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HoWBRd W P/fMlNO
550 1 F?r(i Cj £■ pQfjci '
Be R ke ) ^ y.
Qlft
Dr. Howard Fleming
CAMBRIDGE BIOLOGICAL SERIES.
Qensral Editor :— Arthub E. Shipley, M.A.
FELLOW AND TUTOR OF CHRIST'S COLLEGE, CAMBRIDGE.
ZOOLOGY
llonl^on: C. J. CLAY and SONS,
CAMBRIDGE UNIVERSITY PRESS WAREHOUSE,
AVE MARIA LANE,
AND
H. K. LEWIS,
136, GOWER STREET, W.C.
eiasgoto: 60, WELLINGTON STREET.
l.eip>is: F. A. BROCKUAUS.
j^rtg fiorfc: THE MAC3IILLAN COMPANY.
SombaB ^ Colnttta: ^UCMILLAN & CO. Ltd.
[All Eights reserved.]
ZOOLOGY
AN ELEMENTARY TEXT-BOOK
BY
A. E. SHIPLEY, M.A.,
FELLOW AND TUTOR "OT CHRIST'S COLLEGE, CAMBRIDGE,
AND UNIVERSITY LECTURER IN ADVAS'CED MORPHOLOGY OF THE
INVERTEBRATA;
AND
E. W. MacBRIDE, M.A. (Cantab.), D.Sc. (Lond.),
SOMETIME FELLOW OF ST JOHN'S COLLEGE, CAMBRIDGE,
PROFESSOR OF ZOOLOGY IN M<=GILL UNIVERSITY, MONTREAL.
SECOND EDITION
CAMBRIDGE :
AT THE UNIVERSITY PRESS
1904
• ■ •
Fir$t Edition 190L
Second Edition 1904
• • * •
* k »
V V V « • W 1
* He
PREFACE.
WE have tried in the following book to write an ele-
mentary treatise on Zoology which could readily be
understood by a student who had no previous knowledge of
the subject. We have endeavoured to explain the technical
terms as they occur, and since one of the difficulties proper to
the science of 2iOology is the enormous number and the pro-
digious length of these terms, we have in many cases given
derivations which may help the beginner to fix them in his
mind.
The attempt to construct the book on the plan that each
section is built on what precedes it, has rendered it impossible
to keep the treatment of the various groups at the same level,
for much space is taken up in the earlier chapters in ex-
plaining processes a knowledge of which is assumed in the
later. A book such as we have aimed at is bound to be
progressive, and the later chapters will be intelligible to the
beginner only if he has read the eailier. Thus the part of
this book which deals with the Yertebrata is in many respects
more advanced than those which deal with the several Inverte-
brate groups.
In order to give some account of the leading types of
animal structure within a book of moderate compass, we have
been compelled to make but scanty reference to Histology,
Embryology and Palaeozoology ; in fact the book in the main
deals with the normal strncture of the adult forms of recent
92006
ri PBEFACEL
^ffiimaJn Wberei'er poatdble we luiTe endeaToored to exhibit
this structure w the outcxHne of funetioD and hahiL We have
tried to show that ZcxAogy deals at least as much with liTing
as with dead ofgsxuKma.
In tracLDg the relatkmship of the animals described to one
aaotiiier we have at times put forward hypotheses which we fear
will not commend themselves to all aoologists, bat we have
thought it better to run the risk of submitting views which
further research may compel us to abandon rather than leave
the student with the idea that the object of zoological study
is the mere collection of &cts. We try everyiidiere to make
it dear that the ultimate end of the sdence is tiie disooveiy
of the laws underiying and binding togethtf the fftcta.
At the end of the sections dealing with each phylum a
short table of classification is given. These tables do not
attempt to be complete but are intended to indicate the posi-
tion of the animals mentioned in the text in the general scheme
of cUfisification, and since the book appears in hotik an English
and an American edition, these examples are in most cases
drawn from the British and North American Faunaa
In one respect thiM book differs from many of the ele-
mentary treatises which have appeared within the last few
years. It has been drawn up with an eye to no examination
and does not claim to correspond with any of the numerous
syllabuses and schedules, issued from time to time by the
various Boards of Examiners scattered through the United
Kingdom and North America.
Many of the illustrations are new and whatever merit
they possess is due to the skill of Mr E. Wilson of Cambridge:
and Mr F. M. Hewlett of Christ's College. We owe om
grateful thanks to Mr S. H. Reynolds for permission to us
many of the illustrations of his book on "The Vertebrat
PREFACE. VU
Skeleton/' and to Slessrs Macmillan & Co. and Messrs A. and
C. Black and the Council of the Royal Agricultural Society for
granting the use of certain other illustrations. We are also
much indebted to many friends for help in special chapters.
Mr E. S. Thompson and Mr J. Graham Kerr have read through
the proof-sheets, a most tedious task, as the authors can
abundantly testify ; Dr Harmer, Dr Gadow, Dr Anderson, Dr
Hopkins, Mr G. P. Bidder, Mr J. Stanley Gardiner, Mr R. Evans^
Mr H. H. Brindley, and Mr C. Warburton, have most freely
given us the help of their special knowledge. Whilst saving us
from many mistakes they are by no means responsible for those
that remain. We tender them all our sincere thanks.
A. E. S.
E. W. M.
August y 1901.
8. (&M.
PREFACE TO THE SECOND EDITION.
TN issuing a second edition of this Zoology, which has been
-■- for some time out of print, the authors desire to thank
many critics who have pointed out errors in the book. They
are again indebted for much help to the gentlemen mentioned
in the former Preface, and above all they owe thanks to
Mr H. H. Brindley of St John's College, who has kindly
read the whole of the proofs and whose critical power has
been most unreservedly placed at the use of the authors.
In the subjects which they have made their own Dr Gadow
and Mr L. A. Borradaile of Selwyn College have given the
writers much valued help.
A. E. S.
E. W. M.
J/arcA, 1904.
TABLE OP CONTENTS.
CHAP. PAGE
I. Introduction 1
II. Phylum Protozoa 13
III. Phylum Ooelenterata 42
IV. Phylum Porifera 74
y. Introduction to the Coelomata 83
VL Phylum Annelida 89
VIL Phylum Arthropoda 118
VIII. Phylum MoUusca 210
IX. Phylum EchinodermaU 249
X. Phylum Brachiopoda 291
XL Phylum Polyzoa 297
XIL Phylum Chaetognatha 302
XIII. Introduction to the Phylum Vertebrata; Sub-phyla
I — III. Ilemichordata, Cephalochordata and Uro-
chordata 306
XIV. Introduction to Sub-phylum IV. Craniata. Di?ision I.
Cyclostomata 333
XV. Craniata. Division II. Gnathostomata. Class I. Pisces 368
XVI. Craniata. Division II. Gnathostomata. Class II. Am-
phibia 417
XVII. Craniata. Division II. Gnathostomata. Class III. Rep-
tilia 457
XVIII. Craniata. Division II. Gnathostomata. Class IV. Aves 495
XIX. Craniata. Division II. Gnathostomata. Class V. Mam-
malia 520
XX. Phylum Platyhelminthes 605
XXI. Phylum Nemertinea 626
XXII. Phylum Rotifera 631
XXIII. Phylum Nematoda 639
Index 645
62
LIST OF ILLUSTRATIONS.
riO' PAGE
1. Amoeba protetu 14
2. D\ffliigia urcedata 18
3. Arcella discoides 19
4. Gramia oviformis .... .... 20
5. Polystomella crtspa 22
6. ffeliosphaera tnermis 24
7. Chondrioderma difforme 26
8. Actinophryi sol 27
9. Actinosphaerium eiehhornii 28
10. Vorticella microstoma 29
11. Diagram of Vorticella 30
12. Opalina ranarum 33
13. Paramecium caudatum 34
14. Eugletta viridie 36
15. Clepndrina longa 38
16. Hydra fusca 43
17. Longitudinal section through the body of Hydra . 44
18. Transverse section of Hydra fusca 46
19. Cnidoblast from the body- wall of Hydra fusca ... 47
20. Section tlirough body-wall of Hydra fusca .... 49
21. Obelia helgolandica 50
22. Part of a branch of Obelia 51
23. Free-swimming Medusa of Obelia 52
24. Bougainvillia fructuosa 53
25. (1) Eye of Lizzia koellikeri; (2) Radial section through the
edge of the umbrella of Carmarina hastata ... 55
26. Planula of Clava squamata 56
27. Part of a colony of Akyonium digitatum .... 60
28. Transverse section through a polyp of Alcyonium digitatum
below the level of the oesophagus 61
29. Transverse section through a polyp of Alcyonium digitatum
through the region of the oesophagus . . 61
30. Semi-diagrammatic view of half a simple Coral ... 64
31. Aurelia aurita 67
Xll LIST OF ILLUSTRATIONS.
FIG. PAGE
32. Strobilization of Aurelia aurita ...••• ^^
33. Hormiphora plumosa 70
34. View of a branch of LeucosoUnia showing osculum . 75
35. Vertical section through an osculum of Leticosolenia . 76
36. Section of a flagellated chamber of Spongilla lacustris . 77
37. Section of a portion of Ghrantia extusarticulata ... 78
38. Three transverse sections through a developing Amphioxm
to show the origin of mesoblast 84
39. Two stages in the early development of a common fresh-water
mollusc, Planorbis, to show the origin of the mesoderm . 85
40. Latero-ventral view of an Earthworm, Lumbrictu terrestrnt . 90
41. Anterior view of the internal organs of Lumbricus ierrestrU . 93
42. Six segments from the intestinal region of Lumbricus ierrestrU
dissected so as to show the arrangement of the parts . . 94
43. Diagram of the anterior end of Lumbrictu herculeus to show
the arrangement of the nervous system .... 99
44. Transverse section through Lumbricus terrestris in the region
of the intestine 102
45. View of the reproductive organs of Lumbrictu terrestris . 105
46. Nereis pelagica 109
47. Transverse section through Nereis cultrifera . . . 110
48. Hirudo medicinalis Ill
49. View of the internal organs of Hirudo medicinalis . 114
50. Three stages in the emergence of the adult Dragon-fly from the
larval skin 120
51. A Centipede, Lithobius forficattu 122
52. A male Cockchafer, Melolontha vulgaris . . . 123
53. The Oarden Spider, Epeira diadema, sitting in the centre
of its web 124
54. The mouth appendages of Gammariu neglectus . 125
55. Pedipalp of the large House-spider, Tegenaria guyonii . 126
56. Left mouth-appendages of the Crayfish, Astaciu fluviaiilis 127
57. Asellus aquaticus 128
58. View of the nervous system of the Cockchafer, Melolontha
vulgaris • . . . . 129
59. Sections through the central and lateral eyes of a Scorpion,
Euscorpius italicus 131
60. View of internal organs of male Crayfish, Astacus fluviatilis^
seen from the side 132
61. Views of the gills of the left side of a Prawn, Penaeus semi-
culcatus 135
62. View of internal organs of the male Cockchafer, Melolontha
vulgaris 136
63. Horizontal section through the abdomen of a Spider, Argy-
roneta 137
LIST OF ILLUSTRATIONS. XUl
FIG. PAGE
64. Longitudinal section through the operculum and gills of a
King-crab, LimtUtis 138
65. Longitudinal section through the lung-book of a Spider . 138
66. Male reproductive organs of Astacut flumatilU . . . 141
67. Female reproductive organs of Astacus flumatUis . 141
68. Dorsal view of a female Branchipus 144
69. Side view of male Simocephalia $ima 145
70. Side view of female Simocephalus sima .... 145
71. Lateral view of Cyprii Candida 147
72. Ventral view of a male Cyclops 148
73. Dorsal view of a female Cyclops 149
74. View of Lepat anatifera cut open longitudinally . . 151
75. A Schizopod, Nyctiphanes norwegica 154
76. The Shore-crab, Cardnus maenas 156
77. Female of Diastylis stygia, one of the Cumacea . 158
78. Side view of Gammariu neglectus showing internal organs 159
79. A Wood-louse, Porcellio scaher 160
80. Peripatus capensis 161
81. Peripatus capensisy male, dissected to show the internal
organs 162
82. A Centipede, Lithohitu forficatus 164
83. Lilhobius forficatus ^ dissected to show the internal organs . 166
84. Iidus terrestris 167
85. Two views of a male Cockroach, Stylopyga orientcUis . 169
86. Mouth appendages of /Stylopyga 171
87. Female Cockroach dissected to show the viscera . . 174
88. A Grasshopper, Pachytylus migratorius . . . . 182
89. Larva of Bombyx mori, the Silkworm . . . . 184
90. Cocoon of Boffnbyx tnori 185
91. Silkworm moth, Bombyx tnori 185
92. The Lady-bird, Coccinella septempunctata, and its larva . 187
93. Male, Female and Neuter of the Wood- ant, Formica rufa 187
94. Drone, Queen and Worker of the Honey-bee, Apis mellifi>ca . 188
95. A Wasp, Polistes tepidiis, and its nest . . . . 188
96. The Tsetse-fly, Glossina morsitans 189
97. The Hessian-fly, Cecidomyia destructor . . . . 189
98. The Garden Spider, Epeira diadema, sitting in the centre
of its web 192
99. Front view of the head of a Spider, Textrix denticukUa . 192
100. Pedipalp of the large House-spider, Tegetiaria guyonii . 193
101. Lateral view of the internal organs of a Spider, Epeira
diademata 194
102. Digrammatic view of a palpal organ 196
103. A Phalangid or Harvestman, Oligolophus spinosus . . 197
104. Male and female of the Cheese-mite, Tyroglyphus siro . 198
XIV LIST OF ILLUSTRATIONS.
PIG. PAGE
105. Dorsal and ventral views of the Indian Scorpion, Scorpio
swammerdami 200
106. Dorsal view of the King-crab, Limulus polyphemus . 202
107. Ventral view of the King- crab, LimuLuB polyphemus . 203
108. Side view of a Snail, Helix potnatia, the animal being expanded 21 1
109. Dorsal view of a Snail, Helix pomatia, after removal of the shell 213
110. Helix pomatia, with the pulmonary chamber cut open . 214
111. Longitudinal section of the head of Helix to show the radula 215
112. Dissection of the Snail, Helix pomcUidk, to show the internal
organs 216
113. View of the nervous system of Helix jwmcUia . . . 218
114. Optical section through the auditory vesicle of Pterotrachea
friederid 219
115. Nervous system of the Pond-suail, Litnnaea . . 219
116. Nervous system, osphradium and gills of Haliotis . 220
117. The Pond-mussel, Anodonla mutabilis, with foot expanded
and the empty shell of the same 224
118. Right side o( Anodonta mutabilis with mantle cut away and
gills folded back 226
119. Diagrammatic transverse sections of Anodonta . . . 227
1 20. Right side of A nodonta mutabilis dissected to show the viscera 229
121. Dorsal view of Anodonta mutabilis^ with the upper wall of
the pericardium removed to show the heart . . 231
122. Solen vagina^ the Razor-shell 233
123. Diagrams of a series of Mollusca to show the relations of the
foot and visceral hump to each other and to the antero-
posterior and dorso-ventral axes 234
124. Posterior view of a male Cuttle-fish, Sepia officinalis^ with
the mantle-cavity opened 235
125. A diagram showing the relation of the kidneys to the peri-
cardium in Sepia 237
126. View of heart and chief blood vessels of Sepia cultrata 239
127. Diagrammatic longitudinal section of Sepia to show the
relation to one another of some of the principal viscem . 240
128. Lateral view of the central nervous system of Sepia officinalis 241
129. Ventral view of Sepia qfficinalis dissected so as to show the
nervous system 243
130. Side view of the pearly Nautilus, Nautilus pompilius 245
131. Oral view of a Star-fish, Echinaster sentus .... 250
132. Dissection of the common Star-fish, Asterias rubens, so as to
show the motor, digestive and reproductive organs . 252
133. A Star-fish, Eckinaster sentus, in the act of devouring a
mussel 254
134. Diagram of a transverse section of the arm of a Star-fish . 255
135. Pedicellariae from Asterias glacial is ..... 259
LIST OF ILLUSTRATIONS. XV
PIO. PAOB
136. Dorsal view of a Brittle-star, Ophioglypha bullaia . . 262
137. Diagram of a transverse section of the arm of a Brittl^star . 263
138. Diagram of a longitudinal vertical section through a Brittle-
star 264
139. Oral view of a portion of Ophioglypha bullata . . 265
140. Dorsal view of a Sea-urchin, Strongylocentrui drdbaehiemis,
with the tube-feet expanded 267
141. Dorsal view of the dried shell of the common British Sea-
urchin, Echintu esctUentus 268
142. A gemmiform pedicellaria from Echintu escidentus . . 269
143. Dissection of Echinus escuientus so as to show the structure
of "Aristotle's lantern" 270
144. Diagram of a longitudinal vertical section of a Sea-urchin 271
145. Transverse sections through the madreporite and the radius
of Echinus escuientus 273
146. Dissection of a Sea-urchin so as to show the course of the *
alimentary canal 274
147. The oral field or peristome of Echinus escuientus . . 275
148. The aboral system of plates, or periproct and calyx of
Echinus escuientus 277
149. Dissection of a Sea-cucumber, Holothuria tubulasa, so as to
show the arrangement of the viscera .... 280
150. A Feather-star, Antedon acoela 283
151. Dia*rram of a longitudinal vertical section of the common
Feather- star, Antedon rosacea 284
152. A stalked Feather-star, Rhizocrinus 285
153. Ventral view of the larva of a Sea-cucumber . . . 286
154. Shell of a fossil Brachiopod, TerebratiUa semiglobosa . 292
155. Section through the shell of Waldheimia flavescens . . 292
156. Dissection of Waldheimia australis so as to show the in-
ternal organs 293
157. Longitudinal vertical section of Argiope neapolitana . . 294
158. Portions of two Polyzoan colonies 297
159. Longitudinal vertical section of Plumatella fungosa . 298
160. An avicularium of Bugula 300
161. Ventral view of Sagitta hexaptera 303
162. Transverse sections of Siigitta bipunctata and of Spadella
cephaloptera 304
163. Dolichoglossus kowaleeskiiy a species of Balanoglossus . 307
164. Longitudinal vertical section of Glossobalanus . 309
165. Longitudinal horizontal section of Glossobalanus . . 310
166. Amphioxus lanceolatus seen from the left side . . 311
167. Views of the velum and of the oral cartilages of Amphioxus 311
168. Diagram of longitudinal section through a young embryo of
Amphioxia 312
XVI LIST OF ILLUSTRATIONS.
FIG. PAOB
169. Anterior region of a young Amphioxus seen from the left
side 313
170. Diagrammatic transverse section through the (>haryngeal
region of a female Amphioxus 314
171. Transverse section through the intestinal region of a young
Amphioxus 315
172. Front end of a young transparent Amphioxus . . . 816
173. Anterior portion of the nerve-cord of Amphioxus . 316
174. Longitudinal vertical section through the cerebral vesicle of
Amphioxus 317
175. Transverse section through the middle region of the nerre-
cord of Amphioxus 318
176. A nephridium of Amphioxus, belonging to the left side of
the body 319
177. Portion of a transverse section through the pharynx of Am^
phioxusy in order to show the relations of the excretory
tubule 320
178. Ventral view of an Amphioxus dissected so as to show the
reproductive organs 321
179. Diagrammatic transverse section of Amphioxus to show the
relations of the excretory and genital organs . . . 322
180. Side view of the anterior end of a larva of Ascidia . 324
181. Dorsal view of the anterior end of a larva of Ascidia 324
182. Diagrams showing the changes undergone by a larval Ascidian
in its metamorphosis . . 326
183. Ciona intestinalis 327
184. Dissection of Ciona intestinalis so as to show the internal
organs 328
185. Portion of a colony of Botryllus vioUiceus .... 330
186. Dorsal view of a fully developed asexual person of Salpa
democraiica 331
187. Longitudinal vertical section of ScUpa 332
188. Views of the brain of a Dogfish, Scy Ilium ccUtUus, from
various aspects 335
189. Transverse section through the snout of a Dogfish, ScyUium
canicula 338
190. Ear of Chimaera monstrosa 339
191. Section of an ampulla of the internal ear .... 340
192. Transverse section through the head of an embryo Chick
of the third day of incubation in order to show the origin
of the retina and lens of the eye . . . . . 341
193. Diagram to illustrate the structure of the retina . . 342
194. Diagram of the arterial system of the Dogfish, ScyUium . 351
195. Diagram of the venous system of the Shark, Mustelus ant-
arcticus 354
LIST OF ILLUSTRATIONS. XVU
FIG. PAOB
196. Dissection of the muscles of the eye of Scyllium canicula 355
197. Dingrams illustrating the development of the excretory and
reproductive organs of Craniata 357
198. Diagram of a transverse section through a hypothetical an-
cestral Elasmobranch in order to show the origin of the
excretory and genital organs 359
199. The Musk Lamprey, Petromyzon tcilderi, in the act of
spawning 361
200. Longitudinal vertical section through a female Lamprey,
Petromyzon tnarinus 362
201. Three views of the skull of Petromyzon marinus^ from
different aspects 363
202. Section through the skin of an Elasmobranch showing the
origin of a scale .... .... 370
203. Diagrammatic transver8e section of the jaw of a Shark, Odoftr
taspU americantu 371
204. Lateral view of the skull of a Dogfish, Scyllium canicula . 372
205. Dorso-lateral view of the pectoral girdle and fins of a Dogfish,
Scyllium, canicula 374
206. Dorsal view of the pelvic girdle and fins of a male Dogfish,
Scyllium canicula 375
207. Dissection of Scyllium canicula^ so as to show the viscera
viewed from the ventral aspect 378
208. Dissection of Scyllium canicula^ so as to show the viscera
seen from the right side 380
209. Adult Scyllium canicula, and opened egg-case of the same 382
210. A Ray, Raia mactdata 384
211. Skull of a male Chimaera monstrosa 385
212. Chimaera mtmstrosa 386
213. Lepidoiiren paradoxa 387
214. Dorsal and ventral views of the cranium of Ceratodus miolepis 388
215. Lateral view of the skeleton of Ceratodus miolepii . . 389
216. Diagram of the arterial arches of Ceratodus . . . 390
217. Diagram of the venous system of a Dipnoan . . 391
218. Polypterus 393
219. The Sturgeon, Acipenser sturio 396
220. The right half of the pectoral girdle and the right pectoral
fin of a Cod, Oadus morrhua 398
221. Dorsal and ventral views of the cranium of a Salmon, Salmo
solar, from which the membrane bones have been removed 400
222. Lateral view of the cartilaginous cranium of a Salmon, Salmo
solar 402
223. Mandibular and hyoid arches of a Cod, Gadus morrhua . 403
224. Lateral view of the skull of a Salmon, Salmo solar . 404
225. Dissection of a Roach. Leuciscus rutilus, to show the viscera 406
XVlll
LIST OF ILLUSTRATIONS.
FIG.
22fS. A Cat-fish, Amiunu cat us
227. The Plaice, Pleuronectes platessa
228. The Sea-horse Hippocampus
229. Skeletons of the anterior and posterior limbs of a Newt,
Molge cristata
230. Skeleton of Mdge cristata^ seen from the side .
231. Male and female specimens of Molge cristata .
232. Dorsal, ventral and lateral views of the skull of Molge
cristata
233. Visceral arches of Molge cristata
234. Ventral and lateral views of the pectoral girdle and sternum
of Molge cristata
235. Skeletons of (a) right fore-arm and hand of the Salamander,
Salamandra maculosa^ and ip) the right ankle of the Newt,
Molge cristata
23d. Pelvic girdle of Molge cristata
237. Dissection of a male Molge cristata
238. Diagram of the venous system of a Urodele
239. Diagram of the arterial arches of Molge
240. Dorsal view of the brain of Molge cristata
241. Excretory and reproductive organs of a female Molge cristata
242. Excretory and reproductive organs of a male Molge cristata
243. Larva of Molge cristata
244. Dorsal and ventral views of the cranium of the common Frog,
Rana temporariay from which the membrane bones have
been removed
245. Dorsal and ventral vieivs of the skull of Rana temporaria
246. Lateral and posterior views of the skull of Rana temporaria
247. Visceral arches of (a) a Tadpole, (b) an adult Frog .
248. Pectoral girdle and sternum of (a) a very old male specimen
of Rana temporaria, (b) an adult female Docidophryne
gigantea
249. Diagram of arterial arches of a Frog
250. Dorsal view and dissections of the heart of a Frog .
251. Dorsal view of the brain and spinal cord of a Frog .
252. The excretory and reproductive org^s of (a) a male, and
ip) a female Frog
253. Tadpole of Rana esculenta
254. Section through the scale of a Lizard
255. Ventral view of the pectoral girdle and sternum of a Lizard,
Loemanctus longipes
256. Lateral view and longitudinal section of the skull of a Lizard,
Varanus varius
257. Diagrams of the cranial roof in a Stegocephalan, various
types of reptile and a bird
PAOS
407
409
410
418
420
423
426
427
428
429
429
430
432
433
434
435
436
437
442
443
444
445
446
447
448
449
450
451
458
461
462
464
LIST OF ILLUSTRATIONS. XIX
FTO. PAGE
258. Lateral view of the pectoral girdle of a Lizard, Varanus . 466
259. View of the interior of the mouth of Far anus indicus 468
260. Diagram of the arterial arches of Chamaeleo 469
261. Diagram of the venoas system in Antira and ReptUia 470
262. Excretory and reproductive organs of a male Lizard 471
263. Lateral, dorsal, ventral and posterior views of the skull of
Sphenodon puncUUus 473
264. The hWndL-Ytorm^ AnguU fragilisy a limbless Lizard . 475
265. Dorsal and ventral views of the skull of the common Shake,
Tropidonotus natrix 477
266. Diagram of the arterial arches of a Snake .... 478
267. The Texas Rattlesnake, Crotaliu atrox .... 480
268. (1) Dorsal and ventral views of the carapace of a loggerhead
Turtle, Thalassoc/ielys caretta ; (2) the plastron of a
green Turtle, Chelone mydas 482
269. Ventral view of the skeleton of the green Turtle, Chelone
mydat 484
270. Longitudinal vertical section of the skull of the green Turtle,
Chelone mydas 485
271. Diagram of the arterial arches of a Turtle . 486
272. Ventral view of the skull and dorsal view of the lower jaw
of an Alligator, Caiman latirostris 488
273. The first four cervical vertebrae of a Crocodile, Crocodilus
vulgaris 489
274. Sternum and associated membrane bones of a Crocodile,
Crocodilus palustris 490
275. (a) Left half of the pectoral girdle and (b) the pelvis and
sacrum of an Alligator, Caiman latirostris . . 491
276. Diagram of the arterial arches of a Crocodile . . 492
277. Section through the skin of a Bird showing the developing
feather 497
278. Skeleton of the right wing of a Gannet, Sula alba . . 498
279. Pectoral girdle and sternum of a Peacock, Paco cristatus 499
280. Dorsal and ventral views of the wing of the Wild- Duck,
Anas boschas 500
281. Lateral view of the pelvic girdle and sacrum of the Duck,
Anas boschas 502
282. Skeleton of the common Fowl, Oallus bankina . . 503
283. Lateral and dorsal views of the brain of the Pigeon, Columba
Una 506
284. Anterior, posterior and dorsal views of the third cervical
vertebra of an Ostrich, Struthio camelus . . . 507
285. Diagram of the arterial arches of a Bird .... 508
286. Diagram of the venous system of a Bird .... 509
287. Dissection of the Pigeon, Columba lima . . . . 510
XX LIST OF ILLUSTRATIONS.
no. PAOE
S88. The lungs, kidneys and reproductive organs of the Pigeon,
Columba lima 514
SHO. Hection through the skin of a Mammal showing the develop-
ing hair 521
990. Ventral view of the skull of the Dog, Canit familiarU . 523
]|i)l. Dorsal view of the skull of the Dog, Canis familiarU . 524
902. Dentition of the Dog, Canis familiaris .... 526
993. Dorsal and ventral views of the brain of the Rabbit, Lepui
eunicului 529
994. Hternum and sternal ribs of the Dog, Canis familiaris . 530
99A. Hkeleton of the Rabbit, Lepus cuniculia .... 532
990. Diagrams of arterial arches of Mammals .... 534
997. Diagmm of the venous system of a Mammal . 535
99H. The Duckbill, OmitfMrhynchuM anatinus .... 538
999. Diagram to show the arrangement of the female genital ducts
in Prototheria 538
300. Ventral view of the pectoral girdle and sternum of a Duckbill,
Ornithi>rhynchu» paradoxiu 539
801. Diagram to show the arrangement of the female genital ducts
in Metatheria 540
302. The Rock Wallaby, Petrogale xanthoptu, with young in
tlie pouch 541
HOH. Hkull of Lesuenr^s Kangaroo-rat, Bettongia lesueuri . . 542
•104. The banded Ant-eater, Myrmecobius fasciattu . . . 543
300. Diagrams to show (he arrangement of the female genital
ducts in the Rabbit and Man as types of Entheria . 545
306. Tamandua Ant-eater, Tamandua tetradactyla . 546
807. The six-banded Armadillo, Datypus sexcinctus . . 547
80H. The white-bellied Pangolin, Manis tricuipis . 548
309. Lateral view and longitudinal section of the skull of a young
Ca'ing Whale, Globicephaltu melas 551
310. BkuU of the African Manatee, Manatus senegalentis . . 553
811. Front views of the head of the American Manatee, Manatus
americanus 553
812. An African Jumping-shrew, Macroscelides tetradactylta . 555
313. The Russian Desman, MyogcUe moschata 556
814. Vortical longitudinal section of the skull of a Dog, Canis
familiaris 569
315. The common Skunk, Mephitis mephitica .... 562
316. The Patagonian Sea-lion, Otaria jvbata .... 563
317. The skull of Hyrax (Procavia) dorsalis .... 565
318. Left view of skull of a young Indian Elephant, Elephas indi-
cia, witli the outer sides of the jawbones removed so as
to expose the roots of the teeth 566
319. Bones of. the right fore-foot in living Perissodactyles 567
LIST OF ILLUSTRATIONS. XXI
FIO. PAGE
320. The Indian Rhinoceros, Rhinoceros unicornis . . . 569
321. Stomach of a Sheep cut open so as to show the different
compartments 572
322. Skeleton of a Cape Buffalo, Bubalus caffa .... 573
323. The African Ghevrotain, Dorcatherium aquaticum . . 575
324. The Musk-ox, Ovibos moschatus 577
325. Side view of the skull of the Rabhit, Lepus cuniculus . 578
326. Dorsal view of the skull of the Rabbit, L^us cuniculus . 579
327. The African Flying Squirrel, Anomalurus /ulgens . . 581
328. The Musquash, Fiber zibethicus 582
329. Skeleton of a fruit-eating Bat, Pteropus medium . . 583
330. Female with young of a Bat, Xantharpyia coUaris . . 585
331. Skulls of an old and of a young specimen of the Gorilla,
Ghrilla savagei 586
332. The Ring-tailed Lemur, Lemur catta 587
333. The Orang-utan, Simia satyrus, sitting in its nest . . 589
334. A transparent Turbellarian, Mesostoma splendidum^ show-
ing the viscera 608
335. Planaria polychroOy with everted proboscis . . . 612
336. Diagram of the reproductive and nervous systems of a
Trematode, Distoma hepaticum 614
337. Diagram of the digestive and excretory systems of a Trema-
tode, Distoma hepaticum 616
338. A Tape- worm. Taenia solium 619
339. Transverse section through a mature proglottis of Ta^enia, 620
340. Diagram of a ripe proglottis of Taenia solium . . . 621
341. A Nemertine Worm, Linens geniculatus .... 627
342. A young transparent Nemortino Worm, Cerebratulus fuscus 629
343. A Rotifer Fhsctdaria ; (a) female of Floscularia comuta,
(P) male of Floscularia campanulala .... 632
344. Diagram to show the arrangement of the viscera in Flos-
cularia 633
345. Diagram of a median longitudinal section of a free-swimming
Rotifer 635
346. Ventral view of Hydatina senta 636
347. Dissection of female Ascaris lumhricoides so as to show the
arrangement of the viscera 640
348. Dissection of male Ascaris lumbricoides so as to show the
arrangement of the viscera 642
349. Trichina spiralis, encysted amongst muscular fibres . 643
CHAPTER L
Introduction.
The word Zoology (Gr. {<3ov, an animal; Xoyo?, an account)
denotes the science which concerns itself with animals.
Life*
endeavouring to find out what they are and how they
came into being. It is a branch of the wider science of Biology
(Gr. /?tbs, life, Aoyo?, a discourse) \ which deals with all living things,
plants as well as animals. Before any progress can be made with
the study of Zoology, it is necessary to get clear ideas on two points:
firstly, as to what is meant by life and living things ; and secondly,
as to how an animal is to be distinguished from a plant
The idea implied in calling a thing living, is that in some
respects its existence is similar to our own. Our own existence is
the only thing immediately known to us, the standard with which
we compare everything else. Every material object has certain
points of resemblance to our bodies, inasmuch as all are composed
of matter obe3ring the same laws of chemical affinity, gravitation,
and so forth ; it is necessary therefore to define the amount of re-
semblance which constitutes life. Now everyone knows that human
beings grow, that is, increase in size at the expense of matter
different from themselves called food, and that further, they give
rise at intervals to firesh human beings. These two fundamental
characteristics — the power of growth and of multiplication — define
life ; everything that can increase its bulk by building up foreign
matter into itself and that reproduces its like is said to be alive.
The idea originally underlying the word animal was a self-
moving object, as distinguished from a plant which was regarded
as motionless*. This distinction, however, will not stand close
^ This tenn is too well established to admit of alteration but it implies a
mistranslation of plot. This does not mean Mile' in the physiological sense hot
a period of life^ a career, a life-time or oiroamstanoes of life, environment.
' It is trae that to all general statements of Zoology, as to this, exceptions
eoold be fonnd. The rule followed in this book is to have regard only to the
8. A IL 1
2 INTRODUCTION. [CHAP.
examination. Plants as well as animals move, and although the
motions of animals are conspicuous and such as to catch the eye,
whilst those of plants are usually slow and imperceptible, yet there
is no essential difference between the nature of the movements in
the two cases.
The fundamental difference between animals and plants is to be
Distinction fouud iu the uature of their food. Animals can only
animal* and ^^® ^^ complex substaucos, uot Very diflFerent in
pianu. chemical composition fix)m their own bodies, and
further, they can live on solid food. Plants, on the other hand,
build themselves up out of carbon di-oxide and other gases and water
with a few simple salts in solution, and they only take in fluids or
gases. There are, however, a certain number of living beings which
combine the characters of animals and plants, and the question in
which division they should be ranked is a matter to be determined
only after a study of the special circumstances of each case.
It has been pointed out that our own existence is the original
type from which the idea of life is derived. But we know ourselves
not only as bodies in which growth and reproduction occur, but also
as conscious, thinking beings, and we are naturally inclined to
imagine that animals at least, which not only grow and multiply^
but in many other respects also resemble us, are likewise conscious.
How &r this belief is well-founded is open to serious question, if by
consciousness we mean anything at all resembling our own inner life —
the only consciousness we know anything about. The movements
of the higher animals suggest that they experience the feelings of
fear, anger, desire, etc., and it would be foolish to deny all similarity
between them and man in these respects, but the habit many people
have of uncritically attributing purely human feelings to dogs,
cats, horses, etc., is apt to lead us into serious error. Our fore-
fathers went further than even we are inclined to do and supposed
all natural objects, the sun, wind, trees, etc., to have spirits, that is,
to be conscious. Since we can never learn much about the conscious-
ness of beings with whom we cannot speak, zoologists content them-
selves with looking at animals entirely from the outside, without
enquiring as to whether or no they are conscious ; animals are for
them bodies in which certain changes take place, changes such as
growth, reproduction, movement, and others.
vast bulk of normal cases which gave rise to the idea. The reasons for classify,
ing abnormal oases in one category or another are not general but special, and
have to be considered in each case.
L] PROTOPLASM. 8
A dose study of animals reveals the fact that though the
chemical constitution of no two is exactly alike, yet all contain certain
highly complex substances of very obscure chemical
composition, known as proteids. These substances
occur in the form of a thick, viscous fluid, in which are suspended
iiot only numerous solid granules of most varied composition, but
also minute drops of other fluids. Such a mixture is called by
chemihts an emulsion, and it is the emulsion just'describe'd which is
the seat of all those processes which we call life. This emulsion is
termed protoplasm (Gr. irpturo^, first ; vXaa-fia, a thing moulded).
Further, it has been found that, so long as any sign of life is
visible, this protoplasm is in a continual state of slow combustion,
absorbing oxygen from outside and decomposing with the liberation
of energy, and whilst some of the products of decomposition are
cast off, others apparently reconstitute the original substance by
combining with some of the materials of the food. The energy
liberated is the cause of the movements which constitute the visible
manifestation of life.
An animal then is only the more or less constant form of a flow
of particles ; it may be compared to a flame, which has a constant
form, although the particles which compose it vary from moment to
moment ; unbumed particles coming in at one end and the oxidised
products escaping at the other.
The deepest insight which can be obtained into the nature of
^ . ,, life viewed as a series of changes in the shape and
position of bodies reveals to us this continual
chemical change as the ultimate cause of all manifestations of life.
It is known by the convenient name of metabolism (Gr. fi€TaPo\rj^
chMige, changing). The ultimate object of Zoology is therefore
to discover the nature, cause, and conditions of the metabolism in
the case of every animal ; but the means of attaining this object
are still to seek, and for the most part the zoologist has to be con-
tent with describing and comparing with one another the outer and
visible effects of the metabolism in various cases.
The proteids, which form the essential basis of protoplasm,
consist of carbon, nitrogen, hydrogen, oxygen, and sulphur ; besides
these elements phosphorus, chlorine, potaasium, sodium, magnesium,
calcium and iron are constantly found in the bodies of animals, and
some of them are doubtless chemically combined with the proteid.
Phosphorus is a constituent of nucleic acid, a substance which
in combination with proteid is characteristic of the nucleus (see
1—2
i
4 DJTRODUCTION. [CHAP.
p. 16). Proteids have a percentage composition which yariea
somewhat, though not widely, in different cases.
Carbon Ax)m 50 to 55 per cent
Hydrogen „ 6 5 to 7*3 „ „
Nitrogen „ 15 to 17 "6 „ „
Oxygen „ 19 to 24 „ „
; Sulphur „ -3 to 2-4 „ „
The size of the molecules of which proteids are composed is un-
doubtedly a large one. It is difficult if not impossible to determine
exactly how many atoms are contained in a molecule of a particular
proteid because it is difficult to obtain one such substance in a pure
condition free from admixture with others. The best determinations
which have been made show however that at least 1000 atoms must
be contained in the molecule. But the proteids known to the
chemist are of course taken from the dead bodies of animals and
are themselves to be regarded as products of the decomposition of
the molecules which existed during life. The proteid as the seat
of life has probably a decidedly different composition from the dead
substance. To avoid confusion, we may call the living molecules
biogens.
The biogen molecule is continually absorbing oxygen from the
outside. This process is called respiration or breathing. It
decomposes and some of the products are no longer capable of being
built up again into other biogen molecules and are therefore got rid
of, since otherwise they would interfere with the chemical action,
just as accumulating ashes will eventually put out a fire. The
process of ejecting these waste products is called excretion, the
waste substances themselves, excreta, and the chemical changes
which lead to their production, katabolism (Gr. KaTafiokij, deposi-
tion). The commonest excreta are water, carbon dioxide, urea,
and uric acid; the last two substances containing nitrogen. But
it is not necessary that in all cases excreta should be ejected.
They may remain within the bounds of a mass of protoplasm;
if they are removed from the sphere of chemical action of the
protoplasm this is sufficient. In some animals uric acid is
stored up in this way. Many of the excreta, though injurious
if they remain in the protoplasm, are indirectly usefrd to the
animal after ejection. Such useful excreta are called secre-
tions. Thus, all the hard skeletons of animals are really insoluble
excreta. On the other hand, the gastric juice which digests the
food in the human stomach, and the slime or mucus, which
LJ MOVEMENT. 5
prevents a frog from clr3ring up when taken out of water, are fluid
excreta. A part of the body specially adapted to produce a secre-
tion is termed a gland.
Other products of decomposition reconstitute, as we have seen,
the original molecule by combining with the necessary elements
from the food; this process is known asanabolism (Gr. dva^SaXXctv,
to put back or up) or assimilation. Inasmuch as, generally speak-
ing, from the breaking up of one molecule more than one residue is
produced capable of regeneration, there is an increase in the number
of biogen molecules causing an increase in bulk of the protoplasm,
or growth*.
The regeneration of the biogen takes place at the expense of the
food. Taking in food is called eating, or ingestion. Since how-
ever, the food must penetrate to every portion of the protoplasm
it must be dissolved — a process effected by the chemical action
of certain products of the decomposition of the biogens, known
as ferments. The process is called digestion. The casting out of
an insoluble remnant of the food is called defae cation, and inasmuch
as such remnants have never formed part of the biogen molecule, this
process is carefully to be distinguished from excretion. The accumu-
lation of excreta soon stops metabolism, whereas the intermission
of defalcation need only interfere very slightly with metabolism.
Of the numerous solid particles found in protoplasm some are
secretions, others are solid deposits of partly assimilated food, which
act as reserve stores, others are indigestible remains. The fluid
drops consist largely of water — some have in solution excreta or
secretions ; others contain the results of digestion.
Animals, as we have seen, possess the power of executing move-
ments ; this power is exercised in order to seek their
food and escape their enemies. However complicated
these movements may be, they are all found to be dependent on the
capacity of protoplasm to alter its shape, suddenly contracting and
then slowly expanding. By contraction is meant such an altera-
tion of shape of the moving part as will tend to diminish its surface
but not its bulk; that is, the contracting part tends to assume
a spherical shape; by expansion, on the other hand, is meant
an alteration of shape leading to increase of surface. A bird
flies by contracting the muscles first on one side of the wing, then
on the other; a fish swims by alternate contractions of the two
sides of the fleshy tail. Any part of an animal fitted to execute
1 See Verworn, General Physiology (Engl. Edition), 1899, p. 486.
6 INTRODUCTION. [CHAP.
movements more quickly in one direction than in another and
80 to bring about the movement of the whole animal, is called a
locomotor organ. Protoplasm in which the power of contraction
u highly developed is called muscle.
A contraction is the result of an explosive decomposition of the
living substance; there have been a great many theories as to
how the chemical change brings about the change of shape but,
since all of them account for some of the facts and none of them for
all, there is no need to mention any of them here.
The sudden chemical change which brings about contraction,
although dependent on the unstable character of the biogen
molecule, must be precipitated by some change occurring either
in the living matter itself or in the surrounding medium, just
as an explosion of gunpowder is not brought about without a spark.
In either case the change causing the contraction is known as a
stimulus, and the capacity of contracting under the influence of
stimuli is known as irritability. Thus when a moth flies into a
flame it is acting under the stimulus of light ; when a hungry lion
in the Zoological Gardens rises up and commences running violently
round its cage it is obeying the stimulus of hunger. In the first
case we have to deal with an external stimulus, in the second with
an internal one. Of course since all internal changes are ultimately
due to changes in the surrounding medium, — e.g. hunger to a dis-
appearance by digestion of the food in contact with the stomach, —
the distinction between external and internal stimuli, though con-
venient, cannot be sharply drawn. The power of protoplasm to
originate movement through internal changes is called automa-
tism. In the case of external stimuli we can often observe that
the disturbance caused at the point of application of the stimulus
is propagated to widely difi'erent parts of the animal. Nerves
contain protoplasm in which this power of transmission is powerfully
developed.
We have seen that at some period in the life of all animals
^ ^. when food is abundant, more living matter is formed
than is broken down ; in a word, that the animal
increases in size, grows. But whereas volume increases proportion-
ately to the cube of the length (or breadth), surface increases only
proportionately to the square of the same dimension. Hence the
amount of volume per unit of surface continually ijicreases, and thus
the chemical action between the internal portions of the protoplasm
and the surrounding medium, which can only go on through the
I.] EEPRODUCTION. 7
surface, is slowed down ; in other words, the activity of growth is
checked and when a certain size is reached waste becomes equal to
repair. At this stage there is a tendency for the protoplasm to
divide into two or more pieces of smaUer size. This division into
smaller pieces is called Reproduction, and it is a necessary result
of growth. When an animal divides into two equal portions, the
process is called fission, but when one portion is very much smaller
than the other, the process is known as gemmation ; the smaUer
portion is called the germ, and the larger the parent, since the
latter is — somewhat illogically — regarded as identical with the origi-
nal animal before division. A germ very rarely resembles the parent;
usually it has to undergo a series of changes during growth by
which it at last attains the shape of the animal which gave rise to
it ; this series of changes in shape and size is known as Develop-
ment.
Reproduction in the higher animals is closely associated with
R rod ti another process called Conjugation or Sexual
Union. This process consists in the coalescence with
one another of two portions of living matter. Conjugation probably
occurs in all animals, but the interesting thing about the higher
animals is that they give rise to special germs of two kinds, called
ova (eggs) and spermatozoa respectively, which cannot develope
without first conjugating, one of the first kind uniting with one of
the second.
The ovum is devoid of the power of movement and has a larger
or smaller amount of undigested or at any rate unassimilated food
stored in it; this reserve material is called yolk. The spermato-
zoon, on the other hand, has no such reserve and is in consequence
very much smaller than the ovum, but it possesses in nearly every
case the power of movement by which it is enabled to seek and find
the ovum. Reproduction, which thus requires conjugation before
development can take place is called Sexual Reproduction. In
most cases ova and spermatozoa are developed in different individuals.
The individual giving rise to ova is called the female, that giving
rise to spermatozoa the male. In this case the animals are said
to be bisexuaL When both ova and spermatozoa are developed in
the same individual it is spoken of as hermaphrodite.
It is obvious to the most casual observation that there is an
amazing variety of animals in the world. Closer
observation reveals the fact that while no two
animals are exactly alike, all can be nevertheless sorted into a
8 INTRODUCTION. [CHAP.
number of kinds called species, the individuals composing which —
apart from the difference between males and females — resemble
each other exceedingly closely. Where the observation has been
made, it is always found that the members of a species conjugate
freely with one another; and indeed this is assumed to be the
case in every species ; that is, we group a number of specimens into
a species under the assumption that they can conjugate with one
another, and that young like themselves will develop as the result.
If this can be shown to be not the case, we conclude that a mistake
has been made and that two or more species have been confounded
with one another. It follows that the vast majority of species rest on
provisional hypotheses ; these hypotheses nevertheless possess a very
high degree of probability, for by the use of them only can the great
resemblance between the individuals grouped together in the same
species be accounted for. When, as occasionally happens, members
of different species are fertile inter se, the offspring is termed a
hybrid, and hybrids may or may not be fertile.
It has been pointed out, that whereas germs are in most cases
H r dit exceedingly different from their parents, they never-
and theless in process of growth come to resemble them.
This tendency to reproduce the characters of the
parent is called heredity. If the germ undergoes a large part of
its development within a hard case, like a chick within the eggshell
or in a cavity of the parent's body, it is called an embryo ; if it
moves freely about, it is termed a larva.
In the case of the development of an animal which has originated
sexually, that is from the coalescence of two germs, the tendency is
for it to assume characters intermediate between those of the two
parents. Thus it is easy to see how sexual reproduction tends to
annul the differences existing between members of the same species,
by constantly producing means between them. When therefore a
large number of individuals are found with very close resemblances,
it is a reasonable supposition that the agent, which has caused this,
is sexual reproduction; in other words, that they constitute a
species. It is not however to be assumed that in every case
conjugation results in the production of an animal exactly inter-
mediate in character between the parents. Sometimes the child
resembles closely the father or the mother, a result denoted by
the term prepotency of the father or of the mother. Some-
times in an unexplained way an exaggeration of a character found
in one or both parents is produced. Sometimes even an apparently
I.] CLASSIFICATION. 9
entirely new character arises. Such deviations of the offspring from
the average of the parents constitute variation. If the difference
is striking the individual exhibiting it is called a sport.
It is obvious that so vast a science as Zoology must be divided
into various branches, since the different questions
ofzooiogy. i*' seeks to solve require that special attention should
be given to each side of the subject Thus, the
nature and conditions of the metabolism and the mechanism by
which movements are effected, etc, constitute the subject-matter of
Physiology ; the investigation of the structure of individuals and
of the differences in structure between the various species and the
search for the causes of these differences is termed Morphology ;
whilst Bionomics is the name given to the study of the means
whereby an animal obtains its food and orders its life, in other
words, of its habits. But it must be remembered that all such
divisions are purely arbitrary, and indeed no great progress can be
made in any one department if the others be ignored. Bionomics,
when followed to its sources, passes into Physiology, and in trying
to explain the different structures studied in Morphology constant
recourse must be had to both Physiology and Bionomics.
Of aU divisions of the subject, that of Physiology has been most
neglected; it has indeed only been studied systematically in the case
of man and of a few of the higher animals. Hence this work will be
mainly concerned with the questions of Morphology and Bionomics.
Of these questions, by far the greatest is the problem how the
distinctions between the various species are to be explained. The
question of the " Origin of Species " involves nearly all others in
Zoology.
The distinctions between species are of very different degrees,
so that for convenience species closely resembling
each other are collected into genera — genera into
families — families into orders — orders into classes — and classes
into phyla. These are the names in commonest use, but often the
nature of the subject requires the introduction of further grades of
difference, and the number of grades actually employed depends to
a large extent on the point to which the analysis is pushed.
The only theory of the origin of species which has so far
commanded any considerable agreement amongst
^^pecies. naturalists is the fekmous theory of Charles Darwin.
According to this theory, the resemblances between
a number of living species are due to the fact that these species
10
DTTBODUCnON. [CHAP.
dtfcended fitnn a common ancestral species which possessed the
Mnmon features as characters of its own. Therefore, the degree of
likeness between species is the expression of a nearer or remoter
bkvd relationship, and it logically follows that, since no pwrt of
rK« tnimal kingdom is without resemblances to the rest, if we
•^e far enough in time we reach a period when all the animals
in the world constituted one species.
To a certain extent Darwin's theory was only the expression of
idns that had first occurred to Greek philosophers, and had in one
nirm or other been put forward by many naturalists before him.
His si«cial merit lies in that he pointed out various processes
nresi^nt going on in nature which must lead to the modification
(C ^^ecics.
He i^called attention to the well-known fact, that although the
iFmrinff in general resemble the parents, yet this resemblance is
never exact, and further that the young of one brood often differ
-inite wivepribly from one another, and that these differences are
rtften inherited by the offspring of the individuals showing them,
^nch differences, as has been mentioned above, are denoted by the
rerm Variation.
Acaiu, another fact well-known but usually ignored, was em-
Tihii^^ by Darwin : viz., that if the state of the animal population
(%i the globe remains fairly constant, out of all the young produced
b\- a pftir ^^ parents during their lifetime on an average only two
^]1 gorvive, since if more were to live the species would inevitably
inrrtwse in numbers. Hence since each animal tends to multiply
nt % late at which if unchecked it would soon overrun the globe, a
^vvmpetition must result between the members of each species both
inr food and in the escape from enemies, as a result of which the
'fittest'' will survive. So long as the surroundings of the species
fftmain the same, this struggle for existence will only weed out those
individuals least perfectly adapted to their environment, so that the
{Mecies will be kept up to a high level of adaptation to its surround-
ings. This elimination of imperfect individuals which results in the
arrival of the fittest is known as Natural Selection. Thus
^ can well imagine that if white-haired individuals turned up
mnongst hares, they would be more conspicuous and hence more
^$;aly discovered by the animals which prey on hares. If however
ihe circumstances of a species change, a different class of individuals
^U survive. For instance, if for the greater part of the year the
country inhabited by tiie liares were covered by snow, aa is the case
l] origin op species. 11
in the North of Canada, the whitest-haired indiyidnals would have
the best chance, and from generation to generation would be selected
until the colour of the hare was totally changed. The progressive
modification of species by the agency of natural selection is called
Evolution. If the modification tends towards simplification of
structure it is called Degeneration, if on the contrary it tends
towards great complexity it is spoken of as Differentiation.
So far the theory shows how a species will become slowly modified
as its surroundings change. But it has been postulated that distinct
species have arisen firom the same ancestors. It is of course not
difficult to see that if a species is distributed over a wide area the
conditions in difi'erent portions may vary independently of one
another, and hence the species may become modified in one place
in one direction and in another situation in a different direction by
the agency of natural selection. So long however as the species
inhabits a continuous area this tendency to split up into divergent
groups will be checked by inter-breeding between the sections of
the species which are thus becoming modified in different directions.
But if through geographical changes the species becomes divided
into groups of individuals cut off from access to another, then no
interbreeding can take place and in time two species will be formed.
Thus when birds have been blown far out to sea and have colonised
a distant island they have often given rise to a new species.
The same result may be brought about by the sea overflowing a
part of the area inhabited by the species, an event which we
know firom geology to have often occurred. The important fact to
be borne in mind is that at bottom the evolution of several species
out of one is due to the formation of colonies, and that the same
causes which have led to the differences between the American and
the Englishman have acted again and again in the world's history so
as to produce the marvellous variety of species inhabiting the globe,
the only difference between human and animal colonies being that,
in the latter case, the divergence has become so great that animal
colonists will no longer breed with the original race. Thus, accepting
Darwin's theory, we find it possible to give a rational explanation of
those resemblances between animals which are expressed in a system
of classification \ If the theory be rejected these resemblances are
pure figments of the human mind, and the species must be regarded
* Most of the names employed in classification were in use before Darwin's
▼lews were accepted. The word phylum (Gr. ^DXok, tribe or stock) is howeyer
an exception. This term expresses the central idea of the eyolution theory,
and its proper use is to denote the whole of a group of animals characterised
12 INTBODUCnON. [CHAP. L
as just as independent of one another as are the chemical atoms.
Hence since it is a choice between this explanation or none, the
Darwinian theory is accepted by the oyerwhelming majority of
naturalists.
One or two interesting consequences follow from the acceptance
of this theory. The structural features of animals are to be regarded
as adaptations to their surroundings, since they have been built up
by natural selection. Hence an isolated resemblance in a particular
feature between two species need not necessarily indicate that this
feature was present in the common ancestral species, for similar
surroundings may have evolved a similar modification in two
animals only remotely related. Such similarities are called Homo-
plasy, whereas resemblances believed to indicate blood-relationships
are grouped under the term Homology.
Again, the inmiature forms of some animals are found to exhibit
strong resemblances to the adults of others, and the eggs of all the
highest animals show the strongest general resemblance to the
simplest animals — the so-called Protozoa (Gr. Trpwros, first, iwov,
animal). If these resemblances are to be interpreted in the same
way as those prevailing between adults — and it is illogical to refuse
to do so — ^then we are driven to conclude that most animals in their
development pass through stages when they exhibit many characters
once possessed by their ancestors, commencing at the stage of the
Protozoa. These latter animals, since they are about as simply
constructed as we can imagine living matter to be, may be looked
on as slightly modified survivors of the first animals which appeared
on the globe.
This method of interpreting the changes which occur during
development is what is known as the Recapitulation Theory,
because during Ontogeny (Gr. ov, ovro?, being) or the development
of the individual, nature recapitulates to some extent the develop-
ment of the species in past time, Phylogeny (<;(>vXov, a stock, a race).
There are, however, a great many other factors which have modified
development, and the determination of these and their separation
from the hereditary factor is a task requiring careful study and one
which is as yet far from complete.
by haying the same groand-plan of structure and beUeyed to be the descendants
of a common ancestor, from whom no other living animals are descended.
The essential feature about a phylum is its isolation, in the present state
of our knowledge, from other phyla. Of course it is believed that at bottom
all living beings constituted one phylum, but there are enormous differenoes
in structure which can only be bridged by imaginative hypotheses.
13
CHAPTER n.
Phylum Protozoa.
The Protozoa are distinguished from all other animals (1) by
the fact that they do not produce ova and spermatozoa but that the
whole animal engages in the processes of conjugation and repro-
duction, and (2) by the fact that the protoplasm of the body is never
di£ferentiated into tissues nor exhibits cellular structure (see p. 27) ^
The higher animals are often grouped under the name Metazoa
(Gr. furd, after; C^ov, an animal) in order to contrast them with
the Protozoa, but whereas the Protozoa, since they have a common
structural ground-plan, constitute a phylum in the sense defined
in the last chapter the same is by no means true of the Metazoa.
Hence the name Metazoa does not denote a phylum but is a mere
conyenient collective term.
The term Invertebrata is also a mere collective name; it
is employed to designate all animals which do not belong to the
phylum Vertebrata. Like the name Metazoa its convenience in
promoting terseness of expression is its only justification. The
Protozoa are thus Invertebrata and the Vertebrata are Metazoa.
The phylum Protozoa includes the simplest and lowest
members of the animal kingdom. With few exceptions the members
of this phylum are too small to be seen by the naked eye, and yet
many of them are of great importance in the economy of nature.
In order to fix our ideas we may select one of the simplest
Protozoa as a type for examination. Amoeba, some-
times called the Proteus animalcule, from its power
of continually changing its shape, is found in the mud at the
^ These statements are true of the vast majority of animals classed as
Protozoa. The exceptions are for convenience classified as Protozoa, but it
seems to the authors that in the light of a fuller knowledge they may turn out
to be survivors of that great series of forms which must, if the evolution theory
be true, have intervened between the Protozoa and the Metazoa.
14 PROTOZOA. [chap.
bottom of ditebes, ponda and pools of atagDant water. There are
several species TaiyiQg somewhat in size included under the
generic name Amoeba, all of them, however, are so small as to
necessitate the use of a microscope for their examination. When
magnified an Amo^ki appears like a small, almost transparent lamp
of jelly, in which we can distinguish a thin outer rind and inner
./^ /
'b:
Fia. 1. Amoeba proUutx S80. From Qniber.
sabstancfli. The firrt, called the ectoplasm, is almost abeolatelr
transparent, the second, called the endoplaam, has usually a
grayish tinge, due to the presence of minute solid partacles or
grsQules, and is therefore described as granular. Often indeed,
good sized objects of various shapes and generally of a green or
yellow colour, can be seen in the endoplasm ; these an the
undigested remains of the microscopic plants which the animal has
eaten and are snrronnded by babbles of water, termed vaoaoles.
Amoeba frequently engnlb particles of sand, though fin: what
purpose is unknown ; possibly to render itself less palatable to
animals which might eat it If the Amofba is healthy we shall
see it move. The txanqiarent ectoplasm slowly sends out a
il] amoeba. 16
projection, and then the granular eodoplaam flows into it As of
conrse the size of the animal does not alter, when a process is
thrust out in front, the rest of the animal must follow it by
shrinking away behind ; indeed it would no doubt be more correct
to say, that it is the shrinking or contraction of the animal's body
behind, which forces out the projection in front, for the movement
of an Amoeba, like the movement of every other kind of animal, is
brought about by a series of contractions.
These projections are called by the awkward name of pseudo-
podia (Or. ^cvSi79, false , ttoSiov, a little foot) ; the adjective pseudo-
implies that they are not fixed organs like our own limbs, but are
made at any part of the surface of the body. When Amoeba comes
across anything it desires to eat, it throws out pseudopodia on each
side of it ; these then unite beyond the object, and so the latter
becomes engulfed, so to speak, in the body of the animal, where
it is digested. It may thus be said, that Amoeba flows round its
prey. Once the prey is inside, it is surrounded by a drop of water
poured out of the surrounding protoplasm or enclosed with the food.
There is probably some substance secreted into this water which
acts on the prey and dissolves it.
One of the most marked features in which Amoeba differs from
other animals, from ourselves for instance, is, that it possesses no
separate parts or organs, such as stomach, hearty lungs, etc., fitted
to perform the separate vital actions, or functions as they are
called. It breathes, that is, absorbs oxygen and gives off carbon
dioxide all over the body ; and it likewise excretes, that is, gets rid
of the oxidized protoplasm, at all points of the surface. I^ however,
we are so fortunate as to come across a large Amoeba, which is
at the same time comparatively clear of granules, and moving only
sluggishly, we may be able to make out two definite objects in the
endoplasm. The first of these is called the contractile vacuole
(2, Fig. 1) ; this is a clear round space, which slowly enlarges and
then suddenly vanishes, and then reappears in the same place and
goes through the same series of changes. It is believed that the
cause of this appearance is that at a certain point in the endoplasm
a substance is produced by katabolism with a strong affinity for
water; this substance attracts to itself from the surrounding
protoplasm water, carrying in it the soluble waste products, in fact
draining the protoplasm and forming a drop. This drop swells
until it, so to speak, bursts the covering of protoplasm separating it
from the outside water; the space it occupies then collapses^ but
16 PROTOZOA. [chap.
as soon as the fluid hais escaped the rent in the protoplasm joins
up again, and as the excretory process continues the drop of fluid
again accumulates.
The other object which we may perceive is the nucleus. This
Nucleus ^ ^ spherical body consisting apparently of the same
kind of material as the endoplasm, only slightly denser
(1, Fig. 1). If we, however, kill the animal by running in some iodine
under the coverslip, the nucleus stands out at once in contrast to the
rest of the protoplasm by its property of taking up more iodine and
appearing stained a much deeper colour, and this happens in the
case of any Amoeba, whether we have been able to see the nucleus
whilst it was living or not. The material contained in the nucleus
is an essential part of the body: when deprived of it metabolism
within the protoplasm slackens and finally stops. Nearly all living
things, animals or plants possess one or more nuclei, though in
some rare cases the essential nuclear material is dispersed through-
out the protoplasm. The bigger the plant or animal, the more
nuclei it possesses. The so-called " Flowers of Tan " (Mycetozoa),
which creep over the hides in tan-pits, are some of the few Protozoa
which are distinctly visible to the naked eye ; they may be com-
pared to gigantic Amoebae with branching pseudopodia, and
they have thousands of nuclei. In the case of certain Protozoa
it has been proved that if the animal be broken in pieces,
those bits which contain a nucleus can repair themselves and
continue to live, eventually growing to form an animal like the one
of which they are fragments; but those bits which contain no
nucleus, though they continue to live for a short time, have no
power of feeding themselves nor of growth. On the other hand if
the nucleus be fireed firom protoplasm it dies ; life depends on the
mutual reactions of protoplasm and nucleus.
The reproduction of Amoeba ordinarily takes place by the simplest
Re reduction couceivablo proccss ; the animal divides itself into
and Encyst- two. This proccss is Called fission : and it is found
"**" * that the nucleus always divides into two before the
body as a whole shows any signs of the process. When Amoebae
are exposed to unfavourable conditions, such as the drying up of
their surroundings, they have the power of enclosing themselves in
a cyst. They draw in all their pseudopodia and assume a spherical
form, and the cyst appears as a membrane on the outside which
then thickens. Once enclosed within its cyst. Amoeba can be blown
about like a particle of dust, and in this way we can account for
n.] LOBOSA. 17
the hot that we sometimes find Amoeba in infusions, that is, solu-
tions made by allowing some animal or vegetable matter to stand in
water exposed to the air. If we put some hay or meat into perfectly
pure water and expose it to the air, it will putrefy ; this is due to
the development of minute microscopic plants called Bacteria, the
spores of which are carried by the air : at a later stage, various
Protozoa and sometimes Amoebae will appear. At one time it was
supposed that both Bacteria and Protozoa were spontaneously
developed out of the dead meat, but it has been shown that if the
water and meat be boiled, so as to kill any spores which may be in
them, and the mouth of the vessel plugged with cotton-wool whilst
steam is issuing, so that the air penetrating from outside through
the interstices of the wool has all the spores it may carry strained
off before it comes in contact with the water, neither Bacteria nor
Protozoa will appear. The cyst which invests the body of the
Amoeba is the first instance we have met with of what is called a
secretion. A secretion has already been defined as dead substance
which is of use to the animal, and which is produced by the
decomposition of protoplasm.
In one or two cases an Amoeba enclosed within its cyst has been
seen to break up into a number of rounded germs which were
eventually set free by the breaking of the cyst and each of which
then took on the form of a minute Amoeba. This process is called
sporulation and the germs to which it gives rise spores. It is
unknown whether every species of Amoeba sporulates and if so
under what conditions this occurs.
When we were describing the endoplasm of Amoeba above, we
called it granular, owing to its containing solid particles. When
the highest powers of the best microscopes are used, it appears that
both endoplasm and ectoplasm have a structure comparable to that
exhibited by a mass of soap-bubbles. The walls of the bubbles
consist of the actual living substance which is probably composed
of the biogen molecules ; the cavities are filled with water which
has in solution the products of digestion, from which the living
framework repairs itself, and likewise the excretory products. This
water also conveys in solution the oxygen necessary for life and
removes the carbon dioxide. It is only by means of a structure like
this that the complicated chemical changes which constitute life
can be perfectly carried out by every particle of the living substance.
The granules are temporary deposits in a solid form, either of
S. (ft M. 2
18 PBOTOZOA. [chap.
matter reBulting from katabolism, or of nntritdoiu mttter not yet
aBsimilated.
We must DOW glance at some animals allied to Amoeba, in orda
to gain some idea of the group Protozoa as a whole.
Diffiugia and Arcella are both found in the mud of pools and
ponda; they resemble Amoeba in general structure
but differ from it in being provided with shells. In
consequence of having these they are only ^le to put out
pseudopodia at one spot, the mouth of the shelL The shell of
Diffluffia is composed simply of grains of sand stuck together with a
secretion ; it haa the shape of a pointed egg with the thick end cut
off (1, Fig. 2). Areeih, on the other
1 hand, makes its shell entirely out of
its own secretion ; this is colourless
when thin, but as the animal grows
older the shell becomes thicker and
acquires a characteristic brown colonr,
and we are enabled to recognize that
it consists of chitin. This is really a
name for a class of substances which
are constantly met with in the animal
kingdom and which are probably allied
in composition to uric acid. Out of
chitin, for instance, all insects construct
their hard cases. It seems probable,
that the self-destruction of protoplasm,
which results from the ordinary vital
1. Shell ootopoBed of partiolu functions, may in many cases give rise
Mim»L TSioJdL"' "" *° ^^^'^ ^^ '***' V<»^Y» in Arcella,
the shell is at once a protection and
the ordinary excretion. The shape of this shell is like a watch-glass
with a flat lid testing on it, and in the middle of the lid there is a
round hole through which the pseudopodia come out Sometimes
gas bubbles (7, Fig. 3) can be seen in the body of the animal, which
t«nd no doubt to baUnce the weight of the shelL Owing to the blunt
character of the pseudopodia, Atao^, Diffiugia, Areola and similar
forms are united into a class tenned Lobosa (Gt. Xofiot, a lobe).
The Frotoztion Gromia possesses a thin membranous shell,
FonmiDihn. ^^P*^ somewhat like that of Diglagia: bat the
animal shows two important differences; first, liie
n.] FOBAlflNIFEBA. 19
protoplasm 4^ which the body U composed, besides fillmg the shell,
extends in a thin layer all over its outer suriace (2, Fig. 4), and
secondly, the pseudopodia, vhicli are given off from this layer, are
thin and delicate threads which join and interlace with each other
■0 as to form a network. Gromia seizes its prey by entangling it in
these fine psendopodia ; these then flow together and form a little
island of protoplasm surrounding the captive, which is thus digested
quite outside the main part of the body ; the products of digestion
Pia. B, AntUa Utoide* x 500. From Laid;.
. Bean fMin abova, B. Saen from tha ddo, optioal wotioii. 1. Bhell.
3. Puadopodia. 8. Edge of opening Into uieU. 4. Thread atUahmg
•nimkl to inner fnrboe of ^all. 0. Nnoleai. 0. Food VMnole.
7. Om TaeaoU.
being carried along the psendopodia into the protoplasm which is
inside the shell
We may next consider a rather laiger ProtozSon, allied to
Gromia and like it possessing a shell, which hower^ is composed
not of chitis bnt of calcium carbonate. The name of this animal
is PolyitotiuUa (Fig. 5). Like Gromia it possesses delicate inter-
woreu psendopodia idiich spring from the whole surface, since
there is a thin layer of protoplasm covering the ontside of the
■hell ae well ■■ the main mass inside it. Unlike Gromia, however,
S— 8
. 4. Qromia (rr(fonni« x 250, bat tbe paeadopodia &» leu than one-thlid
their raUtiTe nstnral length. From U. 8. Sohnltze.
Shell. 2. Protoplasm •urronndine shell. 3. Paeudopodia, fnalng
together in placea and Barroanding food partioles anoh ae diatoms.
CHAP, il] fobaminifera. 21
PolystomeUa has a shell which is perforated by a large nmnber of
minute holes, through which pass cords of protoplasm, connecting
the inner and outer parts of the animal Polystomella is therefore
a typical example of the Foraminifera (Lat. foramen^ a hole ;
fero, to carry), a class which includes countless varieties of microscopic
shells, generally composed of calcium carbonate, less frequently
of flint (silica). Gromia is included in the Foraminifera, though it
does not possess the peculiarity indicated by the name, because its
structure as a whole shows that it is really the same kind of animal
There is another most instructive feature of the structure of
Polystomella wherein it differs from Gromia. K we examine the
shell with the low power of a microscope, we shall see that it is
shaped like a rather flat snail shell or the shell of the Pearly
Nautilus. If, however, we dissolve away the shell with dilute acid
so as to expose the proper body of the animal, it will be seen that
this is made up of separate parts, united to each other by two or
three little bridges of protoplasm, and arranged one behind the
other in a spiral series. This is the first example we have met with
of the repetition of similar parts in a definite order, but upon this
principle of the repetition of similar parts the bodies of the most
complicated animals are built up. It is no doubt fundamentally
the same thing as reproduction, only the various units which are
produced, instead of separating frooi each other and leading separate
existences, remain connected, and, as we say, are co-ordinated
to form an individual of a more complex kind. In Polystomella
the various parts are called chambers; a name which properly
belongs, and was first applied to, the segments of the shell enclosing
them. It is worthy of note that it is only the protoplasmic body of
Polystomella which shows this composition out of definite units
arranged in a definite order; there may be one large nucleus or
a considerable number of smaller nuclei, but they are not arranged
in correspondence with the chambers.
The group Foraminifera, of which Gromia and Polystomella are
examples, is of an enormous extent, and includes an immense variety
of forms, the variety being brought about by differences in the
number of chambers and the way they are arranged in series. The
Foraminifera almost all live in the sea; some, like the two we
have described, creep about amongst the sand and debris at the
bottom of pools or other places where the water is quiet; many
others float at the surfeu^e of the ocean, the protoplasm which clothes
the outside of the shell having numerous vacuoles filled with fluid
22 FBOTOZOA. [chap.
probably less dense than the aesrwater, and tbos serving sa floats,
la auch iQconceivable myriads do these floating Foiamiiiifera exists
Fia. S. Polyitomella eriipa. Highly magnified,
1. Shell. 2. Paeiidopodia.
that their empty shells form thick banks of impalpable white chalky
mnd at the bottom of the ocean, and tbe familiar white chalk of
il] radiolabia. 23
our English cliffs and hills is largely made up of the shells of
Foraminifera.
The Foraminifera show the same two methods of reproduction,
viz. fission and sporulation which were mentioned in the case of the
Lobosa. Indeed the progress of research has rendered it probable
that they are found in all classes of Protozoa. The presence of a
hard skeleton has however produced modifications in the process of
fission. When such a form as Polystomella for instance is about to
reproduce by fission the protoplasm emerges firom the old shell and
divides repeatedly into a number of pieces each as large as the
central chamber of an ordinary individual These then secrete
round themselves shells and begin to bud off new chambers and
gradually acquire the size and shape of adults. When on the
contrary Polystomdla sporulates the protoplasm whilst still within
the shell divides into a large number of small rounded pieces — these
acquire hair-like projections called flagella which can be moved
to and fro and by means of which they swim and then escape from
the shell and move freely about. They coalesce with one another
in pairs, and the resultant mass or zygote acquires a shell and
begins to bud off new chambers. Since in spite of the fact that
the zygote has resulted from the union of two spores it is much
smaller than the product of fission — the adult rasulting from the
growth of a zygote is distinguished from that resulting from fission
by the small size of the initial chamber. Hence we can distinguish
a microspheric form resulting from sporulation from a megalo-
spheric form resulting firom fission. Lister has shown that in
Polystomelia there is an alternation of fission and sporulation,
probably more than one generation of fission intervening between
two periods of sporulation.
We may pass now to the consideration of some Protozoa,
which show a good deal of resemblance in many
points to the Foraminifera, though they have very
marked peculiarities of their own. These are the Radiolaria;
they have delicate threadlike interlacing pseudopodia, and their
protoplasm is divided into two parts — an inner and an outer —
by a membranous case having pores, through which the two parts
communicate with each other. This case, the central capsule,
may be compared to the Foraminiferan shell, but the interesting
fiict is that these Badiolaria have in addition to this another skeleton
composed not of chalky — calcareous — but of flinty — siliceous —
substance, as are also some of the shells of the Foraminifera. This
24 FBOTOZOA. [chap.
iinty skeleton may conBist simply of isolated needles sticking out
on all sides from the centre ; oftener, however, it consists of a
beautiful basketwork as in HeliosplKura inermU (Fig. 6), and aome-
Fi9. e. Bebotphatra inermis kZSO, From Bfltschli.
1. Skeleton. 3. Oenttal eapsule. S. Nnclena.
times we find several of these baskets one within the other, like the
Chinese ivory ball. The Radiolaria, like the free-swimming Fora-
minifera, have a bubbly outer protoplasm, and often drops of oil in
the inner protoplasm; these structures serve to sustain them and
they are found floating at the sur&ce of the sea amongst the Fora-
minifera. At the bottom, in medium depths, their flinty skeletons,
though mixed with the calcareous shells of the Foraminifera, do not
affect the general character of the chalky mud (called the Ghbigerina
OOte, from the name of one of the commonest Foraminifera found
in it), but at greater depths, owing to the enormous pressure, the
quantity of carbonic acid dissolved in the water increases very
much — on the same principle that the preaaure inside a soda-water
bottle keeps the gaa dissolved — and all the shells composed of
ohalky matter are dissolved, only the flinty skeletons being left.
The bottom mud here entirely changes its character and is called
Radiolarian ooze.
The next group of Protozoa to be considered is a very remark-
able one, including the largest forms known. The
yee io». go.pj]]g^ "FloweTB of Tan" (Mycetozoa) are brightly
coloured patches, which may be seen on the surface of the oak-hark
used in tan-pits. Similar patches may be seen on old tree stumps
n.] MYCET020A. 25
utd on thfl sattaM of beanstalks which havQ been wet for a con-
dderable time. These patches under the microscope are seen to
tesemble enonnous Amoebae with thin branching pseadopodia,
Tta. 7. Yariooi stagM of Chondriademia difformt. From StTasbiiTger.
A. FlsgellulA laftviiut ajai. B & C. Flogellulu. D young and E older
•moebnlaa. B. Amoeholite fasing to (orm plumodiam. AU x G40.
Q, FlMmodlomxtKL 1. NucUdb.
which are apt to join one another to form networks, although these
networks are muc^ coarser than in the case of the Poraminifeia.
The fluid endoplasm is seen to have a regular flow alternately
backwards and forwards in these pseudopodia ; the movement of
the whole mass in any direction beiog due to the predominance of
the forward flow over the backward, or vice versa. When stained
the protoplasm is seen to include thousands of veiy small nuclei.
The name Mycetczoa literally means Fungus animals (from Gr. p-vicip,
a fungus, Z<^, animals). They are also often called Myxomycetee —
literally Slime-Fuugi, both names having been suggested because
their special mode of reproduction leads some naturalists to con-
sider them to be plants. Their power of encystment is very
marked, the slightest tendency to drought calls it into action, and
then a mass will break up into numerous cysts, which will remain
26 PROTOZOA. [chap,
perfectly passive until wetted. Before reprodnction, the same
process occurs, but the contents of the cyst divide repeatedly so
as to form a mass of small germs — spores — which acquire walls
of cellulose, a constant product of plant Hfe. Such spores arc
called chlamydospores. Some of the protoplasm not used in the
formation of spores forms long threads of cellulose, called collectively
a capillitium, which when wetted expands and so expels the
spores. The appearance of cellulose was the only justification for
regarding these animals as in any way allied to plants, and it is
known that cellulose is quite a constant product in some groups of
animals. The contents of the spore escape as a germ propelling
itself by a vibratile thread called a flagellum (B and C, Fig. 7),
the germ itself being termed a flagellula. This thread is soon
withdrawn and the germ takes on the form of a small Amoeba and
is then called an amoebula (D, E, and F, Fig. 7). Many of these
amoebulae coalesce to form the adult form, which is called the
Plasmodium (0, Fig. 7), a name given to the result of the fusion
of a number of originally separate animals.
The Sun animalcules, or Heliozoa (6r. 17^.109, the sun), which
inhabit, with few exceptions, fresh water, were formerly
confounded with the Radiolaria, but they are in
reality very different from these. They are spherical in shape and
have a large number of stiff pointed pseudopodia sticking straight
out all round them, like the conventional rays in pictures of the
sun. The common and scientific names are taken from this circum-
stance. Since these animals float about, it is not surprising to
find much the same structure in the outer protoplasm as we found
in Badiolaria and the floating Foraminifera. The pseudopodia are
different in character from those of the Badiolaria, since they do
not interlace, nor do they run together when they seize prey ; the
captured food is simply pressed in towards the body by the
bending of the pseudopodia, and when it is brought quite close, a
broad irregular pseudopodium, like one of those of Amoeba, shoots
out and engulfs it. Pseudopodia were defined in the case of
Amoeba as irregular projections shot out at intervals from the body
and soon withdrawn, and the question arises how far we have any
right to call by the same name these stiff projections of the Heliozoa.
They are, however, true pseudopodia, for if the animal be sub-
jected to strong irritation they are all withdrawn. These unimalR
show a most interesting example of the repetition of parts. The
species Actinophrys sol and Actinospkaerium eichhomii are both
n.] HELIOZOA. 27
comparatively cominoQ inhabitants of our ditehes. The fitst is,
howerer, exceedingly miante, not more than -^innr^b of sn inch
in diameter and poasesses only a single nucleus, whereas the second
is large enoogh to be jost visible to the naked eye, and h&s about
SOO nuclei There ia here repetition of the nuclei, but no division
of the protopUem, vheieas in Polyttomdla there ia segmentation of
Tio. 8. Aetinophryt lol x about 800. Ttom Bionn.
1. EetoplMm. 9. EndopUnn. B. Contnctils Tacaole. 4. Food vMniole.
t. Naoleos. 6. Axit of a paeudopodiQm, Btiffei tban the protoplum
«hieh oofen it.
the protoplasm, but no corresponding multiplication of the nucleL
If both were to occur simultaneously and to correspond so that the
body were to consist of a number of segments of protoplasm, each
with its nndens, the animal would be said to be multicellular,
each unit being spoken of as a cell ; but it would no longer be a
Frotoioon.
So far we have been considering animals which, however much
they may differ in details, are all essentially naked
masses of protoplasm, and in them no very definite
organs are set apart for Uie performance of special functions. We
most now examine some Protozoa of a distinctly higher grade of
Btmcture, wherein definite organs exist ; by the word organ being
meant a part of the body definitely fitted to perform some special
function for the general benefit of the whole. If we examine the
<^ V <i!<«£ tv wnMiwis ^KoiHiw x a BhMt Waiifiil animal
1^ ■■•r.r-jA. '^wu/mIu mh wODfla^ tbr ifa^« ijf « blne-bfiU
«tr -: • .DiNfr ji » -untf ttiik-aw ta^ lai a Ma-^ioiied body;
w>M»- a ut --ukI;. .fc « iw 7i *nat ifiiiew «fpc«t. such as,
. 7in.-«^w<). »m. Tut ^met «f d» body oort»-
i)T iC Vii Mil V brjai ami taned iwhrarda ;
- Ill, ^intA. » uSai thr f>mst*M«^ dwn ia a
n.]
CILIATA.
29
Fio. 10. VoHieella
microstoma x about
200.
From Stein.
flattened projection called the disc. Between the peristome and
disc there is a groove, and in this we can make out some short
hair-like structures waving to and fro; there is
a circle, or rather one twist of a spiral of these,
as we can see when the animal turns the surface
of the disc upwards. By the regular rhythmical
bending of these cilia (Lat. cilium, an eyelash)
as they are called, and possibly by the move-
ment of a rolled membrane which projects into
the mouth, a vortex is produced in the water,
which draws particles of food to the Vorticella,
The cilia and the stalk are definite permanent
organs, the first of the kind we have met with.
But the possession of these organs is not by any
means the o)|ly difference between Vorticella
and the lower Protozoa. The shape of the
body, though it varies slightly with the state
of expansion or contraction, is practically con-
stant ; no pseudopodia are given out. This is the
result partly of the possession of a firm membrane covering the
whole of the body, called the cuticle, which is a protective secretion
like the shell of Arcella only much thinner and so intimately con-
nected with the protoplasm under it as to be inseparable; but the
constancy of shape is also due to the fact that the outermost layer
of the protoplasm itself is finely striated, constituting a specially
contractile sheet surrounding the body and distinctly marked off
from the inner protoplasm. This sheet is called the cortical
layer and the striation is caused by the differentiation of the
protoplasm into parallel strings called fibrils, embedded in different
material acting as a cement This arrangement of protoplasm
makes its appearance whenever the contractile power is specially
developed. The stalk, which is entirely composed of this layer,
might almost be regarded as a muscular fibre. The stalk is slightly
twisted and attached in a long spiral to the inner side of an elastic
tube of cuticle. When contraction occurs the stalk is necessarily
thrown into the most evident spiral curves, like a corkscrew ; the
restoration of the form after contraction is due to the elasticity of
the tube of cuticle.
Vorticella possesses a contractile vacuole and a nucleus just as
Amoeba does ; in small nearly transparent specimens both are easily
detected during life; in fact, if the specimen under observation only
30 PBOTOZOA. [chap.
keeps modemtely Btill, we can follow the ezpwisioQ and oontnctioB
of the Tocnole with tiie greatest eaasi The sadeiia is -nry large
and hss more or less the shape of a horee-shoe, thon^ the two ends
are generally at different levels, so that in reality it forms part of a
spiraL If we mn in some iodine it at once absorbs the stain and
stands ont Teiy distinctly ; the VorUceUa, however, frequently shows
1. Diio, 3. Mouth. S. Perutomial groove. i. VibrMile msmbiane in
moDth. 6. Gortical layer. 6. Eudoplaim. 7. Food-Taouoles. Tbe
lut ol the tood-TBouolea is neahng the podtioD ol the taai. B. Pharynx
■liowing tonoation of food-Tacuolsa. 3. Controotile vacaole. 10. Per-
nuneDt reeeptade into which the ooDtraotile Taonole openg. 11. Hioio-
unoUoi. 13. Nuolena. 13. Oontrootile flbrili mnaing into mnsole
in italk. 11. St«lk oontrMted (the axial fibre ahonld touch tbe oatiele
in pl40««).
its dislike to the operation by contractiag its body into the sliape of
a ball and snapping itself off from the stalk : it is then apt to gel
washed away from its position by the inflowing iodine and we may
have to search over the slide to find it When a Vorticella Is
irritated, the peristomial lip is turned in so as to lie against tiie disc,
II.] CILIATA. 81
and thus the groove in which the cilia lie becomes converted into a
tube and so they are efficiently protected.
We have seen above that VorticeUa uses its cilia in order to
produce a miniature whirlpool in the water by means of which
particles of edible matter — ^whether living or not — are drawn
towards it. Since, however, it possesses a firm cuticle and in
addition a specialized outer layer of protoplasm, the question arises
how the food is taken into the interior of the body. If we run
some Indian ink under the cover-glass we shall have a demonstra-
tion of how this is managed. The black particles are caught in
the whirlpool made by the cilia, they course round and round and
finally accumulate in a pit which opens into the ciliated groove
and from the bottom of tiiis they pass one by one into the internal
protoplasm of the body. This pit which obviously passes through
both the cuticle and the outer protoplasm — the cortical layer as it
is called — is termed the pharynx and its opening the mouth.
The particles of Indian ink which have passed into the body are
surrounded by little drops of fluid which are partly swallowed with
it and partly secreted by the protoplasm, in order to effect the
solution of the particle, that is, its digestion. Such a drop is called
a food-vacuole to distinguish it firom the contractile vacuole,
which, as we have seen, has probably an excretory office to perform.
As there is nothing nutritious in Indian ink, the VorticeUa soon
gets tired of trying to digest it, and the particles after having
travelled through the body in a more or less definite tract are
thrust out into the ciliated groove. Since this takes place at only
one spot, there must be a permanent hole in the cuticle here though
we cannot discern it, and this opening may be called the anus.
Therefore in contradistinction to Amoeba, where food can be taken
in and undigested remnants cast out at any spot on the surface,
in Vortkdla it is only at one particular spot that either action
can take place.
The reproduction of VorticeUa is a most interesting process. It
takes place by longitudinal splitting, or, as it is technically called,
fission. The disc splits into two, and the cleft soon reaches right
down to the beginning of the stalk, so that for a time we have two
bodies attached to the same stalk. One of these acquires a new row
of cilia round its base ; soon after the original circle of cilia and
the peristomial groove disappear; the animal then breaks loose
firom the stalk and swimming by means of its new circle of cilia
seeks a new place of rest. The other body remains on the original
w WWTOZOA. [chap.
.ik.^ .»«iw ' «j»4iMM.o^ it«. viffluwuf life. This simple mode of reprodnc-
^ ^ .«^ .^o .'ik -Oi h l(/ii^ ^ine unchecked, but experiments made on
^uiv*. >v;iv«.wi* 'u\»i^ v»^ I«e« allied to Vorticella show that it has a
.u^;. v^^vii v««) wDf^ speaking of reproduction in the introductory
a«^'«v». H«» -U4ttlth>^«^i that in sexual reproduction two germs had
V tt*v vj^iUiur th^&«« they could give rise to a new indiyiduaL
V^^^«^^ -^^^ lihii* has to happen at intervals in the case of
' i^ .M.x<,a» lU OMCC that the reproduction by division may go on in
« H.«uiAV liKUUMT. When this process (conjugation) is about to
.^c >fiwo» ^\k^ individual divides repeatedly by longitudinal division
HU4K'<iv .uiv ^' the new individuals produced breaking away from
i^w xulk, ^ that we have a bunch of minute VorticeUae attached to
'.iw s4^uo sUiilk. Tliis rapid division is clearly comparable to the
(Uvsvaa icrui^ ^^sporulation" which has been already described in
uIk* omm> s.^* the Lobosa and the Mycetozoa. The " spores," as we
iiu^ UH'iii the small Fc^r^zW/o^^ become free and swimming away
c^iUK'h (hem^lves to the sides of the large stalked individuals. There
Uwii ouAU^ 9k\\ interchange of substance between the two individuals
^hioh thuai ailhere to one another; the large nucleus of each breaks
up tuid di^p|>ears and a small subsidiary nucleus, the micronucleus
vU» b^. U), exceedingly difficult to detect at ordinary times, now
vHomM iuto view. It also breaks up and many of the portions
diMAppear, but a part of the micronucleus of the large one passes into
th^ little one and vice versa. In the case of the allies of Vorticella,
wh^ the two individuals which thus conjugate are of the same
SUM), they separate afber the operation, and each goes on dividing on
it« own account. In Vorticella, however, the small individual
«eem8 to be exhausted by the process and is absorbed into the
body of the other. It appears that this process of conjugation is
only effective when it takes place between individuals of different
parentages ; if care is taken to exclude all VorticeUae of foreign
stock from a collection consisting of the descendants of a single one,
either no conjugation takes place, or, if it does take place, it fails
to produce the results which normally follow, viz., increased vigour
of reproduction and other vital processes. When conjugation with
individuals of different parentage is prevented the individuals which
are produced by fission, after a certain number of generations, are
said to be badly formed, unable to feed themselves and die, and
this is the only instance of natural death which is met with amongst
the Protozoa.
like Amoeba, Vorticella encysts and it appears stiU more
n.] CILIATA. 33
frequently than Amoeba in infusions. The Vorticellae which are
fannd under these circumstances are usually small and transparent
and more favourable for observation than those occurring in
ditches. The genus occurs both in fresh and salt water.
Vorticella is but one example of a large cla^s of Protozoa
termed Ciliata, which agree nith it in all the essential points of
structure, but differ in the arrangement of cilia, the absence of a
stalt, and more rarely in the absence of & mouth aud pharynx.
This last feature is found only in those species which live in places
where the surrounding fluid contains dissolved nutriment which can
percolate in at any spot. An example of such a Oiliate is Opalina,
found in the intestine of the Frog. This ^^
animal is thin and plate-like and covered '*^\^ 2
all over with cilia of the same size ar- ^ ^'"
ranged in regular lines; this arrangement
of dlia, which is called the holotrichous t
arrangement (oAot, entire ; dpif, hair), is
always associated with the absence of a
stalk and with a &ee-swimming life. Vor-
ticella, on the other hand, is said to be
peritrichous (xtpi= around). Opalina
is farther remarkable for possessing a large
number of nuclei (1, Fig. 12), which is
a rare occurrence amongst the Ciliata. Fio. 12. Opalina
When, however, division commences it From Brona.
continues until the resulting pieces have 1. NnoUi. 3. Ectoplasm.
only one nucleus each ; they then grow
and do not divide again till they acquire the size they had before
division took place and also the same number of nuclei Hence
we might regard the multipHcation of the nuclei as the real repro-
duction of this form, the division of the protoplasmic body being
of lesser importance and setting in later.
Paramecium is one of the commonest (ree-swimming Ciliata.
It is of an elongated oval outline; seen sideways it has a thin
scoop-like anterior end and a thick posterior part, so that it is
nsnaUy described as slipper-shaped. It is holotrichous like Opalina,
but like Vorticella it possesses only two nuclei, one large and easily
visible and one, the micronucleus, small and difficult to detect. It
haa a well-developed mouth and deep pharynx situated on one
side and lined with specially long cilia. Paramecium is a beautiful
form in which to study the contractile vacuole ; there are two
8. am; 3
34 PBOTOZOA. [chap.
of these preeeot, one in the anterior and another iii the posterior
portion of the aoimaL If one of these vacuoles be vatched it can
be seen to contract and then slowly to re-appesr. Id the process
of reappearance five or eiz isolated drops are seen which elongate
into streaks arranged like the rays of a star. These streaks coalesce
with one another and soon form a perfectly spherical drop.
Paramecium poseessee pecoliar organs named trichocysts
(&, Fig. 13) embedded in the outer layer of the protoplasm. These
FlQ. 13. Faramieiwn
ftboat250. After BitUohU.
1. Moath at bottom of groove. 3, Oeaopbagng. 8. Food vacuole just
being formed. i. Coctraetile Taoaoles. S. TriohoojBtB which hftve
exploded: tlie nnexploded ones line the mitiole. 6. Cilia. 7. NaeleDB.
6. Micron Qcleua. 9. Contractile fibrils.
look like minute rods. When the Paramecium is irritated — as
for instance if it is deluged with dilute iodine — or approaches
IT,] FLAGELLATA. 36
prey it wishes to seize, these are suddenly shot out, assuming the
form of long threads, and they appear to exercise a stunning effect
on any small animal with which they come in contact.
The process of conjugation has been carefully worked out in the
case of Paramecium^ so that some more details may here be given
of what happens in that case. Two individuals about to conjugate
become attached to one another, the larger nucleus in each breaks
up into a number of minute pieces which are apparently used as
food by the rest of the protoplasm — at any rate they gradually
disappear. The smaller nucleus breaks up in eight pieces in each
case, and of these seven are cast out, the eighth divides into two
and of these two one passes over into the body of the other Para-
mecium and fuses there with the remaining piece of the corresponding
smaller nucleus. In this way each Paramecium becomes a zygote.
The two individuals separate, the single nucleus in each divides
twice so that four nuclei are produced, the Paramecium then divides
transversely so that each half has two nuclei, one of which becomes
the large and the other the small nucleus of the new individual
Passing from the Giliata, we next come to a small group called
the Suctoria, which are allied to the Ciliata, for
their buds commence life as holotrichous forms.
When they grow up they frequently become stalked like Vorticella,
lose their cilia, and acquire instead a number of stiff rod-like
outgrowths etiding in knobs ; these structures are termed tentacles.
These are able in some way we do not understand to seize small
animals and suck out their contents. Some secretion must be
produced which eats its way through the cuticle and dissolves
the contents of the prey.
The next group of the Protozoa we shall consider is a very large
Fi eUatft *^^ important one. It is called the Flagellata.
The members of it agree with the Ciliata in having a
fixed shape and a firm cuticle and probably (though this is difficult
to make out in the smaller ones) a specialized cortical layer of
protoplasm; they differ, however, in not having cilia, but in pos-
sessing instead, one or two — ^rarely more — whip-like organs called
flagella, which lash about in the water, and drag the animal after
them by a spiral screw-like motion, just as a steamship is dragged
by the screw when the engines are reversed. We may take as a
type Euglena viridiSy one of the numerous inhabitants of ditches.
This animal has a narrow elongated shape, pointed at one end, and
at the other — which is its front end — it possesses the vestige of
a— 2
36
PROTOZOA.
[chap.
ik phBr3nix, which is exceedingly narrow. It has a flagellum which
aziaes from the phar3mgeal wall near its inner end. Slightly behind
the pharynx there is a small contractile vacuole, and at the one side
of this a small red spot, which may very possibly be associated with
a smatiTeness to light About the middle of the body is a nucleus
which can sometimes be made out as a clear spot in the living
animal, bat which is most satisfactorily observed when the animal is
killed with oemic acid and stained with picrocarmine.
Fio. 14. Englena viridii,
A X 100. B, 0, D, E, F X 200 showing the different shapes assumed by the
aiiiuial during the euglenoid movements. 1. Pharynx. 2. Contractile
Vfuniolo. 8. Pigment spot. 4. Nuclens.
Two features in HJuglena, however, will strike us as very peculiar.
Oue is, that in spite of possessing a cuticle and a cortical layer of
l>n)t^>l>laHm, it is able to change its shape. It does not possess the
IKiwor of throwing out pseudopodia, but it bends its body in the
uioHt (extraordinary way, and contracts it till it is almost spherical
*V\w {HMMiliar wriggling movements which it thus executes are so
uiiliku anything else that they have been called euglenoid. The
rtmMoii Inr their possibility is no doubt that the cuticle is flexible and
tho (Mirtical layer powerfuUy contractile. The other peculiarity is
Mtill iiinni Htriking, and it is that the protoplasm is coloured bright
yrooii and tliat it contains particles of a substance very like starch.
Now (liiiHii tilings indicate that Euglena feeds itself like a plant, and
ilifit it coHHtructs its protoplasm out of carbon dioxide and mineral
ballM iliMMolvod in water in the presence of sunlight. The only points
lliMi'itfnrn that can be suggested in which it differs from plants are
llial' it han a llagollum and moves, and that it does not possess a
(uivming fif futlliilose. These supposed differences, however, will not
Mliihft ifKitniination ; the germs of many undoubted plants, such as,
il] flaqellata. 37
for instance, the sea-weeds, have no cell wall and propel themselves
by means of flagella What justification then, it may be asked,
have we for reckoning Euglena as an animal? What do we mean by
so classing it? It must indeed be admitted that when we come
to deal with the simple Flagellata, the animal and plant kingdoms
merge into one another, and the only valid line of division we can
draw is between forms which feed on solid food, and those which
absorb dissolved nutriment ; and amongst the latter we call those
forms animals which we believe to have been derived from ancestors
which fed on solid food. Now the pharynx in Euglena takes
in solid particles from time to time and these passing into the
protoplasm are apparently digested. We might therefore imagine
either that Euglma is a plant which has acquired a pharynx and is
commencing to live like an animal or else that it is an animal that
has acquired chlorophyll and has commenced to live like a plant
The fact that the pharynx is smaU and of little use is against the
idea that it is an organ which has been newly acquired — as all
organs are acquired — on account of its usefulness. It has the
appearance of being the vestige of a once useful organ and therefore
we conclude that Euglena is an animal which has begun to live like
a plant.
The reproduction of Euglena and of the Flagellata in general is
quite similar to that of the Ciliata ; they increase by longitudinal
division, but they also divide when in an encysted condition into
two or four, or a larger number of germs ; these germs are not
killed by drought When dry they are blown about, and so appear
in infusions. In infusions Bacteria appear first, then Flagellata,
and finally Ciliata.
Many flagellata are devoid of a pharynx altogether, but these
rarely have chlorophyll and subsist on the nutritive substances which
are dissolved in the fluid in which putrefying matter is soaking.
These are reckoned as animals on no very good grounds ; for it is
well known that plants can lose their green matter when they can
get the materials of protoplasm without building it up from carbon
dioxide. How entirely arbitrary the decision is is best shown
by the fact that many forms are claimed by both botanists and
xoologists. For this reason it is convenient to have a name which
denotes simply a living thing without prejudging the question as to
^vhether it is an animal or a plant Such a name is supplied by the
word organism, which is frequently used.
88 PBOTOZOA. [CHAF.
The hat group of Protozoa, the Sporosoa, agree widi the
SiKnoioa Ciliata in posoessing a &m catide and a highly
developed contractile cortical layer, bnt differ in
nerer havbg any organs Bncb as cilia or flagella ; their movements,
which are rery alnggiBh, are carried ont entirely hy contnetioiu
Fto. 16. Cltpttdrina iimga, ttoia larrt of Tipaia, the Uaddy-long-lagB.
Highl; magQitieJ. From Uget.
A, B, C, D, E. Stages of the devclopineiit of C. iunaa, at first vithin and then
pDshiDg its vay oQt of one ot the cells of the intestine of the Tipvla larva.
F. Mature form. O. Two forms conjngating. 1. Cell of intestine
of host. 3. Its nnelcuB.
of the cortex, which give riae to worm-like wrigglbgs. The name
Sporowa which was suggested by the frequently recurring sponUa-
tion which is a marked feature in the life-histoiy is inappropriate,
OS we have seen reason to believe that something analogous occurs
in all Protozoa. All the Sporozoa are parasitic ; that is to say all
live at the expense of some other animal which is termed the host
AH as a matter of fact pass the first period of their existence
II.] SPOROZOA. 89
embedded in the protoplasm of some animal. Some — the Coccidea
— remain throughout life in this position, but others when fully
grown become at any rate partly free, adhering to their hosts only
by one end. Only fluid nourishment is absorbed and consequently
there is neither mouth nor anus. There is never more than one
nucleus, although the body may be divided by partitions running
across the protoplasm into two or even three portions, placed one
behind the other. Reproduction takes place after encystment, and
this encystment is in most cases preceded by conjugation, so that two
individuals are enclosed by a common cyst. The contents of the cyst
break up into spores, which surround themselves with flinty cases and
hence are called chlamydospores (x^/^vs^a cloak). The proto-
plasm inside these spores is sometimes liberated as a small amoeba-
like creature which usually divides into two worm-like forms, which
wander into suitable positions and become metamorphosed into
the adult form. In very many cases, however, from two to eight
worm-like forms are formed by the division of the contents of the
spore before the case breaks. The name falciform embryo has
been given to these germs.
The best known Sporozoa are Monocystis found in the vesicula
seminalis of the earthworm, with a long worm-like undivided body,
Ckpsidrina blattarum found in the intestine of the Cockroach and
C, longa in the intestine of the larval grub of the Daddy-long-legs,
which lives in damp soil. This last form is quite free when adult and
is distinctly divided into two portions.
The ffaemamoeba and Haemomenas which cause Malaria in
man and allied forms which infest other vertebrates are classed with
the Sporozoa.
The Coccidea is the name of one of the sub-divisions whose
members remain entirely enclosed in the protoplasm of the infected
animals throughout life, and in some cases cause disease.
The larger Sporozoa are often easily detected by the intense
opaque white colour of the protoplasm, due to the inclusion of an
immense number of granules. This is in marked contrast with the
translucent protoplasm in which they are embedded.
40 PROTOZOA. [chap.
Phylum PROTOZOA.
The Protozoa are classified as follows : —
Class Gymnomyxa.
Naked forms without distinct cortical layer and capable of
emitting pseudopodia.
Order 1. Lobosa.
Simple forms with blunt pseudopodia which do not form
networks ; with or without a shell.
Ex. Amoeba, Dijlugia, Arcella.
Order 2. Reticularia.
Protozoa with thread-like pseudopodia which form networks ;
a shell is formed and protoplasm covers the outside as well as
the inside.
Suborder (a) Poraminifera. The shell consists of one
or a series of chambers composed of lime or flint.
Ex. Gromia, Folystoniella, Globigeriiia.
Suborder (h) Radiolaria. The shell is a single sac of
membrane. In almost every case there is an additional skeleton
of flinty needles often joined so as to form complicated basket-
works.
Ex. Tkalassicola, Heliospkdera.
Order 3. Myoetozoa.
Protozoa with branching pseudopodia forming coarse net-
works and devoid of skeleton. Reproduction by means of
spores coated with cellulose. The contents of many spores
coalesce to form one individual
Ex. Chondrioderma.
Order 4. Heliozoa.
Protozoa with stiff" radiating pseudopodia. Skeleton when
present only in the form of isolated needles.
Ex. Actinosphaeriwn, Actinophrys,
Class CORTICATA.
Protozoa with a distinct cuticle and almost alwajrs a distinct
cortical layer.
II.] CLASSIFICATION. 41
Order 1. CiUata.
Forms provided with cilia.
Ex. Vorticella, Paramoectum, Opalina.
Order 2. Suctoria.
Forms provided with sucking tentaclea
Ex. Acineta.
Order 3. Flagellata.
Forms provided with flagella.
Ex. Euglena,
Order 4. Sporozoa.
Parasitic forms, devoid of mouth, cilia, flagella or tentacles.
The younger stages at least are cell-parasites.
Ex. MonocystiSy Clepsidrina, Coccidium, Haemamoeba,
42
CHAPTER m.
Phylum Coelenterata.
It is difficult to say what idea the originator of the name
Coelenterata meant to convey. Most animals have hollow
insides (Or. icotXos, hollow ; cktc^ov, inside) ; the Coelenterata how-
ever are distinguished from all the more highly organized groups in
the animal kingdom by containing inside only one set of spaces,
which all communicate with each other and with the exterior
through the moutL
The Coelenterate of simplest structure is undoubtedly the
common fresh-water Poljrp {Hydra), (Pig. 16). K a
mass of weed and other debris from a ditch or even
the edge of a river be placed in a glass vessel along with some of
the water in which it was grown and allowed to settle, a niunber of
these small animals frequently termed polyps will usually be found
collected on the side of the vessel nearest the light. Several
distinct species are collected under the name Hydra. There are
three species recognized in Great Britain; Hydra fusca, about a
third of an inch long when expanded and of whitish yellow colour.
Hydra viridis, a quarter of an inch long, of a green colour, and
Hydra vulgaris, which is almost colourless. Similar species to the
fiiBt two, if indeed they are not identical, are common in Lower
Canada. Hydra fusca may be selected as a tjrpe.
The shape of this animal is that of a minute cylinder. The base
or foot is attached to the surface of the glass by an adhesive disc,
whilst the other extremity carries a circle of delicate thread-like
appendages called tentacles. In the centre of these, near their
point of origin, we can with a lens detect a minute conical ele-
vation, the oral cone (2, Fig. 16), at the end of which is the mouth.
The mouth is the only opening in the body and it leads into a space
which occupies the whole extent of the animal^ so that we might
CHAP. III.]
HYDRA,
43
with justice say that the poljrp is really simply a tube closed at
one end and open at the other : further, the tentacles can be seen
with the microscope to be nothing but thin hollow tubes, opening
into the central one (Fig. 17). The central space is often termed a
stomach, and in the case of Hydra the idea suggested by this
Fio. 16. Hydra futca x about 12.
A. Expanded condition. This specimen ia badding off a young Hydra, It
contains a large food mass in its ooelenteron, probably a Daphnia or some
other fresh-water Crustacean. B. Retracted condition. 1. Mouth.
3. Oral cone. 8. Tentacles. 4. Bud. 5. Endoderm. 6. Foot
term is correct. In other Coelenterata the space performs other
functions besides those of the human stomach, and the term
coelenteron, which does not imply any function, is preferable.
With the microscope, however, we can make out a number of
farther points. If the edge of the animal be carefully focussed it
can be seen that the body-wall consists of two layers, an outer
COELENTERATA. [CHAP.
Fra. 17. A tongitndiiuU seotion through the body of a Hydra: tomewhAt
diagramnutio, the det4ila of th« oelli iMing omitted. Mtgnified.
1. Month. 9. Foot. S. Tentaole. 4. Ooet^taron ot digeative Mvltjr.
6. Ectoderm. 6. Endodeim. 7. HesogloM or itnutnreless lamelM.
a Battaries of UuMd mUi. 9. Twtit. 10. OtH7 with nngle onm.
III.] HYDRA. 45
clear one, termed the ectoderm (Gr. cktos, external ; 8€pfjLa, skin),
and an inner one called the endoderm (6r. IvSov, inside), which
is green in Hydra viridis and brownish in Hydra fusca ; so
that we may speak of a skin as distinct from the lining of the
coelenteron (Figs. 17 and 18). It is further possible to make out
under the microscope that at any rate the outer layer is not
homogeneous, but is composed of separate small pieces. It is
necessary, however, to examine thin sections of specimens which
have been hardened by being soaked in corrosive sublimate or some
similar reagent, before one can reaUy get a good idea of the
structure of the "skin" and of the "inner lining" of the poljrp.
Then it is seen that both are made up of the repetition of similar
parts, and that in each of these parts there is a single nucleus.
Such a portion of protoplasm, marked off from the surrounding
parts by a definite boundary^ is called by Zoologists a cell The
wall or boundary of the cell probably consists of a tliin layer of
some secretion, in many cases, if not in most, traversed by bars or
sheets of protoplasm connecting the cell with its neighbours.
Around this term " cell " many battles have been waged and its
indiscriminate use has led to much misconception.
It used to be said, for instance, that the Coelenterata
were multicellular animals, as opposed to the Protozoa, which
were unicellular. Now it has already been pointed out that the
centre of the vital processes is the nucleus, which controls the
processes going on in the protoplasm, and that in some of the
Protozoa, such as Actinosphaeinum and Opalina, this essential organ
is repeated several hundred times. But an Actinosphaerium or an
Opalina certainly does not correspond to a so-called cell of Hydra,
with its single nucleus ; the relation between them may rather be
defined by saying that, whereas in Actinosphaerium the areas of
control of the various nuclei are not visibly delimited from each
other, in Hydra, on the other hand, this delimitation has to some
extent taken place, leading to the appearance of cell-structure.
But not only are cells to be detected in Hydra ; the cells are not
all of the same kind. Those forming the endoderm are very
big and often have great watery vacuoles near their inner ends ;
they also contain the coloured granules to which the colour of the
animal is due. The cells of the ectoderm or outer skiu, on the
contrary, are much shorter than those of the endoderm and are
more or less pear-shaped, the broader end being turned out. Be-
tween their narrower bases we find groups of very small round cells
46 COELENTEBATA. [CHAP.
(2, Fig. 18). These so-called interatiti&l cells are young cells,
which partly, do doubt, become developed into ordinary ectodeno
cells as the older ceUs die and drop off, and in certain seasons of
the year they increase very much in nnmber at certain spots and
form the reproductive oi^ans (9 and 10, Fig. 17). The two kinds
of organs, male and female, are borne by the same individual ; in
the male organ or testis all the cells remain small and become
converted into the small spermatozoa; in the female organ or
ovary one cell increases very much in size at the expense of the
rest and becomes the egg-cell or ovum (1<^ Fig. 17). There is.
Fig. IB. TronaTerBS Beetion of Hydra fuiea.
1. Ectoderm cells (mjv-epithelial). 2. InlAtetitial ceUB. 8. KemAtoorstt.
4. CoetenteroD. G. Endoderm cells. 6. YoonolM. T, ?ood
granulea. 8. Nuclei.
however, a third change which these interstitial cells may undergo,
which is of the utmost importance to the animaL Some of them
move outwards and become wedged between and even embedded in
the large ectoderm cells near the surface, e&(!h developing in its
interior an oval bag filled with fluid. One end of this bag is
turned into the interior of it, forming a long hollow thread. The
whole bag is called a thread-capsnie or nematocyst (Gr. vijiia,
a l^iread ; Kv'trnt, a bladder) (Fig. 19). If now the cell in which
the thread-capsule is situated contracts, since the fluid in the
o^enle is incompressible, the hollow thread must be quickly turned
m.] HYDBA. 47
inside out and thaa thrust out of the capenle. If the irritation
of akin continnes the whole capanle will be pressed out by the
animaL These thiead-capsoles are most abundantly dereloped in
the tentacles, and a small amount of observation of the habits
of Hydra will show how they are used. If a small Crustacean,
or othei animal, approaches too near a Hydra, the latter makes
Fia. 19. CnidobUtt vith luge Nematocjet f^om tba body-irsU of Bydra fiuea.
Ei^; mftguiSed. From Schneider.
A. Unexp1od«d. B. Exploded. I. CuidoblBSt. 2. Nuolens of onido-
blMt B. Cnidoail. 4. MasoQlar aheath. S. W&ll of
nematocyit. 6. Thread. 7. Beflezed procesBee.
one swift lash with its tentacles and the luckless water-flea is seized
and at the same time paralysed. If we now remove and examine
the prey, we shall find it covered with exploded thread-capsules,
the threads of which have entered its body, and exerted a poisonous
action on it It is possible to induce a Hydra which is beinj;
observed under the microscope to eject its thread-capsules : we
48 COELENTERATA. [CHAP.
have only to irrigate it with a little ten per cent. aolntioQ of common
salt, and from all parts of the skin we shall see first the threads
shot ont, and then the capsules follow.
In the case of a fluid like salt solation, the stimulating action is
no doubt exerted over the whole surface of the animal, but an
examination of the tentacle when it is extended reveals an ar-
rangement for bringing about the explosion of the thread-capsule.
The surface of the tentacle is seen to be covered with little
swellings, in which are collections — one might say, batteries — of
thread-capsules (8, Fig. 17); and from the surface of the ectoderm,
in which they are embedded, delicate hair-like rods project out into
the water (3, Fig- 19). These rods are called cnidocils (6r. kviBtj^
a nettle; Lat. cilium, an eyelash) and are the simplest form of
sense-hairs met with in the animal kingdom. If one of these be
touched, it transmits a stimulus to the cell containing the thread-
capsule, the cuidoblast (6r. kviBtj, a nettle ; jSXaoros, a sprout), as
it is termed ; in response to this stimulus the cell contracts, presses
on and explodes the capsule.
In the first chapter it was pointed out that protoplasm, when it
effects movements, always does so by contracting. We saw, for
instance, that the extrusion of the pseudopodia of Amoeba could be
accounted for by supposing that part of the outside protoplasm
contracted and, so to speak, squeezed out part of the more fluid
interior. In the life of Hydra the principal movements which
occur are the shortening and lengthening of the body and the
tentacles (B, Fig. 16). Now it has been found that in these
movements, the shortening is effected by the contraction of the
ectoderm in a longitudinal direction, and the lengthening by the
contraction of the endoderm in a transverse direction, in con-
sequence of which the animal is rendered thinner and longer. It
has been further ascertained, by the examination of very carefully
prepared longitudinal sections, that each ectoderm cell possesses
at its base a tail running vertically, which is embedded in the thin
layer of jelly sometimes called the structureless lamella or
mesogloea (Gr. /ncVos, intermediate; yXottx, glue), which separates
ectoderm and endoderm (Fig. 20). The endoderm cells similarly
possess short tails, embedded in the jelly, but these run transversely.
These tails then are instances of the tendency of protoplasm, which
contracts regularly in one direction, to be drawn out into fibres in
that direction, or, in other words, we have before us the first step
in the conversion of an ordinary cell into a muscle ceU. * Cells
III.] HTDBA. 49
showing this inodiBcation are termed myo-epithelial (Or. /ivf-*
moscle) : the word epithelial is used to eiguify the arrangement of
cells ID a layer to fonn a pavement or mosaic.
The most important function of the endoderm cells is to digest
the prey which is captured by the tentades and thtnst into the
coeleateron. For this purpose they secrete a fluid which has a
great power of dissolving protoplasm. This fluid, termed digestive
juice, ie poured forth into the coelenteron and a large portion of
tiie prey is dissolved by it and passes by diffuaion into the endo-
derm cells, from which part is transferred in a similar manner to
1. Ectoderm. 2. Endodemi. 3. Meaogloes of BtrDctaieleea lamellft.
4. Kenuito^at. S. Cnidoci!. 6. Unsele-fibres o( actoderm cells
eat MTOH. 7. Naaleas of eatoderm cell. 8. IntarBtitial cella.
9. Cutide. 10. Figment granule. 11. Food grsDale. 12. Maclens
of andi>d«im cell. 13. Flaeellam. 11. Water lacuole.
the ectoderm. Certain portions of the prey, consisting of some of
tiie proteids, resist the aotion of this juice. These are seized by
psendopodia emitted by the endoderm cells and bodily engulfed,
to be subsequently slowly digested in food vacuoles. Any insoluble
parte of the prey, such as cuticle, skeleton, etc., are ejected by the
mooth. Some of the endoderm cells also bear flagella, whose move-
ment doubtless aids the circulation of the fluid in the coelenteron.
We have already seen that Hydra at certain seasons of the
year, vit., the late autumn, produces egg-cells (ova) and male
60
COELENTEBATA.
[chap.
germs (spermatozoa). Tke l&Uer are Bhed oat into the water, and
eventually some of them reach the egg-<»llB and unite with them.
This process is called feTtiliiation, and the fertilized egg-cella
cover themselves with spiny coats and drop off into the mud.
Here they remain through the winter ; in the spring the hard coat
cracks and out issues a minute Hydra.
But Hydra is hy no means limited
to this method of sexual reprodaction
in its power of multiplying itaelC All
tJirough the spring and summer, if it
be well fed, it buds or reproduces itself
by Gemmation. A small swelling
makes its appearance on the side of
the body; this is really a hollow pouch
containing -a cavity in communication
with the Goelenteron (4, Fig. 16). The
walls of the pouch are merely continua-
tions of the body-wall of the Hydra,
and hence consist of the same two
layers. The pouch rapidly lengthens,
and after a while a circle of tentacles
sprouts out from its free end, and a
mouth is formed in the centre. We
thus have a daughter Hydra still in
close connexion with the parent, the
coelentera of the two being in open
communication ; later, however, this
communication becomes closed and the
o£bpring separates from the parent
and leads a free existence. A third
method of reproduction, which probably
rarely occurs except artificially, is
Fission. If a Hydra be divided into
two halves, each half will grow up into
r individual
A large number of the Goelenterata, called the Hydromednsae,
agree with Hydra in iJl essential points of structure ;
the most important point of difference is that in
them the buds do not become separated, but remain
permanently in connection with the parent, and thus compH-
cated colonies are built up (Fig. 21). Other differences of less
Fid. 31. Obetia helgolandica
X 1. From HutUub. Thia
is the hydroid ^eoention
natmal size u it appears
to the Daked eje.
Hydro-
m.] HTDROHEDUSAE, 61
importance are that there is a horny shell, the perisarc (Gr. «pi,
aronod ; irdpi, flesh) (Fig. 32), secreted by the ectoderm at any rate
on the lower portion of the body, also that the tentacles are nearly
1. Eotodenn. 3. Endodemi. 8. Uoatb. i. Coelettteron.
B. Coonouio. B. Peruare. 7. Hydrotbeca, prolonged at base ot
Hydioid u ■ ahelf. 8. BlutOBtyle, a moathlesB hjrdroid bmrlng medau-
bndi. 9. MedosB-liiid. 10. Qonotheca, part of perisaro wbioh proteete
ths madnn-bnda.
always solid, containing, instead of tubular outgrowths of the endo-
deim, a solid ooid of cells (Fig. 22) with firm outer membranes and
52
COELENTEBATA.
[chap.
Medusa.
partially fluid contents, so that the cells have the same kind of
stiffness as a well-filled water-pillow. These cords likewise bnd ont
from the endoderm, but, as apparently the animal does not need the
tentacle cavity which exists in the Hydra, it has disappeared, and
the solid axis is essentially a strengthening or skeletal structure.
As in Hydra, there is an oral cone; and in some species of
Hydromedusae, at any rate, there is an additional row of short
tentacles at the tip of this. It has been stated above that the
buds do not become detached, but there is one kind of bud differing
much in shape from the rest which does become detached. In
such a bud, the whole body becomes very much shorter
and at the same time much flattened out in its lower
portion, so that the main circle of tentacles is widely separated
from the oral cone ; at the apex of the latter there is sometimes a
second circle of small tentacles. The flattened part of the body
becomes concave on the side towards the mouth so as to assume the
form of a bell or umbrella, and, owing apparently to this circum-
stance, the part of the coelenteron which it contains becomes so
pressed together, that by the adhesion of its upper and lower walls,
its cavity for the most part disappearing, it becomes converted into a
concave layer, called the endodermal lamella. Along four lines,
however, the cavity does not disappear (4, Fig. 23), and it also
remains open just beneath the circle
of larger tentacles at the edge of
the bell, so that in this way we have
a circular or marginal canal
established, communicating by four
radial canals with the part of the
coelenteron that still persists in the
oral cone, and opening to the exterior
by the mouth (1, Kg. 23). The
upper surface of the bell is styled
the exumbrella or aboral surface
(Lat. ab, away from ; os, oris, the
mouth) the lower the subumbrella
or oral surface.
The great mass of the bell is
composed of the jelly intervening
between the outer ectoderm on the
convex side and the endoderm. In this jelly solid strings sometimes
appear which give it a firmer consistence. The modification of the
Fio. 28. Free-swimming Medusa
of Ohelia sp.
1. Mouth at end of manubrium.
2. Tentacles.
8. Beproduotive organs.
4. Badial canals.
5. Auditory organ.
m.]
HYDBOUEDUSAE.
Fia. Si. Bougainvitliafmctuoia, xftboat 12. From Allman.
A. The fixed hTdcoid foim with nimieroaB bydroid polTpea and medasae in
-nriotit ittges of development. B. Tbe free swimmiDg sexual Medusa
which hM broken away from A.
64 COELENTERATA. [CHAP.
base of the animal into the shape of an umbrella causes the oral
cone to resemble the handle, hence the name manubrium (Lat.
a handle), by which it is usually designated in a bud of this kind
(1, Fig. 23). Just above the circular canal in most Medusae a fold of
the outer skin grows in towards the oral cone, so as to form a broad
circular shelf: this structure is called the velum (Lat. an awning)
(B, Fig. 24 ; 1, Fig. 25). The bud now breaks loose and swims by
contractions of the bell, aided by vibrations of the velum. Anyone
would now recognise it as a minute jelly-fish, though it really is
quite different in many points from the larger and better known
animals denoted by that term. Zoologists speak of it as a Medusa,
and speak of the stock from which it was budded as a colony
consisting of medusoid and hydroid persons, the latter term
denoting the ordinary buds which resemble Hydra, The terms polyp
and hydranth are also often used to denote a hydroid person.
A medusoid is in many respects more highly developed than
the hydroid person. The ectoderm cells composing the velum
and those forming the lining of the under side of the bell or
sub-umbrella are strongly drawn out into processes which are
muscular. In the velum these are arranged so as to form two
bands running round the edge of the bell or umbrella, one band
being in connection with the upper and another with the lower
layer of cells composing the fold of ectoderm of which the velum
consists. Just, however, where the velum is attached to the bell,
its cells— upper and lower — undergo another and more interesting
modification (4 and 5, Fig. 25). At their bases a tangle of delicate
threads of almost inconceivable fineness appear; these threads are
outgrowths of the cells, but far more delicate than those which
alr^y in Hy&ra we recognised as the forerunners of muscles; the
threads we are now considering are, in fact, nervous in nature,
and the tangles of them connected with the upper and lower layers,
respectively, of the velum, constitute an upper and a lower nerve
ring. Each thread is to be regarded as the tail of an excessively
small ectoderm cell
In Hydra we found the earliest appearance of sense hairs; and
the cells of which they are processes, viz., the cnidoblasts, may be
called sense cells. In the Medusa we meet with definite collections
of sense cells aggregated so as to form sense organs. These are
found close to the position of the nerve ring, either on the velum
itself or immediately outside it at the bases of the tentacles, so
that the stimuli which they receive are easily transmitted to the
UI.] HTDKOHEDUSAB. 53
nerve Hd^. Two main kindB of sense o^;ang are frequeotly foand,
whidi may be ronghly called eybs and ears ; never, howevn, both
kinds in one Medosa. The 'eyes' are little coloured patches of skin;
some of the cells of which end in clear rods while others secrete a
coloured aubatance or pigment Both pigment and rods are neces-
sary if tiiere is to be vision, though we do not understand why. The
eara are little pits in the base of the velum ; they may be open or
tbeb edges may come together, so that the ectoderm lining them is
entirely shut off from the outer skiiL In either case, some of tlie
Fto. 25. I. A. Eya of lififa Ito^Hffari seen from (he Bide magnified B The
ume Been from in front. C. JsoUted oella of the ums Fiom O & B
1. Lena. Z. Fignient cells. S. Percipient cells.
n. Bldiat section through the edge of the umbrella of Carmarina kaitata
■howing Benie-organ and velnm.
1. Yeltun. 3. Jell;. 8. Ciroolar mascles of velam. 4. Upper nerra
ring. C. Lower nerye ring. G. NematocjMs. 7. Badisl Teuel
running into cinmlar TeBsel, lioth lined bj endodem. 8. ContinnatioD
of endodena along abonl aarfaee. 9. Sense orean or tentaoitlocTat.
10. Anditory nerve.
cells forming the walls of the pits secrete particles of lime, others
close to them develope delicate sense hairs. The result is that
vibrations in the water, if they come with a certain frequency, will
affect the heavy particles, and their vibrations ui turn will affect
the sense hairs. There is another kind of infonnation, however,
which organs like ^eee give their possessor, and this is probably still
more impOTtant to the floating Medusa, namely, information as to
the position of the animal with regard to the vertical. In other
56 OOELENTERATA.
words, the Medn.^ leams from them whether it is moving upwards
or downwarda or sideways : for when the aoimal shifts it« poaition,
the heavy particles in the ear-sacs are shifted couformably aod affect
different sen^ cells.
Through these different sense organa etimuli are continnallf
pouring in from the external world. If the etimnli only affected
the contractile cells nearest them irregular movements would result.
The function of the nerve ring, as of all nervous systems, is to co-
ordinate the stimuli, that ia to collect and rearrange and rapidly
distribute them to the whole animal so that a definite reaction of
the whole contractile tissue results, not a series of local reactions
interfering with one another.
The Medusa is very voracious and rapidly increases in sixe. It
feeds on the small organisms of all kinds, both plants and ammftla,
which are found at the surface of the sea. After some time it e
Fia. 96. The ciliated lana or Ptonola oF a BTdrompdngoD, Clara tqvomata.
Magnified. From AUmaii.
A ilE B. Swimming aboat in the sea. C. Coming to tet,t on a rock.
D. Deveioping tenUolea, oral oone and atolon. 1. Tentacles. 3. Oral
coDf. 8. Stolon.
mences to give rise either to eggs or to spermatozoa, which usually
develope in exactly the same way in which they developed in Hij^ra.
ie., from the interstitial cells of tlie ectoderm. The ticcumulations
of these cells, called gonads or generative organs, are borne
either on the under side of the bell (3, Fig, 23). or on the sides of
the manubrium, and it is a curious fact that those Medusae which
have them in the former position usually possess ear-sacs, whereas
when the gonad is situated on the oral cone, ear-sacs are never
present, but eyes may be. The eggs and spermatozoa are both shed
ni.] HYDROMEDUSAE. 57
out into the water and coalesce there, and the fertilized egg developes
into a little oval larva, termed a Planula (Fig. 26), without
tentacles or mouth, and covered all over with cilia. It consists at
first of a hollow vesicle of ectoderm cells, later becoming filled with
a solid plug of endoderm. This little creature swims about for a
while and then attaches itself by one end to a stone or a piece of
sea-weed. The attached end flattens out (C and J), Fig. 26), but
the rest of the animal lengthens and a mouth and tentacles appear
at the firee end and the endoderm becomes hollowed out, so that
the creature takes the form of an unmistakeable hydra-like organism.
It then begins to bud out a branch called a stolon which creeps along
the substratum. From this other polyps will arise, each of which
has only to bud in order to reproduce the colonial stock fi-om which
its parent, the Medusa, was separated. The free-swimming young
or planulae famish good examples of what is meant by the term
larva. This name is given to the young form of any animal when
it is very different to the fully-grown animal and leads a free life.
We have thus learnt that a Medusa gives rise to an egg which
develops into a Hydroid person, which after a time in turn buds off a
Medusa; such an alternation of generations is very characteristic
of a large number of Coelenterata. The Medusa re-
of Genwations. prcsouts a soxual generation, the Hydroid an asexual
generation, and inasmuch as the Medusoid is often
only produced as a bud of the third or fourth order (ie. is budded
from a Hydroid person which has produced similarly from another
Hydroid person), it will be seen that several asexual generations
intervene between two sexual ones. One explanation of this life-
history is that the Medusa is only a specially modified Hydroid, which
has acquired the power of locomotion, in order to disperse the eggs
over a large area, and thus avoid the overcrowding of a limited area
with one species. The swimming beU and velum are contrivances
to enable the bud which bears the eggs to move about. If, however,
this explanation be adopted, it is a most remarkable fact that in
many species the Medusae are very imperfectly developed and
never become free. Such Medusae are usually more or less de-
generate and are termed gonophores. Since the gonophore fails
to fulfil the purpose for which we believe the Medusa to have been
developed we must assume that conditions have now so far changed
that the same wide scattering of the eggs is not now so necessary as
formerly, possibly because the species in question are restricted to
particular strips of the shore. Tubularia larynx found growing on
^S COELENTERATA. [CHAP.
M^w«>0d is a good example of a form with degenerate Medusae,
H^m^^im'illia or Obelia of forms with free Medusae.
The Hydromedusae include a large number of families, most of
whioh are represented by small plant-like forms resembling the
iS^uera just mentioned, but there are several groups which show
warktHl {H'ouliarities and have been regarded by many zoologists as
of oo<e(i\ial rank with the order although they have probably been
d<^rive<l from ordinary Hydromedusae. Of these we may name
vi) tlie IVachymedusae, (ii) the Narcomedusae, (iii) the Siphonophora
M\i\ (iv) the Hydrocorallinae. In the first two groups the eggs
doYolope from the planula stage directly into Medusae, missing out
tJ\e hydroid stage completely. In both cases also the sense-organs
are s)H>oially modified tentacles which are suspended like minute clubs
round the edge of the belL In the Narcomedusae these clubs are
tVtH^ly exposed and the wide baggy stomach occupies the whole under-
nurface of the umbrella, whereas in the Trach3rmedusae the sensoiy
clubs are enclosed in pits (Fig. 25) and the stomach is small and
Huspended from the umbrella by a stalk traversed by the radial canals.
The name Trachymedusae (Gr. Tpa^w, rough) is derived firom the
oirtmmstance that the umbrella is 8ti£fened by numerous ribs of
ondoderm cells and the edge has a thick rim of ectoderm. The
members of the third group are stocks consisting both of medusoid and
hydroid persons which are not attached to any support but which freely
swim or float in the sea. Some of the medusoid persons known as
noctocalyces have taken on the function of locomotor organs and
by their rapid pulsations not only drive themselves through the sea,
but draw after them the rest of the stock much as an engine draws
a train of carriages. A few forms, however, like the Portuguese
Man-of-war, Phi/salia, have no nectocalyces and float passively about.
The popular name of this genus is derived from the shape of the huge
air-containing float from which the persons of the colony are sus-
pended. It has been plausibly suggested that the Siphonophora
have been derived from planulae which attached themselves to the
surface-film of the water instead of to a solid support The surface-
film in consequence of its physical properties acts like an elastic
membrane, and in artificial cultures it can often be seen that some
planulae do attach themselves to this, and in consequence perish.
But if by favourable variations, such as a tendency to cupping of
the base and an inclusion of air-bubbles in the cavity, the stock
were enabled to remain suspended, then it would be placed in a very
favourable position for getting food, and thus it has been suggested
III.] ACTINOZOA. 59
the simply floating Siphonophora have been evolved from Hydro-
medusae. If this view be taken, the three chief divisions of Siphono-
phora represent three successive stages in the adaptation of the group
to a pelagic life. Thus the Fhysaliidae simply float, the Physo-
phoridae float and swim by nectocalyces, whilst the Calycophoridae
have lost the float and trust entirely to their powerful nectocalyces.
The Siphonophora are remarkable for the varieties of person
which compose their colonies. As varieties of the hydroid person
may be named the palpons or tactile persons devoid of a mouth,
but showing their equal rank with the nutritive person by the
possession of similar tentacles. To the category of medusoid persons
belong not only the nectocalyces but the bracts — transparent
sheath-like structures sometimes present, which shelter groups of
persons. This extreme variety of persons is foreshadowed in the
ordinary Hydromedusae. Hydractinia for instance, which grows at
the mouth of whelk shells inhabited by hermit crabs, has palpons
amongst its hydroid persons, but in no case is such extreme diversity
attained as among the Siphonophora. The Hydrocorallinse hydroids
form large colonies and are divisible into nutritive polyps or gastro-
sooids and tentacle-like polyps, the dactylozooids. The skeleton
is massive and they form encrusting growths. The medusoid
persons attain varying degrees of perfection.
The Sea-Anemones are representatives of a second division of
the Goelenterata, which show a decidedly more com-
plicated structure than the animals just considered.
Unfortunately it is very difficult to obtain the ordinary sea-
anemones in a sufficiently expanded condition to make out their
structure, since when irritated they contract so much as to
throw their internal structures into great confusion. Another
animal belonging to the same group is the 'colonial' species
Alcy(mium digitatum, sometimes called "Dead men's Angers.''
It is comparatively easy to paralyse the members of the colony
or i>olyp8 by adding cocaine, or some similar reagent, to the water
in which the colony is living (Fig. 27). If then an expanded polyp
be cut off and examined with a lens, we shall be able to make out
most of its structure. We notice to begin with that there is a
single circle of eight tentacles, each of which has a double row of
short branches, so that it looks like a miniature feather; within the
circle of tentacles there is, however, no trace of an oral cone ; there
is instead a flat disc, slightly sunken in the centre, where we find
the slit-like mouth. If we look in at the lower cut end of the
60
COELESTERATA.
polyp we shall see that the interual cavity or cnelenteron, instead of
being a simple cylindrical space like that of Hijdra, is partiallj
divided into compartiucDts by folds stretching in towards the centre,
but not meeting. These folds are called mesenteries, and there are
eight of them, coiresponding ia Dumber (but not iu position) with the
Fart Qf a colony or Atcyaniwn digllatum x 8, abowing thirteen p
IS BttkgeB at retroctioo uiid eipansioD.
1. Mriutb, 3. MeseDterisB with repmduotiTe csIIb.
8. Oesopbagae. 4. Festhered tentnclea.
tentacles (Fig. 28). We shall further see that the mouth does not,
as in Hydra, open directly into the coelenteron, but leads into a
flattened tube which projecta into the interior of the body. This
tube, the so-called oesophagus or gullet, ia really lined by the
ectoderm, which is merely tucked in at the mouth. Such a tube is
known as a stomodaeum\ The mesenteries, although they end
fieely below, are attached to the Bides of the stomodaeum above,
BO that in this region the coelenteron b divided into a number
of compartments, each of which is prolonged int^ one of the hollow
tentacles (Fig. 29).
' "I have proposed ia deBienata tills ingrowth,. .thoEtomodaeum (arJjuafaiM',
like wXiiaiOt, the road couaecled nith a galewsf ) and Bimilorlj to call snothei
iDgiowth which accompaaiei the rotmation of the second orifice (the anus) of
lh« enteron, the pioctodaeum " (v^nrAt, the anos). Bay Lankesler.
TeotTBl
Fra. 39> Tmurena teotion throngh a polyp of Alej/onium digitatua, through
the legion ot the oesophagns x abont 130. From Hickeoii.
1, Ckvlty of oeuphagiiB. 3. Sipbonogljph. 8. Eotoderm. 4. Meso-
gloM 01 jallj. 5. Endodenn. 6. MQBClel in meunterieB. 7. Inter-
52
COELENTERATA.
[chap.
Medusa.
partially fluid contents, so that the cells have the same kind of
stiffness as a well-filled water-pillow. These cords likewise bud out
from the endoderm, but, as apparently the animal does not need the
tentacle cavity which exists in the Hydra, it has disappeared, and
the solid axis is essentially a strengthening or skeletal structure.
As in Hydra, there is an oral cone; and in some species of
Hydromedusae, at any rate, there is an additional row of short
tentacles at the tip of this. It has been stated above that the
buds do not become detached, but there is one kind of bud differing
much in shape from the rest which does become detached. In
such a bud, the whole body becomes very much shorter
and at the same time much flattened out in its lower
portion, so that the main circle of tentacles is widely separated
from the oral cone ; at the apex of the latter there is sometimes a
second circle of small tentacles. The flattened part of the body
becomes concave on the side towards the mouth so as to assume the
form of a bell or umbrella, and, owing apparently to this circum-
stance, the part of the coelenteron which it contains becomes so
pressed together, that by the adhesion of its upper and lower walls,
its cavity for the most part disappearing, it becomes converted into a
concave layer, called the endodermal lamella. Along four lines,
however, the cavity does not disappear (4, Kg. 23), and it also
remains open just beneath the circle
of larger tentacles at the edge of
the bell, so that in this way we have
a circular or marginal canal
established, communicating by four
radial canals with the part of the
coelenteron that still persists in the
oral cone, and opening to the exterior
by the mouth (1, Kg. 23). The
upper surface of the bell is styled
the exumbrella or aboral surface
(Lat ab, away from ; 05, oris, the
mouth) the lower the subumbrella
or oral surface^
The great mass of the bell is
composed of the jelly intervening
between the outer ectoderm on the
convex side and the endoderm. In this jelly solid strings sometimes
appear which give it a firmer consistence. The modification of the
Fio. 28. Free-swimming Medusa
of Ohelia sp.
1. Moath at end of manabrinm.
2. Tentacles.
8. Beprodnotive organs.
4. Badial canals.
5. Auditory organ.
m.]
BYDROMEDUaAJL
Fio, Si. Bousainelllia /mefuoia, x about 13. From Allman.
A. The fixed Iiydroid form vith numeroua hj'droid pol;p«8 and meduBoa in
wioiu itBgea of derelopment. B. Ibe free BvrimmiDg aeiaal Meduea
vhloh has brokea away from A.
54 COELENTERATA. [CHAP.
base of the animal into the shape of an umbrella causes the oral
cone to resemble the handle, hence the name manubrium (Lat.
a handle), by which it is usually designated in a bud of this kind
(1, Fig. 23). Just above the circular canal in most Medusae a fold of
the outer skin grows in towards the oral cone, so as to form a broad
circular shelf: this structure is called the velum (Lat an awning)
(B, Fig. 24 ; 1, Fig. 25). The bud now breaks loose and swims by
contractions of the bell, aided by vibrations of the velum. Anyone
would now recognise it as a minute jelly-fish, though it really is
quite different in many points from the larger and better known
animals denoted by that term. Zoologists speak of it as a Medusa,
and speak of the stock from which it was budded as a colony
consisting of medusoid and hydroid persons, the latter term
denoting the ordinary buds which resemble Hydra. The terms polyp
and hydranth are also often used to denote a hydroid person.
A medusoid is in many respects more highly developed than
the hydroid person. The ectoderm cells composing the velum
and those forming the lining of the under side of the bell or
sub-umbrella are strongly drawn out into processes which are
muscular. In the velum these are arranged so as to form two
bands running round the edge of the bell or umbrella, one band
being in connection with the upper and another with the lower
layer of cells composing the fold of ectoderm of which the velum
consists. Just, however, where the velum is attached to the bell,
its cells —upper and lower — undergo another and more interesting
modification (4 and 5, Fig. 25). At their bases a tangle of delicate
threads of almost inconceivable fineness appear; these threads are
outgrowths of the cells, but far more delicate than those which
already in Hydra we recognised as the forerunners of muscles; the
threads we are now considering are, in fact, nervous in nature,
and the tangles of them connected with the upper and lower layers,
respectively, of the velum, constitute an upper and a lower nerve
ring. Each thread is to be regarded as the tail of an excessively
small ectoderm celL
In Hydra we found the earliest appearance of sense hairs; and
the cells of which they are processes, viz., the cnidoblasts, may be
called sense cells. In the Medusa we meet with definite collections
of sense cells aggregated so as to form sense organs. These are
found close to the position of the nerve ring, either on the velum
itself or immediately outside it at the bases of the tentacles, so
that the stimuli which they receive are easily transmitted to the
III.] HTDBOHSDUSAE. 55
nerre Ting. Two mam kinds of sense organs are frequently found,
wliich may be ronghly called eyfes and ears ; never, hovever, both
kinds in one Medosa. Tbe 'eyes' are little colouied patches of skin ;
some of the cells of which end in clear rods while others se^ete a
colonred snbatauce or ingment Both pigment and loda are neces-
sary if there is to be Tision, though we do not undeistand why. The
ears are little pits in the base of the velum; they may be open oi
their edges may come together, so that the ectoderm lining them is
entirely abut off from the outer skin. In either case, some of the
Fio. 2S. I. A. B7eof£f»iatof(IfJbfri Been from the tide, magalQcd. B. The
Eaine ieen ttom in front. C. Isolated celli of the ume. From 0. & B.
1. Lena. 3. Pigoient cells. S. Percipient cells.
n. BmUaI section throngh tlie edge of the umbrella of Carmarina haitata
■hoviog HDM-OTijan and velnm.
1, Telam. 9. Jell?. S. Ciicnlir muscles of velum. 1. Upper nerve
ring. 0. Lower nerve ring. G. Nemntocjsts. 7. Bstlial vessel
ttmning into cironUr vessel, both lined by endoderm. 8. Contittuation
of andoderm along ftbortl scrfooe. fi. SeiiM organ or tentacnlocj'at.
10. Anditory nerve.
ceQs forming the walla of the pits secrete particles of lime, others
close to them develope delicate sense hnirs. The result is that
Tilmriions in the vaiet, if they come with a certain frequen<^, will
affect the heavy particles, and their vibrations in tarn will affect
the sense hairs. There is another kind of ioformation, however,
which organs like these give their possessor, and this is probably still
more important to the floating Medosa, namely, information as to
the position of the animal with regard to the vertical. In other
66
COELENTERATA.
[chap.
words, the Medusa learns from them whether it is moving upwards
or downwards or sideways : for when the animal shifts its position,
the heavy particles in the ear-sacs are shifted conformably and affect
different sense cells.
Through these different sense organs stimuli are continually
pouring in from the external world. If the stimuli only affected
the contractile cells nearest them irregular movements would result.
The function of the nerve ring, as of all nervous systems, is to co-
ordinate the stimuli, that is to collect and rearrange and rapidly
distribute them to the whole animal so that a definite reaction of
the whole contractile tissue results, not a series of local reactions
interfering with one another.
The Medusa is very voracious and rapidly increases in size. It
feeds on the small organisms of all kinds, both plants and animals,
which are found at the surface of the sea. After some time it com-
— I
Fio. 26. The ciliated larva or Pianola of a Hydromednsan, Clava tquamata.
Magnified. From Allman.
A <fe B. Swimming about in the sea. G. Coming to rest on a rock.
D. Developing tentacles, oral cone and stolon. 1. Tentacles. 2. Oral
cone. 3. Stolon.
mences to give rise either to eggs or to spermatozoa, which usually
develope in exactly the same way in which they developed in Hydra,
Le., from the interstitial cells of the ectoderm. The accumulations
of these cells, called gonads or generative organs, are borne
either on the under side of the bell (3, Fig. 23), or on the sides of
the manubrium, and it is a curious fact that those Medusae which
have them in the former position usually possess ear-sacs, whereas
when the gonad is situated on the oral cone, ear-sacs are never
present, but eyes may be. The eggs and spermatozoa are both shed
m.] HYDROMEDUSAE. 67
out into the water and coalesce there, and the fertilized egg developes
into a little oval larva, termed a Planula (Fig. 26), without
tentacles or month, and covered all over with cilia. It consists at
fiist of a hollow vesicle of ectoderm cells, later becoming filled with
a solid plug of endoderm. This little creature swims about for a
while and then attaches itself by one end to a stone or a piece of
sea-weed. The attached end flattens out (C and D, Fig. 26), but
the rest of the animal lengthens and a mouth and tentacles appear
at the firee end and the endoderm becomes hollowed out, so that
the creature takes the form of an unmistakeable hydra-like organism.
It then begins to bud out a branch called a stolon which creeps along
the substratum. From this other polyps will arise, each of which
has only to bud in order to reproduce the colonial stock from which
its parent, the Medusa, was separated. The free-swimming young
or planulae furnish good examples of what is meant by the term
larva. This name is given to the young form of any animal when
it is very different to the fully-grown animal and leads a free life.
We have thus learnt that a Medusa gives rise to an egg which
develops into a Hydroid person, which after a time in turn buds off a
Medusa; such an alternation of generations is very characteristic
of a large number of Coelenterata. The Medusa re-
of oenmtions. pwsGiits a soxual generation, the Hydroid an asexual
generation, and inasmuch as the Medusoid is often
only produced as a bud of the third or fourth order (i.e. is budded
from a Hydroid person which has produced similarly from another
Hydroid person), it will be seen that several asexual generations
intervene between two sexual ones. One explanation of this life-
history is that the Medusa is only a specially modified Hydroid, which
has acquired the power of locomotion, in order to disperse the eggs
over a large area, and thus avoid the overcrowding of a limited area
with one species. The swimming bell and velum are contrivances
to enable the bud which bears the eggs to move about. If, however,
this explanation be adopted, it is a most remarkable fact that in
many species the Medusae are very imperfectly developed and
never become free. Such Medusae are usually more or less de-
generate and are termed gonophores. Since the gonophore fails
to fulfil the purpose for which we believe the Medusa to have been
developed we must assume that conditions have now so far changed
that the same wide scattering of the eggs is not now so necessary as
formerly, possibly because the species in question are restricted to
particular strips of the shore. Tubularia larynx found growing on
-^ COELENTERATA. [CHAP.
«^iftv^M '^ A ^Hxl t^xample of a fonn with degenerate Medusae,
j(^MCt-%^««''-^M or (>Mi<i of forms with free Medusae.
^v*V tV>>i^>^^i^^^ include a large number of families, most of
^.V\A 4^v iiv|VN»tM>uted by small plant-like forms resembling the
^v**^^ .^U'iC luoutioned, but there are several groups which show
-*^v:Xnn( isvuliiiritieii and have been regarded by many zoologists as
.^ sv Aiu>'^l muk with the order although they have probably been
<^>i,A\v^( n\KUi ikfdinary Hydromedusae. Of these we may name
^i^ V^N> t\««ohyuicHtu8ae, (ii) the Narcomedusae, (iii) the Siphonophora
^uvt \\\) tht) llydrocorallinae. In the first two groups the eggs
>^\v^ts'|K» fu^m Uie planula stage directly into Medusae, missing out
uW kvv^tv\»i\l Htage completely. In both cases also the sense-organs
MW »|KH>i4^11y modified tentacles which are suspended like minute clubs
vv'iAUv) tht) ixlge of the belL In the Narcomedusae these clubs are
iVsH)|v t)\|Kkd6(i and the wide baggy stomach occupies the whole under-
>uvUvve i»f the umbrella, whereas in the Trachymedusae the sensory
4ub2i are enclosed in pits (Fig. 25) and the stomach is small and
4Vu)^iuitHl from the umbrella by a stalk traversed by the radial canals.
'i\\s imiue Trachymedusae (Gr. rpaxys, rough) is derived firom the
car\Huatitauco that the umbrella is stifiened by numerous ribs of
vuuUult)nu cells and the edge has a thick rim of ectoderm. The
luuiuberd uf the third group are stocks consisting both of medusoid and
liy droiil persons which are not attached to any support but which freely
ttwiui or iioat in the sea. Some of the medusoid persons known as
u t) 0 1 0 e a I y c e s have taken on the function of locomotor organs and
b) tlioir rapid pulsations not only drive themselves through the sea,
but draw after them the rest of the stock much as an engine draws
a train of carriages. A few forms, however, like the Portuguese
Man-of-war, Physalia, have no nectocalyces and float passively about.
The popular name of this genus is derived firom the shape of the huge
air-containing float firom which the persons of the colony are sus-
pended. It has been plausibly suggested that the Siphonophora
have been derived from planulae which attached themselves to the
surface-film of the water instead of to a solid support The surface-
film in consequence of its physical properties acts like an elastic
membrane, and in artificial cultures it can often be seen that some
planulae do attach themselves to this, and in consequence perish.
But if by fikvourable variations, such as a tendency to cupping of
the base and an inclusion of air-bubbles in the cavity, the stock
were enabled to remain suspended, then it would be placed in a very
favourable position for getting food, and thus it has been suggested
III.] ACTINOZOA. 59
the simply floating SiphoDophora have been evolved from Hydro-
medusae. If this view be taken, the three chief divisions of Siphono-
phora represent three successive stages in the adaptation of the group
to a pelagic life. Thus the Physaliidae simply float, the Physo-
phoridae float and swim by nectocalyces, whilst the Calycophoridae
have lost the float and trust entirely to their powerful nectocalyces.
The Siphonophora are remarkable for the varieties of person
which compose their colonies. As varieties of the hydroid person
may be named the palpons or tactile persons devoid of a mouth,
but showing their equal rank with the nutritive person by the
possession of similar tentacles. To the category of medusoid persons
belong not only the nectocalyces but the bracts — transparent
sheath-like structures sometimes present, which shelter groups of
persons. This extreme variety of persons is foreshadowed in the
ordinary Hydromedusae. Hydractinia for instance, which grows at
the mouth of whelk shells inhabited by hermit crabs, has palpons
amongst its hydroid persons, but in no case is such extreme diversity
attained as among the Siphonophora. The Hydrocorallinse hydroids
form large colonies and are divisible into nutritive polyps or gastro-
zooids and tentacle-like polyps, the dactylozooids. The skeleton
is massive and they form encrusting growths. The medusoid
persons attain varying degrees of perfection.
The Sea-Anemones are representatives of a second division of
the Coelenterata, which show a decidedly more com-
plicated structure than the animals just considered
Unfortunately it is very difficult to obtain the ordinary sea-
anemones in a sufficiently expanded condition to make out their
structure, since when irritated they contract so much as to
throw their internal structures into great confusion. Another
animal belonging to the same group is the 'colonial' species
Alcyanium digitatum, sometimes called ''Dead men's fingers."
It is comparatively easy to paralyse the members of the colony
or polyps by adding cocaine, or some similar reagent, to the water
in which the colony is living (Fig. 27). If then an expanded polyp
be cut off and examined with a lens, we shall be able to make out
most of its structure. We notice to begin with that there is a
single circle of eight tentacles, each of which has a double row of
short branches, so that it looks like a miniature feather; within the
circle of tentacles there is, however, no trace of an oral cone ; there
is instead a flat disc, slightly sunken in the centre, where we find
the slit-Iike mouth. If we look in at the lower cut end of the
Ventra!
n diffitatam below the
level of tha oeeophagns x a^ut* 120. from Hickson.
. CoelenteroD. 2. Meseuteiy with free edge. 8. Ectoderm. i. Meao-
gloea or jelly. S. Endoderm, 6. Husdee in mewntery.
DoitAl
Ventral
Fia. 29. Transvarse section through a polj'p of Alcj/ouiuvt digitatum, thcongh
the region of the oesophagna x about 120. From Elckgon.
I. Cavity of oeeophagna, 3. BiphonoglTph. 3. Ectoderm. t. Meso-
gloea or jcily. S. Bndoderm. 6. Mnsclea in meienteriea. 7< Inter*
'--0 catily.
ft <»•
*..
r/iKiXSTKRATA. [CHAP.
i.
tH^w' ts>nTuti. rt- snri A polyp shows us several other
*"' -^^^ IV; i«« J^M we have to deal with the same
^♦^wwtii. ^ ^^ ^^ ^^ Hydra, skin (or ectoderm) and
*""^" ^ I .. » /f,- w.i'viucaiX Between them, however, there is
- ''"""jKr-.^ ^«««rJ« an exceedingly fine membrane in
" " 1 «j.,,. iT**i;.'» ii:okened, formed the substance of the
. *) V«*«r«h '^*** .'^^^>' ^^ fairly thick in the minute sea-
^r f»v«niii'.'^. Aud here contains cells which have
. , , h-r^ :rjv ATtiHlerm. Some of these cells have the
- sp.^rJo. «-^'***'J' "^^8 ^f ^°^®> termed spicules. These
,^» «siin^it where the pol3rp merges into the general
- 1», -r.:%»r *> that they form a kind of stiflF protecting
♦•i **«*' ^'^^ ^^® polyp and over the surface of the
^., ^M^^ «ii«> polyps rise. In the oi^an-pipe coral,
♦I, ^s•%v*i.•v'» in the lower parts of the polyps are so
^,.-^^ *^»*5 thoy form a set of parallel tubes, suggesting
., . - - sx<wi; only the upper part of the polyp, where the
t,- ..♦ « '^ ^^'5 oli>sely aggregated, being capable of movement.
I , ^-s^vviA aIh»vo of the colony as distinct from the polyps,
. ^, ,.„ .^i tho word demands some justification. When we
."•w 't^ *t-'^ <l*o Ilydromedusae, we used the word colony in
. ^ 10 ^lu»lo mass of the polyps which cohered together,
.t;,t kkI AriMOU by the growth of one original polyp. Now
.... ..:».«* aiul its allies, budding does not take place in quite
jL,. aj luHuiuT in which it occurs in Hydra and its allies.
, . X ■• ^*Ak^ IH'lyp growing directly out of another, the coelen-
^. . .iio i^u'tuit Monds out a tube lined only by endoderm. This
V ^«''>'^»# |itishing the ectoderm before it ; but, as between the
,^:^t«ui JkwA ciuloderm there is a thick jelly interposed, the endo-
^^.^^«w but>o oan bniuch without the ectoderm becoming indented.
^;V<v^ ^^^^ ^^^^^^ ^^nds of these tubes reach the surfSekce, there fresh
y^\i\i ^vo ilfvelopod, mesenteries and oesophagus making their
^^x\uaikoo. Something like these tubes does, in fact, occur
•.M^'Oi^^i tlydrouuHliisao: a complete colony is found to consist of
, uumkior (if upright branches ending in polyps but connected at
*vu lia.">nsi I'.v tuluM called stolons which creep along the sea Hoor :
uSo uuiluilonual tiiboM of Alcyonium may be compared to these
lU^Kiusi. tlhi great liitVonMioo being that in their case, owing to the
tUu'iiiitti-^ i>f tltt^ J^^IIy. the ectiHlorm is stretched uniformly over a
iuuttji uf tubed, iuNteail of each tube having its own ectodermal
OiiViuiug ud in tlie llydnmiedusao.
m.] ACTINOZOA. 63
Still examining a section of the poljrp the next point we notice
is the structure of the mesenteries. These end in a free edge
below which is much thickened and folded, and since it stands out
in contrast with the rest of the mesentery as if it were an inde-
pendent structure it has been called a mesenteric filament
(Figs. 28 and 30). The cells composing six of these filaments are
very tall and secrete a juice which digests the prey : the remaining
two filaments are composed of ciliated cells of moderate height
which maintain a constant outward current of water. The surface
of the mesenteries is covered by cells which become very much
folded so as to produce a marked projection from the face of the
mesentery. The cells of the folded area are all produced into
vertical muscle-tails so that together they give rise to one of the
powerful longitudinal muscles (Figs. 28 and 29), by which the
sudden retraction of the polyp is brought about. The slow
expansion is efiected by the reaction of the elastic jelly or mesogloea
and perhaps also by the pressure exerted on the fluid contained in
the body by a layer of circular muscles developed as outgrowths
firom the endoderm cells of the intermesenteric chambers.
A second difierence is found in the position of the eggs and
sperm cells. These are developed from the endoderm on the face
of the mesenteries, very low down in the base of the polyp and
nearer the free edge than the longitudinal muscle. The eggs when
ripe are cast out into the coelenteron and so out by the mouth,
though in many species they come in contact with the male cells
whilst in the coelenteron of the parent.
The gullet has at one side a deep indentation or groove which
is lined by powerful cilia (2, Fig. 29). The groove is termed a
siphonoglyph (Gr. o-t^wv, a tube; y\v<l>ta, to hollow out) and its
cilia keep up an inward current of water whilst the rest of the
gullet is choked with prey, and so fresh supplies of water chaiged
with oxygen are brought in contact with the lining of the coelenteron
and enable it to respire. The two mesenteries with which the lower
end is connected are called the directive mesenteries, they are
situated opposite to the two ciliated mesenteric filaments. By the
cooperation of the latter with the siphonoglyph complete circulation
of the water in the coelenteron is maintained. The ectoderm of
course gets its oxygen directly from the surrounding water.
The ordinary sea-anemones or Zoantharia differ from Alcyo-
nium in very many points. The tentacles, hollow as before, are
never feather-like but always perfectly simple and round, and there
iM COELEMTERATA. [CHAP.
is. iMuitlly a lai^ namber of them amtoged in several coDcentric
>,-uvW The mesenteries also are unmeronB, and extend invards
Iv ditfwvut lengths, bo that we cui distiDgnish primary mesea-
turie* wluch join the gullet from secondary ones which do not.
ttuitk primaiy and secondary are usually ananged in pairs, but
thoM is much variety and all that can be universally asserted
is that they never exhibit exactly the arrangement shown in
Alcyonari^ A very common arrangement is to have six pairs
<.it' primary mesenteries and two siphonogtyphs, one at each end.
S^uoules are never developed and in the ordinary anemones of
our coasts there is no skeleton whatever. These commoner forms
sometimes, though rarely, bud, but there is another large class
of anemones which do form colonies, the bads occasionally arising
as in the Hydromedusae from the body of the parent directly.
These colonial anemones form the hard stony masses called coral
(Pig. 30). If we look at a piece of coral we can see in it cups
Fio. 80. Semi-diogranimatio view of half » limple CoTal, ptirtly after G. C-
Boaraa. On the right tids the tuaues ue Tepreaeated aa trangpareDt to
ahow tha ammgemeut of the theca and septa ; on ijie left side a
I. Tentacle. 2. Month. S. Oeaophagtu. 4. MeMntei;. 5. Heaen.
teric filamanta, free edge of mesentorj. 6. Eotoderm. 7. Endoderm
e. Basal plate. 9. Theca. 10. Columella. 11. Beptmu.
with partitions radiating inwatds, the whole reminding one of the
structure of a sea-anemone: and it was a natural mistake to-
suppose, as the earlier naturalists did, that the hard skeleton was
III.] CORAL. 65
formed inside the body of the poljrps, the partitions representing
the mesenteries. Of course it is difficult to imagine how the animal
could move if it had all that mass of stone inside it. How the
corallum or stony skeleton is formed is a matter of dispute. It
is certainly situated outside the ectoderm, but whether it is secreted
by the ectoderm as a kind of sweat which hardens, or whether the
ectoderm cells are calcified and thrown off, or the ammonium car-
bonate, secreted by all animals, precipitates the calcium carbonate
of the sea water and so forms the skeleton, is not finally decided.
At any rate a calcareous cup is formed in which the polyp sits and
the partitions of the cup indent the base of the animal, pushing
before them folds of the body wall, which project into the coelen-
teron between mesenteries, so that the action of the longitudinal
muscles is not interfered with.
Under the name Cored the skeletons of quite a number of
^^ different kinds of Coelenterata were included besides
Zoantharia.
The so-called Millepore Corals belong to the first division of the
Coelenterata, the Hydrozoa, for Millepora itself gives ofi* quite
typical Anthomedusae and the other genera have gonophores.
The Hydrocorallinae are really distinguished by the fact that the
perisarc only which covers the basal stolons is thick and calcareous.
After a while the stolons enclosed in the skeleton die, but fresh
stolons are thrown out at higher levels, so the skeleton grows in
thickness. The hydroid persons are of two kinds, nutritive persons,
gastrozooids, short and with wide mouths, and tactile persons,
dactylozooids, which surround each gastrozooid in a circle and
which are long and mouthless. Both kinds have short rudimentary
tentacles looking like knobs.
The so-called Organ-pipe coral is, as has been already explained,
an Alcyonarian in which the spicules cohere. Various fossil so-
called corals, e.g., Syringopora, belong to the same category. The
red Neapolitan coral of which ornaments are made is also an
Alcyonarian, the spicules of which are of a bright pink or red
colour and cohere to form a rod in the axis of the colony. In some
spots off the coast of Australia the Alcyonaria with coherent spicules^
are so numerous that they form reefs.
Coral-forming anemones are found all over the world, — one
genus, Caryophyllia, being actually found at low spring tides on
the south-west coasts of England : but it is only in the tropics that
those species are found which keep on buddiug and growing with
S. i&M. 5
66 COELEKTERATA.
Bnfficieut persistence to build up the great teefa which form the
fsmoua coral islands of warmer seas. Of course as soon m the
reef is built up to the surface the polyps cease to grow, and then
the breakers soon pile up broken off pieces ia eufficieot qoancity W
raise the reef above the tide-marks.
A third group of the Coelenterata is constituted by the Acale^^
phae {Gr. dia\>j4i>i, & nettle). These animals ai^^
the Inrger and better known jelly-fish. They are U>
some extent intermediate in charai-ter between the Hydrosoa and
the Actiunzoa. Like the latter their genital cells are developed
from endoderm, and in the larval condition there are meaenieries.
but they do not possess a etomodaeuin.
A common British species, Aurelia aurita, is in snmmer often
cast by thousands on the southern shores of Great Britain. Viewed
from the outside it very much resembles the modusoid persons of
the Hydromedusae. Like them it possesses a awimming bell with
a circle of tentacles at the margin. There is aiso a prumiueut oral
cone or manubrium. This however does not bear real tentacles, hut
the four corners of the rectangular mouth are drawn out into long
frilled lips (3, Fig. 31), along the inner sides of which are open
grooves leading into the gullet. Perhaps the most marked difference
is that the reproductive organs are here, as in the anemones,
swellings of the stomach lining: the eggs and spermatozoa are shed
into the coelenteron and escape by the moutL The generative
oigans have the shape of four semicircular ridges, and along the
inner side of each of these there is a row of filaments composed of
cells somewhat similar to the ceils on the edges of the mesenteries
in the anemones (11, Fig, 31). Nothing like these gastral filar-
meats, as they are called, are found in the Hydromedusae. There
is, further, no velum in the Acalephae, and there is also no nerve
ring. Sense oi^aus however of an exceedingly Interesting kind are
present.
In Aurelia, for instance, there are eight minute tentacles which
stick out from the edge of the bell and are covered by special little
hoodlike outgrowths of the same (9, Fig. 31). Each of these
tentacles contains a hollow outgrowth from the circular canal lined
like it by endoderm. The endoderm cells at the tip secrete a mass
of calcareous particles : the skin cells at the base of the tentacle
have produced nervous fibrillae from their bases and so the tentacle,
as it is caused to sway in one direction or another by the weight of
its heavy end, affects now some of the nerve fibrillae and now
lU.] ACALEPHAB. 67
others, uid so produces the same effect as the stones in the ear
Mc of a medusoid, though the coustniction of the Acalephan organ
is quite different In the TiachTinednsae and Nsrcomedusae, how-
ever, sense tentacles dmilar to those of the Acalephae are found.
Here the edges of the hood often join so as to form a sac enclosing
^ihe organ, whence the name tentaculocj'st (9, Fig. 25).
" It has been proved experimentally that the ordinary stimuli
which cause the rhythmical pulses of the bell proceed &om these
Fto. 31. Aurelia aurita, Somevhat reduced.
1. HoDth. 3. Circnmoral prooesgee. 3. Tentadea on the edge of the
□mbrdla. 4. One of tbs branching pemtdinl camilB. There are foar of
theie, and foot timilar interradial canaU; the perradial conala coireapond
to th« primu? ttomaoh pouches of tha Hydra-tubB, the interradial
mltematA with these. 6. Ooe of the uubranched odradiftl ennftle.
8. The circnlar oannl. 9. Mareinal lappeta hiding tentBoulocyata.
11. Quti&l fllunentB, just outside theae are the genital ridges.
tentacuhx^sts, so that they act like minute brains. How the
co-ordination of the sUmuU proceeding from the eight centres is
brought about we do not know, but it b probably due to the
presence of a very thin diffuse sheet of nerve fibiillae on the under
surface of the bell.
6—2
68 COELEKTEBATA. [CHAP.
It has been mendoiied aboTG that tiiie reprodactive organs are
swellings of the endoderm. The ceutial space or "stomach" is a
wide sac occupying the centre part of the bell and not, as in the
Hydromediisae, confined to a large extent to the oral cone. In
Aurelia this space is prodaced into four lobes, and in the floor of
each lobe is one of the reprodactiye organs. From the edges of the
stomach a number of branching canals lead oat into the circular
canal (4, Fig. 31), all these tnbes being, as it were, burrows in a
continuous sheet of eudoderm cells, which stretches out to the edge
of the disc and really represents a part of the coelenteron, the
cavity of which has been obliterated. It thus corresponds exactly
to the endodermal lamella of the Hydromedusae.
When the %gs fall out of the mouth they are caught in little
pockets and there develope into little Planulae. These, as usual.
Fis. S2. StrobUizatioQ ot AureUa awrita. From Bftn.
A, Hydra-tuba on stolon which ii meepiag on a Laminam. The atoloD is
fonning new bads at 1 and 2. B. I^tet stage or Sanihistoma k 1. The
strobil^ation has began. G. Strobilization foitber adraiicedxS.
D. Free swimming Ephyra stage x T'5, se«D from below. E. The same
seen in pcoGle x T6.
become free and swim about, and finally each fixes itself and
developes into a little polyp, called a Hydra-tuba, not unlike a
Hydra in appearance (A, Fig. 83), but there are nevertheless
important points of difference. l%as there is no oral cone but a
flat oral disc in the centre of which the mouth opens into the
coelenteron. The latter has four ridges projeotiog into it, the
iil] ctenophoba. 69
lower edges of which are free while the upper ones are joined to the
gullet These ridges being produced by the folding of the endoderm
layer they are double and contain between their two limbs a space
filled with jelly. Into this space a prolongation of the ectoderm of
the mouth disc grows down so as to form a '' septal funnel." The
cells composing the septal funnel secrete longitudinal muscular
fibrils, and thus four powerful septal muscles are formed which
senre to shorten the Hydra-tuba. The hydroid persons of the
Hydromedusae have also longitudinal muscles but these are dis-
posed in a uniform sheet round the polyps in question and belong
to the ectoderm cells forming the sides. During a large part of the
year the Hydra-tuba multiplies by budding, just as a Hydra does,
but at certain seasons it undergoes a very remarkable change (B and
C, Fig. 32). The oral disc flattens out very much and its edges
become drawn out into lobes, the tentacles at the same time drop-
ping off. A short oral cone is developed from the centre of the disc,
the mesenteries become perforated and finally the whole flattened-out
top of the Hydra-tuba breaks off and swims away. This is known
as an Ephyra larva (D and £, Fig. 32). It leads a free life and
gradually develops into a large jelly-fish. But long before the
primary oral disc has become free, the part of the Hydra-tuba next
below has been growing out so as to produce a similar disc. This
process, called Strobilization (Gr. a-TpoPiXos, a whorl), is repeated
until the Hydra-tuba resembles a pile of saucers, in which state it is
called aScyphistoma (Gr. <rKv<t>os, a saucer).
We can get some idea as to how this extraordinary development
may have arisen on the following hypothesis: — The original Aca-
lephan wad probably an organism like an anemone with a wide top
and narrow base. In this top the generative organs were developed,
and when the eggs became ripe it broke off and wandered away in
order to disperse the species. The lower part of the polyp regene-
rated the head, exactly as a Hydra can do if the head with its ring of
tentacles be cut off. Later this process of renewal became hurried
on until it commenced before the separation of the head was
complete and thus we have the Scyphistoma stage. It is a strong
support of this theory that there exists a large coral-forming
anemone, Fungia, in which there is a flat top and a stalk, and the
flat top periodically falls off and is renewed.
A third great division of the Coelenterata is constituted by the
animals called Gten ophora (Gr. ktci?, ktcvo?, a comb).
These are widely different from both Hydromedusae
or Actinozoa, even including Acalephae. They never bud and with
■ ^ COELCKTERATA. [CHAP.
,jM;nai jisMptioa htm bo thread cells. In i^Me of these
.ML^.>oi. »«>^*^<^ * •dhesive cells coveited with a secreticm by
<.«Ml'A >M» -Wa«m w the prey. They ue often npped off in the
■».*•*"*■-"* ■''* P"**' "^^^y *" ^"^^ provided with an eLutac tail
4t.'Cv^<Miii. -1^ 'JM i^^ which pnlls in the object to which they have
,^;kw>VM t*^ Ctooophon are free Bwinuning but their locomotion
> NUtKiuiM iwc by the agency of muscular bands bat by eight
<^^ .-^ 'iiiJti whigh na like meridians of longitude over the
Fiq. SS. Bemiphora fbimoia. After Chun. Side riev.
1. Moalh leading inla itonuch. 3. Abonl pcda with leiue orgtn.
8. FDDoeL 4. PudeastriB canal mnninK back toiraids otal poU-
5. One of tfaa eight band] of fuced cilia. 6. One of the eight euub
tanninR tovarda 5. 7. A tentat^ular poach. 6. A tentacle.
0. OelatiDoni linua.
generally oval body from the mouth to the opposite pole (&,
Fig. 33). The cilia in each band are arranged in short transverse
rows, and the cilia in each row are joined at the base and free at
III.] CTENOPHORA. 71
the tip. So each row has the form of a comb, and thus the name
Ctenophora, comb-bearer, is seen to be appropriate. Further the
principal sense organ is situated in the centre of the end of the
animal opposite to the mouth at the spot where the bands of
thickened ectoderm which carry the combs converge. These
thickened ridges of cells are often termed " ribs." If we compare
the animal to a globe, the end at which the mouth is may be
called the oral pole, the opposite end the aboral pole (2, Fig. 38).
The sense organ at the aboral pole is a plate of thickened ecto-
derm the cells of which have developed nerve tails. Similar nerve
tails are developed by the bands of ectoderm which carry the combs.
The cells at the edge of the plate carry cilia fused with one another
which arch over the plate and cover it like a tent. Inside is a
calcareous ball supported on four curved bars, each made of con-
joined cilia, borne by some of the inner cells. This ball acts as a
balancing sense-organ. If the animal inclines to one side the ball
will bear heavily on the support on that side, and stimulate thus
the corresponding ribs, which will thus act more vigorously than the
rest and tend to restore the vertical position.
Like Actinozoa, Ctenophora have a well-marked stomodaeum, and
the true coelenteron is represented by a series of branching canals,
the central one being termed the funnel (3, Fig. 33). The funnel
and stomodaeum are both flattened but in planes at right angles to
one another. The funnel gives off (1) two canals, the so-called
excretory canals, which open at the sides of the sense-organ;
(2) two canals, paragastric, running back towards the mouth
parallel with the stomodaeum (4, Fig. 33); (3) two canals running
each to a branched tentacle, which can be retracted within a pouch
(7, Fig. 33). This branched tentacle is covered with adhesive cells,
there is one on each side of the animal Each tentacle canal gives
off four branches (6, Fig. 33) which lead into the meridional canals
running under the ribs, from the cells lining which both ova and
spermatozoa are produced, Ctenophora being hermaphrodite. The
commonest British form is Hormiphora plumosa, which sometimes
appears in shoals in the seas washing the Atlantic coast of Britain
on the one hand and America on the other. The Ctenophora are
good examples of what are called pelagic organisms, that is to say,
organisms which pass their whole life from the egg to the adult
condition floating at or near the surface of the sea. Such organisms
are the only ones which are found in mid-ocean. Nearer the shore
the waters are filled by a profusion of other animals, but these turn
72 COELENTEBATA. [CHAP.
out on examination to be largely composed of forms which in some
period of their existence are adherent to or creeping on the bottom.
Other purely pelagic groups are the Siphonophora, the Trachy-
medusae and the Narcomedusae.
The Gtenophora contain many forms which difier widely in
appearance from Hormiphora — for instance the Cestum venei-isy or
Venus's girdle, a beautiful transparent ribbon-like creature, a foot
or 80 in length and two or three inches wide. On close examination
the reason of this diversity of shape is found to be that the Cteno*
phora are not really radially symmetrical, but doubly bilaterally
symmetrical That is to say, not only right and left sides are like
one another but also the back and belly are alike, but at the same
time different from the sides. The difference is slight in Hormi'
phora but very strongly marked in Cestum veneris.
Phylum COELENTERATA.
The classification of the Goelenterata is as follows : —
Class I. Hydrozoa.
Goelenterata without mesenteries or gullet lined by ectoderm:
genital cells derived from ectoderm.
Order 1. Hydrida.
Only hydroid persons present, not permanently attached
but capable of locomotion : the buds become free.
Order 2. Hydromedusae.
Composite fixed colonies of hydroid persons from which
medusoid persons are budded off.
Suborder (1) Qjrnmoblastea. Perisarc confined to the
base of the hydroids: medusoids have eyes and bear gonads on
the manubrium.
Suborder (2) Calyptoblastea. Perisarc expanded to form
cups called hydrothecae, into which heads of hydroid persons
can be retracted : medusoids have ears and bear gonads on
under side of umbrella.
Order 3. Narcomedusae.
Only medusoid persons present. The manubrium poorly
developed, the wide stomach occupying the under side of the
belL The sense-organs are reduced tentacles projecting at the
edge of the bell.
III.] CLASSIFICATION. 73
Order 4. Trach3rmedusae.
Forms in which like the foregoing group only medusoid
persons are present, but there is a long manubrium traversed by
the radial canals, and the stomach is only at the bottom of it.
Order 5. Siphonophora.
Free-swimming colonies consisting of hydroid and medusoid
persons in which the base is modified into a float or some of
the medusoids are transformed into swimming organs, or both
arrangements are combined.
Order 6. Hydrocorallinae.
Composite fixed coloDies of hydroid persons : medusoid
persons budded off" in only one or two genera.
Perisarc thick and calcareous, surrounding chiefly the stolons
which are given off at various levels and form a thick mass.
Class II. ACTINOZOA.
Solitary or colonial Coelenterata with gullet lined by ectoderm :
coelenteron provided with radiating mesenteries : genital cells de-
rived from endoderm.
Order 1. Alcyonaria.
Eight mesenteries and eight fringed tentacles : spicules
in the jelly.
Order 2. Zoantharia.
Mesenteries usually in pairs, either six pairs or some
multiple of six : tentacles conical : no spicules but often an
external calcareous skeleton formed by the ectoderm.
Class III. AOALEPHAE
Coelenterata with alternation of generations : mesenteries present
in young, but later becoming absorbed : oral part breaks loose and
becomes developed into a free-swimming organism externally resem-
bling a medusoid : the stalk of the original polyp reproduces the
lost parts.
Class IV. Otenophora.
Very widely different from the two preceding divisions : free-
swimming animals with a sense organ and nervous disc of skin at
the pole opposite the mouth: swim not by muscular contractions
but by vibrations of eight longitudinal bands of cilia radiating from
nervous disc, which bands consist of successive transverse rows of
cilia, the cilia of each row fused at base so as to form a comb-like
structure : only two tentacles, a gullet lined by ectoderm : stomach
represented by a system of branching tubes.
74
CHAPTER IV.
Phylum Porifera.
'l^v >;roup of the sponges or Porif era occupies an almost isolated
position in the animal kingdom. Sponges agree, it is
.u\*rv!vuii, ^^®» ^^ Coelenterata in exhibiting cellular structure
and having their protoplasm arranged in tissues ; and
luilhor iu the fact that all the internal cavities of the body are in
i oiuuiuuication with one another, so that both Coelenterata and
t'mifom might be described as systems of branched tubes. A
\ K»iK)r iuHpection however reveals the fact that the tissues of the
l'urif<&nk are very diflferent from those of Coelenterata and originate
iu a different way from the larva, so that the opinion is gaining
^ivuuil that whereas most, if not all, of the higher groups of
uuiiaals have descended from ancestors which had we seen them
vkv ahould have classed as Coelenterata, Porifera on the other hand
liAVO been independently derived from Protozoa.
lu Coelenterata the colonies can be analysed into persons
^lutnlusoids or hydroids) and stolons, and many of the Porifera show
a like aggregation of persons. But in many forms it is impossible
W t»uggest how many individuals are contained in the branch
system of a single aggregate since all distinctness of individuals is
Uwit. Further analysis shows that the apparent persons or units,
even when most clearly demarcated, are of very varying morpho-
logical value.
The salient peculiarities of sponges will be best appreciated by
, , a short description of one of the simplest types
Lcucoftolenia. *^ iijr »«fi-
known, a sponge called Leucasolenta, which is
common on most clean rocky shores.
In this animal we can recognise a foundation consisting of a
network of horizontal stolons, adherent to some foreign object,
from which a number of upright tubes spring. Each upright tube
CHAP. IV,]
LEDCOSOLBKIA.
75
ends in a large opening, the OBonlnm (1, Fig. 34), which can be
eloeed if the animal be irritated and which in LeuamUma is
partly closed by a perforated membrane. This opening, which at
first sight recatls the moatli of Hydra, is really need for a qnite
different purpose. It is an efferent opening (Lat. ^ero, to
carry ont) and from it the water which has passed through the
animal is expelled. Water enters the internal cavity through a
multitude of very fine pores in the walls of the tube (Fig, 85, and
1, Fig. 37): it is the universal presence of these pores which gives
the name Porif era to the grou'
FlO. M. Tiew of ft bnneh of I^tueetoUnta ep., flhowiDg the sieve-like mem.
brane which Btretchea MToag the oBoalDm, The lower part of the sponge
■bowi spioolee only x 10. From Uinohm.
1. Biere-like membrane.
The wall of the tube is made up of two layers, but we must
guard ourselves against rashly comparing these with the layers of
the body waU of Hydra, and hence it is better to avoid the names
ectoderm and endoderm and adopt the terms dermal and gaatral
layers.
The dermal layer consists of fiat cells which cover the external
surface and extend for a short distance inside the osculnm, and of
cells termed omoebocytes from the resemblance of their movements
to those of an AmoAa ; the whole of the rest of the tube and the
stolons are lined by a tissue consisting of peculiar cells called
eboanocytes (Gr. -jpai/vi, a funnel; kvto;, a hollow vessel), or
76
POBIFERA.
[chap.
collar cells, which alone constitute the gastral layer (3, Fig. 35
and Fig. 36). Each of these is cylindrical and provided with a
funnel-shaped transparent rim called the collar, turned towards
the cavity of the tube. The collars of adjacent cells are not
Fio. 85. Yertioal section throngh an osonlnm with sieT^-like membiana, and
a tube of Leueowlenia sp. Highly magnified. From Minchin.
1. Sieve-like membrane. 2. Outer layer. 3. FlageUated or collar cells
(choanocytes). The pointer shoold have been continued to indicate the
cells lining 5. 4. Spicules. 5. Internal cavity
normally in contact, and the outer part of the cell bodies are widely
separate, so that here the distinctness of the elements of a cellular
tissue is carried to an extreme. From the centre of each collar
a long flagellum arises, and it is by the action of these flagella
IT.] LEDCOSOLENIA. 77
thftt water is drawn in throngh the pores. The sponge lives on
the organisms carried in bf the current ; these appear to be carried
within the collars b7 the miuute whirlpools produced by the
individual flagella: they adhere to the collars and are swallowed
by them and digested by the cells. It will be seen that the collar is
a real Uving structure, not a caticular tube, such as the hydrotheca
of a calyptoblaatic hydroid, and this is further illustrated by the
&ct that it is withdrawn by the collar-cell under certain conditions.
The water after being exhausted of its food is expelled through
the osculum, carrying with it all excreta.
1. NdoIbhc 3. Tkenole. 6. Opeoing into the inner space of the Bponge.
The outer layer of the body-wall consists, in the ordinary con-
dition of the sponge, of fattened cells. These however, especially
in the region of the osculum, have the power of changing their
shape so aa to become shorter and thicker ; in a word they can
contract, although they show no trace of the fibrillae found in all
muscle and in the muscle tails of the contractile cells of Goelen-
terata. The contraction is slow, not quick, as in true muscle.
It has been proved that the pores are formed by specially large
cells, the porocytee, which extend from the outer layer and push
aside the choanocytes, and then become hollowed out.
Between the two layers is Found a certain amount of secretion
which may be termed jelly, in which in many sponges a large
78 PORIFERA. [chap.
namber of cells is found. These form a portion of the dermal layer,
aod are, for the most part, amoeboid. Some of these probably act
as camerB of food and possibly of excreta from one layer to the
other. Others at first very similar give rise to ova and sperma-
tozoa. A third class called scleioblasts — derived in iMtcotolmia
from the fiat cells which cover the surface, but not bo derived in all
sponges — secrete the rods which form the skeleton and which are
termed spicules (Fig. 34, and 6, Fig. 37). In Leucosolmia these
ore calcareous and hare three rays, more or less in one plane — a
Fia. 37. Seotion of a portion of Orantia txttuartiealata. Hlglilj minified.
From Dendj.
1. Opeoings of the inhal&nt oaoalB. 3. Inhalant oanal. 3. Opentng* of
inhaUnt canals into flagellated chamber (proBop;)e). i. Flagellated
chamber. G. Flagellated or eoUar-oells (ohoanoajtes). 6. Bpiculea.
7. Eihalant opening of flagellated chamber.
shape technically named triradiate. One limb is usually directed
parallel with the long axis of the tube, and often bears a fourth ray
or spine making a qoadriradiate spicule. The spicules although
remaining unconnected aie numerous enough to form a loose mesh-
work.
The most important points in which the higher sponges differ
from Leucosolenia are the folding of the outer and
a^jElf* inner layer, the restriction of the choanocytes to
small portions of the latter, and the differentiation of
the body into distinct regions.
IV.] COMPLEX SPONQEa 79
A common sponge on the British coast, Sycon (Grantia) com-
pressutn, will illustrate the first step in this complication. This
animal has the form of a series of flattened thick- walled upright
tubes. The layer lining the central cavity consists of flattened ceUs,
but from this cavity pouches lined by choanocytes extend out into
the substance of the wall. These flagellated chambers, as
they are often called, communicate with the exterior by a series of
inhalant canals which intervene between them and into which
the pores open (Fig. 37).
When a sponge becomes still more complicated the central
cavity becomes broken up into a series of branching canals, which
are termed ezhalant or efferent, and the ciliated chambers become
small and rounded (Fig. 36), each often connected only by a single
opening or prosopyle (Gr. Trpdo-o), forwards ; irvAiy, a gate) with the
afferent system of canals. Numerous oscula are found in one
sponge mass, so that no pretence of discriminating the individual
can be made.
A still further complication arises from the presence of sub-
dermal spaces. These are wide cavities immediately beneath the
surCeu^e of the sponge into which the inhalant pores open and from
which the inhalant canals take their origin. In this way a rind or
crust of the sponge can be separated from a deeper part containing
the flagellated chambers. Sponges are by some of the best authori-
ties divided into two main classes, viz. :
Glass I. Caloabea.
This group includes all those sponges with calcareous spicules
and comparatively large flagellated chambers.
It is divided into two main orders :
Order 1. Homocoela.
Sponges consisting of tubes lined throughout with choano-
cytes.
Order 2. Heterocoela.
Sponges in which the choanocytes are restricted to special
chambers — which may be cylindrical as in Grantia or spherical
as in Leucandra.
Class II. Hexaotineludae.
Sponges in which the skeleton consists of a coherent network of
siliceous spicules each consisting of three axes placed at right angles
80 PORIFERA. [chap.
to one another. The flagellated chambers are large and cylindrical
but are separated from the central space by a system of canals.
The central space may be deep and narrow and covered with a plate
pierced by numerous oscula, or short, open and shallow.
These sponges inhabit as a rule very deep water and most species
are provided with a tuft of long needle-like spicules which root them
in the soft mud which forms the bottom of the sea at these depths.
Class III. Demospongiab.
These sponges derive their name from the fact that their spicules,
which are always siliceous, are arranged in cords so as to form a
network traversing the substance of the sponge. The spicules com-
posing these cords are nearly always cemented together by a homy
elastic material called spongin. The flagellated chambers are always
extremely small and there is never a central chamber. Besides the
skeletal spicules, as those composing the cords are called, smaller
ones called flesh spicules are scattered singly in the intervals of the
network.
There are several exceptional genera in which interesting modi-
fications occur.
Oscarella is totally devoid of any skeleton and has the appear-
ance of a whitish yellow scum on the rocks to which it adheres.
Empongia possess spongin cords but no spicules in them, and for
this reason it can be employed for domestic purposes.
Two fresh-water species, namely, Spongilla lacustris with a bush
like appearance and Ephydatia fluviatilis with an encrusting form,
are often found growing on the side of canals and on the timbers of
river-locks or weirs in Great Britain. The two species are bright
green when they grow in the light, but they are pale flesh-colour
when they grow in the shade. In Canada similar species adhere to
stones in the river St Lawrence.
The larvae of sponges are best understood by a short description
of the simplest form, viz. the larva of Oscarella, This
has the form of a simple hollow sphere of ciliated cells
like the planula of Coelenterata in its first stage. The cells at one
pole lose their cilia, become pigmented and granular and then the
larva fixes itself by the ciliated pole. The whole animal flattens and
the granular cells extend over the ciliated cells which become tucked
IV.] LARVA OF PORIFERA, 81
into the interior and there arranged as an inner lining to a cavity.
The flageUated chambers of the adult arise as small pocket-shaped
outgrowths irom this cavity and the osculum is a later perforation.
The ciliated cells are eventually restricted to these chambers where
they form the choanocytes and all the rest of the sponge is formed
from the granular cells. Other larvae differ from that of Oscarella
in the early multiplication of granular cells which form a solid mass
at one end of the larva and often — indeed generally — of such extent
as to project into the interior.
To compensate for greater dead-weight, so to speak, the ciliated
layer — the locomotor organ of the larva — becomes extended to
surround the granular material, so that we are presented with the
remarkable phenomenon of the internal layer of the larva burst-
ing forth and becoming the outer layer of the adult. This is the
case in the larva of Leucosolenia. In the larvae of other calcareous
sponges, the ciliated cells at first surround the granular cells, but
the latter are afterwards exposed and the larva in this form has
been called an amphiblastula. In the case of most of the Demo-
spongiae the ciliated cells nearly, but not quite, surround the
granular cells, and these last often contain a number of spicules
ready formed in a central bundle which are scattered in all direc-
tions when the sponge flattens on fixation. Comparing the develop-
ment of a sponge with that of the planula of a Coelenterate we see
that in the first the ciliated cells form the internal layer, in the
second the external layer of the adult ; in the first the animal fixes
itself by the pole at which the invagination or intucking of the cells
destined to form the inner layer takes place — in the Coelenterata at
the opposite pole — so that if Coelenterata and Porifera had an
ancestor in common it could only have been an animal like the
organism Vohxxt, consisting of a single sphere of cells — in a word it
would have been classed were it living now as a Protozoon.
The study of the development of sponges like Si/con shows that
at first, after the metamorphosis, the sponge has the form of Leuco-
solenia by a simple cylinder lined by choanocytes. The flagellated
chambers arise as horizontal cylindrical branches on the primitive
chamber and soon become so numerous that their walls come into
contact and the afferent or inhalant canals are simply the crevices
left between these chambers. As the chambers develop, flattened
cells come inwards from the pores and displace the choanocytea
except in the chambers.
S. (bU. 6
82 POBIFERA. [chap. IV.
Porifera then may be defined as animals consisting of branch-
systems of tubes, the principal openings of which are exhalant,
whereas the inhalant openings are minute perforations of the walls.
The wall consists of two layers ; some cells of the inner layer have
the form of choanocytes, whilst the skeleton consists of siliceous or
calcareous needles formed by cells of the outer layer which wander
in, or of spongin. There are never any thread-cells or differentiated
muscle or well-marked nerve-cells, nor any such organs as tentacles.
83
CHAPTER V.
Introduction to the Coelomata,
The last two groups of animals studied, although very different
from one another in most respects, yet agree in this that the
groundwork of their structure is a set of tubes branched in dif-
ferent ways and with walls of varying thickness but consisting
always of two layers with an intervening jelly. It would not be
straining the truth to assert that in the Coelenterata and the
Porifera we find but two tissues, an outer more or less differentiated
skin— the ectoderm with the underlying jelly,— and an inner layer
mainly digestive in function.
The phyla which are next to be considered, and which may be
^ grouped together under the name Coelomata, differ
from the two mentioned above in the possession of
an important organ termed the coelom (Gr. KoiXcofia, a thing
hollowed out). This is often described as a space intervening
between the ectoderm and endoderm, and the term coelomic
cavity or body cavity has been used to describe it. In spite of
the etymological difficulty we propose in the following pages to deal
with this organ under the term coelom, and its cavity under the
term coelomic cavity. In reality it consists of one or more pairs of
sacs with perfectly defined walls lying at the sides of the endo-
dermic tube. In the adult these sacs join each other above and
below the endoderm, and the adjacent walls entirely or partly break
down, and thus one continuous cavity results. The wall of the
coelom and the tissues derived from it are known as the mesoderm.
To describe the coelom as a split or space is to describe it negatively :
with as much justice the endodermic tube might be described as a
split. In each case the real object of consideration is the wall.
If we leave out of account cases in which the facts of develop-
ment have not been fuUy elucidated and confine our attention to
6—2
8i INTRODUCTIOK TO THE COKlXMiT^ [CHAP,
those instances where the wliole histoiy of the coelora has been
ezbaustively worked out, we find that this important oi^an arises
in one of two ways, either (1) by the fonnation of poaches of
the endodennic tube, which become nipped off (Pig. 38) ; or (3) by
the budding of two large cells, formed themselves by budding from
the endoderm (Fig. 39), these cells subsequently growing rapidly
and dividing so as to form bands, the so-called germinal bands,
which subsequently become hollowed out. These initial cells are
termed pole-cells.
The ectoderm U deeply shaded, tbe mesodenn U lightlj shaded, the endederm
— ftlimentarj cansl sad Dotocboid — ia anshaded. A. sbowa the origin
of the paired meaodennal ponchea from the areheDteroii ; the cavity —
coelomio — of tba focmer ia atill id aommnnication with the cavity of the
alimentary oanaJ. The notochotd is ariaing in the middle line from the
stidodetm, and the tabular nerroui system above it ii already separated
from tbe ecCodeim. B. shows the meBodennalpouabeaooinplel^Tahut off;
the; each enclose a cavity, the coelom, and each ooneiBtg of an outer wall
next the ectoderm, the 'somatopleur,' and an inner wall next the endodenn,
the ' Bplancbnopleur.' C. ehowe the mesodermal ponches extending ventrally
beneath the notochord, now completely eeparated from the wall of the
alimentary canal and also round the alimentary canal. The ooelomia
space ia laigsr, and the splancbnopleor is beginnijiB to form mosole-ceUs.
A sharp controveiay haa raged round the question which of
these two processes gives us the best representation of what
occurred in the evolution of Coelomata &om simpler Coelenterata-
like ancestors.
If however we recall the fact that in the Actinozoa the endo-
dermic sac has the form of a series of pouches ranged round a
central cavity, and that the walls of these pouches become coa-
verted into musclea and generative cells exactly as in the case of
the coelom, and that pores exist in many cases placing the cavity of
these pouches in communication with the outside world, we shall
T.] lNTftODnCTIO» TO THE COELOHATA. 85
be indaced to oonclade that the coelom woe probably evolved ftom
l&teral pouches of the gnt and that the mesodenn is therefore
dnived from the primittTe endoderm. Where pole-cells ocout the
cavity of the alimentary canal ia small in proportion to the thickness
of its wall, and the pole-cell might be looked on as a solid pouch.
Fut. S9. T«o sUgea in the earl; deidopment of a oomiDoa fresh-water mollaBO,
Planorbii, to show the origin of the mesoderm cells x S20. From BabL
The wtoderm cells eie deeplj shaded, the endoderm oella ate tuiBhaded.
k. Totmg stage in which the endoderm has not hegnn to be invagmaled ;
it is a lateral optical section. B. Older stage, optical section seen in
front Tiev; the endoderm oella are invaginating, and the two mesoderm
oellfl are aeett on each side. 1. Mesoderm or pole-ceils ; in B, each has
budded ofl another mesoderm cell.
In most Coelomata the mesoderm forms by far the greatest
portion of the body, and it may be roughly stated that the
mesoderm gives rise in the fully developed animal to " the muscles,
the bones, the connective tissue, both arteries and veins, capillaries
and lymphatics, with their appropriate epithelium," and to the ex-
cretory and generative oi^ns.
In the Porifera and in the mora complex Coelenterata, where
the thin structnreleBS lamella of Hydra has swollen into a bul^
mass of jelly such as we find in a Medusa, cells begin to wander
into it &om the ectoderm, and thus a kind of tissue is formed to
which the name mesoderm has unfortunately been applied. We
■ee that its origin and nature are quite different, although both in
Bpongea and Coelenterata it may give rise to the skeleton, and in
86 INTRODUCTION TO THE COELOMATA. [CHAP.
this respect at least it may be regarded as a forerunner of the tme
mesoderms.
The endoderm, after the separation from it of the mesoderm,
forms the lining epithelium of the digestive tube and of its ap-
pendages, which in the higher Vertebrata are the organs known as
lungs, liver, pancreas, and urinary bladder. The basis of the
skeleton of Vertebrata, the gelatinous rod called the notochord,
also arises from it.
In Coelenterata there is one opening only to the digestive sac,
which is used both as a mouth to take in food and
Can^L*'***^ *8 ^^ ^^^^ ^ cast out indigestible material. In the
overwhelming majority of the Coelomata there is a
second opening, the anus, the mouth being restricted to the
function of taking in food. As a consequence the digestive sac
takes the form of a tube open at both ends, and is known in the
higher groups as the alimentary canaL Often this endodermic
tube is much longer than the ectoderm, and so in order to be
contained in the bounds of the ectoderm it has to be bent and
looped on itself.
Hound both mouth and anus the ectoderm is generally tucked
in, so as to form as it were vestibules to the true alimentary canaL
Of these, the ectodermic vestibule to the mouth is called the
stomodaeum, and is found amongst the Actinozoa, where it has
been already described. The proctodaeum is the term applied to
the vestibule around the anus. Although not strictly parts of the
alimentary canal stomodaeum and proctodaeum are usually included
in descriptions of it, and indeed in some cases — Crustacea — ^they
form by far the greatest portion of the apparent digestive tube.
The internal anatomy of the lower animals was first studied by
physicians and others who were primarily interested in human
anatomy. An unfortunate consequence is that a large number of
names are used in the description of simpler animals which are
based on fanciful resemblances between their organs and those of
man. As a consequence many of these names are quite misleading.
To give some instances: the word stomach in the Lobster denotes
part of the stomodaeum, in the Vertebrata it signifies part of the
endodermic tube. The pharynx of an earthworm is the stomo-
daeum, in a fish it includes both stomodaeum and the first part of
the endodermic tube. The term liver has also been much abused.
The names taken from the anatomy of the higher animals
which are customarily used in the description of the alimentary
v.] SHAPE OF THE BODY. 87
canal are as follows: mouth- or buccal-cavity, pharynx,
oesophagus, stomach or crop, gizzard, intestine, and
rectum. They are applied generally to parts of it succeeding
one another in the order above given. The significance of these
will be explained in each case : it would perhaps be more logical to
sweep away altogether these and a host of similar terms employed
to designate other parts of the body, but so deeply are they
engrained in zoological literature that such a course would render
unintelligible most anatomical descriptions of species that we
possess.
Besides forming the outer layer of the skin or epidermis of
the animal and the stomodaeum and proctodaeum, the ectoderm
gives rise to the brain and nervous system and to the essential cells
of the sensory organs.
In the group Coelenterata a general circular outline of the body
Qcner.. predomiBatea. the principal external organs being
Shape of the arranged like the spokes of a wheel around the
^°^^' mouth as a centre. Such an arrangement is spoken
of as a radial symmetry, and is in all probability connected with
the fixed life so common amongst Coelenterates, a condition of
affairs which renders it advantageous to have organs developed so
as, to use a familiar phrase, to be on the look-out all round.
The firee-swimming Medusae, it is true, move always with the
apex of the bell directed forwards, but as has been pointed out (see
p. 55) they are to be regarded as specially modified hydroids, and
they have not modified the radial symmetry so deeply impressed on
them by the habits of ancestral Coelenterata.
In the higher groups of animals there is usually one fixed part
of the body which moves first when the animal changes its position ;
and when such a portion is definitely set aside to move first we can
distinguish the front end of an animal from the hind end. It is
usual to term the former the head or anterior end and the latter
the posterior end, and when an organ such as a man's arm lies
nearer the anterior end (head) than another, as for instance his leg,
we say the former is anterior to the former, and that the latter,
i.e. the leg, is posterior to the former, i.e. the arm. In describing
the parts of an appendage such as the arm it is usual to speak of
the part nearest the base of attachment as proximal and the part
further away as distaL
Corresponding with the appearance of the head as distinct
from the rest of the body, which is in contradistinction termed the
88 INTRODUCTION TO THE COELOMATA. [CHAP. V.
trunk, we find a difference arising between the surfaces of the
body. With few exceptions animals, whether creeping, swimming,
flying or walking, keep the same surface turned towards the eartL
This lower surface is termed the ventral (Lat. venter, belly),
whilst the upper surface or back is termed the dorsal (Lat.
dorsum, back). As a rule the difference in their relationship to
their surroundings induces a difference in the aspect of these two
surfaces, and it is seldom difficult to determine which is the ventral
and which the dorsal surface of the body. As a general rule the
ventral surface of an animal is much lighter in colour than the
dorsal In most Coelomata the nervous system is for the most part
ventral and the chief blood-vessel dorsal, but in the Vertebrata the
reverse is the case. In both the alimentary canal lies between the
chief blood-vessel and the main nervous system.
The two sides of an animal, the right and left, are however
exposed to ]uuch the same conditions and as a rule resemble each
other very closely. When this is the case an animal is termed
bilaterally symmetrical, and it may then be divided in one
plane — and in one plane only — in such a way that each half forms a
reflected image of the other, such as we should see if we held half
the animal up to a looking-glass. This bilateral symmetry may
extend to all the internal organs, as it does in an earthworm or
a crayfish, or it may be confined to the external features and
some of the internal organs only, as in insects or in most verte-
brates, where the coiling of the alimentary canal, etc.', interferes
with the bilateral symmetry of the internal organs.
In some animals, and these are for the most part such as move
sluggishly or have become permanently attached to some sub-
stratum and do not move at all, this bilateral symmetry has been
lost and the two sides do not resemble one another. Such animals
are called asymmetrical The Snail is a familiar example of
such asymmetry. Amongst the Echinodermata (Star-fishes and
Sea-urchins) this asymmetry is replaced by a radial symmetry.
89
CHAPTER VL
Phylum Annelida.
The name Annelida (Lat. annulus, a ring) means ringed, and
refers to the fact that the bodies of the creatures grouped under
this name are built up of a series of parts more or less resembling
each other placed one behind another. This division of the
body into more or less similar parts is called segmentation ;
each part is called a segment (or somite), and the animal is
said to be segmented. Like the symmetry, the segmentation
may be merely external or may affect both the exterior and
a greater or less number of the internal organs.
Sometimes, however, as in the case of the longer
half of an earthworm's body, the segmentation affects all the
organs, and the likeness of one segment to another is so great that
it would be impossible to say what part of the body any given
isolated segment was taken from. More often, however, one or
another of the organs of the body differs in shape or size in
successive segments, and this is the case with the internal organs of
the first twenty segments of the earthworm's body, so that if these
segments were all separated it would not be very difficult to place
them together in their natural order.
K we take an earthworm and kill it by placing it in alcohol for
a few minutes and examine it carefully, we shall see
Earthworm. that the body is composed of some 150 rings, each
fcSurel! ^^ which corresponds with a segment The rings are
separated from one another by slight grooves. At
each end of the body there is an opening, the mouth (2, Fig. 40)
in front and the anus (3, Fig, 40) behind. Besides these, two
slit-like pores with rather swollen lips, situated on the under sur-
face of the fifteenth segment (5, Fig. 40), may be seen. These
are the pores through which spermatozoa are discharged, and
are consequently known as the male genital openings. The
iO
ANNELIDA.
[chap.
uLhur opeaings into the body are minnte and
roquire the aid of a lens to make them out
Thure are paired openings on each segment,
except the first three and the last, situated
lutero-ventrally; these are the openings of the
tubes known as nephridia (Gr. vc^piStov, a
little kidney), which act as kidneys; in addi-
tion to these a median dorsal pore opening into
the body-cavity is situated in each groove behind
the tenth segment (11, Fig. 44). The earthworm
is hermaphrodite, that is, it contains both
male and female organs in its body. Through
two slit-like openings in the ventral surface of
the fourteenth segment the eggs are discharged:
these are called the female generative
openings. Two pairs of pouches called
spermathecae, which are reservoirs for sper-
matozoa received from another worm (v. p. 107),
open, one pair between the ninth and tenth,
the other between the tenth and eleventh
segments, all on the ventral surface.
If a worm killed in alcohol be drawn through
the fingers a certain roughness may be felt
along the sides and lower surface. This rough-
ness is due to the presence of a number of small
bristles, called chaetae (6r. x^^"^* hair), which
project from the body (7, Fig. 40, and Fig. 43).
Each segment bears eight of these chaetae ar-
ranged in four pairs, one pair on each side being
lateral and the other nearer the ventral middle
line. Itisbymeansof the chaetae that the worm
crawls about; since by protruding the chaetae
and implanting them in the soil a fixed point
is obtained from which the anterior end of the
Fio. 40. Latero-ventral yiew of Lumhricut terrestrit,
slightly smaller thftn life-size. From Hatschek
and Cori.
1. Prostomiom. 2. Mouth. 8. Anus. 4. Opening
of oviduct. 5. Opening of vas deferens. 6. Geni-
tal chaetae. 7. Lateral and ventral pairs of chaetae.
zv. xuui. and xxxvn. are the 15th, 82nd, and 87th seg-
ments. The 82nd to the 87th form the CliteUnm.
«v^-^
3
Fio. 40.
VI.J
LUMBBICD8.
body can be pushed forward and to which the hinder end of the
body can be drawn up.
The colour and thickness of the body from the thirty-second to
the thirty-seventh segment differ in adult worms from those of the
ttegments which lie before and behind this band. This la due to
the presence in this region of certain ectodermal glands whose secre-
tion forms tlie cocoons in whicli the eggs are laid. This region of
the body is called the Clitellnm (xxxn — xxxvn, Fig. 40),
The surface of the body of an earthworm is glistenipg and
somewhat slippery. This is dtio to the cuticle, which is a thin
membrane secreted by the ectoderm cells of the stin ; if a dead
earthworm be soaked in water for a few hours the cuticle can be
easily stripped off the body. In the crayfish, insects, etc.. a similar
cuticle is present, but it is much harder and forms an external
protective skeleton; even in the earthworm, where it is soft, it acts
as a protection to the underlying cells, and its smooth surface
enable-s the worm to creep into narrow holes without hindrance.
The chaetae are simply large local thickenings of the cuticle: they
protrude from pockets called chaeta-saca, each of which is a
portion of the ectoderm tucked in. In the bottom of each sac is a
specially large cell which rapidly secretes a column of cuticle and
builds up the chaeta.
If we cut through the skin of an earthworm we do not make
our way into the cavity of the alimentary canal but
Ai.t^y! '"'o ^^^ coelomic cavity, in which not only the
alimentary canal but the blood-vessels, kidneys, re-
productive organs, apparently lie. The relation of the alimentary
canal to the body-cavity might be roughly represented by introducing
a piece of glass tubing loosely into an india-rubber pipe. The
alimentary canal would be represented by the glass tube and the
body-cavity by the space between the glass and the india-rubber.
The coelomic cavity is a very important feature in all the higher
animals; it may become very reduced, as in the Arthropods, but it
is always present, although it may not at first sight be easy to
recognise. There are, however, certain features which it always
presents : (i) it always possesses a proper wall, never being a mere
slit intervening between various organs, and it is always surrounded
by mesoderm ; (ii) its walls give rise to the cells which form the
reproductive cells; (iii) the kidneys, which are primitively tubes
with open ends, open into it.
There is no difficulty in recoguiaing the body-cavity of an
92 ANNELIDA. [CUAP.
earthworm. It is comparatively spacious and is divided by a
iteries of partitions into a number of chambers which correspond in
number and position with the segments of the body. These par-
titions or septa (8, Fig. 41) are pierced by the alimentary canal,
the nervous system and blood-vessels ; they are not complete but
are provided with holes so that the space in one segment is not shut
off from the spaces in the neighbouring segments. Fundamentally
in Annelida the body-cavity consists of a series of pairs of sacs
interposed between the skin (ectoderm) and the gut- wall (endoderm) ;
tliere is in the embryo a pair in each segment, but the walls of
these come into contact above and below the alimentary canal and
then break down, so that the cavities of the right and left sacs
open into one another and a ring-shaped space results. This space
has distinct inner and outer walls of its own which are known col-
lectively as the peritoneum (Gr. ircpt, around ; toVos, a stretched
band).
The septa are formed where the adjacent walls of two sacs,
placed one behind the other, come in contact. If this description
of the relations has been followed it will be seen that the coelom
in the adult consists of a series of ring-shaped spaces, and that
the alimentary canal is not truly in the coelom nor, it may be
added, is tlie nervous system or the blood-system.
Like all similar spaces in animals the body-cavity of an earth-
worm contains a fluid, and in this fluid certain cells float which
change their shape as an Amoeba does, and hence are called
amoebocytes. As a rule the body-cavity is completely shut off
from the outside world, but in the earthworm it opens to the
exterior by means of the dorsal pores (11, Fig. 44), and at times
the fluid which it contains escapes through these holes and pours
over the cuticle. This fluid has a certain poisonous action on
bacteria, and helps to keep the outside of the body clean and
free from parasites. Somewhat similar pores leading from the
exterior to the body-cavity are found in certain fishes.
The first segment is divided into two parts, a lobed lip or prosto-
mium (1, Fig. 43), overhanging the somewhat crescent-shaped mouth,
and a peristomium containing the mouth which leads into an oral
cavity extending through three segments (Fig. 41). There are no
teeth in this cavity and the food is probably sucked in by the action
of the muscular stomodaeum, called the pharynx, which succeeds it
and reaches back to the sixth or seventh s^pnent. This is followed
by the true endodermic tube. The first part is narrow and is
VI.] LUMBRICTJS.
calleil the oeaophaguB; it reaches to the twelfth segment and has '
Uiree pairs of lateral pouches developed on its walla. These pouches
secrete calcareous particles, and hence are tenaed calclferous
glands. The oesophagus dilates behind into a thin-walled sac,
called the crop, situated in the region of segmenta thirteen to six-
teen, and this is separated by a groove from a thick-walled sac,
with bard, homy walls, termed the gizzard, which extends to about
the tnentieth segment. The exact segment in which the above-
mentionedparta of the alimentary
canal lie varies with the amount
of food they contain, the septa
wiiich are pierced by them being
Btretched forward or backward
according to their state of fulness
or empdneas.
Behind the twentieth segment
the intestine stretches without
change to the anus. It is a thin-
walled tube, supported by the
septa between each segment and
sweUing out slightly in each
segment, so that it presents an
outline like a string of beads.
A deep fold, called the typhlo-
sole (Gr. rv<j,\4i. blind; Ti^h^y,
a gutter), runs along the upper
surface of the intestine, project-
ing into its cavity. Its presence
causes the wall of the intestine to
be pushed in, and thus the inter-
nal absorbing portion b increased
(7, Fig. 42). The intestine is
covered everywhere by a number
of cells of a yellow colour.
These form the inner wall of the
uoelomic sac and are actively en-
gaged in excretion.
The exact part that each of
the above-mentioned parts of the alimentary canal plays in digestion
ia not thoroughly understood. The pharynx helps to take food in
by a tinckiug action which ia caused by the contraction of the
Fid. 41. Anterior view of the InteniHl
organs ot in Earthworm, Lumhricui
IflTMtrii. filigbtl; magniSed. From
Bataobeh and Cori.
1. Central gaaglion orbraia. 3. Mus-
calu pharjQi. S. OcEophngQB.
i. Crop. S. UaBoulut gizinrd.
6. lukitine. 7. Nepbridk (the
rebrence lines ionul quil«icftohtbe
nepbri<lja|, S. 8«pta. B. Dond
blood-Tcsael. 10. Htaita. 11.
Spermathecne. 13. Tesionlae
■eminaleB.
TbaBomaii UgorMicfeitotheuumbet
of Ibe •cguionls.
miiscleB ruDniDg from it to the body-wall, resulting in an enlarge-
meut of tlie cavity of the pharynx eo that food may pass in by
stmoBpheric pressure. The food posses down the oesophagus,
being propelled by a seriea of contractions of the walls of the
alimentut7 cana! which push it along; on its passage it is mixed
with the secretions of the calciferous glands. The crop serves
as a resting-place in which the food accumulates before passing into
the gizzard. The hard, horny walls of the last-named chamber help
to grind up the food and render it lit for the action of the juices
which digest it. The process of digestion, or the rendering of the
food soluble, probably takes place in the intestine, and through the
walls of this portion of the alimentary canal the soluble products of
digestion soak, and are taken all over the body by the blood-vessels
and probably also to some extent by the fiuid in the coelom.
Eatadiek and Cori,
Septa. 2. Nephridia. 3, Ventral aarve-cord. 4. Sub-neural
blood-vessel, 6. Nephroalonies, internal fuunel-shaped openings of
Iiepliriilia, 6. Inleatine, 7. Tj^ihlosole. e._ Circular bloodv
9. Yenlial or Bub-ialeatinal blood-TeBsel.
10. Dorsal blood-vesseL
The series of contractions which squeeze the food onwards
towards the anus are known as peristalsis; they constitute the
sole moveaieuts of which tlie alimentary canal is capable and are
carried out by muscles developed from the cells of the inner wall
of the coelom, which pass round the canal like a series of nngt
or tight india-rubber hands.
LUMBRICC3.
The earthworm oats earth and manages to find sufEcient
nouriflhment for its needs in the small amount of organic matter,
broken-domi debris of leases, etc., which is contained in the earth.
The actual minerals of the earth are not digested but are passed
oat of the body in the form of those coiled and thread-like castings
which are so commonly seen on a lawn in the early morning.
Earthn-onna also eat fallen leaves and to this end they drag the
leaf-atalka into their burrows, and on autumn mornings it is a
common sight to see lawns studded with the stalks of horse-
chestnut leaves or the needles of fir trees, the stalks having been
dragged a little way into the burrows by the wonna. The burrows
that they make admit both air and rain to the deeper layers of the
soil, and Ihe earth which they swallow in their burrows is brought
to the GorfacQ and spread about in the form of castings. Thia is
carried on to such an extent that the whole surface of the soil soon
becomes covered by a layer of earth brought up from below. It is
thus clear that the earthworm is of great use as an agricultural
agent.
All the blood-vessels are for the moat part merely crevices
between the coelomic wall on the one haad and the ectoderm and
endoderm on the other. Those described are merely the larger
channels in a continuous network of spaces. The contractile power
which some, like the hearts, dorsal vessel, and sub-intestinal vessel,
possess is due to the presence of a special wall of muscular cells
derived from that part of the coelomic wall which lies next them.
The earthworm is the first animal that we have studied posseas-
ing a distinct and well-marked body-cavity; it is also the first in
which we find a distinct blood-system. In the Coelenterata the
cavity in which digestion is carried on permeates the body in all di-
rections, and the soluble products of digestion are never far from the
tissues or cells which may need them. But in the earthworms the
Alimentary canal is a straight tube separated from a number of the
other systems of organs by a space or coelomic cavity, and hence a
Tascolar system is of great use in conveying the digested products
to where they are most needed. Thus the blood serves to take up
the nutriment from the intestine and distribute it to all the active
cells in the body. The blood is also the medium by which the
waste products resulting irom katabolism are collected and taken to
the appropriate organs whose duty it i» to separate them from
the blood and ca£t them out of the body of the animaL Amongst
96 ANNELIDA, [CHAP.
the products which do not contain nitrogen the most important is
carbon dioxide, which is carried by the blood to the skin and got
rid of through the ectoderm, at the same time as the oxygen
needed for respiration is absorbed.
The dark streak which runs along the body of the worm from
head to tail in the middle line is caused by the dorsal blood-
vessel (10, Fig. 42), in which the blood flows forward. A parallel
sub-intestinal vessel in which the blood flows backwards under-
lies the intestine, and a third but smaller vessel, the sub-neural, lies
still more ventrally under the nerve-cord. The dorsal vessel receives
blood from the yellow cells covering the intestine by two pairs of
minute vessels in each segment, and anteriorly it breaks up into a
network of small vessels which branch over the pharynx. But by
far the larger x)art of the blood from this vessel passes into the sub-
intestinal vessel by means of five pairs of loops, called hearts,
situated in the seventh, eighth, ninth, tenth, and eleventh segments
(10, Fig. 41). Each pair of these hearts encircles the oesophagus
and contracts at regular intervals from above downwards. Their
contractility has suggested the name heart. As they pass from
the dorsal vessel into the sub-intestinal the effect of their con-
tractions is to drive the blood which is passed forvrard on the dorsal
side of the animal into the ventral system, whence it passes toward
the tail. These contractile hearts thus take a large share in main-
taining the circulation of the blood. The sub-intestinal vessel
gives off a special vessel in each segment to the nephridia, and the
blood which is purified in these organs is returned to the dorsal
vessels by another series of vessels. The dorsal vessel and the
sub-neural vessel are put into communication in each segment by
two lateral vessels which lie on the outer wall of the coelom
and which receive numerous small vessels from its substance.
The earthworm breathes through its skin. The blood-system
sends up into the skin innumerable minute vessels or capillaries
which come so near the outer surface of the worm that the oxygen
can pass in from the air into the blood. The name capillary (Lat.
capillus, a hair) was suggested by a comparison of the exceedingly
small calibre of these vessels with the diameter of a human hair.
The blood is red, and the red colour is due to the same substance
which colours our blood, haemoglobin, but there is this difference,
that whereas in Vertebrates the haemoglobin is contained in certain
cells which float in an almost colourless fluid, in the earthworm it
is dissolved in the fluid itself. This substance has a strong attrac-
VI.] LUMBBICUB.
tion for oxfgen whicli it takes up &oin the air that comes into
the neighbouiliood of the skiQ-capillaTies, formiDg a bright red
compound called oxy-haemoglobin. This compound is unetable,
and when the blood in its course round the body encounters a cell
hungry for oxygen, the oxy-haemoglobin is decomposed : the reduced
haemoglobin is purplish in colour. At the same time the cell gives
up carbon dioxide to the blood. The rolatioQs of this gas in the
blood are less understood than those of the oxygen, but like the
latter it is in loose chemical union, though not with the haemo-
globin. In Vertebrate animals the sodium of the blood provides
the means of conveying the carbon dioxide to the respiratory oi^&ns.
When the blood again approaches the skin carbon dio:[ide is
got rid of, oxy-baemoglobin being again formed by fresh oxygen
taken in.
In the Vertehrata the excretion of the waste nitrogenous
material is performed by a pair of compact organs, the kidneys.
In the earthworm this function is carried out by the nephridia,
which fundamentally reaemlile the tubules composing the kidney of
Vertebrates, but are not compai'ted into a solid organ. They are
distributed throughout the body, one pair being situated in each
segment, except the last segment and the first three, which have
no nephridia (7, Fig. 41, and 2, Fig. 42). Each nephridium is a
minute tube, opening at one end on to the surface of the worm
near the outer chaeta of the more ventral pair, and at the other end
into the body-cavity. This inner opening or iiephrostome has
cilia on its funnel-shaped rim, and these Hicker with an untiring
movement The nephrostome does not lie in the same segment aa
the rest of the tube but pierces the anterior septum, and projects
into the cavity of the segment in front, somewhere near the sub-
intestinal vessel Thus each segment contains a funnel-ahaped
opening and a tube which opens externally, but they do not belong
to the same nephridium, The tabe is. not straight but is coiled
and lies aa a white glistening tangle close to the muscular body-
wall. Each nephridium is to be regarded as a portion of the
coelomic sac into which it opens internally. It is, bo to speak, a
tail of this sac which projects backwards into the next one — not, of
couree, pieR'iug it, but indenting, so to speak, its anterior wall.
When we examine a nephridium through a microscope we see
that the waCs of the tube are very richly supplied with minute
blood vessels. The tube is really a cord of glandular cells placed
end to end and traversed by a minute cavity. It is these cells
i
98 ANNELIDA. [CHAP.
which take up the waste nitrogenous matter from the blood and
convey it out of the body. The part of the nephridium nearest the
external opening is swollen so as to form a bladder. The cavity
is here intercellular instead of piercing the cells themselves, and
surrounding it is a muscular wall by the contraction of which the
contents are from time to time expelled.
The blood thus takes digested food to the living cells all over
the body and brings from them certain nitrogenous excreta to the
nephridia, which cast them out of the body. But the nephridia
also exert some action on the other great fluid of the body — the
coelomic fluid — which bathes all the organs of the body. It
has been mentioned above that the funnel-shaped ciliated openings
of the nephridia open into the coelom, so that the fluid of this
cavity can pass out of the body not only by the dorsal pores but by
the tubular nephridia. This fluid has suspended it in numerous
amoebocytes (v, p. 92), and these corpuscles act as scavengers,
taking up into themselves any foreign bodies, such as bacteria,
which have made their way into the coelom, and breaking them up.
The yellow cells (7, Fig. 44), which surround the gut and
form the inner wall of the coelom, are also actively engaged in
extracting nitrogenous waste from the endoderm cells and the blood-
vessels which pass near them. When the excreta have accumulated
to a certain extent in a yellow cell it dies, and its remains fall
out into the coelomic fluid, where they are eaten by the amoebocytes.
These latter then wander to the nephridium and become pressed
close against its wall, the cells of which extract the excreta from
the amoebocytes and pass them into the cavity of the nephridial
tube. The funnel of the nephridium is too small to admit the
amoebocytes — it serves as a flushing apparatus, since its cilia draw
in water from the coelom which is swept down the tube and carries
the excreta into the terminal bladder whence they are from time to
time expelled.
It is probable that the yellow cells represent a primitive mode
of excretion and that originally the whole coelomic wall undertook
this function, the products escaping either by simple pores or by
being taken up by amoebocytes which forced their way out through
the skin, as in Echinodermata. The yellow cells and the nephridia
are then to be regarded as portions of the coelom in which the
power of storing up excreta is specially developed, and in this
limitation of this power to a special area we have the first type of
an excretory organ. A localized excretory organ requires some
VI.] LCMBEICU8. 99
means of bringing to it the prodnctg of katabolism of all portiotiB
of the body — since poisonous excreta are produced by all living
protopldsm— and this means is supplied in the earthworm by the
blood-system and the nmoebocytes.
The earthworm, although it lives in earth, has a clean, glistening
look, and this is partly due to the fact that the coeloraic fluid
is poured out from the doranJ pores (U, Fig. 44) aud keeps the
skin moist and lubricated. This fluid is also antiseptic in its
at.-tion and thus its presence prevents foreign organisms, Buch as
bacteria, which swarm in the mould in which the worm lives,
settling npon the skin and growing there. Numerous glandular
calls belonging to the ectoderm also jinur forth n secretion through
minute pores in the cuticle.
t. ri. nt. :v. Tba Urst, geuoud, third, and tuiirth aegmentB.
1. Tlie prostomium. 2. The wrebrni gBQKlia. 3, The oiroumornl oam-
miasnre. 4. The 6rsl veDtral gnuglitin. 6. Tlie mouth. 6. The
ptuuynx. 7. The donwl and ventral pair of cboetoe. 8. The tactile
DiirTeH lo tlie pcaKtomium. !!. The anterior, middle and ptiflterior
donftl uervea. 10. The auturiiit, middle and poaterior Tenlral neryes.
If WB cut Open an earthworm by a median dorsal incision aud
attentively examine the upper surface of the pharynx
we shall find at its anterior end, tucked awiiy between
it and the skin, two little whitish knobs lying close to
one another. These are the cerebral or supra-pharyngcal
The Ncrvoui
100 ANNELIDA. [CHAP.
ganglia (1, Fig. 41 ; 2, Fig. 43). At their outer ends the supra-
pharyngeal ganglia pass into two cords (3, Fig. 43). If we now
cut away the pharynx and remove the alimentary canal we can
trace these two cords towards the ventral middle line where they
unite and form the first sub-pharyngeal ganglion (4, Fig. 43) :
from this a long white cord — the ventral nerve-cord — ^runs back to
the extreme posterior end of the animal If we examine these
structures with a lens we shall be able to see that the supra-
pharyngeal ganglion gives off small nerves to the sensitive pro-
stomium, and that the ventral nerve-cord swells out between each
pair of septa, that is, in each segment, into a thicker portion which
gives off both dorsally and ventrally and on each side three pairs of
nerves to the surrounding parts. Each of these swellings is termed
a ganglion (6r. yayyXiov, a knot^) (4, Fig. 43).
The nervous system is made up of a number of cells termed
neurons. These, as proved by a study of the development are
ectoderm cells which have become pushed inwards from amongst
the others. Each neuron consists of a body with a comparatively
large nucleus difficult to stain. From the body in one direction is
given off a tuft of root-like processes (which some suppose to be
actual retractile pseudopodia) called receptive dendrites, by
means of which stimuli are received into the cell In the opposite
direction is given off a long straight process called an axon which
may branch once or twice, the branches being called collaterals.
The axon itself and its branches end finally in tufts of root-like
processes which are in close contact but apparently not in continuity
with either a muscle-fibre or the receptive dendrites of another
neuron and are called terminal dendrites.
Through the axon and its branches stimuli are transmitted to
other neurons and to the muscles.
A bundle of collateral branches of axons bending outwards to
convey stimuli to a group of muscles is known as a motor peri-
pheral nerve.
The nervous system of an earthworm thus consists of two
supra-pharyngeal ganglia situated in the third segment, a pair
of connecting cords called commissures which form a ring
round the pharynx, and a ventral cord which swells out into a
ganglion in every segment behind the third. The ring round
the mouth and the solid nature of the nervous system is common
^ TdYY><top was ased by the old medical writers to indicate the swelling or
'* knot" in a muscle caused by cramp.
^n^ LUMBBICtJS. iUl
to nearly all the Invertebrata, and in those which have a bilateral
aymmetry and are segmented there are Bupra-pharyiigeal ganglia
and a ventral nerve-cord bearing Begnientally repeated ganglia.
The earthworm baa no specialized aense-orgnn^, it haa neither
eyes to see, nor nose to smell, nor ears to hear with. Still,
although it in apparently deaf, it is not devoid of the power of
appreciating those stimuli which in us excite the sensation of sight
or smell. A strong light suddenly turned on the anterior end of
the body will cause the worm instantaneously to withdraw into its
burrow, and worms readily recognise the presence of such favourite
food as oniona and raw meat. Their sense of toui^h is well
developed and they are very sensitive to vibrations ; for instance,
a stamp of the foot on the ground wOl cause all those in a.
certain radius to disappear into their burrows. It is further
possible that earthworms |>oaaess other senses with which we are
totally unaoiuaiuted.
In each segment of the worm scattered here and there amongst
the etrtoderm cells are a, number of aense-cells. Ea^h of these has
a minute sense-hair which projects upwards througli a hole in the
cuticle, and by meiuiB of this hair stimuli of various kinds are
received by the outer world. The body of the cell is small — ^juat
large enough to contain the nucleus — and from the base proceeds
an axon which runs inwards and terminates inside the central
nerve-cord in a brush of tenninal dendrites in close contact with
tlie receptive dendrites of a neuron. In tliia way the neurons
receive impressions from the outside world. A bundle of the axons
of eenae-cells proceeding inwards is known as a sensory peripheral
nerve.
llie swelling called a ganglion is due to an aggregation of a
number of the bodies of neurons, so that in this region the nerve-
cord is broader than at other places, though everywhere some bodies
can be seen in transverse section of the cord.
The nervous system is one of the most important organs of the
body. It governs and controls the action of every tissue and cell.
It receives and registers impressions from the outside world and
co-ordinates the movements and activities of every jmrt of the body.
It further serves to put each organ and eatth part of each organ in
communication with all the others, and thus this vast accumulation
of tissues and cellm acts in an orderly way and towards a set
«Dd.
A transveree section of an earthworm, such as can be cut by a
microtome &om a specimen embedded io paratHn wax, is most
inatTucdve, in exhibiting the relation to one another of the various
tissues which make up the body of the earthworm. The outermost
boundary is cou3titut«d by the cuticle (I, Fig. -U), a hardened
secretion poured out by the ectoderm (2, Fig. 44), The ectoderm
. Onticle. 2. Eatodcrm or epidcimis. 3. Ciiculat mnncloa, 4. Doiaal
nerve. S. l/ODgitudinal muaeleB. B. Smuatic cpitbelium.
7. SplnDchnic epitbelium or ;elIow uellH. S. Eododena or epithalium
liDing tbe mteatiDe. 9. Caelnm. 10. Nvphiidium cat iu suctioD.
11. Dorukl pore. 12. Dorsal blood-vcsael lyiiit; along tbe typhloKile
or groove in Ibe wall at intestine. 13. Suh-intcBtinal blood- vessel.
U. Ventral nerve-cord. 15. Snb-neuml blood-vesHel. 16. Ventral nerve.
The dorsal aad veattul net
is composed of tall cylindrical celb, amongst which are isolated
"goblet cells" — that is, cells with a round body situated beneath
the level of the rest and with a long neck. The name is
suggested by their shape. In the body of these cells mucus is
secreted, which is poured forth through a hole in the cnticle
opposite the end of the cell-neck and helps to keep the ii^urface of I
the wonn moist.
Beneath the ectoderm is a thin and hardly perceptible layer of '
jelly fonning a bed on which the ectoderm cells rest. This founda-
tion in called the dermis, and is included inth the ectoderm in tha
ordinary conception of the "skiQ." In contradistinction to the
dermis the ectoderm is often spoken of as the epidermis {Gr.
ftri. Upon).
Beneath the dermis cornea a layer of circular musclea {3, Fig, 44),
and beneath these again a much thicker layer of longitudinal
muscles. The circular muscles consist of a few layers arranged to
form rings round the section. The longitudinal muscles are arranged
very regularly, and in the section they have the form of a series of
feathers (5, Pig. 44), since the individual fibres appear arranged
in oblique rows between which tongues of jelly extend, giving off
Ut«ral branches on which the fibres rest.
Both sete of muscles are composed of muscle-cells. These are
long fibre-like stnictures pointed at both ends. Most of the proto-
plasm is differentiated into fine fibrillae, which indicate (see p. 29)
contractile power. In the centre of the cell is a patch of un-
modified protoplasm with a nucleus. The whole cell may be
compared to a myo-epithelial cell of fiffdni in whtcli the epithelial
part has diminished in size and the tail increased. Nor is this a
fanciful comparison, for the study of development teacher us that
the cell is actually derived in tliis way from the originally »iimple
cells of the wall of the coelomic sac or in the case of the circular
muscles from an ectoderm cell.
T)ie movements of the earthworm can be more easily under-fl
stood when the arrangement of the muscles is known. Tho'l
longitudinal muscles serve to shorten tha body, and as the coelomiG
fluid, like water, is practically incompressible, the diameter of the
animal must be increased, and thus the chaetae can be driven into
the sides of tha burrow. On the other hand, the circular muscles
dimiuigli the diameter of the coelom, and the contained duid being
forced to move in a longitudinal direcrtion stretches the body out.
Tlia holes in the septa equalize the pressure in the various segment* i
by permitting the fluid to escape from one into the next.
Mention has been made above of "jelly" as forming a support^
for the ectoderm and the longitudinal muscles. It forms also the '
main part of the substance of the septa. In the worm and higher
animals generally jelly fulfilling this function is known as con-
104 ANNEUDA. [chap.
nective tissue. Its nature will be more fully dealt with in
the section relating to Arthropoda.
Within the longitudinal muscles there is a layer of cells called the
somatic peritoneum (6, Fig. 44) which forms the immediate wall
of the coelom. As the coelom in a segment of the worm has a ring-
shaped form there is an inner as well as an outer wall of the coelom ;
the former, since it closely invests the alimentaiy canal, is called the
visceral or splanchnic (Lat. viscus; Gr. onrXayx^w, entrail)
peritoneum (7, Fig. 44) — the latter the parietal or somatic
(Lat. paries, an outer wall; 6r. awfia^ body) peritoneum. The
parietal peritoneum is composed of flattened cells ; the visceral
peritoneum, on the other hand, consists of large cubical cells, the
yellow cells already described.
Beneath the visceral peritoneum there is a thin layer of circular
muscles, the splanchnic muscles derived from the peritoneal
layer and forming the agency by which the peristalsis («. p. 94) of
the gut is carried out.
The endoderm (8, Fig. 44) consists of a single layer of long
cylindrical cells bent in dorsally to form the typhlosole. Within
the limbs of this fold the splanchnic peritoneum is very much
thickened.
The dorsal blood-vessel can be seen embedded in the yellow
cells lying in the typhlosole (12, Fig. 44), whereas the ventral vessel
is attached by a membrane to the ventral side of the intestine.
This membrane is really a part of the partition which separated
the two coelomic sacs which originally existed in the segment.
The nerve-cord, apparently lying loosely in the coelom, is sur-
rounded by a layer of cells similar to those forming the somatic
peritoneum of which they once formed a part (14, Fig. 44). Hence
the coelom has extended in a ring-shaped manner round the nerve-
cord exactly as it has surrounded the gut. At the sides of and below
the nerve-cord may be seen sections of vessels, the sub-neural and
latero-neural vessels. The mass of the nerve-cord is made up of the
sections of axons, whilst the nuclei of neurons can be seen forming
a sheath on the outer border of the cord. The fibres are divided
into two bundles by a septum of connective tissue. On the dorsal
surface of the cord there are seen three apparent tubes, these are
sections of the so-called "giant" fibres — colossal axons which are
outgrowths of correspondingly large neurons.
Sections of chaeta-sacs and nephridia may be seen in favourable
sections.
It bas been mentioned above that it is one of the cbaracteristica
of the coelom that the cells lining it should produce
OrB»n«." "* the reproductive cells. This does not mean that
any cell lining the coelom can become an ovum or
a spermatozoon, but that at certain spotti the cells fonnbgpart
of the ooelomic wall turn into either female or male generative cells.
Id the earthworm the paired ovaries (6, Fig. 45) are situated in
the thirteenth segment and may be seen by cutting through the
iutestiike about the region of the gixzard and gradually lifting it up
from behind forwards ; when it is freed up to the twelfth segment
I'krt of the veeiuuU seiuiuiUis U uul u
t«ctto lUid the iaaec opening of the
Froiu Hatiohek and Cori.
'ay uu tlie Uii &iJe to expoae the
ras dslerena. Slii;htly iniLgnified.
1. Speruiatbeuoo. '2. Fannel-Hliaped iatemal opeaingB of the vas deferens,
S, Anterior testis. 4. Vmiicalae seminutes. 5. Ovary altavhpil lo
poateriar wall of aeptum Beporating xti and mi. S. Oviduct traversing
aeptam separating xni and iiv. 7. Vas deferene. S. UUnda in the
tkia. 9. Tentnil nerve. cord. 10. Suptum.
The BoDian Qgures iadioaCe the number of the segmenta.
the ovaries may be seen as minute white pear-shaped bodies lying
one on each aide of the nerve-cord. They are attached by their
broad end to the posterior wall of the septum separating segment
twelve from segment thirteen, and they nre formed by the accii-
malation and growth of some of the cells which cover this septum,
that is, from cells lining this portion of the coelom.
If one of the ovaries he removed and examined under a micro-
scope it will be seen that many of the i^ells composing it are large,
spherical and crowded with granule.^. The largest lie in the
narrow end of the ovary which waves about in the coelomic duid.
106 ANNELIDA. [CHAP.
These cells are the full-grown eggs or ova and when ripe they drop
off from the ovary into the coelom, but are probably at once taken
up by the wide funnel-shaped openings of the oviducts, one of
which is situated opposite each ovary. Like the nephridia, the two
oviducts pierce a septum, the one between the thirteenth and the
fourteenth segments. They are short tubes which open into the
coelom by the above-mentioned funnel-shaped opening in the thir-
teenth segment and to the exterior by a small pore just outside the
inner pair of setae on the fourteenth (6, Fig. 45). They bear on
their course a diverticulum or sac which is called the receptac-
ulum ovorum, in which the ova collect until the earthworm
is ready to make a cocoon to receive them.
The male reproductive cells are formed in the testes, of which
there are two pairs situated in a similar position to the ovaries but
in the tenth and eleventh segments (3, Fig. 45). They are in many
respects similar to the ovaries but are hand-shaped, the broad end
of the hand being attached and the fingers free. Their ducts which
convey away the spermatozoa are called the vasa deferentia(Lat.
vas, vessel; deferens, carrying away). They have similar funnel-
shaped openings to those of the oviducts and they traverse the
septum behind the segment in which these openings lie, but they
do not at once open to the exterior. The two ducts of each side
unite in the twelfth segment, and the common duct thus formed
runs back to open by a pore with swollen lips on the fifteenth seg-
ment, the one behind that on which the oviducts open (7, Fig. 45).
There is, however, one great difference between the male and
female organs. Whereas the ovaries lie freely in the body-cavity
and can be seen readily if the intestine be removed, each pair of
testes and the corresponding inner funnel-shaped openings of the
vasa deferentia are concealed by a certain sac or bag called the
vesicula seminalis, and it is only by cutting away the wall
of this sac that these structures come into view (4, Fig. 45).
Each vesicula seminalis is a flat, oblong bag extending backwards
from the front wall of the segment in which it lies and situated
beneath the alimentary canal. The angles of the front vesicula
seminalis are produced into two long pouches which project upwards
at the sides of the alimentary canal, and are often called lateral
vesiculae seminales, though they ought to be termed lateral horns of
the anterior vesicula seminalis. A similar projection is produced
from the hinder angles of the posterior vesicula seminalis, so that on
opening a worm three pairs of greyish white sacs are seen at the
VI.] LUMBRICUS. 107
sides of the gut. The study of the way in which the vesicula
seminalis is formed shows that the space it contains is really part
of the coelom which has become cut off from the rest \>y the out-
growth of folds frx>m the septa, so that, although at first sight the
testes seem to differ from the ovaries and to be exceptions to the
general rule that reproductive cells have their origin from the walls
of the coelomic cavity, a closer examination shows that this apparent
divergence is not a true one.
Every earthworm has grown up from an egg which has been
fertilized by a spermatozoon. As the earthworm is hermaphrodite,
that is to say, contains both male and female organs, it might be
thought that the spermatozoa of an individual would fertilize its
own ova, but this is not the case. Cross fertilization or the
fertilization of the ova of one individual by the spermatozoa of
another is the rule in Nature, and the earthworm is no exception
to the rule. The method by which the spermatozoa reach the ova
is not clear in all its details, but it is something like this. The
ceUs which are to form the spermatozoa break off from the testes
and whilst lying in the fluid contents of the vesicula seminalis
they divide and the products of the division or spermatozoa de-
velope each a long vibratile tail by whose aid they swim actively
about. Two earthworms then approach each other and the
spermatozoa pass down the funnel-shaped opening and vasa defe-
rentia of each and into the spermathecae of the other. The
earthworms then separate, each carrying away the spermatozoa of
the other.
The spermathecae in which the earthworm stores up the
spermatozoa received from another individual are pockets of the
skin (1, Fig. 45). They belong, strictly speaking, to the female
reproductive system. Seen from the interior of the animal, they
appear as four small white spherical bodies, lying one pair near the
hind end of segment nine, and the other pair near the hind end of
segment ten, and each pair opens by a very short neck or duct on
the grooves between segments nine and ten and ten and eleven, just
inside the outer pair of chaetae. It is through these ducts that
the spermatozoa from another worm enter.
Earthworms lay their eggs in cocoons, which at one time were
mistaken for the eggs themselves. These cocoons are usually
brown and horny and vary in size in different species of earthworm ;
some are about as large as rape seed, others almost equal in bulk to
a small grain of wheat. They are formed from the secretions of the
\^ ^csccsuupUL [chap.
lihKuiiMr ^tihlens cell^ fbund m tdbo clitellmn and at first have
;4 riag-likd shape. The aecretBona hardm when in contact with the
i^K 'Phe tiuimal b^^ins to wriggle out of the band, which at first
aU4i'roaudB it& body in the neighbonriiood of the thirty-eecond to the
tlurty-::iidveuth segment As the band passes over the openings of
th^ ovkducU in the fourteenth segment it carries awajwith it a
cvirtaiu uumber of oYa» and as it passes the orifices of the sperma-
UuKae between the eleventh and tenth and tenth and ninth
!H)^m^its, some of the sp^matozoa which have been received from
«Miother individual are squeezed out Besides ova and spermatozoa
tho oocoou contains a certain amount of a milky and nutritive fluid
in which these cells float ; this is probably supplied by certain other
glauda in the skin of the earthworm. At the moment the last
Hei^ment, that is, number one, is withdrawn, the anterior end of the
iHHHH>u contracts and closes, and as the posterior end of the band-
like ring passes over the head it also closes, so that the cocoon lies
in the earth as a closed vesicle containing eggs, spermatozoa and a
nutritive fluid. The spermatozoa fuse with the ova and firom the
fertilized ova, by division into a number of cells and by the
ditt'erentiation of the cells into muscle cells, epithelial cells,
iligestive cells, nerve cells, etc., a young earthworm is built up.
Before being hatched out of the cocoons the young embryos are
nourished by the milky nutritive fluid in which they float.
lu Great Britain there are several species of earthworm, which
are grouped into two genera, viz. Allolobophora, with
fiSVrm. fourteen species, which, with one exception, have the
prostomium not dove-tailed into the peristomium ;
and Lumbricus, with five species, in which the prostomium is com-
pletely dove-tailed into the peristomium. The above account has
been taken from the anatomy of L. Aerculeus, the largest of our
indigenous species, but with the exception of a few minor details
the account applies to most British earthworms.
Order I. Oligochaeta.
The sub-order to which earthworms belong, the Terricolae,
are for the most part inhabitants of the land, and occur widely
distributed over the Earth, being, as a rule, only absent firom
sandy and desert soils. Some of them are aquatic but not
many. On the other hand the allied sub-order the Limicolae
ave for the most part denizens of fresh water. A few Limicolae
VI.]
POLYCHAETA.
109
possess gUls or finger-like processes well supplied with blood-vessels
which tftke up oxygen from the surrounding water. Both sub-orders
contain numerous genera and families; together they form the order
Oligochaeta, which is characterised by being hermaphrodite, by
haying the reproductive organs few in number and definite in
position, by developing directly from the egg without the inter-
vention of any larval stage, and lastly by the absence of certain
structures which are very characteristic of the other great division
of the true worms or Ghaetopoda.
Order 11. PolychaetaN
The Polychaeta differ from the Oligo-
chaeta, as their name implies, by possessing a
large number of chaetae on each segment.
The sides of each segment are further as a
rule drawn out into hollow flaps or lobes called
parapodia, which bear the chaetae. Each
parapodium may be divided into a dorsal half,
the Notopodium, and a ventral half, the
Neuropodium (15 and 16, Fig. 47). Both
notopodium and neuropodium carry bunches of
chaetae, and each has as a rule one particu-
larly large chaeta, the aciculum, completely
concealed in a very deep chaeta-sac, which is
moved by muscles attached to its base and
serves as a kind of skeleton for the parapodium.
There is usually above the notopodium and
beneath the neuropodium a process called a
cirrus. The dorsal cirrus may be modified
into a gill, and both dorsal and ventral cirri
are absent in some cases.
The coelom is often divided into three
longitudinal compartments by two muscular
partitions (5, Fig. 47) which run from the dorso-
lateral line towi^s the median ventral line near
the nerve-cord. The septa which divide the
coelom in one segment from that in the next
are in many forms incomplete or absent.
As a rule Polychaets have a certain num-
ber of the anterior segments modified to form a head, which usually
Fio. 46. Nereis pel-
agicGf L. After
Oersted.
1 10 ANNELIDA. [CHAP.
wrriww teatftoles and organs for absorbing oxygen from the water,
ckUed braaohtae or gills. They are generally of separate sexes,
uul thtt e^gs develop into a larva nhich swims in the sea and
KrwluiJty uhaug«s and grows np into a worm. This gronp includw
N vury ttrvmt variety of forms, almost all of which are marine.
Wittt tuw uAcuptious they form burrows for themselves, which most
t'liiikilu. S. K|>IJ«tiiu». 3. CirenUr moaclra. 4. IiOii{[itadiDBl
iiiiiuilw. A. Obliijup mnM^lM tomuDg & partition. 6. Bommtio
Lsiii i4 •pllhrlium. 7. Gwloin. 8. SpUuehnia Ujw of peritonenm,
<) ritut; of iiiii-iluiv. 10. Doml Uood-ve^Ml. 11. Toitnd blood-
\iu«'l- Xi- Yfittnl iwrve-coKL 13. Nepbridiom oat in aeotioii.
11. K^\m. 1>^' KotopodiuiD. 16. N«an>podiiim. IT. Donal
ciirtw. ItL Vnitnl cimis. 19. CbMtae. 30. Aoionliun with
iif ihciu (K<iMuii)»Hlly dosert in order to seek prey and to discharge
tliu i'u]iroiliii-iivti ivUs. Some however never leave the burrows,
ttliii^ti ill lliin cuHP oFt«D take the form of tubes composed of a
nutiluUxU iif ihn octodorm.
VI]
HIBUDINEA.
Older III. Hlmdlnea.
BeaideB the Oligochaata and Polychaeta the order Hirudinea,
the members of which are popularly known as leeches, is included
amongst the Chaetopodo. They were for some time regarded as a
distinct order of Annelida, since the great majority of species possess
no chaetae and have other peculiari-
ties ; but the recent discovery of
species possessing chaetae, and the
close resemblance between the develop-
ment of all Hirudiaea and that of
Oligocbaeta, renders it evident that
t^ey are true Cbaetopoda and that tlie
absence of chaetae is a secondary
characteristic.
There is little doubt that the
LcHhH. Hirudinea are closely al-
Extcrnai lied to the Oligochaeta ;
indeed there are certain
families which it is not easy to assign
definitely to either group ; but the
more ^ical forms are easily distin-
guished. Externally leeches may be
recognized by the possession of a sucker
at each end of the body, the anterior
one being formed by the mouth, whilst
the posterior one is a special organ.
By alternately attaching and releasing
these suckers and bending the body
the animal crawls along.
With the exception of BranckeU
lioa, which bears tufted gills, the bodies
of leeches are without external pro-
cesses. There are no parapodia, as in
the Polychaeta, and no branchiae or
tentaclea, and only one genus of the
family has any chaetae. The body is
segmented, and recently it has been
shown that the number of segments is always thirty-three. Some
however of the segments are fused together ; thus for example the
Fio. 46. Hirado medieinalU,
ftbout LCe Bize.
1. Mouth. 3. Posterior
Bucker. 8. SeoaOTy papillae
on the antetior aanulus ot
each Hegment. The remain-
iag four annuli whioh mtJcs
up each tine Begmeut are in-
dicated b; the maikingi on
the doiBol Burlooe.
112 ANNELIDA, [CHAP.
posterior sucker contains traces of six or seven true segments. The
best test of the number is to count the ganglia on the ventral nerve-
cord. But even this is not decisive, because although there are
twenty-one free ganglia in the centre of the body a certain number,
some say five and some six, are fused into the sub- pharyngeal
ganglion, and a certain number, some say seven and some say six,
coalesce to form the ganglion of the posterior sucker. Whichever
view is taken the total number of segments is thirty-three.
The body of the leech is ringed or divided into a number of
annuli. These do not, however, represent the segments, but a
number, varying in the different genera, make up a segment. In
HirudOf the medicinal leech, there are five annuli to a true
segment; in Clepstne, a common fresh- water leech, the number is
three. The real segmentation is, however, to some extent indicated
by markings on the skin.
The animal is covered like the earthworm by a thin cuticle
secreted by the outermost cells, and the ectoderm contains numerous
goblet cells which are especially well-developed over the segments
abutting on the generative orifices. Here they form a clitellum,
and the secretion the cells pour out forms a cocoon in which the
eggs are laid.
The nervous system of a leech does not differ in essentials from
that of the earthworm, but the nephridia, of which
OrglfcM?** there are in Hirudo seventeen pairs, are peculiar.
They are no doubt a modified form of the same
organ as the nephridium of the earthworm, and they consist of
coiled cellular tubes. The outer end communicates with the exterior
through a muscular vesicle. The inner end, or so-called testis lobe,
lies near the testis in the genital segments. The whole is traversed
by a ramifying network of chambers opening by minute pores on
the testis lobe.
The other systems of organs are still more unlike what has been
described in the case of the earthworm and deserve a short account.
Leeches live by sucking the blood or juices of other animab,
usually of Vertebrates. They are divided into two large groups —
(a) the Rhynchobdellidae, which pierce the tissues of their hosts
by means of a fine protrusible stomodaeum, the so-called proboscis,
and {b) the Gnathobdellidae, which bite their prey by means of
homy jaws. The medicinal leech is one that bites, and the tri-
radiate little scar which its three teeth make in the skin was well-
known to our forefathers in the times of bleeding and cupping.
▼l] hirudinea. 113
The three teeth, which are notched like a saw, are really only
thickenings of the cuticle borne by the wall of the pharynx, which
contains many unicellular glands whose secretion prevents blood
from coagulating. Thus the leech when fixed on to its victim by
the oral sucker readily obtains a full meaL
From the pharynx a short narrow tube, the oesophagus, leads
into an enormous dilatation, the crop. This extends to the four-
teenth s^ment and gives o£f on each side a series of eleven pouches
or caeca (Lat eaea^n, blind) which increase in size from before
backward. The posterior caeca are very large and reach back to
the level of the anus, lying one on each side of the intestine. The
leech has the habits of a boa-constrictor. It makes a hearty meal,
absorbing as much as three times its own weight of blood, and the
blood it absorbs is stored up for many months in this enormous
crop. It slowly digests the food in a small globular stomach
situated just behind where the posterior caeca leave the crop. The
stomach opens into a short intestine which ends in the anus, a
minute pore situated dorsally between the posterior sucker and the
body (Fig. 49).
In one genus at least, Acanthobd^lla, the coelomic cavity is
almost as well-developed as in an earthworm, and
is divided up by septa as in that animal. In other
leeches the cavity tends to disappear, becoming in fact filled up
by a great growth of tissue, and thus reduced to a few narrow
channels. In many leeches it contains a fluid closely resembling
the true blood, so that unless very careful microscopic examination
be made these channels may be mistaken for true blood-vessels.
TBe capsules in which the ovaries and testes lie are also parts of
the coelom.
The medicinal leech, owing to a great growth of this above-
mentioned tissue, is almost without a coelomic cavity. When the
body is opened a narrow vessel full of a red fluid is seen running
along the middle dorsal line above the alimentary canaL This is
the dorsal sinus, a remnant of the true coelomic cavity; a similar
sinus runs along the ventral surface underneath the alimentary
canal, which is called the ventral sinus. It communicates with
the dorsal sinus by lateral channels which run between the intestine
and the posterior caeca of the crop. It surrounds the ventral nerve-
cord, which thus seems to float in blood but really lies in the red
coelomic fluid, and it gives off lateral sinuses which surround
the inner openings of the nephridia. The true blood-vessels
& AIL 8
\ \ 4 ASXEUDA. [CHAP.
vvM^^rtf * xyoMl niNMiif: iin Mdk side of the body and con*
uvsimA ifu^tMiKt h^ vn»»T9r» fanuiche« which ran from side to
»le Mow tlie Tentnl Buns. The
Umml nnels (dither anpi4y capillaries
to the nephridia. alimentary canal,
KpiwlactiTe organs, ete., and a very
extensive system to the skin where the
haemoglobin of the blood takes np
oxygen. Except in BranclteUion, which
has special gills, the reepiiation of
leeches is carried on by the skin.
Leeches are, like the earthworm,
Kcproduc- hennaphiodite, but their
"""■ reproductive o^ans differ
in some respects from those of that
animal.
In Lumbricua the testes are re-
peated in two segments only, but in
Hlrudo there are usually nine pairs of
testfis. The cavities of both the testis
and of the ovary are to be regarded as
part of the original coelom ; in strictness
the testes probably correspond to the
vesiculae seminales in an earthworm,
which are part of the coelom, and
enclose the true testis and the sperm-
fiiniiel. Each testicular sac produces
spermatozoa on one side and on the
other side is ciliated. The ciliated
tract is the sperm-funnel and leads into
a short transverse duct which passes
into a lon^tudinal canal termed the
vas deferens, there being one such
canal on each side of the body. At its
II. 41). View of the internal orgnna ai Hirudo medidnalu. On the left side
thu alimentary canal ia shown, but the right hall or this organ hu been
removed to show the eioretor; and reproductive organs.
Head with e;e spota. 2. Mneoolar pharynx. 3. lat diverticulum o(
the erop. i. 11th diverticulum of the crop. S. Stomach.
(1. Itectum. 7. Auub. 6. Cerebral ganglia. 9. Ventral nerve-
curd. 10. Nephridium. 11, Lateral blood-veasel. 12. Teitie.
18. Vaa deferens. 14, Prostate glaud, IS. Penis, 16. Ovary.
17. Uterui— a dilatation formed bj the conjoined oviducts.
yi.] HIRUDINEA. 116
imterior end each vas deferens passes into a convolated mass of
tabes — the so-called epididymis — whose walls secrete a substance
which binds the spermatozoa together into packets called sperma-
tophores. It is to be remembered that the names epididymis,
prostate, etc., are given firom fanciful resemblances to parts in the
anatomy of man by no means homologous with the organs bearing
the same name in the leech. From each epididymis a short duct
passes towards the middle line, and these two ducts fuse and enter
the base of the penis, which is protruded from the segment which
contains the sixth distinct post-oral ganglion.
The penis is simply the muscular end of the conjoined male
ducts or yasa deferentia; it is the organ by which the spermatophore
is deposited in the body of another leech. The spermatozoa in
Ctepsine seem to penetrate the skin at any point and make their way
to the ovaries, where they fertilize the eggs. In other species the
spermatozoa enter in the usual way by the female genital pore.
As in the earthworm, there is but one pair of ovaries. These
are minute filamentous bodies each enclosed in a small coelomic sac.
From each sac a short oviduct proceeds and uniting with its fellow
forms a twisted tube surrounded by many glands. This finally opens
by a median pore on the segment behind the one bearing the male
opening.
Thus in leeches, unlike the condition in the earthworm, the
genital pores are single and median. The medicinal leech lays
its eggs in a cocoon and buries them in holes in the banks of the
ponds it inhabits. Clepsine, one of the Rhynchobdellidae which
is very common in Britain, attaches its eggs to some stone or water-
plant, or in some species carries them about on its ventral surface.
It has developed a quite maternal habit of brooding over the eggs,
and when the young are hatched it carries them about and they
feed on some secretion from its body.
Of the Gnathobdellidae, Hirudo medidnalis is found in Great
Britain, but is commoner in some parts of the Con-
tinent. It is cultivated in some districts, but the
demand for it is decreasing with ihe disappearance of blood-
letting. It becomes mature in three years. In the young stages
it sucks the juices of insects. Another common but small
Gnathobdellid leech is the brownish Nephelis, which frequents our
ponds and pools ; it feeds on snails and planarians. A large species
of the same genus is common in the shallows of the St Lawrence, in
Canada. In waimer climates many leeches take to living on land,
8—2
116 ANNELIDA. [CHAP.
and are a source of great annoyance to travellers whose blood
they suck. Even water-forms do much damage unless carefully
guarded against. Certain species make their way with drinking
water into the throat and back of the mouth, on which they fasten,
and so cause great suffering both to man and cattle.
Phylum ANNELIDA.
This phylum includes segmented animals with, as a rule, a well-
developed coelom and metamerically repeated nephridia. The
cuticle is always thin and flexible, and the nervous system consists
of a pair of supra-oesophageal ganglia, a nerve collar and a ventral
nerve-cord which has a ganglionic swelling in each segment.
Class I. Chaetopoda.
Annelida which possess bristles (chaetae) embedded in pits in
the skin and serving as organs of locomotion, or which are believed
to have once possessed such organs and to have lost them.
Order 1. Oligochaeta.
Chaetopoda which have the chaetae arranged singly or in
pairs and which have neither parapodia nor tentacles : the
generative organs are definitely localized and the sexes are
united in the same individual : development is practically
entirely embryonic : the group inhabits fresh water or damp
earth.
Ex. Lumbrictis, Alhlobopkora,
Order 2. Polychaeta.
Chaetopoda which have the chaetae arranged in bundles of
some size, almost always borne on conspicuous lateral out-
growths of the body termed parapodia : the prostomium has,
as a rule, tactile organs, known as tentacles and palps : there
are no localized generative organs, ova and spermatozoa being
developed from wide stretches of the coelomic wall ; the
sexes are separate : in the development a well-marked larval
stage occurs : with few exceptions the group is marine.
Ex. Nereis,
VI.] HIRUDINEA. 117
Order 3. Hiradinea.
Chaetopoda in which chaetae and parapodia are absent and
which move by means of a muscular sucker developed on the
under surface of the posterior segments : there are no tentacles
and the mouth acts as an anterior sucker: the coelom is
reduced to capsules surrounding the genital cells and to a few
narrow channels : the animals are hermaphrodite, and the
genital pores single and median : the members of this order
live on the juices of other animals, and there are both fresh
water and marine species : development is entirely embryonic.
Ex. Hirudo, Nepkelis, Clepsine.
118
CHAPTER VIL
Phtluh Abthbofoda«
One of the most striking features of the AnnelidA is the hxt
that they are segmented, that is to say their body is divided into a
number of similar parts placed one behind the other like coaches in
a train, each of which to a greater or less extent resembles the part
in firont of it The likeness of the parts to one another yaries.
In some worms we might easily detect from which region of the
body any given segment was taken. In the Earthworm, except
in the region of the clitellum, there is little external difference ;
nevertheless if we consider the internal organs we can dis-
tinguish any of the first twenty segments from any other behind
these and can easily arrange them in their proper order ; but no
matter how long the worm is, all the segments behind the twentieth
resemble one another so closely that it is impossible to assign any
to their right place, except the last of all (v. p. 89).
The animals included in the group of the Arthropoda are
segmented like the Annelida, but with few exceptions
^ the number of segments is small and does not exceed
twenty. The segments have also become more highly differentiated
from one another in consequence of being modified to perform
various functions, and they are more frequently fused together than
is the case in the Annelids.
The Arthropoda have jointed outgrowths called limbs or ap-
pendages. Tliese are always arranged in pairs, and at least one
pair is modified so as to assist in holding and crushing the food*
This character of possessing jointed limbs is what is indicated by
the name Arthropoda (Gr. Sp^pov joint ; toxs foot).
The Arthropoda may be dividoti into three classes : —
L The Crustacea, which includes all the Crabs, Lobsters^
.^^^^^ Cray-fish, Barnacles, Wood-lice, etc, besides oonntless
small forms s\ich as the Water-flea, Cydops, and
many others which inhabit both salt and fi>dsh water.
ARTHROPODA.
II. The A3«TKNNATA, which lEclude all Arthropoda posseBaing
one pair of feelers — antennae — and breathing by means of air tubes
or tracheae. This group is divided into three sub-classes, viz. :
The Prototracheata, a group containing the genus
Peripatus. an animal not found in Europe or in North America,
but which must be mentioned because it seems to be a survival from
an earlier age and because its structure has given us a clue to
mach that was obscure in the anatomy of Arthropods ; it is in
lact in many respects intermediate between tbe Annelids and the
air-breathing Arthropoda.
B- The Myriapoda or Centipedes, the commonest British
examples of nhich are the chestnut-coloured centipede LithMiis
Jorficatut and the block "wire-worm"' Iidua terreslris.
C. The Insecta, the largest group in the Animal Kingdom.
It contains about 250,000 named species, and includes all those
creatures such as Beetles, Flies, Dragon-flies, May-flies, Moths, Beee,
Anla, Wasjis, eh;., which we are accustomed to call insects.
III. The Aiuoui^iDA, includiug the Spiders, Harvestmen,
Mitm and certain larger forms such ag the Scorpion, and Limulus,
the King-crab.
If we go into an old garden and turn over a stone or look
between the bark and the trunk of a decaying tree or examine the
leaves, we may find representatives of each of the four larger classes
mentioned above. The Crustacea may be represented by a Wood-
louse (Fig. 79), the Myriapoda by a Centipede (Figs, 51 and 84),
the Insecta by a Beetle (Fig. 92), and the Arachnida by a Spider
(Fig 53). If we compare these creatures one with another we shall
see that they resemble each other in certain fundamental particulars.
I'o begin with they are all clothed in a hard coating consisting
largely of the homy substance called obitin which
does not form a simple chamber or house in which
the body of the animal lies as a snail lies in its shell, but which is
moulded accurately over all the body and even tucked into all the
openings ao that it forma an exact cast of the soft parts underneath.
Tliis covering is to be regarded as an exaggeration of the cutiole found
in Annelida, and it is called an Exoskeleton in order to dis-
tdoguish it from the internal framework of hard parts found in the
Vertebmta.
:o be confused with the larva of a beetle, Elattr liaeatue, wMch
irini-irorm " Itf the BritiBh agrianUurirt.
k
Vn.] ECDYSIS. ^ 121
Fio. 50.
A. The anterior portion of the body of a Dragon-fly, Ae$ehna cyanea, freed
from the larval ahell. B. The tail being extricated. 0. The whole
body extricated. J>, The perfect insect, ^e wings having acquired
their fall dimensions, resting to dry itself preparatory to the wings being
horizontally extended.
Were this hard exoskeleton of the same consistency all over the
body it would be impossible for the animal to bend its body or
to move at all, but at certain spots, as may be well seen between
the s^fments of a Centipede or between the members of a Beetle's
legs, the exoskeleton has remained soft like the leather joints in a
suit of mail-armour, and thus a certain amount of flexibility is
given to the whole body ; for instance the Armadillo wood-louse
and the Pill-millepede can roll themselves up into spherical balls.
Not only is a hard exoskeleton a hindrance to unlimited
movement but it also interferes with growth. It is
impossible to increase in size when shut up in a hard
unyielding case. Now growth is one of the common characters
of all animals, and the way the obstacle presented by the exoskeleton
of Arthropods to growth is overcome is as follows. At certain
stated times the outer skin or ectoderm of the animal loosens itself
from the inside of the cuticle or investment, which splits or cracks,
usually along the middle of the back ; through the opening thus
formed the body of the animal begins to appear, and gradually
withdrawing each limb from its case it works its way out. The
exoskeleton thus c&st off forms a most accurate mould of tha
animal which has left it, and even includes those portions which are
folded in at the mouth and anus and other openings of the body.
A dragon-fly emerging and freeing itself from its cast skin is shown
in Figure 50.
The skin of the animal when it steps out of its old casing
is quite soft, and it remains so for a varying time, a few hours in
the case of some insects, one to three days in a Cray-fish. During
this period the animal grows. After a longer or shorter time
during which the body remains soft and capable of extension the
secretions of the skin commence to harden, and very soon the
animal is again enveloped in a hard case which rapidly assumes the
colour and appearance appropriate to the species in question.
This moulting of the skin in the Arthropoda is termed the
ecdysis. It takes place at more or less regular times in each
species, in the Cray-fish three or four times or even oftener during
Hi
AETHEOPODA.
[CHiP.
tie first year, the period of most active growth, later but once
uiDUAlly, usually about Midsummer ; the Cockroach moults three
times during the first j'ear, after which the moulta are Annual, but
it does not become adult till after the seventh ecdysta, when it ia
four years old.
If we further examine onr wood-loDSS,
DiviiioDi centipede. beetle, and spider,
of B«i/. ^g gj^ notice at once that
they are all. like the Annelids, bilaterally
symmetrical ; and it may as well be stated
at once that with few exceptions this ia
true of the internal organs as well aa of
the exoskeleton. Another feature oap-
mon to them all b that they posaeai
jointed limbs or appendages. These may
occur in all the segments, as in the wood-
louse and centipede, or the limbs may be
reduced in number and confined to defi-
nite regions of the body, as in the beetle
and spider, but they always exi^ and an
always jointed.
In the body of the centipede we ean
recognise but two regions (Fig. 51), ft
head and a triiuk ; the trunk consisting
of a number of segments, the head appa-
rently of a ningle rounded one whose
really composite nature is shown by the
fact that it carries not one but several
pairs of a])pendagea.
The same may be said of the wood-
loHse (Fig. 79), though here the trunk is
divisible info two parts by the character
of the appendages. The anterior part or
thoras bears walking legs, the posterior
part or abdomen plate-like appendages
which act as respiratory organs. In
neither of these creatures nor in the spider is there any constriction
between the head and the trunk, thai is to say there is no neck.
In the beetle however there is a well-marked neck separating the
head from the rest of the body. The three following segments in
the beetle are again separated from those which come after and
Vm. SL A Centipede, Li-
thobiui fiiTficalui. Dotial
upeot K 13.
1. Aiiteiin>«. 9. Poison
cIbwi, 5tb ptir of append-
sgira. i. Firit paii of
iraUiing Ug«.
VII.] DIVISIONS OF BODY. 123
fonn what ia called the thorax. This part bears the three pairs
of walking limbs and the two pairs of wings. The hindermost
segments, often ten in number in insects, constitute the ahdomen ;
this part of the body ia devoid of jointed limbs, though doubtless
the ancestors of insects once possessed them on all the segments.
Fia. 62. A Male Gookoli&ler, MOohnlha vvlgaHi, Men from kboTe mA Oigh&j
enUcged. After Togt uid Tung.
1. Head, atretchftd forwud. 2. Prothorax. S. Howthom.
4. Uetatbomi. 6. Abdomen. 6. Anterior viDg (eWtron) of rigbt
aide, tamed fomrd. 7. Posterior wing of right side, eipsnded.
B. Uaiillu; palps. 9. Femnr of tbiid right leg. 10. Tibia of third
right lag. 11. Tanas of third r^;ht leg.
In the Insecta the abdomen may be constricted off from the
thorax aa it is in wasps (Fig. 95), or there may be no constrictioo.
If WQ now turn to the spider we shall see that the division of the
body into regions has gone along different lines, and we can
recognise only two principal parts, a so-called cephalo-thorax
or prosoma to which all the appendages are attached, and a
stalked abdomen or fused meso- and meta-soma behind which
is devoid of obvious limbs, though certain little kuobs at its hinder
end, from the summit of which are spun out the silken threads
used in making the web, have been shown to be rudimentary limbs.
The abdomen has lost all trace of external segmentation. In the
harrestmen— Phalangids — long-legged creatures resembling spiders
and found only during the summer months, the constriction between
the cephalo- thorax and abdomen is absent, but the latter is distinctly
divided into segments (Fig. 103).
Thus in the Arthropods the body is divided into segments, and
these s^ments are not all equal and alike, but they have become
variously modified and some of them have fused together, as in the
124 ABTHHOFODA. [CHAP.
head of inBectK. and the abdomen of apiders, so that certun r^ODs
of the body may be distinguished, and this is one of the moBt
ohaiacteristic features of the group.
In all Arthropoda certain of the appendages have lost tha
function of locomotion and are bent round and
brought into connexion with the month. These
moatii or oral appendages assist in catching and holding the food,
and to some extent in biting and tearing it into small pieces.
With the exception of the Arachnida, in which the anangement
Via. fiS. The Ouden Spidt
is somewhat different, and of Peripatua, which has only one pair of
jaw-limbs, the first pair of oral appendages is termed the mandible,
the second is the first maxilla and the third the second maxilla;
the last-named however in the Myriapoda retains the appearance of
a walking leg, although too short to be used for walking. Un the
odter hand in Crustacea a varying number of the appendages im-
mediately encceeding the second maxilla are often turned forward
and assist in the feeding. When this is the case they are termed
maxillipedes (Figs. M and 56).
vn.]
AFPENDAGEa
125
The modification which all these appendages nndergo is similar
in kind. The first stages of it are seen in the Arachnida. Here
the first pair of appendages is always a pair of little claws placed
in front of the mouth, the last joint shutting down on the next
diyision of the limb like a knife-blade
on the handle. After this pair come
others, more leg-like, of which some-
times all and in any case one pair have
inwardly directed projections on their
lowest joints termed gnathobases,
so that when the limbs are brought
together they act like a pair of nut-
crackers (Fig. 55). Or to take another
example, as we pass from the segment
of the Gray-fish or of a Gammarus
which bears the great claws forwards
through the maxillae to the mandible
we find the outer parts of the limb
dwindling in size, and the basal pro-
jection growing bigger (Figs. 54 and
56). In the mandible only a minute
rudiment of the other joints remains,
and is called the palp. In the mandible
of the insect even this has disap-
peared. Limbs which have undergone
these characteristic changes are called
gnathites (6r. yva^os, a jaw).
If we cut open the body of an
Earthworm, a Starfish or
Cavitiea of
Bpdy. ^ Vertebrate, we lay open
a chamber in which the alimentary
Fio. 54. The month append-
ages of Gammarus negUctus,
From Lcackart and Nitsche,
after G. 0. Sars.
1. The left mandible.
2. Its palp.
8. Ist maxilla of left side.
4. 2nd maxilla of left side.
5. Maxillipede of each side to-
gether forming an under lip.
canal and many other organs appar-
ently lie. This chamber is the coelom
or primary body cavity, which has no connexion with the blood
system, though amoebocytes float in the fluid it contains. If we
cut open the body of an Arthropod or of a Mollusc we also open
up a chamber which may be spacious, as in an Insect or a Snail, or
which may be much reduced and filled up by the various organs of
the body and by muscles, as in a Cray-fish or a Mussel. This
cavity however, as development shows, is not similar in its nature to
the coelom of an Earthworm or a Vertebrate, and it further difiers
126
ARTHROPODA.
[chap.
in that it contains blood and is continuous with the cavity of the
heart and Urge blood-vessels. A special name has been given to
this cavity and it is termed the Haemocoel (blood-cavity). The
presence of this secondary body cavity or Haemocoel instead of a
Coolom introduces at once a peculiarity in the physiology of the
circulation of the Arthropoda. Instead of the oxygen-bearing and
food-carrying blood being conveyed all over the body in minute
capillaries which ramify in every part of every tissue, in the animals
in question the tissues are floating in and bathed by the blood,
which surrounds the organs on all sides and is kept in action by
the contraction of a muscular tube — the heart — which opens freely
into the body-cavity or Haemocoel.
A true coelomic cavity
(as is proved bot^ by its
origin and its relation to
the excretory and repro-
ductive organs) is however
found in Arthropods in the
cavities of the reproductive
organs (Fig. 67) and in
certain vesicles connected
wit^ the inner ends of
some of the excretory
organs, such as are found
in the coxal glands of
Arachnids. It is however
obviously much reduced
and takes a smaller part
in the economy of these
animals than it does for instance in the Annelida or Echinodermata.
The skin of an Arthropod like that of an Earthworm includes
Skin and Cm. R^t Only the ectoderm, but a firm support for the
MctivtTiMUft. g|^^^ caUed the dermic The dermis in this case is
(onued of well-developed connective tissue and this tissue also
form^ an investment for every organ in the body, so that,as Huxley
remarks, if all the organs were dissolved away there woold remain
a ci>mpIote ca^l of them in connective tissue. The same statement
i;» true of MoUusca and Vertebrata : it is therefbie important to
obtain a clear idea what connective tissue is.
lt» gTv>undwv>rk is a jeUv-like secretion interrening between
eclKKlcrm and me^xietm> or meiscdeim and endoderm> and thereibre
Fio. 55. Pedipalp of Tegenaria ffuyomi, the
laxge hoase-spider.
1. Coxa. 9. MaziUa, tbe gnathobnse.
S. TroehADter. 4. Femur. 5. PuteUm.
e. Tibi*. 7. TATsas. 8. Palpal organ.
vil]
CONNECTIVE TISSUE.
127
to some extent oomparable with the BtrnctureleBS lamella of Hydra
ox the jelly of a Mednea. Into this substance cells are budded
from the adjacent layers, chiefly from the meeodenn. These cells
add to the secretion, in which fibres soon make their appearance,
crossing each other at various angles. These fibres are to be
looked on as more or less solid precipitates. The cells are found
often flattened against them and connected with neighbouring cells
Fi«. H. Left nonth Rppandagei of Attaeut Jluviatilii, alightl; mRgnified. The
other appendage* are shown in Fig. ttO.
I. Ifandibl*. n. Knt maxlUa. in. Beoond maiiUa (Scaphognathite).
IT. Fint masillipad. V. Second maiilliped. VI. Third maiillip^.
at. Bndopodile. ix. Biopodile. ep. Epipodite. &£ tt <y in in
form a woop Ua dmilatiag vaUr over the ((illA.
by delicate protoplasmic threads. The connective tissue round
the ends of a muscle is modified to form tendon. Here the
fibres aU pursue a parallel course and great tensile strength is
the remit
Oburration <A derelopment shows that connective tissue,
, and blood-vessels all generally arise firom the same
i!*J;
ABTHBOFODA.
[chap.
^^JuiiiMit in tba embryo, which may be compared to the jelly of
V'tMltttttonta. Blood is s portioD of it where the jelly ia fluid,
ttt* fibres tue not developed ud ihe amoebocytes remain molnle.
la. oooneotive tissue the jelly becomes more solid, fibrea ue de-
veloped and the amoebocjrtea become stationary, being converted
isto the ao-oalled connective-tisane corpuscles. It is interesting to
oote that under the abnormal circumstances of a wound the blood
of many animals can develop fibres ; this properly causes what is
known as clotting.
Fio. S7. JirJlui aquatiew.
Mnls viewed from above.
From Lauakul and NitGclie,
after (i. 0. Sin,
1. Anterior antenoBe. S. Fob-
terior aQteimBe. 3^9. Tho-
Taoic limbs. 10. The last
pair o[ abdominal limbs.
11. Tesles withtbeir effer-
•^Btcni li Bbowu black.
The muscular system of the Arthropoda is highly modified as
ThcMuicuiir Compared with the primitive arrangement found in
Byaum. jj^^ Annelida, Instead of a continuous sheath of
muscle there are special bundles of muscular fibres for the purpose
til] MDSCnLAB AND NEBV0TJ8 SYSTEMS. '^V
of moving the Tarioiw hard parte on one another. Each joint of
each limb, for iiutance, ie provided with a piur of muscles which
move it on the next joint. One of these ie called the flexor, or
bmder, and the other the extensor, or straightenei. Heie aa in
Annelida the mueoles are derived irom ^
epithelial celle, bat all trace of this
origin is lost in the adult In the
moscle-cell in many cases the QDclens
has divided, giving tise to several nuclei
which are eurtounded by unmodified
protoplasm. All the reet of the proto-
pksm is converted into fibrillae which
consist of alternately dark and light
Btretches. Such muscles are said to be
striped, and they have the power of
contracting with much greater rapidity
than mnecles of the type found in
Annelida. Muscles of the latter kind
ate called smooth mosclee, and in
Artfaropoda exist in the wall of the
gnt and some other places.
The nervous system of the Arthro-
Ncrtoo* poda is built upon the
»>•"'»■ same plan as that of the
Annelids. It consists in its least
modified form of a pair of closely ap-
proximated supra-oesopbageal ganglia
forming a brain situated in front of the
mouth. Id the head iu Insects, and in
tlie anterior part of the body in those
Arthropods which have no distinct
head. This brain supplies nerves to
certain sense organs, and gives off two
atout corde, one of which passes to the
left, and the other to the right of the oesophagus. These para-
o€eophageal (Gr. vapa, alongside) cords unite together behind the
oeaophague, and where they unite they form a pair of sub-oesophageal
ganglia which send nerves to some or all of the mouth appendages
(Figs. 57 and 58). Behind this comes a chain of ganglia, normally
one pair for each eegment, which supply nerves to the organs and
^ipendages of the segment in which they lie; each pair being
n. AK. 9
FiQ. 68. View of nwrom sjb-
tern of the Cockohftfer, Mtlo-
lontha wlgaTti, After Togt
aiid fang.
1. CerebiBl ganglioo.
2. fiub-oesophageal ganglion.
3. IsC thoiooio ganglion.
4. Slid tboiacio ganglion.
5. 3rd thoracio ganglion.
6. Faa«d abdominal ganglia.
7. Nerves to antennae.
8. Optic HE rvea. 9. Origin
of sympathetic nerves.
10. Abdominal nerves, a pair (o
each segment, which apht
into an anterior and pos-
terior branch.
130 ARTHROPODA, [CHAP.
connected with their successor by a double nerve-coid. These
ganglia do not always remain distinct but show a tendency to fuse
together. Thus in the Cray-fish the supra-oesophageal ganglion is
shown by its development to be formed by the fusion of seyeral
pairs of ganglia ; and the mandibles, both maxillae and the 1st and
2nd maxillipedes are supplied from a single ganglionic mass, the
sub-oesophageal ganglion, which is the result of the fusion of five
primitive ganglia; again in some Flies and in Spiders all the
ganglia behind the mouth have fused into one large nervous mass
situated in the thorax. This fusion takes place to a less extent in
some beetles; for instance in the Cockchafer, Melolantha wUgaris,
the thoracic ganglia remain distinct, but the abdominal have fused
into one mass which has been drawn up into the thorax (6, Fig. 58).
The Crustacea are normally provided with two pairs of long
feelers or antennae (though occasionally, as in the case of the Wood-
louse, one pair may be entirely lost) and the Insects and Centipedes
have a single pair, very conspicuous in some Butterflies and Beetles.
These are organs of touch and frequently of smell ; and in some
cases, such as the Lobster, they also act as hearing organs. They
are supplied with nerves from the brain. No such antennae exist
in the Spiders or Mites, and this serves at once to distinguish the
Arachnids from the other two classes.
The eyes of Arthropoda are peculiarly modified areas of the
ectoderm. Over a certain area some of the ecto-
^*' derm ceils become modified into visual sense-cells.
In these there is a gelatinous rod developed from the outer end
of the cell, and situated on the one side of it (Fig. 59 a) ; whilst
from the base of the cell a nerve-fibre is developed. Usually
several visual cells are pressed together in such a way that their
rods cohere, and in this way a fluted spindle-shaped rod termed the
rhabdome is built up (6, Fig. 59 A and e). This rod, like all such
structures formed in visual cells, is cross-striped or in other words
consists of layers of difiierent densities. Other cells of the visual area
remain as supporting cells, being longer than the surrounding ecto-
derm cells but otherwise unmodified. Pigmeut — universally present
in visual organs — ^is secreted either by these cells (4, Fig. 59 a)
or by amoebocjrtes which have wandered out from the underlying
dermis (8, Fig. 59 b). The cuticle covering the visual area becomes
transparent and greatly thickened, and so acts as a condensing
apparatus or lens. In the larger eyes each group of visual cells
secreting a rhabdome is sharply marked off from the rest and covered
by a separate lens or thickening of the cuticle. Such a group is
▼n.] BEH8E OBOANa 131
termed aretinnl&; and as it is suiroanded by a sheath of pigment
it can only be affected hy light coming from an object directly in
front of it and priq>agated parallel to ita axis. Hence to an
Artbn^Kxl possessing an eye vith many letinulae the outer world
will be presented as a mostuc of light and shade, each letinula giving
an impresnon depending on the intensity of light in the field of view
directlf in front of it. Such a mosaic is an image, and this image
A. TertiMl moUod through a lateral eye of a Scorpion, Eiucorpiui iUtliaa.
B. Diagram of retiaola of a Soorpion'a oentral eye. C. D. E. Tniiii-
*arM leotioD of B taken at diSeieal Isvels. From Lankeater and Bourne.
1. Gntieolar lens. 2. EpiderraiB of the general bodr-gnrface. 8. Base'
ment membrane. 4. Epidermal cells which coatnin pigment. S. Merre
end-eella with nnolei. 6. Rhabdome. 7. Fibr^ of optio nerre.
8. Pigment contained in eonnective tiesne cells.
will be obviously the more detailed and definite the greater the
number of retinuiae in a given area. In some Arthropods,
ench as the common Fly, the eyes cover the greater part of the
head. Eyes with numerous well-defined retinuiae are known as
compound eyes: and they uaually present the appearance of
numerous facets of hexagonal outline, owing to the fact that there
is s luu corresponding to each retinula. In many cases the retinuls
9—2
ARTHBOFODA.
(|<9AP.
AUMENTABY CANAL.
1. AnteoDiile. 3. Antenna. 3. Mandible. i. Mouth, 6. Scale
oreqiuniB of uilcDDa (Hiopodite). 6. Anus. 7. TbIsod. 8. Opening
at TU deleieDB. g. Chals. ID. let nalkiDK leg. 11. 2nd valking
leg. 13. 'itd calking leg. 13. ith walking leg. 14. lei BbdominsI
leg, modiGed- 15. 2ad abdominal leg, sligbtl; modified. 16. 3ril
Kbdomiual leg. 17. 4th abdominal leg. IB. £th abdomimil leg.
19. 6th abdominal leg, forming vith tetaaa the swimming paddle.
30. OesopbasQS. 31. Stomach. 23. Meuejiteron or mid-eaC
3S. Cenical groove. 2i. Intestine. SS. Cerebral uanglion.
86. Pata-oesophogtal nerve-oordB. 27. Ventral nerve-cotiJ. 3H. Eye.
29- Beort. SO. Sternal artery. 31. Sopro-intcstinol artery.
S3. Sub-ial«>tinal artery in abdomen. '63. Sub-in tea tinal artery in
thorax. S4. Ophthalmia artery. 35. Antennary artery. 36. Hepaiio
artery. 37. Testis. 3S. Vas defeirnB. 39. Intental ekeleton.
40. Qreen gtand. 41. Bladder. 42. Eiteroai opening o[ green gland.
is depres-^ed beneath the general surface, and the adjacent ectoderm
eells meet above it. These cells secrete clear glassy rods which
cohere to form a crystalline cone. Thia also happens in some
simple eyes, such as the centra! eyes of the Spider ; here the clear
roda remain unconnected, and the whole upper layer of ectoderm
cells is known as the vitreous layer. In the Cray-fish the compound
eyes are carried on the ends of moveable eye-stalks ; and in Spiders
the eyes, which in these animals are always simple, are sometimes
elevated on a little prominence like a lighthouse, borne on the head
and thorai. The number and position of the eyes in the Spiders
are points of great use in identifying the various species.
Ab a rule the alimentary canal of the Arthropods is about as
DisenivB long as the body, so that it is straight; the Insects
*"'^- however form an exception to this rule, since in their
case the canal is longer than the body, and consequently has to
be coiled or twisted in order to tuck it away in the limited space.
]t was mentioned above that the chitinous exoskeleton of Arthro-
pods is tncked in at both the mouth (stomodaeum or fore-gut)
and anus (proctodaeum or hind-gut), and in many this lining
extends BO far in as to leave but a small part of the ahnientary
canal free from it In some species the hinder end of the stomo-
daeum secretes deposits of chitin, as in the cockroach, or is
hardened by calcareous deposits, as in the lobster or cray-fish, and
thus teeth are formed which lie inside what has been termed the
stomach or gizzard. When the moult or ecdysis of the shell takes
place the linings of the fure- and hind'gut are also cast oET.
The presence of chitin lining parts of the alimentary canal
(orved to discriminate those parte of the canal which ore to be
134 ABTHROPODA« [CHAP.
looked on as merely parts of the skin — the stomodaeum and
proctodaeum — &om the true endoderm. The stomodaeum is usually
divided into a narrow portion leading from the mouth, called the
oesophagus (20, Fig. 60), and an expanded portion containing teeth,
called the stomach (21, Fig. 60). The proctodaeum is usually a
straight cylindrical tube, called the intestine (24, Fig. 60). The
small piece intervening between them is called the Mid-gut or
Mesenteron; it alone corresponds to the human gullet, stomach,
and intestine, and to the whole alimentary canal of a worm behind
the pharynx. In it digestion is carried on and into it opens the
so-called liver, i.e., one pair — rarely more — of glands consisting
of great tufts of branching tubes lined by yellowish-brown cells.
These secrete a fluid that assists in digestion. The food passes in
part into these glands and some of it is there digested.
In most animals the heart is a muscular sac which opens into a
Circulatory systcm of tubcs with muscular walls, called arteries,
apparatus. through which blood is driven to all parts of the
body, finally passing into narrow tortuous passages, the so-called
capillaries, whence it reaches the thin-walled veins through which
it returns to the heart Thus, excepting such fluid as soaks through
the thin walls of the capillaries, the blood is entirely confined within
definite channels which do not open into the body cavity. But in
the Arthropods the state of things is different; the heart (Figs. 60
and 101), which lies in the middle line just below the skin of the
back, opens by a series of slits called ostia into the body-cavity
(haemocoel), and when the heart expands the blood which is in the
body cavity enters these slits, but cannot pass out again through
them when the heart contracts, as each slit has a valvidar arrange-
ment which prevents this. When the heart contracts the blood is
therefore forced forwards and leaves the heart by a vessel — ^the
aorta — or by vessels with various names, which sooner or later
open again into the haemocoel, and so the circuit is completa
The part of the haemocoel in which the heart lies and into which
the ostia open is called the pericardium, and it is separated fit>m
the remainder ol the haemocoel by a horizontal septum called the
pericardial septum, in which however there are perforations. The
pericardium of Arthropoda thus contains blood, and is consequently
widely different from the pericardium of Mollusca or Vertebrata,
which is in both cases part of the coelom.
In those Arthropods which have a localised respiratory system,
and in which the blood takes part in respiration, there is a more
til] CIEOULATION and BE3PIEATI0N. 135
definite course for the blood than that sketched above. The
extent to which blood-vessela with definite walls are developed
varies in the different members of the group ; thus the Scorpion and
King-crab have a mnch more specialized circulatory system than
Fw. 6L
Lett tide of & L&ttk of the Prawn. Ptnaeui, to ehow the origin of the
gills. SliRhtl; magnified. From Claua. L, to L,. Tlie firBt to fiflh
uiibi>l»tat7 limbg. M, to M,. The first to third maiiilipedB. la. 2a, Sa,
7a. Podobranoha. lb, 6b. Anterior arthrob ranch b. lo. 2o. 7o. POB-
terior artliiobranchi. Id, Gd, Td. Plenrobranchg. Of these rudiments
of gillB onl; Dineteen develope. B. heli eide of a fully-grovn Prawn,
Penaau lemieuleatiu, to show faUj-grown giUs. Slightlj magnified.
8. Siopodita of eecond maxilla, which flaps to and fro and ao oaOBes a
ODirent oTei the gills. 9. Eiopodlte of fourth ambulator; limb.
have the Spider and Mites. The blood is very rarely red, but
is usnally slightly tinged with a bluiith colour by a substance acting
in tile same way as haemoglobin, hut differing from it in composition.
In the lower and more simply organized Crustacea, such as the
Kcspiratory wfiter-ffeas, there are no special breathing organs, but
die blood is able to absorb its oxygen and give off its
136 ABTHBOPODA. [CHAP.
carbonic acid ob it courses under the thin skin. But in the larger
and more complicated Crustacea, such as the shrimp and lobster, a
special apparatus is present in the form of gills. These gills are
thiu-walled extensions of the akin which project from the surfiEu»
of the body near the base of the limb or on the side of the thorax
into the surrounding water; inside them the blood flows to and firo
and a cuirent of water washes tbem on
the outside. The gills are classified
according to their point of origin, being
termed podobranchs(la,Fig.61) when
they arise from the proximal joint of
tbelimb, artbrobrancbs(lb,Fig. 81)
when they are outgrowths of the thin
membrane covering the articulation
between the appendages and the body,
and pleurobranchs (Id, Fig. 61) when
they arise from the side of the body
above the insertion of the appendage.
In order to increase the surface of die
gill, it is usually much folded or pro-
duced into a number of small processes.
In a lobster the gills are borne on the
sides of the cephalo-thorax, as the
fused head and thorax is called. There
are twenty on each side, and they are
4. Fused abdominal RiQglis. protected from injury by a broad flap
6. OeBophagus. 6. Mid-gat. „ . i. , i ■ / .^ , . f
7. Small intcBiiDB. 8. Colon, called the branchiostegite, which
9. Bectnm. 10. Malpighian has grown down from the back and
tabnUs, brown portion with - , lll. -.iirj
oaeoa. 11. Malpighian tn- formed a chamber between itself and
bales, dlitfd end. 12, Trachea thesideof the body ; in this cavity the
with TBBioles. 13. TeBteg, ,,, ,, , , ,, ,, , . . r
opening into coiled vaw defo- P^^ "^ concealed. At the iront end oi
tentia. 1*. Penis. 16. Bingla this chamber lies a small paddle, which
ispart of the second maxilla or scapho-
gnathite (Fig. 56 m), which throws out the water from the front
end of the gill chamber two or three times every second and thus
keeps a current of fr«sh water passing into this space behind. This
may be easily demonstrated by adding some coloured granules, such
as carmine or indian-iuk, to the water in which lobsters are living.
Many of the Arthropoda breathe air and their respiratory
mechanism is very peculiar and unlike anything else in the animal
kingdom. Instead of the blood being taken to a gill or lung and
Fro, 69. View of male Cock-
abater, ileloUmtha vatgaTii,
from which the dorsal integu-
ment and heart have been re-
moved to ahow the internal
organe. After Yogt and Yung.
1. Cerebral ganRlioo. S. let
thoracic ganglion. 3. 2nd
kndSrdthoracicgangliatosed.
BESPIBATOSr STSTEH.
137
til]
there purified and then driven with its oxygen all over the body to
every organ and tiasne, the air itaelf is introdaced into the body and
is carried by minnte tubnles to every tissne and cell (12, Fig. 62).
Tboa in these ^nimuli! the blood has loet one of its main functions —
the respiratory — and remains simply a nutritive fluid. The fine
tubules through which the air travels are termed tracheae (Gr.
Tpaxvf, Tpaxfui, Tough, comigated), and the three groups of Myria-
poda, ArachnidB, and Insects are sometimes coUectiveiy termed the
Tiacheata, in contradistinction to the Groatacea, though there is
reason to believe that the tracheae in Arachnida have arisen in a
different way to those in the other two groups. The tracheae open
to the exterior at certain definitely arranged pores termed stigmata,
usnalljr found at the sides of
the body. From these pores
the tracheae pass inwards,
dividing into smaller and
smaller branches which ulti-
mately end in the various
tissues. Each trachea is
reaUy a pouch of skin tucked
into the body, and hence is
lined by chitin continuoua
with the exoskeleton cover-
ing the rest of the body.
The tracheae are kept bom
collapsing by a thickened
ridge of the chitinous lining
which coib round inside the
tube like a spiral of wire
inside a water hose. Oxygen is thus absorbed by all the parts
of the body directly from the air and not ftx)m the blood. This
peculiar mode of respiration has had a profound influence on
Insect stmctuie.
A very primitive Arachnid, lAmulus, the King-crab, which lives
in the sea, breathes by means of what are called gill-books ; these
are piles of delicate leaf-like plates placed one over the other like
the leaves of a book and attached to the posterior surface of the
appendages of the hinder part of the body, which are flattened
(Figs. 64 and 107). When these plates are moved up and down the
leaves of the gill-books fly apart and the water gets in between
them, and oxygen passes from it into the blood which circulates in
Fio. 63. Horizontal seotion throngh the
abdomen of a Spider, dTgyrontta. After
MacLeod. Magnified.
1. Opening to eitetior, tracheal stigma.
2. Terminal traoheae. 8. Lateral
tre^heae. 4. Long books.
138 A&THBOPODA. [CHAP.
the substanca of the leaves. In the Scorpiom, which &re geologioally
the oldest and most primitive group of the Atachnids ^t live od
Fio. M. Seetton throngb the opercnlnii) and gills of k Eiug-cnb, Lfmtdw.
X abont 16. The normKl nmnber of gills id b Limoltu is five, the seotioa
from whjob thla drawing is made shoved only fonr.
land, the arrangement is the
same, only the gill-books and
the plate-like appendages
which carry them are ankaller,
and the books are packed
away into pits on the under
aide of the body, whilst the
highly modified appendages
extend horizontally below so
as to floor in the pits, leaving
only a slit through which air
enters. This arrangement
prevents the gill-book»— now
called lung-books — from dry-
ing up. In other Aiachiuds
the gill or lung'book has been
lost, and only the pit remains^
and this is enlarged and hor-
Pra. 65. Londtndiua] aeation throngh the _.__ j„i.-, ♦!,„ i . * ■
lung bool of > Spider. MagSified. "'" *"*" '°5 "^7' forming
From MacLaod.
Opeuiog to the exterior or atigma.
free edge of the pulmonary lesTes.
SpM« in which the air oiroalateB.
BpMS in trhioh the blood oiraiilateB.
tracheae which may i
all the appearance of Insect
tracheae. The Spiders form
an interesting link, for some
vil] excretory system. 139
of their Inng-books have been thus replaced by tracheae and others
remain as in the Scorpion (Fig. 63). The tracheae of the Anten-
nata have however developed in a different manner. In Peripatus,
the oldest and most primitive member of the group, the stigmata
or openings of the tracheae are scattered irregularly all over the
surface of the body. Each leads into a short straight tube which
ends in a bunch of diverging tracheae. In the Myriapoda there is
usually only one pair to each segment, and the same is the case
with the Insecta, but in them tracheae belonging to successive
segments usually join so as to form longitudinal trunks which may
even (as in the Flies) become swollen so as to form reservoirs of air.
In some of the smaller Crustacea where the cuticle is thin the
exchange of gases between the blood and the surrounding medium
seems to take place all over the surface of the body. Another
mode of exchange is the so-called anal respiration which is met
with in many Phyllopods and Copepods, in Gammarus and Aselltis,
in the larvae of Decapods and in certain Insect larvae. In these
animals the rhythmic contraction of the muscular walls of the
rectum alternately pumps in and expels water carrying oxygen in
and out of the anus. In the Insect larvae the walls of the rectum
are richly supplied with tracheae.
The excretion of the nitrogenous products of katabolism from an
animal's body is a function of fundamental importance.
excrcUon."**"' W® ^avo scou in the Earthworm that this is per-
formed in a series of little tubes called nephridia, one
pair in each segment, and the same is roughly true of Peripatus.
But in the other Arthropods, with few exceptions, where the primi-
tive segmentation is much changed and modified, such structures
do not exist in each segment, but a single pair of excretory organs
suffices for the whole body. In the simpler Crustacea each of these
is a tube with glandular walls (i.e. walls composed of cells which are
filled with excreta), and each tube opens at the base of the second
maxilla, on each side. They are termed the maxillary or shell-
glands (Figs. 69 and 70). In the larger and more complex forms
corresponding organs open on the second antenna (40, Fig. 60).
Here the organ consists of a network of parallel glandular tubes
joining each other at intervals and opening into a thin bladder
which communicates with the outside. The whole is called the
antennary or green-gland. In a few cases both antennary
and maxillary glands co-exist, at least for some time of the animal's
life.
140 ARTHROPODA. [CHAP.
A typical nephridium has been already defined as a tube which
opens at its inner end into the coelont Since the excretory glands of
Crustacea have in some cases at their inner ends thin-walled dilata-
tions which are by most zoologists regarded as portions of the true
coelom the Arthropoda may be said to possess modified nephridia.
In Insects and Mjrriapods the excretory system, like the
breathing apparatus, is peculiar; the waste nitrogenous matter is
taken up by certain tubules called Malpighian tubules, after a
celebrated Italian anatomist named Malpighi (Figs. 62 and 83).
These lie in the body cavity surrounded by the blood ; they do not
open directly into the exterior but into the front end of the procto-
daeum, and through this their excreta leave the body.
In the Arachnids the excretory apparatus is of two kinds which
may coexist. In Scorpions and Spiders there are Malpighian
tubules superficially resembling those of Insects, only shorter and
less numerous, but they open into the endodermic tube or
mesenteron and are therefore endodermic, not ectodermic structures.
There are also organs which, like the green- and shell-glands of the
Crustacea, are to be regarded as modified nephridia, which open at
the one end into a space which is a remnant of the coelom and at
the other to the exterior; they are termed coxal glands, since
they lie mainly in the coxal or proximal joints of the legs. The
contrast between the ordinary earthworm with its numerous pairs
of nephridia and the larger and more active crayfish with its single
pair is a very striking one for which some explanation is sought.
Eisig experimenting on some of the marine Polychaeta discovered
that the ectoderm performed part of the function of excretion. He
fed the animals on a substance (indigo carmine) which was soluble
and was consequently digested but which was got rid of by the
excretory organs. This substance was found in the nephridia,
and also in the ectoderm from which it was secreted into the cuticle
and into the chaetae which, as has been shown (p. 91), are special
developments of the cuticle. Hence we may conclude that in the
Arthropoda with their enormous production of cuticle this function
of the ectoderm has been so strengthened that nephridia have
become superfluous. Peripatus, which alone retains nephridia in
every segment, has indeed the thinnest cuticle of any Arthropod.
With few exceptions Arthropods are bisexual. The reproductive
organs are comparatively simple. Both the ovary
J^IZ^'"'"'^^ (Fig. 67) and the testis (Fig. 66) are continuous with
their ducts, which, in the Crustacea, Arachnids and
some MjTiapods, UBuaJly open to the exterior on the under BUrface
of the middle region of the body und at tlie posterior end of the
body ID Insects and one dirision of the Myriapods. The apace
Flo. 6S. Mate reproductive orgtiiH of Aitacat JluvialiluiiB.hont !}. From
Howes. 1. Right antorior lobo of teatia. 3. Utdiaii posterior lobe of
teHtin. S. Tas defeiena. i. Bitemal opening of vas defereuB.
G. Kight fourth uobulataiy leg in wlucb the vbb deferens opens.
Pin. 67. Female reproductive organs of Aitaeut Jlui'iatUitu about 2. From
Howes. 1. Kight oTiduot. The left ovidnct ia sliowo parti; opened.
3. Btghl lobe ot ovary. 3. Left lobe of ovary with Ibe upper half re-
moved to show the cavity of ovary or ooelom into vhieh the ripe ova drop.
4. Bitemul opening of ovidnot. a. Bight second ambulator; leg on
irhioh the oviduct opens.
inaide thei^e glands, lined by the reproductive cells, is regarded as
part of the coelomic cavity.
The foregoing account of the Arthropoda enables us to give the
following definition of the group r — The Arthropods
tht'owup" "^ *■* bilateral animals with segmented bodies. The
segments are not all alike and frequently fuse one
with another ; some at least hear a pair of jointed limbs, of which
those in the region of the mouth are modified to catcii and bite the
food. The nervous system consists of a supra-oesophage&l mass or
brain, a nervous ring round the oesophagus and a ventral chain of
142 CRUSTACEA. [CHAP.
ganglia sometimes fused into a single mass. A heart is usually
present above the alimentary canal and blood enters it through a
series of paired valvular slits from the haemocoel or blood-cavity.
The sexes are usually distinct. The coelom is much reduced.
This definition is in the main true of all Arthropods, whether
insect, spider, centipede, or crab. We must now consider however
how the various subdivisions of this great group may be dis-
tinguished one from another.
Class I. Crustacea,
The Crustacea are with few exceptions, such as the wood-louse,
inhabitants of the water, and they breathe either through the
general surface of the body or by means of gills. They have as a
rule two pairs of antennae and these as well as their other jointed
limbs are typically biramous, that is, they consist of a basal portion
bearing two prolongations. They have at least three pairs of ap-
pendages converted into jaws.
The Crustacea are usually divided into two groups, the En-
tomostraca (Gr. €VTOfio^, cut in piec^ ; oa-rpaKov, a shell) and the
Malacostraca (6r. /xoAaKo?, supple) ; and each of these is again
divided into four and three Orders respectively.
Sub-class A. Entomostraca.
This group may be regarded as a lumber-room for all Crustacea
which are not included in the well-defined division Malacostraca,
and the only character which can be attributed to all the members
is that of not possessing the marks of Malacostraca.
For the most part they are small Crustacea of simple structure.
The number of their segments varies within wide limits ; some Ostra-
coda having only seven pairs of limbs, whilst in Apus there are sixty-
eight pairs. The dorsal part of their head has, in many cases, grown
backwards and downwards like a mantle to form a large hood or shell,
termed the carapace, which may cover a large part of the body,
and in some cases this becomes divided into two lateral halves hinged
together like a mussel's shell. In many descriptions of Entom-
ostraca the words 'Hhorax'' and "abdomen" are used to describe
Vn.] PHYLLOPODA. 143
regions of the body. Such terms are in strictness applicable only to
the higher Crustacea, where the trunk is sharply differentiated into
two regions distinguished by the character of their appendages.
Amongst the Entomostraca however the appendages of the trunk
form a uniform series : often it is true the last segments are devoid
of appendages, and to these the term abdomen (16, Fig. 68) is usually
applied, but to us this seems an unjustifiable and misleading use of
a term which has an exact significance only amongst Malacostraca.
Entomostraca have no internal teeth in their stomacL As a
rule the young are not like their parents but are larvae of a special
kind called Nauplii; these after a number of ecdyses, during
which the number of segments increases, grow up into adults.
The Nauplius possesses an oval, unsegmented body, a median
simple eye, three pairs of appendages and a large upper lip. The
first pair of limbs representing the first antennae of the adult are
simple and unjointed, the other two pairs have a basal piece and
two branches. The inner branch of one or both pairs has a hook
for masticatory purposes. These two pairs of appendages become
the second antennae and mandibles of the adult ; both are at first
placed behind the mouth.
The Entomostraca consists of the following Orders :
Order I. Phyllopoda.
As the name implies the Phyllopoda (6r. <t>v\kov, a leaf; ^ov?,
a foot) are characterized by possessing flattened leaf-like swimming
limbs. Of these there are at least four pairs but there may be
many more. The larger Phyllopods are not uncommon in Britain ;
one genus, Artemia, taken at Lymington, flourishes in salt-pans in
which the salt is so concentrated as to be fatal to other animals.
Branchipus (Fig. 68) is devoid of the carapace and has an elongated
heart extending throughout the body. It occurs in stagnant water,
and has been recorded in several localities in the south of England.
It is often found in the vicinity of Montreal, in Canada, in the
pools of rain water which have accumulated in disused quarries.
Apu8 is another of the larger forms which was formerly found in
Britain but has not been met with for some years and is possibly now
extinct in this country. It has a large carapace, and its flattened
leaf-like appendages are regarded as primitive types of the Crustacean
limb from which all the numerous modifications of the higher forms
144 CBUSTACEA, [CHAP.
may be derived. Of these eleven psirs are situated in front of the
genital opening and are often termed "thoracic," one pair being
attached to each of the pre-genital seg-
ments of the trunk. Behind the genital
opening there are fifty-two so-called
"abdominal" pain of legs, of which
several pairs are attached to each post-
genital segment except the last two or
three.
The genera Simocephalu» and Dapk-
nia, common in pondA and ditches, both
in England and America, differ from
the foregoing in having fewer s^ments
and in possessing a bivaived catapaca
which completely encloses the body.
The first antennae, or, as they are
generally called, the antennulee, are
small and simple, but the second anten-
nae are very large and forked and pn>>
ject from the shell, and by their htshing
movement carry the animal through the
water (Figs. 69 and TO). The carapace
is to a certain extent transparent, and
through it the beating of the heart,
the circulation of the blood and the
movements of the thoracic leaf-like
appendages may be made out. Within
tiie substance of each valve of the
carapace a coiled glandular tube may
be detected ; this is the shell-gland or
topical excretory o^;an of the Entom-
oatrsca which opens on to the exterior
in the region of the second maxilla.
The male (Fig. 69) is usually smaller
than the female (Fig. 70), and is cer-
tainly very much rarer. The females
lay two kinds of eggs, (i) unfertilized
eggs, which develop in the space inter-
vening between the dorsal side of the
body and the shell which acts as a
brood-pouch, and (ii) fertilized eggs, which are larger and become
Fia.68. Dorsal view of female,
Branchipiu Bp. foaad in a
poDd in SuBBei x about 10,
1, Antennae. 2. Head. 3. Ejen.
4 — 14. The eleven "thoracio"
limbn. IS. The caudal forks.
16. The fifth "abdominal"
w of male Simocephalui ,
nalM. 2. ADtennae. 3. TeetiB.
divertiODlam. 11. H«art. 14
17. Neok OTgao.
Fio, 70. Side riew of female Simocephalvt tima, magnified 1
as Fig. 69. From CDDniDgton. 1. AntenmileH.
3. Mandibles. 1. MaiilUa. 6. Itit pair of legs,
of legs. 7. 8rd pair of legs. 8. 4th pair of lega.
lega. 10. Hepatic diverticolum. 11, Heart.
18. Brood-pouoh. 14. fihell-gland. 16. Brain.
17. Neck organ.
A AM.
HirIiIj magnified. 1. AliteD-
Vaa deferens. 10. Hepatic
:bell-glaDd. 16. Mid-gut.
ti. 2nd pair
0. Gth pair ol
12, OTarj-,
16. U id-gut.
146 CRUSTACEA. [CHAP.
surrounded by a special modification of the brood-pouch called the
ephippium. The nature of the eggs produced is regulated by
favourable or unfavourable conditions of life. At a suitable tem-
perature and with a sufficiency of food and water, the unfertilized
eggs are produced in large numbers at short intervals. Periods of
drought or the cold of winter bring about the formation of eggs
which are fertilized and enclosed in the ephippium. Sheltered by
this case the eggs are enabled to withstand freezing or desiccation
and with a return of suitable conditions a young Daphnia hatches
out from each Qgg to continue the cycle of lifq.
The Phyllopoda are divided into two Sub-orders, viz. : —
Sub-order 1. Branchiopoda.
Long-bodied forms devoid of a brood-pouch and not using
the second antennae as swimming organs.
Ex, Apus, Artemia, Branchipus.
Sub-order 2. Cladocera.
Short-bodied Phyllopoda with a dorsal brood-pouch and
long second antennae.
Ex, Simocephalus, Daphnia,
The Branchiopoda live in fresh-water and as a rule in the stand-
ing water of pools and ponds; they are more rarely found in
brackish or salt water. They swim actively about by means of
the vibrations of their flattened limbs. As a rule aquatic animals
swim with the upper surface towards the surface of the water, but
the Branchiopoda seem very indifferent to this rule, and are quite
frequently seen swimming upside down. The Cladocera also fre-
quently swim upside down, the genus Daphnia however usually in
a vertical position with the head uppermost.
Order II. Ostracoda.
This Order (6r. oo-rpaicioSiy?, shell-like) contains a great number
of species which do not differ greatly from one another. In form
they resemble Daphnia^ but the head does not protrude from
between the valves of the carapace, and some of the internal organs
of the body, viz., the ovary or testis and branches of the liver, are
prolonged into the valves of the carapace. This latter is a very
characteristic structure, consisting, like the shell of the Mussel, of
two valves. It opens by an elastic ligament which tends to pull
VII.] COPEPODA. 147
the Yalves apart, and it closes by the contraction of a muscle which
runs across the body from one vaJve to another. The whole body
is included in the carapace, antennae and all.
Ostracoda have fewer ap-
^n g pondages than any other group
■^ I of Crustacea ; besides the anten-
1-J^^I!?^ M ^^N. nules, antennae, mandibles and
fix ^h// r^ \ \ *^^ P*^^ ^^ maxillae, they possess
V^(^wa^^^^^ jkl..i ^ only two pairs of limbs, and
^"~ ^^ — ^"^^^^^5^0/ these are stout and cylindrical
iv^ * 6 ^^fr- ^z 1^ marked contrast to the ap-
"'^^ pondages of the Phyllopoda. The
1. Antennoles. 2. Antennae. m •
3. Mandibles. 4. ist maxillae. Two pairs of excretory organs
6 2ndmaidllae. 6. Ist pair ^ been described in some
of legs. 7. 2nd pair of legs. . r /n, ^ , ^i_ , „
8. Tail. 9. Eye. species of Ustracoda, the shell-
glands common to all Entom-
ostraca opening at the base of the second maxillae and a pair of
antennary glands opening at the base of the second antennae. The
last named are seldom found except in the Malacostraca.
Both pairs of antennae are jointed, unbranched appendages,
which are used in swimming, another most important distinction
frt)m Daphnia and its allies.
The males differ from the females, which either (Cypris) lay
their ^gs on water-plants or {Cypridina) carry them about within
their shells. The majority of species are found in the sea but
others occur in fresh-water. They are flesh eaters, and as they
exist in great numbers they fulfil the important duty of scavenging
on a small scale, and thus they prevent the accumulation of dead
oiganic matter in the water.
Order III. Copepoda.
This Order (Gr. Kowny, oar ; ^rov?, foot) is also a large one and its
free swimming members exhibit a very characteristic structure and
appearance. The body is of an elongated pear shape, and consists
of a large round head and a tapering trunk of comparatively few
segments. The carapace so characteristic of the preceding order
is entirely absent. The head bears a single median eye in front,
the lateral compound eyes so conspicuous in most Crustacea being
10—2
148
CRUSTACEA.
[chap.
absent. Attached to the head are
five pairs of appendages, two pairs
of nnbranched antennae, a pair of
mandibles and two pairs of max-
illae. The head is not separated
from the trunk by any constriction.
The latter bears four pairs of swim-
ming feet of a typical forked pattern.
Each of these appendages is some-
thing like a X- ^^^ ^^^ ^^ ^^^
limb consists of one or two joints
and is called the protopodite. It
splits at its free end into two
prolongations, the inner of which
is known as the endopodite
and the outer as the exopodite.
Both are flattened, consisting of
stout joints each of which bears
spines, and the whole forms a
convenient paddle. Each limb
is also joined to its fellow of the
opposite side by a transverse
moveable ridge so that the right
cannot move without the left.
By the simultaneous action of all
the limbs of the trunk the animal
is enabled to execute a series of
swift darts through the water;
by the action of the second an-
tennae a slow, gliding movement
is carried out, whilst the max-
illipedes by sweeping movements
search the water for food. A
forked limb is characteristic of
the Crustacea, and is not met
with in other groups of the
Arthropods. It appears over and
over again in all the Orders,
retaining its primitive form in
some instances, as in the ab-
dominal appendages of a Cray-
Fio. 72. Ventral view of male Cyclops
sp. Magnified.
1. Antennule. 2. Antenna.
3. Mandible. 4. 1st maxilla.
5. The two halves of the 2nd
maxillae sometimes called inner
and outer maxillipedes. 6-9. Ist-
4th thoracic limbs. 10. Eye.
11. Bristles near male generative
opening. 12. Caadal fork.
13. Mouth. 14. Copula or
plate connecting the right and
left limb of each pair.
VII.] COPEPODA. 149
fish, but m<ae oiWi by the enppreseion of one part (uBually the
exopodite) and by the development and modification of others, the
origioal form becomes masked and difficult to recognise. When
Fro. TS. DorMl viev of female Cyclopt Ep. MagniGed. Partly after Hartog.
I«t AntsDoa. 3. Sad AnteDna. 3. Eye
6. Oridact. 7. Sp«nnathecB or pouch
of the male. 8. Egg-attcr. ». Caudal (
11. Componad segment, oonaiating of the laF
opening) and the flrst abdominal.
4. Ovary. 5. Utenii,
!or receiving the epennatozoa
rk. 10. Position of anus,
thoracic (bearing the genital
both forks are conspicuously developed the limb is said to be
biramonB. The fonr or five last segments of the Copepod'e body
150 CRUSTACEA. [chap.
bear no appendages. The last is produced into two processes,
forming a caudal- or tail-fork.
The sexes in the free-living species are not markedly different,
but if we examine specimens of such a genus as Cyclops, which is
common in our fresh-water pools, we shall find that in the breeding
season the female carries about with her two egg-sacs (Fig. 73).
These are attached to her body just behind the last pair of append-
ages and project freely at the side. Each egg-sac may contain four
or five dozen eggs which are glued together by a cement-substance.
Such egg-sacs are very characteristic of the Copepoda and are
found even in the parasitic members of the order. Most of the
latter live on fish, and some have acquired the name of ''fish-lice."
Their mouth appendages have lost their biting function and have
become adapted for piercing the tissues of the host on which they
live. Their segmentation is suppressed and their appendages are
reduced and the body has grown out into all sorts of curious
processes. The male is often much smaller than the female and
as a rule retains the crustacean characters more than she does.
Occasionally they are found on the skin of a fish, but more often
they occur in the mouth and on the gills, sometimes half and
sometimes almost wholly embedded in the flesh of their host.
Order IV. Cirripedia.
Some of the Copepods have become so modified by their parasitic
habits that unless we were able to trace their development, in-
cluding the larval forms through which they pass before becoming
adult, we should have difliculty in assigning them to their proper
place amongst the Crustacea. A somewhat similar modification
occurs in the Cirripedia (Lat. cirrus, a tuft of hair ; pes, a foot) and
is associated with a fixed or sessile habit of life. After passing
through a variety of free-swimming larval forms the animal comes
to rest and attaches itself by the anterior end of the body to a stone
or rock, the bottom of a ship, or some other object submerged in
the sea, and then becomes adult.
Like that of the Ostracods tlie body of a Cirripede is enclosed
in a carapace consisting of two valve-like folds which have grown
out from the region of the head, but these are usually strengthened
by five calcareous plates, a right and left scutum, a right and
left tergum and a median carina, and in Balamis, the common
acorn-barnacle of our sea-shores, a further armour of triangular
plates developes in an additional outer fold of skin which encircles
til] cibbipbdia. 151
the body. In Lepas, the barnacle usaally found in clusters on the
bottom of ships, which often seriously impedes their progress, this
ring is absent, but the anterior end of the head bearing the first
Antennae at its end has grown out into a long stalk which lodges
Fia. 7-4. A visw o{ Ltpat aTutHfera, cat open iDDgitudinally to show the iliapo-
sition of tile oTguii. From LeuckarC and Nitache, pertly after CIbdb.
1. StaJk. 2. CariDB. 3. Targam. 4. Scutum. 5. 1st antennae.
6. liandible with " palp " in front. 7. 1st maxilla. 8. 2nd maxilla.
9. The fliz pairs of biramoua thoracic limbs. 10. Labrum. 11. Month.
12. Oesophagns. 13. Liver. 14. Inleetme. 15. Anas. 16. Ovary.
17. Ovidnot. 18. Testes. 19. Vas deferens. 20. Penis,
21. Cement gland and duct. 22. Adductor scntorum muscle, which
closes the carapace. 23. Mantle cavity, i.e., the epaoe iatervening
between the carapace and the body.
some of the internal organs of the body. The second antennae
though present in the larvae are lost in the adult. The rest of the
body is enclosed within the carapace. Around the mouth are a pair
of mandibles and two pairs of maxillae, and the thorax carries six
162 CRUSTACEA. [CHAP.
pairs of biramous many-jointed limbs beset with nnmerons hair-
like spines, the lashing of which kicks food particles towards the
mouth (Fig. 74). These limbs are slender and flexible and thns
differ firom the corresponding limbs of Gopepods.
Like some Gopepods the Cirripedes are without a heart, and
the existence of special respiratory organs is doubtfuL Unlike
other Crustacea they are, as a rule, hermaphrodite, the male and
female reproductive organs being united in one individual A few
species are parasitic, chiefly on other Crustacea, and these have
reached a very extreme stage of degeneration.
Sub-class B. Malacostraoa.
The second of the two large groups into which the Crustacea are
divided contains most of the more familiar forms, such as Crabs^
Lobsters, Shrimps, Wood-lice, etc For the most part the Malac-
ostraca are larger than the Entomostraca and the number of their
segments is a fixed one. With the exception of the first Order,
Leptostraca, which is really a connecting-link between true Malac-
ostraca and the lower forms, this number is nineteen and there are
nineteen pairs of appendages. One of the most marked characters
in the Malacostraca is the differentiation of the trunk into two
distinct regions, the thorax and the abdomen. It is true, as is
mentioned above, that many authors speak of an abdomen in the
Entomostraca, but by this they mean with a few exceptions the
hindermost segments which are devoid of limbs. In any En-
tomostracan if we examine the series of limbs behind the jaws we
shall find that they constitute a continuous series without any
sudden change in their character. In a Malacostracan, on the
other hand, we find an abrupt change at one point in the character
of the limbs. The hinder limbs or swimmerets (pleopods) are
markedly different from the front limbs, for whereas in the swim-
meret both forks of the limb, endopodite and exopodite, are equally
developed, in the last five limbs or the thorax (peraeopods) the
endopodite is large and the exopodite is small or absent. It is this
difference in character which defines the abdomen.
Although the division between the head and thorax is not always
apparent, as a rule we may assign five segments to the head, eight
to the thorax and six to the abdomen, which ends in an unseg-
mented flap called the telson. The reason for this want of &
vil] thoracostraca. 153
definite bonndaTy between head and thorax in the Malacostraca
is that the carapace, which as we have seen is an outgrowth of
the head, has become fiised with the dorsal surface of the thoracic
segments, whilst at the sides it forms freely projecting flaps, which
since they cover the gills are known as branchiostegites (6r. cnrcya),
to cover).
The excretory organ of the Malacostraca opens at the base of
the second antennae and not as in the Entomostraca on the
second maxilla. As a rule the typical larva — the Nauplius — of the
last-named group is not present in the life-history of the Malac-
ostraca, which may hatch out from the egg in a practically adult
condition or may pass through several larval stages, the first of
which 18 the Zoaea, a larva with many appendages, possessing eyes
and in all ways more differentiated than the Nauplius.
Order I. Leptostraca.
The order Leptostraca (Gr. Xcirros, slight, small) contains but
three genera, which are interesting because they form an inter-
mediate stage between the Malacostraca and the Entomostraca.
Like many of the latter they are provided with a bi-valve carapace
which, unlike that of all other Malacostraca, is not fused with the
thoracic segments. Behind the six appendage-bearing segments of
the abdomen there come two more segments without limbs and
the hindermost bears two diverging filaments constituting a " caudal
fork," such as is commonly found amongst the Entomostraca. The
thoracic limbs are flattened and leaf-like, as in Apus, but the
mandible bears a three-jointed feeler or palp and the eyes are
stalked, — ^both, on the whole, Malacostracan characters. The
excretory organ opens on the second antenna, but in the larva the
shell-gland or maxiUary excretory organ is found and traces of it
exist in the adult
The order is marine, and very widely distributed throughout the
ocean. Its members are capable of living and thriving in very foul
water, so foul as to be fatal to most other animals. Nebalia is
the best known genus.
Order IL Thoracostraca.
The Thoracostraca (Gr. ^wpaf, a breast-plate) form a large
group and contain many very different forms. They are placed
together because the carapace has become fused with several of the
IM CEUSTACEA. [CHAP.
tfaoracio aegmeata, so as to form a region known as the cephalo-
thorax, the exoskeletou coTering which is cot jointed and is not
bivalved as in Nebalia. The eves of the Thoncostraca are
compound and almost always are home on moveable stalks. The
Older is divided into four sub-orders.
Sub-order 1. Schlzopoda.
This sub-order includes the lowest of the Thoracostraca. The
name is suggested by the circumstance that all the eight pairs of
thoracic limbs are biramous ; the first and sometimes the second
pair are reduced in size and provided with gnathobases ; they assist
the manibles and maxillae niid hence are termed maxillipedes. It
will occur to most observers that the thoracic feet of the Schizopod
resemble the ordinary form of swimmeret or abdominal appendages
FiQ, 76. Nyetiphanet wjratgica, a Schizopod. Slight!; magnified. From
WatMi. Thu black dots indicate the phosphorescent organi. The gillB
ore Men betneen the uephalothoracio and the abdomin&I appendagaa.
in the more familiar Lobster or Crayfish. This is so ; the swim-
merets of a Schiiopod are however sharply distinguished from
the thoracic limbs by their smaller size. It appears probable
that the first step in the evolution of an abdomea was the
reduction in size of the appendages so as to transform the hinder
part of the body into a powerful swimming fin, and many Schizopods
only use the abdomen in this way, since most of the swimmerets
are very small and appear to be practically functionless. The last
one however is broad and assists the tail in its vigorous strokes.
Some Schizopods have a series of phosphorescent oi^ans which
under certain conditions emit a pale but very perceptible light
VII J DEC APOD A. 155
like iha,t of a glow-worm. This light seems to be controlled by
the animal but its use is not very clear.
There are very interesting differences amongst the genera com-
posing the Schizopoda. The genus Euphausia for instance has
long feathery gills attached to the basal joints of the thoracic legs
and the eggs are not borne about by the mother but hatch out into
Nauplii, which pass through a series of metamorphoses before
becoming adult. In Mysis on the other hand the gills are few and
simple and the eggs are borne under the thorax on flat plates
termed oostegites, which project inwards from the hinder thoracic
appendages. In these two genera we see the beginning of two
tendencies which have led the descendants of primitive Schizopoda
to differentiate themselves in two different directions. One group
have taken to carrying the embryos about until they are fully de-
veloped ; at the same time the gills are reduced and the carapace,
which is essentially a gill-cover, tends to disappear. This group
includes the Stomatopoda, Cumacea and Arthrostraca.
In the other group the gills and carapace are retained, and
though the eggs are for a time carried about attached to the
swimmerets the young one passes through a larval stage before
becoming adult. This group includes the Decapoda.
Sub-order 2. Decapoda.
The Decapoda (6r. Ukol, ten) derive their name from the circum-
stance that the first three pairs of thoracic appendages have become
maxillipedes, that is to say have been modified so as to assist in
mastication, leaving five pairs of large conspicuous limbs which
have lost all trace of an exopodite, for prehension and locomotion.
This group includes the lobsters, cray-fish, shrimps, prawns,
hermit-crabs and crabs, etc. In the division of the crabs, the
Brachyura (Gr. jSpa^vs, short ; ovpa, tail), the abdomen is reduced
in size and turned up and closely applied to the under surface of the
thorax, except when the animal is '' in berry '' and then the masses
of eggs force the abdomen away from the thorax. As a rule crabs
are broader than they are long and the breadth is partly due to the
large gill chambers on each side of the body. The gills are really
outside the body, but are in a special chamber bounded by the
branchiostegite or free edge of the carapace.
The Anomura are in some respects intermediate between the
foregoing and the following divisions. As in the crabs the
156 CRUSTACEA. [cHAP.
abdomen Ib folded somewhat forwaida but the taO-fin is not so much
reduced. The last pair or last tvo pairs of the thoracic limbs are
reduced and turned dorsalwarda. Some species — the heimit-crabs —
shelter themselves in the empty shells of moUascs. to these cases
the abdomen does not develope a hard covering as the animal is
sufficiently protected by its lodging. It remains soft and acquires a
spiral twist as it moulds itself to the interior of its borrowed shelL
VII.] STOMATOPODA. 157
In the lobsters, shrimps, etc., which form the division Macrura
{Gr. fiaKpo^ long ; ovpd, tail), the tail is relatively large and is not
folded up against the thorax.
Some Decapods have left the sea and taken to live on land and
this has in some cases involved a change of structure, the gills
which breathe water being supplemented by the soft vascular
lining to the gill-cavity covered by the branchiostegite which, like a
lung, breathes air.
The group is for the most part marine, though the well-known
fresh-water cray-fishes, Ast(ictis in Europe and Cambarm in North
America, form striking exceptions.
Sub-order 3. Stomatopoda.
The Stomatopoda (Gr. o-ro/xa, a mouth) are a sharply defined
group with few genera, and may be regarded as an offshoot from
the primitive Schizopoda peculiarly specialized. The members
attain a considerable size, some eight inches or more in length.
The carapace is small and only covers the anterior five thoracic
segments ; the appendages of these segments are turned forward
towards the mouth and take part in feeding, and so are termed
maxillipeds. They end in a claw, the last joint shutting down
on the penultimate one like a knife blade into its handle. They
are thus very different from the maxillipeds of Schizopoda or
Decapoda, which are really limbs on the way to become jaWs and
have developed gnathobases. The maxillipeds of Stomatopoda
are grasping, not chewing organs, and have undergone the same
modification as the great claw of the lobster, which might just as
reasonably be called a maxilliped. A fertile source of confusion
in the study of the Arthropoda is the use of names like maxillipede,
thorax, abdomen, etc., to denote different things indifferent groups.
The last three thoracic limbs are for walking ; they are very feeble
and retain a rudiment of the outer fork or exopodite. The
abdomen is large and bears six pairs of flattened swimming limbs,
each of which carries a gill in its outer branch.
Unlike most other Crustacea, Squilla and the other members
of the group do not carry their eggs about with them, but lay them
in the burrows in which they live, and by sitting over them and
moving their abdominal limbs they keep up a current of water which
aerates the eggs. They are exclusively marine and live buried in
the sand or hidden in crevices of the rock. They move actively
and are difficult to catch.
GEUSTAOU.
6nb-ordeT 4. Cnmaces.
The membera of the sub-order Cuinac«a (Gr, xvfta, a. wave, or
billow) are mostly smali; they live in the sea on sandy bottoms at
considerable depths, but come to the surface at night. They an
especially interesting because to a certain extent they are int«i^
mediate in character between the Thoracoetraca and the Arthn-
straca. Thus their paired eyes are not elaikMi aod are some-
times fu8&l U^ether to form a single eye ; the carapace is reduced
BO as to leave several s^meots of the thorax uncovered (Fig. 71)
and on some of the thoracic legs there is a small exopodit«.
Fio. 77. FemiJo DitalylU ttygia k G. After Sm. The o&npace ia repis-
■ented aa trsaepuect to show the gilt
I. CftnpOM. 3. First uiteniia. S. First ieg. 4. Gill borne on
Bnt mkxilliped. 5, 6, 7 anil 8, Beeoad to fifth leg. 9. Free put at
thorax. 10, Abdomen. II. Appendage of the last BecmeDt of tha
abdomea.
liave a single pair of gills borne by the first thoracic limb. In
the female the abdomen, which is long, has lost all the limbs except
the last pair.
Order III. Arthrostraca.
The membera of the Arthrostraca (Gr. afiSpov, a joint; Sm-paKov,
a sheU) have sessile eyes, i.e., without stalks. The carapa*^. which
in most of the above-mentioned groups covers the segmenU of
the thorax, ia absent, and consequently seven of the latter are
usually freely moveable on one another, the first and in rare cases
the second thoracic segment remaining immoveably fused with the
VII.]
ARTHROSTRA.CA.
159
bead. They thua represent a further stage in the same process
which we found going on in Cumacea and Stomatopoda. Only one
of the thoracic appendages is modified so as to form a maxilliped;
there are consequently seven pairs of w&Mng legs attached to the
thorax. In the female these legs hear inwardly directed processes
which together form a hrood pouch in which the eggs develop©.
profile. From
. Tbe
i-Ti. Cepbalothorax. th-uii. Free thoraoio EegmeDta. siv-ui
tix ftbdominsl segmeDta. I. Anterior aDtenna. 3. Poaterior sdiciidb.
B. Haudiblei. i. let msiilk. 6. 2nd maxilla. 6. Maxilliped,
7 — IS. ThorMio limbs. 14 — 16. Three anterior abdominal limbB for
nrimming. IT — 19. Three posterior abdominal limbs for jumping.
20. Heart with six pain of ostia. 31. Ovary. 23. Hepatio diverti-
onla. 38. Pottenor divertienla of the alimentar? canal 34. Median
dorsal diirertiaalam. 35. AlimeDtor; canal. 26. Nervoaa system.
37. Ots in egg poach, formed from lamellae on tbe coioe of the aeoood,
tbild and fourth thoracic limbs.
The Arthiostraca are mostly small animals, living in either salt
or ftesh water ; they assume very different forms, some of them
having a rudimentary abdomen. They are divided into the sub-
orders Amphipoda (Gr. A/i^t, on both ends; n-oSa, feet), which are
for the most part compressed or flattened from side to side
160 ANTENHATA. [CBAP.
(Fig. 78) and carry their gills on their thoracic iqtpendages, and
the Isopoda (Gr. utm, equal ; roSa, feet), which are depressed or
flattened bom above downwards (Figs. 57 and 79), and whose gills
are the modi&ed endopoditea of the appendages of the abdomen.
A typical example of the last named snb-order is the Hog-water
Louse, AseUut aquaticiu (Fig. 57), common in out ponds and
streams, but many of the groups are parasitic and lose most of their
characteristic Crustacean features. As in the case of the Decapods
some genera of Isopoda have forsaken
the sea for a life on land, amongst
which the wood-lice, OnUcua and Por-
cellio, exhibit certain peculiaritjea
usually associated with Insects ; thus
the mandible has no palp, one pair
of antennae is usually lost, and there
are certain tubular air passages be-
lieved to be respiratory burrowed in
the abdominal endopoditea which recall
by their structure the tracheae of air-
breathing Arthropods. This is another
proof that any attempt to group to-
gether all animals possessing tracheae
leads to absurdities.
Fio. 79. A Wood-louse, Por-
ceiiio tcaber x Kboat 2.
From Caviec
Class 11. Antehnata.
Sub-class A, Peototraoheata.
A short account of the genus Penpatus must be given, as this
animal is of a very primitive nature and both its adult structure
and the mode of its development throws much light upon the origin
and anatomy of Myriapods and Insects and indeed on tJie ArUiropods
generally.
The different species of Peripatta are differently coloured, but
they mostly possess a beautiful velvety coat. In shape they
resemble caterpillars but carry two large antennae on their heads,
and at the base of each antenna is an eye. On the under surface
of the head is the mouth and tucked into it on each side is a
toothed jaw. This is an appendage which has been modified so as
to form a true gnathite. At each side of the mouth is a third ptur
of appendages, the oral papillae, from the tips of which a stioky
sUme can be ejected which entangles the insects and spiders on
VII.] ANTENNATA, 161
which the animal lives. The other appendages, which vary in
number in the different species from seventeen pairs to over forty,
have the form of soft cylindrical papillae ending in two claws and
function as walking legs (Fig. 80). The anus is posterior, and at
the base of each leg is a slit-like pore, the opening of a nephridium.
The genital pore is in front of the anus.
Fio. 80. Peripatus eapentU x very slightly. From Sedgwick.
The body cavity is a spacious haemocoel divided into three longi-
tudinal compartments by two bands of muscles which run from its
outer upper angle towards the middle ventral line. The lateral
compartments are continuous with the cavities of the limbs and
lodge the nephridia, the salivary-glands and the nervous system.
The alimentary canal, slime-glands and generative organs lie in the
middle compartment.
The mouth leads into a large muscular pharynx, such as is
found in many Chaetopods. The salivary glands open near this.
They are interesting structures, as development has shown that in
origin they are derived from nephridia, a state of things which
recalls the fact that in certain Oligochaets some of the nephridia
open into the oesophagus. The pharynx leads by a short oesophagus
into a roomy endodermic stomach which reaches back nearly to the
anus, a short proctodaeum only being interposed (Fig. 81).
The structure of the heart and pericardium closely resembles
that of the same organs in Myriapods and Insects.
The animal breathes by bunches of tracheae or short tubes which
pass from the exterior into the tissues and convey air. Their
external openings or stigmata are partly in two rows above and
between the legs and partly scattered irregularly.
At the base of each leg is a nephridium which ends internally in
a vesicle. Embryological research has shown that this vesicle is
a remnant of the true coelom which is spacious in the embryo, but
becomes displaced as development proceeds by the haemocoel.
Enclosed in the proximal part of the leg there is a gland called the
crural gland.
Peripatus is bisexual, and again embryology has demonstrated
& AIL 11
162
ANTENNATA.
[chap.
that the cavity of the sexual
oTgauB is coelomic The male
deposits its spermatozoa io
packets in the body of the
female. It is not known how
they reach the ova but they
are usually found in the ovaiy
and possibly bore their way
through the tissues, as they do
in some leeches. The ducts
of the reproductive organs are
believed to be modified ne-
phridia.
The nervons system con-
sists of abrain and two ventral
cords, which however do not
approach one another but lie
wide apart. They are con-
nected by nine or ten trans-
verse commissures in each
segment (Fig. 81). Posteriorly
the two ventral nerve-cords
fose abovB the proctodaeum,
aa arrangement which recalls
what occurs in certain primi-
tive Mollusca.
There are many species of
Peripatus, which are by some
antborities grouped into three
ot four genera. They are
found in widely separated
parts of the world and afford,
as is often the case wit-h ar-
chaic animals, an excellent
example of "discontinuous
distribution." They have beeu
found in South America ami
the West Indies, in South
Africa, in Australia, New
Zealand and in some of the
Islands of the Malay Archipelaj
After BalToac.
1. AoteTtDoe, abowicg aateaaiaj nerve.
a. Oral papilla. 3, 3', S». lit, Ind
and 10th U^ of right side. 4. Bnin
and ejes. 6. Ciromn-oeaophageal
cord. 6. Veotial Deive-eoTd of nght
side, ahowing the tranHverae oommia-
euree. 7. Pharjni. 8. Stomach.
9. Adqs. 10. Mole generative open-
ing. 11. Salivar; glands. 12. Slime
^lanila aad reservoir. 13. Enlarged
crunil glaod of the 17th leg. U*.
1J'°. 4tli aod lOlh nephiidia of right
;o and in Lower Siam.
VII.] MYRIAPODA. 163
The deyelopment of Peripatus first definitely solved the problem
of the nature of the various spaces in the Arthropod body and has
also thrown much light on some of the peculiarities of insect
embryology. Some species lay eggs and some produce living young,
and thus the genus afifords favourable opportunities for testing
theories as to the effect of development within the body of the
parent on the embryology of the offspring.
That the animal is a most interesting '' missing link '' becomes
evident if we attempt to sum up the Annelidan and the Arthropodan
features of its anatomy. Thus Peripatus resembles Annelida in the
nervous system, the muscular pharynx, the structure of the eyes,
the serially repeated nephridia, the shortness of the stomodaeum
and of the proctodaeum, the thinness of the cuticle and the hollow
nature of the paired appendages ; but in the indications of joints
in the appendages, the reduction in size of the coelomic spaces,
the presence of a wide haemocoel and of tracheae, the nature of
the antennae and of the heart and pericardium, the position of the
genital pore and the presence of true gnathites, Peripatus approaches
the Myriapods and Insects.
In habits these animals are shy and inconspicuous, hiding under
bark or stones and preferring a moist surrounding. They avoid
the light and move with deliberation, testing the ground as they
advance with their antennae.
Sub-class B. Myriapoda.
The Myriapoda (6r. fivpioq, countless) are characterised by the
possession of a head distinct from the rest of the body, bearing
antennae, mandibles and one pair of maxillae, followed by a large
number of segments bearing simple leg-like appendages.
Compared with the Crustacea or Insecta the group is a small
one, yet it contains some thousands of species which, if we except a
few small families, fall readily into two subdivisions (I) Chilopoda,
and (II) Diplopoda. The subdivisions differ markedly from one
another especially in the position of their reproductive openings
which in the Diplopoda are on the third segment behind the head
and in the Chilopod<i are terminal. For this reason some naturalists
break up the sub- class and associate the Chilopoda with the
Insecta.
[chap.
Order I. ChUopoda.
The very active, lithe, chestnut-brawn, rather Serce-lookiiig
little centipede, LithoHus forficatua, which is very common during
the summer months under the bark of old trees, under leaves and
other rubbish, is a good example of the CMlopoda (Gr. x^'*h ^
thoasand) or Centipedes. In the winter it bories itself in the soil
The female lays her eggs from June till August and hastens to
cover each with a thin layer of earth ; otherwise the egg is seized
and devoured by her mate.
If we examine a little more closely
one of these Centipedes, we
fcft?r™'' ^^^ see that the body is
divided into a head followed
by a very narrow segment and then by
fifteen other segments of varying siie.
The head bears a pair of long antennae,
the first appendages, which are constantly
waving about Close behind the point of
origin of these antennae lie the eyea. If
we turn the animal over and observe the
under surface of the head we shall at
once see a pair of lai^e vicious-looking
clawa — the poison claws or fifth pair of
appendages. The tip of each of these is
pierced and, as it strikes the prey, a
drop of poison is squeezed out which soon
kills any insect or larva the Centipede
wishes to eat. Although the tips of the
poison claws are turned forwards beneath
the head, yet these appendages really
spring from the first segment of the trunk,
which is enlarged and is known as the
^ „ „ . , basilar segment. If we separate with a
Fio. 82. A Centipede, Li- ■ - . . ji ^
thoMm /arficatai. Dorsal P*"' Of mounted needles these poison
Mpectxi2. claws we shall see attached to the head
1. Anteouae. 3. Poison the fourth pair of appendages, sometimes
walking le(-s. resemble legs and have undergone little
modification. They are reduced in size
and each has a blunt functionlees gnathobase. In front of these
the third pair of appendages or first maxillae take the form of a
VII.] MYRIAPODA. 165
lobed plate, being united with one another in the middle line.
These cover in their turn the second pair of appendages or man-
dibles which, like those of Insects and unlike those of Crustacea,
consist simply of the blade, there being no palp or feeler.
The fifteen segments Vrhich succeed the one carrying the poison
claws each bear a pair of seven-jointed running legs ending in
a pair of claws.
Near the base of some of the legs — not of all — in the soft skin
uniting the hard dorsal and ventral plates of chitin,
stmcture^ is an oval opening. This leads into a chamber from
which the tracheae pass off. These tubes divide and
subdivide into smaller tubes, which run all over the body and traverse
all the tissues, entering even the smallest cell. They are lined with
a cuticle of chitin and are kept from collapsing by the presence of a
fine spiral thickening of this cuticle which gives them a very charac-
teristic appearance when seen through a microscope. They are full
of air and constitute the respiratory apparatus of the Centipedes.
The existence of such a breathing apparatus, which is confined
to Peripatus, the M3nriapods, the Insects and certain of the
Arachnids, is associated with certain striking features in the in-
ternal anatomy of the body. In most animals the oxygen of the
air is taken up by the blood and carbon dioxide is given out at
certain fixed points called gills or lungs, and the vascular system is
arranged so as to drive the blood through these specialized respira-
tory organs. The blood takes the oxygen to the various tissues
and takes from them the carbon dioxide which is removed from the
body at the same centres. In the Tracheata however the air is
itself conveyed by means of the tracheae to all the cells of the body
and the gaseous exchange takes place on the spot. The blood has
in the Tracheata lost one of its chief functions, the respiratory one,
and exists chiefly as a nutritive fluid bathing the alimentary canal
and taking up from it the soluble food which it conveys to the other
tissues. It is kept in circulation by a contractile heart which lies
along the middle dorsal line of the animal. In Lithobius this heart
has a pair of ostia or openings in each segment, into which the
blood from the pericardium pours, only to be sent out of the heart
again at its anterior end into the general cavity of the body, for
here the heart has an opening and there is no system of smaller
vessels or capillaries.
One of the peculiarities associated with the above-mentioned
method of breathing is the nature of the excretory organs which rid the
166
AKTEMNATA.
[OHAP.
body of its nttrogenouB waste.
In Peripattts ne find more or
less tjpical nephridia and we
meet with mod ificationa of these
ID the coxal-glands of some
Arachuids, bat in the Myria-
poda and in the Insecta these
organs are wanting and their
place is taken by certain out-
growths from the proctodaeum,
called after iin Italian anatomist
Ualptghian tubules. In
iiitAobitis there arc two such
tubules, blind at their free end,
and at the other opening near
the hind end of the alimentary
canal (6, Fig, 83). Their walls
contain traces of uric acid
and urates which they have
taken np from the blood and
which they presumably excrete
through the alimentary canaL
The laBt-named organ is a
straight tube which runs from
one eud of the body to the
other. A pair of salivary glands
pour their secretion into it near
the mouth, but no other di-
gestive glands exist. Lithobius
is carnivorous, living chiefly
upon insects, their larvae and
on earthworms.
A large part of the spuce in
the head is occupied by the
bilobed brain which supplies
the antennae and the mouth
appendages. Tliis hrain is con-
nected by means of para-
ganglionated ventral cord which suppli
rest of the body (Fig. 83).
Myriapods are bisexual, the ovary and testis are continuous with
Fid. S3. Lithobitu JoTfieatu; diaaecled
to show intetasl org&nB x about 2.
Arier Togt and Tung.
I. AntflDDa. 3. Poison claw.
3. Salirary gland. 1. Wallcing legi^
5. Ventral uerre-cord. S. HbJ-
pigbiau tubule. 7. TMioula semin-
alis. 8. Small accesBory glaud.
9. Large accessory gland. 10. Un-
paired testis. 11. AlUnentarj canaL
commissures with & long
i nerves to the legs and the
VII.] MYRIAPODA* 167
tbeir dacts which open to the exterior on the ventral surface of the
last segment.
Order II. Diplopoda.
The second large subdivision of the Myriapoda is well ilhistrated
by the black " wire-worm," lultis terrestris, very commonly found in
Great Britain curled up under stones or burrowing in the soil, where
it is said to do much damage by gnawing the tender roots of
plants, for all Diplopods (Gr. 6(irAdo$, double) are vegetarians.
The wire-worm is a black, shiny cylindrical animal with an
enormous number of legs, in spite of which its movements are much
slower than are those of Lithobius. The terga or dorsal shields are
in this sub-group very much enlarged, whilst the sterna or ventral
shields are very much reduced, and thus it comes about that the
bases of each pair of legs, instead of being separated by the width
of the body, are close together. Another peculiarity in this sub-
division is that each tergum corresponds with two segments and
that each apparent segment bears two pairs of legs and has the
internal organs also duplicated. This double arrangement however
only begins at the fifth segment behind the head.
Pio. 84. lulua terrestrist Bometimes caUed the *' Wire- worm.*' From Koch
xabont 8^.
1. Antennae. 2. Eyes. 8. Legs. 4. Pores for the escape of the
excretion of the stink-glands.
The appendages on the head are : — (i) Short, usually clubbed-
shaped antennae; (ii) mandibles; (iii) a single pair of maxillae
fused into a lobed plate.
Both the first two segments behind the head bear but one pair
of legs, the third has no legs but carries the opening of the
generative ducts. The fourth free segment has one pair of legs, the
remainder two pairs.
The female lulus lays its eggs, some 60 to 100, in an earthen
receptacle she has prepared beneath the surface of the ground.
1 68 ANTENN ATA. [CHAP.
Sub-class C. Insecta
The immense group of Insects far outnumbers in species any
other group of animals and in all probability exceeds in number all
the species of the rest of the animal world. New insects are con-
stantly being discovered and although some quarter of a million
have already been named and to some extent described, it is
believed that at least as many more remain unrecorded.
In spite of these numbers Insects are as a whole a uniform
group and show less diversity in size and structure than many of
the smaller groups, as for instance the Crustacea or the Mollusca.
Probably their great number and small range of structural variation
is not unconnected with the fact that they have found a new
medium in which to pass some part, at any rate, of their life. The
other group of animals which have taken to flying and lead an
aerial life — the birds — show a somewhat similar range of species
accompanied by a uniformity of structure which in their case is
even more marked.
Insects may be characterized by their body being divided into
three distinct regions, the head, the thorax and
feiaurei"** the abdomeu (Fig. 85). The head bears one pair
of antennae and three pairs of gnathites. The
thorax consists of three enlarged segments, each of which bears
on the ventral surface a pair of legs and the two hindermost of
wliich bear on the dorsal surface a pair of wings. The abdomen
consists of a varying number of segments, ten being perhaps the
usual number but fewer often occur. The abdomen bears no
appendages except at the posterior end, where a pair of rod-like
outgrowths — the anal cerci — are often found.
Owing to the similarity of Insects to one another and their great
number the study of them has become a very special branch of
Zoology, which is termed Entomology. The necessity of ex-
tremely detailed study is due to the same cause and a great number
of technical terms are in use for describing the numerous structures
which build up the body of the Insect.
In this short book it will only be possible to indicate a few
points about the anatomy of Insects and we will take as a type the
common Cockroach because it is both a generalized form and not
too small for dissection.
The common Cockroach of the British kitchen is Stylopyga
arierUalis, but a larger form, Periplaneta americana, is often met
I. B, Sida view.
1. AnteDD*. 3. Palp oC HchI maxilla. 3. Protliorai. 4. Anledor
vingt. 6. Femnr of aecood leg. 6. Tibia. 7. Tusus. 6, Cerci
kDftlM. 9- Stflea.
1. Antenna. 2. Haul. S. Piothocai. 4. Anterior wing.
5. Soft skin between terga and Bterna. 6. Sixth abdominal teteum.
7. Bplit portion of tenth abdominal tergam. 8. Cerci analea. 9. States.
10. Coxa of third leg. 11. Trochanter. la. Femnr. 13. Tibia.
14. Tarans. IG. Claws.
170 ANTENNATA, [CHAP.
with on ships and from them makes its way to the docks ; it is also
often found in zoological gardens, etc. PhyUodromia germanica,
a small species, is becoming increasingly common in England.
The whole body of the Cockroach is covered by a chitinous
covering which varies in thickness, from the black hard head to the
thin whitish areas which exist at the joints and which permit
movement of the harder parts on one another. Except in the
head the segments of the body can be detected externally, and, as
in other members of the Arthropoda, the segmentation affects some
only of the internal structures, such as the heart, the tracheae, the
muscles and the nervous system, the other organs of the body not
being influenced by it.
The head of a Cockroach is a flattened structure placed at right
angles to the axis of the body. It is oval in outline, its upper edge
being considerably broader than the lower. It is loosely jointed to
the thorax by a neck which permits considerable movement (Fig.
85). This neck enters the head near its upper edge and below it
the head hangs free. On the upper and outer edge of the head are
a pair of kidney-shaped, facetted eyes of a shining black colour, on
the inner curve of which the antennae or feelers have their origin.
These are long whip structures, often as long or longer than the
body ; they are made up of many joints and during life are in
active movement, now stretched downward as if trying the ground
on which the creature moves and now waving aloft as if testing
the air.
The mouth is on the lower edge of the head and is covered in
front by a small moveable flap called the labrum or upper lip.
At the sides it is protected by the first and the second pairs of
appendages, and behind the fusion of the right and left third pair
it forms a plate called the labium, which completes the boundaries
of the mouth behind (Fig. 86).
If the first pair of mouth-appendages or mandibles be removed
from the head and examined through a lens, each is
.pp.°„"iS,... seen to be a single-jointed stont jaw with a toothed
inner edge which bites against the corresponding part
of its fellow. It is characteristic of the mandibles of all Antennata
to have no palp or remnant of the distal joints of the limb, such as
is almost universally present in Crustacea.
Behind the mandibles and like them situated on each side of
the mouth, are the first maxillae. Each consists of a number of
joints and each joint has a special name. Like the typical
VII.] INSECT A. 171
gnathite of other Arthropods we may regard them as consisting
of a limb-like appendage with out-growths from the basal joints
biting against corresponding processes — gnathobases — of the
fellow appendage. There are two of these gnathobases, the hard
pointed lacinia and an outer portion, the softer galea (B, Fig. 86).
The lowest joints form an L-shaped hinge which, when opened out,
protrudes the jaw. The outer portion of the first maxilla is many-
jointed and is sensory in function, constantly touching and testing
the ground as the animal moves about. It is called the maxil-
lary palp.
The second maxillae are united across the median line and thus
constitute a fold or plate called the labium, which bounds the
ABC
Fio. 86. Mouth-appendages of Stylopyga. Magnified.
A. Mandible. B. Ist maxilla. 1. Cardo. 2. Stipes. 3. Lacinia.
4. Galea. 6. Palp. C. Bight and left 2nd maxillae fused to form
the labium. 1. Submentnm. 2. Mentum. 3. Lignla, corresponding
to the lacinia. 4. Paraglossa, corresponding to the galea. 5. Palp.
mouth behind as the labrum bounds it in front (G, Fig. 86). Each
half may be resolved into elements similar to those of the first
maxillae, the fused basal joints of the pair of appendages form the
mentum and sub-mentum, the galea being represented by the
paraglossa, whilst the inner gnathobase corresponds with the
lacinia and is termed the ligula. As in the case of the first
maxilla the outer joints of the appendage which have a tactile
frmction are termed the labial palp.
The thorax is built up of three segments, the pro-, meso- and
meta- thorax. The skeleton of each segment con-
sists of a dorsal hard piece, the tergum, united
with a ccmesponding ventral piece, the sternum, by a soft in-
172 ANTENNATA. [CHAP.
tervening pleural membrane. The tergam of the first thoracic
segment is clearly visible, but the meso- and meta-terga are
concealed by the wings. The two pairs of wings are formed by
folds of the skin arising from the terga of the meso- and meta-
thorax respectively, and in a state of rest conceal the dorsal surface
of the animal behind the prothorax. The front pair are termed
elytra ; they are hard and horny, one overlaps the other, and they
probably serve more as protectors to the delicate hind wings than
as organs of flight. The posterior wings are thin and membranous
and are of greater area than the elytra, and they constitute the
effective organs in the rare flight of the CockroacL At rest they
are folded like a fan and concealed by the elytra. In Stylopyga
orientalis the wings — as is not uncommon amongst Insects — are
rudimentary in the female.
The ventral plate or sternum of each thoracic segment bears a
pair of legs by means of which the Cockroach scuttles rapidly about.
Each leg consists of a number of joints, viz., a thick flat coxa
applied to and articulating with the sternum ; a minute triangular
joint, the trochanter; a stout joint called the femur; a more
slender one termed the tibia, armed with spines ; then a piece con-
sisting of five short joints called the tarsus, with a whitish hairy
patch under each joint which acts as a sole ; and finally a pair of
terminal claws (Fig. 85). These names, as is too often the case in
Zoology, were suggested by fanciful and misleading comparisons
with the parts of the limb of a vertebrate.
The abdomen consists of ten segments and here the terga and
sterna can be easily seen as they are not obscured by
the insertion of the wings and legs. The eighth and
ninth terga are however both tucked under the seventh and are not
readily seen until the animal is artificially stretched. The tergum
of the tenth or last segment stands out from the hind end of the
animal and is cleft into two lobes. The sterna are equally distinct
but the first is small The abdomen is broader in the female than
in the male, and the seventh sternum is shaped like the bow of a
boat and projects backwards, hiding the posterior sterna and sup-
porting the lower surface of a roomy pouch or cavity in which the
egg-case is formed. In the male the seventh sternum conceals the
eighth and ninth.
The stigmata leading to the tracheae are placed in the soft
pleural membrane connecting terga and sterna.
The abdomen is usually regarded as being without appendages^
VIL] INSECTA. 173
but a pair of jointed cerci anales emerge below the edge of the
tenth tergum in each sex, and in the male the ninth sternum bears
a pair of anal styles. The claim of these structures to be
reckoned as appendages of the same rank as the antennae, the
gnathites and the legs, was at one time not generally conceded,
but appears to be now fairly established for the cerci anales.
In the soft tissue between the tenth tergum and the last visible
sternum, at the hind end of the body, is placed the anus, below
it the single genital pore is situated. The anus is supported by
certain thickened plates in the skin, known as podical plates,
and around the genital orifices are arranged certain rods and bars,
symmetrical in the female but asymmetrical in the male, whose
functions and meaning are obscure, but which are connected with
the processes of copulation and of egg-laying. As we have seen,
this region is in the female enlarged into a genital sac by the
growth and modification of the seventh sternum and the tucking
into the space so formed of the skin carrjdng the eighth and ninth
sterna. The opening of the oviduct is on the eighth sternum and
on the ninth is the single opening of the receptaculum seminis or
spermatheca, which consists of two pouches of unequal size composed
of intumed ectoderm : these are always found full of spermatozoa
in the fertilized female. The spermatozoa apparently leave the
spermathecae when the eggs are being laid and fertilize the ova
whilst they are in the genital sac. Two glands, consisting of
branching tubes, — called colleterial glands — open separately
behind the spermatheca. They secrete a fluid which hardens to
form the egg-capsule in which the eggs are laid. This is moulded
in the genital sac and may often be seen half-protruding between
the distended seventh sternum of the mature female.
When the skin is removed from the dorsal surface of the Cock-
roach the cavity laid open is not a coelom but a
structure! haemocool, and it is largely filled by a loose white
tissue, known as the fat-body, which surrounds the
various internal organs. If the alimentary canal be disentangled
from this it is at once evident that in Insects, unlike other Arthro-
pods, the intestine is longer than the body and the larger portion
of it which lies in the abdomen is coiled in order to stow it away.
Like the digestive tube of other Arthropods a large part of its length
consists of the stomodaeum and proctodaeum. The former consists
of an oesophagus which quickly passes into a large crop in which
the food is stored for a time. The lining of both these regions
174 antennatjL [chap.
bears haira and the muscles in their walla are striped. The crop
is followed by a gizz&rA, which bears intenially six hard chitinotu
teeth, and behind them are fine hairs which act as straiDeis, so
that only finely divided food can pass on into the meeenteron or
chylific ventricle, as the part of tho alimentary canal ie called
which alone is lined by endoderm and is capable of absorbing
noarishment. This tabe is produced in front into seven or eight
Fio.'.ST. A Female Cookroaah, Stylopyga, with the doraal exoakeletoo removed
ftnU diasected to show the viscera. Magnified about 2.
1. Head. 2. Labmm. 3. Anlenna cat short. 4. E;e. 6. Crop.
6. Nervous system of crop. 7. Gizzard. 8. Hepatic caeca. 9. Mid-gut
or mesenteroQ. 10. Malpigfaian tubules. II. Colon. 13. Bectum.
13. Salivary glands. 14. Salivary receptacle. 15. Brain.
16. Ventral nerve-cord with ganglia. 17. Ovary. 18. Spermatheca.
19. Oviduct. 20. Genital pouch in which the egg..coooon is found.
21. Colleteriul glands. 22. Anal cercus.
pouches, the so-called hepatic diverticula. The mesenteron, the
limit of which ia marked by the insertion of the Malpighian tubules,
is succeeded by the intestine or proctodaeum, a long coiled tube
which enlarges posteriorly and opens by the anus. The enlarged
portion is called the rectum (Fig, 87), the anterior coiled [Kirtioii
the colon.
Vn.] INSECTA. 175
Lying along the crop on each side is a pair of branched glands
— the salivary glands — and a bladder termed the salivary
reservoir. All three are provided with long ducts. Those of the
two glands on each side unite to form a single tube which then
receives the duct of the reservoir, and the common ducts of the two
sides open behind the mouth but in front of the second maxillae.
The saliva converts starch into sugar. The secretion of the hepatic
diverticula emulsifies fats and turns insoluble proteids into the
soluble forms (peptones). This secretion seems to pass forward into
the crop and there true digestion is effected. The digested and
dissolved food then passes through the filter of the gizzard into the
mesenteron, where absorption of the nutritious parts is effected, the
undigested portions passing on to the intestine and so out of the
body. The cells of the mesenteron undoubtedly exert some action
on the products they absorb, though we are ignorant of its precise
nature, but in the end they pass on the products of digestion — altered
no doubt — to the blood which everywhere bathes the alimentary
canal, and by it the new material is conveyed all over the body.
The blood is kept in circulation by the heart which lies in the
middle dorsal line close under the skin ; in fact it can be seen
through the skin in the region of the abdomen. It is a long vessel
made up of thirteen chambers corresponding with the three thoracic
and ten abdominal segments, each chamber opening into the one in
front and the whole somewhat resembling a row of funnels fitted one
into another. At the broader hinder end of each chamber is a pair
of ostia or holes through which the blood enters from the peri-
cardium, and there are valves which prevent the blood being forced
out of the ostia or forced backward when the heart contracts, so
that its only course is to flow forward. The pericardium is separated
from the rest of the haemocoel by the pericardial septum, in which
however there are certain holes which permit an interchange of con-
tents between the two cavities. When at rest the pericardial septum
is arched upwards, but it is pulled outwards and flattened by the
periodic contraction of certain muscles attached to its sides called
the alary muscles, thus enlarging the pericardium and causing an
inflow of blood into it from the rest of the haemocoel. This blood
enters the heart when it is relaxed and the ostia are open, and hence
by the alternate contractions of the alary muscles and the muscular
wall of the heart the circulation is maintained.
The anterior end of the heart, called the aorta, opens by a
trumpet-shaped orifice into the haemocoel and the blood pours out
176 ANTENNATA. [CHAP.
of this and bathes all the organs of the body. It thus takes np the
soluble food which has left the alimentary canal and conyejrs it to
those parts of the body where it is needed, and in a similar way it
yields up its superfluous fat to be stored up in the fat bodies and
gives up its waste nitrogenous materials to the Malpighian tubules,
whence they are passed out of the body. It is noticeable that just
as water-plants are as a rule not of a compact shape, but finely
subdivided so as to expose as large a surface as possible to the
surrounding medium, so in the body of the Cockroach the various
organs are long, tubular or diffuse structures offering a large
surface to the nourishing and purifying blood.
The heart contracts almost as frequently as the normal human
heart, Le., about seventy-two times a minute when the Cockroachi is
at rest, but at other times its rate of contracting varies a good deal
The blood is colourless and contains amoeboid corpuscles. It is
slightly alkaline.
It is obvious from the above account that in the Cockroach the
blood is mainly a means of conveying nutriment to the organs and
taking certain waste matter from them, and that unlike what is
usual in other animals, its respiratory function is at a minimum.
Owing to the nature of the tracheae, the air with its oxygen is
taken directly to each organ, almost to each cell, without the
intervention of the blood.
The tracheal system opens to the outer air by ten pairs of oval
pores or stigmata. These lie in the soft integument between the
terga and sterna, one pair just in frx>nt of the mesothorax, one
pair just before the metathorax and eight pairs just in trout of
each of the first eight abdominal segments, so that they seem to be
intersegmental in position. These openings lead into tubes or
tracheae which soon bifurcate and divide. The larger branches
have a definite and symmetrical arrangement. There are dorsal
arches running up towards the heart and ventral arches descending
towards the nerve-cord. These arches are connected with one
another longitudinally by trunks which run on each side of the
pericardium and the nerve-cord. Large trunks also are given
off to the alimentary canal. It follows that should one stigma
become blocked the organs which its tracheae supply are still
provided with air. The finer branches become smaller and smaller
until they become veritable capillaries which penetrate every tissue.
The tracheae being full of air present a glistening silvery
appearance which is unmistakeable. They are prevented from
vil] insecta. 177
collapsing by the presence of a spiral thickening of the chitinous lining
which runs round the interior of the tube just as the wire spiral
strengthens the india-rubber tube of some kinds of garden hose.
Respiration is elTected by the alternate arching up and flattening of
the abdomen, resulting in an alternate increase and diminution of
its volume, which, since the blood is incompressible, secures an
alternate inrush and expulsion of air from the tracheae. In all
probability only the contents of the larger tracheae are affected by
this process ; by diffusion the oxygen from this ** tidal air '' is handed
on to the finer tracheae.
In Insects the tracheal mode of respiration reaches its highest
development and it is accompanied by a correlative diminution and
simplification of the circulatory apparatus, the oxygen of the air
being conveyed directly to and the carbon dioxide removed directly
ttom the cells to the outer air, whilst the blood loses its respiratory
function. It is doubtful how far this state of things is connected
with the peculiar disappearance of the coelom — which presumably
exists only in the cavity of the reproductive organs — because a
similar replacement of the coelom by a haemocoel is found in
Crustacea and Mollusca, where the blood is respiratory and the gills
are compact and active organs ; but probably it is correlated vdth
the modification which the excretory system undergoes and this
again is undoubtedly influenced by the state of the body-cavity.
Peripatus, the most primitive Arthropod, has typical nephridia,
each of which opens internally, not into a general coelom, but into
a small sac which is really a special part of the coelom not com-
municating with any other coelomic space but belonging only to
the nephridium which opens into it. The main body-cavity is a
haemocoel Mollusca also retain a pair of typical nephridia or in the
case of NaiUilus two pairs. These organs open into special coelomic
spaces which are as a rule small, the more spacious cavities of the
body being haemocoelic. Crustacea probably retain nephridia, those
of the fourth segment — shell glands — being persistent in the En-
tomostraca, whilst those of the second segment — green glands —
persist in the Malacostraca. It is not absolutely proved but it
seems probable that the inner ends of these glands represent
coelomic spaces. But even amongst Crustacea, in certain Amphipods
for instance, we find the transference of the function of the nephridia
to outgro?rth8 of the alimentary canal. In Arachnids the nephridia
or coxal-glands show very varying degrees of development, but on the
whole they are tending to die out and to be replaced by Malpighian
a. AM. \^
178 ANTENNATA. [CHAP.
tubules or diverticula of the intestine. Finally in Mjrriapods and
Insects, where the true coelom is reduced to its minimum and
where the tracheal mode of respiration attains a very high degree of
development, all traces of nephridia have disappeared and the waste
nitrogenous matter is excreted solely by the Malpighian tubules.
These are very fine long caecal diverticula, — so fine as to be but
just visible to the unaided eye,— 60 — 80 in number, arranged in six
bundles which open into the beginning of the narrow part of the
proctodaeum from which they are outgrowths. They float in the
blood, winding about amongst the abdominal viscera (Fig. 87).
They contain crystals, probably of urate of soda, which are taken up
from the blood and which leave the body through the intestine.
The nervous system of the Cockroach is constructed on the same
plan as that of the other segmented Invertebrates with which we have
had to do. There is a large supra-oesophageal ganglion or brain
giving off commissures, which encircle the oesophagus and unite
below in a sub-oesophageal ganglion. Together these occupy a
considerable portion of the cavity of the head. The supra-oeso-
phageal ganglion supplies paired nerves to the eyes and to . the
antennae and is thus the sensory centre. The sub-oesophageal
ganglion supplies the mandibles and both pairs of maxillae. From
it two cords pass backward and bear three pairs of ganglia in the
thorax and six in the abdomen. This difference between the number
of nerve ganglia and the number of segments is carried to a much
greater extent in some Insects where, as in Spiders, all the post-
oesophageal ganglia tend to fuse into a common nervous mass in
the thorax (Fig. 58).
The only specialized sense organs are the eyes and the antennae.
The eyes have fundamentally the same structure as those of the
Crustacea : the antennae are the seat of the senses of smell and
taste, and are in addition very delicate tactile organs. The
maxillary palps are also tactile and are constantly touching and
testing the ground on which the Cockroach is moving.
Cockroaches are bisexual. The ovaries in the female consist of
two sets of eight tubes, each of which has developed
from a coelomic sac in the embryo. They unite at
their anterior end into two cords which pass to the dorsal wall of the
thorax and become attached to the pericardial septum, and at their
posterior end they fuse into two short oviducts which join to form a
small uterus (Fig. 87). Each of the sixteen tubes contains cells,
some of which become ova, and as they approach the oviduct the ova
I'Tn.i
INSBOTA,
betMine arranged in a single row. At the same time they increase
greatly in size by the deposition of yolk in the egg, ho that an oviun
just before it leaves the body is of considerable size.
The eggs are apparently fertilized after leaving the uterus by
spermatozoa which emerge from the spermatheca (in which they
have been deposited by t)ie male) situated behind the opening of
the utcni.s. Whilst still in the genital pouch the fertilized eggs
are surrounded by the secretion of the coUeteria! glands which
o]>en behind the spermatheca, and this secretion hardens into the
egg-capsule or cocoon.
The paired testes of the male are functional only during youth
»nd as they diminish in size after they cease to function, they aro
only to be found with difficulty. They he concealed by the fat body
below the terga in the region of the fourth, fifth and sixth aMominal
eegmciits. They look somewhat like elongated bunches of cherries,
their translucent colour strongly contrasting with the opaque
white of the fat body. Two vasa defereutia lead from the testes to
B pair of large reuervoira colled vesiculae semiuaies, which together
form the "mushroom-shaped gland." Iiit() these at an early age
the cells destined to form spermatozoa pass Irum the testes and
there they undei^o their further development. The mushroom-
shaped gland opens to the exterior by means of a short muscular
tube, the ductus ejaculatorius, which has its orifice jnat below the
-anus. The name of the glaud is derived from its form ; it has a
tliick stalk surrounded by a crown of branches. Fertilization and
ovipositioii take place during the summer.
Sixteen eggs are laid in eai^h egg-capsule, and for some seven
or eight days, until the mother finds sumo warm aud secluded
hiding-place to deposit her load, she carries about the capsule half-
protruding from the genital pouch. When the embryos in the eggs
art! fiilly formed, which takes about twelve months, it is said that
they secrete some fluid, probably saliva, which dissolves the upper
^rt of the capsule and so permits of their escape. In Phyllodromia
ggrmaiiirn the mother is said to take a part in freeing her oflspring
from their temporary imprisonment. When they first appear they
are while with dark eyes, but the integument soon thickens and
darkens. They have no wings, but in other respects they resemble
their parents and thus there is no metamorpliusis such as occurs in
the Butterflies and many other Insects. They run actively about,
devouring any starchy food they can find, and when in time they
{[row too large for their coat of mail it splits and a soft Cockroach
180 ANTENNATA. [CHAP.
extricates itself therefrom. The integument soon hardens again.
This casting of the sldn or ecdysis takes place seven times, and after
the seventh moult, when the insect is four years old, it is adult
The Insects are usually subdivided into eight Orders, which
are mainly based (i) on the structure of the gnathites ; (ii) on the
nature of the wings ; (iii) on the amount of Metamorphosis which
the life-history of the Insect presents. A short account of each of
the criteria is therefore subjoined.
The Mouth' Parts {Gnathites) of Insects.
The mouth-parts of Insects can in almost all cases be resolved
into a pair of mandibles which never bear palps and two pairs of
maxillae which are usually provided with palps. In the diflferent
orders of Insects and in different members of the orders these
mouth-appendages show many modifications and are put to a veiy
great variety of uses. One or other part may be suppressed and
disappear, others may coalesce, as is the case with the right and left
second maxillae of the Cockroach, but as a rule traces of all the
gnathites may be found though often much altered. The mouth-
parts of insects have been grouped as follows : (i) Biting, This kind
of mouth is found in the Aptera, the Orthoptera, the Neuro-
ptera and the Coleoptera (v. below), in which orders there is as a
rule no very great difficulty in recognizing the various parts which
have been described in the Cockroach. As an example of the great
variety presented by the mandible, those of the male Stag-beetle,
Lucanus cervus, may be mentioned. In this animal the mandibles
may equal in length the whole of the rest of the body, (ii) Suckino,
This kind of mouth is found in the Lepidoptera or Butterflies.
Here the mandibles are rudimentary, but the gnathobases of the
first maxUlae are much elongated and frequently coiled into what is
sometimes termed the proboscis. Each half is grooved and so
applied to the other as to form a tube, and in some cases the two
halves of the tube are locked together by minute hooks. The palp
of this maxilla is absent or rudimentary. The labium composed of
the second maxilla is an important structure in the larva or
caterpillar, as it forms the spinnerets through which the silk of
the cocoons is excreted, but in the adult it is practically absent
although its palps persist as large hairy structures. The hollow
tube formed by the maxillae is well adapted to suck up the fluids
on which the Lepidoptera live. The suction is performed by a
VII.] INSECTA. 181
X)owerful muscular sac called the suctorial-stomach, which is a
lateral outgrowth of the oesophagus and communicates with it.
(iii) Piercing and Sucking, The Diptera or Flies possess both
sacking and piercing organs, which are as a rule somewhat unequally
developed. The basal portion of the labium or second maxilla is
much elongated and takes the form of a fleshy protuberance which
to some extent ensheaths the other parts. In the house-fly,
Musea domestica, the piercing organs are fused to the labium and
act only as supporting rods for it, but in the Gnat or Mosquito
they are iree and reach a high degree of development. These parts
are overlaid by a somewhat enlarged labrum and between this and
within the grooved labium the pointed stylets lie. Amongst these
a sharp style called the hypopharynx situated behind the mouth
may be distinguished. Two pairs of lateral stylets, identified by
some as the modified mandibles and first maxillae, also exist and
the maxillary palp acts as a sensory organ. The Hemiptera or Bugs
have a very similar set of gnathites in correspondence with their
habit of boring into animals or plants to feed on their juices.
In this Order the mouth-parts when not in use are bent under the
body and lie along the under surface of the thorax. The labium
is jointed and its edges are curved so as to form an incomplete tube,
only the base of which is partly covered by the labrum. Within
this groove four sharply pointed styles — the mandibles and first
maxillae — work. They are as a rule finely toothed like little saws
and are well adapted for piercing the skin. There are no palps,
(iv) Biting and Sucking, The Hymenoptera or Bees and Wasps
have mandibles not unlike those of a Cockroach and use them for
biting and moulding their food of pollen and the wax they secrete
from their bodies. The laciniae of the maxillae form blade-like
structures and their palps have much diminished in size. The labial
palps however are large, and the conjoined median outgrowths from
the labium (corresponding to the ligula of the Cockroach, 3, Fig.
86 c) form a kind of grooved tongue along which the nectar in the
flowers is sucked up.
It thus appears that although the mouth-parts of Insects are
highly modified in connexion with the kind of food they live on and
the modes in which they obtain it, nevertheless the various mouth-
parts have a common ground plan, and although the authorities
differ as to details a fundamental similarity runs through these
appendages in the different Orders.
ANTENNATA.
IVingt Q/' IiniiKls.
1
The wingB of Insects are folds of the integanient, ftfttteiied
HO that r.lie two sides are iu coutuct oq their inneT surfaces. At
certain places however »1its are left and throagh these tracheae
pass taking air to the wings. The ectoderm of both upper and
Flo. H8. Pach<ilj/tui
r. A OtaBsUopper.
under layers is also thickened along certain lines and the prepuce
of these thickenings divides the wing up into a number of areas.
These lines are nsintlly called wing-reins or win(r-nerves, but as
they are neither veins nor nerves it is better to call them nervures.
The presence and disposition of the nervures is of the highest
Vn.] . INSECT A. 183
importance in classification. Wings may be thin, membranous, and
transparent, as in the Grasshopper (Fig. 88) or Dragon-fly (Fig. 50),
where there is an enormous number of nervures, or in the Flies
and Bees, where there are few nervures, or they may be thickened
and strongly chitinised as in the front wings of Beetles. In this
last group the anterior wings are called elytra (6r. cXvrpov, a cover)
and they always meet together in a median longitudinal line,
80 that when they are closed the insect appears to be wingless
(Fig. 92) : in some few cases they have fused together so that the
posterior or flying wings are rendered useless. In one great
division of the Hemiptera one half of the anterior wing is horny
and strongly chitinous, the other and posterior half membranous.
In the Cockroach, as we have seen, the anterior wings tend to
become homy and are of little use in flight (Fig. 85). The posterior
wings of the same insect when at rest are folded together something
like the leaves of a shut fan and many species in several of the
orders fold up their hind wings when not in use. The tucking
away of these wings under the small elytra is a complicated affair
in some Insects such as the Earwig, where the nippers at the end
of the body are said to aid in the process. Many Insects however,
such as the Dragon-flies, Plant-lice, Butterflies and Moths, Flies
and Bees and numerous others, do not fold up their wings but either
bear them erect or lying depressed on the body. In some cases the
wings are quite transparent, but in the Moths and Butterflies they
are covered with a dense fur of flattened scales which can readily
be brushed off as a fine powder oi dust (Fig. 91). It is these scales
which give rise to the beautiful and in some cases gorgeous colouring
of the Lepidoptera.
Two pairs of wings are present as a rule, but the order Diptera
has only the anterior pair, the hind wings being replaced by certain
stalked structures called balancers or hal teres. In the Hymeno-
ptera, the two wings of each side are clamped together by means of
hooks on the hind wing which fit into a ridge on the hinder edge
of the front wings (Figs. 93, 94, and 95). The two wings of each
side thus move as one. It is not uncommon to find isolated
species in which the wings are not developed, for instance, the
females of many Plant-lice and some Moths ; while Fleas, which
are sometimes placed amongst or near the Order Diptera, never
possess wings, though their absence is compensated for by a special
development of the powers of jumping.
184
ANTENNATA.
[chap.
Metamorphosis,
A very large number of animals that live in the water, whether
in the sea or fresh water, hatch out from the egg in a lanral condi-
tion. That is to say, the being which leaves the egg is veiy
unlike the adult in structure and habits, but by growth and a series
of accompanying changes in time passes over into the adult which
is capable of reproducing. These changes constitute the meta-
morphosis. In the life-history of land animals such lanral stages
are rare and indeed hardly exist outside the Insecta and the
Amphibia. As we have seen, the egg of a Cockroach gives rise to a
young Cockroach which differs but little from the adult and gradu-
ally grows into it by a series of small changes, but which never at
any time undergoes a long period of profound rest. But if we con-
sider the case of a Moth or Butterfly we shall find that the egg does
not give rise to an animal resembling a minute Butterfly but to a
worm>like larva or caterpillar, which has no wings and in other
respects is very unlike the Insect which produced the egg. This
caterpillar as a rule eats voraciously and grows rapidly with little
change in form until its fourth ecdysis, when a sadden change
occurs, and the so-called pupal stage supervenes. In this stage
with a few exceptions the animal now called a pupa (Lat. pupa, a
puppet) is motionless and ceases to feed. It may be uncovered and
protected only by the hard-
ened integument or it may
be enclosed in a casing or
cocoon. In the case of
the Silkworm Moth and
some others, this is con-
structed of silk. During
the pupal stage, the ani-
mal undergoes a profound
change, many of its organs
and tissues being broken
up and new ones con-
structed. When this process is completed the pupa casts its skin,
makes its way out of the cocoon and emerges as an imago (Lat.
imago, an image) or perfect insect.
The various orders of Insecta diff^er in the degree to which meta-
morphosis occurs. In the Aptera there is no metamorphosis and
the development is said to be direct. In Orthoptera and Hemi-
Fio. 89. Larva of Bomhyx mori, the Silk-
worm. Life size.
itera there is no quiescent pupa stnge and the chief difference
the larva aad adult is the absence of wings. Here the
metamorphosiB ia said to be incomplete. The
is true of most of the Neuropt«ra. a
Tery varied assembly of Insects, in some forma
pf which however, e.g. the Caddis-flies, a pupal
eatists. Amongst the Lepidoptera, Coleo-
ptera. Hymenoptera and Diptera there is a, well-
Biarked pupal stage, and these orders are said
to have omplete metamorphosis. Various names
have been given to the larvae of Insects without
Tery precise definitions. Those of the Lepido-
ptcra are usually called Caterpillars, They are
often gaudily coloured and bear tufta and
lionches of hair. Besides the three pairs of legs
which are found on the three segments following
the head and which correspond with the legs of
the imago, certain of tlie alidominal segments bear fleshy stumps
called abdominal legs. The larvae of some of the l^aw-flies (Hymeno-
ptera) have a similar bright colouring and resemble Caterpillars, and
like them feed exposed on leaves, etc. Tiie larvae of Beetles and
Jnost Hymeuoptera are aa a rule hidden underground or in galls
wax-comb. They are whitish in colour and unattractive, and
Fig. 90. Cocoon of
Bombt/T auiri, from
wbicb siltc is span.
About Ute BiKB.
Pio. 91. Si!k-worm motli. Iinmhy.r mori.
A. Feanle. B, Male.
are often termed gruba, whilst the footless white larvae of the
Diptfira, which are for the most part deposited in some organic
hilntVLce — whether alive or not — are usually called maggots.
In the following account of Insect Classification we can only
indicate the chief charat'ters of each Order and mention the names
of one or two common members of each.
186 ANTENNATA. [cHAP.
Order I. Aptera.
Wingless Insects, with scales and hairs coyering the body.
The mouth-parts are adapted for biting. They move by running or
by springing by aid of a caudal style which is kept bent forwards
under the abdomen and retained in this position by a yentral hook.
When released from this hook the recoil of this style hurls the
insect into the air. The segments of the thorax are not fused
together and there is no metamorphosis.
Not all wingless Insects belong to this Order. The name
Aptera (Or. airrcpos, wingless) refers to the belief that the ancestors
of these Insects never had wings and that thus they represent a
lower stage of evolution than the rest of the sub-class.
For the most part the Aptera are minute Insects living in
retired spots under leaves or rubbish, in root-gutters, etc., but
they are widely distributed over the world. One of the best known
is the Silver-fish, Lepisma, which hides in disused cupboards, old
chests of drawers, sugar barrels, etc. It runs with great rapidity.
Order 11. Orthoptera.
The Orthoptera (Gr. 6p66^, straight ; TrrcpoV, a wing) have mouth-
parts adapted for biting. The anterior wings are as a rule stiff,
and when the Insect is at rest one overlaps the other, and both
usually cover and conceal the large membranous hinder wings with
which the creature flies. There is an incomplete metamorphosis,
the young being at first without wings.
This Order is a very varied one and doubts exist as to whether
it is a natural one. It includes the Cockroach, whose anatomy has
already been described ; the Earwig, Forfictda ; the Mantis ; the
leaf and stick insects, Phyllium and Phasma ; the Grasshopper
(Fig. 88), Acridium, Pachytylus ; the Locust, Locusta ; the Cricket,
Gryllus \ and many others.
Order III. Neuroptera.
The Neuroptera (6r. vtvpovy a tendon and hence a nervure) have
biting mouth-parts. Both pairs of wings are membranous and used
in flight, and the '' veins " of the wings form a more or less close
network. Metamorphosis complete or incomplete.
This Order, like the preceding, contains many families which,
except as regards the structure of the wings, have little resemblance
to one another. The following are a few of the more widely known
VII.]
INSECTA.
187
species: the White-ant, Termes; the May-fly, Ephemera', the
Dragon-fly, Libettula or Aeschna (Fig. 50) ; the Ant-lion, Myrmeleo ;
the Aphis-lion, Hemerobius ; the Caddis-fly, Phryganea, which in
some respects approaches the Lepidoptera ; and the Thrips, an insect
which injures com crops and certain flowers and is sometimes
elevated to the position of a distinct Order.
Order IV. Coleoptera.
The Coleoptera (Gk. koXco?, a sheath) have mouth-parts adapted
for biting. The anterior wings are hard and homy and fit together
in the middle line with a straight suture. The hind wings are
membranous and folded. The metamorphosis is complete, that is,
there is an active larval stage (Fig. 92), followed by a quiescent
stage during which extensive changes in the internal anatomy take
place.
Unlike the preceding, this order is clearly defined and its
members are on the whole very like one another. It has always
been a favourite order with Ento-
mologists and the number of species
named and described is far greater
than in any other Order. It in-
cludes all the Beetles. For the
most part these Insects are dull in
colour but their firm exoskeleton
gives them a very definite outline
and renders their preservation and
identification comparatively easy,
which may to some extent account for their popularity with
collectors.
Order V. Hymenoptera.
The Hymenoptera (6r. vftcio-nrcpos, membrane-winged) have
mouth-parts adapted for biting and sucking. The ligula of
the labium is long and grooved, whilst the paraglossae are smaU.
Fio. 92. In the centre Coccinella
septempunctata, the Lady-bird
X about 2^, with the larva to the
left X about 2^, and the adult
beetle, natural size, to the right.
3 1
Fio. 98. Formica rufa, the Wood-ant.
1. Female. 2. Male. 3. Neuter.
The mandibles are well-dereloped and the l&ciDi&e of tl
maxillae large. The four wings are alike, membraDoua in t
and the liiad wingH are hooked od to the anterior in siu
way that the two wings of each side move together. They differ
from the wings of the Neuroptera in possessing fewer veins. The
metamorphosis is complete,
This group comprises the Ants, Bees and Wasps. Many of
them live in highly complex vommunities and in their social habtte
and general intelligence they reach a level which is only surpassed
by man himself. The group iucladea the Wood-wasp, Sirv^ ;
assed
; the J
FiK. 05. Politttt (epidtu unci nest.
Saw-fly, Tenthredo; the Gall-fly, Ci/nips; the Ichneumon; the
Ant, Formica ; the Wasp and Hornet, Vfspa ; the Humble-bqa,
liombus ; and the Honey-bee, Apig.
Order VI. Hemiptera.
j-bfl^
The Hemiptera (Gr. ijfu, half) have mouth-part^ arranged for
piercing and auckiug. The basal part of the labium is elongated
VII.] INSECTA. 189
and tubular and the mandible and first maziUa form sharp pointed
stales. The two pairs of vings may be alike or may differ and
the ant6ri(n' pair are is some cases half homy and half membranous.
The metamorphosis is incomplete, there being no quiescent stage.
The membera of Una Order present very great divergence both
of fonn and of size ; they are colloquially known as Bugs and Lice.
Amongst the commoner forms are the Water-boatman, Notonecta ;
the Water-scorpion, N^epa ; the Bed-bng, Acanthia ; the Cicada,
remarkable for its chirping noiae ; the Frog-hoppers, including the
Cuckoo-spit, Apkrophora ; the Plant-louse, Aphis ; the Phylloxera,
which destroys vines ; Scale Insects and lice.
Order VII. Diptera.
The Diptera (Or. Sfnr^pa, two -winged) have mouth-parts
arranged for piercing and sucking. The only difference in this
respect from the Hemiptera consists in the
fact that the sucking tube is partly formed
by the labrum and that the first maxillae
retain palps. Only one pair of wings, the
anterior, are present; the posterior are re-
presented by a pair of short knobs called
baUncers or halteree (Fig. 97). The meta-
morphoeis is complete.
The Diptera or Plies form one of the
largest of the Insect Orders, probably as
large as the Coleoptera, although at present
the nimiber of species of Beetles
named and described is far greater
than that of Flies. Amongst the
commoner genera are the Gnats and
Mosquitoes, Culex ; the Daddy-
long-legs, Tipala; the Gall-fly,
Ceeidomyia (Fig. 97); the Horse-
fly, Ta&anus ; the Bot-fly, Oestrus ;
the common House-By and Blue-
bottle, Mutca, and many othera.
The Flea, PaJex irritans, which is
wingless but endowed with con-
siderable powers of jumping, is
sometimes placed in a Sub-order nf
the Diptera and sometimes in a separate Order.
». 97. Cteidomyia dettructor,
the Heasian.fly.
Insect. 2. Larva. 3. Pnpa,
ir "flax seed." All magDified.
190 ARACHNIDA. [CHAP.
Order VIII. Lepidoptera.
The Lepidoptera (Gk. Xcttis, a scale, '7rT€p6v, a wing) have mouth-
parts adapted for suckiog only. The two pairs of wings are similar
in appearance and covered with scales (flattened spines) which give
rise to the beautiful pattern on the wings but are easily rubbed off.
None of the wings fold up and when not in use are either held
erect or are depressed on each side of the body. The metamor-
phosis is complete.
This Order is very clearly defined and the members show a
marked resemblance one to another. It includes the Butterflies
and Moths, and all of them exhibit a very definite and complete
metamorphosis. The eggs give rise to worm-like larvae known as
caterpillars, which consume much food, generally of a vegetable
nature (Fig. 89). After a considerable time, varying from a few
weeks to three years, the caterpillar comes to rest, and in such
cases as the Silk-worm Moth, Bombyx mori, surrounds itself by a
case or cocoon spun by itself, which furnishes the material silk
(Fig. 90). Within this cocoon, or in some species without forming
a cocoon, the caterpillar forms a pupa, and whilst in this state it
undergoes a very thorough reorganization and gradually the mature
Insect is built up ; after a certain time this emerges and occupies
its comparatively short life in the propagation of its species (Fig. 91).
The female usually deposits its eggs on or near the plants which
serve as food for its offspring.
Class III. Arachnida.
The third large group of the Arthropoda is a very varied one
and contains many animals which differ markedly in their structure
one from another. Perhaps the most distinctive features of the
External Arachuida (Gk. apax*^» * spider ; cTSos, shape) are
features. ^j^ There are no true gnathites. No appendage loses
all other functions and becomes exclusively a jaw, although the
proximal joints of several are prolonged inwards towards the mouth
and help to take up food ; in a word some of the limbs have
developed gnathobases; (ii) The most anterior appendages are
never antennae but always a pair of nippers, termed chelicerae ;
(iii) The active catching and walking legs of the fore part of the
body orprosoma are strongly contrasted with the plate-like modi-
fied limbs of the middle part of the body or mesosoma when the
VII ] . ARANEIDA. 191
latter exist, but in many cases these have disappeared and in others
have become so modified that they are no longer recognisable as
limbs. Nearly all Arachnids moreover agree in having the anterior
end of the body, the prosoma^ as it is called, marked off from the
rest and covered by a single piece, the carapace. The rest of the
body or abdomen is in some forms differentiated into two regions,
the mesosoma and metasoma, but in other cases this distinction
does not exist ; it may be segmented or it may not. The prosoma
bears six pairs of appendages and of these the last four are usually
walking legs. The appendages of the abdomen are connected with
the respiratory function and are much modified, often — in the
terrestrial forms — forming floors for the respiratory chambers. The
breathing apparatus may be tracheal, or in a few marine forms
branchial, or may take the form of respiratory chambers, the last
named and the gills having a peculiar form found only amongst
Arachnida. They consist of '' books " of thin superposed lamellae
attached to the posterior aspect of an appendage. When modified
for breathing air these "books" are called lung-books. When,
as is the case in Limulus, they breathe oxygen dissolved in water
they are called gill-books. The genital orifice is usually on the
anterior end of the abdomen and ventral : the group is bisexual.
Many different Orders are included in the Arachnida, the best
known being perhaps those which include the Spiders, the Harvest-
men, the Mites and the Scorpions. The last named are found only
in warm climates and Mites are too small for investigation with the
naked eye, so that we will take the Spider as an example of
Arachnid structure.
Order I. Araneida.
Spiders belong to the Order Araneida (Lat. aranea, a spider),
in which the abdomen is unsegmented and soft. The second pair
of appendages, the pedipalpi, are leg-like and modified in the male
in connexion with the fertilization of the female. The abdomen
bears certain modified appendages called spinnerets, on which
1 The name cephalothorax is often applied to this region, but the term is
too misleading to be used. The cephalothorax of Decapod Crustacea includes
the first thirteen segments of the body: the prosoma of Arachnida only includes
six, and therefore corresponds roughly to the ''head" of the higher Crustacea.
Similar criticism might be launched against the use of the word ''abdomen,''
bat here the error is too deep-rooted for correction since the term is used in
describing both Cmstacea and Insecta, and in each case in a different sense.
192 ARACHHIDA. [CHAP.
Open the glanda, the secretion of which prodnces the Spider's web.
If we examine such a Spider as Epeira diademata, which is common
enough in English gardens, sitting on or near its wheel-shaped web
Y^^F-^'
Via. 98. The Oarden Spider, Epeira diademata, utting in th« oentre of its mb.
Arter BUnohard.
(Fig. 98), we notice that behi&d the proeoma
there is a slender waist and that this ia
followed by a large swollen abdomen with
no outward trace of division into segments,
or into meeo- and meta-soma.
Tbere are six pairs of appendages, and
Bitcrnai >'' ^^ ^^ °^*^ noticoable that
■tnicture. \^eiQ are no antennae or feelers
to act as sensory organs. Their function is
to some extent taken over by the long walk-
ing legs. The first pair of limbs are called
chelicerae: in i^tra these are two-jointed,
the terminal joint being pointed and folded
1. Head. 2. Eyes, down against the basal joint except when
3. Btual joint of che- , . . ,n.- n,.i ni- c
Ijoerae. being used (Fig. 99). This pair of appen-
4. Claw of ohelioene. dages contains poison glands and the poison
Front Tiow of
the head of a Spider,
Tfxtrix denticulala.
Magnified. From
Warburton.
VII.] ARANEIDA. 193
escapes through an opening at the point of the second joint. By
means of it the Spider can kill insects and seriously hurt larger
animals.
The second pair of i^pendages in the Arachnida are called
pedipalpi (Fig. 100). In Epeira they resemble the walking legs,
but in the male at the final moult the last joint becomes altered
and forms a hollow sac — the palpal organ — which plays an im-
portant part in fertilizing the female.
Then follow four pairs of walking legs each with seven joints
and terminated with two or three claws ; in some species they are
provided with a pad of short hairs called a scopula, which helps
the animal to run on walls and ceilings.
The mouth is very minute, for the Spider does not swallow solid
food but sucks the juices of its prey. It lies between the bases
of the pedipalps, and the basal joint of each of these appendages
has a cutting blade termed the "maxiUa" (2, Fig. 100). It is a
common feature of the Arachnids that the basal joints of one or
more of the pairs of appendages are produced inwards towards
the mouth and act as jaws, but the modification never goes so
far as to obscure the limb-like form of the appendage and so pro-
duce a true gnathite.
On the ventral surface of ' /a#--7
the abdomen just behind i^llJS^
the waist is situated the m^r
genital opening, protected by / ; W^Si
a plate which is the result of \ lUjl^^p-
the fusion of a pair of ap- \\ \^«(lJ^. e
pendages, and on each side of N^^ftj^
this is the slit-like orifice of ^^v \s v\A\\a\V
a lung-book. The lung- ^4^ . ,
books are very remarkable ^ »^^^^^^^^^^
structures. Each opens to the 4 ^
exterior by a pore through ^
which the air enters, and con- Fig. 100. Pedipalp of TegenaHa guyoniiy
. ^ - , V •!. ^ the large house- spider.
sists of a sac the cavity of
which is largely occupied by \.Co-^„ ^^-3. ^TrS".' *'!" F^'^
a number of thin plates in 5. Patella. 6. Tibia. 7. Tarsus.
the substance of which the ^- ^^^P*^^ ^^«*"-
blood circulates, and is thus
brought into close relationship with the air which passes in and
out between the neighbouring plates ; the sac is floored in by a
s. <& M. \^
194 A,IUCHNIDA. [chap.
Bpeciid plate which is & modified appendage (Fige. 63 and 65). Sach
a breathing apparatus is peculiar to the Arachnida. In some
Spiders we find a second pair of Inng-books placed behind ihe
others, and io other species this second pair is replaced by a pair of
tracheae recalling the respiratory mechanism of the Myriapoda or
the Insects (Fig. 63). They have however been independently de-
veloped, and probably owe their origin to the sac of a lung-book
from which the lamellae have disappeared.
1. Month. 2. SnckinR stomach. 3. Ducts at liver. 4. Malpigfaiui
tubaloa. S. Storoorsl pockal. 6. Anua. 7. Dorsal muscle of
sucking etomach. 8. Coecal prolongation of etomoch. 9. CerebnU
giuiglioii giving off nerves to eyes. 10. Bub-oesophogeai ganglionic mass.
11. Heart with three lateral openiiiRS or ostia. 12. Lung-book.
13. Ovary. li. Acioate and pyriform ulk glands. 15. Tubiiliform
silk gland. 16, Ampulliform silk gland. IT. Aggregate or dendrifonn
Bilk glands. 18. Spinnerets or mammillae. 19. Distal joint ofcheli-
cero. 20. Poison gland. 21. Eye. 23. Pericardinin. 38. Teasel
bringing blood from lung sao to pericardium. 31. Arteij.
Near the binder end of the abdomen are four tubercles or
spinnerets, and if these be pushed aside, two more,
shorter in length, come into view. These are the
oif^B which form the web and they have been shown to be vestiges
of abdominal appendages. They are very mobile and are pierced
at their ends by hundreds of minute pores through which the
silk exudes as a fluid, hardening on exposure to the air (18,
Fig. 101).
The silk is secreted by a large number of glands which have
their exit at the above-mentioned pores. Of these in K diademcUa
there are five different sorts and each secretes a special kind of
thread ; for the various lines in a Spider's web differ considerably
VII.] ARANEIDA. 195
one from another, in accordance with the use they are put to.
The circular lines are sticky and help to catch insects for the
Spider's food, the radial lines are stout and form a framework for
the support of circular lines ; the threads with which the Spider
binds up its captured prey di£fer from these, and there is still
another kind of thread with which it constructs its cocoons, and
each kind of line is supplied from diiferent sets of glands.
The dissection of a Spider requires much care, since the organs
almost fill the hody and are completely embedded in the large
masses of the digestive and reproductive glands. The oesopha-
gus, which leads from the mouth, opens into a strong sucking
"stomach," which is really like the stomach of the Cray-fish, a
stomodaeum. This is attached by muscles to the chitinous exo-
skeleton, and when the muscles contract its cavity is enlarged and
thus a sucking action is induced at the mouth (Fig. 101). Behind
this is an endodermic portion of the alimentary canal which gives
off certain caeca or blind tubes, followed by an intestine which
traverses the abdomen and is frirther provided with a number of
ducts which collect the products of a very capacious digestive gland
or " liver." The intestine, which is also lined by endoderm, is fol-
lowed by a short proctodaeum, the proximal portion of which is
swollen up into a pouch called the stercoral pocket. It ends in an
anus situated close behind the spinnerets.
Spiders possess two kinds of organs which excrete waste nitro-
genous material : (i) the Goxal glands, which are true nephridia,
i.e., glandular tubes running between a reduced coelom and the
exterior, and (ii) Malpighian tubules, a pair of simple pouches opening
into the endodermal intestine and thus in their origin differing
from those of Insects. The coxal glands are better developed in
some species, such as the common House-spider, Tegenaria derhatnii,
than is the case in E. diademata^ where they are very degenerate
and where their frinctions seem to have largely passed to the
Malpighian tubules. In fact these structures are an interesting
example of a set of organs degenerating and of their functions
being assumed by another set.
The heart of the Spider is of the same general type as that of
Myriapods ; it is a tube with paired slit-like openings — ostia — at
the sides, through which the blood enters to be driven out again
through certain rather ill-defined vessels to circulate in the spaces
between the various organs.
The nervous system is concentrated ; there is a bi-lobed ganglion
196 ARACHNIDA. [CHAP.
above the oesophagus which gives off nerves to the eyes and the
chelicerae ; this is connected by two lateral cords, which pass one on
each side of the oesophagus, with a large nervous mass situated in
the thorax. From this, nerves pass off to supply the remaining five
pairs of limbs and two nerves arise which pass backward and
1..
Fia. 102. Diagrammatic view of Palpal Organ.
1. Tarsus. 2. Bulb. 3. Yesicula seminalis. 4. Opening of vesicula
semiualis. 6. Conductor. 6. Haematodocha. 7. Alveolus.
supply the abdomen. The only conspicuous sense organs of Spiders
are the eyes, which are ** simple " ; of these in E, diademata there
are four large eyes arranged in a square on the top of the head and
two small ones on each side of the square. This number, eight, is
not uncommon in Spiders, where both the number of eyes and their
disposition are much used in systematic classification.
The male, as is not uncommon amongst the Araneida, is
smaller than the female. The ovaries and testes lie in the abdomen
and have the form of a network of tubes, a form characteristic
of ^Vrachnida ; the spermatozoa are conveyed to the palpal organs
of the pedipalpi of the male and by them introduced into pouches,
the spermathecae of the female. The eggs are fertilized before they
are laid, which latter event usually takes place in October, when they
are enclosed in cocoons of yellowish silk. The young are hatched
out in the following spring and at once begin spinning. By means
of the minute threads they secrete they weave a kind of nest about
the size of a cherry-stone which hangs suspended from some twig or
leaf. At the least disturbance the hundreds of young Spiders in
the nest begin to disperse ; the spherical nest breaks up as into
dust, but when the disturbance is at an end the minute Spiders,
VII.] PHALANGIDA. 197
SO small as to be almost mvisible, re-assemble and agaia form their
little spherical nursery.
The number of species of Spiders is very great and their habits
are very diverse and well worthy of study.
Order 11. I^alangida.
The Phalangids (Gr. ij/SXayY^oy, a venomous kind of spider) or
Harvestmen are in common talk usually classed viith Spiders, but
F:ij. 103. A PhalsDgid or Harvestman, OUgolophui tpii,
I. Chelioeru.
lu, adalt malex 2,
L, second, third, and
they difTer from the latter in having no waist, that is, the abdomen
is not separated from the prosoma by a constriction, and they
breathe entirely by tracheae. They have four long and very
slender pairs of legs, which easily break, and their eyes are some-
198 ABA.CHNIDA. [CHAP.
times elevated &boTe the sur&ce of tihe head on a tubercle like a
look-oat tower. The abdomen is distinctly divided into segments.
Aa a rule these creatures are nocturnal and are nsnally met witli
in dark comers or amongst the stalks of hay or grass. Their long
legs enable them to steal with a gliding spring upon their prey,
foi the most part insects or spiders, for they are carnivorous. They
are dull in colour, grey, brown or blackish, as becomes an animal
that loves the dnsk. About twenty-fonr species have been recorded
in Qreat Britain. Fhalangids die down as winter sets in, but the
eggs last through the cold weather and give rise to a new generation
in the spring.
Order III. Acarina.
The Acarids (Gr. axSpU, a morsel) or Mites form an enormous
order whose function in life is to a large extent to pl&y the
1. Pedipolpi. 2. Chelioerae. 3. 4, 5, 9. First, aecoad, third and fODrtb
volking legs. 7. Chitinoiu thiokeninga mpporting legs. 8. Farrow ~
roand bodj. 9. Reprodactive opening, flanked bj two saokeiB on each
side. 10. Adob. 11. Sockera at liila of anna.
scavenger, and the terrestrial forms confer the same benefits on t^e
dwellers on the Earth that the Ostracoda and many of the smaller
Crustacea do on the aquatic fauna. Many of them however have
adopted parasitic habits and cause disease amongst larger animals,
Vn.] ACARINA. 199
while some induce the formation of galls and other deformities
amongst plants. Most of the Mites, as their name indicates, are of
minute size; but the female Ticks, belonging to the family Ixodidae,
which live amongst the undergrowth of forests on the look-out for
some vertebrate prey, can when they become attached to their
hosts — man, cattle, or even snakes — ^by distending their bodies with
the blood they suck, swell out to the size of hazel-nuts.
Anatomically they are difficult to characterize. like the
Phalangids, they have no waist, and when special breathing organs
are present they take the form of tracheae ; they differ however
from the Phalangids in never showing signs of segmentation. The
chelicerae may be clawed or chelate, like a lobster's claws (Fig. 104),
but they often take the form of piercing stylets and the pedipalpi
may form a sheath to protect them.
The number of species is very great ; amongst the commoner
forms may be mentioned, Tetranychus telarius, often known as
the Bed Spider, which spins webs under leaves in which whole
colonies shelter. This species is believed to do great damage in
hot-houses. Tyroglyphus siro, the Cheese-mite, which burrows in
decaying cheese, and the genus Phytoptus, which causes the conical
galls on lime-trees, maples, etc., are also familiar.
Order IV. Scorpionida.
Scorpions are not found in Great Britain, though they are common
on the Continent of Europe around the Mediterranean basin and
generally in warm climates. They retain a more marked segmenta-
tion than is the case with the other Arachnids we have considered.
The abdomen is very long, distinctly segmented and differentiated
into two portions ; (a) the mesosoma, consisting of seven segments
of the same diameter as the prosoma, bearing the respiratory
appendages ; (b) the metasoma, a much narrower part, consisting
of five segments and a curved spine like a tail at the apex of which
is the opening of a poison gland. The mesosoma has six pairs of
appendages. The first of these forms the genital operculum, a plate
bearing on its posterior aspect the genital pore in both sexes ; the
second are " pectines," curious comb-shaped structures, whose exact
function is not yet determined, but which are morphologically
reduced and thickened gill-books. The third, fourth, fifth and sixth
segments bear each a pair of lung-books, and it has already been
explained that the floors of these are formed of highly modified
ARACHNIDA.
[chap.
1. Chelicera.
walking lege.
Bide of bod;, plei
2. Pedip&lp. 3, 4, S, 6. 3id to 6th appendages, oi
, Lateral ejen. 8. Median eyea, 9. Soft tissae »1
0. 10. The poison stiog or telson.
1 — 6 &s in A. 7. The genital operculum. B. The pectinea. 9, 10,
11, 12. The tour right stigmata leadiog to the (our luug-bookB. 18. The
last segment of the mesoeoma. 14. The third segment of metasoma.
15. The teUon. la eaoh oase the metasoma, which is usually carried bent
forward over the meio- and pro-soma, has been strughtened out.
VII.] 8C0RPI0NIDA. 201
plate-like appendages which in the adult have lost all trace of
their origin from limbs. The seventh segment of the mesosoma
shows no traces of limbs and tapers to join the first segment of
the metasoma. At the posterior end of the fifth metasomatic
s^ment, on the ventral surface, is situated the anus, and behind
this is a conical pointed joint which contains the poison glands
and which forms a very efficient and powerful sting. The whole of
this tail is very mobile and the sting can readily be directed to any
point In life the tail is usually borne turned forward over the
body so that the sting threatens the head.
Both the chelicerae, which are small and short, and the pedipalpi,
which are long and six-jointed, end in nippers, the latter recalling
the appearance of the claws of a lobster. The four pairs of walking
legs end in claws.
The mouth is very minute, for like the Spiders Scorpions only
suck the juices of their prey. They feed for the most part on
Insects and Spiders. The basal joints of the first two pairs of
appendages, like those of the pedipalps in Spiders, are all produced
towards the mouth, forming gnathobases which probably help to
hold their food.
Scorpions usually hide under rocks and stones during the day,
being often very intolerant of heat, but they creep out as dusk
comes on and run actively about. The Scorpion is viviparous, the
young being bom in a condition resembling their parents.
Order V. Xiphosura.
A very peculiar aquatic Arachnid called Limulits, or popularly
the '* King-crab," inhabits the warm seas on the Western side of the
Pacific Ocean and along the shores of the Western Atlantic. It is
a littoral form, that is to say, it lives not far from the shore ; it
burrows in sand or mud at a depth of firom two to six fathoms, often
lying with only its eyes, which are on the top of the body, exposed.
The shape of the body is something like a half-sphere with a
piece cut out and a long spine is attached to the truncated side.
This spine has given the name Xiphosura (Gr. f «^os, a sword ; ovpd,
a tail) to the Order. The half-sphere is hiaged, and the part in
front of the hinge is the prosoma ; the rest is the abdomen or
meso- and meta-soma. On the upper surface of the half-sphere are
a pair of simple eyes near the middle line, and there is a pair of
compound eyes situated further back nearer the edge. The under
surface of the half-sphere is partially hollowed out and concealed in
202 -ARACHlflDA. [chip.
this hollow on each edde of the middle line of the prosomA are six
pairs of appendsgeB. The most anterior of these are typical nipper-
like chelicerae, the next is not specially modified to form a pedipalp,
but it and the remaining four pairs are walking legs. All of them
Fjq. 106. BoraAl view of the EiDg-crabj Linmlui polyphtt
send inwards a spiny gnathobase, which helps to form the border
of the mouth. The sixth pair of limbs end in some flattened blade-
like structures which aaaist in digging and burrowing in the sand
and in extracting the worms which form the principal item of the
diet of the King-crab. The aeventii appendages, or the first on the
VII.] XIPHOSOBA. 208
meBoeomti, take the form of a flattened plate or operculnm which
bears the reprodnctive pores on ita posterior siir&ce. It is bent back
and underlies the eighth, ninth, tenth, eleventh, and twelfth pairs of
appoidages, which are aUo plate-like and each of which bears on
its posterior snrface a gill-book. There is a striking aimilarity
Fta. 1D7. T«iitral view of the King-crab, Limtilui polyphemat x \.
1. Cuapue aoTering pidBoma. 2. Meso- and meta-aoma. 3. TelsoQ.
4. Cbelioent. 6. P«dipalp. 6, T, S. 9. 3rd to 6th appendages,
atnbnlatoi; limtw. 10. Qenital opecoulam tarned forward to sboir the
genital aperture. II, 12, 13, 14. IS. Appendages bearing giU-books.
16. Anna. 17. Month. 18. ChUaria.
between these organs and the " lung-books " of the Scorpion ;
the latter, however, do not project, but are sunk in pite. The
I terminates at the anus, but behind it a long sword-like
204 ARACHNIDA. [CHAP.
tail projects. This post-anal tail corresponds with the swollen
stinging tail or telson of the Scorpion. It is used by the animal
to right itself when it is upset by the motion of the waves.
A curious plate of fibro-cartilage to which muscles are attached
lies inside the body near the ventral surface. It is formed of modi-
fied connective tissue in which a cheesy material termed chondrin
has been deposited in the ground substance, and is largely built up of
interlacing tendons of muscles so that it acts as an internal support-
ing structure or endoskeleton. It is called the endosternite.
Possibly it was a feature of primitive Arthropoda, as similar
endostemites occur in many other Arachnida and in some of the
more primitive Crustacea.
The internal anatomy differs in many points of detail from that
of the Spider, but in essentials there is a fairly close resemblance.
Unlike the Scorpion, Limulus lays eggs and these are fertilized
in the water and pass through what may be termed a larval stage.
In many respects Limulus seems to be related to the extinct
Eurypterina, whose fossil forms are so abundant in the Upper
Silurian and Old Red Sandstone formations ; and like some species
of Limulus they attained a great size, two feet or more in length
being not uncommon. The Eurypterines were aquatic and indeed
seem to form an intermediate stage between the Scorpion and
Limulus^ and confirm us in the conclusion drawn from the anatomy
of Limubis that this animal retains in many points the habits and
structure of the marine ancestors of Arachnida.
Phylum ARTHROPODA.
Bilaterally sjrmmetrical Coelomata whose coelom has undergone
great change. Segmented animals with the segments usually arranged
in groups. Paired hollow and jointed limbs on some of the segments.
Class I. Crustacea.
Aquatic Arthropods usually breathing by gills, with two pairs of
antennae. A limb-bearing thorax usually fused with the head and
followed by a segmented abdomen which may be limbless.
Sub-class A. Entomostraca.
Small, simple Crustacea with varying number of segments. The
stomach has no teeth. The larva is a Nauplius.
VII.] CLASSIFICATION. 205
Order 1. Phyllopoda.
Long-bodied and usually well segmented with a shield-like
shell protecting head and thorax and sometimes abdomen ; with
leaf-like swimming appendages.
Sub-order i. Branchiopoda.
Large-bodied forms with no dorsal brood-pouch, second
antennae not enlarged for swimming, numerous swimming
appendages.
Ex. Apus, Branckipus, Artemia.
Sub-order ii. Cladocera.
Small, short forms with bivalved shell, a dorsal brood-
pouch and enlarged swimming second antennae.
Ex. Daphnia, Simocephalus.
Order 2. Ostracoda.
Usually small forms with body unsegmented. At most
seven pairs of appendages and a rudimentary abdomen, all shut
up in a bivalve shell.
Ex. CypriSy Cypridina,
Order 3. Copepoda.
Usually elongated and clearly segmented but often much
modified by parasitism. Four or five pairs of biramous thoracic
appendages.
Ex, Cyclops, Argulus,
Order 4. Cirripedia.
Sessile animals whose not clearly segmented body is enclosed
in a fold of skin strengthened by calcareous plates. Usually
five biramous thoracic appendages. Hermaphrodite as a rule.
Ex. LepaSf Baktmis,
Sub-class B. Malacostraca.
Large Crustacea as a rule with five segments in the head, eight
in the thorax and six in the abdomen. Nauplius larva very rare.
Order L Leptostraca.
Bivalve shell covering the eight free thoracic segments but
not fused with them, abdomen of eight apparent segments with
anal forks. Thoracic limbs leaf-like.
Ex. Nebalia.
206 ARACHNIDA. [CHAP.
Older 2. Thoracostraca.
All or most thoracic s^ments fiised with head and covered
by a cephalothorax. Eyes as a role stalked.
Sub-order i. Schizopoda.
Eight pairs of biramoos thoracic appendages. Eyes
stalked.
Ex. Mysis.
Sub-order ii. Decapoda.
Thoracic segments fused with head. Last five thoracic
appendages uniramous and used for walking. Eyes stalked.
Division a, Macrura.
Abdomen long.
Ex. Astaais,
Division b, Brachjrtura.
Abdomen short.
Ex. Cancer^ Carcinus.
Sub-order iii. Stomatopoda.
Cephalothoracic shield short. Five pairs of maxillipeds.
Abdomen large and bearing gills on its appendages.
Ex. Squilki.
Sub-order iv. Cumacea.
Four or five free thoracic segments. Two pairs of
maxillipeds. Eyes sessile.
Ex. Cumay Diastylk,
Order 3. Arthrostraca.
Seven, rarely six, free thoracic segments. No cephalo-
thoracic shield. Eyes sessile.
Sub-order i. Amphipoda.
Body laterally compressed. Gills on thoracic appen-
dages.
Ex. Gammarua,
Sub-order ii. Isopoda.
Body dorso-ventrally compressed. Gills on abdominal
appendages.
Ex. Asellus, Parcellioy Oniscu$.
VII.] CLASSIFICATION. 207
Class II. Antennata.
A single pair of antennae and with tracheal respiration.
Sub-class A. Prototracheata.
Soft, caterpillar-like bodies with numerous pairs of appendages.
Nephridia present.
Ex. Peripatus,
Sub-class B. Myriapoda.
Terrestrial, with head well marked off from body, which consists
of many similar segments bearing six- or seven-jointed appendages.
Order 1. Chilopoda.
Animal flattened dorso-ventrally, bases of legs wide apart :
to each tergum corresponds one pair of legs : the segment
following the head has a large pair of poison claws : genital
opening between the last pair of legs.
Ex. Lithobius,
Order 2. Diplopoda.
Animal cylindrical, bases of legs close together : to each
tergum behind the fourth correspond two pairs of legs: no
poison claws : genital opening on the third segment behind
the head.
Ex. lulus.
Sub-class C. Insecta.
Body divided into three regions, head, thorax and abdomen.
Head bears the antennae and three pairs of persistent mouth parts ;
thorax three pairs of walking appendages and usually two pairs of
wings ; abdomen as a rule without appendages.
Order 1. Aptera.
Wingless insects with hairy and scaly bodies ending in
anal filaments. No metamorphosis.
Ex. Lepisma,
Order 2. Orthoptera.
Jaws biting, wings usually unalike. Metamorphosis in-
complete.
Ex. Forfictda^ Stylopygay Phasma^ Acridium^ Gryllus.
208 ARACHNIDA. [CHAP.
Order 3. Neuroptera.
Jaws bitiDg, sometimes sucking. Wings alike, membranous,
with many nervures. Metamorphosis varies.
Ex. Teimes, Ephemera, Libellula, Phryganea,
Order 4. Coleoptera.
Jaws biting. Anterior wings hard and curving together
with a median, straight suture. Metamorphosis complete.
Ex. Coccinettay Melolontha.
Order 5. Hymenoptera.
Jaws biting and licking. Four membranous wings with
few nervures. Metamorphosis complete.
Ex. Formica^ Apis, Vespa,
Order 6. Hemiptera.
Jaws piercing and sucking. Wings alike or different.
Metamorphosis incomplete.
Kx. Acanthia, Cicada, Aphis.
Order 7. Diptera.
Jaws piercing and sucking. Hind-wings reduced, front-
wings membranous. Complete metamorphosis.
Ex. Culea:, Musca,
Order 8. Lepidoptera.
Jaws sucking. Four similar wings covered with scales.
Metamorphosis complete.
Ex. Bambyx.
Class III. Arachnida.
No antennae and no true gnathites. Frosoma of six appendage-
bearing segments followed by a meso- and meta-soma whose appen-
dages are when present usually much modified.
Order 1. Araneida.
Meso- and meta-soma soft, unsegmented. Four to six
spinnerets, two to four lung-books.
Ex. Epeira.
Vn.] CLASSIFICATION. 209
Order 2. Fhalangida.
No waist between pro- and meso-soma which latter with
meta-soma is segmented. Tracheate.
Ex. Oligolophus.
Order 3. Acarina.
No waist. Minute and often reduced forms mostly tracheate.
Ex. Tyroglyphus, Tetranychus.
Order 4. Scorpionida.
Meso-soma seven segmented in adult, meta-soma five seg-
mented and ending in a post-anal poisonous telson. Four
lung-books.
Ex. Scorpio,
Order 5. Xiphosura.
Shield-shaped carapace covers prosoma. Meso- and meta-
soma fused. Gill hooks. The telson forms a spine.
Ex. lAmulus.
S.ftM 14
210
CHAPTER VIIL
Phylum Mollusca.
MoLLirscA (Lat. mollis^ soft) is the name which is given to one
of the largest and most important phyla of the animal kingdom.
In it are included not only our terrestrial snails and slugs and
many fresh-water species but also the oysters, mussels, periwinkles,
whelks and countless other species of "shell-fish," bivalve and
univalve, which crowd the rocks laid bare at low-
descriptfon. Water around our coasts: and in addition to these,
the extraordinary Octopuses, Squids and other forms
of Cuttle-fish belong to the same great phylum. The name Mollusca
seems to have been suggested by the fact that the members of the
phylum do not possess any internal hard parts such as are found in
Man and other vertebrates. This softness of internal constitution
is shared by other classes with no relation to the Mollusca, as for
instance the great group of the Arthropoda. The Arthropods
however possess a horny covering which closely invests them and
following every irregularity of their outlines, so that it seems a
real part of themselves. This is the exoskeleton or cuticle, which
constitutes one of the great difi'erences between them and the
Mollusca. The latter, it is true, possess also an exoskeleton
composed principally of calcareous matter, but this adheres only
to a part of the surface. It is usually very thick and easily
detached, and so it is frequently looked on as a separate thing
&om the animal and is known as the shell. The shell is to be
looked on as a secretion produced by a part of the skin only:
this part of the skin, which almost always projects from the rest
of the body as a flap, is called the mantle. The space between
the mantle-flap and the rest of the body is known as the mantle-
<javity. The mantle-cavity shelters the gills or organs of respira-
tion, and into it open the kidney or kidneys and the anus, and
usually also the genital ducts.
tiil] oastebofoda.
Class I. Qastebopoda.
In order to fix our ideas we may take the common ]
garden snail, Helix aspersa, which has also established
o( 3^11^''*'" ^t^olf throughout considerable areas in North America,
or, if procurable, the larger Helix pomatia, which on
account of its size la easier to dissect, as a type of the Mollnsca.
In Lower Canada the genus Helix is not very abundant, and the
1. MoDth. 3. Anterior tentacles. 8. Eye tentaoles. 4. Edge of muitle.
6. Bespintor; poie. 6. Ann*. 7. Apei of shell. 8. Foot.
9. Bepiodaotive apertitra.
latest species, Helix ctStolabrut, ia rather small for convenient
dissectioD. Livmaea stagnatis, the large river-snail, is however
common and easy to obtain, and its structure is similar in its main
outlines to that of Helix.
The shell is coiled into a spiral form ; the body contained in it
consisto of a visceral hump, coiled like the shell and closely
adhering to it, and of a poTtion which we call the head, neck, and
foot, which can be drawn within the openiug of the shell if the
animal is alarmed, but which under ordinary circumstances is quite
outside it The snail is devoid of anything in the nature of
legs, — an important character of the MoUusca as contrasted with
the Artbropoda, — but the part of the body next the ground is
a flat muscular surface called ^e foot. By means of wave-like
contractions of the longitudinal muscular fibres of this organ the
snail moves along, always preparing the ground for itself by de-
poeitJDg a layer of slime on it. This slime is poured forth irom a
gland which opens in Iront of the foot, just beneath tlie mouth
11—2
212 MOLLUSCA, [chap.
(14, Fig. 111). The foot is one of the most important oigans of
the Mollusca; it takes different shapes in the different groups but
always assists locomotion. In the pond-mussel, for instance, it is
shaped like a wedge, in order to force a path through the soft mud
at the bottom of the ponds in which the animal lives. The
different shapes which the foot assumes afford the chief basis for
the classification of Mollusca.
The head of the snail bears two pairs of feelers, or tentacles,
which are hollow outgrowths of the body-wall (2, 3, Pig. 108) : these
when irritated are protected by being pulled outside in, and so
are brought into the interior of the body. The first or shorter pair
are supposed to be the chief seat of the sense of smell : the second
and longer pair have at their tip a small pair of black eyes. These
eyes are merely minute sacs, the walls of which are made of light-
perceiving cells, connected at their bases with a nerve which leads
to the brain; in the cavity of the vesicle is a horny lens which
nearly fills it up. The eyes of nearly all the Mollusca are con-
structed on the same plan, but in the Cuttle-fish not only is the
vesicle large and spacious and the lens proportionately smaller, but
there is in addition a series of folds of skin surrounding the place
where the eye comes to the surface, which constitute an outer
chamber, and outside this, eyelids, so that the whole organ acquires
a superficial similarity to the human eye.
If we carefully pick away the shell of the animal and lay bare
the visceral hump, brushing away any mucus which may adhere to
the body, we shall see on the right side of the animal a round hole
(5, Fig. 108). A bristle passed through this reaches into a large
cavity separated from the outside by an exceedingly thin walL
This space is nothing but the mantle-cavity, which, as explained
above, is the space comprised between the projecting mantle flap
and the rest of the body. The peculiarity about the snail is that
the mantle edge has become fused to the back of the neck so as to
shut the mantle-cavity off from the exterior, leaving only this little
hole of communication. The mantle-cavities of the marine allies of
the snail, such as the whelk and periwinkle, are not so completely
shut off, inasmuch as in them the mantle flap merely lies against
the neck but is not fased to it, and inside the mantle-cavity there
is a gill. This gill consists of a hollow axis bearing on one or both
sides a close set row of thin plates inside which the blood circulates
and receives oxygen from the water by diffusion. Fresh supplies of
water are drawn into the mantle-cavity by the action of myriads of
VnL] GASTEROPODA. 213
cilia which cover the gill. A gill of this nature is called a
ctenidinm, owing to its comb-like appearance (Gr. mi'iSun-, a small
comb). Now, since the snail breathes air, not water, it has lost the
gill, bnt to compensate for the loss it has changed the whole mantle-
cavity into a lung. The floor of the mantle-cavity, really the back
of the neck, is arched and composed of muscles: when these con-
tract the floor flattens and thus the mantle-cavity is enlarged and
air is drawn in.
The blood is contained in
large vessels running in the
thin roof of the mantle-cavi^ :
these are clearly eeen when the
mantle flap is clipped away
from the neck and turned over
to the right (9, Fig. 109, and
Fig. 110). These vessels are
seen to all converge to the
heart, which consists of two
small oval sacs placed end to
end. That into which the vein
eDt«Ts ia thin-walled and is
called the auricle: the other
thicker one is called the ven-
tricle (Fig. 110); it is the more
muscular of the two and drives
the blood through two arteries
to the body. One of these passes
up to the visceral hump, and
tlie other forward to the head
and neck. In Molluscs which
have gills the auricle always
receives the blood from the gill :
when there is one gill, as is the
case with nearly all the uni-
valves, there is only one auricle :
but where, as in the bivalves
and cuttle-fish, there are two or
even four gills (as in Nautilus)
there are likewise two or four auricles. The heart is surrounded
by a space called the pericardium, which really corresponds to
the body-cavity or coelom of Vertebrates, AnneUds and Echino-
Fta. 109. Htlis pomatia. The animal
ueD from the dorsal side after removal
oftbe shell. From Hatechek and Cori.
1. Auricle of the heart reoeiving pal.
monaryTeiii. 9. An torior tentacles.
3. Bye tentacles. 4. Edgeotmantte.
5. Nephridinm. 6. Liver. 7. Al-
bnmoD gland. 6. PQlmonair vein.
9. Pool.
214 MOLLUSCA. [chap.
denuB, for into it the excretory organ opens and in tiie embiyo
the genital cells are budded from its walL Othsr large spaces
flxiBting in the head and neck have no connexion with tlie
coelom but are really parts of the blood Bystem. Since there are
no regular veioB, except those which ran in the mantle-roof, the
arteries open into irregular spaces. It will be remembered that the
space called pericardium amongst the Arthropods is really a
blood space and that the heart opens into it by
openings called ostia: the coelomic character of the
pericardium of Mollusca is then another distangnishing
feature of the group. It
opens by a narrow ciliated
passage, the reno-peri*
cardial canal, into the
kidney, which ib seen in
the mantle-roof beside the
pericardium {5, Fig. 109).
The kidney looks like a
solid yellow organ; but in
reality it ia a vesicle into
the cavity of which nu-
merous folds project, cover-
ed by the peculiar cells
which have the power of
extracting waste products
from the blood, which fiows
in spaces in the kidney
wall The kidney com-
municates with the exterior
by a narrow thin-walled
tube, the ureter, which
runs along the right side of
the body and opens on
the lip of the respiratory
opening, just above the Fm. no. Beiixpam
opening of the anus (10,
Fig. 112).
The kidney in Mollusca
varies a good deal in
structure, but is always
built on the Bame fuoda-
nith tbe upper wall
of the polmoiiary ehambar cot open aud
folded back. From Hatschek and Cori.
1, Venlcicle. 2. Anterior tentaclsB. 3. Eje
teatacles. 4. Cat edge of maDtle.
6. Respiratory pore. 6. Aoua. 7. Open-
ing of ureter. 8. Foot 9. Amiole
receiving pulmonar; yeln. 10. Bectuin.
11. Nephridium. 12. Upper wall of
palmoDar; chamber.
Vin.] GASTEROPODA. 215
mental plan u that of the SdoU. Where there are two gills there
ue liluwise two kidney b. Often there is no ureter, but the kidney
opens directly to the exterior, as in the cuttle-fish, the whelk
{Bweinum), the limpet (Patella), in the cuttle-fish instead of
irregular spacea there are regular veins in its walls and the folds
coTBied with special cells are only developed over the coarse of
these veins.
Turning now to the digestive system of the snail we notice
several very interesting pecnliaritiee. The mouth is situated in
front, beneath the small pair of tentacles, and there is a cnrved
homy bar, the jaw, in the roof of the mouth. Against the jaw
worlra a rasp-Uke tongue, called the radula, the surface of which
is a homy membrane covered with myriads of minute, recurved
teeth. TTndemeath tiiis membrane there are certain small pieces oi
cartilage to which muscles are attached which pull the cartilages
and the membrane covering them alternately downwards and for-
wards and upwards and btickwards, so that the tongue is worked
against the jaw. Thus the snail is enabled to tear pieces out of
Fio. 111. Inau view o[ right halt ot head of Helix, to show Che arraDgement
of the radula x 2.
1. Moath. 2. Horny jaw. 3. Baduln. 4. Cartilaginoai piece »up-
porting ndnla. 6. Badola MO from which radula grovs. 6. Mnsole
which retraoM the hocoal msae. 7. IntiioBic musclea which rotate the
radola. 8. Cerebial gaoglioo. 9. Pedal and Tisceral ganglia.
10. Oeuiphagni. 11. Anterior tentaclti. 12. Eye tentacle. 13. OriGca
of daet ol Mlivaiy gland. 14. Mucous gland which rona along toot and
openi jQEt imder the month,
the leaves on which it feeds (Pig. 111). A similar organ is found
in all Mollusca, except the Bivalves or Lamellibranchi&ta, and the
number, shape and arrangement of the teeth are an important help
in clasaification. The homy membrane ia continued backward into
2lfi MOLLUSCA. [chap.
a little blind pouch, called the raduU sac: here is its growing'
point, where new teeth are continually being fonned u the old ones
wear away. In the limpet {Patella), this raduia sac is extn-
1 eipoMd.
FharyDi 3 Oesophagaa 3 Salivar; gUnda with dact.
4 Stomscb G Liver 6 Bectum T Anna 6 Eiiluej.
9 laflaled commencemen oF nreter 10 Opening ot reter to eitarior.
11 Ventt ole 12 Anr cle 13 Pu monaiy yb d II Opening
of uephndium mto penca dium 15 0 o test b 16 Commoa duct
of ovo testis IT Albumen g and 18 Fema a duot IS IfaU
dnot 30 SpenDittheea 21 Flagellum 22 Accessory glands.
23 Fetiu. 24 Dart sac 26 Vag nk 26 Eye tentacle
retracted 27 Ante o tentacle retcacl«d 28 Uusde* irhicl)
rebut the bead, phai;iii teutaela eta
Vni.] GASTEROPODA. 217
ordinarilj long, attaining a length two or three times greater than
that of the body. In the cuttle-fish the radala is present and the
jaw is developed into upper and lower beaks, like those of a parrot,
with which the animal tears its prey to pieces. The Bivalves have
lost all trace of both jaws and radula: they live on the microscopic
organisms brought to them in the currents of water which they
produce, and so they do not need to masticate their food.
The radula sac and the muscles and cartilages belonging to the
radula, form a swelling which is called the buccal mass. Behind
this comes the oesophagus or gullet, which appears narrow by
comparison, but its cavity is really as large as the space inside the
buccal mass. The gullet soon widens out into the first stomach or
crop, which is used for storing the food. On the outside or surface
of this two branching whitish structures are seen, the salivary
glands. They secrete a juice which runs forwards through two
tubes, the salivary ducts, opening into the buccal mass. The
saliva mingles with the food as it is being masticated. The crop is
situated in the hinder part of the neck, and behind it the ali-
mentary canal passes under the mantle-cavity and up into the
visceral hump. The great mass of this hump is occupied by a
brownish looking organ, called the liver. This, like the similarly
named organ in the Arthropoda, is a great mass of tubes lined by
cells of a deep brown colour: the tubes join together and event-
ually open by two main tubes, one above and one below, into a
dilatation of the alimentary canal. This swelling is the true
digestive stomach. It is probable that the 'Miver" assists di-
gestion by preparing a fluid which is poured into the stomach:
its function is thus not the same as that of the human liver. In
fact it must be confessed that the name liver has been recklessly
given by the older naturalists to any brown-coloured organ found
near the stomach of an Invertebrate. The part of the alimentary
canal behind the true stomach is called the intestine. It takes
a turn in the liver substance and then runs out of the visceral
hump along the right side of the body to open by the anus, which,
as we have seen, is placed just behind the respiratory opening.
The central nervous system resembles that of the Annelida in
being made up of ganglia, each of which might be compared to a
miniature brain, connected together by means ol commissures, that
is, bands of nerve fibres. The two largest ganglia, which are placed
above the oesophagus one at each side and connected by a com-
missure, are called the supra-oesophageal or cerebral ganglia.
21»
[CHA?.
or sometimes the bnuQ {1, Pig. 113); bat there is no reason to think
that they are any more important to the animal than tJie others.
Underneath the oesophagns there is what at first sight seems to
be a compact nervous mass, connected with the sapia-oesophageal
ganglia by a commisaure on each side forming a nerve collar
(Fig. 113). Closer inspection shows that this mass is perforated
by a hole through which passes the
great anterior artery from the ventricle,
and that from both the lower and
upper halves a separate nerve comes
ofT to go to the cerebral ganglia. Thos
the apparently simple nerve collar con-
sists of two commissures on each side
united in a common sheath. Between
them a minute nerve paases down, to
end finally in a minute membranous
sac hned by ciliated cells and cells
with sense hairs and containing fluid
in which a little ball of carbonate of
lime floats. This sac, the otocyst, is
the only other important senae-oigan,
besides the eyes, which the snail pos<
sesses. It is difficult to dissect, but if
the small bivalve Cyclas be taken,
the shell opened and the foot cut off !■ Cercbrnl gangUou. 3. Ped«1,
and slightly compressed, or if one of ' "" "° "•"" -
the transparent Molluscs, such as
Pterotrachea, which float at the sur-
face of the sea, be examined, it is
perfectly easy to see both otocysts
with the microscope. It used to be
supposed that the function of this organ was to perceive sound, but
whilst it is probable that some vibrations of the air affect it, it is
nearly certain that, like the otocysts of Medusae and Arthiopoda,
its main function is to enable the Mollusc to keep its iialance by
allowiug it to perceive whether it is leaning on one side or not.
As the snail changes its position the little ball inside rolls about
and affects different parts of the wall of the vesicle, and hence
probably different fibres in the nerve which supplies it
Not all Mollusca possess eyes, but all, except perhaps the
Oyster, which never moves, possess otocysts. The experiment has
6. Olfactory nerve.
6. Optio nerve, 7- Plenro-
Derebrol commissure. 8. Pe-
do-cerebnil commisaure. 9.
OeniUl nerve. 10. Nerve to
mantle. 11. Nerve to vi»-
Vni.] OASTKROPODA. 219
been nude in the Gatde-fifih of cattmg them out, and it ia then
found that the animai loses its
power of keeping its balance in
the water and tumbles about
To return to the central
nervous syatenL In the pond-
Boail, Limnaea, the hinder part
of the Bub-oesophageal nervous
masses consists of no less than
five ganglia, strung together on
a short loop of nervous fibres,
which is called the visceral
loop. Of these a pair nearest
the head are called the pleural
ganglia, the next are called
the visceral ganglia, and
the one at the end the ah-
dominal ganglion (Fig. 115).
The &ont and lower part of t^
_ _ sub-oesophageal nervous mass
G. Supporting wila, coQsists of the pedal ganglia,
which send nerves exclusively
to the foot. Pleural and
visceral ganglia can be re-
cognised in the young snail,
but they become indistiu-
guiahably joined in the
adult. In other Molluscs,
such aa the Sea-hare
{Aplysia), or the Ear-shell
{Haliotis)y the visceral loop
is long and the ganglia
widely separated. In these
animals it can be seen that
the pleural ganglia send
nerves to the sides of the
' body, and that from the
Fid. IIS. Nsrvoai ■vatemotLtmnaeA. After ■ < ,.
laoBze-Datbiere. Visceral gangha nerves
1. Cerebnl Baaglion. 3. Pedal ganglioa. COme off which go tO the
guiftlion. 6. Abdominal gangUoa. ""^ ,°' *™ P" °^ Bl"*-
6. ViMBial gaaglian. At the base of each gill
Fio. 114. OptJeal «eotion throngb the
nnditoty veiiote oc ear of Pterotraekea
fiitdrriei, a traaepaieDt pelagia Mol-
Inso X BboDt 150. After Clana.
1. Auditory nerve. 3. Ciliated cells.
S. AnditOT7 celli. ' ~
aaditoi7 cell.
a. OtoUth.
220
MOLLUSCA.
[chap.
there is a patch of thickened skin, called an osphradium (Gr.
6(r<l>paivofiai, to smell), provided with numerous sense-cells, which
enables the animal to test the water which enters its mantle-cavity.
Of course no such organ exists in the Snail The muscles of the
radula are supplied by nerves from a special pair of small ganglia
placed on the buccal mass — the buccal ganglia — connected with the
supra-oesophageal ganglia.
We thus see that the
nervous system of the i
snail consists of a pair of
supra-oesophageal ganglia
connected by commis-
sures with (a) a pair of
pedal ganglia supplying
the muscles of the fo«t
with nerves, (b) an ex-
tremely short visceral
loop, the ganglia on which
are so closely placed as
to become practically con-
fluent with each other,
whence nerves go to all
parts of the body, and
(c) a small pair of buccal
ganglia supplying the
buccal mass. The ner«
vous systems of all Mol-
lusca are built on this
plan : in the bivalves,
however, where there is
no radula, not only are
the buccal ganglia absent,
but the pleural and cere-
bral are fused with one
another, and, as the vis-
ceral loop is long, we find
three widely separated pairs of ganglia, — cerebro-pleural, pedal and
visceral— the last named often termed " parieto-splanchnic," in
different parts of the body. The Cuttle-fish have a closely massed
nervous system, like the snail, which is protected in a kind of
rudimentary skull, made of cartilage.
— . 9
Fio. 116. Nervoas gystem, osphradiam (ol-
factory organ) and giUs of Haliotit, After
Lacaze-Dothiers.
1. Cerebral ganglion. 2. Pedal ganglion.
8. Osphradial ganglion. 4. Pleural
ganglion. 5. Abdominal ganglion.
7. Nerves to mantle. 8. Gills. 9. Pedal
nerves.
VIII.] GASTEKOPODA. 221
The only organs of the snail which remain to be mentioned are
the reproductive organs. These are exceedingly complicated in this
Molloac, both sexes being united in the same individual, a condition of
affairs which is known as hermaphroditism. The essential genital
organ is the ovotestis, a small yellowish patch of delicate tubes
spread out on the surface of the liver, on the inner side of the
uppermost coil of the spire (Fig. 112). This organ produces both
eggs and spermatozoa and both travel down a single tube. Before
the duct reaches the neck it receives the secretion of a large organ,
called the albumen gland. This secretion consists of a fluid
which has proteids in solution and is of high nourishiDg value.
Beyond the albumen gland although externally simple the duct is
divided by a septum into two passages, one for the eggs and one for
the spermatozoa, and still further on it becomes completely divided
into two separate tubes. The female portion opens to the exterior
by a thick-walled muscular part, the vagina, into which a tuft of
tubes — the mucous glands — opens. The vagina also receives the
opening of an organ called the spermatheca, which is a round
sac at the end of a long duct in which the spermatozoa received
from another individual are stored up. In addition to this, a
thick-walled sac called the dart- sac also communicates with the
vagina. .In this sac is found a calcareous rod which is thrown out
into the body of another individual about the time of fertilization.
The male duct opens also into a muscular organ called the penis,
which can be partly everted, that is, turned inside out, and so
protruded. The function of this organ is to transfer the sperma-
tozoa to another individual ; it has a blind pouch projecting
inward beyond the place where the male duct enters it called
theflagellum; intiiisthe spermatozoa are massed together into
bundles called spermatophores. Both penis and vagina have
a common genital opening far forward on the right side of the neck
(Fig. 108).
Few MoUusca have such complicated generative organs as the
snaiL One large group of marine snails, the Opisthobranchiata^
resemble Hdix in being hermaphrodite, but none possess the dart-
sac, and in many the generative opening is placed further back and
connected with the opening of the penis by a groove called the
seminal groove. Hence the penis is obviously derived from a
muscular pit on the side of the head into which the spermatozoa
trickled and was at first unconnected with the generative opening.
In another group of maiine snails, the Prosobranchiata, there is
222 MOLLUSCA. [chap.
a separation of the sexes and the albumen gland is absent. The
penis is not a sac which can be turned inside out^ but a projecting
lobe of the body, often of great size. In the most primitiye
Mollusca — the Solenogastres — the genital organ remains through-
out like a thickening of the wall of the pericardium or coelom ; the
eggs and spermatozoa drop into the pericardium and find their way
out by the nephridia, just as is the case with Annelida.
This is the case also in Cephalopods, where, however, there were
originally four kidneys, and the one or two which serve as generative
ducts are specialized for this purpose; thus the duct is in the male
prolonged into a papilla which serves as the penis. A commoner
case is for the generative organ to be closely connected with one
kidney and to burst directly into it. This is found in the simpler
Prosobranchiata, such as the Limpet {PateUa), the Ear-shell
(HcUiotis) and their allies. In Nucula and the simplest bivalves
there are two generative organs and they open into both kidneys;
in the Pond-mussels {Anodonta and C7ni(?), and the more modified
forms, they open independently close to the kidney opening. There
is little doubt that in all Mollusca the tube convejdng away the
generative products was originally a kidney or a part of one.
Having got some idea of the arrangement of the organs of the
snail we must proceed to consider certain points about
of^dy."*^'^ the form of the body considered as a whole. If we
except the genital opening, the head and neck of the
snail are exactly bilaterally sjonmetrical in their outer form; on
each side there is a taste-tentacle and an eye-tentacle and the
mouth and the opening of the mucous gland are exactly in the
middle line. Most of the ordinary animals we see — birds, quadrupeds,
fishes, insects, worms, etc. — are bilaterally symmetrical with regard
to the exterior and many with regard to the whole body. The
peculiarity of the snail is that, while it follows the ordinary rule as
far as the head, neck and foot are concerned, it departs from it
with respect to the visceral hump and the included organs. The
shell is, as we all know, spiral, but this shape is due to the shape of
the visceral hump contained within it, by the activity of the skin of
which the shell is produced. This spiral shape again is simply due
to one side being longer than the other, and it is connected with
the shortness of the right side that we find the opening of the vent
on the right side. In all bilaterally symmetrical ani'mftlq this
opening is situated in the middle line, but in some of the marine
allies of the snail — the whelk, limpet and others forming the group
VIII.] GASTEROPODA, 223
Prosobranchiata — ^the inequality of the tivo sides of the visceral
hump is carried to such an extent that the anus is brought right
round so as to open nearly over the middle of the neck ; and where,
as in the Ear-shell {Haliotis), there are two gills, the left becomes
pushed over to the right side and the gill belonging to the right
side becomes displaced to the left. Since the visceral ganglia are
connected with the bases of the gills, one side of the visceral loop
becomes pulled over the other in consequence of the displacement
of the gills (Fig. 116). This condition of the nervous system is
called the streptoneurous condition; it exists in all the groups
which are ordinarily termed "sea-snails/' i.e., Prosobranchiata, and
though most of these have only one gill, the twisting of the visceral
loop may be regarded as a proof that they originally had two. In
another large division of the sea-snails, the Opisthobranchiata, the
shell is generally small or has quite disappeared, and since where
this has taken place there seems to have been a tendency to undo
the twisting, the anus becomes pushed back to nearly the middle
line and the visceral loop becomes straightened out and shortened.
There is reason to believe that this last process has gone on in the
snail, though it has kept its shell. It appears then that the curious
spiral form of part of the body and the inequality of the sides
have something to do with the possession of a large shell by a
crawling animal We do not understand very clearly how the one
thing has brought about the other, but we can understand that
there would be a tendency in a tall visceral hump to topple over
to the one side or the other and thus exercise a greater strain on
one side than on the other. Certain it is, at any rate, that the
only existing Mollusca which possess large coiled shells and yet are
bilaterally symmetrical, are the pearly Nautilus and another rare
Cuttle-fish (Spirula), which do not crawl but swim.
The class or primary division of the Mollusca to which the snail
belongs is called the Gasteropoda, on account of the flat smooth
foot or crawling surface which they all possess (Gr. yaor^p, the belly ;
irov9, iroSo?, foot). The shell is typically composed of a single piece,
never of paired pieces ; and from this circumstance is derived the
general term ** univalve" often applied to the Gasteropoda by
collectors ; in one small division of the class (the Isopleura) the
shell is represented by eight pieces placed one behind the other in
the middle line.
LaMELLIBBANCBUTA = PELEOYPODA,
Q_l
The characters mentioned ivt the end of the last section shaiply
(separate the Gaattropodn from another clasa oS
Mmei"."™'" Molksca, the Lnmellibranchiata or Pelecypoda, to
which the coinmoii mussel and innumerable marine
forms, such as the oyster, clam, cockle, etc , belong. The Moliases
belonging to this class have a shell composed of two similar pieces,
the right and left valres, united by a horny flexible piece, the hinge
(Fig. 117). The foot is typically formed like a wedge or axe-hettd,
' miuolM
pDlDt of
Fm. 117. Shell contsiniiig Anodonla mulahilii. and behind it tba mi
so empty left nhell.
1. Points of inwrtion of the unterior protraclor (above) and retractc
iMon) of the abell. I. t'oiat of uissrtioQ at tbe anieiior addaat
3. Point of inBettioa of the poBlerior pioliaoloi of the ibell. i
iniertion of the posterior adductor musole. 6. Lines formed by
ftltachioents of the mantle. 6. Umbo. 7. Dorsul ajphos. i
■ipbOD. 9. Foot protruded. 10. Liaee of growth.
whonoe the name Pelecypoda (6r. jriKiKVi, a hatchet), and is ooed
as a plough to force a way through tbe mud in which the creatuni
live. There are many species of pond- or river-mneselG in Ntnlb
America : Jntxlontn cii'/iiuea ie perhaps tbe commonest in En^and^
but in places Unto pictorum is abundant; A. cygnaea occtitB io
Canada and the United States and in these countries Unio eom-
pianatus is also common. Auy one of these forms will serve our
viil] lamelubranchiata. 225
purpose. The shell is about four inches long and two inches high,
-^ -^ .. and is covered with a black horny layer, the so-called
The SheU. , ^ ^ ^ i
periostracum. The shell is apt in places to be
eroded by the action of the carbonic acid in the water. Under-
neath it is a tiiick slightly translucent layer of crystals of carbonate
of lime, called the prismatic layer. The inner part next the
mantle is composed of thin layers placed one above the other.
This is the mother-of-pearl or nacreous layer, which in many
Molluscs has an iridescent sheen, owing to its action on light.
These three layers are also present in the shell of the snail and in
all other Mollnscan shells, but they are very easily made out in the
shell of the pond-mussel. To the periostracum the colour of the
MoUuscan shell is mainly due. The periostracum and prismatic layers
are formed by the edge of the mantle and if destroyed they cannot be
replaced. The nacreous layer is deposited by the whole surface of
the mantle. If by chance a grain of sand gets wedged in between
the mantle and the shell it is apt to become covered with layers of
mother-of-pearl, and in this way a pearl is formed. The more costly
pearls however arise within the soft parts of the body, usually
encysting around some parasitic larva. The shell is marked by a
series of curved lines running parallel to one another. These lines
mark the limits of growth attained in each year, the amount inter-
vening between two lines being the amount of growth accomplished
in a year. It will be seen that the common focus around which the
curves run is not in the centre of the hinge line, but decidedly
nearer one — the anterior — end. This common focus is called the
umbo, and it represents the shell with which the Unto started life
(6, Fig. 117).
As might be expected from the shape of the shell, the mantle
has the form of two great flaps hanging down at the sides of the
body. The flaps have a free edge in front, below and behind, but
pass into the general wall of the body, with which they fuse, above.
The edges of the mantle flaps are very much thickened and closely
adherent to the shell ; as stated above, it is by these edges alone
that the periostracum and the prismatic layer are formed.
The hinge is strictly speaking part of the shell ; it is secreted
by the ectoderm of the back of the animal between the two mantle
lobes. When the valves of the shell are pressed closely together
the hinge is bent out of shape and by its elasticity it tends to
throw the valves apart; hence when a mussel is dead the valves
always gape.
The two valves in Unio articulate with one another by means
& AH. 15
226 HOLLUSCA. [chap.
of teeth. There are a p&ir of stoat teeth a little in front of the
umbo, on the left valve, working on either aide of one tooth on the
right valve; these are called the cardinal teeth. A long ridge
on the right valve, woridng between two ridgea on the left viln,
ifl called the lateral tooth. Atiodonta derives its name (6r. aV-,
not ; iSovt, ihevrot, a tooth) from the circnmetiuice that the sheD ia
devoid of teeth.
Vta. lis. Bight side ot inodonto nmlabilii with tha mftntls cat ain; H)d tlte
right gilla folded btdk k About 1. From HatBcliek uid Cori.
L Uoath. 2. Addb. 8. Corebro-pIeiiTBl ganglion. 4. Anterior aJdaetov
miucle. 6. Anterior protractor moscle of the shell. S. Betnetor
miucle. T. Dorsal siphon. B. Inner labial p&lp. 9. Foot. 10. Ex-
ternal opening of nejmridinni or organ of BojanoB. 11. Opening of
genital dacL 12. Outer right gill-plate. 13. Inner right gill-i£ue.
14. Tsntral siphon, IG. EpibrSDChial obamber, tha inner lamellae of
the right and left inner gills having been slit apart. 16. Posterior pro-
tractor mus«Ie.
When the shell is removed from the animal the cut ends of the
fibres of two large muscles are seen. These mnscles, which run
transversely from the one valve to the other, are called
the anterior and posterior adductors respectively,
and it is by means of them that, when danger threatens, the animal
closes the valves and shelters foot, gilla and body, within. Just
behind the anterior adductor is a pair of small muscles running into
the foot, and these are the anterior protractors of the shell. A
similar pair, the posterior protractors, are found just in front of the
posterior adductor, and by the combined action of the four the shell is
drawn forward, the foot being (relatively) fixed in the mud (Figs. 118,
121). The foot is thrust forth by the forcing of blood into it, through
the contraction of the muscles which underlie the skin in various parts
of the body. The retractors (of the shell) enable the animal to
LAMELL1BHANCHIAT4,
I move backwards wheu neceaaaiy. A small group of musclea ranniag
from the mantle to be attached to the shell near the umbo puU the
flhell downward and help to plough a furrow in the mud. The
I ftulmal moves by forcing out the foot ajid wedging it in the mud in
front and then drawing tlis body after it.
At the sides of the body on each side we find the hrancbia or
gill, or ctenidium, which as in the Gasteropoda consists of a hollow
\ axis bearing two rows of plates. The cteuidium is. however, highly
1. 119. A. Iiiag»mraittia sectiim thioaeh Aiuitlanta to abow the eiraulaUon
o( tilo blood. B. Beclion througb Anodonta uoar the posterior edga of
the tool. From Hones.
1. Bight auricle. 2. TeDtrlctc. 3. Kebcr'a orgnit. i. 'Veaa, cava,
S. E9«ieiit bmDcbitU trank. 6. Efferent pallial vessel. T. Efferent
bnndiukl vecael. 8. Biaachiae. 0. Afferent branchial vessel.
10. ESecent lenal vessel. 11. Afferecl biKncbial trunk. 12. AHeceitt
ISD&I TuaaL 13. Keotum .
1. Bi^t auricle. 2. Epibranchial Ehamber. 3. VoDtriole. 4. Vena
cava. 6. Non- glandular part of the kidney. 6. Olaadular part of
the kidne]'. 7. Intestine in foot. S. Perioardioni. 9. Shell.
10. Ligament of shell.
ItDodified in Unio. The axis is attaohed high up to the side of
2ie body in front but projects freely into the mantle cavity behind,
rhe plates hare become narrowed bo as to form long filaments,
ind the ends of each row are bent up and are, in the case of the
outer row, fused to the mantle lobe. The bent-up ends of the
ir row are joined to the foot in front and to the corresponding
a of the utenidium of the other side behind, but in the middle
15—2
228 MOLLUSCA. [chap.
they are free, at least in Bome species (Fig. 119). Saccessive fila-
ments of one row are welded together into a plate, called a lamella^
by the fusion of their adjacent edges, leaving only occasional holes
for the percolation of the water, so that individual filaments appear
like ridges on a ploughed field (Figs. 118, 120). The descending
and bent-up ends of the same filament are tied together by cords or
narrow plates of tissue traversiug the space between them. These
cords and plates are called interlamellar junctions, since they
unite two lamellae. The pieces of tissue uniting the filaments are
called interfilamentar junctions, or collectively, subfilamentar
tissue. Gill-plate is the name given to the whole mass composed
of one row of V-shaped filaments : there is thus an outer and an
inner gill-plate on each side, and each gill-plate has two lamellae
formed from the descending and ascending limbs of the filaments,
respectively (Fig. 119). It is this peculiar modification of the
ctenidia which has suggested the name Lamellibranchiata for the
class.
Each V-shaped filament is clothed on its outside, that is, the side
looking away from the concavity of the V, with high ectoderm cells
carrying powerful cilia. By the action of these a strong indraught
of water is produced, the current entering between the posterior
borders of the mantle lobes, which normally gape slightly. On this
current the animal depends both for respiration and for nutrition,
since the food consists entirely of the minute Aninntla and plants
swept in with the water. The normal position of the Mussel is to
have the anterior end deeply embedded in the sand or mud and the
posterior end protruding ; the animal moves only when for some
cause the water becomes unsuitable for its purposes.
Since the upturned ends of the inner rows of filaments of both
ctenidia are united behind the foot, a bridge is formed dividing the
mantie cavity into an upper or epibranchial division and a lower
or hypobranchiaL The gaping opening between the mantle lobes
at the posterior end is similarly divided into an upper portion, the
dorsal siphon, and a lower, the ventral siphon. Since it is the
outer lower surfaces of the filaments which are clothed with cilia,
it is into the ventral siphon and hypobranchial chamber that the
current passes. The lips of both siphons — especially the ventral
siphon — are plentifully beset with small papillae, which are sensitive
to light and shade. If the shadow of the hand be allowed to pass
over them the mantie edges are instantiy drawn together and the
siphons thus closed. In the scallop (Pecten) similar papillae are
LAMELLIBRANCHIATA.
Ideveloped into well-formed eyes. Part uf the water passes through
I the small holes left between the gill-fiJamentB and bo into the
K epibraocbial chamber and escapes by the dorsal siphon, carrying
1 with it the matter cast out from the kidneys and the anus. As it
I percolates throagh the gills the blood which circulates in these
gtws receives oxygen and gets rid of its carbonic acid.
A large part of the water, however, pursues a different i;our3e.
I In front of the gills there are situated two organs called labial
I palps, on each side of the anterior part of the animal (8, Fig. 118).
s-^-
I ], Cerebro-pleuiaJ iiftnglion 2 Cerobio pedal c(iiiiiiiisaur« 3 Oesopliagns.
i. Anlenot proHtuitor moscla 6 Li%er 6 Stomach 7. AorM.
8 Ext«raiil opening of orpnn of Bcijbqds or cephndium 9 Nephio-
■ti>m« or intPraol openniR of the tMne 10 FencuTditim IL Bight
aancle IJ lostt-rior end of vsutride passing into posterior aorta.
13. Bectam. 14. Oluxidular part of nephridiam. 16. Adob,
m. Op«DiD|i of epibnnchial c1]aiiib«r. IT. Teatral aiphoD. 18. Edge
of Bliiill. 19. Cerebio-vUceral commisatire. 20. loCeitiiie. 31. Foot.
23. ReprodnctiTe orgaDS. S3. Pedal gaoglioii ot right side. 24, Motitb.
95. Opeomg of the raproductivs oi^an.
These are triangular flaps, an upper and lower on each side, the
Burfaces of which are covered with grooves clothed with abundant
L cilia on the sides turned towards one another. The two superior
I labial palps are connected by a narrow ridge crossing above the
I mouth ; the two inferior labial palps by a similar ridge beneath it,
[ The mouth thus lies at the bottom of a trough, — the lips of which
[ are formed by the superior and inferior labial palps respectively.
230 MOLLUSCA. [chap.
The mouth is situated beneath the great anterior adductor muscle
which projects beyond it like a forehead. The action of the labial
palps is to direct a large portion of the incommg current into the
mouth, and thus the animal obtains its food.
The alimentary canal shows a considerable resemblance to that
of the snail No trace, however, of radula, buccal mass, crop or
salivary glands, is to be seen. A short oesophagus leads at once
into the stomach, which is a wide sac receiving right and left the
ducts of the two lobes of the liver. The intestine runs vertically
down into the foot, makes several loops there and then turns back
and reaches nearly to the point from which it started, Le,, the
hinder end of the stomach. Thence it pursues a straight course
through the pericardium and over the posterior adductor muscle, to
end in an anal papilla which projects into the epibranchial mantle-
cavity. For pare of its course the ventral wall is infolded towards
the cavity so as to produce a ventral typhlosole comparable to the
dorsal typhlosole in the worm. The straight concluding portion of
the intestine is called the rectum. The pericardium is situated
in the mid-dorsal line posterior to the stomacL The fact that it
surrounds the rectum is the consequence of its origin as a pair of
sacs in the embryo lying to the right and left of the intestine,
which later meet above and below this organ.
There are, as mentioned above, two kidneys or nephridia in the
mussel These, frequently termed the organs ofBoj anus, are
dark coloured bodies situated beneath the floor of the pericardium
on either side of the vena cava. Each consists of a U-shaped tube
lying horizouiaUy, with one limb placed vertically above the other
and the bend directed backwards. The deeper limb is the active
part; it has numerous folds projecting into it which are covered
with dark cells. It opens into the pericardium in front by a
curved slit lined with powerful cilia which produce an outward
current. This of course is the reno-pericardial duct such as has
been already described in the snail The outer and upper limb is
wide and smooth-walled and opens into the deeper limb beneath
the posterior adductor. In front it opens to the exterior through
a pore with thick lips placed just above the place where the
upturned ends of the inner row of filaments are attached to the foot
(Pig. 120).
The kidney, since it is a tube lined with excretory cells and
communicating internally with the body-cavity, is a nephridium
comparable to that of the worm, Lumbrkus, In the worm the
LAMEi.LIBRANCmATA.
231
functioD of the internal opening is to convey to the exterior the
fluid in the body-carity, which contains excretory matter thrown
out by the cells lining the coelom.
The anterior end of tlie perif ardiiim
of the Mussel has a. brownish ted
colour and is prodac«d into nu-
merous httle pockets lined by
jiecaliar cells, which ore excretory
in function (Fig. 119), This por-
tion of the pericardial wall is called
Keber's organ, and the excreta
thrown out by it pass down the
reno -peri cardial canal
The heart consists of a ventricle
which surrounds the rectum, and
tno flat triangular ati rides, the
broad ba^es of which are inserted
into the wall of the pericardium
just over the place where the bent-
np ends of the outer filaments of
the ctenidium are attached to the
mantSe. From the ventricle blood ia
driven forwards by an anterior aorta
dorsal to the rectum, and backwards
by a posterior aorta ventral to the
rectum. From these arteries it
finds its way into a multitude of
irregular spaces in the foot and the
other portions of the body, and
eventually reaches a vessel, called
the vena cava, lying under the
floor of the i>ericardium in the
beiwMn leit uid tight msDile middle lino, between the right and
lfX„"r.'?,l,."'ptaS lef »PPe' li-bs ot the two Iddneji
ohaniber. It. Keber'a orgao. From the vena cava the blood
13. NepbroBioDiB or iawmal streams out through many chan-
Fia. 131. Dorsal view or Jiiodonrn
mutabtU; witlt tha upper wnll
<it tha pericArdinm rcmoveJ to
■how the heart k about I. Alter
HatMhsk and Cori.
1. Foot. 2. Antarior addnclct
miiaclc. 9. Bslmtor mDaclo,
4. DepraSBorlniisalea. S, Pos-
terior protractor ranacle. 6,
Poatnior adduolor muscle. 7.
SotmL aiphoQ. e. Ventrnl
tiphon. 0. Anua. ID. Split
opening of organ of Bojanos.
14. Ventricle. IG. Left auriale.
16. Anterior protnuilur mUBCle.
in the wall of the kidney and
reaches the axis of the ctenidium,
whence it makes its way into the
filaments, especially those of the outer row. From the upturned
edgos of these htst it reaches the mantle and from this tlie auricle.
232 MOLLUSCA. [chap.
Some blood is sent to the lobes of the mantle, as in the snail, and
through the thin skin absorbs oxygen ; this blood is returned direct
to the auricle without passing through the gill ; from this fact it
appears that the mantle lobe as well as the gill is a respiratory
organ.
In the nervous system the cerebral and pleural ganglia on each
side are generally regarded as coalesced, but a distinct pleural
ganglion has been observed in some cases on the cerebro-visceral
commissure anterior to the pericardium. There is a long visceral
loop, ending in two closely conjoined visceral ganglia, placed beneath
the posterior adductor (Fig. 120). On either side of these, just
where the axis of the ctenidium becomes free from the body, is a
thickened patch of yellow ectoderm — the osphradium. This is a
peculiar sense-organ, the function of which, it is believed, is to test
the water passing over the gill as to suitability for respiration.
There is a pair of large otocysts in the foot.
Mussels are male and female : their productive organs are
paired, and consist on each side of a bunch of tubes spreading
through the foot. The ducts are continuous with the walls of the
ovary or of the testis. They open by slit-like orifices just in front
of the opening of the nephridia on each side of the foot The
spermatozoa are swept out by the water passing through the dorsal
siphon and are sucked in by the inhalant currents of female indi-
viduals. The eggs when cast out are detained between the two
lamellae of the outer gill-plate and there fertilized. They develope
into peculiar larvae called Glochidia, provided with a sticky thread
or byssus. A bivalve shell is developed but not the foot. When
a fish passes by the mother expels the Glochidia from the gills, and
they seize hold of the tail or fins of the fish and embed themselves
therein. They develope there for some weeks and change gradually
into the adult form. They show a remarkable sensitiveness to the
presence of fish, but if they fail to attach themselves to one they fall
to the bottom of the water and perish.
Lamellibranchiata as a group have very uniform habits: the
principal points in which they differ from one another are (1) the
degree of complexity which that all-important organ the ctenidium
has attained, and (2) the extent to which the animal is able to burrow.
The simplest forms, such as Nucida, have ctenidia like those of
a Gastropod, a fact which suggests the view now generally held,
that the Lamellibranchs are descended from some primitive type of
Gastropod.
In others, such as the Sea-mussel {Mi/Hlas)» the ctenidia have
-m.] LAMELLIBRANCHUTA. 233
be BUDe eztemal appearance as those of Unio, but the filaments
re vei7 loosely united with one another and their upturned ends
n not fused to the mantle. The foot is small and tongue-shaped,
the animal never burrows and rarely
moves, being fixed by a cord of mucus
caJlod the byssus, secreted byagland
in the hinder part of the foot.
In the Oyster {Ostrea) the foot has
disappeared and the animal passes its
life resting on one side. In the
Scallop (Pectm) the foot has also
atrophied, but the animal is able to
swim through the nater by flapping
the valves of the shell. The Cockle
(Cardium) has a iat^e and powerfol
foot hy which it is enabled to execute
leaps.
Ml/a (sometimes known as the
Clam, tiiough this term is applied to
many Bivalves) and its allies burrow
deeply in the sand and have the edges
of the mantle behind drawn out into
two long tubes closely apposed to one
another, termed the dorsal and ventral
siphons. By means of these tubes
they keep up a connexion with the
surface, BO that the currents of water
are not interrupted. Similar tubular
funnels, though not so much drawn
out, are seen in the Eazor-shell {SoUn)
(Pig. 122). Pkolaa and some others are
able to burrow in rock ; this is said
in some cases to be efTected by an acid
secretion poured out by the flat disc-
like end of the cylindrical foot
Teredo, the ship-worm, burrows in
timber ; the siphons are very long and
covered with a shelly deposit; the
origiiutl valves of the shell are very small compared to this
secondary shelly tube. This animal is very destructive to sub-
merged woodon structures; a wooden pile supporting a pier in
Fia. 123. Boltn vagina, the
Buar-ahell, the shell ii open-
ed ancl the poeterioi pftrt of
Um Diuitle it torn to admit
of thu.
1. Shell. 9. Foot, S. Lb-
U»l palpa. 1. OillB.
5. Tom portdon of muitle.
6. Brutle in ventnl siphon.
7. Bristle in dorsal siphon.
VancouTer was hi eighteen mouths reduced to a mere spongevnl
of vood b; ita ravages.
Class in. Cephalopoda.
A third dasi of the MoDnsca, very differently constitated from
the LamellibraDchiata, is that of the Cuttle-fish, or Cephalopoda.
This pamdoxicftl name,
literallj "head-footed"
(Qr. Kt<t>aki}, head ; tovs,
iroScJs, a foot), is suggested
by the circumstance that
the foot has grown for-
ward and upwards at each
side of the head, and that
these two extensions have
met and coalesced, so to
speak, on the back of the
neck. The edges of this
part of the foot, which
may be called the fore-
foot, are drawn out in-
to strap-iike processes,
which are the arms by
nhicli the animal seizes
its prey. The e<lgos of
the hinder port of the
foot, OQ the other hand,
have become bent round
aud joined beneath the
auimal, so as to form a
tube, the funnel, through
which water is ejected
from the mantle-cavity.
The best known Brit-
lo. 123. DiigTBTna ol s Kties of HoUoaca
to ahow tbe [orm of Iha foot and it*
regiooB and the lelKtioDs of tbe Tisoet*!
hamp to tliD UDtero. posterior and dono-
veulral aire. After Lanki'ster.
A PraBobrancb Goatropod. IL La-
tDellibranoh. III. A Cepbalopod.
A. Anterior autfoce. P. Poilerior ani-
face. D. Dor«J aoiface. V. Ventral
BurTace. 1. Month. 3. Antw.
Sepi.. ""' ^l"""" 8. Mantle-oavity. t. Foot,
lopoda are
the Squid, LoUgo forbesi, often caught by trawlers, to whom it is
known as the 'ink-fish'; Sepia ojficiiialis, the cutlle-fish, taken in
the southern waters, is abundant in the Mediterranean, where it is a
favourite article of food ; Moschitea cirrom with eight arms and a
single row of suckers; Polypus (or Octopus) vulgaris almost c
Plo, 124, Posterior viev of mnls or Sep a qffieinalti x 1 The mantU-M*iV
has been opvued to expose ts contenta
!■ Long ann half pratraded 2 Ash rt arm tlua one a beato-oot.vUzed.
8, Lips Buirouud og liomj jaws moutli i t iterDol opcDiQg of
fniinel. 5 E;o 6 OartiloBinooa kcob on mantle wliivh Qta mta<1
ibt lOcket 9 7 O 11 S Soeket tor 6 0 Auua.
prwBorinttBoIoof IbafunQol II Hep odu tveport IJ. Bightki
pftpilU, 131 \ iBcerai maae. 14. I m.
236 MOLLUSCA. [chap.
fined to the south coast and commoner on the French shores and in
the Mediterranean. Another squid, Ulex illecebrosa, is common in
the Oulf of St Lawrence and on the shores of the eastern United
States. The body of S^ia appears to be composed of a swollen
head separated by a neck from a tapering trunk. When closely
examined, however, the body is seen to be nothing but a long
pointed visceral hump, like that of the snail, but it is not twisted
and is unprotected by an external shelL The mantle, as in the
snail, is a skirt-like fringe of skin, the space between its inner
surface and the visceral hump forming the large mantle-cavity. In
order to compare the animal with the snail it must be placed with
the point of the hump projecting upwards and backwards (Fig. 123).
The so-called head includes the true head, with two enormous eyes
of almost human aspect, surrounded by the fore- foot. The fore-foot
is drawn out into eight short pointed arms, thickly covered on their
inner sides with stalked suckers (Fig. 124), and two very long arms
bearing suckers only at their expanded ends. These latter can be
pulled back into two large pits situated at their bases, and when so
retracted they are completely hidden from view.
The sucker is a cup with a homy rim which keeps the opening
from collapsing. In its base there is a swelling, which is the
end of a muscle running into the stalk, and by the contraction
of this, when the cup is applied to any object, a partial vacuum
is produced. By means of the suckers the Squid can take a firm
hold of its prey.
The hind-foot is the tube, known as the funnel (Figs. 124 and
127). The posterior end of this is overlapped by the hind end of
the mantle; in other words, it projects into the mantle-cavity. The
mantle is veiy muscular; by the contraction of longitudinal
muscles running towards the apex of the hump the mantle-cavity is
widened ; by the contraction of circular muscles it is narrowed, and
by the alternate action of these two sets of muscles, water is sucked
in and forced out of the mantle-cavity.
When, however, the mantle-cavity is contracted, two projecting
pegs on the inner side of the mantle fit into sockets on the outer
side of the funnel (6 and 8, Fig. 124). No water can then escape
over the free edge of the mantle, and all is ejected in a narrow and
forcible stream through the funnel The funnel itself is muscular
and by contraction aids the process ; there is a valve-like projection
inside it which prevents water from being driven back into the
mantle-cavity (Fig. 127).
VIII.]
CEPHALOPODA.
237
Since water is sucked in gently and ejected forcibly the animal
is propelled in the opposite direction, that is backwards, by the
reaction of the stream against the surrounding water. Sepia can
however also swim gently forward by wave-like undulations of the
two lateral fins. These fins are flaps of skin projecting from the
sides of the visceral hump (14, Fig. 124).
It has been said that the visceral hump is unprotected by an
7— .
Fio. 125. A diagram ahowing the relation of the kidneys to the perioardinm
in Sepia,
1. External opening of the kidney into mantle-oavity. 2. Internal opening
of the kidney into the pericardial eoelom. 8. Opening of the right kidney
into the donal sao and henoe into the left kidney. 4. Left kidney,
yentral portion. 6. Beno-perioardial canal. 6. Pericardinm (part of
the eoelom). 7. Branchial heart. 8. Dorsal sao common to both kidneys.
A. Arrow passing into left kidney by external opening from mantle cavity.
D. Arrow passing into right kidney through external opening into median
lobe. 0. Arrow passing into external opening and then into internal
opening, and so into pericardial eoelom. The extension of the eoelom in
which the generative cells arise is not shown in this diagram.
external shell This is not strictly true. On the anterior surface
of the hump there is an oval plate-like shell completely hidden in
a sao formed by the meeting over it of upturned flaps of skin (14,
Fig. 127). From its upper surface project an innumerable number
of delicate calcareous plates parallel to one another, the spaces
between them being filled with gas so as to give lightness.
In one or two living Cephalopoda, as for instance the Pearly
Nautilus (Nautiltis pompilius), and in very numerous extinct forms>
238 MOLLUSCA. [CHAP.
there was a large tabular external shell which might be straight or
coiled, but which always had the peculiarity of having a large
number of septa or transverse plates dividing up its cavity into
chambers, only the last of which contained the visceral hump, the
rest being filled with gas (Fig. 130). In Sepia it is supposed that the
chambers have become so small and shallow that the last one simply
appears as a plate situated on port of the surface of the hump. The
other chambers contain gas as in Nautili^.
Sepia possess tv?o well-formed ctenidia, each consisting of an
axis bearing two rows of thin plates. The axis is suspended
from the body by a membrane, and the ctenidia project forwards
and downwards instead of backwards as in the Lamellibranchiata
(7, Fig. 124).
As in Lamellibranchiata, there are two kidneys which open by
little papillae placed just in front of the bases of the ctenidia
(12, Fig. 124). Just inside the papilla is a narrow opening, the
lips of which are folded so as to make it appear like a rosette.
This is the internal opening of the kidney: it leads into a lateral
prolongation of the pericardium, which is the reno -pericardial
canal (5, Fig. 125). The kidney has the form of a wide sac and may
perhaps be compared to a U-shaped kidney, like that of Unio, in
which the two limbs have become merged in one another.
The wall of the kidney is smooth, except over the course of the
large veins which run beneath its upper and inner walL Here the
epithelium is folded and consists of tall cells which are actively
engaged in extracting excreta from the blood, as is shown by the
rows of granules with which they are filled. From the anterior ends
of the kidney two outgrowths project which inmiediately fuse into
one and constitute a great pouch called the dorsal sac (8, Fig. 125)
stretching upwards and backwards just underneath the shelL This
peculiar extension gives to the two kidneys the form of M, between
the median V and outer limbs of which lies the pericardium.
Posteriorly the cavities of the right and left kidneys also com-
municate with one another.
The pericardium is a wide sac lying between the dorsal sac of
the kidneys and their ventral parts. At the sides it gives ofif the
reno-pericardial canals, whilst the stomach and intestine project
into its roof.
The ventricle of the heart is a spindle-shaped sac Ijang trans-
versely (1, Fig. 126). Into its two ends open the tubular thin-walled
auricles which receive the blood from the ctenidia. From its
viil]
CEPHALOPODA.
239
anterior wall a i>oweiful artery, the anterior aorta, is given oflf
ninning forward above the oesophagus to the head, and a smaller
artery or posterior aorta goes backwards and upwards to supply the
stomach and genital organ. These arteries have regularly formed
branches from which the blood enters definite veins. This formation
of well-defined channels for the Uood is characteristic of the Cephalo-
poda. Of these veins the most important are : (1) the anterior
vena cava ; this is a charmel in the mid- ventral line in front of the
-8
1.
Fio. 126. View of heart and chief blood-vessels of Sepia euUrata.
Partly after Parker and Haswell.
Ventricle. 2. Anrldle. 8. Otenidinm. 4. Anterior aorta. 5. Pos-
terior aorta. 6. Anterior yena cava. 7. Vein from ink-sac.
8. Genital yein. 9. Branchial vein. 10. Branchial heart. 11. Bight
abdominal vein. 12. Vein from the mantle.
kidneys, which forks and sends a branchial vein over each kidney to
the base of each gill ; (2) the abdominal veins ; these are a pair of
large channels which come from the mantle, especially the upper
part of it, and join the forks of the vena cava just before they enter
the gills ; (3) the genital vein ; this is a trunk draining the genital
organ, it runs along the ventral wall of the dorsal pouch of the
kidney and joins the right fork of the vena cava ; (4) a vein from the
ink-sao joins the same fork, and (5) on each side a smaller vein from
the mantle joins the main venous system at the branchial hearts
[OHAK
. Ovary. 3. OeDiCal part of the ooelom. S. Perioardial part of tlw
ooelom ; the teference line touchea the heart. 4. Mantle^avitT. 6. See-
tion of inteatine. 6. Incomplete septum between genital aad perioaidial
ooelom. 7. Ventral limb of kidney. 8. Glaitdalftr tiMOB of kidney.
9. Dorsal limb of kidney. 10. Stomach. 11. Liver dnct
13. " Panoreatia " oaeoB. 13. Liver. 14. Shell. IS. Shell uo.
16. Dorsal homy jaw. 17. Anterior opening ol fonneL 18. Talvs
infimnel. 19. Badula. 20. Lips. 31. Tentral homy jaw.
viil]
CEPHALOPODA.
241
(Fig. 126). Where these yeins come in contact with the kidney
wall the special excretory tissue mentioned above is developed.
A peculiar feature in the circulatory system is the presence of a
pair of muscular swellings of the forks of the vena cava just before
they enter the gills. These are the branchial hearts, the
function of which is to drive the blood into the gills, whereas the
auricles drain it out of them. Each branchial heart projects on the
one side into the kidney and on the other side into the reno-
pericardial canal, and the epithelium of the latter where it covers
the heart is greatly thickened so as to form a cushion, the function
of which is excretory. This, like Eeber's organ in the river-mussel,
is a remnant of the primitive excretory function which probably all
the cells of the coelom once possessed
Fza. 128. Lateral view of the central nervons Bystem of Sepia offlcinalU,
Magnified. From Cheron.
1. Upper buccal ganglion. 2. Nerves connecting bacoal ganglion with
cerebral ganslion. 3. Brachial ganglion. 4. Infundibular ganglion.
5. Pleural ganglion. 7. Supra-oesophageal ganglion. 8. Out
end of optic nerve. 9. Superior ophthalmic nerve. 10. Pallial nerves.
11. Visceral nerve. 12. Anterior nerve to the funnel. 14. Auditory
nerve. 15. Inferior ophthalmic nerve. 16. Nerves to the arm.
The dotted outline represents the buccal mass and the oesophagus.
The alimentary canal of Sepia is constructed on very much the
same plan as that of the snaiL The mouth is situated in the centre
of the arms and surrounded with a frilled lip (Fig. 127). There is a
large buccal mass containing the radula and there are a pair of
powerful jaws shaped like a parrot's beak, moveable on one another,
of which the ventral is the larger. There are two salivary glands
and a loug narrow oesophagus but no crop. The oesophagus widens
behind into the- stomach, which receives, as is usual in Mollusca, the
ducts of the liver. With the stomach is connected a side pouch
a <ftii. 16
242 MOLLUSCA. [chap.
spirally coiled. The liver is enormous, occupying all the anterior
portion of the visceral hump ; the ducts traverse the dorsal
extension of the kidneys, and are in this position covered extern-
ally with excretory tissue which by the older naturalists was termed
''pancreatic caeca" (12, Fig. 127) from a mistaken comparison with
the human pancreas. The intestine is slightly bent on itself and
ends in an oval papilla. A peculiar sac, the ink-bag, the cells
lining which secrete the pigment known as Indian ink or Sepia,
opens by a long duct on this papilla (Fig. 129). When the Cuttle-
fish is alarmed it ejects this ink and darkens the water so much
as completely to escape from view.
The nervous system consists of ganglia even more closely massed
than in the case of the snail. The supra-oesophageal ganglia
form one rounded mass ; they are produced at the sides into the
very much larger optic ganglia which are in close relation to the
eyes (Fig. 128). The pedal ganglion is divided into an anterior
ganglion called the brachial, and a posterior ganglion sometimes
called the infundibular. The brachial ganglion supplies a stout
nerve to each arm, and each nerve swells out into a small ganglion
just where it enters the arm (Fig. 129). The infundibular ganglion
supplies the funnel.
Posterior to the infundibular ganglion are the two pleural
ganglia fused together. These give rise to a visceral loop which
supplies the various internal organs and the gills. From the
same ganglion two short nerves run to the mantle and terminate
in the two large stellate ganglia, which underlie the skin and
supply nerves to all the muscles of the mantle (Fig. 129). The
buccal mass is supplied by two ganglia, superior and inferior, each
representing a pair joined by a minor nerve collar running round
the oesophagus. The inferior ganglion corresponds to the buccal
pair in the snail, the superior is a separated part of the cerebral.
It has been already stated that Sepia possesses complicated
eyes. In the embryo these are like the eyes of the snail, merely
sacs lined by visual cells and containing a transparent homy
secretion which serves as a lens. In fact, in the embryo, the sac is
at first a pit which gradually closes up. Immediately over the spot
where the first pit closed a second pit is formed in which a second
homy lens is formed just over the first one, so that the lens consists
of two pieces, and as in the eye of the Vertebrate, there is an anterior
and a posterior chamber in the eye separated from one another by
the lens.
CEPHALOPODA.
243
Into the aaterior chamber a circular fold projects called the
iris, fulfilling exactly the a&me fimctioa as the iris of the human eye
or the diaphragm in a phot<^aphic camera. Outside and around
the eye a circolar fold acts aa au eyelid.
B ay B tern, ventral view.
1. Three nerves to the arma diesected out. 2. AudUoFy nerve. S, Anterior
nerve to the tuoael. i. Nerve to vena cava. 5. Posterior nerve
to fonoel. 6. Continaation of this nerve. 7. AcoeaHory nerve to
mantle. B. Left nerve to mantle. 9. Stellate ganglion. 10. Com.
mon tmnk o( the visceral loop. 11. Left branch of the viseeisl loop.
13. Nerve to mneolea. 13. Nerve to vUcera. 14, QanRlion en
branchial heart. IG. Nerve of ctenidinm. 16. Ink-bag. IT. Duct
of ink.bag. 18. Lett nidamental gland. 10. Branchial heart.
30. Position of anne. 91. Eitemal opening of kidneys.
The cerebral, pedal and pleur^ ganglia are surrounded by very
tough connective tisane, in which the fibres, although still visible,
244 MOLLUSCA. [CJHAP.
have a cheesy consistence, the tissue being called fibro-cartilage.
In this way a kind of skull is formed, which sends a scoop-like
extension on either side over the back of the eye, covering the
optic ganglia. The edges of the scoop pass into ordinary connec-
tive tissue round the rest of the eye. This tissue forms the wall
of the eyeball.
The otocysts are branched and embedded in the ventral wall
of the skull. They receive nerves from the cerebral ganglia, but as
the nerve fibrils traverse the pedal gauglia they appear to arise from
the latter.
The genital organ in Sepia occupies the apex of the visceral
hump. It is, as examination of young specimens shows, a thicken-
ing of the wall of the coelom, behind the pericardial coelom. The
space into which the eggs and spermatozoa are shed is only shut o£f
from the pericardium by an incomplete partition, so that in Sepia
a state of things persists throughout life which is found only in the
embryos of some other forms (Fig. 127).
The genital duct is present only on one side, the left, and is
produced into a prominent papilla which in the male is used as a
penis (Fig. 124). The outermost part of the duct in the male is
A wide pouch in which the spermatozoa are welded into masses and
•enveloped in cylindrical cases called spermatophores. Just
beyond this the duct receives the excretion of two glands termed
prostate glands, and then narrows into a very fine tube which
opens internally into the coelom. Since in some cuttle-fish the
genital duct is paired and in Nautilus there are two pairs of
kidneys, while the genital ducts of that animal appear to be portions
of the kidney ducts split ofi*, it has been suggested that the genital
duct of Sepia is all that is left of a missing pair of kidneys.
The oviduct is simple, but in the female there are four glands,
the nidamental glands, situated on the wall of the mantle cavity
just outside the kidneys (18, Fig. 129). From the secretion of these
glands tough egg-shells resembling india-rubber cases are made.
The egg is about the size of a pea and when the young cuttle-fish
emerges it is already like the adult.
Cuttle-fish feed chiefiy on crabs, shrimps and other Arthropoda,
using their beaks to break the hard sheU. Some are large enough
to attack men and this circumstance has given rise to many legends.
Gigantic species are sometimes cast dead on the shores of Nova
Scotia, the length of body being ten feet, and of the arms over fifty
feet. The phylum MoUusca finds its climax in the cuttle-fishes.
Vni.] CEPHALOPODA. 245
Modem cnttle-fish hwe a. fairly uniform structure. The two
long tentacnl&r arms are absent in the Octopoda. In Lotigo the
shell is horny, in Polypus it is entirely absent. In Ommatnatrephes,
tiie common cuttle-fish of the Gulf of St Lawrence, the anterior
chamber of the eye is open and the lena bathed with, sea-
water.
Navtilvs is a remarkably interesting cuttle-fish, widely difierent
from Sepia and the others, but closely allied to most
of the extinct fonns. The arms are short, broad, ill-
defined lobes, the suckers being represented by tentacles with raised
ridges round their bases. There is a large external shell coiled
I. lAst oompleted chamber of the shell. 2. Hood part of foot. 3. Shell
maacte. i. Mantle cut away to eipooe (5) the piD-hole fj'e. 6. Outer
mil a! ibetl, some of which U out awa; to bIjow tlie chambeis. 7. Siphon.
8. TentkcnliferoiiB lobes of the foot. 9. Funnel.
forwards in the median plane over the animal's head, so to speak
(Fig. 130). The visceral hump is enclosed in the last chamber and
ftt>m the apex of the hump a membraneous tube called the
siphuncle is given off, which nms through all the other chambers,
piercing the septa. There is a fold of the coantle turned back over
the anterior edge of the shell, the firRt foreshadowing of the shell
sac o{ Sepia.
There are four gills and four kidneys and four auricles in the
heart. Thus Nautilus shows traces of segmentation. The papillae
246 MOLLUSCA. [chap.
of the posterior kidneys are split, one half leading directly to the
reno-pericardial canal, the other into the sac-like kidney. The
reno-pericardial canals thus open directly to the exterior, and the
genital ducts are in such a relation to the anterior kidneys as to
make it probable that they are the reno-pericardial canals belonging
to these, which have acquired independent communication with the
exterior.
Phylum MOLLUSCA.
MoUusca are classified as follows :
Class I. Gasteropoda,
Mollusca with a fiat foot adapted for crawling. There is a buccal
mass and radula; distinct pleural ganglia are present and the shell
is never composed of paired pieces.
Sub-class I. ISOPLEUBA.
Bilaterally symmetrical forms with a shell composed of eight
median plates situated in a longitudinal series. Numerous pairs of
ctenidia.
Ex. Chiton,
Sub-class 11. Anisopleura.
Asymmetrical forms, with the left side of the visceral hump long
in comparison to the right, the anus, kidneys and ctenidia being
shifted forwards.
Division I. Streptoneura.
The arms and ctenidia shifted so far forward that the visceral
loop is pulled into the shape of an eight and the gill is anterior to
the heart.
Order 1. Aspidobranchiata.
Usually two kidneys, two auricles, two ctenidia. The axis
of the ctenidia free and both rows of plates present.
Ex. Haliotis, Patella.
Order 2. Pectinibranchiata.
One kidney, one auricle, one ctenidium in which the axis is
adherent to the mantle and only provided with one row of
plates.
Ex. Buccinum, the Whelk.
VUI.] CLASSIFICATION. 247
Division 11. Euthyneura.
The viflceral loop is untwisted and the gill is posterior to the
heart
Order 1. Opisthobranchiata.
Marine forms with a ctenidium and mantle.
Ex. Aplysia.
Order 2. Pulmonata.
Land and fresh-water forms breathing air, having the
mantle cavity converted into a lung and the ctenidium aborted.
Ex. Helix.
Glass II. SOLENOGASTRES.
Degenerate worm-like Mollusca devoid of shell and foot and
with a ventral ciliated groove. There is a rudimentary radula and
the genital organs burst into the pericardium, the nephridia serving
as genital ducts.
Ex. Proneomenia, Neomenia.
Class III. SCAPHOPODA.
Mollusca with a tubular shell and mantle and a long cylindrical
foot ending in three processes. A buccal mass and pleural ganglia
are present The genital organ opens into the left nephridium.
Ex. Dentalium,
Class IV. Lamellibranchiata (Pelecypoda).
Mollusca with a shell composed of two valves united by a hiuge,
and a mantle of two lobes. The foot is usually wedge-shaped and
the plates of the ctenidia are fused to form gill-plates. No buccal
mass. Pleural ganglia fused with the cerebral.
Sub-class I. Protobranchiata.
Small Lamellibranchiata with a simple ctenidium like that of
Gasteropoda, and large labial palps.
Ex. Nucula.
Sub-class II. Filibranchiata.
Lamellibranchiata in which the filaments of the ctenidium are
loosely united with one another and their bent-up ends are not
united to the mantle.
Ex. Mytilus,
248 MOLLUSCA. [chap. VIII.
Sub-class IIL Eulamellibranchiata«
Lamellibranchiata in which the filaments are welded into a
" lamella " or plate and their bent-up ends are joined to the mantle.
Ex. UniOf Anodonta,
Class V. Cephalopoda.
Mollusca in which the front part of the foot surrounds the head
and is drawn out into sucker-bearing arms whilst the hind portion
of the foot forms a muscular tube. The ganglia are massed together
and protected by a skull : there is a buccal mass with a radula and
two jaws.
Sub-class I. Tbtrabranchiata.
Cephalopoda with four ctenidia, four kidneys, four auricles, a
large external shell, no suckers and very short arms.
Ex. Nautilus.
Sub-class II. Dibranchiata.
Cephalopoda with two ctenidia, two kidneys and two auricles.
The shell enveloped in the mantle and the arms are long and
provided with suckers.
Order I. Decapoda.
Dibranchiata with two long and eight short arms.
Ex. Ommatostrephes, Sepia.
Order II. Octopoda.
Dibranchiata with eight arms of equal length.
Ex. Polyptis (Octopus).
249
CHAPTER IX.
Phylum Echinodermata.
The class of animals known as the Echinodermata comprises
the well-known Star-fish or Five-fingers, the equally well-known
Sea-urchins, the less familiar Sea-cucumbers and Brittle-stars,
lastly the graceful Feather-stars. The name is derived firom two
Greek words, ^ivos, which means hedgehog (and was also used for
the sea-urchin), and Scp/ia, the skin. The prickles and spines with
which many members of this Phylum are covered constitute a
very prominent feature in their appearance. Spines, it is true, are
sometimes absent, but in every case, whether this is so or not, the
skin contains a skeleton consisting either of plates or of rods, and
the spines are merely rods belonging to this skeleton projecting
outwards and still covered by the skin which they push before them.
Class I. ASTEBOIDEA.
The most familiar of all the British Echinoderms is probably
the common star-fish, Asterias rubens, which may be found at low
water on almost any part of the coast where shell-fish, its favourite
food, abound. Very similar species, Asterias vulgaris and Asterias
polaris, abound on the American coast, the first-named on the New
England coast, the second further north in the Oulf of St Lawrence.
The species represented in Fig. 131 belongs to a different genus,
Echinaster, but in all essential features of its anatomy it agrees
with Asterias. Echinaster sentus is common on the N. American
coast. The name ''star-fish" denotes the shape. The body is
produced into five arms or lobes which are arranged like the spokes
of a wheel round the centre of the body or disc, on the under side
of which the mouth is situated. These arms are termed radii, and
the re-entrant angles between them interradiL
250 ECHINODKRMATA. [uKiP
The Btar-fish creeps abimt with its moath downwaids: iti
motion is effected b^ meaiia of numerutia ddictte
semi-traDsparent tentacles. These ore sitostdd in
6*6 grooves which run &long the aoder side of the atius and oon-
verge tow&rds the mouth, where they merge into a
FiQ. 131. Onl view of Echinatlrr ientiii with labe-reet eilended x&boat 1.
Fram Agaeaii.
surrounding that oiwning, These grooves are termed the ambo-
lacral grooves: the tentacles situated in them are called the
tube-feet, and the depressed space round the month in wliicb
all the grooves unite is called the buccal membrane (Lat bueea.
the cheek) or the peristome (Gr. Ttpi, around, aud trrdfia, moutli).
ABTEROIDEA,
So far as we have yet seen the Echinnderms aeem to differ from I
Coeleitterates, which are also radiate aiiimaU, in the details of the ]
arrangement of the organs rather than iu any fundamental features.
The skeleton no doubt is pecnSiar in being embedded in the skin :
bnt the spicules of the Atcyonaria occupy a similar position, although
they rarely cohere to form the definite rods and plates like those
characteristic of Echinodenna. When the soft parts are dissolved
away from one of these rods or plates by caustic |>otash it is s
consist of a delicate network of calcinm carbonate ; and it is found
by ohsenration of the developing young that such a plate is formed -
by a little heap of cells coming together and secreting a lime-
stone rod between them : this rod then branches at both ends and
the branches bifurcate again so that the twigs of the second or
third degree approach each other and joining form a mesh, and this '
process of bifurcating and joining is repeated luitil the plate or
spine is built up. The growth of the primitive rod into the mesh-
work is rendered possible only by the growth of the cells which shed
out the calcium carbonate. These cells remain throughout life,
more or less modified, as a kind of living network interpenetrated by
the skeletal one.
When however we cut a star-fish open we see that the animal
aptiarently cousista of two sacs plained one within the
other. The iunennoet sac or alimentary canal opens
in the centre of the upper surface by a minute opening, the anus,
through wliich undigested matter is thrown out, and on the under
surface by the month. The space or sac which apparently a urronuds
the digestive cavity of the star-fish ia a true coelom : like the
coelom iu a segment of an annelid it has been formed by the union
of two sacs which in the embryo lay right and left of the digestive
tube. Prom its walls the muscles are developed, tlie generative
cells, and also the cells which give rise to the skeleton. Between
the outer wall of the body-cavity and the tnie external skin which ,
corresponds to the ectoderm, there is a mass of more or less
gelatinous substance exactly corresponding to the jelly of a Medusa
or the connective tissue of an Arthropod, which constitutes the
substance of the body-walL Into this material wander cells budded
from the wall of the coelom: these cells from their power of move-
Uieut and appearance can be recognised as amoebocytes. It is
Irom these cells that the skeleton is formed in the way we have
described above: some of them, however, retain their primitive
character and wander about, probably carrying food to the various ,
IX.] DIGESTION. 253
The alimentary canal can most easily be examined by carefiilly
Aiimentaiy Cutting away all the upper parts of the five arms in
canal. qj^q pioco, Cutting along both sides of each arm, then
laisiDg the upper part of the animal and clipping through the
intestine near the anus. By this means the animal is separated
into an upper and lower half and all the internal organs are dis-
played in one piece or the other. The alimentary canal is then
seen to consist of several regions clearly distinguished from one
another. It begins with an exceedingly short gtdlet which passes
at the lips into the buccal membrane already mentioned : the gullet
widens out above into an exceedingly loose baggy stomach produced
into ten short pouches, two situated in the beginning of each arm.
Above the stomach and communicating with it by a wide aperture
lies a flattened pentagonal bag, called the pyloric sac, and from
each of the five angles of this sac there is a tube given off which
runs into each arm, where it is soon divided into two parallel sacs,
each produced into a multitude of little, short pouches. These sacs
are called the pyloric caeca: caecum, Latin "blind,'' being a con-
venient zoological term for a blind poucL The pyloric caeca are
tied to the upper side of the arm, each by two bands of transparent
membrane called mesenteries. From the centre of the pyloric
sac a short straight tube runs to the upper surface of the animal
where it opens by a minute anus : this tube is called the rectum,
a name, as we have seen, commonly given to the last portion of the
digestive tube. The rectum has attached to it two branched
tubes of a brown colour which open into it, called the rectal
glands.
The reason of the division of the digestive sac into various
parts is of course the different uses to which they are put in the
life of the animal ; and we may stop for a moment to enquire what
these uses are.
Star-fish feed chiefly on bivalve shell-fish, such as mussels,
cockles and clams, though they will attack almost any animal.
Their mode of seiziog their prey is very curious. If they are
attacking a bivalve, they bend all their five arms down round it,
thus arching up the central portion of the body. Then the stomach
is pushed out, — this being rendered possible by the turning inside
out of its .edges, which as we saw above, are loose and baggy — and
wrapped around the fated mollusc. The pushing out is effected by
the contraction of some muscle fibres in the body-wall : these tend
to diminish the space which the coelom occupies, and as this is
ECBINODERMATA.
iilled with incompressible fluid, the stomach must be preeeed dqL
After some time has elapsed the stsr-fish relaxes its hold aod iti<
then seen that the shell of the mollusc is completely empty saA u
clean as if it had been scrajved with a knife. It was long a p
how the star-lish succeeded in foix-ing its vii.-tim to relax its mnsdei
and allow the valves to open. It was supposed that the aUmoA
secreted a paralysing poison, but it huv been conclusively |
that this is not the case, but that the stat-hsh drags the valvei of
its victim ajiart by main force, often actually breaking the addactn
muBcles, The pull exercised by the suckers is not nearly strong
Fiii. l.^iS sua b h !■ h aitrr m tu n the act f deToiiring a Mussel.
Madrepono p ate.
enough to open the valves at on e but the star tish has staying
power and eventually the m issel si wly fo ed open. The cells
lining the sto acb n lule u large u nber of goUet^cells (v. p. lOS)
swollen by drop of lear tl ud those of the pyloric sac, on the
other hand 7 esent a d fferent appearan e These are full of minut«
granules and re all the appeara ce of the ells a other animals
which conta n the act ve d gest ve | r nc pie Hence it seems
reasonable to suj pose that the mussel s d gested by the seeretion
of the pylonc sa and its me lage which tious downwards into
the stomal h Kay po t n ren ain ni; und ^esttd s expelled through
the rectum no food ever penetrates uto the pylo c caeca.
The locomot on of the star fish s ffected n the following
manner. The tube-feet which crowd the ambulacra! grooves 1
nt]
WATER-VASCULAR SYSTEM.
255
during life continually extended and retracted. At their ends are
■tcc'vu- flat circular discs, and these disc:^ are pushed against
■yitcm. jjjg etone or rock or whatever else the star-fish is
clinging to. Then by the contractioa of their muscles t}ie centre
of the disc is pulled upwards, and so it is made to adhere in exactly
the same way in which a boy uiakei^ a leather "sucker" adhere to a
■tone. When once the disc is firmly fixed the contraction of the
tube-foot draws the animal after it.
I. IM. mtftia ol a
3. JoUf. S. FeribnuiabiBl i.
4. Peritoiiwl lining of bodj-csTity. 6. A bianoliia.
ckaeiuii. 7. Hesenteiy HupportiDg a caecnm. 8. Spine. 9. Otusiole
in Bkio. 10. Fsdiaelluia. II. Ambnl&cnl OBsiele. IS. Adunba-
laom] oaricle. 13. B&dud trunk of WHtet.VBBoulnr system.
11. Badul leptam Sfparnling the tvo perihaemal spacta. IS. BadisJ
aenv-eoii. • tbieltened band of ectoderm nitb a plexus of nerra-fibrils
noderljiTig it. 16. Aiopulta of tube-foot. 17. Tnbe>foot.
IS. PeribMinal space. 19. Coelooi.
We found that in order to examine the alimentary canal it was
advisable to divide the star-fish into an upper and a lower half. If
WB now cut away the tube-feet and look at the roof of the ambu-
laoml grixjve from wtiich they project, it will be seen that the
groove is roofed in by a double series of calcareous rods, meeting
each other at an angle like the beams of a church-roof (II, Fig. 131).
Tbeae are called the ambulacral ossicles. They can be drawn
together by muscle fibres running from one of a pair to its
fellow just wider the spot where they meet. By this action the
unbtdacral groove is narrowed ; and at the same time, inwardly
256 ECHINODBRMATA [OHAP.
projectiDg spines lining its edges are made to meet, so that the tabe-
feet are entirely protected by a trelliswork of spines. These spines
are attached to rods, called the adambulacral ossicles, firmly
bound to the outer edges of the ambulacral ossicles (12, Fig. 134).
Inside the animal, between the ambulacral plates, a series of pear-
shaped transparent bladders tensely filled with fluid project into
the coelom (Figs. 132 and 134). These are really the swollen upper
ends of the tube-feet and are termed ampullae. They act as
reservoirs into which the fluid contents of the lower part of the foot
are driven when the longitudinal muscles of the tube-foot contract
The bladder-like upper end of the foot has only circular muscles,
and when these contract the fluid is driven back into the lower
part of the tube-foot and it is expanded. The tube-feet, though
from the above description it would seem as if each was capable of
acting without the others, are really all parts of one system : they
are connected by short transverse tubes, with a canal running along
the whole length of the arm immediately under the ambulacral
ossicles, called the radial water-vessel (13, Fig. 134). This
canal and its branches can easily be seen in microscopic sections of
the arms of young star-fish, or they can readily be demonstrated
by cutting oflf the tip of the arm of a fully-grown specimen,
finding the end of the radial tube on the cut surface and inject-
ing it with coloured fluid by means of a fine pipette. The five
radial tubes are connected with each other by a ring-shaped
canal lying just within the peristome, which is called the water-
vascular ring. There are nine small pouches called Tiede-
mann's bodies projecting inwards from the ring canaL In these
are formed the amoebocjrtes which are found floating in the fluid of
the canal, and which arise by budding from the wall of each poucL
From the ring canal also in one interradius, where the tenth
Tiedemann's body if it existed would be found, a tube is given ofi*
which leads to the upper surface of the disc, where it opens by a
sieve-like plate, pierced by numerous minute pores, called the
madreporite (Figs. 132 and 133). This vertical tube receives the
awkward name of the stone-canal because its walls are stiffened
by calcareous deposit ; its cavity is reduced to a mere slit by the
projection into it of an outgrowth of its wall shaped in section
like a T with coiled ends, which is also strengthened by lime.
Although, as we have said, the cavity of the stone-canal is a mere
slit, yet it is lined by long narrow cells carrying most powerful
cilia. In many species of star-fi^h, although not in Asterias, stalked
IX.] NERVOUS SYSTEM. 257
sacB resemUing greatly enlarged ampullae are attached to the water-
yascular ring. These appear to act as reservoirs of fluid for it:
they are known as Folian yesicles after Poli, the naturalist who
first described them.
Now since all the moyements of a tube-foot can be accounted for
by the action of the longitudinal muscles of its lower part and the
circular muscles of the ampulla, the question arises as to what is
the purpose of this apparatus of radial and circular tubes, stone-
canal and madreporite ? There is one interesting little mechanism
which supplies a valuable clue to the answer to this question. This
is a pair of valves placed in the tube-foot at the entrance of the
transverse canal, which unites it with the radial tube. These valves
swing open into the tube-foot when the pressure in the radial tube
is greater than the pressure in the tube-foot, but 'when the pressure
in the latter is the higher they close, so that under no circumstances
can water escape from the tube-foot into the radial canal. So it
appears that there is an arrangement which allows fluid to pass into
the tube-foot but which prevents its return, and this implies that
under ordinary circumstances there must be a loss of fluid from the
tube-foot. We must in fact suppose that when the tube-foot is
driven out by the contraction of the ampulla, the contained fluid
slowly transudes through its thin walls and the loss is supplied from
the radial canaL The pressure in the radial and circular canals is
kept up by the action of the cilia in the stone-canal, by means of
which a slow but steady current is produced, setting in from the
outside through the madreporite.
The function of the whole system of tubes therefore is to keep
the tube-feet full of fluid and thus tense and rigid, so that they can
perform their frinctions properly.
The nervous system of the star-fish is one of the most interesting
Nervous fcaturcs in its anatomy. The ectoderm consists of long
system. delicate cells bearing flagella and interspersed with
goblet-cells similar in appearance to those lining the stomach.
The slime which these cells manufacture covers the surface of the
animal and no doubt protects it from the attacks of bacteria and
microscopic algae. But the chief point of interest is that at the
bases of the long delicate cells there is an indescribably fine tangle
of delicate nerve-fibres which are doubtless outgrowths of some of
the cells. Here and there a nucleus is seen amongst them which
belongs to a neuron — that is, an ectoderm cell which has lost its
connection with the rest and has become pushed down into the
8. <& M. 11
258 ECHINODERBfATA. [CHAP.
fibrillar layer. The ectoderm all over the body is therefore under-
lain by a nervous sheath and is very sensitive, but there are certain
places where the nervous sheath becomes very much thickened and
it is these areas which constitute the true sense-organs and the
central nervous system.
Isolated sense-cells, that is, cells having a stiff protruding hair,
are scattered all over the surface ; but the only spot where they are
collected in groups so as to form true sense-organs is on the tips of
the tube-feet The tube-feet are then practically the only sense-
organs, and since the radial water-tube ends at the tip of an arm in
a ireely projecting tentacle, we might regard the whole radial tube
as a huge, branched, sensitive tentacle. There is the more justifica-
tion for doing this when it is found that the radial tube with its
freely projecting tip is in the young star-fish quite independent of
the outgrowth of the body called the arm, and only secondarily
becomes applied to it. At the base of the end-tentacle there is a
thick cushion of nervous matter in which are excavated a number
of ectodermal pits lined by cells containing orange pigment.
These pits are organs of vision: and it has been experimentally
shown that a star-fish deprived of these organs is insensible to
Ught.
The central nervous system consists of five thick bands of
nervous tissue situated one above each ambulacral groove under-
neath the radial water-tube (Fig. 134). They are termed the
radial nerve- cords and are joined by a circular band of a similar
nature, called the nerve- ring, lying under the water-vascular ring.
Intervening between the radial nerve-cord and the radial water-tube
there are two canals lined by flattened cells and separated from one
another by an imperfect septum (14, Fig. 134). They are caUed
the radial perihaemal canals and are outgrowths firom the
coelom. From their upper walls are derived the muscles which
move the ambulacral ossicles on one another : from their lower walls
a layer of ganglion cells and nerve-fibres, which may be termed the
coelomic nervous system in order to distinguish them bom the
main mass of ganglion cells and fibres which are derived from the
ectoderm. This coelomic nervous system, which is very thin in
the star-fish, seems to serve as the channel by which impulses bom
the radial nerve-cord reach the ambulacral muscles. The five pairs
of radial perihaemal canals are connected with one another by a
circular canal lying above the nerve-ring called the outer perihae-
mal ring. Inside this is another circular canal called the inner
IX.] PEDICEILASUE. 259
perih&em&l ring, vliich is ui espansioQ of the foot of the axial
smns (see p. 360).
The apper or abonl sorface of the star-fish is provided with two
moBt interesting groupB of organs, pedicellariae and
dermal branchiae. The former are minute pincers,
composed of two or rarely three blades moving on a basal piece.
Fia. 135. Pedioellariae from Aiteriat glaciali$. From Cnfoot.
A. CroBBed form X 100. 1. Eotoderm. 2. Bam of leR "jaw." 3. Muscle
olomog the "jaws." 4. Basal ossicle. 6. Hnscle opening the
" jawB." 6. Fibrous bend coDcecting the basal ossicle with ooe of tlie
rods of ths skeleton. 7. Fibres of pedimale.
B. Straight form.
4. Mnsole douDg the "jav
These close when the skin of the back is irritated; their main
purpose appears to be to keep the surface of the animal clear from
loopbytes and other small encrusting organisms. They cover the
thickened bases of the blunt spines with which the back is beset
iMTgBt pedic«ll&riae are scattered in the inter-spacea between the
qnnes and are distinguished &om the smaller by the hct that the
blades do not cross as is the case with these. The larger kind
are also found on the adambnlacral spines.
The pedioellariae are probably little spines of the second order.
In the small blunt-armed star-fish, Asterina gibbosa, there are no
true pedioellariae, but the plates on the back bear small spines
arranged in twos or threes, which act somewhat like pedicellariae
when the akin is irritated.
260 ECHINODERMATA. [CHAP.
The dermal branchiae (5, Fig. 134) are conspicuous in a
star-fish when alive; they are very difficult, on the
other hand, to detect in preserved specimena They
are in fact thin spots on the body-wall, where it consists only of
the ectoderm and the wall of the coelom — closely apposed, the
jelly, fibres and skeletal rods being absent These spots project
like little finger-shaped processes and their purpose is to facilitate
respiration. The fluid in the coelom or body cavity being separated
from the external water by a very thin membrane, the dissolved
oxygen is able to pass from the one fluid to the other with great
ease.
There is no localized excretory organ in the star-fish or indeed
in any Echinoderm. Throughout the phylum so far as is known
this function is performed by the amoebocytes which float in the
coelomic fluid and have been produced by the budding of the cells
forming the wall of the coelom. When charged with excreta the
amoebocytes endeavour to make their way out. This in the star-fish
they effect by accumulating at the base of the dermal branchiae
and working their way through the thin body-wall and so escaping
into the ocean.
The organs of sex in the star-fish are very simple. Both kinds
iieproductive ^^ gorm Cell are aggregated in great feather-shaped
organs. glauds situated in pairs in the bases of the arms and
opening in the angles between the arms or in the inter-radiL The
ten ovaries in the female and ten testes in the male are connected
by a circular cord of immature germ cells called the genital
rachis running round the disc just dorsal to the coelom. This is
embedded in the wall of a tube called the aboral sinus which like
the other spaces in a star-fish, apart from those of the digestive
canal, is an outgrowth of the coelom. The rachis is in turn con-
nected with a pillar of similar cells running alongside the stone-canal
which used to be called the heart, under a mistaken idea of its
function, but which we shall term the genital stolon. The genital
rachis is formed as an outgrowth from the genital stolon and the
latter is an outgrowth from the coelomic wall, so that the genital
cells are derived from the coelomic cells as in other Coelomata.
The genital stolon is interposed between the general coelomic cavity
of the animal and a special division of the same which is called
the axial sinus, and which runs parallel to the stone-canal.
The axial sinus is derived from the anterior portion of the
coelom in the larva. Underneath the madreporite there is still
IX.] OPHIUROIDEA. 261
another diyision of the coelom completely shut oflF from the rest,
which may be termed the madreporic vesicle. It apparently
represents a rudimentary second water-vascular system, since in
exceptional cases it may develope the rudiments of radial canals.
The genital stolon projects into the axial sinus ; it has a brown
colour which no doubt suggested the connection with the blood-
system to the earlier anatomists, but true blood-vessels do not exist
in Echinodermata. The ova and spermatozoa are thrown out into the
water by pores situated on the under or oral surface at the base of
the arms and unite with each other there. The young lead a free-
swimming existence, and are so unlike the star-fish that no one would
ever dream of suspecting that the two had anything to do with
each other. As however these peculiarities are fundamentally the
same in each of the groups of the Echinoderms they will be dealt
with later when the characters of these other groups have been
studied.
The other species of star-fish, which are all grouped together in
the Glass Asteroidea (Gr. dcmjp, a star; €1809, shape), diflfer but little
in really fundamental points from Asterias rubens, Pedicellariae
may, as we have seen, be absent; the arms may be short so that
the shape almost becomes that of a pentagon and the arrangement
of the plates and spines constituting the skeleton may vary very
mucL In one family, the Astropectinidae, there is no anus, the
rectum ending blindly, and the tube-feet have pointed ends. These
star-fish do not climb but run over the surface of the sand.
The number of arms is most often five, but not only do indivi-
dual variations from this rule occur in species where five is the
normal number, but species and even genera and families are
characterised by having a larger number: the common Sun-star,
Sohuier papposus, for instance, has from eleven to thirteen arms.
Class II. Ophiuroidea,
The next order of Echinoderms is termed the Ophiuroidea (Gr.
o^tovpos, serpent- tailed ; cISo?, form) or the Brittle-stars. These like
the star-fish have a body with five arms diverging from a central
disc on all sides like the conventional representation of a star. The
arms are, however, sharply marked off from the central disc, and
they do not, as in the true star-fish, insensibly merge into it, but
are continued along grooves on the under surface to the immediate
neighbourhood of the mouth : further they are exceedingly long
262 ECHINODERMATA. [CHAP.
and flexible sod totally unlike the stiff anne of Atteriat or ita
alliea.
The habits of the aDimal too are veiy different from those of t^
star-fiab. Instead of creeping slowly along by the action of the
tube-feet it springs along by muscular jerks of the arms, s
pushing with four anus and seizing hold in front with one, sometimee
pushing with three and hauling itself along with two. The name
Brittle-star is derived from the readiness with which, if irritated,
t^e animal will snap off an arm.
As might naturally be expected, the most striking differences
from the stat-fish are seen in the arms. No smbulacial groove is
OPHIUBOIDEA.
^parent; the arm being encased in a cuirass consisting of four eeriea
of plates, an upper row, two lateral rows each bearing a row of spines
on ita edge, and an under low (Fig. 137). On close inspection the
short pointed tube-feet may be seen protruding from minute pores
at the sides of the under row of plates. A thin section of the ann
reveals the fact that there really is a apace correapouding to the
ambulacral groove of the star-fish, but that by the approximatiou of
its edges it has become closed off from the outer world so that it
forms a canal, the so-called epineural canal (i, Fig. 137). Above
this canal, at the spot one would term the apex of the ambulacral
Flo. 137. Section Ihroagh
Ditigraniinatio, mBgnifled.
RuiiAl nsrve-card. 3. Bftdial perihaemaL cilduI. 3, Badial watar-
viuoolar oanal. 4. Epioeural cantiL 6. Ventral plate. 0. Tabe-
fool. 7. Pedal BanBlion. 8. Lateral plate. 9. Spine,
10. Donal plate. 11. Coelom. 13. Lonijitiidiiisl maaale.
IS. "Veitebni." 14. Baft tiaaue Bupporting pluiea.
groove in a star-fiah, there ia a ridge of nervous matter covered on
the lower side by cells exactly resembling the skin cells covering
the nerve ridges in Asterias. This is the radial nerve, and above
this again ia a large rounded disc of calcareous matter, the ao-csUed
vertebra. This really corresponds to a pair of ambulacral plates
which have become fused together. So much might be inferred
from the fact that the radial water-tube runs in a groove on its
under Borface, and it is clearly proved by examining young speci-
mens. Each vertebra ia very short, and it not only has rounded
knobs and cupa in order to enable it to sUde on its auccessor and
predecessor, but ia connected to each of them by four great muscles.
264) EGUXNODBBMA.TA. [CBAP.
by the oontractioa of which the arm is moved in uiy direction
(Fig. 137). If ihe two side musclee contract the arm is moved
toward that side, if the two upper, upwards, and so on. These
muscles are the seat of the chief activities of the animal, and it is
not surprising to find that a pair of large nerves comes off between
each two vertebrae to supply them, and that where these nerves
are given off the nerve-cord u thickened and the nerve-cells
increased, so that a string of ganglia is produced strongly recalling
the ventral nerve-cord of the Earthworm, Between the vertabnM
and tlie radial nerve-coid there is a single canal (2, ^. 137), lepn-
senting the pair of radial perihaemal canals in a similar position in
Fio. tSS. A diograEiimatia T«itical wetiOD of sn Ophittroid After Lndwig.
The oircamoral Bjatema of oTgaoa are seen to the left cut aoroBa, their
radial proloDgationB out longitadinallj to the nght
1. Body-wall. 2. Month. 3. Coelom. 3'. Goelom of the arm.
4. Mouth papillae, 5. Toma angalatis. 6. Oral plate. T'. lat am-
balacral Oiainle. 7*, 7', 7*. 2nd to 4th ambulaersl oaaicle or " TBrt»>irae."
8>, 8>, 8*. lat to 9rd Teotral plate. 9. lat oral foot. 10. Tiaiu-
Terse muBcle of the 2Qd joint. 10*. Eiteraal inteiradiat muacle.
10'. Internal iuterradial mnade. (The line should point to the dotted
tiaaue.) 11. Water-vasaolar aTatem ; to the left the oironmoral ring,
to the right the radial Teaael. 12. Folian veaiole. IS. Nerre-Tiug at^
radial nerve ; the Raoglia on the latter are not ahowu. 14. Genital
lachia. 15. Badial perihaemal oanal,
Asteroidea. From the ventral wall of the canal the coelomio
nervous system is formed ; and it is by the greater development of
this system where the nerves to the ambulacral muscles ue given
off Uiat the ganglionic swellings of the nerve-cord are produced.
The vertebrae and these muscles nearly completely fill the arm,
leaving only a small canal above the vertebrae (11, Fig. 137): this
is an outgrowth of the body cavity or coelom, but there is no
branch of the alimentary canal continued into it, as was the case
with the star-fiah.
The digestive sac is here a simple flattened bag lined by cells
somewhat like those lining the pyloric sac of the star-fish. There
OPBIDROIDEA.
is no anus, and the edges of tha stomach cannot be pushed out.
How then, it may be asked, does the Brittle-star eat and of nbat
does its food consist ?
It must be confeHaed that, in spite of their qnick movements and
highly developed nervous system, BrittJe-stars belong in general to
the great army of mud-eaters and scavengers. Where they live —
nsually at the bottom of sea poob and at such depths of the ocean
as to be in still water — the mud or sand is impregnated vrith
decaying animal and vegetable mattor, and the Brittle-stars shovel
tiaa material into their mouths by means of the two pairs of tube-
feet of each arm nhich he nearest the mouth and are called the
oral tube-feet. The interradii between the arms project inwards
over the mouth, as the mouth-angles ; those are lined along their
edges and at their tips with broad blunt spines called teeth and
month papillae, so tltat they form an effi<Ment strainer and prevent
coarse particles entering the stomach (Figs. 138 and 139). The
calcareous plat-e at the apex of each mouth-angle which bears these
sptoea is called the torus angularis (5, Fig. 138).
We saw that in the star-fish the whole surface is covered
vith a sensitive akin, but that the tube-feet act aa sense-organs
266 ECHINODERMATA. [CHAP.
as well as being locomotor in function. In the Brittle-stars the
sole purpose of the tube-feet is to serve as sense-organs; they are
often covered with little warts consisting mainly of sense-cells with
their delicate hairs sticking out all round, just like the batteries of
cnidoblasts in Hydra, and in all cases there is a special nervous
swelling surrounding the base of each tube-foot called the pedal
ganglion (7, Fig. 137). As, however, these tiibe-feet have lost their
power of attaching themselves by a sucking action to objects and
hence are of no use for locomotion, the ampullae have disappeared ;
and as the action of the ampullae is probably the chief cause of the
loss of fluid in the tube-feet of the star-fish, in the Brittle-star, where
the loss must be very smaU, the stone-canal is excessively narrow
and the madreporite instead of being a regular sieve has two pores
only, rarely more. It is very curious to find that the madreporite
is on the underside of the animal; in the young Brittle-star it is
on the edge of the disc, but in each interradius the upper surface
grows more rapidly than the ventral and so it is forced round on to
the underside. To the water-vascular ring are attached four large
Polian vesicles, the interradius occupied by the stone-canal alone
being without one. The tube-feet are the only sense-organs, in a
sense still more real than is the case with star-fish, for in the
Ophiuroidea the rest of the ectoderm, after having given rise to a
cuticle, has disappeared, the solid mail of plates which the animal
possesses appear to render it impervious to sensations of contact.
The organs of sex are very simple ; they are situated in the disc
in the interradii and consist, in each interradius, of several short
pouches. These open into ten sacs, called the genital bursae ;
one pair being placed in each interradius. These sacs are merely
invaginations of the ectoderm which does not here disappear as over
the rest of the body ; they are lined by ciliated cells which keep up
a constant current of fresh water pouring into them and thus they
fulfill the same function as the "dermal branchiae " of Star-fishes.
Class III. ECHINOIDEA.
The general appearance of the dried skeleton of a Sea-urchin or
Echinoid, is familiar to most people, but many would fail to recognize
any resemblance to a star-fish in the slightly flattened sphere
covered with spines. If, however, we are fortunate enough to see
one living, we at once perceive that along five meridians the sphere
is beset with beautiful semi-transparent tube-feet, ending in suckers,
ECniNOIDEA.
exactly like those of the star-fish. In fact, the Sea-urchin might be
desciibed as a star-fiah in which the upper surface had shrank to
insignificant proportious, being repre^iented. by a small patch of
leathery skin at the upper pole : or, if no regard the whole radial
tube with ita tube-feet as one immense branched tentacle and the
arm as ite support, we should say that the arm had been again
Flo. HO. Strongijlofcnirui ilrirbachiciuii^l, Aliutal surfnoo. From AgUBsiz,
I. Expanded tabe-fect. 2. Spines.
merged iu the body ao that the radial tube was bent back in a
curved course. As a matter of fact the end of the radial tube
projecle very slightly beyond the general surface und bears at its tip
a mass of pigment which corresponds with the eye of the star-fish,
though no eye-structure liiis been detected in it. 'lliia is situated
near tiie upper end of the body, just outside the small area of
lesthery skin mentioned above.
268 ECHINODERMATA. [CHAP.
The skeleton of the Sea-urchin is a cuirass of plates fitting edge
to edge, with two openings. Of these the upper (already referred to)
is covered with leathery akin and has the small anus in the centre
of it and is called thepeiiproct (Fig. 148): it is this area which
corresponds to the whole upper surface of the star fish The other
opening is in the centre of the lower surface and is likewise
covered by flexible skin it wrrounds the mouth and is called the
peristome (Fig 147)
1, Adus 2 Leathery akin roand anuB penproct 3 Modreponc plate.
4 Oenitiil plate with gen tal pora S Ooalar plate with eye.
6. Line of junction of ambulocral nod ittterambulactal pUtes. T. Ambn-
lacrnm. 8. Pores through whioh tube-feet piotnide. 9. Boasea
which bear the spiaes.
The cuiraas itself is called the corona and consists of twenty
strips, each made up of s row of plates. Corresponding to each
tube-foot area or radius there are two rows of so-called ambnlscral
plates, and each intervening area or ioterradius is similarly covered
by two rows of large plates. As in Opliiuroids, there is no ambulacral
groove visible from the outside : it is represented by the epioeural
canal, immediately inside which there is the radial nerve-cord.
IX.]
ECHINOIDEA.
269
It 18 necessaiy to bear this in mind when the term ambulacral
plate is used ; the so-called ambulacral plates of an Urchin do not
correspond to the similarly named plates in the star-fish, as they
do not roof in the ambulacral groove, but form a floor for it.
Inside the nerve-cord there is a single radial perihaemal canal as in
the Brittle-star (2, Fig. 145 b). As the plates of the skeleton are
not movable on one another nothing corresponding to the ambu-
lacral muscles of the star-fish exist at least over most of the radius,
and the radial perihaemal canal is separated from the general
coelom only by a thin septum in which the radial water-tube is
embedded For the same reason there is no recognizable coelomic
nervous system.
If the continuous cuirass of the Sea-urchin and the closed
ambulacral groove remind one of an
Ophiuroid, the resemblance ends there;
for in the Urchin the ectoderm, consist-
ing of long slender cells with a tangle of
nerve-fibres at the base, is spread over
the whole surface outside the skeleton,
just as in a star-fisL This sensitive
layer controls, it is found, the move-
ments of the spines, which are among the
most important organs of the Urchin.
These spines, unlike the spines of the
star-fish or Brittle-star, have hollow
bases, which articulate with smooth
rounded bosses on the plates (B, Fig.
145). They are tied to these bosses by a
sheath of muscle-fibres, so that by the
special contraction of any side of the
sheath they can be moved in any direc-
tion. The skin covering the sheath has
developed a specially thick nervous layer.
Sea-urchins such as we have been
describing live on stony or rocky bottoms,
over which they slowly creep by means
of their tube-feet The spines are
pressed against the substratum and keep the animal from rolling
over under the pull of the tube-feet and also help to push it
on. The spines are usually of two distinct sizes, longer primary
spines, and shorter secondary spines. The forest of spines has
a kind of undergrowth of pedicellariae. These are of several
Fzo. 142. A glandular or
gemxniform Pedioellaria
from E. escuUntuixlQ,
From Chadwiok.
270 ECHINODBRHATA. [CHAP.
kinds and are much more highly finished organs than those of
star-fishes ; they have a long stalk, which is portly stafiianed by
a delicate calcareous rod, aad the jaws are three in nomber. One
Fia. 143. AriEtotte's Lantern at E. eievlentat x 3. Pnrtlj from Chadvick.
1. Tipper end of tooth enveloped in lantern membrane. 2. BadEns.
S. Tranaverse muscle of radii, elevator. 4. Depressor mnscles of radina.
S. Jaw. 6. Retractor muscles of the jaws. 7. Protractor of jaws.
8. ADricala. 9. Ampnllae of tnbe-fect. 10. Jnter-ambitl&eral plate.
11. Tooth. 12. Circular watec-vBHcuIar vessel. IS. EpiphTsis.
14. Polian veaiclea. 15. Oesophagus. 16. 'Vontial"blood"-vessel.
17. Oenital stolon. IB. StoDe-oanal. 19. Bectum. SO. Uadre-
poriaplftte.
IX,] ARISTOTLE'S LANTERN. 271
kind hu §hott stumpy jaws, each with a poison bag at its base and
a stiff stalk; these are doubtless weapons of defence and enable the
Urchin to give any unwelcome Tisitor which may come too close a
wann reception. Such pedioeilariae are called gemmiform (Fig. 142).
Another kind, termed tridactyle, has long jaws and a flexible
stalk. It was supposed that these helped the animal to climb by
seiiiiig hold of waving fronds of sea-weed till the tnbe-feet could
get a hold, but this is proved not to be the case. It has been
1. Month, a. iDteatine cut ahort. 3. Siphon. 4. Itectum. S. Anas.
6. VentTftl " blood "-vesael on intestine. T. Dorsal " blood "-vessel
on intastiiu. S. Stone-canal. 9. Madreporio plate. 10. Qenital
rsohiB. II. Water-TasonUr ring. 12. Nerve-ring. 13. Tube-foot
with ampulla. 14. Radial nerve. IS. Radial water-vessel. 16. Polian
veaicle. 17. Moscles ; those on the left pull Aristotle's Lantern out-
wards, those on the right retract it. 18. Ocular plate.
shown that a gentle movement in the water excites the tridactyle
pedicellariae while a stronger movement calls the gemmiform into
activity. Besides these there are two other kinds of pedicellariae.
It seems most probable that these elaborate organs are for the
purpose of protecting the sea-urchin against the attacks of certain
animals which in their absence would either fix themselves on
tiie skin of the Echinoid or even burrow into it. The number
and variety of these organs are an indication of the danger that exists
from this eouicfl.
272 ECHINODERMATA. [CHAP.
The Urchin is provided with five white chisel-like teeth, each of
which slides on a pair of grooved pieces called alveoli, meeting in
a point below. Each pair of alveoli meet in a point where they
clasp the tooth. Above they are united by two pieces called
epiphyses (13, Fig. 143) which meet in an arch. A pair of
alveoli with their epiphyses are often spoken of as a jaw, and
adjacent jaws are joined by stout, inwardly projecting rods called
rotulae. The whole apparatus of five jaws has received the name
of 'Aristotle's Lantern.' This can be pushed out or pulled in
by muscles attached to arches called auriculae, rising from the
inner side of the skeleton (8, Fig. 143). Through the auriculae the
radial water-tube and nerve pass, and thus they correspond in
position to the ambulacral plates of star-fish.
The food of the Urchin consists ordinarily of seaweed which it
gnaws with its teeth. No doubt the little worms and molluscs
always 'found in abundance on the surface of the weed add a flavour
to the repast The alimentary canal is exceedingly unlike those of
the Echinoderms so far studied. The gullet ascends vertically
between the teeth and passes into the intestinal tube which runs in
a spiral right round the body and then turns sharply back and
describes one turn of a spiral in the opposite direction, after which
it bends inwards and runs straight up to the anus (Fig. 146). For
the first part of its course a small tube, the so-called siphon, runs
parallel to it, opening into it at both ends.
The water-vascular ring is situated above the masticatory ap-
paratus and is thus widely separated from the nerve-ring, which is
situated below it : the radial tubes, in consequence, run downwards
along the ''lantern" before bending outwards under the auriculae
(see Fig. 144). The water-vascular ring bears small pouches which
have been termed Polian vesicles. They seem, however, to corre-
spond to Tiedemann's bodies in an Asteroid. The first pair of
tube-feet in each radius are difi'erent to the rest, in that they are
short and not capable of extension, and that their discs are ovaL
These tube-feet protrude through the peristome and are called the
buccal tube- feet; they function as tasting organs, and are
thrown into violent excitement if a piece of eatable matter is put
near them (Fig. 147).
In describing the Asteroidea it was mentioned that the genital
stolon or "dorsal organ '' had been mistaken by former authors for a
heart, and that true blood-vessels were unknown amongst Echino-
dermata. If by blood-vessel is meant a tube with well-defined
n.]
Flo. 115. SeotiODS through ports ol Echinut eicuUntui.
A. A. wctioa at right ftnglw to the i)Une of the Uadreporio plats x 16.
From Chadwiok. 1. Madiepoiic ptate. 2, Pores in the game.
3. Uadreporio Teside. i. Ampulla of ntadreporio plate or dilatation of
Btone-canal into which the pores open. 6. Madrepotia tabe. 6. Oeni-
tal stolon. 7. Axial bIhub.
B. A i«etion at right angles to an ambolacral aiea. 1. Badial nerre-cord.
3. Badialperihaemal oanal. 3. Badial water-canal. 4. Epineuial
oanal. 6. Ampulla. 6. Cavitj ol tube-foot. 7. Ambnlaoral plate.
B. Boh for articnlation of spine. 9. Spine. 10. Uasolea which move
th« spine. 11. Ectoderm.
LAX. V&
274 ECHINQDERHATA. [CHA?.
walls in which there is a definite circulation of fluid thia ia strict^
true.
It roust be remembered, as was pointed out in the chapter on
Arthropoda, that blood-vessels aad connective tissne hare been
derived from the same primitive tissue, which may be compaied to
the jelly of Goelenterata. Now Echinodennata probably lepresent a
stage before the evolution of either blood-vessels or proper coDoective
tissue. Apart from the plates of the skeleton the subetance of the
body-wall has little more consistence than the jelly of an Aurtlia,
FiQ. 146. View of aeft-Urchin, with part of the ihell removed to show the
coarse of the slimeotnrj oansl. From Leackart, after Coiier.
1. Mouth BarTOQDded by five teeth (displaced), 2. Laotem of Ariatotle.
3, Oesophagne, coiled intestine and rectum. 4. Ovaries with ovidactB.
5. The siphon. 6. " Blood -ring." 7. Fold of peritoneum supporting
genital rachis. 8. "Blood-vessel" aooompanjiDg intestine. 9. Ampnllae
at base of tube-feet.
aud readily degenerates into slime. The ground substance has
remained so fluid that it is still traversed by arooebocytes which
cany excreta to the exterior. In Echinoidea along two tracts, one
situated on the same side of the oesophagus as the stone-canal and
the other on the opposite side, the jelly intervening between the
inner wall of the coelom aud the oesophagus has undergone the first
stage in the change to a blood-vesBel. The fibres an scantily
coMXEcnva tissve.
I developed and the amoebocytes are preaent in immense numbers,
whilst the )^und substance has become more fluid and probably
contaiua proteidn, since it stainn with ciirmine like protoplasm.
Tbese tracts are termed dorsal and Tentr&l " blood "-vessels. The
dors«] vessel is on the side next the stoue-canaL These tracts
have not the form of tubes, but are uetworka of irregular iHissages
devoid of proper walls. They accompany the alimentary canal
throughout most of its courHe and it seems as if the products
[ of digestion were areumulated in them. A so-called "blood-ring"
I ctf similar character surrounds the oesophagus just above the water-
I Fw. 1*7. Oral field of Krhinu, fteiil-^Mue. Magnieed. Fiom Kiiktnlliol.
AmboUcniiu with tobe-rmt and spiues.
Ariatotlc'a lantern. 4. Buccal tubp-reet.
mouth > the Perutome.
Bcolar ring and into this the two " vessels " open. A similar ring
It been described in Asteroidea and Ophiuroidea ; iii some species
t the former class a tract of similar substance appears. to run down
e arm just above the uerve-cord in the septum separating the two
ihaemal canals, and the name of these canals (Ur. irtpi. around ;
[, blood) has been suggested by this circumstance.
276 ECHINODERMATA. [CHAP.
Breathing, as one might expect, is carried out wherever the
body-wall is thin enough to allow the oxygen to diffuse through,
that is to say by the tube-feet and by the peristomal membrane.
The tube-feet, as in the star-fish, are provided with large ampullae
which project freely into the great spacious body cavity. Oxygen
thus taken into the fluid filling the tube-feet can be passed into the
body cavity through the ampullae, and there is a curious arrange-
ment to facilitate this. Where the tube-foot passes through the
skeleton it is split into two parallel tubes which reunite below
(B, Fig. 145) : so that on the dried shell we see on the ambulacra!
plate several pairs of pores, each pair corresponding to a single
tube-foot. As the cells lining the inside of the latter are ciliated,
the splitting of the tube is apparently to facilitate the separation of
the upward and downward currents of water.
The peristome has ten branched pouches, situated one pair in
each interradius and projecting outwards. These are the gills,
but it is unreasonable to suppose that all the breathing is done by
them. They communicate not with the general body cavity, but
with a part of it, called the lantern coelom, shut off from the
rest by a septum stretched between the teeth and jaws. Embedded
in the upper wall of this are certain rods called radii, which are
connected with each other and the auriculae by muscles, and by
means of these the upper wall of the lantern coelom can be raised
or depressed and so the pressure inside altered. When these
rods are depressed water is driven out into the gills and there
absorbs oxygen. When they are raised the water is sucked back
into the lantern coelom and the oxygen passes through the thin
wall of the latter into the general coelom.
The organs of sex are alike in external appearance in both sexes
(Fig. 146). They have the form of five great bunches of tubes
hanging down into the body cavity and opening by five small holes
placed in plates called the genital plates, forming the summit of the
interambulacral series on the corona and situated just outside the
periproct (Figs. 141 and 148). In the young Sea-urchin there is a
genital rachis connecting them together, and throughout life there
is a genital stolon alongside the stone-canaL The genital stolon is
relatively much larger in Echinoidea than in Asteroidea, and sur-
rounds the axial sinus in the lower part of its course, so that this
space appears like a cavity excavated in the stolon. Hence by one
author the axial sinus and stolon were mistakenly described as a
nephridium with gkndular walls, and the madreporic vesicle, which
IX.] CLASSIFICATION. 277
IB here mnch eolarged and extends parallel with the axial sinus,
was called by the same author the "accessory kidney."
The EchiDoidea are divided into three Orders : —
I. The ordinary Sea-urchins, such ae we have described, con-
stitute the Order Endoctclica, which live chiefly on rocky and stony
ground. The other two Orders live in sand or mud and have under-
gone singular modiflcations in order to fit them for this kind of life.
Fia. 148. Aboral B;item of platei o( EMnoi ficuUntut x i. From Chadnicb.
They are termed the Irregular or Exocyclic Sea-urchins, because
whereas the anus has become shifted from the upper pole of the
body down one side to the edge, or even to the under-surface of the
more or less flattened body, the madreporite and genital plates still
retain their position. In both Orders the tube-feet of the upper
part of the ambulacra are the main breathing organs, and are
greatly flattened and expanded at the base, while the pores
through which they pass are arranged in two converging curves on
each ambulacrum, the figure produced being compared to a petal
of a flower, hence the name applied to them, viz., petaloid ambulacra.
The special characters of these two Orders are as follows :
II. Cltpbaotboidea or Cake-urchins. They live at or near the
surface of the sand. They still retain their teeth, which are placed
almost horizontally, and they use them as spades to shovel the sand
278 ECHINODERBCATA. [CHAP.
into the moutL All the spines covering the upper surfiftce are
ciliated and so a constant current of water sweeps over the expanded
tube-feet which act as gills. In addition to these tube-feet the
whole aboral surface, radii and interradii included, is covered with a
multitude of minute tube-feet provided with suckers. Similar tabe-
feet are found on the oral surface, but they are confined to the
radii. This immense multiplication of tube-feet is of course due to
the small purchase that any one of them is able to get on such a
yielding material as sand. In a word, the animal moves itself by a
multitude of minute pulls instead of by a lesser number of stronger
pulls as do the Endocyclica. There are calcareous piUars stretching
from the upper to the lower surface of the shell or test, apparently
to enable them to withstand rough usage, since in many cases they
live within reach of the breakers. The best known British species
is Echinocyamus pusillus, a little oval Sea-urchin about the size of a
pea, whence the common name applied to it, viz. Pea-urchin. On
the east coast of North America one species, Echinarachnius parma^
the Sand-dollar, is very common ; this is an extremely flattened
Urchin of circular outline, the shape and size of which have suggested
a comparison with the famous silver-dollar of the United States
currency.
III. Spatangoidea or Heart-urchins. These live buried at
depths of a few inches to a foot beneath the surface of the mud,
and the body is more or less oval or egg-shaped, slightly flattened
underneath. The mouth is sometimes in the centre of the under-
surface and sometimes nearer one end, and is usually crescentic
and always without any trace of jaws. These Urchins have usually
only four of the ambulacra ''petaloid"; the fifth has a few long
tube-feet with expanded fringed discs. In the case of the familiar
British species Echinoca/rdium cordatum it is known that the Urchin
extends these tube-feet from its burrow right up to the surface of
the sand and collects with them deca3dng organic matter lying on
the surface. This is pushed within reach of the buccal tube-feet
and so reaches the mouth.
The Spatangoidea do not use their tube-feet to walk with, but
move by means of spines which are provided with flattened tips,
and so the small tube-feet present in such multitudes in the
Cl3rpeastroidea are absent. Besides these spines they possess peculiar
lines of very small spines covered with cilia, which cause a current
to pass over the gill-like tube-feet. Such rows of ciliated spines are
termed fascioles.
IX.] HOLOTflUROIDEA. 279
Class IV. Holothuroidea.
The fourth group of the Echinoderms is termed the Holothu-
roidea or Sea-cucumbers, and consists of animals of a more or less
sausage-shaped form, with the mouth at one end and the large anus
at the other.
These animals have undergone the same essential modification
as the Sea-urchins, the arms having been re-absorbed into the body
so that the radial tubes run down the side of the body and end
near the vent The nervous system also is situated beneath the
surface, the ambulacral groove being represented by the epineural
canaL The stdn, as in Echinoidea, retains its well-marked ecto-
derm with nervous sheath.
They are however distinguished by some most marked character-
istics:— 1. The skeleton has almost entirely disappeared, being
represented only by grains and prickles of various shapes completely
buried in the skin. 2. The muscular system of the body-wall is
most powerfully developed: there is a pair of strong longitudinal
muscles running inside each radial tube, and transverse muscles run
across each interradius. 3. The buccal tube-feet are highly modi-
fied and are the means by which the animal feeds itself. 4. The
anus is wide and the concluding portion of the intestine termed the
cloaca is strongly muscular, and it is used as a breathing organ,
water being sucked in at the anus and thrown out again. 5. The
stone-canal does not reach the exterior, but terminates in a sieve
plate hanging down into the interior of the body.
The broathing by means of the anus is carried out by certain
organs called gill-trees. These are two great branched tree-
like outgrowths of the hinder part of the intestine, reaching right
through the body cavity to near the mouth (Fig. 149). Water is
taken in by the anus and forced up into the finest branches of these
and no doubt diffuses through into the body cavity under the
pressure set up by the contraction of the muscles of the anus. Hence
it is that the animal is able to dispense with an external madreporite,
and also to obtain the fluid necessary to keep its tube-feet tense
from its own body cavity. From the water-vascular ring one or
moro long-stalked Polian vesicles hang down into the body
cavity.
The muscular body-wall has a very curious effect on the economy
of the animal. When it is irritated it contracts the muscles, and
Fill. 149. View of Bolotkttrta tuJmtoia somewhat diminiBhed. The animal
is opened along the left doreal interradioB and (he viecera are expoeed.
After Ludwig.
1. Tentaclel. 2. Ampnllae of tentacles. 3. Water-vosoulac ring.
4. Polian Teaiole. G. Stone-canals. 6. fiadial water-Tees^
7. Badial longitadinat mosole parti? out away. 3. Beproductive
organ. 9, AJimentary oanaL. 10. Clo&ce., 11. Bwpiiatory trees.
13. Fuitnl "Uood-TeeseL" IB. DcumI "^\i«A-Biewi».''
IX.] HOLOTHUROIDEA. 281
since the fluid in the body cavity is practically incompressible, the
effect is to set up a tremendous pressure. As a result of this the
wall of the intestine near the anus tears and a portion or the whole
of the intestine is pushed out. The gill-trees are the first to go, and
in some species the lower branches of these are covered with a
substance which swells up in sea-water into a mass of tough white
threads in which the enemies of the animal are entangled. A
lobster has been seen rendered perfectly helpless as a consequence of
rashly interfering with a Sea-cucumber. These special branches are
termed Cuvierian organs.
A Holothuroid is only temporarily inconvenienced by the loss of
its internal organs. After a period of quiescence it is again
furnished with the intestine and its appendages. Some species, which
are able to pull in the mouth end of the body with their tentacles,
when strongly irritated snap oflF even this, and yet are able to repair
the loss.
The intestine is a simple looped tube which has three limbs.
One limb runs down towards the anus, the next turns up again
towards the mouth and then bends back into the final limb which
goes towards the anus. These limbs are attached by mesenteries
to different interradii of the body, the first to that which in the
ordinary position of the animal is mid-dorsal, the next to the left
ventral, and the third to the right ventral (Fig. 149).
Accompanying the alimentary canal are so-called dorsal and
ventral "vessels" similar to those of the Echinoidea, and there is
also a ''blood-ring" like that described in the same class. In
Holothuroidea the ventral vessel is close to the alimentary canal
but the dorsal vessel is borne on a little ridge projecting from the
intestine. The alimentary canal is enswathed by minor branches of
the network of which the dorsal and ventral vessels form merely the
large trunks. The whole system thus assumes a very complicated
appearance, but even here it has been shown that there is no
circulation nor even a proper wall to the spaces. The longitudinal
vessels indeed often do not appear to communicate with the blood-
ring.
The buccal tube-feet form a crown of from ten to twenty-five great
branched tentacles, and their different shapes are used to classify
the various families of the Sea-cucumbers. Most species feed
on sand or mud, but one Order can be described only as anglers.
In them the tentacles are long and delicately branched so that
they resemble pieces of sea-weed. The animal stretches them
282 ECHINODERBfATA. [CHAP.
oat, and they become the resting-place of numbers of the mmate
animals which swarm in sea-water. When one tentacle has got a
sufficient freight it is bent round and pushed into the mouth which
is closed on it. It is then forcibly drawn out through the closed
lips so that all the living cargo is swept ojQf.
The organs of sex are similar in nature to those of the Urchins,
but are represented by only one mass of tubes which all unite in a
common opening near the tentacle region, and it is in this region
that the stone-canal opens in the one or two rare cases where it
still opens to the exterior. Hence it appears that whereas in the
irregular Sea-urchins the genital openings and madreporite have
remained fixed while the anus has been shifted, here the anus has
remained in its original position while the genital opening has
been shifted towards the mouth.
The Holothuroidea are divided into the following five Orders.
1. Elasipoda: Sea-cucumbers whose tentacles have shield-
shaped ends drawn out into short processes, devoid of gill-trees,
with the tube-feet of the upper surface of the body modified
into stiff respiratory processes. Live only at great depths in the
ocean.
2. Aspidochirotae : Sea-cucumbers with shield-shaped ends to
the tentacles, — these have also large ampullae so that they can
be individually retracted. With gill-trees and often Cuvierian
organs.
3. Dendrochirotae : Sea-cucumbers with long delicately-branched
tentacles without ampullae. The whole front end of the body can
be pulled in by means of special muscles. Gill-trees present
4. Molpadidae : Sea-cucumbers with tentacles unbranched or
with two or four small lateral branches, and no other tube-feet
except a circle of papillae round the anus. Gill-trees present.
5. Sjmaptidse : Sea-cucumbers in which the tentacles have two
rows of short branches. No tube-feet except these, the radial
canals having also disappeared. No gill-trees. The body-wall is
thin and transparent and oxygen can diffuse through it.
Class V. Crinoidea.
The last group of the Echinoderms is termed the Crinoidea (Gr.
Kplvov, a lily), animals long familiar to collectors of fossils under the
name of lily-encrinites. They differ from other Echinoderms in
IX.] CRINOIDEA. 283
that from the centre of what corresponds to the upper or aboral
surface of other orders, there springs a
jointed stalk by which the animal is
moored to the substiatnm.
Animals of this type were much
more common in past times than now.
La^ masses of limestone are actu-
ally made up of their skeletons. The
modem order of Crinoidea mcludes a
few species sorTiving at great depths
in the ocean, and about the mode of
life of these we know little. There
are, however, besides these a number
of species not sharply marked off from
each other assigned to a family, the
Comatulidae, containing two genera,
Antedon and Actitwmetra, which lire
at moderate depths in the ocean and
which have been thoroughly studied.
These however are exceptional in that
they break off from the stalk when
they are mature and swim about by
muscular movements of the long anns.
The stump of the lost stalk forms a
knob called the centro-dorsal ossi-
cle, which is provided with grasping
processes called ci rri, by means of which the animal can temporarily
attach itflel£
We may select for our type the common Antedon rosacea,
which can easily be captured by the dredge at moderate depths.
This animal has a small disc and ten extremely long arms. It
reminds one of a star-fish, in the fact that on the oral sides of
these arms there are open grooves converging to the mouth, and
that the skin lining these grooves is modified to form nervous bauds
uniting in a ring round the mouth. These ambulacral grooves are
further lined by powerful cilia which cause currents of water carry-
ing small animals to flow towards the mouth, and thus the animal is
fed. The tube-feet are small and apparently of use only as gilla,
those springing from the grooves on the disc alone retaining their
sensory frinction.
The skeleton is peculiar. The ventral side of the body is
Fio. ISO. Anttdan acotla. Car.
A;oDnfcindividD&l X 1^, Alter
CBtpenter.
284 BCHINODERHATA. [CH&P.
covered by a leathery skin but on the aboral side there are first the
centre dorsal ossicle a round knob representing the uppermost
joint of the stem and then five rows of plates called radials
radiating from t These five rows show ua that here as in most
other Echinoderma we have to do with five primitive arms or
radii these ladii however bifurcate the moment they becoms
Fia. 151. Transverse aeation through the disc and base of an arm of
Anttdon Toiacta. After Ludwig.
1. Month. 2. Various sectious of alimeDlArj oaual. 3. Epithelium of
ambulftcral grooTS. i. Nervona lajer of ftmbulaoral groove. 6. Bailial
water-canal. 8. Circuraoral water- vascular ring. 7. Slone-eanals,
e. Pore-canals. 9. Trabeculae trsTeraing the coelom. 10. Axial
coelom oommuniaatiDf; with 11. 11. Coelom of arm. 12. Cini.
IS. Genital stolon giving ofT 14. 14. Branches of genital stolon in
oirn. 16. Badial nerve of dorsal nervous system. 16. "Chambered
organ" in centre of dorsal nervous system, 17, Calcareous reds
developing into trabeculae. 18. Muscles connecting radial and brachial
plates. CD. Centro.dorsal piece. B', K^, R>. First, second and third
radial plate. Br,', Br.' First and second brachial plate.
free from the disc, and bo there are ten arms : the uppermost
plate in each of the five rows having a double facet, on to which
fits the lowest of the rows of plates supporting the arras.
The arms really bifurcate again and again, but in each case one
of the forks does not develops further and forms a pinnule. If in
tiie case of any of the bifurcations both forks were to develope we
IX.] CRINOIDEA.
sfaotUd h&Te an increase in the number of
arms, and indeed speciea of Antedon with
twenty, forty and even one hundred arms
are known.
There is no madreporite, but the whole
of tiie upper soft integument ia riddled
with isolated pores which lead into the
body cavity and are lined by ciliated cells.
The water- vascular ring has hanging down
from it a large number of stone- canals,
which also open freely into the body
cavity. Only one pore and one stone-
can^ exist in the stalked young, but their
position, comparatively near the mouth,
is utterly different from that in any other
Echinoderm. In the adult the cavity of
the coelom is traversed in every direction
by cellular cords called trabeculae.
The anus is situated on the ventral
side of the body in an interradius, the
alimentary canal being coiled in a simple
spire in the disc. We have spoken above
of the ambulacral grooves being lined by
nervous cells, like those forming the radial
nerve in star-fish. This is indeed so, but
the Crinoid possesses another and much
more important nervous system. From
the body cavity five canals are given off
which penetrate the stalk. Iliese canals
swell up in the substance of the ceotro-
dorsal ossicle into chambers, and in the
permanently stalked forms like Bhizo-
erinns or Pentacrinm they form similar
chambers wherever the stalk bears cirri.
The coelomic cells which form the walls
of these canals develope great masses of
nervous fibrillae. In Antedon of course
only the five uppermost chambers remain
when the stalk disappears — they are
termed collectively the chambered
organ — and the nervous lining of these
286 ECHINODERIUTA. [CHAP.
constitutes a kind of brain (Fig. 151), This " brain "ia separated
from the body cavity of the calyx by a shelf-like fold strengthened
by a calcareous plate called the rosette, which represents a circle
of five plates alternating with the columns of radials clearly seen
in more primitive crinoids. From this brain cords go off to the
cirri, and live great cords run upwards perforating the radial rows of
plates and eventually bifurcating pass into the arms perforating the
plates which form the skeleton of the latter. These cords are at
first tubular outgrowths from the
brain, the cells forming the walls
of which become converted into
nervous matter. It has been ex-
perimentally proved that it is this
nervous system which controls the
muscles moving the arms, and
that if the whole soft part of
the disc including the ambulacral
nervous system be removed the
animal swims just as well as
before.
The organs of sex are rounded
masses found in the pinnules and
are really, as in Asteroidea,
Ophinroidea and Echinoidea,
swellings on branches of a genital
rachis. There is also a genital
stolon, which however has no
connection with any of the stone-
canals, but rises from the lachis
to the centre of the dorsal wall of the coelom. The young are
carried on the pinnules for some time and have a very short fr«e
swimming life, very soon settling down and developing into little
pentacrinoids with a jointed stalk. The name " pentacrinoid "
is suggested by their resemblance to Penlticrhiivt. These stalked
young present interesting features in the skeleton found in many
living and fossil Grinoidea but absent in the adult Antedon. Thus
the mouth is guarded by five inter-radial valves each supported
t^ an oral plate, and the rosette is represented by five ossicles.
Leaving aside the Grinoidea, the development of which is known
only in one case and is there evidently much modified, the eggs of
Fio. 153. Ventral view of a Lutk ot
a Holothuriaii taken at Marseillea
X about 100. From Job. Miiller.
Moath. 3. Oesophagns.
Stomach. 4. Rectam.
AnuB. 6. Coelomio sac.
Rndiment of vater-vaacalar Bj'stem.
Ciliated band.
IX.] DIPLEUBDLA.
the othw four groups of EchiDoderms develope into free swiraining
aoimala which for periods varyiog from a fortnight to six weeks lead
a free life at the surface of the ocean. These young are called
Dipleurula larvae and they are, as mentioned, utterly different to
adult Echinoderms : nnlike these, but like most other animals, they
are bilaterally symmetrical (Fig. 1S3). They swim by means of a
powerful longitudinal ciliated ring, drawn out into a number of
arms or processes. They possess a complete alimentary canal,
consisting of oesotihagus, stomach and rectum, while the cnelom is
represented by two sacs lying one at each side of the digestive
tube. These sacs are, as a study of the early development teaches,
portion:^ of the alimentary canal budded off from the rest. One of
the moat interesting features in the development is the fact that
these sacs undergo traDsverse division in the same way as do the
germinal bands of an Annelid. On each side three segments are
formed. The most anterior on each side often coalesce to form a
median sac into which the originally single madreporic pore opens
on the left side : a portion of this sac becomes the axial sinus of
the adult. The middle sections on each side in exceptional cases
deveIo|e each into the nidimente of a water-vascular system showing
tliat this structure was originally paired. That on the right side,
however, normally remains small, whilst the left one takes on the
form of a wreath with five projections, by the union of the two ends of
which the water- vascular ring with the rudiments of the five radial
canals is formed. This is called the by drocoele. The most posterior
divisions form the body cavity of the adnit ; the left one grows in a
ring-shaped manner, encircling, as with a wider ring, the ring of the
hydrocoele, while through the centre of both rings the oesojihagus
of the adult grows. The oesophagus of the larva is usually cast
off, but liometimes, as in the Ophiuroidea, it is directly converted
into that of the adult by being shifted to the left before the rosette
of the water-vas;:ular sy.stem becomes a ring.
The Dipleurulae of the Asteroidea fix themselves at the conclusion
of their larval life by the anterior end of the body, using the prae-
oral lobe as a stalk. The tised stage is omitted in other Eleutherozoa,
but the larva of Antedon nimcea — the only Grinoid whose develop-
ment is known — also converts the prae-oral lobe into a stalk. But
in the case of the Asteroidea the body becomes bent on the stalk in
such a way that the stalk springs from dose to the month of the
adult. The stalk is eventually absorbed and the star-tish commences
itfl adult life, breaks loose from its attachment and moves away.
II tiie ^H
away. ^^|
288 ECHINODERMATA. [CHAP.
In the Crinoid, on the other hand, the mouth becomes rotated away
from the stalk, and the latter seems to spring from the aboral surEace.
The whole of this development seems to point to the conclusion
that the radially symmetrical Echinodermata are derived bom a
bilaterally symmetrical ancestor with traces of metameric s^men-
tation ; that the acquisition of radial symmetry was due in the first
instance to the assumption of a fixed mode of life, followed by the
dwindling of the organs of the right side and the compensating
greater growth in those of the left. The Crinoidea seemed to have
retained the original mode of feeding by means of the current
produced by cilia, and thus their mouth became shifted upwards
away from the stalk into a position favourable for the capture
of floating prey. In the Asteroidea and the other Eleutheroxoa
food is obtained by seizing it with the tube-feet, and hence in
these the mouth was bent downwards so that the stalk seems to
spring from the oral surface.
This development is not only interesting on account of the
extraordinary metamorphosis which the young undergo, but also on
account of the fact that whilst the adult is utterly unlike any of the
other Coelomata, the structure of the young is reconcilable with the
fundamental structure of Annelida and MoUusca, etc. The only
plausible explanation of this is to be found in the hypothesis that
the young represent in a rough sort of way the ancestor fix>m which
the Echinoderms were derived.
When the Vertebrata are dealt with it will be pointed out that
the larvae of the most primitive forms bear a striking resemblance
to those of the Echinodermata, and that in the embryos of many
Vertebrata the coelom undergoes at first a similar division to what
occurs in the Dipleurula, suggesting the conclusion that the hi^est
groups in the animal kingdom are also sprung from the same
ancestor as gave rise to the Echinoderms.
The Phylum Echinodermata is classified as follows :
Sub-Phylum A. Pelmatozoa.
Echinodermata which are fixed to some foreign object during the
whole or part of their existence by a jointed stalk springing from
the centre of the aboral surface.
Class I. Crinoidea.
Pelmatozoa with five long arms which repeatedly fork. The
genital organs are borne in the tips of the branches.
IX.] CLASSIFICATION. 289
Sub-Phylum B. Eleutherozoa.
Echinodermata which are free during the whole of their adult
existence and rarely fixed even during the larval condition. When
the immature form is fixed the stalk springs from the oral surface
near the mouth and is not jointed.
Class I. ASTEROIDEA.
Eleutherozoa with arms (free radii) containing outgrowths of the
alimentary canal and open ambulacral grooves. The arms have
feebly developed muscles and locomotion is effected entirely by the
tube-feet.
Ex. Asterias, Echinaster,
Class 11. Ophiuroidea.
Eleutherozoa with arms sharply marked off from the central disc.
The arms do not contain outgrowths of the alimentary canal and
have closed ambulacral grooves. They have highly developed
muscles, and locomotion is entirely effected by the arms, the tube-
feet being purely tactile.
Ex. Ophioglypha,
Class III. ECHINOIDEA.
Eleutherozoa in which the arms have coalesced with the body,
the radii being arranged like meridians on a sphere. The ambulacral
grooves are closed. The body has a complete armour of closely
adjusted plates and the spines are movably articulated with these
and assist in locomotion.
Order 1. Endocyclica.
Echinoidea in which the anus is in the centre of the aboral
pole and teiBth are present.
Ex. Echinvs.
Order 2. Clypeastroidea.
Echinoidea in which the anus is excentric, the dorsal tube-
feet are flattened and teeth are present.
Ex. Cfypeaster, Echinocr/amus, Eckinarachnius,
290 ECHINODERMATA. [CHAP. IX.
Order 3. Spatangoidea.
Echinoidea with an excentric anus and flattened dorsal
tube-feet but without teeth.
Ex. Spatangus,
Class IV. HOLOTHUROIDEA.
Eleutherozoa resembling Echinoidea in the anus and ambulacra!
grooves ; but with rudimentary skeleton, highly developed muscular
body-wall and greatly enlarged buccal tube-feet by means of which
all the food is obtained.
Ex. Hohthuria,
291
CHAPTER X.
Phylum Brachiopoda.
Brachiofods (Or. Ppaxunv, the arm; ttov^, voSo^, the foot) are
tnie Goelomata and retain the coelom in a primitive and typical
condition. Like the Mollusca, they are not segmented, and the
only trace of a repetition of parts in the group is in a genus called
BkynchoneUa in which the nephridia are repeated, so that we find
two pairs. A similar repetition of the same organs occurs amongst
the Mollusca in Nautilus.
Brachiopods are exclusively marine. They have a shell con-
sisting of two valves, so that at first sight they appear
features, to resemblo the Felecypoda, but in Brachiopods the
shells are placed ventrally and dorsally, and not on
the two sides of the animal as in Mussels. In a few cases such as
that of the primitive genus LingtUa the two valves of the shell are
nearly alike in size and shape and consist largely of homy matter or
chitin. In most cases however the shell is calcareous, and since in
Brachiopoda, as in most bilaterally sjrmmetrical animals, the two
sides resemble one another whilst the back and front are unlike,
each valve of the shell is symmetrically shaped, but the dorsal valve
differs from the ventral, the latter being usually the larger. In a
few cases, such as that of Crania, a British form common in certain
localities, the ventral valve is flat and attached by its whole surface
to the substratum ; all that is then seen is the arched dorsal valve.
Since in the overwhelming majority of Pelec3rpoda the two valves of
the shell are similar in appearance, while each is asymmetrical in
shape, the umbo being situated near the anterior end, it is easy to
distinguish at a glance the shells of the Felecypoda from those of
the Brachiopoda.
The posterior end of the body terminates in a stalk which in
Lingula helps to keep the animal in the holes of the sand in which
it lives. In other forms the stalk is shorter and it is firmly glued
19—2
to a rock so that vheo it has
Fio. 164. Tertbratula lemigloboi
Braohiopod HheU x |.
Dorsal view. B. Lateral
BRACUIOPODA. [CHAP.
fixed itself a Bracbiopod cannot
change ite place of resideoce
(Fig. 157). Each valve of
the shell is lined hj the body-
wall of the animal, but tlie
body does not occupy the
whole of the space between
the two valyes ; it is produced
ioto two folds or flaps called
the mantle-flaps, which an
foBHU g^d hollow Mid contain ex-
tensions of the coelom. These
a. posterior, b. anterioT end. The line secrete the larger part of
between a and bifl called the length, it j^e Yalves of the ghelL In
traversea tha aperture through which , . , .
the etalk pTojects. The line between Ltngula and BOme otlieTS tfae
°!f'f.?';>,'''t'"^'^w '^'T"! free edges of these mantfe-
and f the thickneBS, and between g and ° n i . i i
h is the hiDge-line. folds, lying panllel with the
free edges of the shells, bear a
number of cttaetae which recall those of the ChaetopodL It v
by no means certain that the shell of Brochiopods is an external
secretion like that of Mollusca : it seems possible that it b really
deposited in the connective tissue under the ectoderm.
In most of the thick-shelled forms
the shell is traversed by processes of
the mantle, which nourish it, so that
in dned Brachiopods the shell seems
perforated with a number of pores.
If ne slightly open the valves of
the shell of a living Bracbiopod (so as
^ I fiavetefiu ^ avoid tearing the tissues) and look
in we shall see between the ventral
and dorsal mantle-folda the anterior
body wall of the creature. This some-
tunes runs almost horizontally across
between the space within the valves,
but often slopes obliquely from the
ventral to the dorsal valve of the shell. Part of this wall is modified
to form two long ridges, the ends of which project freely and are called
the arms i they are coiled and are beset with tentacles (Fig. 156).
Running close to the origin of the tentacles is a little lip or flange
BO placed that the two form a groove or gutter. The groove is
shell at II aldheim
Uagnificd
1 Pnsmatio layer formed ii
nective tissue b Epidermal
ia;er e Outer calcareous
lajer ddt The expanded
outer ends of the tubes which
traverse the shell.
lined with cilia and so is the timer face of each tentacle. The
whole of this apparatus is called the lophophore. It might be
described as a ring of tentacles, the ends of which are drawn out so
as to form the arms. It is never quite bo simple as the above
account would lead one to suppose, for the rin); is often produced
into two minor lobes forming the lesser arms situated between the
main ones, and in many genera the two main anna aro raised up
from the level of the body-wall and each is twisted into a spiraL
The dorsal shell may be prolonged into a series of plates and even
into elaborate bands and loops which serve to support such
lophophores.
1. Month. 3. Lophophore. 3. Stomach. 4. I.irer tubes. 6. Median
ridge on dorsal shell. C. Heart. T. loteatine. eliding; blindly.
S. MuHole fiom dorsul valve of shell to atalk. !t. lulernitl funnel -ah aped
opening at □ephridium. 1(1, Stallc. 11. Bodj-watl. 13. Tentacles.
13. Coil or lip, 14. Terminal Lenloctea.
The mouth lies on the middle line at the bottom of the gutter
between the lip in front and the tentacles behind.
Mruetur^ '^^^ lophophore ia thus an organ for catching food and
passing it into the mouth. The cilia which cover the
inner surface of the tentacles and line the gutter set up small
whirlpools in the water so that minute animals and algae becoming
involved in these are swept into the month- In many species the
BBACmtWODA.
tentacles can be protmded between the valves of the shell, uid thiu
the area they affect is enlarged.
The mouth leads into a simple stomach which ends in a flbott
intestine. Both atomach and iutestiae are ciliated,
gland called the liver consisting
of a number of branching tubes
opens on each aide into the
stomach, and as is the esse in
the Crustacea much of the di-
gestion takes place inside these
glands. In the genera of Brach-
iopuiia which have a hinged
shell the intestine ends blindly,
but in those which have no
hinge there is an anus which
may open in the middle line as
in Crania, or on the right side
of the body as in Lingula.
On the dorsal surface of the
stomach is a small, muscular,
contractile vesicle, the heart
(Fig. 156). This givea off a
number of vessels, amongst
others one which passes to
each tentacle, which there-
fore possibly act as respiratory
organs.
The chief part of the nervous
system retains its primitive re-
lation to the ectodenn. Just
in front and just behind the
mouth there are thickenings of Fro. 157. A iongitudinalvertieal median
the ectoderm forming a supra- °" '""
Bection tiuough Argiope ntapoliU
1. Veuttal «heU. 3. Catial oooUiainft
and 3ub-06sophageal ganglion
respectively. The latter con-
trary to the usual rule being
much the larger (Fig. 157).
They are connected by two
lateral cords and give off a
number of nerves, one of which runs to each tentacle. No sense
organs, such as ears or eyes, are known ^ and indeed the fixed
Sub-oesopbogekl
4. Moatb.
Stalk. 7. neiUB
of btoud- vessels. 8. Meilian oreit
on dorsal shell. 9. UembntM
which ilie separftted from shall during
the process of liec&lcificatian.
to Bit still" and sweep little
luth, lias but little need of special-
Bnchiopod, whose "strengtli i
particles of food towards its n
ized sense-organs.
The carit; of the coelom is reduced by the presence of the
alimentary cana], the digestive gland and the heart, but it is still
spacious. It is partially divided up by certain meaenteries which
support the alimentary canal, and it is traversed by several pairs of
musclea Some of these muscles run from valve to valve, and when
they contract close the shell, others beiag situated behind the hinge,
so that when they contract the valves slightly open. Others again
nm from the valves to the inner surface of the stalk and their con-
traction bends the body one way or another and may even serve to
slightly rotate it.
There is— except in one genus — but one pair of nephridia.
These are short tubes which open by large trumpet-shaped openings
(9, Fig. 156) into the coelom ; while their external openings are
situated at the sides of the body behind the lophophore. The cells
lining the nephridia are some of them ciliated, while others are
crowded with coloured granules. As already mentioned, the genua
BhyncKonella possess two pairs of nephridia.
As a rule, in Brachiopods the sexes are separated. The cells
destined to form ova or spermatozoa are derived from those lining
the body cavity. At certain places, usually four in number, the
coelomic cells multiply and build themselves up into ovaries or testes
according to the sex. When they are ripe they fall off into the
coelom and make their way to the exterior through the nephridia.
The spermatozoa are cast into the water by the male, and the female
must bring them within the valves of her shell by the action of the
current set up by the cilia, because the eggs are almost certainly
fertilized as soon as they leave the nephridia. The eggs develope
in certain brood-pouches situated at the sides of the animal which
are formed by a bulging in of the body-wall. A larva is ultimately
formed which leaves the body of the mother and swims about in
the sea by means of a band of ciha. As it is extremely minute,
although it swims quickly it does not get very far, and this probably
accounts for the fact that Brachiopods are usually found in large
□umliers in one place.
Brachiopods are found in all seas. Abont eleven genera have
been dredged around the British Isles, moat of them
■Bd ciuiifica- in comparatively shallow water. lAngvla is usually
'""' found between tide-marks or in shallow watery it lives
296 BRACHIOPODA. [CHAP. 3L
in a tube in the sand, and the bristles round the mouth of the shell
doubtless serve to keep out particles of sand which might otherwise
injure the animal It is found along the East coast of America, in
the Pacific and other places. One species of Brachiopod, Ter^-
bratula teyviUeit has been dredged from a depth of close upon 3000
£ithoms.
Perhaps the chief interest of the group is that it includes an
enormous number of fossil forms which had a very wide distribu-
tion. The extinct forms far surpass both in variety and number
the existing forms. Some species have lived on, — as fiax as we can
judge from the shell, — unchanged from the time when the earliest
fossil-bearing rocks were laid down. They may thus claim to be
one of the oldest groups with which we are acquainted.
The Brachiopoda are classified as follows : —
Glass I. ECABDDTES.
Shell with no hinge and no internal skeleton. The alimentary
canal has an anus.
Ex. Lingula, Crania.
Class II. Testicardines.
Shell with hinge and internal prolongations, chiefly calcareous.
No anus.
Ex. TerebrattUa, Argiope, Waidheimia, BhynchoneUct,
CHAPTER XL
Phylum Polyzoa.
Thb group includBs a great number of species, the iodividuals
of which are bo small as to be barely visible to the naked eye, but
they are with hardly an exception colonial in their habits and the
ooloniee nsually attain a fair size. These colonies take many
shapes, some branching like a tree, others being flattened like a
leaf, while others again are discoidal ; often they are encrusting,
that is to say they form a layer on some sea-weed or rock, for the
m^ority of them are marine.
If one of these colonies be
dried so that the organic mat-
ter shrivels up, a hard skeleton
remains, and this is then seen
to consist of a number of
chambers or " cells," each of
which opens to the exterior
by an orifice, and, as a rule,
communicatos with its neigh-
bouiB. The skeleton may be
calcareous, or chitinons, or
the colony may be gelatinous
in consistency. The dried cell
may be open or closed by a
lid termed the operculum.
Dniing life each of these cells lodges part of the body of a person
of the colony, the "cell" being indeed the cuticle; part however of
the person is not dotbed with cuticle and is normally stretohed
out above the cell — the opening in the dried cell is in fact the
place where the flexible part of the peraon begins. At the end of
this flexible part is the mouth surrounded by a ring of ciliated
Vio. 168. PortlonB of two P0I710UI
oolonieB. Magnifl«d.
A. Smiltia UmdiborovH. a. ATlcnUriQin.
m. Orlfloe of sell. o. Ooeoinm or
Donoh in which the <^ deTelopei.
B. fiUml^ora plumoia, AftarHinokg.
298 POLTZOA. [ORAK
tentacles: on one side is the anua. The flexible put is tensed
the polypide, and the cell the zooecium. If the polj|>ide be
retracted, which occurs when it
is irritated, the anterior end is
inverted and forms the ten-
tacle sheath in which the
tentacles lie. The operculum
when present is a movable fold
of the body-wall thrown back
when the polypide is pushed out,
and covering the opening of the
tentacle sheath when it is re-
tracted.
The animal within the cell
has a U-shaped alimentary canal,
the anna being situated not far
from the mouth, but it is sepa-
rated from it by a ring of tenta-
cles in the centre of which the
mouth lies. This crown of
tentacles, called the lopho-
phore, is not always circular,
jgnt may. be drawn out into a
horseshoe shaped structure (Fig.
IfiS), and in the species in which
it undergoes this modification
there is a small projection, called
the epistome, which overhangs
the mouth, being situated inside
the tentacle ring. The tentacles
are ciliated, and the action of the
cilia brings food to the month,
which leads into an oesophagus
also ciliated, and this enlarges
into a rounded stomach uaaally
produced into a caecum (Fig.
1S9). From this a small intestine,
parallel with the oesophagus,
leads to the anus. From the
abor&l side of the stomach a cord of mesodermic tissue, called the
funicle, usually passes to the body-walL
Fio. 1S9. Viev of right hilt of Pttt-
matelia flmgaia, aligliU; diaema-
matic. After *"'"°" and Nitioha.
1. Lophophore. 3. Mnuth. 8. Epi-
Bloms. i. Anna. 6. Nerve gaaglioa.
6. OesopbagD*. 7. Stomach.
8. IntcBtiite. 9. Edge of fold of
body-wall. 10. WaU of taba.
11. Muscles. 13. Fanicnlni.
18. Bod;-walL 14. Testil.
16. Teitia, more mature, IS. Stato-
bl*Bt. 17. Orat;. 18. Bpermato-
Eoa free in body-eavity. IS. Ten-
The body cavity ia regarded aa truly coelomic, It contains a
fluid in which cella float; it is traversed by the fuoicle and by
numerous strands of meaodermic tissue. The funicle may be the
remains of a median mesentery which om^e separated the coelomic
sacs of the two sides. Sume of the cells of its walla give rise
to reproductive cells, and the body cavity opens to the exterior
in cfirtain individuals which possess an ovary by a short tuhulor
duct, the so-called inter-tentacular organ. This functions as
an oviduct and has Ijeen regarded by some authors as a modihed
uephridium. A portion of the Ixxly ctivity is separated fnim the
rest by a horizontal septum, and forms a space at the base of the
tentacles- Tliis may open into the other part or may be completely
abut off from it.
No heart or blood-veasele are present. It is possible that some
of the nitrogenous waste matter may be got rid of by means of the
inter-tentacular organ, but it has ulso been suggested that these
wa«te products are stored up in certain cells on tlie funicle. From
time to time the tentacles, alimentary canal and nervous system
of an individual undergo degeneration and form a brown mass,
c-alled the brown-hody, which forms a conspicuous feature in the
colony. After a time the bixly-wall, which has not disintegrated,
forms a new set of organs and the brown-body may come to lie in
the stomach of the reconstituted individual. Thence it })asses to
the exterior through the anus. It ia thought that much of the
yraale matter which has accumulated in the body of the animal is,
in this way, eliminated. In certain Phylactolaemata there are ii
jiair of small nephridia opening betweeu the mouth and the anus.
A nerve -ganglion lies between the mouth and anus, situated in
that' part of the body cavity which run.s round the base of the
lophophore.
Polyiioan colonies are usually hermaphrodite. The testes are
as a rule formed by the multiplication of the coelomic cells which
lie at the aide of the body-wall, while the ovary originates from the
funicle or from the body-wall. They may be found iu the same
individual or in different individuals of the same colony. As a rule
the eggs develope within some part of the parent colony, hut they may
be laid, escaping from the body cavity through the inter-tentacular
canal, and then they pass at once into the sea-water. More usually
the early stages of development are passed through in the t«ntac]i
iibeath or iu a special pouch called an ooecium (Kig. i^^), or in
certain " cells " which contain nidinientary individuals. A free
L
J
300 POLTZOA. [chap.
swimming larval form is usnally found, which after a time comee to
rest and by budding fonns a new colony.
Just as in the colonies of Hydrozoa we found different
individuals set apart to perform different functions, so in Folyioi
we find a similar specialization. Certain individuals may be
modified to accommodate and protect the developing egg, bat
perhaps the most remarkable modifications are the Vibracula and
Avicularia of the CfaeUostome Polyzoa. The vibracula are long
i hair-like processes which sweep
through the water; the avicnlam
are two snapping jaws provided
with powerful muscles, like the
claws of a lobster or the be^
of a parrot (Fig. 160). They are
modifications of a "cell" and its
operculum. The avicularia oc-
casionally catch worms, crustacea
and other animals whose pre-
sence might interfere with the
colony, and by their action they
probably prevent the larvae of
encrusting animals settling on the
Polyzoan colony.
Besides the sexual method of
reproduction just mentioned cer-
tain internal buds termed stato-
blasts are formed in the group Phylactolaemsta. Masses of
cells arise from the funicle and become enclosed between two
watchglass shaped chitinous shells whose edges are kept together
by a special ring of cells. As a rule, the Phylactolaemata die
down during the winter, but the statoblasta persist and when spring
recurs give rise to new colonies. A somewhat analogous process
ensures the perpetuation of the species in certain fresh-water
Ctenostomata.
Polyzoa are widely distributed throughout the sea, many occur-
ring in shallow water, but others have been dredged at great
depths. The Phylactolaemata and a few genera from other sub-
divisions are fresh-water. Fossil forms are numerous and the
Coralline Crag, a tertiary deposit, takes its name &om the luge
number of coral-like calcareous forms, sometimes described as
" corallines," which are found in it.
Fio. 160. An AvionUriDm of fiu^ula.
MagQiGed. From Hincks.
b. Beak. c. Chamber reprmenting
the bodj.oaiity of the modified in-
dividual, dm. Muscle irhich opens,
om. muBcle which closea the man-
dible on the bei^. md. Mandible,
the opecoulum of the modified oeU.
p. Stalk.
XL] POLYZOA. 301
There is a small class of Polyzoa with a solid body, i.e., no
coelomic space, and with both ends of the alimentary canal included
in the ring of tentacles, termed the Entoprocta. In this Class
the body consists of a stalk and a *'cup." The edges of the latter are
fringed with a short row of ciliated tentacles surrounding a disc on
which both the mouth and the anus open. When irritated these
tentacles are bent inwards and the contraction of a sphincter muscle
causes the edge of the disc to be drawn over them exactly as happens
in a Sea-anemone. Sometimes in Pedicellaria the '* cup " falls off
and a new one is formed. Beneath the disc is situated a nerve-
ganglion and the genital organs are continuous with a short duct
which opens in the centre of the disc. The excretory system is
either one or two blind, ciliated canals opening between the mouth
and the anus.
All other Polyzoa are grouped together as Ectoprocta, and
these are subdivided into
Order I. Oymnolaemata.
With a few exceptions marine and having a circular
lophophore. Devoid of an epistome.
Suborder (1), Cheilostomata. An operculum covers the
orifice of the cell Avicularia and vibracula often present.
Skeleton with more or less calcareous deposit in it.
Suborder (2), Cyclostomata. Cells tubular and ending in
circular mouths. No operculum. Calcareous skeleton.
Suborder (3), Ctenostomata. Body-wall soft The orifice
of the cell is closed by the coming together of a fringed mem-
brane.
Order II. Fhylactolaemata.
Fresh-water forms with a horseshoe shaped lophophore
(except Fredericella), an epistome, and statoblasts.
302
CHAPTER Xn.
Phylum Chaetognatha,
The Ghaetognatha (xaCrrf, hair; yvdSo^, jaw) are small cylindrical
animals which swim at the surface of the sea- The name is sug-
gested by the circumstance that at the sides of the mouth are two
rows of curved movable bristles by means of which they seize their
prey (e, Fig. 161).
The body has a small rounded head in front and tapers to a tail
posteriorly; it is provided with one or two pairs of flat, lateral
expansions termed fins ; the general shape resembles that of a
torpedo, if we leave the head out of account. The head is sur-
rounded by a fold of the skin forming a hood which is most
prominent at the sides and dorsal surface. Within the hood the
head bears a row of sickle-like hooks whose points when at rest
converge around the mouth, but are capable of being widely di-
varicated. The head also bears one or more rows of stout spines
whose number and arrangement are of importance for the sjrstem of
classification (/, Fig. 161).
The coelom is well developed and contains a fluid in which cells
float. In strictness there are three pairs of coelomic sacs separated
bom one another by transverse and longitudinal partitions. In
the head the coelomic space is practically obliterated by the great
development from its walls of the muscles which move the hooks.
The coelom of the trunk and tail is further divided into right and
left halves by a vertical mesentery, which in the trunk region
supports the alimentary canal (Fig. 162). This mesentery is pierced
by numerous small holes.
The skin is covered by an epithelium more than one layer thick,
some of the cells of which are modified to form sense-organs, while
others project from the surface of the body and are known as
adhesive cells (Fig. 162). Beneath the epithelium is a thin layer
ia. IGl. A venual iii>n of
f Sagilu hexapUTii x 3j.
I Piom O, Hertweg.
' , MoDtb.
, Onry.
d. Ventral
e. Movable
[ho head.
•a tbe head.
h. Oviduc
ANATOMY. SOa
cif jelly called the basemeDt membrane,
and beneath this a layer of muscleB.
Anteriorly the muscles are broken up into
numerous bundles which fill the cavity
of tbe bead, but in the trunk and tail the
mosclesform four distinct bundles, bilater-
ally airauKed, two dorsal and two ventral.
The nervous system consiats of a
dorsally placed ganglion in the head
which gives off two lateral nerves ; these
pa»9 round tbe alimentary canaJ and end
in » ventral ganglion situated (Figs. 161
and 162) near tbe centre of the body.
The cerebral ganglion gives off nerves to
the eyes, the olfactory organ, muscles, etc.,
and both it and the ventral ganglion
are connected with a tangle of nerve-
fibrils lying at tbe base of the ecto-
derm. A pair of eyes exist on the
upper part of tbe head, and behind
the eyes an organ to which an olfactory
function has been assigned. This con-
sists of a ring of modified ciliated epi-
thelium. Gumps of isolated tactile cells
with long hairs surrounded by supporting
cells are scattered over the body and fins
(Fig, 1G2).
The alimentary canal is simple and
straight The mouth — with one excep-
tion— is ventral and it leads into a
pharynx which traverses the bead ; this
passes into an intestine lined by a single
layer of ciliated epithelium amongst
which are some glandular cells. The anus
is situated at the junction of the trunk
and tbe ttiil and — witn one possible ex-
ception— is ventral.
In Spaddla maritmi, the exception
mentioned in the preceding paragraph,
there is a glandular structure in the head
which may be connected with the escre-
304 CHABTOONATHA. [CBAF.
tjon of vaste nitrogenons material, but no oHiei flzcretotr organ it
known and no special respiratory or ciicnlatory organs exist.
The C^iaetognatha are heriDaphtodite. The paired oTariee
(Figs. 161 and 162) lie in the bnink F^on of the body caiitj
supported by a lateral mesentery. When matnie th^ almost fill
the cavity. The oviduct traverses the ovaiy. It is not known hov
the ova make their way into it, but spermatozoa are eometiiiiet
found inside it, so that it acta as a receptaculum seminis. The
oviducts open to the exterior at the upper surface of the lateral fin,
just wliere the trunk passes into the tail
t-^V^^
Fio. 163. A. Transverae aection throngh a ^adeila etphaloptera in the reiciOD
of the Tentr&l ganglion x abont 200. B. TransTerse aeotion throngh a
Sagitta bipwtctata in tha region of the ovary x about 120.
a. InteHtine. i. in A. Ventral ganglion. b. ia B. Ovary. e. in A. A
ciliated aenae-organ. c. in B. Base of the left fin vhioh haa been eat off.
d. in A. Adbesiia celU. d. in B. Lett Tentral masele. e. in A. Ecto-
derm, t. in B. Tentral mesentery, /, Dorsal mesentery, g. Bight fin.
The median mesentery of the trunk region is continued through
the tail, dividing its cavity iuto two ; and in each of these lateral
cavities the cells lining the body-wall are heaped up and form a
testis (j. Fig. 161). The cells divide up into spermatotoa, which
float in the coelomio fluid and are kept in motion by some of the
ciliated cells lining the body cavity. The spermatosoa escape
through a pail of short vasa deferentia which open on the one band
into the coelom and on the other to the exterior on the tail
Each has on its course a well-marked vesicula seminalis (Fig. 161).
The ova are tranqHirent and pelagic The cells destined to form
the reproductive organs of the adult are early set apart and
distinguishable. The development is entirely embryonic, no larval
form being recognizable.
n.] CLASSIFICATION. 305
The Chaetognatha consist of three geneia, Sagitta, Spadella
Qd Krohnia, amongst which some twenty-three species are divided,
lie genera differ from one another chiefly in the arrangement of
ie armature on the head and in the disposition of the fins, which are
lwa3rs horizontally placed and supported by fine skeletal rods. A
mdal fin exists in addition to one (Spadella and Krohnia) or two
Sagitta) pairs of lateral fins.
The Chaetognatha are with hardly an exception pelagic, that
1 they live near the surface of the sea, and as is usually the case
ith animals which frequent the surface of the ocean they are
lansparent. At certain times of the year they are found in
icredible numbers swimming on the surface by the muscular con-
"action of their bodies, their fins acting as balancers and having no
lovement of their own. At other seasons they descend and are
iken at depths varying from 100 to over 1000 fathoms. The cause
r their descent is unknown. Their food consists of Infusoria, small
orae and small Crustacea.
The zoological position of the Chaetognatha is obscure. They
low no relationship with any of the larger groups ; possibly their
earest existing allies are to be found amongst certain aberrant
Fematoda, such as CluMtosomay but at present too little is known
> make any close comparison possible.
& c&M 20
806
CHAPTER XnL
Introduction to the Phylum Vertebrata, Sub-Phyla
Hemichordata, Cephalochordata and Ubochordata.
The Vertebrata comprise almost all the larger anhnah, indadiiig
Man. The name simply means jointed (Latw Tertehra,
of thePhylom. ^ jouit, and ospociaUy a bone of the spinal column),
and refers to the possession of a jointed internal
axis as the main part of the skeleton. In the lowest forms this
axis is not developed, but in place thereof there is a smooth elastic
rod, which has received the name of notochord, literally bad^-
string (6r. vwtov, back ; x^P^» string). In all the members of the
phylum this notochord is present at some stage of development,
although in the higher forms it subsequently becomes sanonnded
and obliterated by the jointed rod or vertebral column. Hence
the name Chordata, which has been proposed for the group, is really
more appropriate ; but as the term Vertebrata has been sanctioned
by long usage it is inadvisable to depart from it
Besides the possession of the notochord there are two other
features by which the Vertebrata are distinguished. They all
possess at some period of their lives slits in the wall of the front
part of the alimentary canaL These slits in the lower forms allow
the water which is taken in at the mouth for purposes of respiration
to escape, and hence they are called gill -slits. Further, the
nervous system takes on the form of a dorsal strip of sensitive
skin — the medullary plate, which becomes wholly or partly
enroUed to form a tube, the neural canal or spinal cord.
There are in all about 32,000 known spedes of Vertebrata,
including aU the more familiar animals— fish, frogs, reptOes, Urds
and mammals ; so that the word animal to the ordinary mind
generally calls up the idea of a vertebrate. Nevertheless the
number of spedes is not much more than half that ci the Mollasca
and is not a tenth that of the described species of Arthropoda.
CHAP. Xni.] HEMICHOKDATA.
Snb-Phylmn L HEMICHOKDATA.
The most primitiTe membeis of the phylum are certain worm-
like tanna, in which it hu taken speciml research to discover tnc«8
Fro. 163. A Dolichoglm4ut ko^uUnkii n I. From Speng«l.
I. ProboMii. 2. CoUu. 3. Tnmk. 4. Mouth. 3. Gill-sLts.
of Vertebrate Btmetnre. They are marioe and live in mnd, passiDg
it through their iutestinee and extracting nutriment from the
ofganic matter it contains : thus they feed and move forwards by
die same process. These animab are termed Hemichordata (Gr.
Tfu, half) on acconnt of the short mdimeutar>' notochord which they
SometimeB they ate called Enteropneosta (6r. wrtv/ui.
308 HEMICHORDATA. [CHAP.
breath) because, like all Vertebrata, they use the anterior portion of
the gut for breathing. There are several genera, DolickoglostuSj
Chlamydothorax, Glossobalanus and others ; Balanoglossus, although
used as a generic name, may also be used as a semipopular name
for any member of the Enteropneusta.
The body of the animal is divided into three portions : (1) &
conical anterior part in front of the mouth, the proboscis; (2) a
swollen cylindrical portion immediately behind the mouth, the
collar ; and (3) a long trunk, at the end of which is the anus.
The proboscis contains one, and the collar and trunk each a pair
of special sections of the coelom or body cavity. The coelomic sacs
of the proboscis and collar communicate with the exterior by ciliated
tubes, the proboscis and collar pores (Figs. 164 and 165). The
cilia produce currents setting inwards : thus the collar and pro-
boscis are kept swollen up and tense with water and form efficient
burrowing instruments. If a Balanoglossus be removed from the
water and laid upon damp sand it is incapable of burrowing and
wriggles helplessly about. As soon however as it is covered by
water the proboscis and collar are seen to dilate and become stiff,
and the proboscis is then inserted into the sand, soon followed by
the collar, whilst the trunk is dragged passively after them. As the
walls of both proboscis and collar are highly muscular the water can
be expelled through the pores and the volume of these r^ons
of the body diminished, but the action of the cilia soon swells them
up again. On the hinder wall of the proboscis cavity there is a
puckered membrane richly supplied with blood-vessels, which is
called the glomerulus and appears to act as a kidney. When the
water in the cavity has become impregnated with excretory products
it is expelled as explained above by a muscular contraction.
The alimentary canal runs straight from the mouth on the
anterior surface of the collar region to the posterior end of the
trunk ; there is neither stomodaeum nor proctodaeum. In most
species in the anterior part of the trunk the canal has an Q-shape in
section, being partially constricted into two tubes, an upper or
branchial into which the gill-slits open, and a lower or oesophageal
along which the mud is passed which the animal has swallowed for
food. The notochord is a hollow tube of cells surrounded by a
tough membrane much thickened beneath (Fig. 164). This tube
opens into the alimentary canal in the collar region and projects
forward into the proboscis as a support for this organ, which is
attached by a very narrow neck to the collar. The whole skin is
NKBTOUB BTSTKM ASD OILL-SLITB.
ensitive, since there is everywhere a layer of nerve-fibriJB under-
fing the ectoderm cells, Uit this fibrillar layer is especially thickened
long the mid-dorsaJ and inid-ventral hnea of the trunk, these two
egions being connected by a ring of nervous tissue immediately
lehind the collar, The dorsal thickening alone is continued into
he collar region, and here it becomes rolled up so as to constitute
I short ueural tube (Kig, 164) which becomes detached from the
a. lU. LongitndiiiRi Tsctical nectioo through the middle Une of GU>»inhaliiniu.
Di&icraiilmiitic.
Probowiis. 3. Collar. 3. Traak. i. Prolianeis cavit;. 6. GlomeMituB.
8, Periowrdinin. 7. Heart. 8. I'toboMia pore, 9. Collar cavil;.
10. Moath. 11. Notoohord. 12. Donal blood- vessd. 13. Oeao-
pho^eal portion of >limeiitar;r caiml. 14. Branohinl legioD of alimentary
canal. ia, VeDtral blood- veBsel. 16. Giil-sUts shoving external and
intornal opeainsB; Hie oatlioeB of tho eitsrnol opeoinKa are dotted.
17. CcDtrnl nervoas system. 18. Dorsal roole ol nervoas Bjstem.
19. Veotrol pocket of proboscis cuvit;.
Ktoderm and aasnmes a deeper position, it may retain however n
lonnection with the ectoderm through several strings of cells with a
Bbrillar sheath, known aa dorsal roota (18, Fig. 164).
There are very numerous gill-slits opening int4) the alimentaiy
anal, in the front part of the trunk region ; they onght rather to be
lalled pouches with a small outer and a large inner opening, The
inner opening of each pouch is divided almost into two by a tongue
irojecting down from its dorsal edge, the so-called tongue-bar.
'bill tongue-bar is specially richly supplied with blood-vessels and
0 may be regarded as the principal respiratory organ. The blood-
Vessels are destitute in most cases of any proper wall : they are
B it were mere crevices between tlie epithelial walla of the gut,
Doelom and skin. There is however a well-detined contractile dorsal
Bbaunel ninning forward into the kidney, the contractility being
confined to the front end in the proboscis where there ia a closed
c with muscular walls, which pulsate rhythmically, situated above
■he blood-vessel. The mc is termed the pericardium, and the
I
Fin. ItiS. LoDRitudiiiBl hori'
ZDDtftl aectiou through Glui-
tabaUtnut. Diagram matic
1. ProboBcia. 2. Collar. 3. Trunk.
4. Proboscis cavity. 5. Olo-
merulue. 6. Pericuidium.
7. Heart. 8. Probosois pore.
9. Collar cavity. 10. Peri-
baemal cavit;. II. Collar
pora. 12. Dorsal blood-
TeBBel. 13. Alimentary canaL
14. Branchial sac wiUi exter-
nal openiDg. IS. Beproduc.
CBPHALOCHOBDATA. [CBAP.
dilated part of the blood-veBsel beknr
it, the heart. This dorsal vecael om-
nituucat«s with a ventr^ vesael in the
tmnk region by two dewending corred
veesels at the aides o£ the collar. Baeh
of the coelomic cavitiea of the tnak
seuda forwards into the collar region a
narrow toogue lying at the side of the
blood-vessel. These tubes from theii
relation to the vessel are called peii-
II haemal tubes (Gt. rtpi, around; aljia,
blood).
The sexual organs or gonads ue
mere packets of cells in the gill region
and behind it, developed from the wall
of the trunk coelom (Fig. 16S). Each
when ripe forms its own opening through
the body-wall.
One point of interest attaching
to the Hemicbordata is that they may
commence life aa free-swimming larvae,
resembling the larvae of the Echino-
dermata, and suggesting the thonght
that perhaps two such different groups
as the Vertebrata and Bchinodermata
may have descended by different paths
from the same simple free-swimming
ancestors.
Sub-Phylum II. CEPHALOCHORDATA.
Leaving the Hemicbordata we next come to some small fish-like
aninuds, the Gephalocbordata, which were formerly all included
under the name Amphioitus, and indeed there is no very strong
reason for breaking up this old genus. The name Amphioxw (<V^
at both ends ; it^, sharp) refers to the shape of the body, which
is long, flattened and pointed ^t both ends. It is remarkable that
we here meet for the first time with a shape very common among
Vertebrates, but almost absolutely unknown elsewhere in the animal
kingdom, viz. a laterally compressed form with narrow ventivl and
NOTOCBORD.
I dors&l regions and deep sidee. It is common to find animala with
I broad backs and belliea and narrow sides, but only Vertebrates show
a. ISfl. AmphioxvM lanceolntua from tha lett siile, about twice nKtOTnl sixe.
After Luikesler. The gooadio pouohes are seen by trangpaiBooy through
the bodf-will ; the aCriam h eipanded so that ita QooF prajeots below ^e
iDetapleural fold ; the GD-rays of the veotral Bn aie indioated between the
atrial pore and aliaB. The dock spot at the base of the Qfty-soooud
mjotome represents the anua.
the reverse condition. In con-
sequence of this peculiar
shape Amphioiria falls on its
side when it ceases moving.
It burrows in the sand, lying
with its mouth just protrud-
ing, and as its tips are fringed
with ciliated rods (Fig. 167)
a current is produced which
brings new water to the gills
and with it small swimming
organisms which serve as food,
At night Amphioxus often
leaves its burrow and e
about, returning instantly to
the sand if alarmed. It can
burrow with either the head
or tail
The notochord is a
smooth cylindrical rod lying
above the gut and running
from end to end of the animal.
It consists of cells, much of
whose body is changed into
a gelatinous substance, and
which are surrounded by an
exceedingly firm membrane
termed the chordal sheath.
In the embryo the notochord
Via. 167.
Telmn of Amphiotiu aeon from the
iniide of the pharyni. Alter luiQ-
[J. hphinoter mnBOle of Tolum.
. leiar lentnclva Ijiug octane the ora!
Dpenitig.
Oral irartilageB of AmpMoxiu, After
J. Mailer, The btual piecea lie end
lo end in thv oiariiiii of the oral
bood, and each baaal piece wnds up
■D axial procoae into the correapuod-
ing oral cirrus.
312
CEPHALOCHORDATA.
[CHAP.
first appears as a groove in the dorsal wall of the gat, so that we
may say that the notochord of the Hemichordata retains a form
which is passed through in development by that of Amphioxw.
In the very young embryo also an indication is seen of the
division of the body into the same three r^ons as we found in the
Hemichordata. Just as in the embryo of Balanogloesus so here, the
embryonic gut gives rise to five outgrowths firom which the coelom of
Fio. 168. Diagrammatic longitudinal section of an embryo of Amphiaxut.
1. Neuropore — anterior opening of the nenral canaL 2. Neural canal.
3. Neurenterio canal. 4. Coelomio groove. 5. Somite divided off
from coelomio groove. 6. Collar-cavity. 7. Head-cavity. 8. Ali-
mentary canal.
the adult is derived. These outgrowths are (1) a median anterior
unpaired pouch, the so-called head-cavity corresponding to the
proboscis-cavity of Balanoglossus ; (2) an anterior pair of pouches,
the collar-cavities, corresponding to the similarly named sections
of the coelom of Balanoglossus ; and finally (3) a pair of groove-like
extensions of the dorso-lateral angles of the gut-cavity, called the
coelomic grooves, developed only at the hinder end of the gut
From the last-named the coelom of most of the body arises, and
they correspond to the trunk-coelom of Balanoglossus (Fig. 168).
The proboscis or prae-oral region is however very small and bent
down ventrally ; its cavity becomes more or less obliterated in the
adult. Dorsally the collar region is narrow from before backwards,
but it extends obliquely downwards and backwards, causing a
slight ridge to appear at the side of the body. This ridge grows
out on each side into a flap, which meets its fellow beneath the
ventral wall of the body and thus they enclose a space, the so-
called atrial cavity (Figs. 170, 171). This still commuidcates
with the exterior through the atrial pore. The gill-slits,
which occur in the front part of the trunk region, open into
COELOU. 313
bia atrial cavity. The atrial flaps, enclosing the atrial cavity, are
Ka obvious arrangement by which the slits are saved from being
looked with the sand in which the creature lives. lu the Hemichor-
data the hinder end of the collar region may extend over one or two
gill'Slita ; the arraDgement in Amphioxiin may he regarded aa a
farther development of this state of aflairB. As in the case of
Hemichordata, the slits of Amplmxus are divided into two, by a
tongue-bar reaching from the upper margin almost to the bottom
of the slit Each slit thus becomes U-shaped (Figa. 169, 172).
M. Atrial cavity, ei. Oral cirri. eft, Notoohord. d.f. Dorsal fin-chambers.
(. Eye-spat. end, Eadoatyle. hfp. Oiiterowing liver i tlie index
tine passes throa^ih one of J. Miiller's "renal papillae." met. Metaplenral
(old. nph. Nephridla. nt. Spinal cord. otf. Olfactory pit.
ph.b. FBriphaiyngeal ciliated band. tb. Tongae-bais. vei. Telnrn.
The upper and anterior [lortion of the collar-cavity becomes
separated from the rest: its inner walls thicken and develops into a
powerful longitudinal muscle which forms the hist myotome
(Or. /ivt, motise, muscle ; ro/iot, a division).
The trunk coelomic cavity breaks up from the beginning into a
iea of pouches called somites, each of which subsequently divides
into au upper and an under part. The inner wails of the upper
parts undergo a similar change to that experienced by the cor-
rraponding port of the coUar-cavity forming a series of myotomes.
The name myotome is given to each of the inelnmericnliy arranged
bundles of muscle-fibres. Each myotome is separated from the ne^t
liy a connective- tissue partitiott. In Ampkioxus the myotomes of
the right side alternate with those of the left, so that the centre of
ft myotome on one side is opposite the connective-tissue partition
.on the other. Each is V-shaped, and they are arranged so <^g .
Hence in a transverse section several myotomes are seen on each
ClCrHA LOCHOKD ATA,
ade of the lic>dy Ihaa we lave two great Benes of Inngitadinol
muscles broken up into my trmes une on each side of the animal,
by the altercate c ntra tion of which powerful side-strokes of the
lavereo apction tlirongL pliarjiitjeal regioD
feiaalo Amphioxiu, Alter Lankeatec and BoTeri, from R. Hertwig.
. Atriid oavity. c. Doraol oo^lom, separated (Tom atrial cavity bj the doabU-
layeccd meoibraue ICBDitD as the ligamenttivt dtiiUcul-ilum. eh. Nolo-
ohord. d.n. Senarirf nerve. e, Eodoelyle, below whioh is tha
eodostylai oaelnm ooalaining the veiitral aorta. /. Fin-ra; of dorsal
fin. g. Gonadic pouoh ooatniniiig ova. H.v. Beiiatie vein lying in
the narrow coelomio epace which Biicrouutis I, the liver or ItepaliB eoeoum.
l.a. Iisft aorU separated Irom the right norta by the hyperpbarrne^
(epibranohial) gtixtve. tu, Lympb-Bpao?. tap, Metapleural fold,
my. LoDeitudiQfll mnBoles of myotomes ; over against the dorsal coelom
theae mOHoles are atraoged Tertically, and form the rectus abdominis of
Schaeider. n l. Spmal cord. p. Pharyni. r. Nephridium.
t,ffl. Transverse or Buhalrial mascles. c.ii. Motor Fpinal oerre. the
fibres of which have the appearutoe of passing directly into the maBola-
flbtM. N.B. The coaiiecuvo tiseue (cutis, notochordal aheath, et«.] and
the coclomic epithelium are indlcaled by the black lines.
fiat boJj propel the aniina! lorwurds. The elaatdcity of the notochord
acts like a fly-wheel in storing
■J/' the force during the latter
part of each stroke and re-
inforcing each striike at ita
comiaencement. The cavity
of the upper division of the
somite persists throughout
life, ajid is known as the
myocoel (15. Fig. 179), the
fold separating it from the
cavity of the lower division
being termed the iutercoe-
lic membrane {i.m. Fig3.
171 and 177).
The lower portions of the
somites fiise with one another
and form a continuous body
cavity round the hinder part
of the alimentary canal i&.c.
Fig. 171). In front, owing to
the presence of gill-slita, there
are formed a right and a left
dorsal eoelomio canal, and a
ventral coelomic tube, or eu-
dostylar coelom, the dorsal
and ventral portions com-
municating with one another
by spaces iu the gill-bara, that
is, in the pieces of body-wall
intervening between the gill-
si ita. These spaces are termed
branchial coelomic canals.
Although at first formed from
backward prolongations of the collar region, the atrial fliips soon
become invaded by the lower ends of the trunk myotomes ; the
ventral muscle however running across the under surface of the
atrial cavity (Fig. 170), which by contracting diminishes its size and
thus espels water, originates from the walls of the lower portions of
tbe collar cavity.
Tha mouth is originalty some distance behind the anterior end,
Fio. 171. TraQ8ver6e Bcctlon tbrougli
poBt. pharyngeal legioo of jonng AmyM-
ozut, to show groapB of remU ct^lla id
floor of Htriuui. After Laakester and
WUUy.
ad. Aorta. dI. Atrinl eavit;. K.C. Body-
eatitf (ooelom). c.e. Central oannl of
Qerve-ootd (n.c). ch. Notoehonl.
d./.c. Fio-oavitv, i.m. Interooelio
tDembrsoe. inC. Intesline. (.m. and
r.n. Left and riflht metapleural foldj.
r.p. One of J. Mil Iter's "renal pspiltae."
#.f.t>. Sub-inleBtinal Teiii.
31ti CKFEULOCHORDATA. [CEAP.
tuiti ou the left side, so that there is a prae-onl portioD of the hoiy
which in the emtxyo is occupied by an aoterior division of die
^r
t'lu. 173. AnWrior portion ot body of jrouog
tiiiiiiipuniut Atnpht'oxiu. After J. Milller, Blight-
ly ullerod.
ch. Notuchord. ct. Oral rim. t. Eye-tpat.
end. BuduBtyle. /.r. Fin-rays. gj, Gill-
ulits ; th« skeletal roda ot the gill-baFB are
iudicated by black linea. n(. Spinal cord, with
piguiout granalee Dear its base. r.a. Down-
t^ivwth from right anrta lying to the right
ot vtl. the velum, with Telar teotocleB pro-
jecting back into pharynx. ir,o. Ciliat«d
epithelial tracts on inner surface of oral
hood.
■4
^.
■H
1^
coelotn corresponding to the proboBcie
cavity of the Hemichordata. Subee-
quently however the atrial flaps extend Fw. 173. Anterior portion ot
.,,... . . J ,1 , spinaloordot .ImfcKtJw;
right to the antenor end, so that a new seen from abors. After
terminal mouth is formed leading into a Schneider,
chamber which is clothed by ectoderm Between^ '^^^^ ^^t^*
and which is therefore to be regarded as
the stomodaeum. The opening of the
stomodaeum now fonns the apparent
mouth, and the lips of this secondary
mouth grow out into rods supported by
gelatinous material and covered with cilia,
the so-called oral cirri, the function
of which has been already explained (Fig. 167). The walls of
the stomodaeum are known collectively as the oral hood. The
position of the primary month is stiU marked by a projecting lip,
the velum, which is produced into ten or twelve delicate tentacles.
These form a filter to prevent coarse material from reaching the
alimentary canal.
eye-Hpot; one of the
branches of the second
pair of cranial nerres
sometimeH arises directly
from the Hpinal oord as
shown on the right ; tu-
ther back are seen the pig-
ment spots of the nene-
NEKVOCa STSTKM.
The neiToiis system is a simple tube with thick Trails and very
oaTTOw cavity. It is almost as extended as the notochord, and lies
above it. It does not however quite reach the front end of the
body. Its extreme front tip is called the cerebral vesicle ; it ha^ a
wide cavity with thin nails, ao that the total diameter is not
iacieued. There is a pit reaching down to it from the external
Pdj. 174. Hediui TsrticBl seotion throogh the nersbial vesicle of Amphiox'it.
After Eupffer.
I. Gttit; of oerebral reaiole, «. Eje-ipot. g.c. Dorenl groap of gasRlion-
cdla. in/' lolundibaliuii. l.o. Olfaotory lobe. Ip. ITnberculum
bIcid, pog.sibly anidimeutary olfactory organ (Fig. 174), and in tlie
wall of the vesicle itself is a maaa of pigmented cells forming an
eye-apot. In the young larva! Amphio-rus this part of the nerve-
tube remains for a considoralile time as an uncovered medullary
plate, and one is inchned to imagioe that it corresponds to the
Benaitive nervous surface of the proboscis in the Hemichordata,
i in the larvae of these animals there is a sensitive plate with
two eye-spots at the apex of the prae-oral lobe, In the wall of the
nerve-tube are to he found two kinds of nerve-cells, via., (a) ordinary
Bmall nerve-colls, the processes of which soon pass outwards into
the peripheral nerves, and (6) very large nerve-cells, the processes of
'hich extend almost thronghout the entire length of the nerve-tube.
The processes of the Utter kind of cell are called "giant fibres'
(g./* and g./^, Fig. 175): they appear to have to do with
J
318 CEPHALOCHOBDATA. [CHAP.
cooidiDating the huisciiIat movements of the khjihhL Bemdee uie
nerve-cella, aa in all nervous systems, there are a certain number of
anpportmg cells (a/. Fig. 175). In the embryo of Ampiioana Hie
whole wall of the nerve-tube consists of a single layer of cells, all of
which abut on the cavity of the tube ; loany of theee cella becone
JTio. ITS. TroaBveTM section through the ipinal cord of Amphioxui in tbe
middle region oF the body. After Bohde.
a. Ciiant fibre. e.e. Central canal. g./K Oiant nerre-fibree, which taaTeiH
tbe Bpinal cord from before beckwerdB. g.f*. Oiant nerre-fibre*. which
traverse tbe spinal cord from behind forverde. ia.p, Moeole-platea, ue.
terminations of the nerva-flbras on the muscles. m-r. Motor nerre-flbies.
n.f. Longitudinal nerve-fibres cut across, t./. Supporting ecUfc
ih, Sheutli of Di:tvB-cord.
afterwards transformed into small round nervs-cells, and recede from
the cavity, ansnroing a more peripheral position : but others retain
their connection with the cavity and become drawn out into fibre-
like supporting cells. From the nerve-cord aie given off two kinds
of nerves, but not at the same level, ao that in a transverse section
one kind only is seen. These are: — (I) sensory nerves, going
directly to the skin nnd hnving a dorsal origin ; (2) motor nerves,
going to the myotomes. The nervous tube and the alimentary
caual at first both reach to the extreme posterior end of the body
and here are connected by a vertical tube, the neurenteric canal
On tbe course of tliis tube the anus is formed. As development
proceeds the anus slowly shifts forwards and the neurenteric canal
m
wmes a aolM atring of cells and disappears. Thus is initiated the
fitrmatioa of a tail, by vhich terni is denoted a portion of the body
Rdevoted entirely to locomotion and freed from all part of the giit,
■ being filled only with muscles. The tail of Amphloxus ncqu'iTea only
■ ft very limited development, but it soon becomes fiurrounded by a
1 tail-Go, at lirst merely made up of the enlarged skin cells, but soon
I becoming a 0ap contaiuiug gelatinous material. A similar fold along
the middle line of the back
forms the dorsal fin, in
which, iu the larva, there
are a series of metameric-
ally arranf,'ed cavities lined
hy distinct epithelium, pro-
bably derivatives of the
myocoelic cavities (rf./c.
Fig. 171). There are also
low fin folds projecting from
I t ■'5' -1 ^■7^.^-_t ^^& thesideaoftheatrialcavity
L ''^ ■H''-A '^' ^^iSB^^^L "'^'^ constituting the lateral
P'-'-:^v\!'" 'jif^^HH^^ \ '^^ metapleural fins (Fig.
'' ^^B^B^^fc 170), and a median ventral
fold between the atrial pore
and anus, called the ven-
tral fin (Fig. 166). The
dors.il and ventral fins are
stilleued by a number of
l^'elatinous rods mora num-
erous than the myotomes
of the corresponding re-
gions of the body.
The alimentary canal of
Ampkioxus is a perfectly
straight tube consisting of
stonodaeum or mouth
gut, pharynx or braii-
lehial gut, and intestine or digestive gut The pharynx has
faking both dorsal and ventral middle lines grooves lined with cilia
luected with each other by a circular groove just inside the velum
Por trne mouth. The ventral groove is called the endostyle or
rkypopharyngeal groove, the upper groove is termed the hy-
■ perpharyngeal, and the connecting groove the peripharyngeal
^aod (Figs. 169,170, 172). The function of these grooves is cuhouB.
I ?ia. 176. AmphioxuM. Nephiidium of the
left lids, with Ibe Detnhboariiitt portion of
tha phuyugeBl vail, at Been in the iiviDg
ooDdition. The round bodies in the aiiil
of the tubule r^ieseut carmine gtaouliis.
Highlj' magnilied. AFMr Boveii.
320 CEPHALOCHOfiDATA. [CHAP.
The endoBtyle produces ft cord of mucua which is worked fonraida
hj its ciUa and pressed up the sides of the periph&ryugeal btnds.
Here it is caught b; the icrushing cuireut of water produced hj the
cilia of the oral cini and swept back along the hyperphaiyngeal
groove to the opening of the intestine, entangling in its passage tlw
small plants and animals carried by the water ; the latter of oonise
escapes into the atrial cavity through the hundred or so long narrow
gill-slits. The intestine is prolonged forward on the right side of the
pharynx into a blind pouch, the so-called liver {I, Pig. 178), which
probably secretes a digestive juice.
Fio. 177. Portion at transverBe section through the phsryni ot Amphioxtu, to
show position of excretory tnbule. After Weiss.
ao Lett aorta. at. Atrial caTity. at.t. Atrial epithelium. c. Coelom,
eh. Notochord. i.m. Id tereoclic membrane. l.d. Docsal wall of atrial
CBTity nph. Nephriiiium. p.b. Gill -bar. ph.t. Bpithelinm
of hyperpharyngeal Rroove. ph.f. Fold attached to giU-bar conUming
branchial coelomic canal, s.fft. Sheath of notochord. (.6. Tongue-hw.
The exeeretory organs of Amphiorus are small and have only
recently been discovered. We have seen that in the region of the
pharynx the coelom has become reduced to a narrow canal,
beneath the pharjnx, and to two dorsal canals at the sides of tiie
notochord (Figs. 170, 177). These latter canals have been described
as having at the level of each tongue-bar a wide funnel leading into
a short tube connecting them with the atrial cavity. The edges of
the funnel are supported by strings crossing the coelomic canal and
inserted in its wall. Goodrich has recently re-examined these organs
HI.}
EXCRETORr AKD VASCULAR SYSTEMS.
321
Und according to his account they do not open into tlie coelom but
iid intera&Uy in branches beset with aoleuocytes, or cells provided
I the choanocytea of Spongei^ with a
Dollar inside which a flagelhiin flickers.
ITbe same author lias desiMibed -similar
Btmctuies in the Polycbaeta, and holds
them to be radically distinct from the
wide-moutlied, simple nephridia of the
Uollusca and of some Ohaetopoda which
e terms coelonioducts. These tubes
re the nephridia, and taken collective-
r constitute the kidney. It has been
proved that carmine injected into the
Boimal is excreted by them. Besides these
■ number of thickened patches of the atrial
epithelium, discovered by Johannes Miiller
wad called by him renal papillae, are
thought to assist in excretion (Pigs. 169
md 171).
The blood system is exceedingly sim-
ile. The blood from the elementary canal
B brought back by a 8ub-int«stinal vein,
which like a broad river is often subdivided
into two or three parallel channels which
then reunite with one another ; in a word
it is more a plexus than a tube. It
runs to the tip of the liver on its outer
ride, returns on its inner side, and pursues
3 then as a single channel under
the pharynx, where it is called the V e n t ral
<torta. In this region it is contractile,
dmiviog its muscles from the walla of the
Tsntial coelomtc tube. Vertical branchial
TeaMls called arterial arches are given
flS; tliese ascend in the gill nepta, that
u, the portions of the wall of the pharynx
intervening between the gill-alits. Arriv-
: at the dorsal line of the pharsmx
a vessels empty into two longitudinal
8, the dorsal aortae, which further
: unite into one (Figs. 170 and 171). The tongue-bars abn
Fio. ITS. Amph'oxw lUt-
Bscted from the ventral
side X 3. After ItAthke,
sligbtl; Altered.
an. AnuB. at. PositioD of
atrial pore; thoexteDBiOQ
oF the atriam behind this
point is indicated by the
dotted line puBing over
to the light lid* of i, the
intestine. '. £ndOBtyle.
;;. Gonadic poaches. 1.
Liver, m. EntraQ(>a to
mouth with the oral cirri
lying over it. p. Pharynx.
tx
3SS CEPHALOCHOBDATA. [CHAF.
coDtain Teasels emp^ring into the dorsal aortae ; then commomcate
with the branchial vessels tbrougti what are called synaptionlae,
that is, cross pieces tying the tongue-bar to both sides of the gill-
slit which it divides (Fig. 172).
Both gill-bar and tongue-bar are strengthened with rods of
gelatinous tissue. These are the precursors of the visceral
arches, which form such an important part of the skeUton in the
1. Nerre-cord. 2, Notochord. 3. Myotome. 4. HoUaur wderotome.
S. OoQ&dio ponch. 6. Dorsal coelomic oanaL T. Nephridiam.
8. Branchial costomio canal in gill-bar. 9. Bndoa^lu ooelom.
10. PhaijDi. II. Hyperphuyngeal grooie. 13. Endoatjle.
13. Dorsal aorta. 14. Atrial cavity. 15. Uyoooel.
higher Vert«brata. Similar gelatinous tissue forms the lays of
the dorsal and ventral fins, the sheaths of the notochord and
nerve-cord and the dermis. It differs from ordinary connective-
tisfiue in that although it consiBts of a ground substance with a
deposit of fibres in it, it contains no amoebocytee or " connective-
tisBue corpuscles." The fibres in ordinazy connective-tissue are
lai^Iy if not entirely produced by the metabolic activity of the
Wnoebocj'tes ; but in Amp/'i'irus it appears that tbey are produced
by the cells of the coelom, ectoderm and endoderm which adjoin
the connective-tiasue. Thus the sheath of the notochord is deposited
partly by the cells of the notochord, but chiefly by a hollow out-
growth from the myotome called the sclerotome (4, Pig. ITS), the
fin-ray by a coolomic sac (dj'.c. Fig. 171) which disappears in the
adult, the rods of the gill- and tougue-bars largely by the epithelium
of the pharynx. The connective-tissue of the Cephalochordata is
therefore in a peculiarly interesting primitive condition ; and that
of the Hemichordata has the same structure.
The reprodnctive organs ore very simple in construction. The
es are separate, and ovaries an<I testes closely resemble each
other in external appearance (Fig. 178). They take the form of
squarish masses, called guuadic pouches, embedded iu the outer
walla of the atrial cavity. Wlieu ripe they burst into the atrial
cavity, the eggs escape through the mouth or atrial pore, the
spermatozoa through the atrial pore. The fertilized egg developes
ito a free-swimming larva of a remarkable form. There are
Lo atrial folds covering the gills, but one set of slits is developed
long before the other, and the mouth appears on the left side. It
has been proved that the sexual organs are outgrowths from the
lower ends of the myotonies, and remain throughout hfe connected
with these hy strings of ceils (Fig. 179).
The Hemichordata and C-ephalochordata are found all over the
tropical and temperate regions of the world wherever a suitable
aubstratum is found. The Hemichordata burrow in mud rich in
decaying matter, but the Cephalochordata prefer clean sand, their
fooiJ as we have seen consisting of swimming organisms,
Sub-Phylum HI. TUNICATA on I'ROCHORDATA.
By many the group of Tuuicata or Urochordata would be
considered the lowest portion of the phylum Vcrtebrata, and if we
had regard only to the adult structure this could not well be denied,
for in the adult hardly a trace of the Vertebrate relationship is
discernible. But the Tunicate commences life as a larva showing a
redeveloped structure in several important points than .4 mpA/oj-«s
jposseaHes at any period of its life-history, and hence we must regard
" 9 simple organization of the adult as a degraded rather than a
primitive condition of affairs.
1\— 1
DROCHOBDATA.
[chap.
ID. ISO. Side view of the {interior end of a larvft of Aicidia which has been
frte-BwimiuiDg for two dajs k 8TS. Fio. IBl. Dorsal Tiew of the Mine.
After Eowaleweky.
. Moath. 3. The connection o( the bmin with the itomodaenm.
3. EndoB^le. 4. Intestine. 6. Branchial oavit^. 6. let gill-slit
7. 3nd gill-Blit. 8. Atrial opening. 9. Blood oorpnaoUs, 10. CaTit;
of biun. 11. Dorial nerre-tnbe. 12. Kotooboid. IS. Hnscles.
14. Filing organs. IG. Otocfst. 16. Eye,
till.] LARVA. 325
f
H The typical Tuniijate larva is often called the Ascidian tadpole
I . becauBe ita form recalls that of the well-known larva
^P of the frog. It attains a leDf^h of about a quarter of
Bu inch, and consists of a small round trunk and a tUu vertical
F tail four or five times au long aa the trunk. The tail is the organ
of locomotion, and is provided with a sheet of muscles on either side
by the alt4?mat6 contraction of which powerful aide-strokes are
Metuted and the animal is propelled forwani (13, Fig. 181). The
tftil is stitfeued by a well -developed notochord— which does not
:8xteQd into the trunk, hence the name " Urochonlata " (Ur. oipii,
.tail ; x°P^' " string). A uniform flap of skin, a continuous
fin, forma a liorder to the tail. The trunk contains the enlarged
ryus which opens hy a narrow mouth in front : and laterally
communicates with the exterior by two ciliated openings — the gill-
riits. Its ventral wall is swollen out into a pocket which causes the
vnder lip to protrude as a bulky chin. In this pocket we find
developed a ciliated groove, theendostyle. having the same position
s the organ similarly named in Amp&ioa^us. On the chin outside
le three peculiar warts which secrete a sticky slime and which are
used by the larva to fix itself to surrounding objects. The pharynx
Wds l>ehind into a short iutestijte which is attached to the ectoderm
liigh up on the side far in ailvance of the root of the tail. Hence
'■ the priwcas of shifting forward the anus and the corresponding
development of a purely muscular tail have been carried much
further in the Ascidian tadpole thau in AmpAioiPus.
The nervons syKtem in the tail is a simple neural tube ; but in
the trunk it expands into a thin walled vesicle, the so-called sense-
vesicle, which is the rei>reseutative of the cerebral vesicle of Ampki-
ojvt and the forerunner of the brain of the higher Vertebrata.
As in the larva of A mphtarun, the sense-vesicle opens to the exterior,
but the spat where this occurs is involved in the invagination which
forma the stomodaeum. The tube connecting the sense-vesicle and
the stomodaeum is called the neuropore (2, Figs. I8U and 181).
Part of the side-wall of this vesicle is modified so as to form a cup-
shaped eye with a .-iimplu cuticular lens directed inwards. From the
roof liangs a ball of lime suspended by a pillar of celts ; this acts aa
an otiiiith, and the whole forms a rudimentary ear.
Tlius both in the structure of tlie nervous system and the
position of the anus, the Ascidian tadpole is more advanced than
the Ampkiiixiii.
Although, as we have seen, both mouth and anus are present,
yet they c&niiut I
gel&tinonM matter,
ectodenn c«lls and
UBOGHOSDATA.
nfiod, tor tltey are closed by a sheet of
This is the test which is secreted by the
invelopes the whole body, bo that during iu
brief free-swimniing life the
Asciilian takes no food.
After swimuiing for a
nhort time tlie larv-a fi^es
itself by ttt
phalli"'"' chin-warla to a
suitable sub-
stratiun and undergoes a
very rapid metamorphosiB.
Tlje tail Hlirinks and is ab-
sorbed , notticboni and nerre-
tulje disappear : the srose-
veaicle also disappears, only
its hinder thickened wall
persisting as the adult gan-
glion (6, Pig. 182). 'ITie
neuropore however peisista
and developes into a maaa
of tubes underlyiog the
ganglion, which is called
the sub-neural gland. It«
opeiung acquirer a i-reseent
form with thickened lips,
and is called the dorsal
tubercle. Meanwhile the
i-liin grows enormously, so
as to rotate the mouth up
and away from the sab-
stratum, and thus the long
axis of the pharynx becomes
Fro. 192. DiaETain of the liximi luid obuieea .■ i - . j r i. - _
undergone by a Wval J,ri<K«n. Prom vertical instead of horuMD-
Lanke»tef- tal. The skin of the region
1. HoDtb. 2. Anns. s, oill-Blita. nhere the anus becomes
i. In A, Dotochord: in B ftnd 0. vnniBhmi! -. . i ■ ji i
tail. 6. In A, taU. 6. Brttia. Situated 18 depressed so as
to form a groove. This be-
comes confluent with the outer parts of the two gill-slits, so ivs to
form a single dorsal cavity termed the atrial-cavity, the opening of
which is not far from the mouth. It must be noticed that this
STRUCTURE.
cavity does not correspond to the simi-
larly named cavity In AmpMoj^is: in
the case of the lost-uauied animal the
atrial walls originate &om the dorsal
edges of the gill-slits and meet one
aaother beneath the animal ; whereas
iu the ITrocliordata they arise (roiu the
ventral edges of the slits, and are united
with one another on the dorsal edge.
Thegill-alitstliemselvesbecomeL^hanged
by tlie growth of numerous |iartitiona,
transverse to the axis of the phatynx,
into a series of narrow slits ; and then
by the formation of another series of
stronger bars parallel to the long axis,
into a veritable ciliated trellis- work.
All this trellis-work is supported by
homy rods like the gill-bars of Amphi-
(uriu. The t«st thickens enonncualy
and becomes invaded by a finger-like
outgrowth from the hinder part of the
body, which carries blood-vessels to it
and buds off cells into it which nourish
it and change its character. With these
changes the adult form is attained.
Few would see any resemblance to a
Vertebrate in the motionless sac-like
body fixed to a stone or rock and look-
ing more like a plant than an animal
(Fig. 183).
Nevertheless, the Tunicate in some
points, even when adult,
recalls the structure of
A mpktoirws. Thus we
eBCOunter a ring of delicate toutatles
a short tUstance inside the
mouth strikingly recalling
the velar tentacles of Am-
phivxva. Asinthat animal
also there is a lung hypo-
pharyngeal groove or
structure of
animal at
inUtU<uiii4n 1. Tbe live
Id teat I some □[ the oig&nB
can he seen, an the teat ia semi.transpAreDt.
Man til. 3. Atri&l (iriflct. B. Anus.
1. Ueaitalpore. 5. MusoleB. 6. Stomaoh.
T> Iiitotitiiie. 8. Ueptodactive organB.
0, Stalk attached to a roak. 10. Tentacular
ring. 11. Peripharyogoal ring. 12. Bittin.
Tio. 184, TieiT or Ciona iniatinalit lying on its right side. Both the liraiu
and the atridl oavitieB haTe been opened lij longitudinal inoiaiona.
1. Mouth. 2. T^ntaclel. 3. Periphorfngeal groove. 4. Fer-
(orutiid wallB of braQchial aao. 5. Endostjle. 6. Oesophageal
opening lending tiova the brsoohial sac to tbe gtomaob, rather diagram-
matic 7. Stomach. 8. Intestine slioning tjphlosole; port of it remofed
to show Enbjacent atractoies. 9. Bectnm. 10. Anna. II. Atiial
aperlnte. 12. Inner anrface of mantle ahontng longitodinal and trans-
Terse muscle Gbres. 13. Dorsal tuberale. 14. Subnenral gland and
brain. 15. Cut edge of brauohial aac. IC. Heul IT. Oval?.
16. Fore of vas deferens. The openings of the oviduct and the vaa defer«DK
are shown enlai^ed to the right. 19. Tealioular tubes on intestine.
80. Oviduct. 31. Beptnin ahatting off that port of the bodj-okviQ
which containa the heart, atomacli and generative organa. ^^^_
endoBtyle passing in front iuto a peripharyngeal band, and
8e(.^reting a cord of mucus which is worked forward. This muctis is
torn into strings by the inrustiing current of water and swept back-
wards to the opening of the oesophagus, entangling in it food
particles jnst aa in Amphioxug. Instead of a hyperpharyngeal
groove, there is a seriei< of tags hanging down from the dorsal wall
of the pharynx, called languets. These in life curve round so
■8 to form a row of hooks supporting and dire'^ting the mucous
Btriuga.
The oesophagus leads into a dilated stomach which bends on
itself and leads into an intestine which after ono or two coils runs
forward and opens into the atrial ciivity. Its ventral wall is folded
inwards, forming a typhloaole similar to that of an Earthworm. Aa
lal the straight terminal portion of the intestine is called the
rectum. Near the anus open the ducts of the ovary and testes,
for the animals are hermaphrodite. These organs are branched
clumps of tubes, the testis being spread over the surface of the
Btotuach, the ovary forming a mass between the stomach and
intestine. Oviduct and vas deferens are closely applied to one
another, the vas deferens being the more superficial The latter
opens by a rosette of small pores, the ovary hy a broad opening, and
IK> the water from the gill-slits, as it parses out of the atrial cavity,
sweeps away the sexual cells.
On the ventral side of the pharynx is a V-shaped heart, which
is enclosed in a space called the pericardium. The heart is only
a specially thickened part of a ventral blood-veasei, which lies im-
mediately under the endostyle and communicates through a network
of vessels in the gill trellis-work with the dorsal blood-vesseL
Waves of contraction pass over the heart so as to drive the blood
forward. After a certain interval the direction of these waves ia
Teveraed, so tliat the blood alternately goes to the dorsal vessel from
the heart and vice term. With the e-\ce]>tion of the heart, however,
the blootl-veasels do not seem to have definite walls, and are really,
an in the Enteropneusta, crevices left between various organs.
The sluggish life of the Ascitlian lias as its only external
nanifestatiou the sudden closing of the mouth and atrial cavity
Vy spliincters, and the consequent ejection of water — whence the
popular name Sea Squirt. In consequence metabolism is at a low
level and not much waste is prodiK'ed. A good deal of tbis
waste is probably got rid of by the throwing off of the mantle from
time to time, but for the rest no definite excretory organ is required.
nROCHOBDATA-
T he nilrogenona excretion is stored up as crystals of insoluble unn
acid in little vesicles attached to the hinder part of the intestine.
These vesicles, together with the cavities of the genital organs and
the pericardium, may be looked on as the remnants of the coelom, so
that here a similar phenomenon has taken place (■<> what was met
with in the case of ArthropodB, namely an obliteration of the coelom
through the expansion of blood-vessels.
The Tunicata or Urochordata abound on every rocky shore and
exhibit a surprising diversity of form. Their priucipal divisiuni
are ns follows.
Class 1. CoPELATA or Lahvacea.
Small forms which retain the larval condition thronghoul
life. The gill-slits are undivided and the anus ventrB,l, There
is no atria] cavity : each of the two j^ilUslits opens <lirectly
to the exterior. The tail is usually carried bent forward at a
ttharp angle with the body. A temiwraty teat devoid of bl(
vessels is found : the animal when disturbed wriggles out
and forms another.
Class II. The AaiPA.
Forms which have lost the
tail with its nerves and mnsclea.
These are divided into
Order I. The Aacidl-
aceae, fixed forms.
Older II, Tlie Thali-
aoeae, which have second-
arily acquired the power of
swimming by contractions of
the whole body carried out
by transverse bauds
muscle.
The Ascidiaceae constil
the great bulk of the Urochor-
data. Some of them, such as the
Fm. iftS. Two gronps ot individuals form taken as a type in the
of Bwryiiuj pioiiw^u., afier Milna general description given above,
Edwards. Magnified. " i- n ^
1. Moutb opening;. 2. Conunoi
at a
'1^
oat .
)hor- I
olooea ot the gtaup.
remain solitary throughont life,
but otbetB bud and form colonua
XIIL]
embedded in a common teat ; these ore called Compound Ascidians.
But the group is not a, natural one, since budding is carried out in
diflf^Tont ways in different Emilias, and han therefore probably
originated several times. The
commonest method is by the
outgrowth of a hollow finger-
shaped process of the pharynx,
called a stolon, arising at the
hinder end of the endostyle,
which becomes divided into
pieces, each forming a bud.
On tlie other hand in Botnj)-
tug a difTerunt method b fol-
lowed, since in this la.'^e the
buda originate simply as little
pockets of the atrial-wall of
tlie parent. Bofri/llua is one
of the most beautiful colonial
forms : in it the bitds are
arranged in circles ; the atrial
openingE of the members of
a circle open into a common
pit in the centre called the
cloaca- Pyrosoma is a free
floating colonial form, with
the shape of a cylinder open at
both ends, the atrial cavities
of the constituent persons
opening on the inner surface,
their mouths on the outer.
The Thaiiaceae are extra- p,^ ^^_ j,„^ ^^^ ^, ^ iMj-growr,
flpecimen of the aoHUiy form of Sntpa
dtmoeratica X ahoxxt 10. Tvum Biuulu,
I
ordinary forms. They have
tlie shape of cylinders with
lkenouth.t.„e«d=„dtl,« '-pL^lti'"! ao^r™ 'o"''
atrial opening »t the other,
and tlieir body is surrounded
wholly or partly with muscular
hoiips like tlie hoops encasing
a tiurrel. The commonest
form is Stilp/e, which at intervals may be seen in countless
numbers swimming at the surface of the sea. In this anima
preaeDliog
pharynx, the Bo-oalled "gin." !l. En-
dDBtfle. 4. Peripharyngeal band.
5. Brain. 6. Ciliated pit. 8. "Nu-
oleuB," consiBtini; □( stomaeh, iiver. in-
letline. 9. Stolon or row of fooiiB.
ID. Processes of muDtle. 11. Uonlh.
332 UROCHORDATA. [CHAP. XUL
the test is of a glassy transparency. The two original atrial
openings or gill-slits of the larva do not become divided by
partitions, but develope into two huge vacuities in the side walls
of the pharjmx, reducing its dorsal wall to a mere band, the so-
called " gill." There are two distinct forms of this animal, a sexual
and an asexual, one giving rise to the other, so that here we have
a case of "alternation of generations.'' In the asexual form we
find an endostyle-process or stolon which gives rise to a chain of
Fio. 187. Semi-diagrammatic view of left side of Salpa, From Herdman.
1. Branchial aperture. 2. Atrial aperture. 3. Anus. 4. Branchial sac.
5. "Gill." 6. Sub-neural gland. 7. Endostyle. 8. Heart.
9. Oesophagus. 11. Languet. 12. Muscle bands. 13. Nerve
ganglion. 14. Embryo in ovisac. 15. Peribranchial cavity.
16. Peripharyngeal band. 17. Stomach. 18. Testes. 19. Test.
20. Sub-neural gland.
small sexual forms which one by one drop ofif. Each sexual form
produces only one egg. This when fertilised does not give rise to
a tailed larva, but becomes attached to the atrial wall of the
mother by a knob of maternal tissue containing blood-vessels, called
the placenta, which is embedded in a disc of embryonic tissue,
through which nourishment diffuses from mother to embryo. In
this position it grows up into an asexual form and eventually
breaks loose and swims away.
333
CHAPTER XIV.
Introduction to Sub-Phylum IV, Craniata.
The Cyclostomata.
All the remaming Vertebrata are distinguished by possessing a
skuU and brain, and are grouped together as Craniata. The Craniata
are separated by a deep gap from the lower forms : but they them-
selves present a fedrly continuous and graded series from the lowest to
the highest forms, and their comparative anatomy, especially when
we take into account the fossil representatives of the sub-phylum,
gives us a fairly good idea of the course which the evolution of
Vertebrata has pursued ; so much so indeed, that the group might
be compared to the fairly reliable and complete records of a country
during the historical period, whilst the Hemichordata, Cephalo-
chordata and Urochordata represent the few scattered and scarcely
decipherable documents of prehistoric epochs.
The Craniata are defined, as we have seen, by the possession of
a skull and a brain, though these are only two of the
many characters which distinguish them from the
other Vertebrata. The skull is composed of either cartilage or
bone; and even in cases where the adult skull is completely bony, in
the embryo the bone is partly, at any rate, represented by cartilage.
Cartilage and bone are really only two peculiar modifications of
connective tissue whose fundamental characters it may be
useful to recall There is in every case a gelatinous ground
substance traversed by fibres, and applied to these fibres are cells,
which are connected with one another by delicate threads of
protoplasm and which secrete the greater part of the ground sub-
stance and fibres contained therein. In cartilage, the ground
substance becomes cheesy in consistence, the fibres being masked,
and the cells are arranged by twos and threes in little pockets.
In bone, on the other hand, the cells remain single while the
334 INTRODUCTION TO CRANIATA. [CHAP. XIU.
ground substance becomes hardened by depositions of phosphate
and carbonate of lime. The spaces occupied by the cells are
known as lacunae, and the delicate processes which connect the
cells give rise to the capillary canals known as canaliculi in the
dried bone, whilst the spaces occupied by blood-vessels traversing
the bone are known as Haversian canals.
In the simplest form the skull consists of two pairs of pieces of
cartilage, one pair embracing the front end of the
skuii!"***^* notochord and termed the parachordals. In front
of these is the second pair, the trabeculae, united
behind and before with each other but diverging in the middle
so as to embrace between them the pituitary body, which is
described with the brain. The parachordals develope ridges which
wall in the sides of the brain and may form a roof over its hinder
portion.
The brain is only the enlarged and modified anterior end of the
neural tube, and the existence of a skull is correlated with the
presence of neural arches protecting the hinder part of the
nervous system. These arches consist of paired pieces of cartilage
meeting above the neural tube. They have been shown to be formed
as solid outgrowths of the myotomes which represent the hollow
sclerotomes of Amphiaxtts, and hence it may be that the cranium
itself is derived from the walls of the most anterior myotomes which
early become fused with one another and otherwise modified.
Haemal arches, paired pieces of cartilages with their upper
ends implanted in the sheath of the notochord and their outer ends
directed downwards, are also always present, and like the neural
arches are derivatives of the myotomes. In the region of the tail
the haemal arches meet each other so as to form a V beneath the
notochord, but in the trunk they simply project out between
adjacent myotomes as transverse processes, the ends of which
may become movable on the basal parts and are then known as
ribs'.
The brain of all Craniata is sharply divisible into three primaiy
regions called fore-brain, mid-brain and hind-
brain (Fig. 188). Of these the first is certainly
the enlarged and highly developed representative of the sense
vesicle of the Urochordata and of the cerebral vesicle of Amphioxus.
^ This statement applies to the transverse processes of the lower Craniata :
those of the higher Craniata are secondary outgrowths from the neural arches.
BefUtum eatu!iu. DiBseotion of thebnin •nd of soma of the oraoial
as. A. VentcBl oiow. B. Dorsal view. C. Lougitadmal median
Mctiou. D. Diagmm of embrfoiiic hnia nhowinH the Ihree primuy
, Cerebmm. 3. Pineal stalk. &. Olfactory lobe. i. Cerabial hemi'
cphcza. G. ThalameDcephulou. 6. Pituitary body. 7. Optio lobea.
~ "Iptia lobes. 9. Cerebellum. 10. Root of the hind-brain,
laperiot obliqne muBcle. 12. Internal rectas muscle. 13. Sup-
■otiu muMle. 14. Eiternal rcclun muicle. 16. Kinth or
pfaaryngeal nerre. 16. Branch of vaguH Derre to aeoond
1 clefi. 16a. Branch of vagus nerve to tliiid branchial
'. Main tnittk of vuriu to fourth and fifth gill-slits, to
blnal line and to viscpta. ii. Optio aerve. im. In A, oplie ahiaama.
tv, V, VI, VD. VIII, IX and x. Hoots of faurih to tenth l^rBIlial nerves. In
I), I, II, III rciireBent the first, second and third primaty veBtoIes of tbo
-cnbfToiue brain.
336 INTRODUCTION TO CRANIATA. [CHAP.
In the embryo it is a simple thin-walled vesicle, the lateral walls of
which become changed into the retina or the essential s^isoiy
portion of the eye. This, as is the case in the Ascidian
tadpole, has its perceptive surface turned inwards towards the
brain cavity. The nerves by which the eyes are connected with the
brain are really the narrowed connections of the lateral portions of
the fore-brain with the central portion. The roof of the fore-brain
remains thin throughout life and from it a stalk arises leading to a
third median eye, the so-called pineal body, vestigial in all living
forms. From the front wall of the fore-brain an outgrowth takes
place, giving rise to a bilobed vesicle termed the cerebrum, each
of the two lobes of which it is composed being termed a cerebral
hemisphere. This in the higher Craniata is the seat of the more
complex mental processes, but in the lower it appears to be intimately
connected with the organ of smelL The cerebrum in these cases
remains thin-roofed, but its base thickens owing to a great develop-
ment of nervous matter. In order to distinguish it fix>m the
cerebrum the original fore-brain is denoted by the name thal-
amencephalon. This pituitary body is compounded of a
downgrowth of nervous tissue from the fore-brain with a portion of
tissue evaginated and constricted ofif from the lining of the buccal
cavity. It represents the sub-neural gland of the Urochordata, and
in the higher Vertebrates produces a substance which is of im-
portance to the normal metabolism of bone and connective tissue,
and recent research suggests that its secretion also influences the
activity of the kidneys.
The mid-brain acquires thick lateral pouches, the so-called optic
lobes : the hind-brain remains thin-roofed, except in front where a
transverse nervous band, the cerebellum, is formed. The cere-
bellum is believed to be the portion of the brain intimately con-
nected with the semicircular canals of the ear and to have for its
function the control of the muscles so as to maintain the equilibrium
of the body. The rest of the hind-brain is termed the medulla
oblongata or spinal bulb; it controls the beating of the heart, the
respiratory movements and other vital processes. The hinder part
of the neural tube is known as the spinal cord, and it developes
thick walls, so that its cavity is exceedingly smaU.
The essential element in the nervous system of Vertebrata, as in
all other nervous systems, is a kind of cell which has been variously
styled nerve-cell, ganglion-cell and neuron. This last name is
undoubtedly the best, as it avoids the old misapprehension that re-
garded ibe d
'E STRUCTUKK OK NERVOUS SYSTEM.
rve-cell and neTve-fibre as two indepeDdent stmctureB.
On page 54 it was pointed out that the Dcrve-fibre
ia a very fine basal outgrowth of a modified ecto-
S'tem?"'"' denii cell which is the Derve-cell. The cell, inchiding
its outgrowth, is termed the neuron. Important
disroveriee Iiave recently been made on the minute atructure of the
Dervons system of Vertebrata, and we are now able to form a
simple and connected idea of the principles on which it ia built np.
Ongiuating as a simple strip of ectoderm which becomes rolled up
so as to form a tube, it k at first composed of cells which extend
through its entire thickness and which all abut on the cavity of
the tube. Some retain this position Ijut developc branches and
deposit a large amount of cuticnlar suhstance in their protoplasm:
these, constituting the supporting elements of the system, are termed
collectively neuroglia. Other cells retire from the cavity of the
tuhe, becoming more or less rounded in form, but developing a
number of outgrowths: these cells are the neurons. Each neuron
is provided with a number of branching processes, sometimes
arising from a single thick stem; these are cailed receptive den-
drites (Gr. &€v&pov. a, tree), and they receive impulses. Impulses
&T« transmitted through one long basal process, called the axis-
cylinder process or a.\on, which ends in a tuft of processes
often thickened at the tips, which are called terminal dendrites.
Tlie name axis-cylinder is suggested by the circumstance that
amongst Vertebrata this process is in many cases surrounded by
a fatty sheath of a conspicuous white colour, called the myelin ;
a proccis with or without this sheath making up what is known
as a nerve-fibre. The tuft of dendrites in which the axon ends is
found to be in close contiguity either with the receptive dendrites
of another neuron, by which means the impulse is transmitted
from one neuron to another, or else with the muscle-plate of
a mnscle-fibre, hy which means the fibre is stimnhited. The
muscle -plate is a disc of protoplasm with several nuclei situated
at tlie side of the muscle-fibre. The axon may give off several
branches termed collaterals. These like the main stem end in
tufts of dendrites ; in this way an impulse may spread over several
paths. The receptive dendrites of a neuron may also receive
impulses from the terminal tufts of several axons, and in this way
impulses are co-ordinated and c-ombincd.
As mentioned above, the skull and brain are by no means the
only characters which distinguish the Craniata from other Ghordata.
8. Si HI. 22
338 INTRODDCTION TO CRANIATA. [CHAP.
PeihapB the next in importance is the posaeesion of three well-
developed paits of aenee-orguis, nose, eyes and eats.
ar^"~ Of these the noae is the most simply conatructed.
It consists merely of a pair of pits in the skin at the
most anterior portion of the body, the lining of vhich developes
ridges covered with sensory cells, having an olfactory function
(Fig. 189). The essential element in all sense-organs is the sense-
cell, which resembles the neuron in possessing a basal procesB
terminating in a tuft of dendrites by which the stimulus is trans-
mitted as an impulse through a neuron, for in Craniata a sense-cell
is never in direct communicatioD with a muscle-fibre. An olfactory
sense-cell differs from a neuron in possessing one or more stiff
peripheral processes projecting from the surface of the body, by
which stimuli are received from the external world. These are
termed sense-hairs, and they are excessively delicate in structure.
Sense-cells are never combined by themselves into an epithelium:
they are always intermixed with stiff supporting cells which usually
have at the base several root-like branches. The front end of tJte
brain comes in direct contact with the wall of the nasal sac and the
axons of the sensory cells stretch into the brain, thus constituting
the olfactory nerve (Fig. 188).
XIT.] AUDITORT ORGAN. 339
The ears are alao at first pits of the skin placed further back at
the sides of the hind-brain. In the lower forms these pite retain a
narrow connectioD with the exterior throughout life through a long
Fia. 190. Eur of Chimaera mimitro$a L. x about 4. From BetziuB. Seen
from the inner side.
1. External apeitnre od roof of skull. Tbe wall of 2, the "duotuB endo-
lymphaticus," ig partlj removed to show that it ie a tube. 3, Anterior,
4, poHterior, and d, horizontal getmciroiiler canals. 6, Anterior,
7, external, and 8, posterior ampnllae. 9. Sacenlue. 10. Auditor;
or 8th nerve.
tube called the dnctaa endolymphaticus (2, Pig. 100). In the
hi^ier forms this tube is still recognizable bat no longer opens to
iha exterior. Each pit contains lyioph and becomes constricted in
22—2
340 INTRODUCTION TO CBANIATA. [CHAP.
the middle into an upper portion, the utricaluB, and a lowec
portion, the sacculus. With the exception of the Cycloetomata
the former gives rise to three flat outgrowths placed in planet
at right angles to one another (Fig. 190). liiese oatgrowtha
become converted into half-rings hy the meeting of their vails
in the middle of each, and in this way three semicircnlar
canals are formed, called respectively anterior, posterior and
horizontal. The primary function of the whole organ, like that
of the otocyats of Medunae, Crustacea and Molluscs, is to enable
the animal to perceive its position. Where each semicircQlar
canal arises from the utriculus it is swollen, and the swelling
FiQ. 191. SectioD of ui ampulla of the intemaJ Eai.
1. Senae-cell bearing a long faair. 2. SenBe-hair. S. Nerre tenm-
nation blanching round haae of seose-cell (dendrites of a deeply plaoed
□earon). 4. Interstitial cell. S. OelatinoQB cap in vhich the
senso -hairs are embedded.
is termed an ampulla. The wall of each ampulla projects
inwards, and the projection contains cells with exceedingly long
sense-hairs which project into the cavity of the ampulla (Fig. 191).
The free ends of these hairs are embedded in a gelatinous cup,
and thus the whole organ is admirably adapted to record change of
position in any direction, since any change of position can be
completely analysed into movements in three planes. The lower
part of the organ or sacculus has cells adapted to be stimulated
by vibrations in the snrrounding lymph. It often contains cal-
careous ' ear-stones.' In higher forms it gives off a spiral tube, the
cochlea, which contains the true aaditory sense-cells. These form
the organ of Corti, a more complex structure than the sensory
epithelium of the sacculus and ampullae, but resembling it in
consisting of hair-cells which are embraced by the receptive den-
THE ETE,
diites of DeuroD8. The grouiied cells of the neurona of all these
■ensoiy atnieturea form the several auditory ganglia. Both
id ear have cartilaginous or bony coats which become finnlf
coQoected with the skull; these are kuowu as the sense-capsules.
The eye is the most complicated, and in the higher Craniata by
&r the moat important, of the sense-organs. In its origin, as we
have seen, it is the lateral portion of the fore-brain which when
constricted off is known as
the primary optic vesicle (Fig.
192). Tlie outer wall of this
becomes miwlified into a sen-
sory epithelium called the
retina. This consists of a
row of visual cells, their free
ends dire<;ted inward towards
the brain and produced into
the characteristic striated
rods. Beneath these sense-
cells lie a number of neurons,
the dendrites of which, miiig-
Ung with the dendrites of the
sensory cells, give rise to a
ci)mparntively thick bed of
nervous tissue. Long, however,
before the sense-cells are de-
veli>ped, the primary vesicle of
the eye has completely altered
ita shape. The outer wall has
become pushed in on the inner
so as to completely reverse the
•hape of the sac (Fig. 19^).
Its cavity is reduced to a
slit, and it takes on the form of a very deep double cup with
its concavity directed outwards. This is the cavity of the eyeball,
or so-called secondary optic vesicle, the clear gelatinous connec-
.tive tissue inside which is known as the vitreous humour. The
connective tissue surrounding the vesicle peripherally fonns a tough
fibrous or even cartilagioous capsule called the sclerotic coat,
lined by a thin vascular tissue, the choroid coat. The sensitive
.and nervous outer layer of the primary vesicle is known as the
retio&, the other layer (which becomes loaded with pigment) as
Flo. 192. Tranaveise lectioD (hraugli a
third diij Chick to show origin o( the
l«ti|]a from the brain and of the lens
from the eotoderm. Highly msgnilied.
1. Cavity Qf brain. 2. Ontar lajer
of retina surrODndioR the black,
thicker layer which will form the rods
nud coneu. S. LeiiB uriniuR ns a
hol}ow invagination. 4. Pineal
boilj' origiuiiting. 5. Embrjonio
342
INTEODUCnON TO CBAKIATA.
[CHAP.
die pigment epithelium of the retina. If we analyse the
structure of the retina, we find that it has fundamentally the
game structure as the central nervous system of which, as ita
origin shows, it is leally a part. Thus there are a uTimber of
branched and cuticularized supporting cells called fibres of
Mil Her, extending throughout the whole thickness of the retina,
and the main mass of the retina is made up of nenroug. There
is, however, in addition a layer of characteristic visnal cells;
Fio. 193. Diagram to illugtnte structure of & retina. The wrerftl "lajren"
are indicated by the DumerftU III, Ac. in order from within (vitreous
humour) ontwaraa.
1. Gone. 2. Bod. 3. NncleoB of rod-sell. 4. Small aearon.
5. Large neuron. 6. Pigment epithelium. 7. Fibie of MiiUer or a
supporting cell.
that is to say, of sense-cells, with a comparatively thick striated
rod in place of the ordinary sense-hair. Visual rods have already
been described in the eyes of Anthomedusae (p. 55) and of
Arthropoda (p. 131); they occur wherever the capacity for vision
b developed. In the retina of Graniata there are two varieties of
visual cell, called respectively rod-cells and cone-cells. In t^
first, the visual rod is narrow and cylindrical, and the body of the cell
beneath is filamentous with a rounded swelling for the nucleus; the
basal process ends in an unbranched knob, that is to say, in a single
THE RETINA.
dendrite, In the cone-cell the rod is conical with a broad base, to
hich the body of the cell coutainiug the nucleus is immediately
applied; the btisal process ends in the normal manner in a tuft of
dendrites. The baaal processes of both kinds of sense-cell are is
cloae relation to the receptive dendrites of a layer of neurons with
small cell bodies; the axis-cylinder processes of these in turn end
close to the receptive dendrites of a layer of neurons with large
cell bodies situated close to the outer basal surface of the retina,
which give rise to the fibres ci^ostitiiting the optic nerve. Taking
ft general view therefore we may say that the retina is a sensory
epithelium cousistiug of a layer of sense-cells underlaid by
two layers of neurons. Before its structure was thoroughly under-
stood, however, the appearance of the retina in transverse section
was a hewilderiug mass of fibres and nuclei, iu which for descrip-
tive purposes different layers were distinguished. These, reckoning
them iu the order proceeding from the inner side of the eyeball
towards the lens, were as follows: — (a) the layer of rods and
cones; (/>) the outer nuclear layer (ti. Pig. 193) consisting of the
bodies of the visual cells containing their nuclei; (e) the outer
molecular layer (v. Pig. 193) consisting of sections of the basal
processes of the visual cells and of the receptive dendrites of the
neurons with small cell bodies ; (of) the inner unclear layer (fv. Fig.
193) consisting of the bodies of the above neurons; (e) the inner
molecular layer (in. Fig, 19.')) consisting of sections of the baaal
processes of the above neurons und of the receptive dendrites of the
neurons with large cell boilies; (/) the layer of nerve-cells consist-
ing of the bodies of the last-named neurons ; and finally (g) the
layer of nerve-fibres consisting of the basal processes of the last-
named neurons which constitute the optic nerve.
The remainder of the eye Is to be looked on as a part of the
skin of the side of the hea<l which has been rendered transparent
in order to allow light to reach the retina. It consists of a lens
■nd cornea, separated by a chamber containing the aqncoug
Humour. The lens is an originally hollow plug of ectoderm cells,
which breaks loose from the skin and lies in the mouth of the
idary optic vesicle (Pig. 192). The skin outside the lens forms
the cornea, which is transparent The cornea being joined to
the edges of the sclerotic completes the boundary of the eyeball,
as the fully -elaborated sense-organ may be termed, If the above
description ha.'; been followed it will be seen that in a Craniate
light must reach the visual cells through their basal aud not
344 INTRODUCTION TO CRANIATA. [CHAP.
through their^ visual ends. As this is contrary to the almost
universal rule obtaining throughout the animal kingdom, we cannot
believe it to be a primitive arrangement. Bather we must believe
that when the eye was being evolved the rods of the visual cells were
directed towards the light, and that the epithelium of which they
form a part was exposed and not rolled up into a neuial tube ; in a
word, that the front portion of the nervous system of Vertebrata at
any rate was once a plate of sensitive skin. It is most su^estive
to note that in the larva of the Hemichordata we find such a
plate with two eye-spots at the apex of the prae-oral lobe.
The external layer of the skin or ectoderm of Graniata is quite
peculiar in the animal kingdom, in that it consists not of one, but of
many layers of cells. On closer inspection, however, it is seen that
the deepest layer, consisting of columnar cells alone, really repre-
sents the ectoderm of the other phyla. This layer
instead of becoming directly converted into cuticular
substance, as, for example, in the Arthropoda, buds off flattened
cells from its outer surface which become bodily converted into
homy matter and scale off. The ectoderm rests on a specially firm
bed of connective tissue called the dermis.
A very peculiar feature in the Craniata is the character of the
scattered sense-cells of the skin. These end in
sense filaments embedded in the ectoderm, not pro-
jecting beyond it. These filaments have however grown enormously,
and with their growth the bodies of the cells with the nuclei have
come to lie deep down in the body. Here they form segmentally
arranged packets of cells lying at the side of the nerve-cord and
known as the spinal ganglia. They are connected with the nerve-
cord by their basal outgrowths or nerve-tails, which constitute the
dorsal roots of the spinal nerves corresponding to the dorsal sensory
nerves of Amphioxus. To each myotome a motor nerve is given off,
as in Amphioxus y but in the Craniates the fibres of this nerve are
bound up for a certain distance with the long peripheral hairs of the
sense-cells constituting the spinal ganglia, so as to form a compound
sensory-motor nerve, which is then said to have a dorsal sensory
and a ventral motor root
The power of transmitting and modifying impulses, characteristic
of the nerve-cell, is merely one of the fundamental properties of all
protoplasm, specially developed. It therefore probably resides to a
small extent in all cells. In the ectoderm from its exposed con-
dition this function has been largely exercised, and hence the
CRANIAL NERVES.
nervous system of most aniniaU coDsists of modiiied ectoderm
cells. But the eudodenuic tube is likewise stimulated by the
passage of food through it and it is therefore not surprising to
learu that some of its cells deveiope nerve-tails and are
converted into sinaJJ neurons. In this way a tangle or plesua
of fibres with intermixed cells is formed, which is the basis of the
nervous system of the gut, or 'sympathetic' system. In most groups
of animals the endodermic nervous system is never developed beyond
this point ; but in Craniata this plexus is connected with portions
of the spinal ganglia at regular intervals which early separate from
the rest and are called the sympathetic gangha. These ganglia
retain their connectiou with the spinal cord by nerves imlled the
rami communicantes, in which motor fibres going to the
alimentary canal are included. Successive sympathetic ganglia
are connected by a longitudinal commissure, and so there is a
chain of sympathetic ganglia on each side of the spinal cord.
It is usual to reckon ten liairs of nerves as appertaining to the
brain, but these are of very unequal value. The first or olfactory
pair are really drawn-out portions of the cerebrum. In the lower
Craniata these parts have the shape of swellings connected by
narrow stalks with the brain, and these stalks were confused with
nerves (Fig. I8S). The terminal swelling comes into close contact
with the epithelium of the nasal sac, and a large number of small
nerves— the true olfactory nerves — connect the two. The second
or optic nerve is formed by nerve-fibres growing along the stalk
uniting the primary optic vesicle with the brain (Fig. 192). The
nerve fibrils which run in this stalk go mainly but not entirely to the
opposite side of the brain. Thus in the Boor of the thalamencepbalou,
or primitive fore-brain, there is a crossing of fibres proceeding from
the two eyes. This part of the floor becomes nipped off as a groove
from the rest — and is known as the optic chiasma. The chiasma
is connected with the combination of the stimuli received by the
two eyes so as to produce single vision, each side of the biain
recfliviag impulses from both eyes. The third or motor oculi,
the fourth or patheticus, and the si:cth or abduceus nerves are
motor nerves, supplying the eye muscles derived from tho head
cavity, the collar cavity and tlie first myotome respectively. The
fifth or trigeminal, and seventh or facial, are most interesting
nerves, being sensory as well as motor, and the sense-organs they
supply iu the lower Craniata are peculiar. These organs are scattered
over the prae-oral part of the body or snout and the sides of the
hend, and are known as the mucona caoaU. On the snout they
have the shape of deep tubes swelling out at the bottom into sacs ot
aiiipiilloe ; and on the head, of canals communicatii^ at intervals witli
the exterior by vertical tubes. Certain of the cells lining these tnbes
devetope blunt, freely projecting sense-hairs, recalling the oharai'ter of
the auditoty cells, whilst others secrete the mucus with which the
tubes are filled and whence they derive their namei. It is probable
that the function of these organs is somewhat allied to that of the
ear, balancing combined with hearing (or at any rate, perception of
vibrations), for it has been proved that a &sh deprived of its eyes is
still able to guide itself along tortuous passages so long os this
organ remains intact, and this is explicable only on the assnuipdoa
that the reflected pulses of the water are felt by these organs The
branches of the fifth and seventh nerves wliich supply them are
usually for some distance in close juxtaposition and are known as
the ophthalmic nerves. The eighth or auditory cranial nerve
goes to the ear, and arises in such close proximity to the seventh
that it may be regarded as a specialized branch of it, the ear itself
being very possibly a highly specialized mucous canal. The motor
divisions of the fifth and seventh are distributed to the region of
the mouth and to that of the first gill-slit respectively. They both
fork ; the upper branch of the lifth goes to the upper jaw and the
lower to the lower jaw, while one branch of the seventh passes in
front and the other behind the spiracle. The ninth or glosso-
pharyngeal nerve is similarly forked round the first true gill-
slit (Fig. 1R8). The tenth or vagus or pneumogastric nerve,
which is certainly a compound one, gives off a branch to each of
the remaining slits, to which it bears a relation similar to that
borne by the ninth nerve to the second slit. The main stem of the
nerve passes along the alimentary canal and sends nerves to its
muscles and to those of the heart, alt these muscles being develop-
ments of the inner or splanchnic wall of the unsegmented coelom.
The tentli nerve has also in the lower Craniata a sensory dii-ision.
This separates from it soon after it leaves the brain and posse?
backward, supplying an immensely long mucous canal, called the
lateral line, which extends from head to tail along the mid-lateral
portion of the body and is provided with a series of openings to the
exterior. On account of its extensive area of distribution the tenth
nerve has received the name of vagus (wandering).
The alimentary canal exhibits a marked ditt'erence from 1
condition found in the lower Chordato. The gill-slits are redi^
ALIMENTARY CANAL.
tn Dumber, there being as a. rule uot more than eight: it would
indeed be more correct to speak of them as gilli
t«n«i"""*^ pouches. Ill this reapect Oaniata agree with the
Hemichordata in contrast tfl the Cephalochordata and
Hrochordata. No trace of a tongue-bar has however been found in
any Craniate.
The endostyle bet-omes shut nif from the pharynx and
thus loses entirely its original fuuction ; it branches and forma
a mass called the thyroid gland. The evil results attendant on
its removal or diseased condition and experiments on liring animals
show that it secretes into the system a substance which has a
beneficial influence on metabolism, especially as regards the " tone "
of the nerviius system and the growth of connective tissue.
The sub-neural gland of the tlrochordata, on the other hand,
seems to be represented by a structure called the jiituitary body.
This, like the sub-neural gland. Is a dorsal pocket of the etomodaeum,
but it becomes cut off from all connection with the mouth and
intimately associated with a downgrowth of the brain, called the
infundibulum, tn form an organ having an influence on the
well-being of the animal (see p. 336). Since in the case of the
Urochordata the sub-neural gland is fashioned out of the persistent
communiuatinn of the sense vesicle with tbe exterior, one is tempted
to regard the clo^e connection of the infundibulum and the pituitary
body as remnants of the former connection of the brain and stomo-
daeum in the aucestora of the Craniata. Some authors maintain
that a rudiment of the infundibulum is to be seen even in ths
cerebral vesicle of Amphiarus (see Pig. 174).
Except in the lowest forms the alimentary canal Is differentiated
into several well-marked divisions. There is to begin with a
stomodaeum lined by an epithelium consisting of many layers
similar to that forming the epidermis. The first division of tho
endodermal tube is called the pharynx, and into this the gill-slita
open, Tbe line of demarcation between ectixlerni and endoderm
is entirely obliterated in the adult. Following on the pharynx
is a tube of narrow diameter, termed the oesophagus or
which leads into the stomach. The stomach, consists of the
first of the loops into which the alimentary canal is bent
sequence of being longer than tho body, it is a greatly dilated
portion of the canal and in it the food is stored until a large
amount of digestion is accomplished. As in other animals, the food
ia moved from place to place by peristaltic contractions of the vis-
I
348 INTRODUCTION TO CRANIATA. [CHAP.
ceral muscles derived firom the inner wall of the coelom. There is a
particularly powerful girdle of these called the pyloric sphincter,
which by remaining contracted keep the distal end of the stomach,
the so-called pylorus, closed until the work of digestion is
accomplished, when they relax and allow the food to pass on into
the next division of the canal, the intestine. The walls of the
proximal part of the stomach are produced into small pouches, the
lining cells of which secrete a substance called pepsiji, which has
the power of turning the proteid of the food into soluble peptone.
Pepsin is an example of the class of substances known as
digestive ferments or enzymes : these are complex substances of
unknown constitution which have the power of effecting a large
amount of chemical change without themselves undergoing a
permanent alteration. The object of their action on food-stuffs is
to render them soluble, and therefore fitted for absorption by the
wall of the canal. Pepsin is active only in an acid medium, and
free hydrochloric acid is found in the contents of the stomach in
small quantities, produced by special cells in the waUs of the
pouches just mentioned.
An organ called the liver is very conspicuous (Pig. 207).
It consists of a ventral outgrowth of the gut, arising just behind
the stomach, which extends forwards and branches into an immense
tree-lik^ mass of tubes welded together by connective tissue into a
solid mass extending forwards and nearly obliterating the front part
of the body cavity. Whether this organ really performs the same
function as the so-called liver in Amphioxus is doubtful. It has
been proved that the function of the Craniate liver is largely the
elaboration of an alkaline fluid called the bile. This is partly
excretory in nature, but has an important influence upon the
processes of digestion and absorption in the intestine. The main
stem of the liver tubes is called the bile-duct; there is often a
lateral outgrowth from this which acts as a reservoir for the bile,
called the gall-bladder. Besides this, the liver cells can form from
the sugar brought to it from the intestine a substance called
glycogen, allied to starch in composition, which acts as a reserve of
carbohydrate material available for the system as needed. Among
other influences which the liver exercises on the chemical processes
of the body is the very important one of transforming the nitro-
genous waste products into a suitable form (urea or uric acid) for
excretion by the kidneys.
Another outgrowth from the intestine arises sometimes just
behind the opening of the bile-rtuct, sometimes from the duct
itself. This ontgrowtli, like the liver, branches into a tree of tubes
whi'-h are hound together by connective tissue to form a solid mass,
though one of much smaller size than the bver. This organ is
called the pancreas and it produces a secretion called pancreatic
juice, by which the process of digestion is completed. This juice
contains three ferments : these are amylo-pftin, which converts
Starch into soluble sugar; trypsin, which, acting only in an
aikahne medium, converts proteid into |>eptone and simpler de-
rivatives; and ateapsin, which splits np fat into soluble fatty
acids and glycerine. The fatty acids unite with the alkalis present
in the mixed contents of the intestine to form soluble soaps, and
these are absorbed along with the glycerine, a reconstruction into
fat taking place in the intestinal epithelium.
The intestine is always somewhat longer than the body. Hence
it must be to some extent looped or twisted (Fig, 207), though this
may express itself only in a slight curvature. A fold projecting into
it in some forma represents the typhloaole of the Urochordata and
19 known as the spiral valve, since it shares in the twisting. In
the intestine ihe digested food is absorbed and transferred to the
blood-vessels and lymph-canals. The last portion of the intestine
ia usually of larger diameter than the rest and is called, when thus
distinguishable, the large intestine. In it the indigestible
, material is elaborated into faeces for expulsion by the anus.
The blood system of the Craniate is distinguished by the posses-
sion of a large and well-developed heart, which, like
■yBWrn.*""" '''^ heart of the Urochordata, is an enlargement and
specia.hzation of part of the ventral vessel. The space
■ in which it apparently lies — really, into which it protrudes, — is called
the pericardiuin, and is only an anterior part of the coelom shut
off from the rest by the development of a, transverse septum. The
heart is constricted into four chambers, becoming successively more
thirk-walled aa we proceed forwards, and named, beginning from
behind, the sinus venosuK. the atrium, the ventricle and the
COBUs arteriosus (Fig. 195). It is bent into an S-shape, so
that the sinus venosus is dorsal and posterior, the atrinm dorsal and
anterior, the ventricle ventral and posterior, and the conus arteriosus
ventral and anterior, The conns arteriosus leads into the ventral
aorta, which gives off the arterial arches ; the.te are branches
which ascend between the gill-sacs and ramify on their walls. From
the gills the blood collects into epibranchial vessels which join
350 INTRODUCTION TO CRANIATA. [OHAP.
to form two longitudinal vessels on the dorsal wall of the pharynx,
the roots of the dorsal aorta. These unite behind the pharynx
into a single dorsal aorta, giving blood to all the hinder part of the
body. The forward extensions of the two longitudinal epibranchial
vessels carry blood to the head and are known as the carotid
arteries. There can be little doubt that the impulse leading to the
evolution of the heart came from the necessity of having a strong
force to drive the blood through the capillary channels on the walls
of the gill-^acs.
In the embryos of all Graniates the number of these paired
connections between the ventral aorta and the roots of the dorsal
aorta is six, but the two anterior pairs, viz., those traversing the
wall of the pharynx parallel with those parts of its supporting
skeleton known as the mandibular and hyoidean visceral arches
respectively (see pp. 371 and 372), are found in adult forms only
as remnants in connection with the carotid arteries. Whatever
may have been the case in primitive forms, these first two arterial
arches have now no part in aerating the blood, this function being
performed by the succeeding four pairs of arches, along whose
course only are gill-sacs developed. We shall see that the arterial
system near the heart is in all groups of Craniata a modification of
the six pairs of arterial arches now described.
The fore-limb is supplied by a vessel called the subclavian
artery, but the origin of this differs in the several classes of
the phylum. In Amphibia, Lizards and Mammalia other than
Getacea, it arises from the epibranchial artery near or behind the
sixth branchial arch, while in Crocodiles, Turtles, Birds and
Cetaceans its origin is from the ventral end of the third branchial
arch. As in both Lizards and Cetaceans these two vessels exist
side by side, but only one of them supplying the fore-limb, it is
clear that the subclavian arteries are not homologous throughout
the group.
Each chamber of the heart is separated from the one behind by
valves, which are flaps of membrane free to move in one direction so
as to open and admit blood from behind, but restrained by tendinous
chords from being driven further back than so as just to meet when
the chamber contracts, and thus prevent any backward movement of
the blood. In the con us there may be several transverse rows of
pocket valves. These valves as their name implies are loose
pockets of membrane which are pressed flat against the wall of the
conus during the forward movement of the blood, but which when
XIT.] CIBCULATOHT SY8TBU. 351
the coDUB cODtnctB become filled with blood and swollen out ao as to
meet one another and prevent the reflux of blood into the ventricle.
The development of Uie liver has exerciaed a profound influence
and their branobe* ii
352 INTRODUCTION TO CRANIATA. [CHAP.
on the afferent part of the blood system coiresponding to the
hinder part of the sub-intestinal vein of Amphioams. The vast
mass of tubes projecting into it has broken it up into a network of
capillary channels called the hepatic portal system. In front of
this, where it enters the sinus venosus, it is known as the hepatic
vein ; behind, branches from the walls of the intestine so overshadow
the original ventral trunk that this, embedded between the limbs
of the spiral valve, appears as merely a small branch of the com-
posite trunk or portal vein.
The blood from the muscles and kidneys, in a word, from the
dorsal and outer parts of the coelom, collects into two longitudinal
channels called the cardinal veins. These empty into the sinus
venosus by transverse trunks called ductus CuvierL These trans-
verse trunks divide the veins into anterior cardinals returning
blood from the head, and posterior cardinals returning it from
the rest of the body. In the tail the two posterior cardinals are
represented by the median caudal vein, which further forward splits
into two. Just as the course of the original sub-intestinal vein has
been obstructed by the growth of the liver, so that of the posterior
cardinal has been choked by the growth of the kidney tubes.
The blood from the tail and hind limbs is forced to filter amongst
these in a series of narrow channels called the renal -portal
system. The front part of the vein retains the name posterior
cardinal : the hinder part is called the renal-portal vein. Since
the kidney tubes also receive blood from the dorsal aorta they, like
the liver, have a double supply.
The blood of Craniata has in addition to the ordinary amoebo-
cytes a much larger number of oval or round cells impregnated
with haemoglobin, called red blood-corpuscles. Haemoglobin
has been mentioned when describing LumbricuSj in which worm
it is found diffused in the blood fluid. The great characteristic
of haemoglobin is its power of forming a bright red, unstable
compound with oxygen. This compound is formed in the respira-
tory organ and carried by the circulation to all parts of the
body. In the capillaries it is broken up and the oxygen absorbed
by the tissues. The haemoglobin having lost its oxygen changes in
colour, and the impure blood which leaves the tissues is in conse-
quence bluish. From the tissues the blood takes up carbon dioxide
which, like the oxygen, is conveyed in loose chemical combination,
though with the sodium of the blood instead of with the haemo-
globin. The carbon dioxide is set free in the respiratory organs.
CIRCULATORY SYSTEM.
On page 128 it was pointed out that both blood and connective
tissue have been derived from a jelly-like secretion auch as is found
in Coelenteiata. This in the embryo ooelomate animal fills up the
interstices between ectoderm, endoderm and uoelomic sacs, these
interstices being collectively termed the primary body-cavity or
haemacoeL It was also pointed out there, that whereas in the
part nf the jelly which was converted into connective tissne a large
mimber of fibres were developed, in the portion destined to form
Uood, on the contrary, no fibres appeared and the jelly remuned
fluid, and in consequence the amoebocytes which had wandered into
H from the neighbouring epithelia were able freely to move about.
In Annelida, Arthropoda and Mollusca certain of the blood-Bpaees
acquire muscular walla derived from the adjacent coeloniie sacs,
Ud thereby attain contractility which may be specially localized in
t dilatation called the heart, 'i^he spaces with muscular walls are
Ithe arteries. In CVaniata a further differentiation has taken place :
we find not only a definite heart and arteries leading away from it,
litit also eipially definite veins leading into it as described above,
ftnd arteries and veins are c-onnected with one another by narrow
channels called capillaries with well-marked walls. Heart,
ftrteries, veins and capillaries are all lined by a single layer of
flattened cells called an endothelium, which has been developed
from the flattening out and union of a certain number of amoebo-
eytes. The capillaries possess no other wall, but arteries and veins
intside this a wall of elastic and fibrous connective tissue in
which is embedded a zone of circular muscle-fibres. These structures
fie all derived from the adjacent coelomic sacs. The muscles of
blood vessels do not contract rhythmically and spontaneonsly like
ihosi! of the heart, but are in a state of continued contrai-tion called
tone, This t«ne is under the control of the nervous system through
Ihe medium of special " vasomotor " fibres, and thus the supply of
blood to an organ can be varied according to its needs.
In Craniatii however, outside the definite arteries, veins and
flBpiUaries, there exists a large portion of the haemocoel in the
1 of irregular channels and interstices, in many cases without
definite walls, an endothelium being found only in the larger trunks.
I system of spaces is known as the lymphatic system. It
eontainR a clear fluid in which amoebocytes float, but no haemo-
|[lubin -containing cells, and at one or several points the main
trunks of the system open into the large veins. The finer branches
ipf the system ramify amongst all the organs of the body. There
354 INTRODUCTION TO CBANIATA. [CHIP.
is no circulatory onrrent in tKe lymph canals except in thoea
belonging to the viBcera, but there are v&lves arranged so that vidi
eTei7 contracUon of neigbbounng mnwles some flnid can pu
foTwarda in one direction but
not backwards.
It will be aeon Hat in
Oraniata, unlike Aitfaropoda
and MoUnsca, the blood, being
everywhere confined to veaaeli
with definite walls, does not
directly bathe the tiaanes of
any organ ; bnt that materials
most first diffuse through the
walla of the blood- veesels into
the lymph-spaces before they
can reach the tissue. One
explanatioD of the separatioti
of the lymph-eystem from the
blood-system is that the hae-
moglobin is not diffused in
the fluid of the blood, bnt is
carried in cells which have no
power of moTement in them-
Flo. I9S. Dugnm ol the yeaoa»
Bjatem of MaMtelUM aiilarelicut.
From T. J, Pm)t«r.
1. Orbital fiaas. 3. Hroidnn
vein. 3. Daotiis Cn*iei.
4. Anteiioi caidinal Tciii. 5.
JngDlar vein. 6. Codqb arteii.
osos. 7. Ventricle. 8. Atrium.
9. SIddb TenoooB. 10. Hep»I)0
Tein. 11. LiTVT. 19. Hepatic
vein. 13. Hepatic port&l Teiii.
14. Left cardiDal TCin. 15. Bra-
chial Tetn. 16. Sab-claTiall
teiD. IT. Gimmi. IS. Poa-
lerior cardiDal reiti. 19. Sper-
matic Tein. SO. lateral Tein.
31. Reoal-portal niiH bom
eaodal Tein to kidne;. 33.
Bigfat poatnioT cardinal vein.
33. AlimeulaiT oanaL M. Vein
coDuei^tinf: orbital sinases. 35.
Sub-iDtettinal vein. 36. Eidnef.
" Pelvic tvin. 34. Cloacal
Caodaln
39. FemonJ n
30.
XIV.]
355
selves Did these cells enter the iTrnph-eystem they would speedily
block ita finer channels.
The supply of smoebocytes to both blood uid lymph is provided
for by widely distributed actively growing nodules of cells which
bud off amoebocytes into the adjacent lymph-chaDuels. These
packets of cells are called lymphatic glands : the largest collection
is in the spleen, an organ having several other functions, which is
attached to the mesentery just dorsal to the posterior end of the
stomach.
Fiu. 196. Dorsal view of bead of Sct/llium caiiicula x 1, The right orbit has
been exposed so as to ahoir the masolea that move tbe eye and the aecoad
and fourth nervea.
1. LeoB of the eye. 3. Superior reotua moRcle ot tbe eyeball. 8. Ei-
ternal (or posterior) rectus muscle. 4. Inferior rectus muscle, S. In-
ternal {or anterior) rectuE muscle. 6. Inferior oblique muscle.
7. Superior oblique muaole ; the slender nerve eiit«riiiR this muscle is tbe
fomrUi enuiial. 8. Second cranUl or optic nervo, the nerve of sight.
The muscles of tlie Crani&ta like those of the Cephalochordata
■ ate developed from the inner walls of a, aeries of dorsal
coelomic pockets, in a word, from myotomes. Unlike
Uiat of iha Cephalochordata the trunk coelom does not become at
first completely divided into separate sacs, the ventral portions of
which fuse later. In the Graniata this stage is Bkip]>ed in develop-
ment, and the coelom appears tVom the first as a pair of elongated
sacs undivided below, but segmented above. After the complete
23—2
356 INTRODUCTION TO CRANIATA. [CHAP.
sepaxation of the dorsal portions as myotomes the ventral parts of
the two sacs unite beneath the intestine, whilst above it their walls
become apposed, forming the vertical sheet of tissue known as the
mesentery, in which the intestine is slung.
It is necessary of course for the efficient action of the eyes that
they should be movable, and this is brought about by the space
around the eyeball becoming converted into a cavity called the
orbit, which in the lower Craniata is continuous with the anterior
cardinal vein, and thus contains blood (Figs. 195 and 196). To
each eyeball six muscles are attached, two arising from the anterior
part of the orbit and inserted one above and one below the eyeball,
and named respectively the superior and inferior oblique ; and
four arising close together from the posterior comer of the orbit and
inserted on the eyeball, one above and one below, the superior and
inferior recti, and one antero-laterally, the internal or anterior
rectus, and one postero-laterally, the external or posterior
rectus.
The proboscis and collar coelomic cavities of the Hemichordata
are represented in the Craniata by two cavities found in the embryo
on each side, in advance of all the myotomes, termed the head-
cavities. The most anterior, termed the pre-mandibular, is
joined to its fellow by a narrow canal running underneath the eyes
— the pair really constitute a bilobed cavity — from whose walls the
inferior oblique, superior, inferior and internal recti muscles are
developed.
The collar-cavities are represented by the mandibular-
cavities, a pair of long, narrow cavities running down the sides of
the mouth and curving up over the eye on each side. From the
wall of this portion of the cavity the superior oblique muscle is
derived. The external rectus muscle arises from the first myotome.
The muscles derived from the anterior head-cavity are supplied by
a common nerve, the third cranial ; the superior oblique is supplied
by the fourth, and the external rectus by the sixth cranial.
Most of the muscles which compress or expand the gill-sacs are
derivatives of the wall of the unsegmented ventral portion of the
coelom. From the inner wall of this part of the coelom all the
muscles of the alimentary canal, which in Craniata are longitudinal
as well as circular, arise, as do the muscles in the walls of the
blood-vessels. From the myotomes are derived the muscles by
which the locomotion of the animal as a whole is carried out. In
the lower Craniata these have the same simple arrangement as was
XIV.] URINO-aENITAL OSQANS. 357
found in &e cue of Amphtams, but in the higher forma where the
roovemente are complicated by the development of limbs, these
muscleB are divided into numerous bundles with a very complex
airangement. All the muscles derived from the myotomes are
composed of striated fibres. Most of those governing the move-
ments of the alimentary canal and blood-vessels are composed of
smooth fibres, but to this statement the muscles of the heart form
an exception.
Fia. 197. Dugrama illDBtrating the development of the urino-genital argaui
of Craniato. [For full etplaDBtiou see seotioat on Elatmobrouobii and
Amphibia.]
A. l>avelopment of pronephroB and Begmental duct, B. Atrophy of pio-
nephroB, development of mesonaphroB. C. OifferentiatioD of pro- and
meBonephric dacta. D. Development of toetanephroa, male t^pe.
E. Female type. 1. AUantoio bladder. 4. Gonad. 6. iDteatine.
7. HeBOnephrio duct. 8. Nephrostome. 9. Metanephrio duot.
10. Metsnephros. 12, Ovan', 13. Oviduot. 14. Fronephroa.
16. Archinephrto daot. 16. Testia.
The excretory and reproductive organs are closely related
in development, and by recent research their relation
omna''*" ** *** those of the Cephalochordata has been made
tolerably plain. The unit in the excretory system
is a tube opening into the body-cavity at one end and at the other
into a longitudinal duct which opens into the proctodaeum behind.
358 iNTBODucrrioN to crakiata. [chap.
If it opened to the exterior directly it would be essentially identical
with the nephridium which constitutes the excretory organ of
Annelida and Mollusca. Of these tubes in the Graniata there are
two kinds: the first or pronephric tubules, called collectively the
pronephros, develope in continuity with the duct into which they
open. This is called the archinephric duct, or sometimes the
Wolffian duct, after Caspar Wolff, who first saw it develope in
the embryo. The pronephric tubules are situated at the upper and
outer angle of the unsegmented coelom, a position exactiy corre-
sponding to that of the nephridia of Amphioxus, except that in the
Craniata they are not developed in the shortened branchial region
but immediately behind it From the root of the mesentery
opposite the inner openiDgs of the pronephric tubule a swelling
projects into the body-cavity. It is covered by a thin layer of
peritoneum and is richly supplied with blood-vessels by branches
from the aorta. The cells of the peritoneum appear to extract
water and excreta from the blood and pour it into the coelom, whence
they are excreted by the pronephric funnels. This structure is
termed a glomerulus.
If the homology of the two sets of organs be accepted — and in
view of Goodrich's researches it must be regarded as doubtful — the
somewhat startling conclusion follows that the atrial cavity of
Amphioxus must be the homologue of the archinephric duct This
conclusion, however, must not be expressed in the form that the
archinephric duct is derived from the atrial cavity, but rather that
both seem to be developments of a primitive groove, overhung by a
longitudinal ridge which may be called the Wolffian ridge and
which corresponds to the atrial fold in Amphioxus, This view is
to some extent supported by recent observations on the development
of the archinephric duct It appears probable that this arises as a
solid ingrowth of ectoderm, a method of development which, from
the study of other cases where it occurs, may legitimately be regarded
as a modified form of invagination or intucking of ectoderm. The
exceptional development of the Wolffian ridge in Amphioxm, so as
to form a veil over the gills and wall in the atrial cavity, is perhaps
advantageous in a burrowing animal. Van Wijhe, to whom we owe
the first clear account of the head cavities, is a strong supporter of
the view of the ectodermal origin of the archinephric duct just
mentioned. It ought however in justice to be mentioned that other
observers do not accept this view and confidentiy assert that the
archinephric duct is derived firom the mesoderm. They regard it as
developed out of a series of secondary connections between the
nepUridia juat as the ureter is formed, and similar to connections
between the nephridia found in some Polychaeta.
The pronephric tubules are developed only in the larval form,
and so far as is known they persist in no adult Craniate. They
become replaced by the second kind of tubules, termed the meso-
aephric tubules, which, like the pronephric, open into the coulom,
Diftgiamnintic tmnsverBe Beclion of ii hypothetionl unoeBtnl Elftsmo-
sh to hIiow origin of tddbI and genital orgluiB. On the left side & later
1. Ncm-cord. 3. Notoohord. S. Mjutome.
6. Ventral nolarotome. B. Nephrotome. 7,
6. Archinephriii duel as an open RrooTe. 9.
gland. 10. Aorta. 11. AlimenUiy cannJ.
coelom. 13. Mesouephric tcbuie. 11.
in. Seminal tubule.
I. Iiiiraal aolerotome-
Pronephric tubale.
Radiment of genital
12. Uii»ei;ment«d
Archiuephrio duct.
but unlike these Hwell out immediately beyond this, forming thin-
walled capsules, termed the Malpighian capsules, into which a
glomerulus, that is a thin-wallecl plug coutainiug a plexus of
blood vessels, projet'ts. Its function is similar to that of the
glomenilas opposite the pronephric tubules.
The mesonepluric tuhules are developed from the necks connect-
ing the myotome with the general coelom, that in, from the lower
end of the myotome, a position corresponding to the ]ioiat of origin
■Wi jsrniuocccRMP to craniata« [chap.
t d« ^smioaL iQaw^ ii JLjimiMfftui. These necks, which may be
«im«i«^ :% !^u.i-v sxi mjdeis% mmL j»mt ^nt the myotomes, curve roond
>a«fc ^^tiirrr rMKUMC^ Jtcu 'SM icrr&iKfiiiAf AucL It IS the central
•«M.tr a tiM tts.>uj.« VBKii jwetld out to fotm the Malpighian capsule.
^ 'M» -^vifr ><ngp»oiwi ^bac die mesonephiic tsbules are the homo-
i^i*«0^ i an 4!t»uaii sacs of Aw^kiaru*^ and this suggestion
«^t«i»«q^ ^(4iurt 3um the &ct that the genital cigans in the lower
rtba«<^«jk rtftcinace from the lower ends of the ncphrotomes, just
«a«4> .OftiM euctf the general coelom, and oonseqnently the genital
«li(:teiifr iM :U tiTst segmented. The change of function suggested
vo^w^ ?«Muit» at first sight a little forced, but ve must remember
U14U lu v'iui^^^ Vertebrata, as in Annelida, the whole coelomic
^^^il 'Mkl pcubably an excretory function, and henoe if permanent
'.u^Maii ot temporary pores for the discharge ot genital products
s%u>» tormed, these pores would allow the escape of excreta thrown
Mjii, by the ueighbouring portions of the coelom, the excretory
tuucciou of which would therefore be stimulated.
The genital rudiments soon coalesce to form continuous ridges
Licvjcv-'tiug into the general coelom on either side of the root of the
lucdoiitery. lu the female the sexual cells or ova, when ripe, drop
into the coelom and are conveyed to the exterior by an oviduct
opouiug into the body-cavity with a wide funnel The oviduct
luriaea from a groove in the dorsal coelomic wall, the edges of which
uioet. Posteriorly it opens into the proctodaeunu In the male, on
the other hand, the sexual cells arrange themselves in tubes, the
:iOiniuiferous tubules, which retain in most Craniata a perma-
uent connection with certain of the mesonephric tubules through a
set of tubes called the testicular network which like the organs
they connect are derived from the nephrotomes. The archinephric
Uuot therefore acts as vas deferens or male duct. Since through
the opening of the proctodaeum not only the faeces are expelled but
also the excretory products and spermatozoa from the archinephric
duct, and ova from the oviduct, this aperture has received the
uame of cloaca, the Roman name for 'sewer.'
Division I. Cyclostomata.
Tiie C-raniata are divided into two main groups, namely, the
DyuluMtomata and the Gnathostomata. The former division,
(litttingiiished by the absence of true visceral arches and of jaws,
iucliulas at the present day only a few, probably degenerate, worm-
like animalH, with short tails like Impfiuxus, and with naked
akina. The name Cyclostomata means Unuud mouthed (6k. kvkKo^
a circle ; tTro/ia, mouth) and alludes to the cmumstaDces that the
edges of the mouth are atiffeued by a ring shaped
cartiluge the aunulaj- cartilage, bo that the mouth
cannot be closed (2 Fig 201) There la a piston shaped tongue i
supported by a lingual cartilage, and the whole is protruded hj
a miucle attached to the annular cartilage in the lips (Fig. 200).
Both the tip of the tongue and the walls of the stomodaeum are
Iwset with horny teeth, developed from the agglutinated cells of
the akin. The expansion of the atomodaeum causes the mouth to
act like a sucker, and the whole animal is thus enabled to adhere
to some foreign body, such as a stone, or to some victim, nsually
a fish, in which case the rasp-like tongue works a hole in the fiesh
of tlie prey. The atomodaeum is greatly elongated and is liupported
in ite roof by several broad cartilages, the so-caIIe<l labial carti-
lages ; in consequence the eyes and gill-slits appear to be pushed
very far back.
I
^^^^^881 CTCLOSTOXATA.
^P
1^ IV conditiaB of ths mfM-orgimij U
one of the roost marked
I ^ /^j^ ^^
nil!
H
,'
;; jK^^
J ■ X " 1
^H
1 tll^
1
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il
n
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-2
1 iJ\
! . ^-1
1- lis"
^^^^H Kfl
mSUfrj-~
=■ s^»a
^^H N
»
r^H/-/ 5
;- ii-n
^^^1 Q
I iSUl
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SMflh
ir:ii^
■a- f ■
E„ S ..9
fS .12 S
t^ 111
1 ii
^^^^^^^^^H \ nCr% Ji^or '^
^ l-tf
^^^^^H '^ \ «u^
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^^^^^^^^
■^ single sac placed far back in coD8e<iuence of the elongation of the
K Btomodaeam, as above explained. This
single Bac is diawit «i»
B-OBGANS AND GILL-SLITS.
into a loDg tube passing beneath the brain, and in one Order,
the Myxinidae or Hag-fisbes, this opens into the roof of the i
atomodaeum. The tube-like prolongattOQ is really the pituitary
body, which in the embryo developes close to the nasal sai-. The
groove counectiDg the tivo organs becomes closed so as to form a
canal, and then by the great development of the suctorial mouth
the external openings of the two orgiius are widely removed from
one another.
The eye developes no proper cornea or aijueous humour, the
lens remaining in connection vitb the skin. The ear is represented
either by two semicircular canals and a vestibule (or sacculus)
in the Lamprey, or by a single membranous tube in the Hag-fish.
The gill-slits, usnally aeven in number, have the form of regular
1. Honiy teeth. 2. Annular cartilaga. 8. Anterior Iftbial curtiU^.
4, FoBlerior Isbiftl cHrtilaire. 5. Naaal capEnls. H. Auditory aapsnle,
T. Don&l portion of trabeoulne. 8. Lutenil distal labial cartilage.
fl. Lingual flartilajK, 10. Brnnohial bikskct. 11. Cartil agin hub cup
■upporting perionrdimn. 13. 8)ie«tb at notocbonl. 13. Anteciur
neural orchea taeed together.
gill-sai's, recalling those of the Hemichordata, only williout the
tongiie-bara. The external opening is circular; the connection
with the gullet, on the other hand, is a vertioiti slit (Pig. 200).
The whole set of sacs is sti])ported on a framework of cartilage
consisting of longitudinal dorsal and ventral bars, connecting c
pieces pass between the sat^s and give otf branches encircling their
outer openings (Pig. 2iil). The whole of the branchial basket,
as it 18 called, is a development of the dennb and baa nothing to
do with the visceral arches of the Craniata, as will be shown
later.
364 CTCLOSTOKATA. [CHAP.
The commencemeiit of the txne alimentary canal is marked, as
in Amphioxus, by a velum. What corresponds to the hyper-
pharyngeal groove in that animal is in many species of Cyclostomata
completely constricted off from the remainder of the goUet and is
known as the oesophagus, though this word is used in a different
sense from that in which it is used in the case of the Gnathostomata.
The lower part of the gullet which communicates with the gill-slits
ends blindly behind and is called the respiratory tube.
The hinder part of the alimentary canal is a nearly straight
tube, the spiral valve having a very slight deviation from a straight
course. There is no dilatation of any kind in its course. The
large liver empties its secretion by the bile-duct, which opens into
the intestine a short distance behind the branchial region.
The skull consists of the simplest elements, viz. the trabeculae,
with a wide hole for the infundibulum, and the parachordals,
forming only a slender arch over the hinder part of the brain^ but
developing a low side wall throughout their extent with which the
simple auditory capsule is fused. The nasal capsule is represented
by cartilage stiffening the nasal tube. The brain is remarkable
for having a thin membranous roof except just at the front end
of the hind brain where a narrow band of nervous matter represents
the cerebellum.
The only fins present consist of a fringe of skin similar to that
found in Amphioxus surrounding the hinder end of the body in the
vertical plane. This fringe is divided by a notch into an anterior
(or dorsal) and a caudal fin. The dorsal fin is supported by
cartilaginous rays situated above the neural arches which protect
the spinal cord ; the caudal fin has, in addition to these, rays situated
below the haemal arches. A caudal fin of this description, which
the notochord divides into two equal lobes, is called diphycercal.
Besides the neural arches (13, Fig. 201) and small haemal arches
in the tail no other cartilage is developed in connection with the
axial skeleton, the notochord with its thick fibrous sheath persisting
unchanged throughout life.
The pericardium is not completely separated from the remainder
of the body-cavity, and the genital organs take the form in both
sexes of a single median ridge projecting into the body-cavity (21, Fig.
200). No connection of the testis tubules with the kidney tubules
exists, nor is there any trace of an oviduct, both ova and sperma-
tozoa being freely shed into the body-cavity and escaping by two
abdominal pores or simple openings in the body-wall placed
Tentrally to the openings of tfie kidneys. loasmucli as these latter
open directly to the exterior and are quite independent of the
opening of the intestine, which is placed more ventrally, we may
Btate that no cloaca has yet been developed.
Living Cyoloatomata, represented by a single class which may
be called Maraipobranchii (Gr. ^a'po-iTros, a pouch),
are divided into two families : (i) Petkomyzohtidae,
(ii) Myxinidae.
(i) In the first family, familiarly Isniura as the Lampreys, the
pituitary body appears a-s a blind ])rocess from the nasal sac : each
gill-sac opens directly to the exterior, and the hyperpharyngeal
groove is separated fmm the rest of the alimentary canal aa a
distinct tii1>e, the so-called oesophagus.
The Lampreys {Petromi/zon) are conspifuous in the early spring,
when they ascend small brooks to spawn. Several sjwcies inhabit
the rivers of Great Britain, Canada and the United States, but the
differences between them are trifling, depending mainly on the
development of the homy teeth covering the tongue. One species,
Prtromt/zim marintts, attaining a much larger size than the others,
inhabits the sea. It may reach a length of three feet, whereas the
other forms do not grow longer than from ten to twelve inches.
Tlie e^'gs of Lampreys develope into a moat interesting larval
form which stands in many respects nearer to the other Craniates
tlian does the adtdt and supplie.s an intermediate stage between
Amphiii^iie and an ordinary Craniate. This larva is called the
Ammocoetes, and its mode of life resembles on the whole that of
Amphioj:u». Like that animal the Ammocoetes lives ou what the
cturentB of water, prrjduced by the cilia inside the velum, bring.
The thyroid gland, which, as we have seen, represents the
endostyle, remains open, and still performs its primitive funution of
Becreting a cord of mucus, which is c-iirriod up dorsally by a ciliated
groove, the peripharyngeal band, situated just behind the velum.
Tile hyjierpharyngeal groove is represented by a doraa! strip of
ciliated cells, the current produced by which sweeps the mucus
backward into the alimentary canal just as it does in Amphioj-ug,
The tubular suctorial stomodaeum is represented by a hood-like
upper lip and a distinct short under lip, and when the mouth is
contracted the velum is produced into tentacles just as in the
Urochordata and in AmpAioaiiB. The lateral eyes are exceedingly
rudimentary, but there is a large pineal eye, and the nasal sac
has a median septum.
rifti
366 ONATHOSTOMATA. [CHAP.
(ii) The Myxinidae are characterued by the persistent connectioii
of the pituitary body with the stomodaeam, so that there is a tabe
leading from the nasal sac to the moutL There are eight tentacles
called barbels at the sides of the mouth, and there is no special
oesophagus distinct from the rest of the gullet. The skin has a
double series of mucous glands placed at the sides of the body, and
so much mucus can be thrown out that a large amount of water can
be rendered semi-solid. The intestine has no spiral valve. The
Myxinidae are the animals known as Hag-fish. They adhere to fish
on whose flesh they feed, but, uulike the Lampreys, they can
actually burrow into their victims so that the stomodaeal region is
completely buried. In connection with these habits the stomodaeal
region is enormously elongated, and the eyes remain in a rudimmitaiy
condition, whilst the gill openiogs are pushed very far back.
The Myxinoids include two genera, BdeUostoma and Myaine,
In the former, which is a genus inhabiting the southern Atlantic
and Indian Oceans, the gill-sacs are seven in number on each side
and open separately ; in Myxine, on the other hand, each external
opening of the six gill-sacs is drawn out into a long tube, and the
tubes of each side curve back and unite to open by a common
atrial pore placed so far back that the animal can insert almost half
its length into the body of its victim without interfering vrith its
breathing. The portal vein is rhythmically contractile. Myxine
is common on both the Atlantic and Pacific coasts of North
America and on the European coast.
Division II. Gnathostomata.
The great division of the Gnathostomata includes all the remain-
ing Craniata, and is characterised by the development of definite
visceral arches, jaws and paired limbs. The visceral arches
are jointed rods developed from the inner or splanchnic wall of the
coelom ; they cannot therefore be considered as corresponding to
the branchial basket of Cyclostomata. They are placed in the
forms which retain gill-slits between these openings, and hence are
often called gill-bars. The first pair of visceral arches lie in the
sides of the mouth, and consist on each side of two pieces, hinged
on one another and called the upper and underjaws respectively.
By the motion of these on one another the mouth can be opened
and closed. The nose is always represented by two sacs and the
ear has three semicircular canals.
XIV.] CLASSIFICATION. 367
The Gnatho8tomata are divided into five classes. In the first
three of these the temperature of the body varies with that of the
surrounding medium.
Class I. Pisces.
Gnathostomata with fins supported by fin-rays and breathing
chiefly by gills.
Class II. Amphibu.
Gnathostomata with pentadactyle or five-fingered limbs and
without fin-rays. Gills and gill-slits functional in the young but
generally entirely lost in the adult. An amnion is not formed in
the embryo. The skin is soft and moist.
Chiss III. Reptilu.
Gnathostomata with pentadactyle limbs. The young are bom
similar to the adult and in embryonic life develope an amnion.
Skin with horny scales.
Class IV. AvBS.
Gnathostomata agreeing with Reptilia in most points, but
having a constant temperature independent of that of the surround-
ing medium : the skin is provided with feathers instead of scales
and the fore limb is used as a wing.
Class V. Mammalia.
Gnathostomata agreeing in many points with Reptilia, but
clothed with hair instead of scales. The body, like that of Aves,
has a constant temperature independent of that of the surrounding
medium. The young are nourished after birth by the secretion
of certain glands of the mother termed milk glands or mammary
glands.
368
CHAPTER XV.
Sub-Phylum IV. Craniata.
Class L PiscBSL
The class Pisces, or true Fishes, are not, as many would imagine,
characterized by their gills (since some Amphibia
retain these throughout life), but by their Hns. In
addition to the vertical flap of skin with which we have become
acquainted in the case of the Cephalochordata and the Gyclostomata,
we find typically two pairs of lateral flaps, an anterior pair called
the pectoral fins, and a posterior pair known as the pelvic fins
(Figs. 205 and 206). Both from a study of their development and
their condition in the oldest fishes, it is believed that the paired fins
are derived from the division of two originally continuous lateral
flaps, of which the intermediate portions have disappeared. In the
embryo the remains of these ridges are known as the Wolffian
ridges, which can be with some probability identified with the
flaps overhanging the groove that, as is held by some, becomes
converted into the primitive kidney duct. If this be so, we have
representatives of the lateral fins in the walls of the atrial cavity of
Amphioxus, of which the rudimentary folds known as the meta-
pleural folds form part If we accept this view it follows, since
Gyclostomata possess a kidney duct, that they once possessed either
a continuous lateral fin or the two pairs possessed by modem fishes.
While the possession of paired fins discriminates Pisces from
the lower Vertebrata, the forms of these members equally sharply
mark Pisces off from the class with which they are most nearly
allied, namely. Amphibia. In all Pisces the limb or fin is a blade-
like organ which never exhibits the slightest resemblance to the
typical form familiar to all in the human limb, but Amphibia
have as the representative of the paired fins limbs in which the
Ian of the human arm and leg can be at once recognised. The
lade-like type of fin ia known as the ichthyopterygium (ix^vt,
fish; TTTfpvytov, a little wing), the other type of limb aa the
leirnpterygium (x"'pi the band). Piacea therefore are detioed
' the poeseasioQ of iehthyopterygia.
The m&diau and the paired fins are stretched on a skeleton with
two-fold origio, (i) a aeries of borny or cartilaginoua rods or
iterygiophores which auppiirt the baaal part of the fins, and
!) a series of homy fibres or bony dermal fin-rays which support
le distal part of the fioa. In moat Orders of fishes these are not
xternally diacernible aa they are covered by muscles and akin, but
1 the median fins of the Teleostiimi the former series have sunk
ito the body, and the dermal fin-rays being covered with a thin
'anslucent skiu without scales become more or less apparent.
The class Pisces is divisible into four Orders, namely, the
ilaamobranchii, the Holocepbali, the Dipnoi and the Teleo-
tomi. These Orders can also be distinguished in the case of fossil
sh, though the differences become less marked as we proceed back-
pard in time, and many indications point to the conclusioo that the
lon ancestors of the four Orders would, if we could examine
hem, be classed as Etasmobranchii. Hence the Elasmobranchti may
termed the basal group of the Pisces, although modem Elasmo-
ranchii, like all modem auimals, are ^ipecialized in many respects.
Order I. Elasmobranchii.
The Elasmobranchii are dii^tinguisbed (i) by not possessing any
gill-cover or operculum, as it is called, each gill-sac
opening separately to the surface ; (ii) by the absence
' an air-bladder opening into the alimentary canal ; and (iii) by
le absence of large bones in the skeleton. In addition to these
^ative characters, they are distinguished (iv) by the possession of
peculiar scJiIe (inito characteristic of the Order.
This scale, tlie so-called placoid scale, consists of a httle spike
attached to a small plate at its inner end. The plate
Er""* consists of true bone : the sjiike of a modtticatiou of
tme bone called dentine. Dentine is distinguished
Dm bone by possessing no HaveD^ian canals or spaces occupied
f blood-vessels, nor even lacunae, since the cells of the connective
gsue, out of which it is formed, remain external to the dentine.
heir protoplusmic processes known as dentine fibres do however
370 ELASHOBBAHCHII. [CHAP.
penetrate it and give rise to canale called dentinal canals. The
core of soft connective tissue is called the dentinal pulp.
The spike therefore may be described as a little wart of dermis
calcified on the ontside. It pushes the ectoderm befor« it, and it
becomes encrusted with crystals of carbonate of lime fonning the
enamel layer (Pig. 20*2). These closely set crystals are secreted by
the inner or basal ends of the ectoderm cells. One would natnrsll;
expect that stnicturea like scales, which are closely arranged all ovet
the body, would also invade the stomodaenm, which is merely a put
of the skin. This we find to be the case, but here the scales are
very greatly enlarged in size and changed in function ; they are the
well-known teeth which are used for the purpose of retaining and
lacerating prey which has been seized. The spike of the tooth is
usually flattened and blade-like, and provided with strongly serrated
Fio. 202. S«ctioD thtoQgh the skia of ui Elasmobraneb HbowiDg (ormfttion
of s dermal spine. Highl; magnified.
1. Horny lajer o( eotodenn. 2. Miilpigliian layer. 3. Colunmu cells
of ectoderm secretiDR 4. 4. Ensmel. 5. Dentine (black). S. Dentinkl
palp. 7. Bony bsasi plate. 8. ConnectiTe lissae.
edges. Fusions of several teeth can occur. The teeth are developed
in a deep fold of skin, part of the stomodaeum, situated just inside
the lower jaw, and usually speaking only the outermost row are in
use at one time, the skin working forward the next set as each row
wears out.
The skull is much better developed than is the case in the
Cyctostomes. lu the cranium the parachordals and
^''""' trabeculae give rise to a firm continuous plate, in
which the pituitary fossa is reduced to a minute hole ; there b a
bigb and wcU-developed side wall and the roof extfiiids a long
distance forward. The sense-tap sulea, nasal and auditory, are well
developed and tirmly united with the cranium, 'i'he eyes are 1arg«
;»nd highly developed, and the aide wall of the cranium is indented
to make room for the spacious orbits in whi«h the eyes move. There
W a considerable part of the head in front of the brain, which uHually
■Iso projects in ^nt of the mouth. Thi.s is the rostrum or snont,
And it is supported by three cartilaginous rods, one ventral and two
dorsal, projecting from the front end
of the cranium. These rods are the
forerunners of the ethmoidal region
in other forma. In most species the
'Opening i.if the nasal sai- is connected
with the mouth by a groove called the
Ofo-naaal groove (Fig- 307). There
are nsually six gill-clefts and seven
visceral arches in Elaamobranchs. The
■first cleft, sometimes called the spi-
racle, is rudimentary and in some
cases entirely absent. On the other
hand there is one family, the Noti-
danidae, with two extra clefts behind,
3 that there are in all eiglit clefts and
ine visceral arches in this family.
The first pair of visceral arches
Ebnn as we liave seen the jaws. The
upper jaw is known as the palato-
pterygo-<[uadrate bar, a compound
Appellation derive<l from the names of
lihe bones by which it is represented in
bhe higher forme; tiie ti-rm is sometimes
ihorteoed to pterygo-ijuadr&te. The lower jaw is called Meckel's
trtilage or mandibular bar: in front a strong ligament, the
iD^alled elhmo-jialatino ligament, attaches the upper jaw to the skull.
The second pair of an^hes is spoken of as the hyoid. and this too is
divided into two portions, an upper, the hyomandibnlar, which is
firmly cimnectcd to the cranium just below the auditory cajwule,
and a lower, the ceratohyal (Fig. SO-i), The upper jaw is con-
nected with the cranium either directly, by articulation with the
brariinm iu front of the auditory region, an arrangement called
kutostylic mid prevailing among recent HIasmobrauchs only in
Fio. 203. Diagrnm of a Beotion
ttirougli tlie jnvt of u Shark,
Odtmliapid amrrieonu; show-
luK the Bucoession oC teeth.
From Bcjnolda.
1. Teeth in use. a. Teeth in
*. Carli.
Uge i>r the jaw. S. ICooruBt-
itig calcibcatioii of caruliige.
6. Connective tissue " "
toderia liniug the m
372 ELASHOBRANCHU. [CEAT.
the Notidanidae ; or the upper jaw has lost ita articnlating proem
with the craninm and is instead firmly connected or slung b;
ligament into the hyomandibular, which thos suspends t^e jaw
from the skull. This arrangement, called hyostylic, is that seen m
the majority of fishes. A modification, termed am phistylic,occnn
in Cestracion, where the jaw is slung by the hyomandibular but alsD
has acquired direct articulation with the skull behind the oibii
The remaining visceral arches have only a muscular connection with
the skull and are termed the branchial arches, since to their mdea
Fto. 304. Lateral view of the akull of ■ Dogfish {SeyUium eanieuia) x j. From
Bejmolds.
1. Nasal capsule. 3. Rostmni. 3. laterorbitol aimal for the pftssage of
a blood-Teese). 4. Foramen far h;aidean artery. 6. Foramen for the
exit of the ophthalmic branches of Vth aod Tilth nerves. 6. Foramen
throoRh which the external carotid leaves the orbit. 7. Orbilo-nowl
foramen vhioh allowH a blood-vessel to reaoh the noBe. 8. Auditory
capsule. 9. Foramen through vhich the external carotid enters the orbit.
10, Ethmo- palatine ligament. 11. Fatato-pteryEO-quadrate har.
12. Meckel's cartilage. 13. Hyomandibular. 14. Cel»to-b];al.
16. Pharj'ngo- branchial. 16. E pi -branchial. 17. CeiAto.brsnchial.
18. Gill-rH3's ; nearly all have been out off short for the sake of clear-
neaa. 19. E»tra. branchial. U. III. IV. V. Va. VDa. IX, X. foratnioa
are attached the gills. The branchial arches are jointed into several
pieces, which are placed in an oblique position and so arranged that
when they are raised by the levatores arcnum — muscles attaching
them to the skull— they diverge and expand the gill-sacs lying
between them. The segments of each branchial arch are typically
four in number, named respectively pharyngo-branchial, epi-
branchial, cerato-branchiat, and hypo-branchial. The first-
named are situated in the dorsal wall of the pharynx and are
horizontal in direction ; the epi- and cerato-branchial stifien the
sides of the pharynx — the cerato-branchial being the main portion
XV.] VI30BRAL ARCHES. 373
of the arch, whilst the hj'po -branchial pieces are found in the
veDtral wall of the pharynx and converge to unite in a median
plate, the basi-branchial. To the ceruto- brunch iaJs are attached
a number of thin rods of cartilage which run outwards in the wall
of the gill-eac and are called gill-rays. Lying outside the visceral
arches are a varying number of cartilaginous rods. Those situated
at the sidea of the f^pe are called labial cartilages, those external
to the hinder visceral arches extra-branchials (11), Fig. 204).
They are equivalent to gill-rays which have become detached from
the arches.
The lirst gilt-slit, called the spiracle, is situated between the
jaw and the hyoid just outside the internal ear (Fig. 208). It is
a narrow tube, and its use in the more typical forms appears to be
to allow vibrations to come more closely in contact with the ear, and
in some cases to admit the wat«r for breathing. The other slits are
really flattened sacs, the walls of which are raised up into thin folds
richly supplied with blood-vessels, which are the true gills and are
supported hy the gill-rays. A rudimentary gill, the pseudobranch,
is sometimes developed ou the front wall of the spiracia No gill ia
developed on the posterior wall of the last gill-sac.
In EUsmobrauchs wo find, as in Cyclostomata, well -developed
dorsal (or neural) and ventral (or haemal) archas,
column. '* with their ends deeply embedded in the thick sheath
of the notochurd. This sheath has been converted
into cartilage by amoebocytes wandering into the gelatinous layer
secreted by tlie cells of the notochord, and it is divided into
separate pieces called centra. Between the centra the sheath
remoina membranous, and in the middle of each centrum the
uotOL-hord becomes very much narrowed, so that instead of being
a uniform rod it ia like a row of beads. The haemal arches meet
beneath in the tail, but further forward they stretch out horizon-
tally and become jointed; ttieir outer segments are the ribs, thia
is the ftrst apjiearance of these organs. There are usually twice as
many neural arches as there are centra, and every alternate one is
small and does not meet its fellow, and hence is called an inter-
calary piece: the haemal arches are as numerous as the centra.
The cranium, visceral arches and centra are all strengthened by a
calcareous deposit in the ground substance of the cartilage. This
calcihed cartilage is to lie carefiiUy distinguished from trite bone,
represented in Klasmobranchs by the bases of the scales and t«eth.
The primitive tail-fin of Vertebrata, as we have seen, ia a fringe
374 ra.ASUOBRANCHU. [CHiP.
surrounding the end of the taiL Only a smaD and narrow rem-
nant of this persists in Etasmobranchs, the whip-like end of tbs
tail being bent up ; beneath it there is a well-marked fin, and Uiii
together with the remains of the primitive caudal fin constitute &
secondary tail-fin, which is now denominated heterocercal, since
the axial skeleton does not divide it into two equal parte (Fig. 208).
The paired fiua are attached to hoops of cartilage (tlie limb
arches), called respectively Uie pectoral and pelvic
giidles, the pectoral being situated just behind the
last gill-cleft, the pelvic just in front of the anns. The pectonl
Fro. 205. Doi«o-l>tersl view of the pecloni girdle and fins of a Dof^ita,
Seyllium canicula, > ]. From Reynolds. The gaps betweeo tb« ladialis
are blackened.
1. Hollow in the midTentral part of the pectoral girdle which iapporta the
pericardiam. 2, Dorsal (Hcapalar portion) of pectoral girdle. 3. Mett-
pteryginm. 4. MeBO-pterygium. 6. Pro-pteJTginm. 6. Pro-pterTgial
radial. 7. Meso>pter>')iial radial. 8. Meta-ptei7gial radial. 9. Out-
line of the distal part of the fin which is supported b; homy fin'raya.
girdle extends a considerable distance up the side of the animal:
the pelvic b little more than a transverse bar. llie fins in modeni
Elasmobrauchs are of what is called the uniseriate type, ihat is
to say, there is a thick jointed main axis with cardlagiaons rays
attached only to its anterior border. Fossil Elasmobrauchs show in
one case, PUaracantkus, a bisetiate fin with rays attached to boUi
borders; and in another, C'ladon^tttcAe^ a atili more primitive con-
ditiou, where the fin is merely a lateral flap supported by parallel
bats of cartilage. By the coalescence of these at the base the axis
was formed, and later by the disappearance of the rays on one side,
the imiseriate fin.
In the pectoral tin the basal portions of some of the rays
coalesce to form two large cartilages called propterygium and
tnesopterygium, whilst the axis ilself is called the metaptery-
gium. In the pelvif fin of the male the axis bears distally a
grooved rod which is termed the clasper, and ia used in trans-
ferring spermatozoa to the female. The axis is called the basi-
pterygium. The distal joints of the
rays in both pectoral and pelvic fins
are made up of numerous small carti-
lages called radialia.
Tlie brain of Elasmobranchs is re-
markable for tlie great
development of the ol-
factory lobes, which are in close contact
with the nasal sac and are attached
by a narrow stalk to the cerebrum.
This is only imperfectly divided into
two hemispheres and has nervous
tissue on its roof as well as it« floor.
The cerebellum is developed into a
great flap which projects back and
covers the thin roof of the medulla
oblongata (Fig. 188). It ha» also
lateral ontgruwths called cerebellar
lobes.
The alimentary canal is consider-
ably longer than the ' body and is
consequently folded. It has, as a matter of fact, a U-shape:
the first limb and a jiart uf the next constitute the
c«n»i"'"'"^ stomach, which is marked off' from the intestine by
a constriction and a powerful development of the
circular muscles forming a sphincter or circular muscla To the
posterior aspect of the loop is attai^hed the prominent spleen. The
intestine, although outwardly straight, is probably derived from a
corkscrew coil by the adhesion of successive turns : for the " spiral
valve " which, as we said, is merely a ventral unfolding, has a very
I
icj, 20C. Dorsal view of tb«
))elvic girdle and &n> ot a
male Dogfinh. .SeijUium d
rula. From Beynolda.
Peine Rinlle. 2. B
jitervgiuiiK 3. CldBper.
i. ItiiilialiiL.
376 ELASMOBHANCHIL [CHAP.
strongly marked spiral coarse. The liver opens by tiie bile-duct
into the beginning of the intestine, and close to its opening k
situated that of the duct of the pancreas. A small gland of unknown
function, the rectal gland, opens into the hinder end of the
intestine.
The pericardium is almost completely separated from the rest of
the coelom, communicating only by two narrow holes with it. Hbt
heart has the tjrpical structure described in the last chapter (see
p. 349). In the conus there are at least two transverse rows of
pocket- valves, occasionally more. The arterial arches arising from
the ventral aorta run up between successive-gill sacs and break
up into capillaries on the surface of the gills : from these the blood
is collected by vessels in the form of loops completely surrounding
the gill-sacs. From these loops four pairs of epibranchial vessels
arise and run backwards in the dorsal wall of the pharynx con-
verging to form the single dorsal aorta, which supplies blood to all
the hinder part of the body. The last gill-sac has a gill only on
its anterior border; the blood from this does not reach the dorsal
aorta directly but is connected by a transverse vessel with the loop
surrounding the preceding gill-sac. The dorsal aorta gives off on
each side a subclavian artery to the pectoral fin and then four
median arteries which run down through the mesentery and supply
the alimentary canal. These are named the coeliac, anterior
mesenteric, lieno-gastric and posterior mesenteric arteries
respectively (Fig. 194). The most anterior, the coeliac, has two
important branches, (1) one supplying the liver and the proximal
part of the stomach with arterial blood, and (2) the other supplying
the anterior part of the intestine and the pancreas. The anterior
mesenteric artery supplies the greater part of the intestine and
sends branches to the reproductive organs. The lieno-gastric
supplies the posterior part of the stomach and the spleen and
part of the pancreas. The posterior mesenteric supplies the rectal
gland. After giving branches to the genital organs, kidneys and
pelvic fins, the aorta continues its course into the tail as the caudal
artery. From the two most anterior branchial loops a pair of vessels
arise running forward in the dorsal wall of the pharynx and at the
same time converging. These are the common carotid arteries,
which supply blood to the head. Each divides into two main
branches, an external carotid, which pierces the floor of the
orbit and supplies the eye and the jaw, and an internal carotid,
which pierces the floor of the skull near the middle line and supplies
ABTERIES AMD VEINS. 377
the brain. The paeudo-branch on the front wall of the spiracle
Teceives its blood from the hyoidean artery which, branchiug
from the loop BurroundiDg the first gill-sac, ruus forward in the
Toof of the mouth parallel with the common carotid artery and
eventually joins the internal carotid. In the venous system the
anterior portion of the sub-intestinul vein is represented hy
I pair of hepatic veins returning the blood from the liver,
opening into the sinus venosus close to the middle line, whilst
the posterior portion has dwindled to a small vein embedded
between the folds of the spinil valve; this however is joined by
branches from the sides of the intestinal wall to form the main trunk
of the portal vein. Both anterior and posterior cardinal
veins are represented by wide, somewhat irregular spaces, E&ch
Hiterior cardinal has an expansion called the orbital sinus which
enrrounds the eye. The two orbital sinuses communicate by an
interorbita,! canal tunnelled m the base of the skull The blood
from the ventral sides of the gill-sacs and pharynx is returned to
the Ductus Cuvieri by a pair of independent triinks called the
jugular veins. These are each connected with the anterior cardinal
, of its side by the hyoidean vein lying in a groove on the
byoiuaudibular cartilage {Fig. 195). The blood from the tail is
returned by a median caudal vein lying beneath the caudal artery
and like it enclosed between the centra and the united ventral ends
of the haemal ari'hes. At the level of the posterior etid of the
Ifidneys the caudal vein divides into the two renal portal veins
lying on the outer edges of the kidneys. These veins, as has been
alreoily explained (see p. 353), are the hinder portions of the
poeterior cardinal veins which break up into the renal [HDrtal system
of capillaries. These filter amongst the kidney tubules and reunite
DQ the inner side of the kidney to form the spacious posterior
canlinal sinuses, as the front portions of the posterior cardinals are
Darned. These two sinuses lying ventrally to the kidneys partly
coalesce. Each sinus curves forwards and outwards to join the
Ductus Cuvieri and at tliis point it is met by the large subclavian
vein returning blood from the pectoral fin. The pelvic vein receives
the blood from the side of the cloaca by the cloacal vein and the
blood from the pelvic fin by the femoral vein. It then opens into
a longitudinal trunk, called the lateral vein, which runs along the
BJde of the body beneath but parallel to the posterior cardinal vein,
The lateral vein iu front receives the brachial vein from the ventral
tide of the t>ectoraI fin (not to be confounded with the subclavian
t. Left noris. 2. Moutb. 3. Fectornl Go. i
S. Aperture of cloaca. G, Pericardia! cavity. 7. Vtotriole.
arleriogiiE. S. Auricle. 9. SiuiiB venosus. 10. Coelomic openii
of OTidnets. 10'. PnlcLtorni ligament. 11. Shell-gland. 12. O^
duct. 13. Ovar; refltcted over to the right to as to show 13, which lii
external to the attachment of the ovary. 14. Liver. 15, Proximal '
limb of stomach. 16. Distal limb of stoniach. 17. Intestine.
18. Reotam. 19. Spleen. 2Q. Pancreas. 21. Pancreatic duct.
22. Bile-dad. 23. Dorsal fio. 04. Spinal cord. 26. Noto-
ohord in centrum of vertebra. 36. Oaudal artery. 27, Caudal
2S. Lateral line. 39. Myotomes. SO. Abdominal poree. a.
patio artery. ft. Inteslinul branch of anterior mesenterio artery.
c. Lieno-gastric artery. d. OaBtric branch of lieno-fcutric artery
{posterior gastric artery}. t. Splenic brancli of lieno. gastric arterji
/. Portal vein. 3. InteHtiniil vein. ft. Splenic veic
from the dorsal side of the same organ) and then opens into the
Ductus Cavieri. Tlie ckiacal veins farther give off median branches
which tmite and then distril>ute blood to the viscera, so that some
blood from the pelvic fin may also return to the heart through a
portal system.
The ovary is a single ridge of the dorsal coelomic wall; the
oviducts are long and united far iu front so as to open by
common internal opening, situated ventral to the liver (Fig. 207).
In the middle of its length each oviduct baa an enlargement caused
by a thickening of its walls due to the development of gland
cells. This is called the oviducal gland, and its function is to
secrete the pillow-shaped elastic egg-shell. In all cases a consider-
able amount of development take^ place before the egg is laid : in
many cases development goes so far that the egg-sbell is absorbed,
and the embryo takes in nutriment from the wall of the oviduct
so reaching a very large size before birth. The egg is large and
well charged with yolk. The oviducts unit* posteriorly to open into
the proetodaenm or cloaca behind the anus. There are two large
tcsUs, and those are united anteriorly and connected to the front
end of each of the kidneys, which e.ttend along the entire length of
the abdominal coelom. The anterior region or mesouephros (for
no pronephros is developed) is narrow and its excretory function haa
almost disappeared. The testis is connected with the front end of
the meaonephros by vasa efferentia uniting into a single coiled
tube or epididymis, which structures are derived from mesonephrio
tubules- The arcbinephric duct ha.s also lost its original function
and become a vas deferens, which lies on the ventral surface of the
kidney and conveys spermatozoa from the epididymis to the cloaca.
It enluges at iu hind end into a vesicula seminalia, The
Fio. 208, ScjfUiHTB eanienla J. View of vi
a from the right side.
1. Mnath. 2. Spiracle. 3. Qill-sUta. 1. Oall-bladder. 5. Oeaophagua.
C. Pectoral &d out oft. 7- Veeioula flemiualis lying on melapbros.
8. Tratig. 9. Anterior domal (iu. ID. Pnsterior dorejil &n.
11. Meditui Tsntrsl fin. 12, Dorsal lobe of caadal fin. IU. Ventral
lube of caudal &□. H. Bight lobe of liiei. 15. Proiimsl limb ot
, Btomaoh. 16. Diatal limb of stomaoh. 17. luteHtine. IS. Reatum.
IB. Spleen. 20. Pancrons. 31. RbcHI gland. 22. Bile-duol.
33. Clagpere. 24. Lignment carrying the vasa tfferentio. 2S, Vaa
deferens. a. . Coeliac nrter;. b. Hepatic arter;. c. Anterior gastric
briery. d. Pancreatic branch of the coeliac artery. r. Anterior
mesenterSo artery. /. LieOQ-gastric arlerj. g. Poaterior meaenterio
artery. h. Splenic artery and vein. j. Puatetior mesenteric artery.
k. Portal vcio. I. Intestinal vein.
I»gterior and fiinctioDo.! part, of the Iddiiey ia the metanephros,
sad ita tubules unite iuto about six niaiu ducts, which converge to
form a [iiet»Dephric duct or ureter. There ia also a blind sperm
sac into whose posterior end the veeicula seminalis opens and which
'immediately after receives the ureter. The compound duct thus
formed meets its fellow in the middle line and so there is a single
uriiingenital sinus which opens into the cloaca behind the anus.
In the female the mesouephros is more vestigial than in the male
and itA duct (archinephric duct) is in &ont a very fine tube which
lower down dilates and meets its fellow to form a median urinary
sinus. This receives the ducts from the metanephros, and opens
into the cloaca behind the oviduct.
Actual sexual congress or copulation takes place in the Elasmo-
brauchs; the most posterior rays of the pelvic fins called the
claspers are enlat^ed, and used to distend the cloaca of the female
to allow of the entrance of spermatoEoa (Fig. 208). This is cor-
tL-latiHl with the large size and small number of the eggs and their
long retention in the oviduct. In the mate the spermatozoa are stored
in a swollen portion of the vas deferens, the vesicula seminalis, or
ill special pouches termed the sperm -sacs. It is probable that the
clasiter-, the large eggs and the division of the kidney into two parte
are specializations peculiar to modern Elasmobrancha.
The Elasmobranchs are the Sharks, Dog-fish, Skates and Rays
of our seas. They are almost exclusively marine and are a group
timch detested by tishenuen, since they are excessively voracious
*and their flesh is of little value.
They are divided into two sub-orders, the Selochoidei and the
fiatoidei. The first consists of powerful swimmers with cylindrical
bodies, well-developed tail-fins and moderate pectoral tins ; the
Utter ore ground fish with broad backs and bellies and narrow sides.
whip-like taiU with rudiment&ry tail-Qj), and enormous pectoral &as
extending forward to the extreme end of the snout.
Flu. aiW. A. SriilUum canicula. Rediicod. From Pay.
B. Egg-ease opened lo dio« soan^ ombrso wiih yolk sac.
CT^SSIKICATIOS.
The Sbl&choidei are known as dog-fiahes or sharka, according to
their size. The common Englisli dog-Sab, Srylliu
canioulit, is about two feet long (Piga, 207, 208, and
H)9); another kind, the Spiny dog-fish, Squalus ucunlhia», ia
itinguiahed by haviog a spine, a greatly enlarged Bcale, in front
vf each of the two dorsal fina, This latter genua ia very common
the Atlantic coast of North America, where it ia known aa
he Spiny-dog, The American Smooth dog-fiah. Galea* canis, is
listingmshed from Scyllium by being viviparous. Amongst the
iharks the most remarkable are Zygaena, the Hammerhead, in
irhich the roofs and fioora of the orbits are produced outwarda,
that the eyes are set as it were on peduncles; and Carchiroilon,
ihe great White shark, which has lost its spiracles and poaseases
tail-fin with crescentic under lobe. Owing to their powerful
Iwimming capacities, sharks are as a rule not limited in distribu-
Carchnrodon is the dreaded man-eater of the Adriatic and
ihe warmer seas everywhere. Z;igarna occasionally carries terror
uto the bay of Naples, and apeeic^s of both genera are found ulT the
.merican coast. The Notidanidae are a family with many in-
teresting traits. They poaaeaa one (Huxniirhtig) or two (fleptaiicAus)
txtra gill-clefts, and the upper jaw directly articulatea with the skull
Khind the orbit. Teeth of the same cbaracter as those borne by
iring representatives of this family have been found in tlie Lias
ibales of England. The Port Jaeksoii shark of Australia, Cmtradoii.
H the sole aurviviug ty[)e of another family, representative a of which
tre common in the Coal Measures. In it the snout is reduced so
ihat the mouth ia thrust forward and the jaw is attached to the
ikull in front of the orbit. The teeth are flat and pavement-like
id adapted for cruabing the Molluscs on which the auitnal feeds.
The BatoHiei or Rays are, aa we have said, ground feeders. All
ive the true gill openings on the underside of the body: the
liracle alone opens on the dorsal side and is enlarged. It has in
Sftct in this group taken on the function of pumping water into
^e pharynx, a duty which cannot be conveniently uuderbaken by
ihe mouth when this is burrowing in the mud at the bottom. Ruia
the common akate on both sides of the Atlantic : it has no caudal
in but two dorsals. Turpi-dn is distinguished by a more elongated
lody. The muscles on either side of the head are converted into
electric organs, consisting of batteries of vertical hexagonal tubes
llled with a clear gelutiuous fluid, each tube representing a meta-
lorphoeed uiuscle-hbre. By means of these organs it con inflict
Tha pecUifiU fins are joined in front of the anout. Prinlia
saw-Gsh. It has an immensely elongated rostrum, at the aides (
which lai^e pointed teeth are set; the body is elongated, but i
ahows all the essential features of the Bntoidei. The teeth in the
month, like those of other Batoidei, are flattened. Printis is found
both in the Mediterranean and Caribbean Seaa and elsewhere. In
some of the extinct representatives of the family the upper jaw ia
Attached to the cranium behind the orbit. This variation in the
pUh.'e of attachment indicates tliat the connection between the two
structures is secondary.
The two most interesting fossil representatives of the groups
are C^gdotelacis and Pleiiracuulhoif whose fins are desi'ribed above
(p. 375). ""
Order II. Holocephali.
The second Order of Pisces, the Holocephali, differ from Elasmo-
knchs chiefly in the skeleton ; in the viscera they resemble them
ly closely. The Holocephali are distinguished by having the
Fia. ail. SkoU of a u>le Chi
KkuJ wpsole.
Hubrecht.
Cartilae>Dous appendage to the ethmoid regioD,
n of ElaamobrikDcliii. 3. Breotile ikpp«iid>{te.
Formara by whioh the ophthsJmio nervea lesve the orbit. 5. Forunen
by «hich the opbthalmia branch of the Vtb nerve enters the orbit,
ft. Auditory eapaiile. 7, Interorbitn.) septum. 8. Meckel's CRrtiloge
KrtimlKtiDic with oil ontgronth From the poBterJor part ut tliu palftto-
pterjRO-quadmte cartilage. 9. Teeth. 10. Lsblal cartilage, 11.
III. V. VII. IX. X. foramina for the pasaage of cruoial nerves.
Upper j»w completely confluent with the cranium, a condition called
mo tostylic (Fig. 211) : the orbits are so deeply indented that the
1 ii pressed hack from between them, and tlieir two cuvities are
ily separated by a vertical plate of cartilage, called the inter-
25
HOLOCEPHALL
orbital septum. There is no spiracle and the Uet gill-cleft is ■!»
oloeed. A fold of skin, called the operoulam. extends back over
the gill-slits. The gills are, however, still borne on the valla of
sacs. 'I'he aaout or praeoral part uf the body is aiui^b rednc«d in
sixe and supported only by a siugle rod of cartilage.
The scales bave almost entirely disappeared and are reprcseoted
otUy by the great spine, tbe su-caited icthyudorulite, irhiek
stitTens tbe front edge <^
the dorsal tin, by the teetil
and by the prickles on >
peculiar tentacle situatol
on the snout of the male.
The teetb are confluent,
FonuiDg ridges of dentine
covered with enamel. OF
these there are a pntr in
the lower jaw, called den-
tary plates, and two paits
in the upper, termed vo-
merine and palatine
plates respectively, placed
one behind the other. Each
plate has certain areas,
where the dentine is espe-
cially thickened, called
tritors. The arrangement
of these tritoiB is used in
classifying tbe fossil spe-
cies. Tbe ]>eculiar tentacle
on the head of the male
arises from a pit situated
in the middle line of the
Buout^ and bears sharp
tooth-like scales at its tip.
The QotiK-hordnl sheath
is not broken up into
centra, but in CMmaera it
has developed nitbin it a
large number of calcified
„„,„,, , rings, three to five times
Fio. 213. Chimaera moTutrota, L. °' , ,
,, . , „ , , as numerous as the neural
Male with pTMBsH on snout. B«dueea, ,
aicnes.
The Holocephafi were once a niimerons group ; now they are
represented by three closely allied genera, of which the best known
is Chimatra, sfiuietimes called the Rabbit-fiah, common to the
Mediterranean and bi:i the Atlantic coust of Europe and A&ica.
C. mofistrosa ie found on the East coast of N. America. On the
Pai'ifio coast C. colki occurs in such Euml(ers aa to be a serious
naifiitnce to fishermen. It eata the baits off their tines. It ie
known as the Rat-fish, in allusion to the shape of the tail. Callo-
rkjfttckaa ocours in the temjierate waters of the Southern Hemi-
q»hffl«5. The third genus, IlaiTtolta, is a deep-sea form.
Order III. Dipnoi.
The third Order of Fishes, the Dipnoi, are very interesting
animals, inasmuch as they afford suggestions as to how land animals
were evolved from fishes, They are distinguished by possessing true
lungs, in the form i>f oqo or two sacs opening by a common lube
into the ventral side of the oesophagus. The blood is supplied to
the Kings by vessels given off from the last two paiia of efferent gill-
arteries (Fij;. 216), and it is returned not into the general circula-
tion, but direct to the heart, where it oj)enx into a special section
of the atrium, the left auricle, cut off from the rest by a septum.
Afl in the Holocephali, the upper jiiw is fused with the cranium.
There are four or five gill-clefts and no spiracle. There is a large
gill-cover which completely covers the clefts; it is strengthened in
Crratftt/ug by two strong membrane- hones, tiie so-called squamosal
or pre-operculum, and the operculum; there is also a third
smaller bone called the inter-operculum. The oro-nasal groove
has become closed so as to form a canal, the end of which opens
vithin the stomodaeum as the posterior naris or choana. Owing
to the forward growth of the jaws the mouth has become terminal.
Tlie cranium is not narrowed between the orbits, aud the cartilage
behind is replaced by true boue. there being two exoccipital
k
bonsB at etch aide of the hole called the foramen ma^aum bm
which the spinal cord isaues. Above the foramen magnnm tin
craaium is quite obviously coinjioGed of fused neural and veaUil
arches ; the spiuee of the former and the riba of the latter arc quite
distinct. As in Chimagra the teeth have coalesced to form grett
deutary ridges in the lower jaw and in the roof of the moath,
the fio-called vomerine and i>alatine plates, the timt named being
anterior (Fig. 214).
It will be observed that iu the Dipnoi we for the first time meet
with large bones, and it is instructive to notice under what ciTcam-
stances they appear. The exoccipital bones are quite distinct &om
CkrtilBginoufl put ot tlie qnBilrate with nhioh tha nuadible utieoUl*,
8. a, 4, Booting membnuie-lKioBH. 3. Nares. 6. Orbit. T. Pn-
opercular (a(|UBmoBftl). 8. Second rib. 9. First rSb. 10. Vonnriiii
deoUl piste. 11. Palatine dental pUte. 13. Palato-pletTguii
13. Purasphenoid. 14. Inleropcruuiar.
the calcifications of the cranium met with in the 1
In the latter case there was hardening of tha
Bmi"'"""" "' ground substance of the cartilage; here the bone
is formed in the membrane surrounding the caitiUgt
and eats into and destroys the cartilage. This sort of bane is Cne
cartilage-bono. Besides such bones, however, we have m^l
which are traceable to the fusion of the suiull bony bases of ^
typical scales which we found in Elaamobranchs. Theee Uttle bonj
plates fuse together to form large structures which are then tsotd
XV.] SKELETON.
m em brane- bones. A lirat trace of this
process is seen in the fusion of the teeth
to form compound plates, as in the Holo-
cephali.
The Dipnoi are eel-like tish with elon-
gated whip-like paired fins, and they are
covered all over with thin rounded cycloid
scales. These scales are equivalent to the
enlarged bases of the scales of Elasmo-
branchs without the apikes. On the upper
side of the head these scales have joined
to form median and lateral bones ; in
front near the nasal sacs there are two
smaller bones. The Dipnoi are quite
peculiar among Craniata in having an
unpaired series of large roofing bones on
the top of the head. The palatine dental
plates are supported by a bone which sur-
ronnds and replaces the cartilaginous upper
jaw,and is called the palato-pterygoid.
The roof of the month is sheathed by a great
plate of bone called the parasphenoid,
derived from the bases of vanirfied teeth
(Fig. 211). Beside these there is a
large membrane bone outside the pec-
toral girdle, which is the first trace of a
collar bone or clavicle, and the two
bones already mentioned in the opercular
flap. The sheath of the notochord is
converted into cartilage, but is not di-
vided into centra.
The pured fins are remarkable for
having a long jointed axis and two rows
of rays; they are in a word biseriate
(Fig. 215) like those of the extinct Elas-
Fio. 21S. Lateral view of the skeleton of Ceratodia mioltp'u. After Oiinther.
I, 3, S. Hoofing membrane-boneB. 4. Cartilaginous posterior part of oranium.
E. Pre-operoDlar (squamosal). 6. Opercular. 7. SuborbitaL
6. Orbit. 9. Pectoral girdle. 10. Proximal cartilage of peotoral Gn.
II. Pectoral &□. 13. PeWic girdle. 13. Pelvic Sn. 14. Spinal
ooloniD. IS. Candal fin (diphyoercal).
390
DIPNOL
[chap.
mobranch Pleuracanthus. A fin of this type is called an archi-
pterygium. The tail-fin is of the primitiye type found in Amp^
oxus and Cyclostomata, in which the fringe of skin supported by the
fin-ray is equally developed
above and below the noto-
chord. It is in fact a diphy-
cercal tail.
As was to be expected,
the blood-system has under-
gone interesting modifica-
tions. The conus arteriosus
is long, and as in Elasmo-
branchs and Holocephali hu
several transverse rows of
pocket valves. From its
anterior end four arteries
are given ofi* in a bunch on
each side to the gill arteries
to supply the gills : there is
no ventral aorta. From the
last eflferent vessel on each
the artery going to the lungs
arises. An oblique septum
divides the cavity of the
conus into two in such a
way as to cut ofi* the open-
ings of the last gill arteries
from the front ones, so that
the blood passing to the
lungs does not mingle with
that going on to the head.
Thia is very like the ar-
rangement found in Am-
phibia. The likeness to the
Amphibian blood-system is
increased by the presence
of a median *Weua cava"
which returns the blood fix)m one kidney directly to the heart. One
posterior cardinal vein persists, the other has atrophied except at its
origin from the kidney (Fig. 217).
The lungs are long, wide sacs, extending between the intestine
17
Fig. 216. Diagram of the arterial arches
of CeratoduSf viewed from the venlral
side.
I. II. in. IV. V. VI. First to sixth arterial
arches. 7. Gills. 8. Epibranchial.
10. Anterior carotid. 11. Posterior
carotid. 17. Dorsal aorta. 19. Pul-
monary. 24. Coeliac.
XV.]
CLASSIFICATION.
391
Classification.
and notochord, although their opening into the gullet is ventral.
The gill-arches and gills are on the other hand very small, and
the opening between the gill-cover and the body is narrow.
Only three species of Lung-fish are still living, but the group
has very many fossil representatives. The Australian lung-fish,
Ceratodus /orsteri, has well-developed paired fins (Fig. 215). It
inhabits rivers which at
certain seasons become
foetid with decaying vegetation, and
during this time it breathes air. The
African and South American lung-
fishes {Protopterus annectens and
Lepidosiren paradoxa) have whip-like
paired fins consisting of little more
than the axis of the limb skeleton
(Fig. 213). They bury themselves in
mud during the dry season, a necessary
precaution, since they inhabit swamps
which dry up. Lepidosiren, the South
American form, has been shown to have
larvae witli long feathery external gills,
strikingly recalling the larvae of Amphi-
bians. The young Protopterus has
similar structures and retains traces of
its external gills throughout life. Cera-
iodus, on the other hand, has a develop-
ment practically completed within the
egg-shelL The fossils referable to this
order are very interesting. They occur
in a great variety of forms. Some of
them — referred to a Sub-order called
the Arthrodira — having not only the
head but also the anterior part of the
trunk clothed in great bony plates.
The head skeleton articulated with the
trunk skeleton by ball-socket joints.
The occurrence of Dipnoi in great
numbers in the rocks immediately pre-
ceding in the geological series those in which the first remains of
Amphibia are found is very suggestive.
Fia. 217. Diagram to show ar-
rangement of the principal
veins in a Dipnoan.
1. Sinus venosus — graduaUy
disappearing in the higher
forms. 2. Ductus Cuvieri
= superior vena cava. 3. In-
ternal jugular= anterior car-
dinal sinus. 4. External
jugular = sub-branchial. 5.
Subclavian. 6. Posterior
cardinal, front part = venae
azygos and hemiazygos. 7.
Inferior vena cava. 8. Benal
portal = partly hinder portion
of posterior cardinal. 9. Cau-
dal. The hepatic portal
system is omitted.
392 TELEOSTOMI. [CHAP.
Order IV. Teleostomi.
The fourth Order of Fishes, the Teleostomi, is by far the largest
and contains the overwhelming majority of living fishes. They
differ irom the Dipnoi, in that the lung or air-bladder, as it is
called, receives its blood from the dorsal aorta and returns it to the
general circulation, so that the organ is as a rule not so mudi
respiratory as hydrostatic. The lung is undivided and its opening
has in most cases apparently become shifted up the side of the
throat to the mid-dorsal line. Since the opening of the air-bladder
is dorsal some authorities have held that it is quite a different
organ from the lung, the opening of which is ventral. But it is
very difficult to believe that we have to deal with two totally
distinct organs in Polypterus and Lepidosteus, more especially as
in both these fishes it is probable that the air-bladder subserves
respiration. The air-bladder is never paired : if we suppose it to
represent one lung we can imagine how the opening could be
gradually shifted dorsally. The anus of Urochordata has, we know,
undergone such a shifting.
Another point of difference, distinguishing Teleostomi from the
Dipnoi, is that there are no median membrane-bones on the head,
all the bones being originally paired. Further, a set of membrane-
bones bearing teeth appears in the sides of the mouth outside the
primitive jaws, or, as we may express it, in the lips. These lip-bones
functionally replace the true jaws, and as the mouth has now
received its full armature, the name Teleostomi, or Perfect-mouthed
Fish (tcXcios, perfect; oTo/ia, mouth) has been given to the Order.
As in Elasmobranchs, the upper jaw is joined to the skull only by
the upper half of the hyoid arch, which is ossified as the hyo-
mandibular. There is a strongly developed gill-cover, armed
with several bones, called the operculum. The septa between the
gill-sacs are reduced to narrow bars, so that there are gill-clefts,
not gill-pouches. The gills themselves develope into long triangular
processes freely projecting and attached only at the base. Ofiben there
is a rudimentary gill attached to the posterior aspect of the hyoid
arch. This is called the pseudobranch or sometimes the oper-
cular gilL This is not to be confounded with the pseudobranch
of Elasmobranchii, which is attached to the first visceral arch. The
opening of each nasal sac is divided into two by a bridge and there
18 no oro-nasal groove. The cloaca is divided into two openings;
CBOSSOPTEBYGn.
an tuiterior, the anus, cammiini eating with the intestine, and a
posterior, serving for the discharge of the genital products and
excreta of the kidneys.
It was formerly customary to divide
the fisliea here grouped as Teleostomi into
two Orders, the Teleoatei, or completely
bony tish (oo-Tt'oi', ft bone), and the Ganoidei,
or tiah with shining scales (yavo^, glitter,
brightness). As, however, there is far more
difference between dilTerent families in-
cluded in the Ganoids than there is be-
tween some Ganoids and some Teleostei,
this arrangement is really unnatural.
The Ganoids are in fact composed of
widely different families, retaining certain
priiuitive ehara^'tenstics once shared by
all Teleoetomi. A far more rational divi-
sion of the Teteostomi is that now usually
adopted into Croasopterygii and Actino-
pterygii.
Sub-Order A. Croasopterygii.
The Crosaoptorygii include only two
living genera, Poli/plerii« and C'alamo-
ichtkyi, which inhabit the rivers of Africa.
In former geological periods, however, the
Crossopterygii constituted an immense
group. They are distinguished by retain-
ing the biseriate paired fin with a shortened
and broadened axis covered by scales.
This scaly lobe is consequently fringed by
the rays, whence the name (Kpoairoi, a
fringe; vTfp\i$. wing or fin). The so-called
air-bladder is paired and the two halves
open on the underside of the pharynx.
The spiracle still persists, having a special
little gill-cover strengthened by several
Bmall bones. It has recently been proved
that the air-bladder is a respiratory organ
and tliat the expired air escapes by the
epirocle.
394 TELEOSTOML [CHAP.
The whole body is covered with lozenge-shaped scales covered
by a thick layer of shining enamel, and the dorsal fin is subdivided
into a large number of finlets, each supported by a large stiff ossified
fin-ray (Fig. 218). The head is covered with numerous membrane-
bones arranged in pairs, replacing the cartilage of the cranium.
There are not only exoccipital bones, but also a basi-occipital
situated beneath the foramen magnum, and the front wall of the
auditory capsule is ossified by a pro-otic bone. The notochord
is narrowed in part by the formation of bony centra ; these however
are not, as in the Elasmobranchs, mere rings in the notochordal
sheath, but are formed of the coalesced expanded bases of the bony
neural and haemal arches. The term chorda-centra has been
proposed for centra such as those of Elasmobranchii, formed by the
segmentation of the sheath of the notochord; whilst centra such
as those of the Crossopter}'gii are called arco -centra. The centra
have concavities before and behind, and the space between two
vertebrae is filled with an expanded section of the notochord, which
in the middle of the vertebrae is reduced to a mere thread if not
obliterated altogether. Vertebrae hollowed on each side are said
to be amphicoelous (Gr. d/x</>t, both; koiAo?, hollow).
It is obvious that an axis composed of vertebrae is a much more
efficient organ of support than the flexible notochord with its loosely
adherent neural and haemal arches. Hence it is not surprising to
find that vertebrae have been independently developed in Fishes,
Amphibia and Reptiles, and have had an independent origin even
in difierent families of the same order — the Halecomorphi and
Lepidosteidae, for example. Different investigators therefore in
their endeavours to find exactly corresponding parts
coTumn!*'^** in the vertebral columns of various animals have
arrived at discrepant results. After years of research
however Gadow has been enabled to give a consistent account
of the evolution of the column in all the Graniata, and his account
seems on the whole the most probable.
According to Gadow, all arco-centrous vertebrae originate firom
four pairs of cartilaginous pieces ; some of which may be entirely
suppressed in some vertebrae, but all of which are represented in
some part or other of the column. These are (1) basi-dorsals,
the expanded bases of the neural arches; (2) basi-ventrals, the
expanded bases of the haemal arches (to these when present the rib
is always attached); (3) inter-dorsals, cartilaginous pieces situated
between successive basi-dorsals, and derived from the segmentation
ACTINOFTEBTail.
of the apical ends of the haemal arches which have extended upwards
roimd the notochord; {4) iater-veutrala, cartilagiiimis pieces
pla>.'ed beoeath the notochord alternating with the basi-veiitraU,
and derived from the segmentation of the apical ends of the
neuT&l arches which have extended downwards round the sheath
of tiie notochord.
In an ancestral Craniate therefore corresponding to eat^h myotome
there were ou each side of the notochord four cartilaginous pieces.
These pieces In diSereut groups of animals have been variously
combined with their successors and predecessors, the joint between
two successive vertebrae being formed not between two pieces but
by the absorption of cartilage in the middle of & piece at the ptaee
where the maximum bending occurs.
The Croasopterygii are probably in some respects more nearly
related to the ancestors of Am])hibia than are modern Dipnoi.
Thia view is strengthened by the fact that the air-bladder is
occasionally used as a lung. The young have one large external
gill attached to the operculum. As in the Dipnoi the mouth is
terminal.
Sub-Order B. Actinopterygii.
The Actinopterygii are distinguished by having a uniseriate fin,
the base of which is not covered by scales, avid by having the
opening of the air-bladder dorsal. Among the moat primitive
subdivision is that of the Cuondrumtei, or Stnrgeons. In these hsh
there is a long shovel-shaped snout or prue-oral part of the head,
which is used for shovelling up the mud at the bottom of rivers in
search of prey. This old-fashioned feature is not found in any other
family of the Actinopterygii, all of which have terminal mouths,
The notochord of the Sturgeons has a thick sheath without any
trace of centra, and the only cartilage bones in the cranium are small
ossifications on ita side walls, called the orbitosphenoid and the
alisphenoid bones, and a pro-otic in the front wall of the
auditory capsule. The hyomandibular segment of the hyoid arch is
ossified by two bones — a hyomandibular where it articulates with
the skull, and a symplectic below where it joins the first visceral
arch. A large part of the cranium is covered with a number of
membrane-bones which pa.'-s insensibly into the great scutes or
bony plat«a which cover the body. These latter, like the hones of
the head, are derived from the fusion of scales. Though the mouth
Fio. SIP. Acipent
the Stargeoo. From Day,
is often toothless, there is a
maxilUry bone in the upper li
the pterygoid hone which supports tiie
pterygo<iuadrat« cartilage. A great para-
i^phenoid Hupports the base of the sknil.
The coinmun stuigeon Aripeiifur is
found in the Pacific and North Atlantic,
and enters the rivers of Europe Mid
America. The ovary forms the RusgioD
deUcacy known as caviare. The apcwn-
hill Polynioii, found in the Missis.*in)i,
hae a very broad snout and has lost
nearly all its scutes, but it retains some
at the sides of the tail and a series form-
ing a comb-like fringe along the dorwil
edge of the upjwr lobe of the tail, called
fuK-ra, The extinct members of this
subdivision were clothed all over with
ganoid scales and the membrane-lHines
on the head were fewer and more regular
than in recent forms.
Tlie subdivision of the H.u:,e(xh(08ph[
is represented at the preseut day by only
one species, Amui ritliti, the Bow-fin of
the St Lawrence and other American
rivers. Like /'oti/ji/mis this species has
Lomplet* ampliit'oelous centra formed by
the ftiaion of the expanded bases of the
neural and haemal arches: the craninm
is also largely replaced by bone, not only
behind where the foramen magnum is
encircled by four hones, the supra-occi-
pital, two ex-oceipitals and n basi-
oeoipitai, hut at the sides and in the
snout where a mesethmoid is formed.
In addition there is a complete helmet of
membrane-bones surrutinding the cranium
above and at the sides, and the fiiH have
above a pre-niaxiUa and a maxilla,
and below a dentary, all well proTided
with teeth. The whole body is
XV.] ACTINOPTERYGII. 397
with thin rounded scales. Amia is a voracious fish ahout two
feet long.
The next family, that of the Lepidosteidae, are the most bony
of all fish. They are the Bill-fish or Gar-spikes of the Northern
and Central American and Cuban lakes and rivers. The whole
body is covered with scales like those of Polypterus^ coated with a
thick layer of ganoiu. The jaws are long, and in both the upper
and under lips there is a series of three or four bones bearing teeth,
a rare condition. The skull is as bony as that of Amia, The
vertebral centra have become opisthocoelous, that is to say, each
centrum is convex in front, fitting into a concavity of the hinder
surface of the one in front of it, so that the notochord has almost
disappeared. The ovary, by the fusion of its free edge with the
coelomic wall, has become converted into a sac, to which the funnel
of the oviduct has become adherent, so that ovary and oviduct are
continuous. The spiral valve on the intestine is rudimentary.
The Gar-pike are said to lie in wait among the reeds on the
banks of the lakes, in order to seize small animals visiting the swamp
in their long pincer-like jaws.
The remaining families of the Actinopterygii are grouped to-
gether as Teleostei and have certain well-marked characters in
common which distinguish them from the preceding families grouped
together as the Ganoidei. The first of these characters is the
structure of the tail. In all the Actinopterygii so far mentioned
the tail is heterocercal, though in some, such as Amia, the ventral
lobe is very predominant. In the Teleostean families the ventral
lo))e forms the whole of the tail and is placed in a straight line with
the rest of the body, the end of the notochord being sharply bent
up almost at a right angle with the remainder and surrounded by
a bony sheath. Such an apparently symmetrical tail-fin is called
homocercal, and it is to be sharply distinguished from the really
symmetrical diphycercal tail of the Dipnoi.
Another important point in the anatomy of Teleostei is the
structure of the heart. The conus arteriosus with its several rows
of valves has become completely absorbed into the ventricle. Only
the anterior row of valves remains, separating the enlarged ventricle
from the ventral aorta, at the origin of which there is a non-
contractile swelling, the bulbus arteriosus.
The stomach is distinctly sac-like, the two limbs of the loop of
the alimentary canal of which it is constituted showing a tendency
to coalesce.
398 TELEOSTOML [CHiF.
The iDtefltaue has become longer and more coiled aitd hn
completely lost its spiral ralve. Cloee to the entrance of the bile-
dact there is a aeries of short, blnnt diTerticula of tlie intestiDe,
called pyloric caeca. These were supposed to be a modified tnu
pancreas, bnt the trae pancreas has recently been discovered in tlie
form of a number of very delicate tubes intermixed with the pyloric
caeca. Id do Teleostean, so br aa is known, does the pancreu
form a compact gland. The ov&ry is a hollow orgMi continooiu
with its duct; in this point, it is true, Lepidotteta has Teleostean
characters, bnt in Teleostei the testis is also contjnnons with its
duct, which shorn do relation to the kidney; bo tliat Id the male
I, 2. So pn -clavicle. 3. ClaTicle. 4. Cortcoid. 5. Bckpnla.
6, Accessory piece. 7. OMiSed radialia of the flu. 8. Dcsmal
there is a complete departure from the normal Craniate arrange-
ment. The cloaca has undergone more division than even in the
primitive Actinopteiygii, for the conjoined kidney ducts have an
opening behind and distinct from that of the united genital ducts.
In the brain the roof of the cerebrum is a thio noD-nervous
membrane, but the optic lobes and cerebellum are greatly devdqied.
SKELETON, 399
'Jthe interlacing of the fibres of the two optic nervea, which was
lUliided to above as the optic chiasma, has entirely disappeared,
D that the optic nerve from the left side proi'eed^ Htraiglit to the
ight eye, crossing but not interlocking with those from the right
ade to the left eye. 'flie eyes are exceedingly large, so that in
learlyalt Teleost«i, as in the Holocephali, an inter-orbital eeptuni
B formed, aloog the upper edge of which the olfactury stalks run.
In the skeleton there is hardly a feature which is not ahared by
(ome or other of the members of the more primitive families of
Actinopteiygii, but in the coin bin a lion of features it is
sharao ten Stic, and it is of such an uniform type throughout a
Kge number of families that it merits a special description.
The notochord is constricted by the formation of amphicoelous
centra, which have developed four ridgea projecting
outwards in two planes at right angles to one another.
In the intervals between these ridges the ends of the Deural and
haemal arches are inserted, all being converted into bone. The
pectoral arch is represented by a small plate of cartilage on each
Bide, in which are two bony centres, an upper scapula and a lower
coracoid (Pig. 220). Outside this there is a strong curved mem-
brane-bone, strengthening the hinder border of the opercular slit,
^e clavicle. Thia is connected with the skull by additional
bars, whilst from its lower end a pre-clavicle runs forwanl beneath
bhegilla. Prom tu hinder edge a post- clavicle often projects back
Isto the muscles. The anterior paired lins are attached to the girdle
where the scapula ao<! caracoid join. In them the cartilaginons
skeleton is almost all absorbed, the basal portions of the fin rays
»)ming changed into true membrane-bone and articulating directly
with the pectoral girdle. The pelvic fin has a similar structure, and
tiie pelvic girrlle has quite disappeared.
The cranium is completely covered with bones. Even where
CATtilage persists it is covered with the Iwnea wluch
iu other allied forms have displaced and absorbed the
underlying cartilnge. The cranium, as already mentioned, is so
•trongly compressed between the orbits that it is divided iuto two
portions, an ethmoid region in front of the eyes and an occipital
tegioii behind them, connected by a narrow sphenoid isthmus
running between them. In the carttlagiuoua roof there are several
membranous windows or " fontanelles," The anterior fontauelle
'lies between the nasal sacs ; the posterior fontanelles are a pair of
windows situated one at each side of the aupra-occipital bone.
400 TELEOSTOUI. [CRAP.
The supra-occipital, two exoccipitaU aod & b&si occipitil
form the hindermost portion of the braiD case suirooiiding die
foramen magnum (Fig. 321) The supra occipital, which is sita-
ated in the mid-dorsal line has a great vertical ndge to which Uk
powerful longitud nal muscles of the body are attached. The
auditory capsule is completely replaced by bone above it is
Fia 221 A donal and B ventral view of the craniam of a SmlmoD Salmo
lala from which moat of the membnuie bones hare been removed After
Fu-ker Cart laKe a dott«d
1. SupmoucipiUI. '2. Epiotic. 3. Pterotic. 4. Sphenotic. 5. Frontal.
6. Meitiun ethmoid. T. Parietal. 8. Lateral ethmoid. 9. Pan-
Bphcnoid. 10. Vomer. 11. Eioceipital. 12. Opisthotio.
IS. Aliflphenoid. 14. Oibitospbenoid. 16. Foramen foi p«8aB^
of an artery. 17. Prootic, 18. Articalar Hnrface for hyomandibolar.
II. VII. IX. X. foramina for the passage of cranial nerres.
covered by a pointed epiotic, in front and below by the pro-
otic, behiud by the opisthotic, and on the out«r side by the
pterotic with which the hyomandibuiar articulates. Od its inner
side the capsule is only separated from the brain by membrane. In
the inter-orbital septum there is an orbito-sphenoid in front, an
alisphenoid behind and a sphenotic above partly extending into
the auditory capsule, while below and behind in the base of tin
I skull there is a Y-shaped hone, the hasi-spheooid, just m front of
" the basi-o
r the
li-occipital (Fig. 292). The ethmoid region i
eyes is the part in which most cartilage persists; it is ossified
above by the median ethmoid and on the aides by the lateral
ethmuids. Connected with the cartilaginous upper jaw there is a
lai^e quadrate bone developed where it articulates with the lower
jaw : an ectopterygoid bone replacing the cartilage on the outer
and an entopterygoid on the inner side; lastly a metaptery-
goid above and in front of the quadrate. The palatine hone is
situated in front of the pterygoid and articulates with the lateral
ethmoid. It ossifies around the anterior part of the on},'ina!]y
Cartilaginous upper jnw. In the lower jaw we have a bone,
'e articular, which moves on the quadrate. In the second
"hyoid" visceral arch we find, as in al! hyoatylic lish,
upper segment, the hyomandibular, articulating with the
skull, and a lower segment, the ceratohyal, which supports the
opercular flap and from which in Teleostei bony rays, called
l>Tnncliiostegal rays, extend, on which the membranous part of
the membrane is stretched, as an umbrella on its ribs, The hyo-
landibular segment is formed, as in almost aU Actinopterygii, of
two bones, an upper hyomandibular, Mmu stricto, uniting with
the sloill. and a lower symplectic joined to the quadrate. The
ceratohyal segment likewise is represented by three bones, a main
ceratohyal, a small interhyal uniting the latter to the symplectic,
aod a hypohyal extending iuwards from its lower end. The two
liypohyals are joined by a median bono, the glossohyal. This
mpporte a projection of the floor of the pharynx which is the
wdtment of the tongne. The other visceral arches are eacli com-
post of four bones, except the last, which is rudimentary. The
nppermost segments extend inwards on the roof of the pharynx
tud bear teeth ; they are called the superior pharyngeal bones.
Owing to the forward slope of the visceral arches these bones are
directly above the seventh or last pair of arches, which consist on
each side of a small bone bearing teeth, the inferior pharyngeal
What^jver chewing is done by fish is effected by these bones,
the teeth in the front part of the mouth are chiefly used for
fetaining prey. The presence of teeth on the gill-arches is not
f ta explain. Teeth, as we have seen, are structures develo[)ed
£roiu the dermis and ectoderm, while the gill-arches support tlie
(raiU of the pharynx, which are certaiidy eudodermal. We must
either sup|)ose that some portion of the ectoderm has migrated
402 TELBOSTOMI. [CHtP.
inwards through the gill-slite or that the endodenn has acqniied
tlie power of producing teedi : on the whole the first suppodtian
seems the more probable.
The membrane-bones in the Teleostean skull are nnmeioas and
are traceable to two sources, namely, the scales of the akin and the
bases of the teeth. To the former category belong tJie loofiog bona
1. Supra-occipital. 9. Epiotie. S. Plerotk. 4. Opiathotic.
5. Eioccipiul. 6. Ban-oedpiuL T. PampkcBoid. B. Sphenotic.
9. .Uupbenoid. 10. Orbilosphenoid. 11. Ectethmoid.
13. Olfaclorc pit : ibr Tomerine WMfa kre Geen jan bdov. 14. Prootic.
13. Bku«pbenoi<L 16. Foremen for the paua^ of ui uterv. 17. Ant.
eriot fonUHlk. lA Po«lvrioi fonUneUe. L IL Y. TIL IX. X.
Fonminm for the p43np* of cmiial nerrcs.
of the skuU. the parietals at each side of the sapia-oecipital,
and the great frontals which cover the antowH- fontandle, but
vhioh al$o extend outwards and roof in the oibita. A pair of
delicate nasal bones lie od the nasal sacs. On tbe »de of the bead
there is a I'hain of bones suTTOunding the eje, called tbe orbital
ring, and four Wne» stiffening the apfa pait of the opercular
flap, a pre-operi-nlom in front, an opercnlnm abon and
behind, a sub->.>peronlum below it, and an inler-operculnm
betwwn the pr*-opeiviiloin and the suK^jfiwcahuiL
Tit the fosioD i«f the baf«s of teeth w« mast ask-tibe the ot^iB of
the ^rm: parasphenoid Kine. whkb sttfteits the roof of the Donth
and exTeni:: Wk nnder tb« basi->wipiial. althoodi ia ma TdeoeCean
d<>ei» it bear leeih. SimilariT. in fn<flt ><£ it thoe is tbe Tomer
mmit <Si tw\i K>aee jtMned in tbe middle ttM^ wbicb stall bcir
XT.] SKELETON. 403
teeth in their anterior portions. The palatine and pterygoid
are also traceable to the fusion of groups of teeth placed more
laterally, but in this case the membrane-boDe has become a
cartilage bone by extending into and replacing the c&rtilagiDous
bar beneath it.
The membrane-bones in the lips, which are essentially character-
istic of the Teleostomi, have probably had a double origin— scales of
Fia. 323, Mandibular and by aid arohea of a Cod, Oadu4 morrhiia x }.
Palatine. 2. Ento -pterygoid. 3. Pterygoid. 4. Qaadrate.
S. Sympleotio. 6. Meta- pterygoid. 7. Eyomaodibnlar. 8. Angnlar.
9. Articalar. 10. Den tar;. 11. Inlerhyal. 12. Epibyal.
13. Ceratobyal. 14. Hypohjal. 15, OloBHohyal. 16. BraDChioBtegal
the outer skin united with teeth developed jnst inside the mouth.
There are, in the upper lip, the pre-maxilla in front, the max-
illa behind, and occasionally behind these a third bone, the jugal.
As we have already seen, the number of these upper lip bones is
greater in the Lepidosteidae. In the lower lip there are in &ont
the dentary, behind and on the inner side the aplenial, and be-
hind and below, the angular. The branchioategal rays mentioned
above are membrane-bones, and between those of opposite sides
there is a mediae bone called the basi-branchiostegal.
TaUng a general view of the skeletons thus Car studied, we see
404 TKLEOSTOMI. [0H4P.
that the replftcement of cartUage by cartilage bone tends to take
place first nherevor there i» a joiut. Thns in Di{iuoi we find the
liinder part of the cranium rcpluced by excK-cipitali^, whereas in the
C'hondroatei, where all the sktill and front part of th<> notochurdal
sheath form one solid mass, uo siinh boneg are developed. Again,
in Teleostei, the oidy repW-ement of the lower jaw by cartilage bnne
1, Bopm^OMipitiil. a. Epiotic, 3. rtcrotip. *. Bphunotic. 5, Prubfal
6. Madim ethmoid. 7. Purietal. 8. Mukl. 9. LbcIiitiiiiJ.
10. Sub-orbiul. II. Sapr&-orbitaI, 13. Citrtil»eiDi>aH B«l«TDtio.
18, Ossification in »olorotiij. li- Bnto-pterygoia, 15. Meta-pt«rj'goid.
16. Pulatine. 17. Jugal. 19. Qnadtnte. 19. MuilU. iO. Prt-
maiilla. 31- Alticulai'. 93. Angular. 33. Dsntary. W. Hyonuui-
dibulnr. 35. Rymplectio. 26. Epihyal. 37. Ceratahnl.
ae. Hypohyal, 39. aloaaohyal. 30. Opercular. 81. Snb-opvroular.
83. Infra. oporauUr. 33. Pro-operonlar. 31. SapratempontL
35. Branohioategal rajB. ao. BaBi-bronohiiwtegiJ.
takes place at its proidmal end, where it joins the upper jaw. Then
again we find the lateral ethmoid develoi«d where the front part
of the palatine articulates with the skull, and the articulation
of the hyouiandibiilar has probably had something to do with
bringing about the oasiticatitm of the auditory capsule.
With the exception of the Gaiioidei all the Teleostomi differ
fundanientally from the Elasmobrsnchii and Holocephali in bavii
avra^J
XV.] DEVELOPMENT AND CLASSIFICATION. 405
small eggs. These rapidly develope into larvae with diphycercal
tails and other primitive features which ally modem
lanra^ *"** fish with the aocieut fossil forms. The development
into the adult is very slow and dangerous, and
during this period an enormous number of the young perish. The
habits, distribution and food of these young form one of the most
important economical problems that zoologists of the present day
are seeking to solve.
Since in the animal kingdom small eggs and a prolonged larval
life constitute the more primitive arrangement, and eggs charged
with yolk and cared for by the parent a secondary modification, we
conclude that in this matter the Teleostei have retained primitive
habits. This throws some light on a question which must often
arise in the minds of all students of zoology, namely, how it is that
comparatively primitive forms, like the Elasmobranchs, and highly
modified forms, like the Teleostei, exist side by side? We can
see that in each case there has been some great modification of the
primitive arrangement, in Elasmobranchs in the egg and young, in
Teleostei in the skeleton and scales. It is improbable that any
living animal preserves all the characters of the common ancestor
of the group to which it belongs ; some traits are preserved in one
case, others in another.
There are some 10,000 species of fish included amongst the
Teleostei. The limits of this work forbid us to
Systematic. , . . - mi i
mention more than a very few, and these will be
chiefly the commoner food-fish. It is possible to separate a number
of families, as Physostomi, distinguished by the two ancient char-
acters of having the air-bladder opening into the oesophagus and
having the pelvic fins abdominal in position, that is to say, placed
far back near the vent. All the rest are termed Physoclisti ; in
them the air-bladder is a closed sac having lost its connection with
the oesophagus, and the pelvic fins have been in nearly every case
shifted forwards and are either thoracic, that is, placed just behind
the pectoral fins, or jugular, that is, placed in front of them.
The families of the Physostomi which we shall mention are the
Cat-fish (Siluridae), the Eels (Anguillidae), the Herrings (Clu-
peidae), the Salmon and Trout family (Salmonidae) and the Carp
family (Cyprinidae).
The Cat-fish receive their name from the peculiar appendages
called barbels which hang down from their upper and under lips.
Other fish may have them on the under lip, but in the Siluridae
TELEOSTOMX
[cHir.
^ iii
3 "c » — ■
i-r.
2 is
I ''a
llll
i ll
-^ till
the maxilla bears no teetli and forms only a support for the great
barbel& The Cat-tiahea are uainly a tropical group abounding
in South America and Africa and nearly all are fresh-water. The
forms with bony scutes are confined to South America, others
are naked and without scales. These as a, rule wallow in the
mud at the bottom of the streams they live in. The teeth are
feeble. The skull is not narrowed between the orbita ; the anterior
vertebrae are fused together and the sub-opercular bone is wanting.
The first ray in the dorsal and in the pectoral fin ia replaced by a
strong spine. Several however of the naked species are found
in North America, two l>eing marine Sea-Oats. Iclalurug is thi-
Whits Cat, an excellent food-fish ranging north to New England,
trus is common in the Eastern States, and one species, the
Bnll-head, A. nebulosus, b fonnd in the St Lawrence.
The CypRiBibAK, including the Carp, Gudgeon, Barbel, are allied
to the Silnridae with which they uj,Tee in having the " Weberian
oi^an." This is a modification of the anterior ribs and vertebrae
to fonn a movable chain of bones connecting the air-bladder and
the internal ear and thus enabling the animal to receive impressions
of the pressure in the bladder. The Cyprinidae differ from the
Biluridae in having typical scales and in wanting the maxillary
barlwl and in having a typical skull. Caras/iius awratiis, the Gold-
, belongs here.
The Anocillidae or Eels are long cylindrical creatures with
either small deeply imbedded scales or none. The dorsal, ventral
and caudal fins are contiguous, the pelvic fins being absent The
408 TELEOSTOMI. [CHAP.
skull resembles that of the Cat-fish in not being narrowed between
the orbits, and in having only one or two bones in the giU-
cover. Eels spawn in the sea. Anguilla, the common eel, ascends
streams and even crosses wet grass to get to isolated ponds;
it has small scales. Echelus {Conger)^ the conger eel, is entirely
marine, and devoid of scales ; it attains a length of six feet The
eggs of both species develope into a peculiar ribbon-shaped larva
with colourless blood and slightly developed tail called Lepto-
cephalus.
The Clupeidae or Herrings are distinguished by the fSsu^t that
their maxillae bear teeth and form part of the edge of the jaw, and
further that the maxilla is really composed of two or three pieces
placed end to end, recalling the condition in the Lepidosteidae.
The tail-fin is forked. The genus Clupea, with compressed belly
edged by projecting scales, includes not only the Herrings, which
come in shoals to the English and Scotch and American coasts to
spawn, but also the Shad, a high-backed herring, which frequents
the coasts of Canada and New England and which spawns in the
rivers. The eggs of Clupeidae, as a rule, are large and heavy and
sink to the bottom, unlike those of most Teleostei, which float at
the surface of the sea. The Anchovy, with a projecting snout, and
a rounded belly, the Pilchard and the Sprat also belong to this
family. ITie Sardine is the young Pilchard.
The Salmonidae have a toothed maxilla and a jugal bone in
the upper lip and a small soft fin devoid of rays behind the dorsal,
called the adipose fin. In the female the oviduct has disappeared,
the eggs escaping by two pores. The genus Salmo includes the
well-known Salmon, which ascends rivers to deposit its spawn, and
also the Brown River Trout of Europe, which is permanently
confined to fresh-water. The brook-trout of North America belongs
to a diiferent genus, Salvelinus, and the great King-Salmon of
British Columbia, canned in such enormous quantities, is Oneo-
rki/ncus tschawytscha. From a sportsman's point of view it is
distinguished from the true Salmon by the circumstance that it
does not take the fly. Coregonus, the White Fish of the great
American lakes, much esteemed for its delicate flavour, also be-
longs to this group. The habit of ascending the rivers to spawn
probably points to the conclusion that the whole group was origin-
ally fresh-water, and that the Salmon is a river fish which has
taken to the sea, whereas the Eel is a salt-water fish which has
taken to fresh-water. Whether all the Herring family were ever
XV.]
CLASSIFICATION.
409
firesh-water or not is doubtful, but it is interesting to note that
the Pilchard has a small floating egg.
The great division of the Physoclisti includes five main sub-
divisions, the Anacanthini, the Acanthoptebj, the Pharyn-
oooNATHi, the LoPHOBRANCHii and the Plectoqnathi. The
last two groups are in some respects aberrant.
I. The Anacanthini have all the fin-rays soft and flexible
and the pelvic fins are shifted forward in front of the pectorals.
The Oadidae are the Cod family and include the Cod, Haddock,
Whiting and Pollack. These fishes spawn out at sea, one female
cod producing as many as 9,000,000 eggs. The Pleuronectidae, or
flat fish, also belong here. They are fish with compressed backs
and bellies, and broad sides ; they habitually swim on one side, and
the eye belonging to the side kept downwards is twisted on to the
upper side which deforms the bones of the skuU. The anus is very far
forward, the dorsal and ventral fins both being about equally long ;
the air-bladder is absent The most valued member of this family
in British water is the Sole, Solea^ distinguished by its elongated
shape. Other food-fish belonging to this family are the Flounder,
the Plaice, the Turbot, the Brill and the Dab. On the coasts of
Europe and of North America is found the immense Halibut,
HippoglcsstiSy which may attain a length of 6 feet and a weight of
400 pounds.
Fio. 227. PUuronectes platessa, the Plaice, found from the coast of France to
Iceland.
, 410 TELEOSTOML [CHlP.
II. The AcANTHOPTERi are the spiny-nyed fiah in which the
first rays of the dorsal and ventral fins are converted into bony
dermal Bpines. Many fiunilies of most varied stroctnre are inc^aded
in this subdivision : the tvo best known are the Scokbbidae, in-
cluding the Mackerel and the Pekcidab or Perches. Tha first are
distinguished by the Bmall dorsal fin
supported by spines only, followed by
a long dorsal fin the end of which ii
broken into finleta. In the Percidae
the scales have a toothed posterior
border, that is, they are ctenoid and
the first BpiDOUB dorsal fin is long.
The American fish called Baas belong
to two families, the river-bass being
one of the Centbarcuidae, dieton-
guished by high compressed body and
nndivided dorsal, whilst the sea-basa
belongs to the Serkanidab, a family
closely allied to the Perchea
III. Tha PHARYIfGOaifATHlhwt
the lower pharyngeal bones firmly
united with one another. This division
includes the Labridag or Wrasses, dis-
tinguished by their thick lips and
protrasible prem&xillae ; the Triglwae
or Gurnards, which walk on the spines
of the pectoral fin ; the Gobudae aod
many other small fish.
IV. The LopaoBRANCHii are
peculiar fish covered with rings of
lai^e plates ; their gill processes are
h„ b„„ morf ISStS, cl«b-sh.ped instead of tri.ngul.,, .nd
tbe gillB. are attached in tuits to the side of the
1. Branchial aperture. 2. Pee- clefts ; there are no pelvic fins and
S™i,«,.ch: Tom;: thet.il-fioi.rudimenl.ry. The j...
bones, the pterygoid and maxilla, are
elongated so as to form a long muzzle at the end of which is the
tiny mouth. St/ngnathtis is the Pipe-fish which moves slowly
amongst the long green fronds of the green sea-weed Zostera, which
it resembles, picking off minute Crustacea and Molluscs. It b
common both on the British and American coasts. Hippocampu»,
Fio. 22a. A. The Sea-horse,
Hippocampus 9p. B. Head
of the B
XV.] CLASSIFICATION. 411
the Sea-horse, has the muzzle bent down at an angle with the rest
of the body so as to present a whimsical resemblance to a horse's
head. It anchors itself by curving its tail round weeds, and swims
slowly but with dignity by means of the dorsal fin. This genus is
found in the Mediterranean, on the southern parts of the American
coast and elsewhere. The Lophobranchii show a peculiar mode of
caring for the young ; the male has a brood pouch enclosed by two
folds of skin on the underside of his body in which he carries the
eggs until they are hatched.
V. The Plectognathi resemble the Lophobranchii in being
covered with plates instead of scales and in having lost the pelvic
fins. The pelvic fins are represented by spines or are entirely
absent. The pre-ma2dlla and hyomandibular are immovably fused
to the skull, while the inferior pharyngeal bones remain distinct.
In Ostracion, the trunk-fish, the plates form as compact a cuirass
as the shell of an Echinus : the only flexible spots being around the
articulations of the fins and the lower jaw. In Diodon and Tetro-
don the teeth have coalesced to form great transverse ridges of
enamel, and the dermal plates bear spines which are usually directed
backwards, but which are erected when the body is rendered tense
by swallowing air into the gullet and stomach. These extraordinary
fish are confined to tropical waters ; they haunt small crevices of
the rocks, in which, when the tide retires, very small quantities of
water are left, and it appears that the giUs absorb oxygen fi*om the
air they swallow.
The Pisces are classified as follows :
Order 1. Elasmobranohii.
Pisces devoid of air-bladder or lung ; with placoid scales ;
no bones developed except at the bases of these scales.
Cartilaginous centra formed by the division of the notochordal
sheath and not corresponding to the neural arches. The jaws
slung to the skull by the second arch. No operculum : well-
developed gill-sacs present.
Sub-order (1). Selaohoidei.
Elasmobranohii of cylindrical form with well-developed tail-
fin and pectoral fins of moderate size. Spiracle small or absent.
Ex. Carcharodon^ Scyllium, Acantkias.
Sub-order (2). Batoidei.
Elasmobranchii of flattened form, the tail whip-like and the
412 TELEOSTOIO. [CHAP.
taQ-fin rndimeiitaiy, the pectoral fin veiy large and joined to
the skulL Spiracle veiy large and opening on the doial
snrface, openings of the other gill-slits ventral.
Ex. Rata, Trygon,
Order 2. Holocephali.
Pisces devoid of air-bladder or lung ; the skin naked, a
series of slender bony rings in the onsegmented notochordal
sheath, besides this no other bones. Upper jaw completely
confluent with the skolL An operculum present, well-developed
gill-sacs.
Ex. Ckimaera.
Order 3. Dipnoi.
Pisces with a large lung, sometimes divided into two,
opening by a ventrally situated glottis into the oesophagus:
the atrium of the heart divided into two, the left division
receiving blood from the lung only. The body is covered with
thin flat scales. Membrane-bones covering the skull and roof
of the moutL Cartilage bones in the upper jaw and in the
hinder region of the skull, but the notochordal sheath is
undivided. The upper jaw completely fused with the skulL
An operculum present, the septa between the gill-sacs reduced
so that they become gill-slits.
Ex. Ceratodus, Lepidosireti, Protopterus,
Order 4. Teleostomi.
Pisces with an air-bladder which returns blood into the
cardinal veins, the atrium of the heart being undivided. The
sheath of the notochord sometimes remains undivided, but
when centra are present they are formed by the fusion of the
expanded bases of the neural and haemal arches, not by
the segmentation of the sheath of the notochord. Membrane-
bones in the skull and roof of the mouth, and in addition
a series in both upper and lower lips bearing teeth, situated
outside and replacing functionally the original jaws. Cartilage
bones in the jaws and skull. The upper jaw slung to the skull
by means of the hyoid arch. A well-developed operculum
present : the septa between gill-sacs are so narrowed that they
form gill-slits with long branchial processes. The cloaca divided
into two openings.
XV.] CLASSIFICATION. 413
Sub-order 1. Crossopterygii.
Teleostomi in which the pectoral and pelvic fins have the
form of a lobe covered with scales fringed anteriorly and
posteriorly with fin-rays. The air-bladder is bilobed and its
opening is ventral. The scales are rhomboidal and covered
with enamel
Ex. Polyptertis.
Sub-order 2. Actinopterygii.
Teleostomi in which the paired fins bear rays only on their
posterior borders and in which the base of the fin is never
covered with scales. The opening of the air-bladder is dorsal.
Division A. Ganoidei.
Actinopterygii which retain the optic chiasma, several rows
of valves in the conus arteriosus and a spiral valve in the
intestine. A heterocercal tail
Subdivision (1). Chondrostei.
Actinopterygii clothed with large bony plates which
pass uninterruptedly into the membrane-bones of the
head, the notochordal sheath undivided ; very few cartilage
bones. A long snout projecting in front of the mouth.
Teeth rudimentary.
Ex. Acipenser.
Subdivision (2). Halecomorphi,
Actinopterygii with thin scales ; many cartilage bones
and the notochordal sheath surrounded by well-formed
amphicoelous vertebrae. Mouth terminal.
Ex. Amia,
Subdivision (3). Lepidoateidae,
Actinopterygii with rhomboidal scales covered with
enamel; the skull completely ossified and the vertebrae
opisthocoelous. Jaws very much elongated, each carrying
a row of long teeth.
Ex. Lepidosteus.
414 TELE0S1X)MI. [CHiF.
Division B. Teleostei.
Actinopterygii in which the optic nerves cross without
intermingling, the conus is absorbed into the ventricle, leaving
one row of valves. No spiral valve in the intestine. A
homocercal tail.
Section 1. Physostomi.
Teleostei which retain the opening of the air-bladder
into the alimentary canal ; the pelvic fins are abdominal in
position.
Family (1). Siluridas,
Physostomi with a skin naked or covered with bony
plates ; the skull unconstricted between the orbits, maxilla
without teeth and bearing a long barbel. Weberian chain
present.
Ex. Amiurus, Ictalurus.
Family (2). Cyprinidae.
Physostomi with scales, the skull is constricted between
the orbits, maxilla without teeth or barbeL Weberian
chain present.
Ex. Cyprinus,
Family (3). Anguillidae,
Physostomi devoid of scales^ skull not constricted
between orbits. Weberian chain absent. No reproductive
ducts. A continuous dorsal-caudal-anal fin and no pelvic
fins.
Ex. EcheluSy Anguilla.
Family (4). Salmonidae.
Physostomi with thin scales, the skull constricted
between the orbits, the maxilla forming part of the edge
of the jaw and bearing teeth. A small soft dorsal fin
behind the main dorsal.
Ex. Salmo, Salvelinus, Oncorhyncus,
Family (5). Clupeidae,
Physostomi in most points resembling the last family ;
the maxilla consists of several pieces and there is no soft
dorsal fin.
Ex. Clupea,
XV.] CLASSIFICATION. 415
Section 2. Physoclisti.
The remaining sections of the Teleostei have lost the
opening of the air-bladder into the alimentary canal, so that
it becomes a closed vesicle.
Sub-section 1. Anaoanthini.
Teleostei in which the fin-rays are all soft and flexible, and
the pelvic fins are shifted forward anterior to the pectorab.
Family (I). Gadidas,
Anacanthini of 83nnmetrical shape and not especially
compressed.
Ex. Gadtis.
Family (2). Pleuronectidae.
Anacanthini very much compressed laterally, which
swim always on one side : the eye belonging to the lower
side being rotated on to the upper side.
Ex. Solea^ Flatessa, Hippoglossus,
Sub-section 2. Aoanthopteri.
Teleostei in which some at least of the fin-rays of the
median fins are hard and unjointed.
Family (1). Scombridae.
Elongated Acanthopteri in which there is a short
spinous dorsal fin followed by a long softer one, the hinder
portion of which is broken up into finlets.
Ex. Scomber,
Family (2). Percidae.
Short stout Acanthopteri with one long dorsal fin fol-
lowed by a short one and having a toothed posterior border
to the scales.
Ex. Ferca,
Family (3). Serranldae (Sea Bass).
Closely allied to the Perctdcw^ but distinguished by
having the dorsal fin undivided. Teeth large and numer-
ous ; a large pseudobranch.
416 TELEOSTOMI. [CHAP. XV.
Family (3). Centrdrchidae (River Bass).
Acanthopteri which have a laterally compressed body
and undivided dorsal fin. Teeth small; a small pseudo-
branch.
Sub-section 3. Pharyngognathi.
Teleostei in which the bones (rudimentary fifth gill-arches)
bearing the pharyngeal teeth are firmly united together.
Ex. Lahrus,
Sub-section 4. Lophobranchii.
Teleostei covered with bony plates, the &cial bones elon-
gated so that the jaws are at the end of a tube-like proboscis.
The branchial processes are arranged in tufts and thickened at
their firee ends. The pelvic fins absent.
Ex. Syngnathus, Hippocampus.
Sub-section 5. Plectognathi.
Teleostei covered with bony plates, the pre-maxilla and
hyomandibular immovably joined to the skull. The gills
normal. Pelvic fins absent or represented by spines.
Ex. Ostracion, Diodon, Tetrodon,
417
CHAPTER XVL
Sub-Phylum IV. Craniata.
Glass II. Amphibia.
The class Amphibia includes the familiar frogs and toads, the
less-known newts and salamanders, and some very
ofthe'cuM!* curious worm-like tropical forms which burrow in
the earth. The name means double life (Gr. oifi<l>i,
double ; fiio^, manner of living), and refers to the fact that all the
typical members of the class commence their lives as fish-like larvae,
breathing by gills, and afterwards become converted into land
animals, breathing by lungs. This strongly marked larval type of
development is one of the great distinctions between the Amphibia
and the only other class of Vertebrata with which they could be
confounded, viz., the Reptiles. In the Reptiles, as in the Birds, a
large egg abundantly provided with nutritive material is produced,
and the young animal practically completes its development within
the egg-shell and is bom in a condition dififering from the adult
chiefly in size.
It might at first sight be thought that the fact that Amphibia
breathe air in their later life and live on land would be sufiicient to
mark them off from the fisL But we have already seen that one
order of fisli — ^the Dipnoi — possesses lungs and breathes air, and on
the other hand some Amphibia retain gills throughout life and
rarely if ever leave the water.
The unbridged gap between true fish and Amphibia is to be
found not in the breathing organ but in the structure of the limb.
Fish possess fins — median and paired — which are in both cases
supported by homy rays, as well as an intemal skeleton ; and the
paired fins have an intemal skeleton which has the form of a jointed
axis bearing similar rays on one or both sides (Figs. 205 and 215).
& &M. 27
418
AMPHIBIA.
[chap.
B
The Amphibian limb, on the other hand, is what is known as a
pentadactyle limb; that is to say, it is constructed on the fiamiliar
type of the human limb, and the median fin when present has no
fin rays (Figs. 229 and 231).
The pentadactyle or five-fingered limb (Gr. tcktc, five ; SaKrvXoi a
finger), also called the cheiropterygium (Gr. x^^* ^ hand; vrcpv-
yiov, little wing, hence an appendage), consists of three segments, a
proximal, containing one long bone ; a middle, containing two bones
placed side by side and occasionally fused into one ; and a distal,
containing a series of small squarish cartilages or bones arranged in
lines so as to give rise to a series of diverging rays ; the last-
mentioned constitute the skeleton of the fingers and toes. In the
proximal part of this lowest segment the bones are much crowded
together and the rays tend to coalesce : this part has received a
special name, as has also the portion where the rays although
separate are embedded in the same muscular mass.
The fore-limb is called
the arm, and its divisions
the brachium or upper
arm, the ante-brachium
or fore -arm, and the
manus or hand (b, Fig.
229). The hind limb is
the leg, and its divisions
are the femur or thigh»
the crus or shank, and the
pes or foot (a, Fig. 229).
The manus is divided
into three regions, viz. :
(a) the carpus or wrist
where the rays tend to
coalesce; (6) the meta-
carpus or palm where the
rays although separate are
bound together by flesh
and skin; (c) the digits
or free ends of the rays.
The pes is similarly divided into tarsus or ankle, metatarsus
or sole, and digits or toes.
The bone of the brachium is called the humerus, that of the
femur bears the same name as the segment to which it belongs;
Fio. 229. A. A skeleton of a right posterior,
and B of a right anterior limb of a Newt,
Molge cristata x 1).
1. Femur. 2. Tibia. 3. Fibula.
4. Tibiale. 5. Intermedium. 6. Fibu-
lare. 7. Gentrale of tarsus. 8. Tarsale 1.
9. Tarsalia 4 and 5 fused. I. U. III. IV.
y. Digits. 10. Humerus. 11. Radius.
12. Ulna. 13. Badiale. 14. Intermedium
and ulnare fused. 15. Gentrale of carpus,
the pointing line passes across carpale 2.
16. Carpale 3. 17. Carpale 6.
['thaw of the ante-brachium are called radius and ulna, those M
the crus tibia and fibula (Fig. 229).
The akeletonfl of the pes and manua are typically exactly the
same. Situated proximally close to the middle segment of the limb
is a transverse row of three small bones, the central one being called
the intermedium in both limbs, whilst the outer and inner are
named after the bones of the middle segment of the limb adjacent
to them. Thus we find in the wrist a radiate and ulnare and
in the iiuUle a tibiale and fibnlare. Beyond this row of bonea
there is a tingle central bone which probably belongs to the middle
ray, and beyond it a row of five small bones corresponding to the
digits. This last row are denominated carpalia in the wrist and
tarsalia in the ankle. The individual bones are called carpale
(or tarsale) 1—5 in accordance with the digits opposite which they
are situated.
In almost every case this typical skeleton of nine bones has
onderguoe some modification, owing either to the absenL-d of some
bones or the fusion of others, but in the hind-limb of the lower
Amphibia it la exactly typical. In the higher Amphibia not only
has great reduction of the elements taken place but the radius and
vlna in the fore-limb and the tibia and fibula in the hind-limb have
coalesced, a groove only being left to show their primitive distinct-
ness.
The primitive position of the limbs with reference to the trunk
is, from the study of development, assumed to be one in which they
are stretched out at right angles to it, with the inner surface of the
hand and the sole of the foot directed ventrally and iu such a
position that a line joining the tips of the fingers is parallel to tbe
long ana of the body. If we suppose an imaginary line or axis to
run down ttie centre of each limb, we sball be able to distinguish a
pre-axial from a post-axial aide. In the lower Amphibia the only
change from this position tliat has taken place in the hind-limb is
tliat each segment of the limb is bent at right angles on tiie one
vhich follows it. The fore-lirab is bent similarly, but it is also
rotated backwards so that its upper segment is almost parallel to
the axis of tlie body, and the etbow points backwards. If this
position were maintained the first digit would become e.\teriial; but
the manus in most cases is at the same time twisted forwards so
that the lower end of the radius lies intertial to that of the ulna,
and the raditia thus crosses the ulna in its course. In the higher
Vertebraia this iwialing can be undone and tlie hauii reverteti to
27-2
420
AMPHIBIA.
[CHAP.
an untwisted position. This movement is known as supination,
the reverse movement being known as pronation.
The hind-limb in the higher Amphibia and
other Vertebrata is likewise rotated forward so
that the knee points forward and the first digit
is internal, but this does not occur in the lower
Amphibia, such as Molge.
The pectoral girdle is not essentially dif-
ferent in the lower Amphibia and the more
primitive Teleostomi, but the pelvic girdle is
firmly joined to the transverse process of one of
the vertebrae, which is called the sacraL This
is one of the most distinctive features of all
pentadactyle animals ; it is a consequence of
the adaptation of the pentadactyle limb to raise
the body from the ground (Fig. 230). It is
necessary for this purpose that the limb shoidd
have a firm purchase on the axial skeleton.
Consequently when we find some Amphibia
which never use their limbs for crawling but
only for swimming, we assume that this is a
secondary degenerate condition.
Next to the character of the limb one of
the most distinctive features of Amphibia is
the nature of the skin. Indeed the five great
classes of Qnathostomata— Fishes, Amphibia,
Keptiles, Birds, and Mammals — are each per-
fectly characterised by the nature of their skin.
In a typical Amphibian the skin is soft and
moist and devoid altogether of any ossifications
like the scales of fishes. The skin is a most
important breathing organ, since the lung alone
cannot meet the demand for oxygen, and if the
skin becomes dry and consequently incapable
of absorbing oxygen the animal dies. The
necessary moisture is supplied from a series of
pockets, to form which the ectoderm is pouched
inwards — or to use a more convenient term
* invaginated* — at various points, and the ceUs
lining these pouches have the power of secreting
great quantities of mucus. As the cells become
Fio.230. Skeleton 0
Triton, Molg€ cm
(otaxl.
lO
SKULL AND VERTKBBAL COLCMN.
421
broken np into mucua, Dew e«lls take their place, being biiddeJ off
from tLe underlying Malpighian layer just &s the horny cells are.
These pouches are known as dermnl glands.
The skiill and brain are very characteriptic, recalling in many
points those of the Dipnoi. The axis of the brain appears straight,
as in fishes; in higher Vertebrates this axis is more or less folded.
In contrast, however, with fishes, the cerebral hemispheres of the
fore-brain are relatively large, whereas the cerebellum, usually so
large in fishes, is reduced to a mere band (Fig. 240).
The skull always articulates by two pegs — the occipital con-
dyles— with the first vertebra (Fig. 2a2). It is remarkable for its
extremely flattened shape; the jaws are widely bent outwards so
that the large eyes in no way compress the cranium, which is
thus evenly cylindrical Both membrane- and cartilage -bones are
present, but the ossification is by no means complete. The exact
arrangement of the bones will be given when a type is studied.
The vertebrae are either procoelous (Qr. xjio, in front; koiXot,
hollow), or opisthocoelous (Gr. ointrflo-, behind), that is to say either
concave in front and convex behind, or vice mrsil, and the arrange-
ment may difi'er in allied genera, while amphicoelous vertebrae also
occur.
The vertebrae articulate with one another, not only by the
centra but also by facets called aygapophyses (Gr, ^uyo'v, a yoke),
on the aides of the neural arches. The anterior facets, pre-zygapo-
physes, look upwards and are covered by the posterior facets or
jiost-zygapophyses of the vertebra in front, which look downwards.
The circulatory system closely resembles that of the Dipnoi.
The atriiira is divided into two auricles, and the blood from the lungs
returns direct to the left auricle by the pulmonary veins. A median
▼ein, the inferior cava, returns the blood from the kidneys directly
into the sinus venosus, receiving in its course the hepatic vein.
The anterior portions of the posterior cardinals are much reduced
in size and may be altogether absent.
The lungs open by a common Ht«tn. the laryngeal chamber, into
the throat. The opening is called the glottis, and it« sides are
stiffened with cartilage.
The kidneys and reproductive organs show essentially the same
arrangement as in the Elasmobranchs, the kidney being divided into
B, sexual part connected with the testis and a posterior non-sexual
part. There is one opening for all cjecta. the cloaca.
The ventral wall of the cloaca, however, is produced outwards
422 URODELA. [chap.
into a great thin-walled sac, the allantoic bladder, in which when
the cloaca is closed the urine accumulates. This organ acquires
immense importance in the development of the higher animals and
is found in no fish.
In the larva, which is to all intents and purposes a fish, there are
present those peculiar sense organs called mucous canals, suppUed
by the 5th and 10th nerves, but these are usually lost in the adult
Living Amphibia are divided into three well-marked Orders, vi^
the Urodela, the Anura and the Afoda. The
Urodela (Gr. ovpd^ tail; 817X09, conspicuous) have
long cylindrical bodies and long flattened tails. The limbs are
short and comparatively feeble, barely strong enough to lift the
belly from the ground. Both pairs of limbs are about equal in
size. The Anura (Gr. av-, no; ovpd, tail) have much broader and
shorter bodies; the tail is totally lost and the hind limbs are
powerfully developed and adapted for jumping. The Apoda (Gr.
a-, no, voSa, feet) have lost both pairs of limbs and their cylindrical
bodies give them a worm-like appearance; their habits heighten
the resemblance since they burrow in moist earth. They have
embedded in the skin small bony plates, relics of the scales which
their Stegocephalous-like ancestors once possessed. The tail has
in these animals almost disappeared.
In the Carboniferous rocks the remains of a large number of
Amphibia have been found which have been called Stegooephala
(Gr. arcyos, a roof ; #c€<^aXi7, the head) firom the circumstance that
the head is covered with a compact mosaic of membrane-bones
extending from the mid-dorsal line of the cranium outwards to
the lips. Similar small boDes or scales are found on the ventral
surface. These features bear resemblances t6 what is found in
Dipnoan or Crossopterygian fish from which Amphibia have probably
descended, and the small scales of the Apoda seem to be the last
remnants of this armature. Stegocephala include both long and
short tailed forms, and while some of their descendants — the Laby-
rinthodonta — became highly specialized in the structure of their
teeth and died out in the next geological period, others, in all
probability, gave rise to modern Amphibia.
URODELA.
Returning to the Urodela, which are the most primitive of
modern Amphibia, we find that in Great Britain they are represented
by three species, all belonging to the genus Molge {Triton) and
poiiularly known aa efts or newts. Mutge crletata, the warty eft,
and Molge vulgarU, the lonimou eft, are found m ponds and ditc)ies
all oyer the country, but Slolqg pitlmata is nmuh more local. We
may sele<.'t Molt/e cristala, the greater r warty ett or creeted newt,
as a type of the aaatomy of T r iel Fit, i 1
Via. 231. Motge criilala, the Warty Eft. From Qadov.
Female. 2. Male at the breeding aeaHoD with the frills well developed.
llie auimal in about five or six iDcbes long, half the length being
made up of the tail, which has a continuous fringe of akin, the
median fin. This tin in the male extends forwards to the head
dorsally and is greatly enlarged in the breeding season, but it is at
all times devoid of tin rays,
The akin is clammy, owing to the secretion of the dennal glands:
) dark coloured above and yellow sjjotted with black below. The
oitening of the cloaca is placed behind the hind leg^: it is a
longitudinally placed oval slit which in the male has thickened lips.
The fore-limbs have only four lingers, the innermost corresponding
to the human thumb being wanting, but there are five toes in the
hind-limb. The animal when out of water crawls feebly along, but
it awim.s actively in the wat«r by means of its vertically flattened
tail. The head is flattened dorao- ventral! y and of somewhat oval
outline, and the gape is of moderate e-vtent. The eyes are small
and project but little. The nostrils are very small and situated
at the extreme front end of the snout.
If the newt be carefully watched when out of the water the skin
of the underside of the head between the two sides of the lower
jaw will be seen to throb at regular intervals, being alternately
424 URODEUL [chap.
paffed out and drawn in. It can be further seen that the nostrils
are closed when the skin is drawn in and opened when it is paffed
out. These movements constitute the mechanism of breathing in
the newt. As in the case of the Dipnoi, the paired nasal sacs
communicate with the interior of the mouth by an opening called
the choanae or internal nares, and the air passes through these
from the nostril when the cavity of the mouth is enlarged. When
the cavity of the mouth is compressed the nostril is closed by a flap
of skin constituting a valve, and the air is forced through ihe open
glottis into the lung, whence it is forced out again by the elastic
recoil when the pressure is removed.
If the animal be laid on a board with the ventral side uppermost
and skinned, a thin sheet of muscles, the mylo-hyoid, will be seen
stretching between the two halves of the lower jaw. When this
muscle is relaxed the floor of the mouth is arched upwards and the
underside of the head consequently becomes concave. When the
muscle contracts and straightens the cavity of the mouth enlarges
and air is drawn in. Above the mylo-hyoid (underneath from the
point of view of the dissection) are two longitudinal muscular
bands, and in these are embedded the reduced remains of the
visceral arches to which the gills of the larva were attached
(Fig. 233). These muscles are called genio-hyoid in front of the
arches, sterno-hyoid between them and the pectoral girdle, and
they are continued backwards along the belly as the straight muscles
of the abdomen, the recti abdominis.
These sterno-hyoid muscles can draw the visceral arches
downwards and backwards and probably assist the mylo-hyoid in
depressing the floor of the mouth. The genio-hyoid muscle on
the contrary pulls the arches forwards and helps to restore them
and the floor of the mouth with them to their old position. In this
action muscles called petro-hyoid, which run from the arches to
the outer surface of the auditory capsule, also take part. These
muscles are representatives of the levatores arcuum of fish, and
they raise the arches and consequently the floor of the mouth.
The glottis or opening into the lungs is stiffened at the sides by
a pair of cartilages, which it seems probable are the remains of a
hinder pair of visceral arches : and these cartilages have masdes
attached to their sides which drag them apart and which belong to
the same series as those which raise the arches. Hence the same
muscular action which lifts the floor of the mouth opens the glottis
and admits air into the lungs.
XTLl
425
The remaining muscles of the body are not much altered from
those of the fish. In the tail and the ventral part of the trunk
there are V-shapeil myotomes, but this arrangement is distnrbed in
the neighbourhood of the limbs.
Turning oon to the skeleton we find that the vertebrae bear
stout transverse processes with which are articulated
short rib? (Fig. -^30), The ribs borne by the sacral
vertebra are expanded in accordance with the strain put on them
by the attachment of the ilium. Of the vertebrae those of the tail
are the most primitive since they are composed of all the four
arcualia ; but of these only the basi-dorsalB and the basi-ventraJB
become ossified, and joining together form the bulk of the vertebra,
vhile the inter-dorsals and inter-ventrals, although likewise fusing
together, remain cartili^nous and form the inter- vertebral cartilage.
This either remains continuous and owing to its Bexibility acts as a
joint, or it becomes more or less separated into a cup-and-ball portion.
Joint)! in which the cup belongs to the posterior end of the vertebrae
are called opiathocoelous, eg., in Desmotfitatkim trlton. The basi-
veutrals of the tail vertebrae form long downward haemal arches.
In the trunk the basi-ventrals occur only in early larvae ; in the
Bdult they have disappeared so that the bulk of such vertebra is
formed only by the i>air of" basi-dorsals which alone cany the ribs,
and these to compensate the loss of their capitular process have
guued a new process dorsally &om the tuberculum.
It is of importance to note that in many of the extinct
Stegocephala, e.g., Arctwiiimtunia, the caudal vertebrae were repre-
sented by four pairs of distinct arcualia. wiiile tlie trunk vertebrae
consisted of three separate pairs of pieces, namely the basi-dorsal,
the inter-dorsal and the basi-ventral ; but that in the typical
Lahyrinlhodouta, the highest of the Stegocephala, all these constitnent
pieces were formed into solid vertebrae ; lastly, that in some of the
loweBt, e,g., in Branckiosaurus, each vertebra consisted of a thin
shell of bone surrounding the chorda, and composed of the basi-
duntals and basi-ventrala, which met each other, forming a broad-
based section along the side of the vertebra, both partaking in the
formation of a transverse process which carried tiie rib. The haemal
•rches of the tail are, like the rfba, outgrowths of the basi-ventral,
bat they do not exactly correspond to the ribs, for they are placed
rer the middle line.
In the skull the cranium is cylindrical, being (juite uncom-
pressed between the eyes. The bones of the jaws and £ace are
426 UBODELA. [chap.
widely arched outwuds, bo that the whole skull has a flattened
shape. The nasal aud auditory capsules form easily rect^iuUt
buttresses projecting from the cranium.
Id both the floor aod roof of the cartilaginous craoinm the
proper wall is largely deficient. The deficiency of the roof is the
Fto. 333. A doraal, B ventrtl, and C lateral ti^wb of the skull of a Newt,
Molge ciiitala x 2}. After Parker.
The oartilage ie dotted, the cartilSfte-boiieB are marfced with dotg and daahea, the
membrane- bones are left white.
1. Premaiilla. 3. Anterior narea. 3. Posterior narCK 4. NaaL
G. Frontal. 6. Parietal. 7. Prefrontal. B. Maxilla. 9. FoKd
Tomer and palatine. 10. Paraaphenoid. 11. Orbito«pbenoid.
13. Pterygoid. 13. Squamosal. 14. Pro-otia region of fiiaed eioocipital
and prO'Olic. 15. Quadrate. 16. Calcified cartilage forming the
articular eiirface of the quadrate. 17. Eioceipital regioD of foied
eioccipital and pro-otio. 18. Articalar. 19. Artienlat outilagb
30. Dentary. 21. Splenial. 23. Middle narial passage, a cleft in
the cartilage of the snont filled with connectiTe limoe. IL T. Til. IS.
X. Foramina for the eiit of cranial nerves.
anterior fontanelle, in the floor the greatly enlai^ed pituitary fossa.
But these deficiencies are not seen in the uninjured aknll, because
the hole in the roof is closed in by two pairs of membraoe-bones, the
front&ls and the parietals, and that in the floor ia nnderiaid by
a broad parasphenoid membrane-bone (Fig. S3S).
Unly at its extreme front and hind ends is the wall of the (^aniam
converted into cartil^-bone. In Jront there is oa each aide w
XTt] VISCBBiX AIICHSS. 427
urbito-Bpheo Old bone, in the side wall, extending ioto tlie roof and
floor and ossifying also the hind wall of the nasal sac ; behind, two
exocoipital bones' areplacedat the sides of the forfunen magnum,
which Uiey nearly encircle (Fig. 232). These bones bear the two
condyles, so characteristic of Amphibia, for articulation with the
vertebral column.
The iirat viac^al arch, which constitutes the cartilaginous jaws, is
almost entirely cartilaginous. It consists of an upper part immov-
ably attached to tJie skull, corresponding to the ptery go-quadrate
l)ar or upper jaw of Fish, and a lower part, Meckel's cartilage,
forming the basis of the lower jaw. It will thus be seen that
Amphibia, like Holocephali and Dipnoi, are autostylic. The same
is true of all the higher groups of the Craniata. The upper jaw
consists of two regions, the suspensorium which is fused with the
skull and to which the tower jaw is attached, and the pterygoid
process, a spur of cartilage which runs
forward towards the nasal capsule.
Both suspensorium and the articular
end of Meckel's cartilage are slightly
calciHed. They are denominated quad-
rate and articular in Fig. 2S2, but
there is no true bone present in either
case. The front of the auditory capsule
is ossified by a large bone, the pro-otie,
which in fully adult specimens becomes
confluent with the exoccipital. The
hinder visceral arches in the adult are
present in a very degenerate condition.
Traces of three remain (Fig. 233).
It is usual to speak of the hinder
visceral arches of Amphibia and higher
Vertebrata nn the hyoid apparatus,
simply as the hyoid. The name suggests a misleading com-
parison with the second visceral arch of Fish; it is distiaclly to be
Temembered that the hyoid bone of even Man contains more than
this second arch; a good definition of the hyoid of Amphibia and
higher animals would be "the degenerate remains of the hinder
visceral arches,"
Turning now to the membrane-bones of the skull, we find that it
Fin. aU3. Visfleral archea of
Molfff crittata. The ngsified
parts are Klightl; shaded, the
cartilage ia white. From
Parker.
2. Hyoid arah, 3. First
ViranchiBl arch. 4. Second
branchial aroh. 8. Oopula,
i.e. the median piece coDoeat-
Ing sucoeBaive sccheB.
are equiralent to the lateral o
It oooipitalia exteroa.
tipilaU. Tlia
428
[chap.
is roofed by three p&ire, viz., the n&saU, frontala uid p&rietali.
The nasals of course roof in the nasal saca. In the palate then ti
one median bone, the parasphenoid, and three pairs of lateiil
bones, viz., the vomers in front of the posterior uares, Ha
palatines fiised with them and ruouing along the edges of the
parasphenoid, and lastly the pterygoids underlying tJu pt^-
goid process. Some of tbeee bones are actually built up by the
fusion of the bases of mioute conical teeth in the larva. The
vomers and palatines retain their teeth in the adult, whilst the
parasphenoid loaee them.
The upper lip has tooth-
bearing pre-mazillary snd
maxillary bones developed,
the lower has a dentary on
the outside of Meckel's car-
tilage and a splenial on tlie
inner. Above the maxilla then
is a small pre-frontal bone.
If we examine the skeleton
of the limbe we find that
the pectoral girdle consists of
two plates of cartilage which
Blightly overlap in the mid-
ventral line. The lower half
of each is forked, the foriu
being called precoracoid and
coracoid respectively, 'Hie
centre of each half of Uie
girdle has a hollow termed the
glenoid cavity for the articu-
lation of the arm. All arotmd
the glenoid cavity the gitdle
is converted into bone; there
la a bone termed the scapula
above, and a coracoid bone
below. The nuossified part
of the coracoid is simply
termed the coracoid carti-
lage. The upper part of the
ginlle dorsal to the sci^nlar
bone is called the supra-
Fio. 234. A, ventral, and B, Uteial Tiew
of the Blionlder girdle and Btemum of
an old male Created Newt, Molge Crii-
tata X 3. After Parker.
1. Scapula. 2. Supra- ncapula. B. Cora-
ooid. 4, Oleooid oavity. 6. Pre-
ooracoid. 6. Btammn.
LIMBS AND VISCERA.
XVI.]
scapula. It remains cartil^inons, but
eoncoids are fastened behind to a small
median cartilage called the sternum.
The meaning of this is discussed later.
The manus has only four fingers,
the thumb and the corresponding small
bone in the nrist or carpus having
disappeared and the ulnare and inter-
medium being fused, although they are
distiactinthelar?a(Fig.335A). Other-
wise the limb corresponds to the scheme
given in the beginning of the chapter.
The pelvic girdle on each side is
finnly joined to the rib of the sacral
vertebra, and the two halves meet in the
mid-ventral line. The upper part of
the girdle above the cavity for articula-
tion of the thigh is a bone, the ilium;
below this cavity, which is termed the
acetabulum, is a so-called "ischio-
pubic " cartilage, in the hinder part of
which a small bone, the ischium, is
developed. In the mid-ventral line, in
front of the union of the two halves of
the pelvic girdle, there is a forked piece
of cartilage, the epipubis (Fig. 236).
In the pes the only departure from the
fusion of the tarsalia 4 and 5.
If the muscles be carefully cut
through inthemiddleline
ViKCTK. in > . , ,
and reflected, the body
cavity and the organs contained therein
will be exposed. In general the dif-
ference from the arrangement of the
organs in a dog-fish is only in the
relative size of the organs, in a word,
in details.
The alimentary canal is thrown
into a number of loops. The oeso-
phagus is not in any way sharply
marked off from the stomach, and
is often calcified. The two
Fio. 23S. A, BigLt antebra-
chinm and MiinuB of a larval
Balamandar, Salamandra ma-
caloia. Arter Gegenbaur.
B, BigLt TarBQB aod adjoiDiii([
Bones of Mntgt tp. AfMr
Oegeobaut.
1. lUdiae. 2. Ulna. S. Bad.
iale. 4. Intertnedium.
B. Uluare. 6. Centrale.
7. Carpale 2. B. Carpale S.
9. Carpalel. 10. Carpale
5. 11. Tibia. IS. Fibula.
13. Tibials. 14. Id termed-
iam. 15. Fibnlare.
16. Centrale. 17. Tareale 1.
18. Tarsalia 4 and 6 faeed.
I. II. III. IV. V. Digiw.
typical arrangement is the
430 nSODBLA. [CHiF.
the latter ia nearty etnight, extending only a short way roand ths
bend of tbe first loop. There u a well marked large inteatbe or
rectum, ventral to which hee the bladder The spleen is u
o eipoee the inteniBl orgkDS,
Mflo-hyoid iQiiBcle with genio-hjoid UDdemeith. 3. ConaB krUrilMlli.
3. YeDtriole. 4. Aariole. 5. BinnB renoiilB. 6. C«rotid midi.
7. 5f Btemic arch. S, Pulmoatur Arteiy. 9. Anterior venm cftva of left
Bide. 10. CoraooidB polled oatwards. 11. Liver. 13. Oall-hUdder.
13. Lung. 14. Bpleen. 16. Stomach. 16. lntestin«. IT. B«otnin.
18. Allantoio bladder. 19. Fst-bod;. 20. TeBlea. 31. AnlerKH-
abdominal Teui, dispUoed. 33. Kidney with dact. i '
1-]
CIRCULATION.
I red body lying at the side of the gtomach and attached to
pie DieacDtery. The ducts of the pancreas and liver coalesce into
coininon atem before opening into the intestine.
The newt feeds on small worms aad aquatic insects, which it
fceizes with its jaws. Both upper and lower jaws are armed with
■ minnto teeth, and there are in addition two longitudinal rows of
I teeth on the roof of the mouth borne by the conjoined vomer and
I jialatine on each side. The function of these teeth is not so much
to crush as to retain a hold of the prey, which is swallowed whole.
The tongue is a circular cushion on the floor of the mouth,
supported by the second visceral arch. Its hinder edge is partially
free. The lungs are long, smooth-walled, tube-like elastic sacs,
attached to the liver and other organs at their base, but their tips
float freely in the body-cavity.
The heart lies far forward, between the roots of the lungs,
enclosed in the pericardium. Externally all the four
syutm." divisions of the piscine heart are visible, viz., sinus
venoeua, atrium, ventricle, conus. The venous syHtem
is essentially that of the dog-fish, only the veins are indicated hy
names borrowed from human anatomy. Thus the blood from the
head is returned by two internal jugular veins, representing the
anterior cardiuals of the fislu These are joined by external
jugulars from the auperticial part of the throat and face and hy
a 8ub-clavian vein from each arm. The common trunk formed
by the nnioM of all three is, of course, the Ductus Cuvieri, but it is
called the superior vena cava, and it receives on each side close
to the middle line a posterior cardinal vein. As in fishes, this vein
in its course breaks up into capillaries through the kidney, and
along the outer edge of the kidney, its posterior portion, the renal
portal, may be matie out. The two renal portals when followed
further back are found to coaiesce in the caudal vein wliich
returns the blood from the tail: each receives a sciatic vein from
the ilorsal side of the leg joined by a femoral from the ventral
surface of the limb.
The increased importance of the hind limb has brought with it
this increase in the vessels draining it, wliich are represented only
by the smsJI pelvic vein in fishes.
'Inhere are certain vessels, however, unrepresented in any fishes
except the Dipnoi. These are: first, the pulmonary veins,
which receive the blood from the lungs and open directly into the
left side of the atrium, which is separated from the rest by a septum
432 URODELA. [chap.
and constitutes the left auricle; secondly, the inferior Tens
cava, a large trunk situated in the median dorsal line jtut beneidi
the aorta, which receives most of the blood that has traversed the
kidnejs and conyeys it into the sinus venosus just between the
openings of the two superior venae cavae. The inferior cava
coalesces with the hepatic vein)
returning blood from the liver:
these thus lose their independeat
openings into the sinus veoosiu
which they had in the Dog-fish.
In its hindermost portion between
the kidneys the vena cava joins
the posterior cardinal.
So far the peculiarities of the
Newt are shared by the Dipnoi :
but there remain two veins highly
characteristic of Amphibia. The
muBculo-cutaneons vein re-
ceives blood from the skin and
pours it into the subclavian ; we
have already seen that the skin
is a very important breathing
organ, and this vein returns the
blood which has been oxygenated
in the skin to the heart The
anterior abdominal vein
arises ou the ventral side of the
Fta. 336. Diagram to show urange-
ment of the priQcipsl Veins ol tm
Urodele.
1. SiDusTeDOBQi, gradually disappear-
iDK it
Cuvii
temal jngular = anterior oardioal
diiius. *■ Eitemal jtigular=
Bub-branchial. 5. SubclaviaD.
6. Posterior cardinal, front part.
7. Inferior vena cava. 8. Renal
portal — hinder part of posterit
dinal. 9. Caudal. 10. Sciatic.
11. Femoral. 12. Anterior ab-
dominal.
1 of two forks given off by
the femoral veins ; it runs for-
ward in the mid- ventral line,
eventually joining branches of
the portal vein and entering the
liver. This vein is found also in
the lower Reptiles and in the
embryos of Mammalia, where it is of the utmost importance in both
nutrition and respiration.
When the veins are cut away it is possible to follow out the
arteries. There 18 no ventral aorta, since on each side three arterial
arches arise in a bunch from the &out end of the tubular conns.
The first of these is called the carotid arch, and is derived from
XVI.]
CIRCULATION.
433
IV
14-
V
VI
-14
the third arterial arch of the embryo, but unlike its equivalent
in Dipnoi it does not communicate with the dorsal aorta. It gives
off a lingual artery to the
tongue and throat and then
passes up round the gullet,
to which it gives off some
twigs and continuing as the
common carotid supplies
the upper part of the head
and brain. Just after giv-
ing off the lingual artery
the arch swells up into a
little knot, called the
carotid gland. In this
structure the channel of
the artery is broken up into
a network of fine passages
and its function is believed
to be that of holding back
the blood from entering the
head until, at the close of
the contraction of the ven-
tricle, the blood has return-
ed from the lungs. The
second arch, derived from
the fourth embryonic arch,
supplies most of the blood
to the root of the dorsal
aorta, and on this account
is called the systemic
arcL The fifth and sixth
embryonic arches in later
stages unite on each side
into one trunk, which pass-
ing round the gullet joins
the systemic arch. From
Fio. 239. Diagram of arterial arches of Molge,
viewed from the ventral aspect.
I. II. III. IV. v. VI. first to sixth arterial
arches. 9. Carotid gland. 12. Lingual
^ventral carotid). 13. Common carotid
(dorsal carotid). 14. Systemic arch.
17. Dorsal aorta. 19. Pulmonary.
22. Subclavian (dorsal type). 23. Cuta-
neous. 24. Coeliaco-mesenteric.
the sixth arch is given off
the pulmonary artery which supplies the lung. On this account it
is called the pulmonary arch. The systemic arch on either side
gives off a subclavian artery to the fore-limb : and fix)m its place of
origin it will be seen that this subclavian is of the dorsal type
8. AM. <2!^
434 . UBODELA. [chap.
(p. 350). The subcl&Tians originate close to the junction of die
two srstemic arcbes and each gives off a large branch to the otbv
breathing organ, the skin, which is known aa the cutaneoas arterj.
In Molge the fifth arterial arch disappears, as it does in aU Verte-
brates above the Amphibia, bat in
the allied genus Salamandra it is
retained in the adult
It is comparatiTelf easy to un-
cover the brain and
•jF«em^'^' spinal cord of the
newt owing to the
thinness of the bones which cover
them. The cerebral hemispherea
are long and cylindrical, and devoid
of any other connection with one
another than that by way of the
thalamencephalon ; through the thin
roof of the latter two thickenings in
' its floor, the optic thalami, can
be clearly seen. The mid-brain is
a simple smooth vesicle, and the
cerebellum is a alight inconspicuous
transverse band (Pig. S40).
The olfactory lobe of Amphibia
difTers from that of Pisces in being
separated from the cerebrum only
by a slight constriction. From its
anterior end a brush of nerves is
Fi«. 240. Brain o( Triton, Molge given off which goes to the nasal
sac. The so-called olfactory nerve
1. Ollutoij DerreB, lepretentiag
the olftctoty lobea of the Dog-
Bah. 2. Olfactory lobea.
3. Cerebral hem ilpbere. 1. Thin
roof of thalamenoephalon. 5.
Optic thalami. 6. Pineal bod;.
7. Mid-brain. 8. Cerebellum.
9. Medulla oblongata. Fiom
Barckhardt.
of the Dogfish which is the stalk
connecting the olfactory lobe and
the cerebrum is unrepresented in
the Amphibia.
The coarse of the cranial nerves
is substantially the same as in the
Dogfish ; owing, however, to the
loss of the gills and the mucous canals in the adult, the branches
are simplified. The 9th or glossopharyngeal, as its name implies,
is distributed to the pharynx and tongue. The vagus supplies the
Jaiynx and glottis, but its main stem runs on to the heart and stomach.
XVI,]
DBINO-OENITAL ORGANS.
435
The firBt spinal nerve comes out &ona beliiud the ^rat vertebra und
is called the hypoglossal ; it runs
directlyto the respiraU>ry muscle, the
niylo-hyoid, crossing the vagus and
glossopharyogeal in its course. At
the t^ides of the dorsal aorta the tvro
chains of sympathetic ganglia
can be made out, connected by cross
branches with the spinal nerves.
To turn now to the excretory
system, the kidney
uotBani?" '^^^ ^^ ^^^ wlien the
alimentary canal is
removed. It is a long narrow strip
on each ^ide adjacent to the aorta.
In front it tapers to the merest
tiiread, but behind, close to the
cloEu:s, it thickens somewhat. Along
itft outer edge runs the arcbine])hric
duct, and external to the archi-
nepbric duct is situated the long
viduct.
' The tubules which compose the
kidney retain throughout life the
ciliated openings into the body-
cavity, and if the narrow part of
the kidney be cut off and mounted
in a bttle salt solution it in possible,
at leiiat in small specimens, under
a low power of the microscope, to
see the funnels and to observe the
whirlpools due to the currents pro-
daccil by their cilia.
The genitAl gland in both se.xes
is represented by a pair of ridges
suspended to tlie inner edges of
the front parts of the kidney by
slings of peritoneum similar to the
L mesentery suspending thegut,and on
B this account called mesenteries.
Lin the female the oviduct opens
Fio. 'J41. Urino-Rpnital organs of
a Feraala Mnlgt criifnfo x »bout 5.
I, O^Bry. 2. Bemnftnt of TBM
eflereutift. 3. Remoaotof longi-
tudinal caDnl ooDDeoting tbe T&aa
iifferentisi. 4. Sexual portion
of kidne}'. S. Arobinephric
duct. 6. Ofiduet. 7. Pos-
terior non.nexnal portion ot
kidney. S. Opening of arohi-
nepbric duct. 11. Internal open-
in|{ ot oviJuct. 12, SuspenBoijr
ligaiDEnt. 13. External upea-
ing of oviduct.
436 UBODBLA. [CHiP.
by a ciliated fannel adjointog the root of the lung. The fdnnd
leads into a long convoluted tnbe running back to open into
the cloaca. The testis, which
takes t^e form of two conicil
bodies with their broad eatdi
apposed, or aometimes a m
of tiiree rounded lobes, com-
municates by a nnmbei of
-rasa efferentia with the ant-
erior part of the kidn^,
which is on tins accooot
termed the sexna] portion at
mesonephros. In the mile
the kidney tabules belong-
ing to tite hinder non-sexiul
portion, or metanephros,ue
split off from the archinephiic
duct and unite into a short
common trank, Mud ureter,
which joins the archinephric
duct juBt before the latter
enters the cloaca
It has been stated above
that the genital glands ate
a pair of ridges. In the
larva the inner portions of
the ridges degenerate, the
cells becoming largely coo-
verted into fat-bodiee. In
the adult these &t-bodie8
appear running parallel to the
genital o^ans on the inner
side. They serve as a stote
of nourishment for the eggs
which develope during the
winter-sleep. The Newt, like
other Amphibia, passes the
winter buried in the mud at
Fia. 212. Urino'geoit*) orguii of ft Male
Molge eriitala x kbout 5.
1. Testes. 2. Vun efferentia. 8. Longit-
udinal canal eonnecting the Tasa effer-
entia. 4. Beiaal portion of kidney
showing nephroslomea. 6. Wolffian
duct. 6. BudimeDtar; oviduct. 7. Non-
aemal portion of kidney. 8. Eilemal
opening oC the archinephrio dnot which
has received the ureter 9 made np of
a number of duets tram the posterior the bottom of ponds and takes
part of the kidney. 10. Fat-body. ^^ j^ ^^ convenriou of
Bome of the possible eggs into &t to feed the rest is simply an
n.]
487
example of the aame principle as tlie sacrifice of some of the dogs in
■a Arctic expedition to feeii the rest.
The development of Mf)lg« is interesting. The male emita
the spermatozoa in & bundle which the female then
introdnces into her cloaca, and the eggs commence
their development in the body of the mother. Soon afterwards they
are laid and attached to water plants. After some time larvae are
hatched out wiiich in many respects resemble fishes. They are
provided with three long feathery appendages on each side of the
neck, in which there is a rich blood supply and active circulation.
hese are the external gills found only in Amphibia, Dipnoi and in
'olffpterua. There is also a pair of curious rod-like organs in front
F the gills attached to the sides of the head. These "balancers,"
I they are termed, are possibly a first pair of external gills peculiarly
lodifiod. They have mucous cells at the tip, and by means of
^em the young larva suspends itself for hours at a time to plants.
There is a long fish-like tail, the organ of locomotion, with a (ringed
%a. The fore-limbs are tiny buds. No trace of hind-limbs exists
I the gill-alits are not open.
As deveIo]>nient proceeds the fure-Hmbs make their appearance
provided with only two toes. The gill-clefts, three in number,
appear on each side. AJt«r a considerable time the third finger
l^pears and the hind legs sprout out as buds; still later the fore-
mbs get all four fingers and the hind-limbs five. The animal has
Bow attained the appearance of the adult except in so far aa the
plls are concerned. These are retained for a long time, and excep-
tiially, in Switzerland in high Alpine localities, the larva may
Kcome sexually ripe and never leave the water. More usually with
e closing of the gill-slits and the shrivelling of the ext«rual gilU
fche adult state is attained.
The Urodela have for a long time been divided into two main
poups, according to the presence during adult life of gill-slits
438 UBODELA. [chap.
and gills. Huxley thus divided them into Iohthtoedba and Sau-
MAi^DROiDEA. But this has been criticized as not
ClasBincation. ,.,, t» ^ it
being based upon fundamental characters. Huxley s
IcHTHTOiDEA are those which retain throughout life gill-slits or
external gills or both. Invariably the limbs are reduced in size,
the animals rarely if ever leaving the water. In one case the hind-
limbs have totally disappeared.
North America is the great head-quarters of the Ichthyoidea.
Menopoma {Cryptobranchus) retains one gill-slit throughout life.
This animal attains a length of 18 inches. It is fSedrly common on
the Mississippi and its tributaries. An allied species found in
Japan, and attaining a length of two feet, is the largest living
Amphibian.
Amphiuma is a snake-like animal about 18 inches long, with
one gill-slit It is found in the same region as Menopoma. The
limbs are exceedingly rudimentary, each having only two toes.
Necturus, the Mud-puppy, has small but well-developed limbs.
It retains throughout life two gill-slits and three external gills on
each side. Necturus is abundant in the shallows of the St
Lawrence, wriggling in and out around the roots of aquatic plants.
A somewhat similar animal, Proteus, with more rudimentary limbs,
is found inhabiting the limestone caverns of Camiola in Austria.
Lastly, there is the aberrant Siren, which has a homy beak en-
sheathing the premaxilla and dentary; it has no hind-limbs, but
is similar to Necturus in its gills: it is found inhabiting the
swamps of the Southern United States.
Since the Ichthyoidea possess both gills and lungs it is tempting
at first sight to regard them as the little modified descendants of an
animal just making the transition from water-breathing to air-
breathing life. There are however insuperable difficulties in the
way of such an explanation. If we turn to other groups of the
animal kingdom we find that the first step in fitting an animal for a
land life is the covering up of the respiratory organ so as to protect
it against drying up. But in hardly any fish are the respiratory
organs so exposed as in Necturus, Proteus and Siren,
Further, it was pointed out that the great gap between fishes
and Amphibia is to be found in the structure of the limb. But the
Ichthyoidea do not in any way assist in bridging the gap. On the
contrary their limbs are obviously degenerating, a fact which seems
to show that the aquatic life has been re-acquired. Now when the
similarity between say Necturus and the late larva of Molge is
CLASSIFICATION. iwt J
borne in mind, and the further fact that these larvae may abnormally
become aexiiallf ripe, the conclusion is irresistibly suggested that
the Ichthyoidea are larvae in which the ailult stage has been
suppressed. In the case of one large American newts Amblystoma
tiffrinum, the Urva (the " AxolotI ") often breeds nnder certain
oircumatances and was at one time regarded aa a distinct genus
ISiredon).
The second division of Urodela, the Salamandhoidba, are in
general very similar to Molge, both in appearant^e, anatomy and size.
As in Ichthyoidea, so likewise North America is very rich in
Salamandroidea. These have been divided into families on grounds
of difTerencea in the skeleton which have little effect on the external
appearance. Tlie most abundant are the Amblyrtomatinae repre-
aented by the genus Amldifstoma of which there are many species,
nine being found in the Eastern States and Canada. The members
of this family are distiDguishcd by having the palatine bones
directed transversely, ho that the vomero-palatine rows of teeth
run aiTOBS the roof of the mouth instead of along it, and by
having amphicoeloua vertebrae.. Motga (Diemi/etilu^) mridescetis
ia the common Water-Newt of Lower Canada. It is a member of
the same genus as the English Newt which has been selected for
detailed description, but unlike its English congener the American
species does not develope a crest in the breeding season. These
Newts are representatives of the Salam-^ndhinae distinguished by
having the vomero-palatine teeth in a longitudinal row and by
possessing opisthocoelous vertebrae. The family Dbsmuonatuinae
are closely allied to the Amblystomatinue, but differ from the latter
in possessing a cluster of teeth on the parasphenoid in addition
to the transverse row of vomero-palatine teeth and in having
opisthocflcloua vertebrae. The species of this family are common
Water-Newts in the Eastern United States. Desmogntttlms nigra,
the black Salamander, occurs near Montreal. The Plbtrodon-
TINAE iucludca tlie American Cave- and Laud-Newts which rarely
enter water but wriggle about actively on land. Tliese Newts re-
semble the Desmognathinae in tlieir teeth, but differ in possessing
amphicoeloua vertebrae. Although the most terrestrial in their
habits of the New World Urodela, these animals and some of the
Desmognathinae have undergone an extratirdtnary modification in
their respiratory system. The lungs have disappeared and the
septum between the auricles has l>ccome absorbed : so the animals
depend for their oxygen entirely on their skin and the lining of the
440 URODELA. [chap.
pharynx, the walls of which still execute active respiratoiy movem^ts.
This curious association of terrestrial habits with the absence of longs
suggests the idea that the lung in such Urodela as retain it may be
chiefly used as a hydrostatic organ like the air-bladder of fish, for
were it of prime importance as a respiratory organ it would be diffi-
cult to explain its disappearance in terrestrial forms. SpeUrpes
includes the Cave-Newts, of which there are twenty species in
America and one isolated species in Italy. In these animals the
tongue is long and not adherent to the floor of the mouth. It can
be suddenly protruded and is used to catch insects in the same
way as the tongue of the Anura. This is an exceptional action
amongst Urodela, most of which seize their prey with the jaws.
PUthodcn erythronotus has the typical tongue. This is the common
Land-Newt in the neighbourhood of Montreal, being found under
old logs and in other damp situations.
II. ANURA.
The Anura or Batrachia are at once recognized by their broad,
flattened, tailless bodies and their powerful hind-limbs.
These limbs are not only efficient in jumping but also
in swimming, and the toes are connected with one another by a thin
web of skin in order to aid them in performing this function. The
toes are stretched apart in the back stroke to present a large surface
to the water, in the forward stroke they are folded together and
offer little resistance.
Anura are much more abundant than Urodela and are found all
over the world, whereas the Urodela are restricted to the Northern
hemisphere. They are in fact the dominant Amphibia of the present
day, but they are highly specialized, and the Urodela give a much
better idea of the relation of the Amphibia to the Fishes on the one
hand and the Reptiles on the other, for which reason Molge was
selected as the type.
Besides the absence of a tail, the powerful character of the
hind-limbs and the diff'erences in the skeleton connected therewith,
Anura diff^er from Urodela in the skull and jaws, in the pectoral
girdle, in the heart and lungs, and in the kidneys, genital organs
and development.
Two genera and four species of Anura occur in the British Isles.
Rana temporaria, the common frog, and B. esculenta, the edible
frog (the last named is thought by some not to be indigenous but
1]
ANITHA. 441
» have been introduced), represent the family Rasidae, while the
IryoNiDAE or toads are represented by Bvfo vulgnng, the common
oud, and by B. ealamita, the Natterjack, whioh occurs in numbers
It certain restricteil localities, as a rule those with a Bandy soil.
As the Common Frog, Rana tumporaria, is easily attainable,
the principal points in which it differs from Molge
will be briefly described.
The animal when at rest normally .squats on its haunches,
Opporting itself slightly on its palms. Under these circumstances,
he pelvic ^rdle makes a considerable angle with the vertebral
olonin and the powerful iliac bones raise the skin of the back into
well-marked homp, the ao-ealled sacral prominence.
The gape is enormous, and is caused by the lower end of the
nspensorium, or part of the skull to which the lower jaw is
^d, slanting backwards instead of projecting directly downwards
I in Urodela. The tongue is fixed to the floor of the mouth in
ront, but is free behind ; it can be ra|>idly thrust out of the mouth
\f bending the posterior end forwards and it can be ils rapidly
etracted. It is used to whisk the insects on which the aniinal
nds into the mouth.
Behind tlie eye is a circular patch of thin, tightly stretched skin,
Phis is the ear-drum or tympanic membrane, which closes ex-
eniatly the Eustachian pouch of the gullet. It is believed that
his pouch or tympanum is the remains of the first gill-cleft, the
pirach) of Elasmobrauch fishes. Sound impinging on the ear-drum
I conveyed to the wall of the ear capsule by a row of several small
Utilages, the so-called columellar chain of the ear. In the
trodela sound has to find its way as best it can through the skin
Dd muscle of the iiead to the auditory organ. All Anura possess
Bnstachian pouches and a. columella auris, but all do not have
, well-developed ear-drum.
The skin is most loosely attached to the muscles underneath.
ATge spaces containing lymph are interposed between tliem.
Siese lymph spaces form a protection against the danger of
lying up. There arc two pairs of sacs placed, one pair just
etween the upper ends of the pectoral girdle, and another pair
t at the sides of the rudimentary stump of a tail, which have the
ower of contraction and pump the surplus lymph into the veins of
be neighbourhood. These are called the anterior and posterior
urs of lymph-hearts.
Turning now to the skeleton we observe many points of
442 JLNUEJL [CXiP.
difference between the Frog and the Newt The ribs in the Fnig
are indiBdnguiahably fused with the transverse prooeasea; in laj
few Annra are they distinct and they are always radimentaiy. TU
vertebrae differ from those of the Urodela in the entire snpprenon
of the inter-ventral element so that the centnim is constracted ont
of basi-dorsal, inter-dorsal and bad-vential elements, the last
named being very rudimentary. In some Annra the baai-ventnl
piece is entirely absent, and in this case, since the centmm i)
constructed entirely of dorsal elements, the notochord is found for
a considerable period of development lying in a groove on its under
surface. This is the so-called epichordal type of development.
Fia. 2H. A, Dorsal, and B, Ventnl view of the Cmiiam ot a Cominon Fnc,
Ratta lemporaria, from which the membrsne'bonea have most); betn
removed X 2. After Psrket.
1. Bpbenethmoid. 2. Palatine. 3. PleiTiioid. 4. Smapciuorian.
5. Colamella. 6. Eiocoipital. 7. Ventral oortUsfiiiioua waltof
cranium. 8. Pro.otio. 9. Anterior fontanelle. 10. Bi^t
posterior fontanelle. 11. Quadratojngal. 19. Ntual capsok.
n. V. VI. IX. X. tonimiDB for exit of cranial nerrea.
The tail vertebrae are represented by a bony style, the nrostyla
Besides it there are only nine vertebrae. The transverse processes,
or " diapophyses " of the ninth or sacral vertebn, to which ii
attached the ilium, are either cylindrical as in Rana, or ^ey in
more or less wide and flat as is the case in Bnfo and ffyla. In
most cases to the distal end of the diapophyais is attached a nodols,
the rudimentary rib, which may either fiise with the diapophysis la
in Bana or remain distinguishable throughout life as in AlyUi.
The skull is constructed on the same plan as tliat of Molgi,
but it is broader and flatter; this is due to the wide arcfabf
ont of the upper jaws, leaving a very lai^ opening between them
avi.]
443
sniJ the cranium. The cause of this again is to he sought in the
large protruding prominent eyes, ao marked a feature of all Anura.
The floor of the cartit.iginou.t cranium is complete in the Frog, the
pituitary' fossa having shrunk to insignilicant dinieusions. The
orbitoBphenoids have coalesced to form a box-like bone which ossifies
only in the front part of the cranium but also in the hinder parU
of the nasal aae, and is called the spheuethmoid. The parietal
IB fused with the fronlal.
Tlie suspensorinm sends fonvard a pterygoid process which
Spbeaethmoiil. 3. FrnDtti-piu-ietaJ. 3. Pterygoid.
6. ExoocipitBl, 7. PaiAKpheaoid. B, Prn-otii. 9. QuitdraU>jni!Bl.
10. Maxilla. 11. NhhbL 13. Premaxilla. IS. Anterior D»res.
14. Vomi^r. 15. Posterior naiM. 16. Palittine. 19. Colnniells.
1». Qa*d»te. 20, Oooipital oondyle, U. Optio foramen. V. VII.
Foramen (or exit ol trigeminal and facial nerveB. IX. X. Foramen [or
exit of gtORSopharyngeai anJ pnoumogaatric nerveH.
becomes attached to the skull in the uasul region. Underneath the
posterior part of the pterygoid process there is a pterygoid bone
which Burroiinda it and partly replaces it. The pterygoid sends out
ft fork which underlies that part of the auspensorium which forms
ftn articulation for the lower jaw. The front part of the pterygoid
process where it bends in to rejoin the skull in ossitied by the
palatine, which like the pterygoid iias ijecome a cartilage bone.
The palatine is transverse to the axis of the nktill, as in Ambty-
ttoma. Neither palatine nor pt«rygoid bears teeth, but the vomers
444 ANUBA. [chap.
bear a little group of teeth towards their hinder edge. Then
vomerine teeth are used for crushJDg the food.
The upper lip has a series of three bones on each aide, readung
completely to the suapensorium, an additional qnadrsto-jugal
being added to the two present in the NewL The presence of tJiii
bone suggests that the ancestors of the Annra are to be sought
amongst that highly modified group of the Stegocephala termed the
L&byrinthodonta. In them u
B > I , in the Annre the interventral
element was absent but at
any rate in the older forms
the basi-dorsals, the basi-ven-
trals and the inter-dorsals
were distinct pieces. Iq all
Anura there is a la^e mem-
brane-bone of a characteristic
T-shape, known as the squa-
mosal, lying outside the sua-
pensonuuL In the lower Up
there is a splenial and a
deutary, whilst in front the
cartilaginous lower jaw is re-
placed by a pre-deotary
bone. In the frog only the
premaxilla and maxilla and
vomer bear teeth. MostAnuia
agree with the Frogs in this,
but the Toad, Btffo, and its
allies are entirely toothless.
The hinder visceral arches
are reduced to a still more
rudimentary condition than
those of Molge. They are
represented by a thin plate
of cartilage called the basi-liugual with short blunt processes, of
which only the last pair, which embrace the glottis, are ossified
(Fig. 247). This pair are termed the thyio-hyals. The whole
"hyoid" is thus the remains of the visceral arches.
The pectoral girdle is much more strongly developed than in
the Urodela. The coracoid and pre-coracoid processes are joined
at their inner ends by a longitudinal bar, the epicoracoid, so as to
Fio. 246. A, LaMnl view at the Skull,
B, Posterior view of the Crsninin, of k
ConiDion Frog, Rana temporaria n 2.
Alter Parker.
1. Sphenethmoid. 2. Fronto- parietal.
3. Pterygoid, i. Squamosal. 6. Tjm-
panic membrane. 6. ExoccipitaJ.
7. Paraepbenoid. B. Pro -otic.
9. Quadiatojugal. 10. Maxilla.
II. Nasal. 12. PremaiiUa. 13. An-
terior nares. 14. Pre-dentary.
15. Dentary. 16. Splenial. IT. Basi-
lingual plate, 19. Quadrate.
30. Columella. 21. Occipital condyle.
22. Anterior coma of tbe hyoid (cerato-
hyal). 23. Foramen magnum. II.
IX. X. Foramioa for the eiit of cranial
XVI.] SKELETON. 445
enclose a space called the coracoid foramen. The two epicoracoids
are in the frog firmly united in the middle line. In many Anura
however they merely overlap (Fig. 248, B).
The upper portion of the pectoral girdle is ossified by a bone
called the scapula. As in Urodela, however, the cartilage projects
a long way beyond it, and this portion is called the supra-scapula
and may become partially ossified. There is a distinct coracoid
bone ossifying the coracoid process, and the pre-coracoid is under-
lain by a membrane-bone called the clavicle. In firont of the
pectoral girdle in the middle line lies a small rounded piece of
cartilage called the episternum, followed by a bony piece, the
omosternum. Behind the girdle in a similar position is a carti-
B
Fiu. 247. Visceral arches of Amphibia. A. Rana temporaria adult. After
Parker. B. Tadpole of Bana, Affcer Martin St Ange.
In A the ossified portions are slightly shaded, while the cartilaginous
portions are left white.
1. Basilingual plate. 2. Hyoid arch. 3. First branchial arch. 4. Second
branchial arch. 5. Third branchial arch. 6. Fourth branchial
arch. 7. Th7roh7al= fourth branchial arch.
laginous bar with a flattened end, ensheathed by a bone called
the sternum; the flattened end is called the xiphisternum.
The omosternum has proved to be composed of a portion budded
off by the conjoined epicoracoids. The sternum is supposed to be
the first sign of the breast-bone of higher Vertebrates, but as their
breast-bone originates in connection with long ribs, which meet one
another in the mid-ventnd bone, this must be considered doubtful.
In the arm the two points to be noticed are the complete fusion
of the radius and ulna into one bone, and the reduction of the
carpus, in which there are only six bones, three of the distal small
bones having coalesced and the centrale being absent. The first
digit or poll ex is rudimentary.
In the pelvic girdle there is no epipubis: the ilium is a very
long cylindrical bone : the ischium ossifies most of the ischio-pubic
446 ANDRA. [chap.
cartilage and is closely apj^ied to its fellow. In the leg the tilnt
and fibula are fused into one bone, vhicb is about the same Iwgtli
as the femur. The ankle is remarkably elongated, the tibiale aod
the iibiale being long cylindrical bones, easily mistaken for tiu
middle segment of the limb. The distal bones of the tarsus ban
nearly disappeared, only two or three small nodules being present
on tjie axial side. The longest toe is the fourth, that correspond-
ing to the human big toe (hallux) is the shortest It is a matta
of great interest to see on the inner side of tite foot a spur
supported by a small bone which may be the vestige of a sixth
Fia. 248. Shoulder- girdle and Steninni of
An old male CommoD Frog, Bana ttmporaria.
An adull lemsle, Docidopkryiu gigantta. After Parker, to illnitiat* the
'a Arcifera.
In both A and B the left Buprasoapola is remOTed. The parte tuiahBded
are ossified; those marked vith email dota causiet of hjaline cartilage, thoie
marked vith large dota of calcified oartilage.
1. Caloifled cartilage of auprascapula. 2. OaaiSed poitioa of enprasoaptda.
3. ScapQla. 4. Coracoid. 5. Epicoraooid. 6. Praooraooid.
7. ClaTicle. 8. Oleooid oarit;. 9. Coracoid foramen. 10. Epi-
stemnm. 11. Omostemum. IS. Slemam. 13. Xiphiatemom.
digit. It is a common occurrence for the number five to be
diminished, but very rare for it to be increased. It is believed that
the pentadactyle limb is derived Irom a Jin like that of the Dipnoi
by a shortening of the main axis and a reduction in the number of
rays, and it would be not unnatural to expect to find in the lower
groups of land animals traces of extra rays.
The main difierences between the circulatory system of the Frog
and that of the Newt we to be found in the arterial system. Not only
aa in the Newt does the fifth arterial arch of the embryo disappear
altogether, but the sixth becomes entirely cut off from the aorta and
jcvl] circulation. MV
in addition to supplying the lung it sends a large branch to the stdn,
for which reason it is called the pulmo-cutaneoue arch. The
conus arteriosus, na in Moiije, has two transverse rows of pocket
TiJves, one near the heart and one near the outer end, but in the
Frog there is in addition a longitudinal valve with a free
ventral edge running j^omewhat obliquely from the one row of
valTea to the other. When
the ventnde tontructs it
18, at hrst, full of venous
blood from the right auricle
At this stage the conus is
relaxed a condition fthich
inges the longitmiinul
valve in such a way as to
divert the blood almost
exclusively into the pul
nionary (las.^ages whose
width and shortneis also
&T0UTS itt flow intn
them As these beiome
filled the i onus Lontract"
and this ha? the effect i>f
jnakmg the longitudimil
valve he against the open
inga into the pulmonary
anhes and ao ]irevi.titing
any more blood entering
them while at the same
time the path into the
systemic arches is widely
opened By this time Mjote
of the blood has returned
from the lungs to the left
auricle, and so mixed blood
jmaHes tothehinderportion j jj jjj jy y y|
of the body. When the arches. 9. Carotid gland.
pressure in the ventricle
rises to its highest point,
the last blood, which is
almost completely arterial,
— aU from the right auricle having been driven out, — is able to
iitb artarial
12. Lingual
tral carolid). 1.1. Common c?arotid
(doraa! carolid). U. Syatemic arch.
17. Dorsal Borta. 19. Pulino-cutaiieoas
artery. 22. Subclaviaa (dorsal type).
2i. Coeliaoo-" """ '"
448
[cBir.
overcome the reeistance in the carotid gl&nd and go to the hud,
which coQtaiuB the oi^ns having the greatest need tar thoronj^
oxygenated blood.
The posterior cardinal veins are represented only by their faindet
portions, the renal portab, all the blood from the kidneys being
earned by the infenor vena cava.
The brain of the Frog and of Annra in general is more hi^r
B. The SI
the ail
IB venoBua baving been opened np, to alio*
C. The same, disaeeted from (be front, the ventral nU together wilt one at
the auiicuIo-veDtrioular valves having been removed.
1, Ventricle. 2. Bight auricle. S. Left auriole. 4. Tmncna arter.
iOBQB. S. Carotid arch. 6. Lingual artery. T. Carotid kIsoiL
6. Carotid artery. 9. Systenuc arch. 10. Pnlmoentaneoui arch-
il. Innominate vein. 12. Subclavian vein. IS. Vena cava inferior.
14. Venn cava superior. 16. Opening of sLnua venoana into right auricle.
16. Fulmonai; vein. IT. Aperture of entry of pnlmonary veia.
18. Semi-lunar valvea. 19. Longitndinal valve. 20. Point ot
origin of palm ocatsn ecus arch. 21. Rod passed from ventricle into Uir
truncus arterioBua, indicating the courae taken by blood which flows into
the carotid and aortic archea.
developed than that of the Urodela. Thua (Fig. 251) the olfactoiy
lobes of the cerebral hemispheies are connected together, and Uie
optic lobes of the mid-brain are well developed.
It was pointed out (p. 368) that the limbs of Vertebrates are in
all probability derived frvim two lateral flaps of skin — two longi-
tudinal fins. The muscles in these fins were originally prolongations
I«f the myotomeB, and the nerves
of couiee branches of the
motor nerves going to the myo-
tomea. Now as these longitudinal
Baps were converted into paired
fins, and these by a continual
narrowing of their bases acquired
greater distinctness from the body,
the jmrtioiis of the myotomes
supplying the innsuulature and
the nerves in connection there-
with became so to speak bunched
togetlier nt the base of the liuib.
In adult Craniata all trace of the
original nietameric arrangement
of the limb muscles ia lost ; but
the metamerism of the nerves
can still lie seen, and the bundles
of these supplying tiie pectoral
and the pelvic limbs are known
as the brachial and the sciatic
plexus respectively. In the
Prog, where the limbs are of far
greater importance to the life of
the animal than are the fins to
fish, the nerves forming the
brachial and the sciatic plexus
»re powerful trunks (Fig. 251,
2. 3, and 7—10).
The InngB are shorter than
in tile Newt but much
wider, and their inner sur-
face ia covered with a
network of low ridges
which much increases their
area. The kidney is a
comparatively short and
broad organ, very different
from the long tajieriiig
organ of the Newt. The
testis ia connected by vasa
s. AM.
Fis. 9.51. Brain and Spinnl Cord ot a gene-
mJiiied Annmn. In tbe PhADerogloafla the
Ist Epiool nervH is euppresaed. x sbODt 3.
a. Cerebral heminpbpre. b. OlfaoCorj' lobe,
c. Bye. d. Tbttlamencfphalon. e. Optio
lobeii. (. Cfrelielluin. g. Medulla
□bloDgata. h. Fourth ventricle, i. 8pmal
oord. I. Olfactory nerves. II. Optio
nerve, in. Oculomotor nerve. IV. Fath-
fltip-aB, V. Fiftli nerve. VII, Faoial
nerve. VIII, Auditory nerve, IX, OIodbo.
pharyngeal norve. X. V%Ka» necve.
1—10, First to tenth spinal nervea, 2 and
U imile to form the brachial, and 7, 8 and
tt, to form the Kiiatia plexua.
450 ANURA. [can.
efferentia with certain special tubulea of the kidney. These tubnka
do not open into the archinephric duct, but into a special dnct
which runs along the surface of the kidney and opens into tike
archinephric behind. Thus in a somewhat different way the
separation of urine and spermatozoa is carried out quite u
Fra. 252. The Frog.
A. The QriDo-geniUl argoDB of the m&le, diaaected from the froat, ahet
removal from the bod;. From Howes.
B. The urino-geniUI organs ol the female, dealt with in the same manner u
the above, except that, in order to eliow the natural relations of the month
of the oviduct, the left lung and a poition of Iha oesoph^OB were also
removed from the body.
A- 1. Fat-body. 2. Fold of peritoneum supporting tbe teatis. 8. Effereot
dnctB of testis. 4. Ducts of veeicula tiemmalia. 6. Veaioola seminaUa.
6. Archinephiio duct. T. Cloaca. 8. Orifio* of ureter.
9. Proctodaeom. 10. AUaatoic bladder. 11. Rectum. 12. Kidney.
13. TeatiB. 14. Adrenal body.
B. 1. Oeaophagaa. 2. Moutb of oviduct. S. Left Inng. 4. Corpui
odipoaua. 5. Left ovary. G. Atchiaephrio dnet. 7. Ovidact.
a. Allantoic bladder. 9. Cloaca. 10. Aperture of ovidnot
11. Aperture of archinepbrio duct. 12, Prootodaeom. 13. Fold of
peritoneum supporting the ovary. 14. Kidney.
efficiently as m the Newt. The archinephric duct has a number
of pouches developed on its walls which collectively form the
vesicula seminalis in which the spermatOEoa are stored op. In
Bombinator the vaaa efferentia apparently open directly into the
archinephric dnct in front of the kidney.
:ti.]
REPRODUCTION.
461
Lying on the ventral surface of the kidney near its inner edge is
Q elongated body called the adrenal body (Fig. 252 a, 14). This
Drg&Q is found under various forms in most Vertebrates ; it has
been recently shown to be derived from a peritoneal furrow which
nes shut off from the general coelom and loses its cavity,
[ortniag a solid rod of cells. Experiments made ou higher animals
knd the obHcrvatioa of cases where it is attacked by disease, show
tiiat the adrenal bodies, like the thyroid, produce an "internal
secretion. " The substances [wured into the blood by both these
organs are essential to the proper conduct of metabolism, that of
the adrenal bodies being stimulating to the muscular tissues in
particular.
The eggs develope entirely outside the body, and there is a large
thiu-walled swelling of the oviduct in which the ripe eggs accumulate
'. Maloicl. From
a. 'Jd3. Tadpole of liaiut r
I. PoFBiJ Bm. '2. Tail ebciwbg lo.Totomea. 3. Hinii-limb.
iust before being discharged. The male clasps the female round
waist and remains in this ijoaition sometimes for weeks, uttering
loud croaks at intervals until the eggs are discharged. When
the eggs are discharged he emits the spermatozoa on to them. The
eroaks are made by pumjiing the air from the lungs through the
glottis into the pharynx and vice versa. The pharynx has usually
two side pouches, the vocal sacs, which become inflated with air.
It ia thus possible for the frog to croak when under water.
The development is in many respects different from that of
Urodela, Soon after the young are hatched they acquire, it is true,
three external gills on each side, hut there is no trace of Hmbs and
the gili-alits are closed, and as the mouth does not open into the
alitneutary canal no food is taken. Later the gill-sHts appear; but
Hap of skin, the gill-cover, grows back from the second visceral
arch (the hyoid) and covers up the gill-slits and the external gills.
The external gills then bood disappear. The two gill-covers
452 ANURA. [chap.
unite with one another beneath the animal, so only one little
opening to the gill-chamber remains, usually on the left aide. The
mouth has by this time opened into the alimentary canal, and it is
provided with two horny ridges, one above and one below, besides
rows of little homy prickles. The homy jaws crop the water-weeds
upon which the tadpole lives.
The larva is now the well-known tadpole, with a rounded body
and a long flat tail, with which it swims. The limbs gradually grow,
but for a long time the front limbs are hidden beneath tiie gill-
cover. When they finally burst through the animal sheds its homy
jaws and leaves the water. For a short time the tail is retained,
but absorption soon removes all trace of it and the development is
complete.
The Anura are divided into two main groups according to the
development of the tongue. In the Aglossa it is
alio""* ^ entirely absent and the two Eustachian tubes have a
common opening into the phaiynx. This curious
group only includes two genera. In one species, Pipa americana,
the Surinam toad, the eggs are emitted from the protruded oviduct
on to the back of the female, and here the young pass through
the tadpole stage enclosed in deep pockets of the moist skin. This
species as its popular name implies is an inhabitant of S. America.
In the PhanerogloBsa, on the other hand, the tongue is well-
developed, being usually free behind, and in this case used to
flick the prey, which consists of insects, into the capacious mouth.
The Eustachian tubes are separate. The Phaneroglossa are divided
into the Arcifera and the Firmistemia. In the fiurst division
the two epicoracoids of each side overlap (Fig. 248, B); in the
second they are firmly united in the middle line (Fig. 248, A).
The first division includes several families, but the two largest and
most important are those of the toads or Bufonidae and the tree
frogs or Hylidae.
The toads have no teeth whatever: their wrinkled skin is beset
with wart-like poison glands in the upper parts, while numerous
little homy spines occur superficially in the epidermis. They only
enter the water at the breeding season and toads are in many
respects more adapted to a land life than are frogs. Two species
live in Great Britain; Bt{fo vulgaris, found everywhere, and £u/o
calamita, the natterjack, a species with comparatively feeble hind-
limbs, which crawls and (}oes not jump. The natterjack fr^uents
sandy places and is thus local in its distribution.
OUSSIFIOA.TION.
One species of Bufo (li. amertcana) is found in the north of North
America. But besides the Bufonidae another family of the Arcifera,
the pRLOBiTiDAE, whioh have teeth, is represented by Scaphiopu^i, &
bnrrowing species, provided with a sharp spur on the inner side of
each foot, whence the name " spade-foot " toad.
The HvLiDAE have teeth on the vomers and on the upper jaw,
but their moat remariiable peculiarity consists in the possession of
fleshy cushions underneath tlie terminal joints of the digits, the
bones of which are bent up atid claw-like. By means of these
cushions the Hylidae are able to adhere to smooth vertical surfaces,
and so climb trees, in which they mostly live, only approaching the
water for the purpose of laying their eggs. There is no species of
this family in Great Britain and only one in Europe. In North
America there are several species belonging to three genera; ffgta,
Churopkiliuf, and Acrts.
The FiRMisTBRmA have the two epicoracoids fused in tlie
middle line and include the Frogs or Ranidae, There is only one
epecies, Rana temporariit, which is here taken as the tyi)e of the
Ainira, really native to Great Britain, but there exist a few
eolonies of the common European species, Rana esculenta, mostly
in the Eastern Counties. The frogs of this species are most powerful
croakers, and as their name implies they are used as food. It is
believed that they were introduced by monks from Europe, who
before the Reformation used to pay periodical visits to England to
supervise their property.
In Cauada and the Northern United States there are eight
Bpecies of frogs. A species believed to be identical with Rana
temporarla is found, hut the two commonest are Rana virescens, of
a green ground colour with lines of velvety black patches, and
the great Bidl-frog, Rana catesbiana,, which attains three or four
times the size of Rana temporttria, and is of browuish-yellow
colour, peppered over with minute black dots.
HI. AFODA.
The order Apoda is, as has already been mentioned, dis-
tioguished by the entire absence of limbs and the worm-like
sp]iearance and habits of its members. In the skeleton the reten-
tion of a complete roof of bones over the space between cranium
and upper lip, known as the temporal fossa, and the existence of
454 APODA. [chap.
minute bony scales embedded in the dennis, are featnres retained
from the Stegocephala. In accordance with their retiring bnrrowiDg
habits the members of this Order have very small eyes, which in
some cases are rendered quite functionless by being concealed under
the skin. The internal anatomy is in many respects like that of
the Urodela, but the pulmonary arterial arch does not in all cases
join the aorta. These animals often live at some distance from
water and the larval development is passed through inside the
egg-shell, but even there the embryo developes large external gills.
The species of this family are restricted to the tropics ; Ichthyaphi
is found in India, Coecilia in South America, and Hypageophis in
Africa. The extinct Stegocephala have been alluded to many times.
Under this comprehensive head are comprised all the fossil Amphibia,
remains of which are found in the Goal Measures and the Red
Sandstones overlying them. It has been already pointed out that
some of them, like Branchiosaurus, appear in the structure of the
vertebral column to be the forerunners of the Urodela, while others,
like the Lahj/rinthadonta, appear to lead on to the Anura. Besides
these, limbless forms are also known, and there seems to be some
probability that these were the ancestors of the Gymnophiona.
Hence within this ancient group the beginnings of the division of
the Amphibia into the three Orders by which it is now represented
had already shown themselves.
The class of recent Amphibia is divided as follows :
Order 1. URODELA.
Amphibia retaining throughout life a long tail.
Family (1) Amphiumidae.
Both the upper and lower jaws are furnished with teeth
Fore and hind limbs small Eyes small and devoid of lids.
The gill-slits are in a vanishing state, the gills disappear in
the adult.
Ex. Amphiumay Ctyptobratichus japanicus, G. (Menopoma)
aUeghaniensis the Hell-bender.
Family (2) Salamandridab.
Both the upper and lower jaws are furnished with teeth.
Eyes with movable lids. No gills or gill-slits in the adult
Ex. Molge, Salamandra, Desmognathus, Plethodon, Am-
blystoma.
XVI.] CLASSIFICATION. 456
FamUy (3) Protetdae.
Both the upper and lower jaws with teeth. Eyes without
lids. Maxillary bones absent. With permanent gills.
Ex. Proteus, Necturus,
Family (4) Sirenidae.
Both jaws are toothless. The hind limbs, the maxillary
bones and the eyelids are absent. With permanent external
gills.
Ex. Siren.
Order 2. ANURA.
Amphibia which lose when adult all trace of tail, hind-limb
much more powerful than the fore-limb and used for leaping.
Group I. Arcifera.
Phaneroglossa in which the epicoracoids of opposite
sides overlap.
Family (1) Discoglossidae.
Arcifera with a round disc-shaped tongue, adherent at the
whole of its base ; vertebrae opisthocoelous. Teeth in the
upper jaw only.
Ex. Discoglossus, Bambinatar,
Family (2) Pelobatidae.
Arcifera with a protrusible tongue, dilated sacral ribs and
with teeth in the upper jaw only.
Ex. Pelobates, Scaphiopus.
Family (3) Bufonidae.
Like the previous family, but without any teeth.
Ex. Bt{fo.
Family (4) Hylidae.
Arcifera with dilated sacral ribs, with teeth in the upper
jaw and adhesive discs on the fingers and toes.
Ex. Hyla, Charqphilus, Acris.
Family (5) Cystignathidae.
Arcifera with cylindrical sacral ribs.
Ex. Psetidis, Ceratophrys.
456 AMPHIBIA. [chap. XVL
Group II. Firmistemia.
PhaneroglcMssa in which the epicoiacoids are firmly
united in the middle line.
Family (6) Engyotomatidae.
Finnistemia with dilated sacral ribs.
Ex. Engystoma.
Family (7) Ranidab.
Firmistemia with cylindrical sacral ribs.
Ex. Rana,
Order 3. APODA.
Amphibia of worm-like appearance, without limbs or tail
and with vestigial eyes.
Ex. Coecilia, Hypogeophis, Ichthyophis.
467
CHAPTER XVII.
Sub-Phylum IV. Craniata.
Class III. Reptiles.
The name Reptile denotes literally anything that creeps (Lat.
General Char- ^^P^ ^r r^to, to cTawl). Zoologically the term
cteristica. denotes cold-blooded quadrupeds which are covered
rith horny scales and which lay large eggs, inside the shells of
irhich the whole development is completed.
But it is not merely the size of the egg nor even the character
)f the embryonic development which distinguishes Reptiles from
\jnphibia. There are isolated cases of species of Amphibia in
irhich the development is practically completed within the egg-shell,
mt in all Amphibia the whole egg becomes converted into the body
if the larva. In Reptiles on the other hand part of the egg is made
nto a hood termed the amnion, which is wrapped around the body
if the embryo. This structure is cast off entirely at birth and the
round caused by its tearing is healed. With it is also cast off a
portion of the urinary bladder — ^the allantois in the stricter and
iriginal sense — which extends into the amnion and appears to
ubserve respiration during embryonic life. In strictness, therefore,
•nly a part of the egg is converted into the body of the embryo.
This peculiar mode of development is shared by Birds and
Mammals, for which reason these two classes are often included with
he Reptiles in the term Amniota.
Next to the development perhaps one of the most characteristic
eatures of Reptiles is the nature of their skin. They are typically
overed with scales which are widely different from the scales of
isL The latter are essentially areas of the dermis hardened by the
leposition of lime with sometimes the addition of a layer of crystals
rom the basal ends of the ectoderm cells (enamel).
438 BEPTILIA. [chap.
The scale of the Reptile on the contrary is nothing bat an ana
of the homy layer of the ekin where the cells are coDrerted into
horn or Keratin and are adherent to one another. In the mass tS
the scale the horn is rendered brown by the presence of pigment,
bat the outermost layer is composed of clear cells and is known as
the epitrichial layer. A corresponding layer covers the embiyot
of Birds and Mammals, but is shed before birth. A stonghing
or ecdysis of the scaly epidermis ia a constant feature of the
Reptilia. It may take place bit by bit, or as is the case widi
many Sauria the whole ' skin ' is cast in one piece.
The dermal glands so characteristic of the Amphibia ha*e
almost totally disappeared, being restricted to a small area, as, for
Fia. 364. Section through the Scale of a LiBurd.
1. Epitrichial layer. 2. Heavily comiBed oellB forming the scale. 8. Pig-
ment cell, i. Ordinary cells of horn; Uyer. 6. Innermost Halpigbian
layer. 6. Dermis.
instance, the front of the thigh in a lizard. It follows that a Keptale
is essentially a dry-skinned animal and by no means a "slimj
beast."
Besides the structure of the skin Reptiles are distinguished from
Amphibia by many other points in the anatomy. Thus the skull
has a larger number of cartilage bonee, and includes what maf
be considered primitively part of the vertebral region dnce the
hypoglossal nerve (see p. 435) is now a cranial nerve. The skull
articulates with the vertebral column by one condyle. In the heart
the conuH> arteriosus has disappeared and the ventricle is partly
divided. The sexual part of the kidney is entirely disjoined from
the asexual
The lungs have to some extent acquired a spongy texture, and
the mechanism for inhaling and exhaling air is usnally to be fmnd
CLASSIFICATION. f^H
in t^e ribs, not in the hyoid or remains of the hinder visceral
KTcbes as in the Amphibia.
Living Rflptiles are divided into five Orders, of which one
consists only of one species, Sphenodon punctatug, found iu New
Zealand. This animal is the type of the Order (i) Rhyncho-
oephaJa, and is especially intere.^tiDg as not only being to some
extent intermediate in stniL'ture between other Orders of living
Reptiles, but as recalling very closely the structure of some of the
oldest fossil Reptiles known to us ; indeed it retains in many
respects a structure which we believe wa^ possessed by the common
ancestors of the remaining four groups. These are the (ii) LacertUla
(Lizards), the (iii) Ophidia (Snakes), the (iv) Chelonia {Turtles
and Tortoises) and lastly the (v) Crocodilia (Alligators and
Crocodiles). Of the five Orders only the secoud and third are repre-
sented in Great Britain and these by very few species ; in North
America the last four are well represented. The Lacertilia and the
Ophidia are the most closely related and they are often grouped
together under the same term SAURIA.
Ab type we may select the i-ommon lizard, Lacrta vlvipara,
which may be seen on very warm days disporting
^_''"'' itself iu sandy and stony places in the south of
England. On the Continent it and allied species
»re far more abundant ; iu the South of Europe in summer the
whole country is alive with lisards. Almost every step in the
country causes two or three specimens to rush rapidly away into some
retreat, either a hole under a stone or a cleft in the bark of a tree.
The English Lizard has roughly the shape of a Newt, but there
is a distinct neck region in front of the fore-limb, and the limbs are
sufficiently powerful to completely raise the belly well above the
ground and also to run at a compariitively rapid rate. Both mauns
id pes have five digits which end in aharji claws. The body is
covered all over with minute scales (Fig. 254), of which the prevail-
ing colour is reddish-brown above, and orange passing into yeUow
benoath. On the ventral surface and the top of the head the scales
are larger and arranged in pairs. The ear-drum is situated at the
bottom of a slight pit, which is the first appearance of the outer
ear. It is not developed in all Reptiles.
The anal opening is a transverse slit at the root of the tail
behind the hind pair of legs. In front of the thigh the scales are
perforated by a row of pores, the opt-nings of the only dermal glands
which the lizard possesses.
i60 REFTILIA. [chap.
TorDing at once to the skeleton, we find that the TCTtebnl
column consists of procoeloos yertebrae. All the
vertebne articalate with one another by oyeriapping
&cets called pre- and post-zygapophyses as in Amphibia.
Although extemaUy similar to the vertebrae of Amphibia, the
▼ertebrae of the Lizard and of Reptiles generally are fonned of
different elements. Thus the basi-dorsal and inter-doisal have been
suppressed, while the basi-ventral forms an interyertebral disc of
cartilage which in the tail bears a pair of processes united with one
another to form a Y-shaped chevron bone, recalling in its sh^
the haemal arches of fish. In the neck r^ion the basi-ventrals each
bear a bony wedge which is called the sub-vertebral wedge bone.
The centrum is formed by the united pair of enlarged inter-ventrals,
while the basi-ventrals are partly converted into intervertebral pads,
and partly into small parts which occasionally are ossified as the
so-called intercentra. The rib has shifted its position so that the
capitulum is attached to the front end of the centrum (inter- ventral)
behind the basi-ventral to which it belongs. The tubercular attach-
ment is represented by ligament. There are two sacral vertebrae
which have expanded transverse processes with which the ribs are
fused. Behind these come the vertebrae of the tail — the caudal
vertebrae. Each of these bones is made up of two halves, an
anterior and a posterior, which are but loosely connected with
one another. The consequence is that when a Lizard is seized by
the tail this organ in many species snaps in two, one of the vertebrae
breaking into an anterior and a posterior half.
All vertebrae in front of the sacrum, except the first two, have
distinct ribs attached to their transverse processes. The first two
are called respectively the atlas and axis vertebra. The first is as
in the case of Amphibia a mere ring. It is composed of the first
pair of neural arches united with the first pair of basi-ventrals, and
is therefore to a certain extent homologous with one of the inter-
vertebral discs. The second has a well-marked centrum, to the
front of which is attached a peg-like process — the so-called odon-
toid process — which projects through the ring of the atlas. This
odontoid process is quite unrepresented in the Amphibia, but it is
characteristic of all Reptiles and Birds and Mammals. It is formed
by the first pair of inter-ventrals and is therefore the first centrum.
In young specimens it can be seen to be separated from the centrum
of the second vertebra by an unossified disc representing the second
pair of basi-ventrals.
The ribs in front of the jjectoral girdle remain quite short — this
region is the cervical or neck region. Immediately beliind the
pectoral girdle the riba are very long
and curved so as to half encircle the
body like the hoops of a barrel.
The foremost have attached to their
lower ends cartilaginous bars — the
sternal ribs — which are in turn
united with a cartila^nous sternum
in the middle line. This structure
has the form of a lozenge -shaped
plate with a hole in the middle,
ending behind in tvro forks to which
some of the posterior sternal ribs
are attached. The whole sternum
has arisen from the junction of the
sternal ribs one with another. First
those of the same side unite to form
a eternal band, and then these two
bands unite in front hut remain
separate behind. The hole in the
middle also is a place where they do
Dot unite.
The flkuU is distinguished from
the Amphibian skull by many
features. The jaws do not arch
outwards at the sides of the cranium,
as in the frog, but are bent inwards **• S"*"!*! ^'^•^^ not united.
1 1 ■ r, 1 ■ 1 1 ■! J- SloniBl nh.
Bnderneath it. Belnud. the cartilage
of the cranium is completely replaced by four bones — by the supra-
occipital above the foramen magnum, the ex-occipitals at the sides
of this opening, and the basi -occipital beneath. This last bone
bears a single knob or condyle which articulates with the atlas
Tertebra. To t!ie formation of this condyle the ex-occipitals in
some degree coutribute. The basi-occipital and the single condyle
and the supra-occipital are highly characteristic of all Reptilia — as
is also the basisphenoid bone. This is a bone replacing the
eartitaginous floor of the cranium just in front of the basi-occipital.
The paraspheinoid so characteristic of Amphibia is reduced to a
mere splint attached t« the front of the basisphenoid.
'ITie anterior part of the cranium is so compressed between the
Via. 255. Ventral view of the
Shoalijer~Giritle &diI Sternuni of
a Lizard. LofTnanttiii longipei
« 2. After Parker.
1. Interclsviole. , 2. Clavicle.
S. Scapula. 4. Coracoid.
5. Precoraeoidal process. 6. Glen-
^^m
462 REPTILCA. [CB&P.
lai^e eyes that ita c&vity completely disappears and it becomes re-
placed by a vertical sheet of membrane, the inter- orbital septan.
It follows that in the dried skull the two orbits apparently open
widely into one another. Almost the entire brain is poshed back
Fio. 25G. A, Lateral v
1. Premnxilla. 2. MaiilU. 3. Nasal. 4. Lateral ethmoid. 6. Sapia-
orbilal. 6. Lachrymal. 7. Frontal. S. PoatlrontBl. 9. PrefrontaL
10. BasiaphcDoid. 11. Pro-otic. 12. Epi.otic. 13. Pterygoid.
14. Epipterygoid (colmuella oraoii). 15. Jugal. 16. TraDBvene bone.
17. I'araspheDoiil. 18. Quadrate. 19. Parietal. 20. SqnamoeaL
21. Supratempoial. 22. Bxoccipital. 23. Dentar?. 34. SpleDiaL
25. Sapra-angnlar. 26. An^^laF. 27. Coronoid. 28. AiiicaUT.
29. Tomer. 30. Basi-ocoipital. 31. Orbitoapbenoid.
behind the eyes into the hinder part of the cranitim. Only the
olfactory stalks run through holes in the npper part of the septum.
The orbitosphenoid of Urodela and the spbenethmoid of the frog
XVII.] SKELETON. 463
are quite unrepresented, though in some of the larger lizards allied
to Lacerta there is a minute orbitosphenoid bone in the upper part
of the inter-orbital septum (31, Fig. 256). The inter-orbital septum
is certainly a characteristic of the primitive Reptilia. It has how-
ever been lost in some of the most recent and highly modified forms.
The auditory capsule as in Teleostei is completely converted
into bone, but it is ossified by three bones only, anepi-otic above,
which fuses with the supraoccipital, an. opisthotic behind, which
joins the exoccipital, and a pro-otic which remains distinct.
There is no trace of the pterotic bone so characteristic of Teleostei.
As in Amphibia the first visceral arch is represented by an upper
half consisting of a suspensorium with a pterygoid process, and a
lower half — Meckel's cartilage. In the upper half, however, the
cartilage is completely replaced by bone. The suspensorial portion
forms the quadrate bone, which is attached to the side of the
auditory capsule. The pterygoid process is completely ossified by
the pterygoid bone behind and the palatine in front.
A curious bone characteristic of the Lacertilia excluding the
Amphisbaenidae, and called the epipterygoid or columella
bone, nins from the pterygoid vertically up to the parietal. This
bone is however found only in some Lacertilia, not in Reptiles
generally.
The two pterygoid bones however, instead of arching outwards
converge, under the base of the cranium, and they articulate with
outgrowths from the basisphenoid, called basipterygoid processes.
The palatines are united in front with the floor of the nasal capsule :
tliey bear on their inner sides slight ridges which project somewhat
into the cavity of the mouth. These ridges support a flap of the
lining of the mouth, the palatal flap, which is most characteristic
of all Reptilia but is not found in any Amphibian (Fig. 259). It is
a first trace of the process which ends in the higher animals and
even in some Reptiles in the division of the mouth-cavity into an
upper air-passage and a lower food-passage.
The end of MeckeFs cartilage which articulates with the quad-
rate is converted into a bone, the articulare. Three pairs of the
hinder visceral arches are preserved. These retain their rod-like
form as in Urodela, the median connecting pieces (copulae) remain-
ing small.
The membrane-bones of the skull are one of its most character-
istic features. The roofing bones are the same as in the Urodela —
paired nasals, frontals and parietals. On the roof of the mouth
464 KEPTILIft. [OHtf.
there are two vomers and a parasplieiioid. The vomers, howevw,
are rod-like, toothless and placed close together, and the pa>»-
gpheuoid is a small rndiment.
The bones of the side of the bead and the npper lip fonn a moet
Stegooephalan {Mattodomaunu giganteut, ftbont ODe-flflMoth lut. liM,
after E. Fraasj. B. (ieneralized Rbjnobooephftlaa uid CrooodUUn.
C. (ieoeialized LRcertilUn, often losing even the ucade here iodinUd.
D. Generalized Bird. /r. Frontal. j. Jogal. I. Lktenl temponl
tossa, la. Lachrymal, mx. Maxilla, n. Naiial opening, na. NmoL
0. Orbit, pa. Parietal, jitnx. Prenuiiilla. pr/. Prsfrontal. ptf. FoM-
troDtal. pto. PoBt-orbital. qj. Quadrato-jagoi. qu. Quftdiste. i. Sopia-
peculiar scaffolding which is widely separated from the craninm.
The Lizard is in an intermediate condition between the Stegocephak,
where a continuous sheet of bones extends from the craoiom to
the upper lip, and modem Amphibia, where all those boDes have
JtVn.] SKELETON. 465
disappeared, leaving a large vn^utty between the craDium and upper
Kp.
In front in the upper lip there is a premaxilla bearing teeth
ibllowed by a maxilla in which there are alao teeth. The maxilla
joined to the pterygoid by an eetopterygoid or transverse
bune. Between the maxilla and frontalon the side of the face are two
bones known tm prefrontal and lachrymal. The line of t>OQei< in
the npper Up is continued by the jugal. This nnJtes with a bone
placedbehiud the eye termed the post frontal, which joins both the
frontal and parietal. Thus the eye is surrounded by a ring of bone.
The squamosal is a characteriHtii- V-ahaped bone. The apex
of the V artioidates with the upper aide of the quadrat* : of the
•two arms one is directed forwards and meets the postfrontal, thus
forming a bony bar parallel to the cranium which is called the upper
emporal arcade, Tlie other limb in directed backwards and
awards and meets a cre^t on the parietal eo that a bridge is formed
ixtending over the hinder part of the cranium, The space in the
iried skull existing between this bridge and the iTanium is called
he post- temporal fossa. In many reptiles, including most
jacertilia, there is a similar sgiace between the cranium and
the lateral bridge formed by the junction of the squamosal and
postfrontal. This space ia roofed over in Lacerta by two membrane-
buues calleil supratemporals, but when uncovered it is known as
the supratemporal fossa.
Finally, the space intervening between the quadrate and jngal on
fcbe side of the face is known as the latero-temporal fossa. In
f^iAenadoH, Crocoditia and a very large number of extinct Beptilea it
B bounded below by a quadrato-jugal Iwne which joins the jugal
» the quadrate. When the ipiadrato-jugal is present the series of
>anee consisting of maxilla, jugal am) quadrato-jugal is known as the
ower temporal arcade. The upper temporal arcade is formed
Bwe have seen by the postfrontal and the squamosal. The loss of
e quadrato-jugal in Lacertilia is doubtless connected with the
■eater mobility of the jaws. In some lizards, notably in Geckos,
the quadrate can move slightly on its articulation with the skull,
can also the pterygoid on tlie basipterygoid process. When
tlte lower jaw is pulled downwards and backwards by its depressor
nuscle it tends to throw the lower end of the quadrate slightly
forwards: the pterygoid slides on the basigphenoid, and pushing
the ectopterygoid tilts the maxilla wtightly upwards. With the
tnaxilla all the other bones of the face move, and the membranous
K. * .M, 30
466 SEFTILIA. [CBiP.
iaterorbital eeptam pennits the ethmoidal re^on of the craoinm to
be slightly bent on the hinder portion.
The cartilaginous lower jaw is ensheaUied bf five distinct
membrane bones. The dentary and splenial occnpy the same
positions as in Teleostomi and Urodela. The angular clamps the
under aide of the articulare, the cartilage bone replacing die upper
end of the cartilaginoiui jaw. The supra-angular lies above the
angular on the outer side of the articular. The coronoid is a
small projection on the upper edge of tiie jaw.
The pectoral girdle is at first sight exceedingly complicated, but
in reality it consists of the same parts as in the Anura. Above the
c&rity for articulation of the arm — the glenoid cavity — there is the
cartilaginous scapula ; below the girdle forks into a coracoid and
precoracoid united by an epicoracoid. The cartilage bones pieaent
are the scapula, precoracoid and coracoid. The cartilage abow
the scapular bone ia slightly calcified but is not converted into
bone; this region as in Am^Jiibia is called the supra-scapnl^
Along the inner edge of the supra-scapula, scapula and precoracoid
TMns a strong membrane-bone, the
clavicle which reaches a median bone,
the T-shaped interclavicle. Thi»
bone underlies the sternum. The two
epicoracoid cartilages join the ant«riiH
edges of the sternum (Figs. 255 and
258).
The space between the coracoid
and precoracoid is called the coracoid
fontanelle. Since in the Urodela it
is not closed by an epicoracoid it ma;
be regarded as a hay or indentation m
the lower half of the originally sim[^
pect^iral girdle. The condition of
affairs in Urodela throws considerable
tight on what occurs in certaia other
Lacertilia, such as the American
Iguana. There we find that a similar deep indentation has become
developed on the inner side of both scapula and coracoid, so that
projections are formed to which the names mesosc&pula and
mesocoracoid have been given. These are not ossified by sepa-
rate bones but are regions of the scapula and coracoid bones.
The fore-limb of the lizard might be taken as the tgrpe of the
t, Supraac&pala. 2. Sc&pulft.
3. OleDoid cavity. 4. Co-
racoid. £■ Clavicle,
terclavicle. 7. J
coidal process.
pvn.] SKELETON. 467
I pentadai;ty]e limb, since there are five tiogers and the i-arpns has
r ftll the nine bones developed.
) The pelvic gir'Ue differs markedly from that of any Amphibian,
, in that iu ite lower portion there is a hole called the obturator
' foramen, corresponding to the cora«oid foramen in the pectoral
> girdle. The girdle is ossified by three bones, viz., a vertical ilium
I articulating with the ribs of the sacral vertebrae, a pubis ossifying
the anterior limb of the lower half of the girdle and an ischium
osaifyiog the posterior limb. Both pubis aiid iscliium meet their
I fellows in the middle line ; such a union is termed a symphysis.
^The two obturator foramina are closed below and at the same time
Keparated from one another by a loiigitudiual ligament which may
^kave u certain amount of ossification in it. All three Iranes con-
^Bibut« to the formation of the acetabulum, the cavity for the
Huiiculation of the femur.
W The presence of the obturator foramen and a distinct pubis is
characteristic of all Reptiles, Birds, and Mammals, and at once
distinguishes them from Amphibia.
On the hinder edge of the pubis there is a projection which is
called the lateral process. In some e.\tinct reptiles this process
was extraordinarily long and ossified by a distinct bone, which has
been called the post-ptibis. It is the post-pubis which forms the
BO-called pubiis of Birds and Miimmals.
The most marked feature of the hind limb is the formation of a
shaqily- marked "ankle" joint. There is one place and one only
where the foot bends on the shank : whereas in Urodela bending
can (H'cur at any place in the mosaic of small bones which forms
the tarsus.
In the lizard all the three upper bones of the tarsus are joined
to form a horizontal bar. The lower bones have almost entirely
coalesced with the corresponding metatarsals, only the third and
fourth of the series being distinguishable. Thus the lizard has what
has been called an inter-tarsal joint — an arrangement which is
highly characteristic of many Reptiles and of all Birds.
All trace of the division of the muscles into myotomes has
disappeared, but the innermost layer of the muscles
of the flanks has become divided secondarily into a
aeries of bands connecting eacli rib with its successor. Thesd
bands are termed the intercostal muscles and each consists of an
external and an internal layer of fibres. The fibres of the external
layer slope upwards aud forwards and, in contracting, cause the nbs
468 BEPTILIA. [CHiF.
to rotate forwards ; the fibres of the inner layer slope npwvds and
backwarda aad have the reverse effect. Respiration is effected by
the pulling forwards and backwatdi
of the ribs by these intercostal
ausclee. In their relaxed cod-
ditioD the rit» slant strongly back-
wards. When they are pulled
forward by musclee attaching thea
to the anterior vertebrae and bf
the external intercostals, diey rot-
ate forwards so as to stand out
at right angles to the vertebnl
column and thus enlarge the cmvi^
of the chest, that is, the ooeloDL
The diminution of pressure in tin
air-tight cavity at once causes u
inrush of air through the glfrttii,
the elastic luogs are expanded and
their walls closely follow the chat
wall It will be noticed that the
mechanism of inspiration is voj
different from that of Amphibisai
(p. 424). The network of low ridgei
which is found already on the aaa
side of the Frog's lung has iu tin
Reptile greatly increased in com-
plexity. The primary ridges ire
much higher, and between them an
lower secondary and even tertiai;
ridges : the cavity of the lung is ai
it were partly filled up by a spongr
mass. In all Sanrians however the
central cavity is easily rect^niud
as a wide space : whilst in Croco-
diles and Tortoises, still more so in
Birds and Mammals, it is lepn-
sented only by the bronchial
tubes.
The lungs are connected widi
the glottis by a comparatively long
stalk, the trachea or windpipe, which is stiffened if rings </
1. Posterior or internal nares,
2. Palatal folds. S. Internal
opening of EDstachian tabes.
XVII.] ORAL CAvnr. 469
csrtilage. A aimil&r structure is found amoDgst Amphibia in the
Gyninophiona and in a few Urodela. Immediately below the glottis
the trachea is enlarged. The enlarged portion is stiffened by a
large, broad, ring-shaped
cartilage, the cricoid, to
which are articulated two
arytenoid cartilages. The
whole structure consisting
of the dilatation of the
trachea and iu cartilages
ia called the larynx.
The Lizard like the
Prog lives principally on
insects and ia provided
with a long mobile tongue
cleft at the tip, by means
of which the prey are
whisked into the mouth.
The tongue is free in front
and attached behind, the
opposite arrangement to
what is found in the Frog.
The teeth are simple and
conical, and are implanted
in a groove on the inner
side of the bones bearing
them. As the Lizard grows
they become actually fused
with the bone along the
aide of the groove.
When a Frog's mouth
is forced open, amongst the
most striking features of
the roof of the mouth are
the two large eyeballs shin-
ing through. When we
open the mouth of a lizard
nothing of the eyes can be
seen. There is projecting
inwards from the upper lip on each side a flap, the palatal flap.
This does not meet it« fellow in the middle line, a cleft existing
I. II. ni. IV. V. VI. First to siith arterial
■rchea. 12. Tracheo-litigLiftl (veotral
carotid). 13. Common carotid (doreal
carotid). lH. Bigbt ajstemlo arch.
16. Lett ajBleniio »roh. 17. Dorsal
aorta. 19. Fulmonary. 20. In-
nomiaate. 21. Soapular (equivalent
of subclaTian ofveatraltype). 22. Sub-
clavian (dorsal type). 24. Coeliao.
470
REPTILIA.
[chip.
between them. These flaps conceal the eyeballs and the ww*
openings of the Eustachian tubes which lead up to the ear-dmin.
Palatal flaps as already mentioned are found in iJl Beptilia.
Turning now to the circulatory system we find that the conns
arteriosus no longer exists as such, having been cleft into three
trunks down to its commencemeiit
in the yentricle. One of these
trunks is ventral and slightly pos-
terior to the others, and gives rise
to the two arterial arches, which
as pulmonary arteries supply the
lungs and have no connection
with the aorta. The other two
arterial tninks form the right and
left roots of the aorta. They cross
each other at their origin, that
which passes to the right of the
oesophagus arising from the left
of the ventricle and vice ver9d.
The third pair of arterial arches,
corresponding to the carotid arches
of Amphibia, are well developed
in the lizard. They have a
common stem which arises from
the right systemic arch. In some
Lizards the longitudinal epibrsn-
chial vessel of the embryo persists
between the carotid and systemic
arches on either side, so that in
this respect a Lizard may be even
more primitive than a Newt. In
others, as in all other Reptiles, this
connecting link has disappeared.
The ventricle has projecting
into its cavity two imperfect par-
titions or septa. One is the con-
tinuation of the division between
the two auricles, the other is a ridge which arises from the ventral
side and tends to separate the opening of the pulmonary arteries
frrom that of the right and left aortic arches. When the ventricle
at first begins to contract it is full of venous blood fit)m the right
Fio. 261. Diagram to show arrange-
ment of the principal veins in the
Anura and Reptilia,
1. Sinus venosus, gradually disappear-
ing in the higher forms. 2. Duc-
tus Cuvieri= superior vena cava.
3. Internal jugular = anterior card-
inal sinus. 4. External jugular
= sub-branchial. 5. Subclavian.
6. Posterior cardinal, front part
= vena azygos. 7. Inferior
vena cava. 8. Renal portal =
hinder part of posterior cardinal.
9. Caudal. 10. Sciatic = internal
iliac. 11. Pelvic. 12. Anterior
abdominal. 18. Femoral =
external iliac.
t : by the time arterial blood has commenced to euter it from
le left auricle, the veutral septum meiitiooed above has been driven
against the opposite wall, ao aa to shut off the pulmonary trunk
from the rest of the ventricle and prevent its receiving any more
blood. The left aortic arch, which axiaes on the right, receives
mostly venous blood from the right auricle, the right aortic arch
arterial blood from the left auriule, and it is from this arch, aa
mentioned above, that the
carotid arteries ari^. Hence
the head receives compara-
tively arterial blood, and
all the rest of the body
minted blood. The lingual
artery of Amphibia is re-
presented in Reptiles by a
vessel {tracheo-lini^nal or
"ventral carotid") which
arises from the carotid arcli
oear tlie middle bne and
supplies the tongne tra' hea
and muscles of the neck
and shoulder.
The vessels supplying
the fore-limb arise together
from the right s>stemic
arch in the case of Lizards
instead of na in Anura from
both right and left arches
tliey are subclavians of the
dorsal type (see p. 33u),
but in Chelonians and
Crocodiles the eubt-lavians
are ventral in origin, com-
ing off from tiie carotid
trunk on either side close
to its division into ventral
and dorsal carotids. In
Lixarda this "ventral subclavian" is represented by the scapular
artery which runs to the shoulder region.
The veins, on the whole, flosely resemble those of Molge,
There is however no large cutaneous vein, and the anterior part of
I the posterior cardinal, now called the vena azygos, is found only
Fio. 362. UrinogenitiiJorgnnBotMiiteLitard,
1. Testis. 2. Vns deferens — archinephria
dact. 3. EpiJidyiniB^ (msNOQephras).
4. Kidney — motajiephrOH. 3. Uruter.
d. Bkdtler. 7. Rectam out an<] turned
back. 6. Cloftca laid open. t). Open*
inK of ViiB daferena. 10. Groove Uading
to opening of penis. 11. Pfnia. 13. Dor-
sal fiorla.
472 REPTILIA. [chip.
on the right side, where it receives the numerous intercostal veins,
returning the blood fix)m the muscles connecting the ribs. The
renal-portal, sciatic, femoral and anterior abdominal veins have the
same arrangement as in the Urodela.
The brain is distinguished by the comparatively laige sixe of
the cerebral hemispheres, which overlap the thalamencephalon above
and at the sides. They end in fix)nt in large pear-shaped olfactoiy
lobes. The cerebellum is a high vertical ridge and is thus much more
prominent than in any Amphibian. The remainder of the hind
brain, the medulla oblongata, includes a longer portion of the spinal
cord than it does in Amphibia, for the hypoglossal nerve arises from
its side and escapes through an aperture in the exoccipital bone.
This nerve is reckoned the twelfth cranial, not the eleventh, for
there is a trunk called the spinal accessory or eleventh cranial
This arises by several roots from the side of the medulla oblongata,
joins the vagus in a ganglion, and then leaving the skull supplies
some of the neck muscles. In the Ophidia this nerve is not dis-
tinguishable from the vagus.
In the genital organs, the Lizards and Reptiles generally are
distinguished from Amphibia by the complete separation of the
mesonephros from the metanephros or functional part of the kidney.
The persisting part of the mesonephros, now known as the epididy-
mis, is only developed in the male, where it is closely connected
with the testis. As in the Newt it receives the vasa efferentia. In
the female the oviduct is shorter and has a wider internal funnel
than in the Amphibia, and it is also placed further back so as to
be rather nearer to the ovary. This is an arrangement suited to
the large size of the eggs, which are too heavy to be drawn any
distance by the current produced by the cilia of the oviduct.
The egg is fertilized whilst still in the oviduct The male lizard
has two organs called copulatory sacs or penes, situated, one on
each side, on the hinder wall of the cloaca. These, when not in
use, are hollow pouches opening into the cloaca. When in use they
are turned inside out, and are then seen to have grooves leading to
the openings of the vasa deferentia or archinephric ducts.
Most lizards lay their eggs in crevices amongst stones and
allow them to be hatched by the heat of the sun. In all cases a
considerable amount of development goes on before they are laid.
In the English species Lacerta vimpara the young burst through
the egg-shell and use up all the yolk whilst they are still in the
oviduct, so that in common parlance they are bom alive, that is,
as little lizards and not as eggs.
Order I. Rhynchocephala.
As mentioned above, the order Hhynchoi-eph&ls ts represented
by the single species, Sph/rtioJon punrtatm, found only in New
Zealand. This is a very Lizard-like animal. The back is covered
with small scales which in the middle line form a comb-Uke crest :
A
Fla. 3G3. Skull of Splienudo/i pmielatut v 1.
, Lateral. B. Dorsal. C. Venlra!. D. Posterior. After toq Zittel.
Promaiills. S. Nasftl. 8. Prefronliil. i. Prontnl. 5. Poal-
froDtol. 6. Parietal. 7. (iiituinioBnl. 6. Quadratojugal, 9. Quad-
rate. 10, Postorbital. II. Jugal. IS. Maxilla. 13. Vonii
14. Palstine. 16. Pte(7(!oid. IK. Eato pterygoid or traDaTerse bor
17. EioooipiCtil. IB. EpipterfROi^ 19' BaKiBphenoid. 30. Bnpra-
(emporal foaua. 21. Latt^ral temporal fossa. 23, Orbit. 23. Post-
temporal fosBn. 34. Korainen magnum. 25. Anterior nari
26. Inlprpftrii-lal foramea, 27. Denlnrj. 28. Supra-angulf
00. Articular.
tiie belly is covered with large square scales. In the skeleton and
m&le genital organs, however, Spheaodon is widely different from
the IiiEard. The ({uadrate in the skull is quite immovable, beiug
firmly clamped by the Bi|uamosal anil iiiLtdnttojiigal. I'he latero-
temporal fossa is thus completely bounded below and the supra-
temporal fossa is uncovered. Between the parietals is a gap called
474 REPnLiA. [chap.
the interparietal foramen : in this is sitoated the tip of the
pineal body which has here all the characters of a simple eye.
The animal has teeth when young, but they become worn away,
while the edges of the maxilla and premaxilla become converted
into cutting edges.
The vertebrae are amphicoelous, and the basi-ventrak, repre-
sented by the sub-vertebral wedge bones and chevrons, are placed
beneath the interspaces between the vertebrae throughout the neck,
trunk and tail, and not as in Lizards in the neck and tail regions
only.
The ribs have three divisions, there being a small intermediate
piece intercalated between the dorsal and sternal rib. From the
dorsal rib a hook-like outgrowth, the uncinate process, projects
backwards, which overlaps the next rib as in Crocodiles and Birds.
Behind the sternum there is a long series of rod-like bones, the
so-called abdominal ribs, embedded in the muscles of the belly.
They are placed parallel to the direction of the sternal ribs, that is,
they slope obliquely forwards and inwards. They are regarded as
membrane bones and supposed to correspond to the ventral bony
scales of the Stegocephala.
All these peculiarities of the skeleton are found in many of the
oldest fossil reptiles.
There is no proper copulatory organ : the cloaca is used for this
purpose as in the Urodela.
From a condition in many respects represented at the present
day by Sphenodon, the ancestors of living reptiles appear to have
diverged in two directions.
On the one hand, the original stock gave rise to descendants
with long flexible bodies and extensible jaws — this latter feature
involving of course a movable quadrate. The cloacal opening
became converted into a transverse slit and copulatory organs
became developed behind it. This stock includes the Snakes and
Lizards which are often included in the one comprehensive Order
the Sauria.
On the other hand, the descendants of the common ancestral
form diverged in the direction of heavily armoured forms, in which
membrane bones underl}ing the scales were developed and in which
the jaws are very powerful, the quadrate remaining immovably
clamped by the quadratojugal. The cloacal opening became a
longitudinal slit and developed the single median copulatory organ
on its front walL This stock includes the Turtles and Crocodiles.
SAURIA.
We now tarn to the Saubia. Moat people would imagioe that
the task of distinguishing a lisard from a snake was an easy one.
But if we were to collect together all the limbless species of
Reptiles we should find not only that they differ very much from
one another in the structure of the skull and in other points, but
that they are more nearly related to different families of lisards
than to one another. There is no doubt that the snake-like forms
have been derived from four-limbed reptileB like lizards, for some of
Ftn 964 A limblHBi Llaord ttffuti jragUn the bltod worm hIi^I I ly reduced.
tham have rudimentary vestiges of limhs. It is evident then that
there must be an advantage in certain situations in getting rid of
limbs, and it is further evident that the effect of this advantage
has been that not only in one but in many families of liiurds
some species have lout their limbs. The kind of life to which a
snake-like form is suited is a lurking one amongst crevices in
atones, or thick vegetation, or in the aoil, where movement is heat
effected by wrigghng and limbs wtudd be in the way.
Under these circumstances, we mut^t either class together all
limbless Sauria as snakes, and thus give up the idea that the
tnembers of an Order must necessarily be descended from the same
ancestral species, or else we must select one group as the true
Bnakos (Ophidia), the members of which have many other characters
in common besides the negative one of having no limbs. This
476 REPnuA, [chap.
latter coarse is that which has been adopted by Huxley, who defines
true snakes somewhat arbitrarily as those forms which have lost all
trace of the pectoral girdle and of the urinary bladder, although
they may retain traces of hind-limbs.
Order II. Lacertilia.
The Lacertilia then include all species of Sauria which have the
right and left halves of the mandibles connected by a sutural
symphysis and which retain a urinary bladder and some trace of the
pectoral girdle. In all other characters they are a very diversified
group. Most of them possess well developed limbs, movable
eyelids and movable quadrate bones, but a good many species
belonging to specialised burrowing families have no limbs and
scarcely a trace of the pectoral girdle, while the eyes are concealed
beneath the skin and the quadrate has become more or less im-
movable. Some, e.g., Draco volans, have the hinder ribs expanded
so as to press out two expansions of skin and form a parachute-like
expansion on each side, by means of which they are supported as
they flit from tree to tree in great leaps. Most feed on insects,
worms, &c. like the English lizards ; some are large enough to seize
mice and birds and frogs. The limbless forms are represented in
England by the Blind- or Slow- worm, Anguis fragilis, and in North
America by the allied Glass-snake, Gphisaurus ventralis. These
animals have skulls like that of Lacerta and rudiments of pectoral
girdles. Besides the Blind-worm, the Common Lizard, Lctcerta
vivipara, and the Sand- Lizard, Lacerta agUis, are British.
In North America four families of Lizards are represented, one
being that of the limbless Anguidae, while the most remarkable
of the others is that of the Iquanidae. These animals have
short thick tongues and overlapping scales which form a crest of
spines on the head and back and round the throat. Phrynosoma
douglasiy the horned ''toad," is found all through the Central
States and even penetrates into Ontario ; it is the sole lizard
found in Eastern Canada.
Order III. Ophidia.
The Ophidia, or true snakes according to definition, have the
right and left halves of the mandible connected by an elastic band ;
they are also devoid of a urinary bladder and of any trace of a
XYll'] OPHIDIA. 477
pectoral girdle. Beaides this however they have a large immber
of other characters which severally are shared by some families
of Lizards but which collectively are found only in the Ophidia,
The vertebrae in additiou to the zygapophyses on the sides of
the nenrsl arch have median bosses and pits by wluch they &t Into
one another, called respectively zygantra and zygosphenes (Gr.
avTpov, a cave or hollow ; o-'^ijV, a wedge). There are no stem&I ribs
nu: 383. Dorsal (Id the left) und ventral (to the tight) Tiews o( the akull of tite
Cammoii Snnke, TVopiifonudu tialrix. After Porker.
1. Preioixilloe (fu»d). 2. Anterior niiree. 3. XaaaL 4. PrefroDtsL
6. Frontal, 6. Pftrietiil. 7. Maxilla, S. TmnBrerm bone.
n, Palatine. ID, PCerytioid, 11. Pro.otio. 13. Eiocoipitol.
IB. Supra-nccipital. 14, Opinthotic. 15. Epi-otic. 10. Quadrate.
17. ParBsphr>Doiil. 18. BasiBphenoid. 19. BaBJ-oeoipital. 20. Ocolp-
ital condyle. 21. Splenial, 22. DeaCarv. 23. Angular. 24. Artionkr,
25, Snpra-anKular. 26. Coronaid. 27. Vomer. 2B. Squaniaesl.
IX. X. Forumina for the oiDth and Eanth oraoial nerveB,
or sternum, but the dorsal ribs are elongated and curved ventrally,
and a snake literally walks on the ends of them ; it is in a sense a
vertebrate centipede.
In the skull the chief point to be noticed is the extreme mobility
of the jaws. The jugal aa well as the riuadrat^jugal have disap-
peared, the pterygoids no longer articulate with the base of the
skull, and the quadrate itself is pushed away from the cranium by
the w^uamosal, which is a rod-like bone (Fig. -265). Some authoritiea
hold that this bone is not the representative of the s'luamosal, but
represents the aupra-temporal of Lawrtu. 'I'he result of this
airangement is that when the lower jaw is pulled down, the
*78 REPTILU. [chip.
quftdrate is quite free to thrust the pterygoid forwaid amd push np
the maxilla by means of the transverse bcme ; that is to say there
is the same mechanism aa was described in the lizard, only more
easily set in motion and
capable of much more more-
ment. Hie halvfls of the
mandible, or lower jaw, are
connected 1^ elastic fibres,
and thus they can be widely
separated. The restilt of this
is, that a snake has an enot^
mouB gape and can swallow
prey almost as large as itself.
Snakes of qnite moderate
size dispose of &ogs, birds,
&c. The large Pythons of
India can cmsh an ttnimal
lai^r than a half-grown sheep
into a shapeless mass by
coiling themselves around it,
and they then swallow it
whole.
The hyoid, including
under that name the remains
of all the hinder visceral
arches, is vestigial, consisting
of a single bone on each
side. This permits of the
pulling of the glottis far
forward between the halves
of the mandible when Uie
Flo. 266. DiasTam of Arterial Arohes ot . i ■ i ■ n _
Bnake Tiewed fram the ventral «pect. ">"»»! is engaged m swaUow-
inif its prey, this shifting of
I. 11. ni, IV. V. VI, First to siith arterial **.,. ^ ,■'.' ^,
archea. 12. Tracheal (Tentral carotid), position being necessary to
13. CommoQ carotid (dornal oarotidj. IS. prevent choking.
Bigbt ByBtemic arch. 16. Lett tyeteiaie r it i ii iL l •
arch. 17. Dorsal aorta. 19. Pol- ^^ "le StuU tne Drain 61-
monarj. 24. CoaUac. fends forwards between the
eyes and there is consequently
no interorbital septum. That this is a secondary and not a
primary state of afTaii^ is shown by the fact that the front part of the
brain is protected at the sides by downward extensions of the frontkl
Ixvil,] OPHIDIA. 47» 1
I and parietal bones, whereas iu aiiinials such as the Urodela andV
I Mammalia, where an iiiterorbital septum has never been formed, the >
!>ide-walls of the cranium are constituted by the orbitoephenoid ftod
aJisphenoid bones. It is curious to tind this aljsenue of an interorbitsl
septum in a family of limbless lizards, the Auphisgaenidae. What
relation, if any, it has to the anake-like habits it is hard to guess.
The two eyelid)^ have coalesced to fonn an extra guard in front I
of the eye, but there is a traus]>areiit i>ortion in the lower one "
through which the animal can see. The outer covering of scales is
Khed periodically, half-a-dozen times every year or oftetier, and
replaced by a new set formed by the activity of the ectoderm, and
during this process, since the covering of the eye is affected, the J
snake is blind.
Due lung is small, and the other (the right) greatly elongated, I
the hinder part being i^uite smooth.
The heart resembles that of Lizards both in structure and the 1
mode of distributing the arterial and venous blood. The differences
l)etween the vascular systems of a Snake and a Lizard depend chiefly
on the absence of limbs and the correlated great development of the
vertebral column, ribs and their musi'nlature as organs of locomotion
in the Snake. Thus the subclavian arteries are absent from the
right systemic arch, while the vertebral and caudal arteries e
veins are well devehiped. Another diD'erence is that the I
pulmonary artery is very slightly developed, in connection with
the reduced condition of the left lung.
Snakes are divided into many families, of which two are repre-
sented in Great Britain and three in the temperate parts of North
America. A rough classification would divide them according to
their habits into: ('() those which poison their prey, {!>) those which
crush their prey, and (r) those which swallow their prey directly.
Those which crush their prey are confined to the tropics ; those
which swallow their prey directly are the non-venomous snakes,
and ate representetl in both England and North America by the
family Coluiiridak. In this family the maxilla is long and bears
numerous teeth, as do also the pterjgoid and the lower jaw.
The head is much broader behind than at the muzzle. There are
about thirty species belonging to eighteen genera in North Amcr
of which y^rfpidiimttin tnrtalis, the garter-snake freijuently met
with in Canada, is one of the commonest ; and in Kngland the
family is represented by two species, the smootli-snake, CortmtUa
ianms, and the grass- or ring-snake, Tropidoiuitua luitn-x.
480 R&PTTLu. (cur.
I'be veiiamciiH snakes in America belong b> two families. In
the first, the ELAPruAE, the maxilla ia a long bone and beats in
front two large teeth which are gruoved, to allow the secretion of
glanda in the lip to trickle down into the wounil which they make.
The teeth behind are not grooved. The American Harlequin
Snake, ICJapg fahius. belongs to this family. This anake receiva
its name from its brilliant colours; it has iieventeeu crimsoD tings
bordered with yellow. Another family is that of tite Vipkridjie.
The maxilla is much shortened and bears one enormous fang,
which when the mouth is closed lies against the roof of the mouth :
when the mouth is opened the maxilla is rotated by means of the
ecto-pter>'goid, so as to erect the tooth. The typical Rattlesnake—
Crolalut horridat oi C airox — derives its name from an apj
Xvn.} CBELONIA. 481
of about H t<) 9 looaely coEnected homy rings which it bears at the
end of its tail, the shaking of which makes a noise like a rattle.
This is one of the most deadly snakes known : it is found all over
the Unitod Stales in mountainous places and enters Canada. Like
ftll Ckotalinak or Pil-vipers it lias a sensory pit between eye and
nose- The English Adder, Vipera berm, is, like all the Old World
Viperinae, devoid of such pits.
Order IV. Chelonia.
The Chelonia or Turtles are the most pecidiar order of the
Beptilia. In some respects they are nearest to the Amphibia, but
they are highly specialized. Their leading peculiarity is the pos-
session of two great shields, a dorsal the carapace and a ventral
the plastron, composed of bones firmly connected together, so that
most of the organs of the body are enclosed in a box. The homy
scales which cover in this box are very large and form what is
known as tortoise-shell. The carapace is formed of a central row of
neural plates which are espansions of the spines of the dorsal
vertebrae with a nuchal plate in front of these and a pygal
behind, the two last-named being of dermal origin.
On each side there are costal plates ; this name is given to
broad expansions of the outer surfaces of the ribs (Fig. 2(i8). The
ribs curve inwards to join the centrum, and since this, as in all
Reptiles, is formed by the interventral, each rib is nearly opposite
the interspace between two centra and sometimes itnites with
them both. The transverse process is represented by the exi>anBioQ
of the neural plate which meets the costal plate. The almost
horizontally directcil outer ends of the ribs are received into a
aenes of dermal bones called marginals, which form the edge
of the carapace.
The plastron is formed of one unpaired and several paired bones
(Fig. 269). The median bone, called the entoplastron. is believed
to correspond to the intcn.'lavicle of other Reptiles. The first pair
are called epiplastra and probably represent the clavicles of
other forms. The posterior pairs are called hyoplastra, hypo-
3)lastra and xiphiplastra respectively; they are firmly joined to
'the marginals.
In front and behind the plastron and carapace are 8e|mrated by
joft flexihie skin ; their edges project so as to form roof and floor
to cavities into which the bead and neck and arms in front and the
[CHif.
1. 266 AD
To T a
Buperh a Lo
composed are
Nuchn pate
4. Marginal ]
8. First verCc
aa and B
och y
nt a wo
ta Afte Ow
n In A the outlines of tb>
ne» I which the CBrapiee i«
S. b. 7. TboiMia vertdm.
ield.
■hil tb
penned
2 F
^bral ehield.
B h b
bj gh
9. Costal Bb
C. The Plastron of a Orcen Turtle, Chelone mydat x f. (Cunb. Una.)
1. Epiplastron (clavicle). 2, EQtoploatron (interolaviole). 3, HroplMtnii
[cleitbiDm]. 4. HjcopIoBtrai), 6. XipbiplutiOD.
XVII.] OHELONIA. 488
legB and tail behind can be withdrawn. A Btudy of the develop-
ment of modem Chelonia and of the anatomy of fo.sail siieciea makes
it plain that the anceaitora of the preHent furms were provided with
a carapace composed entirely of dermal bonee underlying the homy
ales, jnst as is the case with Crocodilia. This dennal carapace
however was gradually replaced by the development of bony ex-
LDsionB of the ribs and neural arches ; though remnants of it
t in the nuchal, pygal and marginal plates.
There is no trace of sternal ribs or sternum ; but the pectoral
and pelvic girdles o<M;upy the peciJiar position of being within
instead of outside the ribs, a conaeiiuence of the almost horizontal
direction of these. The girdles are in fact converted into pillars or
struts which keep the plastron and carapace apart. In front the
scapula forms a vertical pillar which has a ventral process — the
acromion — projecting inwards beyond the articulation with the
coracoid. This process is unique amongst recent ReptiHa but existed
in the Ple^iosauria. The coracoid slopes backwards and inwards.
The ilium and pubis serve to support the carapace posteriorly. The
pelvic girdle is similar to that of a Lizard but the pertoral girdle
has no epicoracoid. The limbs are essentially similar to those of
the Lizard but the toes are shorter and blunter. The neck is extra-
ordinarily flexible ; the vertebrae composing it fit one another by
cup and ball joiots, one is ami)hieoelous, another is biconvex. The
dorsal vertebrae have flat faces.
The skull is devoid of teeth and the premaxilla and maxilla are
short. Both they and the dentary have sharp cutting edges en-
she&tbcd in horn so as to form a beak. In all species the orbit is
iiicin'led with a bouy ring and the ectopterygoid or transverse bone
B wanting. The jmlatal crest on the palatine is hardly perceptible.
The squamosal does not usually join either the jiostfrontal or
parietal, hence the upper temporal arcade is absent and there is
no distiui-tion between the supra-temporal and latero-temporal
fossae. In the marine C'hehne and its allies however the post-
frontal, si[uamosal, parietal and quadratojugal coalesce to form a
sheet of bone from the crest of the skull to the lip. roofing over a
cavity lying at the side of the cranium and containing muscles.
Breathing is performed as in Amphibia, by a mylohyoid muscle
and other muscles causing movements of the hinder visceral arches,
of which there are three pairs.
The heart in structure and mode of action resembles that of
Lizards and Snakes, the left-hand gnteim^uG^cjmTgm^^oo^^
484 EEPnUA. [chap.
chiefly Tenons to the viscera, while the right-hand one sapplies the
head, trunk and limbs with blood which is much more arterialised
than that in the other arch (p. 470). The fore-limbs are howerer
supplied by a different vessel &om the subclavian of the Limttl
Lower jaw or mandible. 3. Nuchal plate. 3, Ventral piocess of sopuU.
the Acromion. 4. Scapula (much forcahortened). S. Marginal bolK.
6. Coracoid. 7. Ilium. 6. Pubis. 9. IscliiaiD. 10. Centrum
o( vertebra. 11. Humerus. 12. Kadiua. 13. Dlna. It. Cupo).
IS. Femor. 16. Tibia. 17. Fibula.
486
We have already aoen (page 350) that in some vertebrates the
Mtery to the fore-limb arises from the systemjc atuh on its dorsal
Gounte to join its fellow, while in others tbe fore-lioib receives its
blood from an artery given off from the ventral end or commencement
of the systemic arch or else Irom the ventral end of the third arch
near its division into dorsal and ventral carotids. As tbe vessel to
Hie fore-hmb is always called a subclavian artery it is convenient to
sxpress the fact that this vessel is not homologous throughout the
W
10
Fill. 'iTO. IianRiludinal vertical section throttgb tbe Cranium of a, Gtec^n Turtle.
Clithme mydat x |.
Pitrietkl. 8. Squaniosal. 3. Quadrate. 4. Bosisphenoid. 5. Baid-
ocoipital 6. QuadrntojuR&l. 7. Pro-ulic. S. Opialhotic. 9. Pter^j^id.
10, Pftlatine. 11. KikI paaaed into uuriol passage. 12. Eioccipital.
13. Epi'Otio fused to nupra-ocoipitftl. 14. Supra-occipilal. 16. Pre-
lunxiUa. 10. Maxilla. IT. Jiigal. IH. Fostrroiital. 19. Tomer.
20. PretfouUI. ai. PfOQtal. T 1 * 3. VII. Vni, IX, X. XI. XU.
foTiuuiiia tor the i^iiC of uiunial oenea.
rertebrate groups by the terms "dorsal subclavian" and "ventral
vobclavian." In Amphibians and Lizards the subclavian is of the
dorsal type, bat in Chelonians and, as we shall see, in (.Crocodiles
•bo the arm is supplied by a ventral subclavian, a vessel which is
homologous with the "scapular" artery to tbe shoulder muscles in
■ A Liwird. The venous .system in all chief respects is like that already
d&Dcribed m the Lizard.
The copulatory organ is a grooved rod attached to the front
rati of the cloaca. The groove leads to the openings of the male
hicts, the vasa deferentia,
486
HEPTILIA.
[CHiP.
The members of the order Che1oni& have very Tarioas habits and
modes of life. Some are vegetable feeders, others purely aiunuL
None are found in Great Britain, but the representatives of six
groups are fouod in temperate North America. These are
(1) The TBSTCDnriDAE
or Land Tortoises.
(3) The Emtdid&e w
Fond Turtles.
(3) The CiNoarBESiDAE
or Box Turtles.
(4) The Chbltdsidie
or Snapping Turtles.
(5) The Trioittchidai
or Mud Turtles.
(6) The Chblonidax or
Marine Turtles.
The TBSTUDiNiDAEhaTe
a very arched carapace snd
short club-like limbs io
which the toes are taghUj
bound together by "I""
Only a few species, TettuSo
pdyphemus, the burrowing
Gopher, and Ci^ado Caro-
lina, the Box Tortoise, ue
known in temperate North
America.
The Emtdidae are re-
presented by many qtedo.
In this &mily the carapm
has a wide horizontal nu^
gin and the toes are con-
nected by a web. Most of
the species are aquatic, s
few however are almost u
terrestrial as the Tem-
DiNiDAB. Ckrytemys pida,
the painted Pond Turtle,
ranges north into the St Lawrence.
The CmusTERHiDAE have a long and narrow carapace widi the
margins produced downwards; it is highest behind. The fixmt pu^
I. II. III. IV. V. VI First to eiith arterial
niches. 12 Tracheal (Tentral carotid).
13. Common carotid (dorsal carotid]. 15.
BiRbt systemic arch Ifi Left Byst^mic
arch. 17. Dora&l aorta. 19. Fuluonar?.
20. InnomiDate. 21. Sabclavian (veutial
type). 24. Coeliac.
tnd sometimes the bind part, of the plostroD move like a liinge od
the rest and close in the head and tail, whence the name Box
Turtle. Sole genua ChtDstemum, e.g., pt^nnsj/lvnnicnm.
The CiiELYDitiDAE are the so-called Alligator- or Snapping-
Turtles. The head, nei'k and tail are all large and cannot be
completely protected between the uarapace and plastron. The
carapace is highest in front. The jaws are hooked and powerful
and the animals are very vicious. Chdijdra SfTjmitina, the
~'itiapp<.>r," is one of the commonest of American turtles. It is
ibund everywhere from Canada to the tropica.
The Trionvchidae or Mud Turtles have no horny scales ; both
carapace and plastron are covered with leathery skin. There is a
soft pig-like Bnout ; only the three centre toes have claws. They
Beek their food by burrowing in tlie bottom of ponds.
The Chblosih.ie are distinguished liy their peculiar akuU and
the absence of many or all of the nails. Their e.xtremities have
become flattened and form very efficient paddles.
Order V. Crocodilia.
The last and higliest order of the Reptilia is the Crocodilia.
These animals agree with the Chelouia in haviug a series of bony
plates underlying the horny scales of the akin, also in having an
immovable quadrate and a single median copnlatory organ.
'llie Crocodiles are of large size and are decidedly Lii^ard-like in
their general appearance, the chief observable external difference
between them and the Liwertilia being in the jawa, which are
exceeduigly long in companaon with the rest of the skull, so tb&t
the gape is very wicle.
The dermal plates form rings on the tail, but on the body, as in
Clielonia, they form a dorsal and a ventral shield separated by inter-
vening softer skin. In many Crocodiles the ventral shield is very
rudimentary.
Ill the (general arrangement of the bones and the temporal
fossae the skull resembles that of Spheuodon : but there are great
differences in the jaws and palate. The maxilla is very long and is
armed with conical teeth which are implanted in distinct sockets
or alveoli, the bone having grown up round their bases.
The two palatal folds have met so as to completely divide the
upp«r air passage from the lower food passage : both the palatines
and the pterygoids being completely iinited in the middle line
488 REPTILIA. [CHAP.
(Fig. 374). The cboanae or poaterior ntireg are therefore aitiuted
very far l>ack direcUy over the glottis, whilst the external nostril it
at the tip of the snout
In consequence of this position of the external nostril the
1. Premaiilla. 2. Mmilla. 3. FalatiDe. 4. Pterygoid. S. Pofterioi
narea, 6. TmnflverBe bone. 7. Posterior palatine vaonity, 8. Anterior
palatiiie laoQity. 9, Basi-occipital. 10. Openio;; of median
Euatachian canal. II. Jugal. IS. Quadra tojogal. 13. Qnsdnte.
14. Dentary. 15. Splenial. 16. Coronoid. IT. Sapra-angolar.
18. Angular. 19. Articular. 20. Lateral temporal fosHa. 91. Open-
ings For the passage o( blood-vesaela supplying tbe alveoli of the teeth.
crocodile can lie for hours hidden under the water with only the tip
of the snout exposed, and so surprise any nnwary animal coming
to the water to drink.
All the cervical and trunk vertebrae and some even of the
caudal vertebrae bear ribs. The manner in which these ribs an
articulated to the atlas and axis vertebrae throws much light on
tbe relation of these peculiar vertebrae to the rest. Thns we
observe that the first pair of ribs are articulated with their heads
to the lower part of tlie atlait, showing that this represents a basi-
Tentral homologous with the intervertebral cartilaginous pads of the
rest of the column. The head^ of the second pair of riba are united
to an intervertebral cartilage separating the odontoid proceas from
the centrum of the second vertebra. This cartilage ia therefore the
Becond basiventral, and the odontoid process is the first interventral,
'lomoiogous with the centra of all succeeding vertebrae. The
tubercle of each of the second pair of ribs has also an attachment
to the odontoid process lying obliiiuely above and behind the
capitular attachment and hence the centrum of the axis vertebra
has no rib attached to it. The third pair of ribs has shifted its
capitular attachment back ou the centrum of the third vertebra.
This backward sliifting of
the capitular attachment
lias taken place in all suc-
iceeding vertebrae, and the
liead of thp rib is attached
directly under its tubercle.
In the trunk, as we proceed
backwards, the capitular
atlachmL>ut to the centrum
gra<iually raised till it
reaches the transverse pro-
and is confounded with
the tubercular attachment,
uid the hindennost ver-
tebrae are single headed.
There are abdominal
ba,aa in SpAfTtodon; they
Are arranged in transverse
TOWS, each row on each side
Oonaisting of three or four bones (Fig. 374).
The pectoral girdle consists of simply a scapula and coracoid,
tiie latter reaching the sternum, nhich is cartilaginous but protected
rentrally by an interclavicle (Fig. 275). In the fore-limb the carpus
has retained three bones in the pro.ximal row, but the distal row
consists of ft block of cartilage representing the first nnd second
carpalia and a bone representing the remaining tliree. There ia
consequently an intercarpal wrist-joint corresfionding to the inter-
tarsal joint common to Reptiles.
The pelvic girdle is very peculiaj. The ilium is broad and
Fio. 273. Ficflt four Cervical Vertebrae of a
Crocodile, C, vutgnri: Partly after von
Zittcl.
1. Menral spioe of atlas, 'i. Lateral portion of
atlas. 3. Odoutoid proocBB. 4. Ventral
portion of atlas. 6. Neural spine of aiis,
6. PoBtEjRSpophyaia of fonrth vertebra.
7. Tubercalai portion of fourth cervical rib.
8. First cervical rib. 9. Second cervical
rib. 10. Conveic posterior surface of
centram of fonrtli vertebra.
490 REPTIUA. [chap.
rounded above and joins the two sacral vertebrae. The tnie pidn«
is a small round bone inserted and fused with the anterior edge of
the ischium and ilinm but what is ordinarily called the pubis, or
better the epipubis, is ■
bone directed fonntrds
which does not meet ito
fellow, nor does it foim
any part of the socket
for the femur or aceta-
bulum (Fig. 275). TTiiB
so-called pubis or epi-
pubia can be compared
only to that of TJrodeli
and Marsupials. Ihe
tarsus, like the carpus,
is much reduced and
modified. It consists d
a proximal row of two
bones, one of which, dte
fibulare or caloanenm,
forms a distinct heeL
The distal row consisto
of two bones, one repre-
senting the first, second
and third tarsalia, the
other the fourth and
fifth.
The heart of the
Crocodile ts remarkable
for the fact that the
septum in the ventricle
has grown forwards bo
as to completely divide
it into two halves, the
right and left Tentricle&
The left root of the aorta
arises from the right
ventricle and crosses the
right root, which arises from the left ventricle and gives off the
two carotids. The left root therefore receives venous blood from
the right auricle and the blood sent to the trunk is mixed. In
Fia. 274 Sternum and asBooiated MembTane.
bones of a Crocodile, C. palvttrii x }.
The last pair of aUIomiDal ribs vhich are united
with the epipnboB by a plate of cartilage Lave
been omitted.
I. luterclavicle. 2. Steraam, 3. Sternal
rib. 4. Abdominal splint rib. E. Sternal
CHOCODIUA.
addition there is a small passage, the foramen of PaniEza, joining
the two trunks where they cross, so that the blood leaving the right
«rch to go to the carotid is also somewhat mixed. The right
common or dorsal carotid is very reduced, the left-hand vessel
supplying both aides of the head. The fore-limb receives blood by
a subclavian of the ventral type, as iu Chekmiatts. The lung is no
longer a simple sac, but has thick spongy walls and the central passage
is reduced to a narrow tube. In the brain the cerebellum is large
and oylindrical.
., Bcapuls. S. Cur&ooid. S. lal^^rotariule. 4. tilenoid Mvi^.
PelvJR and Haorum of an Alligator, Caiman laliroilrh x 1-
2. Isuhiuni. !l. True pubis. 4. Epipiibis (so-called pubis],
irnl vertatrae. 7. Union
prezygapophjsiB.
All these peculiarities of the iotenial organs may be termed
foresliadowings of what is found in Birds and Mammals, and hence
Crocodiles are styled rightly the highest of the Reptiles.
Crocodiles are inhabitants of rivers and swamps and spend most
of their life in the water. The best known and classical example is
the Crocodile of the Nile, Crocodilitx nilotiont. There is but one
Biiecies in the southern states of North America, the Alligator,
j\ lliifiitor misiisaipiensh, which has a much shorter and broader
snout than the Crocodile. This animid lies for hours absolutely
motionless at the surface of the water so as to greatly resemble a
492 BEPTir-u.
log, and thus entrap any unwary animal which may renture near.
The Gavial, Gavlaiia gangettcua. in India is remarkable for iu
excessively long and narrow jaws.
So far OS we can learn from fossils the Reptjlea seem to have
been the dominating type
of land animals in the agei
whiih intervened between
the close of the Coal e^Hich
" \ '2 '2 II y. and the end of the Chalk
period when the white lime-
Btoue which uoustitutes the
Southern cliffs of Britain
wajn depoeiterl as a Bediment
in the ijuiet waters which
covereil what is now West
eru Europe. A rough sketch
of the history of the CI—
lis deduced from fossils
be given here.
I'he Reptilia i
have arisen from the St«g(V
CL'phala. At least included
in the latter group are saae
forms like Eryopn and Oi-
rotas in which the bune«
flanking the notoohord.
which have not yet united
80 ns to form vertebrTio, Kt
represented by basidor^a,
basiventrals, and inlerveii-
Fi.., aw. DingiMB of Arlerial AreliB" of tfO'ls, the interdorsal as ill
CrcModile viewed from the ventral ispeot. a|l Reptilia being BUpprtiss-
I. n. UI. IV. V. n. First to dxth Brterinl p^. while in the skull the
UToheB. 13. Tmoheiil (ventmt oarotiil). , . - -. i . •
13. Common pfttotid (dotstil oarotid) [righl basl-OCCipital region 13 0881-
tide nearly atrophied], 15. Biwht nys- fied. In the Sandstones
temic Broh. Ifi. Left (jetomio woh. , . , i_ (> , -
17. Dorsal aorta. 19. Pulmonary. 80. In- 'ymg above the Coal in-
nominale. 21. SubcUviao (ventral type), dubitable lleptiles with
fuUyfonued vertebrae make
their appearance. Some of these, termed the Pariasauria, still recall
the Stegocephala in possessing a comjilete roof of dermal bones
covering the skull. At the same time allied forms termed Then-
theO^I
'ossilij^^H
eee^^H
XVII.] CROCODILIA. 493
morpha showed gaps in this armour of dermal bone corresponding
to the supratemporal and laterotemporal fossae, the latter being
exceedingly small and often not present The limbs in all these
early Reptiles were short and stout, the fore and hind limbs being of
nearly the same size. Some of the Theromorpha in possessing teeth
divided into incisors, canines and molars, and in having the lower
jaw partly supported by the squamosal, approached the characters
of Mammalia. Another allied group were the Dicynodontia, which
agreed with the Theromorpha in having a large supratemporal
fossa but differed in having the teeth reduced to two tusks in front
or completely absent. It is believed that these were the forerunners
of the Chelonia.
In the same period we meet a large number of forms with supra-
temporal and laterotemporal fossae equaUy developed, these were
the Rhynchocephala of which Sphenodon now is the sole survivor.
From this group in the following age were developed (a) Water-
Reptiles — the Plesiosauria — with long swan-like necks and limbs
transformed into flippers by the shortening of the bones of the
arm and leg, and (6) Land-Reptiles — the Dinosauria — with greatly
developed limbs ; in some cases the whole weight being borne by
the hind-limbs, the fore-limbs being short and used for prehensile
purposes only. In a still later period from the less specialized
Dinosauria were developed (1) the Crocodilia, which reverted to
the water but retained limbs fit for progression, and (2) Pterosauria,
possibly flying reptiles in which the "wing" was a flap of skin
supported by the greatly elongated 5th finger. The forerunners of
modern Sauria are found only in the Chalk period in the form of
long-bodied aquatic Reptiles with however the characteristic loss of
the quadrato-jugaL There remain to be mentioned the whale-like
Ichthyosauria, which since they possess only a supratemporal fore-arm
seem to be sprung from the Theromorpha. The limbs were converted
into flippers more thoroughly than in the case of the Plesiosauria,
the limb-bones being reduced to round nodules and the fingers
increased in number by forking. There was no neck and no sternum
but a series of ** abdominal ribs " as in Rhynchocephala.
The class Reptilia is classified as follows :
Order 1. Rhynchocephala.
Reptilia devoid of special copulatory organs and with an
immovable quadrate.
Ex. Sphenodon.
494 BEPTILIA. [chap. XVIL
SAURIA.
Order 2. Lacertilia.
Reptilia with two copulatory sacs on the posterior
wall of the cloaca : with a moyable quadrate, with a
pectoral girdle, and with the rami of the lower jaw united
by a symphysis.
Ex. La-certa, Anguis,
Order 3. Ophidia.
Reptilia with two copulatory sacs on the posterior wall
of the cloaca : with a movable quadrate but with no trace
of a pectoral girdle ; with the rami of the lower jaw
united by ligament.
Ex. Crotalus, Vipera, Tropidanotus,
Order 4. Chelonia.
Reptilia with one median copulatory organ on the anterior
wall of the cloaca and an immovable quadrate. No sternum
and the ribs expanded horizontally to form a dorsal shield:
a ventral shield of dermal bone. No teetL
Ex. Testudo, Chelone,
Order 5. Crocodilia.
Reptilia with one median copulatory organ on the anterior
wall of the cloaca and an immovable quadrate. A well-developed
sternum, joined by the ribs. With many alveolar teeth.
Ex. Crocodilus, AUigator, Gavialis,
495
CHAPTER XVIII.
Sub-Phylum IV. Craniata.
Class IV. AvBs.
It is probable that if the first child one met were asked to
describe a bird, he would say that birds were animals
act*erirtic8. **^ which Were covered with feathers and had wings to
fly with. Though it often happens that the marks
by which the ordinary person distinguishes one animal from another
are not those which seem most important to a Zoologist, yet in this
case the Zoologist could not find more important features to serve
as the basis of a definition of the class Aves or Birds.
Birds then are vertebrate animals in which the fore-limb is
modified into a wing or flying organ and in which the body is
covered with feathers. Bats likewise have the fore-limb con-
verted into a wing, but they are covered with hair, not feathers,
and their wing is not constructed on the same plan as that of the
bird.
Birds are sometimes classed along with the Reptiles as Saurop-
6 id a, since they have a good many features in common with them,
and are thus contrasted with the Mammalia, or ordinary quadrupeds.
This, however, gives a wrong view of the relationships of the three
groups. Both Birds and Mammals are believed to be descended
from Reptilian-like ancestors, and it is an open question whether
the changes which Birds have undergone are not at least as im-
portant as those which have taken place in Mammals in the process
of their evolution from ancestors which, had they lived now, would
have been termed Reptiles.
Birds agree with Reptiles in that they lay large eggs from which
the young are hatched in a form closely resembling the parent;
they are like Reptiles also in the structure of their jaws — the lower
496 AVES. [chap.
jaw consisting of five bones and articulating with a quadrate
bone — and in the structure of the hinder part of their skulls, of
their breast-bones and of their ankle-joints. The yertebrae very
rarely have epiphyses like those of Mammals, though these are
found in Parrots. As in Reptiles, the number of neck vertebrM
is variable. Like Reptiles, Birds have nuclei in the red corpuscles
of the blood, and the sole remaining complete systemic arch goes to
the right (Fig. 285), like the principal arch in Reptiles. On the
other hand, they are ** warm-blooded," that is to say, the temperature
of the body remains practically the same whether the surrounding
air gets hot or cold ; it is in fact higher than that of any mammal :
the ventricle of the heart is completely divided into two, and in
addition to the wings and feathers, the structure of the leg and
hip-bones and of the brain, distinguishes them firom any living
Reptile.
Strange as the statement may appear, it is true, nevertheless,
that the feathers are really scales like those found in
lizards, immensely developed and with the edges
frayed out. Like scales, they are epidermal, that is, developments
of the outer or homy layer of skin. The area which is about to form
the feather becomes raised into a little finger-shaped knob by the
growth of the deep layer of the skin or dermis which carries the
blood-vessels. The little knob thus formed is in turn sunk in a
pit called the follicle, the skin immediately surrounding it being
depressed. Thus the lowest part of the feather is a little hollow
tube of horny cells formed round the knob of dermis, but the
upper part, like the scale of a lizard, is formed only on one side
of the knob, and this part as it is pushed away by the growth of
the deeper parts becomes frayed out so as to form the vane of
the feather. In the latter we can distinguish a central stem or
rhachis, and two rows of lateral branches or barbs, which are
kept in position by a number of secondary processes or barbules.
The barbules bear little hooks which interlock with one another.
Down consists of small feathers growing between the bases of
the larger ones. Li these the barbules are absent, so that the
barbs are not held together but float freely about, forming a kind
of fluff. When a bird is plucked it is seen that the feathers are
confined to certain tracts (pterylae) separated by others called
apteria devoid of feathers or covered only with down feathers.
Thus in most birds the mid-ventral and mid-dorsal lines are
apteria. The colour of the feathers is partly due to coloured
XTni.] FEATHERS. 497
snbstftncee or pigments in the epidermal cella imd partly to minute
structural detail which causes interference of the light reflected
from them.
The ving is the foreleg of the Inid. One can easily recognise
the parts corresponding to upper arm, fore-arm and hand, but the
latter is highly modified and specialised for the important function
of canying the long primaries or hand quills. When the wing
is at rest the upper arm extends backwards, the fore-arm is sharply
Epidennii. 2. Malpighiao Ibtbi of the epidenuiB. 3. Dennis.
4. Toang luther. S. Follicle round base of feather. 6. Dermal
papilla whioh developee blood veaaels and ia the organ of i:
the feather.
bent up on this, while the wrist is sharply bent down. When
the wing is expanded these are partially, but never entirely,
straightened out, so that a bird begins the down-stroke of the
wing with the arm bent in a very similar way to that in which
a swimmer's arm is bent when he strikes back with it. In the
hand we find as a role three digits, the first, second and third.
These have thdr fint joints, the metacarpal bones, closely united
8. AH. 32
498 ATES. [CHiP.
together. Id Man Uie metacarpals of tlie variooB fingere are onitod
by skill and fiesh which conBtitute ihe palm, bnt thety are mov-
able on one another, whereas in the bird the metacarpals of the
second and third digits are firmly joined at both ends. The index
has in addition to the metacarpal, in most birds, three other smiQ
bones called phalanges, of which the end one sometitnes catrica
a daw : the third digit has only one bone or phalanx besides the
metacatpal The metacarpal of the first digit or thamb is Toy
small, but is likewise completely fused
with the other metacarpals. Besides this
the thumb has two joints and often •
claw.
Compared with the arm or fore-leg <^
other animals the arm of a bird strikes one
as having very little fiesh. This is be-
cause the muscles, especially those on the
fore-arm, have comparatively short bellies
but very long tendons, in correlatioa with
the often very much lengthened bones,
one of which, the ulna, serves as support
of the secondaries or arm-qoills.
The movements which constitute fly-
ing, namely, the powerful down-stroke of
the whole arm and the slower up-stroke,
are carried out by the immensely developed
Wing of a Oumet, Sula pectoral muscles, great fieshy masses which
"*■ cover the breast-bone or sternum. This
'a.""™- 2; sSi bon.ha..more„rle..p»r-,ih.i,edo«t-
metaoarpal. 0. Tbird line, rounded in front and pointed behind,
S'SS*"' 7°' KS "le ribs eodiDg in it. sides (Pig. S79).
digit ^ 8. jE'hird digit. Jn accordance with the tendency in ill
birds to develope the body into a long
neck and a rounded trunk, we find evidence
that the number of ribs encircling the bodjr
and joining the sternum has been reduced.
Not only do we find small free ribs connected with the hinder
cervical vertebrae, but attached to the sternum are outgrowths
called costal and xiphoid processes (Fig. 279) which are regarded
as the remains of sternal ribs the dorsal halves of which ate
vestigial or lost If we picture to ourselves the pectoral giidle
being thrust backwards and the pelvic girdle forwards so as to crowd
Flo. 276. Bones of the right
Ihe distal phalangea of
the thmnb and oeeond
digit were wanting in the
specimen from which this
£gure was drawn.
XTHI.]
3KELBT0N.
the viscera into n small space ve shall realize the meaning of the
differences between the skeleton of the trunk of a Reptile and that
of a Bird. From the middle line of the sternum projecte a great
vertical crest Btrettrhing outviards, called the carina or keet, and it
B from the sides of this mainly that the pectoral muscles take their
origin. There are two main muacleE on each side. First the pect-
oralis major on the surface, which passes into a tendon attached
» the upper end of the humerus. The contraction of this muscle
lings alwiit the down-stroke of the wing, the effective stroke in
flying. Underneath the pectoralis major is situated the pectoralia
much smaller muscle. Its tendon passes underneath
tbe arch formed by the clavicle
&nd the coracoid bone, the latter of
which, as in Reptiles, connects the
fihoulderhUde firmly with the ster-
Having passed through this
arch the tendon is attached to the
back of the humerus, so that the
contraction of the muscle pulls the
humerus and thus the wing upwards
uid backwards and not downwards,
the upper end of the coracoid acting
as a pulloy round which it passes.
Returning to the wing, we must
now notice how the feathers are
uraoged. The great (juill feathers
are attached chiefly to the upper
and posterior edge of the hand, but
there are also a large number which
! implanted in the posterior aur-
e of the ulna. These two groups
i feathers are pushed one over the
other when the wing is folded, just
like the silk of a closed umbrella, but when the wing is stretched
out they oidy overlap very slightly, and thus a coherent and
practically air-tight surface is formed. Those feathers which are
attached to the hand are called primaries (6, Fig. 280. G), those
arising from the ulna, secondaries (8, Fig, 280, C); a few arising
from the upper arm are called tertiaries; any air which might
escajie between the bases of the long feathers is stopped by an
uppn layer of shorter feathers, called coverts (1, 2, 3. 5 and 7,
~^~" ' 32— ».,
1. Cftiina of tha stemuiD. 2. Cora-
coid. 3. Soapula. 4. Clavicle.
6. Costal process. 6. SurfuieB
tor BrtieDldtioD with tbe etemnl
ribfl. 7. PoBli-riot (xiphoid)
atid oblique proceaseB.
{CBU.
XVni.] FLIGHT. 501
Fio. 280. Wing of a Wild Daok, Ancu bosehas x ^.
A. Bight wing seen from the dorsal side, with the coverts removed. B. Left
wing disarticalated and seen from the ventral side, with the coverts
removed. G. The dorsal side of a right wing. D. The ventral side
of a left wing. From Wray.
In A and B. 1. Humems. 2. Badins. 8. Ulna. 4. Radial carpal.
5. Ulna carpal. 6. First phalanx of first digit. 7. Second metacarpal.
8. Third metacarpal. 9. First phalanx of second digit. 10. Second
phalanx of second digit. 11. Vestigial qaill. 12. Tertiariee.
13. Secondaries. 14 — 17. Primaries.
In G and D. 1, 2, 8, 6, and 7. Coverts. 4. Bastard wing. 6. Primaries.
8. Secondaries. 9, 10. Tertiaries.
Fig. 280, C and D). Air is prevented from escaping in front by the
hand, which is stretched out in a vertical plane, and by two folds of
skin, one in the angle between fore-arm and upper arm, the other
between the upper arm and the body. The name bastard wing
is given to a tuft of feathers borne by the thumb (4 Fig. 280, G
and D).
The full mechanical explanation how the down-stroke of the
wing not only prevents a bird from falling but urges
it onwards is not completely understood, and much
of what is generally accepted is too complicated for an elementary
text-book, but the broad principles involved may be simply set
forth. A bird when it is in the air, like any other heavy body,
is continually falling : the blow of the wing has therefore not only
to effect a forward impulse, but also an upward one sufficient
to compensate for the distance the bird has fallen between two
strokes. These impulses are derived from the elastic reaction of
the air compressed by the down-stroke of the wing. When the
wing is expanded, it is slightly convex above and concave beneath.
This arises from the fact that the quill feathers are attached to
the upper edge of the webbed limb and project gently downwards
and backwards, so that there is a space left which is bounded
behind by the quills and in front by the bones and web of the
limb. Now if this space had a symmetrical shape the air would
be compressed in such a way that the resultant impulse would be
directly upwards ; but it is not symmetrical, for its roof has a very
steep slope in front and a very gentle one behind, and the air is
compressed in such a way that an oblique reaction results, a
reaction which we can resolve by the parallelogram of forces into
an upward and an onward one. So much for the flight of a bird in
still air. The air is, however, very rarely still, and the currents
which exist are never quite horizontal, but generally inclined
502 ATsa [chap. xvm.
slightly upwards, since the lowest layer of air is checked by firiction
against the ground, and birds which are good flyers can, by in-
clining their wings at the proper angle, obtain quite sufficient
support from the play of the current against the wing without
exerting themselves to any great extent. This is called soaring,
and can be seen beautifully in the flight of the Gkuinet. In this
manoeuvre birds are assisted by the tail, which is really a fan-
shaped row of strong feathers attached to the coccyx, that y&j
snuST vestige of a true taU or portion of the ver^biid column
extending behind the anus, which modem birds possess (Fig. 282).
In this region the vertebrae are thin discs, several of which may be
soldered together so as to form a bone called the pygostyle.
Fio. 281. Lateral view of the Pelyis and Saomm of a Dock, Aruu boscJuu x {.
1. Iliam. 2. Isohiom. 8. Pubis. 4. Pectineal process, the radiment
of the prepabis corresponding to the pubis of the Lizard. 5. Ace-
tabulum. 6. Ilio-ischiatic foramen. 7. Fused rertebrae. 8. Facet
on which the projection on the femur, the trochanter, plays.
The legs of birds can be shown to be constructed on essentially
the same type as those of Heptiles, but modified so as to
position. ^ enable them to support the body in an upright position.
The arrangements to efiect this are very interesting,
as they differ markedly from those found in the human skeleton.
In the pelvic girdle the ilia are lengthened so as to be
attached to a considerable number of vertebrae, six or more, and
so a firm attachment of the limb to the main skeleton is effected.
In Reptiles only two vertebrae are joined to the ilium, but in
their case the weight of the body is supported on all four limbs,
whereas in a Bird the whole vertebral column has to be balanced
about two points of support, and hence the ilium must be quite
Fio, SS9. Skeleton of the Common Fowl, e , GaUui bantiva x i.
1, Fremuills. 2. Nasal. 3. Lachrymal. 4. Frontal. E. MitDdfble.
6. Lover temporal arcade in region of qaodratoiiiga]. 7. Tympanio
nvi^r. S. Ceiriool vertebraa. %. Ulna. 10. Humeraa.
IL BadioB. 13. Carpo-metaoarpHB. 13. First phalanx c( aeoood
digit. 14. Third digit. 16. Second dJgiL 16. Qinm.
17. Cio-isohiatia foramen. 16. Pygoatyle. 19. I'emnr.
30. Tibio-Ursaa. 21. Fibnla. 22. Patella. 23. Tarso-
netatantu. 24. First toe. 25. Second toe. 26. Third toe.
27. Fourth toe. 26. Spoi. 29. Pubis. SO. IschiQin.
SI. Olaviole. S2. Coraooid, S3. Keet of steraom. 34. Xiphoid
proeesi. Th« forked boas jast In ^nt of 7 la the QnaAnte.
504 AVES. [chap.
immovably strapped to the vertebral column. The resalt of this
has been atrophy of some of the hinder ribs, and the ventnd
halves of some of these form the xiphoid processes of the stemnm.
The ischium is directed backwards parallel to the hinder part of
the ilium, and often fused with it so as to surround a space
called the ilio-ischiatic foramen. The pubis is a very slenda
bone which is also directed backwards. It is in fact a post^ubis
corresponding to the lateral process on the pubis of the lizard (see
p. 467). Except in the Ostrich the two pubes never unite with
one another ventrally to the cloaca, as they do in Beptiles and
Mammals, the absence of a pubic symphysis facilitatiug the laying
of the egg, which is very large relatively to the size of the animal
The thigh is bent sharply forwards and the shank backwards, and
the ankle is raised to a coDsiderable height above the ground by
the great length and upward direction of the bones of the sole or
metatarsals (Fig. 282). Thus a Bird walks on its toes and like
Heptiles possesses an intertarsal ankle-joint. In Birds however, in
order to give firmness to the leg, the metatarsals are closely united
together and the small bones of the tarsus have entirely disap-
peared, the proximal row having been incorporated with the tibia,
while the distal bones have fused with the metatarsals. Thus in
an adult Bird the ankle-joint is a simple hinge between two
compact bones, the upper being a tibio-tarsus, the lower a tarso-
metatarsus. There are usually four toes, but the first, corre-
sponding to the human great toe, is sometimes, like the fifth,
absent, while its metatarsal remains distinct from the other three.
This toe, except in Steganopodes, is generally directed backwards.
The raised sole of the foot really constitutes the visible "leg" of
most birds, the thigh being altogether, and the shank mostly, buried
in the feathers. In many birds the sole is plated by scales which
are raised homy plates of skin, similar to the scales of Reptiles.
The most characteristic features about a bird, next to the limbs
and feathers, are certainly the head and neck. The
Neck! *" skull is high and arched behind in order to make
room for the comparatively large brain; in front it
slopes gradually downwards to the pointed beak, which is encased
in a hard homy sheath. The bones which underlie this beak are
(above) the premaxilla and (below) the dentary bone of the lower
jaw. No modem bird possesses teeth, and the maxilla, which
usually carries most of the teeth in animals which have them, is
very small and confined to the cheek behind the gape, whereas the
XVIII.] SKELETON. 505
premaxilla is very large. Behind the maxilla two other slender
bones, the jugal and quadratojugal, complete the lower temporal
arcade as in Ghelonia and Crocodilia, but the jugal never sends up
a process behind the orbit and the post-orbital is a mere process of
the frontal bone, so that the orbit and the temporal fossa open into
one another. The eyes are of great size : a bird has little or no sense
of smell, and governs its life mainly by the sense of sight : in corre-
spondence with this the orbits or eye-sockets are so enlarged that the
skull between them is reduced to a thin vertical plate, the inter-
orbital septum, in which there is no brain cavity. This great
development of the eye-sockets and the obliteration of the brain
cavity between them is not, however, confined to Birds : it is found
as already mentioned in many Heptiles also, and is indeed one
of the several points in which a bird's skull may be said to be
Reptilian. It is however characteristic of Birds, as opposed to
Reptiles, that this interorbital septum is largely converted into
bone. In its hinder and upper portions it is composed of orbito-
sphenoid bones, like those found in Teleostean fishes, which support
the exit of the optic nerve, but in its lower part it is composed of a
vertically compressed presphenoid bone corresponding to that
which ossifies the front part of the floor of the cranium in
Mammalia. In front the interorbital septum is continuous with
the intemasal or ethmoid septum : this latter is ossified by a
mesethmoid bone, which unites, but not quite immovably, with the
presphenoid. The hinder part of the floor of the cranium is ossified
by the basioccipital and basisphenoid bones, and the front of the
latter is drawn out into a long spur called the basisphenoidal rostrum.
Underlying the basisphenoid there is a membrane-bone called the
basitemporal, a relic of the parasphenoid of Fishes and Amphibians.
In some Reptiles traces of the front part of this bone remain, but
never any of the hinder portion, and this is an indication that Birds
are descended from a type of Reptile more primitive in some respects
than any now existing. Other points of resemblance to Reptiles
are that the lower jaw is made up of no less than five distinct
bones interlocking with each other ; and that instead of there being
a direct hinging or articulation of the lower jaw to the skull, a
bone called the quadrate is interposed, as in Reptiles, which
articulates on the one hand with the lower jaw and on the other with
the skull. This quadrate bone is movable, and to it in front are
jointed the bones of the palate, the pterygoids and palatines,
which slide on, but are not fixed to, the base of the sktdL Hence
506
AYES.
[chap.
when the lower jaw is opened, ie., palled down, these bones ue
pushed forward, and the upper beak, to which they are fastened m
front, is slightly tilted up, thus increasmg the width of the g^ie.
In parrots the front part of the skull, including the bones of the
face, has an actual joint with the hinder part of the skull. Thus it
follows that in spite of the presence of a quadratojugal the quadrate
is movable. It is to be remembered however that the quadrato-
jugal is here a small flexible bone, very unlike the great bony bar
of Ghelonia and Crocodilia. The hyoid apparatus consists of the
second and third pairs of visceral arches. The second pair, which
a....
.«-
Fio. 283. Brain of Pigeon, Columba livia x about 2.
1. Olfactory lobes. 2. Cerebral hemispheres. 8. Pineal gland. 4. Optic
lobes. 4 a. Optio chiasma. 5. Cerebellum. 6. Lateral lobe of
cerebellum. II. Optic nerves. III. Motor oculi. IV, Patheticas.-
v. Trigeminal. VI. Abduoens. VII. Facial. Vm. Auditory.
IX. Glossopharyngeal. X. Vagus. XI. Spinal aooessoiy.
XII. Hypoglossal.
correspond to the hyoid of Fishes, are very short and consist mainly
of the median piece or glosso-hyal which is closely connected to
the median piece of the third pair. The latter are elongated rods
to which are attached the muscles which protrude the tongue. As
in the Reptilia, the skull has one central knob or condyle for
articulation with the backbone, not two, as is the case with the
Amphibia and Mammalia.
vra.]
THE BRAIK.
607
The features peculiar to the Bird are, firstly, the great elonga-
tioD of the premaxiUa CAirying the beak — this causes the nostrils to
be placed at the baae of the snout instead of at the tip, as is the case
with Reptiles; secondly, the enormous size of the orbit and the
absence of any bony bar to separate it from the temporal fossa, the
hollow on the side of the Eiktill. in which are situated the muscles that
close the jaws; and thirdly, the height and arched character of
the hinder part of the skull, which lodges the brain. The bones of
the skull are usually indistinguishably united in the adult, are
hollow and contain air, and are in consequence very light, as be&ts
an animal which flies. Similar air spaces also exist in the larger
hones of the trunk and limbs. The insects, which also have taken
to the air, have somewhat analogous air reservoirs. Like insects,
birds are represented
by a large number of
species which all exhibit
great uniformity of
structure.
When the brain is
examined, the meaning
of many o
the peculi-
arities of the skull is
seen. What we might
perhaps, with a little
loosenesB, call the organs
of thought, the hemi-
spheres of the fore-
brain, are greatly en-
larged, being high and
rounded. The parts of
the brain supplying the
Doee, the olfactory
lobes, are on the other
band very small and
poorly developed, in accordance with the feebly-developed nasal sacs,
the sense of smell being but slight, as mentioned above (Fig. 383).
The brain is bent sharply on itself, so that the optic lobes of the
mid-brain— portions connected largely with vision — are pressed down-
wards and the hemispheres are brought close to the cerebellum,
Fia. 284. Third Cervical Vertebra of an Oitrich,
Struthio camtlai < 1. A, anterior. B, poa-
terioF. C, dorsal view. A and B after Uivut.
I. Neural spine. 2. Neural oanal, 3. Pre-
ij-gapophyeia. 4. PoBlajgapopbysie. 6. Pos-
terior artieular anrTace of ceotrum. 6. Anterior
articalar surface of eentnim. 7. Canal
between the uapitulum and toberuulum ot the
rudimenlury rib. W. Hypoi«phyBiB, a
median veairal outgrowth of ceatrun).
508
AYES.
[chap.
which, in contradistinction to what is the case in most leptiles, is
large and transversely wrinkled. Evidence is accumulating that
an important function of the cerebellum is to coordinate motor
impulses proceeding from higher parts of the brain to the skeletal
muscles.
All birds have compara-
tively long necks (Fig. 38S),
and the vertebrae which form
the support of this part of the
body have the soifaoes with
which they articulate with one
another shaped like saddles,
being concave firom side to
side and convex from above
downwards infirontand exactly
the opposite curvatures behind
(Fig. 284). This arrangement
allows great freedom of move-
ment, and, as all know, a bird
is able to twist the head com-
pletely round and look straight
backwards. In do-
ing so of course it
squeezes the skin
of one side of the neck and
stretches that of the other,
and so the great jugular
vein, which carries blood from
the head, is liable to be blocked
on one side (Fig. 286). To
obviate this difficulty^ the two
Fio. 285. DiaRTam of Arterial Arches of jugulars are connected by a
a Bird viewed from th. ventral aspect. ^^^ piece just under the he«d.
'• S;,hS-/^I- '^aJ!:SV1nt?<^ BO tJ«^t the blood from both
13. Common carotid (dorsal carotid), sides can always have a free
14. Systemic arch. 17. Dorsal aorta. ^«oo««.« Tk^ ^«^i^*J «^»^^
19. Puhnonary. 20. Innominate. 21. Passage. The carotid artenes,
Sabclavian (ventral type). 24. Coeliac. which take blood to the head,
come close together at the base
of the neck and run up just under the vertebrae. As they are placed
close to the axis of rotation and are further protected by curved
Vascular
System.
xvni.]
VASCULAR SYSTEM.
509
6
6
rods growing out firom the vertebrae and forming arches over them,
they are never compressed, however much the bird twists its neck.
Turning now to the consideration of the internal organs^ we
have first to notice the structure of the heart. In Birds the
ventricle is completely divided into two, a condition found only in
the Crocodiles among reptiles, and even
there the great trunks leaving the two
parts of the ventricle communicate. In
Birds only one systemic arch remains
complete; this passes round to the
right, coming off firom the left half of
the ventricle ; in Heptiles, it will be
recollected, the left fellow of this one
was still present. From the systemic
arch there arises an innominate artery
for either side, which splits up into a
ventral carotid, reduced as compared with
that of reptiles but, as in their case,
8uppl3ring the trachea, and into a dorsal
or common carotid to the head and a
subclavian to the breast and wing. The
subclavian artery which arises fix)m the
ventral carotid divides into a brachial
artery of moderate size for the wing and
a very much larger pectoral artery which
supplies the pectoral muscles. These, as
we have seen, are the real seat of the
activities of the wing. The subclavian
of Birds corresponds in origin with that
of Chelonians and Crocodiles and so is
the ventral type of subclavian, as opposed
to the dorsal type found in Lizards and
Amphibians. The arteries supplying the
lungs, the pulmonaries, which, as in
the Heptiles, have no longer any con-
nection with the systemic arch, come off
firom the right side of the heart; one
passes to each side to reach the lungs.
The arteries of the hinder part of the
trunk agree in their general arrangement
with those of Reptilia and Amphibia. In the venous system the
Fio. 286. Diagram to show
arrangement of the prin-
cipal Veins of a Bird.
1. Sinns venosas— gradn-
ally disappearing in the
higher forms. 2. Dnotas
Cavieri = superior vena
cava. 8. Internal jognlar
= anterior cardinid vein.
5. Sabclayian. 6. Poste-
rior cardinal, front part.
7. Inferior * vena cava.
8. Benal portal = hinder
part of posterior cardinal.
9. Candal. 10. Sciatic.
12. Goccygeo-mesenteric.
18. Femoral. 14. Ana-
stomosis of jugnlars.
[OBU
Fio. 287. TbeobiefViBcerauf the Pigeon, C^olumbiliirfa x|.
1. Tnchea. i. ThjmaE gland. 8. OeMphagna. i. Crop. fi. Syrinx.
. Heart. 7. Liver. 6. Oizzaid.
11. Small intestiae. 12. Keotum.
IG. Led carotid. 16. Left aobclaTian.
wter]'. 19. Bight aubclaTivi. 20.
alia major moBcla cot acrou.
Dnodenimi.
13. Cloac*. 14. Air-BUi.
IT. Bight ouotid. 18. Bmchul
HoHleiofBfiuix. 21. Peotor
BESPl RATION. W^
eonnectioa of the two jugulars baa been already referred to.
The juguiflT joins a large subclavian vein to iorm the superior
vena cava. The largest part of the subclavian vein, like that
of the correBponding artery, is mode up of a pectoral vein re-
turning blood from the pectoral muactea. The front parts of
the posterior cardinal veins have diaapireared : but their hinder
parts remain aa the renal-portal veins which as usual arise by the
bifurcation of the caudal vein and receive on each side a femoral
and a sciatic vein from the leg. The renal-portal pours its blood
into the inferior vena cava, not as in Amphibia and Reptiles through
A syBtem of capillaries, but directly by a single vessel channelled
through the substance of the kidney. Hence in Birds the kidney
tubules receive blood only from the aorta and do not, as in the
lower Craniata, ^e^^eive a double supply. From the point where the
caudal vein divides into the two renal-portals a vein is given off
vbich descends into the mesentery and opens into the posteiior
mesenteric branch of the portal veiu, thus establishing a connection
between the portal and cardinal systems of veins. This vein ia
called the coccygeo-meseuteric (12, Fig. 386), and is quite
peculiar to Birds.
The lungs are firmly fitted in against the ribs; they do not, as
io most Beptiles or as in ourselves, hang freely in a cavity; their
most remarkable fe-ature is the possession of great thin-
walled bladder-shaped outgrowths, the air-sacs, of
which the prolongations extend even into the bones.
There are nine of these great air-sacs, one placed at the base of the
neck, and the other eight situated in pairs at the sides of the body
oavity under the ribs (Fig. 287). When the ribs are in their normal
position, the air-sacs are expanded, but when the ribs are pulled
backwards so as to compress the air-sacs, air is driven out; when
the ribs and wall of the body behind come into their natural
position again, the air-sacs are expanded and air rushes in, filling
the lungs on its way. Breathing out or exj)iration is therefore the
ftctive function, drawing in air ia an elastic reaction, the opposite
to what ia the case in man and other mammals. The windpipe
or trachea is long, and the hoops of cartilage which stiffen it form
complete rings, so that it is not easily compressed (Fig. 287). Like
moat other land vertebrates, birds have a larynx or organ of voice
at the top of the trachea formed in the usual manner by the en-
largement of some of these rings of cartilage, and the stretching
512 AYES. [chap.
of a thin membrane between them and two special cartilageB, the
arytenoids, which lie at the opening of the windpipe into the
gullet.
The effective organ of voice in Birds, the syrinx, is found
much deeper down, at the spot, namely, where the windpipe spKtB
into two tubes, the bronchi, which lead to the lungs. The last
rings surrounding the trachea just before it bifurcates are more or
less fused with one another so as to form a box with stiff walls called
the tympanum. The inner walls of the bronchi, just where th^
join one another, are thin and membranous, and constitate a
membrana tympaniformis interna. From the fork a flexible
yalye, termed the membrana semilunaris, projects up into the
tympanum, and as here the cartilage rings have the form of half-
hoops, which are drawn togeth^ by special mnsdes, the width of
the opening of the bronchus into the windpipe is smalL When air
is forcibly expelled the yalye aboye mentioned is set vibrating like
the reed in an organ-pipe, and by this mechanism the song is
produced. The muscles which connect the half-rings together (in-
trinsic muscles) and two which connect the syrinx with the sternum
(extrinsic muscles) by altering the tension of the sides of the
trachea, and consequently the rate at which it vibrates, change the
pitch of the note produced. A S3rrinx such as we have described is
found in the vast majority of birds. It is termed a broncho-tracheal
syrinx because both bronchi and trachea are concerned in its forma-
tion. In a few North American birds a tracheal Sjnrinx is found in
which the organ of voice is constituted by a portion of the tracfaes
where the rings are thin and delicate, so that the sides are flexible.
In a few birds allied to the Cuckoo there is a bronchial syrinx, a thin
flexible membrane being formed about the middle of each bronchos
by the incompleteness of some of the rings.
The alimentary canal commences with the buccal cavity or
stomodaeum, partially divided by the palatal flaps into an upper
air-passage, and a lower food-passage. The tongue,
s^temt.^^ which is pointed and homy, ensheaths the glosso-
hyal bone ; it is protruded by the action of muscles
which pull the enlarged third visceral arch forwards. Behind the
tongue open the ducts of the sub-maxillary glands; at the
comers of the gape the parotid glands pour their secretion into
the mouth, whilst at the sides of the tongue the sub-lingual
glands open. All these glands are pouch-like outgrowths of the
XVra.] DIGESTION. 513
ectodenn of the stomodaeum and secrete a mucus which assists in
swallowing the food, and occasionally (as in Woodpeckers) in
causing the prey to adhere to the tongue. The names indicate the
position of the glands, as for instance, parotid (Gr. irapa, beside,
o^s, (oTo^y the ear). Following on the buccal cavity and indis-
tinguishably fused with it is the endodermal pharynx into which
the glottis opens, and also the persistent remains of the first pair
of gill-sacs, the Eustachian tubes. The pharynx leads into a long
gullet lying dorsal to the trachea, which eyentually passes into the
stomacL The gullet in the Pigeon and many other birds deyelopes
a large thin-walled outgrowth on the ventral side called the crop.
This is used as a storehouse for the food, and in the Pigeon
may be found full of unaltered seeds. The stomach has a most
characteristic form in Birds; it is sharply divided into two regions,
an anterior egg-shaped one called the proventriculus, and a large
posterior flattened one called the gizzard. In the walls of the
proventriculus are found the pepsin-forming glands, while on the
other hand the endoderm of the gizzard developes a horny lining
which is thin in Birds that live on an animal diet, but very thick in a
grain-eating Bird like the Pigeon, where it forms upper and lower
hardened plates. When by the contraction of the greatly thickened
visceral muscles of this part of the alimentary canal the upper and
lower plates are brought together, a crushing-mill is produced by
which the food is broken up. The action of this mill is assisted by
the habit which many Birds possess of swallowing fragments of
stona A collection of these, sometimes including fragments of
glass, may be found on opening the gizzard of a Pigeon. It is a
great development of this habit which has earned for the Ostrich its
reputation of flourishing on a diet of nails, penknives and match-
boxes. The liver in Birds is remarkable for possessing two ducts,
one opening as usual close to the pyloric end of the stomach and
one into the distal end of the first loop of the intestine. The
pancreas of Birds has from one to three ducts. The intestine is
folded into four or five loops, the arrangement of which has been
made use of as a basis for classification. It ends by passing into a
short rectum or large intestine, which is marked by a pair of out-
growths, the intestinal caeca. Their size varies much, from long
and wide blind sacs, as for instance in the common fowl, Ducks>
Geese and other herbivorous birds, to (^uite small vestiges as in the
Pigeon and in fish- and flesh-eating birds. The rectum ends in an
enlargement termed the urodaeum, the upper part of which receives
514 AVIS. [chip.
ducts of Uie kidneys and reproductive organs, while into the donl
wall of the lower and outer part a glandular ponch t^ onkiMWii
function, called the bursa Fabricii (12, Fig. 988), apeoB. This
becomes smaller and sometimes entirely disappears in the adult Bird.
Fio. SSe. The Lungs, Eidneye ftnd Qonada of a Pigeon, Columba Ittna x\.
I. Treehea. 2, BTonohiu. 3. Long. 4. Suprarsiul bodj. fi. Ovtrj.
6. Ovidaot. T. Lobes of kidney. 8. Ureter. '9. Aorta. 10. Boim
Fabrioii. II. Beotum. 12. Opening of bnrw Fabrioii. IS. Opening!
ot ureters. 14. Opening of ovidact. 16. Cut peotoral mnaole.
The structure of the kidneys and reproductiTe oi^ans is es-
sentially the same as in the Reptilia. The meta-
orgmoi. '""""' Dcphros lu both sexes is distinctly divided into
lobes. The mesonephros is represented by a small
lobed epididymis closely adherent to the testes. The suprarenal
body (4, Fig. 288) is homologous with the adrenal of Amphibia.
In most Birds there is no special organ for copulation, the whole
end of the cloaca being turned inside out for this purpose, just as in
Amphibia and Rhynchocephala. That this however is a secondary
and not a primary state of affairs is suggested by the existence in
Ostriches and some other Birds of a long penis on the dorsal wall
of the cloaca similar in structure to one of the penes or copulatory
3 of the Lizard.
There is only one functional ovary, the left ; an instance of the
economy one observes throughout animated nature, for there is
always a tendency when organs become expensive, that is, so large
aa to be a serious tax on the system, to reduce their number, and
the production of eggs of the size of a Bird's is a great drain on
the organism. There are two oviducts, but the right is small and
useless. It must he remembered that the true egg formed by the
ovary is the yolk ; the white and the shell are additions derived
from the oviduct.
The nests which Birds build and their care for the nestlings,
^^_—_,_,. whom they in some cases feed at short intervals for
^^^^^r" about seventeen hours out of the twenty-four, are
^^^^Bpown to all. Most also are well aware that many birds
^^PQlKA to other lands as winter sets in. It is less well known that
quite as many migrate to lands further north on the approach of
spring. Few imagine the enormous distances which are covered
by birds on the wing. They constantly pass from the Bermuda
Islands to the Bahamas, 600 miles, without a rest. Many species
which have their home in North Africa go every spring to North
Siberia to build their nests. They fly, when migrating, at such
heights in the air as to be quite invisible and attain a pace which
seems hardly credible. There is no doubt, however, that very large
cumbers perish in crossing the sea.
Remains of fossil birds earlier than the tertiary period are
very rare, but a few exceedingly interesting specimens have,
however, been obtained. The principal of these is Arcliaeopteryx,
represented by two specimens from the quarries in lithographic
atone at Solenbofen in Germany. This remarkable bird had a long
tail like that of a lizard, to each vertebra of which a jiair of feathers
was attached ; the fingers of the wing bore claws and the bones of
the palm (uietaearpals) were free from one another. In the skull
^e premaxilla was as usual eusheathed in a horny beak but the
maxilla bore teeth.
In all these points Archoixtptitryx may be said to retain reptilian
characters. Two other fossil birds {HesperomU and Ichthyomie) had
33—2
516 AYES. [chap.
teeth in the maxillae but in other respects their structure was like
that of modem birds.
The classification of Birds presents great difficulties. They
used to be divided into six Orders, Yiz., Cubsobbs,
cation?^^" ^^ running birds ; Natatores, or swimming birds;
Grallatores, or wading birds; Scansobbs, or
climbing birds; Raptores, or birds of prey; and finally, the
Insessores, or perching birds, a division which includes all our
songsters, besides crows, rooks, magpies, sparrows and many others
Such a classification is, however, no longer accepted, because it gives
fundamentally wrong ideas about the true relationships of birds.
The aquatic birds, for instance, include totally different types,
such as the Gull and the Duck, which have been derived bom quite
distinct families of land birds. All are agreed, however, in sepa-
rating the Ostriches and their allies from all the rest as a great
main division, the Ratitae (Lat ratisy a raft) : but it is doubtfol
if this is a ' natural ' group. They are distinguished by possessing
a dwindled wing, which is useless for flight This leads to the
dwindling of the great wing-muscles, the pectorals, and the con-
sequent disappearance of the crest on the breast-bone to which they
are attached, and of the collar-bone, or clavicle. The breast-bone,
having no longer a keel, has been compared to a raft» whence
the name was suggested. The palate is also more like that of a
Reptile than is the case with other Birds, for the pterygoid bones
are firmly united to the basi-sphenoid by means of a basi-pteiygoid
process which springs from the last-named bone and articulates
with the posterior end of the pterygoid. The upper jaw therefore
cannot be bent up. The vomers also are very large and only united
in front Behind they join the basi-sphenoid and prevent the
palatines from touching that bone.
These birds have enormously powerful legs and can run at a
tremendous pace. The feathers are no longer required to form a
compact surface, and hence the barbs have no barbules ; this is the
cause of the soft downy character which is so characteristic of
them and makes them so prized for ornament The true Ostrich,
StruthiOy is found in Africa, Rhea in South America, the Cassowary,
CasuariuSj in New Guinea, the Emeu, Dromaeus, in Australia, and
the smallest Ratite bird, the Kiwi, Apteryx^ in New Zealand. In
historical times, however, New Zealand had the largest of all
Ratitae, the Moas, fyinomis, which had thigh bones larger and
thicker than those of a horse.
XVIU.] CLASSIFICATION. 617
All other birds are called Carinatae (Lat. carina ^ a keel), and
are distinguished by having a keel or crest on the sternum and well-
developed flying muscles. It is impossible to define with any
certainty any large main groups into which they can be divided,
bnt the number of smaller natural groups is very large. Here we
can only briefly allude to two main points in which birds differ from
one another and which are relied on in classification.
These are : — (1) The form of the palate : this resembles that of
the Ostriches only in one family, the Tinamous. This type of
palate is called dromaeognathous. In all other Carinatae the
palatines slide on the base of the skull. The maxillae send plates
inwards towards the middle line dorsal to the palatines, called the
maxillo-palatines. When these are united and the vomers small or
absent, or when they unite with the vomers, as in the Duck and
Hawk, the bird is said to have a desmognathous palate; when
the maxillo-palatines remain separate, as in the Fowl, and the
vomers form a conspicuous rod pointed in front, the palate is
schizognathous; finally when the maxillo-palatines remain sepa-
rate and the vomers form a truncated wedge in front but diverge
behind, aegithognathous is the term used. (2) Secondly, the
manner the young are cared for is an important feature. Nearly all
birds sit on or incubate their eggs. The Megapodes, or Mound-birds
of Australia, however, merely collect a heap of grass and leaves, and
leave the eggs to be hatched by the heat developed in fermentation.
The young, e.g., of the Pheasant, Game-birds, Ducks, when hatched
are able to run about and feed themselves (nidifugae) or they
leave the egg in a helpless condition, blind, and have to be fed by
the parents (nidicolae), for instance those of the Passeres or
Songsters, which require constant care and attention for a long time.
These last are considered by leading ornithologists to be the most
highly developed of all birds, both as to their intellect and their
structure, so that it is hardly too much to say that the increasing
sacrifice of the parents on behalf of the young has had its reward, in
the improvement it has brought about in all the faculties of the race.
The class Aves is classified as follows :
Sub-class I. AllOIIA£ORNITH£S.i
The three fingers and their metacaipals remain separate, each
with a claw. Both jaws with alveolar teeth ; tail without pygostyle ;
wings with well-developed remiges.
Only example, Archaeopteryx,
518 AYES. [chap.
Snb-class II. NBOiEunTHES._
Metacarpals fused.
Division I. Ratitae.
Flightless ; without a keel on the sternum ; williout a
pygostyle. Coracoid and scapula fused.
Ex. /Si^ru^^, African Ostrich; .S^ao, American Ostrich;
Dramaeus, Emeu ; Casuarius, Cassowary ; Apteryx^ EiwL
Division II. Odontoloae.
Marine, flightless, without sternal keel ; teeth in furrows.
Ex. Hesperomis,
Division III. Carinatae.
Without teeth, with a keeled stem^um.
Family (1) Colymbiformes (Divers and Grebes). Planti-
grade, nidifugous, aquatic, all toes webbed.
Ex. Colymbus, Diver ; Podiceps, Orebe.
Family (2) Sphenisciformes (Penguins). Nidicolous; wings
transformed into rowing paddles ; feathers small and scale-like.
Ex. Spheniscfis, Penguin.
Family (3) Procellariiformes (Petrels). Nidicolous, well
flying, pelagic ; sheath of bill compound.
Ex. Procellaria, Petrel; Puffinus, Pufl&n; Diomedea,
Albatross.
Family (4) Giconiiformes. Swimmers or waders ; desmo-
gnathous with basipterygoid processes; without copulatoiy
organ.
Ex. Sulay Gannet; Pelecanus, Pelican ; Ardea, Heron;
Ciconia, Stork ; Phoenicapterus, Flamingo.
Family (5) Anseriformes (Ducks and Gfeese). Nidifugous ;
desmognathous with basipterygoid processes ; with copulatoiy
organ ; palate bearing hard, homy, parallel ridges.
Ex. AnaSy Duck ; Anser, Goose ; Cygnus, Swan.
Family (6) Falconiformes (Birds of Prey). Nidicolous;
desmognathous ; beak powerful with decurved tip.
Ex. Falco, Falcon ; Aquila, Eagle ; CcUAartes, Turkey
Buzzard.
XVIII.] CLASSIFICATION. 619
Family (7) Tmamiformes (Tinamous). Nidifiigous; williout
pygostyle ; palate dromaeognathoos.
. Ex. Tinamtu, Tinamon.
Family (8) Galliformes (Game birds). Nidifdgons ; schizo-
gnathous. •
Ex. GcUlfM, Common Fowl; Phcwanus, Pheasant;
Tetrao, Grouse.
Family (9) Groifonnes (Cranes and Rails). Waders, nidi-
fugous; schizognathous.
Ex. BcMus, Bail ; Fulica, Coot ; Grtu, Crane.
Family (10) Charadriiformes (Plovers, Gulls and Pigeons).
Schizognathous.
Ex. Charadrius, Plover; Larua^ GuU; Pteroctes, Sand-
grouse ; Columba, Pigeon.
Family (11) Cuculiformes (Cuckoos and Parrots). Desmo-
gnathous.
Ex. CuciUtu, Cuckoo ; Psittacus, Parrot.
Family (12) Coraciiformes. Nidicolous.
Ex. Coracias, RoWer ; Upupa, Hoopoe; Alcedo, Eing-
fisher; Stria^ Barn-owl; Caprimulgus, Nightjar; Cypselus^
Swift ; Pictis, Woodpecker.
Family (13) Passeriformes. Nidicolous ; aegithognathous.
Ex. Passer, Sparrow ; Turdus, Thrush ; Hirundo,
Swallow; Alattda, Lark; Corvus, Crow.
520
CHAPTER XIX.
Sub-Phylum IV. Craniata.
Class V. Mammalia.
The class Mammalia (Lat. mammae, breasts), the last division
General ^^ ^^^ phylum Vertebrata, includes those animals
Character- which suckle their young. like the Birds, their
temperature is constant and they have the ventricle
of the heart completely divided into two halves. But they differ
from Birds in never possessing feathers ; only in one Order is the
fore-arm converted into a wing, and even in this case the arrange-
ment of the parts is quite different from that in the Bird's wing.
Besides these characters however there are a large number of
others in which, while Mammals differ from both Birds and Reptiles,
the last-named two groups agree with one another, so that for a
long time the opinion was held that Mammals were vastly further
removed from Reptiles than were Birds ; and indeed if only modem
Reptiles were considered this could not well be denied. If however
we examine the remains of the Reptiles which have existed on the
earth in past time, we come to the conclusion that the better way
to state the difference would be to say that, whereas Birds might be
traced back to Reptiles not very unlike modem lizards, Mammals
are derived from a type which has died out, leaving no modem
representatives. Thus Mammals are in all probability an older
group than Birds since they are presumably derived from the
Theromorpha and birds from some Rhynchocephalan ancestor.
Just as feathers constitute an indubitable mark of a Bird, so
true hairs are equally characteristic of Mammals. It is true that
the word hair is loosely used, being often applied for instance to the
delicate flexible spines of caterpillars, which are constructed on a
totally different plan to the hairs of Mammals. A hair in the
zoological sense is a rod composed of closely packed cells converted
UP. XIX.J
HAIR.
into horn, and under a microscope the outline of these celk con be
seen like a. mosaic on the surface of the hair, the outermost onea
overlapping each other like slates on a roof with the same function
of letting the water run off.
We §aw that a feather originated as a little knob, the outside
of which was composed of horuy cella, while the interior consisted
of soft living tiaaue supplied with blood-vessels ; a hair on the other
hand makes its appearance as a cylinder of horny cells growing down
from the epidermis into the dermis underneath. This cylinder then
becomes split into an outer sheath and an inner core, the latter of
which elongates and forms the hair, while the former remnina
Km. 389. Section throu(;li Ihe Skin of ii Mmuniiil. HigLlj magnified.
DiagranunatLC.
I. Onter liyer of dead homy cells uhich are rubbed off (ram time to time,
Stratum cameum. 2. Deeper iayet of oells retainiag tbeir protoplaBm,
.Sriviluin Slalplghii, 1 and 2 form the epidemiia and are ectodemwl in
origin. 3. DermiB or Corfuni. 4. A bnir. G. Sweat-gland.
6. Openiog of the duct of the aweat-gland. 7. SebaoeouB or fat gland.
8. Erector moBcle of the hair. 9. Connective tissue Bbres nf the dermie.
10. Blood- veseel. II. Vamular papilla at base of the bair follioie.
stationary and constitutes the follicle of the hair. The growth of
the hair is rendered possible by a little plug of dermis carrying
blood-vessels, which is pushed up into the lower end of the hair.
In consequenci' of the rich supply of food brought by these vessels
to the deep cells of the ectoderm lying above them, these cella
bud off homy cells with great rapidity and persistence, and in this
way a column of homy cells is formed which pushes out the older
I put of the hair and causes the whole stracture to assume a great
522 MAMMALIA. [CHAF.
length, sometimes equalliDg that of llie body. The plug of dennis
is called the papilla of the hair. In a few cases hairs may be
aggregated so as to form overlapping scales, and practically all
Mammals have nails or claws on the fingers and toes which resemble
essentially the corneous reptilian scale.
There is one respect in which Mammals and Birds agree with
each other and differ from all other kinds of animals, and this is
that their body temperature is considerably higher than that of thdr
usual surroundings and is capable of varying with safely to the
extent of only a few degrees. This condition of a constant tempera-
ture is known as the homoiothermal (so-called "warm-blooded")
condition and differs strikingly from the poikilothermal (so-called
" cold-blooded ") one of other animals, in which the body tempera-
ture varies with that of the surroundings and is usually only one or
two degrees above the latter. The temperature of a Bird or Mammal
is maintained constant by regulation both of the loss of heat by
radiation at the surface and of the manufacture of heat by tissue
oxidation.
Perspiration or sweat is also characteristic of Mammals. This
consists of a fluid secreted by certain cells of the epidermis which
remain soft and are not converted into horn like most of the outer
cells. The cells which manufacture the perspiration are arranged
to form long tubes called sweat-glands, which penetrate far below
the epidermis into the dermis underneath (Fig. 289). The pro-
duction of sweat is a factor in the regulation of the body temperature
and by it also certain excreta leave the body. The fluid poured oat
carries off a certain amount of heat and by its evaporation cools the
skin. Besides the sweat-glands there are other tubes which are
invaginations of the epidermis and consisting of a special kind of
cell. These tubes, sebaceous glands, open into the hair follicles.
They secrete the fatty substance or sebum which gives the natural
gloss to the hair (Fig. 289).
Mammals, as we have seen, feed their young after they are bom
by suckling them, that is providing them with milk. This milk is
a peculiar fluid produced by the mammary glands, consisting of
epidermal tubes crowded together over certain areas of the ventral
surface. They open at certain spots, raised above the general level,
which constitute the nipple or teat. Many zoologists belieTe
that the mammary glands are really only modifications of the
ordinary sweat-glands and sebaceous glands, for in the lowest Mam-
mals there is no special raised skin area which can be called a teat
THE SKULL.
Aa regards their in-
ternal structure the
great differences be-
, tween Mammals on the
one hand and Reptiles
and Birds on the other,
are to be found in the
skull, the brain and the
limbs and, t<L> a lesser
extent, in the heart and
the arrangement of the
great arteries and veins,
Turning first to the
fikull, we find that in a
Mammal instead of hav-
ing only one knob or
condyle to fit into a
cap on the first vertebra,
as is the case with Birds
and Reptiles, the skull
has two, which are pro-
jections of the exocci-
pital bones that wall in
the sidesof the foramen
magnum, whereas in
Birds the single condyle
is an outgrowth of the
basi-occipital bone that
forms the floor of the
foramen magnum (Fig.
S90). In Reptiles, more
especially the Chelonta,
the so - called single
condyle is really trifid,
the lateral parts being
formed by the exoc-
cipitals and the basal
le by the basi-occipital.
Prom this condition it
IB easy to see how
the conditions in Birds
1. Bupia-oocipital. 3. FoFamen ma^Dum.
3. Occipital condyle. 4. TTinpaliio bulla.
6. BBsi-occipitBl. B. BaBi'Sphenoid. 7. Et-
ternal auditory meatiiH. 8. Glenoid fasaa.
9. Foramen lacenimmedliiro. upertare Ibroagh
vhich the iatemal carotid paBsea to the bnuD.
10. Postglenoid [oramen. 11. Alispheaoid.
12. Presphenoid. 13. Vomer. 1*. Jagel.
15. Ftarygoid. 16. Palatal proeeas of
potatine. IT, Palatal pro<ies8 of maiUla.
18. PoBterior palatine toromen. 19. Ant-
erior palatine foramen. 20, Palatal proceaa
ot preinaiilla. 31. Opening of tube in
aliApbenuid bone tbrongb which tlie carotid
artery paaees 22. Hole fot passage of
BnBtncbiaii tube. 33. FrooesH of squamosal
to act as a stay for condyle of lower jaw.
It— XU. Exits of cranial nerrea. i 2, Second
incidore. C. Canine. pm 1, pm 4. Fint
and lonrth premolar. m 1. First molar.
624 HAHH&UA. [chap.
and higher Beptiles on the one hand and in Mammak on the
other may have been derived. Then the brain instead of lying
behind the eyes extends forward between and above them ; then
is consequently no interorbital septum, and the side walls of tbe
brain-case are thoroogh-
ly and firmly ossified,
not merely represented
by ft vertical plate im-
perfectly ossiGed, as in
a Bird, or neariy entirely
membtanous, as in some
Reptiles. These walls
are in &cl constitnted
of ftlisphenoid bones
behind and orbi to-
sphenoid bones in
front, whilst a strong
mesethmoid bone is
developed in the inttx-
nasal septnm. This
septnm is prolonged
beyond the bones of tbe
face by a cartilaginous
plate forming the sup-
port of a flexible noee
or mnzzle ; this is a
feature quite peculiar to
Mammals. The base of
the cranium is com-
pletely ossified, not only
behind by the baai-occi-
pital and basi-ephenoid
bones but in front by
the pre-ephenoid bones.
To the last-named the
a Dog,
Fio. 391. DorMl view of the Cranium of a
CanU familiarii r
1. Sapra-oeoipital. 3. Parietal. 9. Frontal.
4. Mosol. e. Haxilla (facial portion).
6. Premaxilla. 7. Sqaomosal. 8, Jugal.
10. FoBtorbital procsBs of frontal. 11. Infra-
orbital foramen. 13. Anterior palatine
foramen. 13. LachrTmol foramen, il. First
ineiBOr. e. Canine. pm 4. Fourth pre-
conjoioed vomers are
attached forming a wedge-shaped mass which projecta downwards
and divides the air-space above the palatal folds into two. The
name (Lat. vomer, ploughshare) is derived from the shape of the
bone in Mammals ; it is inappropriate as a description of its shape
in other Craniata. The pterygoid bones take the form ctf thin
XIX.] THE SKULL. 525
vertical plates ; they are attached throughout their whole length to
the side wall of the cranium in the region of the alisphenoid. As in
Grocodilia and desmognathous Birds the palatal folds are united in
the middle line ; the bones supporting them are processes of the
piemaxiUary, maxillary and palatine bones. Between the pterygoid
bones however the palatal folds form a purely muscular bridge,
called the soft palate, which ends posteriorly in a projecting lobe>
called the uvula, lying close to the glottis. The processes of the
palatine bones always meet so as to form a bony bridge, called the
hard palate ; those of the premaxilla and maxilla do so to a
certain extent, leaving however vacuities known as the anterior
palatine foramina (19, Fig. 290). (The posterior palatine
foramina are small holes in the palatine bones for the passage
of blood-vessels.) As in Chelonia, there is only a lower temporal
arcade, which is formed mainly by the cheek-bone or jugal. There
is however no quadratojugal, and the jugal joins a process of the
squamosal, which is a large bone covering the side of the skull and
almost concealing the conjoined bones of the auditory capsule from
view. It is characteristic of Mammalia that these bones, which in
the embryo are distinct from one another, unite to form a single
bone, called the per io tic, which is fused to the squamosal. In
Beptiles, on the other hand, the epiotic joins the supraoccipital and
the opisthotic the exoccipital, while the prootic remains distinct
The outer ear, the funnel-shaped passage leading into the tympanum,
which is termed the meatus auditorius externus, is surrounded
by a bone called the tympanic, often swollen into a rounded form
and then termed the tympanic bulla. There is often a tube-like
prolongation of this bone into the base of the ear-flap or pinna.
There is no quadrate recognizable as such, the lower jaw con-
sisting of a single dentary bone on each side, which articulates with
a smooth cup-shaped facet on the squamosal, called the glenoid
cavity. Occupying the position of the pre-frontal bone in Reptiles
is a small bone called the lachrymal. This bone derives its name
from the fact that it is pierced by a hole called the lachrymal
foramen (13, Fig. 291) which permits of the passage of a duct
leading from the orbit to the cavity of the nose. This duct carries
oiF the excess of tears (Lat. lacrima, a tear), the secretion of the
lachrymal gland, a development of the epidermis between the eyelid
and the eye. The lip-bones, the pre-maxilla and maxilla, are
well developed and like the dentary normally bear teeth, all of
which are implanted in distinct sockets formed by the upgrowth of
526
MAMMALIA.
[chap.
the bone which bears lliem. Many of these teeth aie rooted, that
is to say, after a certain time the dermal papilla on iriiich the
tooth is moulded becomes constricted at the base, so as to be
connected by only a narrow neck with the adjacent ocmnectife
tissue, this appearing in the dried tooth as a small hole thiongli
which a blood-vessel passes. The term root is applied to the
dentine surrounding the narrow neck. When it is formed, growth
of the tooth ceases.
The teeth of Mammalia are amongst their most chancteristic
Fia. 292. Dentition of a Dog, CanU familiari* x (.
i 2. Second inoisor. c. Canine. pm 1, pm 4. First and foorth premolaza.
m 1. First molar.
organs ; they are more differentiated than those of other Graniata,
and their peculiar structure enables us to identify many fossil
remains as mammalian.
They are typically differentiated into four kinds, viz. incisors or
cutting teeth, canines or stabbing teeth, premolars and molars,
which taken together are termed cheek-teeth or back-teeth (Fig.
292). The incisors are borne by the premaxilla and have sharp,
.»«.]
527
Btmght edges adapted for cutting luoraeb of conyeoient size from
the food. The canines and hinder teeth are borne by the maxilla.
The canines, popularly known as the eye-teeth, are pointed teeth
used for the purpose of killing prey or for defence againet enemies,
or in the tights which occur among males for the possession of
females. The premolars liave at least one cutting edge, often two
or more parallel to one another ; they are used to cut up the
morsels which have been taken into tlie mouth. Finally the molars
have hroad surfaces with which the food is sufficiently hroken up
to permit of its being swallowed. The teeth of the lower jaw are
of course all borne by the dentary, and they are divided into the
same varieties as those in the upper jaw. In Elasmobranohii,
&£ we have seen, the teeth are enlarged scales developed on a
fold of skin which is itivaginated within the lip, and as one row
of teeth becomes worn out another takes its place, the skin bearing
the old teeth slipping forward over the lip. In the higher Craniata
tliia fold is represented by a solid wedge of ectoderm, called the
enamel organ, but in Amphibia and Reptilia it only bears one
row of teeth. In Mammalia it normally produces two, the first of
which lasts only for a short time during the youth of the animal,
and is known as the milk dentition ; the teeth belonging to this
row are pushed out of the gum by those of the second row, or
permanent dentition, which last throughout the life of the
animal. In the milk dentition there are only incisors, canines, and
molars ; the milk molars are succeeded by the premolars of the
permanent dentition, while the permanent molars have no pre-
decessors and are regarded as belated members of the first dentition.
The teeth of Mammalia have undergone profound modifications in
accordance with the different habits assumed by diUerent members
of the class, and are one of the principal features on which ita
division into Orders is baaed.
From a study of the dentition of living Mammals the con-
mMmi is arrived at that the typical number of teeth, that is to
wSff&B number which the common ancestral form possessed, may
Httartamated at 44, i.e., 11 on eachsideof each jaw, made up of three
' incisors, one canine, four premolars, and three molars. This fact la
expressed by the fonnula q-,^t"' ., , where the upper line denotes
the teeth on each side of the upper jaw and the lower line those on
each side of the lower jaw.
The complete absence of the quadrate bone in the upper and of
528 MAMHAUA. [chap.
the articular in the lower jaw has given rise to much speculation is
to what has become of these elements, which are so constantly
present in Aves and Reptilia and are distinctly represented by
cartilage even in Amphibia. For a long time the favourite theoiy
was that they had been metamorphosed into the so-called ossicuU
auditds or bones of hearing. In Anura, Reptilia, and Aves sound
is conveyed from the ear-drum or tympanic membrane to the wall
of the auditory capsule by a single rod, called the columella auris.
In Mammalia however the connection is effected by a chain of three
small bones called the malleus (Lat hammer), incus (Lat. anvil)
and stapes (Lat. stirrup) respectively, the last named being
apposed to a membranous spot in the auditory capsule, called the
fenestra ovalis, while the malleus is in contact with the ear-drum.
Now since in the embryo both malleus and incus are represented
by blocks of cartilage which are for some time in continuity with
MeckeFs cartilage (v. p. 356), it was natural to suppose that they
were representatives of the articular and quadrate bones which in
lower Graniata are portions of the first visceral arch. The study
however of the extinct Reptiles which show the closest approximation
to Mammalia has rendered another view more probable. In the
Theromorpha, as these are called, the quadrate is very small, and
is enveloped in the huge squamosal which extends downwards and
backwards and forms part of the articulation for the lower jaw.
This tendency to the covering of the quadrate is also observable to
a slight extent in living Chelonia ; and in this group the quadrate
is observed to be bent around the anterior wall of the outer ear or
meatus auditorius externus and the Eustachian tube. Taking
everything into consideration it appears probable that the quadrate
is represented in Mammalia by the tympanic bone which like the
quadrate of Chelonia encircles the outer ear, and that the ossicula
auditfis owe their origin to the segmentation of the columella auris,
their intimate connection with Meckel's cartilage being paralleled by
the fusion of the columella and the Meckel's cartilage in Crocodilia.
This tendency to fusion of the columella and lower jaw is interpreted
as meaning that the columella is a relic of the hyomandibular bone
of fishes, and that in the ancestors of terrestrial Vertebrata the auto-
stylic articulation was derived from the hyostylic.
The articular bone has probably entirely disappeared in Mam-
malia ; when it was no longer used as an articulation it would first
cease to ossify and then become indistinguishable from the rest of
Meckel's cartilage. Doubtless a similar fate would have overtaken
XIX.] BRAm.
the quadrate but for its secondary use as a. protection to the
tympajiic cavity and as a frame for the tympanic membrane.
The chief peculiarity of the brain as compu«d with Beptilee is
Fill. '2!)3. Brain ot Rabbit. Lrpui cutiicvlui x 3,
A, Daraul aspect. B. Ventral lupect.
I, 01hct<tr>' lobe. 2. PitniUry body. 3. Cnira cerebri. i. Pineal
gLuid. 5. Anterior pair of corpora qaadngemiaa. 6. Pods Varolii.
T. Cerebellnm. 8. Lnttiral lobe of cetebeUum. 0, Flocculai lobe of
oerebellum. 10. Medulla obi oo^ta. 11. Sylvian liBBute saparating
the frontal lobe 12 from the temporal lobe behind. I. Origin of tint
or oKaoCory nerves. n. Optic or second nerves arising from tbe optio
etuBMma. III. Third or motor oouli nerve. IV. Fourth or pathelieus
nerve. V. Fifth or trigeminal nerve. VI. Sixth or abdaceus r "
VU. Seventh or facial nerve. VIU. Eighth or auditory i
EC. Ninth or glosBopharyDgeal nerve. X. Tonth or vagus r
XI. Eleventh or spinal accessory nerve. Xil. Twelfth or hypoglossal
e. AM.
S4
630 MAMMALIA. [CHAP.
the greater development of the cerebral hemispherea, in pn>-
portion to the bind brain or cerebellum. The former overiap
completely and conceal the thalamencephalon and the mid-btain,
and they are connected with one another by a great transverse bend
of nerve-fibreB, called the corpus calloBum. It is custoniarf to
map out the surface of the hemispheres into regions, in order to
facilitate description in delimiting the areas concerned with t^
development of specific sensations and with the control of specific
movements. These regions are called frontal, parietal, occipital,
and temporal lobes. The temporal lobe is separated &om the
frontal by a deep groove, called the Sylvian fissure (11, Fig.
393, A). How well the increased size of the cerebrum is re-
flected in the shape of the cranium will be seen when it is
recollected that the frontals and parietab, which represent merely
the membrane covering the anterior
fontanelle, not only form the roof
of the cranium but a large part td
its domed side wall; and tiirther
that the orbitosphenoid and aU-
spheaoid, which are portione of the
cartilaginous biwn-case, are restrict-
ed to the base of the sknlL The
cerebrum has in fact protruded
through the anterior fontanelle,
pufihing the membrane before it
The same condition is observatJe
in Birds, but not in Reptiles or
Amphibia. The cerebellum how-
ever is also well developed, just aa
in Birds, having indeed in addition
to the lateral lobes ao outer pair
of lateral projections, called floe-
culi, embedded in a hollow of the
bone that covers the inner ear (Pig:
293). The two halves of the cere-
bellum are connected with one
um'la n^ihown^ another by a conspicuous band of
fibres in the floor of the brain, called
the pons Varolii.
The nose, except in aquatic Mammalia, is a highly developed
sense-organ. The epithelium lining it is produced into scroll-like folds
1. PrBHtemam. 2. First sterne-
br& of meBoeteraum. 3. Laet
Bternebra ot mvaoit^raum.
4. XiphiBtemani. The flatMned
cartilasi
the liphietenium
6. First sternal rib.
K.]
531
rhich are supported by thiu plates of bone arising from the meseth-
Doid, and called ethmoturbiDaly. Above, where the mesethtonid
Dins the orbitosphenoid, bo nutnerouB are the apertures in it to
How the bundles of nerve-fibres from the olfactory cells to pass to
lie bmin, that this part of the bane is reduced to a sieve, whence
t has received the name of cribriform plate. From the maxilla,
rhich forms the outer wall of the lower part of the nasal tube, a
lilar scroll -like bone, theniaxillo-turbinal, arises, which supports
I corresponding fold of epithelium. This fold however is supplied
mly by the second division of the fifth nerve, aud is not believed to
uve any olfactory function, but merely to act as a Hlter to ftee the
nrushiiig air from grosser particles before it reaches the delicate
olfactory epithelium.
The neck region of Mammals (with rare exceptions) always
ODsists of seven vertebrae, and thus whereas a long-necked bird
tke a anan has numerous short vertebrae in this region, in a
Dug-necked Mammal like the giraffe the same region consists of
even immensely long vertebrae. The sternum of Mammals also is
leculiar, consisting of distinct pieces or sternebrae. The first of
hese is called the presternum, and bears a crest for the attacb-
oent of the pectoral muscles ; the last ends in u Bpa<le-like xiphoid
artilage, and is called the xiphisternum. The intervening
•gmenta constitute the sternebrae of the mesosternum. The
Dwer ends of a pair of ribs are attached opposite the junction of
iwo sternebrae (Fig. 294).
In Mammalia aa in other Ainniota the centrum is fonned from
he interventrals, and the head of the rib is articulated between two
rertebrae ; the articulation is not shifted on to the vertebra a^ in
^ocodilia. The vertebrae have occasionally in the neck region cup
od ball articulations like those of Amphibia, Beptilia and Avea,
iBt elsewhere the thick intervertebral cartilage allows of sufficient
lending, aud the centra have flat ends which ossify late and for some
ime form separable discs of bone called epiphyses. These do not
epresent any new elements in the centrum, but only ii method of
leaification found also iu the limb-bones. This method consists in
&B ensheathing membrane or periosteum first forming a tube of
3 round the centre of the cartilage, the ends of which remain
aoft and capable of further growth, being only replaced by bone
vfaen growth is diminit^hing, aud united with the main ossification
when growth has ceased.
In the fore-limha of Mammals the chief point to be noticed is
[chap.
the reduction in size of the pectoral girdle to which the fore-
limbs are attached. The lower part of thie, the coracoid, which
in Birds and Reptiles ia a lai^, strong bone meeting the stamnn,
Fio. 295. Skaleton of Rabbit, Lepui cuaicutut.
is here, with the exception of a few primitive forms, a small hixk
with no connection at all with the sternum. Hence the pectonl
girdle ia much more movable than ia elsewhere the caae, and takes
ax.) SSKLKTON. 5S3
part in the movemeDts of the limb. It is therefore not surprising
to find that thi} upper portion of the girdle, the shoulder-blade or
Bcapula, is broad, affording a large surface for the attachment of
muscles ; and that its surface is still further increased by the
presence of a sharp vertical ridge rising up along its middle line
(Fig. 295). To the end of this spine, as it is called, the collar-
bone or clavicle is attached ; this bone extends inwards to the
Btemum and is loosely connected with it. In some Mammab the
clavicle is absent.
The general form of the pelvic girdle to which the hinder
limbs are attached is not very unlike that of Birds ; but there are
two important differences. First, the ilia or hip-bones are attached
only for a veiy short distance to the backbone ; and secondly, the
lower bones of the girdle, the pubis and ischium, meet their
fellows of the opposite side in front of the belly beneath the
»nti9, whereas in Birds they do not even approai-li each other in
this place, though in RAea the ischia do meet dorsal to the anus.
It follows that this i)art of the body is extensible in Birds and
be litre tched as the large egg passes out through the
oviduct.
The leg of Mammals differs from that of Birds and Reptiles
in that the ankle-joint is situated between the bones of the
shank (the tibia and the fibula) and the small bones of the ankle,
instead of in the middle of these small bones (Fig. 295). The
keel-bone or calcaneum is one of the uppermost tier of ankle-
bones and corresponds to the bone called fibulare in the general
Bcheme of the peutadactyle limb. It is prolonged into the heel,
to which the -great gastrocnemial muscles which form the calf of
the leg and which raise the heel are attached.
Turning now to the blood system of Mammals we find that the
red blood corpuscles which give the colour to the blood are imlike
those of other Vertebrates. They have no nuclei and are bicou-
cave, while they are also much smaller and (except in Camels and
Llamas) round, not oval, as in all lower Vertebrates. Like Birds,
but unlike most Reptiles, the Mammals have a four- chambered
heart; the main blood-vessel, the aorta, is supplied by the left
^Btemic arch alone, the right one being cut off ^m connection
with it and being represented by the common trunk of the right
carotid and subclavian arteries, the so-called innominate artery
(Fig. 296), this being exactly the converse of the arrangement in
Birds.
[chap.
The Teatr&l carotid arteries, which va have seen are rednced in
Birds as compared with Reptiles and AmphibiaoB, m osoallf
Flu. 396. Diagram of krtm'ui Ai«beB of MsmmtU, viewed from the t
A. Of all MammaU except OeUoeana.
L II. lU. IV. V. VI. First to sixth arterial anshea. 19. Tentnl oantia
(small or absent). 13. Commoa carotid (dorsal carotid). 14. Syit-
•~ " • -^ - ... 19
B. Of Narwhal, representine Cetaoeans.
I. U. ni. IV. V. VI. Firet to sixth arterial arches. 19. Ventral eaiotil
(small). 13. Common carotid (dorsal carotid). 14. Bystemio trdi.
17. Dorsal aorta. IS. Doctas arterloaos. 19. Pulmonary. SO Innomin-
ate. 21. Subclaiian (ventral t;pe). 23. Inteioortal (eqaiTaknt to
subclavian of dorsal tjpe). 24. Coeliao.
absent in Mammals, though they may exist as qtiitd small vessels,
the trachea and other stmctnres in the neck receiving blood from
CIBCDLATION AND HESPIRATION.
'he »ub- f
XIX.]
the comuiou or dorsal carotid on ita way to the head. The
cJavian artery is of the dorsal type as in Lizards and Amphibians
ill all Mammals except Cetaceans, in which Order the fore-limb or
paddle obtains blood by an art«ry corresponding in origin with
that to the fore-limb of Cheloiiians, Oocodiles and Birds, i.e., a
"ventral subclavian." The "dorsal
subclavian " poflaeesed by most
Mammals is also found in Cetaceans,
but it is distributed to the ribs and
their muscles as the "intercostal
artery."
It is an interesting feature of
the arterial system of a Mammal
that in consequence of the embryo
receiving its oxygen from the ma-
ternal blood, the connection between
the systemic and pulmonary arches
persists in an uiireduced condition
until birth. This connection is
known aa the ductus arteriosus,
and through it the blood from the
right ventricle is passed direct to
the dorsal aorta. The pulmonary
arteries are quite small during this
period, and by these arrangements
circulation of blood through the
aa yet functionleas lungs is avoided.
At birth the ductus arteriosus
shrinks and is rapidly reduced to
a solid rord, while the enlarging
pulmonary vessels provide for the
deviation of the venous blood to
the now expanded lungs.
In the venous system the blood
from the head is returned by ex-
ternal and internal jugular veins,
the former being much the larger.
The hinder portions of the posterior cardinal veins have quite
disappeared and the caudal vein is continued directly into the inferior
vena cava, so that there is no longer even the outward appearance
o^a. renal-portal system. Tha anterior portions of the posterior
III.2QT. Din^irftm to show arrange-
ment of the piiDoipsl Veins in a
Mumm&l.
SimiH renoBUB — gradually dU-
uppeariDg in llie higher [orma.
B. DootUB Oovicri = superior vena
cava, 8. iDlernaijuRUlar^an-
terior oordinal sinDa. t. El-
la rnal jugular = sah-hranohiaL
6. Subclavian. 6. Poaterior
cardinal front part= venae azygoi
and hemiazygos, 7. Inferior vena
uava. 9- Caudal, 10. Boiotio
— ioternal ilioo. 13. Femoral
= external iliac.
536 MAMMALIA. [CHAP.
cardinals, however, persist as the venae azygos and hemiazygos,
which on each side receive the veins from the spaces between
the ribs — the intercostal veins. Only that on the right — the vena
azygos — ^reaches the ductus Cuvieri (superior vena cava) ; the left
cardinal or vena hemiazygos developes a transverse branch through
which its blood joins that of the right cardinal, and the veins from
the legs, instead of traversing the kidneys, empty at once into a
great vena cava inferior situated in the middle line of the back,
which is joined higher up by two short veins from the kidneys
(Fig. 297).
One of the most interesting peculiarities of Mammals is their
breathing mechanism. It will be remembered that whereas the
Amphibia simply swallow air, in the Beptiles the size of the chest
cavity is enlarged by pulling the ribs forward and then separating
them, and as the lungs are closely attached to the wall of the
chest, they are likewise enlarged and air rushes into them. In
Mammals this same mechanism exists, but in addition there is a
totally independent means of pumping air into the lung. This is
rendered possible by the existence of a diaphragm, a partition
convex in front which separates the coelom of the chest from the rest
of the body cavity. This partition is partly muscular, and when the
muscle contracts the whole membrane is tightened and necessarily
flattens, with the result that the chest cavity is enlarged and air
enters the lungs. The action of the diaphragm in fact is precisely
similar to that of the muscular floor of the mantle cavity of the
snail. The diaphragm is attached ventrally to the xiphoid carti-
lage, dorsally to the vertebral column, and laterally to the ventral
edges of the hinder ribs which do not reach the sternum. By it the
coelom of the mammal is separated into a thoracic division in front
and an abdominal one behind. Since therefore all the vertebrae
which bear recognisable ribs which reach the sternum belong to
the thoracic region, they are termed thoracic vertebrae, while the
ribless vertebrae of the abdominal region are denominated lumbar.
In the digestive system the principal peculiarity of Mammals is
the high state of development of the salivary glands. These
glands are much branched tubular outgrowths of the ectoderm of
the mouth-cavity or stomodaeum ; they secrete a fluid which
moistens the food and is swallowed with it, thus helping digestion.
They are foreshadowed by small glands in frogs and snakes, but
in Mammals they form three large masses, viz. the sub-lingual,
underneath the tongue, the sub-maxillary, under the angle of
XIX.J
SALITABY 01AKD8.
the jaw, and the parotid, just under the ear. Glands In simil&r 1
pOBitioDH are found in some Birds, but those of Mammalia secrete I
in addition to mucua a ferment, called ptyalin, which turns T
starch into sugar, so that the secretion which is called aaliya I
ia a true digestive juice. The developmeot of the large intestine ]
withdraws water irom the undigested residue of the food, thus
reducing it to a semi-solid mass or faeces, which is also a cliaracter-
istic of the Mammalian alimentaiy canal.
Mammala are divided into three great primary divisions or I
sub-claasea according to the structure of the ovary and oviduct ]
and tu the stage of development attained by the
young at birth. The lowest forms have large eggs
like those of birds: in the higher forms the egg ia at first small
but has the power of absorbing nourishment from the wall of the
oviduct, which is here enlarged to form a womb or uterus.
the highest division a special organ for the nourishment of the
einl»70, the placenta, is develojied, as an enhtrgenient of the
embryonic bladder.
The sub-cUsses are called :
I. Prototherk, or primitive mammals,
II. Metatiikbia, or modified mammals.
III. ECTHERiA, or perfect mammals.
Snb-clasa I. PaoToTHEBiA.
The Prototheria include two extraordinary animals, the Or-
nithorhynchus (Piatypus), or duck-billed mole, and the Echidna, or
spiny ant-eater, which are found only in Australia, New Guinea
and Tasmania. In these animala Urge e^'gs with a lirm ithell are <
laid in a nest and incubated by the mother, and in harmony with
this arrangement the two oviducts are large throughout the whole
of their length, and do not join each other at any point but open
along with the intestine into a common vent or cloaca, as is the
caae with Birds and Ueptiles. The ureters do not open into the
bladder as they do in all other Mammalia, but they iind the blmlder
open separately into the cloaca. In the male a copniatory organ or
penis is present opening into the cloaca behind, and in front pro-
tntded from the cloaca. After they are hatched the young receive
mUk from tlie mother. There is uu toat, but the fluid from tb«
milk glands aeems to soak into the hair and theuce is sucked bf
the young. Before birth the young re-
i^ive no nourishment at all from ihe
mother, but subsist on the abundant yolk
of the egg.
The skeleton of the Prototheria pre-
sents many interesting features of agree-
ment with the Reptiles; thus the Tertebtae
have no epiphyses, and there is not only
a complete coracoid articulating with the
sternum, but also two pre<:oravoids whicb
overlap. Underneath these there are two
clavicles and a. T-shaped interclavicle, so
that the shoulder-girdle recalls the com-
plicated one of the libird.
Ornithorhynchus has webbed feet and
hves in the water, feeding on worms and
insects, whii-h it digs out of the mnd by
its broad, shovel-like snout, whence the
name Daok-bill (Fig. 29S). It cnuba^
FiQ. 39S. Diagram to illn
(rate the arraDi;EiimDt
the TeniBle genital duuts
the Prototberia.
1. Ovary, 2. Oviducal
funnel. S. Oviduct,
i. Op«niDg into oloaoa.
ite prey by means of horny plates, wliich are really patches of the
hardened gum : when it is young, however, it has true calcareona
teeth, two or three on each side of each jaw, but these it loses when
it grows older. These teeth are covered by several rows of small
points or tubercles. Similar teeth are found amongst the oldest
remains of Mammals which are known, the so-called Multituber- i
calata.
Echidna lives on ants and other insects, which it ensnares by I
putting out its tongue covered
with sticky saliva. Like other
ant-eaters it has a long snout
and no teeth. It is covered with
stiff spines like a porcupine.
Sub-class II. Mbtatheria.
The division Metatheria in-
cludes the curious pouched Mam-
mals of Australia and the neigh-
bouring islands and the Opossums
of America. In these auimais
the egg is exceedingly small,
and the egg-tulie is divided into
Ml Upper part of correspondingl}-
narrow diameter, called the Fal-
lopian tube, and a lower, wider
part, called the uterus. In
this latter the small egg lies for
a while and rapidly grows and
developes, absorbing food &om
the nterus through the thin egg-
membrane, since there is never
any egg-shell. Beneath the
uterus comes the lowest part
of the egg-tube, the so-called
vagina. The two vaginae come into close contact with each other
above and then diverge, both opening below apparently into the
lowest part of the bladder, as do the vasa deferentia in the mate.
What seems to be the lowest part of the bladder is really the front
portion of the cloaca, which has become separated from the part
behind that receives the opening of the intestine. This common
Fin. sou. VeuCmiviuwortheShoalder-
girdle and Steranm of a Duckbill,
OmiChorhynchun paradoxal x |.
Alter Purkur.
1 ud 3. Scapula, 3. Coracoid.
4. Precoracoid. 6. Gienoid
oavil;. 6. laterclavisk. 7. ClBviole.
a. PreBteraum, 0. Third aeg.
DioDtDrmesuslemiiiii. 10. Sternal
rib. II. lotertoediate rib. 13. Var-
tebrnl rib.
540
MAMMALIA.
[chap.
vestibule for excretory and reproductive ducts is called the nrino-
genital sinus, and its opening is distinct from that of the intestine
or anus, although the two openings are still surrounded by a common
muscle. From the spot where the vaginae meet above a pouch
called the median vagina is often developed. This ends blindly
in the young female, but in the mature female it acquires an
opening into the urinogenital sinus and through this opening the
embryo is bom, the lateral vaginae serving merely to admit the
spermatozoa from the male.
When the young are bom they appear
not as eggs but as little mammals, which
are however exceedingly small in sixe.
They are then placed by the mother, who
is said to transfer them with her lips, in
a pouch made by a fold of skin on the
lower part of her body, whence the name
Marsupials (Lat marsupium, a pouch),
often given to these animals. A pair of
sesamoid or epipubic bones run forward
from the pubes. They are ossificatioDs
of a tendon of the extemal oblique muscle.
Similar stmctures are found in Proto-
theria, in Crocodiles and in Urodela.
The young are quite incapable of feeding
themselves, and therefore the mother by
compressing the muscles of the belly
squeezes the milk-gland and forces milk
down their throats. In order to allow
the young one to breathe at the same
time, the back of the soft palate is
wrapped round the upper end of the
windpipe, which projects into the throat so that the air passes from
the nose straight down the windpipe whilst milk flows down at the
sides of the air-passage into the stomach.
In the mandible the angle, that is to say the lower and posterior
end, is as a rule prolonged inwards as a horizontal shelf of bone.
By this feature fossil skulls are recognized as belonging to the
Metatheria.
The living Metatheria are divided into two great orders, of which
the first is mainly carnivorous and the second herbivorous, though
some members of both are insectivorous. The first order is termed
Fio. 301. Diagram to illus-
trate the arrangement in
the female genital dacts of
the Metatheria.
1. Ovary. 2. Ovidncal
funnel. 5. Fallopian
tnbe. 6. Uterus.
7. Vagina. 8. Median
vaginal pouch. 9. Uri-
nogenital vestibule.
METATBERIA.
PoLTPRQTODOSTiA ; the animalB compoaing it h&ve &t least four
incisors on each side of the \i\>\^t jaw uiid three on each eide of the
Ds, foremost; dSoKr«5,
lower, whence the name (Qr. xoAu, many ; t
teeth). The Diprotodontia, as the second Order is called, derive
their name from the circumetance that in the lower jaw there is
one large pointed incisor on each side, the others being rudimentary
or absent, so that ouly two prominent teeth are observable <Gr. 2>-,
tvo). The Poljrprotodontia are represented lu America by tbt;
family of the Opoasums, Didelphytdae, which is confined to thiit
continent It includes 'J4 speoiea, most of which are fomnl in
Mexico, Central Am erica, and Brazil, but one, the Vii^niui
opossum, Didelphjfg rirglniana. ranges north as far as the soatli
bank of the Hudson river. In all Uie Didelphyidae the great toe
is large and can be separated from the other toes so as «itb them bi
grasp a support; thus it is said to be 'prehensile.' In Australia
the Polyprotodontia are represented by three families, viz. the
Dasvurid.u:, the Per.*melidae and the Notortctidae. The
first family includes the animals known as native cats, whicb
resemble the American opossums, but are distingiiiahed from them
by the smaller number of incisor teeth and by having a rudi-
mentary first digit in both fore- and hind-feet, whereas in tbe
Didelphyidae, as we have seen, this digit is long and prehensile.
The largest member of the family is Thylacinits a/nacephaliM,
the Tasmauian wolf, now conhned to tlie wilder parts of Tas-
mania: it has a sktiU which strikingly resembles that of a dog;
in its habits it resembles a wolf and is very destructive to sheep.
The Banded Ant-eater, Myrmt>mt)itts fatdatm, is an aberrsut
member of the same family which lives on insects, capturing them
with ita long tongue. The insects are made to adhere to this
organ by the viscid saliva. The teeth, though rudimentary, ar«
distinct. There is no pouch: the young when first bom cling to
the teatfl and conceal themselves in the long hair of the mother's
abdomen. The Pekamelidae or Bandicoots are small animals some-
what resembling Rabbits and Hares in their appearance but n
HBTATHEBU.
pointed muEzlee ; they are remarkable in possesFung a type of t
characteristic of the Biprotodootia. The Notobtctidab include ti
single genas Notm-yctes, which io habits and appearance resembi
the Mole, a eimitar mode of life having brought about similu-
moditications of structure.
The Order Diprotodontia includes a number of species confined,
vitii one exception, to Australia and the neighbouring islands.
One species, the only living representative of the family Epanor-
THIDAB, has been recently found in South America. This animal,
which has received the name CaenoteatHs ullgluogua, has feet like |
Banded Ant.eaMr, Myrmecobiui fa$ciatu
\ the DiDELPHriDAE, and this circumstance renders it possible that ]
it has been independently evolved from that family, whereas
the other members of the Order .seem to have been derived
from forme like the Peramelid.ve. The typical Diprotodontia
have the secoud, third, fourth and fifth toes of the Iiind-foot
united by a web of skin. The fourth is the strongest toe,
the fifth ia a little shorter, but usually nearly as stout as the
fionrth ; the second and third, though as long as the fourth, are j
544 MAMBfALIA. [CHAP.
much more slender, while the great toe is often rudimentaiy.
Exclusive of the Epanorthidae there are three femuliee in the
Sub-order. The first family, the Phasoolomtidae, consist of one
genus, Phascolomys, the Wombat, represented by three species. The
Phasoolomtibae are distinguished by possessing only one incisor on
each side of the upper jaw, and as both upper and lower incisors
are chisel-shaped the dentition resembles that of a Beaver or Rat
Wombats are heavy animals with a shuffling gait, about the sue
and appearance of a Badger.
The second family, the Phalanqeridae, or Australian opossums,
have normally three incisors on each* side of the upper jaw; the
fore- and hind-limbs are of about the same size and the great toe
is prehensile. These are small animals which like squirrels live in
trees, and several species possess a parachute-like membrane ex-
tending from fore- to hind-limb, by the aid of which they sustain
themselves in the air during their great leaps from tree to tree.
Phascolarctus, the so-called native Bear, is a clumsy tailless Phs-
langer, in which the prehensile great toe is specially well developed.
The Macropodidae, or Kangaroos, are the most peculiar family of
Diprotodontia, and indeed of the Metatheria. They resemble the
Phalangeridae in having three upper incisors on each side, but di£fer
totally in the structure of the limbs. The fore-limbs are so small
as to be used only for grasping, and locomotion is effected by a
series of leaps carried out by the hind-limbs aided by the powerful
tail. The sole of the hind-foot is excessively narrow, the second
and third digits being represented by bones so slender that they
take no part in supporting the body. McuyroptAS giganteus, the
gray Kangaroo or ''Old Man," may obtain a height of from 4 to 5
feet. The fourth toe of the hind-foot has a powerful claw wiUi
which when the animal is brought to bay it has been known to
rip open a dog. The allied genus Petrogaie includes smaller species,
called Rock Wallabies, with only a short claw on the hind-foot
As their name implies they frequent rocky regions. The so-caUed
Kangaroo-rats, Bettangia and others, are nocturnal animals of small
size, which live on leaves, grass, and roots, the last of which they
dig up with their fore-paws.
Sub-class III. EUTHERIA.
The highest division of the Mammalia, the Eutheria, includes
all the most familiar animals, hedgehogs, rats, rabbits, cats, dogs,
XIX.]
EUTHERIA.
545
lions, tigers, horses, oxen, whales, elephants, monkeys, up to and
including man himself. In them as in the Metatheria the egg is
exceedingly small, in Man and the domestic animals for instance,
it varies from ^^ to -^ inch in diameter. The upper part of the
oviduct, the Fallopian tube, is consequently narrow; the uterus is
however enlarged, for the egg not only lies there a long time —
called the period of gestation or pregnancy — but as it is
developing into the young mammal a special organ called the
placenta is developed, which grows out and becomes interlocked
7 ■-
B
B
4
Fio. 305. Diagrams to illustrate the arrangement of the female genital dncts in
an Entherian Mammal. A. Babbit. £. Man.
1. Ovary.
2. Oviducal funnel. 5. Fallopian tube. 6. Uterus.
7. Vagina. 8. Urino-genital sinus.
with folds in the wall of the uterus. This organ is nothing but an
enormous development of the bladder of the embryo, which is
called the allantois, and which is also developed in the embryo
of Birds and Reptiles, where it subserves respiration and lies above
the embryo beneath the egg-shelL In Eutheria the surface of the
allantois is covered with vascular outgrowths called villi, which fit
into pits on the wall of the uterus. Both the membrane covering
the allantois and the lining of the uterus degenerate, allowing the
blood-vessels of mother and embryo to come into close contact.
The placenta becomes gorged with blood driven into it by the heart
of the developing embryo, and at the same time the uterus becomes
congested and loses its epithelium, so that the blood of the mother
and that of the young approach very closely to each other. They
S. <fi; M.
35
separated only hy the thin uuter wntl of the placenta, so tbt
nourishment diBTiiacB tTiim one to the other, and the hlocx
embryo h oxygeuated and its carbon dioxide removed by the
maternal blood. So close is the connection, that when the embryo
is born and passes out of tiie uterus, carrying with it the placenta,
the latter in most coses tears open the vessels in the wall of Ha
uterus and the mother loses a considerable quantity of blood. Tim
lowest i>artB of the tno oviducts are completely joined and pan
into a sin^i^le pa.ssage, tlie vagina, while the middle portions, ot
uteri, are sometimes quite separate as in the rabbit (A, Fig. 305),
sometimes partly united a.9 in the cat, rarely completely joined u
in monkeys and man (B, Fig. :)05). In one or two Metatheria a
placenta such as has been described has been recently discovemd,
but it is of very small extent. These facts lead us to believe tlot
Metatheria are degenerate descendants of early Eutheria, and «f
may take as a further mark of degeneracy the almost complete
disappearance of the milk set of teeth.
Order 1. Edentata.
"When we take a general survey of the orders or main divwn
into which the Eutlieria are divided we And that we have three or
ma^^
From Proe. ZimI.
four strange groups, the relations of which to the others are moat
difficult to decide. These include the cnrious Edentata of South
America, comprising three families, the Bradvpodidae or Sloths, the
MYRUBCOPU^aiBAE or American Ant-eaters, and the Da^vpouUUA
F
■
m
EDENTATA. 547 ^H
pr Armadillos.
With these the South African forms, included in ^|
[he families Manidae oi
""~"'°~ 1
^m »
i
^1 t
^
r^'^^^^A ^^1
^H f
1
^m 1
1
Hf V
Hi
1
1 J
P* Oape Anb-eatera, are
!■ a matter of doubt. ^^
The name mi^auB "toothless," aud was ^|
IL ' '" '
^
J
to be devoid of teeth. This is only the cabr with one small f&mily,
the Ant-eaters, or Mtrmecophaoidae, which, like Ecliidtui, have
lust their teeth through disuse. In the rest tliere we teetli,
but front teeth are always wanting. In the adult none of the
teeth have enauiel and all are similar to each other. The
hands and feet are armed with great curved cUwh. adapted
for holding on to BUpporta. not for grasping or attacking, and
incapable of being retracted or pulled back. Consequently the
hands and feet are like hooks, an which the animals walk
clumsily, bending the fingers under them. The apparent want
FiQ. 308. W1litl^lleUied Pangolin, Manit triaupU,
of utility is however explained when the animals are looked at tn
their natural anrrnundings. It is then seen that one family, the
Sloths (Bradvpuuidak), spend all their time climbing about on trees,
on the leaves of which they feed. There is a remarkable adaptation
which probably helps them to escape detection by their enemies.
The surface of the hairs is grooved and affords a resting-place for a
unicellular Alga which causes the animal to have a greenish appeur-
ance so as to be almost invisible amidst the foliage. The second
family include the true Ant-eaters or Mtrmbcophagidak ; in these
the strong claws are used for pulling down and digging up ant-hills.
The muKzle is long and toothless. There is a very long Umga^
:XIX.] MARINE HAHSUL8. 549 \
and enormous salivary glaodM, the sticky secretion of which entraps
the ants. The Tamandua Ant-eater, Tamandua tvtradactj/la, of
Central and South .\inerica, is arboreal in its habits and lives in the
dense primeval forests of the New World : it uses its strong
claws for i-)imbing and has a prehensile tail. The third Eamily,
the Armadillos or Dasypodidae, can dig with such rapidity that a
comparatively large animal will scoop out a burrow for itself in a
few minutes. These Armadillos are also very remarkable as being
the only Mammals in which the dermis or deeper skin developes
into hard bony plates such as we find in Turtles and Crocodiles,
whilst the hair on the upper part of the body is replaced by homy
scales like those of snakes and lizards, covering the bony plates.
It is thought that in comparatively recent times, geologically
speaking, South America was an island, and just a^ Australia has
preserved some curious animals which could never have held their
ground against the powerful lions and tigers and wolves of the Old
World, so in South America evolution seems to have run a course
of its own.
Id Africa there are found two other genera of Ant-eaters, Manis,
the scaly Ant-eater, also found in Eastern Asia, and Oriicten^us,
the Cape Ant-eater, both of which are usually classed under the
Edentata. Mank has the hair agglutiaated to fonn overlapping
scales, but has no dermal plates and no teeth. M. frlcuapis is
arboreal in its habits. Orycteropvs has peculiar folded teeth and
scanty liair, It is termed by the Boers the Aard-vark or Earth-pig
and is nocturnal in its habits, sleeping during the day in burrows
which are usually found in tlie neigh bfjurhood of the large ant-
mounds so commou on the veldt. Neither genus is believed now to
have any close alhuity with true Edentata, their reproductive
organs being markedly difi'erent from those of the S. American
forms, and they arc provisionally grouped together in an Order
termed the Effodiehtia.
MARiys Mammals,
The second and third strange groups, the relations of which to
the rest of the Mammals are unknown, are the two
Mammau groups inhabiting the sea, viz., the Whales or Cstacka,
and the Sea-cows or Siiienia. Both of these have some
peculiarities in common, due to their having adapted themselves
to special and— for a Mammal— unnatural conditions. Thus both
Whales and Sea-cows have lost all outward trace of hind-limbs,
k
550 MAMMALIA. [CHAP.
although a pair of small bones representing them are found
embedded in the body. In both the tail has become flattened,
developing flukes or fins at the sides, and, as in Fishes, it is
by strokes of the tail that these Mammals principally move. Bnt
whereas in Fishes the tail moves from side to side, here, in accordance
with the necessity for coming to the surface to breathe, it moves up
and down. Both Whales and Sea-cows have lost nearly all hair ;
Whales retain only one or two traces about the lips, while in Sea-
cows there are scanty bristles all over the body and the lips are
thickly covered. The other Mammals which have taken to the sea,
the Seals and their allies, are provided with a thick coating of hair
(see p. 538).
We saw that the nose in Fishes was a sense-organ, adapted
for stimulation by gases and other odoriferous substances dissolved
in the water. When land-animals were evolved, the air needed for
breathing was drawn in past the nose ; the oro-nasal groove leading
from the nose to the mouth, which was at first an open gutter,
became changed into a closed channel, the nasal passage, and the
nose became modified for stimulation by vapours mixed with air.
In the marine Mammals air is still drawn in through the nasal
passage, but they are concerned no longer with perceiving things
which emit vapours into the air, but rather like fishes, with
substances dissolved in the surrounding water. Since the true nose,
the sense-organ, owing to its new connection with breathing, cannot
be used for perceiving substances in the water, it ceases to be of
use, and becomes vestigial : the nasal bones shrink away into small
remnants and the nasal opening is placed far back on the snont,
near what appears to be top of the animal's head.
Order II. Cetacea.
Tlie Order of Whales is distinguished by the great rounded
cranium and by the elongation of the bones of the face and jaws.
These support an immense prow-like snout formed chiefly of fiit,
which is an admirable buttress of defence for the animal's skuL
The supra-occipital bone is of great size and forms the posterior
surface of the cranial dome, interposing between the small
parietals and meeting the frontal The frontals develope great
orbital plates flanking the face, beneath which is the small orbit
bounded below by the slender jugal. In Whales also the teats are
situated far back, as they are in cows, and the mother forces the
milk down the young one's throat; for in the Whale, as in the
young marsupial, the windpipe auci uose are directly connected ;
only here the conoection la.'^ta tLrotigh life and allows a Whale to
smm through the water with its mouth open whilst it breathes at
the same time,
A ■! '?
Bosi-oooipiul. 2 Eiocoipitiil. 3. Bupra-oocipitAl. 4. Buuphenoid.
6. Aliflphenoid. n. Parietal. 7. luCerpanetat IIiBed with S,
8. Prunpheiioid. 8. Orbitoapbenoid. 10. Frontal. 11. Meaethmoid,
la. IVrnpsoia. 13. Periotiii, 14. Squamosal. IS. Jugtil.
lii. Vomer. 17. PnlatiDf. 18. Pterygoid. 19. Nasal.
30. UuillB. 31. Premaxilla. 2-i. Mandible. iS, Anterior
Whales are divided into Sub-orders, the whalebone Whales or
Mystacui-eti and the toothed Whales or Odoxtocsti. In the
latter there are numerous f*eth, but they are all aHke and simple
(Fig. 3U9), and the maxilla developes a ^Teat crest which conceals the
orbital plate of the froutal. The great Sperm-whale, I'kyeeter
macrocep/ialus, of the Soutliern Seas, has teeth ouly in the lower jaw
and feeds on cuttle-fish and fishes, gripping the long flexible arms
of the former by pressing them against the upper jaw. Spermaceti
552 MAMBIALIA. [CHAP.
oil is the melted-down fat of this monster. The Ca'ing or Pilot
Whale {Ghbicephalus melas), which also feeds chiefly on cattle-fish,
has teeth on both upper and lower jaws (Fig. 309). Pilot-whales are
social in disposition, and the herds are occasionally driven into bays
or fiords in the North Atlantic and captured. Smaller Toothed
Whales are found round the coast of Britain which have teeth in
both jaws. Others are known as the Porpoise, Phocaena, the
Dolphin, Delphinus, and the Grampus, Orca, The common Por-
poise, Ph, communis^ is the most abundant and best known of
British Cetaceans. It is not more than six feet long and is often
cast ashore. In the Gulf of St Lawrence the White Whale, Delphin-
apterus leucas, is fairly common. It attains a length of twelve feet
The whalebone Whales, Mystcicoceti, have no teetL The
orbital plate of the frontal is uncovered and there is a small
ethmo-turbinal covered with olfactory epithelium. They are all
large animals, although they feed on the smallest prey, such as
minute pelagic moUusca, jelly-fish and Crustacea. The " whale-
bone'' or baleen consists of a large number of homy plates hanging
down like curtains from the palate into the cavity of the mouth.
These are placed in pairs, one on each side of the mouth, one pair
behind the other, and the fellows of a pair nearly meet in the middle.
The lower edges of these plates are frayed out so as to form a fringe
or strainer. After the whale has taken water into its mouth it
raises its tongue against the edges of the plates and allows the
water to trickle out through the strainer described above; all the
small animals taken in the water are thus retained and then
swallowed. The best quality of whalebone is obtained from the
Right Whale, BaUtena mysticetus, an animal about fifty feet long,
found only in the Arctic regions. The great Rorqual Whale,
Balaenoptera sibbaldi, ha^ a fin in the middle of its back, and
attains a length of from 60 — 80 feet ; it is the largest animal now
found on the globe and is very abundant. The lesser Rorqual,
Balaenoptera rostraia, is a smaller animal some 30 feet in length.
On two occasions at least the animal has strayed up the St Lawrence
as far as Montreal where it has been starved to death in fresh water.
The head of Balaenoptera is much shorter than Balaena and the
whale-bone is shorter and coarser.
Order III. Sirenia.
Sea-cows differ from whales in so many respects that they cannot
have any close relation with them. They are vegetable-feeders, and
I browse on sea-weeds and other water-plaota. As these habits oe-
Lcessitate their staying under the water for some coDsidemble time,
Ktiie bones are heavy and solid, quite different in structure from the
Pio. a
Skn1l of Arrico.!) Manatee, Man
<1-
I bones of whales, which are mucli more spongy iu texture. The skull
long, not rounded, and the fate bones are only moderately
I developed. The parietals are uot pushed aside by the development
■ of the supra- occipital ; the Hupra-orbital plate of the frontal is flm&ll,
iVfaile the orbit is large and bounded below by a very powerful jugaL
#
\ Fiu. 811. Front
Bbooing Ibe
divaricntod.
iew ot bead of American Manatee. Miinatiii americanui,
e», nosIriU and moath. A, with the lobes gf the upper Up
, with lliy lip contracted. From Murie.
The teeth are broad and crushing, and frout teeth sometimes are
fennd developed as tusks. Tliere is no such snout as is found in
I Whales, but there are large movable lips by means of which food
1 (Fig. 311). The teats are placed on the breast as in Bats,
554 MAMMALIA. [CHAP.
Monkeys and Man, and the mother holds the young under the arm,
which is quite flexible and not a mere fin as in whales. It is
supposed that the legends of mermaids have been suggested to
sailors by the sight of these strange parents holding their young
above water. There are two genera, each represented by a single
species ; the Manatee, Manatus, found on the warmer parts of tiie
coasts of the Atlantic and in the estuaries of its rivers, both in
America and Africa, and the Dugong, ffalicorey found all around
the coasts of the Indian Ocean and round Australia, where it is
fished for and eaten. Until 1768 a third species, Rhytina steUeri^ of
great size — 20 to 25 feet long — inhabited some islands in the Behring
Sea. It had no teeth, homy plates on the gum supplying their
place. This species was exterminated by Russian seal-hunters.
Leaving aside these curious groups of animals, we find that
the relations to one another of the remaining Mammals are
more easily understood. We have first of all to deal with the
Insectivora.
Order IV. Insectivora.
This is a group of small animals which, as their name impUes,
feed chiefly on insects. They have three or four sharp pointed
cusps on each of their back teeth, adapted for piercing the armour of
insects, while their front teeth in both jaws are directed outwards
so that they act like a pair of pincers in seizing the prey. The
Insectivora are plantigrade, that is, they place the whole palm aud
the whole sole on the ground when they walk (Figs. 312, 313) ; in
nearly every case they have the full number (five) of fingers and toes ;
they have long flexible snouts projecting beyond the mouth and
their brains are of a low and simple structure, the surface of the
cerebral hemispheres being smooth, while they leave the cerebellum
uncovered. In many cases there is a shallow cloaca surrounded by
a sphincter into which both anus and urinogenital passage open.
They possess an allantoic placenta, but this covers only a small
portion of the surface of the uterus, and indeed in this respect they
are hardly more advanced than those Metatheria which retain an
allantoic placenta. The Insectivora, as may be seen from the de-
scription, are a very primitive group, and like other primitive groups
consist of a number of families widely differing from one another
in structure. Taking a broad view we may say that the tropical
families exhibit the highest grade of structure. Thus the Galeo-
PITHEOIDAE, or flying shrews, represented by the genus Galeapithecus,
INSECnVOBA.
SS5
liave ft parachute-like expanaion of skin extending from neck to
hand, forming a web includiog the fingera. A similar expansion of
akin reaches from wrist to foot, forming a weh between the toes, and
tliere is a piece of skin connecting the two lega behind. There is
a ring of bone round the orbit, and the symphysis pubis is long and
strong. The I'uPAirDAE, or Tree-ahrews, have likewise the orbit
encircled by bone and a strong symphysis pubis, but they are devoid
of any paraohute-like extension of akin. They are small animals
with large eyes and long furry tails ; both these groups are confined
to the Malay archipelago and India and both inhabit trees.
K>%^
Fill. S12. AfricaD Jumping-HhreTr, Mae
radaelylan x }. From
The Machosceudae have no bony ring round the orbit but they
poBsess a strong symphysis puhiti. Their moat marked chaf acteriatic
18 an elongated foot (soe fig. 312) which euables them to make groat
I springs. Hence the name Jum ping-shrews. They are represented
by 14 species distributed over Africa.
The three families which represent the Insectivora in Great
Britain are all of a lower type. Not only ia the orbit never
I muTDimded by bone but the zygomatic arch is slender and sometimes
lUHlULU.
even absent. The braiii cavity ia very small and the symphysis
pubis is very abort ; sometimea the ptibes are uniteil imly by ligament
The first of these families ia the Ebinaceioab, or Hedgehogs, diit-
tingiiinhed by the slender zygomntio arc^h, and by the tympanic lieiiig
iu the foriu of a riog. The well-known Hedgehog. Erinaam
gurtipm'Ui, is intermediate in nize between a rat and & rabbit. It hu
the fur intermixed with sjiines, and when alarmed rau roll JMlf
into a ball, tucking iu head, limbs and tail, and in this condition cao
bid defiance to ite enemiea. All Erinaceidae are not of this character;
Fid. 31S. BassisD DeamaD, Mgogale motchata.
the rat-like Gymnura from India and the Malay i>enim
without spines.
The other two families are the Shrew-mice {Soricidak) am!
the Moles (Talpidae); theae are represtented in both Great Britain
and North America, but the latter country is without Hedgehogs.
The Soricidae have lost the zygomatic arch altogether, the pnbes
are disconnected and the tympanic is ring-like. As the popular
name implies these are mouse-like animals covered with for.
There are three British species, Sorex vuU/nris, about the siw of
an ordinary mouse, 8ore-x pygmaeus, one of the smallest I
XIX.]
WSECTIVORA.
657
known, and Crosstypu« fodlem, the Wftter-ahrew, distinguished by
baviag the feet frayed with stiff hairs to «id in swimming. The
North AmericaE Blarina has the aspect of a Mole with ite small
eyes and rudimentary outer ears. It is failed the Mole-ahrew, but
ita normal arms and hands at once distinguish it from the true
Idoles. 'Ilie true Moles, Talpibae, are above all characterised by
tiie greatly enlarged hands and powerful though short arms by
which they are adapted for a burrowing life. To make room for the
large haniU iu narrow burrows the front segment of the sternum ia
greatly elongated, thus c.irrj'ing the pectoral girdle and limbs forward
on to the neck, where there is room for them. The clavicles are short,
almost sijuare bones, and the humerus of the arm is short and stout.
The zygomatic arch is pre-sent and the tsTupauic is a bulla. The
Talpidae are represented in Great Britain by Talpa europaea, the
common Mole, wbtch feeds on earthworms, constructing a complicated
system of underground passages through which it hunt's its prey.
In North America the commonest is perhaps Condi/lura eristnta, the
Star-nosed Mole, the snout of which is encircled by a ring of fleshy
outgrowtlis.
The Russian Desman, Myogalf moackatn, once extended as far
west as Britain, It lives in burrows by the water-side and feeds
chiefly on fresh-water insects and their larvae. In correspondence
with ite mode of life the hind-feet are webbed and the tail large and
compressed, forming an efticient swimming organ. It is hunted for
its fur.
There still remain four families to be mentioned, each of which
however ia represented by a few species. These are interesting
because, (1) They have a more primitive type of molar tooth than any
other living Mammals ; (2) In their distribution, like the ancient
genus Peripatus, they belong to the southern hemisphere, only over-
stepping it when they go into the West Indies. The tyjie of tooth
18 the tri -tubercular, which is found in the oldest remains of Mammals
known ; it is distinguished by the reduction of the characteristic
cusps of tlie insectivoran tooth to three which form the points of a
triangle, Of these primitive families the CuRVsocuLnRiiiAi: are the
Golden Moles of the Ca|>e, so-called from the iridescent sheen of
the fur. They have the reduced eyes and enlarged hands and anna
of the ordinary Mole, but these hands and arms are placed not at
the sides of the neck but at the sides of the thorax, the ribs of
which are bent inwards to create hollows for their reception. The
q'gomatic arch is present and the tympanic is a bulla. The remain-
ing familira have lost the zygomatic arch and the tympanic ia a mere
ring. I'hese are ( I ) Potamugaliuae, represented liy a single species,
Water-slirewa from Central Africa with a flattened tail, short limhe
and ui> clnviclfs, (2) S'.ilf.nodontidae, and (3) Ckntbtidae, turn
closely allied families of small hog-like animals with stout hmbi,
the hrst from Cuba and Hayti and the second from MadagsMii:
Thi' moat interesting ciri:unjstance about the Insectivora is titt
fact that when Ly means uf foaaiU we trace back the higher group*
of mammak they seem all to merge imperceptibly into forma which
from their teeth and general organisation we should clase ae Id-
sectivura. There is therefore really good ground for supposing Uut
the living Insectivora, though modified in spet^'ial details, ueverthe-
lesfl represent, so far as their general organisation is concerned, the
earliest type of Eutheria which appeared on the gtol>e. From these
original Insectivores advance seems to have tnken place ^ong five
lines:— I., some Insectivora toolc to attacking larger prey, including
tht^Ir own less fortunate relatives, and gradually developed into the
Gamivora or Sesh-eating mammals: II., some became vegetable
feeders and gave rise to the great group of hoofed animals, relying
either on their swiftness, size or strength for defence: III., some
took to burrowing and developed into gnawers or Rodenb;, relying
chiefly on their burrows for safety: IV., some took to the air, the
fore-limb becoming changed into a wing ; these are the Bats : V., the
remainder took to escaping into trees when liard pressed, and
eventually gave rise to the great group of the Primates which
includes Monkey and Man.
Order V. Gamivora.
fSin
The Gamivora are distinguished above all by their teeth (Rg,-
292). They have small iiistguificant front teeth or incisors, but
the eye-teeth or canines, situated in tliemaxilla just where it meets
the premaxilla, are large and pointed. With these the animal
aeizeu and kills its prey. The premolars have cutting edges, consist-
ing typically of a large central cusp and two smaller ones, one in
front and one behind. The molars with the exception noted belo*
are broad and crushing (Piga. 292 and 3U). The last ptt;mohu- in
the upj>er jaw and the first molar Ju the lower jaw constitute what
are called the carnassia! leeth. These are very laige blade-like
teeth which bite on one another like a pair of scissors. The upper
one has enlarged central and posterior cusps, the anterior ouqp
being small or n&ntiBg; the lower carnasHial haa an anterior blade-
lihe pnrtioD consisting of two casps and a. posterior flattened portion
or heel. The nails are sharp curved claws.
The most familiar examples of this class of animals are our Doga
and Gats. The wild ancestors of the domesticated pets are unknown,
though the dog's ancestors were no douht allied to the wolf, whereas
the cat ia probahly descended from Bome species belonging to the
M. 31-1. Vertical longitudiniil neution Uken a little to iUe left ot the middle
lias through the Skoll o( a Doj;. Caiii' /amiliiirii x^.
Sopra-tKWipiWil. 2. Inlerpariela!. 3. Parietal. i- FronttiL 5. Cribii-
lona plate. 6. Nasal. 7. MeBelbmoid. tt. Maxilla, 9. Tomer.
10. Ethmo-turbinal. II. Maiilio-turbinal. 13. Pcemaiilla. 13. Oooip-
ilal condyle. 14. Basi .occipital. 16. Tjmpaaic bulla. 10. BaBJ-Bphenoii).
17. Pterygoid. 18. Palatine. 19. Ali-aphenoid. 30. Internal auditory
meatm, the paaaage for the eiehtta nerve to the internal ear. 21. Tentoriom,
a fold of calcified oonncctive tiaaue projeotin); into the oraoial cavity and
separating the oerebrnm from the cerebellum. 22. Forameu laceiom
p<nteriufl, the paBnage for the tenth nerve, 33. Flooculat foaaa,
the cavity in which the Boccular lobe of the oerebellan) in lodged.
34. CoToaoid priH^eBB. 25. Condyle. 30. Annie. 37. Maudibnlar
symphyBJs. 28. Inferior dental toramen. 39—31. tegmenta of the
aet^ond visceral arob. 29. Styto-byal. 30. Epi-byal. 31, Cerato-
hyal. 32. Basi-hya!. 33. Thyro-hyat, the third visceral amh,
XII. Condylar foramen, the sperturo through which the twelfth cranial
nerve leaves the skull.
East, allied to but distinct from the Wild Cat, Feli'g catus, atill
Ibund in remote parts of Scotland and possibly in the mountains of
North Wales. Possibly the domestic cat has originated from the
Cafire Cat, F. rafra, which extends throughout Africa and was
oonsidered sacred by the ancient Egyptians, who embalmed their
560 MAMMALIA. [CHAP.
bodies in such amazing numbers that their mummies have been
exported from Egypt and used as manure.
In the Dog, Ganis familiaris, and the other members of the
family Canidae, the muzzle is long and the teeth numerons.
Their arrangement can be expressed by the dental formula
i- o > c. -, pm. 7 m. ^ = 42, where the upper line shows the teeth in
6 1 4 o
the upper jaw, the under line those in the lower. The first
figure denotes incisors, the second canines, the third premolars
and the last molars. The hindermost back teeth, or molars, are
still broad. The fore-legs cannot be used for grasping. The daws
are comparatively blunt and cannot be retracted.
In the domesticated Cat on the other hand the muzzle is short,
3 1
and the teeth reduced in number, the formula being L o > ^ t »
3 1.
pm. f^yUi. Y = 30, whilst the fore-limbs can be used for seizing. The
claws are very sharp, and can, when not in use, be completely
retracted or rather raised, so as not to wear the points. In all these
respects Cats are more perfectly adapted for a carnivorous life than
Dogs, these latter still retaining traces of their descent from a
different kind of mammal. Just as the Wolf, C. lupus, the Jackal,
C. aureus, and the Fox, C, vulpes — the last-named the only wild
species of Canis found in Britain — are species of dogs distinguished
from each other by size and slight peculiarities of hair, etc., so the
Lion, F. leo, the Tiger, F. tigris, the Leopard or Panther, F. pardus^
the hynx, F. lyn^, and the Puma, F, coticolor (frequently called a
"Panther" in America, where it is found from Canada to Patagonia),
are all Cats. The differences in the colour of the skin which help to
distinguish them are in all probability due to the fact that the
colours are protective, enabling the animals when in their natural
surroundings to escape the notice of their prey. Thus Lions, which
as a rule live in dry and rather open places, are of dun colour ; the
stripes of the tiger's skin deceptively resemble the alternating
shadows and sunlit strips of ground found amongst the reeds in
which they live ; the spots of the leopard are undiscoverable amidst
the alternating patches of light and shade caused by the sunlight
struggling through the interstices of the foliage of a forest
The Bears, Ursidae, represent a third type of Camivora. They
are plantigrade, placing the whole sole of the foot on the ground ;
the molars are blunter than those of the Cats and Dogs and very
rj OABNITORA. 561
broad, the camassials are broa<l and the premolars Tsry small and
often fall out ; the upper camasaial is a comparatively Bmall tooth
and the heel of the lower camasaial is l&i^er than the blade ; these
{Mctili&rities are connected with the fact that the Bears are not
merely flesh feeders but can live partly on a vegetable diet. ITie
'Town Bear of Europe, Ursus arctos, which used to be abundant in
Britain, is so nearly allied to the Grizzly Bear, V. hfrrribilis, of
the Roi^ky Mountains, that the latter ia by some authorities placed
in the former spei^ies. In Eaateru Canada, especially in the Province
if Quebec, the Black Bear, Ursus americamis, is very abundant and
ifi trapped for its fur. It is usually an inoffensive animal, feeding
on berries and bark, but occasionally, especially when it has cubs,
it will attack man.
The Stoats, Weasels, Martens, Minks, Polecats, Otters, Badgers
and Skunks, forming the family Mdstelidae, are sometimes supirosed
to be allied to the Bears, but are really very distinct. They have very
long necks, slender, flexible bodies and short limbs, and their habits
are exceedingly bloodthirsty and ferocious. The chief resemblances
to Bears are found in the skull and teeth, but the contrast in general
build and in gait — the Mustelidae are digitigrade — is very striking.
Six species of Mustelidae nre found in Great Britain : (1) The Otter,
Lutrn vuli/arin, an animal which has webbed toes and a long, some-
irhat flattened tail. It lives on fish, passing much of its time in the
Tcater, (a) Tiie Badger, Mtdes tajrus, a heavy, somewhat clumsy
animal with btunt claws and short limbs, leading a nocturnal,
burrowing life and feeding on mice, reptiles, insects, fruit, acorns
and roots. (3) The Pine Marten, Mustela martes. (4) The Polecat,
■Putoriug/oetidm, which feeds on small mammals, birds, reptiles and
i^gs, and has a disa^eable odour. The Ferret is a domesticated
Tariety of the Polecat, (o) Tbo Weasel, Pulorius vulgaris. In cold
tegioQB the Weasel turns white in winter. (6) The Stoat, Pulorius
grmitieua, which also turns white in cold climates except the tip of
ita tail, which remains blacL Its fur is much prized. These last
four are I'loseiy related species with long, slender bodies, sharp
curved claws and ferocious habits.
In North America there is an interesting family, the Peo-
croNiDAE, intermetliate between the Ursidae and Mustelidae. The
tnembers of this family have sharp muzzles but clumsy bodies and
abort necks ; the Raccoon, Proc^it htor, is the most familiar. It
is omnivorous. The Mustelidae are represented by otters, martens
and a remarkable form, the Skunk, MepkUia mepkitiat (Fig. 315),
& <t M. 36
HAMXAUA.
which prodacea a secretioD of such repnlaive odour as to make it
avoided by other animals and a temir to man. It la strikingly
marked and aflFords a mucb-ii noted example of naming coloratiuo ;
its conspicuous colour eoabliiig woiild-be euemiee to dii^tinguish it§
poBsessor from less offensive prey. The Viverkidae should be
neutioDed although they are a tropical gruup. In general shape
they resemble the Mustelidae. iiut in the shape of the carDaasial
teeth and in the division of the auditory bulla by a septum they
agree nith the Felidae. The best-knovm members of the family are
the African and Indian Civet Cats ( I'ltrrra rivetta and V. :iMha)
FjQ. 8iB. The Coninion Skank. Mrph>
from whose perineal glands the civet of commerce is obtained.
Fossil remains connect the Viverridae and Mnstelidiie and one would
not be far astray in calling them "primitive cats."
The Carnivora mentioned hitherto are often grouped together as
the Carxivora vera or Fissipedia. The second grouj) of recent
Carnivora is represented by the seals and is terme<i the PiyifiPKJ>lA.
The name is derived from the fact that fingers and toes are united
by webs of skin. The Seals are almost as purely marine animals
as the Whales and Sea-oows, but they have become adapted to
their sorroundiogs in quite a different way. Thus their fur_ia_
cIoBe and thick, and thej are protected a^tunst the cold of the
water by it, instead of being covered all over by a. thick layer of
fat as are the Whales. The tail is short and insiguiiicaDt, but
they make a powerful stern oar by directing the feet backwards
parallel to the body so that the soles are turned up. Thus the feet
■ct just in the same way m the tail does in a whale, making up and
Aovm strokes and driving the animal forward. The whole u])per
port of the limb h burieil in the body. lu one group, the true Bared
or Seal-skin Seals, Otahiid.^e (the fur of some ajKcies of which is
used for making .jackets), the feet can be turned forward when the
ftnita&l comes on land. There are also some traces of an external
Pia, Sie. The FuUgonian Sea-Lion, Olariujubala. From tlolnter.
[ ear, whence comes the name Otariidai; ot Eared Seals which is
[ pveii to them (Fig. 316). They are confined to the Pacific coast of
I Amerii-'a. The Walnis, Trkhechus rosmarua, of the Arctic seas, is
the representative of a second family, the Triciiechidae. No
external ear ia present but here also the feet can be turned forward.
The canine teeth of the upper jaw are very long and give the animal
I a fierce appear(iu'.'6, They arc however chiefly used for digging up
I Wvalves from the mud and for climbing on the blocks of ice in the
I Arctic regions where the animal is found. The name " Old Man "
I aometimes given to it by wiialers is siiggested by the tuftB of gray
I hair on the sides of the face, The common Greenland Seal, Pkocn
IJii—l
564 MAMMALIA. [CHAP.
vitulina, and the Gray Seal, HcUichoerus grypuSy are the two species
of Phocidae, the third and last family of the Pinnipedia, regolaily
found round about the British coast in out-of-the-way places.
The members of this family have harsh fur and no trace of an
ear-flap and are unable to turn their feet forward, so that when
they come on land they shuffle along entirely by the aid of their
fore-limbs. They are in fact the most thoroughly adapted for
aquatic existence of all the Pinnipeds. Phoca mtulina is common
on the eastern shores of Canada and New England.
Order VI. Ungulata.
The great group of the Ungulata or hoofed animals represents
the second line of evolution from the primitive Insectivores. Here
we find that all power of grasping with the limbs is absent and the
feet are purely adapted for running, the toes being encased in hard
blunt nails which are called hoofs. At the present time the
Ungulata include a number of very diverse forms. But it most
be remembered that a large proportion of the group is extinct,
and that to some extent the fossil forms serve to connect the very
heterogeneous members of the group that still exist.
Sub-Order I. Sub-ungolata.
In former times there existed a great assemblage of big and
often clumsy animals belonging to the Ungulata in which the toes
were all nearly equal in length and the bones of the wrist arranged
in parallel longitudinal series. The Sub-ungulata at one time
spread over the earth and in South America, which became isolated
in early times, they gave rise to a great variety of forms. Some of
these mimicked the descendants of the Ungulata, and formed one of
the most striking examples of parallel evolution. Only two famiUes
of the Sub-ungulata, as these animals are called, survive till
the present day. These are the Elephant family, Pboboscideae,
and the family of the Hy^rax, Hyracidae.
Hyracidae.
The Hyrax (Procavia) is the coney mentioned in the Bible.
The Hjrracidae are small, not unlike rabbits in ap-
Hyraddac. pearaucc, but their hind-feet closely resemble those
of the Rhinoceros. Their front teeth are, it is true,
somewhat chisel-shaped, aa in the B.odentia, but there are four of
tiiese below and two above, which is quite UDlIke the arraagetnent
D the rabbit. It is possible howBver that the two teeth reckooed
U lower posterior iocisors may really be (.'anities, since they do not,
like the other ineisors and like those of the Rabbita, grow throughout
life (Fig. 317). These aaimals are found throughout Africa except
IS.]
PROBOSCIDEAE.
565
Pia. 817. S)iMolHyTaxiProeavia]dor^aiii-'ii.
Nasal. S. PuriaUl. 3. Eiterna! auditory meatus. 4. Prooos*
uiipiMl.
Jagal. G. Laohrjmal raramen.
in the north and also in Arabia and Syria. Only one genus is now
'ognized, Hi/ra-r {I'roeavia), with several species. Most of thesf
live Amongst rocks, in mountains and in stony places, hut some
fre<iueut the trunks and large branches of trees and sleep in holes.
Pkobwideae.
The Klephant is too well known to need much description, but it
may be pointed out that the trunk is really a long flex-
ible snout, an excesaiYe exaggeration of what is found
in Insectivores, and that the tuaks are front teeth, only
those in the upper jaw being develojied (thoiigh in some extinct
eleph&nts, as for instance in some species of Mastodon, both upper
and lower incisors were present while in Ditiolkerium the tusks were
developed in the lower jnw only), and finally that the upper parts of
the arms and legs are i|uite free from the body, instead of being, as
unually the case with oiammals, buried iaaide the general contour
of the body. There are only two living species, the A&ican Elephiint,
Elirphas Oifricaniis. inhabiting the forest region of tropical Africa
and bunted for its tusks, and the Indian Elephant, Elciihas inJirua,
inliftbitiug the jungles of India, Further India, Ceylou and Sumatra,
566 HAHMALIA. [CBAP.
which is frequently domesticated. The caninee are loet and haie
left DO traces. The molars ancceed one another in a horizontal row,
nerer more than two being at any one time functional (Fig. 318).
The ridges on these teeth when worn present the appearance
of parallel bands in the Indian Elephant but in the African thep
form diamond shaped lozenges The ears of the latter are veiy
large and the trunk ends m two nearly equal prehensile "lips"
attached to its lower margin. In the Indian Elephant the ean
are smaller there is but one finger like Lp " at the end of the
1. Ei-occipital. 2. Parietal. S. Frontel. 4. SqnamouL S. JngaL
6. Premaiilla. 7. Maiilla. 9. Supnt-oocipitkl. 13. Bui.oecipiuL
14, Poatorbitftl proocBB of the frontal. IS. Laafai7ni*L 16. PteiTgoid
proceBB of the ali-sphenoid. i 1. Incisor. nimS, mini. Third ud
fourth milk molars. m 1. First molar.
trunk and this is attached to the upper edge of the end of the
trunk. The skull is very massive, but the extarior gives an
erroneous impression of the size of the brain-case because the bones
are enormously thickened and contain laige air-spaces, especially
in older specimens, where the &ontals may attain a tliicknesB of
one foot. Till recent times (geologically speaking), an extinct
elephant, Mastodon, inhabited North America, Europe and parts
of Asia. Its remains are being constantly dug up &om the bottom
of gravel-pita and miunli«&. Some species of Mastodon had tusks in
both jaws ; id most tho tnoUr teett were covered with tubercles
like those of the pig, Instead of ridges of enamel. Another fossil
species aUied to the Indian Elephant but covered with thick fiit,
the Mammoth, EUphas primigeni-H&, had formerly au extensive
range around the North Pole and at one time was common in
Britain.
Sub-Order 11. Ungulata vera.
All the rest of the Unguliitn, have the thigh and the upper arm
more or less hurled in the body, whilst the heel and the wrist are
raised in walking so that the creature goes along on the tips of its
Fio. 819- Bonea of right Fore-foot of existing PeritiodiKlylf. A. Tapir,
Tapinu indicui x j. B, Hhioooeroa, Rhinoeenu latnatrmiii ^ ]. C, Horse,
Equut caballat x t,
Onneiform (nlnare). J. Lnmir (inter-medinin). m. Magnam (third
distal tsu- pal J. p. PhiSoiai. R. Radias, >. Souplioid IradiHle).
' '. Trapezoid (seoond diatal carpal), tm. TrapeKium (Srat distal DnrpaJ).
toes. The bones of the wrist are arranged in transverse rows, the
; members of two adjacent rows alternating with one another. The
I first digit in both fore- and hind-limbs is entirely absent. These
I true Ungulatefi, Unqulata vera, as they are csdled, are divided
■ ioto two great groups: (1) the Perissodactyla, in which there
568 MAMlfALIA. [CHAP.
is an odd number of toes and in which the true central axis of both
arm and leg runs down through the centre of the third finger or toe
(Fig. 319), and (2) the Artiodactyla, in which there is an even
number of toes, and in which the axis of the limb passes down
between the third and fourth toes (Fig. 322).
Division I. PERISSODACTYLA.
The Perissodactyla were formerly a numerous class of animals,
but now three families alone survive, the tapirs, Tapiribae;
the various species of rhinoceros, Rhinocerotidas ; and the horse
and numerous species of ass, Equidae.
Of these the oldest and most primitive are the Tapiridab. They
still have four toes on the fore-feet, which is an even
number ; but as they have only three on the hind-feet
and in both fore- and hind-feet the axis of the limb runs through the
third toe, there is no doubt that they are to be classed with the Peris-
sodactyla (Fig. 319). The snout is long and flexible, longer than
the snout of the Insectivores but not so long as the snout of the
Elephant. A most interesting feature in the natural histoiy of the
Tapirs is that they are now found only in two widely separated parts
of the world, viz., the north of South America and in the Malay
Peninsula with the neighbouring islands of Borneo and Sumatra.
We need not however suppose that there was at one time a land
bridge across the Pacific, for in recent rocks we find remains of Tapirs
all over Europe, Asia and America, so that the present species are
to be regarded as two separated remnants of a great race of animals
which once had a very wide distribution. Their present range
affords an often quoted example of what is known as ''discontinuous
distribution."
The Rhinocerotidae are represented at the present day by the
genus Rhinoceros, The Rhinoceros is a heavier and
tidac!"°^*'^° clumsier animal than the Tapir ; it has three toes on
both fore- and hind-feet and no projecting snout
Its chief peculiarity however is the horn which it carries so to speak
on the bridge of its nose. The horn has no bony core, and as it is
entirely composed of homy matter may be said to be a mass of hairs
stuck together. There are several species found in Asia and in
Africa; the best known is perhaps the Indian, R. unicornis (Fig.
320) ; the Javan, R, so?idaictis, is smaller. Both these species
have but one horn. Two-horned rhinoceroses (the two horns stand-
perissodacttlT
ing one behind the other) are now found in the Malay PeninG
Borneo and in Sumatra {Ji. samatrensh), while in Africa there a
several species ; the commonest, R, f'icornis, is frequently shewn 1
in uienogtiTiea. It is supposed that the idea of the unicorn J
was derived from the one-homed rhinoceros, but if this be so thel
imagination must liavo played a powerful part in evolving the!
gracefiii animal which figures in the royal arms out of the clumsy,!
rhinoceros.
The general appearance of the harae, Equun caballus, ial
suiiiciently well known, but the structure of
feet, which, next to the wings are the most highlrj
specialized organs of locomotion in the animal kingdom, demand>j
carcfiU attention.
The apparent "knees" of the horse correspond to the joints aim
tile wrist and the ankle, the true elbow and knees are concealed ia.l
the body of the animal, although the motion of these joints cAn he I
clearly seen if a running horse be watched, A horse walks on thfl'j
very points of its tinger and toe-nails, and it possesses only one finger j
on each band and one toe on each foot (C, Fig. 31'J), the fingers and J
toes corresponding to the outer fingers, the toes of the Rhinoceros
being represented merely by bones entirely concealed beneath the skin |
and applied like splints to the great middle finger and toe resgiec- J
lively. Thas the whole limb instead of being a loosely jointecl]
flexible organ for gi'aaping, becomes a firmly jointed lever bending!
only in one plane and suitable for quick locomotion.
570 MAMMALIA. [CHAP.
The Horse, as we know it, has been domesticated and bred by
man for thousands of years and is doubtless very unlike its wild
ancestor. The wild animals at present existing which are called
Wild Horses are all more like donkeys, with longer ears and widi-
out the peculiar wisp-like tail of the Horse ; they are also all more
or less striped. The Zebras and Wild Donkeys are found in Africa
on the great plains in the south, in the deserts of Syria and Persia
and in the central plains of India. Another African form, the
Quagga, has become extinct in recent times. In America when
discovered there were no horses, although the horse has since nm
wild there; but in the most recent geological period the horse
abounded in America and why it should have died out in a country
which afterwards proved to be well suited for it is a mystery. In
the same country in the deposits formed at the bottom of great lakes
are found the remains of a series of animals which form a complete
chain from a true horse which appears in the newest deposits to
animals which not only are more primitive than Tapirs but which
must even be reckoned as Sub-ungulata, for they have five fingers
and five toes but had the bones of the wrist and ankle in longitudinal
series. This series of forms is one of the most complete evidences of
evolution known to geologists.
Division II. ARTIODACTYLA.
Unlike the Perissodactyla, the Artiodactyla or even-toed Ungul-
ates constitute an immense assemblage of animals, and until the
invention of modern fire-arms were the dominant animals on the
great plains of Africa and also of North America. The Artiodactyla
may be divided into a higher and a lower section.
The lowest section may broadly be called the Pigs, SuiNAS,
„ . They retain four toes on fore- and hind-feet have a
snout endmg m a round flat surface and are all gross
feeders, eating not only roots of various kinds but also small animals
if they come in their way. Their teeth are covered with tubercles
a good deal blunter than the cusps on the teeth of an Insectivore
but still of the same essential nature. Such teeth are termed
bunodont, whence the name Bunodontia (Gr. ^ovyo9, a hill or
mound) has sometimes been applied to this division. The Hippo-
potamus, the sole representative of the family Hippopotamidab, is
nothing but an enormous Pig ; it differs from the ordinary Pig in
having all its toes of equal length, whereas in the true Pig the
Xa.] AHTIODAOTTLA. 571
outer (second and fifth) toes are small and do not rea^^h the grouniL
The Hippopotamus spends moat of its time in rivers and swamps
feeding on the reedy vegetation of such places. It has exceedingly
powerful jaws and when wounded haa heen known to crush a canoe
between them. The true Pig belongs to the Family Suidae and is
a domesticated variety of the wild boar, Sua Kcrq/a, which, as is well
known, survived in England until the middle agee and still exists
in Europe. In the male the canines, or eye-teeth, are jwwerfuUy
developed, those of the lower jaw projecting upwards outside the
mouth. In the Babirusa, Babirusa af/urus, of Celebes, the upper
canines do not enter the mouth but are bent upwards and pass
through special holes in the skin, curving back over the head like
horns. They grow persistently, their roots being kept open. The
Pigs are not strictly vegetable feeders but are really scavengers,
eating every vegetable or animal sub.'itance they encounter, the
food they seek especially consisting of roots. A very interesting
genus, the Peccary, is rejiresented by two species, Dieotyks tajafU
and JJ. lahiatus, which inhabit the American continent. The
former ranges from Patagonia to the Red River of Arkansas, the
latter between Paraguay and British Honduras. The name means
' two navels ' and was suggested by the presence of a large gland in
the middle of the back resembling a navel. On the hind-foot the
fifth toe is wanting, so that there are only three toes ; but the position
of the axis of symmetry is still between the third and fourth toes.
The Peccaries go in droves and are most dangerous antagonists;
climbing a tree is the only chance of safety to a hunter who meets
a herd.
When we leave the Pigs we have t« deal with the higher
section of the Artiodactyla, the Seiesodontia or
/fUMiIfAlfTiA, which include most of our domestic
animals, the cow, sheep, goat, camel, etc., as well as all the deer and
antelopes. The latter name is derived from the habit of ruminating,
thslia of bringing the food back from the stomach into the mouth after
it has heen swallowed and chewing it again. Corresponding to this
habit we find that the stomach has acquired a complicated structure.
Just where the gullet opens into it we find a large pouch projecting
laterally with the walls covered with little projections or papillae ;
this is called the paunch or rumen. Just below the oesophagus is
another smaller pouch divided by a constriction from the first (Fig.
821). The second pouch is called the reticulum because its walls
are raised into intersecting folds producing cavities like the cells o
572
ICAMHALIA.
[chap.
a honeycomb. The food mixed with nliTa is swallowed without
chewing, and after traretsing the oeaopbagns it is driven from mmen
to reticulum and back by the action of the mosclee and well soaked
with gastric juice. After some time it is pressed np again into the
mouth and thoroughly gronnd ap by the great broad premolar and
moUr teeth. When swallowed for the second time it is oeariy
flnid. It now passes down a groove or channel in the side of the
gullet enclosed between two ridges. Beaching the spot where the
gullet opens into the stomach, the grooves are continned along
the upper wall of the stomach and the fluid food is led away from
Fig. 321. Stomach of a Sheep, o
t open to show the var
Oesophagus. 2. Bumen.
3. Retionliim.
4. Pulteriam
the paunch into the third division of the stomach, the manypliee
or psalterium, which has numerons folds of membrane projecting
into its cavity; by means of these the food is completely filtered
from uU the solid matter it contains. It then passes on into the
fourth and last compartment, the abomasum, whose walls are raised
into but a few ridges and which is lined with an epithelium con>
taining numerous gastric glands. This leads into the dnodennni
or first part of the intestine, in which the digestion is completed.
The teeth of the Ruminants have no distinct tubercles like those
of the Fig, since these projections have become confluent so u
XIX.] ABTIODACTYLA. 573
to form bard cnrved ridges of enamel ; and as the jaws shift on each
other Bideways, the npper and lover back teetb produce a grinding
action jnat as two miUstones do. The name Selbnodontia
(Qr. (T<X)Jt^, the moon) has been given to the Ruminantia on
account of the crescentic ridges on their teeth, which are termed
selenodont. It is interesting to note aa evidence of the more
advanced stmcture of the Rnminantia aa compared with the Snina,
574 MAMMAUA. [chap.
that the selenodont teeth always pass through a bunodont stage
in their development. The canines in the upper jaw are long in
the male Moichus, who no doubt uses them in his fight for the
possession of the female. The lower canines howeyer are usually
placed close to the lower front teeth and are indistinguishable
from them. There are — with few exceptions — no front teeth in the
upper jaw, and the grass is bitten off by pressing the lower front
teeth against a patch of hardened gam.
The feet of the Ruminants are organs beautifully formed for quick
motion; the ideal which Nature has so to speak striyen to attain
being the same in their case as in that of the horse, though she
has had to start from a different basis. As in the case of the horse,
the end in view has been a firm jointed lever moving only in one
plane; but in Ruminantia this has been attained by keeping two
fingers and two toes and so to speak glueing them together except
in the bones of the hoof. Ruminants, like Horses, walk on the
points of their finger- and toe-nails; the metacarpals of the third
and fourth digits are frised together, while of the outer fingers and
toes only vestiges remain which hardly ever reach the ground, and
often do not appear externally. The "cloven hoof" is therefore
formed by the nails of two fingers or two toes (Fig. 322).
The families composing the division Ruminantia are the Tragu-
LiDAE or Chevrotains; the Camelidae or Camels
(Tylopoda); theCERViDAEor Deer; the GmAFFTDAE or
Giraffes ; the Antilocapridae which has but one species, the ProDg-
buck, Antilocapra americana\ and the Bovidab or hollow-homed
cattle (Cavicomia) including antelopes, goats, sheep and oxen.
The Tragulidae comprise some small animals found in Afiica
and India, in which the foot is intermediate in structure between
that of the pigs and that of the higher Ruminants : the outer toes
are complete although very slender, and the two inner imperfectly
joined with one another. The stomach and teeth however are like
those of a Ruminant, except that there is no third compartment
or psalterium. The African Chevrotain from the West Coast is
larger than its Asiatic allies (Pig. 323). It fi^uents water-courses
and is said to have the habits of a pig.
The Camels are familiar to all as far as their general appearance
is concerned. The humps — of which the Arabian camel, Cantebu
dromedarius, has one, and the Bactrian or Asiatic camel, C. bactri-
anus, two — are masses of fat, reserve material on which the animal
supports its life when deprived of food. In the foot the main
ARTIODACTYLA.
weight rests on a pad behind the hoofs ; these latter are separated
from each other, bo that the aninial has a broader support than a
cow or a deer. A camel does not walk on its finger- and toe-naiK
but on the last joints of the fingers and toes. The stomach has no
psalteriam, but both the rumen and reticulum have a large number
of wat«r-cells, that is deep poucb-like outgrowtlis in which a quite
undriukable fluid is stored. It will be noted that all the peculi-
arities of the structure of the Camel which have just been mentioned
are directly related to the exigencies uf a life on arid, sandy wastes.
Fifl. aas. The AAican Water- CheTrotam, Tforeathtrii
Thus the diverging toes and leathery pad on the foot enable them
*to aecure a broader surface of the yielding sand on which to support
tiie animal'»< weight : the humps are a prnvisinn of food and the
water-cells in the stomach contain a supply of fluid to serve the
animal in its long wanderings from oasis to oasis over the desert.
The Arabian (.'amel is only known in the domesticated state, but
the Bactrian Camel ranges wild over some of the more inaccessible
r^ons of Central Asia.
It is a remarkable and interesting fact that we find some
members of the Camel tribe in South America. Those animals, the
576 MAMMALIA. [CHAP.
Llama, Auchenia glama; the Vienna, A. vicugna; the Alpaca,
A. paces; and the Huanaco, A, huanacas'y live in the Andes. They
have no humps but possess long fleeces which are used for making
cloth. The skeleton of one of these animals is almost indistingoish-
able from that of a camel, and they have the same stupid, stubborn
ways as their relatives in the Old World. It is curious to see in
the stomach the same provision as is found in the camel, although
water is, as a rule, plentiful enough where the Llama lives.
The higher Ruminants are divided into two main groups accord-
ing to the character of their horns. In the Gebvidae or true Deer
the horns are bony outgrowths of the frontal bones. The horns are
shed every year and are nearly always branched. They may be
termed antlers to distinguish them from the true horns of the
Bovidae. The antlers are usually confined to the male, but in the
Reindeer, Rangifer tarandus, which is called the Caribou in Canada,
they also occur in the female. When the antler has attained it8
full growth the blood supply ceases and the skin peels off". In a
rim round the base called the "fur" absorption takes place, so that
the greater part is easily detached. In the Cavicomia or Bovidae,
the core of the horn is an unbranched bony outgrowth into which
air spaces continuous with the cavity called the frontal sinus of the
skull often extend. This core is permanent and is covered by a hard
horny sheatli made of compacted hairs. Two small families occupy
an intermediate position, these are the Gibaffidae, represented by
the Giraffe, Giraffa camelopardalis, and the Okapi, Okapiajoinstonii,
and the Antilocapridae represented by the Prongbuck, Antilocapra
americana. The Giraffe is now confined to the Ethiopian region ;
it is a conspicuous inmate of zoological gardens, on account of its
extraordinarily long neck, in which however there are as usual only
seven vertebrae. The Giraffe has two short horns, unbranched and
covered throughout with soft fur. The Okapi is a forest giraffe with
a comparatively short neck. In the Prongbuck, which is found in
the prairies of North America, the horn bears a small lateral branch
and is covered with a homy sheath, and this sheath, but not the
horn itself, is shed once a year.
In the family Bovidae are included everything from an Antelope
to an Ox, and, strange as it may appear, we have practically a
complete series of links filling up the gap between the graceful
light-limbed Gazelle and the thick-necked Buffalo, so that we cannot
say very precisely where Antelopes end and Oxen begin. The
Musk-ox, Ovibos moschatus (Fig. 324), which ranges over the
ABTlODACryLA.
Arctic wastes of Canada in large herds, ia iEt«nnediate in some
respects between the Sbeep ami tlie Gtoats on the one hand and
the Oxen on the other, but ia more closely allied to the former
series.
At present in Britain there are but two indigenous species of
deer found wild, the Red-deer of Si-otland, Cervus elaphut, and the
Boe-deer, Caprenim cupritea ; the Fallow-deer, C. dama, is probably
an introduced species, and at present ia only represented in Britain
by semi-domesticated animala. In Roman times there were wild
Oxen, and some suppose that a breed of wild Oxen kept at Chilling-
ham in Northumberland and in one or two other large parks are
ideacended from these ancestors.
Fio. S24. The Maek-Ox, '.
n Canada a large variety of the Red-deer, the Wapiti, Ca-mts
cariailenitU, is found, also the Reindeer or Caribou, Biinffifer
taraiiiiitit, and the Elk or Moose, Akv/i machlh, with short bull-like
neck and broad fan-like horns. Throughout the whole of Eastern
America the so-called " red-deer," Cariacus virgwianvn, is found in
the mountains. The Bovidaa are represented by the Musk-ox, Ombos
noacAatus, with homs curved like a ram, and by the Rocky Mountain
6oat, Ilaphceros mrintanus. Until recently the American Bison, the
■o-ealled "Buffalo," Bimjt americanim, ranged in enormous herds over
the Western plains of North America ; but before lft83, — with the
exception of a few 8<.-attBred stragglers which are "protected," — this
magnificent animal had been e-iterminated.
MAMMALIA.
Order VII. Bodentia.
[COAP.
TKe Rodentia or Gnawers (Lat rodo, to gnaw) are another of the
main divisiona of the Mammalia and include our rabbits, hares,
squirrels, rats and mice, besides the porcupine, beaver, guinea-[ng
and many other foreign species. These are aH sharply marked oB
iirom other mammals by the structure of their teeth. The incisors,
of which there are typically only oue pair in each jaw, are chisel-
Fio. S25. Side view of the Skull of the Babbit, Lrpa* amieulia.
1. Nas&l bone. 3. LachrTinal bone. 3. Orbito-gphenoid. 4, Frontal.
5. Optic foramen. 6. Orbital groove far ophthaimic diviaion of trigemioU
nerve. 7. Zygomatic proc«BB of Bi^uamoaal. 8. Fariet&l. 9. SquunouJ.
10. Supra -occipital. 11. Tympanic booe. 12, External auditory
meatus. 14. Lover inciaor. 15. Anterior premolar tootb. 16. Anterioi
upper inoiaor. IT. Mandible. 18. Maxilla. 19. PremaiiUa.
20. Occipital condyle.
shaped and covered with hard enamel on their outer sides only.
They constantly grow and are only kept down to proper size by
continual gnawing and rubbing against each other (Fig. 326). If
one of the t«eth is destroyed the opposite one grows until it may
pierce the other jaw, prevent the mouth from being opened, and thu
starve the animal to death. There are no canines, so that then
is a great space or diastema between the front teeth and back
teeth. The claws are always blunt and nail-like, and walking is
done on the last joints of fingers and toes, not as in the case of the
an.]
Ungulates on the points of the nails (Fig. 295). Our Eoglish
Rodents are the Hares and Rabbits, Lepiridae ; the Sijuirrels,
ScnmtDAE ; the Voles, Rata and
Mice, MnRiDAE; and the Dor-
mouse, t)ie sole British repreeen-
tstive of the family Mvoxidae.
In Korth America there are
allied species, and in addition
the Ground -sfjuirrels, or Chip-
munks, Tamias, and three
species of Woodchuck or Mar-
mot, Arctomys; also Porcupines,
represented by the common
Canadian Port; a pine, Erethizim
tUH-mtim, the Beaver. Castor
eanatietinix, and many others.
Hy»trix cristata is the Porcu-
pine of tSouthern Earope and
Morlhem Africa. The guinea-
pig ia probably a domesticated
variety of the South American
■pecies C<M>ia cutler i These
various species are very like
each other in their general
anatomy, but differing in the
character of their molars, in their fi
far and in their tails.
Hares and Rabbits consti-
tute the DUPLIVIDEXTA TA ,
one of the two Sub-orders into
which the Order is divided.
The name is derived from the possession of an estra pair of upper
iDcisors, which however are so small as to be uselet^s. The tail is
short and the cusps of the premolar and molar are joined ho as Ui
form ridges or folds running across the tooth. The Common Hare,
iepus limyius, and the Mountain Hare, L. variabilu. are both
British ; they have longer legs than the tlurd British form, the Kabbit,
£. euniculm, and have fewer young at a time. Id the temjierate
part of North America there are at least six species of Dupliciden-
teta all referable to the genus Lepus. Of these the most interesting
Leptts wmericantit and Lepus campiatria. The fur of both
V\—t.
I. 336. Dor3&l view of tbe SkuU of n
B&bbit, I.tpiu runiculut.
1. Nas&I bone. 4. Frontal. 7, Vto-
cesa ot Bqiiamoiukl supporting tbe jaKal.
8. Paris tnl. iO. Supra -occipititl.
12. External auditory mBHtiis. 13.
Allele of lover JHW. IT. Interparietal.
580 MAMMAUA. [chap.
these species turns white at the tips in winter, enabling the animab
to escape observation on the snow-covered ground.
L. americanus, the Northern Hare, is abundant in New England
and Eastern Canada : its summer fur has a cinnamon colour. L
campestris is the famous "Jack-Rabbit" of the western prairies,
which has fur of a yellowish-grey colour in summer. It can ran
with great swiftness.
The remaining Rodentia are called Simplwidektata, and
possess only two incisors above, one on each side.
The Squirrels, Sciuridae, are distinguished by their bushy tail,
their large hind limbs and the fact that the cusps on their back
teeth are distinct Sciurus vtdgaris is the common British Squirrel;
it extends from Ireland to Japan. Two species are very common in
Canada and New England, viz., Sciurus kudsonicus, the Red Squirrel,
and S, carolinensis, the Grey Squirrel These lively little animals
can be seen in autumn disporting themselves in the trees lining the
avenues of the suburbs of Montreal. Sciuropterus Tokms is the
Flying Squirrel ; this animal is provided with a furry expansion of
the skin of its sides joining the elbow and knee. This expansion
forms a parachute-like membrane which supports it in its great
leaps from tree to tree. In these manoeuvres it is assisted by l^e
broad flattened tail The Fl3dng Squirrel is common in the temperate
part of the United States. A similar but larger species {8. sabrinus)
may be seen at dusk leaping from tree to tree on the Mountain of
Montreal. AnomalurvSy found in West and Central Africa, is also
a Flying Squirrel, the skin of whose sides is prolonged into a
parachute-Uke membrane (Fig. 327). It differs from Sciuropterus
however in having a round tail provided with homy scales under-
neath, which assist in climbing, and in having its "parachute''
supported by a cartilaginous rod arbing from the elbow.
The Mice and Rats, Muridae, have naked tails with scales
underneath. The ordinary Rat is the brown Norway Rat, Mus
decumanuSy which was introduced some time ago into England and
has almost ever3rwhere driven out the old English Black Rat,
M. rattus. The Common British Mouse is M. musculus: the
Wood-mouse, M. sylvaticus, and the Field-mouse, M, minutus, also
occur in Britain. The Water-rat or Vole, Arvicola, is distin-
guished from the true Rat by the fact that the cusps on its back
teeth, instead of being rounded as in the true Rat, are angular.
A. amphibius, the Water-vole, A. agrestis, the Field- vole, which
often does much damage to crops, and A. glarealus, the Bank-vole,
IIS.] HODEVTIA. 581
I Tepresent the genus in Britain. The Dormouse, Munrardiniis
[ avellanarhis, which like the Squirrel passes the winter in a hole in a,
iias a long bushy toil, and, in outwaid appearance at any rate
more resembles a tiny sijuirrel than a rat In its aknll it resemhiea
I tJie MuRiDAB, bat it differs from both Squirrels and Rats in not
£^-.-
127. The itriOBD Flying Sqnirre!, Jrwmalurut/ulgeHa.
I a caectim on the intestine. On this a^^count it, along
with five or six allied speeiea from Europe and Africa, haa been
separated &s a distinct family, the Mvh.xidae.
Amongst the most interesting Amerii^an Rodents are the Beaver,
the Porcupine, the Ground-squirrel, the Marmots and the Musquash.
The Beaver, Castor canad^Htia. has a broad flat tail, suited for
fwimming, which is covered with horny scales. The Beaver, by
ueaDS of its shar]) incisors, cuts down trees growing on the banks of
-streams, so that they fall across streams thus damming them up
lod raising the level of the water so as to cover the entrance to their
burrows. By this means large tracts of country have been converted
into Bwamp. The Porcupines (Hystricidae) have some of their haira
^veloped into siiurp spines which make them awkward objects to
[OHUl
handla In the Canadian Poraipioe, Emthizon Jorsahis. the eploes
are concealed by tlie fur. The commonest Ground-squirrel of
North Ainericii is the (.'liipmunk. Taming, an active little anini^
with hirge eyes and a short hairy tail. Tlie Prairie Manoo^
CyiUTmyn, the so-called Prairie-dog, lives in commimities, burrowing
in the ground. Its home is often shared by a small burrowing
Owl, Athetie niiiicularia, and by a Rattlesnake, which jirubablf ,
eats the young Marmots. The Musquash or Mnsk-Rat, j
The Mu*iiift«h. f,
zibetkicus, one of the MuRmAK, is peculiar to North America,
and very widely distributed in suitable places (Fig. 328). It is
aquatic, living on roots and water-plauts and is most active at night
It constructs burrows in the Iwinks of streajna, the openings of which
are under water. Its fur is valuable.
Order VIII. Cheiroptera.
^v^
The Cheiroptera (Gr. xtq>, a hand ; -uTtpov, wing), or Bats, havs
not in their general orgunization, in teeth or brain or stomach,
departed far from the Ini^ectiTora ; their great distinguishiiij
feature is the modification of the arm into a wing. As in Birds, the
fore-arm is bent up on the upper arm, the wrist bent down on the
fore-arm; but unlike Birds' wings the flying membrane is of skin, till
SIX.] CHEIROPTERA.
greater part of which is stretched between the fingers of die tive-
fingered hand, only the smaller part extending, ax in Birds, between
the elbow and the side of the body. The hand ih enormous, the
little linger being, as a rule, very greatly developed and as long as
the rest, while the thumb alone is small and is not included in the
fruit-estiiiR Batx about }.
I. Ola*iclc. 3, Keeled iteniTiiii. S. Scapula, t. Hnmerui. 6. lUiIia*.
«. Ulna. 7. Little fiiiger. S. Thumb. 9. Uium. 111. Pubie.
11, Isvliium. 12. Olittiratar forameii. 13. Femar. U, Tibia.
15, Fibula. lU. Tutna.
584 MABfMALIA. [CHAP.
membrane bat ends in a hook-like nail (Fig. 329). Part of the
membrane extends down the thighs^ and in some even the tail is
involved. The knees are turned outwards and backwards, a most
extraordinary position which would mean dislocation if the hip-joint
of any other mammal were forced into it but which is rendered
possible in Bats owing to the fact that in them the pubes are not
directed inwards so as to meet one another in a symphysis but slope
outwards and are consequently widely separated from one another
(Fig. 329). When the Bat crawls it hooks itself along with its
thumb-nail and pushes itself awkwardly with its hind feet. It has
a most awkward gait and the animal is consequently very helpless
when not flying.
One of the most extraordinary things about Bats is the
development of sensitive patches of skin on the teyce for the
purpose of perceiving faint disturbances in the air. It has been
shown that the eyes of Bats, although apparently normal, are
really degenerate, that in fact the layer of visual rods in the retina,
which is the special organ of light-perception, is most imperfectly
developed. To compensate for this we find, in some species, the
outer ear, in others the skin around the nostrils, in others
again the skin on the lips and chin, developed into corions out-
growths richly supplied with nerves. By means of these sense-
organs Bats are enabled to avoid obstacles, and la blind Bat, let
loose in a room across which numerous strings have been stretched,
will fly about without touching one. Owing to their powers of
flight Bats are exceedingly widely distributed and extend to small
oceanic islands where there are no other mammaU. The true blood-
sucking Bat or Vampire, Desmodus rufxts, is found in Central and
in South America. Its back teeth are rudimentary, but its front
teeth are razor-edged. Pteropus, the so-called Flying Foxes or
Fox-bats, of India and Madagascar, belonging to the family Ptero-
PiDAE, are the largest Bats known; they feed exclusively on fruit, and
the cusps on their teeth are blunter than is usual amongst Bat^
The African Xantharpyia^ one species of which frequents the
interior of the Pyramids and other dark ruins in ^Bgypt (Fig. 330)
belongs to the same family. In Great Britain there are some fifteen
species of Bat divided amongst five genera. Of these the Long-eared
Bat, Plecotus auritus ; the Whiskered Bat, Vespertilio mystacinus ;
the Horse-shoe Bats, Rhinolophus hipposiderus and R. ferrumequi-
nam ; the Barbastelle, Synotus barhasteUus ; and the Pipistrelle,
Vesperugo pipistrellus ; represent the genera. Besides the species
Ot^er IX. Primates.
The l&9t Order of the Mammnlia i$ tliat of the Primates, Khiuh
ioilude Leniura, Monkeys and Man. As was mentioned before, this
order is characteristically arboreal, that is to say they live among
trees, climhing from braach to brauch. This circumstance may
explain why they retAio certaiu primitive characteristics found else-
where only amongst the Insiectivoni, Thus the thigh and upper
ami are quite free fmm the body and the whole sole and palm He
plac«d OQ the ground when walking ; and there are five tingen sad
five toes. On the other hand tlie eyes are pushed round to the
front of the skull instead of being placed at the sides of the head,
and the jiigal joins llie poat-orbital process of the frontal, so tlwt
Fio. 391. Half front *iew of llie skulls. A, ot an old, B, of a ^oiing Gorilla.
aoHUa mBiijiH " i-
1. Parietal. 3. Sagittal orpsl. 3. Frontol. 4. Sapra-orbit»l ridge.
S. SqaamoBsl. 6. Maxilla. 7. External aoditor; mentua.
the orbit ia surrounded by a bony ring (Pig. 331). Some at least
of the toes have flat nails. The big toe is shorter than the rest,
and, except in Man, can be separated from them so as to be used
for grasping. In most but not in all Monkeys the thumb oan be
used similarly, so that monkeys are said to have four hands. There
are two large mammae or nipples situated on the breast. Other
mammae when present are vestigial and situated behind the func-
tional ones.
There are two great divisions of the Primates, the Lemcroidea
and the Axtbropotdea. The first of these includes some curious
little animals, of which the majority are found in the Island of
587
Madagascar, the rest in Africa, India and the Malay Archipelago.
Many of the species are nocturnal, move silently and have large
Byes, whence the name Lomur (Lat. lemurei. goblins, spectres).
These animals have heads recalling those of rata, with no suggestion
of the hiiinaii face, and in their hrains and some other points they
are far lielow the Monkeys. The cerebral hemispheres do not cover
the (.'erebellum; the placenta of the embryo is spread evenly all
over the surface of thf nteru-; ;iriif tlicre are nccasiiitially additional
t'ici. 333. The KiDg.tniled Lemul, Lemur calla.
mammae on the abdomen. Their iociaor teeth are separated in the
middle line, but, as in all Primates, there are never more than two
on each side. The Ring-tailed Lemur, Lemur cnttii (Fig. 332), is
said to be an exception to the rule that the group is arboreal and
to live amongst rocks and bushes, but other authorities say that it
lives in troops amongst the forests of Madagascar. It is a gentle,
grooefol creature with a plaintive cry.
588 MAMMALIA. [CHAP.
The Anthropoidea^ including the true monkeys and man, are
distinguished by the fact that the bony ring surrounding the orbit
sends inwards a plate of bone, which completely separates the orbit
from the temporal fossa. Further, the cerebral hemispheres conceal
the cerebellum when the brain is viewed from above ; the placenta
is highly developed and concentrated on one part of the wall of the
uterus, and there are never more than two mammae. This sub-
order of Primates is divided into five families, viz., Hapalibab,
Cebidab, Cercopithecidae, Simiidae, and Hominidab, the last being
constituted of the single species. Homo sapiens, man.
The Hapalidae and Cebidab are confined to South and Central
America, and are sometimes grouped together as Platyrrhini
(Or. TrXarvs, broad ; pi9, piv6^^ nose). The animals belonging to this
section have a broad internasal septum and three pairs of premolar
teeth. The tympanic bone is without a tube-like prolongation.
The Hapalidae or Marmosets are small, furry animals inhabiting
the forests of Brazil and Columbia; they have the least ape-like
feet of any of the Anthropoidea. The great toe is small and it
alone has a flat nail ; all the other toes and all the fingers heta
curved claws. There are only two pairs of molars. The Cebidab
have flat nails on their fingers and toes and three pairs of molars,
making with the premolars six cheek-teeth on each side of each
jaw, the largest number found amongst Anthropoidea. The Cebidae
have prehensile tails which assist them in climbing. The genus
Ateles includes the Spider-monkeys, in which this function of the
tail is prominent, the under side of this organ being naked and
scaly so as to allow the animal to obtain a hold. The genus Cebus
has the tail hairy all round ; several species of this genus are often
seen in captivity.
The Cbrcopithecidab and Simiidae are confined to the Old
World. They constitute the section Catarrhiiti, characterised
by the possession of a narrow internasal septum, a spout-like
prolongation of the tympanic bone extending into the base of the
ear-flap, and the reduction of the number of premolar teeth to two
pairs, whilst there are always three pairs of molars. The Cer-
GOPiTHEOiDAE have the legs as long as the arms, or longer, and go
habitually on all-fours. There are always bare patches of thick
callous skin on the buttocks forming the so-called ischial callosities,
on which the animals rest when they assume a sitting posture,
and there is in almost every case a well-developed taiL This family
include the Indian and African monkeys, among them the Bandar-
their two feet, which like those of a ba,by show & tendency la
turn inwards under them ; they usually steady themselves by
bending forward so that their knuckles touch the gTOUod. Foui
genera are included in this section, vii. Bylobales, Simla, GorUla
and Anthrnpopilhteax. /fi/lolxtt«s inchide several species knon
B8 Gibbons, inhabiting South-Gastem Asia and the Malay Archi-
pehkgD. lliese are apes with exceedingly long arms ; they a»rame
a completely upright positioo wheu on the ground and ruti along
holding up their long arms in the air as if they were baUndng
poles. In their power of supiwrting themselves without any help
from the arms they approach man ; but in other respeota they
depart widely from him, as for instance in the brain, where the
cerebellum is not completely covered by the cerebrum. .SVwm is
represented by a single species, j8. satyrus, the Orang-utan, a large
animal about 4^ feet high, which is found in the islands of Borneo
and Sumatra. This animal walks ou two feet supporting itself on
its knuckles. It lives however almost entirely in trees, constnicting
a sort of nest for itself out of bram-bes (Fig. 338). It is remarkable
for its high rounded cranium enclosing the large brain, whii-h
presents the closest approximation to the human brain of all the
brains of apes. The cranium is however still overshadowed by the
bones of the face and lower jaw. There exists only a single species
of Gorilla, viz., G. savaget, confined to a limited region of Eiiuatorial
A&ica. This is tlie largest of all tlie apes, reaching a height of b\
feet. It is distinguished from Simia by its shorter arms and more
receding forehead. 7'he skull of the young Gorilla strikingly re-
sembles a child's skull, but in the adult it is deformed by the
development of great bony ridgea which give attachment ti> the
muscles of the face (Fig. 331). Ai>thry)opithtxus is represented
only by A. troghdytrs. the Chimpanzee, which lives in Western
Africa in the same region as the Gorilla but has a wider distribution.
It is distinguished by its shorter arms, which do not reach below
the knee, and by its smoother and rounder skull. It do^ not
reach a height of more thau 's feet and is on the whole the most
Man-like of all the Simiidae, though each of the other species of
the family approaches more closely to the human standard in some
particular feature.
Man is distinguished above alt by the great size of the brain,
which is double the size of that of the highest monkey, and by the
modification of the leg m aa entirely to support the body, in
consequence of which the big toe is no longer used for graspii^
Borne hold that it was this latter mudificatioii which brought about
the great development of the tnteUigecce of Maa, arguiug that
vbeu once the hand was entirely at the service of the brain the
raried usea to which it covild be put would give the opportunity for
the use of the mind. This seems jirobable, but the great factor
which lias stiuiulated the mentnl development of Man is his habit
of liviug together io societies and umlertakiug concerted enterpriees
for the benefit of the community. To this power of combination
inly intellect but also language and morals may eventually be
traced back. Man did not make society, it was tiociety that made
Man.
Men are divided into three great races which are as distinct
from one another as are many groups of allied species amongst
other animals. All races of Men are however mutually fertile
1)ut a niijted race ahows a tendency to revert to one or other
of the parent races — this is true at any rate of mixtures which
have taken place within the historical period. Many authorities
explain the peculiarities of some island populations on the as-
fumptiou tbat they are due to an early crossing of two of the
'principal races at a time when perhaps their leading features were
less fixed than they are now. The three races alluded to are
characterised as follows : —
(i) Ulotrichi. Woolly hair charai^terized by numerous close,
often interlocking, spirals, 1— ilmm. in diameter. The liair of the
head is usually long in the Melanesians and very short in the
Negritos and Bushmen. It is almost invariably black. Ellipsoidal
transverse section.
Ex. Bushmen, Negrillos, Negritos, Negros and Bautus, Papuans
and Melanesians.
(ii) Cymotrichi. Wavy hair; undulating or it may form a
curve or imperfect spiral from one end to the other (aa in the Indo-
nesians), sometimes the extremity forms long curls {as in some
Europeans and Todas), in another variety the hair is rolled spirally
irm clustering rings or curls a centimetre or more in diameter
(as in Australians, some Dravidiana and Ethiopians). The hair of
non-European peoples is generally black, with often a brownish or
reddish tinge. Ovul in transverse section.
Ex. Dravidiaus, Australians, Etiiiupiana, Semites, Mediterra-
ns, Europeans, Indo-Afghans, Indonesians, Polynesians, Arme-
592 MAMMALIA. [CHAP.
(iii) Leiotriohi. Straight or smooth hair. Lank hair that
usually £edls straight down, occasionally with a tendency to become
wavy (as in the Finns, some Amerinds). It is almost inyariably
black. Circular in transverse section.
Ex. Lapps, Ugrians, Turko-Tartars, Northern and Southern
Mongols, Northern, Central and Southern Amerinds, Patagonians,
Eskimo.
The fossil representatives of the class Mammalia are exceedbgly
numerous. It would lead us too far to give even such a general
account of them as was given of fossil Reptilia, but a few hints as
to the light thrown by them on the ancestry of existing groups may
be given here. Mammalia seem to have been derived from Uie
early Reptilia of the Sandstones overlying the Coal Measures. One
group of these, the Theromorpha, in showing the division of the
teeth into three kinds, and in the envelopment of the quadrate by
the squamosal, might almost be regarded as the direct ancestors.
Unfortunately the succeeding rocks are mostly of marine origin, and
in them few and fragmentary remains of Mammalia are preserved.
Some of these show small molars covered with many cusps similar
to the teeth of Omithorhynchus and these teeth are classified as
the remains of an Order Midtituberculata, the members of which
are supposed, like Ornithorhyncus, to have had a reptilian arrange-
ment of the genital organs. The remains are principally lower
jaws, but in one case a scapula with a facette for a coracoid and an
interclavicle have been found which bear out the conclusions founded
on the jaws. At the same time other jaws have been found which
show teeth of a different kind. These have molar teeth of the
tritubercular pattern, but the angle of the jaw is inflected and these
have been referred to the Metatheria. As however the latter group
owe some of their peculiarities to degeneracy it would be better to
regard these jaws as remains of the direct forerunners of Eutheria
from which the Metatheria represent a side line.
When we come to the sands and clays lying above the Chalk
which constitute the Tertiary ''rocks,'' we find in many localities
a rich assemblage of remains of undoubted Mammalia of the
Eutherian type. The oldest horizon shows remains of animals called
Condylarthra and Creodonta. Both groups are small plantigrade
animals, with 44 teeth, but in the first group the cusps of the
tritubercular molars are blunt, and in the second sharp and pointed.
In this small distinction the beginning of the cleft which widens
XIX.] PRIMATES. 593
into the chasm now separating Ungalata and Carnivora is seen.
Modern Insectivora are the little modified descendants of the
Creodonta. In the next horizon traces of the Primates appear as
Lemuroidea, the marks discriminating them from Creodonta being
the enlargement of the orbit and its surrounding leg bone, while the
molar teeth have a fourth tubercle. At the same time the Gondyl-
arthra show horse-like forms (Phenacodus), still with five fingers
and five toes and of the sub-ungulate tjrpe, but true Ungulata now
appear with the bones of wrist and ankle in transverse rows and
reduced number of toes. The earliest of these, the Lophiodontidae,
were Perissodactyla, and in the shape of the face some recall the
horse, others the rhinoceros, though the limbs were like those of
tapirs. The cusps on the teeth were four in number, and were
commencing to coalesce into ridges. Rodentia also make their
appearance as Tillodontia, animals with one pair of large incisors
in each jaw, but with the other incisors and the canines present,
easily derivable from the Creodonta. Passing further on, the origin
of the Artiodactyla becomes apparent in the next horizon, a host
of small pig-like animals making their appearance which in higher
formations gradually differentiate themselves into the families of
Artiodactyla. The ancestors of the South American Edentata,
which at the previous horizon were not separable from Creodonta
except by the fact that the tritubercular molars lost their enamel
late in life, become at this period distinguished by the restriction
of the enamel to bands and the reduction of the incisors. Still
higher in the series bats (Cheiroptera) make their appearance, little
different from what they are at present.
In the horizon above this the ancestors of whales are fouud, as
the Archaeoceti with well-developed nasal bones, the nostrils placed
about the middle of the snout, and with double-rooted serrated molar
teeth, derivable from the tritubercular type by the development of
additional cusps, all like the original three being in the same line.
Tnie Carnivora distinguished by the camassials have likewise been
by this time developed from the Creodonta ; in the Ungulata the
earliest forms of Camels and of Tragulidae have appeared.
Once formed Carnivora rapidly become differentiated, for in the
next period Felidae and Viverridae had already appeared, and
contemporaneously with them the first deer (Protoceratidae) and
the earliest Sirenia with visible hind-limbs {Halitherium), Still
higher the Elephants (Proboscideae) appear represented at first by
forms with both lower and upper tusks or even lower alone
S. A M. oo
594 MAMMALIA. [CHAP.
(Aliistodon and Dinotherium). At the same time the deer first
appear with antlers and the rhinoceros acquires a horn, and the
family of bears (Ursidae) is commencing to be distinct from the
primitive dog-like Camivora, the gradual reduction in size of the
premolars, and the carnassial marking the change. True Apes
(Anthropoidea) here succeed the Lemuroidea.
In the next period the Giraffe (Samotkerium), Hyrax and
Orycteropus appear and so practically the whole group of Mammalia
has made its appearance, the remaining changes consisting chiefly
in the extinction of many forms either completely, or partially, so
that their representatives are now restricted to limited areas. It
will be noted how completely the geological evidence bears out
the idea of the central position of the group Insectivora among
Mammalia.
The Class Mammalia is divided as follows :
Sub-class 1. Prototheria.
Mammalia which lay large eggs and in which the two oviducts
are completely separated, and there is a persistent cloaca. No
placenta.
Ex. OmithorhynchnSy Echidna,
Sub-class 2. Metatheria.
Mammalia in which the young are bom in a most imperfect
condition, and are carried by the mother in a pouch on the
abdomen. The oviducts are differentiated into vagina, uterus
and Fallopian tube, the two vaginae partially united. The cloaca
is divided into an anus and a urinogenital aperture. An allantoic
placenta may or may not be developed but when present is more
or less vestigial In all cases there is an adhesion between the
yolk-sac of the embryo and the uterus.
Order I. Polyprotodontia.
Metatheria with four or five incisors on each side of the
upper jaw and with at least three pairs of incisors of approxi-
mately equal size in the lower jaw.
Family (1) Didblphyidae.
Polyprotodontia with a large opposable great toe, the
XIX.] CLASSIFICATION. 595
other digits of the hind-foot being subequal in size.
American.
Ex. Didelphys.
Family (2) Dasytjridae.
Polyprotodontia with a rudimentary great toe, the other
digits of the hind-foot subequal in size. Australian.
Ex. Thylacinus,
Family (3) Pebamelidae.
Polyprotodontia with a rudimentary great toe, the
other digits of the hind-foot united by a web of skin, the
second and third being excessively slender: the muzzle
long and pointed. Australian.
Ex. Perameles,
Family (4) Notoeyctidae.
Polyprotodontia with rudimentary eyes, an enlarged
manus and burrowiug habits. Australian.
Ex. Notoryctes,
Order 11. Diprotodontia.
Metatheria with not more than three incisors on each side
of the upper jaw, and with, as a rule, one pair of large chisel-
shaped incisors in the lower jaw, the other lower incisors being
vestigial or absent.
Family (1) Epanoethidab.
Diprotodontia with all the toes of the hind-foot free
from one another and subequal American.
Ex. Coenolestes.
Family (2) Phascolomyidae.
Diprotodontia with the toes of the hind-foot united by
a web of skin: only one pair of chisel-shaped incisors in
upper jaw: limbs subequal. Australian.
Ex. Phascolomys,
Family (3) Phalangeridae.
Diprotodontia in which the toes of the hind-foot are
united by a web of skin, the great toe being well-developed,
38—2
596 MAMMALIA. [CHAP.
free from the web, and opposable to the rest: limbe sub-
equal: three incisors on each side of the upper jaw.
Australian and Papuan.
Ex. Phalanger.
Family (4) Macbopodidae.
Diprotodontia in which the toes of the hind-foot are
united in a web of skin and the great toe is rudimentary:
the fore-limbs very short and suited only for grasping:
three incisors on each side of the upper jaw. AustraliaD
and Papuan.
Ex. Macropus, BetUmgia, PetrogcUe.
Sub-class 3. Eutheria.
Mammalia in which the young are bom able to suck and in
which there is no pouch. The two vaginae are always completely
confluent. The cloaca is divided into an anus and a urino-
genital aperture. An allantoic placenta always present and greatly
developed.
Order I. Edentata.
Eutheria devoid of enamel on the teeth and withont
median teeth ; the limbs are, as a rule, provided with heavy
hook-like claws : uterus simple and globular : placenta dome-
shaped.
Family (1) Bradypodidab.
Limbs long and the fore-limbs greatly longer than the
hind-limbs: fiace short: arboreal in habit South American.
Ex. Bradtfpus.
Family (2) Myrmeoophagidae.
limbs short and stout: muzzle exceedingly long: no
teeth. South American.
Ex. Myrmecopluiga.
Family (3) Dasypodidab.
Limbs short and stout: muzzle long with numerous
teeth : a shield of dermal bones covered by homy scales.
South American.
Ex. Dasyptts.
XIX.] CLASSIFICATION. 597
Family (4) Manidae.
Coyered externally with large, oyerlapping homy scales:
no teeth: long protractile tongue. Asian and African.
Ex. Mcmis.
Family (5) Oeyctbropodidab.
Covering of bristly hairs: teeth numerous and heter-
odont: no thumb on anterior limb: femur with a third
trochanter. African.
Ex. Orycteropus.
Order II. Effodientia.
Eutheria resembling Edentata in teeth and claws but with
bicomuate uterus and zonary or diffused placenta.
Order III. Cetacea.
Large aquatic Eutheria which have lost the hind-limbs and
have developed horizontal flukes on the tail. The fore-limb is
a paddle : the cranium is globular and the teats are posterior.
Sub-order 1. Mystacooeti.
Cetacea devoid of teeth in the adult and with plates
of whalebone in the mouth.
Ex. Balaena, Balaenoptera.
Sub-order 2. Odontoceti.
Cetacea with teeth at any rate on the lower jaw and no
whalebone.
Ex. Physeter, Globicephalus, Delphinapterm, Phocaena,
Order IV. Sirenia.
Aquatic Eutheria, with limbs and tail as in the Cetacea:
the cranium is cylindrical and the teats pectoral
Ex. Manatus, Halicore,
Order V. Insectivora.
Small plantigrade Eutheria, with pointed cusps on the
molar teeth : the brain of low type : a flexible snout often
present. The more familiar families are
Family (1) Erinaceidae.
Insectivora with the body covered with harsh spines :
limbs subequal.
Ex. Erinaceus,
598 MAMMALIA. [CHAP.
Family (2) Soricidae.
Small mouse-like Insectivora with soft far.
Ex. SoreXf Blarina.
Family (3) Talpidab.
Mouse-like Insectivora with rudimentary eyes and large
hands adapted to burrowing.
Ex. Taipa^ Condylura^ MyogaU,
Order VI. Camivora.
Eutheria with sharp recurved claws and powerful canine
teeth : the premolars adapted for clipping flesh : the incisors
smaU,
Sub-order 1. Fissipedia.
Carnivora with separated digits : a distinct camassial tooth
and one or more broad molars.
Family (1) Felidae.
Fissipedia with short face and a reduced number of pre-
molar and molar teeth : with retractile claws.
Ex. Fells,
Family (2) Canidae.
Fissipedia with long face and full number of premolar
teeth : claws non-retractile.
Ex. CanU,
Family (3) Ursidab.
Fissipedia with long face : teeth blunt and partially
adapted for a vegetable diet: plantigrade in gait.
Ex. Ursus,
Family (4) Pbocyonidae.
Fissipedia with a sharp pointed muzzle and reduced
number of teeth, otherwise like Ursus.
Ex. Procyon.
Family (5) Mustelidab.
Fissipedia with long necks and exceedingly flexible
bodies : a reduced number of teeth : in the skull and in the
XIX.] CLASSIFICATION. 599
shape of the carnassial tooth they resemble Ursidae but
they are digitigrade in gait
Ex. Lutra, Males, Mustelus, Mephitis.
Sub-order 2. Pinnipedia.
Aquatic Carniyora with the toes united by a web of skin :
the tail is rudimentary, but the two hind-limbs are turned
backwards and closely apposed so as to form a paddle: no
distinct carnassial tooth and no broad molars.
Family (1) Otarhdae.
Pinnipedia still retaining a trace of the external ear,
and capable of turning the hinder-limbs forward so as to
walk on land.
Ex. Otaria.
Family (2) Trichbohidab.
Pinnipedia devoid of external ear, but capable of
walking on land : the upper canines form long tusks.
Ex. Trichechus,
Family (3) Phocidab.
Pinnipedia devoid of external ear, and incapable of
turning the feet forward, so that when on land they can
only wriggle along with the help of their anterior limbs :
the canines not specially enlarged.
Ex. Phoca,
Order VII. Ungulata.
Eutheria with limbs adapted entirely for progression, the
terminal phalanx of each functional digit is enclosed in a short
blunt nail.
Sub-order 1. Sub-ungalata.
Ungulata with short sub-equal toes, and with the bones of
the carpus and tarsus arranged in parallel longitudinal series.
Family (I) Hyracidab.
Small Sub-ungulata with a very short snout : a pair of
chisel-like incisors in each jaw.
Ex. Hyrax (Proccma).
^pj maxmaujl [chap.
iMTgt Sdb-van^sEm wA a iot lamg flexible SMmt
trcnk' ««ed br preka»3K: "ariBM* ^i^^K ^'^ curved,
feKKBf te^ : mtf:ias% ¥crr bnad, oaij <ne pair in use it
UksIssi isL vikk Tilt bcnes oc &t cups^ aad tusos are
unficced ia tEiftSTetse p?«%, libe BeaibeB <d saeeewve rovs
Drri^cn L Pizsgiic
j.:tt
IS v^acc. isfre 2^. -wrsL zize exfiefOciii&, an nn-
•r^vea &:i]nber *:•£ <r.£^ is tatdt Irsb. aad im viiicli die axis
of fVKaKtrr paa-ei dirovc^ libe t£frd
P<7rLs*>iuCT*ja vhh fcor dscxts i^ i^ iire-emb mai three
the •izri-Jiirb :
Ex. RiiM^Kitf ;•«.
Fajzih- 3 KidZJi
FensdikrCT^ vim onir ice i ■[li r i dtt:h xr tcdi
of dsiciu. aad in wiibl-^ ube axk cf mbmiiij f^»e» %em«n
•ibe 'loird aai S>sr:h di^ift. t&OK d^ift ^<B^f flaoened avna^
» as tofenn tvvffVHKttnlhnlw^f mcjiaadBC.
XIX.] CLASSIFICATION. 601
Section A. Biinodontia.
Artiodactyla with comparatively simple stomachs : the
cusps on the molar teeth are separate.
Family (1) Hippopotamidae.
Large Bunodontia with four subequal toes in both fore-
and hind-limbs.
Ex. Hippopotamus,
Family (2) Suidae.
Bunodontia of moderate size, in which the two outer
toes though complete are shorter than the others.
Ex. 8us, Babirtisa, Dicotyles.
Section B. Selenodontia.
Artiodactyla with complex stomachs adapted for ruminating :
the cusx>s on the molars coalesce so as to form crescents.
Family (1) Tragulidae.
Small Selenodontia without horns, and with only three
compartments in the stomach : the outer toes although
excessively slender are still complete.
Ex. Trcbgulus,
Family (2) Camelidae.
Selenodontia without horns, with only three compart-
ments in the stomach : the outer toes entirely absent, the
inner toes slightly diverging below, the weight resting on
a pad behind them.
Ex. CameluSy Auchenia.
Family (3) Cervidae.
Selenodontia with antlers in the form of bony outgrowths
of the frontal boue shed annuaUy : four compartments in
the stomach : the second and fifth digits incomplete.
Ex. CervuSj Cariacus, Capreolus, Bangifer, A Ices,
Family (4) Bovidae.
Selenodontia with horns which are outgrowths of the
frontal, never shed, and covered with a thick homy sheath :
602 MAMBfAUA. [chap.
four compartments in the stomach: ihe second and fifth
toes rudimentary.
Ex. Bos, Ovis, Ovibos, Haploceros.
Family (5) Giraffidae.
Selenodontia with short horns which are outgrowths of
the frontal, never shed, and permanently covered with soft
fur : immensely elongated neck and very long limbs.
Ex. Giraffa.
Family (6) Antilocapridae.
Selenodontia with branched horns which are outgrowths
of the frontal covered with a homy sheath. This sheath is
shed annually.
Ex. Antilocapra,
Order VIII. Rodentia.
Eutheria with one large pair of chisel-shaped incisors in
each jaw growing throughout life and no canines. The
Rodentia walk on the whole surface of the last joint of the
digit, not on the extreme tip as do the Ungulata : the nails are
blunt but not usually hoof-like.
Sub-order 1. Duplicidentata.
Rodentia in which there is a second pair of rudimentary
incisors in the upper jaw.
Ex. Lepus.
Sub-order 2. Simplioidentata.
Rodentia in which there is only one pair of incisors in the
upper jaw.
Ex. SciuruSy Tamias, Mus, Fiber, Arvicola, Mmcardinm,
Cdstm', ErethizoUy Hystrix, Cavia,
Order IX. Cheiroptera.
Eutheria in which the fore-limb is converted into a wing,
the hand being greatly enlarged and the fingers elongated in
order to support the wing-membrane ; the leg small and the
knee-joint rotated backwards : teeth and brain resembling
those of the Insectivora.
Ex. VespertiliOy Vesperugo, Ehtnolopkus, JTantharpyia,
XIX.] CLASSIFICATION. 603
Order X. Primates.
EutJieria with long limbs, the brachium and femur not being
buried in the body: five digits in each limb, some of them
having flat nails : the great toe or thumb or both are opposable
to the other digits. The orbits are rotated on to the anterior
aspect of the skull and are completely surrounded by bone :
the brain is large.
Sub-order 1. Lemuroidea.
Primates in which the orbit is merely surrounded by a bony
ring: front teeth separated by a space in the middle line.
Ex. Lemwr,
Sub-order 2. Anthropoidea.
Primates in which the orbit is completely separated from
the temporal fossa by an inwardly projecting sheet of bone:
front teeth in contact in the middle line.
Section (1) Platyrrhini.
Anthropoidea with a broad intemasal septum, three pairs
of premolar teeth and a simple tympanic bone : the great toe
opposable to the other toes : the thumb imperfectly or not at
all opposable to the other fingers.
Family (1) Hapalidas.
Small thickly furred Platyrrhini with a flat nail on the
great toe only, claws on all the other digits : two molar
teeth on each side.
Ex. Hapale, Midas,
Family (2) Cbbidab.
Platyrrhini with flat nails on all toes : three molar teeth
on each side.
Ex. A teles f Cebtis,
Section (2) Catarrhini.
Anthropoidea with a narrow intemasal septum, two pairs
of premolar teeth and three pairs of molars in each jaw.
The tympanic bone has a tube-like prolongation. The great
toe is opposable to the other toes, the thumb imperfectly op-
posable to the other fingers.
604 MAMMALIA. [CHAP. XIX.
Family (1) Gebcx)Pitheoidab.
Gatarrhini with anns not longer than their legs : bare
patches on the buttocks: with rare exceptions a well-
developed tail
Ex. Macacus, Semnopithecus.
Family (2) Simiidae.
Gatarrhini with arms much longer than legs and a
semi-erect gait: no tail.
Ex. Gorilla, Hykbates, Simia, Anthropqpithecus.
Section 3. Hominidae.
Anthropoidea with arms of moderate length and long legs :
the foot entirely adapted to support the body, the great toe
not opposable to the other toes : the thumb completely oppos-
able to the other fingers : the upright attitude habitual : no
tail: brain very large.
Ex. Homo.
605
CHAPTER XX.
Phylum Platyhelminthes.
From the Earthworm up to Man we have been considering
^ . animals which either in tJie embryo or in the adult
Introduction. , , , ,
exhibit the coelom in a characteristic and unmistak-
able form. Such a space is indicated even in the Actinozoa,
where the endoderm lining the lateral compartments of the
cbelenteron gives rise to the muscular bands and the generative
organs, performs the excretory functions and is probably the
homologue of the mesoderm of higher forms. If this be so the
space in the Actinozoa surrounded by this '' endoderm " is equiva-
lent to a coelom, but one not yet shut off from the digestive tube.
Thus from the Coelenterata to Man we have traced a series of
organisms all of which possess in some form or other this particular
organ. Since Vertebrates include Man and are among the most
highly organized animals at present living on the earth, we have
placed them last in the series of Goelomata, but this must not be
taken to indicate that there is any kind of progression through all
the series of lower animals up to Man. The vertebrate ancestor of
Man probably separated whilst still of exceedingly simple structure
from the ancestors of other animals, and there has been independent
progress along many different lines, culminating for instance in an
Insect, a Cuttlefish and a Sea-urchin.
Leaving now the Coelomata we must consider a few phyla which
we cannot definitely assert to be Coelomata. All of these groups
possess between the ectoderm and endoderm a mass of various
tissues, muscular, connective, excretory and generative, hollowed
out by spaces or traversed by systems of tubes ; but it has not yet
been shown in the case of any one of them that this mass of tissues
has had in the embryo the form of sacs lying at the sides of the
fidimentary canal from the walls of which the said tissues have been
differentiated.
Ib the case of snine of the following phyla it is reasoiiAbte to
expect that fuller knowledge will show that they are coelomate.
but at present this has not been definit«ly proved, and thus it
seems wore logical to consider them apart irom the orgauisim
which undoubtedly possess a coelora.
The Phyla that follow are all Metaxoa and duce they poaaeea ik>
notochord are Invertebrates.
The Platylielininthes consist of three large classes, (i) TDRBElf
LARiA, (ii) Trehatodes and (iii) Cestoda. These three groups
contain animals which are bilaterally symmetrical, each half of the
body being a reSection of the other. The alimeutiiry canal may be
entirely lost, but when present it has only one aperture, which
serves Ixjth as mouth and anua. as in the case of the Coelenterat^
A separate anus is never found, and there is no evidence from ihe
study of development that the ancestors of Platyhelminthes ever
possessed such an opening to the alimentary canal. The alimentary
cavity is practically the only cavity in the animal, as there is do
space between the skin and the intestine which could be compared
to the body-cavity of other animals, and except for the narrov
cavities of the excretory system and the genital ducts the bodies of
these animals are solid. The excretory system, often termed the
wateT'Vascular system, the function of which is the ridding the
body of the waste nitrogenous materials which, as explained before,
result from the cataboUsm of hving protoplasm, is in its structure
eminently characteristic of the Phylum. It consists of a series uf
narrow tubules permeating the body in every direction; these ou
the one hand communicate with larger tubes which open on to the
surface of the body, and on the other receive a lai^ number of still
smaller tubules each of which ends in a cell with a single cilium
hanging into the end of the tubule. The constant flickering of
this cilium is thought to keep the fluid contents of the tubule in
motion. Such a cell is termed a flame-cell from the fancied
resemblance of the motion of the ciliiim to the flickering of a
flame. The Platyhclmiethes usually contain both male and female
reproductive organs in the same animal, and it is characteristic of
them to have a special portion of the ovary called the yolk-
gland or vitellarium, set apart to produce small yolk-filled cells,
which serve as food for the perfect ova during the early et^ss of
development.
L
XX.] , PLATTHELMINTHEa 607
Class I. TUBBELLABIA.
The Turbellaria are free-liTing animals, and as a rule swim about
in the sea or in firesh-water ponds or streams. A few, however, have
taken to living amongst moist earth, and some species, e.g.,£ipalium
kewense, are occasionally met with in hot-houses all over the world,
being probably imported with the roots of some tropical orchid or
fern. Other species of land Turbellaria are common in the Tropics.
Turbellaria are all very soft animals and capable of considerable
change of outline. In their native habitat they are not easy to see,
many of them having colours which imitate the sea- weeds, etc.,
amongst which they live, and many appear only at night from their
hiding-places. If, however, a bunch of red sea-weed be shaken out
in some clean sea-water in a white china dish, as a rule many of
these animals can be seen swimming with an undulating motion
like a Sole or clinging to the sides of the dish.
One of the commonest species in the fresh- water ponds of Great
Britain is Mesostoma ehrenbergii, a flat leaf-like organism, perhaps
half an inch long, the transparency of whose tissues permits at
times the examination of some of the internal organs. The whole
of the outer layer of cells — ^tiie ectoderm — bears innumerable cilia,
by whose action the animal glides slowly along when it does not
swim by the undulations of its whole body. Within this ectoderm
are certain circular and longitudinal muscle-fibres, and these
surround a mass of cells called the parenchyma. This consists
of cells of a stellate shape, united with one another by their out-
growths, the interstices between the cells being filled by a semi-fluid
jelly-like substance. The parenchyma may be regarded as a primitive
form of connective-tissue in which the nervous system, alimentary
canal and excretory and reproductive systems are embedded.
The ectoderm cells secrete a great deal of mucus, mingled with
which are a number of little rod-like bodies called rhabdites.
The exact use of these is not clearly known ; in their formation
they recall the nematocysts of the Coelenterata. Like the nemato-
cysts they are extruded on irritation. The mucus forms a bed
over which the animal moves and in which the cilia work, so as to
propel the animal
The mouth of the Mesostoma is, as its name indicates, near the
centre of the body, on the ventral surface. It leads at once into a
pharynx with very muscular walls which can act like a sucker.
This pharynx can be withdrawn into the body or pushed a little
PLATYHEUUNTHE9. [CHU,
Bi*iD,al)owiDgtvoe;ee. 3. Fharftii tanoanding the month. 8. Food
VBcaole in an eadoderm cell. 4. Eotodeim. 6. Teatii Ipng ftbov«
dimentaty oanal, abowiiie developing spermatozDo. 6. Mnscle fibieb
7. QeDitiil atrium. B. OlandB of the genitttl atrioiD. 9. Penis.
ID, Shell-glandB BtUTOundiiig the tpermatheoa. 11. OsnnuiQiih
12. Titalkriiun.
TDBBBLLARIA.
iway out of the mouth. The chamber in which it lies and which
Fgives it room to pUy in and out, ia an ectodennal pouch called the
pharynx-sheath. This is small in Mesostoma, but in other Tur-
beliarians it may be much larger, and the pharynx ia consequently
capable of stretching out a long distanc& This is the case, for
instance, with the fresh-water genua Planaria (Pig. 335).
Certain glands, called salivary glands, open into the cavity of
the alimentary canal at the inner end of the pharynx, and then the
cavity opens into the stomach, which is a sac-like structure with
no other openiug than the mouth lying in the centre of the body.
The cells lining this cavity are, like the endoderm cells of Hydra,
amoeboid, aod they take up purticlea of food into themaelvea in the
same way that an Amoeba does. This primitive form of digestion
has been lost in most of the Coelomata, wliere the digestive cells
pour out solvent fluids into the cavity of the alimentary canal, and
■the food is rendered soluble in this cavity before being absorbed.
In the Turbellaria, as in the Coelenterata, this secondary method of
digestion coexists with the amoeboid method.
Mesostoma is carnivorous and eats small worms, minute cma-
tacea and insect hirvae. It uses its mucus to ensnare and entangle
ita prey. Its method of devouring them recalls the habits of the
Btarfish. It holds them fast by means of the pharynx, using this
as a sucker. The ao-called saUvary glands secrete a strong di-
gestive fennent which rapidly dissolves the Hesh of the victim,
teduciug it partly to a fluid condition and partly to a disintegrated
mass of particles. There is no vascular system to distribute the
digested food to the different parts of the body, so that these
products must be passed from cell to cell through the solid body
until they arrive where they are ueedeti. The undigested parts are
passed out through the mouth.
The two maio ducts of the excretory or water-vasoular system
open near the sides of the mouth, ea<;h then passes upwards towards
the dorsal surt'ace and divides into two longitudinal vessels, cue
runnin;:! towards the head, the otiier towards the tail These four
longitudinal branches give off innumerable finer ones, which sub-
divide until each branchlet ends in a flame-cell. These latter are
very minute and require a high power of the microscope aod very
careful focussing to see.
The nervous syHtem conaists of a large ganglion called the brain,
divided by a aliallow depression into two lobes. It is situated in
front of the mouth near the anterior end of the animal, embedded
610 PLATYHELMINTHES. [CHAP.
in the parenchyma. It gives off a pair of nenres which ran forward
to the tip of the body, and another pair of rather stoat nenres
which ran back, one on each side of the phai3mz, to the taiL Tbe
nerves give off fine branches which are distributed all over the body.
A pair of eyes of a simple structure lie on the upper surface of the
brain.
The male organs consist of two long sac-like testes which lie
above the alimentary canal and are directly continuous with their
short ducts, the vasa deferentia. These ducts unite to form the
muscular penis which communicates with the genital atrium through
which it can be protruded. The proximal portion of the penis is
swollen up to form a bulb called the vesicula seminalis^ in which
the spermatozoa are stored up before being transferred to another
individual The female organs consist of a large ovary on each side,
divided by constrictions into numerous lobes; these are not well
marked in the species represented in Fig. 334. The whole of one
ovary and the greater part of the other produce only yolk-cells and
are therefore to be regarded as yolk-glands or vitellaria. The
basal lobe however of one of the ovaries (11, Fig. 334) produces ova
capable of development; this is the ovary (sensu stricto) or germ-
arium. The two oviducts, or as they are generally styled, llie
vitellarian ducts, are directly continuous with the yolk-glands and
lead directly into the genital atrium. Near their common opening
a thick muscular pouch opens into the atrium. This is the sperma-
theca which receives the spermatozoa firom another individual, and
emits them on to the ova as tJiey pass its opening. Around tiie
spermatheca are certain glands called the shell-glands, which also
open into the atrium. The secretion of these glands forms llie
egg-cases in which one egg and many yolk-cells are enclosed. As
the egg-cases are formed they pass into two great sac-like dive^
ticula of the atrium, one situated on each side of the body, called
the uteri. In these they are carried about by the animal for some
time, but are eventually laid, and become attached to water-plants
by the stickiness of their outside layer. There are two kinds of
these egg-cases in Mesostomay one thin-walled, called ''summer
eggs," and the other thick-walled, called "winter eggs." The former
are believed to contain ova fertilized by the spermatozoa of the same
individual; these develope rapidly, devouring the surrounding yolk-
cells and the resulting young hatch out in April and May. These
when they arrive at maturity cross-fertilize one another, and as a
result the thick-walled capsules termed "winter-eggs" are produced,
TOKBELLARIA.
iwhicli lie dormant during the winter, whilst the parent turns opaque,
make to the bottom of the water and dies. In the spring young are
hatched from the winter eggs, which produce when mature summer
tgg?, and in some cases are supposed after laying these to live on
And produce the winter eggs of the next season; but in this respect
^e various species probably differ from one another.
The Turbellaria are a large group, and fall naturally into two
nain divisions, vis., the Bhabdocoelida with a rod-like gut (Gr.
fid^&oi, a staff) and the Dendrocoelida with a branched one
(Gr. Bfv&ijov, a tree). Each of these divisions is again subdivided ;
'thus the Order Bhabdocoelida includes the Sub-orders Acoela,
Alloiocoela, and Rhabdocoela, whilst the Dendrocoelida are
.divided into Polyclada and T&iclada.
To turn firat to the divisions of the Rhabdocoelida, the Sub-
order Acoela includes extraordinary forms in which there is no
digestive cavity; the alimentary canal is represented by a porous
; of endoderm cells, amongst the interstices of which the
digested food soaks. The eudoderm completely fills the space
Burroonded t>y the ectoderm and muscle layers ; there is no
parenchyma. In almost every case there is a muscular pharynx
by which the animal adheres to its prey, and through which a
peendopodium-like mass of endoderm is protruded. This protrusion
Becretea a solvent which disintegrates the victim, and it then
oigulfa the product after the manner of an Amoeiia. In e
cases, however {Cojimluta}, the endoderm is infested with small
green Algae, and the animal lives largely on the compounds formed
ly these, needing only a scanty diet of Protozoa and Diatoms to
supplement its internal provision.
The genital organs are simple; the ovaty ie not divided into
Titellarium and germarium and no yolk-cella are produced. It has
seen suggested that the Acoela are the most primitive of all the
phylum, and that they have been directly derived from large
Diultinucleate Protozoa, but their development makes it possible
that their peculiarities are due to degeneracy.
The Alloiocoela have a pareuchyma and a. hollow alimentary
eanal which has elightly developed lateral lobes. The testes are
represented by scattered masses of cells without distinct ducts;
and the spermatozoa apparently hnd their way to the main vasa
defetentia by passing through the interstices of the parenchyma.
The germaria are two in number and have long ducts opening into
the genital atrium distinct from those of the vitellarla.
39—2
612 PLATYHELMINTHES. [CHAP.
The Bhabdocoela are tJie most highly developed fomis of the
Rhabdocoelida ; their alimentaiy canal is cylindrical and smroiuidfid
by a mass of extremely watery parenchyma which simalates a body
cavity. The arrangement of the genital organs has been described
above.
The first division of the Dendrocoelida, the Tbiclada (Or.
rpi-, triple, Kkahv;, a branch), derive their name from the circixm-
stance that there are three main branches of the alimentaiy canal,
one in the middle line running forward from the inner end of the
pharynx, and one ronning backwards at each side of the phaiynz.
There is a pair of germaria formed from the most anterior brandies
of the great lobed ovaries ; they discharge into the same ducts as
the vitdlaria. The utems is an unpaired sac The group includes
marine, freshwater and terrestrial form& Planaria (Dendrocoelum)
is a common form in the streams of both Britain and Canada.
4
Fio. 835. Planaria polychroa x about 4.
1. Eye. 2. Ciliated slit at side of head. 3. Moath of probosois. 4. (hi-
line of the pharynx sheath into which the pharynx can be withdiawn.
6. Beprodactive pore.
The Polyclada are a marine group and are thou^t by some
authorities to be the most primitive of all Turbellaria. Their
name is suggested by the fact that the alimentary canal consists of
many branches radiating from a central stomach into which the
large pharynx opens. The ovary is a lobed organ not divided into
vitellarium and germarium. The eggs are laid in plate-like masBas
bound together by slime. They develope into free-swimming young
known as Miiller^s larvae. These are little oval organisms provided
with a ciliated band drawn out into eight longitudinal loops, and
on these the cilia are arranged in transverse rows fused at the base
so as to resemble the combs of the Gtenophora. The resemblance
of these ciliated loops to the ** ribs " of the Gtenophora suggested
to Lang the idea that Turbellaria were Gtenophora which had
become adapted to a creeping life, in which a marked bilateni
XX.] TITRBELLARIA. 613
symmetry had replaced the generally radial arrangement of the
organs of the normal Gtenophora^ though traces of the latter
arrangement remain in the Polyclada. The brain on this view
wonld be the apical plate which had shifted forward ; the stomach
with its radiating branches would correspond to the funnel of the
Ctenophora and the canals in connection therewith; the pharynx
sheath would represent the stomodaeum, the so-called '* stomach"
of the Ctenophora; but the eversible pharynx, the copulatory
organ, and above all the excretory system must be regarded as new
acquisitions. This view, which at first was not received with much
favour, has received strong support by the investigation of a marine
organism known as Ctenoplana. This is a flattened animal re-
sembling a Polyclade in shape and in the circumstance that the
ventral surface is covered with cilia with which it creeps. It
possesses however an apical plate of thickened nervous ectoderm
supporting a mass of otoliths on bars of fused cilia, and there are
eight short "ribs" radiating from this plate. These ribs as in
Ctenophora are thickened bands of ectoderm bearing combs of cilia
fused at the base. The funnel and its canals are represented by a
lobed alimentary canal, continued on each side into a tentacle
canal, firom the end of which springs a long retractile tentacle.
The genital organs have their independent ducts opening directly
to the exterior. In all these respects therefore Ctenoplana is inter-
mediate between the Polyclada and the Ctenophora. If we accept
Lang's theory it is evident that on this view the Platyhelminthes
are not true Coelomata. The evolution of the more complicated
systems of genital organs amongst the Turbellaria out of the simpler
arrangement in the Polyclada, has probably been the result of
laying the eggs in numbers surrounded by a capstde. This led to
a struggle amongst the eggs, resulting in the sacrifice of the smaller
to tJie needs of the larger ova, and this to the production of weak
ova to serve as food for the others, with the consequent differentia-
tion of the ovary into germarium and vitellarium.
Class II. Trematoda.
The remaining two groups of Platyhelminths have taken to a
parasitic mode of life and this has to a great extent influenced
their organization. The term parasite is applied to an animal
which lives at the expense of another without destroying its life.
The Trematodea have lost the external ciliation of the skin, the
nATTHELHIlITHES. [CHIP.
, UoDth. 2. Phuynz. S. Nerre-ring. i. Chief longitadiiul Dim
6. Begiimiiig of alimentuy canal. 6. OpeniDg of penia. 7. Taoank
nfminalia. 8. Dtenia. 9. Orarj. 10. SheU-^and. 11. Antaicf
teitii. 13. Foaterioc tMtia. 18. ToUc-Blandi. 14. Yudr' -
XX.] TBEHATODA.
ectodenn being ereryvbere covered with cuticle. In other features
of their anatomy they present a great reaemblimce to the 'IVidade
Tuibeltaria, and one family.the Temsocephaiidab, may be described
as intermediate between the two classes of Flatyhelminths eiuce its
members atill retain patches of ciliat«d sldn. For the most part
they live on or in the bodies of Vertebrates, attaching themselves
either to the skin or to the alimentary canal or its outgrowths.
One of the moat characteristic features of Trematoda ia to be
found in the suckera by which they adhere to their prey. Often
indeed the lips of tbe mouth aie thickened and mascular so as to
conatitutfl an oral sucker, but there is always a ventral adhesive
disc provided with suckera or hooks or both. The mouth is
situated at or near tbe anterior end of tbe body; it leads into an
oral funnel opening into a muscular pharynx, which by alternate
expansion and contraction pumps in the juices of the prey. Its
action is thus differenl from that of tbe pbarymc of Turbeilaria,
which, as we have seen, can act as a protmsible sucker. Behind
tbe pharynx the alimentary canal divides into two parallel forks
running back to the posterior end of the body, and beset with
branches which in some cases may unite with one another across
tbe middle line. It thus resembles what the aUmeutary canal of a
Triclade would become were the mouth shifted to the anterior end
of tbe body. The nervous system is remarkable for the fact that
several trunks of equal size are given off from each side of tbe brain.
The repreductive organs resemble those of a Rhabdocoele like
Metostoma ; thus the germarium is developed only on one ovary,
of which it is a basal brauch, and tbe testes each consist of a
lobed organ directly continuous with the vas deferens. Tbe main
peculiarities are as follows : there is no spermatbeca ; the spermat-
ozoa from another individual enter either by a dorsal pore or two
lateral i>ores, leading into a canal or canals which join the oviducts
where tbey unite with one another. These ducts, totally unrepre-
sented in Turbeilaria, are called tbe "canals of Laurer." Further,
the genital atrium is situated on the anterior part of tbo body in
front of the ventral sucker. There is no uterus comimrable with
that of Turbeilaria ; the ao-called uterus being a long coiled tube
composed of the conjoined oviducts (vitellarian ducts). Finally
tbe testes are so large that there is not room for them side by
side, hut in order to atow them away one is situated behind the
other.
Trematoda are divided into two Orders called respectively the
I
I
Fia. SST. Diugiom of digestive And eicretary Bjateai ot Din
X about 8. Frum Leuokoit.
1. Mouth. 2, PlmiTiii. 3. Eeproduotive pore. 1. Branch of kUm-
entsi? oanol. 6. Branches of eicretor^ tiysteu ~
opeuiug of ejLcretorj' BjelBm. 7. NBrve-ring.
TREMATODA. 617
MoxooENEA and the Diqenej.. In the first named the egg gives
rise to a larva ^bich derelopea continuouslj into the adult ; the
m^a organ of adhesion is a disc situated at the posterior end of the
hody and anoed with suukers or hooks, usually both, and there are
two lateral vaginae from which the c;an,iU of Laurer lead inwards.
The excretory system opens by two dorsal pores. One of the
commoiiBst of the Monogenea is Polt/domum inUgernmum, found
in the bladder of the Frog. This animal has an adhesive disc
bearing six suckera. The fertilized egg of Polyatomum is discharged
through the cloaca of the Frog into the water. After some time a
larva hatches out which has a forked alimentiLry canal, but which
is without genital organs and has no suckers, although the posterior
adhesive disc is clearly differentiated. It is provided with a
number of transverse bands of cilia by means of which it swims
about until it finds a tadpole, to the ekin of which it attaches
itself. It creeps into the branchial chamber of its host and loses
ita cilia, and commences to develope genital organs and suckera.
About the time of the tadpole's metamorphosis the Trematode
wanders down the alimeutary canal into the bladder. Sph/ranura
ntkri is an allied form parasitic on the skin of the Urodele
NfcCurus. Ita posterior disc carries two large suckers and two
hooka.
The DiOEHEA give rise to larvae which become parasitic in
some animal, where they give rise by gemmation to several gener-
ations of secondary larvae, which develope into adult forms only
when they are swallowed by a second animal. The life-hiatory
therefore includes an alternation of generations and is only com'
pleted in two hosts. The Digenea further differ from the Mono-
genea in having as main adhesive organ a sucker situated on the
anterior part of the ventral surface, in having only a single " canal
of Laurer " which opens on the dorsal surface, and finally in the fact
that the main trunks of the excretory system coalesce to form a
single trunk which opens to the exterior by a median posterior pore.
The Liver-fiuke, Disloma hepaticum, is au example of the Bigenea ;
it is parasitic in the liver and bde-ducts of the sheep, causing a
wsating disease called sbeep-roU It gives rise to a larva consisting
of a solid mass of cells, the outermost layer of which is ciliated,
This larva cannot survive unless it reaches a pond-snail of the
species Limnaea truneatula. Id the pulmonary chamber of this
animal it loses its cilia, enlarges and becomes hollow, forming a
structure called the B|iorricyst, which sometimes divides into two
I
618 PLATTHELM1NTHE8. [CHAP.
or more. Germ cells are budded off from the wall of the sporocyst
into the cavity. These by division form masses which develope
into secondary larvae called rediae, provided with a mnscnlar
pharynx and a sac-like alimentary canaL These larvae have a pair
of blunt processes on the under side near the posterior end, by the
aid of which they move. They force their way out of the sporocyst
and enter the tissues of the snail, being found especially in the
liver. From the inner sur&ce of their body-wall germ cells aie
budded off which give rise to other rediae, which escape from the
parent by an opening near the anterior end. After a time the
rediae give rise to larvae of a third kind called cercariae.
These have suckers like the adult, and a forked alimentary canal
with a pharynx ; they are provided with a tail stiffened by a rod of
gelatinous tissue recalling the Vertebrate notochord. By the aid of
the tail they work their way out of the snail and attach themselves
to blades of grass. The tail then falls off and they enclose them-
selves in a cyst of mucus, and remain there till they are eaten by a
sheep, from whose intestine they pass into the liver, where they
develope genital organs and become mature.
Class III. Cestoda.
The Cestoda are sharply distinguished from the two preceding
classes of Platyhelminthes by the total absence of an alimentary
canal. They are all internal parasites, living in the alimentary
canal of their hosts, and absorb the half-digested juices of their
hosts through all parts of their skin.
As in Trematoda, there is a well-marked cuticle which protects
the animal from the action of the digestive juice of the host
The ectoderm has undergone aA extraordinary modification. Its
cells have become long and filamentous, having long narrow necks,
the body of the cell with the nucleus being pushed downwards
into the subjacent tissues. These necks are however of very
various lengths, and so the ectoderm, although fundamentally a
single layer of cells, presents the appearance of a thick band of
many layers of nuclei. The ectoderm cells intermixed with longit-
udinal muscles form the cortical zone of the animal Inside
this and surrounded by the circular muscles is the medullary
zone of parenchyma, in which the genital organs and the excretory
and nervous systems are embedded. Many of the cells of the
parenchyma secrete calcareous matter and form the so-called calc-
areous corpuscles.
Fio. 888. Tae»ia»oUuM. Slightly magnified.
Entire vorm sbowing head and proglottides. I. Saoker on head.
3. Qenital porei. B, BipepToglottis.
Head. 1. Bottellnm. 3. Eooka. 8. Sookera. 4. Keck. 5. Cora-
menoement ot atrobiiization.
0. Bipe proglottid broken oft from worm. 3. Bemains of vaa deferens and
" ' — ' " Branehed otenu crowded with eggs.
oiidno
620 PLATTHELHINTHES. [CHAP.
Each portion of the body of & Cest«de which contains ths
reptoductiTe oigana is called a proglottis, and ia budded off from
the anterior portion which is called the bead. The latter is pro-
vided with suckers, and generally, in addition, with a circle of hooks
sitnated on a promiaence called the rostellum (1, Fig. 338b).
With the head the Cestode adheres to its host; its hinder part
or neck buds off proglottides in which new seta of reproductive
orgaoji are formed, and this process is repeated an indefinite number
of times so that a chain of proglottides is formed. The oldest
proglottis is thus the hindermost. This method of segmentation
ia called strobilization on accottnt of its resemblance to the
formation of the Ephjiae by a Hydra-tnba (p. 65); it differs from
Bio. 389. TruiSTerte aectioD throngh a mature proglottis of Taenia x kboat 13.
1. Gnticle. 2. LoDg'necked cells o( ectoderm. 3. 'Longitudinal miucle
fibres cot across. V 4. La;er of oiranlar maBolcB. C. Split in uie
pareneli:n>ia which lodges a calcareana oorpnsde. ' 6. Ori^. 7. Teatit
with nuwBes of male gemi'OeUi forming spermatoEoa. ^'8. Lonsitadiiul
exoretoi? csDal. 9.\'lrODgitndinal nene-(x>Td. 10, Uteraa. 11. Oridact.
the segmentation of the Annelida, where the new segments arise
not is the neck but in the tail.
The excretory system consists of a larger and a smaller trunk
on each side, which unite in the last proglottis to end in a con-
tractile vesicle opening by a median posterior pore. In each pro-
glottis the trunks on each side are connected with their fellows on
the opposite side by transverse canals. The nervous system consists
of a ring in the head, whence two Utetal trunks ariso. There is no
braia — the impressions the animal receives from the outside world
being few and simple.
The reproductive organs have the same general stractnre as
those of the Trematoda. The vitellarium is however often unpaired,
3X] CE3T0DA. 621
whereas there is usually a pair of germaria. There is a luge
nterns (8, Fig. 340) which appeats to be a lateral outgrowth
from die oonjoiDed oTiducte. From the circumstance that in
primitive Cestoda this uterus opens to the exterior independently
of the genital atrium it is believed that it correaponda to the canal
of Laurer in the Digenetio Trematoda. If this be so the functions
of the genital atrium and Laurer's canal have been exchanged in
Cestoda, for in Trematoda the atrium permits eggs to escape
whilst Laurer's canal admits spermatozoa from another individual,
in Cestoda tliese spermatozoa enter through the atrium whilst the
canal is enlarged to form a uterus. The testes aie in Cestoda
1. LoDgitadlnal mtM-TMonlar canal. 2. Transverw water-vuonlar canal,
S. Th defereDB. 4. Tagina. G. Ovaiy. 6. Yolk-gland. 7. Sliell-
gUnd. 8. Utems. 0. Testea. 10. LoDgitadiaal nerve.
represented by a multitude of small rounded bodies (7, Fig. 839,
9, Fig. 340) from which excessively fine ducts are given off uniting
to form the single vas deferens ending in the penis. As the
proglottis gets older the eggs all pass into the uterus, which swells
enormously, displacing and destroying the other organs. In this
condition the proglottis drops off. This process is continually being
repeated so that a single parasite keeps on casting off portion after
portion, each charged with ova capable of developing. In this way
622 PLATTHELMIKTHES. [CHAP.
a Cestode fimdy lodged in the alimentary canal of its host can
produce an almost indefinite number of eggs.
In the more primitive Cestoda the egg-cases, which as in Trema-
toda contain an ovum and a multitude of yolk-cells, escape from
the detached proglottis through the opening of the uterus into
water. In a short time a larva hatches out, consisting of an outer
layer of ciliated cells surrounding a soUd internal mass which deve-
lopes six chitinous hooks. After swimming in the water for a short
time the larva is swallowed by an aquatic animal, loses its outer
layer of cells, thus exposing the hooks and becoming what is now
termed an onchosphere. In the more modified Cestoda the utenu
has no external opening, and the eggs escape from the proglottis only
by decay. The remains of the proglottis, including the eggs, are
swallowed by some animals, and soon after an onchosphere hatches
out, no cilia being formed. In every case the onchosphere bores
through the alimentary canal of its host, and is carried by the
blood-stream to a suitable spot in the tissues where it fixes itsell
Once fixed, tiie larva increases very much in size and gen^idly
becomes hollow so as to resemble a bladder. An infolding or
invagination of part of the outer layer now takes place, forming
a pouch, on the inner side of which the suckers and hooks of the
adult head make their appearance. The pouch is then turned
inside out and a well-marked head is thus formed. The larva is
now known as a bladder-worm or Cysticercoid and is found
parasitic in a great number of animals. A very common form is
Cysticerctis pUiformis found in the coelom of the Rabbit attached
to the mesentery. Coenurus cerebralis is a dangerous Cysticercoid
in which the bladder can become as large as a plum and on which
not one but numerous heads are formed. It is found lodged in the
brain of the sheep and other domestic animals and causes the
disease known as gid or staggers. A still more dangerous form is
Echinococcus polymorphus, in which the bladder may become as
large as a man's head. This enormous vesicle buds off from its
inner surface secondary vesicles on each of which numerous heads
are formed. This parasite is found in the Pig, Sheep and even
Man, in the liver and other internal organs.
The Cysticercoid can complete its development only when
its first host is eaten by anotiier animal Then the bladder is
cast off whilst the head firmly attaches itself by its hooks and
suckers to the alimentary canal of its new host and conmiences to
bud off proglottides. Though the adult may attain an immense
XX.] CESTODA. 623
length (as much as 20 feet) it is a much less dangerous parasite
than the larva, and rarely produces worse symptoms than giddiness
and a certain amount of abdominal pain. The adults are found
chiefly in carnivorous animals, above all in the Dog, Wolf and allied
species. Thus Cysticercus piriformis becomes Taenia serrata,
Coenurus cerebralis gives rise to Taenia coenurus, and Echinococcus
polymorphtis to Taenia echinococcus, all three infesting the alim-
entary canals of the Dog and its allies. The common Taenia
solium found in the human intestine is developed from a Cysticercoid
found in the muscles of the Pig.
Bothriocpphalus latus, which may attain a length of 30 feet, is
the largest Cestode found in Man. It belongs to a more primitive
division of the class than Taenia, for it gives rise to a free-
swimming ciliated larva, which is swallowed by the Pike or the
Perch. In this it developes into a solid larva which gives rise to
the adult when the fish is eaten by man.
It is obvious that an animal which like a Digenetic Trematode
or a Cestode depends for its survival on such a combination of
lucky chances as that of transference frx)m one particular species of
animal to another animal of a definite kind must develope large
powers of reproduction. In the Trematode this is chiefly manifested
in the power of the larva to reproduce itself asexually, but in the
Cestoda the power is in most cases only developed when the animal
is in the adult condition. Considerable discussion has taken place
as to whether the process of strobilization is, or is not to be
regarded as a production of new individuals. When we recollect
that the separated proglottides often retain life for some time after
being cast out of their host, it would seem that there was much to
be said in favour of regarding them as sexual individuals and the
head as an asexual one. The most probable view on the whole is
that of Lang, who suggests that in the ancestor of modem Cestoda
the hinder part of the body which contained the genital organs was
separated at maturity, as occurs in the case of some Polychaeta
When the Cestode took to living in the alimentary canals of
Yertebrata, the abundant food supply and favourable temperature
stimulated the powers of regeneration so that the missing part was
quickly reproduced, and by the hurrying on of this process of
regeneration the process of strobilization was evolved, exactly as
occurred in the Scyphistoma of Aurelia. It is interesting to
notice that Arckigetes, found mature in the coelom of the Oligo-
chaet Tub\fe:c, is the only Cestode which completes its development
624 PLATYHELMINTHES. [CHAF.
elsewhere than in a Vertebrate, and in this case only one proglottis
is produced, which never separates from the head. To the posterior
end of this proglottis an appendage is attached representing the
bladder of the Oysticercoid, in which the six hooks of the oncho-
sphere still remain embedded.
The Platyhelminthes are classified as follo?7B:
Class I. TURBELLARIA.
Platyhelminthes with soft, usually leaf-like bodies and a ciliated
ectoderm : rhabdites are often present : free-living.
Order I. Rhabdocoelida.
Turbellaria with a straight, rod-like alimentary canal and
a protrusible pharynjc.
Sub-order 1. Acoela.
The digestive system is represented by a mass of endo-
derm cells which contains no cavity: a short pharynx and
single otocyst are present.
Sub-order 2. Alloiocoela.
The digestive canal is lobed : the testes are scattered.
Sub-order 3. Rhabdocoela.
The digestive canal is rod-shaped, the pharynx pro-
trusible.
Order II. Dendroooelida.
Turbellaria with a branched alimentary canaL
Sub-order 1. Triclada.
The alimentary canal has three main branches, one
running forward and two running back. Male and female
openings united.
Sub-order 2. Polyclada.
The alimentary canal has many branches sometimes
anastomosing. Male and female openings as a rule distinct.
Manne.
XX.] CLASSIFICATION. 625
Glass 11. Trehatoda.
Parasitio Plaiyhelminilies with usually leaf-like, rarely cylin-
drical bodies : no cilia on ectoderm : forked alimentary canal :
ventral sucker or suckers and hooks often present : not segmented.
Order I. Monogenea.
Trematodes with a sucker or suckers at the posterior end
and in some cases another anteriorly. Often external parasites
or in the mouth, nose or branchial cavities. Development
direct
Order II. Digenea.
Trematodes with a sucker at the anterior end and another
on the ventral surface or posteriorly. Internal parasites and
their organs of adhesion more weakly developed than in the
Monogenea. Development with an alternation of generations.
Glass III. Gestoda.
Parasitic Platyhelminthes with elongated and usually segmented
body : no mouili or alimentaiy canal : suckers and hooks present
but on the head only : the segments break off when ripe.
8. d:M.
40
626
CHAPTER XXL
Phylum Nemebtinea.
Thb Nemertines belong to that category of animaLs which wonld
by most people be styled "wonns"; that is to say they are long,
soft-bodied animals, without limbs or appendages of any kind, which
progress by ondulatory movements of the body. Most Nemertines
are marine, living under stones and amongst seaweed ; a few are
found in fresh-water and one or two species are terrestrial
They swim in a graceful, undulating fashion, but they are much
more sluggish in their movements than Annelida. It is a conmion
and characteristic sight to see an isolated contraction passing
slowly back along the body. Some species are minute, others,
e.g. Lineus marinus, attain a length approaching 100 fL, and aie
perhaps the longest animals known.
The ectoderm consists of long, narrow, ciliated cells. In this
they resemble the Turbellaria, but they differ from the latter
animals profoundly in the structure of the alimentary canaL This
organ is straight and unbranched ; it begins in a mouth placed a
short distance behind the anterior end of the body, and it ends in
an anus placed at the extreme posterior end. For most of its
course the alimentary canal is sacculated; that is, produced at
the sides into a series of short broad pouches ; otherwise it is not
differentiated in any way.
The most characteristic organ of the Nemertine is the pro-
boscis. This is a long tube lying above the alimentary canal,
ending blindly behind, and opening to the exterior in front. The
proboscis is a part of the outer skin invaginated, and when retracted
it is surrounded by a closed space lined by a well-defined epithelium
called the proboscis-sheatL This space contains a watery fluid,
and its wall beneath the epithelium possesses powerful circular
CBAP. XXI.]
musclee. When these contract the proboscis is partially forced out
of ths sheath by being tnroed ineide out and coosequeutly pro-
trndiDg from the front end of the body at the same time. It can
never be completely turned inside out, for certain cords traversing
the proboscis-sheath restrain it At the point in \t& wall which is
at the anterior end when the process of turning inside out haa
reached its utmost limits.
there is in the higher Nem-
ertinee a short lateral pouch
in which a homy spike, the
atylet, is secreted. Round
the base of this open poison-
glands, so it can be seen that
the proboscis is an offensive
o^an for seizing prey. So
far as we know all Nemertines
are carnivorous. Amongst the
lower Nemertines the stylet
is not developed, nevertheless
the proboscis cao be employed
to catch prey ; it is quickly
thrust out and coiled spiraUy
round the victim and then
retractefl so as to push the
prey into the mouth. This
retraction is brought about
by a muscular band which
attaches the end of the pro-
boscis to the sheath. The land
Nemertines (Geonemertes) are
said to travel by thrusting
out the proboscis, attaching
it to foreign objects and
drawing np the body after it.
Underneath the ciliated
ectoderm of Nemertines there
is a series of powerful circular and longitudinal musclai : these
layers are continued, but in the reverse order, on to the walls of
the proboscis, since this is only invaginated skin. Undei* extreme
irritation tlie extended proboscis is sometimes torn from the
body — by the heightened pressure of the fluid in the sheath —
40—2
628 NEMEBTINEA. [CHAP.
and in one instance such a disjoined proboscis was mistaken o&
account of its active contractions for a now species of Nemertine.
There is a well-defined central nervous system amongst Jfeam-
tines, consisting of a pair of ganglia lying at the front of and abo?e
the mouth — ^less frequently at the sides of it — and connected by a
commissure which passes above the proboscisHsheath. The hinder
parts of the ganglia are more or less distinctly separated as posterior
lobes, and come into close relation with curious pouches of invagi-
nated ectoderm, termed cephalic pits (Fig. 341), which seem in
some cases at any rate to subserve the respiration of the nesrvom
tissue, for the latter in some species contains haemoglobin. The
ganglia are continued backwards into two powerful nerve-cords
lying at the sides of the body. In Hie lower species these cords
can be seen to Ue just beneath the ectoderm and to be but thicker
portions of a sheath of nerve-fibrils extending all round the body,
and derived from the bases of the ectoderm cells. In the higher
species the nerve-cords lie well within the muscles, and this sheath
is not so evident
Sense-organs in the form of eyes of simple structure often occur
immediately over the region of the ganglia.
The interstices between the various organs inside the muscles
are filled up with connective tissue, but there exist three longi-
tudinal tubes with well-defined walls which are regarded as blood-
vessels. Two of these tubes lie at the sides of the alimentary caDal,
and one is situated above it and below the proboscis-sheath. These
vessels are connected anteriorly by arches and they unite wiili one
another in both the head and taiL
The excretory organs have the form of a pair of branched tubes
opening at the sides of the body not far behind the cephalic pits.
Their branches end blindly and the terminations of these are closely
applied to and even indent the wall of the lateral blood-vessel,
while in each termination there is a tuft of cilia.
The Nemertinea are dioecious. The generative organs are ex-
ceedingly simple, coDsisting in both sexes of packets of cells
situated along the sides of the body alternating with the pouches
of the alimentary canaL No permanent genital ducts exist, but
when the ova and spermatozoa are ripe they appear to make tem-
porary ducts for themselves. The egg developes in many cases into
a remarkable larva called a Pilidium. This is shaped something
like a policeman's helmet with ear lappets. The edge of the
helmet, including the lappets, is fringed with powerful cilia, and
SXt] ANATOI
there is besides a tuft of long
cilia at the apex. Underneath the
helmet is the opening of the mouth,
which leads into a sac-Uke gut de-
void uf an anus.
The adult is developed from the
Pilidium iu an extraordinor}- way.
Four invaginations of eotodenn
appear on the under aide of the
larva, at the sides of the alimentary
canal. These grow both upwards
and inwards until they completely
Burround the canaL The inner walls
of the pockets form the ectoderm
of the adult. When the process is
complete the alimentary canal sur-
manded by the new ectoderm drops
out of the Pilidium and forms the
Nemertine.
Many species of Nemertine are
found on the firitish coast. As
examples we may mention Lineus
(Fig. 341), a long tliin form without
atylete in the proboscis, and Tstra-
gtemma, a short broad form with
four eyes and stylets in the pro-
boscis.
The Nemertines, so far as our
present knowledge extends, form a
completely isolated group in the
B.iiitnfl.1 kingdom.
From the circnmstanoos that
some Rhabdocoel Turbellarians have
a protrasible organ in the anterior
part of the body, and that the ex-
cretory organs of Nemertines bear
a certain resemblance to those of
PUtyhelminthes, it has been sup-
posed that Nemertines and Platy-
helminthes are allied. The totally
different character of tlie generative
Flo. 342. Cerelmilflui futcui.
Young trsDtipareiib form x 7.
After Biirgar. i
1. Cephalic slits. 3. Opening
leading into the retracted pco-
boscia. 3. Dorsut oommissnre
of nervous sjBtcm. 4. Ventral
commiBBure. 5. limin. 6. Post-
etior lobe of brain which oomea
into connaction with the cephalla
slit. 7. Mouth. 8. Frobouis
sheath. 9. Lateral vessel.
10. FroboBois. 11. Poooliea ot
alimeutarj canal. 13. Stomodt.
630 NEMERTINEA. [CHAP. XXL
organs in the two groups and the presence of an anus in Nemertines
tell strongly against this view, and indeed the resembhiuces will
not stand minute investigation.
Of all the groups, however, about the nature of whose so-called
''mesoderm" we are in doubt, tiie Nemertines have perhaps the
greatest probability of turning out to be true Coelomata. The
cavity of the proboscis-sheath, termed Rhynchocoelom by German
authors, may very possibly be part of a true coelom ; but we are
not justified in assuming this until more exact observations have
been made on its development.
The Nemertinea are divided into classes in accordance with the
condition of the nervous system and tiie arrangement of the layers
of muscles in the skin. These classes are as follow :
Class I. Peotonemertinl
A nervous sheath underlies the entire ectoderm ; the lateral
nerve-cords, mere thickenings of this sheath, are situated oat-
side the layers of muscles : no stylets in the proboscis.
Ex. CarineUa,
Class II. Mesonemertini.
A nervous sheath underlies the entire ectoderm ; the lateral
nerve-cords are more deeply situated, lying between the outer
circular and the inner longitudinal muscles : no stylets in the
proboscis.
Ex. Cephalothrlx,
Class III. Hetebonemebtinl
A nervous sheath surrounds the body. Both it and the
nerve-cords lie inside a special layer of longitudinal muscles,
which are derivatives of the ectoderm cells, but outside all the
other muscles : no stylets on the proboscis.
Ex. Lineus, Cerebratulus.
Class IV. Metanbmertinl
No nervous sheath but definite peripheral nerves : the
lateral nerve-cords lie within all the muscle layers : the
proboscis is armed ¥nth stylets.
Ex. Tetrastemma, Geonemertes, MalacobdeUa,
Classes I — III are often united as the Class Anopla, charac-
terised by the absence of stylets in the proboscis. Glass IV is
sometimes termed Enopla (i.e. armed) to contrast it with the
remaining Nemertines or Anopla.
631
CHAPTER XXIL
Phylum Rotifera,
The Botifera are minute animals mostly confined to firesh water;
a few only being found in the sea. Many of them swim about by
means of a loop of cilia which encircles the front end of the body,
but some are sessile. The motion of these cilia induced the early
observers to think that the animal had wheels in front, whence the
name (Lat., rota, a wheel ; fero, to carry). There is a complete
transparent alimentary tube, ending in an anus situated on the
dorsal side in front of the hind end of the body, the latter forming
a ventral projection called the foot. The first part of the tube is
a stomodaeum, and lined like the rest of the skin with cuticle.
This cuticle is thickened to form teeth which work on one another,
the whole organ being called a mastax The activity of the
mastax enables one at once to distinguish a Rotifer from other
minute animals.
Floscularia comtUa, often termed F. appendicidata, is a widely
distributed species. It lives in ponds, ditches and pools, usually
attached by its posterior end to some water-weed or other body
and surrounded by a gelatinous tube into which the animal can
retire. The length of the animal when extended is 0*2 to 0*3 mm.
The body is covered by a thin cuticle, and may be divided into
three regions, the head, the trunk and the foot When the animal
is extended the last-named is stretched out and smooth, but it is
wrinkled when the animal withdraws into its tube. It terminates
in a disc, on which opens the duct of two large glands which
secrete an adhesive substance, by means of which the foot is
anchored.
The anterior end of a Rotifer, on which the mouth opens, is
called the disc. In Floscularia this is produced into five long
tentacle-like processes fringed with stiff bristles which serve as a
net to entangle small animals and plants. The cilia which produce
632 BOTIFERA. [CBiF.
the cnrrent b^ means of which the prey is captared are mtoated
inside the rinf; of tentacles. They take the form of a horaeshoe-
shaped band open doisally, the mouth being sitoated in the centie
B. F, eampanuiata. Hal« magnified. 1. Teeianlk wmImIm. 2. feois.
of the hoTse-shoe. This band of oilia is termed the velum : in
other Botifera it is a complete circle bat is folded back on itself in
such a way that a loop is produced which lies dorsal to the mouth.
XXIL] ANATOHr.
This loop 18 called tlie trochns; it
osofdlf consiats of more powerful cilia
than &e rest of the Tolam, which is
tmned the ciDgnlum. The groove
between the two bands in which the
month lies is covered with fine cilia.
In the genns Rotifer the trochns is
composed of two almost circular lobes,
which were described as wheels by the
first naturalist who observed them, and
this circumstance, as we have Bsid,
sni^ested the name given to the genne
and afterwards bestowed on the whole
pbjlnm.
Within the cnticle which covers the
bod^ ia the ectoderm. This takes the
form of a protoplasmic layer with
scattered nnclei, showing no cell-
outlines. It snrronnds a spacious body-
cavity, probably a haemocoel, which
contains a fluid with no amoebocytes ;
in this float the various organs of the
body connected more or less closely
together by connective tissue-cells.
The muscles do not form a oontiniions
layer underneath the ectoderm as is
the case with the Platyhelminthea and
the Nemertinea but consist of isolated
bands, chiefly longitudinal, which re-
tract the disc and the foot and beud
the body in various ways, the recovery
of its original shape being due largely
to the elasticity of the cuticle.
The food, which consists of
Protozoa and other small organ-
isms, is swept into the month by
the action of the surrounding
cilia. The mouth leads Utrough
a wide vestibule into an oeso-
phagus, which is ciliated and
projects down into the so-called
giizard or mastax which, next
Pia. BM. Diagram of fJweuJ-
Cirolfl of tentoeleB bMiiag brlEtlw.
2. Telnm. S. MoothleadiugtOTMtl-
baje. 4. Brain. fi. OeBOphagDB
Opening of oloaca.
10. Strands of mnaolea. 11. Tolk-
gl&nd part of avajy. 12. Oraiian
paitof ovary, 18. Ovidnct. H. Ei-
oretoi; duct opening into Ifi, □rituiy
bladder. 16. A Ug with a tolt of
oilia. IT. Longitadinal and oimUai
maielM in foot.
634 BOTIFERA. [chap.
to the ciliary rings on the head, is the most characteristic organ of
a Botifer. The vestibule, oesophagus and mastax are all part of
the stomodaeum. The cuticle lining the mastax is thickened so as
to produce the trophi, which are hard, chitinous, chewing organs ;
of these there are typically three, two mallei and an incus on
which they strike. The incus, a Y-shaped piece, consists of two
rami and a central piece or fulcrum. Each malleus is composed
of a manubrium and an uncus or head, which may be toothed
The shape and arrangement of these hard parts is of great yalae
in dassificatioiL In some species the mallei are absent altogether,
and the two rami of the incus then work against one another like
two lateral teeth. In the Notommatidae the mallei can be pro-
truded through the mouth and are used to cut into the cells of
Algae on which the animals browse. In Floscularia and its allies
there is a dilatation of the stomodaeum, called the crop, interposed
between the mastax and the '' oesophagus," and the latter hangs
down into the crop just as a funnel might hang into a tumbler:
the crop can be everted through the mouth.
After passing between the jaws the food enters the stomach,
which is lined with cilia ; here the food loses its original colour and
becomes tinged with the brown secretion of the walls of the stomach.
In most forms two salivary glands open into the gizzard and two
gastric glands into the stomach, but these have not been clearly
made out in JFlosciilaria. The stomach is separated by a con-
striction from the ciliated rectum, and this ends in a non-ciliated
proctodaeum into which the genital and excretory organs open.
The alimentary canal of Rotifera, like that of the lower Vertebrats,
thus terminates in a cloaca.
The excretory system consists of two longitudinal ducts con-
sisting of columns of perforated cells, which bear a number of small
tags hanging freely into the body-cavity (Fig. 845). Each tag
consists of a cavity in which are several flagella, which show
during life the peculiar flickering motion which is usually asso-
ciated with the excretory system of Platyhelminths. In JFTas-
cularia four or five pairs of tags have been seen. The longitudinal
ducts are usually connected by a transverse duct just under the
disc, and they open as a rule into a capacious bladder which
contracts at intervals and expels its contents into the cloaca and
thus out of the body. It has been calculated that in some species
this bladder expels a bulk of fluid equal to that of the animal
about every ten minutes, and this fluid must be replaced by
water which diffuses through the body-walL This water doubtless
tL]
AN^TOHT.
brings with it oxygen and camea off carbonic acid which it has
taken up from the tissues.
The principal part of the nervous system is a bilobed ganglion
called the brain. This liea just under the disc ou the dorsal side of
the mastax ; it bears two red
eyes in Fhscularia. In Notom-
mala the brain is large, and on
it more than one pair of eyes are
situated. In tbe Bdelloida there
is alflo a ganglion on the ventral
side of the mastax, and a pair of
circumoesopbageal cords unite
this with the brain. In Floscu-
laria, as in Rotifera generally,
there are three well-marked sense
organs called antennae, con-
sisting of prominences bearing
stiff sense-hairs ; one is situated
in the mid-doreal line, two are
latero- ventral ; these latt«r are
in some genera fused with one
another.
As in the Platyhelminthes,
so in Rotifers, the ovary, which
occupies a good deal of space in
the body-cavity, usually consists
of a vitellarium or yolk-gland
andagermariumor trueovary.
The Utter lies between the former
and the stomach ; it is incon-
spicuous and is more or less
hidden by the large cells of the
vitellarium. Both glands may
be paired. They are enclosed in
a membrane continuous with the
oviduct which opens into the
doaca behind the excretory duct
The above description relates
chie&y to the female Floscularia. and in fact until 1S74 the male
waa unknown. It is much smaller than the female (B, Fig. 343).
As a rule the male Rotifer has a single circlet of cilia, a brain,
excretory system and muscles all more or less reduced, but
Fig, 313, Diagram of
AnuB. 9. Brain. 8. TroobaB.
i, Cingnloro. 8. Glwiil "
r>. OloacB. 7. Cuticta. ^
derm. 9. DoraoJ antenna. I
11. A cilialed " Wg" "' "^^ einre-
toi7 system. 13. Intastina.
13. Masciea. 14. Moutb. IS. Ne-
pbridial tnha. Iii. Ovnm. 17. Ori-
<iuot. 18. Ovaiy. '" "— —
30, Stomaob. '
22. Vitellarium.
there is uo mouth oi alimeDtary
After Plate. Mugnified.
1. LnUral uitennu. 3. Bladder.
9. CiDgulom. 4. Egga. 6. Yitet-
Itirium or ]ro1k-gl>ud. G. Foot-
gland. 7. Oiziatd. 8. OaBlrie
gland. 9. GGmiAriDm or otut.
10. Lobes of "grooTa" bearing atiff
Betae. 11. Intestine. 12. Eicrelorj
tube. 13. Mnath. 14. Ciliated tag
of the exoietory BjBtem. 15. Oeeo-
phagiiH. IG. Benol commiBBiire
or transTeree tulie uniting kidneys
BbDvemouth. 17. Stoma«h oTerlud
by repcoduolive nrgana, 18. Tro-
ohiu. 19. Uterus.
Hsdatin
smta IB one of the couunonest
can&l The testis is I&rge and tlie
penis is introduced into the
cloaca of the female, or in Bome
cases is thrust through the mil
of the body, and then the tggs
are probably fertilized in the
ovary.
Floscularia lays two kinds of
oggs during the summer, both of
which are thought to develope
parthenogenetically. Buth kind«
accuaiulate between the foot and
the tube in which the mother
lives. The larger eggs, which
average five to eight in number,
produce females ; tbe smaller eggs,
whose origin seems to be deter-
mined by tbe temperature, may
amount to eighteen or twenty.
These produce the males. 'IV
wards the autnmn tbe males
fertilize the females, and the
resulting eggs termed " winter-
eggs" are clothed with a thick
shell capable of witbst&Dding
cold and drought These live
through tbe winter and give rise
to females in the spring. A
similar alternation of summer
and winter eggs is met with in
certain Crustacea (Phyllopoda
and Ostracoda).
Kotifera are cosmopolitan, but
as a rule they inhabit fresh
water; about 700 species are
known, of wliich only oae-t«Dth
live in the sea or in hrackiah
water. One species, Bynchaeta
baltica, is pelagic and phoapbot-
escent A few ore parasitic
Botifers, and is usoally to
xxil] classification. 637
be met with swimming about amongst the algae of green ponds.
It possesses a shortly elongated, cylindrical body (Fig. 346). The
disc bears a circular cingulum separated by a groove from the
trochus; in this groove are five prominences bearing stifi* setae.
The posterior end of the body tapers and ends in a bifurcated foot
on which a pair of glands open.
A great many of the Bdelloida live amongst the roots and
leaves of mosses, etc., and these can survive being dried up for a
long time, the body shrinking and sealing itself up in the cuticle.
Apart from the species which possess this power Kotifera as a class
are short-lived, and this is especially true of the males.
In certain respects, such as the nature of their excretory organs
and of their ovaries, the Rotifers show some resemblance to the
Flatyhehninthes ; but they differ from them profoundly in the
alimentary canaL The velum, in its typical form consisting of
trochus and cingulum, has been compared to the ciliated band
which encircles the Trochophore larva. This band like the velum
is seen on close inspection to consist of a prae-oral and a post-oral
loop. The Trochophore larva is found in the life-history of the
Polychaeta and some of the more primitive Mollusca, and it is
believed by many to represent a common ancestral form. Should
the comparison of the Botifera with this larva be a just one we
must regard the Botifera as having been derived from the common
stock of Annelida and Mollusca and to be therefore a very ancient
group. There are however difficulties which arise when the com-
parison is carried into details, so for the present it is better to
regard the Botifera as a completely isolated phylum.
Leaving out of sight a few parasitic and aberrant forms the bulk
of the Botifera are classified as follows :
Glass I. BmzoTA
Botifera in which the foot is not retractile but forms a
permanent organ of attachment. The animal lives in a tube.
Ex. Moscularta.
Class II. Bdelloida.
Botifera which creep like a leech, using the foot as a sucker.
They are provided with a protrusible adhesive proboscis on the
638 BOTIFERA. [chap. XXIL
dorsal surface, by which the anterior end of the animal may be
made to adhere.
Ex. Rotifer.
Glass m. Ploima.
Botifera which swim freely, only occasionally attaching
themselves by the forks of the bifurcated foot
Ex. Hydatina, Synchaeta, Notommatd.
Glass IV. SCIRTOPODA.
Rotifera provided with hollow movable outgrowths from
the body by means of which they leap.
Ex. Pedalion,
6.S»
CHAPTER XXin
Phylum Nematoda,
The Nematoda include a very great number of species commonly
termed Thread-Worms, or from the shape of their cross section
Round- Worms. Certain species attain a great length, as long as
a man, but more commonly they are small and insignificant and
often microscopic. The general shape of the body is cylindrical,
usually pointed slightly at each end ; the surface is smooth with at
most a few bristles, so that they easily insinuate themselves into
the cracks in the damp earth, or between the tissues of the animals
and plants in which for the most part they live.
As a rule, like most animals which pass their time in the dark,
Nematodes are white or whitish-yellow in colour. The body is
glistening and smooth, but not slimy. It is ensheathed in a thick
cuticle, which is in some cases ringed. No locomotor organs exist,
and the animals progress by wriggling, bending first to one side
and then to the other. The cuticle, which is moulted about four
times during the life of the animal, is secreted by an underlying
layer called the ectoderm, in which no trace of cell limits can be
detected, but nuclei are scattered in it. Along the middle dorsal
and middle ventral line and along each side this layer is thickened
and projects inward. The median ridges support two nerves, the
lateral ridges two canals, which are believed to be excretory.
By these ectodermal thickenings the body-wall is divided
into quadrants. In each quadrant there is a layer of longi-
tudinal muscle-fibres of very peculiar appearance. In all muscle-
fibres there is a patch of unmodified protoplasm surrounding
the nucleus, the rest being modified into those fibrils which are the
visible sign of a heightened contractile power. In the Nema-
toda, in which all metabolism is at a low ebb, only the outer-
NEIUTODA. [CHiP.
most layer of the mosde-cell is eonvrated
into Ebrila, the great balk consisting of
nomodified protoplasm, which is oflea
diawB out into an internal process nm-
Disg towards the dorsal or ventral ecto-
dermal ridge. Muscle-cells of each ■
character are known only in Ifematoda.
The body-wall, which has just been
described, encloses a space which is
traversed from end to end by the alim-
entary canaL This Bpace i^ fall of i
fluid in which amoebocytes float and it
farther lodges the reproductive Bystem.
It has no epithelial lining and appeiis
to be a haemacoele. Besides this there
is no circulatory system or heart
The mouth is terminal and is usuallj
surrounded by certain papillae or lobes,
often three or six in number. It lead^
into an oesophagus, usually with a bri-
angular cavity and thick muscalar wtlls
(Fig. 347). The oesophagus may be
immediately followed by a second mus-
cular bulb, called the pharynx, whidi
sometimes has an armature of some
bristles or spines. Both oesophagus
and pharynx are parts of the stomo-
daeum. Then foUows the intestine,
which is by &r the largest part of the
alimentary canal. The muscular oeso-
phagus no doubt acts as a sucking organ,
bat there are no muscles and no cilia
in the intestine. It is a simple tube
formed of a single layer of cells, which
both inside and out secrete a tiiin
cutide. Posteriorly it passes into a
proctodaeum with muscular walls, and
Pio, 347. Female Aiearit tumbricoida, cat open along (ha meduui dcmal
line to ihow ths internal oigans x 1.
The moBcaUr oesopliaguB. 3. The iuteetiae. 3. The ov»xj. i. The
DtecuB. S. The vagina. 6. Ita eitenial opening. 7. The
excretory canal*. 8. Their opening.
XXIII.] ANATOMY. 641
this terminates in the anus situated a little in front of the end of
the taiL
The nervous system consists of a ring round the oesophagus,
which sends off in front six nerves to the mouth and its papillae,
while behind it also gives off six nerves, the two more important of
which run down the body in the above-mentioned median dorsal
and ventral ectodermic ridges. Transverse commissures unite these
main nerve-tranks at irregular intervals. With the exception of
certain hairs and papillae to which a tactile sense has been ascribed,
and in the free-living species certain eye-spots, no organs of sense
are known in the Nematoda.
The excretory function is usually assigned to two long tubes
which run along the lateral thickenings of the ectoderm. These
tubes end blindly behind, but anteriorly the tubes approach one
another ventrally and open by a common pore in the middle ventral
line some little distance behind the mouth (Fig. 347). Each of these
tubes is stated to consist of one immensely elongated hollow cell.
Nematoda are with few exceptions bisexual The male is often
smaller than the female and frequently has a curved tail. In both
sexes the reproductive organs are tubular. In the male the organ
consists of a long tapering tube much folded on itself opening into
the proctodaeum close to the anus. In the uppermost and narrowest
part of the tube there is a mass of protoplasm with nuclei ; lower
down the mother-cells of the spermatozoa become separated, while
the lowest part contains ripe spermatozoa. The names testis and
vas deferens are given to the upper part and lower part respectively
of this organ, but the whole is one continuous structure developed
from a single cell in the embryo. In the female there are two
similar tubes which unite to open in the mid-ventral line by an
exceedingly short median piece termed the vagina. The vagina is
situated about one-third the body-length from the head. In each
tube it is usual to distinguish an upper ovary consisting of a mass
of nucleated protoplasm, a middle oviduct where the bodies of the
egg-cells have become separated from one another, and lastly a
uterus where the eggs after fertilization are each provided with a
shell. Each tube however, like the testis of the male, is developed
in the embryo from a single cell.
In order to introduce the spermatozoa the male distends the
vagina of the female by inserting two cuticular hairs, developed
from the lining of the proctodaeum, called copulatory spicules.
It is a most peculiar characteristic of the Nematoda, which they
s. & M. 41
642
NEMATODA.
[chap.
share with the great group Arthropoda, that no cilia are found in
any organ of their body. Even the spermatozoa have no flagella bat
move in an amoeboid manner. This absence of cilia, which are foond
in every other group of the animal kingdom except Arthropods and
in many plants, has received hitherto no explan-
ation. It is possibly correlated with the strong
tendency of the protoplasm in both phyla to
produce chitin. The eggs of Nematoda have
a structure well adapted for histological in-
vestigation, and have been much utilized in
researches on the behaviour of the nucleus
before and during fertilization. As a rule the
eggs are laid, but there are many species which
produce their young fully formed.
Comparatively few species are free-living
throughout their whole career, but these few
are interesting. They are of small size and
inhabit damp earth or mud, one family being
marine. The mouth is often provided with
movable spines and there are frequently eyes.
These features suggest a relationship with Uie
Ghaetogaatha, which, like the Nematoda, have
a thick cuticle and only longitudinal muscles;
and the idea receives support from the existence
of a group of small marine '' worms ** called the
Chaetosomatidae, which are probably also to
be regarded as free-living Nematodes. These
animals have two semicircles of movable bristles,
situated one at each side of the mouth, and
in addition a double ventral row of similar
spines by means of which they creep about
Should this conjecture turn out to be well
founded the Nematoda must be regarded as
Goelomata, and it is interesting to speculate
what has become of their coelomic sacs. Pos-
sibly, as in the Arthropoda, these have been
reduced in size by the development of a
haemocoele and are now represented only by the excretory and
genital tubes ; but until fuller details of the development both of
Nematoda and Ghaetognatha are known it would be unsafe to pursue
these speculations further.
B
Fio. 848. Aacaris lum-
bricoideBf cut open
along the dorsal
middle line x 1.
1. Oesophagus. 2. Int-
estine. 3. Testis.
4. Vas deferens.
5. Lateral excretory
canals.
^xul]
FABASITISH.
643
Fla. 349 Tnch na iptralu, eDcysted
amongBt mnscnlar fibrei. Highl; mas-
nified. Attet Leookut.
Taking the free-living forma as Btarting-point we can arrange
the other fomiliee of Nematoda in an ascending scale of increasing
panaitinn, cnlminating in a form like Trtc&tna spiralis which is a
perpetual parasite. This Nematode inhabits the intestine of ite
host (Pig, Man &c) where it lays its eggs. From theee egga
Iwrvae hatch out which bore through the walla of the intestine and
get into the circulation by which they are earned all over the body
Hiey encyst themselves m __
ihe muscles (Fig 349} and
do not develope further nn
leas the flesh of their host is
eaten by another animal in
whose intestine they become
matoreand then the cycleof
development recommences.
Their natural host is the
Rat ; the Pig is a secoodary
host and being a gross feeder no donbt often devours rats and the
remains of its own species, and thns the parasite is propagated.
IVtekina can however live perfectly well in Man, as the prevalence
of the disease Trichinosis testifies. This disease is contracted by
eadog insufficiently cooked pork infested by the encysted larvae of
THektna. These become mature in the human intestine, and give
rise to a second generation which cause severe and occasionally fatal
symptons by boring through the intestinal wall
Most Nematodes pass the earlier part of their existence in
damp earth, during which they are known as Khabditts larvae and
bear a strong resemblance to some of the &ee-Iiving forma Tplen-
cktu tritici forms the so-called Ear-cockles in wheat ; those are
brown galls replacing the wheat-grains and filled with encysted
Nematodes. If the grains are beaten to the earth by rain the
worms escape irom the cysts and climb up the wheat stalks, where,
afW a generation which live in the flower, they again enter the
grains. In Bphaerularia bombi the males and females live together
in damp earth, but the fertilized female enters the body of a bee
and here developes into a great sac filled with eggs. In Syngamm
trachealis the eggs are laid in damp earth, and here develope into
larvae, which are swallowed by poultry and develope in their wind-
pipes into the sexual form, causing the disease called Gapes, which
is often fatal. Mlaria aangainis-hominit lives in the human lym-
phatic glands ; the embryos escape into the blood, whence they are
41—2
644 NEMATODA. [CHAP. XXIH.
taken up by the Mosquito in whose body they develope. When the
mosquito bites they make their way again into the blood of man.
They are believed to be the cause of the strange tropical diseases
associated with the name Elephantiasis. But it would lead us too
far to enumerate all the modifications of the life-history produced
by parasitism. Suffice it to say that the Nematoda are perhaps the
most successful of all parasites ; there is scarcely a phylum in the
animal kingdom which they do not attack. A smooth slippeiy
body which as a general rule causes little inconvenience to the host
and a low grade of metabolism requiring small supplies of oxygen
seem to have been the leading features in their success.
INDEX.
Names of genera are printed in italics. The figures in thick
type refer to am, Ulustration. In aU cases the references are to
the page.
Abdomen/ 122, 152, 168, 172, 191
Abdominal, 405
Abdominal ganglion, 219
Abdominal pores, 864
Abdominal ribs, 474
Abdncens nerve, 345
Abomasum, 572
Aboral pole, 71
Aboral sinus, 260
Acalepbae, 66, 73
Aeanthia, 189, 208
Acanthias, 411
Acanthobdellat 118
Acantbopteri, 409, 410, 415
Acarids, 198
Acarina, 198, 209
Aoetabolum, 429, 467
Acicolum, 109
AcinetOt 41
Acipemer. 396, 418
Aooela, 611, 624
Acopa, 830
Acridium, 186, 207
Aerit, 453, 455
Acromion, 483
Aetinometra^ 288
ActinopkrySf 26, 27, 40
Aotinopterygii, 395, 413
Aetinosphderium^ 26, 28, 40, 45
Actinozoa, 59, 73
Adambulaoral ossicles, 256
Adder, 481
Adductor muscles, 226
Adhesive cells, 70
Adrenal body, 451
Aegithognathous, 517
Aeichna, 120, 121, 187
Aglossa, 452
Air-bladder, 892
Air-sacs, 511
Alary muscles, 175
Alauda, 519
Albatross, 518
Albumen-gland, 221
Alcedo, 519
Alcei, oil, 601
Alcyonaria, 65, 73
Alcyoniumf 59, 60, 61, 62
Alimentary canal, 86 ; of Arthropods,
133; of Echinoderms, 253, 272, 274;
of Hirudoj 114 ; of Lamellibranchs,
230; of sea-urchin, 274; of Sepia,
241 ; of Vertebrates, 308, 319, 329,
847, 364, 376, 429
Alisphenoid, 395, 400
Allantoic bladder, 422
Allan tois, 457, 545
Alligatw, 459, 488, 491, 494
Alligator-turtles, 487
Alloiocoela, 611, 624 !
Allolobophora, 108, 116
Alpaca, 576
'* Alternation of generations," in Coe-
lenterata, 57 ; in Tunicata, 332
Alveoli, 272, 487
Alytei, 442
Ambly stoma, 439, 448, 454
Amblystomatinae, 439
Ambulacral grooves, 250
Ambulacral ossicles, 255
Ambulacral plates, 268, 269
Amia, 396, 397, 413
Amiurua, 407, 414
Ammocoetes, 365
Amnion, 457
Amniota, 457
Amoeba, 13, 14, 40; in infusions, 17
Amoebocytes, 92, 98, 251
Amoebula, 26
646
INDEX.
Amphibia, 367, 417; classification of,
422
Amphiblastola, 81
Amphicoeloas, 394
AmphioxuM, 310, 8U, SIS, 818, 814,
813, 816, 817, 818, 819, 890, 8S1,
832, 347, 358; origin of mesoblast
in, 94
Amphipoda, 159, 206
Amphisbaenidae, 463, 479
Ampbistylic, 372
Amphiuma, 438, 454
Amphiamidae, 454
Ampulla, 840
Ampullae, 256
Amylopsin, 349
AnaboUsm, 5
Anacanthini, 409, 415
Anal cerci, 168
Anal respiration, 139
Anal styles, 173
Anas, 001, 002, 518
Anchovy, 408
Anguidae, 476
Anguilla, 408, 414
AnguilUdae, 405, 407, 414
Anguia, 475, 476, 494
Angular bone, 403, 466
Animal, 1
Animals and plants, 2
Anisopleura, 246
Ankle, 504
Annelida, 89; classification of, 116
Annular cartilage, 361
Annuli, 112
Anodonta, 222, 224, 226, 227, 229, 281,
248
AnomaluruSf 580, 581
Anomura, 155
Anopla, 630
Aruer^ 518
Anseriformes, 518
Ant, 187, 188
Ant-eater, American, 546, 548 ; banded,
542, 043; Cape, 547, 549; scaly, 547,
549; spiny, 537; Tamandua, 046,
549
Ante-brachium, 418
Antedon, 288, 284, 285
Antelope, 574, 576
Antennae, 119, 170
Antennary gland, 139
Antennata, 119, 160, 207
Antennules, 144
Anterior, 87
Anterior abdominal vein, 432
Anthropoidea, 586, 588, 603
Anthropopithecu$t 590, 604
Antilocapra, 574, 576, 602
Antilocapridae, 574, 576, 602
Antlers, 576
Ant-lion, 187
Anura, 422, 440; dassifioation of,
452, 455
Anus, 31, 86, 349
Aorta, 175, 350, 861, 583
Aphu, 189, 206
Aphis-lion, 187
Aphrophora, 189
Apit, 188, 208
Aplysia^ 219, 247
Apdda, 422, 453, 456
Appendages of Arthropoda, 124
Aptera, 180, 184, 186, 207
Apteria, 496
Apteryx, 516, 518
Apu$, 142, 143, 146, 206
Aqueous humour, 343
Aquila^ 518
Arsohnida, 119, 190, 208 .
Araneida, 191, 208
AreeUa, 18, 19, 40
Arc?uuopteryXt 515, 517
Arohaeomithes, 517
Archego$aurut, 425
Archigetes, 623
Archinephric duct, 358
Arohipterygium, 890
Arcifera, 452, 455
Arco-centra, 394
Arctomys^ 579
Ardea, 518
Argiope, 294, 296
Argrdus, 205
Argyroruta, 187
"Aristotle's lantern," 270, 272
Armadillo, 047, 549
Arms, of Brachiopods, 292; of Mol-
luscs, 234
Artemia, 143, 146, 205
Arterial arches, 321
Arthrobranchs, 136
Arthrodira, 391
Arthropoda, 118; appendages of^ 124;
classification of, 118,204; definition
of, 141
ArthroBtraca, 155, 158, 206
Articular bone, 401
Articulare, 463
Articulation, 505
Artiodactyla, 568, 570, 600
Arvicola, 580, 602
Arytenoid cartilages, 469, 512
AscariSt 640, 642
Aicidiat 324, 886
Ascidiaoeae, 330
Ascidian tadpole, 325, 828
AaeUut, 188, 160, 206
Aspidobranchiata, 246
Aspidochirotae, 282
Ass, 570
Assimilation, 5
IND£X«
647
A»iacu9, 127, 182, 188, 141, 157, 206
Aiteritu, 249, 252, 269, 289
Asteroidea, 249, 261, 287, 288, 289
Astropeotinidae, 261
Asymmetry, 88, 222
AUlet, 588, 603
Athene, 582
Atlas, 460
Atrial cayity, 312
Atrial pore, 812
Atrium, 349
Auchenia, 576, 601
Auditory cranial nerve, 846
Auditory ganglia, 841
Auditoiy ossicles, 528
Aurelia, 66, 67, 68
Auricle, 432
Auriculae, 272
Automatism, 6
Autostylio, 371, 885
Aves, 867, 495; classification of, 516
Avicularia, 800
Axial einus, 260
Axis, 460
Axis-cylinder process, 837
Axolotl, 439
Axon, 100, 837
Bahirusa, 571, 601
Bacteria, 17
Badger, 561
Balaena, 552, 597
Balaenoptera, 552, 597
Balanoglossus, 807, 308, 312
Balanus, 150, 205
Baleen, 552
Banded. ant-eater, 542, 643
Bandicoots, 542
Bank-vole, 580
Barbary ape, 589
Barbastelle, 584
Barbel, 407
Barbels, 366, 405
Barbs, 496
Barbules, 496
Barn-owl, 519
Barnacle, 161
Basement membrane, 303
Basi-branchial plate, 873
Basi-branchiostegal bone, 403
Basi-lingual cartilage, 444
Basilar segment, 164
Basipterygium, 375
Basisphenoid, 461
Bass, 410
Bastard wing, 501
Bat, 495, 582, 688
Batoidei, 381, 383, 411
Batrachia, 440
Bdelloida, 637
Bdellottoma, 866
Bear, 560
Beaver, 579, 581
Bed-bug, 189
Bee, 181, 183, 188
Beetle, 183, 185, 187
Bettongia, 642, 544, 596
BUe, 348
Bile-duct, 848
BUl-fish, 897
Biogens, 4
Biology, definition of, 1
Bionomics, 9
Bipalium, 607
Biramous, 149
Birds, 495, 518
Birtb, 546
Biseriate, 374
Bisexual, 7
Bison, 577
Bivalves, 215, 217, 220, 222, 224
Black bear, 561
Bladder, 422
Blanna, 557, 598
Blind-worm, 476, 476
Blood, 128, 352, 353
Blood-sucking Bat, 584
Blue-bottle, 189
Body cavity, 83
Bombinator, 450, 455
BombuM, 188
Bomhyx, 184, 186, 190, 208
Bone, 333; evolution of, 888
Bo$, 602
Bot-fly, 189
Bothriocephalut, 623
Botryllus, 880, 331
Bougainvillia, 68, 58
Bovidae, 574, 576, 601
Bow-fin, 396
Box tortoise, 486
Box turtles, 486
Brachial ganglion, 242
Brachial plexus, 449
Brachiopoda, 291; distribution and
classification of, 295
Brachium, 418
Brachyura, 155, 206
Bracts, 59
Bradypodidae, 546, 548, 596
Bradyptu, 596
Brain, 334, 375, 448, 507
Branchellion, 111, 114
Branchiae, 110, 259, 260
Branchial arches, 372
Branchial basket, 363
Branchial coelomic canals, 815
Branchial hearts, 241
Branchiopoda, 146, 205
Branehio$aunUt 425, 454
Branchiostegal rays, 401
Branchiostegite, 136, 158
648
l^NDEX.
Branehipus, 143, 144, 146, 205
Breathing, 4
Brill, 409
Brittle-stars, 249, 261, 862, 263, 264,
260
Bronchi, 512
Bronchial tubes, 468
Brook-trout, 408
Brown bear, 561
Brown-body, 299
Bubalua, 678
Buocal-cavity, 87
Buccal mass, 217
Buccal membrane, 250
Buccal tube-feet, 272
Buceinum, 215, 246
Buds, 50
BufFaJo, Cape, 678; American, 577
JBii/o, 441, 442, 444, 452, 455
Bufonidae, 441, 452, 455
Bug, 181, 189
Bugulttt 800
Bulbus arteriosus, 397
BuU-frog, 453
Bull-head, 407
Bunodont, 570
Bunodontia, 570, 601
Bursa Fabricii, 514
Butterfly. 180, 183, 184, 190
Byssus, 232, 233
Caddis-fly, 185, 187
Caeca, 113
CaenoUateSf 543, 595
Caflre cat, 5o9
Caiman, 468, 491
Ca'ing whale, 661, 552
Cake-urchin, 277
Calamoichthys, 393
Calcaneum, 490, 533
Calcarea, 79
Calcareous substance, 23
Calciferous glands, 93
CallorhynchuSf 387
Calycophoridae, 59
Calyptoblastea, 72
Cambarus, 157
Camel, 574
Camelidae, 574, 601
Camelus, 574, 601
Canaliculi, 334
Canals of Laurer, 615
Cancer, 206
Canidae, 560, 598
Canis, 628, 624, 626, 680, 669, 560, 598
Capillaries, 353
Capillary, 96
Capillitium, 26
Cajpreolus, 611, 601
Caprimulgtu, 519
Carapace, 142, 191, 481
CaraMtius, 407
Carbon dioxide, 4, 96, 352
Careharodon, 383, 411
Carcimu, 166, 206
Cardinal teeth, 226
Cardinal veins, 352, 877
Cardium, 233
Cariacua, 511, 601
Caribou, 576, 677
Carina, of Cirripedia, 150; of Atoi,
499
Carinatae, 517, 518
Carinella, 630
Carmarina, 06
Camassial teeth, 558
Camivora, 558, 598
Carotid arch, 432
Carotid arteries, 350, 376
Carotid gland, 433
Carp, 405, 407
Carpale, 419
Carpalia, 419
Carpus, 418
CartUage, 333
Cartilage bone, 388
Caryophyllia, 65
Cassowary, 516, 518
Castor, 579, 581, 602
CasuariuM, 516, 518
Cat, 559, 560
Catarrhini, 588, 603
Caterpillar, 184, 185, 190
Cat-fish, 405, 407
Cathartei, 518
Caudal vein, 352, 377, 431
Cave-newts, 439, 440
Carta, 579, 602
Cavicornia, 574, 576
Cebidae, 588, 603
Cehut, 588, 603
Ceeidomyia, 189
Cell, 27, 45
Cellulose, 26
Centetidae, 558
Centipede, 119, 122, 164, 166
Centra, 373
Central capsule, 23
Centrarchidae, 410, 416
Centro-dorsal ossicle, 283
Cephalic pits, 628
Cephalochordata, 310
Cephalopoda, 234, 248
Cephalopods, 222
Cephalo-thorax, 123, 136, 191
Cephalothrix, 630
Cerato-branchial segment, 372
Ceratodus, 387, 888, 889, 890, 391,
412
Ceratohyal, 371, 401
Ceratopkrys, 455
Ceroariae, 618
INDEX.
649
Cerci anales, 173
Gercopitbeoidae, 588, 604
Cerebellar lobes, 375
Cerebellum, 336, 364, 507
Cerebral ganglia, 217
Cerebral hemisphere, 336
Cerebratulus, 629, 630
Cerebrum, 336
Cervidae, 574, 576, 601
Cervus, 577, 601
Cestoda, 606, 618, 625
Cestracion, 372, 383
Cestum, 72
Cetacea, 549, 550, 597
Chaeta-saos, 91
Chaetae, 90
Chaetognatha, 302
Chaetopoda, 109, 116
Chaetosoma, 305
Chaetosomatidae, 642
Chamaeleo, 469
Chambered organ, 285
Charadrilformes, 519
CkaradriuSf 519
Cheese-mite, 198, 199
Cheilostomata, 301
Cheiroptera, 582, 602
Cheiropterygium, 369, 418
Chelicerae, 190, 192
Chelone, 482, 483, 484, 486, 494
Chelonia, 459, 481, 494
Chelonidae, 486, 487
Chelydra, 487
Chelydridae, 486, 487
Chevron bone, 460
Chevrotain, 574, 676
Chick, 341
ChUopoda, 163, 164, 207
Chimaera, 839. 386, 886, 387, 412
Chimpanzee, 590
Chipmunk, 579, 582
Chitin, 18, 119
Chiton. 246
Chlamydospores, 26, 89
Chlamydothorax, 308
Choana, 387, 424, 488
Choanocytes, 75
Chondrin, 204
Chondriodermay 26, 40
Cbondrostei, 395, 413
Chorda-centra, 394
Chordal sheath, 311
Chordata, 306
Choroid coat, 341
ChorophiluSt 453, 455
ChrysemySf 486
Chrysochioridae, 557
Chylific ventricle, 174
Cicada, 189, 208
CiconUif 518
Ciconiiformes, 518
Cilia, 29
Ciliata, 27, 41
Cingulum, 633
Cinostemidae, 486
Cinostemum, 487
Ciona, 887, 828
Circular canal, 52
Circulatory system, of Amphibia, 421,
431, 446; of Arthropoda, 184; of
Ayes, 508; of Cephaloohordata, 821;
of Cephalopods, 241; of Craniata,
349, 861, 364; of Dipnoi, 390; of
Elasmobranchs, 376 ; of Mammals,
533; of BeptUes, 470, 484
Cirri, 283
Cirripedia, 150, 205
Cirrus, 109
Cittudo, 486
Civet-cats, 562
Cladocera, 146, 205
Cladoselache, 375, 385
Clam, 224, 233
Chisper, 375, 381
ClasseH, 9
Classification, 9
Clava, 56
Clavicle, 389, 399, 445
Clepsidrina, 88, 39, 41
CUpsine, 112, 115, 117
Clitellum, of Lumbricut, 91, 108; of
Hirudo, 112
Cloaca, 279, 360
Clupea, 408, 414
Clupeidae, 405, 408, 414
Clypeaster, 289
Clypeastroidea, 277, 289
Cnidoblast, 48
Cnidocils, 48
Coccidea, 39
Coceidium, 41
Coceinella, 187, 208
Coccygeo-mesenteric, 511
Coccyx, 502
Cochlea, 340
Cockchafer, 123, 129, 130, 186
Cockle, 224, 233
Cockroach, 168, 183, 184, 186; ecdysis
of, 122
Cocoon, of cockroach, 179 ; of Hirudo,
112; of Lumbricus, 106, 107; of
silk-worm, 184, 186
Cod. 898, 408, 409
Coecilia, 454, 456
Coelenterata, 42 ; classification of, 72 ;
general shape of body of, 87
Coelenteron, 43
Coeliac artery, 376
Coelom, 83, 605; of Annelids, 109,
113; of Arthropods, 125, 177; of
Brachiopods, 292, 295 ; of Cephalo-
chordata, 318; of Chaetognatha,
€50 JNO
803 ; of Echiiiod«nni, S51 ; of Hemi-
oboidaU, 306; of HoUiiHa, SIS; of
TertebniM, SS5
CoeloDwUi, SS
Coelomic uvitj, 88; in Aithn>podB,
196; in Lumbrieut, 91; in leeohM,
118
Codomia groovet, 812
Coelomio flnid, 98, 09
Coelomia nervoDB ayilem, 358
Co*IoiuodiicW, 3-21
Coe,mn.>, 6-2->, fiSa
CoUopMra, 180, ISS, 187, 308
Collftr. 76, 3oa
CoUsr-ciivitieB, SIS. 866
Collar «1U. 76
Oollu pore, 806
CollAteralB, 100, 337
CoUeterisl gUuds, 173
Colon, 174
Colon;, Coelenterate, 50, Bi, M, 63;
PoljEosn, 897
Colnbridae, 479
Cabimia, S06, SID, B14. G19
Colnaiellfl, 463
ColamelU auria, 411, 528
Columellar cbain. 441
Coljmbi formes. 518
Colymhai, SIB
Com&tulldoe, 2K3
CommiBBuros, 100, 317
CDDinioa ciirotid, 433
Compoand Ascidi&ns, 381
Camponnd «;e8, 181
CondjlBB, 431. 606
Condylma, 567, 698
Cone-eel la, 343
Cone;, 664
Conger eel, 408
Conjugation, 7; in Vortieetia, 33; in
Paranmium, 35
Connectire tissue, 104, 136, 374, 833,
833
CoQBcioUHDeita. 2
ConuR arteriosus. S49, 850
Coni-olufa, CI
Co-ordinated parts, 31
CopeUts, 8ao
Copepoda, 147, 306
Copalatory sacs, 479
Copulfttoty BpiculcB, 6*1
Coraciai. 51il
Co racii formes. 619
Coraooid, 399, 438, 466, 5S3
Coracoid cartilage, 438
Coraeoid fontanelle, 466
Coral, 64. lIS
Coral iBLind!-, 66
Coralline Crag, 800
Corallam, 66
Coregonui, 408
ComM, 848
Corona, 3B8
Conmelia, 479
CoroDoid, 466
Corpus callosnin, 680
Cortioal Uyar, 39
Cortioal SODS, 618
Cortioata, 40
Connu, 619
Coatal platea, 481
Costal process, 498
Coverts, 499
Coxa, 173
Ooial gUnds, 140, 166
Cnb*. 166, IH
Crane, 619
Crania, 991, 394, 896
Cranial bones, 887, 899
Cranial nsrres, 844
Craoiata, 833
Cray-flih, 130, ua, 188; Md7si«of,Ul
Crested uewt, Ul
Cribriform plate, 681
Cricket. IMfi
Cricoid, 469
Cn'CDCui, 493
Crinoidea, 389, 388
Crocodiles, 469, 474. 487
Crooodilia, 459, 466, 487, 493, 494
Crocodjiiu, «B*, 4M>, 491, 4M, 494
Crop, 87, 93, 113, 173, 917, 613
Cross fertilization, 107
Cro»soptPi7Rii, 393, 413
CroUlina^, 481
!a!„/.
I, 494
Crow, 519
Crural gland, 161
Cms, 416
Crustsoea, 118, 143, 904
Cnji.l.:h,-micl.>,>. 438, 464
CrTstalline cone, 133
Ctenidium. 913, 337, 238
Ctiiinid BcUes. 410
Ctenophora, 69, 78
Clenoptana. 613
ri,.„<>htn|,l,lU, 801
Cnckoo, 619
Cnolioo-spit, 189
Cuooliforniei', 519
Cucula; 519
Culri, 189, 208
Ciinio, 2(tB
Cnmacea, 16S, 158, 906
Cnnores, 516
Cotaneoos artery, 434
Cuticle. 29, 91
Cuttle-fish, 910, 313, 915, 317, 319,
330, 334
Cnrierian organs, 281
CycUu, 218
INDEX.
651
Cycloid scales, 389
Cyclopia 148, 149, 160, 205
Cjdostomato, 301, 338, 360
Cygntu, 518
Cymotrichi, 591
Cynips, 188
Cynomyi, 582
Cypridina, 147, 205
Cyprinidae, 405, 407, 414
CyprinuSt 414
CyprU, 147, 205
CypseluSf 519
Cyst, 16, 25, 39
Cysticercoid, 622
Cyitieereui, 622, 623
Cystignathidae, 455
Dab, 409
Dactylozooids, 59, 65
Daddy-long-legs, 189
Daphnia, 144, 146, 205
Dart-sac, 221
Dasypodidae, 546, 549, 596
Dasyputt 547, 596
Dasyuridae, 542, 595
"Dead men's fingers," 59
Decapoda, 155, 206, 248
Deer, 574, 676
Defaecation, 5
Degeneration, 11
DelphinapteruSt 552, 597
Delphinutf 662
Demospongiae, 80
Dendrites, receptive and terminal, 100,
337
Dendrochirotae, 282
Dendrocoelida, 611, 624
Dendrocoelum, 612
Dental formula, 627, 560
Dentalium, 247
Dentary bone, 396, 403, 428
Dentary plates, 386
Dentinal canals, 370; pulp, ih.
Dentine, 369
Dermal branchiae, 259, 260
Dermal glands, 421
Dermal layer, 75
Dermis, 103, 126, 344, 496
Desman, 556, 557
Desmodu8f 584
Desmognathinae, 439
Desmognathous, 517
Desmognathus, 426, 439, 454
Development, definition of, 7
Diaphragm, 636
Diapophyses, 442
Diastema, 578
Diastylu, 158, 206
Dibranchiata, 248
JHcotyUs, 571, 601
Dicynodontia, 493
Didelphyidae, 542, 594
Didelpkys, 542, 595
DiemyctiluSf 439
Di£ferentiation, 11
Difflugia, 18, 40
Digenea, 617, 625
Digestion, 5
Digestive ferments, 5, 348, 849, 537
Digestive juice, 49
Digestive system, of Birds, 512; of
Echinoderms, 253 ; of HeUx, 215 ;
of Platyhelminthes, 609, 611, 615,
616; of Vertebrates, 348
Digits, 418
DinomUt 616
Dinosauria, 493
Dinotheriuntf 566
Dtodon, 411, 416
Diomedeay 518
Diphycereal-fin, 864; -tail, 890, 897
Dipleurula, 287
Diplopoda, 163, 167, 207
Dipnoi, 369, 387, 412
Diprotodontia, 541, 543, 595
Diptera, 181, 183, 185, 189, 208
Disc, 29, 249, 631
Discoglossidae, 465
DiscoglosstUt 466
Discontinuous distribution, 162, 568
Distal, 87
DUtoma, 614, 616, 617
Diver, 618
Docidophrynet 446
Dog, 623, 624, 626, 630, 609, 560
Dog-fish, 381, 383; see Seyllium
Doli€hoglo$8U8f 807, 308
Dolphin, 662
Donkey, 570
Dorcatherium, 676
Dormouse, 579, 681
Dorsal, 88
Dorsal blood-vessel, 96
Dorsal sac, 238
Dorsal tubercle, 326
Down, 496
Draco, 476
Dragon-fly, 120, 121, 183, 187
Dromaeognathous, 617
Dromaeus, 616, 618
Duck, 602, 616, 517, 518
Duckbill, 638, 689
Ductus arteriosus, 635
Ductus Cuvieri, 352
Ductus ejaculatorius, 179
Ductus endolymphaticus, 839
Dugong, 664
Duplicidentata, 579, 602
Eagle, 518
Ear, 56; outer, 459; of Gasteropod,
219; of Vertebrates, 889, 840, 863
652 iSB
£BC-c[>ckleB, tun
Ear-abell, 21D. 3«, 33a, 228
Eared Beals, 5GS
Esrtb-pig, 54U
Earthwoim, 69 ; British tpceiaa of, 108
Earwig, IHS. 1h6
EoardiDes. 2it6
EcdjaU, 1-21. IHO, 458
Eeluhu, 408. 414
£fh<(ln<i, &3T, S39, 694
£ch<n«rachniu,. 378, 389
Eehinaitir, 21!), 3W, >M, 389
Echinoeardiam, 378
£ehinoeocfU(. 623, 638
Mchiaoeyamui. 278, 389
Echinodennala, 349; olsaaifleatioti of,
288
BohinoideB, 366; BabdiviuoDs of, 277,
289
Eehimu, U», 3S9, 370, 3T8, STE, STT, 389
Eolodenn, 46
EcloploBm, 14, 17
EctoprooU, 301
Bctopterygoid, 401, 46fi
Edentata, 646. 596
Eels, 405. 407
EffflreDt, 76
Effodientia, 649, 697
Eft, 431
EgK-«il. 4tl
EggB.of IJirdB. ol6; of Clodooen, 144;
of CockroucJi, 179; of T«l«ostonii,
40G
Egg-aaca of Copepoda, 149, 160
Elapidae, 480
Elaps, 480
I ; classification of.
Elssipoda. 2»2
ElaHimilirauchii,
383, 411
ElattT, 119
ElephaDt, 564, 6fi6, 5M
Elephat. 6S5, 061, 600
Eleatberozoa. 288, 389
Elk, 677
Elytra, 173, 183
Embrro, definition of, 8; of Amphi-
oxui, 313, SIH; of SeuUmm, m
Emeu, £10, 519
Emydidae, 48fl
Enamel, 370
Enaiuol ortton. 527
EncTStmeut, 16
End'oCTclira. 377, 289
Endndi'tiH. 45
Bndodermal lamella, 63
Endoplasm, 14, 17
Endopodite, 148
Endoskeleton. 204
EndoBteniiCe, 204
EndoBtytar ooelom, 316
Endoatyle, 319. 825, 339, 347
EndotheliuDj, 353
Engyftoma, iM
Engystouialidae, 466
EnopU, 630
EnteropneuBta, 307
EnlomolORy. 1G8
EctomoetrDca. 112. 204
EntoptiLBtron. 481
EntuprwU, 301
Eotopterjgoid, 401
Enzymes, 348
Eponorthidae, 543, 595
Epeira. IM. 1B3. 193, IM, 196, 196, 908
Epktmtra, 187, 308
Ephippiam, 146
Ephydalia, 80
Epbyra, 69
G pi branchial Kegment, 373
E pi branchial lessels, 349
Epicbordol, 443
Epicoracoid, 444, 466
Epidermal, 496
Epidermis, N7, 103
Epididymis, IJ5, 379. 478
Ept neural canal, 363, 368
EpioCic. 400. 463
Epipbyaca, 373, 531
Eplplastra, 481
Epipterjgoid, 463
Epipnbis, 439
Episteraam, 446
Epistome, 398
Epithelial. 49
Epitricbial layer, 458
EquidsB, 668. 669, 600
Equut, MT, 669, 600
EreUiiion, 679, 682. 602
Erinaceidte, 666, 597
Eri»aefui. 556. 397
Ergopi, 493
Ethmoid region, 371. 399, 401
EthmotarbinalH, 531
Eufflaut, 35, SB, 4!
Euglenoid, 36
EalaraeUibroDchiata, 348
Euphautia, 155
Eurnpterina, 304
Etucorpiiu, ISl
Evipongia, 80
Eustachian pouch. 441
Entheria, 687, 544, 506
Eutbyoeara, 247
Evolation, 11
Excreta, 4
Eicretion, 4
Excretory organ, 98
Excretory ayttem. of Aithropodi, 1S9,
196; of Lumbrieiu, 97; of Flatj-
helminthee, 606, 609, <1«, 617 ; of
Botifert, 634 ; of Tntebratei, S30,
S6T, >W, 435, 460
INDEX.
653
Ezhalant, 79
Exoocipital bones, 387, 427
Ezopodite, 148
ExoskeletoD, 119, 121
Extensor mascle, 129
Extrarbranchials, 373
Exumbrella, 52
Eye, of Arthropods, 130, 181, 154, 178,
196; of Lizzia^W; of Mollnscs, 212,
242; of Vertebrates, 341, 366, 363
Facial nerves, 345
Faeces, 349, 587
Falciform embryo, 39
Falcon, 518
Falcomformes, 518
Fallopian tnbe, 539
Fallow-deer, 577
Families, 9
Fascioles, 278
Fat-body, 173
Feathers, 496
Feather-stars, 249, 288, 284, 286
Felidae, 598
Felis, 559, 560, 598
Female, 7
Femoral vein, 431
Femur, 172, 418
Fenestra ovalis, 528
Ferments, digestive, 5, 348, 349, 537
Ferret, 561
Fertilization, 50
Fiber, 682, 602
Fibres of MfiUer, 342
FibrUs, 29, 103
Fibula, 419
Fibulare, 419, 533
Field-mouse, 580
Field-vole, 580
Filaria, 643
FiUbranchiata, 247
Fins, 237, 364, 368, 874, 876
Firmistemia, 452, 453, 456
Fishes, 368
Fish-Uce, 150
Fission, 7, 16 ; in Vorticellat 31 ; in
Hydra^ 50
Fissipedia, 562, 598
Five-fingers, 249
Flagellata, 35, 41 ; reproduction of, 37
Flagellated chambers, 79
Flageliula, 26
Flagellum, 23, 26, 35 ; of Helix, 221
Flame-cell, 606
Flamingo, 518
Flea, 183, 189
Flexor muscle, 129
Flight of birds, 501
Flocculi, 530
Flotcularia, G31, 682, 688, 637
Flounder, 409
Flowers of tan, 16, 24
Fly, 181, 183, 189
Flying-foxes, 584
Flying-squirrel, 580, 681
Fontanelles, 399
Food, of animals and plants, 2
Foot of Molluscs, 211, 212, 284
Foramen magnum, 388
Foramen of Panizza, 491
Foraminifera, 18, 21, 40
Fore-gut, 133
Forficula, 186, 207
Formica, 187, 188, 208
Fowl, 608, 517, 519
Fox, 560
Fox-bats, 584
Fredericella, 301
Fresh-water mussel, 224
Fresh-water polyp, 42
Frog, 417, 441, 453
Frog-hoppers, 189
Frontals, 402, 426, 428
Fruit-eating Bat, 688
Fulcra, 396
Fulica, 519
Functions, 15
Fungia, 69
Funicle, 298
Funnel, 71, 234, 236
Gadidae, 409, 415
OadiM, 898, 408, 415
Galea, 171
Galeopithecidae, 554
GaUopithecus, 554
Galeus, 383
Gall-bladder, 348
Gall-fly, 188, 189
Galliformes, 519
Gallus, 608, 519
Game-birds, 517, 519
Gammarus, 136, 169, 206
Ganglion, 100
Gannet, 498, 518
Ganoidei, 393, 397, 413
Gapes, 643
Gar-pikes, 397
Gasteropoda, 211, 223, 246
Gastral filaments, 66
Gastral layer, 75
Gastrozooids, 59, 65
Gavial, 492
Gavialis, 492, 494
Geckos, 465
Gemmation, 7 ; in Hydra, 50
Gemmiform, 269, 271
Generative openings, 90
Genio-hyoid, 424
Genital bursae, 266
Genital openings, 89
Genital rachis, 260
G54
0«Dibtl stolon, 360
QenitiTe organa, 56
Q«niu, 9
Oamemertu, 637, 630
Germ, 7
Oerm&rium, 610, flSfi
Oenniniil bandi. M
OeatatioD, 646
Gmotfibree. 104, S17
(iibboDS. SUO
(^l-buH, 366
Oill-bookfl, 137, m. 191
Oill-oi
', ISl
OiU-pUte, 228
GUl-rajs, 873
Gilla, of ArthropodB. 13S, 136, 1S8 ;
of BtaMhellion, 111 ; of Echinoids,
276: of ElasmobruichB, 873; oC
10; of Helix, 312 j of
NiTti,
110
Onenland leal, 663
Green turtle, 463, 48t, 4U
QtKj teal, G64
Grey eqniirel, 680
GtippiuK oeU», TO
OrisEly bear, 561
Gromia. 18, 10, 10
GroUDd-squirrel, 378, 683
Groape. 519
Growth, 6, 6
Grabs, IBS
Qmitormes, 619
Onu. S19
Gnjiliu. lefl. 207
Guilgeoii, 4U7
Guiiiea-pis- 579
Gull, my. Sl<l
Gullet, 60, 347
Gamarda, 410
Gill-BlitB, 306, 309, 313, 346, 863
GUl-ti
I, 279
airaffa, 676, (
Giraffe. 674, 676
Glraffidae, 674, 676, 602
Giizard. 87, 93. 174. 518
Gland. 6
OlMa-aaake, 476
Glenoid cavity. 428, 406, 526
Globicfphalui, «S1, S62, 697
Globigtrina, 40
OlobigfTMui Oifin. 34
Glochidia. 232
QlomeralUK. 30S, 368, 869
Qlottinat IBS
QlBuobaUinui, 30i^, S09, 310
Gionohj'al. 401, 606
Glosaophaiyngcal uerve, S46
QlottiH, 421
Oljcogen. 3.lfi
Gnat, 181, 189
GoathiteB. 126, 170, 160
ODatbubatita. 125. 171. 190
GiiatiiobaelHdi.e, 113, 115
GnatlioBtumata, 360, 366
Goat. 577
GobiiJae. 410
GobUt-celln. 103
Golden mule, 657
Gold-fiBb, 407
Oooads, 66
GonophorcB, 57
Goose. 618
Gopher, 486
aorilla, US, 590. 601
GrallaloreK. 510
Grampus, 552
Graiiiia, 78, 7!)
GraBBhorper, 183, 183, 166
Orebe, 618
Green-glaud, 139
Oj-n,
Gym,
lobla-
., 301
. 556
Haddock, 409
Baemal Arches. 334, 373
Raemamatba, 39. 41
Hnemocoel, 12C, 3iA
Haemoglobio, %. 362
Ha.
39
Hag-fish, 363. 366
Hair. 520
Halecomorphi, S96, 118
Halihut, 409
Haiicharna, S64
Balicort, 654, 097
HaliotU, 319, 330, 332, 338, 346
Hnllui, 446
HaltereH, 183. 1B9
Hammerhead ehatk, 869
Hafiilf, 603
Hapalidae, 6S8, 603
Haptocerot, S77, 603
Hard palate, 626
Hare, 579
HarleqniD snake, 480
Harriotta, 387
Han*e>ilmcii. 123, 191, 1»T
Havecaian caualx. 334, 369
Hawk, 617
Hfftd, 87, 16*. 504
Head-cavity, 312. 366
Heart, 134. 31<J. 350; of Lt(mMciu,96
Heart- urcbinB. 273
Hedgehog, 6Sf>
lUliarpliacra, M, 40
Heliozoa, 36. 40
Helix, 311, 318, 31«, 310, Sl«, >U, 347
Hell-bender, 464
Hemerobiiu, 187
INDEX.
655
Hemiazygos, 536
Hemiohordata, 307, 323
Hemiptera, 181, 183, 184, 188, 208
Hepatic diverticula, 174
Hepatic portal system, 352
Hepatic vein, 352, 377
Heredity, 8
Hermaphrodite, 7, 90
Hermaphroditism, 221
Hermit-crab, 156
Heron, 518
Herrings, 405, 408
He$perorniSy 515, 518
Hessian-fly, 189
Heterocercal tail, 374, 397
Heterocoela, 79
Heteronemertini, 630
Hexactinellidae, 79
Hind.gut, 183
Hinge, 224, 225
HippocamptUf 410, 416
Hippoglo88U8f 409, 415
Hippopotamidae, 570, 601
HippopotamuSf 570, 601
Hirudinea, 111, 117
Hirudo, 111, 114, 115, 117
HirundOf 519
Hog-water loose, 128, 160
Holocephali, 369, 385, 412
Holothuria, 280, 290
Holothoroidea, 279, 290; subdiviBions
of, 282
Holotrichous, 33
Hominidae, 588, 604
Homo, 588, 604
Homocercal tail, 397
Homocoela, 79
Homoiothermal, 522
Homology, 12
Homoplasy, 12
Honey-bee, 188
Hoof, 564
Hoopoe, 519
Hormiphoraj 70, 71
Homed *' toad," 476
Hornet, 188
Horse, 667, 569
Horse-fly, 189
Horse-shoe Bat, 584
Host, 38
House-fly, 181, 189
Huanaco, 576
Humble-bee, 188
Humerus, 418
Hybrid, 8
Hydatina, 636, 638
Hydra, species of, 42, 43, 44, 46, 47,
49 ; cell of, 45 ; reproduction oif, 50
Hydractinia^ 59
Hydranth, 54
Hydra-tuba, 68, 69
Hydrida, 72
Hydrocoele, 287
Hydrocorallinae, 58, 59, 65, 78
Hydroid person, 54, 57, 59
Hydromedusae, 50, 72
Hydrozoa, 72
Hyla, 442, 453, 455
Hylidae, 452, 453, 455
HylohaUt, 590, 604
Hymenoptera, 181, 183, 185, 187, 208
Hyoid, 360, 371, 427
Hyoidean artery, 377
Hyomandibular, 371, 392, 395, 401
Hyoplastra, 481
Hyostylic, 372
Hyperpharyngeal groove, 319
Hypo-branchial segment, 372
Hypogeophis, 454, 456
Hypoglossal nerve, 435, 458
Hypohyal, 401
Hypopharyngeal groove, 319, 327
H3rpopharynx, 181
H3rpoplastra, 481
Hyracidae, 564, 599
Hyrax, 564, 666, 599
Hystricidae, 581
Hyttrix, 579, 602
Ichneumoti, 188
Ichthyodorulite, 386
Ichthyoidea, 438
IchthyopMs, 454, 456
Ichthyopterygium, 369
Ichthyomis, 515
Ichthyosauria, 493
Ictalurus, 407, 414
Iguana, 466
Iguanidae, 476
Ilio-ischiatic foramen, 504
Ilium, 429, 533
lUex, 236
Image, 131
Imago, 184
Impulses, 337
Incus, 528, 634
Indian ink, 242
Infundibular ganglion, 242
Infundibulum, 347
Infusions, organisms in, 17
Ingestion, 5
Inhalant, 79
Ink-bag, 242
Innominate artery, 533
Insecta, 119, 168, 207
Insectivora, 554, 597
Insessores, 516
Intercalary piece, 373
Interoentra, 460
Interclavide, 466
Intercoelic membrane, 315
Intercostal muscles, 467
656
INDEX.
Interfilamentar janctions, 228
Interhyal, 401
Interlamellar junctionB, 228
Intermedium, 419
Inter-operculum, 387
Inter-orbital septum, 886, 462, 505
Interparietal foramen, 474
Interradii, 249
Interstitial oells, 46
Inter-tarsal joint, 467
Inter-tentacular organ, 299
Intestine, 87, 348, 349
Invertebrata, 13
Iris, 243
Irritability, 6
Isohiopubic cartilage, 429
Ischium, 429, 583
Isopleura, 223, 246
Isopoda, 160, 206
lulus, 119, 167, 207
Ixodidae, 199
Jackal, 560
Jack-rabbit, 580
Jaw, 272, 366, 871
JeUy, 48, 52, 62, 77, 108, 358
Jelly-fish, 54, 66
Jugal bone, 403, 465, 505
Jugular, 405
Jugular- vein, 431, 508
Jnmping-shrew, 656
Kangaroo, 544
Kangaroo-rat, 642, 544
Katabolism, 4
Keber's organ, 231
Kidneys, 97
King-crab, 137, 138, 201, 202, 208
Kingfisher, 519
King-salmoD, 408
Kiwi, 516, 518
Krohnia, 305
Labial cartilages, 361, 373
Labial palp, 171, 229
Labium, 170, 171
Labridae, 410
Labrum, 170
Labrus, 416
Labyrinthodonta, 422, 425, 444, 454
Lacerta, 459, 472, 476, 494
Lacertilia, 459, 476, 494
Lachrymal, 465, 525
Lacinia, 171
Lacunae, 334
Lady-bird, 187
Lamella, 228
Lamellibranchiata, 215, 224, 247
Lamprey, 361, 362, 868, 365
Land nemertiucs.
Land-newts, 439, 440
Land-reptiles, 493
Land tortoises, 486
Languets, 329
Langur, 589
Lantern coelom, 276
Large intestine, 349
Lark, 519
Larus, 519
Larva, 8; of Acalephae, 66; of Am-
phibia, 422, 437, 451, 452; of Ces-
toda, 622; of Echinoderms, 287;
Ephyra-, 69 ; of Holothorian, 886;
of Hydromedusae, 66, 57; of In-
sects, 184, 187; of Lamprey, 365;
of Nematodes, 648; of Nemertines,
628; of PenaeuSj 186; of Sponges,
80; of Teleostomi, 405; of Trema-
todes, 617; of Tunicata, 325; of
Turbellaria, 612
Larvacea, 330
Larynx, 469, 511
Lateral-line, 346; -process, 467; -tooth,
226; -vein, 377; vessels, 96
Latero-temporal fossa, 465
Leeches, 111
Leiotrichi, 592
Lemur, 586, 687, 603
Lemuroidea, 586, 603
Lens, 130, 343
Leopard, 560
Lepas, 161, 205
Lepidoptera, 180, 183, 185, 190, 208
Lepidosiren, 887, 391, 412
Lepidosteidae, 397, 413
Lepidosteus, 392, 413
Lepisma, 186, 207
Leporidae, 579
Leptocephalus, 408
Leptostraca, 153, 205
Lepug, 629, 632, 678, 679, 602
LeueUcuSy 406
LeucosoUniaj 74, 76, 76, 81
Levatores, arcuum, 372, 424
Libellula, 187, 208
Lice, 189
Lieno-gastric artery, 376
Life, 1, 3
Ligula, 171
Lily-encrinites, 282
Limbs of Amphibia, 418
Limicolae, 108
Limnaea, 211, 219, 617
Limpet, 215, 216, 222
Limiilus, 137, 188, 191, 201, 208, 808,
204, 209
Linem, 626, 627, 620, 630
Lingual cartilage, 361
Lingula, 291, 292, 294, 295, 296
Lion, 560
Lithobius, 119, 122, 164, 166, 207
Liver, 86, 217, 320, 348, 351
INDEX.
657
Liver-fluke, 617
Lizard, 459, 461, 462, 471, 476, 476;
scale of, 408
Lizzia^ 60
Llama, 576
Lobosa, 18, 40
Locomotor organ, 6
Locttsta, 186
Loemanctus, 461
Loggerhead tartle, 482
LoUgo, 234, 245
Long-eared Bat, 584
Longitudinal valve, in Rana^ 447
Lophobranchii, 409, 410, 416
Lophophore, 293, 298
Lower temporal arcade, 465
Ltucanusy 180
Lumbar vertebrae, 536
Lumhncus, 89, 90, 93, 94, 99, 102, 100,
116; British species of, 108
Lung-books, 138, 191, 193
Lung-fish, 387, 391
Lungs, 387, 431, 511
Lutra, 561, 599
Lymph, 441
Lymphatic system, 353
Lymph-hearts, 441
Lymph-spaces, 441
Lynx, 560
Macaeus, 589, 604
Mackerel, 410
Macropodidae, 544, 596
Macroputj 544, 596
Macroscelidae, 555
MacroscelideSf 000
Macrura, 157, 206
Madreporio vesicle, 261
Madreporite, 256
Maggots, 185
Malaeobdella, 630
Malacostraoa, 142, 152, 205
Male, 7
Malleus, 528, 634
Malpighian capsules, 359
Malpighian layer, 421
Malpighian tubules, 140, 166, 176,
178
Mammalia, 367, 520 ; classification of,
537, 594; fossil representatives of,
592
Mammals, 467
Mammary glands, 522
Mammoth, 567
Man, 586, 588, 590
Manatee, 008, 554
Manatus, 008, 554, 597
Mandible, 124
Mandibular-arches, 850 ; -bar, 371 ;
-cavities, 356
Manidae, 547, 597
S. <fc M.
Manis, 048, 549, 597
MantU, 186
Mantle, 210
Mantle-cavity, 210, 212, 228
Manubrium, 54
Manus, 418
Manyplies, 572
Marginal canal, 52
Marginals, 481
Marine mammals, 549
Marine turtles, 486
Marmosets, 588
Marmot, 579, 582
Marsipobranchii, 365
Marsupials, 540
Marten, 561
Mastax, 631
Mastodon, 565, 566
Ma»todonsauTU8i 464
Maxilla, 124, 193, 396, 403, 465, 504
Maxillary- bone, 396; -glands, 139;
-palp, 171
Maxillipedes, 124
Maxillo-turbinal, 531
May-fly, 187
Meatus auditorius extemua, 525
Meckel's cartUage, 371, 463
Median fin, 423
Median vagina, 540
Medulla oblongata, 336
Medullary plate, 306
Medusa, 02, 54
Medusoid person, 54, 59
Megalospheric form, 23
Megapodes, 517
MeUs, 561, 599
Melontha, 128, 129, 130, 186, 208
Membrana semilunaris, 512
Membrana tympaniformis interna, 512
Membrane bones, 389
Menopoma^ 438, 454
Men turn, 171
Mephiti$, 561, 062, 599
Mesenteric arteries, 376
Mesenteric filament, 63
Mesenteron, 134
Mesentery, 60, 63, 64, 253, 356, 435
Mesethmoid, 396
Mesoblast, 84
Mesocoracoid, 466
Mesoderm, 83, 85
Mesoderm cells, 80
Mesogloea, 48
Mesonemertini, 630
Mesonephric tubules, 359
Mesonephros, 379, 436
Mesophyterygium, 376
Mesoscapula, 466
Mesosoma, 123. 190, 191
Mesostemum, 531
Mesostoma, 607^ 608
42
658
INDEX.
Meso-thorax, 171
Metabolism, 3
Metacarpals, 497
Metacarpus, 418
Metamorphosis, 184, 826
MetaDemertini, 680
Metanephros, 881, 486
Metapterygium, 375
Metapterygoid, 401
Metasoma, 123, 191
Metatarsus, 418
Metatheria, 687, 539, 594
Meta-thoraz, 171
Metazoa, 18
Mioronudeus, 82
Microspberic form, 28
Midas, 608
Mid-gut, 184
Milk, 522
Millepore coral, 65
Mink, 561
Mites, 191, 198
Moa, 516
Mole, 556, 557
Mole-shrew, 557
Mo^e, 418, 420, 428, 426, 427, 428, 429,
480, 483, 484, 480, 486, 437, 439, 454
MoUusca, 210; classiiioation of, 246
Molpadidae, 282
Monkey, 586, 588
Monocystit, 39, 41
Monogenea, 617, 625
Moose, 577
Morphology, 9
Moachites, 234
Mo»chu$, 574
Mosquito, 181, 189
Moth, 183, 184, 186, 190
Mother-of-pearl, 225
Motor nerves, 344, 846
Motor oculi, 845
Motor peripheral nerve, 100
Mound-birds, 517
Mouse, 579, 580
Mouth, 31, 86
Mouth-angles, 265 ; -cavity, 87 ; -papil-
lae, 265
Mouth-appendages, of Astactu, 127 ; of
Oammarust 126 ; of Insects, 170, 171,
180
Movement, 5
Mucous canals, 346
Mucous glands, 221
Mud-puppy, 438
Mud turtles, 486, 487
Miiller's larva, 612
MulticeUular, 27, 45
Multiplication, 1, 5
Muridae, 579, 580
Mus, 580, 602
Mutca, 181, 189, 208
MuBcardiwu, 581, 602
Muscle, 6; of Arthropods, 128; of
Lamellibranchs, 226; of Urodela,
424
Muscle-cell of LumbrieuM, 108
Muscle-plate, 887
Musculo-cutaneous vein, 432
Musk-lamprey, 861
Musk-ox, 576, 6T7
Musk-rat, 582
Musquash, 682
Mussel, 210, 224
Mwtela, 561, 599
Mustelidae, 561, 598
Mustelut, 864
Mya, 283
Myoetozoa, 16, 24, 40
Myelin, 337
Mylo-hyoid, 424
Myocoel, 815
Myo-epithelial, 49
MyogaUy 666, 557, 598
Myotome, 313
Myoxidae, 579. 581
Myriapoda, 119, 168, 207
Myrmecohias^ 542, 648
Myrmecophaga, 596
Myrmeoophagidae, 546, 548, 596
Myrmelfo, 187
My»ig, 155, 206
Mystacoceti, 551, 552, 597
Mytilxu, 232, 247
Myxine, 366
Myxinidae, 865, 866
Myxomycetes, 25
Nacreous layer, 225
Narcomedusae, 58, 67, 72
Nans, 387, 424
Narwhal, 684
Nasals, 428
Natatores, 516
Natterjack, 441, 452
Natural selection, 10
Nauplius, 148, 153, 155
NauHlut, 177, 213, 228, 237, 244, M6,
248
Neapolitan coral, 65
Nebalia, 153, 164, 205
Neck, 122; of Birds, 508
Nectocalyoes, 58
Necturus, 438, 455
Nematocyst, 46
Nematoda, 639
Nemertinea, 626
Neonunia^ 247
Neomithes, 518
Nepa, 189
Nephelis, 115, 117
Nephridium, of Amphioxu$, 819, SSI ; of
Arthropods, 140, 177; of Craniatea,
INDEX.
659
358; of Hirudo, 112; of Lumbricw,
90, 97 ; of Molluscs, 222, 230
Nephrostome, 97
Nephrostomes, 360
Nereu, 109, UO, 116
Nerve-ring, 54, 56, 258
Nerves, 6 ; cranial, 344 ; Ist to 10th, 345
Nenrons system, of Arthropods, 129,
178, 195 ; of Brachiopods, 294 ; of
Gephalopods, 242 ; of Chaetognatha,
303; of Echinoderms, 257, 285;
functions of, 100; of Gasteropods,
217; ofHaliotU, 220; of Helix, 217,
218; of Lamellibranchiata, 232; of
Lumbrictu, 99 ; minute structure of,
336 ; of Nematodes, 641 ; of Nemer-
tines, 628; of Platyhelminthes, 609,
614,615; ofBotifers,635; o( Sepia,
241, 248; of Vertebrates, 309, 317,
325, 336. 344, 434, 472
Nervous threads, 54
Nervures, 182
Nests, 515
Neural-arches, 334, 373; -canal, 306;
-tube, 309
Neurenteric canal, 318
Neuroglia, 337
Neuron, 100, 336, 337
Neuropodium, 109
Neuropore, 325
Neuroptera, 180, 185, 186, 208
Newt, 417, 423, 439
Nidamental glands, 244
Nidicolae, 517
Nidifugae, 517
Nightjar, 519
Nipple, 522
Nitrogenous, 97
Nose, 888, 362
Notidanidae, 371, 383
Notochord, 86, 306, 308, 311
Notommata, 635, 638
Notommatidae, 634
Notonecta, 189
Notopodium, 109
Notoryctes, 543, 595
Notor}xtidae, 542, 543, 595
Nuchal plate, 481
Nucleic acid, 3
Nucleus, 14, 16
Nucula, 222, 232, 247
NyctiphaneXf 164
Obelia, 60, 61, 62, 58
Oblique muscles, 356
Obturator foramen, 467
Occipital bones, 396
Occipital region, 399, 400
Octopoda, 248
OcU^, 234, 248
Odontatpit, 871
Odontoceti, 551, 597
Odontoid process, 460
Odontolcae, 518
Oesophagus, 60, 87, 93, 347, 364, 865
Oestrus, 189
Okapi, 576
Okapia, 576
Olfactory lobes, 607
Olfactory nerves, 345
Oligochaeta, 108, 116
OHgoJophus, 197, 209
Ommatostrephes, 245, 248
Omostemum, 445
Onchosphere, 622
Oncorhynctts, 408, 414
Oniscus, 160, 206
Ontogeny, 12
Oecium, 299
Oostegites, 155
Opalina, 88, 41, 45
Opercular ^1, 392
Operculum, 297, 386, 387, 392; of
Limulus, 138
Ophidia, 459, 476, 494
Ophioglypha, 262, 266, 289
Ophisaurus, 476
Ophiuroidea, 261, 289
Ophthalmic nerves, 346
Opisthobranchiata, 221, 223, 247
Opisthocoelous, 397, 421
Opisthotic, 400, 463
Opossums, 542, 544
Optic-chiasma, 345, 399; -ganglia, 242;
-lobes, 336, 507; -nerve, 345; -thala-
mi, 434; -vesicle, 341
Oral-cartilages, 811 ; -cirri, 316 ; -cone,
42; -hood, 316; -plate, 286; -pole,
71 ; -tube-feet, 265
Orang-utan, 689, 590
Orbit, 356
Orbital ring, 402
Orbitosphenoid bone, 395, 400, 427
Oca, 552
Orders, 9
Organ of Corti, 340
Organism, 37
Organ-pipe coral, 65
Organs, 15, 27
Organs of Bojanus, 230
Omithorhynchtu, 537, 688, 689, 594
Oro-nasal groove, 371
Orthoptera, 180, 184, 186, 207
Orycteropodidae, 547, 597
OrycteropuSy 549, 597
Oscarella, 80
Osculum, 75
Osphradium, 220, 232
Ossicula auditiis, 528
Ostia, 134, 165, 175
Ostracian, 411, 416
Ostracoda, 146, 205
660
INDEX.
Ostrea, 233
Ostrioh, 504, 607, 613, 516, 518
Otana, 563, 599
Otariidae, 563, 599
Otocyst, 218, 244
Otolith, 325
Otter, 561
Ovary, 46; of LumbricuSf 105
Ovihos, 576, 677, 602
Ovidacal gland, 379
Oviduct, 106, 435
Ovit, 602
Ovotestis, 221
Ovum, 7; of Hydra ^ 46
Owl, 582
Ox, 574, 576
Oyster, 210, 218, 224, 233
Pachytylus, 182, 186
Palatal flap, 463, 469
Palatine bone, 401, 403, 428, 505
Palatine foramina, 525
Palatine plates, 386
Palato-pterygoid, 389
Palato-pterygo- quadrate bar, 371
Palp, 171
Palpal organ, 193, 196
Palpons, 59
Pancreas, 349
Pangolin, 648
Panther, 560
PapiUa, 522
Parachordals, 334, 364
Paragastric canals, 71
Paraglossa, 171
Paramecium^ 33, 34, 41; conjugation
of, 35
Para-oesophageal cords, 129
Parapodia, 109
Parasite, 613
Parasitic, 38, 613
Parasphenoid, 389, 396, 402, 426, 428
Parenchyma, 607
Pariasauria, 492
Parietal peritoneum, 104
Parietals, 402, 426, 428
Parotid glands, 512, 513, 537
Parrot, 619
Patser, 519
Passeres, 517
Passeriformes, 519
Patella, 215, 210, 222, 246
Patheticus nerves, 345
Paunch, 571
PavOf 499
Peacock, 499
Pea-urchin, 278
Peccary, 571
Pecten, 228, 233
Pectines, 199
Pectinibranchiata, 246
Pectoral girdle, 874
Pectoral mnscles, 499
Pedal ganglion, 242
Pedalion, 638
Pedicellaria, 301
Pedicellariae, 269, 269, 271
Pedipalp, 191, 198
Pelagic, 305
Pelagic organisms, 71
PelecanuSf 518
Pelecypoda, 224, 247
Pelican, 518
Pelmatozoa, 288
PelobateSf 455
Pelobatidae, 453, 455
Pelvic girdle, 374, 876, 502
PenaciUf 136
Penguin, 518
Penis, 115, 221, 472
Pentacrinoids, 286
PentacrinuSt 285
Pentadactyle, 418
Pepsin, 348
Peraeopods, 152
Perameles, 596
Peramelidae, 642, 595
Perca, 415
Perches, 410
Percidae, 410, 415
Pericardium, 134, 329, 349
Perihaemal-canals, 258, 275 ; -rings,
258; -tubes, 310
Periosteum, 531
Periostracum, 225
Periotic, 625
Peripatus, 119, 160, 161, 162, 177, 207
Peripharyngeal band, 319, 329
Periplaneta, 168
Periproct, 268
Perisarc, 51, 65
Perissodactyla, 567, 668, 600
Peristalsis, 94
Peristome, 28, 250, 268
Peritoneum, 92
Peritrichous, 33
Periwinkle, 210, 212
Perspiration, 622
Pes, 418
Petaloid ambulacra, 277
Petrel, 518
Petrogale, 641, 544, 596
Petro-hyoid, 424
Petromyzon, 861, 862, 863, 365
Petromyzoutidae, 365
PhalangeTf 696
Phalangeridae, 544, 595
Phalanges, 498
Phalangida, 197, 209
Phalangids, 123
Phaneroglossa, 452, 455
Pharyngeal bones, 401
INDEX.
661
Pharjngo-branchial segment, 872
Pharyngognathi, 409, 410, 416
Pharynx, 31, 86, 87, 92, 347, 640 ; of
Amphioxus, 820
Pharynx-Bheath, 609
PhatcolarctuSf 544
Phascolomyidae, 544, 595
Phagcolomyty 544, 595
Phagiantis, 519
Phasma, 186, 207
Pheasant, 517, 519
Phoca, 563, 599
Phocaena, 552, 597
Phocidae, 564, 599
PhoenicapteruSj 518
PholiM, 233
Phosphorescence, 154
Phryganea, 187, 208
Phrynosoma, 476
Phylaotolaemata, 300, 801
PhyUium, 186
Phyllodromia, 170, 179
Phyllopoda, 143, 205
Phylloxera, 189
Phylogeny, 12
Phylum, 9, 11
Phy$aliay 58
Physaliidae, 59
Physeter, 551, 597
Physiology, 9
Physoolisti, 405, 409, 415
Physophoridae, 59
Physostomi, 405, 414
PhytopUts, 199
PiciM, 519
Pigeon, 606, 610, 513, 614, 519
Pigment epithelium, 342
Pigs, 570
Pilchard, 408
Pilidium, 628
Pilot-whale, 552
Pine marten, 561
Pineal body, 336
Pineal eye, 365
Pinna, 525
Pinnipedia, 562, 599
Pipa, 452
Pipe-fish, 410
Pipistrelle, 584
Pisces, 367, 368; classification of, 411
Pituitary body, 334, 336, 347, 368
Pit-vipers, 481
Placenta, 332, 537, 545
Placoid scales, 369
Plaice, 409
Planaria, 609, 612
Planorbis, origin of mesoderm, 66
Plantigrade, 554
Plant-louse, 183, 189
Plants and animals, 2, 25, 86
Pianola, 66, 57
Plasmodium, 26
Plastron, 481, 482
Platetsa, 415
PlatyhelminUies, 605 ; classifioation
of, 624
Platypus, 537
Platyrrhini, 588, 608
Plecotus, 584
Plectognathi, 409, 411, 416
Pleopods, 152
Plesiosauria, 493
PUthodon, 440, 454
Plethodontinae, 439
PUuracanthus, 374, 385
Pleural ganglia, 219
Pleural membrane, 172
Pleurobranohs, 186
Pleuronectes, 409
Pleuronectidae, 409, 415
Plexus, 345
Ploima, 638 •
Plover, 519
Plumatella, 298
Pneumogastric nerve, 346
Pocket valves, 350
Podical plates, 173
PodicepSj 618
Podobranchs, 136
Poikilothermal, 522
Poison-glands, 627
Polecat, 561
Pole-cells, 84
Polian vesicles, 257, 279
Polistetj 188
Pollack, 409
PoUex, 445
Polyohaeta, 109, 116
Polyclada, 611, 612, 624
Polyodon, 396
Polyp, 42, 64, 62
Polypide, 298
Polyprotodontia, 541, 594
Polypterw, 392, 898, 413
Polypus, 234, 245, 248
Polystomella, 19, 22, 27, 40
Polystomum, 617
Polyzoa, 297; classification of, 301
Pond-mussel, 222, 224
Pond- snail, 219
Pond turtles, 486
Pons Varolii, 530
Porcellio, 160, 206
Porcupine, 679, 581
Pores, 75; dorsal, 92
Porifera, 74; classification of, 79;
larva of, 80
Porocytes, 77
Porpoise, 552
Portal system, 352, 877
Portuguese man-of-war, 68
Post-axial, 419
42—3
662
Fost^Uriele. 899
PoaterioT. 87
pMlfroDUl, 465
PMt-pnbii, 467
PoH-iempond tosm, 465
P<>M-irg»poph;fe«, 421, 460
Potamogalidae, 538
Pnirie-doK, or -mumot, 603
Pravii, lu
Pie-aiUI, 419
Pie-cUvirle, 399
Preconuoid, 428
Pre-dentary bone, 444
Pra-froDUl, 438, 465
Pt,'j^T^a«-:>. .-.l.-i
Pte-iusiidiLLiliii ^ikkiiy, 3G6
Pre-inuilla, 3<J6. 1U3. 504
Pre-opercnlum, 387
Prepolenoj. 8
Preaphenoid, 305
pTMteniiiii], 631
Pr.-/-fNT'-'l'in-.-, 431, 460
Vnn.-.n.-. ll.T, 199
FrimateB, 586, 603
FiUmalic lajrer, 225
FrUtii. 3H4
ProboBoideae, 564, 565, 600
Pn>bo«iii, IbO, 30H, 626
Probowiii.poKi, 3U8; -Bhcath, 636
Prucatio, 564, HB. 6»9
pTOrillaria. alft
ProcellariifotiiieH, 518
ProewloUK, 421
Proctodaeum, 60. 86, 138, 134
Procyon. 561. 598
Procjonidae, 561, 698
PronatioD, 420
JVimrumnt;.., 247
Fronepbric tabulea, 368
Pronepbroa, 358
Prongbuali. 674. 57G
Pro-olic, »95, 437
ProplerfRium, 375
ProwbrancbiaU. 2^1, 332, 233
Prosoma, 123, 190, 191
Prooopjle. 79
ProsUie tilands, 344
Prox torn i HID. 93
PraCfctire coloration. 560
Proteidae, 456
Proteids, 3, 4
ProUm, 4S«, 465
Proteus animaloule, IS
Pro- thorn. 171
FrotobnncblaU, 347
Prolunemertini, 630
Protoplaam. 1. 3, 5
Protopodite, 118
Protopl/nu, S91, 413
Prototberia, 637, 694
Prototracbeata, 119. 160, 307
Protozoa, 13, IS: in infnaioiu, 17;
olaBsification of, 40
Protractor mosclea, 826
i^yentticnlDB, 513
Proiimal, 87
Psttlltriuni. 372
r.tiul,.. J.i5
P.-^^Tid^bmnch. 378, 392
l>e«\idop..diii. lo. 36, 4a
Piiltaeut, 519
PUToeU*, 519
I'Uropidae, 581
PleropuM, Ml. 584
PtfTotaaria, 493
Flerotie, 400
Pleralraehea, 318, Ua
PWrygiophores. 869
PtCT7goid bone, 396, 403, 438, 606
Pter^Roid proc«u, 437
Pter^-lae. 496
P^alin, aai
Pubis, 633
Puffin, 518
Pules, 1«9
Pnlmo-onUneoDB arch, 447
Pulmonarj arch, 483, 609
Pulmonary veina-, 431
Pabnonata, 347
Puma. 560
Pupa. 184
Pypai flat,., 4B1
Pjgo-.vlt, 502
Pyloric. caeca. 353, S98; -aae, 35S;
-aphincter, S48
Pjlomt, 848
I^naoma, 331
r;thon, 478
(joadrate bone, 401, 505
Quadrato-juiial bona, 144, 465, 505
Qnagga. 670
Babbit, DM, »sa, BW, 678, BT9
Babbit-flHh, 387
Racooon. 661
Badial canala, 63
Badial nerve-oordi, 258
Badi&l perihaemal oauals, 368
Badial water-veaael, 256
Badiale, 419
Bodialia, B7S
Radiala, 384
Badii, 349
Badiolaria, 23, 40
Badiolarian ooie, 34
Badina, 419
Badula, ais
Radola-Bao, 316
Baia, S88, WC, 113
INDEX.
663
BaU, 519
Rallus, 519
Bami communicantes, 345
Rana, 440, 4ia, 4i3, 444, 446, 446, 461,
453, 456
Rangifer, 576, 577, 601
Banidae, 441, 453, 456
Baptores, 516
Bat, 579, 580
Bat- fish, 387
Batitae, 516, 518
Battlesnake, 480
Bays, 381, 883
Bazor-shell, 233
Becapitulation theory, 12
Beceptaculum ovorum, 106
Beotal gland, 253, 376
Becti abdominis, 424
Bectum, 87, 174, 230
Bectus muscles, 356
Bed blood-corpusoles, 352
Bed-deer, 577
Bedia, 618
Bed spider, 199
Bed squirrel, 580
Beindeer, 576, 577
Benal papillae, 315, 321
Benal-portal veins, 352, 377
Beno-pericardial canal, 214, 238
Bepetition of parts, 21, 26
Beproduction, 7; by fission, 16, 23,
31, 50; by sporulation, 17, 23, 82
Beproductive cells, 105
Beproductive system, of Annelids, 105,
114 ; of Arthropods, 140, 141, 178,
196; of Brachiopods, 295; of Ces-
toda, 620; of Echinoderms, 260,
276; of Molluscs, 221, 222, 232, 244 ;
of Nematodes, 641 ; of Polyzoa, 299,
300; of Botifers, 636; of Trema-
todes, 614, 615; of Turbellaria, 610;
of Vertebrates, 323, 367, 869, 379,
435, 450, 472, 514
Beptilia, 367, 457; classification of,
459, 493; fossil representatives of,
492
Bespiration, 4
Bespiratory system, of Arthropods,
136, 165, 176; of Birds, 511; of
Mammals, 536
Bespiratory tube, 364
Beticulari'a, 40
Beticulnm, 571
Betina, 336, 841, 342
Betinula, 131
Betractor muscles, 226
Bhabdites, 607
Bbabditis, 648
Bhabdocoela, 611, 612, 624
Bhabdocoelida, 611, 624
Bhabdome, 130
Bhachis, 496
Rhea, 516, 518
Rhinoceros, 667, 568, 669, 600
Bhinocerotidae, 568, 600
Rhinolophuf, 584, 602
Rhizocrinwt, 286
Bhizota, 637
BhynchobdelUdae, 112, 115
Bhynchocephala, 459, 473, 498
Bhynchoooelom, 630
RhynchoneM, 291, 295, 296
Rhytina, 554
Bibs, 334, 373
Bight whale, 552
Biver-bass, 410, 416
Biver-trout, 408
Boach, 406
Bock-wallaby, 641, 544
Bodent|a, 578, 602
Bods and cones, 342
Boe-deer, 577
Borqnal whale, 552
BoUer, 519
Bosette, 286
Bostellum, 620
Bostrum, 371
Rotifer, 633, 688
Botifera, 631; classification of^ 687
Botulae, 272
Bound-worms, 639
Bumen, 571
Buminantia, 571
SacculuB, 340
Sacculated, 626
Sacral prominence, 441
Sacral vertebra, 420; 442
Sagitta, 803, 804, 305
Salamander, 417, 429, 439
Salamandra, 429, 434, 454
Salamandridae, 454
Salamandrinae, 439
Salamandroidea, 438, 439
Saliva, 537
Salivary-ducts, 217; -reservoir, 175
Salivary glands, of Helix, 217; of
Lithobius, 166; of Mammals, 536;
of Mesostoma, 609; of Styhpyga,
175
Salmo, 400, 402, 404, 408, 414
Salmon, 400, 402, 404, 405, 408
Salmonidae, 405, 408, 414
Salpa, 881, 882
Salvelinru, 408, 414
Sand-dollar, 278
Sand-grouse, 519
Sandlizard, 476
Sardine, 408
Sauria, 459, 475, 494
Sanropsida, 495
Saw-fish, 384
BtM-Aj. ISS, IS8
ScMle-itiMets, 1^
Scalea. of El»nDobruicbii, 869; of
Bepliles, tM
Scallop, 328, 233
Seal; uil-«AteT, 5i7, 5V.>
Bcanaam, 51G
Sfaphiopur, 453, 455
Sc&pbnniBtbite. 136
Scsphopoda, 247
BMpnlB, 999, 438, 468
Scapular arterj'. 471
SobizoKiiBthoaB, 617
Bohizupoda. 154, 20fl
Scintic plpxud, 449
Sciatic vein, 431
Scirtopoda, 038
ScmriJ&«. G79, 5S0
SeiurepUnu, 580
Beiunu, 580, 603
Scleroblaita, 78
Sclerotic coat, 341
Seomher, 415
Bcombridae, 410, 415
Boopula, 193
Scorpio, too. 309
Scorpion, ISl, 191, 199, MO
Boorpionida, 199, 209
Seotophitut, 585
Bcat«0, 395
Scutum, 150
SeyUium, 330, SS8, SSI, SBS, ITS, tT«,
JTS, 3TS. 3B0, SC3, 411
SoyiiluNtonm. es. 69
Bea-miemoiiefl, .^il, S3
Sea-baM, 410, 416
Sea-eowB, 549, 062
Sea-cucumber 349, 379, 880
SBa-hore, S19
Ses-lior«e, 410
Sea-lioD, Ki
Sea-mDSBel, i^-I
Sea-snails, 323
Bea-«qairt, 329
SeB-urchiDn, 249, 366, M8, 874
Seal, 550
Seal-skin seal, 663
Sebaoeoas filands, 539
Sebum. 622
Seoondarief. 498, 499
Secretion, 4. 17
Segmentation, 811, 118
Selachnidei, 381, SS3, 411
Sek-ijodout. r,V.
8eU'no;ionliB, o71, S73, 601
Semicirculnr ciiuBlf, 340, 363
Seminiferons tubules, S60
SemtiopitkKW. 589, 604
Sense-capeules, 341; -cell, 338, 844;
-hairs. 48, 54, 338: ■orniiB, 64,
130, 338, 363
Sensory p«ripber»l necre, 101
Stpia, 334, ISO, SIT, 819. MO, Ml,
848, 348
Septa, 93
Serotine, 565
Serranidae. 410. 41S
Seiual reprodnotion, 7, B
Beiual onion, 7
Shad, 408
Sharli, sn. 383
Bheep, 571, STl
SbeU, of Brachiopodt, 391, 9H; of
UollDsci, 310, 323, SH, 325
Shell-Gsb. 910
Sbell-glanda. 1S9. 610
Ship-worm, 33S
Shore-crab, 156
Sh rev -mice. 666
Siliceoos substance. 88
Silk, 194
Silk-worm, 184
SUk-vonn molh, m, 190
Silnridae, 405, 414
Silver -fish, 166
Simi„. ess. 5',ia. (M
Simiidae. 588, oKO. 604
Simwtphalui. 144, lU, 146, 801
SiiiipiicideDtat». am, 603
Sinux, dorsal and ventral. 118
Sinus venoKus. 349
Siphon. 2-28, 272
8ipho.ioRlyph. 6S
Siphouophora. 58, 59, 78
Sipbuncle, 245
Siridan. 43U
Sir™, 438, 455
Sirenia, 649. 663. 597
Siren idae, 465
Strtx, 188
Skates, 381, 883
Skeletal, spicnles, 80
Skeleton, of Amphibia, 417, 490, 435,
44-j; of Birds, lye, wO, soa; of
Kcliiuodernis, 360, 268; of Fiabet.
;)88. H9, 399 ; of Mammala, 681 ;
of heptilen, 4MI. 481
Skin, 15. 314, 3T0, 631
Skimh. 661. 661
SlothH, 646, 548
Sloughing, 453
, 476
Slug, 1
Smooth dog-Gsh, SSS
Smooth mnsclee, 139
Snail. 311
Snakes, 459, 474, 476
SDBpper, 4B7
Snapping tnrtlea, 486, 487
Soaring of birds, £03
Soft palate, 636
INDEX.
665
SoUuter, 261
Sole, 409
Solea, 409, 415
Solen, 233
Solenocytes, 321
SolenodoDtidae, 558
Solenogastres, 222, 247
Somatic peritoneum, 104
Somite, 89, 313
Songsters, 517
Sorex, 556, 598
Soricidae, 556, 598
Spadella, 303, 804, 305
Sparrow, 519
Spatangoidea, 278, 290
Spatangus, 290
Species, 7; origin of, 9
SpelerpeSf 440
Spermathecae, of HeUx, 221 ; of Lum-
bricuSf 90, 107 ; of Mesosioma, 610
Spermatophores, of Helix ^ 221; of
Hirudo, 115 ; of Sepia, 244
Spermatozoa, 7 ; of Hirudo, 115 ; of
Hydra, 46 ; of Lumbricus, 107
Sperm sac, 381
Sperm-whale, 55]
Sphaerularia, 643
Sphenethmoid, 443
Sphenisciformes, 518
Spheniscus, 518
Sphenodon, 459, 465, 473, 493
Sphenotic, 400
Sphincter, 375
Sphyranura, 617
Spicules, 62, 78, 80
Spider, 123, 134, 136, 137, 138, 191,
193, 193, 194, 196; web of, 194
Spider-monkejs, 588
Spinal cord, 306, 316, 818, 336
Spinal ganglia, 344
Spine, 533
Spines, 269
Spinnerets, 191, 194
Spiny ant-eater, 537
Spiny dog-fish, 383
Spiracle, 346, 371, 373
Spiral valve, 349
Spirula, 223
Splanchnic muscles, 104
Splanchnic peritoneum, 104
Spleen, 355, 430
SplenUl bone, 403, 428, 466
Sponges, 74 ; complex, 78 ; larva of, 80
Spongilla, 77, 80
Spongin, 80
Spoon-bill, 396
Spores, 17, 26, 39
Sporocyst, 617
Sporozoa, 38, 41
Sport, 9
Sporulation, 17, 23
Sprat, 408
Squalus, 383
Squamosal, 387, 444, 465
Squid, 210, 234, 236
Squilla, 157, 206
Squirrel, 579, 580
Stag-beetle, 180
Stapes, 528
Star-fish, 249, 262, 304, 866
Star-nosed mole, 557
Statoblasts, 300
Steapsin, 349
Steganopodes, 504
Stegocephala, 422, 425, 454, 492
Stellate ganglia, 242
Stercoral pocket, 195
Sterna, 167
Sternal ribs, 461
Sternebrae, 531
Sterno-hyoid, 424
Sternum, 171, 172, 429, 445
Stigmata, 137, 139
Stimulus, 6
Sting-ray, 384
Stoat, 561
Stolon, 57, 62, 65, 260
Stomach, 43, 86, 87, 347
Stomatopoda, 155, 157, 206
Stomodaeum, 60, 86, 133, 134, 316,
347
Stone* canal, 256
Stork, 518
Streptoneura, 246
Streptoneurous, 223
Striated rods, 841
Striped muscles, 129
Strix, 519
Strobilization, 68. 69, 620
Strongylocentrus, 367
Structureless lamella, 48
Struthio, 607, 516, 618
Sturgeon, 395, 896
Stylet, 627
Stylopyga, 168, 169, 171, 174, 207
Subclavian artery, 350, 431
Subfilamentar tissue, 228
Sub-intestinal vessel, 96
Sub-lingual glands, 512, 536
Sub-maxillary glands, 512, 536
Sub-mentum, 171
Sub- neural gland, 326
Sub-pharyngeal ganglion, 100
Sub-umbrella, 52
Subungulata, 564, 599
Sub-vertebral wedge, 460
Suctoria, 35, 41
Suctorial stomach, 181
Suidae, 571
Suinae, 570, 601
Sula, 498, 518
Summer-eggs, 146, 610, 636
666
INDEX.
Sun-star, 261
Supination, 420
Supra-angular, 466
Supra-oesopbageal ganglia, 217, 242
Supra-pharyngeal ganglia, 99
Supra-acapula, 429, 466
Supra-temporal fossa, 465
Surinam toad, 452
Sut, 571, 601
Suspensorium, 427, 441
Swallow, 519
Swan, 518
Sweat-glands, 522
Swift, 519
Syeon, 79
Sylvian fissure, 530
Symmetry, bilateral, 88, 122, 222;
radial, 87
Sympathetic nervous system, 345
Symphysis, 467
Symplectic, 395, 401
Synapticulae, 322
Synaptidae, 282
Synehaeta, 636, 638
SyngamuSt 643
Syngnathus, 410, 416
SynotuSf 584
Syringopora, 65
Syrinx, 512
Systemic arch, 433
Tabanus, 189
Tadpole, Ascidian, 325, 336; of i2a?ia,
461
Taenia, 619, 620, 621, 623
Tail, 319
Talpa, 557, 598
Talpidae, 556, 557, 598
Tatnandua, 546, 549
Tamias, 579, 582, 602
Tape-worm, 619
Tapir, 667, 568
Tapiridae, 568, 600
Tapirus, 667, 600
Tarsale, 419
Tarsalia, 419
Tarsus, 172, 418
Tasmanian wolf, 542
Teat, 522
Teeth, origin of, 370; of Mammalia,
626, 642, 558
Tegeiiaria, 126, 193, 195
Teleostei, 393, 397, 414
Teleostomi, 369, 392 ; classification of,
405, 412
Telson, 152
Tenmocephalidae, 615
Temporal arcades, 465
Temporal fossa, 507
Tendon, 127
Tentacle sheath, 298
Tentades, 42; of Actinosoa, 60; of
Hydromednsae, 52; of NereU, 110
Tentaoulooyst, 67
Tenthredo, 188
Terebratula, 292, 296
Teredo, 233
Terga, 167
Tergum, 150, 171
Termes, 187, 208
Terricolae, 108
Tertiaries, 499
Testioardines, 296
Testicular network, 360
Testis, 46, 106, 641
Testudinidae, 486
Tettudo, 486, 494
Tetrabranchiata, 248
Tetranychiu, 199, 209
Tetrao, 519
Tetrastemma, 629, 630
Tetrodon, 411, 416
Textrix, 192
Thalamencephalon, 336
Thalas$ieola, 40
Thalasaochely*, 482
Thaliaoeae, 330, 331
Theromorpha, 492
Thoracic, 405
Thoracic vertebra, 536
Thoracostraca, 153, 206
Thorax, 122, 152. 168, 171
Thread-capsule, 46
Thread-worms, 639
Thripi, 187
Thrush, 519
Thylacinus, 542, 595
Thyro-hyals, 444
Thyroid gland, 347, 365
Tibia, 172, 419
Tibiale, 419
Ticks, 199
Tiedemann's bodies, 256
Tiger, 560
Tinamiformes, 519
Tinamou, 519
Tinamut, 519
Tipula, 189
Toad, 417, 441, 444, 452
Tone, 353
Tongue, 431
Tongue-bar, 309
Toothed whales, 551, 552
Torpedo, 383
Tortoise-shell, 481, 482
Tortoises, 459, 486
Torus angularis, 265
Trabeculae, 285, 334, 364
Trachea, 119, 137, 165, 176, 468
Tracheata, 137, 165
Trachymedusae, 58, 67, 73
Tragulidae, 574, 601
INDEX.
667
Tragulus, 601
Transverse bone, 465
Transverse processes, 884
Tree-frogs, 452, 468
Tree-shrews, 665
Trematoda, 606, 613, 625
Trichechidae, 568, 599
Tricheckua, 563, 699
Trichina^ 648
Trichinosis, 643
Trichocysts, 34
Tridada, 611, 612, 624
Tridactyle. 271
Trigeminal nerves, 846
Tnglidae, 410
Trionyohidae, 486, 487
Triradiate, 78
Triton, 420, 422, 484, 487
Tritors, 386
Trochanter, 172
Trochns, 688
Trophi, 684
Tropidonotust 477, 479, 494
Trout, 405. 408
Trunk, 88
Trunk-fish, 411
Trygon, 384, 412
Trypsin, 849
Tsetse-fly, 189
Tube-feet, 260
Tuhifex, 623
Tubipora, 62
Tubularia, 57
TtLbulipora, 297
Tunicata, 323
Tupaiidae, 665
Turbellaria, 606, 607, 624
Turbot, 409
Turdus, 619
Turkey buzzard, 618
Turtles, 469, 474, 481
Tylenchus, 643
Tylopoda, 674
Tympanic, 526
Tympanic bulla, 525
Tympanic membrane, 441, 628
Tympanum, 441, 612
Typhlosole, 93
Tyroglyphus, 198, 199, 209
Ulna, 419
Ulnare, 419
Ulotrichi, 691
Umbo, 226
Uncinate process, 474
Uncus, 684
Ungulata, 664, 599
Ungulata vera, 667, 600
Unicellular, 46
Unio, 222, 224, 226, 227, 248
Uniseriate, 874
Univalve, 228
Upper temporal arcade, 466
Upupa, 619
Urea, 4
Ureter, 214, 881, 486
Uric acid, 4, 166
Urinary sinus, 881
Urinogenital organs, 867
Urinogenital sinus, 381, 640
Urochordata, 323
Urodaeum, 618
Urodela, 422 ; classification of, 438,
464
Urostyle, 442
Ursidae, 660, 698
Ursus, 661, 598
Uterus, 687, 689
Utriculus, 340
Uvula, 626
Vacuole, food-, 14, 31 ; contractile-, 16,
31, 33
Vagina, 221, 689, 641
Vagus nerve, 346
Vampire, 684
Varanus, 462, 466, 468
Variation, 8, 10
Vas deferens, 106, 360, 641
Velum, 54, 811, 816, 364, 632
Vena azygos, 471, 636
Vena cava, 231, 431, 482, 686
Ventral, 88
Ventricle, 349
Venue's girdle, 72
Vertebra, 263
Vertebral column, 878, 894, 421
Vertebrata, 306
Vesicula seminalis, 106, 879, 881
Vespa, 188, 208
Vespertilio, 684, 686, 602
Vetperugo, 684, 686, 602
Vestibule, 863
Vibracula, 300
Vicuna, 576
VilU, 645
Vipera, 481, 494
Viperidae, 480
Visceral arches, 822, 850, 866, 871,
427
Visceral ganglia, 219
Visceral hump, 211
Visceral loop, 219
Visceral peritoneum, 104
VitelUrium, 606, 686
Vitreous humour, 841
Viviparous, 201
Viverra, 662
Viverridae, 662
Vole, 679, 680
VolvoXt 81
Vomer, 402, 428, 524
668
INDEX.
Vomerine plates, 386
VortieeHa, 28, 89, SO, 41 ; reproduetion
of, 31
Waldheimia, 298, 898, 296
Wallaby, 541
Walras, 563
Wapiti, 677
Warty eft, 488
Wasp, 181, 188
Water-boatman, 189
Water-newt, 439
Water-rat, 580
Water-reptilefl, 493
Water-scorpion, 189
Water-shrew, 557
Water-Tascolar system, 255, 256, 606
Water-vole, 580
Weasel, 561
Whalebone whales, 551, 552
Whales, 549, 550
Whelk, 210, 212, 215
Whinkered bat, 584
White-ant, 187
White-cat, 407
White-fish, 408
White-Khark. 383
White-whale, 552
Whiting, 409
Wild l)oar, 571
Wild dock, 001
Windpipe, 511
WinKS of Insects, 182 ; of Birds, 497,
499, 000
Winter-egiirs, 146, 610. 63€
Wire-worm, 119. 18T
Wolf, 56i»
WolfBan-dnct, 358; -ridge. 558, 368
Womb, 537
Wombat. 544
Wood-ant, 187
Woodchnck, 579
Wood-loose, 122, 180
Wood-mouse, 580
Woodpecker, 519
Wood-wasp. 188
Wrass, 410
Xaniharpyia, 584. 585, 602
Xiphiplastra. 481
Xiphistemom, 445, 531
Xiphoid process. 498
Xiphosnra, 201. 209
Tellow-cells, in Lumlirinut, 93, 98
Yolk, 7, 515: -gland. 606
Zebra, 570
Zoaea, 153
Zoantharia, 63, 73
Zooecinm, 298
Zoolof^y, definition of, 1 ; o:«ject of, 3 ;
subdivisions of, 9
Zygaena, 383
Zygantra, 477
ZyKapophyses, 421
Zygosphenes, 477
Zygote, 23
cambbidoe: pbintbi> bt j. and o. f. cult, at the UNIVEBSITY PmBBS.
D74a Shipley, n.h. 3ii006
655 ZocLogy.
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