BIOLOGY
LIBRARY
S
ZOOLOGY
AN ELEMENTARY TEXT-BOOK
BY
SIR A. E. SHIPLEY, G.C.B.E., Sc.D.,
Hon.D.Sc. (Princeton), F.R.S.
MASTER OF CHRIST'S COLLEGE, CAMBRIDGE
AND UNIVERSITY LECTURER IN ZOOLOGY
AND
E. W. MAcBRIDE, M.A. (Cantab.),
D.Sc. (Lond.), Hon.LL.D. (M c Gill), F.R.S.
SOMETIME FELLOW OF ST JOHN'S COLLEGE, CAMBRIDGE
PROFESSOR OF ZOOLOGY IN THE IMPERIAL COLLEGE OF SCIENCE .AND
TECHNOLOGY, LONDON
FOURTH EDITION
CAMBRIDGE
AT THE UNIVERSITY PRESS
1920
BIOLOGY
LIBRARY
G
First Edition 1901.
Second Edition 1904.
Third Edition 1915.
Fourth Edition 1920.
PREFACE TO THE THIRD EDITION
IN the eleven years which have elapsed since the publication
of the second edition of this Text-book the science of
Zoology has made such advances that it has become necessary
to re-write considerable portions of this book. The brilliant
work of Dr Goodrich on the nature and development of
nephridia has caused us to reconsider our position with regard
to the nature of these organs and we have now confined the
name nephridium to the excretory organs of Platyhelminthes,
Nemertinea, Rotifera, Annelida and Amphioxus, and have no
longer applied the term to the excretory organs of Arthropoda,
Mollusca and Brachiopoda.
The chapter on Protozoa has had to be radically changed
and we are indebted to Mr Dobell for valuable hints on this
subject. The newer discoveries in the laws of inheritance are
dealt with in the Introduction.
The chapters dealing with Platyhelminthes, Nemertinea,
Rotifera and Nematoda have been moved to a position follow-
ing Coelenterata and preceding Annelida. A short chapter
on Gephyrea has been added and the chapter on Arthropoda
has been largely rewritten. In the second edition detailed
accounts of a type of Arachnida and of Insecta were given
to these we have now added a detailed account pf the anatomy
of the Crayfish as a type of the Crustacea, as experience
has shown that only by the detailed study of types can the
elementary student form clear images of Animals as " going
machines." Indeed throughout the book we have endeavoured
to avoid describing structure unless function was indicated at
the same time.
433872
vi PREFACE
In the section of the book dealing with Vertebrata many
changes have been made. In the chapter on Fishes, we
have endeavoured to bring clearly before the student's mind
that the existing piscine population of the world's waters consists
of two types of fish, the bony and the cartilaginous, and that the
so-called Ganoids and Dipnoi comprise very few species, the
last survivors of groups now nearly extinct. Sketches of the
modern classification of Bony Fish and of Birds have been
given so that the student may grasp to some extent the principles
on which modern systematists proceed. Lastly, in the section
dealing with Mammalia, considerable alterations were inevitable.
Our largely increased knowledge of Theromorphous Reptiles
has rendered untenable the view of the hornology of the ear-
ossicles of Mammalia formerly accepted by us, and the brilliant
discoveries of Dr Andrews have settled the position of Elephants
and Sirenia.
Besides those whose work we have mentioned above we owe
thanks to Mr H. H. Brindley of St John's College, and to
First Lieutenant J. T. Saunders of Christ's College, for much
helpful criticism.
We are grateful for the reception which has been accorded
to the second edition : we hope that the changes we have
alluded to may increase the usefulness of the book.
A. E. S.
E. W. M.
1st January, 1915.
PEEFACE TO THE FOURTH EDITION
ONLY a few changes have been made in the text of the last
edition. Of these, those most worthy of mention are (1) the
incorporation of Prof. Jennings' most interesting observations on
the motion of Amoeba, which has involved the discarding of
Prof. Ehumbler's hypothesis which was adopted in the third
edition ; (2) the inclusion of some new and interesting results
on the physiology of the bivalve Mollusca ; (3) the adoption of
Dr Ridewood's results on the development of centra, which have
narrowed the gap between the so-called arco-centra and chorda-
centra ; and (4) the rewriting of the section dealing with Human
races in accordance with the views of Ripley, Elliot-Smith,
Keith and other modern Anthropologists.
A. E. S.
E. W. M.
I wish to state that owing to pressure of duties as Vice-
Chancellor, and other claims on my time, the Fourth Edition has
been revised and seen through the Press by Prof. MacBride, and
any improvements that appear in it are solely due to him.
A. E. S.
TABLE OF CONTENTS
CHAP.
I.
II.
III.
IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
XII.
XIII.
XIV.
XV.
XVI.
XVII.
XVIII.
XIX.
XX.
XXI.
XXII.
XXIII.
XXIV.
XXV.
INTRODUCTION
PHYLUM PROTOZOA
PHYLUM COELENTERATA
PHYLUM PORIFERA
PHYLUM PLATYHELMINTHES
PHYLUM NEMERTINEA .
PHYLUM KOTIFERA
PHYLUM NEMATODA
INTRODUCTION TO THE COELOMATA ....
PHYLUM ANNELIDA
PHYLUM GEPHYREA .... .
PHYLUM ARTHROPODA
PHYLUM MOLLUSCA . . . . . . .
PHYLUM ECHINODERMATA
PHYLUM BRACHIOPODA .
PHYLUM POLYZOA .
PHYLUM CHAETOGNATHA . . ....
INTRODUCTION TO THE PHYLUM VERTEBRATA, SUB-PHYLA
I III, HEMICHORDA, CEPHALOCHORDA AND URO-
CHORDA
INTRODUCTION TO SUB-PHYLUM IV, CRANIATA. DIVISION I.
CYCLOSTOMATA ,
CRANIATA. DIVISION II.
DIVISION I. ANAMNIA.
CRANIATA. DIVISION II.
DIVISION I. ANAMNIA.
GNATHOSTOMATA. SUB-
CLASS I. PISCES
GNATHOSTOMATA. SUB-
CLASS II. AMPHIBIA
CRANIATA. DIVISION II.
TION TO AMNIOTA
CRANIATA. DIVISION II.
DIVISION II. AMNIOTA.
CRANIATA. DIVISION II.
DIVISION II. AMNIOTA.
CRANIATA. DIVISION II.
DIVISION II. AMNIOTA.
INDEX
GNATHOSTOMATA. INTRODUC-
GNATHOSTOMATA. SUB-
CLASS III. REPTILIA .
GNATHOSTOMATA. SUB-
CLASS IV. AVES .
GNATHOSTOMATA. SUB-
CLASS V. MAMMALIA
PAGE
1
15
49
84
92
113
119
127
133
138
167
174
284
326
370
376
381
385
413
452
519
563
567
606
636
728
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Amoeba proteus . . . 16
2. Difflugia urceolata 20
3. Arcella discoides ......... 21
4. Gromia oviformis 23
5. Polystomella crispa 24
6. Heliosphaera inermis 27
7. Chondrioderma diforme 29
8. Actinophrys sol ......... 30
9. Actinosphaerium eichhornii ....... 31
10. Euglena viridis 32
11. Vorticella microstoma 36
12. Diagram of Vorticella . . . . . . . . 37
13. Paramecium caudatum 40
14. Opalina ranarum ......... 42
15. Clepsidrina long a .43
16. Hydra fusca ...... 50
17. Longitudinal section through the body of Hydra ... 51
18. Transverse section of Hydra fusca 53
19. Cnidoblast with large nematocyst from the body -wall of
Hydra fusca 54
20. Section through body- wall of Hydra fusca ... 56
21. Preparation of part of the body -wall of Hydra to show the
nerve-cells 56
22. Diagram of Hydra to show the arrangement of the nerve- cells 57
23. Obelia helgolandica .58
24. Part of a branch of Obelia 59
25. Free-swimming Medusa of Obelia .60
26. Bougainvillia fructuosa 61
27. (1) Eye of Lizzia koellikeri ; (2) Kadial section through the
edge of the umbrella of Carmarina hastata showing sense
organ and velum 63
28. The ciliated larva or Planula of a Hyclromedusan, Clava
squamata 65
29. Part of a colony of Alcyonium digitatum . . . 69
LIST OF ILLUSTRATIONS
30. Transverse section through a polyp of Alcyonium digitatum
below the level of the oesophagus ..... 70
31. Transverse section through a polyp of Alcyonium digit atum
through the region of the oesophagus .... 70
32. Semi-diagrammatic view of half a simple Coral ... 73
33. Aurelia aurita ...... ... 76
34. Strobilisation of Aurelia aurita ...... 77
35. Hormiphora plumosa ........ 79
36. View of a branch of Leucosolenia showing sieve-like mem-
brane which stretches across the osculum ... 85
37. Vertical section through an osculum with sieve-like mem-
brane, and a tube of Leucosolenia ..... 86
38. Section of a flagellated chamber oiSpongilla lacustris, showing
the flagella and collar cells ..... . 87
39. Section of a portion of Grantia extusarticulata . . . 88
40. Two flame-cells or solenocytes from the nephridium of an
Annelid worm ......... 93
41. Mesostoma splendidam, drawn from a compressed individual ;
the cilia and rhabdites are omitted . . . . . 95
42. Planaria polychroa, with everted proboscis . . . .100
43. Diagram of the reproductive and nervous systems of a
Trematode, Distomum hepaticum ..... 102
44. Diagram of the digestive and excretory systems of a Trema-
tode, Distomum hepaticum ...... 104
45. A Tape-worm, Taenia solium . ..... 1 07
46. Transverse section through a mature proglottis of Taenia. 108
47. Diagram of a ripe proglottis of Taenia solium . . . 109
48. Lineus geniculatus . . . . . . . . . 114
49. Cerebratulus fuscus. Young transparent form . . . 116
50. A Rotifer, Floscularia ; (a) female of Floscularia cormda,
(b) male of Floscularia campanulata . . . . 120
51. Diagram of Floscularia ......... 121
52. Diagram of a Rotifer . . . ..... 123
53. Hydatina senta. Ventral view ...... 124
54. Female Ascaris lumbricoides cut open along median dorsal
line to show the internal organs ..... 128
55. Male Ascaris lumbricoides cut open along the dorsal middle
line ........... 130
56. Trichina spiralis, encysted amongst muscular fibres . . 131
57. Three transverse sections through a developing Amphioxusio
show the origin of mesoblast from endodermal pouches . 134
58. Two stages in the early development of a common fresh-water
mollusc, Planorbis, to show the origin of the mesoderm
cells ........... 135
59. Latero- ventral view of an Earthworm Lumbricus terrestris . 139
LIST OF ILLUSTRATIONS XI
FIG. PAGE
60. Anterior view of the internal organs of Lumbricus terrestris . 142
61. Six segments from the intestinal region of Lumbricus
terrestris, dissected so as to show the arrangement of the
parts . 143
62. Diagram of the anterior end of Lumbricus herculeus to show
the arrangement of the nervous system . . . . 149
63. Transverse section through Lumbricus terrestris in the region
of the intestine and of a dorsal pore 151
64. View of the reproductive organs of the earthworm, Lumbricus
terrestris 154
65. Nereis pelagica 158
66. Transverse section through Nereis cultrifera . . . 159
67. Hirudo medicinalis ........ 160
68. View of the internal organs of Hirudo medicinalis . . 163
69. Dissection of Sipunculus nudus . . . . . . 172
70. The Common Crayfish, Astacus fluviatilis, seen from the side 177
71. Astacus fluviatilis, viewed from beneath . . . . 178
72. Left mouth-appendages of Astacus flumatilis . . . 183
73. The Crayfish, Astacus flumatilis, split into two by a median
cut extending along the mid-dorsal line and viewed from
the side ] 90
74. Diagrams to illustrate the process of " ecdy sis " in Arthropoda 1 94
75. Male reproductive organs of Astacus fluviatilis . . . 195
76. Female reproductive organs of Astacus flumatilis ... 195
77. Dorsal view of a female Branchipus ..... 206
78. Side viaw of male Simocephalus sima . . . . . 207
79. Side view of female Simocephalus sima . ... . 207
80. Lateral view of Cypris Candida 209
81. Ventral view of a male Cyclops . . . . . . 210
82. Dorsal view of a female Cyclops 211
83. View of Lepas anatifera cut open longitudinally to show the
disposition of the organs 213
84. A Schizopod, Nyctiphanes norwegica ...... 216
85. The Shore-crab, Carcinus maenas, ventral aspect . . 218
86. Left side of a larva of the Prawn, Penaeus, to show the origin
of the gills . . 219
87. Female of Diastylis stygia, one of the Cumacea . . . 221
88. The mouth appendages of Gammarus neglectus . . . 222
89. Gammarus neglectus. Female bearing eggs seen in profile . 223
90. Asellus aquaticus. Male viewed from above . . .' 224
91. A Wood-louse, Porcellio scaber 224
92. Peripatus capensis 225
93. Peripatus capensis, male, dissected to show the internal
organs 227
94. A Centipede, Lithobius forficatus . . ... . . 229
xii LIST OF ILLUSTRATIONS
no. PAGE
95. Lithobius forficatus, dissected to show the internal organs 230
96. lulus terrestris, sometimes called the "Wire-worm" . . 231
97. Two views of a male Cockroach, Stylopyga orientalis . 234
98. Mouth appendages of Stylopyga 235
99. Female Cockroach dissected to show the viscera . . 239
100. A Grasshopper, Pachytylus migratorius .... 247
101. A male Cockchafer, Melolontha vulgaris . . . 248
102. Larva of Bombyx mori, the Silkworm . . . . 249
103. Cocoon of Bombyx mori * . 250
104. Silkworm moth, Bombyx mori . . .... . 250
105. The Lady-bird, Coccinella septempunctata, its larva, and the
adult beetle 254
106. View of internal organs of the male Cockchafer, Melolontha
vulgaris 255
107 View of the nervous system of the Cockchafer, Melolontha
vulgaris .......... 255
108. Male, female and neuter of the Wood-ant, Formica rufa . 256
109. Drone, queen and worker of the Honey-bee, Apis mellifica . 256
110. A Wasp, Polistes tepidus, and its nest .... 256
111. . The Tsetse-fly, Glossina morsitans . . . . . 257
112. The Hessian-fly, Cecidomyia destructor .... 257
113. The Garden Spider, Epeira diademata, sitting in the centre
of its web 260
114. Front view of the head of a Spider, Textrix denticulata . 261
115. Pedipalp of the large House-spider, Tegenaria guyonii . 262
116. Horizontal section through the abdomen of a Spider,
Argyroneta . . . *> ... . . . . . 263
117. Longitudinal section through the lung-book of a Spider . 263
118. Lateral view of the internal organs of a Spider, Epeira
diademata . * . . . : .... . . . 264
119. Diagrammatic view of a palpal organ .... 265
120. A Phalangid or Harvestman, Oligolophus spinosus . . 267
121. Male and female of the Cheese-mite, Tyroglyphus siro, seen
from the ventral side . ..... .... . . . . 268
122. Dorsal and ventral views of the Indian Scorpion, Scorpio
swammerdami . . . ...... ". . . 270
123. Sections through the central and lateral eyes of a Scorpion,
Euscorpius italicus . . . . . . . 271
124. Dorsal view of the King-crab, Limulus polyphemus . . 273
125. Ventral view of the King-crab, Limulus polyphemus. . 274
126. Longitudinal section through the operculum and gills of a
King-crab, Limulus . . . . . . . . 275
127. Side view of a Snail, Helix pomatia, the animal being
expanded 285
128. Dorsal view of a Snail, Helix pomatia, after removal of the shell 287
LIST OF ILLUSTRATIONS XI ii
TIG. PAGE
129. Helix pomatia, with the pulmonary chamber cut open . 288
130. Longitudinal section of the head of Helix to show the radula 289
131. Dissection of the Snail, Helix pomatia, to show the internal
organs . . . . . ; . . 290
132. View of the nervous system of Helix pomatia . . . 292
133. Optical section through the auditory vesicle of Pterotrachea
friederici . 293
134. Nervous system of the Pond-snail, Limnaea . . . 293
135. Nervous system, osphradium and gills of Haliotis . . 294
136. The Pond-mussel, Anodonta mutabilis, with foot expanded
and the empty shell of the same ..... 298
137. Eight side of Anodonta mutabilis with mantle cut away and
gills folded back . 300
138. Diagrammatic transverse sections of Anodonta . . . 301
139. Eight side of Anodonta mutabilis dissected to show the
viscera . . . . . . . . . 303
140. Dorsal view of Anodonta mutabilis, with the upper wall of
the pericardium removed to show the heart . . . 306
141. Solen vagina, the Eazor-shell 308
142. 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 31 1
143. Posterior view of a male Cuttle-fish, Sepia officinalis, with
the mantle- cavity opened . . .. . .313
144. A diagram showing the relation of the kidneys to the peri-
cardium in Sepia . . . ... . . 314
145. View of heart and chief blood vessels of Sepia cultrata . 316
146. Diagrammatic longitudinal section of Sepia to show the
relation to one another of some of the principal viscera . 318
147. Lateral view of the central nervous system of Sepia officinalis 319
148. Ventral view of Sepia officinalis dissected so as to show the
nervous system . . . . . . . . . 320
149. Side view of the pearly Nautilus, Nautilus pompilius . 322
150. Oral view of a Star-fish, Echinaster sentus .... 327
151. Dissection of the common Star-fish, Asterias rubens, so as to
show the motor, digestive and reproductive organs . . 329
152. A Star-fish, Echinaster sentus, in the act of devouring a
mussel . . . . . . . . . . 331
153. Diagram of a transverse section of the arm of a Star-fish 332
154. Pedicellariae from Asterias glacialis . . . . . 336
155. Dorsal, upper or aboral view of a Brittle-star, Ophiocfh/pha
bullata ... 339
156. Section through an arm of an Ophiuroid . . . . 340
157. A diagrammatic vertical section of an Ophiuroid . . 341
158. Oral view of part of the disc and arms of Ophioglypha bullata 342
xiv LIST OF ILLUSTRATIONS
FIG. PAGE
159. Strongylocentrus drb'lachiensis 344
160. Dorsal view of the dried shell of the common British Sea-
urchin, Echinus esculentus ...... 345
161. A glandular or gemmiform pedicellaria from Echinus
esculentus 346
162. Dissection of Echinus esculentus so as to show the structure
of "Aristotle's lantern" 347
163. Diagram of a longitudinal vertical section of a Sea-urchin . 348
164. Transverse sections through the madreporite and the radius
of Echinus esculentus 351
165. Dissection of a Sea-urchin so as to show the course of the
alimentary canal 352
166. The oral field or peristome of Echinus esculentus , . 353
167. The aboral system of plates, or periproct and calyx of
Echinus esculentus 355
168. Dissection of a Sea-cucumber, Holothuria tubulosa, so as to
show the arrangement of the viscera .... 358
169. A Feather-star, Antedon acoela ...... 361
170. Diagram of a longitudinal vertical section of the common
Feather-star, Antedon rosacea 362
171. A stalked Feather-star, Rhizocrinus .... 363
172. Ventral view of a larva of a Holothurian . . . . 364
173. Shell of a fossil Brachiopod, Terebratula semiglobosa . 371
174. Section through the shell of Waldheimia Jlavescens . . 371
175. Dissection of Waldheimia australis so as to show the in-
ternal organs 372
176. Longitudinal vertical median section of Argiope neapolitana 373
177. Portions of two Polyzoan colonies . 376
178. Longitudinal vertical section of Plumatella fungosa . . 377
179. An avicularium of Bugula 379
180. Ventral view of Sagitta hexaptera 382
181. . Transverse sections of Sagitta bipunctata and of Spadella
cephaloptera . 383
182. A Dolichoglossus kowalevskii ...... 387
183. Longitudinal vertical section of Glossobalanus . . . 388
184. Longitudinal horizontal section of Glossobalanus . . 389
185. Amphioxus lanceolatus seen from the left side . . . 391
186. Views of the velum and of the oral cartilages of Amphioxus 391
187. Diagrammatic longitudinal section of an embryo of
Amphioxus 392
188. Anterior region of a young Amphioxus seen from the left side 393
189. Diagrammatic transverse section through the pharyngeal
region of a female Amphioxus . . . . . 394
190. Transverse section through the intestinal region of a
young Amphioxus 395
LIST OF ILLUSTRATIONS XV
FIG. PAGE
191. Anterior portion of body of young transparent Amphioxus 396
192. Anterior portion of the spinal cord of Amphioxus . . 396
193. Median vertical section through the cerebral vesicle of
Amphioxus 397
194. Transverse section through the middle region of the spinal
cord of Amphioxus ........ 398
195. A nephridium of Amphioxus, belonging to the left side of
the body 399
196 Portion of a transverse section through the pharynx of
Amphioxus, in order to show position of the excretory
tubule 400
197 Ventral view of an Amphioxus dissected so as to show the
reproductive organs ........ 401
198 Diagrammatic transverse section of Amphioxus to show the
relation of the excretory and genital organs . . . 402
199. Side view of the anterior end of a larva of Ascidia. . 405
200. Dorsal view of the anterior end of a larva of Ascidia . 405
201. Diagrams showing the changes undergone by a larval
Ascidian in its metamorphosis . . . . 406
dona intestinalis . ....... 407
View of Ciona intestinalis lying on its right side . . 409
204. Two groups of individuals of Botryllus violaceus . . -410
205. Dorsal view of a fully-grown specimen of the solitary form
of Salpa democratica . . . . . . . 411
206. Semi-diagrammatic view of left side of Salpa . . . 412
207. Views of the brain of a Dogfish, Scyllium catulus, from
various aspects . . . . . . . . 415
208. Transverse section through the snout of a Dogfish, Scyllium
canicula . 418
209. Ear of Chimaera monstrosa ....... 419
210. Section of an ampulla of the internal ear . . . . 420
211. 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 . . . 421
212. Diagram to illustrate the structure of the retina . . 423
213. Diagram of the arterial system of the Dogfish, Scyllium . 432
214. Diagram of the venous system of the Shark, Mustelus
antarcticus . . . . . . . . . 435
215. Dissection of the muscles of the eye of Scyllium canicula 436
216. Diagrams illustrating the development of the excretory and
reproductive systems in Craniata ..... 438
217. Diagram of a transverse section through a hypothetical an-
cestral Elasmobranch in order to show the origin of the
excretory and genital organs 441
218. The Musk Lamprey, Petromyzon uiilderi, in the act of spawning 444
XVI LIST OF ILLUSTRATIONS
FlO;
219. Longitudinal vertical section through a female Lara prey,
Petromyzon marinus ... ....
220. Three views of the skull of Petromyzon marinus, from
different aspects . . . .
221. Section through the skin of an Elasmobranch showing
formation of a dermal spine ......
222. Diagram of a section through the jaw of a Shark, Odon-
taspis americanus .
223. Lateral view of the skull of a Dogfish, Scyllium canicula .
224. Dorso-lateral view of the pectoral girdle and fins of a Dogfish,
Scyllium^ canicula . ...
225. Dorsal view of the pelvic girdle and fins of a male Dogfish,
Scyllium canicula . ... .
226. Dissection of Scyllium canicula, so as to show the viscera
viewed from the ventral aspect .....
227. Dissection of Scyllium canicula, so as to show the viscera
seen from the right side .... ,
228. Scyllium canicula, and opened egg-case of the same .
229. A Ray, Raia maculata .......
230. Skull of a male Chimaera monstrosa .
231. Chimaera monstrosa ........
232. Diagrams illustrating the mode of formation of the vertebral
column in Teleostei . 474
233. Lateral view of the cartilaginous qranium of a Salmon, Salmo
salar ........ . 476
234. Dorsal and ventral views of the cranium of a Salmon, Salmo
salar, from which the membrane bones have been re-
moved . . . 477
235. Mandibular and hyoid arches of a Cod, Gadus morrhua . 478
236. Lateral view of the skull of a Salmon, Salmo salar . . 480
237. The right half of the pectoral girdle and the right pectoral
fin of a Cud, Gadus morrhua ...... 482
238. Dissection of a Roach, Leuciscus rutilus, to show the brain,
gills, and viscera . 485
239. Diagram illustrating the arrangement of the heart and
branchial vessels in a Teleostean fish .... 488
240. A Cat-fish, Amiurus catus 492
241. The Plaice, Pleuronectes platessa . . . . . . 494
242. Three stages in the development of the vertebral column
of Lepidosteus . - . . . . . . . 497
243. Three stages in the development of the vertebral column
_of Amia .
244. The Sturgeon, Acipenser sturio ......
245. Polypterus .........
246. Lepidosiren paradoxa . . . . .
LIST OF ILLUST11ATIONS XV11
Diagram of the arterial arches of Ceratodus viewed from
the ventral side . 505
Diagram of the venous system of a Dipnoan ... 507
Lateral view of the skeleton of Ceratodus miolepis . . -508
Dorsal and ventral views of the cranium of Ceratodus
miolepis .......... 510
Skeletons of the anterior and posterior limbs of a Newt,
Molge cristata 520
Skeleton of Triton, Molge cristata, seen from the side . 522
Male and female specimens of Molge cristata . . . 525
Diagram illustrating three stages in the development of
the vertebral column of an Opisthocoelous urodela . 526
Dorsal, ventral and lateral views of the skull of Molge
cristata .......... 529
Visceral arches of Molge cristata. . . . . . 531
Ventral and lateral views of the pectoral girdle and sternum
of Molge cristata 532
Skeletons of (a) right fore-arm and hand of the Salamander,
Salamandra maculosa, and (6) the right ankle of the Newt, .
Molge cristata . . . . . . . . 533
Pelvic girdle of Molge cristata . . , . . . 533
Dissection of a male Molge cristata . . . . . 534
Diagram of .the venous system of a .Urodele . . . 536
Diagram of the arterial arches of Molge . . . . 537
Dorsal view of the brain of Molge cristata . . . 538
Excretory and reproductive organs of a female Molge cristata 539
Excretory and reproductive organs of a male Molge cristata 540
Larva of Triton, Molge cristata ...... 541
Diagrams illustrating the development of the procoelous
vertebral column in Anura . . 546
Dorsal and ventral views of the cranium of the common Frog,
^jRana temporaria, from which the membrane bones have
mostly been removed . . . . . . . ^ 547
Dorsal and ventral views of the cranium of Rana temporaria 548
Lateral view of the skull and posterior view of the cranium
of Rana temporaria . . . . . . . . 549
Visceral arches of (a) Rana temporaria, adult, (6) Tadpole
of Rana . .. . ' ... . .. . ... . 550
Shoulder-girdle and sternum of (a) an old male specimen
of Rana temporaria, (6) . an adult female Docidophryne
gigantea . . . . . . . . . 551
Diagram of arterial arches of a Frog viewed from the
ventral aspect ......... 552
Dorsal view and dissections of the heart of a Frog . . 553
Dorsal view of the brain and spinal cord of a Frog . . 554
xviii LIST OF ILLUSTRATIONS
FI(J. PAGE
276. The excretory and reproductive organs of (a) a male, and
(b) a female Frog 556
277. Tadpole of Rana esculenta ....... 557
278. Two stages in the development of the front part of the
vertebral column of an Amniote (the Lizard) . . 564
279. Section through the scale of a Lizard . . . . 568
280. Ventral view of the shoulder-girdle and sternum of a Lizard,
Loemanctus longipes ........ 570
281. Lateral view and longitudinal section of the skull of a Lizard,
Varanus varius . . . . . . . . . 572
282. Diagrams of the cranial roof in a Stegocephalan, various
types of reptile and a bird, showing modifications in the
postero-lateral region .......
283. Lateral view of the shoulder-girdle of a Lizard, Varanus .
284. View of the interior of the mouth of Varanus indicus
285. Diagram of the arterial arches of Chamaeleo . . .
286. Diagram of the venous system in Anura and Reptilia
287. Excretory and reproductive organs of a male Lizard
288. Lateral, dorsal, ventral and posterior views of the skull of
Sphenodon punctatus ... ...
289. A limbless Lizard, Anguis fragilis, the Blind-worm .
290. Dorsal and ventral views of the skull of the Common Snake,
Tropidonotus natrix
291. Diagram of the arterial arches of a Snake ....
292. The Texas Rattlesnake, Crotalus atrox ....
293. (1) Dorsal and ventral views of the carapace of a Loggerhead
Turtle, Thalassochelys caretta ; (2) The plastron of a Green
Turtle, Chelone mydas .......
294. Ventral view of the skeleton of the Green Turtle, Chelone
mydas ..........
295. Longitudinal vertical section through the cranium of the
Green Turtle, Chelone mydas ......
296. Diagram of the arterial arches of a Turtle viewed from
ventral surface
297. Palatal aspects of the cranium and of the mandible of an
Alligator, Caiman latirostris ......
298. The first four cervical vertebrae of a Crocodile, Crocodilus
vulgaris ..........
299. Sternum and associated membrane bones of a Crocodile,
Crocodilus palustris ........
300. (a) Left half of the shoulder-girdle and (6) the pelvis and
sacrum of an Alligator, Caiman latirostris . . .
301. Diagram of the arterial arches of a Crocodile
302. Section through the skin of a Bird showing a developing
feather
LIST OF ILLUSTKAT1ONS XIX
FIG. PAGE
303. Bones of the right wing of a Gannet, Sula alba . . 609
304. Shoulder-girdle and sternum of a Peacock, Pavo cristatus 610
305. Dorsal and ventral views of the wing of the Wild-Duck,
Anas boschas ......... 612
306. Lateral view of the pelvis and sacrum of a Duck, Anas
boschas 613
307. Skeleton of the common fowl, <, Gallus bankiva . . 615
308. Lateral and dorsal views of the brain of the Pigeon, Columba
livia 617
309. Anterior, posterior and dorsal views of the third cervical
vertebra of an Ostrich, Struthio camelus . . . 618
310. Diagram of the arterial arches of a Bird .... .620
311. Diagram of the venous system of a Bird .... 621
312. The chief viscera of the Pigeon, Columba lima . . . 622
313. The lungs, kidneys and gonads of the Pigeon, Columba
livia 626
314. Section through the skin of a Mammal showing the develop-
ing hair 637
315. Ventral view of the cranium of the Dog, Canis familiaris 639
316. Dorsal view of the cranium of the Dog, Canis familiaris . 640
317. Dentition of the Dog, Canis familiaris .... 642
318. Diagrams showing the evolution of the ear-bones in Mam-
malia . . . . . 644
319. Dorsal and ventral views of the brain of the Rabbit, Lepus
cuniculus 646
320. Diagrammatic transverse section of the bony cochlea and
its contained sense-organ in a Mammal. . . . 648
321. Sternum and sternal ribs of the Dog, Canis familiaris . 649
322. Skeleton of the Rabbit, Lepus cuniculus . . . . 651
323. Diagrams of arterial arches of Mammals .... 653
324. Diagram of the venous system of a Mammal . . . 654
325. The Duckbill, Ornithorhynchus anatinus .... 657
326. Diagram to show the arrangement of the female genital
ducts in the Prototheria 657
327. Ventral view of the shoulder-girdle and sternum of a Duckbill,
Ornithorhynchus paradoxus ...... 658
328. Diagram to show the arrangement of the female genital
ducts of the Metatheria . . 659
329. The Rock Wallaby, Fetrogale xanthopus, with young in
the pouch 660
330. Skull of Lesueur's Kangaroo-rat, Bettongia lesueuri . . 662
331. The banded Ant-eater, Myrmecobius fasciatus . . . 663
332. Diagrams to show the arrangement of the female genital
ducts in the Rabbit and Man as types of Eutheria . 665
333. Tamandua Ant-eater, Tamandua tetradactyla . . . 666
XX LIST GF ILLUSTRATIONS
FIG.
334. The six-banded Armadillo, Dasypus sexcinctus .
335. The white-bellied Pangolin, Manis tricuspis
336. An African Jumping-shrew, Macroscelides tetradactylus
337. The Russian Desman, Myogale mosohata . . .
338. Vertical longitudinal section through the skull of a Dog,
Cams familiaris . . .
339. The Common Skunk, Mephitis mephitica ....
340. The Patagonian Sea-lion, Otaria jubata . .
341. Lateral view and longitudinal section of the skull of a young
Ca'ing Whale, Globicephalm melas .....
342. The skull of Hyrax (Procavia) dorsalis ....
343. Eight view ' of skull of a young Indian Elephant, Elepkas
- indtcus, with the outer sides of the jawbones removed
so as to expose the roots of the teeth ....
344. Bones of the right fore-foot of existing Perissodactyles .
345. The Indian- Rhinoceros, Rhinoceros unicornis ...
346. Stomach of a Sheep cut open so as to show the different
- compartments . . .
347. Skeleton of a Cape Buffalo, Bubalus caffa ....
348. The African Water-chevrotain, Dorcatherium aquaticum .
349. The Musk-ox, Ovibos moschatus
350. Skull of the African Manatee, Manatus senegalensis .
351. Front views of the head of the American Manatee, Manatus
americanus . . .
352. Side view of the skull of the Rabbit, Lepus cuniculus
353. Dorsal view of the skull of the Rabbit, Lepus cuniculus .
354. The African Flying Squirrel, Anomalurus fulgens
355. The Musquash, Fiber zibethicus ......
356. Skeleton of -a fruit-eating Bat, Pteropus medius . .
357. Female with young of a Bat, Xantharpyia collaris .
358. Skulls of an old and of a young specimen of the Gorilla,
- Gorilla savagei
359. The Ring-tailed Lemur, Lemur catta
360. The Orang-utan, Simia satyrus, sitting in its nest .
CHAPTER I
INTRODUCTION
THE word Zoology (Gr. woi/, an animal; Xoyos, a discourse)
denotes the science which concerns itself with animals,
endeavouring to find out what they are and how they
came into being. It is a branch of the wider science of Biology
(Gr. /3io9, life, Ao'yos, 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 obeying 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 called
food, which is different from themselves and that further, they give
rise at intervals to fresh 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 2 and this distinction, is broadly speaking true.
1 This term is too well established to admit of alteration but it implies a
mistranslation of /Jt'os. This does not mean 'life' in the physiological sense but
a period of life, a career, a life-time or circumstances of life, environment.
2 It is true that to all general statements of Zoology, as to this, exceptions
could be found. The rule followed in this book is to have regard only to the
S. & M. 1
2 " INTRODUCTION [CH.
The'so-icalled movements' t)F' plants are almost always due to the
growth of new parts and are not to be compared with the movements
of animals which are the result of the alteration of relative position of
fully formed organs.
Another fundamental difference between animals and plants is to
Distinction be found in the nature of their food. Animals can
animals and on ^ ^ ve on com pl ex substances, not very different
plants. i n chemical composition from their own bodies, and
further, they can live on solid food. Plants, on the other hand, build
themselves up out of carbon dioxide and other gases and out of 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 of
extremely low and primitive character 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
primarily not as bodies in which growth and reproduction occur, but
rather 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 far 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 which 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 1 ; animals are for
vast bulk of normal cases which gave rise to the idea. The reasons for classify-
ing abnormal cases in one category or another are not general but special, and
have to be considered in each case.
1 The science of Comparative Psychology endeavours to make deductions
about the minds of animals from their actions.
I] PROTOPLASM 3
them bodies in which certain changes take place, changes such as
growth, reproduction, movement, and others.
A close study of animals reveals the fact that though the
chemical constitution of no two is exactly alike, yet all contain
certain allied highly complex substances of very
Protoplasm. i i v i
obscure chemical composition, known as proteids.
These substances occur in the form of a thick, viscous solution in
water; this is what is called by chemists a colloid solution or sol.,
which on very slight provocation passes into a gelatinous solid, or
gel. This mixture of sol. and gel. is termed protoplasm (Gr. TT/OWTOS,
first ; TrXaor/xa, 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; unburned 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
Metabolism. . ^
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. neTaftoXij,
change, 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, potassium, sodium, magnesium,
calcium and iron are constantly found in the bodies of animals, and
some of them are doubtless chemically combined with the proteid.
12
4 INTRODUCTION [CH.
Phosphorus is a constituent of nucleic acid, a substance which
in combination with proteid is characteristic of the nucleus (see
p. 18). Proteids have a percentage composition which varies
somewhat, though not widely, in different cases.
Carbon from 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, and so 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. Kara/3oAry, deposi-
tion). The commonest excreta are water, carbon dioxide, urea,
and uric acid ; the last two substancQS contain 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 the chemical action going
on in 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 useful to the
animal after ejection. Such useful excreta are called secre-
l] ASSIMILATION 5
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
prevents a frog from drying 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. ava.pd\Xeiv,
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 1 .
It is believed that both biogen and proteid molecules are of the
nature of compound amino-acids. An amino-acid is an acid in which
not only is the place of the central acid radicle corresponding to
the sulphur in sulphuric acid or the phosphorus in phosphoric acid
taken by a group of atoms containing carbon but this carbon group
contains also NH 2 the radicle of ammonia. As a consequence an
amino-acid can act not only like an acid in combining with an
alkali but like an alkali combining with an acid it is both an acid
and a compound ammonia and has in consequence two hands
and owing to this circumstance it can combine with another group
similar to itself by uniting so to speak its acid hand with the
alkaline hand of the new group or vice-versa and so build up a
complex chain.
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 products of
digestion must be assimilated ; in order that this may be accom-
plished they are decomposed until quite simple substances are
formed ; in a word the amino-acid chain constituted by the ingested
proteid is broken into its individual links. The casting out of an
insoluble remnant of the food is called defaecation, and inasmuch
as such remnants have never formed part of the biogen molecule,
1 See Verworn, General Physiology (Engl. Edition), 1899, p. 486.
6 INTRODUCTION [CH.
this process is carefully to be distinguished from excretion. The
accumulation of excreta soon stops metabolism, whereas the
intermission of defaecation 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 or faeces. The
fluid drops contained in it 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
Movement. / -i i TT
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, by 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
movements more quickly in one direction than in another and
so to bring about the movement of the whole animal, is called a
locomotor organ. Protoplasm in which the power of contraction
is 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
l] REPRODUCTION 7
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 in consequence of internal changes is called
automatism. In the case of external stimuli we can often observe
that the disturbance caused at the point of application of thq
stimulus is propagated to widely different 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 decreases as size
increases, and thus the chemical action between the internal portions
of the protoplasm and the surrounding medium, which can only
go on through the 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 smaller 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 smaller portion is called the germ, and the larger
the parent, since the latter is somewhat illogically regarded as
identical with the original 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 development.
Reproduction in the higher animals is closely associated with
another process called conjugation or sexual
union. This process consists in the coalescence with
one another of two portions of living matter. Conjugation probably
8 INTRODUCTION [cH.
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 develop
without first conjugating, one of the first kind uniting with one of
the second. The lowest animals also produce such germs in many
cases, but sometimes they are all alike and at other times they are
different in size. Sometimes indeed they are almost indistinguishable
from true ova and spermatozoa. The name gamete is employed
therefore to designate conjugating germ cells irrespective of their
size.
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 is termed the male. In this case the species of
animals is said to be bisexual. When both ova and spermatozoa
are developed in the same individual it is spoken of as her-
maphrodite.
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
number of kinds called species, the individuals composing which
apart from the difference between males and females and difference
due to age 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
l] HEREDITY 9
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 in the majority of
cases are not fertile.
It has been pointed out, that whereas germs are in most cases
exceedingly different from their parents, they never-
Heredity - . i i i
and theless in process 01 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. In a large number of
cases where father and mother differ from one another by some
well-marked character unconnected with their sex the child resembles
closely the father or the mother, a result denoted by the term
prepotent applied to the parent which the offspring resembles.
When however the children resulting from such a union are mated
together, some of the grandchildren resemble one grandparent and
some the other grandparent : three-fourths resemble the prepotent
grandparent, and the character which they inherit is called the
dominant character, and one fourth the other grandparent and
the character which reappears in them is called the recessive
character. When the grandparents differ in two characters, the
same law holds with respect to each character, i.e. three-fourths of
the offspring resemble one grandparent and one fourth the other
but not all the same children fall into the same group in the case
of each character, and so some children inherit the dominant
character from one parent and the recessive from another, and thus
10 INTRODUCTION [CH.
two new types are formed. Individuals belonging to the same
species which differ from one another in well-marked characters
are termed varieties, and the laws governing the inheritance of
character when two varieties are mated together were worked out
by an Augustinian monk named Mendel, whose work has been
repeated and extended by a flourishing school of modern investiga-
tors. These laws show how when two varieties of a species exist,
new varieties can result from their crossing, but they throw no light
on a question of cardinal importance, how the varieties themselves
came into existence in the first case. In a few cases however, the
sudden appearance of these new varieties has been actually recorded.
In all these cases the new variety may be described as a cripple ; it
is characterised by the loss or imperfect development of some character
found in the normal form. A variety is to be discriminated from a
race ; a race is a subdivision of a species occupying usually a definite
area and discriminated from neighbouring races by a multitude of
small characters.
It is obvious that so vast a science as Zoology must be divided
into various branches, since the different questions it
of B zooi C h gy. 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 all. divisions of the subject, that of Physiology has been most
neglected it has indeed been studied systematically only 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 dis-
tinctions between the various species are to be explained. The question
of the "Origin of Species" involves nearly all others in Zoology.
l] ORIGIN OF SPECIES 11
The distinctions between species are of very different degrees,
so that for convenience species closely resembling
Classification.
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
naturalists is the famous theory of Charles Darwin.
According to this theory, the resemblances between
a number of living species are due to the fact that these species
are descended from a common ancestral species which possessed the
common features as characters of its own. Therefore, the degree of
likeness between species is the expression of a nearer or remoter
blood relationship, and it logically follows that, since no part of
the animal kingdom is without resemblances to the rest, if we
recede 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
ideas that had first occurred to Greek philosophers, and had in one
form or other been put forward by many naturalists before him.
His special merit lies in that he pointed out various processes
at present going on in nature which must lead to the modification
of species. He recalled attention to the well-known fact which we
have just discussed, that although the offspring in general resemble
the parents, yet this resemblance is never exact, and further that
the young of one brood often differ quite perceptibly from one
another, and that these differences are often inherited by the off-
spring of the individuals showing them.
Again, another fact well-known but usually ignored, was em-
phasised by Darwin : viz., that if the state of the animal population
of the globe remains fairly constant, out of all the young produced
by a pair of parents during their lifetime on an average only two
will survive, since if more were to live the species would inevitably
increase in numbers. Hence since each animal tends to multiply
at a rate at which if unchecked it would soon overrun the globe, a
competition must result between the members of each species both
for food and in the escape from enemies, as a result of which the
" fittest " will survive. So long as the surroundings of the species
12 INTRODUCTION [CH.
remain the same, this struggle for existence will only weed out those
individuals least perfectly adapted to their environment, so that
the species will be kept up to a high level of adaptation to its
surroundings. This elimination of imperfect individuals which results
in the survival of the fittest is known as Natural Selection.
Thus we can well imagine that if white-haired individuals turned
up amongst hares, they would be more conspicuous and hence more
easily discovered by the animals which prey on hares. If however
the circumstances of a sp'ecies change, a different class of individuals
will survive. For instance, if for the greater part of the year the
country inhabited by the hares were covered by snow, as is the case
in the North of Canada, the whitest-haired individuals 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 from the same ancestors. It is of course not
difficult to see that if a species is distributed over a wide area the
conditions in different 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
inter-breeding 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 from 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
I] HOMOLOGY 13
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 1 . If the theory be rejected these resemblances are
pure figments of the human mind, and the species must be regarded
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 of gradual evolution is accepted by the over-
whelming majority of naturalists. Differences however exist as to the
nature and origin of the variations out of which evolutionary change
is built up. It has been shown that the minute differences between
brothers and sisters on which Darwin relied are usually non-inheritable.
Larger variations occurring at rarer intervals are strongly inherited
but as already mentioned these are of the nature of pathological
defects and are utterly unlike the marks which divide natural species.
Of quite recent years some evidence has been brought forward to show
that increased use which leads to increased size produces inheritable
effects. The selection would then operate in causing the survival
of those that responded most actively to the needs imposed by the
environment.
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-
1 Most of the names employed in classification were in use before Darwin's
views were accepted. The word phylum (Gr. QvKov, tribe or stock) is however
an exception. This term expresses the central idea of the evolution theory,
and its proper use is to denote the whole of a group of animals characterised
by having the same ground-plan of structure and believed 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 differences
in structure which can only be bridged by imaginative hypotheses.
14 INTRODUCTION [ CH - l
plasy, whereas resemblances believed to indicate blood-relationships
are grouped under the term homology.
Again, the immature 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. TT/XOTOS, first, o>oi/,
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 thart 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. Some of 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, OVTOS, being) or the development of
the individual, nature recapitulates to some extent the development
of the species in past time, Phylogeny (, flesh) (Fig. 24), secreted by the ectoderm at any rate
on the lower portion, of the body, also that the tentacles are nearly
always solid, containing, instead of tubular outgrowths of the endo-
derm, a solid cord of cells (Fig. 24) with firm outer membranes and
partially fluid contents, so that the cells have the same kind of
stiffness as a well-filled water-pillow. These cords likewise grow 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
Hydro medusae, 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 bases of the longer tentacles
which spring from the flattened part of the body are connected
together by a web of skin, which constitutes in this way an
umbrella or bell. The endoderm al
canals of the tentacles within
this web are termed radial canals.
The radial canals are at first
quite separate from one another,
but they soon acquire broad fringes
of endoderm at their sides, and
these unite with those of adjacent
canals so as to form a continuous
sheet of endoderm, the endoderm
lamella. The radial canal branches
within this lamella and some branches
meet those of adjacent canals and
form a circular or marginal canal.
Other branches lead into extra ten-
tacles so that in Obelia there may
be a large number of tentacles at
the edge of the umbrella although there are only four radial canals.
In other species the young bud has the same number of tentacles as
FIG. 25
Free-swimming Medusa
of Obelia sp.
Mouth at end of manubrium.
Tentacles.
Keproductive organs.
Radial canals.
Auditory organ.
IIIJ
HYDROMEDUSAE
61
Fro. 26. Bougainvillia fmctuom, x about 12. From Allman.
A. The fixed hydroid form with numerous hydroid polyps and medusae in
various stages of development. B. The free-swimming sexual Medusa
which has broken away from A.
(52 COELENTERATA [CH.
there are radial canals, but as it grows the primary tentacles branch
and become bunches of tentacles. The upper surface of the bell is
styled the ex umbrella 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 union of certain of the tentacles by means of a web
so as to simulate 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. 25). 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. 26; 1,
Fig. 27, II). 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 term polyp is an
unfortunate one.. It really refers to the swollen end piece of a
hydroid person carrying the mouth and tentacles. The early
naturalists supposed this to be something distinct from the lower
stalk-like portion of the body which they called the "coenosarc." 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. 27,
II). 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
Ill]
HYDROMEDUSAE
63
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. This nervous system
differs from the nerve cells which were described in Hydra in that
the processes of the cells are longer and finer in proportion to the
size of the body of the cell and that the cells are more numerous and
that their processes run more or less parallel to one another. Certain
of the nerve cells have their bodies still wedged in between neigh-
bouring ectoderm cells : in this case the nerve process issues from
the base of the cell and the cell is termed a sense cell.
II. ,6
FIG. 27. I. A. Eye of Lizzia koellikeri seen from the side, magnified. B. The
same seen from in front. C. Isolated cells of the same. From 0. & R.
Hertwig.
1. Lens. 2. Pigment cells. 3. Percipient cells.
II. Radial section through the edge of the umbrella of Carmarina hastata
showing sense organ and velum.
1. Velum. 2. Jelly. 3. Circular muscles of velum. 4. Upper nerve
ring. 5. Lower nerve ring. 6. Nematocysts. 7. Radial vessel
running into circular vessel, both lined by endoderm. 8. Continuation
of endoderm along aboral surface. 9. Sense organ or tentaculocyst.
10. Auditory .nerve.
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, although they possess no nerve processes or fibres.
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 immedi-
ately outside it at the bases of the tentacles, so that the stimuli
which they receive are easily transmitted to the nerve ring. Two
64 COELENTERATA [CH.
main kinds of sense organs are frequently found, which may be
roughly called eyes and ears; never, however, both kinds in one
Medusa. The " eyes " are little coloured patches of skin, some of
the cells of which end in clear rods, while others secrete a coloured
substance or pigment. Both pigment and rods are necessary if
there is to be a vision, though we do not understand why. The ears
are little pits in the base of the velum ; they may be open or
their edges may come together, so that the ectoderm lining them is
entirely shut off from the outer skin. In either case, some of the
cells forming the walls of the pits secrete particles of lime, others
close to them develop 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 in turn will affect
the sense hairs. There is another kind of information, however,
which organs like these give their possessor, and this is probably still
more important to the floating Medusa, namely, information as to
the position of the animal with regard to the vertical. In other
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 comfortably and affect
different sense cells.
It is a very interesting fact that " Eyed " Medusae or Antho-
medusae arise from hydroid stocks in which the perisarc is confined
to the base and in which the first or mother person is taller than the
daughters which sprout from her. Such forms are called Gymno-
blastea. " Eared " Medusae or Leptomedusae arise from stocks in
which the mouth and tentacles are covered by a cup of perisarc called
the " hydro thcca" and in which the stem is built up by a daughter
sprouting from the mother hydroid's neck and a grand-daughter
from the daughter's neck and such forms are called Calyptoblastea.
Graptolites or " Pen-stones " from the Ordovician slates of Cumber-
land are extinct Calyptoblastea.
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
Ill]
HYDROMEDUSAE
65
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-
mences to give rise either to eggs or to spermatozoa, which usually
develop in exactly the same way in which they developed in Hydra>
i.e., 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. 25), 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
out into the water and coalesce there, and the fertilised egg develops
A C
FIG. 28. The ciliated larva or Planula of a Hydrornedusan, Clava Squamata.
Magnified. From Allman.
A & B. Swimming about in the sea. C. Coming to rest on a rock.
D. Developing tentacles, oral cone and stolon. 1. Tentacles. 2. Oral
cone. 3. Stolon.
into a little oval larva, termed a Planula (Fig. 28), without
tentacles or mouth, and covered all over with cilia. It consists at
first of a hollow vesicle of ectoderm cells, which later becomes 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. 28), but
the rest of the animal lengthens and a mouth and tentacles appear
at the free end and the endoderm becomes hollowed out, so that
the creature takes the form of an unmistakable 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
S. &M. 5
66 COELENTERATA [CH.
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 repre-
O f Generations sents a sexual generation, the Hydroid an asexua.l
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 was 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 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. It is an interesting fact that those
species in which the hydroid persons develop strongly and bud
frequently, so as to form a complicated branching system, generally
have degenerate Medusae, whilst in those species on the contrary
which have free Medusae the hydroid stock buds feebly or not at all
and is usually small and poorly developed. Tubularia larynx found
growing on seaweed is a good example of a form with degenerate
Medusae, Bougainvillia or Obelia of forms with free Medusae.
The Hydromedusae include a large number of families, most of
which are represented by small plant-like forms resembling the
genera just mentioned, but there are several groups which show
marked peculiarities and have been regarded by many zoologists as
of co-equal rank with the order although they have doubtless
been derived from ordinary Hydromedusae. Of these we may name
Ill] SIPHONOPHORA 6V
(i) the Trachymedusae, (ii) the Narcomedusae, (iii) the Siphonophora
and (iv) the Hydrocorallinae. These four groups together with
Hydra and the Hydromedusae constitute the first primary division
of Coelenterata which is termed the Hydrozoa.
In the first group the eggs appear to develop from the planula
stage directly into Medusae, missing out the hydroid stage com-
pletely, but there is some evidence to show that a more correct
interpretation of what happens would be to say that the egg develops
into a modified hydroid which is then converted into a Medusa by the
appearance of a web connecting the tentacles. The sense organs are
specially modified tentacles which are suspended like minute clubs
round the edge of the bell. In the Narcomedusae the planula
develops into a reduced hydroid which attaches itself to the inner
surface of the bell of a Medusa belonging to a different group.
Medusoid buds are produced by this person and set free. The
sensory organs are short clubs which are freely exposed and the wide
baggy stomach occupies the whole under-surface of the umbrella,
whereas in the Trachymedusae the sensory clubs are enclosed in pits
(Fig. 27, II) and the stomach is small and suspended from the
umbrella by a stalk traversed by the radial canals. The name
Trachymedusae (Gr. rpaxvs, rough) is derived from the circumstance
that the umbrella is stiffened by numerous ribs of endoderm cells and
the edge has a thick rim of ectoderm. The Siphonophora 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.
In most Siphonophora some of the medusoid persons known as
nectocalyces become locomotor organs and by their rapid pulsa-
tions 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.
Some species, however, like the Portuguese Man-of-war, Physalia,
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 suspended. 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 of ordinary
Hydromedusae 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
52
68 COELENTERATA [CH.
were enabled to remain suspended, then it would be placed in a very
favourable position for getting food, and it has been suggested that
the simply floating Siphonophora have thus been evolved from Hydro-
medusae. If this view be taken, the three chief divisions of
Siphonophora represent three successive stages in the adaptation of
the group to a pelagic life. Thus the Physaliidae simply float,
the Physophoridae 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 Hydrocorallinae are really distinguished by the fact that the
peris arc which only 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. Most genera produce only gonophores
but Millepora give rise to free Medusae devoid of mouth or tentacles
in which the genital organs are developed from the manabrum.
The Sea-Anemones are representatives of a second division of
Actinozoa ^ e 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
Alcyonium digitatum, sometimes called "Dead men's fingers." It
Ill] ACTINOZOA 69
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. 29). 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
-,.4
FIG. 29. Part of a colony of Alcyonium digitatum x 8, showing thirteen polyps
in various stages of retraction and expansion.
1. Mouth. 3. Mesenteries with reproductive cells.
2. Oesophagus. 4. Feathered tentacles.
polyp we shall see that the internal cavity or coelenteron, instead of
being a simple cylindrical space like that of Hydra, is partially
divided into compartments by folds stretching in towards the centre,
but not meeting. These folds are called mesenteries, and there are
eight of them, corresponding in number (but not in position) with the
tentacles (Fig. 30). We shall further see that the mouth does not,
as in Hydra, open directly into the coelenteron, but leads into a
flattened .tube which projects into the interior of the body. This
tube, the so-called oesophagus or gullet, is really lined by the
70
COELENTERATA
Dorsal
[CH.
Ventral
FIG. 30. Transverse section through a polyp of Alcyonium digitatum below the
level of the oesophagus x about 120. From Hickson.
1. Coelenteren. 2. Mesentery with free edge. 3. Ectoderm. 4. Meso-
gloea or jelly. 5. Endoderm. 6. Muscles in mesentery.
Dorsal
2
Ventral
Transverse section through a polyp of Alcyonium digitatiun, through
the region of the oesophagus x about 120. From Hickson.
Cavity of oesophagus. 2. Siphonoglyph. 3. Ectoderm. 4. Meso-
gloea or jelly. 5. Endoderm. 6. Muscles in mesenteries. 7. Inter-
mesenteric cavity.
FIG. 81.
1.
Ill] ALCYONIUM 71
ectoderm, which is merely tucked in at the mouth. Such a tube is
known as a stomodaeum 1 . The mesenteries, although they end
freely below, are attached to the sides of the stomodaeum above,
so that in this region the coelenteron is divided into a number
of compartments, each of which is prolonged into one of the hollow
tentacles (Fig. 31).
A microscopic section of such a polyp shows us several other
interesting points. We see that we have to deal with the same
layers which we met with in Hydra, skin (or ectoderm) and
coelenteron lining (or endoderm). Between them, however, there is
the jelly, which was present as an exceedingly fine membrane in
Hydra, and which, greatly thickened, formed the substance of the
bell of the Medusa. This jelly is fairly thick in the minute sea-
anemone we are examining, and here contains cells which have
wandered into it from the ectoderm. Some of these cells have the
power of secreting thorny rods of lime, termed spicules. These
spicules are very abundant where the polyp merges into the general
surface of the colony, so that they form a kind of stiff protecting
crust round the base of the polyp and over the surface of the
colony from which the polyps rise. In the organ-pipe coral,
Tubipora, the spicules in the lower parts of the polyps are so
felted together that they form a set of parallel tubes, suggesting
the pipes of an organ ; only the upper part of the polyp, where the
spicules are not yet closely aggregated, being capable of movement.
We have spoken above of the colony as distinct from the polyps,
and this use of the word demands some justification. When we
were dealing with the Hydromedusae, we used the word colony in
the sense of the whole mass of the polyps which cohered together,
and which had arisen by the growth of one original polyp. Now
in Alcyonium and its allies, budding does not take place in quite
the simple manner in which it occurs in Hydra and its allies.
Instead of one polyp growing directly out of another, the coelen-
teron of the parent sends out a tube lined only by endoderm. This
tube grows, pushing the ectoderm before it; but, as between the
ectoderm and endoderm there is a thick jelly interposed, the endo-
dermal tube can branch without the ectoderm becoming indented.
Where the free ends of these tubes reach the surface, there fresh
1 "I have proposed to designate this ingrowth... the stomodaeum ( tne restriction of the choanocytes to
small portions of the latter, and the differentiation of
the body into distinct regions.
A common sponge on the British coast, Si/con (Grantia) com-
pressum, 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 cells,
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
IV] LARVA OF POKIFERA 89
inhalant or afferent (Lat. ad, to; fero, I carry) canals which
intervene between them and into which the pores open (Fig. 39).
When a sponge becomes still more complicated the central
cavity becomes broken up into a series of branching canals, which
are termed exhalantor efferent, and the flagellated chambers become
small and rounded (Fig. 38), each often connected only by a single
opening or prosopyle (Gr. Trpoo-w, forwards; -rrvXrj, 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
surface of the sponge into which the pores open and from which
the afferent 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.
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 tacked
into the interior and there arranged as an inner lining to a cavity.
The flagellated chambers of the adult arise as small pocket-shaped
outgrowths from 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 multipli-
cation of granular cells which form a solid mass at one end of the
larva, and often, indeed generally, this mass is 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 so as to surround the granular material, so that
we are presented with the remarkable phenomenon of the internal
layer of the larva bursting 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.
90 PORIFERA [CH.
In the case of most of the Demospongiae 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 directions when the sponge flattens on
fixation. Comparing the development 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 Coelenterate 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 Volvoa, consisting
of a single sphere of cells in a word were it living now it would
have been classed as a Protozoon.
The study of the development of sponges like Sycon shows that
at first, after the metamorphosis, the sponge has the form of Leuco-
solenia, i.e. 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 choanocytes from
the walls of the central chamber into the flagellated chambers.
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.
Sponges are by some of the best authorities divided into three
main classes, viz. :
Class I. CALCAREA.
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.
IV] CLASSIFICATION 91
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. HEXACTINELLIDAE.
Sponges in which the skeleton consists of a coherent network of
siliceous spicules each consisting of three axes placed at right angles
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.
It is a most interesting fact that the flints which form regular rows
in our English chalk have been proved in many cases to contain the
remains of Hexactinellid sponges. As the chalk is a deposit on the sea-
bottom similar to the globigerina ooze on the floor of the Atlantic
one would expect it to have been richly sown with these sponges.
Class III. DEMOSPONGIAE.
These sponges derive their name from the fact that their spicules,
which are always siliceous, are arranged in cords so as to form a net-
work traversing the substance of the sponge. The spicules composing
these cords are nearly always cemented together by a horny elastic
material called s p o n g i n. The flagellated chambers are always extreme-
ly 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 appearance
of a whitish yellow scum on the rocks to which it adheres. Euspongia
possess spongin cords but these cords have 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. .
CHAPTER Y
PHYLUM PLATYHELMINTHES
THE name Platyhelminthes (Gr. -rrAarvs, flat; eX/uvs, 2X/uv#os, a
worm) means simply "flat worms." The word worm is a popular
expression not capable of any very exact definition. It connotes in
the popular, mind a low wriggling animal without conspicuous ap-
pendages. The animals belonging to the phylum of Platyhelminthes
are almost always of a flattened shape. They agree with the
Coelenterata in possessing only one opening to the alimentary
canal and this, as in Coelenterata, functions as a mouth through
which nourishment is taken in. Between ectoderm and endoderm
there intervenes a mass of tissue which strongly recalls the tissue
making up the body of a Ctenophore. This tissue is called paren-
chyma and its basis is a mass of stellate cells embedded in a ground
substance. The processes of many of these cells are metamorphosed
into muscle fibres, and these muscle fibres are arranged in longi-
tudinal, circular and vertical layers. The Platyhelminthes are
distinguished from Ctenophora by three main features. (1) They
have a definite nervous system separated from the ectoderm, which
consists of two large closely connected masses in the anterior part of
the body called the brain, from which two bands of nerve fibres run
backwards along the two sides of the body which are termed lateral
nerve cords. The swellings termed ganglia (Gr. ya'yyXioi/, a knot)
are produced by an accumulation of the bodies of nerve cells.
The cords consist mainly of their outgrowths which constitute nerve
fibres, although cell bodies are not entirely restricted to the ganglia
but are also scattered along the course of the cords in lesser
numbers. (2) They possess reproductive organs which do not
discharge directly either to the exterior or into the alimentary canal,
but which are connected with the exterior by long complicated
tubes termed genital ducts. (3) They possess a definite excretory
system. With regard to the last-named point it is to be noted that
CH. V]
EXCRETORY SYSTEM
93
in all the animals which we have so far studied excretion seems to
be performed by each cell for itself. In a sense this is true of all
animals all protoplasm must be continually producing excreta so
long as it is living and these excreta must somehow be got rid of.
So long as protoplasm is arranged (as in most Coelenterata) in the
form of thin layers of cells lining tubes, excreta are easily voided
into the cavities of the tubes, or in the case of ectodermal cells
directly to the exterior.
When however we have thicker masses of cells such as are met
with in the parenchyma of Platyhelminthes, then their excreta must
pass into the fluid in which they are
bathed, i.e. the fluid that fills the space
between ectoderm and endoderm, into
which the cells forming the parenchyma
pass. As the percentage of excreta in
this fluid rises it tends to become
poisonous to the cells unless the ex-
creta are in some way crystallised out
from it. This then is the function of
an excretory organ it precipitates the
excreta in the body-fluids in its cyto-
plasm. The precipitated excreta may
be retained in the excretory cell as
insoluble granules till it dies and drops
off, or they may be redissolved and cast
forth as an external secretion by that
cell. The ectoderm seems to have been
the original excretory organ, and the
first distinct excretory organs which we
encounter in Platyhelminthes for the
first time appear to arise as tubular
ingrowths of ectoderm into the paren-
chyma. These ingrowths branch re-
peatedly and each branch terminates in
a peculiar cell known as aflame-cell or
solenocyte. "Such a cell is hollowed
out by an extension of the excretory
tube which ends blindly within it and is
lined by a cuticular substance. From the blind end there grow
out one or more flagella which project into the tube and by their
vibration suggest the flickering of a flame. Water passes through
FIG. 40. Two flame-cells or
solenocytes from the ne-
phridium of an Annelid
worm. (After Goodrich.)
1. Flagellum of the flame-
cell. 2. Branch of the
nephridial tube leading into
the flame-cell. 3. Nucleus
of flame-cell. 4. Main
tube of the nephridium.
94 PLATYHELMINTHES [CH.
the thin wall of the tube by osmosis and dissolves the excreta
which the cells forming the wall of the tube cast out into it. Such
a branched tube ending in flame-cells is known as a nephridium
(Gr. v/m,
a thing hollowed out). This, like the primary body-cavity, is often
described as a space intervening between the ectoderm and endo-
derm, and the terms coelomic cavity and body-cavity have 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 endodermic tube. In the adult these
sacs join each other above and below the endoderm, and the adja-
cent 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
134 INTRODUCTION TO THE COELOMATA [CH.
or space is to describe it negatively : with as much justice. the endo-
dermic tube might be described as a split. In each case the real
object of consideration is the wall, and this is the point where the
coelom which the Germans appropriately name the secondary body-
cavity differs fundamentally from the primary body-cavity, for the
outer wall of the latter is merely the ectoderm. In many animals
such as Mollusca the two types of body-cavity coexist, and indeed
in all the higher animals the vessels or tubes which convey the
blood may be said to be remnants of the primary body-cavity.
ABC
FIG. 57. Three transverse sections through a developing Amphioxus to show
origin of mesoblast from endodermal pouches x 435. From Hatsehek.
The ectoderm is deeply shaded, the mesoderm is lightly shaded, the endoderm
alimentary canal and notochord is unshaded. A. shows the origin
of the paired mesodermal pouches from the archenteron ; the cavity
coelomic of the former is still in communication with the cavity of the
alimentary canal. The notochord is arising in the middle line from the
endoderm, and the tubular nervous system above it is already separated
from the ectoderm. B. shows the mesodermal pouches completely shut off;
they each enclose a cavity, the coelom, and each consists of an outer wall
next the ectoderm, the " somatopleure," and an inner wall next the endoderm,
the " splanchnopleure." C. shows the meso dermal pouches extending ven-
trally beneath the notochord, now completely separated from the wall of
the alimentary canal and also round the alimentary canal. The coelomic
space is larger, and the splanchnopleur is beginning to form muscle-cells.
If we leave out of account cases in which the facts of develop-
ment have not been fully elucidated and confine our attention to
those instances where the whole history of the coelom has been
exhaustively worked out, we find that this important organ arises
in one of two ways, either (l) by the formation of pouches of
the endodermic tube, which become nipped off (Fig. 57) ; or (2) by
the proliferation of two large cells, formed themselves by budding
from the endoderm (Fig. 58), which subsequently grow rapidly
and divide so as to form bands, the so-called mesoderm ic bands,
these bands later become hollowed out. These initial cells are
termed pole -eel Is.
IX]
INTRODUCTION TO THE COELOMATA
135
A sharp controversy has raged round the question which of
these two processes gives us the best representation of what
occurred in the evolution of Coelomata from simpler Coelenterata-
like ancestors.
If however we recall the fact that in the Actinozoa the endo-
dennic sac has the form of a series of pouches ranged round a
central cavity, and that the walls of these pouches become con-
verted into muscles and generative cells exactly as does the wall of
the coelom, and that pores exist in many cases placing the cavity of
these pouches in communication with the outside world, we shall
FIG. 58. Two stages in the early development of a common fresh-water mollusc,'
Planorbis, to show the origin of the rnesoderm cells x 320. From Kabl.
The ectoderm cells are deeply shaded, the endoderm cells are unshaded.
A. Young stage in which the endoderm has not begun to be invaginated ;
it is a lateral optical section. B. Older stage, optical section seen in
front view ; the endoderm cells are invagiriating, and the two mesoderm
cells are seen on each side. 1. Mesoderm or pole-cells ; in B, each has
budded off another mesoderm cell.
be induced to conclude that the coelom was probably evolved from
lateral pouches of the gut and that the mesoderm is therefore
derived from the primitive endoderm. Where pole-cells occur the
cavity of the alimentary canal is small in proportion to the thickness
of its wall, and the pole-cell might be looked on as a solid pouch.
In most Coelomata the mesoderm or coelomic wall forms by far
the greatest portion of the body. In the phyla which we have here-
tofore considered there are usually, as we have already mentioned,
136 INTRODUCTION TO THE COELOMATA [CH.
cells in the primary body-cavity. To such cells the name meso-
derm has also unfortunately been applied and great ambiguity has
resulted from this practice. The term mesenchyme has been pro-
posed for these cells and it is to be hoped that it will be more
generally adopted so that the name mesoderm may be confined to
the coelomic wall. The origin of mesenchyme is different in different
cases. In Actinozoa it appears to arise mainly from the ectoderm,
in Ctenophora from the endoderm. In Platyhelminthes it arises
principally from the endoderm. In the higher Coelomata it arises
partly from the ectoderm but principally from the outer wall of the
coelom. Everywhere it gives rise to connective tissue and to
the tissues developed from this (tendon, cartilage, bone, etc.),
whereas the coelomic wall or true mesoderm gives rise to the gene-
rative cells and their ducts, and the main parts of the muscular
system including the muscular coats of the principal blood-vessels.
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.
We have already seen that the ectoderm can be intucked both
at mouth and anus so that both in front and behind there is an
ectodermal section of the alimentary canal. The anterior of these
sections we have already learnt is called the stomodaenm and the
posterior the proctodaeum. In Crustacea these sections form by far
the greatest sections of the alimentary 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 stomot
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
canal are as follows: mouth- or buccal-cavity, pharynx,
IX] INTRODUCTION TO THE COELOMATA 137
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.
CHAPTER X
PHYLUM ANNELIDA
THE name Annelida (Lat. anmilus, 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.
Segmentation. " . PIT
sometimes, however, as in the case ot 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.
If we take an earthworm and kill it by placing it in alcohol for
The a few minutes and examine it carefully, we shall see
Earthworm. that the body is composed of some 150 rings, each
Matures! ^ 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. 59)
in front and the anus (3, Fig. 59) behind. Besides these, two
slit-like pores with rather swollen lips, situated on the under sur-
face of the fifteenth segment (5, Fig. 59), may be seen. These
are the pores through which spermatozoa are discharged, and
CH. X]
LUMBRICUS
139
are consequently known as the male genital
openings. The other openings into the body
are minute and require the aid of a lens to
make them out. There are paired openings on
each segment, except the first three and the
last, situated latero-ventrally; these are the 6"'
openings of the nephridia; in addition to
these a median dorsal -pore opening into the
body-cavity is situated in each groove behind
the tenth segment (11, Fig. 63). The earth-
worm 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 gene-
rative openings. Two pairs of pouches called
spermathecae, which are reservoirs for sper-
matozoa received from another worm (y. p. 97),
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 (Gr. x at/T *?> hair), which
project from the body (7, Fig. 59, and Fig. 62).
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. It is by means of 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
Fm. 59. Latero-ventral view of Lumbricus terrestris,
slightly smaller than life-size. From Hatschek
and Cori.
1. Prostomium. 2. Mouth. 3. Anus. 4. Opening
of oviduct. 5. Opening of,vas deferens. 6. Geni-
tal chaetae. 7. Lateral and ventral pairs of chaetae.
xv, xxxn, and xxxvn are the 15th, 32nd, and 37th seg-
ments. The 32nd to the 37th form the clitellum. FIG. 59.
xv
XXXVII
140 ANNELIDA [CH.
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 dift'er in adult worms from those of the
segments which lie before and behind this band. This is due to
the presence in this region of certain ectodermal glands whose secre-
tion forms the cocoons in which the eggs are laid. This region of
the body is called the clitellum (xxxn xxxvn, Fig. 59).
The surface of the body of an earthworm is glistening and
somewhat slippery. This is due to the cuticle, which is a thin
membrane secreted by the ectoderm cells of the skin ; if a dead
earthworm be soaked in water for a few hours the cuticle can be
easily stripped off the body. As we have already seen a similar
cuticle is present in Trematoda, Cestoda, Nematoda and Rotifera,
but in the two groups last mentioned 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 enables 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-sacs, 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
Anatomy! * n * * ne coeloniic cavity, in which not only the
alimentary canal but the blood-vessels, kidneys and
reproductive organs apparently lie. The relation of the coelom in
the earthworm to the ectoderm and endoderm may be illustrated in
the following way. Take a piece of leaden gas-tube or of thick glass
tubing to represent the endodermic tube or alimentary canal, slide
over it a series of hollow rubber rings so that these rings are pressed
closely against one another in longitudinal series. Then pull a
cotton casing over the whole thing and so we shall have a rough
model of the body of an earthworm. The cotton casing will repre-
sent the ectoderm and the rubber rings collectively the coelom.
From this we learn that the coelom of the earthworm consists not
of one but of a series of cavities there being one ring-shaped cavity
in each somite, and that these cavities are separated from one
another by transverse walls which are called septa or dissepi-
ments. Each cavity has its own proper wall which is termed
X] LUMBRICUS 141
peritoneum (Gr. Trepi, around; TO'VOS, a string). Where this wall
adjoins the ectoderm it is called parietal or somatic peritoneum
(Lat. paries, an outer wall ; Gr. o-w/xa, body), where it impinges on
the gut it is called visceral or splanchnic peritoneum (Lat.
viscus-, Gr. cnrXayx vov ) entrail). A septum consists of two layers
of peritoneum one forming the hinder wall of the coelomic space
in front and the other the front wall of the coelomic space behind,
and intervening between the two there is a certain amount of
mesen chyme in the form of connective tissue and also channels for
the blood. Each septum is pierced with a small hole in the mid-
ventral line so that fluid can pass from one coelomic cavity to the next.
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 coelom 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. 63), 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, viz. (a) a lip or pro-
stomium (], Fig. 62), overhanging the somewhat crescent- shaped
mouth, and (6) a peristomium containing the mouth which leads
into an oral cavity extending through three segments (Fig. 60).
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 segment.
This is followed by the true endodermic tube. The first part is
narrow and is called the oesophagus; it reaches to the twelfth
segment and has three pairs of lateral pouches developed on its
walls. These pouches secrete calcareous particles, and hence are
termed calciferous glands. Their formation has recently been
carefully investigated by Stephenson and it is interesting. The most
anterior pair open widely into the oesophagus of which they are
merely lateral dilatations : folds project^into their cavities. As we
pass back the free edges of these folos^unite so that the spaces
between them form a series of tunnels and these tunnels make up
the middle and posterior pair of glands. The oesophagus dilates
behind into a thin- walled sac, called the crop, situated in the region
142
ANNELIDA
[CH.
of segments thirteen to sixteen, and this is separated by a groove
from a thick-walled sac, with hard, horny walls, termed the gizzard,
which extends to about the twentieth segment. The exact segment
in which the above-mentioned parts of the alimentary canal lie varies
with the amount of food they contain, the septa which are pierced
by them being stretched forward or backward according to their
state of fulness or emptiness.
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
swelling out slightly in each
segment, so that it presents an
outline like a string of beads.
A deep fold, called the typhlo-
sole (Gr. rvcf>\6<;, blind; o-wX^V,
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 its inter-
nal absorbing surface is increased
(7, Fig. 61). The intestine is
covered everywhere by a number
of cells of a yellow colour.
These form the inner wall of the
coelomic sac and are actively
engaged in excretion.
The exact part that each of
the above-mentioned parts of
the alimentary canal plays in
digestion is not thoroughly
understood. The pharynx helps
to take food in by a sucking
action which is caused by the
contraction of the muscles run-
ning from it to the body-wall,
resulting in an enlargement of
the cavity of the pharynx so
that food may pass in by
atmospheric pressure. The food passes down the oesophagus,
being propelled by a series of contractions of the walls of the
FIG. 60. Anterior view of the internal
organs of an Earthworm, Lumbricus
terrestris. Slightly magnified. From
Hatschek and Cori.
1. Central ganglion or brain. 2. Mus-
cular pharynx. 3. Oesophagus.
4. Crop. 5. Muscular gizzard.
6. Intestine. 7. Nephridia (the
reference lines do not quite reach
the nephridia). 8. Septa.
9. Dorsal blood-vessel. 10. Hearts.
11. Spermathecae. 12. Vesiculae
seminales.
The Koman figures refer to the number
of the segments.
LUMBRICUS
143
alimentary canal which push it along ; on its passage it is mixed
with the secretions of the calciferous glands. It has been sug-
gested that since the decaying vegetation on which the worm feeds
is strongly acid in character the calcareous particles secreted by the
calciferous glands tend to neutralise these acids. 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 fit 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
FIG. 61. Six segments from the intestinal region of an Earthworm, Lumbricua
tcrrestris, dissected to show arrangement of parts. Magnified. From
Hatschek and Cori.
1. Septa. 2. Nephridia. 3. Ventral nerve-cord. 4. Sub-neural
blood-vessel. 5. Nephrostomes, internal funnel-shaped openings of
nephridia. 6. Intestine. 7. Typhlosole. 8. Circular blood-vessels.
9. Ventral or sub-intestinal blood-vessel. 10. Dorsal blood-vessel.
digestion soak, and are taken all over the body by the blood-vessels
and probably also to some extent by the fluid in the coelom.
The series of contractions which squeeze the food onwards
towards the anus are known as peristalsis; they constitute the
sole movements of which the 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 rings
or tight india-rubber bands.
The earthworm eats earth and manages to find sufficient
nourishment for its needs in the small amount of organic matter,
144 ANNELIDA [CH.
broken-down de"bris of leaves, etc., which is contained in the earth.
The actual minerals of the earth are not digested but are passed
out 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.
Earthworms also eat fallen leaves and to this end they drag the
leaf-stalks 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 worms. The burrows
that they make admit both air and rain to the deeper layers of the
soil, and the earth which they swallow in their burrows is brought
to the surface and spread about in the form of castings. This 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 remnants of the primary body-cavity
which is nearly obliterated as the result of the expansion of the
secondary body-cavity or coelom they may be described as being
merely crevices between the coelomic wall on the one hand and the
ectoderm and endoderm on the other. Those mentioned below
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. A few of the blood-vessels seem also to
have an inner wall consisting of flattened cells this is known as
an en dot helium. Its origin is curious and interesting. In the
blood of the earthworm as in that of almost all animals there are
floating cells which, like those in the coelom, resemble Amoeba in
the power of crawling and of emitting pseudopodia; certain of these
amoebocytes adhere to the walls of the crevice which constitutes
the blood-vessel, become flattened and make in this way an almost
complete plating of cells.
The fluid in the primary body-cavity is the medium into which
the digested product of the food diffuses from the endoderm cells,
and in which the excreta accumulate until they are removed by the
excretory organ. The oxygen necessary for the respiration of the
mesenchyme cells must also diffuse into it through ectoderm or
endoderm or both. Hence this fluid which is the basis of blood has
three main functions : (a) it conveys the products of digestion to
X] LUMBRICUS 145
the internal cells of the body, (6) it conveys excreta to the excretory
organ, and (c) it conveys to the internal cells of the body the
oxygen necessary for their respiration.
The most important blood-vessels of the earthworm are as follows :
(1) a dorsal blood-vessel visible through the skin as a dark streak
which runs along the body of the worm from head to tail in the middle
line (10, Fig. 61); (2) a parallel sub-intestinal vessel which
underlies the intestine, and (3) a third but smaller vessel, the
sub- neural, which lies still more ventrally under the nerve-cord.
There are also two latero-neural vessels lying one at each side of
the sub-neural vessel, but as they are connected with it at frequent
intervals the three together may be regarded as practically one
vessel. 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. Two vessels in each segment
connect the ventral vessel with the network of fine blood-vessels
which covers the surface of the alimentary canal, and the ventral
vessel and the dorsal vessel are connected by means of five pairs
of loops, called hearts, situated in the seventh, eighth, ninth, tenth,
and eleventh segments (10, Fig. 60). The dorsal vessel and the sub-
neural vessel are put into communication in each segment by two
parietal vessels which lie on the outer wall of the coelom and
which receive numerous small vessels from its substance. Each
nephridium is connected by one vessel with the ventral vessel and
by another with the parietal vessel.
The earthworm breathes through its skin. The parietal vessel
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-
tion for oxygen, which it takes up from the air that comes into
the neighbourhood of the skin-capillaries, forming a bright red
compound called oxy-haemoglobin. This compound is unstable,
and when the blood in its course round the body encounters a cell
S. & M. 10
146 ANNELIDA fen.
hungry for oxygen, the oxy-haemogiobin is decomposed : the reduced
haemoglobin is purplish in colour. At the same time the cell gives
up carbon dioxide to the blood. The relations 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 organs.
When the blood again approaches the skin carbon dioxide is got rid
of, oxy-haemoglobin being again formed by fresh oxygen taken in.
The earthworm is the first animal which we have so far studied
in which there is any flow of the blood in a definite direction in
a word a circulation. Movements of the fluid contained in the
vessels of the Nemertine worms in various directions are doubtless
occasioned by the contractions of the body muscles of those long
thin animals in the Rotifera owing to their small size the whole
bulk of the fluid is so small that the molecular movements of
diffusion are enough to thoroughly mix it up. The direction of
movement of the blood in the dorsal vessel in the Earthworm can
be seen through the skin. Waves of contraction are seen to begin
in the hinder end of this vessel and to travel forwards, pushing
the blood in front of them. In the other vessels the direction of
the flow can be inferred from the existence of valves. These are
flaps projecting inwards from the walls of the vessels into their
cavities. They are arranged in pairs so as to open only in one
direction. When they swing in the opposite direction they come
together and close the cavity of the vessel. The blood must there-
fore flow in the direction in which the valves open. In the dorsal
vessel there is in each segment a pair of valves opening forwards.
Where the parietal vessel joins the dorsal vessel there is a pair
of valves opening upwards, and lastly in each heart there is at
each of three different levels a pair of valves opening downwards.
Hence we infer that as blood flows forwards in the dorsal vessel,
blood pours into it from the parietal vessel which has ascended
from the sub-neural vessel along the outer side of the body. Some
of this blood has doubtless passed into the dermal plexus, as the
network of fine vessels is termed which underlie the skin and are
connected with the parietal vessel. In this plexus the blood has been
recharged with oxygen. Blood passes from the dorsal vessel down-
wards into the ventral vessel through the hearts, and as this latter .
vessel is devoid of muscles and valves it is to be regarded as a reservoir
in which the blood is stored and from which it passes out in all
X] LUMBRICUS 147
directions. Thus some of it descends to the sub-neural vessel by
a vessel situated in each septum. Some of it streams out to the
gut and enters the plexus of fine vessels surrounding it in which it
absorbs the products of digestion and passes by other vessels into
the dorsal vessel; and some of it streams out to the nephridia, is
there relieved of its nitrogenous excreta, after which it passes on to
the parietal vessel. Blood from neural vessels and nephridia passes
upwards in the parietal vessel to pour into the dorsal vessel.
In the earthworm the excretion of the waste nitrogenous
material is carried out by the nephridia. 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. 60, and 2, Fig. 61). The nephridia differ from those
of Platyhelminthes, Nemertinea and Rotifera, (1) in being un-
branched, since each consists of a single coiled tube, and (2) in
that each opens into the coelom at its inner end by a funnel termed
the nephrostome. This nephrostome has cilia on its funnel-shaped
rim, and these flicker with an untiring movement. The nephro-
stome does not lie in the same segment as 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-shaped opening and a tube which
opens externally, but they do not belong to the same nephridium.
The tube is not straight but is coiled and lies as a white glistening
tangle close to the septum in front. Close inspection shows it to
be completely enveloped in a loose fold of the peritoneum forming
the hinder wall of the septum.
When we examine a nephridium through a microscope we see
that the walls 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
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
102
148 ANNELIDA [CH.
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 in it numerous
amoebocytes (v. p. 141), and these corpuscles act as scavengers,
taking up into themselves any foreign bodies, such as bacteria,
which have made their way into the coeloin, and breaking them up.
The yellow cells (7, Fig. 63), 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 escape by the dorsal pores since the funnel of the
nephridium is too small to admit the amoebocytes it serves merely
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.
In the yellow cells we see evidence that the coelomic wall takes
part in the process of removing excreta from the blood, and as we
ascend in the scale of animal life we shall find that the primitive
ectodermic nephridia are more and more replaced by structures
derived from the coelomic wall.
The earthworm, although it lives in earth, has a clean, glistening
look, and this is partly due to the fact that the coelomic fluid
is poured out from the dorsal pores (11, Fig. 63) and keeps the
skin moist and lubricated. This fluid is also antiseptic in its
action, and thus its presence prevents foreign organisms, such as
bacteria, which swarm in the mould in which the worm lives, from
settling upon the skin and growing there. Numerous glandular
cells belonging to the ectoderm also pour forth a secretion through
minute pores in the cuticle.
If we cut open an earthworm by a median dorsal incision and
attentively examine the upper surface of the pharynx
System. 6 we sna ^ nn( l a ^ its anterior end, tucked away between
it and the skin, two little whitish knobs lying close
to one another. These are the cerebral or supra-pharyngeal
ganglia (1, Fig. 60; 2, Fig. 62). At their outer ends the supra-
pharyngeal ganglia pass into two cords (3, Fig. 62). 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 ventral ganglion (4, Fig. 62): from
this a long white cord the ventral nerve-cordruns back to
LUMBRICUS
149
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 or
ganglion which gives off both dorsally and ventrally and on each
side three pairs of nerves to the surrounding parts.
The nervous system of an earthworm thus consists of two
supra-pharyngeal ganglia situated in the third segment, a pair
FIQ. 62. Diagram of the anterior end of Lumbricus herculeus to show the
arrangement of the nervous system. After Hesse.
i, n, m, iv. The first, second, third, and fourth segments.
1. The prostomium. 2. The cerebral ganglia. 3. The circumoral com-
missure. 4. The first ventral ganglion. 5. The mouth. 6. The
pharynx. 7. The dorsal and ventral pair of chaetae. 8. The tactile
nerves to the prostomium. 9. The anterior, middle and posterior
dorsal nerves. 10. The anterior, middle and posterior ventral nerves.
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 are features common
to nearly all the Invertebrata, and in those which have a bilateral
symmetry and are segmented there are supra-pharyngeal ganglia
and a ventral nerve-cord bearing segmen tally repeated ganglia.
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 part of the body.
150 ANNELIDA [CH.
It further serves to put each organ and each part of each organ in
communication with all the others, and thus this vast accumulation
of tissues and cells acts in an orderly way and towards a set end.
It is built up by the repetition of a special type of cell called the
neuron or nerve-cell. This cell consists of a body containing
the nucleus and processes. From the body is given off a straight
fine process called the ax on, which ends in a tuft of processes
called terminal dendrites. From the other end of the cell a
coarse process proceeds outwards, ending in a tuft of processes
called receptive dendrites. These receive impressions which
are transmitted to the axon and passed on either to other neurons
or to muscles.
The 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 earthworm has no specialised sense organs, it has neither
eyes to see, nor nose to smell, nor ears to hear with. Still,
although it is 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 onions and raw meat. Their sense of touch is well
developed and they are very sensitive to vibrations ; for instance,
a stamp of the foot on the ground will cause all those in a
certain radius to disappear into their burrows. It is further
possible that earthworms possess other senses with which we are
totally unacquainted.
In each segment of the worm scattered here and there amongst
the ectoderm cells are a number of sense cells. Each of these has
a minute sense hair which projects upwards through a hole in the
cuticle, and by means of this hair stimuli oi various kinds are
received from the outer world. The body of the cell is small just
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 terminal dendrites in close contact with
the receptive dendrites of a neuron. In this way the neurons
receive impressions from the outside world. A bundle of the
axons of sense cells proceeding inwards is known as a sensory
peripheral nerve. The receptive dendrites of the neurons
receive the impressions from the sensory nerves and pass them on
LUMBRICUS
151
to other neurons and eventually to muscles. A bundle of axons
passing out to a muscle is called a motor peripheral nerve.
A transverse section of an earthworm, such as can be cut by a
microtome from a specimen embedded in paraffin wax, is most
instructive, in exhibiting the relation to one another of the various
tissues which make up the body of the earthworm. The outermost
16
Fro. 63. Transverse section through Lumbricus terrestris in the region of the
intestine and of a dorsal pore. Magnified.
1. Cuticle. 2. Ectoderm or epidermis. 3. Circular muscles. 4. Dorsal
nerve. 5. Longitudinal muscles. 6. Parietal peritoneum.
7. Visceral peritoneum or yellow cells* 8. Endoderm or epithelium
lining the intestine. 9. Coelom. 10. Nephridium cut in section.
11. Dorsal pore. 12. Dorsal blood-vessel lying along the typhlosole
or groove in the wall of intestine. 13. Sub-intestinal blood-vessel.
14. Ventral nerve-cord. 15. Sab-neural blood-vessel. 16. Ventral nerve.
The dorsal and ventral nerves are added diagrammatically. The other
structures are drawn from nature.
boundary is constituted by the cuticle (1, Fig. 63), a hardened
secretion poured out by the ectoderm (2, Fig. 63). The ectoderm
is composed of tall cylindrical cells, 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
152 ANNELIDA [CH.
secreted, ' which is poured forth through a hole in the cuticle
opposite the end of the cell-neck and helps to keep the surface
of the worm moist.
Beneath the ectoderm is a thin and hardly perceptible layer of
connective tissue forming a bed on which the ectoderm cells rest.
This foundation is called the derm is, and is included with the
ectoderm in the ordinary conception of the "skin." In contra-
distinction to the dermis the ectoderm is often spoken of as the
epidermis (Gr. ri, upon).
Beneath the dermis comes a layer of circular muscles (3, Fig.
63), 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, Fig. 63), since the individual fibres appear
arranged in oblique rows between which tongues of connective
tissue extend, giving off lateral branches on which the fibres rest.
Both sets of muscles are composed of muscle-cells. These are
long fibre-like structures pointed at both ends. Most of the proto-
plasm is differentiated into fine fibrillae, which indicate (see
p. 33) contractile power. In the centre of the cell is a patch of
unmodified protoplasm with a nucleus. The whole cell may be
compared to a myo-epithelial cell of Hydra in which the epithelial
part has diminished in size and the tail increased. Nor is this a
fanciful comparison, for the study of development teaches us that
the cell is actually derived in this way from the originall} 7 ' simple
cells of the wall of the coelomic sac or in the case of the circular
muscles from an ectoderm cell.
The movements of the earthworm can be more easily under-
stood when the arrangement of the muscles is known. The
longitudinal muscles serve to shorten the body, and as the coelomic
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 the burrow. On the other hand, the circular muscles
diminish the diameter of the coelom, and the contained fluid being-
forced to move in a longitudinal direction stretches the body out.
The holes in the septa equalise the pressure in the various segments
by permitting the fluid to escape from one into the next.
Within the longitudinal muscles there is a layer of cells called
the parietal peritoneum (6, Fig. 63) which forms the immediate
wall of the coelom. The parietal peritoneum is composed of
flattened cells; the visceral peritoneum which forms the inner
X] LUMBRICUS 153
wall of the coelom, 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 visceral muscles derived from the peritoneal layer
and forming the agency by which the peristalsis (v. p. 143) of the
gut is carried out.
The endoderm (8, Fig. 63) 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. 63), 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 parietal
peritoneum of which they once formed a part (14, Fig. 63). 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, which
are sections of the so-called "giant" fibres colossa 1 axons which
are outgrowths of correspondingly large neurons.
Chaeta-sacs and nephridia cut across may be seen in some
sections of the worm.
It has been mentioned above that it is one of the characteristics
of the coelom that the cells lining it should produce
the reproductive cells. This does not mean that
any cell lining the coelom can become an ovum or
a spermatozoon, but that at certain spots the cells forming part
of the coelomic wall turn into either female or male generative cells.
In the earthworm the paired ovaries (5, Fig. 64) are situated in
the thirteenth segment and may be seen by cutting through the
intestine about the region of the gizzard and gradually lifting it up
from behind forwards ; when it is freed up to the twelfth segment
the ovaries may be seen as minute white pear-shaped bodies lying
one on each side of the nerve-cord. They are attached by their
broad end to the posterior wall of the septum separating segment
154
ANNELIDA
[CH.
twelve from segment thirteen, and they are formed by the accu-
mulation 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 be removed and examined under a
microscope it will be seen that many of the cells composing it are
large, spherical and crowded with granules. The largest lie in the
narrow end of the ovary which waves about in the coelomic fluid.
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
7
FIG. 64. View of reproductive organs of the Earthworm, Lumbricus terrestris.
Part of the vesicula seminalis is cut away on the left side to expose the
testis and the inner opening of the vas deferens. Slightly magnified.
From Hatschek and Cori.
1. Spermathecae. 2. Funnel-shaped internal openings of the vas deferens.
3. Anterior testis. 4. Vesioulae seminales. 5. Ovary attached to
posterior wall of septum separating xn and xiu. 6. Oviduct traversing
septum separating xm and xiv. 7. Vas deferens. 8. Glands in the
skin. 9. Ventral nerve-cord. 10. Septum.
The Roman figures indicate the number of the segments.
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. 64). They bear on
their course a diverticulum or sac which is called the recepta-
culum ovorum, in which the ova collect until the earthworm
is ready to make a co-coon 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. 64). They are in many
respects similar to the ovaries but are hand-shaped, the broad end
X] LUMBRICUS 155
of the hand being attached and the fingers free. Their ducts which
convey away the spermatozoa are called the vasa efferentia.
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 com-
mon duct thus formed runs back to open by a pore with swollen
lips on the fifteenth segment, i.e. the one behind that on which the
oviducts open (7, Fig. 64). It is termed the vas defer ens.
Since both genital ducts and nephridia are tubes opening at the
inner end into the coelom and at the other end to the exterior, it
used to be supposed that they were the same kind of thing, in a
word that the genital ducts were modified nephridia. The study
of their development has proved that such is not the case. The
genital duct arises as an outgrowth of the coelomic sac it is
therefore termed a coelomiduct. The nephridium is always an
ingrowth from the ectoderm. The so-called nephridia of Mollusca
are really modified coelomiducts, and are not comparable with the
nephridia of Annelida. The ovaries of the earthworm 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. 64). Each vesicula seminalis is a flat, oblong bag ex-
tending 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 semiuales, though they ought to be termed
lateral horns of the anterior vesicula seminalis. Similar projections
are produced from the hinder angles of both of the anterior
and of the posterior vesiculae seminales, so that on opening a worm
three pairs of grayish white sacs are seen at the 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 by the outgrowth of folds from 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 repro-
ductive cells have their origin from the walls of the coelomic
cavity, a closer examination shows that this apparent divergence
is not a true one.
156 ANNELIDA [CH.
Every earthworm has grown up from an egg which has been
fertilised 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- ot an individual would fertilise its
own ova, but this is not the case. Cross fertilisation or the
fertilisation 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
cells 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-
velop each a long vibratile tail by whose aid they swim actively
about. Two earthworms then approach each other and place their
ventral surfaces in contact. The heads of the pair are turned in
opposite directions. Since the ventral surfaces are slightly grooved
a sort of tube is formed by the opposition of the two worms, and
the pair are bound together by a mantle of slime secreted by the
goblet cells. The spermatozoa of one of the pair, which acts as
male in this embrace, pass down the sperm funnels and vasa
deferentia into the tube formed by the adpressed ventral surfaces
of the worms. The spermathecae of the one which acts as female
are filled from this tube. The earthworms then separate, one
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. 64). 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
peculiar ectoderm cells found in the clitellum and at first have
a ring-like shape. The secretions harden when in contact with the
air. The animal begins to wriggle out of the band, which at first
X] LUMBRICUS 157
surrounds its body in the neighbourhood of the thirty-second to the
thirty-seventh segment. As the band passes over the openings of
the oviducts in the fourteenth segment it carries away with it a
certain number of ova, and as it passes the orifices of the sperrna-
thecae between the eleventh and tenth and tenth and ninth
segments, some of the spermatozoa which have been received from
another individual are squeezed out. Besides ova and spermatozoa
the cocoon contains a certain amount of a milky and nutritive fluid
in which these cells float ; this is probably supplied by certain other
glands in the skin of the earthworm. At the moment the last
segment, that is, number one, is withdrawn, the anterior end of the
cocoon 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 from the
fertilised ova, by division into a number of cells and by the
differentiation of the cells into muscle cells, epithelial cells,
digestive 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.
In Great Britain there are several species of earthworm, which
are grouped into two genera, viz. Allolobophora, with
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. herculeus, 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 from sandy
and desert soils. Some of them are aquatic but not many. On
the other hand the allied sub-order the Limicolae are for the
most part denizens of fresh water. A few Limicolae possess gills
or finger-like processes well supplied with blood-vessels which take
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
158
ANNELIDA
[CH.
having 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 orChaetopoda.
Order II. Polychaeta.
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 maybe divided into a dorsal half,
the notopodium, and a ventral half, the
neuropodium (15 and 16, Fig. 66). 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. 66) which run from the
dorso-lateral line towards the median ventral
line near the nerve-cord. The nephridia lie
beneath these muscular partitions. It is of
great * nterest to not i ce taat i n a & w genera
they do not terminate internally in a funnel
which opens into the coelom but terminate like the nephridia of
Platyhelminthes, Nemertinea and Rotifera in a group of flame-cells
or solenocytes. The sexes are separated in Polychaeta, and the
genital cells of each sex are developed from extensive stretches of
the coelomic wall in every segment throughout a considerable region
FIG. 65. Nereis pe-
Oersted L * After
POLYCHAETA
159
of the hinder part of the body. Genital ducts in the form of wide
ciliated funnels are likewise developed in many segments, but only
acquire openings to the exterior at the time of sexual maturity.
Sometimes they open into the tube of the nephridium. Such
combinations of nephridium and coelomiduct have been called
nephromyxia. The part of the animal containing the ripe sexual
cells sometimes breaks off from the head end and floats at the
surface of the sea. The head end may then grow a new series
a a .
FIG. 66. Transverse section through Nereis cultrifera, slightly simplified.
The parapodia are shown in perspective. Magnified.
.. Cuticle. 2. Epidermis. 3. Circular muscles. 4. Longitudinal
muscles. 5. Oblique muscles forming a partition. 6. Parietal
layer of epithelium. 7. Coeloin. 8. Visceral layer of peritoneum.
9. Cavity of intestine. 10. Dorsal blood-vessel. 11. Ventral blood-
vessel. 12. Ventral nerve-cord. 13. Nephridium cut in section.
14. Ova. 15. Notopodium. 16. Neuropodium.' 17. Dorsal
cirrus. 18. Ventral cirrus. 19. Chaetae. 20. Aciculum with
muscles at inner end.
of hinder segments. The septa which divide the coelom in one
segment from that in the next are in many forms incomplete or
absent.
As a rule Polychaeta have a certain number of the anterior
segments modified to form a head, which often carries tentacles;
organs for absorbing oxygen from the water, called branchiae
or gills are also often developed sometimes from the head some-
times from the middle region of the body. Polychaeta are generally
160
ANNELIDA
[CH.
of separate sexes, and the eggs develop into a larva which swims
in the sea and gradually changes and grows up into a worm. This
group includes a very great variety of forms, almost all of which
are marine. With few exceptions they form burrows for themselves,
which most of them occasionally desert in order to seek prey and
to discharge the reproductive cells. Some however never leave the
burrows, which in this case often take the form of tubes composed
of a secretion of the ectoderm.
1
Order III. Hirudinea.
Besides the Oligochaeta and Poly-
chaeta the order Hirudinea, the
members of which are popularly known
as leeches, is included amongst the
Chaetopoda. They were for some time
regarded as a distinct order of Annelida,
since the great majority of species
possess no chaetae and have other
peculiarities; but the recent discovery
of species possessing chaetae, and the
close resemblance between the develop-
ment of all Hirudinea and that of
Oligochaeta, renders it evident that
they are true Chaetopoda and that the
absence of chaetae is a secondary
characteristic.
There is little doubt that the
Hirudinea are closely al-
lied to the Oligochaeta;
indeed there are certain
families which it is not easy to assign
definitely to either group ; but the
more typical forms are easily distin-
guished. Externally leeches may be
recognised 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.
Leeches.
External
features.
FIG. 67. Hirudo medicinalis,
about life size.
1. Mouth. 2. Posterior
sucker. 3. Sensory papillae
on the anterior annulus of
each segment. The remain-
ing four annuli which make
up each true segment are in-
dicated by the markings on
the dorsal surface.
X] HIRUDINEA 1(31
With the exception of Branchellion, which bears tufted gills,
the bodies of leeches are without external processes. There are
no parapodia, as in the Polychaeta, and no branchiae or tentacles,
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 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 first ventral 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
ffirudo, the medicinal leech, there are five annuli to a true
segment ; in Clepsine, 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 which the goblet cells pour out forms a co.coon
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
Organ* 1 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 are best
described as U-shaped rods of cells. One end of the U com-
municates with the exterior by a muscular vesicle; the other
end is unconnected with anything else, but from the end con-
nected with the muscular vesicle a delicate cord of cells proceeds
inwards and terminates in a structure something like a minute
cabbage situated in a sinus above the testis. This termination is
called the testis lobe. The whole nephridium is traversed by a
S. & M. 11
162 ANNELIDA [CH.
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 animals,
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 (6) the GNATHOBDELLIDAE, which bite their prey by means
of horny jaws. The medicinal leech is one that bites, and the
triradiate little scar which its three teeth make in the skin was
well-known to our forefathers in the times of bleeding and cupping.
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 segment and gives off on each side a series of eleven pouches
or caeca (Lat. caecum, 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. 68).
In one genus at least, Acanthobdella, the coelomic cavity is
almost as well-developed as in an earthworm, and is
Coelom. .
divided up by septa as in that animal, but 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.
The capsules in which the ovaries and testes lie are also parts of
the coeloin.
HIRUDINEA
163
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 comprise a vessel running
on each side of the body and con-
nected together by transverse branches
which run from side to side below the
ventral sinus. These lateral vessels
further supply capillaries to the
nephridia, alimentary canal, repro-
ductive organs, etc., and a very ex-
tensive system to the skin where the
haemoglobin of the blood takes up
oxygen. Except in Branchellion, which
has special gills, the respiration of
leeches is carried on by the skin.
FIG. 68. View of the internal organs of Hirudo medicinalis. On the left side
the alimentary canal is shown, but the right half of this organ has been
removed to show the excretory and reproductive organs.
1. Head with eye spots. 2. Muscular pharynx. 3. 1st diverticulum of
the crop. 4. llth diverticulum of the crop. 5. Stomach.
6. Kectum. 7. Anus. 8. Cerebral ganglia. 9. Ventral nerve-
cord. 10. Nephridium. 11. Lateral blood-vessel. 12. Testis.
13. Vas deferens. 14. Prostate gland. 15. Penis. 16. Ovary.
17. Uterus a dilatation formed by the conjoined oviducts.
112
164 ANNELIDA [CH.
Leeches are, like the earthworm, hermaphrodite, but their
Reproduc- reproductive organs differ in some respects from
tion - those of that animal.
In Lumbricus the testes are repeated in two segments only,
but in Hirudo there are usually nine pairs of testes. 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-funnel. 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 longitudinal canal
termed the vas deferens, there being one such canal on each side
of the body. At its anterior end each vas deferens passes into a
convoluted mass of tubes the so-called epididymis whose walls
secrete a substance which binds the spermatozoa together into
packets called spermatophores. 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 base of
the penis is surrounded by glandular cells which discharge into it
and which collectively are termed the prostate gland. They form
a milky fluid in which the spermatophores are bathed. It is to be
remembered that the names epididymis, prostate, etc., are given from
fanciful resemblances to parts in the anatomy of man by no means
homologous with the organs bearing the same name in the leech.
The penis is simply the muscular end of the conjoined male
ducts or vasa deferentia; it is the organ by which the spermatophore
is deposited in the body of another leech. The spermatozoa in
Clepsine seem to penetrate the skin at any point and make their way
to the ovaries, where they fertilise 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
X] HIRUDINEA 165
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 oh some secretion from its body.
Of the Gnathobdellidae, Hirudo medicinalis is found in Great
Britain, but is commoner in some parts of the Con-
Habits, etc. . _ . .
tinent. It is cultivated in some districts, but the
demand for it is decreasing with the 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 warmer climates many leeches take to living on land,
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 coelorn 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 localised and the sexes are
united in the same individual : development is practically
entirely embryonic : the group inhabits fresh water or damp
earth.
Ex. Lumbricus, Allolobophora.
166 ANNELIDA [CH. X
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 localised 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.
Order 3. Hirudinea.
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.
Sub-order 1. Acanthobdellidae. . ;
Leeches which retain a few pairs of chaetae and have spacious
coelomic cavities divided by septa.
Ex. Acanthobdella.
Sub-order 2. Rhynchobdellidae.
Leeches which have lost all chaetae and in which the coelom
is reduced to a series of narrow channels. The stomodaeum
can be everted and is termed a proboscis.
Ex. Clepsine (Glossipkonia).
Sub-order 3. Gnathobdellidae.
Leeches which have lost chaetae and have a reduced coelom.
The stomodaeum is not eversible but forms a sucker provided
with three thickened muscular ridges covered with rough cuticle
which act as jaws.
Ex. Hirudo, NepMis.
CHAPTER XI
PHYLUM GEPHYREA
IN the older books of zoology under the head of Annelida a
subdivision is included which is termed Gephyrea. The Gephyrea
were defined as Annelida which had lost all signs of the metameric
segmentation of the body and in which moreover the ventral nerve-
cord is uniform in diameter throughout and in which there are no
septa dividing successive coelomic cavities from one another. What
remains of Annelid character is as follows: (1) The possession of
a dorsal brain, nerve-collar and ventral nerve -cord. (2) The pos-
session of a spacious body-cavity or coelom from whose walls, in the
majority of cases, the genital cells are produced. (3) The possession
of tubes opening to the exterior which in most cases combine the
functions of excretory organs and genital ducts. The group used
to be divided into Gephyrea nu da which burrowed in sand and
mud, and Gephyrea tubicola which lived in clear water sheltered
in leathery tubes secreted by the ectoderm. The Gephyrea nuda were
further divided into (a) Armata, which possessed a smaller or larger
number of chaetae embedded in the skin and which had an elongated
praeoral lobe or prostomium, and into (6) Inermia which were
devoid of chaetae and of prostomium, but in which the anterior part
of the body could be turned outside in or introverted like the finger
of a glove.
Modern research seems to indicate that in the Gephyrea nuda
we have confounded together three quite distinct groups whose
connection with one another is more than doubtful. These are
as follows : (1) The Echiuroidea which possess chaetae embedded
in the skin, a much elongated, grooved and ciliated prostomium,
and in which the anus is at the posterior end of the body. (2) The
Sipunculoidea in which there is no prostomium, but in which the
front part of the body can be introverted into the hinder part, and
in which the anus is situated far forward on the dorsal surface of
168 GEPHYREA [CH.
the body. (3) The Priapuloidea which agree with the Sipunculoidea
in having no prostomium and in having the front region of the
body introversible, but in which the anus is terminal.
Now the development of Echiuroidea demonstrates that this
group really does belong to the Annelida, for the larva is distinctly
divided into segments and each segment contains a section of the
coelom. Since they possess at least a pair of chaetae they are
Chaetopoda, and since the generative cells are developed from the
wall of the coelom covering the ventral blood-vessel along the whole
length of the body, and since the same organs act as excretory
organs and genital ducts, they are to be regarded as modified
Polychaeta. They are in fact Polychaeta which have ceased to
burrow and which pass their lives in one spot, feeding themselves
by what is brought to them by the current of water produced by
the cilia lining the under surface of the prostomium. In the genus
Bonellia, which is found in the Mediterranean, the prostomium
is produced at its anterior end into two muscular flaps which are
used for seizing prey. The prostomium of Bonellia when fully
extended is 10 to 15 times as long as the animal, and this is a
remarkable instance of the way in which any organ of the body can
be increased in size indefinitely by the action of natural selection if
it becomes of importance in obtaining food for its possessor, for it
must be remembered that the enormous " proboscis" of Bonellia is
strictly comparable with the insignificant lobe which overhangs the
mouth in the earthworm.
One striking peculiarity of the Echiuroidea may be mentioned
and that is, that in addition to possessing anterior nephridia which
serve as genital ducts, they likewise possess a pair of peculiar
nephridia which open into the hindermost part of the alimentary
canal. These terminate internally in a multitude of small ciliated
funnels opening into the body-cavity These funnels are scattered
all over the surface of the nephridia.
The Sipunculoidea are not closely connected with the Annelida.
The features which they have in common with them are distinctive,
not merely of Annelida but of a wide range of animals which retain
the coelom in a more or less primitive condition, and these only
show that both Annelida and Sipunculoidea belong to the Coelom ate
division of Metazoa. Since the line joining mouth and anus is to
be looked upon as the dorsal surface, it follows that the main part of
the length of these animals is to be regarded as being made up of
a great protrusion of the ventral surface of the body. The same is
Xl] MAIN DIVISIONS 169
true of the Gephyrea tubicola and there are a great many other
features in which the Gephyrea tubicola and the Sipunculoidea
resemble one another. We may therefore with great plausibility
regard these two groups as forming an independent group of animals
or phylum for which the name Gephyrea may be reserved, the
Echiuroidea being removed to the Polychaeta and the Priapuloidea
being left on one side for the present as a completely isolated group
until we know more about their development.
The Priapuloidea differ not only from the Sipunculoidea but
from all the groups classed together as Gephyrea in the character
of their excretory and genital organs. The genital organs are in the
form of sacs, from the walls of which the ova and spermatozoa are
produced, and which are directly continuous with the genital ducts,
of which there are a pair opening to the right and left of the anus.
When young specimens are examined no genital organs or genital
ducts are to be found, but in their place two typical nephridia
which end internally in a number of branches, each branch terminat-
ing in a flame-cell or solenocyte. As the animal grows, pouches are
given off from the nephridial duct, the blind ends of which
develop into the genital organs whilst the nephridial duct
becomes the genital duct. Numerous specimens of the genus
Priapulus, which has two branched gills protruding from the hinder
part of the body, are found embedded in black mud in moderate
depths in the Firth of Clyde.
The Gephyrea tubicola consist of a number of species which are
grouped in a single genus PJwronis. The British species are minute
creatures about of an inch long. The mouth is surrounded by
hollow ciliated tentacles which spring from a lip or platform termed
a lophophore, and this lophophore is not circular but drawn out
at the side into two arms which project dorsally and give the
whole the form of a horse-shoe. These tentacles are supplied with
branches from dorsal and ventral blood-vessels and serve for
respiration as well as to bring food. The anus is situated on the
dorsal surface far forward and two ciliated funnels which serve both
as genital ducts and excretory organs open at the sides of it. When
Phwonis is young it swims about in the sea by means of an oblique
ciliated band running behind the mouth and much resembles the
larva of some Annelids. There is a large prostomium in the form
of a hood overhanging the mouth and the anus is at the posterior
end of the body. As the larva grows an intucking of the skin
on the ventral surface makes its appearance. This becomes attached
170 GEPHYREA [CH.
to the intestine, and when the critical period of growth has arrived,
the hood or prostomium is cast off : the ventral pouch becomes
turned inside out and pulls out the intestine into a loop and this
everted pouch constitutes the greater part of the body of the
Phoronis.
The largest of the Sipunculoidea is the species Sipunculus
nudus which is found burrowing in the sand and mud in the
Mediterranean. It is however used as a type for study by students
of zoology in this country, and as species of the same genus occur
on the American coast we may give a brief description of its
anatomy and its habits. The animal is shaped somewhat like a
sausage, and may attain a length of 10 11 inches and a diameter of
nearly an inch. The front part of the body which can be retracted
and which we may name the introvert is covered with minute
papillae. The rest of the body is marked by a series of longitudinal
grooves crossed by transverse ones so that the skin is divided into
a series of squares. There is a well-developed cuticle somewhat
loosely attached to the ectoderm beneath, and in the ectoderm are
a series of glands, each of which consists of a number of oval cells
arranged in the form of a shallow cup. The mouth is situated
at the end of the introvert and is surrounded by what can only
be described as a frilled membrane (a, fig. 69). This is represented
in other genera by a horse-shoe of ciliated hollow tentacles lying
dorsal to the mouth. This membrane is richly supplied with blood-
vessels and seems to serve as gatherer of the minute particles of
organic matter on which the animal feeds. The blood-vessels
communicate with a main reservoir, the dorsal blood-vessel (c, fig. 69)
which lies above the oesophagus. When blood passes from this
into the membrane the latter becomes swollen out.
The animal burrows its way into muddy sand and feeds on it as
well. If it is removed from the sand it turns and twists the
introvert about, alternately retracting it and pushing it out until
it finds sand of the proper consistency, when the introvert is driven
in. It then becomes fixed in its new position by the appearance of
a swelling on it immediately behind the mouth. It is then retracted
and this action since the introvert is fixed necessarily draws the
body after it. When the body is fixed the introvert is again
extruded and so movement goes on.
When a Sipunculus is opened by a cut along the dorsal surface we
find that we have cut into a spacious coelom undivided by any
septum whatever. The most conspicuous organs which strike the
Xl] SIPUNCULUS 171
eye of the observer are the alimentary canal and four great retractor
muscles of the introvert (i, fig. 69). These latter structures are
arranged as a dorsal and ventral pair, they broaden out towards
their posterior ends and are all inserted in the body-wall at the
same distance from the mouth. Immediately behind the line of
their insertion a slight thickening of the coelornic epithelium may
be observed running round the body; this is the rudiment of the
genital organ. From it in periods of genital ripeness the genital
cells are produced and budded off into the coelomic cavity and
float in the coelomic fluid. The alimentary canal runs back to
the posterior end of the body, here .it bends and runs forward to
the anus. It is therefore bent in the form of a U, and the two
limbs of the U are twisted round each other in a spiral fashion.
From the recurrent or ascending limb of the U not very far
from the anus there is given off a blind pouch (/, fig. 69). This
pouch varies extraordinarily in length in different individuals,
sometimes it is a mere vestige, sometimes it is half as long as the
body. The walls of the alimentary canal are extremely thin,
they can hardly be touched without rupturing them, and yet the
canal is crammed with sharp fragments of shells and other debris,
and it is extraordinary that these never seem to penetrate it.
The thinness of the walls of the alimentary canal are probably
in relation to the poor development of the blood-system, because
though there are two blood-vessels on the dorsal side and one on
the ventral side of the alimentary canal connected by a ring vessel
immediately behind the mouth, yet they extend only a short distance
backwards and their main function seems to be to expand the
"frilled membrane" to which they give off numerous branches.
The products of digestion must therefore diffuse directly into the
coelomic fluid, and the effective mixing up of this is aided by the
so-called " urns." These are cups of ciliated cells which are formed
on the coelomic wall where it covers the dorsal blood-vessel and are
budded off into the fluid.
The organs which function both as kidneys and as excretory
ducts are a pair of so-called u brown tubes," which lie beneath the
alimentary canal and open on the ventral surface some little distance
behind the end of the introvert (h, fig. 69). They receive their
name from the colour of the pigment (probably excretory) in their
walls. They may be described as blind pouches, with however
a lateral ciliated opening leading into the body-cavity and situated
near the external opening. They much resemble the "anterior
172
GEPHYTREA
[OH.
-'6
FIG. 69. Dissection of Sipunculus
nudus.
a. Frilled membrane surrounding
the mouth.
b. Ventral nerve-cord.
c. Dorsal blood-vessel.
d. Oesophagus.
e. Cut ends of the intestinal coil.
/. Anus.
g. Bush-bodies.
h. Brown tube.
i. Retractor muscle.
;'. Blind pouch or caecum.
XI] SIPUNCULUS 173
nephridia " of Echiuroidea, and this was one excuse for including
the latter among Gephyrea. Attached to the sides of the intestine
near the anus are two branched outgrowths termed bush-bodies.
These (g, fig. 69) were formerly compared to the posterior nephridia
of Echiuroidea ; but they have been shown to be thickenings of the
visceral peritoneum whence floating cells (amoebocytes) are budded
off into the coelomic fluid.
The nervous system consists of a small squarish supra-oesophageal
ganglion or brain which is beset by a number of curious lobes called
fungiform processes. Above the brain there is a ciliated canal
leading up to the external surface of the body this is doubtless
sensory in character. The ventral nerve-cord (b, fig. 69) shows no
ganglionic thickenings of any kind, it is connected with the brain
by a long "nerve-collar" which runs through the whole length of
the introvert. In order to avoid the risk of straining these delicate
cords when the introvert is suddenly shot out they are flanked on
either side by a special muscle which takes the strain when the
introvert is stretched.
The larva of Sipunculus in many ways resembles that of
Phoronis. As in the latter larva, an oblique postoral band of cilia
is the chief organ of locomotion. There is also as in the Phoronis
larva a praeoral lobe, the greater part of which is eventually cast
off. The anus is at first terminal but becomes slowly displaced
on to the dorsal surface by the outgrowth of a ventral protrusion,
so that what takes place with cataclysmal suddenness in Plwronis
is effected by a gradual process in. Sipunculus. The study of
development therefore reinforces the arguments drawn from the
study of adult anatomy that the two groups of Sipunculoidea and
Phoronidea are akin, and it would be a great advantage if the old
term Gephyrea were exclusively devoted to them.
CHAPTER XII
PHYLUM ARTHROPODA
ONE of the most striking features of the Annelida is the fact
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 front of it. The likeness of the parts to one another varies. In
some worms we might easily detect from which region of the body any
given segment was taken. In the Earthworm we found, that, except
in the region of the clitellum, there is little external difference;
nevertheless if we consider the internal organs we can distinguish
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. 142).
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. These are always arranged in pairs, and almost always
at least one pair is modified so as to assist in holding and crushing
the food. These modified limbs are termed gnathites (Gr. -yvdOos,
jaw). This character of possessing jointed limbs is what is indicated
by the name Arthropoda (Gr. apOpov, joint ; TTOV?, foot).
The strength of these outgrowths lies in the thickness of the
cuticle secreted by the ectoderm surrounding them. The thickness
of the cuticle which constitutes the exoskeleton is the distin-
guishing feature of all Arthropoda.
CH. XIl] MAIN DIVISIONS 1*75
The exoskeleton not only furnishes an external armour but
penetrates between the limbs of inturned folds of ectoderm termed
apodemes into the interior of the body and furnishes support for
the muscles.
The Arthropod* may be divided into the following classes :
I. The CRUSTACEA, possessing two pairs of feelers (antennules
and antennae) and three pairs of jaws which include
all the Crabs, Lobsters, Crayfish, Barnacles, Wood-
lice, etc., besides countless small forms such as the Water-flea,
Cyclops, and many others which inhabit both salt and fresh
water.
II. The ANTENNATA, which include all Arthropoda possessing
one pair of feelers antennae and breathing by means of air tubes
or tracheae. This group is divided into three sub-classes, viz. :
A. The Prototracheata, a group containing the genus
Peripatus, an animal riot 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 much
that was obscure in the anatomy of Arthropods: it is in fact in
many respects intermediate between the Annelids and the air-
breathing Arthropoda.
B. The Myriapoda or Centipedes, the commonest British
examples of which are the chestnut-coloured centipede Lithobius
forficatus and the black "wire-worm 1 " lulus terrestris.
C. The Insect a, 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, Bees,
Ants, Wasps, etc., which we are accustomed to call insects.
III. The ARACHNIDA, devoid of feelers but having a small
pair of claws (chelicerae) as first appendages, and having as jaws mere
processes of their walking legs. This class includes the Spiders,
Harvestmen, Mites and certain larger forms such as the Scorpion,
and Limulus, the King-crab.
IV. The PANTOPODA, with chelicerae but devoid of jaws
altogether,-a group of small animals incorrectly termed "sea-spiders."
They are marine and may be found under stones between tide marks
on our coast.
V. The TARDIGRADA or "Bear Animalcules." These are
minute microscopic Arthropoda found amongst moss and decaying
1 This is not to be confused with the larva of a beetle, Elater lineatus, which
is also called a " wire- worm" by the British agriculturist.
176 ' ARTHROPODA [CH.
vegetation. They have a few pairs of stumpy legs each ending in
two claws. They are devoid of antennae, jaws and chelicer-ae.
In order to get a clear and definite idea of the structure of the
Arthropoda we shall select for closer examination the common fresh-
water Crayfish which belongs to the class Crustacea. This in England
is Astacus fluviatilis, an animal which when full grown is six inches
long, but in America the "common" crayfish is represented by
various species of the allied genus Cambarus : the common denizen
of the St Lawrence is Cambarus virilis, a smaller and more slender
creature than the English crayfish, not exceeding five inches in
length. The crayfish looked at from above is seen to be composed
of a nearly cylindrical anterior portion the cephalo-thorax and
a hinder more flattened portion divided by constrictions into a series
of similar rings placed one behind the other and at once recalling
the segments of an earthworm. This jointed portion is called the
abdomen. The cephalo-thorax is covered above by a hard horny
skeleton called the carapace (c, fig. 70) and the rings of the
abdomen are similarly covered by pieces of a similar skeleton which
are called terga. Close inspection shows that a similar though
thinner covering extends over the joints between the cephalo-thorax
and the abdomen and between the various rings of the abdomen
in fact the whole body of the crayfish has a continuous covering
of horny matter, thin in some places, thick in others, which is to be
regarded as an exaggeration of the cuticle found in the worm. The
same is true of all Arthropoda and to this circumstance may be
traced directly or indirectly most of the characteristics of the
phylum. The thick pieces of the skeleton are known as scle rites
and the thin flexible portions which permit of the movement of one
sclerite on the other are termed arthrodial membranes.
Each segment of the abdomen has a pair of outgrowths movably
articulated with it called appendages. These differ from the
parapodia of Polychaeta chiefly in being flexible only at certain
places, and in being on the whole of simpler form. Like the typical
parapodium, each consists of a basal piece and two forks, an outer or
dorsal called the exopodite and an inner or ventral called the endo-
podite. The basal piece is called the pro topodite. As compared
with the parapodia of a worm the appendages spring more from the
ventral surface and less from the sides, and hence the dorsal branch
of the parapodium corresponds to the outer branch of the limb.
The ventral surface of the segment is protected by a narrow
sclerite called the sternum and between successive sterna there are
XII]
ASTAC0S
177
broad intersternal arthrodial (i.s, Fig. 71) membranes which permit
of a great amount of downward bending of the abdomen, for in
such a movement they must of necessity be much puckered. On
the outer side of the insertion of the limb there is a short sclerite
running to the tergum, called the epimeron. The bent down edge
of the tergum is distinguished as the pleuron but there is no line
of demarcation between it and the rest of the tergum.
s. & M. 12
ARTHROPODA
[CH.
Fia. 71.
Astacusfluviatilis, viewed from beneath,
have been removed.
The appendages on one side
Anus. ap.arth. Arthrodial apodeme. ap.par. Paraphragmal apodeme.
b.ch. Branchial chamber. e. Epistome. g.a. Female genital aperture.
g.g. Opening of the green gland, i.s. Intersternal membrane. Ib. Labrum.
md. Mandible. mt. Metastoma. mx.l. First maxilla. mxp.I. The
first maxillipede. rs. Rostrum. s.14, s.20. The fourteenth and
twentieth sterna respectively. t. Telson. Arabic figures denote the
segments, Roman figures the appendages.
XII] ASTACUS 1*79
When the abdomen is bent upwards each tergum is found to
articulate with both its successor and predecessor by two points
situated one at each side. Each tergum slides to a certain
extent under its predecessor: and each has a smooth part called
the tergal facet, over which its successor slides.
The last division of the abdomen is a flat semicircular piece
without appendages, which is divided into two by a transverse joint
and on the under surface of which the anus is situated. This is
called the t els on, and in the lower Crustacea it is represented by
a pair of appendages called the caudal fork between which the
anus lies it is believed that in the crayfish these appendages
have coalesced to form the telson. The last regular segment
bears a pair of appendages, both forks of which exopodite and
endopodite have taken on the form of broad triangular valves
(xx, Fig. 71). These can be folded the one under the other and
the whole limb can be concealed under the telson but they can also
be spread out at the sides of the animal's body so as to make with
the telson a broad terminal fan.
By means of this fan the animal is able to execute a manoeuvre
which is of the utmost value to it when it is pursued by its enemies.
It bends the abdomen quickly and sharply downwards, striking the
water with the outstretched fan and the reaction of the water drives
the whole animal suddenly backwards. In this way the crayfish
can back into a crevice between stones, whilst keeping its eyes fixed
on its enemy.
In the case of the next three segments of the abdomen the
protopodite is composed of a stout cylindrical sclerite. Both exo-
podite and endopodite on the contrary are made up of a large number
of short disc-like joints, so that these divisions of the limb are
exceedingly flexible. They are furthermore fringed with "hairs,"
that is to say delicate spines of cuticle in no way comparable to the
structures -called hairs in Mammalia (see p. 636). It is instructive
to notice the contrast between these structures and the chaetae of
Chaetopoda. The Chaetae as we have seen are solid pillars of cuticle
in which the oldest part is the tip. The "hairs" are on the contrary
hollow structures containing at first an axis of ectoderm. The term
seta has been proposed for them, and it is preferable to hair as the
latter term suggests a false comparison.
The appendages under discussion those belonging to the third,
fourth and fifth segments of the abdomen are termed swimmerets
(sw, Fig. 70) and are much better developed in some of the lower
122
180 ARTHROPOD A [CH.
Crustacea, such as the Shrimps, and by means of them the animal
is enabled to swim forwards. The crayfish is too bulky to be
completely supported by the action of these appendages but when
the crayfish . creeps forwards by means of its other appendages,
these by their vigorous motion support the abdomen and prevent
it from resting on the ground, and aid the whole forward movement.
The appendages borne by the first two segments of the abdomen
are obviously constructed on the same plan as those borne by the
other segments but they have undergone great modification. From
the fact that they differ greatly in the two sexes we should be led
to suspect what proves to be the case, that this modification has
taken place in consequence of their being used in connection with
the sexual function. As is often the case with sexual appendages
they vary much in shape from species to species and hence are of
great value in classifying crayfish. In the male of Cambarus virilis
the endopodite of the appendage belonging to. the second segment
is in its basal portion transformed into a rigid unjointed rod, whilst
the endopodite of the appendage belonging 'to the first segment is
transformed throughout its whole extent except the extreme tip into
a grooved rod, whilst the exopodite is completely absent. When
the appendages of the two segments are pressed together a tube
is formed by the juxtaposition of the endopodites on each side, and
through this tube the germ cells of the male are conveyed to the
female. In the female the appendages of the second segment are
like those of the third, fourth and fifth, whilst the appendages of the
first segment are reduced to tiny vestiges.
Turning now to the carapace which covers the cephalothorax
we find that it is divided into an anterior and a posterior portion by
the cervical groove (cv.g, Fig. 70), a well marked transverse
groove which crosses it. The portion of the animal in front of this
groove is termed the head, whilst the part behind is called the
thorax. The thorax is marked by two longitudinal grooves which,
starting from the cervical groove run backwards to the hinder edge
of the carapace. The two grooves are termed branch iocardiac
grooves (br.c, Fig. 70) and the lateral areas marked off by them are
known as the branchiostegites or gill-covers (Gr. /Jpay^ia gills,
oreyav to cover) (be, Fig. 70) and do not really form the lateral walls
of the body but form two flaps which project at the sides and
between which and the body the gills are lodged.
If we examine the under-side of the thorax we observe that it
bears a number of long jointed appendages, between the bases of
XII] ASTACUS 181
which a series of very short sclerites are situated, which quite
evidently correspond to the sternites of the abdomen. Hence we
conclude and the conclusion is confirmed by a study of the allies
of the crayfish that the thorax is composed of a number of segments
like those constituting the abdomen which have secondarily become
fused with one another through the thickening of the arthrodial
membranes. The appendages above-mentioned differ in many
respects from those of the abdomen. To begin with they are not
forked, they consist of a limited number of exceedingly stout joints,
and they are very much longer than those attached to the abdomen.
It is usual to speak of them as legs, distinguishing the appendages
of the abdomen asswimmerets. If we select for careful examination
the last leg we find that it consists of 7 segments which are named,
in the order proceeding from the base to the apex of the limb, coxo-
podite, basipodite, ischiopodite, meropodite, carpopodite,
propodite, dactylopodite. Many of these names are suggested by
fanciful analogies with the divisions of the human limb as the prefixes-
cox- (Lat. coxa thigh), dactyl- (Gr. SaKTvAos finger) and others testify.
It is indeed becoming usual to employ the English words wrist, hand
and finger, for carpopodite, propodite and dactylopodite respectively,
but it must be remembered that there is no real correspondence
between the parts of the arthropodan and the human limb. From
a comparison with the more anterior limbs of the crayfish it appears
that the coxopodite and basipodite represent the protopodite of the
swimmeret and the remaining five joints correspond to the endopodite.
The dactylopodite or "finger" is a sharp-pointed segment. On the
coxopodite of the last leg there is found in the male a small round
opening. This is the aperture of the male genital duct and
through it the male germ cells are shed into the tube formed by the
first two appendages of the abdomen. Proceeding forwards in our
examination of the appendages we find that the next leg is in all
respects similar to the one described, but the three preceding legs
are distinguished by the fact that each terminates in a claw.
This claw is due to a simple modification of the two terminal
joints. The hand (propodite) is prolonged into a stiff spine which
with the finger (dactylopodite) constitutes a pair of pincers. Of the
three legs terminating thus, the first is by far the largest and strongest
and has the joints constituting the claw very much enlarged. It is
termed the chela, and it is the organ by which the crayfish obtains
its food and defends itself against its enemies.
In order to give the chela rather more rigidity than the other
182 ARTHROPOD A [CH.
legs possess, the basipodite and ischiopodite are fused into one
segment: this is effected simply by the thickening of the cuticle
covering the arthrodial membrane between the two segments men-
tioned so as to destroy its flexibility. The crayfish feeds on any
small animals that it can catch, it seizes water-snails for instance
dragging them out of their shells and tearing them to pieces with
its chelae, and also greedily seizes on any dead fish it may come
across.
The chela is the first of the long leg-like appendages of the
animal, and as of these there are in all 5 pairs, the crayfish is said
to be a Ten-footed Crustacean and to belong to the order De capo da
(Gr. 8e/ca ten, TTOVS foot).
The remaining 8 legs are used to enable the animal to creep
cautiously forward, the abdomen being supported by the vigorous
action of the swimmerets.
On the coxopodite of the third claw-bearing leg there is in the
female a small round opening which is the aperture of the oviduct.
In front of the chela there are still to be found three pairs of
appendages attached to the thorax but these are very much shorter
than the "legs" and diminish rapidly in size as we proceed forward,
so that the hindermost entirely conceals the rest. These appendages
.are termed maxillipedes which literally means foot-jaws (Lat.
maxilla jaw, pes foot) ; this name was given to them because they were
supposed to be intermediate in character between the other limbs
and the jaws. This is true, but all the jaws of the crayfish are, as
we shall see directly, modified limbs, hence the term foot-jaw is not
distinctive. The maxillipedes might with propriety be termed
"secondary jaws" for the corresponding limbs in the lower Crustacea
have no resemblance to jaws and hence we conclude that the maxilli-
pedes have only recently been modified in this direction, and may
be expected to show still the first stages of the change. This indeed
proves to be the case. If we examine the third and hindermost
maxillipede we can see that it consists of exactly the same segments
as the other thoracic limbs, but that the ischiopodite and basipodite
are each prolonged inwardly into a sharp edge, so that when the two
limbs of opposite sides are brought into contact in the middle line,
the sharp edges mentioned above act like the cutting parts of a pair
of nut-crackers. The meropodite and the "wrist," "hand" and
"finger" are smaller in proportion to the ischiopodite than is the
case with the corresponding segments of the limbs behind, so that
we see that the first step towards converting a leg into a jaw is to
XII]
ASTACUS
183
develop sharp cutting edges on the basal segments and to diminish
the size of the distal segments. The cutting edges are termed
gnathobases. This change becomes more and more marked as we
proceed forwards. Thus in the second maxillipede the distal joints
are reduced to three (the finger being absent) and the ischiopodite
is as long as all three put together and finally in the first maxillipede
the basipodite and coxopodite are greatly enlarged and produced
FIG. 72. Left mouth appendages of Astacusftuviatilis, slightly magnified.
The other appendages are shown in Fig. 73.
I. Mandible. II. First maxilla. III. Second maxilla (Scaphognathite).
IV. First maxilliped. V. Second maxilliped. VI. Third maxilliped.
en. Endopodite. ex. Exopodite. ep. Epipodite. ex & ep. Scapho-
gnathite, i.e. enlarged exopodite which in III forms a scoop for circulating
water over the gills.
into cutting edges (gnathobases) and the whole endopodite is reduced
to two tiny segments, which, taken together, are not as long as the
basipodite.
A remarkable feature about the maxillipedes is that they each
possess a well developed exopodite in the form of a whip-like filament
184 ARTHROPOD A [CH.
springing from the basipodite. We thus possess in the third maxilli-
pede an exactly intermediate link between the swimmeret and the
"leg," for it resembles the former in its forked character and the latter
in the segments into which the endopodite is divided. Since in the
lower Crustacea the forked type of limb is the rule we have every
reason for supposing that the "legs" once had an exopodite which
they have lost and indeed in one family of Shrimps vestigial exo-
podites are found, and so we regard the third maxillipede as the
typical limb of the crayfish, from which by modification all the other
types have been derived. The use of the exopodites will be pointed
out when the respiration of the crayfish is described.
Turning now to the head region we find that it is covered by the
carapace, an unjointed shield, which closely invests it above and at
the sides and is produced in front into a pointed spine called the
rostrum (rs, Fig. 70). The shape of this spine is a useful mark
in discriminating one species from another. At its base on either
side is a curved indentation the eye-socket or orbit, from which
the eye springs. The shield which covers the back of the thorax
and forms the branchiostegites is a direct prolongation of the
covering of the head. When we examine the corresponding parts
of the body in the lower Crustacea we find that from the head there
projects backward a large free fold of skin covering the thorax on the
back and sides but not in any way adherent to it, and the segments
of the thorax are freely movable like those of the abdomen. Hence
we conclude that in the crayfish a similar outgrowth of the head
region exists but that it has become adherent to the thorax along
the mid-dorsal line whilst still projecting freely at the sides.
On the under side of the head there are two sterna in front of
the mouth the first excessively narrow, the second broader and
termed the epistome (e, Fig. 71). These sterna are immovably
fixed to one another and to the upper lip. This last is termed the
labrum (/6, Fig. 71) ; it is a curved bar overhanging the mouth
which has the shape of a longitudinal slit. Behind the mouth are
two small lobes termed the metastoma (mt, Fig. 71) and at the sides
of the mouth the head bears three pairs of appendages which are
modified so as to form jaws, making with the maxillipedes six pairs
of jaws altogether. The hindermost of these is called the second
maxilla or simply the maxilla. It is a thin and blade-like limb not
unlike the first maxillipede in front of which it lies. The two
segments of the protopodite, the basipodite and the coxopodite are
each produced into gnathobases fringed with small spines 3 the
XII] ASTACUS 185
endopodite is a short unjointed filament whilst the exopodite is
a broad jaw -like plate called the scaphognathite.
The first maxilla ormaxillulaisa still slenderer limb than the
second maxilla the exopodite is absent and the endopodite represented
by a tiny filament, whilst from the basal joints two gnathobases are
developed. The foremost of the three jaws is termed the mandible.
It is much stronger and thicker than any of the jaws described
except the third maxillipede, though in general form it recalls the
first maxilla. There is one strong toothed gnathobase which has
two edges, an outer cutting or " incisor " edge and an inner crushing
or "molar edge/' the exopodite is absent and the endopodite is a two-
jointed appendage much smaller than the gnathobase, which is
termed the palp.
We can now form to ourselves some idea of the process of
mastication in the crayfish. The flesh of the prey is torn into
fragments by the chelae; these are then passed to the third maxilli-
pede and then gradually worked forward through the whole series
of jaws, becoming broken into finer and finer fragments before enter-
ing the mouth. The delicate maxillae appear to act like combs,
removing the softer particles from the more resistant ones these
last being finally ground up by the stronger mandibles.
In front of the mouth there are to be found two pairs of
appendages which are modified to act as feelers, and by means of
these the crayfish explores the neighbouring water. These are the first
and second pairs of antennae, the first pair being sometimes termed
antennules (an ', Fig. 70) whilst the phrase antenna without quali-
fication denotes the second pair (an", Fig. 70). These appendages are
proved by a study of development to have originally belonged to the
region behind the mouth and to have been gradually shifted forwards
during the course of growth. It is characteristic of Crustacea as
distinguished from the other Arthropoda that they have two pairs
of appendages in front of the mouth acting as feelers. The second
or large antenna commences by a protopodite consisting of the
usual two joints which are very short and broad. On the under
surface of the coxopodite is a rather conspicuous knob of cuticle
the summit of which is pierced by a hole. This is the opening
of the kidney (g.g, Figs. 70 and 71). The exopodite is represented
by a flat oblong scale the squarne which is freely movable on
the protopodite and which serves as a floor to the eye-socket. The
endopodite is represented by a long filament two thirds the length
of the body, the basal joints of which are stout and fairly long but
the distal joints are disc shaped, so that the whole is exceedingly
1 86 ARTHROPODA [CH.
flexible. Armed with this long antenna the crayfish explores the
width and extent of the various nooks and crannies amongst the
stones in the river bed in which he hides himself.
The first antenna or antennule is a much smaller organ. The
protopodite consists of three stout joints, not two, as is the case with
the thoracic protopodites, and hence we cannot label any of them
basipodite or coxopodite. On the upper surface of the most proximal
is an open pit the entrance to which is guarded by a fringe of
bran ched setae. This is the otocystor rudimentary ear, the structure
and function of which will be explained later. Both exopodite and
endopodite have the form of flexible filaments made up of a multi-
tude of joints, the exopodite being by a little the longer and attaining
about half the length of the head. On the under surface of each of
its joints are two tufts of fine setae which are flattened and the tips
of which are obtuse. These are believed to be olfactory in function
so that the senses of smell and hearing are situated in the antennule.
If a crayfish be watched when at rest it will be noticed that the
antennules are in constant movement; the animal twitches them
first in one direction and then in another. If now a piece of some-
what stale fish be dropped into the water near the animal, in a little
while as soon as the odour therefrom has had time to diffuse, the
twitching becomes much more violent and is now confined to the
vertical plane joining the animal and the food and soon the crayfish
creeps forward and secures the tasty morsel. It appears therefore
that the animal not only perceives odours by means of the antennule,
but by moving it about is able to discover the direction from which
the odour has emanated.
In front of the first antennae are situated the eyes which
form the summits of two short unjointed stalks freely movable
on the carapace. Whether the eye-stalks are to be regarded as
appendages comparable with the others is a disputed question. In
the time of Huxley it was regarded as self-evident that they were
appendages. Later when due weight was given to the facts that
in many of the lower Crustacea the eyes are mere convex areas of
the carapace, and that in none of them are the eye-stalks movable,
it was considered more probable that the eye-stalks were simply
portions of the carapace which had become movable to enable the
eyes to have a wider range of vision. The study of development
has however shown that the absence of an eye-stalk is a secondary
condition of affairs and the remarkable fact that in some Shrimps
when the eye-stalk with its contained optic ganglion is torn out, an
XII] ASTACUS 187
antenna-like organ grows in its place, suggests that after all the
eye-stalk may be an appendage which we might perhaps compare to
the "antennae" on the prostomium of a Polychaete worm.
The crayfish like all Crustacea is primarily adapted to a water-
breathing life, though like many members of its class it is able to
pass short periods out of the water if its respiratory organs be kept
moist. These organs are feathery outgrowths of the body and limbs
termed gills or branchiae. By cutting away the branchiostegite of
one side the structure and arrangement of these organs can be
observed. Commencing behind we find in the English crayfish
(Astacus fluviatiUs) a small gill springing from the thin side- wall
of the thorax high above the insertion of the last leg. This gill,
from its place of origin termed apleurobranch (Gr. irXtvpov side),
is absent in the species of Cambarus. It has the form of a fila-
mentous stem beset with small flattened branches on all sides,
through the thin walls of which the oxygen dissolved in the water
diffuses inwards to the blood.
Proceeding forwards we find above the other thoracic legs no
pleurobranchs (though in the Crabs [Brachyura] there is quite
a series of them), but attached to the arthrodial membrane which
connects the fourth leg to the body there are two gills, one placed
above the other, which from their position may be termed arthro-
branchs. These gills are similar in structure to the pi euro -
branch, but there is in addition a gill attached to the coxopodite
of the limb, of rather a different structure. It commences in a
circular basal plate from which springs a flattened stem called the
lamina beset with two series of branches. This gill is termed
a podobranch because it springs from the limb itself.
The 4th, 3rd, and 2nd legs, the chela or 1st leg and the
third maxillipede have each attached to their bases and arthrodial
membranes, a podobranch and two arthrobranchs, the second
maxillipede has only a podobranch and the lower arthrobranch,
whilst attached to the base of the first maxillipede there is a
structure called an epipodite, which is a lamina devoid of gill
filaments and must be regarded as a rudimentary gill. Hence
if we construct a chart showing the arrangement of the gills
of the English crayfish, we find remains of four parallel series
of gills y^ll \ \ " . The extent to which each series
,/Q e ___ e /
is developed really depends on the shape of the branchial cavity,
188 ARTHROPOD A [CH.
that is, the space enclosed between the branchiostegite and the
side walls of the thorax. Thus as mentioned above, the Crabs
having a high branchial chamber of shorter length than that of the
crayfish have preserved more of the pleurobranchs and lost more
of the podobranchs.
In order that the gills may be able to carry out their functions
properly the water which bathes them must be constantly changed.
In other phyla of the animal kingdom, notably the Mollusca, this
is effected by means of cilia but cilia are an impossibility to an
Arthropod since the ectoderm everywhere seems to have an irre-
sistible proclivity to produce cuticle.
In the absence of cilia a current of water is caused to pass over
the gills by the action of the scaphognathite, that is, the exopodite
of the second maxilla. This is a fan-shaped plate fitting into the
extreme front corner of the branchial chamber. During the life of
the animal it is in constant vibration, and it literally bales the
water out of the front end of the branchial chamber, causing a current
of fresh water to enter the hinder and l<^MBfcd of the chamber
between the edge of the branchiostegite anclH Rises of the legs.
The whip-like exopodites of the maxillipedes ai^Wpcaphognathite ;
they whisk away from the sides of the animal thewater which the
scaphognathite has baled out. The constant shaking of the gills in
consequence of the motion of the legs must aid in ridding them of
the film of water which might cling to their surfaces.
Turning now to the internal anatomy, if the carapace be clipped
away from the mid- dorsal region of the head and the thorax, and
the terga removed from the segments of the abdomen, a general
view of the internal organs will be obtained. In the extreme front
is seen the brain at the sides of which two roundish glandular
masses, the kidneys, are situated: behind these the so-called
''stomach" with its attached muscles. Behind the stomach we find
the heart floating in a sac termed the pericardium, whilst in the
abdomen we find a mass of muscle which, as we approach the peri-
cardium, breaks up into strands which are attached to the sides of
the thorax.
Although the heart and its vessels are the structures which
naturally present themselves first on commencing dissection, yet it
will be more convenient to describe the alimentary canal first of all.
This canal differs sharply from the type found in most other groups
of animals in the large part of its length which is constituted
by the stomodaeum and the proctodaeum. The part lined by
XII] ASTACUS 189
endoderm is reduced to exceedingly small dimensions and yet, from
experiments made on other Crustacea, we have every reason for
believing that it is this part alone which is capable of digesting
and absorbing nourishment. Hence it comes about that the nourish-
ment must be supplied to it in the form of the finest powder, and
so a Crustacean and the same is true more or less of all Arthro-
poda is quite incapable of either swallowing its prey whole or
even of bolting large morsels of food.
From the mouth the so-called oesophagus ascends upwards and
slightly forwards till it expands into the so-called stomach, which is
divided by a deep transverse indentation into an anterior "cardiac"
portion and a posterior "pyloric" portion, these names being sug-
gested by fanciful analogies with parts of the human stomach. Both
oesophagus and stomach are simply portions of the stomodaeum
and of course like the rest of the ectoderm are covered with cuticle
internally. In the case of the stomach this cuticle is thickened in
places so as to form firm sclerites some of which have tooth-like pro-
jections which are brought together by the action of muscles attached
to the stomach and so constitute a mill by means of which the food
which has already been torn into fragments by the gnathites is
ground up into a powder. This powder is sifted through a sieve of
setae which guard the entrance to the pyloric sac ; in this way only
the finest grains reach the short portion of the intestine lined by
endoderm. The muscles which cause the grinding action of the
stomach are two pairs, termed the anterior gastric and poste-
rior gastric respectively. These are longitudinal bands arising
from the skin under the carapace and inserted in the sclerites in the
stomach wall. The anterior gastric muscles arise from the anterior
part of the carapace and are attached to a transverse sclerite in the
upper wall of the cardiac portion of the stomach termed the cardiac
ossicle, whilst the posterior gastric muscles arise from the posterior
part of the carapace and are attached to a sclerite called the pyloric
ossicle which runs transversely in the upper wall of the pyloric
portion of the stomach. The action of these muscles is to drag
asunder the cardiac and pyloric ossicles and to stretch the wall of
the stomach between them. When the muscles relax the elasticity
of the lining of the stomach restores it to its former shape. With
each end of the cardiac ossicle there articulates a sclerite called
the pterocardiac ossicle which curves downwards and backwards
along the side of the stomach, and similarly with each end of the
pyloric ossicle a zygocardiac ossicle articulates which curves
190
AllTHBOPODA
[CH.
Fig. 73.
XII] ASTACUS 191
FIG. 73. The Crayfish, Astacus fluviatilis, split into two by a median cut
extending along the mid- dorsal line and viewed from the side.
1. Antennule. 2. Antenna. 3. Mandible. 4. Mouth. 5. Squame
of antenna. 6. Anus. 7. Telson. 8. Male genital opening.
9. Chela. 10. First walking leg. 11. Second walking leg. 12. Third
walking leg. 13. Fourth walking leg. 14. The first abdominal
appendages modified for copulation. 15. The second abdominal ap-
pendages also modified for copulation. 16. The first swimmeret.
17. The second swimmeret. 18. The third swimmeret. 19. The
tail fan last abdominal appendage. 20. Oesophagus. 21. "Stomach."
22. Mesenteron. 23. Cervical groove. 24. Intestine. 25. Cerebral
ganglion. 26. Nerve-collar. 27. Ventral nerve-cord. 28. Eye.
29. Heart. 30. Sternal artery (ventral part). 31. Abdominal
artery. 32, 33. Sternal artery (sub-neural part). 34. Ophthalmic
artery. 35. Antennary artery. 36. Hepatic artery. 37. Testes.
38. Vas deferens. 39. Apodemes. 40. Kidney (glandular part).
41. Kidney (bladder). 42. Kidney (opening).
downwards and forwards on the lateral wall of the stomach to
meet and articulate with the pterocardiac ossicle. The lower
end of the zygocardiac ossicle is produced inwards into a comb-like
lateral tooth. The cardiac, pyloric, pterocardiac and zygocardiac
ossicles form a hexagonal frame of rods jointed together; so that
when the two ends are pulled apart the sides come inwards and
the lateral teeth meet and collide. But this is not all; to the
centre of the cardiac ossicle is articulated *a median sclerite, the
urocardiac, running directly backwards, and to the centre of the
pyloric is articulated a similar sclerite, the prepyloric, running
downwards into the groove dividing the urocardiac and pyloric
divisions of the stomach till it meets the urocardiac ossicle.
Articulating with both is the median tooth, a sclerite projecting
into the stomach. When the cardiac and pyloric sclerites are
dragged apart the urocardiac ossicle draws the median tooth forward
whilst the end of the prepyloric ossicle rotates it upwards and turns
the biting surface of the tooth forward and it comes into contact
with the lateral teeth. By the action therefore of the gastric
muscles the three teeth are caused to collide. The whole arrange-
ment is termed the gastric mill.
The portion of the intestine lined by endoderm is termed the
mesenteron and it is not more than -^ inch long: it is produced
dorsally into a slight pouch called the caecum, whilst at each
side it is joined by the duct of a large gland called the liver.
This organ might be described as a pair of trees of tubes: it
consists on each side of a branched outgrowth of the mesenteron
the cells lining which are impregnated with pigment and produce
a juice which has a powerful digestive action on the food. It
192 ARTHROPODA [CH.
thus corresponds in function to the pancreas of the Vertebrata
rather than to the liver (see p. 429). What cannot be digested
passes out by the perfectly straight intestine which is simply the
proctodaeum and is of course lined by cuticle. The alimentary
canal is surrounded by a series of spaces which used to be
regarded as equivalent to the coelom of the Annelida. This
however is not a correct view of their nature. The spaces in
question are simply blood spaces. From the study of the develop-
ment of the simplest known Arthropod, Peripatus, it is concluded
that the coelomic cavities, which in the embryo are just as well
represented as they are in Annelida dwindle in size as growth
advances and are represented finally merely by the cavities of the
kidneys and of the generative organs, whilst the blood spaces enlarge
and take on the character of a body-cavity which is then termed
a haemocoele in order to distinguish it from the true coelom. In
Peripatus there is corresponding to each segment a pair of coelomi-
ducts, the so-called " nephridia " which open internally into minute
thin-walled sacs, the remnants of the coelomic sacs. In the crayfish
however there is but one pair of greatly enlarged "nephridia" which
open in front of the mouth by pores situated as already described
on the coxopodites of the second antennae. Each of these kidneys
consists. of an oval thin-walled sac, developed by an intucking of
ectoderm, termed the ureter, in which the excretion accumulates,
and by the muscular contraction of which it is expelled, and of a
greenish glandular mass situated beneath the ureter, which is the
secreting portion of the kidney. This latter portion consists of a net-
work of tubes opening into one another, connected on the one hand
with the ureter and on the other with a small thin- walled sac the-
end sac which is the last trace of the coelomic cavity belonging
to this segment. The tubes are lined with excretory cells and since
the whole organ is bathed in blood the network arrangement of the
tubes permits of the exposure of a large surface to the surrounding
fluid from which the excreta are attracted by the excretory cells.
It must however excite no small surprise that an active and
muscular animal like the crayfish should be able to accomplish its
excretion by means of a single pair of excretory organs whilst
sluggish animals like the Annelida and even Peripatus require a
pair of such organs in each segment.
We are forced to the conclusion that some other organ must
assist the "nephridia" in carrying out their function, for there is no
question that the active metabolism of the crayfish must produce
XII] ASTACUS 193
more waste than that of the worm. Some experiments which Dr
Eisig of Naples made on the Capitellidae, a family of Polychaeta,
seem to throw light on this subject. When he injected into these ani-
mals a coloured poison like indigo-carmine, a large part was excreted
by the nephridia, the cells of which became deeply coloured with the
material they extracted from the coelomic fluid. Part was however
got rid of by the skin, and was thrown off mixed with the substance
of the cuticle and was even incorporated with the chaetae. From
these facts Dr Eisig concluded that a portion of the waste products
of metabolism was eliminated through the skin. Now in the crayfish
the ectoderm consists of a single layer of pillar-shaped cells, which
are continually secreting at their outer ends the material called
c hi tin which contains nitrogen and is stated by some authorities to
be chemically allied to guanin and uric acid, substances which are in
many animals produced by the kidneys. As this secretion goes on
the shell increases in thickness, and confines the growth of the
animal. So at intervals this hard casing of dead matter is thrown
off: the old shell cracks along the mid-dorsal line, and the animal
gradually extricates itself, and the cuticular lining of the stomo-
daeum and proctodaeum is cast at the same time (Fig. 74). The
whole process is called ecdysis, and it occurs five or six times in the
first year, twice in the second year and after that once a year. After
each ecdysis the skin remains soft and growth can take place, but
of course during this period as the animal is defenceless it remains
hidden. Thus the tendency of the ectoderm to produce chitin has
not only governed the form which the locomotor and masticatory
organs have assumed but it has had the indirect effect of causing
the eoelom and nearly all the excretory organs to disappear, since
the skin has assumed most of the excretory functions.
The genital organs have the same shape and position in both
males and females : they are situated beneath the pericardial septum
which is a sheet of connective tissue forming the floor of the peri-
cardium. In each sex the organ has a trilobed shape; there are
a pair of anterior lobes and a single median posterior lobe. It is
hollow and is connected with the exterior by a pair of ducts which
spring from the sides just where the paired anterior lobes pass into
the posterior one, and open to the exterior by a pair of pores
situated in the male on the coxopodite of the last pair of thoracic
legs, but in the female on the coxopodites of the third pair (in each
case counting the chela as the first leg). From the cells lining the
cavity of the gonad are produced the ova, which are about the size
S. & M. 13
B
PIG. 74.
CH. XII]
ASTACUS
195
FIG. 74. To illustrate the process of " ecdysis " in Arthropoda.
A. The anterior portion of the body of a Dragon-fly, Aeschna cyanea freed
from the larval shell. B. The tail being extricated. C. The whole
body extricated. D. The perfect insect, the wings having acquired
their full dimensions, resting to dry itself preparatory to the wings being
horizontally extended.
of pellets of shot and are filled with a dark red yolk. These when
ripe are shed to the exterior through, the short straight oviduct
and become attached to the swimmerets of the abdomen by their
adhesive coats, and in this position they are fertilised and accom-
plish their development, becoming free from the mother only when
they have become little crayfish.
FIG. 75.
76.
FIG. 75. Male reproductive organs of Astacus fluviatilis x about 2. From
Howes. 1. Eight anterior lobe of testis. 2. Median posterior lobe
of testis. 3. Vas deferens. 4. External opening of vas deferens.
5. Eight fourth ambulatory leg in which the vas deferens opens.
FIG. 76. Female reproductive organs of Astacus fluviatilis x about 2. From
Howes. 1. Eight oviduct. The left oviduct is shown partly opened.
2. Eight lobe of ovary. 3. Left lobe of ovary with the upper half
removed to show the cavity of ovary or coelom into which the ripe ova
drop. 4. External opening of oviduct. 5. Eight second ambulatory
leg on which the oviduct opens.
From the lining of the testes male germ-cells are formed we
say advisedly, male germ-cells not spermatozoa, for these cells are
utterly unlike spermatozoa. They are rounded saucer-shaped cells
with a central nucleus and a number of curved spines sticking out
tangentially from the surface by means of which they adhere to the
132
196 ARTHROPODA [CH.
ova. The nucleus is in the centre at the bottom of a chitinous tube
which seems capable of being turned inside out and thus forcing the
nucleus into the ovum. The male duct or vas deferens is long and
coiled, and for part of its length is lined by cells which produce a
milky fluid in which the male cells float. When this fluid with its
contained cells escapes from the male pore it is received by the tube
formed by the two first pairs of appendages of the abdomen, and the
male then seeks the female and turning her on her back, discharges
the fluid on to the eggs.
Nothing could more strongly illustrate the proclivity which the
protoplasm of the Arthropoda has towards the production of cuticle
than the substitution of these motionless male cells with their spiny
covering for the active motile spermatozoa. One cannot but believe
that spermatozoa would be more advantageous, especially for aquatic
animals, and other groups of the Arthropoda such as the Arachnida,
have managed to retain them, but in these Crustacea the set towards
the production of cuticle appears to be so strong that they have
become an impossibility. The study of the development of Peripatus
teaches us, that not only are the genital organs of Arthropoda
remnants of coelomic sacs but that the genital ducts are the remnants
of the coelomiducts or " nephridia " opening into these sacs. There-
fore, in the crayfish there are three pairs of " nephridia " left ; one
pair acting as kidneys, one as oviducts, one as vasa deferentia.
The nervous system of the crayfish is constructed on the same
type as that of the Annelida, differing in details only, though these
details are most instructive. It consists of a brain, situated in front
of the mouth, communicating by means of a nerve-collar, which
encircles the oesophagus, with a ventral chain of ganglia. The
differences are as follows. In the Annelida the nuclei of the
neurons are scattered all along the ventral cord, being only less
numerous in the commissures than in the ganglia. In the Crus-
tacea, and indeed all Arthropoda except Peripatus, the nuclei are
confined to the ganglia and the commissures consist of axons (nerve-
fibres) only. Further, in most Annelida the cord is apparently a
single one, though the microscope shows that it consists of a
double strand of fibres but in the crayfish it is clearly a double
one in thorax and apparently a single one in the abdomen.
Finally the ganglia of several adjacent segments show in some
cases a tendency to coalesce so that there are considerably fewer
ganglia than segments as indicated by the appendages. Thus the
brain supplies nerves not only to the eye region which we may
suppose to represent the prostomium of Annelida but also to the
XII] ASTACUS 197
two pairs of antennae which were originally pairs of appendages
situated behind the mouth, whilst the first ganglion of the ventral
chain termed the sub-oesophageal sends nerves to all the primary
jaws and to the first two pairs of maxillipedes, so that it represents
five ganglia fused together. The ganglion which supplies the third
maxillipede is separated from the sub-oesophageal ganglion only by
a groove, and Huxley considered it a part of the sub-oesophageal,
which on this reckoning would -supply all the jaws. Each of the
"legs" and of the swimmerets is supplied by a separate ganglion,
though the ganglia for the fourth and fifth legs are very close
together. The commissures between the ganglia for the third and
fourth leg diverge widely to allow the sternal artery to pass between
them.
In higher Crustacea such as the Crabs the coalescence of the
ganglia has gone much further so that all the jaws and all the
thoracic appendages are supplied by a single ganglion.
The principal sense organs of the crayfish are the eye and the
ear. The eye is a modification of the ectoderm covering the tips of
the eye-stalks. It consists fundamentally of a number of pits of
ectoderm each of which becomes filled with the secretion of the
cells forming its walls. It is termed a compound eye to distinguish
it from the eyes found in other Arthropoda which consist of a
single pit of ectoderm. Starting from the surface each pit consists
of a pair of lens cells which secrete ordinary cuticle rather more
vigorously than the surrounding ectoderm. Hence a slight con-
vexity of the cuticle is occasioned which acts as a. plano-convex
lens to concentrate light on the pit. Below the lens cells is a circle
of four cells, each of which secretes on its inner side a mass of clear
material the conjoined secretions of the four cells constitute a
.clear body termed the crystalline cone. Below these again come
a circle of six or seven visual sense cells, each of which develops the
characteristic visual rod on its inner side whilst from its basal
end a nerve fibre proceeds inwards. The visual rods all coalesce
to form a fluted striated spindle called the rhabdome and the
group of visual cells is termed the retinula.
Each eye-pit is surrounded by dense black pigment contained in
amoebocytes which wander into this position from the surrounding
blood. As a result of this investment of pigment the only light
which can penetrate the pit and affect the retinula consists of rays
very nearly parallel to the axis of the pit. All slanting and oblique
light will be absorbed by the pigment layer, and so the retinula is
198 ARTHROPODA fcH.
stimulated by the colour and intensity of the light proceeding from
a small area of the outside world directly in front of it. Since the
eye consists of a great number of pits, it follows that an image is
formed as a mosaic or pattern of light and shade, depending on the
extent to which each individual retinula is stimulated. The fine-
ness and exactness of the image will depend on the number of
eye-pits and retinulae, The principle of the formation of this
image is exactly similar to that on which the image is formed in
the human eye viz. the concentration of the light from a particular
area of the outside world on a particular element of the eye, only
that the form of the human lens enables a much larger beam of
light to be concentrated on each element, and the number of
elements is large, so that the image in the crayfish's eye is dimmer
and coarser than the image in our own. The sensations from all
the various eye-pits are transmitted by the basal fibres of the
retinula cells to the optic ganglion situated in the centre of the
eye-stalk, by which they are combined and the resultant image is
transmitted to the brain.
The optic ganglion is developed by a budding of the ectoderm
cells along the side of the stalk. In shrimps, as already mentioned,
when this ganglion is destroyed an antenna-like organ is developed
in place of the eye, but if it remains intact the stump of the eye-
stalk will produce a new eye.
The ear is a very much simpler organ than the eye. It ib
merely an open ectodermic pit, lined with cuticle, situated on the
upper surface of the basal segment of the antennule. The entrance
is guarded by rows of feather- like setae which extend from the
side across the opening. Over the bottom of the pit are several
parallel rows of delicate simple setae, the bases of which are in
close association with sense cells, and the nerve fibrils proceeding
from these cells form the auditory nerve, which goes to the brain.
These delicate setae it may easily be imagined will respond to
vibrations traversing the water : and the information thus conveyed
to the animal may warn it against the approach of its enemies,
though these vibrations would not be perceptible to our ears as
sound. But experiments have shown that as is the case with so many
ears, another and different function is carried out by the organ
to which the perception of vibrations may be quite subsidiary, viz.
the perception of the position of the animal with regard to the
vertical or the perception of balance. These experiments were
carried out on the sea crayfish Palinurus. The ear-pit contains
Xll] ASTACUS 199
particles of grit or sand which will roll into different positions and
stimulate different sense-cells for each new position which the
animal assumes. When however the animal undergoes ecdysis the
cuticle lining the ear-pit is shed and with it these grains of grit.
After each ecdysis therefore the animal must obtain fresh grains
of sand from outside. Now the experimenter kept specimens of
Palinurus in a tank till they shed their shells which he immedi-
ately removed. The animals were then placed in filtered sea-water
to which some grains of magnetic oxide of iron were added. In a
day or two when the new shell had hardened and the crayfish
regained their activity the experimenter approached the tank with
a powerful magnet. The animals then set themselves at right
angles to the lines of magnetic force; they behaved as if the
magnetic attraction were the force of gravity. This could only be
^ explained on the assumption that they regulated the positions of
their bodies in accordance with the position of the particles of grit
in the ears in other words the balancing function of the ear was
proved.
The sense of smell is also situated in the antennule and is no
doubt one of the most important senses the animal has, but the
only organs which can be associated with it are the small flattened
setae on the exopodite already described. The sense of touch is
probably associated with the small setae scattered all over the body.
Each of these is inserted by means of a tiny arthrodial membrane
in the shell and is consequently moveable, and sense cells are
situated at the bases of many of them which must be stimulated
when anything moves these tiny levers.
The muscles of the crayfish practically all consist of bundles of
longitudinal fibres which must be regarded as remnants of the walls
of the vanished coelomic sacs. There are no circular muscles,
except those surrounding heart and arteries, for the comparatively
rigid shell in which the animal is enclosed would make circular
muscles useless. The muscles may be divided into trunk muscles
and appendage muscles, and we may treat of the latter first. The
skeleton of each segment of each appendage articulates with each
succeeding and preceding segment, so that it can move with respect
to each of them in only one plane. To effect this movement two
muscles are necessary, an extensor, or straighterier, and a flexor,
or bender. Since the skeleton is outside the muscles, the flexor
muscle is placed on the opposite side of the limb from that towards
which it is bent, the reverse of the condition which prevails in the
200 ARTHKOPODA [CH.
human liinb where the skeleton is internal. In each segment of each
limb (except the most distal) there are four muscles, two flexors and
two extensors connecting it with its predecessor and successor, but
the plane in which any one segment can move on its successor is
different from that in which it moves on its predecessor ; in fact,
there is a different plane of movement between every pair of segments,
so that by the combined movement of every joint the limb can be
bent into any position. [The construction of the crayfish's limb
has been imitated by a firm of American instrument makers who
have produced a lens-holder on this plan which can be bent into any
shape.] The muscles which move the mandibles are very powerful,
the adductor which brings them together forming a great fleshy
mass at the side of the stomach. Each abdominal segment is
connected with the next by a pair of flexors and extensors, and
since the downstroke is, as we have seen, the motion by which the
crayfish swims backwards the flexors form a very much thicker bed
of flesh than do the extensors. The intestine lies above the flexors
and below the extensors. From the first segment of the abdomen
extensors and flexors pass into the thorax, in each case breaking up
into several slips of muscle which are inserted in different segments
of the thorax, indicating that the segments of the thorax, though
now immovably fused with one another, were once movable. The
cells of which the muscles are composed are very different from
the muscle-cells described in the Annelida. Muscle-cells of that
description are, it is true, found in the muscular walls of the heart
and arteries and intestine of the crayfish, but the muscles by which
the quick movements of the body-segments and appendages are
carried out are composed of muscle-cells of a more complex kind.
These are much longer than the spindle-shaped muscle-cells of
Lumbricus, and are clothed with a delicate cuticle called the sarco-
lemma; they each have numerous nuclei which are embedded in
unmodified protoplasm, and the remainder of the protoplasm is
converted into contractile fibrils. These fibrils are of a composite
nature, being made up of alternate discs of a lighter, apparently
semi-fluid, material and a darker solid doubly -refracting material.
Each fibril is divided into a series of segments or sarco styles, each
sarcostyle consists of a disc of doubly refracting or anisotropic
substance with a disc of singly refracting isotropic substance on
each side. Each sarcostyle is separated from the next by a thin
membrane, " Krause's membrane." When contraction occurs the
isotropic substance is absorbed by the anisotropic which swells and
XII] ASTACUS 201
at the same time becomes lighter in colour. Such muscles are
able to carry out much more rapid contractions than is the case
with the unstriped smooth muscles, and as they recover from the
state of contraction with great rapidity many quickly succeeding
contractions can be carried out. In the case of the Mosquito,
which produces its note by the vibration of the wings, it has been
calculated that at least 5000 contractions a second must be
effected by the wing-muscles. Speaking broadly, muscles of this
type are found only in Arthropoda and Vertebrata, but they occur
in other groups of the animal kingdom in the case of isolated muscles
(cf. jaw-muscles of Echinoidea), where rapid and powerful movements
are required.
The muscles are inserted m the skin, but in the thorax this is
folded inwards between the segments so as to produce wedges
termed apodemes which project into the body cavity and give
attachment to the flexor muscles. The apodemes are, of course,
stiffened by a deposit of chitin between the two layers of ectoderm
of which they are composed. Between all the segments which bear
the "legs," except the last, two apodemes project inwards on each
side, one arising from the side, called the endopleurite, and one
from the ventral surface, called the endosternite. The two endo-
sternites of opposite sides meet in an arch, enclosing the sternal
canal, in which lies the nerve cord. On its outer side the endo-
sternite forks and one fork, termed the arthrodial apodeme
(ap.arth, Fig. 71), meets a corresponding process of the endopleurite,
and the two form a strengthening wall round the insertion of the
limb. The endosternite has a third process, termed the para-
phragmal (ap.par, Fig. 71), which passes forward to unite with
the endopleurite in front, so that a somewhat complicated internal
skeleton results. At each ecdysis the chitin which stiffens the
apodemes is moulted, and at that time the apodemal fold could
be straightened out. In some Crustacea, though not in the cray-
fish, very marked changes in the shape of the animal are brought
about at ecdysis by the smoothing out of apodemes, and the
development appears to proceed by sudden jerks.
Connective tissue has already been mentioned in the case of the
Platyhelminthes, Rotifera and Annelida, but in these animals it attains
little development compared with that which it reaches in the case
of the Arthropoda. It consists, it will be remembered, of a semi-
fluid ground-substance, corresponding to the jelly of Coelenterata,
which becomes invaded by amoebocytes. These by their metabolism
202 ARTHROPODA [CH.
manufacture bundles of white tough fibres which interlace in such
a way as to produce a membrane of great strength. A special
development of this connective tissue underlies the ectoderm and
is termed dermis it is included along with the ectoderm in the
popular term skin. But connective tissue is ubiquitous in the
crayfish, if as Huxley said we could imagine the essential cells of
every organ dissolved there would remain a cast of the whole in
connective tissue.
Blood may be regarded as a tissue of the same kind as connective
tissue only here the ground-substance is thoro uglily fluid, the
amoebocytes or blood cells not depositing fibres. As already
mentioned, in the crayfish all the crevices between the various
organs are occupied by blood, these cavities taken together being
termed thehaemocoele. Of these the largest is the pericardium,
a space just under the dorsal wall of the thorax which is divided
from the rest by the horizontal pericardial septum a structure
which from observations on the development of other Arthropoda we
learn to be derived from the dorsal portions of the coelomic sacs,
which have flattened out and lost their cavities. The pericardium
communicates with certain vertical canals in the thin side-walls of the
thorax (i.e. the true walls, not the branchiostegite), termed branchio-
cardiac canals. These canals are in communication with the gills,
and through them the blood that has absorbed oxygen there is re-
turned to the pericardium. Each gill has a hollow stem traversed
by a longitudinal septum which divides its cavity into two spaces,
an upper and a lower, only communicating at the tip. The branchio-
cardiac canal communicates solely with the upper passage, whilst
the lower communicates with the ventral sinus already mentioned,
in which the nerve-cord lies, from which the impure blood passes
to the gills.
Returning to the pericardium we find suspended in it by
fibrous cords, termed the alae cordis, the heart. This is an
oval muscular sac with three pairs of openings, termed ostia
(Lat. ostium, a door). Each ostium is provided with two flaps
which open inwards, but which when the heart is full of blood are
pressed .together so that they meet and prevent the blood from
escaping. Thus the heart receives the blood from the pericardium.
When the heart contracts the blood is driven out on all sides
through vessels with strong muscular walls called arteries. There
are six main arteries one called the abdominal goes backwards
over the intestine, and gives off a branch immediately behind the
Xll] ACTACUS 208
heart called the sternal artery. This artery goes directly down-
wards and passing between the commissures connecting the third
and fourth pairs of thoracic ganglia divides into anterior and pos-
terior branches which lie beneath the nerve-cord and give blood to
it (30, Fig. 73). From the heart an ophthalmic artery is given
off which runs forwards over the dorsal surface of the stomach and
eventually gives branches to the eyes and antennules. In addition
there proceed forwards from the heart two pairs of arteries, the
antennary and the hepatic. The first pair supply the antennae;
each gives off on its way a large branch to the stomach, called the
gastric artery. The hepatic arteries are more deeply situated,
they run forward and break up into branches which are distributed
to the tubes of the liver. The muscles surrounding the arteries, as
in Vertebrata (see p. 434), do not carry out rhythmical contractions,
but keep up a steady pressure on the blood, called tone. When
the arteries are traced they break up into branches which finally
open into the spaces of the haemocoele.
So far no mechanism has been described which drives the blood
to the pericardium. It seems to find its way there by the constant
pressure from behind of the blood driven out from the heart.
Reviewing the structure of the animal we see that the production
of chitin by the ectoderm leads to the jointing of the appendages
from which the name Arthropod is derived, leads further to the
loss of cilia and the consequent necessity of the peculiar respiratory
mechanism, and to the disappearance of the coelom and most
of the excretory organs, and consequently to the peculiar form of
the genital organs. In fact, it would be hard to name a character
of the Arthropoda as distinguished from the Annelida which is not
directly *r indirectly traceable to the existence of the chitinous
shell.
Class I. CRUSTACEA.
The Crustacea are with a 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 or
are believed to have once possessed two pairs of antennae and these
as well as their other jointed limbs are typically biramous, that is,
they consist of a basal portion or protopodite bearing two prolonga-
tions, the endopodite and the exopodite. They have at least three
pairs of appendages converted into jaws.
204 ARTHROPODA [CH.
The Crustacea are usually divided into two groups, the En-
tomostraca (Gr. CVTO/X.OS, cut in pieces ; oo-rpaKov, a shell) and the
Malacostraca (Gr. //.aAaKo'?, supple) ; and each of these again is
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
Ostracoda 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 ; but unlike the carapace
of the Malacostraca it does not become fused with the terga of
the thorax. In many descriptions of Entomostraca the words
" thorax " and " abdomen " are used to describe 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. 77) 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 stomach. 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
XII] PHYLLOPODA 205
the second antennae and mandibles of the adult ; both are at first
placed behind the mouth.
The Entoinostraca consists of the following Orders :
Order I. Phyllopoda.
As the name implies the Phyllopoda (Gr.
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^^ the silk .
and tissues being broken wornu Life size,
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 differ in the degree to which
metamorphosis occurs. In the Aptera there is no metamorphosis
and the development is said to be direct. In Orthoptera and
250
ARTHROPODA
[CH.
Hemiptera there is no quiescent pupa stage and the chief difference
between the larva and adult is the absence of wings in the former.
Here the metamorphosis is said to be incom-
plete. The same is true of Ephemeroptera,
Isoptera and Paraneuroptera. Amongst the Le-
pidoptera, Coleoptera, Hymenoptera and Diptera
there is a well-marked pupal stage, and these
orders are said to have complete metamorphosis.
Various names have been given to the larvae of
Insects without very precise definitions. Those of
the Lepidoptera are usually called Caterpillars.
They are often gaudily coloured and bear tufts
and bunches 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 the abdominal
segments bear fleshy stumps called abdominal
The larvae of some of the Saw-flies (Hymenoptera) have
a similar bright colouring and resemble Caterpillars, and like
them feed exposed on leaves, etc. The larvae of Beetles and most
Hymenoptera are as a rule hidden underground or in galls or wax-
comb. They are whitish in colour and unattractive, and are often
Fm. 103. Cocoon of
Bombyx won, from
which silk is spun.
About life size.
B
FIG. 104. Silk-worm moth, Bomlyx mori,
A. Female. B. Male.
termed grubs, whilst tlje footless white larvae of the Diptera,
which are for the most part deposited in some organic substance
whether alive or not are usually called maggots. The wingless
young of Orthoptera and of the other orders in which incomplete
metamorphosis occurs are termed nymphs.
In the following account of Insect Classification we can only
indicate the chief characters of each order and mention the names
of one or two common members of each.
XII] ORDERS OF INSECTS 251
Order I. Aptera.
Wingless Insects, with scales and hairs covering 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 ventral 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 (Gr. aTrrepos, 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 roof-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. Machilis is
a small insect found between tide marks in seaweed. In it the
abdominal exponents have small vestigial appendages.
Order II. Orthoptera.
The Orthoptera (Gr. op0os, straight; irrepoV, 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, Forficula ; the praying insect,
Mantis; the leaf and stick insects, Phyllium and Phasma; the
Grasshopper (Fig. 100), Pachytylus', the Locust, Locusta; the
Cricket, Gryttus ; and many others.
Order III. Paraneuroptera, or Dragon-flies.
The Paraneuroptera (Gr. vevpov, 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 is incomplete.
252 AETHROPODA [CH.
This order includes the Insects familiarly known as Dragon-flies.
Two of the best known genera are Libellula and Aeschna (Fig. 74).
A number of other small orders of Insects agree with the Para-
neuroptera in possessing two pairs of membranous wings with
numerous nervures. These were formerly grouped with the Para-
neuroptera in one large order termed the Neuroptera and this
course was adopted in former editions of this book. Continued
research has shown that amongst these "nerve-winged" insects
profound differences occur both as to the character of the mouth-
parts and the nature of the metamorphosis ; and in consequence
the old group of the Neuroptera has been divided up, and its
divisions given the rank of orders. A few only of these orders
will be mentioned here, viz.:
Order IV. Ephemeroptera or Day-flies.
In these Insects the nymph stage is passed in water and lasts a
long time, in some cases as much as two years. Breathing is
effected by the so-called tracheal gills wing-like organs projecting
from the sides of the abdomen in which tracheae ramify. These have
been recently shown to be modified abdominal appendages. Oxygen
diffuses from the water into the air in these closed tracheae and
thence into the blood, instead of as in the gills of animals of true
aquatic ancestry, directly into the blood. From this circumstance
it is clear that the nymph represents a terrestrial not an aquatic
ancestor. The imago takes no food, it emerges from the cuticle of
the nymph in the evening and hovers over the water for a few hours
during which time mating and laying of eggs is accomplished. The
gnathites though vestigial are of the biting type. Ephemera, the
May-fly, is the commonest British form.
Order V. Isoptera, Termites or White Ants.
In these Insects the gnathites are like those of the Cockroach, of
a strongly marked biting type. They live in large colonies which
include one perfect sexually developed female (the queen) and one
ripe male at least, and a very large number of imperfectly developed
wingless females which are divided into two varieties, termed
respectively the workers with small heads and the soldiers with
enormous heads and powerful jaws. They live on decaying wood
and burrow in it, never exposing themselves to the light if it can be
XII] OKDERS OF INSECTS 253
avoided. Wings are only developed on the sexually ripe Insects at
the time when they swarm out from the nests and when cross
fertilisation can take place. Isoptera are confined to the tropics
and are fearfully destructive of furniture, clothing, etc. Two forms,
Caktermes and Eutermes come as far north as Sicily.
Order VI. Thysanoptera, or Corn-flies.
These are minute black Insects which infest flowers including
under that title the inflorescences of corn and other grasses. The
wings are fringed with hairs The basal parts of the maxillae
coalesce to form a tube. One mandible only is developed and this
forms a curved stylet. The nymph resembles the adult except in
possessing no wings, but a motionless pupal stage intervenes
between larvae and adult forms Thrips is the common British
genus.
Order VII. Trichoptera, or Caddis-flies.
In these Insects a sucking tube is formed by the coalescence of
both pairs of maxillae and the mandibles are vestigial or entirely
absent in the imago, so that as -in Lepidoptera nutrition has to be
obtained from such sources as honey, in which a preliminary stabbing
of the host-plant is not required. The wings are covered with
hairs, which may be compared to the scales on the Lepidopteran
wing, since these latter are only flattened hairs. The larva resembles
the larva of Ephemeroptera: it has biting mouth-parts and tracheal
gills attached to the abdomen and is aquatic in habit. It constructs
for itself a case of bits of stone or shell which ensheaths and pro-
tects the abdomen and which when larval life is over serves as a
case to protect the pupal or motionless stage which intervenes
between the larval and imaginal stages. Phryganea is a British
example of this order.
Order VIII. Neuroptera (sensu stricto).
These Insects possess biting mouth-parts. The larvae are some-
times terrestrial and sometimes aquatic and in the latter case they
possess tracheal gills which like those of Day-fly nymph are modified
abdominal legs. The wings of the adult are devoid of hairs. There
254 ARTHROPODA [CH.
is always a quiescent pupal stage : Sialis the Alder-fly, much used
by anglers, Myrmeleon the Ant-lion, Hemerobius the Aphis-lion and
Chrysopa the Golden- eye lace-winged fly are examples of this order
found in Britain.
Order IX. Coleoptera
The Coleoptera (Gr. /coAeo'?, a sheath) or Beetles have mouth-
parts adapted for biting. The anterior wings termed elytra (sing.
elytron) are hard and horny and meet in the middle line of the
back in a straight suture and conceal the abdomen. The hinder
wings are membranous and folded and used for flight. There is a
grub-like larva with biting mouth-parts and a quiescent pupa which
takes no food. The metamorphosis is consequently complete. This
order has always been a favourite one with collectors, because its
firm exoskeleton renders preservation and identification easy, and
so the number of species of it named and described is much greater
than in the case of any other order of insects. At least 90,000
species are known. One of the most familiar British beetles is
Coccinella, the Lady-bird, in which
the elytra are bright red in colour
diversified by black dots ; it is one
of the greatest friends of the
gardener, as it devours plant-lice.
The so-called Black-beetle as we
have alread seen is not a Beetle
FIG. 105. In the centre Coccinella
septempunctata, the Lady-bird at all but belongs to the Orthoptera,
beetle, natural size, to the right, for example we dissect one of our
larger British beetles such as the
Cockchafer or June-bug (Melolontha) and compare its anatomy with
that of the Cockroach we cannot fail to be struck by the compara-
tive specialisation of the former insect as compared with the latter.
Thus in the Cockchafer the branches of the tracheae end in vesicles
(Fig. 106), the Malpighian tubes are reduced to two which are
beset with pouches; there is a huge tubular eversible organ, the
penis, for transmitting the spermatozoa to the female, and the entire
abdominal chain of ganglia is fused with and indistinguishable
from the last thoracic ganglion (Fig. 107). The reader should
compare with this the account given of the anatomy of the
cockroach on pp. 233 244.
XIl]
ORDERS OF INSECTS
255
FIG. 106. FIG. 107.
FIG. 106. View of male Cockchafer, Melolontha vulgaris, from which the dorsal
integument and heart have been removed to show the internal organs.
After Vogt and Yung.
1. Cerebral ganglion. 2. 1st thoracic ganglion. 3. 2nd and 3rd
thoracic ganglia fused. 4. Fused abdominal ganglia. 5. Oesophagus.
6. Mid-gut. 7. Small intestine. 8. Colon. 9. Rectum.
10. Malpighian tubules, bro-wn portion with caeca. 11. Malpighian
tubules, distal end. 12. Trachea with vesicles. 18. Testes, opening
into coiled vasa deferentia. 14. Penis. 15. Single vas deferens.
FIG. 107. View of nervous system of the Cockchafer, Melolontha vulgaris.
After Vogt and Yung.
1. Cerebral ganglion. 2. Sub-oesophageal ganglion. 8. 1st thoracic
ganglion. 4. 2nd thoracic ganglion. 5. 3rd thoracic ganglion.
6. Fused abdominal ganglia. 7. Nerves to antennae. 8. Optic
nerves. 9. Origin of sympathetic nerves. 10. Abdominal nerves,
a pair to each segment, which split into an anterior and posterior branch.
Order X. Hymenoptera.
The Hymenoptera (Gr. v^o'-Trrepo?, membrane-winged) have
mouth-parts adapted for biting and sucking. The ligula of the
labium is long and grooved, whilst the paraglossae are small. The
mandibles are well developed and the laciniae of the first maxillae
large. The four wings are alike, membranous in texture, but with
vastly fewer nervures than the wings of insects belonging to the
" Neuropterous " orders, and the hind wings are hooked on to the
anterior in such a way that the two wings of each side move
together. The metamorphosis is complete.
256
ARTHROPODA
[CH.
This group comprises the Ants, Bees and Wasps. Many of
them live in highly complex communities, in which small sterile
females act as " workers," and in their social habits and general
intelligence they reach a level which is only surpassed by man him-
1.
Fm. 108. Formica rufa, the Wood-ant.
Female. 2. Male. 3. Neuter.
Worker-bee.
Queen-bee.
Drone.
FIG. 109. Apis mellifica, the Honey-bee.
FIG. 110. Polistes tepidus and nest.
self. The group includes the Wood-wasp, Sirex ; the Saw-fly,
TentJiredo; the Gall-fly, Cynips; the Ichneumon ; the Ant, Formica-,
the Wasp and Hornet, Vespa\ the Humble-bee, fiombus; and the
Honey-bee, Apis.
XII]
ORDERS OF INSECTS
257
Order XL Hemiptera.
The Hemiptera . (Gr. i}/u, half) have mouth-parts arranged for
piercing and sucking. The basal part of the labium is elongated
and tubular and the mandible and first maxilla form sharp pointed
styles. The two pairs of wings may be alike or may differ and
the anterior pair are in some cases half horny and half membranous.
The metamorphosis is incomplete, there being no quiescent stage.
The members of this order present very great divergence both
of form and of size ; they are colloquially known as Bugs and Lice.
Amongst the commoner forms are the Water-boatman/JVbfowecta ;
the Water-scorpion, Nepa ; the Bed-bug, Acanthia ; the Cicada,
the " Cicala " of Italy, remarkable for its chirping noise ; the Frog-
hoppers, including the Cuckoo-spit, Aphrophora ; the Plant-louse,
Aphis; the Phylloxera, which destroys vines and Scale Insects from
one of which the dye Cochineal is prepared.
Order XII. Diptera.
The Diptera (Gr. 8t-7TT6pa, two-winged)
have mouth-parts arranged for piercing and
sucking. The chief 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. In addition to the styles formed
by the elongation of the mandibles and the
laciniae of the first maxillae there is a fifth
style, the hypopharynx, situated
middle line which represents an
elongated chin and carries the duct
of the salivary gland. Only one pair
of wings, the anterior, are present ;
the posterior are represented by a
pair of short knobs called balancers
or halteres (Fig. 112). The meta-
morphosis is complete.
The Diptera or Flies form one
of the largest of the Insect Orders,
probably as large as the Coleoptera,
although at present the number
of species of Beetles named and
S. & M.
Ill
the
FIG. 111. Glossina mor~
sitans, the Tsetse-fly.
FIG. 112. Cecidomyia destructor,
the Hessian-fly.
1. Insect. 2. Larva. 3. Pupa,
or "flax seed." All magnified.
17
258 ARTHROPODA [CH.
described is far greater than that of Flies. Amongst the commoner
genera are the Gnats and Mosquitoes, Gulex ; the Daddy-long-legs,
Tipula-, the Gall-fly, Cecidomijia (Fig. 112) ; the Horse-fly, Tabanus;
the Bot-fly, Oestrus; the common House-fly and Blue-bottle, Musca,
and many others.
Order XIII. Siphonaptera.
The Fleas, of which the commonest is termed Pulex irritans, are
wingless but endowed with considerable powers of jumping. They
were formerly classed with the Diptera, but are now regarded as
a type of a separate order, the Siphonaptera (sometimes called
Aphaniptera).
In the Fleas the mandibles form stylets with saw -like edges and
there is a short hypopharynx. The maxillary palps are long but the
basal portions of these appendages are broad and triangular and
not converted into stylets. The labial palps are very long and
grooved and form sheaths for the mandibles and the hypopharynx.
The metamorphosis is complete, the larva is worm-like and lives on
animal refuse. The body of the adult is much compressed from
side to side, which is an unique feature among Insects.
Order XIV Lepidoptera.
The Lepidoptera (Gk. Ac?'?, a scale, irrepor, a wing) have mouth-
parts adapted for sucking 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. 102). 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 famishes the material silk
(Fig. 103). Within this cocoon, or in some species without forming
a cocoon, the caterpillar forms a pupa, and whilst in this state it
XII] AEACHNIDA 259
undergoes a very thorough reorganisation 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. 104). The female usually deposits its eggs on or near the
plants which serve as food for its offspring.
Class III. AEACHNIDA.
The third large group of the Arfchropoda 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 Arachnida (Gk. apcr^, a spider; etSos, shape) are
features. Q 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 or prosoma are strongly contrasted with the plate-like modi-
fied limbs of the middle part of the body ormesosoma when the
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 1 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 in the most primitive marine forms consists of
gills. In the many land forms these gills are retained but are
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,"
but here the error is too deep-rooted for correction since the term is used in
describing both Crustacea and Insecta, and in each case in a different sense.
172
260
ARTHROPODA
[CH.
enclosed in respiratory chambers. In other land forms tracheae
assist the respiratory chambers and in still others entirely replace
them. The gills have 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 shall 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
FIG. 113. The Garden Spider, Epeira diademata, sitting in the centre of its web.
After Blanchard.
XII] SPIDER 261
of appendages, the pedipalpi, are leg-like and modified in the male
in connection with the fertilization of the female. The abdomen
bears certain modified appendages called spinnerets, on which
open the glands, the secretion of which produces 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 well-shaped web
(Fig. 1 1 3), we notice that behind the prosoma
there is a slender waist and that this is
followed by a large swollen abdomen with
no outward trace of division into segments,
or into meso- and meta-soma.
There are six pairs of appendages, and
External it is at once noticeable that
there are no antennae or feelers
to act as sensory organs. Their function is
to some extent taken over by the long walk- FIG. 114. Front view of
ing legs. The first pair of limbs are called "* < t $>*
eh el i c era e ; in Epeira these are two-jointed, Magnified. From
the terminal joint being pointed and folded
down against the basal joint except when 1 - Head - 2 - E y es -
, . 8 , /TV ,,x mi r 3 - Basal J lnt f che '
being used (rig. 114). Tnis pair 01 appen- Hcerae.
dages contains poison glands and the poison 4 - Claw of chelicerae.
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 appendages in the Arachnida are called
pedipalpi (Fig. 115). 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 "maxilla" (2, Fig. 115). It is
a common feature of the Arachnids that the basal joints of one
or more of the pairs of appendages develop gnathobases and act
as jaws, but the modification never goes so far as to obscure
262
ABTHROPODA
[CH.
1. Coxa.
"maxilla." 3. Trochanter. 4. Femur.
5. Patella. 6. Tibia. 7. Tarsus.
8. Palpal organ.
the limb-like form of the appendage and so produce a true
gnathite.
On the ventral surface
of the abdomen just behind
the waist is situated the
genital opening, protected by
a plate ; on each side of this
is the slit-like orifice of a
lung-book. The lung- books
are very remarkable struc-
tures. Each opens to the
exterior by a pore through
which the air enters, and
1 consists of a sac the cavity
FIG. 115. Pedipalp of Tegenaria guyonii, O f which is largely occupied
the large house-spider. , , ,, . , ,
by a number of thin plates
2. Gnathobase, the so-called j n the substance of which
the blood circulates and is
thus brought into close rela-
tionship with the air which
passes in and out between the neighbouring plates ; the sac is
floored in by a special plate which is a modified appendage (Figs. 116
and 117). Such a breathing apparatus is peculiar to the Arachnida.
In some Spiders we find a second pair of lung-books placed behind
the others, and in other species this second pair is replaced by a
pair of tracheae recalling the respiratory mechanism of the Myria-
pods or the Insects (Fig. 116). They have however been indepen-
dently developed, and probably owe their origin to the sac of a
lung-book from which the lamellae have disappeared. Certain
branches of these tracheae situated near the middle line are be-
lieved to be modified tendons of the abdominal muscle, for in all
Arthropoda the tendons of the muscles are formed by hollow
involutions of the ectoderm lined by chitinous cuticle.
Near the hinder 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
organs 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. 118).
Spinnerets.
XII]
SPIDER
263
The silk is secreted by a large number of glands which have
their exit at the above-mentioned pores. Of these in E. diademata
there are five different sorts and each secretes a special kind of
thread ; for the various lines in a Spider's web differ considerably
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
3 4
Fio. 116.
FIG. 117.
Fm. 116. Horizontal section through the abdomen of a Spider, Argyroneta.
After MacLeod. Magnified.
1. Opening to exterior, tracheal stigma. 2. Terminal tracheae.
3. Lateral tracheae. 4. Lung-books.
FIG. 117. Longitudinal section through the lung-book of a Spider. Magnified.
From MacLeod.
1. Opening to the exterior or stigma. 2.
leaves. 3. Space in which the air circulates.
the blood circulates.
Free edge of the pulmonary
4. Space in which
the support of circular lines ; the threads with which the Spider
binds up its captured prey differ from these, and there is still
another kind of thread with which it constructs its cocoons, and
each kind of line is supplied from different sets of glands.
The dissection of a Spider requires much care, since the organs
almost fill the body and are completely embedded in the large
264 ARTHROPODA [CH.
masses of the digestive and reproductive glands. The oesopha-
gus, which leads from the mouth, opens into a strong sucking
"stomach," which, like the stomach of the Crayfish, is really 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. 118). Behind
this is an endodermic portion of the alimentary canal which gives
14 18
Fio. 118. Diagram of a Spider, Epeira diademata, showing the arrangement
of the internal organs x about 8. From Warburton.
1. Mouth. 2. Sucking stomach. 3. Ducts of liver. 4. Malpighian
tubules. 5. Stercoral pocket. 6. Anus. 7. Dorsal muscle of
sucking stomach. 8. Caecal prolongation of stomach. 9. Cerebral
ganglion giving off nerves to eyes. 10. Sub-oesophageal ganglionic
mass. 11. Heart with three lateral openings or ostia. 12. Lung-book.
13. Ovary. 14. Acinate and pyriform silk glands. 15. Tubuliform
silk gland. 16. Ampulliform silk gland. 17. Aggregate or dendriform
silk glands. 18. Spinnerets or mammillae. 19. Distal joint of
chelicera. 20. Poison gland. 21. Eye. 22. Pericardium.
23. Vessel bringing blood from lung sac to pericardium. 24. Artery.
off two caeca or blind tubes which project forwards ; from each of
these four smaller pockets arise one projecting into the base of each
walking leg ; behind these comes an intestine which traverses the
abdomen and is further provided with a number of ducts which
collect the products of a very capacious digestive gland or "liver."
The hinder portion of this intestine is swollen up into a pouch
called the stercoral pocket. Following the intestine comes
a short proctodaeum lined by ectoderm which ends in an anus
situated close behind the spinnerets.
Spiders possess two kinds of organs which excrete waste nitro-
genous material : (i) the coxal glands, which are coelomiducts, like
the "nephridia" of Peripatus, i.e., glandular tubes running between
a reduced coelom and the exterior, and (ii) Malpighian tubules, a
XIl] SPIDER 265
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 derhamii, than is the case in E. diademata,
where they are very degenerate and where their functions seem to
have largely passed to the Malpighian tubules. In fact these struc-
tures 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
FIG. 119. Diagrammatic view of Palpal Organ.
1. Tarsus. 2. Bulb. 3. Vesicula seminalis. 4. Opening of vesicul a
seminalis. 6. Conductor. 6. Haematodocha. 7. Alveolus.
The nervous system is concentrated ; there is a bi-lobed ganglion
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
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.
266 ABTHROPODA [CH.
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 Arachnida; 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 palpal organ is a bulb-like
outgrowth of the pedipalp or second appendage of the male.
The base of the bulb, the so-called haematodocha, is elastic and
marked by a spiral groove it is attached to the terminal joint
of the pedipalp in such a way that this joint partially ensheathes
it forming a so-called alveolus round it. The bulb and its base,
the haematodocha, contain a sac, the vesicular seminalis, which
opens by a narrow duct on the apex of the pointed extremity of
the bulb. This needle-like point is protected by a spiral outgrowth
from the bulb coiled round it which is called the conductor.
The male Spider deposits its seminal fluid on a web. It then
inserts into this fluid the point of the bulb, the blood pressure
in the pedipalp is then diminished and the diminished pressure
causes the fluid to be sucked up into the bulb. When the male
copulates the pressure in the haematodocha is increased and this
forces the spermatozoa out into the genital opening of the female.
The eggs are fertilised 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, so small
as to be almost invisible, re-assemble and again 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 II. Phalangida.
The Phalangids (Gk. ^>aXayyiov, a venomous kind of spider) or
Harvestmen are in common talk usually classed with Spiders, but
they differ from the latter in having no waist, that is to say, the
abdomen is not separated from the prosoma by a constriction, and
XII]
PHALANG1DA
267
they breathe entirely by tracheae. They have four long and very
slender pairs of legs, which easily break, and their eyes are some-
times elevated above the surface of the head on a tubercle like a
look-out tower. The abdomen is distinctly divided into segments.
As a rule these creatures are nocturnal and are usually met with
in dark corners or amongst the stalks of hay or grass. Their long
Fro. 120. A Phalangid or Harvestman, Oligolophus spinosus, adult male x 2.
1. Chelicerae. 2. Pedipalps. 3, 4, 5 and 6. First, second, third, and
fourth legs.
legs enable them to steal with a gliding spring upon their prey,
for the most part insects or spiders. They are dull in colour, grey,
brown or blackish, as becomes an animal that loves the dusk. About
twenty-four species have been recorded in Great Britain. Phalangids
die down as winter sets in, but the eggs last through the cold weather
and give rise to a new generation in the spring.
268
ARTHROPODA
Order III. Acarina.
[CH,
The Acarids (Gk. d/cu/ae's, a morsel) or Mites form an enormous
order whose function in life is to a large extent to play the
scavenger, and the terrestrial forms confer the same benefits on the
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,
FIG. 121. Tyroglyphus siro, seen from the ventral side. A. Female.
B. Male. Magnified. From Leuckart and Nitsche.
1. Pedipalpi. 2. Chelicerae. 3, 4, 5, 6. First, second, third and fourth
walking legs. 7. Chitinous thickenings supporting legs. 8. Furrow
round body. 9. Eeproductive opening, flanked by two suckers on each
side. 10. Anus. 11. Suckers at side of anus.
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, when they become attached to their hosts
man, cattle, or even snakes can, by distending their bodies with
the blood they suck, swell out to the size of hazel-nuts.
Anatomically Mites are difficult to characterise. 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
Xll] SCORPIONIDA 269
chelicerae may be clawed or chelate, like a lobster's claws (Fig. 121),
but they often take the form of piercing stylets and the gnathobases
of 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 Red 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 Pkytoptus, 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 , (6) 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 which project freely and are not
enclosed in respiratory chambers. 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
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
segment, 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.
270
ARTHROPOD A
[CH.
FIG. 122. A. Dorsal view of an Indian scorpion, Scorpio swammerdamix%*
B. Ventral view of the samex|.
A. 1. Chelicera. 2. Pedipalp. 3, 4, 5, 6. 3rd to 6th appendages, or
walking legs. 7. Lateral eyes. 8. Median eyes. 9. Soft tissue
at side of body, pleura. 10. The poison sting or telson.
B. 16 as in A. 7. The genital operculum, 8. The pectines. 9, 10,
11, 12. The four right stigmata leading to the four lung-books. 13. The
last segment of the mesosoma. 14. The third segment of metasoma.
15. The telson. In each case the metasoma, which is usually carried bent
forward over the meso- and pro-soma, has been straightened out.
XII]
SCORPION1DA
271
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
B
FIG. 123.
A. Vertical section through a lateral eye of a Scorpion, Euscorpius italicus.
B. Diagram of retinula of a Scorpion's central eye. C, D, E. Trans-
verse section of B taken at different levels. From Lankester and Bourne.
1. Cuticular lens. 2. Epidermis of the general body-surface. 3. Base-
ment membrane. 4. Epidermal cells which contain pigment. 5. Nerve
end-cells with nuclei. 6. Khabdorne. 7. Fibres of optic nerve.
8. Pigment contained in connective tissue cells.
appendages, like those of the pedipalps in Spiders, are all produced
towards the mouth, forming gnathobases which probably help to
hold their food.
The eyes of Scorpions are simpler than those of Spiders and are
amongst the simplest type of eye found amongst Arthropoda. As
Fig. 123 shows, the lateral eyes are simply shallow pits of the
ectoderm. The cells forming one of these pits secrete more cuticle
272 AKTHROPODA [CH.
than the neighbouring ectodermal cells, and this thicker patch of
cuticle forms the lens. Some of the pit-cells secrete visual rods
on their lateral surfaces. Several of these rods coalesce to form a
characteristic rhabdome, or striated spindle characteristic of
Arthropodan eyes. The bases of the cells which secrete the rods are
prolonged into nerve fibres. The central eyes have a layer of clear
cells lying above the visual cells ; this is the crystalline layer and
acts the part of an additional lens. The visual cells of the central
eye are arranged in groups called retinulae, consisting of six or
seven cells which surround a. central rhabdome.
Scorpions usually hide under rocks and stones during the day,
being often very intolerant of heat, but they cfeep out as dusk
comes on and run actively about. The Scorpion is viviparous, the
young being born in a condition resembling their parents.
Order V. Xiphosura.
A very peculiar aquatic Arachnid called Limulus, 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 from 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 (Or. &'iovpo 15
FIG. 184. Longitudinal hori-
zontal section through Glos-
sobalanus. Diagrammatic.
1. Proboscis. 2. Collar. 3. Trunk.
4. Proboscis cavity. 5. Glo-
merulus. 6. Pericardium.
7. Heart. 8. Proboscis pore.
9. Collar cavity. 10. Peri-
haemal cavity. 11. Collar
pore. 12. Dorsal blood-
vessel. 13. Alimentary canal.
14. Branchial sac with ex-
ternal opening. 15. Repro-
ductive organs.
390 CEPHALOCHORDA [CH.
The Cephalodiscida exhibit the same three regions of the body
as the Balanoglossida, but these are very differently developed.
The proboscis becomes a flat glandular shield bent down over the
mouth. It secretes the material out of which the house or tube
is constructed. The collar region is prolonged into hollow arms
which are beset by rows of ciliated tentacles which waft microscopic
swimming organisms into the mouth. The central nervous system
remains as a plate of exposed ectoderm. The trunk is short and
rounded and the anus is shifted on to the dorsal surface. There
is never more than a single pair of gill-pores, and in minute forms
these may be absent. From the ventral surface springs a stalk
from which buds are produced which grow up into new persons.
Prof. Gilchrist has shown that the individuals of a Cephalodiscid
colony can emerge from their tubes and creep out. They fix them-
selves to the substratum by the ventral surface of their praeoral lobes
or proboscides exactly as the larva of an Asteroid does. (See p. 366.)
Cephalodiscus with twelve arms and one pair of gill-pores is fairly
abundant in the Antarctic and Southern Atlantic Oceans.
Rhabdopleura, with two arms and no gill-pores, which is found
fairly abundantly in moderately deep water in the North Sea, was
formerly described as a Polyzoon. The absence of gill-pores in
Rhabdopleura is no doubt a secondary modification due to the very
small size of the individuals, for we find that as the size of animals
of the same build is diminished, respiratory organs tend to disappear.
One point of interest attaching to the Hemichorda is that
they may commence life as free-swimming larvae, resembling the
larvae of the Echinodermata, and suggesting the thought that
perhaps two such different groups as the Vertebrata and Echi-
nodermata may have descended by different paths from the same
simple free-swimming ancestors.
In dealing with the larvae of Echinodermata it was pointed out
that the middle section of the coelom called the hydrocoele, which
develops into the water-vascular system of the adult, has been
compared to the collar coelom of Hemichorda. This comparison
is supported by the condition of the collar region in Cephalodiscida,
where, as we have seen, it is produced into outgrowths very like the
radial canals of Echinodermata and beset with tentacles which may
be compared to tube feet.
Sub-phylum II. CEPHALOCHORDA.
Leaving the Hemichorda we next come to some small fish-like
animals, the Cephalochorda, which were formerly all included
under the name Amphioxus, and indeed there is no very strong
reason for breaking up this old genus. The name Amphioxus (a//,i
XVIll]
SHAPE JN EELATION TO HABITS
391
at both ends ; ovs, sharp) refers to the shape of the body, which
is long, flattened and pointed at both ends (Fig. 185). It is remark-
FIG. 185. Amphioxus lanceolatus from the left side, about twice natural size.
After Lankester. The gonadic pouches are seen by transparency through
the body- wall ; the atrium is expanded so that its floor projects below the
metapleural fold ; the fin-rays of the ventral fin are indicated between the
atrial pore and anus. The dark spot at the base of the fifty-second
myotome represents the anus.
able that we here meet for the
first time with a shape very
common among Vertebrates,
but very uncommon elsewhere
in the animal kingdom, viz. a
laterally compressed form with
narrow ventral and dorsal
regions and deep sides. It
is common to find animals
with broad backs and bellies
and narrow sides, but rare
except amongst Vertebrates to
find the reverse condition. In
consequence of this peculiar
shape AmpMoxus falls on its
side when it ceases moving.
It burrows in the sand, lying
with its mouth just protrud-
ing, and as its lips are fringed
with ciliated rods (Fig. 186)
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 swims
about, returning instantly to
the sand if alarmed. It can
burrow with either the head
or tail.
A. Velum of Amphioxus seen from the
inside of the pharynx. After Lan-
kester.
v.sp, sphincter muscle of velum.
v.t. velar tentacles lying across the
oral opening.
B. Oral cartilages of Amphioxus. After
J. Miiller. The basal pieces lie end
to end in the margin of the oral
hood, and each basal piece sends up
an axial process into the correspond-
ing oral cirrus.
392
CEPHALOCHORDA
[CH.
The notochord is a smooth cylindrical rod lying above the
gut and running from end to end of the animal. It consists of
cells, the greater part of the bodies of which are changed into a
gelatinous substance, and which are surrounded by an exceedingly
firm membrane termed the chordal sheath. In the embryo
the notochord first appears as a groove in the dorsal wall of the
gut, so that we may say that the notochord of the Hemichorda
retains a form which is passed through in development by that of
Amphioxus.
In the very young embryo also an indication is seen of the
division of the body into the same three regions as we found in the
Hemichorda. Just as in the embryo of Balanoglossida so here, the
embryonic gut gives rise to five outgrowths from which the coelom of
FIG. 187. Diagrammatic longitudinal section of an embryo of Amphioxus.
1. Neuropore anterior opening of the neural canal. 2. Neural canal.
3. Neurenteric canal. 4. Coelomic groove. 5. Somite divided off
from coelomic groove. 6. Collar cavity. 7. Head cavity. 8. Ali-
mentary canal.
the adult is derived. These outgrowths are (1) a median anterior
bilobed pouch, corresponding to the proboscis cavity of Balanoglos-
sida; this divides at once into two, giving rise to the so-called head
cavities; (2) an anterior pair of pouches, the collar cavities,
corresponding to the similarly named sections of the coelom of
Balanoglossida ; 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 Balanoglossida (Fig. 187). 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, and here becomes
fused with the lower divisions of the trunk cavities, (v. infra.)
XVIIl]
DIVISIONS OF COELOM
393
The upper and anterior portion of the collar cavity becomes
separated from the rest : its inner walls thicken and develop into
a powerful longitudinal muscle which forms the first myotome
(Gr. /xv?, muscle ; ro/xos, a division).
The "trunk coelomic cavity breaks up from the beginning into a
series of pouches called somites, each of which subsequently divides
into an upper and an under part. The inner walls of the upper
parts undergo a similar change to that experienced by the corre-
sponding part of the collar cavity, forming a series of myotomes.
The name myotome is given to each 'of the metamerically arranged
bundles of muscle-fibres. Each myotome is separated from the next
by a connective-tissue partition. In Amphioxus the myotomes of
the right side alternate with those of the left, so that the centre of
a myotome on one side is opposite the connective-tissue partition
on the other. Each is V-shaped, and they are arranged so <^{.
o!f
ci
end tb m
FIG. 188.
Anterior region of young Amphioxus from left side,
the renal tubules inserted after Boveri.
After Willey ;
at. Atrial cavity, ci. Oral cirri, ch. Notochord. d.f. Dorsal fin-cli ambers.
e. Eye-spot. end. Endostyle. hep. Outgrowing liver ; the index
line passes through one of J. Miiller's "renal papillae." met. Metapleural
fold. nph. Nephridia. nt. Spinal cord. olf. Olfactory pit.
ph.b. Peripharyngeal ciliated band. tb. Tongue-bars. vel. Velum.
Hence in a transverse section several myotomes are seen on each
side of the body. Thus we have two great series of longitudinal
muscles broken up into myotomes, one on each side of the animal,
by the alternate contraction of which powerful side-strokes of the
flat body propel the animal forwards. The elasticity of the notochord
acts like a fly-wheel in storing the force during the latter part of
each stroke and reinforcing each stroke at its commencement.
The cavity of the upper division of the somite persists throughout
life, and is known as the myocoel and the fold separating it from
394
CEPHALOCHOEDA
[CH.
the cavity of the lower division is termed the intercoelic mem-
brane (i.m. Figs. 190 and 196).
mp
FIG. 189. Diagrammatic transverse section through pharyngeal region of a
female Amphioxus. After Lankester and Boveri, from E. Hertwig.
at. Atrial cavity, c. Dorsal coelom, separated from atrial cavity by the double-
layered membrane known as the lig amentum denticulatum. ch. Noto-
chord. d.n. Sensory nerve. e. Endostyle, below which is the
endostylar coelom containing the ventral aorta. /. Fin-ray of dorsal
fin. g. Gonadic pouch containing ova. h.v. Hepatic vein lying in
the narrow coelomic space which surrounds I, the liver or hepatic coecum.
La. Left aorta separated from the right aorta by the hyperpharyngeal
(epibranchial) groove. ly. Lymph-space. mp. Metapleural fold,
containing a lymph-space, my. Longitudinal muscles of myotomes ; over
against the dorsal coelom these muscles are arranged verticairy, and form the
rectus abdominis of Schneider. n.t. Spinal cord. p. Pharynx.
r. Nephridium. t.m. Transverse or subatrial muscles. v.n. Motor
spinal nerve, the fibres of which have the appearance of passing directly
into the muscle-fibres. N.B. The connective tissue (cutis, notochordal
sheath, etc.) and the coelomic epithelium are indicated by the black lines.
XVIIl]
DIVISIONS OF THE COELOM
395
The lower portions of the somites fuse with one another and
form a continuous body cavity round the hinder part of the
alimentary canal which is called the splanchnocoel (
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 conus 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
the conus contracts become filled with blood and swollen out so
as to meet one another and prevent the reflux of blood into the
ventricle.
432
INTKODUCTION TO CRANIATA
[CH.
The development of the liver has exercised a profound influence
on the afferent part of the blood system corresponding to the
hinder part of the subintestinal vein of Amphioxus. The vast
External Carotfd
Afferent
branchial 5
FIG. 213. Diagram of the ventral and dorsal aortas and their branches in
Scy Ilium x about 1.
XIX] CIRCULATORY SYSTEM 433
mass of liver-tubes projecting into this vein has broken it up into a
network of capillary channels called the hepatic portal system.
In front of this, where the vein 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 composite 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 Cuvieri. 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 part
of the vein in front of the kidney retains the name posterior cardinal :
the hinder part is called the renal-portal vein. A vessel running
along the inner side of each kidney and collecting the blood which
percolates through it from the renal-portal .vein is termed the sub-
cardinal vein. The vessels of the renal-portal system apparently
do not give off capillaries to the kidney tubules ; these latter receive
all their blood supply from branches of the dorsal aorta.
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 the earthworm Lumbricus, in
which it is found diffused in the blood fluid. The great character-
istic 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 combina-
tion, though with the sodium of the blood instead of with the
434 INTRODUCTION TO CRANIATA [CH.
haemoglobin. The carbon dioxide is set free in the respiratory
organs.
On page 202 it was pointed out that both blood and connective
tissue have been derived from a jelly-like secretion such as is found
in Coelenterata. This in the embryo coelomate animal fills up the
interstices between ectoderm, endoderm and coelomic sacs, these
interstices being collectively termed the primary body-cavity or
haemacoel. It was also pointed out there, that whereas in that
part of the jelly which was converted into connective tissue a large
number of fibres were developed, in the portion destined to form
blood, on the contrary, no fibres appeared and the jelly remained
fluid, and in consequence the amoebocytes which had wandered into
it from the neighbouring epithelia were able freely to move about.
In Annelida, Arthropoda and Mollusca certain of the blood-spaces
acquire muscular walls derived from the adjacent coelomic sacs,
and thereby attain contractility which may be specially localised in
a dilatation called the heart. The spaces with muscular walls are
the arteries. In Craniata a further differentiation has taken place :
we find not only a definite heart and arteries leading away from it,
but also equally definite veins leading into it as described above,
and arteries and veins are connected with one another by narrow
channels called capillaries with well-marked walls. Heart,
arteries, 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-
cytes. The capillaries possess no other wall, but arteries and veins
have outside this a wall of elastic and fibrous connective tissue in
which is embedded a zone of circular muscle-fibres. These structures
are all derived from the adjacent coelomic sacs." The muscles of
blood-vessels do not contract rhythmically and spontaneously like
those of the heart, but are in a state of continued contraction called
tone. This tone is under the control of the nervous system through
the medium of special "vasomotor" fibres, and thus the supply of
blood to an organ can be varied according to its need.
In Craniata however, outside the definite arteries, veins and
capillaries, there exists a large portion of the haemocoel in the
form of irregular channels and interstices, in many cases without
definite walls, an endothelium being found only in the larger trunks.
This system of spaces is known as the lymphatic system. It
contains a clear fluid in which amoebocytes float, but no haemo-
.globin-coiLtaining cells, and at one or several points the main
XIX]
LYMPHATIC SYSTEM
435
trunks of the system open into the large veins. The finer branches
of the system ramify amongst all the organs of the body. There
is no circulatory current in the lymph canals except in those
belonging to the viscera, but
there are valves, arranged so
that when the lymph vessels
are squeezed by the increase
in diameter . of neighbouring
muscles when these contract,
fluid can pass forwards in one
direction but not backwards.
It will be seen that in
Craniata, unlike Arthropoda
and Mollusca, the blood, being
everywhere confined to vessels
with definite walls, does not
directly bathe the tissues of
any organ ; but that materials
must first diffuse through the
walls of the blood-vessels into
the lymph-spaces before they
can reach the tissue. One
explanation of the separation
FIG. 214. Diagram of the venous
system of Mustelus antarcticus.
From T. J. Parker.
1. Orbital sinus. 2. Hyoidean
vein. 3. Ductus Cuvieri.
4. Anterior cardinal veiu. 5.
Jugular vein. 6. Conus arteri-
osus. 7. Ventricle. 8. Atrium.
9. Sinus venosus. 10. Hepatic
vein. 11. Liver. 12. Hepatic
vein. 13. Hepatic portal vein.
14. Left cardinal vein. 15. Bra-
chial vein. 16. Subclavian
vein. 17. Gonad. 18. Pos-
terior cardinal vein. 19. Sper-
matic vein. 20. Lateral vein.
21. Eenal portaK veins from
caudal vein to kidney. 22.
Eight posterior cardinal vein.
23. Alimentary canal. 24. Vein
connecting orbital sinuses. 25.
Subintestinal vein. 26. Kidney.
27. Pelvic vein. 28. Cloacal
vein. 29. Femoral vein. 30.
Caudal vein.
17 -Y\ t-
30
436
INTRODUCTION TO CRANIATA
[CH.
of the lymph-system from the blood-system is that the haemoglobin
is not diffused in the fluid of the blood, but is carried in cells
which have no power of movement in themselves. Did these cells
enter the lymph-system they would speedily block its finer channels.
The supply of amoebocytes to both blood and lymph is provided
for by widely distributed actively growing nodules of cells which
bud off amoebocytes into the adjacent lymph-channels. These
packets of cells are called lymphatic glands : the largest collection
FIG. 215. Dorsal view of head of Scyllium caniculaxl. The right orbit has
been exposed so as to show the muscles that move the eye and the second
and fourth nerves.
1. Lens of the eye. 2. Superior rectus muscle of the eyeball. 3. Ex-
ternal (or posterior) rectus muscle. 4. Inferior rectus muscle. 5. In-
ternal (or anterior) rectus muscle. 6. Inferior oblique muscle.
7. Superior oblique muscle ; the slender nerve entering this muscle is the
fourth cranial. 8. Second cranial or optic nerve, the nerve of sight.
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.
The muscles of the Craniate like those of 'the Cephalochorda
are developed from the inner walls of a series of dorsal
Coelom.
coelomic pockets, in a word, from myotomes. Unlike
that of the Cephalochorda the trunk coelom does not become at
first completely divided into separate sacs, the ventral portions
of which fuse later. In the Craniate this stage is skipped in
XIX] MUSCULAR SYSTEM 43*7
development, and the coelom appears from the first as a pair of
elongated sacs undivided below, but segmented above. After the
complete separation 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. 214 and 215), but
which in the higher Craniata is a lymph space. 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 corner 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 cavity and collar cavities of the Hemichorda are
represented in the Craniata by two pairs of cavities found in the
embryo, in advance of all the myotomes, termed the head- cavities.
The anterior of these, termed thepre-mandibular, is joined to its
fellow by a very 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, joining the splanchnocoel behind and curving up
over the eye on each side. From the wall of the dorsal 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 arise ; these in Craniata are longi-
tudinal as well as circular, and the muscles in the walls of the blood-
vessels also arise from the coelomic wall. From the myotomes are
438
INTRODUCTION TO CRAN1ATA
[CH.
2 1
FIG. 216. Illustrating the development of
systems in Craniata.
A.
The pronephros in functional activity, the mesonephric tubules being
formed. B. The pronepbros degenerating, the mesonephros in func-
tional activity. C. The mesonephros connected with the genital
organs by vasa efferentia in its anterior portion, the pelvis of the meta-
nephros and the metanephric tubules being formed. D, E, represent the
condition which is found in the higher Craniata. D. The condition in
the female. The mesonephros connected with the ovary by vasa efferentia
and in process of degeneration disconnected from the mesonephric duct.
The metanephros fully formed and also the oviduct. E. The
condition in the male. The capsules of the mesonephros have disappeared.
The metanephros is fully developed, the oviduct is vestigial. F. The
condition in the embryo Elasmobranch. The mesonephros is connected by
vasa efferentia to the genital organ. The oviduct is arising by a splitting
of the longitudinal duct. G. The condition in the female Elasmobranch,
the hinder portion of the mesonephric duct alone persists and receives the
metanephric tubules. The oviduct is separated from the longitudinal
kidney duct. H. The condition in the male Elasmobranch. The
mesonephros is connected with the testes, the oviduct is vestigial.
XIX] EXCRETORY SYSTEM 439
1. The pronephrio chamber produced by the fusion of several nephrotomes.
I 1 . The pronephric tubules. 2. The Malpighian capsules of the
meson^phros. 2 1 . The primary mesoaephric tubules. 2 2 . The
secondary mesonephric tubules. 3. The peritoneal funnels of the
mesonephros. 4. The vasa efferentia and the longitudinal duct which
unites them. 5. The Malpighian capsules of the metanephros.
5 1 . The ureter. 6. The archinephric duct. 7. Young genital
organ. 8. Ovary. 9. Testes. 10. Oviduct. 11. Vestigial
oviduct iu male. 12. Rectum.
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 found in the case of Amphioxus, but in the higher
forms where the movements are complicated by the development of
limbs, these muscles are divided into numerous bundles with a very
.complex arrangement. All the muscles derived from the myo tomes
are composed of striated fibres. Most of those governing the move-
'm'ents of the alimentary canal and. blood-vessels are composed of
smooth fibres, but to this statement the muscles of the heart form
an exception. These latter, the cardiac muscles as they are
named, are cross-striated, but they are nevertheless very different
from the cross-striated muscles derived from the myotomes. The
cardiac muscles are short, thick fibres clearly divided by transverse
septa into the cells to which they owe their origin. Each cell has
a single nucleus. Neighbouring fibres are connected together by
cytoplasmic bridges so that they contract together. Muscles derived
from the myotomes consist of long fibres, each the product of a
single cell but each containing numerous nuclei. These nuclei are
scattered throughout the substance of the fibre, each embedded in
a little islet of unmodified cytoplasm.
The excretory and reproductive organs are closely related
in development, and by recent research their relation
enital to those of the Cephalochorda 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.
The section of the body-cavity into which it opens is termed the
n e p h r o t o m e. The nephrotome is really a portion of the segmented
division of the body-cavity lying immediately beneath the myotome
into which at first it open's ; it is also connected with the splanch-
nocoel below.
The kidney tube is in fact an outgrowth of the nephrotome ;
the longitudinal duct, which is termed the archinephric duct seems
440 INTRODUCTION TO CRANIATA [CH.
to be made up by the fusion of the outer portion of successive kidney
tubules. The kidney in Vertebrates is usually said to be divided into
an anterior, a middle and a posterior region termed pronephros,
mesonephros, and metanephros respectively, but these three
portions are of very different values. The pronephros consists of
two or three, rarely five or six tubules, which are outgrowths from
nephrotomes which lie immediately below the region of the gills for
which reason the pronephros is sometimes termed the head-kidney.
In each nephrotome there is formed a protrusion from its inner
wall which abuts on the dorsal aorta. The protrusion takes
the form of a plug containing a plexus of blood-vessels projecting
into the cavity of the nephrotome. From this cavity the blood is
only separated by a thin layer of epithelium, so that water can
pass by diffusion from the blood into the nephrotome. This plug
is termed the glomerulus. These anterior nephrotomes fuse with
one another so as to form one cavity on each side and this cavity,
the so-called " pronephric chamber," sometimes becomes completely
shut off from the splanchnocoel (as in Fish), sometimes (as in
Amphibia) its opening into the splanchnocoel enlarges so that it
ceases to be distinguishable from the latter space. The pronephros
only persists during the early larval condition of the animal. As
the animal grows it entirely disappears. It is to be looked on as
a precocious development of the most anterior tubules of the kidney
to serve the needs of larval life.
The middle portion of the kidney is called the meson ephros.
In this region the nephrotomes remain separated from one another
and constitute what are known as the Malpighian capsules of
the kidney, and into each of these capsules a glomerular plug pro-
jects. In the lower Craniata (Elasmobranch, Fishes, Amphibia) the
nephrotomes retain their connection with the splanchnocoel by
long necks which become ciliated and are known as ciliated
peritoneal funnels, but in all the higher Craniata the nephro-
tomes become definitely shut off from the splanchnocoel. The
nephrotome or Malpighian capsule can bud off a similar smaller
capsule which in turn produces a kidney tubule, the so-called
secondary tubule. The tubule produced by the original nephro-
tome is called the primary tubule. The secondary tubule opens
into the longitudinal duct which becomes enlarged so as to receive
primary and secondary tubules. The longitudinal duct thus be-
comes somewhat moniliform, i.e. with alternate swollen and
narrow places (C, Fig. 216). In the hinder region of the kidney or
xix]
EXCRETORY SYSTEM
441
metanephros there is essentially the same structure as in the
mesonephros, but not only primary and 'secondary but tertiary
tubules are produced, and all these tubules open into a single
enlargement of the archinephric duct, which is termed the pelvis
of the kidney. This pelvis tends to be separated by a constric-
tion from the rest of the archinephric duct, and the neck of the
communication between the two constitutes the ureter, and as the
animal grows in length the ureter is drawn out into a long tube.
(E, Fig. 216).
FIG. 217. Diagrammatic transverse section of an Elasmobranch embryo in
order to show the development of renal and genital organs.
1. Nerve-cord. 2. Notocbord. 3. Myotome. 4. Dorsal sclerotome.
5. Ventral sclerotome. 6. Nephrotome. 7. Splancbnocoel.
8. Mesonephric tubule. 9. Avcbinephric duct. * 10. Eudiment
of genital organ. 11. Vas efferens. 12. Dorsal aorta.
33. Alimentary canal.
The mesonephros, or rather some of its primary tubules, enter
into close connection with the genital organ. The genital cells in
Craniata at their first appearance seem to consist of groups of cells,
segmentally arranged, and these cells originate from the inner wall
of the splanchnocoel just below the point where it communicates
with the nephrotome. As they increase in number and bulk the
segmental arrangement is obliterated, but from each originally
separate mass of cells strings of cells originate which grow inwards
into the connective tissue above the splanchnocoel and constitute
the genital tubes. These genital tubes meet and connect up with
442 INTRODUCTION TO CRANIATA [CII.
a series of tubular outgrowths from some of the primary nephro-
tomes of the mesonephros, which constitute what are called the
vasa efferentia.
In the male the genital tubes persist throughout life and form
the seminal tubes which make up the testes, and the ripe
spermatozoa find their way out through the vasa efferentia, the
mesonephric tubules and the archinephric duct, and this latter thus
constitutes a vas deferens. In the female the vasa efferentia
disappear, the genital tubes termed egg-tubes remain solid and
their terminal cells enlarge and form ova, which are thus left
isolated in the centre of a mass of connective tissue called the
ovarian stroma. At the period of ripeness these eggs swell so
much as to burst through this stroma into the splanclmocoel,
whence they escape by pores situated near the anus (Eels and
Lampreys) or by tubes, the oviducts opening in the same position,
which seem to have been developed from grooves in the roof of the
splanclmocoel leading to the pores. The oviducts of Elasrno-
branchii are peculiar in that they seem to be formed by a splitting of
the archinephric duct (F, G, H, Fig. 216).
The mesonephros is thus distinguished from the metanephros by
being the sexual region of the kidney. In most cases it persists
throughout life only in the male, vestiges only being found in the
female, but in some primitive types of fish, such as the Sturgeon
and in Amphibia, mesonephros and metanephros are not clearly
differentiated from one another, and a fully developed metanephros
with pelvis and ureter is only found in Reptiles, Birds and Mammals.
If the above description has been followed it will be evident
that the nephrotomes of Craniata correspond closely in position and
origin to the gonadic pouches or gonocoeles of Amphioxus and have
nothing to do with the excretory organs of that animal.
They are in fact coelomiducts, and it appears probable that
they originally served as outlets for the genital products and
correspond to the pores which are formed in the walls of the
.gonocoeles of Amphioxus at the period of sexual maturity. They
still function as outlets for the spermatozoa in most Craniata,
and the reason wliy they have ceased to serve as passages for the
eggs is probably to be found in the circumstance that the eggs of
all Craniata have become swollen in size owing to the accumulation
of yolk so that they are no longer able to pass through such narrow
passages as the kidney tubules afford, and hence have to find their
way out in another manner.
XIX] CYCLOSTOMATA 443
The excretory function of the kidney tubules on this view would
not be their original one; it would be a secondary function which
had gradually supplemented the primary one. It must be remem-
bered that the function of the whole coelomic wall is excretory, and
any convenient opening which allows its contents to escape may
develop into an excretory tube. This change of function has almost
certainly occurred in Polychaeta, Annelida and in Mollusca, as well
as in Craniata. Since the archinephric duct opens into the terminal
portion of the alimentary canal behind, the faeces (as the indigest-
ible remnants of the food are termed), the true excreta and the
genital cells are all expelled through the same opening, which on
this account has received the name cloaca which the Romans
bestowed on their common sewer.
DIVISION I. CYCLOSTOMATA.
The Craniata are divided into two main groups, namely, the
Cyclostomata and the Gnathostomata. The former division,
distinguished by the absence of true visceral arches and of jaws,
includes at the present day only a few, probably degenerate, worm-
like animals, with short tails like Amphioxus, and with naked
skins. The name Cyclostomata means Round-mouthed (Gk. KVK\O?,
a circle ; ord/xa, mouth), and alludes to the circumstance that the
edges of the mouth are stiffened by a ring-shaped
cartilage, the annular cartilage, so that the mouth
cannot be closed (2, Fig. 220). There is a piston-shaped tongue
supported by a lingual cartilage, and the whole is protruded by
a muscle attached to the annular cartilage in the lips (Fig. 219).
Both the tip of the tongue and the walls of the stomodaeum are
beset with horny teeth, developed from the agglutinated cells of
the skin. The expansion of the stomodaeum 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, usually
a fish, in which case the rasp-like tongue works a hole in the flesh
of the prey. The stomodaeum is greatly elongated and is supported
in its roof by several broad cartilages, the so-called labial carti-
lages ; in consequence the eyes and gill-slits appear to be pushed
very far back.
The condition of the sense-organs is one of the most marked
characteristics of the Cyclostomata. The nose is represented by a
single sac placed far back in consequence of the elongation of the
444 CYCLOSTOMATA [CH.
stomodaeum, as above explained. This single sac is drawn out
into a long tube passing beneath the brain, and in one order,
the Myxinidae or Hag-fishes, this opens into the roof of the
stomodaeum. The tube-like prolongation is really the pituitary
body, which in the embryo develops close to the nasal sac. The
groove connecting the two organs becomes closed so as to form a
canal, and then by the great development of the roof of the suc-
torial mouth the external openings of the two organs are widely
removed from one another, although internally their cavities com-
municate with one another.
FIG. 218. The Musk Lamprey, Petromyzon wilderi, in the act of spawning.
From Bashford Dean and Sumner.
The eye develops no proper cornea or aqueous humour, the
lens remaining in connection with the skin. The ear is represented
either by two semicircular canals and a vestibule (or sacculus)
in the Lamprey, or by a single circular membranous tube in the
Hag-fish which corresponds to the vestibule and one semicircular
canal.
The gill-slits, usually seven in number, have the form of regular
gill-sacs, recalling those of the Hemichorda, only without the
xix]
GILL-SACS
445
tongue-bars. The external opening is circular; the connection
with the gullet, on the other hand, is a vertical slit (Fig. 219).
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The whole set of sacs is supported on a framework of cartilage
which in its complete form as seen in the Lampreys, consists of
446
CYCLOSTOMATA
[CH.
longitudinal dorsal and ventral bars, and connecting cross-pieces pass-
ing between the sacs which give off branches encircling their outer
openings (Fig. 220). The whole of the branchial basket, as it is
called, is a development of the dermis and has probably nothing to
do with the visceral arches of the Craniata, as will be shown
later. Since however bars corresponding to true visceral arches are
found in Hemichorda and Cephalochorda, it is almost certain that
their absence in Cyclostomata is a secondary phenomenon, and
indeed, as we shall see immediately, remnants of true visceral
arches are possibly represented by certain cartilages connected with
the skull. The reason for their disappearance is a difference in the
FIG. 220. A, dorsal, B, lateral, and C, ventral view of the skull of Petromyzon
marinus x 1 (after Parker).
1. Horny teeth. 2. Annular cartilage. 3. Anterior labial cartilage.
4. Posterior labial cartilage. 5. Nasal capsule. 6. Auditory capsule.
7. Dorsal portion of trabeculae. 8. Lateral distal labial cartilage.
9. 'Lingual cartilage. 10. Branchial basket. 11. Cartilaginous cup
supporting pericardium. 12. Sheath of notochord. 13. Anterior
neural arches fused together.
method of expanding the branchial sacs from that which obtains in
all other Craniata. For whereas in these latter the branchial sacs
are expanded by the spreading out of the visceral arches like the
ribs of an umbrella and are contracted when these arches fall
together, in Cyclostomata each sac has its own radiating and
circular muscles which enable it to contract and expand like a
heart, and the rhythm can be reversed since water can and does
enter as well as leave the gill-slits by the external pores when the
animal has its mouth applied' to a victim.
The commencement of the true alimentary canal is marked, as
in Amphioxus, by a velum. What corresponds to the byper-
pharyngeal groove in that animal is in many species of Cyclostomata
XIX] SKELETON 447
completely constricted off from the remainder of the gullet 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
in these cases 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,
which form only a slender arch over the hinder part of the brain,
but develop also a low side wall throughout their extent with which
the simple auditory capsule is fused. There is a loop of cartilage
attached to each parachordal termed the subocular arch and
a curved bar of cartilage behind this which is attached above to the
skull and passes down along the pharynx. In Myxiuoidea the latter
encircles the pharynx and unites with its fellow in the mid-ventral
line and joins the cartilage supporting the tongue. This second
arch is termed the hyoid, and with some plausibility both it and
the subocular bar are regarded as degenerate remains of the first
two visceral arches of other Craniata. The nasal capsule is re-
presented 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 which represent the neural arches
which protect the spinal cord ; the caudal fin has, in addition to
these, rays situated below which are to be regarded as haemal arches.
A caudal fin of this description, which the notochord divides into
two equal lobes, is called diphy cereal.
Besides the neural ar-ches (13, Fig. 220) 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.
448 CYCLOSTOMATA [CH.
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.
219). No connection of the testis tubules with the kidney tubules
exists, nor is there any trace of an oviduct, since both ova and
spermatozoa are freely shed into the body-cavity and escape by two
abdominal pores or simple openings in the body-wall placed
ventrally to the openings of the kidneys. Inasmuch 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
state that no cloaca has yet been developed.
Living Cyclostomata, represented by a single class which may
be called Marsipobranchii (Gr. uapo-tTro?, a pouch),
Classification. .. . .. .
are divided into two orders : (i) PETROMYZONTIDA,
(ii) MYXINOIDEA.
(i) In the first order, familiarly known as the Lampreys, the
pituitary body appears as a Wind process from the nasal sac : each
gill-sac opens directly to the exterior, jind the hyperpharyngeal
groove is separated from the rest of the alimentary canal as a
distinct tube, the so-called oesophagus.
The Lampreys (Petromyzoii) are conspicuous in the early spring,
when they ascend small brooks to spawn. Several species 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 horny teeth covering the tongue. One species,
Petromyzon marinus, 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.
The eggs of Lampreys develop into a most interesting larval form
which stands in many respects nearer to the other Craniates
than does the adult and supplies an intermediate stage between
Amphioxus and an ordinary Craniate. This larva is called the
Ammocoetes, and it's mode of life resembles on the whole that of
Amphioxus. Like that animal the Ammocoetes lives on what is
brought by the currents of water, produced by the cilia inside the
velum. The thyroid gland, which, as we have seen, represents the
endostyle, remains open, and still performs its primitive function of
secreting a cord of mucus, which is carried up dorsally by a ciliated
groove, the peripharyngeal band, situated just behind the velum.
The hyperpharyngeal groove is represented by a dorsal strip of
ciliated cells, the current produced by which sweeps the mucus
XIX] CLASSIFICATION 449
backward into the alimentary canal just as it does in Amphi-
oxus.
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
Urochorda and in Amphioxus. The lateral eyes are exceedingly
rudimentary, but there is a large pineal eye, and the nasal sac
has a median septum.
(ii) The MYXINOIDEA -are characterised by the persistent connec-
tion of the pituitary body with the stomodaeum, so that there is a
tube leading from the nasal sac to the mouth. There are eight ten-
tacles 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
Myxinoidea are the animals known as Hag-fish. They adhere to fish
on whose flesh they feed, but, unlike 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 rudimentary
condition, whilst the gill openings are pushed very far back.
The Myxinoidea include two genera, Bdelkstoma and Myxine.
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 with its
breathing. The branchial basket is vestigial in this genus. The
portal vein is rhythmically contractile, and thus constitutes an
accessory heart for the purpose of forcing venous blood through the
capillaries of the liver. 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, arid is characterised by the development of definite
visceral arches, jaws and paired limbs. The visceral arches
s. & M. 29
450 GNATHOSTOMATA [CH.
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 under jaws 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.
The Gnathostomata are divided into five classes which can be
grouped into two sub-divisions. In the first sub-division, termed
Anamnia, which includes Pisces and Amphibia, the whole of the
egg is converted into the body of the embryo, and though a ventral
protrusion of the hind gut termed the allantois may be formed,
this does not function as a special embryonic organ. In the second
sub-division, termed Amniota, a portion of the egg is converted
into a hood termed an amnion, which envelops the body of the
embryo and is cast off at birth, and the allantois is enlarged during
embryonic life and functions as respiratory or nutritive organ. The
greater part of the allantois is cast off with the amnion at birth,
and only the stump persists in the adult and functions as urinary
bladder. In the first three of these the temperature of the body
varies with that of the surrounding medium.
SUB-DIVISION I. ANAMNIA.
Class I. PISCES.
Gnathostomata with fins supported by fin-rays and breathing
chiefly by gills.
Class II. AMPHIBIA.
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 allantois is formed which
functions as a urinary bladder in the adult, but has no function in
the embryo. The skin is soft and moist.
SUB-DIVISION II. AMNIOTA.
Class III. REPTILIA.
Gnathostomata with pentadactyle limbs. The young are born
similar to the adult. The allantois is greatly enlarged in the
XIX] CLASSIFICATION 451
embryo and has the function of a respiratory organ. The skin
develops horny scales.
Clas-s 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.
292
CHAPTER XX
SUB-PHYLUM IV. CRANIATA
DIVISION IT. GNATHOSTOMATA.
SUB-DIVISION I. ANAMNIA
Class I. PISCES
THE class Pisces, or true Fishes, are not, as many would imagine,
characterised by their gills (since some Amphibia
retain these throughout life), but by their fins. In
addition to the vertical flap of skin with which we have become
acquainted in the case of the Cephalochorda and the Cyclostomata,
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. 224 and 22.5). 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. It is
possible even probable that the wall of the atrial cavity of Amphi-
oxus is homologous with this lateral fold : if this be so we may
argue that the absence of lateral fins in the Cyclostomata is a
result of secondary degeneration since Amphioxus represents a
much more primitive level in the evolution of the Vertebrate stem
than Cyclostomata.
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 representatives of the paired fins limbs in which the
plan of the human arm and leg can be at once recognised. The
blade-like type of fin is known as the ichthyopterygium
CH. XX] MAIN DIVISIONS 453
a fish; TTTcpvyiov, a little wing), the other type of limb as the
cheiropterygium (x et 'p> the hand). Pisces therefore are defined
by the possession of ichthyopterygia.
The median and the paired fins are stretched on a skeleton with
a two-fold origin, (i) a median series of cartilaginous or bony rods or
pterygiophores which support the basal part of the fins, and
(ii) a double series of horny fibres or bony dermal fin-rays which
support the distal part of the fins. The horny fibres are termed
ceratotrichia, the bony dermal rays lepidotrichia; both are
from the modification of the superficial layer of the dermis which
immediately underlies each side of the fin-blade.
Taking a broad view of the various types of fish living at the
present time, we find that the old common-sense division of the
group into Cartilaginous fish or Chondrichthyes and Bony Fish
or Osteichthyes is endorsed by the latest scientific writers on
the subject. Cartilaginous fish have no true bone ; calcareous
matter may be, and often is deposited in the cartilage which is then
said to be calcified, but the characteristic structure of cartilage
persists. They are further characterised by possessing a peculiar
form of scale termed the placoid which is a hollow .tooth-like
structure. They never possess an outgrowth from the alimentary
canal containing air termed an air-bladder, the nostril or opening
to the nasal sac is undivided and the eggs are few and large and
are fertilised internally and have already undergone a considerable
portion of their development when laid. In many, perhaps in most,
cases the egg shell is absorbed in the oviduct and the embryo
derives nourishment from the secretions of the oviduct and grows to
a relatively enormous size before being bom. To give an instance :
the Canadian Spiny Dog-fish Squalus acanthias attains a length of
three or four feet and its ripe embryo may be eighteen inches in
length.
In Osteichthyes on the contrary the bone is always present and
the cartilage of the skull is always replaced by it to a greater or
less extent : an air bladder is developed as an outgrowth from the
alimentary canal behind the gill region, the opening to the nasal
sac is divided into two by a bridge of bone : placoid scales may be
present and indeed usually are present in the region of the stomo-
daeum but they are underlain and connected together by calcifications
of the dermis which constitute the real effective scales of the
Osteichthyes. The eggs are always small and in the vast majority
of cases are fertilised externally and pass through a long larval
454 CHONDKICHTHYES [CH.
development before attaining the adult condition. Even in the few
aberrant cases where fertilisation is internal and where the young
are produced viviparously these young are nevertheless very small
compared to the size of the parents.
Sub-class I. CHONDRICHTHYES.
v
The Chondrichthyes include all the creatures known as Sharks,
Dog-fish and Rays whilst the Osteichthyes include all other fish.
The placoid scale, the only form of skin defence developed in this
sub-class is a little spikelet consisting of a substance called
dentine coated with enamel. The spikelet covers a little cone-
like projection of the dermis, and it is covered in turn by the epider-
mis or true ectoderm. Dentine is a hard substance produced by
the calcification of the ground substance of the dermal connective
tissue. It differs from bone in the fact that it includes no cells
within it but from the cells of the connective tissue in the cavity
which it surrounds and which is called the pulp-cavity, processes
are given off which penetrate the dentine and give rise to canals
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 outside. It pushes the ectoderm before it, and it
becomes encrusted with crystals of carbonate of lime forming the
enamel layer (Fig. 221). These closely set crystals are secreted by
the inner or basal ends of the ectoderm cells. One would naturally
expect that structures like scales, which are closely arranged all over
the body, would also invade the stomodaeum, which is merely a part
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
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 Chondrichthyes are divided into two orders, viz. the Elasmo-
branchii and the Holocephali. In the former group the visceral
arches are all distinct from the cranium. The gills are borne on
XX] MAIN DIVISIONS 455
the walls of gill-sacs, and there is no common gill-cover to protect
the external openings of the gills ; the anterior external margin of
each gill-sac being produced into a slight flap which can close the
opening when it is pressed down. The skin is well covered with
placoid scales, and the teeth are not fused together. In the Holo-
cephali on the contrary, the upper half of the first visceral arch
which in Elasmobranchii forms, the upper jaw is indistinguishably
fused with the cranium. There is a common gill-cover, the opercu-
lum, developed as a flap of skin arising from the hyoid arch which can
FIG. 221. Section through the skin of an Elasmobranch showing formation
of a dermal spine. Highly magnified.
1. Horny layer of ectoderm. 2. Malpighian layer. 3. Columnar cells
of ectoderm secreting 4. 4. Enamel. 5. Dentine (black). 6. Dentinal
pulp. 7. Connective tissue.
cover all the gill -slits, and the septa dividing the gill -slits from each
other are reduced in breadth, the gill-folds arising from the walls of
the gill-sacs project slightly beyond the outer edges of the septa.
The teeth are fused together to form great dentinal ridges with
specially hard parts called tritors and the skin is naked, placoid
scales being only developed on a peculiar tentacle which the male
has developed on his head and which he uses to seize the female
during copulation.
Order I. Elasmobranchii.
The Elasmobranchii includes the vast majority of fish classed as
Chondrichthyes, and we shall therefore describe the structure of a
typical Elasmobranch in order to give an idea of the organisation of
Chondrichthyd fish. In a typical Elasmobranch the skull is much
456
ELASMOBRANCHII
[CH.
3
:-* 2
better developed than in Cyclostomata. In the cranium the
parachordals and trabeculae are firmly fused together so as to form a
continuous plate and the pituitary fossa is reduced to a minute hole ;
there is a high and well-developed side wall and the roof extends a long
distance forward. The sense-capsules, nasal and auditory, are well
developed and firmly united with the cranium. The eyes are large
and highly developed, and the side wall of the cranium is indented to
make room for the spacious orbits in which the eyes move. There
is a considerable part of the head in front of the brain, which usually
also projects in front of the mouth. This is the rostrum or snout,
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 forms. In many species the
opening of the nasal sac is connected
with the mouth by a groove called the
or o nasal groove (Fig. 226). There
are usually six gill-clefts and seven
visceral arches in Elasmobranchs. 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,
so that there are in all eight clefts and
nine visceral arches in this family.
The first pair of visceral arches
form as we have seen the jaws. The
upper jaw is known as the palato-
pterygoquadrate bar, a compound
appellation derived from the names of
the bones by which it is represented in
the higher forms : the term is sometimes
shortened to pterygoquadrate. The lower jaw is called Meckel's
cartilage or mandibular bar: in front a strong ligament, the
so-called ethmopalatine ligament, attaches the upper jaw to the skull.
The second pair of arches are spoken of as the hyoid, and this too is
divided into two portions, an upper, the hyomandibular, which is
firmly connected to the cranium just below the auditory capsule,
and a lower, the ceratohyal (Fig. 223). The upper jaw is
FIG. 222. Diagram of a section
through the jaw of a Shark,
Odontaspis americanus, show-
ing the succession of teeth.
From Eeynolds.
1. Teeth in use. 2. Teeth in
reserve. 3. Skin. 4. Carti-
lage of the jaw. 5. Encrust-
ing calcification of cartilage.
6. Connective tissue. 7. Ec-
toderm lining the mouth.
XX] SKULL 457
connected with the cranium either directly, by articulation with the
cranium in front of the auditory region, an arrangement 'called
autostylic and prevailing among recent Elasmobranchs only in
the Notidariidae ; or else- the upper jaw has lost its articulating
process with the cranium and is instead firmly connected or slung
by ligament into the hyomandibular, which thus suspends the jaw
from the skull. This arrangement, called hyostylic, is that seen in
the majority of Elasmobranchs. A modification, termed amphi-
stylic, occurs in Heterodontidae, where the jaw is slung by the
hyomandibular but also has acquired direct articulation with the
skull in front of the orbit. The remaining visceral arches have only
FIG. 223. Lateral view of the skull of a Dog-fish (ScylUum caniculi) x -. From
Reynolds.
1. Nasal capsule. 2. Rostrum. 3. Interorbital canal for the passage of
a blood-vessel. 4. Foramen for hyoidean artery. 5. Foramen for the
exit of the ophthalmic branches of Vth and Vllth nerves. 6. Foramen
through which the external carotid leaves the orbit. 7. Orbitonasal
foramen which allows a blood-vessel to reach the nose. 8. Auditory
capsule. 9. Foramen through which the external carotid enters the
orbit. 10. Ethmopalatine ligament. 11. Palatopterygoquadrate bar.
12. Meckel's cartilage. 13. Hyomandibular. 14. Ceratohyal.
15. Pharyngobranchial. 16. Epibranchial. 17. Ceratobranchial.
18. Gill-rays; nearly all have been cut off short for the sake of clear-
ness. 19. Extrabranchial. n, in, iv, v, va, vna, ix, x. Foramina
for cranial nerves.
a muscular connection with the skull and are termed the branchial
arches, since to their sides 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
arcuum 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
pharyngobranchial, epibranchial, ceratobranchial, and
hypobranchial. The first-named are situated in the dorsal wall
458 ELASMOBRANCHII [CH.
of the pharynx and are horizontal in direction ; the epi- and cerato-
branchial stiffen the sides of the pharynx the ceratobranchial
being the main portion of the arch, whilst the hypobranchial pieces
are found in the ventral wall of the pharynx and converge to imite
in a median plate, the basibranchial. To the ceratobranchials
are attached a number of thin rods of cartilage which run outwards
in the wall of the gill-sac and are called gill-rays. Lying outside
the visceral arches are a varying number of cartilaginous rods.
Those situated at the sides of the gape are called labial cartilages,
those external to the hinder visceral arches extrabranchials (19,
Fig. 223). They are equivalent to gill-rays which have become
detached from the arches.
The first gill-slit, called the spiracle, is situated between the
jaw and the hyoid just outside the internal ear (Fig. 227). 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
to admit the water for breathing. It is often entirely suppressed.
The other slits are really flattened sacs, the walls of which are sup-
ported by the gill-rays and are raised up into thin folds richly
supplied with blood-vessels, which are the true gills. A rudimen-
tary gill, the pseudobranch, is sometimes developed on the front
wall of the spiracle. No gill is developed on the posterior wall
of the last gill-sac.
In Elasmobranchs we find, as in Cyclostomata, well- developed
dorsal (or neural) and ventral (or haemal) arches,
coTumn bral with their ends deeply embedded in the thick sheath
of the notochord. This sheath consists partly of the
primary sheath secreted by the notochordal cells which has been
converted into cartilage by amoebocytes wandering into it and partly
of a secondary sheath derived from the sclerotome (v. page 414), and
it is divided into separate pieces called centra. Between the centra
the sheath remains membranous, and in the middle of each centrum
the notochord becomes very much narrowed, so that instead of being
a uniform rod it is like a row of beads. The haemal arches meet
beneath in the tail, but further forward they stretch out horizontally
and become jointed; their outer segments are the ribs, and this is
the first appearance of these organs. The ribs project at the level
of the centre of the fleshy masses formed by the myotomes. The
inner segments of these arches are termed basiventrals. The ribs
do not correspond to the outgrowths of the basiventrals in the tail
because in one genus of the Osteichthyes (Polypterus] we find two
sets of ribs on each side of the vertebral column one above the
xx]
VERTEBRAL COLUMN
459
other : the upper set correspond to the ribs of Elasmobranchs, the
lower to the ribs of other fish and to the haemal arches of Elasmo-
branchs. 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 intercalary piece: the haemal
arches are generally as numerous as the centra but occasionally
there may be ventral intercalary pieces. The cranium, visceral
arches and centra are all strengthened by a calcareous deposit
in the ground substance of the cartilage. This calcified cartilage
4...
Fio. 224. Dorsolateral view of the pectoral girdle and fins of a Dog-fish,
Scyllium canicula, xf From. Reynolds. The gaps between the radialia
are blackened.
Hollow in the midventral part of the pectoral girdle which supports the
pericardium. 2. Dorsal (scapular portion) of pectoral girdle. 3. Meta-
pterygium. 4. Mesopterygium. 5. Propterygium. 6. Propterygial
radial. 7. Mesopterygial radial. 8. Metapterygial radial. 9. Out-
line of the distal part of the fin which is supported by horny fin-rays.
is to be carefully distinguished from true bone, which is entirely
absent in Elasmobranchs.
The primitive tail fin of Vertebrata, as we have seen, is a fringe
surrounding the end of the tail. Only a small and narrow remnant
of this persists in Elasmobranchs, the whip-like end of the tail being
bent up ; beneath it there is a well-marked fin, and this together
with the remains of the primitive caudal fin constitute a secondary
460
ELASMOBRANCHII
[CH.
Limbs.
tail-fin, which is now denominated heterocercal, since the axial
skeleton does not divide it into two equal parts (Fig. 227).
The paired fins are attached to hoops of cartilage (the limb
arches), called respectively the pectoral and pelvic
girdles, the pectoral being situated just behind the
last gill-cleft, the pelvic just in front of the anus. The pectoral
girdle extends a considerable distance up the side of the animal:
the pelvic is little more than a transverse bar. The fins in modern
Elasmobranchs are of what is called the uni seriate type, that is
to say, there is a thick jointed main axis with cartilaginous rays
attached only to its anterior border. Fossil Elasmobranchs show in
one case, Pleuracantkus, abiseriate fin with rays attached to both
borders ; and in another, Cladoselacfie, a still more primitive con-
dition, where the fin is merely a lateral flap supported by parallel
bars 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 uniseriate fin. In Cladoselache there seems to have been no
limb girdle. This is a newer development and must be regarded
as a strengthening of connective tissue at the base of the fin in
order to provide a firm insertion for the muscles moving the fin.
In the pectoral fin the basal portions of some of the rays
coalesce to form two large cartilages
called propterygium and meso-
pterygium, whilst the axis itself is
called the metapterygium. In the
pelvic fi.n of the male the axis bears
distally a grooved rod which is termed
the clasper, and is used in transfer-
ring spermatozoa to the female. The
axis is called the basipterygium.
The distal joints of the rays in both
pectoral and pelvic fins are made up
of numerous small cartilages called
radialia.
The brain of Elasmobranchs is re-
markable for the 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
FIG. 225. Dorsal view of the
pelvic girdle and fins of a
male Dog-fish, ScylUum cani-
cula. From Reynolds.
1. Pelvic girdle. 2. Basi-
pterygium. 3. Clasper.
4. Radialia.
Brain.
XX] CIRCULATORY SYSTEM 461
two hemispheres and has nervous tissue on its roof as well as its
floor. The cerebellum is developed into a great flap which projects
back and covers the thin roof of the medulla oblongata (Fig. 207).
It has also lateral outgrowths called cerebellar lobes.
The alimentary canal is considerably longer than the body and
is consequently folded. It has, as a matter of fact, a U -shape:
the first limb and a part of the next constitute the
cfnl entary stomach, which is marked off from the intestine by
a constriction and a powerful development of the
circular muscles forming a sphincter or circular muscle. To the
posterior aspect of the loop is attached 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 infolding, has a very
strongly marked spiral course. The liver opens by the bile-duct
into the beginning of the intestine, and close to its opening is
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. The
heart has the typical structure described in the last chapter (see
p. 430). 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, lienogastric and posterior mesenteric arteries
respectively (Fig. 227). 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
462 ELASMOBRANCHII [CH.
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, 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
the brain. The pseudobranch on the front wall of the spiracle
receives its blood from the hyoidean artery which, branching
from the loop surrounding the first gill- sac, runs forward in the
roof of the mouth parallel with the common carotid artery and
eventually joins the internal carotid. In the venous system the
anterior portion of the subintestinal vein is represented by
a 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 spiral 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. Each
anterior cardinal has an expansion called the orbital sinus which
surrounds the eye. The two orbital sinuses communicate by an
interorbital canal tunnelled in 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 trunks called the
jugular veins. These are each connected with the anterior cardinal
vein of its side by the hyoidean vein lying in a groove on the
hyomandibular cartilage (Fig. 213). 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 arches. At the level of the posterior end of the
kidneys the caudal vein divides into the two renal portal veins
lying on the outer edges of the kidneys. These veins, as has been
already explained (see p. 433), are the hinder portions of the
posterior cardinal veins which break up into the renal portal system
of capillaries. These filter amongst the kidney tubules and reunite
XX] GENITAL ORGANS 463
on the inner side of the kidney to form the spacious posterior
cardinal sinuses, as the front portions of the posterior cardinals are
named. These two sinuses lying ventrally to the kidneys partly
coalesce. Each sinus curves forwards and outwards to join the
ductus Cuvieri and at this point it is met by the so-called sub-
clavian vein which returns blood from the region of the shoulder 1 .
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 side of the body beneath but parallel to the
posterior cardinal vein. The lateral vein in front receives the brachial
vein from the ventral side of the pectoral fin (not to be confounded
with the subclavian from the dorsal region of the pectoral girdle) and
then opens into the ductus Cuvieri. The cloacal veins further give
off median branches which unite and then distribute 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, its
fellow which is indicated in the embryo having dwindled and dis-
appeared ; the oviducts are long and united far in front so as to open
by a common internal opening, situated ventral to the liver (Fig.
226). In the middle of its length each oviduct has 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. The egg is large and
well charged with yolk. The oviducts unite posteriorly to open
into the proctodaeum or cloaca behind the anus. There are
two large testes, and these are united anteriorly and connected
to the front end of each of the kidneys, which extend along the
entire length of the abdominal coelom. The anterior region of
the kidney or mesonephros (for no pronephros is developed) is
narrow and its excretory function has almost disappeared. The
testis is connected with the front end of the mesonephros by vasa
efferentia. These vasa efferentia eventually open into a single
coiled duct. This duct is the archinephric duct which has also
lost its original function and become a vas deferens; it lies on the
ventral surface of the kidney and conveys spermatozoa from the
mesonephros to the cloaca. It enlarges at its hinder end into a
vesicula seminalis. The posterior and functional part of the
1 This vein has been described as receiving blood from the pectoral fin, but
O'Donoghue has shown that this is a mistake, and that its blood is derived
solely from the region of the shoulder.
10-
21
14
b- -/ -;
-14
-16
CH. XX] EXCRETORY SYSTEM 465
FIG. 226. ScylUum canicula ? . Ventral view of viscera.
1. Left naris. 2. Mouth. 3. Pectoral fin. 4. Pelvic fin.
5. Aperture of cloaca. 6. Pericardial cavity. 7. Ventricle. 7'. Conus
arteriosus. 8. Auricle. 9. Sinus venosus. 10. Coelomic opening
of oviducts. 10'. Falciform ligament. 11. Shell-gland. 12. Ovi-
duct. 13. Ovary reflected over to the right so as to show 12, which lies
external to the attachment of the ovary. 14. Liver. 15. Proximal
limb of stomach. 16. Distal limb of stomach. 17. Intestine.
18. Rectum. 19. Spleen. 20. Pancreas. 21. Pancreatic duct.
22. Bile-duct. 23. Dorsal fin. 24. Spinal cord. 25. Noto-
chord in centrum of vertebra. 26. Caudal artery. 27. Caudal vein.
28. Lateral line. 29. Myotomes. 30. Abdominal pores. a. He-
patic artery. b. Intestinal branch of anterior mesenteric artery.
c. Lienogastric artery. d. Gastric branch of lienogastric artery
(posterior gastric artery). e. Splenic branch of lienogastric artery.
/. Portal vein. g. Intestinal vein. h. Splenic vein.
kidney is the metanephros, and its tubules unite into about six
main ducts, which are termed ureters. These unite with one another
a very short distance from the cloaca to form a metanephric duct
or common ureter. There is also a blind sperm sac into whose
posterior end the vesicula 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 urino-genital
sinus which opens into the cloaca behind the anus. In the female
the mesonephros is more vestigial than in the male and its duct
(the archinephric duct) is in front a very fine tube which lower down
dilates and meets its fellow to form a median urinary sin us. This
receives the five or six ureters on each side from the metanephros,
and opens into the cloaca behind the oviduct. There is thus no
common ureter in the female, and the so-called common ureter of
the male is formed in quite a different way from that in which the
ureter of the higher Craniata is formed (see Fig. 216, G, H).
Actual sexual congress or copulation takes place in the Elasmo-
branchs ; the most posterior rays of the pelvic fins called the
claspers are enlarged, and used to distend the cloaca of the female
to allow of the entrance of spermatozoa (Fig. 227). This is cor-
related with the large size and small number of the eggs and their
long retention in the oviduct. In the male the spermatozoa are
stored in a swollen portion of the vas deferens, the vesicula\
seminalis, or in special pouches termed the sperm-sacs. It is
probable that the claspers, the large eggs and the division of the
kidney into two parts are specialisations peculiar to modern
Elasmobranchs.
The Elasmobranchs are the Sharks, Dog-fish, Skates and Rays
of our seas. They are almost exclusively marine and are a group
s. & M. 30
FIG. 227.
CH. XX] SELACHOIDEI 467
FIG. 227. Scyllium canicula
N gd. 9
* ?ll
~ .
23 -3
S "*< ^
bp
OQ
5 .2
8
"" ft
5 a..
g .
d ^ >rC <-^
O
fi rt
486 TELEOSTEI [CH.
often swollen into a kind of urinary bladder which descends to open
behind the anus by a separate opening. The testis has a duct
which issues from its hinder end and unites with its fellow to open
by a genital opening between the anus and the kidney opening
(Fig. 238).
The researches of Prof. Kerr on some of the more archaic types
of Osteichthyes have made it probable that the testis duct is to be
looked on as a posterior sterile extension of the testis itself, and
sections of the " duct " confirm this, because it is seen to be more
of the nature of a network of tubes than a single duct. According
to Jungersen it opens into the kidney duct in the embryo, and this
connection may be regarded as a single posterior vas efferens ; the
portion of the genital duct close to the opening may be regarded as
a split-off portion of the kidney duct.
In the female the ovary is similarly continuous with a short
wide oviduct which joins its fellow to open by a genital opening.
But in some primitive families of Teleostei, such as Salmon and
Eels, the oviduct is absent and the ovary dehisces its ova into the
splanchnocoel, and, as in Cyclostomata, the ova escape by abdo-
minal pores. Investigation into development shows that the
oviduct arises as a groove in the peritoneum leading to the pore,
and that this groove is bounded on one side by a fold which is
nothing more than a sterile extension of the ovarian ridge itself.
The brain of a Teleostean differs from that of Chondrichthyid
fish (1) in the reduction of the cerebral hemispheres to their basal
portions, which correspond to the so-called corpora striata in the
human brain. The roof of the cerebrum is a thin sheet of non-
nervous membrane continuous with the roof of the third ventricle ;
(2) in the solution of the optic chiasma. This, it may be remem-
bered, is a band of nervous tissue grooved off from the floor of the
thalamencephalon, in which run fibres from both eyes to both sides
of the brain. In the Teleostean this is split into two separate nervous
stalks each connecting one eye with the opposite side of the brain
only. Since the eyes of a Teleostean fish owing to its compressed
shape receive images of quite different objects, it is of no use trying
to combine them ; (3) in the protrusion of the cerebellum forwards
into the cavity of the mid-brain as the so-called valvula cerebri.
In the cranial nerves the sole point which calls for remark is
a cutaneous branch of the 5th, which is distributed to -the bases
of all the paired and unpaired fins where there are developed
taste-buds.
XX] CIRCULATORY SYSTEM 487
The olfactory lobes are sometimes connected with the cerebrum
by very long stalks (Cod family), but at other times they are sessile
(most other Teleostei).
In the blood system the main difference between Teleostei and
Chondrichthyes lies in the fact that in the former group the con us
of the heart has disappeared as a distinct chamber, since it becomes
merged in the ventricle, which has thereby become enlarged. There
is only one transverse row of pocket valves, and these are situated
at the origin of the ventral aorta, and correspond to the most distal
pair in Chondrichthyes. The ventral aorta is thickened at its origin
by an increase of fibrous tissue, but this swelling, termed the
bulb us arteriosus, is not rhythmically contractile. Besides this
peculiarity of the heart we find that in Teleostei the four epibran-
chial arteries on each side, instead of converging to join the dorsal
aorta, join a ring-shaped vessel termed the circulus cephalicus,
from which two posterior carotid arteries are given off in front
to supply the brain and from which behind the dorsal aorta arises.
The efferent branchial vessels do not form loops round the gill-clefts
as in Chondrichthyes, but the efferent vessel from the hinder wall of
the first cleft, i.e. the cleft between the hyoid and first branchial
arches, gives off a branch which runs round the ventral end of the
cleft and carries blood to the pseudobranch. From the pseudo-
branch blood is carried by an ophthalmic artery, which runs
forward to supply the vascular choroid investment of the eye, and
is connected with its fellow by a bridge above the parasphenoid.
From this bridge go off arteries to the brain in front of the posterior
carotids. These branches of the ophthalmic arteries are known as
anterior carotids (Fig. 239).
The egg of the Teleostean fish develops into a larva which,
although showing special characters in each family of the group, has
certain general characters as well. Thus it possesses a continuous
fin-fold in place of the separate dorsal caudal and anal fins of the
adult. The notochord is at first quite unconstricted, because there
are no centra, and it runs straight to its termination : the end is
not bent up. Pectoral fins alone are developed, and the excretory
organ is a pronephros, consisting of a single closed chamber on
each side, from the inner wall of which is developed a glomerulus.
From this chamber a single pronephric tubule leads into the archi-
nephric duct. When the adult form has been attained the fish is
far from having reached the adult size, and in general several years
must elapse before sexual maturity is attained.
488
TELEOSTEI
[CH.
To give an account of the classification of an enormous group
like the Teleostei would far exceed the limits of this book ; the
latest authority (Tate Regan) recognises no less than 35 primary
divisions, and it would be useless, even if it were possible, for the
student to memorise the characters of all these. All we can
attempt to do is to give some account of some groups, mainly of
those which are of economic importance, because they constitute an
important source of food. Before doing so we may briefly mention
GUI slits 1-5
"Epibnanchia/
^%'
Afferent
Arteries
1-4
Dors&l
Aorta.
FIG. 239.
Diagram illustrating the arrangement of the heart and branchial
vessels in a Teleostean fish.
some of the characters which are relied on by taxonomists in
dividing Teleostei into groups.
First in importance of these must be reckoned the position of
the pelvic fins. In primitive forms these are placed a considerable
distance behind the pectoral fins as in Chondrichthyes. This position
is known as the abdominal one. But in very many Teleostei the
pelvic fins are moved forward until they are immediately behind
the pectoral fins and the pelvic girdle articulates with the cleithra.
This position is known as the thoracic one. In some families (as
for instance in the Cod family, and in the Flat-fish family) they are
XX] MAIN DIVISIONS 489
moved still further forwards till the pelvic girdle is attached to the
front lower end of the cleithra, and so the pelvic fins are actually
in front of the pectoral. This position is known as the jugular.
Next to the condition of the pelvic fins is the condition of the
air-bladder. The function of this organ is to enable the fish to
adjust its weight to the density of the water in which it lives.
In the more primitive families the air-bladder is connected with
the pharynx by a duct opening in the mid-dorsal line and the fish
swallows air into its bladder. In the majority of Teleostei the
air-bladder is shut off altogether from the alimentary canal and
secretes its contained gases from the blood : a thickening in its
wall richly supplied with blood-vessels, being termed the gas-gland.
In the more primitive families the maxilla bears teeth and forms
part of the gape behind the premaxilla, but in the vast majority
of Teleostei the maxilla is a toothless bone embedded in the cheek
and passing up behind the premaxilla. When the mouth is opened
the lower end of the maxilla rotates forward and pushes out the
premaxilla which is then said to be protrusible. In a large number
of the more modified Teleostei certain of the lepidotrichia covering
the dorsal, pectoral and pelvic fins are fused together to form hard
pungent spines, and in very large groups of families, the pelvic fin
possesses one such spine followed by five articulated rays. This
arrangement is almost as constant as five fingers on the hands of
men and monkeys.
The great sub- order CLUPEIFORMES is characterised by ab-
dominal pelvic fins, an air-bladder with a duct and the maxilla
forming part of the gape. The coracoid has an anterior fork
termed the mesocoracoid. This group includes amongst other
families the Clupeidae or Herring family, and the Salmonidae
(Salmon and Trout and White-fish).
The Clupeidae have a single dorsal fin and the air-bladder
sends processes forward which extend into the auditory capsules
and come close to the internal auditory sac, and thus this sense
organ is directly affected by changes of pressure in the air-bladder.
The genus Clupea includes the Herring, Sprat and Pilchard as well
as the Shad, which is a more deep bodied form. The Anchovy dis-
tinguished by its projecting snout is Engraulis.
The Herring is probably the most important food-fish. It lives
in comparatively deep water at a moderate distance from the coast,
but comes into shallow water to spawn, its eggs being attached to
stones. It is usually caught when on this spawning migration.
490 TELEOSTEI [CH.
In spite of the enormous toll on its numbers levied by the fisheries
of Northern Europe it appears to be actually on the increase. The
Pilchard is a smaller fish which lays floating eggs as does also the
Anchovy. The true or French Sardine is the young Pilchard.
Whitebait consists of the fry of the Herring.
The Salmonidae are distinguished by having a small fin-fold
devoid of rays (the adipose fin) behind the dorsal fin. The air-
bladder is a simple sac and the oviducts are very short tubes
unconnected with the ovary.
The genus Salmo includes the Salmon and Trout. Salvelinus is
the Char (called the Trout in America) and Coregonus is called the
White-fish in America and by various names in England. Salmon
and Trout are well known as sporting fish in this country, they are
esteemed as delicacies for the table but do not furnish a source
of food comparable in importance with the Herring. But on the
Pacific coast of America, allied genera are netted in enormous
numbers, and their flesh packed in tins is sent all over the world.
All the Salmonidae spawn in fresh water and the young fish passes
one or two years in fresh water before going to the sea, and may
(as in River Trout) pass all its life there. It is to be concluded that
the Salmonidae furnish a rare instance of a family of fish primitively
fresh -water, some species of which have regained the sea and are
able to maintain themselves there. Coregonus, the White-fish of
the great lakes of America and the " Pollan " of Lough Neagh in
Ireland, is much esteemed for the delicacy of its flavour.
The sub-order ANGUILLIFORMES includes the Eels. In these fish
the caudal and pelvic fins are lost, and the dorsal and anal fins
have extended till they meet at the extremity of the tail and form
a continuous fringe round the hinder end of the body. In this
way a tail fin is produced which resembles that of the larva, but
its apparent primitive character is due to secondary degeneration.
Such a tail fin is called gephyro cereal. Scales are reduced to
vestiges deeply embedded or are absent altogether. The air-bladder
has a duct, and the oviducts as in the Sahnonidae are represented
only by abdominal pores.
In the skull the cranium is not narrowed between the orbits,
the premaxilla and in some cases the maxilla is lost, and the
symplectic is not developed, since the hyomandibular bone is joined
directly to the quadrata. The pectoral girdle is no longer con-
nected with the skull, the post-temporal bone being absent. Some
fish belonging to this group, such 'as the common Eel, live partly
XX] MAIN DIVISIONS 491
in the sea but periodically ascend rivers. Classed with Salmon
as anadromous fish, the Eels in reality form a complete con-
trast to them for they ascend the rivers to feed and return to
the sea to spawn. They lay their eggs on the Atlantic slopes,
i.e. where the drop from shallow depths to abysmal depths begins.
The egg develops into an extraordinary larva termed Lepto-
cephalus, in some ways resembling Amphioxus, and like it
devoid of red blood corpuscles. These larvae change to minute
Eels termed Elvers as thin as a wire and a few inches long, and
in this condition they ascend the rivers. They leave the water
and wriggle over damp grass at night in order to reach isolated
ponds. It has been plausibly suggested that the Eels were origin-
ally estuarine fish and spawned close to the coast ; but as the coast
subsided under the sea, their original spawning place to which
they have remained faithful has been buried far out under the
Atlantic.
The sub-order OSTARIOPHYSI is characterised by having ab-
dominal pelvic fins, an air-bladder with a duct, and a remarkable
chain of bones on each side of the vertebral column connecting the
anterior end of the air-bladder with the auditory capsule. This
chain is termed the "Weberian chain and it consists of a triangular
bone, the "tripus," probably a modified rib, which impinges on
the air-bladder, of a Y-shaped "intercalare," and finally of a
cylindrical " scaphium " which rests against a membranous window
in the periotic capsule. The scaphium is supposed to be the neural
arch (basidorsal) of the first vertebra. The coracoid has a meso-
coracoid branch and the pelvic fins are abdominal in position.
This remarkable group of fish includes the families Cyprinidae
(Carp, etc.) and Siluridae (Cat-fish). The former family is charac-
terised by the presence of normal scales, and the protrusibility of
the premaxilla, but the protrusibility is not effected by the motion
of the maxilla. The Cyprinidae include the Carp, Cyprinus (species
of which constitute the "gold" and silver fish), and the Roach,
Loach, Gudgeon and Minnow in fact the majority of the fish
which inhabit our rivers and lakes. The Siluroids or Cat-fish derive
their name from the numerous tentacle-like appendages (barbels)
which adorn their mouths. One specially long one is borne by the
maxilla. Certain of the fin rays of the dorsal and anal fins are
developed into spines. As in Eels the brain case is unconstricted
between the orbits and the symplectic is absent. Ordinary scales
are never present. Either as in the Cat-fish of North America the
492 TELEOSTEI [CH.
skin is naked, or as in the South American forms the body is
covered with large shining scutes, on the surface of which are
placoid denticles (Fig. 240).
The Siluridae are nearly all fresh-water, none are found in
England. Amiurus, the Horned Pout, is a common North American
fish and is eaten.
The HAPLOMI or Pike-like fish are characterised by possessing
abdominal pelvic fins and a duct of the air-bladder, but they are
distinguished from the Ostariophysi by having no Weberian ossicles
and from the Clupeiformes by the fact that the pectoral girdle has
no " mesocoracoid " projection.
The maxilla usually forms part of the gape. This group of
normal, somewhat unspecialised fish includes the families Esocidae,
with Esox the well-known pike, esteemed for its flavour and dis-
liked for its destrucfciveness on still more valuable fish.
FIG. 240. A Cat-fish, Amiurus catus. Diminished. From Cuvier and
Valenciennes.
The group PEECESOCES, as its name implies, is transitional between
the sub-orders of Pike-like and Perch-like fish. The pelvic fins are
always behind the pectoral and never attached to the cleithrum,
but the air-bladder has no duct. This group includes the family
Mugilidae in which the pelvic bones are attached to the postcleithra.
The best known genus is Mugil, the Grey Mullet, one of the food-fish
most esteemed for its flavour. As the Mullet feed on minute
organisms, which are filtered from the water by strainer-like pro-
cesses extending from the gill-arches, they cannot be taken by bait,
but must be caught by drawing nets round the shoal, i.e. by seining.
The great sub-order PERCOMORPHI or Perch-like fish are charac-
terised by Tate Regan as the central group of Teleostei, for not only
do they include a large number of families, but they seeni to have
XX] MAIN DIVISIONS 493
given rise to a good many of the groups which are now regarded
as primary divisions of the Teleostei. The sub-order is characterised
by the fact that the pelvic bones articulate with the cleithra, and
hence the pelvic fins are thoracic or jugular in position. The air-
bladder is closed, the maxilla is toothless, and there are stiff spines
in the dorsal, anal and pelvic fins, except in one or two primitive
families the pelvic fin has one spine and five soft rays.
Only a few of the families of this enormous sub-order can be
mentioned. The Percidae, including the Common Perch, Perca,
and the Centrarchidae, including the Black River-Bass of North
America (Micropterus), are closely related, the first family being
divided from the second by having the dorsal fin divided into
spinous and soft fins, and by having fewer spines in the anal fin.
The River- or Lake-Bass is one of the fish most esteemed by anglers
as a sporting fish. The Serranidae closely resemble the Centrarchidae,
but have one of the circumorbitals produced inwards as a shelf
supporting the eye-ball. These are the Marine Perch, including the
fish called in America Sea-Bass, which are highly esteemed for the
table. The Mullidae or Red Mullet are distinguished by their ves-
tigial teeth and by having two barbels ; they are food-fish but much
inferior in flavour to the Mugilidae. The Sparidae include the fish
called the Sea-Bream, also fish of economic value distioguished from
Mullidae by their large teeth, which are cutting in front and crush-
ing at the sides. The Labridae or Wrasses are distinguished by the
union of the lower pharyngeal bones in the middle line and by
having pointed teeth like a dog's at the sides of the jaws. The
Wrasses include many tropical fish renowned for their brilliant
colours, indeed our own Wrasses assume gay colours at the breeding
season. The Scombridae, or Mackerel family, are distinguished by
having the spinous dorsal fin made up of a few feeble spines arid by
having the hinder part of the soft dorsal broken up into finlets. The
body has a characteristic shape ; it narrows behind so as to form a
stalk for the tail fin which is greatly enlarged and deeply forked.
The Mackerel, Scomber scombrus, is a most valuable food-fish. It
occurs in shoals chiefly off the West and East coasts and is caught
by seining.
The Tunny (Thunnus thynnus) is one of the largest of food-
fish ; it is 10 feet in length. It is fished chiefly in the Mediterranean
and forms a valuable fishery.
The HETEROSOMATA or Flat fish (often called the Pleuro-
nectidae) are devoid of all rigid spines in their fins and have the
494
TELEOSTEI
[CH.
pelvic fins moved forward into a jugular position. For this reason
they were formerly placed near to the Cod family, but Tate Regan
has shown that they must be regarded as having sprung from the
Percomorphi. One primitive genus, Psettodes, still possesses spines
the dorsal fin. The Heterosomata derive their name from the fact
that they habitually lie on one side, which is usually white, whilst
both eyes are twisted on to the upper side which is deeply pig-
mented. The air-bladder is lost. These fish, which are captured
by the trawl net which is dragged over the bottom, include a large
proportion of our most valued food-fish such as the Plaice (Pleuro-
nectes platessa) (Fig. 241), the Flounder (P. flesus), the Dab (P.
FIG. 241. Pleuronectes platessa, the Plaice, found from the coast of France to
Iceland.
limander), the Lemon Sole (Glyptocephalus microcephalus\ the
Turbot (Psetta maxima), the Brill (Psetta laevus), the Sole (Solea
vulgaris] and the Halibut (Hippoglossus), which may 'attain a length
of 10 feet and weigh 400 Ibs.
As everyone knows, the Sole is one of the most valued fish, and
appears chiefly at the tables of the rich, whilst the Plaice is the food
of poorer people.
The reason for this is curious : all fistrowe their palatability to
some peculiar chemical substance in the muscles which gives them
their characteristic flavour. In the Plaice, as in most fish, the
substance is present in the fish when living, and consequently unless
XX] MAIN DIVISIONS 495
they are eaten just after being caught, this fugitive substance dis-
appears and the flesh becomes comparatively tasteless. But in the
Sole the characteristic flavour is only developed two or three days
after death in consequence of the formation of some characteristic
substance by incipient decomposition. Hence the Sole is a tasty
fish even when it is brought long distances.
The GADIFORMES or Cod-like fish are fish with a peculiar mixture
of primitive and secondary characters. Thus the pelvic fins are
moved into a jugular position ; the original tail fin supported by
the hypural bones has disappeared and is replaced by a new tail fin
formed by the separation of portions from the dorsal and anal fins,
and supported by the neural and haemal spines. There are no spines
developed in any of the fins, and the pelvic fins may have 10 or
12 rays. These features all imply specialisation, but on the other
hand there is an extension of the cranial cavity forwards above
the interorbital septum, and this contains the long stalks of the
olfactory lobes of the brain.
This group includes the food-fish known as the Cod (Gadus
morrhua), the Saithe (sometimes called the Coal-fish) (G. virens),
the Pollack (termed the Lithe in Ireland) (G. pollachius), the
Haddock (G. aeglefinus) and the Whiting (G. merlangus), the Hake
(Merlucius vulgaris) and the Ling (Molva vulgaris).
The Cod, which is captured by line and bait is perhaps the
most sought after food-fish in the world. This is due to (1) the
ease with which it can be preserved in the dried condition and so
carried long distances, (2) the stable and satisfying character of its
flesh ; it is said to be the only fish which can be eaten daily year in
and year out as a staple of diet without provoking nausea.
In their pursuit after Cod the French fishermen were led further
and further into the Atlantic, and this led to the discovery of Canada,
and even yet the Cod-fishery attracts a population of between 20,000
and 30,000 to the desolate ice-bound shores of Labrador. British
fishermen who formerly found the Hake in their own territorial
waters now pursue it further and further South till they go to the
Atlantic off the coast of Morocco to find it.
It is obvious that if a fishery is to be an economic success, the
fish must be taken in enormous numbers at a time, and this is only
possible if they are caught when they congregate in shoals. That
branch of Zoology known as Fishery Science has for its object the
determination of the whole course of the life history of fish of
economic value, and of the causes which determine their migrations.
496 TELEOSTEI [CH.
Armed with this knowledge Fishery Science can aid the fisherman
by enabling him to find the shoals of fish, and also in some cases by
protecting the fish against undue depletion of their numbers at
critical periods of their lives ; and in this way conserving the
"harvest of the sea."
We now turn to consider the aberrant orders of Osteichthyes and
the first we shall mention is the Aetheospondyli, including the
single genus Lepidosteus, the bony Gar -Pike of the lakes and
rivers of North America.
Order II. Aetheospondyli.
The Aetheospondyli are Ganoids, i.e. they are covered all
over with bony rhomboidal scales with a shining covering of ganoin
and the free edges of the scales are beset with placoid denticles.
But there is no essential difference between the so-called scutes of
the South American Siluroids and these ganoid scales, so that they
cannot be regarded as a diagnostic character of the order. The
Aetheospondyli differ from the Teleostei and agree with the
Chondrichthyes in certain characters which must be regarded as
archaic, i.e. derived from the common ancestor of both groups
of fish. These archaic characters are (1) the testis is connected
with the kidney by a series of vasa efferentia and the archinephric
duct serves also as sperm duct, (2) the division of the heart known
as the con us is distinct and has several transverse rows of pocket
valves, (3) there is an optic chiasma containing fibres from both
eyes, beneath the fore-brain, (4) there is the rudiment of a spiral
valve on the intestine. The peculiar features of Aetheospondyli
concern the vertebral column and the skull. In the vertebral column
of the young Lepidosteus distinct dorsal and ventral intercalaries are
present as well as basidorsals and basiyentrals (neural and haemal
arch-pieces). All these arch-pieces are derived from groups of cells
budded from the inner walls of the myotomes, but if we consider the
pieces derived from any one myotome, then the dorsal intercalary
lies behind the basidorsal and the ventral intercalary lies in front of
the basiventral (Fig. 242, A).
Now in discussing the vertebrae of Teleostei, we saw that the
bony ring constituting the centrum connected the basidorsal of one
myotome to the basiventral of the myotome in front of it.
In Lepidosteus the main mass of the centrum is constituted by
a ring of bone connecting the basidorsal derived from one myotome
with the basiventral belonging to the myotome in front. The arches.
xx]
AETHEOSPONDYLI
497
are at first cartilage, but become ossified. The dorsal and ventral
intercalaries belonging to the same myotome become connected
by an intervertebral ring of cartilage which constricts and
finally obliterates the notochord between the centra. Then this
ring undergoes absorption in its centre, so that a joint cavity
is formed (synovial cavity) arid the front half, which is concave,
becomes attached to the vertebra in front and ossified, and the
Fio. 242.
Three stages in the development of the vertebral column of
Lepidosteus.
Stage in which basidorsals, basiventrals, and intercalaries are all separate.
Stage in which basidorsals and basiventrals are connected by a bony ring,
and in which the intercalaries have fused to form a cartilaginous ring in
which a space, the rudiment of the synovial cavity, is appearing.
Stage of the completed vertebra.
Basidorsal. 2. Notochord. 3. Basiventral. 4. Dorsal inter-
calary. 5. Ventral intercalary. 6. Bony ring connecting basi-
dorsal and basiventral. 7. Synovial cavity. Dotting, cross-hatching,
etc. as in Fig. 232.
hinder half, which is convex, becomes attached to the vertebra
behind, and likewise ossified, i.e. replaced by bone, so that it comes
about that the vertebrae acquire articular surfaces by which they can
glide on one another. If this description has been followed, it will
be seen that a vertebra consists of the basidorsal and the smaller
part of the dorsal intercalary belonging to one myotome, and of the
basiventval and the larger part of the ventral intercalary belonging
s. & M. 32
498 AETHEOSPONDYLI [CH.
to the myotome in front. Vertebrae which have hollow articular
surfaces behind are termed opisthocoelous (Gr. OTTIO-^O-, behind).
The skull is just as well ossified as that of a Teleostean, but it
lacks the supra-occipital, the cartilage in that region being covered
here by two dermal bones called supratemporals.
The upper jaw articulates with the pro-otic behind the eye, so
that the jaw is doubly supported, since hyomandibular and sym-
plectic are also developed, but its amphistylism is different from
that of Teleostei. Covering the inner side of the lower jaw mem-
brane bones, termed splenial and supra -angular are developed.
The tail fin is a rounded lobe derived from the ventral lobe of
a heterocercal tail. The vestigial dorsal lobe is perhaps represented
by a vertical line of fulcra (i.e. /^-shaped ganoid scales), which
cover its anterior border.
The jaws are long and bill-like, and the maxilla is represented
by several bones in series. The fish lies in wait for its prey amidst
reeds on the shallow border of lakes. Its air-bladder is produced
into pockets like the alveoli of the lung of a land animal, and the
fish swallows air and emits it, so that it is probable that the air-
bladder is partly used as a respiratory organ.
Order III. Protospondyli.
The Protospondyli include, like the Aetheospondyli, only a
single genus, Amia, represented by a single species, Amia calva,
the Bow-fin, inhabiting the lakes and rivers of North America. The
Protospondyli show the same archaic features as the preceding
group in the matter of vasa efferentia, conus, optic chiasma and
spiral valve ; further, they have short wide oviducts opening
internally into the body cavity by wide funnels, whereas in
Aetheospondyli, as in most Teleostei, ovary and oviduct are con-
tinuous. The Protospondyli are, above all, distinguished by the
structure of the vertebral column. In the young fish dorsal and ven-
tral intercalaries are present as well as neural and haemal arches,
and all these arch pieces become connected with each other by
bony rings which form centra, but the centra so formed resemble
those of Teleostei in being amphicoelous and enclosing between
them portions of the notochord, and in the tail the centra are
doubly as numerous as the myotomes, a centrum bearing dorsal
and haemal arches alternating with one devoid of both. From
the study of development it appears that the arch-bearing
centrum is formed chiefly by a bony ring connecting the basi-
xx]
PHOTOS POND Y LI
499
dorsal with the basiventral. It is termed the postcentrum. The
archless centrum or precentrum is formed chiefly by a bony ring
connecting the dorsal intercalaries with the ventral intercalaries.
Where the tail merges into the trunk the precentrum may be
seen to become attached to the postcentrum. A vertebra of
the trunk consists, therefore, of the basidorsal of one myotome
FIG. 243. Three stages in the development of the vertebral column of Amia.
A. Stage when basidorsals, basiventrals and intercalaries are separate.
B. Stage when basidorsals and basiventrals are connected by a ring of bone,
and likewise dorsal and ventral intercalaries.
C. Stage of formation of complete vertebra in the trunk and of precentrum
and postcentrum in the tail. The hinder part of the figure shows the
condition in the tail, the front that in the trunk.
1. Basidorsal. 2. Notochord. 3. Basiventral. 4. Dorsal inter-
calary. 5. Ventral intercalary. 6. Bony ring connecting basidorsal
and basiventral. 7. Bony ring, connecting intercalaries. i. Arch-
less precentrum. n. Arch-bearing postcentrum. in. Complete
vertebra in the trunk. Dotting, etc. as in previous figure.
and of the basiventral and the dorsal and ventral intercalaries
of the myotome in front.
The tail fin agrees in shape with that of Lepidosteus, but fulcra
are absent, since the scales of Amia are "cycloid," i.e. thin and
devoid of both ganoin and placoid denticles.
322
500 CHONDEOSTEI [CH.
In the skull there is no supra-occipital, but two supratemporals
occupy its place. The upper jaw is short and normal, i.e. resembles
that of Teleostei, but the lower jaw has the splenial bone and in
addition there is a dermal bone, the gular plate, on the under side
of the throat between the halves of the jaw. The air-bladder is like
that of Lepidosteus, and Amia appears to use it as an organ of
respiration when the water becomes foul.
Numerous fossil fish belong to the Protospondyli, and in most
cases their pre- and postcentra do not -even form rings, but oblique
wedges, and no complete centra are formed even in the trunk.
Order IV. Chondrostei.
The Chondrostei or Sturgeons include four genera divided
into two families. They agree with the two preceding orders in
possessing the archaic features of vasa efferentia, conus, optic
chiasma and spiral valve, and the oviducts are short and open by
wide funnels into the coelom.
The Chondrostei are distinguished by the condition of the
vertebral column. As in the two preceding orders, dorsal and
ventral intercalaries are present as well as neural and haemal
arches, but only the neural and haemal arches Become ossified, and
that incompletely ; the notochord is invested with an unsegmented
cartilaginous sheath, which is a modification of its own sheath. No
centra are formed. A large number of the arch-pieces are fused into
a cartilaginous tube and amalgamated with the great cartilaginous
cranium. The tail fin is typically heterocercal, and the front edge
of the dorsal lobe is covered with a line of fulcra. The rostrum
of the skull is produced into a great prae-oral snout which is
used for stirring up the mud in which the fish finds the worms
on which it feeds. The jaws are feeble, devoid of teeth and
attached only to the skull by the hyoid arch. It is an interesting
fact that not only the hyomandibular cartilage, but also some of the
pharyngobranchials, articulate with the cartilaginous skull. The
spiracle usually persists and has a rudimentary gill (pseudobranch)
on its anterior wall. Bones replacing the cartilage are very feebly
developed. In very old fish parethmoid and orbitosphenoid bones
may appear, as well as pro-otics and opisthotics. In the upper
jaw there is always a palatine bone and sometimes ectoptery-
goids, metapterygoids and quadrates, but the cartilage is merely
invested it still persists. In the second arch there is a
xxj
SKULL
well- developed hyomandibular and sym-
plectic, and the middle portions of the
ceratohyals and ceratobranchials are also
invested by bone.
Dermal bones are well developed both
on the upper surface and sides of the
head. The rostrum and occipital region
are covered by numerous bones, and the
typical series of paired bones on the roof
of the skull may become separated by an
intercalated secondary series of median
membrane bones. In the upper lip a
maxilla, but no premaxilla, is developed,
in the lower lip a dentary bone appears.
On the roof of the mouth there is in
front a single bone representing the
vomer, and behind it an immense para-
sphenoid. The region of the pectoral
girdle is covered by membrane bones
having in general the same arrangement
as -in Teleostei, but between the two
cleithra there are two clavicles which
meet in the mid" ventral line. These
bones, absent in Teleostei, are present
in most land animals, and must have
been inherited from the common an-
cestor from which fish and land animals
are derived.
Living Chondrostei fall into two
families, viz. the Acipeuseridae, including
Acipenser and Scapkirhynckus, which
possess five longitudinal rows of great
bone scutes on the body, which appear
to merge insensibly into the dermal
bones of the head, and the Polyodon-
tidae, in which the body is naked except
for vestigial scales embedded in the skin,
and there is no series of median dermal
bones on the roof of the head. The
dorsal lobe of the tail fin retains, how-
ever, its series of fulcra (Fig. 244).
Caviare is prepared from the ovaries
FIG. 244. Acipenser sturio,
the Sturgeon. From Day.
502 POLYPTERINI [CH.
of members of both families, from Polyodontidae in America and
from Acipenseridae in Russia.
The Acipenseridae are, like Salmon, anadromous fish, spawning
in fresh water, but, with the exception of one or two species, seeking
their living in the sea. The Polyodontidae, so far as is known, are
fresh-water. Acipenser is found occasionally off the British coast,
but abounds in the rivers of Russia and the Black Sea. Polyodon is
a denizen of the Mississippi.
To the order Chondrostei belong a large number of fossil fish, and
as we recede backwards in geological times the peculiar features of
the Sturgeon gradually fade out. The rostrum in older forms is
shorter, a premaxilla as well as a maxilla is present, and both bear
teeth (as the maxilla does in the young Polyodon); the body is
clothed with shining " ganoid " scales, like those of Lepidosteus and
Amia, and the whole animal looks very like an ordinary fish, but is
destitute of an ossified backbone and, so far as is known, of car-
tilage bone in the skull.
These extinct fish are termed "Palaeoniscids," and in this case
their evolution into Sturgeons has been a degeneration, not an
advance, in structure.
Order V. Polypterini.
The Polypterini include two genera, Polypterus and Cala-
moichthys, both confined to the rivers of Africa. This order agrees
with the three preceding in the archaic features of conus, optic,
chiasma, and spiral valve, but it agrees very nearly with Teleostei
in the character of the male organs. As in that order there is a
sterile posterior prolongation of the testes consisting of a central
duct with a network of sterile tubes around it, and this portion of
the testes, as in the young Teleostei, communicates with the hinder
portion of the archinephric duct by a single tube which may be
looked on as a single posterior vas efferens. In the female the
oviduct is short and opens by a wide funnel into the coelom.
The Polypterini further agree with the Teleostei in the character
of the vertebral column, which consists of well ossified amphicoelous
vertebrae bearing two sets of ribs, viz. dorsal ribs, which correspond
to the "epipleurals" of Teleostei and the ribs of Chondrichthyes,
and ventral ribs, which correspond to the ribs of Teleostei and all
other Osteichthyes.
The peculiarities of Polypterini are to be found in their fins
xx]
RESPIRATORY ORGANS
503
and in their respiratory organs. Thus the tail fin is a symmetrical
fringe round the end of the body, and resembles the tail fin of the
Teleostean larva. Such a primitive type
of fin is called diphycercal. The dorsal
fin is broken up into a series of finlets,
each beginning with a stout spine (whence
the name Polypterus, lit. many fins),
and the pectoral fin has a median scaly
lobe round which the dermal fin rays (lepi-
dotrichia) form a fringe, whence the name
Crossopterygii (lit. fringe-fmned, Gr. Kpov-
a-oL, a fringe), which Huxley bestowed on
the order. The air-bladder is deeply
bilobed, the left lobe being much larger
than the right one, and the two lobes
unite into a median duct, which opens on
the ventral side of the pharynx an
arrangement which recalls that of the
lungs of land animals and the Poly-
pterus, like A mia and Lepidosteus, swallows
air, which it uses for respiratory purposes,
the used air escaping by the spiracle,
which persists and has a little gill-cover
of its own. The larva possesses a long
feather-shaped external gill attached to
the hyoid arch, resembling the gills borne
by Amphibian larvae. Here again we see
features which seem to be derived from
the common ancestor of fish and land
animals.
The body is covered with rhomboidal
shining ganoid scales, beset with placoid
denticles, like those of Lepidosteus. In
the skull the jaws are articulated as in
Teleostei ; there is a hyomandibular bone,
but no symplectic, and in the lower jaw a
splenial bone is developed, and on the
under side of the throat a pair of gular
plates. The vomers are paired, and in
the dermal pectoral girdle clavicles are
present, as in Chondrostei. The pectoral is uniseriate with three
FlG - 245 -
504 DIPNOI [CH.
basals, as in Elasmobranchia. Of these the two outer are ossified,
while the central one remains cartilage.
Calamoichthys is an eel-like form, but agrees in all essentials
with Polypterus. With the Polypterini were formerly associated
a large number of fossil fish common in the Devonian and Car-
boniferous strata, which Goodrich has separated under the name
OSTEOLEPIDOTI. These agree with Polypterini in having a diphy-
cercal tail and a scaly lobe in the pectoral fin, and in having
shining rhomboid scales. It appears, however, that the pectoral
fin is biseriate, of the type to be described in the next order, and
according to Goodrich the scales which he terms cosmoid, have
a different structure from the ganoid scales. In cosmoid scales,
under a very thin layer of shining substance, there is a row of
pulp-cavities from which radiate dentinal canals, suggesting that
this layer of the scales is derived from the fusion of placoid
denticles.
Order VI. Dipnoi.
The Dipnoi, or Lung-fish, including the genera Protopterus
from the swamps of Africa, Lepidosiren from the swamps of South
America, and C&ratodus from the Australian rivers, are distinguished
FIG. 246. Lepidosiren parafloxa. Male, showing the feathered pelvic fins of
the breeding season. Much reduced. From Graham Kerr.
for their power of breathing air as well as water. In the case of
Lepidosiren and Protopterus this is necessary, because the swamps
in which they live dry up in the dry season, a time which the
fish pass through buried in the mud, enclosed in air-containing
chambers or cocoons which communicate with the surface by
breathing-pores. . Ceratodus inhabits rivers in which the water turns
foetid at certain seasons of the year from decaying vegetation, and
during this period it breathes air. The air-bladder is bilobed in
Protopterus and Lepidosiren, undivided in Ceratodus ; its walls are
developed into pockets or sacculi, like those of the lungs of land
animals, and the two lobes unite to form a duct which passes
xx]
CIRCULATOKY SYSTEM
505
to the left of the pharynx and opens into it in the mid-ventral
line as in Polypterini. In Ceratodus a similar duct leads from
the undivided sac to the pharynx. But the power of using the air-
bladder to breathe air is one which is shared by the Protospondyli,
the Aetheospondyli, and the Polypterini : the really characteristic
features of Dipnoi are to be found in the modifications of the
vascular system, which resemble closely those found in the
^Poster/or
Carotid
Anterior
Carotid f^ EpibranchiaJ
essds 1-4
FIG. 247. Diagram of the arterial arches of Ceratodus,
viewed from the ventral side,
lowest land animals, the Amphibia, and strongly support the view
that Dipnoi in most points retain the structure of that group of fish
from which land animals were "derived.
Thus we find that the atrium of the heart is divided by a
septum into a large right and a small left auricle, and that whereas
the right auricle receives its blood from the sinus veuosus, the left
receives blood direct from the lobes of the air-bladder, or as we
506 DIPNOI [CH.
shall term them the lungs, by two pulmonary veins. The conus
of the heart is spirally twisted and contains several transverse rows
of pocket valves. In Ceratodus one valve in each row is enlarged
so as to touch one in the next row, and in this way an obliquely
longitudinal valve is foreshadowed, which becomes a definite struc-
ture in Lepidosiren and Protopterus. There is no ventral aorta ;
the afferent branchial arteries, of which there are four or five pairs,
arise in two groups one group from the distal end of the conus,
whilst the hinder group, though becoming distinct at the end of
the conus, really arises from its dorsal surface some distance back.
The longitudinal valve is inserted in such a way that when the free
end is pressed against the wall of the conus the valve covers the
openings of this hinder group of afferents. The efferent arteries
are five in number on each side, each made up of a pair of vessels,
one of which drains the gill on the front of the arch and one the
gill on the back. The spiracle is lost, and the first cleft has a gill
only on its anterior border. In Ceratodus this gill is a "pseudo-
branch," supplied by a branch from the first efferent running
round the ventral edge of the cleft. The vessel which carries the
blood from this gill, as in Teleostei, is a carotid artery (Fig. 247).
In Protopterus, however, this hyoidean gill receives an afferent
vessel from the ventral aorta, and its efferent joins the dorsal aorta.
In this genus and in Lepidosiren there are no gills on the hinder
wall of the hyoidean cleft, on either wall of the next cleft, and
on the front wall of the third cleft, corresponding afferent and
efferent vessels form one continuous "arterial arch." The arteries
supplying the lungs, i.e. the pulmonary arteries, arise from a stem
formed by the junction of the last two or three efferents ; the first
two efferents on each side form a distinct stem opening separately
into the dorsal aorta.
During the contraction of the heart the oblique longitudinal
valve is pressed down so as to close the entrance to the last two
afferent arteries on each side. The valve is so situated that the
blood which pours into the atrium from the sinus venosus is directed
by it to the openings of these last two afferents, and so the bulk of
it is directed to the lung, whilst the blood from the left auricle
which enters the other side of the ventricle is shut off by the valve
from entering the last two afferents, and goes forward to enter the
first two afferents which spring from the anterior part of the conus,
and so through the carotids to the head that passing through
the hyoidean gill receiving a further purification. A very similar
xx]
CIRCULATORY SYSTEM
507
arrangement will be described when we come to deal with Amphibia.
But the resemblance to the vascular system of land animals does
not end here. The blood brought to the kidneys by the renal
portals filters through them, arid emerges into two subcardinal veins
running along the inner sides of the
kidneys. In Ceratodus these two sub-
cardinals are prolonged forwards in the
usual way as two posterior cardinal
veins which enter the ductus Cuvieri,
but a median vein, the vena cava in-
ferior, arises by two forks from the
subcardinals and passes forwards to
enter the sinus venosus of the heart.
In Protopterus and Lepidosiren much
the same arrangement is found, but
the left posterior cardinal has dis-
appeared. Prof. Kerr, to whom more
than to anyone else we owe the eluci-
dation of the anatomy and develop-
ment of these fish, suggests that the
vena cava arose through the long lobe
of the liver touching and effecting an
adhesion with the dorsal wall of the
splanchnocoel in the region of the
kidneys. In this way some of the
blood from the subcardinals can enter
the branches of the hepatic vein, and a
short road was thus provided by which
it could reach the heart, and the en-
largement of this channel formed the
inferior vena cava (Fig. 248).
When we turn to the kidneys and
the generative system, the researches
of Prof. Kerr have brought to light
an interesting series of modifications.
In all three genera the oviduct opens
by a funnel into the coelom, but it is much longer than in most
Osteichthyes. In all three genera kidney ducts and generative ducts
open with the alimentary canal into a cloaca, as in Chondrichthyes.
In Ceratodus the testis is connected with the kidney by a number
of vasa efferentia. These arise from a longitudinal duct running
FIG. 248. Diagram to show ar-
rangement of the principal
veins in a Dipnoan.
1. Sinus venosus gradually
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. Renal
portal= partly hinder portion
of posterior cardinal. 9. Cau-
dal. The hepatio portal
system is omitted.
508
DIPNOI
[CH.
-to
along the testis which acts as a collecting
duct. A quite similar arrangement is
found in the lower Amphibia as well (as
already described) as in Chondrichthyes.
In Lepidosiren the hinder part of the
testis is sterile and consists mainly of this
longitudinal duct with some rudimentary
tubules, and this portion alone is con-
nected with the kidney by five or six vasa
efferentia.
Finally, in Protopterus there is the
same sterile extension of the testis, and
this is connected with the kidney by a
single vas efFerens which joins the neck
of the capsule of one of the kidney
tubules. If vas efFerens and tubules were
simplified into a single wide tube we
should reach the condition of Polypte-
rus, and if this duct were split off from
the archinephric duct and acquired a dis-
tinct opening to the exterior, we should
reach the condition of Teleostei.
The alimentary canal has a spiral
valve, as in other archaic groups of fish.
The brain of Protopterus and Lepido-
siren resembles that of Chondrichthyes
and Amphibia in having definite cerebral
hemispheres with nervous matter all
round, but that of Ceratodus is like the
brain of Osteichthyes in having only a
membranous roof. The opening of the
nasal sac is divided into two as in almost
all Osteichthyes, but the whole sac lies, as
in Chondrichthyes, on the under side of
the snout, and the inner opening is within
the stomodaeum, thus foreshadowing
FIG. 249. Lateral view of the skeleton of Ceratodus mlolepis. After Giinther.
1, 2, 3. Boofing membrane bones. 4. Cartilaginous posterior part of cranium.
5. Pre-opercular (squamosal). 6. Opercular. 7. Suborbital.
8. Orbit. 9. Pectoral girdle. 10. Proximal cartilage of pectoral fin.
11. Pectoral fin. 12. Pelvic girdle. 13. Pelvic fin. 14. Spinal
column. 15. Caudal fin (diphycercal).
vm
or'
XX] SKELETON 509
the choana or posterior nostril of Amphibia. A further resem-
blance to Amphibia is found in the fact that the taste-buds
scattered over the body in all other Pisces are in Dipnoi confined
to the region of the mouth. The eggs of Protopterus and Lepi-
dosiren develop into larvae extraordinarily like the larvae of
Amphibia but with four, not three, feathery external gills on each side
attached to the gill-arches. Traces of these gills remain through-
out life in Protopterus. We see then that Dipnoi present strong
resemblances to Amphibia in the anatomy of their "soft parts,"
and also resemblances to primitive Chondrichthyes, and we shall be
disposed to agree with Prof. Kerr that they are nearly related to
the old group of fish which first migrated from the seas into the
rivers and finally reached swamps liable to dry up, and became in
this way ad^)ted to life on land, and so gave rise to all land
animals. Strange to say, this conclusion has been attacked by
some able zoologists who, basing their conclusions on the skeleton,
regard all resemblances between Dipnoi and Amphibia as deceptive.
We must therefore turn our attention to the skeleton and see how
far these conclusions are justified.
In the backbone of Dipnoi there are no vertebrae. The noto-
chord is surrounded by a thick sheath which as in Chondrichthyes
is transformed into cartilage by the invasion of cells derived from
the cartilage forming the bases of the neural and haemal arches.
These arches are partly transformed into bone, but intercalaries are
absent or vestigial and developed irregularly. Neural and haemal
arches are ossified. There is a diphycercal fin forming a fringe
round the hinder end of the body as in Teleostean larvae and in
Amphibian larvae also and there are no separate anal or dorsal fins.
The paired fins are of the type called biseriate, i.e. they consist of
a jointed axis of pieces of cartilage to which are attached on each
side a series of jointed branches termed rays. Such fins have been
found in the extinct Osteolepidoti and in the extinct Chondrichthyid
P lew acanthus. Such a fin is termed an archipterygium. In
Protopterus and Lepidosiren the axis is developed into a long whip-
like filament, and the rays are vestigial and attached only to the
base of the axis.
In the skull the upper jaw is completely fused with the cranium,
and the teeth in both jaws are amalgamated to form great deutary
plates as in Holocephali. Only a pterygoid bone is developed in the
upper jaw and premaxilla and maxilla are absent. The cranium
is ossified mainly by two great exoccipital bones behind, but
510 DIPNOI
orbitosphenoids are also present (Fig. 250). Of the bony plates
derived from fused teeth there are two pairs which represent the
vomers, and palatine bones are situated on the roof of the mouth.
In the lower jaw there is a membrane bone, the dentary, which
carries on each side another dental plate. But the roofing bones of
the skull consist of two median bones one behind the other, flanked
by a lateral bone on each side, and it appears to be mainly on this
ground as also on the absence of premaxilla and maxilla that rela-
tionship to the Amphibia is denied, because in Amphibia the roofing
bones form a paired series, as in most Osteichthyes, and premaxilla
...-10
FIG. 250. Dorsal (to the left) and ventral (to the right) views of the cranium of
Ceratodus miolepis. After Giinther.
1. Cartilaginous part of the quadrate with which the mandible articulates.
2, 3, 4. Hoofing membrane bones. 5. Nares. 6. Orbit. 7. Pre-
opercular (squamosal). 8. Second rib. 9. First rib. 10. Vomerine
dental plate. 11. Palatine dental plate. 12. Pterygoid. 13. Para-
sphenoid. 14. Interopercular.
and maxilla are present and bear teeth, and the upper jaw, though
fused with the cranium before and behind, and not movable on it,
is not completely fused with it. But of course the most ardent
supporter of the view that Dipnoi are related to the ancestors of
Amphibia would admit that it is a very long time since the two
groups were separated from one another, and that modem Dipnoi
have undergone changes in the meantime. As a matter of fact,
when we examine fish which are regarded as fossil Dipnoi, chiefly
on account of the fusion of their teeth into plates and the shape of
their fins, we find that premaxilla and maxilla are present, and
that the head is covered with numerous roofing bones, the most
XX] MAIN DIVISIONS 511
conspicuous of which form a paired series between which a median
series is beginning to appear (as happens also in Acipenser). We
conclude therefore that these differences between Amphibia and
modem Dipnoi are due to degeneration on the part of the latter
and are not primitive. The gill-arches of modern Dipnoi are simple
rods with at most a single joint, as in Amphibia, and the bones of
the opercular flap are represented by a single bone which strongly
resembles the squamosal in Amphibia in position.
The body is covered with thin scales deeply sunk in the skin.
These scales have a well developed bony layer covered with dentine.
The scales of extinct Dipnoi resembled those of Osteolepidoti in
possessing a superficial layer of pulp-cavities covered with a thin
layer of ganoin. The scales of both recent and fossil fish agree in
having little solid spines covering their margins, not to be con-
founded with placoid denticles such as cover both margins of the
scales of Lepidosteus, Polypterus and some Siluroid fish. Modem
Dipnoi are divided into two suborders, viz. :
(1) Monopneumona, including Ceratodus, characterised by the
undivided air-bladder, the well- developed archipterygial paired fins,
the hyoidean pseudobranch, the complete series of gills, the mem-
branous roof of the brain, and the fact that the young emerge from
the egg like the adult.
(2) Dipneumona, including Lepidosteus and Protopterus, charac-
terised by the bilobed air-bladder, the vestigial paired fins devoid
of fin-rays and resembling filaments the true gill on the hyoid arch
and the reduction of the other gills, the nervous roof to the brain,
the fact that the larvae have external gills and the eel-like form of
the adult.
Before dismissing the Pisces and passing on to consider land
animals, we may endeavour to sum up the general conclusions to
which our study has led us.
The most primitive fish must have resembled in many points
the Chondrichthyes, as for example in possessing no bone and in
having as sole skeleton the placoid denticles. The Chondrichthyes
have been enabled to survive to the present day chiefly by the
development of the oviduct into a womb and the great advantage
which this gives in enabling them to launch their young fully equipped
for the battle of life instead of turning them loose as helpless larvae
as do almost all Osteichthyes. The air-bladder of Osteichthyes
corresponds to the lungs of land animals and from observations on
the development of lungs we are led to regard these as a posterior
512 DIPNOI [CH.
pair of gill pouches the external openings of which have become lost.
In Polypterus> Protopterus and Lepidosiren both lungs are preserved
and, as in land animals, they join a duct which opens into the
pharynx by a median ventral opening. In Ceratodus the opening
is also median and ventral but. there is only one lung. In the other
Osteichthyes, it is probable that only one lung has been preserved
but the opening has become shifted to the mid- dorsal line. Finally
the circumstance that all archaic Osteichthyes use the air-bladder
for respiration leads to the suggestion that the group was evolved in
shallow waters near land and has since re-invaded the sea, gradually
displacing its original inhabitants the Chondrichthyes.
CLASSIFICATION.
Class PISCES.
Sub-class I. CHONDRICHTHYES. Pisces in which the skeleton is
formed of cartilage strengthened by deposits of calcareous matter
but in which no true bone is developed. The skin is protected only
by placoid denticles composed of dentine. There is no air-bladder,
the nostril is undivided and the eggs are few and large, a large part
or the whole of development being completed before laying.
Order I. Elasmobranchii. Chondrichthyes in which there is
no common gill-cover or operculum, in which the skin is covered
with placoid denticles and in which the upper jaw, though it may
articulate directly with the skull, is not fused with it. The noto-
chordal sheath is segmented into distinct centra.
Sub-order 1. Selachoidei. Active free-swimming Elasmo-
branchii with cylindrical or spindle-shaped bodies in which the gill-
slits are placed above the level of insertion of the pectoral fin which
is of moderate size and not joined to the skull.
Ex. Hexanchus, Heptanckus, Heterodontus (Cestracion), Scyl-
lium, Squalus, Galeus.
Sub-order 2. Batoidei. Sluggish bottom-living Elasmo-
branchii with flattened bodies. Openings of the gill-slits situated
on the ventral surface beneath the insertion of the pectoral fin which
is of great size and the front end of which is joined to the skull,
Ex, Raia t Trygon, Pristis.
XX] CLASSIFICATION 513
Order II. Holocephali. Chondrichthyes in which there is an
opercular flap springing from the hyoid arch and covering the gill-
slits, in which the skin is naked, the placoid scales being restricted
to the frontal tentacle of the male and to spines in front of the
unpaired fins. The upper jaw is fused with the skull and the noto-
chordal sheath is not divided into centra.
Ex. Ckimaera, JRhinocMmaera, Harriotta, Cattorhynchus.
Sub-class II. OSTEICHTHYES. Pisces in which true bone is
present, at least in the form of dermal plates covering the head, and
of flat scales covering the body and connecting together the bases
of the placoid denticles if these are present. Bone is also present
in every case as a partial or complete investment of the cartilage
of the skull. An air-bladder is developed as an outgrowth of the
alimentary canal behind the gill region. The septa between the
gill-sacs are narrowed so that these become mere slits and a gill-
cover or operculuin is developed from the hyoid. The nostril is
divided into two openings, the eggs are small and the young
emerge from them as larvae which undergo a long period of
development before becoming adult.
Order I. Teleostei. Osteichthyes in which the notochord is
surrounded and obliterated by bony amphicoelous centra developed
from the connective bone outside the proper notochordal sheath.
Between the centra the notochord persists. . No intercalary arches
are developed. The cartilage of the skull is covered by and largely
replaced by bone and in particular a large median supra-occipital
bone is always developed. The upper jaw is amphistylic articulating
with the skull in front and supported by the hyoid behind. No
splenial bone is developed in the lower jaw and there are no clavicles
in the pectoral girdle. The tail is homocercal. The optic chiasma
in the brain is resolved into two distinct nerves. The conus is
amalgamated with the ventricle, and only one transverse row of pocket
valves persists. There is no special valve in the intestine. The
testis has a special duct opening by a special pore and in both sexes
excretory ducts, genital ducts and alimentary canal open to the
exterior by separate apertures.
Sub-order 1. Clupeiformes. Teleostei in which the pelvic
fins are abdominal in position, the air-bladder has an open duct, the
coracoid develops a mesocoracoid branch and in which there are no
hard spines in the fin rays. The maxilla bears teeth and forms
part of the gape,
S. & M. 33
514 PISCES [CH.
Family 1. Clupeidae. Clupeiformes in which the oviduct is
continuous with the ovary, air-bladder penetrates the skull and
there are no adipose fins.
Ex. Clupea, Engraulis.
Family 2. Salmonidae. Clupeiformes with short oviducts with
wide funnels, air-bladder normal. An adipose fin behind the dorsal.
Ex. Salmo, Salvelinus, Coregonus, etc.
Sub-order 2. Anguilliformes. Teleostei devoid of pelvic fins,
and in which the pectoral girdle is disconnected from the skull.
Air-bladder with open duct. No mesocoracoid and no hard spines in
the fins. The premaxilla is lost, the maxilla if present bears teeth.
Ex. Anguilla.
Sub-order 3. Ostariophysi. Teleostei with abdominal pelvic
fins and an open duct to the air-bladder. With a " Weberian chain "
of ossicles connecting air-bladder and skull. A mesocoracoid is
present.
Family 1. Cyprinidae. Ostariophysi in which the skin has
normal thin cycloid scales. There is an interorbital septum and
the symplectic is present. The maxilla does not bear a barbel.
Ex. Cyprinus.
family 2. Siluridae. Ostariophysi in which the skin is naked
or covered with ganoid scales beset with placoid denticles. The
cranial cavity extends between the eyes, the symplectic bone is
absent. The maxilla is toothless and carries a long barbel.
Ex. Amiurus.
Sub- order 4. Haplomi. Teleostei with abdominal pelvic fins
and an open air duct to the bladder. No mesocoracoid and no
Weberian chain.
Family. Esocidae. Supra-occipital separates the parietals.
Ovaries and oviducts continuous with one another.
Ex. Esox.
Sub-order 5. Percesoces. Teleostei in which the pelvic fins
are close behind the pectoral fins but not attached to the cleithra.
The duct of the air-bladder is closed.
Family. Mugilidae. Percesoces in which the pelvic bones are
attached to the postcleithra.
Ex. Mugil.
XX] CLASSIFICATION 515
Sub-order 6. Percomorphi. Teleostei in which the pelvic
bones are attached to the cleithra and in which the fins are conse-
quently thoracic or jugular in position. The duct of the air-bladder
is closed. Hard spines are developed in dorsal and anal fins and the
skeleton of the pelvic fin usually consists of one spine and not more
than five soft rays.
Family 1. Percidae. Percomorphi in which the dorsal fin is
split into two fins, the front one alone having spines.
Ex. Perca.
Family 2. Centrarchidae. Percomorphi in which the dorsal fin
is undivided.
Ex. Micropterus.
Family 3. Serranidae. Percomorphi in which the dorsal fin is
undivided and in which a .shelf supporting the eye- ball is developed
from one of the circumorbital bones.
Ex. Serranw.
Family 4. Mullidae. Percomorphi with undivided dorsal fin
and with a shelf for the eye-ball but with vestigial teeth and long
gill rakers.
Ex. Mullus.
Family 5. Sparidae. Percomorphi with undivided dorsal fin
and a shelf for the eye-ball ; the teeth are large, cutting in front,
crushing at the sides.
Family 6. Labridae. Percomorphi with undivided dorsal fin,
no shelf for the eye-ball ; the lower pharyngeal bones fused to form
a single plate.
Family 7. Scombridae. Percomorphi with a few feeble spines
in the dorsal fin and series of finlets behind the soft dorsal.
The body is attenuated behind forming a stalk for the large caudal
fin.
Ex. Scomber, Thynnus.
Sub-order 7. Heterosomata. Teleostei which habitually swim
lying on one side in which both eyes are twisted on to the upper
side of the head. Pelvic bones articulate with the cleithra, the air-
bladder is lost. No hard spines are developed in the fins (except
in one genus, Psettodes).
Ex. Hippoglossus, Plewronectes, Psetta, Psettodes, 8olea.
332
516 PISCES [CH.
Sub-order 8. Gadiformes. Teleostei in which the pelvic fins
are attached to the cleithra and are jugular in position, and in which
the duct of the air-bladder is closed. No hard spines are developed
in any of the fins and the primitive caudal fin is lost and replaced
by a new caudal developed from portions of the anal and dorsal fins.
A remnant of the cranial cavity persists above the interorbital
septum in which the long stalks of the olfactory lobes lie.
Ex. Gadus, Merlucius.
Order II. Aetheospondyli. Osteichthyes in which the noto-
chord is surrounded and entirely suppressed by the formation of
opisthocoelous centra with well developed articulating surfaces.
The articulating surfaces are developed out of dorsal and ventral
intercalary cartilages which become ossified. No supra-occipital
bone in the skull which is otherwise well ossified. The jaws are long
and the maxilla represented by a series of bones. The upper jaw
articulates with the skull behind the orbit but is still supported by
hyomandibular and symplectic. Splenial and supra-angular bones in
the lower jaw The tail fin a rounded lobe, the body is covered
with ganoid scales beset with denticles forming fulcra on the anterior
border of the tail fin. The conus is distinct in the heart and the
optic chiasma in the brain. Ovary and oviduct are continuous and
the testis discharges through the kidney by vasa efferentia. A
spiral valve on the intestine. Air-bladder opens into pharynx in
mid-dorsal line.
Ex. Lepidosteus.
Order III. Protospondyli. Osteichthyes in which dorsal and
ventral intercalaries are present and join to form archless pre-
centra at least in the tail region, the arch-bearing postcentra being
formed from a ring connecting neural and haemal arch-pieces
(basidorsals and basiventrals). Both pre- and postcentra are am-
phicoelous. No supra- occipital in the skull which .is otherwise
well ossified. The jaws are short, the maxilla is a single tooth-
bearing bone. Splenial bone in lower jaw. A single gular plate
on the under side of the throat. Tail fin a rounded lobe, body
covered with thin cycloid scales. The conus distinct in the heart
and the optic chiasma in the brain. Oviduct short, opening into
coelom by a wide funnel. Testis discharging through the kidney
by vasa efFerentia. A spiral valve on the intestine. Air-bladder
opens into pharynx in mid-dorsal line.
Ex. Amia.
XX] CLASSIFICATION 517
Order IV. Chondrostei. Osteichthyes in which dorsal and
ventral intercalaries are present as well as neural and haemal
arches but in which no centra are found, the notochord being per-
sistent arid surrounded by an unsegmented cartilaginous tube.
Few or no cartilage bones present in the cranium, jaws feeble and
toothless connected to the skull only by hyoid. Numerous dermal
bones on the head and the pectoral girdle. Clavicles present
between the cleithra. Tail fin heterocercal with a row of fulcra on
anterior lobe. Conus distinct in heart, optic chiasma in brain.
Oviduct short and opening by a wide funnel into the coelom, testis
discharging through kidney by vasa efferentia. 'Air-bladder opens
into pharynx in the mid- dorsal line.
Family 1. Polyodontidae. Skin naked or with vestigial scales
deeply embedded.
Ex. Polyodon, Psephurus.
Family 2. Acipenseridae. Skin covered with five longitudinal
rows of bony scutes.
Ex. Acipenser, ScapMrhynchus.
Order V. Polypterini. Osteichthyes in which the notochord
is surrounded and partly obliterated by amphicoelous bony centra
resembling those of Teleostei. Both dorsal and ventral ribs
present. Skull well ossified but devoid of supra-occipital bone. A
splenial in the lower jaw and a pair of gular plates on the throat.
Spiracle persistent and covered with a special cover formed from
the postorbital bone. Clavicles present in pectoral girdle, pectoral
fin with a median scaly lobe. The skin covered with ganoid scales
beset with placoid denticles. A diphycercal tail fin. Conus distinct
in heart and optic chiasma in brain. Oviduct short, opening by a
wide funnel into coelom. Testis with special duct joining kidney
duct near its external aperture. A spiral valve on intestine. Air-
bladder bilobed and opening on ventral side of pharynx.
Ex. Polypterus, Calamoichthys.
Order VI. Dipnoi. Osteichthyes in which there are intercalary
pieces but no centra, the notochord being surrounded by an un-
segmented cartilaginous sheath. Few cartilage bones in skull, a
median series of dermal roofing bones. The upper jaw fused with
cranium, no premaxilla or maxilla. A diphycercal tail, body covered
with thin cycloid scales, paired fins typically long and biseriate.
518 PISCES [CH. xx
Conus distinct in heart with a spiral longitudinal valve, atrium
divided into right and left auricles, an inferior vena cava present
and pulmonary veins returning blood from air-bladder to heart.
An optic chiasma in brain. Oviduct opens by a funnel into coelom.
A spiral valve on intestine, air-bladder opens in mid-ventral line of
pharynx.
Family 1. Monopneumona. Air-bladder undivided, young
without external gills.
Ex. Ceratodus.
Family 2. Dipneumona. Air-bladder bilobed, young with
external gills.
Ex. Protopterus, Lepidosiren.
CHAPTER XXI
SUB-PHYLUM IV. CRANIATA
DIVISION II. GNATHOSTOMATA
SUB-DIVISION I. ANAMNIA
Class II. AMPHIBIA
THE class Amphibia includes the familiar Frogs and Toads, the
less known Newts and Salamanders, and some very
curious worm-like tropical forms which burrow in
the earth. The name means double life (Gr. d/i^f,
double ; fitos, 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 born in a condition differing 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 sufficient to
mark them off from the fish. But we have already seen that the
older orders of Bony Fish use their air-bladders as lungs to assist
in respiration, 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 horny rays, as well as an internal skeleton ; and the
paired fins have an internal skeleton which has the form of a jointed
axis bearing similar rays on one or both sides (Figs. 224 and 249).
520
AMPHIBIA
[CH.
The Amphibian limb, on the other hand, is what is known as a
pentadactyle limb ; that is to say, it is constructed on the familiar
type of the human limb, and the median fin when present has no
fin-rays (Figs. 251 and 253).
The pentadactyle or five-fingered limb (Gr. TreWe, five ;
a finger), also called the cheiropterygium (Gr. \tip, a hand;
yiovj 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 antebrachium
or fore-arm, and the
man us or hand (B, Fig.
251). 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. 251).
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 ;
FIG. 251. A. Skeleton of a right posterior,
B. skeleton 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. Centrale of tarsus. 8. Tarsale 1.
9. Tarsalia 4 and 5 fused, i, n, HI, iv,
V. Digits. 10. Humerus. 11. Eadius.
12. Ulna. 13. Badiale. 14. Intermedium
and ulnare fused. 15. Centrale of carpus,
the pointing line passes across carpale 2.
16. Carpale 3. 17. Carpale 5.
XXI] SKELETON OF LIMBS 521
those of the antebrachium are called radius and ulna, those of
the crus tibia and fibula (Fig. 251).
The skeletons of the pes and manus 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 radiale and ulnare and
in the ankle a tibiale and fibulare. Distal to this row of bones
there is a single central bone which probably belongs to the middle
ray, and still more distally situated a row of five small bones cor-
responding to the digits. This last row are denominated carp alia
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
undergone some modification, owing either to the absence of some
bones or the fusion of others, but in the hind-limb of the lower
Amphibia it is exactly typical. In the higher Amphibia not only
has great reduction of the elements taken place but the radius and
ulna 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 in such a
position that a line joining the tips of the fingers is parallel to the
long axis of the body. If we suppose an imaginary line or axis to
run down the centre of each limb, we shall be able to distinguish a
pre-axial from a postaxial side. In the lower Amphibia the only
change from this position that has taken place in the hind-limb is
that each segment of the limb is bent at right angles on the one
which follows it. The fore-limb is bent similarly, but it is also
rotated backwards so that its upper segment is almost parallel to
the axis of the body, and the elbow points backwards. If this
position were maintained the first digit would become external; but
the manus in most cases is at the same time twisted forwards so
that the lower end of the radius lies internal to that of the ulna,
and the radius thus crosses the ulna in its course. In the higher
Vertebrata this twisting can be undone and the hand reverted to
522
AMPHIBIA
[CH.
an untwisted position. This movement is known as supination,
the reverse movement being known aspronation.
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 Osteichthyes, 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. 252). It is
necessary for this purpose that the limb should
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 Gnathostomata Fishes, Amphibia,
Reptiles, 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 cells
lining these pouches have the power of secreting
great quantities of mucus. As the cells become
FIG. 252. Skeleton of
Triton, Molge cris-
tata x 1.
XXlJ AXIAL SKELETON 523
broken up into mucus, new cells take their place, being budded off
from the underlying Malpighian layer just as are the horny cells.
These pouches are known as dermal glands.
The skull and brains are very characteristic, 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, and, as in Dipnoi, have a roof
consisting of nervous matter, whereas the cerebellum, usually so
large in fishes, is reduced to a mere band (Fig. 263).
The skull always articulates by two pegs the occipital con-
dyles with the first vertebra (Fig. 255). 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 (Gr. irpo, in front; KoiAos,
hollow), or opisthocoelous (Gr. oVio-0o-, behind), that is to say either
concave in front and convex behind, or vice versa, and the arrange-
ment may differ in allied genera, while amphicoelous. vertebrae also
occur.
The vertebrae articulate with one another, not only by the
centra but also by facets called zygapophyses (Gr. vyoV, a yoke),
on the sides of the neural arches. The anterior facets, prezygapo-
physes, look upwards and are covered by the posterior facets or
postzygapophyses of the vertebra in front, which look downwards.
The circulatory system closely resembles that of the Dipnoi.
The atrium is divided into two auricles, and the blood from the
lungs returns direct to the left auricle by the pulmonary veins. A
median vein, 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 stem, the laryngeal chamber, into
the throat. The opening is called the glottis, and its sides are
stiffened with cartilage.
The kidneys and reproductive organs show essentially the same
arrangement as in the Elasmobranchs, the kidney being divided into
a sexual part connected with the testis and a posterior non-sexual
part. There is one opening for all ejecta, the cloaca.
524 AMPHIBIA [CH.
The ventral wall of the cloaca, however, is produced outwards
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, supplied
by the 5th and 10th nerves, but these are usually lost in the adult.
Living Amphibia are divided into three well-marked orders,
viz. the URODELA, the ANURA and the APODA. The
URODELA (Gr. ovpd, tail ; S-fjXos, 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. dv-, 110 ; 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-j no, : TTOVS, TroSo's, a foot) 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 fish-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 STEGOCEPHALA
(Gr. ore/OS, a roof ; KaX->j, the head) from 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 bones or scales are found on the ventral
surface. These features show resemblances to what is found in
Dipnoan fish from which Amphibia are 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 Labyrinthodonta
became highly specialised in the structure of their teeth and
died out in the next geological period, others, in all probability,
gave rise to modern Amphibia.
Order I. Urodela.
Returning to the Urodela, which are the most primitive of
modern Amphibia, we find that in Great Britain they are represented
XXI]
URODELA
525
by three species, all belonging to the genus Molge (Triton) and
popularly known as Efts or Newts. Molge cristata, the Warty Eft,
and Molge vulgaris, the Common Eft, are found in ponds and
ditches all over the country, but Molge palmata is much more local.
We may select Molge cristata, the Greater or Warty Eft, or Crested
Newt, as a type of the anatomy of Urodela (Fig. 253).
The animal is about five or six inches long, half the length being
made up of the tail, which has a continuous fringe of skin, the
median fin. This fin 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 fin-rays.
FIG. 253. Molge cristata, the Warty Eft. From Gadow.
1. Female. 2. Male at the breeding season with the frills well developed.
The skin is clammy, owing to the secretion of the dermal glands :
it is dark coloured above and yellow spotted with black below. The
opening of the cloaca is placed behind the hind-legs: it is a
longitudinally placed oval slit which in the male has thickened lips.
The fore-limbs have only four fingers, 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 swims actively in the water by means of its vertically flattened
tail. The head is flattened dorso-ventrally and of somewhat oval
outline, and the gape is of moderate extent. 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
526
UKODELA
[CH.
jaw will be seen to throb at regular intervals, being alternately
puffed 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 puffed
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 openings called
Fio. 254. Diagram illustrating three stages in the development of the vertebral
column of an Opisthocoelous Urodela.
A. Stage in which basidorsals, basiventrals and intercalaries are separate.
B. Stage in which basidorsals and basiventrals have united with one another
and in which the intercalaries have united to form an intervertebral pad of
cartilage in which a synovial cavity is just appearing. This stage is per-
manent in some Urodela.
0. Stage in which the vertebrae are complete.
1. Basidorsal. 2. Notochord. 3. Basiventral. 4. Dorsal inter-
calary. 5. Ventral intercalary. 6. Synovial cavity. Dotting,
cross-hatching, etc. as in Figs. 232 and 242.
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 the open
glottis into the lung, whence it is forced out again by the elastic
recoil when the pressure is removed.
XXl] RESPIRATORY MUSCLES 527
If the animal be laid on a board with the ventral side uppermost
and skinned, a thin sheet of muscles, the mylohyoid, 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 mylohyoid (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. 256). These muscles are called geniohyoid in front of the
arches, stern ohyoid 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 sternohyoid muscles can draw the visceral arches
downwards and backwards and probably assist the mylohyoid in
depressing the floor of the mouth. The geniohyoid 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 petrohyoid, 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 (see p. 457),
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 muscles
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 thej mouth opens the glottis
and admits air into the lungs.
How these muscles co-operate to effect the regular pumping of
air in and out of the lungs has been thoroughly investigated only
in the case of the Frog, and will be described when we come to
deal with that animal.
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-shaped myotomes, but this arrangement is disturbed in
the neighbourhood of the limbs.
Turning now to the skeleton we find that the vertebrae bear
stout transverse processes with which are articulated
short ribs (Fig. 252). The ribs borne by the sacral
528 UEODELA [CH.
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 pairs
of arch-pieces ; but of these only the basidorsals and the basi-
ventrals become ossified at first, and joining together form the bulk
of the vertebra, each basidorsal, as in fish, becoming connected with
the basiventral belonging to the myotome in front, while the dorsal
and ventral intercalaries, although likewise fusing together, remain
cartilaginous and form the intervertebral cartilage. This either
remains continuous and owing to its flexibility acts as a joint,
or it becomes More or less separated into two portions which
articulate TO&h one another, one forming a cup and the other a ball.
Joints in wbi(!h the cup belongs to the posterior end of the vertebrae
are called opisthocoelous, e.g., in Desmognathus triton, bu^he most
frequent form of joint is one in which the ball forms the posterior
and the cup the anterior portion of the vertebra. Such vertebrae
are said to be procoelous. The portions 6i the intervertebral
cartilage eventually become ossified and joined to the previously
formed centrum. When the intervertebral cartilage does not form
a joint but remains soft, the bony vertebrae in the dried skeleton
appear to have the form of an hour-glass with cups at both sides
to be in fact amphicoelous, but they differ fundamentally from the
amphicoelous vertebrae of Teleostei in that in these fish a portion
of the notochord persists between two adjacent vertebrae, whereas
in Urodela the notochord is obliterated between two successive
vertebrae. The basiventrals of the tail vertebrae form long
haemal arches.
In the trunk the basiventrals appear only in young larvae ; in
the adult they disappear so that the bulk of such vertebrae is formed
only by the pair of basidorsals to which the ribs become secondarily
attached by the formation of an outgrowth from the basidorsal
termed the tubercular process (Fig. 254).
It is of importance to note that in many of the extinct
Stegocephala, e.g., Archegosaurus, the caudal vertebrae were repre-
sented by four pairs of distinct arch-pieces, viz. basidorsals, basi-
ventrals, and dorsal and ventral intercalaries, while the trunk
vertebrae consisted of three separate pairs of pieces, namely the
basidorsal, the dorsal intercalary, and the basiventral ; but that in
the typical Labyrinthodonts, the highest of the Stegocephala, all
these constituent pieces were united into solid vertebrae ; lastly,
that in some of the lowest, e.g., in Branchiosaurus, each vertebra
VERTEBRAL COLUMN
529
xxi]
consisted of a thin shell of bone surrounding the chorda, and
composed of the basidorsals and basiventrals, which met each
other, forming a broad-based section along the side of the vertebra,
both parjbaking in the formation of a transverse process which
"carried the rib. It is of course possible and even probable that
in these extinct forms dorsal and ventral intercalaries were present,
FIG. 255. A. dorsal, B. ventral, and C. lateral view of the skull of a Newt,
Molge cristata x 2. After Parker.
The cartilage is dotted, the cartilage bones are marked with dots and dashes,
the membrane bones are left white.
1. Premaxilla. 2. Anterior nares. 3. Posterior nares. 4. Nasal.
5. Frontal. 6. Parietal. 7. Prefrontal. 8. Maxilla. 9. Fused
vomer and palatine. 10. Parasphenoid. 11. Orbitosphenoid.
12. Pterygoid. 13. Squamosal. 14. Pro-otic region of fused exoccipital
and pro-otic. 15. Quadrate. 16. Calcified cartilage forming the
articular surface of the quadrate. 17. Exoccipital region of fused
exoccipital and pro-otic. 18. Articular. 19. Articular cartilage.
20. Dentary. 21. Splenial. 22. Middle narial passage, a cleft in
the cartilage of the snout filled with connective tissue. n, v, vn, ix, x.
Foramina for the exit of cranial nerves.
forming intervertebral cartilages which were not ossified, for as we
have just seen this state of affairs is found in some living Urodela.
The haemal arches of the tail are, like the ribs, outgrowths of the
basiventrals, but they do not exactly correspond to the ribs, for they
are placed nearer the middle line.
S. & M.
34
530 URODELA [CH.
In the skull the cranium is cylindrical, being quite uncom-
pressed between the eyes. The bones of the jaws and face are
widely arched outwards, so that the whole skull has a flattened
shape. The nasal and auditory capsules form easily recognisable
buttresses projecting from the cranium.
In both the floor and roof of the cartilaginous cranium the
proper wall is largely deficient. The deficiency of the roof is the
anterior fontanelle, that of the floor the greatly enlarged pituitary
fossa. But these deficiencies are not seen in the uninjured skull,
because the hole in the roof is closed in by two pairs of dermal
bones, the frontals and the parietals, and that in the floor is
underlaid by a broad parasphenoid dermal bone (Fig. 255).
Only at its extreme front and hind ends is the wall of the cranium
converted into cartilage bone. In front there is on each side an
orbi to sphenoid bone, in the side wall, extending into the roof
and floor and ossifying also the hinder wall of the nasal sac ; behind,
two exoccipital bones are placed at the sides of the foramen
magnum, which they nearly encircle (Fig. 255). These bones bear
the two condyles, so characteristic of Amphibia, for articulation
with the vertebral column. There is no basi-occipital ossification,
and in this point again Amphibia resemble Dipnoi.
The first visceral arch, which constitutes the cartilaginous jaws, is
almost entirely cartilaginous. It consists of an upper part immov-
ably attached to the skull, corresponding to the pterygoquadrate
bar 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 resemble Holocephali and Dipnoi in this point. If we
call this condition autostylic we do not do justice to the full extent
of the resemblance between Dipnoi and Amphibia, for the jaw in
the Notidanidae, which is movably articulated with the cranium,
is also said to be autostylic. The name holostylic has been
proposed for the condition of immovable junction between the
cartilaginous upper jaw and the cranium, and this name we shall
adopt. 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 lower 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 calcified. They are de-
nominated quadrate and articular in Fig. 255, but there is no
true bone present in either case. The front of the auditory capsule
XXI]
SKULL
531
is ossified by a large bone, the pro-otic, which in fully adult
specimens becomes confluent with the exoccipital. The hinder
visceral arches in the adult are present in a very degenerate con-
dition. Traces of three remain (Fig. 256).
It is usual to speak of the hinder visceral arches of Amphibia
and higher Vertebrataas the hyoid apparatus, or simply as the
hyoid. The name suggests a misleading comparison with the
second visceral arch of Fish ; it is distinctly to be remembered 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 dermal bones of
the skull, we find that it is roofed by
three pairs, viz., the nasals, frontals
and parietals. The nasals, of course,
roof in the nasal sacs. In the palate
there is one median bone, the para-
sphenoid, and three pairs of lateral
bones, viz., the vomers in front of the
posterior nares, the palatines fused
with them and running along the edges
of the parasphenoid, and lastly the
pterygoids underlying the pterygoid
process. Some of these bones are
actually built up by the formation of a
network of bone around the bases of
minute conical teeth in the larva. The vomers and palatines
retain their teeth in the adult, whilst the parasphenoid loses them,
but in other genera of Urodela the parasphenoid may retain its
teeth throughout life. When we were describing the skull of a
Teleostean fish, bones named palatine and pterygoid (viz., ecto-
pterygoid, entopterygoid and metapterygoid) were mentioned, but
these were regarded as cartilage bones, i.e., as bones which arise
in the connective tissue surrounding cartilage, and which sub-
sequently eat into the cartilage, destroy it, and replace it.
Dermal bones, on the contrary, as the name implies, arise in
the dermis or the connective tissue underlying the ectoderm. Now
there is one situation where the dermis teuds.to become the "peri-
chondrum," or connective tissue surrounding cartilage, and that
is the stomodaeum or buccal cavity, whose lining membrane tends
to be tightly stretched over the supporting visceral arches. Hence
342
FIG. 256. Visceral arches of
Molge cristata. The ossified
parts are slightly shaded, the
cartilage is white. From
Parker.
2. Hyoid arch. 3. First
branchial arch. 4. Second
branchial arch. 8. Copula,
i.e. the median piece connect-
ing successive arches.
532
URODELA
[CH.
bones originally dermal bones, like the pterygoid and palatine
bones in Urodela, in more completely ossified animals, such as the
Teleostei (and as we shall presently see in the higher Amphibia
also), have begun to eat into the subjacent cartilage and thus to
deserve the name of cartilage bones.
The upper lip has tooth-
bearing premaxillary and
maxillary bones developed,
the lower has a dentary on
the outside of Meckel's car-
tilage and a splenial on the
inner. Above the maxilla there
is a small prefrontal bone.
If we examine the skeleton
of the limbs we find that
the pectoral girdle consists of
two plates of cartilage which
slightly overlap in the mid-
ventral line. The lower half
of each is forked, the forks
being called precoracoidand
coracoid respectively. The
centre of each half of the
girdle has a hollow termed the
glenoid cavity for the articu-
lation of the arm. All around
the glenoid cavity the girdle
is converted into bone ; there
is a bone termed the scapula
above, and a coracoid bone
below. The un ossified part
FIG. 257. A. ventral, and B. lateral view c , u -,
of the shoulder girdle and sternum of of the coracoid IS Simply
an old male Crested Newt, Molge cris- termed the coracoid carti-
tata x 3. After Parker. , m i . ,
lage. The upper part of the
3. Cora-
coid. 6. Sternum. bone is called the supra-
scapula. It remains carti-
laginous, but is often calcified. The two coracoids are fastened
behind to a small median cartilage called the sternum. The
meaning of this will be discussed later.
The manus has only four fingers, the thumb and the cor-
responding small bone in the wrist or carpus having disappeared
XXI]
INTERNAL ORGANS
533
and the ulnare and intermedium being
distinct in the larva (Fig. 258, A). Other-
wise the limb corresponds to the scheme
given in the beginning of the chapter.
The pelvic girdle on each side is
firmly 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. 259).
In the pes the only departure from the
typical arrangement is the fusion of
the tarsalia 4 and 5.
If the muscles be carefully cut
through in the middle line
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 re-
lative 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 the
latter is nearly straight, extending only
a short way round the bend of the first
loop. There is a well-marked large in-
testine or rectum, ventral to which
lies the bladder. The spleen is an
oval red body lying at the side of the
stomach arid attached to the mesentery.
fused, although they are
A B
FIG. 258. A. Eight antebra-
chium and manus of a larval
Salamander, Salamandra
maculosa. After Gegenbaur.
B. Right tarsus and adjoining
bones of Molge sp. After
Gegenbaur.
1. Radius. 2. Ulna. 3. Bad-
iale. 4. Intermedium.
5. Ulnare. 6. Centrale.
7. Carpale 2. 8. Carpale 3.
9. Carpale 4. 10. Carpale
5. 11. Tibia. 12. Fibula.
13. Tibiale. 14. Intermed-
ium. 15. Fibulare.
16. Centrale. 17. Tarsale 1.
18. Tarsalia 4 and 5 fused.
i, n, m, iv, v. Digits.
FIG. 259. Pelvic girdle of Molge
cristata from below x 4.
1. Epipubis. 2. Ischiopubic
cartilage. 3. Ilium. 4. Is-
chium.
534.
URODELA
[CH.
The ducts of the pancreas and liver coalesce into a common stem
before opening into the intestine.
The newt feeds on small worms and aquatic insects, which it
Fia. 260. A male Molge cristata cut open so as to expose the internal organs,
about natural size.
1. Mylohyoid muscle with geniohyoid underneath. 2. Conus arteriosus.
3. Ventricle. 4. Auricle. 5. Sinus venosus. 6. Carotid arch.
7. Systemic arch. 8. Pulmonary artery. 9. Anterior vena cava of left
side. 10. Goracoids pulled outwards. 11. Liver. 12. Gall-bladder.
13. Lung. 14. Spleen. 15. Stomach. 16. Intestine. 17. Bectum.
18. Allantoic bladder. 19. Fat-body. 20. Testes. 21. Anterior
abdominal vein, displaced. 22. Kidney with duct. 23. Pancreas.
XXI] CIRCULATORY ORGANS 535
seizes with its jaws. Both upper and lower jaws are armed with
minute teeth, and there are in addition two longitudinal rows of
teeth on the roof of the mouth borne by the conjoined vomer and
palatine 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
divisions of the piscine heart are visible, viz., sinus
venosus, atrium, ventricle, conus. The venous system
is essentially that of the Dog-fish, only the veins are indicated by
names borrowed from human anatomy. Thus the blood from the
head is returned by two internal jugular veins, representing the
anterior cardinals of the fish. These are joined by external
jugulars from the superficial part of the throat and face and by
a subclavian vein from each arm. The common trunk formed
by the union 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 made out. The two renal portals when followed
further back are found to coalesce in the caudal vein which
returns the blood from the tail: each receives a sciatic vein from
the dorsal 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, which are represented only
by the small pelvic vein in fishes.
There 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
and constitutes the left auricle; secondly, the inferior vena
cava, a large trunk situated in the median dorsal line just beneath
the aorta, which receives most of the blood that has traversed the
kidneys and conveys it into the sinus venosus just between the
536
URODELA
[CH.
openings
of the two superior venae cavae. The inferior cava
coalesces with the hepatic veins
returning blood from the liver :
these thus lose their independent
openings into the sinus venosus
which they had in the Dog-fish.
In its hindermost portion between
the kidneys the vena cava pins
the subcardinal veins, i.e. the
collecting trunks formed by the
blood which has percolated
through the kidneys from the
renal portal, and which open into
the posterior cardinal veins in
front.
So far the peculiarities of the
newt are shared by the Dipnoi :
but there remain two veins highly
characteristic of Amphibia. The
musculocutaneous 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 an-
terior abdominal vein arises on
the ventral side of the body near
the cloaca from the union of two
forks given off by the femoral
veins ; it runs forward 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 respira-
tion ; it has been compared to the lateral veins of Chondrichthyes
(see p. 463) which are supposed to have become shifted inwards
towards the mid- ventral line and to have partly coalesced.
When the veins are cut away it is possible to follow out the
arteries. There is no ventral aorta, since on each side three arterial
arches arise in a bunch from the front end of the tubular conus.
10
FIG. 261. Diagram to show arrange-
ment of the principal veins of an
Urodele.
1. Sinus venosus, gradually disappear-
ing in the higher forms. 2. Ductus
Cuvieri = superior vena cava. 3. In-
ternal jugular = anterior cardinal
sinus. 4. External jugular =
sub-branchial. 5. Subolavian.
6. Posterior cardinal, front part.
7. Inferior vena cava. 8. Renal
portal = hinder part of posterior car-
dinal. 9. Caudal. 10. Sciatic.
11. Femoral. 12. Anterior ab-
dominal.
XXI]
CIRCULATORY SYSTEM
537
-14
The first of these is called the carotid arch, and is derived from
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
arch. 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 (Fig.
262). The fifth arch dis-
appears in Molge, as in all higher Vertebrates, but it is retained
throughout life in the allied genus Salamandra. From the sixth
arch is given off the pulmonary artery which supplies the lung. On
this account it is called the pulmonary arch. The subclavian
FIG. 262. Diagram of arterial arches of Molge,
viewed from the ventral aspect.
i, n, in, rv, 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. Coeliacomesenteric.
53S
URODELA
[CH.
1
Nervous
system.
artery to the fore-limb on either side is given off just where the
systemic arch unites with its fellows to form the dorsal aorta: hence
it will be seen that this subclavian is of the dorsal type (p. 343).
Each subclavian gives off a large branch to the other breathing organ,
the skin, which is known as the cutaneous artery.
It is comparatively easy to un-
cover the brain and
spinal cord of the
newt owing to the
thinness of the bones which cover
them. The cerebral hemispheres
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 slight inconspicuous
transverse band (Fig. 263).
The olfactory lobe of Amphibia
differs from that of Chondrichthyes
and Gadiformes among Pisces in
being separated from the cerebrum
only by a slight constriction. From
its anterior end a brush of nerve
fibres is given off which goes to the
nasal sac. These constitute the ol-
factory nerve. The stalk connecting
the olfactory lobe and the cerebrum
is unrepresented in the Amphibia.
The course of the cranial nerves
is substantially the same as in the
Dog-fish; owing, however, to the
loss of the gills and the mucous
canals in the adult, the branches are
simplified. The 9th or glosso-pharyngeal, as its name implies, is
distributed to the pharynx and tongue. The vagus supplies the
larynx and glottis, but its main stem runs on to the heart and
stomach.
Fm. 263. Brain of Triton, Molge
cristata x about 8.
1. Olfactory nerves, representing
the olfactory lobes of the Dog-
fish. 2. Olfactory lobes.
3. Cerebral hemisphere. 4. Thin
roof of thalamencephalon. 5.
Optic thalami. 6. Pineal body.
7. Mid-brain. 8. Cerebellum.
9. Medulla oblongata. From
Burckhardt.
XXI]
URINO-GENITAL SYSTEM
539
Urino-geni
tal organs.
The first spinal nerve comes out from behind the first vertebra and
is called the hypoglossal ; it runs
directly to the respiratory muscle, the
mylohyoid, crossing the vagus and
glossopharyngeal in its course. At
the sides of the dorsal aorta the two
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
can be seen when the
alimentary canal is
removed. It is a long narrow strip
on each side adjacent to the aorta.
In front it tapers to the merest
thread, but behind, close to the
cloaca, it thickens somewhat. Along
its outer edge runs the archinephric
duct, and external to the archi-
nephric duct is situated the long
oviduct.
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 little salt solution it is possible,
at least in small specimens, under
a low power of the microscope, to
see the funnels and to observe the
whirlpools due to the currents pro-
duced by their cilia.
The genital gland in both sexes
is represented by a pair of ridges
suspended to the inner edges of
the front parts of the kidney by
slings of peritoneum similar to the
mesentery suspending the gut, and on
this account called mesenteries.
In the female the oviduct opens
FIG. 264. Urine-genital organs of
a female Molge cristata x about 5.
1. Ovary. 2. Bemnant of vasa
efferentia. 8. Kemnant of longi-
tudinal canal connecting the vasa
efferentia. 4. Sexual portion
of kidney. 5. Archinephric
duct. 6. Oviduct. 7. Pos-
terior non-sexual portion of
kidney. 8. Opening of archi-
nephric duct. 11. Internal open-
ing of oviduct. 12. Suspensory
ligament. 13. External open-
ing of oviduct.
540
URODELA
[CH.
by a ciliated funnel adjoining the root of the lung. The funnel
leads into a long convoluted tube running back to open into
the cloaca. The testis, which
takes the form of two conical
bodies with their broad ends
apposed, or sometimes a row
of three rounded lobes, com-
municates by a number of
vasa efferentia with the an-
terior part of the kidney,
which is on this account
termed the sexual portion or
mesonephros. In the male
the kidney tubules belong-
ing to the hinder non-sexual
portion, or metanephros, are
split off from the archmephric
duct and unite into a very short
common trunk, the ureter,
which joins the archinephric
duct just before the latter
enters the cloaca (Fig. 265).
It has been stated above
that the genital glands are
a pair of ridges. In the
larva the inner portions of
the ridges degenerate, the
cells becoming largely con-
verted into fat-bodies, i.e.
lobes of peritoneum filled with
connective tissue in which
the cells secrete large drops
of fat (stearate of glycerine)
in their interiors and thus
become swollen fat cells. In
the adult these fat-bodies
8. External appear running parallel to the
FIG. 265. Urine-genital organs of a male
Molge cristata x about 5.
1. Testes. 2. Vasa efferentia. 3. Longi-
tudinal canal connecting the vasa effer-
entia. 4. Sexual portion of kidney
showing nephrostomes. 5. Wolffian
duct. 6. Eudimentary oviduct. 7. Non-
sexual portion of kidney,
opening of the archinephric duct which
has received the ureter 9 made up of
a number of ducts from the posterior side. They serve as a store
part of the kidney. 10. Fat-body. , . , f ,-,
ot nourishment tor the eggs
which develop during the winter-sleep. The newt, like other
XXI] DEVELOPMENT 541
Amphibia, passes the winter buried in the mud at the bottom
of ponds and takes no food. The conversion of some of the possible
eggs into fat to feed the rest is simply an example of the same
principle as the sacrifice of some of the dogs in an Arctic ex-
pedition to feed the rest.
The development of Molge is interesting. The male emits
the spermatozoa in a bundle which the female then
introduces 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 which 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.
These are the external gills found only in Amphibia, Dipnoi and in
FIG. 266. Larva of Triton, Molge cristata x 5. Showing external gills.
After Eusconi.
Polypterus. There are also a pair of curious rod-like organs in front
of the gills attached to the sides of the head. These "balancers,"
as they are termed, are possibly a first pair of external gills peculiarly
modified. They have mucous cells at the tip, and by means of
them 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 fringed
fin. The fore-limbs are tiny buds. No trace of hind-limbs exists
and the gill-slits are not open.
As development proceeds the fore-limbs make their appearance
provided with only two toes. The gill-clefts, three in number,
appear on each side. After a considerable time the third finger
appears and the hind legs sprout out as buds ; still later the fore-
limbs get all four fingers and the hind-limbs five. The animal has
now attained the appearance of the adult except in so far as the
gills are concerned. These are retained for a long time, and excep-
tionally, in Switzerland in high Alpine localities, the larva may
become sexually ripe and never leave the water. More usually with
542 UEODELA [CH.
the closing of the gill-slits and the shrivelling of the external gills
the adult state is attained.
It has been recently pointed out that the development of the
Newt's fore-limb may afford a hint as to how the pentadactyle limb
was evolved from the fin of a fish. Prof. Broom has made the
plausible suggestion that this took place by the gradual freeing of
the anterior rays from the fin-membrane so that the limb was used
for a time both to walk on and swim with, exactly as occurs in the
pelvic fin of the modern gurnard (Trigla) where the anterior rays
are freed from the membrane and are used by the fish to walk on
the bottom. This freeing of the rays must have been a progressive
process the fin-membrane shrinking as it was less and less used.
The fingers of the Newt's hand appear one after the other and the
oldest known foot-print of a land animal which is found in the
Devonian rocks shows traces of only two well-developed toes.
The Urodela have for a long time been divided into two main
groups, according to the presence during adult life of gill-slits
and gills. Huxley thus divided them into ICHTHYOIDEA arid SALA-
MANDROIDEA, and we shall adopt this mode of classi-
fying Urodela although we fully admit that the group
Ichthyoidea does not represent a single stem but probably several
stems in the same condition. It is advisable to base classification
on blood relationships when this is clear and undoubted, and this is
possible in the case of the larger groups. But to follow out blood-
felationship in minute detail is a very speculative matter in which
the opinions of zoologists differ sharply, and if classification is to be
continually altered in relation to such speculations no finality will
b.e obtained and great inconvenience will result. Huxley's Ichthy-
oidea 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.
tylenopoma (Cryptobranchus) retains one gill-slit throughout life.
This animal attains a length of 18 inches. It is fairly 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.
XXI] MAIN DIVISIONS 543
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 Carniola in Austria.
Lastly, there is the aberrant Siren, which has a horny 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 at first
sight tempting 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
borne in mind, and the further fact that these larvae may abnormally,
become sexually ripe, the conclusion is irresistibly suggested that the*
Ichthyoidea are larvae in which the adult stage has been suppressed.;
In the case of one large American newt, Amblystoma tigrinum, the
larva (the " Axolotl ") often breeds under certain circumstances and
was at one time regarded as a distinct genus (Siredon).
The second division of Urodela, the SALAMANDROIDEA, are in :
general very similar to Molge, both in appearance, anatomy and size*
As in Ichthyoidea, so likewise in Salamandroidea is North
America very rich. These have been divided into families on grounds;
of differences in the skeleton which have little effect on the external
appearance. The most abundant are the AMBLYSTOMATINAE repre-
sented by the genus Amblystoma of which there are many species,^
nine being found in the Eastern States and Canada.; The members
of this family are distinguished by having the palatine bones,
directed transversely, so that the vomeropalatine rows of teeth
run across the roof of the mouth instead of along it, and by having
544 URODELA [CH.
so-called amphicoelous vertebrae, i.e. vertebrae in which the inter-
vertebral discs remain cartilaginous, not true amphicoelous vertebrae
as in fish. Molge (Diemyctilus) mridescens is 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 develop
a crest in the breeding season. These Newts are representatives of
the SALAMANDRINAE distinguished by having the vomeropalatine
teeth in a longitudinal row and by possessing opisthocoelous vertebrae.
The family DESMOGNATHINAE are closely allied to the Amblystoma-
tinae, 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 opisthocoelous vertebrae. The
species of this family are common Water-newts in the Eastern
United States. Desmognathus nigra, the Black Salamander, occurs
near Montreal. The PLETHODONTINAE includes the American Cave-
and Land-newts which rarely enter water but wriggle about actively
on land. These Newts resemble the Desmognathinae in their teeth,
but differ in possessing amphicoelous vertebrae. Although the
most terrestrial in their habits of the New World Urodela, these
animals and some of the Desmognathinae have undergone an extra-
ordinary modification in their respiratory system. The lungs have
disappeared and the septum between the auricles has become ab-
sorbed : so that the animals depend for their oxygen entirely on their
skin and the lining of the pharynx, the walls of which still execute
active respiratory movements. This curious association of terrestrial
habits with the absence of lungs 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 difficult to explain its disappearance
in terrestrial forms. Spelerpes includes the Cave-newts, of which
there are twenty species in America and one isolated species in 1
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. Plethodon erythronotus has the typical Urodele
tongue. This is the common Land-newt in the neighbourhood of
Montreal, being found under old logs and in other damp situations.
XX I] ANUEA 545
Order II. Anura.
The Anura or Batrachia are at once recognised by their broad,
flattened, tailless bodies and their powerful hind-limbs.
Structure. m .
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 specialised, 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 differences in the skeleton connected therewith,
Anura differ 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 temporaries, the Common Frog, and R. esculenta, the Edible
Frog, represent the Family RANIDAE, but the latter of these two
species is very possibly not indigenous but may have been introduced
from the continent, while the BUFONIDAE or Toads are represented
by Bufo vulgaris, the Common Toad, and by B. calamita, the
Natterjack, which occurs in numbers in certain restricted localities,
as a rule those with a sandy soil.
As the Common Frog, Rana temporaria, is easily attainable,
The Fro ^ e principal points in which it differs from Molge
will be briefly, described.
The animal when at rest normally squats on its haunches,
supporting itself slightly on its palms. Under these circumstances,
the pelvic girdle makes a considerable angle with the vertebral
column and the powerful iliac bones raise the skin of the back into
a well-marked hump, the so-called sacral prominence.
The gape is enormous, and is caused by the lower end of the
suspensorium, or part of the skull to which the lower jaw is
s. & M. 35
546
ANURA
[CH.
hinged, slanting backwards instead of projecting directly downwards
as in Urodela. The tongue is fixed to the floor of the mouth in
front, but i free behind ; it can be rapidly thrust out of the inouth
by bending the posterior end forwards and it can be as rapidly
retracted. It is used to whisk the insects on which the animal
feeds into the mouth.
Behind the eye is a circular patch of thin, tightly stretched skin.
FIG. 267. Three diagrams illustrating the development of the procoelous ver-
tebral column in Anura.
A. Stage in which basidorsals, basiventrals and intercalaries are separate.
B. Stage in which the basidorsals have extended downwards to form the
main mass of the vertebra and in which the dorsal intercalary has formed
an intervertebral cartilaginous pad in which a synovial cavity is appearing.
The distal part of the basiventral has disappeared.
C. Stage of the completed vertebra.
1. Basidorsal. 2. Notochord. 3. Basiventral. 4. Dorsal inter-
calary. 5. Intervertebral pad. 6. Synovial cavity of cartilage.
7. Vestigial rib. Dotting, cross-hatching, etc., as in Figs. 232, 242 and
254.
This is the ear-drum or tympanic membrane, which closes ex-
ternally the Eustachian pouch of the gullet. It is believed that
this pouch or tympanum is the remains of the first gill-cleft, the
spiracle of Elasmobranch fishes. Sound impinging on the ear-drum
is conveyed to the wall of the ear capsule by a slender cartilaginous
rod ensheathed in its middle part by bone, the so-called columella
auris. In the Urodela sound has to find its way as best it can
through the skin and muscle of the head to the auditory organ.
XXI] VERTEBRAL COLUMN 547
All Anura possess Eustachian pouches and a columella auris,
but all do not have a well-developed ear-drum.
The skin is most loosely attached to the muscles underneath.
Large spaces containing .Jjm&tL are interposed between them.
These lymph spaces form a protection against the danger of
drying up. There are two pairs of sacs placed, one pair just
between the upper ends of the pectoral girdle, and another pair
just at the sides of the rudimentary stump of a tail, which have the
power of contraction and pump the surplus lymph into the veins of
the neighbourhood. These are called the anterior and posterior
pairs of lymph-hearts.
7
FIG. 268. A. dorsal, and B. ventral view of the cranium of a Common Frog,
Ratio, tempo raria, from which the membrane bones have mostly been
removed x 2. After Parker.
1. Sphenethmoid. 2. Palatine. 3. Pterygoid. 4. Suspensorium.
5. Columella. 6. Exoccipital. 7. Ventral cartilaginous wall of
cranium. 8. Pro-otic. 9. Anterior fontanelle. 10. Eight
posterior fontanelle. 11. Qnadratojugal. 12. Nasal capsule,
ii, v, vi, ix, x. Foramina for exit of cranial nerves.
Turning now to the skeleton we observe many points of
difference between the frog and the Newt. The ribs in the frog
are indistinguishably fused with the transverse processes; in very
few Anura are they distinct and they are always vestigial. The
vertebrae differ from those of the Urodela in the entire suppression
of the ventral intercalary element, so that the centrum is constructed
out of basidorsal, interdorsal and basiventral elements, the last
named being vestigial. In some Anura the basiventral piece is
entirely absent, and in this case, since the centrum is constructed
entirely of dorsal elements, the notochord is found for a considerable
period of development lying in a groove on its under surface. This
352
548
ANTJRA
[CH.
is the so-called epichordal type of development. The tail vertebrae
are represented by a bony style, the uro style. Besides it there are
only nine vertebrae. The transverse processes, or " diapophyses "
of the ninth or sacral vertebra, to which is attached the ilium, are
either cylindrical as in ftana, or they are more or less wide and flat
as is the case in Bufo and Hyla. The diapophysis does not, like the
so-called parapophysis of Teleostei, represent the proximal portion
of the rib but is a secondary outgrowth of the neural arch-piece or
basidorsal and the rudimentary rib is represented by a nodule
A B
10
FIG. 269. A. Dorsal view of the skull of a Common Frog (Rana temporaria) x 2.
B. Ventral view of the same. Both figures after Parker.
In this and in Figs. 270 and 272 the cartilage is dotted, cartilage bones are
marked with dashes, membrane bones are left white.
1. Sphenethmoid. 2. Frontoparietal. 3. Pterygoid. 4. Squamosal.
6. Exoccipital. 7. Parasphenoid. 8. Pro-otic. 9. Quadratojugal.
10. Maxilla. 11. Nasal. 12. Premaxilla. 13. Anterior nares.
14. Vomer. 15. Posterior nares. 16. Palatine. 18. Columella.
19. Quadrate. 20. Occipital condyle. n. Optic foramen. v, vn.
Foramen for exit of trigeminal and facial nerves. ix, x. Foramen for
exit of glossopharyngeal and pneumogastric nerves.
attached to the distal end of this diapophysis, which may either fuse
with the diapophysis as in Rana or remain distinguishable through-
out life as in Alytes (Fig. 267).
The skull is constructed on the same plan as that of Molge,
but it is broader and flatter ; this is due to the wide arching
out of the upper jaws, leaving a very large opening between them
and the cranium. The cause of this again is to be sought in the
large protruding prominent eyes, so marked a feature of all Anura.
The floor of the cartilaginous cranium is complete in the frog, the
pituitary fossa having sunk to insignificant dimensions. The
orbitosphenoids have coalesced to form a box-like bone which ossifies
xxi]
SKULL
549
not only in the front part of the cranium but also in the hinder parts
of the nasal sac, and is called the sphenethmoid. The parietal
is fused with the frontal.
The suspensorium sends forward a pterygoid process which
becomes attached to the skull in the nasal region. Underneath the
posterior part of the pterygoid process there is a pterygoid bone
which surrounds it and partly replaces it. The pterygoid sends out
a fork which underlies that part of the suspensorium which forms
an articulation for the lower jaw. The front part of the pterygoid
process where it bends in to rejoin the skull is ossified by the
palatine, which like the pterygoid has become a cartilage bone.
The palatine is transverse to the axis of the skull, as in Ambly-
stoma. Neither palatine nor pterygoid bears teeth, but the vomers
bear a little group of teeth towards their hinder edge. These
vomerine teeth are used for crushing the food, and are present in
species like the Toad where the teeth borne by premaxillae and
maxillae have been lost.
The upper lip has a series of
three bones on each side, reach-
ing completely to the suspen-
sorium, an additional quadra-
tojugal being added to the
two present in the Newt. The
presence of this bone suggests
that the ancestors of the Anura
are to be sought amongst that
highly modified group of the
Stegocephala termed the Laby-
rinthodonta. In them as in the
Anura the ventral inter-calary
element was absent but at any
rate in the earlier forms the
basidorsals, the basiventrals and
the interdorsals were distinct
pieces. In all Anura there is a
large m embrane bone of a charac-
teristic T-shape, known as the
squamosal, lying outside the
suspensorium. In the lower lip
there is a splenial and a dentary,
whilst in front the cartilaginous
lower jaw is replaced by a pre-
FIG. 270. A. Lateral view of the skull
of a Common Frog, Rana temporaria
x 2. B. Posterior view of the skull of
the same. Both figures after Parker.
1. Sphenethmoid. 2. Frontoparietal.
3. Pterygoid. 4. Squamosal. 5. Tym-
panic membrane. 6. Exoccipital.
7. Parasphenoid. 8. Pro-otic.
9. Quadratojugal. 10. Maxilla.
11. Nasal. 12. Premaxilla. 13. An-
terior nares. 14. Predentary.
15. Dentary. 16. Splenial. 17. Basi-
lingual plate. 19. Quadrate.
20. Columella. 21. Occipital condyle.
22. Anterior cornu of the hyoid (cerato-
hyal). 23. Foramen magnum. ir,
ix, x. Foramina for the exit of cranial
neives.
550 .ANURA [CH.
dentary bone. In the frog only the premaxilla and maxilla and
voiner bear teeth. .Most Anura agree with the Frogs in this, but,
as already mentioned, the Toad, Bufo, and its allies are entirely
toothless (Figs. 269, 270).
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 basilingual with short blunt processes, of
which only the last pair, which embrace the glottis, are ossified
(Fig. 271). This pair are termed the thyrohyals. 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 precoracoid processes are joined
at their inner ends by a longitudinal bar, the epicoracoid, so as to
enclose a space called the coracoid foramen. The two epicoracoids
FIG. 271. Visceral arches of Amphibia. A. JRana temporaria adult. After
Parker. B. Tadpole of Rana. After 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. Thyrohyal = fourth branchial arch.
are in the frog firmly united in the middle line. In many Anura
however they merely overlap (Fig. 272, 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 suprascapula and
ijv, a wedge). There
588
REPTILIA
[CH.
are no sternal ribs 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 as well as
the quadratojugal have dis-
appeared, the pterygoids no
longer articulate with the
base of the skull, and the
quadrate itself is pushed
away from the cranium by
the squamosal 1 , which is a
rod-like bone. (Fig. 290).
The result of this arrange-
ment is that when the lower
jaw is pulled down, the
quadrate is quite free to
thrust the pterygoid for-
ward and push up the
maxilla by means of the
transverse bone ; that is
to say there is the same
mechanism as was described
in the Lizard, only more
easily set in motion and
capable of much more move-
ment. The halves of the
mandible, or lower jaw, are
connected by elastic fibres,
and thus they can be widely
separated. The result of this
is that a Snake has an enor-
mous gape and can swallow
prey almost as large as itself.
Snakes of quite moderate
size dispose of frogs, birds, etc. The large Pythons of India can
crush an animal larger than a half-grown sheep into a shapeless
1 This so-called squamosal corresponds to the upper branch of the squamosal
of Lacerta, and represents the tabular bone.
24
FIG. 291. Diagram of arterial arches of
Snake viewed from the ventral aspect.
i, n, in, iv, v, vi. First to sixth arterial
arches. 12. Tracheal (ventral carotid).
13. Common carotid (dorsal carotid). 15.
Eight systemic arch. 16. Left systemic
arch. 17. Dorsal aorta. 19. Pul-
monary. 24. Coeliac.
XXIII] OPHIDIA 589
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 the animal is engaged in swallowing
its prey, this shifting of position being necessary to prevent choking.
In the skull the brain extends forwards between the eyes and
there is consequently no interorbital septum. That this is a
secondary and not a primary state of affairs is shown by the fact
that the front part of the brain is protected at the sides by down-
ward extensions of the frontal and parietal bones, whereas the animals
such as the Urodela and Mammalia, where an interorbital septum
has never been formed, the side-walls of the cranium are constituted
by the orbitosphenoid and alisphenoid bones. It is curious to find
this absence of an interorbital septum in a family of limbless Lizards,
the AMPHISBAENIDAE. What relation, if any, it has to the snake-
like habits it is hard to guess.
The two eyelids have coalesced to form an extra guard in front of
the eye, but there is a transparent portion in the lower one through
which the animal can see. The outer covering of scales is shed
periodically, half-a-dozen times every year or oftener, 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 snake is blind.
One lung is small, and the other (the right) greatly elongated,
the hinder part being quite smooth.
The heart resembles that of Lizards both in structure and the
mode of distributing the arterial and venous blood. The differences
between 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 musculature as organs of locomotion
in the Snake. Thus the subclavian arteries are absent from the
right systemic arch, while the vertebral and caudal arteries and
veins are well developed. Another difference is that the left
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 : (a) those which poison their prey, (b) those which
crush their prey, and (c) those which swallow their prey directly.
590 REPTILIA [CH.
Those which crush their prey are confined to the tropics ; those
which swallow their prey directly are the non-venomous snakes, and
are represented in both England and North America by the family
COLUBRIDAE. In this family the maxilla is long and bears numerous
teeth, as do also the pterygoid and the lower jaw. The head is
much broader behind than at the muzzle and passed into the trunk
without any constriction to mark a neck. There are about thirty
FIG. 292. The Texas Rattlesnake, Crotalus atrox, reduced. From Stejneger
after Baird and Girard.
species belonging to eighteen genera in North America, of which
Tropidonotus (Eutainia) sirtalis, the Garter-snake frequently met
with in Canada, is one of the commonest; and in England the
family is represented by two species, the Smooth-snake, Coronella
laevis, and the Grass- or Ring-snake, Tropidonotus natrix.
The venomous Snakes in America belong to two families and
these two families are not closely allied and have quite different
XXIII] CHELONIA 591
kinds of poison clearly indicating that the poison producing power
has been independently evolved in different families of the Ophidia.
In the first, the ELAPIDAE, the maxilla is a long bone and bears in
front two large teeth which are grooved, to allow the secretion of
glands in the lip to trickle down into the wound which they make.
The poison acts directly on the nervous system of the victim para-
lysing the nerve centres which control respiration and heart action.
The teeth behind are not grooved. The American Harlequin
Snake, Elaps fulvius, belongs to this family. This Snake receives
its name from its brilliant colours ; it has seventeen crimson rings
bordered with yellow. Another family is that of the VIPERIDAE.
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
ectopterygoid, so as to erect the tooth. The poison in this family
causes the blood of the victim to clot in its veins. The typical
Rattlesnake Crotalus korridus or C. atrox derives its name from
an appendage of about 8 to 9 loosely connected horny 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 United States in mountainous places and enters
Canada. Like all CROTALINAE or Pit-vipers it has a sensory pit
between eye and nose. The English Adder, Vipera berus, is, like
all the Old World VIPERINAE, devoid of such pits. Speaking
generally poisonous snakes may be recognised by their extremely
swollen cheeks behind which there is a slightly narrowed neck,
which passes into the trunk. The swelling of the cheek is due to
the great enlargement of the poison-gland, which is a modified salivary
gland (see p. 655) opening into the mouth.
Order III. Chelonia.
The Chelonia or Turtles are the most peculiar order of the
Reptilia. In some respects they are nearest to the Amphibia, but
they are highly specialised. 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 horny
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 expansions of the spines of the dorsal
vertebrae with a nuchal plate in front of these and a
behind, the two last-named being of dermal origin*
592
REPTILIA
[CH
FIG. 293. A. dorsal and B. ventral view of the carapace of a Loggerhead
Turtle, Thalassochelys caretta. After Owen. In A the outlines of the
superficial horny scales constituting the tortoise-shell are indicated by
heavy lines, whilst the outlines of the bones of which the carapace is
composed are represented by lighter lines.
1. Nuchal plate. 2. First neural plate. 3. Second costal plate.
4. Marginal plate. 5. Pygal plate. 6. Eib. 7. Thoracic vertebra.
8. First vertebral shield. 9. Costal shield.
C. The Plastron of a Green Turtle, Chelone my das x |. (Camb. Mus.)
1. Epiplastron (clavicle). 2. Entoplastron (interclavicle). 3. Hyoplastron
(cleithrum). 4. Hypoplastron. 5. Xiphiplastron.
XXIIl]
CHELONIA
593
On each side there are costal plates; this name is given to
broad expansions of the outer surfaces of the ribs (Fig. 293). The
ribs curve inwards to join the centrum, and since this, as in all
Reptiles, is formed by the ventral intercalary, each rib is nearly
opposite the interspace between two centra and sometimes unites
FIG. 294. Ventral view of the skeleton of Chelone mydas, the Green Turtle
x about . The plastron has been removed.
1. Lower jaw or mandible. 2. Nuchal plate. 3. Ventral process of scapula,
the acromion. 4. Scapula (much foreshortened). 5. Marginal bone.
6. Coracoid. 7. Ilium. 8. Pubis. 9. Ischium. 10. Centrum
of vertebra. 11. Humerus. 12. Radius. 13. Ulna. 14. Carpus.
15. Femur. 16. Tibia. 17. Fibula.
8. & M. 38
594 REPTILIA [CH.
with them both. The transverse process is represented by the
expansion of the neural plate which meets the costal plate. The
almost horizontally directed outer ends of the ribs are received into
a series of dermal bones called marginals, which form the edge
of the carapace.
The plastron is formed of one unpaired and several paired bones
(Fig. 293) The median bone, called the entoplastron, is believed
to correspond to the interclavicle of other Reptiles. The first pair
are called epiplastra and probably represent the clavicles of
other forms. The posterior pairs are called hyoplastra, hypo-
plastra and xiphiplastra respectively; they are firmly joined to
the marginals.
In front and behind the plastron and carapace are separated by
soft flexible skin ; their edges project so as to form roof and floor
to cavities into which the head and neck and arms in front and the
legs and tail behind can be withdrawn. A study of the develop-
ment of modern Chelonia and of the anatomy of fossil species makes
it probable that the ancestors of the present forms were provided
with ,a carapace composed entirely of osteoderms underlying the
horny scales, just as is the case with Crocodilia. This dermal cara-
pace however was gradually replaced by the development of bony
expansions of the ribs and neural arches ; though remnants of it
persist in the nuchal, pygal and marginal plates.
There is no trace of sternal ribs or sternum ; but the pectoral
and pelvic girdles occupy the peculiar position of being within
instead of outside the ribs, a consequence 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 among recent Reptilia but existed"
in the extinct Plesiosauria. 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 pectoral girdle has no epicoracoid. The limbs are essentially
similar to those of the Lizard but the toes are shorter and blunter.
The neck is extraordinarily flexible ; the vertebrae composing it fit
one another by cup and ball joints, one is amphicoelous, the next
is biconvex and so on. The dorsal vertebrae have flat faces.
The skull is devoid of teeth and the prem axilla and maxilla
are short. Both they and the dentary have sharp cutting edges
ensheathed in horn so as to form a beak. In all species the orbit is
XXIII]
CHELONIA
595
encircled with a bony ring and the ectopterygoid or transverse bone
is wanting. The palatal crest on the palatine is hardly perceptible.
There is but one temporal arcade which is chiefly composed of jugal
and quadratojugal bones. When the squamosal joins the postfrontal
as it^does in a few cases no fossa intervenes between this union and
the jugal-quadratojugal bar. Chelonia as already explained are
Monapsid reptiles and descended from a different stock from that
which gave rise to the other groups of Reptiles. In the marine
21
V &
VII 10
FIG. 295. Longitudinal vertical section through the cranium of a Green Turtle,
Chelone mydas x f .
1. Parietal. 2. Squamosal. 3. Quadrate. 4. Basisphenoid. 5. Basi-
occipital. 6. Quadratojugal. 7. Pro-otic. 8. Opisthotic. 9. Pterygoid.
10. Palatine. 11. Bod passed into narial passage. 12. Exoccipital.
13. Epi-otic fused to supra-occipital. 14. Supra-occipital. ' 15. Pre-
maxilla. 16. Maxilla. 17. Jugal. 18. Postfrontal. 19. Vomer.
20. Prefrontal. 21. Frontal. v 1 and 2, vn, vm, ix, x, xi, xii.
Foramina for the exit of cranial nerves.
Chelone and its allies the postfrontal, squamosal, 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. The parietals send downwards two vertical
plates which meet upward extensions of the pterygoids.
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 systemic arch conveying blood
382
596
EEPTILIA
[CH.
chiefly venous to the viscera, while the right-hand one supplies the
head, trunk and limbs with blood which is much more arterialised
than that in the other arch
(p. 581). The fore-limbs
are however supplied by a
different vessel from the
subclavian of the Lizard.
We have already seen (p.
451) that in some verte-
brates the artery to the
fore-limb arises from the
systemic arch on its dorsal
course to join its fellow,
while in others the fore-
limb receives its blood from
an artery given off from the
ventral end or commence-
ment of the systemic arch
or else from the ventral
end of the third arch near
its division into dorsal and
ventral carotids. As the
vessel to the fore-limb is
always called a subclavian
artery it is convenient to
express the fact that this
vessel is not homologous
throughout the vertebrate
groups by the terms "dorsal
FIG. 296. Diagram of arterial arches of subclavian" and "ventral
a Turtle viewed from ventral surface. SUDC lavian." In Amphi-
i, 11, m, iv, v, vi. First to sixth arterial -. i LiWrU th^ ^iih
arches. 12. Tracheal (ventral carotid). Dian f an( ^ ^ lzam
13. Common carotid (dorsal carotid). 15. clavian is of the dorsal
Eight systemic arch. 16. Left systemic i . ov i
arch. 17. Dorsal aorta. 19. Pulmonary. ^P 6 ' but m Chelonians
20. Innominate. 21. Subclavian (ventral and, as we shall see, in
type). 24. Coeliac. Crocodiles also, the arm is
supplied by a ventral subclavian, a vessel which is homologous with
the "scapular" artery to the shoulder muscles in a Lizard. The
venous system in all chief respects is like that already described in
the Lizard.
The copulatory organ is a grooved rod attached to the front
XXIII] CHELONIA 597
wall of the cloaca. The groove leads to the openings of the male
ducts, the vasa deferentia.
The members of the order Chelonia have very various habits and
modes of life. Some are vegetable feeders, others purely animal.
None are found in Great Britain, but the representatives of six
groups are found in temperate North America. These are
(1) The TESTUDINIDAE or Land Tortoises.
(2) The EMYDIDAE or "Pond Turtles.
(3) The CINOSTERNIDAE or Box Turtles.
(4) The CHELYDRIDAE or Snapping Turtles
(5) The TRIONYCHIDAE or Mud Turtles.
(6) The CHELONIDAE or Marine Turtles.
The TESTUDINIDAE have a very arched carapace and short club-
like limbs in which the toes are tightly bound together by skin. Only
a few species, Testudo polyphemus, the burrowing Gopher, and Cistudo
Carolina, the Box Tortoise, are known in temperate North America.
The EMYDIDAE are represented by many species. In this family
the carapace has a wide horizontal margin and the toes are con-
nected by a web. Most of the species are aquatic, a few however
are almost as terrestrial as the TESTUDINIDAE. Chrysemys picta,
the Painted Pond Turtle, ranges north into the St Lawrence.
The CINOSTERNIDAE have a long and narrow carapace with the
margins produced downwards ; it is highest behind. The front part,
and sometimes the hind part, of the plastron moves like a hinge on
the rest and close in the head and tail, whence the name Box
Turtle. Sole genus Cinosternum. C. pennsylvanicum is the most
northerly species.
The CHELYDRIDAE are the so-called Alligator- or Snapping-
Turtles. The head, neck and tail are all large and cannot be
completely protected between the carapace and plastron. The
carapace is highest in front. The jaws are hooked and powerful
and the animals are very vicious. Chelydra serpentina, the
"Snapper," is one of the commonest of American turtles. It is
found everywhere from Canada to the tropics.
The TRIONYCHIDAE or Mud Turtles have no horny scales ; both
carapace and plastron are covered with leathery skin. There is a
soft pig-like snout ; only the three centre toes have claws. They
seek their food by burrowing in the bottom of ponds.
The CHELONIDAE are distinguished by their peculiar skull and
the absence of many or all of the nails. Their extremities have
become flattened and form very efficient paddles.
598
BEPTILIA
[CH.
~* Order IV. Crocodilia.
The last and highest order of the Reptilia is the Crocodilia.
These animals agree with the Chelonia in having a series of osteo-
derms underlying the horny scales of the skin, also in having an
immovable quadrate and a single median copulatory organ, hut in
spite of these resemblances, they seem to belong to the same stock
.& 14
21 *
13
FIG. 297. Palatal aspect, A. of the cranium, B. of the mandible of an Alligator,
Caiman latirostris x 4j .
1. Premaxilla. 2. Maxilla. 3. Palatine. 4. Pterygoid. 5. Posterior
nares. 6. Transverse bone. 7. Posterior palatine vacuity. 8. Anterior
palatine vacuity. 9. Basi- occipital. 10. Opening of median
Eustachian canal. 11. Jugal. 12. Quadratojugal. 13. Quadrate.
14. Dentary. 15. Splenial. 16. Coronoid. 17. Supra-angular.
18. Angular. 19. Articular. 20. Lateral temporal fossa. 21. Openings
for the passage of blood-vessels supplying the alveoli of the teeth. .
as Sauria and Uhynchocephala ; they are Diapsid not Monapsid in
their skulls. It must be remembered that many families of Lizards
possess osteoderms.
The Crocodiles are of large size and are decidedly Lizard-like in
their general appearan.ce, the chief observable external difference
between them and the Lacertilia being in the jaws, which are
XXIII] CROCODILIA 599
exceedingly long in comparison with the rest of the- skull, so that
the gape is very wide.
The osteoderms form rings on the tail, but on the body, as in
Chelonia, they form a dorsal and a ventral shield separated by inter-
vening softer skin. In many Crocodiles the ventral shield is very
rudimentary.
In the general arrangement of the bones and the temporal
fossae the skull resembles that of Sphenodon : 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
upper air passage from the lower food passage : both the palatines
and the pterygoids being completely united in the middle line
(Fig. 297). The choanae or posterior nares are therefore situated
very far back directly over the glottis, whilst the external nostril is
at the tip of the snout.
In consequence of this position of the external nostril the
crocodile can lie for hours hidden under the water with only the
tip of the snout exposed, and so surprise any unwary 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 are
articulated to the atlas and axis vertebrae throws much light on
the relation of these peculiar vertebrae to the rest. Thus we
observe that the first pair of ribs are articulated with their heads
to the lower part of the atlas, showing that this represents a basi-
ventral homologous with the intervertebral cartilaginous pads of the
rest of the column. The heads of the second pair of ribs are united
to an intervertebral cartilage separating the odontoid process from
the centrum of the second vertebra. This cartilage is therefore the
second basiventral, and the odontoid process is the first interventral,
homologous 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 obliquely 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 have shifted their
capitular attachment back on the centrum of the third vertebra
(Fig. 298). This backward shifting of the capitular attachment has
taken place in all succeeding vertebrae, and the head of the rib is
attached directly under its tubercle. In the trunk, as we proceed
600
EEPTILIA
[CH.
backwards, the capitular attachment to the centrum is gradually
raised till it reaches the transverse process and is confounded with
the tubercular attachment, and the hindermost vertebrae are single
headed. There are abdominal ribs, as in Sphenodon ; they are
arranged in transverse rows, each row on each side consisting of
three or four bones (Fig. 299).
The pectoral girdle consists of simply a scapula and coracoid,
the latter reaching the sternum, which is cartilaginous but protected
ventrally by an interclavicle (Fig. 300). In the fore-limb the carpus
has retained three bones in the proximal row, but the distal row
consists of a block of car-
tilage representing the first
and second carpalia and a
bone representing the re-
maining three. There is
consequently an intercarpal
wrist joint corresponding to
the intertarsal joint com-
mon to Reptiles.
The pelvic girdle is very
peculiar. The ilium is
broad and rounded above
and joins the two sacral
1. Neural spine of atlas. 2. Lateral portion of rpv v j
atlas. 3. Odontoid process. 4 Ventral vertebrae. The pubis does
portion of atlas. 5. Neural spine of axis. not form any part of the
6. Postzygapophysis of fourth vertebra, i j /. ,1
7. Tubercular portion of fourth cervical rib. ndary the aceta-
8. First cervical rib. 9. Second cervical bulum or socket for the
rib. 10. Convex posterior surface of i j /> ,1 f mi
centrum of fourth vertebra. head of the femur. This
is completed by a small
bone termed the acetabular bone. This exclusion of the pubis
from the boundary of the acetabulum is a feature of modern
Crocodiles, because in extinct Crocodiles the pubis took its proper
share in forming the border of the acetabulum. The tarsus, like the
carpus, is much reduced and modified. It consists of a proximal
row of two bones, one of which, the fibulare or calcaneum, forms
a distinct heel. The distal row consists of two bones, one repre-
senting the first, second and third tarsalia, the other the fourth
and fifth.
The heart of the Crocodile is remarkable for the fact that the
septum in the ventricle has grown forwards so as to completely
divide it into two halves, the right and left ventricles. The left
FIG. 298. First four cervical vertebrae of a
Crocodile, C. vulgar is. Partly after von
Zittel.
XXIII]
CROCODILIA
601
5
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 ad-
dition there is a small
passage, the foramen
of Panizza, joining the
two trunks where they
cross, so that the blood
leaving the right arch to
go to the carotid is also
somewhat mixed. The
right common or dorsal
carotid is very reduced,
the left-hand vessel
supplying both sides of
the head (Fig. 301).
The fore-limb receives
blood by a subclavian of
the ventral type, as in
Chelonians. The lung
is no longer a simple sac,
but has thick spongy
walls and the central
passage is reduced to a
najrow tube. In the
brain the cerebellum
is large and cylindrical.
All these peculiari-
HVe nf f>io infor-nol
Organs' may be termed
foreshadowingS of what
/, -, . -o' i
is found in Birds and
Mammals, and hence
Crocodiles are styled
rightly the highest of living 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, Crocodilus niloticus. There is but one
299. Sternum and associated membrane
bones of a Crocodile, G. palustris x $ .
The last pair of abdominal ribs which are united
witl1 the epipubes by a plate of cartilage have
been omitted.
^ Interclavicle . 2 . sternum . 3 . Sternal
rib. 4. Abdominal splint rib. 5. Sternal
band '
602
KEPTILIA
[CH.
species in the southern states of North America, the Alligator,
Alligator mississipiensis, which has a much shorter and broader
snout than the Crocodile. This animal lies for hours absolutely
motionless at the surface of the water so as to greatly resemble a
log, and. thus entrap any unwary animal which may venture near.
The Gavial, Gavialis gangeticus, in India is remarkable for its
excessively long and narrow jaws.
So far as we can learn from fossils the Reptiles seem to have
been the dominating type of land animals in the ages which inter-
3 ^^*^- 4
FIG. 300. A. Left half of the pectoral girdle of an Alligator, Caiman lati-
rostris x-f .
1. Scapula. 2. Coracoid. 3. Interclavicle. 4. Glenoid cavity.
B. Pelvis and sacrum of an Alligator, Caiman latirostris x \.
1. Ilium. 2. Ischium. 3. Acetabular bone. 4. Pubis. 5. Aceta-
bular foramen. 6. Neural spines of sacral vertebrae. 7. Union of
the two ischial bones. 8. Process bearing prezygapophysis.
vened between the close of the Coal epoch and the end of the Chalk
period when the white limestone which constitutes the southern
cliffs of Britain was deposited as a sediment in the quiet waters
which covered what is now Western Europe. A rough sketch of
the history of the class as deduced from fossils may be given here.
The Reptilia seem to have arisen from the most primitive forms
included under the title Stegocephala. At least there are some
forms like Eryops and Cricotus included in the latter group in which
the bones flanking the notochord, which have not yet united so as to
XXIll]
EXTINCT FORMS
603
VI
form vertebrae, are represented by basidorsals, basiventrals, and
ventral intercalary pieces, the dorsal intercalary piece as in all
Reptilia being suppressed, while in the skull the basi-occipital
region is ossified. In the Sandstones lying above the Coal in-
dubitable Reptiles with
fully formed vertebrae
make their appearance.
Some of these, termed
the Cotylosauria, still re-
call the Stegocephala in
possessing a complete
roof of dermal bones
covering the skull.
The descendants of
the Cotylosauria in the
next period split into two
stocks, in one of these
the Monapsida, the cover-
ing of dermal bones on
the head was reduced in
such a manner to leave
one broad temporal bar.
The limbs in all these
early Reptiles were short
and stout, the fore- and
hind-limbs being nearly
of the same size. One
group of the Monapsida,
the Theromorpha, were
distinguished by having
the teeth differentiated
into incisors, canines and
molars and in having the
dentary very large and ar-
ticulating with the squa-
mosal, the other bones of
the lower jaw being re-
duced in size. These are
almost certainly the ancestors of Mammalia.
In another group of Monapsida the teeth were reduced to a
pair of tusks in the upper jaw or were totally absent. This group
FIG. 301. Diagram of arterial arches of
Crocodile viewed from the ventral aspect.
i, n, in, iv, v, vi. First to sixth arterial
arches. 12. Tracheal (ventral carotid).
13. Common carotid (dorsal carotid) [right
side nearly atrophied]. 15. Eight sys-
temic arch. 16. Left systemic arch.
17. Dorsal aorta. 19. Pulmonary. 20. In-
nominate. 21. Subclavian (ventral type).
24. Coeliac.
604 REPTILIA [CU.
termed the Dicynodontia are believed by some to have been the
forerunners of the Chelonia.
A third group of Monapsida was constituted by the great group
of whale-like Reptiles known as Ichthyosauria in which the neck was
absent and the limbs were transformed into flippers the fingers
being represented by long rows of squarish bones. The fingers
frequently branched and supernumerary fingers were formed. Some
exceptionally well preserved specimens show that the animals when
alive possessed a dorsal fin.
The other division of the Cotylosaurian stem consisted of forms
in which supratemporal and laterotemporal fossae were equally de-
veloped ; these were the Diapsid Reptiles. The Rhynchocephala as
represented by Sphenodon are almost unmodified survivors of the
early Diapsida. 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 was
borne by the hind-limbs, the fore-limbs being short and used for
prehensile purposes only. In a still later period from the less
specialised Dinosauria were developed (l) the Crocodilia, which
reverted to the water but retained limbs fit for progression, and
(2) Pterosauria, 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 showing the characteristic loss of
the quadratojugal.
The class Reptilia is classified as follows :
Order I. Rhynchocephala.
Reptilia devoid of special copulatory organs arid with an
immovable quadrate.
Ex. Sphenodon.
Order II. Sauria.
Reptilia with paired dorsal copulatory organs and a
movable quadrate.
Sub-order 1. Lacertilia.
Sauria which retain a pectoral girdle and a urinary
bladder ; in which the rami of the lower jaw are united by a
symphysis. Limbs present or absent.
Ex. Lacerta, Anguis.
XXIII]
CLASSIFICATION
605
Sub-order 2. Ophidia.
Sauria devoid of pectoral girdle and of urinary bladder ;
in which the rami of the lower jaw are united by an elastic
ligament. Limbs absent.
Ex. Crotalus, Vipera, Tropidonotus.
Order III. 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 teeth.
Ex. Testudo, Chelone.
Order IV. 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, Alligator, Gavialis.
CHAPTER XXIV
SUB-PHYLUM IV. CRANIATA
DIVISION II. GNATHOSTOMATA
SUB-DIVISION II. AMNIOTA
Class IV. AVES
IT is probable that if the first child one met were asked to
describe a bird, he would say that birds were animals
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 Hep tiles asSaurop-
sida, 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 ancestor^ 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
jaw consisting of five bones and articulating with a quadrate
CH. XXIVJ STRUCTURE OF FEATHERS 607
bone and in the structure of the hinder part of their skulls, of
their breast-bones and of their ankle-joints. As in Reptiles, the
number of neck vertebrae 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. 310), 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 from any living Reptile.
Strange as the statement may appear, it is true, nevertheless,
that the feathers are really scales like those found in
Lizards, but immensely developed and with the edges
frayed out. Like' scales, they are epidermal, that is, developments
of the outer or horny 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 as this part is pushed away by the growth of the
deeper parts it becomes frayed out so as to form the vane of the
feather (Fig. 302). In the latter we can distinguish a central stem
or rachis, 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. In 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
substances or pigments in the epidermal cells and partly to minute
structural detail which causes interference of the light waves re-
flected from them.
608
AVES
[CH.
The wing is the fore-leg of the bird. 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 carrying the long primaries or hand quills. When the wing
is at rest the upper arm extends backwards, the fore-arm is sharply
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
FIG. 302. Section through the skin of a Bird showing a developing feather.
Highly magnified.
1. Epidermis. 2. Malpighian layer of the epidermis. 3. Dermis.
4. Young feather. 5. Follicle round base of feather. 6. Dermal
papilla which develops blood-vessels and is the organ of nutrition of
the feather.
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 rule three digits, the first, second and third.
These have their first joints, the metacarpal bones, closely united
together. In Man the metacarpals of the various fingers are united
by skin and flesh which constitute the palm, but they are mov-
able on one another, whereas in the bird the metacarpals of the
XXIV]
SKELETON OF TRUNK
609
second and third digits are firmly joined at both ends. The index
or second finger has in addition to the metacarpal, in most birds,
three other small bones called phalanges, of which the end one
sometimes carries a claw : the third digit has only one bone or
phalanx besides the metacarpal. The metacarpal of the first
digit or thumb is very small, but is like-
wise completely fused with the other
metacarpals. Besides this the thumb has
two joints and often a claw.
Compared with the arm or fore-leg of
other animals the arm of a bird strikes one
as having very little flesh. This is be-
cause the muscles, especially those on the
fore-arm, have comparatively short bellies
but very long tendons, in correlation with
the often very much lengthened bones,
one of which, the ulna, serves as support
of the secondaries or arm-quills.
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
pectoral muscles, great fleshy masses which
cover the breast-bone or sternum. This
bone has a more or less pear-shaped out-
line, rounded in front and pointed behind,
the ribs ending in its sides (Fig. 304).
In accordance with the tendency in all
birds to develop the body into a long-
neck and a rounded trunk, we find evidence
that the number of ribs encircling the body
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. 304) which are regarded
as the remains of sternal ribs the dorsal halves of which are
vestigial or lost. If we picture to ourselves the pectoral girdle being
thrust backwards and the pelvic girdle pushed forwards so as to crowd
the viscera into a small space we shall realise the meaning of the
differences between the skeleton of the trunk of a Reptile and that
of a Bird, but it must not be supposed that the great length of a
s. &M. 39
FIG. 303. Bones of the right
wing of a Gannet, Sula
alba x .
1. Humerus.
3. Ulna,
metacarpal.
metacarpal.
or pollex.
digit. 8.
The distal phalanges of
the thumb and second
digit were wanting in the
specimen from which this
figure was drawn.
2. Radius.
4. Second
5. Third
6. Thumb
7. Second
Third digit.
610
AVES
[CH.
bird's neck is a measure of the extent to which the pectoral girdle
has been pushed back. From the relation of the cervical spinal
nerves to the sympathetic ganglia it is certain that the greater part
of the length of the neck must be regarded as due to a secondary
zone of growth. From the middle of the sternum projects a great
vertical crest stretching outwards, called the carina or keel, and
it is from the sides of this mainly that the pectoral muscles take
their origin. There are two main muscles on each side.. First
the pectoralis major on the surface, which passes into a tendon
attached to the upper end of the humerus. The contraction of this
muscle brings about the down-stroke of the wing, the effective stroke
in flying. Underneath the pectoralis major is situated the pectoralis
minor, a much smaller muscle. Its tendon passes underneath
the arch formed by the clavicle
and the coracoid bone, the latter of
which, as in Reptiles, connects the
shoulder-blade firmly with the ster-
num. Having passed through this
arch which is termed the foramen
triosseum because it is bounded by
three bones, viz. clavicle, coracoid and
scapula, 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 and backwards and not
downwards, the upper end of the
coracoid acting as a pulley round
which it passes.
Returning to the wing, we must
now notice how the feathers are
arranged. The great quill feathers
are attached chiefly to the upper
and posterior edge of the hand, but
there are also a large number which
are implanted in the posterior surface of the ulna. These two groups
of 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 only 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. 305, C), those
FIG. 304. Shoulder-girdle and ster-
num of Peacock, Pavo cristatus
xf.
1. Carina of the sternum. 2. Cora-
coid. 3. Scapula. 4. Clavicle.
5. Costal process. 6. Surfaces
for articulation with the sternal
ribs. 7. Posterior (xiphoid)
and oblique processes.
XXIV] MECHANISM OF FLIGHT 611
arising from the ulna, secondaries (8, Fig. 305, C); a few arising
from the upper arm are called tertiaries; any air which might
escape between the bases of the long feathers is stopped by an
upper layer of shorter feathers, called coverts (1, 2, 3, 5 and 7,
Fig. 305, 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. Each of these folds is
termed a patagium. The name bastard wing is given to a tuft
of feathers borne by the thumb (4, Fig. 305, C 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 the patagia.
Now if this space had a symmetrical shape the air would be com-
pressed 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
slightly upwards, since the lowest layer of air is checked by friction
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 Gannet. In this
392
Fig. 305.
CH. XXIV] SKELETON OF HIND-LIMBS 613
FIG. 305. Wing of a Wild Duck, Anas boschas x $.
A. Eight wing seen from the dorsal side, with the coverts removed. B. Left
wing disarticulated and seen from the ventral side, with the coverts
removed. C. The dorsal side of a right wing. D. The ventral side
of a left wing. From Wray.
lu A and B. 1. Humerus. 2. Eadius. 3. Ulna. 4. Eadial 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 quill. 12. Tertiaries.
13. Secondaries. 14 17. Primaries.
In C and D. 1, 2, 3, 5, and 7. Coverts. 4. Bastard wing. 6. Primaries.
8. Secondaries. 9, 10. Tertiaries.
manoeuvre birds are assisted by the tail, which is really a fan-
shaped row of strong feathers attached to the coccyx, that very
small vestige of a true tail or portion of the vertebral column
extending behind the anus, which modern birds possess (Fig. 307).
In this region the vertebrae are thin discs, several of which may be
soldered together so as to form a bone called the pygostyle.
FIG. 306. Lateral view of the pelvis and sacrum of a Duck, Anas boschas x f .
1. Ilium. 2. Ischium. 3. Pubis. 4. Pectineal process, the rudiment
of the prepubis corresponding to the pubis of the Lizard. 5. Ace-
tabulum. 6. Ilio-ischiatic foramen. 7. Fused vertebrae. 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 Reptiles, but modified so as to
enable them to support the body in an upright position.
The arrangements to effect this are very interesting,
as they differ markedly from those found in the human skeleton. On
the other hand they agree with the modifications of the hind limb
found in those extinct Dinosauria which were bipedal.
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.
614 AVES [CH. XXIV
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
immovably strapped to the vertebral .column. The result of this
has been atrophy of some of the hinder ribs, and the ventral
halves of some of these form the xiphoid processes of the sternum.
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 slender
bone which is also directed backwards. It is in fact a postpubis
corresponding to the lateral process on the pubis of the Lizard (see
p. 577). Except in the Ostrich the two pubes never unite with
one another ventrally to the cloaca, as they do in Reptiles and
Mammals, the absence of a pubic symphysis facilitating 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 considerable height above the ground by
the great length and upward direction of the bones of the sole or
metatarsals (Fig. 307). Thus a Bird walks on its toes and like
Reptiles 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 absent, while
its metatarsal remains distinct from the other three. This toe,
except in Steganopoda, is directed backwards. In the Parrot the
fourth toe is also directed backwards. In the Cuckoo the fourth
toe is directed backwards but can be turned forwards at will. In
swimming and diving birds the second, third and fourth toes are
generally connected by a web of skin. Only in Steganopoda is
the hallux included in this web and in these birds this toe is
turned forwards like the rest. In other swimming and diving birds
the hallux is either absent or when present is free from the web and
turned 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
FIG. 307. Skeleton of the Common Fowl, tne y are never
13. Common carotid (dorsal carotid), compressed, however much
14. Systemic arch. 17. Dorsal aorta, ik U*-J H- *. M i
19. Pulmonary. 20. Innominate. 21. the bird twisfcs lts neck -
Subclavian (ventral type). 24. Coeliac. Turning now to the con-
sideration 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
XXIV]
CIRCULATORY SYSTEM
621
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 from the left half of the ventricle ;
in Reptiles, 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, sup-
plying the trachea, which splits up into
a ventral carotid, as in Reptiles, but re-
duced as compared with the correspond-
ing vessel in them, and into a dorsal or
common carotid which supplies the
head and a subclavian which supplies
the breast and wing. The subclavian
artery which arises from 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 Fm - 311 - Dia S r a m to show
, f i arrangement of the prm-
lungs, the pulmonaries, which, as m O i pa i veins of a Bird.
the Reptiles, have no longer any con- i. sinus venosus gradually
nection with the systemic arch, come off
from the right side of the heart; one
passes to each side to reach the lungs
(Fig. 310). 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
connection of the two jugulars has been
already referred to. The jugular joins
a large subclavian vein to form the
superior vena cava. The largest part of the subclavian vein, like
that of the corresponding artery, is made up of a pectoral vein
returning blood from the pectoral muscles. The front parts of
10
10
disappearing in the higher
forms. 2. Ductus Cuvieri
= superior vena cava.
3. Internal jugular = an-
terior cardinal vein. 5. Sub-
olavian. 6. Posterior car-
dinal, front part. 7. In-
ferior vena cava. 8. Renal
portal = hinder part of pos-
terior cardinal. 9. Cau-
dal. 10. Sciatic. 12. Coc-
cygeomesenteric. 13. Fe-
moral. 14. Anastomosis
of jugulars.
622
AVES
[CH.
12
FIG. 312. The chief viscera of the Pigeon, Columba livia x f .
1. Trachea. 2. Thymus gland. 3. Oesophagus. 4. Crop. 5. Syrinx.
6. Heart. 7. Liver. 8. Gizzard. 9. Duodenum. 10. Pancreas.
11. Small intestine. 12. Rectum. 13. Cloaca. 14. Air-sacs.
15. Left carotid. 16. Left subclavian. 17. Right carotid. 18. Brachial
artery. 19. Eight subclavian. 20. Muscles of syrinx. 21. Pector-
alis major muscle cut across.
XXIV] RESPIRATORY SYSTEM 623
the posterior cardinal veins have disappeared: but their hinder
parts remain as 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 system 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, receive a double supply. From the point where the
caudal vein divides into the two renal portals a vein is given off
which descends into the mesentery and opens into the posterior
mesenteric branch of the portal vein, thus establishing a connection
between the portal and cardinal systems of veins. This vein is
called the coccygeomesenteric (12, Fig. 311), and is quite
peculiar to Birds.
The lungs are firmly fitted in against the ribs; they do not, as
in most Reptiles or as in ourselves, hang freely in a cavity; their
most remarkable feature is the possession of great thin-
sjStem. rat ry 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
cavity under the ribs (Fig. 312). 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.
Breathing out or expiration is therefore the active function
drawing in air is an elastic reaction, the opposite to what is the
case in Man and other Mammals, It must be remembered that in
the lungs of Birds as indeed of those of all other land animals the
air which is breathed in or out, the tidal air as it is termed, is only
a fraction of the total air contained in the lung. Oxygen and other
gases pass from the tidal air to the residual air and vice versa by
the swift process of gaseous diffusion and as the torrent of tidal air
rushes past the lungs into the air-sacs the limgs abstract oxygen
from it, both on its way in and on its way out. This double
oxygenation of the air in each complete set of respiratory move-
ments is perhaps the reason for the extraordinary activity and
strength of Birds 'in proportion to their size.
The windpipe or trachea is long, and the hoops of cartilage
624 AVES [CH.
which stiffen it form complete rings, so that it is not easily com-
pressed (Fig. 312). Like most other land vertebrates, birds have a
larynx or organ of voice at the top of the trachea formed in the
usual manner by the enlargement of some of these rings of cartilage,
and the stretching of a thin membrane between them and two
special cartilages, the arytenoids, which lie at the opening of the
windpipe into the gullet. The larynx however appears to be
functionless, and the effective organ of voice in Birds, the syrinx,
is found much deeper down, at the spot, namely, where the wind-
pipe splits 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 their successors and predecessors so as to
form a box with stiff walls called the tympanum. The inner walls
of the bronchi, just where they join one another, are thin and mem-
branous, and constitute a membrana tympaniformis interna.
From the fork a flexible valve, termed the membrana semi-
lunaris, projects up into the tympanum, and as here the cartilage
rings have the form of half-hoops, which are drawn together by
special muscles, the width of the opening of the bronchus into the
windpipe is small. When air is forcibly expelled the valve above
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 (intrinsic 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 syrinx
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 formation. In a few North American
birds a tracheal syrinx is found in which the organ of voice is
constituted by a portion of the trachea 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 bronchus 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 flaps as
Systfm. tlve we nave seen are stiffened by the maxillopalatines.
The tongue, which is pointed and horny, ensheaths
the glossohyal bone; it is protruded by the action of muscles
XXIV] ALIMENTARY CANAL 625
which pull the enlarged third visceral arch forwards. Behind the
tongue open the ducts of the submaxillary glands; at the
corners of the gape the parotid glands pour their secretion into
the mouth, whilst at the sides of the tongue the sublingual
glands open. All these glands are pouch-like outgrowths of the
ectoderm 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. Trapa, beside,
ov9, WTO?, 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 eventually passes into the
stomach. The gullet in the Pigeon and many other birds develops
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 develops 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
stone. 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. It has been recently
proved that the pancreas of all Amniota originates as three pouches
of the intestine behind the pouches which give rise to the liver a
dorsal pouch and two ventral pouches. All these pouches divide
S. & M. 40
626
AVES
[CH.
and give rise to tufts of tubes. The ventral ducts disappear, the
tufts of tubes which were connected with them acquire secondary
connections with the dorsal tuft whose duct now serves to discharge
the products of all three tufts and which persists as the adult
pancreatic duct. In Birds, however, all the three pancreatic ducts
appear to persist. The intestine is folded into four or five loops,
15
FIG. 313. The lungs, kidneys and gonads of a Pigeon, Columba lima x-f.
1. Trachea. 2. Bronchus. 3. Lung. 4. Suprarenal body. 5. Ovary.
6. Oviduct. 7. Lobes of kidney. 8. Ureter. 9. Aorta. 10. Bursa
Fabricii. 11. Kectum. 12. Opening of bursa Fabricii. 13. Openings
of ureters. 14. Opening of oviduct. 15. Cut pectoral muscle.
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 quite small vestiges as in the Pigeon and in fish- and flesh-
eating birds. The rectum ends in an enlargement termed the
XXIV] URINO-GENITAL SYSTEM 627
urodaeum, the upper part of which receives ducts of the kidneys
and reproductive organs, while into the dorsal wall of the lower and
outer part a glandular pouch of unknown function, called the bursa
Fabricii (12, Fig. 313), opens. This becomes smaller and some-
times entirely disappears in the adult Bird.
The structure of the kidneys and reproductive organs is es-
sentially the same as in the Reptilia. The meta-
oiga n ns. genitai nephros in 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. 313) 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 Khynchocephala. That this however is a secondary
and not a primary state of affairs is suggested by the existence in
Ostriches and some other Birds (Anseriformes) of a long penis on
the dorsal wall of the cloaca similar in structure to one of the
penes or copulatory sacs of the Lizard.
There is usually 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 as 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. In the case of a few birds of prey it has been
recently shown that the right ovary can produce fully developed
eggs as well as the left. There are two oviducts, but the right
is small and useless. It must be 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 about seventeen hours out of the twenty-four,
are well known to all. Most also are aware that many birds
migrate 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
402
628 AVES [CH.
seems hardly credible. There is no doubt, however, that very large
numbers 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 Archaeopteryx,
represented by two specimens from the quarries in lithographic
stone at Solenhofen in Germany. This remarkable bird had a long
tail like that of a lizard, to each vertebra of which a pair of feathers
was attached ; the fingers of the wing bore claws and the bones of
the palm (metacarpals) were free from one another. In the skull
the premaxilla was as usual ensheathed in a horny beak but the
maxilla bore teeth.
In all these points Archaeopteryx maybe said to retain reptilian
characters. Two other fossil birds (Hesperornis and Ichthyornis) had
teeth in the maxillae but in other respects their structure was like
that of modern birds.
The classification of Birds presents great difficulties. They are
a modern and very successful group of animals and
evolution in them is proceeding rapidly. Older
taxonomists were wont to classify them by the shapes
of their beaks and their claws; modern taxonomists are perhaps
too apt to reject these as external characters " of a purely adaptive
nature." Such comments raise some fundamental questions on
which a few words may be said here. If the evolution theory be
justified .all characters in animals are adaptive : they have either
been directly acquired in response to the demands of the environ-
ment, or they are the secondary result of the adaptation of other
organs to the environment. Now the thought underlying the dis-
trust of external characters as a basis of classification is that they
in their form represent the most recent adaptations since they
come first into contact with the environment; the more deeply
situated organs it is thought, are more slowly affected and hence
represent more ancient adaptations, and therefore afford indications
of the affinity of animals whose external features have become
different. There is a good deal to be said for this principle but
it must be used with caution. As Herbert Spencer pointed out
long ago, the alimentary canal, the most internal organ of all,
comes into close and direct relation to the environment.
The bones on which systematists are wont to lay what seems to
us an overwhelming amount of stress alter quickly and directly
according to the development of the muscles which are attached to
XXIV] TYPES OF PALATE 629
them and the development of these muscles is an expression of
the habits of the animal a feature which is eminently subject
to adaptive variations.
Such organs as the heart, the kidneys and the genital organs
are perhaps less variable than those we have just mentioned, but
these afford little or no help in classifying birds since their
structure throughout Aves is extraordinarily uniform. Another
objection to using internal organs as a basis for classifying Aves
is that the dissection of different types and the comparative
description of the internal organs have been so incompletely ac-
complished that according to one of the best bird specialists, the
external characters furnish just as reliable data as the ill-known
internal organs, In classifying we must endeavour to group together
birds showing as many points of agreement as possible and frankly
admit that the question of the affinities of many groups is at
present an unsolved problem. The points at present most relied
on in classification are the structure of the palate and the amount
of care given to the young. With regard to both these points we
recognise in some birds archaic features which they share with
the Reptiles. These enable us to separate a more primitive stratum
from a more advanced stratum of Birds. Huxley long ago showed
that four types of palate are found amongst modern birds which
are as follows :
(1) The dromaeognathous palate. In this type the vomers are
large and flat and embrace the rostrum of the basisphenoid bone
behind and prevent the pterygoids and palatines from touching
it. The pterygoids are united to the basisphenoid by processes
termed basipterygoid processes. A palate such as this presents
considerable resemblances to the palate of Spkenodon.
(2) The schizognathous palate. In this type the vomers
coalesce in front to form a pointed bone ; they are small behind
and the pterygoids and palatines rest on the basisphenoidal rostrum
and can play up and down on it. The maxillopalatine bones do
not unite in the middle line.
(3) The aegithognathous palate. This type greatly resembles
the preceding but differs from it in that the vomers unite in front
to form a bluntly truncated bone and diverge behind.
(4) The desmognathous palate. In this type the vomers have
the same form as in the second type but they are smaller and may
occasionally be absent altogether. The maxillopalatine bones are
united in the middle line so as to form a bony palate.
630 AVES [CH.
With regard to the care of the young, the Mound-builders of
Australia (Megapodidae) exhibit the most primitive conditions, for
they do not even sit on their eggs, but bury them in a mass of
decaying vegetation, so that they may be hatched by the heat of
fermentation just as Reptiles bury their eggs where they may be
hatched by the heat of the sun. All other birds sit on their eggs.
But in the case of some birds, such as the common hen, when the
chicks are hatched they are covered with down and are able to run
about and feed themselves : such chicks are said to be nidifugous.
In the case of other Birds, such as the Swallow, the chicks emerge
from the egg in a blind, naked condition and have to be fed with
unremitting care by the parents : such chicks are said to be
nidicolous: and this is certainly a more modified condition of
affairs than the nidifugous condition.
If we now, starting from Archaeopteryx, ask ourselves what the
most primitive form of bird was like, we may arrive at certain
probable conclusions. Birds, we have already concluded are derived
from Reptiles, and they must have originated from active tree-
climbing Reptiles of moderate size, which jumped from branch to
branch, for in this way only can we understand how the power of
flying was evolved.
The wings in the first birds must have been actively functional,
for only by their functional importance can we account for their
evolution ; but we need not credit the first birds with great powers
of flight any more than the first aviators, whose short flights pale
into insignificance in comparison with the flying feats of to-day.
Now there is one group of birds which to a large extent retain these
primitive characters to-day : these are the Game-Birds, the so-called
Cock-like Birds (Galliformes). They roost in trees for the most part
and make short flights only when they are disturbed or alarmed.
Their young are nidifugous.
Included in this group are two remarkable genera. In one of
these, the South American Tinamou, the palate is of the dromaeo-
gnathous type, and there is a penis in the dorsal wall of the cloaca.
In the other (OpistJwcomus) the chick, when it emerges from the
egg, has claws on the thumb and index finger and the wing feathers
are not developed, and for the first few days of its life it runs about
over the branches like the arboreal reptile from which the group of
Birds is descended. It is in fact a bird larva. In all other Galli-
formes, except the Tinamou, the palate is schizognathous and there is
no penis. It is customary to separate the Tinamou on this account
XXI V] MAIN DIVISIONS 631
from the other Game-Birds and make it the type of a primary
division, the Tinamiformes, but in all essentials it is a Game-Bird
which retains primitive characters. In one respect, however, the
Game -Birds are not primitive, but secondary ; they are for the most
part grain eaters.
Now the primitive Birds had teeth, and we may assume that in
its leaps from branch to branch the ancestral reptile chased some-
thing more active than seeds. With great probability we may con-
clude that the original bird was insectivorous, and it is useful to
remember that this is true of the chicks of very many species the
adults of which are not insectivorous.
A number of 'large flightless Birds agree with the Tinamou in
possessing a dromaeognathous palate and in having a penis. These
are grouped together as RATITAE, because the breast-bone has lost
its keel and has become raft-like, and the clavicles have disappeared.
These are secondary degenerative changes due to the loss of the
power of flight, and another such change is found in the loss of
barbules, in consequence of which the feathers have a soft downy
consistence. This is because they are not required to form a firm
surface with which to beat the air. It is this character which makes
them prized for ornament.
The Ratitae include the true Ostrich (Struthid) from Africa with
two toes, the Rhea from South America with three toes, the Emeu
(Dromaeus) from Australia and the Cassowary (Casuarius) from
New Guinea with three toes. All these species have powerful legs
and can run at a great rate. Finally we have the Kiwi (Apteryx)
from New Zealand with four toes, the smallest Ratite Bird, but in
that country there formerly existed the largest of all Ratites, the
Moas (Dinornis), which had thigh bones thicker than those of a
horse. These, though now extinct, survived into the human period.
The Tinamiformes and Galliformes, and all other Birds, are
grouped as CARINATAE, but this is a most illogical proceeding, as
individual species among them have lost the power of flight, and lost
in consequence, or very nearly lost, the carina or keel on the sternum.
And the Ratitae are certainly not descended from a common Ratite
ancestor, but represent different types of archaic birds which have
independently lost the power of flight owing to the circumstances in
which they have found themselves. In the Ratitae of New Zealand
this was certainly due to the absence of carnivorous mammals.
Reverting now to Birds of more modern type and passing over the
Galliformes, we find in the group of Divers (Colymbiformes)
632 AVES [CH.
aquatic, swimming and diving Birds with flattened legs nidifugous
young and schizognathous palate. The Diver (Colymbus) is well known
on our northern coasts ; it is called the Loon in N. America.
Another form common to England and N. America is the Grebe
(Podiceps\ in which the toes are fringed with separate webs not united
into a common web. The Procellarii formes, which include the
Petrel (Procellarius), and the Albatross (Diomedea), are also swim-
ming and diving Birds, but they differ in being nidicplous and in
retaining the curious primitive character in having the covering of
the bill made up of several plates, recalling the scales of Reptiles,
whereas in most Birds it consists of a single horny sheath, which no
doubt has been produced by the fusion of several Such scales. The
Penguins (Sphenisciformes) are known to all frequenters of the
London Zoological Gardens by the upright gait and curious paddle-
like wings in which the feathers have degenerated into scales. The
toes are webbed, for these also are swimming and diving Birds which
use the wings as well as the feet to swim with. The palate is schizo-
gnathous. All the Penguins belong to the Southern Hemisphere.
More familiar are the Duck-like Birds (Anseriformes) distin-
guished by the series of transverse horny ridges on the palate,
extending to the edges of the bill and enabling these Birds to
either crop water plants or to hold struggling aquatic prey, like
frogs. The toes are webbed and the palate desmognathous. The
Anseriformes include all our Swans, Ducks and Geese.
Equally well characterised are the Birds of Prey or Falcon-like
Birds (Falconiformes), distinguished by their powerful arched beak
with cutting edges, the desmognathous palate and above all by the
cruel curved talons on their toes. These claws are the real weapons
of attack the beak is only used to tear off the flesh of the prey
when it has been killed. The Golden Eagle, our largest Bird of
Prey, has been known to kill a full-sized cat with a single blow
of its claws.
The Ciconii formes, or Stork-like Birds, are a more diversified
group. They have a desmognathous palate and usually a long
spear-like beak, with which they impale the fish on which they
feed. This group includes not only the Storks and Herons in
which the legs are long and the toes free, but the so-called
Steganopoda (Pelicans and Gannets), in which all four toes are
included in one web and the legs are short.
The Gruiformes, or Crane-like birds, including the Cranes and
Rails are often confounded with some of the Ciconiiformes, as many
XXIV] CLASSIFICATION 633
of them are wading birds with long legs, but they are distinguished
by having a schizognathous palate and by having the hallux or big
toe inserted in the leg higher up than the other toes.
The Charadriiformes, or Plover-like Birds, include Plovers, Gulls
and Pigeons. They are usually Birds with short legs and powerful
wings. Like the Gruiformes, they have a schizognathous palate.
The Cuculiformes,. or Cuckoo-like Birds, include the two very
different groups of the Cuckoos and Parrots, united by the desmo-
gnathous palate and the turning of the fourth toe back parallel to
the hallux; whether these two groups are really closely related
is doubtful.
The Coraciiformes, Roller-like Birds named after the Roller
(Coracias), include such diverse groups as Owls, Swifts, King-
fishers and Woodpeckers, and can only be described as a lumber
room a mere temporary convenience. Most of the Birds in it have
weak legs and descend very little to the ground, and, though nidi-
colous, do not make nests, but live in holes.
The Passeriformes, or Sparrow-like Birds, distinguished by an
aegithognathous palate and by being nidicolous and constructing
nests, are to be regarded as the most finished products of bird-
evolution. They include, besides Crows, Magpies, Shrikes, Swallows
and Jays, all our native songsters, and in the sub-division Oscines
alone, which includes the best songsters, there are 5000 species.
Sub-class I. AECHAEORNITHES.
The three fingers and their metacarpals remain separate, each
with a claw. Both jaws with alveolar teeth ; tail without pygostyle ;
wings with well- developed remiges.
Only example, Archaeopteryx.
Sub-class II. NEORNITHES.
Metacarpals fused.
Division I. Ratitae.
Flightless ; without a keel on the sternum ; without a
pygostyle. Coracoid and scapula fused.
Ex. Struthio, African Ostrich ; Rhea, American Ostrich ;
Dromaeus, Emeu ; Casuarim, Cassowary ; Apteryx, Kiwi.
Division II. Odontolcae.
Marine, flightless, without sternal keel; teeth in furrows.
Ex. Hesperornis (extinct).
634 AVES [CH.
Division III. Carinatae.
Without teeth, with a keeled sternum.
Tribe 1. Colymbiformes (Divers and Grebes). Plantigrade,
nidifugous, aquatic, toes webbed.
Ex. Colymbm, Diver; Podiceps, Grebe.
Tribe 2. Sphenisciformes (Penguins). Nidicolous ; wings
transformed into rowing paddles ; feathers small and scale-like.
Ex. Spheniscus, Penguin.
Tribe 3. Procellariiformes (Petrels). Nidicolous, good fliers,
pelagic; sheath of bill compound.
Ex. Procellaria, Petrel; Puffinus, Puffin; Diomedea,
Albatross.
Tribe 4. Ciconiiformes. Nidicolous ; swimmers or waders ;
desmognathous with basipterygoid processes.
Ex. Sula, Gannet ; Pelecanus, Pelican ; Ardea, Heron ;
Ciconia, Stork ; Phoenicopterus, Flamingo.
Tribe 5. Anseriformes (Ducks and Geese). Nidifugous;
desmognathous with basipterygoid processes ; with copulatory
organ; palate bearing hard, horny, parallel ridges.
Ex. Anas, Duck ; Anser, Goose ; Cygnus, Swan.
Tribe 6. Falconiformes (Birds of Prey). Nidicolous ; des-
mognathous ; beak powerful with decurved tip ; talons long
and curved.
Ex. Falco, Falcon; Aquila, Eagle; Cathartes, Turkey-
Buzzard.
Tribe 7. Galliformes (Game-Birds). Nidifugous; schizo-
gnathous.
Ex. Gallus, Common Fowl; Phasianus, Pheasant;
Tetrao, Grouse.
Tribe 8. Tinamiformes (Tinamous). Like Galliformes but
without pygostyle and with dromaeognathous palate.
Ex. Tinamus, Tinamou.
Tribe 9. Gruiformes (Cranes and Rails). Waders, legs
long, nidifugous ; schizognathous.
Ex. Rallus, Rail ; Fulica, Coot ; Grus, Crane.
XXIV] CLASSIFICATION 635
Tribe 10. Charadriiformes (Plovers, Gulls and Pigeons).
Schizognathous, legs short.
Ex. Charadrius, Plover ; Larus, Gull ; Pterocles, Sand-
grouse ; Columba, Pigeon.
Tribe 11. Cuculiformes (Cuckoos and Parrots). Desmo-
gnathous, fourth toe either permanently reversed or reversible
at will.
Ex. Cuculus, Cuckoo; Psittacus, Parrot.
Tribe 12. Coraciiformes. Nidicolous, but nest in holes,
arboreal, legs feeble.
Ex. Coracias, Roller ; Upupa, Hoopoe ; A kedo, King-
fisher; Stria, Barn-owl; Caprimulgus, Nightjar; Cypselus,
Swift; Picus, Woodpecker.
Tribe 13. Passeriformes. Nidicolous, construct elaborate
nests ; aegithognathous.
Ex. Passer, Sparrow; Turdus, Thrush; Hirundo,
Swallow; Alauda, Lark; Corws, Crow.
CHAPTER XXV
SUB-PHYLUM IV. CRANIATA
DIVISION II. GNATHOSTOMATA
SUB-DIVISION II. AMNIOTA
Class V. MAMMALIA
THE class Mammalia (Lat. mammae, breasts), the last division
of the phylum Vertebrata, includes those animals
General * J
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 modern lizards, Mammals
are derived from a type which has died out, leaving no modern
representatives. Thus Mammals are almost certainly descended
from the extinct group Theromorpha and birds from some Rhyn-
chocephalan 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
into horn, and under a microscope the outline of these cells can be
CH. XXV]
STRUCTURE OF HAIRS
637
seen like a mosaic on the surface of the hair, the outermost ones
overlapping each other like slates on a roof with the same function
of letting the water run off.
We saw that a feather originated as a little knob, the outside
of which was composed of horny cells, while the interior consisted
of soft living tissue 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 tine 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 remains
FIG. 314. Section through the skin of a Mammal. Highly magnified.
Diagrammatic.
1. Outer layer of dead horny cells which are rubbed off from time to time,
Stratum corneum. 2. Deeper layer of cells retaining their protoplasm,
Stratum Malpighii. 1 and 2 form the epidermis and are ectodermal in
origin. 3. Dermis or Corium. 4. A hair. 5. Sweat-gland.
6. Opening of the duct of the sweat-gland. 7. Sebaceous or fat gland.
8. Erector muscle of the hair. 9. Connective tissue fibres of the dermis.
10. Blood-vessel. 11. Vascular papilla at base of the hair follicle.
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 consequence of the rich supply of food brought by these vessels
to the deep cells of the ectoderm lying above them, these cells
bud off horny cells with great rapidity and persistence, and in this
way a column of horny cells is formed which pushes out the older
part of the hair arid causes the whole structure to assume a great
length, sometimes equalling that of the body. The plug of dermis
MAMMALIA [CH.
is called the papilla of the hair, it obviously corresponds to the
knob of dermis in the base of the feather, and so a hair might be
compared to a feather consisting only of the shaft and sunk in a
very deep and narrow pit of the skin (Fig. 314). 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 horny 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 their
usual surroundings and is capable of varying with safety 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. 314). 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 out
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 consist 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. 314).
Mammals, as we have seen, feed their young after they are born
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. It has been recently shown
that the mammary glands are simply enlarged and modified sebaceous
xxv]
SKULL
639
glands. In the lower
Mammals these glands
arise in connection with
rudimentary hairs (the
milk hairs) which are
later shed.
As 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, to a lesser
extent, in the heart and
the arrangement of the
great arteries and veins.
Turning first to the
skull, we find that in a
Mammal instead of hav-
ing only one knob or
condyle to fit into a
cup 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 sides of 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.
315). In Reptiles, more
especially the Chelonia,
the so-called single con-
dyle is really trifid,
the lateral parts being
-22
FIG. 315. Ventral view of the cranium of a Dog,
Canis familiar is x f .
1. Supra-occipital. 2. Foramen magnum.
3. Occipital condyle. 4. Tympanic bulla.
5. Basi-occipital. 6. Basisphenoid. 7. Ex-
ternal auditory meatus. 8. Glenoid fossa.
9. Foramen lacerum medium, aperture through
which the internal carotid passes to the brain.
10. Postglenoid foramen. 11. Alisphenoid.
12. Presphenoid. 13. Vomer. 14. Jugal.
15. Pterygoid. 16. Palatal process of
palatine. 17. Palatal process of maxilla.
18. Posterior palatine foramen. 19. An-
terior palatine foramen. 20. Palatal process
of premaxilla. 21. Opening of tube in
alisphenoid bone through which the carotid
artery passes. 22. Hole for passage of
Eustachian tube. 23. Process of squamosal
to act as a stay for condyle of lower jaw.
ii xn. Exits of cranial nerves. i 2. Second
incisors. c. Canine. pml, pm4. First
and fourth premolar. m 1. First molar.
640
MAMMALIA
[CH.
formed by the exoccipitals and the basal one by the basi-occipital.
From this condition it is easy to see how the conditions in Birds
and higher Reptiles on the one hand and in Mammals on the
other may have been derived. Then the brain instead of lying
behind the eyes extends forward between and above them ; there is
consequently no interorbital septum, and the side walls of the brain-
case are thoroughly and
firmly ossified, not merely
represented by a vertical
plate imperfectly ossified,
as in a Bird, or nearly
entirely membranous, as
in some Reptiles. These
walls are in fact consti-
tuted behind by bones
termed alisphenoids
which in reality corre-
spond to the epipterygoids
of Reptiles (see p. 572).
These "alisphenoids "are
applied to the wall of
the cranium above but
below they diverge out-
wards and join the ptery-
goid bone just as do the
epipterygoids in Lac&rta.
In front, the lateral walls
of the cranium are con-
stituted by orbitosphe-
noid bones, whilst a
Fm.316. Dorsal view of the cranium of a Dog, strong mesethmoid
Canis famiiiaris x|. bone is developed in the
1. Supra-occipital. 2. Parietal. 3. Frontal, internasal septum. This
4. Nasal. 5. Maxilla (facial portion).
6. Premaxilla. 7. Squamosal. 8. Jugal,
10. Postorbital process of frontal. 11. Infra-
orbital foramen. 12. Anterior palatine
foramen. 13. Lachrymal foramen, il. First
c. Canine, pm 4. Fourth pre-
13
12
septum is prolonged be-
yond the bones of the
face by a cartilaginous
plate forming the support
of a flexible nose or
muzzle ; this is a feature quite peculiar to Mammals. The base
of the cranium is completely ossified, not only behind by the
occipital and basisphenoid bones but in front by the presphenoid
incisor,
molar.
XXV] SKULL 641
bones. To the last-named a wedge shaped bone termed the vomer
is attached which projects downwards and divides the air-space
above the palatal folds into two. The name (Lat. vomer, plough-
share) is derived from the shape of the bone in Mammals; it is
inappropriate as a description of its shape in other Craniata.
Recent discoveries in the Theromorpha make it plain that the
Mammalian vomer is the representative oftheparasphenoid bone
of Amphibia and the lower Reptiles. The vomers of Amphibia and
Reptilia are represented in the Theromorpha by a pair of small
bones termed prevomers attached to the underside of the internasal
septum in front of the unpaired bone which corresponds to the
vomer of Mammalia. The pterygoid bones take the form of thin
vertical plates ; they are attached throughout their whole length to
the side wall of the cranium by the " alisphenoid." As in Croco-
dilia and desmognathous Birds the palatal folds are united in the
middle line; the bones supporting them are processes of the pre-
maxillary, 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. 315). (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 peri-otic, which is fused to the squamosal.
In Reptiles, on the other hand, the epi-otic joins the supra-occipital
and the opisthotic the exoccipital, while the pro-otic remains
distinct. The outer ear, the funnel-shaped passage leading into
the tympanum, which is termed the meatus auditorius ex-
ternus, 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.
s. & M. 41
642
MAMMALIA
[CH.
There is no quadrate recognisable 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 prefrontal 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. 316) which permits of the passage of a duct
leading from the orbit to the cavity of the nose. This duct carries
FIG. 317. Dentition of a Dog, Canis familiaris xj.
Second incisor. c. Canine. _P m l> pm4. First and fourth premolars.
ml.
pml, pm4.
First molar.
off 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 premaxilla 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
the bone which bears them. Many of these teeth are rooted, that
is to say, after a certain time the dermal papilla on which the
tooth is moulded becomes constricted at the base, so as to be
XXV] TEETH 643
connected by only a narrow neck with the adjacent connective
tissue, this appearing in the dried tooth as a small hole through
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 characteristic
organs ; they are more differentiated than those of other Craniata,
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.
317). The incisors are borne by the premaxilla and have sharp,
straight edges adapted for cutting morsels of convenient 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 against enemies,
or in the fights which occur among males for the possession of
females. The premolars have 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 the mouth. Finally the molars
have broad surfaces with which the food is sufficiently broken 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 Elasmobranchii, as
we have seen, the teeth are enlarged placoid denticles developed 013.
a fold of skin which is invaginated 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
this fold is represented by a solid wedge of ectoderm, called the
enamel organ, and in Amphibia and Reptilia it produces succes-
sive rows of teeth throughout life as they are needed. In Mam-
malia 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 predecessors and are regarded as belated
members of the first dentition. The teeth of Mammalia have
412
644
MAMMALIA
[CH.
undergone profound modifications in accordance with the different
habits assumed by different members of the class, and are one of
the principal features on which its division into orders is based.
From a study of the dentition of living Mammals the con-
clusion is arrived at that the typical number of teeth, that is to
--7
FIG. 318. Four diagrams to illustrate the evolution of the ear-bones in Mam-
malia. The diagrams represent the bones of the back of the lower jaw
viewed from the inner side. The tympanic membrane is cross hatched
and cartilage bones are covered with small circles, whilst membrane bones
are left unshaded.
A. Condition in early Theromorphous Reptile. The articular and quadrate
are large, and the dentary does not meet the squamosal.
B. Condition in later Theromorphous Eeptile. The dentary has met the
squamosal, and the quadrate and articular are reduced in size.
C. Condition in hypothetical form, the link between Theromorpha and Mam-
malia. The supra-angular has begun to extend along the border of the
tympanic membrane.
D. Condition in primitive Mammalia (Prototheria).
1. Squamosal. 2. Dentary. 3. Supra-angular. 4. Articular (= Malleus).
5. Quadrate (= Incus). 6. Columella auris ( = Stapes). 7. Tympanic
membrane.
say, the number which the common ancestral form possessed, may
be estimated at 44, i.e., 11 on each side of each jaw, made up of three
incisors, one canine, four premolars, and three molars. This fact is
Q "I A Q
expressed by the formula , where the upper line denotes
o . 1 . 4 . o
the teeth on each side of the upper jaw and the lower line those on
each side of the lower jaw.
XXV] EAR-OSSICLES 645
The apparent absence of the quadrate bone in the upper and of
the articular in the lower jaw has given rise to much speculation as
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 theory
was that they had been metamorphosed into the so-called ossicula
auditus 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, and this theory has been practically proved to be true by the
extensive series of discoveries of extinct Theromorphous Reptiles
made in the last ten years. Some of these Reptiles have become so
mammalian in their general appearance that their isolated teeth and
bones would certainly be regarded as mammalian remains if they
were found separated from the rest of the skeleton. In these
Reptiles the dentary bone of the lower jaw becomes progressively
larger and the other bones, including the articular, become smaller
and crowded into the hinder angle of the lower jaw. This enlarged
dentary acquires an articulation with the squamosal and the
quadrate bone becomes reduced in size, till it is no larger than
the columella auris with which it articulates. The stapes, since it
rests against the fenestra in the peri-otic capsule, evidently repre-
sents the columella auris of Birds and Reptiles. The reduced
quadrate represents the incus and the articular becomes the
malleus. The tympanic bone, which encircles the outer ear and
to which the ear-drum is attached, is not represented by cartilage,
but is a dermal bone. It is believed to be the representative of the
supra-angular bone which lies on the outside of the Reptilian lower
jaw above the angular (Fig. 318).
This view of the homology of the ear- ossicle, which is deduced
from the comparative anatomy of the Theromorpha is strongly
supported by the developmental history of these ossicles in the
higher Mammalia. The malleus is for a considerable time a block
of cartilage, which is part of the rod forming the cartilaginous lower
jaw and only becomes separated from it comparatively late in
development, whereas the incus is segmented from the upper half
646
MAMMALIA
[CH.
of the first visceral arch, as it should be if it represents the
quadrate.
The chief peculiarity of the brain as compared with Reptiles
is the greater development of the cerebral hemispheres, in
FIG. 319. Brain of Eabbit, Lepus cuniculus x 2.
A. Dorsal aspect. B. Ventral aspect.
1. Olfactory lobe. 2. Pituitary body. 3. Crura cerebri. 4. Pineal
gland. 5. Anterior pair of corpora quadrigemina. 6. Pons Varolii.
7. Cerebellum. 8. Lateral lobe of cerebellum. 9. Floccular lobe of
cerebellum. 10. Medulla oblongata. 11. Sylvian fissure separating
the frontal lobe 12 from the temporal lobe behind. i. Origin of first
or olfactory nerves. n. Optic or second nerves arising from the optic
chiasma. in. Third or motor oculi nerve. iv. Fourth or patheticus
nerve. v. Fifth or trigeminal nerve. vi. Sixth or abducens nerve.
vn. Seventh or facial nerve. vni. Eighth or auditory nerve,
ix. Ninth or glossopharyngeal nerve. x. Tenth or vagus nerve,
xi. Eleventh or spinal accessory nerve. xn. Twelfth or hypoglossal
nerve.
XXV] BRAIN 647
proportion to the hind-brain or cerebellum. The former overlap
completely and conceal the thalamencephalon and the mid brain,
and they are connected with one another by a great transverse band
of nerve-fibres, called the corpus callosum. It is customary to
map out the surface of the hemispheres into regions, in order to
facilitate description in delimiting the areas concerned with the
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 from the
frontal by a deep groove, called the Sylvian fissure (11, Fig.
319, 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 parietals, which represent merely
the membrane covering the anterior fontanelle, not only form the
roof of the cranium but a large part of its domed side wall ; and
further that the orbitosphenoid and alisphenoid, which are portions
of the cartilaginous brain-case, are restricted to the base of the
skull. The cerebrum has in fact protruded through the anterior
fontanelle, pushing the membrane before it. The same condition is
observable in Birds, but not in Reptiles or Amphibia. The cere-
bellum however is also well developed, just as in Birds, having
indeed in addition to the lateral lobes an outer pair of lateral pro-
jections, called flocculi, embedded in a hollow of the bone that
covers the inner ear (Fig. 319). The two halves of the cerebellum
are connected with one 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
which are supported by thin plates of bone arising from the meseth-
moid, and called ethmoturbinals. Above, where the mesethmoid
joins the orbitosphenoid, so numerous are the apertures in it to
allow the bundles of nerve-fibres from the olfactory cells to pass to
the brain, that this part of the bone is reduced to a sieve, whence
it has received the name of cribriform plate. From the maxilla,
which forms the outer wall of the lower part of the nasal tube, a
similar scroll-like bone, the maxilloturbinal, arises, which supports
a corresponding fold of epithelium. This fold however is supplied
only by the second division of the fifth nerve, and is not believed to
have any olfactory function, but merely to act as a filter to free the
inrushing air from grosser particles before it reaches the delicate
olfactory epithelium.
648
MAMMALIA
[CH.
The ear of Mammalia is distinguished by the development of a
region termed the cochlea which is not present or at any rate clearly
differentiated in the ears of the lower Vertebrates. It is a spirally
coiled outgrowth of the sacculus of the ear, which replaces the
simple retort-like lagena which is the outgrowth from the sacculus
in Birds and Reptiles. From a study of its minute structure it
appears that it is not the homologue of the lagena, which is still
represented in Mammals by a slight vesicular enlargement of the tip
FIG. 320. Diagrammatic transverse section of the bony cochlea and its con-
tained sense-organ in a Mammal.
1. Scala vestibuli. 2. Scala media (the real sense-organ). 3. Scala
tympani. 4. The pillars of Corti. 5. The tunnel of Corti.
6. Outer auditory cells. 7. Inner auditory cells. 8. Supporting
cells. 9. Basilar membrane. 10. Keissner's membrane.
11. Membrana tectoria. 12. Auditory nerve.
of the cochlea, but is rather a special development of the region at
the base of the lagena connecting it with the sacculus. The special
peculiarity of the cochlea is the organ of Corti, a development of
the epithelium forming the basal wall of the cochlea. This consists
of a double series of articular rods meeting each other above like the
beams of a roof. Between the opposite members of the series is a
space, the so-called tunnel of Corti. On the outer side of each
series are several rows of sensory (auditory) cells each carrying
xxv]
INTERNAL EAR
649
numerous short hairs. Underlying the sensory epithelium between
the divergent legs of the rods of Corti and beyond them is stretched
a connective tissue membrane consisting of parallel fibres termed
the basil a r membrane, and one theory of hearing is that these
fibres vibrate like piano strings in harmony with tones of different
pitch and stimulate the hair cells above them. The roof of the
cochlea is a thin layer of cells termed Reissner's membrane (10, Fig.
320), and from the inner side of the cochlea a flap termed the
membrana tectoria projects into its cavity. This is supposed
to act as damper to the vibrations of the sense-hairs when these
vibrations become excessive. The
cochlea, often termed the mem-
branous cochlea or scala media,
is enclosed in an expansion of the
peri-otic capsule of the same shape
termed the osseous cochlea. In-
side the osseous cochlea run two
lymph spaces, one lying above the
membranous cochlea, termed the
scala vestibuli, and the other
below the membranous cochlea,
termed the scala tympani. These
two spaces communicate with one
another round the tip of the mem-
branous cochlea. The scala tympani
ends externally against a membra-
nous window in the peri-otic bone
termed the fenestraovalis. There
is another membranous window in
the same bone called the fenestra
rotunda, behind which lies the scala
vestibuli and against which the stapes
impinges externally, and when a
vibration strikes the ear-drum, it is
transmitted by malleus, incus and
stapes to the fenestra rotunda and hence when it reaches the top of
the cochlea to the scala tympani. Along the lymph in this it comes
till it reaches the base of the cochlea. As the pulse passes along the
scala tympani it is transmitted through Reissner's membrane to the
cavity of the sense organ or scala media. Thus it stimulates the
hair cells which respond to tones of different pitch and hence
FIG. 321. Sternum and sternal ribs
of a Dog, Canis familiar is x .
1. Presternum. 2. First sterne-
bra of mesosternum. 3. Last
sternebra of mesosternum.
4. Xiphisternum. The flattened
cartilaginous plate terminating
the xiphisternum is not shown.
5. First sternal rib.
650 MAMMALIA [CH.
apparently only the Mammal has an apparatus for analysing a sound-
disturbance into its component parts. The outer ear or ectodermal
involution leading to the drum is in Mammalia guarded by an
external lobe termed the pinna of the ear.
The neck region of Mammals (with rare exceptions) always
consists of seven vertebrae, and thus whereas a long-necked Bird
like a Swan has numerous short vertebrae in this region, in a
long-necked Mammal like the Giraffe the same region consists of
seven immensely long vertebrae. The sternum of Mammals also is
peculiar, consisting of distinct pieces orsternebrae. The first of
these is called the presternum, and bears a crest for the attach-
ment of the pectoral muscles ; the last ends in a spade-like xiphoid
cartilage, and is called the xiphisternurn. The intervening
segments constitute the sternebrae of the mesosternum. The
lower ends of a pair of ribs are attached opposite the junction of
two sternebrae (Fig. 321). The division of the sternum into seg-
ments is supposed to be due to the strains exercised on it by the
sternal ribs owing to their movements in aid of respiration.
In Mammalia as in other Amniota the centrum is formed from
the ventral intercalaries, and the head of the rib is articulated
between two vertebrae ; the articulation is not shifted on to the
vertebra as in Crocodilia. The vertebrae have occasionally in the
neck region cup and ball articulations lit > those of Amphibia,
Reptilia and Aves, but elsewhere the thick intervertebral cartilage
allows of sufficient bending, and the centra have flat ends which ossify
late and for some time form separable discs of bone called epip hy ses.
These do not represent any new elements in the centrum, but only
a method of ossification found in the limb-bones of Amphibia,
Reptilia and Aves as well as in Mammalia. This method is as
follows: the ensheathing membrane or periosteum first forms a
tube of bone round the centre of the cartilage, the ends of which re-
main soft and capable of further growth; these terminal "epiphysial"
cartilages are only replaced by bone when growth is diminishing,
and are united with the main ossification when growth has ceased.
In the fore-limbs of Mammals the chief point to be noticed is
the reduction in size of the pectoral girdle to which the fore-
limbs are attached. The lower part of this, the coracoid, which
in Bir.ds and Reptiles is a large, strong bone meeting the sternum,
is here, with the exception of a few primitive forms, a small hook
with no connection at all with the sternum. Hence the pectoral
girdle is much more movable than is elsewhere the case, and takes
xxv]
PECTOKAL GIRDLE
651
part in the movements of the limb. It is therefore not surprising
to find that the upper portion of the girdle, the shoulder-blade or
scapula, is broad, affording a large surface for the attachment of
FIG. 322. Skeleton of Babbit, Lepus cuniculus x |. In sitting position.
muscles; and that its surface is still further increased by the
presence of a sharp vertical ridge rising up along its middle line
(Fig. 322). To the end of this spine, as it is called, the
652 MAMMALIA [CH.
collar-bone or clavicle is attached; this bone extends inwards to
the sternum and is loosely connected with it. In some Mammals
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 very short distance to the backbone ; and secondly, the
lower bones of the girdle, the pub is and ischium, meet their
fellows of the opposite side in front of the belly beneath the
anus, whereas in Birds they do not even approach each other in
this place, though in Rhea the ischia do meet dorsal to the anus.
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. 322). The
heel-bone or calcaneum is one of the uppermost tier of ankle-
bones and corresponds to the bone called fibulare in the general
scheme of the pentadactyle limb. It is prolonged into the heel,
to which the great gastrocnemius muscle which forms the calf of
the leg and which raises the heel is attached.
Turning now to the blood system of Mammals we find that the
red blood corpuscles which give the colour to the blood are unlike
those of other Vertebrates. They have no nuclei and are bicon-
cave, while they are also much smaller and (except in Camels and
Llamas) are circular, not oval discs 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 systemic arch alone, the right one being cut off from con-
nection with it and being represented by the common trunk of the
right carotid and subclavian arteries, the so-called innominate
artery (Fig. 323), this being exactly the converse of the arrange-
ment in Birds.
The ventral carotid arteries, which we have seen are reduced in
Birds as compared with Reptiles and Amphibians, are usually
absent in Mammals, though they may exist as quite small vessels
but the trachea and other structures in the neck receive blood from
the common or dorsal carotid on its way to the head. The sub-
clavian artery is of the dorsal type as in Lizards and Amphibians
in all Mammals except Cetaceans, in which order the fore-limb or
paddle obtains blood by an artery corresponding in origin with
that to the fore-limb of Chelonians, Crocodiles and Birds, i.e., a
xxv]
CIRCULATORY SYSTEM
653
" ventral subclavian." The " dorsal subclavian " possessed by most
Mammals is also found in Cetaceans, but it is distributed to the
ribs and their muscles as the "intercostal artery."
13
24
Fio. 323. Diagram of arterial arches of Mammals, viewed from the ventral
aspect.
A. Of all Mammals except Cetaceans.
i, n, in, iv, v, vi. First to sixth arterial arches. 12. Ventral carotid
(small or absent). 13. Common carotid (dorsal carotid). 14.. Syst-
emic arch. 17. Dorsal aorta. 18. Ductus arteriosus which in the
embryo connects the pulmonary and systemic arteries. . 19. Pulmonary.
20. Innominate. 22. Subclavian (dorsal type). 24. Coeliac.
B. Of Narwhal, representing Cetaceans.
i, n, in, iv, v, vi. First to sixth arterial arches. 12. Ventral carotid
(small). 13. Common carotid (dorsal carotid). 14. Systemic arch.
17. Dorsal aorta. 18. Ductus arteriosus. 19. Pulmonary. 20. Innomin-
ate. 21. Subclavian (ventral type). 22. Intercostal (equivalent to
eubclavian of dorsal type). 24. Coeliac.
654
MAMMALIA
[CH.
It is an interesting feature of the arterial system of a Mammal
that in consequence of the embryo receiving its oxygen from the
maternal blood, the connection between the systemic and pulmonary
arches persists in an unreduced condition until birth. This connec-
tion is known as the ductus arte-
riosus, 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 as
yet functionless lungs is avoided.
At birth the ductus arteriosus
shrinks and is rapidly reduced to
a solid cord, while the enlarging
pulmonary vessels provide for the
deviation of the venous blood to the
now expanded lungs (18, Fig. 323).
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 caudal vein is continued directly
into the inferior vena cava, so that
there is no longer even the outward
appearance of a renal portal system.
This is due to the formation of a
cross connection or anastomosis be-
tween the two posterior cardinal veins
immediately behind the kidneys and
to the subsequent disappearance of
the right posterior cardinal in front
of this, the left posterior cardinal
extending through the subcardinal
branch round the inner side of the
left kidney to join the inferior vena
cava where it issues from the kidneys. In consequence of this
re-arrangement the left posterior cardinal assumes the appearance
and functions of a posterior portion of the inferior vena cava. The
right posterior cardinal persists only as the right common iliac vein
into which the veins of the right leg empty themselves and as the
13
10
13
10
FIG. 324. Diagram to show arrange-
ment of the principal veins in a
Mammal.
1. Sinus venosus gradually dis-
appearing in the higher forms.
2. Ductus Cuvieri = superior vena
cava. 3. Internal jugular = an-
terior cardinal sinus. 4. Ex-
ternal jugular = sub-branchial.
5. Subclavian. 6. Posterior car-
dinal front part = venae azygos
andhemiazygos. 7. Inferiorvena
cava. 9. Caudal. 10. Sciatic
= internal iliac. 13. Femoral
= external iliac.
XXV] RESPIRATORY MOVEMENTS 655
right renal vein. The anterior portions of the posterior 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 develops a transverse branch through which
its blood joins that of the right cardinal (Fig. 324).
One of the most interesting peculiarities of Mammals is theiri
breathing mechanism. It will be remembered that whereas the
Amphibia simply swallow air, in the Reptiles 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 (see p. 287). The diaphragm is attached ventrally to the
xiphoid cartilage, 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. The thoracic division is
divided into two pleural cavities, one surrounding each lung,. by
the pericardium. Since 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 four large masses, viz. the sublingual,
underneath the tongue,, the submaxillary, under the angle of
the jaw, the parotidjust under the ear, and the suborbital inside
656 MAMMALIA [CH.
the orbit. The ducts of all four open into the buccal cavity. Glands
in similar positions are found in some Birds, but those of Mammalia
secrete in addition to mucus a ferment, called ptyalin, which turns
starch into sugar, so that the secretion which is called saliva is
a true digestive juice. The large development of the large intestine
causes most of the water to be absorbed from the undigested residue
of the food, thus reducing it to a semi-solid mass or faeces, which
is also a characteristic of the Mammalian alimentary canal.
Mammals are divided into three great primary divisions or
sub-classes according to the structure of the ovary and oviduct
and to the stage of development attained by the
Classification. . . . . ; , . . ,
young at birth. The lowest forms have comparatively
large eggs like those of birds in which abundance of yolk is de-
veloped : in the higher forms the egg is 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. In the highest
division a special organ for the nourishment of the embryo, the
placenta, is developed, as an enlargement of the embryonic
bladder.
The sub-classes are called :
I. PROTOTHERIA, or primitive Mammals.
II. METATHERIA, or modified Mammals.
III. EUTHERIA, or perfect Mammals.
Sub-class I. PROTOTHERIA
The Prototheria include two extraordinary animals, the Or-
nithorhynchus (Platypus), or Duck-billed Mole, and the Echidna, or
Spiny Ant-eater, which are found only in Australia, New Guinea
and Tasmania. In these animals large eggs with a firm shell 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
case with Birds and Reptiles. The ureters do not open into the
bladder as they do in all other Mammalia, but they and the bladder
open separately into the cloaca. In the male a copulatory organ or
penis is present lying beneath the ventral wall of the cloaca and
opening into it in front and protruded from the cloaca behind.
After they are hatched the young receive milk from the mother.
xxv]
PROTOTHERIA
657
There is no teat, but the fluid from the milk-glands seems to soak
into the hair and thence is sucked by the young. Before binh
FIG. 325.
Fio.326. Diagram to illus-
trate the arrangement of
the female genital ducts
in the Pro'totheria.
1. Ovary. 2. Oviducal
funnel. 3. Oviduct.
4. Opening into cloaca.
S. & M.
The Duckbill, Ornithorhynchus anatinus.
the young receive a certain amount of
nourishment from the mother but the egg
does not become adherent to the wall of the
oviduct. The egg of Echidna for instance
swells from a diameter of 2 millimetres to
a diameter of 4 millimetres and more in its
passage through the oviduct. A consider-
able amount of food is supplied by the
abundant yolk in the egg. After birth
the egg is carried by the female Echidna
in a ventral pouch of skin on the abdomen.
The female Ornithorhynchus has no such
pouch.
The skeleton of the Prototheria pre-
sents many interesting features of agree-
ment with the Reptiles ; thus the vertebrae
have no epiphyses, and there is not only
a complete coracoid articulating with the
sternum, but also two precoracoids which
42
658
MAMMALIA
[CH.
,-1
overlap. Underneath these there are two clavicles and a T-shaped
interclavicle, so that the shoulder-girdle recalls the complicated one
of the Lizard.
Ornithorhynchus has webbed feet and lives in the water, feeding
on worms and insects, which it digs out of the mud by its broad,
shovel-like snout, whence the name Duck-bill (Fig. 325). It crushes
its prey by means of horny plates, which are really patches of the
hardened gum : when it is young, however, it has true calcareous
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-
culata.
Echidna lives on ants and other insects, which it ensnares by
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. METATHERIA.
The division Metatheria in-
cludes the curious pouched Mam-
mals of Australia and the neigh-
bouring islands and the Opossums
of America. In these animals
the egg is exceedingly small,
and the egg-tube is divided into
an upper part of correspondingly
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. The egg-shell dis-
appears and the egg then de-
velops a close adhesion with the
wall of the uterus. Through
this adhesion nourishment is
absorbed and the embryo in con-
sequence grows and develops
FIG. 327. Ventral view of the shoulder-
girdle and sternum of a Duckbill,
Ornithorhynchus paradoxus x f .
After Parker.
1 and 2. Scapula. 3. Coracoid.
4. Precoracoid. 5. Glenoid
cavity. 6. Interclavicle. 7. Clavicle.
8. Presternum. 9. Third seg-
ment of mesosternum. 10. Sternal
rib. 11. Intermediate rib. 12. Ver-
tebral rib.
xxv]
METATHERIA
659
rapidly. The allantois, however, always remains small and though
in one or two cases it may contract an adhesion with the outermost
layer of cells of the developing egg and through this with the wall
of the womb yet this adhesion is temporary and does not persist till
birth. Most of the nourishment is absorbed through an adhesion
between egg and womb in the ventral region of the yolk-sac. Be-
neath 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 male.
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
vestibule for excretory and reproductive ducts is called the urino-
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 urino-genital sinus and through this opening the
embryo is born, the lateral vaginae serving merely to admit the
spermatozoa from the male.
The penis or copulatory organ is a
thickening surrounding the opening of the
urino-genital sinus in the male, it is
directly continuous with the neck of the
bladder, and through it with the vasa
deferentia.
When the young are born they appear
not as eggs but as little mammals, which
are however exceedingly small in size.
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 ossifications
of a tendon of the external oblique
muscle. Similar structures are found in
FIG. 328. Diagram to illus-
trate the arrangement in
the female genital ducts of
the Metatheria.
1. Ovary. 2. Oviducal
funnel. 5. Fallopian
tube. 6. Uterus.
7. Vagina. 8. Median
vaginal pouch. 9. Uri-
no-genital vestibule.
422
660
MAMMALIA
[CH.
Prototheria, in Crocodiles and in Urodela. The young are quite
incapable of feeding themselves, but each becomes attached to the
opening of one of the ducts of the milk-gland, and the area of
attachment becomes drawn out into a teat, and therefore the
FIG. 329. Petrogale xanthopw. The Rock Wallaby with young in pouch.
After Vogt and Specht.
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
XXV] METATHERIA 661
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. The pouch is however absent in some of
the more primitive Marsupials, and recent research has demon-
strated that it has arisen by the fusion of a number of separate
depressions, one of which is formed round the attachment of each
embryo.
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 recognised 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
FIG. 330. Skull of Lesuenr's Kangaroo-rat, Bettongia lesueuri. To exhibit
Diprotodont type of dentition.
POLYPROTODONTIA; the animals composing it have at least four incisors
on each side of the upper jaw and three on each side of the lower,
whence the name (Gr. iroXvs, many ; 717x0x09, foremost; oSou?, oSoWcs,
teeth). The DIPROTODONTIA, as the second order is called, derive
their name from the circumstance that in the lower jaw there is
one large pointed incisor on each side, the others being rudimentary
or absent, so that only two prominent teeth are observable (Gr. oYs,
doubly). The Polyprotodontia are represented in America by the
family of the Opossums, DIDELPHYIDAE, which is confined to that
continent. It includes 24 species, most of which are found in
Mexico, Central America, and Brazil, but one, the Virginian
Opossum, Didelphys virginiana, ranges north as far as the south
bank of the Hudson river. In all the Didelphyidae the great toe
is large and can be separated from the other toes so as with
them to grasp a support; thus it is said to be "prehensile." In
662
MAMMALIA
[CH.
many of the more primitive. Didelphyidae there is no pouch. In
Australia the Polyprotodontia are represented by three families,
viz. the DASYURIDAE, the PERAMELIDAE and the NOTORYCTIDAE.
The first family includes the animals known as native Cats, which
resemble the American Opossums, but are distinguished 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 the
Didelphyidae, as we have seen, this digit is long and prehensile.
The largest member of the family is Thyladnus cynocephalus,
FIG. 331. Banded Ant-eater, Myrmecobius fasciatus x.
the Tasmanian Wolf, now confined to the wilder parts of Tas-
mania: it has a skull which strikingly resembles that of a Dog;
in its habits it resembles a Wolf and is very destructive to Sheep.
The Banded Ant-eater, Myrmecobius fasciatus, is an aberrant
member of the same family which lives on insects, capturing them
with its long tongue. The insects are made to adhere to this
organ by the viscid saliva. The teeth, though rudimentary, are
distinct. There is no pouch: the young when first born cling to
the teats and conceal themselves in the long hair of the mother's
abdomen. The PERAMELIDAE or Bandicoots are small animals
XXV] METATHERIA 663
somewhat resembling Rabbits and Hares in their appearance but with
pointed muzzles ; they are remarkable in possessing a type of foot
characteristic of the Diprotodontia. The NOTORYCTIDAE include the
single genus Notwyctes, which in habits and appearance resembles
the Mole, a similar mode of life having brought about similar
modifications of structure.
The order DIPROTODONTIA includes a number of species confined,
with one exception, to Australia and the neighbouring islands.
One species, the only living representative of the family EPANOR-
THIDAE, has been recently found in South America. This animal,
which has received the name Caenolestes uliginosus, has feet like
the DIDELPHYIDAE, 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
forms like the PERAMELIDAE. The typical Diprotodontia have the
second, third, fourth and fifth toes of the hind-foot united by a web
of skin. The fourth is the strongest toe, the fifth is a little shorter,
but usually nearly as stout as the fourth; the second and third,
though as long as the fourth, are much more slender, while the
great toe is often rudimentary. Exclusive of the EPANORTHIDAE
there are three families in the sub-order. The first family, the
PHASCOLOMYIDAE, consists of one genus, Phascolomys, the Wombat,
represented by three species. The PHASCOLOMYIDAE are distin-
guished 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 size and appearance of a
Badger.
The second family, the PHALANGERIDAE, 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 Pha-
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 differ
totally in the structure of the limbs. The fore-limbs are so small
664 MAMMALIA [CH.
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. Macropus giganteus, the
Gray Kangaroo or " Old Man," may attain a height of from 4 to 5
feet. The fourth toe of the hind-foot has a powerful claw with
which when the animal is brought to bay it has been known to
rip open a dog. The allied genus Petrogale 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-called
Kangaroo-rats, Bettongia 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,
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 T ^j- 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
with folds in the wall of the uterus. This organ is a result of an
enormous development of the allantois. In Eutheria, the egg
contracts an adhesion with the wall of the uterus over its whole
surface, but that part of the surface against which the corrugated
and richly vascular allantois impinges is covered with vascular out-
growths called villi, which fit into pits on the wall of the uterus.
It is this area which is called the allantoic placenta. The rest
of the surface of the egg is termed the umbilical placenta. This
region is non-vascular, and through it nourishment is absorbed in
Metatheria. In the lower Eutheria some nourishment is absorbed
through the umbilical placenta for a considerable part of the period
of pregnancy, but in the higher Eutheria it is early destroyed by
an extension of the allantois round the egg. Both the membrane
xxv]
EUTHERIA
665
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 are separated only by the thin outer wall of
the placenta, so that nourishment diffuses from one to the other,
and the blood of the embryo is oxygenated and its carbon dioxide
removed by the maternal blood. So close is the connection, that
when the embryo is born and passes out of the uterus, carrying
FIG. 332
Diagrams to illustrate the arrangement of the female genital ducts
in an Eutherian Mammal. A. Babbit. B. Man.
1. Ovary.
2. Oviducal funnel. 5. Fallopian tube.
7. Vagina. 8. Urino-genital sinus.
6. Uterus.
with it the placenta, the latter in most cases tears open the vessels
in the wall of the uterus and the mother loses a considerable quan-
tity of blood. The lowest parts of the two oviducts are completely
joined and pass into a single passage, the vagina, while the middle
portions, or uteri, are sometimes quite separate as in the Rabbit
(A, Fig. 332), sometimes partly united as in the Cat, rarely com-
pletely joined as in Monkeys and Man (B, Fig. 332). In one or two
Metatheria, as already mentioned, a placenta such as has been
described has been recently discovered, but it is of very small
extent, and does not persist until birth. These facts lead us to
believe that Metatheria are degenerate descendants of early Eutheria,
666
MAMMALIA
[CH.
and we may take as a further mark of degeneracy the almost com-
plete disappearance of the milk set of teeth. The penis has the
same structure as in Metatheria.
Order I. Edentata.
When we take a general survey of the orders or main divisions
into which the Eutheria are divided we find that we have three or
four strange groups, the relations of which to the others are most
difficult to decide. These include the curious Edentata of South
America, comprising three families, the BRADYPODIDAE or Sloths, the
MYRMECOPHAGIDAE or American Ant-eaters, and the DASYPODIDAE
or Armadillos. With these the South African forms, included in
the families MANIDAE or Scaly Ant-eaters and ORYCTEROPODIDAE
- mm
Fia. 333. Tamandua Ant-eater, Tamandua tetradactyla. From Proc. Zool.
Soc. 1871.
or Cape Ant-eaters, are usually grouped, though their relationship
is a matter of doubt, and it seems clear that they have no close
relationship to the South American forms, for which reason we shall
use for these African families the name Effodientia. The name
Edentata means " toothless," and was given to the animals of this
group by the early naturalists because they supposed them to
be devoid of teeth. This is only the case with one small family,
the Ant-eaters, or MYRMECOPHAGIDAE, which like Echidna, have
lost their teeth through disuse. In the rest there are teeth,
but front teeth are always wanting. In the adult none of the
teeth have enamel and all are similar to each other. The
hands and feet are armed with great curved claws, adapted
for holding on to supports, not for grasping or attacking, and
xxv]
EDENTATA
667
incapable of being retracted or pulled back. Consequently the
hands and feet are like hooks, on which the animals walk
I
clumsily, bending the fingers under them. The apparent want
of utility is however explained when the animals are looked at in
668 MAMMALIA [CH.
their natural surroundings. It is then seen that one family, the
Sloths (BRADYPODIDAE), 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 appear-
ance so as to be almost invisible amidst the foliage. The second
family include the true Ant-eaters or MYRMECOPHAGIDAE ; in these
the strong claws are used for pulling down and digging up ant-hills.
The muzzle is long and toothless. There is a very long tongue,
FIG. 335. White-bellied Pangolin, Manis tricuipis.
and enormous salivary glands, the sticky secretion of which entraps
the ants. The Tamandua Ant-eater, Tamandua tetradactyla, of
Central and South America, is arboreal in its habits and lives in the
dense primeval forests of the New "World : it uses its strong
claws for climbing and has a prehensile tail. The third family,
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 develops
into hard bony plates like the osteoderms of Reptilia, whilst the
XXV] EFFODIENTIA 669
hair on the upper part of the body is replaced by horny 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 as 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 also in South America evolution seems to have run
a course of its own.
Order II. Effodientia.
The African group formerly classed with the South American
Edentata consists of two genera each representative of a family and
both are ant-eaters. The MANIDAE are represented by Manis, the
Scaly Ant-eater, which has the hair agglutinated to form overlapping
scales, but has no dermal plates and no teeth. This genus is also
found in Eastern Asia. M. tricuspis is arboreal in its habits. The
ORYCTEROPODIDAE are represented by the Cape Ant-eater, Orycteropus,
which has peculiar folded teeth and scanty hair. 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 the
neighbourhood of the large ant-mounds so common on the veldt.
The womb and the placenta in this group are of quite a different
type from that which is found in true Edentata, and this is one of
the main reasons for separating the two groups. In Edentata the
two uteri have coalesced to form a single dome-shaped uterus,
whereas in Effodientia the two uteri have coalesced only at their
lower portions and a forked or "bicornuate" uterus is the result.
Order III. Insectivora.
This is a group of small animals which, as their name implies,
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 and
the whole sole on the ground when they walk (Figs. 336, 337) ; 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
670 MAMMALIA [CH.
uncovered. In many cases there is a shallow cloaca surrounded by
a sphincter into which both anus and urino-genital passage open.
They possess an allantoic placenta, but this covers only a portion
of the surface of the egg, the rest of the surface of the egg being
occupied by an umbilical placenta. In this respect they are hardly
more advanced than those Metatheria which retain an allantoic
placenta. The Insectivora, as may be seen from the description,
are a very primitive group, and like other primitive groups consist
of a number of families widely differing from one another in struc-
ture. Taking a broad view we may say that the tropical families
exhibit the highest grade of structure. Thus the GALEOPITHECIDAE,
or Flying-shrews, represented by the genus Galeopithecus, have a
parachute-like expansion of skin extending from neck to hand,
forming a web including the fingers. A similar expansion of skin
reaches from wrist to foot, forming a web between the toes, and
there is a piece of skin connecting the two legs behind. There is
a ring of bone round the orbit, and the symphysis pubis is long and
strong. The TUPAIIDAE, or Tree-shrews, have likewise the orbit
encircled by bone and a strong symphysis pubis, but they are devoid
of any parachute-like extension of skin. 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.
The MACROSCELIDAE have no bony ring round the orbit but they
possess a strong symphysis pubis. Their most marked characteristic
is an elongated foot (see Fig. 336) which enables them to make great
springs. Hence the name Jumping-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 is the orbit never
surrounded by bone but the zygomatic arch is slender and sometimes
even absent. The brain cavity is very small and the symphysis pubis
is very short ; sometimes the pubes are united only by ligament.
The first of these families is the ERINACEIDAE, or Hedgehogs,
distinguished by the slender zygomatic arch, and by the tympanic
being in the form of a ring. The well-known Hedgehog, Erinaceus
europaeus, is intermediate in size between a rat and a rabbit. It has
the fur intermixed with spines, and when alarmed can roll itself
into a ball, tucking in head, limbs and tail, and in this condition can
bid defiance to its enemies. All Erinaceidae are not of this character;
the rat-like Gymnura from India and the Malay Peninsula is
without spines.
xxv]
INSECTIVORA
671
The other two families are the Shrew-mice (SORICIDAE) and
the Moles (TALPIDAE) ; these are represented in both Great Britain
and North America, but the latter country is without Hedgehogs.
The Soricidae have lost the zygomatic arch altogether, the pubes
are disconnected and the tympanic is ring-like. As the popular
name implies these are mouse-like animals covered with fur.
There are three British species, JSorex vulgaris, about the size of
an ordinary Mouse, Sorex pygmaeus, one of the smallest Mammals
known, and Crossopus fodiens, the Water-shrew, distinguished by
FIG. 336. African Jumping-shrew, Macroscelides tetradactylus x
Peters.
From
having the feet frayed with stiff hairs to aid in swimming. The
North American Blarina, has the aspect of a Mole with its smali
eyes and rudimentary outer ears. It is called the Mole-shrew, but
its normal arms and hands at once distinguish it from the true
Moles. The true Moles, TALPIDAE, are above all characterised by
the greatly enlarged hands and powerful though short arms by
which they are adapted for a burrowing life. To make room for the
large hands in narrow burrows the front segment of the sternum is
greatly elongated, thus carrying the pectoral girdle and limbs forward
672 MAMMALIA [CH
on to the neck, where there is room for them. The clavicles are short,
almost square bones, and the humerus of the arm is short and stout.
The zygomatic arch is present and the tympanic is a bulla. The
TALPIDAE are represented in Great Britain by Talpa europaea, the
Common Mole, which feeds on earthworms, constructing a complicated
system of underground passages through which it hunts its prey.
In North America the commonest is perhaps Condylura cristata, the
Star-nosed Mole, the snout of which is encircled by a ring of fleshy
outgrowths.
The Russian Desman, Myogale moschata, belongs to the Mole
family 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 its mode of life the hind-feet are
webbed and the tail large and compressed, forming an efficient
swimming organ. It is hunted for its fur (Fig. 337).
There still remain four families to be mentioned, each of which
however is 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 type of tooth
is the tri-tubercular, which is found in the oldest remains of Mammals
known : it is distinguished by the reduction of the characteristic
cusps of the insectivoran tooth to three which form the points of a
triangle. Of these primitive families the (1) CHRYSOCHLORIDAE are
the Golden Moles of the Cape, so-called from the iridescent sheen of
the fur. They have the reduced eye and enlarged hands and arms
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
zygomatic arch is present and the tympanic is a bulla. The remain-
ing families have lost the zygomatic arch and the tympanic is a mere
ring. These are (2) POTAMOGALIDAE, represented by a single species,
Water-shrews from Central Africa, with a flattened tail, short limbs
and no clavicles, (3) SOLENODONTIDAE, and (4) CENTETIDAE, two
externally similar but not closely allied families of small hog-like
animals with stout limbs, the first from Cuba and Hayti and the
second from Madagascar.
The most interesting circumstance about the Insectivora is the
fact that when by means of fossils we trace back the higher groups
of Mammals they seem all to merge imperceptibly into forms which
from their teeth and general organisation we should class as
xxv]
1NSECTIVOKA
673
Insectivora. There is therefore really good ground for supposing
that the living Insectivora, though modified in special details, never-
theless represent, so far as their general organisation is concerned, the
earliest type of Eutheria which appeared on the globe. From these
original Insectivores advance seems to have taken place along four
lines : (I) some Insectivora took to attacking larger prey, including
their own less fortunate relatives, and gradually developed into the
Carnivora or flesh-eating Mammals: (II) some became vegetable
FIG. 337. Eussian Desman, Myogale moschata.
feeders and gave rise to the great group of hoofed animals, relying
either on their swiftness or on their size and strength for defence:
(III) some took to burrowing and developed into gnawers or Rodents,
relying chiefly on their burrows for safety : (IV) some took to climbing
trees when hard pressed, and of these some (a) developed the power
of leaping from tree to tree into the power of flying, the fore-limb
becoming changed into a wing; these are the Bats; the rest
(6) remained purely tree dwellers, and eventually gave rise to the
great group of the Primates which includes Monkey and Man.
S. &M.
674 MAMMALIA [CH.
Order IV. Carnivora.
The Carnivora are distinguished above all by their teeth (Fig.
317). They have small insignificant front teeth or incisors, but
the eye-teeth or canines, situated in the maxilla just where it
meets the premaxilla, are large and pointed. With these the animal
seizes 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 below
are broad and crushing (Figs. 317 and 338). The last premolar in
the upper jaw and the first molar in the lower jaw constitute what
are called the carnassial teeth. These are very large blade-like
teeth which bite on 'one another like a pair of scissors. The upper
one has enlarged central and posterior cusps, the anterior cusp
being small or wanting ; the lower carnassial has an anterior blade-
like portion consisting of two cusps and a posterior flattened portion
or heel. The nails are sharp curved claws.
The most familiar examples of this class of animals are our Dogs
and Cats. The wild ancestors of the domesticated pets are unknown,
though the Dog's ancestors were no doubt allied to the Wolf, whereas
the Cat is probably descended from some species belonging to the
East, allied to but distinct from the Wild Cat, Fells catus, still
found in remote parts of Scotland and possibly in the mountains of
North Wales. Possibly the Domestic Cat has originated from the
Caifre Cat, F. caffra, which extends throughout Africa and was
considered sacred by the ancient Egyptians, who embalmed their
bodies in such amazing numbers that their mummies have been
exported from Egypt and used as manure.
In the Dog, Canis familiaris, and the other members of the
family CANIDAE, the muzzle is long and the teeth numerous.
Their arrangement can be expressed by the dental formula
i. - , c. - , pm. - m. - = 42, where the upper line shows the teeth in
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 claws are compara-
tively blunt and cannot be retracted.
In the domesticated Cat, which is a typical member of the
Family Felidae, on the other hand the muzzle is short, and the
xxv]
CAKNIVORA
675
teeth reduced in number, the formula being i. ?, c . - t pm. -,
m. - = 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
19 a a
FIG. 338. Vertical longitudinal section taken a little to the left of the middle
line through the skull of a Dog, Canis familiaris x .
1. Supra-occipital. 2. InterparietaL 3. Parietal. 4. Frontal. 5. Cribri-
form plate. 6. Nasal. 7. Mesethmoid. 8. Maxilla. 9. Vomer.
10. Ethmoturbinal. 11. Maxilloturbinal. 12. Premaxilla. 13. Occip-
ital condyle. 14. Basi-occipital. 15. Tympanic bulla. 16. Basisphenoid.
17. Pterygoid. 18. Palatine. 19. Alisphenoid. 20. Internal auditory
meatus, the passage for the eighth nerve to the internal ear. 21. Tentorium,
a fold of calcified connective tissue projecting into the cranial cavity and
separating the cerebrum from the cerebellum. 22. Foramen lacerum
posterius, the passage for the tenth nerve. 23. Floccular fossa,
the cavity in which the floccular lobe of the cerebellum is lodged.
24. Coronoid process. 25. Condyle. 26. Angle. 27. Mandibular
symphysis. 28. Inferior dental foramen. 29 31. Segments of the
second visceral arch. 29. Stylohyal. 30. Epihyal. 31. Cerato-
hyal. 32. Basihyal. 33. Thyrohyal, the third visceral arch,
xii. Condylar foramen, the aperture through which the twelfth cranial
nerve leaves the skull.
respects Cats are more perfectly adapted for a carnivorous life than
Dogs, since these latter still retain traces of their descent from a
different kind of Mammal. Just as the Wolf, C. lupus, the Jackal,
G. 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
432
676 MAMMALIA [CH.
Lion, F. leo, the Tiger, F. tigris, the Leopard or Panther, F. pardus,
the Lynx, F. lynx, and the Puma, F. concolor (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 it lives ; 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, UESIDAB, represent a third type of Carnivora. 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
broad, the carnassials are broad and the premolars very small and
often fall out ; the upper carnassial is a comparatively small tooth
and the heel of the lower carnassial is larger than the blade ; these
peculiarities are connected with the fact that the Bears are not
merely flesh feeders but can live partly on a vegetable diet. The
Brown Bear of Europe, Ursus arctos, which used to be abundant in
Britain, is so nearly allied to the Grizzly Bear, U. horribilis, of
the Rocky Mountains, that the latter is by some authorities placed
in the former species. In Eastern Canada, especially in the Province
of Quebec, the Black Bear, Ursus americanus, is very abundant and
is 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 remains of fossil Carnivora demonstrate
that the Ursidae were derived from primitive types of Canidae in the
Miocene period.
The Stoats, Weasels, Martens, Minks, Polecats, Otters, Badgers
and Skunks, forming the family MUSTELIDAE, are sometimes supposed
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 are found in Great Britain : (1) The Otter,
Lutra vulgaris, an animal which has webbed toes and a long, some-
what flattened tail. It lives on fish, passing much of its time in the
xxv]
CARNIVORA
677
water. (2) The Badger, Meles taxus, a heavy, somewhat clumsy
animal with blunt 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,
Putorius foetidus, which feeds on small mammals, birds, reptiles and
eggs, and has a disagreeable odour. The Ferret is a domesticated
variety of the Polecat. (5) The Weasel, Putorius vulgaris. In cold
regions the Weasel turns white in winter. (6) The Stoat, Putorius
erminem, which also turns white in cold climates except the tip of
its tail, which remains black. Its winter fur is much prized and is
FIG. 339. The Common Skunk, Mephitis mephitica.
termed Ermine. These last four are closely related species with
long, slender bodies, sharp curved claws and ferocious habits.
In North America there is an interesting family, the PRO-
CYONIDAE, intermediate between the Ursidae and Mustelidae. The
members of this family have sharp muzzles but clumsy bodies and
short necks ; the Raccoon, Procyon lotor, is the most familiar. It
is omnivorous. The Mustelidae are represented by Otters, Martens
and a remarkable form, the Skunk, Mephitis mephitica (Fig. 339),
which produces a secretion of such repulsive odour as to make it
678 MAMMALIA [OH.
avoided by other animals and a terror to man. It is strikingly
marked with sharply contrasted black and white patches but these
alternations of shade tend to conceal it by breaking up its outline as
seen in the pale moonlight when it sallies forth to seek its prey.
The VIVERRIDAE should be mentioned although they are a tropical
group. In general shape they resemble the Mustelidae, but in the
shape of the carnassial teeth and in the division of the auditory bulla
by a septum they agree with the Felidae. The best-known members
of the family are the African and Indian Civet Cats ( Viverra civetta
and V. zibetha) from whose perineal glands the civet of commerce
is obtained. Fossil remains connect the Viverridae and Mustelidae
and one would not be far astray in calling them " Primitive Cats."
The Carnivora mentioned hitherto are often grouped together as
the CARNIVORA VERA or FISSIPEDIA. The second group of recent
Carnivora is represented by the seals and is termed the PJNNIPEDIA.
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-cows, but they have become adapted to
their surroundings in quite a different way. Thus their fur is
close and thick, and they are protected against 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 insignificant, 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
act just in the same way as the tail does in a Whale, making up and
down strokes and driving the animal forward. The whole upper
part of the limb is buried in the body. In one group, the true Eared
or Seal-skin Seals, OTARIIDAE (the fur of some species of which
is used for making jackets), the feet can be turned forward when
the animal comes on land. There are also some traces of an
external ear, whence comes the name OTARIIDAE or Eared Seals
which is given to them. They are confined to the Pacific coasts
of America and Asia. Species termed " Sea-lion " (Otaria jubata)
thrive well in captivity, and are often seen in Zoological Gardens
(Fig. 340). The Walrus, Trichechus rosmarus, of the Arctic seas,
is the representative of a second family, the TRICHECHIDAE. No
external ear is present but here also the feet can be turned forward.
The canine teeth of the upper jaw are very long and give the animal
a fierce appearance. They are however chiefly used for digging up
bivalves from the mud and for climbing on the blocks of ice in the
Arctic regions where the animal is found. The name " Old Man "
xxv]
CARNIVOEA
679
sometimes given to it by whalers is suggested by the tufts of gray
hair on the sides of the face. The common Greenland Seal, Phoca
vitulina and the Gray Seal Halichoerus grypus, both of which are
found round the British coasts in out-of-the-way places, belong to
the third family PHOCIDAE, the members of which are distinguished
by having no ear-flaps and by being unable to turn their feet for-
wards. For this reason when they are on land they can only move
by wriggling on their abdomens aided by movements of the fore-
limbs. Phoca vitulina is common on the eastern coasts of Canada
and the United States of America.
FIG. 340. The Patagonian Sea- Lion, Otariajubata. From Sclater.
Order V. Cetacea.
The order of Whales includes Mammals thoroughly adapted to
an aquatic life which pass all their life in the water. The great
majority of them are confined to the sea but a few are found in the
great rivers. In consequence of their mode of life they have under-
gone great changes of structure. Thus all external trace of the
hind-limbs has disappeared although a pair of small bones "repre-
senting the pelvic girdle are found embedded in the body. The
fore-limbs have become flippers. The fingers are bound together by
skin to their very tips and the number of joints (phalanges) in each
680 MAMMALIA [CH.
finger has been greatly increased ; the limb is buried in the body
almost to the wrist. The terminal vertebrae of the tail have become
flattened and have expanded transverse processes (diapophyses).
These support a flattened tail fin which is extended in the horizon-
tal plane not in the vertical plane like that of true Fish. Whales
progress by moving the tail fin up and down, whereas in Fish the
movement is from side to side.
All hair has disappeared, only one or two hairs being found in
the region of the lips in the embryo and these disappear when the
adult state is reached.
The body is covered with a thick layer of fat termed blubber,
which preserves the heat of the body and thus in a different way
the Whale is as well protected against the cold water as is a Seal
which has retained its thick furry coat. It is for the sake of the
blubber which is used for making oil that Whales are principally
hunted now-a-days. The skull 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 fat,
which is an admirable buttress of defence for the animal's skull.
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 frontals. The frontals develop great
orbital plates flanking the face, beneath which is the small orbit
bounded below by the slender jugal. The nasal organ has almost
totally disappeared : the vestigial nasal bones overhang an almost
vertical air passage which leads from the choanae to the external
nares. These latter open by a single opening termed the blow-hole
placed far back on the upper surface of the head. The epiglottis
and the arytenoid cartilages surrounding the glottis are prolonged
upwards into a kind of cone which is tightly embraced by a down-
ward prolongation of the soft palate : and thus the mouth can be
opened widely and enormous quantities of water taken into it, whilst
all the time air can pass uninterruptedly from the blow-hole to the
lungs and vice versa. When a Whale rises to the surface to
breathe, it empties its lungs by a strong blast just before it actually
reaches the surface, and in this way an ascending column of hot moist
air is produced. The moisture rapidly condenses into water, the
column seen from the deck of a ship looks like a jet of sea- water,
and in common parlance the Whale is said to " spout." In Whales
also the teats are situated far back, as they are in Cows, and the
connection of larynx and soft palate which enables the adult to
XXV] CETACEA 681
breathe and eat at the same time enables the mother Whale to force
milk down the young one's throat without choking it.
It is an interesting fact that the nasal organ should have become
vestigial in Whales whereas in Fish, it is a large and important sense
organ. But we must remember that the nasal organ was originally
evolved for the purpose of perceiving substances dissolved in water :
but that when land animals were evolved from Fish this organ became
adapted to perceive gaseous substances in the air which was drawn
past the opening of the nasal organ. Now the Whale is interested
in substances dissolved in the water, not in gaseous odours in the
air, but as an air-breathing animal it could not admit water to its
nasal organ without the risk of choking, and hence this organ has
lost its function and become vestigial.
The external ear is liable to become a great nuisance to an animal
which spends so much of its time beneath the surface of the water
as every swimmer and diver knows to his cost. Hence in Whales it
is reduced to capillary dimensions so as to exclude the water as
much as possible. In a Porpoise six feet long, it is of the dimensions
of a pin hole. It is certain therefore that Whales do not hear through
the outer ear : they hear through the bones of the head as a fish
does. This point was made clear by experiments designed to find out
the best means of detecting a submerged submarine.
Whales are divided into sub-orders, the whalebone Whales or
MYSTAGOCETI and the toothed Whales or ODONTOCETI. In the
latter there are numerous teeth, but they are all alike and simple
(Fig. 341), and the maxilla develops a great crest which conceals the
orbital plate of the frontal. The great Sperm-whale, Physet&r
macrocephalus, of the Southern Seas, has teeth only 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
oil is the melted-down fat of this monster. The Ca'ing or Pilot
Whale (Globicephalus melas), which also feeds chiefly on cuttle-fish,
has teeth on both upper and lower jaws (Fig. 341). 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. Of these we may name 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. It abounds in the Firth of Clyde. In the Gulf of
St Lawrence the White Whale, Delphinapterus leucas, is fairly
common. It attains a length of twelve feet.
682
MAMMALIA
[CH.
The whalebone Whales, Mystacoceti, have no teeth. The
orbital plate of the frontal is uncovered and there is a small
ethmoturbinal covered with olfactory epithelium. They are all
large animals, although they feed on the smallest prey, such as
minute pelagic mollusca, jelly-fish and Crustacea. The "whale-
18
FIG. 341. A. lateral view, and B. longitudinal section of the skull of a young
Ca'ing Whale, Globicephalus melas x .
accipital. 4. Basisphenoid.
Interparietal fused with 3.
Frontal. 11. Mesethmoid.
Squamosal. 15. Jugal.
Pterygoid. 19. Nasal.
Mandible. 23. Anterior
bone " or baleen consists of a large number of horny 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
Basi-occipital. !
5. Alisphenoid.
8. Presphenoid.
12. Tympanic.
16. Vomer.
20. Maxilla,
nares.
2. Exoccipital. 3. Supra-
6. Parietal. 7.
9. Orbitosphenoid. 10.
13. Periotic. 14.
17. Palatine. 18.
21. Premaxilla. 22.
XXV] CETACEA 683
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, Balaena mysticetus, an animal about 50 feet long,
found only in the Arctic regions. The Great Rorqual Whale,
Balaenoptera sibbaldi, has a fin in the middle of its back, and
attains a length of 60 80 feet ; it is the largest animal now
found on the globe and is very abundant. The Lesser Rorqual,
Balaenoptera rostrata, 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
whalebone is shorter and coarser.
In Eocene deposits remains of primitive toothed Whales are found
which have been termed " Zeuglodonts," because the teeth have two
distinct roots and were at first mistaken for two teeth fused together,
hence the name (Gr. ^evyXry, loop of a yoke ; 68ovs, oSoVrcs, teeth, lit.
yoked-teeth). The teeth were distinguishable into incisors, canines
and trenchant cheek-teeth like the premolars of the Dog. These
remains give reason to believe that the land-mammal from which
Cetaceans were derived was a member of the group Creodonta an
extinct group which might be described either as primitive Carnivora
or as intermediate between Insectivora and Carnivora. This group
was distinguished by the possession of small incisors, large canines and
trenchant cheek-teeth carrying three cusps like those of primitive
Insectivora but no carnassial teeth were differentiated. It is quite
possible that Seals (Carnivora Pinnipedia) are likewise directly
derived from Creodonta since they also have no carnassial teeth.
In this case Whales and Seals would represent two independent
adaptations of primitive Carnivora to aquatic life, but the means by
which the adaptation was effected are totally different in the two
cases, for the hairy coat of Seals is functionally replaced by the
blubber of Whales whilst the powerful tail fin of Whales is represented
by the hind-legs of Seals.
Order VL Ungulata.
The great group of the Ungulata or hoofed animals represents
the second line of evolution from the primitive Insectivora. Here
we find that all power of grasping with the limbs is absent and the
684 MAMMALIA [CH.
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 must
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 1. Sub-ungulata.
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 members of the other sub-order of the Ungulata,
and formed one of the most striking examples of parallel evolution.
Only two families of the SUB-UNGULATA, as these animals are
called, survive at the present day. These are the family of the
Hyrax, HYRACIDAE, and the Elephant family, PROBOSCIDEAE.
HYRACIDAE.
The Hyrax (Procavia) is the Coney mentioned in the Bible.
The Hyracidae are small, not unlike rabbits in ap-
pearance, but their hind-feet closely resemble those
of the Rhinoceros. Their front teeth are, it is true,
somewhat chisel-shaped, as in the Rodentia, but there are four of
these below and two above, which is quite unlike the arrangement
in the rabbit. It is possible however that the two teeth reckoned
as lower posterior incisors may really be canines, since they do not,
like the other incisors and like those of the Rabbits, grow throughout
life (Fig. 342). These animals are found throughout Africa except
in the north and also in Arabia and Syria. Only one genus is now
recognised, Hyrax (Procavia), with several species. Most of these
live amongst rocks, in mountains and in stony places, but some
frequent the trunks and large branches of trees and sleep in holes.
PROBOSCIDEAE.
The Elephant is too well Ijnown to need much description, but it
may be pointed out that its trunk is really a long fiex-
ikle snout > an excessive exaggeration of what is found
in Insectivores, and that its tusks are front teeth, only
XX V] PKOBOSCIDEAE 685
those in the upper jaw being developed, and finally that the upper
parts of the arms and legs are quite free from the body, instead of
being, as is usually the case with Mammals, buried inside the general
contour of the body. There are only two living species, the African
Elephant, Elephas africanus, inhabiting the forest region of tropical
Africa and hunted for its tusks, and the Indian Elephant, Elephas
indicus, inhabiting the jungles of India, Further India, Ceylon and
Sumatra, which is frequently domesticated. The canines are lost
and have left no traces. The molars succeed one another in a
horizontal row, never more than two being at any one time functional
(Fig. 343). The ridges on these teeth when worn present the appear-
ance of parallel bands in the Indian Elephant, but in the African
1.1
1.1
FIG. 342. Skull of Hyrax (Procavia) dorsalis x .
1. Nasal. 2. Parietal. 3. External auditory meatus. 4. Process
of the exoccipital. 5. Jugal. 6. Lachrymal foramen. il. First
incisor.
they form diamond-shaped lozenges. The ears of the latter species
are very large and the trunk ends in two nearly equal prehensile
" lips " attached to its lower margin. In the Indian Elephant the
ears are smaller; there is but one finger-like "lip" at the end of
the trunk and this is attached to the upper margin of the
trunk. The skull is very massive, but the exterior gives an
erroneous impression of the size of the brain-case because the bones
are enormously thickened and contain large air-spaces, especially
in older specimens, where the frontals may attain a thickness of
one foot. The evolution of the Elephant from an ordinary type of
pig-like animal has been elucidated by the labours of Dr Andrews.
In the Glacial Period which immediately preceded the one in which
we are living, a hairy Elephant the Mammoth (Elephas primigenius]
686
MAMMALIA
[CH.
roamed over Northern Europe and Asia and was hunted by primitive
man. In older deposits we come on the remains of Elephants known
as Stegodon and Mastodon in which the ridges crossing the molars
of Elephants reveal their character by breaking up into pointed
cusps like those on the teeth of Insectivores. In the earlier species
of Mastodon a rudimentary pair of lower incisors is present in
addition to the tusks. In Miocene deposits remains of a creature
termed Tetrabelodon are found in which there was only a short trunk,
but which possessed a pair of long lower incisors in addition to the
... ii
FIG. 343. Skull of a young Indian Elephant, Elephas indicus, seen from the
right side, the roots of the teeth have been exposed x .
1. Exoccipital. 2. Parietal. 3. Frontal. 4. Squamosal. 5. Jugal.
6. Premaxilla. 7. Maxilla. 9. Supra-occipital. 13. Basi-occipital.
14. Postorbital process of the frontal. 15. Lachrymal. 16. Pterygoid
process of the alisphenoid. i 1. Incisor. mm 3, mm 4. Third and
fourth milk molars. m 1. First molar.
upper tusks. In the contemporaneous Dinotherium these lower
incisors formed downwardly curved tusks and the upper incisors
were absent. The animal could not have used these inwardly
curved incisors for offence but must have used them for grubbing
up roots. Finally in the Eocene period a beast is found with com-
paratively short upper and lower incisors and the trunk was not
better developed than it is in Insectivora. It adds to the interest
of these discoveries to know that the remains of all this ancestral
xxv]
UNGULATA VERA
687
chain of animals are found in the same region (N. Africa) in de-
posits lying directly above one another. Dr Andrews seems to have
discovered the actual locality where the evolution of the Elephant
occurred, a discovery which it has fallen to the lot of few to make.
Sub-order 2. Ungulata vera.
All the rest of the Ungulata have the thigh and the upper arm
more or less buried in the body, whilst the heel and the wrist are
raised in walking so that the creature goes along on the tips of its
FIG. 344. Bones of right fore-foot of existing Perissodactyles. A, Tapir,
Tapirus indicus x 4. . B, Khiaoceros, Rhinoceros sumcCtrensis x . C, Horse,
Equus cdballus x ^.
e. Cuneiform (ulnare). I. Lunar (intermedium). m. Magnum (third
distal carpal). p. Pisiform. R. Eadius. . Scaphoid (radiale).
td. Trapezoid (second distal carpal). tin. Trapezium (first distal carpal).
U. Ulna. u. Unciform (conjoined 4th and 5th distal carpals).
ii v, second to fifth digit. From Flower.
toes. The bones of the wrist are arranged in transverse rows, the
members of two adjacent rows alternating with one another. The
first digit in both fore- and hind-limbs is entirely absent. These
true Ungulates, UNGULATA VERA, as they are called, are divided
into two great groups: (1) the PERISSODACTYLA, in which there
is an odd number of toes and in which the true central axis of both
688 MAMMALIA [CH.
arm and leg runs down through the centre of the third finger or toe
(Fig. 344), 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. 347).
Division I. PERISSODACTYLA.
The Perissodactyla were formerly a numerous class of animals,
but now three families alone survive, the Tapirs, TAPIRIDAE;
the various species of Rhinoceros, RHINOCEROTIDAE ; and the Horse
and numerous species of Ass, EQUIDAE.
Of these the oldest and most primitive are the TAPIRIDAE. 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. 344). 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 history 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 Eocene 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 "dis-
continuous distribution."
The RHINOCER'OTIDAE are represented at the present day by the
genus Rhinoceros. The Rhinoceros is a heavier and
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 horny 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. 345); the Javan, R. sondaicus, is smaller. Both these species
have but one horn. Two-horned Rhinoceroses (the two horns stand-
ing one behind the other) are now found in the Malay Peninsula,
XXV J PERISSODACTYLA 689
Borneo and in Sumatra (R. sumatrensis\ while in Africa there are
several species; the commonest, R. bicornis, is frequently shown
in menageries. It is supposed that the idea of the unicorn
was derived from the one-horned Rhinoceros, but if this be so the
imagination must have played a powerful part in evolving the
graceful animal which figures in the royal arms out of the clumsy
Rhinoceros.
The general appearance of the Horse, Equus caballus, is
Equidae. sufficiently well known, but the structure of its
feet, which, next to the wings are the most highly
specialised organs of locomotion in the animal kingdom, demand
careful attention.
FIG. 345. Indian Khinoceros, Rhinoceros unicornis. From Wolf.
The apparent "knees" of the Horse correspond to the joints of
the wrist and the ankle, the true elbow and knees are concealed in
the body of the animal, although the motion of these joints can be
clearly seen if a running Horse be watched. A Horse walks on the
very points of its finger and toe-nails, and it possesses only one finger
on each hand and one toe on each foot (C, Fig. 344), the fingers and
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
respectively. Thus the whole limb instead of being a loosely
jointed flexible organ for grasping, becomes a firmly jointed lever
bending only in one plane and suitable for quick locomotion.
S. & M. 44
690 MAMMALIA [CH.
' 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, but there is some evidence that this wild ancestor still
exists as Equus przewalskii, a small species of Horse with large head
and bristly mane, which still roams over the steppes of Central
Asia. An excellent specimen of this species could formerly be seen
by visitors to the London Zoological Gardens. It showed a consider-
able resemblance not only to pictures of Horses found on remnants
of ancient pottery but to existing breeds of Horse found in isolated
parts of Northern Europe, such as the Icelandic Pony and the
" Hest " of "Western Norway. It had a peculiar tail which consists
of a bushy wisp of comparatively short hairs as in the modern Horse ;
but from the centre of this bunch a tassel of very long hairs hangs
down. Rude drawings of Horses with tails just like this are found
on the flint tools of early man. The Zebras and Wild Donkeys
have longer ears than the Horse, and they afe all more or less
striped ; they have not got the peculiar wisp-like tail of the Horse.
Such animals 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 run 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 on
ancient alluvial plains 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 are like Tapirs but which
are even more primitive since they retain a vestige of the thumb on
the hand and a trace of a fourth toe in the foot. This series of
forms is one of the most complete evidences of evolution known to
geologists, and it seems clear that the evolution of the Horse must
have taken place in this part of America.
Division II. ARTIODACTYLA.
f
Unlike the Perissodactyla, the Artiodactyla or even-toed Un-
gulates constitute an immense assemblage of animals, and until the
invention of modern fire-arms they were the dominant animals on
XX V] ARTIODACTYLA 691
the great plains of Africa and also of North America. The Artio-
dactyla may be divided into a higher and a lower section.
The lower section may broadly be called the Pigs, SUINA.
They retain four toes on fore- and hind-feet, have a
snout ending in 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. jSowo's, a hill or
mound) has sometimes been applied to this division. The Hippo-
potamus, the sole representative of the family HIPPOPOTAMIDAE, 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
outer (second and fifth) toes are small and do not reach the ground.
The Hippopotamus spends most of its time in rivers and swamps
feeding on the reedy vegetation of such places. It has exceedingly
powerful jaws and when wounded has been known to crush a canoe
between them. The true Pig belongs to the family SUIDAE and is a
domesticated variety of the Wild Boar, Sus scrofa, which, as is well
known, survived in England until the middle ages and still exists
in Europe. In the male the canines, or eye-teeth, are powerfully
developed, those of the lower jaw projecting upwards outside the
mouth. In the Babirusa, Bdbirusa alfurus, 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 substance they encounter, the
food they seek especially consisting of roots. A very interesting
genus, the Peccary, is represented by two species, Dicotyles taja$u
and D. labiatus, 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.
442
692
MAMMALIA
[CH.
Ruminantia.
When we leave the Pigs we have to deal with the higher
section of the Artiodactyla, the SELENODONTIA or
JRUMINANTIA, 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 ruminat-
ing, that is of bringing the food back from the stomach into the
mouth after it has been swallowed and chewing it again. Correspond-
ing 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
FIG. 346. Stomach of a Sheep, cut open to show the various chambers.
Oesophagus. 2. Kumen. 3. Eeticulum. 4. Psalterium.
5. Abomasum.
6. Duodenum.
papillae; this is called the paunch or rumen. Just below the
oesophagus is another smaller pouch divided by a constriction from
the first (Fig. 346). The second pouch is called the reticulum
because its walls are raised into intersecting folds producing cavities
like the cells of a honeycomb. The food mixed with saliva is
swallowed without chewing, and after traversing the oesophagus it
is driven from rumen to reticulum and back by the action of the
muscles and well soaked with gastric juice. After some time it is
pressed up again into the mouth and thoroughly ground up by the
great broad premolar and molar teeth. When swallowed for the
xxv]
ARTIODACTYLA
693
second time it is nearly fluid. It now passes down a groove or
channel in the side of the gullet enclosed between two ridges.
Reaching the spot where the gullet opens into the stomach, the
grooves are continued along the upper wall of the stomach and the
fluid food is led away from the paunch into the third division
of the stomach, the manyplies or psalterium, which has
numerous folds of membrane projecting into its cavity; by means
694 MAMMALIA [CH.
of these the food is completely filtered from all the solid matter it
contains. It then passes on into the fourth and last compartment,
the ab omasum, whose walls are raised into but a few ridges and
which is lined with an epithelium containing numerous gastric
glands. This leads into the duodenum 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 Pig, since these pro-
jections have become confluent so as to form hard curved ridges of
enamel; and as the jaws shift on each other sideways, the upper
and lower back teeth produce a grinding action just as two mill-
stones do. The name SELENODONTIA (Gr. o-cXywj, 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 as evidence of the more advanced structure of the Ruminantia
as compared with the Suinae, that the selenodont teeth always pass
through a bunodont stage in their development. The canines in
the upper jaw are long in the male Moschus, who no doubt uses
them in his fight for the possession of the female. The lower
canines however are usually placed close to the lower front teeth
and are indistinguishable from them. There are with few ex-
ceptions no front teeth in the upper jaw, and the grass is bitten
off by pressing the lower front teeth against a patch of hardened
gum.
The feet of the Ruminants are organs beautifully formed for quick
motion ; the ideal which Nature has so to speak striven 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 fused 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. 347).
The families composing the division Ruminantia are the TRAGU-
LIDAE or Chevrotains ; the CAMELIDAE or Camels
(Tylopoda); the CERVIDAE or Deer; the GIRAFFIDAE
or Giraffes; the ANTILOCAPRIDAE which has but one species,
the Prong-buck, Antilocapra americana; and the BOVIDAE or
xxv]
ARTIODACTYLA
695
hollow-horned cattle (Cavicornia) including Antelopes, Goats, Sheep
and Oxen.
The TRAGULIDAE comprise some small animals found in Africa
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
FIG. 348. The African Water- Chevrotain, Dorcatherium aquaticum.
larger than its Asiatic allies (Fig. 348). It frequents water-courses
and is said to have the habits of a Pig.
The CAMELIDAE are familiar to all as far as their general appear-
ance is concerned. The humps of which the Arabian Camel, Camelus
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
weight rests on a pad behind the hoofs ; these latter are separated
from each other, so that the animal has a broader support than a
Cow or a Deer. A Camel does not walk on its finger- and toe-nails,
696 MAMMALIA [CH.
but on the last joints of the fingers and toes. The stomach has no
psalterium, but both the rumen and reticulum have a large number
of water-cells, that is deep pouch-like outgrowths in which a quite
undrinkable 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 of a life on arid, sandy wastes.
Thus the diverging toes and leathery pad on the foot enable them
to secure a broader surface of the yielding sand on which to support
the animal's weight : the humps are a provision 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 Camel is only known in the domesticated state, but
the Bactrian Camel ranges wild over some of the more inaccessible
regions of Central Asia.
It is a remarkable and interesting fact that we find some
members of the Camel tribe in South America. These animals, the
Llama, Auchenia glama ; the Vicuna, A. vicugna ; the Alpaca,
A. pacos; and the Huanaco, A. huanacos; 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 indistinguish-
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 CERVIDAE 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 its
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 Cavicornia 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 sheath made of compacted hairs. Two small families occupy
an intermediate position, these are the GIRAFFIDAE, represented by
the Giraffe, Girqffa camelopardalis, and the Okapi, Okapia johnstani,
XXV] ARTIODACTYLA 697
and the ANTILOCAPRIDAE represented by the Prong-buck, 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 and also the rudiment of a third
median horn in the form of a projection of the nasal bones. The
Okapi is a forest Giraffe with a comparatively short neck. In the
Prong-buck, which is found on the prairies of North America, the
horn bears a small lateral branch and is covered with a horny
sheath, and this sheath, but not the horn itself, is shed once a
year.
FIG. 349. The Musk-Ox, Ovibos moschatus.
In the family BOVIDAE is 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. 349), which ranges over the
Arctic wastes of Canada in large herds, is intermediate in some
respects between the Sheep and the Goats on the one hand and
the Oxen on the other, but is 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 Scotland, Cervus elaphus, and the
698 MAMMALIA [CH.
Roe-deer, Capreolus capraea ; the Fallow-deer, G. dama, is probably
an introduced species, and at present is only represented in Britain
by semi-domesticated animals. 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
descended from these ancestors.
In Canada a large variety of the Red- deer, the "Wapiti, Cervus
canadensis, is found, also the Reindeer or Caribou, Rangifer
tarandus, and the Elk or Moose, Alces machlis, with short bull-like
neck and broad fan-like horns. Throughout the whole of Eastern
America the so-called "Red-deer," Cariacus virginianus, is found in
the mountains. The Bovidae are represented by the Musk-ox, Ovibos
moschatus, with horns curved like a ram, and by the Rocky Mountain
Goat, Hapkceros montanus. Until recently the American Bison, the
so-called "Buffalo," Bison americanus, ranged in enormous herds over
the Western plains of North America ; but before 1883, with the
exception of a few scattered stragglers which are "protected," this
magnificent animal had been exterminated.
Until the introduction of modern fire-arms the Artiodactyla were
in their way as successful and rapidly evolving a group as Teleostean
Fish or as Birds. In a comparatively short time, however, all except
the domesticated breeds or species specially preserved for sport will
be exterminated. As it has been discovered that they harbour in
their blood the dreaded parasite which causes sleeping-sickness it is
probable that in regions infested by this disease their preservation
for purposes of sport will be of short duration. In Tertiary rocks
numerous families of extinct Ungulates are found which completely
fill the gaps existing between Suidae and Tragulidae on the one
hand and Traerulidae and Bovidae on the other.
Order VII. Sirenia.
The Sirenia or Sea-cows agree with the Cetacea or Whales in
the manner in which they are adapted to an aquatic life. Thus all
trace of hind-limbs has been lost, a pair of bones representing the
pelvic girdle alone remaining, the fore-limbs have become flippers,
'the tail is broadened and there is a tail fin with horizontal flukes.
Underneath the skin there is a thick layer of fat and the hairy coat
is reduced to a few scanty hairs scattered over the skin. The lips,
however, are covered with numerous thick bristles. The nasal organ
is rudimentary. Apart from these resemblances which are due to
xxv] SIRENIA 699
adaptation to a similar mode of life, the Sirenia differ from the
Whales so profoundly that no direct relationship can be assumed to
exist between the two groups. The Cetacea are all flesh-eaters but
the Sirenia are vegetable feeders and browse on sea-weeds and other
water-plants. As these habits necessitate their staying under the
FIG. 350. Skull of African Manatee, Manatus senegalensisy.\ t
water for some considerable time, the bones are heavy and solid,
quite different in structure from the bones of Whales, which are
much more spongy in texture. The skull is long, not rounded, and
the face bones are only moderately developed. The parietals are
FIG. 351. Front view of head of American Manatee, Manatus americanus,
showing the eyes, nostrils and mouth. A. with the lobes of the upper lip
divaricated. B. with the lip contracted. From Murie.
not pushed aside by the development of the supra-occipital; the
supra-orbital plate of the frontal is small, while the orbit is large
and bounded below by a very powerful jugal. The teeth are broad
700 MAMMALIA [CH.
and crushing, and front teeth sometimes are found developed as
tusks. There is no such snout as is found in Whales, but there are
large movable lips by means of which food is seized (Fig. 351). The
teats are placed on the breast as in Bats, and the mother when
nursing supports the young with its head above water by means of
the flipper which is more flexible than the flipper of a Whale. It
has been suggested that the tails of Mermaids may have been
suggested to sailors by the sight of these strange mothers holding
their pups on their arms. There are two genera: (1) Manatus, the
Manatee found in the warmer parts of the coastal waters of the
Atlantic and in the estuaries of its rivers both in America and
Africa, and (2) the Dugong, Halicore, 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, stelleri, of great size,
20 25 ft. long, inhabited some islands in the Behring Sea. It
had no teeth, their place being supplied by horny plates on the
gums. This species was exterminated by Russian hunters. Re-
mains of extinct species of Sirenia with front teeth and vestigial
hind-limbs have been discovered and the structure of these renders
it probable that Sirenia are descended from some primitive Ungulate
allied to the Eocene ancestor of Elephants.
Order VIII. Rodentia.
The Rodentia or Gnawers (Lat. rodo, to gnaw) are another of the
main divisions of the Mammalia and include our Rabbits, Hares,
Squirrels, Rats and Mice, besides the Porcupine, Beaver, Guinea-pig
and many other foreign species. These are all sharply marked off
from other mammals by the structure of their teeth. The incisors,
of which there are typically only one pair in each jaw, are chisel-
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. 352). If
one of the teeth is destroyed the opposite one grows until it may
pierce the other jaw, prevent the mouth from being opened, and thus
starve the animal to death. There are no canines, so that there
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
Ungulates on the points of the nails (Fig. 322). Our English
Rodents are the Hares and Rabbits, LEPORIDAE ; the Squirrels,
xxv]
RODENTIA
701
SCIURIDAE; the Voles, Rats and Mice, MURIDAE; and the Dormouse,
the sole British representative of the family MYOXIDAE. In North
America there are allied species, and in addition the Ground-
squirrels, or Chipmunks, Tamias, and three species of Woodchuck
or Marmot, Arctomys; also Porcupines, represented by the common
Canadian Porcupine, Erethizon dorsatus, the Beaver, Castor cana-
densis, and many others. Hystrix cristata is the Porcupine of
Southern Europe and Northern Africa. The Guinea-pig is probably
a domesticated variety of the South American species Cavia cutleri.
19
20
14
FIG. 352. Side view of the skull of the Eabbit, Lepus cuniculus.
1. Nasal bone. 2. Lachrymal bone. 3. Orbitosphenoid. 4. Frontal.
5. Optic foramen. 6. Orbital groove for ophthalmic division of trigeminal
nerve. 7. Zygomatic process of squamosal. 8. Parietal. 9. Squamosal.
10. Supra-occipital. 11. Tympanic bone. 12. External auditory
meatus. 14. Lower incisor. 15. Anterior premolar tooth. 16. Anterior
upper incisor. 17. Mandible. 18. Maxilla. 19. Premaxilla.
20. Occipital condyle.
These various species are very like each other in their general
anatomy, but differing in the character of their molars, in their
fur and in their tails.
Hares and Rabbits constitute the DUPLICIDENTATA, one of
the two sub-orders into which the order is divided. The name
is derived from the possession of an extra pair of upper incisors,
which however are so small as to be useless. The tail is short
and the cusps of the premolar and molar are joined so as to form
ridges or folds running across the tooth. The Common Hare,
702
MAMMALIA
[CH.
Lepus timidus, and the Mountain Hare, L. variabilis, are both
British; they have longer legs than the third British form, the
Rabbit, L. cuniculus, and have fewer young at a time. In the
temperate part of North America there are at least six species of
Duplicidentata all referable to the genus Lepus. Of these the most
interesting are Lepus americanus and Lepus campestris. The fur
of both these species turns
white at the tips in winter,
enabling the animals to escape
observation on the snow-covered
ground.
L. am&ricanm, the North-
ern 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-gray colour in
summer. It can run with
great swiftness.
The remaining Rodentia are
called SIMPLICIDENTATA, 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 vulgaris is
the common British Squirrel;
it extends from Ireland to
Japan. Two species are very
common in Canada and New
England, viz., Sciurus hudsonicus, the Red Squirrel, and S. caro-
linensis, the Gray Squirrel. These lively little animals can be
seen in autumn disporting themselves in the trees lining the
avenues of the suburbs of Montreal. Sciuropterus volans 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
FIG. 353. Dorsal view of the skull of a
Babbit, Lepus cuniculus.
1. Nasal bone. 4. Frontal. 7. Pro-
cess of squamosal supporting the jugal.
8. Parietal. 10. Supra-occipital.
12. External auditory meatus. 13.
Angle of lower jaw. 17. Interparietal.
xxv]
RODENTIA
703
forms a parachute-like membrane which supports it in its great
leaps from tree to tree. In these manoeuvres it is assisted by the
broad flattened tail. The Flying Squirrel is common in the temperate
part of the United States. A similar but larger species (S. sabrinus)
may be seen at dusk leaping from tree to tree on the Mountain of
Montreal. Anomalurus, found in West and Central Africa, is also
called a Flying Squirrel, since the skin of its sides is prolonged into
a parachute-like membrane (Fig. 354). It differs from Sciuropterus
however, in having a round tail provided with horny scales under-
neath, which assist in climbing, and in having its "parachute"
FIG. 354. The African Flying Squirrel, Anomalurus fulgens.
supported by a cartilaginous rod arising from the elbow. In reality
Anomalurus is a surviving member of a primitive group of Rodentia
termed PROTROGOMORPHA, intermediate in character between Squirrels
and Mice, most of which are extinct.
The Mice and Rats, MURIDAB, have naked tails with scales under-
neath. The ordinary Rat is the brown Norway Rat, Mus decumanus,
which was introduced some time ago into England and had almost
everywhere driven out the old English Black Rat, M. rattus. Of
704 MAMMALIA [CH.
recent years however this latter species has increased its numbers
and it is now holding its own. The Common British Mouse is
M. musculus : the Wood-mouse, M. sylvaticus, and the Field-mouse,
M. minutus, also occurs in Britain. The Water-rat or Vole, Arvicola,
is distinguished 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. ampkibius, the Water-vole, A. agrestis, the Field- vole, which
often does much damage to crops, and A. glareolus, the Bank- vole,
represent the genus in Britain. The Dormouse, Muscardinus avella-
narius, which like the Squirrel passes the winter in a hole in a tree,
has a long bushy tail, and, in outward appearance at any rate more
FIG. 355. The Musquash, Fiber zibethicus.
resembles a tiny Squirrel than a Rat. In its skull it resembles the
MURIDAE, but it differs from both Squirrels and Rats in not
possessing a caecum on the intestine. On this account it, along with
five or six allied species from Europe and Africa, has been separated
as a distinct family, the MYOXIDAE.
Amongst the most interesting American Rodents are the Beaver,
the Porcupine, the Ground-squirrel, the Marmots and the Musquash.
The Beaver, Castor canadensis, sole representative of the family
CASTORIDAE, has a broad flat tail, suited for swimming, which is
covered with horny scales. The Beaver, by means of its sharp
incisors, cuts down trees growing on the banks of streams, so that
they fall across streams thus damming them up and raising the
xxv ] CHEIROPTERA 705
level of the water so as to cover the entrance to their burrows. By
this means large tracts of country have been converted into swamp.
The Porcupines (HYSTRICIDAE) have some of their hairs developed into
sharp spines which make them awkward objects to handle. In the
Canadian Porcupine, Erethizon dorsatus, the spines are concealed by
the fur. The commonest Ground-squirrel of North America is the
Chipmunk, Tamias, an active little animal with large eyes and a short
hairy tail. The Prairie Marmot, Cynomys, the so-called Prairie-dog or
Ground-hog is also a Ground-squirrel with a very short tail. It lives
in communities, burrowing in the ground and its home is often shared
by a small burrowing Owl, Athene cunicularia, and by a Rattlesnake,
which probably eats the young Marmots. The Musquash or Musk-rat,
Fiber zibethicus, one of the MURIDAE, is peculiar to North America,
and very widely distributed in suitable places (Fig. 355). It is
aquatic, living on roots and water-plants and is most active at night.
It constructs burrows in the banks of streams, the openings of which
are under water. Its fur is valuable.
Order IX. Cheiroptera.
The Cheiroptera (Gr. x/>, a hand ; vrcpov, wing), or Bats, have
not in their general organisation, in teeth or brain or stomach,
departed far from the Insectivora; their great distinguishing
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, the
greater part of which is stretched between the fingers of the five-
fingered hand, only the smaller part extending, as in Birds, between
the elbow and the side of the body. The hand is enormous, the
little finger 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
membrane but ends in a hook-like nail (Fig. 356). 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. 356). When the Bat crawls it hooks itself along with its
thumb-nail and pushes itself awkwardly with its hind feet. It has
&. & M. 45
706
MAMMALIA
[CH.
a most awkward gait and the animal is consequently very helpless
when not flying.
FIG. 356. Skeleton of Pteropus medius, a fruit-eating Bat x about .
1. Clavicle. 2. Keeled sternum. 3. Scapula. 4. Humerus. 5. Eadius.
6. Ulna. 7. Little finger. 8. Thumb. 9. Ilium. 10. Pubis.
11. Ischium. 12. Obturator foramen. 13. Femur. 14. Tibia.
15. Fibula. 16. Tarsus.
One of the most extraordinary things about Bats is the
development of sensitive patches of skin on the face for the
purpose of perceiving faint disturbances in the air. It has been
xxv]
CHEIROPTERA
707
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
FIG. 357. Female and young of Xantharpyia collaris. From Sclater.
outer ear, in others the skin around the nostrils, in others
again the skin on the lips and chin, developed into curious out-
growths richly supplied with nerves. By means of these sense-
organs Bats are enabled to avoid obstacles, and a blind Bat, let
452
708 MAMMALIA [CH.
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 Mammals. The true Blood-sucking
Bat or Vampire, Desmodus rufus, is found in Central and in South
America. Its back teeth are rudimentary, but its front teeth are
razor-edged. Pteropus, which includes the so-called Flying Foxes or
Fox-bats of India and Madagascar, belongs to the family PTEROPIDAE;
these are the largest Bats known; they feed exclusively on fruit, and
the cusps on their teeth are blunter than is usual amongst Bats.
The African Xantkarpyia> one species of which frequents the
interior of the Pyramids and other dark ruins in Egypt (Fig. 357)
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 Mpposiderus and R. ferrumequi-
numj the Barbastelle, Synotus barbastellus ; and the Pipistrelle,
Vesperugo pipistrellus ; represent the genera. Besides the species
just mentioned there are three more species of Vesperugo and three
more of Vespertilio in Britain. South America has a large fauna
of peculiar Bats, but the North American forms are allied to the
British, although the species are distinct. The Serotine, Vesperugo
serotinus, is the only species common to the two regions. Scotophilus
humeralis is one of the most familiar species peculiar to North
America.
Order X. Primates.
The last order of the Mammalia is that of the Primates, which
includes Lemurs, Monkeys and Man. As was mentioned before, this
order is characteristically arboreal, that is to say most of its members
live among trees, climbing from branch to branch. This circum-
stance may explain why they retain certain primitive characteristics
found elsewhere only amongst the Insectivora. Thus the thigh and
upper arm are quite free from the body and the whole sole and palm
are placed on the ground when walking; and there are five fingers
and five toes. On the other hand the eyes are pushed round to the
front of the skull instead of being placed at the sides of the head,
and the jugal joins the postorbital process of the frontal, so that
the orbit is surrounded by a bony ring (Fig. 358). Some at least
of the toes have flat nails. The big toe is shorter than the rest,
xxv]
PRIMATES
709
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 can 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 LEMUROIDEA
and the ANTHROPOIDEA. The first of these includes some curious
little animals, of which the majority are found in the Island of
Madagascar, the rest in Africa, India and the Malay Archipelago.
Many of the species are nocturnal, move silently and have large
eyes, whence the name Lemur (Lat. lemu/res, goblins, spectres).
These animals have heads recalling those of rats, with no suggestion
Fm. 358. Half front view of the skulls, A. of an old, B. of a young Gorilla,
Gorilla savagei x .
1. Parietal. 2. Sagittal crest. 3. Frontal. 4. Supra-orbital ridge.
5. Squamosal. 6. Maxilla. 7. External auditory meatus.
of the human face, and in their brains and some other points they
are far below the Monkeys. The cerebral hemispheres do not cover
the cerebellum; the placenta of the embryo is spread evenly all
over the surface of the egg, and there are occasionally additional
mammae on the abdomen. Their incisor 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 catta (Fig. 359), 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,
graceful creature with a plaintive cry.
710
MAMMALIA
[CH.
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 at first spread all over the surface of the egg but later becomes
highly developed and concentrated on one part of the wall of the
FIG. 359. The Eing-tailed Lemur, Lemur catta.
uterus, and there are never more than two mammae. This sub-
order of Primates is divided into five families, viz., HAPALIDAE,
CEBIDAE, CERCOPITHECIDAE, SIMIIDAE, and HOMINIDAE, the last being
constituted of the single species, Homo sapiens, Man.
The HAPALIDAE and CEBIDAE are confined to South and Central
America, and are sometimes grouped together as PLATYRRHINI
(Gr. TrAarvs, broad ; pi's, pu/o?, nose). The animals belonging to this
XXV] PRIMATES Til
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
FIG. 3GO. The Orang-utan, Simia satyrus, sitting in its nest. From a specimen
in the Cambridge Museum.
alone has a flat nail; all the other toes and all the fingers bear
curved claws. There are only two pairs of molars. The CEBIDAE
have flat or slightly curved nails on their fingers and toes and
three pairs of molars, making with the premolars six cheek-teeth
712 MAMMALIA [CH.
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 CERCOPITHECIDAE and SIMIIDAE are confined to the Old
World. They constitute the section CATARRHINI, 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-
COPITHECIDAE 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
includes the Indian and African monkeys, among them the Bandar-
log of Kipling's Jungle Tales. One species, Macacus inuus, the
Barbary ape, is found on the Rock of Gibraltar, and this is the only
species which enters Europe. It is remarkable for being completely
tailless. Semnopithecus entellus is the sacred Langur of India, and
owing to its immunity from persecution has become very abundant.
The SIMIIDAE include those Monkeys which in structure and
appearance most resemble Man. In this family the tail is completely
absent, the arms are longer than the legs, and the gait might be
described as that of a baby learning to walk. They never go
completely on all-fours, but usually shuffle along unsteadily on
their two feet, which like those of a baby show a tendency to
turn inwards under them; they usually steady themselves by
bending forward so that their knuckles touch the ground. Four
genera are included in this section, viz. Hylobates, Simia, Gorilla
and Anthropopithecus. Hylobates include several species known
as Gibbons, inhabiting South-Eastern Asia and the Malay Archi-
pelago. These are Apes with exceedingly long arms; they assume
a completely upright position when on the ground and run along
holding up their long arms in the air as if they were balancing
poles. In their power of supporting themselves without resting the
arms on the ground they approach Man ; but in other respects they
depart widely from him, as for instance in the brain, where the
XXV] PBIMATES 713
cerebellum is not completely covered by the cerebrum. Simla is
represented by a single species, 8. satyrus, the Orang-utan, a large
animal about 4j feet high, which is found in the islands of Borneo
and Sumatra. This animal walks on two feet supporting itself on
its knuckles. It lives however almost entirely in trees, constructing
a sort of nest for itself out of branches (Fig. 360). It is remarkable for
its high rounded cranium enclosing the large brain, which presents
the closest approximation to the human brain of all the brains of
Apes. The cranium is however still small compared to the bones
of the face and lower jaw. Of the next genus Gorilla only a single
species exists, viz. G. savagei, confined to a limited region of Equa-
torial Africa. This is the largest of all the apes, reaching a height
of 5J feet. It is distinguished from Simla by its shorter arms and
more receding forehead. The skull of the young Gorilla strikingly
resembles a child's skull, but in the adult it is deformed by the
development of great bony ridges which give attachment to the
muscles of the face (Fig. 358). Anthropopithecus is represented
only by A. troglodytes, 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 does not
reach a height of more than 5 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 and the Chimpanzee is more purely arboreal in
its habits than the other Simiidae.
Man is distinguished above all 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 so as entirely to support the body, in
consequence of which the big toe is no longer used for grasping.
Some hold that it was this latter modification which brought about
the great development of the intelligence of Man, arguing that
when once the hand was entirely at the service of the brain the
varied uses to which it could be put would give the opportunity for
the use of the mind. This seems probable, but the great factor
which has stimulated the mental development of Man is his habit
of living together in societies and undertaking concerted enterprises
for the benefit of the community. To this power of combination not
only intellect but also language and morals may eventually be traced
back. Man did not make society, it was society that made Man.
The general circumstances of the Evolution of Man are becoming
714 MAMMALIA [OH.
quite clear; just as the Marmot may be described as a ground-squirrel,
so Man may be described as a ground-ape. In the warm Miocene
Epoch a luxuriant forest covered a large part of Europe and Asia and
in this forest Simiidae abounded, and remains of genera intermediate
between the Gibbon and Chimpanzee have been found in France. In
succeeding Pliocene and Pleistocene times the climate became colder,
the mountains were covered with glaciers, the forest receded and
was replaced by steppes over which roamed myriads of grazing
animals. Under these circumstances, the more enterprising Simiidae
descended from the trees and began to assemble in troops to chase
the smaller animals they found on the plains and so Man was
evolved. He is a product of the Glacial Epoch.
The Human species is divided into a great many races which are
more distinct from one another than allied species in other groups
of animals, but all of which so far as is known are more or less
fertile amongst each other. They differ in the shape of the skull
which may be broad (brachycephalic) or long (dolichocephalic) in
the hair which may be curly, wavy or lanky, in stature and the
proportions of the limbs. We cannot in this short treatise describe
all these races ; many of these such as the Esquimaux, the Bushmen
and the Australians, are represented by small numbers and are dying
remnants of primitive man, but we must briefly refer to the great
dominant races which make up the bulk of the world's population.
These are :
(1) The Negroes, dark skinned, dolichocephalic, curly haired
people with thick skulls and weak ankles which form the bulk of
the population in Equatorial Africa and also inhabit the larger
islands of the Malay Archipelago where they are called Melanesians;
they have never evolved a native civilization.
(2) The Mongols, yellow-skinned brachycephalic lanky haired
people with slit-like eyes; these include all the Chinese and
Japanese as well as the less civilized and wandering tribes of Siberia
and the Malays who inhabit the Western part of the Malay Archi-
pelago. The natives of North America or Amerinds are supposed
to be an offshoot of this race distinguished by an arched nose and
slit-like nostrils.
(3) The Alpine race, brachycephalic people with lanky or wavy
hair, short in stature, a race resembling the Mongols but distinguished
by lighter complexion and abundant hair. This race originated in
Western Asia but invaded Europe in prehistoric times subjugating
the previous inhabitants. They form the bulk of the people of
central Europe; the Russian and German peasantry as also those of
XXV] FOSSIL REPKESENTATIVES 715
central France belong to this race and they have contributed to the
population of the British islands.
(4) The Mediterranean race, swarthy skinned dolichocephalic
people with wavy hair and dark eyes, the original inhabitants of Europe
in post-glacial times and the first race to evolve a civilization. To this
race belong the Arabs, the ancient Egyptians, as well as the modern
peasantry of that country, the Southern Italians, the Spanish,
Portuguese and Moors, and the Bretons and Gascons in France, and
the small dark people of Wales, Cornwall, the Western Highlands
and Ireland.
(5) The Nordic race, fair skinned dolichocephalic people with
wavy hair and blue eyes. This race originated near the Baltic and
spread south conquering and organising the whole of Europe. It
represents not only a large and virile section of the population but
the aristocracies and ruling houses of Europe. To it belonged (a)
The "heroic" Greeks who fought at Troy and the "Dorian"
founders of Sparta. (6) Probably also the ancient "Patrician"
families of Rome, (c) The Goths, Germans and allied Barbarians
who overran and conquered the Roman Empire, (d) The Saxon
invaders of Britain, (e) The Norman invaders of Britain and Europe.
In its purest form it is found at the present time in the Scandinavian
Peninsula. Modern History may be said to be due to the initiative
and prowess of this race. The Alpine race has developed craftsman-
ship, they were the first to use metal tools whilst the Mediterranean
race evolved the ancient Egyptian civilization the oldest in the
world.
The fossil representatives of the class Mammalia are exceedingly
numerous. It would lead us too far to give even such a general
account of them as was given of fossil Reptiliaj 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 the
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, are now regarded as the ancestors of the class.
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 Ornithorhynchus and these teeth are classified as
the remains of an order MULTITUBERCULATA, the members of which
are supposed, like Ornithorhynchus, to have had a reptilian arrange-
ment of the genital organs. The remains are principally lower
716 MAMMALIA [CH.
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 or Basal Eocene 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 is
seen which widens into the chasm now separating Ungulata and
Carnivora. Modern Insectivora are the little modified descendants
of the Creodonta, whilst the so-called " Sub-ungulata " may be
regarded as survivors of the Condylarthra which have undergone
modifications in their dentition. In the next horizon or Lower
Eocene traces of the Primates appear as Lemuroidea, the marks
discriminating them from Creodonta being the enlargement of the
orbit and its surrounding ring of bone, while the molar teeth have
a fourth tubercle. At the same time the Condylarthra begin to
show Horse-like forms (Phenacodus), still with five fingers and five
toes and of the Sub-ungulate type, but true Ungulata now appear
with the bones of wrist and ankle in transverse rows and a reduced
number of toes. The earliest of these, the Lophiodontidae, were
Perissodactyla, and iii 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; these forms are
easily derivable from the Creodonta. The origin of the Artiodactyla
becomes apparent in the next horizon, the Middle Eocene, 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
XXV] CLASSIFICATION 7 17
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 (Upper Eocene) the ancestors of Whales
are found, as the Archaeoceti (Zeuglodon) 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. True Carnivora distinguished by the
carnassials have likewise been by this time developed from the
Creodonta ; amongst the Ungulata the earliest forms of Camels and
of Tragulidae have appeared, as well as the forerunners of Elephants
and Sirenia.
Once formed, Carnivora rapidly become differentiated, for in the
next period (Oligocene) 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
(Mastodon 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 Carnivora, the gradual reduction in size of the
premolars, and of the carnassial marking the change. True Apes
(Anthropoidea) here succeed the Lemuroidea.
In the next period (Miocene) 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 I. PROTOTHERIA.
Mammalia which lay large eggs and in which the two oviducts
are completely separated, and there is a persistent cloaca. No
placenta.
Ex. OrnitkorhynchuSj Echidna.
718 MAMMALIA [Cfl.
Sub-class II. METATHERIA.
Mammalia in which the young are born 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 and the two vaginae are partially united. The
cloaca is divided into an anus and a urino-genital aperture. An
allaritoic placenta may or may not be developed but when present
is more or less vestigial. In all cases there is an umbilical placenta
consisting of 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. Didelphyidae.
Polyprotodontia with a large opposable great toe, the
other digits of the hind-foot being subequal in size.
American.
Ex. Didelphys.
Family 2. Dasyuridae.
Polyprotodontia with a rudimentary great toe, the other
digits of the hind-foot subequal in size. Australian.
Ex. Thylacinus.
Family 3. Peramelidae.
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.
9
Family 4. Notoryctidae.
Polyprotodontia with rudimentary eyes, an enlarged
manus and burrowing habits. Australian.
Ex. Notoryctes.
Order II. 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.
xxv ] CLASSIFICATION 719
Family 1. Epanorthidae.
Diprotodontia with all the toes of the hind-foot free
from one another and subequal. American.
Ex. Caenolestes.
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,
free from the web, and opposable to the rest, the second and
third toes very slender : limbs subequal : three incisors on
each side of the upper jaw. Australian and Papuan.
Ex. Phalanger.
Family 4. Macropodidae.
Diprotodontia in which the toes of the hind-foot are
united in a web of skin, the second and third toes are slender
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. Australian and Papuan.
Ex. Macropus, Bettongia, Petrogale.
Sub-class III. EUTHEBIA.
Mammalia in which the young are born 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 without median
teeth ; the limbs are, as a rule, provided with heavy hook-like
claws; uterus simple and globular: placenta dome-shaped.
Family 1. Bradypodidae.
Limbs long and the fore-limbs considerably longer than
the hind-limbs: muzzle short with few teeth: arboreal in
habit. South American.
Ex. Bradypus.
720 MAMMALIA [CH.
Family 2. Myrmecophagidae.
Limbs short and stout: muzzle exceedingly long: no
teeth. South American.
Ex. Myrmecophaga.
Family 3. Dasypodidae.
Limbs short and stout: face long with numerous teeth:
a shield of dermal bones covered by horny scales. South
American.
Ex. Dasypus.
Order II. Effodientia.
Eutheria resembling Edentata in teeth and claws but with
bicornuate uterus and zonary or diffused placenta.
Family 1. Manidae.
Covered externally with large, overlapping horny scales :
no teeth : long protractile tongue. Asian and African.
Ex. Manis.
Family 2. Orycteropodidae.
Covered with bristly hairs: teeth numerous and heter-
odont: no thumb on anterior limb. African.
Ex. Orycteropus.
Order III. Insectivora.
Small plantigrade Eutheria, with pointed cusps on the
molar teeth : the brain of low type : a flexible snout often
present. The more familar families are
Family 1. Erinaceidae.
Insectivora with the body covered with harsh spines:
limbs subequal.
Ex. Erinaceus.
Family 2. Soricidae.
Small mouse-like Insectivora with soft fur.
Ex. Sorex, Blarina,
Family 3. Talpidae.
Mouse-like Insectivora with rudimentary eyes and large
hands adapted to burrowing.
Ex. Talpa, Condylura, Myogale.
Order IV. Carnivora.
Eutheria with sharp recurved claws and powerful canine
teeth: the premolars adapted for clipping flesh: the incisors
small.
XXV] CLASSIFICATION 721
Sub-order 1. Pissipedia.
Carnivora with separated digits : a distinct carnassial tooth
and one or more broad molars.
Family 1. Felidae.
Fissipedia with short face and a reduced number of pre-
inolar 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. Canis.
Family 3. Ursidae.
Fissipedia with long face: teeth blunt and partially
adapted for a vegetable diet : plantigrade in gait.
Ex. Ursus.
Family 4. Procyonidae.
Fissipedia with a sharp pointed muzzle and reduced
number of teeth, otherwise like Ursus.
Ex. Procyon.
Family 5. Mustelidae.
Fissipedia with long necks and exceedingly flexible
bodies : a reduced number of teeth : in the skull and in
the shape of the carnassial tooth they resemble Ursidae
but they are digitigrade in gait.
Ex. Lutra, Meles, Mustela, Mephitis.
Family 6. Viverridae.
Fissipedia with long necks and exceedingly flexible
bodies; a reduced number of teeth, but the teeth are
more numerous than in the Felidae. In the skull and
the shape of the carnassial tooth they resemble the Felidae.
Ex. Viverra.
Sub-order 2. Pinnipeclia.
Aquatic Carnivora 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.
S. & M. 46
722 MAMMALIA [CH.
Family 1. Otariidae.
Pinnipedia still retaining a trace of the external ear,
and capable of turning the hind-limbs forward so as to
walk on land.
Ex. Otaria.
Family 2. Trichechidae.
Pinnipedia devoid of external ear, but capable of walking
on land : the upper canines form long tusks.
Ex. Trichechus.
Family 3. Phocidae.
Pinnipedia devoid of external ear, and incapable of
turning the feet forward, so that when on land they can
(%ly wriggle along with the help of their anterior limbs:
the canines not specially enlarged.
Ex. Phoca.
Order V. 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. Mystacoceti.
Cetacea devoid of teeth in the adult and with plates of
whalebone in the mouth.
Ex. Balaena, Balaenoptera.
Sub-order 2. Odontoeeti.
Cetacea with teeth at any rate on the lower jaw and no
whalebone.
Ex. Physeter, Globicephalus, Delphinapterus, Phocaena.
Order VI. 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-ungulata.
Ungulata with short subequal toes, and with the bones of
the carpus and tarsus arranged in parallel longitudinal series.
Family 1. Hyracidae.
Small Sub-ungulata with a very short snout : a pair of
chisel-like incisors in each jaw.
Ex. Hyrax (Procavia).
XX V] CLASSIFICATION 723
Family 2. Proboscideae.
Large Sub-unguiata with a very long flexible snout
(trunk) used for prehension:' incisors long and curved,
forming tusks : molars very broad, only one pair in use at
a time.
Ex. Elephas.
Sub-order 2. Ungulata vera.
Ungulata in which the bones of the carpus and tarsus are
arranged in transverse rows, the members of successive rows
alternating with one another. The first digit is lost.
DIVISION I. PERISSODACTYLA.
Ungulata in which there is, with rare exceptions, an un-
even number of digits in each limb, and in whichjfche axis of
symmetry passes through the third digit.
Family 1. Tapiridae.
Perissodactyla with four digits in the fore-limb and three
in the hind-limb : a short flexible snout.
Ex. Tapirus,
Family 2. Rhinocerotidae.
Perissodactyla with three subequal digits in each limb :
one or two median horns without bony cores carried on the
nasal bones.
Ex. Rhinoceros.
Family 3. Equidae.
Perissodactyla with only one complete digit in both
fore- and hind-limbs.
Ex. Equus.
DIVISION II. ARTIODACTYLA.
Ungulata in which there is almost always an even number
of digits, and in which the axis of symmetry passes between
the third and fourth digits, these digits being flattened against
each other so as to form two symmetrical halves of a cylinder.
Section A. Bunodontia (Suina).
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.
462
724 MAMMALIA [CH.
Family 2. Suidae.
Bunodontia of moderate size, in which the two outer
toes though complete are shorter than the others.
Ex. Sus, Babirusa, Dicotyles.
Section B. Selenodontia.
Artiodactyla with complex stomachs adapted for ruminating:
the cusps 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. Tragulus.
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 bone shed annually : four compartments in
the stomach : the second and fifth digits incomplete.
Ex. Cervus, Cariacus, Capreolus, Rangifer, Alces.
Family 4. Bovidae.
Selenodontia with horns which are outgrowths of the
frontal, never shed, and covered with a thick horny sheath :
four compartments in the stomach : the 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, four compartments in the stomach : immensely elongated
neck and very long limbs.
Ex. Giraffa.
XXV] CLASSIFICATION 725
Family 6. Antilocapridae.
Selenodontia with branched horns which are outgrowths
of the frontal covered with a horny sheath. This sheath is
shed annually but not the core of the horn. Four com-
partments in the stomach.
Ex. Antilocapra.
Order VII. Sirenia.
Aquatic Eutheria, with limbs and tail as in the Cetacea :
the cranium is cylindrical and the teats pectoral.
Ex. Manatus, Halicore.
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. Simplicidentata.
Rodentia in which there is only one pair of incisors in the
upper jaw.
Ex. Sciurus, Tamias, Mus, Fiber, Arvicola, Muscar-
dinus, Castor, Erethizon, 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. Vespertilio, Vesperugo, Ehinolophus, Xantharpyia.
Order X. Primates.
Eutheria with long limbs, the brachium and femur not being
buried in the body : five digits in each limb, some of them
726 MAMMALIA [CH.
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. Lemur.
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 A. Platyrrhini.
Anthropoidea with a broad intern asal 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. Hapalidae.
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. Cebidae.
Platyrrhini with flat or slightly curved nails on all toes :
three molar teeth on each side.
Ex. Ateles, Cebus.
Section B. Catarrhini.
Anthropoidea with a narrow internasal 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.
Family 1. Cercopithecidae,
Catarrhini with arms not longer than their legs : bare
XXV] CLASSIFICATION 727
patches on the buttocks : with rare exceptions a well-
developed tail.
Ex. Macacus, Semnopithecus.
Family 2. Simiidae.
Catarrhini with arms much longer than legs and a
semi-erect gait : no tail.
Ex. Gorilla, Hylobates, Simia, Anthropopithecus.
Section C. 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.
INDEX
Names of genera are printed in italics. The figures in thick
type refer to illustrations. In all cases the references are to pages.
Aard-vark, 669
Abdomen, 176, 179, 180, 232, 233, 237,
243, 259
Abdominal artery, 202
Abdominal ganglion, 293
Abdominal pores, 448
Abdominal ribs, 584
Abducens nerve, 425
Abomasurn, 694
Aboral pole, 80
Aboral sinus, 337
Acanthia, 257, 281
Acanthobdella, 162, 166
Acanthobdellidae, 166
Acarids, 268
Acarina, 268, 282
Acetabulum, 533, 576
Aciculum, 158
Acineta, 47
Acipenser, 473, 501, 517
Acipenseridae, 501
Acoela, 98, 111
Acopa, 411
Acridium, 280
Acris, 559, 562
Acromion, 594
Aetinometra, 361
Actinophrys, 29, 30
Actinosphaerium, 29, 30. 31, 52
Actinozoa, 68, 78, 80, 82
Adambulacral ossicles, 333
Adder, 591
Adductor muscles, 300, 301
Adhesive cells, 78
Adrenal body, 557
Aegithognathous palate, 629
Aeschna, 194, 195, 252
Aetheospondyli, 473, 496, 516
Afferent, 89
Aglossa. 558, 561
Air-bladder, 453, 489, 491, 498, 503,
504, 513, 514, 516
Air-sacs, 623
Alary muscles, 240
Alauda, 635
Albatross, 632, 634
Albumen gland, 295
Alcedo, 635
Alces, 698, 724
Alcyonaria, 73, 82
Alcyonium, 68, 69, 70, 71, 72
Alimentary canal, 142 ; of Arthropods,
188; of Birds, 624; of Craniata, 427;
of Echinoderms, 330, 350, 352; of
Hirudo, 163 ; of Lamellibrancbs,
305; of Nemertines, 113; of sea-
urchin, 352; of Sepia, 317; of Verte-
brates, 385, 395, 400, 446, 461, 508
Alisphenoid, 476, 610, 647
Allantoic bladder, 524
Allantoic placenta, 664, 670
Allantois, 450, 563, 659, 064
Alligator, 568, 598, 602, 605
Alligator-turtles, 597
Alloiocoela, 98, 99, 112
Allolobophora, 157, 105
Alpaca, 696
Alpine race, 714
" Alternation of generations," in Coe-
lenterata, 65 ; in Tunicata, 412
Alveoli, 349, 599
Alytes, 548, 558
Amblystoma, 543, 549, 561
Amblystomatinae, 543
Ambulacral grooves, 327, 340
Ambulacral muscles, 341
Ambulacral ossicles, 333
Ambulacral plates, 341, 346, 354
Amerind, 714
Amia, 473, 498, 499, 503, 516
Amino-acid, 5
Amiurus, 492, 514
INDEX
729
Ammocoetes, 448
Amnion, 450, 563
Amniota, 450, 563, 564, 565, 566, 567
Amoeba, 15, 16, 141 ; in infusions, 19
Amoebidea, 34, 46
Amoebocytes, 141, 148, 173, 328
Amoebula, 28
Amphibia, 431, 442, 450, 452, 510, 519 ;
classification of, 560
Amphiblastula, 89
Amphicoelous, 474
Amphioxus, 390, 391, 392, 393, 394,
395, 396, 397, 398, 399, 400, 401,
402, 428, 439, 446 ; origin of meso-
blast in, 134
Amphipoda, 222, 279
Amphisbaenidae, 589
Amphistylic, 457
Amphiuma, 542, 561
Amphiumidae, 561
Ampulla, 420
Ampullae, 333, 353
Amylopsin, 429
Anabolism, 5
Anal cerci, 233
Anal fin, 482
Anal styles, 237
Anamnia, 450, 452
Anas, 612, 613, 634
Anaspides, 224
Anchovy, 489, 490
Anguidae, 586
Anguilla, 514
Anguilliformes, 490, 514
Anguis, 585, 586, 604
Angular bone, 575
Animal, 1
Animals compared with plants, 2
Anisopleura, 323
Anisospores, 27
Anisotropic substance, 200
Ankle, 521, 614
Annelida, 125", 138, 155, 168 ; classifica-
tion of, 165
Annular cartilage, 443
Annuli, 161
Anodonta, 298, 299, 300, 301, 303, 306,
325
Anomalurus, 703
Anomura, 217
Anopheles, 45
Anopla, 118
Anostraca, 268, 277
Anser, 634
Anseriformes, 632, 634
Ant, 256
Ant-eater, American, 666,668; banded,
662 ; Cape, 666, 669 ; scaly, 666, 669 ;
spiny, 656; Tamandua, 666, 668
Antebrachium, 520
Antedon, 361, 362, 363, 364, 365, 366
Antelope, 692, 695
Antennae, 175, 176, 208, 233
Antennary gland, 209
Antennata, 175, 225, 280
Antennules, 185, 186, 208
Anterior, 136
Anterior abdominal vein, 536
Anterior fontanelle, 647
Anterior gastric muscles, 189
Anterior nephridia, 168
Anthropoidea, 709, 710, 716, 726
Anthropopithecus, 712, 727
Antilocapra, 694, 6^7, 725
Antilocapridae, 694, 697, 725
Antlers, 696
Ant-lion, 254
Anura, 524,544, 546, 579; classification
of, 558, 561
Anus, 38, 136, 167, 480
Aorta, 240, 432, 433, 654
Aphaniptera, 258, 282
Aphis, 257, 281
Aphis-lion, 254
Aphrophora, 257
Apis, 256, 281
Aplysia, 293, 324
Apoda, 524, 560, 562
Apodemes, 175, 201
Appendages of Arthropoda, 176
Aptera, 245, 249, 251, 280
Apteria, 607
Apteryx, 631, 633
Apus, 204, 205, 215, 277
Aquatic Carnivora, 721
Aqueous humour, 423, 444
Aquila, 634
Arachnida, 175, 259, 276, 282
Araneida, 260, 282
Arcella, 20, 21
Archacopten/x, 628, 630, 633
Archaeornithes, 633
Archegosanrus, 528
Archigetes, 111
Archinephric duct, 439
Archipterygium, 509
Arcifera, 558, 562
Arctomys, 701
Ardea, 634
Argiope, 373, 375
Argyroneta, 263
"Aristotle's lantern," 347, 349
Armadillo, 666, 667, 668
Arms, of Brachiopods, 371; of Mol-
luscs, 312
Artemia, 205, 208, 277
Arterial arches, 402
Arthrobranchs, 187
Arthrodial membranes, 176
Arthropoda, 174; appendages of, 179;
classification of, 175, 277
Arthrostraca, 217, 221, 279
Articular bone, 477, 480, 574
730
INDEX
Articulation, 617
Artiodactyla, 688, 690, 723
Arvicola, 704, 725
Arytenoid cartilages, 579, 624
Ascaris, 128, 130
Ascidia, 405
Ascidiacea, 411
Ascidian, 406
Asellus, 222, 224, 279
Aspidobranchiata, 324
Aspidochirotae, 360, 368
Ass, 688
Assimilation, 5
Astacus, 176, 177, 178, 183, 187, 190,
195, 278
Asterias, 326, 329, 336, 367
Asterina, 337
Asteroidea, 326, 338, 364, 365, 366, 367
Astropectinidae, 338
Asymmetry, 296
Ateles, 712, 726
Athene, 705
Atlas, 565
Atrial cavity, 393
Atrial pore, 393
Atrium, 97
Auchenia, 696, 724
Auditory cranial nerve, 426
Auditory ganglia, 421
Auditory ossicles, 645
Aurelia, 75, 76, 77, 111
Auricle, 535
Auriculae, 349
Automatism, 7
Autostylic, 457, 470
Aves, 451, 606, 629 ; classification of,
633
Avicularium, 379
Axial sinus, 336, 338
Axis, 565
Axis-cylinder process, 417
Axolotl, 543
Axon, 150, 417
Axonosts, 481
Babirusa, 691, 724
Bacteria, 19, 34
Badger, 677
Balaena, 683, 722
Balaenoptera, 683, 722
Balancers, 248, 257
Balanoglossida, 386, 392
Balanoylosstis, 386, 387
Balanus, 212, 278
Baleen, 682
Banded ant-eater, 662
Bandicoots, 662
Bank-vole, 704
Barbary ape, 712
Barbastelle, 708
Barbels, 449, 493
Barbs, 607
Barbules, 607
Barnacle, 212, 213
Barn-owl, 635
Basement membrane, 382
Baseosts, 481
Basibranchial plate, 458
Basidorsals, 475, 496, 499
Basilingual cartilage, 550
Basilar membrane, 649
Basilar segment, 228
Basi-occipital bone, 475, 571
Basipodite, 181
Basipterygium, 460
Basisphenoid, 476, 571
Basiventrals, 458, 475, 496
Bass, 493
Bastard wing, 611
Bat, 606, 705, 706
Batoidei, 467, 469, 512
Batrachia, 544
Bdelloida, 123, 125, 126
Bdellostoma, 449
Bear, 676
Bear animalcules, 175
Beaver, 663, 701, 704
Bed-bug, 257
Bee, 175, 246, 248, 256
Beetle, 246, 250, 254
Bettongia, 661, 664, 719
Bile, 429
Bile-duct, 429
Biogen molecule, 4, 5
Biogens, 4
Biology, definition of, 1
Bionomics, 10
Bipalium, 94
Biramous, 203, 210
Birds, 296, 567, 606, 632
Birth, 659, 665
Biseriate, 460, 504, 509, 517
Bisexual, 8
Bison, 698
Bivalves, 205, 284, 289, 291, 292, 294,
296
Black bear, 676
Bladder, 486, 533, 659
Blarina, 671, 720
Blastocoele, 115
Blind pouches, 171, 290, 401
Blind tubes, 264
Blind-worm, 585, 586
Blood, 187, 203, 432, 433, 665
Blood-sucking bat, 708
Blue-bottle, 258
Body cavity, 133
Body-wall, 56
Bombinator, 557, 562
Bombus, 256
Bombyx, 249, 250, 258, 282
Bone, 413, 474; evolution of, 509
INDEX
731
Bonellia, 168
Books, 260
Bos, 724
Bot-fly, 258
Bothriocephalus, 110
Botryllus, 410, 411
Bour/ainvillia, 61, 66
Bovidae, 694, 696, 724
Bow-fin, 498
Box tortoise, 597
Box turtles, 597
Brachial ganglion, 319
Brachial plexus, 555
Brachiopoda, 370; distribution and
classification of, 375
Brachipod shell, 371
Brachium, 520
Brachyura, 217, 279
Bracts, 67
Bradypodidae, 666, 668, 719
Bradypus, 719
Brain, 188, 414, 460, 554, 619, 669
Branchellion, 161, 163
Branchiae, 161, 336, 337
Branchial arches, 457, 478
Branchial basket, 446
Branchial coelomic canals, 395
Branchial hearts, 317
Branchiocardiac canals, 202
Branchiocardiac grooves, 180
Branchiosaurus, 528, 560
Branchiostegal rays, 481
Branchiostegite, 180, 184, 214
Branchipus, 205, 206, 208, 277
Breathing, 4
Brill, 494
Brittle-stars, 326, 339, 340, 341, 342
Bronchi, 624
Bronchial tubes, 579
Brood-pouch, 206
Brown bear, 676
Brown-body, 378
Brown tubes, 171
Bubalus, 693
Buccal-cavity, 136
Buccal commissure, 310
Buccal ganglia, 310
Buccal mass, 291, 310
Buccal membrane, 327
Buccal tube-feet, 350
Buccinum, 289, 324
Buds, 59
Buffalo, Cape, 693; American, 698
Bufo, 545, 547, 549, 559, 562
Bufonidae, 545, 559, 562
Bug, 245, 257
Bugula, 379
Bulbus arteriosus, 487
Bull-frog, 559
Bunodont, 691
Bunodontia, 691, 723
Bursa Fabricii, 627
Bush-bodies, 173
Butterfly, 244, 248, 249, 258
Byssus, 307, 308
Caddis-fly, 253
Caeca, 162
Gaenolestes, 663, 718
Caffre cat, 674
Caiman, 598, 602
Ca'ing whale, 681, 682
Cake-urchin, 356
Calamoichthys, 473, 502, 517
Calcaneum, 600, 652
Calcarea, 90
Calcareous substance, 26
Calciferous glands, 142
Callorhynchus, 472, 513
Galotermes, 253, 281
Calycophoridae, 67
Calyptoblastea, 82
Cambarus, 176, 220
Camel, 694
Camelidae, 694, 724
Camelus, 695, 724
Canaliculi, 414
Canals of Laurer, 103
Cancer, 279
Canidae, 676, 720
Cam's, 639, 640, 642, 649, 674, 675, 720
Capillaries, 145, 434
Capillary, 145
Capillitium, 28
Capreolus, 698, 724
Caprimulgus, 635
Carapace, 176, 204, 230, 259, 594
Carbon dioxide, 2, 4, 17, 20, 145, 433
Carcharodon, 467
Carcinus, 218, 279
Cardinal teeth, 300
Cardinal veins, 432, 462
Cardium, 308
Cariacus, 698. 724
Caribou, 69j6, 698
Carina, of Cirripedia, 212; of Aves, 610
Carinatae, 631, 634
Carinella, 117
Carmarina, 63
Carnassial teeth, 674
Carnivora, 674, 720
Carotid arch, 537
Carotid arteries, 431, 462
Carotid gland, 537
Carp, 491
Carpale, 521
Carpalia, 521
Carpopodite, 181
Carpus, 520
Cartilage, 413
732
INDEX
Cartilage bone, 474
Caryophyllia, 74
Cassowary, 631, 633
Castor, 701, 704, 725
Casuarius, 631, 633
Cat, 674, 675, 676
Catarrhini, 712, 726, 727
Caterpillar, 249, 250, 258
Cat-fish, 491, 492
Cathartes, 634
Caudal fork, 179
Caudal vein, 433, 462, 535
Cave-newts, 544
Cavia, 701, 725
Cavicornia, 695, 696
Cebidae, 710, 726
Cebus, 712, 726
Cecidomyia, 257
Cell, 30, 52
Cellulose, 28, 33
Centetidae, 672
Centipede, 175, 228, 229, 230
Centra, 458
Central capsule, 26
Centrarchidae, 493, 515
Centro-dorsal ossicle, 361
Cephalic pits, 115
Cephalochorda, 383, 390
Cephalodiscida, 390
Cephalodiscus, 390
Cephalopoda, 311, 325
Cephalopods, 296
Cephalo-thorax, 176, 180, 259
Cephalothrix, 117
Ceratobranchial segment, 457
Ceratodus, 473, 505, 506, 508, 510, 511,
518
Ceratohyal, 456, 478
Cercariae, 105
Cerci anales, 237
Cercopithecidae, 710, 712, 726
Cerebellar lobes, 461
Cerebellum, 416, 447, 619
Cerebral ganglia, 292
Cerebral hemisphere, 416
Cerebratulus, 116, 117
Cerebrum, 416
Cervidae, 694, 696, 724
Cervus, 697, 724
Cestoda, 106, 112
Cestracion, 468
Cestum, 81
Cetacea, 679, 699, 722
Chaeta-sacs, 140, 153
Chaetae, 139, 167, 179
Chaetoderma, 325
Chaetognatha, 381
Chaetopoda, 158, 165, 179
Chaetosoma, 384
Chaetosomatidae, 130
Chamaeleo, 578
Chambered organ, 364
Character, 9
Charadriiformes, 633, 635
Charadrius, 635
Cheese-mite, 268, 269
Cheilostomata, 380
Cheiroptera, 705, 725
Cheiropterygium, 435, 520 -
Chela, 181, 182
Chelicerae, 176, 259, 261
Chelone, 592, 593, 595, 605
Chelonia, 568, 591, 605
Chelonidae, 597
Chelydra, 597
Chelydridae, 597
Chevrons, 569
Chevrotain, 694, 695
Chick, 421
Chilopoda, 228, 280
Chimaera, 419, 471, 472, 513
Chimpanzee, 713
Chipmunk, 701, 705
Chitin, 20, 193, 201, 229
Chiton, 323
tHTlamydospores, 28
Chlamydothorax, 386
Chlorophyll, 33, 34
Choanae, 599
Choanocytes, 85
Choanoflagellata, 34, 47
Chondrichthyes, 453, 488, 512
Chondrin, 275
Chondrioderma, 29
Chondrostei, 473, 500, 517
Chordal sheath, 392
Chordata, 385 ,
Choroid coat, 422
Chorophilus, 559, 562
Chromatin, 18, 27
Chromidium, 21, 25, 27
Chrysemys, 597
Chrysochloridae, 672
Chrysopa, 254, 281
Chylific ventricle, 238
Cicada, 257, 281
Ciconia, 634
Ciconiiformes, 632, 634
Cilia, 35, 47
Ciliata, 34, 35, 47
Ciliated funnels. 169
Cingulum, 121
Cinosternidae, 597
Cinosternum, 597
Ciona, 407, 409
Circular canal, 60
Circulatory system, of Amphibia, 523,
535, 552; of Arthropoda, 202; of
Aves, 621; of Cephalochorda, 402;
of Cephalopods, 316; of Craniata,
430, 432, 435; of Dipnoi, 506;
of Elasmobranchs, 461; of Mam-
INDEX
733
mals, 652, 653 ; of Eeptiles, 580
588
Cirri, 361
Cirripedia, 212, 278
Cirrus, 158
Cistudo, 597
Civet cats, 678
Cladocera, 208, 277
Cladoselache, 460, 470
Clam, 298, 308
Clasper, 460, 465
Classes, 11
Classification, 10, 13
Clava, 65
Clavicle, 501, 503, 517
Cleithra, 516
Clepsidrina, 43, 44, 48
Clepsine, 161, 164, 166
Clitellum, of Lumbricus, 140, 156;
of Hirudo, 161
Cloaca, 122, 412, 443, 463, 465, 523
Clupea, 489, 514
Clupeidae, 489, 514
Clupeiformes, 489, 513
'Clypeaster, 368
Clypeastroidea, 356, 368
Cnidoblast, 55
Cnidocils, 55
Coccidea, 44, 45, 48
Coccinella, 254, 281
Coccygeo-mesenteric, 623
Coccyx, 613
Cochlea, 421
Cockchafer, 248, 254, 255
Cockle, 298, 308
Cockroach, 233, 239, 243, 245, 246,
247, 249; ecdysis of, 244
Cocoon, of cockroach, 243 ; of Hirudo,
161 ; of Lumbricus, 154, 157 ; of silk-
worm, 249, 250
Cod, 478, 482, 495
Coecilia, 560, 562
Coelenterata, 49; classification of , 81;
general shape of body of, 49
Coelenteron, 50
Coeliac artery, 461
Coelom, 133; of Annelids, 158,
162; of Arthropods, 192, 238; of
Brachiopods, 371,374; of Cephalo-
chorda, 393 ; of Chaetognatha, 381 ;
of Echinoderms, 328; of Henri-
chorda, 386; of Molluscs, 288; of
Vertebrates, 436
Coelomata, 133
Coelomic cavity, 133; in Arthropods,
192; in Cephalochorda, 393; in
Lumbricus, 140; in leeches, 162
Coelomic fluid, 147, 148
Coelomic grooves, 392
Coelomic nervous system, 336
Coelomiducts, 296
Coenurus, 110
Coleoptera, 245, 250, 254, 281
Collar, 85, 86, 386, 387
Collar-cavities, 392, 437
Collar cells, 85, 87
Collar pore, 386
Collaterals, 417
Colleterial glands, 238
Colloid solution, 4, 19
Colon, 238
Colony, Coelenterate, 59, 62, 69, 71;
Polyzoan, 376
Colubridae, 590
Columba, 617, 622, 626, 635
Columella, 572
Columella auris, 546, 645
Columella cranii, 572
Colymbiformes, 631, 634
Colymbus, 632, 634
Comatulidae, 361
Commissures, 149, 291
Common carotid, 537
Compound Ascidians, 411
Compound eye, 197
Conchostraca, 208, 277
Condyles, 523, 618
Condylura, 672, 720
Cone-cells, 422
Coney, 684
Conjugation, 7, 8 ; in Paramecium, 41
Connective tissue, 152, 201, 350, 413
Consciousness, 2
Contractile vacuole, 17, 32, 38
Contraction, 6
Conus arteriosus, 430
Convolute, 98
Co-ordinated parts, 25
Copelata, 410
Copepoda, 209, 277
Copulatory sacs, 582
Copulatory spicules, 130
Coracias, 633, 635
Coraciiformes, 633, 635
Coracoid, 483, 532, 575, 576, 633, 650
Coracoid cartilage, 532
Coracoid fontanelle, 576
Coral, 73, 74
Coral islands, 74
Coralline Crag, 380
Corallum, 74
Coregonus, 490, 514
Cornea, 424
Corona, 346
Coronella, 591
Coronoid, 575
Corpus callosum, 647
Cortical layer, 33
Cortical zone, 106
Corvus, 635
Costal plates, 593
Costal process, 609
734
INDEX
Cotylosauria, 603
Coverts, 611
Coxa, 236
Coxal glands, 230, 264
Coxopodite, 181, 182
Crabs, 217, 218
Crane, 634
Crania, 370, 373, 375
Cranial bones, 475, 479
Cranial cavity, 516
Cranial nerves, 538
Craniata. 413. 414, 438
Crayfish, 176, 177, 178 ; ecdysis of, 193
Crested newt, 525
Cribriform plate, G47
Cricket, 251
Cricoid, 579
Cricotus, 602
Crinoidea, 361, 367
Crocodiles, 568, 584, 598
Crocodilia, 568, 575, 598, 604, 605
Crocodilus, 600, 601, 603, 605
Crop, 137, 141, 162, 238, 291, 625
Cross fertilisation, 156
Crossopterygii, 503
Crossopus, 671
Crotalinae, 591
Crotalus, 590, 591, 605
Crow, 635
Crural gland, 226
Crus, 520
Crustacea, 136, 175, 203, 277
Cryptobranchus, 542, 561
Crystalline cone, 197
Crystalline sac, 305
Crystalline style, 305
Ctenidium, 287, 302, 315
Ctenoid scales, 483
Ctenophora, 78, 83, 92
Ctenoplana, 100
Ctenostomata, 380
Cuckoo, 633, 635
Cuckoo-spit, 257
Cuculiformes, 633, 635
Cuculus, 635
Culex, 258, 282
Cuma, 279
Cumacea, 217, 221, 279
Cutaneous artery, 538
Cuticle, 17, 36, 140, 179
Cuttle-fish, 284, 286, 289, 291, 293,
294, 309
Cuvierian organs, 359, 360
Cyclas, 292
Cycloid scales, 483, 517
Cyclops, 210, 211, 277
Cyclostomata, 380, 413, 443
Cygnus, 634
Cynips, 256
Cynomys, 705
Cypridina, 209, 277
Cyprinidae, 491, 514
Cyprinus, 491, 514
Cypris, 209, 277
Cypselus, 635
Cyst, 19, 28, 45
Cysticercoid, 110, 111
Cysticercus, 110
Cystoflagellata, 34
Dab, 494
Dactylopodite, 181
Dactylozooids, 68
Daddy-long-legs, 258
Daphnia, 205, 206, 208, 277
Dart-sac, 295
Darwin, 11, 13
Dasypodidae, 666, 668, 719
Dasypus, 667, 719
Dasyuridae, 662, 717
Daughter-cysts, 30
"Dead men's fingers," 68
Decapoda, 182, 217, 278, 325
Decomposition, 4, 5, 6
Deer, 694, 696
Defaecation, 5, 6
Degeneration, 12
Delphinapterus, 681, 722
Delphinus, 681
Demospongiae, 91
Dendrites, receptive and terminal, 150,
422
Dendrochirotae, 360, 368
Dendrocoelida, 99, 112
Dendrocoelum, 99
Dental formula, 644, 674
Dentalium, 325
Dentary bone, 480, 510
Dentary plates, 471
Dentinal canals, 454; pulp, 454
Dentine, 454
Dermal branchiae, 337, 344
Dermal glands, 523
Dermal layer, 85
Dennis, 152, 202, 424, 607
Desman, 672, 673
Desmodus, 708
Desmognathinae, 543
Desmognathous palate, 632, 635
Desmpgnathus, 528, 544, 561
Development, definition of, 7
Diaphragm, 655
Diapophyses, 547
Diastema, 700
Diastylis, 221, 279
Dibranchiata, 325
Dicotyles, 691, 724
Dicynodontia, 604
Didelphyidae, 661, 662, 663, 717
Didelphys, 661, 717
Diemyctilus, 543
Differentiation, 12
INDEX
735
Difflugia, 20, 21, 22
Digenea, 105, 112
Digestion, 5
Digestive ferments, 5, 428, 429, 656
Digestive juice, 57
Digestive system, of Birds, 624 ; of
Echinoderms, 330 ; of Helix, 289 ;
of Platyhelminthes, 96, 98, 104,
101 ; of Vertebrates, 429
Digits, 520
Dinoflagellata, 34, 47
Dinornis, 631
Dinosauria, 604
Dinotherium, 686
Diomedea, 632, 634
Diphycercal fin, 447, 509 ; tail, 517
Dipleurula, 365
Diplopoda, 228, 231, 280
Dipneumona, 511, 518
Dipnoan, 507
Dipnoi, 473, 504, 517
Diprotodontia, 661, 663, 718
Diptera, 245, 248, 250, 282
Disc, 35, 36, 119, 326
Discoglossidae, 559, 562
Discoglossus, 562
Discontinuous distribution, 226, 688
Distomum, 102, 104, 105
Diver, 634
Docidophryne, 551
Dog, 639, 640, 642, 649, 675, 676
Dog-fish, 465, 467 ; see Scy Ilium
Dolichoglossus, 386, 387
Dolphin, 681
Donkey, 690
Dorcatherium, 695
Dormouse, 701, 704
Dorsal blood-vessel, 144
Dorsal pore, 139
Dorsal sac, 315
Dorsal tubercle, 407
Down, 607
Draco, 586
Dragon-fly, 175, 194, 246, 248, 252
Dromaeognathous palate, 629, 634
Dromaeus, 631, 633
Duck, 612, 613, 632, 634
Duckbill, 657, 658
Ductus arteriosus, 654
Ductus Cuvieri, 433
Ductus ejaculatorius, 244
Ductus endolymphaticus, 420
Dugong, 700 '
Duplicidentata, 701, 725
Eagle, 632, 634
Ear, 64 ; ampulla of, 420 ; internal,
420; outer, 569; of Gasteropod,
293; of Vertebrates, 418, 419, 420,
444
Ear-bones, 644
Ear-cockles, 131
Eared seals, 678
Ear-shell, 293, 294, 296, 297
Earth-pig, 669
Earthworm, 147, 408 ; British species
of, 157
Earwig, 247, 251
Ecardines, 375
Ecdysis, 193, 194, 244, 567
Echidna, 656, 657, 658, 717
Echinarachnius, 356, 368
Echinaster, 326, 327, 331, 367
Echinocardium, 356, 368
Echinococcus, 110
Echinocyamus, 356, 368
Echinodermata, 326 ; classification of,
367
Echinoidea, 344 ; subdivisions of, 355,
368
Echinus, 345, 346, 347, 351, 353, 355, 368
Echiuroidea, 167, 168
Ectoderm, 52, 179
Ectoplasm, 16, 19, 33
Ectoprocta, 380
Ectopterygoid, 477, 574
Edentata, 666, 719
Eels, 490, 491
Effodientia, 669, 719
Eft, 525
Egg-cell, 53
_ 3, 8, 13 ; of Birds, 627 ; of Cla-
docera, 206 ; of Cockroach, 243 ; of
Teleostei, 491
Egg-sacs of Copepoda, 211
Elapidae, 591
Elaps, 591
Elasipoda, 360, 368
Elasmobranch embryo, 441
Elasmobranchii, 455; classification of,
467, 512
Elater, 175
Elephant, 684, 685, 686
Elephas, 685, 686, 722
Eleutherozoa, 366, 367, 368
Elk, 698
Elpidia, 369
Elytra, 236, 246
Embryo, definition of, 9 ; of Amphi-
oxus, 392, 398 ; of Scyllium, 468
Emeu, 631, 633
Emulsion, 3
Emydidae, 597
Enamel, 454
Enamel organ, 643
Encystment, 19
Endocyclica, 355, 368
Endoderm, 52
Endoderm lamella, 60
Endoplasm, 16, 19
Endopleurite, 201
Endopodite, 179, 180, 209
736
INDEX
Endoskeleton, 275
Endosporeae, 28, 46
Endosternite, 201, 275
Endostylar coelom, 395
Endostyle, 400, 404, 408, 427
Endothelium, 434
Engraulis, 489, 514
Enopla, 118
Enteropneusta, 386
Entomology, 233
Entomostraca, 204, 277
Entoplastron, 594
Entoprocta, 380
Entopterygoid, 477
Enzymes, 428
Epanorthidae, 663, 718
Epeira, 260, 261, 264, 265, 282
Ephemera, 252, 281
Ephemeroptera, 252, 281
Ephippium, 206
Ephydatia, 91
Ephyra, 78
Epibranchial segment, 457
Epibranchial vessels, 430, 461
Epichordal, 547
Epicoracoid, 550, 575
Epidermal, 607
Epidermis, 137, 152
Epididymis, 164, 582
Epineural canal, 340, 346
Epi-otic, 476, 571
Epiphyses, 349, 650
Epiplastra, 594
Epipterygoid, 572
Epipubis, 533
Episternum, 550
Epistome, 377
Epithelial, 57
Epitrichial layer, 567
Equidae, 688, 689, 723
Equus, 687, 689, 723
Erethizon, 701, 705, 725
Erinaceidae, 670, 720
Erinaceus, 670, 720
Eryops, 602
Esocidae, 492, 514
Esox, 492, 514-
Ethmoid region, 456, 475, 476
Ethmoturbinals, 647
Eucarida, 217
Euglena, 32, 33
Euglenoid, 33
Eulamellibranchiata, 325
Euphausia, 217
Euphausidacea, 278
Eurypterina, 275
Euscorpius, 271
Euspongia, 91
Eustachian pouch, 545
Eutermes, 253, 281
Eutheria, 656, 664, 719, 722
Euthyneura, 324
Evolution, 12
Excreta, 4, 5
Excretion, 4
Excretory organs, 5, 168
Excretory system, of Arthropods, 192,
264 ; of Lumbricus, 147 ; of Platy-
helminthes, 92, 96, 104, 103; of
Kotifers, 123 ; of Vertebrates, 401,
438, 439, 441, 539, 556
Exhalant, 89
Exoccipital bones, 475, 530
Exopodite, 179, 180, 188, 210
Exoskeleton, 174, 175, 254, 284
Exosporeae, 28, 46
Expansion, 6
Extensor muscle, 199
Extrabranchials, 458
Exumbrella, 62
Eye, of Arthropods, 186, 209, 233,
271, of Lizzia, 63, 64 ; of Molluscs,
286, 320; of Vertebrates, 421, 436,
444
Facial nerves, 426
Faeces, 6, 430, 656
Falciform embryos, 44
Falcon, 634
Falconiformes, 632, 634
Fallopian tube, 658
Fallow-deer, 698
Families, 11
Fascicles, 357
Fat-body, 238
Feathers, 607
Feather-stars, 326, 361, 362, 363
Felidae, 674, 720
Felis, 674, 676, 720
Female, 8
Femoral vein, 535
Femur, 236, 520
Fenestra ovalis, 649
Ferments, digestive, 5, 428, 429, 656
Ferret, 677
Fertilisation, 58
Fiber t 704, 725
Fibres of Miiller, 422
Fibrils, 36, 152
Fibula, 521
Fibulare, 521, 652
Field-mouse, 704
Field-vole, 704
Filaria, 131
Filibranchiata, 324
Fins, 314, 447, 452, 459, 460
Firmisternia, 558, 559, 562
Firth of Clyde, 169
Fishes, 452
Fish-lice, 212
Fission, 7, 19, in Vorticella, 38; in
Hydra, 58
Fissipedia, 678, 720, 721
Five-fingers, 326
INDEX
737
Flagella, 33
Flagellate, 31, 33, 46 ; reproduction of,
33
Flagellated chambers, 89
Flagellula, 28
Flagellum, 25, 28, 34; of Helix, 295
Flame-cells, 93, 401
Flamingo, 634
Flea, 248, 258
Flexor muscle, 199
Flight of birds, 611
Flocculi, 647
Flosculana, 119, 120, 121, 122, 123,
124, 126
Flounder, 494
Flowers of tan, 18, 27.
Fly, 245, 248, 257
Flying-foxes, 708
Flying- squirrel, 702, 703
Fontanelles, 479
Food, of animals and plants, 2
Food-vacuoles, 16
Foot of Molluscs, 285, 286, 311
Foramen magnum, 583
Foramen of Panizza, 601
Foraminifera, 22,
Forficula, 251, 280
Formica, 256, 281
Fowl, 615, 626, 634
Fox, 675
Fox-bats, 708
Fredericella, 380
Fresh-water mussel, 298
Fresh- water polyp, 49
"Frilled membrane," 171
Frog, 519, 545, 559
--^.Frog-hoppers, 257
Frontal bones, 479
Frontals, 530, 531
Fruit-eating bat, 706
Fulcra, 498
Fulica, 634
Functions, 17
Funicle, 377
Funnel, 80, 311, 312, 314
Gadiformes, 495, 516
Gadus, 478, 482, 495, 516
Galea, 236
Galeopithecidae, 670
Galeopithecus, 670
Galeus, 467, 512
-GFSft-bladder, 429
Gall-fly, 256, 258
Galliformes, 631, 634
Gallus, 615, 634
Game-birds, 631, 634
Gametes, 22
Gammarus, 222, 223, 279
Ganglion, 161
Gannet, 609, 634
8. &M.
Ganoidei, 473
Gapes, 131
Gar-pikes, 496
Gastral filaments, 75
Gastral layer, 85
Gastropoda, 285, 297, 323
Gastrozooids, 68
Gavial, 602
Gavialis, 602, 605
Geckos, 575-
Gemmation, 7 ; in Hydra, 58
Gemmiform, 348
Generative openings, 139
Generative organs, 64
Geniohyoid, 527
Genital bursae, 343
Genital ducts, 168
Genital openings, 13$
Genital rachis, 337
Genital stolon, 338
Genus, 10
Geonemertes, 114, 118
Gephyrea, 167, 173
Gephyrea nuda, 167
Gephyrea tubicola, 167
Gephyrocercal fin, 490
Germ, 7, 8, 9
Germarium, 97, 124
Gestation, 664
Giant-fibres, 153, 398
Gibbons, 712
Gill-bars, 450
Gill-books, 260, 274, 275
Gill-cover, 558
Gill-plate, 302
Gill-rays, 458
Gills, of Arthropods, 187, 219, 220,
275; of Branchellion, 161, 163; of
Echinoids, 354 ; of Elasmobranchs,
458; of Haliotis, 294; of Helix,
286 ; of Nereis, 159
Gill-sac, 444, 458
Gill-slits, 385, 388, 393, 427, 444
Gill-trees, 357
Giraffa, 696, 724
Giraffe, 696, 697
Giraffidae, 696, 724
Gizzard, 137, 142, 238, 625
Gland, 5
Glass-snake, 586
Glenoid cavity, 532, 575, 642
Globicephalus, 681, 682, 722
Globigerina ooze, 26
Glochidia, 307
Glomerulus, 388, 440
Glossina, 35, 257
Glossobalanus, 386, 388, 389
Glossohyal, 478, 618
Glossopharyngeal nerve, 427
Glottis, 523
Glycogen, 429
47
738
INDEX
Gnat, 245, 258
Gnathites, 174, 235, 245
Gnathobases, 183, 185, 235, 259
Gnathobdellidae, 162, 165
Gnathostomata, 449, 451
Goat, 697
Goblet-cells, 151
Golden mole, 672
Gold-fish, 491
Gonads, 64
Gonophores, 66
Goose, 634
Gopher, 597
Gorilla, 709, 712, 72?
Grampus, 681
Grantia, 88
Grasshopper, 246, 247, 251
Grass-suake, 591
Gravitation, 1
Gray-fish, 407
Grebe, 634
Greenland seal, 679
Green turtle, 592, 593, 595
Gregarinidea, 44, 48
Grey seal, 679
Grey squirrel, 702
Gripping cells, 78
Grizzly bear, 676
Gromia, 22, 23
Ground-hog, 705
Ground-squirrel, 704, 705, 714
Grouse, 634
Growth, 1, 2, 7
Grubs, 250
Gruiformes, 634
Grus, 634
Gryllus, 251, 280
Gudgeon, 491
Guinea-pig, 700
Gull, 633, 635
Gullet, 69, 428
Gurnard, 543
Gymnoblastea, 81
Gymnolaemata, 380
Gymnophiona, 560
Gymnura, 670
Haddock, 495
Haemal arches, 414, 458
Haematodicha, 266
Haematoflagellata, 35
Haemocoel, 192, 434
Haemoglobin, 45, 145, 434
Haemosporidia, 44, 45, 48
Hag-fish, 444, 449
Hair, 636
Halibut, 494
Halichoerus, 679
Halicore, 700, 725
Haliotis, 293, 294, 296, 297, 324
Hallux, 551
Halteres, 248, 257
Hammerhead shark, 467
Hapale, 726
Hapalidae, 710-726
Haploceros, 698, 724
Haplomi, 514
Hard palate, 641
Hare, 701
Harlequin snake, 591
Harriotta, 472
Harvestmen, 260, 266, 267
Haversian canals, 414
Head, 232, 616
Head-cavity, 392, 437
Heart, 202,430, 431; ofLumbricus, 145
Heart-urchins, 356
Hectocotylization, 322
Hectocotylus, 322
Hedgehog, 671
Heliosphaera, 26, 27
Heliozoa, 28, 31, 46
Helix, 285, 287, 288, 289, 290, 292,
295, 324
Hell-bender, 561
Hemerobius, 254, 281
Hemiazygos, 655
Hemichorda, 386, 403
Hemiptera, 245, 247, 250, 257, 281
Hepatic diverticula, 238
Hepatic portal system, 433
Hepatic vein, 433, 462
Heptanchus, 512
Heredity, 9
Hermaphrodite, 8, 139
Hermaphroditism, 295
Hermit-crab, 217, 218
Heron, 634
Herrings, 489, 490
Hesperornis, 628, 633
Hessian-fly, 257
Heterocercal tail, 460, 481
Heterocoela, 91
Heterodontidae, 457
Heteronemertini, 117
Hexactinellidae, 91
Hexanchus, 512
Hinge, 298, 300
Hippoglossus, 494, 515
Hippopotamidae, 691, 723
Hippopotamus, 691, 723
Hirudinea, 160, 166
Hirudo, 160, 163, 164, 166
Hirundo, 635
Hog-water louse, 222, 224
Holocephali, 472, 475, 513
Holothuria, 358, 368
Holothurian, 364
Holothuroidea, 357, 368 ; subdivisions
of, 360
Holotricha, 47
Holotrichous, 39
Hominidae, 710, 727
Homo, 710, 727
INDEX
739
Homocercal tail, 481
Homocoela, 90
Homoiothermal, 638
Homology, 13
Homoplasy, 13
Honey-bee, 256
Hoof, 684
Hoopoe, 635
Hoplocarida, 220, 278
Hormiphora, 79, 81
Horned pout, 492
Horned "toad," 587
Hornet, 256
Horse, 687, 689
Horse-fly, 258
Horse-shoe bat, 708
Host, 44
House-fly, 245, 258
Huanaco, 696
Humble-bee, 256
Humerus, 520
Hybrid, 9
Hydatina, 124, 126
Hydra, species of, 49, 50, 51, 53, 54, 56,
57; cell of, 52; reproduction of, 58
Hydractinia, 68
Hydranth, 62
Hydra-tuba, 77, 77, 78
Hydrida, 81
Hydrocoele, 365
Hydrocorallinae, 66, 68, 82
Hydroid person, 62, 65, 68
Hydromedusae, 59, 75, 81
Hydromedusan, 65
Hydrozoa, 67, 81
Hyla, 547, 559, 562
Hylidae, 558, 559, 562
Hylobates, 712, 727
Hymenoptera, 246, 248, 250, 255, 281
Hyoid, 455, 531, 550
Hyoidean artery, 462
Hyomandibular, 456, 478, 500, 503
Hyoplastra, 594
Hyostylic, 457
Hyperpharyngeal groove, 400
Hypo-branchial segment, 457
Hypogeophis, 560, 562
Hypoglossal nerve, 539
Hypohyal, 478
Hypopharyngeal groove, 400, 408
Hypopharynx, 245, 257
Hypoplastra, 594
Hyracidae, 684, 722
Hyrax, 684, 685, 722
Hystricidae, 705
Hystrix, 701, 725
Ichneumon, 256
Ichthyodorulite, 471
Ichthyoidea, 542
Ichthyophis, 560, 562
Ichthyopterygium, 452
Ichthyornis, 628
Ichthyosauria, 604
Iguana, 576
Iguanidae, 587
Ilio-ischiatic foramen, 614, 615
Ilium, 528, 533, 565
Image, 198
Imago, 249
Impulses, 418
Incus, 122, 645
Indian ink, 317
Inermia, 167
Infundibular ganglion, 319
Infundibulum, 428
Infusions, organisms in, 19
Ingestion, 5
Inhalant, 89
Ink-sac, 317
Innominate artery, 652
Insecta, 175, 280
Insectivora, 669, 720
Intercalary piece, 459
Intercentra, 569
Interclavicle, 576
Intercoelic membrane, 395
Intercostal muscles, 577
Interfilamentar junctions, 302
Interhyal, 478
Interlamellar junctions, 302
Intermedium, 521
Interoperculum, 480
Interorbital septum, 470, 571, 616
Interparietal foramen, 583
Interradii, 326
Interstitial cells, 53
Intertarsal joint, 577
Intertentacular organ, 378
Intestine, 137, 428, 429
Introvert, 170
Invertebrata, 15
Iris, 321
Irritability, 6
Ischiopodite, 181
Ischiopubic cartilage, 533
Ischium, 533, 565, 652
Isopleura, 298, 323
Isopoda, 222, 279
Isoptera, 281
Isospores, 27
lulus, 175, 231, 232, 280
Ixodidae, 268
Jackal, 675
Jack-rabbit, 702
Jaw, 349, 449, 456
Jelly, 55, 57, 69, 87, 201, 434
Jelly-fish, 62, 75
Jugal, 641, 699
Jugal bone, 479, 574, 616
Jugular, 489
Jugular-vein, 535, 620
Jumping-shrew, 671
472
740
INDEX
Kangaroo, 663
Kangaroo-rat, 661, 664
Katabolism, 4, 17
Keber's organ, 306
Kidneys, 97, 193, 196, 484
King-crab, 272, 273, 274, 275
Kingfisher, 635
Kiwi, 631, 633
Krohnia, 384
Labial cartilages, 443, 458
Labial palp, 236, 304
Labium, 235, 236
Labridae, 493
Labrum, 235
Labyrinthodonta, 524, 528, 546, 560
Lacerta, 569, 582, 586, 604
Lacertilia, 568, 586, 604
Lachrymal, 574, 642
Lacinia, 236
Lacunae, 414
Lady-bird, 254
Lamella, 302
Lamellibranchiata, 289, 298, 302, 307,
309, 324
Lamprey, 444, 445, 446, 448
Land nemertines, 114
Land-newts, 544
Land-reptiles, 604
Land tortoises, 597
Langerhans, islets of, 430
Languets, 408
Langur, 712
Lantern coelom, 354
Large intestine, 430
Lark, 635
Larus, 635
Larva, 9; of Amphibia, 524, 541, 557,
558; of Cestoda, 109, 110; of
Echinoderms, 365 ; Ephyra-, 78;
of Holothurian, 364 ; of Hydro-
medusae, 65, 66 ; of Insects, 249,
254; of Lamprey, 448; of Nema-
todes, 132 ; of Nemertines, 116 ;
of Penaeus, 219 ; of Sponges, 89 ;
of Teleostomi, 487 ; of Trema-
todes, 103- of Tunicata, 404; of
Turbellaria, 99
Larvacea, 410
Larynx, 579, 624
Lateral-line, 427 ; -process, 577 ; -tooth,
300; -vein, 463; vessels, 145
Laterotemporal fossa, 575
Laverania, 45, 48
Leeches, 160
Leiotrichi, 714
Lemur, 709, 710, 726
Lemuroidea, 709, 726
Lens, 197, 423
Leopard, 676
Lepas, 213, 278
Lepidoptera, 245, 248, 250, 258, 282
Lepidosiren, 504, 506, 507, 508, 509,
518
Lepidosteus, 496, 497, 499, 500, 502,
503, 511, 512, 516
Lepisma, 251, 280
Leporidae, 700
Leptocephalus, 491
Leptostraca, 215, 278
Lepus, 646, 651, 701, 702, 725
Leucandra, 91
Leuciscus, 485
Leucosolenia, 84, 85, 86, 89, 90
Levatores arcuum, 457, 527
Libellula, 252
Lice, 257
Lienogastric artery, 461
Life, 1-3
Ligula, 236
Lily-encrinites, 361
Limbs of Amphibia, 520
Liinicolae, 157
Limnaea, 105, 285, 293
Limpet, 289, 290 t 296
Limulus, 260, 272, 273, 274, 275, 283
Linens, 113, 114, 117
Lingual cartilage, 443
Lingula, 370, 371, 373, 375
Lion, 676
Lissoflagellata, 35, 47
Lithobius, 228, 229, 230, 280
Liver, 136, 291, 401, 429, 433
Liver-fluke, 105
Lizard, 569, 570, 572, 580, 580, 581,
585; scale of, 568
Lizzia, 63
Llama, 696
Lobosa, 20
Locomotor organ, 6
Locusta, 251
Loemanctus, 570
Loggerhead turtle, 592
Loligo, 312, 322
Long-eared bat, 708
Longitudinal valve, in Rana, 552
Lophophore, 169, 372, 374
Lower temporal arcade, 575
Lucanus, 245
Lumbar vertebrae, 655
Lumbricus, 139, 142, 143, 149, 151, 154,
165, 200 ; British species of, 157
Lung-books, 260, 262, 263
Lung-fish, 504
Lungs, 504, 506, 512, 535, 623
Lutra, 676, 721
Lymph, 546
Lymphatic system, 434
Lymph-hearts, 547
Lymph-spaces, 546
Lynx, 676
INDEX
741
Macacus, 712, 727
Mackerel, 493
Macropodidae, 663, 718
Macropus, 664, 719
Macroscelidae, 670
Macroscelides, 671
Macrura, 219, 278
Madreporic vesicle, 338
Madreporite, 334
Maggots, 250
Malacobdella, 118
Malacostraca, 204, 209, 214, 242, 278
Male, 8
Malleus, 122, 645
Malpighian capsules, 440
Malpighian layer, 523
Malpighian tubules, 231, 238, 254, 264
Mammalia, 451, 636 ; classification of,
656, 717; fossil representatives of,
714
Mammals, 577
Mammary glands, 638
Mammoth, 685
Man, movements of, 2, 708, 709, 710,
712, 713
Manatee, 699, 700
Manatus, 699, 700, 725
Mandible, 208, 209, 232
Mandibular-arches, 431 ; -bar, 456 ;
-cavities, 437
Manidae, 666, 669, 719
Manis, 668, 669, 719
Mantis, 251
Mantle, 284
Mantle-cavity, 284, 286, 30
Manubrium, 62, 122
Manus, 520
Manyplies, 693
Marginal canal, 60
Marginals, 594
Marine turtles, 597
Marmosets, 711
Marmot, 701, 704, 705
Marsipobranchii, 448
Marsupials, 661
Marten, 677
Mastax, 119, 122
Mastigophora, 34
Mastodon, 686
Mastodonsaurus, 573
Maxilla, 209, 232, 261, 574, 616
Maxillary-bone, 479 ; -palp, 236
Maxillipedes, 182, 187, 209
Maxilloturbinal, 647
May-fly, 175, 252
Meatus auditorius externus, 641
Meckel's cartilage, 456, 574
Median fin, 525
Median vagina, 659
Mediterranean race, 715
Medulla oblongata, 416
Medullary plate, 385
Medusa, 60, 62, 63, 64, 65, 66
Medusoid person, 62, 67
Megalospheric form, 26
Meganucleus, 37
Megapodidae, 630
Meles, 677, 721
Melontha, 248, 254, 255, 281
Membrana semiluuaris, 624
Membrana tympaniformis interna,
624
Mendel, 10
Menopoma, 542, 561
Mentum, 236
Mephitis, 677, 677, 721
Merlucius, 516
Mesenteric arteries, 461
Mesenteric filament, 71
Mesenteron, 239
Mesentery, 68, 69, 72, 330, 437, 539
Mesethmoid bone, 476
Mesoblast, 134
Mesocoracoid, 576
Mesoderm, 133, 136
Mesoderm cells, 135
Mesogloea, 55
Mesonemertini, 117
Mesonephros, 440, 540
Mesophyterygiura, 460
Mesoscapula, 576
Mesosoma, 259
Mesosternum, 650
Mesostoma, 94, 95
Meso-thorax, 236, 248
Metabolism, 3, 6
Metacarpals, 608
Metacarpus, 520
Metamorphosis, 249, 406
Metanemertini, 118
Metanephros, 440, 441, 465, 540
Metapterygium, 460
Metapterygoid, 477
Metasoma, 259
Metatarsus, 520
Metatheria, 656, 658, .715, 717
Meta-thorax, 236, 248
Metazoa, 15
Mice, 700, 701
Micronucleus, 37
Micropterus, 515
Microspheric form, 26
Midas, 726
Milk, 638
Millepore coral, 74
Mink, 676
Mites, 260, 268
Moa, 631
Mole, 671, 672
Molecules, 4, 5
Mole-shrew, 671
Molge, 520, 522, 525, 529, 531, 532, 533,
534, 537, 538, 539, 540, 541, 543, 545,
548
742
INDEX
Mollusca, 284; classification of, 323
Molpadidae, 360
Mongol, 714
Monkey, 708, 709, 710, 712, 713
Monocystis, 44, 48
Monogenea, 103, 112
Monopneumona, 518
Moose, 698
Morphology, 10
Moschites, 312
Moschns, 694
Mosquito, 245, 258
Moth, 6, 175, 248, 249, 250, 258
Mother-cyst, 30
Mother-of-pearl, 299
Motor nerves, 425, 426
Motor oculi, 425
Motor peripheral nerve, 151
Mound-builders, 630
Mouth, 38
Mouth-angles, 343; -cavity, 136;
-papillae, 343
Mouth-appendages, of Astacus, 183 ; of
Gammarus, 222; of Insects, 235, 244
Movements, 2, 3 ; of animals, 10
Mucous canals, 426^--
Mucous glands, 295
Mud-puppy, 542
Mud turtles, 597
Mugil, 514
Miiller's larva, 99
Mullus, 515
Multicellular, 30, 52
Multiplication, 1, 5
Muridae, 701, 703
Mm, 703, 725
Musca, 245, 258, 282
Muscardinus, 704, 725
Muscle, 6; of Arthropods, 201; of
Lamellibranchs, 300; of Urodela, 527
Muscle-cell ofLumbricus, 152
Muscle-plate, 417
Musculo-cutaneous vein, 536
Musk-lamprey, 444
Musk-ox, 697, 697
Musk-rat, 705
Musquash, 704
Mussel, 284, 298
Mustela, 677, 721
Mustelidae, 676, 677, 678, 721 /
Mustelus, 435
Mya, 308
Mycetozoa, 18, 27, 28, 46
Myelin, 417
Mylohyoid, 527
Myocoel, 395
Myodocopa, 209, 277
Myo-epithelial, 57
Myogale, 672, 673, 720
Myonemes, 33, 34, 86
Myotome, 393
Myoxipae, 701, 704
Myriapoda, 175, 228, 280
Myrmecobius, 662, 663
Myrmecophaga, 719
Myrmecophagidae, 666, 668, 719
Myrmeleon, 254, 281
Mysidacea, 278
Mysis, 216, 217, 278
Mystacoceti, 681, 682, 722
Mytilus, 308, 324
Myxine, 449
Myxinoidea, 448, 449
Myxomycetes, 28
Nacreous layer, 299
Narcomedusae, 66, 75, 82
Naris, 526, 599
Narwhal, 653
Nasals, 531
Natterjack, 545, 559
Natural selection, 12
Nauplius, 204, 215, 216
Nautilus, 242, 287, 297, 315, 321, 322,
325
Neapolitan coral, 74
Nebalia, 215, 278
Neck, 122 ; of Birds, 624
Nactocalyces, 67
Necturus, 542, 561
Negro, 714
Nematocyst, 53
Nernatoda, 127
Nemertinea, 115, 121
Neome'hia, 325
Neornithes, 633
Neosporidia, 47
Nepa, 257
Nephelis, 165, 166
Nephridium, of Amphioxus, 399, 401 ; of
Hirudo, 161 ; of Lumbricus, 139,
147 ; of Nemertines, 115 ; of Platy-
helminthes, 94, 105 ; of Eotifers, 123
Nephrostome, 147
Nephrotome, 439, 440
Nereis, 158, 159, 166
Nerve-cells, 56, 57
Nerve-ring, 62, 64, 335
Nerves, 7 ; cranial, 424 ; 1st to 10th, 425
Nervous system, of Arthropods, 196,
242, 265 ; of Brachiopods, 373 ; of
Cephalopods, 317 ; of Chaetognatha,
382; of Echinoderms, 335, 364;
functions of, 148; of Gastropods,
291; of Haliotis, 294; of Helix, 291,
292 ; of Lamellibranchiata, 307 ; of
Lumbricus, 149 ; minute structure of,
417 ; of Nematodes, 129 ; of Nemer-
tines, 115 ; of Platyhelminthes, 96,
102, 103; of Eotifers, 123; of Sepia,
319, 320 ; of Vertebrates, 388, 397,
404, 417, 424, 538, 582
Nervous threads, 62
Nervures, 246
INDEX
743
Nests, 627
Neural-arches, 414, 458; -canal, 385;
-tube, 388
Neurenteric canal, 399
Neuroglia, 417
Neuron, 150, 417, 418
Neuropodium, 158
Neuropore, 406
Neuroptera, 245, 253, 281
Newt, 519, 525, 543
Nidamental glands, 321
Nidicolous, 630
Nidifugous, 630
Nightjar, 635
Nipple, 638
Nitrogenous, 147
Noctiluca, 34
Nordic race, 715
Nose, 418, 443
Notidanidae, 456, 467
Notochord, 136, 385, 388, 392
Notommata, 123, 126
Notommatidae, 122
Notonecta, 257
Notopodium, 158
Notoryctes, 663, 718
Notoryctidae, 662, 663, 718
Notostrace, 208, 277
Nuchal plate, 591
Nuclear sap, 18
Nuclear wall, 18
Nucleic acid, 4
Nucleus, 4, 18
Nucula, 296, 307, 324
Ri/ciiphanes, 216
Nymphon, 283
Obelia, 58, 69, 60, 66
Oblique muscles, 437
Obturator foramen, 576
Occipital bones, 483
Occipital region, 475
Octopoda, 325
Octopus, 312, 325
Odontaspis, 456
Odontoceti, 681, 722
Odontoid process, 570
Odontolcae, 633
Oesophagus, 70, 137, 141, 428, 447, 448
Oestrus, 258
Okapi, 696
Okapia, 696
Olfactory lobes, 619
Olfactory nerves, 425
Oligochaeta, 157, 165
Oligolophus, 267, 282
Ommatostrephes, 312, 322, 325
Omosternum, 550
Onchosphere, 109
Oniscus, 223, 279
Ontogeny, 14
Onychophora, 225, 279
Ooecium, 378
Oostegites, 216
Opalina, 42, 52
Opercular bone, 480
Opercular flap, 480
Opercular membrane, 481
Operculum, 376, 377, 470 ; of Limulus,
275
Ophidia, 568, 587, 605
Ophioglypha, 339, 342, 367
Ophisaurus, 586
Ophiuroid, 340, 341
Ophiuroidea, 339, 367
Ophthalmic nerves, 426
Opisthobranchiata, 295, 297, 324
Opisthocoelous, 498, 523, 526
Opisthogoneata, 228, 280
Opisthotic, 476, 571
Opossums, 661, 663
Optic-chiasma, 425, 496, 516, 517, 518;
-ganglia, 319; -lobes, 416, 619;
-nerve, 425; -thalami, 538; -vesicle,
422
Oral-cartilages, 391 ; -cirri, 396 ; -cone,
49; -hood, 397; -plate, 365; -pole,
80; -tube-feet, 343
Orang-utan, 711, 713
Orbit, 437
Orbitosphenoid bone, 476, 530
Orca, 681
Orders, 11
Organ of Corti, 421
Organism, 34
Organ-pipe coral, 74
Organs, 17, 35
Organs of Bojanus, 305
Onithorhynchus, 656, 657, 658, 717
Oronasal grooves, 456
Orthoptera, 249, 250, 251, 280
Orycteropodidae, 666, 720
Orycteropus, 669, 720
Oscarella, 89
Osculum, 84
Osphradium, 294
Ossicula auditus, 645
Ostariophysi, 491
Osteichthyes, 453, 473, 513
Ostia, 230
Osteolepidoti, 504
Ostracoda, 208, 277
Ostrea, 308
Ostrich, 614, 618, 627, 631, 633
Otaria, 679, 721
Otariidae, 678, 721
Otocyst, 292, 321
Otolith, 406
Otter, 677
Ova, 8
Ovary, 53 ; of Lumbricus, 154
Ovibos, 697, 724
Oviducal gland, 463
Oviduct, 154, 465, 539
744
INDEX
Ovis, 724
Ovotestis, 295
Ovum, 8 ; of Hydra, 53
Owl, 705
Ox, 695, 697
Oxygen, 3, 17
Oyster, 284, 292, 298, 308
Pachytylus, 247, 251
Palatal flap, 573, 580
Palatine bone,, 477, 531, 617
Palatine foramina, 641
Palatine plates, 471
Palato-pterygo-quadrate bar, 456
Palinurus, 198, 199
Palp, 235
Palpal organ, 261, 265
Palpons, 67
Pancreas, 429
Pangolin, 668
Panther, 676
Pantopoda, 175, 283
Papilla, 638
Parachordals, 414, 447
Paragastric canals, 80
Paraglossa, 236
Paramecium, 39, 40, 47; conjugation
of, 41
Paraneuroptera, 280
Parapodia, 158
Parapophyses, 414
Parasite, 101
Parasitic, 44, 101
Parenchyma, 94
Parethmoid, 476, 477
Parietal peritoneum, 152
Parietals, 479, 530, 531
Parotid glands, 625, 655
Parrot, 635
Passer, 635
Passeriformes, 633, 635
Patella, 289, 290, 296, 324
Patheticus nerves, 425
Pathogenic, 34
Paunch, 692
Pavo, 610
Peacock, 610
Pea-urchin, 356 -
Peccary, 691
Pecten, 303, 308
Pectines, 269
Pectinibranchiata, 324
Pectoral girdle, 459, 460
Pectoral muscles, 610
Pedal ganglion, 343
Pedalion, 126
Pedicellina, 380
Pedicellariae, 336, 346, 348
Pedipalp, 261, 262
Pelagic, 384
Pelagic organisms, 81
Pelagothuria, 369
Pelagothuriidae, 369
Pelecanus, 634
Pelecypoda, 298, 310, 324
Pelican, 634
Pelmatozoa, 367
Pelobates, 559, 562
Pelobatidae, 559, 562
Pelvic girdle, 460, 613
Penaeus, 219
Penguin, 634
Penis, 164, 295, 582
Pentacrinoids, 365
Pentacrinus, 365
Pentadactyle, 520
Pepsin, 429
Peracarida, 217-221, 222
Peraeopods, 214
Perameles, 718
Peramelidae, 662, 718.
Perca, 493, 515
Percesoces, 492, 514
Perches, 493
Percidae, 493, 515
Percomorphi, 493, 515
Pericardium, 389, 408, 430, 448
Perihaemal-canals, 336, 353; -rings,
336; -tubes, 389
Periosteum, 650
Periostracum, 299
Periotic, 649
Peripatus, 175, 196, 225, 227, 242,
264, 279
Peripharyngeal band, 400, 408
Periplaneta, 233
Periproct, 346
Perisarc, 60
Perissodactyla, -687, 688, 723
Peristalsis, 153
Peristome, 35, 327, 346
Peritoneum, 141
Peritricha, 47
Peritrichous, 39
Periwinkle, 284, 286
Perspiration, 638
Pes, 520
Petaloid ambulacra, 356
Petrel, 634
Petrogale, 660, 664, 719
Petrohyoid, 527
Petromyzon, 444, 445, 446, 448
Petromyzontidae, 448
Phalanger, 718
Phalangeridae, 663, 718
Phalanges, 609
Phalangid, 266, 267
Phalangida, 266, 282
Phaneroglossa, 558, 562
Pharyngeal bones, 479
Pharyngo-branchial segment, 457
Pharynx, 32, 33, 96, 128, 136, 141,
428; of Amphioxus, 401
INDEX
745
Pharynx-sheath, 96
Phascolarctus, 663
Phascolomyidae, 663, 718
Phascolomys, 663, 718
Phasianus, 634
Phasma, 251, 280
Pheasant, 634
Phoca, 679, 722
Phocaena, 681, 722
Phocidae, 679, 722
Phoenicopterus, 634
Pholas, 308
Phoronis, 173
Phosphorescence, 216
Phryganea, 253, 281
Phrynosoma, 587
Phylactolaemata, 378, 379
Phyllium, 251
Pfiyllodromia, 233, 244
Phyllopoda, 205, 277
Phylloxera, 257
Phylogeny, 14
Phylum, 11, 13
Physalia, 67
Physaliidae, 67
Physeter, 681, 722
Physiology, 10
Physophoridae, 67
Phytoptus, 269
Picus, 635
Pigeon, 617, 622, 625, 626, 635
Pigment epithelium, 422
Pigs, 691
Pilchard, 490
Pilidium, 116
Pilot-whale, 681
Pine marten, 677
Pineal body, 416
Pineal eye, 449
Pinna, 641
Pinnipedia, 678, 721
Pipa, 558, 561
Pipistrelle, 708
Piroplasma, 45
Pisces, 450, 452; classification :>f,
512
Pituitary body, 414, 416, 427, 444
Pit-vipers, 591
Placenta, 412, 656, 664
Placoid scales, 453
Plaice, 494
Planaria, 99, 100
Planorbis, origin of mesoderm, 135
Plantigrade, 669
Plant-louse, 248, 254, 257
Plants and animals, 2, 25, 36
Planula, 65
Plasmodium, 28
Plastron, 591, 592
Platyhelminthes, 92 ; classification 01,
111
Platypus, 656
Platyrrhini, 710, 726
Plecotus, 708
Pleopods, 214
Plesiosauria, 604
Plethodon, 544, 561
Plethodontinae, 544
Pleur acanthus, 460, 470
Pleural ganglia, 293
Pleural membrane, 236
Pleurobranchs, 187
Pleuronectes, 494, 515
Ploima, 126
Plover, 635
Plumatella, 377
Pneumogastric nerve, 427-
Pocket valves, 431
Podical plates, 237
Podiceps, 634
Podobranchs, 187
Podocopa, 209, 277
Poikilothermal, 638
Poison-glands, 114
Polecat, 676
Pole-cells, 134
Polian. vesicles, 334, 350, 359
Polistes, 256
Pollack, 495
Polian, 490
Pollex, 551
Polychaeta, 158, 166
Polyclada, 98, 99, 112
Polyodon, 473, 502, 517
Polyodontidae, 517
Polyp, 49, 50, 62, 71
Polypide, 377
Polyprotodontia, 661, 717
Polypterini, 473, 502, 517
Polypterus, 502, 503, 512, 517
Polypus, 312, 322, 325
Polystomella, 22, 24, 25, 26, 30
Polystomum, 103
Polyzoa, classification of, 376
Polyzoan colonies, 376
Pond-mussel, 296, 299
Pond-snail, 293
Pond turtles, 597
Pons Varolii, 647
Porcellio, 224, 279
Porcupine, 701, 705
Pores, 85; dorsal, 141
Porifera, classification of, 84, 85, 90 ;
larva of, 89
Porocytes, 87
Porpoise, 681
Portal system, 433, 462
Portal vein, 462
Portuguese man-of-war, 67
Post-axial, 521
Posterior gastric muscle, 189
Postfrontal, 574
Postpubis, 577
Post-temporal fossa, 575
746
Postzygapophyses, 523, 569
Potamogalidae, 672
Prairie-dog, or -marmot, 705
Prawn, 219
Pre-axial, 521
Precoracoid, 532
Predentary bone, 549
Prefrontal, 532, 574
Pregnancy, 664
Premandibular cavity, 437
Premaxilla, 509, 616
Prepotency, 9
Presphenoid, 616
Presternum, 650
. Prezygapophyses, 523, 569
Primaries, 608, 610
Primates, 710, 725
Prismatic layer, 299
Pristis, 470, 512
Proboscideae, 684, 722
Proboscis, 113, 245, 387
Proboscis-pore, 386; sheath, 113
Procavia, 684, 685, 722
Procellaria, 634
Procellariiformes, 634
Procoelous, 523
Proctodaeum, 69, 136, 137, 193
Procyon, 677, 721
Procyonidae, 677, 721
Proglottis, 106
Progoneata, 228, 280
Pronation, 522
Pronephros, 440
Prong-buck, 694, 697
Pro-otic, 476, 531
Propodite, 181
Propterygium, 460
Prosobranchiata, 295, 296, 297
Prosoma, 259, 261, 283
Prosopyle, 89
Prostate glands, 321
Prostomium, 141, 168
Protective coloration, 676
Proteidae, 561
Proteids, 3; composition of, 4
Proteus, 543, 561
Proteus animalcule, 15
Pro-thorax, 236
Protobranchiata, 324
Protonemertini, 117
Protoplasm, 3, 4, 5, 6, 15, 17, 18
Protopodite, 209
Protopterus, 506, 507, 509, 512, 518
Protospondyli, 473, 498, 516
Prototheria, 656, 717
Protrotracheata, 175, 225, 279
Protozoa, 13, 14, 15; in infusions, 19;
classification of, 46
Protractor muscles, 301
Proventriculus, 625
Psalterium, 693
Psephurus, 517
INDEX
Psetta, 515
Psettodes, 494, 515
Pseudobranch, 458, 506
Pseudopodia, 17, 22, 27, 29, 31, 55
Psittacus, 635
Pterocles, 635
Pteropidae, 708
Pteropus, 706, 708
Pterosauria, 604
Pterotic, 476
Pterotrachea, 292, 293
Pterygiophores, 453
Pterygoid bone, 509, 531, 617, 629
Pterygoid process, 530, 531
Pterylae, 607
Ptyalin, 656
Pubis, 652
Puffin, 634
Pulex, 258, 282
Pulmocutaneous arch, 552
Pulmonary arch, 537, 621
Pulmonary veins, 535
Pulmonata, 324
Puma, 676
Pupa, 249
Putorius, 677
Pygal plate, 591
Pygostyle, 613
Pyloric-caeca, 330; -sac, 330; -sphinc-
vQYy 4^o
Pylorus, 428
Pyrosoma, 412
Python, 588
Quadrate bone, 477, 617, 618
6 a i7 ra 618 U8al b ne> 549 ' 575 ' ^ 16 '
Quagga, 690
Eabbit, 646, 651, 665, 70] 702
Eabbit-fish, 472
Kaccoon, 677
Eadial canals, 60, 369
Radial nerve-cords, 336
Eadial perihaemal canals, 336
Eadial water-vessel, 333
Eadiale, 521
Eadialia, 460
Eadials, 363
Eadii, 326
Eadiolaria, 26, 27, 31, 46
Eadiolarian ooze, 27
Eadius, 521
Eadula, 289
Eadula-sac, 291
Raia, 469, 470, 512
Bail, 634
Eallus, 634
Eami communicantes, 425
Eana, 545, 547, 548, 549, 550 551
557, 559, 560
INDEX
V47
Rangifer, 696, 698, 724
Kanidae, 545, 559, 560, 562
Eat, 703, 704
Rat-fish, 472
Ratitae, 631, 633
Rattlesnake, 590
Rays, 465, 469
Razor-shell, 308
Recapitulation theory, 14
Receptaculum ovorum, 154
Rectal gland, 330, 461
Recti abdominis, 527
Rectum, 137, 238, 305
Rectus muscles, 437
Red blood-corpuscles, 433
Red-deer, 698
Redia, 105
Red spider, 269
Red squirrel, 702
Reindeer, 697, 698
Renal papillae, 395, 401
Renal-portal veins, 435, 462
Reno-pericardial canal, 288, 315
Repetition of parts, 24, 29
Reproduction, 7; by fission, 19, 26,
38, 58; by sporulation, 19
Reproductive cells, 154
Reproductive system, of Annelids, 154,
164 ; of Arthropods, 192, 195, 243,
266 ; of Brachiopods, 374 ; of Ces-
toda, 108; of Echinoderms, 337,
354 ; of Molluscs, 295, 296, 307, 321 ;
of Nematodes, 129; of Polyzoa, 378,
379; of Rotifers, 124; of Trema-
todes, 102, 103 ; of Turbellaria, 97 ;
of Vertebrates, 403, 438, 441, 463, '
539, 557, 582, 627
Reptilia, 450, 567, 579; classification
of, 568, 604; fossil representatives
of, 602
Respiration, 4
Respiratory system, of Arthropods,
229, 241; of Birds, 623 ; of Mam-
mals, 655
Respiratory tube, 447
Reticulum, 692
Retina, 416, 422, 423
Retinula, 271
Retractor muscles, 301
Rhabdites, 94
Rhabditis, 131
Rhabdocoela, 98, 99, 112
Rhabdocoelida, 98, 111
Rhabdome, 197
Rhachis, 607
Rhea, 631, 633
Rhinoceros, 687, 688, 689, 723
. Rhinocerotidae, 688, 723
Rhinochimaera, 472, 513
Rhinolophus, 708, 725
Rhizocrinus, 363
Rhizomastigina, 34, 46
Rhizopoda, 42, 46
Rhizota, 126
Rhynchobdellidae, 162, 165, 166
Rhynchocephala, 568, 582, 604
Rhynchonella, 370, 374, 375
Rhytina, 700
Ribs, 414, 438
Right whale, 683
River-bass, 493
River-trout, 490
Roach, 485
Rock-wallaby, 660, 664
Rodentia, 700, 725
Rods and cones, 422
Roe-deer, 698
Roller, 633
Rorqual whale, 683
Rosette, 365
Rostellum, 106
Rostrum, 456
Rotifer, 121, 123, 126
Rotifera, 121; classification of, 126
Rotulae, 349
Round-worms, 127
Rumen, 692
Ruminantia, 692
Sacculated, 113
Sacculus, 421
Sacral prominence, 545
Sacral vertebra, 522, 547
Sagitta, 382, 383, 384
Salamander, 519, 533, 544
Salamandra, 533, 537, 561
Salamandridae, 561
Salamandrinae, 543
Salamandroidea, 542, 543, 561
Saliva, 656
Salivary-ducts, 291; -reservoir, 238
Salivary glands, of Helix, 291; of
Lithobius, 231; of Mammals, 655;
of Mesostoma, 96; of Stylopyga,
238
Salmo, 476, 477, 480, 490, 514
Salmon, 476, 477, 480, 489, 490, 491
Salmonidae, 489, 490, 514
Salpa, 411, 412
Salvelinus, 490, 514
Sand- dollar, 356
Sand-grouse, 635
Sand-lizard, 586
Sardine, 490
Sauria, 568, 585, 586, 604, 605
Sauropsida, 606
Saw-fish, 470
Saw-fly, 250, 256
Scale-insects, 257
Scales, of Elasmobranchii, 455 ; of
Reptiles, 568
Scallop, 303, 308
748
INDEi
Scaly ant-eater, 666, 669
Scaphiopiis, 559, 562
Scaphirhynchus, 473, 501, 517
Scaphognathite, 183, 185
Scaphopoda, 325
Scapula, 483, 532, 594
Scapular artery, 581
Schizognathous palate, 633, 634
Schizopod, 216
Schizopoda, 215, 220, 278
Sciatic plexus, 555
Sciatic vein, 535
Scirtopoda, 126
Sciuridae, 701, 702
Sciuropterus, 702, 703
Sciurus, 702, 725
Scleroblasts, 87
Sclerotic coat, 422
Scomber, 493, 515
Scombridae, 493, 515
Scopula, 261
Scorpio, 270, 282
Scorpion, 260, 269, 270, 271
Scorpionida, 269, 282
Scotophilus, 708
Scutes, 483, 496
Scutum, 212
Scyllium, 415, 418, 432, 436, 457, 459,
460, 464, 466, 467, 468, 512
Scyphistoma, 77, 78
Scyphozoa, 75, 83
Sea-anemones, 68, 73
Sea-bass, 493
Sea-bream, 493
Sea-cows, 678, 698
Sea-cucumber, 326, 357, 358, 359,
360
Sea-hare, 293
Sea-lion, 679
Sea-mussel, 308
Sea-snails, 297
Sea-spiders, 275
Sea-squirt, 410
Sea-urchins, 326, 344, 345, 352, 354,
355
Seal, 678
Seal-skin seal, 678
Sebaceous glands, 638
Sebum, 638
Secondaries, 609, 611
Secretions, 5, 19
Segmentation, 138, 174
Selachoidei, 467, 512
Selection, natural, 12, 13
Selenodont, 694
Selenodontia, 692, 694, 724
Semicircular canals, 420, 444
Semnopithecus, 712, 727
Sense-capsules, 421; -cell, 63, 199, 418,
421, 422 ; -hairs, 55, 63, 418, 422 ;
-organs, 63, 199, 418, 443
Sensory peripheral nerve, 150
Sepia, 312, 313, 314, 316, 317, 318,
319, 320, 321, 322, 323, 325
Septa, 140
Serotine, 708
Serranidae, 493, 515
Serranus, 515
Sexual reproduction, 8, 9
Sexual union, 7 ; reproduction, 8
Shad, 489
Shark, 456, 465
Sheep, 692
Shell, of Brachiopods, 370, 371 ; of
Molluscs, 284, 297, 298, 299
Shell- fish, 284
Shell-glands, 97, 206
Ship-worm, 308
Shore-crab, 218
Shrew-mice, 671
Shrikes, 633
Shrimps, 219
Siales, 253, 281
Siliceous substance, 26
Silicoflagellata, 34, 46
Silk, 262
Silk- worm, 249
Silk-worm moth, 250, 258
Siluridae, 491, 514
Silver-fish, 251
Simla, 711, 712, 727
Simiidae, 712, 713, 727
Simocephalus, 205, 207, 208, 277
Simplicidentata, 702, 725
Sinus, dorsal and ventral, 163
Sinus venosus, 430
Siphon, 303, 350
Siphonaptera, 258, 272
Siphonoglyph, 72, 73
Siphonophora, 66, 67, 82
Siphuncle, 323
Sipunculoidea, 167, 168, 170
Sipunculus, 170, 172, 173
Siredon, 543
Siren, 542, 561
Sirenia, 698, 699, 700, 725
Sirenidae, 561
Sirex, 256
Skates, 465, 470
Skeletal spicules, 91
Skeleton, of Amphibia, 519, 522, 527,
547 ; of Birds, 609, 613, 615 ; of
Echinoderms, 327, 345 ; of Fishes,
474, 508, 509 ; of Mammals, 650 ;
of Eeptiles, 569, 591
Skin, 52, 424, 455, 637, 517
Skunk, 676, 677
Sloths, 666, 668
Sloughing, 567
Slow-worm, 586
,Slug, 284
Smittia, 376
Smooth dog-fish, 467
Snail, 284, 285
INDEX
749
Snakes, 568, 585, 587
Snapper, 597
Snapping turtles, 597
Soaring of birds, 611
Soft palate, 641
Solaster, 338
Sole, 494
Solea, 494, 515
Solen, 308
Solenocytes, 93, 401
Solenodontidae, 672
Solenogastres, 296, 325
Somite, 138, 393
Songsters, 633
Sorex, 671, 720
Soricidae, 671, 720
Spadella, 383, 384
Sparrow, 635
Spatangoidea, 356, 368
Species, 8; origin of, 11
Spelerpes, 544
Spermathecae, of Helix, 295; of Lum-
bricus, 139, 156 ; of Mesostoma, 97
Spermatophores, of Helix, 295 ; of
Hirudo, 164 ; of Sepia, 321
Spermatozoa, 8 ; of Hirudo, 164 ; of
Hydra, 53; of Lumbricus, 156
Sperm-sac, 465
Sperm-whale, 681
Sphaerularia, 131
Sphenethmoid, 548
Sphenisciformes, 634
Spheniscus, 634
Sphenodon, 568, 575, 583, 604
Sphenotic, 476
Sphincter, 461
Sphyranura, 103
Spicules, 71, 88, 91
Spider, 260, 261, 262, 263, 264, 265,
266, 275; web of, 262
Spider-monkeys, 712
Spinal cord, 385, 396, 398, 416
Spinal ganglia, 424
Spine, 651
Spines, 346
Spinnerets, 261, 262
Spiny ant-eater, 656
Spiny dog-fish, 467
Spiracle, 426, 456, 458
Spiral valve, 430, 516
Spirula, 297
Splanchnic peritoneum, 153
Spleen, 436, 533
Splenial bone, 498, 516, 532, 575
Sponges, 84; complex, 88; larva of, 89
Spongilla, 87, 91
Spongin, 91
Spores, 19, 28-, 45
Sporocyst, 105
Sporozoa, 43, 44, 47
Sporulation, 19
Sprat, 489
Squalus, 453, 467, 512
Squame, 185
Squamosal, 549, 574, 575, 585, 595
Squid, 284, 309, 312
Squilla, 220, 279
Squirrel, 702, 703, 704
Stag-beetle, 245
Stapes, 645
Star-fish, 326, 327, 329, 332
Star-nosed mole, 672
Statoblasts, 379
Steapsin, 429
Steganopodes, 632
Stegocephala, 524, 528, 560, 602
Stellate ganglia, 319
Stercoral pocket, 264
Sterna, 232
Sternal ribs, 594, 609
Sternebrae, 650
Sternohyoid, 527
Sternum, 236, 237, 532, 550
Stimulus, 6-7
Sting-ray, 470
Stoat, 676
Stolon, 65, 71, 338
Stomach, 17, 50, 86, 87, 347
Stomatopoda, 217, 220, 279
Stomodaeum, 69, 136, 166, 396, 427
Stone-canal, 334
Stork, 632
Streptoneura, 323
Streptoneurous, 297
Striated rods, 421
Strix, 635
Strobilisation, 77, 78, 106
Strongylocentrus, 344
Structureless lamella, 55
Struthio, 618, 631, 633
Sturgeon, 501, 502
Stylet, 114
Stylopyga, 233, 234, 235, 239, 280
Subclavian artery, 431, 535
Subfilamentar tissue, 302
Sub-intestinal vessel, 145
Sublingual glands, 625, 655
Submaxillary glands, 625, 655
Sub-mentum, 236
Sub-neural gland, 407
Sub-pharyngeal ganglion, 148
Sub-umbrella, 62
Sub-ungulata, 684, 722
Sub-vertebral wedge, 569
Suctoria, 42, 47
Suctorial-stomach, 245
Suidae, 691
Suinae, 691, 723
Sula, 609, 634
Summer-eggs, 98, 124, 206
Sun-star, 338
Supination, 522
750
INDEX
Supra-angular, 498, 516, 575
Supra-occipital, 516
Supra-oesophageal ganglia, 173, 294,
319
Supra-pharyngeal ganglia, 148
Suprascapula, 532, 576
Supratemporal fossa, 575
Surinam toad, 558
Sus, 691, 724
Suspensorium, 530, 545
Swallow, 630, 633
Swan, 632
Sweat-glands, 638
Swift, 633
Sycon, 88
Sylvian fissure, 647
Symmetry, bilateral, 296
Sympathetic nervous system, 425
Symphysis, 576
Synapta, 368
Synapticulae, 402
Synaptidae, 360, 368
Syncarida, 224, 279
Synchaeta, 125, 126
Syngamus, 131
Synotus, 708
Syringopora, 74
Syrinx, 624
Systemic arch, 537
Tabanus, 258
Tabulare, 574
Tadpole, Ascidian, 406; of Rana,
550, 557
Taenia, 107, 108, 109, 110
Tail, 399
Talpa, 672, 720
Talpidae, 671, 672, 720
Tamandua, 666, 668
Tamias, 701, 705, 725
Tanaidacea, 222
Tape-worm, 107
Tapir, 687, 688
Tapiridae, 688, 723
Tapirus, 687, 723
Tardigrada, 283
Tarsale, 521
Tarsalia, 521
Tarsus, 236, 520
Tasmanian wolf, 662
Teat, 638, 680
Teeth, origin of, 454 j of Mammalia,
642, 661, 672
Tegenaria, 262, 265
Teleostei, 474, 479, 496, 498, 513;
classification of, 488, 513
Telosporidia, 48
Telson, 179, 214
Temnocephalidae, 101
Temporal arcades, 574
Temporal fossa, 618
Tendon, 262
Tentacle sheath, 377
Tentacles, 49, 377; of Actinozoa, 69;
of Hydromedusae, 60; of Nereis, 159
Tentaculocyst, 76
Tenthredo, 256
Terebratula, 371, 375
Teredo, 308
Terga, 176, 231
Tergum, 150, 236
Terricolae, 157
Tertiaries, 611
Testicardines, 375
Testis, 53, 129, 154, 523
Testudinidae, 597
Testudo, 597, 605
Tetrabranchiata, 325
Tetranychus, 269, 282
Tetrao, 634
Tetrastemma, 117, 118
Textrix, 261
Thalamencephalon, 416
Thalamophora, 31, 46
Thalassicola, 40
Thalassochelys, 592
Thaliaceae, 411, 412
Theromorpha, 603
Thoracic, 488
Thoracic vertebra, 655
Thoracostraca, 215, 278
Thorax, 232, 233, 236
Thread-capsule, 53
Thread-worms, 127
Thrips, 253, 281
Thrush, 635
Thylacinus, 662, 717
Thynnus, 515
Thyrohyals, 550
Thyroid gland, 427, 4*8
Tibia, 236, 521
Tibiale, 521
Ticks, 268
Tiedemann's bodies, 333
Tiger, 676
Tinamiformes, 634
Tinamou, 634
Tinamus, 634
Tipula, 43, 258
Toad, 519, 545, 549, 558
Tone, 434
Tongue, 535
Tongue-bar, 389
Toothed whales, 681
Torpedo, 470
Tortoise-shell, 591, 592
Tortoises, 568, 597
Torus angularis, 343
Trabeculae, 363, 414, 447
Trachea, 175, 230, 241, 263, 579
Tracheata, 230
Trachymedusae, 67, 75, 82
Tragulidae, 694, 698, 724
Tragulus, 724
INDEX
751
Transverse bone, 574
Transverse processes, 416
Tree-frogs, 559
Tree-shrews, 670
Trematoda, 101, 103, 106, 112
Trichechidae, 678, 721
Trichechm, 678, 721
Trichina, 131
Trichinosis, 131
Trichocysts, 39
Triclada, 98, 99, 112
Tridactyle, 349
Trigeminal nerves, 426
Trigla, 543
Trionychidae, 597
Triradiate, 88
Triton, 522, 525, 538, 541
Tritors, 471
Trochanter, 236
Trochus, 121
Trophi, 122
Trophozoites, 44
Tropidonotus, 587, 591, 605
Trout, 489, 490
Trunk, 434, 499
Trygon, 470, 512
Trypanosoma, 35
Trypsin, 429
Tsetse-fly, 257
Tube-feet, 327
Tubifex, 111
Tubipora, 71
Tubularia, 66, 78
Tubulipora, 376
Tunicata, 404
Tupaiidae, 670
Turbellaria, 94, 96, 100, 111
Turbot, 494
Turdus, 635
Turkey buzzard, 634
Turtles, 568, 585, 591
Tylenchus, 131
Tylopoda, 694
Tympanic, 641
Tympanic bulla, 641
Tympanic membrane, 545, 645
Tympanum, 545, 624
Typhlosole, 153
Tyroglyphus, 268, 269, 282
Ulna, 521
Ulnare, 521
Umbilical placenta, 664
Umbo, 299
Uncinate process, 584
Uncus, 122
Ungulata, 684, 722
Ungulata vera, 687, 723
Unicellular, 52
Unio, 296, 299, 300, 302, 325
Uniseriate, 460
Univalve, 298
Upper temporal arcade, 574
Upupa, 635
Urea, 4
Ureter, 288, 465, 540
Uric acid, 4, 231
Urinary sinus, 465
Urinogenital organs, 438, 439
Urinogenital sinus, 465, 659
Urochorda, 404
Urodaeum, 627
Urodela, 524; classification of, 542,
560
Urodele, 536
Urostyle, 547
Ursidae, 676, 721
Ursus, 676, 721
Uterus, 656, 658
Utriculus, 420
Uvula, 641
Vacuole, food-, 16, 38; contractile-,
17, 38, 39
Vagina, 129, 295, 659
Vagus nerve, 427
Vampire, 708
Varanus, 572, 576, 577
Variation, 9
Varieties, 10
Vas deferens, 129, 154, 155, 442
Velum, 62, 63, 121, 391, 397, 446
Vena azygos, 581, 655
Vena cava, 306, 535, 536, 654
Ventricle, 430, 535
Venus's girdle, 81
Vertebra, 341
Vertebral column, 458, 523
Vertebrata, 385
Vesicula seminalis, 155, 463, 465
Vespa, 256, 281
Vespertilio, 708, 725
Vesperugo, 708, 725
Vestibule, 444
Vibracula, 379
Vicuna, 696
Villi, 664
Vipera, 591, 605
Viperidae, 591
Visceral arches, 403, 431, 446, 450,
535, 549, 550
Visceral ganglia, 293, 433
Visceral hump, 285
Visceral loop, 293
Visceral muscles, 153
Visceral peritoneum, 153
Viscous fluid, 3
Vitellarium, 97, 124
Vitreous humour, 422
Viverra, 678
Viverridae, 678
Viviparous, 272
752
INDEX
Vole, 701, 704
Volvox, 90
Vomer, 531, 549, 559, 574, 641
Vomerine plates, 471
Vorticella, 35, 36, 37, 38, 39, 41, 42,
47; reproduction of, 38
Waldheimia, 371, 372, 375
Wallaby, 660
Walrus, 678
Wapiti, 698
Warty eft, 625
Wasp, 246, 256
Water-boatman, 257
Water-frog, 559
Water-newt, 543
Water-rat, 704
Water-reptiles, 604
Water- scorpion, 257
Water-shrew, 671, 672
Water-vascular system, 96, 332, 333
Water-vole, 704
Weasel, 676
Weberian chain, 491
Weberian ossicles, 492
Whalebone whales, 682
Whales, 664, 679
Whelk, 284, 286, 289
Whiskered bat, 708
White-ant, 252
White-fish, 489, 490
White-shark, 467
White-whale, 681
Wniting, 495
Wild boar, 691
Wild cat, 674
Wild duck, 612
Windpipe, 623
Wings of Insects, 246 ; of Birds, 608,
609, 612
Winter-eggs, 98, 125
Wire-worm, 175, 231
Wolf, 675
Womb, 656
Wombat, 663
Wood-ant, 256
Woodchuck, 701
Wood-louse, 223, 224
Wood-mouse, 704
Woodpecker, 633
Wood-wasp, 256
Wrass, 493
Xantharpyia, 707, 708, 725
Xiphiplastra, 594
Xiphisternum, 550, 650
Xiphoid process, 609
Xiphosura, 272, 283
Yellow-cells, in Lumbricus, 142, 148
Yolk, 8, 627; -gland, 97
Zebra, 690
Zoaea, 215
Zoantharia, 73, 82
Zooecium, 377
Zoology, definition of, 1 ; object of, 3 ;
subdivisions of, 10
Zygaena, 467
Zygantra, 587
Zygapophyses, 523
Zygosphenes, 587
Zygote, 26
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' ' ' ' - '
FEB 13 1939
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DEC 2 1 1948
nrn 1 9 1949
MAY" l I jqr-
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UNIVERSITY OF CALIFORNIA LIBRARY
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