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LONDON 


PRINTED  BY  SAMUEL  BENTLEY, 

Bangor  House,  Shoe  Lane. 


A 


GENERAL  OUTLINE 


THE  ANIMAL  KINGDOM, 

AND 

MANUAL  OF  COMPARATIVE  ANATOMY. 


BY  THOMAS  RYMER  JONES,  F.Z.S. 


PROFESSOR  OF  COMPARATIVE  ANATOMY  IN  KING’S  COLLEGE,  LONDON; 
FULLERTAN  PROFESSOR  OF  PHYSIOLOGY  TO  THE  ROYAL  INSTITUTION  OF  GREAT  BRITAIN, 

&C.  &C. 


ILLUSTRATED  BY 

THREE  HUNDRED  AND  THIRTY-SIX  ENGRAVINGS. 


LONDON: 

JOHN  VAN  VOORST,  1,  PATERNOSTER  ROW; 


M.DCCC.XLT. 


Digitized  by  the  Internet  Archive 
in  2018  with  funding  from 
University  of  Toronto 


https://archive.org/details/generaloutlineofOOjone 


To  RICHARD  OWEN,  Esq.,  F.R.S. 

&c.  ike.  ike. 


THE  FOLLOWING  PAGES  ARE  INSCRIBED 


BY  HIS  SINCERE  FRIEND, 


THE  AUTHOR. 


VIII 


PREFACE. 


analogy.  Discussions  of  this  kind  have  been  carefully 
avoided  in  the  following  pages :  to  collect  from  every 
available  source  the  ascertained  facts  connected  with 
anatomical  structure,  and  to  arrange  the  grand  divisions 
of  the  animal  world  in  conformity  with  progressive  de- 
velopement  as  we  advance  from  humbler  to  more  com¬ 
plex  types  of  organization,  has  been  the  chief  aim  of  the 
Author;  and,  if  he  has  at  all  succeeded  in  divesting  so 
important  a  subject  of  those  technicalities  which  not  un- 
frequently  impede  the  progress  of  the  general  reader, 
his  labour  has  not  been  thrown  away. 

To  the  Physiologist  little  apology  is  necessary  for  the 
production  of  a  work  intended  to  exhibit  at  one  view  the 
leading  facts  of  Comparative  Anatomy.  In  this  country, 
unfortunately,  so  extended  a  view  of  Nature  is  considered 
as  being  by  no  means  essential  to  a  correct  intelligence 
of  the  laws  of  animal  life,  and  as  a  branch  of  professional 
education  has  been  hitherto  completely  neglected.  Our 
illustrious  countryman  John  Hunter  entertained  a  dif- 
ferent  opinion.  May  the  fire  which  he  first  kindled 
amongst  us,  and  which  has  since  his  time  been  kept  alive 
by  the  fostering  care  of  that  College,  the  depository  of 
his  invaluable  works,  soon  burst  forth,  and  irradiate  the 
realms  of  science  as  brightly  as  the  great  founder  of 
Comparative  Physiology  foresaw  that  it  might  ! 


PHYSIOLOGICAL  INDEX 


NERVOUS  SYSTEM. 

Page  Sec. 

General  classification  of  Animals,  in  accordance  with  the  condition  of  .  6 —  8 


Acrita  ....... 

• 

6—  8 

Nematoneura  ....... 

* 

99—132 

Anatomy  of  the  nervous  system  in 

Linguatula  taenioides  .... 

• 

101—135 

Ascaris  lumbricoides  ..... 

• 

103—140 

Notommata  clavulata  .... 

• 

124—163 

Actheres  percarum  ..... 

• 

132—173 

A  stems  ...... 

• 

158—199 

Echinus  ...... 

# 

171—211 

Holothuria  ..... 

# 

178—219 

Siponculus  ...... 

• 

183—225 

Homogangliata  ...... 

184—227 

Anatomy  of  the  nervous  system  in 

Hirudo  medicinalis  ..... 

• 

198—240 

Myriapoda  ..... 

• 

229—273 

Insecta  ...... 

• 

270—312 

Changes  that  take  place  in  the  condition  of  the  nervous 

system 

during  the  metamorphosis  of  Insects 

• 

303—349 

Crustacea  ...... 

• 

336—372 

Motor  and  Sensitive  tracts  in  the  nervous  centres  of  Homogangliata 

340—375 

Heterogangliata  ..... 

351—387 

Anatomy  of  the  nervous  system  of 

Cirrhopoda  ..... 

• 

355—391 

Brachiopoda  ..... 

• 

367—400 

Tunicata  ...... 

• 

372—408 

Conchifera  ..... 

• 

391—425 

Gasteropoda  ...... 

• 

415—452 

Pteropoda  ..... 

• 

427—468 

Cephalopoda  ...... 

• 

457—499 

Nautilus  Pompilius  .... 

• 

457—500 

Vertebrata  .  ..... 

• 

484—520 

Anatomy  of  the  nervous  system  of 

Fishes  ...... 

521—557 

Reptiles  ...... 

• 

576—633 

Birds  ...... 

• 

607—675 

Mammalia  ...... 

• 

691—796 

ORGANS  OF  THE  SENSES. 

Sense  of  Touch 

in  Polyps  .  .  .  .  .  . 

• 

22—  28 

in  Holothuria  ...... 

• 

178—219 

in  Siponculus  ...... 

• 

180—181 

in  Leech  ...... 

199—240 

Antennae  of  Myriapoda  . 

• 

225—267 

Sense  of  touch  in  Insects  .... 

274—317 

111  W  1  H  O  IU.U  •  •  »  • 

• 

Tentacula  of  Gasteropoda  .... 

• 

402—439 

- Pteropoda  . 

• 

425—466 

X 


PHYSIOLOGICAL  INDEX 


Tactile  organs  of  Cephalopoda 
Sense  of  touch  in  Reptiles 

- in  Birds 

- in  Mammalia 

Sense  of  Taste 
in  Insects 
in  Crustacea 
in  Cephalopods 
in  Fishes 
in  Reptiles 
in  Birds 
in  Mammals 

Sense  of  Smell 
in  Insects 
in  Crustacea 
in  Nautilus  Pompilius 
in  Fishes 
in  Reptiles 
in  Birds 
in  Mammals 


Sense  of  Vision. 

Red  specks  observable  in  Acrita 

• - in  Rotifera 

- in  Lamproglena  pulchella 

Eyes  of  Leech 
Simple  ocelli  of  Insects 
Compound  eyes  of  Insects 
Eyes  of  Crustacea 

- - the  Scallop  ( Pecten )  . 

- Snail 

- other  Gasteropoda 

- Nautilus  Pompilius 

- Cuttle-fish 

- - -  Fishes 

- Reptiles  .... 

- —  Birds 

- Mammalia  .... 

Sense  of  Hearing 

in  Insects  .... 

in  Crustacea  .... 

in  Cuttle-fishes  .... 

in  Fishes  ..... 

in  Reptiles  .... 

in  Birds  ..... 
in  Mammalia  .... 


Page  Sec. 
460—501 
584—645 
608—676 
703—825 


275—318 

343—378 

462—503 

510—544 

555—611 

608—677 

673—752 


275—319 

343—378 

463-504 

521—558 

578—633 

608—678 

692—800 


64—  92 
124—162 
134—177 
199—241 

276— 321 

277— 321 
343—379 
391—426 
402—439 
416—452 
464—506 
466—507 
522—560 
578—634 
609—679 
695—805 


275—319 
344—380 
470—512 
526—568 
580—638 
614  —  684 
699—819 


LOCOMOTIVE  ORGANS. 

Condition  of  muscular  system  in  Acrita 

- - - Ccelelmintha 

- Bryozoa 

- Rotifera 

- Epizoa 

Suckers  of  Star-fishes  .... 

Suckers  of  Echini  .... 

Spines  of  Echini  ..... 
Suckers  of  Holothuria  .... 
Muscular  system  of  Siponculus 
Locomotive  organs  of  the  Leech 

■ - Earthworm 

Setae  of  Dorsibranchiate  Annelidans 


6—  8 
102—139 
111—147 
121—159 
132—172 
149—190 
163—204 
163—205 
173—214 
180—221 
191—234 
201—224 
213—258 


PHYSIOLOGICAL 

INDEX. 

XI 

Page  Sec. 

FeetofJulus  .... 

,  , 

225—268 

- -  Scolopendra 

•  •  • 

.  228—272 

Legs  of  Insects  .... 

•  • 

240—282 

Mechanical  structure  of  the  feet  of  Insects 

•  •  • 

.  241—283 

Wings  of  Insects  .... 

•  « 

246—287 

Muscular  system  of  Insects 

•  •  • 

.  250—292 

Spinning  organs  of  Arachnidans 

316—363 

Locomotive  organs  of  Crustacea 

•  •  • 

.  319—364 

Muscles  of  Cirrhopoda 

• 

356—392 

Arms  of  Brachiopoda 

•  •  • 

.  363—398 

Mantle  of  Ascidia  .... 

•  • 

369—402 

Foot  of  Conchifera  . 

•  •  « 

.  381—415 

Byssus  of  Mussel  and  Pinna 

•  • 

383—417 

Apparatus  for  opening  and  closing  the  shells  of  Conchifera 

.  384—418 

Muscular  system  of  Snail 

•  • 

395—430 

Locomotive  organs  of  Pteropoda 

•  •  • 

.  424—465 

Tentacula  and  suckers  of  Cuttle-fishes 

.  • 

431—474 

Sails  (so  called)  of  Argonaut 

.  435—477 

Arms  and  float  of  Nautilus  Pompilius 

•  • 

437—479 

Locomotive  apparatus  of  Argonaut 

• 

.  443—485 

Fins  and  muscular  system  of  Fishes 

•  • 

500—537 

Limbs  of  Reptiles 

•  •  • 

.  542—590 

Muscular  system  of  Reptiles 

•  • 

555—610 

Locomotion  of  Birds 

•  •  « 

.  591—657 

Muscular  system  of  Mammalia 

•  • 

660—740 

SKELETONS  OF  INVERTEBRATA. 

Horny  and  calcareous  framework  of  Sponges 
Shells  of  Infusoria  .... 

Polyparies  of  Polyps  ...... 

Fungidas  ....  .  . 

Cortical  Polyps  ..... 

Tubiporidae  ..... 

Sertularidae  .  ..... 

Internal  plates  of  V elella  and  Porpita 

Cells  of  Bryozoa  ...... 

Shells  of  Rotifera  ..... 

Skeletons  of  Echinodermata. 

Crinoidag  ...... 

Asteridae  ...... 

Echinidae  ...... 

Skeletons  of  Homogangliata  ..... 

Myriapoda  ...... 

Insecta  ...... 

Arachnida  ..... 

Crustacea  ...... 

Structure  and  growth  of  the  shells  of  Mollusca  : 

Cirrhopoda  ...... 

Brachiopoda  ..... 

Tunicata  ...... 

Conchifera  ..... 

Gasteropoda  ...... 

Cephalopoda  ..... 

F'irst  appearance  of  an  internal  skeleton  ( Endo-skeleton ) 

SKELETONS  OF  VERTEBRAE  A. 

a.  Cuticular  skeleton,  or  Exo-skeleton. 

Dermo-skeleton  of  Fishes 

Growth  of  hair  and  other  epidermic  appendages 

Ilorns  of  the  Deer  ..... 


13—  16 
53—  74 
30—  42 
18—  21 
29—  40 
34—  48 
45—  63 
69—  97 
110—146 
118—155 

136—180 

147—189 

160—202 

184—228 

224—266 

238—279 

306—351 

319—364 

352—389 

363—398 

369—402 

384—419 

418—458 

440—482 

439—481 


506—541 

687— 788 

688— 790 


Xll 


PHYSIOLOGICAL  INDEX. 


b.  Osseous  skeleton,  or  Endo- skeleton  :  Page  Sec. 

General  view  of  the  skeleton  of  Vertebrata  ....  477 — 518 

Osteology  of  Fishes  ......  489 — 522 

- Reptiles  .......  544 — 593 

- - - Birds  ......  592 — 658 

- - -  Mammalia  .......  633 — 710 


NUTRITIVE 

Digestive  Organs  of  Aciiita. 

Sponges  .... 
Fungiae  .... 
Alcyonium  .... 
Hydra  viridis 
Cortical  Polyps 
Tubipora  musica 

Sertularidae  .... 
Actinia  .  .  . 

Polygastrica 
Acalephie 

Hydatid  .... 

Trichina 

Taenia  .... 

Distoma 

Planaria  .... 

Diplozoon  .  .  . 

Echinorynchus 

Digestive  Organs  of  Nematoneura. 

Linguatula  taenioides 
Ascaris  lumbricoides 
Bryozoa 

Rotifera  .... 

Epizoa. 

Actheres  percarum 
Lamproglena  pulchella 

Echinodermata. 

Asterias 

Echinus  .... 

Holothuria 

Siponculus  .... 

Digestive  Organs  of  Homog angliata. 
Annelida. 

Leech  .... 

Earthworm 

Dorsibranchiata  . 

Tubicola  .... 

Myriapoda. 

Julus  .... 

Scolopendra 

Insecta. 

Mouths  of  Insects 
Alimentary  canal  of  Insects 
- of  Arachnida 


SYSTEM. 


15—  17 
18—  21 
27—  37 
23—  29 

34—  46 

35—  48 
45—  64 
40—  55 
56—  79 
71—  99 
81—110 

83— 114 

84— 115 
87—118 
89—119 
92—122 
95—126 


100—134 
.  103—141 

108—145 
.  122—160 


131—171 

134—177 


151  —  192 
.  166—207 

174—215 
.  180—222 


192—235 
.  203—246 
215—260 
.  221—265 


226—269 

229—274 


254—295 
.  260—301 
310—356 

.  328—367 


Crustacea 


PHYSIOLOGICAL  INDEX. 


Xlll 


Digestive  System  of  Heterogangliata. 

Cirrhopoda  ..... 

Page  Sec. 
356—393 

Brachiopoda  ..... 

. 

.  365—399 

Tunicata  ..... 

•  • 

370 — 405 

Conchifera  ...... 

• 

.  378—413 

Gasteropoda. 

Snail  ..... 

•  . 

395—430 

Mouths  of  Gasteropoda  .... 

• 

.  410—445 

Alimentary  canal,  &c. 

. 

413—448 

Pteropoda  ...... 

• 

.  424—466 

Cephalopoda  ..... 

• 

445—487 

Digestive  System  of  Vertebrata. 

Fishes. 

Teeth  of  .  .  , 

. 

.  510—544 

Digestive  apparatus  of 

• 

515—545 

R EPTILES. 

Teeth  of  ..... 

.  556—61 1 

Alimentary  system  of 

•  « 

561—619 

Birds  ...... 

• 

597—664 

Mammalia. 

Teeth  of  ..... 

•  • 

663—744 

Alimentary  apparatus  .... 

• 

.  677—759 

RESPIRATORY  AND  CIRCULATORY 
Rotifera  ...... 

SYSTEMS. 

.  125—164 

Asterias  ..... 

155—195 

Echinus  ...... 

• 

.  170—209 

Holothuria  .  .  ... 

175—216 

Siponculus  ...... 

• 

.  181—223 

Leech  ...... 

195—237 

Earthworm  ...... 

. 

.  204—247 

Dorsibranchiate  Annelidans 

217—262 

Insects  ...... 

# 

.  264—306 

Arachnidans  ..... 

311—358 

Crustacea  ...... 

.  329—368 

Cirrhopoda  ..... 

357- — 394 

Brachiopoda  ..... 

• 

.  366—400 

Tunicata  ..... 

370—403 

Oyster  ...... 

• 

.  378—412 

Snail  ...... 

397—433 

Gasteropoda  ..... 

• 

.  403 — 440 

Pteropoda  ..... 

427—467 

Cephalopoda  ...... 

• 

.  451—494 

Fishes  ...... 

517  — 553 

Reptiles  ...... 

• 

.  564—626 

Birds  ...... 

602—671 

Mammalia  ...... 

• 

.  682—778 

GENERATIVE  SYSTEM. 

Fiissparous  Generation 

in  Polygastrica  ..... 

. 

59—  85 

in  Annelida  ...... 

• 

.  211—254 

Gemmiparous  Generation 

in  Sponges  ..... 

. 

16—  19 

in  Fungia  ...... 

• 

19—  23 

in  Ilydra  viridis  .  ... 

• 

25—  33 

XIV 


PHYSIOLOGICAL  INDEX. 


Generative  System  in 

Tubipora  ..... 

Acalephae  .... 

Sterelmintha  .... 

Coelelmintha. 

Ascaris  lumbricoides 
Hermaphrodism  of  Syngamus  trachealis 
Rotifera  ..... 

Epizoa  ...... 

Asterias  ..... 

Echinus  ..... 

Holothuria  ..... 

Siponculus  ..... 

Leech  ..... 

Earthworm  ..... 

Nais 

Dorsibranchiate  Annelidans 

Myriapoda  ..... 

Insects  ...... 

Arachnidans  .... 

Crustacea  ..... 

Cirrhopoda  .  . 

Brachiopoda  ..... 

Tunicata  ..... 

Conchifera  ..... 

Snail  ..... 

Gasteropoda  ..... 

Pteropoda  ..... 

Cephalopoda  ..... 

Fishes  ..... 

Reptiles  ...... 

Birds  ..... 

Mammalia  ..... 

LYMPHATIC  SYSTEM. 

In  Fishes  ..... 

In  Reptiles  ..... 
In  Birds  ..... 

In  Mammalia  ..... 


In  Fishes 
In  Reptiles 
In  Birds  . 
In  Mammals 


URINARY  SYSTEM. 


DEVELOPEMENT  OF  THE  EMBRYO. 

In  Adheres  percarum  ..... 
Ova  of  Earthworm  ..... 
Metamorphoses  of  Myriapoda  .... 

- Insects  .... 

- Crustacea  .... 

- -  Cirrhopoda  . 

Embryo  of  Cuttle-fish  ..... 
Metamorphosis  of  the  Tadpole 
Changes  in  vascular  system  of  Tadpole 
Developement  of  the  chick  in  ovo  . 

Anatomy  of  the  ovum  of  Ornithorynchus  paradoxus 
Anatomy  of  marsupial  ovum 
Developement  of  the  placental  fetus 


Page  Sec. 

36—  49 

78—107 

82—111 

105— 142 

106— 144 
127—166 
133—174 
158—198 
172—212 
178—218 
183—226 
200—242 
207—249 
209—252 
219—263 
230—275 
279—323 
315—361 
344—381 
357—395 
367—401 
403—407 
393—427 
399—435 
417—453 
428—470 
472—513 
530—576 
585—648 
616—687 
706—833 


517—552 

563—624 

602—670 

682—776 


520—555 

584—646 

615—685 

704—831 


133—175 

209—251 

227—271 

288—336 

348—386 

361—397 

475—516 

539—589 

572—630 

620—697 

707—834 

714—839 

728—858 


GENERAL  INDEX 


CLASSIFICATION  OF  THE  ANIMAL  KINGDOM. 


ACRITA. 


Page 


Sponges 

Polyps 

Polygastrica 

Acalephae 

Sterelmintha 


12 

17 

50 

64 

79 


NEMATONEURA 


99 


Coelelmintha 

Bryozoa 

Rotifera 

Epizoa 

Echinoclermata 


99 

107 

117 

128 

135 


HOMOGANGLIATA 


184 


Annelida 

Myriapoda 

Insecta 

Arachnida 

Crustacea 


188 

224 

231 

306 

319 


HETEROGANGLIATA 


.  351 


Cirrhopoda 

Brachiopoda 

Tunicata 

Conchifera 

Gasteropoda 

Pteropoda 

Cephalopoda 


352 

362 

368 

375 

394 

423 

430 


VERTEBRATA 


476 


Fishes 

Reptiles 

Birds 

Mammalia 


488 

537 

591 

632 


A  GENERAL  OUTLINE 


OF 


THE  ANIMAL  KINGDOM. 


CHAPTER  I. 

ON  CLASSIFICATION. 

(1).  From  the  earliest  periods  to  the  present  time,  the  great 
desideratum  in  Zoology  has  been  the  establishment  of  some  fun¬ 
damental  system  of  arrangement,  which,  being  universal  in  its 
application,  should  distribute  the  countless  beings  surrounding  us 
into  natural  groups  or  divisions,  such  as  might  be  subdivided 
into  classes,  orders,  and  genera,  by  obvious  differences  of  structure 
in  the  tribes  composing  them,  and  thus  enable  the  Zoologist  at 
once  to  indicate  the  position  which  any  unknown  animal  ought 
to  occupy  in  the  scale  of  existence,  and  its  relations  with  other 
creatures. 

(2.)  Aristotle,  the  father  of  our  science,  was  the  first  who  at¬ 
tempted  a  scientific  division  of  the  animal  world  ;  *  the  outlines 
of  his  system  were  rude  in  proportion  to  the  necessarily  limited 
knowledge  at  his  disposal,  although  his  efforts  were  gigantic, 
and  still  excite  our  warmest  admiration.  This  acute  observer  ad¬ 
mitted  but  two  great  sections,  in  one  or  other  of  which  all  known 
beings  Avere  included,  the  highest  comprehending  creatures  pos¬ 
sessed  of  blood,  ( i .  e.  red  blood,)  corresponding  to  the  vertebrata 
of  modern  authors  ;  the  lowest  embracing  animals  which  in  his  view 
were  exsangueous,  or  provided  with  a  colourless  fluid  instead  of 
blood,  and  corresponding  to  the  invertebrata  of  more  recent 
Zoologists. 

(3.)  Linnseus,  like  Aristotle,  selected  the  circulatory  system  as 


*  I ! istoria  Animalium. 


ON  CLASSIFICATION. 


9 

/v 

tlie  foundation  of  liis  arrangement,*  dividing  the  animal  creation 
into  three  great  sections,  characterized  as  follows : 

I.  Animals  possessed  of  warm  red  blood,  and  provided  with  a 
heart  containing  four  compartments,  viz.  two  auricles  and  two 
ventricles.  Such  are  the  mammalia  and  birds. 

II.  Animals  with  red  cold  blood,  their  heart  consisting  of  but 
one  auricle  and  one  ventricle,  as  he  believed  to  be  the  case  in 
reptiles  and  Jishes. 

III.  Animals  possessed  of  cold  white  sanies  instead  of  blood, 
having  a  heart  consisting  of  a  single  cavity  which  he  designates  an 
auricle  :  under  this  head  he  includes  insects  and  all  other  inverte¬ 
brate  animals,  to  which  latter  he  gives  the  general  name  of  vermes , 
worms. 

W e  shall  not  in  this  place  comment  upon  the  want  of  anatomi¬ 
cal  knowledge  conspicuous  in  the  above  definitions,  or  the  insuffi¬ 
cient  data  afforded  by  them  for  the  purposes  of  Zoology.  The  appa¬ 
ratus  of  circulation,  being  a  system  of  secondary  importance  in  the 
animal  economy,  was  soon  found  to  be  too  variable  in  its  arrange¬ 
ment  to  warrant  its  being  made  the  basis  of  zoological  classification, 
and  a  more  permanent  criterion  was  eagerly  sought  after  to  supply 
its  place. 

(4.)  Among  the  most  earnest  in  this  search  was  our  distinguished 
countryman  John  Hunter,  who,  not  satisfied  with  the  results  ob¬ 
tained  from  the  adoption  of  any  one  system,  seems  to  have  tried  all 
the  more  vital  organs,  tabulating  the  different  groups  of  animals  in 
accordance  with  the  structure  of  their  apparatus  of  digestion,  of 
their  hearts,  of  their  organs  of  respiration,  of  their  generative 
organs,  and  of  their  nervous  system,  balancing  the  relative  im¬ 
portance  of  each,  and  sketching  out  with  a  master  hand  the 
outlines  of  that  arrangement  since  adopted  as  the  most  natural 
and  satisfactory. 

The  result  of  the  labours  of  this  illustrious  man  cannot  but 
be  of  deep  interest  to  the  zoological  student,  and  accordingly  an 
epitome  of  his  ideas  upon  the  present  subject  is  here  concisely 
given. 

The  apparatus  of  digestion  appears  to  be  among  the  least 
efficient  for  the  purpose  of  a  natural  division  ;  as  the  separation 

*  Systema  Naturae  Vindobonae,  1767.  Thirteenth  Edition. 

t  Descriptive  and  illustrated  Catalogue  of  the  Physiological  series  of  Comparative 
Anatomy,  contained  in  the  Museum  of  the  Royal  College  of  Surgeons  in  London,  — 
Yol.  111.  Part  I.—  1835. 


OK  CLASSIFICATION. 


of  animals  into  sucli  as  have  a  simple  digestive  cavity,  receiving 
and  expelling  its  contents  by  the  same  orifice,  and  such  as  have 
an  aperture  for  the  expulsion  of  the  contents  of  the  alimentary 
canal  distinct  from  that  by  which  food  is  taken  into  the  stomach, 
is  by  no  means  of  practical  utility,  although  this  circumstance,  as 
we  shall  afterwards  see,  has  been  much  insisted  upon. 

Hunter’s  arrangement  of  the  animal  kingdom  in  conformity 
with  the  structure  of  the  heart,  was  a  great  improvement  upon 
that  of  Linnseus,  founded  upon  the  same  basis.  He  divides  in 
this  manner  all  animals  into  five  groups. 

I.  Creatures  whose  hearts  are  divided  into  four  cavities — Mam¬ 
malia  and  Birds. 

II.  Those  having  a  heart  consisting  of  three  cavities  —  Rep¬ 
tiles  and  Amphibia .* 

III.  Animals  possessing  a  heart  with  two  cavities —  Fishes 
and  most  Mollusca. 

IV.  Animals  whose  heart  consists  of  a  single  cavity  —  Articu¬ 
lated  Anivials. 

V.  Creatures  in  which  the  functions  both  of  stomach  and  heart 
are  performed  by  the  same  organ,  as  in  Med  usee. 

We  shall  pass  over  Hunter’s  sketches  of  arrangements  founded 
on  the  respiratory  and  reproductive  organs,  as  offering  little  satis¬ 
factory  ;  but  the  researches  of  this  profound  physiologist  upon  the 
employment  of  the  nervous  system  for  the  purpose  of  zoological 
distribution,  did  much  to  approximate  a  more  natural  method  of 
classification,  afterwards  carried  out  with  important  results. 

(5.)  The  appearance  of  the  u  Animal  Kingdom  distributed  in 
accordance  with  its  organization”  of  Cuvier,  formed  a  new  and  im¬ 
portant  era  in  Zoology.  In  this  we  find  all  creatures  arranged  in 
four  great  divisions,  Vertebrata,  Mollusca,  A rticulata,  and 
Radiata.  These  divisions,  with  the  exception  of  the  first,  are 
named  from  the  external  appearance  of  the  creatures  composing 
them,  nevertheless  the  three  first  are  defined  by  characters  exclu¬ 
sively  drawn  from  their  internal  organization,  the  arrangement  of 
the  nervous  system  being  essentially  the  primary  character  of  dis¬ 
tinction,  and  have  been  found  to  be  strictly  natural  ;  whilst  the 
last  division,  characterized  by  the  appellation  of  Radiata,  in  the 
formation  of  which  the  structure  of  the  nervous  system  has 

*  For  the  important  discovery  that  the  heart  of  the  Amphibia  is  divided  into  three 
cavities,  instead  of  being  composed  of  a  single  auricle  and  ventricle,  we  are  indebted  to 
Professor  Owen.  Vide  Zool.  Trans.  Vol.  I. 


4 


ON  CLASSIFICATION. 


been  allowed  to  give  place  in  importance  to  other  characters  of 
secondary  weight,  obviously  embraces  creatures  of  very  dissimilar 
and  incongruous  formation. 

The  Yertebrata  are  distinguished  by  the  possession  of  an 
internal  nervous  centre  or  axis,  composed  of  the  brain  and  spinal 
cord,  which  is  enclosed  in  an  osseous  or  cartilaginous  case,  and  placed 
in  the  median  plane  of  the  body,  giving  off  symmetrical  nerves, 
which  are  distributed  to  all  parts  of  the  system.  This  general 
definition  indicates  a  large  division  of  the  animal  world,  which, 
by  secondary  characters  drawn  from  the  structure  of  their  organs 
of  respiration  and  circulation,  is  separable  into  mammals,  birds, 
reptiles,  amphibia,  and  fishes. 

The  Mollusca  have  a  nervous  system  constructed  upon  a  very 
different  type,  and  do  not  possess  any  vertebral  column  or  articu¬ 
lated  skeleton.  The  nervous  centres  consist  of  several  detached 
masses  placed  in  different  parts  of  the  body,  without  regularity 
of  distribution  or  symmetrical  arrangement  ;  and  the  entire  group 
is  obviously  natural,  although  Cuvier  has  ranged  in  it  some  creatures 
which,  in  the  structure  of  their  nervous  system,  differ  essentially 
from  those  comprised  in  his  own  definition. 

The  class  of  Articulated  Animals  is  likewise  well  cha¬ 
racterized  by  the  nervous  system,  which,  in  all  the  members  of  it, 
is  composed  of  a  double  series  of  ganglia  or  masses  of  neurine, 
arranged  in  two  parallel  lines  along  the  abdominal  surface  of  the 
body,  united  by  communicating  cords,  and  from  which  nerves  are 
given  off  to  the  different  segments  of  which  the  body  consists. 

But  the  fourth  division  of  Cuvier,  namely,  that  of  Zoophytes 
or  Radiated  Animals,  is  confessedly  made  up  of  the  most  hete¬ 
rogeneous  materials,  comprising  animals  differing  in  too  many 
important  points  to  admit  of  their  being  associated  in  the  same 
group  ;  and  the  efforts  of  subsequent  Zoologists  have  been  mainly 
directed  to  the  establishment  of  something  like  order  in  this 
chaotic  assemblage. 

(6.)  The  evident  relation  which  the  perfection  of  the  nervous 
system  bears  to  that  of  animal  structure,  and  the  success  of  Cuvier 
in  selecting  this  as  the  great  point  of  distinction  in  the  establish¬ 
ment  of  the  higher  divisions  of  the  animal  kingdom,  necessarily 
led  succeeding  naturalists  still  to  have  recourse  to  this  important 
part  of  the  economy  in  making  a  further  subdivision  of  the 
Radiata  of  Cuvier.  In  some  of  the  radiated  forms,  indeed, 
nervous  filaments  are  distinctly  visible,  and  such  are  among  the 


ON  CLASSIFICATION. 


D 


more  perfectly  organized  of  the  group ;  these,  therefore,  have 
been  classed  by  themselves,  and  designated  by  Mr.  Owen  the 
Nematoneueose*  division  of  the  animal  world;  while  those 
which  are  apparently  without  the  least  trace  of  distinct  nervous 
matter,  have  been  formed  by  Mr.  M‘Leay  into  a  group  by  them¬ 
selves,  to  which  he  has  given  the  denomination  of  Acrita.*[* 

(7.)  There  can  be  no  doubt  that  the  nervous  matter  must  be 
regarded  as  the  very  essence  or  being  of  all  creatures,  with  which 
their  sensations,  volition,  and  capability  of  action  are  inseparably 
connected ;  and  such  being  the  case  it  is  a  legitimate  inference, 
that  the  capacities  and  powers  of  the  several  tribes  are  in  im¬ 
mediate  relation  with  the  developement  and  perfection  of  this 
supreme  part  of  their  organization,  and  their  entire  structure  must 
be  in  accordance  with  that  of  the  nervous  apparatus  which  they 
possess.  The  nature  of  the  limbs  and  external  members,  the 
existence  or  nonexistence  of  certain  senses,  the  capability  of  loco¬ 
motion,  and  the  means  of  procuring  food,  must  be  in  strict  cor¬ 
respondence  with  the  powers  centred  in  the  nervous  masses  of 
the  body,  or  in  that  arrangement  of  nervous  particles  which 
represents  or  replaces  them. 

Granting  the  accuracy  of  the  above  view,  it  is  obvious,  that 
if  exactly  acquainted  with  the  structure  and  elaboration  of  the 
nervous  apparatus  in  any  animal,  we  might  to  a  great  extent  pre¬ 
dicate  the  most  important  points  in  its  economy,  and  form  a 
tolerably  correct  estimate  of  its  powers  and  general  conformation. 
But,  unfortunately,  such  knowledge  is  not  always  at  our  disposal : 
in  the  lower  forms  of  the  animal  world  especially,  we  are  far  from 
being  able  to  avail  ourselves  of  such  a  guide,  and  it  will  probably 
be  long  ere  our  improved  means  of  research  permit  us  to  apply  to 
practice  the  views  which  Physiology  would  lead  us  to  adopt. 

The  grand  divisions  of  the  animal  kingdom,  grounded  upon  the 
principal  varieties  in  the  arrangement  of  the  nervous  system,  we 
shall,  however,  proceed  to  consider,  leaving  to  future  occasions 
those  comments  which  a  consideration  of  the  structure  of  par¬ 
ticular  groups  will  force  upon  our  notice. 

* 


a  thread ;  N-vpiv,  a  nerve. 


t  «,  priv. ;  xgivM,  to  discern. 


ON  CLASSIFICATION. 


6 


1st  Division. — Acrita* * * §  (M‘Leay);  Cryptoneura ,  (Rudolplii)‘f' 

Protozoa ,j  Oozoa.§ 

(8.)  In  animals  belonging  to  this  division,  no  nervous  filaments  or 
masses  have  been  discovered,  and  the  neurine  or  nervous  matter  is 
supposed  to  be  diffused  in  a  molecular  condition  through  the  body, 
mixed  up  with  the  gelatinous  parenchyma  of  which  they  consist. 
Possessing  no  brain  or  central  mass,  to  which  external  impressions 
can  be  transmitted,  or  nervous  filaments  calculated  to  conduct 
sensations  to  distant  points  of  the  system,  or  associate  muscular 
movements,  they  are  necessarily  incapable  of  possessing  those 
organs  which  are  dependent  upon  such  circumstances  ;  instruments 
of  the  external  senses  are  therefore  totally  wanting,  or  their  ex¬ 
istence  at  least  is  extremely  doubtful ;  the  contractile  molecules  of 
their  bodies  are  not  as  yet  aggregated  into  muscular  fibre.  The 
alimentary  apparatus  consists  of  canals  or  cavities,  permeating  the 
parenchyma  of  the  body,  but  without  distinct  walls,  as  in  the 
higher  divisions,  where  it  floats  in  an  abdominal  cavity.  The 
vascular  system,  where  at  all  perceptible,  consists  of  reticulate 
channels,  in  which  the  nutrient  fluids  move  by  a  kind  of  cyclosis. 
Their  mode  of  reproduction  is  likewise  conformable  to  the  diffused 
state  of  the  nervous  and  muscular  systems ;  not  only  are  most 
of  them  susceptible  of  being  multiplied  by  mechanical  division, 
but  they  generate  by  spontaneous  fissure,  as  well  as  by  gemmae, 
ciliated  gemmules,  and  true  ova.  Many  appear  to  be  made  up  of 
a  repetition  of  similar  parts,  forming  compound  animals  of  various 
forms,  and  different  degrees  of  complexity.  In  this  division  are 
included 

1.  Sponges. 

2.  Polyps. 

3.  Polygastric  animalcules. 

4.  Acalepliae. 

5.  Parenchymatous  Entozoa  or  Sterelmintha. 

*  Horae  Entomologicae,  Vol.  I.  Part  II.  page  202.  We  adopt  the  term,  however, 
a.ccording  to  its  improved  application  by  Mr.  Owen,  viz.  to  the  exclusion  of  the  higher 

organized  Polyps  and  Entozoa,  and  the  admission  of  part  of  the  Radiata  of  Macleay. 

t  Beytriige  sur  Anthropologic.  1812.  £  first;  2 Zov,  animal. 

§  'fiov,  an  egg;  2 wov,  animal,  so  called  by  Carus,  because  they  resemble  the  eggs  or 
rudiments  of  more  perfect  forms. 


ON  CLASSIFICATION. 


7 


Second  Division. — Nematoneura  (Owen).* 

(9.)  In  the  second  division  of  the  Radiata  of  Cuvier,  the  nervous 
matter  is  distinctly  aggregated  into  filaments,  and  in  some  cases 
nuclei  of  neurine,  which  may  be  regarded  as  rudimentary  nervous 
centres,  have  been  noticed.  It  is  to  be  lamented,  however,  that  in 
this  most  interesting  group  of  animals,  in  which  we  have  the  first 
developement  of  most  of  the  organs  subservient  to  the  vital 
functions,  the  extreme  minuteness  of  some  genera,  and  the  diffi¬ 
culty  of  distinctly  observing  the  nervous  system  in  the  larger 
species,  has  prevented  our  knowledge  regarding  their  organization, 
in  this  particular,  from  being  of  that  satisfactory  character  which  it 
is  to  be  hoped  it  will  hereafter  attain  to. 

Owing  to  the  want  or  imperfect  condition  of  the  nervous  centres, 
the  nematoneura  are  necessarily  incapable  of  possessing  external 
organs  of  the  higher  senses,  the  general  sense  of  touch  being  as  yet 
the  only  one  of  which  they  are  indubitably  possessed ;  yet  in  their 
muscular  system  they  are  much  more  efficiently  provided  than  the 
acrite  orders,  as  the  developement  of  nervous  threads  of  communi¬ 
cation  renders  an  association  of  muscular  actions  possible ;  and 
therefore,  co-apparent  with  nervous  filaments,  we  distinguish  in  the 
structure  of  the  nematoneura  distinct  fasciculi  of  muscular  fibre, 
and  powers  of  locomotion  of  a  much  more  perfect  description. 

The  digestive  apparatus  is  no  longer  composed  of  canals  merely 
excavated  in  the  parenchyma  of  the  body,  but  is  provided  with 
distinct  muscular  and  membranous  walls,  and  loosely  attached  in 
an  abdominal  cavity. 

The  circulation  of  the  nutritious  fluid  is  likewise  carried  on  in  a 
separate  system  of  vessels,  distinct  from  the  alimentary  apparatus, 
yet  still  unprovided  with  a  heart,  or  exhibiting  pulsations  for  the 
forcible  impulsion  of  the  contained  blood. 

The  fissiparous  mode  of  reproduction  is  no  longer  witnessed, 
an  obvious  consequence  of  the  increased  complexity  of  struc¬ 
ture,  and  these  animals  are  for  the  most  part  androgynous,  or 
capable  of  producing  fertile  ova,  without  the  co-operation  of  two 
individuals. 

Among  the  nematoneura,  therefore,  we  include 

*  Cyclopaedia  of  Anatomy  and  Physiology.  Article,  Acuita. 


8 


ON  CLASSIFICATION. 


1.  Bryozoa,  or  Polyps,  with  ciliated  arms. 

2.  Rotifera. 

3.  Epizoa. 

4.  Cavitary  Entozoa  or  Ccelelmintha. 

5.  Echinodermata. 

The  reader  will  perceive,  that  this  division,  however  well  sepa¬ 
rated  from  the  preceding  by  physiological  characters,  is,  in  a 
zoological  point  of  view,  principally  composed  of  groups  detached 
from  the  members  of  other  orders.  The  Bryozoa  are  evidently 
dismemberments  of  the  family  of  Polyps,  from  which  they  differ  in 
their  more  elaborate  internal  organization.  The  Ccelelmintha  are 
more  perfect  forms  of  the  Parenchymatous  Entozoa.  The  Roti¬ 
fera,  formerly  confounded  with  the  Infusoria,  exhibit  manifest 
analogies  with  the  articulated  Crustaceans,  as  in  fact  do  the 
Epizoa.  The  Echinodermata  alone  appear  to  form  an  isolated 
group,  properly  belonging  to  the  division  under  consideration. 

Third  D  ivision. — Homogangliata  (Owen)  ;  Arliculata  (Cu¬ 
vier)*  ;  A nnulosa  (Macleay)  ;  Diploneura  (Grant).' *f* 

(10.)  The  articulated  division  of  the  animal  kingdom  is  charac¬ 
terized  by  a  nervous  system,  much  superior  in  developement  to  that 
possessed  by  the  two  preceding,  indicated  by  the  superior  propor¬ 
tionate  size  which  the  ganglionic  centres  bear  to  the  nerves  which 
emanate  from  them.  The  presence  of  these  central  masses  of  neurine, 
admits  of  the  possession  of  external  senses  of  a  higher  class  than  could 
be  expected  among  the  Acrita  or  Nematoneura,  and  gives  rise  to 
a  concentration  of  nervous  power,  which  allows  of  the  existence  of 
external  limbs  of  various  kinds,  and  of  a  complex  muscular  system 
capable  of  great  energy  and  power  of  action. 

The  nervous  centres  are  arranged  in  two  parallel  lines  along  the 
whole  length  of  the  body,  forming  a  series  of  double  ganglia  or 
brains,  belonging  apparently  to  the  individual  segments  of  which 
the  animal  is  composed.  The  anterior  pair  placed  invariably  in 
the  head  above  the  oesophagus,  and  consequently  upon  the  dorsal 
aspect  of  the  body,  seems  more  immediately  appropriated  to  the 
higher  senses,  supplying  nerves  to  the  antennae,  or  more  special  in¬ 
struments  of  touch,  to  the  eyes,  which  now  manifest  much  com¬ 
plexity  of  structure,  to  the  auditory  apparatus  where  such  exists, 

*  The  Cirri  peel  a  are  excluded  from  the  Articulata  of  Cuvier. 

1  he  Entozoa  and  Rotifera  are  included  in  the  Diploneura  of  Dr.  Grant. 


ON  CLASSIFICATION. 


9 


and  probably  to  the  senses  of  taste  and  smell.  This  dorsal  or 
anterior  pair  of  ganglia,  which  evidently  is  in  relation  with  the 
higher  functions  of  the  economy  of  the  creature,  is  brought  into 
communication  with  the  series  of  nervous  centres  placed  along  the 
ventral  aspect,  by  means  of  filaments  which  embrace  the  msophagus, 
and  join  the  anterior  pair  placed  beneath  it ;  the  whole  system 
may  therefore  be  regarded  as  a  series  of  independent  brains  destined 
to  animate  the  segments  of  the  body  in  which  they  are  individually 
placed.  Such  a  multiplication  of  the  central  organs  of  the  nervous 
system,  is  obviously  adapted  to  the  elongated  forms  of  the  vermi¬ 
form  orders,  but  from  the  want  of  concentration  which  such  an 
arrangement  implies,  this  type  of  structure  is  still  very  inferior  in 
its  character.  As  the  articulata  become  more  perfect  in  their  out¬ 
ward  form,  the  number  of  the  brains  becomes  diminished,  while 
their  proportionate  size  increases  ;  and  thus  in  the  carnivorous 
Insects,  Arachnida  and  Crustacea,  they  are  all  united  into  a  few 
great  masses,  which,  becoming  the  general  centres  of  the  entire 
system,  admit  of  a  perfection  in  their  external  senses,  a  precision 
in  their  movements,  and  an  energy  of  action,  of  which  the  detached 
character  of  the  ganglia  in  the  lower  tribes  was  incapable. 

(11.)  This  dependence  of  the  perfection  of  the  animal  upon  the 
concentration  of  the  central  masses  of  the  nervous  system,  is  strik¬ 
ingly  proved  by  the  changes  perceptible  in  the  number  and  arrange¬ 
ment  of  the  ganglia,  during  the  progress  of  an  insect  through  the 
different  stages  of  its  existence.  In  the  elongated  body  of  the  worm¬ 
like  caterpillar,  each  segment  possesses  its  appropriate  pair  of  ganglia, 
and  the  consequence  of  such  diffusion  of  its  nervous  apparatus,  is 
apparent  in  its  imperfect  limbs,  its  rude  organs  of  sense,  its  sluggish 
movements,  and  general  apathy,  but  as  it  successively  attains  to 
more  mature  forms  of  existence,  passing  through  the  different  me¬ 
tamorphoses  which  it  undergoes,  the  nervous  ganglia  gradually 
coalesce,  increase  in  power,  as  they  diminish  in  number,  until  in 
the  imago  or  perfect  state,  having  arrived  at  the  greatest  concen¬ 
tration  compatible  with  the  habits  of  the  insect,  we  find  it  endued 
with  new  and  far  more  exalted  attributes,  the  organs  of  its  senses 
are  more  elaborately  formed,  it  possesses  limbs  which  previously  it 
would  have  been  utterly  incapable  of  wielding,  its  movements  are 
characterized  by  their  activity  and  precision,  and  its  instincts  and 
capabilities  proportionately  enlarged  and  exalted. 

The  Homogangliate  division  of  the  animal  world  is  extremely 
natural,  and  includes  the  following  classes  : — 


10 


ON  CLASSIFICATION. 


1.  Cirripeda.  4.  Insecta. 

2.  Annelida.  5.  Araclmida. 

3.  Myriapoda.  6.  Crustacea. 

Fourtli  Division. — Heterogangliata  (Owen)  ;  Mollusca 
(Cuvier)  *  ;  Cyclogangliata  (Grant). 

(12.)  The  characters  of  this  division  are  well  defined,  and  the  irre¬ 
gular  and  unsymmetrical  forms  of  the  bodies  of  most  of  the  genera 
which  compose  it,  in  exact  relation  with  the  arrangement  of  the 
nervous  apparatus. 

As  in  the  articulata  there  is  a  large  nervous  mass  placed  above 
the  oesophagus,  which  supplies  the  principal  organs  of  sense,  but 
the  other  ganglia  are  variously  dispersed  through  the  body,  although 
always  brought  into  communication  with  the  supraoesophageal 
portion  by  connecting  filaments.  Throughout  all  the  forms,  we 
find  a  distinct  relation  between  the  size  and  developement  of  the 
nervous  centres,  and  the  perfection  of  the  animal,  indicated  by  the 
senses  and  organs  of  motion  with  which  it  is  provided. 

This  division  includes 

1.  Tunicata.  4.  Gasteropoda. 

2.  Conchifera.  5.  Pteropoda. 

3.  Bracliiopoda.  6.  Cephalopoda. 

Fifth  Division. — Yerterrata  (Cuvier);  Myelencepliala  (Owen); 

Spinicerebrata  (Grant). 

(13.)  The  arrangement  of  the  nervous  centres  in  the  highest  or 
vertebrate  division,  indicates  the  greatest  possible  concentration  and 
developement.  The  ganglionic  masses  assume  a  very  great  pro¬ 
portionate  size  when  compared  with  the  nerves  which  emanate  from 
them,  and  are  principally  united  into  a  long  chain,  denominated 
the  cerebro-spinal  axis  or  cord,  which  is  enclosed  in  a  cartilaginous 
or  bony  canal,  occupying  the  dorsal  region  of  the  animal.  The 
anterior  extremity  of  the  cerebro-spinal  axis  is  made  up  of  those 
ganglia  which  are  more  especially  in  relation  with  the  principal  senses 
and  the  higher  powers  of  intelligence,  forming  a  mass  denominated, 
from  its  position  in  the  skull  which  encloses  it,  the  encephalon. 
It  is  with  the  increased  proportionate  developement  of  this  portion, 
that  the  intelligence  of  the  animal  becomes  augmented ;  in  the 
lower  tribes,  the  cerebral  masses  scarcely  exceed  in  size  those 

4 

*  The  Cirripeda  are  included  in  the  Mollusca  of  Cuvier. 


ON  CLASSIFICATION. 


11 


which  form  the  rest  of  the  central  chain  of  ganglia,  but  as  we 
advance  from  fishes  towards  the  higher  forms  of  the  vertebrata,  we 
observe  them  to  preponderate  more  and  more  in  bulk,  until  at 
last  in  man  they  assume  that  extraordinary  developement  adapted 
to  the  exalted  position  which  he  is  destined  to  occupy.  It  is  in 
the  cerebral  ganglia,  therefore,  that  we  have  the  representative  of 
the  supracesophageal  masses  of  the  articulated  and  molluscous 
classes,  which,  as  we  have  already  seen,  preside  especially  over  the 
senses,  and  correspond  in  their  proportions  with  the  capabilities  of 
the  tribes  of  animals  included  in  those  divisions.  The  spinal  cord, 
as  the  rest  of  the  central  axis  of  the  nervous  system  of  vertebrata 
is  denominated,  is  made  up  of  a  succession  of  ganglia,  in  communi¬ 
cation  with  symmetrical  pairs  of  nerves  connected  with  them,  and 
which  preside  over  the  generally  diffused  sense  of  touch,  and  the 
voluntary  motions  of  the  body.  But  besides  the  cerebro-spinal  sys¬ 
tem,  we  find  in  the  vertebrated  classes  another  set  of  nervous  centres, 
to  which  nothing  corresponding  has  been  satisfactorily  identified  in 
the  lower  divisions  ;  namely,  the  sympathetic  system ,  which  mainly 
controls  the  involuntary  movements  of  the  body  connected  with  the 
vital  functions. 

The  vertebrata  are  further  distinguished  by  the  possession  of 
an  internal  organized  skeleton,  either  composed  of  cartilage  or 
bone,  which  is  made  up  of  several  pieces,  and  serves  as  the  general 
support  of  the  frame,  forming  a  series  of  levers  upon  which  the 
muscles  act. 

This  last  division  of  the  animal  world  embraces  the  following 

O 

classes  : — 

1 .  Fishes.  4.  Birds. 

2.  Amphibia.  5.  Mammalia. 

3.  Reptiles. 

Such  will  be  the  classification  which  we  shall  adopt  in  the 
following  pages  ;  and  although,  perhaps,  the  definitions  of  the  five 
great  groups  may  be  considered  by  the  scientific  reader  as  some¬ 
what  scanty,  enough,  we  trust,  has  been  said  to  render  intelli¬ 
gible  the  terms  which  we  shall  hereafter  have  frequent  occasion  to 
employ. 

(14.)  A  question  naturally  presents  itself  in  this  place  which  re¬ 
quires  consideration  : — May  we  expect,  as  we  advance  from  the  lower 
types  of  organization  to  such  as  are  more  perfect,  to  be  led  on 
through  an  unbroken  and  continuous  series  of  creatures,  gradually 
rising  in  importance  and  complexity  of  structure,  each  succeeding 


12 


ON  CLASSIFICATION. 


tribe  of  beings  presenting  an  advance  upon  the  preceding,  and 
merging  insensibly  into  that  which  follows  it  ?  A  very  slight 
investigation  of  this  matter  will  convince  us  of  the  contrary.  Each 
group,  in  fact,  will  be  found  to  present  points  of  relationship  with 
several  others,  into  all  of  which  it  passes  by  connecting  species  ;  as 
a  circle  would,  at  different  points  of  its  circumference,  touch  others 
placed  around  it.  This,  however,  will  be  best  illustrated  as  we 
proceed. 


CHAPTER  IT. 


ON  SPONGES. 


Porifera ,  Grant — Amorphozoa  (Blainville). 

(1 5.)  The  great  circles  to  which  we  may  compare  the  animal  and 
vegetable  kingdom,  like  the  smaller  circles  to  which  allusion  was 
made  at  the  close  of  the  last  chapter,  touch  each  other  ;  or,  in 
other  words,  there  are  certain  forms  of  organization  so  closely 
allied  to  both,  that  it  is  difficult  to  say  precisely  in  which  they 
ought  to  be  included.  Such  are  the  sponges,  which,  although  by 
common  consent  admitted  into  the  animal  series,  will  be  found  to 
be  excluded,  by  almost  every  point  of  their  structure,  from  all  the 
definitions  of  an  animal  hitherto  devised.  What  is  an  animal  ? 
How  are  we  to  distinguish  it  as  contrasted  with  a  mineral  or  a 
vegetable  ?  The  concise  axiom  of  Linnaeus  upon  this  subject  is 
well  known, — u  Stones  grow  ;  vegetables  grow  and  live  ;  animals 
grow,  live,  and  feel.”  The  capability  of  feeling,  therefore, 
formed,  in  the  opinion  of  Linnaeus,  the  great  characteristic  sepa¬ 
rating  the  animal  from  the  vegetable  kingdom  ;  yet,  in  the  class 
before  us,  no  indication  of  sensation  has  been  witnessed  ;  contact, 
however  rude,  excites  no  movement  or  contraction  which  might 
indicate  its  being  perceived  ;  no  torture  has  ever  elicited  from  them 
an  intimation  of  suffering  ;  they  have  been  pinched  with  forceps, 
lacerated  in  all  directions,  bored  with  hot  irons,  and  attacked  with 
the  most  energetic  chemical  stimuli,  without  shrinking  or  exhibit¬ 
ing  the  remotest  appearance  of  sensibility.  On  the  other  hand, 
in  the  vegetable  world  we  have  plants  which  apparently  feel  in 


PORIFERA. 


IS 


this  sense  of  the  word.  The  sensitive  plant,  for  example,  which 
droops  its  leaves  upon  the  slightest  touch,  would  have  far  greater 
claims  to  be  considered  as  being  an  animal  than  the  sponges  of 
which  we  are  speaking. 

The  power  of  voluntary  motion  has  been  appealed  to  as  exclusively 
belonging  to  the  animal  economy  :  yet,  setting  aside  the  spontane¬ 
ous  movements  of  some  vegetables,  the  sponge,  rooted  to  the  rock, 
seems  absolutely  incapable  of  this  function,  and  the  most  micro¬ 
scopic  scrutiny  has  failed  to  detect  its  existence. 

The  best  definition  of  an  animal,  as  distinguished  from  a  vege¬ 
table,  which  has  as  yet  been  given,  is,  that  whereas  the  latter  fixed 
in  the  soil  by  roots,  or  immersed  perpetually  in  the  fluid  from 
which  it  derives  its  nourishment,  absorbs  by  its  whole  surface  the 
nutriment  which  it  requires  ;  the  animal,  being  generally  in  a 
greater  or  less  degree  capable  of  changing  its  position,  is  provided 
with  an  internal  receptacle  for  food,  or  stomachal  cavity,  from 
which,  after  undergoing  the  process  of  digestion,  the  nutritious 
matter  is  taken  up.  But  in  the  case  of  the  sponge  no  such 
reservoir  is  found ;  and  in  its  place  we  find  only  anastomosing 
canals  which  permeate  the  whole  body,  and  convey  the  circumam¬ 
bient  medium  to  all  parts  of  the  porous  mass. 

The  last  circumstance  which  we  shall  allude  to  as  specially 
appertaining  to  the  animal  kingdom,  is  derived  from  the  chemical 
composition  of  organized  bodies.  Vegetables  contain  but  a 
small  proportion  of  azote  in  their  substance,  whilst  in  animals  this 
element  exists  in  considerable  abundance,  causing  their  tissues 
when  burned  to  give  out  a  peculiar  odour  resembling  that  of 
burned  horn,  and  in  this  particular  sponges  differ  from  vegetable 
matter. 

(16.)  The  common  sponge  of  commerce  is,  as  every  one  knows, 
made  up  of  horny,  elastic  fibres  of  great  delicacy,  united  with  each 
other  in  every  possible  direction,  so  as  to  form  innumerable  canals, 
which  traverse  its  substance  in  all  directions.  To  this  structure 
the  sponge  owes  its  useful  properties,  the  resiliency  of  the  fibres  com¬ 
posing  it  making  them,  after  compression,  return  to  their  former 
state,  and  leaving  the  canals  which  they  form  open,  to  suck  up 
surrounding  fluids  by  capillary  attraction. 

The  dried  sponge  is,  however,  only  the  skeleton  of  the  living 
animal :  in  its  original  state,  before  it  was  withdrawn  from  its  native 
element,  every  filament  of  its  substance  was  coated  over  with  a  thin 
film  of  glairy  semifluid  matter,  composed  of  aggregated  transparent 


14  PORI  FE II  A. 

globules,  which  was  the  living 
part  of  the  sponge,  secreting,  as 
it  extended  itself,  the  horny 
fibres  which  are  imbedded  in  it. 

The  anastomosing  filaments  which 
compose  the  skeleton  of  such 
sponges,  when  examined  under  a 
microscope,  and  highly  magnified, 
appear  to  be  tubular,  as  represented 
in  fig.  1 .  c. 

Many  species,  although  exhibit¬ 
ing  the  same  porous  structure, 
have  none  of  the  elasticity  of  the 
officinal  sponge,  a  circumstance 
which  is  due  to  the  difference  ob¬ 
servable  in  the  composition  of  their 
skeletons  or  ramified  frame-work. 

In  such  the  living  crust  forms 
within  its  substance  not  only  tenacious  bands  of  animal  matter, 
but  great  quantities  of  crystallized  spicula,  sometimes  of  a  calca¬ 
reous,  at  others  of  a  silicious  nature,  which  are  united  together  by 
the  tenacity  of  the  fibres  with  which  they  are  surrounded.  On 
destroying  the  softer  portions  of  these  skeletons  either  by  the  aid 
of  a  blow-pipe  or  by  the  caustic  acids  or  alkalies,  the  spicula  re¬ 
main,  and  may  readily  be  examined  under  a  microscope  :  they  are 
then  seen  to  have  determinate  forms,  which  are  generally  in  rela¬ 
tion  with  the  natural  crystals  of  the  earths  of  which  they  consist ; 
and  as  the  shape  of  the  spicula  is  found  to  be  similar  in  all  sponges 
of  the  same  species,  and  not  unfrequently  peculiar  to  each,  these 
minute  particles  become  of  use  in  the  identification  of  these 
bodies.* 

Crystallized  spicula  of  this  description  form  a  feature  in  the 
structure  of  the  sponge  which  is  common  to  that  of  many  vege¬ 
tables,  resembling  the  formations  called  Raphides  by  botanical 
writers.  Some  of  the  principal  forms  which  they  exhibit  are  de¬ 
picted  in  fig.  lab,  which  likewise  will  give  the  reader  a  general 
idea  of  the  appearance  of  the  silicious  and  calcareous  sponges, 
after  the  destruction  of  their  soft  parts  has  been  effected  by  the 
means  above  indicated.  The  figures  d,  e ,  f,  and  g,  exhibit 
detached  spicula  of  different  forms  highly  magnified.  The  most 

*  Savigny  (Jules  Caesar)  Zoologie  d’Egypte — gr.  fol.  Paris,  1809. 


Fig-  1. 


PORI  FEE- A. 


15 


convenient  method  of  seeing  them  is  simply  to  scrape  off  a  few 
particles  from  the  incinerated  sponge  upon  a  piece  of  glass,  which, 
when  placed  under  the  microscope,  may  be  examined  with  ordinary 
powers. 

(17.)  On  placing  a  living  sponge  of  small  size  in  a  watch-glass  or 
small  glass  trough  filled  with  sea-water,  and  watching  it  attentively, 
something  like  a  vital  action  becomes  apparent.*  The  entire 
surface  is  seen  to  be  perforated  by  innumerable  pores  and  aper¬ 
tures,  some  exceedingly  minute,  opening  on  every  part  of  its  peri¬ 
phery  ;  others  of  larger  dimensions,  placed  at  intervals,  and  gene¬ 
rally  elevated  upon  prominent  portions  of  the  sponge.  Through 
the  smaller  orifices  the  surrounding  water  is  continually  sucked  as  it 
were  into  the  interior  of  the  spongy  mass,  and  it  as  constantly  flows 
out  in  continuous  streams  through  the  larger  openings.  This  con¬ 
tinual  influx  and  efflux  of  the  surrounding  fluid  is  produced  by  an 
agency  not  yet  discovered,  as  no  contraction  of  the  walls  of  the 
canals,  or  other  cause  to  which  the  movement  may  be  referred,  has 
ever  been  detected  ;  we  are  as¬ 
sured,  however,  that  it  is  from 
the  currents,  thus  continually 
permeating  every  portion  of 
its  substance,  that  the  general 
mass  is  nourished.  The  annex¬ 
ed  diagram,  fig.  2  rz,  will  give 
the  reader  an  idea  of  the  most 
usual  direction  of  the  streams  : 
the  entering  fluid  rushes  in  at 
the  countless  pores  which  occu¬ 
py  the  body  of  the  sponge  ; 
but,  in  its  progress  through  the 
canals  in  the  interior,  becomes 
directed  into  more  capacious 
channels,  communicating  with 
the  prominent  larger  orifices,  through  which  it  is  ultimately  ejected 
in  equable  and  ceaseless  currents.  Organized  particles,  which  ne¬ 
cessarily  abound  in  the  water  of  the  ocean,  are  thus  introduced 
into  the  sponge  on  all  sides,  and  are  probably  employed  as  nutri¬ 
ment,  whilst  the  superfluous  or  effete  matter  is  continually  cast 
out  with  the  issuing  streams  as  they  rush  through  the  fecal  ori¬ 
fices.  The  growth  of  the  sponge  is  thus  provided  for,  the  living 

*  Dr.  Grant,  in  the  New  Edinburgh  Philosophical  Journal,  1827. 


Fig.  2. 


16 


PORIFERA. 


gelatinous  portion  continually  accumulates,  and,  as  it  spreads  in 
every  direction,  secretes  and  deposits,  in  the  form  peculiar  to  its 
species,  the  fibrous  material  and  earthy  spicula  which  characterise 
the  skeleton. 

(18.)  From  this  description  of  the  structure  of  a  sponge,  it  will 
be  apparent  that  all  parts  of  the  mass  are  similarly  organized  :  a 
necessary  consequence  will  be,  that  each  part  is  able  to  carry  on, 
independently  of  the  rest,  those  functions  needful  for  existence. 
If  therefore  a  sponge  be  mechanically  divided  into  several  pieces, 
every  portion  becomes  a  distinct  animal. 

(19.)  The  multiplication  of  sponges,  however,  is  effected  in 
another  manner,  which  is  the  ordinary  mode  of  their  reproduction, 
and  forms  a  very  interesting  portion  of  their  history.*  At  certain 
seasons  of  the  year,  if  a  living  sponge  be  cut  to  pieces,  the  chan¬ 
nels  in  its  interior  are  found  to  have  their  walls  studded  with  yel¬ 
lowish  gelatinous  granules,  developed  in  the  living  parenchyma 
which  lines  them  ;  these  granules  are  the  germs  or  gemmules 
from  which  a  future  race  will  spring ;  they  seem  to  be  formed  in¬ 
differently  in  all  parts  of  the  mass,  sprouting  as  it  were  from  the 
albuminous  crust  which  coats  the  skeleton,  without  the  appearance 
of  any  organs  appropriated  to  their  developement.  As  they  in¬ 
crease  in  size,  they  are  found  to  project  more  and  more  into  the 
canals  which  ramify  through  the  sponge,  and  to  be  provided  with 
an  apparatus  of  locomotion  of  a  description  which  we  shall  fre¬ 
quently  have  occasion  to  mention.  The  gemmule  assumes  an 
ovoid  form,  fig.  2  B,  and  a  large  portion  of  its  surface  becomes 
covered  with  innumerable  vibrating  hairs  or  cilia,  as  they  are  de¬ 
nominated,  which  are  of  inconceivable  minuteness,  yet  individually 
capable  of  exercising  rapid  movements,  which  produce  currents  in 
the  surrounding  fluid.  As  soon  therefore  as  a  gemmule  is  suffi¬ 
ciently  mature,  it  becomes  detached  from  the  nidus  where  it  was 
formed,  and  whirled  along  by  the  issuing  streams  which  are  ex¬ 
pelled  through  the  fecal  orifices  of  the  parent,  it  escapes  into  the 
water  around.  Instead,  however,  of  falling  to  the  bottom,  as  so  appa¬ 
rently  helpless  a  particle  of  jelly  might  be  expected  to  do,  the  cease¬ 
less  vibration  of  the  cilia  upon  its  surface  propels  it  rapidly  along, 
until,  being  removed  to  a  considerable  distance  from  its  original, 
it  attaches  itself  to  a  proper  object,  and,  losing  the  locomotive  cilia 
which  it  at  first  possessed,  it  becomes  fixed  and  motionless,  and 


*  Professor  Grant — loc.  cit. 


ON  POLYPS. 


17 


developes  within  its  substance  the  skeleton  peculiar  to  its  species, 
exhibiting  by  degrees  the  form  of  the  individual  from  which  it 
sprung.  It  is  curious  to  observe  the  remarkable  exception  which 
sponges  exhibit  to  the  usual  phenomena  witnessed  in  the  reproduc¬ 
tion  of  animals,  the  object  of  which  is  evident,  as  the  result  is 
admirable.  The  parent  sponge,  deprived  of  all  power  of  movement, 
would  obviously  be  incapable  of  dispersing  to  a  distance  the  numerous 
progeny  which  it  furnishes  ;  they  must  inevitably  have  accumulated 
in  the  immediate  vicinity  of  their  place  of  birth,  without  the  possi¬ 
bility  of  their  distribution  to  other  localities.  The  seeds  of  vegetables, 
sometimes  winged  and  plumed  for  the  purpose,  are  blown  about 
by  the  winds,  or  transported  by  various  agencies  to  distant  places  ; 
but,  in  the  present  instance,  the  still  waters  in  which  sponges  grow 
would  not  have  served  to  transport  their  progeny  elsewhere,  and 
germs  so  soft  and  delicate  could  hardly  be  removed  by  other 
creatures.  Instead  therefore  of  being  helpless  at  their  birth,  the 
young  sponges  can,  by  means  of  their  cilia,  row  themselves  about 
at  pleasure,  and  enjoy  for  a  period  powers  of  locomotion  denied  to 
their  adult  state. 


CHAPTER  III. 

ON  POLYPS. 

Zoophytes  of  old  Authors — Phytozoa  (Ehrenberg). 

(20.)  It  is  not  surprising  that  many  members  of  the  extensive 
family  upon  a  consideration  of  which  we  are  now  entering,  should 
have  been  regarded  by  the  earlier  naturalists  as  belonging  to  the 
vegetable  kingdom,  with  which,  in  outward  appearance  at  least, 
numerous  species  have  many  characters  in  common.* 

Fixed  in  large  arborescent  masses  to  the  rocks  of  tropical  seas, 
or  in  our  own  climate  attached  to  shells  or  other  submarine  sub¬ 
stances,  they  throw  out  their  ramifications  in  a  thousand  beautiful 
and  plant-like  forms  ;  or,  incrusting  the  rocks  at  the  bottom  of  the 
ocean  with  calcareous  earth  separated  from  the  water  which  bathes 
them,  they  silently  build  up  reefs  and  shoals,  justly  dreaded  by 
the  navigator,  and  sometimes  giving  origin,  as  they  rise  to  the 
surface  of  the  sea,  to  islands  which  the  lapse  of  ages  clothes  with 

*  Tournefort,  Institutiones  Rei  Herbaria,  4to.  1719. 

C 


18 


ON  POLYPS. 


luxuriant  verdure,  and  peoples  with  appropriate  inhabitants.  Va¬ 
rious  indeed  are  the  forms  which  these  creatures  offer  to  the  zoolo¬ 
gist  ;  and  the  classification  of  them,  even  at  the  present  day,  is  a 
subject  of  much  doubt  and  uncertainty.  Without  entering  fur¬ 
ther  into  the  subject  of  their  division  into  groups  and  families 
than  is  connected  with  our  purpose  of  examining  the  main  features 
of  their  economy,  wTe  shall  select  some  of  the  most  marked  varieties 
for  description,  commencing  with  the  simplest  and  least  elabo¬ 
rately  formed. 

(21.)  W e  have  already  seen  that  in  the  Sponges  the  living  portion 
of  the  animal  was  composed  of  a  gelatinous  film,  which,  without  any 
apparent  organization,  was  possessed  of  the  power  of  extracting  nutri¬ 
ment  from  the  water  around  it,  of  deriving  from  the  same  source  ani- 
malized  materials  and  earthy  particles,  which  wrere  deposited  within 
its  texture,  and  used  in  constructing  a  porous  frame-work  or  skele¬ 
ton  ;  and,  moreover,  that  the  same  semifluid  parenchyma  could  de- 
velope  from  its  substance  germs,  which  became  ultimately  expanded 
into  other  beings  resembling  that  from  which  they  sprung  ;  we  shall 
therefore  be  prepared  to  find,  in  the  class  upon  which  wre  are  enter¬ 
ing,  like  results  produced  by  equally  simple  means. 

Among  the  calcareous 
structures,  derived  from 
the  tropical  seas,  which 
are  usually  known  by  the 
general  terms  of  Madre¬ 
pores,  Corals,  &c.  and 
which,  from  the  beauty  of 
their  structure,  form  the 
ornaments  of  our  cabinets, 
few  are  more  common  than 
those  denominated  F un- 
giae  and  Meandrinae,  — 
animals  belonging  to  the 
group  M adrep hyl l icea  of 
systematic  zoologists. 

These  masses  consist  of  thin  plates  or  laminae  of  various  dimensions 
(fig.  3.)  disposed  in  different  directions  in  different  species,  but  in 
the  Fungia  Agariciformis ,  which  we  have  selected  as  an  example, 
radiating  from  a  common  centre,  and  forming  a  circular  mass  resem¬ 
bling  a  mushroom.  When  living  in  its  native  element,  every  part  of 
the  surface  of  this  stony  skeleton  was  encrusted  with  a  film  of  animal 


Fig.  3. 


ON  POLYPS. 


1  9 


matter,  clipping  down  into  tlie  interstices  of  tlie  plates,  and  cover¬ 
ing  the  whole  frame- work.  In  the  figure,  the  darker  portion  indi¬ 
cates  the  living  crust ;  whilst  from  the  lighter  parts  it  has  been  re¬ 
moved,  to  show  the  stony  skeleton  itself.  There  are  no  arms  or 
moving  parts  adapted  to  the  prehension  of  food,  and  no  separation 
of  organs  adapted  to  the  performance  of  the  vital  functions  has 
hitherto  been  described  ;  the  thin  membranous  film  apparently 
absorbs  the  materials  of  its  support  from  the  water  of  the 
ocean,  and  deposits  within  its  substance  the  calcareous  par¬ 
ticles  which  it  secretes,  moulding  them  into  the  form  peculiar 
to  its  skeleton,  which  it  gradually  enlarges  as  its  own  extent 
increases. 

(22.)  The  gelatinous  investment,  however,  gives  certain  dubious 
indications  of  vitality,  and  possesses  the  power  of  contracting  itself 
so  as  to  retire  between  the  laminae  of  its  skeleton  when  roughly 
handled,  and  thus  conceal  itself  from  injury.  Upon  the  surface  of 
the  soft  crust  are  seen  a  number  of  vesicles  indicated  in  the  figure, 
which  were  regarded  formerly  as  rudimentary  tentacula,  from  the 
circumstance  of  their  being  able  to  contract  and  vary  their  dimen¬ 
sions  ;  recent  observations  however  lead  to  the  belief  that  they  are 
cavities  filled  with  air,  and  serving  an  important  purpose  in  the  eco¬ 
nomy  of  the  creature, — namely,  that  of  preventing  it  from  being 
turned  upside  down  by  the  occasional  agitation  of  the  ocean, — as  in 
such  case  the  animal  has  been  found  by  experiment  to  have  no  power 
of  restoring  itself  to  its  former  position,  and  consequently  perishes  : 
these  air-vessels  may  therefore  be  looked  upon  as  floats,  which,  ren¬ 
dering  the  upper  surface  more  buoyant  than  the  inferior,  materially 
assist  in  preventing  such  an  accident  ;  for,  as  it  lies  quite  loose  and 
unattached  upon  the  surface  of  the  sand,  it  is  subject  to  be  lifted 
up  from  its  bed  by  any  sudden  roll  of  the  sea,  and  deposited  at  a 
considerable  distance  from  its  former  place. 

(23.)  The  reproduction  of  fungiae  is  effected  by  the  developement 
of  sprouts  or  gemmae,  which  pullulate  from  the  animal  substance  as 
buds  issue  from  a  plant,  and  remain  for  some  time  fixed  to 
the  parent  by  a  species  of  foot-stalk,  which  sustains  them  until 
they  have  attained  to  a  considerable  size  ;  the  young  fungiae  being  up¬ 
wards  of  an  inch  in  diameter  before  they  become  detached.  When 
mature,  they  separate  from  the  top  of  the  stony  peduncle  which  hi¬ 
therto  supported  them  ;  and  at  this  time,  the  skeleton  of  the  young 
fungia,  when  divested  of  its  fleshy  part,  shows  a  circular  opening 
beneath,  through  which  the  radiating  plates  of  the  upper  surface 

c  2 


20 


ON  POLYPS. 


are  visible.  In  a  sliort  time  a  deposit  of  calcareous  matter  takes 
place,  which  cicatrizes  the  opening,  the  marks  of  which  however  can 
be  traced  for  a  considerable  period,  until  at  length  the  increase  of 
this  secretion  continuing  with  the  growth  of  the  animal,  entirely 
obliterates  all  appearance  of  its  having  existed. 

In  the  earliest  period  of  its  developement,  the  foot-stalk  by 
which  the  young  is  united  to  the  parent,  as  well  as  its  radiating 
disc,  is  entirely  enveloped  with  the  soft  parts  of  the  animal ;  but  as 
the  upper  portion  spreads,  and  assumes  its  characteristic  form,  the 
pedicle  is  left  naked,  and  the  gelatinous  coating  extends  only  to  the 
line  where  the  separation  afterwards  takes  place. 

(24.)  It  is  generally  supposed  that  the  calcareous  matter  which 
forms  the  skeleton  of  these  madrepores  is  perfectly  external  to  the  liv¬ 
ing  crust  which  secretes  it,  and  accordingly  is  absolutely  inorganic, 
and  removed  from  the  future  influence  of  the  animal  which  produced 
it.  Such  a  supposition  appears,  however,  at  variance  with  the  facts 
above  stated,  and  incompatible  with  many  circumstances  connected 
with  the  history  of  the  lithophytous  polyps.  On  trying  to  detach  the 
soft  envelope  from  the  surface  of  the  skeleton,  the  firmness  of  their 
adherence  would  render  such  a  want  of  connexion  improbable, — they 
appear  to  be,  as  it  were,  incorporated  with  each  other  ;  and  besides, 
the  separation  of  the  fungia  from  the  peduncle  which  joined  it  to 
its  parent  during  its  earlier  growth,  necessarily  supposes  a  power  of 
removing  the  calcareous  particles  after  their  deposition.  It  is 
therefore  almost  demonstrable  that  the  earthy  matter  secreted 
by  the  polyp  is  deposited  in  the  tissue  of  its  substance,  and 
still  remains,  in  a  greater  or  less  degree,  subject  to  absorption 
and  removal :  of  this,  however,  we  shall  have  fuller  evidence 
hereafter. 

(25.)  It  is  astonishing  how  nearly  the  animal  and  vegetable  king¬ 
doms  approximate  each  other  in  the  lower  orders  of  these  calcareous 
zoophytes.  Admitting  the  animal  nature  of  fungia,  we  find  calcareous 
skeletons,  essentially  similar  in  their  chemical  composition,  produced 
by  a  large  tribe  of  organic  forms,  long  classed  with  the  creatures  we 
are  now  considering,  which  modern  observations  have  clearly  shown 
to  be  of  vegetable  nature.* 

These  are  the  Corallines,  (Linn.)  which,  although  so  nearly  re¬ 
sembling  the  skeletons  of  polyps,  that  Cuvier,  Lamarck,  and  others, 
scrupled  not  to  admit  them  into  the  animal  circle,  have  been  proved 

Schweigger,  Anatomisehe  Plivsiologische  Untersuchungen  iiber  Covallen.  Berlin, 
1819.  J 


ON  POLYrS. 


21 


by  microscopical  researches  to  possess  the  cellular  structure  apper¬ 
taining  to  vegetable  organization,  and  are  thus  placed  beyond  the 
limits  of  our  present  investigations. 

(26.)  We  have  hitherto  spoken  of  animals  which  do  not  appa¬ 
rently  possess  any  stomach  or  oral  aperture, — any  apparatus  for 
the  purpose  of  the  digestion  or  prehension  of  food.  Before  describ¬ 
ing  the  more  complex  forms  of  polyps,  we  will  now  select  a  group 
of  that  class  of  animals,  in  which  the  organs  provided  for  these  pur¬ 
poses  are  easily  recognisable ;  and,  as  the  simplicity  of  their  orga¬ 
nization  will  well  exhibit  the  principal  points  in  the  physiology  of  the 
acrita,we  shall  detail  at  some  length  the  facts  known  concerning  them. 

The  Hydrje,  or  fresh- water  polyps,  are  common  in  the  ponds  and 
clear  waters  of  our  own  country  ;  they  are  generally  found  creeping 
upon  confervae  which  float  upon  the  surface,  and  may  readily  be  pro¬ 
cured  in  summer  for  the  purpose  of  investigating  the  remarkable  cir¬ 
cumstances  connected  with  their  history.  4> 

The  body  of  one  of  these 
simple  animals  consists  of  a 
delicate  gelatinous  tube,  con-  j 

tracted  at  one  extremity,  which 
is  terminated  by  a  minute 
sucker,  and  furnished  at  the  op¬ 
posite  end  with  a  variable  num¬ 
ber  of  delicate  contractile  fila¬ 
ments,  placed  around  the  open¬ 
ing  which  represents  the  mouth. 

In  the  Hydra  viridis ,  {Jig. 

4, 1,)  the  species  most  common 
amongst  us,  the  tentacular  fila¬ 
ments  are  short,  and,  when  elon¬ 
gated  to  the  utmost,  are  not 
equal  to  the  length  of  the  body ; 
but  in  the  long-armed  species 
Hydra  fusca,  {Jig.  4,  )  they 

are  much  prolonged,  and  of  extreme  tenuity.  If  placed  in  a  small  glass 
tube,  one  side  of  which  is  flattened,  these  animals  may  readily  be  sub¬ 
mitted  to  microscopical  examination,  and,  from  their  transparency, 
their  entire  structure  is  easily  made  out.  When  highly  magnified,  the 
whole  body  is  seen  to  consist  of  a  granular  substance,  generally  of  a 
greenish  hue,  the  granules  being  loosely  connected  by  a  semifluid 
albuminous  matter ;  but  the  most  minute  research  reveals  no  fur- 


ON  POLYPS. 


tlier  appearances  of  organization  :  there  is  no  trace  of  muscular 
fibre  or  of  nervous  substance,  not  the  slightest  indication  of  vessels 
of  any  hind,  nor  any  apparatus  destined  to  the  function  of  repro¬ 
duction  ;  such  is  the  hydra,  offering  in  every  particular  a  good 
example  of  the  acrite  type  of  structure. 

The  young  naturalist  would  scarcely  be  prepared  to  see  an 
animal  of  this  description  waging  continual  war  with  creatures 
much  more  perfectly  organized  than  itself ;  endowed  with  consi¬ 
derable  capability  of  locomotion  ;  possessed  not  only  of  a  refined 
sense  of  touch,  but  able  to  appreciate  the  presence,  and  seek  the 
influence  of  light ;  and  exhibiting  moreover  a  tenacity  of  life  and 
power  of  reproduction  almost  beyond  belief :  a  little  observation, 
however,  will  convince  him  that  it  possesses  all  these  attributes, 
and  enable  him  to  share  in  some  degree  the  astonishment  with 
which  Trembley,  their  enthusiastic  discoverer,  first  witnessed  and 
described  them.* 

(27.)  The  hydra  is  not  like  most  other  polyps,  fixed  and  station¬ 
ary ;  but  can  roam  about  and  change  its  situation  according  to  circum¬ 
stances.  Its  usual  mode  of  progression  is  by  creeping  along  the 
stems  of  aquatic  plants,  or  upon  the  sides  of  the  glass  in  which  it 
is  confined  :  attaching  first  the  little  tubercle  at  its  posterior  ex¬ 
tremity  to  the  surface  upon  which  it  moves,  it  slowly  inflects  its 
body  {Jig.  4,  3),  and  fixing  its  oral  tentacles,  moves  along  in  the 
manner  of  a  leech,  by  a  succession  of  similar  actions.  This  method 
of  advancing  is,  from  the  small  size  of  the  animal,  necessarily  slow  ; 
and  a  march  of  a  couple  of  inches  will  require  several  hours  for  its 
performance  :  but,  when  arrived  at  the  surface  of  the  water,  it  adopts 
a  more  speedy  course  ;  suspending  itself  by  the  tail  as  by  a  minute 
float,  and  hanging  with  its  mouth  downwards,  it  rows  itself  about 
with  its  tentacles,  or,  wafted  by  the  wind,  can  travel  to  a  consider¬ 
able  distance  without  effort. 

(28.)  When  left  free,  the  hydrse  are  found  to  select  positions  most 
exposed  to  the  influence  of  light,  assembling  at  the  surface  of  the 
ponds  which  they  inhabit,  or  seeking  that  side  of  the  glass  in  which 
they  are  confined,  that  is  most  strongly  illuminated.  That  they 
are  able  to  appreciate  the  presence  of  light  is  therefore  indubitable  ; 
yet  with  what  organs  do  they  perceive  it  ?  We  are  driven  to  the 
supposition  that,  in  this  case,  the  sense  of  touch  supplies  to  a  certain 
extent  the  want  of  other  senses,  and  that  the  hydrse  are  able,  as 

*  Trembley,  Memoires  pour  servir  a  l’Histoire  des  Polypes  d'eau  douce.  Leyde, 
1744. 


ON  POLYPS. 


23 


an  Italian  author  elegantly  expresses  it,  palpare  la  luce,”  to  feel 
the  light. 

(29.)  The  tentacles  placed  around  the  mouth  are  eminently  sensi¬ 
tive,  and  the  smallest  particles  which  impinge  upon  those  organs  in 
their  expanded  state  appear  to  excite  a  perception  of  their  presence  ; 
yet  their  movements,  as  well  as  those  of  the  whole  body,  are  extremely 
slow  and  languid  :  it  wTould  be  difficult  therefore  to  imagine  that 
creatures  apparently  so  helpless  should  be  able  to  obtain  other 
prey  than  such  as  had  no  power  of  resistance  ;  and  we  could  scarcely 
believe,  were  it  not  a  matter  of  continual  observation,  that  the  most 
active  little  animals,  entomostraca,  the  larvae  of  insects,  and  even 
minute  fishes,  form  their  usual  food. 

When  the  hydra  is  watching  for  prey,  it  remains  expanded, 
(fig-  4,  1,  2, 5,)  its  tentacula  widely  spread  and  perfectly  motionless, 
waiting  patiently  till  some  of  the  countless  beings  which  populate  the 
stagnant  waters  it  frequents,  are  brought  by  accident  in  contact 
with  them :  no  sooner  does  an  animal  touch  one  of  the  filaments 
than  its  course  is  arrested  as  if  by  magic  ;  it  appears  instantly  fixed 
to  the  almost  invisible  thread,  and  in  spite  of  its  utmost  efforts  is 
unable  to  escape  ;  the  tentacle  then  slowly  contracts,  and  others  are 
brought  in  contact  with  the  struggling  prey,  which  thus  seized  is 
gradually  dragged  towards  the  orifice  of  the  mouth,  that  opens  to 
receive  it,  and  slowly  forced  into  the  interior  of  the  stomach. 

(30.)  We  are  naturally  led  to  ask,  what  is  the  nature  of  the  action 
by  which  a  passing  animal  is  thus  seized  ?  Trembley  supposed  that 
the  filamentary  arms  were  besmeared  with  an  adhesive  secretion 
like  bird-lime,  by  which  the  victim  became  glued  to  the  tentacle  ; 
this  however  can  hardly  be  the  case,  as  the  exercise  of  the  power  of 
retaining  prey  seems  quite  under  the  control  of  the  hydra  :  when 
hungry,  seven  or  eight  monoculi *  will  be  captured  and  swallowed  in 
succession  ;  but  when  thus  gorged  with  prey,  or  when  indisposed  to 
take  food,  although  these  animals  may  touch  the  tentacula  again 
and  again,  they  escape  with  impunity. 

(31.)  Arrived  in  the  stomach  of  the  polyp,  the  animal  which  has 
been  swallowed  is  still  distinctly  visible  through  the  transparent 
body  of  the  hydra,  which  seems  like  a  delicate  film  spread  over  it : 
(Jig.  4,  4,)  gradually  the  outline  of  the  included  victim  becomes 
indistinct,  and  the  film  which  covers  it  turbid  ;  the  process  of  diges¬ 
tion  has  begun  ;  the  soft  parts  are  soon  dissolved  and  reduced  to  a 


*  Minute  crustaceous  animals,  possessing  considerable  strength  and  agili‘y* 


24 


ON  POLYPS. 


fluid  mass,  and  the  shell  or  hard  integument  is  expelled  through  the 
same  aperture  by  which  it  entered  the  stomach. 

W e  will  not  even  hazard  a  conjecture  concerning  the  process  by 
which  digestion  is  effected  in  this  case,  our  knowledge  of  animal 
physiology  is  by  no  means  sufficiently  advanced  to  render  any 
attempt  at  explanation  useful ;  we  will  rather  pass  on,  and  enquire 
in  what  manner  the  nutritious  parts  of  the  food  are  conveyed  into 
the  system  of  the  polyp.  We  have  already  observed  that  no 
traces  of  vessels  of  any  kind  have  as  yet  been  detected  in  the 
granular  parenchyma  of  which  the  creature  seems  to  be  composed ; 
coloured  globules  are  seen  floating  in  a  transparent  fluid,  which,  in 
the  Hydra  viridis ,  are  green_,  although  in  other  species  they 
assume  different  tints.  When  the  food  has  been  composed 
of  coloured  substance,  as,  for  example,  red  larvae,  or  black 
planarice ,  the  granules  of  the  body  are  seen  to  acquire  a  simi¬ 
lar  hue,  but  the  fluid  in  which  they  float  remains  quite  trans¬ 
parent  ;  each  granule  seems  like  a  little  vesicle  into  which 
the  coloured  matter  is  conveyed,  and  the  dispersion  of  these 
globules  through  the  body  gives  to  the  whole  polyp  the  hue  of 
the  prey  which  it  has  devoured ;  sometimes  the  granules  thus 
tinted  are  seen  to  be  forced  into  the  tentacula,  from  whence 
they  are  driven  again  by  a  sort  of  reflux  into  the  body,  pro¬ 
ducing  a  kind  of  circulation  or  rather  mixing  up  of  the  granular 
matter  which  distributes  it  to  all  parts.  If,  after  having  thus 
digested  coloured  prey,  the  polyp  is  made  to  fast  for  some  time, 
the  vesicles  gradually  lose  their  deepened  hue  and  become  com¬ 
paratively  transparent.  The  granules,  therefore,  would  seem  to 
be  specially  connected  with  the  absorption  and  distribution  of 
nutriment. 

(82.)  Rapid  as  is  the  action  of  the  stomach  upon  food  introduced 
into  it,  it  has  no  effect  upon  other  parts  of  the  animal  when  immersed 
in  its  cavity  :  the  arms,  for  example,  of  the  long-armed  hydra  are 
frequently  coiled  around  its  prey  during  the  process  of  its  solution, 
without  receiving  the  slightest  injury.  This  circumstance  may 
not  appear  very  remarkable,  but  it  has  been  found  that  other 
polyps  of  the  same  species  are  equally  able  to  resist  the  solvent 
action.  Trembley  once  saw  a  struggle  between  two  of  these 
creatures  which  had  seized  upon  the  same  animal ;  both  had  partially 
succeeded  in  swallowing  it,  when  the  largest  put  au  end  to  the 
dispute  by  swallowing  its  opponent  as  well  as  the  subject  of  con¬ 
tention.  Trembley  naturally  regarded  so  tragical  a  termination 


ON  POLYPS. 


25 


of  tlie  affray  as  the  end  of  the  swallowed  polyp’s  existence,  but  he 
was  mistaken  ;  after  the  devourer  and  his  captive  had  digested 
the  prey  between  them,  the  latter  was  regurgitated  safe  and  sound, 
and  apparently  no  worse  for  the  imprisonment. 

(S3.)  W e  will  now  proceed  to  consider  the  mode  of  reproduction  of 
these  simple  animals.  When  mature  and  well  supplied  with  food, 
minute  gemmules  or  buds  are  seen  to  become  developed  from  the 
common  substance  of  the  body  ;  they  spring  from  no  particular 
part,  but  seem  to  be  formed  upon  any  portion  of  the  general  sur¬ 
face.  These  gemmae  appear  at  first  like  delicate  gelatinous  tu¬ 
bercles  upon  the  exterior  of  the  parent  polyp  ;  but,  as  they  increase 
in  size,  they  gradually  assume  a  similar  form,  become  perforated  at 
their  unattached  extremity,  and  develope  around  the  oral  aperture 
the  tentacula  characteristic  of  their  species. 

During  the  first  period  of  the  formation  of  these  sprouts,  they 
are  evidently  continuous  with  the  general  substance  from  which 
they  arise ;  and  even  when  considerably  perfected,  and  possessed  of 
an  internal  cavity  and  tentacula,  their  stomach  freely  communicates 
writh  that  of  their  parent  by  a  distinct  opening,  so  that  food 
digested  by  the  latter  passes  into  the  stomach  of  the  young  one, 
and  serves  to  nourish  it.  As  soon  as  the  newly-formed  hydra  is 
capable  of  catching  prey,  it  begins  to  contribute  to  the  support  of 
its  parent ;  the  food  which  it  captures  passing  through  the  aperture 
at  its  base  into  the  body  of  the  original  polyp.  At  length,  when 
the  young  is  fully  formed  and  ripe  for  independent  existence,  the 
point  of  union  between  the  two  becomes  more  and  more  slender, 
until  a  slight  effort  on  the  part  of  either  is  sufficient  to  detach 
them,  and  the  process  is  completed. 

This  mode  of  increase,  when  the  animals  are  well  supplied  with 
nourishment,  and  the  temperature  is  favourable,  is  extremely  rapid  ; 
sometimes  six  or  seven  gemmae  have  been  observed  to  sprout  at  once 
from  the  same  hydra,  and,  although  the  whole  process  is  concluded 
in  twenty-four  hours,  not  unfrequently  a  third  generation  may  be 
observed  springing  from  the  newly-formed  polyps  even  before 
their  separation  from  their  parent :  eighteen  have  in  this  manner 
been  seen  united  into  one  group,  so  that,  provided  each  individual 
when  complete  exhibited  equal  fecundity,  more  than  a  million 
might  be  produced  in  the  course  of  a  month  from  a  single  polyp. 

(34.)  But  perhaps  the  most  remarkable  feature  in  the  history 
of  the  hydra  is  its  power  of  being  multiplied  by  mechanical 
division.  If  a  snip  be  made  with  a  fine  pair  of  scissors  in 


26 


ON  POLYPS. 


tlie  side  of  one  of  these  creatures,  not  only  does  the  wound  soon 
heal,  but  a  young  polyp  sprouts  from  the  wounded  part ;  if  it  be 
cut  into  two  portions  by  a  transverse  incision,  each  soon  deve- 
lopes  the  wanting  parts  of  its  structure  ;  if  longitudinally  di¬ 
vided,  both  portions  soon  become  complete  animals ;  if  even  it 
be  cut  into  several  parts,  every  one  of  them  will  rapidly  assume  the 
form  and  functions  of  the  original ;  the  inversion  of  its  body,  by 
turning  it  inside  out,  does  not  destroy  it ;  on  the  contrary,  the  ex¬ 
terior  surface  assumes  the  office  of  a  stomachal  cavity,  and  that 
which  was  originally  internal  will  give  birth  to  buds,  and  take 
upon  itself  all  the  properties  of  the  skin. 

(35.)  Cortical  compound  Polyps. — From  what  we  have  said  con¬ 
cerning  the  two  preceding  families  of  polyps, —  one  composed  of 
animals  consisting  entirely  of  a  gelatinous  crust  which  invests  a  fixed 
and  immoveable  skeleton  ;  the  other  exhibiting  active  and  hungry 
creatures,  provided  with  an  internal  digestive  cavity,  and  endowed 
with  the  capability  of  seizing  and  devouring  living  prey, — we  are 
prepared  to  examine  the  more  complex  structure  of  compound 
polyps,  which  combine  in  themselves  the  characteristics  of  both 
families.  The  compound  polyps  consist  of  a  mass  of  gelatinous 
matter,  which  indicates,  by  its  power  of  contraction  upon  the  appli¬ 
cation  of  stimuli,  a  degree  of  sensation  ;  and  of  a  great  number  of 
hydrseform  polyps,  which  spring  from  the  surface  of  the  common 
body,  and  are  individually  capable  of  seizing  and  digesting  prey, 
the  nutriment  thus  gained  being  appropriated  to  the  nourishment  of 
the  general  mass.  The  animals  of  this  division  are  provided  with 
numerous  mouths  and  stomachs,  each  endowed  with  a  power  of 
independent  action. 

Although  essentially  similar  in  their  habits,  the  compound 
polyps  present  various  modifications  of  structure,  which  natu¬ 
rally  leads  them  to  be  grouped  in  distinct  families.  Some¬ 
times  the  central  common  mass  is  entirely  soft  and  gelatinous, 
its  surface  being  covered  with  minute  cells  in  which  the  polyps 
are  lodged ;  such  are  the  Alcyonidce.  Sometimes  the  common 
body  secretes  large  quantities  of  calcareous  matter  in  the  same  man¬ 
ner  as  the  Fungia ,  which,  being  deposited  in  its  interior,  forms 
arborescent  masses,  presenting  upon  their  surface  multitudes  of 
cells,  generally  distinguishable  after  the  removal  of  the  outer 
crust,  in  each  of  which  when  alive  a  polyp  existed  :  these  form 
the  family  of  Madrepores .  The  central  axis  is  not  unfrequently 
quite  solid  and  smooth  upon  the  surface,  offering  no  cells  for  the 


ON  POLYPS. 


lodgment  of  tlie  hydrseform  mouths  ;  being  sometimes  composed  of 
hard  and  dense  calcareous  substance,  or  else  flexible  and  horny  in 
its  texture  :  such  are  the  Corallida  or  family  of  corals,  properly  so 
called.  The  internal  central  axis  is,  moreover,  in  another  family, 
composed  of  several  pieces  united  together  by  the  living  crust 
which  secretes  them ;  and  such  individuals,  being  free  and  unat¬ 
tached,  are  probably  able  to  change  their  position  at  pleasure : 
these  form  the  family  of  Pennatula .  These  groups  are,  however, 
merely  modifications  of  the  same  general  type  of  structure,  although 
differing  in  certain  minor  points  of  their  organization,  so  as  to  render 
an  examination  of  each  form  needful  for  our  purpose. 

(36.)  Alcyonidce. — This  family  includes  several  genera,  known  by 
the  names  of  Alcyonium,  Lobularia,  Cydonium,  & c.,  being  charac¬ 
terized  by  having  no  solid  axis  developed  in  the  interior  of  the  com¬ 
mon  body.  The  Cydonium 
Mulleri  ( fig .  5,  1,)  will  give 
the  reader  a  good  idea  of  the 
general  appearance  of  one  of 
these  compound  animals.  The 
central  mass,  or  polypary,  is 
entirely  soft,  being  of  a  gelati¬ 
nous  or  rather  subcartilagi- 
nous  texture.  Its  density  varies 
with  the  state  of  the  animal, 
being  more  firm  when  the  crea¬ 
ture  is  contracted  or  hardened 
by  immersion  in  spirits  of 
wine,  than  when  alive  and  ex¬ 
panded.  Upon  cutting  into 
it,  it  is  found  to  be  intersected 
by  tough  fibrous  bands,  and 
not  unfrequently  contains  calcareous  spicula  dispersed  through  its 
substance ;  no  muscular  fibre  or  nervous  matter  has  ever  been  de¬ 
tected  in  its  composition,  and  its  interior  is  permeated  by  nume¬ 
rous  wide  canals  variously  disposed.  The  alcyonidse,  therefore,  may 
justly  be  looked  upon  as  intimately  related  to  the  sponges  in  the 
structure  of  their  common  body,  differing  from  them  principally  in 
the  polyps  which  occupy  the  cells  upon  their  surface. 

(37.)  The  polyps  which  fill  these  cells  resemble  so  many  hydra,  in 
their  external  configuration,  from  which,  however,  they  differ  in  the 
number  of  tentacula  surrounding  the  mouth.  In  the  hydra  we 


Fig.  5. 

1 


28 


ON  POLYPS. 


find  sometimes  five,  sometimes  six,  or  more  of  these  appendages ; 
but  in  all  the  cortical  polyps  there  are  eight.  The  tentacles,  also, 
are  not  unfrequently  pinnated  or  slightly  fringed  on  each  side,  but 
never  provided  with  moveable  cilia.  The  body  of  the  polyp,  when 
withdrawn  from  its  cell,  is  somewhat  globular,  and  more  complex 
in  its  structure  than  that  of  the  hydra.  In  Jig .  5,  2,  a  diagram  is 
given,  representing  the  Alcyonium  exos ,  in  which  the  following 
parts  may  be  distinguished.  The  stomach*  is  considerably  dilated, 
and  terminates  inferiorly  in  a  tubular  prolongation,  6,  which  ex¬ 
tends  into  the  substance  of  the  common  mass,  into  which  it  most 
probably  conveys  nourishment.  But  the  main  difference  observ¬ 
able  between  the  alcyonidse  and  the  hydra  consists  in  the  possession 
of  a  reproductive  organ  or  ovary,  in  which  the  germs  of  its  progeny 
are  developed.  This  consists  of  a  tubular  filament,  c,  lodged  in 
the  cell  which  the  polyp  inhabits,  which  opens  by  one  extremity 
into  the  bottom  of  the  stomach,  into  which  the  ova  when  mature 
are  conveyed,  and  they  are  ultimately  ejected  through  the  mouth, 
«,  as  represented  in  the  figure. 

(38.)  Few  objects  exhibit  to  the  naturalist  a  more  beautiful  spec¬ 
tacle  than  the  compound  animals  of  which  we  are  speaking.  When 
found  upon  the  shore  contracted  and  deformed,  it  would  be  diffi¬ 
cult  to  imagine  that  they  were  really  organized  beings,  much  less 
possessed  of  the  elaborate  conformation  we  have  described  ;  yet,  on 
placing  one  of  them  in  a  tumbler  of  sea-water,  and  watching  it 
attentively  with  a  magnifying  glass,  its  true  nature  is  gradually  re¬ 
vealed  :  the  central  mass  expands  in  all  directions,  exhibiting  the 
cells  upon  its  surface,  from  which  in  time  the  countless  flower-like 
polyps  are  protruded,  and,  stretching  out  their  arms  in  all  directions, 
wait  for  the  approach  of  prey.  A  scene  like  this  naturally  leads  us 
to  make  a  few  observations  upon  some  points  of  physiology  con¬ 
nected  with  their  economy  :  several  questions  obtrude  themselves 
upon  us,  which,  although  applicable  to  the  whole  group  of  com¬ 
pound  polyps,  may  be  well  discussed  in  this  place. 

(39.)  That  there  is  a  community  of  nutrition, — or,  in  other  words, 
that  food  taken  and  digested  by  the  individual  polyps  is  appropriated 
to  the  support  of  the  general  body, — appears  to  be  indisputable,  and 
is  generally  admitted  ;  but  is  there  a  community  of  sensation  so  as  to 
render  the  entire  mass  one  animal,  capable  of  consentaneous  move¬ 
ments,  or  is  each  polyp  independent  of  the  rest  in  its  sensations 
and  actions  ?  Upon  this  there  are  different  opinions  :  some  regard- 
*  Spix  (Jean),  Memoire  pour  servir  a  I’histoire  de  rAlcyonium  exos. 


ON  POLYPS. 


29 


ing  the  whole  as  a  single  animal,  each  part  being  in  communication 
with  the  rest,  and  thus  participating  in  the  feelings  and  movements 
of  the  others  ;  whilst  some  consider  each  polyp  as  a  distinct  crea¬ 
ture,  independent  of  the  rest.  The  solution  of  this  problem  is 
a  matter  of  some  difficulty ;  but  there  are  several  facts  recorded  by 
observers,  which  may  in  some  measure  enlighten  us  upon  the  sub¬ 
ject.  From  the  absolute  want  of  nervous  filaments,  which 
might  bring  into  communication  distant  points  of  the  body, 
we  might  theoretically  deny  the  possibility  of  any  combina¬ 
tion  of  actions  ;  and  experiment  teaches  us  that  the  assumption 
is  correct. 

If  when  one  of  these  animals  is  fully  expanded,  transparent  and 
soft,  any  point  of  its  surface  be  rudely  touched,  the  whole  body 
does  not  immediately  shrink,  but  the  point  only  where  the  irrita¬ 
tion  was  applied  appears  to  feel  the  impression  ;  this  part  shortly 
becomes  more  dense,  opaque,  and  a  depression  is  seen  gradually  to 
appear.  If  the  shock  be  severe,  and  extensively  diffused  over  the 
body,  the  contraction  slowly  extends  to  the  whole  mass ;  the  most 
violent  local  injury,  indeed,  seems  to  be  totally  unperceived  at  re¬ 
mote  parts  of  the  body  :  whilst  a  general  shock,  such  as  striking  the 
vessel  which  contains  the  expanded  polyp,  produces  a  simultaneous 
contraction  of  the  whole.*  The  polyps,  however,  exhibit  much 
greater  irritability,  and  their  movements,  from  their  rapidity,  form 
a  striking  contrast  to  the  languid  contractions  of  the  connecting 
central  mass  ;  but  that  they  have  a  community  of  life  appears  im¬ 
probable  :  they  seem  to  act  quite  independently  of  each  other ; 
when  one  is  touched  and  suddenly  retracts  itself  within  its  cell,  it 
is  true  that  those  in  the  neighbourhood  will  likewise  not  unfre- 
quently  retire,  but  this  circumstance  may  be  accounted  for  by  the 
sudden  movement  of  their  neighbour  ;  for,  as  the  polyps  often  touch 
each  other  with  their  tentacles,  there  is  no  cause  for  urging  a  com¬ 
munity  of  substance  to  explain  it.j* 

(40.)  Maclreporidce. — Were  we  to  imagine  one  of  the  alcyonidse 
capable  of  secreting  not  merely  the  calcareous  spicula  which  are 
mixed  up  with  the  softer  portions  of  its  body,  but  abundant  quan¬ 
tities  of  carbonate  of  lime,  which,  being  stored  up  in  the  centre  of 
its  substance,  should  form  a  dense  calcareous  axis  encrusted  with 
the  uncalcified  part  of  the  living  animal,  and  perforated  at  its  sur- 

*  Professor  Grant,  Lectures  on  Comparative  Anatomy,  —  Lancet  for  1833-4, 
vol.  ii.  p.  261. 

t  Quoy  et  Gaimard,  Zoologie  du  Voyage  de  rilranie.  Paris,  1834. 


30 


OX  POLYPS. 


face  so  as  to  form  innumerable  cells  or  lodges  containing  the 
polyps  which  provide  nourishment  for  the  general  mass,  we  should 
have  a  good  general  idea  of  the  structure  of  the  tribe  of  polyps 
which  now  comes  beneath  our  notice. 

The  shallower  parts  of  the  tropical  seas  contain  countless  forms 
of  madrepores,  known  to  us,  unfortunately  but  too  often,  only  by 
the  earthy  skeletons  which  the  beauty  of  their  appearance  induces 
the  mariner  to  bring  to  our  shores.  These  calcareous  masses 
assume  more  or  less  an  arborescent  appearance,  spreading  to  a 
considerable  extent,  so  as  to  cover  the  bottom  of  large  tracts  of  the 
ocean,  and  not  unfrequently  they  play  an  important  part  in  pro¬ 
ducing  geological  changes  which  are  continually  witnessed  in  the 
regions  where  they  are  abundant. 

(41.)  The  extent  of  our  knowledge  of  the  animals  themselves  is, 
unfortunately,  but  very  limited.  That  the  entire  skeleton,  whatever 
its  form,  is  encrusted  with  living  substance  ;  that  the  cells  contain 
polyps,  resembling  more  or  less  those  of  the  alcyonidse,  and  which 
provide  for  the  nutrition  of  the  whole, — is  pretty  much  the  extent 
of  our  information  concerning  them  :  and  should  the  scientific 
naturalist  ever  be  placed  in  circumstances  where  he  can  more  closely 
examine  them  in  their  living  state,  there  is  scarcely  a  department 
of  science  in  which  his  labours  could  be  more  beneficially  employed 
than  in  the  investigation  of  their  structure  and  history. 

(42.)  That  the  madrepores,  from  the  immense  masses  of  chalky 
material  which  they  accumulate  in  the  regions  inhabited  by  them,  not 
unfrequently  become  the  cause  of  excessive  danger  to  the  mariner, 
by  raising  the  bottoms  of  the  shallow  seas  which  they  frequent,  so 
as  to  render  regions  once  covered  with  deep  water  no  longer  navi¬ 
gable,  or  filling  up  by  their  accumulation  the  bays  and  harbours  of 
the  South  Seas, — is  undeniable;  and  a  knowledge  of  this  fact  justly 
makes  the  navigator  cautious  in  passing  through  the  localities  where 
they  most  abound.  Yet  the  imagination  of  authors  has  not  seldom 
far  exceeded  the  truth  in  detailing  the  circumstances  connected  with 
them.  That  the  harbour  of  Tinian,  so  extolled  in  the  Voyages  of 
Lord  Anson  and  others,  is  now  choked  up  with  the  skeletons  of 
madreporegynous  polyps,  is  readily  credited ;  that  islands  are  gra¬ 
dually  formed,  where  none  existed,  by  the  agency  of  these  creatures, 
is  equally  authenticated ;  and  that  madrepores  are  found  in  strata 
much  elevated  above  the  level  of  the  seas  in  the  neighbourhood,  is 
a  fact  attested  by  many  voyagers.  Yet  when  we  are  told  of  coral 
reefs,  some  hundred  miles  in  length,  entirely  formed  by  the  agency 


ON  POLYPS. 


31 


of  these  apparently  insignificant  creatures, — of  perpendicular  cliffs 
rising  from  immense  depths,  which  are  altogether  the  produce  of 
their  secretions, — we  have  only  to  turn  to  the  details  in  our  posses¬ 
sion,  concerning  their  habits  and  mode  of  increase,  to  assure  us  of 
the  inaccuracy  of  such  statements.*  In  the  hot  climates  in  which 
the  saxigenous  corals  abound,  they  are  found  to  frequent  shallow 
bays  and  sheltered  spots,  where  they  can  enjoy  the  full  influences 
of  light  and  air,  unexposed  to  the  agitation  of  the  ocean,  which, 
were  it  to  beat  continually  upon  them,  would  infallibly  destroy 
their  delicate  substance :  in  such  situations,  the  sub-marine  rocks 
become  gradually  encrusted  with  the  calcareous  skeletons  which 
they  produce ;  and  if  undisturbed,  in  the  lapse  of  years,  successive 
generations  will  of  course  deposit  such  large  quantities  of  calcareous 
matter  as  to  form  beds  of  considerable  thickness.  That  there  are 
at  the  bottom  of  the  ocean  bold  and  precipitous  cliffs,  rising  from  a 
depth  of  1000  or  1200  feet,  their  broad  tops  approximating  the 
surface  of  the  ocean,  every  one  will  admit,  without  having  recourse 
to  the  labours  of  madrepores  to  account  for  their  formation,  although 
the  sheltered  portions  of  the  summits  of  such  mountain  ridges 
afford  an  eligible  position  for  their  increase.  In  such  situations, 
therefore,  they  accumulate,  and  slowly  deposit  continually  increas¬ 
ing  masses  of  earth  upon  the  brow  of  these  sub-marine  mountains, 
until  at  last  the  pile  approaches  the  surface  of  the  sea,  and  even  at 
low  water  remains  uncovered  by  the  waves.  The  further  elevation 
of  the  rock,  as  far  as  the  polyps  are  concerned  in  its  construction,  here 
ceases  ;  but  a  variety  of  causes  tends  gradually  to  heap  materials 
upon  the  newly  appearing  island  :  storms,  which  tear  up  the  bottom 
of  the  sea,  perpetually  throw  to  the  surface  sand  and  mud  ;  which 
becoming  entangled  among  the  madrepore,  and  matted  together 
with  sea-weed,  forms  a  solid  bed  over  which  the  waves  have  no 
longer  any  power.  The  circumference  of  the  islet  is  perpetually 
augmented  by  the  same  agency :  sea-weeds  and  vegetable  sub¬ 
stances  cast  upon  it,  by  their  decay  cover  its  top  with  vegetable 
mould ;  and  if  its  proximity  to  other  land  permit  the  united  action 
of  winds  and  currents  to  bring  the  germs  of  vegetation  from  neigh¬ 
bouring  coasts,  they  take  root  in  the  fresh  soil,  and  soon  clothe  with 
verdure  a  domain  thus  rescued  from  the  ocean. 

(43.)  The  coasts  described  by  Cook  and  Bougainville,  whereon 
strata  of  coral  are  found  much  elevated  above  the  level  of  the  sea, 
are  undoubtedly  of  volcanic  origin.  The  bottom  of  the  ocean, 

*  Quoy  etGaimard,  Op.  cit. 


ON  POLYPS. 


32 

crusted  over  by  thick  masses  of  madrepore,  has  been  suddenly 
heaved  up  by  one  of  those  stupendous  convulsions  of  nature,  pro¬ 
bably  produced  by  the  sea  finding  its  way  into  some  sub-marine 
volcano ;  and  rocks  and  corals,  raised  from  their  beds  by  the  tre¬ 
mendous  explosion  so  produced,  give  birth  to  islands  and  elevated 
tracts  of  country,  such  as  are  met  with  in  the  South  Seas. 

Cor allidje. — The  Corallidse  are  compound  polyps  of  appa¬ 
rently  more  perfect  organization  than  those  forming  the  last  family. 
The  polypary  or  central  axis,  which  supports  the  external  or  living 
crust,  is  solid,  without  cells,  and  variously  branched  ;  the  larger 
species  resembling  shrubs  of  great  beauty,  frequently  coloured  with 
lovely  hues,  and  studded  over  their  whole  surface  with  living 
flowers,  for  such  the  polyps  which  nourish  them  were  long  consi¬ 
dered  even  by  scientific  observers.  The  central  stem  of  these 
zoophytes  differs  much  in  its  composition  in  different  families ; 
sometimes  being  of  stony  hardness,  in  other  cases  it  is  soft  and 
flexible,  resembling  horn  ;  and  not  unfrequently  it  is  formed  of  both 
kinds  of  material  :  it  is  however  always  produced  by  the  living 
cortex,  which  secretes  it  in  concentric  layers,  the  external  being 
the  last  deposited. 

The  example  which  we  shall  select  for  special  description  is  the 
Coral  of  commerce,  Corallium  rubrum ,  (Jig.  6.)  from  which  we 
derive  the  material  so  much  prized  in 
the  manufacture  of  ornaments. 

(44.)  The  red  coral  is  principally 
obtained  in  the  Mediterranean.  When 
growing  at  the  bottom  of  the  sea,  it 
consists  of  small  branched  stems,  en¬ 
crusted  with  a  soft  living  investment, 
by  which  the  central  axis  is  secreted, 
and  studded  at  intervals  with  polyps 
possessing  eight  fringed  arms,  and 
capable  of  being  contracted  into 
cells  contained  in  the  fleshy  covering, 
but  not  penetrating  the  stem  itself. 

The  skeleton  or  polypary  of  the  coral  is  of  extreme  hardness,  and 
susceptible  of  a  high  polish  ;  a  circumstance  to  which  the  estima¬ 
tion  in  which  it  is  held  is  principally  owing.  But  in  other 
genera  of  this  family,  the  central  axis,  instead  of  being  con¬ 
structed  of  calcareous  matter,  is  formed  of  concrete  albumen,  and 
resembles  horn  both  in  appearance  and  flexibility  ;  such  are  the 


ON  POLYPS. 


33 


Fig.  7. 


Gorgon iee  of  tlie  Indian  Ocean.  In  the  Isis  Hippuris  (jig.  7,  B) 
the  central  axis  is  alternately  composed  of  both  these  substances, 
exhibiting  calcareous  masses  united  at  intervals  by  a  flexible  mate¬ 
rial,  allowing  the  stem  to  bend  freely  in  every  direction.  The 
object  of  such  diversity  in  the  texture  of  the  polypary  of  the  Coral- 
hdce  will  be  at  once  apparent  when  we  consider  the  habits  of  the 
different  species  :  the  short  and  stunted  trunks  of  Cor  allium , 
composed  of  hard  and  brittle 
substance,  are  strong  enough 
to  resist  injuries  to  which  they 
are  exposed ;  but  in  the  tall 
and  slender  stems  of  Gor- 
gonia  and  Isis ,  such  brittle¬ 
ness  would  render  them  quite 
inadequate  to  occupy  the  si¬ 
tuations  in  which  they  are 
found,  and  the  weight  of 
the  waves  falling  upon  their 
branches  would  continually 
break  in  pieces  and  destroy 
them  ;  this  simple  modifica¬ 
tion,  therefore,  of  the  nature 
of  the  secretions  with  which 
they  build  up  the  skeleton 
which  supports  them  allows, 
them  to  bend  under  the  passing  waves,  and 
otherwise  inevitable  destruction. 


secures  them  from 


(45.)  Upon  making  a  transverse  section  of  one  of  these  poly¬ 
paries,  (Jig.  7,  A,)  the  solid  axis  is  distinctly  seen  to  be  made  up 
of  layers  arranged  in  a  somewhat  undulating  manner  around  the 
centre,  and  successively  deposited  by  the  living  cortex  :  the  growth 
of  the  stem,  in  the  harder  species  at  least,  is  very  slow,  and  several 
years  are  necessary  to  its  maturity ;  a  circumstance  which  has  ren¬ 
dered  it  needful  to  impose  strict  laws,  forbidding  the  Mediterranean 
coral-fishers  to  disturb  too  frequently  the  same  localities,  which  are 
only  visited  at  stated  periods. 

(46.)  The  deposition  of  solid  matter  in  the  soft  bodies  of  these 
polyps  is  not  confined  to  the  production  of  the  central  stem,  but  in 
many  even  of  the  Keratophyta*  cretaceous  particles  are  extensively 


*  An  old  name  for  polyps  with  a  horny  axis,  horn ;  (fnirov,  a  stem  ;  as  distin¬ 

guishing  them  from  the  stony  polyps,  Liihophytci,  Xdo;,  a  stone  ;  Qurov. 


D 


ON  POLYPS. 


34 

diffused  through  the  cortex,  which  not  unfrequently  is  likewise 
gorgeously  coloured  by  secretions  of  different  hues.  In  the  Gor- 
gonise,  a  section  of  one  of  which  ( Gorgonia  verrucosa)  is  repre¬ 
sented  in  Jig.  7,  A,  the  earthy  matter  in  the  crust  is  so  abundant, 
that,  even  when  dried,  it  will  retain  in  some  measure  its  natural 
form,  and  exhibit  the  tints  peculiar  to  the  species. 

The  structure  of  the  individual  polyps  of  the  Corallidae,  as  far 
as  we  are  acquainted  with  their  history,  resembles  that  of  one 
of  the  polyps  of  the  Alcyonidse  already  described  (§36)  ;  and  the 
prey  obtained  by  each,  goes  to  the  support  of  the  general  mass. 
Their  reproduction  is  undoubtedly  from  germs  developed  in  in¬ 
ternal  filamentary  ovaria,  which  escape  either  through  the  mouth, 
as  in  Alcyonium,  or  else,  as  Cavolini*  supposed,  through  apertures 
placed  between  the  origins  of  the  tentacles. 

(47.)  Pennatulidce. — This  family  belongs  likewise  to  the  divi¬ 
sion  of  cortical  polyps,  and  agrees  with  the  two  last  in  most  points, 
the  principal  distinction  consisting  in  the  character  of  the  internal 
axis  which  supports  the  body.  In  some  species  this  part  is  reduced 
in  fact  to  a  ligamentous  mass,  interspersed  with  calcareous  granules  ; 
but,  in  the  most  typical  forms,  the  skeleton  consists  of  several 
pieces,  capable  of  moving  upon  each  other.  The  whole  animal, 
in  such  cases,  resembles  a  feather,  the  stem  supporting  lateral 
branches,  upon  which  the  polyps  are  arranged.  From  the  circum¬ 
stance  of  these  compound  animals  being  unattached  to  any  foreign 
support,  they  have  been  supposed  to  be  capable  of  swimming  at 
large  in  the  sea,  by  the  voluntary  movements  of  their  articulated 
branches,  a  fact  strongly  contested  by  many  modern  zoologists  ; 
but,  as  we  can  say  nothing  from  our  own  observation  upon  this 
subject,  we  must  leave  the  question  open  to  future  investigation. 
Many  species  are  eminently  phosphoric. 

Tubiporida ?. — We  now  have  to  speak  of  a  class  of  polyps  very 
different  in  their  construction  from  those  which  have  been  described. 
Instead  of  encrusting  an  internal  solid  skeleton,  the  Tubiporidse  are 
enclosed  in  a  calcareous  or  coriaceous  sheath  or  tube,  from  the  ori¬ 
fice  of  which  the  polyp  is  protruded,  when  in  search  of  prey :  these 
are  named  by  authors  Vaginated  Polyps. 

(48.)  The  Tubipora  musica  (Jig.  8,  a)  is  the  species  which  has 
been  most  carefully  studied,  and  the  details  connected  with  its  or¬ 
ganization  will  be  found  of  the  highest  importance,  as  affording  a 

*  Cavolini  (Philippe),  Memorie  per  servire  alia  storia  di  Polipi  marini.  4to.  Naples, 
1785. 


ON  POLYPS. 


35 


clue  to  the  investigation  of  other  forms,  to  be  mentioned  hereafter.* 
The  Tubiporae  live  in  society,  but  do  not  appear  to  be  organically 
united  as  the  compound  polyps;  a  group  of  these  animals  presents 

Fig.  8. 


Fig.  9. 


several  stages  of  tubes,  placed  one  above  another  ;  the  tubes  are  ge¬ 
nerally  straight,  and  nearly  parallel  to  each  other,  but  appear 
slightly  to  diverge,  as  ra¬ 
diating  from  a  common 
centre  ;  they  are  separated 
by  considerable  intervals, 
and  reciprocally  support  each 
other  by  horizontal  laminae 
of  the  same  substance  as 
the  tubes  themselves,  which 
unite  them.  From  each  tube 
issues  a  little  membranous 
animal  of  a  brilliant  grass- 
green  colour,  the  mouth 
being  surrounded  by  eight 
tentacles,  which  are  furnished 
along  their  edges  with  two  or 
three  rows  of  minute  fleshy 
papillae.  Within  the  mouth 
of  the  specimen  examined  by 
M.  Lamouroux,  was  found  an 

*  Anatomie  de  Tubipore  Musical,  par  M.  Lamouroux, — in  the  Zoology  of  Quoy  et 
Gaimard,  Voyage  de  l’Uranie. 

n  2 


SG 


ON  POLYPS. 


oval  membranous  sac,  blit  not  in  sufficient  preservation  to  be 
properly  described.  This  was  most  probably  the  stomach. 

(49.)  Around  this  sac,  alternating  with  the  tentacles,  are  eight 
triangular  filaments,  {Jig.  9;  1  e,)  which  are  at  first  free  and 
floating,  but  they  soon  become  attached  to  a  membrane  which 
lines  the  calcareous  tube  ;  and,  gradually  diminishing  in  size,  they 
extend  through  its  whole  length.  These  filaments  are  analogous 
to  the  ovaries  of  the  Corail  idee  and  Pennatulidee  ;  their  inner  sur¬ 
face,  in  mature  individuals,  is  studded  with  ova  of  different  sizes 
attached  to  them  by  short  pedicles  ( fig .  9  ;  3). 

(50.)  At  the  point  where  the  ovigerous  filaments  reach  the  ten¬ 
tacles,  a  membrane  is  observable  which  assumes  the  shape  of  a 
funnel  when  the  animal  retires  into  its  shell,  and  at  the  open  end 
of  the  funnel  the  membrane  is  seen  to  fold  outwards,  and  become 
continuous  with  the  calcareous  tube;  (Jig.  9  ;  1,5;)  its  inner  sur¬ 
face  indeed  is  prolonged  under  the  form  of  a  thin  pellicle  over  all 
that  part  of  the  interior  of  the  tube  which  is  inhabited  by  the 
polyp,  terminating  at  a  kind  of  diaphragm  composed  of  the  same 
hard  substance  as  the  tube  itself.  The  remains  of  these  diaphragms 
are  found  in  the  interior  of  old  tubes  at  various  distances  from 
each  other. 

The  funnel-shaped  membrane  does  not  terminate  suddenly  at  its 
point  of  junction  with  the  calcareous  tube  ;  the  latter,  indeed,  is  a 
continuation  and  product  of  the  first,  the  calcareous  substance  being 
evidently  deposited  in  this  gelatinous  membrane,  in  the  same  man¬ 
ner  as  phosphate  of  lime  is  deposited  in  the  bones  of  very  young 
subjects,  changing  its  soft  texture  into  hard,  solid  substance.  The 
manner,  therefore,  in  which  this  tube  is  formed,  cannot  be  compared 
to  the  mode  of  formation  of  the  shells  of  Serpulce  or  the  shells  of 
mollusca ;  in  the  latter  case  it  is  a  secretion  from  the  skin,  almost 
an  epidermic  product,  but  in  these  polyparies  there  is  a  real  change 
of  soft  into  solid  substance,  which  is  effected  gradually,  but  not 
deposited  in  layers. 

(51.)  When  the  tube  has  acquired  a  certain  height,  the  animal 
forms  the  calcareous  horizontal  plate  which  unites  it  to  those 
around ;  the  still  membranous  upper  part  of  the  tube  extends 
itself  horizontally  outwards  around  the  aperture,  (Jig.  9  ;  2,  5,) 
doubling  itself  so  as  to  form  a  circular  fold  ;  this  part  of  the 
membrane  is  no  longer  irritable  ;  its  internal  surfaces  unite  so  as 
not  to  interrupt  the  continuity  of  the  tube ;  carbonate  of  lime  is 
gradually  deposited  within  it,  and  soon  a  prominent  partition,  com¬ 
posed  of  two  lam  ell  se,  soldered  together  through  almost  their  entire 


ON  POLYI’S. 


37 


extent,  surrounds  the  tubular  cell.  Generally  many  polyps  of  tlie 
same  polypary  form  these  partitions  at  the  same  time  and  upon  the 
same  plane.  In  this  case  the  gelatinous  margins  of  the  folded  mem¬ 
brane  unite,  no  space  is  left  ;  and  they  ultimately  become  most  inti¬ 
mately  soldered  together,  and  the  solid  plane  or  stage  (fig.  8)  is 
formed.  If  the  animal  constructs  its  partition  against  a  tube  already 
perfect  and  solidified,  it  fixes  its  collar  to  its  sides,  so  that  the  point 
of  junction  is  imperceptible  ;  but  when  it  is  quite  insulated,  as  at  5, 
Jig.  8,  the  horizontal  collar  is  still  formed,  and  it  then  assumes 
somewhat  of  an  octagonal  shape.  The  tube-forming  membrane 
exhibits  no  appearance  of  vessels  or  other  traces  of  organization. 

When  the  polyp  is  withdrawn  within  its  cell,  its  tentacles  form 
a  cylindrical  fasciculus  {Jig.  9,  c)  ;  the  papillae  which  partially  cover 
them  being  laid  upon  each  other  like  the  leaflets  of  some  mimosa 
when  asleep. 

The  protrusion  of  the  creature  from  its  tube  is  accomplished  by 
the  contraction  of  the  membrane,  6,  inserted  into  its  neck. 

(52.)  How  the  eggs  formed  upon  the  oviferous filaments  issue  from 
the  polyp,  has  not  been  ascertained  :  it  is  most  probable,  from  their 
size,  that  they  are  not  expelled  during  the  life  of  the  parent  ;  but 
that,  when  it  dies,  the  eggs  all  come  out  of  the  tube,  except  one, 
which  developes  itself  in  the  old  cell  ;  the  rest  fixing  themselves 
upon  the  neighbouring  stage,  there  to  form  a  new  story  of  tubes. 
The  germs,  during  the  first  period  of  their  developement,  have  no 
organs  distinguishable,  not  even  the  rudiment  of  a  tube  ;  each  ap¬ 
pears  to  consist  of  a  simple  gelatinous  membrane  folded  upon  itself, 
(Jig.  9 ;  4,  c,)  and  forming  upon  the  stage  upon  which  it  is  fixed  a 
little  tubercle  resembling  a  small  Zoanthus  or  other  naked  zoophyte. 
This  tubercle  gradually  elongates,  and  assumes  the  form  of  a  polyp, 
provided  with  all  its  organs ;  but  the  sac  which  encloses  it  is  still 
gelatinous  at  its  upper  part,  and  membranous  near  the  base, 
(Jig.  9  ;  4,  bj  where  it  gradually  diminishes  in  thickness,  and, 
becoming  calcareous,  gives  to  the  animal  the  general  appearance  of 
its  original. 

(53.)  In  Tubularia  indivisa  the  structure  of  the  tentacula  around 
the  mouth  is  different  from  what  has  been  described  in  Tubipora  mu- 
sica,  although  in  the  principal  points  of  its  structure  the  resemblance 
between  the  two  is  very  great ;  when  the  Tubularia  is  expanded,  its 
protruded  portion  is  seen  to  be  furnished  with  two  circles  of  arms, 
one  placed  around  the  opening  of  the  mouth,  the  other  at  a  consi¬ 
derable  distance  beneath  it,  (Jig.  10  ;  1,)  and  nearly  on  a  level  with 
the  inferior  circle  a  second  aperture  (Jig*  10  ;  1,  a)  is  observable, 


38 


ON  POLYPS. 


Fig.  10. 


communicating  with  that  portion  of  the  body  which  is  lodged  within 
the  tube,  and  resembling  a  second  mouth.  A  remarkable  action  has 
been  observed  to  take  place  in  these  parts  of  the  polyp,  producing  a 
continual  variation  in  their  form  ;*  a  fluid  appears  at  intervals  to  be 
forced  from  the  lower  compartment  into  the  space  intervening  be¬ 
tween  the  two  rows  of  tentacula,  which  becomes  gradually  dilated 
into  a  globular  form  (Jig-  10  ;  2  and  3.)  This  distension  continues 
for  about  a  minute,  when  the  upper  part,  contracting  in  turn, 
squeezes  back  the  fluid  which  fills  it  into  the  lower  compartment 
through  the  opening  a ,  which  then  closes  preparatory  to  a  repeti¬ 
tion  of  the  operation.  The  intervals  between  these  actions  were, 
in  the  specimen  observed  by  Mr.  Lister,  very  evenly  eighty 
seconds.  In  Tubularia  indivisa  the  sheath  or  cell,  Z>,  which  en¬ 
closes  the  polyp,  is  perfectly  diaphanous,  allowing  its  contents  to 
be  readily  investigated  under 
the  microscope.  When  thus 
examined,  a  continual  circu¬ 
lation  of  particles  was  visi¬ 
ble,  moving  in  even,  steady 
currents  in  the  direction  of 
the  arrows  (fig.  10;  1)  along 
slightly  spiral  lines  represent¬ 
ed  in  the  drawing.  The  par¬ 
ticles  are  of  various  sizes, 
some  very  minute,  others 
apparently  aggregations  of 
smaller  ones  ;  some  were 
globular,  but  they  had  gene¬ 
rally  no  regular  form.  In 
fig.  3,  d,  a  series  of  longitu¬ 
dinal  lines  are  perceptible, 
which  most  probably  are  ovi- 
gerous  filaments,  resembling 
those  of  Tubipora  musica. 


Actimadoc. —  The  next  family  of  polyps,  from  the  fibrous 
character  which  the  substance  of  their  bodies  assumes,  have  been 
named  by  zoologists  ii  Fleshy  Polyps They  differ  indeed  re¬ 
markably  from  the  soft  gelatiniform  structures  which  have  hitherto 
come  under  our  notice,  exhibiting  traces  of  muscular  fibre  which 
are  not  to  be  mistaken. 


*  Lister,  on  the  structure  and  functions  of  Tubular  and  Cellular  Polypi. — Philoso¬ 
phical  Transactions,  1834. 


ON  POLYPS. 


39 


Fig.  12. 


Although  the  genera  composing  this  division  are  exceedingly 
numerous,  and  vary  much  in  their  external  characters,  they  will 
be  found  more  or  less  to  conform  in  the  essential  points  of  their 
organization  with  the  subject  which  we  have  chosen  as  the  type  of 
this  extensive  tribe,  and  of  which,  being  common  upon  our  own 
coasts,  the  reader  will  have  little  difficulty  in  procuring  specimens 
for  examination. 

(54.)  The  body  of  an  FlS-  ll- 

Actinia  when  moderately 
expanded,  (Jig.  11,)  is  a 
fleshy  cylinder,  attached 
by  one  extremity  to  a 
rock,  or  some  other  sub¬ 
marine  support ;  whilst 
the  opposite  end  is  sur¬ 
mounted  by  numerous 
tentacula,  arranged  in  se¬ 
veral  rows  around  the  oral 
aperture  {fig.  1 2) .  When 
these  tentacula  are  expand¬ 
ed,  they  give  the  animal 
the  appearance  of  a  flower, 
a  resemblance  which  is 
rendered  more  striking  by 
the  beautiful  colours  which 
they  not  unfrequently  as¬ 
sume  ;  and  hence  in  all 
countries  they  have  been 
looked  upon  by  the  vulgar 
as  sea-flowers,  and  distin¬ 
guished  by  names  indica¬ 
tive  of  the  fancied  resem¬ 
blance.  Their  animal  na¬ 
ture  is  however  soon 
rendered  evident  by  a  little  attention  to  their  habits ;  when 
expanded  at  the  bottom  of  the  shallow  pools  of  salt-water  left  by 
the  retreating  tide,  they  are  seen  to  manifest  a  degree  of  sensibility, 
and  power  of  spontaneous  movement,  which  we  should  little  an¬ 
ticipate  from  their  general  aspect.  A  cloud  veiling  the  sun  will 
cause  their  tentacles  to  fold,  as  though  apprehensive  of  danger 
from  the  passing  shadows  :  contact,  however  slight,  will  make 


40 


ON  POLYPS. 


them  shrink  from  the  touch  ;  and  if  rudely  assailed,  they  com¬ 
pletely  contract  their  bodies  so  as  to  take  the  appearance  of  a  hard 
coriaceous  mass,  scarcely  distinguishable  from  the  substance  to 
which  they  are  attached. 

(55.)  It  is  in  seizing  and  devouring  their  prey  however  that  the 
habits  of  the  Actinise  are  best  exemplified  ;  they  will  remain  for 
hours  with  their  arms  fully  expanded  and  motionless,  waiting  for 
some  passing  animal  which  chance  may  place  at  their  disposal,  and 
when  the  opportunity  arrives,  are  little  inferior  to  the  Hydrse  in  their 
voracity  or  powers  of  destroying  their  victims.  Their  food  generally 
consists  of  crabs  or  shell-fish,  animals  apparently  far  superior  to 
themselves  in  strength  and  activity,  but  even  these  are  easily  over¬ 
powered  by  the  sluggish  yet  persevering  grasp  of  their  assailant. 
No  sooner  are  the  tentacles  touched  by  a  passing  animal  than  it  is 
seized,  and  held  with  unfailing  pertinacity  ;  the  arms  gradually 
close  around  it  ;  the  mouth,  placed  in  the  centre  of  the  disc,  ex¬ 
pands  to  an  extraordinary  size  ;  and  the  creature  is  soon  engulph- 
ed  in  the  digestive  bag  of  the  Actinia,  where  the  solution  of  all  its 
soft  parts  is  rapidly  effected,  and  the  hard  undigestible  remnants 
speedily  cast  out  at  the  same  orifice. 

The  Actinim,  although  exceedingly  voracious,  will  bear  long 
fasting  :*  they  may  be  preserved  alive  for  a  whole  year,  or  per¬ 
haps  longer,  in  a  vessel  of  sea-water,  without  any  visible  food  ;  but 
when  food  is  offered,  one  of  them  will  devour  a  crab  as  large  as  a 
hen's  egg,  or  two  muscles  in  their  shells  :  in  a  day  or  two  the 
shells  are  voided  through  the  mouth,  perfectly  cleared  of  the  soft 
parts  which  they  contained. 

(56.)  The  Actinise,  like  the  Hydrse,  possess  the  power  of  chang¬ 
ing  their  position  :  they  often  elongate  their  bodies,  and,  remaining 
fixed  by  the  base,  stretch  from  side  to  side  as  if  seeking  food  at  a 
distance  ;  they  can  even  change  their  place  by  gliding  upon  the 
disc  which  supports  them,  or  detaching  themselves  entirely,  and 
swelling  themselves  with  water,  they  become  nearly  of  the  same 
specific  gravity  as  the  element  which  they  inhabit,  and  the  least 
agitation  is  sufficient  to  drive  them  elsewhere  ;  Reaumur  even 
asserts  that  they  can  turn  themselves  so  as  to  use  their  tentacles  as 
feet,  crawling  upon  the  bottom  of  the  sea  ;  but  this  mode  of  pro¬ 
gression  has  not  been  observed  by  subsequent  naturalists : — when 
they  wish  to  fix  themselves,  they  expel  the  water  from  their  dis- 


*  Encyclopaedia  Londinensis,  art.  Actinia. 


ON  POLYPS. 


41 


tended  body,  and  sinking  to  tlie  bottom  attack  themselves  again 
by  the  disc  at  their  base,  which  forms  a  powerful  sucker. 

(57.)  From  this  sketch  of  the  outward  form  and  general  habits 
of  these  polyps,  the  reader  will  be  prepared  to  examine  their  internal 
economy,  and  the  more  minute  details  of  their  structure.  On  ex¬ 
amining  attentively  the  external  surface  of  the  body,  it  is  seen  to 
be  covered  with  a  thick  mucous  layer  resembling  a  soft  epidermis, 
which  extending  over  the  tentacula,  and  the  fold  around  the  aper¬ 
ture  of  the  mouth,  is  found  to  coat  the  surface  of  the  stomach 
itself ;  this  epidermic  secretion  forms  in  fact  a  deciduous  tunic 
which  the  creature  can  throw  off  at  intervals.  On  removing  this, 
the  walls  of  the  body  are  seen  to  be  made  up  of  fasciculi  of  mus¬ 
cular  fibres,  some  running  perpendicularly  upwards  towards  the 
tentacula  ;  and  others,  which  cross  the  former  at  right  angles,  pass¬ 
ing  transversely  round  the  body  ;  the  meshes  formed  by  this  in¬ 
terlacement  are  occupied  by  a  multitude  of  granules  apparently 
of  a  glandular  nature,  which  give  the  integument  a  tuberculated 
aspect :  these  granules  are  not  seen  upon  the  sucking  disc  at  the 
base.  The  tentacula  are  hollow  tubes,  composed  of  fibres  of  the 
same  description.  The  stomach  is  a  delicate  folded  membrane, 
forming  a  simple  bag  within  the  body  ;  it  seems  to  be  merely  an 
extension  of  the  ex¬ 
ternal  tegument,  some¬ 
what  modified  in  tex¬ 
ture  ;  it  is  closed  infe- 
riorly,  the  same  orifice 
serving  both  for  the  in¬ 
troduction  of  food,  and 
the  expulsion  of  effete 
or  indigestible  matter. 

(58.)  On  making  a 
section  of  the  animal,  as 
represented  in  Jig.  13, 
the  arrangement  of  these 
parts  is  distinctly  seen  : 
a  being  the  muscular 
integument ;  b  the  ten¬ 
tacula  formed  by  the 
same  fibrous  membrane ; 
and  c  the  stomach, 
which  is  apparently  de- 


Fig.  13. 


42 


ON  POLYPS. 


rived  from  it.  Between  tlie  digestive  sac  c,  and  the  fibrous  ex¬ 
terior  of  the  body  a,  is  a  considerable  space  d,  divided  by  a  great 
number  of  perpendicular  fibrous  partitions,  /,  into  numerous  com¬ 
partments,  which  however  communicate  freely  with  each  other,  and 
likewise  with  the  interior  of  the  tentacula,  as  seen  at  e.  Every 
tentacle  is  perforated  at  its  extremity  by  a  minute  aperture  b , 
through  which  the  sea-water  is  freely  admitted  into  these  compart¬ 
ments,  so  as  to  bathe  the  interior  of  the  body  ;  and  when  from 
alarm  the  animal  contracts  itself,  the  water  so  admitted  is  forcibly 
expelled  in  fine  jets  through  the  holes  by  which  it  entered.  There 
can  be  no  doubt  that  the  surrounding  fluid,  thus  copiously  taken 
into  the  body,  is  the  medium  by  which  respiration  is  effected ;  and 
every  one  who  has  been  in  the  habit  of  keeping  Actiniae  in  glass 
vessels  for  the  purpose  of  watching  their  proceedings,  must  have 
noticed  that  as  the  fluid  in  which  they  are  confined  becomes  less 
respirable,  from  the  deficiency  of  air,  the  quantity  taken  into  the 
body  is  enormous,  stretching  the  animal  until  it  rather  resembles 
an  inflated  bladder  than  its  original  shape. 

(59.)  It  is  in  the  compartments  which  are  thus  at  the  will  of  the 
creature  distended  with  water,  that  we  find  the  organs  of  reproduc¬ 
tion,  which  here  assume  a  developement  far  exceeding  what  we  have 
noticed  in  other  zoophytes.  On  raising  a  portion  of  the  mem¬ 
brane  which  forms  the  stomach,  as  at  f9  we  see  lodged  in  each  par¬ 
tition  an  immense  number  of  ova  attached  to  a  delicate  transparent 
membrane,  and  arranged  in  large  clusters,  g.  The  ovigerous  mem¬ 
brane  which  secretes  these  eggs  is  represented  unravelled  at  h  ;  it  is 
through  its  whole  extent  bathed  with  water  admitted  into  the  compart¬ 
ment  in  which  it  is  lodged,  a  circumstance  which  provides  for  the  re¬ 
spiration  of  the  ova  during  their  developement.  The  convoluted  ovary 
is  seen  to  terminate  by  a  minute  aperture  near  the  bottom  of  the  sto¬ 
mach  k ,  into  which  when  mature  the  young  escape.  The  eggs  found  in 
the  ovaria  are  round  and  of  a  yellow  colour,  resembling  minute  grains 
of  sand  :  it  is  probable  that  sometimes  they  are  hatched  after  thfeir  ex¬ 
pulsion,  but  it  is  likewise  asserted  by  numerous  authorities  that  the 
young  are  not  unfrequently  born  alive.  The  manner  in  which  the 
ova  are  extruded  has  been  long  a  matter  of  controversy,  and  perhaps 
cannot  yet  be  regarded  as  definitively  ascertained.  Our  own  dissec¬ 
tions  would  lead  us  to  concur  with  those  anatomists  who  describe 
them  as  escaping  from  the  ovaria  into  the  bottom  of  the  stomach, 
whence  they  have  been  seen  to  escape  by  the  mouth  fully  formed  : 
it  is  possible,  however,  that  they  may  likewise  be  expelled  with  the 


ON  TOLYPS. 


43 


streams  of  water  forced  by  tlie  contractions  of  the  animal  through 
the  orifices  at  the  extremities  of  the  tentacula. 

The  Abbe  Dicquemare#  relates  several  curious  experiments  on 
the  multiplication  of  these  animals  by  mechanical  division.  When 
transversely  divided,  the  upper  portion  still  stretched  out  its  ten¬ 
tacles  in  search  of  food,  which,  when  seized,  sometimes  passed 
through  its  mutilated  body,  but  was  occasionally  retained  and  di¬ 
gested.  In  about  two  months  tentacles  grew  from  the  cut  ex¬ 
tremity  of  the  other  portion,  which  soon  afterwards  began  to  seize 
prey.  By  similar  sections  he  even  succeeded  in  making  an  animal 
with  a  mouth  at  each  end. 

(60.)  The  entire  organization  of  the  Actinia  is  evidently  very  supe¬ 
rior  to  that  of  any  animals  which  have  been  described  in  the  preceding 
pages  ;  the  muscular  fasciculi,  now  for  the  first  time  distinctly  recog¬ 
nisable,  give  an  energy  to  their  contractions  very  different  from  the 
languid  movements  of  the  gelatinous  polyps.  The  Actinia  can  in¬ 
deed  hardly  be  classed  in  the  acrite  division  of  the  animal  kingdom  ; 
the  developement  of  muscular  fibre  which  it  presents,  presupposes 
the  existence  of  nervous  filaments,  and  we  might  a  priori  infer 
their  existence.  Spix,  many  years  ago,  described  a  nervous  sys¬ 
tem,  which  he  believed  he  had  discovered,  in  the  neighbourhood 
of  the  base,  or  sucking  disc  by  which  the  animal  attaches  itself  to 
foreign  bodies  ;  in  which  situation  he  was  led  to  look  for  it,  by  ob¬ 
serving  that  when  galvanic  shocks  were  sent  through  the  body, 
convulsive  movements  were  excited  most  distinctly  in  this  part, — 
and  also  from  the  supposition  that  the  organ  of  attachment,  here 
placed,  must  necessarily  be  the  most  abundantly  endued  with  sen¬ 
sibility.  j* 

Having  raised  the  longitudinal  muscles  by  a  slight  incision  near  the 
middle  of  the  base  or  disc  of  attachment,  he  thought  he  perceived  an 
interlacement  formed  by  some  pairs  of  nodules,  disposed  around  the 
centre,  which  communicated  by  several  cylindrical  threads  ;  from 
each  nodule  two  filaments  ran  forwards,  one  accompanying  the  lon¬ 
gitudinal  fleshy  fasciculi,  the  other  penetrating  to  the  internal 
longitudinal  septa,  which  have  likewise  a  muscular  character.  Suc¬ 
ceeding  anatomists  have,  however,  totally  failed  in  their  endeavours 
to  detect  the  arrangement  here  described  ;  and  which  indeed,  did  it 
exist,  would  be  contrary  to  every  analogy  with  which  we  are  ac¬ 
quainted.  It  is  more  probable  that  the  nervous  system  consists  in 

*  Philosophical  Transactions,  1773. 

t  Spix  (Jean)  Annales  du  Museum,  tome  13. 


44 


ON  POLYPS. 


a  delicate  thread,  which  we  are  pretty  well  convinced  we  have  de¬ 
tected  running  round  the  roots  of  the  tentacles,  embedded  in  a 
strong  circular  band  of  muscle  which  surrounds  the  orifice  of  the 
stomach,  and  acts  the  part  of  a  powerful  sphincter  in  closing  the 
aperture. 

(61.)  After  the  account  which  has  been  given  of  the  general 
structure  of  the  Actinia,  the  mechanism  by  which  the  tentacula  are 
expanded  and  withdrawn  will  be  easily  understood  :  these  do  not, 
like  the  horns  of  a  snail,  become  inverted  and  rolled  up  within  the 
body,  but  owe  their  different  states  of  extension  entirely  to  the 
forcible  injection  of  water  into  the  cavities  which  they  contain.  We 
have  seen  already  that  the  interior  of  each  tubular  arm  communi¬ 
cates  freely  with  the  space  which  intervenes  between  the  stomach 
and  the  external  integument,  a  space  which,  at  the  will  of  the 
animal,  is  filled  with  sea- water  drawn  through  the  orifices  seen  at  the 
extremity  of  each  arm  :  when  these  minute  orifices  are  closed,  and 
the  body  of  the  creature  contracted,  the  water,  being  violently  forced 
into  the  tentacula,  distends  and  erects  them,  as  when  watching  for 
prey ;  and,  on  the  other  hand,  when  emptied  of  the  fluid  thus 
injected,  they  shrink  and  collapse.  This  circumstance,  so  easily 
seen  in  the  Actinise,  will  probably  enable  us  to  account  for  similar 
phenomena  observable  in  other  polyps,  the  internal  economy  of 
which  is  by  no  means  so  conspicuous. 

(62.)  The  next  tribe  of  polyps  which  presents  itself  to  our  notice, 
differs  widely  from  the  preceding  families  in  outward  form,  as  well 
as  in  many  important  features  of  internal  structure.  It  would  seem, 
indeed,  to  comprise  animals  distinguished  from  each  other  by  so 
many  important  circumstances,  and  yet  so  intimately  related  by  ex¬ 
ternal  configuration,  that  it  is  difficult  to  separate  them,  or  to  leave 
them  in  the  same  group. 

It  was  imagined  a  few  years  ago,  before  accurate  researches  had 
been  made  concerning  the  internal  structure  of  these  zoophytes, 
that  in  all  the  compound  species  the  polyps  or  mouths  of  the 
general  mass  were  in  their  essential  structure  analogous  to  the 
Hydra,  being  simple  digestive  sacs,  without  more  complication  of 
structure  than  we  have  found  those  of  the  cortical  polyps  to  possess. 
Recent  investigations,  however,  have  shown  that  amongst  the 
species  ranged  by  Cuvier  under  the  head  of  Tubular  Polyps, 
“  Polypes  a  Tuyaux many  are  exceedingly  complex  in  their 
organization,  possessing  the  outward  form  of  the  simpler  kinds,  but 


ON  FOLYrS. 


45 


furnislied  with  a  complete  digestive  canal,  and  approximating  in 
their  general  economy  very  superior  orders  of  animals.  These  latter 
would  appear  to  be  distinguishable  by  the  nature  of  the  tenta¬ 
cles  around  the  mouth,  which,  in  all  the  families  as  yet  examined, 
we  have  found  to  be  smooth  or  merely  fringed,  as  they  are  indeed 
in  some  of  the  tubular  polyps  hereafter  to  be  noticed  ;  but,  in  the 
more  perfect  species,  the  arms  are  covered  with  vibratile  hairs  or 
cilia,  forming  important  agents  in  securing  prey  :  such  have  been 
separated  by  Ehrenberg  into  a  distinct  class,  under  the  title  of 
Bryozoa,  and  have  been  recently  designated  by  Dr.  Arthur  Farre, 

ClLIOBRACITI  ATE  POLYPS. 

Further  observation  is  necessary  before  the  boundaries  of  these 
important  divisions  can  be  accurately  laid  down;  we  shall  neverthe¬ 
less,  without  entering  upon  a  question  foreign  to  our  present  sub¬ 
ject,  arrange  them  in  conformity  with  the  analogies  of  their  internal 
structure,  rather  than  of  their  outward  general  form,  and  defer  the 
consideration  of  the  ciliobrachiate  division  to  another  place. 

(63.)  In  the  unciliated  tubular  polyps,  the  common  body  of 
the  animal,  instead  of  encrusting  a  solid  skeleton,  is  enclosed  in  a 
horny  sheath,  which  it  traverses  like  the  pith  of  a  tree,  follow¬ 
ing  all  the  ramifications  of  the  branched  stem  of  the  polypary  : 
to  the  central  part  are  attached,  at  intervals,  cells  opening  exter¬ 
nally,  in  which  the  polyps  which  provide  nourishment  for  the  whole 
are  lodged. 

Zoophytes  of  this  description  are  readily  found  on  our  own 
coasts,  and  the  microscopic  observer  can  scarcely  enjoy  a  richer 
treat  than  the  examination  of  them  affords.  In  order  to  study 
them  satisfactorily,  it  is  necessary  to  be  provided  with  several 
glass  troughs,  of  different  depths,  in  which  the  living  animals 
immersed  in  their  native  element  may  be  placed  :  in  this  situa¬ 
tion,  if  the  water  be  carefully  renewed  at  short  intervals,  they  will 
live  for  some  time. 

(64.)  On  examining  a  piece  of  one  of  these  polyparies  with  a  good 
glass,  the  tubular  horny  envelope  is  seen  to  be  filled  with  granular 
matter;  and,  on  attentively  watching  it,  globules  will  be  seen  moving 
in  different  directions,  producing  a  sort  of  circulation  or  cyclosis 
very  much  resembling  what  is  observable  in  some  plants.  The  glo¬ 
bules  thus  moving  do  not  appear  to  be  contained  in  vessels,  but  steal 
in  slow  currents,  ascending  along  the  sides,  and  returning  down  the 
middle  in  an  opposite  direction,  as  represented  by  the  arrows  in 
fig.  14. 


46 


OK  POLYPS. 


(65.)  It  has  been  generally  stated  that  the  living  pith  exuded  from 
its  surface  the  horny  matter  which,  by  its  concretion,  forms  the 
tube  or  external  skeleton  investing  the  whole  ;  the  accuracy  of  such 
a  supposition,  however,  may  well  be  questioned.  We  have  already 
seen,  in  the  Tubipora  musica,  that  the  calcareous  tube  investing  that 
polyp  was  produced  by  the  interstitial  deposit  of  earthy  matter  in 
the  membrane  which  formed  originally  its  outer  case.  In  the  tribe 
of  zoophytes  which  we  are  now  speaking  of,  we  shall  find  the 
exterior  tube  to  be  formed  in  a  way  precisely  similar.  On  referring 
to  the  diagram,  (fig.  14,)  the  mode  of  its  growth  will  be  rendered  in¬ 
telligible:  the  soft  part  or  living  axis  of  the  polypary  is  seen  to  be 
contained  in  two  distinct  layers  ;  the  inner  one  composing  the 
digestive  sac  of  the  polyp,  and  embracing  the  granular  matter, 
which  seems  to  be  the  special  seat  of  the  nutritive  process  ;  the 
outer  or  tegumentary  layer,  5,  after  leaving  the  tentacula,  may 
be  traced  down  the  sides  of  each  polyp  to  the  bottom  of  the  cell, 
where  its  course  is  arrested  by  a  slight  partition,  at  which  point 
it  turns  outwards,  lining  the  interior  of  the  cell  as  far  as  its  margin, 
where,  as  in  the  Tubipora ,  it  is  seen  to  be  continuous  with  the 
horny  matter  itself.  It  is  this  tegumentary  membrane,  then,  which 
forms  by  its  develope-  14, 

ment  the  entire  skele¬ 
ton  :  as  it  expands,  it 
gives  origin  to  the  cells 
and  branches  character¬ 
istic  of  the  species;  and, 
from  being  at  first  quite 
soft  and  flexible,  it  gra¬ 
dually  acquires  hardness 
and  solidity  by  the  de¬ 
position  of  corneous 
matter  in  its  sub¬ 
stance. 

The  cells  thus  formed 
are  inhabited  by  polyps 
analogous  to  those  which 
provide  nourishment  for 
the  cortical  families ;  but 
differing  in  the  number 
and  appearance  of  the 
tentacula,  which  are 


ON  POLYPS. 


47 


here  studded  with  minute  tubercles,  but  never  provided  with  cilia. 
Few  objects  are  more  admirable  than  these  polyps,  when  watched 
with  a  good  microscope  :  protruding  themselves  beyond  the  mouths 
of  their  cells,  they  inflect  their  bodies  in  all  directions  in  quest  of 
prey,  waiting  till  some  passing  object  impinges  upon  their  tenta- 
cula,  which  is  at  once  seized  and  conveyed  into  the  stomach  with 
a  rapidity  and  dexterity  almost  beyond  belief. 

The  multiplication  of  these  singular  animals  appears  to  take  place 
in  three  different  modes  : — 1st,  by  cuttings,  as  in  plants  ;  Sndly, 
by  off-shoots,  or  the  formation  of  new  branches  bearing  polyps  ; 
3dly,  by  gemmules  capable  of  locomotion. 

(66.)  The  first  mode  strikingly  resembles  what  is  observed  in  the 
vegetable  kingdom  ;  for  as  every  branch  of  the  plant-like  body 
contains  all  the  parts  necessary  to  independent  existence,  it  can 
hardly  be  a  matter  of  surprise  that  any  portion,  separated  from  the 
rest,  will  continue  to  grow  and  perform  the  functions  of  the  entire 
animal. 

(67.)  The  second  mode  of  increase,  namely,  by  the  formation  of 
new  branches  and  polyps,  seems  more  like  the  growth  of  a  plant  than 
the  developement  of  an  animal.  We  will  consider  it  under  two 
points  of  view  :  first,  as  regards  the  elongation  of  the  stem  ;  secondly, 
as  relates  to  the  formation  of  fresh  cells  containing  the  nutritive 
polyps.  On  examining  any  growing  branch,  it  will  be  found  to  be 
soft  and  open  at  the  extremity,  and  through  the  terminal  orifice, 
the  soft  tegumentary  membrane  above  described  as  forming  the 
tube  by  its  conversion  into  hard  substance  is  seen  to  protrude  ;  the 
skeleton  is  not  therefore  merely  secreted  by  the  enclosed  living 
granular  matter,  but  it  is  the  investing  membrane,  which  continually 
shoots  upwards,  and  deposits  hard  material  in  its  substance,  as  it 
assumes  the  form  and  spreads  into  the  ramifications  peculiar  to 
its  species. 

(68.)  Having  thus  lengthened  the  stem  to  a  certain  distance,  the 
next  step  is  the  formation  of  a  cell  and  a  new  polyp,  which  is  accom¬ 
plished  in  the  following  manner  the  newly  formed  branch  has  at 
first  precisely  the  appearance  and  structure  of  the  rest  of  the  stalk 
of  the  zoophyte,  {Jig.  15,  1,)  being  filled  with  granular  matter, 
and  exhibiting  in  its  interior  the  circulation  of  globules  already 
described,  moving  towards  the  extremity  along  the  sides  of  the 
tube,  and  in  an  opposite  course  in  the  middle  ;  the  end  of  the 
branch,  however,  before  soft  and  rounded,  soon  becomes  perceptibly 

*  Lister,  Philosophical  Transactions,  Loc.  cit. 


48 


ON  POLYPS. 


dilated.  After  a  few  hours  the  branch  is  visibly  longer,  its 
extremity  more  swollen,  and  the  living  pith  is  seen  partially  to 

Fig.  15. 


have  separated  itself  from  the  sides  of  the  tube,  the  boundaries 
of  which  become  more  defined  and  undulating  (2).  The  growth 
still  proceeding,  the  extremity  is  distinctly  dilated  into  a  cell,  in 
which  the  soft  substance  seems  to  be  swollen  out,  so  as  to  give  a 
rude  outline  of  the  bell- shaped  polyp  (8),  but  no  tentacula  are  yet 
distinguishable  ;  a  rudimentary  septum  is  now  visible  stretching 
across  the  bottom  of  the  cell,  through  the  centre  of  which  the 
granular  matter,  now  collected  into  a  mass  occupying  but  a  portion 
of  the  stem,  is  seen  to  pass.  The  polyp  and  cell  gradually  grow 
more  defined,  (4,  5,  6,)  and  the  tentacula  become  distinguish¬ 
able  ;  the  cell,  moreover,  is  seen  to  be  continued  inwards  by  a  mem¬ 
branous,  infundibular  prolongation  of  its  margin  (7),  which  imme¬ 
diately  reminds  us  of  the  funnel-shaped  membrane  of  Tubipora 
(§  50),  and  its  office  is  no  doubt  similar.  As  the  developement 
proceeds,  the  tentacles  become  more  perfect  (8),  and  the  polyp  at 

length  rises  from  its  cell  to  exercise  the  functions  to  which  it  is 

© 

destined. 

(69.)  The  third  mode  of  multiplication,  or  that  by  reproductive 
gemmules,  seems  to  be  specially  adapted  to  the  diffusion  of  the 


ON  POLYPS. 


49 


species  ;  and  as  it  is  peculiar  to  zoophytes  of  this  description, 
we  shall  dwell  upon  it  at  some  length.  At  certain  periods  of  the 
year,  besides  the  ordinary  cells  which  contain  nutritive  polyps, 
others  are  developed  from  different  parts  of  the  stem,  which  may  be 
called  female  or  fertile  polyps,  although  usually  simply  termed 
the  vesicles.  The  cells  of  this  kind  are  much  larger  than  the 
nutritive  cells,  and  of  very  different  forms ;  they  are  moreover 
deciduous,  falling  off  after  the  fulfilment  of  the  office  for  which 
they  are  provided.  They  are  produced  in  the  same  manner  as 
the  rest  of  the  stem,  by  an  extension  of  the  tegumentary  mem¬ 
brane,  ( fig .  14,  6,)  which,  as  it  expands  into  the  form  of  the  cell, 
becomes  of  a  horny  texture  ;  it  may  be  traced,  however,  over  the 
opening  of  the  cavity,  where  it  sometimes  forms  a  moveable  oper¬ 
culum.  The  cell  being  thus  formed  from  the  expansion  and  subse¬ 
quent  hardening  of  the  tegumentary  membrane,  it  remains  to  explain 
the  origin  of  the  reproductive  germs  which  soon  become  developed 
in  its  interior.*  These  are  seen  to  spring  from  the  inner  or  nutritive 
layer  of  the  polyp  (a),  to  which  they  are  attached  by  pedicles,  re¬ 
garded  by  authors  as  fulfilling  the  office  of  umbilical  cords  during 
their  early  growth.  As  the  germs  expand,  they  gradually  advance 
towards  the  opening  of  the  cell,  where,  as  they  are  protruded, 
each  becomes  covered  with  a  layer  derived  from  the  tegumentary 
membrane  ( f)  which  closed  the  orifice,  and  protruding  externally, 
has  very  much  the  form  and  appearance  of  a  young  polyp,  for 
which  indeed  it  has  often  been  mistaken.  We  are  assured,  how¬ 
ever,  that  this  supposition  is  erroneous,  and  that  the  polypiform 
bodies  are  only  external  capsules  inclosing  the  real  germs  (e), 
from  which  young  polyps  are  to  be  formed.  *f-  On  tearing  open 

one  of  these  capsules  when  the  included  germs  are  ripe,  the  latter 
are  seen  to  be  rounded  grains  of  a  gelatinous  appearance,  covered 
externally  with  minute  cilia,  which,  like  those  of  the  gemmules  of 
the  sponge,  enable  them  to  swim  about  at  pleasure  in  search  of  a 
proper  locality  whereon  to  fix  their  permanent  habitation.  These 
ciliated  gemmules  are  highly  irritable,  and  frequently  contract 
their  bodies  into  different  shapes  during  their  progress  through  the 
water  ;  but  at  length,  when  about  to  fix  itself,  each  gemmule  becomes 
flat  and  circular,  and  assumes  a  radiated  appearance,  resembling  a 
minute  grey  star,  having  the  interstices  between  the  rays  filled  with 

*  Loefling.  Muller’s  Archives,  1826. — Lister,  Loc.  cit. 

f  Professor  Grant,  Edinb.  New  Philosoph.  Journal,  1827.  Observations  on  the 
spontaneous  motions  of  the  Cainpanularia  Dichotoma,  &c. 

E 


50 


POLYGASTRICA. 


a  colourless  transparent  matter,  which  seems  to  harden  into  horn. 
The  grey  matter  swells  in  the  centre,  where  the  rays  meet,  and 
rises  perpendicularly  upwards,  surrounded  by  the  transparent  horny 
substance,  so  as  to  form  the  trunk  of  the  new  zoophyte.  The  rays 
first  formed  are  obviously  the  fleshy  central  substance  of  the 
roots ;  and  the  portion  of  that  substance  which  grows  perpendi¬ 
cularly  upwards  forms  the  fleshy  part  of  the  stem,  from  which  in 
due  time  polyps  become  developed. 


CHAPTER  IV. 

POLYGASTRICA. 

Animalcula  Infusoria. — Auct. 

(70.)  Previous  to  the  discovery  of  the  microscope,  it  was  little  sus¬ 
pected  that  animals  existed  of  such  minute  size  as  totally  to  elude 
the  search  of  unassisted  vision  ;  much  less  that  every  drop  of  water  in 
which  animal  or  vegetable  substances  have  been  allowed  to  decay, 
swarms  with  numberless  forms  of  living  beings  ;  that  countless 
millions  inhabit  every  stagnant  pool  or  running  stream  ;  nay,  that 
every  drop  of  the  surface  of  the  ocean  is  in  itself  a  little  world, 
peopled  by  innumerable  active  creatures,  as  various  in  their  out¬ 
ward  forms  as  they  are  elaborately  adapted  by  their  internal  organi¬ 
zation  to  the  circumstances  in  which  they  live. 

The  terms  Infusoria  and  Animalcula,  as  first  used  by  the  earliest 
discoverers  of  these  beings,  were  applied  to  an  immense  number  of 
creatures  widely  differing  from  each  other  in  every  particular  except 
in  the  minuteness  of  their  size,  which  had  previously  concealed 
them  from  observation.  The  germs  of  embryo  polyps,  the  larvae 
of  insects,  and  all  microscopic  forms  of  being,  including  the  won¬ 
derful  tribes  of  living  atoms  which  inhabit  various  secretions  in  the 
interior  of  other  animals,  were  thus  thrown  together  in  one  heteroge¬ 
neous  and  chaotic  group,  without  reference  to  the  structure,  rela¬ 
tions  or  habits  of  the  creatures  so  denominated.  This  motley 
assemblage  has,  however,  by  subsequent  laborious  investigations, 
been  separated  and  arranged  so  as  in  some  measure  to  enable  us  to 
acquire  accurate  notions  concerning  the  animals  formerly  confounded 
under  one  common  designation. 


POLYGASTRICA. 


51 


(71.)  The  character  which  distinguishes  the  class  of  microscopic 
creatures  which  first  offers  itself  for  consideration,  is  derived  from 
the  nature  of  the  digestive  apparatus  with  which  the  creatures  com¬ 
posing  it  are  provided  this  consists  of  a  number  of  internal  sacs 
generally  regarded  as  stomachs,  which  are  easily  distinguishable  with 
the  microscope,  and  form  a  feature  in  their  economy  so  peculiar, 
that  they  are  from  this  circumstance  alone  at  once  recognised  as  an 
exceedingly  natural  and  well-defined  group,  allied  with  each  other  in 
the  general  details  of  their  history,  and  exhibiting  most  astonishing 
powers,  not  met  with  in  other  forms  of  being.  In  order  to  investigate 
the  facts  which  will  be  hereafter  stated,  connected  with  the  history  of 
these  animals,  the  young  naturalist  must  be  provided  with  a  good 
microscope,  furnished  with  glasses  capable  of  magnifying  objects 
from  200  to  1000  diameters, — the  last  will  be  seldom  needed  ;  but 
a  power  of  one-fourth  of  an  inch  focus  will  be  indispensable.  As 
some  practice  and  dexterity  is  requisite  in  prosecuting  researches  of 
this  description,  a  few  hints  relative  to  the  best  methods  of  procur¬ 
ing  and  observing  animalcules  will  not  be  improper  in  this  place. 
It  would  be  needless  to  advert  to  the  situations  in  which  they  are 
to  be  found ;  every  stream  and  stagnant  pool  contains  some  forms 
in  countless  numbers  ;  but,  in  order  to  obtain  many  uncommon 
species,  a  little  care  is  necessary.  The  lemnce,  or  duck-weed 
should  be  skimmed  from  the  surface  of  ponds  which  are  exposed 
to  the  rays  of  the  sun,  or  the  green  film,  which  not  unfrequently 
covers  stagnant  waters  ;  and  from  these  sources  examples  of  most 
tribes  may  readily  be  collected  :  or  else  recourse  may  be  had  to 
infusions  of  various  vegetable  substances, — of  hay,  chopped  straw, 
or  the  leaves  of  plants,  which,  if  left  in  open  glass  vessels,  and 
fully  exposed  in  the  open  air  to  the  influence  of  the  sun,  will  in  a 
few  days  swarm  with  polygastric  animals,  sometimes  not  to  be  pro¬ 
cured  by  other  means. 

A  drop  of  water  derived  from  any  of  these  sources,  if  placed 
upon  a  thin  plate  of  glass,  and  covered  with  a  film  of  talc,  will  rea¬ 
dily  enable  the  observer  to  examine  the  beings  which  inhabit  it  ; 
or  if  it  be  deemed  advisable  to  insulate  the  larger  species,  they 
may  be  separated  from  the  rest  with  a  feather,  and  placed  in  small 
tubes  or  flat  troughs  in  filtered  water,  and  their  developement  and 
mode  of  increase  watched  from  day  to  day. 

(7 2.)  We  shall  now  proceed  to  describe  some  of  the  most  common 
forms  which  the  Polygastrica  thus  procured  exhibit.  In  all  water 

E  2 


*  Ehrenberg. 


52 


POLY  GAS  TRIG  A. 


containing  putrefying  vegetable  matter,  innumerable  moving  points 
are  visible,  scarcely  distinguishable  except  under  the  highest  powers 
of  the  microscope,  but,  when  magnified  to  the  utmost,  assum¬ 
ing  the  appearance  represented  at  Jig.  16,  1  :  these  have  been 
termed  Monads;  and,  as  they 
may  well  be  supposed  to  be 
the  smallest  creatures  in  ex¬ 
istence,  have  been  regarded 
as  the  limit  of  the  animal 
world  ;  their  minuteness,  in¬ 
deed,  is  incalculable.  Dr. 

Ehrenberg  *  has  described 
monads  which  are  not  larger 
than  from  -y&o y  to  t^o  o  of  a 
line,  and  which  appeared  to 
be  separated  from  each  other 
by  intervals  not  greater  than 
their  diameter.  Each  cubic 
inch  of  the  water  in  which 
they  are  found  must  contain, 
therefore,  800,000  millions  of 
these  animalcules,  estimating 
them  to  occupy  but  one-fourth 
of  its  space.  A  single  drop,  brought  under  the  field  of  the  micro¬ 
scope,  and  not  exceeding  one  cubic  line  in  diameter,  will  there¬ 
fore  contain  500  millions,  equal  to  the  whole  number  of  human 
beings  upon  the  surface  of  the  globe.  Well  may  the  mind, 
overwhelmed  with  wonder  at  such  an  astounding  fact,  launch 
into  visionary  speculations  when  contemplating  it ;  and  we  are 
little  surprised  to  see  the  fertile  imagination  of  Buffon  figuring  all 
animal  and  vegetable  bodies  as  composed  of  aggregations  of  these 
living  particles,  believing  them  to  be  the  primitive  materials  of 
which  organized  substances  are  made  up. 

(73.)  The  Proteus,  ( Amaba  E .)  Jig.  16,  2,  is  not  frequently  met 
with,  but  affords  a  singular  example  of  an  acrite  animal.  It  ap¬ 
pears  under  a  good  glass  to  be  an  atom  of  transparent  jelly,  which 
perpetually  changes  its  form  by  contractions  of  different  parts  of  its 
body ;  at  one  time  being  a  roundish  mass,  then  expanding  into  a  linear 

*  Ehrenberg’s  valuable  researches  concerning  the  Polygastrica  are  to  be  found  in 
the  Transactions  of  the  Berlin  Academy,  Abhandlungen  der  Academie  von  Berlin, 
vols.  68,  69,  and  71. 


POLY  GASTRIC  A. 


53 


figure,  and  again  shooting  out  processes  of  its  substance  in  various 
directions,  so  as  to  assume  all  kinds  of  shapes  with  the  greatest 
facility. 

The  Flask  animalcule,  ( Enchelis ,)  fig.  1 6,  3  ;  the  Trichoda 
sol ,  fig.  16,  4  ;  the  Euglena  viridis ,  fig.  16,  5  ;  the  Gonium 
jyectorale,  fig.  16,  6;  the  Trachelius  anas ,  fig.  16,  7  ;  the  Para¬ 
mecium  aurelia ,  fig.  16,  8;  the  Navicula ,  fig.  16,  9  ;  the  Vibrio 
Spirillum ,  fig.  16,  10  ;  and  the  Vorticella  Stentor,  fig.  1  6,  11, — will 
give  the  reader  an  idea  of  the  most  common  species  of  these  crea¬ 
tures,  the  structure  of  which  we  shall  now  proceed  to  investigate. 

(74.)  With  regard  to  their  external  covering,  the  Polygastrica  may 
be  divided  into  two  parallel  groups,  in  one  of  which  the  body  is  en¬ 
tirely  soft,  whilst  in  the  other  the  animals  are  enclosed  in  a  delicate 
transparent  shell  :  the  former  are  termed  nuda ,  or  naked  ;  the 
latter  loricata ,  or  loricated  animalcules.  The  shells  of  the  lori- 
cated  division  vary  much  in  form  ;  sometimes  being  mere  transparent 
shields  covering  the  back,  as  in  Euplsea  Charon  ( fig .  17,  4)  ;  at 
others  they  would  seem  to  be  capable  of  opening,  like  the  bivalve 
shells  of  mollusca,  as  in  the  minute  Naviculse^g.  16,  9.  Delicate 
as  these  shells  are,  and  requiring  the  most  accurate  examination, 
even  with  a  good  microscope,  to  detect  their  presence,  we  shall  be 
surprised  to  find  that  they  play  an  important  part  in  nature,  mak¬ 
ing  up  by  their  immense  accumulation  for  their  diminutive  size. 
We  have  before  us,  while  writing  this,  a  specimen  of  pulverulent 
matter  collected  upon  the  shores  of  Lake  Lettnaggsjon,  two 
miles  and  a  half  from  Urnea  in  Sweden,  which  from  its  extreme 
fineness  resembles  flour  :  this  has  long  been  known  by  the  natives 
of  the  region  where  it  is  plentiful,  under  the  name  of  Bergmehl  or 
mountain  meal,  and  is  used  by  them,  mixed  up  with  flour,  as  an 
article  of  food  ;  experience  having  taught  them  that  it  is  highly 
nutritive.  On  examination  with  the  microscope,  the  Bergmehl  is 
found  to  consist  entirely  of  the  shells  of  loricated  infusoria,  which, 
having  been  accumulating  from  age  to  age  at  the  bottom  of  the  waters 
in  which  the  living  animals  are  found,  form  a  stratum  of  considera¬ 
ble  thickness.  Nor  is  this  all  :  for,  when  agglomerated  and  mixed 
up  with  siliceous  and  calcareous  particles,  these  exuvise  become  con¬ 
solidated  by  time  into  masses  of  flint  and  marble,  in  which  the 
shape  and  characters  of  the  shells  are  perfectly  distinguishable,  so 
that  even  the  species  of  the  animalcules  to  which  they  originally 
belonged  is  easily  made  out. 

(75.)  The  movements  of  the  polygastrica,  when  seen  under  the 


54 


POLYGASTRICA. 


microscope,  are  exceedingly  vivacious;  and  although,  many  of  them 
inhabit  a  space  not  larger  than  the  point  of  a  needle,  they  swim 
about  with  great  activity,  avoiding  each  other  as  they  pass  in  their 
rapid  dance,  and  evidently  directing  their  motions  with  wonderful 
precision  and  accuracy.  Our  next  enquiry  therefore  must  be  con¬ 
cerning  the  organs  of  locomotion  which  they  possess.  These  are 
of  various  kinds,  and  are  arranged  differently  in  different  species. 
In  the  smallest  animalcules,  monads ,  & c.  no  locomotive  organs 
have  been  satisfactorily  detected ;  yet  even  in  some  of  these 
Mons.  F.  Dujardin  perceived  one  or  more  filaments  of  extreme 
tenuity  attached  to  their  globular  bodies,  which  he  regards  as 
instruments  for  progression.  These  filaments  he  describes  as  not 
exceeding  -30-00  0  of  a  millimetre  in  diameter,  and  consequently 
requiring  the  utmost  penetration  of  the  microscope  for  their  detec¬ 
tion.  In  Am<zba  dijjliiens  (Jig*  1  6,  2)  organs  of  locomotion  are 
formed  at  the  pleasure  of  the  animal,  by  shooting  out  processes 
from  different  parts  of  its  semifluid  substance,  which  may  be  used 
as  fins  or  legs,  as  occasion  requires.  Some  are  provided  with  stj/li, 
or  articulated,  stiff,  bristle-like  organs,  which  are  moveable,  and 
perform  in  some  measure  the 
office  of  feet,  and  with  uncini , 
or  little  hooks,  serving  for  at¬ 
tachment  to  foreign  bodies  ; 
these  are  seen  in  Euplaa 
Charon  (Jig.  17,  4). 

(76.)  But  the  most  impor¬ 
tant  locomotive  agents  are  the 
cilia, *  with  which  the  Poly- 
gastrica  are  generally  fur¬ 
nished  (Jig.  17;  1,  2,  3). 

On  attentively  examining  most 
forms  of  these  creatures,  espe¬ 
cially  those  of  comparatively 
large  size,  the  body  will  be 
seen  in  some  cases  to  be  en¬ 
tirely  covered  with  minute 
vibrating  hairs,  or  at  least 
furnished  with  such  appen¬ 
dages  on  some  part  of  its  surface.  The  existence  of  these  cilia 
is  leadily  detected  by  a  practised  eye,  even  when  using  glasses 

*  C ilium,  an  eye- lash. 


Fig.  17. 


POL  YG  AST  RICA. 


55 


of  no  very  great  magnifying  power,  by  tlie  peculiar  tremulous 
movement  which  they  excite  in  the  surrounding  fluid,  somewhat 
resembling  the  oscillations  of  the  atmosphere  in  the  neighbour¬ 
hood  of  a  heated  surface  ;  but  on  applying  higher  magnifiers,  espe¬ 
cially  if  the  animalcule  is  in  a  languid  state,  the  motion  is 
seen  to  be  produced  by  the  action  of  the  delicate  filaments 
of  which  we  are  speaking.  It  is  extremely  difficult  accurately 
to  define  the  motion  of  the  individual  cilia  ;  it  is  most  probable 
that  each  forms  by  its  rotation  a  cone,  the  apex  of  which  will  be 
at  the  root  of  the  organ — 'this  at  least  is  the  opinion  of  the  best  ob¬ 
servers,  and  the  combination  of  such  movements  gives  rise  to  cur¬ 
rents  in  the  water,  serving  a  variety  of  purposes  in  the  economy  of 
these  minute  creatures.  The  vibrating  organs,  notwithstanding 
their  indescribable  minuteness,  vary  considerably  in  size  ;  and  it  is 
more  than  probable  that  in  those  monads,  and  other  species,  in 
which  their  existence  has  not  been  detected,  the  apparent  want  of 
them  is  owing  to  the  imperfection  of  our  means  of  investigation. 
A  few  years  ago,  indeed,  some  species  now  distinctly  proved  to  be 
covered  with  cilia,  were  looked  upon  as  being  absolutely  deprived 
of  locomotive  apparatus,  as  the  Volvox  globator  (Jig.  SO)  ;  and 
few  greater  proofs  can  be  given  of  the  superiority  of  the  microscopes 
now  at  our  disposal,  than  the  fact  of  our  being  able,  not  only  to 
detect  with  facility  their  existence  on  the  surface  of  the  parent 
volvox,  but  even  upon  the  young  vol voces  before  their  birth. 

(77.)  The  cilia,  as  has  been  already  observed,  are  sometimes 
dispersed  over  the  whole  body,  either  arranged  in  parallel  rows  or 
scattered  irregularly ;  they  are,  however,  most  frequently  only  met 
with  in  the  neighbourhood  of  the  mouth,  in  which  position  they 
are  always  most  evident  :  here  they  produce,  by  their  vibration, 
currents  in  the  surrounding  fluid  which  converge  to  the  oral  aper¬ 
ture,  and  bring  to  the  mouth  smaller  animalcules,  or  particles  of 
vegetable  matter,  which  may  be  floating  in  the  neighbourhood,  and 
thus  ensure  by  an  admirable  contrivance  an  abundant  supply  of 
food,  which  without  such  assistance  it  would  be  almost  impossible 
for  these  little  creatures  to  obtain. 

(78.)  We  may  be  expected,  in  this  place,  to  make  a  few  obser¬ 
vations  concerning  the  agency  by  which  these  numberless  and 
almost  invisible  organs  are  made  to  perform  their  rapid  move¬ 
ments.  The  subject  is  one  of  no  little  difficulty,  and  in  the 
present  state  of  our  knowledge  probably  inexplicable.  Ehrenberg 
indeed  asserts,  that  round  the  base  of  every  cilium  is  an  appa- 


56 


POLYGASTRICA. 


ratus  of  radiating  muscular  fibres,  to  the  successive  contractions  of 
which  the  rotation  of  the  cilium  is  owing.  Such  an  arrangement 
is,  to  say  the  least,  hard  to  be  conceived,  for  in  this  case  we  must 
attribute  to  these  acrite  beings  an  elaboration  of  structure  of  infi¬ 
nite  complexity  ;  and  in  creatures  so  small,  how  can  the  human 
mind  imagine  the  cilia  to  be  wielded  by  many  millions  of  distinct 
and  independent  muscles,  as  such  a  supposition  would  infer  ? 
Some  authors  attempt  to  get  rid  of  the  difficulty  by  ascribing  the 
apparent  ciliary  movement  to  the  rapid  undulations  of  mem¬ 
branous  fins  ;  others  altogether  deny  its  existence,  asserting  that 
the  vibratory  appearance  is  caused  by  the  mingling  of  some  secre¬ 
tion  which  exudes  from  the  surface  of  the  animalcule  with  the  sur¬ 
rounding  fluid,  in  the  same  manner  as  the  union  of  spirit  of  wine 
and  water  gives  rise  to  an  oscillation  of  particles  visible  to  the 
naked  eye  :  to  these  suppositions,  however,  we  barely  allude,  be¬ 
cause  we  are  convinced  that  any  one  who  with  a  good  microscope 
and  an  unbiassed  mind  investigates  the  subject,  will  be  con¬ 
vinced  that  the  cilia  are  such  as  we  have  described  above, 
however  unable  he  may  be  to  conjecture  the  cause  of  their 
movement. 

(79.)  The  mouth  of  the  polygastrica  is  generally  a  simple  and 
extremely  dilatable  orifice,  and,  with  a  few  rare  exceptions,  is  un¬ 
provided  with  any  masticating  organs  ;  yet  in  JVassula  elegans , 
(Jig-  17,  1,)  and  a  few  kindred  species,  Ehrenberg  describes  a 
dental  system  of  a  most  extraordinary  description  :  this  consists  of 
a  prominent  cylinder  (u),  of  which  an  enlarged  view  is  given  at  a, 
composed  of  numerous  long  teeth  adapted  to  seize  and  bruise 
materials  used  as  food. 

(80.)  The  digestive  apparatus  itself,  from  the  peculiarity  of  its 
structure,  has  given  the  character  usually  employed  to  distinguish 
the  entire  class  :  it  is  described  as  consisting  essentially  of  a 
number  of  internal  sacculi,  varying  from  four  to  two  hundred  in 
number  in  different  species.  These  sacs  are  readily  distinguishable 
without  any  preparation,  but  are  rendered  more  conspicuous  by 
feeding  the  animalcules  with  pure  carmine  or  indigo,  the  coloured 
particles  of  which  substances  they  eagerly  swallow.  In  one  large 
division,  called  Anentera,  the  sacculi  or  stomachs  are  said 
to  arise  by  separate  tubular  pedicles  from  the  mouth  itself 
(fig-  18,  1);  whilst  in  others,  Enterodela,  there  is  supposed 
to  be  a  complete  intestinal  canal,  terminated  by  a  mouth  and 
anus,  to  which  the  sacculi  or  stomachs,  as  they  are  called, 


POLYGASTRICA . 


57 


are  appended  :  sometimes  tlie  Fig.  18. 

mouth  and  anus  are  lodged  in 
the  same  fossa,  and  the  intes¬ 
tinal  canal  forms  a  circle  in  the 
body  (Anopisthia,  Ehren.),  as 
in  the  Vorticella  ( fig .  18,  2)  :  or 
else  the  mouth  and  anus  are  placed 
at  opposite  extremities  of  the  body, 
through  which  the  intestinal  tube 
passes  either  in  a  straight  course,  * 
or  exhibiting  several  flexuous  curves 
in  its  passage.  (Enantiotreta 
and  Allotreta,  Ehren.)  {fig. 

18,  3  and  4.)  When  neither  the 
mouth  nor  anus  are  terminal,  as 
in  Kolpoda ,  {fig-  19  ;  7,  a,  5,) 
such  animals  belong  to  the  group 
denominated  Katotreta  by  the 
same  author. 

(81.)  However  imposing,  from  their  completeness,  the  views  of 
Ehrenberg  concerning  the  digestive  system  of  the  polygastrica  may 
be,  and  sanctioned  as  they  are  by  almost  general  consent,  we  can¬ 
not  pass  over  a  subject  of  so  much  importance  without  expressing 
ourselves  as  being  far  from  admitting  their  accuracy  in  all  respects, 
and  we  must  say  that  our  own  observations  upon  the  structure  of 
the  polygastrica  have  led  us  to  very  different  conclusions.* 

The  positions  of  the  mouth  and  anal  aperture  we  are  well 
assured,  by  frequent  examination,  to  be  such  as  are  indicated  by 
the  illustrious  Professor  of  Berlin  ;  but  with  regard  to  the  tube 
named  by  him  intestine,  and  the  stomachs  appended  thereto,  our 
most  patient  and  long-continued  efforts  have  failed  to  detect  the 
arrangement  depicted  in  his  drawings.  In  the  first  place,  as  re¬ 
gards  the  function  of  the  sacculi,  which  he  looks  upon  as  the  organs 
in  which  digestion  is  accomplished ;  in  carnivorous  animalcules 
which  devour  other  species  we  might  expect,  were  these  the 
stomachs,  that  the  prey  would  at  once  be  conveyed  into  one  or 
other  of  these  cavities  ;  yet,  setting  aside  the  difficulty  which  must 
manifestly  occur  in  lodging  large  animalcules  in  these  microscopic 


*  It  may  be  proper  to  state  that  the  microscope  used  in  these  and  similar  re¬ 
searches  to  which  allusion  will  he  made,  is  a  compound  achromatic,  made  hy  Ross 
of  London  ;  and  the  powers  employed,  of  and  x  of  an  inch  focus. 


58 


POLYGASTRICA. 


sacs,  and  having  recourse  to  the  result  of  actual  experience,  we 
have  never  in  a  single  instance  seen  an  animalcule,  when  swallowed, 
placed  in  such  a  position,  but  have  repeatedly  traced  the  prey  into 
what  seemed  a  cavity  excavated  in  the  general  parenchyma  of 
the  body. 

In  the  second  place,  the  sacculi  have  no  appearance  of  being 
pedunculated,  and  consequently  in  a  certain  degree  fixed  in  defi¬ 
nite  positions  :  during  the  last  two  hours  we  have  been  carefully 
examining  some  beautiful  specimens  of  Paramecium  aurelia, 
(Jig-  18,  4,)  an  animalcule  which,  from  its  size,  is  peculiarly 
adapted  to  the  investigation  of  these  vesicles  ;  and  so  far  from 
their  having  any  appearance  of  connection  with  a  central  canal,  as 
represented  in  the  figure  copied  from  Ehrenberg,  they  are  in  con¬ 
tinual  circulation,  moving  slowly  upwards  along  one  side  of  the 
body,  and  in  the  opposite  direction  down  the  other,  changing 
moreover  their  relative  positions  with  each  other,  and  resembling 
in  every  respect  the  coloured  granules  which  have  been  described 
(§31,)  as  visible  in  the  gelatinous  parenchyma  of  the  hydra. 

With  respect  to  the  central  canal,  (Jig-  18  ;  2,  8,  4,)  we  have 
not  in  any  instance  been  able  to  detect  it,  or  even  any  portion  of 
the  tube  seen  in  the  figures,  much  less  the  branches  represented  as 
leading  from  it  to  the  vesicles  or  stomachs,  as  they  are  called. 
Even  the  circumstances  attending  the  prehension  of  food  would 
lead  us  to  imagine  a  different  structure  ;  witness  for  example  the 
changes  of  form  which  Enchelis  pupa  undergoes  when  taking  prey, 
as  shown  in  fig.  16,  8,  where  it  is  represented  in  the  act  of  devour¬ 
ing  a  large  animalcule,  almost  equal  to  itself  in  bulk,  and  is  seen  to 
assume  a  perfectly  different  shape  as  it  dilates  its  mouth  to  receive 
the  victim,  with  which  its  whole  body  becomes  gradually  distended. 
Such  a  capability  of  taking  in  and  digesting  a  prey  so  dispropor¬ 
tionate,  would  in  itself  go  far  to  prove  that  the  minute  sacculi 
were  not  stomachs ;  as  it  evidently  cannot  be  in  one  of  these  that 
digestion  is  accomplished. 

(82.)  Looking  at  the  above  facts  as  a  whole,  we  cannot  mistake 
the  analogy  which  there  is  between  the  organization  of  the  so- 
named  Polygastrica  and  of  the  Hydra  viridis ;  there  is  the  same 
dilatable  body  in  which  the  solution  of  food  takes  place,  and  the 
same  granular  vesicles  by  which  the  nutritious  portions  are  ab¬ 
sorbed  :  that  the  vesicles  become  coloured  by  the  coloured  food 
given  to  the  animalcule,  cannot  be  considered  as  a  proof  of  their 
being  stomachs,  as  in  the  experiments  of  Trcmblcy,  above  nar- 


POL  VG  AST  ltIC  A. 


59 


rated,  tlie  granules  which  circulate  in  the  body  of  the  hydra 
became  dyed  with  the  juices  of  the  animals  with  which  it  was  fed, 
precisely  in  a  similar  manner. 

The  reproduction  of  the  polygastric  animalcules  is  effected  in 
various  ways,  and  not  unfrequently  the  same  individual  would 
appear  to  propagate  in  two  or  three  different  modes. 

(83.)  The  first  is  by  external  gemmules  or  buds,  resembling 
those  by  which  the  hydra  is  multiplied  which  sprout  like  minute 
gelatinous  tubercles  from  the  surface  of  the  body,  and,  gradually 
attaining  the  shape  of  their  parent,  develope  the  cilia  characteristic 
of  their  species,  and  soon  become  independent  beings,  although 
they  do  not  attain  to  their  full  growth  until  some  time  after  their 
separation. 

(84.)  A  second  mode  of  reproduction  is  witnessed  in  the 
Volvox,  and  others  of  similar  conformation.  In  these  animalcules 
(Jig.  19, 1,)  the  parent  is  a  delicate  green  transparent  globe,  which 
under  a  good  microscope  is  seen  to 
be  entirely  covered  with  cilia,  whose 
action  produces  currents  in  the  water, 
the  course  of  which  is  represented  by 
the  arrows  in  the  figure  ;  impelled  by 
these  cilia,  the  little  globe  makes  its  //  j 
way  with  a  revolving  motion  through 
the  element  which  it  inhabits.  In 
the  interior  of  the  volvox,  the  observer 
readily  discovers  other  smaller  globes 
of  a  dark  green  colour,  which  a  little 
attention  will  prove  to  be  young  vol- 
voces,  exactly  resembling  the  larger 
one  which  contains  them,  and  covered 
in  like  manner  with  vibratile  cilia,  by 
the  assistance  of  which  they  swim 
about  in  the  body  of  their  parent 


Fig.  19. 


V  *  •  •  .  *  *  ' 

®  *  -  .  •  •  -jr 

f«:**:*  » v 
y. :  v  - 
•  ■  *  Vvx 


A-\>x 

and  seem  to  have  ample 
space  for  their  motions.  At  length,  when  the  imprisoned  gem- 
mules  are  ripe  for  exclusion,  the  skin  of  the  original  volvox  bursts, 
(Jig.  19,  2,)  and  the  young  ones,  (Jig.  19,  3,)  escaping  through 
the  fissure,  enter  upon  a  wider  stage  of  existence  :  yet,  even  before 
their  escape,  the  gemmules  of  a  third  generation  are  seen  within 
their  bodies,  which,  gradually  enlarging,  are  destined  to  terminate 
by  their  birth  the  life  of  the  newly  liberated  beings. 

(85.)  The  most  usual  mode  of  propagation  however  is  by 


60 


POLY  GASTRIC  A. 


Fig.  20. 


spontaneous  fissure,  or  division  of  the  body  of  an  adult  animalcule 
into  two  or  more  portions,  each  of  which  is  perfect  in  all  its  parts. 
This  singular  kind  of  fjeneration,  by  which  the  old  animalcule 

O  O  " 

literally  becomes  converted  into  two  or  more  young  ones,  is 
accomplished  in  various  ways,  which  will  require  separate  notice. 

In  the  oval  forms  of  the  polygastrica,  the  line  of  separation 
generally  divides  the  body  transversely  into  two  equal  portions, 
by  a  process,  the  different  stages  of  which  are  represented  in 
Jig.  20  ;  1,  2,  3.  The  body 
of  an  animalcule  about  to  di¬ 
vide  in  this  manner  becomes 
at  first  slightly  elongated, 
and  a  line  more  transparent 
than  the  rest  of  its  body  is 
seen  to  cross  its  middle  por¬ 
tion  :  a  constriction  becomes 
gradually  apparent  at  each 
extremity  of  the  line  of  divi¬ 
sion,  which  soon  grows  more 
decided,  and  at  length  the  12 
two  parts  are  only  united 
by  a  narrow  isthmus,  (Jig. 

19,  3,)  which,  getting  thinner 
and  thinner,  allows  a  slight  k 
effort  on  the  part  of  either  of 
the  now  nearly  distinct  por¬ 
tions  to  tear  itself  from  the  other  half,  and  complete  the  separation. 

In  some  elongated  species  (Jig.  20,  4)  the  fissure  is  effected  in 
a  longitudinal  direction,  the  separation  gradually  proceeding  from 
the  posterior  to  the  anterior  extremity  of  the  body  (Jig.  20,  6)  ; 
yet  even  in  these  the  division  is  occasionally  transverse,  the  newly 
formed  creature  appearing  truncated  at  one  end  (Jig.  19,  5)  for 
some  time  after  the  completion  of  the  process. 

(86.)  The  mode  of  generation  in  Convallaria,  a  group  of  which 
is  seen  at  Jig.  20,  11,  is  very  curious;  and  from  the  different 
forms  which  the  young  assume  during  the  progress  of  develope- 
ment  much  confusion  has  occurred,  each  stage  of  its  growth  having 
been  described  as  the  permanent  appearance  of  a  distinct  species. 
This  beautiful  animalcule  seems  to  be  propagated  in  several 
ways  :  sometimes  this  is  effected  by  external  gemmules,  which 
appear  like  minute  points,  scarcely  more  than  toV o  of  a  line  in 


POLY  GASTRIC  A. 


61 


diameter,  upon  the  pedicles  of  the  adult  convallarise  ;  these  in  time 
become  pedunculated,  and,  although  still  very  small,  exhibit  the 
cilia  upon  the  margins  of  their  delicate  cups  ;  in  this  state  they 

were  called  bv  Schrank  Vorticellce  monedica ?.  The  Convallarise 

%> 

generally  however  multiply  by  fissure,  the  bell-shaped  cup  at  the 
extremity  of  their  highly  irritable  pedicles  separating  longitudinally 
into  two  ;  but  the  progress  of  this  division  requires  our  particular 
notice,  as  the  unpractised  observer  might  be  considerably  puzzled 
on  witnessing  some  of  the  phenomena  attending  it. 

The  adult  animalcule,  seen  with  its  pedicle  fully  extended, 
(Jig.  20,  9,)  when  it  is  alarmed,  shrinks  by  throwing  its  stem  into 
spiral  folds  (10)  :  in  the  latter  figure,  the  bell  or  body  of  the 
animalcule  is  seen  to  have  extended  considerably  in  breadth,  pre¬ 
paratory  to  its  becoming  divided  into  two  distinct  creatures.  At 
11,  the  commencement  of  its  division  is  depicted;  the  separation 
gradually  extending  from  the  base,  or  ciliated  extremity,  to  the 
point  where  the  body  is  attached  to  its  stem.  When  the  division 
has  extended  thus  far,  (12,)  the  newly  formed  portion  is  seen  with 
surprise  to  have  become  furnished  with  cilia  at  both  ends,  and, 
when  finally  detached,  (IS,)  only  at  the  opposite  extremity  to 
that  on  which  they  originally  existed  ;  it  then,  freed  from  its  pe¬ 
dicle,  and  thus  losing  the  great  characteristic  of  its  species,  swims 
about  at  large,  exhibiting  forms  represented  at  11,  15,  16,  17,  all 
of  which  have  been  described  as  distinct  species  by  different 
writers  ;  at  last  it  puts  forth  a  new  stem,  and,  assuming  the  adult 
form,  becomes  fixed  by  its  pedicle  to  some  foreign  body. 

(87.)  This  fissiparous  mode  of  reproduction  is  amazingly  pro¬ 
ductive,  and  indeed  far  surpasses  in  fertility  any  other  with  which 
we  are  acquainted,  not  excepting  the  most  prolific  insects  or  even 
fishes.  Thus  the  Paramecium  aurelia ,  if  well  supplied  with 
food,  has  been  observed  to  divide  every  twenty-four  hours,  so  that 
in  a  fortnight,  allowing  the  product  of  each  division  to  multiply  at 
the  same  rate,  16,381  animalcules  would  be  produced  from  the  same 
stock ;  and  in  four  weeks  the  astonishing  number  of  268,135,156 
new  beings  would  result  from  a  continued  repetition  of  the  process  : 
we  shall  feel  but  little  surprise,  therefore,  that  with  such  powers  of 
increase  these  minute  creatures  soon  become  diffused  in  countless 
myriads  through  the  waters  adapted  to  their  habits. 

(88.)  The  capability  of  spontaneous  division  is  one  of  the  most 
distinctive  attributes  of  the  acrite  type  of  structure ;  and  was  the 
organization  of  these  animalcules  as  simple  as  it  was  supposed  to 


62 


POLY"  GASTRIC  A. 


be  a  few  years  ago,  when  they  were  thought  to  be  mere  specks  of 
living  gelly,  imbibing  nourishment  at  every  point  of  their  surface, 
which  became  diffused  through  all  parts  of  the  homogeneous  tex¬ 
ture  of  their  bodies,  such  a  mode  of  multiplication  would  be  per¬ 
fectly  intelligible,  and  every  step  of  the  process  easily  understood  : 
but  setting  aside  the  conformation  of  their  digestive  apparatus, 
which,  as  we  have  before  observed,  is  in  our  opinion  not  satisfac¬ 
torily  determined,  there  are  many  circumstances  attending  the 
operation,  which  would  indicate  a  power  of  developing  new  organs 
in  the  construction  of  every  fresh  individual,  which  must  be  looked 
upon  as  a  very  interesting  feature  in  their  history.  Thus  a  new 
oral  orifice,  surrounded  with  cilia,  must  be  formed  upon  the  poste¬ 
rior  segment  of  each  divided  animalcule,  while  an  anal  aperture  is 
developed  upon  the  anterior  half.  In  JVassula  elegans  (Jig.  17, 1) 
the  dental  apparatus  u,  complex  as  its  structure  seems  to  be,  must 
be  formed  upon  a  new  part  of  the  body  preparatory  to  every  sepa¬ 
ration  ;  and  accordingly,  in  the  plates  which  Ehrenberg  gives  of  the 
reproduction  of  this  animalcule,  a  new  mouth  or  dental  cylinder  is 
actually  seen  to  sprout  from  the  hinder  half  of  the  creature  before 
its  transverse  fissure  is  complete.  These  structures  therefore,  and 
others  hereafter  to  be  mentioned,  must  continually  be  called  into 
existence  at  new  and  distant  parts  of  the  system. 

(89.)  We  have  as  yet  only  spoken  of  those  forms  of  fissiparous 
generation  in  which  the  original  animalcule  divides  either  trans¬ 
versely  or  longitudinally  into  two  portions  ;  yet  there  are  instances 
where  several  new  beings  result  from  a  like  process.  In  Gonium 
pectorale  (Jig.  1 6,  6)  the  entire  animalcule  seems  to  consist  of 
sixteen  globules  enclosed  in  a  delicate  film  or  capsule  ;  which, 
divides  both  in  a  transverse  and  longitudinal  direction,  so  as  to 
separate  into  four  portions,  each  composed  of  one  large  and  three 
smaller  globules,  which,  after  their  separation  from  the  rest,  swim 
freely  about,  and  soon  develope  the  parts  and  assume  the  appear¬ 
ance  of  the  parent.  In  Gonium  pulvinatum  the  offspring  is  still 
more  numerous  ;  the  parent  resembles  a  square  piece  of  delicate 
membrane,  and,  on  assuming  its  full  growth,  is  seen  to  be  marked 
by  three  transverse  and  as  many  longitudinal  lines,  crossing  each 
other  at  right  angles,  and  dividing  the  original  into  sixteen  smaller 
squares,  which  soon  separate  from  each  other,  and  become  as  many 
detached  beings. 

(90.)  Productive  as  the  above-mentioned  modes  of  increase 
are,  it  would  seem  that  they  are  not  the  only  sources  of  propagation 


POLY  GASTItICA. 


63 

in  the  polygastric  class  of  animals ;  as  many  tribes  have  been 
observed  to  be  produced  from  ova  or  spawn,  as  well  as  by  fis¬ 
sure  and  gemmation.  The  Kolpoda  cucullus  (jig.  20,  7)  is 
one  in  which  Elirenberg  succeeded  most  perfectly  in  detecting  this 
kind  of  generation,  but  he  has  likewise  observed  it  in  many  others. 
The  ova  seem  to  be  produced  in  the  general  parenchyma  of  the 
body,  without  the  visible  existence  of  any  organ  specially  destined 
to  their  formation  ;  and,  when  mature,  are  expelled  in  a  delicate 
reticulate  mass  (Jig.  20,  8).  Elirenberg  even  describes  some 
contractile  vesicles  discovered  to  exist  in  many  species,  which  he 
regards,  though  perhaps  without  sufficient  grounds,  as  being  a 
male  apparatus  provided  for  the  fertilization  of  the  ova  previous  to 
their  expulsion.  In  Paramecium  aurelia  (Jig.  17,  2)  these  were 
two  in  number,  (a,  g,)  placed  at  the  two  extremities  of  the  body, 
each  seeming  to  consist  of  a  delicate  irritable  central  portion, 
from  which  he  could  see,  on  gently  pressing  the  animalcule  be¬ 
tween  two  plates  of  glass,  eight  canals  issuing  in  a  radiating  manner 
and  diverging  toward  all  parts  of  the  body ;  these  became  gradually 
enlarged  as  the  vesicle  contracted,  and,  on  the  contrary,  became 
narrow  and  disappeared  as  the  vesicle  dilated.  The  contractile 
organs  were  detected  in  twenty-two  species  belonging  to  very 
different  families  ;  but  the  radiating  canals  were  only  seen  in  two, 
viz.  Paramecium  aurelia  and  Ophryoglena  :  their  appearance  in 
Nassula  elegans,  Stentor  polymorphic,  and  Euplotes  charon ,  is 
seen  in  Jig.  17  ;  1,  3,  4,  h.  The  function  of  these  organs 
Elirenberg  believes  to  be  connected  with  the  secretion  of  a  fecun¬ 
dating  fluid,  which,  being  dispersed  by  their  contraction  through 
the  body,  serves  to  fertilize  the  ova. 

(91.)  No  circulation,  properly  so  called,  has  been  seen  in 
the  polygastrica  ;  neither  have  vessels  of  any  kind  been  satisfac¬ 
torily  made  out.  There  is  however  in  Paramecium  aurelia ,  as  has 
been  already  mentioned,  a  constant  sap-like  movement  in  the  gra¬ 
nular  matter  of  the  body,  which  is  easily  detected,  and  was  described 
by  Gruithuysen :  this  appearance  Ehrenberg  attributes  to  the 
movements  of  the  intestine ;  but  as  we  have  been  quite  unable  to 
detect  the  arrangement  which  he  indicates,  or  to  reconcile  the  ap¬ 
parent  course  of  the  globules  with  the  supposed  direction  of  the 
alimentary  tube,  we  are  still  inclined  to  regard  the  flow  of  particles 
alluded  to  as  analogous  to  what  has  been  described  as  existing  in 
the  stems  of  polyps.  Neither  do  we  find  any  distinct  apparatus 
devoted  to  respiration  in  these  minute  beings  :  the  cilia  upon  the 


ACALEPH.E. 


64 

surface,  by  the  constant  currents  which  they  excite,  necessarily 
ensure  a  continual  supply  of  aerated  water,  which  bathing  the 
whole  body  exposes  every  part  to  the  influence  of  oxygen,  and 
Ehrenberg  thinks  that  he  has  even  perceived  the  existence  of  a 
delicate  net-work  of  minute  canals  hollowed  out  in  the  periphery 
of  some  species,  which,  if  filled  with  nutritive  juices,  might  be 
regarded  as  the  first  rudiments  of  a  vascular  system. 

(92.)  The  nervous  matter,  or  neurine,  which  we  must  suppose 
to  exist  in  a  molecular  state  mixed  up  with  the  tissues  of  the  body, 
has  never  been  detected  in  an  aggregated  form  ;  nevertheless,  upon 
many  species,  when  observed  under  good  glasses,  it  is  easy  to  see 
one  or  two  extremely  minute  red  or  brown  specks,  which  have 
been  conjectured  to  be  eyes,  though  probably  without  further 
reason  for  the  supposition  than  the  resemblance  which  they 
exhibit,  in  colour  at  least,  to  the  visual  organs  of  some  ento- 
mostracous  Crustacea  :  in  some  cases,  these  points  exist  only  in 
the  young  animalcule  prior  to  its  birth ;  thus  in  Eudorina 
elegans ,  an  animal  resembling  the  Volvox  in  its  mode  of  gene¬ 
ration,  the  offspring,  while  confined  in  the  body  of  their  parent, 
are  each  seen  to  be  furnished  with  a  red  speck,  as  well  as  a  long 
bristle,  which  is  exserted  through  the  parent  envelope  ;  but  as  soon 
as,  by  the  rupture  of  the  sac,  the  contained  gemmules  are  set  at 
liberty, — a  time  when  we  should  imagine  the  faculty  of  vision  to  be 
most  useful, — the  red  point  disappears  ;  and,  were  that  the  only 
means  of  appreciating  the  presence  of  light,  we  might  suppose  the 
liberated  animalcules  to  be  deprived  of  the  power  of  seeing  when 
most  capable  of  enjoying  it. 


CHAPTER  V. 

Acaleph.e,  (Cuv.) 

(93.)  The  fourth  class  of  acrite  animals  is  scarcely  inferior  to 
that  last  described,  either  in  numbers  or  interest.  The  ocean  in 
every  climate  swarms  with  infinite  multitudes  of  animals,  which, 
from  their  minuteness  and  transparency,  are  almost  as  impercepti¬ 
ble  to  the  casual  observer  as  the  infusoria  themselves  ;  their  exist¬ 
ence  being  only  indicated  by  the  phosphorescence  of  some  species, 
which,  being  rendered  evident  on  the  slightest  agitation,  illuminates 


ACALEPH.E. 


65 


the  entire  surface  of  the  sea.  All  however  are  not  equally  minute, 
some  grow  to  a  large  size ;  and  their  forms  are  familiar  to  the  inha¬ 
bitants  of  every  beach,  upon  which,  when  cast  up  by  the  waves, 
they  lie  like  masses  of  gelly,  melting  as  it  were  in  the  sun,  inca¬ 
pable  of  motion  and  exhibiting  few  traces  of  organization,  or 
indications  of  that  elaborate  structure  which  more  careful  examina¬ 
tion  discovers  them  to  possess.  Their  uncouth  appearance  has 
obtained  for  them  various  appellations  by  which  they  are  fami¬ 
liarly  known,  as  sea-gelly,  sea-blubber,  or  gelly- fishes ;  whilst, 
from  disagreeable  sensations  produced  by  handling  most  of  them, 
they  have  been  called  sea-nettles,  stingers,  or  stang-fishes.  The 
faculty  of  stinging  is  indeed  the  most  prominent  feature  in  their 
history,  so  that  their  names  in  almost  all  languages  are  derived 
from  this  circumstance  :  they  were  known  to  the  older  naturalists 
by  the  title  of  Urtica  marina;  and  the  word  at  the  head  of  this 
chapter,  applied  by  Cuvier  to  the  entire  class,  and  originally  used 
by  Aristotle,  is  of  similar  import  a  nettle). 

There  are  few  subjects  which  come  under  the  observation 
of  the  physiologist  more  calculated  to  excite  his  astonishment 
than  the  history  of  these  creatures.  If  he  considers,  in  the  first 
place,  the  composition  of  their  bodies,  what  does  he  find  ? — an 
animated  mass  of  sea-water,  for  such  in  an  almost  literal  sense 
they  are.  Let  him  take  a  medusa  of  any  size,  and  lay  it  in  a 
dry  place  ;  it  will  be  found  gradually  to  drain  away,  leaving  nothing 
behind  but  a  small  quantity  of  transparent  cellular  matter,  almost 
as  delicate  as  a  cobweb,  which  apparently  formed  all  the  solid 
frame-work  of  the  body,  and  which,  in  an  animal  weighing  five  or 
six  pounds,  will  scarcely  amount  to  as  many  grains ;  and  even  if 
the  water  which  has  escaped  from  this  cellulosity  be  collected  and 
examined,  it  will  be  found  to  differ  in  no  sensible  degree  from  the 
element  in  which  the  creature  lived.  The  conclusion  therefore 
at  which  he  naturally  arrives  is,  that,  in  the  medusae,  the  sea-water 
collected  and  deposited  in  the  delicate  cells  of  an  almost  imper¬ 
ceptible  film  becomes  in  some  inscrutable  manner  instrumental 
to  the  exercise  of  the  extraordinary  functions  with  which  these 
creatures  are  endowed.  The  Acalephse  have  been  divided  by 
zoologists  into  groups  distinguished  by  the  nature  of  their  means 
of  progression  :  in  describing  therefore  the  organs  of  locomotion, 
with  which  we  commence  their  history,  the  reader  will  be  made 
acquainted  with  the  principal  modifications  of  outward  form  which 
they  exhibit. 


66 


AC  ALEPHJS. 


(94.)  Pulmonigrada. — The  most  ordinary  examples  of  the 
acalephee  found  in  our  climate,  when  examined  in  their  native 
element,  are  seen  to  be  composed  of  a  large  mushroom-shaped 
gelatinous  disc,  from  the  inferior  surface  of  which  various  pro¬ 
cesses  are  pendent,  some  serving  as  tentacula,  others  for  the  pre¬ 
hension  of  food.  In  Rhizostoma  (Jig-  SI)  the  central  pedicle 
resembles  in  structure 
and  function  the  root  of 
a  plant,  being  destined 
to  absorb  nourishment 
from  the  water  in  which 
the  creature  lives.  The 
body  of  one  of  these 
medusae  is  specifically 
heavier  than  the  water 
of  the  ocean,  and  would 
sink  but 
for  some  effort  on  the 
part  of  the  animal. 

The  agent  employed 
to  sustain  it  at  the  sur¬ 
face,  and  in  some  mea¬ 
sure  to  row  it  from  place 
to  place,  is  the  um¬ 
brella-shaped  expansion 
or  disc,  which  is  seen  continually  to  perform  movements  of  con¬ 
traction  and  dilatation,  repeated  at  regular  intervals  about  fifteen 
times  in  a  minute,  having  some  resemblance  to  the  motions  of  the 
lungs  in  respiration,  whence  the  name  of  the  order  ( pulmo ,  the 
lung;  grcidior ,  I  advance).  By  these  constant  movements  of  the 
disc,  the  medusa  can  strike  the  water  with  sufficient  force  to 
insure  its  progression  in  a  certain  direction  when  swimming  in 
smooth  water,  but  of  course  utterly  inefficient  in  stemming  the 
course  of  the  waves,  at  the  mercy  of  which  these  animals  float. 
The  tentacula,  in  such  species  as  are  provided  with  these  organs, 
are  likewise  capable  of  contractile  efforts,  and  may  in  some  slight 
degree  assist  as  agents  of  impulsion,  although  they  are  destined  to 
the  exercise  of  other  functions.  The  locomotive  disc,  when  cut 
into,  seems  perfectly  homogeneous  in  its  texture,  nor  is  any 
fibrous  appearance  recognisable  to  which  its  movements  could  be 
attributed  ;  but  in  the  larger  species  its  inferior  surface  appears 


consequently 


ACALEPHiE. 


67 


corrugated,  as  it  were,  into  minute  radiating  plicse,  which  seem 
to  contract  more  energetically  than  the  other  portions,  and  re¬ 
semble  a  rudimentary  developement  of  muscular  fibre. 

(95.)  Ciliograda. — In  the  Ciliograde  acalephfe,  the  organs  of 
motion  are  of  a  very  different  description,  consisting  of  narrow 
bands  of  vibratile  cilia  variously  disposed  upon  the  surface  of 
the  body,  which  in  their  motions  and  office  resemble  those  of 
the  polygas  trie  animalcules. 

In  the  globular  forms  of  Beroe  {Jig.  22)  the  cilia  are  generally 

Fig.  22. 


arranged  in  eight  longitudinal  bands,  and  appear  to  be  attached  to 
subjacent  arches  of  a  firmer  consistence  than  the  rest  of  the  body. 
They  are  generally  quite  naked,  but  in  Pandora  are  lodged 
between  folds  of  the  skin,  which  will  close  over  and  completely 
conceal  them ;  their  motion  is  extremely  rapid,  and  sometimes 
only  recognisable  by  the  currents  which  they  produce,  or  the 
iridescent  hues  which  play  along  the  arches.  The  ciliary  action 
seems  to  be  perfectly  under  the  control  of  the  animal,  as  it  can 
retard  or  stop  their  motions  at  pleasure,  sometimes  arresting  the 
play  of  one,  two  or  more  rows,  whilst  the  rest  continue  in  rapid 
vibration,  and  thus  changing  its  course,  or  causing  its  body  to 
revolve  in  any  direction.  In  some  of  the  Ciliograda,  the  loco¬ 
motive  cilia  are  of  considerable  size  ;  and  in  Cydippe  pileus  their 
structure  has  been  particularly  examined  by  Dr.  Grant.*  In  this 
animal  each  cilium,  instead  of  being  a  simple  filament,  seems  to 
be  made  up  of  several,  arranged  side  by  side,  so  as  to  form  a  flat 
membranous  organ,  not  unlike  the  fin  of  a  fish  (Jig.  22 ;  3,4): 
the  individual  filaments  appear  tubular  when  viewed  under  a 
powerful  magnifier,  and  are  slightly  curved  backwards,  so  that 

*  Transact.  Zoolog.  Society  of  London,  vol.  i. 

F  2 


68 


ACALEPII.E 


the  whole  apparatus  gives  not  a  very  bad  representation  of  the 
paddle-wheel  of  a  steam-boat.  The  cause  of  their  movements  is 
however  as  little  evident  in  the  Beroeform  acaleplue  as  in  the 
minute  Polygastrica.  Under  the  arches  which  support  them 
are  vessels  containing  a  fluid,  which  Dr.  Grant  imagines  may  in 
some  manner  be  injected  into  the  tubular  structure,  and  thus  cause 
them  to  become  erected  ;  but  how  their  rapid  motions  are  excited, 
is  still  far  from  being  explicable. 

But  one  of  the  most  beautiful  examples  of  a  ciliated  medusa 
is  seen  in  the  Girdle  of  Venus  ( Cesium  Veneris)  23). 


Fig.  23. 


This  creature  is  a  long,  flat,  gelatinous  riband,  the  margins  of 
which  are  fringed  with  innumerable  cilia,  tinted  with  the  most 
lovely  iridescent  colours  during  the  day,  and  emitting  in  the  dark 
a  phosphorescent  light  of  great  brilliancy :  in  this  animal  too, 
which  sometimes  attains  the  length  of  five  or  six  feet,  canals  may 
be  traced  running  beneath  each  of  the  ciliated  margins,  analogous 
to  those  which  exist  in  the  Beroe,  and  no  doubt  answering  a 
similar  purpose. 

(96.)  Physograda. —  In  the  third  division  of  acalephae,  de¬ 
nominated  by  Cuvier  “  Acalephes  Hydrostatiques,”  the  body  is 
supported  in  the  water  by  a  very  peculiar  organ,  or  set  of  organs, 
provided  for  the  purpose.  This  consists  of  one  or  more  bladders, 
capable  of  being  filled  with  air  at  the  will  of  the  animal,  which 
are  appended  to  the  body  in  various  positions,  so  as  to  form  floats 
of  sufficient  buoyancy  to  sustain  the  creature  upon  the  surface  of 
the  sea  when  in  a  state  of  distension  ;  but,  when  partially  empty, 
allowing  it  to  sink,  and  thus  escape  the  approach  of  danger.  In 


ACALEPH  E 


69 


Physalus,  (Jig.  24,)  known  to  sailors  by  tlie  name  of  the  Por¬ 
tuguese  man-of-war,  the  swim-  p^  24. 

ming-bladder  is  single,  and  of 
great  proportionate  size,  so  that 
when  full  of  air  it  is  exceed¬ 
ingly  buoyant,  and  floats  con¬ 
spicuously  upon  the  waves.  The 
top  of  this  bladder  bears  a  crest, 
c,  of  a  beantiful  purple  colour, 
which,  presenting  a  broad  surface 
to  the  wind,  acts  as  a  sail,  by  the 
assistance  of  which  the  creature 
scuds  along  with  some  rapidity. 

The  air-bladder  is  endowed  with 
a  considerable  power  of  contrac¬ 
tion,  and,  when  carefully  exa¬ 
mined,  two  orifices  are  observ¬ 
able,  one  at  each  extremity,  (aJJ 
through  which,  upon  pressure, 
the  contained  air  readily  escapes  ; 
a  provision  which  enables  the 
creature  to  regulate  its  specific 
gravity  at  pleasure,  and,  when  alarmed,  at  once  to  lessen  its  buoy¬ 
ancy  by  diminishing  the  capacity  of  its  swimming-bladder,  and 
to  sink  into  the  waves.  The  nature  of  the  air  with  which  the 
little  voyager  distends  its  float  has  not  been  accurately  deter¬ 
mined  ;  but  it  is  undoubtedly  a  secretion  furnished  at  pleasure 
when  at  a  considerable  distance  from  the  surface,  although  the 
mode  of  its  production  is  still  unknown. 

Among  the  diversified  forms  of  the  Hydrostatic  acalephee,  few 
are  more  elegant  than  one  named  by  Peron  Cuvieria  cariso- 
chroma  (Jig-  27).  In  this  beautiful  medusa  we  find  the  floats 
arranged  like  a  string  of  pearls  around  the  margin  of  its  circular 
body  ;  which,  thus  supported,  spreads  its  long  and  delicate  fila¬ 
mentary  tentacles  to  a  considerable  depth,  in  search  of  passing 
food,  as  it  swims  upon  the  tranquil  bosom  of  the  ocean. 

(97.)  Cirrigrada .  —  The  Cirrigrade  acalephse  form  a  very 
remarkable  family,  peculiarly  distinguished  by  the  possession  of 
an  internal  solid  support  or  skeleton  secreted  in  the  substance 
of  their  soft  and  delicate  bodies.  In  Porpita  (Jig.  25)  this 
consists  of  a  flat  plate  of  semicartilaginous  texture,  (2,)  evi- 


70 


acalephj:. 


clently  deposited  in  *•  Fl8'  25 

thin  secondary  lami¬ 
nae,  which  gradually 
increase  in  size  as  the 
animal  advances  in 
,  the  inferior 
being  the  largest  and 
last  formed.  When 
examined  after  its  removal  from  the  body,  this  fragile  skeleton  is 
seen  to  be  extremely  porous  or  cellular ;  and,  the  pores  being 
filled  with  air,  it  is  specifically  lighter  than  water,  a  circumstance 
which  may  contribute  to  the  buoyancy  of  the  animal,  even  when 
alive. 

The  lower  surface  of  Porpita  is  furnished  with  numerous  appen¬ 
dages  called  cirri,  some  of  which  appear  to  be  organs  of  prehension, 
but  perform  also  the  office  of  oars,  which  in  this  species  are  the 
principal  agents  in  progression  ;  yet  in  other  Cirrigrada,  as  Velella 
and  Rataria ,  besides  the  horizontal  lamella,  which  forms  the  whole 
skeleton  of  Porpita,  there  is  a  second  subcartilaginous  plate  rising 
at  right  angles  from  its  upper  surface,  and  supporting  a  delicate 
membranous  expansion,  which  rises  above  the  water  and  exposes  a 
considerable  surface  to  the  wind,  so  as  to  form  a  very  excellent 
sail.  To  perfect  so  beautiful  a  contrivance,  in  Rataria  the  crest 
is  found  to  contain  fibrous  bands,  apparently  of  a  muscular  nature, 
by  the  contractions  of  which  the  sail  can  be  lowered  or  elevated  at 
pleasure. 

(98.)  Diphyda. — The  last  family  of  aealeplise  derives  its  name 
from  the  singular  appearance  of  the  creatures  which  compose  it : 
each  animal,  in  fact,  seems  to  consist  of  two  portions  so  slightly 
joined  together,  that  it  is  by  no  means  easy  to  understand  the 
nature  of  the  con-  26. 

nection  which  ex¬ 
ists  between  them ; 
and  from  the  per¬ 
fect  transparency 
of  their  bodies, 
which  is  such  that 
it  is  with  great 
difficulty  they  are 
discoverable  even 
in  small  quanti- 


AC  ALEPPLE. 


71 


Fig.  27. 


ties  of  sea-water,  our  knowledge  of  their  internal  structure  is  at 
present  extremely  imperfect.  The  annexed  figure  of  Diphyes  cctm- 
panulifera  {Jig.  26)  will  give  the  reader  a  general  idea  of  their 
form.  The  two  bell-shaped  portions  of  which  the  creature  may 
there  be  seen  to  consist,  are  constantly  found  united  together,  and 
seem  to  compose  but  one  animal,  although  they  might  readily  be 
conceived  to  be  distinct  creatures  ;  the  apex  of  the  posterior  part 
is  received  into  a  cavity  in  the  other  portion,  but  the  connection 
between  the  two  is  so  slight,  that,  when  preserved  in  spirits  at 
least,  the  slightest  touch  is  sufficient  to  tear  them  asunder  ;  their 
principal  bond  of  union  appears  to 
be  a  delicate  filament,  which,  arising 
from  the  anterior  compartment, 
passes  through  the  whole  length 
of  the  posterior  portion.  This 
strange  compound  body,  concern¬ 
ing  the  structure  of  which  our 
knowledge  is  very  imperfect,  swims 
through  the  water  with  consider¬ 
able  rapidity,  urged  forward  by  the 
alternate  contractions  of  the  two 
campanulate  halves,  which  con¬ 
tinually  take  in  and  eject  the  cir¬ 
cumambient  fluid,  with  sufficient 
force  to  propel  the  creature  in  an 
equable  and  uniform  course. 

(99.)  Interesting  as  the  acalephse 
may  justly  be  considered  when  we 
contemplate  the  singular  beauty  of 
their  external  configuration,  and 
the  wonderful  design  conspicuous  in 
their  locomotive  organs,  a  more  in¬ 
timate  acquaintance  with  their  habits  and  economy  will  be  found  to 
disclose  many  facts  not  less  curious  in  themselves  than  important  in  a 
physiological  point  of  view.  In  the  higher  animals  we  are  accustomed 
to  find  the  nutritive  apparatus  composed  of  several  distinct  systems  ; 
one  set  of  organs  being  destined  to  the  prehension  of  food,  another 
to  digestion,  a  third  to  the  absorption  of  the  nutritious  parts  of  the 
aliment,  a  fourth  provided  for  its  distribution  to  every  part  of  the 
body,  and  a  fifth  destined  to  ensure  a  constant  exposure  of  the  cir¬ 
culating  fluid  to  atmospherical  influence.  These  vital  operations 


V  I /I 


ACALEPH.E. 


72 

are  carried  on  in  vessels  specially  appropriated  to  each  ;  but,  in  the 
class  of  animals  of  which  we  are  now  speaking,  we  find  but  a 
single  ramified  cavity  appropriated  to  the  performance  of  all  these 
functions,  and  exhibiting  in  the  greatest  possible  simplicity  a 
rough  outline,  as  it  were,  of  systems  afterwards  to  be  more  fully 
developed. 

In  the  Pulmonigrade  acalepha,  we  have  the  best  illustration  of 
this  arrangement :  in  these  the  stomach  or  digestive  cavity  is  ex¬ 
cavated  in  the  centre  of  the  disc,  and  is  supplied  with  food  by  a 
mechanism  which  differs  in  different  species.  In  Rhizostoma, 
(Jig.  21),  which  receives  its  name  from  the  nature  of  the 
communication  between  the  stomach  and  the  exterior  of  the 
body,*  the  organ  destined  to  take  in  nourishment  consists  of  a 
thick  pedicle,  composed  of  eight  foliated  divisions,  which  hang 
from  the  centre  of  the  disc.  Each  of  these  appendages  is  found 
to  contain  ramifying  canals,  opening  at  one  extremity  by  nu¬ 
merous  minute  apertures  upon  the  external  surface,  whilst  at  the 
opposite  they  are  collected  into  four  large  trunks  communicating 
with  the  stomach ;  as  the  Rhizostoma  therefore  floats  upon  the 
waves,  its  pendent  and  root-like  pedicle  absorbs,  by  the  numerous 
oscules  upon  its  exterior,  such  food  as  may  be  adapted  to  its 
nutrition,  finding  most  probably  an  ample  provision  in  the  mi¬ 
croscopic  creatures  which  so  abundantly  people  the  waters  of  the 
ocean.  The  materials  so  absorbed  are  conveyed  through  the  canals 
in  the  interior  of  the  arms  into  the  stomachal  cavity,  where  their 
solution  is  effected. 

But  it  is  not  upon  this  humble  prey  that  some  of  the  medusae 
feed  ;  many  are  enabled,  in  spite  of  their  apparent  helplessness,  to 
seize  and  devour  animals  which  might  seem  to  be  far  too  strong  and 
active  to  fall  victims  to  such  assailants  :  Crustacea,  worms,  mollusca, 
and  even  small  fishes  are  not  unfrequently  destroyed  by  them.  In¬ 
credible  as  this  may  seem  when  we  reflect  upon  the  structure  of  these 
feeble  beings,  observation  proves  that  they  are  fully  competent  to 
such  enterprises.  The  long  tentacula  or  filaments,  with  which 
some  are  provided,  form  fishing-lines  scarcely  less  formidable  in 
arresting  and  entangling  prey  than  those  of  the  Hydra  ;  and,  in  all 
probability,  the  stinging  secretion  which  exudes  from  the  bodies  of 
these  medusse  speedily  paralyzes  and  kills  the  animals  which  fall 
in  their  way.  The  mouth  of  these  acalephse  is  a  simple  aperture 
leading  into  the  gastric  cavity,  and  sometimes  surrounded  with 


*  'P get,  a  root ;  ar'ofjLa.,  a  mouth. 


acaleph.e. 


78 


tentacula,  which  probably  assist  in  introducing  the  food  into  the 
stomach. 

In  C assiopea  Borbonica ,  the  principal  agents  in  procuring 
nourishment  are  numerous  retractile  suckers,  (Jig.  28,  a ,)  terminat¬ 
ing  in  small  violet- 
coloured  discs,  which 
are  dispersed  over  the 
fleshy  appendages  to 
the  under  surface  of 
the  body  ;  the  stem 
of  each  of  these  suck¬ 
ers  is  tubular,  and 
conveys  into  the  sto¬ 
mach  nutritive  mate¬ 
rials  absorbed  from 
animal  substances  to 
which  they  are  at¬ 
tached  during  the 
process  of  imbibing  food. 

(100.)  The  above  examples  will  suffice  to  give  the  reader  an  idea  of 
the  most  ordinary  provisions  for  obtaining  nourishment  met  with 
in  the  Pulmonigrada  :  we  will  therefore  return  to  consider  the 
structure  of  the  stomach  itself,  and  of  the  canals  which  issue  from 
it,  and  convey  the  digested  nutriment  through  the  system.  In 
Cassiopea  Borbonica ,  which  will  serve  to  exemplify  the  general 
arrangement  of  these  parts  in  the  whole  order,  the  stomach  ( fig . 
28)  is  a  large  cavity  placed  in  the  centre  of  the  inferior  surface  of 
the  disc,  and  is  apparently  divided  into  four  compartments  by  a 
delicate  cruciform  membrane  arising  from  its  inner  walls.  Into 
this  receptacle  all  the  materials  Fig.  29. 

collected  by  the  absorbing  suck¬ 
ers  are  conveyed  through  eight 
large  canals,  and  by  the  process  of 
digestion  become  reduced  to  a 
yellowish  pulpy  matter,  which  is 
almost  fluid,  and  which  is  the 
pabulum  destined  to  nourish  the 
whole  body.  From  the  central 
stomach  sixteen  large  vessels 
arise,  (Jig-  29,  c,)  which  ra¬ 
diate  towards  the  circumference 


74 


AC  ALEPHyE. 


of  the  disc,  dividing  and  subdividing  into  numerous  small  branches, 
which  anastomose  freely  with  each  other,  and  ultimately  form  a 
perfect  plexus  of  vessels  as  they  reach  the  margin  of  the  mush¬ 
room-shaped  body  of  the  creature.  The  radiating  vessels  are 
moreover  made  to  communicate  together  by  means  of  a  circular 
canal  (Jig.  29,  e)  which  runs  around  the  entire  animal,  so  that 
every  provision  is  made  for  an  equable  diffusion  of  the  nutritive 
fluid  derived  from  the  stomach  through  the  entire  system.  Now, 
if  we  come  physiologically  to  investigate  the  nature  of  this 
simple  apparatus  of  converging  and  diverging  canals,  we  cannot 
but  perceive  that  it  unites  in  itself  the  functions  of  the  digestive, 
the  circulatory,  and  the  respiratory  systems  of  higher  animals  : 
the  radiating  canals,  which  convey  the  nutritive  juices  from  the 
stomach  through  the  body,  correspond  in  office  with  the  arteries 
of  more  perfectly  organized  classes ;  and  the  minute  vascular 
ramifications  in  which  these  terminate,  situated  near  the  thin 
margins  of  the  locomotive  disc,  as  obviously  perform  the  part  of 
respiratory  organs,  in  as  much  as  the  fluids  which  permeate  them 
are  continually  exposed  to  the  influence  of  the  air  contained  in  the 
surrounding  water,  the  constant  renewal  of  which  is  accomplished 
by  the  perpetual  contractions  of  the  disc  itself. 

(101.)  Before  closing  our  description  of  the  alimentary  system  of 
the  Pulmonigrade  acalephse,  we  must  mention  some  accessory  organs 
of  recent  discovery  which  are  in  connection  with  it.  Eschscholtz* 
describes  a  series  of  elongated  granular  bodies,  placed  in  little  de¬ 
pressions  around  the  margin  of  the  disc,  which  seem  to  be  of  a 
glandular  nature,  and  apparently  communicate  by  means  of  minute 
tubes  with  the  nutritious  canals  :  these  he  regards  as  the  rudiments 
of  a  biliary  system.  Other  observers  assign  a  similar  office  to  a 
cluster  of  blind  sacculi  or  caeca,  which  are  connected  in  some 
species  with  the  commencement  of  the  radiating  tubes  ;  it  is, 
however,  scarcely  necessary  to  observe  that  such  surmises  relative 
to  the  function  of  minute  parts  are  but  little  satisfactory. 

(102.)  The  Ciliograde  acalephee,  although  their  digestive  system 
varies  considerably  in  its  general  arrangement  from  what  has  been 
described  in  the  Pulmonigrade  division,  will  be  found  to  exemplify 
in  an  equally  perfect  and  perhaps  more  striking  manner  the  for¬ 
mation  of  the  vascular  and  respiratory  systems  from  an  extension 
of  the  nutritive  canals.  In  the  Beroeform  species  (Jig.  22)  the 

*  System  der  Acaleplien.  Berlin,  1829. — Annales  des  Sciences  Nat.  vol.  xxviii. 
p.  251. 


AC  A  LEPHyE. 


75 


alimentary  canal  passes  straight  through  the  globular  or  barrel¬ 
shaped  body,  commencing  at  one  extremity  by  two  prominent  and 
sensitive  lips.  No  apparatus  of  prehension  is  here  needful ;  for,  as 
these  animals  swim  along  by  the  action  of  their  cilia,  the  water 
passes  freely  through  this  capacious  channel,  and  brings  into  the 
stomach  materials  proper  for  food.  From  both  extremities  of  the 
digestive  cavity  arise  vascular  canals  which  empty  themselves  into 
two  circular  vessels,  one  surrounding  the  oral,  and  the  other  the 
anal  portions  of  the  body  :  from  these  two  rings  eight  double  vessels 
arise,  which  run  longitudinally  from  one  pole  to  the  other  of 
the  creature  beneath  each  of  the  cartilaginous  ribs  upon  which 
the  cilia  are  placed  ;  and  from  these,  others  more  minute  arise, 
which  are  distributed  in  a  delicate  network  through  the  sub¬ 
stance  of  the  animal.  In  the  Beroe,  therefore,  we  must  regard 
the  vessels  which  convey  the  nutritive  juices  beneath  the  ciliated 
arches,  not  merely  as  arteries,  but  as  organs  of  respiration  ;  for, 
thus  placed  close  beneath  the  outer  surface  of  the  body,  the  water, 
which  is  perpetually  made  to  rush  over  them  by  the  ciliary  move¬ 
ments,  will  serve  to  aerate  the  fluid  contained  within. 

The  Cestum  Veneris  (Jig-  23)  is  nearly  allied  to  the  Beroe  in 
the  arrangement  of  its  nutritive  apparatus,  notwithstanding  the 
difference  of  form  observable  in  these  Ciliograde  medusae.  In  Ces¬ 
tum  the  digestive  cavity,  which  is  exceedingly  short  in  comparison 
with  the  length  of  the  animal,  passes  transversely  across  the  body 
in  a  straight  line  from  one  side  to  the  other,  as  represented  in  the 
engraving  (Jig.  23)  ;  but  the  details  of  its 
structure,  and  the  nature  of  the  vessels  aris¬ 
ing  from  it,  will  be  best  understood  by  a 
reference  to  the  enlarged  diagram  of  these 
parts  given  in  the  annexed  figure  (Jig.  30). 

The  mouth  (i)  is  a  rhomboidal  depression 
seen  near  the  centre  of  the  body,  between 
the  two  lateral  rows  of  locomotive  cilia 
which  extend  from  one  end  of  the  animal  to 
the  other.  From  the  mouth  arise  two 
tubes,  (j,j9)  which  terminate  in  a  globular 
cavity  common  to  both  ;  these  would  seem 
to  constitute  the  digestive  apparatus  :  and 
a  straight  and  narrow  tube  (o),  prolonged 
to  the  margin  of  the  body  opposite  to  that 
which  the  mouth  occupies,  may  be  regarded 


Fig.  30. 


mimiiii  ii 


76 


ACALEPH.E. 


as  an  intestine  through,  which  the  residue  of  digestion  is  discharged. 
From  around  the  oral  extremity  of  the  stomach,  and  from  the  glo¬ 
bular  cavity  in  which  the  two  principal  canals  terminate,  arise  ves¬ 
sels,  (7,  t ,  tj  which  diverge  so  as  to  form  a  cone  at  the  base  of  which 
they  all  empty  themselves  into  two  circular  canals,  one  surrounding 
the  mouth,  and  the  other  encircling  the  anal  aperture  ;  which  pre¬ 
cisely  correspond  with  the  vascular  rings  already  described  in  the 
Beroe  :  and,  from  these,  four  long  vessels,  or  branchial  arteries  as 
they  might  be  termed,  (p,  p-,  </,  </,)  are  prolonged  beneath  the  four 
ciliated  margins  all  around  the  body.  But,  besides  these  four  nutri¬ 
tive  vessels,  two  others  (x,  x)  arise  from  the  anal  ring  which  run 
inwards  towards  the  centre  of  the  animal,  and  afterwards,  assuming 
a  longitudinal  direction,  seem  to  distribute  nourishment  to  the  me¬ 
dian  portions  of  the  body.  The  cseca  or  blind  tubes,  ( n ,  n ,)  ap¬ 
pended  to  the  intestine,  may  possibly  furnish  some  secretion  use¬ 
ful  in  digestion,  although  we  are  perhaps  scarcely  warranted  in 
saying  decidedly  that  they  are  the  rudiments  of  biliary  organs.* 

Our  information  concerning  the  nutritive  apparatus  of  the  other 
orders  of  acalephse  is  very  limited.  In  Physalus  (Jig-  24)  and 
Porpita  (Jig.  25),  the  suckers  appended  to  the  body  would  seem 
to  be  the  organs  by  which  food  is  taken  into  the  system  ;  but,  of 
the  internal  arrangement  of  the  parts  subservient  to  its  digestion 
and  distribution,  little  has  been  determined  satisfactorily. 

(103.)  Extraordinary  as  must  appear  the  powers  which  these 
animals  possess  of  seizing  and  dissolving  other  creatures,  apparently 
so  disproportioned  to  their  strength,  and  the  delicate  tissues  which 
compose  their  bodies,  there  are  other  circumstances  of  their  history 
equally  remarkable,  which  in  the  present  state  of  our  knowledge 
are  still  more  inexplicable.  If  a  living  medusa  be  placed  in  a 
large  vessel  of  fresh  sea- water,  it  will  be  found  to  secrete  an  abun¬ 
dant  quantity  of  glairy  matter,  which,  exuding  from  the  surface 
of  its  body,  becomes  diffused  through  the  element  around  it  so 
copiously,  that  it  is  difficult  to  conceive  whence  materials  can  be 
derived  from  which  it  can  be  elaborated.  Of  the  origin  of  this 
fluid  we  are  ignorant,  although  certain  glandular-looking  granules 
contained  in  the  folds  of  the  pedicle  have  been  looked  upon  as 
connected  with  its  production. 

(104.)  We  are  equally  at  a  loss  to  account  for  the  pro¬ 
duction  of  the  irritating  secretion  in  which  the  power  of  stinging 

*  Delle  Chiaje,  Memorie  per  servire  alia  storia  degli  Animali  senza  vertebre  del 
regno  di  Napoli.  4to.  1823 — 1825. 


ACALEPH.E. 


77 


seems  to  reside,  but  it  is  observed  that  the  tentacula  seem 
to  be  more  specially  imbued  with  it  than  other  parts  of  the 
body.  Perhaps  the  most  remarkable  property  of  the  acalephse 
is  their  phosphorescence,  to  which  the  luminosity  of  the  ocean, 
an  appearance  especially  beautiful  in  warm  climates,  is  princi¬ 
pally  due.  We  have  more  than  once  witnessed  this  pheno¬ 
menon  in  the  Mediterranean,  and  the  contemplation  of  it  is  well 
calculated  to  impress  the  mind  with  a  consciousness  of  the  profu¬ 
sion  of  living  beings  existing  around  us.  The  light  is  not  con¬ 
stant,  but  only  emitted  when  agitation  of  any  kind  disturbs  the 
microscopic  medusae  which  crowd  the  surface  of  the  ocean  :  a  pass¬ 
ing  breeze,  as  it  sweeps  over  the  tranquil  bosom  of  the  sea,  will 
call  from  the  waves  a  flash  of  brilliancy  which  may  be  traced  for 
miles  ;  the  wake  of  a  ship  is  marked  by  a  long  track  of  splendour ; 
the  oars  of  your  boat  are  raised  dripping  with  living  diamonds  ; 
and,  if  a  little  of  the  water  be  taken  up  in  the  palm  of  the  hand 
and  slightly  agitated,  luminous  points  are  perceptibly  diffused 
through  it,  which  emanate  from  innumerable  little  acalephee  scarce¬ 
ly  perceptible  without  the  assistance  of  a  microscope.  All,  how¬ 
ever,  are  not  equally  minute  ;  the  Beroes,  in  which  the  cilia  would 
seem  to  be  most  vividly  phosphorescent,  are  of  considerable  size  ; 
the  Cestum  Veneris,  as  it  glides  rapidly  along,  has  the  appearance 
of  an  undulating  riband  of  flame  several  feet  in  length  ;  and  many 
of  the  larger  Pulmonigrade  forms  shine  with  such  dazzling  bright¬ 
ness,  that  they  have  been  described  by  navigators  as  resembling 
44  white-hot  shot”  visible  at  some  depth  beneath  the  surface. 
This  luminousness  is  undoubtedly  dependent  upon  some  phospho¬ 
rescent  secretion,  but  its  nature  and  origin  are  quite  unknown. 

(105.)  The  principal  instruments  of  sensation  in  the  acalephse  are 
the  tentacula  and  suckers,  which,  under  various  forms,  are  append¬ 
ed  to  different  parts  of  the  body,  and  which  are  individually  capa¬ 
ble  of  contraction  and  elongation  to  a  considerable  extent.  In  the 
discophorous  forms,  these  are  frequently  appended  to  the  margin 
of  the  disc  (Jig-% 7)  ;  sometimes  they  are  only  found  around  the 
aperture  of  the  mouth.  In  P  or  pita  and  Physalus  they  are  nu¬ 
merous,  and  hang  in  clusters  from  the  inferior  surface  of  the  body  : 
but  the  most  beautiful  tentacular  apparatus  is  that  which  is  met 
with  in  the  Beroe  ( Cydippe )  pileus;  this  is  represented  in  Jig.  22  ; 
1 ,  a,  a ,  and  consists  of  two  very  long  and  delicate  filaments, 
many  times  exceeding  the  length  of  the  body  when  extended  to 
their  full  length  ;  from  these  arise  others  of  still  greater  tenuity, 


78 


ACALEPH.E. 


which  are  likewise  capable  of  spontaneous  elongation.  When  not 
in  use,  these  organs  are  retracted  within  the  body,  and  lodged  in 
two  membranous  sheaths  visible  in  the  drawing,  from  which  they 
are  protruded  at  the  pleasure  of  the  animal,  and,  as  they  expand, 
gradually  uncurl  the  spiral,  secondary  tentacula  by  movements 
which  are  singularly  graceful  and  elegant. 

In  Medusa  aurita  there  are  seen  around  the  circumference  of 
the  locomotive  disc  certain  red  spots,  which  Ehrenberg  regards  as 
eyes,  without  however  adducing  the  slightest  proof  that  they 
possess  any  claims,  derived  either  from  their  structure  or  function, 
to  the  name  which  he  is  pleased  to  give  them. 

(106.)  Most  anatomists  have  failed  to  detect  nervous  filaments 
even  in  the  largest  medusse  ;  nevertheless  Ehrenberg  is  inclined  to 
believe  that  in  some  Pulmonigrade  species  a  delicate  thread,  which 
encircles  the  margin  of  the  disc,  is  to  be  regarded  as  nervous,  as 
well  as  others,  which  he  describes  as  being  visible  around  the  base 
of  the  pedicle.  In  the  Beroe  ( Cydippe )  p  ileus ,  (Jig.  22,)  Pro¬ 
fessor  Grant*  regards  a  double  cord  which  runs  around  the  oral 
extremity  of  the  alimentary  canal,  of  which  an  isolated  view  is 
given  at  Jig.  22,  2,  as  constituting  the  nervous  system  ;  this  ar¬ 
rangement,  however,  has  not  been  confirmed  by  later  observations, 
and  we  are  inclined  to  think  that  the  vascular  circle  which  sur¬ 
rounds  the  mouth  (§  102)  of  the  Beroeform  species  has  been  in 
this  case  mistaken  for  nervous  fibre. 

(107.)  We  know  little  satisfactorily  concerning  the  mode  of  gene¬ 
ration  in  the  acalephse,  the  opinions  of  authors  upon  this  subject 
being  in  the  last  degree  vague  and  contradictory.  Confining  our¬ 
selves  to  the  examples  which  have  been  selected  as  best  adapted  to 
put  the  reader  in  possession  of  the  principal  facts  known  concerning 
the  class  under  consideration,  we  find  the  organs  usually  regarded 
as  the  agents  of  reproduction  assuming  very  different  forms.  In 
Cassiopea  Borbonica ,  the  parts  which  Delle  Chiaje  describes  as 
ovaria,  are  four  membranous  tubes  filled  with  granular  matter,  and 
placed  above  the  stomach  (Jig.  28,  c)  ;  from  each  of  these  a  canal 
issues,  which,  dividing  into  several  smaller  branches,  opens  by  as 
many  minute  orifices  into  four  cavities  placed  around  the  stomach, 
into  which  the  sea-water  is  freely  admitted. 

According  to  Gaedej*  and  Eysenhardt, j  the  ovaria  examined 

*  Transactions  of  the  Zoological  Society,  vol.i. 

*J*  Beytrage  zur  Anatomie  und  Physiologie  der  Medusen.  Berlin,  1816.  8vo. 

t  Zur  Anatomie  und  Naturgeschichte  der  Quallen  ;  Bhizostoma  Cuvierii. — Mem.  de 
l’Academie  Leopold  des  cur.  de  la  Nature. 


STERELMINTHA. 


79 


in  other  forms  of  the  Pulmonigrada  occupy  a  similar  position,  and 
at  certain  seasons  of 
the  year  become  re¬ 
markably  distended 
with  ova  ;  but,  from 
the  observations  of 
these  writers,  it 
would  seem  that  the 
young  medusa  are 
hatched  in  the  ova- 
ria,  and  afterwards 
escape  in  a  very  per¬ 
fect  state  of  deve- 
lopement.  One  of 
the  ovaria  of  M edusa 
aurita  is  represented 
in  the  annexed  figure, 

{Jig.  31,  1,)  taken 
from  Ehrenberg,s  ela¬ 
borate  plates  of  the 
anatomy  of  this  animal,  in  which  «,  b  indicate  the  extremities  of 
the  convoluted  organs  in  which  the  germs  are  developed.  The 
gemmules,  when  mature,  are,  according  to  this  author,  covered  with 
locomotive  cilia  like  those  of  sponges  and  polyps  (2). 

In  Physalus  the  ova  would  seem  to  be  generated  by  the 
long  undulating  filaments  attached  to  the  lower  surface  of 
the  body,  and  in  Beroe  the  ovaria  are  seen  to  form  clusters 
around  the  alimentary  canal ;  but  we  are  ignorant  of  the  mode 
of  their  developement,  and  of  the  circumstances  connected  with 
the  exclusion  of  the  young. 


Fig.  31 . 


CHAPTER  VI. 

STERELMINTHA. 

Parenchymatous  Entozoa.  (Cuv.) 

The  Entozoa,  as  the  name  implies,  are  nourished  within  the 
bodies  of  other  animals,  from  the  juices  of  which  they  derive  their 
sustenance.  It  may  naturally  be  supposed  that  living  under  such 


80 


STERELJVIINTHA. 


circumstances,  deprived  of  all  power  of  locomotion,  as  is  gene¬ 
rally  a  necessary  consequence  of  the  localities  in  which  they  are 
found,  debarred  from  the  influences  of  light,  and  absolutely  de¬ 
pendent  upon  the  fluids  which  bathe  their  bodies  for  nutriment, 
the  entozoa  have  little  occasion  for  that  elaborate  organization 
needful  to  animals  living  in  immediate  communication  with  exter¬ 
nal  objects. 

W e  find  therefore,  among  these  creatures,  some  whose  structure 
is  more  simple  than  that  of  any  other  animals,  in  adaptation  to  the 
circumscribed  powers  of  which  they  are  capable.  Yet,  however  ap¬ 
parently  insignificant  some  may  appear  from  their  diminutive  size, 
they  not  unfrequently  become  seriously  prejudicial  to  the  animals 
in  which  they  are  found,  by  the  prodigious  numbers  in  which  they 
exist,  or  from  their  growth  in  those  organs  more  especially  essential 
to  life,  and  not  a  few'  of  them  from  their  dimensions  alone  some¬ 
times  prove  fatal.  The  annexed  figure  (Jig.  32)  represents  a 
Ligula  developed  in  the  abdominal  cavity  of  a 
fish.  There  are- probably  no  races  of  animals 
which  are  not  infested  with  one  or  more  species 
of  these  parasites,  from  the  microscopic  infu¬ 
soria  up  to  man  himself,  and  sometimes  several 
different  forms  are  met  with  in  the  same  spe¬ 
cies,  to  which  they  would  appear  to  be  peculiar, 
and  even  in  some  cases  the  entozoa  would 
seem  themselves  to  enclose  other  species  para- 
sitically  dwelling  in  their  own  bodies.  Neither 
is  their  existence  confined  to  any  particular 
parts  ;  they  are  met  with  in  the  alimentary 
canal,  in  the  liver,  the  kidneys,  the  brain,  the 
arteries,  the  bronchial  passages,  the  muscles 
and  cellular  tissue,  and  in  fact  in  almost  all  the 
organs  of  the  body. 

(109.)  It  would  appear  that  some  of  the  ordinary  secretions  of  ani¬ 
mals  are,  when  in  a  healthy  state,  naturally  inhabited  by  innumerable 
active  beings,  scarcely  equalling  in  bulk  some  of  the  most  minute 
infusoria,  and  consequently  requiring  the  highest  magnifiers  to 
detect  even  their  presence.  The  best  known  of  these  are  found  in 
the  seminal  fluid,  and  of  their  size  the  reader  may  form  some  judg¬ 
ment  by  the  following  calculations  upon  this  subject.  Reil  esti¬ 
mated  the  length  of  those  found  in  man  at  the  3~o  o'Voo'  part  of  an 
inch,  or  at  the  25,000th  part  of  a  line,  and  their  breadth  at  the 


STERELMINTHA 


81 


tliousandtli  part  of  the  diameter  of  a  hair  ;  and  Clifton  Wintring- 
ham,  in  order  that  our  ideas  concerning  them  should  be  as  perfect 
as  possible,  recorded  his  estimate  of  the  weight  of  one  of  these 
animalcules,  which  he  supposed  might  be  about  the  hundred  and 
forty  thousand  millionth  part  of  a  grain  !*  Notwithstanding  their 
inconceivable  minuteness,  however,  the  Zoosperms  have  each  a 
definite  and  symmetrical  figure,  which  is  peculiar  to  their  species, 
so  that  those  taken  from  different  animals  may  be  recognized  by 
their  outward  form.  In  quadrupeds  they  have  generally  the  ap¬ 
pearance  of  minute  tadpoles,  with  flattened  globular  bodies,  termi¬ 
nated  by  long  tails  of  extreme  tenuity  ;  but,  in  fishes  and  inverte¬ 
brate  animals,  they  are  often  without  tails,  sole-shaped,  or  even 
globular.  Nothing  of  course  is  known  concerning  the  internal 
organization  of  these  living  atoms. 

(110.)  The  Cystiform  Sterelmintha ,  which  are  generally  known 
by  the  name  of  Hydatids ,  are  the  simplest  in  structure  ;  and  with 
these,  therefore,  we  shall  commence  our  enquiry  into  the  economy 
of  these  creatures.  The  Ccenurus  cerebralis ,  (Jig.  S3,)  one  of 


Fig.  33. 


the  most  common,  is  met  with  in  the  brains  of  sheep,  and  is  the 
cause  of  a  mortal  disease  but  too  well  known  to  the  farmer ;  it  is 
likewise  occasionally  met  with  in  other  ruminating  quadrupeds, 
and,  by  partially  destroying  the  substance  of  the  brain,  soon  proves 
fatal.  This  entozoon,  represented  in  the  figure  of  its  usual  size, 
consists  of  a  delicate  transparent  bladder,  the  walls  of  which, 

*  De  Blainville,  (H.  M.  D.)  Manuel  d’Actinologie.  Paris,  1834.  8vo. 

G 


82 


STERELMINTITA. 


during  the  life  of  the  creature,  are  visibly  capable  of  sponta¬ 
neous  contractions  on  the  application  of  stimuli.  To  this  bladder, 
or  common  body,  are  appended  numerous  heads,  or  rather  mouths, 
ay  hi  ch  are  individually  furnished  with  an  apparatus  of  hooks  and 
suckers,  {Jig.  83,  2,  a,  bj)  calculated  to  fix  them  to  the  surrounding 
tissues,  whence  they  derive  nourishment. 

(111.)  The  Cysticerci,  or  common  hydatids,  agree  in  the  main 
features  of  their  structure  with  the  Ccenurus,  but  are  provided 
with  only  one  head  or  oral  orifice  resembling  those  of  Coenurus 
{Jig.  34,  2).  These  Fi£.  34. 

animals  are  found  in 
almost  all  the  viscera  of 
the  body  ;  and  not  un- 
frequently,  especially  in 
pigs,  exist  in  great  num¬ 
bers,  not  only  in  the 
liver,  which  is  their  most 
usual  seat,  but  in  the 
cellular  texture  of  the 
muscles,  and  even  in 
the  eyes  themselves. 

The  human  frame  is  not 
free  from  their  ravages, 
and,  Avlien  they  abound, 
serious  consequences 
frequently  result  from 
their  presence. 

The  Cysticercus 
crassicollis  is  less  fre¬ 
quently  met  with  than 
the  ordinary  hydatid  (C.  tenuicollis).  In  this  animal  the  head 
is  provided  with  a  prehensile  apparatus  analogous  to  that  found 
in  the  last  described  species ;  a  structure  which  resembles  pre¬ 
cisely  what  Ave  shall  afterwards  find  in  the  Tcenioe  or  tape-Avorms, 
with  which  these  creatures  are  closely  related  in  a  zoological  point 
of  vieAv.  Even  in  external  form  they  are  allied  to  the  cestoid 
Avorms,  as  may  be  seen  in  the  annexed  figure,  in  which,  notAvith- 
standing  the  vesicular  character  of  the  posterior  part  of  the  body, 
the  anterior  portion  is  distinctly  divided  into  segments. 

(112.)  The  mode  of  reproduction  in  these  entozoa  resembles 
that  of  the  Yolvox  globator.  They  propagate  by  internal  gem- 


S  TER  ELM  I  NTH  A. 


83 


mules,  which  grow  from  the  membranous  walls  of  the  sac  ;  and 
which,  having  attained  a  certain  growth,  become  detached,  and  are 
found  floating  in  the  glairy  fluid  contained  in  the  interior  of  the 
parent. 

(113.)  It  is  difficult  even  to  conjecture  the  manner  in  which 
these  parasites  first  obtain  admission  to  the  localities  where  they  are 
found,  and  some  zoologists  have  been  content  to  allow  the  possi¬ 
bility  of  their  being  spontaneously  generated  :  but  the  present 
state  of  our  knowledge  can  scarcely  sanction  the  occurrence  of 
such  developements.  It  seems  more  probable  to  imagine  that 
the  entozoa  exist  in  some  other  form  under  other  circumstances, 
but  that,  when  introduced  into  tlie  body,  their  eggs  may  be 
conveyed  by  the  circulating  fluids  to  a  nidus  proper  for  their 
developement,  where  their  inordinate  growth  is  due  to  the 
abundant  supply  of  already  animalized  food  placed  within  their 
reach,  and  the  exalted  temperature  at  which  they  are  kept. 

(114.)  The  Trichina  spiralis  {fig.  35)  is  an  entozoon  hitherto 
only  found  in  the  human  body, 
and,  although  of  recent  dis¬ 
covery,  several  cases  of  its  oc¬ 
currence  are  recorded.  This 
minute  worm  is  found  in  im¬ 
mense  numbers  imbedded  in 
the  cellular  intervals  between 
the  muscular  fibres,  and  in 
some  instances  all  the  vo¬ 
luntary  muscles  seem  full  of 
these  creatures,  exhibiting, 
when  viewed  with  the  naked 
eye,  an  appearance  imitated 
in  the  annexed  figure  ( fig .  35,  c .)  *  On  examining  the  white 
specks  attentively  under  the  microscope,  every  one  of  them  is 
seen  to  be  a  flask-shaped  vesicle,  apparently  formed  of  condensed 
cellular  membrane,  in  which  the  minute  animal  is  lodged ;  and 
when  this  outer  covering  is  ruptured,  as  at  (a),  the  worm  escapes. 
A  magnified  view  of  the  entozoon  is  given  at  (5),  coiled  up  in  the 
position  in  which  it  is  seen  prior  to  the  destruction  of  the  sac 
which  enclosed  it.  The  body  seems  to  be  filled  with  granular 

*  For  the  knowledge  which  we  possess  of  the  anatomy  of  Trichina,  we  are  princi¬ 
pally  indebted  to  the  researches  of  Professor  Owen  and  Dr.  Arthur  Farre;  though 
it  was  first  discovered  by  M.  Hilton.  Vide  Zool.  Trans,  vol.  i. 


Fig.  35. 


84 


STERELMINTHA. 


matter,  which  escapes  when  the  worm  is  torn  asunder  (d)  ;  hut 
whether  it  possesses  a  true  alimentary  tube,  is  not  as  yet  satis¬ 
factorily  determined. 

(115.)  The  Tania,  or  tape-worms,  are  among  the  most  inter¬ 
esting  of  the  Sterelmintha,  whether  wre  consider  the  great  size  to 
which  they  sometimes  attain,  or  the  singular  construction  of  their 
compound  bodies.  Several  species  of  these  worms  infest  the  human 
body,  and  many  other  forms  of  them  are  met  with  in  a  variety 
of  animals.  They  are  usually  found  in  the  intestinal  passages, 
where,  being  amply  provided  writh  nutritious  aliment,  they  fre¬ 
quently  grow  to  enormous  dimensions,  being  not  unusually 
twenty  or  thirty  feet  in  length,  and  some  have  been  met  with 
much  longer  ;  it  is  therefore  manifest  how  prejudicial  their  pre¬ 
sence  must  prove  to  the  health  of  the  animals  in  which  they 
reside,  and  we  are  little  surprised  at  the  emaciation  and  weak¬ 
ness  to  which  they  generally  give  rise. 

The  Tania  solium ,  the  species  most  usually  met  with  in  the 
human  subject,  at  least  in  our  own  country,  is  that  which  we  select 
for  description.  The  body  of  this  creature  consists  of  a  great 
number  of  segments  united  together  in  a  linear  series  ( fig .  36)  : 
the  segments  which  immediately  succeed  to  the  head  are  very  small, 
and  so  fragile  that  it  is  ^ig.  36. 

rarely  that  this  part  of 
the  animal  is  obtained 
in  a  perfect  state  ;  they 
gradually  however  in¬ 
crease  in  size  towards 
the  middle  of  the  body. 

Each  segment  of  the 
tape-worm  might  be  re¬ 
garded  as  a  distinct  ani¬ 
mal,  for  every  one  of 
them,  with  the  excep¬ 
tion  of  the  smallest,  or 
those  in  the  vicinity  of 
the  head,  is  found  to 
contain  a  complete  ge¬ 
nerative  apparatus ;  yet 
the  alimentary  tubes 
are  common  to  them 
all,  those  of  each  joint 


STERELMINTHA. 


85 


freely  communicating  with  the  nutritive  canals  of  the  adjoining 
segments.  The  first  joint  of  the  Taenia,  which  may  be  called  the 
head,  differs  materially  in  structure  from  all  the  rest ;  it  is  in  fact 
converted  into  an  apparatus  by  means  of  which  the  entire  animal 
derives  its  nourishment.  This  part  in  the  Taenia  solium,  when 
highly  magnified,  is  found  to  be  somewhat  of  a  square  shape ; 
in  the  centre  is  seen  the  mouth,  surrounded  with  a  circle  of 
minute  spines,  so  disposed  as  to  secure  its  retention  in  a  posi¬ 
tion  favourable  for  imbibing  the  chyle  in  which  it  is  immersed. 
Around  this  prominent  mouth  are  placed  four  suckers,  which  are 
no  doubt  additional  provisions  for  the  firm  attachment  of  the  head 
of  the  worm.  In  other  Taeniae  the  structure  of  the  oral  segment  is 
variously  modified  :  thus  in  Taenia  lata  the  aperture  of  the  mouth 
has  no  spines  in  its  vicinity  ;  in  Bothryocephalus  there  are  only 
two  longitudinal  sucking  discs  ;  in  Floriceps  these  are  replaced 
by  four  proboscidifonn  prolongations,  covered  with  sharp  recurved 
spines,  which,  being  plunged  into  the  coats  of  the  intestine,  form 
effectual  and  formidable  anchors  :  yet  the  intention  of  all  these 
modifications  is  the  same,  namely  to  retain  the  mouth  in  a  position 
adapted  to  ensure  an  adequate  supply  of  nutritious  juices. 

(116.)  The  alimentary  canal,  which  extends  from  the  mouth,  is  a 
double  tube,  which  may  be  traced  through  the  whole  length  of  the 
body,  without  any  other  perceptible  communication  with  the  ex¬ 
terior  than  the  oral  orifice  in  the  centre  of  the  head  :  at  the  com¬ 
mencement  of  every  segment,  moreover,  there  is  a  cross-canal,  which 
communicates  with  the  corresponding  canal  of  the  opposite  side 
{Jig-  37,  a ),  so  as  to  facilitate  a  free  distribution  of  the  nutrient 
fluids.  In  some  species  a  delicate  vascular  network  is  perceptible 
in  the  parenchyma  of  the  body,  which  may  likewise  be  connected 
with  the  nutritive  function. 

(117.)  A  distinct  generative  system  is  found  in  every  segment  of 
these  remarkable  animals ;  and,  judging  from  the  number  of  eggs 
produced  by  each,  we  are  at  a  loss  to  reconcile  the  disproportion 
which  exists  between  the  extreme  fertility  of  the  Teenise,  and  the 
comparative  rareness  of  their  occurrence.  The  ovaria  in  which  the 
eggs  are  produced  are  of  great  relative  size,  occupying  the  centre 
of  each  joint.  In  the  annexed  figure  {Jig.  37),  which  represents 
one  of  the  segments  of  the  Tsenia  solium  highly  magnified,  the 
ovigerous  organ  {b)  is  seen  to  consist  of  a  central  cavity,  from  the 
circumference  of  which  radiate  a  great  number  of  crncal  tubes  ; 
these  at  certain  seasons  are  filled  with  granular  ova.  From 


86 


STERELMIN T H A . 


the  central  portion  of  this  ramified  ovary  issues  a  wide  canal  or 
excretory  duct  (c),  which  may  be  traced  to  a  prominent  tu¬ 
bercle  placed  on  the  lateral 
margin  of  every  segment  (e), 
where  it  terminates  in  a  mi¬ 
nute  pore  opening  externally. 

This  canal,  which  may  be 
called  the  oviduct,  is  seen 
just  before  its  termination  in 
the  external  pore  to  be  joined 
by  a  delicate  tube  (d),  which 
appears  as  a  dark  line  under 
the  microscope,  and  derives 
its  origin  from  a  small  bulb  or 
vesicle,  and  may  be  regarded 
as  most  probably  furnishing  a 
secretion  serving  to  fertilize 
the  ova  prior  to  their  expul¬ 
sion  ;  such,  at  least,  is  the 
office  generally  assigned  to  it. 

Many  thousands  of  eggs  must  be  produced  from  such  multiplied 
sources  of  reproduction  ;  and  yet  how  are  they  preserved  and 
replaced  in  circumstances  favourable  to  their  developement  ? 
Fortunately  it  is  rare  to  meet  with  more  than  one  of  these 
creatures  at  the  same  time,  taking  up  a  residence  in  the  same 
individual ;  and,  in  fact,  the  species  which  has  been  specially  the 
subject  of  our  description  is  often  called,  par  excellence ,  “  the 
solitary  worm,”  from  this  circumstance.  Yet  what  becomes  of 
the  reproductive  germs  furnished  in  such  abundance  ?  Do  they, 
as  was  the  opinion  of  Linneus,  live  in  a  humbler  form  in  stagnant 
waters  and  marshes,  until  they  are  casually  introduced  into  the 
body  of  some  animal,  where,  being  supplied  profusely  with  food 
and  placed  in  a  higher  temperature,  they  attain  to  an  exuberant 
developement  ?  Or  are  the  germs  thus  numerous  in  proportion  to 
the  little  likelihood  of  even  a  few  of  them  finding  admission  to  a 
proper  nidus  ?  To  these  questions  we  can  only  reply  by  conjec¬ 
tures  ;  and,  interesting  as  the  subject  is,  few  are  more  entirely 
involved  in  mystery. 

(118.)  In  the  Fluke,  Distoma  ( Fasciola ,  Linn.)  hepaticum ,  we 
have  an  entozoon  of  more  complex  and  perfect  structure ;  one  of 
those  forms,  continually  met  with,  which  make  the  transition  from 


Fig.  37. 


STE  It  ELM  I  NT  II  A. 


87 


one  class  of  animals  to  another  so  insensible,  that  the  naturalist  hesi¬ 
tates  with  which  to  associate  it.  In  the  Distoma,  in  fact,  notwith¬ 
standing  its  intimate  relationship  with  the  Tsenioid  Sterelmintha, 
the  first  rudiments  of  nervous  filaments  are  apparent,  and  we  find 
its  whole  organization  approximating  the  nematoneurose  type  rather 
than  strictly  exhibiting  the  simple  structure  common  to  the  Acrita. 

The  Distoma  is  commonly  found  in  the  liver  and  biliary  ducts 
of  sheep,  and  other  ruminants,  deriving  nourishment  from  the 
fluids  in  which  it  is  immersed.  The  body  of  the  creature, 
which  is  not  quite  an  inch  in  length,  is  flattened,  and  resembles 
in  some  degree  a  minute  sole  or  flat-fish.  At  its  anterior  extre¬ 
mity  is  a  circular  sucker  or  disc  of  attachment,  by  which  it  fastens 
itself  to  the  walls  of  the  cavity  in  which  it  dwells,  as  well  as  by 
means  of  a  second  sucker  of  similar  form,  placed  upon  the  ventral 
surface  of  the  body.  In  the  annexed  diagram  (jig.  38)  the 
posterior  sucker  has  been  removed, 
in  order  more  distinctly  to  exhibit 
the  internal  structure  of  the  animal. 

The  name  which  this  entozoon  bears 
seems  to  have  been  given  to  it  from 
a  supposition  that  it  possessed  two 
mouths,  one  in  each  sucker ;  whereas 
the  anterior  or  terminal  disc  (a)  only  is 
perforated,  the  other  being  merely  an 
instrument  of  adhesion.  The  ali¬ 
mentary  canal  ( b )  takes  its  origin  from 
the  mouth  as  a  single  tube,  but  soon 
divides  into  two  large  branches,  from 
which  ramifications  arise  which  are 
dispersed  through  the  body,  each  ter¬ 
minating  in  a  blind  clavate  extre¬ 
mity.  These  tubes,  from  being 
generally  filled  with  dark  bilious  matter,  are  readily  traced,  even 
without  preparation  ;  or  they  may  be  injected  with  mercury  intro¬ 
duced  through  the  mouth. 


Through  the  walls  of  the  ventral  surface  of  the  body,  two 
nervous  filaments  (c)  are  discoverable,  crossing  over  the  root  of 
the  anterior  sucker  or  acetabulum,  and,  gradually  diverging,  may 
be  observed  to  run  in  a  serpentine  course  towards  the  caudal 
extremity,  where  they  are  lost :  it  would  even  seem  that  on  either 
side  of  the  oesophagus  there  is  a  very  slight  ganglion,  from  which 


88 


STERELMINTIIA. 


other  nervous  filaments  arise  to  supply  tlie  suckers,  and  tlie 
anterior  part  of  the  body. 

The  organs  of  generation  in  the  fluke  are  very  voluminous, 
occupying  with  the  ramifications  of  the  alimentary  tubes  the 
whole  of  the  interior  of  the  animal :  in  the  diagram  they  are 
not  represented  on  the  right  side,  in  order  that  the  distribution 
of  the  intestine  may  be  better  seen  ;  and  on  the  left  side  the  ali¬ 
mentary  vessels  are  omitted,  to  allow  the  general  arrangement  of 
the  sexual  system  to  be  more  clearly  intelligible. 

These  animals  would  seem  to  be  completely  hermaphrodite, 
not  only  possessing  distinct  ovigerous  and  seminiferous  canals, 
which  open  separately  at  the  surface  of  the  body,  but  even 
provided  with  external  organs  of  impregnation,  so  that  most 
probably  the  co-operation  of  two  individuals  is  requisite  for  mutual 
fecundity. 

To  commence  with  the  female  generative  system,  we  find  the 
ovaria  (A)  occupying  the  whole  circumference  of  the  body. 
When  distended  with  ova,  the  ovigerous  organ  is  of  a  yellow 
colour ;  and,  when  attentively  examined  under  the  microscope,  is 
seen  to  be  made  up  of  delicate  branches  of  vesicles  united  by 
minute  filaments,  so  as  to  have  a  racemose  appearance.  From 
these  clusters  of  ova  arise  the  oviferous  canals,  which,  uniting  on 
each  side  of  the  body  into  two  principal  trunks,  discharge  their 
contents  into  the  large  oviducts  (g).  The  oviducts  terminate  in 
a  capacious  receptacle  (e),  usually  called  the  uterus ;  and  from 
this  a  slender  and  convoluted  tube  leads  to  the  external  orifice, 
into  which  a  hair  (d)  has  been  inserted.  On  each  side  of  the 
uterus  we  find  a  large  ramified  organ,  made  up  of  csecal  tubes, 
( f ,)  which  opens  into  the  uterine  cavity,  and  no  doubt  furnishes 
some  accessory  secretion  needful  for  the  completion  of  the  ova. 

The  male  apparatus  occupies  the  centre  of  the  body.  The 
testes  (A-),  in  which  the  spermatic  fluid  is  secreted,  consist  of 
convoluted  vessels  of  small  calibre,  arranged  in  close  circular 
folds,  and  so  inextricably  involved,  that  it  is  difficult  to  get  a 
clear  idea  of  their  arrangement ;  but  towards  the  middle  of  the 
mesian  line  they  become  more  parallel,  and  terminate  in  two 
larger  trunks  (z),  (one  of  which  has  been  removed  in  the  figure,) 
which  are  enclosed  and  hidden  in  the  seminal  vessels.  These 
great  canals,  which  run  side  by  side  in  a  longitudinal  direction, 
become  gradually  much  attenuated  (/),  and  terminate  in  the  root 
or  capsule  of  the  penis  (m).  The  external  male  organ  (?i)  is 


STERELM1NTHA. 


89 


placed  a  little  anterior  to  the  orifice  which  leads  to  the  female 
parts  ;  it  is  a  short  spiral  filament,  distinctly  traversed  by  a  canal, 
and  perforate  at  the  extremity,  so  as  indubitably  to  perform  the 
office  of  an  instrument  of  intromission. 

(119.)  The  Planari.e,  although  they  do  not  inhabit  the  interior 
of  other  animals,  are  so  nearly  allied  in  every  part  of  their  organi¬ 
zation  with  the  Flukes ,  ( Distoma ,)  that  their  history  cannot  be 
more  appropriately  given  than  in  this  place.  The  Planariee  are 
common  in  ponds  and  other  stagnant  waters  ;  they  are  generally 
found  creeping  upon  the  stems  of  plants,  or  amongst  the  healthy 
confervse  which  abound  in  such  situations,  and  wage  perpetual 
war  with  a  variety  of  animals  inhabiting  the  same  localities.  The 
body  of  one  of  these  minute  creatures  appears  to  be  entirely 
gelatinous,  without  any  trace  of  muscular  fibre  ;  *  yet  its  motions 
are  exceedingly  active,  and  it  glides  along  the  plane  upon  which 
it  moves  with  a  rapid  and  equable  pace,  of  which  the  observer 
would  scarcely  expect  so  simple  a  being  to  be  capable ;  or,  by 
means  of  two  terminal  suckers,  progresses  in  the  manner  of  a 
leech.  No  agglomeration  of  nervous  fibre  has  hitherto  been  sa¬ 
tisfactorily  detected  in  the  Planarise  ;  nevertheless,  many  species 
possess  two  red  specks 
upon  the  anterior  part 
of  the  body,  which,  as 
in  other  cases,  have 
been  unhesitatingly 
pronounced  to  be  eyes, 
although  their  claim 
to  such  an  appellation 
is  not  only  unsubstan¬ 
tiated  by  any  proofs 
derivable  from  their 
structure,  but  com¬ 
pletely  negatived  by 
experiments,  which  go 
to  prove  that  in  the 
pursuit  of  prey  no 
power  of  detecting 
the  proximity  of  their 
food  by  the  exercise  of 
sight  is  possessed  by 
any  of  them. 


Fig.  39. 


*  Duges,  Annales  des  Sciences  Nat. 


90 


STERELMINTHA. 


The  phenomena  which  have  been  observed  connected  with  the 
multiplication  of  the  Planariee  by  division  are  analogous  to  those 
which  we  have  witnessed  in  other  acrite  animals  ;  for  it  has  been 
proved,  that  if  an  individual  be  cut  to  pieces,  every  portion  continues 
to  live  and  feel,  from  whatever  part  of  the  body  it  may  be  taken  ; 
and,  what  is  not  a  little  remarkable,  each  piece,  even  if  it  be  the 
end  of  the  tail,  as  soon  as  the  first  moment  of  pain  and  irrita¬ 
tion  has  passed,  begins  to  move  in  the  same  direction  as  that  in 
which  the  entire  animal  was  advancing,  as  if  the  body  was  actuated 
throughout  by  the  same  impulse,  and,  moreover,  every  division, 
even  if  it  is  not  more  than  the  eighth  or  tenth  part  of  the  crea¬ 
ture,  will  become  complete  and  perfect  in  all  its  organs. 

The  mouth,  in  a  few  species  of  Planarise,  is  placed  at  the  an¬ 
terior  extremity  of  the  body,  but  generally  it  is  found  to  occupy  the 
middle  part  of  the  ventral  surface.  Its  structure  is  quite  peculiar, 
and  admirably  adapted  to  the  exigencies  of  the  creature :  it  con¬ 
sists  of  a  wide,  trumpet-shaped  proboscis,  (Jig'.  39,  3  and  4,)  which 
can  be  protruded  at  pleasure,  and  applied  to  the  surface  of  such 
larvae  or  red-blooded  worms  as  may  come  within  reach,  so  as  to 
suck  from  them  the  juices  which  they  contain  ;  or,  if  the  prey  be 
small,  animalcules  and  minute  Crustacea  are  seized  by  it  and  con¬ 
veyed  into  the  digestive  canals.  The  internal  organs  appropriated 
to  nutrition  resemble  in  all  essential  points  those  of  the  Distoma ; 
they  consist  of  a  multitude  of  blind  tubes,  hollowed  out  in  the 
parenchyma  of  the  body,  which,  when  distended  with  coloured 
substances,  are  sufficiently  distinct.  The  principal  trunk,  (Jig.  39, 
1,)  which  communicates  with  the  proboscidiform  mouth,  soon  di¬ 
vides  into  three  primary  branches  ;  one  of  which  runs  along  the 
median  line  of  the  body  towards  the  anterior  extremity,  whilst  the 
other  two  are  directed  backwards  towards  the  tail.  From  these 
central  canals  secondary  ones  are  given  off,  which  permeate  all  parts 
of  the  body.  There  is  no  anal  aperture,  so  that  of  course  the 
residue  of  digestion  is  expelled  through  the  mouth  ;  but  the  nature 
of  the  process  by  which  defecation  is  thus  effected  is  curious  : 
the  Planaria,  slightly  bending  its  body,  is  seen  to  pump  up  through 
its  proboscis  a  quantity  of  water,  with  which  all  the  branches  of  the 
alimentary  ramifications  are  filled  ;  the  creature  then  contracts, 
and,  forcibly  ejecting  the  contained  fluid,  expels  with  it  all  effete 
or  useless  matter. 

Besides  the  arborescent  tubes  in  which  digestion  is  accomplished, 
a  rudimentary  vascular  system  is  distinctly  visible,  by  which  the 


STERELMINTIIA. 


91 


nutritive  juices  are  dispersed  through  the  system.  This  consists 
of  a  delicate  network  of  vessels,  arising  from  three  large  trunks, 
one  placed  in  the  centre  of  the  dorsal  aspect,  and  the  other  two 
running  along  the  sides  of  the  animal  ( Jig .  39,  2). 

(120.)  The  Planarim  are  perfectly  androgenous,  as  each  indi¬ 
vidual  possesses  a  distinct  male  and  female  generative  system ;  but 
they  are  not  apparently  self-impregnating,  as  the  co-operation  of  two 
individuals  has  been  found  needful  for  the  mutual  fertilization  of 
their  ova.  In  every  one  of  these  animals  tw'o  distinct  apertures 
are  seen  to  exist  upon  the  ventral  surface,  at  a  little  distance  be¬ 
hind  the  root  of  the  proboscis ;  the  anterior  of  which  gives  issue  to 
the  male  organ,  while  the  posterior  leads  to  the  oviferous  or  fe¬ 
male  parts. 

In  Planaria  tremellaris ,  the  penis,  which  during  copulation  is 
protruded  from  the  anterior  orifice,  ( Jig .  39,*  6,)  is  a  white,  con¬ 
tractile  body,  enclosed,  when  in  a  retracted  state,  in  a  small  oval 
pouch;  it  is  perforated  by  a  minute  canal,  and  receives  near  its  root 
two  flexuous  tubes,  which  gradually  decrease  in  size  as  they  diverge 
from  each  other,  until  they  can  no  longer  be  traced.  These  are 
the  seminiferous  vessels  (Jig-  39,  5,  a).  The  posterior  genital 
orifice,  which  leads  to  the  female  organs,  communicates  with  a  small 
pouch,  or  uterus,  as  it  might  be  termed  (Jig-  39,  5,  b)  :  into  this 
open  two  lateral  oviducts,  which  run  on  each  side  of  the  male  ap¬ 
paratus  and  of  the  proboscis  ;  these  are  very  transparent,  and  only 
recognisable  under  certain  circumstances  by  the  ova  which  they 
contain.  In  Planaria  lactea  the  oviduct  opens  into  the  uterine 
cavity  by  a  single  tube,  which,  passing  backwards,  divides  into  two 
equal  branches ;  and  both  of  these,  again  subdividing,  ramify 
extensively  among  the  cseca  derived  from  the  stomach.  We 
likewise  find  in  this  species  two  accessory  vesicles,  which  pour 
their  secretions  into  the  terminal  sac. 

(121.)  The  Diplozoon  paradoxum  is  another  form,  which, 
though  it  cannot  strictly  speaking  be  classed  with  the  entozoa,  is 
so  nearly  allied  to  Distoma  in  its  internal  structure,  that  its 
anatomy  will  be  most  conveniently  examined  in  this  place. j' 

This  remarkable  animal,  as  its  name  imports,  is  literally  pos¬ 
sessed  of  two  bodies,  precisely  resembling  each  other  in  every 
particular,  and  united  by  a  narrow  communicating  band,  so  as  to 
form  but  one  animal,  the  nutrient  canals  of  one  division  commu- 

*  This  figure  represents  two  Planariae  as  they  appear  in  the  act  of  sexual  inter- 

t  Nordmann. 


course. 


92 


STERELMINTHA. 


mcating  most  freely  with  those  of  the  opposite  half.  We  might 
be  led  to  imagine  such  an  extraordinary  arrangement  as  the  result 
of  some  monstrous  connexion  of  two  separate  creatures,  did  not 
observation  show  that  the  conformation  is  perfectly  natural  and 
common  to  all  the  species. 

Each  half  of  the  body  of  the  Diplozoon  possesses  a  mouth  and 
digestive  apparatus, 
a  distinct  set  of  vas¬ 
cular  channels,  in 
which  a  circulation  of 
the  nutritive  juices 
is  evident,  and  more¬ 
over  contains  a  com¬ 
plete  and  indepen¬ 
dent  generative  sys¬ 
tem  ;  but  in  the 
annexed  diagram, 

{Jig.  40,)  for  the 
sake  of  clearness, 
these  are  only  par- 
shown,  the  ali¬ 
mentary  organs  alone 
being  seen  upon  the 
left  portion,  whilst 
in  the  opposite  the 
organs  of  reproduc¬ 
tion  are  displayed : 
the  reader,  there¬ 
fore,  will  imagine  similar  parts  to  exist  on  both  sides  of  the 
body. 

These  animals,  which  are  of  very  small  size,  being  not  more 
than  two  or  three  lines  in  length,  are  found  attached  to  the  gills 
of  the  bream,  {Cyprinus  brama ,)  from  which  they  absorb  nutri¬ 
ment.  They  are  fixed  in  this  position  by  twro  sucking  acetabula, 
resembling  those  of  Distoma ,  (Z>,  b ,)  which  are  seen  on  each  side 
of  the  mouths,  and  also  by  four  oval  membranous  appendages 
( m ,  m)  attached  to  the  opposite  extremities  of  the  body,  upon 
which  likewise  suckers  are  placed,  so  that  at  all  four  extremities 
the  creature  is  provided  with  instruments  of  adhesion. 

(122.)  The  mouths  («,  a)  are  two  orifices  of  a  somewhat  semi¬ 
circular  form,  and  at  the  lower  margin  of  each  two  teeth  arc  per- 


Fig,  40. 


STERELMINTHA. 


93 


ceptible,  which  are  either  merely  provisions  for  fixing  the  mouth 
firmly  when  in  the  act  of  imbibing  food,  or  else  they  may  act  as 
lancets,  by  scarifying  the  surface  from  which  nourishment  is  de¬ 
rived.  From  the  outer  orifice  we  may  trace  a  canal  which  extends  a 
little  way  into  the  body,  and  becomes  slightly  dilated  ;  into  the 
bottom  of  this  cavity  a  small  tongue-shaped  organ  (d)  is  seen  to 
project,  having  its  surface  perforated  by  a  number  of  exceed¬ 
ingly  minute  holes,  which  indeed  might  be  looked  upon  as  the 
real  mouths  destined  to  imbibe  the  nutritious  juices,  and  convey 
them  to  the  stomach.  The  stomach,  (c,c,  c,  c,  c,)  which  has 
been  partly  removed  on  the  right  side  of  the  figure,  is  a  wide 
canal,  extending  through  the  whole  length  of  both  divisions  of 
the  body,  and  passing  by  a  capacious  cross-branch  from  one  half 
to  the  other,  so  that  the  nutriment  taken  in  by  either  mouth  will 
pass  freely  to  the  opposite  side.  From  these  central  channels 
great  numbers  of  blind  canals  issue,  resembling  those  of  Distoma 
and  Plariaria,  which  ramify  extensively ;  there  is,  however,  no 
anal  orifice  or  outlet  for  excrementitious  matter. 

(123.)  But,  besides  the  ramifications  of  the  alimentary  canal, 
other  vessels  are  discernible,  running  through  the  parenchyma  of 
the  Diplozoon,  where  nutritious  fluids  circulate,  and  which  corre¬ 
spond  to  the  vascular  arrangement  met  with  in  Planaria.  Of 
these  the  main  trunks  only  are  represented  in  the  figure ;  the 
branches  given  off  from  them,  which  are  very  numerous,  being  for 
the  sake  of  distinctness  entirely  omitted.  Each  half  of  the  body 
contains  four  of  these  vessels,  (/,  /,)  which  run  from  one  extremity 
to  the  other.  In  these  a  fluid  is  observed  to  move,  running  in 
the  directions  indicated  by  the  course  of  the  arrows  in  the  diagram  ; 
namely,  in  two  of  them  from  the  head  toward  the  posterior  end  of 
the  body,  and  in  the  other  two  in  an  opposite  direction.  This  ru¬ 
dimentary  circulation  must  be  for  the  purpose  of  more  perfectly 
diffusing  through  the  system  the  fluids  which  result  from  the 
process  of  digestion,  and  which  are  probably  taken  up  by  imme¬ 
diate  osculation,  between  the  terminations  of  the  branches  from 
the  stomach,  and  the  origins  of  the  vascular  system. 

Upon  the  opposite  side  of  the  figure  is  given  a  diagram  of 
the  arrangement  of  the  generative  apparatus  insulated  from  sur¬ 
rounding  parts,  so  as  to  give  the  reader  a  distinct  view  of  the 
different  organs  composing  it. 

(124.)  As  in  the  two  last  described  species,  we  find  both  oviger- 
ous  and  impregnating  organs  constituting  complete  hermaphrodism, 


94 


STEREL  M  I  NT  II  A. 


and  this  not  on  one  side  only  of  the  creature,  but  on  both  ;  all 
the  parts  being  precisely  similar  in  the  two  lateral  halves. 

The  ovarium  is  not  distinguishable  as  a  distinct  viscus,  the 
gems  or  granular-looking  ova  (e)  being  apparently  diffused  through 
the  parenchyma  of  the  body  around  the  alimentary  channels. 
From  this  situation  the  ova  are  taken  up  by  two  long  oviducts, 
which,  turning  upon  themselves  near  the  mouth,  are  seen  to  per¬ 
form  a  long  course  through  the  anterior  part  of  the  body,  until  at 
(f)  they  unite,  and  immediately  expand  into  a  capacious  intestini- 
form  cavity,  or  uterus,  (g),  from  which  the  eggs  escape  when 
mature  through  a  lateral  aperture  (/z). 

The  male  or  seminiferous  apparatus  is  quite  unconnected  with 
the  female  organs,  and  its  structure  is  easily  distinguishable.  The 
testicle  (z‘)  is  a  small  pear-shaped  vesicle,  from  which  a  duct  may 
be  traced,  which  ends  in  a  long  cirrus  (fc),  represented  in  the 
figure  as  coiled  up  in  a  spiral  form ;  but  when  unrolled  it  is  of 
considerable  length,  and  analogous  both  in  structure  and  office 
to  the  male  organ  of  Distoma. 

(125.)  W  e  now  arrive  at  the  most  perfect  type  of  structure  found 
in  the  Parenchymatous  Entozoa,  which  leads  us  by  a  gradual  trans¬ 
ition  to  the  more  highly  organized  forms  which  are  possessed  of 
a  distinct  nervous  apparatus.  The  reader  will  observe  that  in 
all  the  preceding  genera  the  alimentary  canal  has  consisted  en¬ 
tirely  of  nutritive  canals  excavated  in  the  substance  of  the  body, 
and  unprovided  with  any  outlet  distinct  from  the  mouth  adapted 
to  the  discharge  of  the  residue  of  digestion.  From  the  nature  of 
their  food,  indeed,  we  might  be  led  to  infer  the  reason  of  such  a 
structure ;  for  living,  as  these  creatures  do,  upon  juices  already 
completely  animalized  and  prepared  for  the  purposes  of  nutrition, 
the  assimilation  of  the  materials  provided  for  them  constitutes 
nearly  the  entire  process  of  alimentation.  The  same  con¬ 
formity  to  one  type  has  been  also  visible  in  the  nature  of  the 
reproductive  system  ;  all  the  species  which  we  have  as  yet  ex¬ 
amined,  except  perhaps  the  Planarise,  having  possessed  indepen¬ 
dent  powers  of  propagation,  either  containing  no  visible  organs 
appropriated  to  the  developement  of  the  germs  which  they 
produce,  or  possessing  both  an  ovigerous  and  impregnating 
apparatus  combined  in  the  same  body.  The  Entozoa  acantho- 
cephala>  of  which  we  are  now  about  to  speak,  will  be  found  still 
to  exhibit  a  digestive  system  analogous  in  structure  to  that  which 
exists  universally  among  the  Sterelmintha ;  but  in  the  organs 


STE HELMINTH A. 


95 


of  reproduction  we  find  a  mani¬ 
fest  analogy  with  higher  classes  in¬ 
dicated  in  the  complete  separation 
of  the  sexes,  which  we  now  for 
the  first  time  meet  with,  the  ovig- 
erous  and  impregnating  organs  be¬ 
ing  found  in  separate  and  distinct 
individuals. 

The  Echinorynchus  gigas  is  the 
species  which  has  undergone  the  most 
complete  investigation,*  and  will 
serve  as  an  example  of  the  usual 
structure  of  the  Acanthocephala. 

(126.)  The  Echinorynchi  inhabit 
the  intestinal  canal  of  various  ani¬ 
mals,  to  the  walls  of  which  they  fasten 
themselves  by  a  singular  contrivance. 
In  the  animal  under  consideration, 
which  is  found  in  the  intestines  of 
the  hog,  the  head  (a,  jig.  41  ;  1,  2, 
3)  is  represented  by  a  retractile  pro¬ 
boscis,  armed  externally  with  four 
circlets  of  sharp  recurved  hooks, 
which,  when  plunged  into  the  coats 
of  the  intestine,  serve  as  secure  an¬ 
chors  by  which  the  creature  retains 
itself  in  a  position  favourable  to  the 
absorption  of  food.  In  jig.  41,  1, 
2,  this  aculeated  proboscis  is  repre¬ 
sented  of  its  natural  size  relative  to 
the  body  of  the  entozoon,  as  it  ap¬ 
pears  when  fully  protruded  ;  but, 
when  not  in  use,  the  spinous  part 
is  retracted,  and  concealed  by  the 
mechanism,  of  which  an  enlarged 
view  is  given  at  Jig.  3.  When 
extended,  the  position  of  the  organ 
is  indicated  by  the  dotted  lines  ; 
but  in  the  drawing  the  whole  or- 
gan  is  represented  as  drawn  inwards 


*  Cloquet,  Anatomie  des  Vers  intestiuaux,  Paris,  1824. 


96 


STEllE  LMINTHA. 


and  lodged  in  a  depression  formed  by  tlie  inversion  of  the  in¬ 
tegument,  so  as  completely  to  hide  it  within  the  body.  This 
inversion  is  produced  by  the  contraction  of  two  muscular  bands, 
(d,  e,)*  which  arise  from  the  inner  walls  of  the  body,  and  are 
inserted  into  the  root  of  the  proboscis  around  the  oesophagus  : 
two  other  muscles,  ( b ,  6,)  antagonists  to  the  former,  arise  near 
the  spines  themselves  ;  and  these,  aided  by  the  contractions  of 
the  walls  of  the  body,  are  the  agents  by  which  the  protrusion 
of  the  head  is  effected.  Although  the  teeth  or  spines,  which 
render  this  organ  so  formidable,  are  merely  epidermic  appendages, 
they  are  found  to  be  rendered  erect  or  depressed  at  the  will 
of  the  creature  ;  and  it  is  therefore  probable  that,  minute  as  they 
are,  they  have  muscular  fibres  connected  with  them  serving 
for  their  independent  motions :  these  spines,  moreover,  are  not 
always  confined  to  the  head  ;  but  in  many  intestinal  worms  are 
found  on  various  parts  of  the  body,  wherever  their  office  as 
instruments  of  attachment  is  by  circumstances  rendered  needful. 

(127.)  The  digestive  system  of  the  Echinorynchus  is  extremely 
simple.  The  mouth  is  a  minute  pore  placed  at  the  extremity  of  the 
proboscis,  which  communicates  with  two  slender  canals,  at 

first  of  great  tenuity,  but  towards  the  middle  of  the  body  assum¬ 
ing  something  of  a  sacculated  appearance.  Towards  the  tail 
these  vessels  gradually  diminish  in  size  until  they  are  no  longer 
distinguishable  ;  but  they  have  not  been  seen  to  give  off  any 
branches,  or  to  communicate. with  each  other. 

Near  the  origin  of  these  nutrient  tubes  are  two  large  caeca,  nearly 
an  inch  in  length,  called  lemnisci ,  {fig.  41,  1  and  2,  d,  d,)  which 
are  probably  connected  with  the  digestive  function. 

(128.)  The  female  Echinorynchus  is,  as  is  usually  the  case  in 
Dioecious  Entozoa,  considerably  larger  than  the  male,  as  may  be 
seen  in  the  figure.  In  the  former  {fig.  41,  1)  the  ovary  (c)  is  a 
capacious  organ  occupying  the  centre  of  the  body,  and  extending 
along  its  entire  length.  When  minutely  examined,  it  is  found  to 
consist  of  two  compartments  or  distinct  sacs,  one  occupying  the 
dorsal,  the  other  the  ventral  aspect ;  the  two  tubes  being  separated 
by  a  septum.  The  dorsal  ovary  commences  near  the  tail,  at  g,  by 
a  cul-de-sac ;  and,  enlarging  as  it  runs  forward,  terminates  near  the 
point  c,  by  uniting  with  the  ventral  portion.  The  anterior  part 
of  the  canal  {b)  is  common  to  both  divisions  of  the  ovary ;  and 
from  this  the  ventral  tube  runs  backwards  to  the  posterior  end  of 

*  These  muscles  are  seen  of  their  natural  size  in  fig.  1  at  e,  e. 


STERELMINTIIA. 


97 


tlie  body,  where  it  ends  in  a  narrow  duct,  which  opens  externally 
at  h.  It  would  seem  therefore  that  the  last-mentioned  opening 
is  the  only  excretory  passage  from  the  ovarium  ;  the  connection 
apparent  in  the  figure,  between  the  common  sac  ( b )  and  the  root 
of  the  proboscis,  being  merely  of  a  ligamentous  character. 

(129.)  The  generative  system  of  the  male  Echinorynchus  is  re¬ 
presented  in  Jig.  41,  2.  The  organs  which  secrete  the  fecundating 
fluid  ( J \  g)  are  two  cylindrical  vesicles  attached  at  one  extremity 
by  minute  filaments  to  the  walls  of  the  body  :  from  each  of  these 
arises  a  duct  (/?),  and  the  two,  uniting  at  i,  form  a  common  excretory 
canal.  This  canal  speedily  dilates  into  a  number  of  sacculated 
receptacles  in  which  the  secretion  of  the  testes  accumulates,  and 
from  them  a  duct  leads  to  the  root  of  the  penis  (m).  The  penis 
or  organ  of  intromission,  when  extended,  protrudes  through  the 
aperture  p ,  placed  at  the  anal  extremity  of  the  body  ;  but  when 
retracted  it  is  folded  up,  and  lodged  in  a  conical  sheath  (o).  The 
protrusion  and  retraction  of  this  part  of  the  male  apparatus  is 
effected  by  a  very  simple  mechanism  :  two  muscles,  (/,  /,)  arising 
from  the  inner  walls  of  the  body,  are  inserted  into  the  base  of  the 
sheath,  (mj  and  serve  to  draw  it  inwards  ;  and  two  others,  (n,  nj) 
inserted  at  the  same  point,  but  arising  from  the  posterior  ex¬ 
tremity  of  the  animal,  by  their  contraction  force  outwards  the 
intromittent  organ,  an  arrangement  precisely  corresponding  with 
that  by  which  the  movements  of  the  proboscis  are  provided  for. 

(130.)  In  Distoma  perlatum 
(Jig.  42),  we  have  another  example 
of  organization  intermediate  be¬ 
tween  that  which  is  most  usual 
among  the  Sterelmintha,  and 
what  we  shall  afterwards  meet 
with  in  the  more  perfect  entozoa. 

The  animal  in  question  resembles 
most  closely  in  its  outward  form 
the  liver-fluke  of  which  we  have 
already  spoken,  and  possesses  a 
similar  suctorial  apparatus.  In 
the  annexed  figure  (Jig.  42),  the 
oral  disc  only  is  seen,  the  ventral 
sucker  having  been  removed  for 
the  sake  of  displaying  the  interior 
of  the  animal,  as  in  the  diagram  of 


Fig.  42. 


II 


98 


STERELMINTHA. 


Distoma  hepaticum  already  given  {Jig.  88).  On  comparing  tlie  two 
we  are  at  once  struck  with  the  superior  concentration  of  all  the 
systems  of  the  body,  visible  in  Distoma  perlatum.  The  ali¬ 
mentary  canal  (Jig.  42,  tf)  commences,  as  in  the  former  example, 
by  an  aperture  situated  in  the  oral  sucker  ;  but,  instead  of  ramifying 
through  the  parenchyma  of  the  body,  is  contained  in  an  abdo¬ 
minal  cavity,  in  which  it  floats  in  common  with  the  other  viscera. 
The  oesophagus  (a)  is  a  simple  flexuous  tube  terminating 
abruptly  in  two  lateral  and  more  capacious  intestines,  ( b ,  Z>,) 
terminated  by  blind  dilated  extremities,  which  form  the  digestive 
apparatus. 

Two  vascular  canals  (d,  d)  are  seen  on  each  side  of  the  body, 
which  ramify  extensively,  but  of  these  the  principal  trunks  only 
are  represented. 

(181.)  The  Distoma  perlatum  is  allied  to  the  Sterelmintha  in 
the  liermaphrodism  of  its  generative  organs,  and  the  parts  subservient 
to  reproduction  will  be  found  analogous  in  structure  and  arrange¬ 
ment  to  what  we  observed  to  be  the  usual  conformation  in  that 
order.  The  ova  would  seem  to  be  produced  in  the  parenchyma 
of  the  body,  as  in  the  fluke  ;  from  this  situation  they  are  con¬ 
veyed  by  two  canals  ( e )  into  a  capacious  receptacle  (J ‘),  from 
which  arises  the  tortuous  oviduct  (g),  represented  in  the  en¬ 
graving  distended  with  eggs.  Near  its  termination  the  oviduct 
is  joined  by  two  secerning  vesicles  having  their  interior  appa¬ 
rently  of  a  villous  texture.  These  vesicles  are  regarded  as 
being  the  testes,  and  are  supposed  to  pour  out  an  impregnat¬ 
ing  secretion,  by  which  the  ova  are  rendered  fertile  as  they 
pass  out  of  the  body.  The  external  aperture  through  which 
the  eggs  are  discharged  is  placed  upon  a  prominent  tubercle 
(?),  which,  if  mutual  impregnation  is  essential  in  these  animals, 
may  indeed  perform  the  office  of  an  intromittent  instrument. 


CCELELMINTHA. 


99 


CHAPTER  VII. 

NEMATONEURA. 

CCELELMINTHA*  (Owen). 

Vers  Intestinaux  cavitaires  (Cuv.)  ;  Nematoidea  (Rudolplii). 

(132.)  The  entozoa  which  belong  to  the  nematoneurose  division 
of  the  animal  kingdom  have  long  been  separated  in  zoological  clas¬ 
sification  from  those  which  have  been  described  in  the  last  chapter, 
on  account  of  the  superiority  of  their  internal  organization.  In 
the  Sterelmintha,  or  parenchymatous  forms,  we  have  seen  the 
digestive  process  carried  on  in  canals  simply  excavated  in  the  sub¬ 
stance  of  the  body,  without  any  anal  outlet  for  the  discharge  of 
superfluous  matter ;  the  nervous  system  either  perfectly  diffused 
through  the  tissues,  or  but  obscurely  visible  even  in  the  most  per¬ 
fect  species,  and  the  muscular  tissue,  as  a  necessary  consequence, 
scarcely  aggregated  into  distinct  fibres  :  the  sexes,  moreover,  except 
in  the  Echinorynchi ,  which  form  the  transition  from  the  more  im¬ 
perfect  to  the  more  elevated  type  of  structure,  have  been  invariably 
combined  in  the  same  individual.  But  we  now  arrive  at  a  point 
in  the  scale  of  animal  developement  at  which  the  nervous  fibre  be¬ 
comes  for  the  first  time  distinctly  recognisable,  forming  a  more 
perfect  means  of  intercourse,  if  we  may  be  allowed  the  expression, 
between  the  different  parts  of  the  body  ;  the  muscular  contractions, 
being  thus  more  intimately  associated,  assume  far  greater  energy, 
and  muscular  fasciculi  are  distinguishable,  arranged  in  precise  and 
definite  directions  ;  the  alimentary  canal  is  visible  as  a  separate 
and  distinct  tube,  enclosed  with  other  viscera  in  an  abdominal 
cavity ;  and  the  ovigerous  and  impregnating  sexual  organs  arc 
found  to  exist  in  different  individuals.  Still,  however,  we  find 
no  nervous  centres  developed,  or  the  ganglia  which  exist  are  so 
extremely  minute  and  rudimentary  that  in  no  case  can  wre  suspect 
the  existence  of  organs  appropriated  to  the  higher  senses  ;  the 
sensations  of  all  the  tribes  composing  this  division  of  the  animal 
world  are  therefore  apparently  limited  to  the  generally  diffused 


*  ko1Xo(3,  hollow — t\y,ivi-iv6o(>,  a  worm. 


H  2 


100 


COELELMINTIIA. 


g 


sense  of  toucli  and  its  modifications,  to  which  the  perception  of 
taste  and  odours  must  he  referred. 

(138.)  The  Linguatula  tamioides  (Jig.  48, 1 )  is  the  first  example 
which  we  shall  select  to  illustrate  the  structure  of  the  Ccelel- 
mintha.  This  ento-  Fig.  43. 

zoon,  which  is  gene¬ 
rally  found  to  inhabit 
the  frontal  sinus  of 
quadrupeds,  is  about 
three  inches  in  length, 
and  as  many  lines  in 
breadth,  at  the  broadest 
part  of  its  body.  In 
external  form  it  has 
some  resemblance  to 
the  tape- worm,  being 
divided  into  slightly  im¬ 
bricated  segments;  but 
in  its  internal  structure 
it  is  widely  different, 
especially  as  relates  to 
the  arrangement  of 
the  generative  organs, 
which,  instead  of  being 
multiplied  until  they 

are  nearly  as  numerous  as  the  segments  of  the  body,  (§  117,) 
form  but  one  continuous  system. 

The  Linguatula  is  invested  externally  with  a  delicate  cuticle, 
easily  separable  by  maceration,  so  as  to  peel  off  as  represented  in 
the  figure.* 

(184.)  Around  the  mouth  (j^g.43,1,  a),  are  several  oval  pits  or 
cavities  containing  as  many  sharp,  recurved  hooks  by  which  the  an¬ 
terior  extremity  of  the  body  is  securely  attached  to  the  walls  of  the 
frontal  sinus,  and  the  mouth  retained  in  a  position  adapted  to 
secure  an  adequate  supply  of  nutritive  material. 

The  mouth  itself  is  a  simple  aperture,  from  which  a  short  and 
narrow  oesophagus  leads  to  a  dilated  cylindrical  stomachal  cavity, 
(Jig-  43,  2,  «,)  that  forms  a  somewhat  capacious  receptacle  for 
food  ;  to  this  succeeds  a  straight  intestinal  tube  (f),  which  tra- 


B 


*  Owen,  Transact.  Zool.  Soc.  vol.  i. 


CCELELMINTHA. 


101 


verses  the  whole  length  of  the  body,  and  terminates  by  an  anal 
aperture  at  the  extremity  of  the  tail. 

(185.)  The  nervous  system  of  the  Linguatula  is  distinctly  de¬ 
veloped.  It  consists  of  a  central  ganglion,  situated  beneath  the  oeso¬ 
phagus. ,  from  which  eight  pairs  of  nervous  filaments  proceed  in  dif¬ 
ferent  directions  :  of  these  the  greater  number  are  distributed  to  the 
parts  immediately  around  the  mouth,  but  the  posterior  pair  (o,  o), 
which  is  by  far  the  most  considerable  in  size,  runs  backwards  along  the 
ventral  aspect  of  the  body,  taking  first  a  wavy  or  serpentine  course, 
but  afterwards  becoming  straight ;  these  nerves  may  be  traced  for 
some  distance  until  they  are  gradually  lost  in  the  integuments,  to 
which  they  are  distributed. 

It  will  be  seen  that  in  such  a  condition  of  the  nervous  apparatus, 
we  have  a  type  of  structure  decidedly  superior  to  what  has  been 
observed  in  any  of  the  parenchymatous  entozoa,  and  adapted  to 
the  situation  in  which  the  Linguatula  is  generally  found  ;  a  situa¬ 
tion  which  allows  of  considerable  change  of  position,  and  of  some 
selection  as  regards  the  food  which  it  imbibes.  The  muscular 
movements,  therefore,  being  more  perfectly  associated  by  the  de- 
velopement  of  nervous  filaments,  exhibit  a  greater  energy  of  action  ; 
and  although  the  nervous  matter  is  not  as  yet  sufficiently  concen¬ 
trated  to  allow  of  the  possession  of  organs  appropriated  to  the 
higher  senses,  there  is  provision  made  by  the  clevelopement  of  the 
rudimentary  sub-oesophageal  ganglion  for  more  delicate  sensibility 
in  the  neighbourhood  of  the  mouth,  adequate,  no  doubt,  to  the 
perception  and  choice  of  such  aliment  as  may  be  best  adapted  to 
nutrition. 

(186.)  The  female  Linguatula ,  as  is  generally  the  case  among 
the  dioecious  entozoa,  is  considerably  larger  than  the  male.  The 
generative  organs  exhibit  a  peculiar  arrangement,  and  form  nu¬ 
merous  convolutions  in  the  body,  which  are  visible  through  the 
semi-transparent  integument  {Jig.  48,  1). 

The  ovary  {Jig.  48,  2,  g)  is  a  narrow,  minutely  granulated 
body,  running  along  the  two  anterior  thirds  of  the  dorsal  aspect  of 
the  body.  It  terminates  about  half  an  inch  from  the  head  in 
two  capillary  tubes  (c  c),  which  pass  on  each  side  of  the  stomach 
and  nervous  cords,  embracing  them  as  in  a  ring.  These  two  tubes 
unite  behind  the  mouth  into  a  common  canal  or  oviduct,  through 
which  the  eggs  escape;  but,  before  their  junction,  each  receives  a 
duct  derived  from  a  glandular  sacculus  (e,  e),  destined  no  doubt  to 
furnish  some  secretion  essential  to  the  completion  of  the  ova. 


102 


CffiLELMINTHA. 


The  oviduct  formed  by  the  junction  of  the  oviferous  canals  which 
embrace  the  oesophagus,  is  very  narrow  at  its  commencement,  but 
after  running  backwards  for  some  distance  it  dilates  a  little,  and, 
becoming  much  convoluted,  it  winds  around  the  alimentary  tube 
in  numerous  and  extremely  complex  gyrations  (rf).  Towards  the 
lower  third  of  the  body,  the  coils  become  less  numerous  and  more 
distant  from  each  other,  and  are  seen  to  contain  brown  ova  in  scat¬ 
tered  masses,  until  at  length  the  oviduct  assumes  a  course  parallel 
to  that  of  the  intestine  (e),  and  accompanies  it  to  the  anus,  in  the 
vicinity  of  which  it  terminates. 

The  ova  are  of  a  firm  resisting  texture,  and  do  not  lose  any 
of  their  form  or  contour  by  drying ;  hence  they  may  preserve  their 
vitality  for  a  long  period  under  very  different  circumstances,  and 
be  ready  to  assume  the  actions  of  developement  when  deposited  in 
a  fit  situation. 

(137.)  In  the  male  Linguatula ,  the  structure  of  the  generative 
apparatus  is  very  simple.  Two  long  convoluted  tubes,  which  float 
loosely  in  the  abdominal  cavity,  secrete  the  seminal  or  impreg¬ 
nating  fluid  ;  and  these  tubes,  which  may  be  called  the  testes,  ter¬ 
minate  by  forming  a  single  canal  or  vas  deferens,  leading  to  the 
external  organs  appropriated  to  sexual  union,  which  are  two  fili¬ 
form  appendages  found  in  the  neighbourhood  of  the  head,  through 
which  the  fecundating  secretion  is  expelled. 

(138.)  The  only  other  example  which  will  be  necessary  to  illustrate 
the  structure  of  the  Ccelelmintha,  is  an  evident  approximation  to 
the  annulose  type  of  animal  organization.  The  Ascaris  lumbri- 
coides  indeed,  as  its  name  imports,  so  strongly  resembles  some  of 
the  annelida  in  its  external  configuration,  that  the  zoologist  who 
should  confine  his  attention  to  outward  form  alone,  might  be 
tempted  to  imagine  the  affinities  which  unite  them  much  stronger 
than  a  comparison  of  their  anatomical  relations  would  sanction. 
This  entozoon  is  found  in  the  intestines  of  many  animals,  and  is 
endowed  with  some  considerable  capability  of  locomotion  adapted 
to  the  circumstances  under  which  it  lives ;  for  in  this  case  the 
worm,  instead  of  being  closely  imprisoned  in  a  circumscribed  space, 
may  traverse  the  entire  length  of  the  intestines  in  search  of  a  con¬ 
venient  locality  and  suitable  food. 

(139.)  In  accordance  with  such  an  enlarged  sphere  of  existence, 
we  observe  muscular  fibre  distinctly  recognisable  in  the  tissue  which 
composes  the  walls  of  the  body,  not  as  yet  indeed  exhibiting 
the  complete  characteristics  of  muscle  as  it  is  found  in  higher 


CtELELMINTHA. 


103 


animals,  but  arranged  in  bundles  of  contractile  filaments,  run¬ 
ning  in  determinate  directions,  and  thus  capable  of  acting 
with  greater  energy  and  effect  in  producing  a  variety  of  move¬ 
ments. 

In  this  rudimentary  state,  the  muscular  fibre  does  not  possess 
the  density  and  firmness  which  it  acquires  when  completely  de¬ 
veloped  ;  it  has,  when  seen  under  the  microscope,  a  soft  gelatinous 
appearance,  apparently  resulting  from  a  deficiency  of  fibrin  in  its 
composition;  the  transverse  striae,  usually  regarded  as  characteristic 
of  the  muscular  tissue  of  the  more  perfect  animals,  are  not  yet 
distinguishable,  and  the  individual  threads  are  short,  passing  over 
a  very  small  space  before  they  terminate.  On  examining  the 
arrangement  of  these  fasciculi,  they  are  seen  to  be  disposed  in 
two  layers,  in  each  of  which  they  assume  a  different  course  ;  thus 
in  the  outer  layer  they  are  principally  arranged  in  a  longitudinal 
direction,  while  the  inner  stratum  of  fibres  is  placed  transversely, 
affecting  a  spiral  course,  so  as  to  encircle  the  viscera.  From  this 
simple  structure  various  movements  result ;  by  the  action  of 
the  longitudinal  fasciculi  the  whole  body  is  shortened,  by  the 
contractions  of  the  spiral  layer  an  opposite  effect  is  produced, 
or  by  the  exertion  of  circumscribed  portions  of  the  muscular  in¬ 
tegument  lateral  flexions  of  the  body  are  effected  in  any  given 
direction.  These  motions  in  the  living  worm  are  vigorous  and 
easily  excited  by  stimuli ;  they  are  therefore  abundantly  sufficient 
for  the  purpose  of  progression  in  such  situations  as  those  in  which 
the  creature  lives,  and  enable  it  to  change  its  place  in  the  intes¬ 
tines  with  facility. 

(140.)  The  nervous  system  of  the  A  scar  is  is  strictly  conformable 
to  the  nematoid  type.  Around  the  mouth  or  anterior  part  of  the 
oesophagus,  there  appears  to  be  a  delicate  nervous  ring,  probably 
specially  connected  with  the  association  of  such  movements  of 
the  oral  extremity  as  are  essential  to  the  imbibition  of  nourish¬ 
ment.  From  this  oral  ring  proceed  two  long  nervous  filaments, 
(Jig.  44,  e,  e,)  one  of  which  runs  backwards  along  the  dorsal 
aspect  of  the  body,  while  the  other  occupies  a  similar  position 
upon  the  ventral  surface.  The  last-named  filament  is  described 
by  Cloquet  as  dividing  in  the  female  Ascaris ,  at  the  point  where 
the  termination  of  the  organs  of  generation  issue  from  the  body 
(Jig.  44,  ??i),  so  as  to  enclose  the  termination  of  the  vagina  in  a 
nervous  circle. 

(141.)  T  he  digestive  apparatus  in  this  order  of  intestinal  worms  is 


104 


CCELELMINTHA. 


very  simple.  In  Ascaris  lumbricoides ,  tlic 
{Jig.  44,  a,)  wlien  highly  magnified, 
is  seen  to  be  surrounded  by  three 
minute  rounded  tubercles  ;  into  each 
of  these,  fasciculi,  derived  from  the 
longitudinal  muscles  of  the  body, 
are  inserted  in  such  a  manner  as  to 
cause  the  separation  of  the  tuber¬ 
cles,  and  consequent  opening  of  the 
mouth,  which  is  again  closed  by  a 
sphincter  muscle  provided  for  the  e 
purpose.  To  the  mouth  succeeds  a 
short  oesophagus,  (Jig.  44,  1  &  2,  bj 
which  is  separated  by  a  constriction 
from  the  rest  of  the  alimentary 
canal,  and  would  seem,  from  the 
muscularity  of  its  walls,  to  be  an 
agent  employed  in  sucking  in  the 
liquid  food  upon  which  the  crea¬ 
ture  lives.  The  true  digestive  ca¬ 
vity  (Jig.  44,  1  &  2,  c,  c)  is  a  sim¬ 
ple  and  extremely  delicate  tube, 
which  arises  from  the  oesophagus, 
and  without  presenting  any  appear¬ 
ance  indicative  of  separation  into 
stomach  and  intestine,  gradually  en¬ 
larges  as  it  proceeds  backwards, 
until  it  terminates  at  the  hinder 
extremity  of  the  body  by  a  narrow 
aperture  (Jig.  44,  1  &  2,  d.) 

It  would  seem  that  the  food  of 
these  entozoa  being  already  ani- 
malized  by  having  undergone  a  pre¬ 
vious  digestion,  requires  little  further 
preparation  ;  and  we  are  little  sur¬ 
prised  at  finding  in  the  generality  of 
the  Coelelmintha  no  accessory  glan¬ 
dular  apparatus  appended  to  the  di¬ 
gestive  canals  for  the  purpose  of 
furnishing  auxiliary  secretions.  In 
two  species  only  have  tributary 


CfELELMINTHA. 


105 


secreting  organs  been  detected ;  in  one  example,  Gnathostoma 
aculeatum ,  (O  wen,)  found  in  tlie  stomach  of  the  tiger,  and  which 
is  remarkable  as  possessing  a  pair  of  rudimentary  jaws,  four  slen¬ 
der  elongated  ceeca  are  appended  to  the  mouth,  into  which  they 
pour  a  fluid  analogous,  no  doubt,  to  that  of  the  salivary  glands.* 
In  a  species  of  ascaris,  found  in  the  stomach  of  the  dugong,  Mr. 
Owen  likewise  discovered  a  csecal  appendage  opening  into  the  ali¬ 
mentary  tube  at  some  distance  from  the  mouth,  and  which,  without 
much  stretch  of  imagination,  may  be  regarded  as  the  first  and  sim¬ 
plest  rudiment  of  a  biliary  system,  j' 

In  further  prosecuting  our  inquiries  concerning  the  process 
of  nutrition  in  these  entozoa,  we  must  now  speak  of  a  peculiar 
structure  first  noticed  by  Cloquet,^  and  apparently  intimately 
connected  with  the  assimilation  of  nutriment.  Projecting  from 
the  inner  surface  of  the  abdominal  cavity,  especially  in  the  dorsal 
and  ventral  regions,  there  is  a  great  number  of  gelatinous,  spongy 
processes  ( appendices  nourr icier s),  which,  although  they  have  no 
apparent  central  cavity,  would  seem  to  be  appended  to  vascular 
canals  seen  upon  the  lateral  aspects  of  the  body  :  it  is  probable, 
therefore,  that  their  office  is  to  absorb  the  nutritive  juices,  which 
exude  through  the  delicate  walls  of  the  intestine,  and  convey  them 
into  the  circulatory  apparatus  ;  or  they  may  be  reservoirs  for  nou¬ 
rishment,  analogous  to  the  adipose  tissue  of  higher  animals. 

(142.)  In  the  Cadehiintha  the  sexes  are  separate,  and  the  genera¬ 
tive  organs,  both  of  the  male  and  female,  exhibit  great  simplicity 
of  structure.  In  the  female  Ascaris ,  the  aperture  communicating 
with  the  ovigerous  apparatus  is  placed  upon  the  ventral  aspect  of 
the  body,  a  little  anterior  to  the  middle  of  the  worm  ( fig .  44, 1,  m). 
This  opening  leads  into  a  wide  canal  (/),  usually  called  the  uterus  ; 
and  from  the  last-mentioned  organ  arise  two  long  and  undulating 
tubes,  which,  diminishing  in  size,  run  towards  the  posterio  ex¬ 
tremity,  where  they  become  completely  filiform,  and  turning  back 
upon  themselves  are  wound  in  innumerable  tortuous  convolutions 
around  the  posterior  portion  of  the  alimentary  canal,  until  the 
termination  of  each  becomes  nearly  imperceptible  from  its  extreme 
tenuity.  In  these  tubes,  which  when  unravelled  are  upwards  of 
four  feet  in  length,  the  ova  are  formed  in  great  numbers,  and 
are  found  to  advance  in  maturity  as  they  approach  the  dilated 

*  Owen,  Proceedings  of  the  Zoological  Society,  Nov.  1836. 

t  Preparation,  No.  429  A. — Mus.  Coll.  Surg.  Phys.  Catalogue,  p.  121. 

|  Cloquet,  Anatomie  des  Vers  Intestinaux  ;  Paris,  1824. 


106 


CCE  LELMINTHA. 


terminal  receptacle  common  to  both  oviducts  (/),  from  which  they 
are  ultimately  expelled. 

(148.)  The  male  Ascaris  lumbricoides  is  considerably  smaller  than 
the  female,  and  the  structure  of  its  generative  system  remarkably 
similar  to  what  has  been  just  described  in  the  other  sex.  The  testis 
or  gland,  which  secretes  the  impregnating  fluid,  is  a  single,  delicate, 
tubular,  filament  {fig-  44,  2,  f),  which  when  unravelled  is  found 
to  be  nearly  three  feet  in  length,  and  is  seen  winding  in  close  and 
almost  inextricable  folds  around  the  middle  and  hinder  parts  of 
the  intestine.  The  termination  of  this  tube  (g)  may  be  traced  to 
the  tail  or  anal  extremity  of  the  worm,  where  it  ends  in  a  fila¬ 
mentary  retractile  penis  (f),  in  which  the  microscope  exhibits  a 
minute  receptacle  wherein  the  seminal  fluid  accumulates  prepara¬ 
tory  to  its  expulsion.  During  copulation,  the  penis  of  the  male 
is  introduced  into  the  vulva  of  the  female,  by  which  it  is  firmly 
embraced,  and  the  different  positions  which  the  external  parts 
occupy  in  the  two  sexes  is  evidently  an  arrangement  favourable 
to  their  intercourse. 

(144.)  There  are  few  more  striking  exemplifications  of  that  gra¬ 
dual  transition  by  which  we  are  led  from  one  type  of  structure  to 
another,  than  we  meet  with  in  tracing  the  progressive  separation 
of  the  sexes  as  we  advance  from  the  monoecious  to  the  dioecious 
families  of  the  entozoa.  Leaving  those  forms  of  hermaphroditism 
in  which  the  male  and  female  parts  are  both  found  in  each  division 
of  the  body,  we  find  in  Syngamus  trachealis  an  animal  “  in  which 
the  male  is  organically  blended  by  its  caudal  extremity  with  the 
female,  immediately  anterior  to  the  slit-shaped  aperture  of  the 
vulva,  which  is  situated  as  usual  near  the  anterior  third  of  the 
body.  By  this  union  a  kind  of  hermaphroditism  is  produced  ; 
but  the  male  apparatus  is  furnished  with  its  own  peculiar  nutrient 
system,  and  an  individual  is  constituted  distinct  in  every  respect, 
save  in  its  terminal  confluence  with  the  body  of  the  female.  This 
condition  of  animal  life,  which  was  conceived  by  Hunter  as  within 
the  circle  of  physiological  possibilities,  (see  Animal  (Economy, 
p.  46,)  has  hitherto  been  only  exemplified  in  this  single  species 
of  entozoon,  the  discovery  and  true  nature  of  which  is  due  to 
the  sagacity  and  patient  research  of  Dr.  Charles  Theodore  Yon 
Siebold.”* 


*  Cyclop,  of  Anat.  and  Pliys.  ;  article  Entozoa,  by  Professor  Owen.  Vide  Siebold, 
in  Weigmann’s  Archives,  1835. 


BRYOZOA. 


107 


Fig.  45. 


CHAPTER  VIII. 

Bryozoa*  (Ehrenberg)  ;  Oiliobrachiate  Polypi  (Farre). 

(145.)  It  is  only  within  the  last  few  years  that  microscopical  re¬ 
searches  have  revealed  to  naturalists  the  real  structure  of  a  series  of 
animals  originally  confounded  with  the  simpler  polyps,  with  which, 
as  far  as  external  form  is  concerned,  they  are  indeed  intimately 
related.  The  observations  of  Milne  Edwards,- *f*  Audouin,  Ehren¬ 
berg, £  and  Thompson, §  gradually  led  the  way  to  more  correct 
and  precise  ideas  concerning  the  more  highly  organized  genera  ; 
and  Dr.  Arthur  Farre,  ||  by  a  series  of  investigations,  followed 
up  with  exemplary  industry  and  perseverance,  seems  to  have  com¬ 
pleted  our  knowledge  of  the  anatomical  details  of  these  creatures, 
in  a  manner  which  leaves  few  points  of  their  economy  unknown. 

We  shall  select  an  in¬ 
dividual,  named  by  Dr. 

Farre  Bowerbankia  den- 
sa ,  as  an  illustration  of 
the  general  structure  of 
the  Bryozoa,  partly  from 
the  complete  manner  in 
which  its  organization  has 
been  developed  in  the  me¬ 
moir  alluded  to,  and  partly 
because  we  have  had  fre¬ 
quent  opportunities  of  ve¬ 
rifying  the  accuracy  of  the 
descriptions,  and  the  ex¬ 
treme  fidelity  of  the  draw¬ 
ings  by  which  it  is  illus¬ 
trated. 

The  animal  Bowerban¬ 
kia ,  which  is  only  about 
a  line  in  length,  inhabits  a 

*  Bgvov,  sea-moss — Z uov,  an  animal. 

t  Annales  des  Sciences  Naturelles,  for  Sept.  1828,  and  July  1836. 

J  Symbol®  Physic®. 

§  Zoological  Researches  and  Illustrations,  Memoir  v.  \  Cork,  1830. 

||  Philosoph.  Trans.  Part  2,  for  1837. 


108 


BRYOZOA. 


delicate  and  perfectly  transparent  tube  of  horny  texture,  which 
arises  from  a  repent  stem,  common  to  a  great  many  individuals, 
found  aggregated  in  small  patches  upon  the  surface  of  Flustra 
foliacea ,  upon  which  they  are  apparently  parasitic. 

The  mouth  is  surrounded  by  ten  long  and  slender  tentacula, 
{Jig-  45,)  which,  during  the  expanded  state  of  the  animal,  are 
kept  quite  straight  and  motionless,  as  represented  in  the  drawing. 
Each  tentacle  is  provided  upon  its  outer  aspect  with  a  series 
of  stiff  and  immoveable  spines,  probably  serving  to  keep  off  any 
foreign  bodies,  which,  by  their  proximity,  might  interfere  with  the 
ciliary  movements  immediately  to  be  described. 

Besides  the  stiff  spines,  the  tentacula  are  covered  with  an  im¬ 
mense  number  of  vibrating  cilia,  which  at  the  will  of  the  animal  are 
thrown  into  most  rapid  movement,  so  as  to  produce  strong  and 
continuous  currents  in  the  surrounding  fluid,  by  which  particles 
floating  in  the  neighbourhood  are  hurried  along  with  great  velocity. 
From  the  direction  of  the  streams  produced  by  the  cilia,  namely, 
to'wards  the  mouth,  we  at  once  perceive  the  utility  and  beauty 
of  the  contrivance  which  compensates  to  a  great  extent  for  the 
fixed  condition  of  the  Bryozoon  ;  animalcules  floating  in  the  vi¬ 
cinity  no  sooner  come  within  the  influence  of  the  currents  so  pro¬ 
duced,  than  they  are  forced  towards  the  mouth,  which  is  placed 
at  the  roots  of  the  tentacula,  and,  being  at  once  seized,  are  imme¬ 
diately  swallowed. 

The  tentacula  themselves,  notwithstanding  their  immobility  dur¬ 
ing  the  process  of  watching  for  prey,  are  highly  irritable,  and  sensi¬ 
ble  of  the  slightest  contact.  No  sooner  does  an  animalcule  im¬ 
pinge  upon  any  part  of  their  surface,  than  the  tentacle  touched 
bends  with  extraordinary  quickness,  as  if  endeavouring  to  strike  it 
towards  the  mouth  ;  and,  if  the  object  be  sufficiently  large  to  touch 
several  at  the  same  moment,  all  the  tentacula  simultaneously  co¬ 
operate  in  seizing  and  retaining  it. 

(146.)  The  existence  of  the  cilia  upon  the  tentacula  would  seem  to 
be  characteristic  of  the  Bryozoa,  and  is  invariably  accompanied,  as 
far  as  our  information  extends  at  present,  with  a  digestive  apparatus 
of  far  more  complex  structure  than  what  we  have  seen  in  the  un- 
ciliated  polyps,  for  in  the  class  before  us,  besides  the  stomach,  we 
find  a  distinct  intestinal  tube  and  anal  outlet.  In  the  specimen 
under  consideration  the  organization  of  the  alimentary  organs  is 
even  rendered  more  elaborate  than  is  usual  in  the  class,  from  the 
addition  of  a  gizzard  or  cavity  in  which  the  food  is  mechanically 


BRYOZOA. 


109 


bruised  before  its  introduction  into  the  proper  stomach.  The 
mouth  is  placed  in  the  centre  of  the  space  enclosed  by  the  tcnta- 
cula  ;  it  appears  to  be  a  simple  orifice,  incapable  of  much  distension, 
through  which  the  particles  of  food  brought  by  the  ciliary  action 
pass  into  a  capacious  oesophagus,  (j%.  45,  a ,  1,  2,)  which,  gradually 
contracting  its  dimensions,  ends  in  a  globular  muscular  organ  to 
which  the  name  of  gizzard  has  been  applied.  (3)  The  walls  of  this 
viscus  are  composed  of  fibres  which  radiate  from  two  dark  points 
seen  in  the  figure,  and  its  lining  membrane  is  covered  with  a  great 
number  of  hard  horny  teeth,  so  disposed  as  to  represent,  under  the 
microscope,  a  tesselated  pavement.  The  contractions  of  the  giz¬ 
zard  are  vigorous  ;  and,  from  the  structure  of  its  interior,  its  office 
cannot  be  doubtful. 

To  the  gizzard  succeeds  a  stomach  45,  a ,  4,)  which  is  studded 
with  brown  specks  apparently  of  a  glandular  nature,  and  probably 
representing  a  biliary  apparatus.  The  intestine  leaves  the  stomach 
at  its  upper  portion,  close  to  the  gizzard  (5)  ;  and,  running  parallel 
with  the  oesophagus  towards  the  tentacula  (6),  terminates  at  the  side 
of  the  mouth  (7),  in  such  a  position  that  excrementitious  matter  is  at 
once  whirled  away  by  the  ciliary  currents.  The  whole  intestinal 
apparatus  floats  freely  in  a  visceral  cavity,  which  contains  a  transpa¬ 
rent  fluid,  and  encloses  distinct  muscular  fasciculi,  which  we  shall 
speak  of  in  another  place. 

The  process  of  digestion  in  this  minute,  yet  highly  organized  being, 
is  well  described  by  Dr.  Farre  in  the  memoir  above  mentioned. 

“  The  little  animal,  when  in  vigour,  is  seen  projecting  from  its  cell 
with  the  arms  extended,  and  the  cilia  in  full  operation  ;  the  upper 
part  of  the  body  being  frequently  turned  from  side  to  side  over  the 
edge  of  the  cell,  the  extremity  of  which,  from  its  peculiar  flexibility, 
moves  along  with  it.  The  particles  carried  to  the  mouth  in  the 
vortex  produced  by  the  action  of  the  cilia,  after  remaining  a  little 
while  in  the  pharynx,  are  swallowed  by  a  vigorous  contraction  of 
its  parietes,  and  carried  rapidly  down  the  oesophagus  and  through 
the  cardia  to  the  gizzard,  which  expands  to  receive  them.  Here 
they  are  submitted  to  a  sort  of  crushing  operation,  the  parietes  of 
the  organ  contracting  firmly  upon  them,  and  the  two  dark  bodies 
being  brought  into  opposition.  Their  residence,  however,  in  this 
cavity,  is  only  momentary,  and  they  are  immediately  propelled  into 
the  true  stomach  below,  where  they  become  mixed  up  with  its 
contents,  which,  during  digestion,  are  always  of  a  dark,  rich,  brown 
colour,  being  tinged  with  the  secretion  of  its  parietal  follicles.” 


110 


BRYOZOA. 


The  food  appears  to  be  retained  for  a  considerable  time  in  the 
stomach,  and  may  be  frequently  seen  to  be  regurgitated  into  the 
gizzard,  whence,  after  having  been  again  submitted  to  its  opera¬ 
tions,  it  is  returned  to  the  stomach.  Here  it  is  rolled  about  by  the 
contraction  of  its  parieties,  and  at  its  upper  part  is  frequently  sub¬ 
mitted  to  a  rotating  motion.  This  rotation  of  particles  is  chiefly 
near  the  pyloric  orifice  ;  and  a  mass  may  be  occasionally  seen  pro¬ 
jecting  through  the  pylorus  into  the  intestine,  and  rotating  rapidly 
in  the  direction  of  the  axis  of  the  orifice.  In  an  animal  having  a 
similar  form  of  pylorus  to  this,  but  in  which  the  parts  were  more 
transparent,  I  could  distinctly  see  the  cilia  by  which  this  rotation 
is  effected  surrounding  the  orifice.” 

The  granular  matter,  after  rotating  for  some  time  at  the  pylorus, 
(a  provision  for  preventing  its  too  rapid  escape  from  the  stomach,) 
passes  into  the  intestine,  where  it  accumulates  in  little  pellets, 
which  are  rapidly  pushed  by  the  contraction  of  the  intestine  to¬ 
wards  the  anal  orifice,  through  which  they  are  expelled  from  the  body. 

The  tube  or  cell  inhabited  by  this  bryozoon  is  of  exquisite  struc¬ 
ture,  and  the  mechanism  concerned  in  the  protrusion  and  retraction 
of  the  animal  of  great  simplicity  and  beauty. 

The  inferior  two-thirds  of  the  cell  in  the  species  under  considera¬ 
tion  is  hard  and  corneous,  but  perfectly  transparent :  the  upper 
third,  on  the  contrary,  is  flexible,  and  so  constructed  as  to  form  a 
very  complete  operculum  by  which  the  entrance  is  guarded.  The 
flexible  part  consists  of  two  portions,  the  lower  half  being  a  simple 
continuation  of  the  rest  of  the  cell,  while  the  upper  is  composed  of 
a  circle  of  delicate  bristle-shaped  processes  or  setae,  which  are  ar¬ 
ranged  parallel  to  each  other  around  the  mouth  of  the  cell,  and  are 
prevented  from  separating  beyond  a  certain  distance  by  a  membrane 
of  excessive  tenuity  which  connects  them  ;  this  membrane  is  evi¬ 
dently  analogous  to  the  infundibular  termination  of  the  cells  of 
polyps  already  described. 

When  the  bryozoon  retires  into  its  abode,  the  setae  and  soft  ter¬ 
mination  of  the  cell  are  gradually  folded  inwards  in  the  manner 
exhibited  in  the  annexed  figures  {Jig.  46),  which  represent  the 
various  stages  of  the  process.  The  oesophagus  surmounted  by  its 
tentacula  descends  first,  whilst  the  integument  of  the  upper  part  of 
the  body  begins  to  be  inverted  at  the  point  where  it  has  its  insertion 
around  the  base  of  the  tentacles  (c).  As  the  descent  of  the  tenta¬ 
cula  proceeds,  the  inversion  of  this  membrane  continues ;  and  when 
the  extremities  of  the  arms  have  reached  the  level  of  the  extremi- 


ties  of  tlie  setse,  it  is  seen  to  form  a  complete  slieatli  around  them. 
The  animal  being  thus  retracted,  the  next  part  of  the  process  is  to 
draw  in  the  upper  portion  of  the  cell  after  it.  The  setse  are  now 
brought  together  in  a  bundle  (Jig.  46,  2,  a),  and  are  gradually 
drawn  inwards,  inverting  around  them  the  rest  of  the  flexible  por¬ 
tion  of  the  cell  until  they  form  a  close  fasciculus  (Jig.  46,  3  &  4,  a), 
occupying  the  axis  of  the  opening  of  the  tube,  and  forming  a  com¬ 
plete  protection  against  intrusion  from  without. 

(147.)  The  muscular  system  exhibits  the  earliest  appearance  of 
muscular  fibre.  The  filaments  are  unconnected  by  cellular  tissue, 
and  have  a  watery  transparency  and  smooth  surface,  neither  do 
they  exhibit  cross  markings  or  a  linear  arrangement  of  globules, 
even  when  examined  under  the  highest  powers  of  the  microscope. 

The  muscles  may  be  divided  into  two  sets,  one  serving  for  the 
retraction  of  the  alimentary  apparatus,  the  other  acting  upon  the 
setse  around  the  mouth  of  the  cell,  and  serving  for  the  inversion  of 
its  flexible  portion.  The  bundles  of  muscular  fibre  which  act  upon 
the  alimentary  canal  are  two  in  number,  and  arise  from  near  the 
bottom  of  the  cell :  one  of  these  is  inserted  into  the  stomach 
(Jig.  45,  a,  8)  ;  the  other  passes  upwards  along  the  side  of  the 
oesophagus  (Jig.  45,  a,  9),  to  be  attached  in  the  vicinity  of  the 
tentacula  :  the  latter  fasciculus  is  evidently  the  great  agent  in 
drawing  the  animal  into  its  retreat,  and  in  doing  so  it  throws  the 
alimentary  canal  into  close  sigmoid  folds. 

The  muscles  which  close  the  operculum  are  arranged  in  six 
distinct  fasciculi ;  they  arise  from  the  inner  surface  of  the  upper 
hard  part  of  the  cell,  and  act  upon  the  upper  flexible  portion  of  the 
tube  and  upon  the  setse  (Jig.  46,  d,  d). 

The  mode  in  which  the  protrusion  of  the  tentacula  is  effected  is 


112 


BRYOZOA. 


not  so  easily  explained ;  it  would  seem  that  the  lining  membrane  of 
the  shell  is  furnished  with  circular  muscular  fibres,  so  disposed  as  by 
their  action  to  compress  the  fluid  contained  in  the  visceral  cavity,  and 
thus  tend  to  elongate  the  body.  Dr.  Farre,  however,  believes  the 
alimentary  canal  itself  to  be  the  great  agent  in  effecting  this  object, 
and  he  conceives  it  to  possess  a  power  of  straightening  itself  from  the 
flexures  into  which  it  is  thrown  during  the  retracted  state  of  the 
animal. 

(148.)  The  Flustr^e  and  Eschars  are  intimately  allied  to 
Bowerbankia  in  all  the  details  of  their  structure,  as  we  are 
assured  by  the  researches  of  Dr.  Milne  Edwards  concerning  these 
singularly  aggregated  forms  of  Bryozoa.* 

The  cells  of  the  F lustra  and  Eschar ce  are  disposed  side  by 
side  upon  the  same  plane,  so  as  to  form  a  common  skeleton  of  a 
coriaceous  or  horny  texture.  The  individual  cells,  which  are  ex¬ 
tremely  minute,  vary  in  shape  in  different  species  ;  and  the  orifice 
of  each  is  generally  defended  by  projecting  spines,  or  sometimes 
by  a  moveable  operculum,  or  lid,  which  closes  the  orifice  in  the 
contracted  state  of  the  animal.  The  extension  of  one  of  these 
skeletons  is  effected  by  the  regular  addition  of  new  cells  around 
the  circumference  of  the  F lustra ,  those  of  the  margin  being,  of 
course,  the  most  recent;  and  the  latter  are  not  unfrequently found 
inhabited  by  healthy  animals,  whilst  in  the  older  or  central  ones 
the  original  occupants  have  perished. 

The  facts  which  have  been  observed  relative  to  the  formation  of 
these  cells  possess  a  high  degree  of  interest,  and  materially  support 
the  views  already  given  concerning  the  formation  of  the  tubes  of 
zoophytes  in  general  ;  proving  that  the  calcareous  matter  to  which 
their  hardness  is  owing  is  not  a  mere  exudation  from  the  surface  of 
the  animal,  but  is  deposited  in  an  organized  tegumentary  membrane, 
from  which  it  can  be  removed  with  facility  by  means  of  extremely 
dilute  muriatic  acid.  When  so  treated,  a  brisk  effervescence  is  pro¬ 
duced,  the  cells  become  flexible  and  are  easily  separated  from  each 
other,  but  they  are  not  altered  in  form,  and  evidently  consist  of  a  soft 
and  thick  membrane,  forming  a  sac  containing  the  digestive  organs  of 
the  creature.  In  this  state  the  opening  of  the  cell  is  no  longer  de¬ 
fined  as  it  was  before,  but  the  membranous  cell  appears  continuous 
with  the  tentacular  sheath.  We  see,  therefore,  that  in  these  crea¬ 
tures  the  cell  is  an  integrant  part  of  the  animal  itself,  not  a  mere 

*  Recherches  Anatomiques,  Physiologiques,  et  Zoologiques  sur  les  Eschares.  Ann. 
des  Sciences  Nat.  for  1836. 


BRYOZOA. 


113 


*  calcareous  crust  moulded  upon  the  surface  of  the  body,  being  a 
portion  of  the  tegumentary  membrane,  which,  by  the  molecular 
deposit  of  earthy  matter  in  its  tissue,  ossifies  like  the  cartilage  of 
higher  animals  without  ceasing  to  be  the  seat  of  nutritive  move¬ 
ment.  It  is  evident,  likewise,  that  what  is  called  the  bodv  of  the 
Bryozoon  constitutes,  in  fact,  but  a  small  portion  of  it,  principally 
consisting  of  the  digestive  apparatus. 

As  to  the  operculum  destined  to  close  the  entrance  of  the 
tegumentary  cell,  it  is  merely  a  lip-like  fold  of  the  skin,  the 
marginal  portion  of  which  acquires  a  horny  consistence ;  while,  at 
the  point  where  it  is  continuous  with  the  general  envelope,  it  re¬ 
mains  sufficiently  soft  and  flexible  to  obey  the  action  of  the  mus¬ 
cles  inserted  into  it. 

(149.)  The  tegumentary  sac,  deprived  of  its  carbonate  of  lime, 
seems  to  be  formed  of  a  tomentous  membrane,  covered,  especially 
upon  its  outer  side,  with  a  multitude  of  cylindrical  filaments  disposed 
perpendicularly  to  its  surface,  and  very  closely  crowded  together. 
It  is  in  the  interstices  left  by  these  fibres  that  the  calcareous 
matter  appears  to  be  deposited  ;  for,  if  a  transverse  section  be 
examined  with  a  microscope,  the  external  wall  is  seen  not  to  be 
made  up  of  superposed  layers,  but  of  cylinders  or  irregular  prisms 
arranged  perpendicularly  to  the  axis  of  the  body. 

But  the  above  are  not  the  only  arguments  adduced  by  Milne 
Edwards  in  confirmation  of  our  view  of  the  mode  in  which  these 
skeletons  are  held  in  vital  connection  with  the  animal.  On  ex¬ 
amining  the  cells  at  different  ages,  it  is  found  that  they  undergo 
material  changes  of  form. 

This  examination  is  easily  made,  since  in  many  species  the 
young  spring  from  the  sides  of  those  first  formed,  and  do  not  sepa¬ 
rate  from  their  parents  ;  each  skeleton,  therefore,  presents  a  long 
series  of  generations  linked  to  each  other,  and  in  each  portion  of  the 
series  the  relative  ages  of  the  individuals  composing  it  are  indicated 
by  the  position  which  they  occupy.  It  is  sufficient,  therefore,  to 
compare  the  cells  situated  at  the  base,  those  of  the  middle  portion, 
those  of  the  young  branches,  and  those  placed  at  the  very  extremi¬ 
ties  of  the  latter.  When  examined  in  this  manner,  it  is  seen  that  not 
only  does  the  general  configuration  of  the  cells  change  with  age,  but 
also  that  these  changes  are  principally  produced  upon  the  external 
surface.  For  instance,  in  the  young  cells  of  Eschar  a  cervicornis , 
the  subject  of  these  observations,  the  walls  of  which  are  of  a  stony 
hardness,  the  external  surface  is  much  inflated,  so  that  the  cells  are 


i 


BRYOZOA. 


114 

very  distinct,  and  the  borders  of  their  apertures  prominent ;  but  by 
the  progress  of  age  their  appearance  changes,  their  free  surface  rises 
so  as  to  extend  beyond  the  level  of  the  borders  of  the  cell,  and 
defaces  the  deep  impressions  which  marked  their  respective  limits. 
It  results  that  the  cells  cease  to  be  distinct,  and  the  skeleton  pre¬ 
sents  the  appearance  of  a  stony  mass  in  which  the  apertures  of  the 
cells  only  are  visible. 

It  appears  evident,  therefore,  that  there  is  vitality  in  the  sub¬ 
stance  composing  these  stony  walls  ;  and  the  facts  above  narrated 
appear  only  explicable  by  supposing  a  movement  of  nutrition  like 
that  which  is  continually  going  on  in  bone. 

(150.)  The  anatomy  of  these  Bryozoa  differs  slightly  from  that 
of  Bowerbankia.  The  crown  of  ciliated  tentacula  is  inserted  into 
the  extremity  of  a  kind  of  proboscis,  which  is  itself  enclosed  in  a 
cylindrical  retractile  sheath.  From  the  margin  of  the  opening  of 
the  cell  arises  a  membrane  equalling  in  length  the  contracted  ten¬ 
tacles,  and  serving  to  enclose  them  when  the  animal  retires  into  its 
abode.  These  appendages,  thus  retracted,  are  not  bent  upon  them¬ 
selves,  but  perfectly  straight  and  united  into  a  fasciculus,  the 
length  of  which  is  nevertheless  much  less  than  that  of  the  same 
organs  when  expanded. 

By  the  opposite  extremity  to  that  fixed  to  the  margin  of  the 
opening  of  the  cell,  the  tentacular  sheath  unites  with  a  tolerably 
capacious  tube,  the  walls  of  which  are  exceedingly  soft  and  deli¬ 
cate  ;  and  near  the  point  of  their  union  we  may  perceive  a 
fasciculus  of  fibres  running  downwards  to  be  inserted  upon  the 
lateral  walls  of  the  cell  :  these  fibres  appear  to  be  striated  trans¬ 
versely,  and  are  evidently  muscular  ;  their  use  cannot  be  doubted  : 
when  the  animal  wishes  to  expand  itself,  the  membranous  sheath 
above  alluded  to  becomes  rolled  outwards,  everting  itself  like  the 
finger  of  a  glove  as  the  tentacles  advance.  The  muscular  fasciculi 
are  thus  placed  between  the  everted  sheath  and  the  alimentary 
canal,  and  by  their  contraction  they  must  necessarily  retract  the 
whole  within  the  cell. 

The  first  portion  of  the  alimentary  tube  is  inflated,  and  much 
wider  than  the  rest ;  it  forms  a  kind  of  chamber,  in  which  the 
water  set  in  motion  by  the  vibration  of  the  cilia  upon  the  tentacles 
appears  to  circulate  freely.  The  walls  of  this  chamber  are  ex¬ 
tremely  delicate  ;  the  soft  membrane  forming  them  is  puckered,  and 
appears  traversed  by  many  longitudinal  canals  united  by  minute 
transverse  vessels  ;  this  appearance,  however,  may  be  deceptive. 


BRYOZOA. 


115 


Beneath  the  first  enlargement,  the  digestive  apparatus  becomes 
narrower,  but  immediately  expands  again,  and  offers  at  this 
point  a  certain  number  of  filiform  appendages,  which  appear  to 
be  free  and  floating  in  the  interior  of  the  cell.  To  the  second 
cavity  succeeds  a  narrow  canal,  opening  into  a  third  dilatation, 
generally  of  a  spherical  form.  From  the  last-named  viscus 
issues  a  kind  of  intestine,  which  soon  bends  upon  itself  and  be¬ 
comes  attached  to  an  organ  of  a  soft  and  membranous  texture, 
having  the  appearance  of  a  csecum,  and  which  seems  to  be  con¬ 
tinuous  superiorly  with  the  digestive  tube  ;  the  latter  continues 
its  progress  towards  the  upper  part  of  the  cell,  and  ultimately  ter¬ 
minates  by  a  distinct  anal  aperture  upon  the  upper  aspect  of  the 
tentacular  sheath. 

The  operculum  which  closes  the  cell  in  Flustra  and  Fschara  is 
moved  by  two  muscular  fasciculi  inserted  into  the  internal  face  of 
this  valve  by  the  intermedium  of  two  filaments  analogous  to  ten¬ 
dons  :  by  their  inferior  extremity,  these  muscles  are  attached  to 
the  walls  of  the  cell ;  and  when,  by  its  own  elasticity,  the  operculum 
is  turned  back,  and  the  mouth  of  the  cell  thus  opened,  they,  by 
their  contraction,  can  close  it  like  a  door. 

(151.)  A  very  singular  form  of  Bryozoon  is  met  with  in  fresh 
water,  of  which  the  Cristatella  Muceclo *  is  an  example  that  has 
undergone  minute  investigation. 

The  Cristatella  {Jig.  47,  3)  consists  of  a  common  body  or  enve¬ 
lope  (d),  which  is 
membranous,  and 
slightly  cordifonn  ; 
its  surface  is  tubercu- 
lated,  and  it  is  incapa¬ 
ble  of  contraction.  In 
this  outer  covering 
several  individuals 
are  contained, but,  al¬ 
though  produced  from 
one  another,  they  are 
only  aggregated,  be¬ 
ing  lodged  in  distinct  tubular  cells.  The  body  of  each  animal 
appears  to  consist  of  a  digestive  canal,  constricted  once  or  twice 

*  M.  Turpin,  Etude  microscopique  de  la  Cristatella  Mucedo,  espece  de  polype 
d’eau  douce. — Ann.  des  Sciences  Nat.  for  1837.  Also,  another  memoir  upon  the  same 
subject,  by  M.  P.  Gervais. — Ibid. 

i  2 


116 


BRYOZOA. 


in  its  course,  and  terminated  by  an  anal  orifice.  When  these 
creatures  are  extended,  the  upper  part  of  the  body  protrudes  from 
the  cell  ;  the  tentacular  apparatus  being  supported  on  a  kind  of 
neck,  whereon  the  mouth  ( a )  is  easily  seen,  and  near  it  the  anus. 

On  each  side  of  the  mouth  the  body  divides  into  two  arms, 
which,  when  spread  out,  resemble  a  horse-slioe,  being  flattened  and 
blunt  ;  and  upon  the  arms  are  arranged  about  a  hundred  slender, 
transparent,  and  retractile  tentacles,  disposed  on  each  side  and 
upon  the  summit,  like  the  barbs  of  a  feather  ;  and  all  covered  with 
an  infinite  number  of  cilia,  whose  action  produces  currents  directed 
towards  the  mouth,  hurrying  in  that  direction  organized  particles 
contained  in  the  wrater. 

The  three  individuals  that  thus  inhabit  the  same  general  cover¬ 
ing  are  produced  at  two  distinct  generations ;  the  two  lateral 
being  the  offspring  of  the  central  one,  derived  from  it  by  a  pro¬ 
cess  of  gemmation,  but,  when  complete,  they  are  evidently  quite  se¬ 
parate  from  and  independent  of  their  parent. 

(152.)  From  what  is  known  concerning  the  propagation  of  the 
Bryozoa,  it  would  appear  that  their  reproduction  is  effected  in 
several  different  ways. 

The  most  ordinary  is  by  the  developement  of  gemmae  or  buds, 
that  sprout  from  the  parent  stem  in  the  branched  species,  or,  as 
in  the  Flush'#  and  Eschar #,  are  derived  from  the  sides  of  con¬ 
tiguous  cells. 

A  second  mode  of  increase  is  by  the  production  of  ciliated 
gemmules  capable  of  locomotion.  These  gemmules  have  been 
attentively  examined  by  Dr.  Farre  in  the  paper  above  alluded  to, 
and  the  nature  of  the  ciliary  action  by  which  they  are  moved  most 
satisfactorily  investigated,  as  we  shall  elsewhere  have  occasion  to 
notice  more  particularly  ;  but  the  organs  wherein  the  reproductive 
gemmules  are  developed  are  as  yet  undescribed. 

The  Cristatella  seems  to  be  developed  in  an  ovum,  provided 
with  a  shell  of  extremely  singular  construction.  In  fig.  47,  2, 
the  investment  of  one  of  these  extraordinary  eggs  is  represented 
prior  to  the  exclusion  of  the  embryo  Bryozoon,  its  natural  size 
being  shown  in  the  same  figure  ( o  •  the  external  surface  is 
seen  to  be  covered  with  numerous  long  processes  arising  perpen¬ 
dicularly  from  it,  and  each  terminates  in  a  minute  double  hook, 
adapted  apparently  to  fix  the  egg  upon  marine  plants  at  the  sur¬ 
face  of  the  water :  but  how  these  hooks  become  developed  is  still  a 
mystery  ;  it  would  seem  impossible  that  an  ovum  so  formidably 


ROTIFER  A. 


117 


armed  could  be  expelled  from  the  parent  animal  in  the  usual 
way ;  we  must  therefore  suppose  that  the  spines  grow,  or  become 
hardened  at  least,  subsequently  to  the  birth  of  the  ovum.  Since  the 
discovery  of  this  microscopic  egg  in  a  recent  state,  similar  bodies 
have  been  detected  in  great  numbers  in  a  fossil  condition  im¬ 
bedded  in  flint ;  a  fact  which,  in  conjunction  with  what  has  been 
already  stated  (§74)  concerning  the  occurrence  of  the  shells  of 
loricated  infusoria  in  the  same  situation,  tends  materially  to  show 
that  masses  of  flint  are  agglomerations  of  siliceous  particles  inclos¬ 
ing  immense  quantities  of  the  debris  of  organized  bodies.* 

That  the  bryozoa  are  very  far  superior  to  the  polyps  in 
all  the  details  of  their  structure,  will  now  be  sufficiently  mani- 
test.  The  ciliated  tentacula,  although  selected  as  affording  the 
most  convenient  character  for  the  guidance  of  the  Zoologist 
from  the  constancy  of  their  coexistence  with  elaborately  or¬ 
ganized  internal  viscera,  are  probably  only  organs  of  secondary 
importance  in  a  physiological  point  of  view  ;  for  the  analogies 
between  this  class  and  that  which  will  form  the  subject  of  our 
next  chapter  are  not  to  be  mistaken,  and  the  transition  from  one 
to  the  other  is  so  gradual,  that  where  observation  has  failed  in  com¬ 
pletely  developing  the  anatomy  of  the  animals  we  have  been 
considering,  the  facts  which  have  been  ascertained  concerning  the 
Rotiferous  Animalcules,  will  go  far  towards  supplying  the  defi¬ 
ciency. 


CHAPTER  IX. 

fRoTiFERA  ( Ehrenberg ). 

(153.)  The  class  of  animals  that  next  presents  itself  for  our 
consideration  was,  until  very  recently,  confounded  with  the  chaotic 
assemblage  of  minute  creatures  to  which  the  name  of  Infusorial 
Animalcules  was  indiscriminately  applied;  but  the  information  at 
present  in  our  possession  concerning  their  internal  structure  and 
general  economy,  while  it  exhibits,  in  a  striking  manner,  the  assi¬ 
duity  of  modern  observers,  and  the  perfection  of  our  means  of  ex¬ 
ploring  microscopic  subjects,  enables  us  satisfactorily  to  define  the 
limits  of  this  interesting  group  of  beings,  and  assign  to  them  the 
elevated  rank  in  the  scale  of  zoological  classification  to  which,  from 
their  superior  organization,  they  are  entitled. 

*  Turpin,  Ann.  des  Sciences  Nat.  1837.  t  Rota,  a  wheel;  fero,  I  bear. 


118 


ROTIFERA. 


The  character  whence  the  class  obtains  its  name  is  derived  from 
the  peculiar  organs  placed  upon  the  anterior  part  of  the  body, 
which  are  subservient  to  locomotion,  and  assist  in  the  prehension 
of  food  ;  these  consist  of  circlets  of  cilia  variously  disposed  in  the 
neighbourhood  of  the  mouth,  and  having,  when  in  action,  the  ap¬ 
pearance  of  wheels  spinning  round  with  great  rapidity,  so  as  to  pro¬ 
duce  strong  currents  in  the  surrounding  water.  Yet,  notwithstand¬ 
ing  this  peculiar  structure  of  the  locomotive  apparatus,  the  Roti¬ 
fer  a  present  very  marked  relations  with  the  Bryozoa,  described 
in  the  last  chapter  ;  and  the  conversion  of  the  ciliated  tentacula  of 
the  latter  into  the  rotatory  organs  of  the  present  class  is  effected 
by  several  intermediate  forms,  which  would  seem  to  indicate  a 
closer  alliance  between  the  two  than,  from  an  examination  of  the 
more  typical  genera  of  each,  we  should  be  inclined  to  suspect. 

( J  54.)  The  annexed  engraving  of  the  Stephanoceros  Eichornii* 
(Jig.  48)  exhibits  an  48. 

animal  that  would  seem 
to  be  one  of  the  connect¬ 
ing  links  by  which  this 
transition  is  accomplish¬ 
ed  ;  the  transparent  cell, 
and  ciliated  tentacula 
around  the  mouth,  would 
indicate  this  creature  to 
be  a  Bryozoon  ;  but  the 
tentacula  are  no  longer 
the  stiff  and  slender  arms 
which  we  have  seen  in 
BowerbaiiJcia ,  but  are  vi¬ 
sibly  stunted  and  thick¬ 
ened  at  their  base,  thus 
approximating  in  character 
the  cilia-bearing  lobes  of 
a  Rotifer  ;  while  the  inter¬ 
nal  organs,  the  pharynx, 
gizzard,  and  stomach,  in 
this  animal  conform  ex¬ 
actly  to  the  type  of  structure  common  to  the  Rotifera  properly  so 
called. 

(155.)  The  body  of  one  of  the  wheel  animalcules  is  enclosed  in 

*  Ehrenberg. 


ROTIFEltA. 


119 


a  delicate  transparent  envelope  of  considerable  consistency,  often 
terminating  at  tlie  upper  extremity  in  wavy  indentations  or  tooth- 
like  processes,  as  in  Brachionus  arceolaris*  {fig.  49,  c,  c  ).  This 
harder  integument  is  essentially  analogous  to  the  cell  of  a  Bryo- 
zoon,  but  in  this  case  is  so  constructed  as  to  allow  the  animals  to 
move  at  large  in  the  element  they  inhabit,  instead  of  being  per¬ 
manently  fixed  to  the  same  locality.  Continuous  with  the  free 
margin  of  the  shell  is  a  delicate  membrane  connecting  it  with  the 


Fig.  49. 


bases  of  the  cilia-bearing  lobes  around  the  mouth,  so  as  to  allow 
those  organs,  when  not  in  use,  to  be  retracted  within  the  cell  by  a 
mechanism  resembling  that  provided  in  Bowerbankia  for  the  re¬ 
traction  of  the  tentacula. 

To  the  posterior  extremity  of  the  body  is  generally  appended  a 
pair  of  forceps  composed  of  two  moveable  pieces  {figs.  50  and 
51),  used  as  anchors  or  instruments  of  prehension;  and  by 
means  of  these  the  little  creatures  fix  themselves  to  the  confervm 
or  aquatic  plants  amongst  which  they  are  usually  found.  In 
Brachionus  urceolaris  the  prehensile  forceps  {fig.  49,  o  p,)  is  at¬ 
tached  to  the  extremity  of 
a  long  flexible  tail  in  which 
the  muscular  fibres  des¬ 
tined  for  its  motions  are 
distinctly  visible. 

(156.)  The  cilia,  whose 
action  produces  the  ap¬ 
pearance  of  wheels  turn¬ 
ing  upon  the  anterior  part 
of  the  body,  are  variously 
disposed,  and  from  their 
arrangement  Ehrenberg 
has  derived  the  characters 
whereon  he  bases  the  di¬ 
vision  of  the  class  into 
orders.  The  peculiar 
movements  excited  by  the 
vibration  of  these  organs, 
was  long  a  puzzle  to  the 
earlier  microscopic  observers,  who,  imagining  them  to  be  really 
wheels  turning  round  with  great  velocity,  were  utterly  unable  to 


*  The  engravings  of  the  Rotifera  are  all  copied  from  Ehrenberg’s  papers.  Abhand- 
lungen  der  Koniglichen  Akademie  der  Wissenchaften  zu  Berlin,  for  1833. 


120 


ROTIFER  A. 


conceive  what  could  be  the  nature  of  the  connection  between  such 
appendages  and  the  body  of  the  animal.  The  apparent  rotation 
has,  however,  been  long  proved  to  be  an  optical  delusion,  and  to 
be  produced  by  the  progressive  undulations  of  the  cilia  placed  in 
the  neighbourhood  of  the  mouth. 

(157.)  With  respect  to  the  agents  employed  in  producing  the 
ciliary  movement  in  the  rotifera,  we  are  as  much  in  ignorance  as  we 
are  concerning  the  cause  of  the  same  phenomenon  in  the  polygastrica. 
Ehrenberg  describes  the  cilia  as  arising  from  a  series  of  lobes  as  re¬ 
presented  in  Notommata  clavulata  (Jig.  51  a);  these  he  regards  as 
being  muscular,  and  capable  of  producing  by  their  contractions  the 
rapid  vibrations  of  the  fibrillee  attached  to  them.  We  confess, 
however,  that  such  lobes,  even  was  their  existence  constant,  seem 
very  clumsy  instruments  for  effecting  the  purpose  assigned  to  them, 
and  it  is  not  easy  to  conceive  how  the  rapid  and  consecutive  undu¬ 
lations  to  which  the  appearance  of  rotation  is  due  can  be  produced 
by  organs  of  this  description. 

The  observations  of  Dr.  Arthur  Farre*  concerning  the  ciliary 
movements  visible  upon  the  gemmules  of  some  of  the  Bryozoa  appear 
best  calculated  to  throw  light  upon  the  nature  of  the  action  of  these 
wonderful  appendages,  and  to  explain  the  cause  of  the  apparent 
rotatory  motion  of  the  so-called  wheels  of  the  rotifera.  The  very 
accurate  observer  alluded  to  remarks  that  under  high  powers,  the 
cilia  have  the  appearance  of  moving  in  waves,  in  the  production  of 
each  of  which  from  a  dozen  to  twenty  cilia  are  concerned,  the 
highest  point  of  each  wave  being  formed  by  a  cilium  extended  to 
its  full  length,  and  the  lowest  point  between  every  two  waves  by 
one  folded  down  completely  upon  itself,  the  intervening  space  be¬ 
ing  completed  by  others  in  every  degree  of  extension,  so  as  to  pre¬ 
sent  something  of  the  outline  of  a  cone.  As  the  persistence  of 
each  cilium  in  any  one  of  these  positions  is  of  the  shortest  possible 
duration,  and  each  takes  up  in  regular  succession  the  action  of  the 
adjoining  one,  that  cilium  which,  by  being  completely  folded  up, 
formed  the  lowest  point  between  any  two  waves,  in  its  turn  by  its 
complete  extension  forms  the  highest  point  of  a  wave  ;  and  thus, 
while  the  cilia  are  alternately  bending  and  unbending  themselves, 
each  in  regular  succession  after  the  other,  the  waves  only  tra¬ 
vel  onward,  whilst  the  cilia  never  change  their  position  in  this  di¬ 
rection,  having,  in  fact,  no  lateral  motion. 

The  whole  of  the  ciliary  movements  arc  so  evidently  under  the 
control  of  the  animal  as  to  leave  not  the  slightest  doubt  in  the 


*  Phil.  Trans,  for  1837. 


It  OTIFERA. 


m 


mind  of  tlie  observer  upon  this  point.  The  whole  fringe  of  cilia 
may  be  instantly  set  in  motion,  and  as  instantaneously  stopped,  or 
their  action  regulated  to  every  degree  of  rapidity.  Sometimes  one 
or  two  only  of  the  waves  are  seen  continuing  their  action,  whilst 
the  remainder  are  at  rest ;  or  isolated  cilia  may  be  observed  slowly 
bending  and  unbending  themselves,  while  the  others  are  quiescent. 
It  is  by  the  constant  succession  of  these  movements  that  the  eye  is 
seduced  to  follow  the  waves  which  they  seem  to  produce,  and  thus 
the  apparent  rotation  of  the  wheels  is  easily  understood. 

(158.)  Such  being,  as  we  conceive,  the  nature  of  the  ciliary  motion, 
we  will  proceed  to  examine  the  uses  to  which  it  is  made  subservient  in 
the  class  of  animals  under  consideration.  A  very  slight  examina¬ 
tion  of  one  of  these  creatures  under  the  microscope  will  show  that 
the  cilia  answer  a  double  purpose  ;  if  the  Rotifer  fixes  itself  to 
some  stationary  object  by  means  of  the  anal  forceps,  it  is  precisely 
in  the  position  of  a  Bryozoon  ;  and  the  ciliary  action,  by  producing 
currents  in  the  water  all  directed  towards  the  oral  orifice,  ensures 
a  copious  supply  of  food  by  hurrying  to  the  mouth  whatever 
minute  aliment  may  be  brought  within  the  range  of  the  vortex  thus 
caused  ;  or,  on  the  other  hand,  if  the  animal  disengages  itself  from 
the  substance  to  which  it  held  by  its  curious  anchor,  the  wheels 
acting  upon  the  principle  of  the  paddles  of  a  steam-boat  carry  it 
rapidly  along  with  an  equable  and  gliding  movement. 

(159.)  The  whole  ciliary  apparatus  when  not  in  use  is  retracted 
within  the  orifice  of  the  shell,  and  lodged  in  a  kind  of  sheath  formed 
for  it  by  the  inversion  of  the  tegumentary  membrane.  The  muscular 
fasciculi  by  which  this  is  effected  are  very  conspicuous ;  they  arise 
from  the  lining  membrane  of  the  shell,  and  run  in  distinct  fasci¬ 
culi  in  a  longitudinal  direction  to  be  inserted  into  the  lobules 
whereon  the  cilia  are  arranged  ( fig .  50,  h ,  li). 

But,  besides  these  retractor  muscles,  other  fasciculi  of  muscular 
fibres  are  seen  to  run  transversely,  (fig*  50,  i,  z,  )  crossing  the  for¬ 
mer  at  right  angles :  these  are,  most  probably,  the  agents  pro¬ 
vided  for  the  extrusion  of  the  wheel-like  apparatus ;  for,  aris¬ 
ing,  as  they  do,  from  the  inner  membrane  of  the  hard  integument, 
they  will,  by  their  contraction,  compress  the  fluid  in  which  the 
viscera  float,  and,  forcing  it  outward  towards  the  orifice  of  the  shell, 
it  will,  of  course,  push  before  it  the  wheels,  so  as  to  evert  the  te¬ 
gumentary  membrane  connecting  them  with  the  shell,  by  unrolling 
it  like  the  finger  of  a  glove,  and  thus  they  will  cause  the  rotatory 
organs  to  protrude  at  the  pleasure  of  the  animal. 


\m 


ROTIFER A. 


We  have  already  described  the  means  whereby  the  Rotifera  pro¬ 
cure  a  supply  of  food,  namely,  by  exciting  currents  in  the  surrounding 
water  ;  the  materials  so  obtained  pass  at  once  into  a  pharynx,  the 
capacity  of  which  would  seem  to  vary  considerably  in  different 
species :  from  the  pharyngeal  receptacle  it  is  conveyed  into  a 
singularly  constructed  gizzard,  to  be  bruised  and  broken  down 
by  an  apparatus  provided  for  that  purpose ;  thus  prepared  it  is 
allowed  to  enter  a  third  cavity,  wherein  digestion  is  accomplished, 
which  may  be  called  the  stomach,  and  this,  after  becoming  gradu¬ 
ally  constricted  in  its  diameter,  terminates  at  the  caudal  extremity 
of  the  body. 

(160.)  The  usual  arrangement  of  the  digestive  apparatus  will  be 
readily  understood  on  reference  to  the  annexed  figures ;  thus,  in  Ste- 
phanoceros  Eichornii ,  (Jig-  48,)  the  pharynx  (a)  is  very  capacious, 
receiving  readily  the  materials  brought  into  it  by  the  ciliated 
arms ;  the  gizzard  ( e )  is  a  small  globular  viscus,  containing  the 
instruments  of  mastication  hereafter  to  be  noticed ;  while  the 
digestive  cavity  properly  so  called  (A),  which  presents  no  per¬ 
ceptible  division  into  stomach  and  intestine,  extends  from  the 
gizzard  to  the  anal  aperture. 

In  Brachionus  urceolaris  (Jig-  49)  the  pharynx  or  oesopha¬ 
gus  (e)  is  less  capacious ;  the  gizzard  (f)  exhibits  through  its 
transparent  coats  the  peculiar  dental  organs  placed  within  it ; 
and  the  stomach  (g)  is  seen  partially  folded  upon  itself  by 
the  retraction  of  the  body.  We  observe  moreover  in  this 
animal,  appended  to  the  commencement  of  the  stomach,  two 
large  csecal  appendages  ( h  A),  which  were  scarcely  perceptible  in 
the  last  figure,  and  which  no  doubt  are  of  a  glandular  nature, 
furnishing  some  fluid  to  be  mixed  up  with  the  bruised  aliment 
contained  in  the  stomach,  to  assist  in  the  digestive  process.  To 
these  secreting  caeca  Ehrenberg  has  chosen  to  give  the  name  of 
pancreas,  but  for  what  reason  it  is  difficult  to  conjecture,  since  the 
first  rudiments  of  a  pancreas  are  only  met  with  in  animals  far 
higher  in  the  scale  of  animal  existence  ;  every  analogy  indeed  would 
lead  us  to  denominate  these  caeca  the  first  rudiments  of  a  liver, 
by  far  the  most  important  and  universal  of  the  glandular  organs 
subservient  to  digestion,  and  in  a  variety  of  creatures  we  shall 
afterwards  find  it  presenting  equal  simplicity  of  structure.  In 
the  Notommata  centrura  (Jig-  50,  g,  g),  the  caeca  are  merely 
two  pouches  opening  into  the  top  of  the  stomach,  whereas  in 
Notommata  clavulata  there  are  six  of  these  appendages  (Jig- 


ROTIFERA. 


123 


51,  e,  e)  communicating  with  that  enlarged  portion  of  the 
digestive  canal  (c)  which  may  be  looked  upon  as  the  proper 
stomach. 

(161.)  We  must  now  revert  to  the  consideration  of  the 
dental  apparatus  contained  in  the  gizzard,  represented  in  situ  in 
(Jig.  49,/),  and  exhi¬ 
bited  on  a  still  larger 
scale  in  (/g.  50,  2). 

This  curious  masticat¬ 
ing  instrument  consists 
of  three  distinct  pieces 
or  teeth,  which  are 
made  to  work  upon 
each  other  by  the  con¬ 
tractions  of  the  gizzard, 
so  as  to  tear  in  pieces  or 
bruise  all  matters  made 
to  pass  through  the 
cavity  containing  them. 

The  central  piece  (Jig. 

50,  2,  b)  may  be  com¬ 
pared  to  an  anvil  pre¬ 
senting  upon  its  upper 
surface  two  flattened 
facets  ;  and  upon  these 
the  other  two  teeth,  that  might  without  much  stretch  of 
fancy  be  compared  to  two  hammers,  act.  Each  of  the  superior  teeth 
(Jig.  50,  a,  a)  may  be  described  as  consisting  of  two  portions 
united  at  an  angle  :  the  larger  portion,  or  handle  as  it  might  be 
called,  serves  for  the  attachment  of  muscles ;  whilst  the  other 
part  is  free  in  the  cavity  of  the  gizzard,  and  works  upon  the  facets 
of  the  anvil,  the  edge  being  apparently  divided  into  teeth  resem¬ 
bling  those  of  a  comb,  and  evidently  adapted  to  bruise  or  tear 
substances  submitted  to  their  action.  Such  is  the  transparency 
of  the  whole  animal,  that  the  effect  of  these  remarkable  masti¬ 
cating  organs  upon  the  animalcules  used  as  food  is  distinctly 
visible  under  a  good  microscope,  and  if  the  Rotifer  be  compressed 
between  two  pieces  of  glass,  so  as  to  break  down  the  soft  textures 
of  its  body,  the  teeth  may  from  their  hardness  be  procured  in  a 
detached  state  for  minute  examination.  The  whole  apparatus 
described  above  evidently  resembles  very  closely  the  kind  of 


124 


ROTIFER  A. 


stomach  met  with  in  tlie  Crustacea,  to  which  the  rotifcra  will  be 
found  gradually  to  approximate. 

(162.)  Notwithstanding  the  microscopic  size  of  the  Rotifera,  and 
the  consequent  difficulty  of  detecting  the  more  minute  details  of 
their  structure,  Ehrenberg  thinks  he  has  succeeded  in  discovering 
filamentary  nerves,  and  even  nervous  masses,  distributed  in  different 
parts  of  their  body  ;  an  arrangement  which  not  only  would  account 
for  the  complete  association  of  their  voluntary  movements,  but 
would,  from  the  presence  of  ganglia,  render  these  animals  capable  of 
possessing  some  of  the  local  senses  ;  indeed  Ehrenberg  imagines  he 
has  discovered  such  to  exist  in  the  shape  of  red  specks,  to  which  he 
gives  the  name  of  eyes.  The  organ  alluded  to  is  a  minute  red 
spot,  indicated  in  the  figures  {Jig.  49  and  50,  c)  ;  nevertheless,  no 
organization  has  been  described  of  such  a  nature  as  to  entitle  us 
unhesitatingly  to  designate  it  an  organ  of  vision,  even  if  it  should, 
as  he  intimates,  invariably  be  in  connection  with  a  nervous  mass, 
which,  from  examining  his  drawing  of  the  arrangement  of  the 
nerves,  we  should  have  little  expected  to  be  the  case. 

(163.)  The  nervous  system  of  Notommata  clavulata ,  as  describ¬ 
ed  by  this  indefatigable  observer,  is  represented  in  fig.  51.  It  would 
seem  to  consist  of  several  minute  nodules,  exhibiting  a  somewhat 
symmetrical  arrangement,  and  disposed  apparently  in  pairs  ;  some 
of  these  nodules,  which  are  about  ten  in  number,  communicate 
Avith  each  other  by  delicate  filaments,  whilst  others  seem  to  be 
quite  insulated  from  the  rest. 

Every  one  who  is  acquainted  with  the  difficulty  of  conducting 
microscopical  observations,  especially  with  the  high  powers  needful 
in  detecting  structures  so  minute  as  the  nerves  of  the  Rotifera,  will 
be  exceedingly  cautious  in  admitting  the  complete  establishment  of 
facts  involving  important  physiological  principles  ;  and  we  cannot 
help  thinking  that  Ehrenberg  has  been  misled  by  some  appearances 
which  it  is  impossible  for  the  most  correct  observer  always  to  guard 
against,  in  assigning  to  the  rotifera  an  arrangement  of  the  nervous 
system  so  totally  different  from  what  is  met  with  in  any  other  class 
of  animals,  as  that  represented  in  his  figure  from  which  our  engrav¬ 
ing  has  been  accurately  copied. 

All  our  ideas  of  the  physiology  of  the  nerves  would  lead  us  to 
suspect  some  error.  The  uses  of  ganglia,  as  far  as  we  know  at 
present,  are  either  to  associate  nerves  derived  from  different  sources, 
or  to  serve  as  centres  for  perception,  or  else  they  are  for  the  con¬ 
centration  of  nervous  energy.  The  position  of  the  ganglia  depicted 
in  the  figure  as  being  in  relation  with  the  nervous  threads  would 


ROTIFERA. 


125 


scarcely  seem  to  be  consistent  with  either  of  the  above  offices,  and 
therefore  we  cannot  but  regard  the  observations  which  have  been 
hitherto  recorded  concerning  the  nervous  system  of  the  rotifcra  as 
far  from  being  complete. 

(164.)  In  addition  to  the  elaborate  organization  described  above, 
the  Prussian  naturalist  conceived  that  he  had  discovered  a  vascular 
apparatus,  consisting  of  transverse  vessels,  51,  w,  n,)  in  which 
he  supposed  a  circulation  of 
the  nutritive  fluids  occurred. 

But  the  vascular  character  of 
the  transverse  striae  visible  in 
this  position  is  more  than 
doubtful,  as  there  seems 
every  reason  to  suppose  that 
the  appearance  depicted  in 
the  figure  is  due  to  the 
existence  of  the  transverse 
muscular  bands  whereby  the 
extrusion  of  the  rotatory  ap¬ 
paratus  is  effected,  analogous 
to  those  occupying  a  similar 
situation  in  the  Bryozoa  :  in 
fig.  50,  i,  these  transverse 
fasciculi  are  distinctly  de¬ 
lineated,  and  their  nature 
is  at  once  evident. 

(165.)  The  mode  in  which 
respiration  is  effected  in  the 
class  of  animals  under  consi¬ 
deration  has  been  a  subject  of  much  dispute.  Some  have  supposed 
the  contact  of  water,  applied  to  the  general  surface  of  the  body, 
sufficient  for  the  aeration  of  the  nutritious  juices,  especially  as  its 
constant  renewal  would  be  ensured  by  the  ciliary  movements. 
Bory  St.  Vincent,  *  on  the  contrary,  regarded  the  rotatory  cilia 
as  real  gills,  resembling  those  of  fishes  ;  and  mistaking  the  move¬ 
ments  of  the  gizzard  for  the  contractions  of  a  heart,  conceived  these 
animalcules  to  be  even  superior  to  insects  in  the  organization  of 
their  vascular  system.  Ehrenberg,  moreover,  thinks  that  he  has 
discovered  an  internal  respiratory  apparatus  of  a  most  extraordinary 
description.  In  Notommata  centrura  ( Jig .  50  )  he  remarked 

*  Diet,  des  Sciences  Naturelles  ;  art.  Rotifera. 


126 


ROTIFER  A. 


seven  vibrating  points  on  one  side,  and  six  on  the  other,  attached 
to  two  long  and  undulating  viscera,  (/,  /,)  which  he  elsewhere 
describes  as  being  the  testes  of  the  animal  :  the  above-mentioned 
points  were  never  at  rest,  and  appeared  to  be  placed  in  determinate 
positions  opposite  to  each  other.  Accurate  observations,  he  says, 
have  shown  each  to  be  a  peculiar  little  organ,  provided  with  a  tail 
resembling  that  of  a  note  in  music,  and  to  be  thrown  into  vibration 
by  three  little  vesicles  or  folds  of  their  inflated  extremity  ;  these 
organs  floated  freely  in  the  abdominal  cavity  by  their  enlarged 
portion,  while  by  their  tail  they  were  attached  to  the  long  tubular 
organ  above  referred  to  {figs.  49  and  50). 

Ehrenberg’s  first  idea,  on  seeing  these  organs,  was,  that  they 
formed  a  vascular  system,  executing  movements  of  pulsation  ;  but 
he  now  considers  them  as  internal  branchiae,  or  organs  of  respira¬ 
tion,  to  which  the  external  water  is  freely  admitted  in  the  following 
manner. 

In  many  species  of  the  rotifera,  we  find,  projecting  from  the  neck 
of  the  animal,  a  horny  tubular  organ,  called  by  Ehrenberg  the  Calcar 
or  spur  {figs.  49  d,  and  50  b)  ;  this  he  at  first  considered  to  be 
the  male  organ  of  sexual  excitement,  but  he  now  regards  it  as  a 
syphon  or  tube  of  respiration,  through  which  the  circumambient 
water  passes  freely  into  the  cavity  of  the  body.  He  thinks,  more¬ 
over,  that  the  periodical  transparency,  and  the  alternate  distension 
and  collapse  of  the  animal,  seen  to  occur  regularly  in  almost  all  the 
Rotifera,  are  produced  by  the  introduction  of  water  into  the  visceral 
cavity,  and  its  subsequent  expulsion  therefrom,  upon  which  action 
the  fluctuations  observed  in  the  interior  of  the  body  would  there¬ 
fore  depend.  The  supposition  that  water  is  injected  in  this 
manner  into  the  body  seems  to  be  favoured  by  other  appear¬ 
ances  ;  for,  when  the  internal  cavity  is  thus  filled,  all  the  viscera 
appear  isolated,  so  that  the  boundaries  of  each  can  be  distinctly 
seen,  but  when  the  water  is  discharged  they  approximate  each 
other,  their  limits  become  confounded,  and  the  external  membrane 
of  the  body  assumes  a  crumpled  appearance. 

Upon  reviewing  the  above  account  of  the  mode  of  respiration  in 
the  rotifera,  we  must  say  that  we  consider  that  the  office  assigned 
to  the  little  organs  called  internal  branchiae  is  extremely  proble¬ 
matical,  especially  as  we  have  but  the  most  vague  intimations  con¬ 
cerning  the  existence  of  a  circulating  system  at  all,  much  less  of 
such  a  double  circulation  carried  on  in  arteries  and  veins  as  the 
presence  of  such  organs  would  infer.  “  I  presume, ”  says  Ehrenberg, 


ROTIFERA. 


127 


that  the  branchise  possess  a  vascular  system  ;  for,  when  the  local 
contractions  occur  in  the  body  of  the  animal,  we  see  distinctly  a 
certain  number  of  filaments  (vessels  ?)  loose  and  delicate.”  The 
opinions  of  the  Professor  himself  concerning  the  nature  of  the 
organs  which  he  describes  being  so  indefinite,  we  must  pause  before 
adopting  the  physiological  views  to  which  their  admission  would 
lead ;  more  especially  as,  from  the  very  fact  of  the  whole  visceral 
cavity  being  perpetually  filled  with  aerated  water,  the  existence  of  any 
localized  organs  of  respiration  could  hardly  be  esteemed  necessary. 

(166.)  The  last  subject  which  we  have  to  consider  relative  to  the 
internal  economy  of  the  rotifera  is,  the  conformation  of  their  gene¬ 
rative  apparatus,  which  now  assumes  a  considerable  perfection  of 
developement.  The  reproductive  system  is  composed  apparently 
of  two  distinct  parts  :  the  one  subservient  to  the  formation  of  the 
ova  ;  the  other  destined  either  to  furnish  some  secretion  essential  to 
the  completion  of  the  egg,  or,  as  is  more  probably  the  case,  secret¬ 
ing  a  fertilizing  fluid  by  which  the  impregnation  of  the  ova  is 
effected  prior  to  their  escape  from  the  body. 

The  ovary,  as  we  might  term  it,  or  female  portion  of  the  system, 
{Jigs.  48  c,  49  m,  n ,  50  A-,  kf  51  fj  is  a  transparent  sacciform  organ, 
in  which,  at  some  seasons,  the  eggs  are  distinctly  perceptible  through 
the  pellucid  coverings  of  the  animal,  as  represented  in  the  figures. 

The  male  organs,  or  testes,  as  we  may  call  them,  are  two  in  number 
( figs.  50  /,  and  50  h)  ;  they  resemble  long  wavy  cseca,  extending 
nearly  the  whole  length  of  the  animal,  and  terminating  near  the  oral 
extremity  by  closed  extremities.  It  is  to  these  organs  that  the  small 
appendages  mentioned  above  as  organs  of  respiration  are  appended  ; 
and,  should  the  latter  not  perform  the  office  of  respiratory  branchiae, 
they  are  most  probably  organs  of  secretion,  such  as  in  many  other 
animals  we  shall  see  appended  to  the  spermatic  tubes. 

Both  the  ovigerous  organ  and  the  two  seminiferous  vessels 
terminate  in  a  common  receptacle  (Jig-  51,  g,)  that  may  be  named 
the  cloaca  ;  this  consists  of  a  transparent  vesicle  endowed  with 
great  irritability,  in  which  the  fertilization  of  the  ova  is  apparently 
effected,  the  eggs  being  here  brought  in  contact  with  the  secretion 
of  the  testes  before  they  escape  through  the  excretory  passage 
(Jig.  51,  d). 

The  ova  of  the  rotifera,  before  they  are  hatched,  form  very  in¬ 
teresting  objects  for  the  microscope  ;  as  the  movements  of  the  in¬ 
cluded  young,  and  even  the  action  of  the  cilia  forming  their 
wheel-like  organs,  may  be  distinctly  seen  through  the  exquisitely 
transparent  investment  of  the  egg. 


128 


EPIZOA. 


CHAPTER  X. 

Epizoa. 

(167.)  Not  only  are  tlie  internal  parts  of  living  animals  occasion¬ 
ally  made  tlie  residence  of  creatures  adapted  by  tlieir  organization  to 
live  under  such  circumstances,  but  there  is  an  extensive  class  of 
beings  destined  to  an  equally  parasitical  life,  so  constructed  as  to 
be  capable  of  attaching  themselves  to  the  external  parts  of  other 
creatures,  from  which  they  suck  the  nourishment  suited  to  their 
nature. 

These  parasites  are  commonly  found  to  infest  Fishes,  Crustaceans, 
and  other  inhabitants  of  fresh  and  salt  water;  generally  fixing 
themselves  in  positions  where  an  abundant  supply  of  animal  juices 
can  be  readily  obtained,  and  where,  at  the  same  time,  the  water  in 
which  they  are  immersed  is  perpetually  renewed  for  the  purpose  of 
respiration.  The  gills  of  fishes,  therefore,  offer  an  eligible  situa¬ 
tion  for  their  developement,  as  do  the  branchiae  of  the  lobster  ;  or 
they  are  sometimes  found  attached  in  great  numbers  to  the  interior 
of  the  mouth  in  various  fishes,  deriving  from  its  vascular  lining,  or 
from  the  abundant  secretions  met  with  in  such  a  locality,  a  plentiful 
supply  of  food,  while  they  are  freely  exposed  to  the  currents  of 
water  which  the  mode  of  respiration  in  the  fish  brings  in  contact 
with  them. 

(168.)  Allied,  however,  as  these  creatures  are  in  the  nature  of 
their  mode  of  life  to  the  entozoa,  it  is  easy  to  perceive  that,  from 
their  residence  upon  the  surface  of  the  body,  they  enjoy  a  far  greater 
capability  of  action,  and  a  more  enlarged  intercourse  with  the  ex¬ 
ternal  world  ;  so  that  we  are  not  surprised  at  finding  them  possessed 
of  organs  which  in  both  the  Sterelminthoid  and  Ccclelminthoid 
entozoa  would  have  been  entirely  useless.  In  none  of  the  indi¬ 
viduals  of  either  of  those  classes,  therefore,  have  we  found  external 
organs  developed  ;  but  in  the  Epizoa *  we  perceive,  in  a  very  in¬ 
teresting  form,  the  first  sproutings  as  it  were  of  articulated  mem¬ 
bers,  which  in  higher  classes  attain  their  perfect  developement. 

The  least  elaborately  organized  of  these  animals  exhibit,  indeed, 
exceedingly  grotesque  and  singular  shapes,  resembling  rather  im- 

*  Eti,  upon  ;  ^oovy  an  animal. 


EPIZOA. 


129 


perfect  embryos  than  mature  beings ;  the  first  buddings  of  external 
limbs  in  the  earlier  period  of  foetal  developement  imitating  not 


very  remotely  the  appearance  of 
the  rudimentary  appendages  re¬ 
presented  in  the  annexed  figure* 
(Jig-  52).  But  this  resem¬ 
blance  is  not  confined  merely  to 
a  fancied  similarity  in  outward 
form ;  it  exists  in  the  physio¬ 
logical  relation  that  there  is 
between  the  embryo  and  the 
Epizoon,  and  seems  dependent 
upon  that  great  principle  which 
inseparably  connects  the  perfec¬ 
tion  of  an  animal  with  the  cha¬ 
racter  of  its  nervous  system  : 
the  nerves  of  the  Epizoa  are 
simple  filaments,  the  ganglia 
being  indistinct  or  scarcely  de- 


Fig.  52. 


veloped  ;  and  the  imperfection 

of  the  limbs  is  a  necessary  consequence.  In  the  same  manner,  in 
the  earliest  stages  of  foetal  growth,  when  we  know  that  the  nerves  are 
as  yet  but  mere  threads,  it  is  interesting  to  observe  the  resemblance, 
even  in  outward  appearance,  between  the  embryo  in  this  transitory 
stage  of  its  growth,  and  the  permanent  condition  of  the  Epizoa 
which  we  are  considering. 

(1 69.)  A  great  number  of  species  of  these  parasites,  generally  de¬ 
scribed  under  the  name  of  Lerneans,  have  been  observed  by  authors, 
and  it  would  seem  indeed  that  each  is  peculiar  to  a  particular  kind  of 
fish.  The  varieties  observable  in  their  outward  form  are,  of  course, 
exceedingly  great ;  but  the  examples  depicted  in  the  figure,  namely, 
the  Leriuea  gobina ,  found  in  the  branchiae  of  Coitus  Gobio  and 
Lerruza  racliata ,  which  infests  the  mouth  of  Coryphcena  rupestris , 
will  make  the  reader  sufficiently  acquainted  with  their  general  ap¬ 
pearance  and  external  structure.  In  the  former  parasite,  of  which  an 
anterior  and  posterior  view  are  given  in  the  engraving  (a,  b ),  the 
appendages  seen  upon  the  head  and  sides  of  the  body  answer  the 
purpose  of  hooks  or  grappling  organs,  whereby  the  creature  re¬ 
tains  its  position  ;  and  so  firm  is  its  hold  upon  the  delicate  covering 
of  the  gills,  that,  even  after  the  death  of  the  fish,  it  is  not  easily 


Miiller  (Othone  Frederico)  Zoologia  Danica,  1788. 


K 


130 


EPIZOA. 


detached.  In  the  second  example,  (c,  d,)  besides  the  rudimentary 
limbs,  the  lower  surface  of  the  head  and  ventral  aspect  of  the  body 
('0  are  covered  with  sharp  spines  calculated  to  increase  very 
materially  the  tenacity  of  its  hold  upon  the  surface  from  which  it 
imbibes  food.  The  sacculi  appended  to  the  posterior  part  of 
the  animal  are  receptacles  for  the  eggs,  and  will  be  explained 
hereafter. 

These  examples,  however,  are  taken  from  the  most  imperfectly 
organized  Epizoa  ;  but,  as  we  ascend  to  more  highly  developed 
species,  we  shall  at  once  see  how  gradually  an  approximation  is 
made  to  the  articulated  outward  skeleton,  and  jointed  limbs,  met 
with  in  the  homogangliate  forms  of  being,  until  at  last  the  zoolo¬ 
gist  remains  in  doubt  whether  the  more  elaborately  constructed 
ought  not  to  be  admitted  among  the  crustacean  families,  which 
they  most  resemble. 

(170.)  The  Adheres  percarum  ( Jig .  53)  is  one  of  those  spe¬ 
cies  most  nearly  allied  to  the  Articulata  ;  and,  the  details  of  its 
anatomy  having  been  fully  investigated  by  Nordmann,^  it  will 
serve  as  a  good  example  of  the  type  of  structure  which  prevails 
throughout  the  class. 

The  Adheres  is  found  to  infest  the  perch  (Ferca  fluvialilis), 
adhering  firmly  to  the  roof  of  the  mouth,  to  the  tongue  or  some¬ 
times  even  to  the  eyes  of  that  fish  ; 
in  which  situations  it  is  concealed  by 
a  brownish  slimy  secretion,  so  that 
its  presence  might  easily  escape  the 
notice  of  a  casual  observer. 

The  female,  which  is  represent¬ 
ed  in  the  figure,  is  about  two  lines 
in  length ;  the  male,  which  differs 
materially  from  the  other  sex  in  many 
points,  is  considerably  smaller. 

The  outer  covering  of  the  body  of 
these  little  creatures  is  at  once  seen  to 
have  assumed  a  horny  hardness  ap¬ 
proximating  the  density  of  the  cover¬ 
ings  of  the  articulated  classes,  and  in¬ 
dications  are  even  perceptible  of  a 
division  into  segments  :  the  distinct¬ 
ion,  moreover,  between  the  trunk 
(cep halo-thorax),  to  which  the  limbs 

*  Mikrographische  Beitnige  zur  Naturgeschichte  tier  wiibellosen  Thiere  ;  Berlin,  1832. 


Fig.  53. 


EPIZOA. 


131 


are  appended,  and  the  abdomen,  wherein  the  viscera  are  lodged, 
is  obvious. 

The  rude  and  imperfect  limbs  that  we  have  seen  in  the  Lerneans 
are  visibly  more  perfect  in  their  entire  construction  ;  and  in  the  fe¬ 
male  the  posterior  pair  of  these  appendages  is  converted  into  a  most 
singular  instrument  of  attachment,  by  which  it  fixes  itself  to  the 
gums  of  the  fish.  The  hinder  pair  of  extremities  alluded  to  (Jig. 

53,  b,  b)  are,  in  fact,  enormously  developed;  they  curve  forward  after 
their  origin  from  the  posterior  part  of  the  trunk,  and  are  so  much 
extended  that  they  project  considerably  beyond  the  head  of  the 
creature,  where,  becoming  considerably  attenuated,  the  two  are 
joined  together  by  a  kind  of  suture,  and  support,  upon  the  point 
where  they  are  united,  a  cup-shapecl  organ  whereby  the  creature 
fixes  itself.  This  singular  instrument,  represented  upon  an  enlarged 
scale  at  fig.  54,  1,  is  of  cartilaginous  hardness,  and  resembles  a  little 
bowl,  the  inside  of  which  is  studded  with  sharp  teeth,  and  calcu¬ 
lated  not  only  to  act  as  a  powerful  sucker,  but,  from  the  hooks 
within  its  cavity,  it  is  capable  of  taking  a  most  tenacious  hold 
upon  the  lining  membrane  of  the  mouth. 

The  other  members  (fig.  53,  o)  are  much  less  developed,  but 
are  nevertheless  so  constructed  as  to  assist  materially  in  fixing  the 
Epizoon  ;  they  are  represented  upon  a  very  enlarged  scale  in  fig. 

54,  2,  where  the  outer  pair  (a,  a)  are  seen  to  exhibit  in  the  transverse 
lines  indented  upon  their  surface  the  first  indication  of  articulated 
members  ;  and  their  extremities,  armed  with  minute  hooks,  evidently 
form  powerful  agents  for  prehension.  Internal  to  these  are  two 
other  jointed  organs,  still  more  feeble  in  their  construction,  the 
ends  of  which  ( b ,  b),  being  armed  with  three  spines,  will  assist 
in  effecting  the  same  object. 


(171.)  The 


Fig.  54. 


mouth  itself  (fig. 
54,2,  c)  is  formed 
upon  similar  prin¬ 
ciples,  the  exter¬ 
nal  orifice  being 
surrounded  with  a 
circle  of  minute 
recurved  spines 
well  calculated  to 
ensure  its  firm  ap¬ 
plication  to  the 


k  2 


132 


ETIZOA. 


surface  from  which  nourishment  is  obtained  ;  and,  within  this, 
rudimentary  jaws  furnished  with  strong  teeth  are  visible,  adapted, 
no  doubt,  to  scarify  the  part  upon  which  the  mouth  is  placed,  in 
order  to  ensure  an  adequate  supply  of  food.  In  the  male  Adheres , 
the  sucking-bowl  possessed  by  the  female  does  not  exist  ;  the  pre¬ 
hensile  organs  being  merely  four  stout  articulated  extremities, 
armed  at  the  end  with  strong  prehensile  hooks. 

As  we  might  suppose,  from  the  nature  of  the  food  upon  which 
this  creature  lives,  the  alimentary  system  is  extremely  simple.  The 
oesophagus,  the  course  of  which  is  represented  by  dotted  lines  in  the 
last  figure,  terminates  in  a  straight  digestive  canal  (aj  which  passes 
through  the  centre  of  the  abdomen,  but  no  separation  between  sto¬ 
mach  and  intestine  is  visible  :  the  entire  tube,  from  the  transverse 
constrictions  visible  upon  its  surface,  has  a  sacculated  appearance, 
and  is  perceptibly  dilated  towards  the  centre  of  the  abdominal 
cavity  ;  after  which  it  again  diminishes  in  size  as  it  approaches  the 
anal  orifice  (5),  situated  at  the  posterior  extremity  of  the  body. 

Near  the  termination  of  its 
course,  the  alimentary  canal 
passes  through  a  loop  formed 
by  transverse  bands  (??,  ??),  and, 
moreover,  seems  to  be  retained 
in  its  position  by  radiating  fibres 
apparently  of  a  ligamentous  cha¬ 
racter,  but  which  has  been  de¬ 
scribed  as  representing  a  biliary 
apparatus. 

.)  The  muscular  system 
of  this  animal  is  far  more  perfect 
in  its  arrangement  than  in  the 
preceding  classes,  and  the  deli¬ 
cate  fasciculi  which  move  the 
rudimentary  limbs  are  visible 
through  the  transparent  integument  (Jig.  54).  In  the  abdomen, 
the  muscles  form  longitudinal  and  transverse  bands,  which  intersect 
each  other  at  right  angles  (Jig.  55,  d)  ;  an  arrangement  not  very 
different  from  what  we  have  already  seen  in  the  rotiferous  ani¬ 
malcules. 

(178.)  The  nervous  system  appears  to  consist  principally  of  two 
long  filaments  (Jig.  55,  c),  which  run  beneath  the  alimentary  ca¬ 
nal  :  but  it  is  extremely  probable  that  these  communicate  with  some 


EPIZOA. 


133 


minute  ganglia  in  the  neighbourhood  of  the  head  ;  at  least,  the 
perfect  structure  of  the  oral  apparatus,  and  the  developement 
of  the  limbs,  would  seem  to  indicate  such  a  type  of  structure. 

(174.)  The  generative  organs  in  the  female  Adheres  consist  of 
two  parts ;  the  ovaria,  wherein  the  eggs  are  formed,  contained  in 
the  abdominal  cavity  {Jig.  53,  d,  d),  and  of  two  external  append¬ 
ages,  or  egg-sacs  (Jig.  53 which  are  attached  to  the  pos¬ 
terior  extremity  of  the  body  for  the  purpose  of  containing  the 
eggs  until  their  complete  developement  is  accomplished ;  this  ar¬ 
rangement  we  shall  again  have  an  opportunity  of  examining  in 
the  entomostracous  crustaceans. 

The  internal  ovaria  (Jig.  55,  /*),  when  distended  with  ova, 
occupy  a  great  part  of  the  cavity  of  the  abdomen,  and  present  a 
racemose  appearance  ;  but  when  empty,  as  represented  upon  the 
opposite  side  of  the  same  figure  (e),  each  is  found  to  be  a  simple 
blind  canal,  with  sacculated  walls,  opening  externally  by  an  ori¬ 
fice  (g,  g ),  through  which  the  ova  are  expelled  into  the  egg-sacs, 
where  their  developement  is  completed. 

(175.)  It  would  seem  that,  even  when  the  eggs  are  hatched,  the 
excluded  young  are  far  from  having  attained  their  perfect  or  adult 
form  ;  but  undergo,  at  least,  two  preparatory  changes  or  metamor¬ 
phoses,  during  which  they  become  possessed  of  external  organs 
so  totally  different  from  those  they  were  furnished  with  on  leaving 
the  egg,  that  it  would  be  difficult  to  imagine  them  to  be  merely 
different  states  of  existence  through  which  the  same  animal  passes. 

On  first  quitting  the  egg,  the  young  Adheres  is  in  fact  by  no 
means  adapted  to  the  parasitical  life  to  which  it  is  subsequently 
destined  ;  possessing  no  organs  of  prehension  like  those  of  the  adult, 
but  merely  two  pairs  of  swimming-feet,  each  armed  with  a  brush  of 
minute  hairs,  and  calculated  to  propel  it  through  the  water.  Be¬ 
fore,  however,  the  first  change  is  effected,  another  set  of  feet  may 
be  perceived  through  the  transparent  external  covering,  encased 
as  it  were  in  the  first ;  when  these  are  completely  formed,  the 
original  skin  falls  off,  displaying,  in  addition  to  two  new  pairs 
of  swimming-feet,  three  pairs  adapted  to  prehension ;  and  it  is 
only  when  the  second  set  of  feet  is  thrown  off  in  a  similar  manner 
that  the  animal  assumes  its  perfect  or  mature  form. 

(176.)  The  affinities  between  the  more  highly  organized  Epizoa 
and  the  Crustacea  are  evidently  very  strong;  yet,  independently 
of  the  different  character  of  the  nervous  svstem,  there  is  another 
important  distinction  between  them,  derived  from  their  compara- 


134 


EPIZOA. 


tive  anatomy.  In  the  Crustacea,  the  organs  of  circulation  and 
respiration  are  well  developed  and  easily  recognisable  ;  but,  in  the 
class  we  are  now  considering,  no  parts  adapted  to  either  of  those 
functions  have  hitherto  been  satisfactorily  discovered  :  neverthe¬ 
less,  that  the  Epizoa  form  a  gradual  transition  from  the  humbler 
creatures  we  have  hitherto  examined  to  the  great  division  of  ar¬ 
ticulated  animals,  must  be  obvious  to  the  most  superficial  observer. 

(177.)  In  Lamproglena  pulchella  we  have  a  still  more  decided 
approximation  to  the  crustacean  type  of  structure,  and  the  rudimen¬ 
tary  feet  arranged  in  symmetrical  pairs  are  as  numerous  as  the 
segments  of  the  body.  The  limbs,  however,  are  as  yet  only 
adapted  to  secure  a  firm  hold  upon  the  structures  to  which  this 
parasite  attaches  itself,  namely,  the  gills  of  the  chub  ( Cyprinus 
Jeses ),  in  which  situation  it  is  most  usually  found.  The  two  an¬ 
terior  pairs  (Jig-  56,  Z>,  c)  are  far  more  large-  Fig.  56. 

ly  developed  than  those  which  are  placed 
upon  the  posterior  parts  of  the  animal,  and 
are  apparently  strengthened  by  a  cruciform 
cartilaginous  frame-work  seen  through  the 
transparent  integument.  The  first  pair  of 
these  holding  feet  consists  of  two  robust 
and  powerful  hooks,  terminated  by  simple 
horny  points  ;  whilst  the  second,  which  are 
likewise  unciform,  terminate  in  trifid  prongs, 
and  are  evidently  equally  adapted  to  pre¬ 
hension.  The  four  pairs  of  members  which 
succeed  to  these  are  mere  rudiments,  and 
can  be  of  little  service  as  organs  of  attach¬ 
ment  ;  but,  to  make  up  for  their  imperfec¬ 
tion,  we  find  at  the  posterior  extremity  of 
the  body,  between  the  orifices  of  the  ovaria 
(g),  a  pair  of  cartilaginous  suckers  well  cal¬ 
culated  to  fix  this  part  of  the  animal. 

The  muscular  system  is  readily  seen 
through  the  transparent  skin  :  four  longitudinal  bands  are  visible 
(d),  running  from  one  end  to  the  other,  and,  besides  these,  broad 
transverse  fasciculi  are  discernible  in  the  fifth  and  sixth  segments  of 
the  body ;  from  the  nature  of  the  feet,  however,  and  general  struc¬ 
ture  of  the  creature,  we  must  imagine  the  existence  of  muscles 
provided  for  the  movements  of  each  articulated  member,  although, 
from  their  extreme  minuteness,  they  escape  detection. 


ECHINODERMATA. 


135 


The  opening  of  the  mouth  is  placed  in  the  centre  of  the  space 
bounded  by  the  four  anterior  prehensile  hooks  ;  and  the  alimen¬ 
tary  canal  is  a  simple  tube  passing  straight  through  the  body  to 
the  tail,  where  the  anal  orifice  is  distinguishable.  The  walls  of 
the  intestine  have  a  reticulated  appearance,  being  covered  with  a 
kind  of  glandular  net-work,  which  probably  constitutes  a  biliary 
apparatus. 

(178.)  In  a  creature  thus  highly  organized  we  may  well  expect  to 
find  senses  of  proportionate  perfection,  and  in  Lamproglena  their 
existence  is  no  longer  doubtful.  The  eyes  are  distinctly  apparent, 
of  a  reddish  colour ;  but  as  yet,  as  in  the  lowest  crustaceans, 
united  into  one  mass.  The  antennse  likewise,  which  may  be  re¬ 
garded  as  special  instruments  of  touch,  are  well  developed ;  and, 
both  in  number  and  position,  resemble  those  which  characterise 
the  crustacean  orders,  to  which  we  are  thus  conducted  by  almost 
imperceptible  gradations. 

The  reproductive  organs  are  entirely  similar  to  those  of  Adheres 
already  described.  Those  of  the  female,  represented  in  the  figure, 
consist  of  sacciform  ovaria,  in  which  the  ova  are  secreted :  and 
from  these,  when  mature,  the  eggs  are  expelled  through  two  simple 
triangular  orifices  situated  on  each  side  of  the  anus. 


CHAPTER  XL 
Echinodermata.*  (Cuv.) 

(179.)  The  last  class  of  beings  belonging  to  the  Nematoneurose 
division  of  the  animal  world  seems,  upon  a  partial  survey,  to  be  com¬ 
pletely  insulated,  and  distinct  from  all  other  forms  of  living  crea¬ 
tures  ;  so  peculiar  is  the  external  appearance,  and  even  the  internal 
organization  of  the  families  which  compose  it.  The  casual  observer 
who  should,  for  the  first  time,  examine  a  star-fish  or  a  sea-urchin, 
two  of  the  most  familiar  examples  of  the  Echinodermata 
met  with  upon  our  own  shores,  would  indeed  find  it  a  difficult 
task  to  associate  them  with  any  other  class,  or  to  imagine  the  affi¬ 
nities  whereby  they  are  related,  either  to  the  simpler  animals  we  have 
already  described,  or  to  more  perfect  forms  of  existence  hereafter  to 
be  mentioned :  they  would  seem  to  stand  alone  in  the  creation, 

*  ”E %Dios,  a  hedgehog  ;  the  skin. 


136 


ECHINODERMATA. 


without  appearing  to  form  any  portion  of  that  series  of  develope- 
ment  which  we  have  hitherto  been  able  to  trace. 

But  this  apparent  want  of  conformity  to  the  general  laws  of 
developement  vanishes  on  more  attentive  examination ;  so  that  we 
may  not  only  trace  the  steps  by  which  every  family  of  this  exten¬ 
sive  class  merges  insensibly  into  another,  but  perceive  that,  at  the 
two  opposite  points  of  the  circle,  the  Echinodermata  are  inti¬ 
mately  in  relation  with  the  Polyps  on  one  hand,  while  on  the 
other  they  as  obviously  approximate  the  annulose  animals,  to  which 
the  most  perfectly  organized  amongst  them  bear  a  striking  resem¬ 
blance. 

It  would  be  impossible  within  our  present  limits  to  do  more 
than  lay  before  the  reader  the  most  important  types  of  structure 
which  the  Echinodermata  exhibit  ;  it  must,  nevertheless,  be  under¬ 
stood  that  innumerable  intermediate  families  connect  the  different 
genera  ;  so  that,  however  dissimilar  the  examples  we  have  selected 
for  the  purpose  of  exhibiting  their  general  habits  and  economy 
may  appear,  the  gradation  which  leads  from  one  to  another  is 
easily  traced. 

(180.)  Crinoidce. — We  have  already  found  that  many  tribes  of 
polyps  secrete  calcareous  matter  in  large  quantities,  so  as  to  con¬ 
struct  the  solid  skeletons  or  polyparies,  which  generally  seem  to 
be  placed  external  to  their  soft  and  irritable  bodies,  but  occasion¬ 
ally,  as  in  Pennatula ,  within  the  living  substance.  Let  us  for  a 
moment  suppose  a  polyp  supported  upon  a  prolonged  stem,  and 
that,  instead  of  depositing  the  earthy  particles  externally,  they 
should  be  lodged  in  the  substance  of  the  polyp  itself,  so  as  to  fill 
the  pedicle,  the  body,  the  tentacula  around  the  mouth  and  all  the 
appendages  belonging  to  the  animal  with  solid  pieces,  of  definite 
form  ;  such  pieces  being  connected  together  by  the  soft  parts,  and 
surrounded  on  all  sides  with  irritable  matter,  would  thus  form  a 
complete  internal  skeleton,  giving  strength  and  support  to  the 
entire  animal,  and  at  the  same  time  allowing  flexure  in  every  di¬ 
rection.  A  polyp  so  constituted  would  obviously,  when  dried, 
present  an  appearance  similar  to  what  is  depicted  in  the  annexed 
engraving  ( Jig .  57),  representing  an  Encrinoid  Echinoderm  in 
its  perfect  condition.  That  animals  thus  allied  to  polyps  in 
their  outward  form  have  in  former  times  existed  in  great  num¬ 
bers  upon  the  surface  of  our  planet  is  abundantly  testified  bv  the 
immense  quantities  of  their  remains  which  are  met  with  in  various 
calcareous  strata,  but  their  occurrence  in  a  living  state  is  at 


ECIIINOUEIIMATA. 


137 


Fig.  57. 

present  extremely  rare :  one 
minute  species  only  lias  been 
detected  in  our  own  seas  ;* 
while  specimens  of  larger 
growth,  such  as  that  repre¬ 
sented  in  the  engraving,  deriv¬ 
ed  from  tropical  climates,  are 
so  seldom  met  with,  that  it  is 
fortunate  that  one  or  two  ex¬ 
amples  have  been  found  —  to 
reveal  to  us  the  real  structure 
of  a  race  of  animals  once  so 
common,  but  now  almost  com¬ 
pletely  extinct.  The  body  of 
the  Encrinus  (Jig-  57,  a)  (or 
pelvis,  as  the  central  portion 
of  the  animal  is  termed  by 
geological  writers,)  is  com¬ 
posed  of  numerous  calcareous 
plates,  varying  in  shape  and 
arrangement,  so  as  to  become 
important  guides  to  the  identification  of  fossil  species  ;  from  this 
central  part  arise  the  large  rays  (b,  5),  each  furnished  with  a  double 
rowT  of  articulated  appendages,  which,  as  well  as  the  arms,  are,  no 
doubt,  instruments  for  seizing  prey  and  conveying  it  to  the 
mouth,  situated  in  the  centre  of  the  body  near  the  point  a. 
This  part  of  the  animal,  when  found  in  a  fossil  state,  from  its  re¬ 
semblance  to  a  flower,  has  received  the  common  name  of  a  “  lily- 
stone.1’ 

The  body  above  described,  with  the  rays  proceeding  from  it,  is 
supported  upon  a  long  pedicle  (e),  composed  of  numerous  pieces  ; 
and,  upon  the  sides  of  the  stem,  similarly  constructed  filamentary 
branches  are  fixed  (d,  d)  at  equal  intervals.  The  skeleton  of  an  En- 
crinite  consists,  therefore,  of  thousands  of  regularly  shaped  masses 
of  calcareous  earth  kept  together  by  the  living  and  irritable  flesh 
in  which  they  are  imbedded,  and  it  is  to  the  contractions  of  this 
living  investment  that  the  movements  of  the  animal  are  due  ;  but 
after  the  death  of  the  creature,  and  the  consequent  destruction  of 
its  soft  parts,  the  pieces  of  the  earthy  frame-work  become  sepa¬ 
rated  and  fall  asunder,  forming  the  fossil  remains  called  “  TrochiJ 

*  Thompson  (J.  W.),  Memoir  concerning  the  Pentacrinus  Europaeus ;  Cork,  1827,  4to. 


138 


ECH  INODE  It  MATA. 


and  known  in  tlie  northern  districts  of  our  own  island,  where  they 
are  very  abundant,  as  44  St.  Cuthberf  s  beads 

Of  the  internal  structure  of  the  Encrinites  nothing  is  satisfac¬ 
torily  known.  That 
they  possessed  a  dis¬ 
tinct  mouth  and  anal 
aperture  is  evident, 
from  the  structure  of 
the  plates  of  the  body ; 
but  this  is  the  extent 
of  our  information 
concerning-  them.* 

(181.)  Asteridce. — 

In  order  to  convert  an 
Encrinus  into  an  ani¬ 
mal  capable  oflocomo- 
tion,  and  able  to  crawl 
about  at  the  bottom 
of  the  sea,  little  fur¬ 
ther  would  be  requi¬ 
site  than  to  separate 
the  body  and  arms  from  the  fixed  pedicle  upon  which  they  are  sup¬ 
ported,  and  we  should  have  an  animal  resembling  in  every  particular 
the  star-fishes.  The  Comalula ,  for  example,  {Jig.  58,)  one  of  the 
lowest  of  the  asteroid  Echinodermata,  might  be  looked  upon  as  an 
animal  thus  detached.  The  central  part,  or  body,  which  contains 
the  viscera,  is  made  up  of  numerous  calcareous  pieces,  having  in 
its  centre  a  stelliform  mouth,  and  near  this  is  a  tubular  orifice  which 
might  be  regarded  as  an  anus.  Around  the  margin  of  the  central 
disc  arise  five  stunted  arms  which  immediately  divide  into  a  variable 
number  of  long  radiating  branches,  composed,  like  those  of  the  En¬ 
crinus,  of  innumerable  articulated  earthy  masses  enveloped  in  a  liv¬ 
ing  and  irritable  integument.  We  find,  moreover,  issuing  from 
the  sides  of  every  one  of  the  prolonged  rays,  a  double  row  of  se¬ 
condary  filaments,  each  containing  an  internal  jointed  skeleton,  and 
capable  of  independent  motion.  The  complicated  arms  of  the  Co- 
matula ,  therefore,  are  not,  like  those  of  a  polyp,  merely  adapted 
to  seize  prey  ;  but,  from  their  superior  firmness,  may  be  used  as 
so  many  legs,  enabling  the  animal  to  travel  from  place  to  place. 

*  For  a  detailed  account  of  the  fossil  Encrinites,  the  reader  is  referred  to  “  A  Natural 
History  of  the  Crinoidea,  or  lily-shaped  animals,  by  J.S.  Miller  ;  4to.  Bristol,  1821. 


ECH I  NODERM  AT  A. 


130 


Setting  out  from  this  point  to  trace  the  gradual  developement  of 
organization  in  the  Echinodermata,  we  shall  observe  a  progressive 
concentration  of  their  entire  structure.  The  central  part,  or  vis¬ 
ceral  cavity,  so  small  in  the  Comatula  when  compared  to  the 
complicated  rays  derived  from  it,  enlarges  in  its  proportional  di¬ 
mensions  as  the  viscera  contained  within  it  become  more  perfect 
in  their  structure  ;  whilst,  on  the  other  hand,  the  radiating  or  po¬ 
lyp  form,  so  visible  in  Encrinus  and  Comatula,  becomes  obliterated 
by  degrees,  until,  at  length,  almost  all  vestiges  of  it  are  lost,  or  but 
obscurely  recognisable. 

In  the  Gorgonocephalus  (Jig.  59),  the  proportionate  size  of  the 
rays  when  compared  with  that  of  the  central  disc  still  preponde¬ 
rates  very  considerably,  although  even  here  some  concentration  is 
manifest.  The  secondary  articulated  filaments  appended  to  the 
rays  of  Comatula  are 
no  longer  recognis¬ 
able,  their  place  be¬ 
ing  supplied  by  the 
continual  division 
and  subdivision  of 
the  rays  themselves ; 
the  same  end,  how¬ 
ever,  is  obtained  in 
both  cases,  for  the 
numerous  jointed 
and  flexible  rays 
of  Gorgonocephalus 
still  form  so  many 
legs,  enabling  the 
creature  to  drao-  it- 

O 

self  along  the  bottom  of  the  sea,  or  to  entwine  itself  among  the 
submarine  plants,  as  well  as  supplying  the  office  of  tentacula  in 
securing  food. 

Continuing  our  progress  towards  more  perfect  forms  of  these 
remarkable  animals,  we  at  length  arrive  at  genera  in  which  the 
rays  become  divested  of  all  elongated  appendages,  either  in  the  shape 
of  articulated  lateral  filaments  or  dichotomous  ramifications.  In 
Oph  iurus ,  for  instance  (Jig.  60),  the  rays  are  long  and  simple,  re¬ 
sembling  the  tails  of  so  many  serpents — a  circumstance  from  whence 
the  name  of  the  family  is  derived  ;  nevertheless,  on  each  side  of 
every  ray  we  still  trace  moveable  lateral  spines,  which,  although 


Fig.  59. 


140 


ECHINODEKMATA. 


but  mere  rudiments  of  what  we  have  seen  in  Comatula ,  may  still 
assist  in  locomotion,  or  perhaps  may  contribute  to  retain  the  prey 
more  firmly  when  seized  by  the  arms.  The  rays  themselves  are 
composed  of  many  pieces  curiously  imbricated  and  joined  together 
by  ligaments,  so  that  they  are,  from  their  length  and  tenuity,  ex¬ 
tremely  flexible  in  all  directions,  and  serve  not  only  for  legs  adapt¬ 
ed  to  crawl  upon  the  ground,  but  are  occasionally  serviceable  as 
fins,  able  to  support  the  animal  in  the  water  for  a  short  distance 
by  a  kind  of  undulatory  movement.  The  body,  or  central  disc, 
is  beautifully  constructed,  being  made  up  of  innumerable  pieces  ac¬ 
curately  fitted  together.  The  mouth  occupies  the  centre  of  the 
ventral  surface,  and  is  surrounded  by  radiating  furrows  in  which 
are  seen  minute  apertures  that  give  passage  to  a  set  of  remark¬ 
able  prehensile  organs,  to  be  described  hereafter  :  these  are  calcu¬ 
lated  to  act  as  suckers,  and  so  disposed  as  either  to  fix  the  body  of 
the  animal,  or  to  retain  food  during  the  process  of  deglutition. 


Fig.  60. 


Leaving  the  Ophiuri ,  we  are  led  through  a  long  series  of  almost 
imperceptible  gradations  to  animals  apparently  of  most  dissimilar 
structure.  The  star-fishes  ( Asterias )  {Jig.  65)  form  the  next  step  : 


ECIIINODERMATA. 


141 


in  these,  from  the  increased  size  of  the  body,  the  rays  are  united  at 
their  origin,  and  become  so  much  dilated  as  to  contain  prolongations 
of  the  viscera  lodged  in  their  interior  ;  an  arrangement  not  met  with 
in  Ophiuri  and  other  slender-rayed  Asteridse.  The  dilatation  of 
the  central  part  proceeds,  and  in  the  same  proportion  the  rays  be¬ 
come  obliterated  ;  so  that  at  length,  the  asteroid  shape  becoming 
totally  lost  by  the  progressive  filling  up  of  the  interspaces  between 
the  rays,  we  arrive  ultimately  at  completely  pentagonal  forms,  the 
sides  of  the  pentagon  being  perfectly  straight  lines. 

(182.)  It  is  extremely  interesting  to  remark  the  changes  which 
occur  in  the  nature  of  the  locomotive  organs  during  these  diversi- 
fications  of  external  figure.  We  have  seen  that,  in  the  lower 
Echinodermata  possessing  long  and  flexible  rays,  such  organs  were 
fully  adequate  to  perform  all  movements  needful  for  progression  ; 
but  as  the  mobility  of  these  parts  is  diminished  by  their  gradual 
curtailment,  and  the  filling  up  of  the  spaces  between  them,  some 
compensating  contrivance  becomes  indispensably  necessary,  and 
accordingly  we  find  an  apparatus  gradually  developed,  well  cal¬ 
culated  to  meet  the  exigencies  of  the  case.  In  Ophiurus 
we  have  already  mentioned  the  existence  of  protrusible  suckers 
around  the  opening  of  the  mouth,  well  adapted,  from  their  posi¬ 
tion,  to  take  firm  hold  of  food  seized  by  the  animal ;  and  it  is  by 
increasing  the  number  of  such  organs  that  ample  compensation 
is  made  for  the  loss  of  motion  in  the  rays  themselves.  On  ex¬ 
amining  the  lower  surface  of  an  Asterias ,  even  in  those  forms 
which  most  approximate  a  right-lined  pentagon  in  their  marginal 
contour,  the  number  of  rays  will  still  be  found  to  be  distinctly  in¬ 
dicated  by  as  many  furrows  radiating  from  the  mouth,  and  indicat¬ 
ing  the  centre  of  each  division  of  the  body.  These  ambulacral 
furrows,  as  they  are  termed,  exhibit,  when  examined  in  a  dried 
specimen,  innumerable  orifices  arranged  in  parallel  rows,  through 
each  of  which,  when  alive,  the  animal  could  protrude  a  prehensile 
sucker,  capable  of  being  securely  attached  to  any  smooth  surface. 

No  verbal  description  can  at  all  do  justice  to  this  wonderful 
mechanism,  even  leaving  out  of  the  question  the  means  by  which 
each  individual  sucker  is  wielded,  for  of  this  we  shall  speak  here¬ 
after  ;  but  let  any  of  our  readers,  when  opportunity  offers,  pick 
up  from  the  beach  one  of  these  animals,  the  common  star-fish  of 
our  coast,  which,  as  it  lies  upon  the  sand  left  by  the  retiring 
waves,  appears  so  incapable  of  movement,  so  utterly  helpless  and 
inanimate  ;  let  him  place  it  in  a  large  glass  jar  filled  with  its 


112 


ECHINODEllMATA. 


native  element,  and  watch  the  admirable  spectacle  which  it  then 
presents  : — slowly  he  perceives  its  rays  expand  to  their  full  stretch, 
hundreds  of  feet  are  gradually  protruded  through  the  ambulacral 
apertures,  and  each,  apparently  possessed  of  independent  action, 
fixes  itself  to  the  sides  of  the  vessel  as  the  animal  begins  its  march. 
The  numerous  suckers  are  soon  all  employed,  fixing  and  detaching 
themselves  alternately,  some  remaining  firmly  adherent  while  others 
change  their  position  ;  and  thus,  by  an  equable  gliding  movement, 
the  star-fish  climbs  the  sides  of  the  glass  in  which  it  is  confined, 
or  the  perpendicular  surface  of  the  submarine  rock. 

But  it  is  not  only  as  agents  in  locomotion  that  the  ambulacral 
suckers  are  used  ;  helpless  as  these  creatures  appear  to  be,  they 
are  among  the  most  formidable  tyrants  of  the  deep,  as  will  be 
readily  admitted  by  any  one  who  watches  them  in  the  act  of  de¬ 
vouring  prey.  When  seizing  its  food,  the  rays  of  the  Asterias 
are  bent  towards  the  ventral  aspect  so  as  to  form  a  kind  of  cup, 
in  the  centre  of  which  is  the  opening  of  the  mouth  ;  the  cup  thus 
formed  will,  to  a  certain  extent,  lay  hold  of  a  passing  victim,  but, 
without  other  means  of  securing  it,  the  grasp  would  scarcely  be 
very  formidable  to  animals  possessed  of  any  strength  ;  armed,  how¬ 
ever,  as  the  rays  have  been  found  to  be,  with  hundreds  of  tena¬ 
cious  suckers,  escape  is  almost  impossible,  for  prey  once  seized 
is  secured  by  every  part  of  its  surface,  and,  in  spite  of  its  utmost 
efforts,  is  speedily  dragged  into  the  mouth  and  engulphed  in  the 
capacious  stomach,  where  its  soft  parts  are  soon  dissolved. 

But  to  continue  our  survey  of  the  class  before  us.  Having  ar¬ 
rived  at  the  point  at  which,  by  the  diminution  of  the  rays  and 
consequent  extension  of  the  central  part,  the  body  has  assumed 
a  pentagonal  outline,  we  may  now  advance  in  an  equally  gradual 
manner  to  those  globular  species,  of  which  the  Echinus ,  or  sea- 
urchin ,  is  the  type  or  most  perfect  example. 

(183.)  Echinidce. — In  the  Scutellcc  (Jig.  61),  we  have  a  flat  and 
shield-like  body,  in  which  even  the  angles  of  the  margin  are  lost, 
and  the  whole  circumference  acquires  a  circular  form  ;  but  still  the 
five  radiating  ambulacra  are  visible  upon  the  centre  of  the  disc,  al¬ 
though  evidently  imperfectly  developed  when  compared  with  those 
of  the  Asteridae  above-mentioned.  The  nature  of  the  integument 
has,  in  fact,  become  so  changed  in  its  texture,  that  another  modi¬ 
fication  of  the  locomotive  organs  is  here  imperatively  called  for, 
and  the  means  of  progression  are  therefore  proportionately  altered. 
In  the  Asteridm,  the  integuments,  especially  upon  the  dorsal  as- 


ECHINODERMATA. 
Fi«-.  61. 


143 


pect,  are  always  more  or  less  composed  of  a  coriaceous  material,  or, 
at  least,  of  solid  pieces  so  articulated  together  as  to  permit  of  con¬ 
siderable  flexibility  ;  but  in  the  Echinidse  tlie  nature  of  the  external 
covering  is  very  different,  for  these  creatures  are  completely  en¬ 
cased  in  a  dense  calcareous  shell,  composed  of  numerous  angular 
pieces  accurately  fitted  together  and  incapable  of  movement.  The 
Scutella ,  moreover,  bury  themselves  beneath  the  surface  of  the 
sand,  a  situation  in  which  suckers  would  be  of  little  use,  but  for 
which  these  animals  are  admirably  adapted  by  a  contrivance  not  less 
calculated  to  excite  the  admiration  of  the  observer.  The  exterior 
of  the  shell  is  entirely  covered  with  minute  appendages,  resembling, 
when  seen  with  the  naked  eye,  delicate  hairs,  but  which,  when  ex¬ 
amined  under  a  microscope,  are  found  to  be  spines  of  most  elaborate 
structure,  as  may  be  seen  from  the  magnified  view  of  one  represent¬ 
ed  in  the  annexed  figure  {Jig-  61).  Innumerable  as  these  spines 
are,  every  one  of  them  is  articulated  to  the  shell  by  a  kind  of  ball- 
and-socket  joint,  and  susceptible  of  being  moved  in  all  directions, 
so  that  by  their  combined  efforts  the  Scutella  can  speedily  bury  itself, 
either  for  the  purpose  of  procuring  food,  or  of  eluding  observation. 

(184.)  From  the  flat  Scutellcc ,  the  passage  to  the  globose  Echi- 
nida  is  most  gradual ;  and  a  beautiful  series  of  connecting  forms, 
many  still  existing  as  living  species,  but  a  still  greater  number  found 
only  in  a  fossil  state,  demonstrate  the  gradual  expansion  of  the 
shell,  and  its  conversion  into  the  spherical  figure  seen  in  the  Echinus 
esculentus  (Jig.  62).  The  Echinus  in  shape  resembles  an  orange, 


144 


ECHINODERMATA. 


its  dense  calcareous  crust  enclosing  the  viscera  within  its  cavity, 
while  the  locomotive  apparatus  is  placed  upon  the  external  surface. 
The  mouth  is  a  simple  orifice  in  the  shell  placed  at  one  extremity 
of  its  axis,  and  through  it,  as  represented  in  the  figure,  the  points 
of  five  singular  teeth  project  externally  ;  while  the  anal  aperture 
occupies  the  opposite  pole  of  the  sphere.  The  instruments  of 
locomotion  occupy  the  entire  superficies  of  the  shell,  and  consist 
of  two  distinct  sets  of  organs  adapted  to  different  uses.  The  first 
consists  of  a  multitude  of  sharp  purple  spines,  every  one  of  which 
is  articulated  to  a  distinct  and  prominent  tubercle  whereon  it 
moves.  These  numerous  spines,  therefore,  which  are  essentially 
similar  in  their  office  to  those  we  have  already  described  in  Scutella , 
differing  only  in  proportionate  size,  are  so  many  inflexible  legs 
upon  which  the  Echinus  rolls  itself  from  place  to  place,  or  by  their 
assistance  it  can  bury  itself  in  the  sand  with  the  greatest  facility. 
But  these  wonderfully  constructed  animals  are  by  no  means  con¬ 
fined  to  this  mode  of  progression  ;  for,  impossible  as  it  might 
appear  from  their  outward  appearance,  they  are  able  to  climb 
rocks  in  search  of  food,  and  thus  destroy  the  corallines  and 
shell-fish  upon  which  they  principally  feed.  In  order  to  effect  this, 
we  find  the  shell  perforated  with  ten  rows  of  small  orifices  so 
disposed  as  to  form  five  pairs  of  ambulacra  extending  from  one 
pole  to  the  other  :  through  these  apertures  a  system  of  long 
suckers  is  made  to  pfe.  62 

issue,  which  protrud¬ 
ing,  as  represented 
in  the  figure  (Jig- 
,  beyond  the 
points  of  the  spines, 
can  be  firmly  fixed 
to  any  smooth  sur¬ 
face,  and,  like  the 
suckers  of  Asterias , 
become  locomotive 
agents. 

(185.)  Holothu- 
ruloe. — Having  trac¬ 
ed  the  developement 
of  the  Echinodermata  from  the  polypiform  Encrinite  to  the  globu¬ 
lar  Echinus ,  we  now  shall  find  them  perceptibly  approximate  an 
annulose  or  worm-like  form.  In  the  Holothuria  (Jig- 'IQ),  the 


E  C  H I N  0  D  E  Ii  M  A  T  A 


145 


commencement  of  this  change  is  perceptible  :  instead  of  being  com¬ 
posed  of  hard,  calcareous  pieces,  the  integuments  of  the  body  now 
become  soft  and  irritable,  a  few  thin  laminae  of  earthy  matter 
around  the  mouth  being  the  only  vestiges  of  the  shell  and  the 
spines,  of  course,  are  no  longer  met  with  ;  the  suckers,  however, 
remain,  and,  when  protruded  through  innumerable  apertures  dis¬ 
tributed  over  the  surface  of  the  body,  Fig.  63. 

they  still  form  the  principal  instruments 
of  progression. 

(186.)  Fistularidce . — At  length,  in 
the  last  division  of  the  class,  even  the  loco¬ 
motive  suckers  are  lost,  and  the  only  ex¬ 
ternal  resemblance  left  between  the  now 
worm-like  body  and  the  forms  above 
enumerated  is  met  with  in  the  radiating 
tentacula  which  surround  the  mouth. 

The  apodous  Echinodermata,  “Ecliino- 
dermes  sans  pieds,”  of  Cuvier  have 
indeed  been  expunged  from  the  list 
of  radiated  animals  by  some  modern 
writers,  but  in  every  point  of  their  in¬ 
ternal  structure  we  shall  find  them 
offer  too  many  points  of  similarity  to 
permit  of  their  expulsion  from  the  class 
under  consideration,  although  they  evi¬ 
dently  form  the  connecting  link  between 
the  Radiata  and  the  lowest  families  of 
the  articulated  division  of  the  animal 
kingdom.  The  genus  Fistulciria  (Jig. 

63)  strikingly  exhibits  approximation  to 
the  outward  form  of  the  Annelida  ; 
and  the  anatomy  of  these  creatures, 
which  we  shall  afterwards  consider, 
equally  indicates  the  affinities  which 
unite  them. 

(187.)  We  have  already,  when  speak¬ 
ing  of  the  general  division  of  the  Echino¬ 
dermata,  put  the  reader  in  possession  of 
all  that  is  satisfactorily  known  concern¬ 
ing  the  structure  of  the  Orinoid*  ge- 


*  KolvoV)  a  lily  ;  u^o;,  like. 


146 


ECIIINODERMAT  A. 


nera  ;  our  knowledge  of  those  singular  animals  being  entirely  derived 
from  the  exterior  conformation  of  two  recent  species,  and  from  the 
mutilated  skeletons  of  fossil  Encrinites,  which  exist  in  such  abun¬ 
dance  in  the  limestone  strata  of  our  own  country. 

Commencing,  therefore,  with  the  A st eridee,*  we  shall  now  enter  at 
once  upon  the  consideration  of  the  anatomy  of  such  species  as  have 
been  most  carefully  examined,  and  merely  notice  incidentally  the 
modifications  which  occur  in  the  disposition  of  various  organs  in 
kindred  genera. 

(188.)  On  examining  a  living  Asterias ,  the  outer  covering  of  its 
body  is  found  to  be  composed  of  a  dense  coriaceous  substance,  in  which 
numerous  calcareous  pieces  are  apparently  imbedded.  The  cori¬ 
aceous  integument  is  generally  coloured  externally  with  lively  tints, 
and  is  evidently  possessed  of  considerable  irritability,  as  it  readily 
shrinks  under  the  knife,  or  upon  the  application  of  various  stimuli. 
When  cut  into,  it  has  a  semicartilaginous  hardness,  and  fibrous 
bands,  almost  resembling  tendon  in  their  aspect,  may  be  seen  to 
radiate  from  the  centre  of  the  body  towards  the  extremities  of  the 
rays.  There  is  no  doubt  that  the  movements  of  the  rays  are 
effected  by  the  contractions  of  this  fibrous  membrane  ;  and  that, 
especially  in  the  most  polyp-like  forms,  as  in  Comatula  and  Gor- 
gonocephalus ,  the  irritable  skin  is  the  principal  agent  in  effecting 
locomotion. 

Besides  the  calcareous  matter  deposited  in  its  interior,  this  outer 
covering  of  the  star- fish  appears  to  furnish  several  secretions  of 
different  descriptions.  The  colouring  matter  upon  its  surface  is  no 
doubt  one  of  these ;  as  is  a  reddish  fluid  which  exudes  from  the  in¬ 
tegument  of  A.  rubens,  and  is  of  so  caustic  a  quality  as  occasion¬ 
ally  to  produce  great  irritation  of  the  skin  in  persons  by  whom 
individuals  of  this  species  are  incautiously  handled :  moreover,  in 
A.  aranciaca ,  the  whole  animal  is  coated  with  a  thick  mucus,  so 
dense  and  filamentous  that  it  may  be  raised  in  thin  films  resembling 
a  cobweb,  and  might  easily  be  taken  for  a  cuticular  covering. 

The  exterior  of  the  body  is  generally  rendered  rough  and  un¬ 
even  by  various  structures,  either  imbedded  in  the  substance  of 
the  coriaceous  skin  or  projecting  from  its  external  surface.  We 
have  already  described  the  articulated  pieces  attached  to  the  rays  of 
Comatula  and  others,  which  seem  to  be  the  most  perfectly  de¬ 
veloped  forms  of  these  cutaneous  appendages.  In  the  common 
star-fish  of  our  own  coast,  similar  spinous  processes,  but  composed 

*  The  name  of  this  family,  and  of  its  typical  genus,  is  derived  from  a  star. 


ECHINOjDERMATA. 


147 


of  but  one  calcareous  piece,  are  attached  to  the  inferior  margins  of 
each  ray,  sometimes  in  several  rows ;  and,  being  still  moveable,  they 
may  be  useful  in  seizing  prey,  or  even  as  assisting  in  progression. 
Upon  the  dorsal  aspect  of  the  body  are  other  calcareous  projec¬ 
tions,  exhibiting  a  great  variety  of  forms,  so  as  to  render  the  en¬ 
tire  surface  of  the  animal  uneven  and  tuberculated. 

But  the  most  remarkable  appendages  to  the  integument  of  the 
Asterias  are  minute  bodies,  which  have  been  named  by  authors 
Pedicellaria ?,  and  have  been  looked  upon  by  many  naturalists  as 
distinct  animals,  allied  to  polyps  in  structure,  and  living  parasiti- 
cally  upon  star-fishes  and  other  Echinodermata.  Each  of  these 
curious  processes  consists  of  a  short  stem  fixed  by  one  extremity  to 
the  skin  of  the  Asterias,  and  terminating  at  the  opposite  end  in 
two  or  three  points  resembling  in  some  respects  the  prongs  of  a 
fork  :  the  stem  itself  does  not  seem  to  be  perforated  by  any  canal ; 
but,  nevertheless,  the  terminating  points  are  found  to  be  highly 
irritable,  and  quickly  seize  hold  of  any  minute  body  placed  between 
them.  Some  writers  regard  these  bodies  as  organs  of  prehension, 
used  under  certain  circumstances  for  fixing  the  animals  which 
possess  them  ;  but,  from  their  small  size  and  general  appearance, 
they  seem  but  ill  adapted  to  such  an  office. 

(189.)  The  skeleton  or  calcareous  framework  imbedded  in  the 
skin  of  the  Asteridse  is  by  no  means  the  least  remarkable  part  of 
their  structure  :  this  consists  of  several  hundred  pieces  variously 
disposed,  and  for  the  most  part  fitted  together  with  great  accuracy; 
being  either  firmly  soldered  to  each  other,  as  we  have  seen  them 
to  be  in  the  formation  of  the  calcareous  box  that  constitutes  the 
central  portion  of  Opliiurus ,  or  united  by  ligaments,  so  as  to  allow 
of  a  considerable  degree  of  motion  to  take  place  between  them,  as  in 
the  rays  of  Opliiurus ,  Gorgonoceplialus ,  and  other  asteroid  forms. 

In  the  generality  of  star-fishes,  the  arrangement,  and  indeed  the 
entire  character  of  the  calcareous  plates,  differs  materially  in  differ¬ 
ent  parts  of  the  body;  and,  even  in  different  species,  considerable 
modifications  are  observable.  In  the  coriaceous  integument  form¬ 
ing  the  dorsal  parietes  of  the  animal,  the  pieces  in  many  cases 
seem  rather  to  be  represented  by  calcareous  granules  disseminated 
through  the  interior  of  the  skin,  or  in  other  cases  they  are  ar¬ 
ranged  in  lines  anastomosing  with  each  other  in  all  directions,  so  as 
to  represent,  when  the  skin  is  dried,  a  rude  network  of  solid  par¬ 
ticles,  upon  the  exterior  of  which  the  various  cutaneous  appendages 
already  noticed  are  sustained. 

l  2 


ECHINODERMATA. 


148 

It  is,  however,  upon  the  ventral  aspect  of  the  Asterias  that  the 
skeleton  assumes  its  most  perfect  developement ;  the  floor  of  every 
ray  is  made  up  of  a  continuous  series  of  detached  pieces,  or  verte¬ 
brae,  as  they  are  generally  called,  fitted  to  each  other  and  united  by 
a  strong  ligamentous  substance,  so  as  to  form  a  succession  of  joints, 
upon  which  the  flexibility  of  the  ray  depends.  The  pieces  around 
the  mouth  constitute  a  strong  circular  framework  enclosing  the  oral 
aperture,  from  which,  as  from  a  centre,  the  rest  of  the  skeleton 
radiates.  The  joints  forming  the  floor  of  the  ray  succeed  to  this  ; 
these  are  partially  represented  in  Jig.  67,  where  the  soft  parts 
having  been  removed  from  the  ray  marked  Z>,  their  general  arrange¬ 
ment  is  displayed. 

The  vertebree  thus  exposed  are  individually  composed  of 
several  pieces,  and  each  is  articulated  by  oblique  facets  to  those 
which  precede  and  follow  it  ;  a  kind  of  union  which  admits  of 
considerable  motion,  and  provides  for  the  flexibility  of  the  ray, 
so  as  to  render  it  capable  of  executing  those  movements  which 
are  requisite  for  the  purpose  of  progression,  or  of  seizing  prey. 
The  connection  of  the  vertebrse  is  effected  in  such  a  manner, 
that  between  each  pair  of  calcareous  plates  minute  orifices  are  left, 
which  in  the  entire  state  of  the  ray  are  seen  to  be  arranged  in  a 
quadruple  series ;  these  holes  give  passage  to  the  locomotive 
suckers,  and  from  this  circumstance  have  been  named  the  am¬ 
bulacra!  holes ,  while  the  furrows  seen  upon  the  ventral  surface 
into  which  they  open  are  designated  the  ambulacral  grooves 
(. fig •  64). 

(190.)  The  singular  organs  which,  at  the  will  of  the  animal,  are 
protruded  through  the  ambulacral  apertures,  forming  the  principal 
agents  whereby,  in  the  generality  of  species,  locomotion  is  effected, 
next  require  our  notice.  In  the  annexed  figure  (Jig.  64)  they 
are  seen  fully  extended,  projecting  for  some  distance  beyond  the 
margins  of  the  ambulacral  grooves  which  occupy  the  centre  of  each 
ray,  every  one  of  them  being  furnished  at  its  extremity  with  a 
sucking  disc,  adapted  to  take  firm  hold  upon  any  smooth  surface. 
The  mechanism  by  which  these  suckers,  or  feet,  as  they  are  usually 
called,  are  extended  from  the  body  and  again  retracted,  is  very 
simple.  That  portion  of  each  foot  which  is  external  to  the  shell 
is  a  muscular  tube,  closed  at  one  extremity,  namely,  that  where- 
unto  the  sucker  is  appended ;  whilst,  by  the  opposite,  it  communi¬ 
cates  through  the  corresponding  ambulacral  hole  with  a  globular 
contractile  vesicle  situated  within  the  body  of  the  animal.  Both 


ECHINODElt  JNI A  T  A . 


149 


Fig.  64. 


tlie  tubular  foot,  and  the  vesicle  appended  to  it,  are  endowed  with 
a  power  of  independent  action,  so  that,  if  the  vesicle  contracts,  the 
fluid  within  it  is  forced  into  the  external  tubular  portion  of  the 
organ,  which  thus  becomes  distended  and  rendered  erect ;  but  if,  on 
the  other  hand,  the  muscular  tube  shrinks  in  turn,  the  contained 
fluid  is  forced  back  again  into  the  internal  vesicle,  and  the  whole 
foot  collapses.  The  arrangement  referred  to  will  be  easily  intel¬ 
ligible  on  reference  to  the  rough  diagram  in  the  next  page,  which 
represents  a  longitudinal  section  of  one  of  the  rays  of  the  Asterias 
depicted  above.  The  internal  vesicles  {Jig.  65,  1,  li)  occupy  the 
floor  of  each  segment  of  the  body,  and,  when  viewed  from  above, 
(Jig.  67,  d,)  the  entire  series  resembles  strings  of  transparent 
beads  placed  above  the  rows  of  ambulacral  apertures,  through  which 
they  communicate  with  the  tubular  feet  (Jig.  65,  1,  g).  In  Jig. 
65,  2,  three  of  these  organs  are  represented  in  different  states  of 


150 


ECHINODERMATA. 


extension,  and  tlieir  whole  structure  is  developed.  The  foot,  (/, 
is  shown  protruded  to  its  full  extent;  the  vesicle,  much  contracted, 
has  forced  the  fluid  which  it  contained  into  the  external  tube  (i), 
whereby  it  is  rendered  tense  and  prominent.  The  muscular  coats, 
which  invest  the  exterior  of  the  protruded  portion,  are  likewise  de¬ 
picted  ;  the  internal  layer  (&),  immediately  in  contact  with  the 
membranous  canal  continued  from  the  vesicle,  is  made  up  of  longi¬ 
tudinal  bands  passing  from  the  root  of  the  organ  towards  the 
sucker  at  its  extremity,  while  the  outer  layer  (/)  consists  of  cir¬ 
cular  fibres, — -an  arrangement  evidently  adequate  to  the  performance 
of  all  required  movements. 

The  other  portions  of  this  diagram  represent  the  feet  in  differ¬ 
ent  stages  of  protrusion  :  in  jig.  65,  2,  c,  the  vesicle  being  par¬ 
tially  contracted,  the  tubular  portion  is  seen  in  a  medium  state  of 
distension  ;  and  at  5,  the  sucker  is  shown  in  a  still  more  retracted 
state,  the  contained  fluid  having  been  completely  expelled  from 
the  muscular  tube,  and  driven  back  into  the  vesicle,  which  is  dis¬ 
tended  to  the  utmost. 

Fig.  65. 


The  fluid  that  thus  fills  the  suckers,  and  performs  so  important 
a  part  in  causing  all  their  movements,  is  not  secreted  by  the  vesi¬ 
cles  in  which  it  is  contained,  but  is  conveyed  into  them  by  a 
special  vascular  apparatus,  (g,  f,  )  from  which  branches  are  given 
off  to  each  tube.  The  nature  of  the  fluid,  however,  and  the  ar¬ 
rangement  of  the  vessels  through  which  it  flows,  will  be  more 
properly  discussed  hereafter. 


ECHINODERMATA. 


151 


(191.)  The  whole  inner  surface  of  the  elaborately  constructed 
box  which  forms  the  skeleton,  as  well  as  the  integuments  of  the 
star-fish,  is  lined  by  a  thin  membrane,  aptly  enough  called  the  pe¬ 
ritoneum  ;  for,  like  the  serous  tunic  so  named  in  higher  animals,  it 
not  only  spreads  over  the  walls  of  the  body,  but  is  reflected  there¬ 
from  upon  the  contained  viscera,  so  that  they  are  completely  in¬ 
vested  by  it,  each  viscus  having  a  distinct  mesenteric  fold  by 
which  it  is  supported  and  retained  in  situ. 

(192.)  The  mouth  of  the  Asterias  occupies  the  centre  of  the  lower 
surface  of  the  body  (fig.  65,  a).  It  is  usually  described  as  being 
a  simple  orifice  entirely  destitute  of  teeth,  although  it  is  not  impro¬ 
bable  that  the  osseous  ring  around  it,  and  the  articulated  spines 
thereunto  attached,  may,  to  a  certain  extent,  perform  the  office  of 
a  dental  apparatus. 

The  oesophagus  is  very  muscular,  and  susceptible  of  great  dila¬ 
tation,  its  parietes  being  gathered  into  deep  longitudinal  folds. 
The  stomach  (fig-  65,  b )  is  a  wide  sacculated  bag,  occupying  the 
central  portion  of  the  body,  and,  like  the  oesophagus,  is  evidently 
calculated  to  undergo  considerable  distension.  There  is  no  anal 
orifice,  and  consequently?  as  in  the  polyps,  the  indigestible  parts 
of  the  food  are  again  expelled  through  the  mouth.  The  walls  of 
the  stomach,  as  well  as  those  of  the  oesophagus,  contain  muscular 
fibres,  and  are  further  strengthened  by  fibrous  bands,  apparently 
of  a  ligamentous  character,  derived  from  the  peritoneal  covering 
which  spreads  over  its  outer  surface.  Ten  narrow  canals  open  by 
as  many  distinct  orifices  into  the  sides  of  the  stomach  ;  each  of 
which,  after  a  short  course,  expands  into  a  capacious  caecum 
(fig-  65,  1,  c). 

The  whole  of  the  digestive  apparatus  is  displayed  in  fig.  66 : 
every  one  of  the  five  rays  contains  two  of  the  caecal  prolongations 
derived  from  the  stomach  or  central  bag  (a)  ;  and  in  the  rays  marked 
c,  d,  e,  these  organs  are  represented  in  situ,  but  at  jf,  they  are 
seen  raised  from  their  natural  position  and  carefully  unravelled,  so 
as  to  display  more  distinctly  their  complicated  structure.  When 
thus  unfolded,  the  caeca  present  an  arborescent  appearance,  the 
central  canal  being  dilated  into  numerous  lateral  sacculi,  from 
which  in  turn  secondary  pouches  are  given  off ;  and  in  this  manner 
innumerable  ramifications  are  formed,  so  that  the  extent  of  internal 
surface  is  enormously  increased,  as  may  be  seen  in  the  ray  g,  in 
which,  the  upper  walls  of  the  caeca  having  been  removed,  their 
sacculated  internal  structure  is  rendered  visible. 


152 


ECHINODERMATA. 


(193.)  With  respect  to  the  exact  office  of  these  capacious  ap¬ 
pendages  to  the  stomach,  there  exists  some  diversity  of  opinion. 


It  is  scarcely  possible  that  they  can  be  at  all  instrumental  in  the 
digestion  of  food,  the  passages  by  which  they  communicate  with 
the  central  cavity  being  too  narrow  to  admit  any  solid  substance 
into  their  interior  ;  the  digestive  process  would  therefore  seem  to 
be  entirely  accomplished  in  the  receptacle  into  which  the  food  is 
first  introduced.  But  there  is  every  evidence  to  prove  that, 
although  they  can  have  little  part  in  digestion,  they  are  inti¬ 
mately  connected  with  the  absorption  of  nutriment ;  and  thus, 
although  possessing  no  excretory  orifice,  they  must  be  looked  upon 
as  strictly  analogous  in  function  to  the  intestinal  canal  of  other 
animals  :  the  great  extent  of  surface  which  they  present  internally 
would  alone  lead  to  this  supposition,  even  did  not  the  nature  of  the 
material  usually  found  in  them,  namely  a  pultaceous  creamy  fluid, 
evidently  a  product  of  digestion,  abundantly  confirm  this  view  of 
til  eir  nature.  The  matter  seems,  however,  to  be  put  beyond  a 
doubt  by  the  arrangement  of  the  vascular  system  connected  with 
these  organs,  as  the  veins  which  ramify  so  extensively  through  their 
walls  are  here,  as  in  other  Echinodermata,  the  only  agents  by 
which  the  absorption  of  chyle  can  be  effected  ;  this  will  be  evident 
when  we  examine  the  organs  subservient  to  the  circulation  of  the 
nutritious  fluids. 

Those  physiologists  who  have  adopted  a  different  view  of  the 
nature  of  the  crncal  appendages  to  the  stomach,  consider  them  to 
be  adapted  to  the  secretion  of  some  fluid,  and  probably  represent- 


ECHINODEltMATA. 


153 


ing  a  biliary  apparatus.  Their  enormous  extent,  however,  would 
alone  lead  us  to  dissent  from  such  a  conclusion  ;  more  especially  as 
another  organ  has  been  pointed  out  to  which  the  functions  of  a 
liver  have  been  assigned.  This  is  situated  upon  the  base  of  the 
stomach  {Jig.  66,  5),  and  is  a  yellow  or  greenish-yellow  racemose 
sacculus,  which  opens  into  the  bottom  of  the  digestive  sac  by  a  free 
aperture  :  the  contents  of  this  organ,  moreover,  resemble  bile  both 
in  taste  and  colour.* 

In  the  slender-rayed  genera,  such  as  Opliiurus ,  the  cm  cal 
appendages  are  not  met  with;  but  their  deficiency  appears  to  be 
supplied  by  the  plicated  walls  of  the  stomach  itself,  the  nu¬ 
merous  folds  of  which  resemble  lateral  leaflets  attached  to  the  cen¬ 
tral  cavity.  We  are  unacquainted  with  the  precise  organization  of 
the  alimentary  canal  in  Comatula ;  but,  from  the  orifices  visible  in 
the  shell,  it  would  appear  that  in  this  genus,  as  well  as  in  some 
Crinoid  species,  the  digestive  tube  was  furnished  with  an  anal 
aperture. 

(194.)  The  star-fishes,  grossly  considered,  might  be  regarded  as 
mere  walking  stomachs  ;  and  the  office  assigned  to  them  in  the  eco¬ 
nomy  of  nature,  that  of  devouring  all  sorts  of  garbage  and  offal  which 
would  otherwise  accumulate  upon  our  shores.  But,  as  we  have 
already  seen,  their  diet  is  byno  means  exclusivelylimited  to  such  ma¬ 
terials,  since  crustaceans,  shell-fish  of  various  kinds,  and  even  small 
fishes,  easily  fall  victims  to  their  voracity.  Delle  Chiaje  found  a 
human  molar  tooth  in  the  stomach  of  an  individual  which  he  exa¬ 
mined.  Neither  is  the  size  of  the  prey  upon  which  they  feed  so 
diminutive  as  we  might  suppose  from  a  mere  inspection  of  the  orifice 
representing  the  mouth  ;  for  this  is  not  only  extremely  dilatable, 
but,  as  we  have  found  to  be  the  case  in  the  Actiniae,  the  stomach 
is  occasionally  partially  inverted,  in  order  more  completely  to 
embrace  substances  about  to  be  devoured.  Shell-fishes  are  fre¬ 
quently  swallowed  whole ;  and  a  living  specimen  of  Chama  anti- 
quata ,  Lin.,  has  been  taken  from  the  digestive  cavity  of  an  Asterias 
in  an  entire  state.  It  appears,  moreover,  that  it  is  not  necessary  for 
testaceous  mollusca  to  be  absolutely  swallowed,  shells  and  all,  to 
enable  the  Asteridse  to  obtain  possession  of  the  enclosed  animal, 
as  they  would -seem  to  have  the  power  of  attacking  large  oysters, 
to  which  they  are  generally  believed  to  be  peculiarly  destructive, 
and  of  eating  them  out  of  their  shells.  The  ancients  believed  that, 
in  order  to  accomplish  this,  the  star-fish,  on  finding  an  oyster  par- 

*  Delle  Chiaje,  op.  eit. 


154 


ECHINODERMATA. 


tially  open,  cunningly  inserted  one  of  its  rays  between  the  valves, 
and,  thus  gradually  insinuating  itself,  destroyed  its  victim.*  Mo¬ 
dern  observations  do  not,  as  far  as  we  are  aware,  fully  bear  out  the 
above  opinion  of  our  ancestors  as  to  the  mode  in  which  star-fishes 
attack  oysters ;  although  the  destruction  which  they  cause  is  pretty 
generally  acknowledged.  The  observations  recorded  by  M.  Eudes 
Deslongchamps  upon  this  subject  are  however  exceedingly  curious,  j' 
As  the  waves  had  receded  from  the  shore,  so  as  to  leave  only  one 
or  two  inches  of  water  upon  the  sand,  he  saw  numbers  of  Asterias 
rubens  rolling  in  bunches,  five  or  six  being  fastened  together  into 
a  sort  of  ball  by  the  interlacement  of  their  rays.  He  examined  a 
great  number  of  such  balls,  and  constantly  found  in  the  centre  a 
Bivalve  Mollusc  ( Mactra  Stultorum ,  Lin.)  of  an  inch  and  a 
half  in  length.  The  valves  were  invariably  opened  to  the  extent 
of  two  or  three  lines,  and  the  star-fislies  were  always  ranged  with 
their  mouths  in  contact  with  the  edges  of  the  valves. 

On  detaching  them  from  the  shell  which  they  thus  imprisoned, 
he  found  that  they  had  introduced  between  the  valves  large 
rounded  vesicles  with  very  thin  walls,  and  filled  with  a  transparent 
fluid.  Each  Asterias  had  five  of  these  vesicles  ranged  around 
its  mouth,  but  they  were  of  very  unequal  size  ;  generally  there 
were  two  larger  than  the  rest,  equal  in  size  to  large  filberts, 
while  the  other  three  were  not  bigger  than  small  peas.  These 
vesicles  appeared  to  be  attached  to  the  Asterias  by  short  pedicles, 
and  at  the  opposite  end  of  each  was  a  round  open  aperture,  through 
which  the  fluid  contained  in  the  vesicle  flowed  out  drop  by  drop. 
No  sooner  was  the  animal  detached  from  the  shell  that  it  was  thus 
sucking,  than  the  vesicles  collapsed  and  became  no  longer  distin¬ 
guishable.  The  Mactree  were  all  found  to  be  more  or  less  de¬ 
voured,  some  having  only  their  adductor  muscles  left;  but,  howrever 
little  they  had  been  injured,  all  had  lost  the  power  of  closing  their 

*  This  may  be  gathered  from  Aldrovando,  who  writes  as  follows  :  “  Alii  ostrea- 
rum  hostes  sunt  Stellae  marinas  molla  crusti  intectae,  verdtam  crudeliter,  (ut  ^Elianus, 
lib.  ix.  cap.  22,  ait,)  inimicae  ut  base  ipsas  exedant  et  conficiunt.  Ratio  insidiarum  quas 
eis  moliuntur  ejusmodi  est.  Cum  testacea  suas  patefaciant  conchas,  ciim  vel  refri- 
geratione  egent,  vel  ut  aliquid  pertinens  ad  victum  incidat ;  eae,  uno  de  suis  sive  cruribus 
sive  radiis  intra  testas  ostreae  hiantis  insito  eas  claudi  prohibens,  carne  implentur.” — 
Testae,  lib.  iii.  page  487.  Thus  likewise  Oppian, 

“  Sic  struit  insidias,  sic  subdola  fraudes 
Stella  marina  parat,  sed  nullo  adjuta  lapillo 
Nititur,  et  pedibus  scabris  disjungit  hiantes.” 

t  Bulletin  des  Sciences  de  M.  le  Baron  Ferussac,  vol.  x.  p.  296. 


ECHINODERMATA. 


155 


valves  and  were  apparently  dead  :  nevertheless  there  was  nothing 
to  lead  to  the  supposition  that  only  dead  shell-fishes  were  attacked, 
so  that  it  is  difficult  to  imagine  how  the  delicate  vesicles  above  de¬ 
scribed  escaped  injury  from  the  closing  of  the  valves.  M.  Deslong- 
champs  thinks  that  probably  the  Asterias  pours  into  the  shell  a 
torpifying  secretion,  and  thus  ensures  the  death  of  its  victim. 

(195.)  The  absorption  of  the  nutritious  portions  of  the  food  in 
the  Echinodermata  is  entirely  accomplished  by  the  veins  distributed 
upon  the  coats  of  the  digestive  cavities,  so  that  the  chyle  resulting 
from  digestion  is  at  once  introduced  into  the  vessels  appropriated 
to  circulation. 

In  Asterias ,  the  intestinal  veins  form  a  fine  vascular  network, 
covering  the  stomach  and  the  ten  digestive  cmca.  The  venous 
trunks  derived  from  all  these  sources  unite  to  form  a  circular 
vessel  (Jig.  67,  e),  which  likewise  receives  branches  derived  from 
the  ovaria  and  other  sources. 


Fig.  67. 


c 

The  circular  vein  thus  formed,  which  seems  to  be  the  common 
trunk  of  the  venous  system,  communicates  with  another  vas¬ 
cular  circle  placed  around  the  mouth  (s),  by  means  of  a  dilated 


ECHINODERM  AT  A. 


156 

vertical  tube  of  communication  (/),  which,  from  its  muscular  ap¬ 
pearance  and  great  irritability,  Tiedemann  regards  as  being  equiva¬ 
lent  in  function  to  a  heart.  The  circle  around  the  mouth  (s) 
would  seem  to  be  arterial  in  its  character ;  and  from  it  branches 
are  derived  which  supply  the  various  viscera  of  the  body. 

But  besides  the  vessels  above  described,  apparently  so  disposed 
as  to  collect  and  distribute  the  nutrient  fluids,  there  is  another 
set  of  canals  appropriated  to  the  supply  of  the  numerous  vesicles 
connected  with  the  locomotive  suckers  (§  190)  ;  these  Tiedemann 
regards  as  being  totally  unconnected  with  the  vascular  system 
properly  so  called,  and  considers  the  fluid  contained  in  them  as  quite 
of  a  different  nature.  Belle  Chiaje,  on  the  contrary,  asserts  that 
the  two  sets  of  vessels  are  derived  from  each  other,  and  describes  a 
peculiar  apparatus  connected  with  them  as  performing  an  important 
part  in  effecting  the  protrusion  of  the  suckers. 

The  circular  vessel  around  the  mouth,  which  forms  the  central 
receptacle  of  the  vascular  system,  resembles  a  sinus  analogous  to 
those  of  the  dura  mater  in  man  ;  and  is  lodged  in  a  groove  between 
the  oral  circle  of  vertebrae  and  the  pieces  of  the  skeleton  articu¬ 
lated  therewith.  Connected  with  the  sinus  above  mentioned,  and 
placed  regularly  in  the  interspaces  between  the  rays,  are  several 
oval  vesicles  {Jig.  67,  A',  A),  filled  with  a  reddish- coloured  transpa¬ 
rent  fluid.  These  vesicles,  which  in  Asterias  aranciaca  are  seven¬ 
teen  in  number,  communicate  by  distinct  ducts  with  the  central 
sinus,  and  are  regarded  by  Belle  Chiaje  as  reservoirs  in  which 
the  nutritive  fluids  accumulate  until  expelled  by  the  contraction  of 
the  vesicles.  Besides  the  arteries  above  described  as  arising  from 
the  vascular  circle  around  the  mouth,  according  to  the  author  last 
mentioned,  vessels  are  given  off  which  communicate  with  the  am¬ 
pullae  connected  with  the  ambulacral  suckers,  apparently  for  the 
purpose  of  supplying  to  them  the  fluid  which  they  contain.  These 
vessels  are  seen  to  run  along  the  floor  of  each  ray,  and  to  give  off 
lateral  branches  communicating  with  every  vesicle,  as  represented  in 
the  enlarged  sketch  (Jig.  62,  2g).  By  this  arrangement  it  would 
seem  that  the  contractile  organs  (Jig.  65,  2  e.)  appended  to  the 
vascular  sinus  are  in  reality  antagonists  to  the  tubular  structure 
of  the  feet,  and  serve  as  receptacles  for  fluid,  which,  by  their  con¬ 
traction,  they  can  force  into  the  whole  system  of  locomotive  suckers 
whenever  the  feet  are  brought  into  action. 

The  above  view  of  the  arrangement  of  the  vascular  system  of 
Asterias  is,  however,  by  no  means  universally  admitted  to  be  cor- 


ECHINODERMATA. 


157 


rect.  Professor  Sharpey  agrees  with  Tiedemann  in  the  opinion  that 
the  vessels  of  the  feet  form  a  system  perfectly  distinct  from  that  of 
the  blood-vessels,  and  even  supposes  that  the  fluid  by  which  the 
ambulacral  tubes  become  distended  is  neither  more  nor  less  than 
pure  sea- water. 

(196.)  Before  quitting  this  part  of  our  subject,  we  must  briefly 
mention  a  singular  organ,  apparently  intimately  connected  with  the 
circular  vessel  around  the  mouth,  and  called  by  Tiedemann  the  sand 
canal.  This  organ  is  represented  mfig.  67,  enclosed  in  the  same 
sheath  as  the  dilated  vessel  (j6),  upon  the  right  side  of  which  it  is 
placed ;  it  appears  to  communicate  by  one  extremity  with  an  isolated 
calcareous  mass  of  a  rounded  figure,  seen  upon  the  exterior  of  the 
dorsal  surface  of  the  star-fish,  while  by  its  opposite  extremity  it 
opens  apparently  into  the  circular  sinus  which  surrounds  the  mouth. 
The  tube  itself  Dr.  Sharpey  describes*  as  being  about  the  thickness 
of  a  surgeon’s  probe,  and  composed  of  rings  of  calcareous  substance 
connected  by  a  membrane,  so  that  viewed  externally,  it  is  not  unlike 
the  windpipe  of  a  small  animal.  On  cutting  it  across,  it  is  found  to 
contain  two  convoluted  laminae  of  the  same  nature  as  its  calcareous 
parietes,  which  are  rolled  upon  themselves  in  a  longitudinal  direction 
in  the  same  manner  as  the  inferior  turbinated  bones  of  an  ox.  The 
convoluted  arrangement  becomes  more  complete  towards  the  upper 
end  of  the  tube,  where  the  internal  laminae,  as  well  as  the  external 
articulated  portion,  join  the  dorsal  disc,  appearing  gradually  to  be¬ 
come  continuous  with  its  substance.  The  use  of  this  curious  organ 
is  quite  unknown,  although  a  variety  of  conjectures  have  been 
hazarded  upon  the  subject.  The  most  probable  appears  to  be  that 
of  Dr.  Sharpey,  who  suggests  that,  should  the  fluid  which  distends 
the  feet  and  the  vessels  connected  with  them  be  indeed  sea-water, 
it  may  be  introduced  and  perhaps  again  discharged  through  the 
pores  of  the  disc  by  means  of  the  calcareous  tube,  which  will  thus 
serve  as  a  sort  of  filter  to  exclude  impurities. 

(197.)  The  Asterias  possesses  no  organs  specially  appropriated 
to  respiration  ;  but  the  sea-water,  being  freely  admitted  into  the 
general  cavity  of  the  body  through  a  set  of  minute  membranous 
tubes  seen  upon  the  exterior  of  the  animal,  bathes  all  the  viscera, 
and  consequently  ensures  a  complete  exposure  of  the  circulating 
fluids  to  the  influence  of  oxygen,  —  the  whole  peritoneal  surface  per¬ 
forming  the  office  of  a  respiratory  apparatus.  The  mechanism  by 


*  Cyclopaedia  of  Anatomy  and  Physiology  ;  art.  Echinodermata. 


158 


ECHINODERMATA. 


which  the  surrounding  element  is  thus  drawn  into  the  body,  and 
the  process  by  which  its  expulsion  is  effected,  are  not  accurately 
known  ;  nevertheless,  apparently  with  a  view  to  ensure  a  continual 
circulation  of  aerated  water  through  all  parts  of  the  system,  the 
entire  surface  of  the  membrane  which  lines  the  shell,  as  well  as  that 
which  forms  the  external  tunic  of  the  digestive  organs,  has  been 
found  to  be  covered  with  multitudes  of  minute  cilia,  destined  by 
their  ceaseless  action  to  produce  currents  passing  over  the  vascular 
membranes,  and  thus  to  ensure  a  perpetual  supply  of  oxygenated 
water  to  every  part.*  But  it  is  not  only  on  the  peritoneal  surfaces 
that  the  existence  of  cilia  has  been  detected,  they  are  found  to  be 
extensively  distributed  over  the  external  surface  of  the  body,  within 
the  cavities  of  the  tubular  feet,  and  even  over  the  whole  internal 
lining  of  the  stomach  and  cseca. 

This  amazing  apparatus  of  vibratile  cilia  must  necessarily  serve 
some  important  purpose  in  the  economy  of  these  creatures  ;  and 
Professor  Sharpey,  to  whose  observations  upon  ciliary  motion  phy¬ 
siology  is  deeply  indebted,  regards  them  as  being  most  probably 
subservient  to  respiration. 

(198.)  The  organs  belonging  to  the  reproductive  system  in  the 
Asterida  exhibit  the  greatest  possible  simplicity  of  structure  :  there 
is  no  distinction  of  sex,  neither  have  any  parts  been  discovered  in 
connection  with  the  ovigerous  organs,  which  can  be  regarded  as 
ministering  an  accessory  secretion.  The  ovaria  {Jig-  67,  /,  l)  are 
slender  cseca  arranged  in  bunches  around  the  oesophagus,  two  dis¬ 
tinct  groups  being  lodged  at  the  origin  of  each  ray.  In  Asterias 
aranciaca  ( Jig .  67),  the  excretory  ducts  are  not  easily  seen ;  but 
in  the  twelve-rayed  star-fish,  especially  if  examined  when  these 
organs  are  in  a  gravid  state,  each  ovary  may  be  observed  to  com¬ 
municate  externally  by  a  wide  aperture,  which  perforates  the  osseous 
circle  encompassing  the  mouth.  {Fig.  65,  f.) 

(199.)  In  order  to  complete  the  history  of  the  Asterida ,  we  have 
yet  to  mention  the  nervous  apparatus  with  which  they  are  furnished. 
This  consists  of  a  simple  circular  cord,  which  runs  around  the 
mouth  of  the  animal ;  from  this  ring,  three  delicate  filaments  are 
given  off  opposite  to  each  ray,  one  of  which,  according  to  Tiede- 
mann,  runs  along  the  centre  of  the  ambulacral  groove  upon  the 
under  surface  of  the  body,  and  gives  minute  twigs  to  the  locomo¬ 
tive  suckers  placed  on  each  side  of  its  course  ;  the  other  two  fila- 

*  See  the  article  Cilia  by  Dr.  Sharpey,  in  the  Cyclopaedia  of  Anatomy  and  Physiology. 


ECHINODERMATA. 


159 


ments  pass  into  tlie  visceral  cavity,  and  are  probably  distributed  to 
tlie  internal  organs.  There  are  no  ganglia  developed  on  any  part 
of  this  nervous  apparatus  ;  or  at  least,  if,  as  some  writers  assert, 
ganglionic  enlargements  are  visible  at  the  points  whence  the  ra¬ 
diating  nerves  are  given  off,  they  are  so  extremely  minute  as  not 
in  any  degree  to  merit  the  appellation  of  nervous  centres. 

(200.)  Such  an  arrangement  can  only  be  looked  upon  as  serving 
to  associate  the  movements  performed  by  the  various  parts  of  the 
animal,  for  no  portion  of  these  simple  nervous  threads  can  be  re¬ 
garded  as  being  peculiarly  the  seat  of  sensation  or  perception. 
But  this  inference  is  not  merely  deducible  from  an  inspection  of 
the  anatomical  character  of  the  nerves  ;  it  is  based  upon  actual 
experiment.  We  have  frequently,  when  examining  these  animals 
in  a  living  state, — that  is,  when  with  their  feet  fully  developed 
they  were  crawling  upon  the  sides  of  the  vessels  in  which  they 
were  confined, — cut  off  with  scissars  successive  portions  of  the 
dorsal  covering  of  the  body  so  as  to  expose  the  visceral  cavity  ;  but, 
so  far  from  the  rest  of  the  animal  appearing  to  be  conscious  of  the 
mutilation,  not  the  slightest  evidence  of  suffering  was  visible  :  the 
suckers  placed  immediately  beneath  the  injured  part  were  inva¬ 
riably  retracted ;  but  all  the  rest,  even  in  the  same  ray,  still  continued 
their  action,  as  though  perfectly  devoid  of  participation  in  any 
suffering  caused  by  the  injury  inflicted.  Such  apathy  would  in¬ 
deed  seem  to  be  a  necessary  consequence  resulting  from  the  defi¬ 
ciency  of  any  central  seat  of  perception,  whereunto  sensations  could 
be  communicated ;  nevertheless  Ehrenberg  insists  upon  the  exist¬ 
ence  of  eyes  in  some  species  of  star-fish,  attributing  the  function  of 
visual  organs  to  some  minute  red  spots  visible  at  the  extremity  of 
each  ray,  behind  each  of  which  he  describes  the  end  of  the  long 
nerve  which  runs  along  the  ambulacral  groove  as  expanding  into  a 
minute  bulb.  We  must  however  confess,  that  the  proofs  adduced 
in  support  of  such  a  view  of  the  nature  of  these  spots,  appear  to  us 
to  be  anything  but  satisfactory;  and  as  we  have  already  stated  in 
the  first  chapter  the  physiological  objections  which  may  be  urged 
against  the  possibility  of  any  localised  organ  of  sense  being  co¬ 
existent  with  a  strictly  nematoneurose  condition  of  the  nervous  sys¬ 
tem,  they  need  not  be  repeated  here.  The  general  sense  of  touch  in 
the  Asteridse  is  extremely  delicate,  serving  not  only  to  enable  them 
to  seize  and  secure  prey,  but  even  to  recognise  its  presence  at  some 
little  distance,  and  thus  direct  these  animals  to  their  food.  Any 
person  who  has  been  in  the  habit  of  fishing  with  a  line  in  the 


160 


ECllINODERMATA. 


shallow  bays  frequented  by  star-fishes,  and  observed  how  frequently 
a  bait  is  taken  and  devoured  by  them,  will  be  disposed  to  admit 
this;  yet  to  what  are  we  to  attribute  this  power  of  perceiving  exter¬ 
nal  objects  ?  It  would  seem  most  probably  due  to  some  modifi¬ 
cation  of  the  general  sensibility  of  the  body,  allowing  of  the  per¬ 
ception  of  impressions  in  some  degree  allied  to  the  sense  of  smell 
in  higher  animals,  and  related  in  character  to  the  kind  of  sensation 
by  which  we  have  already  seen  the  Actiniae  and  other  polyps 
able  to  appreciate  the  presence  of  light,  although  absolutely  de¬ 
prived  of  visual  organs. 

(201.)  The  Echini,  however  they  may  appear  to  differ  in  out¬ 
ward  form  from  the  Asteridce,  will  be  found  to  present  so  many  points 
of  resemblance  in  their  general  structure,  that  the  detailed  account  we 
have  given  above,  of  the  organization  of  the  last-mentioned  family, 
will  throw  considerable  light  upon  the  still  more  elaborately  con¬ 
structed  animals  which  now  present  themselves  to  our  notice. 

The  j Echinida:,  as  we  have  already  observed,  differ  from  the 
star-shaped  Echinodermata  in  the  nature  of  the  integument  which 
encloses  their  visceral  cavity,  as  well  as  in  the  more  or  less  circular 
or  spherical  form  of  their  bodies  ;  so  that  the  locomotive  apparatus 
with  which  they  are  furnished  is  necessarily  modified  in  its  cha¬ 
racter  and  arrangement. 

(202.)  The  shell  of  an  Echinus  (Jig.  68, 1)  is  composed  of  innu- 

Fig.  68. 


1 


ECIIINODERMATA. 


161 


merable  pieces  accurately  joined  together,  so  as  to  form  a  globular 
box  enclosing  the  internal  parts  of  the  animal,  but  perforated  at 
each  extremity  of  its  axis  by  two  large  openings,  one  of  which 
represents  the  mouth,  and  the  other  the  anus. 

The  calcareous  plates  entering  into  the  composition  of  this  ex¬ 
traordinary  shell  may  be  divided  into  two  distinct  sets,  which  differ 
materially  in  size,  as  well  as  in  the  uses  to  which  they  are  subser¬ 
vient.  The  larger  pieces  are  recognisable  in  the  figure  by  hemisphe¬ 
rical  tubercles  of  considerable  size  attached  to  their  external  surface, 
adapted,  as  we  shall  afterwards  see,  to  articulate  with  the  moveable 
locomotive  spines.  Each  of  these  larger  plates  has  somewhat  of  a 
pentagonal  form;  those  which  are  situated  in  the  neighbourhood  of 
the  mouth  and  anal  aperture  being  considerably  the  smallest,  and 
every  succeeding  plate  becoming  progressively  larger  as  they  ap¬ 
proximate  the  central  portion  of  the  shell  :  the  entire  series  of 
pieces  in  each  row  resembles  in  figure  the  shape  of  the  space 
included  between  two  of  the  lines  which  mark  the  degrees  of  lon¬ 
gitude  on  a  terrestrial  globe,  broad  at  the  equator,  but  gradually 
narrowing  as  it  approaches  the  poles  ;  an  arrangement,  of  course, 
rendered  necessary  by  the  spherical  form  of  the  creature.  There 
are  ten  rows  of  these  tuberculated  plates  ;  but  as  they  are  disposed 
in  pairs,  each  row  of  large  pieces  being  united  by  a  zig-zag  suture 
with  another  of  a  similar  description,  there  are  in  reality  only  five 
large  segments  of  the  shell,  each  supporting  a  double  row  of 
tubercles. 

The  reader  must  not,  however,  conclude  that  the  great  central 
tubercles  above  mentioned  are  the  only  parts  of  the  shell  to  which 
spines  are  affixed  ;  hundreds  of  smaller  elevations  are  disseminated 
over  the  surface,  to  which  smaller  spiculm  are  appended,  although, 
from  their  diminutive  size,  these  are  of  secondary  importance  in 
locomotion. 

The  five  large  double  segments  which  thus  form  the  greater  por¬ 
tion  of  the  calcareous  shell  are  separated  from  each  other  by  the 
interposition  of  ten  rows  of  perforated  plates,  likewise  disposed  in 
pairs,  and  composed  of  much  smaller  pieces  than  those  which  sup¬ 
port  the  tubercles  ;  hundreds  of  foramina,  which  pierce  these  ambu- 
lacral  bands,  give  passage  to  as  many  tubular  feet  or  protrusible 
suckers,  in  every  respect  resembling  those  of  Asterias,  and  dis¬ 
tended  by  a  similar  apparatus. 

It  is  impossible  by  any  verbal  description,  at  all  commensurate 
with  the  limits  of  our  present  undertaking,  adequately  to  explain 

M 


162 


EC  H  INODE  II  MATA. 


tlie  more  minute  contrivances  visible  in  the  disposition  of  every 
portion  of  tliese  wonderfully  constructed  coverings :  it  is  sufficient 
for  our  present  purpose  to  observe  that  tlie  globular  crust  of  an 
Echinus  is  made  up  of  several  hundred  polygonal  pieces  of 
different  sizes,  and,  although  presenting  every  variety  of  outline, 
generally  approximating  more  or  less  to  a  pentagonal  form ;  that 
these  pieces  are  so  accurately  and  completely  fitted  to  each  other, 
that  the  lines  which  unite  them  are  scarcely  to  be  distinguished 
even  upon  the  most  minute  examination  ;  and  that  from  the  union 
of  so  many  distinct  and  dissimilar  plates  results  a  firm,  compact,  and 
beautiful  box,  similar  to  that  represented  in  the  figure.  The  first 
question  which  naturally  suggests  itself  on  examining  a  shell  of  this 
description,  is  concerning  the  object  to  be  attained  by  such  remark¬ 
able  complexity  ;  it  would  appear  indeed,  at  first  sight,  that  a  simple 
calcareous  crust,  had  it  been  allowed  to  exude  from  the  entire  sur¬ 
face  of  the  Echinus,  would  gradually  have  moulded  itself  upon  the 
body  of  the  creature,  and  thus  have  formed  a  globular  shell  with¬ 
out  suture,  but  answering  every  purpose  connected  either  with 
support  or  defence. 

(208.)  Avery  little  investigation,  however,  will  suffice  to  show  the 
necessity  for  the  elaborate  arrangement  to  which  we  have  alluded. 
In  the  first  place,  as  we  shall  immediately  see,  the  earthy  matter  is 
not  deposited  upon  the  surface  of  the  body,  but  within  the  soft 
external  integument  by  which  it  is  secreted  ;  the  interior  of  the 
shell  being  filled  with  sea-water,  in  which  the  viscera  are  loosely 
suspended.  But  a  second  and  more  important  reason  for  the  em¬ 
ployment  of  so  many  pieces  in  the  construction  of  the  shell  of  an 
Echinus  is  to  be  derived  from  examining  the  mode  in  which  the 
animal  grows ;  was  it  to  retain  the  same  dimensions  throughout  the 
whole  period  of  its  life,  or  could  it  at  stated  intervals  cast  off  its 
old  investment,  and  secrete  a  new  and  more  capacious  covering,  as 
growth  rendered  the  change  necessary,  a  simple  earthy  crust  would 
have  been  sufficient,  without  the  presence  of  such  an  immense 
number  of  sutures  and  joinings.  The  calcareous  plates  of  the 
Echinus,  it  must  be  remembered,  are  merely  secreted  from  the 
soft  parts,  having  no  vital  action  going  on  within  them,  by  which, 
as  in  the  bones  forming  the  skeletons  of  vertebrate  animals,  a  con¬ 
tinual  deposition  of  fresh  particles  could  be  effected,  allowing  of 
extension  by  interstitial  deposit.  How,  therefore,  could  the  growth 
of  the  animal  be  provided  for  ?  How  is  the  gradual  expansion  of 
the  entire  shell,  thus  composed  of  a  dense  and  extra  vascular  crust, 


E  C II I  NODE  R  MATA. 


163 


to  be  effected  ;  and  that  without  ever  deranging  the  proportions  of 
the  whole  fabric,  or  necessitating  a  loosening  of  its  parts  ?  No 
other  contrivance  could  apparently  have  been  adequate  to  the  pur¬ 
pose:  nevertheless,  by  the  structure  adopted,  we  see  how  admirably 
the  growth  of  Echinus  proceeds  in  all  directions;  for  the  living  and 
vascular  membrane  which  covers  the  whole  external  surface  of  the 
body  dips  down  between  the  edges  of  the  various  calcareous  pieces, 
and  continually  deposits  around  the  margin  of  each,  successive 
layers  of  earthy  particles,  which,  assuming  a  semi-crystalline  ar¬ 
rangement,  progressively  increase  the  dimensions  of  each  individual 
plate.  But  the  continual  augmentation  in  size,  which  is  thus 
going  on,  is  attended  with  no  change  in  the  mathematical  figure  of 
any  given  piece  of  the  skeleton  ;  so  that,  as  they  all  increase  in 
diameter  by  the  unceasing  deposition  of  earthy  matter  around  the 
circumference  of  every  plate,  the  spherical  shell  gradually  expands, 
without  in  any  degree  altering  its  form  or  relative  proportions, 
until  it  has  acquired  the  mature  dimensions  belonging  to  its 
species. 

(204.)  The  tubular  suckers  or  retractile  feet,  which  are  pro¬ 
truded  at  the  pleasure  of  the  animal  from  the  countless  minute 
apertures  seen  in  the  ten  rows  of  ambulacral  plates,  are  so  similar 
in  all  essential  points  to  those  of  Asterias  already  described, 
that  little  further  need  be  said  concerning  their  structure,  or  the 
mechanism  by  which  their  motions  are  effected.  The  tubular  part 
of  each  foot  communicates  with  the  interior  of  the  shell  by  two 
branches  which  pass  through  two  apertures,  and  these  branches  in 
some  species  (as  Echinus  saxatilis )  receive  offsets  from  the  ves¬ 
sels  which  run  along  the  centre  of  each  ambulacral  groove,  and 
convey  to  the  feet  the  fluid  by  which  their  distension  is  effected. 
In  Echinus  esculentus  the  feet  open  into  a  plexus  of  vessels, 
formed  in  leaf-like  membranes,  equal  in  number  with  the  feet,  and 
disposed  in  double  rows  upon  the  inner  surface  of  the  ambulacral 
pieces,*  by  the  intervention  of  which  they  are  connected  with  the 
canals  above  mentioned. 

(205.)  The  tubercles  upon  the  external  surface  of  the  shell  of 
the  Echini  support  a  corresponding  number  of  long  spines,  which, 
as  well  as  the  apparatus  of  suckers,  are  employed  as  locomotive 
agents.  These  spines  vary  materially  in  their  form  and  propor¬ 
tionate  size,  and  even  in  their  internal  structure  and  mode  of 

*  Cyclopaedia  of  Anat.  and  Phys.  ;  art.  Eciiinoderm ata. 

M  2 


164 


ECHINODERMATA. 


growtli,  as  may  be  readily  seen  by  a  comparison  of  different 
species.  Thus,  in  the  flattened  forms  of  Scutella  and  allied 
genera,  they  are  so  minute  as  to  require  the  employment  of  a  mi¬ 
croscope  for  their  investigation  ;  in  Echinus  esculentus  (Jig-  62) 
they  are  sharp,  and  almost  of  equal  length  over  the  entire  surface 
of  the  animal;  while  in  the  specimen  represented  in  the  an¬ 
nexed  figure  (Jig.  69),  the  shell  of  which  we  have  already 

Fig.  69. 


examined  when  divested  of  these  appendages,  the  length  of  the 
spines  which  are  articulated  upon  the  large  tubercular  plates  fully 
equals  the  transverse  diameter  of  the  body  of  the  creature,  and  in 
some  cases  they  are  even  found  much  more  largely  developed. 
Every  spine,  examined  separately,  is  seen  to  be  united  with  the 
tubercle  upon  which  it  is  placed  by  an  apparatus  of  muscular  and 
ligamentous  bands,  forming  a  kind  of  ball-and-socket  joint,  allow¬ 
ing  of  a  considerable  extent  of  motion.  In  Jig.  68,  2,  the  structure 
of  this  articulation  is  exhibited.  The  large  tubercle  (a)  supports 
upon  its  apex  a  smaller  rounded  and  polished  eminence,  perforated 
in  the  centre  by  a  deep  depression  :  the  bottom  of  the  spine, 
moreover,  (c)  is  terminated  by  a  smooth  hemispherical  cavity 
accurately  fitted  to  the  projecting  tubercle,  so  that  the  two  form 
complete  articular  surfaces.  The  bonds  of  union  connecting  the 
spine  with  the  shell  are  of  two  kinds  :  in  the  first  place,  there  is  a 
stout  ligament  ( a ,  c),  extending  from  the  little  pit  seen  upon 
the  centre  of  the  tubercle,  to  a  corresponding  depression  visible 
upon  the  articular  surface  of  the  spine,  resembling  very  accurately 


ECHINODERMATA. 


165 


the  round  ligament  found  in  the  hip-joint,  and  obviously  a  provi¬ 
sion  for  the  prevention  of  dislocation. 

The  whole  joint  is  moreover  enclosed  in  a  muscular  capsule, 
composed  of  longitudinal  fibres  ( b ,  b )  arising  from  the  circum¬ 
ference  of  each  tubercle,  and  inserted  all  around  the  root  of  the 
spine :  these  fibres  therefore,  which  must  in  fact  be  regarded  as 
merely  derived  from  the  general  irritable  skin  that  clothes  the  shell 
externally,  are  the  agents  which,  acting  immediately  upon  the 
spine,  produce  all  the  movements  of  which  it  is  capable. 

(206.)  The  next  thing  to  be  accounted  for  in  the  history  of 
these  elaborately  constructed  animals  is  the  growth  of  the  spines 
themselves,  which,  as  we  have  already  seen,  are  completely 
detached  from  the  rest  of  the  shell,  to  which  they  are  only 
secured  by  the  central  ligament,  and  by  the  muscular  capsule 
enclosing  their  base.  To  account,  therefore,  for  the  production 
of  organs  so  completely  insulated  as  the  spines  appear  to  be, 
especially  when  we  consider  that  there  is  no  vascular  communi¬ 
cation  between  them  and  the  body  of  the  Echinus,  would  appear 
to  be  a  matter  of  some  difficulty;  and  in  fact,  had  we  not  already 
seen  in  the  polyps  the  amazing  facility  with  which  calcareous 
matter  was  secreted  by  the  living  textures  of  those  animals,  it 
would  be  almost  impossible  to  conceive  by  what  process  their 
growth  was  effected.  On  examining  one  of  these  appendages,  taken 
from  a  species  in  which  they  are  largely  developed,  when  fresh, 
before  its  parts  have  become  dry,  every  portion  of  its  surface  is 
seen  to  be  invested  with  a  thin  coat  of  soft  membrane,  derived 
from  that  which  covers  and  secretes  the  whole  shell,  of  which 
indeed  the  muscular  capsule  enclosing  its  articulation  with  the 
tubercle  is  only  a  thickened  portion. 

The  living  covering  of  the  spine  therefore,  like  the  crust  which 
invests  the  cortical  polyps,  is  the  secreting  organ  provided  for  its 
growth,  depositing  the  earthy  particles  separated  from  the  waters  of 
the  ocean,  layer  after  layer,  upon  its  outer  surface,  so  as  to  form  a 
succession  of  concentric  laminae,  of  which  the  outer  one  is  always 
the  last  formed.  The  calcareous  matter  thus  deposited  has  more 
or  less  completely  a  crystallized  appearance  ;  and  on  a  transverse 
section  of  the  organ  being  made,  and  the  surface  polished  by 
grinding,  the  whole  process  of  its  formation  is  at  once  rendered 
evident.  Such  sections,  indeed,  form  extremely  beautiful  and 
interesting  subjects  for  microscopical  examination,  as  nothing  can 
exceed  the  minute  accuracy  and  mathematical  precision  with  which 


166 


ECHINODERMATA. 


eacli  particle  of  every  layer  composing  them  appears  to  have  been 
deposited  in  its  proper  place :  indeed,  if  the  zootomist  would  fully 
appreciate  the  minuter  details  connected  with  their  organization, 
it  is  only  by  the  employment  of  the  microscope  that  he  will 
arrive  at  adequate  ideas  concerning  them  ;  for  it  is  not  in  the  num¬ 
ber  and  variety  of  the  pieces  entering  into  the  composition  of  the 
skeleton  of  one  of  these  animals,  the  extraordinary  apparatus  of 
prehensile  suckers  with  which  they  are  furnished,  or  the  singular 
locomotive  spines  upon  the  exterior  of  the  shell,  that  he  will  find  the 
most  remarkable  features  of  the  history  of  the  Echini ;  it  is  only  by 
a  minute  examination  of  the  intimate  structure  of  each  of  these 
parts  that  the  mechanism  conspicuous  throughout  can  be  properly 
understood. 

(207.)  The  calcareous  pieces  which  surround  the  mouth  of  the 
Echinus  are  not  so  immoveably  consolidated  as  those  composing  the 
rest  of  the  shell,  but,  on  the  contrary,  admit  of  considerable  move¬ 
ment,  by  which  the  prehension  of  food  is  more  easily  effected.  The 
mouth  itself  (Jig.  68,  1)  is  a  simple  orifice,  through  which  the 
points  of  five  sharp  teeth  are  seen  to  protrude.  These  teeth 
obviously  perform  the  office  of  incisors,  and,  from  their  sharpness 
and  extreme  density,  are  well  calculated  to  break  the  hard  sub¬ 
stances  usually  employed  as  food.  The  points  of  such  incisor 
teeth,  although  of  enamel-like  hardness,  would  nevertheless  be 
speedily  worn  away  by  the  constant  attrition  to  which  they  are 
necessarily  subjected,  was  there  not  some  provision  made  to  ensure 
their  perpetual  renewal  ;  like  the  incisor  teeth  of  rodent  quadrupeds, 
they  are  therefore  continually  growing,  and  are  thus  always  pre¬ 
served  sharp  and  fit  for  use.  In  order  to  allow  of  such  an  arrange¬ 
ment,  as  well  as  to  provide  for  the  movements  of  the  teeth,  jaws 
are  provided,  which  are  situated  in  the  interior  of  the  shell ;  and 
these  jaws,  from  their  great  complexity  and  unique  structure,  form 
perhaps  the  most  admirable  masticating  apparatus  met  with  in  the 
whole  animal  kingdom  ;  we  must  therefore  entreat  the  patience  of 
our  readers  while  we  describe  at  some  length  the  parts  connected 
therewith.  The  entire  apparatus  removed  from  the  shell  is  repre¬ 
sented  in  (Jig.  70),  and  consists  of  the  following  parts  :  There  are 
five  long  teeth,  (c,  c,)  each  of  which  is  enclosed  in  a  triangular  os¬ 
seous  piece,  ( a ,  aj)  that  for  the  sake  of  brevity  we  will  call  the  jaws. 
The  five  jaws  are  united  to  each  other  by  various  muscles, 
(A-,  /r,  i,  *,)  so  as  to  form  a  pentagonal  pyramid,  having  its  apex 
in  contact  with  the  oral  orifice  of  the  shell,  while  its  base  is  con- 


ECHINODERMATA. 


167 


nected  with  several  bony  levers,  by  means  of  numerous  mus¬ 
cles  provided  for  the  movements  of  the  whole.  These  parts  we 
must  now  proceed  to  describe  seriatim.  The  teeth  {Jig.  71,  a) 
resemble,  at  the  part  protruded  from  the  mouth,  long  three- 

Fig.  70. 


sided  prisms,  and  at  this  point  they  are  extremely  hard  and  brit¬ 
tle  :  each  tooth  is  fixed  in  a  socket  passing  through  the  jaw, 
{Jig-  71,  e,)  from  which  it  projects  by  its  opposite  extremity, 
{Jig-  71,  a ,)  that  may  be  called  the  root  of  the  tooth,  where,  instead 
of  being  of  glassy  hardness  like  the  point  ( a )  which  issues  from  the 
mouth,  it  is  flexible  and  soft,  resembling  fibres  of  asbestos,  and 
is  covered  by  a  membrane  apparently  connected  with  its  secretion. 
The  jaws,  which  thus  support  and  partially  enclose  these  teeth,  are 
five  in  number :  when  examined  separately,  each  is  found  to 
resemble  in  figure  a  triangular  pyramid,  the  external  surface 
{Jig-  71,  e,)  being  smooth,  and  presenting  eminences  provided 
for  the  attachment  of  muscles ;  while  the  other  two  sides 
(Jig-  71,  b,  b,)  are  flat,  and  marked  with  transverse  grooves, 
so  as  to  have  the  appearance  of  a  fine  file.  When  the  five  jaws 
are  fixed  together  in  their  natural  positions,  they  form  a  five¬ 
sided  conical  mass,  aptly  enough  compared  by  Aristotle  to  a 
lantern,  and  frequently  described  by  modern  writers  under  the 
name  of  the  “  lantern  of  Aristotle.”  When  thus  fitted  to 
each  other,  the  two  flat  and  striated  sides  of  each  jaw  are  in 
apposition  with  the  corresponding  surfaces  of  two  others,  so  that 


168 


ECHINODERMATA. 


there  are  ten  grinding  surfaces  formed,  between  which  the  food 
must  pass  preparatory  to  its  introduction  into  tire  digestive  canal. 
This  arrangement  will  be  easily  understood  by  referring  to 

Fig.  71. 


Jig.  71,  1,  in  which  three  of  these  jaws,  each  containing  its  in¬ 
cisor  tooth,  are  represented  in  situ,  the  two  others  having  been 
removed. 

The  five  curious  jaws  described  above  are  fixed  together  by  a 
set  of  muscles,  {Jig.  70,  A*,  k ,)  consisting  of  short  fibres  passing 
between  the  external  edges  of  the  contiguous  segments  of  the 
lantern,  and  evidently  capable  of  powerfully  approximating  the 
grinding  surfaces  and  rubbing  them  upon  each  other.  The  jaws, 
moreover,  are  provided  with  five  other  osseous  pieces  (c/,  r/,) 
arranged  in  a  radiating  manner  between  the  bases  of  the  different 
segments,  with  which  they  are  connected  by  ligaments,  and  like¬ 
wise  by  the  pentagonal  muscle  (?,  z,)  which  runs  from  one  to 
the  other. 

The  above  described  parts  complete  the  apparatus  required  for 
connecting  the  different  portions  of  this  remarkable  mouth,  but 
the  movements  of  the  whole  are  effected  by  a  very  complicated  set 
of  levers  and  muscles  which  must  next  be  noticed. 

The  levers  attached  to  the  jaws  are  five  long  and  slender  pro¬ 
cesses,  {Jig.  71,  1  d,  dj  each  arising  from  the  central  extremity  of 
one  of  the  radiating  osseous  pieces,  (c,  c,)  and  arching  outwards  con¬ 
siderably  beyond  the  base  of  the  lantern,  to  terminate  by  a  forked 
extremity.  But  there  are  likewise  other  processes  projecting  from 
the  inner  surface  of  the  shell ;  these,  two  of  which  are  seen  in 
(Jig.  70,  b ,  Z>,)  are  also  five  in  number,  and  are  placed  around  the 
orifice  of  the  mouth  :  they  are  generally  perforated  in  the  centre, 


E  CHI  NODERM  AT  A. 


169 


so  as  to  resemble  so  many  bony  arclies ;  and  from  them,  as  well  as 
from  the  spaces  which  separate  them,  numerous  muscles  derive 
their  origin.  Of  these  muscles,  ten  arise  from  the  spaces 

between  the  arches,  two  being  inserted  into  the  outer  edge  of  the  base 
of  each  jaw;  so  that  the  effect  produced  by  their  contraction,  when 
they  all  act  in  concert,  will  be  to  approximate  the  whole  mass  of 
the  mouth  to  the  oral  aperture  of  the  shell,  and  of  course  cause 
the  points  of  the  incisor  teeth  to  protrude  externally  ;  or,  if  they 
act  separately,  they  can  draw  the  base  of  the  lantern  in  any  di¬ 
rection,  or  cause  the  grinding  surfaces  of  the  jaws  to  work  against 
each  other. 

The  antagonists  to  the  muscles  last  mentioned  are  ten  others, 
(g,  g ,)  arising  from  the  extremities  of  the  arches  themselves,  and 
running  in  a  radiating  manner  towards  the  apex  of  the  lantern,  so 
that  the  point  of  each  piece  or  jaw  receives  a  muscle  from  two  of 
those  processes.  These  fasciculi,  from  the  manner  in  which  the 
arches  project  into  the  cavity  of  the  shell,  will  draw  inwards  the 
entire  mass ;  or,  if  they  act  separately  upon  the  jaws  to  which  they 
are  individually  fixed,  they  will  produce  movements  precisely  op¬ 
posite  to  those  caused  by  the  contractions  of  the  muscles  derived 
from  the  spaces  between  the  bony  processes  ;  or,  if  both  sets  should 
act  in  concert,  they  become  the  antagonists  of  the  muscles  («,  i,k9  k ,) 
which  connect  the  jaws  to  each  other,  and  by  causing  the  separa¬ 
tion  of  the  different  pieces  they  necessarily  enlarge,  not  only  the 
opening  of  the  mouth,  but  all  the  passage  leading  to  the  oesopha¬ 
gus  through  the  axis  of  the  lantern. 

Yet  even  these  are  not  all  the  muscles  which  act  upon  the 
masticating  apparatus  ;  ten  others,  (A,  A,)  arising  in  pairs  from  the 
middle  of  the  interspaces  between  the  arches,  are  connected  with 
the  bifurcated  extremities  of  the  slender  curved  processes,  (e,  e,) 
each  of  which  receives  a  muscle  from  two  contiguous  spaces ;  and, 
from  the  length  of  the  levers  upon  which  these  muscles  act,  we 
may  well  conceive  the  force  with  which  they  will  influence  the 
motions  of  the  whole  mass  of  the  jaws. 

Such  is  the  complex  structure  of  the  mouth  of  Echinus  escu- 
lentus  ;  a  piece  of  mechanism  not  less  remarkable  on  account  of  the 
singularity  of  its  construction,  than  as  exhibiting  an  example  of 
the  sudden  developement  of  a  dental  system,  of  which  not  a 
vestige  is  visible  in  any  other  of  the  Echinoderm  families.  In 
others  of  the  Echinidce  having  the  shell  much  depressed,  the 
dental  lantern  is  modified  in  form,  and  proportionately  flattened. 


170 


E  CHI  NODERM  A T  A . 


but  tlie  different  parts  care  essentially  similar  to  those  we  have 
described. 

(S08.)  The  oesophagus  {Jig.  72,  o/,)  is  continued  from  the  termi¬ 
nation  of  the  central  canal,  which  traverses  the  axis  of  the  lantern, 


and  after  a  short  course  termi¬ 
nates  in  a  much  wider  portion  F,S-  72- 

of  the  digestive  tube,  into  which 
it  opens  on  the  lateral  part  of 
its  csecal  origin  in  a  manner 
precisely  resembling  the  com¬ 
munication  between  the  large 
and  small  intestines  of  man. 

The  dilated  alimentary  tube, 

(c,)  which  presents  no  separa¬ 
tion  into  stomach  and  intestine, 
is  continued  in  a  winding 
course  around  the  interior  of  the 
shell,  which  it  twice  encircles, 
and,  becoming  slightly  con¬ 
stricted,  terminates  at  the  anal 
orifice  of  the  shell  (z).  The 
walls  of  the  intestine  are  ex¬ 
tremely  delicate  ;  although  they 
may  be  distinctly  seen  to  con¬ 
tain  muscular  fibres,  and  are 
covered  with  innumerable  vas¬ 
cular  ramifications.  The  external  tunic  of  the  whole  canal  is  de¬ 
rived  from  the  peritoneum,  which  lines  the  entire  shell,  invests  the 
dental  lantern,  and  forms  sundry  mesenteric  folds  as  it  is  reflected 
upon  the  other  viscera. 

(209.)  The  system  of  vessels  provided  for  the  circulation  of  the 
blood  has  been  differently  described  by  different  authors,  a  circum¬ 
stance  by  no  means  surprising  when  we  consider  the  great  difficulty 
of  tracing  such  delicate  and  extensively  distributed  canals.  Ac¬ 
cording  to  Delle  Chiaje,  the  course  of  the  nutritious  fluid  is  as 
follows.  A  large  vein  runs  along  the  whole  length  of  the  intes¬ 
tine,  from  the  anus  to  the  oesophagus,  where  it  terminates  in  a 
vascular  ring  surrounding  the  mouth  ;  into  which,  as  in  Astcrias, 
the  contractile  vesicle,  which  he  considers  to  be  a  receptacle  for 
the  nutrient  fluid,  and  the  antagonist  to  the  tubular  feet,  like¬ 
wise  opens.  The  intestinal  vein  he  regards  as  the  great  agent 


ECIIINODERMATA. 


171 


in  absorbing  nourishment  from  the  intestine,  and  conveying  it 
to  the  vascular  circle  around  the  oesophagus,  from  which  the 
arteries  are  given  off  to  supply  the  whole  body.  These  arte¬ 
ries  are,  1st,  a  long  vessel  to  the  intestine,  which  runs  along 
its  whole  length,  and  anastomoses  freely  with  the  branches 
of  the  intestinal  vein.  2ndly,  Five  arteries  to  the  parts  con¬ 
nected  with  the  mouth.  3rdly,  Five  dorsal  arteries  which  run 
along  the  interior  of  the  shell,  between  the  ambulacral  rows 
as  far  as  the  anal  orifice,  at  which  point  each  dorsal  artery  leaves 
the  osseous  box,  through  an  aperture  specially  provided  for  its 
exit,  and,  arriving  upon  the  outer  surface  of  the  shell,  supplies 
the  soft  external  membrane,  and  in  some  species  may  be  traced 
back  again  between  the  rows  of  ambulacral  suckers  as  far  as  the 
mouth.  These  dorsal  arteries,  like  the  corresponding  vessels  in  Aste- 
ricis ,  supply  the  vascular  origins  of  the  innumerable  protractile  feet. 

(210.)  We  found  in  the  star-fish  that  respiration  was  provided  for 
by  the  free  admission  of  the  external  element  into  the  interior  of  the 
body ;  and  in  Echinus  the  aeration  of  the  blood  is  effected  in  an 
equally  simple  manner.  The  sea-water  is  copiously  admitted  into 
the  peritoneal  cavity  by  a  set  of  membranous  tubes  provided  for 
the  purpose ;  and  its  due  circulation  over  the  lining  membrane  of 
the  shell,  as  well  as  over  the  outer  surfaces  of  the  intestine  and 
other  viscera,  is  provided  for  by  ciliary  movements  visible  in  all 
those  situations,  and  likewise  upon  the  vascular  laminee  connected 
with  the  origins  of  the  feet.* 

Nevertheless,  besides  this  diffused  respiration,  Delle  Chiaje  re¬ 
gards  a  series  of  pinnated  tentacula  in  the  neighbourhood  of  the 
mouth  as  being  in  some  degree  capable  of  performing  the  office  of 
branchiae.  These  organs,  which  are  protruded  through  a  row  of  dis¬ 
tinct  orifices  placed  around  the  oral  aperture  of  the  shell,  are  emi¬ 
nently  vascular ;  and  as  they  present  a  large  surface  to  the  action  of 
the  water,  and  receive  numerous  vessels  from  the  circular  vessel 
which  surrounds  the  mouth,  they  may  no  doubt  very  well  contri¬ 
bute  to  the  complete  exposure  of  the  blood  to  the  influence  of  the 
surrounding  medium. 

(211.)  Little  is  known  concerning  the  nervous  system  of  the 
Echini :  a  few  delicate  filaments  have  been  observed  in  the  neigh¬ 
bourhood  of  the  oesophagus,  apparently  of  a  nervous  character, 
which  renders  it  probable  that  a  nervous  ring  is  placed  in  that  vici¬ 
nity,  resembling  that  already  described  in  Asterias  ;  its  presence, 


*  Dr.  Sharpey,  loc.  cit. 


ECHINODERMATA. 


172 

however,  owing  to  the  complexity  of  the  dental  apparatus,  has  not 
been  satisfactorily  demonstrated,  although  analogy  would  lead  us 
to  infer  the  existence  of  such  an  arrangement. 

(212.)  The  Echini,  like  the  star-fishes,  exhibit  no  distinctions  of 
sex  :  all  are  fertile,  and  in  the  structure  of  their  reproductive  organs, 
display,  if  possible,  greater  simplicity  of  arrangement  than  even  the 
Aster  idee  above  described.  The  ovaria  are  five  delicate  mem¬ 
branous  bags,  quite  distinct  from  each  other,  which  open  exter¬ 
nally  by  as  many  delicate  tubes,  or  oviducts,  as  we  may  term  them. 
The  apertures  through  which  the  eggs  escape  are  easily  seen  upon 
the  outer  surface  of  the  shell,  placed  around  the  anus ;  and  are  re¬ 
cognisable  not  merely  by  their  size,  but  from  the  circumstance  of 
each  perforation  being  placed  in  the  middle  of  a  distinct  oval 
plate  of  the  shell,  distinguished  by  zoological  writers  as  the  ova¬ 
rian  pieces.  The  membranous  sacs  in  which  the  ova  are  secreted 
vary  in  size,  in  proportion  to  the  maturity  of  the  eggs  contained 
within  them,  and  at  certain  times  of  the  year  are  enormously  dis¬ 
tended :  it  is  in  this  state  that  the  44  roe  of  the  sea-egg,”  as  the 
ovaria  are  commonly  called,  is  used  as  an  article  of  food  ;  and  in 
some  countries,  especially  upon  the  shores  of  the  Mediterranean, 
they  are  eagerly  sought  after,  when  in  season,  by  divers  employed 
to  procure  them. 

(213.)  Holothuridce. — The  name  applied  by  naturalists  to  the 
animals  composing  the  next  family  of  Echinodermata  is  derived 
from  a  Greek  word  of  uncertain  application  (oXoQoupiov).  In 
common  language  they  are  generally  known  by  the  appellation 
of  44  sea-cucumbers and  in  fact,  to  a  casual  observer,  the  resem¬ 
blance  which  they  bear  to  those  productions  of  the  vegetable 
kingdom,  both  in  shape  and  general  appearance,  is  sufficiently 
striking.  The  surface  of  these  animals  is  kept  moist  by  a 
mucus,  which  continually  exudes  through  innumerable  pores, 
and  appears  to  be  secreted  by  minute  follicles  imbedded  in  the 
substance  of  the  skin.  The  integument  which  covers,  or  rather 
forms  the  body,  is  entirely  destitute  of  those  calcareous  pieces 
which  encase  the  Echini  and  Star-fishes  ;  but  appears  to  consist  of  a 
dense  fibrous  cutis  of  considerable  thickness,  covered  externally 
with  a  thin  epidermic  layer.  Beneath  the  cutis  is  another  tunic  com¬ 
posed  of  strata  of  tendinous  fibres  crossing  each  other  in  the  midst  of 
a  tissue  of  a  semicartilaginous  nature,  which  is  capable  of  very  great 
distension  and  contraction,  and  serves  by  its  elasticity  to  retain  the 
shape  of  the  body.  Within  this  dense  covering  are  seen  muscular 


ECHINODERMATA. 


173 


Fig.  73. 


bands  running  in  different  directions,  which  by  their  contraction 
give  rise  to  the  various  movements  of  the  creature  ;  of  these  muscle 
five  strong  fasciculi 
assume  a  longitu¬ 
dinal  course,  pass¬ 
ing1  along  the  entire 
length  of  the  ani¬ 
mal  from  the  mouth 
to  the  cloaca,  and 
in  the  interspaces 
between  these  cir¬ 
cular  and  oblique 
muscles  are  readi¬ 
ly  distinguishable. 

The  whole  of  this 
muscular  case  is 
lined  with  a  deli¬ 
cate  membrane  or 
peritoneum,  from 
which  processes 
pass  inwards,  to 
support  the  various 
viscera. 

(214.)  But  al¬ 
though  the  calca¬ 
reous  shell  of  the 
Echinus  is  thus  to¬ 
tally  lost,  the  lo¬ 
comotive  suckers  or 
feet  already  de¬ 
scribed  are  still 
the  principal  agents  employed  in  progression.  In  many  species, 
as  in  that  represented  in  the  annexed  figure,  (Jig.  73,)  these  organs 
are  distributed  over  the  whole  surface  of  the  animal,  and  are  pro¬ 
truded  through  countless  minute  orifices  which  perforate  the  in¬ 
tegument.  In  other  cases,  as  in  H.  frondosa ,  they  are  arranged 
in  five  series,  resembling  the  ambulacra  of  an  Echinus  ;  and  in  some 
instances  they  are  only  found  upon  the  middle  of  the  ventral  sur¬ 
face  of  the  body,  that  forms  a  flattened  disc  upon  which  the  ani¬ 
mal  creeps,  somewhat  in  the  manner  of  a  snail.  The  ambulacral 
feet  themselves,  represented  on  an  enlarged  scale  at  (c),  pre- 


174 


ECIIINODEItMATA. 


cisely  resemble  in  all  the  details  of  their  structure  those  of  the 
Asterias,  and  their  protrusion  and  retraction  are  effected  in  the 
same  manner ;  but,  in  addition  to  these  organs,  we  find  in  some 
genera  moveable  hooks  or  spines  (Jig.  73,  d,)  which  are  likewise 
retractile,  and  most  probably  assist  in  locomotion. 

(215.)  The  mouth  is  a  round  aperture,  as  wide  as  a  goose-quill, 
placed  in  the  centre  of  a  raised  ring  at  the  anterior  extremity  of 
the  body  {Jig.  73,  a).  Around  the  oral  orifice  is  placed  a  circle  of 
tentacula,  which  are  apparently  extremely  sensible,  and  serve  per¬ 
haps  not  only  as  instruments  of  touch,  but  as  prehensile  organs 
used  for  the  capture  of  prey,  or  for  assisting  in  deglutition. 
When  the  sphincter  muscle  which  closes  the  mouth  contracts,  the 
tentacles  are  withdrawn,  and  become  no  longer  visible  externally  ; 
in  this  state,  on  opening  the  animal  (Jig.  74,  5,)  they  are  found 
to  resemble  long  caeca  appended  to  the  commencement  of  the 
oesophagus,  which  have  been  described  by  some  authors  as  forming 
a  salivary  apparatus. 

The  total  deficiency  of  any  external  skeleton,  or  calcareous  frame¬ 
work,  precludes,  of  course,  the  possibility  of  the  existence  of  any 
complex  dental  apparatus  resembling  the  u  lantern  of  Aristotle 
the  only  vestige  of  the  complex  teeth  of  the  Echinidae  which  here 
remains  is  a  small  circle  of  calcareous  pieces,  surrounding  the  opening 
of  the  mouth  :  these  plates,  from  their  extreme  friability,  have  been 
aptly  enough  likened  to  laminae  of  dried  paste  ;  they  may  indeed 
in  some  slight  degree  be  efficient  in  bruising  food  taken  into  the 
mouth,  but  it  is  more  probable  that  they  merely  form  points  of 
insertion  to  the  longitudinal  muscles  of  the  body,  which,  thus  fixed 
around  the  circumference  of  the  oral  orifice,  will  by  their  contrac¬ 
tion  powerfully  dilate  that  aperture  for  the  purpose  of  taking  in 
nourishment. 

The  alimentary  canal  is  of  great  length,  but,  like  that  of  the 
Echinus,  presents  no  stomachal  dilatation ;  from  the  mouth, 
(fig-  74,  a,)  in  which  a  bristle  is  placed,  it  descends  to  the  anal 
extremity  of  the  body,  where,  turning  upon  itself,  it  again  mounts 
up  towards  its  commencement,  whence  turning  back  again,  and 
forming  numerous  convolutions,  (d,  d,  d,)  it  once  more  passes 
backwards,  and,  becoming  restricted  near  its  termination,  opens 
into  a  large  membranous  cavity  (e)  which  may  be  called  the 
cloaca.  Throughout  the  whole  of  this  long  course,  the  alimentary 
tube  is  surrounded  with  a  membrane  derived  from  the  peritoneal 
lining  of  the  visceral  cavity,  which  forms  delicate  mesenteric  folds 
connecting  it  to  the  walls  of  the  body,  and  supporting  it  through 


ECHINODERMATA. 


175 


its  entire  length.  The  whole  intestine  is  generally  found  distended 
with  sand,  in  which  may  be  detected  the  debris  of  corals,  algse, 
fuci,  and  other  marine  substances. 

(£16.)  In  the  structure  of  the  respiratory  apparatus,  the  Holothu- 
ridse  differ  materially  from  the  rest  of  the  Echinodermata,  and  in 
fact  from  all  other  animals.  In  the  Asterida  and  Ecliiiiidee ,  the 
reader  will  remember  that  respiration  was  effected  by  the  free 
admission  of  sea- water  into  the  interior  of  the  animal,  which,  thus 
penetrating  to  every  part  of  the  body,  rendered  the  existence  of 
special  respiratory  organs  unnecessary.  In  the  Holothuria  like¬ 
wise  the  aeration  of  the  circulating  fluid  is  provided  for  by  allow¬ 
ing  the  surrounding  element  freely  to  enter  into  the  internal  parts 
of  the  creature ;  but  in  this  case,  instead  of  bathing  the  surfaces  of 
the  viscera,  the  water  is  confined  in  a  peculiar  system  of  ramifying 
canals,  forming  a  structure  of  great  beauty,  and,  from  its  singularity, 
extremely  interesting  in  a  physiological  point  of  view.  We  have 
seen  that  the  intestinal  canal  terminates  in  a  membranous  recep¬ 
tacle  or  cloaca  (Jig.  74,  e,)  contained  within  the  cavity  of  the 


Fig.  74. 


176 


ECHINODERMATA. 


abdomen,  to  the  walls  of  which  it  is  attached  by  delicate  fleshy 
bands  :  this  cloacal  cavity  communicates  with  the  exterior  of  the 
body  by  a  wide  orifice  twice  as  large  as  the  aperture  of  the  mouth, 
through  which,  in  the  figure,  a  bristle  (f)  has  been  passed ;  it  is 
by  this  hole  that  the  water  required  for  the  purpose  of  respiration 
is  taken  in,  and  it  is  then  forced  by  the  muscular  walls  of  the  cloaca 
itself  through  the  whole  system  of  respiratory  canals  by  which  its 
distribution  is  effected.  The  organs  of  respiration  commence  at 
the  upper  part  of  the  cloaca,  near  the  termination  of  the  intes¬ 
tine,  by  a  large  opening  leading  to  a  wide  membranous  tube,  which 
immediately  divides  into  two  vessels  (g,  g,)  forming  the  main 
trunks  of  the  beautiful  arborescent  branchise,  which  extend  to  the 
opposite  extremity  of  the  body,  giving  off  in  their  course  numerous 
lateral  branches  that  divide  and  subdivide,  so  as  to  form  what  has 
been  not  inaptly  termed  the  “  respiratory  tree,”  until  they  ulti¬ 
mately  terminate  in  minute  vesicular  caeca,  into  which  the  water 
derived  from  the  cloaca  of  course  penetrates.  One  division  of  this 
elegant  apparatus  is  maintained  in  close  contact  with  the  walls  of 
the  body  by  a  series  of  delicate  tendinous  bands,  while  the  other 
becomes  applied  to  the  convolutions  of  the  intestines,  with  which 
it  is  likewise  united.  It  is  this  last-mentioned  division  which 
would  appear  to  be  specially  provided  for  the  oxygenization  of 
the  nutritive  fluids  taken  up  by  the  intestinal  veins. 

(217.)  The  circulation  of  the  blood  in  the  Holothuria ,  as  in 
the  Echinus ,  is  still  but  imperfectly  understood,  and  considerable 
difference  of  opinion  upon  this  subject  will  be  found  in  the 
writings  of  anatomists.  According  to  Tiedemann,*  innumerable 
small  veins  collect  the  blood  and  nutritive  products  of  diges¬ 
tion  from  the  intestine,  and  convey  them  into  a  large  central 
vessel,  {Jig.  74,  f,  «,)  from  whence  the  circulating  fluid  passes 
by  other  trunks  (/,  /,)  to  the  respiratory  tree  ;  hence  it  is  re¬ 
turned  by  vessels  (partly  represented  at  m)  to  the  intestinal 
artery  ( k ),  by  which  it  is  again  distributed  over  the  intestinal 
parietes. 

Delle  Cliiaje  gives  a  different  account  of  the  arrangement  of 
the  vascular  system  in  these  creatures,  which  he  seems  to  have 
investigated  with  his  usual  untiring  perseverance.  According  to 
the  last-mentioned  anatomist,  the  blood  is  taken  up  from  the  in¬ 
testines  by  a  complicated  system  of  veins,  the  main  trunks  of  which 


*  Anat.  der  Rohren,  Holothurie;  fol.  1316. 


ECHINODERMATA. 


177 


are  indicated  in  tlie  annexed  diagram  (Jig.  75)  by  the  letters 
c,  e,  p,  p ,  q  ;  these  communicate  with  each  other  not  only  by 
the  intervention  of  numerous 
anastomosing  branches,  (d,  d,) 
but  likewise  by  means  of  de¬ 
licate  vascular  plexuses  (a) 
passing  between  them.  All 
these  veins  terminate  in  two 
large  venous  canals  (o),  which 
convey  the  blood  and  nutri¬ 
ment  absorbed  from  the  in¬ 
testine  to  a  vascular  circle 
(g),  placed  around  the  com¬ 
mencement  of  the  oesopha¬ 
gus,  which  corresponds  with 
the  circular  vessel  around 
the  mouth  of  the  Echinus. 

This  circle  Delle  Chiaje  re¬ 
gards  as  the  centre  of  the 
arterial  system,  in  communi¬ 
cation  with  which  is  the  con¬ 
tractile  vesicle  (/)■>  which  he 
looks  upon  as  a  reservoir  for 
the  nutritive  fluid.  From  the  circular  vessel  various  arteries  are 
given  off ;  large  branches  pass  into  the  tentacula  around  the 
mouth  («),  so  that  these  organs,  besides  being  instruments  of  touch, 
from  the  extent  of  surface  that  they  present,  and  their  great  vas¬ 
cularity,  are  most  probably  important  auxiliaries  in  respiration. 
Five  other  large  arteries,  derived  from  the  same  source,  (k,  &,  /,) 
pass  backwards  to  supply  the  integuments  of  the  body,  and  also  to 
communicate  by  small  cross  branches  with  the  little  vesicular 
organs  connected  with  the  locomotive  suckers,  which  in  the 
opinion  of  Delle  Chiaje  are  distended  with  the  same  blood  as 
that  which  circulates  through  the  rest  of  the  body.  The  descend¬ 
ing  arteries,  thus  destined  to  supply  the  integument  and  distend 
the  prehensile  suckers,  run  in  the  centre  of  each  of  the  five  lon¬ 
gitudinal  fasciculi  of  the  muscular  tunic  of  the  skin  as  far  as  the 
cloaca,  and  exhibit  in  their  distribution  a  remarkable  exception  to 
the  usual  arrangement  of  the  arterial  system,  which  is  generally 
found  to  divide  and  subdivide  continually  into  smaller  and  still 
smaller  canals,  but,  in  the  case  before  us,  there  would  seem  to  be 

N 


178 


ECHINODERMATA. 


no  diminution  in  the  size  of  the  main  trunks  as  they  approach 
their  termination  ;  and  the  cross  branches  given  off  in  their  course, 
instead  of  ramifying,  all  end  in  the  minute  ambulacral  vesicles,  to 
the  injection  of  which  they  would  appear  to  be  subservient. 

(218.)  The  generative  system  of  the  Holothuria  is  essentially 
similar  to  that  found  in  the  Asteridse,  consisting  of  long  ovigerous 
caeca,  without  any  superadded  parts  which  might  be  regarded  as  con¬ 
tributing  to  the  impregnation  of  the  ova.  The  germs  are  secreted 
in  slender  ramified  tubes  (Jig-  74,  A,  A,)  which  are  collected  into 
one  great  bundle,  and  open  externally  by  a  common  canal  in  the 
neighbourhood  of  the  mouth,  not  into  the  oesophagus  as  Cuvier 
supposed,  but  upon  the  back  of  the  animal.  These  generative 
caeca  at  certain  times  of  the  year  become  enormously  distended, 
being  at  least  thirty  times  larger  than  when  not  in  a  gravid  state  ; 
if  examined  at  this  period,  they  are  found  to  contain  a  whitish, 
yellowish,  or  reddish  fluid,  in  which  the  ova  are  suspended,  but 
nothing  is  known  concerning  the  mode  of  the  expulsion  of  the 
eggs,  or  their  subsequent  developement. 

(21.9o)  The  special  instruments  of  touch,  the  only  sense  allotted 
to  these  animals,  are  the  branched  tentacula  around  the  mouth, 
which  seem  by  far  the  most  irritable  parts  of  the  body.  The 
nervous  system  is  so  obscurely  developed  that  even  Delle  Cliiaje 
was  unable  to  detect  any  traces  of  its  existence  ;  nevertheless 
there  is  little  doubt  of  the  presence  of  nervous  threads  in  the 
muscular  envelope  of  the  animal,  although,  from  the  dense  tissues 
in  which  they  are  imbedded,  it  is  next  to  impossible  to  display  their 
course  ;  most  probably,  as  in  the  Echinus  and  Asterias,  these  com¬ 
municate  with  a  circular  cord  which  embraces  the  oesophagus.  No 
ganglia  have  as  yet  been  discovered  even  in  the  Holothuria ;  and 
consequently,  although  the  muscular  actions  of  the  body  are  no 
doubt  associated  by  nervous  filaments,  the  movements  of  these 
creatures  appear  due  rather  to  the  inherent  irritability  of  the 
muscular  tissues  themselves,  than  to  be  under  the  guidance  and 
control  of  the  animal.  In  many  species,  the  slightest  irritation 
applied  to  the  surface  of  the  body  causes  such  powerful  contrac¬ 
tions  of  the  integument  that  the  thin  membranes  of  the  cloaca, 
unable  to  withstand  the  pressure,  become  lacerated,  and  large 
portions  of  the  intestine  and  other  viscera  are  forced  from  the  anal 
aperture.  So  common  indeed  is  the  occurrence  of  this  circum¬ 
stance  as  to  have  induced  the  older  anatomists  to  suppose  that,  by 
a  natural  instinct,  the  animals  when  seized  vomited  their  own 


ECH1N0DERMATA. 


179 


bowels.  It  is  in  fact  extremely  difficult  to  obtain  perfect  speci¬ 
mens  of  the  Holothuridse,  from  the  constant  occurrence  of  this  ac¬ 
cident  :  but,  although  annoying  to  the  naturalist,  such  a  pheno¬ 
menon  affords  the  physiologist  an  important  lesson,  teaching  that 
here,  as  in  the  lower  Zoophytes,  the  muscular  system  possesses  an 
innate  contractile  power,  which  would  seem  only  to  be  destroyed 
by  incipient  putrefaction  ;  but  so  little  is  this  contractility  under 
command,  that,  once  excited  to  an  inordinate  extent,  it  becomes 
totally  unmanageable,  even  though  its  continuance  inevitably  causes 
the  destruction  of  life. 

(220.)  Fistularidtf, — In  order  to  complete  our  account  of  the 
organization  of  the  Echinodermata,  we  have  still  to  investigate  the 
structure  of  the  Fistularidcc ;  a  group  which,  from  the  external 
appearance  of  the  individuals  composing  it,  and  the  total  absence  of 
the  tubular  feet  met  with  in  other  families,  has  been  improperly 
separated  by  some  modern  writers  from  the  class  under  consideration. 
Nevertheless,  we  shall  find  the  position  assigned  to  these  animals  by 
Cuvier  to  be  in  strict  accordance  with  the  character  both  of  their 
outward  form  and  internal  structure  ;  only,  instead  of  placing  them 
with  the  lowest  of  the  Echinoderms,  they  would  have  been  more 
properly  situated  at  the  head  of  the  class,  as  most  nearly  ap¬ 
proximating  the  Annelida  in  all  the  details  of  their  economy.  We 
have  already  given  a  description  of  the  outward  form  of  a  Fistu- 
laria  (§  186),  and  seen  the  completely  annulose  condition  of  its 
body,  although  the  radiating  tentacula  around  the  mouth  are  evi¬ 
dently  analogous  to  those  of  the  Holothuria  already  described.  We 
are  indebted  to  the  patient  researches  of  Pallas  and  Delle  Chiaje*  for 
almost  all  that  is  known  concerning  the  anatomical  structure  of  these 
animals,  and  the  descriptions  of  the  Siponculus  phalloides  and  bala- 
nophorus  have  left  little  to  be  desired  by  the  systematic  zootomist. 

The  Siponculus  inhabits  shallow  seas,  concealing  itself  at  the 
bottom  in  holes  which  it  excavates  in  the  sand.  Having  once 
located  itself,  it  is  seldom  found  to  quit  its  concealment,  but,  re¬ 
taining  its  hold  upon  the  sides  of  the  retreat  which  it  inhabits  by 
dilating  the  posterior  part  of  its  body,  it  occasionally  protrudes  its 
head  from  the  orifice,  either  for  the  purpose  of  procuring  food,  or 
of  respiring  more  freely  the  element  in  which  it  lives. 

These  animals  are  much  sought  after  by  fishermen,  who  employ 
them  as  baits  for  their  hooks  ;  and  one  species,  Siponculus  edulis , 
is  used  in  China  as  an  article  of  food. 

*  Storia  e  Notomia  delle  Animale  senza  Vertebre  del  Regno  di  Napoli. — Napoli,  1823. 

N  2 


180 


ECHINODERMATA. 


(221.)  The  body  is  covered  externally  with  a  delicate  cuticle, 
easily  separable  by  maceration  or  immersion  in  spirit  of  wine ;  and 
when  thus  detached  it  forms  so  loose  a  covering,  that  Linnseus, 
deceived  by  the  appearance  of  an  animal  thus  preserved,  applied  to 
it  the  name  of  Siponculus  saccatus. 

The  muscular  investment,  placed  beneath  the  skin,  is  composed 
of  strong  fasciculi  arranged  in  three  distinct  layers.  The  external 
stratum  is  disposed  in  circular  rings,  beneath  which  spiral  fibres 
may  be  observed  crossing  each  other  at  various  angles  ;  and  lastly, 
the  inner  coat  is  made  up  of  about  thirty  powerful  longitudinal 
bands,  extending  from  one  extremity  of  the  body  to  the  other. 
Such  an  arrangement  is  evidently  sufficient  for  the  general  move¬ 
ments  of  the  creature  ;  but,  in  order  to  facilitate  the  retraction  of  the 
tentacular  apparatus  around  the  mouth,  eight  additional  muscles 
surround  the  oesophagus,  and  by  their  action  the  whole  of  the  oral 
apparatus  is  completely  inverted  and  drawn  inwards. 

The  tentacula  around  the  oral  orifice  are  the  principal  agents 
employed  in  seizing  and  swallowing  food,  an  office  to  which  they 
are  peculiarly  adapted  by  their  great  sensibility  and  power  of  con¬ 
traction  ;  but,  as  we  have  found  to  be  generally  the  case  among 
the  Echinodermata,  sand  and  fragments  of  shell  form  the  great 
bulk  of  the  contents  of  the  intestine,  so  that  it  is  by  no  means 
easy  to  state  precisely  the  nature  of  the  food  upon  which  the 
Siponculi  are  nourished. 

(222.)  The  structure  of  the  alimentary  canal,  and  of  the  nutrient 
apparatus,  conforms  too  accurately  with  what  we  have  already  seen 
in  Holothuria  to  permit  of  a  moment’s  hesitation  concerning  the 
relationship  which  exists  between  the  apodous  Echinodermata 
and  the  Holothuridse.  The  oesophagus  (Jig.  76,  b )  is  narrow,  and 
soon  dilates  into  a  kind  of  stomachal  receptacle  (c)  ;  but,  although 
the  diameter  of  the  intestinal  tube  is  at  this  point  perceptibly 
larger  than  in  any  other  part  of  its  course,  there  is  no  other  pecu¬ 
liarity  to  distinguish  it  from  the  rest  of  the  intestine.  In  the 
Annelida,  the  digestive  apparatus  is  invariably  straight,  travers¬ 
ing  the  body  from  one  extremity  to  the  other,  a  circumstance  which 
distinguishes  them  remarkably  from  the  Echinoderms  we  are  now 
considering  ;  for  in  Siponculus  we  find  a  digestive  canal,  six  or 
seven  times  the  length  of  the  animal,  within  which  it  is  folded 
upon  itself  in  various  distinct  convolutions.  Leaving  the  stomach, 
if  we  may  so  call  the  dilatation  above  alluded  to,  it  passes  down 
(d,  (/,  c/,)  nearly  to  the  tail,  where  it  is  reflected  upon  itself,  and 


ECHINODEllMATA. 


181 


Fig.  76* 


■nNVI/w 


mounts  lip  again  as  far  as  the  point  where  it  commenced  ;  here  it 
again  turns  back,  and,  once  more  reaching  the  bottom  of  the  tegu¬ 
mentary  sac,  becomes  a  second 
time  directed  upwards,  and  re¬ 
ascends  as  far  as  the  point  (e), 
where  the  anus  is  situated. 

It  is  easy  to  account  for  this 
extreme  length  of  the  intestine 
when  we  consider  the  nature  of 
the  materials  used  as  food,  and 
the  small  proportion  of  nutri¬ 
ment  contained  among  the  sand 
and  broken  shells  which  fill  the 
digestive  canal  :  but  the  re¬ 
markable  position  of  the  anal 
aperture  is  only  explicable  by  a 
reference  to  the  peculiar  habits  of 
the  creature ;  for  living  as  it  does 
in  a  narrow  excavation  bored  in 
the  sand,  from  which  it  seldom 
issues,  had  the  excrements  been 
discharged,  as  in  Holothuria, 
through  a  terminal  orifice,  their 
accumulation  at  the  bottom  of 
the  hole  would  soon  expel  the 
animal  from  its  retreat  ;  but,  by 
the  arrangement  adopted,  it  is 
only  necessary  that  the  anterior 
part  of  the  body  should  be  pro¬ 
truded  from  its  concealment, 
and  the  excrementitious  matter 
may  be  cast  out  without  incon¬ 
venience.  The  intestine  is  retained  in  situ,  and  supported  at 
all  points,  by  innumerable  tendinous  bands,  which  arise  from  the 
interior  of  the  muscular  walls  of  the  body,  and  form  a  kind  of 

mesenterv. 

•> 

(223.)  In  Siponculus ,  the  character  of  the  circulating  system  is  in 
all  essential  points  strictly  analogous  to  that  of  the  other  Ecliinoder- 
mata ;  and  moreover,  from  the  superior  concentration  visible  in 
every  part,  we  have  the  multiplied  organs  of  the  other  families  ex¬ 
hibiting  so  much  simplicity  of  arrangement,  that,  whatever  may 


182 


ECH I  NODERM  AT  A. 


have  appeared  obscure  or  complicated  in  our  description  of  Echi¬ 
nus  and  Holothuria  will  receive  elucidation  from  the  diagram¬ 
matic  form  in  which  all  the  organs  connected  with  the  circulation  of 
the  blood  are  represented  in  the  adjoined  figure.  The  intestinal 
vein  (m)  may  be  traced  along  the  entire  length  of  the  alimentary 
canal  ;  commencing  near  the  anal  extremity  of  the  bowel,  it  fol¬ 
lows  all  its  convolutions,  and  receives  from  every  part  the  minute 
vessels  which  ramify  over  the  intestinal  walls.  These  venous 
ramifications  undoubtedly  perform  the  office  assigned  to  the  lac- 
teals  of  higher  animals,  and  imbibe  the  nutritive  particles  furnished 
by  digestion,  which,  of  course,  are  conveyed  into  the  great  venous 
trunk  (m).  Arrived  opposite  to  the  termination  of  the  oesopha¬ 
gus,  the  intestinal  vein  divides  into  two  vessels  :  one  performing 
the  office  of  a  branchial  artery,  by  conveying  a  part  of  the  blood 
to  the  respiratory  organs  in  the  neighbourhood  of  the  mouth ;  the 
other,  which  we  may  call  the  aorta,  distributing  the  remainder  to 
all  parts  of  the  tegumentary  system.  The  branchial  vessel  (?j) 
runs  from  the  bifurcation  of  the  intestinal  vein  to  the  base  of  the 
oral  tentacles,  where  it  forms  a  vascular  circle  around  the  com¬ 
mencement  of  the  cesophagus,  analogous  to  that  which  we  have  seen 
in  Holothuria  ;  and  in  connexion  with  this  circular  vessel  we  find 
the  “  ampulla  Poliana  ”  (//),  which  Delle  Chiaje  conceives  to  be 
here,  as  in  other  cases,  a  receptacle  for  the  circulating  fluid.  From 
the  vascular  circle  around  the  mouth,  vessels  are  given  off,  to  ramify 
minutely  through  the  substance  of  the  tentacula  (o),  so  that  these 
appendages  may  be  considered  as  respiratory  organs,  like  those  of 
Holothuria.  The  other  vessels  derived  from  the  oral  circle  have 
not  been  traced  ;  but  we  may  conclude  from  analogy  that  arteries 
supplying  the  mouth  and  alimentary  canal  are  furnished  from  this 
source. 

The  aorta  (o)  is  the  other  large  vessel  derived  from  the  intes¬ 
tinal  vein,  and  is  seen  to  pass  in  a  flexuous  course  from  its  origin 
to  the  posterior  extremity  of  the  body,  following  the  median  line, 
and  giving  off  transverse  branches  on  both  sides  opposite  to  every 
ring  of  the  muscular  integument.  At  the  commencement  of  the 
aorta  is  a  dilated  vesicle  (/),  which  may  be  looked  upon  as  a  heart 
(auricle,  Delie  Chiaje).  The  vesicle  alluded  to  is  of  a  conical 
form,  the  apex  of  the  cone  being  directed  towards  the  tail 
of  the  animal ;  and,  from  the  impossibility  of  making  mercury 
pass  from  the  aorta  through  this  organ  in  the  direction  of  the 
intestinal  vein,  it  is  probable  that  it  contains  an  apparatus 


ECHINODERMATA. 


183 


of  valves  so  disposed  as  to  prevent  any  retrograde  motion  of  the 
blood.  At  the  termination  of  the  aorta  there  appears  to  be  a 
second  enlargement,  to  which  the  name  of  ventricle  has  been 
given,  and  which  is  perhaps  also  capable  of  contraction,  so  as 
to  assist  in  the  propulsion  of  the  circulating  fluid.  The  blood 
of  these  animals  is  of  a  purple  colour  in  the  veins,  but  red  in  the 
arterial  vessels. 

(224.)  We  have  seen  that  the  tentacula  are,  from  their  vascu¬ 
larity,  well  adapted  to  fulfil  the  office  of  a  respiratory  apparatus  ;  but 
it  may  be  presumed  that  they  are  not  the  only  agents  by  which 
respiration  is  accomplished.  Upon  the  outer  surface  of  the  body, 
in  the  neighbourhood  of  the  anal  opening,  two  apertures  are  visible, 
which  lead  into  two  long  sacculi  (  f,  j)),  the  entrance  being 
guarded  by  muscular  fibres  (g)  :  their  texture  presents  transverse 
and  longitudinal  strise,  and  they  contract  spontaneously  even 
after  the  animal  is  dead  ;  internally  they  are  lined  with  a  mucous 
membrane.  The  use  of  these  organs  is  not  precisely  known  ; 
Cuvier  regarded  them  as  belonging  to  the  generative  system, 
while  Delle  Chiaje  looks  upon  them  as  respiratory  organs,  inter¬ 
mediate  in  structure  between  the  arborescent  tubes  of  Holothuria , 
and  the  respiratory  vesicles  which  we  shall  afterwards  find  in  some 
of  the  Annelida. 

(225.)  In  this  elevated  form  of  the  Echinodermata,  so  nearly 
allied  to  the  Homogangliate  type,  we  may  naturally  expect  a 
more  complete  clevelopement  of  nervous  ganglia  than  we  have  yet 
met  with  in  the  class ;  and  accordingly  we  find,  upon  the  an¬ 
terior  part  of  the  oesophagus,  two  little  nervous  tubercles  (i), 
from  which  nervous  filaments  issue  to  be  distributed  to  different 
parts  of  the  body ;  one  of  these  in  particular  may  be  traced 
along  the  whole  length  of  the  intestine  from  the  mouth  to  the 
anus. 

(226.)  We  are  entirely  ignorant  concerning  the  mode  of  repro¬ 
duction  in  these  creatures,  as  no  generative  apparatus  has  as  yet 
been  distinctly  pointed  out.  Nevertheless,  at  certain  seasons  of 
the  year,  on  opening  the  visceral  cavity,  it  is  found  to  be  filled 
with  a  fluid  of  a  reddish  tint,  in  which  thousands  of  minute  white 
bodies  resembling  millet-seeds  are  seen  to  float :  should  these 
be  ova,  they  are  probably  expelled  through  an  orifice  which  exists 
in  the  vicinity  of  the  tail. 


184 


CHAPTER  XII. 

HOMOGANGLIATA  (Owen). 

Articulate  (Cuv.)  ;  Annulosa  (Mac  Leay). 

(227.)  The  third  great  division  of  the  animal  kingdom  includes 
an  immense  number  of  living  beings  adapted  by  their  conforma¬ 
tion  to  exist  under  a  far  greater  variety  of  circumstances  than  any 
which  wTe  have  hitherto  had  an  opportunity  of  examining.  The 
feeble  gelatinous  bodies  of  the  Acrita  are  obviously  only  adapted 
to  an  aquatic  life  ;  and  accordingly  they  are  invariably  found  either 
to  inhabit  the  waters  around  us,  or  to  be  immersed  in  the  juices  of 
living  animals  upon  which  they  subsist.  The  Nematoneura, 
likewise,  are  all  of  them  too  imperfect  in  their  construction  to 
admit  of  their  enjoying  a  terrestrial  existence,  for,  possessing  no 
nervous  centres  adequate  to  give  force  and  precision  to  their  move¬ 
ments,  they  are  utterly  incapable  of  possessing  external  limbs 
endowed  with  sufficient  power  and  activity  to  be  efficient  agents  in 
ensuring  progression  upon  land  ;  neither  are  any  of  them  furnished 
with  those  organs  of  sense  which  would  be  indispensable  for  the 
security  of  creatures  exposed  to  those  innumerable  accidents  to 
which  the  inhabitants  of  a  rarer  element  are  perpetually  obnoxious  : 
the  Nematoneura  therefore  are,  from  their  organization,  neces¬ 
sarily  confined  to  a  watery  medium. 

But  the  type  of  structure  met  with  in  the  Homogangliata 
admits  of  far  higher  attributes,  and  allows  the  enjoyment  of  a  more 
extended  sphere  of  existence :  senses  become  developed  propor¬ 
tionate  to  the  increased  perfection  of  the  animal ;  limbs  are  pro¬ 
vided  endowed  with  strength  and  energy  commensurate  with  the 
developement  of  the  nervous  ganglia  which  direct  and  control 
their  movements  ;  and  instincts  are  manifested  in  relation  with  the 
increased  capabilities  and  more  exalted  powers  of  the  various 
classes  as  they  gradually  rise  above  each  other  in  the  scale  of 
animal  developement. 

(228.)  The  most  obvious,  though  not  the  most  constant,  cha¬ 
racter  which  distinguishes  the  creatures  we  are  now  about  to  de¬ 
scribe,  is  met  with  in  their  external  conformation  ;  they  are  all  of 
them  composed  of  a  succession  of  rings  formed  by  the  skin  or 


HOMOGANGLIATA. 


185 


outward  integument,  which  from  its  hardness  constitutes  a  kind 
of  external  skeleton,  supporting  the  body,  and  giving  insertion  to 
the  muscles  provided  for  the  movements  of  the  animal.  In  the 
class  Cirrhopoda  alone  is  this  external  characteristic  wanting, 
and  the  Homogangliate  organization  masked  by  a  tegumentary  tes¬ 
taceous  coat  of  mail,  which  they  seem  to  have  borrowed  from  the 
molluscous  type.  In  the  lowest  forms  of  the  Articulata  the 
body  is  extremely  elongated,  and  the  rings  proportionately  nu¬ 
merous  ;  the  integument  moreover  is  soft  and  yielding,  and,  as  a 
necessary  consequence,  the  limbs  appended  to  the  different  seg¬ 
ments  are  feeble  and  imperfect :  such  is  the  structure  met  with  in 
the  worms,  or  Annelidans,  properly  so  called. 

As  we  advance,  we  perceive  the  tegumentary  rings  to  become 
less  numerous,  and  the  skin  of  a  denser  and  more  firm  texture, 
adapted  to  support  the  action  of  stronger  and  more  powerful 
muscles  ;  the  limbs  likewise  become  more  elaborately  formed,  their 
movements  more  free  and  energetic,  and  the  instruments  of  sight 
and  touch  begin  to  assume  considerable  perfection  of  structure. 
This  state  of  developement  we  find  in  the  Myriapoda  or 
Centipedes. 

In  the  Insects  the  concentration  of  the  external  skeleton  is 
still  more  remarkable,  and  the  integument  assumes  a  hardness 
and  solidity  proportioned  to  the  vigorous  movements  of  which 
the  limbs  are  now  capable  ;  the  rings  or  segments  of  the  body, 
hitherto  distinct,  become  more  or  less  firmly  soldered  toge¬ 
ther  in  those  parts  where  the  greatest  strength  and  firmness  are 
necessary,  and  scarcely  any  traces  are  left  to  indicate  their  ex¬ 
istence  as  separate  pieces ;  so  that,  instead  of  exhibiting  that 
succession  of  similar  segments  seen  in  the  Centipede,  the  body 
is  apparently  divided  into  three  distinct  portions,  viz.  the  head, 
which  contains  the  organs  of  the  senses  and  the  parts  of  the 
mouth ;  the  thorax ,  sustaining  the  limbs  or  instruments  of  pro¬ 
gression  ;  and  the  abdomen ,  enclosing  the  viscera  subservient  to 
nutrition  and  reproduction. 

In  the  fourth  division  of  articulated  animals,  namely  the 
Arachnidans  or  Spiders ,  a  still  greater  consolidation  of  the 
external  skeleton  is  visible  ;  for  in  them  even  the  separation 
between  the  head  and  the  thorax  is  obliterated,  and  it  is  in  the 
abdomen  only  that  the  segments  of  the  body  are  recognisable. 

Lastly,  in  the  Crustaceans  we  have  various  modifications  of 
the  outward  skeleton  adapted  to  the  habits  of  the  different  tribes  ; 


186 


H  O  M  O  G  A  N  G  L I A  T  A . 


in  tlie  least  perfect  species,  which  are  all  aquatic,  the  rings  of  the 
skeleton  are  perfectly  distinct  and  separate,  resembling  those  of 
the  Myriapoda  ;  but  in  the  stronger  and  more  predacious  tribes,  the 
pieces  of  the  head  and  thorax  become  solidly  fixed  together ;  and  in 
those  forms  most  adapted  to  a  terrestrial  life,  namely,  the  crabs, 
almost  all  traces  of  distinction  between  the  thoracic  segments  are 
lost  in  the  construction  of  the  calcareous  shield  which  covers  and 
protects  their  whole  body. 

(229.)  We  see  therefore  in  the  above  rapid  sketch  of  the  dif¬ 
ferent  classes  which  compose  the  articulated  division  of  the  animal 
kingdom,  that,  as  their  organization  assumes  greater  perfection, 
the  different  segments  of  the  external  skeleton  coalesce  and  become 
united  together,  so  as  to  give  greater  strength  to  those  parts  which 
are  more  immediately  connected  with  locomotion  or  the  destruc¬ 
tion  of  prey  ;  let  us  now  examine  the  nature  of  the  nervous  appa¬ 
ratus  which  characterises  the  Homogang  li  at  a,  and  observe  the 
relation  which  the  outward  form  of  the  body  bears  to  the  arrange¬ 
ment  of  this  primary  system  of  the  animal  economy.  In  tracing 
the  developement  of  animal  structure,  on  the  first  appearance  of 
any  new  apparatus,  it  is  by  no  means  unusual  to  find  it  repeated 
again  and  again  in  the  same  creature,  divided  as  it  were  into 
distinct  portions,  prior  to  its  appearance  in  its  more  highly  organ¬ 
ized  and  perfect  condition.  Thus  in  Coenurus  cerebralis,  §  110, 
the  reader  will  remember  numerous  mouths  were  dispersed  over 
different  parts  of  the  simple  sac  composing  the  stomach  of  the 
animal ;  in  the  compound  Polyps,  §  36,  innumerable  digestive 
organs  ministered  to  the  support  of  one  common  mass  ;  in  the 
Tape-worm,  §  117,  the  generative  apparatus  was  repeated  in  nearly 
every  segment  of  its  compound  body  ;  and,  did  we  choose  to  antici¬ 
pate,  other  examples  might  be  adduced,  derived  from  the  more  per¬ 
fect  animals,  exemplifying  the  same  fact.  We  shall  not  be  sur¬ 
prised,  therefore,  to  find  that,  on  the  first  developement  of  a 
nervous  system  provided  with  ganglionic  masses,  these  nervous 
centres,  or  brains  as  we  might  term  them,  are  very  numerous,  and, 
instead  of  being  united,  are  located  in  different  parts  of  the  system. 
In  the  humblest  forms  of  the  Annulosa  it  would  seem  indeed  that 
every  ring  of  the  body  contained  a  complete  nervous  apparatus, 
consisting  of  a  pair  of  ganglia  and  a  set  of  nerves  destined  to 
supply  the  particular  segment  in  which  they  are  lodged.  All  these 
different  brains,  belonging  to  the  individual  segments,  communicate 
with  each  other  by  nervous  filaments,  so  that  a  continuous  chain  is 


HOMOGANG  LI  AT  A. 


187 


formed,  passing  along  the  whole  length  of  the  body.  With  the 
exception  of  the  anterior  pair  of  ganglia,  or  that  contained  in  the 
first  ring,  which  we  may  call  the  head  of  the  worm,  the  nervous 
centres  are  arranged  along  the  ventral  region  of  the  body,  that  is, 
beneath  the  alimentary  canal  ;  but  the  anterior  pair  itself  is  inva¬ 
riably  placed  upon  the  dorsal  aspect  of  the  animal,  and  communi¬ 
cates  with  the  rest  by  a  nervous  collar  which  embraces  the  com¬ 
mencement  of  the  oesophagus.  The  nervous  masses  placed  along 
the  belly  would  seem  to  preside  specially  over  the  movements  of 
the  segments  to  which  they  belong,  and  to  have  little  to  do  with 
sensation  or  the  perception  of  external  objects  ;  whilst  the  anterior 
or  cephalic  pair,  from  the  constancy  of  their  communication  with 
the  organs  of  the  senses,  would  appear  peculiarly  in  relation  with 
the  perceptive  faculties  of  the  creature. 

(230.)  It  may  be  taken  as  a  general  law,  that  the  perfection  of 
the  nervous  system  of  any  animal  may  be  estimated  by  the  propor¬ 
tionate  size  of  the  central  ganglia  connected  with  it,  upon  the 
developement  of  which  both  the  energy  of  the  actions  of  the 
body  and  the  completeness  of  perception  depend  ;  and,  by  follow¬ 
ing  out  this  great  principle,  we  shall  be  easily  able  to  account  for 
the  progressive  steps  by  which  the  Articulata  become  more  and 
more  perfectly  organized,  as  we  trace  them  in  the  series  above  in¬ 
dicated.  In  proportion  as  we  have  found  the  segments  of  the 
body  to  become  less  numerous,  the  appended  limbs  stronger,  the 
outward  skeleton  more  dense,  and  the  muscular  powers  more  ener¬ 
getic,  we  shall  find  the  abdominal  ganglia  to  diminish  in  number 
by  becoming  consolidated  into  larger  masses,  increasing  in  size  and 
energy  in  accordance  with  the  developement  of  the  limbs  over 
which  they  preside :  and  in  the  same  manner  we  shall  observe  the 
senses  assume  greater  perfection  of  structure,  and  the  instincts 
become  more  developed,  as  we  find  the  cephalic  or  anterior  pair  of 
brains  increasing  in  proportionate  bulk. 

These  observations  will  suffice  to  introduce  the  student  to  the 
Homogangliate  division  of  the  animal  world,  and  to  direct  his  at¬ 
tention  to  thos6  physiological  points  connected  with  the  nature  of 
their  nervous  system  which  will  be  more  fully  laid  before  him  in 
the  following  pages. 


188 


CHAPTER  XIII. 

Annelida.*  Red-blooded  Worms.  (Cuv.) 

(231.)  The  lowest  class  of  articulated  animals  comprehends  an  ex¬ 
tensive  series  of  creatures  generally  grouped  together  under  the  com¬ 
mon  name  of  Worms.  In  the  outward  form  of  their  bodies  many 
of  them  resemble  some  of  the  more  perfect  Entozoa,  and  we  need 
not  therefore  be  surprised  that  in  ordinary  language  they  are  not 
unfrequently  confounded  together.  But  whatever  may  be  the 
similarity  in  outward  appearance  between  the  more  perfect  intes¬ 
tinal  worms,  and  the  animals  belonging  to  the  class  upon  the  con¬ 
sideration  of  which  we  are  now  entering,  the  examination  of  their 
anatomical  structure  will  at  once  show  that  they  differ  widely  from 
each  other,  and  have  thus  been  properly  separated  by  a  consi¬ 
derable  interval  in  all  the  more  modern  systems  of  zoological 
arrangement. 

(232.)  The  principal  characters  which  serve  to  distinguish  the 
Annelida  from  other  forms  of  the  animal  world  are  readily  appre¬ 
ciated  ;  and,  when  once  pointed  out,  will  be  found  sufficient  for  the 
guidance  of  the  most  superficial  observer.  The  body  is  always 
considerably  elongated,  and  composed  of  a  succession  of  rings  or 
segments,  which,  with  the  exception  of  the  first  and  last,  scarcely 
differ  from  each  other  except  in  size.  Each  ring  is  generally 
.  found  to  be  furnished  with  a  set  of  short  spines  or  setae,  calcu¬ 
lated  to  assist  in  locomotion  ;  but  in  no  instance  are  these  animals 
provided  with  articulated  legs.  The  first  segment  of  the  body, 
which  may  be  called  the  head,  contains  the  mouth,  sometimes 
provided  with  a  formidable  apparatus  of  jaws  ;  and  is  also  generally 
furnished  with  eyes,  and  variously  shaped  tentacula,  which  are 
apparently  instruments  of  touch.  The  last  segment  also,  which 
is  generally  the  smallest,  occasionally  presents  setiform  appen¬ 
dages,  and  occasionally  a  prehensile  sucker,  used  as  an  organ  of 
progression. 

Their  blood  is  remarkable  for  its  red  colour,  and  circulates 
in  a  double  system  of  arteries  and  veins  ;  respiration  is  effected 
either  in  membranous  sacculi  contained  within  the  body,  or  by 
means  of  arborescent  tufts  appended  to  various  parts  of  their  ex- 


*  Annellus,  a  little  ling. 


ANNELIDA. 


189 


ternal  surface  ;  they  are  moreover  almost  all  hermaphrodite,  and 
generally  require  the  congress  of  two  individuals  for  mutual  im¬ 
pregnation. 

(283.)  These  animals  are  separated  by  Cuvier  into  three  distinct 
orders,  distinguished  by  the  nature  and  position  of  their  organs  of 
respiration  ;  they  are  as  follows  : 

Abranchia. — In  this  order  there  is  no  respiratory  apparatus 
visible  externally,  but  on  each  side  of  the  body  a  series  of  minute 
apertures  may  be  detected,  whereby  the  surrounding  medium  is 
admitted  into  numerous  internal  delicate  sacs,  over  which  the 
blood-vessels  are  seen  to  ramify  ;  these  form  apparently  the  re¬ 
spiratory  system  :  the  sacculi  themselves,  and  the  ducts  by  means 
of  which  they  communicate  with  the  external  apertures,  are  de¬ 
lineated  in  Jig.  80,  2,  m. 

This  order  comprises  two  distinct  tribes,  that  differ  widely  in 
their  habits  and  external  appearance :  the  first  comprehends  the 
Leeches  ( Annelida  suctoria ),  distinguished  by  the  existence  of 
a  prehensile  sucker  at  each  extremity  of  the  body  ;  while,  in 
the  second,  instruments  of  attachment  are  totally  wanting,  the 
only  external  appendages  to  the  body  being  a  number  of  minute 
and  almost  imperceptible  bristles,  which  project  from  the  different 
segments  and  assist  in  progression  :  such  are  the  Earth-worms, 
&c.  ( Annelida  terricolaj 

Dorsibranchiata. — In  the  second  order  the  respiratory  appa¬ 
ratus  consists  of  numerous  vascular  tufts,  a  pair  of  which  is  ap¬ 
pended  to  the  outer  surface  of  every  ring  of  the  body,  or,  in  some 
cases,  only  to  those  near  the  middle  of  the  animal.  The  organs  of 
locomotion,  which  are  likewise  attached  to  each  segment,  assume 
various  forms,  but  are  generally  composed  of  short  moveable  spines, 
or  packets  of  retractile  bristles,  probably  destined  to  perform  the 
office  of  oars.  In  the  annexed  figure,  (Jig.  77,  1,)  which  repre¬ 
sents  the  Leodice  antennata ,  the  general  form  of  these  animals  is 
well  seen,  as  is  the  most  usual  arrangement  of  the  branchial  tufts 
and  locomotive  setae.  In  Jig.  77,  2,  showing  an  imaginary  trans¬ 
verse  section  of  one  of  the  segments,  the  relative  positions  of  the  oars 
(c,  d,  e),  and  of  the  branchial  appendages  (Z>),  are  likewise  indicated. 

Tubicola. — The  two  preceding  orders  of  Annelidans  are 
erratic  ;  but  in  the  third  we  find  creatures  inhabiting  a  fixed  and 
permanent  residence,  which  encloses  and  defends  them.  This  is 
generally  an  elongated  tube,  varying  in  texture  in  different  species. 
Sometimes  it  is  formed  by  agglutinating  foreign  substances,  such 


190 


ANNELIDA. 


as  grains  of  sand,  small  shells,  or  fragments  of  various  materials,  by 
means  of  a  secretion  which  Fig.  77. 

exudes  from  the  surface  of  the 
body,  and  hardens  into  a  toueh 
membranous  substance,  such  is 
the  case  of  Terebella  Medusa 
(Jig.  96).  In  other  cases,  as 
in  the  Serpula  contortuplicata 
( fig .  78),  the  tube  is  ho¬ 
mogeneous  in  its  texture, 
formed  of  calcareous  matter 
resembling  the  shells  of  cer¬ 
tain  bivalve  mollusca,  and  ap¬ 
parently  secreted  in  a  similar 
manner.  These  tubes  are  ge¬ 
nerally  found  encrusting  the 
surface  of  stones  or  other  bo¬ 
dies  which  have  been  immersed 
for  any  length  of  time  at  the 
bottom  of  the  sea  ;  they  are 
closed  at  one  end,  and  from  the 
opposite  extremity  the  head  of 
the  worm  is  occasionally  pro¬ 
truded  in  search  of  nourish¬ 
ment.  It  must  be  evident  that, 
in  animals  thus  encased,  the 
character  of  the  respiratory  ap¬ 
paratus  must  be  considerably 
modified  ;  instead  therefore  of 
the  numerous  branchiae  ap¬ 
pended  to  the  segments  of  the 
body  which  we  have  found  in 
the  Dorsibranchiate  order,  the 
respiratory  tufts  are  all  at¬ 
tached  to  the  anterior  extre¬ 
mity  of  the  creature,  where 
they  form  most  elegant  arbo¬ 
rescent  appendages,  generally 
tinted  with  brilliant  colours, 
and  exhibiting,  when  expanded, 
a  spectacle  of  great  beauty.  In 
some  species,  as  in  that  repre- 


l 


ANNELIDA. 


191 


sented  in  the  annexed  figure,  there  is  a  remarkable  provision  made 
for  closing  the  entrance 
of  the  tube  when  the 
animal  retires  within  its 
cavity.  On  each  side 
of  the  mouth  is  a  fleshy 
filament  resembling  a 
tentacle ;  but  one  of 
these,  sometimes  the 
right  and  sometimes 
the  left,  is  found  to  be 
considerably  prolonged, 
and  expanded  into  a 
funnel-shaped  opercu¬ 
lum,  which  accurately 
fits  the  orifice  of  the 
shell,  and  thus  forms 
a  kind  of  door,  well 
adapted  to  prevent  in¬ 
trusion  or  annoyance 
from  external  enemies. 

(231.)  Abranchia. — The  common  Leech  ( Hirudo  medicinalis ) 
affords  the  most  interesting  example  of  a  suctorial  Annelide.  The 
outward  form  of  one  of  these  animals  is  familiar  to  every  one,  and 
their  general  habits  too  well  known  to  require  more  than  a  very 
brief  notice.  The  body  is  very  extensible,  and  divided  by  a  great 
number  of  transverse  lines  into  numerous  rings,  extremely  apparent 
in  the  contracted  state  of  the  animal,  but  nearly  imperceptible 
when  the  body  is  elongated.  The  skin  is  soft,  being  merely  a  thin 
cuticular  pellicle  separable  by  maceration  ;  and  the  surface  is  lubri¬ 
cated  by  a  copious  secretion  of  mucus.  Beneath  the  cuticle  is  a 
layer  of  coloured  pigment,  upon  which  the  colours  of  the  animal 
depend  ;  but  the  cutis,  or  true  skin,  is  so  intimately  connected  with 
the  muscular  integument  of  the  body,  that  its  existence  as  a  distinct 
tunic  is  scarcely  demonstrable.  The  muscular  covering  or  walls  of 
the  body,  which  form  a  kind  of  contractile  bag  enclosing  the 
viscera,  is  found,  upon  accurate  dissection,  to  consist  of  three 
distinct  strata  of  fibres  running  in  different  directions.  The 
outer  layer  is  composed  of  circular  bands  passing  transversely  ; 
in  the  second,  the  fibres  assume  a  spiral  arrangement,  decussating 
each  other ;  while  the  internal  layer  is  made  up  of  longitudinal 


Fig.  78. 


192 


ANNELIDA. 


muscles,  extending  from  one  end  of  the  creature  towards  the  oppo¬ 
site.  Such  an  arrangement  is  evidently  adequate  to  the  produc¬ 
tion  of  all  needful  movements,  and  capable  of  giving  rise  to  all 
the  motions  connected  with  the  elongation,  contraction,  or  lateral 
inflexions  of  the  body  used  in  progression. 

At  each  extremity  of  the  animal,  the  muscular  coat  expands  into 
a  flattened  fleshy  disc,  composed  of  circular  and  radiating  fasciculi, 
which,  when  applied  to  a  smooth  surface,  perform  the  office  of 
suckers,  and  thus  become  important  instruments  of  prehension. 
There  are  no  vestiges  of  external  limbs ;  nevertheless,  with  the 
simple  mechanism  above  described,  the  leech  is  able  to  crawl  with 
considerable  rapidity  along  the  surface  of  subaquatic  plants,  or  even 
to  swim  with  much  facility  through  the  water.  The  first  method 
of  locomotion  is  accomplished  by  means  of  the  terminal  suckers  : 
supposing  the  posterior  disc  to  be  attached,  the  animal  elongates 
its  body  to  the  utmost,  and  then  fixes  the  sucker  placed  at  the 
opposite  extremity  ;  this  done,  the  hinder  parts  are  drawn  forward 
and  again  fixed,  preparatory  to  a  repetition  of  the  process.  In 
swimming,  the  whole  body  is  elongated,  and  by  some  partial  con¬ 
tractions  of  the  muscular  integument,  not  precisely  understood, 
assumes  the  appearance  of  a  flattened  band,  and  in  this  condition 
the  leech  makes  its  way  through  the  element  which  it  inhabits, 
by  successive  undulatory  movements  of  the  body  performed  with 
much  grace  and  elegance. 

(235.)  The  mouth  of  the  leech  is  an  exceedingly  perfect  appa¬ 
ratus,  adapted  not  only  to  the  destruction  of  those  minute  aquatic 
animals  which  constitute  its  usual  food,  but,  as  is  universally 
known,  admirably  fitted  to  extract  blood  from  the  higher  animals  ; 
combining,  in  its  operation,  the  offices  both  of  the  cupping-glass 
and  the  scarificator. 

The  mouth  is  situated  near  the  centre  of  the  anterior  sucker,  so 
that  the  oral  aperture  is  firmly  applied  to  any  surface  upon  which 
this  part  of  the  animal  is  fixed.  Around  the  entrance  of  the 
oesophagus  are  disposed  three  minute  cartilaginous  teeth,  im¬ 
bedded  in  a  strong  circle  of  muscular  fibres  ( fig .  79,  1).  Each 
tooth  has  somewhat  of  a  semicircular  form,  and,  when  accurately 
examined  with  a  microscope,  is  found  to  have  its  free  margin  sur¬ 
mounted  with  minute  denticulations  ( fig .  79,  2),  so  as  to  resem¬ 
ble  a  small  semicircular  saw.  On  watching  a  leech  attentively 
during  the  process  of  biting,  the  action  of  these  teeth  is  at  once 
evident ;  for,  as  the  skin  to  which  the  sucker  is  adherent  is 


ANNELIDA. 


193 


rendered  quite  tense,  the  sharp  serrated  edges  of  the  teeth  are 
pressed  firmly  against  it,  and,  a  sawing  movement  being  given  to 
each  cartilaginous  piece  by  the  strong  contractions  of  the  muscular 
fibres  around  the  neck,  these  instruments  soon  pierce  the  cutis  to 
a  considerable  depth,  and  lay  open  the  cutaneous  vessels,  from 
which  the  creature  sucks  the  fluid  which  its  instinct  prompts  it  to 
seek  after  with  so  much  voracity.  The  position  of  the  teeth 
around  the  opening  of  the  mouth,  as  represented  in  the  subjoined 
figure,  (fig\  79,  a,)  will  at  once  explain  the  cause  of  the  tri-radiate 
form  of  the  incision  which  a  leech-bite  invariably  exhibits. 

On  contemplating  Fig.  79. 

this  singular  dental  ap¬ 
paratus  found  in  the 
medicinal  leech,  and 
considering  the  na¬ 
ture  of  the  food  upon 
which  it  usually  lives, 
it  is  difficult  to  avoid 
arriving  at  the  conclu¬ 
sion  that  such  a  struc¬ 
ture,  which  is  indeed 
only  met  with  in  one 
or  two  species,  is  ra-  B  A 

tlier  a  provision  in¬ 
tended  to  render  these  creatures  subservient  to  the  alleviation  of 
human  suffering  than  necessary  to  supply  the  wants  of  the  animals 
themselves.  In  the  streams  and  ponds  which  they  usually  in¬ 
habit,  any  opportunity  of  meeting  with  a  supply  of  the  blood  of 
warm-blooded  vertebrata  must  be  of  rare  occurrence,  so  that 
comparatively  few  are  ever  enabled  to  indulge  the  instinct 
which  prompts  them  to  gorge  themselves  so  voraciously  when 
allowed  to  obtain  it :  neither  does  it  appear  that  the  blood 
which  they  swallow  with  so  much  avidity  is  a  material  properly 
suited  to  afford  them  nourishment  ;  for  although  it  is  certainly 
true  that  it  will  remain  for  a  considerable  time  in  its  stomach, 
without  becoming  putrid,  yet  it  is  well  known  that  most  fre¬ 
quently  the  death  of  the  leech  is  caused  by  such  inordinate  reple¬ 
tion,  provided  the  greater  portion  of  what  is  taken  into  the  body 
is  not  speedily  regurgitated  through  the  mouth. 

(236.)  The  internal  digestive  apparatus  is  evidently  adapted  in 
the  construction  of  all  its  parts  to  form  a  capacious  reservoir  for  the 

o 


194 


ANNELIDA. 


reception  of  fluids  taken  in  by  suction  :  the  stomach  indeed,  with 
the  numerous  lateral  appendages  opening  from  it  on  each  side, 
would  seem  to  fill  the  whole  body  ;  and,  being  extremely  dilatable, 
allows  the  animal  to  distend  itself  to  a  wonderful  extent,  so  that 
it  is  not  unusual  to  see  a  leech,  when  filled  with  blood,  expanded 
to  five  or  six  times  the  dimensions  which  it  presented  in  an  empty 
state. 

The  stomach  itself  {fig.  80,  1,  h ,  z,)  occupies  about  two 
thirds  of  the  visceral  cavity  ;  on  opening  it,  as  represented  in  the 
figure,  it  is  seen  to  be  divided  by  delicate  septa  into  nine  or 
ten  compartments,  which  communicate  freely  with  each  other. 
In  each  compartment  we  observe  two  lateral  orifices  leading  into 
as  many  wide  membranous  pouches  (Zr),  which  although  shrunk 
and  flaccid  when  in  an  undistended  state,  as  they  are  seen  in  the 
figure,  are  easily  filled  with  fluid  introduced  into  the  stomach,  and 
are  then  swelled  out  into  very  capacious  bags.  Perhaps  the  sim¬ 
plest  way  of  obtaining  a  correct  idea  of  the  relative  sizes  and 
general  arrangement  of  these  organs,  is  to  make  a  cast  of  their 
internal  cavities  when  in  a  state  of  distension  ;  this  is  readily 
effected  by  placing  a  dead  leech  in  warm  water  until  it  is  slightly 
heated  :  in  this  state  the  pipe  of  a  small  injecting  syringe  can  be 
introduced  into  the  oesophagus  so  as  to  fill  the  stomach  and  caeca 
with  common  wax  injection  ;  and,  if  the  body  be  immediately  re¬ 
moved  into  a  vessel  of  diluted  muriatic  acid,  the  soft  parts  will 
be  speedily  destroyed,  leaving  an  exact  model  of  the  interior. 
It  will  then  be  seen  that  the  lateral  caeca  increase  gradually  in 
size  as  they  approximate  the  posterior  extremity  of  the  body,  until 
the  last  pair  (rf)  become  so  large  as  nearly  to  fill  up  the  space 
intervening  between  the  end  of  the  stomach  and  the  anal  boundary 
of  the  visceral  cavity.  AVhat  is  the  exact  nature  of  these  capa¬ 
cious  sacs  which  thus  open  into  the  stomach  of  the  leech  ?  Are 
they  prolongations  of  the  digestive  surface,  or  are  they  glandular 
caeca  provided  for  the  secretion  of  some  auxiliary  fluids  poured  into 
the  stomach  P  These  are  questions  which  admit  of  considerable 
discussion.  On  the  one  hand,  there  can  be  little  doubt  that,  when 
the  leech  is  filled  with  blood,  the  various  caecal  pouches  become 
likewise  distended,  and  they  are  apparently  as  well  calculated  to 
effect  the  digestion  of  their  contents  as  the  stomach  itself.  Those 
physiologists,  however,  who  embrace  a  different  opinion,  support  their 
views  by  referring  to  the  structure  of  analogous  parts  found  in  other 
Annelidans  :  in  Aphrodita  aculeata ,  for  example,  the  representa- 


ANNELIDA. 


195 


tives  of  the  wide  pouches  met  with  in  the  leech  are  narrow  and 
branched  tubes  terminating  in  blind  extremities,  to  which  it  is 
usual  to  assign  the  office  of  separating  a  biliary  secretion  ;  and, 
according  to  this  view,  we  may  regard  the  cseca  of  the  leech  as  the 
simplest  rudiments  of  the  assistant  chylopoietic  glands, — the  first 
pair  (g,  g-),  from  their  proximity  to  the  mouth,  maybe  destined 
to  furnish  a  salivary  fluid,  and  the  succeeding  ones  to  perform  the 
functions  of  biliary  follicles. 

The  small  size  of  the  intestine  (e),  when  compared  with  the 
capacious  stomach  described  above,  is  remarkable  :  it  commences 
by  a  minute  orifice  from  the  termination  of  the  digestive  cavity, 
and  becoming  slightly  enlarged  passes  in  a  straight  line,  lodged 
between  the  two  posterior  cseca,  to  the  anus,  which  is  an  almost 
imperceptible  aperture  placed  at  the  root  of  the  posterior  sucker  ; 
four  small  and  apparently  glandular  masses  are  appended  to  this 
short  canal,  but  their  nature  is  unknown.  The  entire  alimentary 
apparatus  is  retained  in  situ  by  numerous  membranous  septa, 
(m,  ra,)  passing  between  its  outer  walls  and  the  muscular  parietes 
of  the  body. 

(237.)  It  has  already  been  mentioned,  that,  in  the  abranchiate 
Annelidans,  the  organs  provided  for  respiration  are  a  series  of 
membranous  pouches,  communicating  externally  by  narrow  ducts  or 
spiracles,  as  they  might  be  termed,  into  which  aerated  water  is 
freely  admitted.  These  respiratory  sacculi,  in  the  leech,  are  about 
thirty-four  in  number,  seventeen  being  visible  on  each  side  of  the 
body  :  they  are  extremely  vascular  ;  and  in  connection  with  every 
one  of  them  there  is  a  long  glandular-looking  appendage,  repre¬ 
sented  in  the  figure,  (Jig.  80,  2,  m,)  that  was  looked  upon  until 
recently  as  being  intended  to  furnish  some  important  secretion, 
but  which  recent  discoveries  have  shown  to  be  connected  with  the 
propulsion  of  the  blood  over  the  walls  of  the  breathing  vesicle,  in  a 
manner  to  be  explained  immediately.  It  would  seem,  however,  that 
the  respiratory  function  is  not  exclusively  carried  on  by  the  agency 
of  the  lateral  sacculi :  the  entire  surface  of  the  body  is  permeated 
by  innumerable  delicate  vascular  ramifications  ;  and,  from  the  thin¬ 
ness  of  the  integument,  it  is  evident  that  the  blood  which  tra¬ 
verses  the  cutaneous  net-work  thus  extensively  distributed  must 
be  more  or  less  completely  exposed  to  the  influence  of  oxygen 
contained  in  the  surrounding  medium  ;  nay,  it  would  even  appear 
from  careful  examination  of  the  movements  of  the  blood,  as  seen 
in  the  transparent  bodies  of  some  of  the  Hirudinida ,  that  a  kind 


o 


196 


ANNELIDA. 


of  vicarious  action  occurs  between  the  capillary  vessels  of  the  shin 
and  those  of  the  respiratory  sacs,  so  that  when  the  circulation  pro¬ 
ceeds  languidly  through  one  set  of  vessels,  it  is  carried  on  with 
greater  activity  in  the  other. 

Fig.  80. 

I  2  3 


(238.)  The  vessels  appropriated  to  the  distribution  of  the  circu¬ 
lating  fluid  in  the  leech  are  rudely  sketched  in  Jig.  80,  3.  There  is 
no  heart,  but  the  movements  of  the  blood  are  entirely  due  to  the 
contractions  of  the  canals  in  which  it  flows.  The  principal  vascu¬ 
lar  trunks  are  four  in  number,  which,  although  they  all  communi¬ 
cate  extensively  with  each  other,  perform  distinct  offices  in  effect¬ 
ing  the  circulation  ;  two  of  them  being  specially  connected  with 
the  supply  of  the  general  system,  while  the  other  two  seem  sub¬ 
servient  to  the  distribution  of  the  blood  over  the  respiratory 
sacculi. 


ANNELIDA. 


197 


The  two  systemic  trunks  (f,  g)  run  along  the  mesian  line  of 
the  body  ;  one  upon  the  dorsal,  and  the  other  upon  the  ventral 
aspect.  The  dorsal  vessel  (  f)  seems  to  be  arterial  in  its  cha¬ 
racter,  and  no  doubt  corresponds  in  function  with  the  heart  of 
more  perfect  forms  of  the  articulata  ;  receiving  the  blood  from  all 
parts  of  the  system,  as  well  from  the  respiratory  vessels  as  from 
the  venous  capillaries,  and  by  successive  undulatory  contractions, 
which  may  be  observed  to  proceed  from  the  tail  towards  the  an¬ 
terior  extremity,  propelling  it  through  all  the  arterial  branches 
derived  from  it.  The  ventral  vessel  (g),  on  the  contrary,  seems 
to  be  venous,  collecting  the  blood  after  its  passage  through  the 
systemic  capillaries,  and  returning  it  partly  into  the  dorsal  artery 
from  which  it  set  out,  and  partly  to  the  lateral  vessels  for  the 
purpose  of  undergoing  respiration. 

The  two  lateral  vessels  (a,  c )  are  appropriated  to  the  supply 
of  the  respiratory  system,  and  in  them  the  blood  moves  in  a  circle 
quite  independent  of  that  formed  by  the  dorsal  artery  and  ventral 
vein,  although  they  all  communicate  freely  by  means  of  cross 
branches,  those  passing  from  the  lateral  vessels  to  the  dorsal 
being  called  by  M.  Duges*  dorso-lateral ,  while  those  which 
join  the  lateral  trunks  to  the  ventral  canal  are  the  latero-abdo- 
minal  branches  of  that  observer.  The  movement  of  the  blood 
in  the  lateral  or  respiratory  system  of  vessels  is  quite  distinct 
from  that  which  is  accomplished  in  the  clorso-ventral  or  systemic 
trunks :  sometimes  it  passes  down  the  vessel  marked  a,  from  the 
head  towards  the  tail,  and  in  an  opposite  direction  on  the  other 
side  of  the  body ;  but  in  a  short  time  the  movement  of  the  cur¬ 
rents  will  be  seen  to  become  completely  reversed,  so  that  an  un¬ 
dulatory  motion,  rather  than  a  complete  circulation,  is  kept  up. 
By  this  action  of  the  lateral  canals  the  blood  is  made  perpetually 
to  pass  and  repass  the  respiratory  sacculi ;  and,  opposite  to  each 
of  these,  branches  are  given  off  which  form  so  many  independent 
vascular  circles,  representing  very  closely  the  minor  or  pulmonary 
circulation  of  higher  animals. 

(239.)  Oh  examining  attentively  one  of  the  respiratory  pouches 
(jig.  81,  f),  its  membranous  walls  are  seen  to  be  covered  with  very 
fine  vascular  ramifications,  derived  from  two  sources :  the  latero-ab- 
dominal  vessel  (d)  gives  off  a  branch  (e),  which  is  distributed  upon 
the  respiratory  sacculus ;  and  there  is  another  very  flexuous  vas- 


*  Annales  ties  Sciences  Nat.  vol.  xv. 


198 


ANNELIDA. 


cular  loop  (/>)  derived  from  tlie  lateral  vessel  itself  («),  which  ter¬ 
minates  by  ramifying  upon  the  vesicle  f,  in  a  similar  manner.  The 

Fig.  81. 


walls  of  the  loop  Z>,  are  extremely  thick  and  highly  irritable  ;  but, 
on  tearing  it  across,  the  internal  cavity  or  canal  by  which  it  is 
perforated  is  seen  to  be  of  comparatively  small  diameter,  so  that  we 
are  not  surprised  that,  although  such  appendages  to  the  respira¬ 
tory  sacs  were  detected  and  well  delineated  by  former  anatomists,* 
their  nature  was  unknown,  and  they  were  supposed  to  be  glandular 
bodies  appropriated  to  some  undiscovered  use.  From  the  ar¬ 
rangement  above  described,  it  is  evident  that  small  circular  cur¬ 
rents  of  blood  exist,  which  are  independent,  to  a  certain  extent,  of 
the  general  circulation  ;  since  opposite  to  each  membranous  bag  a 
portion  of  the  fluid  contained  in  the  lateral  vessel  (a)  is  given  off 
through  the  muscular  tube  ( b ),  which  thus  resembles  a  pulmonary 
heart,  and  after  being  distributed  over  the  walls  of  the  respiratory 
vesicle,  and  in  this  manner  exposed  to  the  influence  of  oxygen, 
the  blood  returns  into  the  general  circulation. 

(240.)  The  nervous  system  of  the  leech  (Jig.  80,2,  k)  consists  of 

*  Delle  Chiaje,  op.  cit.  —  Moquin  Tandon,  Monographic  sur  la  famille  des  Iliru- 
dinees,  4to.  Montpellier,  1827. 


ANNELIDA. 


199 


a  long  series  of  minute  ganglia  joined  by  connecting  filaments  ;  of 
these,  about  twenty-four  are  situated  along  the  ventral  surface  of 
the  body.  The  anterior  pair,  or  that  immediately  beneath  the 
oesophagus,  is  larger  than  the  rest,  forming  a  minute  heart-shaped 
mass,  which  is  united,  by  a  delicate  nervous  collar  embracing  the 
gullet,  with  two  small  nodules  of  neurine  situated  upon  the  dorsal 
aspect  of  the  mouth.  The  two  minute  ganglia  last  mentioned 
form  that  portion  of  the  nervous  system  most  intimately  connected 
with  sensation  ;  for,  while  the  nervous  filaments  given  off  from  the 
abdominal  ganglia  are  distributed  to  the  muscular  integuments  of 
the  body,  the  nerves  which  issue  from  the  supra- oesophageal  pair 
supply  the  oral  sucker,  where  the  organs  of  the  senses  are  situated. 
In  all  the  homogangliata,  indeed,  it  is  exclusively  from  this  ce¬ 
phalic  pair  of  ganglia  that  the  nerves  appropriated  to  the  instru¬ 
ments  of  the  senses  are  derived,  and  we  shall  therefore  not  hesitate 
in  the  following  pages  to  apply  to  this  part  of  the  nervous  system 
of  the  articulata  the  name  of  brain  ;  considering  it  to  be  strictly 
analogous,  in  function  at  least,  with  the  cerebral  masses  of  more 
highly  organized  beings. 

When  we  regard  the  minute  size  of  these,  as  yet  rudimentary 
nervous  centres,  we  cannot,  however,  expect  to  find  them  asso¬ 
ciated  with  any  very  perfect  apparatus  of  sensation.  The  oral 
sucker,  indeed,  seems  to  possess  a  more  delicate  sense  of  touch 
than  the  rest  of  the  body,  adapting  it  to  examine  the  surface  to 
which  it  is  about  to  be  fixed  ;  and  probably  the  leech  may  enjoy 
in  some  measure  perceptions  corresponding  with  those  of  taste  and 
smell.  These  senses  have  been  found  to  exist  in  many  of  the 
animals  we  have  already  described  ;  but  in  the  Hirudinida  we 
have,  in  addition,  distinctly  formed  organs  of  vision,  exhibiting, 
indeed,  the  utmost  simplicity  of  structure,  but  nevertheless  cor¬ 
responding  in  the  perfection  of  their  developement  with  the  con¬ 
dition  of  the  cerebral  masses  in  relation  with  them. 

(241.)  The  eyes  of  the  leech  are  eight  or  ten  in  number,  and  are 
easily  detected  by  the  assistance  of  a  lens  under  the  form  of  a  semi¬ 
circular  row  of  black  points,  situated  above  the  mouth  upon  the  suck¬ 
ing  surface  of  the  oral  disc  ;  a  position  evidently  calculated  to  ren¬ 
der  them  efficient  agents  in  detecting  the  presence  of  food.  The 
structure  of  these  simple  eyes,  according  to  Professor  M tiller,* 
does  not  as  yet  present  any  apparatus  of  transparent  lenses  adapted 


*  Annales  des  Sciences  Nat.  vol.  xxii. 


200 


ANNELIDA. 


to  collect  or  concentrate  the  rays  of  light ;  but  each  ocellus,  or  vi¬ 
sual  speck,  would  seem  to  be  merely  an  expansion  of  the  terminal 
extremity  of  a  nerve  derived  immediately  from  the  brain,  spread 
out  beneath  a  kind  of  cornea  formed  by  the  delicate  and  transparent 
cuticle  :  behind  this  is  a  layer  of  black  pigment,  to  which  the  dark 
colour  of  each  ocular  point  is  due. 

(242.)  Leeches,  like  the  generality  of  the  Annelida,  are  herma¬ 
phrodite,  every  one  possessing  two  complete  systems  of  generative 
organs,  one  subservient  to  the  impregnation,  the  other  to  the  produc¬ 
tion  of  the  ova;  nevertheless  these  animals  are  not  self-impregnating, 
but  the  congress  of  two  individuals  is  essential  to  fecundity. 

Commencing  with  the  male  organs,  we  are  not  surprised  to  find 
the  testes  divided  into  numerous  distinct  masses,  or  rather  repeated 
again  and  again  in  conformity  with  a  law  to  which  we  have  already 
alluded  (§  229).  The  glands  which  apparently  secrete  the  semi¬ 
nal  fluid  are  about  eighteen  in  number  ( fig .  80,  2,  e,  f),  arranged 
in  pairs  upon  the  floor  of  the  visceral  cavity.  Along  the  external 
edge  of  each  series  there  runs  a  common  canal,  or  vas  deferens , 
which  receives  the  secretion  furnished  by  all  the  testicular  masses 
placed  upon  the  same  side  of  the  mesian  line,  and  conveys  it  to 
a  receptacle  (d),  where  it  accumulates.  The  two  reservoirs,  or 
vesicula:  seminales ,  if  we  may  so  call  them,  (d,  d,)  communicate 
with  a  muscular  bulb  (c)  situated  at  the  root  of  the  penis.  The 
penis  itself  (a)  is  frequently  found  protruded  from  the  body  after 
death  ;  it  is  a  slender  tubular  filament,  which  communicates  by  its 
origin  with  the  contractile  bulb  (c),  and,  when  retracted,  is  lodged 
in  a  muscular  sheath  ( b ).  The  male  apparatus  is  thus  complete  in 
all  its  parts  :  the  fecundating  secretion  derived  from  the  double  row 
of  testes  is  collected  by  the  two  vasa  deferentia,  and  lodged  in  the 
receptacles  (d,  d)  ;  it  is  thence  conveyed  into  the  muscular  cavity 
(c)  situated  at  the  root  of  the  male  organ  of  excitement,  through 
which  it  is  ultimately  ejected. 

(243.)  The  ovigerous  or  female  sexual  organs  of  the  leech  are 
more  simple  in  their  structure  than  those  which  constitute  the  male 
system  ;  they  open  externally  by  a  small  orifice  situated  immediately 
behind  the  aperture  from  which  the  penis  is  protruded,  the  two 
openings  being  separated  by  the  intervention  of  about  five  of  the 
ventral  rings  of  the  body.  The  vulva,  or  external  canal,  leads  into 
a  pear-shaped  membranous  bag  (fig.  80,  2,  g),  which  is  usually, 
but  improperly,  named  the  uterus.  Appended  to  the  bottom  of 
this  organ  is  a  convoluted  canal  (//),  which  communicates  with  two 


ANNELIDA. 


201 


round,  whitish  bodies  ;  these  are  the  ovaria.  The  germs,  there¬ 
fore,  which  are  formed  in  the  ovarian  corpuscles,  escape  through  the 
tortuous  duct  (h)  into  the  uterus  (g),  where  they  are  detained  for 
some  time  prior  to  their  ultimate  expulsion  from  the  body.  The 
exact  nature  of  the  uterine  sacculus,  as  it  is  called,  is  imperfectly 
understood  :  some  regard  it  as  a  mere  receptacle  wherein  the  se¬ 
minal  fluid  of  the  male  is  received  and  retained  until  the  ova  come 
in  contact  with  it  as  they  pass  out  of  the  body,  and  thus  are  sub¬ 
jected  to  its  vivifying  influence  ;  other  physiologists  believe  that  the 
germs  escape  from  the  ovaria  in  a  very  immature  condition,  and  sup¬ 
pose  that  during  their  sojourn  in  this  cavity  they  attain  to  more  com¬ 
plete  developement  before  they  are  ripe  for  exclusion  ;  while  some 
writers  go  so  far  as  to  assert  that  leeches  are  strictly  viviparous,  in¬ 
asmuch  as  living  young  have  been  detected  in  the  interior  of  this 
viscus  :  but  all  these  suppositions  are  easily  reconcileable  with 
each  other  ;  there  is  no  doubt  that  the  seminal  liquor  is  depo¬ 
sited  in  this  reservoir,  during  the  copulation  of  two  individuals, 
neither  would  any  one  dispute  that  the  ova  are  collected  in  the 
same  cavity  before  they  are  expelled  from  the  body ;  as  to  the 
discussion  whether  the  young  are  born  alive  or  not,  or,  as  it  is  ge¬ 
nerally  expressed,  whether  leeches  are  oviparous  or  viviparous,  it  is 
in  this  case  merely  a  question  of  words,  for  in  a  physiological  point 
of  view  it  can  make  not  the  slightest  difference  whether  the  ova 
are  expelled  as  such,  or  whether,  owing  to  their  being  retained  by 
accidental  circumstances  until  they  are  hatched  internally,  the 
young  leeches  make  their  appearance  in  a  living  state. 

(244.)  Abranchia  terricola. — The  second  division  of  those  Anne- 
lidans  which  possess  no  external  organs  of  respiration  are  easily  dis¬ 
tinguishable  from  the  suctorial  worms  by  the  different  construction 
of  their  instruments  of  locomotion.  They  live  in  general  beneath 
the  surface  of  the  ground,  either  perforating  the  soil  in  all  direc¬ 
tions,  as  the  Earthworms  ( Lumbrici ),  or  burying  themselves  in  the 
mud  upon  the  sea-shore,  where  many  of  them,  called  Naides , 
(Nats,  Lin.)  live  a  semi-aquatic  life.  In  conformity  with  such 
habits,  their  entire  structure  is  adapted  to  a  subterranean  existence, 
and  their  bodies  so  organized  as  to  enable  them  to  burrow  with 
facility  through  the  dense  and  unyielding  materials  in  which  they 
are  usually  found.  Whoever  has  attentively  watched  the  opera¬ 
tions  of  an  earthworm  when  busied  in  burying  itself  in  the  earth, 
must  have  been  struck  with  the  seeming  disproportion  between  the 
laborious  employment  in  which  it  is  perpetually  engaged,  and  the 


202 


ANNELIDA. 


means  provided  for  enabling  it  to  overcome  difficulties  apparently 
insurmountable  by  any  animal  unless  provided  with  limbs  of  extra¬ 
ordinary  construction,  and  possessed  of  enormous  muscular  power. 
In  the  mole  and  the  burrowing  cricket  we  at  once  recognise  in 
the  immense  developement  of  the  anterior  legs  a  provision  for 
digging,  admirably  adapted  to  their  subterranean  habits,  and  cal¬ 
culated  to  throw  aside  with  facility  the  earth  through  which  they 
work  their  way  ;  but  in  the  worms  before  us,  deprived  as  they 
appear  to  be  of  all  external  members,  feeble  and  sluggish  even  to 
a  proverb,  where  are  we  to  look  for  that  mechanism  which  enables 
them  to  perforate  the  surface  of  the  ground,  and  to  make  for  them¬ 
selves,  in  the  hard  and  trodden  mould,  the  pathways  which  they 
traverse  with  such  astonishing  facility  and  quickness  ? 

(245.)  The  structure  of  the  outer  fleshy  integument  of  the  earth¬ 
worm  resembles  in  every  respect  that  of  the  leech  already  described, 
both  in  the  annular  arrangement  apparent  externally,  and  the  disposi¬ 
tion  of  the  muscular  strata.  The  suctorial  discs,  however,  which 
in  the  leech  formed  such  important  instruments  of  progression, 
are  here  totally  wanting ;  and  the  annular  segments  of  the  body, 
as  they  approach  the  anterior  extremity,  become  gradually  dimi¬ 
nished  in  size,  so  as  to  terminate  when  the  worm  is  fully  stretched 
out  in  a  fine  point,  near  the  apex  of  which  is  the  opening  of  the 
mouth.  But  there  is  another  circumstance  in  which  the  external 
anatomy  of  the  terricolous  Annelides  differs  materially  from  what 
we  have  seen  in  the  suctorial  Abranchia  :  in  the  latter,  the  tegu¬ 
mentary  segments  were  quite  naked  upon  their  outer  surface  ;  but  in 
the  Lumbrici,  of  which  we  are  now  speaking,  every  ring,  when  ex¬ 
amined  attentively,  is  found  to  support  a  series  of  sharp  retractile 
spines  or  prickles ;  these,  indeed,  are  so  minute  in  the  earthworm, 
that,  on  passing  the  hand  along  the  body  from  the  head  backwards, 
their  presence  is  scarcely  to  be  detected  by  the  touch,  but  they  are 
easily  felt  by  rubbing  the  animal  in  the  opposite  direction ;  a  cir¬ 
cumstance  which  arises  from  their  hooked  form,  and  from  their 
points  being  all  turned  towards  the  tail.  These  differences  be¬ 
tween  the  external  structure  of  the  suctorial  and  setigerous  Abran¬ 
chia ,  minute  and  trivial  as  they  might  seem  to  a  superficial  ob¬ 
server,  are  however  all  that  are  required  to  convert  an  aquatic 
animal  into  one  adapted  to  a  subterranean  residence,  as  will  be 
evident  to  any  one  who  observes  carefully  the  manner  in  which  the 
earthworm  bores  its  way  through  the  soil  in  which  it  lives.  The 
attenuated  rings  in  the  neighbourhood  of  the  mouth  are  first  insi- 


ANNELIDA 


203 


nuatecl  between  the  particles  of  the  earth, 
which,  from  their  conical  shape,  they  pene¬ 
trate  like  a  sharp  wedge  ;  in  this  position 
they  are  firmly  retained  by  the  numerous 
recurved  spines  appended  to  the  different 
segments  :  the  hinder  parts  of  the  body  are 
then  drawn  forwards  by  a  longitudinal  con¬ 
traction  of  the  whole  animal ;  a  movement 
which  not  only  prepares  the  creature  for 
advancing  further  into  the  soil,  but  by  swell¬ 
ing  out  the  anterior  segments  forcibly  di¬ 
lates  the  passage  into  which  the  head  had 
been  already  thrust :  the  spines  upon  the 
hinder  rings  then  take  a  firm  hold  upon  the 
sides  of  the  hole  thus  formed,  and,  prevent¬ 
ing  any  retrograde  movement,  the  head  is 
again  forced  forward  through  the  yielding 
mould,  so  that,  by  a  repetition  of  the  pro¬ 
cess,  the  animal  is  able  to  advance  with  the 
greatest  apparent  ease  through  substances 
which  it  would  at  first  seem  utterly  impossi¬ 
ble  for  so  helpless  a  being  to  penetrate. 

(246.)  The  alimentary  canal  of  the  earth¬ 
worm  is  straight  and  very  capacious.  Its  great 
size,  indeed,  is  in  accordance  with  the  nature 
of  the  materials  employed  as  food,  for  it  is 
generally  found  distended  with  earth  ;  and, 
indeed,  by  the  older  physiologists  these 
creatures  were  generally  regarded  as  afford¬ 
ing  proof  that  the  nourishment  of  animals 
was  not  exclusively  derived  from  animal  and 
vegetable  substances,  since  in  this  case  they 
supposed  nutriment  to  be  obtained  from 
matter  belonging  to  the  mineral  kingdom. 
This  supposition,  however,  has  been  long 
since  exploded,  for  it  is  not  from  the  earth 
that  nourishment  is  afforded,  but  from  the 
decaying  animal  and  vegetable  particles 
mixed  up  with  the  soil  taken  into  the  sto¬ 
mach  ;  so  that  the  exception  to  the  general 
law  of  nature  supposed  to  exist  in  the  earth- 


204 


ANNELIDA. 


worm  has  no  foundation  in  truth.  The  whole  intestinal  tract  of 
one  of  these  animals  is  represented  in  the  figure  {Jig-  82)  :  it  con¬ 
sists  of  a  wide  oesophagus  which  terminates  in  a  crop-like  dilata¬ 
tion  ;  to  this  succeeds  a  muscular  gizzard  (&),  and  a  long  sacculated, 
intestine  (/,  /)  which  passes  in  a  direct  line  to  the  anus. 

(247.)  The  circulation  of  the  blood  in  the  terricolous  Annelidans 
has  been  the  subject  of  much  discussion,  and  until  recently  was  but 
very  imperfectly  understood.  In  the  earth-worm  there  are  three 
principal  trunks  connected  with  the  vascular  Fig.  83. 

system,*  the  arrangement  of  which  is  repre¬ 
sented  in  the  annexed  diagram  {Jig-  83). 

First,  a  dorsal  vessel  (a)  runs  along  the  whole 
length  of  the  back  in  close  contact  with  the 
intestine  {Jig-  82,  o,  o),  upon  which  it  lies  ; 
this  vessel  is  tortuous,  and  exhibits  constant 
movements  of  contraction  and  dilatation,  by 
which  the  blood  is  propelled  in  continuous 
undulations  from  the  tail  towards  the  head. 

Two  other  large  vessels  occupy  the  ventral 
region  of  the  body  :  of  these,  one  {Jig-  83,  Z>), 
which  we  shall  call  the  ventral  vessel ,  runs 
immediately  beneath  the  alimentary  tube  ; 
while  the  other,  which  is  situated  close  un¬ 
der  the  skin,  and  consequently  beneath  the 
ventral  chain  of  ganglia  composing  the  nervous 
system,  by  which  it  is  separated  from  the  last, 
may  be  distinguished  as  the  sub- ganglionic 
vessel.  These  three  great  trunks  are  united 
by  important  branches,  and  form  two  distinct 
systems  :  one  of  which  is  deeply  seated,  being 
distributed  to  internal  viscera ;  the  other  is 
superficial,  giving  off  innumerable  vessels  to 
the  integuments  of  the  body,  which,  by  rami¬ 
fying  through  the  skin,  form  an  extensive  vas¬ 
cular  surface  adapted  to  respiration. 

The  ventral  vessel  (6),  like  the  dorsal  (a), 
may  be  traced  quite  to  the  anterior  extremity 
of  the  worm,  where  numerous  small  anastomosing  branches  unite 
the  two  trunks  :  but  these  inosculations  are  of  little  consequence 
in  describing  the  circular  movement  of  the  blood  ;  a  more  impor- 

*  M.  Duges,  Annales  des  Sciences  Nat.  vol.  xv. 


ANNELIDA. 


20  5 


tant  communication  being  established,  through  which  the  blood 
passes  freely  from  one  to  the  other,  by  the  intervention  of  seven  or 
eight  pairs  of  large  canals,  situated  in  the  immediate  neighbourhood 
of  the  generative  apparatus,  with  which  indeed  they  are  interwoven. 
Each  of  these  voluminous  vessels  (d)  is  composed  of  a  series  of 
swellings,  or  rounded  bead-like  vesicles,  endowed  with  consider¬ 
able  contractile  power  ;  and  they  form  together  a  kind  of  heart  of 
remarkable  construction,  which  propels  the  blood  received  from  the 
dorsal  trunk  into  the  ventral  tube  (b). 

Along  the  rest  of  the  body,  the  communication  between  the 
dorsal  and  ventral  trunks  is  repeated  at  each  ring  by  canals  which 
are  much  smaller  than  the  bead-like  or  moniliform  vessels,  and 
have  no  vesicular  arrangement ;  they  (g  and  e)  run  perpendicu¬ 
larly  upwards,  embracing  the  alimentary  canal,  and  giving  off 
branches  at  right  angles,  which  divide  into  innumerable  ramifi¬ 
cations  so  as  to  cover  the  whole  intestine  with  a  delicate  vascular 
net- work ;  these  may  be  called  the  deep-seated  ab  domino-  dor  sal 
branches. 

The  sub- ganglionic  vessel  (c)  may  be  looked  upon  as  arising 
from  the  termination  of  the  dorsal  vessel,  with  which  it  is  evi¬ 
dently  continuous  at  the  anterior  extremity  of  the  body.  At  the 
posterior  edge  of  every  segment,  a  delicate  branch  is  given  off  from 
this  sub-ganglionic  tube  (f),  which,  running  upwards  in  the  same 
manner  as  those  derived  from  the  ventral  trunk,  joins  the  dorsal, 
and  receives  in  its  course  a  large  anastomosing  branch  from  the 
deep  ab  domino- dor  sal  canal  which  corresponds  to  it.  From  this 
system  of  superficial  vessels  arises  a  cutaneous  net-work,  analogous 
to  that  described  above  as  covering  the  digestive  viscera  which  tra¬ 
verses  the  skin  in  all  directions. 

Let  us  now  trace  the  blood  in  its  circulation  through  this  ela¬ 
borate  system.  In  the  dorsal  vessel  (a)  the  sanguineous  fluid 
passes  from  the  tail  towards  the  head ;  at  the  anterior  extremity  of 
the  body  it  passes  partly  into  the  sub-ganglionic  vessel  (c),  through 
the  anastomosing  branches,  and  partly  into  the  ventral  vessel  ( b ), 
into  which  it  is  forcibly  driven  by  the  contractions  of  the  monili¬ 
form  canals.  In  both  the  ventral  and  sub-ganglionic  trunks,  there¬ 
fore,  the  course  of  the  blood  is  necessarily  from  the  head  towards 
the  tail ;  and  the  circulating  fluid  is  continually  returned  to  the 
dorsal  canal  by  the  deep  and  superficial  abdomino-dorsal  vessels 
(e,  f,  g ),  completing  the  vascular  circle. 

On  reviewing  the  above  arrangement,  we  immediately  perceive 


206 


ANNELIDA. 


that,  notwithstanding  the  similarity  observable  in  the  distribution 
of  the  ventral  and  sub-ganglionic  systems  of  vessels,  in  a  physio¬ 
logical  point  of  view  they  are  subservient  to  very  different  func¬ 
tions  ;  the  former  representing  the  systemic,  the  latter  the  pul¬ 
monary  circulation.  The  blood  derived  from  the  dorsal  trunk  by 
the  moniliform  hearts  (<7)  is  supplied  by  the  ventral  vessel,  which 
may  be  compared  to  an  aorta,  over  the  surface  of  the  viscera,  and 
the  remnant  of  this  blood,  after  furnishing  materials  for  nutrition, 
is  returned  to  the  dorsal  canal  by  the  deep  vessels  e,  g ;  but  that 
portion  of  the  circulating  fluid  which  passes  from  the  termination 
of  the  dorsal  tube  into  the  sub- ganglionic  trunk,  not  only  serves 
for  the  nourishment  of  the  skin  and  muscular  integument,  but  at 
the  same  time  is  brought  in  contact  with  the  air  as  it  passes  through 
the  cutaneous  net-work,  and  is  thus,  more  or  less,  replenished 
with  oxygen  before  it  is  again  returned  to  the  general  circulation. 
The  sub-ganglionic  canal  is,  therefore,  a  kind  of  pulmonary  artery, 
and  the  dorsal  drives  to  the  moniliform  vessels  a  mixed  fluid, 
composed  partly  of  venous  blood  derived  from  the  viscera,  and 
partly  of  arterial  derived  from  the  superficial  or  sub-cutaneous 
system. 

(248.)  We  see,  therefore,  that  the  extensive  diffusion  of  vascular 
canals  immediately  beneath  the  surface  of  the  skin  must  undoubtedly 
contribute  materially  to  effect  those  changes  in  the  blood  which 
are  analogous  to  those  produced  by  respiration  in  the  higher  ani¬ 
mals  ;  but  it  would  seem  that  this  is  not  the  only  provision  made 
for  the  aeration  of  the  circulating  fluids.  It  is  long  since  Willis* 
described  the  existence  of  a  series  of  pores  upon  the  back  of  the 
earthworm,  which  he  regarded  as  stigmata,  and  had  remarked 
that  air  blown  into  these  openings  is  dispersed  between  the  mus¬ 
cular  integument  and  the  intestine,  so  that  it  passes  readily  from 
one  segment  to  another.  Duges  repeated  these  experiments  with 
the  same  result,  and  found  that  the  pores  alluded  to,  instead  of 
terminating  in  muciparous  follicles,  as  they  were  supposed  to  do 
by  many,  penetrate  into  the  interior  of  the  body,  so  that  air  in¬ 
jected  into  one  of  them  passes  freely  along  the  membranous  com¬ 
partments  which  surround  the  intestine,  and  escapes  through  other 
neighbouring  orifices.  In  like  manner  water  is  found  to  be 
taken  into  the  body  through  the  same  apertures,  from  which  it  is 
often  given  out  in  great  abundance  when  the  animal  is  too  rapidly 
dried  by  exposure  to  the  sun,  or  irritated  by  external  stimuli : 

* 


De  A  nima  Brutoium,  4to.  1672. 


ANNELIDA. 


207 


aerated  water  tlms  taken  into  tlie  system,  and  brought  immediately 
in  contact  with  the  deep-seated  vascular  net-work  dispersed  over 
the  intestinal  parietes,  must  therefore  necessarily  contribute  to  the 
respiratory  function.  Nevertheless,  in  addition  to  all  this,  we  find 
in  every  segment  of  the  body  a  pair  of  membranous  vesicles  {fig. 
82,  v )  communicating  externally  by  lateral  orifices,  apparently 
analogous  to  the  respiratory  vesicles  of  the  leech  ;  and,  in  fact,  by 
many  authors  they  have  been  described  as  constituting  the  breath¬ 
ing  apparatus.*  Their  real  office,  however,  is  but  imperfectly 
understood ;  they  evidently  have  not  the  same  relation  with  the 
circulatory  system,  which  the  lateral  sacculi  of  the  leech  have  been 
found  to  exhibit ;  are  they  then  merely  secreting  follicles  destined 
to  furnish  a  mucosity  for  lubricating  the  external  surface  of  the 
body,  or  are  they  aquiferous  tubes  adapted  to  introduce  water  into 
the  interior?  Future  observations  must  determine  these  ques¬ 
tions. 

(249.)  Few  points  connected  with  the  history  of  the  earthworm 
have  given  rise  to  so  much  speculation  as  the  manner  of  their  repro¬ 
duction.  The  generative  organs  have  long  been  known  to  be  lodged 
in  the  anterior  part  of  the  body,  their  position  being  indicated 
externally  by  a  considerable  enlargement  or  swelling  which  extends 
from  the  seventh  to  about  the  fourteenth  segment,  counting  from 
that  in  which  the  mouth  is  situated.  On  opening  this  portion  of 
the  animal,  a  variable  number  of  white  masses  are  found  attached 
to  the  sides  of  the  crop  and  gizzard  {fig.  82,  A,  A,  A),  which  have 
long,  by  general  consent,  been  looked  upon  as  forming  the  repro¬ 
ductive  system  ;  some  having  been  regarded  as  representing  the 
testes,  others  the  ovaria :  yet  so  delicate  are  the  connections 
which  unite  these  glandular  masses,  and  such  the  difficulty  of 
tracing  the  ducts  whereby  they  communicate  with  the  exterior 
of  the  body,  that  the  functions  to  which  they  are  individu¬ 
ally  appropriated  have  given  rise  to  much  discussion.  The 
Lumbrici  have  been  generally  acknowledged  to  be  hermaphrodite, 
that  is,  possessed  of  organs  adapted  both  to  the  formation  and 
fertilization  of  ova ;  and  it  is  likewise  well  understood  that  the 
congress  of  two  individuals  is  essential  to  the  fecundity  of  both, 
as,  in  the  earlier  summer  months,  the  mode  in  which  they  copulate 
is  a  matter  of  constant  observation.  At  such  times  two  of  these 
animals  are  found  to  come  partially  out  of  the  ground  from 
contiguous  holes,  and,  applying  together  those  segments  of  their 


*  Sir  E.  Home.  Lectures  ou  Comp.  Anat.  4  vols.  4to.  1323. 


208 


ANNELIDA. 


bodies  in  which  the  generative  glands  are  situated,  are  observed 
to  remain  for  a  considerable  time  in  contact,  joined  to  each  other 
by  a  quantity  of  frothy  spume  which  is  poured  out  in  the  neigh¬ 
bourhood  of  the  sexual  organs.  No  organs  of  intromission,  how¬ 
ever,  have  ever  been  distinguished,  neither  until  recently  had  the 
canals  communicating  between  the  sexual  orifices  and  the  testicular 
or  ovarian  masses  been  satisfactorily  traced  ;  so  that  Sir  Everard 
Home*  was  induced  to  believe  that,  in  the  kind  of  intercourse 
above  alluded  to,  there  was  no  transmission  of  impregnating  fluid 
from  one  animal  to  the  other,  but  that  the  excitement  produced 
by  mutual  contact  caused  both  the  ovaria  and  testes  to  burst,  so 
that  the  ova  escaping  into  the  cells  of  the  body  became  there 
mingled  with  the  spermatic  secretion,  and  being  thus  fertilized  the 
ova  were  hatched  internally,  and  the  young,  having  been  retained 
for  some  time  in  the  cells  between  the  intestine  and  the  skin, 
were  ultimately  ejected  through  apertures  which  were  supposed  to 
exist  in  the  vicinity  of  the  tail.  There  is,  however,  little  doubt 
that  what  Sir  E.  Home  conceived  to  be  young  earthworms  were 
in  reality  parasitical  Entozoa,  and  that,  in  the  mode  of  their  pro¬ 
pagation,  the  animals  we  are  describing  exhibit  but  little  deviation 
from  what  we  have  already  seen  in  the  leech. 

(250.)  According  to  M.  Duges,f  the  arrangement  of  the  sexual 
parts  is  represented  in  the  diagram  {Jig.  84).  The  testicles  (5)  are 
placed  in  successive  segments  of  Fig.  84. 

the  body  from  the  seventh  back¬ 
wards  ;  they  vary  in  number  in 
different  individuals  from  two  to 
seven  :  but  whether  this  variety 
depends  upon  a  difference  of 
species,  or  is  only  caused  by  the 
posterior  pairs  becoming  atrophied 
when  not  in  use,  is  undetermined. 

Each  testis  is  fixed  to  the  bot  ¬ 
tom  of  the  ring  in  which  it  is 
placed  by  a  short  tubular  pedicle 
that  opens  externally  by  a  very 
minute  pore  through  which  a 
milky  fluid  can  be  squeezed. 

The  testicular  vesicles  of  the 
same  side  of  the  body  all  com- 

*  Lectures  on  Comp.  Anat.  vol.  iii. 


ANNELIDA. 


209 


Fig.  85. 


municate  by  a  common  canal  ;  and  the  contained  fluid,  which  like 
the  seminal  secretion  of  other  animals  contains  animalcules,  can 
readily  be  made  to  pass  from  one  to  another. 

The  ovaria  (c)  are  eight  large 
white  masses  of  a  granular  texture, 
from  which  arise  two  delicate  tubes 
or  oviducts  ;  these  have  no  connection 
with  the  testes,  but,  running  back¬ 
wards,  they  become  dilated  into  two 
small  vesicles  at  their  termination 
(d),  and  open  by  two  apertures  or 
vulvse  seen  externally  upon  the  six¬ 
teenth  segment  of  the  body  :  in  these 
ducts  eggs  have  been  detected  as  large 
as  pins’  heads. 

(251.)  The  eggs, when  laid,  are  two 
or  three  lines  in  length.  In  figure  85, 
a,  one  of  them  enclosing  a  mature  em¬ 
bryo  is  delineated ;  its  top  is  seen  to 
be  closed  by  a  peculiar  valve-like 
structure  adapted  to  facilitate  the 
escape  of  the  worm,  and  opening 
(Jig.  85,  b)  to  permit  its  egress. 

Another  remarkable  circumstance  ob¬ 
servable  in  these  eggs  is,  that  they  very  generally  contain  double 
yolks,  and  consequently  two  germs,  so  that  a  couple  of  young 
ones  is  generally  produced  from  each. 

(252.)  The  generative  system  of  the  Nais  presents  a  somewhat 
different  arrangement  to  that  which  exists  in  the  earthworm.  The 
swollen  part  of  the  body  in  which  the  sexual  organs  are  placed,  occu¬ 
pies  a  space  of  five  or  six  rings,  beginning  at  the  eleventh.  On  each 
side  of  the  eleventh  segment  is  a  minute  transverse  slit  (Jig.  86,  b ) 
communicating  with  a  slightly  flexuous  canal  which  terminates 
in  a  transparent  pyriform  pouch  or  vesicle.  The  latter  con¬ 
tains  a  clear  fluid,  in  which  minute  vermiform  bodies  are  seen 
to  float,  and  most  probably  represents  the  testis.  The  twelfth 
segment  likewise  exhibits  two  openings,  each  placed  upon  the 
centre  of  a  little  nipple  (c),  these  are  the  orifices  leading  to 
the  female  portions  of  the  sexual  system.  The  ovaria  ( d ,  e) 
are  composed  of  four  large  and  several  smaller  masses  of  a 
granular  character,  and  from  them  proceed  long  and  tortuous 


210 


ANNELIDA. 


Fig.  86. 


oviducts,  which  just  before  their  termination  at  the  lateral  openings 
(c)  become  thick  and  glandular.  These  animals  most  likely  co¬ 
pulate  like  the  earthworm,  and  lay  their 
eggs  in  a  similar  manner.  We  have  al¬ 
ready  seen  in  the  Lumbricus  terrestris 
ova  containing  two  yolks,  and  consequently 
giving  birth  to  two  animals  ;  but  in  the 
Nais  every  egg  produces  ten  or  a  dozen 
young  ones,*  or,  perhaps  we  ought  rather 
to  say,  that  what  appears  to  be  a  single 
egg  is  in  fact  merely  a  capsule  enclosing 
several  distinct  ova  from  which  a  numerous 
progeny  arises.  The  manner  in  which 
these  compound  eggs  are  formed  is 
easily  understood,  when  we  consider  the 
structure  of  the  oviduct  described  above. 

The  granular  germs  escape  no  doubt 
separately  from  the  ovaria,  and  remain 
distinct  from  each  other  as  they  pass 
along  the  tortuous  canal  which  leads  to  e 
the  external  opening  ;  but  at  length,  ar¬ 
riving  at  the  thick  and  glandular  portion 
(c)  of  the  oviferous  tube,  several  of  them 
become  enclosed  in  a  common  investment 
secreted  by  the  walls  of  the  oviduct,  and 
are  expelled  from  the  body  with  the  out¬ 
ward  appearance  of  a  simple  egg. 

(253.)  Besides  the  ordinary  mode  of  pro¬ 
pagation  by  ova,  it  has  long  been  ascertained 
that  some  of  the  Annelida  at  least  are  re¬ 
produced  by  spontaneous  division.  Bonnet,  Muller,  and  Duges,  all 
agree  that  this  is  the  case  with  certain  species  of  Nais  ;  and  in  Nais 
jiliformis  the  process  of  separation  has  been  witnessed  from  its  com¬ 
mencement  to  its  termination.  The  division  was  seen  to  occur 
near  the  middle  of  the  body  of  the  animal,  the  posterior  half  re¬ 
maining  motionless  upon  the  mud  of  the  bottom  of  the  vessel, 
whilst  the  anterior  portion  buried  itself  as  usual  ;  after  some  days 
the  truncated  extremity  of  the  hinder  part  was  observed  to  become 
swollen,  transparent,  and  vascular,  and  ultimately  to  assume  the 
complete  structure  of  the  mouth  of  the  perfect  animal ,*  it  then 


*  Duges,  loc.  cit. 


ANNELIDA. 


211 


buried  itself  in  tlie  mud,  and  no  doubt  there  completed  its  de¬ 
velop  ement. 

(254,)  It  is  very  generally  believed,  that  even  the  earthworm  may 
be  multiplied  by  mechanical  sections,  the  separated  portions  repro¬ 
ducing  such  parts  as  are  removed  in  the  experiment,  and  again 
becoming  perfect.  Careful  experiments  made  to  ascertain  how  far  the 
statements  of  former  authors  upon  this  subject  are  substantiated, 
prove  that  the  assertion  is  not  entirely  without  foundation,  al¬ 
though  by  no  means  to  the  extent  indicated  in  their  writings.  It 
would  indeed  be  easily  credited  that  the  removal  of  the  hinder 
part  of  the  body  of  an  earthworm  would  not  necessarily  destroy  the 
anterior  portion,  since  no  organs  absolutely  essential  to  existence 
are  removed  by  the  operation,  and  even  the  course  of  the  circu¬ 
lating  fluids  would  not  be  materially  interrupted  by  the  mutilation  ; 
but  that  the  hinder  moiety  should  be  able  to  reproduce  the  mouth, 
gizzard,  and  stomach,  the  complicated  apparatus  of  moniliform 
vessels  and  the  sexual  organs,  contained  in  the  anterior  segments, 
could  scarcely  be  deemed  possible,  and  the  assertion  has  been 
satisfactorily  disproved  by  actual  observation.  On  cutting  an 
earthworm  in  two,  the  anterior  portion  is  found  in  fact  generally 
to  survive  ;  and  the  wound  caused  by  the  operation,  becoming 
gradually  constricted,  is  soon  converted  into  an  anal  orifice,  render¬ 
ing  the  animal  again  complete  in  all  parts  necessary  for  its  ex¬ 
istence.  This,  however,  is  by  no  means  the  case  with  the  posterior 
portion  ;  for  although  it  will  exhibit,  for  a  very  long  period,  indica¬ 
tions  of  vitality,  no  signs  of  reproduction  have  been  witnessed,  and 
it  invariably  perishes. 

(255.)  Nevertheless,  although  it  is  thus  proved  that  the  earthworm 
cannot  be  multiplied  by  mechanical  division,  it  is  undeniably  able 
to  reproduce  small  portions  of  its  body,  the  removal  of  which  does 
not  implicate  organs  essential  to  life.  In  the  experiments  of 
M.  Duges,*  for  example,  it  was  found  that  four,  or  even  eight,  of 
the  anterior  rings  might  be  cut  off  with  impunity,  although  the 
cephalic  pair  of  ganglia,  the  mouth,  and  a  part  of  the  oesophagus 
were  necessarily  taken  away.  In  worms  thus  mutilated,  after  the 
lapse  of  from  ten  to  thirty  days,  a  conical  vascular  protuberance 
was  observed  to  sprout  from  the  bottom  of  the  wound  ;  and,  in 
eight  or  ten  days  later,  this  new  part  had  become  so  far  developed, 
that  not  only  all  the  lost  rings  were  apparent,  but  even  the  upper 
lip  and  mouth  had  assumed  their  normal  form,  and  the  animal 
again  began  to  eat  and  bury  itself  in  the  earth. 

r  2 


*  Loc.  cit. 


212 


ANNELIDA. 


(256.)  Dorsibranchiata. — -We  have  gone  too  minutely  into  the 
anatomy  of  the  two  preceding  orders  of  Annelidans  to  render  an 
equally  detailed  account  of  the  structure  of  the  Dorsibranchiata  ne¬ 
cessary  ;  we  must  therefore  restrict  our  observations  to  those  points 
in  which  remarkable  variations  from  what  has  already  been  described 
present  themselves  to  our  notice.  These  worms  are  all  inhabit¬ 
ants  of  the  sea  ;  and  although  upon  our  own  coasts  they  seldom 
attain  to  very  considerable  dimensions,  rarely  exceeding  a  few 
inches  in  length,  in  tropical  climates  some  species  are  found  of 
comparatively  gigantic  proportions,  having  their  bodies  composed 
of  four  or  five  hundred  segments,  and  occasionally  measuring  four 
feet  from  one  end  to  the  other. 

W e  have  already  seen  (§  233)  that,  in  the  more  perfectly  or¬ 
ganized  forms  of  these  worms,  each  segment  of  the  body  supports 
certain  external,  moveable  appendages  adapted  to  assist  in  locomo¬ 
tion,  which  are  usually  called  the  feet,  or  more  properly  the  oars ; 
they  present  great  diversity  of  appearance,  and,  from  the  nature  and 
arrangement  of  the  different  parts  composing-  them,  are  of  material 
assistance  to  the  systematic  zoologist,  as  they  afford  important 
characters  for  the  establishment  of  generic  and  specific  differences. 
In  the  section  of  Leoclicea  antennata  already  given,  {Jig.  77,  2,) 
these  parts  are  seen  in  a  very  intelligible  form,  and  are  visibly 
composed  of  three  distinct  structures  adapted  to  different  uses. 
The  first,  which  occupies  the  uppermost  position,  is  the  respiratory 
apparatus  (b)  ;  in  Leodicea  its  structure  is  extremely  simple, 
being  composed  of  a  central  stem  from  which  a  single  series  of 
vascular  filaments  is  sent  off,  giving  the  organ  a  pectinated  ap¬ 
pearance  ;  but  in  other  cases  the  branchial  tuft  is  far  more  con¬ 
siderably  developed,  dividing  and  subdividing  into  minute  ramifi¬ 
cations,  and  thus  offering  a  more  considerable  surface  to  the 
surrounding  element.  In  most  instances,  as  in  Leodicea  {Jig. 
77,  I),  these  respiratory  arbuscles  are  placed  along  the  entire 
length  of  the  body,  being  appended  to  every  segment,  with  the 
exception  perhaps  of  a  few  of  the  most  anterior ;  nevertheless,  in 
some  species,  their  distribution  is  more  partial,  and  their  presence 
is  restricted  to  a  few  rings  of  the  animal. 

In  Arenicola  piscatorum ,  for  instance,  {Jig.  87,)  a  worm 
met  with  abundantly  upon  our  own  coasts,  and  eagerly  sought 
after  as  a  bait  by  fishermen,  who  dig  it  from  the  holes  which 
it  excavates  in  the  sand,  the  branchiae  ( b )  are  confined  to  the 
central  portion  of  the  body,  where  they  form  on  each  side  a  series 


ANNELIDA. 


213 


of  bundles  which  are  remarkable  during  the  life  of  the  creature 


for  their  beautiful  red  colour,  derived  from 
the  crimson  blood  which  circulates  copious¬ 
ly  through  them. 

But  the  organs  of  respiration  in  the  Dor- 
sibrancliiate  Annelidans  are  not  always  arbo¬ 
rescent  ;  on  the  contrary,  they  are  not  un- 
frequently  spread  out  into  thin  membra¬ 
nous  lamellae,  or  resemble  fleshy  crests  or 
vascular  tubercles  ;  still,  whatever  their 
form,  their  office  is  the  same,  and  the  vessels 
spread  over  them,  presenting  an  extensive 
surface  with  which  the  water  is  brought  in 
contact,  the  blood  is  oxygenated  as  it  passes 
through  them. 

(257.)  The  second  class  of  organs  to  be 
enumerated  as  entering  into  the  composi¬ 
tion  of  the  lateral  appendages,  are  soft,  fleshy, 
and  sub-articulated  processes  called  cirri 
{Jig-  77,  2,  c,  d) ;  these  are  generally  two  in 
number,  and  belong  one  to  the  ventral  and 
the  other  to  the  dorsal  oar  :  their  precise 
office  is  not  well  understood  ;  but  as  in 
some  of  the  segments,  especially  in  the 
neighbourhood  of  the  head,  they  assume  a 
tentacular  form,  they  have  with  some  pro¬ 
bability  been  regarded  as  instruments  of 
touch. 

(258.)  The  seta  {fig-  77,  2,  d)  are  per¬ 
haps  the  most  efficient  agents  in  progression. 
These  are  long  and  stiff  hairs  disposed  in 
bundles  and  implanted  into  strong  muscular 
sheaths.  Each  packet  of  setae  can  be  retracted 
within  the  body  to  a  certain  extent,  and 
again  protruded  by  the  action  of  the  tubular 
supports  from  which  they  arise,  and,  being 
capable  of  independent  action,  these  organs 
must  be  looked  upon  as  so  many  power¬ 
ful  fins,  well  calculated  to  propel  the 
creature  through  the  element  which  it  in¬ 
habits. 


Fig.  87. 


Gr 


ANNELIDA. 


214 


Fig.  88. 


Nothing  can  exceed  the  splendour  of  the  colours  which  orna¬ 
ment  some  of  these  fasciculi  of  hairs  ;  they  yield,  indeed,  in  no 
respect  to  the  most  gorgeous  tints  of  tropical  birds  or  to  the  bril¬ 
liant  decorations  of  insects  :  green,  yellow,  and  orange,— blue, 
purple,  and  scarlet, — all  the  hues  of  Iris  play  upon  them  with  the 
changing  light,  and  shine  with  a  metallic  effulgence  only  com¬ 
parable  to  that  which  adorns  the  breast  of  the  humming-bird. 
But  it  is  not  for  their  dazzling  beauty  merely  that  these  setse  are 
remarkable  ;  they  are  not  unfrequently  important  weapons  of  de¬ 
fence,  and  exhibit  a  com¬ 
plexity  of  structure  far  be-  , 
yond  anything  to  be  met  A 
with  in  the  hair  of  higher  jk 
animals.  In  the  Aphro¬ 
dite  hispida ,  for  example, 

{Jig.  88,  a,)  they  are  per¬ 
fect  harpoons  ;  the  point 
of  each  being  provided 
with  a  double  series  of 
strong  barbs,  (Jig.  88,  b,) 
so  that  when  the  creature 
erects  its  bristles,  much 
more  formidable  than  those 
of  the  porcupine,  the  most 
determined  enemy  would 
scarcely  venture  to  attack 
it. 

But  here  we  cannot  help 
observing  an  additional 
provision,  rendered  neces¬ 
sary  by  the  construction  of  these  lance-like  spines.  We  have 
before  noticed  that  the  bundles  of  setse  are  all  retractile,  and  can 
be  drawn  into  the  body  by  the  muscular  tube  from  which  they 
spring.  It  would  be  superfluous  to  point  out  to  the  reader  the 
danger  which  would  accrue  to  the  animal  itself  by  the  presence  of 
such  instruments  imbedded  in  its  own  flesh,  as  by  every  movement 
of  the  body  they  would  be  inextricably  forced  into  the  surrounding 
tissues.  The  contrivance  to  obviate  such  an  accident  is  as  beau¬ 
tiful  as  it  is  simple.  Every  barbed  spine  is  furnished  with  a 
smooth,  horny  sheath,  (Jig.  88,  a,  bj  composed  of  two  blades, 
between  which  it  is  lodged  ;  and  these,  closing  upon  the  barbs  when 


ANNELIDA. 


215 


Fig.  89. 


they  are  drawn  inwards,  effectually  protect  the  neighbouring  soft 
parts  from  laceration. 

(259.)  In  the  Aphrodite  above  alluded  to  we  have  an  additional 
appendage  developed  from  the  upper  part  of  each  lateral  oar,  in  the 
shape  of  a  broad  membranous  scale,  which,  arching  inwards  over 
the  back  {Jig.  89,  c),  forms  with 
its  fellows  a  series  of  imbricated 
plates,  or  Elytra,  as  they  are  tech¬ 
nically  named  ( Jig.  88,  a)  ;  and 
beneath  these  the  branchial  organs 
are  lodged.  Each  of  the  elytral 
scales  is  formed  by  a  double  mem¬ 
brane,  between  the  laminae  of  which 
at  certain  seasons  the  eggs  are 
found  to  be  deposited  ; — a  situation 
evidently  adapted  to  ensure  the  ex¬ 
posure  of  the  ova  to  the  influence  of  the  surrounding  element, 
and  thus  to  provide  for  the  respiration  of  the  embryo.* 

(260.)  The  structure  of  the  mouth  in  the  Dorsibratichiate  Anne- 
lidans  is  very  peculiar.  The 

first  portion  of  the  alimentary  >s'  ' 

canal  or  stomach,  as  it  is  most  53 

erroneously  called  by  some 
writers,  is  muscular  ;  and 
certainly,  when  seen  in  a  dead 
Annelide,  it  might  easily  be 
taken  for  a  digestive  cavity. 

Nevertheless,  during  life,  this 
part  of  the  alimentary  ap¬ 
paratus  is  destined  to  a  widely 
different  office  ;  for  it  is  so 
constructed,  that  at  the  will 
of  the  animal  it  can  be  com¬ 
pletely  everted,  turned  inside 
out,  and,  when  thus  pro¬ 
truded  externally,  it  forms  a 
very  singular  proboscis,  used 
in  seizing  food,  and  frequent¬ 
ly  armed  with  powerful  teeth  of  singular  construction.  The  an¬ 
nexed  figure  (Jig.  90,  a),  representing  the  head  of  one  of  these 

*  JVJ  ilne  Edwards,  Ann.  des  Sciences  Nat.  vol.  xxvii. 


216 


ANNELIDA. 


worms  ( Goniada  a  chevrons ,  Milne  Edwards),  will  give  a  good 
idea  of  tliis  curious  organ  when  fully  displayed ;  and  in  Jig.  90, 
b,  the  mechanism  is  exhibited  by  which  its  protrusion  and  re¬ 
traction  are  accomplished.  The  whole  apparatus  is  there  seen  to 
consist  of  two  muscular  cylinders,  placed  one  within  the  other,  but 
continuous  at  their  upper  margin  (b),  or,  to  use  a  familiar  illustra¬ 
tion,  the  proboscis  may  be  compared  to  the  finger  of  a  glove 
partially  inverted  ;  it  is  obvious  that  in  this  case,  if  the  inner  cylin¬ 
der  be  drawn  inwards,  —  that  is,  into  the  mouth, — the  whole 
structure  becomes  shortened,  until  at  last  it  is  entirely  retracted 
into  the  oral  cavity  ;  whereas,  on  the  contrary,  if  the  outer  tube 
is  made  to  protrude,  it  expands  at  the  expense  of  the  inner  one, 
which  is  gradually  drawn  forwards.  The  internal  surface  of  this 
remarkable  proboscis  is,  moreover,  variously  modified  in  its  struc¬ 
ture,  so  as  to  adapt  it  to  the  prehension  of  different  kinds  of  prey. 
In  Amphinome ,  for  instance,  the  orifice  of  the  mouth  is  a  thick, 
fleshy,  and  callous  circle  (Jig.  93,  h ,  c,  d),  and  the  surface  of  the 
exserted  proboscis  is  covered  with  delicate  transverse  ruga?,  evi¬ 
dently  so  arranged  as  to  give  tenacity  to  its  gripe.  In  Goniada  it 
supports  two  distinct  sets  of  horny  teeth,  provided  for  very  differ¬ 
ent  uses  ;  one  set,  which  is  exposed  when  the  proboscis  is  un¬ 
rolled  to  a  very  small  extent,  consists  of  a  series  of  linear  horny 
plates,  (Jig.  90,  a,  d,)  and  probably  forms  a  kind  of  file,  or  ra¬ 
ther  a  scraper,  with  which  the 
animal  excavates  the  subterra¬ 
nean  galleries  in  which  it  lives. 

The  other  set  does  not  make  its 
appearance  till  the  proboscis  is 
more  completely  expanded,  and 
is  evidently  an  instrument  of  pre¬ 
hension,  formed  by  two  horny 
hooks  (Jig.  90,  b,  a ,  h)  placed 
upon  an  elevated  ridge  near  the 
entrance  of  the  oesophagus,  so  as 
to  take  a  secure  hold  of  any  vic¬ 
tim  seized  by  this  curious  mouth. 

In  Phyllodoce  laminosa  the 
teeth  form  a  circle  of  semi-carti¬ 
laginous  beads,  encompassing  the 
extremity  of  the  proboscis  when 
that  organ  is  pushed  out  to  its 


ANNELIDA. 


217 


full  length  (Jig.  91,  />),  an  arrangement  well  adapted  to  hold  and 
perhaps  to  crush  their  prey. 

But  the  most  formidable  jaws  are  met  with  in  some  of  the 
Nereidiform  species,  as  in  Leodicea  antennata ,  of  which  a  figure 
is  given  above  (Jig.  77).  When  the  proboscis  of  one  of  these 
creatures  is  slightly  everted,  the  extremities  of  three  pairs  of 
strong  horny  plates  emerge  from  the  mouth  ;  of  these,  one  pair 
terminates  by  forming  a  powerful  hooked  forceps,  while  the  others 
present  strong  denticulated  margins  (Jig.  92,  a,  a,  6,  c).  The 

Fig.  92. 

B  A 


L/\  j 


nature  of  these  teeth  will  be  better  seen  by  a  glance  at  b  in  the 
same  figure,  where  they  are  represented  upon  an  enlarged  scale, 
as  they  appear  when  detached  from  their  connections. 

(261.)  The  alimentary  canal  of  the  Dorsibranchiate  Annelidans 
offers  little  which  requires  special  notice.  It  invariably  passes  in  a 
direct  line  from  the  termination  of  the  proboscis  to  the  anal  extremity 
of  the  body.  In  the  Nereid ce  it  is  provided  with  numerous  lateral 
pouches,  somewhat  resembling  those  of  the  leech .  In  Aphrodite 
these  lateral  cseca  are  very  long,  slender,  and  branched  at  their 
extremities,  so  that  they  have  been  thought  by  some  to  be  secret¬ 
ing  organs,  representing  the  liver.  In  Arenicola  we  find  at  the 
termination  of  the  oesophagus  (fig.  94,  J)  two  large  coecal  ap¬ 
pendages  (e)  of  unknown  office,  while  the  rest  of  the  tube  (c)  is 
entirely  covered  with  minute  sacculi,  the  walls  of  which  are  de¬ 
cidedly  glandular,  and  secrete  a  fluid  of  a  greenish-yellow  colour. 

(262.)  The  course  of  the  principal  trunks  of  the  circulating  system 
in  the  Dorsihranchiata  bears  a  general  resemblance  to  what  we  have 
already  seen  in  the  Abranchiate  order,  modified,  of  course,  by  the 
variable  position  of  the  branchial  tufts  ;  but  with  respect  to  the 


218 


ANNELIDA. 


minuter  details 
connected  with 
the  arrangement 
of  the  vessels  our 
information  is  but 
vague  and  unsa- 

O 

tisfactory.  The 
investigation,  in¬ 
deed,  is  attended 
with  considerable 
difficulty.  The 
annexed  figure  of 
an  elaborate  dis¬ 
section  of  an  Am- 
phinome  (A.  ca- 
pillata ),  copied 
from  one  of  the 
beautiful  draw¬ 
ings  contained  in 
the  Hunterian 
Collection,*  af¬ 
fords  an  example  0 
of  a  circulating 
system  in  which 
the  propulsion  of 
the  blood  is  ef¬ 
fected  entirely  by 
vessels,  without 
the  intervention 
of  any  muscular 
cavities  or  heart. 

In  this  animal 
the  respiratory 
organs  are  penni- 
form  appendages 

1 1 

*  Descriptive  and  </ 
illustrated  Catalogue 
of  the  Physiol.  Series 
of  Comp.  Anat.  in  the 
Mus.  Royal  Coll.  Sur¬ 
geons,  London,  vol.  ii. 
pi .  xiv. 


Fig.  93. 


ANNELIDA. 


219 


placed  along  the  bach,  and  these  external  vascular  tufts  communi¬ 
cate  with  delicate  plexuses  of  vessels  situated  in  the  interior  of  the 
body,  called  the  branchial  plexuses.  In  the  figure  the  branchial 
plexuses  of  the  left  side  only  are  represented  (</,  </,  q ),  and  of 
these  one  marked  q'  has  been  turned  aside.  The  blood  and  nutri¬ 
tious  fluids  derived  from  the  whole  alimentary  tract  are  collected 
by  the  large  ventral  intestinal  vein  (w,  n,  n),  and  conveyed  to  the 
branchial  plexuses  through  the  numerous  vessels  (o,  o,  o),  some  of 
which  (o',  o',  o')  are  displaced  in  the  drawing  in  order  that  their 
connections  may  be  better  seen.  Besides  the  blood  and  nutriment 
thus  derived  from  the  intestine,  the  branchial  plexuses  receive  the 
circulating  fluid  from  all  the  segments  of  the  muscular  envelope  by 
separate  veins  ( p ,  p),  and  thus  the  blood  from  all  parts  is  brought 
to  the  gills  and  exposed  to  the  influence  of  oxygen. 

After  undergoing  respiration,  the  blood  is  collected  from  the 
branchial  plexuses  by  the  lateral  veins  (r,  r,  r)  ;  from  which, 
through  communicating  vessels  ( s ,  s9  s),  it  passes  into  the  aorta 
or  great  dorsal  vessel  ( t ,  t ,  t ),  to  be  distributed  through  the  body. 
From  the  aorta  large  trunks  ( v ,  v)  are  given  off  to  form  the  intes¬ 
tinal  artery  (ze,  w ),  which,  ramifying  over  the  intestine,  communi¬ 
cates  with  the  intestinal  vein  ( n ,  w),  and  thus  completes  the  vas¬ 
cular  circle.* 

In  the  Nereidce ,  the  aorta,  or  dorsal  vessel,  runs  along  the  whole 
length  of  the  back,  and  in  each  ring  offers  a  perceptible  fusiform 
dilatation,  so  that  it  has  a  beaded  appearance ;  at  every  segment  it 
gives  off  lateral  branches,  every  one  of  which  is  furnished  with  a 
little  rounded  vesicle,  which  Delle  Chiaje  conceives  to  be  a  distinct 
heart  or  contractile  cavity,  calculated  to  assist  in  the  propulsion  of 
the  contained  blood. 

In  Arenicola  the  arrangement  of  the  vascular  trunks  seems  to 
be  very  nearly  similar  to  that  found  in  the  earthworm  ;  but,  instead 
of  the  moniliform  hearts,  (§  247,)  two  large  contractile  sinuses 
communicate  between  the  dorsal  and  ventral  vessels  {Jig-  94,  Z>,  b). 

(268.)  The  reproductive  organs  of  iheDorsibranchiateAnnelidaiis 
are,  perhaps,  less  known  than  those  of  any  other  animals.  Cuvierf* 

*  The  parts  indicated  in  the  drawing  by  letters  not  referred  to  in  the  text  are  the 
following : — a,  a,  the  ventral  surface  of  the  segments  of  the  body  ;  e,  e,  the  ventral 
oars  or  packets  of  bristles  ;  f,  f,  the  ventral  cirri,  or  feelers  ;  g,  the  anal  cirri ;  h ,  the 
anus ;  i,  i,  k,  k,  the  bases  of  the  dorsal  and  ventral  oars,  with  their  surrounding  mus¬ 
cles  ;  /,  l,  the  dorsal  longitudinal  muscular  bands ;  m,  m,  the  ventral  longitudinal 
muscular  bands. 

t  Le9ons  d’Anatoinie  Comparee,  vol.  v.  p.  186. 


220 


ANNELIDA. 


I 


observed  in  the  anterior  part  of  the  body  of  Arenicola  five  grey 
vesicles  resembling  the  ovaria  of  the  earthworm  ;  and  he  was  led 
to  conclude,  in  conformity  with  the  Fi  g4< 

then  generally  received  opinion,  that 
the  ova  escaped  from  these  vesicles 
into  the  cellular  structure  between 
the  intestine  and  the  walls  of  the 
body.  It  is,  however,  probable  that  the 
granular  bodies  (Jig.  94,  m,  in )  usu¬ 
ally  found  in  that  situation  are  para¬ 
sitical  Entozoa,  as  those  of  the  earth¬ 
worm  have  been  proved  to  be. 

In  the  Nereis ,  Delle  Chiaje  de¬ 
scribes  the  ovaria  as  two  long  and  ex¬ 
tremely  delicate  caeca,  occupying  the 
posterior  half  of  the  visceral  cavity, 
and  offering  various  constrictions  and 
dilatations  in  their  course  ;  these 
caeca  terminated  by  distinct  apertures 
in  the  neighbourhood  of  the  anus, 
and  when  gravid  were  found  to  be 
filled  with  granular  ova  of  a  greenish 
colour. 

(264.)  In  one  species  of  Nereis  (N. 
prolifer  a),  Muller*  observed  repro¬ 
duction  to  take  place  by  spontaneous 
division ;  a  mode  of  propagation  which, 
although  common  among  the  Net  idee, 
had  not  previously  been  seen  in  any 
of  the  Dorsibranchiate  families.  The 
process  of  division  is  represented  in 
the  appended  figure  (Jig.  95) ;  the 
hinder  part  of  the  body,  including 
about  seventeen  segments,  is  seen  to 
be  gradually  separated  from  the  ante¬ 
rior  or  larger  portion,  and,  moreover, 
at  the  point  of  separation  a  new  head 
with  eyes  and  tentacular  cirri  is  dis¬ 
tinctly  formed.  “  In  one  case,”  says 


'  Olillio  Fred.  Muller,  Zoologia  Danica,  pi.  lii.  fig.  6,  fol.  1788. 


ANNELIDA. 


221 


Miiller,  I  found  a  mother  to  which 
three  fetuses  of  different  ages  ap¬ 
peared  in  one  length.  The  mother 
had  thirty  pedate  segments  ;  the 
youngest  daughter,  or  that  nearest 
the  mother,  had  eleven,  but  the  head 
Avas  not  yet  developed.  The  most 
remote  had  seventeen  rings,  with  both 
head  and  eyes,  and,  moreover,  the 
tail  of  the  mother  ;  the  middle  one 
had  seventeen  segments,  and  a  head. 

The  two  posterior  were  broken  off 
from  the  mother  by  pressure  :  in  the 
last,  or  oldest,  was  found  a  black  sub¬ 
stance  filled  with  white  spots  ;  and  the 
white  spots,  when  squeezed  from  the 
body,  were  oval,  each  marked  with  a 
pellucid  speck.  Were  they  eggs  ?  If 
so,  how  were  they  formed  in  a  young 
one  still  adhering  to  the  body  of  its 
parent  ?  In  the  middle  one  were  si¬ 
milar  spots,  but  smaller.  W ere  they 
younger  eggs  ?” 

Some  curious  speculations  have  been  entertained  by  continental 
writers  relative  to  this  mode  of  propagation.  The  tail  of  the  ori¬ 
ginal  Nereis  is  still  the  tail  of  its  offspring,  and,  however  often  the 
body  may  divide,  still  the  same  tail  remains  attached  to  the  hin¬ 
der  portion,  so  that  this  part  of  the  animal  may  be  said  to  enjoy 
a  kind  of  immunity  from  death. 

(265.)  Tubicola . — Our  knowledge  of  the  last,  or  tubicolous  di¬ 
vision  of  the  Annelidans,  is  very  limited  ;  it  may,  indeed,  be  said  to 
be  confined  to  an  acquaintance  with  their  external  configuration,  for 
the  few  unconnected  accounts  which  are  given  by  authors  relative 
to  their  internal  anatomy  are  so  obviously  based  upon  pure  sup¬ 
position,  that,  perhaps,  the  zootomist  who  should  enjoy  favourable 
opportunities  of  inspecting  the  larger  species  in  a  fresh  state,  could 
hardly  make  a  more  valuable  contribution  to  our  science  than  by 
giving  an  account  of  the  organization  of  these  interesting  animals. 
We  have  already  described  the  different  kinds  of  tubes  in  which  these 
Annelidans  live  (§  238  ),  and  given  a  representation  ( jig .  78)  of 
the  calcareous  tube  secreted  by  the  Serpula  contortuplicata :  the 


ANNELIDA. 


222 

annexed  figure  represents  the 
curious  habitation  of  the  Te- 
rebella  Medusa,  constructed 
by  cementing  together  minute 
shells  and  other  small  bo¬ 
dies.  In  neither  case  is  there 
any  muscular  connection  be¬ 
tween  the  worm  and  its  abode, 
so  that  the  creature  can  be 
readily  drawn  out  from  its 
residence  in  order  to  ex¬ 
amine  the  external  appen¬ 
dages  belonging  to  the  indi¬ 
vidual  segments  of  its  body. 
When  thus  displayed  ( Jig . 
97),  the  modifications  con¬ 
spicuous  in  the  structure  of 
the  lateral  oars  are  at  once 
seen  to  be  in  relation  with 
their  circumscribed  move¬ 
ments,  and  offer  a  wide  con¬ 
trast  to  the  largely  developed 
spines,  setae,  and  tentacular 
cirri,  met  with  in  the  Dorsi- 
branchiata.  In  the  upper 
part  of  the  body,  rudimentary 
protractile  bunches  of  hairs 
are  still  discernible,  but  so 
feebly  developed  that  their 
use  must  evidently  be  restrict¬ 
ed  to  the  performance  of  those 
motions  by  which  the  protru¬ 
sion  of  the  head  is  effected  ; 
while  upon  the  posterior  seg¬ 
ments  even  these  are  oblite¬ 
rated,  the  only  organs  at¬ 
tached  to  the  riims  bein^ 

O  O 

minute  foot -like  processes 
adapted  to  the  same  office. 
The  tentacular  cirri,  which 
were  likewise  distributed 


Fig.  96. 


ANNELIDA. 


along  the  entire  length  of  the 
Dorsibranchiate  order,  are  here 
transferred  to  the  head,  where  they 
form  long  and  delicate  instruments 
of  touch,  and,  most  probably,  assist 
materially  in  distinguishing  and 
seizing  prey  ;  the  branchiae,  like¬ 
wise,  are  no  longer  met  with  upon 
the  segments  enclosed  within  the 
tegumentary  tube,  but  are  placed 
only  in  the  immediate  vicinity  of  the 
head,  where  they  form  fan-like  ex¬ 
pansions,  or  ramified  tufts,  so  ar¬ 
ranged  as  to  be  most  freely  exposed 
to  the  surrounding  medium.  The 
mouth  placed  at  the  origin  of  the 
tentacular  cirri  is  a  simple  orifice 
closed  with  a  valve-like  flap  or  up¬ 
per  lip,  but  is  unprovided  with  any 
dental  structure.  The  alimentary 
canal  is  generally  a  simple  and 
somewhat  capacious  tube  which  tra¬ 
verses  the  axis  of  the  body  ;  but  in 
some  species,  as  in  Sabella  yavo- 
nina ,  it  assumes  a  spiral  course, 
making  close  turns  upon  itself  from 
the  mouth  to  the  anal  aperture, 
which  is  always  terminal.  The  cir¬ 
culating  system  probably  resembles, 
in  its  general  arrangement,  that 
of  the  Dorsibranchiate  worms,  the 
course  of  the  vessels  being  modified 
in  accordance  with  the  altered  posi¬ 
tion  of  the  branchiae  ;  but  of  this 
we  have  no  certain  knowledge,  nei¬ 
ther  are  we  acquainted  with  the  na¬ 
ture  of  the  generative  apparatus, 
and  the  scattered  remarks  of  au¬ 
thors  upon  this  subject  are  to  the 
last  degree  vague  and  unsatisfac¬ 
tory. 


Fig.  97 . 


224 


CHAPTER  XIV. 

Myriapoda/* 

(266.)  The  Annelidans  examined  in  the  preceding  chapter,  with 
the  singular  exception  of  the  earthworm,  are  only  adapted  to  an  aqua¬ 
tic  life  ;  the  soft  integument  which  forms  their  external  skeleton  and 
the  setiform  and  tentacular  organs  appended  to  the  numerous  seg¬ 
ments  of  their  elongated  bodies,  are  far  too  feeble  to  support  them 
in  a  less  dense  and  buoyant  element,  so  that  when  removed  from 
their  native  waters  they  are  utterly  helpless  and  impotent.  Sup¬ 
posing,  however,  that,  as  a  mere  matter  of  speculation,  it  was  in¬ 
quired  by  what  means  animals  of  similar  form  could  be  rendered 
capable  of  assuming  a  terrestrial  existence,  so  as  to  seek  and  obtain 
prey  upon  the  surface  of  the  earth,  and  thus  represent  upon  land 
the  Annelidans  of  the  ocean  :  a  little  reflection  would  at  once  in¬ 
dicate  the  grosser  changes  required  for  the  attainment  of  such  an 
object.  To  convert  the  water-breathing  organs  of  the  aquatic 
worms  into  an  apparatus  adapted  to  aerial  respiration  would  be  the 
first  requisite.  The  second  would  be  to  give  greater  density  and 
firmness  to  the  tegumentary  skeleton, — to  allow  of  more  power¬ 
ful  and  accurately  applied  muscular  force,  by  diminishing  the  num¬ 
ber  of  segments  composing  the  annulose  covering, — and  also  by 
converting  the  lateral  oars  into  jointed  levers  of  support  sufficiently 
strong  to  sustain  the  weight  of  the  whole  body,  to  provide  instru¬ 
ments  of  locomotion  fitted  for  progression  upon  the  ground.  Yet 
all  these  changes  would  be  inefficient  without  corresponding  modi¬ 
fications  in  the  character  of  the  nervous  system  :  the  lengthened 
chain  of  small  ganglia  found  in  the  aquatic  worms  would  be  quite 
inadequate  to  wield  muscles  of  strength  adapted  to  such  altered  cir¬ 
cumstances  ;  the  small  encephalic  brain  would  be  incompetent  to 
correspond  with  more  exalted  senses,  so  that,  as  a  necessary  conse¬ 
quence  of  superior  organization,  the  nervous  centres  must  be  all 
increased  in  their  proportionate  developement  to  adapt  them  to 
higher  functions. 

The  changes,  which  our  supposition  infers  would  be  requisite 
for  the  conversion  of  an  aquatic  Annelidan  into  a  land  animal,  are 
precisely  those  which  we  encounter  when  we  turn  our  attention 
from  the  creatures  described  in  the  last  chapter  to  the  Myria- 
poda,  upon  the  consideration  of  which  we  are  now  entering : — 


*  f. /.ugix? ,  ten  thousand,  i.e.  many  ;  tfovt,  a  foot. 


MYRIAPODA. 


225 


they  form  the  transition  from  the  red-blooded  worms  to  the  class 
of  insects,  and  are  intermediate  between  the  two  in  every  point  of 
their  structure. 

(267.)  The  body  of  a  Myriapod  is  composed  of  a  consecutive 
series  of  segments  of  equal  dimensions,  but,  unlike  those  of 
the  generality  of  the  Annelida,  composed  of  a  dense  semi-calca¬ 
reous,  or  else  of  a  firm  coriaceous  substance;  and  to  every  segment 
is  appended  one  or  two  pairs  of  articulated  legs,  generally  termi¬ 
nated  by  simple  points. 

The  anterior  segment  or  head,  besides  the  organs  belonging 
to  the  mouth,  contains  the  instruments  of  sensation,  consisting  of 
simple  or  compound  eyes,  and  of  two  long  and  articulated  organs 
called  antenna,  generally  regarded  as  appropriated  to  the  sense  of 
touch,  but  which  probably  are  connected  with  other  perceptions  less 
intelligible  to  us. 

The  air  required  for  respiration  is  taken  into  the  body  through 
a  series  of  minute  pores  or  spiracles  placed  on  each  side  along  the 
entire  length  of  the  animal,  and  is  distributed  by  innumerable 
ramifying  tubes  or  tracheae  to  all  parts  of  the  system. 

The  number  of  segments,  and  consequently  of  feet,  increases 
progressively  with  age  ;  a  circumstance  which  remarkably  distin¬ 
guishes  the  Myriapoda  from  the  entire  class  of  insects,  properly  so 
called. 


(268.)  The  Myriapoda  may  be  divided  into  two  families,  origin- 
allyindicated  by  Linnaeus  :  the  Julidce ,  or  millepedes  ;  and  the  S co¬ 
lop  endrida,  or  centipedes  ;  each  of  which  will  require  our  notice. 

Julida.  —  The  lowest  division,  Fig.  98. 

which  derives  its  name  from  the 
Julus ,  or  common  millepede,  is 
most  nearly  allied  to  the  Anneli- 
dans,  both  in  external  form,  and 
also  in  the  general  arrangement 
of  its  different  organs  ;  this,  there¬ 
fore,  we  shall  first  examine,  and 
select  the  Julus  terrestris ,  one 
of  the  species  most  frequently 
met  with,  as  an  example  of  the 
rest.  These  animals  {Jig.  98,  a) 
are  generally  found  concealed  un¬ 
der  stones,  or  beneath  the  bark  of 
decaying  timber,  where  they  find 


Q 


226 


MY  It  I A  POD  A. 


subsistence  by  devouring  decomposing  animal  and  vegetable  sub¬ 
stances.  The  body  is  long  and  cylindrical,  composed  of  between 
forty  and  fifty  hard  and  brittle  rings,  which,  with  the  exception  of 
those  forming  the  head  and  tail,  differ  but  slightly  from  each  other. 
Every  segment  supports  two  pairs  of  minute  feet,  arising  close  to 
the  mesian  line  upon  the  under  or  ventral  surface  ;  but  these  feet, 
although  distinctly  articulated  (Jig.  98,  c),  are  as  yet  extremely 
small  in  comparison  with  the  bulk  of  the  animal,  and  are  evidently 
but  mere  rudiments  of  the  jointed  legs  developed  in  more  highly 
organized  forms  of  homogangliate  beings ;  so  that  the  movements 
of  the  Julus  are  very  slow,  and  the  creature  seems  rather  to  glide 
along  the  ground,  supported  on  its  numerous  but  almost  invisible 
legs,  than  to  walk.  When  at  rest,  the  body  is  rolled  up  in  a 
spiral  form  (fig.  98,  e),  the  feet  being  concealed  in  the  con¬ 
cavity  of  the  spire,  and  thus  protected  from  injury. 

(269.)  The  mouth  resembles  in  structure  that  of  the  larva  of 
some  insects,  and  is  furnished  with  a  pair  of  stout  horny  jaws,  mov¬ 
ing  horizontally,  and  provided  at  their  cutting  edges  with  sharp  den- 
ticulations,  so  as  to  render  them  effective  instruments  in  dividing 
the  fibres  of  rotten  wood,  or  the  roots  and  leaves  of  vegetables, 
which  are  usually  employed  as  food  ;  and  the  alimentary  canal, 
which  is  straight  and  very  capacious,  is  generally  found  filled  with 
materials  of  this  description. 

(270.)  In  most  points  of  their  internal  organization,  the  Myria- 
poda  resemble  insects  ;  and  we  should  only  anticipate  the  obser¬ 
vations  which  will  be  more  conveniently  made  hereafter,  did  we 
enter  into  any  minute  description  of  their  anatomy  :  we  shall,  there¬ 
fore,  in  this  place,  simply  confine  ourselves  to  the  notice  of  those  pe¬ 
culiarities  which  occur  in  the  animals  under  consideration,  by  which 
they  are  distinguished  from  insects,  and  entitled  to  rank  as  a  dis¬ 
tinct  class.  We  have  seen  that  in  such  of  the  Annelida  as  have 
been  most  carefully  investigated,  the  orifices  of  the  sexual  organs 
are  situated  near  the  anterior  part  of  the  body,  not,  as  is  invariably 
the  case  among  insects,  at  the  caudal  extremity  :  in  this  particular 
the  Julidte  still  present  analogies  with  the  red-blooded  worms ; 
for  in  them  the  external  openings  of  the  male  parts  are  situated  im¬ 
mediately  behind  the  base  of  the  seventh  pair  of  legs,  and  are  found 
to  be  placed  upon  minute  mammillary  protuberances,  which  are 
each  furnished  with  a  sort  of  hooked  scale,  adapted  to  hold  the 
female  during  the  process  of  impregnation. 

In  the  female,  also,  the  sexual  orifices  are  advanced  very  far 


MYItlAPODA. 


227 


forward,  being  situated  in  the  vicinity  of  tlie  head,  between  the 
first  and  second  segments  ;  the  sexes,  however,  as  in  insects,  are 
perfectly  distinct,  and  the  conformation  of  the  internal  organs 
coincides  with  that  type  of  structure  which  is  common  to  the  insect 
orders. 

(271.)  Another  important  distinction  between  these  animals  and 
insects  properly  so  called,  is  met  with  in  the  mode  of  their  growth 
and  developement.  Insects,  as  we  shall  more  fully  explain  here¬ 
after,  undergo  a  more  or  less  complete  change  in  their  outward 
form  as  they  advance  through  several  preparatory  stages  to  their 
mature  state :  during  the  progress  of  these  changes,  which  consti¬ 
tute  what  is  usually  called  the  metamorphosis  of  insects,  they  are 
invariably  unable  to  perpetuate  their  species  ;  and  it  is  only  in  then- 
last  or  perfect  condition,  which  is  ordinarily  of  very  short  duration, 
that  the  sexual  organs  attain  their  perfect  developement,  and  are 
fit  for  reproduction.  In  this  state  all  true  insects  have  six  legs, 
which  is  one  of  the  most  important  characters  of  the  class.  The 
Myriapoda,  likewise,  undergo  several  changes  of  form  as  they  ad¬ 
vance  to  maturity ;  but  these  changes  principally  consist  in  the 
repeated  acquisition  of  additional  legs,  so  that  in  their  perfect 
condition,  instead  of  the  limited  number  of  six  legs  met  with 
in  insects,  these  organs  have  become  extremely  numerous.  The 
progress  of  these  transi¬ 
tions,  from  their  imma¬ 
ture  to  their  fully  de¬ 
veloped  state,  has  been 
well  observed  by  De 
Geer  *  and  Savi  ;*f  and 
the  result  of  their  ob¬ 
servations  is  here  given, 
in  order  that  the  rea¬ 
der  may  compare  the 
different  steps  of  the 
process  with  what  we 
shall  afterwards  meet 
with  in  the  more  highly 
organized  articulata. 

The  eggs,  (Jig.  99, 

*  Memoires  pour  servir  ii  l’Histoire  ties  Insectes.  7  vols.  4to.  Stockholm,  1778. 

t  Osservazione  per  servire  alia  storia  di  uua  specie  di  Julus  communissima.  Bo¬ 
logna,  1817. 

Q  2 


Fi° •.  99. 

B 


228 


MYRIAPOD  A. 


Fig.  100. 


a,  )  which  arc  very  minute,  are  deposited  in  the  earth  or  vege¬ 
table  mould  in  which  the  Jiilus  is  usually  met  with.  When  first 
hatched,  the  young  Myriapod  is  of  course  exceedingly  diminu¬ 
tive ;  at  that  period  it  resembles  a  microscopic  kidney-bean,  and 
is  completely  destitute  of  legs  or  other  external  organs.  After 
a  few  days  the  embryo  Julus  changes  its  skin,  and,  throwing  off 
its  first  investment,  appears  divided  into  distinct  segments,  and 
furnished  with  a  head,  a  pair  of  simple  eyes,  a  pair  of  antennse, 
and  six  jointed  legs  attached  to  the  anterior  rings  of  the  body 
(Jig.  99,  b,  c).  Some  days  subsequent  to  its  first  moult,  the 
skin  is  again  cast,  and  the  millepede  acquiring  larger  dimensions  is 
seen  to  possess  seven  pairs  of  ambulatory  extremities,  which  are, 
however,  still  placed  only  upon  the  anterior  segments  (Jig.  99,  d). 
When  twenty-eight  days  old,  they  again  throw  off  their  outward 
covering,  and  assume,  for  the  first  time,  their  adult  form  :  they 
then  consist  of  twenty-two  rings,  and  have  twenty-six  pairs  of 
feet ;  but,  of  these,  only  the  eighteen  anterior  pairs  are  used  in 
progression.  At  the  fourth  moult  the  number  of  legs  is  increased 
to  thirty-six  pairs ;  and  at  the  fifth,  at  which  time  the  body  be¬ 
comes  composed  of  thirty  segments,  there 
are  forty-three  pairs  of  locomotive  organs. 

At  last,  in  the  adult  state,  the  male  has 
thirty-nine  and  the  female  sixty-four  rings 
developed;  but  it  is  not  until  two  years  after 
this  period  that  the  sexual  organs  appear, 
and  the  animals  become  capable  of  repro¬ 
duction. 

(272.)  Scolopendrida. — In  the  second 
family  of  Myriapoda  we  have  a  very  striking 
illustration  of  the  manner  in  which  the  de- 
velopement  of  the  nervous  centres  proceeds 
step  by  step  with  that  of  the  external  limbs. 

The  slow-moving  Julidrn  possess  in  their 
rudimentary  feet  organs  adapted  to  their 
condition,  and  their  feeble  powers  of  locomo¬ 
tion  are  in  relation  with  their  vegetable 
diet  and  retiring  habits.  But  in  the  pre¬ 
daceous  and  carnivorous  Scolopendra  (Jig. 

100),  which,  although  it  lurks  in  the 
same  hiding-places  as  the  Julus,  obtains 
its  food  by  pursuing  and  devouring  insects, 


iiso 


MYRTAPODA. 


229 


far  greater  activity  is  indispensable,  and  accordingly  we  find  the 
segments  of  the  body,  and  the  extremities  appended  to  them,  ex¬ 
hibiting  a  perfection  of  structure  adapted  to  greater  vivacity  and 
more  energetic  movements. 

This  is  at  once  evident  upon  a  mere  inspection  of  their  out¬ 
ward  form  ;  the  individual  segments  composing  the  animal  are 
much  increased  in  their  proportionate  dimensions,  and,  instead  of 
being  cylindrical,  each  division  of  the  body  is  flattened  and  pre¬ 
sents  a  quadrangular  outline.  In  order  to  give  greater  flexibility  to 
the  body,  instead  of  the  semi-crustaceous  hard  substance  which  forms 
the  rings  of  the  Julus,  the  integument  is  composed  of  a  tough  and 
horny  substance,  forming  two  firm  plates,  one  covering  the  back,  the 
other  the  ventral  aspect  of  the  segment,  while  all  the  lateral  part 
is  only  incased  in  a  flexible  coriaceous  membrane  with  which  the 
individual  rings  are  likewise  joined  together.  Such  an  external 
skeleton  is  obviously  calculated  to  give  the  greatest  possible  free¬ 
dom  of  motion,  and  thus  to  enable  the  Scolopendra  to  wind  its 
way  with  serpent-like  pliancy  through  the  tortuous  passages  in 
which  it  seeks  its  prey. 

(273.)  The  ventral  chain  of  ganglia  belonging  to  the  nervous 
system  presents  a  series  of  nervous  centres  of  dimensions  proportioned 
to  the  increased  bulk  of  the  segments  in  which  they  are  lodged,  and 
thus  fitted  to  direct  the  movements  of  more  perfect  limbs.  The 
legs,  therefore,  as  a  necessary  consequence,  become  proportionably 
powerful,  divided  into  distinct  joints,  and  provided  with  muscles 
calculated  to  bestow  on  them  that  activity  essential  to  the  pursuit 
and  capture  of  active  prey.  Thus,  then,  by  a  simple  concentra¬ 
tion  of  the  nervous  masses  composing  the  abdominal  chain  of 
ganglia,  we  have  the  slow-moving  and  worm-like  Julus ,  which  wre 
have  seen  to  be,  in  consequence  of  its  feebleness,  restricted  to  live 
upon  roots  and  dead  substances,  converted  into  the  active  and 
powerful  Scolopendra ,  well  able  to  wage  successful  war  with  the 
strongest  of  the  insect  tribes,  and  not  unfrequently  formidable 
from  its  size  even  to  man  himself. 

(274.)  The  mouth  of  the  Scolopendra  is  a  terrible  instrument 
of  destruction  ;  being  provided  not  only  with  horny  jaws  resembling 
those  of  insects  hereafter  to  be  described,  but  with  a  tremendous 
pair  of  sharp  and  curved  fangs,  ending  in  sharp  points,  and  per¬ 
forated  near  their  termination  by  a  minute  aperture,  through  which 
a  poisonous  fluid  is  most  probably  instilled  into  the  wound  in¬ 
flicted  by  them.  It  is  to  this  structure  that  the  serious  conse- 


230 


MYRI APODA. 


quences,  which  in  hot  climates  not  nnfrequently  result  from  the 
bite  of  one  of  these  animals,  must  no  doubt  be  attributed. 

(275.)  In  their  internal  anatomy  the  S colop endr idee  resemble 
insects  even  more  nearly  than  the  Julies.  The  alimentary  canal  is 
straight  and  intestiniform,  but  of  much  smaller  diameter  than  that  of 
the  vegetable-eating  Myriapoda.  It  presents  an  oesophagus,  and  a 
small  muscular  gizzard  ;  but  there  is  no  perceptible  division  into 
stomach  and  intestine.  The  respiratory  and  circulating  sys¬ 
tems,  as  far  as  they  are  understood,  seem  to  correspond  with 
what  we  shall  afterwards  find  to  exist  in  the  larva  of  insects.  In 
the  position  and  arrangement  of  the  sexual  organs  the  Scolopen- 
dridse  complete  the  transition  between  the  Annelidans  and  insects, 
properly  so  called  ;  for,  while  in  Julus  we  have  found  them  still 
occupying  the  anterior  part  of  the  body  as  in  the  former  class,  in 
the  Scolopendra  they  are  removed  to  the  tail.  The  structure  of 
the  male  organs  is  remarkable.  The  testes  are  seven  in  number, 
and,  on  opening  the  posterior  segments  of  the  animal,  they  are 
found  closely  packed  in  parallel  lines  :  each  testis  is  composed  of 
two  fusiform  parts  precisely  similar  to  each  other,  and  from  both 
ends  of  every  one  of  these,  which  is  hollow,  arises  a  narrow  duct, 
so  that  there  are  fourteen  pairs  of  ducts  arising  from  the  fourteen 
secreting  organs.  The  ducts  all  end  in  a  common  canal,  which 
gradually  becomes  enlarged  and  tortuous,  and  terminates  by  a 
distinct  aperture  in  the  vicinity  of  the  anus.  Just  prior  to  its  ter¬ 
mination  the  common  ejaculatory  duct  communicates  with  five 
accessory  glands,  four  of  which  are  intimately  united  until 
unravelled,  while  the  fifth  is  a  simple  caecum  of  considerable 
length.* 

The  ovarian  system  of  the  female  Scolopendra  is  a  single  tube, 
apparently  without  secondary  ramifications. 

Some  Scolopendrae  (S.  phosphorea )  emit  in  the  dark  a  strong 
phosphorescent  light ;  and  one  species  (A.  electrical  is  able  to 
give  a  powerful  electrical  shock  to  the  hand  of  the  person  who  in¬ 
advertently  seizes  it. 


Vide  Cyclop,  of  Anat.  and  Phys.  art.  Generation,  organs  of. — Comp.  Anat. 


231 


CHAPTER  XV. 

Insecta. 

(276.)  The  word  Insect  has  at  different  times  been  made  use  of 
in  a  very  vague  and  indeterminate  manner,  and  applied  indiscrimi¬ 
nately  to  various  articulated  animals.  *  In  the  restricted  sense  in 
which  we  now  use  it,  we  include  under  this  title  only  such  of  tlie 
Homogangliata  as  in  their  perfect  or  mature  state  are  recog¬ 
nisable  by  the  following  characters,  by  which  they  are  distinguished 
from  all  other  creatures. 

The  body,  owing  to  the  coalescence  of  several  of  the  segments 
which  compose  their  external  skeleton,  is  divided  into  three  prin¬ 
cipal  portions  ;  the  Head ,  the  Thorax ,  and  the  Abdomen.  The 
Head  contains  the  oral  apparatus,  and  the  instruments  of  the 
senses,  including  the  antennse  or  feelers ,  which  are  articulated 
organs  presenting  great  variety  of  shape,  but  invariably  only  two 
in  number.  The  Thorax ,  formed  by  the  union  of  three  segments 
of  the  skeleton,  supports  six  articulated  legs,  and  sometimes  four 
or  two  wings  ;  these  last,  however,  are  frequently  wanting.  The 
Abdomen  is  destitute  of  legs,  and  contains  the  viscera  connected 
with  nutrition  and  reproduction. 

(277.)  But  insects,  before  arriving  at  that  perfect  condition  in 
which  they  exhibit  the  above-mentioned  characters,  undergo  a  series 
of  change,  both  in  their  outward  form  and  internal  structure,  which 
constitute  what  is  generally  termed  their  metamorphosis.  When 
this  is  complete,  as  for  example  in  the  butterfly,  the  insect,  after 
leaving  the  egg,  passes  through  two  distinct  states  of  existence 
before  it  arrives  at  maturity  and  assumes  its  perfect  form.  The 
female  butterfly  lays  eggs  which  when  hatched  produce,  not  but¬ 
terflies,  but  caterpillars, — animals  with  elongated  worm-like  bodies, 
divided  into  numerous  segments,  and  covered  with  a  soft  coriaceous 
integument  (Jig.  105,  a).  The  head  of  the  caterpillar  is  provided 
with  horny  jaws  and  several  minute  eyes  ;  the  legs  are  very  short, 
six  of  them  which  are  attached  to  the  anterior  rings  being  horny  and 
pointed,  while  the  rest  of  variable  number  appended  to  the  posterior 

*  The  word  Insect,  derived  from  the  Latin  word  Insecta,  simply  means  divided  into 
segments. 


232 


INSECT A. 


part  of  the  body  are  soft  and  membranous.  The  caterpillars,  or 
larva,* * * §  live  for  some  time  in  this  condition,  and  frequently  change 
their  skin  as  they  increase  in  size,  until  at  length,  the  last  skin  of 
the  larva  being  thrown  off,  the  animal  presents  itself  in  quite 
a  different  form,  enveloped  in  an  oblong  case,  without  any  ex¬ 
ternal  limbs,  and  almost  incapable  of  the  slightest  motion,  re¬ 
sembling  rather  a  dead  substance  than  a  living  creature  ;  it  is  then 
called  a  chrysalis ,  nymph,  or  pup af  {Jig.  105,  b). 

On  examining  attentively  the  external  surface  of  this  pupa,  we 
may  discern,  in  relief,  indications  of  the  parts  of  the  butterfly  con¬ 
cealed  beneath  it,  but  in  a  rudimentary  condition.  After  some  time 
the  skin  of  the  pupa  bursts,  and  the  imago ,  or  perfect  insect,  issues 
forth,  moist  and  soft,  with  its  wings  wet  and  crumpled  ;  but  in  a 
few  minutes  the  body  dries,  the  wings  expand  and  become  stiff, 
and,  from  being  a  crawler  upon  the  ground,  the  creature  is  con¬ 
verted  into  a  gay  and  active  denizen  of  the  air  {Jig.  105,  c). 

Such  is  the  progress  of  the  metamorphosis  when  complete  ;  but 
all  insects  do  not  exhibit  the  same  phenomena.  Those  genera 
which,  in  their  mature  condition,  have  no  wings,  escape  from  the 
egg  nearly  under  the  same  form  as  they  will  keep  through  life  ;  these 
form  the  Insecta  Ametabola J  of  authors  :  and  even  among  those 
tribes  which,  when  perfect,  possess  instruments  of  flight,  the  larva 
frequently  differs  from  the  complete  insect  only  from  its  wanting 
wings,  and  the  pupa  is  recognisable  by  being  possessed  of  these  organs 
in  an  undeveloped  or  rudimentary  state  ;  an  example  of  this  is 
seen  in  the  house-cricket,  {Jig.  102,)  in  which  a  represents  the 
imago;  b,  the  pupa;  c,  the  full-grown  larva;  d,  the  young  just 
hatched  ;  and  e,  the  eggs. 

(271 .)  The  extensive  class  of  insects  has  been  variously  arranged 
by  different  entomologists,  and  distributed  into  numerous  orders. § 
Among  the  different  systems  which  have  been  given,  we  select  the 
following  as  best  calculated  to  render  the  reader  acquainted  with 

*  So  called  by  Linnaeus,  because  in  this  condition  the  perfect  form  of  the  insect  is 
concealed  as  it  were  under  a  mask.  Larva,  Lat.  a  mask. 

t  The  two  first  of  these  names  are  purely  fanciful ;  the  last  is  derived  from  pupa, 
a  baby  wrapped  up  in  swaddling  bands. 

J  a,  without ;  y.ira.£oXri,  change. 

§  The  classification  of  insects  here  given  is  that  of  Burmeister,  which  we  select 
without  giving  any  opinion  as  to  its  relative  merits  compared  with  others  adopted  by 
different  entomologists,  but  simply  as  being  most  convenient  for  our  present  purpose. 
— Manual  of  Entomology,  translated  from  the  German  of  Dr.  Hermann  Burmeister  by 
W.  E.  Shuckard,  8vo.  1836. 


INSECTA. 


233 


the  transformations,  as  well  as  the  principal  forms,  to  which  allu¬ 
sion  will  be  made  in  subsequent  pages. 

I.  Insecta  Ametabola. — The  larva  resembles  the  perfect 
insect,  but  is  without  wings.  The  pupae  of  such  species  as  have 
wings  in  their  imago  state  possess  rudiments  of  those  organs. 
The  pupa  runs  about  and  eats. 

a.  With  sucking  mouths  composed  of  four  fine  setae  lying  in 
a  sheath. 

1st  Order.  Hemiptera .* — In  such  insects  of  this  order  as  pos¬ 
sess  wings,  which  when  present  are  always  four  in  number,  the 
anterior  or  upper  pair  are  generally  coriaceous  in  their  texture  for 
one  half  of  their  extent,  while  the  posterior  portion  is  thin  and 
membranous  ;  a  circumstance  from  which  the  name  of  the  order  is 
derived.  The  Notonecta  or  water  boatman ,  ( Jig .  101)  is  a 


Fig.  101. 


A 


-S3 


B 


familiar  example  ;  c  and  d  represent  immature,  and  f  mature 
larvae.  The  pupa,  g,  h,  differs  little  in  outward  form  from  the 
perfect  insect  e,  but  possesses  only  the  rudiments  of  wings. 

/3.  Having  mouths  furnished  with  jaws,  or  distinct  mandibles 
and  maxillae. 

2nd  Order.  Orthoptera. j* — In  this  order  the  perfect  insect  pos¬ 
sesses  four  wings,  the  posterior  pair  being  the  largest ;  and,  when 
at  rest,  these  are  folded  both  in  a  transverse  and  longitudinal 

*  w/u,i<nis,  half;  wngov,  awing. 


t  O^os,  straight, 


284 


INSECT A. 


direction.  The  anterior  wings  are  of  a  denser  texture,  resembling 
leather  or  parchment.  To  this  order  belongs  the  common  house- 
cricket  ( Gryllus  domesticus ),  of  which,  as  well  as  of  its  eggs, 
larvae,  and  pupa,  figures  are  here  given  ( Jig .  102). 

Fig.  102. 


3rd  Order.  Dictyotoptera .* — This  order  comprises  the  cock¬ 
roaches,  in  which  the  wings  are  four  in  number  when  they  exist ; 
but  they  are  generally  of  equal  size,  and  never  folded. 

II.  I  nsecta  Metabola.  —  The  larva  is  a  worm  either 
with  or  without  legs.  The  pupa  is  quiet ;  or,  if  it  moves,  it  does 
not  eat. 

4tli  Order.  Neuropterar f*  —  Insects  having  four  equally  large 
or  equally  long  wings  with  reticulated  nervures,  and  mouths  pro¬ 
vided  with  strong  lateral  jaws.  The  most  perfect  examples  of  this 
order  are  the  dragon-flies  ( Libellula ),  the  largest  of  the  insect 
„  inhabitants  of  our  own  country.  The  perfect  insect  (Jig.  103), 
equally  remarkable  for  its  beautiful  form,  powerful  flight,  and  car¬ 
nivorous  habits,  is  among  the  most  formidable  tyrants  of  its 
class  ;  while  the  larvse,  which  abound  in  our  ditches  and  stagnant 
pools,  are  eminently  destructive  to  their  aquatic  companions.  The 
larva  (Jig.  104,  b)  possesses  six  articulated  legs  ;  while  the 
pupa  a,  which  certainly  forms  an  exception  to  the  general 

t  vtugov,  a  nerve  ;  vrrsgov,  a  wing. 


*  'Six.ruwros,  reticulated  ;  a  wing. 


INSECTA. 


235 


rule  given  above,  is  not  only  furnished  with  rudimentary  wings, 
but  is  eminently  rapacious,  and  possesses  in  the  structure  of  its 


Fig.  103. 


mouth,  to  be  described  hereafter,  peculiar  facilities  for  gratifying 
its  blood-thirsty  disposition. 

In  other  orders,  the  wings  are  always  unequal ;  the  pos¬ 
terior,  and  sometimes  both  pairs,  not  unfrequently  being  wanting. 

a.  Mouths  adapted  to  sucking. 

5th  Order.  Diptera* —  Instead  of  posterior  wings,  we  find  in 
this  order  pedunculated  appendages  called  halteres  or  poisers.  The 
mouth  contains  a  soft  proboscis,  and  is  usually  armed  with  several 
setse  and  provided  with  a  pair  of  palpi ;  of  such,  the  common 
house-fly  affords  a  familiar  instance. 

6th  Order.  Lepidoptera.' |' — The  insects  belonging  to  the  lepi- 
dopterous  order  are  possessed  of  four  wings,  which  are  generally 
covered  with  microscopic  scales,  frequently  exhibiting  the  most 
beautiful  colours  :  the  larvse  are  provided  with  feet  and  a  dis- 


*  (§/-?,  -rr^ov),  with  two  wings. 


"t  a  scale  ;  wrigov. 


236 


INSECTA. 


tinct  head  ;  the  mouth  of  the 
perfect  insect  is  a  long  spiral 
proboscis. 

The  butterflies,  so  conspi¬ 
cuous  for  their  beauty,  are 
well-known  representatives  of 
this  order ;  and  the  usual 
forms  of  these  insects  in  the 
larva,  pupa,  and  imago  state 
are  familiar  to  all  {fig.  105, 
a,  b,  c). 

/3.  Mouths  with  distinct 
biting  jaws. 

7th  Order.  Hymenoptera 
—  Possessing  four  naked 
wings  traversed  by  ramose 
nervures.  Larvae  generally 
without  head  or  feet,  but 
sometimes  with  both.  Wasps, 
Bees,  &c. 

8th  Order.  Coleoptera. — 
In  this  last  order,  the  ante¬ 
rior  wings  are  converted  into 
dense  horny  cases 
or  elytra ,  be¬ 
neath  which  the 
posterior  pair,  a- 
dapted  to  flight, 
are  folded  up 
when  the  insect 
is  at  rest.  The 
larvae  possess  a 
head,  and  are 
sometimes  pro¬ 
vided  with  feet, 
but  not  always. 

The  Coleopte¬ 
rous  division  of 
the  insect  world 
embraces  the  ex- 


Fig.  104. 


/  / 


Fig.  105. 


*  vgnv-tvos ,  a  membrane ;  vrrtgov. 


B 


INSECTA. 


237 


tensive  tribe  of  beetles,  both  terricolous  and  aquatic ;  of  the 
former,  we  have  an  example  in  the  common  cock-chaffer  {Melo- 
lontha ),  of  which  a  figure  is  here  given,  as  well  as  of  the  different 
stages  of  its  developement  {fig-  106,  a,  b,  c,  d,  e).* 

Fig.  106. 


Having  thus  introduced  the  reader  to  the  chief  orders  com¬ 
posing  the  vast  class  of  insects,  our  next  object  must  be  to  ex¬ 
amine  more  in  detail  the  principles  upon  which  these  animals  are 
constructed,  both  as  regards  their  external  organization,  and  the 
nature  and  arrangement  of  their  internal  parts.  We  shall  speak 
of  them  in  the  first  place  only  in  their  perfect  condition,  leaving 
all  observations  relative  to  the  metamorphosis  to  which  they  are 
subject  for  subsequent  consideration. 

*  It  would  be  foreign  to  our  present  purpose  to  do  more  than  enumerate  other  orders 
of  insects  which  have  been  formed  by  different  authors ;  of  these,  the  following  are 
the  most  important. 

Dermaptera  (Leach),  skin;  vngov,  a  wing.  Earwigs  (Forficula). 

Trichoptera  (Leach),  6^ — Tgi%o;,  hair  ;  -rrz^ov.  May-flies  (Phryganea). 

Aphaniptera  (Kirby),  u,<Qa.vns ,  invisible  ;  <mgov.  Fleas  (Pulex). 

Aptera,  airngo;,  without  wings.  Wingless  insects. 

Parasita,  (Latreille).  Lice  (Pediculus). 

Thysanoura  (Latreille),  6v<ru.v-ov gog,  bushy-tailed.  Spring-tails  (Lepismenae). 


238 


INSECTA. 


(279.)  Insects,  examined  generally,  differ  from  all  other  articu¬ 
lated  beings  in  one  remarkable  circumstance — they  are  capable  of 
flight — can  maintain  themselves  in  the  air  by  means  of  wings  :  it  is 
true,  indeed,  that  some  species  are  met  with  in  all  the  orders  de¬ 
scribed  above,  which  are  apterous,  being  destitute  of  such  organs  ; 
but  these  form  exceptions  to  be  noticed  hereafter.  Such  a  mode  of 
progression,  through  so  rare  a  medium  as  that  of  the  atmosphere, 
necessarily  demands  an  exercise  of  muscular  power  of  the  most 
vigorous  and  active  description,  and  a  correspondent  strength  and 
firmness  in  the  skeleton  upon  which  the  muscles  act.  It  is  suffi¬ 
cient  to  cast  a  glance  at  the  external  construction  of  any  of  the 
Annelidans  or  Myriapoda,  which  have  come  under  our  notice,  to  be 
convinced  that  in  such  animals  flight  would  be  impossible  under  any 
circumstances  :  their  long  and  flexible  bodies  present  no  point  to 
which  efficient  wings  could  be  appended  ;  neither  is  any  part  of  their 
divided  skeleton  possessed  of  sufficient  strength  to  support  the  action 
of  muscles  so  forcible  and  energetic  as  would  be  indispensable  to 
wield  the  instruments  used  in  flying,  or  raise  the  body  above  the 
surface  of  the  ground. 

Similar  changes,  therefore,  to  those  which  we  found  requisite  in 
order  to  convert  the  aquatic  Annelide  into  the  terrestrial  Myriapod, 
must  be  still  further  carried  out  before  the  animals  last  mentioned 
could  be  adapted  to  become  inhabitants  of  the  air.  The  number  of 
segments  composing  their  elongated  bodies  must  be  materially  re¬ 
duced  ;  certain  parts  of  the  skeleton  must  be  strengthened  in  order 
to  sustain  the  efforts  of  muscles  sufficiently  strong  to  raise  the 
weight  of  the  animal  ;  and,  in  the  last  place,  the  nervous  ganglia, 
by  a  like  concentration  of  hitherto  separated  parts,  must  be  gather¬ 
ed  into  masses  of  increased  power  sufficient  to  animate  the  more 
vigorous  muscles  with  which  they  are  in  relation. 

(280.)  Such  changes  are  precisely  those  which  are  most  remark¬ 
able  when  we  compare  the  external  appearance  of  a  centipede  with 
that  of  a  winged  insect :  the  entire  number  of  segments,  and  conse¬ 
quently  the  proportionate  length  of  the  latter,  is  obviously  reduced. 
The  head  is  seen  to  be  more  distinct  from  the  rest  of  the  body,  to 
which  it  is  connected  by  a  moveable  joint.  The  three  anterior  seg¬ 
ments  of  the  trunk  become  largely  developed,  and,  from  the  density 
of  their  substance,  form  by  far  the  strongest  part  of  the  skeleton, 
constituting  what  is  called  the  thorax  of  the  insect ;  they  are, 
moreover,  generally  united  together,  especially  the  two  posterior, 
so  as  to  be  consolidated,  as  it  were,  into  one  piece  ;  and  to  these 


INSECTA. 


239 


rings  only  the  organs  of  locomotion  are  appended.  The  remaining 
segments  of  the  body  are  much  less  firm  in  their  texture,  especially 
in  insects  with  hard  or  horny  wing-covers,  in  which  indeed  they  are 
almost  of  a  membranous  consistence,  so  as  to  increase  as  far  as  pos¬ 
sible  the  lightness  of  the  animal  in  parts  where  strength  is  not  re¬ 
quired.  Here  then  is  an  annulose  skeleton  adapted  to  flight ; 
dense  and  unyielding  where  support  is  required  for  the  attachment 
of  the  locomotive  organs,  but  thin  and  flexible  elsewhere. 

(281.)  The  above  conditions  being  required  in  the  arrangement 
of  the  pieces  which  compose  the  outward  framework  of  the  body  in 
insects,  we  may  easily  conceive  that  the  mode  of  union  between 
the  various  segments  above  described  is  by  no  means  a  matter  of 
indifference,  inasmuch  as  very  different  degrees  of  motion  are  re¬ 
quired  between  the  individual  rings.  In  the  Annelida  and  My¬ 
riapods  a  very  simple  kind  of  junction  was  sufficient  ;  for  in  them 
the  segments  were  all  united  by  the  mere  interposition  of  a 
thinner  coriaceous  membrane,  extending  between  their  contiguous 
margins  ;  but  in  insects  several  kinds  of  articulation  are  met 
with  in  the  construction  of  the  trunk  adapted  to  the  mobility 
of  different  regions. 

The  first  mode  of  connection  is  effected  by  suture ,  or  rather  by 
a  species  of  u  harmony”  as  it  is  technically  termed  by  anatomists  ; 
two  plates  of  the  skeleton  being  accurately  and  immoveably  fitted 
to  each  other,  but  without  being  decidedly  fastened  together  by 
serrated  edges.  This  kind  of  junction  is  met  with  in  the  thorax, 
and  serves  an  important  purpose  ;  for  at  the  point  of  union  both 
plates  are  bent  inwards,  and  prolonged  internally,  so  as  to  form 
numerous  partitions  and  processes  from  which  the  muscles  mov¬ 
ing  the  wings  and  legs  derive  extensive  origins. 

A  second  means  whereby  the  pieces  of  the  thorax  are  fastened 
together  is  by  symphysis ,  in  which  a  somewhat  soft  membrane 
is  interposed  between  two  plates,  so  as  to  admit  of  a  slight  degree 
of  motion. 

More  extensive  movement  is  required  between  the  pieces  which 
compose  the  abdomen  ;  for  in  this  region  that  rigidity  and  firm¬ 
ness  which  are  essential  in  the  construction  of  the  thorax,  would 
be  highly  disadvantageous,  inasmuch  as  the  abdominal  viscera  must 
be  subject  to  constant  variations  in  bulk,  caused  either  by  food 
taken  into  the  intestines,  or,  in  the  case  of  the  female,  by  the  de- 
velopement  of  the  eggs  after  impregnation.  The  rings  of  the 
abdomen  are,  therefore,  united  by  a  membrane  passing  from  one 


240 


INSECTA. 


to  another ;  but  so  loosely,  that  the  edges  of  the  individual  plates 
wrap  over  each  other  to  some  extent,  and  thus  may  be  separated 
by  the  slightest  pressure  from  within. 

But  in  other  regions  there  is  an  absolute  necessity  for  a  mode 
of  communication  intermediate  in  character  between  the  two  kinds 
mentioned  above  ;  having  neither  the  firmness  of  the  one,  nor 
the  mobility  of  the  other.  This  is  more  especially  the  case  in 
the  junction  between  the  head  and  the  anterior  segment  of  the 
thorax,  and  also  between  the  last-named  segment  and  the  middle 
piece  of  the  thorax,  in  those  cases  where  these  two  parts  are  not 
joined  by  suture.  The  joint  employed  in  this  case  is  of  very 
beautiful  construction,  resembling  in  some  respects  that  formed 
by  a  ball  and  socket ; —  a  conical  prolongation  of  one  segment  is 
admitted  into  a  smooth  cavity  excavated  in  the  corresponding 
margin  of  the  other,  and  secured  in  this  position  by  muscles  and 
an  external  ligament.  Such  an  articulation  is  of  course  capable  of 
being  firmly  fixed  by  muscular  action,  but  at  the  same  time  admits 
of  sufficient  freedom  of  motion  to  allow  rotation  in  all  directions. 

(282.)  The  legs  of  insects,  as  we  have  already  stated,  are  in¬ 
variably  six  in  number,  one  pair  being  attached  to  each  of  the  three 
thoracic  segments.  Considered  separately,  every  leg  may  be  seen 
to  consist  of  several  pieces,  connected  together  by  articula¬ 
tions  of  different  kinds,  which  require  our  notice.  The  first  di¬ 
vision  of  the  leg,  or  that  in  immediate  connection  with  the  thorax, 
to  which  it  is  united  by  a  kind  of  ball-and-socket  joint,  enclosed 
in  a  strong  membranous  capsule,  and  possessing  very  various  de¬ 
grees  of  motion  in  different  insects,  is  called  the  hip  (coxa);  and 
upon  this,  as  upon  a  centre,  the  movements  of  the  limb  are  per¬ 
formed.  To  the  extremity  of  the  coxa  a  small  moveable  piece  is  at¬ 
tached,  called  the  trochanter  ;  to  which  succeeds  the  thigh  (femur), 
which  is  the  thickest  and  most  robust  of  all  the  divisions  of  the 
limb.  The  next  piece,  called  the  shank  (tibia),  is  occasionally  of 
considerable  length,  and  is  connected  to  the  last  by  a  hinge  ;  to  its 
extremity  is  appended  the  foot  (tarsus),  composed  of  a  consecutive 
series  of  small  segments,  varying  in  number  from  five  to  one,  the 
last  of  which  is  armed  with  claws,  or  other  appendages,  adapted 
to  different  kinds  of  progression.  These  divisions  of  the  leg  the 
reader  will  easily  recognise  ;  they  are  for  the  most  part  united 
together  by  articulations  so  constructed  as  to  allow  simply  of  flexion 
and  extension,  which  will  be  best  understood  by  inspecting,  in 
some  large  insect,  the  junction  between  the  femur  and  the  tibia, 


INSECTA. 


241 


* 


or  the  knee-joint,  as  we  might  term  it.  Upon  the  upper  ex¬ 
tremity  of  the  tibia  the  observer  will  find  on  each  side  a  precise 
semicircular  furrow,  behind  which  is  a  concentrical  but  smaller 
ridge,  and  still  further  back  a  circular  depression  or  fossulet.  On 
examining  the  corresponding  surfaces  of  the  femur ,  he  will  detect 
a  ridge  accurately  corresponding  to  the  above-mentioned  furrow  ; 
behind  this  a  furrow  corresponding  to  the  preceding  ridge,  and  still 
further  back,  a  minute  elevation  adapted  to  the  fossulet  of  the 
tibia,  wherein  it  is  fastened  by  a  minute  but  very  strong  ligament. 
Such  ridges  and  grooves,  when  fitted  into  each  other,  form  a  joint 
evidently  admitting  of  a  free  and  hinge-like  motion,  while  from 
its  structure,  dislocation  is  almost  impossible. 

(283.)  The  above  general  description  of  the  leg  of  an  insect  will 
prepare  us  to  examine  various  modifications  in  outward  form  and 
mechanical  arrangements  by  which  these  simple  organs  are  adapted 
to  progression  under  a  great  diversity  of  circumstances.  When, 
indeed,  we  reflect  how  extensively  this  class  of  animals  is  distri¬ 
buted,  and  the  variety  of  situations  in  which  insects  live,  we  are 
led  to  expect  corresponding  adaptations  in  the  construction  of  their 
instruments  of  locomotion;  and  in  this  our  expectations  will  not 
be  disappointed. 

In  the  generality  of  terrestrial  species,  the  last  segment  of  the 
tarsiis  or  foot  is  provided  with  a  pair  of  strong  horny  hooks,  which 
are  available  for  many  purposes,  being  used  either  for  creeping 
upon  a  moderately  rough  surface,  for  climbing  or  for  clinging  to 
various  substances. 

Such  simple  hooks,  however,  would  not  always  serve.  In  the 
case  of  the  louse  (Pediculus)  for  example,  that  is  destined  to 
climb  slender  and  polished  hairs,  such  prehensile  organs  could  be 
of  little  use.  The  structure  of  the  foot  is  therefore  modified  ;  the 
tarsus  in  this  insect  terminates  in  a  single  moveable  claw,  which 
bends  back  upon  a  tooth-like  process  derived  from  the  tibia,  and 
thus  forms  a  pair  of  forceps  fitted  to  grasp  the  stem  of  the  hair  and 
secure  a  firm  hold. 

Many  insects,  especially  those  of  the  Dipterous  order,  are  able 
to  ascend  the  smoothest  perpendicular  planes,  or  even  to  run  with 
facility,  suspended  by  their  feet  in  an  inverted  position,  along  sub¬ 
stances  which,  from  their  polished  surfaces,  could  afford  no  hold  to 
any  apparatus  of  forceps  or  booklets.  In  the  common  flies  ( Mus - 
cidcc ),  the  exercise  of  this  faculty  is  of  such  everyday  occurrence, 
that,  wonderful  as  it  is,  it  scarcely  attracts  the  attention  of  ordinary 


R 


242 


INSECTA. 


observers.  The  foot  of  the  house-fly,  nevertheless,  is  a  very  curious 
piece  of  mechanism  ;  for,  in  addition  to  the  recurved  hooks  pos¬ 
sessed  by  other  climbing  species,  it  is  furnished  with  a  pair  of 
minute  membranous  flaps  (fig.  107,  c),  which,  under  a  good  mi¬ 
croscope,  are  seen  to  be  covered  with  innumerable  hairs  of  the  ut¬ 
most  delicacy :  these  flaps,  or  suckers  as  they  might  be  termed, 
adhere  to  any  plane  surface  with  sufficient  tenacity  to  support  the 
whole  weight  of  the  fly,  and  thus  confer  upon  it  a  power  of  pro¬ 
gression  denied  to  insects  of  ordinary  construction. 

Fig.  107. 


In  Bibio  febrilis  (fig.  107,  b)  the  sucking  discs  appended  to 
the  foot  are  three  in  number,  but  in  other  respects  their  conforma¬ 
tion  is  the  same. 

In  Cymbex  lutea  (fig.  107,  d)  the  arrangement  of  the  suckers 
is  different,  one  large  and  spoon-shaped  disc  being  attached  to  the 
extremity  of  each  tarsal  joint.  Moreover,  in  this  case  there  is 
another  singular  structure, — two  spur-like  organs  project  from  each 
side  of  the  extremity  of  the  tibia,  each  being  is  provided  with 
a  sucking  disc,  while  the  two  together  form  a  strong  prehensile 
forceps. 

In  some  water-beetles  ( Dytiscida: )  the  feet  are  armed  with  a 
still  more  elaborately  constructed  apparatus  of  suckers ;  but  in  this 
case,  as  they  are  only  met  with  in  the  male  insect,  they  perhaps 
ought  rather  to  be  looked  upon  as  a  provision  made  for  the  purpose 


INSECTA. 


243 


of  securely  holding  the  female  during  sexual  union,  than  ns  being 
specially  connected  with  locomotion. 

In  the  anterior  legs  of  the  male  Dytiscus  the  three  first  joints  of 
the  tarsus  are  excessively  dilated,  so  as  to  form  a  broad  circular 
palette :  on  examining  the  inferior  surface  of  this  expanded  portion 
under  a  microscope,  it  is  seen  to  be  covered  with  an  immense  num¬ 
ber  of  sucking-cups  (Jig.  107,  f),  two  or  three  being  much  larger 
than  the  rest,  but  they  form  collectively  a  wonderful  instrument  of 
adhesion. 

The  middle  pair  of  legs  of  the  same  beetle  (Jig.  107,  a)  exhibit 
a  somewhat  similar  structure  ;  but,  in  this  case,  the  disc  upon  which 
the  sucking  apparatus  is  placed  is  much  elongated,  and  the  suckers 
are  all  of  small  dimensions. 

In  the  female  Dytiscus  (Jig.  109,  c)  this  configuration  of  the 
tarsus  is  wanting,  and,  moreover,  the  surface  of  the  back  is  marked 
with  deep  longitudinal  grooves  that  do  not  exist  in  the  male  insect, 
but  seem  to  be  an  additional  provision  for  facilitating  the  inter¬ 
course  of  the  sexes  in  these  powerful  aquatic  beetles. 

(284.)  Another  mode  of  progression  common  among  insects  is 
by  leaping,  to  which,  from  their  extraordinary  muscular  power,  these 
little  beings  are  admirably  adapted.  The  common  flea,  for  example, 
(Pulex  irritam ,)  (Jig.  HO),  will  leap  two  hundred  times  its  own 
length  ;  and  many  Orthoptera  possess  a  power  of  vaulting  through 
the  air  scarcely  less  wonderful,  of  which  the  cricket  affords  a  fami¬ 
liar  instance.  In  such  insects  (Jig.  102,  a,  b)  the  thighs  of  the 
posterior  legs  are  enormously  dilated,  and  the  length  of  these 
limbs  is  much  greater  than  that  of  the  anterior  pair.  When  dis¬ 
posed  to  leap,  such  insects  bend  each  hind-leg,  so  as  to  bring  the 
tibia  into  close  contact  with  the  thigh,  which  has  often  a  longitudi¬ 
nal  furrow  armed  on  each  side  with  a  row  of  spines,  to  receive  it. 
The  leg  being  thus  bent,  they  suddenly  unbend  it  with  a  jerk, 
when,  pushing  against  the  plane  of  position,  they  spring  into  the 
air.*  In  many  of  these  saltatorial  tribes  the  tarsus  is  furnished 
with  very  curious  appendages,  either  provided  for  the  purpose 
of  taking  off  the  jar  when  the  animal  alights  from  its  lofty 
leaps,  j'  or  else  by  their  elasticity  they  may  act  like  firm  cushions, 
adapted  to  give  greater  effect  to  the  spring  which  raises  the  insect 
from  the  ground.  In  the  magnified  view  of  the  tarsus  of  an  Abys- 

*  Kirby  and  Spence,  Introduction  to  Entomology,  4  vols.  8vo. 
f  Sir  E.  Home,  Phil.  Transact.  1816. 

n  2 


244 


INSECT A. 


sinian  grasshopper  (Jig- 107,  e)  the  arrangement  of  these  organs  is 
well  exhibited. 

(285.)  The  next  modification  in  the  structure  of  the  legs  is  met 
with  in  such  species  as  burrow  beneath  the  surface  of  the  ground,  of 
which  mode  of  progression  the  most  remarkable  example  is  seen  in  the 
mole-cricket  ( Gryllo-talpa  vulgaris )  (Jig-  108).  In  this  creature 

Fig.  103. 


the  anterior  segment  of  the  thorax,  whereunto  the  fore-legs  are  ap¬ 
pended,  is  wonderfully  enlarged,  and  of  great  strength,  while  the 
legs  themselves  are  equally  remarkable  for  their  enormous  bulk  and 
muscularity.  The  tibia  is  excessively  dilated,  and  terminates  ob¬ 
liquely  in  four  sharp  and  strong  spines.  The  whole  of  the  tarsus 
would,  at  a  first  glance,  appear  to  be  wanting  ;  but  on  inspection  it 
is  found  to  consist  of  three  joints  placed  upon  the  inner  side  of  the 
tibia,  the  two  first  being  broad  and  tooth-shaped,  while  the  last 
piece  is  very  small,  and  armed  with  two  hooks.  The  direction  and 
motion  of  these  hands  is  outwards,  thus  enabling  the  animal  most 
effectually  to  remove  the  earth  when  it  burrows,  and  by  the  help  of 
such  powerful  instruments  it  is  astonishing  how  rapidly  it  buries 
itself.* 

(286.)  Similar  examples  of  adaptation  in  the  mechanical  structure 
of  the  legs  of  insects  might  be  multiplied  indefinitely  ;  we  shall, 

*  Kirby  and  Spence.  Introd.  to  Ent.  vol.  ii.  p.  362. 


INSECTA. 


245 


however,  select  but  one  other  illustration  before  leaving  this  part 
of  our  subject,  namely,  the  conversion  of  these  organs  into  instru¬ 
ments  for  swimming,  whereby,  in  aquatic  insects,  they  become  adapt¬ 
ed  to  act  as  oars.  Nothing  is,  perhaps,  better  calculated  to  excite 
the  admiration  of  the  student  of  animated  nature  than  the  amazing 
results  obtained  by  the  slightest  deviations  from  a  common  type 
of  organization  ;  and  in  examining  the  changes  required  in  order  to 
metamorphose  an  organ  which  we  have  already  seen  performing 
such  a  variety  of  offices  into  fins  adapted  to  an  aquatic  life,  this 
circumstance  must  strike  the  mind  of  the  most  heedless  observer. 
The  limbs  used  in  swimming  exhibit  the  same  parts,  the  same 
number  of  joints,  and  almost  the  same  shape,  as  those  employed  for 
creeping,  climbing,  leaping,  and  numerous  other  purposes  ;  yet  how 
different  is  the  function  assigned  to  them  !  In  a  common  water 
beetle  already  referred  to,  the  Dytiscus  marginalis  {Jig-  109,  c), 

Fig.  109.  ^ 


the  two  anterior  pairs  of  legs,  that  could  be  of  small  service  as  in¬ 
struments  of  propulsion,  are  so  small  as  to  appear  quite  dispropor¬ 
tionate  to  the  size  of  the  insect,  while  the  hinder  pair  are  of  great 
size  and  strength  ;  the  last-mentioned  limbs  are,  moreover,  removed 
as  far  backwards  as  possible  by  the  developement  of  the  hinder  seg¬ 
ment  of  the  thorax,  in  order  to  approximate  their  origins  to  the 
centre  of  the  body,  and  the  individual  segments  composing  them 


are  broad  and  compressed,  so  as  to  present  an  extensive  surface  to 
tlie  water,  which  is  still  further  enlarged  by  the  presence  of  flat  spines 
appended  to  the  end  of  the  tibia,  as  well  as  of  a  broad  fringe  of 
stiff  hairs  inserted  all  around  the  tarsus.  The  powerful  oars  thus 
formed  can  open  until  they  form  right  angles  with  the  axis  of  the 
body,  and  from  the  strength  of  their  stroke  are  well  adapted  to  the 
piratical  habits  of  their  possessors,  who  wage  successful  war  not 
only  with  other  aquatic  insects  and  worms,  but  even  with  small 
fishes,  the  co-inhabitants  of  the  ponds  wherein  they  live. 

The  same  principles  are  carried  out  even  more  perfectly  in  the 
construction  of  the  swimming  legs  of  the  water-boatman  (Noto- 
necta ),  a  kind  of  water-bug.  The  resemblance  of  this  creature 
(J!g- 101,  g,  h)  to  a  boat  with  its  oars,  cannot  escape  the  most  in¬ 
attentive  examiner;  and  the  similarity  is  still  further  increased  by 
its  manner  of  swimming ;  for,  as  it  preys  upon  insects  that  have 
been  accidentally  drowned  by  falling  into  the  water,  it  usually  rows 
itself  about  upon  its  back,  because  in  such  a  position  it  can  best 
watch  for  its  victims. 

(287.)  The  wings  of  insects,  when  present,  are  invariably  attached 
to  the  two  posterior  segments  of  the  thorax,  which,  as  we  have  al¬ 
ready  seen,  are  strengthened  in  every  possible  manner,  so  as  to  afford 
a  support  of  sufficient  density  and  firmness  to  sustain  the  violent  ex¬ 
ertions  of  the  muscles  inserted  into  the  organs  of  flight. 

In  the  most  perfectly  organized  families  the  wings  are  four 
in  number,  as  in  the  Neuroptera  (Jig.  108),  the  Hymenoptera 
(Jig.  129),  the  Orthoptera  (Jig.  102),  the  Dictyoptera,  the  He- 
miptera  (Jig.  101),  the  Lepidoptera  (Jig.  105),  and  the  Cole- 
optera  (Jig.  106). 

In  the  Dipterous  insects  there  are  only  two  wings,  which  are 
fixed  upon  the  central  segment  of  the  thorax  ;  while,  in  the  posi¬ 
tion  usually  occupied  by  the  posterior  pair,  we  find  a  pair  of  pe¬ 
dunculated  globular  bodies,  usually  named  the  Halteres  or  poisers, 
as  in  the  gnat  (CulexJ  (Jig.  131,  f). 

But,  in  every  one  of  the  orders  above  enumerated,  there  are 
certain  families  which,  throughout  the  whole  period  of  their  exist¬ 
ence,  are  never  provided  with  wings  at  all  ;  and  these  by  many 
entomologists  have  been  formed  into  an  order  by  themselves,  under 
the  name  of  Apterous  insects.  In  the  opinion  of  Burmeister,* 
whose  classification  we  have  adopted,  such  an  arrangement  is 
purely  artificial,  inasmuch  as  it  must  embrace  insects  of  most 

*  Manual  of  Entom.  }>.  623. 


INSECT A. 


247 


dissimilar  kinds.  In  proof  of  this,  lie  adduces  the  fact,  that  in  the 
same  family  we  not  unfrequently  meet  with  both  winged  and  ap¬ 
terous  species  nearly  related  to  each  other ;  and  in  many  cases  the 
males  possess  wings,  while  the  females  of  the  same  insect  are  en¬ 
tirely  destitute  of  such  appendages.  In  such  cases,  the  metamor¬ 
phosis  is  necessarily  what  is  called  incomplete ,  inasmuch  as  the 
organs  which  characterize  the  perfect  state  are  not  developed.  Thus, 
in  the  flea  ( Pulex  irritans )  {Jig.  110),  the  wings  never  become 
apparent,  and  the 
thorax  in  conse¬ 
quence,  even  in 
the  imago  state, 
does  not  exhibit 
that  develope- 
ment  and  con¬ 
solidation  of  its 

met  with  in  wing¬ 
ed  genera.  The  flea,  however,  cannot  on  this  account  be  looked 
upon  as  any  other  than  the  imago  or  complete  insect,  for  it  will 
be  found  to  have  undergone  all  the  preparatory  changes.  The 
flea,  when  it  issues  from  the  egg,  is  in  fact  a  worm-like  and  foot¬ 
less  larva,  in  which  condition  it  lives  about  twelve  days.  When 
about  to  become  a  pupa,  it  spins  for  itself  a  little  silky  cocoon, 
wherein  it  conceals  itself,  until,  having  thrown  off*  its  last  skin, 
it  appears  in  its  mature  form,  deprived  indeed  of  wings,  that,  under 
the  circumstances  in  which  it  lives,  would  be  useless  appendages, 
but  still  with  this  exception  corresponding  in  every  particular  with 
other  insects  in  their  imago  state. 

(288.)  The  wings  of  insects  differ  much  in  texture.  In  the  Neu- 
roptera ,  by  far  the  most  powerful  fliers  met  with  in  the  insect 
world,  all  four  wings  are  of  equal  size,  and  consist  of  a  thin  mem¬ 
branous  expansion  of  great  delicacy  and  of  a  glassy  appearance, 
supported  at  all  points  by  a  horny  network  {Jig.  103).  Few 
things  are  met  with  in  nature  more  admirable  than  these  struc¬ 
tures  ;  they  present  indeed  a  combination  of  strength  and  lightness 
absolutely  unequalled  by  anything  of  human  invention,  and  as 
instruments  of  flight  they  far  surpass  the  wings  of  birds,  both 
in  the  power  and  precision  of  their  movements,  inasmuch  as  these 
insects  can  fly  in  all  directions, — backwards,  or  to  the  right  or  left, 
as  well  as  forwards.  Leeuwenhoek*  narrates  a  remarkable  instance 

*  Leeuw.  Epist.  6,  Mart.  1717. 


parts  invariably 


248 


IKSECTA. 


in  which  lie  was  an  eye-witness  of  tlie  comparative  capabilities  of 
tlie  Dragon-fly  and  the  Swallow,  as  relates  to  the  perfection  of  their 
flio-ht.  The  bird  and  the  insect  were  both  confined  in  a  mena- 

O 

gerie  about  a  hundred  feet  long,  and  apparently  their  powers  were 
fairly  tested.  The  swallow  was  in  full  pursuit,  but  the  little  crea¬ 
ture  flew  with  such  astonishing  velocity,  that  this  bird  of  rapid 
flight  and  ready  evolution  was  unable  to  overtake  and  entrap  it ; 
the  insect  eluding  every  attempt,  and  being  generally  six  feet 
before  it.  44  Indeed,”  say  the  authors  from  whom  we  quote 
the  above  anecdote,*  44  such  is  the  power  of  the  long  wings  by 
which  the  dragon-flies  are  distinguished,  and  such  the  force  of  the 
muscles  which  move  them,  that  they  seem  never  to  be  wearied  with 
flying.  I  have  observed  one  of  them  ( Anax  Imperator ,  Leach) 
sailing  for  hours  over  a  piece  of  water, — sometimes  to  and  fro,  and 
sometimes  wheeling  from  side  to  side,  and  all  the  while  chasing, 
capturing,  and  devouring  the  various  insects  that  came  athwart  its 
course,  or  driving  away  its  competitors, — without  ever  seeming- 
tired  or  inclined  to  alight.” 

In  Hymenopterous  insects  (Jigs.  128  and  129),  the  wings  are 
much  more  feebly  organized,  but  their  structure  is  similar ;  the 
nervures,  or  horny  ribs,  supporting  the  membranous  expansion, 
are  comparatively  few,  and  in  the  Diptera  they  are  still  less  nu¬ 
merous. 

In  several  orders  the  anterior  pair  of  wings  are  converted  into 
shields  for  the  protection  of  the  posterior  ;  such  is  the  case  in  the 
Orthoptera,  many  of  the  Hemiptera,  and  more  especially  in  the 
Coleopterous  genera.  In  the  latter,  indeed,  they  are  very  dense 
and  hard ;  and,  being  nearly  unserviceable  in  flight,  the  hinder  pair 
are  necessarily  developed  to  such  a  size  as  to  present  a  very  ex¬ 
tensive  surface  (Jig-  106,  a),  and  when  in  repose  are  closely 
folded  up  beneath  the  elytra,  and  thus  carefully  preserved  from 
injuries  to  which  they  would  be  constantly  exposed  without  such 
provision  for  their  security. 

(289.)  The  above  observations  relate  only  to  the  general  disposi¬ 
tion  and  connection  of  the  different  parts  of  the  skeleton,  and  loco¬ 
motive  appendages  connected  with  it;  it  remains  for  us  now  to  speak 
more  fully  of  the  texture  of  the  external  integument,  and  those 
modifications  which  it  presents,  adapting  it  to  various  purposes. 

The  hard  covering  of  an  insect,  like  the  skin  of  vertebrate 
animals,  consists  of  three  distinct  layers.  The  outer  stratum  or 

*  Kirby  and  Spence,  op.  cit.  p.  351, 


1NSECTA. 


249 


epidermis  is  smooth,  horny,  and  generally  colourless,  so  that  it 
forms  a  dense  inorganic  film  spread  over  the  whole  surface  of  the 
body.  Immediately  beneath  the  epidermis  is  a  soft  and  delicate 
film,  the  rete  mucosum ,  which  is  frequently  painted  with  the  most 
lively  hues,  and  gives  the  characteristic  colouring  to  the  species.  The 
third  and  principal  layer  is  the  true  skin  or  cutis ,  which  is  gener¬ 
ally  of  a  leathery  texture,  and,  especially  in  the  elytra  of  beetles, 
of  considerable  thickness  :  this  layer  is  abundantly  supplied  with 
nutritive  juices,  and  in  its  substance  the  bulbs  of  hairs,  scales,  and 
similar  appendages,  to  be  described  hereafter,  are  embedded  and 
nourished. 

(290.)  The  wings  are  mere  derivations  from  this  common  cover¬ 
ing,  and  are  composed  of  two  delicate  films  of  the  epidermis,  stretch¬ 
ed  upon  a  strong  and  net-like  framework.  Every  membranous  wing 
is  in  fact  a  delicate  bag  formed  by  the  epidermic  layer  of  the  in¬ 
tegument,  and  in  the  recently  developed  insect  can  be  distinctly 
proved  to  be  such,  by  simply  immersing  the  newly  escaped  imago 
in  spirit  of  wine,  which  gradually  insinuates  itself  between  the 
still  fresh  and  soft  membranes ;  and,  filling  the  cavity  enclosed  be¬ 
tween  them,  distends  the  organ  until  it  represents  a  transparent 
sacculus  in  which  the  ribs  or  nervures  of  the  wing  are  enclosed.* 
This  structure,  however,  is  only  to  be  displayed  while  the  wings, 
after  being  withdrawn  from  the  pupa-case,  are  still  soft  and  moist, 
for  they  soon  become  so  intimately  united  with  the  horny  frame¬ 
work  upon  which  they  are  extended,  that  they  seem  to  form  a 
single  membranous  expansion. 

The,  ribs  or  nervures,  whereby  the  two  plates  of  the  wing  are 
thus  supported,  are  slender  hollow  tubes,  filled  with  a  soft  paren¬ 
chyma,  in  the  interior  of  some  Burmeister  detected  an  air-vessel 
recognisable  by  the  texture  of  its  walls,  and  a  minute  nervous 
filament. 

(291.)  We  have  still,  in  order  to  complete  our  description  of  the 
external  anatomy  of  an  insect,  to  describe  certain  appendages  which 
not  unfrequently  clothe  the  exterior  of  the  skeleton,  and  exhibit 
great  diversity  of  appearance  in  different  tribes.  These  may  be 
divided  into  spines ,  hairs ,  and  scales  ;  and,  however  much  they 
may  appear  to  be  distinct  structures,  all  these  are  essentially  very 
nearly  related  to  each  other. 

The  spines  are  horny  processes  developed  from  the  epidermis  ; 
and  sometimes,  especially  in  the  Coleopterous  order,  as  in  some 

*  Heusinger,  System  der  Hystologie,  2  Ilett. — Burmeister,  op.  cit.  p.  224, 


250 


INSECTA. 


lamellicorn  beetles ,  exhibit  considerable  dimensions.  These  spines 
are  sometimes  bifurcated  or  branched ;  but,  whatever  their  shape  or 
size  they  never  grow  from  bulbs  implanted  in  the  cutis,  but  are 
mere  prolongations  of  the  exterior  layer  of  the  integument. 

The  hairs  in  their  mode  of  growth  appear  to  resemble  those  of 
quadrupeds,  inasmuch  as  they  are  secreted  from  roots  embedded  in 
the  substance  of  the  cutis  or  true  shin  :  they  are  fine  horny  cy¬ 
linders,  and  frequently  are  found  to  be  branched  and  divided  like 
the  feathers  of  birds  ;  but  the  manner  of  their  formation  will  be 
more  conveniently  discussed  hereafter. 

The  wings  of  the  Lepidoptera  are  covered  with  minute  flat 
scales  of  various  shapes,  and  not  unfrequently  tinted  with  the  most 
beautiful  colours  ;  such  scales,  nevertheless,  are  in  reality  only 
flattened  hairs,  into  which  indeed  they  frequently  degenerate  by  in¬ 
sensible  transitions,  and,  moreover,  they  grow  from  bulbs  of  pre¬ 
cisely  similar  construction.  The  variety  of  colours  exhibited  by 
the  scales  of  a  butterfly  depends  upon  a  film  of  pigment  interposed 
between  the  two  plates  of  transparent  epidermic  matter  forming 
each  ;  but  the  gorgeous  hues  derived  from  this  source  must  not  be 
confounded  with  the  iridescent  tints  for  which  they  are  not  un¬ 
frequently  remarkable,  as  these  have  a  very  different  origin  :  the 
surface  of  every  scale,  that  with  the  changing  light  reflects 
evanescent  prismatic  colours,  is  seen,  when  examined  under  a  micro¬ 
scope,  to  be  marked  with  regular  parallel  striae  of  exquisite  minute¬ 
ness  ;  and  such  a  surface,  even  when  grossly  imitated  by  human  art, 
has  been  found  to  give  rise  to  the  brilliant  appearances  exhibited 
by  polarized  light. 

(292.)  The  muscular  system  of  insects  has  always  excited  the 
wonder  and  astonishment  of  the  naturalist,  in  whatever  point  of  view 
he  examines  this  part  of  their  economy, — whether  he  considers  the 
perfection  of  their  movements,  the  inconceivable  minuteness  of 
the  parts  moved,  or  the  strength,  persistence,  or  velocity  of  their 
contractions.  Insects  are  proverbially  of  small  comparative  dimen¬ 
sions — “  minims  of  nature” 

“  that  wave  their  limber  fans 
For  wings,  and  smallest  lineaments  exact. 

In  all  the  liveries  decked  of  summer’s  pride  j” 

their  presence,  indeed,  around  us,  is  only  remarked  as  conferring 
additional  life  and  gaiety  to  the  landscape  ;  and,  except  when  by 
some  inordinate  increase  in  their  numbers  they  make  up  by  their 
multitude  for  their  diminutive  size,  the  ravages  committed  by  them 


INSECTA 


251 


are  trifling  and  insignificant.  Far  otherwise,  however,  would  it  be, 
if  they  attained  to  larger  growth,  and  still  possessed  the  extra¬ 
ordinary  power  with  which  they  are  now  so  conspicuously  gifted  ; 
they  would  then,  indeed,  become  truly  the  tyrants  of  the  creation, — 
monsters  such  “  as  fables  never  feigned  or  fear  conceived,” — fully 
adequate  to  destroy  and  exterminate  from  the  surface  of  the  earth 
all  that  it  contains  of  vegetable  or  of  animal  life. 

We  have  already  seen  that  the  flea  or  the  grasshopper  will 
spring  two  hundred  times  the  length  of  its  own  body ;  that  the 
dragon-fly  possesses  such  indomitable  strength  of  wing,  that  for  a 
day  together  it  will  sustain  itself  in  the  air,  and  fly  with  equal 
facility  and  swiftness  backwards  or  forwards,  to  the  right  or  to 
the  left,  without  turning ;  that  the  beetles  are  encased  in  a 
dense  and  hard  integument,  impervious  to  ordinary  violence  ;  and 
we  might  add,  that  the  wasp  and  the  termite  ant  will  penetrate 
with  their  jaws  the  hardest  wood.  Neither  is  the  velocity  of  the 
movements  of  insects  inferior  to  their  prodigious  muscular  power. 
“  An  anonymous  writer  in  Nicholson’s  Journal,”  say  Kirby  and 
Spence,  “  calculates  that  in  its  ordinary  flight  the  common  house¬ 
fly  ( Musca  domestica )  makes  with  its  wings  about  six  hundred 
strokes,  which  carry  it  five  feet  every  second  ;  but,  if  alarmed,  he 
states  their  velocity  can  be  increased  six  or  seven-fold,  or  to  thirty 
or  thirty-five  feet  in  the  same  period.  In  this  space  of  time  a 
race-horse  could  clear  only  ninety  feet,  which  is  at  the  rate  of 
more  than  a  mile  in  a  minute.  Our  little  fly,  in  her  swiftest 
flight,  will  in  the  same  space  of  time  go  more  than  the  third  of  a 
mile.  Now,  compare  the  infinite  difference  of  the  size  of  the  two 
animals  (ten  millions  of  the  fly  would  hardly  counterpoise  one 
racer),  and  how  wonderful  will  the  velocity  of  this  minute  crea¬ 
ture  appear  !  Did  the  fly  equal  the  race-horse  in  size,  and  retain 
its  present  powers  in  the  ratio  of  its  magnitude,  it  would  traverse 
the  globe  with  the  rapidity  of  lightning.”* 

Let  the  reader,  therefore,  imagine  for  an  instant  that  great  law 
of  nature,  which  restricts  the  dimensions  of  an  insect  within  certain 
bounds,  dispensed  with  even  in  a  single  species.  Suppose  the 
wasp  or  the  stag-beetle  dilated  to  the  bulk  of  a  tiger  or  of  an 
elephant  • —  cased  in  impenetrable  armour  —  furnished  with  jaws 
that  would  crush  the  solid  trunk  of  an  oak — winged,  and  capable  of 
flight  so  rapid  as  to  render  escape  hopeless  ; — what  would  resist 
such  destroyers,  or  how  could  the  world  support  their  ravages  ? 

*  Kirby  and  Spence,  op.  cit.  vol.  ii.  p.  358. 


252 


1NSECTA. 


Such  is  the  comparative  strength  of  insects.  Let  us  now  pro¬ 
ceed  to  examine  the  muscles  to  which  it  is  owing — their  structure 
and  general  arrangement. 

(293.)  The  muscles  consist  of  bundles  of  delicate  fibres,  that 
arise  either  from  the  inner  surface  of  the  segments  composing  the 
skeleton,  or  else  from  the  internal  septa  (§  281.)  which  project  into 
the  thorax.  The  fibres  themselves  are  of  a  white  or  yellow  colour  ; 
and  so  loosely  are  they  connected  by  cellular  tissue,  that  they  may 
be  separated  by  the  slightest  touch. 

All  the  muscles  of  an  insect  may  be  arranged  in  two  great 
divisions ;  the  first  including  those  that  unite  the  different  seg¬ 
ments  of  the  body  ;  the  second,  those  appropriated  to  the  move¬ 
ments  of  the  limbs,  jaws,  and  other  appendages  :  the  former  are 
entirely  composed  of  fleshy  fibres ;  the  latter  are  provided  with 
tendinous  insertions,  by  which  their  force  is  concentrated  and  made 
to  act  with  precision  upon  a  given  point  of  the  skeleton. 

The  connecting  muscles  are  generally  arranged  in  broad  parallel 
bands,  arising  from  the  inner  surface  of  a  given  segment,  and 
passing  on  to  be  inserted  in  a  similar  manner  into  another  seg¬ 
ment,  so  that  by  their  contraction  the  cavity  in  which  they  are 
lodged  is  diminished  by  the  approximation  of  the  different  rings : 
these  have  no  tendons. 

The  locomotive  muscles  of  course  take  their  character  from  the 
joints  of  the  limb  upon  which  they  act ;  and,  as  we  have  already 
seen  that  these  movements  are  generally  confined  to  those  of  a 
hinge,  the  muscular  fasciculi  may  be  conveniently  grouped  into 
two  great  classes,  —  the  flexor  muscles,  that  bend  the  joint ;  and 
the  extensors ,  by  which  it  is  again  straightened,  and  brought  back 
to  its  former  position.  This  simple  arrangement  will  be  best 
understood  by  an  inspection  of  the  appended  figure  {Jig.  Ill), 
representing  the  muscles  of  the  leg  of  a  cockchafer  {Melolontha 
vulgaris ),  as  they  are  depicted  by  Strauss  Durckheim.*  In  the 
thigh,  for  example,  there  are  two  muscles,  one  of  which  bends, 
the  other  straightens,  the  tibia.  The  flexor  {Jig.  Ill,  a )  arises 
from  the  lining  membrane  of  the  femur,  and  is  inserted  by  a  ten¬ 
don  into  a  process  of  the  tibia  in  such  a  manner  as  to  flex  the 
leg  upon  the  thigh  ;  while  its  antagonist  (Z>),  attached  to  a  process 
derived  from  the  other  side  of  the  joint,  has  an  opposite  effect,  and 
by  its  contraction  extends  the  leg.  In  the  tibia  there  are  like- 

*  Considerations  generates  sur  l’Anat.  comp,  des  Animaux  Articnles,  auxquelles  on 
a  joint  l’Anatomie  descriptive  du  Ilanneton.  1  vol.  4to.  Paris,  1828. 


INSECTA. 


253 


wise  two  muscles,  so  disposed  as  move  the 
entire  tarsus  and  foot.  The  extensor  (f)  of 
the  tarsus  is  the  smallest ;  it  arises  from  the 
lower  half  of  the  interior  of  the  tibia,  and  is 
inserted  into  the  margin  of  the  first  joint  of 
the  tarsus  :  but  the  flexor  of  the  foot  (c),  aris¬ 
ing  from  the  upper  half  of  the  cavity  of  the 
tibia,  ends  in  a  delicate  tendon,  which  passes 
through  all  the  tarsal  segments,  to  be  fixed  to 
the  flexor  tendon  of  the  claw-joint  upon  which 
it  acts  ;  and,  as  it  traverses  the  penultimate 
joint,  it  receives  the  fibres  of  an  accessory 
muscle  ( d ).  The  extensor  of  the  claw  (e) 
is  likewise  placed  in  the  penultimate  tarsal 
segment,  and  strikingly  exhibits,  by  its  small 
comparative  size,  the  feebleness  of  its  action, 
when  compared  with  the  flexors  of  the  same 
joint. 

It  would  be  superfluous  to  describe  more 
in  detail  the  disposition  of  individual  muscles, 
as  the  above  example  will  abundantly  suffice 
to  give  the  reader  an  idea  of  the  general  ar¬ 
rangement  of  the  muscular  system,  not  in  in¬ 
sects  only,  but  in  all  the  articulata  provided 
with  jointed  extremities. 

(294.)  The  substances  employed  as  food  by  insects  are  various, 
in  proportion  to  the  extensive  distribution  of  the  class.  Some  de¬ 
vour  the  leaves  of  vegetables,  or  feed  upon  grasses  and  succulent 
plants  ;  others  destroy  timber,  and  the  bark  or  roots  of  trees  ;  while 
some,  more  delicately  organized,  are  content  to  extract  the  juices  of 
the  expanding  buds,  or  sip  the  honeyed  fluids  from  the  flowers. 
Many  tribes  are  carnivorous  in  their  habits,  armed  with  various 
weapons  of  destruction,  and  carry  on  a  perpetual  warfare  with  their 
own  or  other  species  ;  and  again  there  are  countless  swarms  ap¬ 
pointed  in  their  various  spheres  to  attack  all  dead  and  putrefying 
materials,  and  thus  to  assist  in  the  removal  of  substances  which,  by 
their  accumulation,  might  prove  a  constant  source  of  annoyance 
and  mischief.  Such  differences  in  the  nature  of  their  food  demand 
of  course  corresponding  diversity  in  the  construction  of  the  in¬ 
struments  employed  for  procuring  nourishment,  and  accordingly 
we  find  in  the  structure  of  the  mouths  of  these  little  beings  innu- 


254 


INSECTA. 


merable  modifications  adapting  them  to  different  offices.  The 
mouths  of  all  creatures  are  constructed  upon  purely  mechanical 
principles ;  and  in  few  classes  of  the  animal  world  have  we  more 
beautiful  illustrations  of  design  and  contrivance  than  in  that  before 
us  : — -jaws  armed  with  strong  and  penetrating  hooks  for  seizing 
and  securing  active  and  struggling  prey,  —  sharp  and  powerful 
shears  for  clipping  and  dividing  the  softer  parts  of  vegetables, — 
saws,  files,  and  augers  for  excavating  and  boring  the  harder  parts 
of  plants,  —  lancets  for  piercing  the  skin  of  living  animals,  — 
siphons  and  sucking  tubes  for  imbibing  fluid  nutriment  ;  —  all 
these,  in  a  thousand  forms,  are  met  with  in  the  insect  world, 
and  thus  provide  them  with  the  means  of  obtaining  food  adapted 
to  their  habits,  and  even  of  constructing  for  themselves  edifices 
of  inimitable  workmanship. 

(295.)  Parts  of  the  mouth. — The  mouths  of  insects  may  be  di¬ 
vided  into  two  great  classes, — those  which  are  adapted  for  biting, 
forming  what  is  called  a  perfect  or  mandibulate  mouth  ;  and  those 
which  are  so  constructed  as  only  to  be  employed  in  sucking,  consti¬ 
tuting  the  suctorial  or  haustellate  mouth.  It  is  in  the  former  of  these 
divisions  that  all  the  parts  composing  the  oral  apparatus  are  most 
completely  developed .  we  shall  therefore  commence  by  describ¬ 
ing  the  different  pieces  of  which  a  perfect  mouth  consists,  viz. 
an  upper  and  an  under  lip,  and  four  horny  jaws.  We  select  the 
dragon-fly  (fig  112,  a)  as  an  example.  The  upper  lip  ( labrum , 

Fig.  112. 


b)  is  a  somewhat  convex  corneous  plate,  placed  transversely  across 
the  upper  margin  of  the  cavity  wherein  the  jaws  are  lodged,  so  that, 
when  the  mouth  is  shut,  it  folds  down  to  meet  the  under  lip  (la- 


bium ),  and  these  two  pieces  more  or  less  completely  conceal  the 
proper  jaws,  which  are  lodged  between  them. 

The  upper  pair  of  jaws  ( mandibula )  are  two  hard  and  powerful 
hooks  (c),  placed  immediately  beneath  the  upper  lip,  and  so  ar¬ 
ticulated  with  the  cheeks  that  they  move  horizontally,  opening  and 
shutting  like  the  blades  of  a  pair  of  scissors.  Their  concave  edge 
is  armed  with  strong  denticulations  of  various  kinds,  sometimes  fur¬ 
nished  with  cutting  edges,  that,  like  sharp  shears  will  clip  and  di¬ 
vide  the  hardest  animal  and  vegetable  substances  ;  sometimes  they 
form  sharp  and  pointed  fangs,  adapted  to  seize  and  pierce  their 
victims ;  and  not  unfrequently  they  constitute  a  series  of  grinding 
surfaces,  disposed,  like  the  molar  teeth  of  quadrupeds,  to  triturate 
and  bruise  the  materials  used  as  food.  The  variety  of  uses  to  which 
these  mandibles  can  be  turned  is  indeed  amazing.  In  the  car¬ 
nivorous  beetles,  their  hooked  points,  more  formidable  than  the 
teeth  of  the  tiger,  penetrate  with  ease  the  mailed  covering  of  their 
stoutest  congeners  ;  and  in  the  dragon-fly  they  are  scarcely  less 
formidable  weapons  of  destruction.  In  the  locust  tribes  these 
organs  are  equally  efficient  agents  in  cutting  and  masticating  leaves 
and  vegetable  matters  adapted  to  their  appetites ;  while  in  the 
wasps  and  bees  they  form  the  instruments  with  which  these  insects 
build  their  admirable  edifices,  and,  to  use  the  words  of  a  popular 
author,  supply  the  place  of  trowels,  spades,  pick-axes,  saws,  scissors, 
and  knives,  as  the  necessity  of  the  case  may  require. 

Beneatfi  the  mandibles  is  situated  another  pair  of  jaws,  of  similar 
construction,  but  generally  smaller  and  less  powerful ;  these  are 
called  the  maxilla  (f). 

The  lower  lip,  or  labium  (e),  which  closes  the  mouth  inferiorly, 
consists  of  two  distinct  portions,  usually  described  as  separate 
organs, — the  chin  ( mentum ),  that  really  forms  the  inferior  border  of 
the  mouth  ;  and  a  membranaceous  or  somewhat  fleshy  organ,  repos¬ 
ing  upon  the  chin  internally,  and  called  the  tongue  ( lingua )  of  the 
insect  (d). 

All  these  parts  enter  into  the  composition  of  the  perfect  mouth 
of  an  insect,  and,  from  the  numerous  varieties  that  occur  in  their 
shape  and  proportions,  they  become  important  guides  to  the  ento¬ 
mologist  in  the  determination  and  distribution  of  species.  For 
more  minute  details  concerning  them,  the  reader  is  necessarily  re¬ 
ferred  to  authors  who  have  devoted  their  attention  specially  to  this 
subject  ;  we  must  not,  however,  omit  to  mention  certain  appen¬ 
dages  or  auxiliary  instruments  inserted  upon  the  maxilla  and  the 
labium ,  usually  named  the  palpi,  or  feelers,  and  most  probably 


256 


INSF.CTA. 


constituting  special  organs  of  touch,  adapted  to  facilitate  the  appre¬ 
hension  and  to  examine  the  nature  of  the  food.  The  maxillary 
feelers  (palpi  maxillares )  are  attached  to  the  external  margin  of 
the  maxillse  by  the  intervention  of  a  small  scale  and  very  pliant 
hinge,  and  consist  of  several  (sometimes  six)  distinct  but  ex¬ 
tremely  minute  pieces  articulated  with  each  other.  The  labial 
feelers  (palpi  labiales)  are  inserted  into  the  labium  close  to  the 
tongue,  or  occasionally  upon  the  chin  ( mentum )  itself.  The  joints 
in  the  labial  palpi  are  generally  fewer  than  in  the  maxillary,  but  in 
other  respects  their  structure  and  office  appear  to  be  the  same. 

In  the  suctorial  orders  of  insects  we  have  the  mouth  adapted  to 
the  imbibition  of  fluid  nutriment,  and  consequently  constructed 
upon  very  opposite  principles  ;  yet,  notwithstanding  the  apparent 
want  of  resemblance,  it  has  been  satisfactorily  demonstrated  by  Sa- 
vigny*  that  the  parts  composing  a  suctorial  mouth  are  fundament¬ 
ally  the  same  as  those  met  with  in  the  mouth  of  mandibulate  in¬ 
sects,  but  transformed  in  such  a  manner  as  to  form  a  totally  differ¬ 
ent  apparatus. 

According  to  the  distinguished  authors  of  the  44  Introduction  to 
Entomology,”']'  there  are  five  kinds  of  imperfect  mouth  adapted  to 
suction,  each  of  which  will  require  a  separate  notice. 

(296.)  The  first  is  met  with  among  the  Hemiptera,  and  is 
to  perforate  the  stalks  and  buds  of  vegetables,  in  order  to 
procure  the  juices  which  they  contain  ;  or  in  some  bugs  it 
is  employed  to  puncture  the  integument  of  living  animals  for  a 
similar  purpose.  This  kind  of  mouth  is  exhibited  in  Jig.  113: 
first,  there  is  a  long  jointed  sheath  (d), 
which  is  in  fact  the  lower  lip  (labium),  con¬ 
siderably  elongated,  and  composed  of  three 
or  four  parts  articulated  together ;  second¬ 
ly,  there  is  a  small  conical  scale  covering  the 
base  of  the  sheath  last  mentioned,  and  re¬ 
presenting  the  upper  lip  ;  and  between  these 
are  four  slender  and  rigid  bristles  or  lancets 
(scalpella)  (c)  that,  when  not  in  use,  are 
lodged  in  a  groove  upon  the  upper  surface 
of  the  sheath  so  as  to  be  concealed  from  view. 

These  lancets  are,  in  reality,  only  the  man- 

*  Savigny  (Jules  Cesar),  Memoires  sur  les  animauxsans  vertebres,  8vo.  Paris,  1816. 

t  Kirby  and  Spence,  vol.  iii.  p.  463. 


Fig.  113. 


d 


INSECT A. 


257 


dibles  and  maxillae  strangely  altered  in  tlieir  form  and  excessively 
lengthened,  so  as  not  merely  to  become  efficient  piercing  instru¬ 
ments,  but  so  disposed  as  to  form  by  their  union  a  suctorious  tube, 
through  which  animal  or  vegetable  fluids  may  be  imbibed.  This  kind 
of  mouth,  when  not  employed,  is  usually  laid  under  the  thorax  be¬ 
tween  the  legs,  in  which  position  it  is  easily  seen  in  most  Hemi- 
ptera  :  in  some  families,  as,  for  example,  in  the  plant-lice  (Aphides), 
it  is  of  extraordinary  length  ;  thus,  in  the  aphis  of  the  oak  it  is  three 
times  as  long  as  the  whole  body  of  the  insect,  projecting  posteriorly 
like  a  tail,  and  in  the  Jir-aphis  it  is  still  longer. 

(297.)  The  second  kind  of  mouth  is  that  met  with  among  the 
Diptera ,  and  from  its  construction  in  some  tribes  we  may  well  under¬ 
stand  how  they  are  enabled  to  become  so  seriously  annoying.  The 
gnat  and  the  mosquito  furnish  sufficiently  well-known  examples  of 
the  formidable  apparatus  in  question,  which,  in  the  horse-fly  (Taba- 
nus ),  seems  to  attain  its  maximum  of  developement.  The  oral 
organs  of  the  Diptera  are  composed  of  a  sheath  or  proboscis,  that 
represents  the  lower  lip  of  the  mandibulate  insects  ;  it  is  sometimes 
coriaceous  or  horny  in  its  texture,  or  in  other  cases,  as  in  the  com¬ 
mon  flesh-fly,  soft  and  muscular,  and  folds  up  when  at  rest  in  such  a 
manner  as  to  form  two  angles,  representing  the  letter  Z.  At  the 
base  of  this  sheath  or  proboscis  there  is  a  small  upper  lip,  between 
which  and  the  sheath  are  lodged  the  setae,  knives  or  lancets,  which 
form  such  terrible  instruments  for  cutting  or  piercing  the  skin  of 
their  victims.  These  cutting  parts  vary  in  number  from  one  to 
five  :  when  they  are  all  present,  the  upper  pair  ( cultelli ,  or  knives ) 
represent  the  mandibles  of  a  perfect  mouth,  the  two  lower  ones 
(scalpella,  the  lancets)  are  the  maxillae,  the  fifth  or  middle  piece 
(glossarium)  is  the  tongue,  and  between  them  all  is  the  oral 
opening.  The  strength  of  the  above  piercing  instruments  varies 
greatly  ;  in  the  gnat  they  are  finer  than  a  hair,  very  sharp  and 
barbed  occasionally  on  one  side ;  while  in  the  horse-fly  they 
are  flat,  like  the  blades  of  a  lancet  or  penknife :  occasionally 
they  are  so  constructed  as  to  form  a  tube  by  their  union,  through 
which  the  liquid  aliment  is  sucked  up  and  conveyed  into  the 
stomach. 

(298.)  The  mouth  of  the  flea,  although  described  by  Kirby  and 
Spence  as  forming  a  distinct  type  of  structure,  differs  very  little 
from  that  of  the  Diptera  described  above,  as  will  be  at  once  evi¬ 
dent  on  inspecting  the  accompanying  figure,  reduced  from  a  beau¬ 
tiful  drawing  by  Mr.  W.  Lins  Aldous. 

s 


258 


INSECTA. 


Fig.  1 14* 


In  this  insect  the  piercing  organs  are  two  sharp  and  razor-like 
instruments  (Jig-  114,  d,  d ),  placed  on  each  side  of  the  elongated 
tongue  (e),  and  enclosed  in  a  sheath  (c,  c),  probably  formed  by 
pieces  representing  the  mandibles  of  mandibulate  insects.  Two 
palpi  or  feelers  (a,  a ),  and  a  pair  of  triangular  plates  ( b ,  5),  com¬ 
plete  this  remarkable  apparatus. 

(299.)  Another  kind  of  mouth  adapted  to  suction,  and  which  seems 
to  differ  more  widely  from  the  perfect  form  than  any  we  have  as 
yet  examined,  is  that  which  we  meet  with  in  moths  and  butterflies. 
This  singular  organ  is  adapted  to  pump  up  the  nectareous  juices 
from  the  cups  of  flowers,  and  is  necessarily  of  considerable  length,  in 
order  to  enable  the  insect  to  reach  the  recesses  wherein  the  honeyed 

*  Head  of  the  flea,  as  represented  by  the  Solar  microscope  in  Canada  balsam  ;  dedi¬ 
cated  by  permission  to  the  President  and  Members  of  the  Entomological  Society,  by 
W.  Lins  Aldous. 


INSECTA. 


259 


stores  are  lodged.  When  unfolded,  the  apparatus  in  question  repre¬ 
sents  a  long  double  whip-lash  (fig.  115,  a,  b ,  c,  d),  and,  if  carefully 

examined  under  the  micro-  ... 

rig.  115. 

scope,  each  division  is  found 
to  be  made  up  of  innumer¬ 
able  rings  connected  toge¬ 
ther,  and  moved  by  a  dou¬ 
ble  layer  of  spiral  muscular 
fibres,  that  wind  in  oppo¬ 
site  directions  around  its 
walls.  When  not  in  use, 
the  proboscis  is  coiled  up 
and  lodged  beneath  the 
head  ;  but  when  uncurled 
its  structure  is  readily  ex¬ 
amined.  Each  of  the  two 
long  filaments  composing 
this  trunk,  which,  in  fact,  are  the  representatives  of  the  maxillae 
excessively  lengthened,  is  then  seen  to  be  tubular  ;  and,  when  they 
are  placed  in  contact,  it  is  found  that  their  edges  lock  together  by 
means  of  minute  teeth,  so  as  to  form  a  central  canal  leading  to  the 
orifice  of  the  mouth.  It  is  through  this  central  tube,  formed  by 
the  union  of  the  two  lengthened  maxillae,  that  fluids  are  imbibed. 
Burmeister,  however,  asserts  that  the  cavities  contained  in  each  divi¬ 
sion  likewise  communicate  with  the  commencement  of  the  oesophagus, 
so  that  the  Lepidoptera  have,  as  it  were,  two  mouths,  or  rather  two 
separate  methods  of  imbibing  nourishment ;  one  through  the  com¬ 
mon  canal  formed  by  the  junction  of  the  whip-like  jaws,  the  other 
through  the  cavities  of  the  filiform  maxillae  themselves  :  such  an 
arrangement,  however,  which  would  be  quite  anomalous,  may  rea¬ 
sonably  be  doubted.  In  this  mouth,  therefore,  all  the  parts,  except 
the  maxillae,  would  seem  at  first  sight  to  be  wanting ;  they  may, 
nevertheless,  be  detected  upon  a  very  careful  examination,  and 
rudiments  of  the  upper  lip,  of  the  mandibles,  of  the  lower  lip,  as 
well  as  of  the  labial  and  maxillary  palpi,  be  distinctly  demonstrated. 

(300.)  The  last  kind  of  mouth  to  which  we  shall  advert,  is  that 
met  with  in  the  louse  tribe  ( Pediculi )  ;  but,  from  the  extreme  mi¬ 
nuteness  of  the  parts  composing  it,  the  details  of  its  structure  are 
but  imperfectly  known.  It  seems  to  consist  of  a  slender  external 
tube,  wherein  a  sharp  sucker,  armed  with  barbs  adapted  to  fix  it 
securely  during  the  act  of  sucking,  is  lodged ;  when  feeding,  the 

s  2 


260 


INSECTA. 


barbed  piercer  is  denuded  and  plunged  into  the  skin,  where  it  is 
retained  until  a  sufficient  supply  of  nourishment  has  been  obtained. 

(301 .)  Inviting  as  the  subject  is,  we  are  compelled  by  the  strictly 
general  character  of  our  investigations  to  abstain  from  entering  upon 
further  details  concerning  the  mouths  of  perfect  insects,  and  conse¬ 
quently  to  omit  noticing  innumerable  secondary  modifications  in 
the  mechanical  structure  of  the  oral  organs  of  these  little  animals. 
When  we  turn  our  attention  to  the  consideration  of  their  internal 
viscera,  connected  with  the  preparation  and  digestion  of  so  many 
different  materials,  we  may  well  expect  to  find  equal  variety  of 
conformation  ;  and,  in  fact,  the  course,  dimensions,  and  relative 
proportions  of  the  alimentary  canal  will  be  seen  to  be  different  to 
a  greater  or  less  extent  in  almost  every  species.  Considered  as  a 
whole,  the  internal  digestive  apparatus  of  insects  must  be  regarded 
as  a  delicate  membranous  tube,  in  which  the  digestion  of  the  sub¬ 
stances  used  as  food  is  accomplished,  partly  by  mechanical  and 
partly  by  chemical  agents  :  for  the  former  purpose,  gizzard-like 
muscular  cavities  are  not  unfrequently  provided  ;  and,  to  fulfil  the 
second,  various  fluids  are  poured  into  the  canal  in  different  parts  of 
its  course  :  the  arrangement  of  the  cavities,  and  the  nature  of  the 
secreting  vessels,  however,  will  be  modified  in  conformity  with  the 
necessities  of  the  case,  and  certain  parts  will  be  found  to  exist,  or 
to  be  deficient,  as  circumstances  may  require  :  it  would  be  absurd, 
therefore,  to  attempt  to  describe  particular  examples  ;  our  observa¬ 
tions  must  be  of  general  application,  and  such  as  will  enable  the 
reader  to  assign  its  proper  functions  to  any  organ  which  may  pre¬ 
sent  itself  to  his  notice.  The  first  part  of  the  digestive  appara¬ 
tus  is  disposed  in  the  same  manner  in  all  insects,  and  is  a  slender 
canal,  arising  from  the  mouth  and  passing  straight  through  the  tho¬ 
rax  into  the  cavity  of  the  abdomen  ;  this  portion  represents  the 
oesophagus  (Jig-  116,  a,  a ;  117,  o).  The  stomach  and  intestine 
succeed  to  this,  and,  if  the  body  of  the  insect  be  very  thin,  their 
course  also  passes  nearly  in  a  direct  line  to  the  tail ;  but  in  those 
families  which  have  the  abdomen  thick  and  largely  developed,  espe¬ 
cially  if  herbivorous,  the  intestine  becomes  much  elongated,  and 
winds  upon  itself  in  various  convolutions  :  nevertheless,  however 
tortuous  the  canal  may  be,  its  windings  are  never  sustained  by  any 
mesentery  or  peritoneal  investment ;  the  air-tubes,  that,  as  we  shall 
afterwards  see,  permeate  the  body  in  all  directions,  form  a  sufficient 
bond  of  connection,  and  one  which  is  better  adapted  to  the  wants 
of  these  animals. 


INSECT A. 


261 


Fig.  116. 


We  must  now  examine  more  minutely  the  different  portions  of 
which  the  alimentary  canal  may  consist,  premising  at  the  same 
time  that  the  structures  mentioned  do  not  invariably  exist  together, 
as  sometimes  one  part,  and  sometimes  another,  may  be  entirely 
wanting,  or  only  found  in  a  very  rudimentary  condition.  They 
are  the  Crop,  the  Gizzard ,  the  Stomach ,  the  Small  Intestine , 
and  the  Large  Intestine. 

(302.)  The  Crop ,  or  Sucking- Stomach,  as  it  is  called  by  some 
writers,  is  only  met  with  in  Hymenoptera,  Lepidoptera,  and  Di- 
ptera, — insects  which  have  no  gizzard.*  In  bees,  wasps,  and  other 
Hymenoptera,  it  is  a  simple  bladder-like  distension  of  the  oesophagus 
{Jig.  116,  h)  ;  in  butterflies  and  moths  it  forms  a  distinct  bag, 
that  opens  into  the  side  of  the 
gullet  {Jig.  117,  v,  v )  ;  while  in 
the  Diptera  it  is  a  detached  ve¬ 
sicle,  appended  to  the  oesophagus 
by  the  intervention  of  a  long  thin 
duct.  This  organ,  which  in  bees 
is  usually  called  the  honey  blad¬ 
der,  is  regarded  by  Burmeister, 
who  founds  the  opinion  upon  the 
result  of  experiments  made  by  / 

Treviranus  upon  living  insects,  as  p 
being  not  merely  a  receptacle  for  ^ 
food  resembling  the  craw  of  birds, 
as  Ramdohr  j*  and  Meckel  con¬ 
sider  it,  but  as  being  a  sucking  instrument  for  imbibing  liquids, 
by  becoming  distended,  as  he  expresses  it,  and  thus,  by  the  rare¬ 
faction  of  the  air  contained  within  it,  facilitating  the  rise  of  the 
fluids  in  the  proboscis  and  oesophagus.  It  must,  however,  be 
confessed  that  there  is  something  very  anomalous  in  the  idea  of  a 
delicate  bag  having  the  power  of  distending  itself ;  its  muscular 
walls  might  indeed  contract ,  but  that  a  thin  sacculus  should  forci¬ 
bly  expand  itself  would  be  a  fact  new  to  physiology. 

(303.)  The  Gizzard  is  found  in  insects  which  possess  mandibles, 
and  live  upon  solid  animal  or  vegetable  substances.  It  is  a  small 
round  cavity  with  very  strong  muscular  parietes,  situated  just  above 
the  stomach  properly  so  called,  and,  like  the  gizzard  of  granivorous 
birds,  is  employed  for  the  comminution  of  the  food  preparatory  to 


*  Burmeister,  op.  cit.  p.  125. — Treviranus,  Vermischte  Schriften. 
t  Ramdohr,  liber  die  Verdauungswerkzeuge  der  Insecten.  Ilalle,  1811. 


INSECTA. 


262 

its  introduction  into  the  digestive  stomach.  In  order  to  effect  this, 
it  is  lined  internally  with  a  dense  cutieular  membrane,  and  occa¬ 
sionally  studded  with  hard  plates  of  horn  or  strong  hooked  teeth, 
adapted  to  crush  or  tear  in  pieces  whatever  is  submitted  to  their 
action. 

When  bruised  in  the  gizzard,  the  food  passes  on  into  the  proper 
stomach,  which  is  generally  a  long  intestiniform  organ  {fig.  116, 
d,  d),  extending  from  the  crop  or  gizzard  to  the  point  where  the 
biliary  vessels  discharge  themselves  into  the  intestine.  The  size 
and  shape  of  this  organ  will  vary  of  course  with  the  nature  of  the 
food.  Thus,  in  the  butterfly  (fig.  117,  b ),  which  scarcely  eats 
at  all,  or  sparingly  sips  the  honey  from  the  flowers,  it  is  very  mi¬ 
nute  ;  but,  in  insects  which  live  upon  coarse  and  indigestible  mate¬ 
rials,  it  is  proportionately  elongated  and  capacious. 

(304.)  The  stomach  generally  ends  in  the  Small  Intestine  {fig. 
116,  e  ;  117,  «),  but  this  is  occasionally  entirely  wanting,  so  that  the 
stomach  seems  to  terminate  immediately  in  the  colon  or  large  intes¬ 
tine,  which  is  the  terminal  portion  of  the  alimentary  canal  :  when 
much  developed,  the  small  intestine  is  sometimes  divided  by  a  con¬ 
striction  into  two  parts,  to  which  the  names  of  Duodenum  and  Ilium 
have  been  applied  by  entomological  writers.  The  colon  {fig. 
116,^;  117,  A)  is  separated 
from  the  small  intestine  by 
a  distinct  valve;  and,  in  con¬ 
nection  with  its  commence¬ 
ment,  a  wide  blind  sacculus 
or  caecum  is  often  met  with. 

(305.)  Wemay  now  no¬ 
tice  the  secerning  organs  that 
pour  fluids  in  to  different  parts 
of  the  digestive  apparatus  ; 
beginning  with  those  which 
open  into  the  oesophagus  in 
the  vicinity  of  the  mouth, 
and  examining  them  in  the 
order  of  their  occurrence  as 
we  proceed  backwards. 

The  first  are  the  salivary 
vessels ,  which  terminate  in 
the  neighbourhood  of  the 
mouth  itself,  into  which  they  seem  to  pour  a  secretion  analogous  to 


Fig.  117. 


INSECTA. 


263 


saliva.  These  glands  are  principally  met  with  in  suctorial  insects, 
but  not  unfrequently  among  the  mandibulate  orders.  Their  form 
varies  ;  but  they  are  generally  simple  slender  tubes,  that  float 
loosely  among  the  juices  of  the  body,  from  which  they  separate  the 
salivary  fluid.  There  are,  for  the  most  part,  only  two  of  these 
organs  {Jig.  117,  s,  s)  ;  but  in  fleas  ( Pulex ),  and  bugs  ( Cimex ), 
there  are  four,  and  in  a  water-bug  (JVepa),  there  are  six  such 
vessels,  all  of  which  open  into  the  cavity  of  the  mouth.  The 
fluid  supplied  by  the  salivary  glands  is  usually  merely  intended  to 
facilitate  deglutition  ;  but  there  are  cases  in  which  the  saliva  is  ex¬ 
cessively  acrid  and  irritating,  acting  as  a  kind  of  poison  when  in¬ 
fused  into  a  puncture  made  by  the  mouth  :  this  is  especially  re¬ 
markable  in  many  bugs  and  gnats,  and  is  the  chief  cause  of  the 
pain  and  inflammation  frequently  occasioned  by  their  bite. 

Besides  the  proper  salivary  vessels,  there  are  other  glands,  or 
rather  cseca,  which  open  into  the  stomach  itself,  occasionally  cover¬ 
ing  that  organ  over  its  entire  surface,  as  is  the  case  in  some  water- 
beetles  (Hydrophilus)  ;  these,  no  doubt,  secrete  a  fluid  subser¬ 
vient  to  digestion  ;  but  whether  of  a  peculiar  description,  or  allied 
to  saliva  in  its  properties,  is  unknown. 

The  third  kind  of  auxiliary  vessels  connected  with  the  intestinal 
canal  of  insects,  is  supposed  to  furnish  a  secretion  analogous  to 
the  bile  of  other  animals,  and  consequently  to  represent  the  liver. 
The  bile-vessels  (Jig.  116,  A,  h;  Jig.  117,  g,  g )  are  generally  four, 
six,  or  eight  in  number,  but  occasionally  much  more  numerous  ; 
they  are  usually  of  great  length,  but  exceedingly  slender,  and  wind 
around  the  intestine  in  all  directions.  When  unravelled,  they  are 
found  to  terminate,  in  the  neighbourhood  of  the  pylorus  (Jig.  J 17, 
A,  n),  close  to  the  commencement  of  the  intestine,  at  which  point 
the  secretion  produced  by  them  is  mixed  with  the  food  after  it  has 
undergone  the  process  of  digestion. 

Appended  to  the  termination  of  the  alimentary  tube,  close  to 
its  anal  extremity,  other  vessels  are  met  with  in  some  insects  that 
are  looked  upon  by  authors  as  being  allied  in  function  to  the  kid¬ 
neys  of  higher  animals  ;  but  apparently  this  opinion  rests  upon 
very  doubtful  grounds.  They  indubitably  furnish  some  secretion, 
the  use  of  which  is  perhaps  connected  with  defecation  ;  but  that  it 
is  of  the  same  character  as  the  fluid  separated  by  the  renal  organs 
of  vertebrata  may  well  be  called  in  question,  as  no  such  parts  are 
distinctly  recognisable  until  we  arrive  at  much  more  elevated  forms 
of  life  than  the  insects  we  are  now  considering.  There  is,  how- 


264 


INSECTA. 


ever,  another  reason  for  rejecting  the  opinion  that  these  accessory 
vessels  secrete  urine,  and  that  is,  that  they  are  only  met  with  in  a 
few  beetles  and  some  species  of  Orthoptera  ;  a  circumstance  that 
alone  would  be  sufficient  to  disprove  such  a  supposition. 

In  the  vertebrate  animals,  as  the  reader  is  well  aware,  the  nu¬ 
tritious  products  of  digestion  are  taken  up  by  a  system  of  absorb¬ 
ing  vessels,  that  ramify  extensively  over  the  coats  of  the  intestine, 
and  the  nutriment  is  thus  conveyed  into  the  mass  of  the  circu¬ 
lating  fluid  by  ducts  appropriated  specially  to  this  office  ;  in 
animals  of  less  perfect  structure  than  these,  such  as  the  Mollusca, 
the  veins  themselves  absorb  the  nutritive  materials.  But  in  insects, 
in  which  we  find  neither  absorbents  nor  veins,  a  different  arrange¬ 
ment  is  necessary ;  and,  in  the  little  creatures  before  us,  nutrition 
appears  to  be  carried  on  by  the  simple  transudation  of  the  chyle 
through  the  coats  of  the  intestine,  so  that  it  escapes  into  the 
general  cavity  of  the  abdomen,  where,  as  we  shall  see  when  we 
examine  the  arrangement  of  their  circulating  organs,  it  is  im¬ 
mediately  mixed  up  with  the  blood.  This  transudation  has  in¬ 
deed  been  actually  witnessed  by  Ramdohr  and  Rengger,*  and 
even  analyzed  by  the  last-mentioned  physiologist,  who  found  it  to 
consist  almost  entirely  of  albumen. 

(306.)  The  respiratory  organs  of  the  Insecta,  as  well  as  their 
circulatory  apparatus,  are  constructed  upon  peculiar  principles,  and 
are  evidently  in  relation  with  the  capability  of  flying,  which  distin¬ 
guishes  these  minute  yet  exquisitely  constructed  articulated  animals. 
Any  localized  instruments  for  breathing,  whether  assuming  the  shape 
of  branchiae  or  lungs,  would  materially  have  added  to  the  weight  of 
the  body,  and  moreover  have  rendered  necessary  an  elaborate  ap¬ 
paratus  of  arteries  and  veins  for  conveying  the  blood  to  and  fro 
for  the  purpose  of  purifying  it  by  securing  its  exposure  to  the  in¬ 
fluence  of  air.  By  the  plan  adopted,  however,  all  these  organs  are 
dispensed  with  ;  and  the  organs  of  respiration,  so  far  from  increasing 
the  weight  of  the  animal,  actually  diminish  its  specific  gravity  to 
the  greatest  possible  extent.  The  blood,  in  fact,  in  insects  is  not 
brought  to  any  given  spot  to  be  exposed  to  oxygen,  but  the  air  is 
conveyed  through  every  part  of  the  system  by  innumerable  tubes 
provided  for  that  purpose,  and  thus  all  the  complicated  parts 
usually  required  to  form  a  vascular  system  are  rendered  unnecessary. 
These  observations,  however,  only  apply  to  the  insect  in  its  perfect 

*  Physiologisehe  Untersuchungen  liber  den  thierischen  Haushalt  der  Insekten* 
8vo.  1817. 


INSECT A. 


£65 


state ;  for  in  tlie  larva  and  pupa  condition,  where  flight  is  not 
possible,  various  additional  organs,  frequently  of  considerable  bulk, 
are  provided,  that  we  shall  speak  of  in  another  place.  If  we 
examine  the  external  skeleton  of  any  large  insect,  a  beetle  for  ex¬ 
ample,  we  shall  find  between  the  individual  segments  of  the  body 
minute  apertures  or  pores  ( spiracles )  through  which  the  air  is 
freely  admitted  ;  these  openings,  ten  in  number,  on  each  side  of 
the  body,  are  situated  in  the  soft  membrane  interposed  between 
the  different  rings,  and  not  in  the  rings  themselves, — a  provision  for 
the  purpose  of  allowing  their  orifices  to  be  opened  or  closed  at 
pleasure,  instead  of  being  rigid  and  motionless.  The  margin  of  the 
spiracle  is  frequently  encompassed  by  thick  horny  lips,  which  may 
be  approximated  by  muscles  provided  for  the  purpose,  so  that  the 
opening  can  be  shut  at  pleasure,  in  order  to  exclude  any  extraneous 
substances  that  might  otherwise  obtain  admission  :  in  many  insects 
indeed,  especially  in  beetles  which  crawl  upon  the  dusty  ground, 
an  additional  provision  is  necessary  to  prevent  the  entrance  of  foreign 
matter,  and  in  such  cases  the  spiracles  are  seen  to  be  covered  with 
a  dense  investment  of  minute  and  stiff  hairs,  so  disposed  as  to 
form  a  sieve  of  exquisite  fineness ;  a  beautiful  contrivance,  by  which 
the  air  is  filtered,  as  it  were,  before  it  is  allowed  to  pass  into 
the  breathing-tubes,  and  thus  freed  from  all  prejudicial  particles. 
From  every  spiracle  is  derived  a  set  of  extremely  delicate  tubes 
(trachea),  that  pass  internally,  and  become  divided  and  subdi¬ 
vided  to  an  indefinite  extent,  penetrating  to  every  part  of  the 
body,  and  ramifying  through  all  the  viscera,  so  that  air  is  thus 
supplied  to  the  entire  system.  Upon  more  minutely  inspecting 
these  air-tubes,  they  are  found  to  assume  various  forms  in  different 
parts  of  the  body,  being  sometimes  simple  tubes  of  exquisite  deli¬ 
cacy  ;  in  other  cases  they  present  a  beaded  or  vesicular  structure, 
and  in  many  insects  they  are  dilated  at  intervals  into  capacious  cells 
or  receptacles,  wherein  air  is  retained  in  great  abundance.  The  figure 
in  the  following  page  (Jig.  118),  taken  from  Strauss  Durckheim’s 
elaborate  work  upon  the  anatomy  of  the  cockchafer,  will  illustrate 
this  arrangement.  The  spiracles,  situated  at  the  points  respectively 
marked  by  the  letters  a ,  c,  d ,  e,f,  g,  h ,  i,  open  into  two  wide  air- 
trunks,  disposed  longitudinally  along  the  whole  length  of  the 
body  :  from  these,  innumerable  secondary  branches  are  given  off, 
many  of  them  being  seen  to  dilate  into  oval  vesicles,  from  which 
smaller  trachese  proceed  ;  while  others,  without  any  vesicular  en¬ 
largement,  plunge  at  once  into  different  textures,  and  supply  the 


266 


INSECTA. 


viscera  and  internal  organs.  rIhe  muscular  system,  the  legs,  the 
wings,  the  alimentary  canal,  and  even  the  brain  itself,  are  permeated 
in  all  directions  by  these  air- conducting  tubes,  and  thus  the 
oxygen  penetrates  to  every  corner  of  the  body. 

(307.)  There  is  one  Fig,  118. 


circumstance  connected 
with  the  tracheae,  which 
is  specially  deserving 
of  admiration,  whether 
we  consider  the  obvious 
design  of  the  contriv¬ 
ance,  or  the  remarkable 
beauty  of  the  struc¬ 
ture  employed.  It  is 
evident  that  the  sides 
of  canals,  so  slender  and 
delicate  as  the  tracheae 
of  insects,  would  in¬ 
evitably  collapse  and 
fall  together,  so  as 
to  obstruct  the  passage 
of  the  air  they  are 
destined  to  convey  ; 
and  the  only  plan 
which  would  seem  cal¬ 
culated  to  obviate  this 
would  appear  to  be,  to 
make  their  walls  stiff 
and  inflexible.  In¬ 
flexibility  and  stiffness, 
however,  would  never 
do  in  this  case,  where 
the  vessels  in  question 
have  to  be  distributed 
in  countless  ramifica¬ 
tions  through  so  many 
soft  and  distensible  viscera  ;  and  the  problem,  therefore,  is,  how 
to  maintain  them  permanently  open,  in  spite  of  external  pres¬ 
sure,  and  still  preserve  the  perfect  pliancy  and  softness  of  their 
walls.  The  mode  in  which  this  is  effected  is  as  follows :  —  Be¬ 
tween  the  two  thin  layers  of  which  each  air-vessel  consists,  an 


INSECTA. 


267 


Fig.  119. 


elastic  spiral  thread  is  interposed  (fig.  119,  a ),  so  as  to  form  by 
its  revolutions  a  firm  cylinder  of  sufficient  strength  to  insure  the 
calibre  of  the  vessel  from  being  diminished,  but  not  at  all  inter¬ 
fering  with  its  flexibility,  or  obstructing  its  movements  ;  and  this 
fibre,  delicate  as  it  is,  may  be  traced  with  the  microscope,  even 
through  the  utmost  ramifications  of  the  tracheae,  —  a  character 
whereby  these  tubes  may  be  readily  distinguished. 

(308.)  We  must  now  consider 
the  mechanism  by  which  air  is  per¬ 
petually  drawn  into  the  body  of 
the  insect,  and  again  expelled.  If 
the  abdomen  of  a  living  insect  be 
carefully  watched,  it  will  be  found 
continually  performing  movements 
of  expansion  and  contraction  that 
succeed  each  other  at  regular  in- 
tervals,  varying  in  frequency,  in 
different  species,  from  twenty  to 
fifty  or  sixty  in  a  minute,*  but 
occurring  more  rapidly  when  the 
insect  is  in  a  state  of  activity  than 
when  at  rest.  At  each  expansion 
of  the  abdomen,  therefore,  air  is 
sucked  in  through  all  the  spiracles, 
and  rushes  to  every  part  of  the 
body  ;  but,  when  the  abdomen 
contracts,  it  is  forcibly  expelled  through  the  same  openings. 
Burmeister  even  supposes  that  the  humming  noises  produced 
by  many  insects  during  their  flight,  must  be  referred  to  the  vi¬ 
bration  caused  by  the  air  streaming  rapidly  in  and  out  of  the 
spiracular  orifices.  Insects  which  live  in  water  are  obliged,  at  short 
intervals,  to  come  to  the  surface  to  breathe,  at  which  time  they 
take  in  a  sufficient  quantity  of  air  to  last  them  during  the  period 
of  their  immersion  ;  but  if  the  spiracles  are  closed  by  any  acci¬ 
dent,  or  by  the  simple  application  of  any  greasy  fluid  to  the  ex¬ 
terior  of  their  body,  speedy  death,  produced  by  suffocation,  is  the 
inevitable  result. 

(309.)  A  moment’s  reflection  upon  the  facts  above  stated,  con¬ 
cerning  the  respiration  of  insects,  will  suggest  other  interesting  views 
connected  with  the  physiology  of  these  little  creatures.  It  is  evident, 

*  Sorg,  Disquisitio  Phys.  circa  Ilesp.  Lnsectorum  et  Verminum. 


268 


INSECTA. 


in  the  first  place,  that  their  blood  is  all  arterial ;  they  can  have  no 
occasion  for  veins,  as  they  have  no  venous  blood,  the  whole  of  the 
circulating  fluid  being  continually  oxygenized  as  its  principles  be¬ 
come  deteriorated.  The  perfection  of  their  muscular  power,  their 
great  strength  and  indomitable  activity,  are  likewise  intimately 
related  to  the  completeness  of  their  respiration  ;  so  that  the  vital 
energies  of  the  muscular  system  are  developed  to  the  utmost,  en¬ 
dowing  them  with  that  vigorous  flight  and  strength  of  limb  which 
we  have  already  seen  them  to  possess.  It  must  likewise  become 
apparent,  that,  as  the  blood  i-s  freely  exposed  to  the  influence  of 
oxygen  in  every  portion  of  the  insect  to  which  the  air-tubes  reach, 
one  great  necessity  for  the  existence  of  a  circulatory  apparatus  is 
entirely  done  away  with,  and  as  we  have  observed  before,  all  those 
parts  of  the  vascular  system  required  in  other  animals  for  the  pro¬ 
pulsion  of  the  vitiated  blood  through  pulmonary  or  branchial  organs, 
are  no  longer  requisite  ;  so  that,  by  dispensing  with  the  compli¬ 
cated  structures  usually  provided  for  this  purpose,  the  body  is 
considerably  lightened.  The  circulation  of  the  nutritive  fluids  is 
in  fact  limited  to  their  free  diffusion  amongst  all  the  internal 
viscera,  and  is  effected  in  the  following  manner : — If  we  ex¬ 
amine  the  back  of  a  silkworm,  or  of  any  transparent  larva,  a  long 
pulsating  tube  is  seen  running  beneath  the  skin  of  the  back,  from 
one  end  of  the  body  to  the  other  ;  its  contractions  may  readily  be 
watched  ;  they  are  found  to  begin  at  the  posterior  extremity,  and 
are  gradually  continued  forwards,  so  that  the  vessel  presents  a 
continual  undulatory  movement,  by  which  the  fluid  contained  in 
its  interior  is  pushed  from  the  tail  towards  the  head.  This  dorsal 
vessel,  which  may  be  so  well  observed  in  the  thin-skinned  larva, 
exists  likewise  in  the  perfect  insect,  although  from  the  opacity  of 
the  integument,  its  movement  is  no  longer  apparent,  except  by  the 
vivisection  of  the  animal. 

(810.)  This  dorsal  vessel,  or  heart  as  we  shall  call  it  for  the  sake 
of  brevity,  is  organized  in  a  very  singular  manner ;  for,  instead  of 
being  a  closed  viscus,  it  communicates  most  freely,  through  several 
wide  lateral  apertures,  with  the  cavity  of  the  abdomen,  and  from 
thence  derives  the  blood  with  which  it  is  filled.  The  dorsal  vessel 
is  widest  in  the  abdominal  region  ;  but  is  continued,  nevertheless, 
through  the  thorax  into  the  head,  where  it  terminates  as  a  simple 
or  furcate  tube,  that  is  not  closed,  but  open  at  the  extremity. 

The  structure  of  this  remarkable  heart  has  been  fully  investi¬ 
gated  by  Strauss  Durckheim,*  and  is  extremely  curious  ;  it  con- 


*  Op.  cit 


INSECT A. 


269 


sists,  in  the  cockchafer ,  of  eight  distinct  compartments,  sepa¬ 
rated  from  each  other  by  as  many  valves  formed  by  productions 
from  the  lining  membrane,  and  so  disposed  that  the  blood  passes 
freely  from  the  hinder  chambers  into  those  which  are  placed  more 
anteriorly,  but  is  prevented  from  returning  in  the  opposite  di¬ 
rection. 

Each  compartment  of  the  dorsal  vessel  communicates  by  two 
wide  slits,  likewise  guarded  by  valves,  with  the  cavity  of  the 
belly,  so  that  fluids  derived  from  thence  will  readily  pass  into  the 
different  chambers,  but  cannot  again  escape  through  the  same 
channel.  The  arrangement  of  these  valves  will,  however,  be  best 
understood  by  reference  to  the  accompanying 
figure  {Jig.  120),  representing  a  magnified  view 
of  the  interior  of  a  portion  of  the  heart  of  the 
cockchafer,  as  depicted  by  the  celebrated  en- 
tomotomist  above  alluded  to.  The  organ  has 
been  divided  longitudinally,  so  that  one  half  only 
is  represented  in  the  figure  upon  a  very  large 
scale.  The  compartments  (a,  a,  a)  are  distinctly 
composed  of  circular  muscular  fibres ;  the  large 
valves  (d,  d)  separate  the  individual  chambers, 
allowing  the  blood  to  pass  in  one  direction  only, 
viz.  towards  the  head  ;  while  the  openings  (c), 
likewise  closed  by  semilunar  membranous  valves, 
admit  blood  from  the  cavity  of  the  abdomen,  but 
effectually  prevent  its  return. 

(311.)  Let  us  now  consider  the  movements  of 
the  circulating  fluids  produced  by  the  contractions 
of  this  apparatus.  The  chyle  or  nutritive  material 
extracted  by  the  food,  exudes,  as  we  have  already  seen,  by  a  species 
of  percolation  through  the  walls  of  the  intestine,  and  escapes  into 
the  cavity  of  the  abdomen,  where  it  is  mixed  up  with  the  mass  of  the 
blood,  which  is  not  contained  in  any  system  of  vessels,  but  bathes 
the  surfaces  of  the  viscera  immersed  in  it.  When  any  compartment 
of  the  heart  relaxes,  the  blood  rushes  into  it  from  the  abdomen, 
through  the  lateral  valvular  apertures  ;  and  as  it  cannot  re¬ 
turn  through  that  opening  on  account  of  the  valves  (c)  that 
guard  the  entrance,  nor  escape  into  the  posterior  divisions  of  the 
heart  by  reason  of  the  valves  (d),  the  contraction  of  the  dorsal 
vessel  necessarily  forces  it  on  towards  the  head.  When  it  arrives 
there,  it  of  course  issues  from  the  perforated  termination  of  the 


270 


INSECTA. 


heart,  but  does  not  appear  to  be  received  by  any  vessels,  and 
therefore  becomes  again  diffused  through  the  body.  The  diffused, 
character  of  the  circulation  met  with  in  insects  may  easily  be  made 
a  matter  of  observation  in  many  of  the  transparent  aquatic  larvse 
that  are  readily  to  be  met  with.  When  any  of  the  limbs  of  these 
larvae  are  examined  under  a  powerful  microscope,  continual  cur¬ 
rents  of  minute  globules  are  everywhere  distinguishable,  moving 
slowly  in  little  streams  ;  some  passing  in  one  direction,  others  in 
the  opposite  :  but  that  these  streams  are  not  contained  in  vascular 
canals  is  quite  obvious,  from  the  continual  changes  which  occur  in 
the  course  of  the  globules  ;  their  movements,  indeed,  rather  re¬ 
semble  those  of  the  sap  in  chara ,  and  other  transparent  vegetables, 
in  which  the  circulation  of  that  fluid  is  visible  under  a  microscope. 

The  organs  appropriated  to  furnish  the  different  secretions  met 
with  in  the  economy  of  insects,  are  modified  in  their  structure  to 
correspond  with  the  character  of  the  circulation,  and  are  invariably 
simple  tubes  or  vesicles  of  various  forms  immersed  in  the  fluids  of 
the  body,  from  which  they  separate  their  peculiar  products.  The 
poisonous  saliva  of  bugs,  and  the  innoxious  salivary  fluid  of  other 
insects  ;  the  bile  and  auxiliary  secretions  subservient  to  digestion  ; 
the  venom  which  arms  the  sting  of  the  wasp,  and  the  silky  en¬ 
velope  of  the  caterpillar, — are  all  derived  from  the  same  source,  and 
in  some  mysterious  manner  elaborated  from  the  blood  by  variously 
formed  vessels  :  but  of  this  we  have  already  given  many  examples, 
and  others  will  present  themselves  in  the  following  pages. 

(312.)  In  the  nervous  system  of  the  Insecta,  we  have  many 
interesting  illustrations  of  that  gradual  concentration  of  the  parts 
composing  it,  and  consequently  of  increased  proportionate  deve- 
lopement  of  the  nervous  centres,  corresponding  with  the  more  active 
movements  and  higher  faculties  by  which  the  class  before  us  is  so 
remarkably  distinguished  from  those  forms  of  articulated  animals 
that  we  have  hitherto  had  an  opportunity  of  examining.  The  su- 
pra-oesophageal  ganglion,  or  brain,  assumes  a  preponderance  of  size 
in  relation  to  more  perfect  organs  of  sense,  and  to  instincts  of 
more  exalted  character  ;  the  chain  of  ganglia  placed  along  the  floor 
of  the  abdomen,  is  composed  of  a  few  large  masses  of  sufficient 
power  to  animate  the  strong  and  energetic  muscles  of  the  limbs  ; 
and,  moreover,  anatomists  have  detected  the  existence  of  an  addi¬ 
tional  nervous  apparatus,  apparently  representing  the  sympathetic 
system  of  vertebrate  animals,  which  is  distributed  to  the  viscera  ap¬ 
propriated  to  digestion  :  each  of  these  divisions  will  therefore  re¬ 
quire  a  separate  notice. 


INSECTA 


271 


The  brain,  or  encephalic  ganglion  {Jig.  121,  1),  is  a  nervous 
mass  of  considerable  size  placed  above  the  gullet ;  it  consists  es- 

Fig.  121. 


sentially  of  two  ganglia  united  into  one  mass,  and  from  it  all  the 
nerves  appropriated  to  the  special  instruments  of  the  senses  are  de¬ 
rived,  so  that  it  may  naturally  be  regarded  as  the  chief  seat  of  sens¬ 
ation  and  intelligence.  The  nerves  originating  from  this  common 
sensorium  are  seen  upon  an  enlarged  scale  in  Jig.  122  :  they  are  the 
optic  {Jig.  122,  a ),  supplying  the  eyes,  and  the  antennal  (Jig. 
122,,  e),  which  run  to  the  special  instruments  of  touch,  or  antenna , 


272 


INSECTA. 


organs  of  a  very  singular  character  that  we  shall  examine  more  mi¬ 
nutely  hereafter.  Two  other  cords  of  variable  length  (Jig-  122, 
g,  g)  are  given  off  from  the  inferior  aspect  of  the  brain,  and  serve 
to  connect  it  with  the  anterior  ganglion  of  the  ventral  chain  (Jig- 
122,  A),  to  which  some  writers  have  thought  proper  to  give  the 
name  of  cerebellum ,  though  upon  what  grounds  it  is  difficult  to 
conjecture  ;  the  mass  last  mentioned  gives  off  various  nerves  to 
supply  the  parts  connected  with  the  mandibles ,  maxilla, ,  and  other 
organs  of  the  mouth. 

The  rest  of  the  ventral  chain  of  ganglia  forms  a  continuous  series 
(fig-  121,  2,  3,  4,  5,  6,  7,  8)  of  nervous  centres  arranged  in  pairs, 
and  united  to  each  other  by  double  cords  of  communication,  but  they 
vary  much  in  number  and  relative  magnitude  in  different  families. 
Those  situated  in  the  thorax  are  usually  of  the  greatest  proportion¬ 
ate  size,  inasmuch  as  they  furnish  the  nerves  that  supply  the  mus¬ 
cles  of  the  wings  and  legs  ;  the  succeeding  ganglia  give  branches  to 
the  abdominal  segments  ;  and  the  last,  which  is  commonly  of  consi¬ 
derable  bulk,  supplies  the  sexual  organs  and  the  extremity  of  the 
colon. 

(313.)  It  is  the  general  opinion  of  modern  physiologists  that  the 
intimate  composition  of  the  nervous  apparatus  described  above  is  by 
no  means  so  simple  as  it  appears  to  ordinary  observation  ;  and,  since 
the  experiments  of  Sir  Charles  Bell  and  Majendie  demonstrated 
the  existence  of  distinct  columns  or  tracts  in  the  spinal  axis  of  ver¬ 
tebrate  animals,  various  anatomists  have  endeavoured  to  show  that 
corresponding  parts  may  be  pointed  out  in  the  ventral  chain  of  ar¬ 
ticulated  animals.  There  can,  indeed,  be  no  doubt  that  this  por¬ 
tion  of  the  nervous  system  of  an  insect  corresponds  in  every  parti¬ 
cular  with  the  medulla  spinalis  ;  and  if,  in  the  one  case,  the  nerves 
which  preside  over  the  general  muscular  movements  arise  from  a 
different  column  to  that  whence  the  nerves  that  correspond  with 
the  periphery  of  the  body  originate,  while  those  which  regulate  the 
motions  of  respiration  emanate  from  a  distinct  tract,  we  might  rea¬ 
sonably  suppose  a  similar  arrangement  to  exist  in  the  structure  of 
the  nervous  system  we  are  now  examining.  It  has,  in  fact,  been 
well  ascertained  that  the  nerves  given  off  to  the  muscular  system  of 
the  Homogangliata  are  not  derived  from  the  ganglionic  masses  them¬ 
selves,  but  from  the  cords  which  connect  them  together,  while  the 
nerves  distributed  to  the  integument  and  external  parts  of  the  body 
communicate  immediately  with  the  ganglia.  These  different  modes 
of  origin  give  presumptive  evidence  that  at  least  two  distinct  tracts 


INSECTA. 


O' 


rs 


Fi°-.  122. 


exist  in  tlie  central  axis  of  insects  ;  but,  from  the  extreme  minute¬ 
ness  of  the  different  parts,  it  is  not  easy  satisfactorily  to  demonstrate 
them  separately.  In  the  larger  Articulata,  however,  as  for 
example  in  the  crustaceans,  two  distinct  columns  of  nervous 
matter  are  readily  detected:  it  will,  therefore,  be  more  convenient 
to  defer  the  investigation  of  this  interesting  subject  until  we  have 
an  opportunity  of  describing  these  parts  upon  an  enlarged  scale ; 
enough  has  been  said  at  present  to  enable  the  reader  to  compare 
the  nervous  axis  of  an  insect  with  that  of  a  lobster,  and  draw  correct 
conclusions  from  the  comparison. 

(314.)  The  last  division  of  the  nervous  apparatus,  which  we  have 
already  mentioned  as  being  the  representative  of  the  sympathetic 
system,  consists  of  two  portions;  one  corresponding,  in  distribution 
at  least,  with  the  nervus  vagus  of  Vertebrata,  while  the  other 
represents,  apparently,  the  sympathetic  ganglia.  The  nervus  vagus, 
as  we  shall  call  it,  and  which  has  been  named  by  Swammerdam* 
and  Cuvier  the  recurrent  nerve ,  arises  {Jig.  122,  b,  b)  by  two  roots 
from  the  opposite  extremities  of 
the  brain  close  to  the  origins  of 
the  antennal  nerves.  The  nervous 
cords  thus  derived  soon  unite  to 
form  a  minute  central  ganglion 
(Jig.  \22,  i),  from  which  proceeds 
a  single  nerve  (Jig.  \22,  f,  k), 
that  runs  with  the  gullet  (/)  be¬ 
neath  the  brain,  and  spreads  in  deli¬ 
cate  ramifications  upon  the  oesopha¬ 
gus  as  far  as  the  muscular  stomach  (Jig.  \2\,  9,  9),  or  to  the  gizzard, 
when  that  organ  exists. 

(315.)  The  Sympathetic  system,  properly  so  called,  consists 
of  four  small  ganglia  (Jig.  121,  c,  c ,  l,  /),  the  two  anterior  of 
which  communicate  with  the  brain,  and  with  each  other  by 
means  of  connecting  filaments.  These  ganglia  are  closely  applied 
to  the  commencement  of  the  oesophagus,  and  supply  it  with  minute 
nerves. 

(316.)  Various  are  the  conjectures  entertained  by  different  au¬ 
thors  concerning  the  senses  possessed  by  the  members  of  the  insect 
world,  and  the  organs  subservient  thereunto.  The  possession  of 
certain  sources  of  perception  has  been  alternately  granted  and  denied, 


*  Biblia  Natura?. 


274 


INSECTA. 


tlie  nature  of  their  sensations  has  been  a  fruitful  subject  of  inquiry, 
and  some  physiologists  have  even  gone  so  far  as  to  deny  the  corre¬ 
spondence  of  the  impressions  derived  by  insects  through  the  medium 
of  their  senses  with  those  which  we  ourselves  receive.  It  would 
lead  us  far  out  of  our  course  did  we  even  advert  to  the  multiplicity 
of  opinions  and  conjectures  promulgated  from  various  sources  rela¬ 
tive  to  these  inquiries,  and,  perhaps,  with  little  addition  to  our 
real  knowledge.  It  is  true  that  we  cannot  deny  the  possibility  of 
the  existence  of  other  modes  of  sensation  than  those  familiar  to  us  ; 
but  it  is  likewise  evident  that,  as  we  can  never  have  the  most  remote 
conceptions  concerning  their  nature,  speculations  respecting  them 
are  calculated  to  lead  to  very  unsatisfactory  conclusions.  We  must 
from  necessity  take  our  own  senses  as  the  standard  of  comparison, 
limiting  our  inquiries  to  examine  how  far  insects  possess  means  of 
intercourse  with  the  external  world  similar  to  those  which  we  enjoy, 
and,  when  we  find  certain  faculties  to  exist,  to  investigate  the  struc¬ 
ture  of  the  organs  by  which  they  are  exercised. 

(317.)  The  sense  of  touch  is  indubitably  bestowed  upon  all  in¬ 
sects  ;  and,  to  judge  from  the  perfection  of  the  edifices  which  they 
build,  and  the  precision  of  their  usual  operations,  this  must  be  ex¬ 
tremely  delicate.  It  is  sufficient,  however,  to  look  at  the  external 
construction  of  the  skeletons  of  Articulata,  to  perceive  that  the 
hard  and  insensible  integument  spread  over  the  entire  surface  of 
their  bodies  is  but  little  calculated  to  receive  tactile  impressions. 
The  antennae,  or  feelers  as  they  are  popularly  called,  have  been 
very  generally  regarded  as  being  peculiarly  instruments  of  touch  ; 
and  whoever  watches  the  proceedings  of  an  insect  in  which  these 
appendages  are  largely  developed,  will,  we  apprehend,  easily  con¬ 
vince  himself  that  they  are  employed  to  investigate  surrounding 
objects  by  contact.  Strauss  Durckbeim  regards  the  feet  as  being 
specially  appropriated  to  the  sense  of  feeling,  but  this  opinion 
seems  quite  inadmissible.  Burmeister  places  the  exercise  of  touch 
exclusively  in  the  palpi  attached  to  the  maxillse  and  labium,  and 
observes  that  in  the  larger  insects,  such  as  the  predatory  beetles, 
the  grasshoppers,  humble-bees,  and  many  others,  the  apex  of  the 
palpus  is  dilated  into  a  white  transparent  and  distended  bladder, 
which,  after  the  death  of  the  insect,  dries  up,  and  is  no  longer 
visible.  This  bladder  he  looks  upon  as  the  true  seat  of  the  sense 
in  question,  and  remarks  that  the  main  nerve  of  the  maxillse 
and  of  the  tongue  spreads  to  it,  and  distributes  itself  upon  its 
superior  surface  in  minute  ramifications. 


INSECTS. 


27  5 


(318.)  Whether  taste  exists  in  insects  as  a  distinct  sense  may 
admit  of  dispute ;  the  tongue,  already  described,  seems  but  little 
adapted  to  appreciate  savours,  and,  seeing  this,  it  is  obvious  that 
all  opinions  assigning  the  function  of  tasting  to  other  parts  are 
purely  conjectural. 

(319.)  Many  insects  are  certainly  capable  of  perceiving  odours  ; 
of  this  we  have  continual  proof  in  the  flesh-fly  and  other  species, 
that  are  evidently  guided  to  their  food,  or  select  the  position  in  which 
to  deposit  their  eggs,  by  smell ;  but  where  the  olfactory  apparatus 
is  lodged  is  still  a  matter  of  doubt.  The  antenna  and  the  palpi 
have  each  had  the  power  of  smelling  assigned  to  them,  but  without 
much  plausibility.  The  respiratory  stigmata  have  been  pointed 
out  as  performing  the  office  of  examining  the  air  admitted  for  the 
purpose  of  breathing  ;  yet  other  authors,  with  equal  probability, 
look  upon  the  ultimate  ramifications  of  the  tracheae  as  forming  one 
extensive  nose.  The  interior  of  the  mouth  has  been  indicated  by 
Treviranus;*  while  Kirby  and  Spence  find  in  the  Necrophori,  and 
other  insects  remarkable  for  acuteness  of  smell,  an  organ  in  close 
connection  with  the  mouth,  to  which  they  attribute  the  perception 
of  odoriferous  particles  :  this  is  a  cavity  situated  in  the  upper  lip, 
containing  a  pair  of  circular  pulpy  cushions  covered  by  a  membrane 
transversely  striated  or  gathered  into  delicate  folds. 

(320.)  We  are  scarcely  better  informed  concerning  the  organs  of 
hearing ,  but  that  insects  are  capable  of  perceiving  sounds  is  proved 
by  the  fact  of  many  tribes  being  capable  of  producing  audible  noises 
by  which  they  communicate.  There  seems,  indeed,  to  be  little 
doubt  that  the  auditory  apparatus  is  in  some  way  or  other  con¬ 
nected  with  the  antennae.  Some  have  supposed  that  these  slender 
and  jointed  organs,  supplied,  as  they  are,  with  large  nerves,  are 
themselves  capable  of  appreciating  sonorous  vibrations.  Bur- 
meisterj*  thinks  that,  as  in  crabs  and  lobsters,  it  is  at  the  base 
of  the  antenna  that  the  ear  is  situated,  and  observes  that  if  we 
examine  the  insertion  of  these  appendages  we  shall  detect  there 
a  soft  articulating  membrane  which  lies  exposed,  and  is  rendered 
tense  by  the  movements  of  the  antenna,  —  this  he  looks  upon 
as  representing  the  drum  of  the  ear,  and  conceives  that  it  is  so 
placed  as  to  receive  impressions  of  sound,  increased  by  the  vibratory 
movements  communicated  to  the  antennse  by  the  sonorous  undula¬ 
tions  of  the  atmosphere. 


*  Vermischte  Schriften,  vol.  ii. 


t  Op.  cit.  p.  296. 
T  2 


276 


INSECT A. 


In  some  motlis,  Treviranus* * * §'  has  discovered  structures  which 
would  seem  to  be  indubitably  real  auditory  organs.  He  found  in 
front  of  the  base  of  each  antenna  a  thin  membranous  drum,  behind 
which,  large  nerves,  derived  from  those  supplied  to  the  antennae, 
spread  themselves  out ;  but  this  apparatus  has  not  been  detected 
in  other  insects. 

(321.)  The  eyes  of  insects  are  of  two  kinds,  simple  and  com¬ 
pound  ;  the  former  being  insulated  visual  specks,  while  the  latter 
consist  of  agglomerations  of  numerous  distinct  eyes,  united  so  as  to 
form  most  elaborate  and  complex  instruments  of  sight. 

Some  insects,  as  the  Dictyotoptera  and  Thysanoura ,  only 
possess  simple  eyes  ;  others,  as  for  example  the  Coleoptera,  have 
only  compound  eyes  ;  but  in  general  both  kinds  exist  together. 
In  the  Sir  ex  gigas  ( Jig .  128),  for  instance,  besides  the  large 
hemispherical  organs  of  sight,  situated  at  the  sides  of  the  head, 
three  simple  spots  are  seen  upon  the  vertex,  which  are  likewise 
appropriated  to  vision. 

The  structure  of  the  eyes  has  been  most  minutely  investigated 
by  several  distinguished  entomotomists,  and  the  labours  of  Marcel 
de  Serres,j-  Joh.  Muller, j  Strauss  Durckheim,§  and  Duges,||  have 
done  much  to  dispel  the  mistaken  notions  entertained  by  preceding 
anatomists. 

The  simple  eyes  consist  of  a  minute,  smooth,  convex,  transpa¬ 
rent  cornea,  in  close  contact  with  which  is  a  small  globular  lens  ; 
behind  this  lens  is  placed  the  representative  of  the  vitreous  humour, 
upon  which  a  nervous  filament  spreads  out,  so  as  to  form  a  retina  : 
the  whole  is  enclosed  in  a  layer  of  brown,  red,  or  black  pigment, 
which,  bending  round  the  anterior  surface  of  the  eye,  forms  a  dis¬ 
tinct-coloured  iris  and  pupillary  aperture.  Such  an  arrangement 
evidently  resembles  what  is  met  with  in  higher  animals,  and  is 
remarkable  for  its  simplicity ;  but  it  is  far  otherwise  with  the  com¬ 
pound  eyes  of  insects,  for  these  are  constructed  upon  principles  so 
elaborate  and  complex,  that  we  feel  little  surprise  at  the  amaze¬ 
ment  expressed  by  early  writers  who  examined  them,  although 
their  ideas  concerning  their  real  structure  came  far  short  of  the 
truth. 

*  G.  R.  Treviranus,  Annalender  Wetterau.  Gesel.  f.  d.  Ges.  Naturk.  vol.  i.  1809. 

t  Mem.  sur  les  Yeux  composes,  et  les  Yeux  lisses  des  Insectes.  —  Montpel.  8vo. 
1813. 

t  Zur  Vergleichenden  Physiologie  des  Gesichtssinnes,  8vo.  1826. 

§  Annales  des  Sciences  Nat.  tom.  xviii.  j|  Ibid.  tom.  xx. 


INSECTA. 


277 


The  compound  eyes  of  insects  are  two  in  number,  situated  on 
the  lateral  aspects  of  the  head,  the  form  of  each  being  more  or  less 
hemispherical.  When  examined  with  a  microscope,  their  surface 
is  seen  to  be  divided  into  a  multitude  of  hexagonal  facets,  between 
which,  minute  hairs  are  generally  conspicuous.  The  number  of 
facets  or  corneae,  for  such  in  fact  they  are,  varies  in  different 
genera  :  thus,  in  the  ant  ( Formica )  there  are  50  ;  in  the  common 
house-fly  ( Musca  domestica ),  4000  ;  in  some  dragon-flies  ( Libel - 
lula ),  upwards  of  12,000.  In  butterflies  ( Papilio )  17,355  have 
been  counted,  and  some  Coleoptera  ( M or  della )  possess  the  as¬ 
tonishing  number  of  25,088  distinct  cornese. 

But  in  order  to  appreciate  the  wonderful  organization  of  these 
remarkable  organs  of  sight,  it  is  necessary  to  examine  their  internal 
structure  :  every  cornea  is  then  found  to  belong  to  a  distinct  eye, 
provided  with  a  perfect  nervous  apparatus,  and  exhibiting  its  pe¬ 
culiar  lens,  iris,  and  pupil ;  thus  being  completely  entitled  to  be 
considered  a  distinct  instrument  of  vision. 

By  attentively  examining  FiS>  123  • 

the  annexed  figure,  repre¬ 
senting  a  section  of  the  eye 
of  the  cockchafer  ( Melolon - 
tha ),  as  displayed  by  Strauss 
Durckheim,  the  whole  struc¬ 
ture  of  the  organ  will  be 
understood.  The 
optic  nerve  (Jig-  123,  o), 
derived  immediately  from 
the  supra-oesopliageal  mass 
of  nervous  matter,  swells 
soon  after  its  origin  into  a 
rounded  ganglion,  nearly 
half  as  large  as  the  brain  it¬ 
self.  From  the  periphery 
of  the  ganglion  so  formed 
arise  a  considerable  number  of  secondary  nerves  (5),  which  are 
very  short,  and  soon  come  in  contact  with  a  layer  of  pigment  ( d )  ; 
that  in  the  cockchafer  is  of  a  brilliant  red  colour,  and  is  placed 
concentrically  with  the  convex  outer  surface  of  the  eye.  Behind 
this  membrane,  called  by  Strauss  the  common  choroid,  the  second¬ 
ary  optic  nerves  ( b )  unite  to  form  a  membranous  expansion  of 
nervous  matter  (c)  which  may  be  denominated  the  general  retina. 


278 


INSECTA. 


From  the  nervous  expansion  so  formed  arise  the  proper  optic 
nerves  (e),  appropriated  to  the  individual  eyes  or  ocelli ,  as  we  shall 
term  them.  These  nervous  filaments  are  as  numerous  as  the 
facets  of  the  cornea,  and  traverse  the  common  choroid  to  radiate  to¬ 
wards  the  individual  eyes  whereunto  they  are  respectively  destined, 
and  the  structure  of  which  we  must  now  proceed  to  examine. 
In  fig-  123,  b,  a  portion  of  the  circumference  of  the  compound 
eye  is  represented  upon  a  very  large  scale,  in  order  to  show  the 
construction  of  the  hexagonal  ocelli  that  enter  into  its  composi¬ 
tion.  Each  cornea  (i)  is  a  double  convex  lens,  adapted  by  its 
shape  to  bring  to  a  focus  the  rays  passing  through  it.  Behind 
every  lens  so  constituted  is  placed  an  hexaedral  transparent  prism 
(h),  which  from  its  office  may  be  compared  to  the  vitreous  hu¬ 
mour  of  the  human  eye  ;  and  it  is  upon  the  posterior  extremity 
of  these  prisms  that  the  proper  optic  nerves  (Jig.  123,  a,  e)  spread 
themselves  out,  so  as  to  form  so  many  distinct  retinae.  When  we 
reflect  upon  the  extreme  minuteness  of  the  parts  above  alluded  to, 
we  may  well  expect  slight  discrepancies  to  occur  between  the  ac¬ 
counts  given  of  them  by  different  anatomists.  Strauss  Durckheim 
represents  every  optic  nerve  as  terminating  in  a  minute  pyriform 
bulb  (Jig.  123,  b,/),  and  points  out  a  dark  layer  of  pigment  (g*), 
which  forms  a  choroid  tunic  proper  to  each  ocellus  ;  while,  accord¬ 
ing  to  Muller  and  Duges,  the  vitreous  humours  (h)  are  conical,  and 
terminate  posteriorly  in  a  sharp  point,  upon  which  the  terminal 
expansion  of  the  optic  nerve  spreads  out  without  any  pyriform 
enlargement :  they  likewise  deny  the  existence  of  the  proper 
choroid  ( g )  in  the  situation  indicated  by  Strauss,  but  find  a  black 
pigment  situated  immediately  behind  the  cornea,  that  at  first  sight 
would  appear  to  be  continuous  over  the  whole  surface  of  the  eye. 
Even  Cuvier  seems  at  one  time  to  have  adopted  this  opinion  ; 
Muller,  however,  found  that,  upon  carefully  removing  the  internal 
structures  of  the  organ,  leaving  the  pigment  untouched,  the  dark 
varnish  in  question,  although  very  thick  at  the  lines  of  union  of 
the  different  facets,  where  it  is  continuous  with  a  choroid  that 
separates  the  individual  ocelli,  yet  towards  the  centre  of  each  facet 
it  becomes  exceedingly  thin,  and  at  the  very  centre  is  quite  want¬ 
ing,  so  that  a  minute  perforation  or  pupil  is  thus  left,  through 
which  the  rays  of  light  enter.  The  existence  of  the  secondary 
optic  nerves  (b)  and  common  retina  (c)  is  likewise  disputed  by 
Muller  and  Duges,  who  consider  the  proper  optic  nerves  to  arise 
immediately  from  the  surface  of  the  brain. 


INSECTA. 


279 


(322.)  With  regard  to  the  wonderfully  complex  structure  of  these 
organs,  Strauss  Durckheim  suggests,  that,  the  eyes  of  insects  being 
fixed,  nature  has  made  up  for  their  want  of  mobility  by  their 
number,  and  by  turning  them  in  all  directions  ;  so  that  it  might  be 
said  that  these  little  animals  have  a  distinct  eye  for  every  object. 
But  here  we  are  naturally  tempted  to  inquire,  whether  insects  see 
at  the  same  time  distinctly  with  every  one  of  these  eyes,  or  if  they 
distinguish  with  one  eye  only.  Upon  this  point  Strauss  Durek- 
heim  observes,  that,  if  they  saw  clearly  with  all,  the  great  number 
of  images  would  necessarily  produce  confusion,  and  would  prevent 
creatures  so  organized  from  paying  special  attention  to  any  deter¬ 
minate  point.  It  is  probable,  therefore,  that  one  ocellus  only  is  at 
any  given  time  placed  in  circumstances  precisely  adapted  to  the 
complete  examination  of  an  object,  the  animal  seeing  things  imper¬ 
fectly  with  the  rest,  in  the  same  manner  as  we  see  objects  situated 
nearer  to  us  or  further  off  than  that  upon  which  we  fix  our  atten¬ 
tion  ;  so  that,  according  to  this  supposition,  insects  would  see  very 
distinctly  with  one  eye  only,  exactly  as  we  see  confusedly  an  ex¬ 
tensive  landscape,  although  we  only  distinguish  a  small  part  of  it. 

(323.)  In  all  insects  the  sexes  are  quite  distinct,  and  the  genera¬ 
tive  apparatus,  both  of  the  male  and  female,  consists  of  various  se¬ 
creting  organs  with  their  excretory  ducts :  in  the  male,  such  glands 
furnish  the  impregnating  secretions  ;  and,  in  the  female,  give  origin 
to  the  ova,  and  pro-  p-  124> 

vide  the  covering 
wherein  the  eggs  are 
enveloped. 

(324.)  Commenc¬ 
ing  with  a  descrip¬ 
tion  of  the  male  or¬ 
gans,  we  find  in  the 
cockchafer  various 
parts  represented  in 
the  accompanying 
figure,  taken  from 
the  admirable  work 
of  Strauss  already  so 
often  quoted.  The 
testicles  of  Melolon- 
tha  ( fig .  124,  a,  a) 
are  six  in  number 
on  each  side  of  the 


280 


INSECTA. 


body ;  but,  in  tbe  engraving,  those  of  one  side  only  are  delineated. 
Every  testis  consists  of  a  vesicular  organ,  hollow  internally,  which, 
being  immersed  in  the  juices  of  the  insect,  separates  therefrom 
the  seminal  fluid.  Six  ducts  ( b ,  b ,  b)  may  be  called  Vasa 
defer entia ,  and  convey  the  spermatic  liquor  into  a  common 
canal  (c,  c),  of  considerable  length  and  much  convoluted. 
Although  slender  at  its  commencement,  this  tube  ultimately 
expands  into  a  wider  portion  (d),  wherein,  no  doubt,  the  semen 
accumulates,  and  which  has  been  called  by  authors  the  vesica 
seminalis. 

The  canal  (d)  terminates  by  joining  the  corresponding  duct 
from  the  opposite  side  (dr)  to  form  a  common  tube  (g),  but  just 
at  the  point  of  junction  they  are  joined  by  two  long  auxiliary 
vessels  (f,f)  that  have  been  named  sperm-vessels ,  gluten-vessels , 
and  gum-vessels ,  by  different  authors,  but  which  appear  to  be 
appropriated  to  the  production  of  some  fluid,  perhaps  analogous  to 
the  prostatic  fluid  of  mammalia,  whereby  the  bulk  of  the  seminal 
liquor  is  increased  in  order  to  facilitate  its  expulsion.  Each  of 
these  auxiliary  vessels  consists  of  two  parts, — along  and  much  con¬ 
voluted  portion  (e,  e,  e),  forming  the  secreting  organ ;  and  a  dila- 
tation  (y  ),  that  must  be  looked  upon  as  a  reservoir  for  the  fluid 
elaborated.  The  common  canal  (g)  receives  all  these  secretions  ; 
it  is  at  first  enclosed  in  a  kind  of  sheath  (^),  but,  soon  becom¬ 
ing  muscular,  it  dilates  into  a  strong  contractile  canal  (g,  i),  called 
the  ductus  ejaculatorius ,  which  is  continued  to  the  extremity  of 
the  penis. 

The  intromittent  organ  itself  is  composed  of  two  parts ;  a  pro- 
trusible  corneous  tube  (/,  /),  and  an  external  horny  sheath  ( n ,  n), 
in  which  the  former  is  usually  concealed  and  protected. 

(325.)  Great  variety,  of  course,  exists  in  the  number,  form,  and 
general  arrangement  of  all  the  parts  alluded  to  in  the  above  descrip¬ 
tion,  when  examined  in  different  insects.*  In  the  hive-bee,  for 
example,  the  testes  ( fg .  125,  a)  are  only  two  in  number,  and 
are  simple  oval  vesicles  ;  the  vasa  deferentia  (5,  b)  are  short ;  and 
the  seminal  receptacles  ( c )  form  membranous  sacculi.  The  aux¬ 
iliary  secreting  organs  (d),  although  placed  in  the  same  position 
as  in  Melolontha,  are  represented  by  capacious  caeca ;  while  the 
common  excretory  duct  (e)  swells  into  a  strong  and  muscular  bag 

*  For  more  ample  details  relative  to  the  various  forms  of  the  testis  in  insects,  the 
reader  is  referred  to  the  Cyclop,  of  Anat.  and  Phys.  ;  art.  Generation,  Organs 


of. 


INSECTA. 


281 


( f ),  which  constitutes  the  ejaculatory 
apparatus.  Still,  however,  it  is  easy  to 
see  that,  although  diversified  in  appearance, 
the  parts  here  found  are  essentially  similar 
to  those  met  with  in  the  cockchafer,  and 
represent  respectively  the  same  organs. 

(826.)  The  female  apparatus  of  reproduc¬ 
tion  presents  a  general  correspondence,  both 
in  form  and  arrangement,  with  the  sexual 
parts  of  the  male  insect.  The  ovaria  are 
simple  secreting  sacculi,  or  elongated  tubes, 
in  which  the  germs  or  ova  are  produced, 
instead  of  the  seminal  liquor  ;  and  the 
excretory  canals,  or  egg-passages,  with  the 
organs  appended  to  them,  although  appro¬ 
priated  to  different  functions,  strikingly  re¬ 
semble  the  organs  met  with  in  the  other 
sex. 


Fig.  125. 


In  the  female  of  Melolontlia  the  ovaria  are  long  tubes,  form¬ 
ing  two  distinct  fasciculi,  symmetrically  situated  on  the  two  sides 
of  the  body.  At  their  commencement  {Jig-  126,  u ,  u )  the  ovi- 
gerous  tubes  are  slender,  and  the  ova  which  they  contain  at  this 
point  are  in  a  very  rudimentary  state  of  developement ;  they  ge¬ 
nerally  dilate,  however  ( t ,  t ,  t,  t ),  and,  as  they  expand,  the  ova  are 
seen  to  attain  larger  dimensions.  Near  its  termination  each  ova¬ 
rian  tube  assumes  a  granulated  texture  (5,  s ),  and  they  all  ulti¬ 
mately  open  into  the  corresponding  excretory  canal  (r,  r). 

All  the  ovarian  tubes  of  one  side  are  united  into  a  bundle,  by 
a  ligament  ( v ,  a),  which  Joh.  M tiller*'  traced  to  the  dorsal  vessel, 
and  believed  to  be  a  vascular  canal  adapted  to  bring  blood  imme¬ 
diately  into  the  tubes  wherein  the  ova  are  formed  ;  but  no  satis¬ 
factory  evidence  has  been  adduced  in  proof  of  the  existence  of  such 
an  extraordinary  communication,  and  the  thread  in  question  is  most 
probably  a  mere  ligamentous  connection. 

(827.)  Taking  the  higher  animals  as  a  standard  of  comparison,  we 
may  suppose  the  formation  of  the  eggs  in  these  tubes  to  be  accom¬ 
plished  in  the  following  manner  : — In  the  upper  part  of  the  tube  ( u ) 
is  formed  the  yolk,  enclosed  in  its  peculiar  membrane,  and  provided 
with  that  wonderful  germ  from  which  after  impregnation  the  future 
being  is  to  be  developed  ;  as  the  yolk  slowly  descends  to  the  more 


*  Nova  Acta  Phys.  Med,  n.  c.  vol.  xii.  part  ii. 


282  INSECTA. 

dilated  parts  of  the  canal  126, 

(?,  £),  it  becomes  clothed 
with  the  albumen  which 
constitutes  the  white  of 
the  egg;  and  ultimately, 
before  quitting  the  nidus 
of  its  formation,  receives 
from  the  granular  termi¬ 
nation  of  the  ovary  its 
last  integument  or  shell. 

Thus  completed,  it  passes 
into  the  excretory  canal 
(r,  r)  ;  and  this,  meeting 
the  corresponding  tube 
derived  from  the  ovaries 
of  the  opposite  side,  joins 
it  to  form  the  common 
oviduct  (/)  through  which 
the  egg  is  conducted  out 
of  the  body. 

(828.)  But  we  must 
now  advert  to  certain  ap¬ 
pendages  connected  with 
the  common  oviduct. 

These  are  of  two  kinds  ;  the  glut  en- secret  or  s  and  the  spermaiheca . 

The  gluten-secretors  (Jig.  126,  p,  p)  are  glandular  caeca 
opening  into  the  common  egg-canal,  and  are  apparently  destined 
to  furnish  a  glutinous  fluid  with  which  the  eggs  become  invested 
before  they  are  expelled  from  the  body  and  thus  they  are  fre¬ 
quently  united  into  long  chains  and  variously  shaped  masses  ;  or 
else  the  adhesive  varnish  thus  secreted  serves  to  glue  the  ova  in 
situations  favourable  to  the  developement  of  the  embryo. 

The  other  organ,  or  spermatlieca  {Jig.  126,  w,  o),  has  a  widely 
different  office,  being  a  receptacle  provided  to  receive  the  seminal 
secretion  of  the  male  during  copulation  :  it  is  always  situated  upon 
the  upper  aspect  of  the  oviduct,  into  which  it  opens  by  a  small  ori¬ 
fice  surrounded  by  a  thickened  margin  or  sphincter,  embracing  the 
neck  of  the  bag,  and  so  disposed  as  either  to  retain  the  enclosed  fluid, 
or  to  allow  it  to  escape  into  the  oviduct.  That  this  organ  really  does 
receive  and  retain  the  seminal  liquor  is  proved  by  the  presence  of 
seminal  animalcules  in  its  contents  ;  but  the  matter  has  been  placed 


INSECTA, 


283 


beyond  a  doubt  by  the  experiment  of  John  Hunter,*  who  actually 
succeeded  in  fecundating  the  eggs  of  an  unimpregnated  female,  by 
applying  to  them  a  little  of  the  fluid  contained  in  its  cavity :  but 
that  the  reader  may  comprehend  fully  the  reason  of  such  an  arrange¬ 
ment,  it  is  necessary  to  consider  the  circumstances  under  which 
insects  propagate. 

In  most  animals,  sexual  union  may  be  repeated  several  times 
during  the  life  of  individuals,  but,  in  insects,  intercourse  between 
the  sexes  is  permitted  to  take  place  but  once  ;  and  this  solitary 
congress  must  suffice  for  the  impregnation  of  all  the  ova,  however 
numerous,  and  however  imperfect  may  be  the  developement  of 
some  of  them  at  the  time  when  the  embrace  occurs. 

Let  us  take  the  hive-bee  as  an  example  ;  in  the  females  of  this 
insect  the  ovigerous  tubes  (Jig.  1 27,  «,  a)  are  excessively  numerous, 
and  the  eggs  produced  in  them  may  amount  to  between  20,000  and 
30,000  :  these  eggs,  of  course,  arrive  at  maturity  in  succession, 
and  not  all  at  once  ;  so  that  at  the  moment  when  the  queen-bee 
meets  her  selected  mate,  perhaps  the  majority  of  the  ova  are  not 
in  a  sufficiently  mature  condition  to  be  rendered  fertile.  Never¬ 
theless,  the  meeting  of  the  sexes  cannot  be  repeated ;  for  no  sooner 
has  copulation  taken  place  than  the  favoured  male  dies,  and 
by  a  simultaneous  butchery  all  the  other  males,  or  drones  as 
they  are  commonly  designated,  are  Fig.  127. 

destroyed  by  the  working  inhabit¬ 
ants  of  the  hive.  The  quantity 
of  the  fecundating  liquor,  there¬ 
fore,  supplied  by  one  connection, 
must  serve  to  fertilize  all  the  eggs 
produced  during  the  lifetime  of  the 
queen-bee  ;  and  for  this  purpose  it 
is  stored  up  in  the  spermatheca 
(Jig.  127,  c),  so  that,  how  numer¬ 
ous  soever  may  be  the  eggs  formed, 
they  are  all  vivified  as  they  pass  out  through  the  oviducts  ( b ,  e), 
and  thus  come  in  contact  with  the  orifice  of  the  reservoir  of  semen. 

In  Meloe  variegatus  (Jig.  121)  the  ovaria  (d)  consist  of 
wide  and  capacious  sacs,  covered  externally  with  innumerable 
glandiform  vesicles,  opening  into  the  cavity  of  the  ovary  (e).  The 
gluten-secretor  ( h )  and  the  spermatheca  (g)  are  seen  as  in 
Melolontha,  appended  to  the  common  oviduct  (f ) ;  but  the  sperma- 


*  Home’s  Lectures  on  Comp.  Anat.  vol.  iii.  p.  370. 


284 


INSECT A. 


theca  lias  a  small  accessory  vesicle  (i)  connected  with  it,  not  found 
in  the  former  examples. 

(329.)  In  many  insects,  especially  of  the  Hymenopterous  order, 
the  generative  apparatus  is  terminated  externally  by  peculiar  instru¬ 
ments  provided  for  the  purpose  of  introducing  the  eggs  into  a 
proper  situation.  This  is  particularly  remarkable  in  the  Ichneu¬ 
mons ,  which  deposit  their  ova  in  living  caterpillars ;  and  in  the 
saw-flies  ( Tenthredo ),  whose  eggs  are  insinuated  into  the  sub¬ 
stance  of  the  leaves,  or  even  of  the  branches  of  trees.  T o  describe 
all  the  contrivances  employed  for  this  purpose  would  lead  us  far 
beyond  our  prescribed  limits  :  one  example  of  an  organ  of  this 
description  must  suffice. 

In  the  Sir  ex  gigas  (Jig.  128)  the  ovipositor  consists  appa- 


Fig.  128. 


rently  of  three  pieces  of  considerable  length,  seen  in  the  figure  to 
project  from  the  inferior  margin  of  the  abdomen.  Of  these  pieces, 
two  form  a  sheath  enclosing  a  third,  called  the  terebra ,  or  borer,  which 
in  the  Tenthredo  contains  two  saws  of  extremely  beautiful  construc¬ 
tion,  as  we  learn  from  an  account  of  them  given  by  Professor  Peck, 
and  quoted  by  Kirby  and  Spence  :*  the  original  description,  which 
it  would  be  unpardonable  to  abbreviate,  is  as  follows  : — “  This  in¬ 
strument,”  says  Professor  Peck,  “  is  a  very  curious  object  ;  and,  in 
order  to  describe  it,  it  will  be  proper  to  compare  it  with  the  tenon- 
saw  used  by  cabinet-makers,  which,  being  made  of  a  very  thin  plate  of 
steel,  is  fitted  with  a  back  to  prevent  its  bending.  The  back  is  a  piece 

*  Introd.  to  Entom.  vol.  iv.  p.  161. 


INSECT A. 


285 


of  iron,  in  which  a  narrow  and  deep  groove  is  cut  to  receive  the  plate, 
which  is  fixed  :  the  saw  of  the  Tenthredo  is  also  furnished  with  a 
back,  but  the  groove  is  in  the  plate,  and  receives  a  prominent  ridge 
of  the  back,  which  is  not  fixed  (to  the  saw),  but  permits  the  saw 
to  slide  forward  and  backward  as  it  is  thrown  out  and  retracted. 
The  saw  of  artificers  is  single,  but  that  of  the  Tenthredo  is  double, 
and  consists  of  two  distinct  saws  with  their  backs  :  the  insect,  in 
using  them,  first  throws  out  one,  and  while  it  is  returning  pushes 
forward  the  other ;  this  alternate  motion  is  continued  till  the  inci¬ 
sion  is  effected,  when  the  two  saws,  receding  from  each  other,  con¬ 
duct  the  egg  between  them  into  its  place.” 

(330.)  With  respect  to  the  number  of  eggs  laid  by  insects  it 
varies  in  different  species  ;  the  flea,  for  example,  lays  about  twelve, 
and  many  Diptera  and  Coleoptera  average  perhaps  fifty  :  but  others 
are  far  more  prolific ;  among  moths,  for  example,  the  silkworm  pro¬ 
duces  500,  and  some  from  1000  to  2000  :  the  wasp  (  Vespa  vulgaris ) 
deposits  3000 ;  the  ant  (Formica),  from  4000  to  5000.  The 
queen-bee  is  said  by  Burmeister  to  lay  from  5000  to  6000  ;  but 
Kirby  and  Spence  consider  that  in  one  season  the  number  may 
amount  to  40,000  or  50,000,  or  more.  Yet,  surprising  as  this 
latter  statement  may  appear,  the  fecundity  of  the  queen-bee  is  far 
inferior  to  that  of  the  white-ant  (Termes  fatalis)  ;  for  the  female 
of  this  insect  extrudes  from  her  enormous  matrix  innumerable  eg-ors 

oo 

at  the  rate  of  sixty  in  a  minute,  which  gives  3600  in  an  hour, 
86,400  in  a  day,  and  2,419,200  in  a  lunar  month  :  how  long  the 
process  of  oviposition  continues  in  the  termite  is  unknown  ;  but,  if 
it  wrere  prolonged  through  the  entire  year,  the  amazing  number  of 
211,449,600  eggs  would  proceed  from  one  individual ;  setting,  how¬ 
ever,  the  number  as  low  as  possible,  it  will  exceed  that  produced  by 
any  known  animal  in  the  creation. 

(331.)  The  Aphides,  or  plant-lice,  furnish  a  remarkable  instance 
of  fecundity.  In  these  insects  it  has  been  satisfactorily  ascertained 
by  Bonnet,  Lyonnet,  and  Reaumur,  that  a  single  sexual  intercourse 
is  sufficient  to  impregnate  not  only  the  female  parent,  but  all  her 
progeny  down  to  the  ninth  generation  !  The  original  insect  still 
continues  to  lay  when  the  ninth  family  of  her  descendants  is  capa¬ 
ble  of  reproduction  ;  and  Reaumur  estimated  that  even  at  the  fifth 
generation,  a  single  Aphis  might  be  the  great-great-grandmother  of 
5,904,000,000  young  ones. 

(332.)  Innumerable  are  the  means  employed  by  nature  to  keep 
the  balance  between  the  increase  and  destruction  of  the  insect  tribes, 


286 


INSECT A. 


and  countless  enemies  are  provided  for  the  purpose  of  checking 
their  inordinate  accumulation. 


(333.)  Among  the  most  remarkable  provisions  for  preventing  su¬ 
perabundant  fertility,  is  that  law  which  compels  the  most  prolific 
insects  to  live  in  large  societies,  and  permits  but  one  female  out  of 
a  multitude  to  lay  eggs.  As  an  example  of  this,  we  may  take  the 
hive-bees,*  so  remarkable  for  their  elevated  instincts  and  industri¬ 
ous  habits.  A  swarm  of  bees  consists,  first  of  females,  whose  sex¬ 
ual  organs  remain  permanently  in  an  undeveloped  condition,  usu¬ 
ally  called  the  Workers  {fig.  129,  a)  ;  secondly,  of  perfect  males  or 
drones  (c)  ;  and  thirdly,  of  a  solitary  fertile  female,  called  the  Queen 
(b),  which  gives  birth  to  all  the  progeny  of  the  hive  ;  and  thus, 
instead  of  20,000  or  30,000  eggs  being  furnished  by  every  one  of 
as  many  females,  one  female  only  is  permitted  to  be  instrumental 
in  perpetuating  the  species. 

(334.)  The  termite  ants  likewise,  were  it  not  for  a  similar  restric¬ 
tion,  would  soon,  by  their  overwhelming  increase,  depopulate  whole 
regions  of  the  earth,  and  render  the  countries  in  which  they  are 
met  with  absolutely  uninhabitable  by  their  extreme  voracity.  A 
community  of  termites  is  said  to  consist  of  five  different  members, 
namely,  winged  males  and  females  (fig.  130,  a)  ;  apterous  neu¬ 
ters,  or  soldiers,  which  have  large  heads  furnished  with  strong  pro¬ 
jecting  mandibles  (b)  ;  unwinged  pupae,  having  a  smaller  head,  and 
the  rudiments  of  wings  only  (c)  ;  and,  lastly,  of  similarly  formed 
larvee,  or  workers  (d),  differing  from  the  latter  only  in  wanting 
the  rudiments  of  wings.  The  following  is  a  brief  history  of  the 
establishment  and  growth  of  a  colony  of  these  insects,  as  narrated 
by  Burmeister.j~  At  the  termination  of  the  hot  season,  the  young 

*  For  ample  details  concerning  the  habits  of  these  interesting  creatures,  the  reader  is 
referred  to  Dr.  Bevan’s  work  on  the  Honey-Bee,  its  Natural  History,  Physiology,  and 
Management,  vol.  I,  12mo.  Lond.  t  Op.  cit.  p.  535. 


INSECT A. 


287 


males  and  females  disclosed  in  a  nest  quit  it,  and  appear  upon  the 
surface  of  the  earth,  where  they  swarm  in  innumerable  hosts  and  pair. 
The  busied  workers  then  convey  a  chosen  male  and  a  female  back 
into  the  dwelling,  and  imprison  them  in  the  central  royal  cell,  the 
entrances  to  which  they  decrease  and  guard  ;  through  these  apertures 
the  imprisoned  pair  then  receive  the  nutriment  they  require.  The 
male  now,  as  amongst  all  other  insects,  speedily  dies  after  the  im¬ 
pregnation  of  the  female  has  been  effected  ;  but  the  female  from  this 
period  begins  to  swell  enormously  from  the  developement  of  her 
countless  eggs,  and,  by  the  time  she  is  ready  to  commence  laying, 
her  abdomen  is  about  1500  or  2000  times  larger  than  all  the  rest 
of  her  body  ( Jig .  130,  e).  During  the  period  of  this  swelling  the 

Fig.  130. 


C  B  D 

workers  remove  the  walls  of  the  royal  apartment,  uniting  the  nearest 
cells  to  it,  so  that,  in  proportion  to  the  increase  of  the  body  of  the 
queen,  the  size  of  the  abode  she  inhabits  is  also  increased.  She 


288 


INSECTA. 


now  commences  laying  eggs,  and,  during  tlie  process,  the  abdomen 
exhibits  a  continual  undulatory  motion,  produced  by  the  peristaltic 
movement  of  the  egg-ducts ;  while  the  workers  convey  away  the 
eggs  as  they  are  laid,  and  deposit  them  in  the  distant  rearing-cells 
of  their  wonderful  habitation.  The  reader  will  be  able  to  form 
some  idea  of  the  relative  proportions  and  outward  appearance  of 
the  edifices  erected  by  these  comparatively  minute  beings  by  the 
group  of  their  citadels  represented  in  the  back-ground  of  the  figure  ; 
but  to  describe  them  more  minutely  would  lead  us  into  details 
unconnected  with  our  subject.* 

(835.)  The  eggs  of  these  little  animals  vary  much  in  shape  and 
external  configuration  ;  so  that,  from  the  beauty  of  their  forms  and 
exquisite  sculpture,  some  of  them  are  interesting  objects  for  the 
microscope. 

(336.)  We  have  already  spoken  concerning  the  metamorphosis 
which  insects  undergo  during  the  progress  of  their  developement  from 
the  form  under  which  they  first  leave  the  egg  to  their  mature  con¬ 
dition,  when  they  become  fertile,  and,  in  most  instances,  acquire 
those  instruments  of  flight  so  generally  characteristic  of  their  perfect 
state.  Before  entering  upon  a  more  minute  inquiry  concerning 
the  physiological  principles  upon  which  the  important  changes  in 
question  depend,  and  the  phenomena  attending  the  process,  it  will 
be  advisable  to  cite  a  few  more  examples  illustrative  of  the  most 
interesting  varieties  of  metamorphosis  signalized  by  authors.  Fa- 
bricius  distinguishes  five  different  kinds  of  metamorphosis,  and  has 
applied  a  different  name  to  each. 

The  first  class  comprises  all  insects  of  which  the  larva  is  a  mag¬ 
got  entirely  deprived  of  legs,  that  after  having  changed  its  skin,  or 
moulted,  a  certain  number  of  times,  becomes,  previous  to  its  last 
change,  incased  in  an  oval  horny  sheath,  or  pupa-case,  whereon  not 
the  least  trace  of  the  limbs  of  the  mature  insect  is  to  be  detected  ; 
such  pupae  are  absolutely  without  the  power  of  motion,  and  are 
distinguished  by  the  name  of  coarctate  :  examples  of  this  sort  of 
metamorphosis  are  met  with  in  the  common  house-flies  ( Muscidee ), 
and  the  forms  of  their  larvae  and  pupae  are  familiar  to  every  one. 

Of  the  second  kind,  technically  named  obtected ,  the  Lepido- 
ptera  furnish  well-known  instances.  The  changes  which  occur  in 
the  developement  of  the  silkworm,  represented  in  the  annexed 
figure  (Jig.  131),  may  readily  be  witnessed.  In  such  insects  the 
full-grown  caterpillar,  having  enclosed  itself  in  a  silken  ball,  throws 


*  Vide  Smeathman,  Phil.  Trans,  vol.  lxxi.  1781. 


INSECTA. 


289 


dages  of  the  perfect  insect  is  strongly  indicated  upon  the  exterior  of 
the  chrysalis  (a),  though  these  parts  are  still  closely  wrapped  up  in 
the  external  covering. 

(337.)  The  third  form  of  metamorphosis,  called  incomplete ,  is 
seen  in  the  Hymenoptera,  and  in  many  Coleopterous  insects.  The 
maggot,  in  such  tribes  as  exhibit  this  kind  of  change,  is  sometimes  a 
simple  worm  deprived  of  feet  or  other  external  organs,  or  in  other 
species  these  parts  exist  in  a  very  imperfect  condition  ;  in  the  pupa, 
however,  the  form  of  the  legs  and  antennse  is  perfectly  distinct,  and 
even  the  wings  may  be  seen  as  rudiments  projecting  from  the  thorax. 
This  kind  of  chrysalis  we  have  seen  in  the  cockchafer  (Jig.  106,  b), 
in  which  the  grub  (c)  possessed  feebly  developed  legs  ;  and  in  the 
hive-bee,  although  the  larva  (Jig.  132,  a,  c,  d ,  e,  f)  has  no  legs  or 
exterior  appendages,  in  the  pupa  (b)  all  the  limbs  of  the  perfect 
bee  are  recognised  with  the  utmost  facility.  Yet  all  these  organs 
are  still  enclosed  in  distinct  cases  (theca),  to  each  of  which  names 
have  been  applied  by  entomological  writers ;  and  it  is  only  on 
throwing  off  the  integument  which  thus  imprisons  the  mature  in¬ 
sect,  that  the  bee  makes  its  appearance  in  a  capacity  to  begin  its 
active  and  industrious  existence  in  the  winged  state. 


off  its  last  skin,  and  becomes  a  quiescent  pupa ;  but  while  in  this 
state  the  position  of  the  rudiments  of  the  wings  and  other  appen- 


Fig.  131. 


290 


INSECT A. 


Those  insects  whose  larva  only  differs  from  the  imago  in  not 
being  possessed  of  wings  (Jig.  102),  Fabricius  regarded  as  under¬ 
going  a  semi-complete  metamorpho-  Fig.  132. 

sis  ;  and  when  the  perfect  insect  did 
not  acquire  wings  at  all,  but  pre¬ 
cisely  resembled  the  pupa,  he  called 
the  latter  complete. 

(388.)  But  there  are  innumer¬ 
able  examples  of  metamorphosis 
which  will  not  conform  to  any  of 
the  above  definitions,  and  in  some 
of  them  the  phenomena  exhibited 
are  not  a  little  remarkable.  We 
have  already  mentioned  the  changes 
which  the  dragon-fly  undergoes 
(figs.  103,  104),  and  have  seen 
that  in  this  case  there  is  no  very 
striking  resemblance  between  the 
pnpa  and  the  adult  creature,  but,  on  the  contrary,  that  very  won¬ 
derful  changes  occur  during  the  last  stage  of  the  metamorphosis. 
The  pupa  lives  in  water ;  and,  besides  six  jointed  legs  adapted  to 
climb  the  stems  of  subaquatic  plants  in  search  of  prey,  is  pos¬ 
sessed  of  a  very  peculiar  locomotive  apparatus,  whereby  it  can 
propel  itself  through  the  element  which  it  inhabits.  Appended  to 
the  posterior  extremity  of  the  abdomen  we  find  three  or  five  leaf¬ 
like  appendages,  which  the  creature  continually  opens  and  closes, 
and  at  the  same  time  takes  in  a  quantity  of  water,  sufficient  to 
fill  the  muscular  termination  of  the  rectum,  which  is  expanded  for 
the  purpose  ;  this  water  is,  at  intervals,  forcibly  expelled,  mingled 
with  bubbles  of  air,  and  thus  effects  the  propulsion  of  the  animal 
by  a  mechanism  which  human  ingenuity  has  imperfectly  attempted 
to  imitate. 

But  the  contrivance  above  mentioned  is  also  made  subservient  to 
respiration  ;  for,  from  the  observations  of  Cuvier,*  it  appears  that 
the  interior  of  the  rectum  exhibits  to  the  naked  eye  twelve  longi¬ 
tudinal  lines  of  black  spots  arranged  in  pairs  ;  and  these,  when  ex¬ 
amined  under  the  microscope,  are  found  to  be  composed  of  little 
conical  tubes,  from  which  branches  go  off  to  join  the  principal 
longitudinal  trachem  that  distribute  air  through  the  body. 

Another  remarkable  peculiarity  is  met  with  in  the  structure  of 

*  M6m.  de  la  Soci6te  d’Histoire  Nat.  p.  48. 


INSECTA. 


291 


the  mouth  of  these  aquatic  larvae,  for  the  oral  apparatus  here  forms 
an  instrument  of  prehension  adapted  to  seize  prey  at  a  distance, 
and  constitutes,  in  fact,  a  kind  of  projectile  forceps  of  a  very 
curious  construction.  Let  the  reader  contrast  the  following  de¬ 
scription  with  that  already  given  of  the  oral  organs  of  the  dragon¬ 
fly  (§  295),  and  observe  the  remarkable  difference  : — <c  Conceive,” 
say  Kirby  and  Spence,*  “  your  under  lip  to  be  horny  instead  of 
fleshy,  and  to  be  elongated  perpendicularly  downwards,  so  as  to 
wrap  over  your  chin  and  extend  to  its  bottom  ;  that  this  elonga¬ 
tion  is  then  expanded  into  a  triangular  convex  plate  attached  to  it 
by  a  joint,  so  as  to  bend  upwards  again,  and  fold  over  the  face  as 
high  as  the  nose,  concealing  not  only  the  chin  and  the  first-men¬ 
tioned  elongation,  but  the  mouth  and  part  of  the  cheeks  :  conceive, 
moreover,  that  to  the  end  of  this  last-mentioned  plate  are  fixed  two 
other  convex  ones,  so  broad  as  to  cover  the  whole  nose  and  temples  ; 
that  these  can  open  at  pleasure,  transversely,  like  a  pair  of  jaws,  so 
as  to  expose  the  nose  and  mouth,  and  that  their  inner  edges, 
where  they  meet,  are  cut  into  numerous  sharp  teeth  or  spines,  or 
armed  with  one  or  more  long  and  sharp  claws  :  — you  will  then 
have  as  accurate  an  idea  as  my  powers  of  description  can  give  of 
the  strange  conformation  of  the  lip  in  the  larvae  in  question,  which 
conceals  the  mouth  and  face  precisely  as  I  have  supposed  a  similar 
construction  of  your  lip  would  do  yours.  You  will  probably 
admit  that  your  own  visage  would  present  an  appearance  not  very 
engaging  while  concealed  by  such  a  mask  :  but  it  would  strike 
still  more  awe  into  the  spectators  were  they  to  see  you  first  open 
the  two  upper  jaw-like  plates,  which  would  project  from  each 
temple  like  the  blinders  of  a  horse  ;  and  next,  having  by  means 
of  the  joint  at  your  chin  let  down  the  whole  apparatus,  and  un¬ 
covered  your  face,  employ  them  in  seizing  any  food  that  presented 
itself,  and  conveying  it  to  your  mouth.  Yet  this  procedure  is 
that  adopted  by  the  larvae  provided  with  this  strange  organ. 
While  it  is  at  rest,  it  applies  close  to  and  covers  the  face. 
When  the  insects  would  make  use  of  it,  they  unfold  it  like  an 
arm,  catch  the  prey  at  which  they  aim  by  means  of  the  mandibu- 
liform  plates  {Jig.  KM),  and  then  partly  refold  it  so  as  to  hold 
the  prey  to  the  mouth  in  a  convenient  position  for  the  operation 
of  the  two  pairs  of  jaws  with  which  they  are  provided.” 

(339.)  The  metamorphoses  of  the  gnat  ( Culex )  are  not  less 
interesting.  The  female  deposits  her  eggs  upon  the  surface  of  the 

*  Introd.  to  Entom.  vol.  iii.  p.  126. 

u  2 


292 


INSECTA. 


water,  in  which  her  offspring  are  destined  to  pass  the  earlier  pe¬ 
riods  of  their  existence,  gluing  the  ova  together  at  the  moment  of 
their  extrusion,  so  as  to  unite  them  into  a  boat-like  mass  {fg- 
133,  a)  of  such  beautiful  construction  that  the  little  bark  swims 
secure  from  injury,  even  during  the  roughest  weather.  The  in¬ 
dividual  eggs  are  of  a  conical  form  {fig-  133,  b,  Z>,  c),  and  are 
closed  at  their  inferior  extremity  by  a  kind  of  lid  (d),  provided 
to  give  egress  to  the  mature  embryo.  The  larva  (c),  represented 
upon  a  magnified  scale  at  e,  bears  not  the  slightest  resemblance 
to  the  perfect  insect,  and  is  provided  with  a  singular  modification 
of  the  respiratory  apparatus  adapted  to  its  habits.  The  head  is 
large,  and  carries  two  ciliated  organs  (g,  g),  which  by  their 
movements  bring  food  towards  the  mouth  ;  the  thorax  is  even 
larger  than  the  head,  and  is  furnished  with  fin-like  bunches  of 
minute  hairs,  as  likewise  are  the  segments  of  the  abdomen.  To 
the  extremity  of  the  tail  is  appended  a  group  of  moveable  leaflets 
or  fins,  so  disposed  that  by  their  action  they  sustain  the  larva  at 
the  top  of  the  water,  where  it  generally  remains  suspended  with 
its  head  downwards.  Such  a  position  would  obviously  render 
respiration  impossible,  was  there  not  a  corresponding  arrangement 
of  the  breathing  organs  to  allow  of  free  communication  with  the 
air.  For  this  purpose,  the  respiratory  tracheee  are  found  to  be 
connected  with  a  tube  appended  to  the  antepenultimate  segment 
of  the  abdomen,  the  perforated  extremity  of  which,  being  raised 
above  the  water,  procures  from  the  atmosphere  the  oxygen  re¬ 
quired  for  respiration.  After  several  moults,  the  larva,  having 
attained  its  full  growth,  enters  the  pupa  state,  and  in  this  con¬ 
dition  still  remains  an  inhabitant  of  the  water,  and  occupies  a 
position  near  the  surface.  A  remarkable  change,  however,  is  visible 
in  all  parts  of  its  structure  :  the  head  and  thorax  (Jig.  133,  d) 
are  consolidated  into  one  large  mass,  under  which  the  lineaments 
of  the  mature  insect  may  be  detected  ;  while  the  tail  still  con¬ 
tinues  to  be  the  agent  employed  in  natation.  The  condition  of 
the  respiratory  organs  is,  moreover,  completely  altered  :  the  tube 
fixed  upon  the  antepenultimate  segment  of  the  larva  has  totally 
disappeared,  and,  instead  of  it,  we  find  two  tubes  appended  to  the 
back  of  the  thorax  ;  these,  although  they  perform  the  same  office 
as  the  anal  pipe  of  the  larva,  are  thus  displaced,  in  order  to  cor¬ 
respond  with  the  altered  position  in  which  the  animal  now  swims  ; 
the  back  of  the  thorax,  and  not  the  tail,  being  nearest  to  the 
surface,  as  represented  in  the  drawing  (d).  The  necessity  for 


INSECTA. 


293 


this  change  of  posture,  and  consequent  removal  of  the  apparatus 
for  taking  in  air  from  one  part  of  the  body  to  another,  will  be  at 
once  obvious  when  we  consider  the  circumstances  under  which 
the  perfect  insect,  having  completed  its  developement,  emerges 
from  its  pupa  investments  and  enters  upon  an  aerial  existence. 
The  problem  to  be  solved  is,  how  shall  the  mature  gnat  escape 
from  the  water  without  being  wetted  ?  and,  when  we  consider 
that  neither  the  larva  nor  the  pupa  possesses  instruments  of  lo¬ 
comotion  capable  of  enabling  it  to  leave  its  native  element  by 
crawling  on  shore,  the  difficulties  attending  the  change  appear 
almost  insurmountable.  It  is  evident  that,  while  swimming  in 
the  position  in  which  the  larva  floats  (Jig.  133,  c),  the  last 

Fig.  133. 


change  could  not  by  possibility  be  accomplished,  as  the  bursting 
of  the  integument  would  at  once  admit  the  water  to  the  sub¬ 
merged  gnat,  and  drown  it  at  the  moment  of  its  birth  ;  but  by 
the  new  arrangement  the  metamorphosis  is  easily  effected,  and 
that  in  a  manner  so  beautiful,  that  it  is  hard  to  say  which  is 
most  admirable,  the  simplicity  of  the  contrivance,  or  the  perfection 
with  which  the  object  is  accomplished.  No  sooner  has  the  en¬ 
cased  imago  become  fitted  for  its  escape,  than  the  pupa,  rendered 
more  buoyant,  raises  its  back  above  the  surface  :  the  protruded 
portion  of  the  pupa-case  soon  dries,  and  gradually  begins  to  split 
in  a  longitudinal  direction,  so  as  to  form  by  its  expansion  a  boat 


294 


INSECTA 


wherein  the  gnat  swims  upon  the  top  of  its  native  pond  ;  and  sus¬ 
tained  in  this  frail  bark,  formed  by  its  late  skin,  it  gradually  ex¬ 


tricates  its  legs  and  wings  from  their  coverings,  and  is  kept  per¬ 
fectly  dry  until  the  expansion  of  its  instruments  of  flight  enables 


INSECTA. 


295 


it  to  soar  into  the  air  and  quit  for  ever  the  raft  so  singularly  pro¬ 
vided  for  its  use. 

(340.)  Having  thus  become  acquainted  with  the  various  con¬ 
ditions  under  which  insects  arrive  at  maturity,  and  the  principal 
forms  that  they  exhibit  during  the  different  stages  of  the  meta¬ 
morphosis,  the  reader  will  be  prepared  to  investigate  more  mi¬ 
nutely  the  changes  in  progress  during  the  process,  and  the  gradual 
developement  of  the  organs  which  successively  make  their  appear¬ 
ance.  On  examining  the  viscera  of  a  Caterpillar ,  they  are  found 
scarcely  at  all  to  resemble  those  of  the  butterfly  or  moth,  into 
which  a  larva  of  this  description  is  ultimately  matured.  The 
jaws  {Jig.  136,  5,  5),  widely  different  both  in  structure  and 
office  from  the  proboscis  which  represents  them  in  the  perfect 
insect  {Jig.  115),  are  strong  and  horny  shears  adapted  to  cut 
the  leaves  of  vegetables  and  other  coarse  materials  used  as  food ; 
the  oesophagus  {Jig,  134,  g ,  A)  is  strong,  muscular,  and  capa¬ 
cious  ;  and  the  stomach  (A,  z‘),  in  capacity  corresponding  with 
the  extraordinary  voracity  exhibited  by  the  larva,  passes  insen¬ 
sibly  into  a  wide  intestine  {i,  m),  the  line  of  separation  being 
only  indicated  by  the  entrance  of  the  biliary  vessels  (A)  that  wind 
in  numerous  convolutions  around  the  posterior  half  of  the  alimen¬ 
tary  canal.  It  is  sufficient  to  contrast  this  arrangement  of  the 
digestive  organs  with  what  we  have  already  described  in  the  but¬ 
terfly  {Jig.  117),  to  appreciate  the  amazing  dissimilarity:  it  would 
be  difficult  indeed  to  imagine,  did  not  anatomy  convince  us  of  the 
fact,  that  the  digestive  apparatus  of  the  imago,  with  its  slender 
oesophagus,  dilated  crop,  short  sacculated  stomach,  long  and  con¬ 
voluted  small  intestine,  and  capacious  colon,  was  derived  from  a 
gradual  modification  of  such  viscera  as  those  we  have  just  been 
considering.  The  salivary  glands  of  the  caterpillar  {Jig.  1 34,  q ,  r) 
are  large  cylindrical  caeca,  and  their  ducts  ( p )  pour  into  the 
mouth  an  abundance  of  saliva  proportioned  to  the  coarse  nature 
of  the  materials  used  as  food. 

The  sides  of  the  body  are  traversed  by  the  wide  longitudinal 
tracheae,  «,  A,  c,  that  communicate  on  the  one  hand  with  the 
lateral  spiracles,  and  on  the  other  give  off  at  regular  intervals 
the  air-tubes  {d9  e,  e,  e,  e),  which  ramify  most  minutely  over  all 
the  viscera,  and  convey  the  atmospheric  air  throughout  the  entire 
system. 

Besides  the  above  organs,  there  are  other  viscera,  which,  al¬ 
though  of  considerable  importance  to  the  caterpillar,  would  be 


296 


INSECTA. 


utterly  useless  to  the  imago,  and  consequently  are  more  or  less 
completely  wanting  in  the  mature  state. 

The  whole  body  of  the  larva  is  filled  with  a  peculiar  fatty 
tissue  (Jig.  called  by  entomologists  the  rete ,  epiploon , 

or  fat-mass.  This  material,  found  in  great  abundance  in  mature 
and  well-fed  larvae,  consists  of  an  oily  or  greasy  substance  enveloped 
in  a  most  delicate  cellulosity,  and  seems  to  correspond  to  the  fat  of 
higher  animals,  like  which  it  is  indubitably  a  product  of  digestion, 
and  a  repository  of  superabundant  nourishment,  stored  up,  no 
doubt,  for  the  sustenance  of  the  animal  during  its  helpless  con¬ 
dition  in  the  dormant  or  pupa  state — serving  like  the  fat  of  hiber¬ 
nating  quadrupeds,  for  food  during  the  confinement  of  the  imago. 

(341 .)  But  the  most  re¬ 
markable  peculiarity  of  the 
larvte  under  consideration, 
is  the  presence  of  an  appa¬ 
ratus  employed  for  produc¬ 
ing  a  tenacious  thread  of 
extreme  delicacy,  appro¬ 
priated  by  different  species 
to  various  purposes.  In 
many  cases  {fig.  105),  it 
is  made  subservient  to  lo¬ 
comotion  ;  and  by  its  assist¬ 
ance,  as  by  a  rope,  the 
larva  can  suspend  itself 
from  any  object,  or  let  it¬ 
self  down  from  one  branch 
to  another  in  search  of 
food.  The  most  import¬ 
ant  uses  however  to  which 
this  thread  is  applied  are  connected  with  the  concealment  and  pro¬ 
tection  of  the  quiescent  and  defenceless  pupa ;  either  furnishing  the 
means  of  suspending  the  chrysalis  in  a  place  of  safety*  {fig-  135), 
or,  as  is  the  case  with  the  silk-worm  {fig.  131),  supplying  the 
material  with  which  the  caterpillar  encases  itself  preparatory  to 


Fig.  135. 


*  For  a  most  amusing  account  of  the  manner  in  which  some  chrysalides  manage  with¬ 
out  any  external  limbs  to  suspend  themselves  by  the  tail  in  a  position  of  security,  the  rea¬ 
der  is  referred  to  Kirby  and  Spence,  vol.  iii.  page  207.  The  figure  above  given  illustrates 
the  different  steps  attending  the  process.  The  larva,  a,  having  spun  some  loose  silk,  and 
fixed  it  upon  the  under  side  of  a  leaf  or  other  suitable  object,  suspends  itself  therefrom 


INSECTA. 


297 


throwing  off  the  last  skin  of  the  larva.  The  thread  of  the  last- 
named  insect,  the  silk-worm,  is  of  great  tenacity  ;  and,  notwith¬ 
standing  its  fineness,  may  be  wound  off  from  the  cocoon  in  a  con¬ 
tinuous  thread,  forming  the  important  article  of  commerce,  silk. 

(342.)  Nothing  can  be  more  simple  than  the  apparatus  provided 
in  caterpillars  for  the  production  of  this  valuable  commodity: — 
Placed  on  each  side  of  the  intestine  are  two  long  and  tortuous  se¬ 
creting  cseca  {fig.  134,  v ,  a,  y),  that  separate  from  the  surrounding 
juices  of  the  body  a  tenacious  viscid  fluid  which  is  liquid  silk.  The 
viscid  secretion  thus  formed  is  in  the  silk-worm  of  a  golden  yellow 
colour,  and  is  conveyed  by  the  excretory  ducts  of  the  secerning 
organs  ( v ,  z )  to  the  labium  or  under-lip,  where  the  ducts  terminate 
at  the  base  of  a  tubular  instrument,  the  fusulus  or  spinnaret , 
through  which  the  silk  is  drawn  {fig.  136,  c).  The  fusulus  of 
the  silk-worm,  represented  in  the 
annexed  figure  upon  an  enlarged 
scale,  is  a  simple  nipple-shaped  pro¬ 
minence,  perforated  at  its  extre¬ 
mity,  and  surrounded  by  four  rudi¬ 
mentary  palpi.  When  about  to 
spin,  the  larva,  by  placing  the  ex¬ 
tremity  of  its  spinnaret  in  contact 
with  some  neighbouring  object,  al¬ 
lows  a  minute  drop  of  the  glutin¬ 
ous  secretion  to  exude  from  its  ex¬ 
tremity,  which,  of  course,  adheres 
to  the  surface  upon  which  it  is 
placed  :  the  head  of  the  silk-worm 
being  then  slowly  withdrawn,  the 
fluid  silk  is  drawn  out  in  a  delicate 
thread  through  the  aperture  of  the  spinnaret,  its  thickness  being 
regulated  by  the  size  of  the  orifice,  and,  immediately  hardening 
by  the  evaporation  of  its  fluid  parts,  forms  a  filament  of  silk  which 
can  be  prolonged  at  the  pleasure  of  the  animal  until  the  contents 
of  its  silk  reservoirs  are  completely  exhausted. 

(343.)  Such  is  the  structure  of  the  larva  of  a  Lepidopterous  insect, 

by  its  hind-legs.  The  skin  of  the  caterpillar  then  gradually  splits  down  the  back  (b,  c), 
and  is  slowly  pushed  upwards  towards  the  tail  of  the  chrysalis.  The  pupa  now  lays 
hold  of  the  old  skin,  nipping  it  between  the  rings  of  the  abdomen,  and  hanging  in  this 
posture  inserts  the  apex  of  the  tail,  which  is  covered  with  hooks  for  the  purpose,  into 
the  silk  previously  deposited,  and  thus  remains  fixed  in  safety  (d.) 


298 


IN SECT A. 


and  the  arrangement  of  its  internal  viscera,  when  arrived  at  maturity, 
has  been  already  described.  We  have  yet,  however,  to  mention 
the  series  of  phenomena  observable  during  the  progress  of  its 
growth,  and  the  mode  of  its  expansion  from  the  minute  size  that 
it  exhibits  on  leaving  the  egg  to  the  full  dimensions  which  it  ulti¬ 
mately  acquires.  In  order  fully  to  understand  the  circumstances 
connected  with  this  part  of  our  subject,  it  is  necessary  to  premise 
that  the  outer  integument  of  most  larvae  is  of  a  dense  corneous  tex¬ 
ture,  coriaceous  in  some  parts,  but  quite  hard  and  horny  in  others. 
In  the  second  place,  it  is  but  very  slightly  extensible  ;  and  more¬ 
over,  as  is  always  the  case  with  epidermic  structures,  is  not  per¬ 
meated  by  any  vascular  apparatus,  and  consequently  is  absolutely 
incapable  of  growth  when  once  formed.  This  epidermis  encases 
every  portion  of  the  larva;  the  body,  the  legs,  the  antennae,  the 
jaws,  and  all  external  organs  are  closely  invested  with  a  cuticular  en¬ 
velope,  such  as,  from  its  want  of  extensibility,  would  form  an  insu¬ 
perable  obstacle  to  developemcnt  was  there  not  some  extraordinary 
provision  made  to  meet  the  necessity  of  the  case.  The  plan  adopt¬ 
ed  is  to  cast  off  at  intervals  the  old  cuticle  by  a  process  termed 
moulting ;  an  operation  which  is  repeated  several  times  during  the 
life  of  the  insect  in  its  larva  condition,  and  is  accomplished  in  the 
following  manner : — The  caterpillar  becomes  for  a  few  days  slug¬ 
gish  and  inactive,  leaves  off  eating,  and  endeavours  to  conceal  it¬ 
self  from  observation.  The  shin,  or  more  properly  the  cuticle, 
becomes  loosened  from  the  subjacent  tissues,  and  soon  a  rent  ap¬ 
pears  upon  the  back  of  the  animal,  which  gradually  enlarges  in  a 
longitudinal  direction,  and  the  imprisoned  insect,  after  a  long  series 
of  efforts,  at  length  succeeds  in  extricating  itself  from  its  old  cover¬ 
ing,  and  appears  in  a  new  skin  of  larger  dimensions  than  the  one  it 
replaces,  which  however  in  all  other  particulars  it  closely  resembles. 
With  the  old  epidermis  the  larva  throws  off  all  external  appendages 
to  the  cuticle  :  the  horny  coverings  of  the  jaws,  the  corneae  of  the 
eyes,  the  cases  of  the  claws  are  all  removed  ;  and  many  writers  have 
even  found  attached  to  the  exuviae  an  epidermic  pellicle  that  had 
formed  a  lining  to  the  rectum,  and  delicate  prolongations  of  the 
cuticle  derived  from  the  interior  of  the  larger  ramifications  of  the 
air-tubes.  Absurd,  indeed,  have  been  the  explanations  given  by 
various  writers  of  the  nature  of  the  process  under  consideration. 
Swammerdam  and  Bonnet,  nay,  even  our  own  illustrious  entomo¬ 
logists  Kirby  and  Spence,  believed  that  even  at  the  birth  of  the  ca¬ 
terpillar  all  these  skins  existed  ready  formed  one  beneath  the  other, 


INSECT A. 


299 


and  that  the  most  external  being  removed  at  intervals  displayed  in 
succession  the  shins  placed  underneath.  Surely  the  advocates  of 
this  extraordinary  theory  could  scarcely  have  reflected  upon  the  real 
object  of  the  moults  in  question — namely,  to  provide  a  succession  of 
larger  coverings  proportioned  to  the  continually  increasing  bulk  of 
the  larva, — when  they  advocated  this  strange  doctrine,  alike  at  vari¬ 
ance  with  observation  and  sound  physiological  principles  :  the  epi¬ 
dermis  and  all  cuticular  structures  are  mere  secretions  from  the  sub¬ 
jacent  cutis  or  true  skin ;  and  it  can  be  no  more  necessary  to  suppose 
the  pre-existence  of  so  many  skins  in  order  to  explain  the  moults  of 
a  larva,  than  to  imagine  that  because,  when  in  our  own  persons  the 
cuticle  is  removed  by  the  application  of  a  blister,  a  new  layer  of  epi¬ 
dermis  is  again  and  again  produced,  man  should  possess  as  many 
skins  one  beneath  the  other.  Nothing,  in  fact,  can  be  more  simple 
and  free  from  the  miraculous  than  the  whole  process  :  at  certain  pe¬ 
riods,  when  the  old  cuticle  becomes  too  small  for  the  rapidly  enlarg¬ 
ing  dimensions  of  the  insect,  it  becomes  gradually  loosened  and  se¬ 
parated  from  the  vascular  and  living  skin  or  cutis  by  which  it  was 
originally  secreted,  and,  a  new  secretion  of  corneous  matter  taking 
place,  a  fresh  and  more  extensive  layer  of  cuticle  is  slowly  formed, 
and  then  the  old,  dry,  and  dead  epidermis  being  quite  detached,  is 
split  by  the  exertions  of  the  larva,  and  the  newly  secreted  layer  placed 
beneath  it  appears  ;  when  the  old  skin  is  at  length  completely 
thrown  off,  the  newly  formed  one  soon  hardens  by  exposure,  and  the 
re-clothed  caterpillar  assumes  again  its  former  activity  and  habits. 

(344.)  Neither  is  the  change  from  the  larva  to  the  pupa  or  chry¬ 
salis  less  easily  explained,  although  regarded  by  our  forefathers  as 
being  so  mysterious  and  astonishing  a  phenomenon.  According 
to  the  hypothesis  above  alluded  to,  after  removing  three  or  four 
skins  in  the  embryo  larva,  the  anatomist  ought  to  have  arrived  at 
the  totally  different  pupa-case  ready  formed,  and  only  waiting  for 
the  removal  of  the  coats  above  it  to  exhibit  its  characteristic  form. 
Leaving  however  such  visionary  notions,  let  us  examine  the  real 
nature  of  this  portion  of  the  metamorphosis.  The  reader  will 
bear  in  mind,  that,  whatever  the  form  of  the  exterior  or  epidermic 
crust,  it  is  merely  a  dead  and  extra-vascular  secretion,  unchange¬ 
able  when  once  deposited.  But  the  living  skin  or  cutis ,  beneath 
it,  is,  during  the  whole  process  of  the  metamorphosis ,  undergoing 
great  and  important  changes,  increasing  in  size  only,  during  the 
larva  condition  ;  but,  when  perfectly  organized,  developing  itself 
at  different  points,  and  expanding  into  variously  shaped  organs 


300 


INSECTA. 


which  did  not  previously  exist.  In  the  dragon-fly,  for  example 
{Jig.  104),  when  the  cutis  had  become  expanded  to  its  mature 
larva  condition,  it  secreted  from  its  surface  the  external  epidermic 
crust  which  gives  form  to  the  larva,  n  ;  this  outward  integument 
remains,  of  course,  unchanged  when  once  formed,  and  retains  the 
same  appearance  during  the  whole  period  of  the  existence  of  the 
insect  in  its  larva  state  :  but  underneath  this  cuticle,  and  con¬ 
sequently  concealed  from  observation,  the  growth  of  the  living 
dermis  still  goes  on,  and  important  organs  begin  to  appear,  which 
had  no  existence  when  the  last  larva-investment  was  secreted. 
The  wings  have  sprouted  as  it  were  from  the  shoulders,  and 
already  have  attained  to  a  certain  growth  ;  the  old  integument  of 
the  larva  becomes  useless,  and  a  new  one  is  wanted;  the  process 
already  described  is  repeated, — the  old  cuticle  becomes  detached 
from  the  surface  of  the  body,  and  the  cutis  begins  to  secrete  for  it¬ 
self  a  new  covering  moulded  upon  its  own  shape  :  the  newly  form¬ 
ed  wings,  therefore,  and  other  newly  developed  processes  of  the 
dermis ,  secrete  horny  coverings  for  themselves  in  the  same  manner 
as  other  parts  of  the  surface  of  the  body  ;  and  thus,  when  the  in¬ 
sect  leaves  its  old  skin,  and  once  more  escapes  from  confinement, 
it  presents  to  view  the  wing-cases  which  distinguish  the  pupa. 

Whatever  may  be  the  form  of  the  pupa,  its  covering  is  secreted 
in  a  similar  way  ;  it  is  the  living  and  vascular  skin  which,  though 
concealed,  continually  grows  more  perfect  in  its  parts,  and  the 
cases  secreted  by  it  at  distant  intervals  correspond  in  shape  with 
the  different  phases  of  its  developement. 

(345.)  After  having  attained  the  pupa  state,  the  last  steps  of  the 
process  are  completed,  and  the  dermic  system  becomes  fully  de¬ 
veloped  in  all  its  parts.  The  oral  apparatus  attains  its  perfect  con¬ 
dition  ;  the  wonderfully  elaborate  structure  of  the  eyes  is  com¬ 
pleted  ;  the  antennae  assume  their  full  developement ;  the  legs  en¬ 
closed  in  those  of  the  pupa  attain  their  mature  form  ;  and  the 
wings,  which  have  been  continually  growing,  although  concealed  in 
the  wing-cases  of  the  pupa,  acquire  their  ultimate  size  :  the  per¬ 
fect  insect  is  ready  for  liberation,  and,  enclosed  in  its  last  covering, 
creeps  out  of  the  water  in  which  it  has  so  long  resided  to  enter 
upon  a  new  state  of  existence.  Fixing  itself  upon  some  plant  in 
the  neighbourhood  of  its  birth-place,  the  imprisoned  dragon-fly  splits 
its  pupa-case  along  the  back  (Jig.  137,  a),  and  slowly  extricates 
its  head  and  body  ;  draws  its  wings  from  their  coverings,  and 
its  legs  from  those  of  the  pupa  as  from  cast-off  boots  ;  and  at 


INSECTA. 


301 


length  (Jig.  137,  n),  getting  its  body  from  its  now  useless  cover¬ 
ing,  it  becomes  entirely  free.  The  wings,  before  soft  and  crumpled, 
slowly  expand  (Jig.  137,  c)  ;  the  nervures  harden,  the  extended 
membranes  dry,  and  Fig,  137. 

in  a  short  time  the 
winged  tyrant  of  the 
insect  world  (Jig. 

103)  commences  his 
aerial  career. 

(346.)  A  strong 
argument  in  favour 
of  the  above  views 
concerning  the  pro¬ 
duction  of  successive 
skins  from  the  der¬ 
mis,  is  derived  from 
the  phenomena  at¬ 
tending  the  cure  of 
wounds  in  insects. 

If  a  perfect  insect 
be  wounded,  the 
wound  is  never  heal¬ 
ed  at  all  ;  and,  if  a 
larva  or  pupa  is 
similarly  injured,  the 
wound  remains  un¬ 
cicatrised  until  the 
next  moult,  when 
the  newly  formed  in¬ 
tegument  is  found 
to  exhibit  no  traces 
of  the  injury  : —  the 
secreted  and  extra- 
vascular  cuticle  can 
not  cicatrise ;  but  the 

living  and  vascular  dermis  is  not  only  able  to  repair  injuries  in¬ 
flicted  upon  itself,  but,  in  secreting  the  next  investment,  to  obliter¬ 
ate  all  indications  of  their  occurrence. 

(347.)  The  changes  above  described  are  produced  by  the  pro¬ 
gressive  developement  of  the  dermic  or  tegumentary  system  ;  the 
parts  of  which,  as  we  have  already  seen,  becoming  strengthened  and 


302 


INSECT A. 


consolidated  by  degrees,  ultimately  acquire  that  density  of  struc¬ 
ture  which  the  external  skeleton  of  the  insect  exhibits  in  its 
perfect  or  imago  state.  But,  while  this  extraordinary  metamor¬ 
phosis  is  going  on  externally,  other  changes  not  less  important 
are  in  progress  in  the  interior  of  the  body.  The  size  of  the 
alimentary  canal,  and  the  shape,  proportionate  dimensions,  and 
general  arrangement  of  the  different  parts  composing  it,  are  se¬ 
cretly  and  imperceptibly  undergoing  variations  in  accordance  with 
the  altered  necessities  of  the  animal.  We  have  already  seen  a 
conspicuous  example  of  this  in  Lepidopterous  insects,  §  340  ;  and, 
in  other  orders,  equally  striking  instances  might  easily  be  selected. 
One  of  the  most  remarkable  is  met  with  in  many  Hymenoptera , 
as,  for  example,  in  bees  (Apis),  wasps  (Vespa),  and  ant-lions 
(Formica- leo),  as  well  as  in  most  of  the  Ichneumonidee.  In  all 
these  genera,  the  larva  being  concealed  in  a  close  cell  during  its 
developement,  under  circumstances  which  would  render  the  evacu¬ 
ation  of  excrementitious  matter  an  obvious  inconvenience,  both 
the  larva  and  pupa  (Jig.  132)  are  entirely  without  either  intes¬ 
tinal  canal  or  anal  orifice  :  what  little  excrement  is  produced  by 
the  digestion  of  the  highly  nutritive  substances  wherewith  these 
larvae  are  fed  being  collected  in  a  blind  cavity  or  caecum  placed 
behind  the  stomach,  until  the  accomplishment  of  the  last  change  ; 
at  which  period  the  insect,  liberated  from  its  confinement,  becomes 
provided  with  a  pervious  intestine,  and  able  to  get  rid  of  feculent 
matter. 

The  fat-mass  (§  340),  which  at  the  close  of  the  larva  state  has 
reached  its  maximum  of  developement,  is  gradually  absorbed  du¬ 
ring  the  concealment  of  the  insect  in  its  pupa-case,  its  nutritive 
portions  being  no  doubt  appropriated  to  the  nourishment  of  the 
pupa  ;  so  that  in  the  mature  insect  the  fatty  material  has  almost 
entirely  disappeared,  nothing  being  left  in  its  place  but  the  dense 
cellular  web  in  which  the  fat  had  been  deposited. 

The  silk-secreting  apparatus  of  such  genera  as  possess  the  means 
of  spinning  a  silken  thread  is  peculiar  to  the  larvae  ;  and,  after 
the  commencement  of  the  pupa  state,  no  traces  of  its  previous  exist¬ 
ence  are  to  be  detected. 

(348.)  But,  while  the  above-mentioned  organs  disappear,  others 
become  developed  ;  and  the  perfect  insect  is  found  to  possess  vis¬ 
cera,  for  which  a  skilful  anatomist  might  seek  in  vain  in  the  earlier 
stages  of  its  existence.  The  generative  system  appears,  at  first,  to 
be  absolutely  wanting  in  the  larva ;  but  Herold,*  after  much 

*  Entwickelungsgeschichte  der  Schmetterlinge,  1815,  4fo. 


INSECTA. 


303 


patient  investigation,  succeeded  in  detecting  the  undeveloped  ru¬ 
diments  of  the  future  sexual  organs  both  of  the  male  and  female. 
It  is  during  the  maturation  of  the  pupa  that  these  important  parts 
expand ;  and,  before  the  disclosure  of  the  imago,  they  are  found  to 
have  attained  their  complete  proportions,  so  as  to  be  ready  to  per¬ 
form  their  functions  as  soon  as  the  expansion  of  the  wings  endows 
the  insect  with  means  of  locomotion  sufficiently  perfect  to  ensure 
the  due  dispersion  of  the  species. 

(349.)  It  is  in  the  nervous  system,  however,  that  the  most  in¬ 
teresting  phenomena  are  observable  ;  and  in  the  lessons  afforded  by 
watching  the  correspondence  between  the  state  of  the  animal  during 
the  several  phases  of  its  existence  and  the  developement  of  the  ner¬ 
vous  ganglia,  the  physiologist  cannot  fail  to  recognise  those  great 
and  general  principles  upon  which  our  arrangement  of  the  animal 
creation  is  based.  In  the  worm-like  larva  the  ganglia  are  numerous 
but  of  small  dimensions ;  too  feeble  to  be  capable  of  animating 
powerful  limbs,  or  of  appreciating  impressions  from  the  organs  of 
the  higher  senses :  the  animal  is,  in  fact,  precisely  in  the  condition 
of  an  Annelid  an,  which  it  would  seem  to  represent.  External 
limbs  are  therefore  absolutely  wanting  in  many  larvae ;  in  others 
they  are  represented  by  short  and  stunted  appendages;  and  even  in 
the  most  perfect,  or  hexapod  larvae,  they  are  feeble  instruments  in 
comparison  with  those  of  the  mature  imago.  The  senses  exhibit 
equal  imperfection  ;  and  eyes  are  either  entirely  wanting,  or  are  mere 
ocelli,  simple  specks,  exhibiting  the  lowest  possible  organization 
of  a  visual  apparatus.  But,  as  the  growth  of  the  larva  goes  on,  a 
change  in  the  arrangement  of  the  nervous  system  is  perpetually  in 
progress.  The  series  of  nervous  cords  connecting  the  different  pairs 
of  ventral  ganglia  in  the  larva  (Jig.  138,  a)  become  flexuous  as  the 
insect  attains  the  pupa  state  ;  the  whole  chain  becomes  shorter  ;  the 
brain,  or  encephalic  ganglion,  increases  in  its  proportionate  dimen¬ 
sions  ;  and,  moreover,  several  ganglia,  originally  distinct,  coalesce, 
and  form  larger  and  more  powerful  masses  (Jig.  138,  b).  This  co¬ 
alescence  of  the  ganglia,  which  takes  place  more  especially  in  the 
thoracic  region,  is  evidently  a  preparation  for  the  concentration  of 
greater  power  and  activity  in  this  part  of  the  body  ;  and  although  in 
inactive  chrysalides  this  change  is  not  as  yet  visible  by  its  effects, 
in  the  active  forms  even  the  pupa  is  distinguished  from  the  larva 
by  a  considerable  increase  of  vigour  and  energy  in  its  movements. 
In  the  imago  the  concentration  of  the  nervous  centres  is  carried  to 
that  extent  which  is  adapted  to  the  necessities  of  the  mature  state ; 


304 


INSECT  A. 


their  number  is  still  further  reduced  ( Jig .  138,  c);  their  size,  in  the 
thorax  especially,  considerably  increased ;  and  the  brain,  now  ar¬ 
rived  at  its  maximum  of  developement,  is  furnished  with  the  won¬ 
derful  apparatus  of  eyes  and  other  instruments  of  the  senses, 
which  heretofore  would  have  been  absolutely  useless,  but  now,  with 
the  expansion  of  the  brain,  have  become  suited  to  the  more  ex¬ 
alted  faculties  of  the  insect. 

Fig.  138. 

B  C  A 


Many  insects  are  capable  of  producing  audible  sounds  ;  and  some¬ 
times  the  noises  they  make  are  exceedingly  shrill,  and  may  be  heard 
at  some  distance.  Such  sounds  originate  from  various  causes  in 
different  tribes,  and  it  is  not  always  easy  to  detect  the  mode  of 
their  production.  In  many  beetles  they  are  caused  by  rubbing 
different  parts  of  their  dense  integument  against  each  other,  and 
the  chirping  of  several  Orthoptera  seems  to  have  a  similar  origin  ; 
the  acute  note  that  these  insects  utter  is  apparently  produced  by 
friction,  the  edges  of  their  hard  pergamentaceous  wings  being 


INSECT A. 


305 


Fig.  139. 


either  scraped  against  each  other,  or  against  the  long  and  serrated 
edges  of  their  thighs.  The  buzzing  and  humming  noises  heard 
during  the  flight  of  many  genera  results  from  the  forcible  expul¬ 
sion  of  the  air  as  it  streams  through  the  respiratory  spiracles,  whose 
orifices  Burmeister  imagines  are  furnished  with  vibratory  lami¬ 
nae,  to  the  rapid  movements  of  which  the  noise  may  be  due.  In 
the  genera  Gryllus  and  Cicada  among  the  Orthoptera,  however, 
there  is  a  peculiar  apparatus  specially  provided  for  the  production 
of  the  loud  chirping  to  which  such  insects  give  utterance.  Upon 
the  first  segment  of  the  abdomen,  covered  by  a  broad  moveable 
plate  (fig.  139  «),  there  is  a  large  aperture,  wherein  a  tense  plicated 
membrane  is  observable.  This  membrane  is  acted  upon  internally 
by  certain  muscles  able  to  throw  it  into  rapid  vibration,  and  thus 
give  rise  to  the  sound  in  question. 

(350.)  One  other  point  connected  with  this 
interesting  class  of  animals  requires  brief  notice. 

Many  insects  are  endowed  with  the  faculty 
of  emitting  phosphorescent  light,  which  is 
in  some  species  exceedingly  brilliant.  The 
Elaterkhe  among  beetles  are  pre-eminently  lu¬ 
minous,  and  in  them  the  light  seems  to  be 
principally  given  out  by  two  oval  spaces  upon 
the  thorax,  which  in  the  dead  insect  are  of 


a  greenish  hue ;  during  life,  some  species 
( Elater  noctilucus )  are  so  strongly  phospho¬ 
rescent  as  to  enable  a  person  to  read  a  book 
by  passing  the  animal  over  the  lines.  The  Lampyri  emit  a  light 
of  great  brilliancy ;  and  in  Italy,  during  the  summer  nights,  the 
groves,  illuminated  by  their  incessant  scintillations,  exhibit  a  scene 
equally  strange  and  beautiful.  Such  insects  appear  to  have  a 
power  of  obscuring  or  exhibiting  their  light  at  pleasure  ;  but  the 
nature  of  the  luminous  secretion,  if  such  it  be,  upon  which  their 
luminosity  depends,  has  as  yet  escaped  detection.* 

*  An  interesting  account  of  this  subject  is  to  be  found  in  the  article  Luminousness, 
Animal,  by  Dr.  Coldstream,  in  the  Cyclopaedia  of  Anatomy  and  Physiology. 


X 


306 


CHAPTER  XVI. 

Arachnida.* 

(351.)  The  Arachnidans  long  confounded  with  Insects,  and 
described  as  such  even  by  recent  entomologists,  are  distinguished 
by  characters  of  so  much  importance  from  the  animals  described 
in  the  last  chapter,  that  the  necessity  of  considering  them  as  a 
distinct  class  is  now  no  longer  a  matter  of  speculation.  In  In¬ 
sects,  the  external  skeleton  presents  three  principal  divisions, — 
the  head ,  the  thorax ,  and  the  abdomen  :  but  in  the  spider  tribes, 
the  blood-thirsty  destroyers  of  the  insect-world,  the  separation  of 
the  head  from  the  thorax,  which,  by  increasing  the  flexibility,  ne¬ 
cessarily  diminishes  the  strength  of  the  skeleton,  is  no  longer  admis¬ 
sible  ;  and  the  process  of  concentration  being  carried  a  step  fur¬ 
ther,  the  head  and  thorax  coalesce,  leaving  only  two  divisions  of  the 
body  recognizable  externally,  viz.  the  cephalo-thorax  and  the  ab¬ 
domen.  Insects  in  their  mature  forms  were  found  to  be  invariably 
furnished  with  only  six  legs,  but  in  the  adult  Arachnidans  eight  of 
these  limbs  are  developed.  These  characters  in  themselves  would 
be  sufficient  to  discriminate  between  the  two  orders  ;  but  when  to 
these  we  add,  that  in  the  Arachnidans  the  eyes  are  invariably 
smooth,  the  antennae  of  insects  represented  by  organs  of  a  totally 
different  description, —  that  the  sexual  apertures  are  either  situated 
beneath  the  thorax,  or  at  the  base  of  the  abdomen, — and,  moreover, 
that  in  the  greater  number  of  Arachnidans,  respiration  is  carried  on 
in  localized  lungs  (pulmonibranchia) ,  instead  of  by  tracheae  as  in 
insects,  we  need  not  enlarge  further  in  the  present  place  upon 
the  propriety  of  ranking  the  Arachnida  as  a  separate  class.  These 
animals  may  be  grouped  under  three  principal  divisions  ;  the  first 
of  which  is  evidently  an  intermediate  type  of  organization,  com¬ 
bining  many  of  the  characters  of  the  Insecta  with  the  external 
limbs  and  palpi  of  proper  Arachnida. 

(352.)  The  Arachnida  Tr  ache  are  a,  in  fact,  breathe  by 
means  of  tracheae  resembling  those  of  insects,  which  are  so  ar¬ 
ranged  as  to  convey  air  to  every  part  of  the  system  ;  and  we  may 
therefore  suppose  that  their  circulatory  apparatus,  as  well  as  their 


*  A paxvrj.,  a  spider. 


ARACHNIDA. 


307 


secerning  organs,  conform  more  or  less  to  the  type  of  structure 
met  with  in  the  class  last  described.  The  Mites  ( Acarida )  belong 
to  this  division,  and  form  a  very  numerous  family,  which  is  exten¬ 
sively  distributed.  Some  are  parasitic  in  their  habits,  infesting 
the  bodies  of  insects  ;  and  one,  the  itch-insect  ( Acorus  Scabici), 
is  found  occasionally  upon  the  human  skin.  Many  live  in  cheese 
and  other  provisions,  where  they  multiply  prodigiously ;  and  not 
a  few  inhabit  leaves,  or  are  found  under  stones,  or  beneath  the 
bark  of  trees.  Some  ( Hydraclina )  are  aquatic  ;  but  unfortunately 
in  all,  from  their  extremely  minute  size,  the  investigation  of  their 
internal  viscera  presents  so  many  difficulties,  that  but  little  is 
satisfactorily  known  concerning  their  anatomy  :  even  the  pseudo- 
Scorpionidre ,  which  are  of  larger  growth,  and,  although  still 
breathing  by  tracheae,  approximate  most  closely  to  the  outward 
form  of  the  next  group,  have  been  very  imperfectly  examined. 
The  rest  of  the  Arachnidans  breathe  by  means  of  lungs,  or,  as 
they  are  more  properly  designated,  pulmonary  branchiae ;  and 
consequently,  in  contradistinction  to  the  last-mentioned,  are  called 
by  zoologists  Arachnida  Pulmonaria  : — such  are  the  Scor¬ 
pions  and  Spiders. 

(Fig.  ho.; 


The  Pedipalpi,  forming  the  second  division,  are  at  once  re¬ 
cognised  by  the  peculiarity  of  their  external  configuration.  Their 
palpi,  the  representatives  apparently  of  the  maxillary  palpi  of 
insects,  are  exceedingly  strong,  and  furnished  at  their  extremity 
with  a  prehensile  forceps  ;  the  hinder  part  of  the  body,  correspond¬ 
ing  with  the  abdomen  of  insects,  is  much  prolonged,  and  composed 


x 


308 


ARACHNIDA. 


of  numerous  articulated  segments,  terminated  in  tlie  scorpion  tribe 
by  a  sharp  unciform  sting  {Jig.  140),  armed  with  a  venomous  se¬ 
cretion. 

The  third  section  embraces  the  Araneid.e,  or  Spiders ,  distin¬ 
guished  by  having  the  abdomen  short  and  globular,  and  furnished, 
moreover,  near  its  posterior  termination  with  spinnerets ,  by  means 
of  which  these  animals  manufacture  silken  filaments  applicable  to  a 
great  number  of  purposes,  and  especially  employed  in  constructing 
what  is  usually  named  the  spider’s  web.  The  maxillary  palpi  in 
the  females  are  simple,  and  more  or  less  resemble  feet  ;  but  in  the 
males  they  often  form  a  remarkable  apparatus,  to  be  described  in 
another  place  :  the  jaws  are  also  armed  with  sharp  and  hooked  fangs, 
and  perforated  near  their  points  for  the  emission  of  a  poisonous 
secretion  provided  for  the  destruction  of  their  prey. 

(353.)  Beginning  with  the  first  division,  we  shall  now  proceed 
to  place  before  the  reader  such  facts  as  have  been  ascertained,  con¬ 
nected  with  the  anatomical  structure  of  the  class  under  considera¬ 
tion.  In  the  Acaridse,  or  Mites,  the  skin  of  the  entire  body  is  so 
soft  that  any  annulose  structure  is  scarcely  distinguishable;  the 
division,  however,  into  cephalo-thorax  and  abdomen  is  sufficiently 
evident.  The  eyes  are  minute  black  points,  never  exceeding  four 
in  number  and  resembling  the  oeelli  of  insects.  Eight  feeble  legs 
are  articulated  with  the  thorax,  properly  so  called.  The  mouth 
seems  adapted  to  suction,  and  the  jaws  form  a  piercing  instrument 
barbed  at  the  extremity.  The  structure  of  the  respiratory  stig¬ 
mata  or  spiracles  would  seem  to  differ  very  considerably  from  those 
of  insects.  According  to  I)r.  Auduoin,  in  the  species  which  he 
examined  (Ixodes  Erinacei),*  each  spiracle  resembles  a  spherical 
tubercle  perforated  by  an  infinite  number  of  small  holes,  in  the 
centre  of  which  may  be  remarked  a  larger  circular  plate  ;  and  it 
is  through  these  numerous  foramina  that  the  air  enters  the  body, 
and  gets  into  the  trachea?. 

(354.)  The  Pulmonary  Arachnidans ,  both  of  the  pedipalp  and 
spinning  divisions,  are  strictly  carnivorous  in  their  habits,  living 
upon  the  juices  of  the  insects  they  destroy;  and  we  may  consequent¬ 
ly  expect,  in  the  construction  of  their  alimentary  apparatus,  a  sim¬ 
plicity  proportioned  to  the  facility  with  which  highly  nutritive  food 
composed  of  already  animalized  materials  is  capable  of  being  assi¬ 
milated.  The  mouth  varies  somewhat  in  its  conformation,  and,  if 
we  compare  the  pieces  composing  it  with  those  that  we  have  found 

*  Cyclop,  of  Anat.  and  Phys.  ait.  Araciinida. 


ARACIINIDA. 


309 


mandibulate  insects  to  possess,  we  shall  have  good  reason  for  surprise 
in  noticing  the  strange  uses  to  which  some  parts  of  the  oral  appara¬ 
tus  are  converted.  In  scorpions  (jig.  140),  the  apparent  repre¬ 
sentatives  of  the  mandibles  of  an  insect  are  transformed,  into  a  pair 
of  small  forceps,  each  being  provided  with  a  moveable  claw  ;  these 
therefore  form  of  themselves  prehensile  organs  adapted  to  seize  prey, 
and  hold  it  in  contact  with  the  mouth.  But  it  is  in  the  maxillce 
that  we  find  the  most  extraordinary  metamorphosis ;  for  the  maxil¬ 
lary  palpi,  so  small  in  insects,  are  found  to  be  developed  to  such 
prodigious  dimensions,  that  they  far  surpass  in  size  and  strength 
any  of  the  ambulatory  extremities,  and,  from  their  resemblance  to 
the  claws  of  Crustaceans,  have  given  the  character  from  which  the 
name  of  the  division  is  derived.*  Each  of  these  formidable  organs 
is  terminated  by  a  strong  pair  of  pincers,  and  thus  the  maxillary 
palpi  become  converted  into  potent  instruments  either  for  attack 
or  defence.  The  representative  of  the  labium  of  an  insect  in  the 
Arachnidans  has  no  palpi  connected  with  it. 

(355.)  In  spiders  the  organization  of  the  mouth  is  altogether  dif¬ 
ferent.  The  mandibles  (jig.  142,  o,  o)  are  each  terminated  with  a 
moveable  fang  (c),  which  ends  in  a  sharp  point,  and  is  perforated  near 
its  extremity  by  a  minute  orifice,  from  which,  when  the  spider  bites, 
a  venomous  fluid  of  great  potency  is  instilled  into  the  wound  in¬ 
flicted  ;  such,  indeed,  is  the  malignity  of  this  poisonous  secretion 
that  its  effects  in  destroying  the  life  of  a  wounded  insect  are  al¬ 
most  instantaneous,  and  in  some  of  the  large  American  species  even 
small  birds  fall  victims  to  its  virulence.  The  organ  in  which  the 
poison  is  elaborated  is  represented  in  the  figure  above  referred  to  : 
it  is  a  long  and  slender  bag,  from  which  an  attenuated  duct  may 
be  traced  through  the  body  of  the  mandible  as  far  as  the  perforated 
extremity  of  the  fang. 

The  palpi  connected  with  the  maxillae  of  the  spider  are  termi¬ 
nated  in  the  female  by  a  simple  hook  ;  but  in  the  males  of  many 
species  they  exhibit  a  conformation  slightly  resembling  the  forceps 
of  the  scorpion,  although  provided  for  a  very  different  purpose. 
When  closed  (jig.  141,  e),  the  terminal  part  of  the  palpus  pre¬ 
sents  a  club-like  dilatation,  which,  however,  on  close  inspection 
will  be  found  to  consist  of  several  pieces  (jig.  141,  a,  «,5,c,  d,  e), 
connected  with  each  other  by  articulations,  and  capable  of  being 
opened  out  in  the  manner  represented  in  the  figure.  This  strange 
instrument  wras  formerly  imagined  to  be  the  penis  of  the  male  spi- 

*  Pes,  a  foot ;  palpus,  a  feeler. 


310 


AltACHNIDA. 


Fig.  141. 


der,  and  was  thought  to  contain  the  terminations  of  the  seminal 
ducts :  the  supposition,  however,  has 
been  proved  to  be  erroneous,  for  the 
palpus  is  imperforate,  and  the  sexual 
apertures  of  the  male  are  situated  else¬ 
where,  but  the  organ  in  question  is 
nevertheless  apparently  used  in  the  ^ 
process  of  impregnation,  in  a  manner 
to  be  explained  hereafter. 

(356.)  Both  in  scorpions  and  spiders  the  alimentary  canal  is  ex¬ 
ceedingly  narrow,  presenting  scarcely  any  of  those  dilatations  met 
with  in  the  digestive  organs  of  insects.  This  is  a  natural  consequence 
of  the  nature  of  their  food ;  for,  as  they  live  entirely  upon  animal 
juices  sucked  from  the  bodies  of  their  victims,  there  could  be  little 
necessity  for  the  presence  of  capacious  receptacles  for  nutritious 
matter,  or  for  any  reservoirs  for  the  accumulation  of  effete  ma¬ 
terial. 

In  the  Scorpionidce  there  is  no  stomachal  dilatation  what¬ 
ever  :  a  straight  intestine  passes  directly  from  the  mouth  to  the 
anus,  situated  at  the  extremity  of  the  abdomen  ;  and  the  insertion 
of  the  biliary  vessels  forms  the 
only  distinction  between  its  ven¬ 
tricular  and  intestinal  divisions. 

Five  delicate  cseca  are  derived 
from  each  side  of  the  ventricu¬ 
lar  portion,  and  plunge  into  the 
centre  of  a  fattv  substance  in 
which  the  alimentary  canal  is  em¬ 
bedded.  In  Spiders ,  likewise, 
cseca  are  appended  to  the  com¬ 
mencement  of  the  digestive  ap¬ 
paratus,  and  a  slight  enlargement 
{Jig.  142,  b)  may  be  said  to  repre¬ 
sent  the  stomach,  from  which  a 
slender  intestine  (g)  is  continued 
to  the  anus.  As  in  the  scorpion, 
a  large  quantity  of  fat  (h)  sur¬ 
rounds  the  nutrient  organs,  and 
fills  up  a  great  proportion  of  the 
cavity  of  the  abdomen.  Like 

the  fat-mass  of  the  larva  of  insects,  this  substance  must,  no 


Fig.  142. 


ARACHNIDA. 


311 


doubt,  be  regarded  as  a  reservoir  of  nutriment ;  and  when  the  ha¬ 
bits  of  these  animals  are  considered,  the  precarious  supply  of  food, 
and  the  frequent  necessity  for  long-protracted  fasts,  when  a  scar¬ 
city  of  insects  deprives  them  of  their  accustomed  prey,  such  a 
provision  is  evidently  essential  to  their  preservation. 

(357.)  One  peculiarity  connected  with  the  arrangement  of  the 
chylo-poietic  viscera  of  the  spider  is  the  manner  in  which  the  biliary 
organs  terminate  in  the  intestine ;  for  instead  of  entering  in  the 
usual  position,  namely,  close  to  the  termination  of  the  stomach, 
they  seem  to  pour  their  secretion  into  the  rectum  immediately  in 
the  vicinity  of  the  anus.  At  this  point,  a  kind  of  sacculus  {figs. 
142  and  143,  f)  joins  the  intestine,  into  Fig.  143. 

which  the  branched  tubes  (fig.  143,  o,  o  ; 
fig.  142,  s)  empty  themselves.  This  cir¬ 
cumstance  has  long  been  a  subject  of  in¬ 
teresting  inquiry  to  the  comparative  phy¬ 
siologist.  If  the  fluid  secreted  by  these 
tubes  be  really  bile,  in  what  manner 
does  it  accomplish  those  purposes  usually 
supposed  to  be  effected  by  the  biliary 
secretion  ?  It  would  seem  to  be,  in  this 
case,  merely  an  excrementitious  produc¬ 
tion.  Are  the  cseca  appended  to  the 
stomach  biliary  organs  ?  If  so,  the  apparatus  in  question  may  be 
of  totally  distinct  character,  and  its  product  only  furnished  to  be 
expelled  from  the  system.  In  conformity  with  the  last  supposi¬ 
tion,  many  antaomists  have  been  induced  to  regard  these  vessels 
as  being  analogous  to  the  urinary  secernents  of  more  highly 
organized  animals,  and  have  not  scrupled  to  apply  to  them  the 
appellation  of  renal  vessels :  but  this  hasty  application  of  names 
we  have  already  animadverted  upon  as  being  highly  prejudicial 
to  the  interests  of  science  ;  and  in  this  instance,  as  in  many  others, 
to  wait  for  the  results  of  future  investigations  is  far  more  advisable 
than  rashly  to  assign  a  definite  function  to  a  part,  the  real  nature 
of  which  is  a  matter  of  speculation. 

(358.)  The  respiratory  system  of  the  Pulmonary  Arachnidans  is 
constructed  upon  very  peculiar  principles,  being  neither  composed  of 
gills  adapted  to  breathe  water,  nor  lungs  like  those  of  other  air-breath¬ 
ing  animals,  but  presenting  a  combination  of  the  characters  of  both. 
The  pulmo-branchive  are,  in  fact,  hollow  viscera  resembling  bags  ; 
the  walls  of  which  are  so  folded  and  arranged  in  laminae,  that  a 


312 


Alt  ACHNI D  A. 


considerable  surface  is  presented  to  the  influence  of  oxygen.  It 
is,  indeed,  highly  probable  that  these  organs  are  intermediate  in 
function  as  well  as  in  structure  between  an  aquatic  and  air-breath¬ 
ing  respiratory  apparatus  ;  for,  as  both  the  pedipalp  and  spinning 
Arachnidans  frequent  moist  situations,  the  dampness  of  the  atmo¬ 
sphere  may  be  favourable  to  the  due  action  of  the  air  upon  the 
circulating  fluids  of  these  creatures.  Each  pulmo-branchia  opens 
externally  by  a  distinct  orifice,  resembling  the  spiracle  of  an  in¬ 
sect,  and  is  closed  in  a  similar  manner  by  moveable  horny  lips. 
In  the  scorpion  {Jig.  140)  the  spiracles  are  eight  in  number, 
placed  upon  the  ventral  aspect  of  the  body ;  and  just  in  front  of 
the  first  pair  of  breathing-holes  are  two  remarkable  organs  repre¬ 
sented  in  the  figure,  resembling  a  pair  of  combs,  which  are  appa¬ 
rently  adapted  to  keep  the  spiracular  orifices  free  from  dirt,  and 
thus  prevent  any  obstructions  to  the  free  ingress  and  egress  of  the 
air. 

In  the  Araneidse,  the  form  and  arrangement  of  the  spiracles  is 
somewhat  different  :  according  to  Treviranus,  there  are  four  pairs 
on  each  side  of  the  cephalo-thorax,  situated  immediately  above  the 
insertions  of  the  legs  ;  and  in  addition  to  these  there  is  one  pair 
constantly  found  on  the  under  surface  of  the  abdomen,  and  four 
pairs  of  smaller  apertures  of  less  importance  on  its  upper  part. 

In  order  to  understand  the  manner  in  which  respiration  takes 
place  in  pulmo-branchice  of  the  structure  above  described,  it  is 
necessary  to  suppose  the  existence  of  a  vascular  apparatus,  by 
means  of  which  the  circulating  fluid  is  continually  spread  over  the 
laminae  of  the  respiratory  sacculi,  and  afterwards  returned  to  the 
circulation  in  a  purified  condition.  It  is  true,  that,  owing  to  the 
extreme  difficulty  of  tracing  vessels  of  such  small  dimensions,  the 
continuity  of  the  entire  system  is  rather  an  inference  deducible 
from  agen  eral  review  of  the  facts  ascertained,  than  absolutely  a 
matter  of  demonstration.  We  will,  therefore,  briefly  lay  before 
the  reader  the  data  upon  which  physiologists  found  the  opinions 
entertained  at  the  present  day  relative  to  the  means  whereby  the 
circulation  of  Arachnidans  is  accomplished. 

(359.)  According  to  Treviranus,  spiders  are  provided  with  a  long 
contractile  vessel,  which  runs  along  the  mesial  line  of  the  back,  and 
resembles  in  form  the  dorsal  vessel  of  insects,  although  in  struc¬ 
ture  it  is  widely  different.  In  insects,  it  will  be  remembered,  the 
dorsal  vessel  communicated  freely  with  the  abdominal  cavity  by 
numerous  valvular  apertures,  and  neither  arteries  nor  veins  were 


ARACHNID  A. 


313 


necessary  for  diffusing  tlie  blood  through  the  system  ;  but  in  the 
Pulmonary  Arachnidans  numerous  vascular  trunks  are  given  off 
from  both  sides  of  the  dorsal  heart,  and  are  dispersed  in  all  direc¬ 
tions.  All  the  branches  proceeding  from  the  sides  of  the  dorsal 
vessel  are  presumed  to  be  of  an  arterial  character,  with  the  excep¬ 
tion  of  a  few  large  canals  situated  near  the  junction  of  the  anterior 
and  middle  thirds  of  its  length,  and  these  are  supposed  to  be 
veins*  (branchio- cardiac  vessels)  destined  to  return  the  aerated 
blood  from  the  yulmo-branchirc  into  the  general  circulation. 
Whoever  watches  the  movements  of  the  blood  in  one  of  the  limbs 
of  these  creatures,  will  perceive  that  under  the  microscope  its 
motion  bears  little  resemblance  to  that  observable  in  the  foot  of  a 
frog,  or  in  animals  possessed  of  an  arterial  and  venous  system 
completely  developed.  So  irregular,  indeed,  is  the  course  of  the 
globules,  that  it  would  be  difficult  to  conceive  them  to  be  confined 
in  vessels  at  all  ;  the  whole  appearance  resembles  rather  the  dif¬ 
fused  circulation  seen  in  the  larva  of  an  insect,  than  that  of  a  crea¬ 
ture  possessing  vascular  canals  arranged  in  definite  directions. 
The  only  probable  way  of  accounting  for  such  a  phenomenon  is 
by  supposing  that,  in  this  first  sketch  of  a  vascular  system,  if  we 
may  be  pardoned  the  expression,  the  veins  are  mere  sinuses  or 
wide  cavities  formed  in  the  interstices  of  the  muscles,  through 
which  the  blood  slowly  finds  a  passage.  From  a  review  of  the 
above-mentioned  facts  we  are  at  liberty  to  deduce  the  following 
conclusions  relative  to  the  circulation  of  Arachnidans  : — The 
jmlmo-branchia  being  apparently  the  only  organs  of  respiration, 
the  blood  must  be  perpetually  brought  to  these  structures  from 
all  parts  of  the  system,  to  receive  the  influences  of  oxygen,  and 
again  distributed  through  the  body  : — such  a  circulation  could 
only  be  accomplished  in  circumscribed  channels  ;  some  destined  to 
propel  it  through  all  parts  ;  others  to  collect  it  after  its  distribu¬ 
tion,  and  bring  it  to  the  respiratory  organs  ;  and  a  third  set  to 
return  it  in  a  renovated  condition  to  the  heart.  The  circuit  of  the 
blood  may  therefore  be  presumed  to  be  completed  in  one  or  other 
of  the  following  modes.  The  dorsal  vessel,  or  heart,  by  its  con¬ 
traction  drives  the  blood  through  numerous  arterial  canals  to  the 
periphery  of  the  system  :  the  blood  so  distributed  gradually  finds 
its  way  into  capacious  sinuses,  through  which  it  flows  to  the 
branchial  organs,  and  from  hence  it  re-enters  the  heart  by  the 
branchio- cardiac  vessels  above  referred  to  :  or  else  the  action  of 

*  Dr.  Audouin,  Cyclop,  of  Anat.  and  Pliys.  art.  Arachnida. 


314 


ARACHNIDA. 


the  heart  drives  a  portion  of  the  circulating  fluid  into  the  pulmo- 
branchia  by  the  same  effort  which  supplies  the  rest  of  the  system, 
and  the  blood  so  impelled  to  the  respiratory  organs  becomes,  after 
being  purified,  again  mixed  up  with  the  contents  of  the  veins 
which  return  it  to  the  heart. 

(360.)  In  the  nervous  system  of  spiders  we  observe  that  pro¬ 
gressive  concentration  of  the  nervous  centres,  which  we  have  traced 
through  the  lower  forms  of  the  Homogangliata,  carried  to 
the  utmost  extent.  Spiders  are  appointed  destroyers  of  insects, 
with  which  they  maintain  cruel  and  unremitting  warfare.  That 
the  destroyer  should  be  more  powerful  than  the  victim,  is  essen¬ 
tial  to  its  position  ;  that  it  should  excel  its  prey  in  cunning  and 
sagacity,  is  likewise  a  necessary  consequence ;  and  by  following 
out  the  same  principles,  which  have  already  been  so  often  insisted 
upon,  concerning  the  inseparable  connexion  that  exists  between  the 
perfection  of  an  animal  and  the  centralization  of  its  nervous  gan¬ 
glia,  we  find  in  the  class  before  us  an  additional  confirmation  of 
this  law.  In  scorpions ,  indeed,  the  nervous  masses  composing 
the  ventral  chain  of  ganglia  are  still  widely  separated,  especially 
those  situated  in  the  segments  of  the 
tail :  in  the  cephalo-thorax  they 
are  of  proportionately  larger  dimen¬ 
sions  ;  and,  moreover,  exhibit  this 
remarkable  peculiarity,  that,  instead 
of  being  united  by  two  cords  of 
communication,  there  are  three  inter- 
ganglionic  nerves  connecting  each  di¬ 
vision.  It  is  in  spiders  that  the  con¬ 
centration  of  the  nervous  system 
reaches  its  climax  ;  for  in  them  we 
find  the  whole  series  of  ganglia,  en¬ 
cephalic,  thoracic,  and  abdominal,  ag¬ 
gregated  together,  and  fused,  as 
it  were,  into  one  great  central  brain, 
from  whence  nerves  radiate  to  all 
parts  of  the  body.  The  extent  to 
which  centralization  is  here  carried 
will  be  at  once  appreciated  by  refer¬ 
ence  to  the  annexed  figure  {Jig-  144)  :  the  encephalic  masses 
«,  a,  whence  the  optic  nerves  distributed  to  the  ocelli  are  de¬ 
rived,  are  in  close  contact  with  the  anterior  part  of  a  large 


Fig.  144. 


ARACHNID  A. 


315 


ganglion,  c,  tliat  represents  all  the  abdominal  ganglia  collected 
into  one  mass  ;  and  from  the  posterior  part  of  this,  nerves,  n,  n, 
destined  to  supply  the  parts  contained  in  the  abdomen,  derive 
their  origin.  The  thoracic  ganglia,  e,  e,  are  fusiform,  and  placed 
on  each  side  of  the  mass  c,  with  which  they  are  apparently 
amalgamated  at  one  extremity,  while  from  the  opposite  they  give 
off  the  nerves  appropriated  to  the  legs. 

The  ocelli  or  eyes  of  Arachnidans  have  been  minutely  investi¬ 
gated  by  Muller,*  and  seem  to  present  a  type  of  structure  very  far 
superior  to  that  of  insects.  In  the  Scorpion  this  distinguished  anato¬ 
mist  succeeded  in  detecting  most  of  the  parts  which  enter  into  the 
construction  of  the  eye  of  a  vertebrate  animal ;  and,  moreover, 
a  great  similarity  in  their  arrangement.  The  cornea,  a  globular 
lens,  the  aqueous  and  vitreous  humours,  the  retina  and  choroid 
were  all  found  nearly  in  their  usual  relative  positions  ;  so  that  the 
sense  of  vision  in  these  animals  must  be  extremely  perfect. 

(361.)  The  sexual  organs  of  the  male  and  female  Fig.  145. 
Arachnidans  exhibit  very  great  simplicity  in  their 
structure.  The  testes,  or  secreting  vessels  of  the 
male  spider,  are  two  long  caeca  (Jig.  145,  5),  lodg¬ 
ed  in  the  abdomen,  and  terminating  by  simple 
orifices  at  the  ventral  surface.  No  external  in- 
tromittent  organ  is  perceptible ;  and  it  was  on 
this  account  that  the  peculiar  apparatus  above  re¬ 
ferred  to,  situated  at  the  extremity  of  the  maxil¬ 
lary  palpus,  was  so  long  considered  as  giving  pas¬ 
sage  to  the  impregnating  secretion.  The  singular 
instrument  already  described  (§  355),  would  seem, 
indeed,  to  be  in  some  manner  really  subservient 
to  the  fecundating  process  ;  being  used  most  probably  as  an  exciting 
agent  preparatory  to  the  intercourse  between  the  sexes. 

(362.)  The  ovigerous  system  of  the  female  is  equally  devoid  of 
complication,  and,  like  the  male  testes,  consists  of  two  elongated 
membranous  sacculi,  in  which  the  eggs  are  formed  and  brought 
to  maturity.  The  impregnation  of  the  ova  is  evidently  effected  by 
the  simple  juxta-position  of  the  external  orifices  of  the  two  sexes  : 
yet  such  is  the  ferocity  of  the  female  spider,  that  the  accomplish¬ 
ment  of  this  is  by  no  means  without  risk  to  her  paramour;  for  the 
former  being  far  superior  to  the  male,  both  in  size  and  strength 
(Jig.  146,  a,  b),  would  infallibly  devour  him,  either  before  or  after 

*  Annales  des  Sciences  Nat.  tom.xvii. 


316 


ARACHNIDA. 


the  consummation  of  his  purpose,  did  lie  not  exercise  the  most 
guarded  caution  and  circumspection  in  making  his  advances. 

Fig.  146. 


(363.)  One  peculiar  characteristic  of  the  Araneidce  is  the  posses¬ 
sion  of  a  spinning  apparatus,  whereby  the  threads  composing  their 
web  are  manufactured.  The  instruments  employed  for  this  purpose 

Fig.  147. 


arc  situated  near  the  posterior  extremity  of  the  abdomen,  and 
consist  externally  of  four  spinnerets,  and  twopalpiform  organs  (Jig. 
147  a,  r).  Each  spinneret ,  when  highly  magnified,  is  found  to 
be  perforated  at  its  extremity  by  innumerable  orifices  of  extreme 
minuteness  (^/zg.147,  c),  through  which  the  filaments  are  drawn  ;  so 
that,  unlike  the  silk  of  the  caterpillar,  the  thread  of  the  spider, 
delicate  as  it  is,  is  composed  of  hundreds  of  smaller  cords,  some- 


A RACK N I DA. 


317 


times  woven  together  by  zig-zag  lines,  and  thus  exhibiting  a 
structure  of  exquisite  and  most  elaborate  composition.  The  fluid 
silk,  which,  when  it  is  drawn  through  the  microscopic  apertures 
of  the  spinneret,  affords  the  material  whereof  the  web  is  con¬ 
structed,  is  secreted  in  a  set  of  glands  represented  in  the  sub¬ 
joined  engraving  {Jig.  148).  The  secerning  extremities  of  the 
glandular  tubes  are  composed  of  branched  cseca  (.s),  whence  arise 
long  and  tortuous 
ducts  ( a ,  <2,  a), 
that  become  dilat¬ 
ed  in  their  course 
into  reservoirs  for 
the  secreted  fluid, 
and  terminate  by 
several  canals  at 
the  base  of  the 
external  spinning 
tubuli.  Various 
are  the  purposes 
to  which  the  dif¬ 
ferent  species  of 
the  Araneidse  convert  the  delicate  threads  thus  produced.  Some 
construct  for  themselves  silken  tubes  or  cells,  in  which  to  conceal 
themselves  from  pursuit,  and  from  this  retreat  they  issue  to  hunt 
for  prey  in  the  vicinity  of  their  abode ;  others  strew  their  fila¬ 
ments  about  at  random,  apparently  to  entangle  passing  insects ; 
many  make  nets  composed  of  regular  meshes,  and  spread  them  out 
in  favourable  situations  to  entrap  their  victims  (Jig.  146)  ;  while 
a  few  species,  enveloping  their  eggs  in  bags  of  curious  construction, 
carry  them  about  attached  to  their  bodies,  and  defend  them  with 
the  utmost  courage  and  pertinacity :  even  in  water  these  webs  are 
turned  to  many  singular  uses  ;  and  ropes,  nets,  and  even  diving- 
bells  are  at  the  disposal  of  aquatic  species  furnished  with  this 
extraordinary  spinning  machinery. 

A  few  only  of  the  most  remarkable  applications  of  this  de¬ 
licate  material  can  be  noticed  in  this  place.  The  mason-spiders 
(My gale)  excavate  for  themselves  subterranean  caverns,  in  which 
these  marauders  lurk  secure  from  detection,  even  by  the  most 
watchful  foe  :  nor  could  any  robber’s  den,  which  ever  existed  in 
the  wild  regions  of  romance,  boast  more  sure  concealment  from 
pursuit,  or  immunity  from  observation.  The  construction  of  these 


318 


ARACHNIDA. 


singular  abodes  lias  long  excited  the  admiration  of  the  naturalist  : 
a  deep  pit  is  first  dug  by  the  spider,  often  to  the  depth  of  one 
or  two  feet,  which,  being  carefully  lined  throughout  with  silken 
tapestry,  affords  a  warm  and  ample  lodging ;  the  entrance  to 
this  excavation  is  carefully  guarded  by  a  lid  or  door,  which  moves 
upon  a  hinge,  and  accurately  closes  the  mouth  of  the  pit.  In 
order  to  form  the  door  in  question,  the  Mygale  first  spins  a  web 
which  exactly  covers  the  mouth  of  the  hole,  but  which  is  attached 
to  the  margin  of  the  aperture  by  one  point  only  of  its  circum¬ 
ference,  this  point  of  course  forming  the  hinge.  The  spider  then 
proceeds  to  lay  upon  the  web  a  thin  layer  of  the  soil  collected  in 
the  neighbourhood  of  her  dwelling,  which  she  fastens  with  another 
layer  of  silk ;  layer  after  layer  is  thus  laid  on,  until  at  length  the 
door  acquires  sufficient  strength  and  thickness :  when  perfected, 
the  concealment  afforded  is  complete  ;  for,  as  the  outer  layer  of 
the  lid  is  formed  of  earth  precisely  similar  to  that  which  surrounds 
the  hole,  the  strictest  search  will  scarcely  reveal  to  the  most 
practised  eye  the  retreat  so  singularly  defended. 

Another  spider  ( Clotho  Durandii)  constructs  a  dwelling  equally 
artificial  and  ingenious, — a  kind  of  tent  in  which  it  lives  and  rears 
its  young.  This  tent  is  composed  of  several  superposed  sheets  of 
the  finest  taffeta,  and  its  contour  presents  seven  or  eight  prominent 
angles,  which  are  fixed  to  the  surface  of  the  ground  by  silken  cords. 
The  young  Clotho  at  first  lays  down  only  two  sheets  thus  secured, 
between  which  she  hides  herself ;  but,  as  she  grows  older,  she  con¬ 
tinually  lays  down  additional  coverings,  until  the  period  when  she 
begins  to  lay  her  eggs,  at  which  time  she  constructs  an  apartment, 
soft,  downy,  and  warm,  specially  devoted  to  their  reception.  The 
exterior  sheet  of  the  tent  is  purposely  dirtied  for  the  purpose  of  con¬ 
cealment  ;  but  within,  everything  is  beautifully  clean  and  white. 
The  most  admirable  part  of  the  contrivance,  however,  is  the  per¬ 
fect  safety  afforded  to  the  young  when  the  parent  leaves  her  tent  in 
search  of  food  ;  some  of  the  superposed  sheets  are  fastened  toge¬ 
ther  at  their  edges,  others  are  simply  laid  upon  each  other,  and, 
as  the  parent  herself  alone  possesses  the  secret  which  enables  her 
to  raise  those  layers  by  which  entrance  is  to  be  obtained,  no 
other  animal  can  find  its  way  into  her  impenetrable  abode. 


319 


CHAPTER  XVII. 

Crustacea. 

Insects  and  Arachnidans  are  air-breathing  animals  ;  and,  even 
in  such  species  of  these  two  extensive  classes  as  inhabit  fresh 
water,  respiration  is  strictly  aerial.  No  insects  or  spiders  are 
marine ;  and  consequently  the  waters  of  the  ocean  would  be  utterly 
untenanted  by  corresponding  forms  of  Articulata,  was  there  not 
a  class  of  beings  belonging  to  this  great  division  of  the  animal 
world  so  organized  as  to  be  capable  of  respiring  a  watery  medium, 
and  thus  adapted  to  a  residence  in  the  recesses  of  the  deep. 
Examined  on  a  large  scale,  the  Crustaceans,  upon  the  considera¬ 
tion  of  which  we  are  now  entering,  are  marine  creatures  :  many 
species,  it  is  true,  are  found  abundantly  in  the  lakes  and  ponds 
around  us,  but  these  form  rather  exceptions  to  the  general  rule ; 
and  we  may  fairly  regard  this  extensive  group  of  beings  as  the 
aquatic  representatives  of  the  insects  and  spiders,  with  which  they 
form  a  collateral  series. 

(364.)  The  tegumentary  system  of  the  Crustacea  corresponds 
in  its  essential  structure  with  that  of  insects,  and  consists  of  a 
vascular  dermis,  a  coloured  pigment,  and  a  cuticular  secreted 
layer  which  forms  the  external  shell  or  skeleton :  the  latter, 
or  epidermic  covering,  however,  differs  materially  in  texture  from 
that  of  other  Articulata,  inasmuch  as  it  contains  calcareous  matter 
in  considerable  abundance,  and  thus  acquires  in  the  larger  species 
great  density  and  hardness. 

As  regards  the  mechanical  arrangement 
of  the  skeleton,  we  shall  find  the  same 
general  laws  in  operation  as  we  have  ob¬ 
served  throughout  all  the  annulose  orders, — 
a  continual  centralization  and  progressive 
coalescence  of  the  different  rings  or  ele¬ 
ments  composing  the  external  integument, 
and  a  strict  correspondence  between  the 
degree  to  which  this  consolidation  is  car¬ 
ried  and  the  state  of  the  nervous  system 
within. 

In  the  lowest  forms  of  the  Crustacea 


Fig.  149. 


320 


CRUSTACEA. 


we  have  in  fact  a  repetition  of  the  condition  of  flic  skeleton 
met  with  in  tlie  Myriapoda,  or  in  the  larva  state  of  many  in¬ 
sects  ;  the  whole  body  being  composed  of  a  series  of  similar 
segments,  to  which  are  appended  external  articulated  members  of 
the  simplest  construction  {Jig-  149). 

The  number  of  rings  or  segments  composing  the  body  varies 
in  different  species  ;  but  such  variation  would  seem,  from  the  inter¬ 
esting  researches  of  Milne  Edwards  and  Audouin,  concerning  the 
real  organization  of  articulated  tegumentary  skeletons,  to  be  rather 
apparent  than  real,  inasmuch  as  the  discoveries  of  these  distinguished 
naturalists  go  far  to  prove  that,  whatever  the  state  of  consolidation 
in  which  the  integument  is  found,  the  same  number  of  elements 
or  rings  may  be  proved  to  have  originally  existed  before,  by  their 
union,  they  became  no  longer  distinguishable  as  separate  seg¬ 
ments. 

The  normal  number  of  these  elements  Milne  Edwards  considers 
to  be  twenty-one,  seven  of  which  enter  into  the  composition  of  the 
head,  seven  belong  to  the  thorax,  and  as  many  appertain  to  the  ab¬ 
dominal  region  of  the  body. 

To  illustrate  this  important  doctrine  let  us  select  a  few  examples, 
in  order  to  show  the  manner  in  which  the  progressive  coalescence 
of  the  segments  is  effected. 

In  Talitra  {Jig.  150)  the  cephalic  elements  are  completely 
united,  their  existence  being 
only  indicated  by  the  several 
pairs  of  appendages  ;  one  pair, 
of  course,  belonging  to  each 
ring.  The  first  ring  of  the 
cephalic  region,  in  this  in¬ 
stance,  has  no  external  articu¬ 
lated  member  ;  but  in  higher 
orders  the  eyes  are  supported  upon  long  peduncles  connected  with 
this  element  of  the  skeleton,  that  may  be  regarded  as  the  represen¬ 
tatives  of  those  limbs  which  take  different  names  in  different  regions 
of  the  body.  The  second  and  third  rings  support  jointed  organs 
here  called  antennse  ;  while  the  several  pairs  of  jaws  appertaining  to 
the  mouth  indicate  the  existence  of  so  many  elements  united  toge¬ 
ther  in  the  composition  of  the  head. 

The  seven  segments  of  the  thorax  are  still  distinct,  and  each 
supports  a  pair  of  jointed  organs,  which,  being  used  in  locomotion, 
are  called  legs  ;  the  abdominal  elements,  likewise,  are  equally  free, 


Fig.  150. 


CRUSTACEA. 


821 


and  have  natatory  extremities  developed  from  the  five  posterior 
rings. 

In  the  lobster  ( Astacus  Marinus )  we  find  not  only  the  cephalic 
segments  anchylosed  together,  but  those  of  the  thorax  also  ;  and  al¬ 
though  the  lines  of  demarcation  between  them  are  still  recognisable 
upon  the  ventral  aspect  of  the  body,  superiorly  the  entire  thorax 
and  head  are  consolidated  into  one  great  shield  (cep  halo-thorax) , 
the  abdominal  segments  only  remaining  distinct  and  moveable. 

In  the  Crabs  the  centralization  of  the  external  skeleton  is  carried 
to  still  greater  lengths,  so  as  to  enable  this  tribe  of  Crustaceans  to 
become  more  or  less  capable  of  leaving  their  native  element,  and 
walking  upon  the  shores  of  the  sea,  or  even  in  some  instances  of 
leading  a  terrestrial  existence,  as  in  the  case  of  the  land- crab  of  the 
West  India  islands.  The  abdominal  segments,  however,  still  re¬ 
main  free,  though  proportionately  of  very  small  dimensions ;  and, 
being  no  longer  useful  in  swimming,  the  abdomen  is  folded  beneath 
the  enormously  developed  thoracic  portion  of  the  body. 

In  the  King-Crab  ( Limulus  Polyphemus;  Jig.  151)  even  the 
divisions  of  the  abdomen  are  obli¬ 
terated,  the  whole  body  being  co¬ 
vered  by  two  enormous  shields,  and 
the  tail  prolonged  into  a  formidable 
serrated  spine,  of  such  density  and 
sharpness  that  in  the  hands  of  sa¬ 
vages  it  becomes  a  dreadful  weapon, 
and  is  used  to  point  their  spears 
either  for  the  chase  or  war. 

The  reader  will  at  once  perceive 
the  strict  parallelism  that  may  be 
traced  between  the  changes  which 
occur  during  the  metamorphosis  of 
insects,  and  those  observable  as  we 
thus  advance  from  the  lowest  to 
the  most  highlv  organized  Crusta- 
cean  genera ;  and  even  the  steps 
whereby  we  pass  from  the  Anneli- 
dan  to  the  Myriapod,  and  from 
thence  to  the  Insect,  the  Scorpion,  and  the  Spider,  seem  to  be  re¬ 
peated  as  we  thus  review  the  progressive  developement  of  the  class 
before  us. 

Having  thus  found  that  the  annuli,  or  rings,  which  compose  the 


Fig .  151. 


Y 


322 


CRUSTACEA. 


annulose  skeleton  may  be  detected  even  in  tlie  most  compactly 
formed  Crustacea,  it  remains  for  us  to  inquire,  in  the  next 
place,  what  are  the  principal  modifications  observable  in  the  arti¬ 
culated  appendages  developed  from  the  individual  segments.  This 
inquiry  is  one  of  considerable  interest,  inasmuch  as  it  goes  to  prove 
that,  however  dissimilar  in  outward  form,  or  even  in  function,  the 
limbs  of  Crustaceans  are  mere  developements  of  the  same  elements, 
which,  as  they  remain  in  a  rudimentary  condition  or  assume  larger 
dimensions,  become  converted  into  instruments  of  sensation,  legs, 
jaws,  or  fins,  as  the  circumstances  of  the  case  may  render  needful. 
In  the  lower,  or  more  completely  annulose  forms  {figs.  149  and 
152),  these  members  are  pretty  equally  developed  from  all  the  seg¬ 
ments  of  the  body,  and  are  subservient  to  locomotion,  being  gene¬ 
rally  terminated  by  prehensile  hooks,  or  provided  with  fin-like  ex¬ 
pansions  ;  but,  as  we  advance  to  the  more  perfect  genera,  the  limbs 
assume  such  various  appearances,  and  become  convertible  to  so  many 
distinct  uses,  that  they  are  no  longer  to  be  recognised  as  consisting 
of  similar  elements,  modified  only  in  their  forms  and  relative  pro¬ 
portions.  To  notice  Fig.  152. 

all  the  varieties  which 
occur  in  the  extensive 
class  before  us,  would 
be  to  weary  the  reader 
with  tedious  and  unne¬ 
cessary  details ;  we  shall 
therefore  select  the  De¬ 
capod*  division  of  these 
animals,  as  abundantly  sufficient  for  the  illustration  of  this  part  of 
our  subject.  This  division,  which  includes  the  most  highly  organ¬ 
ized  forms,  has  been  divided  by  writers  into  three  extensive  fami¬ 
lies, — the  Macroura,  or  swimming  Decapods;  the  Anomoura ,  which 
inhabit  the  empty  shells  of  Mollusca  ;  and  the  Brachyura ,  or  short¬ 
tailed  species,  of  which  the  crab  is  a  familiar  specimen.  If  we  take 
the  common  lobster  as  an  example  of  the  first  of  these  groups,  we 
shall  find  that  there  are  five  pairs  of  articulated  limbs  placed  upon 
each  side  of  the  mouth,  which  are  evidently  adapted  to  assist  in 
seizing  and  conveying  into  the  stomach  substances  used  as  food. 
These  singular  organs,  which,  although  entitled  to  be  considered  as 
jaws  so  far  as  their  use  would  indicate  the  name  belonging  to  them, 

*  So  called  from  the  circumstance  of  their  having  five  pairs  of  limbs  so  largely  de¬ 
veloped  as  to  become  ambulatory  or  prehensile  organs. 


CRUSTACEA. 


323 


are  no  less  obviously  merely  modifications  of  articulated  feet ;  and 
tlie  term  foot-jaws  lias  now,  by  common  consent,  become  the  appel¬ 
lation  by  which  they  are  distinguished. 

The  pair  of  legs  which  succeeds  to  the  remarkable  members  last 
referred  to,  is  appropriated  to  widely  different  offices.  The  organs 
in  question  are  developed  to  a  size  far  surpassing  that  attained  by 
any  of  the  other  limbs  and  are  endowed  with  proportionate  strength. 
Each  of  these  robust  extremities  is  terminated  by  a  pair  of  strong 
pincers  (chela)  ;  but  the  two  are  found  to  differ  in  their  structure, 
and  are  appropriated  to  distinct  uses.  That  of  one  side  of  the 
body  has  the  opposed  edges  of  its  terminal  forceps  provided  with 
large  blunt  tubercles,  while  the  opposite  claw  is  armed  with  small 
sharp  teeth.  One,  in  fact,  is  used  as  an  anchor,  by  which  the  lob¬ 
ster  holds  fast  by  some  submarine  fixed  object,  and  thus  prevents 
itself  from  being  tossed  about  in  an  agitated  sea  ;  the  other  is  ap¬ 
parently  a  cutting  instrument  for  tearing  or  dividing  prey. 

To  the  chela  succeed  four  pairs  of  slender  legs,  scarcely  at 
all  serviceable  for  the  purposes  of  locomotion  ;  but,  the  two  ante¬ 
rior  being  terminated  by  feeble  forceps,  they  become  auxiliary  , 
instruments  of  prehension. 

The  articulated  appendages  belonging  to  all  the  abdominal 
segments  are  so  rudimentary  that  they  are  no  longer  recognisable 
as  assistants  in  progression ;  and  it  is  at  once  evident,  when 
we  examine  the  manner  in  which  the  Macroura  use  their  tails 
in  swimming,  that  the  developement  of  large  organs  in  this 
position  would  materially  impede  the  progress  of  animals  pre¬ 
senting  such  a  construction  :  the  false  feet ,  as  these  organs  are 
called,  are  therefore  merely  available  as  a  means  of  fixing  the 
ova  which  the  female  lobster  carries  about  with  her  attached  be¬ 
neath  her  abdomen. 

The  tail  is  the  great  agent  of  locomotion  in  all  the  Macroura 
or  large-tailed  Decapods,  and  for  this  purpose  it  is  terminated 
by  a  fin  formed  of  broad  calcareous  lamella3,  so  arranged,  that 
while  they  will  close  together  during  the  extension  of  the  tail, 
and  thus  present  the  least  possible  surface  to  the  water,  they 
are  brought  out  to  their  full  expansion  by  the  down-stroke  of  the 
abdomen  ;  and  such  is  the  impulse  thus  given,  that,  as  we  are 
credibly  informed,  a  lobster  will  dart  itself  backwards  to  a  dis¬ 
tance  of  eighteen  or  twenty  feet  by  one  sweep  of  this  remarkable 
locomotive  instrument. 

If  we  now  pass  on  to  the  consideration  of  the  Anomourous  De- 

y  2 


324 


CRUSTACEA. 


capods ,  we  find  that  the  external  organs  above  enumerated, 
although  existing  in  precisely  similar  situations,  are  so  far  modified 
in  their  construction  and  relative  proportions  as  to  become  suited 
to  a  mode  of  life  widely  different  from  that  led  by  the  members 
of  the  last  division.  The  Anomoura ,  as  their  name  imports, 
have  tails  of  very  unusual  conformation  : — instead  of  being  en¬ 
cased  in  a  hard  coat  of  mail  as  in  the  Macroura ,  the  hinder  part 
of  the  body  is  soft  and  coriaceous,  possessing  only  a  few  detached 
calcareous  pieces,  analogous  it  is  true  to  those  found  in  the  lobster, 
but  strangely  altered  in  structure. 

These  animals  ( Jig .  153),  usually  known  by  the  name  of 
Soldier-Crabs  or  Hermit-Crabs ,  frequent  level  and  sandy  shores, 

Fig.  153. 


and,  from  their  defenceless  condition,  are  obliged  to  resort  to 
artificial  protection,  dhis  they  do  by  selecting  an  empty  tur¬ 
binated  shell  of  proportionate  size,  deserted  by  some  gasteropod 
mollusc,  into  which  they  insinuate  their  tail  ;  and,  retreating 


CllUSTACEA. 


325 


within  the  recesses  of  their  selected  abode,  obtain  a  secure  retreat, 
which  they  drag  after  them  wherever  they  go,  until,  by  growing 
larger,  they  are  compelled  to  leave  it  in  search  of  a  more  capacious 
lodging.  The  wonderful  adaptation  of  all  the  limbs  to  a  residence 
in  such  a  dwelling  cannot  fail  to  strike  the  most  incurious  ob¬ 
server.  The  chela,  or  large  claws,  differ  remarkably  in  size ; 
so  that,  when  the  animal  retires  into  its  concealment,  the  smaller 
one  may  be  entirely  withdrawn,  while  the  larger  closes  and  guards 
the  orifice.  The  two  succeeding  pairs  of  legs,  unlike  those  of 
the  lobster,  are  of  great  size  and  strength  ;  and,  instead  of  being 
terminated  by  pincers,  end  in  strong  pointed  levers,  whereby 
the  animal  can  not  only  crawl,  but  drag  after  it  its  heavy  habit¬ 
ation.  Behind  these  locomotive  legs  are  two  feeble  pairs,  barely 
strong  enough  to  enable  the  soldier-crab  to  shift  his  position  in  the 
shell  he  has  chosen  ;  and  the  false  feet  attached  to  the  abdomen 
are  even  still  more  rudimentary  in  their  developement.  But  the 
most  singularly  altered  portion  of  the  skeleton  is  the  fin  of  the 
tail,  which  here  becomes  transformed  into  a  kind  of  holding  ap¬ 
paratus,  by  which  the  creature  retains  a  firm  grasp  upon  the  bottom 
of  his  residence.  Fig.  154. 


In  the  Br achy ura ,  or  Crabs,  we  have  at  once,  in  the  concentra¬ 
tion  observable  in  all  parts  of  the  skeleton,  an  indication  of  its 


3  26 


CRUSTACEA. 


being  formed  for  progression  on  land,  or,  at  least,  for  creeping  at 
the  bottom  of  the  sea.  The  tail,  the  great  instrument  of  loco¬ 
motion  in  the  lobster,  is  here  reduced  to  a  rudiment,  and  the  fin 
at  its  extremity  entirely  obliterated ;  the  chela  still  continue 
to  be  the  most  powerfully  developed  of  the  extremities  ;  while  the 
legs,  the  principal  locomotive  agents,  are  either  terminated  by 
simple  points,  as  in  those  species  which  are  most  decidedly  ter¬ 
restrial  in  their  habits,  or  else,  in  the  swimming  crabs,  the  pos¬ 
terior  pair  become  expanded  into  flattened  oars  useful  in  nata¬ 
tion  (Jig*  154). 

(365.)  From  the  extreme  hardness  and  unyielding  character  of 
the  tegumentary  skeleton  in  Crustaceans,  a  person  unacquainted 
with  the  history  of  these  animals  would  be  at  a  loss  to  conceive  the 
manner  in  which  their  growth  could  be  effected.  In  insects  we 
have  seen  that  all  increase  of  size  occurs  prior  to  the  attainment 
of  the  perfect  condition,  and  expansion  is  provided  for  by  the 
moults  or  changes  of  skin  which  take  place  during  the  develope- 
ment  of  the  larva  ;  but  the  Crustacean,  having  acquired  its  mature 
form,  still  continues  to  grow,  and  that  until  it  acquires  in  many 
instances  a  size  far  larger  than  that  which  any  insect  is  permitted 
to  arrive  at. 

The  plan  adopted  in  the  case  before  us,  whereby  growth  is 
permitted,  is  attended  with  many  extraordinary  phenomena.  At 
certain  intervals  the  entire  shell  is  cast  off,  leaving  the  body  for 
the  time  unfettered  indeed  as  regards  the  capability  of  expansion, 
but  comparatively  helpless  and  impotent,  until  such  time  as  a  new 
shell  becomes  secreted  by  the  dermis,  and  by  hardening  assumes 
the  form  and  efficiency  of  its  predecessor. 

We  are  indebted  to  Reaumur,*  who  watched  the  process  in 
the  Cray-fish  ( Astacus  jluviatilis ),  for  what  little  is  known  con¬ 
cerning  the  mode  in  which  the  change  of  shell  is  effected.  In  the 
animal  above  mentioned,  towards  the  commencement  of  autumn, 
the  approaching  moult  is  indicated  by  the  retirement  of  the  cray¬ 
fish  into  some  secluded  position,  where  it  remains  for  some  time 
without  eating.  While  in  this  condition,  the  old  shell  becomes 
gradually  detached  from  the  surface  of  the  body,  and  a  new  and 
soft  cuticle  is  formed  underneath  it,  accurately  representing  of 
course  all  the  parts  of  the  old  covering  which  is  to  be  removed ; 
but  as  yet  little  calcareous  matter  is  deposited  in  the  newly  formed 
integument.  The  creature  now  becomes  violently  agitated,  and 

*  Mem.  de  la  Acad,  des  Sciences,  1718. 


CRUSTACEA. 


327 


by  various  contortions  of  its  body  seems  to  be  employed  in 
loosening  thoroughly  every  part  of  its  worn-out  covering  from 
all  connection  with  the  recently  secreted  investment.  This  being 
accomplished,  it  remains  to  extricate  itself  from  its  imprisonment ; 
— an  operation  of  some  difficulty  ;  and,  when  the  nature  of  the  ar¬ 
mour  to  be  removed  is  considered,  we  may  well  conceive  that  not 
a  little  exertion  will  be  required  before  its  completion.  As  soon 
as  the  old  case  of  the  cephalo-thorax  has  become  quite  detached 
from  the  cutis  by  the  interposition  of  the  newly  formed  epidermic 
layer,  it  is  thrown  off  in  one  piece  after  great  and  violent  exertion  ; 
the  legs  are  then  withdrawn  from  their  cases  after  much  strug¬ 
gling  ;  and,  to  complete  the  process,  the  tail  is  ultimately  by  long- 
continued  efforts  extricated  from  its  calcareous  covering,  and  the 
entire  coat  of  mail  which  previously  defended  the  body  is  discarded 
and  left  upon  the  sand.  The  phenomena  which  attend  this  reno¬ 
vation  of  the  external  skeleton  are  so  unimaginable,  that  it  is 
really  extraordinary  how  little  is  accurately  known  concerning  the 
nature  of  the  operation.  The  first  question  which  presents  itself 
is,  how  are  the  limbs  liberated  from  their  confinement  ?  for,  won¬ 
derful  as  it  may  appear,  the  joints  even  of  the  massive  chela  of 
the  lobster  do  not  separate  from  each  other,  but,  notwithstanding 
the  great  size  of  some  of  the  segments  of  the  claw,  and  the  slender 
dimensions  of  the  joints  that  connect  the  different  pieces,  the 
cast-off  skeleton  of  the  limb  presents  exactly  the  same  appearance 
as  if  it  still  encased  the  living  member.  The  only  way  of  ex¬ 
plaining  the  circumstance,  is  to  suppose  that  the  individual  pieces 
of  the  skeleton,  as  well  as  the  soft  articulations  connecting  them, 
split  in  a  longitudinal  direction,  and  that,  after  the  abstraction 
of  the  limb,  the  fissured  parts  close  again  with  so  much  accuracy 
that  even  the  traces  of  the  division  are  imperceptible.  But  this 
is  not  the  only  part  of  the  process  which  is  calculated  to  excite  our 
astonishment :  the  internal  calcareous  septa  from  which  the  mus¬ 
cles  derive  their  origins,  and  the  tendons  whereby  they  are  inserted 
into  the  moveable  portions  of  the  outer  shell,  are  likewise  stated 
to  be  found  attached  to  the  exuviae  ;  even  the  singular  dental 
apparatus  situated  in  the  stomach,  of  which  we  shall  speak  here¬ 
after,  is  cast  off  and  re-formed  !  And  yet,  how  is  all  this  accom¬ 
plished  ?  how  do  such  parts  become  detached  ?  how  are  they 
renewed?  We  apprehend  that  more  puzzling  questions  than 
these  can  scarcely  be  propounded  to  the  physiologist,  nor  could 
more  interesting  subjects  of  inquiry  be  pointed  out  to  those 


328 


CRUSTACEA. 


whose  opportunities  enable  them  to  prosecute  researches  connected 
with  their  elucidation.* 

(366.)  The  structure  of  the  articulations  which  unite  the  differ¬ 
ent  segments  of  the  skeletons  of  the  Articulata,  and  the  general  ar¬ 
rangement  of  their  muscular  system,  have  already  been  described  ; 
and,  in  the  class  before  us,  these  parts  of  their  economy  offer  no 
peculiarities  worthy  of  special  notice. 

(367.)  Throughout  all  the  Crustacean  families  the  alimentary 
canal  exhibits  great  simplicity  of  arrangement,  and  consists  of  a  short 
but  capacious  oesophagus,  a  stomachal  dilatation  or  cavity  in  which 
is  contained  a  singular  masticatory  apparatus,  and  a  straight  and 

*  Since  writing  the  above,  I  have  been  fortunate  in  procuring  a  very  good  specimen 
of  Astacus  fluviatilis,  obtained  soon  after  casting  its  shell,  and  also  its  newly  cast-off 
covering,  both  of  which  are  in  excellent  preservation.  The  following  is  a  description 
of  the  appearances  observed  in  each  : — All  the  pieces  of  the  exuvium  are  connected 
together  by  the  old  articulations,  and  accurately  represent  the  external  form  of  the 
complete  animal ;  the  carapace,  or  dorsal  shield  of  the  cephalo-thorax,  alone  being  de¬ 
tached,  having  been  thrown  off  in  one  piece.  The  pedicles  of  the  eyes  and  external 
corneae,  as  well  as  the  antennae,  remain  in  situ,  the  corresponding  parts  having  been 
drawn  out  from  them  as  the  finger  from  a  glove  ;  and  no  fissure  of  the  shell  or  rupture 
of  the  ligaments  connecting  the  joints  is  anywhere  visible  in  these  portions  of  the  skele¬ 
ton.  The  auditory  tubercles,  and  the  membrane  stretched  over  the  orifice  of  the  ear, 
occupy  the  same  position  as  in  the  living  cray-fish.  The  jaws,  foot-jaws,  and  ambu¬ 
latory  feet  retain  their  original  connections,  with  the  exception  of  the  right  chela,  which 
had  been  thrown  off  before  the  moult  began  ;  and  the  segments  of  the  abdomen,  false 
feet,  and  tail-fin  exactly  resembled  those  of  the  perfect  creature; — even  the  internal 
processes  derived  from  the  thoracic  segments  ( apodemata )  rather  seemed  to  have  had 
the  flesh  most  carefully  picked  out  from  among  them,  than  to  have  been  cast  away  from 
a  living  animal :  but  perhaps  the  most  curious  circumstance  observable  was,  that 
attached  to  the  base  of  each  leg  was  the  skin  which  had  formerly  covered  the  branchial 
tufts,  and  which,  when  floated  in  water,  spread  out  into  accurate  representations  of  those 
exquisitely  delicate  organs.  No  fissure  was  perceptible  in  any  of  the  articulations 
of  the  small  claws  ;  but  in  the  chela  each  segment  was  split  in  the  neighbourhood 
of  the  joints,  and  the  articulating  ligaments  ruptured.  The  lining  membrane  of  the 
stomach  was  found  in  the  thorax,  having  the  stomachal  teeth  connected  with  it  ;  from 
its  position,  it  would  seem  that  the  animal  had  dropped  it  into  the  place  where  it  lay 
before  the  extrication  of  its  limbs  was  quite  accomplished.  The  internal  tendons  were 
all  attached  to  the  moveable  joint  of  each  pair  of  forceps,  both  in  the  chela  and  in 
the  two  anterior  pairs  of  smaller  ambulatory  legs. 

On  examining  the  animal,  which  had  extricated  itself  from  the  exuvium  described 
above,  the  shell  was  found  soft  and  flexible,  but  contained  a  sufficiency  of  calcareous 
matter  to  give  it  some  firmness,  especially  in  the  claws.  The  tendons  of  the  forceps 
weie  still  perfectly  membranous,  presenting  a  very  decided  contrast  when  compared 
with  the  old  ones  affixed  to  the  discarded  shell.  The  stump  of  the  lost  chela  had  not 
as  yet  begun  to  sprout,  and  the  extremity  was  covered  by  a  soft  black  membrane.  The 
jaws  were  quite  hard  and  calcified,  as  likewise  were  the  teeth  contained  in  the  sto¬ 
mach. 


CRUSTACEA. 


329 


simple  intestinal  tube,  which  passes  in  a  direct  line  from  the  sto¬ 
mach  to  the  last  segment  of  the  abdomen,  where  it  terminates. 

The  description  of  these  parts,  as  they  exist  in  the  lobster, 
will  give  the  reader  a  sufficiently  correct  idea  of  their  general 
disposition  and  structure  ;  nor  are  we  acquainted  with  any  class 
of  animals  in  which  so  little  variety  in  the  conformation  of  this 
portion  of  the  system  is  to  be  met  with. 

The  oesophagus  is  covered  at  its  origin  by  the  several  pairs  of 
foot-jaws  already  alluded  to  ;  the  most  internal  of  which  forms 
a  decided  cutting  apparatus,  resembling  a  pair  of  strong  shears,* 
while  the  rest  are  only  instruments  of  prehension,  or,  perhaps,  of 
sensation  also.  From  the  mouth,  the  oesophagus  runs  directly  up¬ 
wards  to  the  stomach,  which  is  a  considerable  viscus  (Jig.  157,  «), 
a  large  portion  of  it  being  situated  in  that  region  of  the  cephalo- 
tliorax  which  we  should  be  tempted  to  consider  as  the  head  of  the 
animal.  The  pyloric  extremity  of  the  stomach  is  strengthened 
with  a  curious  frame-work  of  calcareous  pieces  imbedded  in  its 
walls,  and  so  disposed  as  to  support  three  large  teeth  placed  near 
the  orifice  of  the  pylorus ;  and,  being  moved  by  strong  muscles, 
teeth  so  disposed,  no  doubt,  form  an  efficient  apparatus  for  bruis¬ 
ing  the  food  before  it  is  admitted  into  the  intestine. 

The  intestine  itself  (5,  5,  b)  runs  in  a  direct  course  to  the 
tail,  imbedded  between  the  two  great  lateral  muscular  masses  that 
move  the  abdominal  segments  ;  and  terminates  upon  the  ventral 
surface  of  the  central  lamella  of  the  terminal  fin  in  a  rounded  ori¬ 
fice  closed  by  a  sphincter  muscle. 

The  liver  (c,  c,  c),  one  half  of  which  has  been  removed  in  the 
engraving,  consists  of  two  large  symmetrical  masses,  enclosing  be¬ 
tween  them  the  pyloric  portion  of  the  stomach,  and  a  third  part  of 
the  length  of  the  intestine.  When  unravelled,  the  minute  struc¬ 
ture  of  the  liver  exhibits  an  immense  assemblage  of  secerning  emea 
agglomerated  into  clusters,  from  each  of  which  a  duct  emanates, 
and  the  continued  union  of  the  ducts  so  formed  ultimately  gives 
origin  to  the  common  hepatic  canal  ( d ),  which  pours  the  bile  de¬ 
rived  from  that  division  of  the  liver  to  which  it  belongs  into  the 
intestine  at  a  very  short  distance  from  its  commencement  at  the 
pylorus.  A  little  below  the  insertion  of  the  two  bile-ducts,  a  so¬ 
litary  long  and  slender  csecum  enters  the  intestine,  but  the  nature 
of  the  secretion  furnished  by  this  organ  is  unknown. 

(368.)  Before  tracing  the  course  of  the  circulation  in  the  Crus¬ 
tacea,  it  will  be  necessary  to  consider  the  character  of  the  apparatus 


330 


CRUSTACEA. 


in  which  the  blood  is  exposed  to  the  influence  of  the  surrounding 
medium  for  the  purpose  of  respiration.  The  lowest  forms  of  these 
animals,  many  of  which  are  so  minute  as  to  require  a  microscope  for 
their  investigation,  are  not,  as  far  as  we  have  yet  been  able  to  ascer¬ 
tain,  possessed  of  any  organs  specially  to  be  regarded  as  belonging  to 
this  important  function  ;  it  would  seem,  indeed,  that  in  creatures 
of  such  small  dimensions,  and  which  are  at  the  same  time  covered 
with  an  integument  of  inexpressible  thinness  and  delicacy,  the  ne¬ 
cessity  for  any  such  organization  was  done  away  with,  the  entire 
system  being  freely  exposed  to  the  vital  element.  In  the  Bran- 
chiopod  Crustacea,  so  called  from  this  circumstance,  the  legs  used 
in  swimming  would  appear  to  be  converted  into  broad-fringed  la¬ 
mellae,  so  thin  that  they  perform  the  office  of  branchiae,  and  render 
needless  the  existence  of  other  instruments  of  respiration.  In 
Daphnia ,  for  example  (Jig*  155),  a  creature  common  in  every 
stagnant  pool,  the  body  is  contained,  as  it  wrere,  between  two 
corneous  plates  open  along  their  inferior  edge.  Through  this 
transparent  envelope  the  legs  may  be  perceived  in  constant  move¬ 
ment,  and,  from  the  extreme  delicacy  of  the  covering  that  invests 
them,  they  evidently  present  to  the  surrounding  medium  a  surface 

Fig.  155. 


of  sufficient  extent  for  the  purpose  of  exposing  the  blood  to  its 
action,  thus  rendering  them  efficient  substitutes  for  branchiae ;  while, 
at  the  same  time,  their  movements  insure  a  perpetual  renovation 
of  the  water  in  contact  with  them,  so  that,  as  a  necessary  conse¬ 
quence,  the  respiratory  process  will  be  accomplished  with  greater 
completeness  in  proportion  as  the  exertions  of  the  animal  become 
more  vigorous.  In  the  Crustacea,  indeed,  we  have  many  interest¬ 
ing  and  beautiful  examples  of  the  connection  between  the  respira¬ 
tory  and  locomotive  organs.  The  amount  of  respiration  must  ne- 


CRUSTACEA. 


331 


cessarily  be  equivalent  to  tlie  expenditure  of  muscular  energy,  and 
a  more  elegant  manner  of  insuring  an  exact  correspondence  between 
the  one  and  the  other,  than  that  adopted,  could  scarcely  be  ima¬ 
gined  ;  for,  by  appending  the  branchiae  to  the  locomotive  agents 
themselves,  the  more  actively  the  latter  are  employed,  the  more 
freely  will  the  former  receive  the  influences  of  the  aerated  water  in 
which  they  are  immersed. 

In  the  Squilla ,  which  swims  by  means  of  the  movements  of  its 
broad  tail,  it  is  the  false  feet  beneath  the  abdominal  segments  that 
become  branchial  organs  ;  and  these,  being  expanded  into  broad 
and  vascular  lamellae,  perform  the  office  of  gills.  In  the  Squilla , 
therefore,  and  similarly  formed  genera,  the  free  movement  of  the 
tail  insures  the  full  and  complete  exposure  of  the  respiratory  struc¬ 
tures  to  the  surrounding  element. 

In  the  highest  Crustacea,  as  the  Decaqioda ,  in  which  legs  of  an 
ambulatory  character  become  such  important  locomotive  agents,  it 
is  principally  to  the  origins  of  these  legs  that  we  find  the  breathing 
apparatus  appended;  and  their  active  motion  will,  consequently, 
powerfully  contribute  to  the  complete  aeration  of  the  blood.  But 
let  us  first  examine  the  structure  of  the  branchiae  themselves  in 
this  highly  organized  division,  and  subsequently  we  will  speak  of 
their  arrangement  and  connections. 

In  the  Lobster,  and  many  other  Macroura ,  the  branchiae  {fig. 
159,  m,  m)  are  pyramidal  tufts,  consisting  of  a  central  stem  covered 
over  with  vascular  filaments  disposed  perpendicularly  to  its  axis,  in 
such  a  manner  that  each  of  these  organs  when  detached  resembles 
in  some  degree  a  small  brush  :  on  cutting  the  stem  across,  it  is 
found  to  inclose  an  artery  and  a  vein,  from  which  innumerable 
branches  are  given  off  to  the  horizontal  filaments  ;  so  that  the  latter 
constitute  a  respiratory  surface  of  great  extent,  which  is  most  freely 
exposed  to  the  surrounding  medium. 

In  the  Crabs  and  Anomoura  the  structure  of  the  branchiae  is 
somewhat  different,  for  in  these  divisions  the  cylindrical  filaments 
are  replaced  by  broad  lamellae  laid  one  above  the  other,  but  in 
every  other  respect  the  arrangement  is  the  same. 

(369.)  The  respiratory  organs  above  mentioned  are  lodged 
in  two  extensive  cavities,  or  branchial  chambers,  placed  upon  the 
sides  of  the  body,  covered  by  the  broad  shield  of  the  ceplialo-thorax 
{fig.  158),  and  lined  by  a  membrane  which  is  reflected  upon  the 
root  of  each  branchia,  so  as  to  become  continuous  with  the  delicate 
layer  that  invests  every  filament  or  vascular  lamella  that  enters  into 
its  composition. 


CRUSTACEA. 


332 


The  branchial  chambers  are  in  free  communication  with  the  ex¬ 
ternal  medium  by  means  of  two  large  apertures,  through  one  of 
which  the  water  enters,  while  it  as  constantly  flows  out  through  the 
other.  The  afferent  canal  is  generally  a  wide  slit  that  allows  the 
water  freely  to  penetrate  to  the  interior  of  the  branchial  cavity;  but 
the  passage  whereby  the  respired  fluid  escapes  after  passing  over  the 
branchiae  is  provided  with  a  valvular  apparatus  so  disposed  as  to 
produce  a  continual  current  in  the  water  contained  in  the  chamber, 
and  thus,  by  insuring  its  perpetual  agitation,  effectually  provides 
for  its  constant  renewal.  The  mechanism  is  as  follows  : — The 
aperture  by  which  the  water  issues  is  in  the’  neighbourhood  of  the 
mouth,  and  is  closed  by  a  broad  semi-membranous  plate  ( Jiabel - 
him)  derived  from  the  root  of  the  second  pair  of  foot-jaws  ;  so  that 
every  motion  of  these  foot-jaws  impresses  a  corresponding  move¬ 
ment  upon  the  valve-like  Jlabellum,  and  in  this  manner  urges  on  the 
passage  of  the  water  out  of  the  cavity  in  which  the  branchiae  are 
lodged. 


Fig.  156. 


But  there  are  other  means  whereby  the  action  of  the  limbs  is 
made  to  assist  in  the  perfection  of  the  respiratory  process.  Thus, 
in  the  lobster,  the  third  pair  of  foot-jaws,  and  each  pair  of  ambula¬ 
tory  legs,  except  the  last,  supports  a  flabelliform  plate  (Jig.  159,  n); 
the  movements  of  which  must  likewise  keep  the  fluid  respired 
in  a  state  of  agitation,  and  moreover,  by  gently  squeezing  and  com¬ 
pressing  the  respiratory  tufts,  powerfully  contribute  to  the  per¬ 
fect  renovation  of  the  water  in  contact  with  the  surfaces  of  the 
branchiae. 

In  the  crab  genera  the 
arrangement  is  slightly  mo¬ 
dified,  for  here  there  are 
three  jiabella  derived  ex¬ 
clusively  from  the  roots  of 
the  foot-jaws  (Jig.  156,  5, 
c,  d) :  of  these,  two  are  im¬ 
bedded  among  the  bran¬ 
chiae  ;  while  the  third,  as 
represented  in  the  figure, 
extends  in  a  crescentic 
form  over  the  external 
surface  of  the  whole  series 
of  those  organs.  The 


end  answered  in  this  case  is  obviously  the  same  as  that  accom- 


CRUSTACEA. 


333 


plisliecl  in  the  lobster,  in  a  different,  and,  perhaps,  more  efficient 
manner.  Fig.  157. 

(370.)  In  the 
lowest  Crustacea  the 
heart  is  a  long  dor¬ 
sal  vessel,  not  very 
dissimilar  in  form 
and  disposition  from 
that  of  insects;  but 
of  course  giving  off 
arteries  for  the  distri¬ 
bution  of  the  blood, 
and  receiving  veins 
through  which  the 
blood,  having  ac¬ 
complished  its  cir¬ 
cuit,  is  returned. 

In  the  Decapoda 
the  organ  becomes 
m  ore  cen  tral  i  ze  d ,  an  d 
in  the  lobster  (Jig. 

157,  e)  the  heart  is 
found  to  be  an  oval 
viscus,  situated  in 
the  mesial  line  of 
the  body,  beneath 
the  posterior  part 
of  the  cephalo-tho- 
rax ;  it  is  composed 
of  strong  muscular 
bands,  and  contains 
a  single  cavity  of 
considerable  size. — 

The  contractions  of 
this  heart  are  very 
vigorous,  and  may 
readily  be  witnessed 
by  raising  the  super¬ 
jacent  shell  in  the 
living  animal. 

Several  large  arte- 


334 


CRUSTACEA. 


ries  are  derived  form  the  above-mentioned  simple  heart.  A  consider¬ 
able  trunk  {Jig.  157, g9)  Fig,  158. 
goes  from  its  anterior 
extremity  to  supply  the 
eyes,  antennae,  stomach, 
and  neighbouring  or¬ 
gans  :  another,  the  he¬ 
patic  (z),  which  is 
sometimes  double,  sup¬ 
plies  the  two  lobes  of 
the  liver  :  a  third  large 
vessel  (h)  supplies  the 
abdominal  or  caudal  re¬ 
gion  :  and  a  fourth,  the 
sternal ,  derived  from 
the  posterior  apex  of 
the  heart,  bends  down 
to  the  ventral  aspect  of 
the  body,  where  it  di¬ 
vides  ;  the  posterior  di¬ 
vision  (/,  /)  supplying 
the  lower  parts  of  the 
abdomen,  while  the  an¬ 
terior  and  larger  divi¬ 
sion  (m)  gives  off 
branches  to  the  legs 
and  foot-jaws  ( n ,  n,  n, 

n ) ;  it  likewise  furnishes 
other  vessels  (0,  o,  0, 

o)  which  are  distribut¬ 
ed  through  the  bran¬ 
chiae. 

The  venous  svstem 
is  made  up  of  large  and 
delicate  sinuses  that 
communicate  freely 
with  each  other,  and 
receive  the  blood  from 
all  parts  of  the  body. 

Those  of  the  dorsal  re¬ 
gion  are  represented  in  the  annexed  figure:  {Jig-  158),- a  large 


CRUSTACEA. 


335 


venous  sinus  (a)  occupies  the  cephalic  region,  and  covers  the  sto¬ 
mach  ;  another  cavity  (5)  lies  immediately  above  the  heart ;  and  a 
series  of  smaller  chambers  ( c ,  c,  c,  c )  are  situated  above  the  muscles 
of  the  caudal  region.  These  cavities,  notwithstanding  their  appa¬ 
rent  extent,  are  very  shallow ;  so  that,  upon  a  transverse  section, 
their  dimensions  are  by  no  means  so  great  as  a  superficial  view 
would  indicate.  The  sinus  (5),  or  that  placed  immediately  over 
the  heart,  communicates  with  that  viscus  by  short  trunks,  the  termi¬ 
nations  of  which  in  the  heart  are  guarded  by  valves  (Jig.  157, 
jf,  /,  f )  so  disposed  as  to  allow  the  blood  to  pass  from  the  sinus 
into  the  heart,  but  prevent  its  return  in  an  opposite  direction. 

(371.)  Such  is  the  apparatus  provided  in  the  lobster  for  the  cir¬ 
culation  of  the  blood.  Our  next  inquiry  must  be  concerning  the 
course  that  it  pursues  during  its  circuit  through  the  body. 

Messrs.  Audouin  and  Milne  Edwards,*  after  very  minutely 
examining  this  subject,  came  to  the  conclusion  that  the  heart  is 
purely  of  a  systemic  character,  being  only  instrumental  in  propel¬ 
ling  the  blood  through  the  body,  but  having  nothing  to  do  with 
the  branchial  circulation  ;  they  conceived  that  the  circulating  fluid, 
having  been  collected  in  the  venous  sinuses,  was  brought  to  the 
roots  of  the  branchise,  over  which  it  was  distributed  by  venous 
tubes,  and  then  returned  to  the  heart  by  vessels  which  they  call 
branchio-cardiac  to  recommence  the  same  course.  The  appended 
figures,  however,  which  are  accurately  copied  from  engravings  of 
the  Hunterian  drawings  in  the  collection  of  the  Royal  College  of 
Surgeons, j-  would  seem  to  give  great  reason  to  doubt  the  accuracy 
of  the  conclusions  arrived  at  by  the  eminent  naturalists  referred 
to  ;  and  to  show  that  the  heart,  instead  of  being  purely  systemic,  is 
partly  branchial,  and  impels  the  blood,  not  through  the  body  only, 
but  also  to  the  respiratory  organs.  This  view  of  the  subject, 
which  we  are  disposed  to  consider  as  the  most  correct,  is  exhibited 
in  the  diagram  annexed.  Setting  out  from  the  heart,  we  find  that 
the  blood  goes  to  all  parts  of  the  body  through  the  different 
arterial  trunks,  and  by  the  great  sternal  artery  (Jig.  157,  k)  is  con¬ 
veyed  to  the  legs,  foot-jaws,  and  false  feet.  But  from  this  same 
artery  (m),  vessels,  o,  o,  o,  o,  are  furnished  to  the  branchise.  The 
branchial  arteries  so  derived  (Jig.  159,  g)  subdivide  into  secondary 

*  Recherches  Anatomiques  et  Physiologiques  sur  la  Circulation  dans  les  Crustaces. 
A nnales  des  Sciences  Nat.  tom.ii. 

t  Catalogue  of  the  Physiological  Series  of  Comparative  Anatomy  contained  in  the 
Museum  of  the  Royal  College  of  Surgeons  ;  vol.  ii. 


386 


CRUSTACEA. 


trunks  (A,  A,  A),  which  ramify  through  the  individual  branchiae,  and 
supply  all  their  appended  filaments.  Having  undergone  exposure  to 

Fig.  159. 


a 


the  respired  medium,  the  blood  is  again  collected  from  the  branchiae 
by  branchial  veins  (A,  A,  A)  represented  on  the  opposite  side  of 
the  body,  and  conveyed  by  the  large  vessel,  /,  to  the  dorsal  sinus 
(Jig.  158,  A),  where,  being  mixed  up  with  the  general  mass  of 
blood  contained  in  the  sinus,  the  circulating  fluid  is  admitted  into 
the  heart  through  the  valvular  orifices  (d,  d),  to  recommence  the 
same  track. 

(372.)  As  might  be  anticipated  from  an  examination  of  the  ex¬ 
ternal  configuration  of  the  different  families  comprised  in  the  exten¬ 
sive  class  we  are  now  considering,  the  nervous  system  is  found  to 
pass  through  all  those  gradations  of  developement  which  we  have 
found  gradually  to  present  themselves  as  wc  have  traced  the  Homo- 
gangliata  from  the  lowest  to  the  most  highly  organized  types  of 
structure.  In  the  most  imperfect  Crustacea,  indeed,  we  find  a 
simplicity  of  arrangement  greater  than  any  hitherto  pointed  out 
even  in  the  humblest  Annelida  ;  a  disposition  of  parts  which  the¬ 
oretically  might  have  been  expected  to  exist,  but  has  only  been 
distinctly  recognised  in  the  class  before  us. 

We  have  all  along  spoken  of  the  nervous  centres  of  the  Arti- 
culata  as  arranged  in  symmetrical  pairs,  although  in  no  example 


CRUSTACEA. 


337 


which  has  yet  occurred  to  our  notice  have  we  been  able  strictly  to 
point  out  the  accuracy  of  such  a  view  of  the  subject.  The  two 
lateral  masses  of  the  supra-cesophageal  ganglion  are  found  united 
into  one  brain  in  the  humblest  forms  of  annulose  animals,  and  even 
in  the  ganglia  forming  the  ventral  series,  although  we  might  pre¬ 
sume  each  to  be  composed  of  two  symmetrical  halves,  the  divisions 
are  most  frequently  so  intimately  blended,  that  their  distinctness 
is  not  susceptible  of  anatomical  demonstration.  In  some  of  the 
Crustacea,  however,  among  those  species  which  have  the  segments 
of  their  external  skeleton  most  perfectly  separate  and  distinct,  the 
nervous  system  is  found  to  present  itself  in  such  a  condition  that 
the  division  into  lateral  halves  is  perfectly  evident ;  and  from  this 
condition  their  progressive  coalescence  may  be  traced  step  by 
step  until  we  arrive  at  a  state  of  concentration  as  remarkable 
as  that  already  noticed  in  the  most  elevated  of  the  Arachnidans. 
It  is  to  Milne  Edwards  and  Audouin  that  we  are  indebted  for 
the  interesting  particulars  connected  with  this  part  of  our  sub¬ 
ject  ;  and  the  results  of  their  investigations  are  of  such  great 
physiological  importance,*  that  the  following  condensed  ac¬ 
count  of  their  labours  cannot  be  omitted  in  this  place.  In 
Talitrus  every  pair  of  ganglia  consists  of  two  separate  nuclei  of 
nervous  substance,  united  by  a  transverse  band  so  disposed  as  to 
bring  them  into  communication  with  each  other,  while  an  anterior 
and  posterior  nervous  filament  derived  from  each  unites  it  with  the 
preceding  and  following  ganglia  of  the  same  side  of  the  body ; 
even  the  encephalic  mass  is  composed  of  two  lateral  portions  united 
by  a  cord  passing  between  them  :  all  these  pairs  of  ganglia,  thir¬ 
teen  in  number,  corresponding  with  the  number  of  the  segments 
of  the  body,  are  exact  counterparts  of  each  other  both  in  size  and 
figure,  so  that  none  seems  to  preponderate  in  energy  over  the  rest  ; 
but  the  anterior  or  encephalic  pair  alone  communicates  with  the 
eyes  and  antennse,  the  only  organs  of  the  senses  as  yet  discernible. 

In  Oniscus  Asellus  a  concentration  of  the  elements  composing 
the  nervous  system  above  described  is  discernible,  and  this  is  found 
to  be  indicated  by  incipient  approximation,  which  takes  place  in 
two  directions ,  one  longitudinal,  the  other  acting  transversely.  In 
the  first  place,  the  entire  number  of  pairs  of  ganglia  is  reduced  to 
ten,  three  pairs  having  become  obliterated  by  coalescence  ;  and, 
moreover,*  while  the  central  portions  still  consist  of  two  lateral 

*  Recherches  Anatomiques  sur  le  Systeme  Nerveux  des  Crustac6s.  Annales  des 
Sciences  Nat.  tom.  xiv. 


z 


338 


CRUSTACEA. 


masses  each,  the  first  and  last  pairs  are  united  into  single  ganglia. 
As  we  rise  to  higher  forms  the  coalescence  still  proceeds  :  all  the 
pairs  of  ganglia  soon  become  united  in  a  transverse  direction,  and 
gradually  the  whole  chain  becomes  shorter  by  the  confusion  of 
several  pairs  into  larger  and  more  powerful  masses. 

In  the  Crab ,  which,  from  its  terrestrial  habits,  holds  a  position 
among  the  Crustacea  equivalent  to  that  which  Spiders  occupy 
among  other  Articulata,  this  centralization  is  carried  to  the  utmost 
extent ;  and  all  the  abdominal  and  thoracic  ganglia  become  agglo¬ 
merated  into  one  great  centre,  from  which  nerves  radiate  to  the 
parts  of  the  mouth  and  instruments  of  locomotion  ( Jig .  160). 

(373.)  But  this  change  Fig.  igo. 

in  the  condition  of 
the  nervous  system 
is  not  only  observ¬ 
able  as  we  proceed 
from  species  to  spe¬ 
cies,  as  they  rise 
higher  in  the  scale 
of  developement ;  si¬ 
milar  phenomena  are 
met  with  in  watch¬ 
ing  the  progress  of 
any  individual  be¬ 
longing  to  the  more 
perfect  families,  as  it  advances  from  the  embryo  to  its  ma¬ 
ture  condition.  Thus  in  the  Cray-fish  ( Astacus  fluviatilis ), 
Rathke*  observed,  that,  when  first  perceptible,  the  nervous  system 
consisted  of  eleven  pairs  of  ganglia,  perfectly  distinct  from  each 
other,  and  situated  on  each  side  of  the  mesial  line  of  the  body. 
The  six  first  pairs  then  unite  transversely,  so  as  to  form  as  many 
single  masses,  from  which  the  nerves  of  the  mandibles  and  foot- 
jaws  emanate ;  while  the  five  posterior,  from  which  the  nerves  of 
the  ambulatory  extremities  are  given  oflP,  remain  separate.  Such  is 
the  state  at  birth,  or  on  leaving  the  egg ;  but  further  changes  occur 
before  the  Cray-fish  arrives  at  maturity.  The  four  anterior  gan¬ 
glia,  which  supply  nerves  to  the  mandibles  and  foot-jaws,  are,  by 
degrees,  all  consolidated  into  one  mass,  and  the  fifth  and  sixth 
likewise  coalesce,  while  the  other  pairs  continue  permanently  dis- 


*  Untersnchungen  iiber  die  Bildung  des  Flusskrebses — in  the  Annales  des  Sciences 
Nat.  tom.  xx. 


CRUSTACEA. 


339 


tinct.  The  reader  will  at  once  recognise  the  resemblance  be¬ 
tween  these  changes  and  those  already  described  as  taking  place 
during  the  progress  of  evolution  in  the  caterpillar :  the  same 
great  law  is,  in  fact,  in  operation  in  both  cases,  and  the  same 
results  are  obtained  from  the  completion  of  the  process.* 

From  a  review  of  the  above  facts,  Milne  Edwards  and  Au- 
douin  arrived  at  the  following  conclusions  : — 1st.  That  the  ner¬ 
vous  system  of  Crustacea  consists  uniformly  of  medullary  nuclei 
(ganglions),  the  normal  number  of  which  is  the  same  as  that  of 
the  segments  or  rings  of  the  body.  £2.  That  all  the  modifications 
encountered,  whether  at  different  periods  of  the  developement  or 
in  different  species  of  the  series,  depend  especially  on  the  more  or 
less  complete  approximation  of  these  nuclei,  and  to  an  arrest  of 
developement  in  some  of  their  number.  3.  That  approximation 
takes  place  from  the  sides  towards  the  mesian  line,  as  well  as  in  a 
longitudinal  direction. 

Fig.  16]. 


(374.)  In  the  Crab  the  distribution  of  the  nerves  is  briefly  as 
follows : — The  encephalic  mass,  or  brain,  which  still  occupies  its 

*  For  a  minute  account  of  the  arrangement  of  the  nervous  system  in  these  animals, 
the  reader  is  referred  to  the  Cyclop,  of  Anat.  and  Phys.  art.  Crustacea  ;  by  Dr.  Milne 
Edwards. 

Z  ^ 


340 


CliUSTACEA. 


position  above  tlie  oesophagus,  and  joins  the  abdominal  centre  by 
two  long  cords  of  connection  ( Jig .  161),  gives  off  nerves  to  the 
eyes  and  muscles  connected  with  them,  as  well  as  to  the  antennae 
and  neighbouring  parts. 

Near  the  centre  of  each  division  of  the  nervous  collar  that 
surrounds  the  oesophagus  is  a  ganglionic  enlargement,  from  which 
arises  a  nerve  that  runs  to  the  mandibles,  and  also  a  very  import¬ 
ant  branch,  apparently  the  representative  of  the  nervus  vagus  of 
insects.  This,  after  ramifying  largely  upon  the  coats  of  the  sto¬ 
mach,  joins  that  of  the  opposite  side  ;  and,  assuming  a  ganglionic 
structure,  is  ultimately  lost  upon  the  intestine. 

The  nerves  of  the  extremities,  derived  from  the  central  abdo¬ 
minal  ganglion,  are  represented  in  the  preceding  figure  (fig-  161), 
which  requires  no  explanation.* 

(375.)  We  have  already  (§  313),  when  describing  the  nervous 
system  of  insects,  hinted  at  the  probable  existence  in  the  Homo- 
gangliata  of  distinct  tracts  of  nervous  matter  in  the  composition 
of  the  central  chain  of  ganglia,  and  in  the  filaments  whereby  they 
are  connected  with  each  other :  reasoning  therefore  from  analogy, 
it  seems  fair  to  presume  that,  if  this  be  the  case,  such  tracts  corre¬ 
spond  with  the  sensitive  and  motor  columns  which  have  been  dis¬ 
tinctly  proved  to  exist  in  the  spinal  axis  of  vertebrate  animals. 
It  is  to  Mr.  Newport  that  we  are  indebted  for  the  first  indication 
of  this  interesting  fact  ;  j'  and  the  accuracy  of  his  observations  is 
readily  demonstrable  by  a  careful  examination  of  the  ganglionic 
chain  of  the  lobster  and  other  large  Crustacean  species.  Each 
ganglionic  enlargement  is,  upon  close  inspection,  clearly  seen  to 
consist  of  two  portions  ;  first  of  a  mass  of  cineritious  nervous  sub¬ 
stance  forming  the  inferior  aspect  of  the  ganglion,  and  of  a  cord  of 
medullary  or  fibrous  matter  which  passes  over  the  dorsal  or 
superior  aspect,  and  appears  to  be  distinct  from  the  grey  substance 
over  which  it  passes  :  supposing,  therefore,  the  longitudinal  chain 
to  consist  of  anterior  and  posterior  fasciculi,  as  in  the  medulla 
spinalis ,  we  have  the  anterior  columns  communicating  with  grey 
substance,  while  the  posterior  are  unconnected  therewith,  but  are 
continued  over  the  ganglion  instead  of  becoming  amalgamated  with 
its  substance.  Another  fact,  which  favours  Mr.  Newport’s  view  of 
this  subject,  is  derived  from  an  examination  of  the  manner  in 
which  the  nerves  given  off*  from  the  central  axis  take  their  origin ; 

*  Vide  Swan  ;  Comparative  Anat.  of  the  Nervous  System.  London,  4to. 

t  Phil.  Transact.  1834. 


CRUSTACEA. 


341 


for  some  of  them  undoubtedly  proceed  from  the  cineritious  portion 
of  the  ganglionic  swelling,  while  others,  derived  from  the  upper 
column,  not  only  have  no  connection  with  the  grey  matter,  but 
arise  at  some  distance  from  the  ganglion  {Jig.  138)  :  judging, 
therefore,  by  the  laws  at  present  established  in  physiology,  there 
seems  reason  to  suppose  that  the  anterior  or  rather  inferior  fasciculi 
are  connected  with  sensation,  while  the  superior  constitute  the 
motor  tract. 

The  reader  who  is  conversant  with  human  physiology  will  at 
once  perceive  that  this  arrangement  is  precisely  the  reverse  of 
that  met  with  in  man  and  other  Vertebrata  :  and  this  consi¬ 
deration,  apparently  of  little  importance,  has  given  rise  to  a  va¬ 
riety  of  curious  speculations  ;  some  anatomists  having  even  gone 
so  far  as  to  assert  that  all  the  organs  of  articulated  animals  are 
in  reality  placed  in  a  similar  inverted  position. 

(376.)  A  more  interesting  inquiry  connected  with  this  part  of 
our  subject  is,  concerning  the  extent  to  which  the  Articulata 
are  susceptible  of  pain.  Is  it  really  true  in  philosophy,  as  it 
has  become  a  standing  axiom  in  poetry,  that — 

“  the  poor  beetle,  that  we  tread  upon. 

In  corporal  sufferance  feels  a  pang  as  great 
As  when  a  giant  dies”  ? 

This  is  a  question  upon  which  modern  discoveries  in  science 
entitle  us  to  offer  an  opinion,  and  the  result  of  the  investigation 
would  seem  to  afford  more  enlarged  views  relative  to  the  benefi¬ 
cence  displayed  in  the  construction  of  animals  than  the  assertion  of 
the  poet  would  lead  us  to  anticipate.  Pain,  “  Nature’s  kind 
harbinger  of  mischief,”  is  only  inflicted  for  wise  and  important 
purposes, — either  to  give  warning  of  the  existence  of  disease,  or  as 
a  powerful  stimulus  prompting  to  escape  from  danger.  Acute 
perceptions  of  pain  could  scarcely,  therefore,  be  supposed  to  exist 
in  animals  deprived  of  all  power  of  remedying  the  one  or  of 
avoiding  the  other.  In  man  the  power  of  feeling  pain  indubitably 
is  placed  exclusively  in  the  brain  ;  and,  if  communication  be  cut  off 
between  this  organ  and  any  part  of  the  body,  pain  is  no  longer 
felt,  wdiatever  mutilations  may  be  inflicted. 

The  medulla  spinalis ,  which,  as  we  shall  see  hereafter,  corre¬ 
sponds  to  the  ventral  chain  of  ganglia  in  articulated  animals,  can 
perceive  external  impressions  and  originate  motions,  but  not  feel 
pain  ;  hence  we  may  justly  conclude  that  in  the  Homogangliata, 
likewise,  the  supra-cesophageal  ganglia,  the  representatives  of  the 


342 


CRUSTACEA. 


brain,  and  the  sole  correspondents  with  the  instruments  of  the 
higher  senses,  are  alone  capable  of  appreciating  sensations  of  a 
painful  character.  Thus,  then,  we  arrive  at  a  very  important  con¬ 
clusion, — namely,  that  the  perception  of  pain  depends  upon  the 
developement  of  the  encephalic  masses  ;  and  consequently,  that,  as 
this  part  of  the  nervous  system  becomes  more  perfect,  the  power 
of  feeling  painful  impressions  increases  in  the  same  ratio  : — or, 
in  other  words,  that,  inasmuch  as  the  strength,  activity,  and  intel¬ 
ligence  of  an  animal,  by  which  it  can  escape  from  pain,  depends 
upon  the  perfection  of  the  brain,  so  does  the  perception  of  torture 
depend  upon  the  condition  of  the  same  organ.  How  far  the  feel¬ 
ing  of  pain  is  acutely  developed  in  the  animals  we  are  now  consi¬ 
dering  is  deducible  from  every-day  observation.  The  fly  seized 
by  the  leg  will  leave  its  limb  behind,  and  alight  with  apparent 
unconcern  to  regale  upon  the  nearest  sweets  within  its  reach : 
the  caterpillar  enjoys,  to  all  appearance,  a  tranquil  existence 
while  the  larvse  of  the  Ichneumon ,  hatched  in  its  body,  devour  its 
very  viscera  :  and  in  the  Crustacea  before  us,  of  so  little  import¬ 
ance  is  the  loss  of  a  leg,  that  the  lobster  will  throw  off  its  claws 
if  alarmed  by  the  report  of  a  cannon. 

(377.)  The  singular  power  of  breaking  off  their  own  limbs, 
alluded  to  in  the  last  paragraph,  is  possessed  by  many  Crustacea, 
and  is  a  very  indispensable  provision  in  their  economy.  We  have 
already  found  the  blood-vessels  of  these  animals  to  be  of  a  delicate 
structure ;  and,  the  veins  being  wide  sinuses  whose  walls  possess 
little  contractility,  the  fracture  of  a  limb  would. inevitably  produce 
an  abundant  and  speedily  fatal  haemorrhage  was  there  not  some  con¬ 
trivance  to  remedy  the  otherwise  unavoidable  results  of  such  a  catas¬ 
trophe.  Should  the  claw  of  a  lobster,  for  example,  be  accidentally 
damaged  by  accidents  to  which  creatures  encased  in  such  brittle 
armour  must  be  perpetually  exposed,  the  animal  at  once  breaks 
off  the  injured  member  at  a  particular  part, — namely,  at  a  point 
in  the  second  piece  from  the  body  ;  and  by  this  operation,  which 
seems  to  produce  no  pain,  the  bleeding  is  effectually  staunched. 

But  the  most  remarkable  part  of  the  phenomenon  remains  to  be 
noticed  : — after  this  extraordinary  amputation  has  been  effected, 
another  leg  begins  to  sprout  from  the  stump,  which  soon  grows  to 
be  an  efficient  substitute  for  the  lost  extremity,  and  gradually, 
though  slowly,  acquires  the  pristine  form  and  dimensions  of  its  pre¬ 
decessor.  A  beautiful  example  of  this  curious  mode  of  reprodu¬ 
cing  a  lost  organ  is  preserved  in  the  Museum  of  Comparative  Ana- 


CRUSTACEA. 


343 


tomy  in  King’s  College,  London,  in  which  the  new  limb  (one  of  the 
cheliferous  claws)  has  already  attained  the  form  of  the  old  chela,  but 
still  remains  soft  and  uncovered  by  calcareous  integument.  The  pro¬ 
cess  of  reproduction  is  as  follows  :  —  The  broken  extremity  of  the 
second  joint  skins  over,  and  presents  a  smooth  vascular  membrane, 
at  first  flat,  but  soon  becoming  conical  as  the  limb  begins  to  grow. 
As  the  growth  advances,  the  shape  of  the  new  member  becomes 
apparent,  and  constrictions  appear,  indicating  the  position  of  the 
articulation ;  but  the  whole  remains  unprotected  by  any  hard  cover¬ 
ing  until  the  next  change  of  shell,  after  which  it  appears  in  a  pro¬ 
per  case,  being,  however,  still  considerably  smaller  than  the  cor¬ 
responding  claw  on  the  opposite  side  of  the  body,  although  equally 
perfect  in  all  its  parts. 

(378.)  The  observations  made  in  a  former  chapter  relative  to  the 
organs  by  which  the  senses  of  touch ,  taste,  and  smell  are  exercised 
in  insects,  are  equally  applicable  to  the  animals  composing  the 
class  before  us ;  for  in  the  Crustacea,  although  we  are  compelled  to 
admit  the  possession  of  the  above  faculties,  we  are  utterly  ignorant 
of  the  mode  in  which  tliev  are  exercised,  and  therefore  it  would  be 
only  an  unprofitable  waste  of  time  to  enter  at  any  length  into  a 
discussion  from  which  no  satisfactory  conclusions  are,  in  the  pre¬ 
sent  state  of  our  knowledge,  to  be  deduced. 

(379.)  The  eyes  of  Crustaceans  are  of  three  kinds,  simple ,  ag¬ 
glomerated,  and  compound. 

The  simple  eyes  {ocelli,  stemmata)  resemble  those  of  spiders,  and, 
like  them,  are  said  to  consist  of  a  cornea,  a  spherical  lens,  a  gelatin¬ 
ous  vitreous  humour,  a  retina  and  deeply-coloured  choroid,  all  occu¬ 
pying  their  usual  relative  positions.  These  eyes  never  exceed  two 
or  three  in  number. 

In  the  agglomerated  eyes,  such  as  those  of  Daphnia  {Jig.  155), 
the  organ  seems  to  be  composed  of  a  number  of  simple  eyes  placed 
behind  one  common  cornea  ;  such  eyes  are  moveable,  and,  in  the 
animal  depicted  in  the  figure,  the  muscles  acting  upon  the  visual 
apparatus,  which  in  this  case  is  single,  are  arranged  so  as  to  form  a 
cone  the  base  of  which  is  formed  by  the  eye  and  may  be  distinctly 
seen  under  a  good  microscope. 

The  compound  eyes  appear  to  be  constructed  upon  the  same  prin¬ 
ciples  as  those  of  insects.  The  cornese  are  extremely  numerous 
and  generally  hexagonal  ;  but  sometimes,  as  in  the  lobster,  they  are 
square.  The  vitreous  humours  equal  the  cornese  in  number,  and 
behind  each  of  these  a  distinct  retina  would  seem  to  be  expanded. 


344 


CRUSTACEA. 


The  compound  eyes  of  Crustaceans  have  not,  however,  as  yet  been 
examined  with  the  same  patient  diligence  as  those  of  the  cock- 
chaffer  ;  so  that,  as  relates  to  their  minute  anatomy,  much  is  still  left 
to  conjecture  and  uncertainty.  One  peculiarity  connected  with 
these  organs  is,  that  in  the  two  highest  orders  of  Crustacea,  hence 
called  Podophthalmia ,  the  eyes  are  placed  at  the  extremity  of 
moveable  pedicles  articulated  with  the  first  cephalic  ring  of  the  ex¬ 
ternal  skeleton,  and  thus  they  may  be  turned  in  various  directions 
without  moving  the  whole  body  at  the  same  time.  This  provision 
was  not  required  in  insects,  owing  to  the  mobility  of  the  head  in 
those  animals;  but  is  absolutely  indispensable  in  the  case  before  us, 
where,  the  head  and  thorax  being  consolidated  into  one  mass,  the 
extent  of  vision  commanded  by  sessile  eyes  would  have  been  ex¬ 
ceedingly  limited,  and  inadequate  to  the  security  of  creatures  ex¬ 
posed  to  such  innumerable  enemies. 

(380.)  It  is  in  the  higher  Crustacea  that  we,  for  the  first  time, 
indubitably  find  a  distinct  auditory  apparatus  ;  and,  from  the 
simplicity  which  the  organ  of  hearing  presents  in  this  its  earliest 
appearance,  an  inquiry  concerning  its  structure  becomes  of  great 
physiological  interest.  In  the  lobster  the  ears  are  situated  upon 
the  under  surface  of  the  basal  joints  of  the  second  pair  of  antennae. 
On  looking  carefully  in  this  situation  the  student  will  find  a  pro¬ 
minent  tubercle  formed  by  the  shell,  the  top  of  which  is  perforated 
by  a  small  circular  opening  covered  with  a  tense  membrane.  Be¬ 
hind  this  orifice  is  placed  a  minute  vesicle  filled  with  fluid,  upon 
which  a  delicate  branch  of  the  antennary  nerve  is  distributed. 
This  constitutes  the  whole  apparatus :  --  the  vibration  of  the  water 
strikes  upon  the  external  membrane,  the  water  in  the  sacculus 
participates  in  the  tremor,  and  the  expanded  nerve  conveys  to  the 
brain  the  sensation  thus  produced. 

In  the  Brachyura ,  or  crabs,  the  membrane  covering  the  external 
orifice  of  the  ear  is  converted  into  a  moveable  calcareous  lamella, 
from  which,  in  some  genera,  a  furcate  process  is  continued  inter¬ 
nally  ;  so  that  the  whole,  when  removed  by  maceration,  has  no 
very  distant  resemblance  to  the  stapes  of  the  human  ear,  and,  like 
it,  seems  to  be  acted  upon  by  muscular  fasciculi,  so  disposed  as  to 
regulate  the  tension  of  the  vibratile  membrane,  and  thus  adapt  it  to 
receive  impressions  of  variable  intensity. 

(381.)  One  of  the  first  circumstances  calculated  to  attract  the 
notice  of  the  anatomist  who  turns  his  attention  to  the  structure  of 
the  generative  system  both  in  male  and  female  Crustacea,  is  the 


CRUSTACEA. 


345 


complete  separation  which  exists  between  the  organs  belonging  to  the 
two  sides  of the  body;  for  not  Fig.  162. 

only  are  the  internal  secret¬ 
ing  viscera  for  the  most  part 
perfectly  distinct  from  each 
other,  but  even  the  external 
sexual  orifices  are  equally  se¬ 
parate  and  unconnected. 

(382.)  Beginning  with  the 
parts  observable  in  the  male, 
we  will  take  the  cray-fish  ( As - 
tacus  jhiviatilis)  as  a  standard 
of  comparison,  and  briefly 
notice  the  principal  variations 
from  the  type  of  structure, 
observable  in  that  species, 
met  with  in  other  genera. 

In  the  cray-fish  and  also 
in  the  lobster,  the  secerning 
organs  or  testes,  when  exa¬ 
mined  in  situ ,  are  found  to  occupy  the  dorsal  region  of  the  thorax, 
lying  upon  the  posterior  part  of  the  stomach. 

Examined  superficially,  the  testes  would  seem  to  form  but  one 
mass  consisting  of  three  lobes  ( Jig .  162,  a ,  «,  b)  ;  but,  on  investi¬ 
gating  the  minute  structure  of  the  organ,  it  is  found  to  be  made  up 
of  very  delicate  secreting  tubes  that  give  origin  to  two  excretory 
ducts  (c,  c).  After  numerous  convolutions,  which  form  a  kind  of 
epididymis  (d),  each  duct,  becoming  slightly  dilated,  terminates  by 
a  distinct  orifice  (f),  seen  upon  the  basal  articulations  of  the  last 
pair  of  ambulatory  legs.  There  is  no  intromittent  apparatus  visible  ; 
but,  according  to  Milne  Edwards,*  the  extremity  of  the  excretory 
duct,  by  undergoing  a  kind  of  tumefaction,  may  be  protruded  exter¬ 
nally,  so  as  to  become  efficient  in  directing  the  course  of  the  fecun¬ 
dating  fluid. 

In  crabs  the  mass  of  the  testis  is  exceedingly  large,  but  in  its 
essential  structure  similar  to  that  of  the  cray-fish,  and  the  external 
opening  of  its  excretory  duct  is  found  to  occupy  the  same  situation: 
in  some  genera,  however,  instead  of  being  placed  upon  the  first 
joint  of  the  last  pair  of  legs,  the  orifices  of  the  male  organs  are 
found  upon  the  abdominal  surface  of  the  last  thoracic  ring  itself. 

*  Cyclop,  of  Anat.  and  Phys.  art.  Crustacea. 


346 


CRUSTACEA. 


(383.)  The  female  generative  organs  of  Crustacea  very  accurately 
resemble  those  of  the  male  ;  and  in  the  unimpregnated  condition  it 
is  not  always  easy,  from  a  superficial  survey  of  the  internal  viscera, 
to  determine  the  sex.  In  Astacus  Fig.  163. 

Jluviatilis ,  the  ovaria  (Jig.  163,  a ) 
occupy  a  position  analogous  to  that 
of  the  male  testis,  and  a  simple 
canal  derived  from  each  side  ( b ,  c) 
conducts  the  eggs  to  the  external 
apertures  found  upon  the  first  joint 
of  the  third  pair  of  legs. 

In  crabs  an  important  addition 
is  made  to  the  female  generative 
system  prior  to  the  termination 
of  each  oviduct  it  is  found  to  com¬ 
municate  with  a  wide  sacculus,  the 
function  of  which  is  apparently  ana¬ 
logous  to  that  of  the  spermatlieca 
of  insects  (§  328),  inasmuch  as  it  seems  to  form  a  receptacle  for  the 
fecundating  secretion  of  the  male,  in  which  the  seminal  fluid  re¬ 
mains  ready  to  impregnate  the  ova  as  they  successively  pass  its 
orifice  during  their  expulsion  from  the  body. 

It  is  not  precisely  known  in  what  manner  copulation  is  effected 
by  these  animals  ;  neither,  indeed,  is  it  positively  ascertained  in 
many  species  whether  the  ova  are  impregnated  prior  to  their 
expulsion  or  afterwards,  although  the  latter  supposition  seems  by 
far  the  most  probable. 

(384.)  The  eggs  are  almost  invariably  carried  about  by  the  female 
until  they  are  hatched,  and  in  order  to  effect  this  various  means 
are  provided.  In  the  Decapoda  they  are  fastened  by  a  stringy 
secretion  to  the  false  feet  under  the  abdomen,  and  a  female  crab 
may  generally  be  readily  distinguished  from  a  male  of  the  same 
species  by  the  greater  proportionate  size  of  this  part  of  their  body. 
In  Asellus ,  a  small  Crustacean  very  common  in  stagnant  water, 
the  male  may  be  observed  during  the  breeding  season  to  carry  the 
female  about  with  him  for  many  days ;  after  which  her  eggs  are 
found  impregnated,  and  enclosed  in  a  membranous  sac  placed  under 
the  thorax,  from  which  when  the  young  are  hatched  they  escape 
through  a  longitudinal  fissure  provided  for  the  purpose.  In  many 
genera,  broad  laminae,  or  scaly  plates,  are  found  upon  the  under 
surface  of  the  body,  beneath  which  the  eggs  are  lodged. 


CRUSTACEA. 


347 


The  more  minute  Crustacea,  or  Entomostraca ,  as  they  are 
called  by  zoologists,  in  their  mode  of  reproduction,  offer  several 
remarkable  variations  from  what  has  been  described  above ;  and  a 
brief  account  of  their  most  interesting  peculiarities  is  therefore 
still  wanting  to  complete  this  part  of  our  subject.  These  little 
creatures,  in  fact,  seem  to  form  a  transition  between  the  class  we 
are  now  considering  and  the  Epizoa ,  which  many  of  them  re¬ 
semble  so  nearly  that  they  are  still  confounded  together  by  many 
authors.  The  female  Entomostraca  frequently  carry  their  ova  in 
two  transparent  sacculi  attached  to  the  hinder  part  of  the  body, 
and  it  is  in  these  egg-bags  that  the  oviducts  terminate  ;  so  that 
the  ova,  as  they  are  formed,  are  expelled  into  the  singular  re¬ 
ceptacles  thus  provided.  Without  such  a  provision,  indeed,  it 
would  be  difficult  to  conceive  how  the  ova  could  possibly  remain 
attached  to  the  parent,  as  they  far  surpass  in  their  aggregate  bulk 
the  size  of  her  entire  body,  and  could  not,  therefore,  by  any  con¬ 
trivance  be  developed  internally  without  bursting  the  crustaceous 
covering  that  invests  the  mother.  J urine,*  Ramdohr, j~  and  other 
authors,  have  carefully  watched  the  generative  process  in  several 
genera,  and  brought  to  light  many  important  and  curious  facts 
connected  therewith.  In  Cyclops ,  a  species  to  be  met  with  in 
every  ditch,  the  impregnation  of  the  ova  is  undoubtedly  effected 
in  the  body  of  the  parent,  and  the  eggs  when  formed  are  expelled 
into  two  oval  sacs  placed  on  each  side  of  the  tail,  which  Jurine  calls 
external  ovaries.  The  number  of  eggs  contained  in  these  sacs 
gradually  increases,  and  they  exhibit  a  brown  or  deep  red  colour, 
until  a  short  period  before  the  growth  of  the  embryo  is  completed, 
when  they  become  more  transparent.  In  about  ten  days  the  eggs 
are  hatched  and  the  young  escape  ;  but  such  is  the  prodigious 
fertility  of  these  little  beings,  that  a  single  female  will,  in  the 
course  of  three  months,  produce  ten  successive  families,  each  con¬ 
sisting  of  from  thirty  to  forty  young  ones. 

In  the  genus  Apus ,  another  plan  is  resorted  to  for  the  protec¬ 
tion  of  the  ova  : — the  eleventh  pair  of  legs,  called  by  Schaefer  \ 
“  womb-legs,”  have  their  first  joints  expanded  into  two  circular 
valves,  which  shut  together  like  a  bivalve  shell,  and  thus  form  a 
receptacle  in  which  the  eggs  are  contained  until  they  arrive  at 
maturity. 

*  Histoire  des  Monocles.  1  vol.  4to.  Gen.  1820. 

f  Materiaux  pour  l’Histoire  de  quelques  Monocles  Alletnands.  4to.  1805. 

t  Apus  pisciformis,  insecti  aquatici  species  noviter  delecUe.  4to.  Ratisbonne,  1757. 


348 


CRUSTACEA. 


In  Daplmia  {Jig.  155)  the  ovariaare  easily  distinguished  through 
the  exquisitely  transparent  shell,  especially  when  in  a  gravid  state ; 
and  the  eggs  after  extrusion  are  lodged  in  a  cavity  situated  be¬ 
tween  the  shell  and  the  exterior  of  the  body,  where  they  remain 
until  the  embryo  attains  its  full  growth. 

(385.)  One  fact  connected  with  the  reproduction  of  the  Entomos- 
traca  is  so  remarkable,  that,  had  we  not  already  had  an  instance  of  the 
occurrence  of  a  similar  phenomenon  in  the  insect  world  ( Aphides ), 
the  enunciation  of  it  would  cause  no  little  surprise  to  the  reader ; 
and,  had  its  reality  been  less  firmly  substantiated  by  the  concur¬ 
rent  testimony  of  numerous  observers  who  have  witnessed  it  in 
many  different  genera  ( Cyclops ,  Daphnia ,  &c.),  it  might  still  be 
admitted  with  suspicion.  In  the  genera  above  mentioned  it  has 
been  ascertained  by  careful  experiments  that  a  single  intercourse 
between  the  sexes  is  sufficient  to  render  fertile  the  eggs  of  several 
(at  least  six,  according  to  Jurine)  distinct  and  successive  gene¬ 
rations. 

Some  authors  have  supposed,  from  the  circumstance  of  all  the 
individuals  which  have  been  met  with  belonging  to  some  genera 
being  females,  that  some  of  these  little  beings  were  hermaphrodite, 
or  self-impregnating ;  but  such  an  opinion  rests  on  very  doubtful 
grounds,  especially  as  there  seems  good  reason  to  believe  that  in 
many  instances  the  forms  of  the  male  and  female  of  the  same 
species  are  so  different  that  they  might  easily  be  mistaken  for 
totally  distinct  animals. 

(386.)  The  last  point  which  vre  have  to  notice,  in  connection  with 
the  history  of  the  Crustacea ,  is,  the  progress  of  their  developement 
from  the  embryo  condition  to  their  mature  state.  This  is  a  sub¬ 
ject  which  has  given  rise  to  considerable  discussion,  especially  as 
relates  to  the  changes  which  occur  during  the  growth  of  the  more 
highly  organized  forms ;  some  authors  contending  that  they  leave 
the  egg  complete  in  all  their  parts,  and  presenting  their  adult  con¬ 
figuration,  while  others  assert  that  they  undergo  changes  so  import¬ 
ant  as  only  to  be  comparable  with  the  metamorphosis  of  insects. 

Among  the  Entomostraca  such  changes  have  been  again  and 
again  witnessed,  and  the  appearances  observed  during  their  growth 
carefully  recorded.  From  these  observations  very  important  results 
have  been  obtained,  inasmuch  as  many  forms  previously  described 
as  distinct  species  have  been  found  to  be  merely  the  same  animal 
in  different  stages  of  developement.  In  Cyclops ,  for  example, 
the  newly  hatched  embryo  possesses  only  four  legs,  and  its  body 


CRUSTACEA. 


349 


is  round,  having  as  yet  no  appearance  of  caudal  appendages ;  of 
young  animals  in  this  condition  Midler  had  formed  a  distinct 
genus  ( Amymone )  :*  in  about  a  fortnight  they  get  another  pair 
of  legs,  and  form  the  genus  Nauplius  of  the  same  author.  They 
then  change  their  skin  for  the  first  time,  and  present  the  form  of 
the  adult,  but  with  antennae  and  feet  smaller  and  more  slender 
than  in  the  perfectly  mature  state.  After  two  other  changes  of 
skin  they  become  capable  of  reproduction. 

Many  of  the  Entomostraca,  as  for  example  Daphnia ,  do  not 
seem  to  undergo  material  alterations  of  form,  but  simply  moult  at 
certain  intervals,  throwing  off  their  old  integument  and  acquiring  a 
new  covering.  Nevertheless,  even  in  the  Decapoda  it  is  pretty 
certain  that  great  metamorphoses  take  place  in  the  external  ap¬ 
pearance  of  the  young  animals,  though  many  contradictory  opi¬ 
nions  concerning  their  nature  are  entertained  by  naturalists. 
Much  confusion,  indeed,  still  exists  connected  with  this  important 
subject.  Cavolini  long  since  announced  that  the  embryo  of  Can¬ 
cer  depressus  exhibited  at  birth  a  singular  and  uncouth  appear¬ 
ance,  of  which  he  gave  a  very  tolerable  representation  ;  j*  and  Mr. 
Thompson,  in  a  late  number  of  the  Philosophical  Transactions, 
has  rendered  it  certain  that  even 
in  the  developement  of  the  com¬ 
mon  crab,  so  different  is  the  out¬ 
ward  form  of  the  newly-hatclied 
embryo  from  that  of  the  adult, 
that  the  former  has  been  describ¬ 
ed  as  a  distinct  species,  and  even 
grouped  among  the  Entomos¬ 
traca,  under  the  name  of  Zoea 
pelagica.  On  leaving  the  egg, 
according  to  the  author  alluded 
to,  the  young  crab  presents  a  cu¬ 
rious  and  grotesque  figure  ( fig . 

164)  :  its  body  is  hemispherical, 
and  its  back  prolonged  upwards 
into  a  horn-like  appendage  ;  the 
feet  are  scarcely  visible,  with  the 
exception  of  the  two  last  pairs,  which  are  ciliated  like  those  of  a 
Branchiopod,  and  formed  for  swimming.  The  tail  is  longer  than 

*  Latreille,  Regne  Animal,  vol.  iv. 

+  Sulla  Generazione  dei  Pesci  edei  Granchi.  4to.  Naples,  1787. 


Fig.  164. 


350 


CRUSTACEA. 


Fig.  165. 


tlie  body,  possesses  no 
false  feet ;  and  the  ter¬ 
minal  joint  is  crescent- 
sliaped,  and  covered 
with  long  spines.  The 
eyes  are  very  large,  and 
a  long  beak  projects 
from  the  lower  surface 
of  the  head. 

In  a  more  advanced 
stage  of  growth  the 
creature  assumes  a  to¬ 
tally  different  shape, 

(Jig- 165,)  under  which 
form  it  has  been  known 
to  naturalists  by  the 
name  of  Megalopa. 

The  eyes  become  pe¬ 
dunculated,  the  cepha- 
lo-thorax  rounded,  the 
tail  flat  and  provided 
with  false  feet,  Fig.  166. 

and  the  chelae 
and  ambulatory 
extremities  well 
developed. 

A  subsequent 
moult  gives  it 
the  appearance 
of  a  perfect 
crab  ;  and  then 
only  does  the 
abdomen  become 
folded  under  the 
thorax,  and  the 
normal  form  of  the  species  recognisable  (Jig.  166). 


351 


CHAPTER  XVIII. 

Heterogangliata*  (Owen)  ;  Mollusca.  (Cuv.) 

(387.)  The  term  Mollusca,  employed  by  Cuvier  to  designate 
the  fourth  grand  division  of  the  animal  world,  is  obviously  derived 
from  a  very  unimportant  circumstance  of  their  organization,  which 
the  tribes  included  in  it  possess  in  common  with  innumerable  forms 
both  of  Acrite  and  Nematoneurose  beings,  whose  soft  bodies  are 
unsupported  by  any  internal  or  tegumentary  framework  of  sufficient 
density  to  merit  the  name  of  a  skeleton.  Subsequent  anatomists 
have  therefore,  however  unwillingly,  been  compelled  to  substitute 
another  name  for  that  given  by  the  illustrious  French  zoologist  to 
this  extensive  class,  the  boundaries  and  relations  of  which,  as  at 
present  admitted,  remaining  precisely  as  they  were  first  established 
by  his  patient  and  unwearied  investigations  relative  to  the  anatomi¬ 
cal  structure  of  the  animals  comprised  within  its  limits. 

It  is  to  the  arrangement  of  the  nervous  system  that  we  must 
again  have  recourse  in  order  to  discover  a  distinctive  appella¬ 
tion  ;  nor  in  this  shall  we  be  disappointed,  for  here  we  at  once  find 
a  character  peculiar  to  this  great  section  of  animated  nature,  and 
generally  applicable  to  the  various  classes  composing  it.  All  the 
Mollusca  present  nervous  ganglia,  which,  in  the  more