direction by the veins, in so great a quantity that it cannot possibly 
be supplied all at once from the food that is taken into the body. It 
is therefore necessary to conclude that the blood in animals is impelled 
in a circle^ and is in a state of ceaseless movement. It must be, more¬ 
over, that this circulation is the act of function of the hearty which 
performs this act or function through the vessels.^ 

§ IT. Influence of the Discovery of the Circulation of the Blood. 

Harvey’s discovery was decisive in several directions. 

Firstly, a word must be said of Harvey in relation to 
his predecessors and successors. Galen and those who 
followed him, including Mondino, Leonardo, Servetus, 
Vesalius, and Fabricius, knew well that blood went forth 
from the heart to the body by the great arteries. They 
knew, too, that there are valves at the roots of these vessels 
which prevent its return. Did they not then see that blood 
could not go on being pumped into the body for ever 
without returning whence it came ? 

This question has often been asked, and there is a com¬ 
plete answer to it. Galen and the others think and speak 
of the blood as irrigating the body. Now in irrigation 
water is led, by a conduit, to channels out into the field. 
Thence the water seeps slowly into the earth. From the 
earth it is absorbed into the substance of the corn or lost 
by evaporation. So thought the ancients of the body. The 
blood that went forth to it was building the tissues and 
was so used up, parts of it being lost in perspiration and 
excretion. Not so Harvey. He saw that the blood did not 
seep in slowly, but rushed through in a mighty torrent. 
Men had yet to see what a terrifically active thing life is. 
It took long to learn, and many of Harvey’s followers failed 



Influence of Discovery of Circulation 115 

to realize it. Thus, Harvey’s contemporary, the philosopher 
Descartes (1596—1650), author of the first text-book of 
physiology (pp. 354—6), accepted the doctrine of the circu¬ 
lation but still spoke of it in the old terms of slow irrigation. 

Next, we note that Harvey was the first to give a really 
adequate explanation, in physical terms, of any bodily 
process. From Harvey’s time to our own the interpretation 
of bodily activities in terms of physics and chemistry has 
been one of the main tasks to which biologists have set 
themselves. Harvey’s work is thus not only the starting- 
point of the modern science of physiology, but it is also 
the first milestone on the road to the modern rationaliza¬ 
tion of biological thought. 

Lastly, we note, in those who follow Harvey, a change 
in 'ittitude towards living processes. Until his day bio¬ 
logical discussion had been full of vague terms intended 
to explain living activities. Such conceptions as ‘innate 
heat’, ‘animal spirits’, ‘pneumatic force’, often merely 
darkened counsel with words. Harvey’s book rang the 
death knell of a whole vocabulary of such mysterious 
phrases. Though they survived for generations, the subse¬ 
quent history of physiology is largely the history of the 
replacement of these vague entities by the simpler con¬ 
ceptions introduced into physics by Galileo (1564—1642) 
and into chemistry by Boyle (1627-91). In this sense 
Flarvey initiates the modern period of biology. 

And yet, in a very curious sense, Harvey belongs to the 
older rather than to the newer dispensation. The biologist 
of our time thinks of himself as advancing into new and 
untrodden tracts. This, however, was not how Harvey 
thought of himself. He was a man of very conservative 
views. He was steeped in Galen. Above all, he proclaimed 
himself an adherent of Aristotle. In enunciating his great 
discovery Harvey almost disclaims originality and suggests 
that it is but a return to Aristotle! 



116 Rebirth of Inquiry 

Thus, although Harvey is beyond question one of the 
great initiators of modern biology, we can also treat him 
as the last of the classical tradition. We shall not meet 
others who work and think in his conservative spirit. 

As we leave Harvey and his quaint quotations of an 
Aristotle misunderstood, we pass into a world not only 
of new discoveries but of a new outlook. Harvey stands 
just on the frontier. His gaze is turned in both directions. 
As the day breaks he salutes the dawn but ever and anon 
he casts a longing glance at the monstrous shadows that 
flee away and give place to the clearer outline of a grander 
landscape. He is in the new world and yet not of it. His 
experimental method is a reconstruction rather than a new 
creation. His stubborn heart is yearning for an im¬ 
possible reunion with Hippocrates and Galen and Aris¬ 
totle. 


Fig. 63. Diagram of embryonic membranes and circulation in bird or reptile. 
Fig. 64. Diagram of embryonic membranes and circulation in mammal. 



63 64 







MALOCOSTEUS INDICUS 
Philippine Islands 
Depth 500 Fathoms 



// MACRURUS FASCIATUS 
Fast coast oFsouthern 
extremity oF South 
America 

Depth 140 Fathoms 


Fig. 65. Some fishes from the deep sea obtained by the Challenger, 





Fig. 66. RENfi DESCARTES, 1596-1650. 
an engraving of the portrait by Franz Hah, 




PART. 11 . THE HISTORICAL FOUNDA¬ 
TIONS OF MODERN BIOLOGY 

IV 

ON THE INDUCTIVE PHILOSOPHY AND 
SOME OF ITS INSTRUMENTS 

§ I. The Change from Medieval to Modern Thought 

T he Revival of Learning, of Art, of Philosophy arose 
in Italy. It was intimately connected with the redis¬ 
covery of the ancient classics and with their more effective 
study. Of these ancient writings those on the sciences 
were late in arrival and last to be understood. 

The movement known as the Renaissance spread 
northwardfrom Italy to France, Switzerland, and Germany, 
and then to England and the Scandinavian countries. It 
was succeeded by the scientific wave which, as with the 
humane studies, having crossed the Alps, reached the 
other continental states before affecting England and the 
Baltic lands. At the end of the sixteenth century the 
northern countries had still produced but two men of 
first-rate scientific importance—the English physicist, 
William Gilbert (1540—1603), and the Danish astronomer, 
Tycho Brahe (1546—1601). As regards biology there had 
been as yet no worker of the front rank north of the Alps. 
The biological sciences have usually lagged behind the 
physical. The first important exposition of biological 
science north of the Alps was the work of William Harvey, 
trained by that true nurse of the sciences, free Padua. The 
pre-eminence of Padua will be understood if it be remem¬ 
bered that there, alone among the universities, religious 
tests were so applied as to be, in effect, nugatory. 

It has been convenient to treat Harvey’s main work as 
the last flower of Renaissance biology rather than the 



1 20 Inductive Philosophy 

first of modern times. The turn of the sixteenth into the 
seventeenth century wrought, however, great changes in 
the philosophical outlook of the age—changes in which 
Harvey’s conservative mind shared only imperfectly. A 
whole series of important thinkers had undermined the 
medieval system of thought and freed it from the tram¬ 
mels of ecclesiastical Aristotelianism. Men were begin¬ 
ning to look to an age when the nature of the physical 
world would be revealed by the new means of investiga¬ 
tion. As is wont to happen at times of intellectual ferment, 
the new methods were actually in general application before 
their mode of action was fully understood or explicitly 
stated. Men of science were employing the inductive philo¬ 
sophy before the philosophers had adequately expounded 
its nature. 

We cannot follow the long line of those who laid the 
foundations of the new philosophy. Four culminating 
figures of this great intellectual movement will, however, 
concern us. These are, in order of seniority, Francis 
Bacon (1561—1639), Marin Mersenne (1588—1648), 
Pierre Gassendi (1592-1655), and, above all, Rene 
Descartes (1595-1650). With them Science passes to 
its modern stage. 

§2. Francis Bacon {1^61— 

How the modern world of scientific ideas differs from 
the old order we can, perhaps, best see by examining the 
philosophy of Francis Bacon. Was he truly a prophet of 
science.? He erred in his view of the real nature of the 
scientific process, nor need we exalt the accuracy of his 
particular vision. But an examination even of his errors 
will help us, who stand upon his shoulders, to see more 
clearly things hidden from ‘the greatest, wisest, meanest 
of mankind’. 

The juristic eminence of Francis Bacon is universally 



Francis Bacon 121 

conceded, the magic of his pen is abundantly evident, the 
ingenuity of his conceptions is generally allowed. But 
with all these powers he fails us in the first demand that 
we make upon a prophet—clarity of vision. His view of 
the vast developments of science in the ages that were to 
follow was far from being clear and undisturbed. More¬ 
over, in applying what he believed to be the method of 
the new science. Bacon showed little skill and had no 
success. He thus failed in some measure as a scientific 
philosopher, and to a still greater extent as a practical 
man of science. 

Let us consider Bacon’s attitude toward the investiga¬ 
tion of Nature. What was this new scientific process which 
he practised worse than he preached.? The answer can 
now be given in a word. The process of scientific dis¬ 
covery is essentially an act of judgement. In ultimate 
analysis a scientific discovery is a work of art. This Bacon 
quite failed to envisage. 

Bacon was for conducting his investigations by collect¬ 
ing all the facts. This done, he thought, the facts might 
be passed through a sort of automatic logical mill. The 
results would then emerge. But this method cannot be 
applied in practice, since facts, phenomena, are infinite 
in number. Therefore we must somehow choose from 
among them, though Bacon thought otherwise. 

How then shall we choose our facts.? Experience shows 
that they only choose profitably who have a knowledge 
of how their predecessors have succeeded or failed in their 
choosing. In other words, the process of choosing facts 
is an act of judgement on the part of a learned chooser^ 
the man of science. So it is also with the process of 
choosing words on the part of the word-chooser whom 
we call a poet. The choice of the man of science, as of the 
poet, is controlled by knowledge of his art—of ‘his sub¬ 
ject’ as we are wont to call it at the Universities or in the 



122 Inductive Philosophy 

laboratories. The man of science, like the poet, exercises 
his judgement to select those things which bear a certain 
relation to each other. And yet no skill in reasoning, 
however deft, no knowledge of the nature of scientific 
method, however profound, no acquaintance with his 
science, however complete, will make a man a scientific 
discoverer. Nor, for that matter, will any learning in the 
lore of metre or of the nature and history of poetry make 
a man a poet. Men of science, like poets, can be shaped, 
but they cannot be made. They must be born with that 
incommunicable power of judgement. 

The scientific man in the prosecution of his art of dis¬ 
covery has to practise three quite different mental pro¬ 
cesses. These may be distinguished as firstly, the choosing 
of his facts; secondly, the formation of an hypothesis that 
links them together; and thirdly, the testing of the truth 
or falsehood of the hypothesis. When his hypothesis 
answers numerous and repeated tests, he has made what 
is usually called a ‘scientific discovery’. It is doubtless 
true that the three processes of choosing facts, drawing a 
hypothesis or conclusion, and testing the conclusion, are 
often confused, in his own thinking, by the man of science. 
Often, too, his demonstration of his discovery, that is 
the testing of his hypothesis, helps him, more or less 
unconsciously, to new acts of judgement, these to a new 
selection of facts, and so on in endless complexity. But 
essentially the three processes are distinct, and one might 
be largely developed while the others were in a state of 
relative arrest. 

In this matter scientific articles, and especially scientific 
text-books, habitually give a false impression. These 
scientific works are composed to demonstrate the truth 
of certain views. In doing so they must needs obscure the 
process by which the investigator reached those views. 
That process consists, in effect, of a series of improvised 



Francis Bacon 123 

judgements or ‘working hypotheses’, interspersed with 
imperfect and merely provisional demonstrations. Many 
hypotheses and many demonstrations have had to be dis¬ 
carded when submitted to a further process of testing. 
Thus an article or book, which tells nothing of these side 
issues, blind alleys, and false starts, is, in some sort, an 
attempt on the part of the investigator to conceal his 
tracks. For this reason, among others, science can never be 
learned from books, but only by contact with phenomena. 

The distinction between the process of discovery and the 
demonstration of discovery was consistently missed during 
the Middle Ages. On this point, in which our thought 
is separated from that of the men of those times. Bacon 
remained in darkness. He succeeded, indeed, in em¬ 
phasizing the importance of the operation of collection of 
facts. He failed to perceive how deeply the act of judge¬ 
ment must be involved in the effective collection of 
facts. 

As an insurance against bias in the collection and 
error in the consideration of facts, Bacon warned men 
against his four famous Idols^ false notions of things, 
erroneous ways of looking at Nature. There were the 
Idols of the Tribe^ fallacies inherent in humankind in 
general, and notably man’s proneness to suppose in nature 
greater order than is actually there. There were the Idols 
of the Cave^ errors inherent in our individual constitution, 
our private and particular prejudices, as we may term 
them. There were the Idols of the Market-place^ errors 
arising from received systems of thought. There were 
the Idols of the Theatre^ errors arising from the influence 
of mere words over our minds (Novum Organum^ 1620). 

But did not Bacon himself fail to discern a fifth set 
of idols } These we may term the Idols of the Academy. 
Their worship involves the fallacy of supposing that a 
blind though learned rule can take the place of judgement. 



124 Inductive Philosophy 

It was this that prevented Bacon from entering into the 
promised land, of which but a Pisgah view was granted 
him. 

Yet despite Bacon’s failure in the practical application 
of his method, the world owes to him some conceptions 
of high importance for the development of science. 

(<2) He set forth the widening intellectual breach which 
separated his day from the Middle Ages. He perceived 
the vices of the scholastic method. In the clarity and vigour 
with which he denounced these vices, he stands above those 
of his contemporaries who were striving toward a new 
form of intellectual activity. 

{¥) He perceived, better than any of his day, the extreme 
difficulty of ascertaining the facts of nature. He forecasted 
the critical discussion that characterizes modern science. 
He missed, however, the important point that the 
delicate process of observation is so closely interlocked 
with discussion that both must almost necessarily be 
performed by the same worker. 

(r) English writers of the later seventeenth century 
concur in ascribing to the impetus of Bacon’s writing the 
foundation of the Royal Society. Thomas Sprat (1635- 
1713), Bishop of Rochester, the first historian of the Society, 
assures us of this (1677), as do Oldenburg and Wilkins, 
its first secretaries. The opinion is fully confirmed by 
Robert Boyle (i 627-9 ^ )> the most effective of its founders, 
and by John Locke (1632-1704), the greatest of English 
philosophers. 

(i/) It is, perhaps, in the department of psychological 
speculation that the influence of Bacon has been most 
direct. The basic principle of the philosophy of John 
Locke is that all our ideas are ultimately the product of 
sensation {Essay concerning Human Understandings 1690). 
This conception is implicit in Bacon’s great work, his 
Novum Organum. Through the ‘practical’ tendency of his 



Francis Bacon 125 

philosophy and especially through Locke, Bacon was the 
rather of certain characteristically English schools of 
thought in psychology and ethics. These have affected 
deeply the subsequent course of scientific development. 

Whatever his scientific failures, we may thus accord 
to Bacon his own claim that ‘he rang the bell which called 
the wits together’. 

§ 3. Rene Descartes (i596—1650) 

The role of Rene Descartes was very different from 
that of Francis Bacon. The great French thinker was the 
first in modern times to produce a complete and effective 
theory of the Universe (Principia philosophiae, Amster¬ 
dam, 1644). This became widely current. Though this 
scheme did not hold the field for long, yet the thought 
of Descartes exercised the most profound influence on 
the whole subsequent course of science. His general view 
of the universe covered also the living things therein. To 
the physical and mathematical sciences Descartes made 
important contributions that are of biological application. 
Notably, the so-called Cartesian co-ordinates, in constant bio¬ 
logical use for graphic methods, were introduced by him 
{La Geometrie, I^eyden, 1637) and still bear his name. 
Further, he has exercised very weighty direct influence 
on the development of physiological thought, especially 
through his Traite de Phomme (Paris, 1664; Latin version, 
Leyden, 1662, pp. 354-5). This book, though not pub¬ 
lished till after its author’s death, was complete by 1637 and 
was the first important work that accepted the circulation 
of the blood. 

Descartes is usually regarded as the founder of modern 
philosophy. In his fascinating Discourse on Method 
(Leyden, 1637) he expounds the procedure that he pro¬ 
posed to adopt in his own investigations. The substance 
of this is still recommended to the scientific worker. 



126 Inductive Philosophy 

though often with less succinctness than characterized 
Descartes. He resolved: 

[a) ‘Never to accept anything as true which I do not clearly 
know to be such, avoiding precipitancy and prejudice and com¬ 
prising nothing more in my judgement than is absolutely clear and 
distinct in my mind. 

{h) ‘Ih divide each difficulty under examination into as many 
parts as possible. 

{c) ‘'Fo proceed in my thoughts always from the simplest and 
easiest to the more complex, assigning in thought a certain order 
even to those objects which in their nature do not stand in a 
relation of antecedence and sequence—i.e., to seek relation every¬ 
where. 

{d) ‘I'o make enumerations so complete and reviews so general 
that I might be assured that nothing was omitted.’ 

Descartes believed that truth is ascertainable solely by 
the application of these principles. His field of ascertain¬ 
able truth includes that occupied by religion. This point 
is important for the subsequent history of science. If he 
be right, revealed religion is superfluous, since the data 
of religion should be ascertainable by the same process 
as the data of science. This was widely held, especially 
in the eighteenth century. Those who took this view came 
to be known as Deists, The school to which they belong 
has exercised great influence on the development of 
science. 

An aspect of the thought of Descartes that has set its 
mark upon modern philosophy is his criterion of truth. 
For him the fundamental test of truth is the clearness with 
which we can apprehend it. Cogito ergo sum^ T think, 
therefore I am’, is the most clearly apprehended of all 
truths. Therefore, our thinking, at least, can be no 
illusion. The cogency of our thought may be denied, but 
that we do think, and that we therefore exist, is sure. In 
some of his further deductions he applies the same 



Descartes 127 

principle less cogently. Thus he holds that the conception 
of the soul as separate from the body is clear and even 
obvious. He maintains that it must be accepted as a 
reality on that account. 

The general conception of the nature of the material 
universe set forth by Descartes places him among the 
moderns, and separates him from his predecessors and 
even from Francis Bacon. We cannot discuss his view 
of the universe, but one of his theses we must consider. 
Descartes, unlike Bacon and unlike the philosophers of 
the Middle Ages, regarded the Universe as infinite. He 
did not hold, as did Bacon, that the earth is at the centre 
of the solar system. This change of view is clearly of 
fundamental importance for astronomy and for any general 
conception of the physical universe. It is, however, less 
widely recognized that it exerted of necessity an equally 
revolutionary influence upon other sciences, including 
biology. The point needs some elucidation. 

The old Aristotelian philosophy of the Middle Ages 
treated the universe as limited by the sphere of the fixed 
stars. In such a finite world—with earth as centre— 
science, that is the observation of Nature, must needs 
occupy a subordinate place. The general scheme of the 
world being known, the sole aim of science, in such a 
world, was to fill in the details. This was doubtless a 
difficult task, but it was terminable. Thus accounts of the 
universe could, on this view, be made so complete that 
at last a man could know all that there was to be known 
about Nature. The undertaking was comparable, let us 
say, to a statement of the possibilities of the game of 
chess. The intricacies of that game are very difficult to 
master, but their complete mastery could be accomplished. 
If a sufficient number of men of sufficient ability were to 
apply themselves systematically to chess problems for a 
sufficient time, the subject could be explored to the very 



128 Inductive Philosophy 

end. The number of possible combinations and positions 
in chess, though very great, is yet limited and is calculable. 

Such was the view of Nature held by the medieval 
thinker. For this reason scientific effort often took the 
‘encyclopedic’ form during the Middle Ages and Renais¬ 
sance. Such attempts to compass all knowledge did not 
then seem by any means foredoomed to failure. The task 
was hard, but why should it be thought insurmountable if 
the universe be finite ? 

Now at the end of the sixteenth and at the beginning of 
the seventeenth century there came a change in this 
attitude. Copernicus (1473—1543) had set forth a scheme 
of the universe, in which the earth did not occupy the 
central-position {De revolutionibus orbium celestium^ Nurem¬ 
berg, 1543). Giordano Bruno (1548—1600) had repre¬ 
sented the universe as infinite \l)e Vinjinito universo, 
London, 1584). The Englishman William Gilbert (1540— 
1603) was the first important disciple of Bruno, and prob¬ 
ably met him in London. The views of Bruno and Gilbert, 
cloaked under the name of Copernicus, were supported by 
Galileo (1564-1642) and by Kepler (1571-1630). The 
details of these men’s work lie outside our discussion, but 
their conception of the endless extension of the universe 
and the acceptance of that view by Descartes necessarily 
affected all the sciences. 

The biological sciences were not in any way exempt. 
For with an infinite universe as a postulate, does not the 
adventure of science take on an entirely new character.? 
There can now be no hope of complete comprehension. 
Is not the field boundless.? Science is no longer a sea to be 
explored and mapped. Seas, even oceans, can be crossed, 
but for science there is no further shore. The task before 
the medieval encyclopedist had been regarded as vast but 
susceptible of ultimate accomplishment. Complete know¬ 
ledge could be attained by extension of the old method. 



Descartes 129 

The stress now came to be laid on intensiveness. Specialism 
became possible, and, though its day was not yet, its 
advent was inevitable. The ‘infinite universe’ rang the 
death knell of the encyclopedist. But more, it rang in 
a new era not for religion and philosophy alone but also 
for science. Of that era Descartes was a herald. 

There is some evidence that we are now living at the 
very end of the scientific era which Descartes initiated, 
and that radically new conceptions are dawning for science. 
It is at least possible that we shall need, in the near 
future, to revise our views as to the scope and end of 
science. It is certain that scientific methods are being 
subjected to more searching analysis than ever before. 

For the completion of the system of Descartes, it was 
necessary for him to include the phenomena presented by 
living things. He was not unsuccessful in his efforts, 
though we must, for the moment, defer their consideration 
(p. 354). But a very important point for us here is that, 
by their attitude toward science, Descartes and Bacon 
became the progenitors of the associations known as the 
‘Scientific Societies’or‘Academies’(p. 135). The essence 
of a scientific academy may be summed up in two words 
'organization’ and ‘specialization’. The organization of 
scientific effort was explicit in the system of Bacon, the 
specialization of scientific effort was implicit in the philo¬ 
sophy of Descartes. 

For the extension of natural knowledge, science has 
come to depend, more and more, upon co-operative effort. 
Patrons of learning played an important part in the earlier 
period. They were the progenitors of the Academies. Very 
helpful to scientific advance have been Collections of living 
things in botanical and zoological gardens, Museums where 
specimens can be studied and inspected, and scientific 
Journals in which the results of research can be set forth. 
Apart from these means of communicating and preserving 



130 Inductive Philosophy 

knowledge, we must note that a new attitude toward 
nature came in with the advent of the microscope. This 
is the biological \ins,Xx\ime.rvt par excellence. We shall devote 
some attention to its introduction (p. 145). 



Fig. 67. The University of Padua about 1600. In the foreground are several 
groups of students. One group is headed by a professor in academic dress. 
Over the door is written Gymnasium omnium disciplinarum, ‘I'he University of 
all departments of learning’, and above this Sic ingredcre ut te ipso quotidie 
doctior e^adas, ‘Enter in such mood that you daily come out wiser’. The 
front ground floor is occupied by shops. In this little building was given the 
most important biological teaching of the sixteenth and seventeenth centuries. 

It still stands almost unaltered. 

§ 4. Early Collections of Plants and Animals 

The first step in the process of making science is the 
systematic collection of facts. In biology this is specially 
aided by botanical and zoological gardens. The habit of 
forming these is of great antiquity. We hear of them from 
Pliny. The monasteries of the Middle Ages often had 
their herb gardens. The plans of several have survived, 


































Collections oj Plants and Animals 131 

together with more than one work on their care. Exotic 
animals, too, were occasionally brought to medieval courts. 
A well-known instance was the elephant sent to Charle¬ 
magne about 800 A. D. The curiosity and luxury of the 



Fig. 68. Sketch of an Indian rhinoceros by Albrecht Diirer. It was made 
from a drawing sent by a friend from Lisbon in 1515. 


Renaissance were, however, specially conducive to the 
formation of such collections. 

Toward the end of the fifteenth century, collections of 
live animals were founded by many princes. This was 
notably the case in Italy. The enlightened Duke Ferrante 
(1433-94) of Naples owned the most famous of con¬ 
temporary animal parks. It contained a giraffe and a 
zebra, two creatures not previously seen in Europe, which 
were gifts from the Caliph of Bagdad. Many animals 
were collected at Florence by Lorenzo the Magnificent 
(1449—92). There was also a collection at Lisbon where, 
for the first time, a rhinoceros was brought in 1513. The 
painter, Albrecht Dvirer, has left a sketch of it (Fig. 68). 

Since the sixteenth century the practice of keeping 
botanical and zoological gardens has been continuous. 
The sixteenth century saw at Padua the establishment of 



132 Inductive Philosophy 

the first botanical garden attached to a university (1545). 
Other Italian universities, notably Pisa (1547) and 
Bologna (1567), soon did the same. Leyden (1577) and 
Montpellier (1598) and Oxford (1621) followed. His¬ 
torically a very important place has been occupied by the 
Jardin des Plantes founded at Paris by Cardinal Riche¬ 
lieu (1585—1642) in 1626. Dried collections of plants— 
Herbaria—began to be formed by private collectors in 
the sixteenth century. 

The exploration of the world soon began to make itself 
felt in biological literature. Voyages of exploration, and 
notably the opening up of America and of the fiast Indies, 
resulted in the recognition of many kinds of foreign plants 
and animals. The Coloquios dos simples e drogas he cousas 
medicinais da India (‘Discourses on the simples and drugs 
of India’, Goa, 1563) of the Portuguese Garcia del 
Huerto (1490—1570) was one of the first books printed in 
India. It contains the first description of Indian plants, 
among them being the coco-nut. The Spaniard Nicolas 
Monardes (1493—1588) performed somewhat the same 
service for America. His work (Seville, 1596) was soon 
Englished under the cheerful title Joyfull Newes out of 
the Newe founde Worlde (London, 1577). It contains 
descriptions of the armadillo, of tobacco, and of many 
other plants and animals. The ingenious Venetian 
traveller, Prospero Alpini (1533—1617), issued his finely 
illustrated work, Pe pi antis Aegyptii, in 1591. It contains 
numerous good figures and descriptions including the 
first account of coffee. The most remarkable early faun- 
istic and floristic work was produced as a combined effort 
by the Academy of the Lynx (p. 135), Plantarum, anima- 
lium, mineralium mexicanorum historia (complete edition, 
Rome 1651). It gives a fully illustrated account of all 
the living things known at the time in Mexico. 

In the sixteenth century many attempts were made to 



Collections oj Plants and Animals 133 

acclimatize exotic plants. One of the best-known instances 
is that of tobacco. A pioneer of its culture was Jean Nicot 
(1530-1600), French ambassador to Portugal, whence he 
brought seeds which he gave to Catherine de Medici (i 519- 
89). After Nicot the plant has been named Nicotianay 
whence the alkaloid nicotine. Other plants acclimatized in 
the sixteenth and seventeenth centuries were the Jerusalem 
artichoke, arrowroot, tomato, maize, pumpkin, and acacia. 
Very remarkable is the case of the agave which, though now 
dominant in the scenery of the Mediterranean area, was 
introduced from Mexico about the middle of the sixteenth 
century. The introduction of the potato and the turnip 
were of very great economic importance. The one provided 
a cheap carbohydrate and antiscorbutic food. The other, by 
making it possible to keep cattle through the winter, has 
made fresh meat an accessible commodity the year round. 

§ 5. Parly Patrons of Science 

In the later sixteenth century it became generally recog¬ 
nized that science was a study whose devotees were some¬ 
what separated from the rest of mankind. They soon 
began to speak of themselves as the curiosi rerum naturae^ 
‘inquirers into Nature’s ways’, ‘the curious’, or ‘the 
virtuosi'. Their peculiar interests and character called for 
some means of intercommunication. 

This need was but imperfectly supplied by correspon¬ 
dence when posts were still uncertain, slow, and costly. 
Thus arose a class of eminent and wealthy patrons of 
science. These amateurs —a noble title, too often now 
debased^—sought to bring together their less fortunate 
colleagues in their houses, or to store their letters for 
subsequent discussion or distribution. 

Such a function was performed in England, in modest 

* The word appears in the higher sense in sixteenth-century French. Thus 
Rabelais (died 1553) speaks of an ‘amateur non seulement des lettres, mais aussi 
des gens lettr<?s’. 



134 Inductive Philosophy 

fashion, by William Gilbert (1544—1603), physician to 
Queen Elizabeth. He was the first Englishman to occupy 
a position of high importance among the ‘curiosi rerum 
naturae’. 

A more influential ‘amateur’ was the wealthy French¬ 
man, Nicholas Fabri de Peiresc (1580—1637). This most 
industrious and learned man acted for many years as a 
general agent for the exchange of scientific knowledge and 
ideas. He made it his business to know every one with 
any scientific attainments, whatever his nationality. His 
enthusiasm was boundless and tireless. He was intimate 
with Galileo, and bought forty telescopes that he might 
verify the discoveries of the great Florentine. He followed 
closely the investigations of Aselli on the lacteals and of 
Harvey on the circulation. He won the philosopher 
Pierre Gassendi (1592-1652) to the study of the works 
of Galileo and Kepler, and thus made a most important 
recruit for science. 

Peiresc left a vast correspondence. It yields a pleasing 
picture of the lives and activities of men of science in the 
early part of the seventeenth century. Other wealthy 
patrons of learning of the time followed a course similar 
to that of Peiresc. 

A very important amateur was the French Minorite 
friar, Marin Mersenne (1588—1648). He was a physical 
investigator. For us his chief importance is for the place 
he occupied as a correspondent and friend of men of 
science. He was intimate with Descartes and was the 
main agent by whom Descartes communicated with other 
learned men. Mersenne was a skilful writer. He trans¬ 
lated important scientific treatises of Galileo and others 
into French, thus acting as a popularizer of science. In 
his cell near Paris the most learned men in France 
habitually gathered. His circle was the origin of the first 
scientific societies in France and England. 



( 135 ) 

§ 6. The First Scientific Societies 

Somewhat like Peiresc in his outlook was the brilliant 
and. wealthy young Italian, Federigo Cesi (1585-1630), 
Duke of Aquasparta. His early death robbed science of 
one of its most forceful advocates. As a youth Cesi drew 
to himself a number of others dedicated to science. These 
young men, despite much opposition, formally banded 
themselves into a scientific society (1609). They named 
it the Academy of the Lynx (‘Accademia dei Lincei’). Soon 
they were joined by Galileo, Peiresc, and others. This 
first scientific academy took the lynx as emblem because 
of its supposedly piercing sight. It was thus natural that 
the improvement in vision given by the microscope should 
make a special appeal to the ‘Lincei’. 

In the event, the Academy of the Lynx made the first 
effective contribution to microscopy (p. 148). The word 
microscope was itself invented by one of the original mem¬ 
bers, Johannes Faber of Bamberg (1574—1629). The 
‘Lincei’ also prepared the first important monograph on the 
Natural History of America (p. 132). With the death of 
Cesi in 1630 the society ceased its activities, though it 
was revived in a later generation. Unfortunately much of 
the co-operative work of the Lincei and practically all 
that of Cesi has disappeared. 

The group of savants around Marin Mersenne was 
more successful in perpetuating itself. It grew in power, 
number, and organization. Without a fixed home, it met 
at the houses of its more influential members. Foreigners 
often visited Mersenne and his circle. Among them were 
men who later became fellows of the English Royal 
Society. Such were the father of vital statistics. Sir William 
Petty (1623—87), and the first secretary of the Royal 
Society, Henry Oldenburg (p. 139). 

Among the more powerful members of the French 



136 Inductive Philosophy 

group was MelchisedecThevenot (1620—92,pp. 140, 158), 
the patron of Swammerdam. It was Thevenot who secured 
the manuscript of that unfortunate Hollander’s Bible of 
Nature (p. 162), and so preserved from loss, perhaps, the 
ablest series of biological investigations of the seventeenth 
century. Stensen (pp. 241, 461) experimented in Theve- 
not’s house, through which there passed a constant stream 
of men of science. Jean Baptiste Colbert (1619-83), the 
minister of the Grand Monarque, Louis XIV, became the 
patron of this society (Fig. 69). In 1668 Colbert gained 
it an official recognition as the Academie des Sciences. The 
early biological work of the Academy, from 1666 onwards, 
was issued chiefly as anatomical descriptions of various 
animals, mostly the work of Claude Perrault (1613—88, 
p. 205). The result was the most sumptuously reproduced 
of all biological works and was distributed as a royal gift. 
(Memoires pour servir a I'histoirc des animaux., Paris a 
Vimprimerie royale, 1771-6 (Fig. 69)). 

The English Royal Society began much as the Academie 
des Sciences. A little later in origin as an informal gather¬ 
ing, it was somewhat earlier in official recognition. The 
Society began in London about 1645. The members 
referred to it as the ‘Invisible College’. The early 
gatherings were often held at Gresham College. Sir 
Thomas Gresham (1519—79) had intended his foundation 
to be a university for London, and some of its ‘professors’ 
were among the earliest members of the Invisible College. 

In 1649 niany members of the Invisible College left for 
Oxford where meetings of the same kind soon began to 

Description o f Fig. 69. 

Louis XIV enters, escorted by Colbert. All the faces are portraits. Different members 
exhibit specimens and apparatus. On the tabic to the left is a microscope and also the 
air-pump recently invented by Boyle (1660). In the background are skeletons of a 
man, a stag, an antelope, and a lion, together with chemical apparatus, growing plants, 
and engineering models. To the right anatomical diagrams, maps, and plans are exhibited, 
and, in the forejground, a telescope, a great concave reflector, a pot of exotic plants, an 
armillary sphere, and a stuffed civet. 











138 Inductive Philosophy 

be held. It was in 1660, the year of the Restoration of the 
British Monarchy, that those assembled at Gresham 
College constituted themselves into a formal society. It 
earned the King’s approval and was incorporated as the 
Royal Society m 1662. 

Before long similar associations were formed in Italy, 
Germany, and Denmark. Scientific societies increased 
steadily though slowly in the eighteenth century. In the 
nineteenth century they began to specialize and their name 
became legion. 

§ 7. The Advent of Scientific Journals 

One of the most familiar manifestations of science in 
our own time is the scientific journal. There are now 
thousands of these in various languages, devoted to various 
branches and aspects of science. 

Early in the second half of the seventeenth century an 
important patron of learning was the Parisian, Denys de 
Sallo (1626-69). the course of his self-imposed task 
this learned man employed copyists to extract for him 
what he regarded as the most remarkable passages that 
he encountered. He was of Colbert’s circle (p. 136), and 
suggested to that Minister of State the publication of such 
extracts at regular intervals. Thus in 1665 was born the 
first scientific periodical, the Journal des Sfavans. 

The journal contained much outside the department 
of science. From the first, however, it undertook to 
publish the scientific discoveries of the day. It was, in the 
beginning, rather what would now be called a ‘review’ 
than a record of original observations. The original ele¬ 
ment gradually became more prominent. Very soon the 
Journal des Sfavans was imitated in England, Italy, 
Germany, Switzerland, and Holland. Before long, more¬ 
over, the Academie des Sciences issued separate volumes in 
addition to its journal. 



Scientific yournah 139 

The Philosophical Transactions of the Royal Society had a 
somewhat similar origin to that of the Journal des Sfavans. 
At first it was a private venture of one of the secretaries of 
the Society. Its early history is of considerable interest. 

In 1662 when Charles II bestowed its charter, the 
Royal Society made a very fortunate choice of two 
secretaries. 

One was the Reverend Dr. John Wilkins (1614-72), 
an old parliamentarian, at whose house in Oxford scientific 
men had been accustomed to meet after the break up of 
the ‘Invisible College’ in London (p. 136). Wilkins, who 
afterwards became a bishop, occupies an important place 
as a philosopher of science. 

The other secretary was Henry Oldenburg (1615—77), 
a native of Bremen, then one of the league of Hansa towns. 
Oldenburg had come to England as diplomatic agent of 
Bremen. Moving to Oxford, he came in contact with the 
chemist Robert Boyle (1627—91), and the other virtuosi 
of that city. Although not himself an original worker, 
Oldenburg had boundless enthusiasm for the new science. 
He conducted on behalf of the Society a vast correspon¬ 
dence with foreign men of science. ‘Foreign members’ 
were early elected, among them being Malpighi (p. 151) 
and Leeuwenhoek (p. 164). 

In 1665, three months after the appearance of the 
Journal des SfavanSy the energetic Oldenburg began on 
his own account the monthly Philosophical Transactions. 
At first they consisted largely of reviews. Their character 
gradually changed until only original contributions were 
included. Later, the responsibility for publication was 
accepted by the Society itself. 

During the seventeenth century the Royal Society pub¬ 
lished also a number of independent scientific treatises. 
Among them were biological monographs by Malpighi, 



140 Inductive Philosophy 

Hooke, and Cirew. None would have seen the light in 
anything like so effective a form had the Society not been 
ready to issue publications independent of its Transactions. 

The object qf these scientific journals has been well 
set forth by Oldenburg himself: 

‘Whereas there is nothing more necessary for the improvement of 
philosophical matters, than the communicating to such as apply 
their studies that way, such things as arc discovered by others; it is 
therefore fit to employ the press to gratifie those whose delight in 
profitable discoveries doth entitle them to the knowledge of what 
this kingdom, or other parts of the world do afford, as well as of the 
progress of the studies, labours and attempts of the curious and learned 
in things of this kind. Such productions being clearly and truly com¬ 
municated, desires after solid and uscfull knowledge may be further 
entertained, ingenious endeavours and undertakings cherished, and 
those conversant in such matters encouraged to search out new 
things, impart their knowledge to one another, and contribute to the 
grand design of improving natural knowledge.’ \ Ahhreviated.\ 

The Italian Academia de Cimento (‘Academy of Experi¬ 
ment^) proceeded along somewhat different lines from 
those of the French and Fmglish societies, in that its 
publications were anonymous and were set out as the 
combined work of the society as a whole. The Cimento 
corresponded with Oldenburg, Thevenot (p. 136), and 
many other eminent men of science. It formed the direct 
inspiration for a German society, but it was nearly a 
generation before the German publication became of 
scientific importance. 

The other scientific journals of the seventeenth and 
eighteenth centuries were formed on the French and 
English model. Those intended for wider reading usually 
imitated the Journal des Sgavans\ those that restricted 
their contributions to the severer type of original contri¬ 
bution followed the Philosophical Transactions. 

The need for specialist journals was not felt until the 



Scientific yournah 141 

end of the eighteenth century. Since then the number has 
become enormous. One of the earliest, in the biological 
series, was The Botanical Magazine^ which is still running 
and has appeared under varying titles since 1777. Among 
the editors have been W. J. Hooker (1785-1865) and his 
son. Sir J. D. Hooker (1817—1911), who between them 
were responsible for it for seventy-six years! 

Almost coincident with the appearance of specialist 
journals was the founding of specialist societies. Of these 
the Linnean Society began to publish its Transactions in 
1791, under the glamour of the name of the great 
naturalist. The Geological Society, founded in 1807, 
began to publish its Transactions four years later. Both the 
Linnean and the Geological Society’s Transactions have 
appeared continuously ever since. 

In France the earliest important biological journal was 
the Ann ales du Museum d'Histoire naturelle. This began in 
1802 and has continued with various changes of title to 
the present day. Cuvier and de Candolle contributed 
largely to its early numbers. 

The German-speaking countries have surpassed all 
others in the number of their biological journals. Worthy 
of special commemoration is the Archiv fur die Physiologie^ 
which began in 1795 edited for a time by 

Johannes Mtiller (p. 388), and the Zeitschriftfur Wissen- 
schaftliche Zoologie, founded by von Siebold (pp. 319, 337) 
andK6lliker(p. 339)in 1848. Bothjournals are still active. 
An influential botanical journal. Flora, appeared first at 
Ratisbon in 1818 and is still in being. 

In the course of the nineteenth century the whole of the 
ever-extending field of science has been covered by the 
formation of Societies and by the publication of their 
journals. In the twentieth century the needs of those who 
are specially interested in the History of Science have been 
met both by associations and by periodical publications. 



142 Inductive Philosophy 

% 8. Early Museums 

The origin of our term ‘museum’ is of some interest. 
In its Greek form it is an adjectival noun applying to the 
Muses. Hence Plato uses the word for ‘a temple of the 
Muses’. Thence it came to be applied to schools for the 
arts and specially for philosophy. The ‘ Museum ’ par 
excellence of antiquity was the great school and library 
founded at Alexandria in the third century b.c. (p. 53). 
To it the word without qualification was customarily 
applied. Among the Latins the word museum was some¬ 
times used for a library. There were no collections in 
antiquity of the kind that we should now call a museum. 
The word itself disappeared with the classical civilization, 
to be revived in the seventeenth century. 

There must, however, always have been a tendency to 
hoard natural curiosities. Even during the Middle Ages 
skeletons and dried specimens formed part of the tradi¬ 
tional stock in trade of the alchemist and the apothecary. 
In the fifteenth century, with the revival of learning, the 
collecting of coins and other antique objects came into 
vogue. Natural curiosities were soon added. The German 
scholar, Georg Agricola (1490—1555), father of minera¬ 
logy and one of the founders of geology, put together 
such a collection. Vesalius, too, had the elements of an 
anatomical museum at his disposal. Among those who 
made scientific collections in the sixteenth century were 
Gesner (pp. 92—4) and Belon (p. 89). Collections of dried 
plants—‘herbaria’—were made by Cesalpini (p. 174) and 
Aldrovandi (p. 94), remains of which are still in existence. 
At Copenhagen the anatomist, Ole Worm (1588-1654), 
had a regular museum of natural curiosities of which a 
good record has come down to us. 

In England the earliest museum of which we have a full 
account was put together by the gardeners John Trades- 



Museums 143 

cant, father and son (1567?—1637; 1608-62). They are 
commemorated in the American plant Tradescantia. The 
younger printed in 1656 a catalogue as Museum Trade- 
scantium: or a collection of rarietiespreserved at South Lambeth 
near London. This collection passed in 1694 to Elias 
Ashmole (1617—92) who installed it at Oxford. Parts 
of this collection have been permitted to survive there. 



Fig’. 70. Montague House, the first home of the British Museum as it ap¬ 
peared tiiward the end of the eightc^enth century. It was built in 1676, Robert 
Hooke (p, 168) being its architect. 

Among them are a couple of fragments of what the 
Tradescant catalogue called a ‘Dodar from the Island of 
Mauritius; it is not able to flie being so big’. This was 
the Dodo (p. 247). 

The first scientific museum in England of real educa¬ 
tional value was that of the Royal Society. Of this a good 
catalogue was printed by Grew (p. 156) in 1681. The 
collection was transferred to the British Museum in 1781. 
Very few of the specimens in Grew’s catalogue can now 
be traced. A famous collection of the period was that 
of Sir Hans Sloane (1660-1753), whose vast hoards were 
acquired by the nation (1759) and formed the nucleus 
of the British Museum (Fig. 66). 

In early days it was very difficult to preserve biological 
















144 Inductive Philosophy 

specimens. They had of necessity to be dry, and thus 
were often deformed and unrecognizable. Three inven¬ 
tions greatly extended museum possibilities. The dis¬ 
covery of alcohol as a preservative, the introduction of 
flint glass, and the devising of methods of injection, were 
all contributions of the seventeenth century. The pre¬ 
servation of dried plants presented, from the first, com¬ 
paratively little difficulty. 

The use of alcohol as a preservative was suggested i'n 
1663 by Robert Boyle, who was himself a collector. The 
idea was soon taken up in other collections, including that 
of the Royal Society. No method has been so helpful for 
the preservation of specimens intended for exact scientific 
investigation. 

Hardly less important has been the introduction of 
flint glass. The older type of glass was unsuitable for 
specimens intended for exhibition. Until the introduction 
of suitable glass in the seventeenth century, full advantage 
could not be taken of alcohol as a preservative. The price 
of flint glass, however, was and still is one of the serious 
items of museum expenditure. 

On account of the high cost of spirit and of glass, there 
was ample room for new methods of preserving dried 
animal specimens. Of these the most effective were injec¬ 
tions of solidifying substances into the vessels. The 
technique of this process was greatly elaborated in the 
seventeenth and eighteenth centuries, notably by the two 
Dutch investigators Regnier de (iraaf (1641-73) and 
Frederick Ruysch (1638—1731). 

The development of the biological museum entered on 
its modern stage in the eighteenth century with the 
formation of John Hunter’s collection (p. 208). From his 
time, museums have been among the main instruments of 
biological advance. They have become linked up not only 
with teaching but also with every form of scientific research. 



( ) 

§ 9- Introduction oj the Microscope 

Until the seventeenth century, naturalists depended 
upon their unaided senses. We now, however, enter upon 
a stage in which the senses become refined and sharpened 
by instrumental aids and especially by the microscope. 
Lenses have played no small part in ushering in the new 
inductive philosophy. Robert Hooke says in his great 
Micrographia (1665) that, by the use of such instruments 
as the microscope, ‘the power of considering, comparing, 
altering, assisting, and improving’ the works of nature can 
be ‘so far advanced by the helps of Arts and Experience, 
as to make some men excel others in their Observations 
and Deductions, almost as much as they do the Beasts.’ 

Lenses, consisting of segments of glass spheres, were 
known in antiquity and were used by the Arabian mathe¬ 
maticians. In Europe they were constructed from the 
thirteenth century onward, Roger Bacon suggested their 
use as spectacles (p, 72), In the sixteenth century 
curiosity in scientific matters heightened the interest in 
magnifying glasses. Leonardo da Vinci (p. 80) made a 
number of experiments on lenses of different kinds, and 
was followed by many others. 

By the end of the fifteenth century spectacles with both 
convex and concave lenses were in use. By the end of 
the sixteenth century they had become generally familiar. 
At that time a spectacle-maker in Holland happened to 
put together a convex and a concave lens in a tube. The 
combination formed what physicists now call a ‘Galilean 
telescope’ when looked through from one end, and a 
‘Galilean microscope’ when looked through from the 
other. A vague rumour of this successful experiment came 
to Galileo. At once he set about constructing a telescope 
of his own. In 1610 he published his great work, Sidereus 
nuncius (‘The Heavenly Messenger’). In it he records for 

2613.3 


h 



146 Inductive Philosophy 

the first time the appearance of the mountains in the moon, 
the rings of Saturn, and the four satellites of Jupiter. 

Galileo was thus the effective inventor of the micro¬ 
scope. Its optical properties were worked out first by 
Johannes Kepler (1571—1630) and by Christiaan Huygens 
(1629—95). lens-makers in the seventeenth 

century improved technical details in the construction of 
the instrument. No one gave a better account of one of 
these early microscopes than Robert Hooke (Fig. 75). 
The development of the microscope and of microscopic 
technique has had incalculable effects on subsequent 
biological investigation. 

Galileo was not himself a biologist. Nevertheless, the 
earliest biological observation with the microscope was 
made by him. An Englishman travelling in Italy in 1610 
wrote that T heard Galileo himself narrate how he dis¬ 
tinguished perfectly with his optic glass the organs of 
motion and of sense in the smaller animals. Especially 
he observed in a certain insect that each eye is covered by 
a thick membrane, perforated with holes like the iron 


Description of Figs. 71-4. 

Figs. 71-2 are engravings of two bees. These originally appeared in a printed 
sheet prepared by the first ‘Academy of the Lynx’ (p. 135) in 1625. A single 
copy of this sheet entitled Melissographia has survived and is in the Lancisian 
Library at Rome. The figures were re-engraved and printed more clearly by 
Francesco Stelluti (1577-1653) in an Italian translation of the Latin poems of 
Persius published at Rome in 1630. Our figures are taken from this. The 
magnification of the bees themselves is 5 diameters. 

Fig. 73. Between the bees is a drawing of the mouth parts of the insect. It is 
magnified about 10 diameters and should be compared with the figure of the 
same structures by Swammerdam some sixty years later (Fig. 88). 

Fig. 74 is a representation of a weevil, magnified 10 diameters. This appeared 
in Stelluti’s Persia for the first time. The long beak-like rostrum, the form of 
the antennae, the joints of the legs, and many other minutiae are accurately 
recorded. A more enlarged detail of the rostrum, magnified about 20 diameters, 
is also shown. The animal is drawn to its natural size in the top right-hand 
corner. 

In both bee and weevil, the compound eyes have impressed the artist. 








148 Inductive Philosophy 

visor of a warrior, thus affording passage to the images of 
visible things’. Galileo was describing the compound eye 
of an insect. 

The first systematic investigation of living things with 
the new instrument was made by the ‘Academy of the 
Lynx’ (p. 135)- A member of it wrote in 1628 that ‘our 
prince (i.e. Federigo Cesi) commissioned an artist to make 
draughts for him of numerous plants hitherto regarded 
by botanists as seedless. But the microscope clearly showed 
them to be teeming with seeds. Such is the wonderful 
and minutely fine dust adherent to the back of fronds of 
ferns, and seen as big as peppercorns.’ 

The dark structures seen on the fronds of ferns are the 
‘indusia’. The spores that emerge from these are not, 
however, of the nature of seeds, but give rise to the 
prothalli or sexual generation^ from which in turn the struc¬ 
tures that we call ferns—really the asexual generation —are 
produced. The knowledge of this was deferred for more 
than two hundred years (pp. 515 ff.). Sporangia of ferns 
were, however, well figured in the seventeenth century 
by Swammerdam (Fig. 182, p. 518). 

Continuing his narrative, our Lincean author tells that 
‘with this microscope Francesco Stelluti, the companion 
of the Lynx, has marvellously set forth the external 
anatomy of the bee. And he has caused to be engraved 
the eyes, tongue, antennae, head, legs, digits, and other 
parts of this little animal.’ 

We have a good record of this investigation. The 
figures of the bee and its parts thus set forth by Stelluti 
are the first illustrations prepared with a microscope that 
were set forth in a printed book. In 1630 Stelluti wrote 
that ‘I have used the Microscope to examine bees and all 
their parts. I have also figured separately all members 
thus discovered by me, to my no less joy than marvel, 
since they are unknown to Aristotle and to every other 



Introduction oj the Microscope 149 

naturalist. And I have caused to be engraved here in 
Rome, in compliment to our noble Lord Pope Urban VIII, 



Fic. 7^. Two forms of microscope used by Hooke (1665). 

'Fhe simpler, abandoned after a little use, is shown in section. It consisted of 
a simple large plano-convex lens as eyepiece and a very small plano-convex 
object glass. The conical space within the tube was filled with water. 

T he more elaborate had a tul)e of about six inches long, which was provided 
with further draw tubes by which it could be lengthened. Focussing was 
brought about by a screw on the nose of the tube. This moved in a ring at¬ 
tached to the stand. The objects, fixed on a pin attached to the base, were 
examined by reflected light obtained from a lamp to which a spherical con¬ 
denser was attached. 

Hooke also used minute simple lenses fixed in a hole in a metal plate, much like 
the microscopes of Leeuwenhoek. 

Fig. 76. Portion of a feather, magnified, from Hooke (1665). The barbules 
and their booklets arc well seen. It is these booklets that give the feather its 
peculiar contexture. 


three enlarged bees, drawn in such detail as was revealed 
by the glasses of the Microscope, and figured from front, 
back, and side’ (Figs. 71-3, 96). 




150 Inductive Philosophy 

Urban VIII was of the family of Barberini, whose crest 
exhibited three bees. These insect drawings stood un¬ 
rivalled in accuracy of detail until the appearance of the 
work of the ‘classical microscopists.’ (See below.) With 
the collapse of the Academy of the Lynx on the death 
of its president in 1630 (p. 135) systematic microscopical 
work fell into abeyance. Such microscopic observations 
as were recorded between 1630 and 1660 were desultory 
and of no great consequence. 

One writer of this period, however, deserves some com¬ 
memoration. Henry Power (1623—68) was an intimate 
friend of Sir Thomas Browne (1605—82). His Experi¬ 
mental Philosophy (London, 1663) contains a section 
‘Microscopical Observations’. The softly glowing music 
of the Religio Medici (1643) has infected it, and Power’s 
English has something of the magic cadence of the great 
stylist. The Experimental Philosophy is among the most 
beautifully written of English scientific books. It contains 
many interesting, though hasty, observations. Writing 
to Sir Thomas Browne in 1649, twelve years before 
Malpighi’s communication of 1661 (p. 151), Power had 
spoken of ‘the minute and capillary channels’ between 
the veins and arteries. He has thus some claim to have 
preceded Malpighi in the completion of Harvey’s dis¬ 
covery of the circulation of the blood (pp. 108 IF.). Power’s 
early death robbed English science of her best spokesman. 

In the last forty years of the seventeenth century there 
arose a series of great investigators who may be described 
as the Classical Microscopists. Of these, two, Hooke and 
Grew, were English; two, Leeuwenhoek and Swammer¬ 
dam, were Dutch; and one, Malpighi, was Italian. It 
is interesting to observe that the more important work of 
all these men, except Swammerdam, was published in 
England. 



( I5I ) 

§ lo. Malpighi (1628—g4) 

Marcello Malpighi studied Philosophy and afterwards 
Medicine at Bologna. Later he became professor of 
Medicine at that University, where most of his life was 
passed. He began to work with the microscope when 
about thirty and acquired great technical skill. In 1667 
the Royal Society wrote to him suggesting that he should 
send them his scientific communications. Most of his 
important discoveries were published in London in special 
volumes issued under the auspices of the Society. 

Malpighi was an excellent draughtsman but a poor 
writer, and his descriptions are much inferior to his 
figures. His Latin style is involved and difficult, and is 
rendered more obscure by vague theoretical explanations. 
He was, moreover, neither apt at devising experiments 
nor skilful in interpreting their results. As an observer, 
however, he has seldom been excelled. 

Malpighi’s first important work was an extension of 
that of Harvey. The Englishman had shown that the 
blood leaves the heart by the arteries to return by the 
veins. He had not, however, seen the ‘capillary vessels’ 
which connect arteries with veins. In 1660 Malpighi 
demonstrated this capillary system in the lung of a frog. 
He hit on the idea of examining the lung by injecting 
water into the pulmonary artery and seeing it issue from 
the pulmonary vein. This washed the blood out of the 
lung and made it more transparent. Thus he could 
examine it easily under the microscope. When he did so, 
the network of capillaries presented itself. He followed 
up the clue and demonstrated capillaries in other parts 
of the body. He wrote to a friend about this time: 

‘While the heart is still beating two movements, contrary in direction, 
are seen in the vessels, so that the circulation of the blood is clearly 
laid bare. The same may be even more readily recognized in the 



152 Inductive Philosophy 

mesentery. By the impulse of the heart the blood is showered down 
in minute streams through the arteries. By repeated division these 
lose their red colour until they approach the branches of the veins.’ 

This loss of colour is a mere optical effect. Under high 
magnification the pigment of the blood, which is confined 
to the red blood-corpuscles, becomes less and less obvious 
as the artery divides, until in the capillaries the red colour 
can hardly be discerned. It can be observed again as the 
capillaries join together to form small veins. 

Malpighi greatly extended the work of Fabricius on the 
development of the embryo. Fabricius had already in¬ 
vestigated the embryonic history of a number of animals, 
notably the chick. Being unprovided with a microscope, 
he had seen and depicted only naked-eye characters. He 
had concentrated on the later stages, paying little attention 
to the very minute earlier stages. Malpighi now stepped 
in with his microscope and made many important emhryo- 
logical discoveries (p. 460). 

Malpighi observed that in the chick, at an early stage, 
a series of vessels, given off by the aorta as it leaves the 
heart, go to encircle the gullet. These disappear or become 
rnqi^fied in a later stage of the development of the animal. 
Msupighi was unaware of the nature and meaning of these 
vessels. Since his time (pp. 470-1) they have played 
an important part in the progress of biological ideas. They 
represent, in fact, the vessels of the gills of a fish. Birds, 
like mammals, are descended from remote fish-like 
ancestors. In their embryonic development they still bear 
traces of this, and among the traces are these vessels of 
the ancient gill-slits (Fig. 162, p. 471). 

Among the most striking of Malpighi’s researches 
was that on the anatomy of the silkworm. It was still 
believed that such minute creatures are devoid of internal 
organs. Malpighi dissected the silkworm under the 
microscope with wonderful skill. He was astonished to 



7 . 

From Malpighi (1675), showing various plant vessels in section. All highly 
magnified. FiG. 77. Large tyloses and medullary rays from chestnut tree. 
Fig. 78. Spiral vessels from fig tree. Fig. 79. Pitted vessels from pine tree. 

system of tubes {tracheae) which are distributed like our 
blood-vessels to every part of the body. The tubes open 
at a series of breathing-holes ranged along the sides of the 
insect s body. Malpighi was the first to observe these 
tracheae and breathing-holes, and he arrived at a correct 
conclusion as to their function. He also demonstrated 
many other important structures in insect anatomy, and 
certain of these still bear his name. 

The bulkiest of Malpighi’s contributions are on the 























154 Inductive Philosophy 

anatomy of plants. His interest in this subject was 
stimulated by a peculiar observation. Walking one day 
in a wood, his eye fell on the broken bough of a chestnut 
tree. He noticed very line threads projecting from the 
fractured surface. Taking a lens he found that they pre¬ 
sented a spiral appearance (Fig. 78). Struck with their 
resemblance to the air-tubes of insects, Malpighi wrongly 
regarded them as subserving the function of breathing. 
These spiral vessels impelled him to investigate plant struc¬ 
ture. Many of Malpighi’s accurate figuresof plant anatomy 
remained unintelligible to botanists until the structures 
that they portray were redescribed during the last century. 

Malpighi’s figures show that he attained to a good 
general notion of the anatomical structure of the stems of the 
higher plants. They exhibit a clear distinction between the 
herbaceous and the woody dicotyledonous stem on the one 
hand, and between the dicotyledons and monocotyledons 
on the other. We see clearly the scattered bundles of 
monocotyledons, the annual rings, medullary rays, and 
rearrangement of fibres at the nodes of the dicotyledons. 
Wood fibres, resin passages, pitted vessels, and tyloses 
are all well represented (Figs. 77-9). 

Malpighi was quite familiar with the outlines of cells, but 
in this he was preceded by Hooke (pp. 168,325). He was 
the first to see and figure the stomata on the undersides of 
leaves, but he could make nothing of their function. He has 
good descriptions of the parts of the flower, but was in the 
dark as to their sexual nature. He also made an interesting 
research on the relation of the mistletoe to its host 
(Figs. 138-9). 

In the study of the development of plants, as with the 
development of animals, Malpighi was a pioneer. He 
gives many figures of the embryo sac and endosperm. He 
Has an admirable and classical account of the germination 
of the bean, laurel, and date-palm. His descriptions of the 



seedling of the pea and of the wheat are no less good. Very 
interesting are his admirable distinctions of the different 
modes of germination of monocotyledons and dicotyledons 
(Figs. 19-20). It is worthy of remark that on the rootlets 
of the bean he figures small tubercles. These we now know 
to be bacterial in origin, and to have a special function in fix¬ 
ing the nitrogen of the atmosphere (pp. 3 7 9 ff.). Malpighi, 
as was inevitable in his day, misinterprets their nature. 


i 



From Malpighi, On gcdls, 1679. Fig. 80. Oak gall cut open. The grub lies 
within. Fig. 81. Magnified view of gall insect, showing the long ovipositor. 
Fig . 8 2. The outline of the abdomen of the insect shows it to be a species of Rhodites, 

Malpighi devoted a special work to galls. Previous to 
him it was believed that these extraordinary growths are 
spontaneously produced. He showed, however, that each 
contains a grub. In some cases he traced the grub to an 
egg, and the egg to a hymenopterous insect. He described 
the long and peculiar egg-laying apparatus (‘ovipositor’) 
of the gall flies (Cynipidae, Fig. 81) in a way that should 
enable us to identify the species. The formation of the gall 
he ascribed to the injection of a special fluid by the insect 
at the time of oviposition. In this he was probably wrong, 
but it was a useful hypothesis which long held its ground. 


1^6 Inductive Philosophy 

§11. Grew (1641-1712) 

Nehemiah Crew was educated at Cambridge and 
Leyden. He practised as a physician in London, and was 
one of the early Fellows of the Royal Society, of which he 
became secretary in 1677. Grew was a pious man and he 
tells us that he was led to the study of vegetable anatomy 
because both plants and animals ‘came at first out of the 
same Hand and are therefore the contrivances of the same 
Wisdom’. Being both parts of God’s design, he thinks 
that plants and animals will present some similarity in 
structure. He is therefore ever looking for animal 
analogies in plants. Not infrequently he finds what he 
seeks. 

‘In the woody parts of plants, which are their bones, the principles 
are so compounded, as to make them flexible without joynts, and 
also elastick. That so their roots may yield to stones and their 
trunks to the wind, or other force, with a power of restitution. 
Whereas the bones of animals being joynted are made inflexible.’ 

Grew gives admirable and elaborate sections of plant 
stems and roots, which bring out clearly the diflFerence in 
structure of the main plant types (Figs. 83—4). Of spiral 
vessels he learned from Malpighi. He followed them in a 
variety of plants and called attention to the fact that they 
never branch. He saw and traced the vessels of seed¬ 
lings (Fig. 86). 

Grew was well aware that the tissues of plants are 
porous, sponge-like, or as we should now say ‘cellular’, 
in structure. He frequently represents the outlines of the 
walls of the ‘cells’, but his view of their nature seems very 
strange. In his great Anatomy of Plants (London, 1682) 
he wrote: 

‘The most unfeigned and proper resemblance we can at present 
make of the whole body of a plant, is to a piece of fine bone lace, 
when the women are working it upon the cushion; for the pith. 



Grew 157 

insertions and parenchyma of the barque, are all extream fine and 
perfect lace work; the fibres of the pith running horizontally, as do 
the threads in a piece of lace; and bounding the several bladders of 
the pith and barque, as the threds do the several holes of the lace; 
and making up the insertions without bladders, or with very small 



Fig. 85. Fibres of wood of fir magnified. From Grew (1682). 


ones, as the same threds likewise do the close parts of the lace, which 
they call the clothwork. And lastly, both the lignous and aer 
vessels, stand all perpendicular, and so cross to the horizontal fibres 
of all the said parenchymatous parts; even as in a piece of lace upon 
the cushion, the pins do to the threds. The pins being also conceived 
to be tubular, and prolonged to any length; and the same lace work 
to be wrought many thousands of times over and over again, to any 
thickness or hight, according to the hight of any plant. And this 
is the true texture of a plant; and the general composure, not only 
of a branch but of all other parts from the seed to the seed.’ 





158 Inductive Philosophy 

Perhaps the most striking of all Grew’s contributions 
is his guess that flowers are the sexual organs of plants. 
He distinguishes the calyx, corolla, and stamens—to 
which he gives the curious name of attire —and pistils. He 
tells that the anthers when they open scatter ‘a congeries 
of many perfect globes or globulets, sometimes of other 
figures, but always regular*. These ‘globes’ are the grains 
of pollen, and Grew figures them for a number of plants. 

Grew tells us that ‘in discourse hereof with our learned 
Sedleian Professor, Sir Thomas Millington, he told me 
he conceived that the attire doth serve as male for the 
generation of the seed. I immediately replied that I was 
of the same opinion; and gave him some reasons for it, 
and answered some objections which might oppose them.’ 
He notices that pollen grains ‘are that body which bees 
gather and carry upon their thighs, and is commonly 
called their bread. For the wax they carry in little flakes 
in their chaps, but the bread is a kind of powder, yet some¬ 
what moist, as are the little particles of attire.' 

§12. Swammerdam (1637—80) 

Jan Swammerdam was the son of an Amsterdam 
chemist who had collected a museum of curiosities. From 
his youth he had a passion for natural history. He helped 
his father with his museum and did not go to Leyden 
University till he was twenty-four, when he began to study 
Medicine. At this time Leyden was the best scientific 
school in Europe, and was fast surpassing Padua (pp. 97, 
106-8, 202-3). 

Swammerdam visited Paris. There he drew the atten¬ 
tion of men of science and especially of the ‘amateur’ 
Thevenot (p. 136) by his marvellous skill as a dissector. 
It was realized, even at this time, that he was a man of 
unstable mind. On his return he published his Algemeene 
Verhandeling von bloedloose diertjens (‘General account of 




Fig. 86. A bean dissected, from Grew (1682). 

Fhe entire bean, natural size, opened and with the surfaces of the cotyledons 
pared away to display their vascular system. This system Grew calls the 
‘seminal root* because he thought the plant drew nourishment through it as the 
older plant does through its root. He distinguished the seminal root from the 
true root or ‘radicle’, which is also here shown, h. Surface view of cotyledon. 
Part of the coats adhere to the top. The cotyledon is cut off from the stem at /. 
r, Cotyledon with the surface layers dissected off to expose the ‘seminal root*. 
The cotyledon is cut off at I as in h, d. The young remainder of the plant dissected. 
The ‘plume or bud’ is at w, the root is below. 7 'he cotyledons have been rut off 
at h. e, Shows the top of the true root cut off and seen in section, A piece of 
the surface layer of the cotyledon, displaying the cellular structure. 


16o Inductive Philosophy 

bloodless animalculae’, Utrecht, 1669, French and Latin 
versions, 1685). It deals with the modes of transformation 
of insects, and brings out the different manner of develop¬ 
ment of the different types of insects. Text and figures are 
equally good, and the book at once obtained popular 



F'lc;. 87. Series showing the development of a Dragon-fly, from Swanirnerdarn 
(1685). Below and to the right the complete insect is seen emerging from its 
last moult with the wings not yet fully unfolded. Swammerdam has beautiful 
descriptions of the expansion of the wings in several species of insects. 

recognition. An essay in the same direction had been 
made a few years previously (1662, Fig. 169) by his fellow- 
countryman Jan Goedart of Middelburg (1620—68). 
Swammerdam, however, far surpassed Goedart in the 
minuteness of his observations and in the intelligence with 
which they were prosecuted. 

Swammerdam came under the influence of a half-mad 
woman who was a religious fanatic. During the remainder 












1 62 Inductive Philosophy 

of his life he suffered from fits of depression. While in 
a state of mental disturbance he produced his Ephemerae 
vita (‘Life of the Ephemera’, i.e. the May-fly, Amsterdam, 
1675). This contains some very remarkable pieces of 
minute anatomy. Among them is a figure of the dissected 
larva which shows the series of nodules or ganglia char¬ 
acteristic of the nervous system of insects, and the 
tracheal system and the musculature as well as the series 
of breathing processes or gills (Fig. 89). The minuteness 
of the work can perhaps be realized from the fact that the 
insect itself is less than an inch long. 

Swammerdam’s mind was now frequently clouded. He 
died at 43 in a condition of great mental distress, having 
burnt much of his work. He bequeathed his manuscripts 
and drawings to Thevenot. On the death of Thevenot the 
papers passed to his heirs, who sold them. Many years later 
they were published under the title of Biblia Naturae (Ley¬ 
den, 1737-8) in two magnificent folios with many plates. 

The Bible of Nature is the finest collection of micro¬ 
scopical observations ever produced by one worker. It 
is astonishing that one with so few years to work and who 
was so often mentally incapacitated, could have accom¬ 
plished so much. Contemporary accounts describe him 
as working with the concentration of a madman. The 
book that is the product of this intense industry is con¬ 
sulted by naturalists to this day. Some of the figures have 
never been excelled. 

Among the most remarkable of the contents of the 
Bible of Nature is the description of the anatomy of the 
bee. The account of the internal organs of this creature 
is truly wonderful. Swammerdam’s descriptions of the 
development of gnats and of dragon-flies are astonishing in 
accuracy and modernness (Figs. 8 7, 90-2). He traced the 
development of the frog, and made fine dissections of the 
tadpole. He figures for the first time the spore cases, now 



Swammerdam 163 

known as sporangia^ of ferns (Fig. 182). These studies 
place him in the front rank of biological observers. 

Nor is it only as an observer that Swammerdam 



90 

Fig. 90. Larva of Cu/ex nemorosus from Swammerdam. It hangs from the 
surface film by the respiratory syphon, which contains two air tubes. These pass 
into two other tubes which traverse the whole length of the body. They supply 
every part wdth air. 

F'ig. 91. Pupa of Culex nemorosus from Swammerdam. I'he animal here 
breathes from tw'^o respiratory trumpets which arise from the thorax. I'hese 
trumpets suspend the creature from the surface film. 

Fig. 92. The same pupa drawn in outline to show internal structure. <2, one 
of the eyes, b, one of the antennae ‘divided into black joints*, dddd^ the legs, 
‘the hinder ones coiled up in a very surprising manner and lying for the most 
part under the wings through which, how’ever, those belonging to one side show 
themselves in this figure*, e e, one of the wings, fff-, ‘eight rings of the body*. 
ggf ‘a beautiful edging belonging to the belly*, by ‘the tail, hanging down with 
its rowing fins’, it, respiratory trumpets. 

exhibited skill. He was also a delicate and judicious 
experimenter, and did something to advance physiological 
knowledge. His very earliest publication (Tractatus 
physico-anatomica-medicus de respiratione usuque pulmonum, 
Leyden, 1667) threw some light on the respiratory pro- 

id 2 



164 Inductive Philosophy 

cesses. He improved the technique of injection (p. 144). 
He demonstrated, also, by a simple but excellently devised 
experiment, that muscles, though they alter in form do 
not alter in size when they contract. This is evidence that 
nothing material passes into the muscle on contraction. 
The fact is now well recognized, but in Swammerdam’s 
day it ran counter to the usual physiological views 
(PP- 399-400). 

§13. heeuwenhoek 

Of all the classical microscopists Antony van I.eeuwen- 
hoek made the most impression on his contemporaries. 
He was born at Delft in 1632, and he lived there until his 
death in his ninetieth year. He never learned any language 
but his own Dutch. At the age of sixteen he went to 
Amsterdam as a shop assistant. He returned soon after 
to Delft where he was given a minor official post and spent 
his time on microscopy. He was entirely without thought 
of worldly advancement. 

Leeuwenhoek always constructed his own microscopes, 
lenses and all. These were sought after, and he some¬ 
times gave one away, but he never sold them. He did not 
show his best instruments, however, and in one of his 
communications he observed that he kept some micro¬ 
scopes absolutely for his own studies, and that ‘through 
these no man living hath looked, save only myself’. 

Leeuwenhoek was peculiar among the classical micro¬ 
scopists in that he worked exclusively with simple lenses. 
At that time compound microscopes always had what is now 
called ‘chromatic aberration’. A simple lens has no such 
drawback but, on the other hand, if the power of such a lens 
is at all high, the area of clear field becomes very small. 
The general principle of construction of Leeuwenhoek’s 
microscopes is quite simple. The method of using them, 
on the other hand, was a matter of very great difficulty. 



Leeuwenhoek 165 

From an early date Leeuwenhoek sent his principal com¬ 
munications to the Royal Society, a practice to which he 
was introduced by De Graaf (pp. 461, 465). The Society 
published them in English or in Latin translations from 
the original Dutch. The observations were conveniently 
collected in four volumes published in Holland. He went 
on making observations almost to the end. In one of his 
later communications he says: 

‘A certain gentleman entreated me to go on in making observations, 
adding that the fruit which ripened in autumn was the most lasting. 
This is now the autumn of my life, I being arrived to the age of 88.’ 

Leeuwenhoek did not apply himself to any topic con¬ 
tinuously for very long. He allowed himself to wander 
through Nature with his microscope, finding new wonders 
at every turn. Many of his observations show great 
acumen, but it is impossible to do justice to such a 
desultory mass. 

Leeuwenhoek extended the knowledge of the capillary 
circulation which Malpighi had discovered, describing 
capillaries in a variety of situations. He followed this by 
a description of the blood-corpuscles, and he truly ob¬ 
served that the blood-corpuscles of fishes and frogs are 
oval, and those of man and mammals round. His figure 
of the nucleus of the red corpuscles of fish is certainly 
the first of its kind. He also described the blood-corpuscles 
of some invertebrates. He is the founder of the science 
of Histology^ that is, the study of the microscopic structure 
of tissues. In particular, he gave excellent accounts of the 
microscopic structure of the muscles (Fig. 93), of the 
lens of the eye, of the teeth, the skin, and other structures. 

Very remarkable is Leeuwenhoek’s work on the so- 
called ‘compound eyes’ of insects. These, as Galileo had 
observed (pp. 146-8), differ from ours in that each is pro¬ 
vided with a number of lenses. Leeuwenhoek showed that 



166 Inductive Philosophy 

these lenses form numerous inverted images. He believed 
that compound eyes endow the insect with quickness of 
sight. As proof he relates how he watched a swallow—the 
swiftest of birds—chasing a dragon-fly over a pond. The 
swallow was baffled by the rapid and unexpected turns of 
the insect. Any one who has tried to catch dragon-flies will 
have earned a respect for the resource of these creatures. 

Certain peculiarities in the life-history of the Aphis 
insects that infest plants are of great interest to biologists. 
To these Leeuwenhoek was the first to draw attention. 
He opened the bodies of several species of aphides in 
search of their eggs. To his surprise he found no eggs, 
but young aphides resembling the parents though natur¬ 
ally much smaller. An aphis of a fortnight old might 
contain as many as sixty young. The birth of these was 
observed. He found no males and he rightly concluded 
that the female aphis reproduces farthenogeneticalh\ that 
is without intervention of a male ilirte^parthenos^ Virgin’, 
^enesisy ‘birth’. See pp. 535-9.) 

Among the best of Leeuwenhoek’s observations are 
those on the development of the ant, on the insect nature 
of cochineal, on the spinning and poison apparatus of 
spiders, and on the development of mussels. In his 
account of the metamorphosis of the flea (Fig. 94), 
I.eeuwenhoek described a mite parasitic upon its larvae. 
This and similar observations gave rise to the lines of the 
satirist Jonathan Swift (1667-1745), on which there have 
since been many variants: 

So naturalists observe, a flea 

Has smaller fleas that on him prey; 

And these have smaller still to bite ’em; 

And so proceed ad infinitum, 

[Poetry, a Rhapsody, 1733) 

Very beautiful communications of Leeuwenhoek are 
the papers on minute freshwater creatures, such as 



Leeuwenhoek 167 

Rotifers, Hydra, and Volvox, objects now well known to 
every explorer of pond life. He and Hooke were the first 
to describe specimens of the group of unicellular organisms 
now known as ‘Protozoa’. Probably Leeuwenhoek’s most 



Fig. 94. Development of Flea, from Leeuwenhoek (1693). <7, Egg. Egg-shell 
after escape of larva, c and d. Stage of pupa, c, Young complete insect. /, Larva. 


remarkable achievement is that he caught a glimpse of 
Bacteria (1683). There can be no doubt, both from his 
figures and his descriptions, that he performed this feat— 
extraordinary with a simple lens. No one but Leeuwen¬ 
hoek recorded bacteria until, in the nineteenth century, the 



168 Inductive Philosophy 

improvement of the microscope made it possible for others 
to see them. And Leeuwenhoek was working with a 
lens made by himself! 

§14. .^00^^ (1635-1703) 

Intellectually Robert Hooke was unquestionably the 
most distinguished of the classical microscopists. He was, 
however, primarily a physical experimenter, and most of 
his best work lies outside our field. Sickly from childhood, 
his health prevented him from receiving a normal educa¬ 
tion. He was, however, a precocious and rapid worker. At 
Oxford he attracted the attention of Robert Boyle. When 
the Royal Society was founded, he entered its service as 
a salaried ‘curator of instruments’. This country has 
produced no more brilliant, ingenious, and inventive 
experimenter, and in certain important matters he anti¬ 
cipated Newton. He was a virulent and acrimonious 
controversialist, jealous and censorious beyond all toler¬ 
able limits, with a spirit warped by congenital infirmities 
of body and temper. 

Hooke’s Micrographia, published in London in 1665, 
opens with a description and figure of his microscope. 
This account is a valuable landmark in the history of the 
subject. The book is made up of a number of observa¬ 
tions. Their chief biological importance is in the accuracy 
and beauty of his figures, which formed a standard for 
generations. Biology is the loser from the application of 
his great intellect to other departments. 

Hooke has a figure of the microscopic structure of cork, 
showing thewalls bounding the cells (Fig. 142). He refers 
to these as cells. That word in our modern biological nomen¬ 
clature comes from him. He shows also cells on the sur¬ 
face of a stinging-nettle leaf, and gives a good account of 
the stinging apparatus of the plant (Fig. 143). An im¬ 
portant botanical observation by him is on a leaf fungus, 



Hooke i 6 g 

the development of which is well displayed. He also gives 
accounts of the development of a mould, of the structure 
of a moss, and of experiments on the sensitive plant. 

Among his figures taken from the animal kingdom are 
many of historical importance. Thus he depicted a 



Fig. 95. A flea, from Hooke (1665). The original figure is nearly eighteen 

inches long. 

Polyzoon for the first time. He discerned the beautiful 
minute markings on fish scales, the structure of the bee’s 
sting, the foot of the fly, and the tongues or ‘radulae ’of 
molluscs. All of these have since become classical subjects 
of microscopical study. He made a fine investigation of 
the structure of feathers (Fig. 76), which was not im¬ 
proved until the nineteenth century. His representations 
of minute insects, spiders, and mites had no rivals for a 
century except those of Swammerdam. Really wonderful 


170 Inductive Philosophy 

are his figures of a gnat and its larva, of the compound 
eyes of a fly, and two perfectly gigantic pictures of a flea 
(Fig. 95) and of a louse. 

§15. Influence of the Classical Microscopists 

A perusal of the writings of the classical microscopists 
gives a first impression that their work, except in the case 
of Grew, is without system or definite objective. It must 
be remembered that these men were entering an unex¬ 
plored region, a field of investigation so novel that its 
very existence had not been suspected. 

The infinite complexity of living things thus revealed 
was as philosophically disturbing as the ordered majesty 
of the astronomical world which Galileo (1564-1642) and 
Kepler (1571—1630) had unveiled to the previous genera¬ 
tion, though it took far longer for its implications to sink 
into men’s minds. Considering the smallness of their 
numbers and the greatness and novelty of the topics that 
they were developing, it is subject for remark that the 
classical microscopists hit upon so many observations of 
fundamental importance, and that the views they pro¬ 
pounded were, on the whole, so rational and coherent. 

One cannot fail to be struck by the isolation of these 
men. As it happens, they were all of eccentric character. 
They form a group almost entirely cut oflF from other 
workers. They had little intercourse with each other, they 
founded no schools, they had no pupils, and they were 
wellnigh without imitators. Thus there is no one of their 
contemporaries that may be placed with them, even in 
the second class. They remained without effective 
followers until the nineteenth century. This is a remark¬ 
able fact and one that awaits adequate explanation. 

But despite the inferiority of their contemporaries and 
successors, the work of the classical microscopists was far 
from being without influence. Their writings were not 



The Influence of the Classical Microscopists 171 

forgotten, but were constantly studied and their observa¬ 
tions not infrequently verified. The knowledge of the 
infinitely minute complexity of the structure of living 
things gave a new and more philosophical trend to bio¬ 
logical thought. Thus the general tone of the biological 
writing that followed them is very diflPerent from that 
which precedes them. Variety and complexity now begin 
to overawe the naturalist. Amidst the multiplicity of 
phenomena, order must be sought if knowledge is not to 
lose itself in detail. So it is that in the age that follows, the 
importance of classification becomes greatly emphasized. 

Intensive research with the compound microscope was 
hardly taken up again until the nineteenth century. Not till 
then were any great practical improvements made in the in¬ 
strument. ‘Achromatic’instruments appeared about 1830. 
An immersion system was introduced by Amici (pp. 506-7) 
in 1840, but it was long before it became available to 
naturalists generally. The modern microscope really dates 
from 1878 when the models of E. Abbe (1840-1908) were 
first constructed in the workshops of Messrs. Zeiss at Jena. 

Soon after, a form of substage illumination was designed 
by Abbe for Koch (pp. 445-8). The placing on the market 
of the new substage condenser by the firm of Zeiss—of 
which Abbe became proprietor in 1888—has had great 
influence on microscopical research. It was the last im¬ 
portant improvement in the ordinary laboratory instrument. 
The ‘ultra-microscope’, introduced in the twentieth cen¬ 
tury, has a quite different application. 

Fig. 96. Heads of Bees from Stelluti (1625). 



V 

RISE OF CLASSIFICATORY SYSTEMS 

§ I. Absence of System in the Early 'Naturalists 

T he sixteenth century ‘fathers of botany’ hardly 
attempted to arrange their plants in any logical order. 
They contented themselves with figures and brief descrip¬ 
tions (pp. 86-8). They recognized kinds or ‘species’ of 
plants, and saw that some kinds resembled each other 
more than they did other kinds. 

With the exploration of foreign lands, it became more 
and more evident that each country has plants and animals 
peculiar to itself. The description of these taxed the 
powers of naturalists. Bewildering confusion ensued. 
Deriving from Aristotle, there was a fairly definite con¬ 
ception of the nature of species, but no satisfactory manner 
of arranging the vast numbers of them. The embarrassing 
character of this accumulation may be illustrated by a 
single handy example. The Theatre of Insects^ written 
about 1590 by Thomas Moufet (pp. 95-6), sets forth the 
sum of contemporary knowledge of the subject. It shows 
us a good observing naturalist, overwhelmed by the wealth 
of material collected from many countries. His description 
of grasshoppers and locusts runs thus: 

‘Some are green, some black, some blue. Some fly with one pair of 
wings, others with more; those that have no wings they leap, those 
that cannot either fly or leap, they walk; some have longer shanks, 
some shorter. Some there are that sing, others are silent. And as 
there are many kinds of them in nature, so their names were 
almost infinite, which through the neglect of Naturalists are grown 
out of use. Now all Locusts are either winged or without wings. 
Of the winged some are more common and ordinary, some more 
rare; of the common sort, we have seen six kindes all green, and 
the lesser of many colours. 



Karly Naturalists 173 

‘The first of the bigger, hath as it were a grass cowle or hood which 
covers the head, neck and almost half the body; the wings come 
from the neck underneath, of a greenish colour, speckled with a few 
small spots, the back green, the belly dusk coloured, the tail or stem 
at the end blackish; it hath a great mouth, and strong big teeth, 
excellently made to devour the fruits withall. The second seems to 
be like this, but that the hood is fastened to the neck; the nose also 
and mouth are more red, and it hath greater spots in the wings. The 
third is of a green countenance, the shanks whitish, the tail black¬ 
ish, the wings beset with greater store of spots, and about the edges 
of a pale red {^Abbreviated from English translation of 

Moufet collected most industriously on his travels, and 
many specimens were sent him. These but befogged him 
the more. He is at his wits’ end for descriptive terms. 
Thus: 

‘I procured one from Barbary that was brought out of Affrick with 
. some cost to us, slender, five inches long, hooded, the head pyra¬ 
midal, very long, out of which almost at the tope came forth two 
little broad cornicles about an inch long, much like that Turbant 
which the I'urkish Janizaries use with two feathers in it.’ 

Moufet’s contemporary, Aldrovandi, treats the group 
of grasshoppers in much the same manner. Belon, Ron- 
delet, and Gesner are in like case. To remedy such 
confusion some system was demanded. The first help 
came from the botanists. 

§ 2. First Attempts at Formal Classification 

An early attempt to arrange plants in accord with their 
structure was made by the Fleming, Matthias de I’Obel 
(1538—1616). He came to England in his youth and 
dedicated his first book (i 570) to Queen Elizabeth. Later 
he was botanist to King James I. The plant known as 
Lobelia is named after him. His most important work 
appeared in 1576. 



174 Rise oj Classijicatory Systems 

De rObel takes the form of the leaf as a basis for 
grouping. As a natural result, he places together many 
quite unrelated plants. He begins well with the Grasses, 
which have narrow, long, simple, pointed leaves. He goes 
on to plants with broader, though still simple, leaves, 
placing together Lilies and Orchids, both of which have 
lance-like leaves with parallel veins characteristic of 
Monocotyledons. But from them he passes to a miscel¬ 
laneous group which contains certain Dicotyledons to¬ 
gether with Ferns! They are thus approximated because 
the highly subdivided fronds of ferns bear a superficial 
resemblance to the ‘compound’ leaves of such forms as 
Tansy or Hemlock. 

Andrea Cesalpini (1519-1603), Professor at Pisa, 
made a more effective attempt. He would arrange plants 
according to their flowers and fruit. On this basis he 
sketched a complete scheme of classification {De Plantis^ 
Florence, 1583). An abortive scheme, following some¬ 
what the same line, was made by Prince Federigo Cesi 
(published posthumously 1630). Part of Cesalpini’s 
scheme was, however, absorbed into the important and 
influential work of Bauhin. It exerted influence also on 
Jung (pp. 179-81), and through him on Ray (pp. 181-3) 
and Linnaeus (pp. 185-92). 

The Swiss, Kaspar Bauhin (i560-1624), was a pupil of 
Fabricius (pp. 107-8) at Padua. He went thence on many 
botanizing expeditions throughout Italy. Returning to his 
native Basel, he spent forty years arranging his botanical 
book, which appeared in the year before his death. 

The great work of Bauhin contains descriptions of 
about six thousand species of plants. In general outline 
it is distinctly inferior to that of Cesalpini. Its merit is 
that it distinguishes rather more clearly between the 
idea of a genus and of a species of plant. 



( 175 ) 

§ 3- What is a Genus? What is a Species? 

The reader will here ask what is meant by these words, 
genus and species ? It is disappointing to be forced to reply 
that no clear definition can be given of them. This answer 
will naturally raise a second question, ‘How then can 
the introduction of such conceptions be a scientific 
advance.?’ The fullest answer available would lead us into 
a very intricate and unsatisfactory philosophical discussion. 
The preparation of a complete answer is the object of 
biological science as a whole. But the reader cannot await 
this consummation, and he will naturally demand at least 
a provisional reply. He must rest in the partial satisfaction 
that there is a partial answer. The question, in fact, lays 
bare one of the weakest points in the present state of 
biological science. 

Living things, as we meet them in the world, exist as 
separate individuals. (There are exceptions to this state¬ 
ment, but they need not detain us.) If we examine a large 
and miscellaneous collection of individuals, we find that 
they fall naturally into separate groups, sharply marked 
off from other groups. Any horse can be distinguished 
from any ass. All the sheep can be separated from all the 
goats. It is true that occasional mules are encountered. 
These are the result of the crossing or interbreeding of 
two species. Such products are, however, rare, and since 
they do not usually propagate their kind, they tend to 
disappear and can, in the first instance, be disregarded. 

These groups into which living things can naturally be 
placed are known as species. So far as direct experience 
goes, species always breed true, in the sense that they never 
produce individuals of other than their own species. 
Horses may produce peculiar, deformed, or monstrous 
offspring, but their foals, however unusual, are always 
recognizable by naturalists as of the horse species. They 



176 Rise of Classificatory Systems 

can never be mistaken for asses or zebras or any other 
kind of similar creature. 

Thus much had been known to naturalists since the time 
of Aristotle. The recognition of the general characters 
of the various species is one of the first demands of biology 
as a science. 

The number of species known was rapidly accumulating 
in the seventeenth century. If any general survey of the 
knowledge of living things was to be obtained, it was 
essential to find some method, some general formula, by 
which these species could be grouped. 

Now it is precisely by the finding of such general 
formulae that science advances. The word science means, 
of course, knowledge^ but that is only its first meaning. 
Science means a particular kind of knowledge. It does 
not mean the picking up of bits and scraps of information, 
here and there, just as they happen to turn up. It means, 
on the contrary, arranged, classified, orderly knowledge. 
Another way of saying this is that science means know¬ 
ledge for which general formulae can be found. The 
progress of science is to be measured by the success men 
have in applying these general formulae to the knowledge 
they have collected. 

Let us apply these principles, as Bauhin applied them, 
to the thousands of species of known plants which pre¬ 
sented themselves to him. He had the species fairly well 
defined. The puzzle was how to arrange them. What 
general formulae could he find for them.? 

It may be said at once that he reached no useful scheme 
of classification for all the species with which he had to deal. 
He took, however, a step towards this end in recog¬ 
nizing more clearly than his predecessors that species 
fall naturally into small groups—and that these groups 
are more distinct from one another than are the species of 
which they are composed. Such groups we now call genera. 



What is a Genus? What is a Species? 177 

It is here convenient to interpolate a piece of knowledge 
concerning genera that was hidden from Bauhin. It has 
been mentioned that we can occasionally cross individuals 
of different species of the same genus. The products are 
mules or ‘hybrids*. But it is far more seldom possible to 
obtain progeny from a cross between individuals belonging 
to different genera. We can cross horse and ass, ass 
and zebra, or zebra and horse. All are species of the 
genus Equus. But we cannot cross any of these with their 
next nearest living representative tapirs, animals of about 
the same size and build. The tapirs form a genus of 
their own, far removed from horses, asses, or zebras. 
There are many animals and plants of different genera 
that are very much nearer to each other than horse and 
tapir, but from which it is impossible to obtain progeny 
by crossing. The difficulties of crossing are rendered 
partially intelligible by the chromosome theory, the 
discussion of which we defer (chaps, xiv and xv). 

So far as plants are concerned, Bauhin reached, in some 
cases at least, a workable division into species and genera, 
and a fairly satisfactory method of describing some of 
these groups. He thus made possible the systematic treat¬ 
ment of vegetable forms. It is not that he attained to an 
exact delimitation of the meaning oigenus or of species. No 
man has done that save by the introduction of demon¬ 
strable error. But what Bauhin did for us was to fore¬ 
shadow a method by which the recognized genera and 
species could be designated, and the distinction between 
different genera and species indicated. In fact, he adum¬ 
brated a system of binary classification which led ulti¬ 
mately to the ‘binomial nomenclature*. 


2613.3 


N 



178 


Rise oj Classijicatory Systems 

§ 4. The Binomial Nomenclature 

To every known species of animal and plant, naturalists 
now attach a scientific name. This name is always in 
Latin and is always double. Thus the common English 
primrose is Primula vulgaris^ the first name Primula being 
the name of thej^(?««J, the second vulgaris that of the species. 

But the primrose of the hedgerows is not the only 
species of Primula. All over England, in meadows and 
pastures, is to be found another species of plant which it 
resembles in many ways. It is usually known as the cow¬ 
slip. The leaves and flowers of the cowslip are very like 
those of the primrose. The plant of the cowslip is, how¬ 
ever, a little less hairy, the flowers are a little smaller and 
darker than those of the primrose, and, unlike the primrose 
flowers, they are grouped at the end of a longish stalk. 
Despite resemblances, cowslip and primrose do not form a 
permanent cross. Naturalists never have any difficulty in 
distinguishing the one from the other. The cowslip is, 
therefore, regarded as a separate species of Primula. The 
name Primula veris (i. e. ‘Primula of spring’) has been 
invented for it. 

Moreover, in the north of England, though not in the 
south, a third Primula is sometimes seen. Its flowers issue 
from the stem much as in the cowslip, but they are 
smaller and of a lilac colour. The leaves too are much 
smaller and their under sides are covered with a white 
mealy down. This is a separate species, called in ordinary 
speech ‘bird’s-eye primrose’, and known to botanists as 
Primula farinosa (i. e. ‘mealy primrose’). 

Primula farinosa is also a native of the United States, 
where Primula vulgaris and Primula veris are not found 
in the wild state. In other countries there are many other 
species of Primula. They are found all over Europe and 
Central Asia, including the Alps, which yield their own 



Binomial Nomenclature 179 

peculiar species. There are other species in China and in 
the Himalaya Mountains, and yet others in North America 
and one in South America. The genus^ in fact, is almost 
world-wide. 

The use of the double Latin name to describe every 
species is known as the ‘binomial nomenclature’. By it 
the arrangement and easy presentation of a vast amount 
of knowledge concerning species is rendered feasible. 

The binomial nomenclature is usually ascribed to 
Linnaeus (pp. 18 5-“92). He was the effective introducer of 
the system and he applied it skilfully, but the idea itself 
is in the books of Bauhin and even of earlier writers. And 
although Bauhin applied the method falteringly, fitfully, 
and inconsistently, we yet look upon him as one of the 
founders of that ‘systematic’ description of living forms 
which is fundamental to biological progress. Bauhin was 
the first of the systematists. The greatest of them, John 
Ray, was born a few years after Bauhin’s death. 

§5- (15*^7-1657) 

A peculiar place in the history of biology is taken by 
Joachim Jung. His real merits have only recently been 
adequately appreciated, but his influence was exerted on 
his immediate successors. 

Jung was born in the free town of Liibeck. Abandon¬ 
ing mathematics for medicine, which he studied at Padua, 
he came under the botanical tradition of Cesalpini. 
Returning north, he held chairs at several of the Hansa 
towns. For the last twenty years of his life he was director 
of a school at Hamburg (1629—57). 

Jung published nothing, perhaps because of the sus¬ 
picion of heresy under which he suflFered. Long after his 
death, certain of his pupils, who had carefully preserved his 
manuscripts, printed them in pious duty {JDoxoscopiae^ 1662, 
Isagogc phytoscopicdy 1679). These printed works became 

N Z 



18o Rise oj Classijicatory Systems 

excessively rare and were little noticed. Fortunately 
in 1660 a manuscript of his writings fell into the 
hands of John Ray, who was deeply impressed by them. 
It was through Ray that the ideas of Jung ’reached 
Linnaeus. 

Jung’s literary form is concise, and suggests well- 
arranged lecture notes. His two little works exhibit not 
only great biological insight but a real genius for classifica¬ 
tion. They undoubtedly approach nearer to the modern 
point of view than any other systematic work of his 
century. This comes out in his terminology. Thus we 
note that in discussing leaves he distinguishes simple and 
compound, pinnate and digitate, paripinnate and imparipin- 
nate, opposite and alternate. These modern terms were 
coined by him. Jung treated the kinds and parts of stems 
and roots with equal skill. He introduced petiole for the 
leaf stalk. The technical terms perianth, stamen, and style, 
in their modern signification, are his invention. He dis¬ 
cerned the true nature of the flowers of the Compositae, 
distinguishing the disk from the ray florets. The whole 
composite ‘flower’ he rightly regarded as an inflorescence 
or capitulum. Perhaps Jung’s greatest intellectual achieve¬ 
ment is his clear division of the departments of botanical 
study into what we should now describe as morphology 
(pp. 216-17), physiology, systematic work, and ecology 
(p. 410). 

Jung knew nothing of the sexual nature of flowers, but 
he used flowers as the foundation of classification. He 
distinguishes clearly such groups as the Compositae, the 
Labiatae, the Leguminosae, by the form of their flowers. 

His manner of naming plants approaches extraordinarily 
near to a formal binomial system. The plants in his 
alphabetical list are almost always given two names. 
The first is a noun and in effect a generic name, the 
second is an adjective and in effect a descriptive specific 



Jung i8i 

name. The method is developed from Bauhin and leads 
on through Ray and Tournefort to Linnaeus. The 
great rarity of Jung’s writings has militated against 
adequate reference being made to them. 

§6. (1627-1705) 

The modest English naturalist, John Ray, was the son 
of a blacksmith. He was sent to Cambridge, where he 
made his mark as a man of varied learning and took to 
making natural history excursions. Thus he rode through 
the Midland and Welsh counties, taking notes on plants 
and collecting dried specimens. In 1660 he published 
a scientific description of all the species of plant that grow 
in the neighbourhood of Cambridge. There had been 
earlier accounts of local plants, but this was the first real 
Flora, i. e. a systematic and searching catalogue of the plants 
of a given locality. In the year of its appearance, Ray 
took orders in the Church of England. 

Soon after this, Ray came in contact with a younger 
enthusiast, Francis Willughby (1635-72). The two re¬ 
solved to prepare a systematic description of the whole 
organic world. Willughby would finance the venture and 
undertake the animals, while Ray was to deal with the 
plants. The friends travelled together on the Continent 
and in England to enlarge their knowledge of natural 
history. Willughby died early and left an annuity to Ray, 
who edited his friend’s work. 

Ray’s next work was a handy Catalogus of British plants 
(1697). This was a complete Flora of the British Isles, 
which became the pocket companion of every botanist of 
this country for generations. It is dedicated to Willughby. 

Ray is, with Linnaeus, the chief founder of the science of 
‘systematic biology’, that is, the science that aims at the 
orderly arrangement of the species of animals and plants. 
After his catalogue of British plants, his next attempt 



i82 Rise oJ Classijicatory Systems 

was on birds, and was based on Willughby (1676). Next 
followed a booklet, Methodus plantarum nova (London, 
1682), which shows the influence of Jung. It demon¬ 
strates the true nature of buds, and uses the now familiar 
division of flowering plants, into Dicotyledons and Mono¬ 
cotyledons. These words were invented by Ray but did not 
appear in print until the issue of the second edition (1703). 
Ray based his system chiefly upon the fruit but also upon the 
leaf and, following Cesalpino and Jung, upon the flower. 

Thus Ray succeeded in indicating many of the larger 
groupings of plants which botanists now call Natural 
Orders^ and thereby took the first decided step towards 
a natural system of classification. In a ‘natural system’ 
all resemblances are taken into account, a value being 
ascribed to them according to their presumed importance. 
A system is said to be ‘artificial’ in so far as resemblances 
and differences in some few particulars only are taken 
into account, independently of all others. 

Ray’s greatest work is his Historia generalis plantarum 
(3 volumes, London, 1686—1704). This huge work con¬ 
tains a most able account of everything then known of the 
structure, physiology, distribution, and habits of plants. 
It does justice, moreover, to the memory of the men from 
whom Ray derived many of his ideas. All the plants 
made known by his predecessors and contemporaries, 
about 18,600 in number, are described methodically and 
clearly. The species are arranged in 125 ‘sections’ of 
which a number are still recognized as ‘Natural Orders’. 
The work earned the special admiration of Cuvier (p. 223). 

Ray’s writings on animals were nearly as important as 
his botanical works. His Historia Piscium (1686), part of 
which is by Willughby, and his Synopsis methodica ani- 
malium quadrupedum et serpentini generis (1693) were 
both of great value. 

The latter work is particularly important for it contains 



Ray 183 

the first truly systematic arrangement of animals. This 
is based primarily upon the toes and teeth. Abundant 
traces of his general arrangement of animals survive 
in modern systems of classification. With much acute¬ 
ness Ray perceived that such forms as the armadillo, the 
hedgehog, and the mole could not be made to fit into 
his scheme, which may be set forth thus: 


< 

h 

o 

5 ? 

J-) 


SINGLE HOOFS (SOLIDIPEDA) 


DOUBLE HOOFS <[ 

(bisulca) 


Chew the cud 
(Ruminantia) 


Do not chew cud 
(Non-ruminantia) 

QUADRUPLE HOOFS (QUADRISULCA) 


i. Horsesj Asses. 

ii. Horns permanent. Cattle^ 
Sheep. 

iii. Horns shed. Deer. 

iv. Pigs. 

V. Rhinoceros^ Hippopotamus. 


TWO TOED . 



'"Toes joined 

( 

FIVE TOED-< 

1 

f Nails J 


J 

1 narrow 1 


^Toes separate^ 

Nails [ 
L broad 


vi. Camel. 

vii. Elephant. 

viii. More than two cutting teeth 
in each jaw. Dog^ Cat. 

jx. Only two cutting teeth in 
each jaw. Rabbity Bearer. 
X. Of human form. Monkey. 


Apart from his great systematic writings, Ray showed 
insight and wisdom in other departments of science, as 
in his private life. In his Wisdom of God Manifested in the 
Works of the Creation (i 691), he set forth the true nature of 
fossils, as petrified remains of species now extinct. This 
was a great advance on current views. He also accepted 
the sexual character of flowers. Toward the end of his 
life he devoted himself to the study of insects. When a 
certain lady of Exeter was judged insane because she 
collected insects, Ray appeared as a witness to her sanity! 
Ray’s work on insects was not published till after his death. 
It combined the system of Aristotle with that of Swammer¬ 
dam (p. 160) and prepared the way for Linnaeus. It was 
regarded by Cuvier with the very greatest respect. 



184 Rise oj Classijicatory Systems 

§ 7. Tournejort (i 656-1708) 

In France an authoritative position somewhat similar 
to that of Ray was occupied by the botanist, Joseph Pitton 
de Tournefort. From his earliest youth Tournefort 
exhibited unrestrainable enthusiasm for the study of 
nature. He travelled much throughout Europe and the 
Near East, diligently collecting plants. From 1683 till his 
death he was a professor at the Jardin des Plantes (p. 132). 

Tournefort was inferior to Ray in philosophic grasp 
as well as in the naturalist’s acumen. His descriptions of 
plants are good. His classification, though convenient, 
is artificial, being based on an inadequate and hollow 
investigation of the form of the flower. He is important 
as a predecessor of Linnaeus in developing both the 
binomial nomenclature and the method of describing 
plants. 

Tournefort denied the sexuality of plants, and classed 
those with small flowers along with those without flowers. 
He thus missed the distinction between dicotyledons and 
monocotyledons. His chief work, the Institutiones rei 
herbariae (1700) is significant as foreshadowing the 
rigid systematic spirit that coloured the biology of the 
eighteenth century. It is beautifully illustrated. The 
third (1719) and subsequent editions were improved by 
Antoine de Jussieu senior (1686—1728; see p. 193). 

Tournefort, following Bauhin, lays great stress on 
genera. His chief contribution to systematic botany lay 
in his method of distinguishing these. Bauhin had given 
only a name to each genus, while the terms that he applied 
to the species were, like those of Jung, purely descriptive. 
Tournefort adds descriptions to the names of the genus. 
The names for the species and varieties, however, are 
almost devoid of description save such as is provided by 
the admirable figures. The method of Linnaeus might 



Tournejort i 8 ^ 

be briefly described as an adaption of Bauhin’s method 
for genera />/us Tournefort’s for species J>/us a descriptive 
method largely his own. 



Fig. 97. Linnaeus with equipment for exploration. From a mezzotint. 
Fig. 98. An oriental species of spurge, Euphorbia apiosy of Linnaeus depicted 
for the first time by Belon (p. 89) in 1555. called it by its native Greek 

name *Apios*. 

§8. Linnaeus (1707—78) 

The Swede, Karl Linnaeus, as a boy was backward and 
destined to be an artisan. His father, a poor clergyman, 
was reluctantly persuaded to send the lad to Lund, and 
afterward to Upsala as a student of medicine. It soon 


186 Rise oj Classijicatory Systems 

became evident that, despite literary defects, he had 
extraordinary application and great aptitude in certain 
directions. 

While a student at Upsala, certain French botanical 
works set Linnaeus examining the sexual parts of flowers. 
Convinced of their importance for the life of plants, he 
conceived the idea of basing a system of classification on 
them. He wrote a short treatise on sex in plants which was 
far from original. He was asked to act as deputy to the 
professor of Botany on the strength of it. 

In 1732 Linnaeus was chosen by the Upsala Academy 
to visit Lapland as a collector. He at once set out alone 
and travelled more than 4,600 miles at a total cost of ^2 5. 
In five months he explored Lapland, and much of northern 
Sweden and Norway. Of his equipment he says: 

‘My clothes were a light coat of linsey-woolsey, leather breeches, a 
round wig, a green leather cap and a pair of half-boots. I carried 
a small leather bag containing one shirt, two pair of false sleeves, 
two v'ests, an inkstand, pen-case, microscope and telescope, a gauze 
cap to protect from gnats, a comb, my journal and a parcel of paper 
for drying plants, my manuscript Ornithology, Flora IJplandica and 
Characteres generici. I wore a hanger at my side, and carried a 
small fowling-piece, as well as an octagonal stock graduated for 
measuring.’ (Fig. 97.) 

Accompanied by two Laps, he crossed the peninsula 
on foot to the Arctic Ocean—itself no mean feat—and 
returned again by a parallel route. After incredible 
fatigues and hardships, climbing precipices, crossing 
torrents, suffering extreme heat and cold and hunger and 
thirst, and constantly pestered by mosquitoes, Linnaeus 
reached again the Gulf of Bothnia, and so home. He had 
observed many wild animals and discovered a hundred new 
species of plants. 

Linnaeus next visited Germany, Holland, England, 
and France. During these travels he made the preliminary 



Linnaeus 187 

draft of his famous work the Systema Naturae. It was first 
published in Holland in 1735. At the same period he also 
issued several botanical works. The most important were 
the Fundamenta botanica (1736), the Genera Plantarum 
(1737)5 the Classes Plantarum (1738). 

On his return to Sweden Linnaeus was appointed Pro¬ 
fessor of Natural History at Upsala. He became an 
extraordinarily popular teacher. Students crowded to him. 
Much of his best work was done by sending them out 
on expeditions. These pupils explored a large part of 
the known world in search of new animal and plant forms. 
Many, it is said one-third, died on these expeditions. 
Many more are commemorated in the Systema Naturae. 
One, Solander (p. 236), accompanied the English explorer, 
Captain Cook, and was long resident in London. 

§9. The 'Systema Naturae' (1735—58) 

Linnaeus had a passion for classification. Not only did 
he draw up classified lists of plants and animals, but he 
also classified minerals and even diseases. To his work 
on plants and animals naturalists still constantly refer. 

It would be a mistake to suppose that it is only in 
classification and nomenclature that Linnaeus has left his 
mark. He also developed a method of formal description 
of organisms which is essentially similar to that still in 
current use. He took the parts of a plant or an animal in 
regular sequence and described them according to a 
recognized rule. This brief and graphic method of 
description, though it tended to become mechanical, was 
yet a great improvement on the verbose accounts common 
till his time. 

Linnaeus succeeded in assigning to every known animal 
and plant a position in his system. This involved placing 
it first in a Class, then in an Order, then in a Genus, then 
in a Species. The Orders were large divisions, each con- 



18 8 Rise of Classijicatory Systems 

taining a number of Genera. The Classes were yet larger 
divisions, each containing a number of Orders. Organisms 
from two different Orders in the same Class, e. g. an 
orchid and a hyacinth, differ from one another less than 
either differs from a daisy, which is in an Order belonging 
to a different Class from either. 

The Linnaean Classes and Orders of Plants were 
primarily those set forth by Tournefort (p. 184). They 
were based on the parts in the flower. The number of 
‘stamens’, or free male parts, in the flower was the founda¬ 
tion of this division into classes. Thus IJnnaean grouped 
plants with one stamen in the Class Monandria, plants 
with two in the Class Diandria, plants with three in 
the Class Triandria, and so on. Each Class was divided 
into orders, according to the number of ‘styles’ or free 
female parts in the flower. Thus, the Class Monandria 
was divided into the Orders Monandria Monogynia with 
one style, Monandria Digynia with two, and Monandria 
Trigynia with three; and so on with the other Classes. 

To take a random example, the spurge Euphorbia Apios 
(Fig. 98, p. 185) which he named, he placed in the Class 
Dodecandria as having its male parts in systems of twelve, 
and in the Order Trigynia as having its female parts in 
systems of three. Of this Order he recognized three genera. 
Of the genus Euphorbia he recognized over a hundred 
species from various parts of the world, the Mediterranean 
species Apios coming to him from the island of Crete. 

As to animals, Linnaeus distinguished the Classes of 
Mammals^ Birds, Reptiles, Fishes, Insects, and Vermes. The 
first four Classes had already been grouped together by 
Aristotle as ‘Animals with red Blood’ (p. 42) or as we 
now call them ‘Vertebrata’. The remaining Classes of 
Insects and Vermes contain, bundled together, all the 
groups of animals without vertebrae. Here Linnaeus was 
behind Aristotle, who had broken up these groups. 



'Systerna Naturae' 189 

This basis of arrangement that Linnaeus adofjted for 
the Animal Kingdom may be thus diagrammatically set 
forth: 


Heart with i or 2 ventricles 
and 2 auricles; 

Blood warm and red. 

Heart with i ventricle and i or 
2 auricles; 

Blood cold and red. 

Heart with i ventricle and no 
auricle; 

Blood cold and colourless. 


[ I. Viviparous. Mammals. 
I2. Oviparous. Birds. 

f 3. Breathing by lungs. 

J Reptiles. 

[4. Breathing by gills. Fishes. 

r 5. With antennae. Insects. 
16. With tentacles. Vermes. 


Some of these distinctions have been revised by more 
modern researches. Thus, there are some Mammals, such 
as the Australian duck-billed Platypus, that are not 
viviparous, but that lay eggs. That animal, however, was 
unknown during the lifetime of Linnaeus. Some of the 
Linnaean Class of Reptiles, which include our ‘Am¬ 
phibians’, breathe “With gills; and only by forcing the term 
can they be said to have but one auricle. Not all of the 
group that Linnaeus called ‘Vermes’, a group broken up 
by Lamarck and now abandoned (p. 293), have colourless 
blood, nor do all possess tentacles. Nevertheless, the 
scheme is workable and gave naturalists something on 
which to build. 

The contribution of Linnaeus to biology that has lasted 
best is his division of living things into genera and species^ 
with his development of the binomial system. Bauhin, 
Jung, Ray, Tournefort, had already attached short descrip¬ 
tive titles, often of two words, to all their species. 
Moreover, a I^eipzig botanist and physician, August 
Quirinus Rivinus (1652—1723), made a definitive sugges¬ 
tion (1690) that no plant-name should contain more than 
two words. Both Ray and Tournefort were quite aware 



190 Rise oj Classijicatory Systems 

of the work of Rivinus. Thus the idea cannot be placed 
wholly to the credit of Linnaeus. But it was Linnaeus 
who secured the general adoption of a system in which 
every species has two names definitely allotted to it. 
The first work in which he undertakes this on an 
extensive scale is his Species Plantarum of 1753. About 
7,300 species are there provided with names, many of 
which are still in use. 

Linnaeus was accustomed to give a rigid definition, in 
his terse Latin, to each genus and species. This method 
has been followed by his successors. His classification has 
been repeatedly revised by more modern naturalists. 
Little is now left of his division into Classes and Orders. 
A number of his definitions of Genera and of Species are, 
however, still accepted. 

When a plant or animal retains the titles given by 
Linnaeus, it is usual to add to them an abbreviation of his 
name. Thus, for instance, naturalists refer to the common 
daisy as Beilis perennis^ J-inn., or to the common frog 
as Rana temporaria, Linn. In general, indeed, it has 
become the custom to add to the Latin terms for any 
species an abbreviated form of the name of the man who 
first bestowed it. 

The great work of Linnaeus is his Systema Naturae. 
It was first drafted in 1735. modified it and amplified 
it a good deal as it went through its many editions. Of 
these, biologists have selected the tenth, which appeared 
in 1758, as their basis. If a species is given its Linnaean 
name by a modern naturalist, it means that adopted in this 
tenth edition. 

Linnaeus attached a generic and specific name even to 
man, who is thus known to naturalists as 'Homo sapiens, 
Linn.’ The designation may be translated ‘Man, the 
reasoner’. Linnaeus included in the genus Homo another 
species, the Orang-outang. This creature he designated 



sterna Naturae ’ 191 

Homo troglodytes^ ‘Man, the cave-dweller’. The decision 
of Linnaeus to unite man and orang in one genus has been 
reversed by his modern successors. Naturalists now con¬ 
sider that there is only a single living species of genus 
Homo^ though the species Homo sapiens is divided into 
several subspecies^ varieties^ and races. 

These terms are applied to divisions of species of 
which the peculiar characters are less marked, and 



Fig. 99. A Swedish warship in pursuit of the vessel containing the Linnaean 
collections in 1784 (R. J. Thornton, 1797). 

usually less constant, than those which separate species. 
The discussion of these distinctions we must defer, 
but we note that subspecies, varieties, and races of 
the same species are nearly always fertile with each 
other. 

Of the subspecies of man, Linnaeus knew the black or 
Negro, the yellow or Mongol, the white or European, 
and the red or American. Since his day, forms of Homo 
have been described in a fossil state which differ from any 
of the living varieties of man far more than any of these 
subspecies differ from each other. They form, therefore, 
separate species of Homo, The best known fossil species 


192 Rise oj Classificatory Systems 

of man is the so-called Homo Neanderthalensis which once 
inhabited Western Europe (p. 310). 

The general ideas of Linnaeus concerning the nature of 
species are of great historical importance. He held that 
species are constant and invariable, a view in which he 
differed from John Ray. ‘There are just as many species 
as there were created in the beginning,’ said Linnaeus, 
and again, ‘There is no such thing as a new species.’ In 
this respect we have departed completely from his 
standpoint. 

When Linnaeus died in 1778 his collections and books 
were bought by a wealthy young English naturalist on the 
suggestion of Banks (pp. 236—8). It is said that the King 
of Sweden sent a war vessel after the ship that bore the 
Linnaean specimens to England. The British proved the 
faster, however, and reached England without mishap 
(Fig. 99). The purchaser of the collection became the 
first president of the English biological association named 
the Linnean Society, which still owns his collections and 
library (p. 141). 

§10. The Successors of Linnaeus 

Linnaeus focussed biological interest on classification, 
especially by external parts. He thus withdrew attention 
from the intimate structure and workings of the living 
organism. The search for new genera and species became, 
for generations, the chief aim of most naturalists, to the 
neglect both of anatomical and of physiological studies. 
The tendency was especially marked among botanists, who 
were esteemed in proportion to the number of flowering 
plants whose characters they could memorize. 

But the Linnaean influence showed itself also in another 
and more attractive manner. Linnaeus had a passionate 
love of wild nature, and the close examination of species in 
a living state provided a stimulus toward that type of 



Successors oj Linnaeus 193 

study to which the term ‘Natural History’ is sometimes 
restricted. The eighteenth century and the early part of 
the nineteenth furnished examples of nature-lovers of high 
ability and great literary power. Thus, the Natural 
History and Antiquities of Selborne (1789) by the Rev. 
Gilbert White (1720-93) and the Wanderings (1825) of 
Charles Waterton (1782—1865) are classics both of the 
F.nglish tongue and of biological expression. In other 
languages there are contemporary works comparable to 
these. 

More in the direct line of the Linnaean tradition were 
the activities of a group of botanists in France. Progress 
in that country was aided by several organized botanic 
gardens and by the devotion of two famous families, de 
Jussieu and de Candolle. 

The family of de Jussieu came from Lyons. Three sons 
of an apothecary of that town all became distinguished 
for their studies of plants. For more than a century and 
a half the stock continued to produce eminent botanists. 
The names of no less than six de Jussieu recur constantly 
in scientific literature. Bernard (1699—1777), the most 
famous, worked first at the Jardin des Plantes and from 
1759 at the garden of Le Trianon at Versailles. There he 
made it his chief task to elaborate a ‘natural system’. He 
sought to arrange living plants after the Linnaean manner, 
though his method was based on somewhat different 
principles. He published nothing, but his nephew and 
assistant, Antoine Laurent de Jussieu (1748—1836), de¬ 
veloped his system and gave it to the world in his Genera 
plantarum secundum or dines naturales disposita (1774). 

The terms ‘Monocotyledons’ and ‘Dicotyledons’, intro¬ 
duced by Ray (i 703) for the two primary sub-divisions of 
flowering plants (p. 182), were popularized by Antoine 
Laurent de Jussieu. He distributed the classes on a 
principle taken partly from Tournefort. This further 
2613.3 


n 



194 Classificatory Systems 

division depended partly on the number and arrangement 
of petals in the flower and partly on the position of the 
stamens with reference to the ovary (Hypogynous = below 
the ovary, Perigynous = around the ovary, Epigynous = 
above the ovary). Thus: 

Classes 


Acotyledons ........ I 

THypogynous . . . . . II 

Monocotyledons < Perigynous . . . . . Ill 

L Epigynous . . . . . IV 

C Hypogynous . . V 

^Apetalous Perigynous . . VI 

(^Epigynous . . VII 

r Hypogynous . . VIII 

Monopetalous < Perigynous . . IX 

Dicotyledons < [.Epigynous . . X, XI 

rHypogynous . . XII 

Polypetalous \ Perigynous . . XIII 

I [^Epigynous . . XIV 

[irregular . . . . .XV 


Of these fifteen classes the ‘Acotyledons’ provide but 
one. This group, which we now know to be no less mis¬ 
cellaneous than vast, includes Fungi, Algae, Liverworts, 
Mosses, and Ferns. It will be seen how overwhelming 
a stress is laid on flowering forms—Monocotyledons and 
Dicotyledons. The artificially symmetrical element in 
this classification, which fits them fairly well, is as 
prominent as in the Linnaean system. The Classes were 
broken up into Orders, Genera, and Species much as 
the Systema Naturae. 

Augustin Pyramus de Candolle (1778—1841) was the 
most distinguished member of a wealthy Genevan family 
which, like the de Jussieu, produced a number of eminent 





Successors oj Linnaeus 195 

botanists. He exhibited life-long industry and unsurpassed 
enthusiasm in botanical research. Most of his investiga¬ 
tions were made in France at a period of the most intense 
scientific activity in that country. The width, depth, and 
philosophic insight of his studies on plants made him no 
unworthy colleague of Cuvier (pp. 223—32)—also by birth 
a Swiss—^who devoted his energies to animal forms. 

In his Elementary Theory of Botany (1813 and many 
later editions), de Candolle set forth his general views. 
There are many parts of this fine work which can still be 
read with profit. The classification which de Candolle 
adopted was far more natural and more deeply based on 
anatomical structure than any yet attempted, nor does it 
exhibit the straining after symmetry of Linnaeus and de 
Jussieu. The classification of de Candolle may be abstracted 
thus (Prodromus systematis naturalis^ Paris, 1824-70) ^: 

1 . Structure ‘cellular’. Scarcely proper seeds. Propagation by 
spores. 

6 families, including Fungi, Lichens, Mosses, and 
Liverworts. 

[A miscellaneous group,] 

II. Spiral vessels. True seeds. Sexual parts not double. 

5 families, including the Ferns and Club mosses. 

[A fairly natural group, wrongly described.] 

III. Spiral vessels scattered in bundles throughout stem. Sexual parts 

obvious. Embryo buried in albuminous substance. Arrange¬ 
ment in threes common. 

18 families, including Cypresses, Grasses, Palms, Irises, 
Orchids, being gymnosperms and monocotyledons. 

[Two natural groups linked as one.] 

IV. Spiral vessels in concentric rings. Sexual parts obvious. 

Embryo not buried in albuminous substance. Numerical 
proportions various. 

85 families, all dicotyledonous. [A natural group.] 

’ In sixteen volumes completed by the author's son Alphonse de Candolle. 



196 Rise oj Classijicatory Systems 

This system, with all its faults and errors, is a real 
attempt at a ‘natural’ classification in that it takes many 
different parts into consideration and in this respect is 
thoroughly modern. It may be placed beside that set 
forth for animals by Cuvier in Le regne animal (pp. 229— 
30), which is based on the whole findings of comparative 
anatomy and physiology and not on the appearance of 
arbitrarily selected parts. 

Independent of Cuvier, however, and in his own time, 
there was one writer who, though better remembered for 
his evolutionary speculations, has left a deep impression 
on classificatory schemes. This was Lamarck (pp. 292-5). 
In his Philosophic %oologique of 1809 he introduced the 
useful term invertebrates (‘invert^bres’). He arranged the 
animal kingdom in fourteen classes thus: 


1. Mammals 

2. Birds 

3. Reptiles 

4. Fishes 

5. Molluscs 

6. Cirripedes 

7. Annelids 

8. Crustaceans 

9. Arachnids 

10. Insects 

11. Worms 

12. Radiates 

13. Polypes 

14. Infusoria 


1 

(■ Vertebrate Animals 


> Invertebrate Animals 




The arrangement is in the form of a ‘scale’ or ladder 
and thus contrasts both in principle and in appearance 
with that adopted by his great rival, Cuvier (pp. 227-30). 



( 197 ) 

§11. Modern Systems oj Classification 

Since the time of Linnaeus almost every important 
biological movement has left its mark on the system of 
classification current in its day. The classification of living 
things adopted by a biological writer may often be treated 
as an epitome of his views on many important biological 
problems, and especially on comparative studies, to which 
we shall presently turn. This was notably the case with 
the system of Cuvier. 

We would stress the fact that, from the time of Linnaeus 
to our own, a weak point in biological science has been 
the absence of any quantitative meaning in our classifica- 
tory terms. What is a Class, and does Class A differ from 
Class B as much as Class C differs from Class 1)1 The 
question can be put for the other classificatory grades, such 
as Order, Family, Genus, and Species. In no case can it 
be answered fully, and in most cases it cannot be answered 
at all. 

Until some adequate reply can be given to such ques¬ 
tions as these, our classificatory schemes can never be 
satisfactory or ‘natural’. They can be little better than 
mnemonics—mere skeletons or frames on which we hang 
somewhat disconnected fragments of knowledge. Evolu¬ 
tionary doctrine, which has been at the back of all classifi¬ 
catory systems of the last half century, provides no real 
answer to these difficulties. To sketch the manner in 
which the various groups of living things arose is a very 
different thing from ascribing any quantitative value to 
those groups. 

It is not possible to discuss all the systems of classifica¬ 
tion that have attracted naturalists since Lamarck, Cuvier, 
and A. P. de Candolle. In bulk, systematic works form 
the main part of biological literature. It is convenient, 
however, to set down the chief features of a scheme 



198 Rise of C/assificatory Systems 

generally acceptable to modern naturalists, based largely 
on the process of development and inspired by evolu¬ 
tionary teaching. It will be appropriate to discuss its 
limitations. 

Firstly, the basic division is into a plant series and 
an animal series. No such absolute distinction can, 
however, be rigidly maintained. There exist many 
organisms which cannot be left definitely in either the 
animal or plant kingdom. Most of these forms of uncer¬ 
tain position are characterized, in some stage of their 
existence, by the possession of a whip-like organ, the 
‘flagellum’. We are, therefore, forced to include a group 
Flagellata in both tables. 

Secondly, modern investigation has shown that there 
are many groups of living things which have no clear 
relation, either in structure or in mode of development, to 
any other group. This is even more the case among 
animals than among plants. Such major groups are known 
as Phyla. Many Phyla contain only a very few species, 
but may not be the less interesting on that account. In 
our table on pp. 199 and 200 we have only been able 
to include the larger Phyla. 

Thirdly, it will be noted that while we divide the animal 
kingdom into two main sub-kingdoms, according as the 
organism is composed of one or of many cells, no such 
attempt has been made with the plant kingdom. In fact 
this mode of division is not satisfactory even for animals, 
and there are animals concerning which we might discuss 
whether they are unicellular or multicellular. For plants, 
however, it will not serve at all. One reason for this is 
fairly apparent. An animal has a definite form with a 
definite body shape and a definite number of organs. But 
a plant presents not so much a form as z pattern. It repeats 
itself over and over again and will do so as long as it lives. 
These patterns which we call plants arise ultimately from 



Modern Classification 199 

a single cell. Now in all the first three groups of plants 
which we enumerate, as well perhaps as in others, there 
are forms which may be either one-celled or many-celled 
according to conditions of life. 

SOME IMPORTANT PLANT PHYLA 

1. Flagellata. Usually unicellular, with one or more lash¬ 

like organs of motion (flagella). Many are 
on the border line between plants and 
animals, e.g. Peridinians (p. 260). 

2. ScHizoPHYTA. Include the Bacteria and the so-called ‘Blue- 

Green Algae’. 

3. Thallophyta. a . Algae. Some are unicellular, some multi¬ 

cellular. Include Brown, Green, and 
Red Algae and Diatoms (pp. 257—8). 
b . Fungi. 

4. Bryophyta. Mosses and Liverworts (p. 520). 

5. Pteridophyta. a , Psilophytales.* Found only as fossils 

(p- 274)- 

h , Lycopodiales. Chiefly extinct. Include 
Lepidodendrons (pp. 276-8), modern 
Club-mosses, &c. 

f. Equisetales. Chiefly extinct. Include 
Calamariae (p. 276) and modern Horse¬ 
tails. 

d, Filicales. I'rue ferns (p. 520). 

6. Spermophyta (‘Seed Plants’). 

a , Pteridospermae ‘Seed Ferns’ (pp. 274-6). 

Found only as fossils. 

b, Gymnospermae. With naked seeds. In¬ 

clude the Cone-bearing plants (p. 520), 
the Cycads, the ‘living fossil’ Ginkgo^ 
and the fossil Cordaites, 

c, Angiospermae. Seeds enclosed in a peri¬ 

carp or seed vessel. Flowering plants, 
divided as Monocotyledons and Dico¬ 
tyledons. 



200 


Rise oj Classijicatory Systems 

SOME IMPORl'ANT ANIMAL PHYLA 

Sub-Kingdom Protozoa. Unicellular Organisms 

1. Flagellata (pp. 260 and 328, note), as above. 

2. Infusoria or Ciliata (p. 337). Nearly all have minute hair¬ 

like cilia covering a large part of the body, e. g. Paramecium, 

3. Sarcodina. Send out lobe-like processes of protoplasm, e.g. 

ulmoeha, 

Sub-Kingdom Metazoa. Multicellular Organisms. 

a, Acoelomata. Without definite body-cavity (p. 284). 

4. Spongiaria. Sponges. 

5. Cnidaria. Hydra,^ Jellyfish (pp. 471-2), and Corals. 

6. Platyhelminthes. Flatworms. Include many parasitic 

forms, e. g. Tapev^orms (p. 452). 

b. Coelomata. With definite body-cavity (p. 284). 

7. Mollusca. Unsegmented forms with small body cavity. 

8. Annelida. Round segmented worms, e.g. Earthworms. 

9. Arthropoda. Jointed organisms with external skeleton. In¬ 

clude Insects, Crustacea, Spiders, &c. 

10. Brachiopoda. An isolated group of extreme antiquity. Shells 

superficially like those of bivalve molluscs. 

11. Echinodermata. J'ive-rayed forms including Starfish, Sea- 

urchins, &c. 

12. Nemathelminthes. Round unsegmented worms. Many are 

parasitic. Free living forms of great importance in soil. 

13. Chordata include the vertebrates (pp. 479-80). 

In leaving the subject of classification, we would call 
attention to the fact that the modern concentration on 
the chromosomes and their behaviour (chaps, xiv and 
xv) has not yet had time to react upon the general 
scheme of classification. There can be no doubt that this 
must happen in due course. 



VI 

RISE OF COMPARATIVE METHOD 


§ I. Comparative Studies in the Seventeenth Century 

R esemblances and differences in intimate struc¬ 
ture drew the attention of naturalists earlier in the case 
of animals than of plants. For most of their course, studies 
of this order have been prosecuted mainly on the higher 
backboned animals. This has had a narrowing effect from 
which biological science has shown signs of recovery only 
in recent times. 

It is necessary also to remember that, until the second 
half of the nineteenth century, the analytical study of forms 
had for its object the exposition of function. Thus com¬ 
parative anatomy was designed to lead up to what we 
should now call ‘comparative physiology’. With the 
general acceptance of doctrines of common descent this 
attitude changed. Naturalists concentrated on demon¬ 
strating the historical relations of organisms with less 
regard to the functions of organs. Thus the evolutionary 
bias divorced physiology from anatomy. 

Man was the first animal whose anatomy was adequately 
explored. With Vesalius that study became exact (pp. 96— 
103). He frequently compared human structures with those 
found in animals, and to this day much of the nomenclature 
of comparative anatomy is strictly appropriate only to man. 

During the sixteenth century many besides Vesalius 
made dissections of animals and compared them with man. 
At the end of the century a lawyer of Bologna, Carlo 
Ruini, undertook a detailed investigation of the anatomy 
of the horse. His treatise is the first devoted exclusively to 
the structure of a single species other than man. The 
monograph of Ruini of the horse (Bologna, 1598) is the 
rival, in exactness and beauty, to that of Vesalius of man. 



202 Rise of Comparative Method 

At Padua, Fabricius ab Aquapendente transmitted the 
tradition of Vesalius to his pupils, William Harvey of 
Folkestone (pp. 109-14, 458-9) and Giulio Casserio of 
Piacenza (1561—1616). The latter succeeded to the chair 
of his master in 1604. Casserio had as strong a comparative 
bias as Fabricius. In his extensive investigations of the 
sense-organs, he habitually followed a structure through 
a long series of widely different species. 

The successor of Casserio at Padua was the Belgian 
Adrian Spigelius (1578—1625), who has left his name on 
an important structure in the liver. He was a very exact 
student of the anatomy of man, but he did a signal dis¬ 
service to science by his formal separation of human from 
comparative anatomy. Curiously enough, the founder of 
the great Paduan anatomical tradition, Vesalius, and its 
destroyer, Spigelius, were both natives of Brussels. 

The evil example of Spigelius was followed for two 
centuries. ‘Anatomy’—that is human anatomy—ceased 
to be a true science and became a mere medical discipline. 
The historian of biology can afford to pass lightly over this 
restricted study until it begins to be informed by a new 
spirit in the late nineteenth century. We shall, however, 
constantly need to refer to the greater human anatomists 
who rose above their medical atmosphere. 

Contemporary with Casserio and Spigelius at Padua, 
Gasparo Aselli (1581—1626) professed anatomy at Pavia. 
His great discovery (published 1627) was that of lacteal 
vessels. These gather and convey the fatty material of the 
food from the intestines. The lacteal vessels converge to 
the so-called thoracic duct., which runs up by the spine to 
open finally into one of the veins. The thoracic duct itself 
was first clearly seen twenty years later by the Frenchman, 
Jean Pecquet (1622—74), at Montpellier in 1647 (Fig. 61). 
Both Aselli and Pecquet worked on dogs. Both would 
have extended their researches to other animals, but for 




Fig. ioo. Anatomical theatre at Padua built for Fabricius about 1590 and 
still intact. Harvey, Casserio, and Spigelius all attended lectures in it. 
From an eighteenth-century stipple engraving. 





204 of Comparative Method 

the intervention of an early death in the case of the first, 
and an even earlier addiction to alcohol in the case of the 
second. 

The thoracic duct, before it opens into the blood system, 
also receives tributaries from a system of vessels, the lym¬ 
phatics^ which ramify throughout the body. The lym¬ 
phatic system was first demonstrated in 1653 by Thomas 
Bartholin (1616—80) of Copenhagen. He was a pupil of 
Severino (see below) and a member of a family that long 
monopolized anatomical posts in Denmark. During the 
eighteenth century an immense amount of detailed work 
was done on the lymphatics, without, however, adding to 
the conception of their role in the animal economy. 

Marco Aurelio Severino of Calabria (1580-1656), long 
professor at Naples, earned the suspicious attentions of 
the Inquisition, perhaps by reason of the anti-Aristotelian 
bias which he shared with his contemporary, Galileo. In 
1645 he issued his Zootomia democritaea, id est anatomia 
generalis totius animantium opificii (‘Democritean Zoology, or 
a general anatomy of the whole animal creation’). Demo¬ 
critus, we recall, was the philosopher to whom Aristotle 
was most opposed. Nuremberg, where this volume was 
published, was out of reach of the Inquisition. In this 
book, now very rare, Severino sought to trace analogies of 
construction in corresponding parts of various animals. 
He had dissected many forms, both vertebrate and in¬ 
vertebrate, but he exhibits no deep understanding of their 
structure. He was, however, convinced that microscopic 
research would throw light on comparative anatomy. 

The classical microscopists began to prove him right. 
Swammerdam investigated the anatomy of the may-fly, of 
the bee, of the snail, and of many other forms, Malpighi 
worked on the silkworm, and Leeuwenhoek studied in¬ 
numerable small creatures. Thus by the later seventeenth 
century, partly through the diffused influence of the Paduan 



Comparative Studies in Seventeenth Century 205 

school, partly under the stimulus of the classical micro- 
scopists, the comparative method of investigating animal 
structure caught fast hold. 

Anatomical monographs of various vertebrates now 
began to appear. Worthy of notice is a series of descrip¬ 
tions of dissections by Claude Perrault sumptuously issued, 
from 1671 onwards, by the French Academic des Sciences 
(p. 136). This included monographs of the beaver, the 
dromedary, the bear, the eagle, the tortoise, and many other 
forms. Comparable to these are treatises of the English 
naturalist Edward Tyson (1650—1708) on the porpoise 
(1680), the rattlesnake (1683), the opossum (1698), and 
the chimpanzee or ‘pigmy’ (1699). In the same category 
are works on the ostrich (1712) and the chameleon (1715) 
by the accomplished Paduan, Antonio Vallisnieri (1661— 
1730), who is commemorated in the familiar water-weed, 
Vallisneria spiralis. 

One of the most remarkable comparative studies of the 
seventeenth century is Crew’s Comparative Anatomy of the 
Stomach and Guts (1681) based on the study of some thirty- 
five species. Grew had himself introduced the term ‘com¬ 
parative anatomy’ in his Comparative Anatomy of Trunks 

(1675)- 

The Belgian, Gerard Blaes (Blasius, 1646-82), who be¬ 
came professor of medicine at Amsterdam, devoted many 
years to a comparative investigation of the structure of 
vertebrate animals. His great Anatome animalium (Am¬ 
sterdam, 1681) is a compendium of previous writings on 
the same subject, but contains some original observations. 
Each animal is treated, organ by organ, in an orderly 
manner, and the work is entitled to respect as the first 
general systematic treatise on comparative anatomy. It 
throws into clear relief the community of structure of the 
larger groups of vertebrate animals, such as birds, rodents, 
and carnivorous mammals. 



2 o 6 Rise of Comparative Method 

The common elements in the structure of the great 
botanical groups are less obvious than those of comparable 
zoological divisions. An excellent start was made, however, 
by Malpighi and Grew. The latter author especially 
attained a view of the structural distinction between roots 
and shoots, and the differences between the systems of 
‘vessels’ in the two. Grew and Malpighi displayed the 
distinction between dicotyledonous and monocotyledonous 
stems, and between both and those of such plants as the 
pines and cypresses, now classed as Gymnosperms (Greek, 
‘with naked seeds’). 

Grew showed remarkable grasp of the relationship of the 
various organs of plants throughout different groups. 
Thus, he traced stems through their modifications, and 
perceived that thorns, for example, are modified branches. 
Of subterranean bulbs he says, quite truly, that ‘the Strings 
(i. e. the ring of adventitious rootlets) only are Roots', the 
Bulb actually containing those Parts which springing up 
make the Leaves or Body; and is, as it were a Great Bud 
under ground’. 

Grew perceived that the growing zone of a stem lies 
near the surface and that ‘the young Vessels and Paren¬ 
chymatous Parts' (pp. 325-6) are formed each year ‘betwixt 
the M^ood and the Barque'. Thus, ‘every year the Barque 
of a Tree is divided into Two Parts, and distributed two 
contrary ways. The outer part falleth towards the Skin', 
and at length becomes the Skin itself. The inmost portion 
of the Barque is annually distributed and added to the 
Wood, the Parenchymatous Part thereof making a new 
addition to the Insertions within the Wood.' 

% 2. Some Eighteenth-century Conceptions of Nature 

Following the great comparative investigations of the 
later seventeenth century, there was a lull in progress. 
Certain philosophical prepossessions tended to obscure 



Eighteenth-century Conceptions oj Nature 207 

good work. Among these was the conception of the 
‘Ladder of Nature’. Aristotle had been content with the 
formal projection of the idea (p. 40). He did not erect it 
as a rigid framework into which all observations were 
to be fitted. This, however, was the policy of many 
eighteenth-century naturalists. 

Prominent among those who thus approached nature 
with preconceived ideas was the Genevan, Charles Bonnet 
(1720—93). It was an age when ‘free-thinkers’ and ‘deists’ 
(p. 126) on the one hand, and Christians on the other, 
inhabited sharply-divided camps. It was the century of 
Voltaire (1694—1778), the scoffer, whose works everybody 
read, and of Archdeacon William Paley (1743—1803), 
whose unphilosophical Evidences of Christianity (1785) 
hypnotized until our own time the University where 
Newton had taught. 

Bonnet was very influential on the Christian side and 
was, in some sense, a predecessor of Paley. He raised the 
doctrine of preformation, or rather of embottement, to the 
rank of a dogma, and both it and the process of partheno¬ 
genesis which he rediscovered (p. 166) he made to serve 
religious ends. Moreover,he stamped upon the comparative 
anatomy of his age a rigid interpretation of the Aristotelian 
ladder of nature. Passing from the most subtle of the 
elements, fire and air, through water and earth, to the 
minerals, it ascended through crystals to living things, 
proceeding via moulds, plants, insects, and worms to fish, 
birds, mammals, and finally to man. Man is the type by 
which other forms must be tested. ‘All beings’, wrote one 
of Bonnet’s followers, ‘have been conceived and formed on 
one single plan, of which they are the endlessly graded 
variants. This prototype is man, whose stages of develop¬ 
ment are so many steps toward the highest form of being.’ 

Such views drew much from the philosophy of Leibniz 
(1646—1716). They pass insensibly into the attitude 



2 o 8 Rise of Comparative Method 

known as Naturphilosophie^ which became very popular in 
Germany (pp. 212—19). This temper has, at times, served 
well the cause of scientific advance, but has seldom been 
conducive to careful comparative studies. Until toward 
the end of the eighteenth century, neither in France nor 
Germany nor England was much important work being 
done in that department. The writings of Bufibn accord 
rather with the evolutionary philosophers (pp. 288—91). 
Fdix Vicq d’Azyr (i 748—94), a busy practising physician, 
almost alone upheld the pure comparative method. 

The work of Vicq d’Azyr, largely based on a com¬ 
parative study of function, leads on to that of Hunter. 
On the other hand, his intensive study of a large variety 
of forms brought him to an application of the ‘principle of 
correlation’ (pp. 223—7), and so links him to Cuvier. Vicq 
d’Azyr made extensive studies of the nervous system. A 
structure in the brain is still called by his name. He con¬ 
stantly compared the anatomy of man to that of other 
mammals. The suggestions arising from his detailed com¬ 
parison of the parts of the fore and the hind limb have 
been of great service for the subsequent development of 
comparative studies. 

§ 3. Hunter (1728—93) 

A remarkable and isolated position is occupied by the 
great English biologist John Hunter. Dull at school, he 
was sent to assist a Glasgow cabinet-maker, but persuaded 
his brother William, an eminent anatomical teacher in 
London, to accept him as his assistant. His real genius 
now declared itself, and he became a very great exponent 
of the comparative method. He distinguished himself as 
a practical surgeon, but his earnings and his powers he 
devoted entirely to science. 

Hunter accumulated a wonderful museum; he paid and 
kept assistants and draftsmen; he even set up his own 



Fig. lor. The crop from a male pigeon, while the female was breeding. It 
is turned inside out to show the development of the mucous membrane on its 
internal surface. This secretes a substance which nourishes the young. (From 
Hunter, 1786.) 









Fig. 102. Ear membranes and their apparatus, from drawings by Clift of 
specimens in Hunter’s collection. From left to right are the structure's in the 
cow, deer, and hare. In the tier below is shown the whole apparatus in these 
animals. In the tier above the membranes and their ossicles only. 






210 Rise of Comparative Method 

printing-press and acted as his own publisher. He per¬ 
formed an enormous number of physiological experiments, 
kept his own menagerie, and never missed an opportunity 
of securing the body of a rare beast for dissection. He 
was interested in fossil no less than living forms (Fig. 103), 
in physiology as much as in anatomy. His energy in 
the pursuit of science was inexhaustible. He was ever 
fearful that he would die with his museum and his papers 
in disorder. In fact, of the great mass of notes that he left 
behind, some were published in the name of another and 
others were wantonly destroyed. 

Hunter willed that on his death his collections should 
be offered to the British Government for purchase at a low 
price. The Prime Minister, the younger Pitt, on being 
approached, answered, ‘What! buy preparations! Why, 
I have not money enough to buy gunpowder 1’ Fortunately 
an old servant was more generous. He devoted himself to 
these despised preparations, though he had to live on seven 
shillings a week. The price of bread rose enormously 
owing to the war, but this zealous man never relaxed his 
ward. Hunter died in 1793. In 1795 Government 
decided to reconsider the matter. The guardian of the 
collection was almost starving, but he held on. In 1799, 
having taken six years to make up its mind, the Govern¬ 
ment bought the collection and handed it over to the Royal 
College of Surgeons of London. Hunter’s old servant was 
appointed curator. At the end of his vigil, the specimens 
were in a better state than on his master’s death. His name 
was William Clift (1775—1849). Though an admirable 
assistant, he was devoid of initiative and made no im¬ 
portant discovery, but he has an honoured place in the 
history of science. 

A spirit informs the Hunterian Museum which is as 
different as can be from the ‘magpie instinct’ which has 
been the motive of many great collections. Here every 



Hunter 211 

object has its place and its reason for being included. 
Hunter had anatomized over 500 species of animals— 
many a great number of times—as well as numerous species 
of plants. He designed to trace systematically the different 
phases of life as exhibited by the organs, the structure, and 
the activities of both animals and plants. 

A few of the biological observations which occupied 
Hunter appeared in the Philosophical Transactions. They 



Fig. 103. Skull of Ichthyosaurus from a drawing by Clift in the collection 

of Hunter. 

show the range of his studies. He was interested in 
monstrosities, and was the founder of their experimental 
investigation. Animal behaviour attracted him, and he in¬ 
vestigated, for example, that of bees. He made many 
experiments on the temperature both of plants and of 
animals. Anything related to animal mechanism particu¬ 
larly appealed to him, and his researches on the air-sacs 
of birds, on the electric organs of fish, and on the structure 
of whales and sea-cows added greatly to knowledge. 

No great naturalist is so refractory to literary treatment 
as Hunter. He was himself lacking in literary power and 
could not put outside himself the thoughts surging in his 
mind. Often we can reach his meaning only by piecing 
together hints and notes. No systematic treatise on any 


2 12 Rise oj Comparative Method 

subject was written by him. His main work is his museum 
and the influence that it has exerted. And yet his real 
monument is not so much the museum itself as his ideal for 
a Museum. There were many museums before his (p. 142), 
but they were seldom more than collections of curiosities, 
exhibitions to illustrate human anatomy, or, at best, at¬ 
tempts to set forth the superficial characteristics of a 
number of species. Hunter created the conception of a 
collection to illustrate the varieties of structure and func¬ 
tion right through the organic series. 

§4. The Naturphilosophen; Kant (1724—1804), Goethe 
(1749-1832), and Oken (1779-1851) 

Hunter was averse from all abstract discussion and had 
no feeling for what is usually called ‘philosophy’. But the 
thought of his age was being given new direction by the 
KOnigsberg philosopher, Immanuel Kant. The change 
was inaugurated by this writer’s famous Critique of pure 
reason (i 771). 

Kant was primarily a mathematician and physicist. His 
mind was slow in developing to its full powers, and his 
philosophical interest emerged only gradually from his 
treatment of scientific problems. Beginning with a world 
of phenomena, of nature, of experience—^the determinate 
world of the man of science—he gradually passed into the 
world of the intelligible, of freedom, of ends. 

To most, the two worlds seem still to confront one 
another. Scientific men of our own time still affirm this 
when they say that ‘teleology is the enemy of science’, 
meaning that the study of purpose, of ends, is inconsistent 
with the adequate description of phenomena. It was 
Kant’s thought that the two attitudes are not opposite 
and irreconcilable. The problem reduces itself to the 
discussion of the relation between our perception of things 
and their real nature. Our perceptions, Kant held, come 



The Naturphilosophen 213 

into relation with the real nature of things through the 
character of our processes of thought. In other words, our 
minds work along the lines that nature wills. Our minds 
are, as it were, attuned to Nature. 

This view has implications with biology. Organisms 
are composed of parts. These are comprehensible only as 
conditions for the existence of the whole. The very 
existence of the whole thus implies an end. True, says 
Kant, nature exhibits to us nothing in the way of purpose. 
Nevertheless we can only understand an organism if 
we regard it as though produced under the guidance of 
thought for the end. 

We may note in passing that in coming to this con¬ 
clusion Kant sets forth the relations of classes of organisms 
as though they were historically related to each other. He 
is thus prepared to accept evolution, and he expressly in¬ 
cludes the possibility of organisms developing from lower 
to higher according to mechanical laws (Kritik der Ur- 
theilskraft, ‘Critique of Judgement’, 1790). 

The opposition, so familiar to the biologist, between 
mechanist and teleological views is, Kant thinks, due to the 
nature of our knowledge, that is of our experience. But 
our thoughts must be distinguished from our experience. 
In thought we pass constantly from the m.echanist view of 
the parts to a teleological view of the whole, and back again. 
Nor do we separate these classes of view unless deflected 
by some specific doctrine that the parts are really separate. 
There is, Kant believes, a hidden basic principle of nature 
which unites the mechanical and teleological. That prin¬ 
ciple may be none the less real because our reason is 
unable to formulate it. In practice, in our use of the 
language of biology, we all accept such a principle, the 
most convinced mechanist no less than the teleologist. 

The inevitable use of the language of teleology by 
naturalists of mechanist views might be illustrated from 



214 ?/ Comparative Method 

innumerable works from Kant’s day to our own. A single 
passage may suffice. It is from a work of 1923 by the 
foremost living exponent of the cell doctrine. Professing 
himself, in this very volume, a determinist and a mechan¬ 
ist, E. B. Wilson (1856-) yet writes: 

‘The cytologist is struck by the extraordinary pains that nature seems 
to take to ensure the perpetuation and accurate distribution of the 
components of the system in cell division. . . . Nothing is more im-- 
pressive than the demonstration of this offered by the nucleus of the 
cell; but its obvious meaning is often disregarded or treated with a 
blind scepticism which pretends that no meaning exists. To our limited 
intelligence it would seem a simple task to divide a nucleus into 
equal parts. ... The cell manifestly entertains a very different 
opinion. Nothing could be more unlike our expectation than the 
astonishing sight that is step by step unfolded to our view by the 
actual performance.^ 

(Italics inserted. From E. B. Wilson, Physical Basis of Life^ 1923.} 

So the modern naturalist returns to the antithesis which 
Kant was seeking to resolve. A new system of philosophy 
has intervened. An imperfect fusion of the Kantian 
scheme with atomistic materialism is, in fact, the working 
philosophy of most modern biologists. 

Kant undoubtedly exerted great influence on the bio¬ 
logical thinkers of his day. His hand is to be traced 
especially in the writings of the ‘Naturphilosophen’. Of 
these Goethe and Oken are the most important. 

From the seventeenth century onward, schemes of 
classification of animals were based upon their anatomy. 
Implicit in such attempts was the conception of some 
uniformity of anatomical plan. But it is remarkable how 
far a science may advance before coherent expression is 
given to its principles. The German poet and philosopher 
Johann Wolfgang von Goethe was perhaps the first since 
Aristotle to point out explicitly that the structures of 
animals exhibit uniformity of anatomical plan. He sought 



The Naturphilosophen 215 

general expressions for the constant factors in their ana¬ 
tomical composition. His generalizations were often 
vague or extravagant, but in directing the search for them 
he rendered many important services. Not the least of 
these was that he persuaded biologists to turn their eyes 
away from the anatomy of man as the type to which all 
other creatures were to be referred. 

Searching for correspondences in the structures of dif¬ 
ferent creatures, Goethe had his first success in 1784. He 
noted that the upper jawbone in man is formed of one 
piece only on each side, whereas in other animals it is of 
two. He inferred that in early life the human upper jaw¬ 
bone must consist of two pieces on each side, and he 
marked out the division between the two. Later he was 
able to demonstrate the truth of his view (1822).’ 

In 1790 Goethe completed an essay on plant meta¬ 
morphosis which exhibits the influence of Kant. He set 
forth three doctrines of great importance. 

(a) The genera of a larger group, such as a Family or 
Order, present something in the nature of variants on a 
common plan. They are all expressions of the same idea. 
The idea of Goethe became the type of A. P. de-Candolle 
(1827, see pp. 194-6) and later writers. 

(^) He amplified the view, hinted by Jung (p. 179) and 
expounded by C. F. Wolff (pp. 462—4), that the various 
parts of the flower are but modifications of leaves. He 
stumbled in details and his scheme was needlessly com¬ 
plex, but he reached an important conception (Figs. 151— 
3 > P- 387)* 

(r) The so-called cotyledons of flowering plants, which 
give their name to the great groups. Monocotyledons and 
Dicotyledons (pp. 181-2), are nothing but the first leaves 
borne by the infant shoot (Fig. 152, p. 387). 

* Vicq d*Azyr had come to similar conclusions in 1780, and Fallopio in 1561. 
Goethe and his circle, however, did not know this. 



216 Rise oj Comparative Method 

Goethe’s Preliminary Sketch to a general introduction to 
comparative anatomy (1795) and his Formation and trans¬ 
formation of living things (1807) set forth several further 
important biological ideas. 

{ft) Extending his view of the leaf origin of the parts 
of flowers, Goethe considered that every living being is a 
complex of independent elements, each referable to one 
type. Thus not only is there a primordial animal and a 
primordial plant, representing the animal ‘idea’ and the 
plant ‘idea’, but also each of the parts of each organism re¬ 
presents one primordial part. This position is now indefen¬ 
sible but can be illustrated by the vertebrae. These, funda¬ 
mentally of the same origin and structure, perform very 
different functions, and have different forms in different 
parts of the backbone. So it is, Goethe believed, with other 
organs. There are in fact animal groups, e.g. the Annelids, 
in which he might have brought out the point better, but 
he did not know enough of their structure. 

((?) Applying this view to the skull, Goethe adumbrated 
the famous vertebral theory, more explicitly set forth by 
Oken. Goethe maintained that the structure of the skull 
can be explained as a fused series of bone groups, com¬ 
parable to the series of vertebrae (pp. 218-19). 

{f) He enunciated a principle that has been termed the 
law of balance, according to which ‘no part can be added 
without something being taken away from another part, 
and vice versa'. This law played a considerable part in 
the biological thought of the succeeding generation. 

(jg) He foresaw the value of embryology for the inter¬ 
pretation of adult structure. Thus he perceived that cer¬ 
tain bones might be shown to be of compound origin by 
tracing them back to the embryo. 

(h) He invented the useful word morphology (Greek 
morphe, form). The word describes the science which 
concerns the structure of living things, the relation 



The Naturphilosophen 217 

of their structures to other living things, the way that these 
structures arise, and the factors that go to their production. 

The Swabian, Lorenz Oken, came very early under the 
influence of the philosophy of Kant. He developed what 
he regarded as the ideas of his master into an extreme form, 
and he became the typical Naturphilosoph. This did not 
prevent him from doing some good routine biological 
work. Despite Oken’s great learning and lofty character, 
there is hardly a biologist of the past with whom the man 
of science of to-day would feel so out of sympathy. On 
this account it is worth devoting a little attention to him. 
Through him, and through our differences from him, we 
may learn something of the nature of our own scientific 
method. 

Before we pass to his forgotten methods we may glance 
at his more positive achievements. Oken gave an in¬ 
teresting forecast of the modern cell doctrine which 
included a remarkable appreciation of the true nature of 
the protozoa (1805, p. 328). He made definite advances 
in embryologicial science. He founded a biological 
journal (/w, 1816—48) which for thirty years published 
articles of unquestioned value. He instituted the type of 
annual meeting of men of science (1821) which has since 
had innumerable imitators, among them being the British 
Association for the Advancement of Science (first meet¬ 
ing: York, 1831). 

Oken’s effort to construct a biology that should reflect 
the actions of the mind appears in a work, the title of which 
may be rendered Foundations of Naturphilosophie, the theory 
of Linnaeus and the classification of animals based thereon 
(1802). For Oken, man is the summit and crown of 
nature. Thus the whole animal kingdom is the representa¬ 
tion of his several activities and organs—naught else, in 
fact, than man disintegrated into the five senses through 
which, alone, his mind can learn of nature. On this basis 



218 Rise of Comparative Method 

there must be five classes of animals, and not more than 
five. These are virtually representatives of the five senses 
of man. They are: 

(a) Dermato%oa^ in which the sense of feeling leads. Invertebrates. 

(b) Glossozoa^ the lowest grade in which a tongue, the organ of taste, 

is developed. Fishes. 

(c) Rhinoxoa^ in which the organ of smell is separated and the 

nostrils take in air. Reptiles. 

(d) Otozoa^ in which the organ of hearing begins to be independent 

and to open externally. Birds. 

(e) Ophthalmozoa which have all the organs perfect with the sense 

of sight leading. Mammals. 

Oken’s personality and the fashion of the day gave him 
great influence. His doctrines are now all forgotten. One 
of them, the vertebral theory of the skull, needs discussion. 

It is an evident fact that the spinal column contains a 
number of repeated units, the vertebrae. To each corre¬ 
sponds a group of nerves and a group of muscles, which 
show similar repetition. Vertebra, nerve, and muscle are 
thus, as we say, ‘segmentally arranged'. This fact is even 
more evident in the embryo than in the adult; and in the 
lower forms, such as fish, than in the higher, such as 
mammals. Modern science has found no solution to the 
puzzle of how in most groups of animals many organs 
come to be segmentally arranged. 

For Oken the idea of segmentation provided a plan on 
which the vertebrate body was built. All parts were seg¬ 
mented. He relates how, resting one day on a walk, he 
sat contemplating the skull of a sheep. It flashed across his 
mind that it was but a group of fused vertebrae. The skull, 
like the rest of the body, was segmented. Thus arose his 
vertebral theory of the skull (i 807). 

Oken pressed the matter further. Some of the seg¬ 
ments of the body of vertebrate animals present ap¬ 
pendages—to wit, the fore and hind legs. Doubtless in 



The Naturphilosophen 219 

the complete type of vertebrate all segments should present 
limbs as they do in some jointed animals, notably Crus¬ 
tacea, Myriapoda, & c. The vertebrate type was, in fact, a 
regular centipede! Were there remains of such limbs in 
the head? Oken found them in the jaw. So also the mouth 
cavity represented a series of segments of the intestines, 
the brain represented a series of segments of the spinal 
cord, and so on. 



Fig. 104. The ‘archetype’ of the vertebrate skeleton according to Owen 
(1846). In the view of Oken, Ow'en, and others the vertebrate skeleton could be 
analysed into a series of completely homologous and very similar segments. Of 
these, several of the anterior elements w^ere supposed to be fused to form the skull. 
Each segment is equipped with a series of rib-like structures with appendages. 
From the first tw'o of these segments the jaws were thought to be formed. Other 
segments developed as limbs. 

This theory carried away Goethe, who had already an 
inkling of it. It misled von Baer, and some of those who 
followed him, into a blind alley of speculation. Even 
Johannes Muller (pp. 388—90) adhered to it, and some of 
his best work was done in the false light that it yielded. The 
conception of the segmented ‘archetype’ was elaborated 
and given colour by several other comparative anatomists, 
of whom Owen was one (Fig. 104). 

§ 5. The Eclipse of Naturphilosophie 

The vertebral theory was refuted by the embryologists 
(p. 470). Here we may note the decisive discovery of 
Martin Heinrich Rathke (1793—1860), the successor of 
von Baer (pp. 464—70) at KOnigsberg. Rathke’s best- 
known discovery was of structures homologous with gill 
slits in bird and mammalian embryos (i 825, p. 471). At a 



220 Rise oj Comparative Method 

certain stageof development these creatures present a series 
of structures which in position and anatomical relations are 
identical with similar structures in fish embryos. In the 
latter they continue to develop into gill slits and their 
associated organs. Malpighi had described arteries arch¬ 
ing round the gullet of the chick embryo in the position 
of these gill slits (p. 152). These arches in the embryo 
were now explained by the presence of other structures 
associated with gill slits. They correspond to the vessels 
that supply the gills in fish. But the skeleton of the gill slits 
in the embryo was found to correspond to certain parts 
attached to and ultimately forming part of the jaw, the organ 
of hearing and the organ of voice in the adult mammal and 
bird. Thus it became impossible to believe that the parts 
of the jaw, &c., had originally been of the nature of limbs. 
So the vertebral theory of the skull became discredited. 

The theory was finally dismissed by T. H. Huxley in 
a classical paper published less than a month before the 
first communication on the origin of species was read by 
Wallace and Darwin (1858). Huxley declared his belief 
that the ‘study of the gradations presented by a series of 
living things may have the utmost value in suggesting 
homologies (p. 222), but the study of development alone 
can demonstrate them’. Thus he placed embryology in 
the position of the arbiter of the structural relationships of 
animals. It was prophetic of the dominant position which 
it came to occupy in evolutionary comparative anatomy. 

The vertebral theory was an extreme manifestation of 
the thought of the German Naturphilosophen. These men 

Description of Fig. io6. 

Fig. 106. Drawings by Leonardo to show the correspondence between the 
horse’s stifle-joint and the human knee, on the one hand, and the horse’s hock and 
the human heel, on the other. Leonardo also attempts to bring out the homology 
of the muscles which link limb to body hi the case of horse and man. He has 
represented the muscles diagrammatically as strap-like bands, to assist in the 
interpretation of their action. 




Fig. 105. Structure of wing in the three classes Reptiles, Mammals, and Birds. 
In each case the fore-limb forms the main part of the apparatus of flight. The 
general plan of the limb is found in all. In this sense we trace homology in various 
parts. The other details are, however, so different in the three cases that it is 
evident that they have arisen quite independently and that the wing in the three 
classes is an analogous and not an homologous structure. 

In the fossil reptile pterodactyls a membrane stretches between fore- and 
hind-limb. The main support is an enormously developed fifth or ‘little’ finger. 
There are three free fingers. The thumb is absent. 

In the mammalian bats the membrane is supported by both limbs, but is 
largely formed by an enormous web between digits 2, 3, 4, and 5. The thumb 
alone is free. 


In the wing of birds the fore-limb alone is involved. The only digits remaining 
are i, 2, and 3, and all are greatly reduced except 2. In the fossil bird Archaeo- 
pteryxxhi^ three digits are still free and provided with claws (Fig. 108), I'he 
expanse of the wing in the bird is formed by feathers and not by a membrane. 
The hind-limb is free and is not involved in the flying apparatus. 

Fig. 106. For description see opposite page. 


222 Rise oj Comparative Method 

were interested in ‘types’, ‘schemata’, ‘ideal forms’. They 
linked them with their conception of Repurpose which lies 
in living things. The later Darwinians, in dismissing this 
doctrine—^this ‘religion’—said that it failed to distinguish 
between analogy and homology. 

The passage just quoted from Huxley is of interest as 
an early use of the important biological term homology 
(Greek ‘agreement’). It was first employed in biology 
to indicate the relation of an organ to the general type. 
Organs were said to be ‘homologous’ with each other when 
they had the same relation to that type. Later, with the 
general advent of the doctrine of descent, homology became 
opposed to analogy. Homology is thus a morphological 
relationship based on descent. Analogy is a physiological 
relationship, without any implication as regards relation¬ 
ship by descent. Thus the human knee, as shown in the 
drawing of Leonardo (Fig. io6, p. 221) is analogous with 
the hock of the horse but homologous with the stifle-joint. 
The distinction was certainly not adequately recognized 
by the Naturphilosophen. 

Naturphilosophie was destroyed by the evolutionary 
view and is now placed among the lumber of forgotten 
theories, but it is well to remember that the method had 
its victories. The paths of discovery are as diverse as the 
human mind. But the Naturphilosophen went to fantastic 
excesses. If Goethe succeeded, it is because he was a man 
of genius and was more interested in Nature than in his 
own method. Others were more interested in their method 
than in Nature. Such men, Oken among them, developed 
enormous and bizarre systems which have now little in¬ 
terest save for the special student of the history of science. 

Naturphilosophie infected other countries besides Ger¬ 
many. Etienne Geoffroy St. Hilaire (1772—1844) in 
France and Richard Owen (pp. 233-5) England carried 
deep marks of its influence. 



Eclipse oj Naturphilosophie 223 

It is the prime task of morphology to analyse the 
bodies of creatures into organs and to compare them with 
those of other creatures. But morphology is a poor thing 
unless it can regard the creature as a whole, and no creature 
is a whole unless alive. This was Goethe’s standpoint 
when he expresses his ‘yearning to apprehend living forms 
as such, to grasp the connexion of their external visible 
parts, to interpret them as indications of the inner activity, 
and so, in a certain sense, to master the whole con¬ 
ceptually’. For him the science of morphology should 
separate itself neither from physiology nor from an under¬ 
standing of the organism as a vitally active work of art. 
‘If the creative spirit brings creatures into being and 
shapes their evolution according to a general plan, should 
it not be possible to represent this plan, if not to the sense, 
at least to the mind.?’ This was the view toward which 
.A. P. de Candolle was working {Organographie vegetale, 
1827, pp. 194—6). This was the view of Cuvier. 

§6. Cuvier (1769—1832) and the Principle of Correlation 
of Parts 

Georges Cuvier has been called the ‘dictator of biology’. 
Few men of science have attained to so influential a posi¬ 
tion. For years he was the admitted leader of science. His 
own investigations determined very largely those of his 
contemporaries. His influence was stimulating to research, 
though it cannot be said that he invariably exerted his 
power with the greatest wisdom. He held strong opinions, 
and tended to suppress views opposed to his own, notably 
those of the evolutionist Lamarck (pp. 292-5), Cuvier 
himself believing firmly in the fixity of species. 

Cuvier was the son of a Swiss Protestant officer in the 
French army. He was born near Belfort, then in the Duchy 
of WUrtemberg. He studied at Stuttgart, and in 1795 
became assistant at the Mus6e d’Histoire NaturelleatParis. 



224 Rise oj Comparative Method 

He rapidly attained distinction by his anatomical descrip¬ 
tions of a variety of animals. In 1800 he published a work 
on fossil elephants which he compared with living species. 
The study of fossil fcrms scon became a separate science, 
palaeontology. Cuvier had a leading part in this develop¬ 
ment. His Recherches sur les ossemens fossiles (1812) is a 
classic. 

The Emperor Napoleon selected Cuvier to direct the 
reform of education in France. This detached him from 
his special studies to which, however, he soon returned. 
On several occasions he was again withdrawn for adminis¬ 
trative functions, but these never permanently held him. 
After the downfall of Napoleon he obtained the favour 
of the restored dynasty. 

With encyclopedic knowledge and boundless energy, 
Cuvier formed vast scientific schemes. He had a capacity 
for winning the aid of the ruling powers, and he brought 
many of his projects to fruition. With the gift of inspiring 
others, and of causing them to work for him, he never 
lacked for skilled assistance. He united general culture to 
comprehensive scientific outlook. Thus he perceived the 
interest and importance of the history of science, and lec¬ 
tured and wrote well upon that subject. His historical 
writings can still be consulted with profit. 

Cuvier was a ‘morphologist’ in Goethe’s sense. He was, 
in fact, under the influence of the great German, and his 
view of organisms was based on their activities as living 
things. The main conception that guided his work was 
the principle of correlation of parts. The nature of this 
principle must be discussed. 

Organs do not exist or function in nature as separate 
entities but as parts of organic living wholes. In these 
living wholes, certain relations are observed which are 
fundamental to their mode of life. Thus feathers are 
always found in birds and never in other creatures. The 



Correlation of Parts 225 

presence of feathers is related to a certain formation of the 
forelimb with reference to its use as wing. This, in its turn, 
is related tocertain formations of thecollar-boneand breast¬ 
bone, with reference to the function of flight; these, again, 
to the form and movement of the chest; these, again, to the 
function of breathing. So the‘principle of correlation’might 



Fig. 107. Owen’s first restoration of Archaeopteryx lithographic a ^ a Jurassic fossil 
bird discovered in 1861 in lithographic slate in Bavaria. 

Fig. 108. Modern restoration of Archaeopteryx, The animal, though covered with 
feathers, has yet many reptilian features, e.g. teeth, claws on fore-limb, and long, 

free, jointed tail. 


be followed through the whole being of the bird, down 
to its minutest parts. Yes, and even to its psychology. 

It is with structure that, for the moment, we are con¬ 
cerned. Given a feather, it is possible to infer that its 
owner had a particular form of collar-bone. Again, given 
a particular form of collar-bone, it is possible to injfer a 
feather. The existence of the extraordinary fossil bird 
Archaeopteryx was, in fact, revealed by the discovery (18 61) 
2613.3 o 



226 Rise oj Comparative Method 

of the impression of a feather (Fig. 107). If enough be 
known of the comparative morphology of the bird group, 
it is possible by the use of this principle to make most 
sweeping inferences.* 

It was not reserved for Cuvier to discover the principle 
of correlation. In an elementary form it is obvious, and it 
is known to us all. If any one were to find a severed hand, 
he would be confident that it had once been attached to 
a human body and not to that of an animal. The race, sex, 
occupation, state of health, &c., of the owner of the hand 
might easily be inferred. The ‘principle of correlation’ is 
the theme of most detective stories. Anatomists before 
Cuvier and back to Aristotle had, to some extent, been 
able to act upon the principle of correlation with reference 
to animal bodies. As with many other scientific principles, 
it was applied long before it was adequately formulated. 

An achievement of Cuvier was that he enunciated this 
principle clearly, and made it the guiding element in his 
work. He refined and extended its application far beyond 
all previous knowledge. As a result of his wide and deep 
studies, the principle could often be brought to bear upon 
the merest fragment of an organized body. 

The principle of correlation was especially of value to 
Cuvier in his studies of fossils, as these are usually frag¬ 
mentary. From fossil elephants he passed to the fossil 
bones of other mammals and of reptiles. He discerned that 
these mostly belonged to species no longer existing. At 
the same time he was constantly working at the skeletons 
of living forms. Thus he came to be in a good position 
to elucidate the relationship between the living and the 
extinct forms. By practice in restoring the missing parts 
of fossil skeletons, Cuvier became able to recognize the 

* Some form of feathers was probably first developed as covering and later 
became connected with flight. The argument, however, holds for living and 
recent and for all but a very few fossil forms. 



Correlation oj Parts 227 

species from a few bones, or even from a fragment of a 
bone. In this he became very expert, and founded a 
method of dealing with extinct forms based on the 
anatomy of extant species that has since proved of the 
greatest value. The science of palaeontology owes to no 
one so great a debt as to Cuvier. 

Inferences correctly made by Cuvier and his followers, 
from small portions of fossil bones, excited great astonish¬ 
ment at the time, and are still sometimes cited with 
wonder. They were, however, the natural outcome of such 
intensive study of the physiology and anatomy of animals 
as had long been applied to the body of man. Further, 
the principle of correlation formed the basis of the whole 
of Cuvier’s classificatory system and of the beautiful and 
exact view that he gave of the animal kingdom. 

§ 7. 'Le Regne AmmaV (1817) 

Cuvier’s most comprehensive effort, and that by which 
he is best known, is Le Regne animal distrihue aprh son 
organisation pour servir de base a Phistoire naturelle des 
animauXy et d'introduction a Vanatomic comparee (first edi¬ 
tion, 1817. Many subsequent editions and translations). 
This formidable work embodies a lifetime of research 
on living and fossil animals. It was the most comprehensive 
biological work since Linnaeus. Knowledge had accumu¬ 
lated in the meantime, and Cuvier had investigated more 
forms than any before him. The work describes a species 
from almost every genus then recognized, and is illustrated 
by hundreds of beautiful plates. 

Cuvier’s arrangement of the animal kingdom, that is to 
say his ‘system of classification’, is of interest. In contrast 
to Lamarck (p. 196) he will have nothing to do with a 
‘scala naturae’. He divides animals into four great em- 
hranchements^ each of which is built on its own peculiar 
and definite plan. 



228 Rise of Comparative Method 

I. VERTEBRATA, animals with a backbone. 

II. MOLLUSCA, such as slugs, oysters, snails, &c. 

III. ARTICULATA or jointed animals, such as insects, spiders, 

and lobsters. 

IV. RADIATA^ a group containing all remaining animals. 

The Radiata is a very miscellaneous collection, but the 
other three are all fairly ‘natural’ groups. 

In placing animals in these groups, Cuvier was guided 
by an analysis of two main sets of functions, which he 
regards as fundamental, together with the organs sub¬ 
servient to them. Firstly, the heart and circulation form 
a kind of centre for what he calls the vegetative functions, 
to which the breathing apparatus is attached. Secondly, 
the brain and spinal cord preside over the animal 
functions and are attached to and served by the muscular 
system. The vegetative and animal activities are reminis¬ 
cent of the vegetative soul and the animal soul of Aristotle 
(p. 38). Indeed, the whole scheme is infused with the 
thought of that naturalist. 

We turn now to the structures and functions manifested 
by the four embranchements. Vertebrata, Mollusca, and 
Articulata are bilaterally symmetrical. Radiata are radially 
symmetrical. Vertebrata have a heart and blood-vessels and 
a continuous brain and spinal cord. Their skeleton is in¬ 
ternal. Its basis is an axis—skull and vertebral column— 
and appendages—fore and hind limbs. Mollusca have a 
heart and blood-vessels. Their nervous system consists of 
discontinuous separate masses. They have no internal 
skeletons, and their muscles are attached to the external 
parts, namely the skin and shell. Articulata exhibit in the 
vegetative parts a functional transition from a system of 
blood-vessels to a tracheal system (Fig. 89). Their nervous 
system consists of two long cords running along the lower 
part of the body. They have a hard external skeleton to 
which muscles are attached. Their limbs are jointed. 



‘jLe Rigne Animal' {i 8 iy) 229 

So far, the position of Cuvier is not greatly different 
from that of a biologist of our own time. His treatment of 
his ‘Radiata’, however, separates him widely from us. 

The Radiata of Cuvier are, according to our standards, 
a random mixture of types. He holds that the Radiata 
have ill-defined nervous and muscular systems, that they 
have no vascular system, and that their bodies tend to 
approach plants in homogeneity. The lower forms are a 
homogeneous pulp devoid of organs. There is nothing in 
all this to which the modern biologist will subscribe. 

The existence of this group, Radiata, in Cuvier’s scheme, 
and the qualities ascribed to them, give an index of the 
progress of biology since his time. The Radiata of Cuvier 
are now split up into a dozen or more Phyla and include 
the vastly important sub-kingdom of Protozoa or unicel¬ 
lular animals. In estimating his work, we must remember 
that there was still no knowledge of the part that the cell 
plays in the animal economy, and that he was devoid of the 
resolving power of the modern ‘achromatic’ microscope 
(p. 171). Further, despite Cuvier’s faith in function as a 
guide to form, the technical study of physiology was still 
too little advanced to be of use to him, and comparative 
physiology as a separate science was non-existent. In assign¬ 
ing to Cuvier his position as the supreme comparative anato¬ 
mist, we are therefore justified in passing over his Radiata 
and in concentrating on his other three embranchements. 

The classificatory system of Cuvier contains Classes, of 
which the titles are still familiar. The scheme may be 
drawn up thus: 

EMBRJNCHEMENT I. VERTEBRAE A 

Class I. Mammalia, identical with the modern Class of the same 
name. 

Class 2. Aves or birds, identical with the modern Class of the same 
name. 



230 Rise of Comparative Method 

Class 3. Reptilia, including, besides reptiles, such forms as frogs 
and newts, now placed iti a separate Class as Amphibia. 

Class 4. Pisces, identical with the modern Class of Fishes, from 
which certain forms, such as lampreys, must now 
be excluded. 

EMBRJNCHEMENT 11 MO LEV SC A 

Class I. Cephalopoda, including forms like the Octopus, and 
almost identical with the modern Class of the same 
name. 

Class 2. Pteropoda, a group of free swimming forms, roughly 
corresponding to the modern Class of the same name. 

Class 3. Gasteropoda, including the ordinary land and water 
molluscs, such as slugs and snails, roughly corresponding 
to the modern Class of the same name. 

Class 4. Acephala, molluscs with two shells, such as the mussels 
and oysters. This Class corresponds to the so-called 
‘bi-valve’ molluscs. 

Class 5. CiRRiPEDiA or barnacles, lliese are not in fact molluscs 
at all, but a group of degenerate Crustacea as was shown 
by Vaughan Thompson (pp. 488-9). 

Class 6. Brachiopoda (p. 200), a very ancient well-defined group, 
not now regarded as related to molluscs. 

EMBRANCHEMENT III ARTICULATA 

Class f. Crusi'acea, much as in modern classifications, but omitting 
the Cirripedia and certain parasitic forms. 

Class 2. Arachnides or spiders, &c., much as in modern classifica¬ 
tions. 

Class 3. Insecta, much as in modern classifications. 

Class 4. Annelides, a miscellaneous and artificial group, many un¬ 
related to each other and none closely related to the 
Crustacea, Spiders, or Insects. The group was broken 
up later by Lamarck. 

This classification was a workable scheme, and much 
superior to anything that preceded it. By its use a naturalist 



'Le Regne Animar 231 

could attain a general survey of the variations in structure 
of the animal kingdom as a whole. 

Apart from the important generalities summed up in 
this classification and apart from his great work in the 
foundation of Palaeontology as a science, Cuvier made two 
very important contributions to comparative studies. 

First was his exploration of the anatomy of the Mol¬ 
luscs. He dissected a great many of these forms. He was 
thus able to give a good general account of the group and 
to place its internal classification on a satisfactory basis. 
No other group except the vertebrata had been so in¬ 
tensively investigated {Memoires pour servir a I'histoire des 
Mollusques, 1817). 

Second was his systematic treatment of the vast Class of 
Fishes. These had, in fact, been among the first animals 
to be scientifically treated, as by Belon (p. 89), Rondelet 
(p. 91), Gesner (p. 92), and Willughby (p. 182). Their 
anatomy had, however, been neglected. Cuvier placed 
their affinities, as revealed by their structure, on an entirely 
new basis. Moreover, he united in his scheme fossil with 
living forms (Histoire naturelle des poissons 1828—31). 

§ 8. The Doctrine of Catastrophes 

The effect on the mind of Cuvier of the discovery of a 
large number of fossil forms may seem strange. 

Cuvier realized that the evidence of Geology showed 
that there had been a succession of animal populations. 
He perceived that vast numbers of species, many no longer 
existing, had appeared upon the earth at different periods. 
But following Linnaeus, he was a firm believer in the fixity 
and unalterability of species, though his contemporary and 
early friend, Lamarck, with whom he had quarrelled, was 
engaged in putting forward the opposite view (pp. 292-5). 

Cuvier had, however, to account for the extinction of 
some forms of life and what seemed to be the creation or 



232 Rise oj Comparative Method 

at least the appearance of new forms. His explanation of 
these remarkable facts was that the earth had been the 
scene of a series of great catastrophes. He believed that of 
the last of these catastrophes we have an historic record. 
It is the flood recorded in the Book of Genesis! He ex¬ 
pressly denied the existence of fossil man. 

‘If there be one thing certain in Geology’, he wrote, ‘it is that the 
surface of our globe has been subject of a great and sudden catas¬ 
trophe of which the date cannot go back beyond five or six thousand 
years; that this catastrophe has overwhelmed the countries previ¬ 
ously inhabited by men and by those species of animals with which 
we are to-day familiar; that it caused the bed of the previous marine 
area to dry up and thus to form the land areas now inhabited; that 
it is since this catastrophe that such few beings as escaped have 
spread and propagated their kind on the newly uncovered lands; 
that these countries laid bare by the last catastrophe had been in¬ 
habited previously by terrestrial animals if not by man and that 
therefore an earlier catastrophe had engulphed them beneath its 
waves. Moreover, to judge by the different orders of animals of 
which remains have been revealed, there were several of these 
marine irruptions.’ 

It will be seen that Cuvier does not commit himself to 
the doctrine of a special creation following each catas¬ 
trophe. What he suggests is that the earth was repeopled 
from the remnant left. This does not explain the appear¬ 
ance of new species in geological time. He believed, how¬ 
ever, that the species which appeared as new came from 
parts of the world still inadequately explored by geologists. 

His followers carried the matter farther and elevated 
his teaching into a doctrine of successive creations. This 
came to assume fantastic forms even in the hands of serious 
scientific exponents. Thus Alcide d’Orbigny (1802—57) 
expounded the science of palaeontology on the basis of 
twenty-seven successive creations (1849)! There were 
many variations on this theme which need not detain us, 
despite the prodigious literature to which it gave rise. 



( 233 ) 

§9- Owen (1804-92) and Palaeontology 

The personality of Cuvier lit up a zeal for comparative 
anatomy and palaeontology which lasted throughout the 
nineteenth century. Of those inspired by this great move¬ 
ment, Owen was perhaps the most typical. He is also 
interesting as he was influenced by Naturphilosophie on 
the one hand and was an obstinate opponent of Darwinian 
evolution on the other. 

Richard Owen, after a few years as surgeon’s appren¬ 
tice, went to Edinburgh University and thence to 
London. In 1827 he became an assistant at the Hunterian 
Museum. From Clift (p. 210), whom he succeeded, 
Owen imbibed a reverence for the work of Hunter. In 
1830 when Cuvier visited London, Owen made his ac¬ 
quaintance and he went to study in Paris. He began at 
once the publication of works on comparative anatomy and 
palaeontology. A continuous stream of these proceeded 
from his pen throughout his active life. 

His monumental Catalogue of the physiological series of 
comparative anatomy contained in the museum of the Royal 
College (5 vols., 1833—8) is still of great value. To identify 
the species from which Hunter’s specimens had been 
derived, Owen dissected a large number of animals. The 
dissections of the rarer of these he carefully recorded, and 
in many cases his accounts of these creatures are still cur¬ 
rently consulted by naturalists. 

Owen next embarked on an immense investigation of 
the teeth of mammals {Odontography^ 1840—5). Teeth, 
being the hardest bones in the body, are most often found 
fossilized. Thus his investigations led him into palaeon¬ 
tology, of which he soon became one of the admitted 
masters. He published many monographs of extinct 
forms. Perhaps his best-known are those of the giant 
bird, the recent but extinct Dinornis of New Zealand 



234 Rise of Comparative Method 

(1846), and the much more ancient giant walking sloth, 
the fossil Mylodon of South America (1842, Fig. 95). 

In 1856 Owen became director of the Natural History 



Fig. 109. Restoration by Owen (1842) of the skeleton of Mylodon robustus. 
This massive creature, as big as a Rhinoceros, was an inhabitant of South 
America. I'here it occupied an area corresponding to that of its diminutive 
arboreal ally, the slender modern sloth Bradypus tridactylus. The skeleton of the 
sloth is represented inset and drawn to scale. Both in size and build it is a great 
contrast to that of the Mylodon, (Compare Fig. no.) 

department of the British Museum. The immense wealth 
of material there gave him unrivalled opportunities, and 
his activity and industry rose to the occasion. His great 
work on the Anatomy and Physiology of the Vertebrates 
(1866—8) was based entirely on personal observation and 


Owe 71 235 

was the most important of its kind since Cuvier. The 
system of classification adopted by Owen has not won 
favour, but as a record of facts the book is still used. 

When Owen first became Director of the Natural 
History Department of the British Museum, that depart¬ 
ment was part of the main museum building and was 
greatly hampered for want of space. As a result of much 
agitation and representation in official quarters, Owen at 
last succeeded in persuading the authorities to move it. 
The magnificent museum at South Kensington is the result. 

In leaving the subject of comparative method we note 
that since the general acceptance of evolutionary theory, 
comparative studies have been almost entirely directed 
by belief as to genetic relationships (chap. viii). The 
alliance of comparative studies with evolutionary doctrine 
has had the effect of focussing attention on structure as 
distinct from function. Comparative physiology almost 
ceased to be studied in the later nineteenth century and is 
only now reviving. Comparative anatomy in its turn be¬ 
came largely a study of developmental stages, and em¬ 
bryology became the comparative study far excellence 
(chap. xiii). 

Fig. 110. Skeleton of Megatherium described by Cuvier as ‘an animal of the 
sloth family, but as big as a rhinoceros’. The first specimen was brought to 
Madrid from the Argentine in 1789. From Cuvier’s Recherches sur les ossemens 

fossiles, 1812. 


VII 


DISTRIBUTION IN SPACE AND TIME 

§1. Early Biological Exploration. Joseph Banks (1743— 
1820) and Robert Brown (1773—1858) 

I N the eighteenth century the practice was begun of 
carrying naturalists on voyages of exploration, with 
equipment for observation and collection. One of the 
earliest expeditions thus provided sailed the Pacific under 
command of James Cook (1728—79). Joseph Banks ac¬ 
companied him. He possessed great wealth and while a 
student at Oxford had paid for a lecturer on botany, the 
professor of the subject having given only one lecture in 
thirty-five years! Banks devoted himself to Natural His¬ 
tory. In 1766 he had accompanied an Admiralty vessel 
to Newfoundland on business concerning the fisheries, 
and had thus gained his first glimpse of wild life. Through 
numerous botanical excursions he had become a com¬ 
petent naturalist. For the voyage with Cook, Banks pro¬ 
vided equipment for biological work. He also engaged 
Daniel Solander (1736-82), a pupil of Linnaeus, as 
naturalist together with four artists. 

The Endeavour, Lieutenant James Cook, 330 tons, 
sailed from Plymouth in August 1768 and was away three 
years. She crossed the Atlantic, doubled Cape Horn, 
turned north-west, and was at Tahiti to observe the transit 
of Venus in June 1769. She now passed south and spent 
six months on the coast of New Zealand. Cook was the 
first to circumnavigate its islands. Banks and his staff 
were very active here, and great additions were made to 
the knowledge of plants, birds, and fish. 

Cook next turned west, and reaching Australia explored 
its eastern seaboard. Cook gave its name to New South 



Biological Exploration 237 

Wales. Botany Bay was so called as being a happy hunting- 
ground for Banks and Solander. By navigating Endeavour 
Strait between Australia and New Guinea, Cook estab¬ 
lished the separateness of these two land masses. 

Many new forms of life were encountered. Of one 
Cook says that 

‘In form it is most like the jerboa [but] as big as a sheep. The head, 
neck and shoulders are very small in proportion to the other parts. 
The tail is nearly as long as the body, thick near the rump, and 
tapering towards the end. Its progress is by successive hops, of a 
great length, in an erect posture. The forelegs are kept bent close 
to the breast. The head and ears bear a slight resemblance to those 
of a hare. This animal is called by the natives kangaroo.' 
\Ahhreviated.^ 

The speed of the kangaroo was found to outstrip easily 
that of the ship’s greyhound. Many other curious animals 
were seen, but the best work was done in collecting plants. 
The herbarium put together by Banks and Solander is at 
the Natural History Museum at South Kensington, and 
has formed the nucleus of a great collection there. The 
map, showing the track of the Endeavour marked in by 
Cook’s own hand, is in the British Museum at Blooms¬ 
bury. The journals both of Cook and Banks still exist. 

The expedition returned in 1771. Cook started his 
second voyage—^again with naturalists on board—in the 
following year. It established a record in that, despite the 
hardships of four years, out of 118 men only four died. 
Of these, three were killed in accidents and one succumbed 
to a disease contracted before he left England. Cook’s 
account of his methods of preserving health on board ship 
is one of the most important pronouncements on the 
subject. 

Banks takes a distinguished place as a patron of science. 
Among those for whom he made a scientific career pos¬ 
sible were the two Austrian artists, the brothers Franz 



238 Distribution in Space and Time 

and Ferdinand Bauer—among the best of all botanical 
draughtsmen—and the botanist Robert Brown. 

Brown began early to exhibit the industry, thoroughness, 
and power of generalization that afterwards distinguished 
him. As a young regimental medical officer, he occupied 
himself with collecting plants. While stationed in Ireland 
he met Sir Joseph Banks, then President of the Royal 
Society. Banks had collected a very fine biological library 
and had greatly extended his herbarium. These were 
placed at Brown’s disposal. Through Banks, Brown was 
appointed as naturalist to a new expedition that sailed in 
July 1801 under Captain Matthew Flinders (i 774—1814), 
recently returned from exploring Australia and Tasmania. 
Ferdinand Bauer (17 60—1826) went as botanical draughts¬ 
man, and William Westall (1781—1850), afterwards well 
known as an artist, accompanied the expedition to paint 
landscapes. Their ship, the Investigator^ 334 tons, was 
fitted for scientific purposes. They arrived in December 
1801 at their first objective. King George’s Sound, in 
Western Australia. 

The whole south coast of Australia was systematically 
explored. Many of the geographical names in that region 
are those given by Flinders. Cape Catastrophe^ west of 
Adelaide, records the loss of a cutter and crew. Close by 
is the Sir Joseph Banks Group of Islands. A little farther on, 
covering the mouth of the great bay of Adelaide is Kan¬ 
garoo Island. Farther east they met the French exploring 
vessel, the Geographe, and named the place Encounter Bay. 

In May 1802 Flinders reached Port Jackson, where he 
met his supply ship and the Geographe again. The crews 
of all three vessels—less scientifically commanded than 
Cook’s—^were suffering from scurvy owing to want of 
fresh food. The Investigator was now unseaworthy. 
Flinders returned to England in another ship, and being 
wrecked, lost Brown’s duplicate specimens and living 



Biological Exploration ^39 

plants. Brown and Bauer remained behind to explore the 
botany of the coasts of Australia and Tasmania. The two 
reached England in 1805, after four years’ absence. 

Brown had collected industriously throughout his 
travels, and Bauer had worked no less well. There was 



Fig. III. Australia with Cook’s outline map inset. The names inserted were 
given as a result of the voyages of Cook and Flinders. 


a collection of 4,000 species of dried plants, many new 
to science. During the homeward voyage Brown busied 
himself with the close study of these, and made many 
important observations in botanical anatomy and physi¬ 
ology. Soon after his return he became Librarian to the 
Linnean Society and in 1810 to Sir Joseph Banks. Xhat 
public-spirited and far-sighted patron of science died in 
1820. By his will he endowed Franz Bauer to enable him 
to continue his work, and left to Brown his house in 






240 Distribution in Space and Time 

London together with his library and collections for life. 
In 1827 Brown permitted the books and herbarium to be 
stored in the British Museum, where they now form the 
nucleus of some very important collections. 

The rest of Brown’s life was passed in the uninterrupted 
production of a long series of important and original 
botanical works. He possessed great penetration and per¬ 
tinacity, combined with unusual powers of generalization. 
He had a whimsical manner of publishing his discoveries. 
These he never announced distinctly but buried in 
memoirs, the titles of which do not suggest the nature of 
their content. Brown was, moreover, curiously secretive. 
Darwin in his autobiography writes that 

‘I saw a good deal of Robert Brown facile princeps hotanicorum as 
he was called by Humboldt (p. 269). He seemed to me to be chiefly 
remarkable for the minuteness of his observations and their perfect 
accuracy. His knowedge was extraordinary great, and much died 
with him, owing to his excessive fear of ever making a mistake. 
He poured out his knowledge to me in the most unreserved manner, 
yet was strangely jealous on some points. I called on him two or 
three times before the voyage of the “Beagle”, and on one occasion 
he asked me to look through a microscope and describe what I saw. 
This I did, and believe now that it was the marvellous currents of 
protoplasm in some vegetable cell (Fig. 147, p. 35 3). I then asked him 
what I had seen; but he answered me, “That is my little secret!” ’ 

Brown’s name is associated with four important topics: 

{a) The Cell Nucleus (pp. 329, 331). 

(/;) The nature of the sexual process in higher plants 
(p. 507 and Fig. 175). 

(f) ‘Brownian movements’ (p. 346). 

id) The microscopical examination of fossil plants. 

In a series of monographs he described the plants 
collected by himself and by many other travellers. All are 
models of exact observation combined with wide and deep 
knowledge. Among the most interesting is his account 



Biological 'Exploration 241 

of the largest flower known. This was first seen in Sumatra 
by a young collector Joseph Arnold (1782-1818) while 
travelling with the great colonial administrator. Sir Stam¬ 
ford Raffles (1781-1826). In memory of these men 
Brown named it Raffiesia Arnoldi. The specimen first seen 
by Arnold 

‘measured a full yard across; the petals being twelve inches from 
the base to the apex, and it being about a foot from the insertion 
of the one petal to the opposite one. 'I'he nectarium would hold 
twelve pints, and the weight of this prodigy we calculated to be 
fifteen pounds. 

‘T.'here were no leaves or branches; so that it is probable that the 
stems bearing leaves issue forth at a different period of the year. 
The soil where this plant grew was very rich, and covered with the 

excrement of elephants.’ [^Abbreviated.^ 

% 

Raffiesia^ as we now know, is parasitic on the roots of 
a vine and is devoid of green leaves. Each flower is either 
male or female. Its mechanism of fertilization is still un¬ 
known, but it is suggested that the elephant is the agent! 

§ 2. Pre-evolutionary Geological Theory 

In antiquity and in the middle ages fossils were 
usually looked on 2iS lusus Naturae^ ‘Nature's little games'. 
Gesner wrote a book on them (1555). The Dane, Niels 
Stensen (1648—86), who spent some years in Italy, dis¬ 
cussed the formation, displacement, and destruction of 
stratified rocks in Tuscany (1669). He recognized the 
organic origin of fossils. Stensen was followed by several 
Italians. Among them Vallisnieri (p. 205) figured many 
marine fossils and recognized the nature of a geological 
fault. The Englishman, Martin faster (1638—1712), took 
the same view, wrote the first book devoted to fossils which 
accepted their organic nature (1678), and made suggestions 
for a geological map. Hooke and Ray had similar views. 

2613.3 R 



242 Distribution in Space and Time 

The works of all these were known to Buffbn (pp. 288— 
91). In his T,poques de la Nature (i 778) he tried to set forth 
a history of the earth. There were seven ‘epochs’. The first 
was the ‘incandescent’ stage. The fifth saw the advent of 
large pachyderms—rhinoceroses, hippopotamuses, ele¬ 
phants—and their wide distribution even in temperate 
climes. The sixth saw the separation of the two con¬ 
tinents. We live now in a seventh epoch—that of man. 

The work of James Hutton (1726-97) has a more 
modern character. He travelled widely in order to study 
rocks, and perceived that it is mostly in stratified rocks 
that fossils occur. He saw clearly that the imposition of 
successive horizontal layers is inexplicable as a result of 
a single great flood but suggests rather a quiet orderly 
deposit over a long period. In his Theory of the Earth 
(1795) he interpreted the strata as having once been the 
beds of seas, lakes, marshes, &c. 

It was soon recognized that rocks often contain frag¬ 
ments from lower layers and that stratified series are often 
tilted, bent, or broken. Many, encouraged by Cuvier’s 
doctrine of ‘catastrophes’ (pp. 231-2), ascribed these 
irregularities to violent upheavals. In this connexion it is 
interesting to observe that the Essai sur la geographie 
mineralogique des environs de Paris (1811) of Alexandre 
Brongniart (1770-1847), though written in collaboration 
with Cuvier, inclines more to the views of Hutton. 

William Smith (1769-1839), a civil engineer, obtained 
an insight into the nature of strata while cutting canals. 
He produced the first coloured geological map (1815). 
His Stratigraphical System of Organised Fossils (1817) 
showed that certain layers have each their characteristic 
series of fossils. Some members of a series are wont to 
occur also in the layer below, others in the layer above, 
others in all three. Therefore changes in the flora and 
fauna which these fossils represent could not have been 



Prerevolutionary Geological Theory 243 

sudden. He saw, too, that the further back we go, the 
less like are the fossils to forms still living. 

A third British geologist, Charles Lyell (1797-1875), 
finally exorcised the catastrophic demon. He took to the 
study of Geology while at Oxford, travelled considerably, 
and was influenced both by William Smith and by 
Lamarck. He saw that the relative ages of the later 
deposits could be determined by the proportion they 
yielded of living and of extinct molluscan shells. In his 
great Principles of Geology (3 vols., 1830—3) he showed 
that rocks are now being laid down by seas and rivers 
and are still being broken up by glaciers, rain, sand¬ 
storms, and the like: that, in fact, geologically ancient 
conditions were in essence similar to those of our time. 
Few books have exercised more influence on the course 
of biological thought. 

We are struck by the overwhelming share of British 
investigators in the early development of geology as a 
science. The very names of the formations suffice to 
establish this fact. Lyell is responsible for Devonian (from 
its predominance in Devonshire), Carboniferous (or ‘coal¬ 
bearing’), Pliocene (Greek ‘more recent’), Miocene (‘less 
recent’), and Eocene (‘dawn of recent’). Sedgwick (p. 245), 
the Cambridge geologist with whom Darwin went on 
geological excursions, invented Cambrian (Cambria — 
Wales), Palaeozoic (Greek ‘ancient life’), and Cainozoic 
(‘new life’). Between the last two formations, John Phil¬ 
lips of Oxford (1800—74) interpolated Mesozoic (‘inter¬ 
mediate life’). Other British contemporaries are respon¬ 
sible for Ordovician and Silurian (the Ordovices and 
Silures are British tribes mentioned by Caesar), Permian 
(from the province of Perm in East Russia), and Cretaceous 
(Latin ‘chalky’). On the other hand Triassic (Latin Trias^ 
‘the number three’) and Jurassic (from the Jura moun¬ 
tains) were titles given by German geologists at the begin- 



244 Distribution in Space and Time 

ning of the nineteenth century. The term Tertiary is older 
and was used by eighteenth-century Italian writers. The 
tertiary formations were held to be the third of a series of 
which the Secondary corresponded roughly to the Mesozoic 
and Palaeozoic, and the Primary to the non-fossil-bearing 
rocks. The word Geology itself was introduced (1779) by 
H. B. de Saussure (1740-99) of Geneva, founder of 
modern mountaineering. 

§ 3. Darwin (i 809—82), the Beagle' (1831—5), and Island 
Life 

The name of Charles Darwin is closely associated with 
that view of the succession of living things summed up in 
the words Organic Evolution. Through this doctrine he 
has profoundly influenced every branch of biological in¬ 
quiry. He has also had a large effect on philosophical, 
political, religious, and ethical thought. To appreciate his 
distinction, it should be remembered that, had he never 
written on Organic Evolution, he would still stand in the 
front rank among naturalists. 

Charles Darwin was the son and grandson of medical 
men. His grandfather, Erasmus Darwin, himself wrote 
on Evolution (pp. 290—1). The family exhibits hereditary 
ability to an extraordinary degree. In all its ramifications 
it has probably produced more men of intellect than any 
other of which we have a clear record. 

After contemplating a career in Medicine while at 
Edinburgh and then in the Church while at Cambridge, 
Darwin took an undistinguished degree. At Cambridge 
the course of his life was determined by a friendship with 
the professor of botany, the Reverend John Henslow 
(1796—1861), a fine, upright, inspiring man with an 
enthusiasm both for his subject and his pupils. Henslow 
was the pioneer of practical elementary teaching in botany. 
Darwin came under his spell. 



Island Life 245 

In 1831 Henslow, with remarkable insight, pressed 
young Darwin to take up geology. After a geological tour 
with the Reverend Adam Sedgwick (1785-1873), the 
first professor of Geology at Cambridge, Darwin received a 
letter from Henslow offering him the position of naturalist 
on the Beagle. He accepted with diffidence. 

The Beagle^ 238 tons, set sail under Captain Fitzroy 
(1805-65) in 1831. Her objective was to extend the 
survey of South America, and to make observations for 
determining longitude. Darwin went as a naturalist with¬ 
out salary, at the invitation of the captain. His working 
place was a narrow space at the end of the chart-room. He 
always held that the need for order and method thus 
imposed was among his best pieces of training. His equip¬ 
ment was meagre. Acting on what seemed the whimsical 
but was really the wise advice of the experienced Robert 
Brown, he took no compound microscope. 

On his return in 1835, Darwin put together some of 
his scientific results. Some of the most significant ap¬ 
peared in the famous Journal of Researches (1839—40). 

In his old age Darwin wrote: 

‘The voyage has been the most important event in my life. I owe 
to it the real training of my mind. The investigation of the geology 
of all the places visited was [specially] important. On first examin¬ 
ing a new district nothing can appear more hopeless than the chaos 
of rocks; but by recording the stratification and nature of the rocks 
and fossils at many prjints, light begins to dawn and the structure 
of the whole becomes more intelligible. I had with me the first 
volume of Lyell’s Principles of Geology, and the book was of the 
highest service.’ {Abbreviated.) 

Among the most important observations made by Dar¬ 
win during his voyage were those on the very peculiar 
animal and plant inhabitants of various isolated oceanic 
islands which have never been connected with continental 
lands. 



246 Distrt/?ution in Space and Time 

Of all islands the most fruitful for the development of 
biological ideas have been the Galapagos, a small volcanic 
archipelago in the Pacific, situated on the equator, some 
500 miles west of the nearest South American coast. They 
are named from the enormous numbers of tortoises 
(Spanish geilnpagd) that once dwelt there. When dis¬ 
covered early in the sixteenth century, the archipelago was 
uninhabited. Later it formed a lurking place for buc¬ 
caneers who were not ideal conservators of local fauna and 
flora. There were probably fifteen species of giant tor¬ 
toise, all indigenous, on the islands. Seven species sur¬ 
vived into the nineteenth century. 

The Galapagos were visited by Darwin in 1835. His 
botanical collections were subsequently (1849-51) in¬ 
vestigated by J. D. Hooker (pp. 251, 549). There is no 
more remarkable passage in Darwin^s Journal of Researches 
than his account of these islands. 

‘Of the flowering plants’, says Darwin, ‘there are 185 species, 100 
confined to this archipelago. It is surprising that more American 
species have not been introduced, considering that the distance is 
only 500 miles from the continent; and that drift-wood is often 
washed on the shores. The peculiarity of the Flora is best shown 
in certain families. Thus there are 21 species of Compositae, of 
which 20 are peculiar; these belong to twelve genera, and of these 
genera no less than 10 are confined to the archipelago! The Flora 
has an undoubted Western American character [without] affinity 
with that of the Pacific. [Moreover] a vast majority of all the land 
animals arc aboriginal. 

Why on these small points of land were there aboriginal inhabitants 
created on American types? I'he islands of the Cape de Verd 
group resemble in all their physical conditions, far more closely the 
Galapagos than these latter resemble the coast of America; yet the 
inhabitants of the two groups are totally unlike, the Cape de Verd 
Islands bearing the impress of Africa, as the Galapagos are stamped 
with America. 

‘[Moreover] the different islands are to a considerable extent in- 



Island ^Lije 247 

habited by a different set of beings. I'hc aboriginal plants of dif¬ 
ferent islands [arc] wonderfully different.’ 


Name of 
Island 

Total 
No. of 
Species 

No. found 
in other 
parts of the 
njoorld 

1 

i No. con- 
I fined to the 
j Galapagos 

No. con¬ 
fined to 
one island 

No. confined to 
the Galapagos 
but found on 
more than one 
island 

James 

71 

33 

38 

1 

30 ! 

8 

Allxjrnarle 

46 

iX 

i 26 

22 1 

4 

Chatham 

3^ 

16 

! I6 

12 1 

4 

Charles 

68 

29 

1 “9 

21 1 

8 


‘In James Island, of the thirty-eight Galapageian plants found in 
no other part of the word, thirty are exclusively confined to this one 
island. In Albemarle Island, of the twenty-six aboriginal Gala¬ 
pageian plants, twenty-two are confined to this one island, that is, 
only four are at present known to grow in the other islands of the 
archipelago; and so on. In like manner the different islands have 
their different species of the [world-wide] genus of tortoise, and of 
the widely distributed American genus of the mocking thrush, as 
well as of two of the Galapageian sub-groups of finches.’ [Greatly 
abbreviated from fourth edition, Y 

Since Darwin’s time, several examinations have been 
made of the fauna and flora of the Galapagos. His general 
results have not been greatly modified. 

A famous case of a peculiar form native to an oceanic 
island is the Dodo of Mauritius. When that uninhabited 
volcanic island was discovered in 1505, it was stocked with 
large, unwieldy, flightless birds. These the Portuguese 
called Doudo^ which in their language means ‘simpleton’. 
Later the Dutch brought live specimens to Europe. 
Several artists depicted it. The Dodo, which was as help¬ 
less and harmless as it was unpalatable, was the prey of 

* The section on the Galapagos islands was considerably altered by Darwin 
from edition to edition of the Journal. In the first three editions most of the 
details here given are not to be found. But the impression carried even by the 
first edition (1839-40) is the same, and he remarks on ‘the entire novelty of the 
fact that islands in sight of each other should be characterized by peculiar faunas’. 



248 Distribution in Space and Time 

every lout that could wield a stick. Towards the end of the 
seventeenth century it became extinct. It was a very 
aberrant member of the pigeon family. 

An allied form was the ‘Solitaire’ of the island of Rod¬ 
riguez, not very distant from Mauritius. It had bony 
knobs on its flightless wings, which it used as clubs in 
self-defence. Its methods were ineffective, for it became 
extinct about 1761. 

The little island of Reunion, also near Mauritius, lost 
another dodo-like bird toward the end of the seventeenth 
century. 

From Mauritius itself have disappeared at least two 
species of parrot, a dove, and two species of coot. A 
number of other birds peculiar to each island have been 
lost from both Reunion and Rodriguez, some surviving 
until the nineteenth century. 

This account of the lost birds of a single group of is¬ 
lands illustrates both the peculiarity and the vulnerability 
of island life. The numbers of the losses are the more im¬ 
pressive when we recall that island fauna is very poor 
in species. The flora has suffered no less severely. Nor 
is man the only destroyer. Dogs, cats, rats, introduced by 
him, have exterminated many peculiar animal forms, while 
hogs, rabbits, and above all goats have completely wiped 
out many island species of plants. 

A tragic example is the biologically important island of 
St. Helena, one of the most isolated of all terrestial spots. 
It is 15° south of the equator, 1,100 miles from the coast 
of Africa, and 1,800 from South America. Discovered in 
1502, it has been inhabited since 1513. Darwin called 
there in 1836. 

When first discovered St. Helena was densely covered 
with forest, now almost utterly destroyed. Its rich soil 
could only be retained on the steep volcanic slopes so long 
as they were protected by the vegetation. This was 



Island Lije 249 

destroyed by imported goats, who were soon aided by the 
reckless waste of man. Extirpation of the highly peculiar 
vegetation caused also the destruction of most of the 
animal species which once lived on the island. 



Fig. 112. The Atlantic currents. 

Fig. 113. The land and water hemispheres, from Huxley’s Physiography of 
1877, when the Antarctic continent was unknown. 

St. Helena has never had indigenous vertebrate fauna 
of any kind on land, though there are many peculiar 
species of shore-haunting fish. No indigenous fresh-water 
animals or plants are known. 

The flora—^what is left of it—is remarkable. The 
Challenger reports recognized 65 species of certainly in- 







2 $o Distribution in Space and Time 

digenous plants; 24 probably indigenous; 5 doubtfully 
indigenous (total 94). There are 38 flowering plants, all 
save one being peculiar to the island. Conspicuous among 
them are Compositae of tree-like proportions. There are 
2 7 ferns, of which 12 are peculiar. Hooker considered that 



Fig. 114. Her Majesty’s Ship Challenger, 1872-6. 


the peculiar species ‘cannot be regarded as close allies of 
any other plants. Seventeen belong to peculiar genera, and 
of the others all differ so markedly from their congeners 
that not one comes under the category of an insular form 
of a continental species.’ 

The best known land animals of St. Helena are the 
beetles. Of the 129 indigenous species all save one are 
peculiar. This degree of individuality is probably unique. 
Of these beetles the great majority are wood-borers, as 
might be expected in an island once forest-clad. 

Of the living forms of St. Helena, the plants are nearly 





Island Lije 2 51 

allied to South American species, while the beetles have 
affinities in descending order of frequency with South 
African, Madeiran, European, and Madagascan forms. 
These affinities are illuminated by the currents around the 
island (Fig. 112). Recent research has shown that viable 
seeds can be carried vast distances by ocean currents. Such 
seeds have been seen to be washed ashore and to germinate 
at St. Helena. Nevertheless, most of the indigenous 
population of St. Helena is descended from forms that 
probably reached the island in Miocene times or earlier. 

Oceanic islands, of which Galapagos and St. Helena are 
examples, have for the last century drawn much attention 
from naturalists. Their extraordinary wealth of peculiar 
forms and their difference from their neighbours—both 
continental and insular—are among the most striking 
phenomena in the distribution of living things. Such facts 
set Darwin thinking of the origin of species. They, more 
perhaps than any other, suggested to him his solution of 
the problem. . . 

§ 4. Oceanic Exploration from the 'Beagle' to the 'Challenger' 

Between 1839 and 1843 the Erebus and Terror explored 
the Antarctic under the comrhand of Sir James Ross 
(1800—62). As naturalist there accompanied him Joseph 
Dalton Hooker (1817-^1911), afterwards director, in suc¬ 
cession to his father, of the Royal Botanic Gardens at Kew 
(1865—85). Hooker took with him Charles Darwin’s 
recently published Journal^ a gift from Lyell. 

Hooker was an industrious collector and skilled sys- 
tematist. None of his numerous writings is of more 
weight than the series which appeared in parts from 1844 
to i860 on the flora encountered by the Erebus and 
Terror. It includes accounts of the plants of the Antarctic 
islands as well as those of Tasmania and New Zealand. 
It may be said to lay the foundation of the systematic study 



252 Distribution in Space and Time 

of plant geography. Its last volume is also interesting as 
the first important botanical work written by an adherent 
of the doctrine of organic evolution. 

The expedition of the Erebus and Terror was important 
for the great depths sounded by Ross. Animal life was 
proved to be abundant as deep as 400 fathoms. Hooker 
also showed the importance in the economy of marine life 
of the minute plants known as diatoms (pp. 256—60). 



Fig. 115. Section through the Wyville Thomson Ridge from NE to SW. 
It will be seen that the surface conditions on the tw'o sides of the ridge arc very 
similar but that the deep water conditions are very different. 


At about this time Johannes Muller was drawing 
attention to the wonderful variety of life in the ocean. He 
was followed by several Scandinavian naturalists, notably 
by Michael Sars (1805—69) and his son, G. O. Sars (1837— 
1927). Studies by them of marine organisms at depths 
down to about 450 fathoms appeared in the ’fifties and 
’sixties. Some of these defep-sea creatures were thought to 
be closely related to fossil forms. It was hoped that the 
depths would yield more ‘living fossils’. 

A new outlook on oceanic exploration was introduced 
by the American naval officer Matthew Fontaine Maury 
(1806—73). He produced a valuable work on navigation 
(1836). In 1839 an accident rendered him permanently 









'Exploration jrom ^Beagle to 'Challenger 253 

lame, and he began to occupy himself in extracting from 
logs of ships the observations of winds, currents, tempera¬ 
tures, and so forth. 

The charts that Maury thus drew up led to such a 
shortening of passages that an international conference 
was called in 1853 to consider further organization of such 
observations. His Physical Geography of the Sea (1855) 



was an important work. Largely as a result of his activities. 
Government meteorological offices were established by 
Great Britain and Germany. 

All the western maritime nations were now actively 
interested in the physical geography of the sea. Moreover, 
numerous and striking advances in the knowledge of 
marine plants and animals had drawn special attention to 
deep-sea forms. In 1866 a transatlantic telegraph cable 
was projected. It was necessary to obtain knowledge of the 
depth and the character of the floor of the Atlantic Ocean. 
Improvements had been made in sounding apparatus. 
Instruments for taking the temperature of the sea-water at 
great depths and for obtaining samples of the deep water 















2 54 Distribution in Space and Time 

had been invented. Scientific cruises by the Admiralty 
vessels Lightning and Porcupine (1870) had brought 

back novel biological data from the North Atlantic and 
from the Mediterranean. 

§5. The ^‘Challenger Expedition (1872—6) and the Rise of 
Oceanography 

The British Admiralty now determined on oceanic ex¬ 
ploration on a hitherto unheard-of scale. The corvette 
Challenger^ Captain George S. Nares (1831-1915)5 2,300 
tons, was commissioned. She carried both sail and steam 
and was fitted with sounding, dredging, and other ap¬ 
paratus for examining deep water. She had biological, 
chemical, and other laboratories, and carried a staff of six 
naturalists under Charles Wyville Thomson (1830-82). 

Leaving Portsmouth in December 1872, she crossed 
and re-crossed the Atlantic. Soundings, dredgings, tem¬ 
peratures, samples of sea-water were constantly taken. 
Biological material, especially from great depths, was 
continuously collected. The Atlantic islands, Madeira, 
Canaries, Azores, Bermudas, Cape Verde, as well as 
Robinson Crusoe’s Island (Juan Fernandez), were visited 
and their plant and animal forms collected. A special 
survey was made of Tristan Da Cunha, a small volcanic 
peak between the Cape of Good Hope and Cape Horn. 

After a call at the Cape, the Challenger visited Kerguelen 
Island, a mountainous mass of desolate land midway be¬ 
tween the Cape and Australia. Abundant fossil remains 
of trees were there found. Much attention was paid to 
the vegetation, which is of great antiquity and allied to 
that of America rather than of Africa, as Hooker had 
already observed. Many species of shore and fresh-water 
algae were found to be peculiar to the island. Proceeding 
southward, the Challenger was the first steamship to 
cross the Antarctic circle. 



Rise of Oceanography 255 

Extensive researches were then made in the Pacific, the 
route leading by Melbourne, New Zealand, Fiji, Torres 
Strait, the Banda Sea, and the China Sea to Hong Kong, 
northward to Yokohama, and across the Pacific by Hono¬ 
lulu and Tahiti, making South America at Valparaiso. 
F'ollowing the coast, the Challenger through the Strait 
of Magellan and reached Sheerness in May 1876. She 
had travelled 69,000 nautical miles and had taken 372 
deep-sea soundings. 

The vast collections of the Challenger were now in¬ 
vestigated by a whole army of naturalists under John 
Murray (1841—1914). The results were issued by the 
British Government in fifty thick folio volumes. These pro¬ 
vide the bcst-worked-out account of a biological expedi¬ 
tion and form the solid bases of a science of oceanography. 

The work made it evident that, for any understanding 
of the life of our planet as a whole, an exact knowledge of 
the physical conditions of the sea is essential. Oceano¬ 
graphy has since developed in a manner which demon¬ 
strates the interdependence of the biological and the 
physical sciences. A study which involves more than two- 
thirds of the earth's surface, and implicates the whole past 
and future history of the other third, is of primary im¬ 
portance to our conception of life as a whole. 

The departure of the Challenger was soon followed by 
that of the United States Government steamer Tuscarora^ 
whose scientific staff investigated the floor of the Pacific. 
Other American and Norwegian expeditions followed in 
rapid succession. Alexander Agassiz (1835-1910), son of 
Louis Agassiz (1807—73, pp. 304,482), was especially pro¬ 
minent in this work. Trained as an engineer, he was able 
greatly to improve the apparatus of oceanic investigation. 
Among his most remarkable results was his demonstration 
that the deep-water animals of the Caribbean Sea are more 
nearly related to those of the Pacific depths than they are 



256 Distribution in Space and Time 

to those of the Atlantic. He concluded that the Caribbean 
was once a bay of the Pacific and that, since Cretaceous 
times, it has been cut off from the Pacific by the uprise of 
the Isthmus of Panama. 

The relation of biological to physiographical know¬ 
ledge is illustrated by another discovery that followed on 
the technical improvements of Agassiz. The Challenger 
naturalists had considered the results of certain dredgings 
in the Atlantic north of Britain. They noted, as did the 
investigators of two other survey ships, a great change in 
the bottom-living fauna along a line between the north¬ 
west of Scotland and the Faroe Islands. This area was 
therefore systematically sounded. A long narrow ridge 
separating the Arctic from the Atlantic waters was thus 
revealed. Entirely different physical conditions were 
found to prevail in the deeper parts of the ocean on the 
two opposite sides of the ridge (Fig. 115). This very 
important geographical feature was named the Wyville 
Thomson Ridge (Fig. 116). Its biological and physical 
exploration has given great impetus to similar work in 
other parts of the world. 

Much new knowledge of marine biology has resulted 
from the investigations carried out by Prince Albert of 
Monaco (1848—1922) in a series of specially equipped 
yachts. Before the twentieth century had dawned, other 
nations had joined in the work. American, Russian, 
Belgian, German, Austrian, Italian, Dutch, and Danish 
expeditions have gone forth. In 1902 there met at Copen¬ 
hagen an International Council for marine exploration. 
As a result, we are beginning to obtain a complete bio¬ 
logical survey of the North Sea. Other areas are yielding 
more information every year. Notably, the detailed in¬ 
vestigation of the Pacific Ocean is being taken in hand by 
the Pan-Pacific Conference, while the biology of the 
Antarctic is being explored by the Discovery expeditions. 



Rise of Oceanography 257 

When the bottom, the depths, and the intermediate 
depths of the ocean have been explored, we shall attain 
to a general view of life in the sea as a whole. This 
reached, it will be possible to create a biological science of 
the sea which will bear analogies to the sciences both of 
physiology and of economics. There is in the sea a com¬ 
plex balance of life as a whole, comparable to that complex 
balance of metabolism which goes to making up the life 
of the individual on the one hand and of communities of 
individuals on the other. 

§ 6. Distribution of Life in the Sea 

More than two-thirds of the earth’s surface is covered 
by sea (Fig. 113). The oceans in relation to their area are 
as shallow as a sheet of water of one hundred yards 
diameter and an inch deep. Yet the greatest ocean depth 
is over seven miles. If a globe of 40 feet diameter repre¬ 
sent the earth (that is, i foot to 200 miles) the highest 
mountain or the deepest sea would be an elevation or 
depression of one-third of an inch. 

There is life in the open sea at every depth, but a 
great concentration near the surface and at the bottom. 
The conditions at the two levels differ greatly. 

The surface teems with vegetable life. There is abun¬ 
dance of the larger ‘sea-weeds’, both around the coasts 
and in parts of the open sea. Sea-weeds, however, are 
insignificant, both in bulk and bionomic importance, as 
compared to the vast flora of microscopic forms. These 
are distributed universally over the surface of the ocean 
and below it for a few hundred feet. 

Of surface-living plants, first in importance are the 
minute unicellular diatoms (Greek ‘cut in two’). These 
are named from the two siliceous valves—the so-called 
‘skeleton’—in which each dwells (Fig. 120). The group 
is very rich in species. Diatoms swarm in vast numbers 

2613.3 


S 



258 Distribution in Space and Time 

in temperate and colder seas. At death they sink and are 
consumed by the inhabitants of greater depths, while 
their insoluble and undigested skeletons form the ‘diatom 
ooze’ that covers a large part of the ocean floor. 

The Dane, Otto Frederik Muller (1730-84), was the 



118 

Plankton, Common unicellular plant forms. 

Fig. 117. Rliabdosphaeraxi^oo. Fig. ii8. Coccosphaeraxi)ioo. Fig. 119. 

Peridinium, from Plymouth Sound x 300. 

Fig. izo. Diagrams of ‘skeleton’ of Coscinodiscusy a genus of box-like diatoms 
of world-wide distribution. 

first to describe diatoms (i 773). He was also the inventor 
of the naturalist’s dredge. The Swede, Carl Adolf 
Agardh (1785—1859), afterwards a bishop, who was 
distinguished both as mathematician and botanist, gave 
the first general account of diatoms. He described forty- 
nine species in his Systema algarum (1824). 

By reason of their beauty the diatoms became a classical 
subject of microscopic research. When the Challenger 
sailed more than 4,000 species were already known. The 
Challenger naturalists found that diatoms so abound 
toward the polar regions as to tint the water. In warmer 




Fig. 121. The character of the sea-bottom corresponds to six general types. 

(1) A zone of Terrigenous Deposit surrounds the land masses and is a result of 
their attrition. 

(2) The main floor of the Ocean is Glohigerina Ooze. This was first described 
in 1S53 simultaneously by American and German observers. It forms the floor 
of most of the Atlantic and Indian and of about one-third of the Pacific Ocean. 
It consists mainly of the minute calcareous skeletons of Glohigerina and allied 
genera of Foraminifera, a group of Protozoa. 

(3) Pteropod Ooze is a variety of (2), in which abound the spindle-shaped 
shells of Pteropod Mollusca. These are disintegrated at depths greater than about 
3,000 metres. It is chiefly an Atlantic formation. 

(4) Red Clay was discovered and named by Wyville Thomson on the Challenger 
in 1873. Its origin is mainly the decomposition of volcanic minerals, but it is 
essentially a residue after other substances have been dissolved out. It is not 
found at less than about 4,300 metres and chiefly in the Pacific. It contains 
numerous nodules of manganese dioxide, often formed round indestructible 
animal remains, as teeth of sharks and ear-bones of whales. 7 'hese are sometimes 
of extinct species, and even of forms so ancient that they occur as fossils in Tertiary 
beds. Common also are globules of meteoric iron. Such remains must fall uni¬ 
formly on all parts of the ocean floor and yet are very rare, except in Red Clay. It 
is thus inferred that this deposit accumulates incomparably more slowly than the 
other types. Red Clay contains very little calcium carbonate, which is dissolved 
at great depths. 

(5) Radiolarian Ooze was recognized by Murray on the Challenger. It is an 
outlier of Red Clay and is a variety of it containing a high proportion of the 
siliceous shells of Radiolaria, a group of pelagic Protozoa. It is almost confined 
to the Pacific. 

(6) Diatom Ooze was first recognized by Murray on the Challenger as the 
characteristic deposit in the neighbourhood of the Arctic Circle. It is formed 
chiefly of the siliceous skeletons of the unicellular plants known as Diatoms. 
There is a complete belt of it in the southern hemisphere. In the northern 
hemisphere it occurs only in isolated areas, since land masses there intervene in its 
characteristic latitudes (between about 45° and about 60''). 

s 2 





2 So Distribution in Space and Time 

waters they found that other lowly vegetable forms, 
notably the Peridinians, take their place. 

The Peridinians have two long whip-like processes 
which, during life, are constantly lashing in characteristic 
grooves (Fig. 119). Their cell-wall is of organic matter 
and is decomposed after death. Many Peridinians are 
luminous. Related to them is the well-known Noctiluca 
miliariSy a common cause of phosphorescence in warm 
waters. Otto Frederik Muller was also the first to describe 
a Peridinian, namely, the immensely numerous Ceratium 
tripos. 

The vast number of individuals and the variety of 
species of the oceanic microscopic flora was not realized 
until about i860. The survey for the first Atlantic cable 
then gave opportunities for oceanic research. The Chal¬ 
lenger naturalists threw much further light on the subject, 
and brought to notice the extreme importance of oceanic 
plant-life. Notably, they showed that the curious and sup¬ 
posedly‘crystalline’oceanic‘Coccoliths’(Figs. 117—18) that 
had given rise to much speculation were of plant origin. 
They are the calcareous products of the microscopic oceanic 
plants, since named Coccolithophoridae. Their skeletons, 
like those of the diatom, persist after death, and form ooze 
at the bottom at moderate depths. At greater depths they 
are dissolved. The distribution of these Coccolitho¬ 
phoridae and of other forms can in part be gathered from 
a map of the sea-bottom (Fig. 121). 

Oceanic plants were studied on the Challenger in con¬ 
junction with the floating fauna with which they dwell 
The mme, plankton (Greek ‘drifting’) was invented for the 
whole community by Victor Hensen (1835—1924) of Kiel. 
The study of plankton has become of great importance. 
Hensen, primarily a physiologist, began it while con¬ 
sidering the production of nutritive substances under 
different meteorological conditions. He thus laid the 



Distribution of Lije in Sea 261 

foundations of the systematic study of the economics of 
the life of the ocean, oceanic bionomics^ as we may call it. 
The subject is fundamental for our conception of the 
course of life as a whole upon this planet. 

An interesting relationship between animal and plant- 
life was revealed by the Challenger in the Sargasso Sea. 
Cireat masses of ‘gulf-weed’ there abound. The bright 



P/ankton. Common unicellular animal forms. 

Fk;. 122. Shell of Globigerina, the spines of which have Ixvn dissolved in 
their fall to the bottom. 

Fig. 123. Hexanastra quadricuspis, new genus and species of Radiolarian 
discovea’d by Challenger naturalists. 

yellow of this plant contrasts with the deep blue of the 
water. For concealment, the shrimps, crabs, and other 
creatures that swarm in the weed are also yellow. In 
general, however, animals that live on the ocean surface 
are colourless. 

Among the fauna as among the flora of the ocean the 
microscopic forms are of far greater economic importance 
than the more impressive larger creatures. Of very great 
significance for the life of the sea are the Foraminifera, 
a group of minute unicellular animals with calcareous 
shells. Species of one genus, Globigerina^ float everywhere 


262 Distribution in Space and Time 

on the surface. The dead shells make up the vast mass of 
Glohigerina ooze which is the usual deposit of the Atlantic 
bottom. Chalk deposits have been formed, in past ages, 
from oozes of this type. 

Nearly all the major invertebrate Phyla contribute to 
the fauna of the open ocean. There are innumerable 
oceanic crustaceans, many very minute. Jelly-fish and 
molluscs abound. The shells of a group of the latter, the 
Pteropods^ form an important constituent of some oozes. 
There are even a few oceanic representatives of such 
essentially land-forms as insects and such essentially 
shore-forms as anemones. One insect was often taken by 
the Challenger in the open ocean. This was a bug (Halo- 
hates^ family Hydrometridae), with a small round wing¬ 
less body and long legs. It lives on the juices of jelly-fish. 
Oceanic anemones, instead of clinging to rocks, have air 
chambers as floats, and like many oceanic species they 
form complex floating colonies. 

All the great vertebrate groups, except the Amphibians, 
have oceanic representatives. 

Of mammals, the whales and porpoise breed at sea. 
Their remote ancestors used to come ashore to breed, as 
do still the seals. 

Of birds, the petrels are the most oceanic. The largest is 
the albatross, whose glidingflighthas always excited wonder. 

Of reptiles, the sea-snakes are viviparous, breed at sea, 
and seldom come to shore. Some species cross the ocean, 
but are usually found near shore. Certain turtles are at 
times seen far out at sea. They, too, usually dwell near 
the coast and always come ashore to breed. 

Fish frequent the surface of the open ocean much less 
than might be supposed. Most fish live about the coast 
and near the bottom. There are, however, some species of 
fish that live at intermediate depths of the open ocean. 
The sea is a vast place, especially for creatures that move 



Distribution oj Lije in Sea 263 

in three dimensions, and the sexes of such fish would have 
especial difficulty in finding one another. The problem 
has been solved in certain cases by the female carrying a 
small male attached to her (Fig. 4^). 

A feature of oceanic surface-life is phosphorescence. 
The Challenger recorded that often the sea was lit up with 
sheets of a diffuse light, where the water was broken 
before the breeze. At other times the water was full of 
luminous specks. This, the commonest form of phos¬ 
phorescence, is due to a variety of small creatures, notably 
crustaceans, each of which gives out its flash. Some 
crustaceans are phosphorescent on their own account; 
others derive their light from phosphorescent food in 
their stomachs. 

The circumstances of life on the ocean floor, as revealed 
by the Challenger and by later expeditions, are entirely 
different from those at the surface. The pressure at 
5,000 fathoms is about five tons to the square inch as 
against fifteen pounds at the surface. No sunlight pene¬ 
trates. Below 200 fathoms all is dark. The temperature 
in the depths is uniform and not much above freezing. 
There are no currents and no seasons. Summer and 
winter, day and night are alike. The temperature is 
almost the same on the equator and at the poles. Condi¬ 
tions are substantially uniform the world over. There is 
no vegetable life to build up the bodies of the animals 
that dwell there. Thus the animals prey only on one 
another. They draw their ultimate supplies from the 
dead matter that rains down from above. 

A large proportion of the animals of the depths are 
blind, with their eyes reduced to rudiments. Many of the 
blind fish and Crustacea have prodigiously long and deli¬ 
cate feelers. Other deep-sea animals have enormously 
large eyes and thus make the best of the light emitted by 
themselves or by other phosphorescent animals. 



264 Distribution in Space and Time 

The results of the deep-sea dredging have been in 
certain respects disappointing. Specimens of numerous 
new genera and species of known families have been 
brought up. Many are interestingly specialized but few 
are widely different from familiar forms. No ‘missing 
links’ have been discovered, no new classes or new orders 
found. 

The Challenger found, as further exploration has con¬ 
firmed, that the plants and animals that inhabit the open 
ocean, whether on the surface or at the bottom, are mostly 
very widespread. An exception must be made for the 
inhabitants of the most extrene depths (Fig. 65). The 
distribution of oceanic forms is determined by such factors 
as temperature, degrees of saltness, intensity of light, pres¬ 
sure, &c. 

The extension of our knowledge of the conditions that 
prevail in the Ocean and in its superincumbent atmosphere 
is leading to a new scientific ideal. As the laws of oceanic 
plant-life come into relation with the corresponding laws 
governing their animal associates, and both with those of 
physical conditions, we begin to perceive a most impressive 
physico-biological parallelism and may one day attain to 
a real ‘physiology’ of the Ocean. The word physiologia 
was, in fact, originally applied to the material working of 
the world as a whole and not to the individual organism. 
Thus William Gilbert (i 540-1603) ushered in the modern 
scientific era with his work on magnetism entitled On the 
Earth as a Magnet^ a New Physiology (London, 1600). 

Apart from the open sea there is, round all the land- 
masses, a relatively shallow ‘continental shelf’. In the 
waters and especially over the shoals of this shelf the 
fishermen do their work. This shelf has its own flora and 
fauna which is of great wealth and variety in all latitudes. 
That of the North Sea is best known, largely as a result 
of co-ordinated international effort since 1902 (p. 256). 



Distribution oj Lije in Sea 265 

There we find two distinct faunas, one in the ‘arctic’ 
regions, where the water is usually of a temperature near 
freezing-point and is very salt, and the other where the 
water, under the influence of the Gulf Stream, is several 
degrees warmer and the salinity varies more (Fig. 116). 

Moreover, on the continental shelf, diflPerent animals 
are found at different depths, so that we can conveniently 



F'ig. 124. The distribution of ocean depth. The shaded areas, distributed 
chiefly around the land masses, are less than 2,000 metres. The large unshaded 
area is between 2,000 metres and 6,000 metres. The black patches are the true 
‘Ocean Deeps’ from 6,000 metres onward. 

distinguish between littoral, sublittoral, and continental 
deep-sea zones, with limiting depths of about one hun¬ 
dred, five hundred, and three thousand feet respectively, 
and each with a characteristic fauna. Finally, within these 
zones again there are distinct communities of animals, 
many very diverse species being always found together. 
These associations are of great importance both economi¬ 
cally and scientifically. Their discovery is to the credit of 
the Danish biological station, and their study is leading 
on to a systematic marine ecology that will take its stand 
by the side of marine bionomics. 




266 


Distribution in Space and Time 

% 7. Distribution of Life on Land 

Peculiarities in the distribution of some living forms 
were remarked by naturalists from the first. In the 
eighteenth century Buffon (pp. 288-91) drew attention to 
‘natural barriers’ delimiting flora and fauna. The nine¬ 
teenth century was well advanced before Lyell convinced 
his readers that present distribution is conditioned by past 



Fig. 125. The main zoogeographical regions. The ‘Australian* region in¬ 
cludes an immense number of islands, too small to appear on the map. 


changes involving the major land-masses. The materials 
obtained by Darwin on the Beagle (published 1839-63), 
brought out striking facts in the geographical distribution 
of animals, both living and extinct. 

In 1858, the year of the classic contribution of Darwin 
and Wallace, appeared the pioneer attempt by P. L. Sclater 
(1829—1913) to divide the world into zoological regions. 
He discussed the perching birds which lend themselves 
for the purpose. Their power of flight is small, they are 
rich in species, and they have been very exactly studied. 

In the meantime, A. R. Wallace (p. 297) had been at 
work on the fauna of the Malay peninsula. He was struck 
both with its resemblances to and with its differences from 











































































Distribution oj Life on Land 267 

that of South America where he had also collected. His 
studies resulted in his Geographical Distribution of Animals 
(1876), still the most important work on the subject. 

Wallace based his discussion on mammals. He fol¬ 
lowed Sclater in dividing the land-surface of the earth 
into six zoogeographical regions. These he named 
Lalaearctic^ Nearctic, Ethiopian^ Oriental^ Australian^ and 
Neotropical (Fig. 125). 

Wallace’s regions have been retained in great part by 
more modern workers. The most important changes since 
his time are (a) the separation by some writers of the 
Madagascar (Malagasy) from the Ethiopian region, (h) 
the general recognition that the Palaearctic and Nearctic 
regions are more nearly allied to each other than to any 
other region, and their union into a Holarctic region, and 
(r) the subdivision of the ‘Australian’ or Pacific region 
(Notogaea). The divisions thus instituted have been 
grouped somewhat as follows: 

1. Holarctic 

2. Ethiopian 

3. Malagasy 

4. Oriental 

Neogaea 5. Neotropical 

r 6. Australian 

Notogaea 7. Polynesian 

18 . Hawaiian 

Wallace demonstrated many remarkable contrasts. 
None is more striking than that between Bali and Lombok, 
near Java. These islands, each about the size of Corsica, 
are separated by a deep strait which at its narrowest 
is but 15 miles. Yet, as Wallace remarked, they ‘differ 
far more in their birds and quadrupeds than do England 
and Japan, the difference being such as to strike even the 
most ordinary observer’. 

The strait between Bali and Lombok, known as 



{ Nearctic 
Palaearctic 



268 Distribution in Space and Time 

Wallace's line, is very deep. It has been generally regarded 
as delimiting the Oriental from the highly peculiar 
Australian zoogeographical region. The zoogeographical 
regions into which the earth’s surface can be divided 
depends upon the particular group of animals chosen. 
It happens, however, that the divisions of geographical 
regions based on mammals accords closely with that based 
on perching birds, and is not vastly different from that 
based on certain invertebrate groups, e. g, the Spiders. 
Very different from these, on the other hand, is the 
division based on such very ancient groups as Reptiles or 
Molluscs. 

Geographical regions are biologically interesting, not 
so much in themselves, but as revealing or summarizing 
the history of the various groups from which they are 
constructed. Thus the distribution in space of living forms 
is ultimately referable to their distribution in time. The 
discussion of the one is little profitable without the other. 

The general principles that determine plant regions are 
similar to those of animals, but their application is some¬ 
what different. The subject has been broached mainly in 
connexion with the flowering plants. These are geologi¬ 
cally younger than the groups on which zoogeographical 
regions are based (Fig. 125). Moreover, temperature and 
moisture are of overwhelming importance in the life of 
plants. Even between countries which present but slight 
differences of climate and are in the same regions of plant 
geography, certain notable floristic differences may occur. 
The lawns of the United States are not pied with daisies; 
the hyacinth, so common in English woods, is not found 
in those of Germany; our common purple foxglove is not 
an inhabitant of Switzerland. It is doubtless material needs 
—of the exact nature of which we are ignorant—and 
not physical barriers, that determine such an apparently 
arbitrary distribution. 



Distribution oj Lije on Land 269 

On the other hand, the means of dispersal of flowering 
plants are more effective than those of vertebrates or of 
most other animal groups. The effects of this are suffi¬ 
ciently evident on oceanic islands. 

A pioneer plant geographer was the German philo¬ 
sopher and traveller, Alexander von Humboldt (1769— 
1859). His interests were largely determined by a youth- 



Fig. 126. Probable distribution of land (dotted) in Cretaceous period. 


ful friendship with a companion of Captain Cook. He 
was the founder of the science of physical geography and 
was the first to delineate ‘isothermal lines’. Von Hum¬ 
boldt began his Kosmos (i 845—7) in his seventy-sixth year. 
This great book did good service in emphasizing the 
relations between the forms and habits of plants and the 
character and soil of their habitat. Humboldt’s presenta¬ 
tion is rendered attractive by his magnificent descriptions 
of tropical vegetation. 

Certain resemblances between the flora of Africa, South 
America, and Australia had impressed Humboldt and 
other naturalists. In 1847 J* Hooker (pp. 251, 549) 
suggested in explanation a land connexion between South 




270 Distribution in Space and Time 

America and Australia as late as Jurassic times. Various 
names, forms, and areas have been ascribed to this now 
fragmented continent (Fig. 126). The known facts are 
marshalled in the ‘theory of continental drift’ which 
regards modern continents as the result of the sundering 
of one vast land mass. 

Attempts to delimit definite plant regions have been less 
successful than those of the zoogeographers. The subject 
was approached by the German naturalist, A. H. R. 
Grisebach (1813—79), of Gottingen, in a series of papers 
leading up to his Vegetation der Erde (1872) and Pflanzen- 
Geographie (1878). These works are detailed lists of 
floras, based primarily on those of the West Indies. They 
show each flora to be adapted closely to its climatic and 
environmental circumstances. Oddly enough, Grisebach 
rejected the doctrine of descent. 

Unsuccessful attempts were next made to divide the 
earth into floral areas, corresponding to the zoogeographi- 
cal regions. Later botanists have mostly laid far more stress 
on climate than on geographical regions. The most success¬ 
ful has been A. F. W. Schimper (1856-1901) of Basel, 
whose Pflanzen-Geographie of 1898 is still in current use. 

A simple scheme of plant distribution that covers a 
very large number of phenomena was set forth by 
W. T. Thiselton-Dyer (1843—1929), director of the Royal 
Botanic Gardens at Kew, who had an enormous floristic 
experience. Thiselton-Dyer (1911) divided the earth’s 
flora into three great primary areas: (a) the North Tem¬ 
perate Zone, (d) the Tropical Zone, and (c) the South 
Temperate Zone. The northern tropic cuts off (a) from 
(b) with considerable accuracy. The southern tropic sepa¬ 
rates (b) from (r) with less precision, and, indeed, {b) and 
(f) are less distinct from each other than are (a) and (p). 
The characteristics of these divisions are as simple as their 
geographical boundaries. 



Distribution of Life on Land 271 

(a) The North Temperate Zone contains most land. 
It is continuous save for the geologically recent break 
at the Bering Straits. It is characterized (i) by needle¬ 
leaved cone-bearing trees; (ii) by catkin-bearing and other 
trees, which form an important family {Amentiferae) that 
lose their leaves in winter; and (iii) by a great number of 
herbaceous plants that die down annually. 

{h) The Tropical Region occupied areas widely sepa¬ 
rated by intervening ocean. It includes the major part of 
Africa, is imperfectly continuous with Southern Asia, and 
discontinuous with tropical America and with the Eastern 
Archipelago. It is characterized (i) by gigantic Mono¬ 
cotyledons, notably the palms, by the natural order 
Musaceae and by the enormous grasses known as ‘bam¬ 
boos’; (ii) by evergreen polypetalous trees and by figs; 
(iii) by the rarity of herbaceous plants which, when 
tropical, are mostly parasitic on other plants. 

(c) The South Temperate Zone occupies very widely 
separated areas of South Africa, South America, Australia, 
and New Zealand. It is characterized by the possession 
of a number of peculiar Natural Orders, which are mostly 
of shrub-like habit. Many are intolerant of moisture. 
Individual species are very numerous and often very 
restricted in area of distribution. 

The great supremacy of the tropical region in wealth 
of forms has been brought out by O. Drude (1852— ). 

Apart from families of very restricted distribution (17) and 
those universally dispersed (92) Drude recognized 131 
families of flowering plants. Of these 30-5 per cent, are 
characteristic of the North Temperate, 52-5 per cent, of 
the Tropical, and 17 per cent, of the South Temperate 
Zone. If genera and species instead of families were 
considered, the wealth of the tropics would be found to 
be far greater. The tropics are the storehouse and perhaps 
the nursery of species. It seems probable that the other 



272 Distriiution in Space and Time 

regions are constantly being invaded from the tropics. 
In general we may say of plants as of animals that their 
distribution in space must be discussed in connexion with 
their distribution in time. 

§ 8. Geological Succession 

We have glanced at the general history of palaeontology 
up to Darwin (pp. 241—4). His optimistic followers 
expected the geological record to reveal a series of forms 
becoming progressively ‘higher’ and ‘more differentiated’. 
Research, they thought, would bring to light a number 
of‘links’ between existing species, genera, families, orders, 
classes, and even phyla. It has now long been apparent 
that such ‘links’ are, in fact, conspicuous by their absence. 

Most major groups of organisms go back very far. It 
is true that ancient forms often present features which 
suggest relationship to other groups. But anything to 
which the palaeontologist can point as actual ancestral 
forms are few indeed. Among higher animals the best 
authenticated and most frequently quoted continuous series 
is that which leads up to the modern horse (Fig. 135). 

The difficulty in tracing ‘direct lines’ is partly intelli¬ 
gible if we assume that new species arise by mutation 
(chap. xv). If we consider larger groups, however, the 
record often makes helpful suggestions without giving 
exact information. Thus the relationship of birds and 
reptiles is fairly clear, as is the line of descent of the sur¬ 
vivors of the immense group of mesozoic reptiles. On 
the other hand, the relationship between amphibia and 
reptiles is extremely obscure. The mammals, too, go 
back very far without any real indication of junction with 
any other group. As regards the junctions of the great 
invertebrate phyla, we gain little if any help from geology. 

The general distribution in time of some of the more 
important classes of vertebrates is shown in the accom- 



Geological Succession 273 

panying diagram (Fig. 127). It will be seen that we are 
in an age of predominance of warm-blooded animals— 
mammals and birds. Reptiles and amphibia, which played 
the leading role in mesozoic times, have greatly waned. 

In the study of fossil plants, Robert Brown did pioneer 
service (1851). The subject owed more, however, to 



Fk;. 127. Diagram of geological succession of higher organisms. The varying 
width of the black bands is an attempt to represent the relative dominance of 
the various classes at the different geological j^eriods. (Animals and plants 
must be considered separately in this connexion.) The time estimates to 
the left must be taken as the roughest of approximations. The numbers to 
the extreme right and the black horizontal lines corresponding to them indicate 
the four great floral transformations (pp. 274—8). 

William Crawford Williamson (i 816—95) Manchester, 
who came early under the influence of William Smith 
(p. 242) and began his work on plants in 1858. 

Williamson demonstrated that in coal are to be found 
gigantic woody forms similar to the higher existing 
flowerless plants, such as horse-tails, ferns, and club- 
mosses. His results met with neglect until 1882, but 
from that time the great importance of palaeobotany, and 
the immense mass of material available in coal and other 
2613.3 


T 
















274 Distribution in Space and Time 

formations have been recognized. This extension of the 
knowledge of fossil plants has been due to many workers; 
to none, however, as much as to D. H. Scott (1854- ) 

who was, at first, an associate of Williamson. The demon¬ 
stration of the relationships of several of the major 
groups of fossil plants to each other has been largely his 
work. 

We turn now to consider the broader results of the study 
of palaeobotany. A plankton flora (p. 260) of algae must 
have existed at a very early date. We can hardly, in the 
nature of the case, have geological evidence for it. In 
time these algae came to be attached and rooted as shore- 
forms and, in the Silurian, reached a high development. 
The land was next invaded. 

A feature of the geological history of land-plants is 
a series of four more or less abrupt changes of the world 
flora. There is no corresponding faunal change and only 
the third transformation can at present be adequately 
explained. 

(a) The First Transformation was from a marine to a 
land flora. 

Of land plants we have no convincing evidence until 
the Upper Silurian. In 1888 Sir J. W. Dawson (i 820—99) 
of Montreal produced a classical restoration from the 
Lower Devonian of the simple marsh-living Psilophyton 
frinceps, since traced tack to the Silurian. It was leafless, 
two feet high, with spiny stems half an inch across. Naked 
oval spore-cases were borne on special curved stems. 
Psilophyton gives its name to the important group Psilo- 
phytales (p. 199). They disappeared with the second 
transformation. Another typical plant of the Upper 
Silurian was the rootless and leafless Aberdeenshire 
Rhynia major. An allied genus to this, Asteroxylon^ bore 
elementary leaves. Asteroxylon and Rhynia apparently grew 
in a peaty soil subject to periodic inundations. 



Fig. 128. Lyginodendron Oldhamium found in the lower Carboniferous. It 
was the first Pteridosperm (seed-fern) of which the seed was identified, and is 
now one of the most completely known of all fossil plants. The piecing together 
of its various fragmentary remains has been the work of nearly a century. 
The foliage was described in 1829, the male organs not till 1905. A contem¬ 
porary dragon-fly is shown near by. From D. H. Scott. Inset is the ripe seed 
studded with glands, from F. VV. Oliver. 

T2 




276 Distribution in Space and Time 

Before the second transformation appear a few ‘seed- 
ferns’ or Pteridosperms (p. 199) and a few Lycopodials 
(giant club-mosses), groups characteristic of the next phase. 
On the whole, however, the transformation is sharp. 

(b) The second transformation led to the coal measures 
of the extremely peculiar flora of which we have con¬ 
siderable knowledge. It included many plants with the 
general habit of ferns. Among these were a few true ferns 
very distantly related to forms now living. More charac¬ 
teristic were the ‘seed-ferns’ or Pteridosperms which, 
though superficially similar to ferns, were not closely 
related to them. A characteristic Pteridosperm was Lygi- 
nodendron 128). Lycopodials were large and numer¬ 
ous and have left an insignificant remnant in the modern 
‘club-mosses’. A characteristic I^ycopodial was the well- 
known Lepidodendron (Fig. 129). One was found some 
years ago in an English coal-mine, measuring 114 feet to 
its first branches. Another beautiful Lycopodial was 
Sigillaria (F\g. 129). 

The commonest plants of the coal-measures are the 
Catamites^ a magnificent group of which our living ‘horse¬ 
tails’ (Equisetum) with their twenty-eight species preserve 
a faint memory. Their size may be gleaned from their 
cones, some of which were a foot long (Fig. 129). 

Very conspicuous were the Cordaitales, called so from 
their leading genus Cordaites. Some important beds of 
coal are entirely made up of their leaves. They were tall, 
slender trees with large simple leaves. The ‘flowers’ were 
catkins, which arose just above the leaves (Fig. 129). 

In carboniferous times there were uniform climate con¬ 
ditions almost all over the world, associated with an equally 
uniform flora. A severe glaciation followed in Permian 
times. It affected an enormous area, including part of 
Australia, India, South Africa, and much of South America, 
then combined into a great southern continent (Fig. 126). 




Glossopteris flourished all over the southern hemisphere 
and extended to within 300 miles of the South Pole. Fossil 
specimens were obtained on the Beardmore Glacier by 
Captain Scott’s expedition of 1912. They were found with 
the dead bodies of the explorers. 

(c) The third transformation appears very suddenly and 
marks the dawn of mesozoic times. For the earliest or 








278 Distribution in Space and Time 

triassic period land conditions were relatively dry. This, 
following the Permian glaciation, may explain the rapid 
change. 

The Pteridosperms are now replaced by a vast array of 
Cycad-like forms, of which a remnant still survives. True 
ferns become numerous but quite different from Palaeozoic 
forms, since most belong to still existing families. The 
Cordaites are succeeded by Conifers allied to existing 
families. The great horse-tails dwindle prodigiously both 
in numbers and size. The giant Lycopods are seen no 
more. Their allies, the club-mosses, become both few and 
modest. A few flowering plants are found. 

(d) The fourth transformation is to the modern flora, 
which becomes evident in the Upper Cretaceous times. 
Flowering plants are its feature. There is nothing primi¬ 
tive about them even at their first known appearance. In 
the Upper Cretaceous, the vegetation looks quite modern. 
Monocotyledons include palms, reeds, lilies. They bear 
about the same proportion to the Dicotyledons as in the 
modern flora. Among Dicotyledons are many modern 
families. From the Middle Cretaceous onward, species 
are encountered of genera that are still represented in our 
modern flora. 

There are two striking features in the geological suc¬ 
cession of plants. First is the disappearance of very highly 
developed groups, Pteridosperms, Psilophytales, Glosso- 
pteris, and the like. Second the immense extension back¬ 
wards of living groups, flowering plants, conifers, ferns, 
&c., without any definite sign of junction either with each 
other or with other groups. 

§ 9. Interrelations of Species 

Only since Darwin has any investigation been made of 
the relative distribution of allied species. This has been 
possible through the development of Ecology into an 



Interrelations oj Species 279 

independent science. The word Ecology was given circula¬ 
tion by Haeckel (1886). It is on the model of Economy 
(Greek oikos^ house, and nomos, law). Haeckel considered 
that the scope of Ecology was to treat of the reciprocal 
relations of organisms and the external world. For this 
discussion plants are specially suitable. The external 
world with which ecologists have had to deal can be 
divided into two departments. 

(<2) The physical conditions, light, temperature, mois¬ 
ture, terrain, &c. 

(b) Other species. 

The Ecology of Plants (1895) by the Dane, E. Warming 
(1841—1924), dealt largely with the former theme. Plant 
Geography upon a Physiological Basis (1898) by the Swiss, 
A. F. W. Schimper (1856—1901), with the latter. These 
two important works have set the subject on its way. 
From the beginning, however, it has been cursed, more 
than most sciences, by a horde of technical terms equally 
hideous, unnecessary, and obfuscating. 

Ecology has elicited some suggestive facts for the 
solution of the problem of the distribution of allied species. 
When, in the light of ecological principles, we examine 
the life-habits of plants in a state of nature, we encounter 
certain evident phenomena that have often been over¬ 
looked. It has always been known that plants are im¬ 
mensely fertile, that a single plant of foxglove, for example, 
produces tens of thousands of seeds. Yet foxgloves do 
not become more common. In fact the relative proportion 
of different plants in a given wild area remains substantially 
the same from season to season. Neither plants nor 
animals often spread beyond their normal haunts. In 
undisturbed country a clump of some particular plant will 
come up in the same spot year after year. So too with 
animals. 

Many plants have special modes of distribution—the 



28 o Distribution in Space and Time 

air-borne seeds of the dandelion occur to the mind. Yet 
such means of distribution evidently do not serve them. 
The surface of the earth does not become covered with 
dandelions, despite the pessimistic opinion of gardeners. 

We tend to think of individual plants as we encounter 
them in fields and gardens. But fields and gardens are 
ploughed and harrowed, hoed and weeded and manured. 
Thus each plant is given its place. Nature has less caring 
for individuals. Plants in nature exist in so-called ‘com¬ 
munities’. These do not usually consist of one species but 
of groups of species. 

In nature, when man has not interfered, every spot 
where life can maintain itself is fully occupied by such 
groups and has been so for ages. The frontiers of com¬ 
munities may be altered a little by extraordinarily wet or 
dry seasons and the like. Despite fecundity, despite 
facilities for distribution, despite apparent strength, it is 
an excessively difficult thing for a foreign individual to 
gain entry into a community—indeed the mind has diffi¬ 
culty in grasping the excessive infrequency of such an 
event. Each district has its own flora and there is as little 
hope of that of a mountain, for instance, invading that 
of a valley at its foot as of the reverse process. Wild 
nature is extraordinarily stable. 

The matter demands illustration from a completely 
wild district where man has never intervened. Mount 
Ritigala is a solitary precipitous peak of 2,800 feet in the 
north of Ceylon. That mountainous island has in general 
a typical damp, tropical climate. The northern part of 
the island where Ritigala is situated is dry and arid. But 
Ritigala is cloud-capped and its peak always moist. 

The flora of Ritigala peak consists mostly of species 
of genera which flourish in the dry zone below. Despite 
the chances of vast ages it has received only 103 species 
characteristic of the wet zone of the island where the 



Interrelations oj Species a8i 

climate is similar to its own. Of these 103 species, 24 have 
fruits suited to carriage by birds, 49 have light seeds, or 
spores suited to carriage by wind. Thus some three- 
fourths of the immigrant species have been brought to 
this remote spot by known means. Yet the poverty in 
species of the immigrant population emphasizes the ex¬ 
treme and almost inconceivable slowness with which 
organisms are diffused in nature and the enormous diffi¬ 
culty encountered by the foreign individual in obtaining 
a foothold in an established community. 

Where Nature has cleared the ground, the phenomena 
are utterly different. The classical instance is the island 
of Krakatoa between Sumatra and Java. In 1883 there 
was a terrific eruption on the island. Life was completely 
exterminated. By 1886 some 17 species of flowering 
plants had re-established themselves on the island. In 
1897 the number had risen to 50, and in 1905 to 137. 
Thus, in 22 years more immigrants had established them¬ 
selves on vacant Krakatoa than had succeeded in geological 
ages on occupied Ritigala! 

Of late years some botanists have found it worth while 
to record minutely the actual distribution of individual 
plants or plant colonies. Such intensive work, especially 
in wild or unsettled areas, has brought some remarkable 
facts to notice. If any genus containing a large number 
of species be taken, some of these species will be rare, 
others less rare, and others common. Now it has often 
been found that the rare species have a particularly 
narrow distribution as compared with the common. In 
some cases it has been shown that a rare species exists 
only in an area of a few square yards. 

It was once thought that such extremely local species 
were failures, driven to mountain peaks or other unfavour¬ 
able sites as their last stronghold. Since the advent of 
the view of the origin of species by mutation (chap, xv). 



282 Distribution in Space and Time 

it has seemed likely that very localized species are, more 
often, new productions. Formed by mutation in isolated 
localities, they are able to perpetuate themselves on an 
isolated spot, though many ages must be needed for their 
spread. A species that is really dying out would be much 
more likely to exist sparsely distributed over a wide area 
than densely concentrated in a narrow one. 

§ lO. Migration 

A very remarkable phenomenon is presented by the 
wandering of animals into distant localities. In the most 
striking cases the process is annual and is associated with 
breeding. Since the days of Aristotle migration has been 
observed among birds, but examples no less regular and 
impressive are known among fishes. Certain mammals, 
as seals, perform similar journeys. Less regular migra¬ 
tions, bearing analogies to those less ordered movements 
of population encountered in the human species, are pre¬ 
sented by many groups, from mammals downwards. 

The attention of many learned naturalists has been 
attracted to the migration of birds. Ray (1676), Linnaeus 
(1757), Gilbert White (1789), Blumenbach of Gottingen 
(1823), and von Baer (1834) treat of it. The subject was 
dealt with by Marcel de Serres of Montpellier (1782— 
1862). From 1822 onward he attempted to correlate the 
geological distribution of animals to their modern geo¬ 
graphical distribution. 

During the next half-century a mass of data concerning 
the movement of birds was collected, especially by 
Scandinavian, Russian, and German naturalists. Among 
the most important facts elicited was that in many genera 
of birds, those species that have the widest northerly have 
also the widest southerly range, and those species which 
go next farthest north in summer pass next farthest 
southward in winter. 



Migration 283 

An extreme case is that of the American Golden Plover. 
It breeds and nests in the extreme north of Canada within 
the Arctic circle around Baffin Bay. It spends the winter 
on the pampas in the south of Argentina (Fig. 130). The 



130 131 

Fig, 130. To show the route of migration and range of the American Golden 

Plover. 

Fig. 131. A part of South America to show the distribution of closely allied 
species of the Chinchona trees from which Quinine is derived. The shaded area 
marks the range of the Andes (Clements R. Markham, i860). Twelve distinct 
species occupy each its own area. 

route taken by this species is now fairly known, as is that 
of a large number of other forms. 

The conditions that determine migration of birds are 
partly understood. They are the usual oecological factors— 
food-supply, light, temperature, moisture, safety from 
enemies, and the rest. The mode of origin of migration 
as well as the method by which these birds find their way 
over vast distances remain a mystery. 





284 Distribution in Space and Time 

At an early date (1878) a suggestion was put forth by 
Wallace: 


‘Suppose’, he said, ‘that in any species of migratory bird, breeding 
can only be safely accomplished in a given area and that during a 
great part of the year sufficient food cannot be obtained in that area. 
Those birds which do not leave the breeding area at the proper 
season will become extinct, which will als(j be the fate of those 
which do not leave the feeding area. If the two areas were, for 
some remote ancestor, coincident, but geological and climatic 
changes gradually diverged, we can understand how the habit of 
migration would become so fixed as to be what we term an instinct. 
It will probably be found that every gradation still exists, from a 
complete coincidence to a complete separation of the breeding and 
subsistence areas.’ 

This prophecy has been largely fulfilled. But its ful¬ 
filment does not bring us much nearer to a knowledge of 
the mechanism by which the bird finds its way, nor will it 
explain the numerous cases in which migration takes place 
over a large part of the earth’s circumference. In this 
connexion fantastic statements have been made which we 
need not reproduce. 

Migration is known in some other animal groups, in 
insects, such as locusts, in mammals, such as seals. None 
is more inexplicable than the seemingly objectless sporadic 
mass-movements of the lemmings. 

Regular migrations in connexion with breeding are 
found in fish. Thus the salmon breeds in rivers—a safe 
retreat—but feeds in the sea. Some few fish reverse the 
process, the most extraordinary and best authenticated 
case being that of the eel. 

The problem of the breeding habits and migratory 
movements of the eel have been before naturalists since 
the days of Aristotle. Rondelet (p. 91), Gesner (pp. 92-4), 
and the other sixteenth-century naturalists discuss them. 
Francis Bacon (p. 120) refers to them. Isaac Walton 



Migration 285 

(1593-1683) expresses the difficulties in a very quaint 
passage in his Compleat Angler (1653). Naturalists of the 
eighteenth century described the eel’s general habits of 
migration. They distinguished two migrational move¬ 
ments in the year, in the autumn to the sea, in the spring 
from the sea. They observed that in the autumn move¬ 
ment the eels were larger than in the spring. It was seen 
that they fed in the rivers but bred in the sea. The 
migration itself, part of which is over-land, was repeatedly 
observed in the nineteenth century. The breeding-place 
was quite unknown but believed to be on coasts and 
estuaries. 

Meanwhile, a group of small laterally compressed 
transparent fishes had been observed early in the nine¬ 
teenth century in the Eastern Mediterranean and the 
Atlantic. The genus Leptocephalus was erected to include 
them. In 1896 G. B. Grass! (1854-1925) of Rome—^who 
afterwards did distinguished work on the parasites of 
malaria in man—made an important discovery bearing on 
a species of Leptocephalus. In the Straits of Messina he 
found a number of specimens transitional between Lepto- 
cephali and young eels. This suggested that the eel bred 
in deep water near the coast. In 1904 the Dane, Johannes 
Schmidt (1877— ), showed that the real breeding- 

ground of the European eel is a small area on the bed of 
the Ocean at a depth of about 300 fathoms to the south¬ 
east of Bermuda. From thence these creatures radiate as 
Leptocephali, increasing in size and becoming more eel¬ 
like as they proceed towards their European home. Even 
more remarkable is the fact that a breeding-ground not 
very far distant produces a very closely allied species which 
passes not to European but to American rivers (Fig. 132). 

Some satisfactory explanation of this extraordinary 
movement is now forthcoming. It has been suggested 
that the breeding-ground was once a freshwater lake or 



286 Distribution in Space and Time 

river within a transatlantic continent now submerged 
(Fig. 109), and that the eels have preserved their ancestral 
breeding-ground and continued to follow their old lines 
of movement. These instinctive reactions would thus be 
older than the main geographical features of our world! 
The eel always bred where he now does, but he still fre¬ 
quents for a part of his life his old haunts—the rivers 



Fic. 132. Distribution of European and American eel. I'he continuous con¬ 
centric curves show the limits of occurrence of the larvae of the European eel, 
the length being given in millimetres. By the time they have attained the length 
of 60 millimetres (vertical shading) they have reached the European and African 
continental shelf. As elvers they ascend the rivers (shaded horizontally). Area 
of distribution of the larvae of the American eel is indicated by concentric dotted 
lines and its adult form by oblique shading. 

from which his breeding-ground is now widely separated 
by continental movement. Further, in the course of ages 
a differentiation must have taken place between the 
American and the Old World eel. The breeding-ground 
of the American eel is now a little further west than that 
of its cogener. The larvae of both species radiate from 
their breeding-ground. The American eel is born in 
warmer waters. Its larval stage is completed in about a 
year, while that of the Old World eel is not completed 
until about three years. Both species tend to spread north- 









Migration 287 

eastward along with the prevalent currents (Fig. 112), 
the American form, however, spreads more northward 
and the European more eastward. Thus, by the time 
the larva of the Old World eel attains to the elver stage, 
it has approached the European continental shelf or has 
entered the Mediterranean. At the end of its first year, 
however, the American species finds itself on the American 
continental shelf. The elvers now ascend the rivers of 
the two continents and pass into the adult stage. The 
countless millions that do not reach the shore never 
develop further and perish as larvae (Fig. 132). 

Fig. 133. Fossil skeleton found in Bavaria in 1788. It was regarded as a bird by 
Blumcnbach (1807). Cuvier identified it (1812) as a flying reptile of a previously 
unknown cla.ss, and named it Pterodactyl. Compare Fig. 105, p. 221. 




VIII 


EVOLUTION 

§ I. Buffon (1707—88) and Erasmus Darwin (1731—1802) 

E ven the most savage and uncultured peoples have 
some idea of species. They must naturally distinguish 
the different animals that they hunt and the various plants 
that they gather. Some, in fact, exhibit great acuteness 
in differentiation between species. Their ideas have, 
however, no formal distinctness. For this we must await 
the advent of science. Many philosophical writers have 
included some idea of evolution in their schemes. We 
shall not consider these but shall concentrate on the con¬ 
crete idea of evolution of organic species by descent. 

We have glanced at the conceptions of species of 
Aristotle (p. 43), Bauhin (pp. 174-9), (P* ^ 79 )> 

others. By most older writers, species are treated, after 
the biblical account, as created once for all. Linnaeus held 
that there are ‘as many species as issued in pairs from the 
hands of the Creator’. Later he admitted that it was in 
some cases difficult to separate one species from another. 
Without fully abandoning his original position, he sub¬ 
stituted, in effect, the genus for the species as the original 
creation, concluding that ‘all the species of one genus 
constituted at first one species’. New species, he thought 
had arisen by intercrossing. The first naturalist of modern 
times clearly to set forth the idea that species are not 
permanent was Buffon. 

George I.ouis Leclerc, Comte de Buffon, scion of a 
distinguished Burgundian family, early showed a taste for 
mathematics and the physical sciences. Gradually he 
moved towards biological problems. He was influenced 
in this by the writings of Stephen Hales (pp. 363-6). The 



Buff on and Erasmus Darwin 289 

wealth and social position of Buffon enabled him to devote 
his time to science. His great industry and natural acute¬ 
ness were applied in obtaining a broadly based knowledge 
of biological matters. His attractive literary style rendered 
very great service in drawing public attention to the value 
and interest of science. He was not a painstaking investi¬ 
gator, but he made many excellent scientific sugges¬ 
tions. 

Buffon’s great Histoire naturelle sought to embrace all 
scientific knowledge, and was the first modern attempt 
of the kind. It appeared in forty-four volumes, and its 
publication occupied fifty-five years (1749—1804), being 
completed after his death by an assistant. It was well 
illustrated. There were several editions and translations. 

Buffon’s popularity led to his belittlement by later 
specialists. Nevertheless many of his ideas acted as a 
ferment in the minds of his scientific successors. His 
influence can be traced in Erasmus Darwin, in Lamarck, 
in Geoffroy St. Hilaire, in Goethe, in Cuvier. His more 
fertile conceptions may be thus summarized: 

(a) The grand demonstration by Isaac Newton (1642— 
that the forces that can be investigated on earth are 

identical with those that move the celestial orbs, deeply 
impressed Buffon. He, too, would consider Nature as 
a whole. But, for Buffon, Nature must include living 
Nature, which Newton had disregarded. Yet Buffon was 
no mere physiological mechanist, like Borelli, for instance 
(p. 356), content to explain the more evident activities of 
the living body. For Buffon all parts and all activities of 
the world are interrelated. 

(b) Arising out of (a) is his attitude to classificatory 
systems, especially that of Linnaeus. These he held to be 
trifling and artificial abstractions, since they fail to present 
living things as part of the general order of Nature. 

(c) In the series of living things he paid little attention 

26 l 3*3 


TT 



290 Evolution 

to the minute differences between species that Linnaeus 
and the systematists were ever seeking. He looked rather 
at the common factors, the likenesses. He sought some 
universal element in living things. The cell doctrine 
(chap, ix), had it been available, would particularly have 
rejoiced him. He fastened, however, on the phenomenon 
of reproduction as a universal accompaniment of life. 
Spermatozoa were then being brought to light in a con¬ 
stantly increasing range of organisms. Knowing nothing 
of the cellular phenomena of sex (chap, xiv), he believed 
that spermatozoa—and comparable bodies which he 
thought he saw in the ovaries—represented units out of 
which individuals could be built. The conception has 
distant affinities with that of the ‘monads’ of the philoso¬ 
pher Leibnitz (1646-1716). It is in some degree antici¬ 
patory of the many nineteenth-century theories of the 
particulate nature of living substance (chap. x). 

(^/) He sought to trace the history of the earth through 
a series of ‘epochs’, fossils providing some key to this 
history (p. 242). 

{e) Buffon expresses himself variously on the subject 
of the fixity of species. He was, however, moving ever 
farther from the position of Linnaeus. He noted that 
animals have parts to which no special or adequate use can 
be ascribed. Thus ‘the pig is not formed on an original 
perfect plan, since it is a compound of other animals. It 
has parts which can never come into action, as lateral toes, 
the bones of which are perfect, yet useless.’ Later he 
conceived that species alter in type from time to time, but 
retain marks of their previous types, as the pig retains its 
disused toes. Then, moving a little farther, he concluded 
that some species are degenerate forms of others. Thus 
the ape is a degraded man, the ass a degraded horse, 
and so on. 

These ideas of Buffon were examined by Erasmus 



Bujffon and Erasmus Darwin 291 

Darwin (1731-1802)5 grandfather of Charles Darwin. 
He excelled as a thinker and critic rather than as an 
observer, but was no mean naturalist. In his Zoonomta\ 
or the Laws of Organic Life (i 794-6), he sums up in clear 
though verbose language the general nature of the diffi¬ 
culties among which Buffon was groping. His solution is 
striking and it is noteworthy that he gathers just those 
classes of facts which most impressed his grandson. 

‘When we revolve in our minds,’ writes Erasmus Darwin, ‘first the 
great changes which we see naturally produced in animals after their 
birth, as in the production of the butterfly with painted wings from 
the crawling caterpillar, or of the (air-breathing) frog from the 
(water-breathing) tadpole; secondly, the great changes by artificial 
cultivation^ as in horses which we have exercised for strength and 
swiftness, or dogs which have been cultivated for strength and 
courage, as the bulldog, or acuteness of smell, as the spaniel, or 
swiftness, as the greyhound; thirdly, the great changes produced by 
climate, the sheep of warm climates being covered with hair instead 
of wool, and the hares and partridges of latitudes which are long 
buried in snow becoming white during the winter months; fourthly, 
the changes produced before birth by crossing or mutilation', fifthly, the 
similarity of structure which obtains in all the warm-blooded animals, 
including mankind, from the mouse and bat to the elephant and 
whale; one is led to conclude that they have alike been produced 
from a similar living filament.’ [Much abbreviated. Italics in¬ 
serted.] 

The ‘filament’ to which he refers is a spermatozoon which 
he regarded, following Buffon, as a sort of biological unit 
(PP; 290, 500). 

Erasmus Darwin thus held that the changes that species 
undergo in the course of time are due to influences that 
bear on the individuals from without. These changes he 
held were passed on to the offspring. This view is now 
known as the inheritance of acquired characters. 



292 


Evolution 


% 2 . Lamarck (1744-1829) and his Successors 

The question of the inheritance of acquired characters 
is among the most discussed of modern biological pro¬ 
blems. Erasmus Darwin was the first to state the thesis. 
Charles Darwin took such inheritance for granted, 
Lamarck, a younger contemporary of Erasmus Darwin, 
made it the key to his evolutionary hypothesis. 

Jean Baptiste de Monet Lamarck (1744—1829) of 
Amiens was educated at a Jesuit College. In 1761, during 
the Seven Years’ War, he entered the army. Failure in 
health forced him to forego a military career. He turned 
to medicine, giving special attention to botany, then an 
important part of the medical curriculum. He became 
intimate with the famous Genevan philosopher, Jean 
Jacques Rousseau (1712-78), who influenced him a good 
deal. Later he worked also with another distinguished 
Genevan, the botanist, A. P. de Candolle (pp. 194-6). 

Lamarck’s first biological work was a flora of France 
(1778). It drew the attention of Buffon, who assisted its 
author to travel and to publish other botanical works. In 
1788 Lamarck took up a botanical post at the ‘Jardin du 
Roi’, now the Jardin des Plantes, at Paris. Owing to 
rearrangement there in 1793 he was forced, at 50, to 
change over to zoology, to which he devoted himself with 
enthusiasm. His best-known work is the Philosophie 
zoologique (1809). Its principles are worked out in 
detail in his Histoire naturelle des animaux sans vertebres 
(1815-22). 

Lamarck was unlucky in his mode of address. His 
literary style is arid. He was personally eccentric. He 
married four times, and had to support a very large family 
on a very small salary. His over-proneness to speculation 
often made him a laughing stock. Many of his views 
were extremely fanciful and were held in light esteem by 



Lamarck and his Successors 293 

his contemporaries in general. Cuvier, the scientific 
dictator of the time, who adhered to the view of the fixity 
of species, formed a low opinion of his abilities. Charles 
Darwin, among his successors, held him in contempt. 
The interest of the theory by which Lamarck is re¬ 
membered was not fully realized until he had long 
been dead. 

As a systematist, Lamarck certainly made important 
and lasting contributions. He separated spiders and 
crustaceans from insects, and defined all these classes. He 
began to bring order into the class Vermes of Linnaeus 
(p. 189), segregating the truly worm-like forms. He also 
made some advance in the classification of the echinoderms. 
He introduced the classification of animals into verte¬ 
brates and invertebrates. 

With his eye fixed on ‘system’ I.amarck was convinced 
that there is a ‘natural sequence’ for living organisms. If 
we knew all the species that are or have been, they would, 
he believed, form a long ladder or scale with compara¬ 
tively few branches. On this scale each species would 
differ but little from its immediate neighbours. 

There are, in fact, existing species which differ very 
considerably from their nearest known allies. Lamarck 
was quite aware of this and he attributed such isolation 
to gaps in our knowledge. Further research would, he 
believed, fill these vacant places. The progress of 
palaeontology seemed to him to offer hopes of such a 
consummation. Lamarck, therefore, argues that all 
systems of classification are really artificial, though neces¬ 
sary as summaries of our knowledge. 

This idea of the continuity of living things led Lamarck 
to consider that the animal and the plant series must, at 
some point, be continuous with each other. He thus 
emphasized the view that living things should be studied 
as a whole, an attitude to which he was helped by having 



294 Evo/utiori 

himself practised as both botanist and zoologist. For this 
unified study he invented the term Biology (1802).^ 

Since Lamarck held that no distinction can ultimately 
be found to exist between species, it seemed to him 
intrinsically improbable that they are permanently fixed. 
He laid much stress on the domesticated animals, which 
vary greatly from their wild originals. Who, seeing a 
greyhound, a spaniel, and a bulldog for the first time, 
would not think of them as different species. Yet all have 
a common ancestor. These variations have been produced 
by selective breeding by man. Variations comparable to 
these in kind, if not in degree, occur also in nature. There 
must be some agent in nature producing these differences. 
This agent, according to Lamarck, is the environment. 
Species, he thought, maintain their constancy of form only 
so long as their environment remains unchanged. 

However strained Lamarck’s conclusions in detail, we 
can now see that he had reached three important and inter¬ 
connected conceptions. 

(a) Species vary under changing external influences. 

(/^) There is a fundamental unity underlying the diver¬ 
sity of species. 

(c) Species are subject to a progressive development. 

Lamarck had now to consider the mechanism of this 
progressive development. What is it.^ How is variation 
caused.? How do changes of environment give rise to 
changes of species ? 

In answering these questions, Lamarck enunciated the 
‘law of use and disuse’ that is inseparably connected with 
his name. He supposed that changes of environment lead 
to special demands on certain organs. These being 

* In the same year the word was used by G. R. Treviranus of Bremen (1776- 
1837) as the title of a book expounding some of the principles of the Naturphilo- 
sophen. The word first appears in English in the modern sense in the Lectures 
on Physiology (edition of 1818) of Sir Wh*lliam Lawrence (1783-1867). 



Lamarck and his Successors 295 

specially exercised become specially developed. Such 
development, or some degree of it, is transmitted to the 
offspring. Thus a deer-like animal, finding herbage 
scanty, took to feeding on leaves of trees. It needed a 
longer neck to reach the leaves. In the course of genera¬ 
tions, the long neck became a more accentuated feature 
of the creature’s anatomy. Thus emerged a beast recog¬ 
nizable as a giraffe. Conversely, useless organs, such as 
the eyes of animals that live in darkness, being unexer¬ 
cised, gradually became functionless and finally dis¬ 
appeared. The character of a longer neck or of defective 
eyes was acquired by the individual in the course of its 
lifetime and transmitted in some degree to its descendants. 

The great assumption here is that acquired characters 
are inherited. Whether they are or are not is still in dis¬ 
pute. In the way suggested by Lamarck, it is certain that 
they are not. But Lamarck’s work has been of value in 
directing the attention of naturalists to one of the most 
important problems in the whole range of biological 
thought. 

Lamarck, moreover, brought the question of the con¬ 
stancy of species into the sphere of discussion. His con¬ 
ception of progressive development, or ‘Evolution’ as it 
is now called, together with certain ideas on the subject 
of homologous changes set forth by his colleague, Etienne 
Geoffroy St. Hilaire (1772—1844), attracted some atten¬ 
tion. Unfortunately the details of Geoffroy’s scheme were 
often fantastic to the last degree. Their refutation resulted 
in all biological speculation falling into disrepute for a 
while. Indeed, most discussion on the subject of Evolution 
during the first half of the nineteenth century was of a 
vague and fanciful character. 

Yet there was a writer whose work bore upon the subject, 
against whom this charge could certainly not be made. 
The Rev. T. R. Malthus (1766—1834) was primarily a 



296 Evolution 

mathematician and economist, not a biologist. His im¬ 
portance is due to his Essay on Population which suggested 
to Darwin and Wallace simultaneously the conception of 
the Struggle for Existence and of the Survival of the 
Fittest. 

The Essay of Malthus was first published anonymously 
in 1798. At that moment political theory was a common 
subject of discussion, especially in connexion with the 
French Revolution. Such topics as the ‘rights of man’, 
‘natural justice’, and the like were in the public mind. 
The utilitarian philosophers, with Adam Smith (1723— 
90), Joseph Priestley (1733—1804), and Jeremy Bentham 
(1748—1832) as their chief spokesmen, formed an ad¬ 
vanced and influential school of thought in England. 
Many believed that a day was dawning when, amidst 
universal peace, all men would enjoy complete liberty 
combined with complete equality. Malthus brought out 
forcefully and systematically the difficulties that must 
arise, in such a state, from over-population. 

In his E,ssay Malthus laid down his famous principle 
that populations increase in geometrical, but subsistence 
at best only in arithmetical ratio. He argued that a stage 
is therefore reached at which increase in population must 
necessarily be limited by sheer want. Thus he held that 
‘checks’ on population are a necessity in order to reduce 
vice and misery. 

§ 3. The 'Origin of Species' and the Validity of its Argument 

After the voyage of the Beagle (1837) Darwin became 
recognized as a painstaking naturalist, remarkable for the 
general breadth of his outlook. He did good work on the 
barnacles and their allies (1851-4, pp. 511-14), became 
known for his investigations of mammalian fossil forms, 
wrote much on geology, and was the author of an admir¬ 
able book on coral reefs (1842). He was, moreover, an 



The ‘ Origin oj Species' 297 

observer of living things, a patient recorder of what he 
saw, a man of reflective mind, and one content to ponder 
long before giving his views to the world. 

‘When on board H.M.S. Beagle^ he writes, ‘I was much struck 
with die distribution of the organic beings inhabiting South 
America, and the geological relations of the present to the past in¬ 
habitants. These facts seemed to throw light on the origin of species. 
On my return, it occurred to me that something might be made of 
this question by accumulating all sorts of facts which could possibly 
bear on it. My first note-book was opened in 1837. In 1838 I read 
Malthus on Population. Being prepared to appreciate the struggle 
for existence which goes on everywhere, it struck me that favour¬ 
able variations would tend to be preserved, unfavourable to be 
destroyed. The result would be formation of a new species. I had 
at last a theory by which to work. After five years’ work I drew up 
some short notes; these I enlarged in 1844, into a sketch of the 
conclusions which seemed to me probable; from that period to the 
present (1858) I have steadily pursued the same object. Mr. 
Wallace, who is now studying the natural history of the Malay 
Archipelago, has arrived at almost exactly the same general conclu¬ 
sions. Sir C. Lyell and Dr, Hooker, who both knew of my work— 
the latter having read my sketch of 1844—^horioured me by think¬ 
ing it advisable to publish, with Mr. Wallace’s excellent memoir, 
some brief extracts from my manuscripts.’ {^Abbreviated,'] 

The naturalist and explorer, Alfred Russel Wallace, 
subsequently made many important contributions bearing 
on the distribution and variation of living forms. The 
publication of the joint essays was in July 1858. It was 
the first public pronouncement in which an effective 
mechanism was suggested to explain the evolution of 
organic forms. 

Darwin did not initiate the doctrine of Organic Evolu¬ 
tion. But, by careful and scientific procedure, he per¬ 
suaded the scientific world, once and for all, that many 
diverse organic forms are of common descent, and that 
species are inconstant and in some cases impossible of 



298 Evolution 

definition. Moreover, he directed scientific attention to 
the occurrence of variation, to its persistence, and to the 
question of its origin and its fate. 

In November 1859 appeared Darwin’s great book the 
Origin of Species by means of Natural Selection. Despite its 
great value and stimulating character and despite the 
conviction that it carried, its arguments are frequently 
fallacious. It often confuses two distinct themes. On the 
one hand there is the question whether living forms have, 
or have not, an evolutionary origin. On the other hand is 
the suggestion that Natural Selection is the main factor 
in Evolution. These themes can be and should be dis¬ 
cussed independently. In the Origin they are inextricably 
confused. 

Darwin claims that ‘complex organs and instincts’ have 
‘been perfected, not by means superior to, though 
analogous with, human reason, but by the accumulation 
of innumerable slight variations, each good for the indi¬ 
vidual’. For this, he says, it is necessary to admit only 
three propositions. 

‘That gradations in the perfection of any organ or 
instinct, either do now exist or could have existed, each 
good of its kind. 

‘That all organs and instincts are, in ever so slight a 
degree, variable. 

‘And, lastly, that there is a struggle for existence leading 
to the preservation of each profitable deviation of structure 
or instinct.’ 

But this assumes that the ‘profitable deviations’ are 
inherited. Thus not three but four propositions are needed. 

After discussing the question of the distribution of 
species in time and space—^which provides the most 
irresistible evidence for organic evolution as an historical 
process (chap, vii)—^he turns to the question of conditions 
under which a variation is perpetuated. 



The ^ Origin of Species' 299 

‘Man does not actually produce variability [in domestic animals]; 
he only exposes beings to new conditions, and then nature acts on 
the organisation, and causes variability. But man can and does 
select variations, and thus accumulate them in any desired manner. 
He thus adapts animals and plants for his own benefit. He can 
largely influence the character of a breed by selecting, in each suc¬ 
cessive generation, individual differences so slight as to be quite in¬ 
appreciable by an uneducated eye. 7 'hat many of the breeds 
produced by man have to a large extent the character of natural 
species, is shown by the doubts whether many are variations or 
aboriginal species. 

‘In the preservation of favoured individuals and races, during the 
constantly recurrent Struggle for Existence, we see the most power¬ 
ful and ever-acting meansof selection. More individuals are born than 
can survive. A grain in the balance will determine which individual 
shall live and which shall die,—which variety or species shall increase 
in number, and which shall decrease, or finally become extinct. 
‘With animals having separated sexes there will in most cases be 
a struggle between the males for possession of the females. T he most 
vigorous individuals, or those which have most successfully struggled 
with their conditions of life, will generally leave most progeny. But 
success will often depend on having special weapons or means of 
defence, or on the charms of the males; and the slightest advantage 
will lead to victory.’ \Ahhreviated,\ 

There are here, as we can now see, a series of fallacies 
and some erroneous assumptions. 

{a) All domestic breeds have not been produced by 
selecting very slight individual differences. On the con¬ 
trary, some domestic breeds certainly and all domestic 
breeds possibly have been produced by breeding from 
individuals which presented very considerable deviations 
from the normal. The systematic study of individual 
variations—except in the isolated case of Mendel—did 
not, however, begin until the last decade of the nineteenth 
century. 

(^) That a natural variation should confer an advantage 



300 Evolution 

is not enough to secure its perpetuation. The advantage 
must be effective and moreover it must be transmissible. 
Now it is difficult to believe that the earlier stages of some 
developments are effective. A wing, for instance, so little 
developed as to confer no power of flight, or at least of 
gliding, would be no advantage. 

(c) It is assumed that ‘advantages’ are inherited. On 
this matter the modern development of the theory of 
heredity (chap, xv) has entirely changed the whole point of 
view presented by Darwin and his contemporaries. 

((^ It is tacitly assumed that species differ from their 
nearer relatives in having some special advantages that 
enable them to adapt themselves to slightly different con¬ 
ditions. In fact, however, allied species are found living in 
identical areas and under identical conditions. This would 
hardly be the case if one had the advantage over the other, 
for then one would flourish and the other decline. There 
are, in fact, very few characters by which species differ 
from their fellow-species of the same genus that can be 
shown to be advantageous. 

‘As natural selection acts solely by accumulating slight, successive 
favourable variations, it can produce no great or sudden modifica¬ 
tion; it can act only by very short and slow steps. Hence the canon 
of “Natura non facit saltum”, which every fresh addition to our 
knowledge tends to make truer, is on this theory simply intelligible. 
We can plainly see why nature is prodigal in variety, though nig¬ 
gard in innovation. But why this should be a law of nature if each 
species has been independently created, no man can explain.’ 

This passage is of necessity rejected with the modern 
laws of hereditary before us. The aphorism of Linnaeus 
‘Nature takes no jumps’ cannot be maintained. Mutants 
are, in fact, jumps, saltus. The whole Mendelian teaching 
on heredity is based on saltus. There is evidence that 
Mendelian factors provide at least one and possibly the 
only effective source of varieties, and certainly the main 



The ^Origin ojSpecies' 301 

source of domestic varieties. As to how varieties pass into 
species we are still in the dark. 

Darwin’s view of Natural Selection as an effective 
agent of Evolution is perhaps at its weakest in dealing 
with the problem of disuse. Here he assumes the inheri¬ 
tance of acquired characters in a form hardly less crude 
than that of Lamarck. 

‘Disuse, aided sometimes by natural selection, will often tend to 
reduce an organ, when it has become useless by changed habits or 
under changed conditions of life; and we can clearly understand on 
this view the meaning of rudimentary organs. But disuse and selec¬ 
tion will generally act on each creature, when it has come to 
maturity and has to play its full part in the struggle for existence, 
and will thus have little power of acting on an organ during early 
life; hence the organ will not be much reduced or rendered rudi¬ 
mentary at this early age. The calf, for instance, has inherited 
teeth, which never cut through the gums of the upper jaw, from 
an early progenitor having well-developed teeth; and we may be¬ 
lieve, that the teeth in the mature animal were reduced, during 
successive generations, by disuse or by the tongue and palate having 
been better fitted by natural selection to browse without their aid; 
whereas in the calf, the teeth have been left untouched by selection 
or disuse, and on the principle of inheritance at corresponding ages 
have been inherited from a remote period to the present day.’ 

Where Darwin concentrates on the theory of descent 
and forgets his own particular explanation, his work rises 
to a convincing eloquence. 

‘If we admit that the geological record is imperfect in an extreme 
degree, then such facts as the record gives, support the theory of 
descent with modification. New species have come on the stage 
slowly and at successive intervals; and the amount of change, after 
equal intervals of time, is widely different in different groups. The 
extinction of species and of whole groups of species, which has 
played so conspicuous a part in the history of the organic world, 
almost inevitably follows. Neither single species nor groups of 
species reappear when the chain of ordinary generation has once 



302 Evolution 

been broken. The gradual diffusion of dominant forms, with the 
slow modification of their descendants, causes the forms of life, after 
long intervals of time, to appear as if they had changed simultane¬ 
ously throughout the world. I'he fact of the fossil remains of each 
formation being in some degree intermediate in character between 
the fossils in the formations above and below, is simply explained by 
their intermediate position in the chain of descent. I'he grand fact 
that all extinct organic beings either belong to the same system with 
recent beings, falling either into the same or into intermediate 
groups, follows from the living and the extinct being the offspring 
of common parents. 

‘lyooking to geographical distribution, if we admit that there has 
been during the long course of ages much migratioji from one part 
of the world to another, owing to former climatal and geographical 
changes and to many occasional and unknown means of dispersal, 
then we can understand, on the theory of descent with modification, 
most of the great leading facts in Distribution. We can see why 
there should be so striking a parallelism in the distribution of organic 
beings throughout space, and in their geological succession through¬ 
out time; for in both cases the beings have been connected by the 
bond of ordinary generation, and the means of modification have 
been the same. We see the full meaning of the wonderful fact, 
which must have struck every traveller, namely, that on the same 
continent, under heat and cold, on mountain and lowland, on deserts 
and marshes, most of the inhabitants within each great class arc 
plainly related; for they will generally be descendants of the same 
progenitors and early colonists. On this same principle although two 
areas may present the same physical conditions of life, we need feel 
no surprise at their inhabitants being widely different, if they have 
been for a long period completely separated from each other; for as 
the relation of organism to organism is the most important of all 
relations, and as the two areas will have received colonists from 
some third source or from each other, at various periods and in 
different proportions, the course of modification in the two areas 
will inevitably be different.’ 

We may summarize very briefly the basic criticism of 
the doctrine of Natural Selection in relation to Evolution. 



The'Origin of Species' 303 

‘Natural Selection means merely that a creature survives.’ 
As to why it survives, or whether its survival be due to 
one character more than another, and as to how it acquired 
that character, the theory gives us no information whatever. 

Darwin himself compared the action of natural selection 
to that of a man building a house from stones of all shapes. 
The shapes of these stones, he says, would be due to 
definite causes, but the uses to which the stones were put 
in building the house would not be explicable by these 
causes. The conception reveals the general weakness of 
Darwinism which treats natural selection as an active agent. 
For when a man builds a house, we have the intervention of 
a definite purpose directed towards 2l fixed end and governed 
by a dearly conceived idea. But these psychic factors have 
no relation to the causes which produced the stones, and 
cannot be compared with the action of natural selection. 

§ 4. The Reception of the Doctrine of Evolution 

The Origin of Species created a revolution in biology, 
and indeed in many other departments of thought. The 
idea that species are not constant was far from new or 
modern. But here for the first time was a careful and 
scientific work, by a cautious and painstaking investigator, 
which set forth a vast amount of evidence on the matter. 
Moreover, the book suggested a simple and apparently 
universally acting biological relationship to explain the 
process of change of form. That relationship, the struggle 
of living forms leading to natural selection by the survival 
of the fittest, is certainly far less emphasized by naturalists 
now than in the years that immediately followed the 
appearance of Darwin’s book. At the time, however, it 
was an extremely stimulating suggestion. 

In 18^2, seven years before the publication of the 
Origin, the philosopher, Herbert Spencer (1820-1903), 
had set forth doctrines of Evolution, in a work where for 



304 Evolution 

the first time that word was used to describe the idea of a 
general process of production of higher from lower forms,* 
The word Evolution was in fact seldom employed by Dar¬ 
win, but Spencer’s application of it rapidly caught on. 

Darwinism and Evolution thus came to be regarded as 
synonymous. The doctrines of Darwin, however, only 
apply and were only meant to apply in the world of life. 
Nor, even in that department are the two words inter¬ 
changeable, for Organic Evolution has frequently been 
conceived quite independently of such ‘Darwinian’ factors 
as Natural Selection or Sexual Selection. 

The works of Herbert Spencer were very widely read 
in the nineteenth century, and did much to spread the 
evolutionary view of life. The phrase ‘Survival of the 
Fittest’ was also coined by Spencer, and has caught on 
as did ‘Evolution’. 

Among English-speaking biologists Lyell and Hooker, 
who had long known Darwin’s views, at once gave assent. 
They were joined by the philosopher, Herbert Spencer, 
by T, H. Huxley, who had previously expressed opinions 
in favour of constancy of species, and by the American 
systematic botanist, Asa Gray (1810—88) of Harvard. 

The story of the rise of Darwinism has been more often 
told than any other incident in the history of science. 
Among its scientific opponents were Owen, the leading 
comparative anatomist of his day, and Louis Agassiz 
of Harvard, a very accomplished naturalist. Both were 
still bemused by Naturphilosophie, as was also von Baer, 
now in extreme old age. All opposed to evolution the 
‘idea’ or ‘type’ of Goethe and Cuvier, a metaphysical con¬ 
ception and of its nature insusceptible of demonstration. 
Owen added the suggestion that with alternation of 
generations or with a series of metamorphoses, new types 

* Lyell had used the word some twenty years earlier, in a similar, though less 
general sense. 



Reception oj the Doctrine oj Evolution 305 

might arise by disintegration of the life cycle into its 
stages. No such disintegration has been demonstrated. 

In Germany, then swept by ‘liberal’ ideas, Darwinism 
made rapid progress. Fritz Muller and Haeckel were 
its leading champions. Its ablest scientific opponent was 
Kolliker. did not deny the inconstancy of specific 
forms and he accepted evolution within the limits of 
certain wider groups. He emphasized what have since 
been recognized as the three weakest points in the 
Darwinian position:— 

(a) the absence of any experience of the formation of 
a species; 

(b) the absence of any evidence that the unions of 
different varieties (i. e. incipient species on Darwin’s 
view) are relatively more sterile than unions of the 
same variety; 

(c) the extreme rarity of true intermediate forms 
between known species, whether living or fossil. 

Kolliker and other critics of Darwin pointed out that 
the ‘chance’ element in Darwin’s scheme was but a veiled 
teleology. Natural selection had been elevated to the rank 
of a ‘cause’, and science has to deal not with causes but 
with conditions. Darwin was occupying himself with 
the ‘might’ and the ‘may be’ and not with things seen 
and proved. 

In France the reception of Darwinism was on the whole 
hostile. The influence of Cuvier was still paramount, and 
positive thinkers such as Bernard gave evolution a cold 
reception. Its advance was slow, though its ultimate 
victory fairly complete. The movement led to the revival 
of interest in Lamarck, and French transformisme^ as 
evolution was called, received a strong Lamarckian tinge. 

Apart from purely destructive criticism, there were a 
number of positive suggestions as to the direction and 
mechanism of evolution. The botanist, Nageli, was the 



3 o 6 Evolution 

most productive in this direction. Much of what he wrote 
on evolution was almost unintelligible, though certain of 
his views retain their interest. These we may enumerate. 

{a) The alteration in the same direction of the condi¬ 
tions of life in allied species (of hawkweed) produce, he 
found, no convergence of characters. Thtis change of 
environment produced ‘no useful variations’.^ 

(b) Evolution proceeds along lines controlled by an 
inner directing force. Under the name orthogenesis this 
idea of determinate evolution was adopted by several 
naturalists, notably by the American palaeontologist, 
E. D. Cope (1840—97). The position is, perhaps, tenable. 
It can only be justified, however, empirically, that is by 
the discussion of numerous examples. 

(f) Evolution does not always proceed by minute 
gradations but may take larger steps. (This had already 
been pointed out by Huxley and Kdlliker.) Nageli 
corresponded with Mendel, whose theory is based on the 
existence of such steps. Unaccountably he failed to 
realize the value of Mendel’s work. 

The whole of modern biology has been called ‘a com¬ 
mentary on the Origin of Species'. In a sense this is true. 
Biologists are now agreed that living forms correspond to 
a limited number of common stocks. For a generation in¬ 
vestigation was directed to the endeavour to trace the 
history of those stocks. The battle of evolution is now a 
stricken field. On the other hand, as to the mechanism 
and the directive forces of evolution we are still in utter 
doubt. The generation to which the Origin of Species was 
delivered followed Darwin blindly. The last decade of 
the nineteenth century ushered in a reaction (chap. xv). 
Until we see a variety pass into a new species the problem 
cannot be said to be approaching solution. 

* Nevertheless evidence has since been produced that the resemblance of some 
species to each other is secondary and may be the result of similar conditions, 



( 307 ) 


§ 5 * Evolutionary History of Living Forms 

As soon as naturalists felt equipped with an ex¬ 
planation of how the diversity of species has arisen, the 
relationship of different groups acquired a new meaning 
for them. Classificatory schemes became summaries of 
history. 

In the great Darwinistic period (1860—1900), natura¬ 
lists concentrated rather on the structure of animals and 
plants than on the workings of their bodies or on their 
habits. The reason is not far to seek. Structures, as they 
were adapted to changed needs, assumed different func- 


. L X X .0. 






Fig. 134. Peripatus capensis from Mo^hy. 


tions or different modes of performing the same function. 
The leg, modified into a wing, changed its manner of 
action. Thorns are but modified branches, bulbs are buds, 
but the functions performed by them are as distinct as are 
the functions of the trunk of the elephant from those of 
the nose of man. Yet the general direction of anatomical 
evolution in wing, thorn, bulb, and trunk are clear, though 
the details require investigation. 

With an easy way of advancing knowledge and obtain¬ 
ing distinction before them, most men, even most men of 
science, do not commonly choose the harder. Thus com¬ 
parative anatomy rather than comparative experimental 
physiology became the representative biological study. 
Even when anatomy was interpreted in embryological 
terms, the stress was still on structure. 

The literature of structural botany and zoology has be¬ 
come bulky almost beyond belief. Out of this vast effort 
have emerged definite and comparatively simple schemes 




3o8 


Evolution 


Recent 


Pliocene 


Mio-Pliocenc 


of classification. The general anatomical relationship 
within the great plant and animal groups have been deter¬ 
mined to a degree that commands sub¬ 
stantially universal consent. Early stages in 
the historical development of some of these 
forms have been reconstructed on sound 
anatomical and embryological grounds. 

Further, for many great groups there have 
been found actual living or fossil organisms 
not profoundly unlike the respective an¬ 
cestral forms which had been pictured. Thus 
naturalists had inferred the characters of the 
ancient parent stock of flowering plants, and 
forms were subsequently discovered bearing 
a remarkable resemblance to this hypo¬ 
thetical ancestral type. Again, Peripatus, a 
curious worm-like creature, regarded as a 
mollusc when first found a century ago 
(1826), was proved by anatomical examina¬ 
tion fifty years later (18 74) to have affinity with 
the insects. It bears many resemblances to 
the reconstructed common ancestor of all the 
insects, of some other groups of creatures with 
jointed limbs, and of Myriapods (Fig. 134). 
Amphioxus^ a tiny transparent animal, though 
highly specialized for a peculiar mode of 
life, reveals many points of similarity to 
the reconstructed fish-like ancestor of the 
vertebrates (pp. 475-7). Knowledge of the 
structure and development of such forms has 
cleared our ideas as to what we mean by a 
‘Flowering Plant’, an ‘Insect’, a ‘Vertebrate’. 
Long before Darwin, study of the geo- 

Fig. 135. To illustrate evolution of foot of modern horse by gradual reduction 
of digits. The horse now walks on its middle Uyc and finger (Huxley 1876). 


Miocene 




Evolution of Living Forms 309 

logical record had revealed a long succession of fossil 
beings differing from, but sometimes linked to, those now 
living. The acceptance of evolutionary views provided a 
key to the existence and nature of this series. It was occa¬ 
sionally found possible to continue a geological series right 
into modern forms, as with the extraordinarily complete 
series illustrating the evolution of the hoof of the modern 
horse (Fig. 135). Again, living forms have been found 



Fig. 136. J, Skull of Helladoiherium from the Miocene of Greece. By Skull of 
young Okapi. C, Skull of Giraffe. (All from Lankester, 1901.) 


which continue geological series believed to have come to 
an end. Such was the case with the Okapi, discovered in the 
twentieth century. This curious creature continues a geo¬ 
logical series which has branched off into the giraffe 
(Fig. 136). 

Perhaps the most striking of such revelations that 
geology has to give us is the picture of the vegetation of 
the coal measures. When they were being laid down, the 
Club-mosses and Horse-tails, now insignificant families of 
small and inconspicuous plants, formed the main part of a 
luxuriant vegetation of giant trees (pp. 276—7, Fig. 129). 

§ 6. Application of the Doctrine of Descent to Man 

There is one species whose origin raised acute contro¬ 
versy. Many ancient and early modern anatomists had 
drawn attention to the likeness of the anatomy of man with 



310 Evolution 

that of the apes. Both Goethe and the American naturalist, 
Joseph Leidy (1823-91), interpreted the separate bone in 
the upper jaw of man (p. 215) as linking him with apes. 

Darwin in the Origin of Species expressed no opinion as 
to the relationship of man to lower forms. Several of his 
supporters, however, notably Huxley and Haeckel, de¬ 
voted attention to the subject. The formal expression of 
Darwin’s views was reserved till 1871, when he issued the 
Descent of Man. Its opening passage tells that ‘Huxley 
has conclusively shown that in every visible character man 
differs less from the higher apes than these do from the 
lower members of the same order of Primates’. This was, 
however, very different from a demonstration of any inter¬ 
mediate form between man and the higher manlike apes. 

A short time before the Origin of Species there had been 
discovered remains of a species exhibiting some of the 
characters of the supposed ancestral human type. The 
long bones and part of the skull of a manlike creature 
were unearthed in 1856 in the small ravine of Neanderthal 
in Rhenish Prussia. 

The skull was misinterpreted as pathological by Vir¬ 
chow. Huxley ultimately recognized it as human, but the 
most ape-like yet found. He held that man is ‘more 
nearly allied to the higher apes than the latter are to the 
lower’. The species to which these bones belong is now 
entitled Homo Neanderthalensis.^ Remains of about fifty 
individuals of this species are now known. It is in dispute 
whether it should be treated in a separate genus Palaean- 
thropus allied to Homo. 

Since the discovery of Neanderthal man, a number of 
other species of fossil man have been discovered. On the 
other hand, several fossil species of apes approaching some¬ 
what nearer than living forms to the human stem have 

* A Neanderthal skull had been found at Gibraltar as early as 1848, but it 
had not been brought to scientific notice. 



Application of Doctrine of Descent to Man 311 

also been found. The ape-man series is now probably as 
complete as that of most comparable mammalian groups. 
About a hundred fossil individuals are known, distributed 
over some eleven species of quaternary and late tertiary 
man. The general conclusion is that the junction of man 
with the apes is farther back than was, for long, supposed. 
Most authorities place the junction in the mid-tertiary or 
even earlier. 

Evolutionary doctrine has not only been extended to 
the structure of man, but also to his habits, his language, 
his customs, his religion, his social organization, even his 
ways of thinking. Thus has arisen the modern science of 
Anthropology. Ultimately the study emerges into a con¬ 
sideration of the higher social units. It then discusses the 
social evolution of man, and develops as Sociology. An¬ 
thropology and Sociology must lean, as sciences, on the 
doctrine of descent. They have much to derive from 
modern criticism of the mechanism by which variation 
and modification is brought about. 

The extension of evolutionary doctrine to man owes a 
deep debt to the French investigator, Jacques Boucher de 
Perthes (1788—1868). He was a civil servant who devoted 
his leisure to antiquarian research. As early as 1830 he 
discovered in the gravels of the river Somme certain flints 
which he believed bore evidence of very ancient human 
workmanship. In 1846 he demonstrated the existence of 
such flints in company with the remains of elephant, 
rhinoceros, and other tropical or extinct forms. In his 
great Antiquites celtiques et antediluviennes (1847—64) he 
established the existence of man from his works in Pleis¬ 
tocene and early Quaternary times. In 1863 he clinched 
this view by discovering near Abbeville a human jaw 
associated with worked flints in a Pleistocene deposit. 

These conclusions were accepted, though with caution, 
by Lyell in his Antiquity of Man (1863). Since that time 



312 'Evolution 

the study of the works and arts of stone-age man has 
developed in parallel with the study of his physical struc¬ 
ture. The successions of Palaeolithic cultures, crafts, and 
art, and their merging into those of the Neolithic are now 
familiar. They have been equated with geological and 
geographical changes. Classic works along these lines are 
he Prehistorique (i 882) of Gabriel de Mortillet (1821-98) 
and the writings of the Abb^ Breuil (1877- )• 

§ 7. Coloration and Mimicry 

A peculiar position in the history of evolution is occu¬ 
pied by the study of the colours of animals. These are 
often protective in nature. Protective resemblance of a 
species to its background must have been known to 
hunters from the beginning. The change of coat of some 
northern animals to white in winter was known to Theo¬ 
phrastus (fourth century b.c.) and has been familiar 
through the ages. From Pliny (first century a.d.) and 
Aelian {c. a.d. 200) onward the power of the chameleon 
to alter its colour according to its surroundings has been 
frequently remarked. In the seventeenth century Redi 
(p. 433) drew attention to the peculiarities of the ‘stick 
insects’ and like forms. The green tree-frog attracted 
Vallisnieri (p. 205) in the eighteenth century. 

In the nineteenth century A. R. Wallace frequently 
commented on protective coloration and colour-changes as 
exhibited in Brazil and in the Eastern Archipelago. Pro¬ 
tective resemblance to background or to inanimate objects 
lends itself well to explanation on the basis of Natural 
Selection. Several modern naturalists have devoted them¬ 
selves to illustration of this theme. It has been worked 
out, in great detail, for instance, in connexion with the 
movement of pigment particles of bottom-living fish, such 
as plaice. The coloration of these creatures has been 
shown to adapt itself to that of their background. 



Coloration and Mimicry 313 

Such devices of concealment are manifestly helpful and 
do not entail any considerable structural modifications. It 
is remarkable that Darwin passed them over in the first 
edition of the Origin, for they would have made ideal 
illustrations of his theory. Nor did he deal with the more 
complex problem of mimicry. 

During the twentieth century the conception of the 
coloration of animals was modified by the work of an 
American artist, Abbott H. Thayer (1849—1921). He 
pointed out that in most animals the back is dark and the 
belly relatively light. This distribution of pigment may be 
explained as an adaptation to conditions of life, if an 
animal stand in a high light its lower part is in the shade. 
This is compensated by the lighter colour. On the other 
hand, the upper part is liable to more brilliant illumina¬ 
tion. This is in its turn compensated by the darker colour. 
Thus the general coloration leads to concealment. 

The simple light and shade scheme is often further 
elaborated. Many animals conspicuous in the museum 
are well concealed in nature. A classical example is the 
tiger, whose bright black and yellow banding above the 
lighter colour below fits in well with his normal sur¬ 
roundings of brilliantly illuminated high grass and reeds. 
The giraffe and the zebra are similarly coloured in a man¬ 
ner that tends to concealment. In many cases, too, a 
conspicuous mark or series of conspicuous marks upon 
the animal’s surface distracts attention from the general 
outline of the creature itself. The ‘dazzle pattern’ camou¬ 
flages its bearer. In yet other cases, as in the salamander, 
the pattern draws attention to the creature. Animals thus 
conspicuously marked are often distasteful or poisonous. 
Many brightly coloured insects are in this category. 

Coloration has always to be considered in relation to 
surroundings and cannot be understood without them. 
The Challenger naturalists found that many Crustacea 



314 Evolution 

drawn from the depths were of a brilliant scarlet. It was 
only later realized that this colour could only be perceived 
in light which includes red rays. In the depths, where 
these Crustacea dwell, the only light is that emitted by 
phosphorescent organisms. From this light, however, red 
rays are absent. There such pigmented forms would not 
be conspicuous. The explanation of the red pigment must 
therefore be sought on internal physiological grounds. 

Very special interest attaches to the problem of colora¬ 
tion and other forms of special development classed under 
the term ‘mimicry’. By mimicry is meant the deceptive 
resemblance of one species to another. The subject was 
brought to notice by Henry Walter Bates (1825—92). 
This superb self-taught naturalist left England in 1848 
with the equally self-taught A. R. Wallace on a collecting 
expedition to Brazil. Bates remained eleven years. He 
had with him both Lyell’s Principles and Darwin’s Journal. 
Before the publication of the Origin he wrote, concerning 
certain butterflies, that on their wings ‘Nature writes, as 
on a tablet, the story of the modification of species’. He 
was vastly impressed with the tropical wealth of species, 
of which he discovered more than 8,000. 

In his classic paper Contributions to the Insect Fauna of 
the Amazon Valley (1861), Bates chose as his text the 
Heliconidae, an American family of butterflies, with but 
two genera and about 150 species. 

‘A most interesting feature of the Heliconidae', he says, ‘is the 
mimetic analogies of which many species are the subject. Many 
inhabit districts tenanted by species which counterfeit them. The 
Heliconidae are the objects imitated, since all have the same family 
facies, whilst the imitating species are dissimilar to their own nearest 
allies—perverted, as it were, to produce the resemblance. This 
resemblance is so close that only after long practice can the true 
be distinguished from the counterfeit, when on the wing. 
‘Hundreds of instances of imitative resemblances could be cited. 



Coloration and Mimicry 315 

Some show a minute and palpably intentional likeness which is 
perfectly staggering. It is not difficult to divine the meaning of 
these analogies. When a Moth wears the appearance of a Wasp, 
we infer that the imitation is intended to deceive insectivorous 
animals, which persecute the Moth, but avoid the Wasp. May not 
the Heliconidc dress serve the same purpose to the Leptalis} Is it 
not probable, seeing the excessive abundance of the one species and 
the fewness of individuals of the other, that the Heliconide is free 
from the persecution to which the Leptalis is subjected ?’ \Slightly 
abbreviated.^ 

This type of resemblance has since become known as 
‘Batesian mimicry’. 

Another early writer on mimicry was the German 
naturalist, Fritz Muller (1821-97). reached his 

conclusions in Brazil. In 1879 Muller described another 
type of the phenomenon. In Batesian mimicry the mi¬ 
micked species is unpalatable or dangerous. Muller 
showed, however, that there are cases in which both 
mimicker and mimicked were unpalatable or dangerous. 

‘If two or more distasteful species be about equally common, 
resemblance brings them a nearly equal advantage. Each step to¬ 
ward resemblance is preserved by natural selection. They would 
always match each other numerically, so that finally one would not 
he able to say which has served as model.’ 

A large majority of the best and most striking cases of 
mimetic resemblance have been described from tropical 
countries. A reason for this is the vastly greater wealth in 
species of the Tropics as against temperate climes. Thus 
Bates says of butterflies ‘about 700 species are found with¬ 
in an hour’s walk of the town [of Para]. The number in 
the British Isles does not exceed 66. The whole of Europe 
supports only 321.’ The number of Brazilian species 
known has greatly increased since his day; the European 
hardly at all. 

Further, these tropical species are often very local and 



316 Evolution 

are most probably of very recent origin. ‘In tropical 
South America’, says Bates, ‘a numerous series of gaily- 
coloured butterflies and moths, of very different families, 
which occur in abundance in almost every locality, are 
found all to change their hues and markings together, as if 
by the touch of an enchanter’s wand, at every few hundred 
yards.’ Further, he remarked that ‘so close is the accord 



Fig. 137. A Central American Membracid Hetcronotus trinodosus. Looked 
at from above the animal looks like an ant. What is apparently the abdomen of 
the ant, <2, can he seen from the side to be a part of the huge overgrowth. The 
insect is concealed l^elow this and its true abdomen is seen at b. 

of some half-dozen species [of widely different genera] 
in each change, that I have seen them in large collections 
classed and named respectively as one species’ (1879). 

There are groups of animals among which almost every 
member is either imitatively or protectively formed and 
coloured. Such are the Membracidae, a large family of 
tropical bug-like creatures containing about forty genera 
and several hundred species. The bizarre shapes of these 
insects have attracted observers for over a hundred 
years. In some Membracidae the adult mimics one species 
and the larva another. A curious feature of the family is 
that the mimicking is not usually caused by any modifica¬ 
tion of the bodily shape, but by an outgrowth which has 
no apparent function save that of imitation (Fig. 137). 



Coloration and Mimicry 317 

Most cases of true mimicry have been adduced among 
insects. A few are known among serpents and birds. In 
modern times a degree of scepticism as to the interpreta¬ 
tion of mimicry has crept in. Thus Bates reports a case 
of mimicry of a bird by an insect! 

Mimicry in plants is of special interest. There are cases 
—of which the English bee-orchis is an example—in 
which a plant seems to imitate an insect. These cases have 
been a complete mystery in the past, but of late a little 
light has been shed upon them. In some cases, at least, 
it has been shown that the insect imitated is the female. 
The male is deceived and visits the flower as a female of 
his own species. 

It must be remembered that the insects are a group 
undergoing rapid modification. There are many reasons 
to believe this, notably the vast number, variety, and 
frequency of mutations, and the variety and complexity 
of social systems among insects. It may thus well be thaf 
some plants that mimic insects are mimicking extinct 
species. The ‘bee-orchis’ in its present state certainly de¬ 
rives no benefit from its mimicry, for it is always self- 
fertilized. 

Despite the enthusiasm with which Darwinian natura¬ 
lists seized on the phenomena of mimicry, difficulties arise 
in explaining it on Darwinian lines. 

Simple protective coloration can certainly often be re¬ 
garded as a pure product of the force of Natural Selection. 
The same cause may be invoked in such a group as the 
Membracidae, which exhibit as a group a tendency to ex¬ 
tensive overgrowth of a part of the body. This over¬ 
growth must take some form. It is an advantage for it 
to be imitative, and the form of the overgrowth involves 
the insect in no important physiological change (Fig. 137). 

But in the case of an insect the bodily form of which 
imitates one of a widely different group, e. g. the fly that 



318 Involution 

imitates a bee or ant, or the butterfly that imitates a wasp, 
considerable anatomical modifications are involved. No 
advantage can be claimed for the early stages of such 
mimicry, and the explanation remains one of the unsolved 
problems of biology. In general it is true to say that the 
phenomena of mimicry are little susceptible of explanation 
by known laws. The literature of the subject is peculiarly 
naive and unscientific. 

§ 8. Parasitism, Saprophytism, Symbiosis 

In the early days of evolutionary theory and in the 
course of the subsequent development of morphological 
detail, great interest was raised in certain exceptional 
modes of living. Apart from the more evident balance of 
life between plants and animals, stand those organisms 
that prey on their victims without destroying them, or 
destroy them but slowly. These are parasites. 

The term parasite is derived from a Greek word mean¬ 
ing primarily ‘mess-mate’, and conveyed originally no idea 
of reproach. It came to imply living at another’s expense, 
and finally assumed the modern sense. Parasitism in its 
biological usage signifies that an organism depends upon 
another organism for its existence. Yet all, or almost all, 
living things are to some extent dependent on other living 
things. It is thus very difficult to say where parasitism 
begins, though there is no doubt of the mode of life of the 
more specialized of parasites. 

The dependence characteristic of the parasitic state 
necessarily demands the service of living hosts. There is 
a very large group of so-called saprophytes (Greek ‘putrid 
growers’). These are organisms that live on organic 
matter, parasites, as it were, on the dead. In practice the 
term parasite has become confined to organisms which 
depend for their existence upon physical association with 
other living organisms or hosts, the relationship being 



Parasitism, Saprophytism, Symbiosis 319 

detrimental to the hosts. The work of Darwin un¬ 
doubtedly focussed attention on the subject. 

On the zoological side the most prominent workers in 
this field have been Rudolph Leuckart (1823—98) and 
Carl Theodore von Siebold (1804—85). Von Siebold was 
pursuing the subject of parasitism before Darwin, and 
even more intensively after Darwin’s publication Cirri- 
pedia (p. 511). Leuckart and von Siebold showed that 
almost every group in the animal kingdom presents para¬ 
sitic forms. Two of these have become of particular 
practical importance, the flat-worms and the protozoa. 

Many flat-worms (^rematoda and Cestodd) are frequently 
parasitic in man and other animals, and are productive 
of disease. They exhibit extreme forms of parasitic 
degeneration and go through a complicated life-history, 
often in two or more hosts of widely different species and 
of different modes of life. Similarly, the Protozoa have 
parasitic forms, which give rise to a variety of diseases of 
which Malaria, Yellow Fever, Amoebic Dysentery, and 
Syphilis are the best known. In response to the practical 
demands made by these conditions, there have arisen in 
the twentieth century the specialized sciences of ‘Helmin¬ 
thology’ (Greek helmins ,a ‘tape-worm’)and ‘Protozoology’. 
Of the latter science a basic work is that of the French 
Army Surgeon, Alphonse Laveran (1845-1922), who 
described the protozoon parasite of malarial fever in 1881. 

In the vegetable kingdom parasitism is at least as wide¬ 
spread as among animals. Pliny, in antiquity, recognized 
the mistletoe as a parasitic plant, and the first biological 
use in English of the word parasite is in relation to plants 
(1727). Even flowering plants exhibit almost every degree 
of parasitism. These vary from the occasional support 
demanded by weak-stemmed climbers such as woodbine, 
and the habit of some orchids of growing on the bark or 
crutch of a tree (epiphytism), through the incomplete parasi- 



320 'Evolution 

tism of the mistletoe, with green leaves but roots embedded 
in its host (Figs. 13 8—9), to the dodder, devoid of green 
colouring matter and dependant on its host for its carbo¬ 
hydrates as well as for its other essential food substances. 



DRAWINGS OF MISTLETOE BY MALPIGHI (1679) 

Fig. 138. A plant and two seedlings growing on a branch of an apple-tree. 

Fig. 139. Magnified section through an apple branch, showing the way that its 
tissues are penetrated by the roots of the mistletoe. 


It is a well-established biological law that unused organs 
degenerate and vanish. The parasite and the saprophyte, 
once having reached the host or the medium in which their 
life is to be matured, have no need for organs of sense, of 








-Spa the 


Parasitism., Saprophytism, Symbiosis 321 

movement or even, in many cases, of digestion. These 
disappear. 

That this disappearance is not related to parasitism as 
such has now become fairly evident. Deterioration or 
simplification of the structure of organisms, whether of 
plants or animals, 
may take place pure- 
ly as the result of 

the character of the I /Tm 

medium in which Fronds 

they live and without Fruit 

any degree of para¬ 
sitism, ofsymbiosis or Malc.>vyr:i 
of fixation. Thus the U-Roots 

cave-living Axolotl, /fife H/ 

which is a relative of ) 

the newt, remains v \ / i ' 

throughout life a Male-^X 
blind, unpigmented 

tadpole. Again, the b a 

duckweeds, which ] 

dwell entirely in u 

water, have become Fig. 140. J, Entire plant duckweed Lemna 

so extremely simpli- inflorescence of duckweed 

^ A polxrhtz^. Both from Arber after Hei^clmaier 

ned that they are not (1868-71). 

distinguishable as 

monocotyledons. Lemna^ for instance, has attained world¬ 
wide distribution, but has lost all distinctness of shoot 
and flower, is devoid of most of the structures of a higher 
plant. Duckweeds very rarely produce flowers, which are 
always of the simplest type (Fig. 140). 

Among the most significant of all plants for the general 
balance of life is the lowly and probably degenerate group 
of organisms known as bacteria. 

The study of the lower fungi and especially of the 


remains 


Male 

Fiowen 


Flower 


Fig. 140. A, Entire plant duckweed Lemna 
gibba. B, Inflorescence of duckweed Spirodela 
polyrhiz^a. Both from Arber after Hej^clmaier 
(1868-71). 


V 



322 ’Evolution 

bacteria was initiated as a separate science by Ferdinand 
Cohn (1828—98) of Breslau, a pupil of Johannes Muller. 
Cohn described a large number of species of fungi para¬ 
sitic on plants. Their differentiation and life-history has 
since become a matter of great economic importance in 
connexion with agriculture. Probably no department of 
biology is now more productive of literature than is plant 
pathology which Cohn initiated. 

But not only ia disease has the study of fungi and their 
plant hosts acquired a new importance. During the last 
two decades of the nineteenth century it became evident 
that the formation of mould or humus was itself largely the 
work of fungi. Schleiden had demonstrated that the roots 
of certain plants are always infected with fungi (1842), 
and A. B. Frank (1839-1900) showed further (1885) 
that in some higher plants germination is impossible with¬ 
out the aid of fungus companions. The relationship is of 
great biological significance. To the fungi which are thus 
necessary for germination Frank gavethenameA^cc/rr^/2<?. 

Experimental evidence has shown that infection by 
bacteria of the alimentary canal of the new-born higher 
animals is necessary to life just as Mycorrhiza is essential to 
seedling plants. The matter, however, needs reinvestiga¬ 
tion in the light of the modern knowledge of vitamins. 

The association of two types of living things thus 
mutually beneficial to each has been termed symbiosis 
(Greek = ‘living together’). Such partnerships are of very 
common occurrence throughout the animal and vegetable 
kingdom. There are even vegetable forms, such as lichens, 
in which, as was first shown by the German botanist 
H. A. de Bary (1831—88), neither partner can exist with¬ 
out the other (18 60). There are animals that have in their 
tissues numbers of green unicellular plants which thrive 
on their waste products, while the animal itself feeds upon 
the compounds elaborated by the plants within it. Such 



Parasitism^ Saprophytism^ Symbiosis 323 

are certain flat-worms which are symbiotic with algae 
{Convoluta Roscoffensis^ 1891). There are many other 
associations of animals and plants of less intimate char¬ 
acter. The study of the wider problems of symbiosis 
comes within the department of Ecology (pp. 278-9). 

A particularly interesting aspect of Ecology is that 
which looks upon the entities that we call organisms as 
symbiotic colonies of different types of being. Thus, for 
example, the wood-eating termites or white ants cannot 
digest the cellulose of the fibres that they consume. This 
is done for them by certain flagellate protozoa which live 
in their intestines. The termite consumes the products 
of activity of these protozoa. Thus the creature called 
a white ant is really a colony of diverse living entities. 
Similarly man depends on organisms for certain of the 
processes which go on in his alimentary canal. The 
creature that we call a ‘man’ is a colony of which innu¬ 
merable bacteria are no less necessary—though more 
replaceable—members than the sapient being that writes 
about them. This ecological theme opens out great vistas 
of development in which organisms can be considered in 
fundamental relation to their living environment. 

The subject of evolution may be pursued into many 
such paths as these. But we must remember that while 
evolution illuminates them, they do not illumine evolution. 
The general position, after seventy years of research, may 
be thus summed up. Evolution is universally accepted 
as a general description of the history of organic forms. 
So far Darwin has completely conquered. When we come 
to the mechanism by which evolution acts, we have made 
little progress. The mechanism that Darwin himself 
suggested has been almost universally rejected—at least 
in the form in which he propounded it. Such broken light 
as is being thrown on the matter is coming from the study 
of sciences of which he had never heard (chap, ix, xiv, xv). 




Fig. 141. CHARLES DARWIN, 1809-82. 

From a painting by W. iV, Ouless in 1875. 




PART III. EMERGENCE OF MAIN 
THEMES OF CONTEMPORARY BIOLOGY 

IX 

CELL AND ORGANISM 

§ I. First Emergence of Cell Doctrine 

T he Latin word cella means ‘a small room'. It is still 
so used in such phrases as a ‘hermit’s cell’ or a 
‘prisoner’s cell’. The Latins applied the same word to 
the cells of a honeycomb. Robert Hooke in his Micro- 
graphia (1665) likened the structure of cork to honey¬ 
comb, describing it as composed of cellulae. He was 
examining the thickened walls of dead cells. Moreover, 
he perceived that the surface of living plants, when 
magnified, appears as broken up into similar little divi¬ 
sions. Here he was looking at the walls of living cells, 
though he failed to recognize their nature (Figs. 142-3). 

A little later, Malpighi, examining sections of plants, 
found them made up of little bodies closely applied to¬ 
gether, each surrounded by a definite wall (Figs. 77-9). 
Such a body he named utriculus (diminutive of uterus^. 
Leeuwenhoek, too, frequently figured cells in both plant 
and animal tissues. He formed no clear conception of their 
real nature. 

Grew observed similar structures. He spoke of the 
structures as cells or bladders. He noticed that in the 
younger parts the cells were juicy, had thin walls, and were 
closely applied. Such parts he called parenchymatous and 
rightly regarded as most actively growing (Figs. 83-4). 
Grew’s word parenchyma (Greek ‘poured in beside’) is an 
ancient term used by the Alexandrian anatomist, Erasi- 
stratus, and still current (pp. 54-5). 

At first the parenchyma seemed crystalline to Grew. 



326 Cell and Organism 

He soon realized that it is more complex. ‘Next to the 
Cuticle (of the bean),’ he says, ‘we come to the Parenchyma. 
I call it parenchyma not that we are so meanly to conceive 
of it as if it were a meer concreted Juyce. For it is a body 
very curiously organiz’d’ {Anatomy of Plants^ 1682). 



I4i '43 


Fig. 142. Magnified outlines of cell-walls on the cut surface of cork, from 

Hooke (1665). 

Fig. 143. Lower surface of leaf of stinging-nettle, from Hooke (1665). The 
outlines of the cells are seen. Here and there along the veins FF arc pointed 
spikes, each of which is set on a flexible base BB. I'hese are the stinging elements. 
There are also other hair-like spikes DD which have not this peculiar structure. 

He went farther and reached a correct view of the origin 
of the vessels. Thus: ‘One single Row or File of Bladders 
(i. e. cells) evenly and perpendicularly piled may some¬ 
times . .. all regularly break one into another and so make 
one continued Cavity.' 

After Leeuwenhoek’s death (1723) little further pro¬ 
gress was made until the nineteenth century. Several 
observers, however, concluded that fat consists essentially 
of masses of ‘cells’, each enormously distended by a drop 
of oil. Now fat had been regarded as ‘non-parenchyma- 






















First Emergence of Cell Doctrine 327 

tous’. This view, therefore, extended the vague cell idea 
beyond the parenchymatous structures. 

Just at the dawn of the nineteenth century the French 
investigator, M. F. X. Bichat (1771-1802), perceived that 
the different bodies and parts may be analysed into certain 
elements of specific appearance and texture. Of these 
he distinguished twenty-one. He likened the structure 
of the body to a woven fabric. His word was ttssu^ an old 
term for a particular kind of rich cloth. 

Bichat, who was a hasty worker and writer, did not use 
the microscope. Early death prevented him from further 
developing the knowledge of the tissues. His work was, 
however, continued by others, and the special study of 
the minute structure of the tissues came to be called 
histology. This term, was introduced by Owen (1844). 
It is really derived from tissue^ for ‘histology^ is formed 
from a Greek word which means ‘something woven\ 

During the seventeenth, eighteenth, and early nine¬ 
teenth centuries knowledge was accumulating of those 
beings whose bodies, as we now know, consist of but one 
cell. Vorticella had been described in 1677, Paramecium 
in 1702, Amoeba in 1755. Several works dealing with the 
organisms of infusions and with other microscopic plants 
and animals had appeared. Such organisms were called 
Infusoria, 

These ‘Infusoria’ did not, however, correspond with 
the group of unicellular creatures to which biologists 
came later to attach that name. Included in the older 
‘Infusoria’ were bacteria and algae as well as small worms, 
rotifers, and many other multicellular forms. This was 
the case, for instance, in the posthumous Animalcula 
infusoria fluviatilia et marina (Copenhagen, 1786) of Otto 
Frederik Muller (p. 258). Moreover, so little was as yet 
realized of the true nature of the Foraminifera that 
Globigerina^ so vastly abundant in northern seas (p. 261), 



328 Cell ajid Organism 

was described in 1826 and later as having affinities with 
the nautilus! Contemporary accounts ascribed a variety 
of imaginary organs to the Infusoria. 

No proper appreciation of the nature of all these forms 
could be made until the general recognition of the higher 
animals as cell aggregates. That view had, in fact, been 
set forth by a naturalist to whose genius biology owes 
more than is sometimes allowed. Oken (pp. 217-19) \nDie 
Zeugung ('^Cieneration’, 1805) enunciated the doctrine 
with considerable clarity: 

‘All organic beings’, he wrote, ‘originate from and consist of ve¬ 
sicles or cells. 1 hesc, when detached and regarded in their original 
process of production, are the infusorial mass or Urschleim whence 
all larger organisms fashion themselves or arc evolved. I'heir 
production is therefore nothing else than a regular agglomeration 
of Infusoria —not, of course, of species already elaborated or perfect, 
but of mucous vesicles which by their union or combination, first 
form themselves into particular species.’ 

Three words in this passage need some commentary. 
Infusoria^ in the terminology of the day, included a great 
many organisms that were not unicellular. Oken, how¬ 
ever, is clearly using the word as nearly equivalent to 
independent organisms consisting of but one cell. By 
Urschleim means something akin to what we mean by 
‘protoplasm', a word not yet invented. By mucous vesicles 
he means living cells. Oken, in fact, was reaching out to 
a conception both of protoplasm and of cell.* 

The passage is an illustration of an interesting feature 
in the history of science. We often encounter, in works of 

* I'he recognition of the Infusoria as a special unicellular group was made 
by Dujardin in 1841. Siebold in 1845 included in his Infusoria both Ciliata and 
Tlagellata. The limits of the group were indicated in 1880 by W. Saville Kent 
in the title of his Manual of the Infusoria including a description of all hntrvon 
flagellate^ Ciliate and Tentaculiferous Protozoa. The first and last class were 
removed by Biitschli in 1887, and the Infusoria thus became equivalent to the 
modern Ciliata, 



First Emergence of Cell Doctrine 329 

exceptional ability, the enunciation of truths that are 
beyond the comprehension of their author. The presenta¬ 
tion of premature views is naturally liable to be confused. 
The vocabulary of an age reflects the interests and beliefs 
of that age. The character of the scientific ideas is 
reflected in the character of contemporary terminology. 
With an inevitably changing vocabulary, we must beware 
of reading into words used in older works meanings that 
are too modern for such connotation. Yet there are 
writers with whom such caution may at times be misplaced. 
Oken can and does use the word cell in the modern sense. 
His works were widely read by his contemporaries, and it 
is more than probable that he inseminated the minds of 
the recognized founders of the cell doctrine. 

A somewhat similar course can be traced in the know¬ 
ledge of certain parts of the cell, and notably of the 
nucleus. The nuclei in the blood-corpuscles of fish had 
been depicted by Leeuwenhoek and by several observers in 
the eighteenth century. In 1823, in a drawing illustrating 
Hunter’s specimens, the artist, Franz Bauer (1758—1840), 
produced figures of these corpuscles. The descriptive 
legend tells that they ‘show the nucleus'. This is, perhaps, 
the first use of the word nucleus in such a connexion. 

In 1831, as a result of his Australian experiences, 
Robert Brown (pp. 237-41) undertook a special study of 
the Asclepiadaceae. These dicotyledonous plants, many of 
Australian origin, are allied to our periwinkles. They 
have, however, a mode of fertilization recalling that of 
the monocotyledonous Orchids, a group in which Brown 
was taking special interest. Brown discerned and figured 
nuclei in the surface layers of cells both in Asclepiadaceae 
and in Orchids. He realized that the nucleus was a regular 
feature of plant-cells, and his use of the word normalized 
it into biological nomenclature. 

Between 1833 and 1838 several investigators described 



330 Cell and Organism 

the cells of various vegetable and animal tissues. Notably 
in 1835 Purkinje (pp. 336—7) drew attention to the micro¬ 
scopic structure of the skin of animals, especially in the 
embryonic state. He pointed out that it was composed of 
packed masses of ‘cellulae’ which he compared to the 
parenchymatous tissue of plants (pp. 32^—6). 

At this time there was working in Berlin C. G. Ehren- 
berg (1795-1876), an old travelling companion of Hum¬ 
boldt (p. 269). Ehrenberg was interested in minute life 
and had the best microscopes at his disposal. He investi¬ 
gated many microscopic forms and watched organisms, 
which we now know to be unicellular, digesting food and 
discharging undigested residue. He was wrong in his 
interpretation of the nature of these organisms, to which 
he ascribed many organs which they do not possess, but 
his finely illustrated writings drew much attention to them. 
His Die Infusionsthierchen ah vollkommene Organismen 
(‘Infusorial animalcules as complete organisms,’ 1838) 
was contemporary with the epoch-making papers of 
Schleiden and Schwann. 

§2. Schleiden (1804-81) and Plant Cells (1838) 

M. J. Schleiden, who began life as a lawyer, was for 
many years professor of botany at Jena, where Oken’s 
most active years had been passed. Despite his great 
ability and originality, an impetuous temper and an 
arrogant character led Schleiden into many errors. He 
had a bias against the dry systematization into which 
botany had fallen—the mere naming, describing, and 
arranging of plants, and the search for new species. To 
the microscopical analysis of structure and growth, on 
the other hand, he eagerly applied himself. 

Schleiden raised this matter in 1838 in his historic paper 
in Muller’s Archiv fUr Anatomie und Physiologie with the 
title ‘On phytogenesis’ (Greek, ‘plant origin’). Schleiden 



Schleiden and Plant Cells {1838) 331 

seized on the idea of the cell as the essential unit of the 
living organism. 

‘There have been many endeavours’, he wrote, ‘to establish 
analogies between animals and plants. All have failed since the idea 
of individual, as used for animals, is inapplicable to plants. Only 
in the lowest plants, in some Algae and Fungi^ for instance, which 
consist of but a single cell, have we an individual in the animal sense. 
Plants, developed in any higher degree, are aggregates of fully indivi¬ 
dualized, independent, separate beings, namely the cells themselves. 

‘Each cell leads a double life; one independent, pertaining to its own 
development alone; the other incidental, as an integral part of a 
plant. I'he vital process of the individual cells, however, form the 
first indispensable and fundamental basis for both vegetable physio¬ 
logy and comparative physiology in general. Thus the primary 
question is, what is the origin of this peculiar little organism^ the 
cellV [Abridged,] 

Schleiden then develops Brown’s views on the nucleus. 
‘Robert Brown’, he says, ‘with his comprehensive native genius, 
first realized the importance of a phenomenon which, though 
previously observed, had remained neglected. In many cells in the 
outer layers of Orchids he found an opaque spot, named by him 
the nucleus of the cell. He traced this phenomenon in the earlier 
stages of the pollen-cells, in the young ovulum, and in the tissues of 
the stigma. The constant presence of this nucleus in the cells of 
very young embryos struck me also. Consideration of the various 
modes of its occurrence led to the thought that it must hold some 
close relation to the development of the cell itself.’ 

From the cell—with its essential element the nucleus— 
Schleiden turned to a consideration of its origin. Here he 
blundered, thinking that cells arise by budding from the 
surface of the nucleus. Certain other activities of the cell, 
however, Schleiden observed with great accuracy. Notably 
he described the active movement of the cell substance, 
known now as ‘protoplasmic streaming’, in the tissues of 
plants (Fig. 147). This also had been observed by Brown 
(p. 240). 



332 Cell and Organism 

% 3. Schwann (181 o~8 2) and Animal Cells (1839) 

Theodor Schwann was a pupil of Johannes Muller. 
He was a simple-minded, pious man who showed a genius 
for research in several departments (pp. 436-7). His 
classic, Mikroskopische Untersuchungen iiber die Veherein- 
stimmung in der Struktur und dem Wachstum der Thiere 
und Pflanzen (‘Microscopical researches on the similarity 
in structure and growth of animals and plants,’ 1839) is 
more searching than the work of Schleiden, It is mainly 
devoted to the investigation of the elementary structure 
of animal tissues which are more difficult of observation 
than those of plants. 

Schwann opens with discussion of cartilage, in which 
cell outlines are observed more easily than in most tissues. 
Of cartilages he says that— 

‘the most important phenomena of their structure and development 
accord with corresponding processes in plants. These tissues 
originate from cells, which correspond in every respect to those of 
vegetables. During development, also, these cells manifest pheno¬ 
mena analogous to those of plants. T he great barrier between 
the animal and vegetable kingdoms, viz. diversity of ultimate 
structure, thus vanishes. Cells, cell-membrane, cell-contents, nuclei, 
in the former are analogous to the parts with similar names in 
plants. Fundamentally, the form of the cell is that of a round vesicle, 
but flattening of cells against one another, the presence of inter¬ 
cellular substance between them in greater or less quantity, and 
lastly, thickening of cell-walls, have all been observed.’ [Abridged,^ 

Schwann extends the discussion to the ovum or egg 
which is the beginning of the animal body. In some 
animals, as the hen, the egg is very large, being distended 
with food-substance—the yolk—and surrounded by a 
layer of protective albumen. In other eggs, as of the frog, 
the amount of yolk and albumen is much less. In yet 
others, yolk and albumen are reduced to a minimum, 



Schwann and Animal Cells {i83g) 333 

as in the microscopic egg of mammals, then recently dis¬ 
covered by von Baer (1828, pp. 465-6). Yet, as Schwann 
suggests, all these different types of egg are essentially 
cells. The egg may be enormously distended, but never- 



Fic;. 144. Drawings by Theodor Schwann to illustrate the nature and origin 
of animal cells. All are highly magnified. 

A, The first step in the origin of cartilage from cellular tissues. At the lower 
part the young cells are without cell-w’alls. In the upper part they have formed 
w'alls and are beginning to secrete cartilaginous substance. Nuclei and nucleoli 
are clearly visible. B shows a piece of rnaturer cartilage, in which the cells are 
einlx’dded in a mass of cartilaginous material. C, D, and E, Pigment cells, 
such as are characteristic of the frog. In the lowest cell, which is contracted, the 
nucleus is concealed by the pignjent. The upper two are more expanded and in 
them nuclei can be seen. F, G, Young cells from a developing feather. T'hese 
cells may enlarge, secrete hard walls, and form the fine spongy tissue of the inner 
part of the shaft of the feather (H), or the cells may elongate, the protoplasm 
become granular, and finally break up into fibres [J-M). These form the tough 
fibrous matter of the outer part of the shaft of the feather. In either case the 
nucleus disappears and the cell dies. F-M show how structures of very diverse 
form can he differentiated from cells of the same type. 

theless the essential cell-elements of nucleus, cell-mem¬ 
brane, &c., are clearly traceable in it. 

Further, the development of the egg into the young 
animal proceeds by division of the egg cell. This pheno¬ 
menon is particularly evident in the earliest stages where the 
act of cell division is now usually referred to as ‘segmenta- 



334 Organism 

tion’. This had been observed in invertebrates by Schwann’s 
contemporaries, Siebold and Sars, in 1837. In 1838 
segmentation was described in the mammalian ovum. 
Schwann himself saw the process in the hen’s egg (18 3 9) and 
treated it as a normal part of embryonic development. Soon 
after (1841) it was seen in the frog’s egg, which has since 
become one of the classical objects for its investigation.^ 

From the egg, which is thus essentially a ‘germ-cell’, 
Schwann proceeds to investigate the adult tissues. His 
treatment of these passes at once far beyond that of 
Bichat. Of the tissues he distinguishes five classes on 
a cellular basis: 

(rt) Tissues in which the cells are independent, isolated, 
and separate. Such is the blood. 

{V) Tissues in which the cells are independent but 
pressed together. Such is the skin. 

(f) Tissues in which the cells have well-developed walls 
that have coalesced to a greater or less degree. 
Such are cartilage, teeth, and bones. 

(if) Tissues in which the cells are elongated into fibres. 
Such are tendons, ligaments, and fibrous tissue. 

(e) Tissues which Schwann regarded as ‘generated by 
the coalescence of the walls and cavities of cells’. 
Here he included muscles and nerves. 

Schwann now passed to a general statement of his 
belief as to the cellular origin and structure of animals 
and plants. His conclusion may be expressed thus: 

{a) The entire animal or plant is composed either of 
cells or of substances thrown off by cells. 

(^) The cells have a life that is to some extent their own. 

(f) This individual life of all the cells is subject to that 
of the organism as a whole. 

This general attitude is still valid. 

' Segmentation had lieen observed in the frog’s egg by several early workers, 
Swammerdam among them. 



Schwann and Animal Cells {1839) 335 

‘The question as to the fundamental power of organized bodies’, 
wrote Schwann, ‘resolves itself into that of the individual cells. We 
must consider the general phenomena to discover what powers exist 
in the cells to explain them. These phenomena may be arranged in 
two natural groups. First, those which relate to the combination 
of the molecules to form a cell. These may be called plastic 
phenomena. Second, those which result from chemical changes 
either in the component particles of the cell itself, or in the sur¬ 
rounding cytohlasterna. These may be called metaholic phenomena.’ 

Two words here which Schwann himself invented 
require explanation. 

Cytoblastema means the substance from which the ‘cyto- 
blast’ or nucleus was supposed to be derived, that is to say 
the protoplasm. The word protoplasm (pp. 336—7) has now 
replaced it. The earlier term was, however, very useful 
in clarifying biological ideas and has had an interesting 
history. 

Metabolic is an adjective which has a noun metabolism. 
It means, etymologically, ‘liable to change’. The changes 
which it indicates are chemical and are those specially 
associated with life. 

The changes which we call metabolic are ceaseless in 
living things. The processes of life involve the constant 
breaking down of complex substances— katabolism. The 
continuance of life involves their constant upbuilding— 
anabolism. These two events, which are related in the most 
intimate fashion, we still describe as metabolism. The idea 
which it represents is of very great biological importance. 
(The words anabolism and katabolism were not used by 
Schwann.) 

§ 4. Extension of the Cell Doctrine in the Plant Kingdom 

Schleiden fastened on the cell theory the false idea that 
new cells were derived by budding from the nucleus, 
which he therefore called the cytoblast (i.e. cell-bud). The 



336 Cell and Organism 

error was left uncorrected by Schwann. Difficulties soon 
arose. 

Karl Nageli (1817-91), a versatile botanist who made 
contributions to several departments of biological thought, 
set himself to throw light on the origin of cells. He made 
microscopic examinations of cell-formation during the 
reproductive process and also at the growing points of 
plants. His researches were pursued upon a great variety 
of forms. The phenomena of cell-division, he found, were 
most easily seen in the lower Algae. In them the movement 
and behaviour of the living and transparent cell-substance 
could be watched. He soon saw reason to abandon the 
view that the nucleus buds off new cells (1842—6). 

Further investigations on the subject were carried on 
by Flugo von Mohl (1805—72), professor of botany at 
Tubingen. He pointed out that the part of the vegetable 
cell just within the cell-membrane must be distinguished 
from the watery sap that occupies the centre. To this 
outer granular mucilaginous material he gave the name 
protoplasm (i 846). The word has entered the general bio¬ 
logical vocabulary. It indicates that part of the cell-sub- 
stance which can alone, in proper sense, be said to be alive. 
In many cells the protoplasm is in constant movement. 

Protoplasm means etymologically ‘first formed'. Ancient 
theological writers designated Adam, the first created 
man, as ‘protoplast'. The Bohemian naturalist, Johannes 
Evangelista Purkinje (1787—1869, p. 330), who had 
received a theological training, used the word in a com¬ 
munication of 1839 On the analogies in the structural 
elements of animals and plants, Felix Dujardin (1801 — 
62) of Toulouse, a most acute and penetrating observer, 
entered in 1835 tipon a critical examination of the relation¬ 
ship of certain protozoa. He used the terms ‘sarcode' for 
protoplasm, and described many of its properties. It was 
von Mohl, however, who gave currency both to the word 



Cell Doctrine in the Plant Kingdom 337 

protoplasm and to the idea which it connotes. A series 
of very important and influential articles by him on 
the vegetable cell brought order into current views on 
the subject. 

In the years that immediately followed, further impor¬ 
tant advances in the knowledge of the cell were made by 
Nageli. By means of chemical examination he proved that 
protoplasm contains nitrogenous matter. He showed that 
in this it differs from certain other constituents of the 
cell, notably the cell-wall and the stored starch. He thus 
added a most significant factor to the conception of 
protoplasm. 

§ 5. The Protozoa in Relation to the Cell Doctrine 

While Schleiden and Schwann, Nageli and Mohl were 
elaborating the conception of the cell, Dujardin was in¬ 
vestigating the old group ‘Infusoria' (1835-41). He 
realized that it contained many unrelated forms, rotifers, 
worms, various algae, &c. The entire body substance 
of the remaining ‘Infusoria' was, he noted, capable of 
contraction, movement, digestion, and other vital processes. 
The surfaces of the bodies of these Infusoria were, he 
observed, more or less clothed with minute movable hair¬ 
like processes or ‘cilia’. These, by their movement, gave 
the organisms their power of progression. Dujardin saw, 
too, that the relatively ‘structureless’ character of the bodies 
of these creatures was in contrast to those of higher animals. 

Several investigators were now reaching out to the 
conception of the Protozoa as organisms consisting each 
of but a single cell. It was Carl Theodor von Siebold 
(1804—84) who gave formal expression to this view in 
his text-book of comparative anatomy of 1845. doing 
so he stressed cilia as the instruments by which many 
Protozoa are able to move. He drew attention also to the 
presence and action of cilia in the organs of higher 



338 Cell and Organism 

animals. In these, however, the ciliated cells being fixed, 
the movements of the cilia, instead of moving the cells, 
have a current-producing action. Twenty years previously 
Purkinje had seen cilia in vertebrates. At that date he 
was unable to express their movement as a form of cellular 
activity. This was now possible to von Siebold (1861). 
The cellular theme was rounded off in the same year by 
the comparative anatomist, Gegenbaur (p. 473), who 
showed, in supplement to Schwann (p. 334), that the eggs 
of vertebrates are to be regarded as cells. 

The synthesis in the ideas of protoplasm, protozoa, and 
egg-cell was made by Max Schultze (1825—74) who suc¬ 
ceeded Helmholtz as professor of anatomy at Bonn. He 
devoted himself to histology, which he studied in a wide 
range of animals. In 1861 he defined the cell as ‘a lump 
of nucleated protoplasm’. His investigations extend to 
plants and to protozoa. In 1863 he introduced the con¬ 
ception of protoplasm as ‘the physical basis of life’. He 
showed that it presents essential physiological and struc¬ 
tural similarities in plants and animals, in lower and in 
higher forms, in all tissues wherever encountered. 

A very important series of systematic advances, in¬ 
volving the conception of the cell, were made by Haeckel 
(pp. 483-4). Perceiving the difficulty of separating the 
animal from the plant kingdoms he introduced a third and 
coequal group, the Protista (1866). The division has not 
proved to be tenable (p. 198), but the conception was useful 
in drawing attention to the great similarity of lowly animals 
and plants. Later Haeckel separated the sponges from 
the protozoa (1869). Extremely important was his clear 
expression of the great generalization that the animal 
kingdom is to be divided into unicellular and multi¬ 
cellular organisms, ‘protozoa’ and ‘metazoa’. This formed 
an integral part of Haeckel’s Studien zur Gastraea 
(1873-84, Fig. 168). 



( 339 ) 


§ 6. Extension of the Cell Doctrine in the Animal Kingdom 

The general interpretation of the tissues on a cellular 
basis in a large number of animal forms was especially 
the task of the Swiss, Albrecht Kolliker (i 817—1905). He 
was a pupil of Oken, Johannes Muller, and Henle, and 
for many years a professor at Wurzburg. 

Kolliker happily initiated his work by applying 
Schwann’s theory to the embryonic development of 
animals (pp. 332-3). He treated the ovum as a single cell 
and the process of development as the result of cell-division 
(1844). The theme was further developed by Siebold 
(1849) Remak (1852). Kolliker did an immense 
amount of good microscopical work and established histo¬ 
logy as a separate discipline. He wrote the first text-book 
on the subject (1852). Nine years later he produced a 
model text-book of embryology. 

The discoveries made by Kolliker in his chosen depart¬ 
ment are innumerable and his work has seldom needed 
correction. We note his account of the essential cellular 
nature of the non-voluntary muscles and his demonstra¬ 
tion that nerve-fibres are no more than elongated pro¬ 
cesses of cells, the bodies of which are either in the central 
nervous system or in ganglia. The division of the nuclei 
during the process of segmentation of the ovum, on which 
Kslliker laid much stress, was first adequately observed 
by his colleagues, Leydig (1848) and Remak (1852). 
Kolliker regarded the nucleus as of especial importance as 
the transmitter of hereditary characters. His views on 
this matter, though seldom quoted, have been followed 
by almost all later workers on the subject. K 5 lliker took 
much interest in the problems of heredity and variation. 
He had not heard of Mendel’s work, but he held the view 
that alteration in the characters of races takes place not 



340 Cell and Organism 

gradually but by means of sudden and spontaneous 
changes, thus preceding De Vries. 

Even more influential than Kolliker was Rudolf Virchow 
(1821—1902). He was for many years a professor at 
Berlin, and a prominent liberal alike in academic and in 
political matters. Virchow’s liberal views found vent in 
the Archiv fiir Pathologic which he edited for fifty-five 
years. It was nominally devoted to the study of disease. 
But the test he applied was not so much whether an article 
referred to pathology as whether it was an important 
contribution to knowledge. Thus it contains a great 
variety of learning. Articles on oriental languages, on 
comparative anatomy and physiology, on anthropology, 
on medieval translations from Greek and Arabic, are inter¬ 
spersed between accounts of the histology of tumours, and 
on the infectious character of fever. 

Virchow’s main additions to biological thought are in 
his great Cellular Pathologic (1858). He analysed disease 
and diseased tissues from the point of view of cell-forma¬ 
tion and cell-structure, much as Kolliker had analysed 
normal tissues. There are departments of pathology that 
Virchow explored so well that they have hardly been 
extended since his day. He set in motion the now familiar 
idea that the body may be regarded ‘as a state in which 
every cell is a citizen’. Disease is a civil war, ‘a conflict 
of citizens brought about by the action of external forces’. 

In the Cellular Pathologic Virchow says: 

‘Where a cell arises, there a cell must have been before, even as an 
animal can come from nothing but an animal, a plant from nothing 
but a plant. Thus in the whole series of living things there rules 
an eternal law of continuous development. There is no discon¬ 
tinuity nor can any developed tissue be traced back to anything but 
a cell.’ 

Virchow crystallized the matter in his famous aphorism, 
Omnis cellula e cellula (‘Every cell from a cell’), to be 



Cell Doctrine in the Animal Kingdom 341 

placed beside Omne vivum ex ovo (‘Every living thing from 
an egg’, Siebold’s reading of Harvey, see p. 459), and 
Omne vivum e vivo (‘Every living thing from a living 
thing’, Pasteur, pp. 439—42). These are three of the widest 
generalizations to which biology has yet attained. They 
were all reached within the ten years around the middle 
of the nineteenth century. 

Since Virchow and Kolliker, the study of the intimate 
structure of cells as distinguished from the tissues has 
become a separate and independent science. Cytology, It 
may be said to emerge into independence with the appear¬ 
ance of O. Hertwig’s Zelle und Gewebe (‘Cell and Tissue’) 
in 1893. Cytology must be distinguished from Histology 
or the study of association of cells in tissues. The study 
of cell-division has become peculiarly important in relation 
to problems of heredity (chap. xv). 

§ 7. Nuclear Phenomena of Cell Division 

After the abandonment of Schleiden’s theory that new 
cells were budded off by the nucleus, it became generally 
held that the nucleus disappears during cell-division to 
reappear in the daughter cells. This was at first the view 
of Kolliker. In the seventies new methods of staining 
microscopic preparations were introduced. These soon 
revealed that the seeming disappearance of the nucleus 
during division was illusory. It was due to certain pro¬ 
found transformations of the nuclear substance. 

The elucidation of these changes has been the work of 
a great number of observers. Eduard Strasburger (i 844- 
1912), professor ofbotany at Bonn, a pupilof Meckel, drew 
attention to the subject by his Zellbtldung und Zelltheilung 
(‘Cell-formation and Cell-division’, editions from 1875 
onwards). He described with great clearness the complex 
and important processes involved in division of plant cells. 

The pioneer work for animals was performed by 



342 Cell and Organism 

Walther Flemming (i 843—1915) of Prague and Kiel. He, 
more than any other, initiated cytology as a special science. 
Much of his best work appeared in his Zellsubstanz, Kern, 
und Zelltheiling (‘Cell-substance, nucleus, and cell- 
division’, 1882). 

Cell-division, as worked out by Strasburger and 
Flemming, may be reduced to a schematic form. The 
division of a cell is led and controlled by the nucleus. In 
a few cases the process is simple and ‘direct’ by a mere 
constriction, first of the nucleus and then of the cell as 
a whole. In most cases it is ‘indirect’. The indirect process 
or mitosis is essentially the same in both plants and animals. 
(Fig. 145). 

In an ordinary resting nucleus there can be distin¬ 
guished a fine network of material that stains deeply with 
basic aniline dyes. This is known as As division 

approaches, the chromatin becomes arranged into a long 
thread, the spireme, that is more or less regular, continuous 
and spiral. The spireme breaks up into a series of separate 
filaments, the chromosomes. Early in the twentieth century 
it had become apparent that the number of these is charac¬ 
teristic for each species. It ranges from two to over two 
hundred. In man it is forty-eight. Despite appearances, 
there is reason to believe that the chromosomes retain 
their identity throughout the life of the cell. 

By the time that the chromosomes are distinguishable 
as separate bodies, other changes have occurred. The 
delicate membrane which normally surrounds the nucleus 
has disappeared. On either side of the nucleus a minute 
body or centrosome has become apparent, ^ while from each 
centrosome there radiate, especially toward the nucleus, 
a series of lines forming a star-like aster. 

The two asters extend until they meet around the 
equator of the nucleus. There the chromosomes collect. 

* Most plants present no centrosomes. 



Nuclear Phenomena oj Cell Division 343 

They then split along their length, and the twin halves 
pass, each in an opposite direction, along the lines of the 
asters toward opposite poles. Thus the split chromo¬ 
somes become clustered in the neighbourhood of the two 



Fig. 145. Diagrams of process of mitosis in animals. A-D, Prophase. 
Ey Metaphase. F, G, Anaphase. H, /, Telophase. Modified from Wilson. 


poles. Around each cluster a fine membrane forms. The 
daughter nuclei are now complete. In the protoplasm 
between the two daughter nuclei a partition appears. 
Thus the cell is divided into two independent cells, each 
with its own nucleus. 

It has been suggested that this complex process is needed 
to effect an equal partition of substance of mother nucleus 
between daughter nuclei. Its further ‘meaning’ has become 





344 Cell and Organisms 

more evident as the chromosome has been studied further 
in more modern times (chap. xv). 

The nomenclature of mitosis tells much of the story 
of its discovery. The term mitosis (Greek ‘thread’) was 
introduced by Flemming in 1882. The useful terms 
cytoplasm and nucleoplasm to describe the protoplasm of 
the cell-body and the nucleus respectively are Stras- 
burger’s (1882). He also gave us the terms prophase 
(Greek ‘appearance before’), metaphase (‘appearance next’), 
and anaphase (‘appearance further’) to describe the three 
consecutive stages of mitosis (1884). Flemming intro¬ 
duced in 1879 the terms chromatin (Greek ‘colour’) for the 
part of the nuclear substance that takes up certain stains. 
This part breaks up into the bodies now called ‘chromo¬ 
somes’ (Waldeyer, 1888). Flemming again is responsible 
for spireme (‘a skein’, 1882); and aster (‘star’, 1892). 

During the twentieth century the extent and exactness 
of our knowledge of cellular structure has increased apace. 
The centrosome—a word introduced by Theodor Boveri 
(1862-1915) ini888—has been found a permanent consti¬ 
tuent of the animal cell. It divides at an early stage of 
mitosis. Around it, there is found in animal cells an array 
of peculiar bodies rendered evident by their affinity for 
metallic salts. These attracted the cytologist Camillo 
Golgi (1884—1926) of Pavia in 1909, and have since been 
known as ‘Golgi bodies’. Many other protoplasmic in¬ 
clusions have been described. Some of them seem to be 
permanent, some transitory inhabitants of the cell-body 
or nucleus. The role of these bodies in the life of the cell 
is, however, not yet clear. 

§ 8. Structure of Protoplasm 

Influenced doubtless by the molecular view of matter, 
there has always been a school that has sought to analyse 
the cell into lesser units. The names invented for these 



Structure oj Protoplasm 345 

hypothetical bodies is legion. Herbert Spencer spoke of 
‘physiological units’, Darwin of ‘gcmmules’, Haeckel of 
‘plastidules’, Weismann of ‘biophores’, Hertwig of 
‘idioblasts’, De Vries of ‘pangens’. In the twentieth cen¬ 
tury, with the rise of biochemistry, many have been dis¬ 
posed to refer protoplasmic behaviour to the activity of 
colloid molecules and especially to groups of amino-acids 
(pp. 382-6). 

All these terms assume a view of life that is untenable. 
They all assume that living things are such by virtue of 
being an aggregate of distinct minute bodies each of which 
is alike and each of which possesses the power of inde¬ 
pendent growth and division. Those who profess this 
simple faith draw comfort by throwing back the mystery 
of life on something that is so small as to be beyond vision. 
Such a solution of the problem can yield philosophical 
satisfaction only if certain other conditions be met. First 
among these is a demonstration that aggregates of non¬ 
living origin should exhibit certain properties which have 
been found only in living things and always in living 
things. These properties are metabolism, repair of injury, 
reproduction, heredity, adaptation to environment, and 
‘memory’, that is to say, conduct determined by previous 
history. In fact, the parts of the cell can be given a meaning 
only in reference to the cell, just as the cell itself can be 
given a meaning only in reference to the organism. Kant 
knew nothing about cells, but he saw the cogency of this 
point long ago (pp. 212--14). 

On the other hand, the question as to whether parts 
of the cell have 2Lny particulate as distinct from independent 
existence is not a question of theory but of observation. 
There is evidence that certain parts of the cell, among 
which are the chromosomes and the centrosomes of both 
animals and plants, the Golgi bodies of animals, and the 
bodies known as ‘plastids’ (p. 377, 384) of plants, persist, 



346 Cell and Organism 

divide, pass from cell to cell, and are derived only from 
bodies like themselves. The behaviour of some of these 
bodies, notably the chromosomes, is partly understood. 
A general discussion of the numerous other particulate 
bodies can be of little value in the present state of our 
ignorance. 

The main physical fact about protoplasm itself is that 
it behaves as a liquid. Of this there is evidence of several 
sorts. The earliest and historically the most interesting 
is that associated with the name of Robert Brown. The 
so-called ‘Brownian movements’ had in fact been observed 
in the eighteenth century by Needham (pp. 434—6). 
Brown, however, was the first to describe them exactly 
in his Microscopic Observations on the Pollen of Plants 
(1828). This work, it may be remembered, was offered 
to the Rev. Mr. Farebrother by the surgeon I^ydgate in 
the novel Middlemarch (begun 1869) by George Eliot 
(1819-80). 

All microscopists are familiar with ‘Brownian move¬ 
ment’. If very minute particles are suspended in a liquid 
of a film which is examined under high magnification, 
a constant dancing movement is seen. The particles seem 
alive. This was Brown’s first thought, for he saw the 
movement first in living substance. Later he found it to 
be a purely physical phenomenon. 

Brownian movement has become of greatly increased 
interest since the systematic investigation of the ‘colloid 
state’. Its new study was initiated by Thomas Graham 
(1805-69, pp. 382-3) in 1861. More recently and in the 
twentieth century. Brownian movements have been shown 
to be related to molecular movement in liquids. 

Brownian movements are visible under suitable condi¬ 
tions in all forms of naked living protoplasm. On the 
death of protoplasm the Brownian movements cease. This 
is because the protoplasm then ceases to be liquid. 



Structure of Protoplasm 347 

Other evidence that living protoplasm is a liquid is 
that it tends to assume a spherical form in a state of shock. 
This was shown as long ago as 1864 by the German 
physiologist, Willy Kiihne (i 837—1900), a pupil of Claude 
Bernard and Virchow. He described the effect of an 
electric shock on those streams of protoplasm in plant 
cells which aroused the wonder of Darwin when demon¬ 
strated by Brown (p. 240). 



Fig. 146. Epidermal cell of earthworm to show’ foam-like structure. 
From Btitschli, 1892. 


It has also long been known that drops of watery liquid 
taken up or secreted by protoplasm take a spherical form. 
This is notably the case in the so-called ‘food vacuoles’ 
of protozoa. The spherical form is due to surface tension 
and is further evidence of the liquid nature of protoplasm. 

High magnification reveals minute granules of various 
sizes in even the clearest protoplasm. The nature and 
classification of these is still in dispute. 

We may thus say that physically protoplasm is a com¬ 
plex colloidal system which commonly behaves as a viscous 
liquid and has particles suspended in it. Many investi¬ 
gators have, however, sought to demonstrate some further 
structure of protoplasm. Of these attempts the most 
important is the alveolar or foam theory first expounded 
in 1878 by the Heidelberg professor, Otto Btitschli 
(1848-1920). He found living protoplasm to have a 


34 ^ Cell and Organism 

honeycomb-like appearance. This he regarded as due to 
a mixture of two liquids of different degrees of viscosity. 
He tried to imitate this mixture mechanically, and he 
believed that his mixtures exhibited some of the reactions 
of protoplasm. In view of the excessively complex condi¬ 
tions that we know to prevail within the living cell, the 
idea seems very naive. Btitschli, however, rendered a real 
service by firmly establishing the fact that protoplasm 
is a fluid. 

There have been innumerable variations on Biitschli’s 
theme of the structure of protoplasm. All are open to a 
double criticism, one practical and the other theoretical. 

On the practical side how far do the microscopical 
appearances represent actual objective conditions or 
mere optical effects.^ Or, again, are they artificial results 
of preliminary treatment.^ These are points that should 
be capable of decision. 

On the theoretical side we may say that while there is 
no reason that protoplasmic activities should not be 
analysed separately, yet the results of such analysis cannot 
explain the living entity. Thus the fact that emulsions 
behave in some respects like living protoplasm does not 
get us nearer to understanding what living protoplasm is. 
It only helps us to understand how some of its behaviour 
is determined. If a man assaults another, his action may 
illustrate the laws of mechanics and may be analysable 
on the principles of Galilean physics. The analysis, how¬ 
ever, will neither explain the feelings of the two nor deter¬ 
mine whether or not the injured man will hit back or go to 
law. Similarly it helps little in understanding the nature 
and conduct of the cell to be told that its protoplasm 
behaves according to the physical and chemical laws 
characteristic of an emulsion. 

In fact, however, the only clear knowledge that has 
emerged concerning the visible structure of protoplasm is 



Structure of Protoplasm 349 

that which has to do with the existence of the particulate 
bodies, and not with their relationship. The alveolar 
structure passes insensibly into the emulsional form, and 
both are included in the conception of the ‘colloid state’. 

§ 9. Cellular Ageings New Growths^ and Tissue Culture 

The study of certain ‘new growths’—of which the best 
known arc cancers—has thrown some light on certain 
extremely important aspects of cell physiology. 

Reliable statistics, now available from an enormous 
population, show that only a very small proportion of 
persons under forty develop cancer. Beyond that age the 
proportion rises as age advances. Cancer, in fact, charac¬ 
terizes the decline of life. This explains why it is so rare in 
wild creatures, for thesenormallydiesoonafterpassing their 
sexual prime. An interesting relationship to the cellular 
activities of the body is involved in this age distribution. 

The cells of cancers descend from other cells or tissues 
of the body. They present an appearance resembling that 
of their normal ancestors. How, then, do they differ from 
them.^ The answer, in so far as any can be given, fits 
our knowledge of the age distribution of cancer. 

Since Virchow (pp. 340—1), cancer-cells have been 
recognized to differ from normal cells not so much in 
structure—so far as that is known— but in conduct. They 
are isolated in the co-operative community of the tissues 
and organs of the body. The cells of the various tissues 
exercise an influence upon each other. According to the 
bodily needs they grow, they develop, they multiply. It 
is just this mutual balance and restraint of a group of cells 
that make us call it an ‘individual’. But the cells that become 
a cancer multiply and give rise to tissues which subserve 
no function, which meet no demand of the cell community, 
which answer no physiological need, which obey none 
of the laws laid down by that power of co-ordination— 



350 Cell and Organisms 

entelechy, or whatsoever we may call it—that informs the 
body as a whole. 

This defiance of the laws of the cellular community is 
accompanied by a feature which gives us a glimpse of 
the meaning of the power of co-ordination. The process 
of ageing, so that at last life ceases, is a function of the 
body as a whole, not of its tissues. It is a property only 
gradually imparted to the tissues. Thus embryonic tissue 
can be propagated for an indefinite time in a suitable 
medium, while normal adult differentiated tissue-cells 
can be propagated in media only with great difficulty or 
not at all. Cancer-cells partake in this respect of the nature 
of embryonic cells. 

What is the power that gives cancer-cells this perverse 
quality.^ There is evidence that no parasitic organism is 
involved. The cumulative results of a generation of 
research point rather to cancer being related to those 
peculiar forms of stimulation of the tissues that are grouped 
together as ‘irritation’. In some cases, at least, the carrier 
of the irritation is of a filterable nature (pp. 454—7). 

Further, it is highly probable that at least two factors 
are involved in the disease. One factor is external, the 
irritant. Another factor is certainly internal, since experi¬ 
ments prove that it is possible, by very intensive hereditary 
accumulation, to increase liability or immunity to cancer. 

Cancer presents us also with an interesting analogy with 
unicellular organisms. In multicellular organisms the 
fertilized egg continues to divide, and after the process 
has gone on for a time cells of two types are produced; 
one type constitutes the individual, the other type is for 
the maintenance of the species. This most important con¬ 
ception attracted the attention of August Weismann. It 
was developed in his famous essay The continuity of the 
Germ-Plasm as the Foundation of a Theory of Heredity (1885, 
pp. 543-7). Weismann distinguished between body-cells 



New Growths and Tissue Culture 351 

and germ-cells. He emphasized the continuing character of 
the germ-cells (Fig. 191), and pointed out that the mortal 
fate of the body-cells was the result of the division of 
labour within the multicellular body. The substance of 
these body-cells is to be distinguished from that of the 
germ-cells or germ-plasm. In certain unicellular organisms, 
on the other hand, the whole creature consists of germ- 
plasm. Such are, for example, the bacteria and certain 
protozoa. In such unicellular organisms there is no body 
as distinct from germ. Of these beings no part is pre¬ 
destined for death, no part need decay, ageing is unknown. 

We can now see how cancer-cells present analogies to 
these lower forms of life. Something has happened to 
them whereby they have shed that mortality that is the 
lot of the other descendants of their cell ancestors. We may 
describe them as in a permanent embryonic state. They 
have come to resemble unicellular organisms. Like them 
they live a life that is for themselves alone, without regard 
to any community. 

A new and promising mode of studying cells in general 
and those ofnewgrowths in particularwas introduced in 1907 
by Ross Harrison (i 87o)of Johns Hopkins University. He 
found that if fragments of living tissues were placed in 
suitable media and kept under suitable conditions, the 
cells would multiply. The great technical difficulties— 
which vary for cells of different origin—^were gradually 
overcome, largely by the efforts of the very skilled experi¬ 
menter, Alexis Carrel (1873— )Rockefeller Institute, 
New York. Certain animal tissues, for example cells from 
the heart of a chick, first planted out in 1912, and still 
growing, breed true and produce cells similar to the 
original type. These results are extremely interesting in 
themselves. They seem, however, contradictory of certain 
others. Thus with some plants a small fragment or even 
a single cell, as with Begonia, may regenerate, not cells 



35 ^ Cell and Organism 

like itself, but a complete plant with all its tissues 
complete. A somewhat similar series of contradictions 
arises from certain mutilation experiments. At present 
these inconsistencies cannot be resolved. 

§ I o. Criticism of the Cell Doctrine 

The ‘Cell Theory* is merely a general formula erected 
to cover a series of observations. It is thus open to 
criticism on the ground either (a) of the accuracy of the 
observations, or (b) of the adequacy of the description of 
the observations. 

Naturalists think and speak of the cell as a separate 
entity cut off from other cells. It is a member of a com¬ 
munity. Nevertheless, in many cases it has been shown 
that cells of multicellular organisms are connected with 
their neighbours by protoplasmic bridges. Much atten¬ 
tion was given to this matter by Strasburger (1901). It 
was soon found that not only in plants but also in animal 
tissues such protoplasmic bridges between cells are 
frequently demonstrable. They are encountered in the 
deeper layers of the skin, where they were seen as long ago 
as 1864 by Max Schulze (p, 338) who, however, inter¬ 
preted them wrongly. 

Certain unicellular organisms pass through a stage in 
which there is a naked mass of undivided protoplasm with 
a number of nuclei. An example is the parasite which 
gives rise to malaria. Certain multicellular organisms pass 
through a similar stage in the course of development. 
Notably this is the case with some insects and Crustacea. 
Further, in some higher animals there are stages in de¬ 
velopment in which the cells act as though free to unite and 
their nuclei to multiply according to local needs. More¬ 
over, in various diseased tissues, of which cancer is a type, 
the cells are often either multinuclear or united by bridges. 

A series of facts of this order persuaded some that the so- 



Criticism oj Cell Doctrine 353 

called multicellular organisms cannot justly be compared 
to a community. These critics would treat the animal 
or plant individual as a continuous mass of protoplasm. 
This mass, they would hold, forms a single morphological 
unit, whether it appears as a single cell, as a cell with many 
nuclei, or as a system of cells. Such a view is to some 
extent supported by the results of experimental em- 
bryology (pp. 492 ff.). 

Of the importance and value of these criticisms of the 
cell theory there can be no doubt. Nevertheless, the 
appearances on which they are based are exceptional and 
refer to special tissues, abnormal states, or particular 
phases of life. There is clearly a tendency in the higher 
multicellular forms to a definite and final separation of 
cells from each other. This is especially marked in the 
most specialized tissues. The most characteristic and 
highly specialized tissues are those of the nervous and 
muscular systems. The separateness of the units of these 
systems has been emphasized by the refinements of 
modern histology. That study seems to leave the cell 
theory as a useful, if inadequate, summary of a very im-* 
portant and significant group of facts. 

During the twentieth century the main course of 
biological thought has been concentrated on the cell. The 
problems of heredity, of sex, of development, of the subor¬ 
dination of parts to the whole, of the essential nature of 
life, all have been reduced to cellular expression. These 
aspects we shall presently consider. 

Fig. 147. Living vacuolated hair cells of potato. Magnified. Arrows indicate 
protoplasmic streaming. From Schleidcn, 1838 (p. 240). 



A a 


2613.3 


X 


ESSENTIALS OF VITAL ACTIVITY 

§ I. Physiology of Descartes and the Early Mechanist School 

T he widest generalization that we can make in the 
department of the biological sciences is a view of the 
nature of life itself. In this connexion the philosophy of 
Descartes has been a moulding force on the whole course 
of scientific thought (pp. 125—9). 

The influence of Descartes on biological theory has 
been exerted through his treatise on physiology. He 
intended this to form part of his philosophical system and 
proposed its issue along with his Discourse on Method. It 
was the period of Galileo’s conflict with the Inquisition. 
The great physicist had but recently been condemned 
(1632). Descartes, nominally loyal to the Church, decided 
to issue his Discourse (1637) without its physiological 
appendix. The physiological section did not appear until 
1662, when its author had been in his grave for twelve 
years. Even then it was in a modified form and in Latin 
(De homine, ‘On Man’). The true version appeared in 
French in 1664. It is the first book that seeks to cover 
the whole field now called ‘animal physiology’. 

Descartes had no extensive practical acquaintance with 
anatomy or physiology. He was fairly well read in these 
subjects, but he did not always understand what he had 
read. For instance, he did not fully appreciate either the 
nature or the implication of Harvey’s discovery of the 
circulation (1628). Realizing, however, that it formed 
the best illustration at hand of the mechanical working of 
the body, he used it gladly though clumsily. Neverthe¬ 
less his ingenuity was such that it would be diflicult to 
exaggerate his influence on later biological thought. 



Physiology of Descartes 355 

Indeed that ‘mechanistic’ view of the nature of life, 
which is prevalent among biologists, had its origin with 
this great philosopher. 

Although the general principles set forth by Descartes 
gained wide acceptance, yet the details of the mechanism 
which he presupposed were entirely imaginary and had 
no real existence. A strong point in the physiology of 
Descartes was the stress laid on the nervous system with 
its power of co-ordinating the various bodily activities. 
Thus stated, his view may seem very modern. Yet he 
was grotesquely wrong in his view of the way in which the 
nervous system performs its functions. 

Descartes held, quite erroneously, that the nerves are 
hollow and provided with a system of valves at the points 
at which they branch. These valves he believed to be 
moved by a series of fibrils passing from the central 
nervous system along the nerves and terminating in the 
valves. He regarded as another factor in the activity of 
the nerves a certain subtle vapour, reaching them from 
the blood. This vapour, he believed, passing from the nerves 
into the muscles, distended the latter and thus brought their 
ends nearer together. Thus was produced what we now call 
a ‘muscular contraction’. The movements of the vapour 
were, he thought, controlled by the valves in the nerves. 

On the basis of these and of certain other imaginary 
contrivances, Descartes sought to elucidate all the work¬ 
ings of the animal body. The actions and reactions of 
animals could, he thought, be explained without the 
invocation of anything in the way of mind, consciousness, 
or feeling. He was thus a pure ‘mechanist’. 

An important part of the theory of Descartes was, 
however, the complete separation of man from all other 
animals. Man, he held, differs from them in his possession 
of a reasoning soul. This, he supposed to be situated in 
a structure in the brain, the pineal body. That body, 


A a 2 



356 ’Essentials oj Vital Activity 

we now know, is developed as an eye in certain fossil 
vertebrate animals and in one living lizard {Sphenodon 
punctatum of New Zealand). Its function in other verte¬ 
brates is not yet clear, but it is found in them all. Des¬ 
cartes held that animals have no soul and therefore no 
need for a pineal body. 

This theory of Descartes was an ingenious attempt to 
explain the enormous difference between the activities of 
man and those of the animals. He held the difference to be 
one of kind. We now hold that, so far as biological 
science has anything to say on this theme, the difference 
is one of degree. It is as well to remind ourselves here 
that this attitude does not in itself exclude the revelation 
by other than purely biological methods, of a true differ¬ 
ence of kind. 

Soon after Descartes, the application of his mechanist 
theory was greatly extended by other workers. The most 
successful was the Italian professor, Cliovanni Alphonso 
Borelli (1608—79), ^ pupil of Galileo. Borelli was an 
excellent mathematician and with his De motu animalium 
(Rome, 1680) he founded the science of muscular 
mechanics, which investigates the action of muscles 
according to the mathematical laws of statics and dyna¬ 
mics. These sciences, in their turn, had been founded by 
Galileo. Many conclusions of Borelli have stood the test 
of time. His success did much to persuade men of the 
value of the Cartesian physiology. 

The suggestions of Descartes and of Borelli as to the 
mechanical workings of the animal body provided a fruit¬ 
ful stimulus to biological investigation. But the Cartesian 
mechanist views, in theiroriginal form, did not long remain 
acceptable to biologists. For generations, however, cer¬ 
tain literary men with scientific tastes, but with little 
practical acquaintance with science, clung to the Cartesian 
doctrines. This was the case with the Paris physician. 



Early Mechanist School 357 

de la Mettrie (1709-51). In 1748 he published his 
famous essay, L'homme machine (‘Man a machine’). It 
was burnt as atheistical. 

De la Mettrie attempted to extend the mechanist view 
from animals to man, pursuing it into all departments of 
human activity. The work, though much read in its day, 
is of little biological importance. It was one member of 
a whole series of expressions of the same view. The great 
Encyclopedic, begun in 1751 and completed in 1772, pro¬ 
vides further examples. Denis Diderot (1713-84), its 
main editor and contributor, exhibited the mechanist 
philosophy also in other works. The fact that both Mettrie 
and Diderot were ‘spermatists’ (pp. 498—9) has a bearing 
on their mode of thought. 

§2. P'an Helmont (1577—1644) and the Beginnings oj 
Chemical Physiology 

Even during the lifetime of Descartes, men of science 
perceived that purely physical devices were inadequate to 
explain all living activity. Chemistry, though still in its 
infancy, was also invoked. Away back in the sixteenth 
century the Swiss, Philippus Aureolus Theophrastus 
Bombastus von Hohenheim (1493-1541), more com¬ 
pendiously known as ‘Paracelsus’, had made attempts to 
equate chemical action with bodily processes. The task 
was more successfully taken up by his follower, van 
Helmont, a contemporary of Descartes. 

The Belgian, Jan Baptist van Helmont, was a medical 
man who spent his life investigating chemical processes. 
He was a very pious Catholic of mystical leanings, whose 
mysticism has deeply affected his literary style, rendering 
his works excessively obscure. He published little during 
his life. After his death, his son collected his writings— 
published and unpublished—^and gave them to the world 
in a Latin volume which he called Ortus medicinae (‘The 



358 Essentials oj Vital Activity 

fount of medicine’, Amsterdam, 1648). The work em¬ 
ployed such an outlandish terminology that it was little 
studied by biologists until the appearance of translations 
(into Dutch 1660, English 1662, and French 1671). It 
was thus, in its effect, contemporary with Descartes 
On man (1662—4). 

Van Helmont, like Paracelsus, considered all physio¬ 
logical processes explicable on a chemical basis. He did 
not regard these processes as acting on their own initiative 
but as being each governed by one of a series of agencies, 
the archaei. This conception also he adopted from Para¬ 
celsus. Van Helmont postulated a regular hierarchy of 
archaei in the various organs. The chief archaeus of all, 
he believed, supplies ‘the reproductive power and is, as 
it were, the internal efficient cause. It has the likeness of 
the thing generated and equips the germ with the powers 
that determine its course of development.’ It thus has 
analogies with the entelechy of Aristotle. Van Helmont 
was, in fact, trying to reconcile the vitalist and the 
chemical view of life. His theories are in opposition to 
those of Descartes, who regarded the seed as of the nature 
of a machine from which, if enough were known, the form 
and activity of the adult could be predicted. 

Van Helmont introduced an entity subordinate to the 
archaei, for which he coined the term bias. The bias 
humanum is responsible for the specifically human func¬ 
tions of man’s body, and other forms of bias preside over 
other physiological processes. 

The physiology of van Helmont is otherwise based upon 
ferments and their action. With alcoholic fermentation 
as the type, he attempted to explain all physiological pro¬ 
cesses, and notably digestion, as due to the action of fer¬ 
ments. This is the most intelligible aspect of his work and 
is, to some extent, in accord with more modern teaching. 

The followers of van Helmont are known as the 



Beginnings oj Chemical Physiology 359 

‘iatrochemists’ (Greek iatros^ ‘physician’). The nomen¬ 
clature employed by them is often extremely bizarre, but 
they were working in a direction that has proved fertile 
for scientific advance. 

The most prominent of the iatrochemists was Franciscus 
Sylvius (1614—72), a very able professor of Medicine at 
Leyden. His name is latinized from De la Boe. Sylvius 
devoted much attention to the study of salts. These he 
recognized as the result of the union of acids and bases, 
and he attained to the idea of chemical affinity—a very 
important advance. He sought to represent almost all 
forms of vital activity in terms of ‘acid and alkali’ and of 
‘fermentation’. Shedding the mysticism of van Helmont 
with its ‘archaei’ and its ‘bias’, he assumed that fermen¬ 
tation, which van Helmont had stressed, is a purely 
chemical process. 

The school of Sylvius and its immediate successors 
added considerably to our knowledge of physiological 
processes—notably by the examination of digestive fluids. 
The action of these has some parallels to that of the micro¬ 
organisms of alcoholic and other fermentation. 

§ 3. Plant Physiology in the Seventeenth Century 

The plant physiology of the seventeenth century was 
of very elementary character as compared to that of 
animals. 

Van Helmont had demonstrated that the solid parts of 
a plant increase in weight apart from anything that they 
take from the soil. This action of plants was contrary 
to the current Aristotelian teaching that plants draw their 
food, ready elaborated, from the earth, 

Malpighi held that the leaves form from the sap the 
material required for growth. He knew that elaborated 
food-substance is distributed from the leaves to the various 
parts of the plants. The sap, he wrongly thought, is 



360 'Essentials of Vital Activity 

brought to the leaves by the fibrous parts of the wood. 
He conceived an imaginary course for this nutrient sap. 
It goes downwards, he thought, into the roots and then 
again upwards to the organs above ground (1671—4). 
This view was fantastically developed by some of his 
contemporaries into a ‘circulation of the sap’, comparable 
to the circulation of the blood in animals. Nor was 
Malpighi much more fortunate in his conception of the 
process of plant breathing. He supposed that air is con¬ 
veyed from the roots by the spiral vessels. The cause of 
this latter error was the close similarity which he thought 
he could discern between the ‘spiral vessels’ of plants and 
the ‘tracheae’ or air tubes (p. 153) of insects. 

The earliest important experimental work on the 
physiology of plants was that of the French ecclesiastic, 
Edm^ Mariotte (died 1684). This able physicist was a 
member of the scientific circle in France which developed as 
the Academie des Sciences (pp. 1 35 - 7 ). Mariotte observed 
the high pressure with which sap rises. He inferred from 
this that there must be something in plants which permits 
the entrance but prevents the exit of liquids. The pressure 
he compared to that of the blood-vessels, in a manner 
afterwards developed by Hales (p. 363). Mariotte held 
that it is sap pressure which expands the organs of plants 
and so contributes to their growth {On the vegetation of 
plants^ 1676 ). 

Mariotte was definitely opposed to the Aristotelian 
conception of a vegetative soul (p. 38). He considered 
that this conception fails to explain the extraordinary fact 
that every species of plant, and even the parts of a plant, 
exactly reproduce their own properties in their offspring. He 
was, so far as plants are concerned, a complete ‘mechanist’ 
(pp. 354-6), and therefore anti-Aristotelian. All the ‘vital’ 
processes of plants were for him the result of the interplay 
of physical forces. He believed, as a corollary to this view, 



Mechanism and Vitalism 361 

that organisms can be spontaneously generated (chap. xii). 
This is a conclusion not often faced by advocates of 
mechanistic theory in modern times. 

§ 4. Stahl (i 660—1734) and the Contest between Mechanism 
and Vitalism 

In the generation that was active in the last quarter 
of the seventeenth and the first half of the eighteenth 
century, there arose an important cleavage of physiological 
interests. The opposition between the ‘mechanist’ and 
the ‘vitalist’ came into clear view. 

Georg Ernst Stahl (1660—1734) was professor at Halle 
and a fashionable and influential physician. He was much 
interested in Chemistry and saddled that science with the 
unfortunate theory oiphlogiston which held its ground until 
the time of Lavoisier. In physiology Stahl set himself 
against the ‘mechanism’ of Descartes. To the French 
philosopher the animal body was a machine. To the 
German physician the word machine expressed exactly 
what the animal body is not. The phenomena character¬ 
istic of the living body are, Stahl considered, governed 
not by physical laws but by laws of a wholly different 
kind. These are the laws of the sensitive soul. 

The sensitive soul of Stahl is, in its ultimate analysis, 
not dissimilar to th&psyche of Aristotle (pp. 15—16). Stahl 
held that the immediate instruments, the natural slaves, 
of this sensitive soul, are chemical processes. Thus his 
physiology develops along lines of which Aristotle could 
know nothing since he lived before the days of chemistry. 
Yet neither this nor the fact that Stahl did not regard 
himself as an Aristotelian can alter the fact that his 
theories are of essentially Aristotelian origin. 

The views of Stahl are scattered through an almost 
incredible mass of writings. His physiological theories 
are, however, best set forth in his classical Theoria medica 



362 Essent/als of Vital Activity 

vera (Halle, 1707—8), which contains an important section 
‘Physiologia.’ 

Almost exactly contemporary with Stahl was a rival 
professor at Halle, Friedrich Hoffmann (1660-1742). 
He also was a skilled chemist and he was nearly as verbose 
as his opponent. In Hoffmann’s view the body is like a 
machine. On the one hand, he separated himself from the 
pure mechanists of the school of Descartes and Boerhaave 
(pp. 354—6) by claiming that bodily movements are exe¬ 
cuted under the influence of properties peculiar to organic 
matter. On the other hand, he separated himself from 
the Stahlian vitalists by denying the need to invoke the 
sensitive soul. He was deeply under the influence of the 
‘monadism’ of the philosopher Leibniz, but attached 
great importance to the mechanism revealed by Harvey. 

It is difficult to select from the huge mass of Hoff¬ 
mann’s writing. His doctrines are perhaps best expressed 
in his Fundamenta physiologiae (Halle, 1718). ‘Life’, he 
there says, ‘consists in the movement of the blood. This 
circular movement maintains the integrity of that complex 
which makes up the body. The vital spirits which come 
from the blood are prepared in the brain and released 
therefrom to the nerves. Through them come the acts of 
organic life which can be reduced to the mechanical effects 
of contraction and expansion.’ 

An important protagonist in the controversy was Her¬ 
mann Boerhaave (1668-1738) of Leyden, one of the 
ablest medical teachers of all time. Boerhaave was also 
skilled in chemistry and takes his place in the history of 
that science. He wrote a text-book of physiology, Institu- 
tiones medicae (Leyden, 1708), which ran through in¬ 
numerable editions and was translated into many lan¬ 
guages. It was the staple work on the subject until the 
appearance of the great treatise of Haller (pp. 366—8). 

Boerhaave goes systematically through the functions 



Mechanism and Vitalism 363 

and actions of the body. All are ascribed to chemical 
and physical laws. He does lip service to the influence of 
mind on the body. In practice, however, he ignores it and 
is as completely mechanist as Descartes. He still believed 
that something material passes down the nerves to cause 
movement, though he had himself published Swammer¬ 
dam’s experiment in disproof thereof (p. 367). The value 
of Boerhaave’s physiological work is in its very clear and 
systematic exposition. 

§5. Hales (1677—1761) on the Physiology of Plants and 
Animals 

In the earlier eighteenth century, physiological writing 
was mainly confined to physicians. The attention of 
naturalists was concentrated on the discovery and arrange¬ 
ment of new forms of vegetable and animal life. Voyages 
of exploration kept them busy. Their work thus tends 
to be uniform and monotonous. From them on the one 
hand and from the speculative physicians on the other, 
Hales stands out for his independence of thought, his 
experimental ingenuity, and his power of lucid statement. 

The Rev. Stephen Hales was educated at Cambridge 
in the mathematical and physical sciences. He became 
interested in botany, using Ray’s Flora of Cambridge 
(p. 181) in his excursions. Most of his years were spent 
as vicar of Teddington in exemplary discharge of parish 
duties, and he led the uneventful life of a man of simple 
habits and serene mind. 

Hales made many inventions of considerable impor¬ 
tance. Best known were his ‘artificial ventilators’ which 
he succeeded in getting fitted to prisons, both English 
and French, then particularly insanitary. Great reduction 
in death-rate ensued. He made useful suggestions for the 
distillation of fresh from salt water, for the preservation 
of eatables, for cleansing harbours, for measuring the 



364 Essentials of Vital Activity 

depth of the ocean by a mercurial pressure gauge, for 
winnowing corn, for preventing the spread of fires, for a 
thermometer for high temperature, and for the use of furze 
for fencing river banks. He also invented the use of the tea¬ 
cup to prevent the crusts of pies and tarts from collapsing! 

The work of Hales on the functional activity of plants 
was the most important until the nineteenth century. His 
Vegetable Staticks (I.ondon, 1727) contains the record of 
a great number of ingeniously devised but simple experi¬ 
ments. Many of these are still repeated in the botanical 
laboratory. Their general idea is to explain the action of 
living plants on the basis of known physical forces. Thus 
he measured the amount of water taken in by the roots 
and the amount given off by the leaves, and so estimated 
what botanists now cafl transpiration. He compared this 
with the amount of moisture in the earth and showed the 
relationship of the one to the other. He made calculations 
of the rate at which water rises in the stems of plants, 
and he showed that this has a relation to the rate at which 
it enters by the roots and is transpired through the leaves. 
He measured the force of upward sap current in stems, root- 
pressure as it is now called. He sought to show that these 
actions of living plants might be explained as a result of 
their structure. With this in view he measured the 
absorption of water by substances with fine pores and the 
movements of water and other fluids in capillary tubes. 

An interesting contribution by Hales was his demon¬ 
stration that the air supplies something material to the 
substance of plants. This we know to be the carbon 
dioxide of the atmosphere. In his day, however, the gases 
of the atmosphere were hardly at all understood. The 
significance of this discovery was therefore overlooked. 
Following upon it, however, he showed with the aid of the 
air-pump, that air enters the plant not only through the 
leaves, but also through the rind. 




Fig. 148. From Hales Vegetable S.tatich (1727). 

a and b exhibit the method adopted by Hales of showing the region of growth. 
A young stem is pricked with holes at known equal distances apart. The 
distance between the holes is measured in the stem when older. Growth takes 
place mainly in the middle part of the internodes. 

f is a sunflower planted when younger in a pot on the top of which a metal 
plate is fixed. Air and water are admitted through a tube fixed to this metal 
cover. By comparing the dry weight of such a plant when it is grown, and the 
loss in the soil in which it grows, it can be proved that something material is 
absorbed into its substance from the air. 

d is an apparatus for measuring the negative pressure resulting from transpira¬ 
tion. The apparatus fixed to the branches is, in effect, a ‘manometer*. 

^ is a similar apparatus for measuring root pressure. 









366 'Essentials of Vital Activity 

showed that just as there is a sap pressure that can be 
measured, so there is a blood-pressure that can be measured, 
and he measured it. Moreover, he perceived that the 
pressure varies under different circumstances. It is differ¬ 
ent in the arteries and the veins. It is different during 
contraction of the heart from what it is during dilation. 
It is different in a failing and in an active heart. It is 
different in large and in small animals. All these differ¬ 
ences Hales measured. He measured, too, the rate of flow 
in the capillaries of the frog. These experiments and con¬ 
clusions of Hales were the beginnings of a quantitative 
development of the science of animal physiology. 

It is specially characteristic of the work of Hales that he 
always sought to give an exact mathematical expression to 
his results. ‘Science is Measurement’ sums up his attitude. 

§ 6. Haller (1708-77) and the Doctrine of Irritability 

Albrecht von Haller (1708-77) was a Swiss of noble 
birth and ample means. After holding chairs in several 
German Universities, he retired to his native Berne. He 
exhibited unparalleled literary and scientific activity and 
stamped his views and methods of approach upon the 
whole range of biological research. He was certainly one 
of the most versatile men that has ever lived. He achieved 
distinction as a poet, botanist, anatomist, philosopher, 
physiologist, and novelist. He carried on a prodigious 
correspondence, was an exceedingly learned bibliographer, 
and was, perhaps, the most voluminous scientific author 
of all time. He took much interest too in the history of 
science. His great works on the bibliography of botany 
and of anatomy are still indispensable. They display judge¬ 
ment and penetration as well as system and almost in¬ 
credible learning. Haller was a lover of his native moun¬ 
tains, and his writings on the natural beauties and the 
flora of the Alps are still of value. 



The Doctrine oj Irritability 367 

Haller’s greatest scientific achievement is his Elementa 
Physiologiae (\..2iViS2innc^ i759~66). This extensive work 
immediately replaced Boerhaave’s Institutiones medicae 
(p. 362). It marks the modernization of the subject. The 
Elementa speaks the language of our own time, and as we 
peruse it we seem to have passed, at last, into a modern 
laboratory. Among the important subjects on which it 
throws new light are the mechanics of respiration, the 
formation of bone, and the action of the digestive juices. 
As regards embryology we note that Haller is an un¬ 
repentant preformationist and is opposed to the teaching 
of his contemporary Wolff (pp. 462—4). 

Haller’s most important contributions to biological 
thought are his conceptions of the nature of living sub¬ 
stance and of the action of the nervous system. These 
formed the main background of physiological thinking 
for a hundred years after his time. They are still integral 
parts of physiological teaching. 

During the seventeenth and early eighteenth centuries 
the favourite doctrine of nervous action presupposed the 
existence of a subtle nervous fluid. Such was the view of 
Descartes (p. 355), Borelli (p. 356), and Boerhaave (pp. 
362-3). An admirable experiment by Jan Swammerdam 
had made this view untenable. But Swammerdam’s work 
was lost until published posthumously in 1736, and so 
the matter stood over till Haller’s time. 

Haller concentrated the problem on an investigation of 
the fibres. A muscle-fibre, he pointed out, has in itself a 
tendency to shorten with any stimulus, and afterward to 
expand again to its normal length. This capacity for con¬ 
traction, Haller, following a predecessor (Francis Glisson, 
1597—1677), called irritability. He recognized irritability 
as an element in the movement of the viscera, and notably 
of the heart and of the intestines. The feature of irritability 
is that a very slight stimulus produces a movement al- 



368 Essentials oj Vital Activity 

together out of proportion to itself, and that it will con¬ 
tinue to do this repeatedly, so long as the fibre remains 
alive. We now recognize irritability as a property of all 
living matter. 

But besides its own inherent force of irritability, Haller 
showed that a muscle-fibre can develop another force. 
This second force comes to it from without, is carried 
from the central nervous system by the nerves, and is that 
by which muscles are normally called into action. Like 
irritability, it is independent of the will, and, like irrita¬ 
bility, it can be called into action after the death of the 
organism as a whole. Haller thus distinguished t\ieinherent 
muscular force from the nerve force. Both these forces he 
further distinguished from the natural tendencies to con¬ 
traction and expansion, which, under changing conditions 
of humidity, pressure, and so on, produce changes in all 
tissues, living or dead. 

Having dealt with the question of movement, Haller 
turned to consider feeling. He was able to show that the 
tissues are not themselves capable of sensation, but that 
the nerves are the channels or instruments of this process. 
He showed how all the nerves are gathered together into 
the brain. These views he supported by experiments and 
observations involving injuries or stimulation to the nerves 
and to different parts of the brain. He ascribed importance 
to the outer part or cortex, but the central parts of the 
brain he regarded as the essential seat of the living prin¬ 
ciple, the soul. 

Throughout his discussion Haller never falters in his 
display of the rational spirit. He develops no mystical or 
obscure themes. Although his view of the nature of the 
soul may lack clarity, he separates such conceptions 
sharply from those which he is able to deduce from actual 
experience. He is essentially a modern physiological 
thinker. 



C 369) 


§ 7. Hunter as Fitalist 

During the earlier eighteenth century, owing to various 
causes, the interests of those who investigated plant 
biology and those who investigated animal activities drifted 
ever wider apart. Hales was almost alone in taking both 
departments into his wide purview. Toward the end of the 
century, with the all-embracing curiosity of Hunter and 
the philosophic probings of Goethe, the two studies drew 
together again. Men began again to consider life as a 
whole. Partly this expressed itself in the school represented 
by the ‘Naturphilosophen’ (pp. 212—19); partly, however, 
by a more naive attitude which is well represented by 
John Hunter. 

Hunter’s older contemporary, Linnaeus (pp. 185—92), 
and his younger contemporary, Cuvier (pp. 223—32), used 
their knowledge of comparative anatomy as a guide to 
the classification and arrangement of living things. These 
were not Hunter’s ways. He was ever seeking the more 
general principles that underlie similarities or dissimi¬ 
larities of structures. The most general principle of all, 
the principle from which Biology takes its name, is that 
mysterious thing called life. Hunter came no nearer to 
answering the question ‘What is life V than later biologists. 
In the course of his search, however, he reached some im¬ 
portant conclusions. 

Hunter considered that, whatever life may be, it is 
something held most tenaciously by the least organized 
beings, and is something that is independent of structure. 
These ideas lead to the conception of protoplasm^ the sub¬ 
stance, simple in appearance, inconceivably complex in 
fact, which seems the inseparable material factor without 
which life is never found. Hunter did not use the word 
protoplasm, which was invented fifty years after his death 
(pp. 336—7), but he was reaching out to this conception. 

2613.3 B b 



370 'Essentials oj Vital Activity 

Life is normally exhibited, according to Hunter, in the 
various activities of living things, and notably in the power 
of healing and repair and renovation. This power is quite 
peculiar to living things, and cannot be paralleled in the 
non-living world. Nevertheless Hunter thought that vital 
activity can be suspended—as, for instance, in the egg. 
He was thus led to investigate what he considered the 
simplest forms of life. In doing so, he discovered what 
was from his point of view a ‘latent heat of life’ set free at 
death. Thus he found that sap removed from a tree con¬ 
geals at freezing-point but that the living tree itself may 
be reduced far below freezing-point before the sap loses 
its viscous or liquid quality. The suggestion was interest¬ 
ing though the phenomena, as we now know, are suscep¬ 
tible of other explanation. He made similar experiments 
on other forms of life to illustrate the same point. He also 
came to regard the heat given off by germinating seeds as 
evidence of something of the nature of a latent heat of life. 

§ 8. The Balance of Life 

Light on the vital activities of plants was thrown by the 
chemist, Joseph Priestley (1733—1804). In his Experi¬ 
ments and observations on different kinds of air (London, 
1774) he demonstrated that plants immersed in water give 
off the gas which we term ‘Oxygen’. He observed, too, 
that this gas is necessary for the support of animal life. 

Priestley’s contemporary, the French chemist, Antoine 
Lavoisier (1743-94), made quantitative examinations of 
the changes during breathing. These displayed the true 
nature of animal respiration and proved that carbon 
dioxide and water are the normal products of the act of 
breathing. 

In the meantime Jan Ingenhousz (1730—99) was in¬ 
troducing the highly important concept of the balance of 
animal and vegetable life. Ingenhousz was an engineer, 



Balance of Life 3 71 

of Dutch origin, educated at Louvain, Leyden, Paris, and 
Edinburgh. He worked in London with Hunter, and was 
in contact with all the scientific movements of his day. He 
travelled widely and wrote on a variety of topics. Nearly 
all his communications exhibit an original outlook. 

In 1779 Ingenhousz published in London his Experi-^ 
merits upon vegetables^ discovering their great power of 
purifying the common air in the sunshine and of injuring it in 
the shade and at night. It contains a demonstration that 
the green parts of plants, when exposed to light, fix the 
free carbon dioxide of the atmosphere. He showed that 
plants have no such power in darkness, but that they then 
give off, on the contrary, a little carbon dioxide. 

This discovery is the foundation of our whole concep¬ 
tion of the economy of the world of living things. Animal 
life is ultimately dependent on plant life. Plants build up 
their substance from the carbon dioxide of the atmosphere 
together with the products of decomposition of dead 
animals and plants. Thus a balance is kept between the 
animal and the plant world. The balance can be observed 
in the isolated world of a small aquarium. 

All this is obvious enough now. But the importance of 
the work of Ingenhousz was at first insufficiently appre¬ 
ciated, despite the labours of Lavoisier on the nature of 
air. Not until vegetable physiology came to be taken up in 
the light of the cell theory was it realized that this power 
of plants to fix carbon dioxide is one of the most significant 
of all the activities of living things (pp. 375-8). 

A discerning Swiss protestant pastor, Jean Senebier 
(1742—1809), of Geneva, had however perceived some of 
the implications of the discovery of Ingenhousz. He 
stated the matter clearly in his Memoires physico-chimiques 
sur rinfluence de la lumiere solaire (Geneva, 1782). 
Senebier was much under the influence of his townsman 
Charles Bonnet (p. 207), who had been feeling his way 

B b 2 



372 'Essentials of Vital Activity 

toward the same idea. He was also the medium through 
which the doctrines of Spallanzani (p. 433) became better 
known. Finally, Senebier stimulated his fellow Genevan, 
Nicholas Theodore de Saussure (1767—1845)—the third 
man of science of that name—to work on the chemistry 
of plant respiration. The subject is clearly expounded and 
assumes its modern form in de Saussure’s Recherches chi- 
miques sur la vegetation (1804). 

§9. T. A. Knight (1759—1838) and Tropisms 

A new field of research in plant physiology was opened 
up by Thomas Andrew Knight. This English country 
gentleman was a correspondent of Sir Joseph Banks 
(pp. 236—8). With the purely practical end of improving 
agriculture he made a surprising number of important 
scientific contributions. He is best remembered by the 
device known as Knight's machine. Germinating plants are 
attached to a rapidly rotating disk which may be in a 
horizontal or vertical position. If the plane of rotation be 
vertical, the line of action of gravitational force is con¬ 
stantly changing while the line of action of centrifugal 
force remains constant with reference to the axis of the 
plant. Under these circumstances the stem of the plant 
grows along the radius toward the centre of the wheel, 
while the root grows away from the centre. 

The reaction of the plant to gravity, which can thus be 
eliminated and replaced by centrifugal force, is now known 
as geotropism (Greek = ‘earthward turning’) introduced 
(1868). Such geotropism is spoken of as ‘positive’ for the 
root and ‘negative’ for the stem. Geotropism is a phe¬ 
nomenon of great importance in living things in general 
and in plants in particular. It is the prototype of a whole 
series of similar reactions that have since been discovered 
in living things, both plant and animal. 

These movements are now known by the more general 



Knight and Tropisms 373 

term of tropisms. They may be defined as the simple and 
non-voluntary reaction of an organism or part of an or¬ 
ganism by movement, growth, or bending in response to 
an external stimulus. We thus phototropism (reaction 

to light), heliotropism (reaction to the sun), and thermo¬ 
tropism (reaction to heat). There are also chemical tro¬ 
pisms, one well-known form being the movement of the 
spermatozoids of ferns and other vascular cryptogams to¬ 
wards malic acid. Some naturalists, notably Jacques I.oeb 
(1859-1924), have ascribed many of the phenomena of 
growth and development to tropisms. The theme has been 
particularly stressed in connexion with the conduct of the 
plants and lower animal forms, but also in the modern de¬ 
partment of Experimental Embryology (pp. 492—6). In 
the higher animals tropisms pass insensibly into reflexes 
(pp. 416 ff.). 

§ 10. Liebig (1802—73) and the Chemistry of Vital Activity 

The work of Priestley, Lavoisier, Ingenhousz, Sene- 
bier, and Knight was appreciated by the English chemist, 
Sir Humphry Davy (1778-1829). He combined their 
views with great ability in his Elements of Agricultural 
Chemistry (London, 1813). The real creator of the 
chemistry of vital activity was, however, the commanding 
German teacher, Justus von Liebig (1802—73). 

Liebig was professor of chemistry first at Heidelberg 
and afterwards at Giessen. He was convinced that all 
vital activity could be explained as the result of chemical 
and physical factors. Over the door of the University 
Laboratory which he founded he had inscribed the dictum 
God has ordered all His Creation by Weight and Measure. 
His great achievement was his application of chemical 
knowledge to the phenomena exhibited by living things. 
He did much to introduce laboratory teaching, and certain 
apparatus which he invented is still in constant use. 



374 Essentials of Vital Activity 

Liebig greatly improved the methods of organic analysis 
and notably he introduced a method for determining the 
amount of urea in a solution. This substance is found in 
blood and urine of mammals, and was the first organic 
compound to be ‘synthetized’, that is to say, built up from 
inorganic materials. It is of very great physiological im¬ 
portance, for it is regularly formed in the animal body in 
the process of breaking down the characteristic nitro¬ 
genous substances known as ‘proteins’ (pp. 384-6). 

Along with his colleague, Friedrich Wohler (1800—82) 
who had already synthetized urea, Liebig wrote a famous 
paper (1832) in which he showed, for the first time, that 
a complex organic group of atoms—a radicle as it is now 
called—is capable of forming an unchanging constituent 
through a long series of compounds, behaving throughout 
as though it were an element. The discovery is of primary 
importance for our conception of the chemical changes 
in the living body. From 1838 onwards, Liebig devoted 
himself to attempting a chemical elucidation of living 
processes. In the course of his investigations he did 
pioneer work along many lines that have since become well 
recognized. Thus he taught the true doctrine, then little 
recognized, that all animal heat is the result of combustion, 
and is not ‘innate’. He also classified articles of food with 
reference to the functions that he conceived they fulfilled 
in the animal economy into fats, carbohydrates, and 
proteins. 

Very important was Liebig’s teaching that plants derive 
the constituents of their food, their carbon and nitrogen, 
from the carbon dioxide and ammonia in the atmosphere, 
and that these compounds are returned by the plants to 
the atmosphere in the process of putrefaction. This 
development of the work of Ingenhousz and of others, made 
possible a philosophical conception of a sort of ‘circula¬ 
tion’ in Nature (p. 379). That which is broken down is 



Liebig and Chemistry oj Vital Activity 375 

constantly built up, to be later broken down again. Thus 
the wheel of Life goes on, the motor power being energy 
from without, derived ultimately from the heat of the sun. 
The wheel turns on and on. Whether it will ever stop 
depends upon its motor at the centre of the solar system. 

It was very unfortunate that Liebig conceived putre¬ 
faction as a purely chemical as distinct from a vital process. 
It took Pasteur long years to displace this view. 

§11. The Chlorophyll System 

From the time of Aristotle the idea had prevailed that 
plants absorb their nourishment exclusively by their roots. 
Van Helmont had shown, however, that something was 
absorbed from the atmosphere (pp. 357-9), but it was long 
before his lead was followed. The ultimate destruction 
of the ancient fallacy proceeded along two lines. Firstly 
there was the investigation of the formation of the carbo¬ 
hydrates, and secondly that of the nitrogenous substances. 
The former we consider here; the latter in the next 
section. 

By far the major part of existing living matter is con¬ 
tained in green plants. These provide the ultimate source 
of aliment for the entire animal kingdom. The economic 
significance of the sources from which the substance of 
plants is replenished cannot, therefore, be exaggerated. A 
most important source is carbohydrate, especially in the 
form of starch, the formation of which is associated with 
the green matter itself. 

In the seventeenth century Leeuwenhoek (pp. 164-8) 
saw starch granules in the tissues of plants and he portrayed 
their remarkable concentric form. We now know that 
starch is built up in the plant from the carbon dioxide 
absorbed from the atmosphere; that starch formation is 
a function of the living cell intimately connected with the 
green substance; and that the process is active only in the 



376 Essentials oj Vital Activity 

presence of light. The name Chlorophyll (Greek = ‘leaf 
green’) was attached to this green substance by the two 
French chemists, Pierre Pelletier (1788—1842) and 
Josephe Caventou (1795—1878) in 1817. 

A step toward the modern position was made by the 
French physician and botanical experimenter Henri 
Joachim Dutrochet (1776—1847). It was already known 
from Ingenhousz (p. 371) and others that the plant as a 
whole gave off oxygen and absorbed carbon dioxide. 
Dutrochet recognized (1837) that only those cells that 
contain green matter are capable of absorbing the carbon 
dioxide. 

Perhaps the most influential botanical teacher of the 
nineteenth century was Julius Sachs (1832—97), a pupil 
of Purkinje (pp. 330, 336). Sachs long professed botany 
at Wiirzburg. After applying himself to morphology he 
turned to physiological investigation. From 1857 onward 
he was immersed in problems of nutrition. He soon be¬ 
came convinced that the chlorophyll is not diffused in tissues 
but is contained in certain special bodies —chloroplasts 
as they were later (1883) named by Schimper (p. 270). 
Sachs showed also that sunlight plays the decisive part in 
determining the activity of chloroplasts in absorption of 
carbon dioxide. Further, chlorophyll is formed only in the 
light. Moreover, in different kinds of light the process of 
carbon dioxide assimilation goes on with different degrees 
of activity. The views and discoveries of Sachs were set 
forth in his great treatise on botanical physiology (1865). 

Important for the discussion of starch formation is the 
process by which the gases of the atmosphere come into 
contact with the tissues of plants. In animals this process 
is more evident, especially in such as mammals in which 
the aeration of the lungs is an active process. Plants, how¬ 
ever, were long in giving up their secret. 

The stomata of plants, or little openings on the surface of 



The Chlorophyll System 377 

the leaves, had long ago been figured by Malpighi (pp. 151— 
6). Dutrochet in 1832 called attention to the fact that 
the stomata communicate with intercellular spaces within 
the substance of the leaf. Nevertheless the manner of entry 
of gases into the leaf system remained in dispute for more 
than half a century. It was not until the ’nineties that the 
stomata were generally recognized as the normal channel 
of gaseous entry. 

The critical experiment that determined opinion toward 
Dutrochet’s view was the outcome of the demonstration 
by Sachs that the appearance of starch in the chloroplasts 
follows immediately the absorption of carbon dioxide. 
Thus the presence of starch can be used as an index of 
carbon dioxide absorption. Leaves and parts of leaves 
were coated with wax so as to occlude the stomata. By 
this beautifully simple experiment it was found that starch 
is developed only in the uncoated parts (1894).’ 

In the course of these discussions, the structure of the 
stomata and the nature of the chloroplasts became much 
better known. This was largely the work of Sachs himself 
seconded by Nathaniel Pringsheim (pp. 522—4). The 
chloroplasts have often, if not always, the power of growth 
and division independent of the cell in which they dwell. 
To such an extent is this the case that it has even been sug¬ 
gested that they are, in effect, separate organisms. Chloro¬ 
plasts are merely one of a class of self-multiplying cell 
inclusions (p. 345), named ‘p^^®tids’ in adoption of a 
term of Haeckel (1866). Plastids are found mainly, but 
not exclusively, in plants. 

The formation of starch in the chloroplast is essentially 
a vital phenomenon. It takes place only in the living 
chloroplast and in the living cell. Chlorophyll is not a 

* Some aquatic plants and certain cryptogams as well as certain fossil forms 
are devoid of stomata. Plants without stomata absorb gases through their 
general surface. 



378 Essentials of Vital Activity 

simple chemical substance. Since 1864 it has been known 
that it consists of a mixture of at least two green substances 
together with at least two yellow pigments. The work of 
sixty years has not sufficed, however, to differentiate the 
function of these constituents. 

It was shown in 1882 by the physiologist T. W. Engel- 
mann (1843—1909) that all parts of the spectrum do not 
activate the chloroplast equally. The red is the most 
efficient, the violet less, and other parts of the spectrum 
hardly at all. 

Little is known of the actual chemical process of starch 
formation, but it is certain that there are intermediate pro¬ 
ducts of which formaldehyde is one. The process is 
reversible, since the carbohydrate can be oxidized into 
carbon dioxide and water. The process is specially active 
in growing seedlings. The formula is usually thus re¬ 
presented : 

COj + HjjO + Light energy ^ HCHO + O.^ 

§12. The Nitrogen Cycle 

We turn now to a consideration of the origin and fate 
of nitrogenous substances in the plant. The earlier nine¬ 
teenth century chemists Gay Lussac, Thenard, Davy, 
Liebig, were well aware of the importance of nitrogen 
in the substance of plants. Liebig persuaded men of 
science that nitrogen was taken up by the roots in the form 
of ammonia compounds and nitrates. He steadied the 
whole physiological position by rejecting the old idea of 
absorption of humus and declaring that ‘carbon dioxide, 
ammonia, and water contain in themselves all the necessary 
elements for the production of all living animal and vege¬ 
table matter. Carbon dioxide, ammonia, and water are also 
the ultimate products of their processes of putrefaction 
and decay’ (1840). 

The French chemist and mining engineer, Jean Bap- 



The Nitrogen Cycle 379 

tiste Boussingault (1802-87) applied himself persistently 
and, in the end, successfully to the nitrogen problem. 
During the ’fifties he proved that plants absorb their 
nitrogen not from the atmosphere but from the nitrates of 
the soil. He showed further that no organic or carbon- 
containing matter is necessary in soil for the growth of 
plants, provided that nitrate be present. Thus the carbon 
in plants must all be derived from the carbon dioxide of 
the atmosphere. He applied quantitative methods in these 



experiments (i860) and was correct in his results so far 
as concerned the plants on which he worked. 

Two decades had not gone by before the question of 
nitrogen nutrition was raised in another form by the 
famous historian of chemistry, Marcellin Berthelot (1827— 
1907). This distinguished man did much important work 
on the synthesis of organic compounds. His investigation 
of plant nutrition fits into this series of his researches. In 
1876 Berthelot showed that free atmospheric nitrogen can 
be fixed by electric discharges. Next he proved that the 
presence of certain sugars aids this process. In 1886 and 
the following years he demonstrated that bacteria acting 
in clay soils are able to fix nitrogen. 

It was now evident that the matter of nitrogen fixation 
was of high economic importance. It was soon taken up 
by many other workers whose discoveries have been of 



380 Essentials oj Vital Activity 

the utmost bionomic importance and have modified our 
view of the ‘nitrogen cycle’ (Fig. 149). 

The nature of this cycle is best brought out by a 
diagram. Its existence has been known since Liebig. 
Many details have since been elicited. But over and above 
the familiar circulation of nitrogen it came to be realized 
that certain plants can obtain this element in a way un¬ 
known to Liebig. The discovery is perhaps the most 
significant addition made since his time to our knowledge 
of the economics of life on land. 

In ancient times it was a rule of agriculture to alternate 
leguminous with corn crops. Virgil in his Georgies ad¬ 
vises the farmer to do this. The rule was not wholly 
forgotten during subsequent ages. In 1686 Malpighi 
investigated the germination of leguminous plants and 
figured minute nodules on the roots of the seedlings 
(Fig. 19). His observations were repeated by de Candolle 
(i825),Treviranus (1853), and others. The nodules were 
further found to contain bacteria (1866). The growth 
of these bacteria was investigated by several observers 
(1878—86) while Berthelot’s work was going forward. 

Despite all these concurrent investigations, the real 
significance of the phenomena presented by the Legu- 
minosae, was not fully grasped until the appearance in 
1888 of a classical paper by the two German investigators 
Hermann Helriegel (1831-95) and H. Wilfarth. They 
proved that these plants can absorb atmospheric nitrogen; 
that they do so by means of their root nodules; that their 
rate of nitrogen absorption is proportional to their nodula- 
tion; and that they can live and grow independently of 
either ammonia or of nitrates. 

Not only is this matter of great economic importance, 
but it has, in more recent time, been brought into line 
with a comparable series of phenomena in other plants. 
The agents of nitrogen fixation in the Leguminosae are 



The Nitrogen Cycle 381 

bacteria. Other organisms in other plants are associated 
with the first growths of the roots of seedlings and often 
with the growing points of roots throughout life. Thus 
the organism that we recognize as a higher plant is, in 
fact, a colony of organisms of very different types. The 
same is true of animals. A man, like a plant, is a complex 
of organisms linked together symbiotically (p. 322). 

To complete the conception, we should develop the 
chemistry and bacteriology of soil. These subjects, how¬ 
ever, have not reached the stage at which a brief summary 
is possible. 

§13. The Chemistry of Protoplasm 

There is an immense literature on the chemical char¬ 
acter of protoplasm as the ‘physical basis of life’. Strictly 
the subject is insoluble since protoplasm can only be in¬ 
vestigated when it has ceased to be the basis of life. We 
may learn what protoplasm takes in and what it throws out. 
But living protoplasm is beyond the reach of the chemist’s 
activities. It is protoplasmic products and dead proto¬ 
plasm that have been the subject of his researches. 

Dead protoplasm consists of a very complex mixture of 
numerous substances. Of these the bulkiest is water. The 
others are largely made up of the complex nitrogenous 
group known as proteins and their derivatives, of the 
lipoids or fatty bodies, and of the carbohydrates or starchy 
substances. The distinctness of these three types was 
made definite by Justus von Liebig in his great textbook 
Organic chemistry applied to agriculture and physiology, 
(i 840). The conception of protoplasm itself as a chemical 
substance was made familiar by T. H. Huxley in his well- 
known essay The Physical Basis of Life (1869). Neither 
used the nomenclature with which we are nowadays 
familiar. 

The Dutch chemist, Gerard Johann Mulder (i 802—80), 



382 Essentials oj Vital Activity 

obtained a certain complex substance to which he attached 
the formula 

C.O N„ 0 „. 

He believed that this was the essential constituent of all 
organized bodies and named \t proteine (1838). Later he 
worked with Liebig who soon found that there was no 
such definite compound. The word, however, was re¬ 
tained for the nitrogenous products of which it was a 
mixture. These came ultimately to be known as proteins. 

The words carbohydrate and lipoid had a similar but 
slower development to that of protein. The three terms 
were employed collectively for the first time with reference 
to protoplasm by the Leipzig pathologist Ernst Wagner 
(1829—89). The conception of living protoplasm as an 
enormously complex mixture of those three types of sub¬ 
stance dates from the appearance of Wagner’s Handbuch 
der allgemeine Pathologie (1862). 

Living protoplasm is liquid (pp. 346-7). Nevertheless 
an elementary acquaintance with its behaviour shows that it 
exhibits a considerable degree of ‘viscosity’, that is, it has 
some of the properties of a sticky or of a jelly-like sub¬ 
stance. Modern views of the intimate structure or composi¬ 
tion of living protoplasm have become closely linked with 
a comparison of its behaviour to that of other substances in 
the colloid (‘glue-like’) state. The study of the colloid state 
is one of the many areas in which the old sciences of chemistry 
and physics have become indistinguishable from each other. 

Much of our knowledge of colloid substances is due to 
the chemist Thomas Graham (1805—69). He performed 
the researches with which his name is associated from 
1850 onward while Master of the Mint in London. The 
term ‘colloid’ was already in use, but he applied it to a 
particular state of matter. He distinguished soluble sub¬ 
stances in general into the two great classes, colloids and 
crystalloids. 



Chemistry of Protoplasm 383 

The apparatus used by Graham was of the simplest 
character possible. There can be no doubt, however, 
either of the originality of his methods or of the great 
importance of his results. He observed that certain 
substances id) pass very slowly into solution, (^) do not 
crystallize, and (r) cannot diffuse or diffuse very slowly 
through organic membranes. Of these substances glue is 
the type, hence the name colloid. In this class are starch 
(compare starch paste), white of egg, gelatine (the basis of 
most table jellies). Opposed to these in all three respects 
are the crystalloids. 

Graham distinguished sharply between colloid and crys¬ 
talloid substances, but was aware that certain substances— 
silica for instance—could exist as either colloid or crystal¬ 
loid. He recognized too that instability was a characteristic 
of colloids. Moreover, he perceived that most colloids are 
of organic origin. He almost foresaw certain modern 
views of the nature of vital activity in his conception that 
the surface energy of colloids ‘may be looked upon as the 
probable primary source of the force appearing in the 
phenomena of vitality’. 

The knowledge of the essential nature of colloids was 
but little extended until the twentieth century. Investi¬ 
gators of our own generation have given a physical in¬ 
terpretation to the differences between the colloid and 
crystalloid states. A solution of substances in either state 
may be looked on as a suspension of solid particles in 
another medium. The difference depends on the size of 
the particles, those of colloids being much larger than those 
of crystalloids. Thus the difference is of degree rather than 
of kind, though there are practical difficulties in accepting 
this theoretical conclusion. 

In colloid solutions the dissolved particles are from 
about 2/i,ooo,oooths of a millimetre in diameter up to 
about fifty times that diameter. Much of the recent pro- 



384 Essentials of Vital Activity 

gress in the knowledge of the colloid state has been due 
to the use of the device known as the ultra-microscope.^ in¬ 
vented in 1903. By its means it is possible, in colloid 
solutions, to see light reflected from the floating particles. 
These particles can, moreover, be observed in a state of 
Brownian movement. 

A valuable conception has been introduced by W. B. 
Hardy (1864—) of Cambridge into the view of colloids 
(1899 onwards). It affects our conception of the events 
which follow on the death of protoplasm. 

Colloidal solutions, such as those of gelatine or white 
of egg, can be ‘fixed’ by certain substances into a more or 
less solid state. This may happen in one of two ways. 
Either the solid elements may form a fine sponge-like 
framework enclosing minute droplets of liquid, or the solid 
elements may aggregate into larger separate particles 
forming an excessively fine emulsion (Fig. 150). The 
method of fixation determines which of these states shall 
result. The microscopic appearance will depend on which 
state is produced. This is the case with protoplasm. Thus 
the structure of dead protoplasm cannot be regarded as 
any real index of the state of living protoplasm. 

This criticism does not, of course, apply to larger proto¬ 
plasmic bodies such as chromosomes (p. 342), plastids 
(p. 345), asters (pp. 342—3), and the like which can be 
seen during life. 

Among the colloids, biologically the most important is 
the vast and varied class known as proteins. They are 
absolutely necessary to the building up of protoplasm. 
Dead protoplasm largely consists of them. They are 
not only essential for growth and repair of living substance, 
but they can be and are used as a source of energy and of 
heat, though the carbohydrates and fats share this function 
with them. Chemically the proteins are all built up of 
very large molecules. The modern chemistry of the pro- 



Chemistry of Protoplasm 385 

teins is based on the work of the great German chemist 
Emil Fischer (1852-1919) from 1882 onwards. 

Emil Fischer demonstrated that proteins are built up 
of linkages or condensations of numbers of molecules of 
the substances known as amino-acids. The members of this 
very peculiar class are characterized by the presence in 
each of one or more NH^ (‘amino’) groups and one or 



Pig. 150. Diagrams to illustrate ‘phases’of colloidal systems. The black is 
the solid, the white the liquid element. A represents an ordinary hydrosoL 
in which very minute solid particles are freely movable. Such a prepara¬ 
tion was made by Faraday early in the nineteenth century with extremely 
finely divided gold. His preparations still preserve their character. B repre.sents 
a piyl. It has an alveolar or honeycomb structure. The liquid drops are im¬ 
prisoned by more or less solid walls. Such a preparation is given by a strong 
solution of gelatine when cooled to the ordinary jelly form. 

more COOH (‘carboxyl’) groups. The former gives 
them basic qualities, the latter acid. According as one 
or the other predominate, the amino-acid acts as a base 
or acid. 

A favourite theory of the nature of protoplasm regards 
it as a mixture of amino-acids. These can become im¬ 
measurably complex by associating with each other in 
varyingly intimate ways. A modern mechanist view of 
life pictures all vital activity as a continuous change and 
interchange of the conditions and relations of amino-acids. 
These, it is held, act through local changes in the degree 
of viscosity. It is a fact, in accord with this view, that 
protoplasm does at times change its viscosity in a regular 
and systematic manner as, for instance, in the process of 
cell division. Many other phenomena of the living cell 




386 Essentials of Vital Activity 

have been interpreted as due to changes in degree of 
viscosity. 

Another aspect of protoplasmic activity is that of en¬ 
zyme action. The word enzyme (Greek ‘in yeast’) was 
introduced by Willy Ktihne (1878) to distinguish a class 
of organic substance which activates chemical change. 
Such enzymes can act on an indefinite amount of material 
without losing their activating power. The living body 
produces a large number of enzymes. These are remark¬ 
ably specific in their action. 

Within the protoplasm, though not of it, are numerous 
materials, the so-called ‘food substances’, which are often 
of relatively simple composition. Under this heading are 
to be included sugars and their derivatives, fats, and the 
‘reserve’ proteins (p.381). 

The problem of the nature of protoplasm thus resolves 
itself into that of the nature of the matrix in which a vast 
variety of controlled reactions are taking place, and the 
ways in which the matrix can influence these reactions. 
The chemical processes at any moment within a single 
cell are of many and varied types. In spite of the smallness 
of cellular dimensions, these must somehow be spatially 
separated from one another. 

A very striking fact concerning the reactions within the 
protoplasmic complex is the ease with which they occur. 
Artificial synthesis of sugars is still barely practicable, but 
within the green cell it is both customary and rapid. Many 
enzymes, capable of this and comparable processes, have 
been extracted from plants. When extracted, these en¬ 
zymes will accelerate reactions which otherwise are almost 
imperceptible, so slow is their pace. Enzymes must be 
almost as numerous as the reactions which correspond to 
cellular activity. The cells of yeast have already yielded 
forty distinguishable enzymes. Of the origin or growth 
of enzymes virtually nothing is known. 



152 


*53 


Drawings made by Goehte to illustrate the morphology of leaves 
(Sec p. 215). 

F'lc;. 151. A monstrous rose. Thestamensare replaced by pctal-likeoxpansions. 
The pistil is reprcwsented by a continuation of the stem on which are petal-like 
and leaf-like structures together wdth others of a character intermediate betw^een 
the two. 

Fig. 152. A seedling bean to illustrate the homology of cotyledons wdth other 
leaves. A plant, IVehoitschia, has since been discovered w'hich does not develop 
beyond this four-leaf stage. 

Fig. 153. Young chestnut branch just emerged from bud. It shows transition 
from scales, through leaf-like scales, to complete leaves. 


C C 2 


XI 


RELATIVITY OF FUNCTIONS 

§ I. Johannes Muller (1801—58) and the haw of Specific 
Nerve Energies 

A new spirit was introduced into Biology in Germany 
by the gifted but short-lived Johannes Muller. He 
ranks among the greatest biologists of all time. 

Muller was the son of a shoemaker. He showed early 
promise, studied Medicine, filled the chair of Anatomy 
and Physiology at Bonn, and was called thence to Berlin. 
His last twenty-five years were crowded with teaching and 
writing. The general direction of modern physiology and 
morphology has been largely determined by him. His 
character and bearing were of a dignified and lofty as¬ 
ceticism, and he approached his labours as a prophetic call. 

In Muller’s Handbook of Physiology (1834—40), the 
results of comparative anatomy, chemistry, and physics 
were for the first time systematically brought to bear on 
physiological problems. His researches on the chemistry 
of the animal body touch on those of Liebig at many 
points. His most important physiological work, however, 
dealt with the action and the mechanism of the senses. 
His explanation of colour sensations, his account of the 
internal ear, his description of the structure and action of 
the organs of voice, were all important starting points for 
modern physiological research. 

The doctrine specially associated with Mtiller’s name is 
the ‘principle of specific nerve energies’. This teaches that 
the kind of sensation, following the stimulation of a sen¬ 
sory nerve, depends not on the mode of stimulation but on 
the nature of the sense organ with which the nerve is 
linked. Thus mechanical stimulation of the nerve of the 



Law of Specific Nerve Energies 389 

eye produces luminous impressions and no other; stimula¬ 
tion of the nerve of hearing gives rise only to an auditory 
impulse, and so on. 

Muller’s doctrine of specific nerve energies is of such 
importance that it is well to consider some of its implica¬ 
tions. 

What do we know of the world in which we live ? Only 
what our senses tell us. But how do our senses convey 
anything to us ? That no man can answer. All we know 
is that certain external events somehow initiate specific 
disturbances in certain nerves, that these nerves convey 
the disturbances to the brain or central nervous system 
and that a sensation then arises. We have a glimmering 
of understanding of the mechanism by which the external 
event elicits a specific nerve impulse. But as to how that 
impulse becomes a sensation, which alone is what we 
experience, and how that experience can give rise to 
something which so alters a nerve or series of nerves that 
it induces action—of these things we are as ignorant as 
Aristotle. There are reasons to believe that ignorant we 
shall remain, and that here is a veil which never can be 
rent by mortal man. 

But consider further. Such external events as we ex¬ 
perience, we know only by their action on our senses. 
Nevertheless from one and the same event we may receive 
utterly different sensations. Thus, an electric stimulation 
of the optic nerve will give rise to a visual sensation; the 
same stimulation of the olfactory nerve yields a sensation 
of smell; of the auditory nerve, a sensation of sound. 
Further, different events may give rise to the same order 
of sensation. Thus it matters not whether the optic nerve 
is stimulated electrically, thermally, or mechanically; in 
each case the sensation will be visual. If our optic nerve 
were grafted to our auditory organ and our auditory nerve 
to our optic organ, we should find ourselves transported 



390 'Relativity oj Functions 

to a world so strange that we cannot form the remotest 
conception of it. To beings with senses different from 
ours, the world would be utterly different. 

The law of specific nerve energies is thus fundamental 
for our view as to the range of validity of scientific method, 
and indeed of experience as a whole. That law is a stand¬ 
ing criticism of the ‘common-sense’ view that the world 
is just as we see it and that its contents, and particularly 
the living things in it, can be exactly and completely 
understood by us. 

The later part of Muller’s short life was given to mor¬ 
phological research. He was one of the founders of the 
modern science of embryology (p. 470). There is hardly 
a group in the animal kingdom on the knowledge of which 
he has not left his mark. Moreover, he worked out the 
microscopic anatomy of glandular and cartilaginous tissues, 
and thus prepared the ground for his pupil Schwann 
(pp. 332—5). Again, his introduction of the microscope into 
the scientific study of disease was carried further by 
another gifted pupil, Virchow (pp. 340-1). There are many 
other special departments which Muller initiated. 

Muller was a convinced vitalist. He laid emphasis on 
the existence of something in the vital process that was 
and must remain insusceptible of mechanical explanation 
or physical measurement. This doctrine, however, oc¬ 
casionally misled him. Thus he held it impossible to 
measure the velocity of a nervous impulse. Yet that 
velocity was measured by his own pupil, Helmholtz, some 
ten years later. 

§2. Karl Ludwig (1816-95) Mechanism 

Less universal as an intellect than Johannes Muller, 
but hardly less important as a teacher, was Karl Ludwig 
(1816—95). perhaps, the most successful of all 

teachers of physiology. Much of the important physio- 



Ludwig and Mechanism 391 

logical research between about 1870 and 1910 was the 
work of his pupils. He published little in his own name. 

Among the many lines of investigation initiated by 
Ludwig, the most remarkable depended on his introduc¬ 
tion of new technical methods. He had an exceptionally 
wide knowledge of the physical sciences, and he excelled 
in mechanical skill and in ingenuity of device. The most 
important invention or rather adaptation of Ludwig is the 
mechanically rotating drum or kymograph (Greek ‘wave 
writer’). This instrument is now in general use for the 
permanent record of all sorts of continuous movement. 
The self-recording barometer is a familiar example. The 
kymograph led to a much wider applications of the method 
of automatic record. Ludwig applied it specially to in¬ 
dicate the movements of breathing as well as the variations 
of the pressure of blood in the arteries. It has since been 
in constant use for recording vital movements and changes 
of many kinds, including the transient electrical distur¬ 
bances associated with nerve impulses. 

An instrument invented by Ludwig is the mercurial 
blood-gas pump. Its purpose is to separate from the blood 
the mixture of gases which it contains. This apparatus 
was indispensable for the investigation of the physiology 
of breathing by Ludwig’s pupil Pflhger (pp. 404-6), and 
modifications of it are still in use. 

Ludwig devoted much attention to secretion. Here 
especially his work gave support to mechanist views. He 
succeeded in showing that the process of secretion can be 
so transformed as to do external mechanical work. Thus 
secretion can be made to fit into the modern physical 
conception of energy (p. 396). 

Ludwig explained many other physiological events on a 
physical or chemical basis. His methods were followed 
and developed by his pupils, and he is largely responsible 
for the mechanistic view of the nature of life that was and 



39 ^ Relativity of Functions 

is prevalent among the leading exponents of the science of 
animal physiology. 

§ 3. The Early French Experimental Physiologists. Claude 
Bernard (1813-7 8) 

French science in general has been more isolated than 
English, German, or Italian. At the beginning of the nine¬ 
teenth century the supreme influence in French biology 
was Cuvier, of whom it has been said that ‘he mastered 
not only his subject but also his opponents’. His destined 
successor was M. F. X. Bichat (1771-1802). He died at 
thirty-one, too early to develop his conclusions. 

Bichat’s analysis of the body into ‘tissues’ (p. 327) 
has survived only in name; in essence it has been rejected. 
Bichat’s basic idea was that the life of the body is the 
resultant of the combined and adjusted lives of the various 
tissues of which it is upbuilt. He held to the conception 
of a definite vital force. The activities of living things he 
regarded as a result of the conflict of this force with 
physico-chemical forces. The latter have full play at 
death, but not till then. In giving a separate life to each 
tissue Bichat, though turning away from the vitalism of 
Stahl (pp. 361—2), and still more from the mechanism 
of Boerhaave (pp. 362—3), was really reviving the old con¬ 
ceptions of Paracelsus and Helmont. 

Bichat’s spiritual successor was Fran9ois Magendie 
(1783-1855). Recognizing ‘vital force’, he regarded it as 
beyond the reach of experiment. But the physico-chemical 
elements of the body he considered to be fully within his 
field, and he threw himself with enthusiasm into their in¬ 
vestigation. He indulged in a perfect orgy of experiments 
that were technically most skilful though seldom philo¬ 
sophically thought out. His most important result was the 
exact demonstration of the doctrine, already set forth by 
Charles Bell (p. 411) that the anterior nerve-roots of the 



Bernard 393 

spinal cord convey the impulses of movement, while the 
posterior convey impulses to the brain that are translated 
into sensation (Fig. 155). 

The pupil and successor of Magendie was Claude 
Bernard. He was a severe and powerful thinker with an 
Olympian intellectual aloofness. Inheriting the technique 
and principles of Magendie, he utterly surpassed him in 
the deep and searching manner in which he devised his 
experiments. 

One of Bernard’s greatest discoveries, the elucidation of 
which occupied over ten years, was that the liver builds up, 
from the nutriment brought to it by the blood, certain 
highly complex substances which it stores against future 
need. These substances, and notably that known as 
glycogen., it subsequently modifies for distribution to the 
body according to its requirements. 

Now Wohler in 1828 had synthetized urea (p. 374). 
This substance was recognized as a final degradation pro¬ 
duct which the body manufactures by breaking down 
substances derived from food. It had also become recog¬ 
nized that the source of bodily energy is this breaking-down 
process. Bernard, by his work on glycogen, demonstrated 
that the body not only can break down but also can build up 
complex chemical substances. This it does according to 
the various requirements of its various parts. 

Bernard thus destroyed the conception, then still 
dominant, that the body could be regarded as a bundle of 
organs, each with its appropriate and separate functions. 
He introduced what we may call a ‘physiological syn¬ 
thesis’, a conception that the various forms of functional 
activity are interrelated and subordinate to the physio¬ 
logical needs of the body. 

No less important, as bearing on this conception, was 
Bernard’s work on the physiology of digestion. Up to 
his time, an elementary knowledge of the facts of digestion 



394 Relativity of Functions 

in the stomach constituted the whole of digestive physio¬ 
logy. While Bernard was working on the glycogenic 
function of the liver, one investigator had suggested that 
the secretion sent forth by the organ known as the 
‘pancreas’, or sweetbread is capable of emulsifying fats. 
This, it was held, is its function in digestion. Another 
worker demonstrated that pancreatic juice acts also on 
starchy matter in food. 

Bernard now showed that digestion in the stomach is 
‘only a preparatory act’. The pancreatic juice, passing 
into the intestine, emulsifies the fatty food substances as 
they leave the stomach, and splits them into fatty acids 
and glycerin. He showed further that the pancreatic juice 
has the power to convert insoluble starch into soluble 
sugar, and that it has a solvent action on such ‘proteins’ 
as have not been dissolved in the stomach. 

A third great synthetic achievement of Bernard was his 
exposition of the manner of regulation of the blood-supply 
to the different parts of the body. This we now call the 
‘vaso-motor mechanism’. In 1840 the existence of muscle- 
fibres in the coats of the smaller arteries was discovered. 
Bernard showed that these small vessels contract and ex¬ 
pand, thereby regulating the amount of blood supplied to 
the part to which they are distributed. This variation in 
calibre of the blood vessels is, he showed, associated with 
a complex nervous apparatus. The reactions of the ap¬ 
paratus depend upon a variety of circumstances in a variety 
of other organs. Thus he again provided an illustration 
of the close and complex interdependence of the various 
functions of the body upon each other. 

Bernard’s clear conception of the interdependence and 
reciprocal relations of the organic functions led him to a 
very valuable generalization. He perceived that the 
characteristic of living things, indeed the test of life, is the 
preservation of internal conditions despite external change. 



Bernard 395 

‘All the vital mechanisms,’ he held, ‘varied as they are, 
have only one object^ that of preserving constant the 
conditions of life in the internal environment’. 

The phrase stamps Bernard’s belief that the living or¬ 
ganism is something sui generis, something quite different 
from everything in nature that is not living. The organism 
has an object, and it uses a mechanism for attaining that 
object. Is this conception infinitely removed from that 
of Aristotle (pp. 37—41).'’ 

What is the internal environment of an organism.? 
Bernard was thinking chiefly of the blood. But if we think 
of a part in terms of cells we see the environment of the 
cell made up of four main factors: 

{a) The neighbouring cells and cell products. 

(^) The substances that are brought to it by the blood. 

(c) The substances that it throws off and that are 
removed from it by the blood. 

(d) The nervous impulses that come to it, the physical 
nature of which is still but very little known. 

To all of these we shall be returning. 

§4. Energetics 

A characteristic phenomenon of life is certainly move¬ 
ment. This is something over and above the molecular 
and atomic movement, or the mechanical change to which 
all matter is subject. Qrganic movement is of relatively 
large and visible masses, is relatively rapid, and is condi¬ 
tioned by an ‘end’ or ‘purpose’. Whatever our view of 
the nature of life, when we seek to describe its exhibitions 
we are forced to use terms which imply such end. Aristotle 
recognized this. He invented the term entelechy or ‘in¬ 
dwelling purposiveness’ to describe the governing prin¬ 
ciple of the organism. 

At first sight it might be thought that the vegetable 
kingdom is exempt from the rule that movement is char- 



396 'Relativity oj Functions 

acteristic of life. This, however, is not the case. Many 
fixed plants pass through a phase in which they move 
freely. Movement is characteristic of the sexual process 
in all plants. It is also characteristic of the phenomena of 
cell division (pp. 341—4). Moreover, in cells of fixed 
plants there is an active streaming of living protoplasm 
(pp. 240, 336, and Fig. 142). Movement, in fact, is as 
characteristic of living protoplasm as is metabolism, of 
which movement is at once an exhibition and a product. 
Movement, like metabolism, may, under some circum¬ 
stances, be reduced to a minimum. 

Physicists have worked out the general principles of the 
transformations of the various forms of energy. These are 
expressed most conveniently in terms of their heat equiva¬ 
lents. Landmarks in the history of the subject are the 
enunciation in 18 24 of his famous ‘axiom’ of the dissipation 
of energy by Sadi Carnot (1796—18 32); the determination 
in 1840-3 of the mechanical equivalent of heat by J. P. 
Joule (18 19—89); and the formulation in 1845 of the law 
of the ‘conservation of energy’ by J. R. Mayer (1814—78) 
and Hermann Helmholtz (1821—94). Until these doctrines 
were available, there could be no true science of energetics, 
either for the biological or non-biological world. 

A fundamental principle of the science of energetics is 
that, in any system, the capacity for doing mechanical work 
tends always to decrease, except in so far as it is increased 
from without. The principle is of great importance 
whether we consider mechanical systems or living bodies. 
It also has its implications in cosmology and philosophy. 

The energy of living things is derived from chemical 
changes. These may be expressed as the oxidation of food 
and of the products of food. The energy of living things 
is utilized in various ways and need not and often does 
not pass through the form of heat. 

A form of energy, associated with liquids, is that known 



Energetics 397 

as ‘surface energy’. When a liquid, such as the protoplasm 
of an Amoeba, is in contact with another liquid, such as 
water, the surface between them has the properties of a 
stretched film. It can therefore do work if the tension of 
this film be decreased, just as the stretched India rubber of 
a catapult can do work when released. Attempts to explain 
the action of protoplasm have been made on this basis. 

For these attempts Amoeba has often been taken as the 
exemplar. The behaviour of this organism can be reduced 
to terms of protoplasmic flow. The flow in this and in 
other protozoa, as well as movements of protoplasm in 
higher beings, could, it was believed, be explained as due to 
changes of surface energy. These changes are in their turn 
due to chemical changes within the protoplasm, which alter 
or suddenly destroy the surface tension at different points. 

The great mathematical physicist J. Clerk Maxwell 
(1831—79) compared the transactions of the material 
universe to ‘a system of credit’. Each transaction consists 
of the transfer of so much credit or energy from one body 
to another. This act of transfer or payment is called work. 
There is no part of the universe accessible to us where the 
ledger has been closed. The transactions are ever going 
on. In the world of life these transactions are very active, 
are largely chemical in nature, and are constantly in op¬ 
posite directions. The transactions in the living organism 
may be summed up in the word metabolism. 

So far as has yet been discovered, the actions of living 
things accord with the general laws of physics and 
chemistry. They have not been shown to break the laws 
of energy. It is true that living things are peculiar systems 
which cannot be imitated, produced, or paralleled, and 
that some of their processes—and notably the progress 
from youth to age—are irreversible.* Nevertheless, so far 

* For some organisms and under some conditions this statement requires 
qualification. 



398 Relativity of Functions 

as can be seen, living things obey the laws of thermo¬ 
dynamics and other rules of physics. Many biologists 
therefore refuse to recognize or discuss the existence of 
anything of the nature of a .‘vital action’. In the present 
stage of research, the conception of ‘vital action’ has no 
place in the physiological laboratory, since physiologists 
are occupied in examining functions separately and not 
in examining organisms as wholes. None of these reasons 
need prevent the biological philosopher from forming his 
own views according to the evidence. 

It must be remembered that the amount of energy con¬ 
sumed by the cell need have no relation to the external work 
done. Some cells, such as those of the muscles and of the se¬ 
cretory cells of the glands, do considerable external work; 
others, as the nerve-cells or the fertilized egg-cells, hardly 
any. But both types demand a good supply of oxygen. 
The work done by the nerve-cells and the egg-cell must, 
therefore, be internal. These cells need energy for the 
maintenance and development of their own structure. The 
demand and search for and the utilization of energy for the 
maintenance of internal structure is altogether characteris¬ 
tic of living things. 

In this connexion it is appropriate to invoke a famous 
illustration by Clerk Maxwell. An established law of 
thermodynamics is that, in a system in which temperature 
and pressure are uniform, and so enclosed that neither 
change of volume nor passage of heat is permitted, no 
inequality of temperature or pressure can be produced 
without expenditure of work. 

But if we look within the system and if we consider it 
not as a uniform mass but as a group of molecules, we 
find that these conditions of uniformity are not fulfilled. 

‘If we conceive’, says Clerk Maxwell, ‘a being whose faculties are 
so sharpened that he can follow every molecule in its course, such 
a being, whose attributes are still as essentially finite as our own. 



Energetics 399 

would be able to do what is impossible to us. The molecules in 
a vessel full of air at uniform temperature are moving with velocities 
by no means uniform. Now suppose that such a vessel is divided 
into two portions, A and B, by a division in which is a small hole, 
and that a being, who can see the individual molecules, opens and 
closes this hole, so as to allow only the swifter molecules to pass 
from A to B, and only the slower to pass from B to A. He will 
thus, without expenditure of work, raise the temperature of B and 
lower that of A in contradiction to the law that we have considered.’ 

‘Clerk Maxwell’s demon* may be looked upon as the 
vitalistic crux. Does our conception of the behaviour of 
inorganic matter provide that uniformity in diversity 
which is demanded for any adequate conception of the 
stream of living things throughout the ages.^ Will it 
explain the apparent purposiveness of the developing 
ovum } Can it account for consciousness and will "i Does it 
cover all the phenomena of life and especially of mind.? 
The vitalist answers these questions in the negative, but 
this denial does not contradict or infringe the laws of 
thermodynamics. 

§ 5. Muscular Action 

Among the higher animals, movement is very evident. 
It is always brought about by the action of muscles. These 
structures were long ago subjected to microscopical an¬ 
alysis. The process began with Leeuwenhoek and Stensen 
in the seventeenth century and continued through a long 
line to Bowman (1840), Kolliker (1851), and beyond. 
These observers have shown that muscles are essentially 
collections of innumerable minute elongated fibres which 
are definitely cellular and are living. Muscle-fibres are 
so constructed that during ‘contraction* their ends, and 
consequently the ends of the muscle itself, are approxi¬ 
mated (Fig. 93). 

The word ‘contraction* must not mislead the reader 



400 ’Relativity oj Functions 

into supposing that either the muscle fibre or the muscle 
becomes smaller in total bulk. Such is not the case. No 
change of bulk takes place during contraction (p. 164). 
What happens within the muscle-fibre during contraction ? 
This has been the subject of microscopic investigation 
since Leeuwenhoek. The optical difficulties are so great 
and their interpretation so various and so unsatisfactory 
that almost nothing has yet been learned as to these 
structural changes. 

As regards chemical aspects of the question we are in 
better case. One important chemical conclusion in con¬ 
nexion with the ‘contraction’ of muscle is that the sugar— 
with which it is kept continuously supplied from the stored 
glycogen of the liver—is changed into another form of 
carbohydrate, lactic acid. The process is not essentially 
an oxidation, for it takes place freely in the absence of 
oxygen. 

A second important conclusion is that recovery from 
contraction is an active chemical process. About one- 
fifth of the lactic acid produced during contraction is nor¬ 
mally oxidized—‘burnt up’—during recovery or relaxa¬ 
tion. The remaining four-fifths of the lactic acid is 
reconverted into glycogen and stored for further use. 

The history of our knowledge of lactic acid and its rela¬ 
tion to muscle tissue is intricate. Lactic acid was originally 
isolated from sour milk in 1780 by the Swedish chemist 
Scheele (1742—86). Its formation in milk was ascribed to 
micro-organisms by Pasteur in 1857 in his epoch-making 
Memoire sur la fermentation apfelee lactique. The same 
acid had been found in meat extract by Liebig in 1832 and 
synthetized in 1850. In the latter year Helmholtz sfiowed 
that muscular contraction resulted in the formation of an 
acid substance. In 1867 Adolf Pick (1829-1901) of 
Cassel, a pupil of Ludwig, showed that muscular contrac¬ 
tion was associated with carbohydrate metabolism. In 



Muscular Action 401 

1871 it was proved that the muscles were the site of the 
chemical regulation of heat in the animal body. In the 
same year Hugo Kronecker (1839—1914), another pupil 
of Ludwig, demonstrated that the acid formed during 
muscular contraction is similar to that in sour milk. The 
role of the muscles in heat regulation was settled during 
the next decade in Ludwig’s laboratory at Leipzig. 

The action of the muscles accords with the ordinary 
laws of mechanics. In antiquity this was perceived with 
some clearness by Galen. He knew of such mechanical 
laws as those of the lever and the pulley set forth by 
Archimedes. Galen applied them to muscular action 
(Fig. 156). 

In the seventeenth century, the impetus given to the 
science of mechanics by Galileo encouraged attempts in 
the same direction. The principle of the parallelogram of 
forces was applied to muscles in general by Niels Stensen 
(1667), and to the muscles of respiration in particular by 
John Mayow (i 668). Giovanni Alfonso Borelli (1608—79) 
of Bologna, a pupil of Galileo, placed muscular mechanics 
on a firm scientific footing. His great De Motu animalium 
(Rome, 1680) seeks to treat all the movements of the body, 
both voluntary and involuntary, on a mechanical basis. 

The mechanics of muscular movement has attracted the 
attention of human anatomists since Borelli. Mechanical 
principles have been invoked in the examination of the 
more rigid parts on which the muscles act. The skeleton, 
and its accessory structures, the cartilages, are formed in 
many respects along the lines best suited to meet the 
muscular stresses and strains that they have to bear. Thus 
the structure of the bones is often close to that which 
would have been given them had they been designed by 
a modern engineer (Fig. 154). 

Ever since Galen, much has been made of this evidence 
for design in the body. The argument, however, cuts both 

2613.3 ud 



402 Relativity of Functions 

ways, for there are many parts of the body the design of 
which is, in fact, very inadequate. Take, for example, the 
eye. That organ is focussed by alteration in the shape of 
the lens—^the result of its elasticity. But the elasticity of the 
lens, like that of a piece of caoutchouc, gradually wears out. 
With advancing age we all have to take to spectacles. Had 



bone has to support the entire weight of the body, the direction of action of 
which is shown by the arrow. B, Vertical section of the thigh bone. The lines 
show the direction of stresses and strains. These correspond with the develop¬ 
ment of bony tissue. This part of the thigh bone is thus constructed much as 
it would have been by an engineer with due regard to economy of material 
and the nature of the material with which he had to work. 

the lens been focussed, like that of a telescope or micro¬ 
scope, by movement backward and forward, no such arti¬ 
ficial device would have been needed. No good working 
optician would send out an instrument so clumsily 
designed as the human eye. 

We may note that the investigation of muscular 
mechanics has been almost exclusively upon the human 
body. It has been in the main a tribute which the science 
of biology has paid to the art of surgery. To complete the 
conception of the body as a muscular mechanism, it would 
be necessary to work out the subject on an evolutionary 



Muscular Action 403 

basis. The ‘entelechy’ (p. 395) or vital force or whatever 
we may call it that shapes our bodies has to work with 
imperfect instruments. Those instruments, both in their 
values and in their shortcomings, can be understood only 
through their evolutionary history. It is this historical 
element which marks them as vital products and separates 
them from those of the inorganic world. 

§ 6. Respiration as Combustion 

The importance of breathing to the animal organism 
cannot be missed. It provides the crude test of life, and 
we do not die until we ‘breathe our last’. The word used 
for ‘spirit’ (Latin sptro^ ‘I breathe’), the theoretical basis 
of life, contains this idea in most languages (pp. 15—16). 
The importance of breathing was recognized in the phy¬ 
siological system of Galen (p. 102). Real advance in the 
knowledge of the subject was, however, deferred until 
Chemistry became a science in the second half of the 
seventeenth century. 

In the nineteenth century, the bare chemical facts of 
respiration being ascertained and their resemblance to 
those of combustion, the organism came to be compared to 
a steam engine. In such a machine, the draught of air leads 
directly to oxidation of the fuel. The accompaniment of 
oxidation is heat which is transformed into work. The 
parallel is now quite familiar. It was drawn in 1842 
by the German physician J. R. Mayer, founder of the 
doctrine of Conservation of Energy (p. 396). 

Arising out of the discussion of the relation of work to 
oxidation in the animal body were two fundamental ques¬ 
tions : 

{a^ What is the essential nature of the combustible 
material ? 

{b^ Where in the body is it consumed ? 

An answer to the former question was reached by Liebig 

D d 2 



404 'Relativity oj Functions 

and his colleagues. Foods were classed as proteins, fats, 
and carbohydrates (pp. 374, 381—2). Of these only the first 
contains nitrogen. It reappears mainly in the urine and 
mainly as urea. The fats and carbohydrates are completely 
oxidized in the body into water and carbon dioxide. It 
thus became possible to calculate the amounts of the food 
substance absorbed from the ratios and amounts of the 
nitrogen compounds and carbon dioxide thrown off and 
the oxygen consumed. 

The answer to the latter question was longer in coming. 
The perfecting of the mercurial blood-pump by Ludwig 
and his pupil E. F. W. Pfliiger (1829—1910) was the main 
factor (p. 391). This instrument extracts from blood the 
contained gases, which can then be analysed. It was thus 
established that oxygen absorbed during breathing is 
taken up in the form of a chemical combination with the 
red colouring matter in the blood corpuscles. This colour¬ 
ing matter, known as haemoglobin, gives up part of its 
oxygen as the blood passes to the tissues, and then returns 
to the lung for a fresh charge. The discharge of oxygen 
in the tissues is accompanied, as is well known, with a 
change in the colour of the blood from scarlet to purple. 
Similarly carbon dioxide is taken up from the tissues and 
discharged in the lung. 

For long there was doubt as to whether and how far 
the oxidation took place in the tissues or the blood. By 
1872 Pfliiger had shown that it took place only in the 
tissues, whither the oxygen is conveyed by the blood, as 
is also the nutriment. Thus the study of respiration was 
brought into relation with that of nutrition. 

Before Pfliiger, the relationship of respiration to animal 
heat was regarded as a blind mechanical process. Thus 
Liebig held that the rate of oxidation and consequent heat 
production is proportionate to the amount of food ab¬ 
sorbed from the alimentary canal and oxygen introduced 



Respiration as Combustion 405 

into the lung, just as the heat of a furnace is a function of 
the fuel consumed and the draught created. In support of 
this he showed that increase in the amount of nitrogenous 
food absorbed is followed by proportional increase in the 
amount of nitrogen excreted. This view, of animal respira¬ 
tion merely as combustion, is untenable, but here, for the 
moment, we shall leave it (see pp. 406—8). 

The conception of the nature of respiration in plants 
was only gradually brought into line with that of animals. 
By the end of the first third of the nineteenth century it 
was known that green plants in the light absorb carbon 
dioxide and give off oxygen, while in the dark they absorb 
oxygen and give off carbon dioxide (pp. 375-8). The 
two processes were held to be of comparable character and 
became known as ‘day respiration’ and ‘night respiration’. 
Liebig went so far as to deny that plants respired at all in 
the proper sense. 

Sachs in the ’sixties was the main agent in the dispersal 
of the confusion that thus arose. The major facts he estab¬ 
lished in connexion with plant respiration were four in 
number: 

{a) Respiration in plants, as in animals, involves ab¬ 
sorption of oxygen and oxidation of assimilated substances. 
This leads to the formation and exhalation of carbon 
dioxide. The process is masked but not suppressed by the 
process of starch formation and the accompanying assimi¬ 
lation of carbon dioxide and discharge of oxygen by the 
chlorophyll apparatus. 

(^) The respiratory process of plants becomes more 
active with rapid growth or metabolic change. 

(c) The streaming movements of protoplasm and other 
active exhibitions of movement by plants are decreased 
and finally cease if oxygen be withheld. 

(i/) If nutrition be suspended, weight is lost. This is 
ascribable to respiration. 



4 o 6 Relativity of Functions 

Thus the respiratory process of plants was brought 
fairly into line with that of animals. The process, as with 
animals, was freely compared to the combustion in an 
engine. Moreover, the process of combustion was re¬ 
garded by Sachs as essentially a consumption of fats and 
carbohydrates which were separately grouped in the 
hypothetical protoplasmic molecule. 

§ 7. Respiration as Relative to Physiological Needs 

During the ’seventies, largely owing to the work of 
Pfluger, it transpired that the view of respiration as com¬ 
bustion is inadequate to explain the phenomena. If no 
food be taken, the amount of nitrogen excreted falls greatly, 
but there is little fall in the amount of oxygen consumed. 
This means that fat and carbohydrate are being oxidized, 
while protein is being conserved. Such is, in general, the 
policy of the animal body. 

The ratios in which protein, fat, and carbohydrate re¬ 
place one another were next determined. These are pro¬ 
portional—^within wide limits—to the energy which they 
liberate by oxidation within the body. Thus the rate of 
oxidation is not determined merely by the rate of food 
supply but is regulated according to the energy require¬ 
ments of the body—and is moreover so regulated with 
great accuracy. 

It should be remembered, however, that even with com¬ 
plete starvation of nitrogenous material, the consumption 
of nitrogen does not cease. It may fall, however, to the 
extraordinarily low level of about 8/i,ooo,oooths of the 
body weight per day (1911). This minute amount of 
nitrogen is obtained by the organism through the break-up 
of its own tissues. 

Just as the rate of oxidation is not determined by the 
food supply, so also it is not determined by the supply of 
oxygen. Again, within wide limits, Pfltiger found that the 



Respiration as Relative to Physiological Needs 407 

amount of oxygen consumed is altered neither by rise nor 
fall of oxygen concentration. It is determined by the 
requirements of the organism—and again the determina¬ 
tion is very exact. 

Similarly—^within wide limits—^the body determines its 
own temperature, whatever the temperature of the sur¬ 
rounding medium. PflUger showed that if the surround¬ 
ing temperature of a warm-blooded animal be lowered, 
the cold evokes, via the nervous system, a rise in heat 
production. The body temperature is maintained at the 
same level. This maintenance is thus a factor determining 
the energy requirements. 

The progress of botanical physiology has been on essen¬ 
tially the same lines. Everywhere consumption has come 
to be seen as no blind process, but as related to the physio¬ 
logical needs of the organism as a whole. The process is 
less evident in the plant than in the animal only because 
the plant is less integrated under a directing mechanism, 
because it is, in short, less an ‘individual’. 

We might go through the whole gamut of functions 
and find them all subservient to the preservation of a 
norm. The science of physiology, like every other science, 
has many ‘loose ends’ which have not yet been traced to 
their connexion with the central theme. But wherever 
research has been long maintained upon a definite line, it 
leads back to this conception of bodily activity regulated in 
subservience to physiological needs. It is a theme that has 
been expounded by many writers, but by none with more 
learning and eloquence than by the English philosopher 
and physiologist, J. S. Haldane (i860— ). The con¬ 

ception gives us the justification of biology as a separate 
science that can never become a department of Chemistry 
and Physics. 

‘Up to a certain point we can understand living organisms mechani¬ 
cally. We can, for instance, weigh and measure them and their 



408 Relativity of Functions 

parts, and investigate their mechanical and chemical properties. 
This enables us to predict certain points in their behaviour. But 
when we look more closely it becomes quite evident that the 
knowledge we gain hardly touches any fundamental physiological 
problem. We cannot escape from the relativity of the phenomena 
we are dealing with. 

‘The only way of real advance in biology lies in taking as our starting 
point, not the separated parts of an organism and its environment, 
but the whole organism in its actual relation to environment, and 
defining the parts and activities in this whole in terms implying 
their existing relationships to the other parts and activities. We can 
do this in virtue of the fundamental fact, which is the foundation 
of biological science, that the structural details, activities, and en¬ 
vironment of organisms tend to be maintained. This maintenance 
is perfectly evident amid all the vicissitudes of a living organism and 
the constant apparent exchange of material between organism and 
environment. It is as if an organism always remembered its proper 
structure and activities; and in reproduction organic ‘memory’, as 
Hering (1870) figuratively called it, is transmitted from generation 
to generation in a manner for which facts hitherto observed in the 
inorganic world seem to present no analogy. We can discover and 
define more and more clearly by investigation these abiding details 
of structure and activity, distinguishing accidental appearances from 
what is really maintained; and this process of progressive definition 
is the work of the biological sciences.’ (J. S. Haldane, 1922.) 

§ 8. Vital Activity of Plants and Animals Approximated 

During the eighteenth and early nineteenth centuries, 
the study of plants had tended to become widely separated 
from that of animals. Thus a true science of ‘Biology' in 
the sense of Lamarck and Treviranus (p. 294) became 
more and more distant. From about i860 plant and animal 
biology drew nearer to each other. It is worth tabulating 
some of the reasons for this. The approximation has had 
and is having an important influence in moulding biological 
thought. 

{d) The methods of respiration and of nutrition in 



Vital Activity oj Plants and Animals 409 

plants and animals have been shown to be basically similar 
despite great apparent differences (pp. 405—6). 

{b') The chlorophyll apparatus is specially characteristic 
of plants, but there are plants that have no chloroplasts and 
there are a few unquestionably animal species that have 
these structures. Moreover the chloroplasts can multiply 
independently of the organism in which they are con¬ 
tained, and the containing organism, in some cases, in¬ 
dependently of the chloroplasts. It has even been shown 
that certain lower forms, which usually contain chloro¬ 
plasts, can, under suitable conditions, thrive through an 
indefinite number of generations after their loss {Euglend). 

Plants are divided from animals by a very indefinite 
line, and the chlorophyll apparatus is found on both sides 
of that line. Its extensive occurrence in the plant world is 
correlated with the stationary habit of the plant. Plants 
cannot go forth to gather their food. They fasten on that 
which comes to them (pp. 375—81). 

(f) The conception of ‘protoplasm’ has had much in¬ 
fluence. That conception was directed by the discovery 
that the living substance of plants is indistinguishable in 
general appearance and in many of its activities from that 
of animals. In all essentials the vital unit, the cell, was 
seen to be the same for plants and animals (pp. 330—7). 

{d) The processes of cellular division (mitosis) and 
sexual cell union (conjugation) are, on the whole, more 
easily traced in plants than in animals. Gradually they 
have been revealed as essentially identical in the two 
kingdoms (pp. 341—4). 

{e) The discovery of the sex processes, especially of the 
flowerless plants (Cryptogams), by Hofmeister and his 
followers (pp. 517—18) led to the conception of an alterna¬ 
tion of generations in plants (p. 520). This was freely 
compared to the well-known phenomena of alternation of 
generations in animals. Modern views of alternating 



410 Kelativity oj Functions 

‘haploid’ and ‘diploid’ cell generations have made the 
analogy still closer (pp. 524—31). 

(/) The general conception of a ‘physiologia’ of life as a 
whole, involving the interdependence of plants and animals, 
has been developing ever since Liebig. It expresses itself 
in such formulae as the ‘nitrogen cycle’ (p. 379). 

{£) The evolutionary view gave a new conception to 
what may perhaps be called the economics of life. There 
arose the tendency to examine the relations of living things 
to each other. This led to the discussion of how com¬ 
munities, especially plant communities, adjust their forms 
and behaviour to factors, such as moisture, heat, light, nutri¬ 
ment, and so forth. Looking back on the history of modern 
botany, one can see much of the work on absorption, nutri¬ 
tion, metabolism, and growth, as well as on geographical 
distribution, converging on to this topic (pp. 370—2). 

Ecology, as this aspect of biology is named, has been 
especially extended to a consideration of the mode of 
association of plants into communities and the relation of 
such communities to one another. The same approach 
may be used to animal communities in relation both to 
each other and to plant communities. 

(h) The essential phenomena on which the modern 
doctrine of heredity is based have been drawn in equal 
measure from the animal and the plant kingdom. Their 
similarity in the two is generally admitted (ch. xv). 

All these movements began to make possible a true 
science of Biology, a science that should treat life as a 
whole. Of that science Darwin was one of the earliest and 
perhaps the ablest exponent. It is certain that from about 
i860, the time of his greatest activity, most departments 
of biology begin to take on a new aspect. 

The aspect in which plants differ most fundamentally 
from animals is in the matter of integration. As we ascend 
the animal series we encounter an ever increasing tendency 



Vital Activity of Plants and Animals 411 

for the general co-ordination of the organism by a nervous 
system. No such tendency is visible in plants. It is to this 
action of the nervous system that we now turn. 

§ 9. The Sensori-motor System 

In the case of plants, the investigation of vital functions 
has chiefly centred either round the cell, or round the 
organism as a member of a community. With animals the 
subject has become differently orientated. The develop¬ 
ments of experimental physiology have here awarded a 
position of peculiar dominance to the nervous system. 

By the time of Haller (pp. 366—8), the naked eye anatomy 
of the nervous system had become quite familiar. It was 
made more exact by several anatomists in the later 
eighteenth century, prominent among them being Vicq 
d’Azyr (p. 208). 

A new physiological phase was opened by Luigi Galvani 
(1737—98) of Bologna, whose name is preserved in the 
‘galvanic battery’. Galvani showed (1791) that if a nerve 
be subjected to a certain type of stimulation, the muscle 
to which it leads will contract. The electrical nature of 
Galvani’s method was revealed by Alessandro Volta 
(1745—1827) of Pavia, who is commemorated in our sys¬ 
tem of ‘voltage’. In the fifth decade of the nineteenth 
century the Berlin Professor, Emil du Bois-Reymond 
(1818—96), pupil and successor of Johannes Mtiller, 
showed that a nervous impulse is always accompanied by 
the passage along the nerve of a change of electrical state. 
He and other investigators demonstrated moreover that 
chemical changes in the muscle accompany contraction. 
These chemical changes are initiated—‘lit up’ we might 
say—by the nervous impulse. 

In the meantime Sir Charles Bell (1774—1842) had 
been at work on the double spinal roots from which most 
of the nerves of the body arise. He showed that of these 



412 Relativity of Functions 

roots, one conveys only sensory elements, while the other 
conveys only motor elements (Fig. 155). The experiments 
of Bell were extended and improved by Frangois Magendie 
(1783-1855, p. 393), the teacher of Bernard and founder 
of the first journal devoted to physiology (1821). Thus 
the investigation of the action of individual nerves became 
possible. 

In the first half of the nineteenth century there appeared 
many comparative studies on the nervous system. Cuvier 
based his classificatory system in part upon the nervous 
reactions (p. 228). He had himself explored the nervous 
system of Molluscs, Starfish, and Crustacea. His influence 
may be traced in a detailed work on the anatomy of the 
vertebrate nervous system prepared under the super¬ 
intendence of Magendie (1825). The subject was ex¬ 
tended by many less distinguished workers. 

The solid researches on a variety of invertebrates by the 
‘Naturphilosoph’ Carl Gustav Carus (1789—1869), Pro¬ 
fessor at Leipzig, and the very refined dissections of in¬ 
sects by the English amateur, George Newport (i 803—54), 
should have drawn attention to the fact that the bodies of 
many invertebrate groups are no less dominated by their 
nervous organization than are those of the vertebrates. 
Yet Franz von Leydig’s (1821-1905) important text-book 
of Comparative Histology (1857), while stressing invertebrate 
forms, did little to emphasize the dominance of the nervous 
system. Not until the appearance of T. H. Huxley’s 
Manual of the Anatomy of the Invertebrated Animals (1877) 
was full stress laid on the complete nervous control in all 
except the lowest members of the animal series. 

Despite the lead of Huxley, the nervous anatomy and 
especially the nervous physiology of the invertebrates has 
remained neglected. But the internal structure of the 
nervous system in the higher animals has been investigated 
with very great detail. It has shown itself to be almost in- 



The Sensori-motor System 413 

conceivably complex. The investigations have been greatly 
helped by the introduction of new technique, at which we 
may now glance. 

The early anatomists, from Vesalius onward, recognized 
that the central nervous system consists of two main 
parts—the grey and the white matter. It was perceived 
that in the brain the grey matter is mostly on the surface, 
while in the spinal cord it is mainly central in position. 

Soon after the foundation of histology as a special 
science, it was observed that white matter consists of 
masses of enormous numbers of fibres, while grey matter 
contains also numerous cells. This was known to Pur- 
kinje (1835, PP- 33 °’ 33 ^) formally set forth by 

Henle (p. 445) in his Allgemeine Anatomie (i 841). It was, 
however, more than forty years before Kolliker proved that 
all nerve-fibres are nothing more than enormously elongated 
processes given off from nerve-cells with which they retain 
continuity (1889). These nerve-cells are to be found either 
in the central nervous system itself or in the various 
ganglia (Fig. 155). 

This discovery of Kolliker gave meaning to a series of 
facts that had long been under observation. As far back 
as 1851 the half French, half English investigator, 
Augustus Volney Waller (1816—70) had demonstrated 
that if a nerve be cut, only the fibres peripheral to the 
injury will degenerate. The reason is that they are cut off 
from the nerve-cell of which they are a branch and in 
whose metabolism they share. As the degenerative char¬ 
acter of nerve-fibres is microscopically easily determinable, 
‘Wallerian degeneration’ placed in the hands of investi¬ 
gators an experimental means of tracing the course of 
nerve-fibres through the nervous system. 

Another system of conducting comparable investiga¬ 
tions has also been developed. In 1873 the Pavia Profes¬ 
sor, Camillo Golgi (1844—1926), introduced a method of 



414 "Relativity of Functions 

depositing metallic salts within various cell structures. 
These deposits are very evident under the microscope. 
Ten years later Golgi succeeded in applying this method 
to the central nervous system. He showed that the cells 
in that system tend to resemble irregular polygons from 
the angles of which project processes, axons^ the essential 
parts of the nerve-fibres which ultimately end in a com¬ 
plicated system of branches, dendrites. The dendrites form 
twig-like ‘arborizations’ round other dendrites linked to 
other cells. Ultimately the system ends in terminal cells 
associated with sense organs, glands, or muscles. 

The method of Golgi has been developed for the sense 
organs as well as for muscles and glands by many investi¬ 
gators. Of these the most prominent has been the Swede, 
Magnus Gustav Retzius (1842—1919). In application to 
the structure of the central nervous system itself, remark¬ 
able work has been done by Ramon y Cajal (1852- ) of 

Madrid, almost the only important scientific investigator 
that Spain has hitherto produced. 

§10. Localization of Nervous Functions 

Such researches stamped upon biology the conception of 
an immensely complex series of systems for the transport 
of nervous impulses. These systems, if intact and work¬ 
ing well, determine the activities, the reactions, the whole 
life of the organism. Most significant work has been done 
during the last half century in the light of this conception. 

Very important for our view of the activity of the higher 
organisms has been the localization of the functions of the 
central nervous system. Work in this department has been 
entirely upon the higher vertebrates, having as ultimate 
aim the elucidation of the nervous and mental phenomena 
of man. Some of the earliest experimental evidence was 
adduced by the Parisian surgeon, Julien Legallois (1770— 
1814). He proved (i 811) that an injury to a certain spot 



Localization oj Nervous Functions 415 

in the medulla oblongata^ a structure that lies at the base 
of the brain, causes cessation of breathing. Here then lies 
a centre controlling this function. 

The Viennese, Franz Joseph Gall (1758—1828), who 
had long been working on the functions of the brain, was 
in Paris when Legallois made his researches. Gall now 
produced in collaboration his monumental treatise on the 
brain and nervous system (i 811). In it the structural dis¬ 
tinction between the white and the grey matter is clearly 
set forth, as well as the excessively intricate character of 
the various tracts (in one of which Gall is still commemo¬ 
rated) which go to make up the brain and spinal cord. 
Gall’s attempt to map out the surface of the brain, the 
‘cortex’, according to function, gave rise to the pseudo¬ 
science of Phrenology. 

Not till long after Gall’s death was cortical localization 
again taken up by investigators of repute. In 1861, how¬ 
ever, the French surgeon, Paul Broca (1824-80) demon¬ 
strated in a post-mortem room at Paris a relationship 
between loss of speech and injury to a definite area of the 
cortex. The work was soon carried into the experimental 
field. 

In 18 70 a very versatile naturalist, Gustav Fritsch (1838— 
91), and a student of insanity, Eduard Hitzig (1838— 
1907), working together at Berlin, found that stimulation 
of certain parts of the cortex regularly produced con¬ 
traction of certain muscles. The Englishman, David 
Ferrier (1843-1928) followed this up by demonstrating 
that other areas of the cortex, which do not evoke mus¬ 
cular activity, are nevertheless functionally differentiated 
(1876). 

In the half century that has since elapsed, the surface 
of the brain has been mapped in great detail. Special areas 
have been associated with movements of different parts 
and different organs. Others are related to various forms 



416 Relativity of Functions 

of sensory discrimination such as sight, sense of position, 
weight, taste, and the like. Yet others are involved in the 
use of language, both in written and spoken form. 

Influential in determining modern views of the action 
of the nervous system have been researches on the nature 



Fig. 155. Diagram to illustrate simplest form of Reflex. An aflferent impression 
from a sense organ to the spinal cord may give rise to an aflerent impulse by a 
purely intra-spinal process. This impulse may be of the nature of a complex 
and balanced muscular act involving a whole system of muscles, some of which 
may be antagonistic to each other. All this may lake place not only uncon¬ 
sciously, without any intervention from the higher nerve centres in the brain, but 
even in an animal from which the brain has been removed. On the other hand, 
channels exist (and are indicated in the diagram) for passage of impressions to 
and impulses from higher centres. These higher centres in many cases control and 
modify the resulting muscular or other action to a greater or less degree. 


of ‘reflex action’, that is, non-voluntary movement in 
response to a sensory stimulus. The conception may be 
traced in physiological writings of the seventeenth and 
eighteenth centuries from Descartes onwards. The term 
‘reflex action’ was invented (1833) by the English physio¬ 
logist Marshall Hall (1790—1857). 

By experiments, chiefly on cold-blooded vertebrates, 
Marshall Hall demonstrated in the spinal cord the nervous 
centres for a variety of reflexes. His papers, culminating 




Localization of Nervous Functions 417 

in his Memoirs on the Nervous System (1837), mark a period 
in the history of nerve physiology. The study of reflexes 
has resulted in the localization of functions in the grey 
matter of the spinal cord much as with the grey matter 
of the cortex. 

Since Hall’s time there has been vast extension of the 
conception of reflexes. Besides the simple nervous arc 
(Fig. 155) there are more complex arcs which depend for 
their action on an elaborate mechanism. Beside ‘spas¬ 
modic’ events, as sneezing, coughing, scratching, &c., 
many of the ordinary acts of life, standing, walking, 
breathing, &c., are expressible as reflexes. The attempt 
has also been made by Pavlov and others to press even 
the ‘instincts’ into the same category, and the cortex has 
been shown to have the power of establishing new reflexes. 
The school that has been thus occupied seeks to explain 
all the reactions and indeed the whole life of the higher 
organisms on a purely objective basis without reference to 
volitional elements (pp. 423—5). 

§11. Nervous Integration 

If the simple reflexes of animal bodies are tested, it will 
be found that they clearly serve certain ends. Lightly 
touch the foot of a sleeping child and it will withdraw it. 
Tickle the ear of a cat and it will shake it. Exhibit savoury 
food to a hungry man and his digestive process will at 
once get to work, his mouth will ‘water’. These instances 
might be multiplied an hundredfold. Such reflexes are ad¬ 
mirably adapted to their ends. Many will continue in an 
animal in which the brain has been removed, provided 
that the spinal cord be still intact. Nevertheless, in the 
higher animals, and especially in man, the reflexes are con¬ 
trollable to a greater or less extent by the will. 

But to leave the question at that would give a false idea 
of the extremely complex functions performed by the 

2613.3 E e 



418 Relativity oj Functions 

central nervous system. Thus, the spinal cord which, to 
the naked eye, is a longitudinal and little differentiated 
nervous mass, is, in fact, a collection of nerve-centres 
which have historically, both in the individual and in the 
race, been formed by the union of a series of separate 
segments. Each segment in this system governs certain 
functions or movements of the body, and the activity of 
each segment is related in various ways to the activity of 
the other segments. There is thus a very complex process 
of ‘integration’ which runs right through the nervous 
system. 

During the present generation, the growing knowledge 
of the bodily functions of chemical and physical nature 
has revealed that these activities are far more largely under 
nervous control and discipline than was formerly con¬ 
ceived to be possible. Thus, the main factor in the activity 
of any part is its blood-supply, but the blood-supply is 
determined, as Bernard showed (p. 394), by the state of 
contraction of the vessels of supply, which are in their 
turn under nervous control. Similar relations prevail for 
the state of nutrition of muscles, for the action of the sweat 
glands of the skin, for the mechanism of childbirth, and 
for a thousand bodily states. The regulation and control 
of all these events, processes, and states has come to be 
called integration. 

The investigation of nervous integration is especially 
associated with the name of Sir Charles Sherrington 
(1861— ) of Oxford. The picture formed of the 

nervous apparatus is that of a machine in which some parts 
work spontaneously, automatically, and with complete uni¬ 
formity; others, though mainly automatic, are susceptible 
of various degrees of alteration and adjustment; others 
need intermittent or constant attention and demand for 
their functioning fresh supplies of energy at longer or 
shorter intervals: while, finally, others have hardly yet 



Nervous Integration 419 

taken a fixed form and are improvised as occasion demands. 
Thus the nervous system is a system of systems of every 
degree of independence. 

These systems, each with a certain individuality of its 
own, date from every stage of evolution, the more ancient 
being, as a rule, the more automatic and the less dependent 
on other systems. The most ancient, the chemical mes¬ 
senger or ‘so-called' ‘hormonic’ system, we share with the 
simplest living things which consist of but one cell. Very 
recent are the factors in the nervous system that are 
specially developed in man as contrasted with the higher 
apes. Such are those associated with the delicate co¬ 
ordination of sensory impressions and motor impulses 
involved in such acts as speaking, reading, writing, and 
the like. Each of these systems, high or low, ancient or 
recent, has its own place in the body. In many cases the 
exact position of the controlling centre is demonstrable, 
and some of the lower systems can function without the 
aid of any other systems save those which control their 
nutrition, 

§12. Beginnings of Comparative Psychology 

When we watch the conduct of any being we ascribe its 
actions to sensations, emotions, motives, thoughts, com¬ 
parable to those which we ourselves experience. In the 
case of human beings this forms an admirable working 
hypothesis and is indeed the theory which carries us 
through life. It is the basis of our laws, our customs, our 
very society. It has held human communities together 
through the ages. The only alternative doctrine is what 
philosophers call solipsism (Latin solus ~ ‘alone' and ipse — 
‘self), the view that self is the only object of real knowledge 
and, in the extreme, the only thing really existent. If any 
individual should push this view beyond a mere philo¬ 
sophic tenet and act as though he believed it, we should 

E e 2 



420 'Relativity of Functions 

regard him as eccentric and antisocial. If he acted con¬ 
sistently with his belief, we should be forced to treat him 
as insane. 

When we contemplate higher animals, dogs for in¬ 
stance, we ascribe to their minds some at least of the 
qualities of our own. The method works within limits. 
In practice a dog shows signs of knowing his master, 
manifests affection for him, exhibits hunger, passion, 
content, and so forth. The application of this ‘common- 
sense’ method is more or less possible according as the 
being with which we deal is more or less like ourselves. 
When, however, we pass to insects, in which the nervous 
system is organized on a wholly different though no less 
complex plan than our own, or to protozoa which exhibit 
no separate nervous system, the task becomes impossibly 
hard. The ‘subjective’ method that reads our minds into 
other beings is here merely misleading. 

With the advent of evolutionary views naturalists turned 
to comparative studies. Comparative anatomy, as being 
the easiest, was the first cultivated. Comparative physio¬ 
logy came much later into the field. A consideration of 
comparative psychology on a scientific, that is on an 
objective, basis was perforce deferred until physiology 
could provide an adequate technique. Since the mind of 
beings other than oneself can only be known through 
their conduct, some exact, some physiological method of 
investigating conduct had to be devised. 

By a truly extraordinary mental ellipsis, a school of 
thinkers now developed the conception that since mind 
can only be known through behaviour, therefore mind has 
no existence. As though we should say that there was no 
Phidias since we can know him only through his sculp¬ 
tures ! From the philosophical point of view this extreme 
‘behaviourist’ position seems hardly worthy of answer, for 
the one thing we do know about ourselves is that we 



Comparative Psychology 421 

think. All else, even our own behaviour, is inference. We 
can, however, discuss behaviouristic interpretation from 
the purely scientific point of view that does not go behind 
phenomena except to other phenomena. That is to say, 
we may adopt the scientific method of limiting our field 
of study and may decide to consider only the phenomena 
of behaviour without forming any hypothesis concerning 
its motive. This is a perfectly sound attitude, provided that 
its necessary limitation is recognized. From this phe¬ 
nomenological point of view, behaviourism is a necessary 
corollary to biological ‘mechanism’. Nevertheless, such 
behaviourism is not, as some behaviourists seem to think, 
inconsistent with vitalism. There are certainly philo¬ 
sophical reasons for rejecting ‘behaviourism’, but rejection 
of ‘mechanism’ is not one of them. 

The extreme mechanist doctrines of some of the early 
followers of Darwin created a great stir in their day. They 
are, however, of little importance for the history of science, 
since they were not based on experimental evidence. But 
a new period was opened in the early ’nineties by two 
investigators who were philosophically poles asunder. 
These were C. Lloyd Morgan (1852- ), of Bristol, 

and Jacques Loeb (1859—1924), first of Strasbourg and 
later of the University of California. 

The basis of Lloyd Morgan’s comparative psychology 
is, in effect, a return to the essential principles of science. 
These, it is said, were laid down in the fourteenth century 
by the great Franciscan opponent of the Papacy, William 
of Ockham (1270—1349), to whom is ascribed the dictum 
‘entities are not to be multiplied beyond necessity’. This 
‘law of parsimony’, sometimes called ‘Ockham’s razor’, is 
fundamental for the logic of science. To this principle 
Lloyd Morgan was appealing when he wrote: 

‘In no case may we interpret an action as the outcome 
of the exercise of a higher psychical faculty, if it can be 



422 Relativity of Functions 

interpreted as the outcome of the exercise of one which 
stands lower in the psychological scale’ (1893). 

But while this was being written, experiments were in 
progress, the interpretation of which reduced the lower 
psychological scale to the level of physico-chemical rules. 
Indeed chemotropism in the case of spermatozoids of ferns 
(pp. 372—3) was already well known. The American school, 
led by H. S. Jennings (1868— ), was making similar 

observations on protozoa, which showed that certain be¬ 
haviour of these creatures also is determinable by physical 
and chemical means. The conception was developed in 
great detail by Loeb and his followers and was extended 
to a large variety of animals, chiefly invertebrates. These 
investigators showed that many actions and attitudes that 
might be thought ‘voluntary’ in the human sense are closely 
controlled by physical conditions. The contemporary 
work of the isolated French amateur, Henri Fabre (1823— 
1915), also demonstrated that a multitude of seemingly 
purposeful acts of insects are performed without reference 
to even the most elementary form of reason, and even 
without regard to the interests of the performer or of his 
species. 

In the meantime Lloyd Morgan had developed his con¬ 
ceptions of the nature of the psychical faculties. He dis¬ 
tinguished three levels of mental activity. Of these the 
lowest sentience, a vaguely conscious state, is possessed by 
all animals, and is described in man by the term ‘affective’. 
Above this stands effective consciousness which we must sup¬ 
pose possessed by such creatures as can profit by experi¬ 
ence. There is evidence to suggest that this too is present 
in all animals, even in protozoa, though it is more obvious 
in the higher orders. Lastly there is the third level, selj- 
consciousness, which can be present only in a small number 
of the higher creatures. 

This scheme, with various modifications and qualifica- 



Comparative Psychology 423 

tions, still holds the field with most thinkers, and has 
provided the outline for the doctrine of ‘emergent evolu¬ 
tion’. The basic criticism to which it is subject from the 
point of view of science is that its ultimate criterion, self- 
consciousness, is not susceptible of measurement or ex¬ 
pression in terms other than itself. This is merely to say 
that self-consciousness is not susceptible of scientific ana¬ 
lysis, which is a very different thing to proving that it has 
no existence. The latter view has, however, been taken 
by some extremists who have been much attracted by 
doctrines arising from recent work on ‘conditioned 
reflexes’. 

§13. Conditioned Reflexes 

Many of the simple reflexes, or automatic movements 
in response to stimulus from the environment, appear very 
early in life, and a number are present before birth. The 
animal exhibits these innate reflexes, without any regard 
to its individual experience as an individual in the world. 
The absence or exaggeration of reflexes, normally innate or 
early acquired, implies some injury or disease of the 
nervous system. A number of these reflexes are, in fact, 
of value to medical men in testing for nervous disorders. 

Beside these innate reflexes, common to the species, 
there are also a number of acquired or conditioned reflexes, 
the development of which depends upon the history of 
each particular individual. They are called ‘conditioned’, 
since their nature depends on the conditions of their es¬ 
tablishment. It will, however, be found impossible to 
draw an absolute distinction between some conditioned 
reflexes and some reflexes that have been acquired very 
recently in evolutionary history. 

The study of conditioned reflexes is the work of the last 
twenty years and is associated closely with the name of the 
Russian physiologist Ivan Pavlov (1849-- ). This 



424 Relativity of Functions 

distinguished investigator has developed a method of 
inquiry into the mechanism of the highest nerve centres 
without appealing to the consciousness of the organism. 
The technique of investigation of conditioned reflexes is 
largely determined by Pavlov’s method of measuring ac¬ 
curately the flow of saliva in dogs—a somewhat slender 
basis, it must be confessed, on which to found a new 
philosophy and psychology. If a hungry dog is shown 
food, his mouth waters—the saliva flow is increased. If a 
bell be rung each time food be given, he comes at last to 
secrete saliva at the sound of the bell, irrespective of food. 
The showing of the food is the unconditioned stimulus, the 
ringing of the bell is the conditioned stimulus. 

Our experience with the dog accords in fact with our 
own and is, in itself, nothing new. Our own dinner bell 
arouses us to the fact that we have an appetite. The new 
feature is the manner, at once exact and objective, in 
which these reflexes can be studied. The chief difficulty 
in their study consists, as in many scientific experiments, 
in limiting the number of ‘variables’. If we are investigat¬ 
ing, let us say, the effect of pressure on a gas, we must be 
sure that the temperature remains constant. If we are 
investigating the effects of temperature, we must take 
steps to secure uniformity of pressure. Such precautions 
are especially difficult in studying the acquired reflexes. 
Pavlov and his assistants have taken immense pains to 
eliminate the sources of error due to ‘multiplicity of vari¬ 
ables’, which in this case means multiplicity of stimuli. 
Their work, like much successful scientific work, has been 
mainly concerned with the perfection of methods. It is, 
however, only with the results that we are here concerned. 
Pavlov has shown that each conditioned reflex is associated 
with a definite part of the cortex of the brain. If that part 
is removed, the reflex disappears. 

An important aspect of the conditioned reflexes is the 



Conditioned Keflexes 425 

manner of their inhibition. Any sort of disturbance, 
curiosity, anxiety, noise, fear, change of light or tempera¬ 
ture may interfere. How well we know this with children 
at their meals! The removal of these interferences has been 
Pavlov’s chief task. Special laboratories have been so con¬ 
structed that the experimental animals are under absolutely 
uniform conditions and do not even see the experimenter. 
Thus conditioned reflexes have been experimentally 
established in relation to many organs, the pupil of the eye, 
the movements of so-called voluntary muscles, even the 
beat of the heart and the process of breathing. The ease 
with which the various kinds of conditioned reflexes can 
be established is very various. Moreover, the strength or 
weakness of the reflex depends largely on the intensity and 
duration of the requisite stimulus. 

Pavlov’s point of view is that, through the medium of 
conditioned reflexes, any part of the nervous system may 
be coupled up with any other part. When we consider that 
the nervous system contains many millions of nerve-cells, 
we can realize the truth that no creature uses more than 
a small fraction of its cerebral powers. Pavlov himself 
holds that however complex mental activity may be, it is 
in essence compounded of successions of acquired and 
modifiable connexions of one neurone with another. Pav¬ 
lov recognizes in the brain no other, no higher function 
than this. He accepts no science of psychology beyond this 
development of neurology. For him, ‘freedom’, ‘curiosity’, 
‘purpose’, are but conditioned reflexes, and religion but 
one of the higher conditioned reflexes. Such a view is an 
extreme development of mechanist doctrine. It is incon¬ 
sistent with vitalistic theory and is equally inconsistent 
with any of the philosophical doctrines, such as emergent 
evolution or holism, which have been elaborated to cover 
the phenomena of life. 



426 Relativity oj Functions 

§14. Mind as Conditioning Life 

During the nineteenth century there was an enormous 
extension of scientific interest in the analytical study of 
animal function by means of physical experiment. 

The exponents of this science of physiology have 
applied themselves mainly to the higher animals. They 
have devoted themselves almost exclusively to an examina¬ 
tion of the parts or functions in the adult or developed 
state. The results have been portentous in bulk, com¬ 
plexity, and interest. Fundamental for the details of 
scientific medicine, they are less useful in helping us to a 
conception of the organism as a whole. 

The animal body is, as it were, a vast and complex 
maze. The physiologist enters it and he wanders there as 
long as he will. But his close and detailed report on its 
paths and walls helps but little toward the exposition of 
the design as a whole. A bird’s-eye view would be more 
productive. Such a glimpse, though blurred and distant, 
has been better obtained by the ‘general physiologist’, 
who has devoted himself to the examination of protoplasm 
and especially of the life, movement, and habits of the lower 
organisms; by the embryologist who has sought out the 
beginnings of the organism; and by the biochemist who 
has analysed the physical and chemical character of the 
products of vital activity. 

The physiologist, in his special studies, is well nigh 
bound to consider isolated functions. He selects respira¬ 
tion, nutrition, muscular movement, the action of the 
nervous system, or the like. But the performance of each 
of the functions of each of the systems is inextricably 
linked with the performance of the functions of all the 
other systems. We are always looking for metaphors in 
which to express our idea of life, for our language is in¬ 
adequate for all its complexities. Life is a labyrinth. But 



Mind as Conditioning Life 427 

a labyrinth is a static thing and life is not static. Life is a 
dance, a very elaborate and complex dance! The physio¬ 
logist cannot consider the dance as a whole. That is be¬ 
yond his experimental power. Rather he isolates a par¬ 
ticular corner or a particular figure. His conception of the 
dance, as thus derived, is imperfect in itself and, moreover, 
in obtaining it he has disturbed the very pattern of the 
dance. The shortcoming of his method becomes fairly 
evident when he seeks to relate his corner to another in 
a far distant part of the dance. 

Moreover, even should he seek to treat the organism 
as a whole, he is still almost bound to consider it as an 
‘individual’, complete and separate in itself, shut off from 
its environment and its history, born, as was Minerva, 
armed and fully equipped from the head of Jove. But in 
fact living beings are not so. There is every degree of in¬ 
dependence of its fellows among organisms. ‘Individuality’ 
comes into prominence only in the more differentiated 
groups. The term is almost inapplicable to plants in which 
physiology is, in effect, the physiology of a community and 
is a study not far, in its conceptions, from that of biono¬ 
mics. The very idea of the ‘individual’ involves an historical 
record which the science of physiology has hitherto almost 
ignored. 

The special development and isolation of the science of 
animal physiology have been largely conditioned by its 
relation to medical studies. The seminal biological ideas 
of the nineteenth century were unquestionably in con¬ 
nexion with Evolution, Biogenesis, Heredity, and the 
Cell Theory. The work of those who professed physiology 
was but little directed by any of these themes except the 
last. The illustration of Evolution has been provided al¬ 
most entirely by the field naturalist and the comparative 
anatomist. The phenomena accompanying the beginnings 
of organisms have been illuminated by the cytologist and 



4^8 Relativity oj Functions 

the experimental embryologist. The activities of the cell 
and its protoplasm have been elucidated mainly by 
botanists. The study of Heredity and Sex has demanded 
specially trained naturalists. ‘Physiology’ has retained a 
peculiarly lonely position among the biological sciences. 

Since the dawn of the twentieth century there have been 
signs of a breakdown of this isolation. Physiology alone 
is, however, of its nature incapable of presenting any pic¬ 
ture of the mode of action of the organism as a whole, 
though modern doctrines of the workings of the nervous 
system have given some explanation of certain forms of 
animal behaviour. 

Yet the functions of the nervous system, like those of 
other systems, are relative to the other functions of the 
body. Not only is respiration, for example, regulated by 
the nervous system, but the nervous system itself is regu¬ 
lated by the character of the respiration. Raise the amount 
of carbon dioxide in the blood, and the respiratory move¬ 
ments are first stimulated and finally diminished via action 
on the respiratory centres. It would be possible to show 
that the same is true of any system or part of a system in 
relation to any other. What picture, then, can physio¬ 
logical processes give us of the interrelated complex of 
activities that we can call an organism i 

The physiologist has found that his science can be best 
prosecuted on the higher animals because the functions of 
these creatures are best differentiated. If he wishes to 
study movement, respiration, nutrition, nervous action, he 
finds in the higher animals separate organs devoted to 
these processes. Such organs he cannot so easily or cannot 
at all find in the lower organisms. In the lowest of all, the 
Protozoa, every process is carried on in a single cell. 

But the most distinctly and clearly developed character¬ 
istics of the highest animals are their mental powers. To 
discuss these in the mechanistic nomenclature adopted by 



Mind as Conditioning Lije 429 

physiology is mere contradiction in terms. The one thing 
that we really know is our own thoughts, and external 
things—including the science of physiology—^we know 
only in relation to these. How then can external things be 
said in any sense ‘to explain’ our thoughts ? It is more in¬ 
telligible to invert the process and to say that phenomena 
—including those of physiology—are parts of our think¬ 
ing, than to say that our thinking can be built up of 
phenomena. 

But if we emphasize the conception of science as dealing 
with phenomena—‘things which appear’—^we reach a 
modus vivendi both for a conception of mind and for the 
findings of science. Having agreed that science shall deal 
only with phenomena, we expressly exclude our own mind, 
which is not an appearance at all but that to which ap¬ 
pearances happen. Science must keep to the phenomenal 
level. On that level she must prosecute physiological 
study. But no amount of that study will truly represent 
an entity in which is any element of mind. Is that element 
of mind found in other organisms than myself.^ Unless 
the solipsist view (pp. 419—20) be taken, this question must 
be answered in the affirmative. The man who answers it 
in the affirmative is a vitalist. 

Fig. 156. The first attempt to inter¬ 
pret graphically in mechanical terms 
the action of muscles and ligaments 
(Vesalius, 1543). 




XII 

BIOGENESIS AND ITS IMPLICATIONS 

§ I • Early Ideas of Infection and Spontaneous Generation 

M any savages think that the properties of any kind 
of matter can be transferred to neighbouring 
matter. They see that decaying animal or vegetable sub¬ 
stance corrupts neighbouring material, or again, that hot 
or cold things make neighbouring things hot or cold. 
Thus for them corruption and incorruption, heat and cold, 
are ‘contagious’, that is, pass from object to object by 
reason of contact. Generalizing, they think many other 
things contagious—a man’s cleanliness and uncleanliness, 
his holiness and unholiness, his power and his weakness. 
This belief is described by anthropologists as ‘sympathetic 
magic’. To the savage, the passage of disease from person 
to person is a normal part of a world full of such magic. 

Man rises in the scale of civilization. Religion crystal¬ 
lizes out from the mass of vague beliefs. Gods now govern 
the fate of man. An epidemic outbreak in the tribe is 
a most impressive event. The gods have dealt the blow. 
It is the unknown that is most dreaded, and ‘the pestilence 
that walketh in darkness’ has ever been more feared than 
‘the arrow that flieth by day’. The Bible strikes a human 
note when the appearance of the very Angel of Death 
at the threshing-floor of Araunah comes as a relief to the 
stricken King of Israel. 

Greek, medieval, and renaissance physicians studied 
epidemics. The Greek man of science remained very 
sceptical concerning the infectious nature of these diseases, 
and indeed concerning infection in general, for that sus¬ 
pect conception came from a magic-ridden world. It was 



Infection and Spontaneous Generation 431 

in the later Middle Ages that physicians, acting on 
promptings from the book of Leviticus, came to realize 
that epidemics are simply outbreaks of disease of a 
peculiarly infectious type. Such disease, it was observed, 
is almost always associated with fever. Theories were 
formed to explain the evident association of infection and 
fever. A common view was that these conditions were 
allied to the phenomena of fermentation or leavening. 
We still speak of‘zymotic’ diseases (Greek zyme, ‘leaven’). 

Ideas on the subject of infection were given some exact¬ 
ness by the Veronese physician, Hieronimo Fracastoro 
(1484—1553). He did much to separate the different types 
of fever, and he sought to classify the infectious diseases. He 
was an ardent follower of Lucretius {c. 98—55 b. c.), the 
Roman atomic philosopher, whose work had been recently 
rediscovered. Following his master, Fracastoro expounded 
the idea that infection of all kinds, including fermentation, 
is the work of minute ‘seeds’ {seminarui) or germs. This 
view remained more or less latent in men’s minds until 
Pasteur’s time. 

The really salient fact in the seventeenth century con¬ 
ception of zymotic disease was, however, not its ‘seminal’ 
origin but its relation to fermentation. Fermentation and 
zymotic disease have indeed much in common. Both are 
associated with rise of temperature, both are infectious, 
both can be propagated indefinitely without diminution 
of the original focus. Moreover, it seemed to early 
observers, who interpreted the facts wrongly, that both 
were capable of being ‘spontaneously generated’, that is, 
of arising without the existence of any predecessor like 
to themselves, of being, in fact, without parents. 

Now this power of spontaneous generation suggested 
to the men of the age that both fermentation and in¬ 
fectious disease partake of the nature of life. Certain 
living things, it was held, could, under certain conditions, 



432 Biogenesis and its Implications 

be spontaneously generated. Moreover, all living things 
have this power of indefinite propagation. Thus the early 
scientific study of infectious disease came to turn on the 
current conceptions of spontaneous generation and of 
fermentation. 

The misleading doctrine of spontaneous generation is 
often laid at the door of Aristotle. It so fell out that when 
that doctrine was first questioned, the authority of Aris¬ 
totle—or rather the contemporary misunderstanding of 
him—^was a very real obstacle to scientific advance. It is 
also true that Aristotle believed in spontaneous generation 
and gave it a place in his biological scheme (p. 42). But 
his error was shared by every naturalist until the seven¬ 
teenth century. Indeed it is hard to see how these men, 
with the knowledge at their disposal, could take any other 
view. It is but just, therefore, that the father of biology 
should be acquitted of any special fault in misleading his 
successors in this matter. 

With the advent of the general use of the microscope 
in the second half of the seventeenth century, new ten¬ 
dencies set in. On the one hand, exploration of minute 
life showed many cases of alleged spontaneous generation 
to have been falsely interpreted. Thus plant galls had 
been regarded as spontaneously generated. Nevertheless, 
Malpighi showed that these curious growths are related 
to insect larvae (p. 155). On the other hand, the micro¬ 
scope revealed minute organisms which seemed to appear 
out of nothing. Thus Leeuwenhoek saw excessively small 
creatures in infusions of hay and other substance (pp. 167— 
8). Such infusions, perfectly clear when first prepared, 
become in a few days or even hours cloudy with actively 
moving microscopic forms. These seemed ‘spontaneously 
generated’. 



(433 ) 

§ 2 . Redi ( 1621 — 97)5 Needham ( 1713 — 81)5 and Spallan¬ 
zani ( 1729 - 99 ) 

The first scientific treatment of the question was made 
toward the end of the seventeenth century. Francesco 
Redi of Florence5 at once poetj antiquary5 physician5 and 
naturalist5 proved by experiment that, if living causes be 
excluded, no living things arise. Using no microscope, 
his work failed to convince those who based their belief 
in spontaneous generation on microscopic appearances. 
Nevertheless, Redi's experiments are faultless so far as 
they go, and his arguments unanswerable so far as they 
apply to flesh-eating flies. He checked his operations by 
what are now called ‘controIs\ 

In his Esperienze intorno alia generaztone degli insetti 
(‘Observations on the generation of insects', Florence, 
1668), Redi tells that he 

‘began to believe that all worms found in meat were derived from 
flies, and not from putrefaction. I was confirmed by observing that, 
before the meat became wormy, there hovered over it flies of that 
very kind that later bred in it. Belief unconfirmed by experiment 
is vain. Therefore I put a [dead] snake, some fish, and a slice of 
veal in four large, wide-mouthed flasks. These I closed and sealed. 
T'hen I filled the same number of flasks in the same way leaving 
them open. Flies were seen constantly entering and leaving the 
open flasks The meat and the fish in them became wormy. In 
the closed flasks were no worms, though the contents were now 
putrid and stinking. Outside, on the covers of the closed flasks a 
few maggots eagerly sought some crevice of entry. 

‘Thus the flesh of dead animals cannot engender worms unless the 
eggs of the living be deposited therein. 

‘Since air had been excluded from the closed flasks, I made a new 
experiment to exclude all doubt. I put meat and fish in a vase 
covered with gauze. For further protection against flies, I placed 
it in a gauze-covered frame. I never saw any worms in the meat, 
2613.3 p f 



434 Biogenesis and its Implications 

though there were many on the frame, and flies, ever and anon, lit 
on the outer gauze and deposited their worms there.’ {Slightly 
abbreviated^] 

It is odd that, despite these admirable experiments, 
Redi continued to believe that gall insects were spon¬ 
taneously generated. This subject was taken up by Vallis- 
nieri (1661-1730) who again demonstrated that the larvae 
in galls originate in eggs deposited in the plants (1700). 
Vallisnieri compared the process of gall formation, as well 
as infection of plants by aphides, to the transmission of 
disease. Other investigators showed that fleas and lice— 
to this day popularly thought to be ‘bred by dirt’—are, 
in fact, bred only by parents like themselves. 

The later history of the doctrine of spontaneous 
generation was long and stormy. The battle raged back 
and forth. On the one hand, it was shown that by screen¬ 
ing, boiling, or chemically treating a medium, the appear¬ 
ance of minute organisms was either delayed or altogether 
avoided. On the other hand, cases were repeatedly adduced 
in which organisms did so appear, despite all precautions. 

About the middle of the eighteenth century the con¬ 
troversy reached an important stage in a discussion be¬ 
tween John Turberville Needham and Lazzaro Spallan¬ 
zani. This debate was virtually repeated a century later 
between Pasteur and his opponents. 

Needham was an English Catholic priest, who made 
some interesting contributions to science. In 1748 he 
published what was in effect a repetition, made in con¬ 
junction with Buffon, of the experiments of Redi of the 
previous century. Needham’s treatment of the problem 
was, however, more refined than Redi’s, since he aimed at 
excluding even the most minute microscopic organisms. 

Needham came to the opposite conclusion for micro¬ 
scopic organisms to that reached by Redi for maggots. 
He boiled mutton broth and placed it in a corked phial 



Redi^ Needham^ Spallanzani 435 

so well closed-with mastic that it was ‘as* good as her¬ 
metically sealed*. He sought thus to exclude the exterior 
air, that it might not be said that animalcules arose from 
air-borne germs. The flask was opened after a few days. 
It was swarming with animalcules. ‘The very first drop 
yielded multitudes perfectly formed, animated and actively 
moving.’ He followed this up with observations on infu¬ 
sions of other animal and vegetable substances. All gave 
the same phenomena with little variation. 

Needham was answered byI>azzaro Spallanzani of Scan- 
diano, an investigator of very great experimental skill. 
Spallanzani, who was in orders and bore the title ‘Abbot’ 
(Abate), was professor successively at Reggio, Modena, 
and Pavia. He made important contributions to several 
departments of biology. Some of his experiments on 
spontaneous generation bore a close resemblance to those 
of Pasteur. 

Spallanzani was dealing with very minute organisms. 
He perceived that the early stages must be minuter still. 
Thus the problem resolved itself into excluding forms of 
life so small as to be beyond the reach of his microscopic 
vision. In his Saggio di osservazioni microscopiche relative 
al sistema della generazione dei signori Needham e Buffon 
(Modena, 1667), he says: 

‘I sought to discover whether long boiling would injure or prevent 
the production of animalcules in infusions. 1 prepared infusions 
with eleven varieties of seeds, boiled for half an hour. The vessels 
were loosely stopped with corks. After eight days I examined the 
infusions microscopically. In all there were animalcules, but of 
differing species. Therefore long boiling does not of itself prevent 
their production.’ [^Abbreviated^] 

Spallanzani then tried excluding air. He placed in¬ 
fusions in five series of flasks. One series was left open. 
The other four series were first sealed with the blow-pipe 
and then raised to the boiling-point. The duration of 

F f 2 



436 Biogenesis and its Implications 

boiling for these four series was respectively a half-minute, 
a minute, a minute and a half, and two minutes. The 
flasks were left for two days. The open series swarmed 
with microscopic organisms. Of the sealed series, that 
boiled for a half-minute contained smaller organisms, 
while the remainder contained only excessively minute 
forms. 

With this clue Spallanzani now raised the time of 
exposure to heat. At last he found that if a sealed flask 
be subjected to the temperature of boiling water for 
between one-half and three-quarters of an hour, no 
development of organisms ensued so long as the flask 
remained sealed. 

The experiments of Needham and Spallanzani were 
much discussed. Some thought the flaw in Spallanzani’s 
method lay in the necessity of air for the development of 
organisms. Heating the air in the sealed flasks, they 
considered, had spoiled it for purposes of generation. 
Spontaneous generation in the presence of unspoiled air 
seemed still to be a possibility. 

Several workers in the early nineteenth century repeated 
Spallanzani’s experiments with improved technique. Thus 
Schwann (pp. 332-5) also proved that no putrefaction 
ensues in fully sterilized broth to which none but air 
previously heated can have access. He was convinced, 
however, that such heated air rests unchanged for vital 
purposes since he was able to show that it will serve for 
animal respiration (1836-7). 

The weak point of such experiments was that they 
sought to prove a universal negative. One positive result, 
and the rest became worthless. Thus some still remained 
convinced of the reality of spontaneous generation. Of these 
the most prominent was the naturalist, Felix Archimfede 
Pouchet (18 00—72). In i859he brought out a large work. 
Heterogenic —his name for spontaneous generation. Its 



Pasteur on Fermentation 437 

elaborate details of cases and conditions of the supposed 
process are now mere curiosities. The fallacies inherent 
in his methods were fully demonstrated by Pasteur. 

§3. Pasteur (1822—95) Fermentation 

Pasteur was by training and profession a chemist and 
especially a physical chemist. When he began his first 
great series of researches, the question of the optical 
action of crystals was much before the scientific world. 
His first scientific successes were obtained on the optical 
action and varieties of the tartrates. These are produced 
in the course of fermentation, and his researches carried 
him from crystalline substances to the ferments which 
make them, from experimental physics to great industrial 
problems. Much of his subsequent work had practical 
issues, but he never faltered in the purity of his scientific 
enthusiasm. 

Pasteur was, however, by no means the first to demon¬ 
strate that fermentation is associated with organisms. 
Thus in 1837 Schwann revealed that yeast consists essen¬ 
tially of a mass of plant-like beings. He showed that the 
presence of these is a condition of the alcoholic fermenta¬ 
tion of sugar. 

In 1854 Pasteur became professor of chemistry at 
Lille, a great industrial centre. There he set himself to 
that study of fermentation which bore him on to the study 
of disease. He made the first important step in 1857, 
when he gave to a local society a paper on the souring of 
milk. This Memoire sur la fermentation appelee lactique is 
a landmark in the history of Biology. He had discovered 
in sour milk a substance that proved to be a ferment that 
produces lactic acid. He isolated the ferment, added it 
experimentally to milk and watched it act. It was, in 
fact, a mass of bacteria of a species nowadays quite 
familiar. 



43 8 Biogenesis and its Implications 

At this stage Pasteur was called to Paris, where the rest 
of his scientific life was passed. He had hitherto been 
primarily a chemist. His work on sour milk led him to 
acquire skill with the microscope. His development of 
microscopic technique made him one of the founders of 
bacteriology, and indeed one of the great biologists of 
all time. 

At this period the current views of fermentation were 
controlled by Liebig (pp. 373-5). That eminent chemist 
regarded fermentation as a peculiarity of organic matter, 
and the fermentational change as ‘of the nature of death'. 
Pasteur’s experiments were to reveal the essential part 
played in it by living organisms. From the first, the teach¬ 
ing of the two men was opposed. For Pasteur, fermenta¬ 
tion was a vital phenomen and demanded the presence of 
living organisms. 

From the souring of milk Pasteur turned again to the 
investigation of the most familiar fermentation, that of 
sugar into alcohol in the making of wine. He found that 
for the formation of wine, essential elements were yeasts 
or moulds which he detected on the skins of the ripening 
grapes. If these were absent, deteriorated or in wrong 
proportions, the fermentation was either arrested or on 
abnormal lines. Pasteur sought to trace the life-history of 
these organisms. He perceived that their mode of growth 
was controlled by their conditions of life. 

Thus Pasteur passed to the diseases and defects of wine. 
Most of these, he found, were due to abnormal ferments. 
Study of the ferments soon suggested that there is a great 
variety of organisms associated with fermentation. Not 
all are of the type of yeasts. Some are quite different 
in form. These are yet smaller and grow often in chains. 
Pasteur’s investigations were summarized in his historic 
Etudes sur le vin (Paris, 1866). 

Pasteur was now quite convinced that fermentation, 



Pasteur on Fermentation 439 

decomposition, and putrefaction are all vital processes. 
It is life that brings about these changes. Innumerable 
minute organisms are perceptible in decomposing material. 
They are the cause of the process of decay. The germs 
of them are brought by the air. 

§ 4. Biogenesis versus Abiogenesis 

A great difficulty was here encountered in the demand 
that Pasteur’s views made on the germ-bearing capacity 
of the air. His critics were not slow to avail themselves of 
this. According to Pasteur, they said, the air must be 
one solid mass of germs! Some held that the organisms 
found in fermenting and decomposing matter were the 
result, not the cause, of these processes. The old idea of 
spontaneous generation still had its advocates. 

By 1859—the year of publication of the Origin of 
Species —Pasteur was engaged in acute controversy on the 
question of the ‘Origin of Life’. Discussion turned round 
what was then regarded as the lowest form of life, the 
bacterium. Were bacteria ever spontaneously generated, 
or were they not? If a supposedly sterilized flask of 
broth ‘went bad’, and bacteria made their appearance in 
it, was it certain that they had come from without ? May 
they not have generated spontaneously within the broth ? 
Must all life, even lives so low, so minute as these, be 
the work of life ? Life must begin somewhere; then why 
not here, at this lowest stage ? 

Pasteur, like his predecessor Spallanzani, had now the 
task of proving a universal negative. The task is im¬ 
possible in formal logic, but science is not formal logic. 
In a few years, with a magnificent series of studies, Pas¬ 
teur so cut away the foundations of the doctrine of 
spontaneous generation that it crumbled into ruin. Bio¬ 
logists now hold that all living things are themselves 
derived from living things and always have been, in so 



440 Biogenesis and its Implications 

far as properly designed experiment can test the matter. 
The crux is the germ-carrying power of the air. 

The most effective criticism of the experiments of 
Spallanzani had been that in boiling his sealed flasks, he 
had also altered the contained air. Early investigators of 
cells were naturally interested in the origin of minute 
forms of life. Despite Schwann (pp. 436-7), the question 
was still essentially in the state in which Spallanzani had 
left it. 

Now if, as Spallanzani and Pasteur believed, the beings 
associated with fermentation come from the air, it should 
be possible to find them there. Pasteur therefore made 
air-filters of gun-cotton and drew air through them. The 
cotton was then dissolved. The deposit that settled at 
the bottom of the vessel revealed numbers of rounded and 
of elongated microscopic bodies. These resembled 
organisms already observed in fermenting substances. 
On the other hand, gun-cotton from filters through which 
air already filtered had been drawn, revealed no such 
structures. The unfiltered air then contained these bodies. 

But it could still be said ‘Yes, these structures that you 
demonstrate are in the air, but they are not alive. It is 
not they, but something far more minute and subtle, that 
gives rise to the swarms of living things that we see in 
fermenting and putrid substances.’ 

To the question thus posed, Pasteur found a complete 
answer. A wonderfully simple but triumphant experiment 
clinched the matter. An infusion of a fermentable sub¬ 
stance is introduced into a flask. The neck, very narrow 
and long but left open, is drawn out into an ‘S’ shape. 
Flask and contents are raised to boiling-point for a long 
time. The source of heat is now withdrawn, but the flask 
is left undisturbed in still air. It so remains for days, 
weeks, months. Its contents do not ferment. Now the 
neck is severed. The fluid within is thus exposed to the 



Biogenesis versus Abiogenesis 441 

fall of atmospheric dust. In a few hours it is fermenting. 
Organisms are demonstrated in it under the microscope 
(Memoire sur les corpuscules organises qui existent dans 
ratmosphere^ 1861, Fig. 157). 

The success of this experiment marks the downfall of 
the doctrine of spontaneous generation. In the two-thirds 
of a century that have since elapsed, it has been shown in 
various ways that if due precautions be taken to exclude 



Fig. 157. Pasteur’s crucial experiment to prove that fermentation or putre¬ 
faction is the result of the action of air-borne organisms. The S-shaped flask 
contains a putrescible fluid such as meat broth. The flask containing the broth 
is subjected to prolonged heating to destroy all organisms. It is then left in 
position with the mouth open. Days, weeks, months, even years, may pass 
without sign of putrefaction. No organisms reach the broth, since any that enter 
the open mouth fall on the floor of the neck and remain there. Sever the neck 
of the flask so that organisms can fall from the air directly on to the surface of the 
fluid and thus multiply. In a few hours putrefaction sets in. This is shown by 
the formation of a film of scum on the surface just l^elow the severed neck. Micro¬ 
scopically the broth is seen to he teeming with organisms. 

living organisms and their eggs, spores, or seeds, no 
fermentation, putrescence, or other production of minute 
life ever takes place. It is all a question of the adequacy of 
the precautions. This adequacy is a question of technique. 

The germ-carrying power of the air was reduced to 
more exact expression by the English experimenter, John 
Tyndall (1820-93). devised beautiful methods for 
determining the physical conditions of aerial purity. He 
also demonstrated the errors in technique that had led 
some observers to oppose Pasteur. Tyndall’s work (1876— 
81) was well presented and widely read. Its appearance 



442 Biogenesis and its Implications 

marks the final abandonment by men of science of the 
doctrine of spontaneous generation. 

Biologists are now united in rejecting this belief, at 
least for organisms as they now exist upon earth. Whether 
spontaneous generation has ever taken place with other 
and yet lower forms of life or elsewhere than on this earth 
is a question on which science cannot, at present, express 
any opinion. 

The word biogenesis (Greek, ‘life-origin’) was coined by 
T. H. Huxley in 1870 to express ‘the hypothesis that 
living matter always arises by the agency of pre-existing 
living matter’. The opposite hypothesis is abiogenesis. 

% 5. Early Work on Microbic Origin of Injections Disease 

Long before Pasteur, it had been suggested that the 
phenomenon of infectious disease might be ascribed to 
minute organisms and to their passage from one host to 
another. In one infection this had been actually demon¬ 
strated. The condition known as ‘the itch’ is both caused 
and carried by a minute creature related to the spiders. 
This ‘itch mite’ is just visible to the naked eye. The 
microscopists of the seventeenth and eighteenth centuries 
had described it, and had cured the disease with ointments 
injurious to the mite. They had even conveyed it experi¬ 
mentally. Moreover, certain diseases of plants were well 
known to be due to and carried by gall insects, aphides, 
and other insects (pp. 155, 433-4). 

An important pioneer of the germ theory of disease was 
the amateur microscopist, Agostino Bassi (i 773—1856), of 
Lodi near Milan. In 1835 ^he first demonstration 

that a vegetable micro-organism could be a cause of 
infection. After prolonged investigation, Bassi proved 
that a certain disease of silkworms was transmissible from 
moth to worm, and that the transmitting material was a 
minute fungus. 



Microbic Origin of Infectious Disease 443 

In 1840 the Berlin anatomist, Jacob Henle (p. 445), 
set forth in detail his theory that infectious disease in 
general is caused and conveyed by invisible forms of life. 
During the next two decades the idea was taken up by 
several other workers. A few minor superficial maladies 
were shown, with a high degree of probability, to be 
related to micro-organisms. The microbic doctrine of 
disease was, however, still vague and generally regarded 
as a scientific heresy. 

In the ’fifties and ’sixties the French silk industry was 
suffering acutely from an epidemic among the silkworms. 
It looked as though the trade might perish altogether. 
The industry depends on the success of cocoon formation, 
as the caterpillar becomes a chrysalid. The caterpillars 
were forming hardly any silk and were dying, or languish¬ 
ing to die as chrysalids. Such few moths as were hatched 
showed signs of disease. 

There were many theories concerning this disastrous 
state of affairs. Certain microscopists had found numerous 
oval corpuscles in the worms and moths. Their association 
with the disease was, however, very vague. 

Pasteur took up the question at the request of the 
French Government. After a long investigation he did at 
last succeed in showing that the corpuscles were the cause 
of the disease. The matter was exceedingly complicated, 
and he made many false starts. He was, in fact, dealing 
not with one disease but with two. He showed that each 
is always associated with its own special organism (Etudes 
sur la maladie des vers a sole, Paris, 1862). 

The general nature of infection was still a mystery, but 
here were two infectious diseases in silkworms shown to 
be associated with microscopic organisms. The hint was 
very valuable. Primarily, it enabled Pasteur to recommend 
measures that saved the silk industry of France. Secon¬ 
darily, it led to discoveries which have opened out entirely 



444 Biogenesis and its Implications 

new departments of biology, initiated a new era in 
medicine, and given a new view of the world of life. 

The next infection on which light was thrown was 
anthrax. This is a very fatal disease of cattle, and is some¬ 
times transmitted to man. As with silkworm disease, rod¬ 
like bodies had been found in the tissues of sick animals. 

The matter had gone farther. A French observer, 
Casimir Davaine (1812—82), after long research, had 
shown that bodies which he called bacteridia are always 
found in the blood of sick animals in numbers propor¬ 
tional to the gravity of the attack. He showed that such 
blood conveys the disease, when inoculated in amounts 
so minute as i/1,000,000th of a drop (1863—8). A 
German observer, C. J. Eberth (1835—1927), had proved 
that the substance conveying the disease could be sepa¬ 
rated from the blood. He had filtered the blood of animals 
suffering from anthrax, and injected the filtrate into 
healthy animals which had nevertheless failed to develop 
the disease (1872). 

The bacteria had also begun to attract the attention of 
botanists. Among them, Ferdinand Cohn (1828—98) of 
Breslau applied himself most successfully to the subject. 
He recognized the great number and variety of bacteria, 
and sought to classify them according to their effect on 
the medium in which they dwelt. He reserved a place 
for those which cause disease. Cohn’s work on bacteria 
in the period 1872—6 clarified the current attitude toward 
these organisms. He is rightly regarded as the father of 
bacteriology. 

Bacteria are a group of lowly plants, perhaps allied to 
the fungi, but entirely without any trace of sexual pro¬ 
cesses. Like fungi, they are without chlorophyll and there¬ 
fore cannot build up organic substance from the carbon- 
dioxide of the air (pp. 375-8). They depend for their sus¬ 
tenance upon the substances in which they live. This 



Mtcrobic Origin oj Injections Disease 445 

existence is described as ‘saprophytic’ (p. 318). The 
derivation of the word implies that they ‘grow in putrid 
substance’. Bacteria are the great agents of decay of all 
kinds, owing to the fact that they set up rapid and pro¬ 
found chemical changes in the organic substances which 
support them. They are also necessary for various vital 
processes. Bacteria fall into two great classes, according to 
their mode of life. The aerobic bacteria flourish only in 
the presence of oxygen; the anaerobic cannot so flourish. 
It happens that the organism of anthrax, which for a 
bacterium is large and conspicuous, is aerobic. 

§ 6. Koch (i 843-1910) on Anthrax 

The achievement of unravelling the life-history of the 
anthrax bacillus belongs to Robert Koch. He had a poor 
education and little culture. He studied medicine at 
Ghttingen. Though an inconspicuous pupil at the time, 
it is yet probable that he was inspired by the theories of his 
teacher, Henle (1809—85), who was himself a pupil of 
Johannes Mtiller. In 1872 Koch settled as a country 
doctor not far from Breslau. He was thrown entirely on 
his own resources. Anthrax broke out among the cattle 
of his district, and he began to study it microscopically. 

Koch found that in anthrax the spleen was specially 
affected. He examined fragments of it microscopically 
and saw the anthrax bacilli as Davaine and Eberth had seen 
them (p. 444). He found that the disease could be con¬ 
veyed to the mouse. Propagating it for twenty generations, 
he recovered the characteristic organisms from the last. 

But the key to Koch’s progress in the study of the 
disease was his discovery that the organism can be grown 
outside the body. He used as soil the body fluids of the 
animal, and especially blood serum. He ascertained with 
exactness the conditions under which growth of the bacilli 
will take place. 



446 Biogenesis and its Implications 

For investigating growth at different temperatures, 
Koch employed a primitive sort of incubator. It was so 
arranged that the temperature could be adjusted. A frag¬ 
ment of spleen of a mouse infected with anthrax was sown 
in a drop of blood serum. This was kept at body tempera¬ 
ture for eighteen hours and examined hourly. The drop 
finally presented microscopically a very characteristic 
appearance. 

In the centre of the preparation, where air could not 
penetrate, the bacilli, being aerobic, suffered from want 
of oxygen. They were there growing very slowly and 
were mostly separated from each other. Farther out, 
where the oxygen supply was better, the bacilli had grown 
longer and many were placed end to end. These organ¬ 
isms, like many of their kindred, when actively multiplying 
tend to grow thus in threads. Yet farther out, the threads 
were so long that they became twisted and bent. The nearer 
to the edge, the longer the threads. In those threads in 
contact with the outer air, little round refringent bodies had 
formed. These were the ‘spores’. They were very highly 
resistant to such destructive influences as heat, chemical 
agents, drying, &c. This fact is of the utmost significance 
for the history of the disease, as Koch fully realized. 

In 1876 the unknown Koch wrote to Cohn at Breslau 
that he was prepared to demonstrate the life-history of the 
anthrax bacillus. Cohn immediately invited him to do so 
in his laboratory. A few days later Koch fulfilled his 
promise. Several men of science were specially invited as 
witnesses. The results were published under Cohn’s 
auspices. Koch’s great paper, T)ie Atiologie der Milz- 
brandkrankheitf begriindet auf die Entwickelungsgeschichte 
des Bacillus Anthracis (‘The causative factors of anthrax 
based on the development of the Bacillus Anthracis’), 
marks the beginning of our exact knowledge of bacterial 
infectious diseases. 



Koch on Anthrax 447 

Koch was now able to devote himself to science. He 
proceeded at once to develop technique. In a short time 
he had made the two contributions that have enabled 
bacteriology to develop as a separate science. First he 
raised the microscopic visibility of bacteria, and second he 
improved the method of cultivating them. 

As regards visibility. The eye does not readily distin¬ 
guish the shape and arrangement of bacteria under the 
microscope. Stains had been occasionally used to raise 
their visibility. The aniline dyes were now available. 
Koch introduced them into bacteriology and elaborated 
methods of staining suitable for a variety of organisms. 
The staining methods commonly employed by modern 
bacteriologists are more or less directly derived from 
those of Koch. Perhaps the greatest triumph of these 
methods is the discovery by Koch himself of the elusive 
tubercle bacillus in 1882. 

As regards methods of cultivation. Early workers on 
bacteria were constantly confused by preparations that 
contained more than one species. Many elaborate methods 
were introduced to obtain growths consisting of but one 
species—‘pure cultures’ as they are now termed. Koch 
adopted, after many trials, the beautifully simple device 
of a transparent medium of jelly-like consistence. The 
fluid from which the organism is to be grown can then 
be diluted indefinitely before it is used to infect the 
medium, and the very smallest quantities can be used. Thus 
colonies of bacteria can be raised, each from very few or even 
from a single organism. Moreover, anaerobic organisms 
can be grown within the medium. The system of cultiva¬ 
tion in transparent media introduced by Koch in 1881 has 
remained in use to this day without substantial alteration. 

A direct result of the use of Koch’s technical methods 
has been the discovery of the causative organisms of a 
large number of diseases. Among these are cholera, 



44 8 Biogenesis and its Implications 

diphtheria, glanders, Mediterranean fever, plague, pneu¬ 
monia, and typhoid. The bacteria of all these are now well 
known. 

§ 7. Immunity 

Koch and his German colleagues thus applied them¬ 
selves with success to the development of bacteriological 
technique and to the discovery of the causative organisms 
of disease. It is a department which we need follow no 
further. In the meantime Pasteur and the school that he 
had founded were studying the powers that the body 
possesses for protection against disease. These studies 
were of the highest practical importance. Here, however, 
we have only to consider certain biological aspects. 

It was well known that many infectious diseases, such 
as measles, scarlet fever, and the like can commonly be 
contracted but once. The sufferer having recovered 
becomes ‘immune’. Further, Pasteur had before him the 
artificial establishment of immunity to small-pox by 
vaccination which is, in effect, a mild form of the disease. 
Pasteur sought a parallel to this. He found it in the 
disease called ‘fowl cholera’. 

He prepared cultures of the germs of fowl cholera and 
noticed a fact that has proved of great significance. If he 
kept the cultures too long and then inoculated fowls with 
them, the fowls developed only a mild attack. Into such 
a fowl, on recovery, he inoculated an ordinary virulent 
culture of the disease. The animal withstood it. It was 
‘immune’. The discovery (i 8 80) opened up a new depart¬ 
ment of biology. 

Pasteur now turned to anthrax, where he found a some¬ 
what similar state of affairs. If a virulent culture of anthrax 
bacilli be kept at a temperature of 42° Centigrade (108® 
Fahrenheit) for eight days, it loses much of its virulence. 
It may then safely be inoculated into susceptible animals. 



Immunity 449 

Further, he found that animals thus treated become 
immune to the disease. He demonstrated this on cattle, 
and ultimately protected millions of them. He carried out 
successful researches of a similar character in other diseases 
of which the best known is hydrophobia. 

The question of the nature of immunity early arose. 
Two rival theories appeared. One of them, associated with 
the name of Elias Metschnikolf (1845—1916), may be 
called the ‘solidist theory’, the other the ‘humoral theory’. 

According to Metschnikoff, infective organisms that 
find their way into the body are engulfed and digested by 
certain cells which he named ‘phagocytes’ (1884, Greek, 
‘devouring cells’). He based his views, in the first 
instance, on invertebrates, and set them forth in detail in 
his Lemons sur la pathologic comparee de ^inflammation 
(1892). The process that he describes certainly takes 
place, but his work threw light chiefly on local inflam¬ 
mation. The general nature of immunity cannot be 
explained by it. 

The humoral theory was stimulated by a very important 
discovery in connexion with the phenomena of immunity, 
made in 1890 by the Prussian army surgeon, Emil von 
Behring (1854-1917). He showed that it is possible to 
produce immunity against tetanus and diphtheria by 
injecting serum from an animal that has been infected 
and has recovered. The serum, then, in these cases at 
least, is the carrier of the immunity. It bears with it the 
antitoxin —a word introduced by Behring. 

The subject of immunity has turned out to be enor¬ 
mously complex. The body, under various forms of 
excitation, is constantly throwing into its blood-stream 
substances which are somehow directly or indirectly 
inimical to the organisms of diseases. Of the chemical 
nature of these substances we have no knowledge. 
They are, however, definitely specific for the disease 



45° Biogenesis and its Implications 

for which the body elaborates them. Nor is the body 
prepared only against attacks of disease. There are 
poisons of known chemical composition against which 
similar immunity may be acquired. Further, it must be 
remembered that whenever we recover from an infectious 
disease, we must have developed some degree of specific 
immunity against it. If we did not, the infecting organism 
would have got the upper hand and we should not have 
recovered. 

No theory yet advanced is adequate to explain all the 
known facts of immunity, or even a large number of 
them. The details of the science of immunity are thus 
not of great importance for us here. What is of impor¬ 
tance is that the study reveals to us the complexity of 
the conditions involved in the ‘internal environment’. 
Just as the functions are active according to physio¬ 
logical needs, so are they active according to pathologi¬ 
cal needs. In disease, as in health, the organism must 
be considered as a whole. The test of life is ever this— 
Does the organism seek to preserve its own norm.^ We 
can no more consider a disease apart from the sufferer 
than we can an organ apart from the organism. We are 
back on that wonderful balance that life alone maintains. 

§ 8. Biology and Disease 

Pasteur and Koch brought the phenomena of disease 
well within the range of biological science. Many con¬ 
temporaries and successors extended their work in many 
departments. The special application of the knowledge 
of disease to the life of man has given a practical direction 
to these researches. With their extension in the domain 
of medicine we are not directly concerned. Yet it is well 
to recall that if the problems of disease are to be regarded 
in a philosophical manner, they must be treated on a 
biological basis. 



Biology and Disease 451 

The sciences are usually developed along the lines of 
the material needs of the day. Special departments are 
established not so much because of a pressing intellectual 
necessity as because of the practical demands of the times. 
Thus develop such sciences as forestry, economic zoology, 
or the study of immunity, which become intensively 
investigated without regard to their general relation to 
the main body of knowledge. Nevertheless, we may some¬ 
times turn from the more special aspects which these 
subjects represent, and consider their position as part of 
a great scientific unity. Let us, in this spirit, consider 
Medicine as a department of Biology, recalling at the 
same time that if Biology is now an independent discipline, 
it first became so, historically, as a department of Medicine. 

There are various departments of medical research 
which, in modern times and with the rapid advance of 
biological knowledge, have been placed in the hands of 
those who follow the study of biology in the academic 
sense. To a few of these lines of work we may briefly refer. 

The study of Protozoa has its own special technique, 
and entered long ago upon the experimental stage. Many 
important and common disorders are of protozoal origin. 
Among them we may recall malaria, certain forms of 
dysentery, syphilis, and sleeping sickness. The investiga¬ 
tion of these and of other diseases is mainly the concern 
of specially trained biologists who have had experience of 
allied forms of Protozoa, and who understand the complex 
life histories of the groups as a whole. Moreover, much 
light has been thrown on human protozoal diseases by 
the study of the protozoal parasites of animals. Thus has 
arisen the study of the specialist science of Protozoology. 

Many diseases are, as we now know, conveyed by 
Insect parasites. Thus malaria and yellow fever are con¬ 
veyed by certain species of mosquito; typhus by certain 
species of louse; plague by certain species of flea; relapsing 

Gg2 



452 Biogenesis and its Implications 

fever by certain species of tick; sleeping sickness by 
certain species of fly. Many other instances might be 
adduced. Close attention to the distribution and life- 
history of such insects has illuminated many obscure and 
little-understood features in the nature of all these diseases. 
There are some insects, moreover, which without being 
carriers of a specific disease, yet distribute infection im¬ 
partially by reason of their habits. Such is the domestic fly, 
which has typhoid, many forms of sepsis, and the very fatal 
infantile diarrhoea to his discredit. Because of facts such 
as these, a special knowledge of the life-history and habits 
of insects is demanded for the advancement of Medicine. 
Thus has arisen the study of Medical Entomology. 

Again, a number of diseases have their origin in the 
action of metazoan parasites, chiefly of the type of flat- 
worms (Trematoda and Cestoda) and round worms 
(Nemathelminthes). These enter usually through the 
digestive or urinary tract, but there is almost no part 
of the body that is not, from time to time, infested by 
them. Many of these forms are parasitic during parts of 
their lives in other animals besides man, and many of 
them have life-histories of excessive complexity involving 
some of the classic cases of alternation of generations 
(pp. 515-22). These forms require very knowledgeable 
interpretation. Thus has arisen Helminthology ((lireek 
helmins, ‘a worm’) as a special science. 

More obviously related to medical studies, as they are 
usually understood, are such sciences as Bacteriology, 
Physiology, Anatomy, and Comparative Anatomy. More¬ 
over, of late years most of the main biological themes have 
appeared in a medical aspect. The problems of heredity, 
of the nature of sex, of the natural term of life, and of life 
as a cycle, of generation, of the nature and origin of species 
as illustrated by man, of the possibility of modifying 
specific characters—all these have their medical aspects. 



Biology and Disease 453 

Further, it has long been known that certain diseases 
affect certain animals and not others, and this has become 
of importance both for the study of the spread of disease 
and for its experimental investigation. The domestic 
animals have been specially studied in this connexion, and 
so we are getting a real science of Comparative Pathology. 

§ 9. Some Failures of the Theory of the Microbic Origin of 
Disease 

The practical results of the study of the microbic origin 
of disease are so impressive that we are apt to forget the 
shortcomings in our knowledge of the nature and life of 
micro-organisms. Thus from the biological point of view 
the first question that we should like answered is, ‘How 
does an infectious disease originate in the first place 
Instead of answer there is almost complete silence. 

All through the animal and vegetable kingdoms we 
encounter the phenomenon of parasitism. The parasite 
lives in or on its host. In that limited habitat, its organs 
are lost and it becomes degenerate. The flea, living on the 
surface of the body, loses its wings. The mistletoe can no 
longer root in earth. Many parasitic plants have lost their 
chlorophyll. Intestinal parasites have lost their sense- 
organs, and among them are forms without digestive canal 
and even without power of movement. It is assumed that 
the bacteria are such degenerate organisms, though we 
are without knowledge of their ancestry. 

How does such a form become parasitic.'^ We are 
entirely in the dark. We are struck with the fact that 
diseases often attack only one particular species, but why 
the fowl, for example, alone suffers from fowl cholera, and 
man alone from typhoid fever, it is hard to say. Why 
should not allied forms be attacked by such diseases.^ 
We can but guess. 

A disease must have started at some time. Without 



454 Biogenesis and its Implications 

raising the question of the origin of life itself, it is evident 
that there must be points in history at which disease germs 
of each type enter a body for the first time, and cause a 
disease for the first time. We hear of historical or con¬ 
temporary records of previously unknown diseases. But 
no one has ever watched the process of the first appearance 
of a disease from the bacteriological point of view. We 
have, therefore, no real knowledge as to whether any 
particular disease is new or not. 

Again, if a disease is traced through history, it is 
evident that its type changes. Scarlet fever, measles, 
influenza, are very different in one year from what they 
are in another. Why.^ Is it that the infective organism 
has changed or is it that the host has changed.^ We know 
nothing on these matters, and the answers that are given 
do but darken counsel with words. 

On these fundamental points our age is as ignorant as 
other ages were. So long as this is so, it is but blind 
optimism that can speak of ‘the secret of disease’ having 
been ‘wrested from nature’. It is no small part of the 
function of science to define the limits of knowledge. 
Unjustified optimism is as much the enemy of science as 
is unreasoning credulity. 

§ lo. Filterable Viruses 

Of late years there has come into view an aspect of 
infectious disease that has bearing on the most funda¬ 
mental biological problems. It has been demonstrated 
that a number of diseases are conveyed by infectious 
material which does not lose its virulence even when 
passed through filters of minute mesh. Filters can be 
constructed which hold back not only bacteria but far 
smaller bodies. In 1892 it was demonstrated that the 
juices of tobacco plants suffering from ‘mosaic disease’, 
when thus filtered, can still convey the infection. In 1897 



Filterable Viruses 455 

the German bacteriologist, Friedrich Loeffler (1852— 
1915), showed that the same is true of the virus of the 
foot-and-mouth disease of cattle. This opened up a new 
line of investigation. 

A great many diseases are conveyed by filter-passing 
viruses. They affect plants, insects, birds, and mammals. 
It is believed that they even affect bacteria themselves. 
The evidence for this, though first adduced in 1915, is, 
however, still the subject of discussion. Among human 
diseases due to a filter-passing virus are measles, mumps, 
hydrophobia, typhus, chicken-pox, small-pox, and perhaps 
influenza and the common cold. In plants some filterable 
virus diseases are conveyed by insects and notably by 
aphides. Filterable viruses may be associated with the 
formation in the infected cell of bodies of considerable 
size. These were first recognized in hydrophobia. 

Seeing that filterable viruses will not increase in the ab¬ 
sence of living cells, attempts have been made by Carrel to 
grow them in pure cultures of particular cells (pp. 351—2). 
These attempts have succeeded. Little, however, has thus 
been learned of the nature of the viruses. 

The theoretical limits of microscopic vision are well-nigh 
attained when particles of a diameter of about i /4,000th 
millimetre (about one twelve-millionth of an inch) be¬ 
come distinguishable. By photographing microscopic 
fields with short rays of ultra-violet light, much smaller 
bodies can, however, now be determined in certain filter¬ 
able viruses. These minute bodies are of various sizes, 
the average diameter being about one-tenth of that of 
the smallest bacillus (say i/40,000th of a millimetre), 
though some are far less. They have a form and history 
very different from bacteria. 

Are these minute beings alive ? The question has been 
raised because of difficulties in which certain biological 
views are involved by this extreme minuteness. 



4^6 Biogenesis and its Implications 

One difficulty is that life is always associated with 
groups of exceedingly complex proteid substances which 
must, of their nature, be very large. Even if these minute 
bodies be mainly proteid—and we have no evidence for 
this—their tiny bulk leaves room for no more than 200 
to 400 proteid molecules. If these little masses are alive 
they must present the whole physiology of living matter 
with its unique combination of chemical flexibility and 
physical stability. They must have a mechanism for 
reproduction. They must adapt themselves to environ¬ 
ment by some degree of resistance to heat, drought, 
poisons. They must vary since, from the same virus, 
strains can be obtained of various degrees of virulence. 

There are doubts, among those who take a mechanistic 
view, as to whether these vital qualities can reside in so 
small a bulk. Some have suggested that filterable viruses 
are not alive but exhibit a passage from the world of 
not-life to that of life. Such doubts need not be shared by 
those who prefer the vitalistic point of view. But even the 
mechanist may take comfort that a few hundred molecules, 
each made up of numbers of variously linked amino-acids, 
afford immense possibilities of variation (p. 385). 

Is life then the mere concomitant of a happy juxta¬ 
position of events in non-living matter. The onus of 
demonstration lies on the mechanist, for the only known 
origin of living things is from other living things. There 
are, however, less formal and more philosophical reasons 
for thinking that life cannot be given a purely chemico- 
physical expression. Some of these we have already con¬ 
sidered, others we shall later consider. 

Fig. 158. A, In fresh blood (with red and white blood corpuscles). The bacilli 
show tendency to elongate. B, Incubated for three hours. The bacilli have 
grown into long threads. C, Incubated ten hours. Threads further elongated 
and coiled. Where oxygen runs short, spores begin to appear. Z), Incubated 
twenty-four hours and exhibiting full spore formation. E, Germination of 
spores, very highly magnified. 









XIII 


DEVELOPMENT OF THE INDIVIDUAL 

§ I. Seventeenth-Century Embryologists 

W ITH the advance of comparative anatomy in the 
sixteenth and seventeenth centuries (pp. 201-6) 
came the beginning of the study of development, embryo¬ 
logy as it is now called. Goiter broached the subject 
(pp. 106-7). Fabricius of Aquapendente (pp. 107-8,202) 
published the first illustrated embryological works. His 
De formato foetu (‘On the form of the foetus’) saw the 
light in 1600. His De formatione ovi etpulli (‘On the for¬ 
mation of the egg and the chick’) appeared posthumously 
in 1621. The former deals well with later stages of the 
embryo, when it has assumed an appearance similar to 
that of the new-born young. The latter, in treating of the 
earliest stages, breaks new ground but contains many 
grave errors. Among these is the representation of the 
parts as distinctly formed at a far earlier date than is the 
case. Fabricius, it must be remembered, had no micro¬ 
scope. Some of his errors passed to an important school 
of later writers, who held that the young animal is from 
the first ‘preformed’ in the egg (Fig. 159). 

During the seventeenth century, there appeared a num¬ 
ber of treatises on embryology. The majority of them 
were befogged by metaphysical speculation. The most 
famous is the De generatione animalium (1651) forced from 
the reluctant William Harvey in his old age. Despite the 
strange conservatism of parts of this work, it contains a 
host of observations and many important conclusions. 
The most significant is set forth on its allegorical title- 
page (Fig. 160). Jove sits enthroned, his eagle by his side. 
He opens an egg—a very Pandora’s box. From it emerge 



Seventeenth-Century Embryologists 459 

many creatures, embryos of man, mammals, reptiles, fish, 
insects. On the egg is inscribed Ex ovo omnia (‘All 
creatures come from an egg’). The phrase is prophetic, 
for Harvey had not seen the minute ova of viviparous 
creatures such as mammals. Harvey does not, in fact. 



Fig. 1^9. A series illustratinjj the development of the chick from Fabricius 
ah Aquapendente (1621). In b and f, of the third and fourth days of incubation, 
the chick is wrongly represented as having almost its adult form. 


attach the exact meaning to the word ovum that it now 
has. His discourse, however, has this of genius, that its 
content is greater than its utterer knew. Save for those 
beings that arise by budding or by fission, all living things 
are derived from eggs or from something analogous thereto. 

Harvey’s treatise is also important as being averse 
to the false doctrine of ‘preformation’. For the most 
part it is very Aristotelian, but Harvey’s philosophical 


460 Development oj the Individual 

prejudices, though they sometimes led him astray, placed 
him in this matter on the side of truth. Observationally, 
too, Harvey’s work stands out. He passed his predecessors 
in the accuracy of his description of the egg, in his account 
of the ovary and oviduct of the hen, and in many points 
in the early history of the incubated egg. 

Embryological study was placed on a firm basis by 
Malpighi (p. 1^2). His De formatione pulli in ovo (‘On 
the formation of the chick in the egg’, 1673) 
incubato observationes (‘Observations on the incubated egg’, 
1689) foreshadowed some of the more important general 
lines of subsequent embryological research and gave an 
exact foundation of knowledge on which to build. 

Despite his observational acuity, Malpighi believed that 
he could discern the form of an embryo in an unincubated 
egg. Nevertheless, the egg which he was examining was 
not really unincubated. No hen had brooded on it, but 
it had been laid two days previously in an unusually hot 
Italian August. This embryo provided a basis for the 
extraordinary doctrine of preformation and its yet more 
extraordinary development, the theory of emboitement or 
encasement (p. 498). On such a shaky foundation have 
been built whole systems of biological philosophy. Nay, 
the very hope of salvation of men such as Bonnet was 
erected upon it ! (p. 207). 

On other and cooler occasions Malpighi was less 
successful. Examining truly unincubated eggs he ‘often 
opened the sac with a needle to see the animal more clearly, 
but it was destroyed by the lightest stroke’. It is testimony 
to the character of this great investigator that his beliefs 
have in no case influenced the drawings of what he saw. 

Apart from the embryo as a whole, Malpighi describes 
stages in the development of certain of its organs. Of 
these he is most successful with the heart. Some of his 
figures of that organ, though inadequately described, are 



Fig. i6o. Part of allegorical title-page of William Harvey, De genera- 
tione animaliumy London, 1651, 


The generative organs of mammals were accurately 
described (1668—73) % Graaf and Stensen, though the 
knowledge oftheir minute ova was long deferred (pp.465-6). 











462 Development oj the Individual 

The spermatozoa, or essential male elements, were figured 
for the first time by Leeuwenhoek in 1679 and soon after 
by several others (Fig. 172). The discovery gave rise to 
strange views as to the nature of generation (pp. 498-500). 

Not until the mid-eighteenth century was the know¬ 
ledge of the developing embryo pushed farther than 
Malpighi had left it. The reason for the arrest was the 
general acceptance of the doctrine of preformation. This 
removed the embryological motive. If all the parts of an 
organism be preformed from the beginning, it were easier to 
investigate them in the grown animal than in the embryo. 

The next important landmark in the history of the 
subject is the work of Wolff. 

§ 2. Wolff (1738—94) and his successors 

The German, Caspar Friedrich Wolff, produced at 21 
his remarkable booklet, Theoria generationis (Halle, 1759). 
Five years later Catherine the Cireat offered him a post 
in Russia. There he published a series of observations 
on the formation of the intestine in the chick (St. Peters¬ 
burg, 1768). Neither work attracted much attention till 
the nineteenth century, when J. F. Meckel (1761-1833) 
issued a German translation of the Observations (Halle, 
1812). Meckel, like Wolff, worked at Halle, where he 
pursued comparative studies with enthusiasm. He has 
left his name on several anatomical structures. He pub¬ 
lished a monograph of the egg-laying mammal, the duck¬ 
billed Platypus, then recently discovered. Meckel was 
a befogged thinker but a very popular teacher, and his 
advocacy of Wolff’s writings gained them wide attention. 

Wolff showed that the organs of plants—leaves, 
stipules, roots, &c.—are developed by differentiation from 
uniform tissues at the tip of the growing shoot or root. 
He was the first to indicate that this growing point con¬ 
sists of an area of undifferentiated tissue. The demon- 



Woljf and his successors 463 

stration had as corollary that the growth of the bud could 
not be a mere process of ‘unfolding’, since during the 
earlier stages the elements of the bud—such as leaves or 
parts of the flower—are not present. These elements appear 
only gradually. They first emerge as tiny prominences in 
undifferentiated tissue at the growing point (Fig. 161). 

The process of emergence is, in appearance at least, 
a true epigenesis (Greek, ‘origin upon’), an event in which 
something appears which was not there before, even in 



Fig. 161. Diagrams of development of leaf and flower-bud after Wolff, 1759. 
Wolff was such a poor draftsman that his figures are difficult to understand 
unless redrawn. This has been done here, using his outlines. 

I'he diagrams, inferior though they are, illustrate the process of ‘epigenesis’. 

A and C represent early magnified stages of the flower of the common l.)ean, 
A being from above, and C from the side. In ( 7 , a is an anther not yet raised on 
its filament, ^ to/are more developed anthers,/being definitely cleft into two 
chambers. B, Vertical section through growing point of yemng cabbage. 

rudiment. Epigenesis was thus opposed to the then pre¬ 
vailing view oipreformation (p. 498) which in the language 
of that day was often denominated evolution (literally 
‘unfolding’). 

Wolff set himself also to examine the formation of the 
parts of the flower. He showed that these appear in the 
first instance exactly as do the leaves, and that the rudi¬ 
ments of leaves are indistinguishable from the rudiments 
of floral parts. This suggested that the parts of the flower 
are of the nature of ‘modified leaves’. 

Wolff made a somewhat similar series of demonstra¬ 
tions in the developing chick. He showed that the 



464 Development oj the Individual 

abdominal organs and notably the intestines, like the parts 
of the plant, develop from apparently homogeneous tissue 
that at first shows no trace of its ultimate fate. 

Wolff’s name is still attached to a structure peculiar 
to the embryo, the development of which he was able to 
trace from such undifferentiated tissue. It is known as the 
‘Wolffian body’ or ‘primitive kidney’. It disappears in later 
life, and does not function in any living vertebrate except 
certain fish. Since Wolff’s time, however, a most primitive 
excretory system, from which the Wolffian body has doubt¬ 
less arisen in the course ofevolution, has been demonstrated 
in that lowly and primitive ‘chordate’, Amphioxus, 

There is an idea in the work of Wolff which yielded 
important results in the nineteenth century. Arising, 
doubtless, out of his researches on the growing points of 
plants, he compares the first rudiments of organs in 
animals to ‘leaflets’. I>ater, in describing various folds 
and layers in the embryo, he compares them to ‘leaves’, or 
‘layers’. This is the beginning of the so-called 

afterwards developed by von Baer and his successors. 

§3. Fon Baer (i 792—1876) and the Mammalian Ovum 

The subject of development was taken up early in the 
nineteenth century by the Russian, Heinrich Christian 
Pander of Riga (1794—1865). He published a beauti¬ 
fully illustrated monograph on the development of the 
chick (Wurzburg, 1817). A close personal friend of 
Pander was von Baer, who introduced the definitive 
modern stage in the study of development. 

The Esthonian, Karl Ernst von Baer, after wandering 
through several universities, settled with his friend Pander 
at Wurzburg. Von Baer was called as professor to Kdnigs- 
berg in 1817. He there prosecuted embryological studies 
inspired by Pander. In 1834 von Baer accepted a chair 
at St. Petersburg, where he passed the rest of his life. His 



Von Baer and the Mammalian Ovum 465 

later scientific work bore on the variety of the races of 
man, but had no relation to embryology. All his writings 
give the impression of great depth and intellectual power. 

Four important advances in embryology are associated 
with von Baer’s name. They are: 

(a) The discovery of the mammalian ovum. 

(b) The proposition known as ‘the germ-layer theory’. 

(c) The law of corresponding stages in the develop¬ 
ment of embryos. 

(d) The discovery of the notochord. 

Of these the first appeared in his De ovi mammalium et 
hominis gene si (‘On the origin of the mammalian and 
human egg’, Leipzig, 1827). The other three were 
adumbrated in his great Entwickelungsgeschichte der Thiere 
(‘Developmental history of animals,’ 2 vols., Konigsberg, 
1828-37). 

Harvey had seen nothing of the ova of mammals (p. 458). 
Apart from the large eggs of birds, reptiles, and amphibia, 
he knew of the ova of fishes. These are quite visible to 
the naked eye, as are those of insects and of the other 
larger invertebrates. It was naturally thought that the 
mammalian ovum must be of size comparable at least to 
that of fish. Now it happens that during the sexual cycle 
of mammals, there form in the ovaries certain peculiar 
bodies, easily visible to the naked eye. These were 
described by Regnier de Graaf (1641—73). The ‘Graafian 
follicles’, as they are called, were erroneously hailed as the 
mammalian ova. 

The error was corrected by von Baer. He saw minute 
objects which he took to be ova in the tubes or oviducts 
leading from ovary to womb. He tried to detect similar 
structures in the ovary. They evidently could not be the 
‘Graafian follicles’, which were far too large. But, with 
his very near-sighted eyes, examining one day the intact 
ovaries, he ‘clearly discerned in each follicle a yellowish 

2«I3.3 H h 



466 Development of the Individual 

point floating freely in the fluid. Opening the follicle I was 
able to examine this point microscopically. It proved to 
be the body already known from the oviduct.’ 

Thus at last the reproductive processes of mammals and 
of man himself were brought into line with those of other 
animals. 

§ 4. The Germ-Layer Theory 

A doctrine associated with von Baer is known as the 
‘germ-layer theory’. The word ‘theory’ has several senses. 
Commonly it indicates an hypothesis which, if accepted, 
would explain a number of observed phenomena. The 
‘Origin of Species by Natural Selection’ is a theory of 
this order. Its supporters hold that the variety of species 
is explained if the action of Natural Selection be accepted. 
The ‘germ-layer theory’ is no theory in this sense. Struc¬ 
tures known as ‘germ-layers’ are visible in the embryo. 
They demonstrably give rise to various organs of the 
body. On these matters there is no room for doubt. The 
germ-layer theory is thus rather a description, in general 
terms, of events which have been observed in many 
organisms and can safely be assumed in others. It is a 
generalization and can only be questioned in the sense 
that we may doubt whether it is adequate. We might 
legitimately say, for instance, that it summarizes the facts 
too simply, or we might doubt whether the germ-layers 
are constant in their action or comparable from group 
to group. 

Von Baer, in the matter of the germ-layers, was carrying 
farther the views of Wolff and Pander. He showed that, 
during the development of certain types of animal, the 
egg or ovum divides into layers of tissue. These layers 
give rise to the various organs of the body. Further, each 
layer gives rise to the same organs throughout various 
groups of animals. Von Baer distinguished four germ- 



Germ-Layer Theory 467 

layers, an inner and outer which were formed first and 
from which were budded off the two intermediate layers. 

At a later date (1845) Robert Remak (1815—65), a 
pupil of Johannes Muller, showed that the two middle 
layers were best treated as one. Thus Remak distinguished 
an ectoderm (Greek, ‘outside skin’), an endoderm (‘inside 
skin’), and a mesoderm (‘middle skin’). He confirmed and 
extended the teaching of von Baer that the skin and 
nervous system are formed from the ectoderm; that the 
notochord (pp. 469-70) and the lining membrane of the 
digestive canal and of the digestive organs are from the 
endoderm; and that the muscular and skeletal and excretory 
systems are from the mesoderm. This is a remarkably 
wide generalization—one of the widest in the whole 
domain of animal biology. It needs some qualification 
but has, on the whole, preserved its usefulness and held 
its ground to the present day. 

§5. The Biogenetic Law 

A contribution to embryological thought for which 
science owes much to von Baer was the view of correspond¬ 
ing stages in the development of the embryo. Von Baer 
applied the doctrine specially to the vertebrate embryo. 
There are traces of this attitude among earlier workers. 
Thus Harvey wrote that Nature ‘by steps similar in all 
animals, goes through the forms of egg, worm, embryo, 
gradually acquiring perfection at each step’ (1628). 
Again, John Hunter about 1790 had put down in his 
notes ‘If we were to take a series of animals from the more 
imperfect to the perfect, we should probably find an 
imperfect animal corresponding with some stage of the 
most perfect’. Meckel (p. 462) expressed the view (i 811) 
that the embryonic stages of higher animals actually 
resemble lower animals. Somewhat similar teaching was 
that of the French anatomist E. R. A. Serres (1787-1868) 

H h 2 



468 Development of the Individual 

who included man in his list. Von Baer corrected this by 
pointing out that lower forms never resemble embryos of 
higher forms, but that embryos of higher and lower forms 
resemble each other more closely the farther we go back in 
their development. 

In a famous passage which drew the attention of Darwin, 
von Baer wrote 

‘The embryos of mammalia, of birds, lizards, and snakes are, in 
their earliest states, exceedingly like one another, both as a whole 
and in the mode of development of their parts; indeed we can often 
distinguish such embryos only by their size. I have two little em¬ 
bryos in spirit, to which I have omitted to attach the names. I am 
now quite unable to say to what class they belong. I'hey may be 
lizards or small birds, or very young mammals, so complete is the 
similarity in the mode of development of the head and trunk in 
these animals. The extremities are still absent, but, even if present, 
we should learn nothing from them in this early stage of develop¬ 
ment, for the feet of lizards and mammals, the wings and feet of 
birds, no less than the hands and feet of man, originate on the same 
fundamental plan.’ 

It is doubtful if this position of von Baer can be rigidly 
maintained. It is true that embryos of different vertebrate 
types are built on the same fundamental plan and bear 
a strong resemblance to each other. But it is probably 
equally true that, if sufficiently carefully studied, they can 
be distinguished from each other. 

Nevertheless, von Baer’s embryological doctrine is of 
great historic and practical importance. Later, when the 
doctrine of Organic Evolution had become generally 
accepted, structural relationship came to be explained as due 
to relationship of descent. The process of development 
then came to be a test of structural relationship. Some 
who stressed this aspect ascribed to von Baer the view, 

* In the earlier editions of the Origin of Species Darwin unaccountably ascribes 
this passage to Agassiz! In his notes, however, he had the ascription correct. 



The Bio genetic Law 469 

epitomized later by Haeckel (pp. 480—5) that Ontogeny 
(individual development) is an epitome of Phytogeny (race 
development). To ascribe this ‘Recapitulation Theory’ 
to von Baer is, however, to read into his work something to 
which his ideas did not extend. Von Baer, though he lived 
till 1876, did not accept the doctrine of organic evolution. 

Like most German writers of his day, von Baer was 
saturated with Naturphilosophie. His views on the 
geometrical and numerical relations of the developing 
organs savour of Pythagoreanism. We need not follow 
these fancies. He has, however, profoundly influenced 
biology through what has become known as his biogenetic 
law. This consists, in effect, of four propositions: 

(ei) In development, general characters appear before 
special. 

(b) From the more general characters are developed 
the less general and finally the special. 

(c) In the course of development an animal of one 
species diverges continuously from one of another. 

(d) A higher animal during development passes through 
stages which resemble stages in development of 
lower animals [Contra Meckel & Serres, p. 467J. 

One of the most remarkable of von Baer’s contributions 
was in connexion with the notochord, or as he called it, 
chorda dorsalis. This cellular rod runs the length of the 
vertebrate embryo, between alimentary canal below and 
nervous system above. It cannot be seen in the adult, 
save in certain fish. Previous investigators had seen it in 
the embryo, but did not perceive its importance. Von Baer 
followed the formation and fate of the chorda dorsalis. He 
showed that it arises from the layer that produces also the 
lining of the alimentary canal,the endoderm (Fig. 165). He 
showed that at a later stage it is broken up by the forma¬ 
tion of the vertebrae. It thus has no place, or at most a very 
minor one, in the anatomy of the higher adult vertebrate. 



47 ° Development oj the Individual 

Its demonstration in embryos, however, not only estab¬ 
lished a criterion for the vertebrate nature of an organism 
but had some extremely important implications for the 
relationship and classification of the vertebrates (pp. 479— 
80 and Figs. 165-7). 

§ 6. The Earlier Morphological Embryologists 

With the knowledge of the mammalian ovum and the 
notochord secure, and wfith such important generaliza¬ 
tions as the germ-layer theory and the biogenetic law, 
embryology advanced rapidly. Development as the key 
to morphology became the watchword of biology even 
before evolutionary teaching provided its special explana¬ 
tion of this relationship. The immediate followers of von 
Baer were essentially morphologists. 

Heinrich Rathke (1793—1860) succeeded both to the 
chair and to the tradition of von Baer at Kbnigsberg. The 
general tendency of his numerous embryological observa¬ 
tions was to destroy the view based on the ‘ideal forms’ 
to which the embryo was attaining as expressed by the 
Naturphilosophen. They took the adult as basis of their 
‘archetype’. Rathke forced back the archetypal con¬ 
ception to earlier developmental stages. Thus in 1829 he 
described gill-slits and gill-arches in embryos of birds 
and of mammals as corresponding to a fish-like stage. 
This exposition of Rathke linked up with observations 
of Malpighi and illustrated the biogenetic law of von 
Baer (Fig. 162). 

In a classical treatise on the lampreys and their allies, 
Johannes Mtlller recognized these creatures as the most 
primitive of true vertebrates (1835-8). He set forth the 
relationships of their gill-arches, though his views were 
vitiated by his continued adhesion to the vertebral theory 
of the skull (pp. 218—20). 

The transformation of the embryonic structures which 



The Morphological Embryologists 471 

in fish form parts of the gills into other organs of higher 
animals—Eustachian tubes, tonsils, thymus gland, hyoid, 
&c.—is now part of stock anatomical teaching. It took 
its place there through the exposition of the leading mor- 



Fig. 162. Diagrams to illustrate fate of arteries supplying gill arches 
(Rathke 1829). 

A, Ideal diagram of primitive condition still encountered in some fish. From 
the single chambered heart H a great vessel goes forth and divides into gill 
arches right and left. I'hese unite and distribute blood to the body. 

In the subsequent diagrams the dark or shaded lines show the vessels which 
persist. The others disappear. 

B, Modification in bird. The heart, Hy now has two ventricles. The great 
vessel from it has divided into a pulmonary artery/> (shaded) and aorta a (black). 
The former is formed from the first, the latter from the second arch. 

Cy Modification in mammal. 

In B and C the artery to the head, c, as well as the artery to the fore-limb, sc, 
are formed, in part, by remains of the arches. 

phological teacher of the later nineteenth century, Carl 
Gegenbaur (1826—1903). 

The germ-layer theory was also soon brought into the 
general field of discussion. Almost the first contribution 
made to science by T. H. Huxley bore on this very 
topic. He perceived that the jelly-fish and their allies 
consist of two cellular layers separated by the jelly-like 
substance. In 1849, writing On the affinities of the 





472 Development oj the Individual 

Medusae^ he made the happy suggestion that these layers 
correspond to the ectoderm and endoderm (p. 467) of 
the embryos of higher animals. Thus the lowly jelly-fish 
are devoid of a mesoderm, and Huxley suggested that the 
presence or absence of this layer can be made the primary 
basis for classifying multicellular animals according to 


A 



Ectoderm^ 

Lower layer 
oP cells 


Segmenbation cavity 


10 


oo 


C 



Fig. 163. Sections of three early stages in development of hen’s egg. 
Contrast Fig. 164. 

Ay Section through germinal disk of egg about the middle of its stay in the 
uterus. I'he cells are shown segmenting off from the yolk. At the edges of the 
disk are seen nuclei still embedded in yolk. 

By Section toward the end of segmentation. I'he ectoderm and endoderm are 
definitely separated and a segmentation cavity has made its appearance. This 
corresponds to the beginning of the gastrula stage, greatly deformed by the 
mass of yolk ectoderm represented as black. Compare Figs. 16^ E and F, 167 Ay 
and 168 D, 

Cy Transverse section of the embryo about the twentieth hour of incubation. 
The ectoderm and endoderm are clearly differentiated from each other. The 
neural groove has appeared. From the junction of ectoderm and endoderm the 
mesoderm is being given off. 


both adult structure and embryonic development. The 
idea has won acceptance. 

The cellular view now began to have its influence on 
the study of development. The earlier embryologists 
worked without any clear conception of a community in 
microscopic structure of the tissues. Wolff and von Baer 



The Morphological Embryologists 473 

speak but vaguely of 'a cellulosity' of certain parts of 
animals. A fine exposition of the new cell doctrine in all 
its bearings was made by Huxley in 1853, It was im¬ 
mediately followed by advances in the conception of the 
development of the embryo. In 1861 Gegenbaur set 
forth the view that all eggs are simple cells. In the same 
year Kolliker published the first general text-book of 
embryology on a cellular basis.^ It is valuable for its lucid 
account of the earliest stages of division of the egg-cell 
in mammals—the process of segmentation as it is now called 
(Fig. 163)—and for its complete grasp and exposition of 
the germ-layer theory. 

§ 7. First Reaction of Evolutionary Theory on Embryology 

Embryological science at this stage came within the 
orbit of the great evolutionary movement. Darwin him¬ 
self early perceived its bearings on his theory of descent. 
In his note-books of 1842 and 1844 he devotes much space 
to embryological discussion relying on von Baer. 

In the Origin of Species (1859) Darwin exhibits a grasp 
of the biogenetic law. He was, however, more at home 
with living nature than with laboratory specimens. 
Characteristically he points out that 

‘A trace of the law of embryonic resemblance sometimes lasts till 
a late age: thus birds of the same genus, and of closely allied genera, 
often resemble each other in their immature plumage; as we see in 
the spotted feathers in the [young of the] thrush group. In the cat 
tribe, most of the species [when adult] are striped or spotted in lines; 
and stripes or spots can be plainly distinguished in the whelp of the 
lion [and the puma].’ [Bracketed clauses added from later edition^] 
‘The points of structure, in which the embryos of widely different 
animals within the same class resemble each other, often have no 
direct relation to their conditions of existence. We cannot, for 
instance, suppose that in the embryos of the vertebrata, the peculiar 

* Earlier summaries were made by G. Valentin, 1835, Th. L. W. BischofF, 
1842, A. Agassiz, 1859 (see p. 482), and H. Rathke, 1861. 



474 Development oj the Individual 

loop-like courses of the arteries near the branchial slits (Fig. 162) 
are related to similar conditions in the young mammal which is 
nourished in the womb of its mother, in the egg of the bird which 
is hatched in a nest, and in the spawn of a frog under water. No 
one will suppose that the stripes of the whelp of a lion, or the spots 
on the young blackbird, are of any use to these animals, or are 
related to the conditions to which they are exposed.’ 

The immediate disciples of Darwin also perceived the 
bearing of individual development on evolutionary theory. 
Several took up the subject with enthusiasm. Prominent 
among these was Fritz Mtiller (1821—97), an eccentric 
pupil of Johannes Muller. Fritz Muller went as a mer¬ 
chant to Brazil. There he studied the development of the 
Crustacea, and published some of his results in his little 
book, For Darwin (1864). This curious document is con¬ 
versational in form but contains much original observation. 

Fritz Muller convinced himself that the complex 
process of development of certain Crustacea is of the 
nature of an ‘historical document’. The various and 
startling phases traversed by these forms during develop¬ 
ment closely resembled, he thought, those through which 
their ancestors had passed. Striking instances of these 
phases had long before been adduced by Vaughan Thomp¬ 
son (Fig. 170), who ascribed no evolutionary significance 
to them. Fritz Muller’s views on ancestral recapitulation 
attracted Haeckel and excited in him an enthusiasm for 
embryology. They were followed by a series of magnificent 
studies from Haeckel’s laboratory by Alexander Kowalew- 
sky (1840-1901), whose papers on the development of 
Amphioxus (1866—77) Tunicates (1866-71) are 

among the most striking in embryological literature. 
They largely determined the general systematic position 
of the vertebrates (Figs. 164—7). 

Amphioxus is a small lancet-shaped marine creature 
which lives half buried in sand and, at times, darts about 



Evolutionary Embryology 475 

freely in the water. In its adult state it has many features 
in common with the lowest vertebrates and with all verte- 



Fig. 164, A-H, Early development of Amphioxus> 

A-Dy Segmentation of the egg. E-M, Later stages shown in section. The cells 
of the ectoderm are represented as black, with white nuclei, the cells of the endo- 
derm and mesoderm as white, with black nuclei. £, F, and G, Formation of 
gastrula (cf. p. 483). H, Beginning of formation of neural canal (that is, the 
formation of central nervous system). In G and H a large posterior cell is seen 
which is the beginning of the mesoderm. For J-M see Fig. 165, p. 476. 

brate embryos. It has a persistent notochord. It has an 
unsegmented nervous system, the front of which is slightly 



























Nt'uropore 

■ Notorhorcj 














478 Development oj the Individual 

the nervous system are continuous, and the liver is a mere 
diverticulum of the gut (Fig. i66). 

The further investigation of Amphioxus has been 
undertaken by many able observers, who have greatly 
refined the work of Kowalewsky. Notably we have learnt 
on the one hand of the peculiarly primitive excretory 
system of Amphioxus, and on the other hand of the high 
degree to which the creature as a whole is adapted to its 
mode of life. But the attitude towards Amphioxus which 
Kowalewsky suggested has remained substantially un¬ 
changed (pp. 479—80). The developmental history of 
Amphioxus is still held to be much like that of a very 
primitive vertebrate, and that to which the development 
of less primitive vertebrates must be compared. 

No less extraordinary were Kowalewsky’s discoveries 
concerning the development of the Ascidians. These are 
curious fixed forms, of which the affinities were then quite 
uncertain. Most naturalists had placed them near the 
molluscs. Kowalewsky showed (Fig. 167) that they have 
a free-swimming larva, that this larva has a notochord and 
has many other features which unite it with the Chordata 
and separate it from the mollusca. The Ascidian larva 
has been compared to a tadpole, which it somewhat 
resembles in general structure and appearance. But, 
unlike a tadpole, its metamorphosis to the adult state is 
reached by regressive stages comparable to those gone 
through by the barnacle (Fig. 170). 

Since Kowalewsky’s time much has been learned con¬ 
cerning the Tunicates, the group to which the Ascidians 
belong. Some forms have been distinguished which 
retain throughout life their larval organization together 
with their notochord and associated structures. Others 
have acquired a secondary free-swimming habit. Yet 
others have been shown to go through extraordinary 
methods of reproduction by branching, by fission, and 



'Evolutionary Embryology 479 

by other exceptional methods. They are now united 
together under the term ‘Urochorda*, and for this group 
as a whole the observations and conclusions of Kowalewsky 
have fairly held their ground. 

These sensational discoveries made it necessary to erect a 
new group which should include Amphioxus, the Tunicates, 
and Vertebrates. This group is of the order of a Phylum, to 
which the name Chordata was given by Balfour in 1880. 

There have been claims from time to time for the 
inclusion of other classes among the Chordates besides 
Vertebrates, Amphioxus, and Tunicates. Mention may 
specially be made of a worm-like creature Balanoglossus, 
In 1884 the English investigator, William Bateson (1861— 
1926), showed that it presents a notochord in its free part 
or proboscis only. This creature and its allies he there¬ 
fore placed in a special Class ‘Hemichorda’. It has also 
been claimed that the free-swimming ciliated larvae of the 
Hemichorda bear strong resemblances to the larvae of 
certain Echinoderms, thereby uniting the vertebrate stock 
with certain non-vertebrate forms. 

Thus we may set forth the current modern classification of 
the Phylum Chordata. It is based on von Baer’s biogenetic 
law, is derived from his discovery of the origin of the noto¬ 
chord, and involves the work of Kowalewsky and of Bateson. 

PHYLUM; CHORDATA {mioyxx, 1880) 

Class I. Hemichorda Balanoglossus and allies. Notochord of 
(Bateson, 1884). larva and adult in proboscis only. 

Larva ciliated, free swimming, and 
resembling that of Echinoderms. 

Class II. Urochorda Tunicata and allies. Notochord in tail 

(Lankester, 1877). only of larva and disappears in adult. 

Lar\'a tadpole-like. Adult a de¬ 
generate form, fixed or secondarily 
may float or swim, or in some cases 
preserve a free life (Fig. 167). 



480 Development of the Individual 

Class III. Cephalochorda jimphioxus and allies. Notochord from 
(Lankester, 1877). tip to tail, develops early and persists 
throughoutlife(Figs. 165-6). Larva 
free swimming and ciliated. Adult 
active and free swimming. Primitive 
kidney (Wolffian body) persists. 

Class IV. Vertcbrata. Notochord runs the length of the body 

in embryo, but is broken up by 
vertebrae in adult. Limbs in all 
except lowest forms. Primitive kid¬ 
ney replaced by newer formations. 
Brain surrounded by cartilaginous 
or bony cranium. 

§ 8. The Systematic Evolutionary Embryologists 

Ernst Haeckel (1834—1919) studied with Johannes 
Muller, Kolliker, Virchow, and Gegenbaur. After an 
expedition to Sicily, he brought out his first important 
contribution. It was on the Radiolaria of the Mediter¬ 
ranean (i860). The Radiolaria are a group of Protozoa 
which have very beautiful and symmetrical skeletons. 
Haeckel was an admirable artist, whose imagination was 
ever prone to rule his brush. His beautifully illustrated 
memoir earned him the chair of Zoology at Jena, which 
he held till 1909. 

It is difficult to estimate Haeckel’s place in the history 
of biology. His faults are not hard to see. For a generation 
and more he purveyed to the semi-educated public a 
system of the crudest philosophy—if a mass of contra¬ 
dictions can be called by that name. He founded some¬ 
thing that wore the habiliments of a religion, of which 
he was at once the high priest and the congregation. A 
large part of his insatiable energy was devoted to propa¬ 
ganda for the great liberal intellectual movement of his 
time, the essential nature of which he misunderstood. In 
science, his peculiar employment of hypothesis had close 



Systematic Evolutionary Embryologists 481 

affinities with that of the scholasticism that he denounced 
and that vitiated alike his observations and his inferences. 
He confidently constructed genealogical trees of living 
things, which now give rise only to a smile. He habitually 
perverted scientific truth to make certain of his doctrines 
more easily assimilable. He invented a bizarre philo- 
sophico-scientific nomenclature, now happily forgotten. 
His graphic talents led him to portray the more beautiful 
forms of minute life in which he saw things less visible 
to eyes devoid of that fire that burned within his own. 

The works of the German apostle of Darwinism now 
rest peacefully on the less accessible shelves of libraries. 
And yet they contain contributions which are still funda¬ 
mental to the fabric of scientific thought. 

In the department of embryology, Haeckel's strong 
points are his great experience of diverse forms of life 
and his fertile and ingenious imagination. He seized on 
von Baer’s law (pp. 468-9) and developed it along his own 
lines. Stimulated by the work of Fritz Mtiller, he trans¬ 
formed the biogenetic law into a series of doctrines to 
which von Baer would never have assented. 

‘Ontogeny, or the development of the organic individual, being the 
series of form-changes which each individual traverses, is imme¬ 
diately conditioned by phylogeny, or the development of the organic 
stock to which it belongs. 

‘Ontogeny is the short and rapid recapitulation of phylogeny, con¬ 
ditioned by the physiological functions of heredity (reproduction) 
and adaptation (nutrition). The individual repeats during the rapid 
and short course of its development the most important of the form- 
changes which its ancestors traversed during the long and slow 
course of their palaeontological evolution. 

‘The complete and accurate repetition is obliterated and abbreviated 
by secondary contraction, as ontogeny strikes out for itself an ever 
straighter course; accordingly, the repetition is the more complete 
the longer the series of young stages successively passed through’ 
{Generelle Morphologies 1866). 

3613.3 I i 



482 Development oj the Individual 

( All this is briefly stated in the phrase ‘Ontology is an 
epitome of phylogeny’. If this rule be correct, there 
should be three biological parallels: («) the history of the 
individual, (h) the history of the species to which the 
individual belongs, and (c) a natural classification or 
system of organic forms which include the species. ) 

These doctrines were neither peculiar to Haeckel nor 
first suggested by him. In the very year of the publication 
of the Origin of Species the great Swiss naturalist, Louis 
Agassiz, published his Essay on Classification (1859). The 
book is, in large part, a summary of the embryological 
knowledge of its day. Agassiz, though firmly opposed to 
evolutionary interpretations, considers that ‘Embryology 
furnishes the best measure of the true affinities existing 
between animals. It affords a test of homologies in contra¬ 
distinction to analogies.’ 

To this familiar conception of classificatory relationship, 
Haeckel, following Fritz Muller, added the idea of evolu¬ 
tion. He developed the theme with more detail than discre¬ 
tion. But by the vigour, bulk, and controversial character 
of his writings, he turned the eyes of naturalists to the study 
of development. He failed to give full weight to the disturb¬ 
ing factor of the mechanical element in the process of de¬ 
velopment. He failed to explain the dropping out of many 
stages and the modifications of others—factors concerning 
many of which we are still in the dark. Naturalists since 
his time have concluded that we cannot, by embryological 
study alone, reach a complete or comprehensive summary 
of the relationships of living forms. C Yet there can be little 
doubt that Haeckel, more than any other man, initiated the 
modern movement which has, in effect, transformed com¬ 
parative anatomy into comparative embryology.) In this 
respect his work is to be contrasted with that of his more 
pedestrian teacher, Carl G«genbaur, the representative of 
comparative anatomy in its older and more classical sense. 



Systematic Evolutionary Embryologists 483 

Haeckel made valuable contributions to the knowledge 
of several important animal groups, notably the Radio- 
laria, the Sponges, and the Medusae. His greatest work 
on the Radiolaria is his magnificent monograph of the 
‘Challenger’ material. Certain of his embryological doc¬ 
trines that are still of value arose from these investigations. 
Of special importance is his gastraea theory, 

Kowalewsky, when investigating the development of Am- 
phioxus and of the Tunicates, observes that these creatures 
develop by the segmentation of the egg into a hollow 
sphere. This sphere in due course invaginates into a cup, 
much as a hollow ball may be invaginated. The inner part 
of the resulting invaginated stage is the endoderm, the outer 
the ectoderm. The mesoderm is given off between the 
two. During subsequent development the invaginated 
sphere elongates. The opening narrows and forms the anus 
of the larva or of the adult. All these stages were noted by 
other observers in the early development of many organ¬ 
isms unrelated to the Chordates (Figs. 164, 167—8). 

Huxley had suggested that jelly-fish have not three 
germ-layers but two (pp. 471—2). The matter was taken 
farther by Haeckel in a monograph of sponges (1872). 
He maintained that the invaginated form, the gastrula^ 
as he termed it (diminutive of Greek gaster^ ‘stomach’), 
occurs as a stage in all multicellular animals. Looking 
always for lines of descent, he pointed out that in the 
sponges and jelly-fish the two-layered gastrula, in a state 
of greater or less complication, is the final body structure. 
Thus the passage of the higher animals through this stage 
represents the historical passage of their ancestors through 
a similar stage. The ‘gastrula’ or ‘gastrea’ theory thus 
illustrated Haeckersversionofthebiogeneticlaw(Fig. 168). 
( Moreover, Haeckel pointed out that many multi¬ 
cellular organisms go through stages represented by {a) 
a single cell, {b) a spherical conglomeration of cells, (J) 

1 i 2 



484 Development oj the Individual 

a hollow sphere, and {d) a gastrula (Fig. 168). He saw 
other stages and invented names for them all. 

Haeckel further propounded the view that the definitive 
body cavity of many animals, coelom, as he called it 
(Greek, ‘hollow’), has a common origin in hollow buds 
from the endoderm. The coelom is a cavity in the 
mesoderm of higher organisms. Other organisms, such 
as the two-layered sponges and jelly-fish, have no mesoderm 
and therefore no coelom. Yet others, such as the flat- 



Fig. 168. Haeckel’s five primary stages of individual development (ontogeny) 
corresponding to five types of independent organisms (1877). 

A, Moner-ula, a hypothetical non-nucleated form that has, as we now know, 
no existence. B, Cytula or one-celled nucleated form. The term is no longer in 
use. C, Morula, a solid sphere of cells of equal size. D, Blastula, a hollow sphere 
of cells, ciliated in free living form. E, Gastrula formed by invagination of D, 

worms, possess a mesoderm which shows no tendency 
to form a coelom. This provides a basis for classification 
of many forms (pp. 200, 338). 

The ‘coelom theory’ was developed by others and 
especially by Haeckel’s pupils, the brothers O. and R. 
Hertwig. Although neither the gastrea theory nor the 
coelom theory are now accepted as originally propounded, 
they still form the main basis of the classificatory arrange¬ 
ment of multicellular animals. 

Despite his very early death, the best representative of 
systematic evolutionary embryology is the Cambridge 
investigator, Francis Maitland Balfour (1851-82). He de¬ 
veloped the more profitable embryonic theories of Haeckel. 



Systematic B/volutionary Embryologists 485 

Balfour’s first work was on the group of cartilaginous 
fishes, to which the sharks and rays belong. They have 
large eggs, loaded with a yolk, comparable in size to that 
of birds. Balfour demonstrated many important parallels 
between the development of these fish and that of Am- 
phioxus. Some of the differences between them were, he 
showed, due to distortion by the yolk (1878). 

Balfour’s great Comparative Embryology (1880—i) was 
issued a few months before his death. It is a masterly 
summary of the subject, a mass of erudition and yet lucid 
and critical, covering the whole field of the development 
both of vertebrates and of invertebrates. It is generally 
acknowledged as the foundation of the modern study of 
embryology. Balfour’s death took place within a few 
weeks of that of the aged Darwin. 

The traditions of Balfour and the theories of Haeckel 
were alike developed and expounded by Edwin Ray 
Lankester (i 847-1929). He was, after Huxley, the most 
prominent English biological teacher of the nineteenth 
century. Lankester produced no systematic treatise of any 
permanent importance. By an immense number of sepa¬ 
rate studies, however, he did much to give their modern 
form to the gastraea theory, the germ-layer theory, the 
coelom theory, and the recapitulation theory. His re¬ 
searches on the development of the Mollusca, Annelids, 
and Arthropoda are largely responsible for the generally 
accepted internal classification of these groups. He did 
a somewhat similar service for the Protozoa and the 
Acoelomate Metazoa (p. 200). 

In Germany the work of Balfour was carried on by 
O. Hertwig. His great embryological text-book appeared 
first in 1886. It is distinguished by clarity of exposition, 
by excellence of arrangement, and by its careful historical 
material. It has established a standard for embryological 
writing. 



486 Development of the Individual 

§ 9. Digression on Metamorphosis 

In most beings the progress from embryo to adult is 
gradual. Some, however, exhibit a series of rapid and 
fundamental changes. Such is the case with the Ascidians 
(pp. 477-8). More familiar phenomena of the same order 
are presented by the insects. Thus, the caterpillar is trans¬ 
formed into a chrysalis and the chrysalis into a winged 
insect in what seems a sudden manner. Such events are 
termed ‘metamorphoses’ (Greek, ‘complete change’). 
This was the title of the great poem by Ovid (43 b.c.— 
A.D. 17). It recounts legends of miraculous change of 
shape and opens: 

In nova fert animus mutatas dicere formas corpora. 

‘My mind is bent to tell of bodies changed into new forms.’ 

Thus the term is peculiarly appropriate to these insect 
changes. Moufet (pp. 95—6) was the first in modern times 
to use the word in this sense, and it was popularized by 
Jan Goedart (i 662, Fig. 166). Insect metamorphoses were 
studied by Swammerdam and others in the seventeenth 
century. 

Of eighteenth-century entomologists none was more 
noteworthy than the Frenchman, Ren6 Antoine Ferchault 
de Reaumur (1683-1757). After a long Jesuit training, 
he applied his varied talents to the whole range of the 
sciences. Among his biological activities we note his 
observations on regeneration in the Crustacea, on the 
locomotion of star-fish, on the electric apparatus of the 
torpedo, on marine phosphorescence, on the growth of 
Algae, on the digestion of birds, on spiders and silk, and 
on the nature of coral organisms. Reaumur’s great Contri¬ 
butions to the History of Insects (12 volumes, 1737—48) is 
remarkable among such works for its physiological inter¬ 
est. In it he discusses the effect of heat on the develop¬ 
ment of insects and their larvae, and has much to say on 



Digression on Metamorphosis 487 

the leaf-boring and gall-forming insects. Throughout he 
emphasizes development and especially metamorphosis. 

Several contemporary naturalists worked on similar 
lines. The Dutch lawyer, Pieter Lyonet (1707-89), pro¬ 
duced with incredible labour in 1740 his famous mono¬ 
graph of the goat moth caterpillar. As a refined anatomical 



Fig. 169. From Goedart (1662) illustrating three different types of insect meta¬ 
morphosis: a is the caterpillar, and b the chrysalis of r, the common ' clouded 
yellow ’ butterfly; d and e are larvae of/, the cockchafer; gand h are maggots 
of /, the blue-bottle fly. 

examination it is still unapproached. The Parisian physi¬ 
cian Etienne Geofffoy (1725-1810) described and figured 
beautifully the metamorphoses of a number of forms. 

Thus by the beginning of the nineteenth century the 
conception of metamorphosis was quite familiar. 

The subject was put on a new footing by the English 
army surgeon, John Vaughan Thompson (1779—1847), 
who settled in Cork in 1816. There for twenty years he 
conducted investigations in marine zoology, which both 
modified and extended the current conception of meta¬ 
morphosis. It has been said of him that ‘no great naturalist 
has ever written so little and that so good’. 



488 Development of the Individual 

Thompson showed that the common shore crab, during 
its development, passes through a series of changes not 
less remarkable than those of insects. He extended his 
discoveries to other groups of Crustacea. Most revolu¬ 
tionary was his discovery of the nature of the Cirripedia 
or barnacles. 



Fig. 170. Developing forms of Crustacea from Vaughan Thompson (1828-30). 


A, ‘Zoea’ shown by I'hompson to be the larval form of the shore crab 
Carcinus moenas. 

B, Stalked compound eye of slightly older ‘zoea’. This type of eye is charac¬ 
teristic of certain groups of higher Crustacea. 

C. Free-swimming Crustacean, proved by Thompson to be the larval form of a 
fixed ‘barnacle’, an organism classed among the Cirripedia. The larva attaches 
itself by its anterior limb or ‘antenna*. This becomes converted into the foot 
or peduncle’ of the adult barnacle. The foot becomes attached to a fixed object 
by cement from the cement gland. The larval form possesses eyes both simple 
and compound. These disappear in the adult barnacle. (Compare Figs. 179 and 
180.) 

D. Compound eye of larval barnacle, which may be compared to B, 

The Cirripedia had already been much studied. 
Cuvier had treated them as a class of his phylum Mollusca 
(p. 230). Cirripedes are immobile, without head, eyes, 
limbs, or obvious joints. They have a shell formed of a few 
calcareous plaques. In general appearance they resemble 
bivalve molluscs. Yet Thompson showed convincingly that 
they pass through a young or larval stage, in which they 
swim freely and are equipped with eyes and jointed limbs. 
These larvae closely resemble certain stages of the develop- 



Digression on Metamorphosis 489 

merit of the shore crab and other Crustacea (Fig. 170). 
With that group they have ever since been classed. 

Since Thompson’s time, metamorphoses no less remark¬ 
able have been traced in a variety of animal forms. The 
most extreme types are encountered among parasitic 
worms, many of which dwell at different periods of their 
lives in several different hosts. 

Such a very extreme type of metamorphosis was inves¬ 
tigated by Thompson himself. Shore crabs are sometimes 
found with a bag-like growth on the abdomen. This is the 
degenerated parasitic body, limbless, eyeless, motionless, 
devoid of mouth, alimentary canal, or sense organs, of 
what was once a free swimming creature. It is herma¬ 
phrodite, that is to say, it contains the sexual organs of 
both sexes—testis and ovary. It contains little else. 
Thompson saw its larval stage and interpreted it as a 
crustacean. It is now classed near to the Cirripedia. 

These observations drew attention to the profound 
effects of parasitism on structure and life history. Numer¬ 
ous and varied investigations have since been made on the 
subject. The general laws of parasitism and the types of 
degeneration that parasitism involves are now well recog¬ 
nized. The phenomenon is found throughout the animal 
and vegetable kingdoms (pp. 318-23). 

§10. Developmental Mechanics 

There has always been a school that seeks to refer all 
biological phenomena to known physical laws. With such 
an end in view the process of development has long been 
the subject of experimental investigation. 

An important pioneer in this work was the Swiss, 
Wilhelm His (1831—1904), who professed anatomy at 
Leipzig. No one before' him described so diligently, 
lucidly, and exactly the minutiae of the development of 
the higher animals and especially of man. He was the chief 



49° Development of the Individual 

agent in the introduction of the instrument for cutting 
serial sections known as the microtome. Its use has become 
an indispensable method of biological research in general 
and of embryological research in particular {Beschreibung 
eines Mikrotoms, 1870). His very exact knowledge of the 
developmental history of man enabled him to attempt an 
explanation of the entire process on mechanical principles. 

In a work on Our bodily structure and the physiological 
problem of its formation (18 74), he compared the various 
layers and organs of the embryo to a series of more or less 
elastic tubes and plates. The local inequalities of growth 
on the one hand and differences in the consistency of 
the tissues on the other, might, he conceived, account for 
the formation of the various organs and structures. 

If we were to accept such forces as in themselves 
adequate to explain development, we should find ourselves 
involved in an ancient fallacy; we should have to admit 
that the originals (primordia or rudiments) of the various 
organs are represented in the germ layers, at least as re¬ 
gards their local behaviour. The germ layers themselves 
would be similarly represented in the parts of the embryo 
in a yet earlier stage, and these would be represented in the 
egg. We thus reach the old doctrine of preformation in 
another dress. Apart from theoretical objections to this 
conception, there is experimental evidence that renders it 
untenable. For a time, however, the evidence that was 
forthcoming, notably that produced by Wilhelm Roux 
(1850-1924), was in its favour. 

Roux was a pupil of Haeckel. In a series of important 
writings collected as The developmental struggle of the parts 
within the organism (1881) he worked out in detail his 
view of a mechanical basis for the functional adaptation 
of the parts to each other. The investigation of function 
implied experiment. Thus in seeking the basis of‘develop¬ 
mental mechanics’ (Entwickelungsmechanik), with which 



Developmental Mechanics 491 

his name is specially associated, Roux passed naturally 
to experiment on the embryo. 

An examination of the process of development along 
the lines suggested by Roux soon revealed the fact that 
development cannot be treated as a uniform process. It is 
divisible into two periods. The first is the true embryonic 
period. During it there are formed the structures that are 
predetermined (Roux’s own term, 1905). It includes all 
that part of the development which takes place until the 
organs function. The second is the period of functional 
development. It is in this second period that the formation 
of the parts is brought about by their specific action. Thus 
structure, according to Roux, determines function, but 
function also determines structure. The statement is 
doubtless true, but as thus analysed it gets us no farther 
towards an explanation of either. A mystery is no less a 
mystery because it is limited in its action in space and time, 
nor even when re-expressed in terms of the unknown. 
Nevertheless, as the creator of the science of Develop¬ 
mental Mechanics and of its handmaid Experimental 
Embryology, Roux rendered enormous service. 

Roux, like his contemporary Weismann and like many 
other naturalists to this day, held that in the fertilized egg¬ 
cell there exists a very complex structure or machine. He 
held further that this structure or machine is divided or 
disintegrated into its constituent but still complex parts, 
structures or machines, by the process of division or 
segmentation of the egg-cell. 

A famous experiment by Roux raised again in a new 
way the old antithesis between preformation and epi¬ 
genesis. In a developing frog’s egg, which had just seg¬ 
mented into two cells, Roux succeeded in destroying one 
without injuring the other (1888). The remaining cell 
developed as a half embryo. 

This result would appear to be interpretable on the 



492 Development oj the Individual 

basis of preformation, one cell containing the germ of one 
half of the frog, the other of the other half. Nevertheless 
this view proved to be untenable. 

O. Hertwig had shown the value of sea-urchins’ eggs 
for the investigation of developmental problems. Hans 
Driesch (1867— ), one of the most important architects 

of modern biological theory, then began to experiment 
with these sea-urchins’ eggs in 1891. He succeeded in 
separating the two cells into which a sea-urchin’s egg had 
segmented, and from each half egg he reared a complete 
larva, half the normal size (1900 onward). Further, he 
obtained complete embryos from yet later stages of segmen¬ 
tation—i/4th, i/8th, and even i/i6th or i/32nd the nor¬ 
mal size. Moreover, it was shown subsequently that if in 
such a frog’s egg as that on which Roux had experimented 
the dead cell be carefully removed, the remaining cell will 
develop as a whole embryo, though of course half the size 
of the normal. These results, contradicting the work of 
Roux, focussed the attention of naturalists on the experi¬ 
mental method in embryology. 

§11. The Science of Experimental Embryology 

Thus arose Experimental Embryology as a separate 
science. It is very recent in its development, and its find¬ 
ings seem sometimes equivocal. We shall, however, 
glance at a few of its more significant results. 

The primary phenomenon of development is the seg¬ 
mentation of the egg-cell. This exhibits great variety in 
eggs of different types. The main factor is the presence of 
yolk. Some eggs, like that of the hen, are masses of yolk 
with the protoplasm of the egg at one pole (Fig. 163). The 
segmentation of such eggs begins at the protoplasmic pole, 
and the yolk is only gradually included in the embryo. 
Other eggs, such as that of Amphioxus, have no yolk and 
segment almost uniformly (Fig. 164), Yet other eggs, such 



Experimental Embryology 493 

as that of the frog, are intermediate. The segmentation in 
the frog’s egg is more active in the region where there is 
less yolk than in the region where there is more yolk. 

That the yolk itself causes thpse differences by its 
mechanical action was proved by O. Hertwig (1897). He 
centrifugalized frogs’ eggs so that the yolk collected at 
one pole and the protoplasm at the other. The result was 
that the frog’s egg segmented only at the protoplasmic 
pole. This view has been since confirmed in many other 
ways on many other animals. 

A characteristic of animals, as distinct from plants, is 
their bilateral symmetry. This feature appears far down 
in scale. Most groups even of protozoa exhibit some 
trace of bilateral symmetry. In higher metazoa, bilateral 
symmetry may become masked, as in the radial sea 
urchins and starfishes or in the spiral snails or hermit 
crabs. Yet all these begin embryonic life as symmetric 
forms. Bilateral symmetry is often less apparent internally, 
as in the intestines and abdominal parts of man, than exter¬ 
nally. Nevertheless developmentally, bilateral symmetry is 
deep rooted among almost all animals. Some eggs, as those 
ofinsects, are visibly bilaterally symmetrical from the begin¬ 
ning. Eggs of many other animals can be shown to have 
an invisible bilaterality. The plane of symmetry is, in some 
cases at least, determined by the point of entry of the sper¬ 
matozoon, as was shown for the frog’s egg by Roux (1903). 
Work on this theme was done by the Oxford embryologist 
J. W. Jenkinson (1871-1915), who demonstrated that in 
some forms the axis of symmetry is determined by ex¬ 
ternal mechanical causes, such as light and gravity (1909). 

Much of the confusion in the early days of experimental 
embryology arose, as we can now see, from the fact that 
eggs belong to one of two classes, according to their 
physiological behaviour during segmentation. Thus there 
are eggs, as those of the sea-urchins, which segment into 



494 Development oj the Individual 

cells each of which can produce a complete animal. (It is 
evident that this power can extend only to a certain degree 
of division.) Such are regulative eggs as distinguished from 
mosaic eggs in which the different regions of the embryo 
develop independently of one another—the loss of one 
piece spoiling the pattern. There are, however, all stages 
between completely regulative eggs and completely 
mosaic eggs. The loss of the regulative power takes place 
at different dates in different eggs and can be either 
retarded or hastened experimentally. 

The factors that determine the development of an egg 
are of different classes. Certain of them, which we may 
call ‘internal factors’, are transmitted from the parents. 
These we shall consider elsewhere (chap. xv). The de¬ 
velopment of these factors depends, however, upon their 
environment. This environment is in part truly biological, 
that is to say, it is made up of the interaction of different 
parts of the embryo upon each other. A simple case of 
this was described by the American cytologist E. B. 
Wilson in the Mollusc Dentalium (1904, Fig. 171). It is, 
in fact, characteristic of living things that they carry with 
them the power of such mutual interaction of their parts. 
This we may call the ‘internal environment’ (pp. 394—5). 

Over and above internal factors and internal environment 
there are external factors that have an influence on develop¬ 
ment. Among these are such forces as gravity, tempera¬ 
ture, electrical and chemical actions, and osmotic pressure. 
All vary within wide limits during normal development. 
All have been experimentally varied within wider limits 
with significant results. The variation of each of these 
factors produces its own characteristic disturbances. 

Extremely interesting results have been elicited in con¬ 
nexion with the power of healing or regeneration of lost 
parts, especially in embryonic and growing animals. 

After the changes of the ‘embryonic’ period, there 



Experimental Embryology 495 

comes a time in the life of every being when the stimulus 
of function is necessary for the development of the part. 
This was perceived by Roux (pp. 490-2). The first appear¬ 
ance of the main trunks of the blood-vessels is an event of 



Fig. 171. Ay Early staj^c of cleavage of Dentalium, 'I'he egg has segiiienteci 
into two nucleated cells, from one of which depends a non-nucleated proto¬ 
plasmic lobe. By Normal larva oi' Dentalium. C, Larva obtained after removal 
of non-nucleated lobe. Neither the apical organ nor the hind region is then 
developed (Wilson, 1904). 

the embryonic period. The formation of the elaborate 
connexions of their branches depends on the development 
of the parts that they supply. This has been proved 
experimentally for these vessels and for numerous other 
organs by many workers. 

A particularly interesting series of events of the ‘func¬ 
tional’ period is provided by the nerves and the tissues 
that they supply. It is a remarkable fact that certain nerves 
are very faithful to certain structures. Despite changes in 
the form, position, and function of these structures in the 
course of evolution, their nerve-supply remains constant. 
Thus the normal nerve-supply of organs and notably of 
certain muscles is very complex, and the normal course of 
certain nerves is extremely intricate. It might be thought, 
therefore, that there is some natural affinity between a 
particular organ and a particular nerve, so that each attracts 
the other and refuses co-operation with more conveniently 
placed neighbours. 






496 Development oj the Individual 

This is in fact in some degree the case. Thus the limb of 
a newt grafted on to another becomes innervated after 
the normal fashion. It is, however, also true that some 
organs can, if suitably ingrafted, be persuaded to form 
quite abnormal connexions. Thus the eye of the am¬ 
phibian Amblystoma can be removed and engrafted in 
another individual in such a way as to acquire its innerva¬ 
tion from the nerve that normally supplies the tongue. 

The whole subject of grafts and their innervation is in 
course of active investigation. Particularly interesting but 
very difficult are experiments of early grafts in the ‘em¬ 
bryonic’ as distinct from the functional stage. The very 
skilful experimenter Hans Spemann (1869- ) has had 

interesting results on the newt. Before the formation of 
the gastrula, he removed a piece of the ectoderm destined 
for the formation of the nerve-cord. For this he sub¬ 
stituted a piece of ordinary ectoderm (not destined to 
form nerve cord) from a newt of another species and 
colour. The difference in colour enabled the fate of the 
engrafted fragment to be traced. It was found to take its 
place in the nerve cord which was formed and completed 
in the normal way (1918). Thus the work of Spemann 
demonstrated that the fate of the ectoderm of the newt 
is not irrevocably determined until after the period of 
development at which this experiment was made. 

The determination of the parts continues throughout 
development. It is a process which never reaches finality. 
Its last exhibition is the power of repair which ceases only 
with death. The process is indeed a reflex of life as a 
whole. What we are in esse we can no longer be in posse. 
The very fact of achievement means a limitation of pos¬ 
sibilities of development. The parallel is more than 
an accidental one. Development, evolution, progress, 
ageing, bring gains that are problematic, but losses that 
are certain. 



XIV 

SEX 

§ I. First Attempts to Analyse the Nature of Generation 

T he process of coming into being has always roused 
human curiosity. Aristotle devoted two of his finest 
treatises to the subject. After ages have not been want¬ 
ing in theories as to the nature of the process, but it was 
many centuries before observation led to doctrines more 
comprehensive than his. 

Without a microscope, it was inevitable that Aristotle 
should hold some organisms to be ‘spontaneously gene¬ 
rated’. Apart from this, he recognized that most animals 
reproduce their kind through the intervention of two 
sexes. It was evident that in reproduction an egg or some¬ 
thing like it was frequently involved. In seeking analogy 
to the egg in those animals in which he had seen no egg, 
Aristotle compared an embryo in its membranes to an egg 
surrounded by its characteristic coverings (Figs. 63—4). 
The egg, he thought, was rendered capable of develop¬ 
ment by the sperm of the male. He believed that this sperm 
had in itself the power to form all parts of the body by 
its action on the ‘egg’. The male element was thus a 
potentiality and not necessarily material. The male 
gave form., the female substance, just as the artist ‘imparts 
shape and form to the material by means of the motion he 
sets up’ {De generatione animalium, i, § 22). 

Opposed to Aristotle were those that held the embryo 
to be formed of material elements derived from both 
parents. This view was especially acceptable to the philo¬ 
sophical sect known as ‘Epicureans’. Their representa¬ 
tive, Lucretius (r. 50 b.c.), assures us that ‘the embryo is 
always formed of two seeds, and whichever parent that 
which is so formed more resembles, of that parent it 



498 Sex 

hath greater share’. To this view Galen and his Arabian 
followers conformed. 

As the Middle Ages and the Renaissance derived their 
biological ideas in part from Aristotle and in part from the 
Arabian Galenists, confusion ensued. So the matter re¬ 
mained until the time of Harvey, who adopted something 
in the nature of a compromise. He greatly stressed the 
role of the egg, thus yielding to the Galenists, but he 
followed Aristotle in regarding the female as impregnated 
‘by a kind of contagion which the male communicates, 
almost as the lodestone does to iron’. He held, with Aris¬ 
totle, that for impregnation nothing material need pass 
from male to female. Fertilization was an act of a mys¬ 
terious essence, the aura seminalis. 

In the later seventeenth century the erroneous doctrine 
of ‘preformation’ unfortunately came to hold the field 
(pp. 460-3). It was now taught that a complete being lay 
in the egg. Only the suitable stimulus was needed to 
cause it to unfold. 

But complication again arose. If the being in the egg 
be complete, it must contain ovaries and ova. And if such 
secondary ova are present, they also must contain com¬ 
plete beings, and so on in a process of emboitement, like 
a series of Chinese boxes. Eve, it was held, had within 
her ovary the forms of all the men and women that were 
to be. One writer estimated them at the very moderate 
figure of twenty-seven million. This remarkable theory 
long held the field. The philosophers and men of science 
who professed it were named ‘ovists’. Their views had 
certain evident theological implications with which we 
are not here concerned. 

A further complication arose. It was found that the 
semen contained animalcules, as they were called, sperma¬ 
tozoa, as we name them to-day. These were depicted by 
Leeuwenhoek in 1679 (Fig. 172 a-c). It was now claimed 



Attempts to Analyse the Nature oj Generation 499 

that the spermatozoon, and not the ovum, contained the 
preformed organism. This was a justification ofthedignity 
of the male! It was also an interpretation—on the basis 
of a misunderstanding—of Aristotle’s view that the ‘male 
contributes form and the female substance'. Some claimed 
to descry a human form in the spermatozoon itself. Thus 
arose the school of the ‘spermatists’. These held that the 



Fig. 172. Spermatozoa as seen in the seventeenth century, a, by c, I^uwenhoek 
from thedog (1679). ^ 3 ^, Hartsoeker from man showing the ‘homunculus* (1694). 
€yfy g, Francois Plantades (Dalenpatius) from man. Cy intact, f and g, broken to 
show the ‘homunculi* (1699). 

testis of Adam must have contained all mankind, as the 
ovists had held for the ovary of Eve! The literature of 
these extraordinary preformationist doctrines is consider¬ 
able (Fig. 172 d-£). 

During the eighteenth century WollF gave a new turn 
to embryology by attacking the doctrine of preformation 
and presenting epigenesis in its stead (pp. 462-3). Many, 
Haller among them, remained unconvinced. The know¬ 
ledge of the essential nature of sexual generation was not 
greatly forwarded by the new discovery, for, though 
spermatozoa were demonstrated in a variety of animals, 
the ovum of mammalia had not been seen, or rather had 
been seen wrongly. The cellular nature of the ovum was 
still unsuspected. The spermatozoa were misunderstood 

K k a 



500 Sex 

and the most bizarre forms sometimes ascribed to them. 
Buffon and Needham, misled by their faith in spontane¬ 
ous generation (chap, xii), compared spermatozoa to the 
superficially similar organisms yielded by infusions. They 
thought that somehow these ‘filaments’ represented the 
primordia of higher forms of life (p. 290). 

§ 2. Early Writers on Pollination 

With this confusion in regard to animal forms it is not 
surprising that the reproductive processes of plants were 
little understood. The general sexual character of flowers 
was foreshadowed by Millington and Grew (p. 158), 
opposed by Malpighi, and supported by Ray. None of 
these contributed any facts of great importance to the 
subject. In 1691, the Roman Jesuit Filippo Buonanni 
(1655-1725) published a polemical treatise attacking 
Redi’s destructive criticism of spontaneous generation 
(p. 433). Buonanni figures the styles of several plants with 
pollen grains actually adherent to them. He found insects 
sometimes in association with these parts of plants, but 
he advanced no further (Fig. 173). 

The conception of sex in plants was first lucidly set 
forth a few years later in a small tract by a professor at 
Ttibingen, Rudolph Jacob Camerarius (1665-1721). 
The work is balanced, based firmly on experiment, and 
frank in its presentation of difficulties. Camerarius first 
made observations on such plants as Dog’s Mercury in 
which the flowers are of different sexes. He says: 

‘In plants in which the male flowers are separated from the female 
on the same plant, I have learnt by two examples the bad effect 
produced by removing the anthers. When I removed the male 
flowers before the anthers had expanded, and also prevented the 
growth of the younger male flowers, but preserved the ovaries, 
I never obtained perfect seeds, but only empty vessels, which 
finally fell exhausted and dessicated,’ 



501 


'Early Writers on Pollination 

He goes on to say that: 

‘In plants no production of seeds takes place unless the anthers have 
prepared the young plant in the seed. It is thus justifiable to regard 
the anthers as male, while the ovary with its style represents the 
female part’ 

Camerarius judiciously added that his theory did not 
apply to non-flowering plants. 



Fig. 173. Process of pollination from Filippo Buonanni (1691). The degree 
of magnification varies greatly in the different figures. 
a. Sexual parts of the flower of a mallow. Althaea hirsuta Linn.; calyx and 
corolla being removed. There are numerous styles^ or separate female organs, 
shown as hair-like lines above. They are surrounded by a large cushion, formed 
of a mass of stamens^ or male structures. 

by Pollen grain of mallow very highly magnified, 
r. Highly magnified style of mallow on which are three pollen grains. 
dy Flower of a valerian, Centranthus ruber. The five petals forming the corolla 
are joined at their bases into a spurred tube. Near its attachment this tube is sur¬ 
rounded by the calyx. Projecting from between the free ends of the petals are the 
sexual parts which consist here of but one style and one stamen. On the end of the 
stamen is an anther bearing pollen grains, shown as black dots. 

Cy PoUen grains of valerian, further enlarged. 

fy Style of valerian with three pollen grains in place on its expanded end or 
stigma. Between the cells, of which the style is composed, a tube, shown as a black 
line, leads to the ovary. 


502 Sex 

The sexual character of flowers was widely canvassed 
in the early eighteenth century. It was formally accepted 
by Linnaeus and incorporated into his system, though in 
a mechanical way. Linnaeus was not interested in physio¬ 
logy, and he used the sexual parts merely as a convenient 
basis for his system of classification (p. i88). 

During the eighteenth century, several botanists suc¬ 
ceeded in using the pollen of one species to fertilize the 
flowers of another. The products had some of the char¬ 
acteristics of both species. The word hybrid was introduced 
to describe these cross-breeds. The Latin hybrida means 
the offspring of a domestic sow and a wild boar, that 
is a cross between varieties, not species. Flowers that 
are hybrids, in the strict sense, that is crosses between 
species, occur occasionally in nature. * The observation of 
these and their formation under cultivation provided ad¬ 
ditional evidence of the sexual character of parts of flowers. 

Joseph Gottlieb Koelreuter (1733-1806), director of 
the grand-ducal botanic garden at Carlsruhe, was in¬ 
terested in hybrids. His book on the sex of plants (1761) 
acknowledges a debt to Camerarius. Koelreuter rightly 
considered that a very important agent in the fertilization 
of flowers is the wind, that some flowers fertilize them¬ 
selves, but that 

‘in flowers in which pollination is not by immediate contact, insects 
are the usual agents, and consequently they alone bring about 
fertilization. It is probable that they render this important service 
if not to the majority of plants, at least to many, for all the flowers 
which we discuss have in them something agreeable to insects’. 

Koelreuter pointed out that there are certain plants with 
flowers of different sexes in which pollination by wind is 
almost impossible. Here he thinks insects must be the 
agents. Such is the case with the mistletoe. He drew 
attention to the distribution of its seeds, later investigated 

* The word ‘hybrid’ has come to be used much more loosely (see chap. xv). 



Ear/y Writers on Pollination 503 

by Darwin. The mistletoe is parasitic, growing only on 
certain species of tree. There must be some means by 
which the seeds find their way from one host to another. 
Koelreuter showed that the carriers are birds. Thus the 
mistletoe depends on two groups of animals, insects and 
birds, for its existence. The ancients believed the seed of 
mistletoe to be conveyed by the excrement of birds. It is 
in fact conveyed by birds wiping their beaks on the bark. 

Koelreuter’s lead was taken up by several German 
workers, but especially by Christian Conrad Sprengel 
(1750—1816), Rector of Spandau. He became so devoted 
to botany that he neglected his duties. He was removed 
from his parish and he removed himself to Berlin, where 
he led a solitary life and was regarded as a crank. His 
book on sex in plants is a work of genius. Its title may be 
translated The Newly Revealed Mystery of Nature in the 
Structure and Fertilization of Flowers (1793). He was so de¬ 
pressed by its reception that he abandoned botany for philo¬ 
logy. There is no evidence that philology was the gainer. 

‘In 1787’, says Sprengel, ‘I observed the lower part of the petals of 
Geranium sylvaticum to be provided with slender rough hairs on the 
inside and on both edges. Convinced that the Wise Framer of 
Nature has not produced a single hair in vain, I pondered on their 
purpose. Suppose the five drops of juice secreted by the five glands 
are for food of certain insects, it is likely that there are means of 
protecting this juice from rain. The flower is upright, but drops 
falling into it cannot reach the juice, being stopped by the hairs. 
An insect is not so hindered. 

‘I examined other flowers and found that several had structures for 
a like end. I now saw that flowers which contain this juice are 
contrived so that it may be accessible to insects but not to rain; 
and that it is for the insects that these flowers secrete the juice, 
which is so secured that they may enjoy it pure and unspoilt.’ 
[Much ahbreviatedJ] 

The flowers of Forget-me-not suggested that the spots 



504 Sex 

on the corolla are placed in relation to the honey glands, 
and he concluded that 

‘the corolla has a particular colour in particular spots, to indicate the 
juice to the insects, that when in search of food they may see 
the flowers from afar and know them for receptacles of juice’. 
[Abbreviated,'] 



Fig. 174. Pollination of Nigella ar^ensis as represented by Sprengel (1793). In 
the centre is the multiple pistil in a single whorl. Around these are several whorls 
of stamens. Around these again is a circle of very small tubular petals filled with 
honey. These are surrounded by a circle of large coloured sepals. When the 
flower first opens the filaments of the outermost whorl bend so that their 
anthers touch the visiting bee. These stamens, being exhausted of pollen, come to 
lie upon the sepals. Next day their place is taken by the next whorl, and so on. 
When all the whorls of anthers are thus exhausted the segments of the pistil 
come into play. Bending down to touch the back of the visiting hce they are 

duly pollinated. 

Sprengel afterwards found that the stigmas of a species 
of Iris cannot be fertilized save by insects, and 

‘that many, perhaps all flowers which have this juice, are fertilized 
by the insects which feed on it The whole structure of such flowers 
can be explained if we consider these points; first, that flowers were 
intended to be fertilized by the agency of insects; second, that insects 
in seeking the juice were intended to sweep off the dust from the 
anthers with their hairy bodies and convey it to the stigma, which is 
provided either with short delicate hairs or with a sticky substance 
to hold the pollen,’ 


^arly Writers on Pollination 505 

He paid special attention to those plants in which the 
two sexes, while occurring on one blossom, yet mature at 
different periods. This process, dichogamy, Sprengel first 
observed in the Rose-bay. He found 
‘the individual flowers fertilized by 
the humble bee, but not by their 
own pollen, for the older flowers are 
fertilized by the pollen which the 
insects carry to them from the 
younger flowers’. Later he found 
exactly the opposite arrangement 
to prevail in a Euphorbia. There the 
pollen is brought by insects only 
from the older flowers. Sprengel’s 
observations on dichogamy are 
specially striking in the case of Love- 
in-a-mist {Nigella, Fig. 174). 

Sprengel concluded that the whole 
structure of nectar-bearing flowers 
is directed to fertilization by insects, 
and can be fully explained by it. 

He found the chief proof of this in 
dichogamy, the details of which he 
traced skilfully. 

Sprengel noted that there are 
flowers which imprison and even 
destroy the insects that serve them. 

He also observed that flowers devoid of attractions for in¬ 
sects are fertilized by the wind or other mechanical means. 
These wind-fertilized flowers always produce, he saw, 
great quantities of very light pollen. He believed that his 
principles explain all the characters of flowers—^position, 
size, colour, smell, form, season of flowering, and the 
like. 

At about the turn of the eighteenth century, several 



Fig. 175. Fertilization 
of Asclepias phytolaccoUes, 
from Robert Brown (1833), 
Rightf Pollen mass which 
has germinated. The pollen 
grains have sent forth their 
tubes, some of which are 
entering and descending 
the style which has been 
laid open. Lefty Enlarged 
detail of pollen grain. 



$06 Sex 

workers were occupying themselves with experiments in 
fertilization of flowers. T. A. Knight (p. 372) wrote his 
Experiments on the fecundation of vegetables (1799) which 
drew far more attention than the incomparably greater 
treatise of Sprengel. Working primarily on peas, Knight 
observed 

‘the variety of methods which nature has taken to disperse the 
[pollen], even of those plants in which it has placed the male and 
female plants within the same empalement. It is often scattered by 
an elastic exertion of the filaments which support it, on the first 
opening of the blossom; and its excessive lightness renders it capable 
of being carried to a great distance by the wind. Its position within 
the blossom is generally well adapted to place it on the bodies of 
insects, and the vellous coat of the numerous family of bees is not 
less well calculated to carry it. “I'he [pollen] is often so placed that 
it can never reach the summit of the [pistil] unless by adventitious 
means; and many trials have convinced me that it has no action on 
any other part.’ 

Knight formulated the view, which long prevailed but 
must now be abandoned, that in no species of plant can 
interbreeding between male and female elements in the same 
flower continue to be productive through many generations. 

§ 3. The Modern Study of Pollination 

The sexual character of flowers being determined, it 
remained to analyse the sexual process. At the beginning 
of the nineteenth century the microscope was still very 
defective. Several physicists were at work upon it. 
Among them was the Italian, Giovanni Battista Amici 
(1784-1860), who had already done good work in as¬ 
tronomy and was a professor of mathematics. This ver¬ 
satile and gifted man succeeded in introducing many 
improvements in the microscope, some of which, such as 
the immersion lens, are still in daily use. 

With one of his improved microscopes. Amici had seen 
streaming movements of protoplasm in the Alga Chara. 



Modern Study of Pollination 507 

In 1823 he was examining the hairs on the stigma of 
Purslane. He then saw a tube given off by the pollen 
grain, and the granular contents perform streaming move¬ 
ments like those in Chara (Fig. 176 A). In 18.30 he even 



Fig. 176. Early figures of pollination. 

A, Amici’s drawing of formation of pollen tube in Purslane, 1823. B, C, D, 
Schleiden’s figures of fertilization in the pumpkin (1845). Schleiden regarded the 
ovum as the male, the pollen as the female element. We have lettered the figures, 
however, according to modern views. 

followed the pollen tubes into the ovary and he observed 
one to find its way into the ovule. 

These observations were repeated a short time after by 
Robert Brown (Fig. 175) and Schleiden (Fig. 176). Unfor¬ 
tunately, the Scot, Brown, was too cautious, and the 



5o8 Sex 

German, Schleiden, too bemused by theory to make the 
right inference from their observations. The work of both- 
on the pollen tubes was overshadowed by further in¬ 
vestigations by the brilliant Amici. 

In 1846 Amici placed the whole matter on a firm 
foundation by his observation of Orchids, which are pecu¬ 
liarly suitable for the investigation of pollination. He 
demonstrated that an egg cell is present in the ‘embryo 
sac’ of the ovule before the pollen tube reaches it; that the 
egg cell is stimulated to further development by something 
brought by the pollen tube; and that this further develop¬ 
ment results in the formation of the embryo. In the 
meantime a firm foundation had been given to the doc¬ 
trine of the nature of ‘cells’ (chap. ix). The examination 
of the sexual process was thus facilitated, and further light 
on the sexual process in plants was thrown by von Mohl 
(p. 336) and by Hofmeister (pp. 516-20). 

Sprengel’s great work remained generally neglected 
during the early nineteenth century. In 1837, Charles 
Darwin became persuaded that intercrossing from flower 
to flower plays an important part in keeping the forms of 
species constant. In 1841, on the advice of Robert Brown, 
he read Sprengel’s book. It impressed him deeply, and 
much of his later work on flowers arose out of it. 

Darwin produced his Fertilization of Orchids in 1862. 
The book is the first in which the pollination process is set 
forth for a whole group of plants. Like so much of Dar¬ 
win’s work, it opened out a new field of research for others. 
Fourteen years later, Darwin published his Effects of Cross 
and Self-Fertilization (1876), which is the complement of 
its predecessor. The earlier book had shown how perfect 
are the means for ensuring cross-fertilization. The later 
discusses why cross-fertilization is important. Darwin had 
been experimenting from 1851 on the lines suggested by 
Knight (p. 506). 



Modern Study oj Pollination 509 

Some extremely interesting discoveries were made by 
Darwin in certain plants which exhibit variations in the dis¬ 
tribution of the sexual parts. Of such species the common 
cowslip is a very good example. Cowslip plants accord 



Fig. 177. The two sexual types of cowslip, Primula •verts Linn., in vertical 
section. Slightly modified from Darwin (1876). The two types were observed 
by the South African naturalist C. H. Persoon (1770-1836) as early as 1794. 
Their interpretation in relation to the visits of insects and the associated process of 
fertilization was provided by Darwin 80 years later. The style leads down to the 
ovary, around which are honey-glands. The proboscis of the insect is inserted 
within the flower to reach this honey. If the insect visit a long-styled form, its 
proboscis will be dusted near the middle with pollen from the anthers. I'his 
pollen will then be in position to adhere to the stigma of a short-styled form, but 
not to the stigma of a long-styled form. On the other hand, if a short-styled 
form be visited, the proboscis will be dusted near its base with pollen. This 
pollen will then be in position to adhere to the stigma of a long-styled form, but 
not to the stigma of a short-styled form. 

to one of two definite types. Their flowers have either along 
style and short stamens or a short style and long stamens 
(Fig. 177). Such species are spoken of as There 

are heterostyled species such as the Purple Loosestrife 
which exhibit three types of individuals. 

Darwin showed that in the cowslip a long-styled in- 



510 Sex 

dividual crossed by another long-styled individual is rela¬ 
tively infertile. To obtain complete fertility the crossing 
of the two forms is needed. This is brought about by the 
adaptation of the different types of flower to the form of 
the visiting insect, so that the pollination of the style of one 
type with the pollen of the other is encouraged. Thus the 
structure of the flower is fully adapted to that of the insect 



Fig. 178. Relative Distribution of Aconite and bumble bee, from Knuth 

(1898). 


Such work created much interest, and several naturalists 
threw themselves into an intensive study of the phenomena 
of pollination. Among these were the brothers Fritz and 
Hermann Mtiller (1829-83). The latter had produced 
in 1873 his classical treatise Fertilization of Flowers by 
Insects and their Reciprocal Adaptation. This was largely 
used by Darwin in his botanical work. Mtiller expressed 
in condensed form the doctrine toward which Knight and 
Darwin had been striving, by his enunciation of the law: 
‘whenever offspring resulting from crossing comes into 
serious conflict with offspring resulting from self-fertiliza¬ 
tion, the former is victorious. Only when there is no 




Modern Study oj Pollination . 511 

struggle for existence does self-fertilization prove satis¬ 
factory for many generations.’ 

Investigations along such lines as those of the Mullers 
were given encyclopaedic shape by Paul Knuth (1854— 
1900) in his Handbook oj Flower Pollination (1898). Not 
only are the actual relationships of insects to many plants 
there demonstrated, but a geographical correspondence 
between many species of plants and insects is tabulated 
(Fig. 178). 

§ 4. Sexual Dimorphism 

In 1851 Charles Darwin published his first independent 
scientific treatise, of the Cirripedia. Vaughan 

Thompson had already made important observations on 
these marine creatures (pp. 488-9). Darwin now discovered 
among the cirripedes or barnacles some remarkable sexual 
relations. The majority of the individuals of this extra¬ 
ordinary group have both male and female organs, that is, 
they are ‘hermaphrodite’. The Cirripedia discharge their 
male sexual elements into the sea and thus fertilize one 
another. This process of cross-fertilization is possible to 
them since, though fixed like plants, they yet, like plants, 
live mostly in groups. The currents of the sea act for 
them as the wind acts for many plants. But while most 
species of Cirripedia are cross-fertilizing, some species 
are capable of self-fertilization. 

The most remarkable sexual phenomena presented by 
the Cirripedia have, however, yet to be considered. Dar¬ 
win showed that in some species there are numbers of 
minute and degenerate males attached to the hermaphro¬ 
dite forms and living a parasitic life upon them. These he 
called ‘complemental males’, since they are not essential to 
the completion of the sexual process. Such complemental 
forms possess, in some cases, certain of the external organs 
of the free-swimming larvae, but their internal organiza- 



itl 

\o\ 



Portion or Wmm/m 

body of Female 

prb'ori oF male embedded 
1 body oF Female 

Fig. 179. Ibla Cumingh', a species of barnacle parasitic on other barnacles. I'he 
male is parasitic on the female. female x i. Lefty male x 40. From Darwin. 

that one form of barnacle described by Darwin is parasitic 
within the body of another species of barnacle. The female 
of this parasitic species exhibits some, but not all, of the 
degenerative changes which have been described in the 
complemental and dwarf males of other species, in addition 
to the degenerative changes common to all Cirripedia (Figs. 
179 and 180). 

Description e^Fic. 180. 

Ay Diagram of hermaphrodite Cirripede. By Hermaphrodite Scalpellum 
Peronii x 2 after Darwin. C, Complemental male of S, Peronii x 20; general 
appearance similar to hermaphrodite form. D, Complemental male of allied 
species S, <vulgare x 30 after Darwin; structure very different from herma¬ 
phrodite form. Ey Female of Alcippe lampas x 10 after Darwin. F, Male of 
lampas x 50 after Darwin, 












514 Sex 

The investigations of Darwin drew attention to the 
extremer manifestations of sexual differentiation which are 
encountered here and there throughout the animal king¬ 
dom. Such ‘sexual dimorphism’ is pften very marked in 
those organisms which exhibit more or less advanced 
stages of parasitism. It is also known, however, in other 
forms as, for instance, in certain oceanic fishes (Fig. i8i), 



Fig, i8i. Sexual dimorphism in Oceanic Angler-fish Edriolycknus Schmidtii, 
Above, female with parasitic male attached. Below, parasitic male which lives 
attached upside down to the female. The creature inhabits middle depths of 
the Western Atlantic, and was first discovered in 1926. 

in rotifers, and in spiders. It is usually the male that is 
dependent on the female. Sexual dimorphism manifests 
itself even among protozoa. 

There is a type of minor sexual dimorphism that was 
much stressed by Darwin. Among many species of birds 
and mammals are forms of ornament or armament, such 
as the clumsy tail of the male peacock or the unwieldy 
antlers of the stag, the beauty and size of which may 
give the possessor advantage over rivals for favour of the 
females. The special development of these organs thus 
leads to more numerous progeny. This process Darwin 




Sexua/ Dimorphism 515 

called ‘sexual selection*. Evidently it can act only within 
the species and can give no advantage over other species. 
In introducing the subject in the Origin of Species (1859), 
Darwin draws attention to what we should now call ‘sex- 
linked characters’ (p. 562). ‘Peculiarities’, he says, ‘often 
appear under domestication in one sex and become 
hereditarily attached to that sex.’ 

§ 5. Alternation of Generations 

A curious aspect of animal life came into view toward 
the middle of the nineteenth century. The Franco- 
German poet Louis Adelaide de Chamisso (1781—1838), 
author of the famous story Peter Schlemihl^ ‘the man who 
sold his shadow’, applied himself with effect, like his 
contemporary Goethe, to biological research. In a work 
On certain animals of the Linnaean class Fermes (1819), he 
described, for the first time, the very peculiar life cycle 
of certain Tunicates, introducing the expression ‘alterna¬ 
tion of generations’. In 1842 the Copenhagen zoologist 
Japetus Steenstrup (1813-97) brought out in Danish his 
work On the Alternation of Generations^ or the Propagation 
and Development of Animals through Alternate Generations. 
He showed that 

‘certain animals, notably jelly-fish and certain parasitic worms, 
habitually produce offspring, which never resemble their parent, 
but which, on the other hand, themselves bring forth progeny, 
which return in form and nature to the grandparents or more 
distant ancestors. Thus the maternal animal does not meet with its 
resemblance in its own brood, but in its descendants of the second, 
third or fourth generation.’ 

Steenstrup wrongly believed that this peculiar process 
‘always takes place with the intervention of a determinate 
number of generations’. 

Steenstrup’s observations drew much attention. Fur¬ 
ther evidence of such alternation of generations was 

l1 2 



5i6 Sex 

rapidly accumulated from a number of different groups in 
the animal kingdom. It was seen to be frequently related 
to an alternation of methods of reproduction. A well- 
known instance is in the common Aphides of roses. These 
creatures are normally female. They produce their young 
without the intervention of any males, that is to say, they 
are parthenogenetic (Greek, ‘pertaining to virgin birth’). 
To this Leeuwenhoek had long ago called attention (p. 166). 
It was now found that at times true males appear among 
the Aphides, and the young are then produced by means 
of a sexual process. Thus there is an alternation of 
parthenogenetic and sexual generations. Alternation of 
generations has since been shown to exist in a number 
of other animal forms. In the plant world, however, the 
process proved to have a particular importance and 
interest (Fig. 190). 

During the early nineteenth century there were many 
random observations and suggestions directed to the 
elucidation of the sexual process of the non-flowering 
plants. Carl NSgeli (l 817—91) made some advance. He 
examined the tiny leaf-like bodies or prothalli that are 
liable to form in moist earth in the neighbourhood of 
ferns. These had been generally regarded as ‘cotyledons’, 
though no clear picture had been formed of the manner 
of reproduction of these plants. On the prothalli Nageli 
observed free swimming spiral objects (1844-6). These 
we now know to be the male elements or spermatozoids of 
the fern (Fig. 183). They could not at the time be thus 
interpreted, for the female elements were unknown until 
Hofmeister revealed them (Fig. 184). 

The scientific career of Wilhelm Hofmeister (i 824—77) 
is unique. Much of the most important biological research 
in England has been done by amateurs. In Germany the 
amateur has taken a much less important place. Yet Hof¬ 
meister, entirely without academic training, not only won 



Alternation oj Generations 517 

for himself the leading position among German botanists, 
but also came to hold an important University chair. The 
consensus of expert opinion places him among the very 
greatest of modern botanists. He was notably distinguished 
for the refinement and beauty of his technical methods, for 
which, it might be thought, training is especially needed. 

Hofmeister left school at fifteen to assist in a shop, but 
used every spare minute for study. He read Schleiden’s 
Outlines oj Scientijic Botany (i 842), which was based on the 
cellular view of the plant. Inspired by this he started at 
nineteen, entirely self-taught, on a series of studies which 
placed him at one bound in the front rank of biologists. 

His first important publication. On the Embryology oj 
Flowering Plants, appeared in 1849 when he was only twenty- 
four. It brought him immediate notice. At that time, despite 
the work of Amici (pp. 506-7), the essential nature of the 
process of fertilization was still little understood. Schleiden 
himself had put forth the perverse notion that the pollen 
tube was the female element, formed the embryo, and was 
fertilized by the ovule which was male (Fig. 176)! Hof¬ 
meister corrected this. His investigation of the process 
of fertilization in the flowering plants contains but one 
important error. He adhered to the ancient Aristotelian 
view of a seminal ‘aura’ (p. 498). Thus he still conceived 
fertilization as a result of ‘diffusion’, thinking ‘the direct 
flow of the contents of the pollen tube into the germinal 
vesicle to be simply impossible’. 

The most important of Hofmeister’s works marked an 
epoch in the history of botany. Its title may be translated 
'Comparative researches on the germination, development, and 
jructijication oj the higher non-flowering plants {Cryptogams)' 
(18 51). Up to Hofmeister’s time, non-flowering plants were 
treated in relation to the known conditions of the flowering 
plants. It was assumed that flowers and seeds are con¬ 
cealed in non-flowering plants, which were therefore called 



518 Sex 

Cryptogams (Greek, ‘hidden marriage’), a term still current. 
Hofmeister, examining the development of these plants, 
revealed a regular and definite alternation of sexual and 
asexual generations in the mosses, ferns, horsetails, and 
liverworts. Throughout these groups, hitherto held to be 



Fig. 182. Spore-bearing apparatus of Polypodium from Swammerdam, a is part 
of the frond of natural size. The black spots mark the collections of spore-cases, 
each covered in with its special roof or ‘indusium’. Below, can be seen a highly 
magnified series of spore-cases or ‘sporangia*. Each sporangium is surrounded 
by a ring-like structure seen on end in b and in its full course in c. The splitting 
or ‘dehiscing* of this ring-like structure causes the dispersal of the spores. The 
condition after dehiscence is shown, somewhat inaccurately, in </. The sporangium 
at e is torn open and the spores within can be seen. 

diverse, he demonstrated an essential unity of develop¬ 
mental plan. In them all he showed that a sexless genera¬ 
tion, which propagates itself by means of spores, alternates 
with another generation, which exhibits the phenomenon 
of sexual union of motile spermatozoids with ova con¬ 
tained in characteristically shaped receptacles known as 
Archegonia (Figs. 183—5). 

Hofmeister was able to give a consecutive account of 




Alternation oj Generations 519 

the life-history of the fern. He traced the spore through 
its development into the little green prothallus or true 
sexual generation. He saw how the prothallus develops 
spermatozoids and archegonia; and how the ovum in the 
latter, under the influence of the spermatozoid, gives rise 
to the more conspicuous and asexual form that we know 
as a ‘fern’. He went on to show that the mode of produc- 



Fig. 183. A series of male cells or ‘spermatozoids* exhibiting essential simi¬ 
larity throughout a series of lower and higher plant forms, a and b from club 
moss, c from moss, dirom liverwort. All these have two flagella and the last is of 
spiral form, e, from a fern, is spiral and has numerous short flagella, or ‘cilia*, 
gathered at one end. f, from a Cycad, is top-shaped with cilia arranged along 
a spiral, and is double. 

tion of the embryo in the pines and their allies is, in certain 
senses, intermediate between that of flowering plants and 
that of ferns and other higher cryptogams. 

Hofmeister extended his investigations into the ovule 
of flowering plants. After tracing the elaborate process of 
its development, he made the suggestion that its earlier 
cell-divisions correspond to the ‘prothallus’ of ferns 
(p. 520), which in flowering plants never leaves the asexual 
generation, is inconspicuous and reduced to a few cells 
(1851-62, Fig. 190). 

It had already been recognized that the conifers have 
affinities with the flowering plants. The old distinction 
between the flowering and flowerless plants had now to be 



520 Sex 

abandoned. What this has meant for botany may be 
gauged by comparing the classification of A. P. de 
Candolle (p. 195) with a modern classification of plants 
(see below). The latter is as much based upon reproduc¬ 
tion as is the classification of animals foreshadowed by 
Aristotle (p, 42), 

Hofmeister spent little space in discussing the wider im¬ 
plications of his valuable contributions to science. The 
formal recognition of the alternating character of the 
generations in all plants was thus left to others. The con¬ 
ception was given wide circulation by the influential text¬ 
book of Sachs, especially from its fourth edition (1874) 
onward. It was adopted and developed by Strasburger, 

On the basis of alternation of generations, we may, 
with Strasburger, set forth the great groups of plants in 
a series (p, 199), thus: 

(a) Thallophyta. Relations between asexual and sexual 
generations in most cases irregular. Sexual reproduction 
by motile spermatozoids. Ovum in archegonium. Water 
the medium of fertilization, 

(b) Mosses, Asexual generation alternates regularly 
with sexual. Sexual the more conspicuous. Asexual 
generation dependent on sexual. Sexual reproduction by 
motile spermatozoids. Ovum in archegonium. Water the 
medium of fertilization, 

(c) Ferns. Asexual generation alternates with sexual 
(‘prothallus’). Asexual more conspicuous and may 
increase vegetatively to an enormous degree. Sexual 
generation has independent life. Sexual reproduction by 
motile spermatozoids. Ovum in archegonium. Water 
the medium of fertilization, 

(d) Conifers, Asexual generation enormously over¬ 
shadows sexual. Sexual generation entirely dependent on 
asexual. Sexual reproduction by non-motile generative cell. 
Ovum in archegonium. Air the medium of fertilization. 



Alternation oj Generations 521 

(e) Flowering Plants. Asexual generation completely 
conceals sexual. Sexual generation may be long deferred 
when reproduction becomes continuously vegetative. 
Sexual reproduction by non-motile generative cell. Ovum 



To illustrate similarity of female reproductive apparatus in mosses, liverworts, 

and ferns. 

Fig. 184. A-D, successive stages in formation of archegonium of a moss. From 
Hofmeister, 1851. 

Fig. 185. A-C, Archegonium of a liverwort. Ay young form. B, mature with 
neck open. C, fertilized ovum dividing. archegonium of a fern, i), 

young form. £, mature. From Strasburger, 1869-71. 

not in archegonium. Air—sometimes with insect aid 
—^the medium of fertilization. 

This striking series of sexual relationships is susceptible 
of exposition on an evolutionary basis. Such has been 
specially the work of F. O. Bower (i 855- ) from 1890 


522. Sex 

onwards. He supposed that plants with archegonia 
originated from algae, as is borne out by their mode of 
reproduction. Gradually spreading to drier and yet drier 
regions—invading the land from the sea—they developed 
a method of reproduction that depended less and less upon 
water as the carrier of their sexual elements. Thus the 
asexual generation has gradually increased in importance, 
finally, in the higher plants, completely concealing the 
sexual. Bower’s views of the origin of the land flora have 
proved generally acceptable. 

§6. Ear/y Observations on Cellular Phenomena of Sexual Union 

Despite the emphasis laid on spermatozoa in contro¬ 
versial writings, their essential role in fertilization was still 
unproven when the nineteenth century dawned. Early in 
the century, filtered semen was shown to be infertile, and 
the semen of infertile males was shown to be devoid of 
spermatozoa. Thus upon the spermatozoa was fastened 
the power of awakening the development of the ovum. In 
1838 Schwann interpreted the ovum as a cell, a conception 
more fully expounded later by Gegenbaur (p. 338). In 
1841 Kolliker (p. 339) succeeded in tracing the develop¬ 
ment of spermatozoa. He showed that they, too, are of 
cellular origin and nature. 

At this time good progress in the knowledge of fer¬ 
tilization was being made from the botanical side. The 
general situation in 1855 was thus expressed by the 
German amateur Nathaniel Pringsheim (1823—94): 

‘The existence of sexuality in plants is now admitted. In flowering 
plants, the necessity o