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A TEXT-BOOK OF ZOOLOGY
MAC.M1I.LAN AND CO., LIMITED
I.O.NTViX . IKiMKAV . CALCUTTA . MADRAS
MELBOURNE
THK MACMILLAN COMPANY
M.\V VflkK . liOSTOX . ( IIK'A(;o
DALLAS . SAN1 KUANCISCO
TUI', MACMILLAN CO. OF CANADA, LTD.
A TEXT-BOOK
OF ZOOLOGY
BY THE LATE
T. JEFFERY PARKER, D.Sc., F.R.S.
PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF OTAGO, DUNEDIN, N.Z.
AND
WILLIAM A. HASWELL, M.A., D.Sc., F.R.S.
EMERITUS PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF SYDNEY, N.S.W.
IN TWO VOLUMES
VOL. II
WITH ILLUSTRATIONS
MACMILLAN AND CO., LIMITED
ST. MARTIN'S STREET, LONDON
1921
COPYRIGHT
First Edition, i8g8.
Second Edition, IQIO
Third Edition, 19.3 1
CONTENTS
SECTION XIII
PHYLUM CHORDATA .
Sub-phylum and Class I. Hemichorda (Adelochorda)
Sub-phylum and Class II. Urochorda ....
1. Example of the Class — Ascidia .
2. Distinctive Characters and Classification .
Systematic Position of the Example .
3. General Organisation
PAGE
1
13
14
20
23
23
Sub-phylum III. Euchorda .
Section I. ACRANIA .
Section II. CRANIATA
42
43
63
Class I. Cyclostomata .
1. Example of the Class — Petromyzon .
2. Distinctive Characters and Classification .
3. Comparison of the Myxinoids with the Lamprey
4. General Remarks .
119
119
133
134
138
Class II. Pisces
Sub-class I. Elasmobranchii
2. Distinctive Characters and Classification
3. General Organisation ....
139
140
1. Example of the^Sub-class — -ScyHium canicula or Hemiscyllium
mode stum ... 140
161
165
V
vi CONTENTS
PHYLUM CHORDATA — continued. PAGE
Class II. Pisces — continued.
Sub -class II. Holocephali . ...... 182
Sub-class III. Teleostomi 190'
1. Example of the Sub -class — Salnio fario 192
2. Distinctive Characters and Classification 211
Systematic Position of the Example 216
3. General Organisation . 217
Sub-class IV. Dipnoi. ... . ... 239
1. Example of the Class — Ceratodus (Neoceratodus or Epicera-
todtis) forsteri 239
2. Distinctive Characters and Classification 249
3. General Remarks 250
Appendix to Pisces — Ostracodermi . . .... 253
Class III. Amphibia ..... 256
1. Example of the Class — Rana temporaria or Rana esculenta . .257
2. Distinctv e Characters and Classification 283
Systematic Position of the Example 285
3. General Organisation 285
Class IV. Eeptilia .... 303
1. Example of the Class — Lacurta 304
2. Distinctive Characters and Classification 323
Systematic Position of the Example 327
3. General Organisation of Recent Reptilia ... . . 327
4. Extinct Groups of Reptiles 360
Class V. Aves 366
1. Example of the Class — Columba livia . .... 367
2. Distinctive Characters and Classification 395
Systematic Position of the Example 404
3. General Organisation . 405
Sub-class I. Archseornithes 405
„ II. Neornithes . ... 407
CONTENTS vii
PHYLUM CHORDATA — continued. PAGE
Class VI. Mammalia . . 432
1. Example of the Class — Lepus cuniculus 432
2. Distinctive Characters and Classification of Recent Mammalia . 462
Sub-class I. Prototheria .... . . . 464
„ II. Theria ... . . 464
Systematic Position of the Example. . . . 474
3. General Organisation .... . . 474
The Mutual Relationships of the Chordata . . . 590
On the Mutual Relations of the Phyla of Animals 596
SECTION XIV
DISTRIBUTION . 599
1. Geographical Distribution 599
2. Bathymetrical Distribution 614
3. Geological Distribution .... . .618
SECTION XV
THE PHILOSOPHY OF ZOOLOGY . .623
SECTION XVI
THE HISTORY OF ZOOLOGY .... 647
APPENDIX — Zoological Literature . . . .671
INDEX . 679
LIST OF ILLUSTRATIONS
VOL. II
FIG. PAGE
714. Balanoglossus ............ 3
715. „ anterior end 4
716. Ptychodera bahamensis 5
717. Balanoglossus, development 7
718. Tornaria . 7
719. „ . . . 8
720. Cephalodiscus dodecalophus, gelatinous investment .... 9
721. „ „ zooicl 10
722. „ „ sagittal section 11
723. Rhabdopleura 12
724. Ascidia 14
725. „ anatomy 15
726. ,, mesh of branchial sac 16
727. „ diagrammatic longitudinal section 17
728. „ transverse section 18
729. ,, dorsal tubercle, ganglion, and associated parts . . . 19
730. ,, sagittal and transverse sections 20
731. Oikopleura 23
732. Appendicularia, diagram 24
733. Botryllus violaceus 25
734. Composite Ascidian, diagram of zooid 25
735. Doliolum 26
736. Salpa democratica, ventral view 26
737. ,, lateral view 27
738. Pyrosoma . 27
739. ,, part of section 28
740. Salpa, lateral view of ganglion 29
741. Ascidian, mature egg 31
742. Development of Clavellina, early stages 32
"43. „ „ later „ 33
744. Larva of Asciclia mammillata 35
745. Metamorphosis of Ascidian, diagrammatic 36
746. Doliolum, tailed larva 38
747. „ asexual stage, lateral view 38
748. „ ,, „ dorsal ,, 39
ix
x LIST OF ILLUSTRATIONS
FIG. PAGE
749. Salpa, late stage in development 40
750. Amphioxus lanceolatus 43
751. „ ,, transverse sections of pharyngeal and in-
testinal regions ...... 44
752. ,, ,, anatomy, diagrammatic .... 47
753. ,, ,, transverse section of pharyngeal region,
diagrammatic ..... .48
754. ,, ,. diagram of vascular system . • . . . 49
755. ,, ,, nephridium 51
756. ,, ,, brain and cerebral nerves .... 52
757. ,, ,, anterior portion of neuron .... 53
758. ,, ,. segmentation of the oosperm ... 54
759. ., ,, formation of gastrula 55
760. ,, ,, development of notochord, neuron, and
mesoderm ....... 56
761. ,, ,. advanced embryo ...... 57
762. ,, .. young larva ....... 59
763. ., ,, more advanced larva ..... 60
764. ,, .. development of atrium 61
765. ,, ,, ,, ,, transverse sections 62
766. Ideal Craniate ... . . . 66
767. Section of skin of Fish . 67
768. Muscular system of Dogfish 68
769. Ideal Craniate, anatomy 69
770. Vertebral column of embryo, transverse section. .... 70
771. Diagram illustrating segmentation of vertebral column ... 71
772. Elements of embryonic cranium 73
773. Diagrams of cartilaginous skull 74
774. .Diagrams of bony skull 77
775. Development of pelvic fins, diagram . . .... 79
776 and 777. Diagrams of limbs and limb-girdles 80
778. Structure and development of tooth 83
779. Structure of liver, diagrammatic ...... .85
780. Diagram of gills .86
781. Diagram of vascular system of Fish 88
782. Diagram of circulation in a Fish 89
783. Diagram of vascular system of embryo of air-breathing Craniate . 92
784. Diagram of heart of Amphibian and Crocodile 93
785. Blood-corpuscles of Frog and Man 94
786. Transverse section of spinal cord ........ 95
787. Diagrams of Craniate brain 98
788. Diagram of cerebral and anterior spinal nerves . . . . . 101
789. Organs of touch .103
790. Sensory canals of head and organs of the lateral line . . . 104
791. Taste-buds . 105
792. Olfactory cells ... 106
793. Section of eye 106
794. Diagram of retina 107
LIST OF ILLUSTRATIONS xi
FIG. PAGE
795. Development of eye ... . 109
796. Muscles and nerves of eye . .110
797. Pineal eye of Sphenodon . ... .111
798. Organ of hearing .... . .112
799. Section of ampulla ... .112
800. Urinary tubule . ... .114
801. Diagrams of urinogenital organs . .115
802. Development of mesoderm in Frog . .117
803. Petromyzon fluviatilis, external views of head . . 120
804. „ marinus , skull, with branchial basket . .121
805. „ „ • 122
806. ,, ,, dissection of female . . . 125
807. „ „ brain . . .127
808. ,, „ „ with olfactory and pituitary sacs . 128
809. ,, ,, development of olfactory and pituitary sacs . 129
810. „ ,. auditory organ 130
811. ,, .. transverse section of trunk .... 130
812. ,, ,, urinogenital sinus and related parts . . 131
813. ,, development . . . 131
814. ,, sections of embryos . . . . 132
815. ,, fluviatilis, head of larva . .... 133
816. Head of Myxine and of Bdellostoma . .135
817. Myxine glutinosa, dissection . . . .136
818. „ auditory organ . . .137
819. Bdellostoma, kidney . .137
820. Palseospondylus gunni . .138
821. Hemiscyllium modestum . . .... 141
822. Scyllium canicula, vertebrae . . . .142
823. Hemiscyllium, skull . . 143
824. ,, visceral arches .... 146
825. ,, pectoral arch and fin . ... 147
826. ,, pelvic arch and fin 147
827. ,, lateral dissection . . 148
828. ,, branchial sac ... 149
829. Scyllium, heart and branchial arteries . . .150
830. Hemiscyllium, blood-vessels . . . .152
831. Scyllium canicula, brain . . .154
832. Hemiscyllium, brain . . 155
833. Syc Ilium catulus, cranial nerves and branchial plexus . . .156
834. ,, canicula, cerebral nerves 157
835. ,, „ urinogenital organs . . . . . .160
836. Hemiscyllium, right kidney and urinary sinus 161
837. Dogfish, egg-case .161
838. Cladoselache fyleri ... . . 162
839. Pleuracanthus ducheni ... 163
840. Acanthodes wardi ... . .... 164
841. Chlamydoselachus angumeus 164
842. Lamna cornubica . . .165
xii LIST OF ILLUSTRATIONS
FIG. PAGK
843. Urolophus cruciatus 16&
844. Centrophorus calceus, dermal denticles 167
845. Scymnus, spinal column . .167
846. Urolophus, skeleton 1 69
847. Heptanchus, skull 170
848. Torpedo-Ray, showing electric organ 172
849. Cestracion galeatus, egg-case 17fr
850. Pristiurus, section of blastoderm 177
851. ,, formation of mesoderm 177
852. Elasmobranch embryo, sections 178
853. Scyllium canicula, embryo 179*
854. Ray, embryo .179
855. Elasmobranch embryo with yolk-sac 180
856. Scyllium canicula, head of embryo . . . . . . .181
857. „ „ „ „ later stage 181
858. Chimsera and Callorhynchus . . .183
859. ,, vertebral column . . . . . . . . .185
860. ,, skull 186
861. Callorhynchus antarcticus, skull 187
862. „ „ brain ..." 188
863. „ „ male urinogenital organs . . . .189
864. ,, ,, embryo in egg-shell .... 191
865. Salmo fario 192
866. „ „ head . 19£
867. „ „ scale 194
868. ,, „ vertebrae 195
869. ,, ,, caudal end of vertebral column 196
870. „ skull 197
871. ,, fario, skull disarticulated 199
872 ,, salar, ,, of young individual 202
873. ,, fario, fin-ray 202
874. ,, ,, shoulder-girdle and pectoral fin 203
875. „ „ pelvic fin 204
876. ,, ,, side dissection 205
877. ,, „ brain 207
878. „ „ eye 208
879. „ ,, auditory organ 209
880. ,, ,, urinary organs 209
881. ,, ,, development 210
882. ,, „ section of blastoderm 210
883. Polypterus bichir 212
884. Acipenser ruthenus '. . .212
885. Lepidosteus platystomus 213
886. Amiacalva 213
887. Rita buchanani 214
888. Gadus morrhua 214
889. Sebastes percoides . . . . . . . . . . .215
890. Labrichthys psittacula . . .215
LIST OF ILLUSTRATIONS xiii
FTC.
891. Ostracioii ...... 216
892. Hippocampus ..... .217
893. Pleuronectes cynoglossus . . • 220
894. Stomias boa .... 221
895. Ctenoid and ganoid scales
896. Polypterus, part of vertebral column .
897. Sturgeon, skull . . 223
898. Polypterus, skull . . . 224
899. „ pectoral fin . . 225
900. „ pelvic fin • 225
901. Gymnotus elect ricus ... • 226
902. Sargus, teeth ... 227
903. Anabas scan dens
904. Lepidosteus, digestive organs ..... • 229
905. Pseudophycis bachus, relation of air-bladder to auditory organ . 230
906. Lepidosteus, brain ...... • 231
907. ,, male organs ....
908. ,, and Amia, female organs . .233
909. Acipenser, Amia, and Lepidostexis, segmentation . 234
910. Polypterus bichir, head of larva .... 235
911. Glyptolepis and Macropoma ..... . 236
912. Palseoniscus and Platysomus . . . • 237
913. Lepidotus and Caturus ..... • 238
914 Ceratodus forsteri ....... . 240
915. ,, ,, anterior portion of skeleton . . . 241
916. „ „ skull, dorsal .... .242
917. „ „ „ ventral .... .242
918. „ ,, pelvic arch and fin .... . 243
919. „ „ lung . . 244
920. „ „ heart and main blood-vessels .... 245
921. „ „ brain ...... .246
922. ,, ,, reproductive organs, female . . 248
923. „ „ development . . . 249
924. Protopterus annectens ....... .251
925. ,, „ skull, shoulder-girdle, and fore -limb . . 252
926. Coccosteus decipiens .......... 253
927. Pteraspis rostrata ........... 254
928. Lanarkia spinosa ..... . 254
929. Drepanaspis gemundenensis ......... 254
930. Cephalaspis ........ . 255
931. Pterichthys testudinarius .... . . . 256
932. Rana temporaria ....... . 257
933. „ „ skeleton ..... . 259
934. „ „ skull . . .261
935. „ „ „ of tadpole . 263
936. ,, esculenta, shoulder-girdle ........ 263
937. ,, ,, ,, ,, transverse section, diagrammatic 264
938. „ „ pelvic girdle ........ 265
xiv LIST OF ILLUSTRATIONS
FIG. PAGE
939. Rana esculenta, muscles . ' 267
940. Rana temporaria, dissection from left side 268
941. ,, esculenta, digestive organs 269
942. ,, temporaria, heart 270
943. „ „ arteries .272
944. „ „ veins 273
945. ,, ,, course of blood and lymph, diagrammatic . . 275
946. „ esculenta, brain 276
947. ., accessory auditory apparatus ....... 277
948. „ esculenta, urinogenital organs, male 278
949. ,, „ „ ,, female 279
950. ,, development 281
951. ,, temporaria, stages in life-history 282
952. Necturus maculatus 286
953. Siren lacertina 286
954. Amphiuma tridactyla 286
955. Salamandra maculosa 287
956. Ccecilia pachynema 288
957. Urodela, structure of vertebral column 290
958. Proteus anguinus, chondrocranium . 291
959. Salamandra atra, skull . 292
960. Ichthyophis glutinosa, skull . ...... 292
961. Protriton, skull 293
962. Salamandra and Amblystoma, shoulder-girdle and sternum . . 294
963. „ pelvic girdle 295
964. ,, heart and chief arteries, larva and adult . . . 296
965. ,, maculosa, venous system : 297
966. Urodela, diagrams of male and female organs 299
967. Nototrema marsupiatum 300
968. Pipa americana 300
969. Ichthyophis glutinosa . . . . ... 301
970. Amblystoma tigrinum (axolotl) 301
971. Lacerta viridis 304
972. Lizard, vertebrae . 306
973. Lacerta agilis, skull 308
974. „ ,, pectoral arch and sternum 311
975. ,, ,, carpus . 311
976. ,, vivipara, pelvis .... 312
977. ,, agilis, tarsus 313
978. ,, ,, general view of viscera ....... 314
979. ,, vii-idis, dissection from ventral aspect 315
980. Lizard, lateral dissection . . 317
981. Lacerta viridis, brain 318
982. ,, vivipara, brain of an embryo 319
983. ,, Jacobson's organs 320
984. ,, sclerotic ossicles 321
985. ,, viridis, membranous labyrinth . . . . . . . 321
986. ,, „ urinogenital organs, male . . . . . . 322
LIST OF ILLUSTRATIONS xv
FIG. PAGE
987. Lacerta viridis, urinogenital organs, female . . . . 322
988. Chamaeleon vulgaris .....
989. Pygopus lepidopus . . . . 329
990. Sphenodon punctatum .... . 330
991. Testudo graeca ... .331
992. Sphenodon, vertebra ... . . 333
993. Python, vertebra . . 332
994. Crocodile, skeleton . . . . . . 334
995. Sphenodon, skeleton ... . 334
996. Crocodile, anterior vertebrae 335
997. Cistudo lutaria, skeleton . 336
998. Chelone midas, transverse section of skeleton 336
999. Tropidonotus natrix, skull . . .... . 337
1000. Crotalus, skull . . . . . 33&
1001. Sphenodon, skull ... . . . 339
1002. Emys europsea, skull 340
1003. Chelone mydas, skull ... . ... 341
1004. Crocodilus porosus, skull . . 342
1005. Crocodile, skull ... . . ... 342
1006. Emys europaea, tarsus ... 342
1007. Alligator, carpus . . .... 342
1008. „ pelvis . . . ... 344
1009. Crocodile, tarsus 344
1010. Monitor, Emys, and Alligator, tongues 346
1011. Chamaeleon, lungs 347
1012. Lacerta muralis, heart 348
1013. Turtle, diagram of heart . . . ... 348
1014. Crocodile, heart . . . . ... 349
1015. Alligator, brain 350
1016. Sphenodon punctatum, pineal eye . ... . . . .351
1017. Alligator, early development 352
1018. Lacerta ...'.. 352
1019. Draco volans 355
1020. Rattlesnake, poison apparatus ........ 356
1021. Bclodon, skull 359
1022. Galesaurus planiceps, skull ... 360
1023. Plesiosaurus macrocephalus . . . . . . . . .361
1024. ,, pectoral arch . . 361
1025. ,, pelvic arch ... ... 362
1026. Ichthyosaurus communis ...... ... 362
1027. Iguanodon bernissartensis 363
1028. ,, mantelli, teeth ... .... 36*
1029. Pterodactylus spectabilis 364
1030. Scaphognathus, skull 365
1031. Ramphorhynchus 365
1032. Edestosaurus 36&
1033. Columba livia, external form . 368-
1034. feathers 369
xvi LIST OF ILLUSTRATIONS
™. PAGE
1035. Structure of feather 370
1036. Development of feather 371
1037. Columba livia, pterylosis . 372
1038. „ bones of trunk 374
1039. ,, „ cervical vertebra . 374
1040. ,, „ sacrum of nestling • . 375
1041. ,, ,, skull of young specimen 376
1042. Diagram of Bird's skull 377
1043. Columba livia, hyoid apparatus 378
1044. ,, ,, columella auris 378
1045. ,, ,, bones of left wing ....... 379
1046. „ „ manus of nestling . . . . . . . 380
1047. ,, „ innominate of nestling 380
1048. ,, „ bones of hind-limb . 381
1049. ,, ,, foot of embryo 381
1050. ,, ,, muscles of wing 383
1051. „ ,, dissection from right side 384
1052. ,, ,, lungs and trachea 386
1053. Diagram of air-sacs of a Bird 387
1054. Columba livia, heart 389
1055. „ ,, vascular system 390
1056. „ „ brain 391
1057. ,, ,, dissections of brain 392
1058. „ „ eye 393
1059. ,, ,, auditory organ 394
1060. ,, ,, urinogenital organs, male 395
1061. „ „ „ „ female ... .395
1062. Apteryx australis 398
1063. „ „ skeleton ... 399
1064. Hesperornis regalis 400
1065. Ichthyornis victor 401
1066. Eudyptes antipodum 402
1067. Archseopteryx lithographica 406
1068. „ „ skull . . .... 407
1069. ,, ,, manus 407
1070. Opisthocomus and Apteryx, wings 408
1071. Gypaetus and Ardea, pterylosis 410
1072. Casuarius, feather 411
1073. Gallus, Turdus, Vultur, Procellaria, and Casuarius, sterna . . 412
1074. Eudyptes pachyrhynchus, skeleton 413
1075. Apteryx mantelli, skull of young specimen, side view . . . 414
1076. ,, ,, ,, ,, ,, dorsal view . . 415
1077. Anas boschas, skull .... 416
1078. Ara, skull ... . 416
1079. Apteryx mantelli, shoulder-girdle 417
1080. Dinornis robustus, skeleton ......... 418
1081. Sterna wilsoni, fore-limb of embryo 419
1082. Apteryx australis, left innominate . . . . . .419
LIST OF ILLUSTRATIONS xvii
FIG. PAGE
1083. Galius bankiva, innominate of embryo . 420
1084. Apteryx oweni, hind-limb of embryo . 420
1085. Galius bankiva, egg at time of laying 423
1086. „ „ blastoderm 424
1087. „ „ two embryos . . 425
1088. ,, „ egg with embryo and embryonic appendages . 426
1089. ,, „ diagrams of development of embryonic mem-
branes . 427
1090. Diagram illustrating the relationships of the chief groups of
Birds . .432
1091. Lepus cuniculus, skeleton with outline of body . . 433
1092. ,, ,, vertebrae .... . 434
1093. „ „ skull . 437
1094. ,, ,, ,, vertical section ... . . 441
1095. ,, ,, carpus with distal end of fore-arm . . 443
1096. ,, ,, sacrum and innominates . . 443
1097. „ ,, skeleton of pes . . . 444
1098. ,, ,, nasal region, vertical section .... 445
1099. ,, ,, lateral dissection of head, neck, and thorax . 446
1100. „ ,, digestive organs .... . 447
1101. „ „ heart . . .449
1102. „ ,, vascular system . 451
1103. „ „ larynx 453
1104. ,, „ transverse section of thorax . . 453
llO.j. „ ,, brain . . . 455
1106. ,, ,, dissections of brain 456
1107. „ ,, brain, vertical section .... . 457
1108. „ ,, urinogenital organs 459
1109. ,, ,, female organs (part) 460
1110. ,, ,, diagrammatic section of ad vanced embryo . 461
1111. Section of human skin . 474
1112. Longitudinal section of hair 475
1113. Development of hair . 476
1114. Echidna aculeata, with pouch and mammary glands . . . 477
1115. Diagrams of development of nipple 478
1116. Ornithorhynchus anatinus . 479
1117. Echidna aculeata . . 479
1118. Didelphys virginiana . 480
1119. Dasyurus viverrinus 480
1120. Petrogale xanthopus . 481
1121. Xotoryctes typhlops 481
1122. Phascolomys mitchelli 482
1123. Phase olarc tos cinereus . . 482
1124. Choloepus didactylus . . . . 483
1125. Dasypus sexcinctus 484
1126. Manis gigantea 485
1127. Orycteropus capensis 485
1128. Orca gladiator .... 486
xviii LIST OF ILLUSTRATIONS
FIQ- PAGE
1129. Hippopotamus amphibius . 488
1130. Eqvuis burchelli . 488
1131. Tapirus terrestris . . . . . . . ... . . 489
1132. Rhinoceros indicus . .... . . 490
1133. Phoca vitulina . . 491
1134. Galeopithecus . .... 492
1135. Synotus barbastellus 49 £
1136. Gorilla .495
1137. Diagram of Mammalian skull . 497
1138. Sagittal sections of Mammalian skulls, diagrammatic . . . 499
1139. Ornithorhynchus, skeleton ........ . 502
1140. Echidna aculeata, skull ..... . 504
1141. Ornithorhynchus, scapula ..... . . 505
1142. Kangaroo, atlas ... 506
1143. Halmaturus xialabatus. skeleton 507
1144. Dasyurus, skull . . . 508
1145. Petrogale penicillata, skull .... ... 508
1146. Phascolomys, skull . ' ... 509
1147. Phalanger, bones of leg and foot 510
1148. Macropus, bones of foot 510
1149. Dasypus sexcinctus, skull .... .... 511
1150. Myrmecophaga, skull, lateral 511
1151. ,, „ ventral 512
1152. Bradypus tridactylus, skull 512
1153. Dasypus sexcinctus, shoulder-girdle 513
1154. Bradypus tridactylus, skeleton 514
1155. ,, ,, shoulder-girdle 515
1156. ,, ,, manus 515
1157. ,, pes . . ... 515
1158. Dasypus sexcinctus, pelvis 516
1159. „ ,, pes .... .... 516
1160. Phocaena communis, skeleton . . . . . . . .517
1161. Balsenoptera musculus, sternum 517
1162. Globiocephalus, skull 518
1163. Halicore australis, skeleton 519
1164. Manatus senegalensis, skull ......... 520
1165. Cervus elaphus, axis . . . . . . . . . 520
1166. Equus caballus, posterior part of skull 521
1167. Ovis aries, skull 523
1168. Hyrax, skull . . . 524
1169. Elephas africanus, skull 524
1170. Cervus elaphus, scapula 525
1171. Tapirus indicus, manus . . . 526
1172. Equus caballus „ . 526
1173. Sus scrof a „ . 526
1174. Cervus elaphus ,, 526
1175. Equus caballus, tarsus 527
1176. Cervus elaphus , ... 527
LIST OF ILLUSTRATIONS xix
FIG. PARK
1177. Siis scrof a, tarsus ..... . 527
1178. Felis tigris, skull . . 528
1179. ,, ,, section of auditory bulla . . . 529
1180. Canis familiaris, skull .... . . 529
1181. Ursus ferox, section of auditory bulla . 530
1182. ,, american us, carpus . . . 530
1183. Felis leo, digit. . . 53')
1184. Phoca vitulina, skeleton .... . 531
1185. Centetes ecaudatus, skull ... ... . 533
1186. Pteropus jubatus, skeleton . . .... 534
1 187. ,, fuscus, skull .... 535
1188. Homo sapiens, skull .... ..... 536
1189. Anthropopithecus troglodytes, skull ..... . 538
1190. Simla satyms, skeleton ... ... . 539
1191. Cynocephalus anubis, carpus ... . 539
1192. Homo, Gorilla, and Simia, foot . 540
1193. Various forms of teeth, sections . . ... . 541
1194. Development of Mammalian teeth ... . . 542
1195. ,, „ . 54-'
1196. Canis familiaris, milk and permanent dentitions . . . 543
1197. Lagenorhynchus, teeth ... 544
1198. Perameles, teeth . 544
1199. Phascolarctos cinereus, front view of skull 545
1200. Macropus major, teeth .......... 546
1201. Sarcophilus ursinus, front view of skull . .... 546
1202. Didelphys marsupialis, teeth . . 546
1203. Orycteropus, section of lower jaw and teeth ... . 547
1204. Sus scrof a, teeth 548
1205. Equus caballus, skull and teeth . . . . 549
1206. Elephas africanus, molar teeth . . ... . 550
1207. Balsenoptera rostrata, lower jaw of fretus, with teeth . . 550
1208. ., section of upper jaw, with baleen . . . 551
1209. Lower carnassial teeth of Garni vora ....... 552
1210. Different forms of stomach in Mammalia 554
1211. Stomach of Ruminant 555
1212. „ ,, Porpoise 555
1213. Liver of Mammal, diagrammatic. ....... 556
1214. Canis familiaris, brain . . 559
1215. Echidna aculeata, sagittal section of brain . . . 560
1216. Petrogale penicillata ,, ,, ,, . . 51111
1217. Orriithorhynchus anatinus, brain 561
1218. Echidna aculeata, brain .... . 561
1219. Macropus major ,, .... . 562
1220. Cogia grayi „ 502
1221. Homo sapiens, sagittal section of nasal and buecal cavities . . 563
1-22. ,, „ ear .... 564
1223. Female organs of Marsupials ........ 566
1224. Uteri of Eutheria . 567
xx LIST OF ILLUSTRATIONS
FIG. PAGK
1225. Homo, sagittal section of ovary . . 568
1 226. Development of Graafian follicle 568
1227. Segmentation of Mammalian oosperm . 570
1228. Lepus cuniculus, embryonic area. . 571
1220. ,, ,, embryos . . 572
1230. Formation of foetal membranes of Mammal . . . 573
1231. Lepus cuniculus, embryo with membranes . 574
1232. Erinaceus, formation of amnioii and trophoblast . . 575
1233. Formation of amnioii in Mammalia .... . 575
1234. Macropus, mammary foetus .... . . 577
1235. Hypsiprymnus rufescens, embryo and foetal membrane . . . 578
1236. Phascolarctos cinereus ,, ,, ,, ,, . 578
1237. Perameles obesula „ „ placenta . 578
1238. Theria and Monotremata, blastula . . 579
1239. Phascolotherium bucklandi, mandible . . 582
1240. Plagiaulax becklesi, mandible . . 582
1241. Diprotodon australis, skeleton 583
1242. Nototherium mitchelli, skull ... . . . 584
1243. Thylacoleo carnifex, skull . . 584
1244. Glyptodon clavipes. skeleton 585
1245. Mylodon robustus . . 585
1246. Squaloclon, teeth . .586
1247. Dinotherium giganteum, skull 587
1248. Tillotherium fodiens, skull 589
1249. Diagram illustrating the mutual relationships of the Chordata . 596
1250. ,, „ ,, „ „ „ „ Phyla of
animals 598
1251. Map showing depths of sea between the British Isles and the
Continent 603
1252. Map showing depths of sea between New Zealand and Australia . 604
1253. Diagram showing the relations of the Zoo-geographical Regions . 614
ZOOLOGY
SECTION XIII
PHYLUM CHORDATA
IN the arrangement which it has been found convenient to
follow in the present work, the Vertebrate animals (Fishes,
Amphibians, Reptiles, Birds, and Mammals), together with the
Cephalochorda or Lancelets, the Urochorda or Ascidians, and
the Hemichorda or Balanoglossus and its allies, are all grouped
together in a single phylum — the Chordata. The main groups
comprised in this assemblage, however, differ so widely from
one another in certain essential points, and the common features
uniting them together are so few, that it has been thought
advisable to depart from the plan of arrangement followed in
connection with the rest of the phyla, and to make a primary
division in this case not into classes, but into sub-phyla. In
accordance with this scheme the phylum Chordata is regarded
as made up of three sub-phyla — the Hemichorda, the Urochorda,
and the Euchorda, the last-mentioned comprising the two sections
Acrania and Craniata or Vertebrata, each of which receives separate
treatment.
The name Chordata is derived from one of the few but striking
common features by which the members of this extensive phylum
are united together — the possession, either in the young condition
or throughout life, of a structure termed the chorda dorsalis or
notochord. This is a cord of specially modified vacuolated cells
extending along the middle line on the dorsal side of the enteric
cavity and on the ventral side of the central nervous system.
In the lower Chordates (the Hemichorda, Urochorda, and
Cephalochorda) the notochord is developed directly and unmis-
takably from the endoderm, and in the first-named group it
remains permanently in continuity with that layer. But in the
Craniata its origin is by no means so definite, and it may originate
VOL. II B
2 ZOOLOGY SECT-
from cells which are not obviously of endodermal derivation. It
may be enclosed in a firm sheath and thus be converted into a
stiff, but elastic, supporting structure. In the Craniata (with a few
exceptions among lower forms) it becomes in the adult replaced
more or less completely by a segmented bony or cartilaginous
axis — the spinal or vertebral column. Another nearly universal
common feature of the Chordata is the perforation of the wall
of the pharynx, either in the embryonic or larval condition only,
or throughout life, by a system of clefts — the branchial clefts ;
and a third characteristic is the almost universal presence at all
stages, or only in the larva, of a cavity or system of cavities, the
neuroccele, in the interior of the central nervous system.
The Chordata are Ccelomata (Vol. I., p. 333), and the mode
of development of the ccelome in the lower sub-phyla is essentially
the same as in the Echinoderrnata (Vol. I., p. 421), the Chsetognatha
(p. 313), and the Phoronida (p. 351) : it is derived, that is to say,
by direct outgrowth from the archenteron. In the Craniata this
enteroccelic origin of the cavity is no longer definitely traceable,
though what appear to be indications of it may be detected in
some cases. The Urochorda are not segmented1 : in the Henii-
chorda there is a division of the ccelome into three parts, each
occupying a definite region of the body, so that the view is
sometimes maintained that these animals are tri-segmented : in
the Cephalochorda and Craniata there are numerous segments, the
nature of which will be referred to later.
SUB-PHYLUM AND CLASS I.— HEMICHORDA (ADELOCHORDA).
A number of worm-like, simply organised animals possessing
a structure which is commonly regarded as of the nature of a
rudimentary notochord, comprising Balanoglossus and certain allied
genera, are so widely removed from the other members of the
Chordata that, if we accept them as Chordates, it is advisable to
consider them as constituting an independent sub-phylum, and to
this the name of Hemichorda or Adelochorda has been applied.
Resembling Balanoglossus in the condition of the supposed noto-
chord, in the division of the body into three regions, sometimes
looked upon as representing three segments, and in certain other
features, are two genera of small marine animals — Cephalodiscus
and Rhabdopleura. These are probably more nearly related to
one another than they are to Balanoglossus, from which they are
separated by well-marked differences, and the Hemichorda may,
therefore, best be regarded as divisible into two classes — one,
the Enteropneusta, comprising only Balanoglossus2 and its imme-
1 Though faint indications of serial repetition of parts are traceable in
certain cases.
2 The name Balanoglossus is here used as a general designation rather
than as a strictly generic term.
xnr
PHYLUM CHOP DATA
/
3
diate allies ; the other, the Ptero-
branchia, including Cephalodiscus
and Rhabdopleura.
External Characters and
Coelome of Enteropneusta.—
Balanoglossus (Fig. 714) is a soft-
bodied, cylindrical, worm-like animal,
the^_ sjirjac^_j)l_whj^h__is__uaifornil^
ciliated. The size varies extremely in
~"~V""" 1 — "~ — ~ . .
the different species, some being quite
small — 2 or 3 centimetres, while other
species are of comparatively large size
and may be as much as 2j_metres in
length. It is ' divisible into three
regions ; in front there is a large
club-shaped hollow organ — the pro-
boscis (pr.) ; immediately behind the
proboscis and encircling its base is a
prominent fold — the collar (co.) ; the
third region or trunk is long and
nearly cylindrical, but somewhat
depressed.
Balanoglossus lives in the sea,
usually in shallow water, burrowing
in sand or mud by means of its pro-
boscis : one species has been found
swarming on the surface of the sea.
Numerous glands in the integument
secrete a viscid matter to which
grains of sand adhere in such a way
as to form a fragile temporary tube.
The proboscis (Fig. 715, prob.) has
muscular walls ; its cavity (pro-
boscis-ccelome) opens on the exterior
usually by a single minute aperture
—the proboscis-pore (prb. po.) — rarely
by two. In some species the pro-
boscis-pore does not communicate
with the proboscis- ccelome, but ter-
minates blindly, and may send off a
narrow tubular diverticulum which
opens into the neuroccele. The nar-
row posterior part or " neck " of the
proboscis is strengthened by a layer
of cartilage-like or chondroid tissue, FIG 714
which supports the blood-vessels. The
collar is also muscular, and contains one
cavity, or two (right and left) cavities
Balanoglossus. En-
tire animal, br. branchial region ;
co. collar ; gen. genital ridges : hep.
prominences formed by hepatic
caeca ; pr. proboscis. (After
Spengel.)
B 2
ZOOLOGY
SECT.
separated from one another by dorsal and ventral mesenteries, and
completely cut off from the proboscis-cavity. The collar-cavity
and also that of the proboscis are crossed by numerous strands of
connective-tissue of a spongy character. The collar-cavity com-
municates with the exterior by a pair of collar-pores — ciliated tubes
leading into the first gill-slit or first gill-pouch.
On the dorsal surface of the anterior part of the trunk is a double
row of small slits — the gill-slits (Fig. 714, br.) — each row situated
brob
dors.v
FlG. 715. — Balanoglossus. Diagrammatic sagittal section of auterior end. card. s. cardiac
sac ; div. diverticulum (supposed notochord) ; dors. n. dorsal nerve-strand ; dors. sin. dorsal
sinus ; dors. •». dorsal vessel ; mo. mouth ; prob. proboscis ; prob. po. proboscis-pore ; prob. skel.
proboscis-skeleton ; venl. n. ventral nerve-strand ; vent. v. ventral vessel. (After Spengel.)
in a longitudinal furrow ; these slits increase in number throughout
life. The most anterior are in some species overlapped by a
posterior prolongation of the collar called the operculum. A
pair of longitudinal genital ridges (gen.) — not recognisable in some
species — which extend throughout a considerable part of the
length of the body both behind and in the region of the gill-slits
(branchial region), are formed by the internally situated gonads :
these ridges are so prominent in some of the genera as to form a
pair of wide wing-like lateral folds. Behind the branchial region
XIII
PHYLUM CHORDATA
5
are two rows of prominences (hep.) formed by the hepatic caeca.
The trunk is irregularly ringed, this annulation, which is entirely
superficial and does not correspond to an internal segmentation,
being most strongly marked behind. The coelome of the trunk
is divided into two lateral closed cavities by a vertical partition
(dorsal and ventral mesenteries).
Digestive Organs. — The mouth (Fig. 715, mo.} is situated
ventrally at the base of the proboscis, within the collar. Into the
dorsal half of the anterior portion of the alimentary canal open
the internal gill-openings. Each of these is in the form of a long
narrow (J , the two limbs separated by a narrow process — the tongue
—which contains a
prolongation of the
body-cavity. In
most of the Entero-
pneusta the internal
gill - openings lead
into gill-pouches
which in turn com-
municate with the
exterior by the gill-
slits. But in the
genus Ptychodera
(Fig. 716) there are
no gill-pouches, the
U -shaped internal
gill-openings leading
directly to the ex-
terior. The gill- FIG. 716. — Ptychodera bahamensis. Transverse section of
pouches are sup-
ported by a chitinoid
skeleton consisting of
a number of separate
parts. Each of these
consists of a dorsal
basal portion and three long narrow lamellae, a median and two
lateral ; the median, which is bifurcated at the end, lies in the
septum or interval between two adjoining gill-sacs ; the two
lateral lie in the neighbouring tongues. In most species a number
of transverse rods — the synapticulcs — connect together the tongues
and the adjoining septa, and are supported by slender processes of
the skeleton.
The posterior part of the alimentary canal is a nearly straight
tube, giving off, in its middle part, paired hepatic cceca, which bulge
outwards in the series of external prominences already mentioned.
Posteriorly it terminates in an anal aperture situated at the
posterior extremity of the body. In the posterior part of its
.c'-
TTV
the branchial region, b. branchial part of alimentary canal ;
b. c:i, coelome of trunk ; d. m. dorsal mesentery ; d. n.
dorsal nerve ; d. a. dorsal vessel ; e. epidermis with nerve
layer (black) at its base ; g. genital wing ; g. p. branchial
aperture encroached upon by tongue (t) ; I lateral septum ;
m. longitudinal muscles ; o. digestive part of oesophagus ;
r. reproductive organ ; t. tongue ; v. ventral mesentery
and ventral vessel ; v. n. ventral nerve. (From Harmer,
Cambridge Natural History, after Spengel.)
6 ZOOLOGY SECT.
extent in some Enteropneusta the intestine presents a ventral
median ridge-like outgrowth of its epithelium — the pygockord.
Throughout its length the intestine lies between the dorsal and
ventral divisions of the vertical partition, which act as mesenteries.
As the animal forces its way through the sand, a quantity of
the latter enters the digestive canal through the permanently
open mouth, and is eventually passed out again by the anus in
the shape of castings, which may be thrown out on the surface
of the sand in a form resembling that taken by the castings of
earthworms.
A series of pores (gastro-cutaneous pores), variously arranged in
the different genera, connect the intestine with the surface.
Notochord or cesophageal diverticulum. — The dorsal wall
of the part of the digestive canal immediately following upon
the mouth gives off a diverticulum (div.) that runs forwards some
distance into the basal part of the proboscis after giving off a
short ventral branch. The diverticulum contains a narrow lumen,
and its wall is composed of a single layer of long and very narrow
cells, each of which contains a vacuole. This layer of cells forming
the wall of the diverticulum is continuous with the epithelium of
the digestive canal itself, the cells being somewhat modified by the
presence of the vacuoles. The diverticulum, owing partly to its
structure, partly to its relations, is usually regarded as representing
the notochord of the typical Chordata. In close relation with this
on its ventral surface is the chitinoid proboscis-skeleton (prob. skel.),
which consists of a median part of an hour-glass shape, and with a
tooth-shaped process, bifurcating behind into two flattened bars
which lie in the anterior region of the oesophagus and support the
opening into the lumen of the diverticulum.
There is a blood-vascular system with dorsal and ventral
longitudinal trunks. The dorsal vessel (dors, v.) lies above the
notochord, and ends in front in a sinus, the dorsal sinus or heart
(dors, sin.), situated in the anterior part of the collar and the neck
of the proboscis, in close contact with the notochord. From
the posterior part of the sinus is given off a vessel which bifurcates
to supply the proboscis. In communication with the sinus in
front are a number of vessels of a bilateral plexus in the glomerulus,
a glandular organ, probably excretory, situated at the anterior end
of the cesophageal diverticulum. From the posterior end of each
half of the glomerulus there passes backwards an efferent vessel
which breaks up into a plexus ; the two plexuses unite ventrally
to form a median ventral plexus continuous behind with the ventral
vessel. The dorsal sinus, having no definite walls, is not contractile ;
but a closed sac, the cardiac sac (card, s.), situated on the dorsal
side of the sinus, has a muscular ventral wall, by the contractions
of which the blood may be propelled.
The nervous system consists of dorsal and ventral strands
xin
PHYLUM CHORDATA
(dors, n., vent, n.) which extend throughout the length of the body.
These are merely thickenings of a layer of nerve-fibres which
extends over the entire
body in the deeper
part of the epidermis.
Here and there are
giant nerve-cells. The
part of the dorsal
strand which lies in
the collar (collar-cord)
is detached from the
epidermis ; it contains
a larger numberj of
the giant nerve-cells
than the rest ; in some
species it encloses a
canal, the neurocoele,
opening in front and
behind ; in others a
closed canal ; in most
a number of separate
Fm.'717. — Development of Balanoglossus. A, stage of
the formation of the first groove (gr.). B, stage in which
the second groovejihas appeared, and the first gill-slit has
become developed, co. collar ; g. si. gill-slit ; pr. proboscis.
(After Bateson.)
cavities. At
Jbrob cauf
cards -
the posterior extremity of
the collar the dorsal
and ventral strands
are connected by a
ring-like thickening,
and there is a thick-
ening also round the
neck of the proboscis.
There are no organs
of special sense ; but
some cells of the epi-
dermis on certain
parts of the proboscis
and on the anterior
edge of the collar
seem to be of the
character of sensory
cells.
Reproductive
Organs. — The sexes
are separate, and often
differ in shape and
colour ; the ovaries
and testes are simple
or branched saccular
organs arranged in a double row along the branchial region of the trunk
and further back ; they open on the exterior by a series of pores.
cil.r
FIG. 718. — Tornaria. Dorsal view. an. anus ; card. .«. cardiac
sac ; cil. r. post-oral ciliated band (membranellse) ; oil. rz.
posterior ciliated ring ; eye, eye-spots on apical plate ; proti.
cao. proboscis-cavity ; proh. po. proboscis-pore. (After
Spengel.)
8
ZOOLOGY
SECT.
The course of the development (Figs. 717-719) differs in different
species. In some it is comparatively direct ; in others there is a
metamorphosis. Impregnation is external. Segmentation is com-
plete and fairly regular, resulting in the formation of a blastula,
which is at first rounded, then flattened. On one side of the
flattened blastula an invagination takes place. The embryo at
this stage is covered with short cilia, with a ring of stronger cilia.
The aperture of invagination closes and the ectoderm and
endoderm become completely separate. The embryo elongates
and a transverse groove (gr.) appears (A) : the mouth is formed
by an invagination in the position of the groove. The anus is
developed in the position
formerly occupied by the
blastopore. Before the
mouth appears there are
formed two diverticula of
the archenteron which
become completely sepa-
rated off, their cavities
subsequently giving rise
to the ccelomic cavities
of the proboscis and of
the collar, and the body-
cavity of the trunk. By
the appearance of a
second transverse groove
(B) the body of the em-
bryo becomes divided
into three parts — an an-
terior, a middle, and a
posterior - - these being
the beginnings respec-
tively of the proboscis,
the collar, and the trunk.
The branchial region is
marked off by the appearance of a pair of apertures — the first
pair of branchial slits (g. si.) — and other pairs subsequently develop
behind these.
In the species that undergo a metamorphosis the embryo assumes
a larval form termed Tornaria (Figs. 718 and 719). This is some-
what like an Echinoderm larva, with a looped ciliated band, some-
times lobed, sometimes produced into tentacles, running along its
anterior part, and a ring of membranellse (cil. r.),m some cases with
a ring of smaller cilia (cil. r2.), round the posterior (anal) end. At
the anterior end, in the middle of the pre-oral lobe, is an ectodermal
thickening— the apical plate — containing nerve-cells and eye-spots,
and, like the apical plate of a trochophore, constituting the nerve-
Fio.~719. — Tornaria. Lateral view. r Lettering as
in Fig. 718 : in addition, int. intestine"; mo. mouth.
(After Spengel.)
xin
PHYLUM CHORDATA
centre of the larva : this disappears in the adult. There is a short
alimentary canal with mouth and anus. The ciliated bands are lost ;
an outgrowth is formed to give rise to the proboscis, and a constric-
tion separates it from the collar ; the hinder part becomes elongated
and narrow to form the body of the animal ; a series of perforations
from the exterior give rise to the branchial pouches. A band of
thickened epithelium has been described on the wall of the oesophagus
and has been supposed to correspond to the structure termed
endostyle to be subsequently
met with in the Tunicata. The
collar-cord is formed by the
separating off of thedeeper'portion
of the ectoderm along the middle
line : or, in other species, by a
sinking down of the whole thick-
ness of the layer, which becomes
cut off to form a medullary plate
with its edges overlapped by the
adjacent ectoderm.
V
Constituting the class Ptero-
branchia are only the two genera
Cephalodiscus and Rhabdopleum.
These both resemble Balano-
glossus in having the body divided
into three parts or regions — a
proboscis with a proboscis-cavity,
a collar with a collar-cavity
communicating with the exterior
by a pair of collar-pores (nephri-
dia in Rhabdopleura), and a
trunk with two distinct- lateral
cavities ; and in the presence
of a structure resembling a noto-
chord with the same relations
to the nervous system as in
Balanoglossus. They both differ
from Balanoglossus in having
the alimentary canal bent on
itself, so that the anal opening is
situated not far from the mouth ;
tentacles arising from the collar ; and in the comparatively small
size of the proboscis. Cephalodiscus, moreover, has only a single
pair of apertures which may be regarded as representing the gill-
slits ; while in Rhabdopleura such openings are entirely absent,
their places being taken, apparently, by a pair of ciliated
grooves. Both forms occur in associations or colonies secreting
Fin. 720.— Cephalodiscus dodecalo-
phus. Gelatinous investment. (After
Mclntosh.)
in the presence of arms bearing
10
ZOOLOGY
SECT
a common case or investment. Both occur in the sea at various
depths.
Cephalodiscus has an investment (Fig. 720) in the form of a
branching gelatinous structure, which is in some species beset with
FIG. 721. — Cephalodiscus dodecalop bus. Entire zooicl. (After Mclntosh.)
numerous short filiform processes, and contains a number of tubular
cavities with external openings, occupied by zooids. The latter
(Fig. 721) are not in organic continuity, so that, though enclosed in a
common investment, they do not form a colony in the sense in which
the word is used of the Polyzoa or the Hydroid Zoophytes. They
XIII
PHYLUM CHORDATA
11
be'
have a feature in common with such a colony that they multiply by
the formation of buds ; but these become detached before they
are -mature. With the collar-region are connected a series of usually
eight to sixteen arms, each beset, except in the case of the male of
one species, with numerous very fine pinnately-arranged tentacles,
and containing a prolongation of the collar-cavity. The proboscis
(Fig. 722, ps.) is a shield- shaped lobe overhanging the mouth ; its
cavity communicates with the exterior by two proboscis-pores
(p. p.). The cavity of the collar communicates with the exterior by
a pair of ciliated passages opening by the collar-pores. Behind the
collar-region on each side is a small area in which the body-wall
and that of the pha-
rynx are coalescent ;
this area is perforated
by an opening - - the
gill-slit. Cilia occur
only on the arms, pro-
boscis, and lateral lips.
A nerve-strand, dorsal
ganglion, or collar-cord ,
containing nerve-fibres
and ganglion-cells, is
situated on the dorsal
side of the collar below
the epidermis, and is
prolonged on to the
dorsal surface of the
proboscis and the dor-
sal surface of the arms.
On the ventral side of
this nerve-strand is a
very slender cylin-
drical cellular cord
(nch.) continuous be-
hind with the epi-
thelium of the pha-
rynx: this is supposed
to represent the diver-
ticulum of Balano-
glossus, and thus to be homologous with the notochord of the
Chordata. A blood-vascular system with heart and cardiac sac like
those of the Enteropneusta is present. In some species of Cephalo-
discus the sexes are united, in most they are separate. The posterior
end of the body is drawn out into a sort of stalk on which the buds
are developed (Fig. 721). A pair of ovaries (ov.) lie in the trunk-
cavity, and there is a pair of oviducts (ovd.) lined by elongated,
pigmented epithelium. The development, which is direct, without a
FIG. 7^-. — Cephalodiscus. Diagram, of longitudinal
section, a. anus ; be1, cceiome of proboscis ; 6c2.
coelome of collar ; be3, coelome of trunk ; int. intestine ;
m. mouth ; nek. supposed notochord ; n. s. nerve-
strand : op. operculuni ; ces. oesophagus ; ov. ovary ;
ovd. oviduct ; ph. pharynx ; p. p. proboscis-pore ; ps.
proboscis ; st. stomach ; stk. stalk. (After Harmer.)
12
ZOOLOGY
SECT.
free-swimming larval stage, takes place in passages in the investment.
According to one account the segmentation is complete, but unequal,
and a gastrula is formed by invagination : according to another, the
segmentation is incomplete, and gastrula is formed by delamination.
The larva bears a striking resemblance to that of Ectoproct Polyzoa.
Rhabdopleura (Fig. 723) occurs in colonies of zooids organically
connected together, and enclosed in, though not in organic con-
FIG. 723. — Rhabdopleura. A, Entire zooid. a, mouth ; b, anus ; c, stalk of zooid ; d, pro-
boscis ; e, intestine ; /, anterior region of trunk ; g, one of the tentacles. (After Ray
Lankester.) B, Diagram of the organisation : median longitudinal section, seen from the
left. a. arm ; an. anal prominence ; col. collar ; col. ne. collar-nerve ; c. s. cardiac sac ; int.
intestine ; m. mouth ; ntc. " notochord " : ce. oesophagus ; pr. proboscis ; pr. c. proboscis-
ccelome ; ret. rectum ; st. stomach ; te. tentacles ; tr. c. trunk-ccelome ; v. n. ventral nerve.
(After Schepotieff.)
tinuity with, a system of branching membranous tubes connected
with a creeping stolon. The collar-region bears a pair of hollow
arms, each carrying a double row of slender tentacles — the whole
supported by a system of firm internal (cartilaginous ?) rods.
There are two collar-pores, each leading into a ciliated canal with an
internal funnel, and a pair of proboscis-pores. The " notochord '
and the nervous system resemble those of Cephalodiscus. The
sexes are united.
xra PHYLUM CHORD ATA 13
Cephalodiscus, of which there are three sub-genera with fifteen
species, has been found at various widely separated localities in the
Southern Hemisphere (Straits of Magellan, Borneo, Celebes, the
Antarctic) : species occur also off the coast of Japan and Korea. Some
live in shallow water : none have been found at a greater depth than
about 300 fathoms. Rhabdopleura has been found at moderate
depths in Norway, Shetland, the North Atlantic, France, the Azores,
Tristan d'Acunha, Celebes, and South Australia. It seems doubtful
if more than one species occurs.
Affinities. — The inclusion of the Hemichorda in the phylum
Chordata is an arrangement the propriety of which is not universally
admitted, and is carried out here partly to obviate the inconvenience
of erecting the class into a separate phylum. On the whole, however,
there seems to be sufficient evidence for the view that, if not the
existing representatives of ancestral Chordates, they are at least
a greatly modified branch, taking its origin from the base of the
chordate tree. The presence of the presumed rudimentary repre-
sentative of a notochord and of the gill- slits seems to point in this
direction. It should, however, be stated that, by some of those
zoologists by whom the members of this group have been most
closely studied, their chordate affinities are altogether denied. If
the Hemichorda are primitive Chordates, the fact is of special
interest that they show remarkable resemblances in some points
to a phylum — that of the Echinodermata — which it has been the
custom to place very low down in the invertebrate series. The
tornaria larva of Balanoglossus exhibits a striking likeness to an
echinopsedium (Vol. I., p. 422), and, though this likeness between
the larvae does not establish near connection, it suggests, at least,
that an alliance exists. Between actinotrocha, the larva of Phoronis
(Vol. I., p. 351) and tornaria there are some striking points of
resemblance ; and a pair of gastric diverticula in the former have
sometimes been compared with the single notochord or oesophageal
diverticulum of the Hemichorda.
SUB-PHYLUM AND CLASS IL-UROCHORDA.
The Class Urochorda or Tunicata comprises the Ascidians or
Sea-Squirts, which are familiar objects on every rocky sea-margin,
together with a number of allied forms, the Salpse and others, all
marine and for the most part pelagic. The Urochorda are specially
interesting because of the remarkable series of changes which they
undergo in the course of their life-history. Some present us with
as marked an alternation of generations as exists among so many
lower forms ; and in most there is a retrogressive metamorphosis
almost, if not quite, as striking as that which has been described
among the parasitic Copepoda or the Cirripedia. In by far the
greater number of cases it would be quite impossible by the study
of the adult animal alone to guess at its relationship with the
14
ZOOLOGY
SECT.
Chordata ; its affinities with that phylum are only detected when
the life-history is followed out, the notochord and other higher
structures becoming lost in the later stages of the metamorphosis.
Multiplication by budding, so common in the lower groups of
Invertebrata, but exceptional or absent in the higher, is of very
general occurrence in the Urochorda.
«
1. EXAMPLE OF THE CLASS — THE ASCIDIAN OR SEA-SQUIRT.
(Ascidia.)
Sea-squirts are familiar objects on rocky sea-shores, where they
occur, often in large associations, adhering firmly to the surface of
the rock. When touched the Ascidian ejects with considerable
force two fine jets of sea- water, which are found
to proceed from two apertures on its upper end.
The shape of the Ascidian, however, can only
be profitably studied in the case of specimens
that are completely immersed in the sea-water,
specimens not so immersed always undergoing
contraction. In an uncontracted specimen (Fig.
724), the general shape is that of a short cylinder
with a broad base by which it is fixed to the
rock. The free end presents a large rounded
aperture, and some little distance from it on one
side is a second of similar character ; the former
aperture is termed the oral, the latter the atrial.
A strong current of water will be noticed, by
watching the movements of floating particles,
to be flowing steadily in at the former and out
of the latter. When the animal is removed from
the water both apertures become narrowed, so
as to be almost completely closed, by the con-
traction of sphincters of muscular fibres which
surround them. At the same time the walls of
the body contract, streams of water are forced through the aper-
tures, and the bulk is considerably reduced.
Body-wall and Atrial Cavity. — The outer layer of the
body-wall is composed of a tough translucent substance forming
a thick test or tunic (Fig. 725, test). This proves when analysed
to consist largely of a substance called tunicine, which is apparently
identical with the cellulose already referred to (Vol. I., p. 15) as a
characteristic component of the tissues of plants, and of rare
occurrence in the animal kingdom. The test of an Ascidian is
frequently referred to as a cuticle, and it is a cuticle in the sense
that it lies outside the ectoderm and is derived from that layer
in the first instance. The cells, however, by the action of which its
substance is added to in later stages, seem to be chiefly derived, not
FIG. 724.— Ascidia,
entire animal seen
from the right side.
(After Herdman.)
PHYLUM CHORDATA
15
or.ap
itrau
tent
pJi.
test
rna.nl
from the ectoderm, but from the underlying mesoderm, from which
they migrate through the ectoderm to the outer surface. These
formative cells of the test are to be found scattered through its
substance. Running through it are also a number of branching
tubes lined with cells, each terminal branch ending in a little
bulb-like dilatation. The interior of each tube is divided into
two channels by a longitudinal septum, which, however, does not
completely divide
the terminal bulb.
Through these tubes
(which are of the
nature of looped
blood-vessels) blood
circulates, passing
along one channel,
through the ter-
minal bulb, and
back through the
other channel.
When the test is
divided (Fig. 725)
the soft wall of the
body or mantle
(mant.}, as it is
termed, comes into
view ; and the body
is found to be freely
suspended within
the test, attached
firmly to the latter
only round the oral
and atrial apertures.
The mantle (body-
wall) consists of the
ectoderm with
underlying layers of
connective -tissue
enclosing muscular
fibres. It follows
the general shape
of the test, and
at the two apertures is produced into short and wide tubular
prolongations, which are known respectively as the oral and
atrial siphons (Fig. 727, or. siph., air. siph.). These are continuous
at their margins with the margins of the apertures of the test, and
round the openings are the strong sphincter muscles by which
closure is effected. In the rest of the mantle the muscular fibres
mant
FIG. 725.— Dissection of Ascidia from the right side. The
greater part of the test and mantle has been removed from
that side so as to bring into view the relation of these layers
and of the internal cavities and the course of the alimentary
canal, etc. an. anus ; air. ap. atrial aperture ; end. endostyle ;
gon. gonad ; gonod. gonoduct ; hyp. neural g!and ; hyp. d.
duct of neural gland ; mant. mantle ; ne. on. nerve-ganglion ;
ces. ap. aperture of oesophagus ; or. ap. oral aperture ; ph.
pharynx ; stom. stomach ; tent, tentacles ; test, test. (After
Herdman.)
16
ZOOLOGY
SECT.
are arranged in an irregular network, crossing one another in all
directions, but for the most part either longitudinal or transverse.
Within the body-wall is a cavity, the atrial or peribranchial cavity
(air. cav.), communicating with the exterior through the atrial
aperture : this is not a coelome, being formed to a great extent by
involution from the outer surface.
Pharynx. — The oral aperture leads by a short and wide oral
passage (stomodceum) into a chamber of large dimensions, the
pharynx or branchial chamber (Fig. 725, ph.). This is a highly
characteristic organ of the Urochorda. Its walls, which are thin
and delicate, are pierced by a number of slit-like apertures, the
stigmata (Fig. 727, stigm.), arranged in transverse rows. Through
these the cavity of the pharynx communicates with the atrial or
peribranchial cavity,1 which completely surrounds it except along
one side. The edges of the stigmata are beset with numerous strong
cilia, the action of which is to drive currents of water from the
pharynx into the atrial cavity.
It is to the movements of these
cilia lining the stigmata that
are due the currents of water
already mentioned as flowing
into the oral and out of the
atrial aperture, the ciliary ac-
tion drawing a current in
through the oral aperture,
driving it through the stigmata
into the atrial cavity, whence
it reaches the exterior through
the atrial aperture. The stig-
mata (Fig. 726) are all vertical
in position ; those of the same
row are placed close together, separated only by narrow vertical bars ;
neighbouring rows are separated by somewhat thicker horizontal
bars ; in all of these bars run blood-vessels. Extending across the
atrial cavity from the body-wall to the wall of the pharynx are a
number of bands of vascular mesodermal tissue, the connectives.
It has been already mentioned that the atrial cavity does not
completely surround the pharynx on one side. This is owing to
the fact that on the side in question, which is ventral in position,
the wall of the pharynx is united with the mantle along the middle
line (Fig. 728). Along the line of adhesion the inner surface of
the pharynx presents a thickening in the form of a pair of longi-
tudinal folds separated by a groove : to this structure, consisting
1 A distinction is sometimes made between the lateral parts of this space
(peribranchial cavities, right and left) and the median unpaired (dorsal) part
(atrial cavity, or cloaca), in which the two peribranchial cavities coalesce, and
which leads to the exterior through the atrial aperture.
FIG. 726. — Ascidia, a single mesh of the
branchial sac, seen from the inside, i. I.
internal longitudinal bar ; /. v. longi-
tudinal vessel ; p. p'. papilte projecting
inwards from the branchial bar ; sg.
stigma ; tr. transverse vessel. (After
Herdman.)
xm
PHYLUM CHORDATA
17
lest
tr.
mant
of the two ventral longitudinal folds with the groove between
them, the term endostyle (end.} is applied. The cells covering the
endostyle are large cells of two kinds — ciliated cells and gland-
cells — the former beset at their free ends with cilia, the action of
which is to drive floating particles that come within their influence
outwards towards the oral aperture, the latter secreting and dis-
charging a viscid mucous matter. Anteriorly the endostyle is
continuous with
a ciliated ridge
which runs cir-
cularly round
the anterior end
of the pharynx.
In front of this
circular ridge,
and running
parallel with it,
separated from
it only by a
narrow groove,
is another ridge
of similar char-
acter : these are
termed the
peripharyngeal
ridges; the
groove between
them is the
peripharyngeal
groove. Dor-
sally, i.e. oppo-
site the endo-
style, the pos-
terior peri-
pharyngeal
ridge passes
into a median,
m u c Ji more
prominent,
longitudinal
ridge, the dorsal
lamina (dors, lam.}, which runs along the middle of the dorsal
surface of the pharynx to the opening of the oesophagus. In the
living animal the lamina is capable of being bent to one side in
such a way as to form a deep groove. The mucus secreted by
the gland-cells of the endostyle forms viscid threads which entangle
food-particles (microscopic organisms of various kinds) ; the cilia
VOL. II C
(tloni
FIG. 727. — Ascidia, diagram of longitudinal section from the left
side, the test and mantle removed, an. anus ; air. cav. atrial
cavity ; atr. siph. atrial siphon ; br. car. branchio-cardiac vessel ;
card. vise, cardio-visceral vessel ; dors. v. dorsal vessel ; gonod.
gonoduct ; lit. heart ; hyp. neural gland ; mant. mantle ; ne. gn.
nerve-ganglion ; oes. oesophagus ; or. siph. oral siphon ; ov. ovary ;
red. rectum ; stigm. stigmata ; stom. stomach ; tent,, tentacles ; test,
test ; tr. v. transverse vessel ; vent. v. ventral vessel ; vise. br.
\iscero-brancliial vessel. (From Herdman, after Perrier.)
18
ZOOLOGY
SECT.
of its ciliated cells drive these forwards to the peribrauchial groove,
around which they pass to the dorsal lamina, and the cilia on the
cells of the latter drive them backwards to the opening of the
oesophagus.
Some little distance in front of the anterior peripharyngeal
ridge, at the inner or posterior end of the oral siphon, is a circlet
of delicate tentacles (Fig. 725, tent.).
Enteric Canal. — The oesophagus (Figs. 725 and 727, CBS.) leads
from the pharynx (near the posterior end of the dorsal lamina) to
the stomach (stom.), which, together with the intestine, lies
embedded in the mantle on the left-hand side. The stomach is a
large fusiform sac
. *3 .
with tolerably thick
walls. The intestine
is bent round into a
double loop and runs
forwards to terminate
an anal aperture
in
(an.} situated in the
atrial cavity. Along
its inner wall is a
thickening — the typli-
losole. There is no
liver ; but the walls
of the stomach are
glandular, and a
system of delicate
tubules, which ramify
over the wall of the
intestine and are con-
nected with a duct
FIG. 728. — Ascidia, transverse sod ion. hi. r. blood-vessels ; Opening illto the
dors. lam. dorsal lamina ; epi. epidermis ; end. endostyle : , •>
gn. ganglion ; hyp. neural gland ; itnix. muscular layer of wall StOmacn, IS SUppOSBQ
of body; peribr. peribranchial cavity; ph. pharynx; test, +n V.p nf j-l,p Tla4-llrp
test ; ms. tr. vascular traberuhe. (After Julin.)
of a digestive gland.
The Ascidian has a well-developed blood-system. The heart
(Fig. 727, ht.) is a simple muscular sac, situated near the stomach
in the pericardium — a cavity entirely cut oft' from the surrounding
spaces in which the blood is contained. Its mode of pulsation is
very remarkable. The contractions are of a peristaltic character,
and follow one another from one end of the heart to the other for
a certain time ; then follows a short pause, and when the con-
tractions begin again they have the opposite direction. Thus the
direction of the current of blood through the heart is reversed at
regular intervals. There are no true vessels, the blood circulating
through a system of channels or sinuses devoid of epithelial
lining, and of spaces or lacunae, forming a haemocoele : in the
pe-ribr
e-pt.
xrti
PHYLUM CHORDATA
19
description that follows, therefore, the word vessel is not used in
its strict sense. At each end of the heart is given off a large
' vessel." That given off ventrally, the branchio-cardiac vessel
(br. car.), runs along the middle of the ventral side of the pharynx
below (externally to) the endostyle, and gives oft' a number of
branches which extend along the bars between the rows of stigmata,
and give off smaller branches passing between the stigmata of
each row. The vessel given oft' from the dorsal end of the heart
—the cardio-visceral (card, vise.) — breaks up into branches which
ramify over the surface of the alimentary canal and other organs.
This system of visceral vessels or lacunae opens into a large sinus,
the viscera-branchial vessel, which runs
along the middle of the dorsal wall of
the pharynx externally to the dorsal
lamina, and communicates with the
dorsal ends of the series of transverse
branchial vessels. In addition to these
principal vessels there are numerous
lacunae extending everywhere through-
out the body, and a number of branches,
given off both from the branchio-
cardiac and cardio-visceral vessels,
ramify, as already stated, in the sub-
stance of the test. The direction of
the circulation through the main vessels
differs according to the direction of the
heart's contractions. When the heart
contracts in a dorso-ventral direction,
the blood flows through the branchio-
cardiac trunk to the ventral wall of
the pharynx, and through the trans- FIG
verse vessels, after undergoing oxygena-
tion in the finer branches between the
stigmata, reaches the viscero-branchial
vessel, by which it is carried to the
system of visceral lacunas, and from
these back to the heart by the cardio-visceral vessel. When the
contractions take the opposite direction, the course of this main
current of the blood is reversed.
The nervous system is of an extremely simple character. There
is a single nerve-ganglion (Figs. 725 and 727, ne. gn., 729, gn., and
730, n.g.) which lies between the oral and atrial apertures, embedded
in the mantle. This is elongated in the dorso-ventral direction,
and gives off at each end nerves which pass to the various parts
of the body.
Lying on the ventral side of the nerve-ganglion is a body — the
neural gland (Figs. 725, 727, hyp. ; Fig. 729, gld., and Fig. 730,
c 2
29. — Ascidia. Dorsal tubercle,
nerve-ganglion, and associated
parts as seen from below, dct. duct
of neural gland ; dors. lam. dorsal
lamina ; yld. neural gland ; gn.
ganglion ; fiitp. dorsal tubercle ;
>ir., ni\ nerves ; periph. peri*
pharyngeal band. (After Julin.)
20
ZOOLOGY
SECT.
n.gl.) — which has sometimes been correlated with the hypophysis
of the Craniata. A duct (Fig. 729, dot., and Fig. 730, gl.d) runs
forward from it and opens into the cavity of the pharynx ; the
termination of the duct is dilated to form the ciliated funnel, and
this is folded on itself to form a prominence, the dorsal tubercle,
which projects into the cavity of the pharynx. The dorsal tubercle
may be a sensory organ : the neural gland may have to do with
excretion.
The excretory system seems to be mainly represented by a
single mass of clear vesicles, without a duct, lying in the second
loop of the intestine. • In the interior of these are found concretions
containing uric acid.
'; Reproductive System. — The sexes are united. The ovary
and the testis are situated close together on the left-hand
-t
test
. - teat
..' mantle
ribrancMal
cavity
e.p.br
Branchial
FIG. 730. — Antero-dorsal part of Ascidia, showing the relations of the layers of the body and
of the nervous system, A, in sagittal section ; £, in transverse section, d. bl. s. dorsal blood-
sinus ; d. I. dorsal lamina ; d. n. dorsal nerve ; d. t. dorsal tubercle ; ect. ectoderm ; en.
endoderm ; e. p. br. epithelium of peribranchial cavity ; gl. d. duct of neural gland ; /. v.
points to the ciliated epithelium covering a longitudinal vessel of branchial sac (pharynx) ;
m. mantle ; n. nerve ; n. g. ganglion ; n. gl. neural gland ; p. br. peribranchial cavity ; pp. b.
peripharyngeal bauds ; sph. oral sphincter ; t., t'. test ; in. tentacle. (After Herdman.)
side of the body in the intestinal loop. Each of them contains
a cavity which, like the pericardium and the cavities of the
excretory vesicles, forms a part of the original coelome. Con-
tinuous with the cavity of each is a duct— oviduct or sperm-duct,
as the case may be — which opens into the atrial cavity close to
the anus.
The development of the Ascidian is described below (p. 30).
2. DISTINCTIVE CHARACTERS AND CLASSIFICATION.
The Urochorda are Chordata in which the notochord is confined
to the tail region, and, in all but the Larvacea, is found only in
xm PHYLUM CHORDATA 21
the larva. The adults, which for the most part are retrogress! vely
metamorphosed in other respects besides the abortion of the
notochord, are sometimes sessile, sometimes free and pelagic ; they
frequently form colonies (fixed or free) by a process of budding,
and in some instances exhibit a well-marked alternation of gene-
rations. The body is enclosed in a test consisting largely of
cellulose. The proximal part of the enteric canal (pharynx) is
enlarged to form a spacious sac with perforated walls, acting as
an organ of respiration. There is a simple heart with a system of
sinuses, all devoid of epithelial lining. The coelome is represented,
apparently, only by the pericardium and by spaces in the interior
of the gonads and of the renal organ. The sexes are united. The
larva is always free-swimming, and is nearly always provided with
a caudal appendage.
Three orders of Urochorda are recognised :—
ORDER 1. — LARVACEA.
Free-swimming pelagic Tunicata with a caudal appendage
supported by a skeletal axis or notochord. The test is represented
by a relatively large temporary envelope, the "house," formed
with great rapidity as a secretion from the surface of the ectoderm
and frequently thrown off and renewed. The pharynx has only
two stigmata, and these lead directly to the exterior. There is no
atrial or peribranchial cavity. The principal nerve-ganglion gives
off a nerve-cord with ganglionic enlargements running to the tail,
along the dorsal aspect of which it passes to the extremity. There
is no reproduction by budding, and development takes place
without metamorphosis.
This order contains only a single family, the Appendiculariidce,
with about nine genera, including Appendiculama and OiJcopleura.
ORDER 2.— THALIACEA.
Free-swimming Tunicata, sometimes simple, sometimes colonial,
never provided with a caudal appendage in the adult condition.
The test is a permanent structure. The muscular fibres of the
body-wall are arranged in complete or interrupted ring-like bands,
or diffusely. The pharynx has either two large or many small
stigmata leading into an atrial cavity which communicates with
the exterior by the atrial aperture. There is usually an alternation
of generations ; there may or may not be a tailed larval stage.
Sub-Order a. — Gyclomyaria.
Thaliacea with a cask-shaped body, having, the oral and atrial
apertures at opposite ends, and surrounded by a series of complete
rings of muscular fibres. There is a tailed larval stage.
ZOOLOGY SECT.
This sub-order contains only one family, the DoliolidcB, with the
three genera, Doliolum, Anchinia, and Dolchinia.
Sub-Order b . — Hemimyaria .
Thaliacea with a more or less fusiform body, with sub-terminal
oral and atrial apertures. The muscular fibres are arranged in
bands which do not form complete rings. There is no tailed larval
stage.
This sub-order is probably best looked upon as comprising only
one family, the Salpidce.
OEDER 3. — ASCIDIACEA.
Mostly fixed Tunicata, either simple or forming colonies by a
process of budding, and, in the adult condition, never provided
with a tail. The test is a permanent structure, usually of con-
siderable thickness. The muscular fibres of the mantle (body-
wall) are not arranged in annular bands. The pharynx is large,
and its walls are perforated by numerous stigmata leading into a
surrounding atrium or peribranchial cavity, which communicates
with the exterior by an atrial aperture. Most undergo a meta-
morphosis, the larva being provided with a caudal appendage,
supported by a notochord similar to that of the Larvacea.
Sub-Order a. — Ascidice simplices.
Ascidians in which, when colonies are formed, the zooids are not
embedded in a common gelatinous mass, but possess distinct tests
of their own. They are nearly always permanently fixed and
never free-swimming.
Including all the larger Ascidians or Sea-Squirts.
Sub-Order b. — Ascidice composites.
Fixed Ascidians which form colonies of zooids, embedded in a
common gelatinous material without separate tests.
This order includes Botryllus, Amarcecium, Diazona, and a
number of other genera.
ORDER 4. — LUCIDA.
Pelagic Tunicata which reproduce by budding, so as to give
rise to hollow cylindrical colonies, open at one or both ends, having
the zooids embedded in the gelatinous wall in such a manner that
the oral apertures open on the outer, the atrial on the inner surface
of the cylinder. There is no tailed larval stage.
This order comprises only one family, the Pyrosomidcs, with one
genus, Pyrosoma.
XIII
PHYLUM CHORDATA
Systematic Position of the Example.
The genus Ascidia, of which there are very many species, is a
member of the family Ascidiidce of the Ascidice simplices. The
Ascidiidse differ from the other families of simple Ascidians by the
unio'n of the following characters : — The body is usually sessile,
rarely elevated on a peduncle. The oral aperture is usually
8-lobed and the atrial 6-lobed. The test is always of gelatinous or
cartilaginous consistency. The wall of the pharynx is not folded ;
the tentacles are simple and filiform. The gonads are placed close
to the intestine.
The genus Ascidia is characterised by having the oral and atrial
apertures not close together, by the dorsal lamina being a continu-
ous undivided fold, and by the ganglion and neural gland being
situated at a little distance from the dorsal tubercle.
3. GENERAL ORGANISATION.
General Features. — The Larvacea are minute transparent
animals, in shape not unlike tadpoles, with a rounded body and a
long tail-like appen-
dage attached to the
ventral side. At the
extremity of the body
most remote from the
tail is the aperture of
the mouth. This leads
into a tolerably wide
pharynx (Fig. 732,
ph.), in the ventral
wall of which (except
in Kowalevskia) is
an endostyle similar to that of the simple Ascidian, but com-
paratively short. Round the pharynx there run obliquely two
bands covered with strong cilia — the peripharyngeal bands, which
join a median dorsal ciliated band. On the ventral side of the
pharynx there are two ciliated openings — the stigmata (stig.), which
communicate with the exterior by short passages — the atrial
canals, situated on either side behind the anus. The axis of the
tail is occupied by a cylindrical rod — the notochord or urochord
(noto.).
A remarkable peculiarity of the Larvacea is the power which
they possess of secreting from the surface, by the agency of certain
specially modified epidermal cells, a transparent envelope which is
frequently discarded and quickly renewed. The chief object of
this structure seems to be the capture of the very minute plankton-
organisms on which the Larvacea feed. In Oikoplciira (Fig. 731)
the " house" is a comparatively large structure within which the
FIG. 7;il. — Oikopleura in "house." The arrows show
the course of the current. (From Herrlman, after Fol.)
24
ZOOLOGY
SECT.
ties n e
oto
or.cip
animal is enclosed : undulatory movements of the tail cause a
current of water to flow in through a pair of incurrent apertures
and out through a single excurrent aperture ; the former are closed
by lattice-work of fine threads, preventing the passage of any but
the smallest organisms. In the interior is an elaborate apparatus
for filtering out the minute organisms from the water as it passes
through. In Appendicularia and Kowalevskia the house also
encloses the animal : in Fritillaria it does not do so.
Among the simple Ascidians there is a considerable degree of
uniformity of structure, and little need be added here to the
account given of the example. The shape varies a good deal : it
is sometimes cylindrical, sometimes globular, sometimes com-
pressed ; usually sessile and attached by a broad base, often with
root-like processes, but in other cases (e.g. Boltenia) elevated on
a longer or shorter stalk.
peri.bd negH,' Most are solitary ; but
some (the so-called social
Ascidians) multiply by
budding, stolons being
given off on which new
zooids are developed,
so that associations or
colonies are formed ;
but the connection be-
tween the zooids is not
close, and their tests
remain distinct and
separate. The test varies
FIG. 732. — Diagram of Appendicularia from the right
side. an. anus; ht. heart; int. intestine; ne. nerve; considerably in COnSlS-
ne'. caudal portion of nerve ; ne. gn.' principal nerve- , v. • ' ^U
ganglion ; ne. gn", ne. gn." first two ganglia of nerve of tency, being Sometimes
tail ; noto. notochord ; ces. oesophagus : or. ap. oral aper- oU^^of n-plafirmnq tra na-
ture ; oto. otocyst (statocyst); peri. bd. peripharyngeal almost geiatl "US T
band ; ph. pharynx ; tes. testis ; stic/. one of the stigmata ; parent Or translucent,
stom. stomach. (After Herdman.) . ,
sometimes tougn and
leathery, occasionally hardened by encrusting sand-grains or frag-
ments of shells, or by spicules of carbonate of lime. Calcareous
spicules may be developed in the substance of the mantle. The
apertures always have the same position and relations, varying only
in their relative prominence. The pharynx varies in its size as
compared with the rest of the internal organs, in the position which
it occupies with regard to the various parts of the alimentary
canal, and in the number and arrangement of the stigmata. The
tentacles are sometimes simple, sometimes compound ; and the
dorsal lamina may or may not be divided up into a system of
lobes or languets (Fig. 734, lang.}.
In the composite Ascidians the zooids are embedded in a common
gelatinous mass formed of their united tests. The gelatinous colony
thus formed is sometimes flat and encrusting, sometimes branched
rz&to
XIII
PHYLUM CHORDATA
25
tsl
or lobed, sometimes elevated on a longer or shorter stalk. In
certain forms the gelatinous substance is hardened by the inclusion
in it of numerous sand-grains. The arrangement of the zooids
presents great differences.
Sometimes they occur
irregularly, dotted over
the entire surface without
exhibiting any definite
arrangement ; sometimes
they are arranged in rows
d rh-
end
slom.
01'
FIG. 733. — Botryllus violaceus.
or. oral apertures ; cl. opening; of
common cloacal chamber. (After
]\lilne-Edwards.)
or
in
regular groups ;
Botrytt-us (Fig. 733) they
form star-shaped, radiating
sets around a common
cloacal chamber into which
the atrial apertures of the
zooids lead, while the oral
apertures are towards their
outer ends. In essential
structure the zooids of such
colonies (Fig. 734) resemble
FIG. 734. — Diagram of a zooid of a colony of Com-
posite Ascidians, in which the zooids are in pairs,
as seen in a vertical section of the colony, an. anus ;
at. atrium ; at', atrium of adjoining zooid ; cl. cloaca
common to the two zooids ; end. endostyle ; gld.
digestive gland ; gn. nerve-ganglion ; h't. heart ;
hyp. neural gland ; lang. languets ; mant. mantle :
or. ap. oral aperture ; ov. ovary ; periph. peripharyngeal
band ; ph. pharynx ; reel, rectum ; stom. stomach ;
te. testis ; tent, tentacles ; 1st. test, or common
gelatinous mass ; v. d. vas deferens. (After Herd-
man.)
the simple Ascidians.
In the free-swimming pelagic Doliolum (Fig. 735) the shape is
widely different from that of the ordinary fixed forms. The body
26
ZOOLOGY
SECT.
is cask-shaped, surrounded, as by hoops, by a series of annular
bands of muscular fibres (mus. bds.). The oral and atrial apertures
(or. ap., atr. ap.), instead of being situated near together at the same
end of the body, are placed at opposite extremities, and the
relations of the various organs have undergone a corresponding
mu-s.bds
6lij
FIG. 735. — Doliolura. Diagram of the sexual t'urin. air. ap. atrial aperture surrounded by
lobes ; atr. car. atrial cavity ; rf. the. dorsal tubercle ; end. endostyle ; ht. heart ; int. intestine ;
mus. bds. muscular bands ; ne . gn. nerve-ganglion ; or. ap. oral aperture ; ov. ovary ; peri. bd.
peripharyngea! band ; ph. pharynx ; xtift. stigma ; storn. stomach ; test, testis. (After
Herdman.)
modification. The test is thin and transparent. Surrounding
each opening is a series of lobes — the oral and atrial lobes — in
which there are sense-organs ; and the first and last of the muscular
hoops serve as sphincters for the two orifices. The oral aperture
mus.Lds end.
or. ap
FIG. 736. — Salpa democratica, usexual form, ventral view. atr. ap. atrial aperture ; branch.
dorsal lamina ; end. endostyle ; ht. heart ; mnx. b'. end
fixed, IS Colonial in One vjew. (^,ter Herdman.)
B
28
ZOOLOGY
SECT.
proc
tent
species, and has the oral and atrial apertures towards one end of the
body, which is somewhat discoid, with its margin produced into
eight tapering processes. It has no eye. In all probability
Octacnemus is more nearly related to the social Ascidians (p. 24)
than to Salpa.
Pyrosoma (Fig. 738) is a colonial Tunicate, the colony assuming
the form of a cylinder, the internal cavity of which, closed at one
end, open at the other, serves as the common cloaca for all the
zooids. The oral apertures (Fig. 739, or. ap.) of the zooids are
situated on the outer surface of the cylinder on a series of papillae.
The colonies of Pyrosoma, which may be from jbwo or three inches
to four feet in length, are pelagic, and are brilliantly phos-
phorescent.
The enteric canal in
Appendicularia (Fig. 732)
consists, in addition to the
pharynx, of a narrow oeso-
phagus, a bilobed stomach,
and a straight intestine
(int.) which opens directly
by an anal aperture (an.)
situated on the ventral
side. The alimentary canal
of the simple Ascidians has
already been described,
and there are few differ-
ences of consequence in
the various families, ex-
cept that in some cases
there is a well-developed
digestive gland or "liver";
FIG. 739.— Part of a section through a Fyrosoma • J/L nnirmndtp frvrm«s fhp
colony, air. ap. atrial aperture ; or. ap. oral aper- 3mpOSH
ture ; proc. processes of test on outer surface of arrangement of the parts
colony : ph. pharynx ; stol. stolon on which are de- . , . ,, . ,
veloped buds giving rise to new zooids ; tent, tentacles. IS tne Same 111 all essential
respects as in the simple.
In the Salpa3 and in Doliolum and Octacnemus the alimentary canal
forms a relatively small dark mass — the so-called nucleus — to-
wards the posterior end of the body ; it consists of oesophagus,
stomach, and intestine, the anal aperture being situated in the
peribranchial or atrial part of the internal cavity.
The heart in all has the simple structure already described in
the simple Ascidian. In one of the genera of Larvacea (Kowalevskia)
it is absent.
The nervous system in Appendicularia consists of a cerebral
ganglion (Fig. 732, ne. gri.) on the dorsal side of the mouth, of a
dorsal nerve which passes from this to a caudal ganglion (ne. gn".)
at the root of the tail, and of a caudal nerve (ne'.) which extends
stoL
PHYLUM CHORDATA
29
from this to the extremity of the tail, presenting at intervals slight
enlargements from which nerves are given off. An otocyst or
statocyst (oto.) is placed in close relation to the cerebral ganglion,
and close to it also is a ciliated funnel ; but there is no neural gland
opening into the pharynx. In one species of Oikopleura a simple
light-perceiving organ, without pigment, is incorporated with the
statocyst. In the simple Ascidians, as we have seen, there is a
single flattened ganglion, representing the cerebral ganglion of
Appendicularia, situated between the oral and atrial apertures ;
and the same holds good of the composite forms. Many of the
simple Ascidians have pigment-spots, probably of a sensory
character, around the oral and atrial apertures. The dorsal tubercle
is always present, but varies in shape in accordance with variations
in the form of the ciliated funnel, which opens on it usually in
FIG. 740. — Salpa. Diagrammatic lateral view of the ganglion and neighbouring parts, at.
wall of atrial cavity ; br. branchia : br. ap. aperture of branchia ; c. c. ciliated crests of
branchia ; c. /. ciliated funnel ; ey. eye ; n. gl. gland (paired) that may represent neural
gland ; ph. wall of pharynx. (After Delage and Herouard.)
conjunction with the duct of the neural gland, of which it forms the
terminal part. The opening may be divided into several smaller
apertures by fusion of its lips : rarely the duct gives off branches
with independent openings. The tubercle with the ciliated funnel
is supplied with nerve-fibres from the ganglion, and is probably a
sensory organ of some kind. The neural gland is usually below the
ganglion, but may be situated above it or on one side. Sometimes
it coalesces with it.
In Salpa and Doliolum there is also a single ganglion (Figs.
735, 736, 737, and 740) situated dorsally, giving off nerves to the
various parts of the body. Salpa has a single tentacle, the so-called
languet (Fig. 737, Ing.), absent in Doliolum. In Salpa there is
a median horse-shoe-shaped eye (Figs. 737, 740), and sometimes
smaller accessory eyes. In Doliolum an eye is not developed, but
there is a pair of otocysts or statocysts. A neural gland and duct
:io ZOOLOGY SECT.
with ciliated funnel are present, in Doliolum ; but in Salpa, though
there are a pair of glands which occupy a position similar to that
occupied by the neural gland (Fig. 740, n. gl.), their correspondence
with the latter is not established, and their ducts have no connection
with the ciliated funnel.
In the simple Ascidian we have seen that the renal organ
consists of a number of large clear vesicles situated in the loop of
the intestine and devoid of duct. In some forms the terminal
portion of the sperm-duct has glandular walls in which concretions
of uric acid have been found. The neural gland is by some
zoologists looked upon as having an excretory function, but there
i& no positive evidence in favour of this view, and no definite
conclusion has yet been reached as to the function which it
performs.
Reproductive System. — The Urochorda are hermaphrodite.
Ovary and testis are in all cases simple organs placed in close
relation with one another. In Appendicularia (Fig. 732) they are
situated in the aboral region of the body. In the simple Ascidians
they may be either single or double, and their ducts, sometimes
very short, sometimes more elongated, open close together into the
atrial cavity. In Pyrosoma there are no gonoducts, the ovary—
which contains only a single ovum — and the testis being lodged in
a diverticulum of the peribranchial cavity. In Salpa also the
ovary contains usually only a single ovum : ovary and testis lie in
close relation to the alimentary canal in the " nucleus," and their
short ducts open into the peribranchial cavity. In Doliolum the
elongated testis and oval ovary have a similar position to that
which they occupy in Salpa, but the ovary consists of a number
of ova.
Development and Metamorphosis. — In the Ascidiacea
impregnation usually takes place after the ova have passed out
from the atrial cavity. But in a few simple, and most, if not all,
compound forms impregnation takes place in the atrium or in a
special outgrowth of the latter serving as a brood-sac, and the ovum
remains there until the tailed larval stage is attained. In certain
composite forms there is a coalescence of the investing layers of
the ovum with the wall of the atrium, forming a structure analogous
to the placenta of Mammals and designated by that term. Self-
impregnation is usually rendered impossible by ova and sperms
becoming mature at different times ; but sometimes both ripen
simultaneously, and self-impregnation is then possible.
A somewhat complicated series of membranes invests the ovum.
The immature ovarian ovum is enclosed in a layer of flat cells—
the primitive follicle-cells — derived from indifferent cells of the
ovary. On the surface of this is developed a structureless basal
membrane. The follicle- cells increase by division and soon form
a sphere of cubical cells. Certain of the cells migrate into the
xin
PHYLUM CHORDATA
31
interior of the sphere so as to form a layer on the surface of the
ovum. Others penetrate into the latter so as to lie in the superficial
strata of the yolk. The layer of cells on the surface of the ovum
are termed the test-cells (Fig. 741, e) : they afterwards develop on
the outer surface a thin structureless layer, the chorion (d), and
internal to them is formed a gelatinous layer (x) through which
the test-cells in a degenerated condition become scattered. Mean-
time, external to the follicle-cells, between them and the basal
membrane, has appeared a layer of flattened epithelial cells ; this,
with the basal membrane, is lost before the egg is discharged.
In all the simple Ascidians. with the exception of the few in which
development takes place internally, the protoplasm of the follicle-
cells (Fig. 741, c) is greatly vacuolated so as to appear frothy, and
the cells become greatly enlarged, projecting like papillae on the
surface and buoying up the developing ovum.
Segmentation is complete and
approximately equal, but in the
eight-cell stage four of the cells
are smaller and four larger :
the smaller, situated on the
future dorsal side, are the be-
ginning of the endoderm ; the
four larger form the greater
part, if not the whole, of the
ectoderm. In the following
stages the ectoderm cells multi-
ply more rapidly than the
endoderm, so that they soon
become the smaller. In the
sixteen-celled stage the em-
bryo (Fig. 742, A) has the
form of a flattened blastula
(placula) with ectoderm on
one side and endoderm on the other, and with a small segmen-
tation-cavity. The transition to the gastrula stage is in most
Ascidians effected by a process intermediate in character between
embolic and epibolic invagination ; in some the invagination is
of a distinctly epibolic character. In the former case the ectoderm
cells continue to increase more rapidly than the endoderm, the
whole embryo becomes curved, with the concavity on the endodermal
side, and the ectoderm extends over the endoderm, the two layers
coming to lie in close contact and the segmentation-cavity thus
becoming obliterated. The concavity deepens until the embryo
assumes the form of a saucer-shaped gastrula with an archenteron
and a blastopore which is at first a very wide aperture extending
along the whole of the future dorsal side. The blastopore gradually
becomes constricted (Fig. 742, B) — the closure taking place from
FIG. 7U. — Ascidian (Ciona). Mature egg
from the oviduct after the basal membrane
and layer of flattened cells have been
thrown off. r. follicle-cells ; d, chorion ;
c, test-cells ; /, ovum ; a-, gelatinous layer.
(From Korschelt and Heider, after Kupffer.)
32
ZOOLOGY
SECT.
before backwards, and the opening eventually being reduced to a
small pore at the posterior end of the dorsal surface.
The embryo elongates in the direction of the future long axis.
The dorsal surface becomes recognisable by being natter, while
the ventral remains convex. The ectoderm cells bordering the
blastopore are distinguished from the rest by their more cubical
shape ; these cells, which form the earliest rudiment of the nervous
system, become arranged, as the blastopore undergoes contraction,
eel
.
eel
nolo
end
end.
ecf
FIG. 742. — Early stages in the development of Clavellina. A, flattened blastula ; B, early
gastrula ; C, approximately median optical section of more advanced gastrula in which the
blastopore has become greatly reduced and in which the first rudiment of the notochord is
discernible ; D, similar view of a later larva in which the medullary canal has begun to be
closed in posteriorly. W. p. blastopore ; ect. ectoderm ; end. endoderm ; med. can. medullary
canal ; nerv. cells destined to give rise to the nerve-cord ; neur. neuropore ; nolo. notochord ;
seg. cau. segmentation cavity. (A and B from Korschelt and Heider, after Seeliger ; C and 1)
after Van Beneden and Julin.)
in the form of a plate — the medullary plate— on the dorsal surface.
On the surface of this plate appears a groove — the medullary groove
—bounded by right and left medullary folds, which pass into one
another behind the blastopore.
The medullary folds grow upwards and inwards over the medul-
lary groove, and unite together (D), the union beginning behind
and progressing forwards in such a way as to form a canal, the
neurocosle, in the hinder portion of which is the opening of the
XIII
PHYLUM CHORDATA
33
mes
noto
neur-
blastopore. In this process of closing-in of the medullary groove
the fold which passes round behind the blastopore takes an im-
p o r t a n t part,
growing forwards * A
over the pos-
terior portion of
the canal. The
blastopore, thus
enclosed in the
medullary canal,
persists for a
time as a small
o p e n i n g — t h e
neurenteric canal
—by which the
neuroccele and
enteric cavity are
placed in com-
munication. At
the anterior end
of the medullary
canal, owing to
its incomplete
closure in this
region, there re-
mains for a time
an opening — the
neuropore (Fig.
743, neur.)-
leading to the
exterior.
A notochord
(Figs. 742, G, D,
743 and 744,
noto.) is formed
from certain of
the cells of the
wall of the arch-
enteron along the
middle line of the
end
side.
Fia. 743. — Later stages in the development of Clavellina. A,
approximately median optical section of a larva in which the
medullary canal (neuroccele) has become enclosed throughout,
communicating with the exterior only by the neuropore at the
anterior end and with the archenteron by the neurenteric canal ;
B, larva with a distinct rudiment of the tail and well-formed
mesoderm-Iayer and notochord. Letters as in preceding figure ;
in addition, mes. mesoderm. (After Van Beneden and Julin.)
dorsal
These are
arranged to form
an elongated cord
of cells which
becomes completely constricted off from the endoderrn of the wall
of the archenteron, and comes to lie between the latter and the
VOL. II D
i{4 ZOOLOGY SECT.
medullary groove. Laterally certain cells of the endoderin, in close
relation to those forming the rudiment of the notochord, divide to
give rise to a pair of longitudinal strands of cells — the rudiments
of the mesoderm (Fig. 743, mes.). During this process of mesoderm-
formation, there are no diverticula developed from the archenteron.
The embryo (Fig. 743, B) now becomes pear-shaped, the narrow
part being the rudiment of the future tail. As this narrow portion
elongates, the part of the enteric cavity which it contains soon
disappears, coming to be represented only by a strand of endoderm
cells, which gives rise in the middle to the extension backwards
of the notochord, laterally to the mesoderm of the tail, and ventrally
to a cord of endoderm cells continuous with the wall of the enteric
cavity in front.
The caudal region increases in length rapidly, and the anterior
or trunk region, at first round, becomes oval. At its anterior end
there appear three processes of the ectoderm, the rudiments of the
adhesive papillce (Fig. 744, adh.), organs by which the larva sub-
sequently becomes fixed. The ectoderm cells at an early stage
secrete the rudiments of the cellulose test ; in the caudal region
this forms longitudinal dorsal and ventral flaps having the function
of unpaired fins.
The medullary canal becomes enlarged at its anterior end. A
vesicular outgrowth from this enlarged anterior portion forms the
sense-vesicle (sens, ves.) The posterior narrow part forms the caudal
portion of the central nervous system (spinal cord). Masses of
pigment in relation to the sense-vesicle early form the rudiment
of the two larval sense-organs, otocyst (or statocyst) and eye.
The part behind this presents a thickened wall with a narrow
lumen. This is known as the ganglion of the trunk. The rudiment
of the neural gland early appears on the ventral wall of a ciliated
diverticulum (cil. gr.) of the anterior end of the archenteron (future
pharynx), which subsequently unites with an outgrowth from the
medullary canal.
The embryonic alimentary canal consists of two regions, a wide
region situated altogether in front of the notochord, and a nar-
rower portion situated behind in the region of the notochord. The
wider anterior part gives rise to the pharynx, the posterior part
to the oesophagus, stomach, and intestine. The mouth-opening is
formed shortly before the escape of the embryo from the egg ; an
ectodermal invagination is formed at the anterior end, and an
endodermal diverticulum from the archenteron grows out to meet
it ; the two coalesce, and the oral passage is thus formed.
The rudiments of the heart and pericardial cavity first appear
as a hollow outgrowth from the archenteron : this subsequently
becomes constricted off and involuted to form a double-walled sac,
the inner layer of which forms the wall of the heart, while the
outer gives rise to the wall of the pericardium.
xrtt
PHYLUM CHORDATA
The first beginnings of the atrial cavity appear as a pair of
invaginations of the ectoderm which grow inwards and form a
pair of pouches, each opening on the exterior by an aperture.
There is a difference of opinion as to some points in the history
of these atrial pouches, and it remains uncertain to what^extent
the ectoderm and endoderm respectively share in the formation
of the atrial cavity. Eventually spaces, into the formation of
which the two ectoclermal diverticula at least largely enter, grow
round the pharynx and give rise to the atrial cavity ; and perfora-
tions, the stigmata, primarily two in number, place the cavity
of the pharynx in communication with the surrounding space.
The two openings of the atrial pouches subsequently coalesce to
form one — the permanent atrial aperture.
It will be useful now, at the cost of a little repetition, to sum-
marise the various characteristics of the larval Ascidian at the
stage when it escapes from the egg and becomes free-swimming
(Fig. 744). In general shape it bears some resemblance to a
FIG. 74 \.— Free-swimming larva of Ascidia mammillata, lateral view. ad/t. adhesive papilla; ;
aft. alimentary canal ; atr. atrial aperture ; til. gr. ciliated diverticuluin, becoming ciliated
funnel ; end. endostyle ; eye, eye ; med. nerve-cord (ganglion of trunk) ; noto. notochord ;
oto. otocyst ; sens. ves. sense-vesicle ; stig. earliest stigmata. (From Korschelt and Heider,
after Kowalevsky.)
minute' tadpole, consisting of an oval trunk and a long laterally-
compressed tail. The tail is fringed with a caudal fin, which is
merely a delicate outgrowth of the thin test covering the whole
of the surface ; running through the delicate fringe are a series of
striae, presenting somewhat the appearance of the fin-rays of a
Fish's fin. In the axis of the tail is the notochord (noto.), which
at this stage consists of a cylindrical cord of gelatinous substance
enclosed in a layer of cells. Parallel with this runs, on the dorsal
side, the narrow caudal portion of the nerve-cord, and at the sides
are bands of muscular-fibres. In the trunk the nerve-cord is
dilated to form the ganglion of the trunk, and, further forwards,
expands into the sense- vesicle (sens, ves.) with the otocyst or
statocyst (oto.) and eye (eye). A prolongation of it unites, as already
stated, with the ciliated diverticulurn from the anterior part of
the pharynx. From the walls of this at a later stage are
developed, on the dorsal side, the ganglion, and, on the ventral,
the neural gland ; the pharyngeal opening (cil. gr.) becomes the
D 2
36
ZOOLOGY
SECT.
ciliated funnel. The enteric canal is distinguishable into pharynx,
oesophagus, stomach, and intestine. The pharynx opens on the
exterior by the mouth : in its ventral floor the endostyle (end.)
has become developed ; its walls are pierced by stigmata, the
reel
FIG. 745. — Diagram of the metamorphosis of the free-tailed larva into the fixed Ascidian. A,
stage of free-swimming larva ; B, larva recently fixed : C, older fixed stage, adh. adhesive
papillae ; air. atrial cavity ; oil. gr. ciliated diverticulum, beconiing ciliated funnel ; end.
endostyle ; ht. heart ; med. ganglion of trunk ; n. gn. nerve-ganglion ; noto. notochord ; or.
oral aperture ; rect. rectum ; sens. ves. sense-vesicle ; stig. stigmata ; stol. stolon ; (. tail.
(From Korschelt and Heider, after Seeliger.)
xm PHYLUM CHORDATA 37
number of which varies. The atrial cavity has grown round the
pharynx, and opens on the exterior by a single aperture only
(atr.). The heart and pericardial cavity have been formed. In
this tailed free-swimming stage the larva remains only a few hours ;
it soon becomes fixed by the adhesive papillae and begins to undergo
the retrogressive metamorphosis by which it attains the adult
condition.
The chief changes involved in the retrogressive metamorphosis
(Fig. 745) are the increase in the number of pharyngeal stigmata,
the diminution, and eventually the complete disappearance, of the
tail with the contained notochord and caudal part of the nerve-
cord, the disappearance of the eye and the otocyst, the dwindling
of the central part of the nervous system to a single ganglion, and
the formation of the reproductive organs. Thus, from an active
free-swimming larva, with complex organs of special sense, and
provided with a notochord and well-developed nervous system,
there is a retrogression to the fixed inert adult, in which all the
parts indicative of affinities with the Vertebrata have become
aborted. The significance of these facts will be considered when
we come to discuss the general relationships of the Chordata.
In some simple Ascidians, and in the composite forms in which
development takes place within the body of the parent, the meta-
morphosis may be considerably abbreviated, but there is always,
so far as known, a tailed larva, except in the genus Anwiella of
the Molgulidce — a family of the simple forms — in which the tailed
stage is wanting and there is only an obscure endodermal rudiment
to represent the notochord.
In Pyrosoma development is direct, without a tailed larval
stage, and takes place within the body of the parent. The ovum
contains a relatively large quantity of food-yolk, and the seg-
mentation is meroblastic. A process, developed at an early stage,
elongates to form the so-called stolon, which divides, by the
formation of constrictions, into four parts, each destined to give
rise to a zooid (tetrazooid). The primary zooid (cyaihozooid) under-
goes atrophy, and at this stage the young colony, composed of four
tetrazooids with the remains of the cyathozooid enclosing a mass
of yolk — the whole invested in a common cellulose test — passes out
from the brood-pouch in which it was developed and reaches the
exterior through the cloaca of the parent colony. By a process of
budding from the four primary tetrazooids, the entire adult colony
is produced.
The development of Doliolum is, in all essential respects, very
like that of the simple Ascidians. There is total segmentation,
followed by the formation of an embolic gastrula ; the larva (Fig.
746) has a tail with a notochord (noto.), and a body in which the
characteristic muscular bands soon make their appearance. This
tailed larva becomes the asexual stage or " nurse." By and by
ZOOLOGY
SECT.
the tail aborts, and two processes, one postero-dorsal, the other
ventral, known respectively as the cadophore (dors, st.) and the
ventral stolon (vent, st.), grow out from the body of the larva. On
the latter are formed a number of slight projections or buds. These
become constricted off, and in the form of little groups of cells,
each consisting of seven strings of cells with an ectodermal invest-
FIG. 746. — Doliolum, late stage in the development of the«tailed larva, air. ap. atrial aperture ;
dors. st. cadophore ; end. endostyle ; ht. heart ; ne. gn. nerve-ganglion ; noto. notoehord ;
or. ap. oral aperture ; vent. st. ventral stolon. (After Uljanin.)
ment, creep over the surface of the parent (Fig. 747, e, and Fig.
748) till they reach the cadophore, to which they attach themselves
after multiplying by division. The cadophore soon becomes
elongated, and the bud-like bodies attached to it develop into zooids.
As the long chain of zooids thus established is further developed,
dors.st
onap
f, si
Fid. 747. — -Doliolum, lateral view of asexual stage, showing the early development of the buds.
atr. ap. atrial aperture ; dors. st. cadophore ; e. embryos passing over the surface from the
ventral stolon to the cadophore ; ht. heart ; ne. gn. nerve-ganglion ; or. ap. oral aperture ;
vent. st. ventral stolon. (After Uljanin.)
the parent Doliolum (Fig. 747) loses its branchiae, its endostyle,
and its alimentary canal ; at the same time the muscle-bands
increase in thickness and the nervous system attains a higher
development, until the whole parent comes to play a part like
that of the nectocalyx of a Siphonophore (Vol. I., p. 161), its
xnr
PHYLUM CHORDATA
39
enib
exclusive function being by its contractions to propel the colony
through the water.
The zooids of the cadophore consist of two sets, differing from
one another in position and in future history — the lateral zooids
and the median zooids. The lateral zooids serve solely to carry on
the nourishment and respiration of the colony, and do not undergo
any further development. Some of the median buds, on the other
hand, become detached and take on the special character of phoro-
zooids. When free, each phorozooid
carries with it the stalk by means of
which it was attached to the stolon ;
on this stalk there have previously
become attached a number of buds
which are destined after a time to be
developed into the sexual zooids.
The succession of stages in the
life-history of Doliolum thus briefly
sketched will be seen to succeed one
another in the following order :— (1)
sexual form ; (2) tailed larva de-
veloped sexually from (1) ; (3) first
asexual form or " nurse," the direct
outcome of (2) ; (4) second asexual
form (phorozooid) developed on the
cadophore of (3) from buds originating
on the ventral stolon ; (5) the young
of the sexual form (1) which are
developed on the stalk of (4).
Salpa, like Doliolum, presents a
remarkable alternation of generations.
In the sexual form, which has already
been described, only one ovum is
developed. The testis becomes mature
T .£ .-, i ,1 i FIG. 748. — Doliolum, dorsal view of
later than the OVUm, and the latter the posterior part of the body of an
is impregnated by sperms from the
testis of an . individual of an older
chain. The development is direct
and takes place within the body of
the parent, the embryo as it grows
projecting into the branchial cavity. The nourishment of the
developing embryo (Fig. 749) is effected by the formation
of a structure — the placenta — through which a close union is
brought about between the vascular system of the parent and that
of the embryo. The placenta of Salpa is partly formed from follicle-
cells and ectoderm- cells of the embryo, partly from the cells of the
wall ofj}he oviduct. Segmentation is complete. The study of the
earlier stages is complicated by the very remarkable and unusual
cfors.slol
lal.bds
me.d.bds
asexual zooid, showing the course
taken by the buds (emb.) over the sur-
face from the ventral stolon (rent,
stol.) to the cadophore (dors, stol.) and
their growth on the latter, lat. bds.
lateral buds ; med. bds. median buds ;
peric. pericardium. (After Barrois.)
40
ZOOLOGY
SECT.
atr-ap kr~
sfom
reel
ebi
circumstance that during segmentation there is a migration in-
wards of some of the cells of the follicle and of the wall of the
oviduct, which enter the segmenting ovum and pass among the
blastomeres. There is uncertainty as to what part these inwardly
migrating cells play in the development of the embryo ; but
probably they act merely as carriers of nourishment, and become
broken up and eventually completely absorbed.
There is no tailed larval stage, and the embryo develops the
muscle-bands and all the characteristic parts of the adult while
still enclosed within the body of the parent and nourished by
means of the placenta. This sexually-developed embryo, however,
does not give rise to a form exactly like the parent, but to one
which differs from the latter in certain less important features and
notably in the absence
of reproductive organs.
The sexually formed
embryo, in other
words, gives rise to
an asexual generation,
which escapes to the
exterior and becomes
free - swimming (Fig.
736). After a time
there is developed a
process or stolonr(s£oL),
on the. surface of which
are formed a number
of bud-like projections.
These increase in size
as the stolon elongates,
and each eventually
assumes the form of
a sexual Salpa. The
stolon with the Salpse attached becomes separated off and swims
about as a chain of zooids in which the reproductive organs are
developed.
Distribution, etc. — The pelagic forms are, as is the case with
most pelagic organisms, of very wide distribution, and none of the
genera are confined to particular oceanic areas. The fixed forms,
both simple and composite, are also of world-wide distribution ;
they are much more abundant in the southern hemisphere than in
the northern — the composite forms attaining their maximum in
the South Pacific area. The depth to which the pelagic forms
extend has not been determined. Fixed forms occur at all depths,
but are much more numerous in shallow water than in deep, and
at great depths are comparatively poorly represented, the simple
forms extending to a greater depth than the composite. Several
FIG. 749. — Late stage in the development of Salpa, showing
the placental connection with the parent, air. ap. atrial
aperture ; br. branchia ; oil. or. ciliated groove ; ebl. elseo-
blast (mass of tissue probably representing a vestige of the
tail) ; end. endostyle ; n. gn. nerve-ganglion ; ces. oesopha-
gus ; or. ap. oral aperture ; peric. pericardium ; pi.
placenta ; reef, rectum ; slol. stolon ; stom. stomach.
(From Korschelt and Heider, after Salensky.)
xrn PHYTAJM CHORDATA 41
genera of pedunculated simple Ascidians seem to he confined to
very great depths.
Though placed so high in the animal series, the Urochorda
exhibit very low functional development. This is chiefly connected
with the sessile condition of most of them. The movements per-
formed by a fixed Ascidian are slow and very limited in character,
being confined to contractions of the mantle ; when the animal is
detached, such contractions may sometimes be observed to result
in a slow creeping locomotion. Even in the free forms the move-
ments are limited to the contractions, of the tail muscles in
Appendicularia, of the muscle-bands of the body-wall in Doliolum,
by which swimming is effected. The mode of obtaining food
resembles that which has already been described in the case of the
Pelecypoda (Vol. I., p. 671), the currents which subserve respira-
tion also bringing in microscopic organic particles to the mouth.
Affinities. — That the Urochorda are degenerate descendants of
primitive Chordates admits of little doubt ; the history of the
development of the Ascidians, taken in connection with the occur-
rence of permanently chordate members of the group (Appendicu-
laria and its allies), is quite sufficient to point to this conclusion.
But the degree of degeneration which the class has undergone—
the point in the line of development of the higher Chordata from
which it diverged — is open to question. According to one view
the Urochorda are all extremely degenerate, and have descended
from ancestors which had all the leading features of the Craniata ;
according to another, the ancestors of the class were much lower
than any existing Craniate — lower in the scale than even Amphioxus
—and had not yet acquired the distinctive higher characteristics
of the Craniates. The complete want of segmentation and the
virtual absence of a coelome seem to point in the latter direction :
the presence in the larva of highly-developed central nervous
system and sense-organs in the former. Appendicularia is hardly
to be regarded as representing a primitive ancestral type ; its
close resemblance to the larva of the sessile Ascidians rather seems
to indicate that it is a persistent larval form — a form in which
sexual maturity has been reached at earlier and earlier stages in
the life-history, and in which the final sessile stage has at last been
lost, the animal having become completely adapted to a pelagic
life. Probably the other pelagic forms — Salpa, Doliolum, Pyrosoma
—were also descended from sedentary ancestors : none of them
shows any character that can be interpreted as primitive.
The nearest existing ally of the Urochorda among lower forms
is probably Balanoglossus. The similarity in the character of
the pharynx, or anterior segment of the enteric canal, perforated
by branchial apertures, is alone sufficient to point to such a connec-
tion ; and further evidence is afforded by the occurrence of a
" notochord " in both, and by the similarity in the development
42 ZOOLOGY SECT.
of the central part of the nervous system. But the notochord of
the larval Ascidian, almost confined to a post-intestinal tail-region,
differs very widely from the structure in Balanoglossus supposed to
correspond to it, which is situated anteriorly and directed forwards ;
moreover, the other differences are so great that the alliance cannot
be a close one, and Balanoglossus and its allies can only be looked
upon as very remotely connected with the stock from which the
Urochorda are descended. Further consideration will be given
to this subject in the general treatment of the relationships of the
Chordata.
SUB-PHYLUM III.- EUCHORDA.
We have seen that the fundamental characters of the Chordata
are the presence of a notochord, of a dorsal, hollow, nervous system,
and of a pharynx perforated by apertures or gill-slits. In none of
the lower Chordata, however, are these structures found in a typical
condition, at least in the adult. In Balanoglossus, Cephalodiscus,
and Rhabdopleura the " notochord " is rudimentary, and in nearly
all Tunicata it is present only in the embryo. In Rhabdopleura
the gill-slits are absent, and in that genus as well as in Cephalodiscus
and the adult Tunicata the nervous system is represented by a
single solid nerve-centre or ganglion, the neuroccele being absent.
In Balanoglossus, moreover, there is a ventral as well as a dorsal
nerve- cord, and it is only in the anterior portion of the latter that
the neuroccele is represented.
In the Euchorda, on the other hand, what have been called the
three fundamental chordate peculiarities are fully and clearly
developed. There is always a distinct notochord extending as a
longitudinal axis throughout the greater part of the elongated
body, and either persisting throughout life, or giving place to an
articulated vertebral column or backbone. The central nervous
system remains throughout life in the form of a dorsal nerve-tube
or neuron containing a longitudinal canal or neurocoele, and the
pharynx is always perforated, either throughout life or in the
embryonic condition, by paired branchial apertures or gill-slits.
In addition to these characters, the mouth is ventral and anterior,
the anus ventral and posterior ; the muscular layer of the body-
wall is primarily segmented, and the renal organs arise as a series
of paired tubules which may represent either nephridia or ccelomo-
ducts. Moreover, there is always an important digestive gland,
the liver, developed as a hollow outpushing of the gut, and distin-
guished by the fact that the blood from the alimentary canal
circulates through it before passing into the general current, thus
giving rise to what is called the hepatic portal system of blood-vessels.
The sub-phylum Euchorda comprises two sections of very unequal
extent.
XTTI
PHYLUM CHORDATA
43
SECTION I. — ACRANIA (CEPHALOCHORDA).
Including only the little fish-like Lancelels.
SECTION II. — CRANIATA (VERTEBRATA).
Including Cyclostomes, Fishes, Amphibians, Reptiles, Birds, and
Mammals.
SECTION I.-ACRANIA (CEPHALOCHORDA).
The section Acrania includes only two families, the Branchio-
stomidcB — containing the genera BrancMostoma (usually known by
the name of one of its sub-genera, Amphioxus), Epigonichthys, and
perhaps some others ; and the Amphioxididce — containing the
pelagic genus Amphioxides, which, however, may not be an adult
form. The differences between the genera and species of
Branchiostomidse are comparatively insignificant, and the following
description will deal exclusively with the best known and most
ml pi
alrp -vcnlfr
orhcL
dors/f
mj/om
or.hd
FIG. 750. — Amphioxus lanceolatus. A, ventral, _B,-»side view of the entire animal.
an. anus ; atrp. atriopore ; al.f. caudal fln ; dr. cirri ; dors.f. dorsal fln ; dars.f. r. dorsal fin-
rays ; fion. gonads ; mtpl. metapleure ; myom. myomeres ; nch. notochord ; or. fid. oral hood ;
vent. f. ventral fin ; vent.f. r. ventral fin-rays. (After Kirkaldy.)
thoroughly investigated species, the Lancelet, Amphioxus lanceo-
latus, found in the English Channel, the North Sea, and the
Mediterranean.
Amphioxus is a small transparent animal, occurring near the
shore and burrowing in sand ; its length does not exceed 5-8 cm.,
or less than two inches. Its form will be obvious from Fig. 750
and from the transverse sections, Fig. 751, A and B. The body
is elongated, pointed at either end, and compressed. The
anterior two-thirds is roughly triangular in transverse section,
presenting right and left sides, inclined towards one another above,
and a convex ventral surface. The posterior third is nearly oval
in section, the right and left sides meeting above and below in
a somewhat sharp edge.
Extending along the whole of the dorsal border is a median
longitudinal fold, the dorsal fin (dors, f.) : this is continued round
44
ZOOLOGY
SECT.
the posterior end of the body and extends forwards, as the ventral
Jin (vent. /.), as far as the region where the oval transverse section
passes into the triangular. The portion of the continuous
median fold which extends round the pointed posterior extremity
of the body is somewhat wider than the rest, and may be
distinguished as the caudal fin (d. /.). In the anterior two-thirds
of the body there is no median ventral fin, but at the junction
of each lateral with the ventral surface is a paired longitudinal
fold, the metapleure (mtpl.), which extends forwards to the oral
hood mentioned in the next paragraph.
Below the pointed anterior extremity is a large median aperture
surrounded by a frill-like membrane, the oral hood (or. hd.), the
A B
srt
a
neu
rni/om ~,
FIG. 751. — Amphioxus lanceolatus. A, transverse section of the pharyngeal region,
a. dorsal aorta ; b. atrium ; c. notochord ; co. ccelome ; e. endostyle ; g. gonad ; tsb. branchial
t lamellse ; td. pharynx ; 1. liver ; nvj. rnyomere ; n. nephridium ; r. neuron ; sn. spinal
nerves. B, transverse section of the intestinal region, atr. atrium ; ccel. ccelome ;
d. ao. dorsal aorta ; int. intestine ; mijom. myomere ; nch. notochord ; neu. neuron ; s. int. ?>.
sub-intestinal vein. (A, from Hertwig, after Lankester and Boveri ; -B, partly after
Rolph.)
edge of which is beset with numerous tentacles or cirri (dr.). The
oral hood encloses a cup-shaped cavity or vestibule, at the bottom
of which is the mouth (Fig. 752, mth.). On the wall of the oral
hood is a specially modified tract of the epithelium divided into
finger-shaped lobes. The cells of this tract, which is known as
the wheel-organ, are provided with long cilia, the movements of
which drive currents of water with floating food-particles backwards
into the pharynx. Along the roof of the vestibule runs a ciliated
groove — the groove of Hatschek. Immediately in front of the
anterior termination of the ventral fin and partly enclosed by the
metapleures is a rounded aperture of considerable size, the atriopore
xra PHYLUM CHORDATA 45
(alrp.), and a short distance from the posterior extremity of the
body is the anus (an.), placed unsymmetrically on the left side of
the ventral fin. The post-anal portion of the body is distinguished
as the tail.
Amphioxus ordinarily lives with the greater part of the body
buried in sand, only the anterior end with the expanded oral
hood protruding. It also swims in the vertical position, and
frequently lies on one side on the sand : it burrows, head foremost,
with great rapidity. A current of water is constantly passing in
at the mouth and out at the atriopore.
Body-wall. — The body is covered with an epidermis (Fig. 751)
formed of a single layer of columnar epithelial cells, some of which
are provided with sensory hairs, while some are unicellular glands.
On the surface of the epidermis is a cuticle perforated by pores. The
epithelium of the buccal cirri presents at intervals regular groups
of sensory cells, some of them bearing stiff sensory hairs, others cilia.
Beneath the epidermis is the dermis, formed mainly of soft connec-
tive-tissue.
The muscular layer (my, myom.) is remarkable for exhibiting
rnetameric segmentation. It consists of a large number— about
sixty — of muscle-segments or myomeres, separated from one another
by partitions of dense connective-tissue, the myocommas, and having
the appearance, in a surface view, of a series of very open V's with
their apices directed forwards (Figs. 750 and 752). Each myomere
is composed of numerous flat, striated muscle-plates, arranged longi-
tudinally, so that each is attached to two successive myocommas.
In virtue of this arrangement the body can be bent from side to
side with great rapidity. The myomeres of the right and left
sides of the body are not opposite to one another, but have an
alternate arrangement. A special set of transverse muscles (Fig.
751, A) extends across the ventral surface of the anterior two-thirds
of the body, lying in the floor of the atrial cavity presently to be
described.
One striking and characteristic feature of the muscular layer of
the body-wall is the immense thickness of its dorsal portion. In
the higher Worms and many other Invertebrates the muscles form
a layer of approximately equal thickness surrounding the body-
cavity, which contains, amongst other organs, the central nervous
system. In Vertebrates, on the other hand, the dorsal body-wall
is greatly thickened, and in it are contained both the nervous system
and the notochord.
Skeleton. — The chief of the skeletal or supporting structures
of the Lancelet is the notochord (Figs. 751 and 752, c, nch.), a
cylindrical rod, pointed at both ends, and extending from the
anterior to the posterior end of the body in the median plane. It
lies immediately above the enteric tract and between the right and
ft myomeres. It is composed of a peculiar form of cellular
44 JZOOLOGV
tissue known as notochordal tissue, formed of large vacuolated cells
extending from side to side of the notochord, and having the
nuclei confined to its dorsal and ventral regions. Around these
cells is a structureless layer, secreted by the cells, enclosed in a
notochordal sheath of connective-tissue, which is produced dorsally
into an investment for the canal enclosing the central nervous
system. The notochord, like the parenchyma of plants, owes its
resistant character to the vacuoles of its component cells being
tensely filled with fluid, a condition of turgescence being thus pro-
duced.
The oral hood is supported by a ring (Fig. 752, sk.) of cartilaginous
consistency, made up of separate rod-like pieces arranged end to
end, and corresponding in number with the cirri. Each piece sends
an offshoot into the cirrus to which it is related, furnishing it with
a skeletal axis.
The pharynx is supported by delicate oblique rods of a firm
material, apparently composed of agglutinated elastic fibres, the
gill-rods (br. r.). These will be most conveniently discussed in
connection with the pharynx itself. The dorsal fin is supported by
a single series and the ventral fin by a double series of fin-rays
(dors. f. r., vent. f. r.), short rods of connective-tissue, continuous
with the investment of the neural canal and separated from one
another by small cavities (lymph-spaces).
Digestive and Respiratory Organs. — The mouth (mth.), as
already mentioned, lies at the bottom of the vestibule or cavity of
the oral hood (or. hd.). It is a small circular aperture surrounded
by a membrane, the velum (vl.), which acts as a sphincter, and has
its free edge produced into a number of velar tentacles (vl. t.}.
The mouth leads into the largest section of the enteric canal,
the pharynx (ph.), a high, compressed chamber extending through
the anterior half of the body. Its walls are perforated by more
than a hundred pairs of narrow oblique clefts, the gill-slits or
branchial apertures (br. cl.), which place the cavity of the pharynx
in communication with the atrium (see below). From the posterior
end of the pharynx goes off the tubular intestine (int.), which extends
backwards almost in a straight line to the anus.
On the ventral wall of the pharynx is a longitudinal groove, the
endostyle (Fig. 751, A, e.), lined by ciliated epithelium containing
groups of gland-cells. Like the homologous organ in Ascidia
(p. 17), the glands secrete a cord of mucus in which food-particles
are entangled and carried by the action of the cilia to the intestine.
A somewhat similar structure, the epipharyngeal groove, extends
along the dorsal aspect of the pharynx : its sides are formed by
ciliated cells, which, at the anterior end of the groove, curve down-
wards, as the peripharyngeal bands, and join the anterior end of
the endostyle.
From the ventral region of the anterior end of the intestine is
Xtll
PH'STLUM CHORDATA
given off a blind pouch,
the liver (Ir.) or hepatic
ccecum, which extends
forwards to the right of
the pharynx : it is lined
with glandular epithelium
and secretes a digestive
fluid.
The gill-slits (br. d.)
are long narrow clefts,
nearly vertical in the
expanded condition, but
very oblique in preserved
and contracted specimens
—hence the fact that a
large number of clefts
always appear in a single
transverse section (Fig.
751, /4, M). The clefts
are more numerous than
the myomeres in the
adult, but correspond in
number with them in the
larva : hence they are
fundamentally m e t a -
meric, but undergo an
increase in number as
growth proceeds.
The branchial lamella}
(Fig. 752, br. sep., Fig.
751, A, kb.), or portions
of the pharyngeal wall
separating the clefts from
one another, are covered
by an epithelium which
is for the most part en-
dodermal in origin, and
is composed of greatly
elongated and ciliated
cells. On the outer face
of each lamella, however,
the cells are shorter and
not ciliated, and are, as a
matter of fact, portions of
the epithelial lining of
the atrium, and of ecto-
dermal origin. Each
48
ZOOLOGY
SECT.
lamella is supported towards its outer edge by one of the branchial
rods (Fig. 752, br. r.) already referred to. These are narrow bars
united with one another dorsally by loops, but ending below in
free extr mities
-J' which are alter-
nately simple
and forked. The
forked bars are
the primary (br.
r. 1), those with
simple ends the
secondary (br. r.
2} branchial rods,
and the lamella;
in which they are
contained are
similarly to be
distinguished as
primary lamellcc
(br. sep. 1} and
secondary or
tongue-lamella;
(br. sep. 2). In
the young con-
dition the two
clefts between
any two primary
lamellae are re-
presented by a
single aperture :
as development
proceeds a down-
growth takes
place from the
dorsal edge of
the aperture,
forming, as in
Balanoglossus (p.
5), a tongue which
extends d o w n-
wards, dividing
the original cleft
into two, and
itself becoming a
secondary lamella. A further complication is produced by the
formation of transverse branchial junctions or synapticulce, sup-
ported by rods connecting the primary septa with one another at
tolerably regular intervals.
FlG.s753. — Amphioxus lanceolatus. Diagrammatic transverse
section of the pharyngeal region, passing on the right through a
primary, on the left through a secondary branchial lamella.
ao. dorsal aorta ; c. derm ; ec. en dostylar portion of ccelome; /. fascia
or investing layer of myomere ; fh. compartment containing fin -ray ;
ff. gonad ; gl. glomerulus (modified part of branchial artery in
relation to nephridium) ; k. branchial artery ; led. pharynx ; Id.
combined atria! and ccelomic wall (ligamentum denticulatum) ;
m. myomere ; int. transverse muscle ; n. nephridium ; of. meta-
pleural lymph-space ; p. atrium ; so. ccelome ; si. ventral aorta ;
sk. sheath of notochord and neuron ; uf. spaces in ventral wall.
(From Korschelt and Heider, after Boveri and Hatschek.)
XIII
PHYLUM CHORDATA
49
The Atrium. — The gill-clefts lead into a wide chamber occupying
most of the space between the body- wall and the pharynx, and
called the atrium (Figs. 751, B, and 752, atr.). It is crescentic in
section, surrounding the ventral and lateral regions of the pharynx,
but not its dorsal portion. It ends blindly in front , opens
externally, behind the level of the pharynx, by the atriopore
(, .'• '-,.,; , ^
•d
B
(- "
ji >^y,,!;Q
'> 7*- SV
i, Iks
JTL _A
FIG. 7(52. — Amphioxus lanceolatus. A, young larva ; D, anterior end more highly
magnified, c. provisional tail-fin ; ch. notochord ; en. neurenteric canal ; d. enteric canal ;
/(. coelome of head ; k. club-shaped gland ; /,;'. its external aperture ; ks. first gill-slit ; m.
mouth ; mr. neuron ; np. neuropore ; se. sub-intestinal vein ; w. pre-oral pit. (From
Korschelt and Heider, after Hatschek.)
system and notochord dorsally, and with the enteric canal
ventrally. At about the level of the ventral surface of the notochord
a horizontal partition is formed in each ccelomic sac (Fig. 760, D),
separating it into a dorsal and ventral portion. The dorsal section
is distinguished as the protovertebra or myotome (ns), and its cavity
as the myoccele or muscle-cavity : the ventral section is called the
lateral plate or splanchnotome, and its cavity forms a segment of the
coelome.
The lateral plates now unite with one another in pairs below the
enteric canal, their cavities becoming continuous : at the same
time the cavities of successive lateral plates are placed in communica-
tion with one another by the absorption of their adjacent (anterior
and posterior) walls. In this way the cavities of the entire series
ZOOLOGY
SECT.
-^
«&
S-fg
« o> C
(J P< CD
811
*< AK
of ventral plates, right and left, unite to
form the single unsegmented coelome of
the adult, their walls giving rise to the
coelomic epithelium.
At the same time the cells of the
splanchnic layer of the protovertebrse
become converted into muscular fibres,
which nearly fill the myoccele, and give
rise to the myomeres : the myocommas
arise from the adjacent anterior and
posterior walls of the proto vertebrae. An
outpushing of the splanchnic layer, at
about the level of the ventral surface
of the notochord, grows upwards be-
tween the myomere externally and the
notochord and nerve-tube internally :
from the cells lining this pouch the con-
nective-tissue sheath of the notochord
and neural canal arises, and perhaps
also the fin-rays. From the parietal
layer of the protovertebrse is formed the
derm or connective-tissue layer of the
skin.
The larva increases in size, and be-
comes very long and narrow, with a
pointed anterior end and a provisional
caudal fin posteriorly (Fig. 763, c). As
growth proceeds, new segments are added
behind those already formed, the noto-
chord grows forwards to the anterior end
of the snout, and the eye-spot (au.) and
olfactory pit appear, the latter as an
ectodermal pit which communicates
with the neuroccele by the still open
neuropore (np.). The mouth (m.) attains
a relatively immense size, still remaining
on the left side.
Additional gill-slits arise behind the
one already mentioned : they all make
their appearance near the middle ventral
line, and gradually shift over to the
right side : at first they correspond
with the myomeres, so that the seg-
mentation of the pharynx is part of the
general metamerism of the body. Alto-
gether fourteen clefts are produced in a
single longitudinal series. Above, i.e.,
xm PHYLUM CHORDATA 61
dorsal to them, a second longitudinal series makes its appearance,
containing eight clefts, so that at this stage there are two parallel
rows of gill-slits on the right-side of the body, and none on the
left. But as growth goes on, the first or ventral series gradually
travels over to the left side, producing a symmetrical arrangement,
and at the same time the first slit and the last five of the first or
definitively left series close up and disappear, so that the numbers
are equalised on the two sides. At first each gill-slit is simple, but
before long a fold grows down from its dorsal edge, and, extending
ventrally, divides the single aperture into two : this fold is the
secondary or tongue-lamella, the original bars of tissue between the
undivided slits becoming the primary lamellae.
While the development of the gill-slits is proceeding, the atrium
is in course of formation. Paired longitudinal ridges, the meta-
pleural folds (Fig. 764, If. rf., Fig. 765, sf.), appear on the ventral
side of the body, behind the;gill-slits, and^gradually extend forwards,
Jl
ap
FIG. 764. — Amphioxus lanceolatus. Ventral aspect of three larvae showing the develop-
ment of the atrium, ap. atriopore ; k. gill-slits ; //. left metapleural fold ; m. mouth ; rf. right
metapleural fold ; w. pre-oral pit. (From Korschelt and Heider, after Lankester and Willey.)
dorsal to the latter, their arrangement being very unsymmetrical
in correspondence with that of the clefts themselves. On the
inner face of each fold, i.e. the face which looks towards its fellow
of the opposite side, a longitudinal sub-atrial ridge (Fig. 765, A, si)
appears, and the two sub-atrial ridges meeting and coalescing, a
canal (B, p) is formed immediately below the ventral body-wall.
This canal is the commencement of the atrium : it is at first quite
narrow, but gradually extends upwards on each side (C, p) until it
attains its full dimensions. It is open, at first, both in front and
behind : the posterior opening remains as the atriopore : the
anterior opening becomes gradually shifted forwards as the fusion
of the sub-atrial ridges proceeds (Fig. 764, B and C), and is finally
completely closed. In this way the gill-slits come to open, not
directly on][the exterior, but into a cavity formed by the union of
paired ridges of the body-wall, and therefore lined by ectoderm.
62
ZOOLOGY
SECT.
The mouth gradually passes to the ventral surface, and undergoes
a relative diminution in size : a fold of integument develops round
it and forms the oral hood, which is probably to be looked upon as
a stomodseum. The endostyle appears on the right of the pharynx
(Fig. 763, fi), and is at first rod-shaped, then V-shaped : ultimately
the limbs of the V unite in the middle ventral line. The gill-slits
increase in number and become more and more vertically elongated.
The provisional caudal fin disappears. The gonads arise from the
outer and ventral regions of the protovertebrse in the form of pouches,
which gradually assume their permanent form.
Distribution.— The Branchiostomidae are very widely dis-
tributed in tropical and warm-temperate seas. Amphioxides has
only been obtained with the tow-net and is, seemingly, of
FIG. 765. — Amphioxus lanceolatus. Diagrammatic transverse sections of three larvse
to show the development of the atrium, ao. aorta ; c. derinis ; d. intestine ; /. fascia
(layer of connective-tissue on inner surface of myomere) ;fh. cavity for dorsal fin-ray ; in.
myomere ; n. neuron ; p. atrium ; sf. metapleural folds ; sfh. metapleural lymph-space;
si. sub-intestinal vein ; sk. sheath of notochord and neuron ; si. sub-atrial ridge ; sp.
coelome. (From Korschelt and Heider, after Lankester and Willey.)
permanently pelagic habit. It differs from Amphioxus in the
absence of oral cirri and of an atrial cavity, the branchial slits
opening directly on the exterior in an impaired ventral row. No
fully mature specimens have yet been found, but the larger speci-
mens have a single row of gonads.
Distinctive Characters.— The Acrania may be defined as
Euchorda in which the notochord extends to the anterior end of
the snout, in advance of the central nervous system. There is no
skull, and no trace of limbs. The ectoderm consists of a single
layer of cells which may be ciliated. The pharynx is of immense
xm PHYLUM CHORDATA 63
size, perforated by very numerous gill-slits, and surrounded by an
atrium. The liver is a hollow pouch of the intestine. There is no
heart, and the blood is almost colourless. The nephridia remain dis-
tinct and open into the atrium. The brain is very imperfectly
differentiated ; there are only two pairs of cerebral nerves ; and the
dorsal and ventral spinal nerves do not unite. There are no paired
eyes, but there is a median pigment-spot in the wall of the brain, and
many others in the spinal cord ; an auditory organ is absent. The
gonads are metamerically arranged and have no ducts. There is a
typical invaginate gastrula, and the mesoderm arises in the form
of metameric ccelomic pouches. The coelome is an enteroccele.
Affinities. — Amphioxus has had a somewhat chequered zoo-
logical history. Its first discoverer placed it among the Gastropoda,
considering it to be a Slug. When its vertebrate character was
made out, it was for a long time placed definitely among Fishes, as
the type of a distinct order of that class ; but it became obvious,
from a full consideration of the case, that an animal with neither
skull, brain, heart, auditory organs, nor paired eyes, with colourless
blood, with no kidneys in the ordinary sense of the word, and with
its pharynx surrounded by an atrium, was more widely separated
from the lowest Fish than the lowest Fish from a Bird or
Mammal.
There was still, however, no suspicion of any connection
between Amphioxus and the Urochorda until the development
of both was worked out, and it was shown that in many
fundamental points, notably in the formation of the nervous
system and the notochord, there was the closest resemblance
between the two. The likeness was further emphasised by the
presence in both forms of an endostyle, an epipharyngeal groove
(dorsal lamina) and peripharyngeal bands, and of an atrium,
and by the obvious homology of the stigmata or gill-slits of Tunicates
with those of Amphioxus. The Urochorda being obviously a
degenerate group, it was suggested that the peculiarities of the
adult Amphioxus might also be due to a retrogressive metamor-
phosis. Of this, however, there is not sufficient evidence, and most
recent investigations have tended to bring the Acrania nearer to
the Craniate Vertebrata, and to remove them further from the
lower Chordata.
SECTION II.— CRANIATA (VERTEBRATA).
The group of the Craniata (Vertebrata) includes all those animals
known as Fishes, Amphibians, Reptiles, Birds, and Mammals, or, in
other words, Vertebrata having a skull, a highly complex brain, a
heart of three or four chambers, and red blood-corpuscles.
In spite of the obvious and striking diversity of organisation
obtaining among Craniata — between, for instance, a Lamprey, a
Pigeon, and a Dog — there is a fundamental unity of plan running
64 ZOOLOGY SECT.
through the whole group, both as to the general arrangement of
the various systems of organs and the structure of the organs
themselves — far greater than in any of the principal invertebrate
groups. The range of variation in the whole of the six classes
included in the division is, in fact, considerably less than in many
single classes of Invertebrata — for instance, Hydrozoa or Crustacea.
Hence, while the plan hitherto adopted of treating the group class
by class will be followed, it will be found convenient to begin by
devoting a considerable space to a preliminary account of the
Craniata as a whole, since in this way much needless repetition
will be avoided.
The Craniata include the following classes and sub-classes :—
CLASS I. — CYCLOSTOMI,
Including the Lampreys and Hags.
CLASS II. — PISCES,
True Fishes, which are again divisible into
Sub-class 1 . — Elasmobranchii,
Including the Sharks and Rays.
Sub-class 2. — Holocephali,
Including the Cat-fish (Chimcera) and the Elephant-fish
( Callorhynchus) .
Sub-class 3. — Teleostomi,
Including the bony Fishes, such as Perch, Cod, Trout, &c., and the
Sturgeons and their allies.
Sub-class 4. — Dipnoi,1
Mud-Fishes.
CLASS III. — AMPHIBIA,
Including Frogs, Toads, Newts, and Salamanders.
CLASS IV. — REPTILIA,
Including Lizards. Snakes, Crocodiles, Turtles, and Tortoises.
CLASS V. — AVES,
Birds.
i The animals included iu Classes I. and II. are all "Fishes" in the broad sense of the word.
XIII
PHYLUM CHORDATA 65
CLASS VI. — MAMMALIA,
Including Hairy Quadrupeds, Seals, Whales, Bats. Monkeys, and
Man.
External Characters. — The body of Craniata (Fig. 766) is
bilaterally symmetrical, elongated in an antero-posterior direction,
and usually more or less cylindrical. It is divisible into three
regions : the head, which contains the brain, the chief sensory
organs, and the mouth and pharynx ; the trunk, to which the
ccelome is confined, and which contains the principal digestive and
circulatory as well as the excretory and reproductive organs ; and
the tail, or region situated posteriorly to the ccelome and anus,
and containing none of the more essential organs. Between the
head and trunk there is frequently a narrow region or neck, into
which the ccelome does not extend. In aquatic Vertebrates the
tail is of great size, not marked off externally from the trunk, and
is the chief organ of locomotion : in terrestrial forms it usually
becomes greatly reduced in diameter, and has the appearance of
a mere unpaired posterior appendage.
The mouth (mth.) is a transverse aperture placed at or near the
anterior end of the head. Near it, sometimes' dorsal, sometimes
ventral in position, are the paired nostrils or anterior nares (na.)—
or in Cyclostomi the single nostril — leading to the organs of smell.
Farther back, on the sides of the head, are the large paired eyes
(e.), and on the dorsal surface there is sometimes more or less
indication of a vestigial median or pineal sense-organ (pn. e.), which
may take the form of an eye. Posterior to the paired eyes are
the auditory organs (an.), the position of which is indicated in
the higher forms by an auditory aperture.
On the sides of the head, behind the mouth, are a series of
openings, the gill-slits or external branchial apertures (e. br. a.
1 — ?) : they are rarely more than seven in number, (Cf. p. 139) and in
air-breathing forms disappear more or less completely in the adult.
In the higher Fishes a fold called the operculum (Fig. 780, op.)
springs from the side of the head immediately in front of the
first gill-slit and extends backwards, covering the branchial
apertures.
On the ventral surface at the junction of the trunk and tail is
the anus (an.). Distinct urinary and genital apertures, or a single
urino-genital aperture, are sometimes found either in front of or
behind the anus, but more commonly the urinary and genital ducts
open into the termination of the enteric canal, or cloaca, so that
there is only a single egestive opening, known as the cloac'il
aperture. On either side of this there may be a small abdominal
pore (ab. p.) leading into the ccelome.
In Fishes and some Amphibians, the trunk and tail are produced
in the middle dorsal line into a vertical fold or median fin, which is
66
ZOOLOGY
SECT.
xm
PHYLUM CHORDATA
67
f
continued round the end of the tail and forwards in the middle
line to the anus. Frequently this continuous fin becomes broken
up into distinct dorsal (d.f. 1 and 2), ventral (v.f.), and caudal (cd.f.)
fins, which may assume very various forms : in the higher classes
all trace of median fins disappears (cf., however, the Cetacea).
Fishes also possess paired fins. Immediately posterior to the
last gill-slit is a more . or less horizontal outgrowth, the pectoral fin
(pet. f.}, while a similar but smaller structure, the pelvic fin (pv.f.),
arises at the side of the
.a Ji a Cf!
anus.
In all Craniata above
Fishes, i.e., from Am-
phibia upwards, t h e
paired fins are replaced
by fore- and hind-limbs
(f.L, h.l.), each consisting
of three divisions— upper-
arm, fore-arm, and hand
in the one case ; thigh,
shank, and foot in the
other. Both hand and
foot normally terminate
in five ringers or digits,
and the pentadactyle limb
thus formed is very char-
acteristic of all the higher
Vertebrata. The paired
fins, or limbs, as the case
may be, are the only
lateral appendages pos-
sessed by Vertebrates.
Body-wall and In-
ternal Cavities. - - The
body is covered extern-
ally by a skin consisting
of two layers, an outer
or epithelial layer, the
epidermis (Fig. 767, Ep.), derived from the ectoderm of the em-
bryo, and an inner or connective-tissue layer, the dermis (Co),
of mesodermal origin. The epidermis is always many-layered,
the cells of the lower layers, forming the stratum Malpighii, being
protoplasmic and capable of active multiplication, while those of
the superficial layers often become flattened and horny, and con-
stitute the stratum corneum. Glands are frequently present in the
skin in the form of tubular or flask-shaped in-pushings of the
epidermis or of isolated gland-cells (B).
Beneath the skin comes the muscular layer. This is always
FIG. 767. — Diagrammatic vertical section of the skin of
a Fish. B, unicellular mucous glands ; Co, derm ;
CS, cuticular margin ; Ep, epiderm ; F, fat ; G, blood-
vessels ; Ko, goblet-cells ; Ko, granule-cells ; S, ver-
tical, rand W, (horizontal bundles of connective-
tissue. (From Wiedersheim's Vertet/rata.)
68
ZOOLOGY
SECT.
3 03
highly developed, and, in the lower Craniata, has the same general
arrangement as in Amphioxus, i.e., consists of zig-zag muscle-
segments or myomeres (Fig. 768, mym.), separated from one another
by partitions of connective-tissue, or myocommas (myc.), and formed
of longitudinally disposed muscle-fibres. The myomeres are not
placed at right angles to the long
axis of the body, but are directed
from the median vertical plane
outwards and backwards, and are
at the same time convex in front
and concave behind, so as to have
a cone-in-cone arrangement (Fig.
769, C). Each myomere. moreover,
is divisible into a dorsal (d. m.)
and a ventral (v. m.} portion. In
the higher groups this segmental
arrangement, though present in
the embryo, is lost in the adult,
the myomeres becoming con-
verted into more or less longi-
tudinal bands having an ex-
tremely complex arrangement.
In the trunk, as shown by a
section of that region, the muscles
form a definite layer beneath the
skin and enclosing the ccelome
(Fig. 769, A and C, ccel). The
muscular layer, as in Amphioxus,
is not of even diameter throughout,
but is greatly thickened dorsally,
so that the coslome is, as it were,
thrown towards the ventral side.
Its dorsal portion, moreover, is
excavated by a canal, the neural
or cerebro-spinal cavity (c. s. c.), in
which the central nervous system
is contained, and the anterior
portion of which is always dilated,
as the cranial cavity, for the brain.
Thus a transverse section of the
trunk has the form of a double
tube. In the head, neck, and
tail (B, D), the coelome is absent in the adult, and the muscles
occupy practically the whole of the interval between the skin and
the skeleton, presently to be referred to : in the tail, however, there
is found a hcemal canal (h. c.) containing connective-tissue, and
representing a virtual backward extension of the ccelome. The
xtti
i'HYLUM CHORDATA
t-.^3 f ,71 « "^ r/> *•* -r^ '/>
i"2 §^3^ .rf «^ £
2^3~3'3g1''*'O'o
VOL. II
70
ZOOLOGY
SECT
sped
C.C
fins, or fore- and hind-limbs, are moved by longitudinal muscles
derived from those of the trunk. All the voluntary or body-muscles
of Crania ta are of the striated kind.
The ccelome is lined by peritoneum (C, pr.), a membrane consisting
of an outer layer of connective-tissue, next the muscles, and an
inner layer of ccelomic epithelium bounding the cavity, and thus
forming the innermost layer of the body-wall. In Fishes the
ccelome is divided into two chambers, a large abdominal cavity
containing the chief viscera, and a small f orwardly-placed pericardia!
cavity (A, pc.) containing the heart, and lined by a detached portion
of peritoneum
known as the peri-
cardium. In Mam-
mals there is a
vertical muscular
partition, the dia-
phragm, dividing the
ccelome into an an-
terior chamber or
thorax, containing
the heart and lungs,
and a posterior
chamber or abdomen
containing the re-
maining viscera.
Skeleton. — The
hard parts or sup-
porting structures
of Craniata fall into
two categories — the
exo skeleton and the
endoskeleton. The
exoskeleton con-
sists of bony or horny
deposits in the skin,
and may be either
epidermal or dermal,
or both, but is never,
like the armour of an Arthropod or the shell of a Mollusc, cuticular.
The epidermal exoskeleton is always formed by the cornification or
conversion into horn of epidermal cells, and may take the form of
scales — as in Reptiles, feathers, hairs, claws, nails, horns, and hoofs.
The dermal exoskeleton occurs in the form of either bony or horn-
like deposits in the derm, such as the scales and dermal fin-rays of
Fishes, and the bony armour of the Sturgeon, Crocodile, or Armadillo.
The endoskeleton, or " skeleton " in the ordinarv sense of the
sh.ncTi-
p.c.l
el.rn
FIG. 770. — Semi-diagrammatic transverse section of the vertebral
column of a Craniate embryo, c. c. central canal ; el. m. ex-
ternal elastic membrane ; h. r. haemal ridges ; n. c. neural tube ;
nch. notochord ; nch. c. notochordal cells ; p. c. t. perichordal
tube ; sh. nch. sheath of notochord ; sk. c. skeletogenous cells
migrating into notochordal sheath ; sk. I. skeletogenous layer ;
sp. cd. spinal cord. (Modified from Balfour and Gadow.)
int PHYLUM CHORDATA 71
word, forms one of the most complex portions of the body, and
presents an immense range of variation in the different classes and
orders. As in Amphioxus, the axis of the entire skeletal system
is formed by the notochord (Fig. 769, nch.}, an elastic rod made of
peculiar vacuolated cells (Fig. 770, nch.}. resembling the pith of
plants, and covered by a laminated sheath (sh. nch.}, with an external
elastic membrane (el. m.) around it. The whole sheath is, in the
Craniata, a cuticular product of the superficial notochordal cells
(nch. c.), i.e., is developed as a secretion from their outer or free
surfaces. The notochord lies in the middle line of the dorsal body-
wall between the cerebro-spinal cavity above and the ccelome below :
it is usually developed, as in the lower Chordata, from a median
longitudinal outgrowth of the dorsal wall of the gut. Posteriorly
it extends to the end of the tail, but in front it always stops short
of the anterior end of the head, ending near the middle of the brain
immediately .
behind a pecu- **•£ /
liar organ, the
pituitary body
(Fig. 769, A,
pty. b.}, which
will be referred
to again in
treating of the
digestive organs
and of the ner-
vous System. -pK} 77j_ — Diagram illustrating the segmentation of the vertebra
The extension column, c. n. t. perichordal tube; h. r. liicmal ridge ; h. t. haema
. . tube ; i. c. /. intervertebral > foramen ; n. t. neural tube ; nch.
Of the nerVOUS notochord. The dotted lines indicate the segmentation into
system in front
of the notochord is one of the most striking differences between the
Craniata and Amphioxus, in which, it will be remembered, the
notochord is prolonged to a considerable distance beyond the
anterior end of the nerve-tube.
In the majority of Craniata the notochord is a purely embryonic
structure, and all but the anterior end of it is replaced in the adult
by the vertebral column. The cells of mesoderm surrounding the
notochord become concentrated around the sheath and give rise
to the skeletogenous layer (Fig. 770, sk. I.), some of the cells of which
(sk. c.) may migrate through the elastic membrane into the sheath
itself. In this way the notochord becomes surrounded by a cellular
investment which soon takes on the structure of cartilage, and may
be called the perichordal tube (Fig. 770. p.c.t., and Fig. 771, c.n.t.}.
The skeletogenous layer also grows upwards, and gives rise to an
inverted tunnel of cartilage, the neural tube (n.c., n.t.}, enclosing
the cerebro-spinal cavity and connected below with the perichordal
tube ; and to paired hcemal ridges (h.r.) of cartilage standing out
F 2
72 ZOOLOGY SECT,
from the sides of the perichordal tube into the muscles : in the
region of the tail these unite below to enclose the hcenial canal (li.t.)
already referred to. Actually, however, the vertebral column thus
constituted is from the first more or less broken up into segments,
and in the higher^ forms is replaced by a chain of bones called
vertebrce which follow one another from before backwards, beginning
a short distance behind the anterior end of the notochord and
extending to the extremity of the tail.
A vertebra consists essentially of the following parts : (1) a
centrum or body (Fig. 769, C, en.) lying below the spinal canal in
the position formerly occupied by the notochord and perichordal
tube, and arising either in the skeletogenous layer proper, or in
the notochordal sheath after its invasion by skeletogenous cells ;
(2) a neural arch (n. a.} which springs from the dorsal surface of
the centrum and encircles the spinal canal, representing a segment
of the neural tube ; and (3) a pair of transverse processes (t. p.)
which extend outward from the centrum among the muscles and
represent segments of the hasmal ridges : to them are often attached
ribs which extend downwards in the body-wall, sometimes between
the dorsal and ventral muscles (/), sometimes immediately external
to the peritoneum (r.). In the anterior part of the ventral body-
wall a cartilaginous or bony sternum or breast-bone may be
developed : in the Amphibia it is an independent structure ; in
the higher classes it is formed by the fusion of some of the anterior
ribs in the middle ventral line. In this way the anterior or thoracic
region of the coelome is enclosed in an articulated bony framework
formed of the vertebral column above, the ribs at the sides, and
the sternum below. The ribs under these circumstances become
segmented each into two parts, a dorsal vertebral rib, articulating
with a vertebra, and a ventral sternal rib with the sternum. In the
tail there is frequently a hcemal arch (Fig. 769, D, h. a.) springing
from the ventral aspect of the centrum and enclosing the heomal
canal. Thus the line of centra in the fully-formed vertebral column
occupies the precise position of the notochord ; the neural arches
encircle the spinal portion of the cerebro-spinal cavity ; the trans-
verse processes, ribs, and sternum encircle the coelome ; and the
hsemal arches similarly surround the haemal canal or vestigial
coelome of the tail. As we ascend the series of Craniata we find
every gradation from the persistent notochord of the Cyclostomata,
through the imperfectly differentiated vertebrae of Sharks and
Rays, to the complete bony vertebral column of the higher forms.
The vertebrse are equal in number to the myomeres, but are
arranged alternately with them, the fibrous partition between two
myomeres abutting against the middle of a vertebra, so that each
muscle-segment acts upon two adjacent vertebrse. Thus, the
myomeres being metameric or segmental structures, the vertebras
are intersegmental.
XTTT
PHYLUM CHORDATA
In connection with the anterior end of the notochord, where no
vertebrae are formed, there are developed certain elements of the
skull or cephalic skeleton, a structure which is eminently charac-
teristic of the whole craniate division, and to the possession of
which it owes its name. The skull makes its first appearance in the
embryo in the form of paired cartilaginous plates, the parachordals
(Fig. 772, pc), lying one on each side of the anterior end of the
notochord (nch), and thus continuing forward the line of vertebral
centra. In front of the parachordals are developed a pair of curved
cartilaginous rods, the trabeculce (tr), which underlie the anterior
part of the brain, as the para-
chordals underlie its posterior
part : their hinder ends diverge
so as to embrace the pituitary
body (pty) already referred to.
Cartilaginous investments are
also formed around the organs
of the three higher senses : a
pair of olfactory capsules round
the organs of smell, one of
optic capsules round the organs
of sight, and one of auditory
capsules (au. c.) round the
organs of hearing. The optic
capsule, which may be either
cartilaginous or fibrous, re-
mains free from the remaining
elements of the skull in accord-
ance with the mobility of the
eye ; it constitutes, in fact, the
sclerotic or outer coat of that
organ. The olfactory capsules
are usually formed in relation FIG. 772. — The elements of the cranium in an
,r , V i -i embryo Salmon, from above, au. c. auditory
to tne trabecillae, and are COn- capsule ; nch. notochord ; pc. parachordal ; pty.
rich,
tinuous with those structures
from an early stage. The
auditory capsules in some cases arise as outgrowths of the para-
chordals, in others as independent cartilages, each of which, how-
ever, soon unites with the parachordal of its own side. As
development goes on, the trabeculse and parachordals become fused
into a single "basal plate (Fig. 773, B, b. cr.) underlying the brain:
the skull-floor thus formed gives off vertical up-growths on each
side which finally close in above to a greater or less extent, and so
give rise to a more or less complete cranium or brain-case enclosing
the brain and the organs of smell and hearing, and furnishing open
cavities or orbits for the eyes.
In the continuous solid cranial box thus formed certain definite
74
ZOOLOGY
SECT.
regions are to be distinguished : a posterior or occipital region,
formed from the parachordals, united or articulated with the
anterior end of the vertebral column, and presenting a large
aperture, the foramen magnum (Fig. 773, B, for. mag.), through
which the spinal cord becomes continuous with the brain ; an
auditory region formed by the two outstanding auditory capsules
(A, au. cp.) ; and a trabecular region, including all the rest. The
latter is again divisible into an interorbital region, between the
orbits or eye-sockets ; an olfactory region, constituted by the
olfactory capsules (olf. cp.), and by a median vertical plate, the
mesethmoid (B, m. eth.), which separates them from one another ;
and a pre-nasal region or rostrum (r) extending forwards from the
B
FIG. 773. — A, diagram of cartilaginous skull from the left side ; B, cranium in sagittal section.
au. cp. auditory capsule ; b. br. 1 — -5, basi-branchials ; b. cr. basis cranii ; b. hy. basi-hyal ;
c. br. cerato-branchial ; c. hy. cerato-hyal ; ep. br. epi-branchial ; ep. hy. epi-hyal ; fan. fon-
tanelle ; for. mag. foramen magnum; h. br. hypo-branchial; h. hy. hypo-hyal ; hy. m.
liyomandibular ; Ib. 1—4, labial cartilages ; mclc. c. Meckel's cartilage ; m. eth. mesethmoid ;
no. 1 — 10, foramina for cerebral nerves ; olf. cp. olfactory capsule ; pal. tju. palato-quadrate ;
ph. br. pharyngo-branchial ; r. rostrum ; s. t. pituitary fossa or sella turcica.
mesethmoid and forming a more or less well-marked anterior
prolongation of the cranium. The cavity for the brain (B) extends
from the foramen magnum behind to the olfactory region in front ;
its floor, formed from the basal plate of the embryo, is called the
basis cranii (b. cr.) : its roof is always incomplete, there being one or
more apertures or fontanelles (fon.) closed only by membrane and
due to the imperfect union above of the side-walls.
In the walls of the brain-case are apertures or foramina for
the passage outwards of the cerebral nerves (vide p. 100). The
most important of these are the olfactory foramina (nv. 1) for the
nerves of smell, situated at the anterior end of the cerebral cavity,
xm PHYLUM CHORDATA 75
one on each side of the mesethnioid ; the optic foramina (nv. 2)
for the nerves of sight, in the interorbital region ; the trigeminal
foramina (nv. ~>) for the fifth nerves, just in front of the auditory
capsule ; the auditory foramina (nv. \n. vomer.
(A, PR. OT.) in front, an opisthotic (OP. OT.) behind, and an
epi-otic (EP. OT.) over the arch of the posterior semicircular canal
of the ear (vide infra). In front of the basi-occipital a bone called
the basi-sphenoid (A and C, B. SPH.) is formed in the floor of the
skull : it appears in the position of the posterior ends of the trabe-
culse, and bears on its upper or cranial surface a depression, the sella
turcica (s.t), for the reception of the pituitary body. Connected
on either side with the basi-sphenoid are paired bones, the
all-sphenoids (AL. SPH.), which help to furnish the side- walls of
the interorbital region. The basi-sphenoid is continued forwards
by another median bone, the pre-fiphenoid (A and D, P. SPH.),
with which paired ossifications, the orbito-sphenoids (ORB. SPH),
78 ZOOLOGY SECT
are connected and complete the side-walls of the interorbital region.
The basi-occipital, basi-sphenoid, and pre-sphenoid together form
the basis cranii of the bony skull. A vertical plate of bone, the
mesethmoid (M. ETH.), appears in the posterior portion of the
cartilage of the same name, and the outer walls of the olfactory
capsules may be ossified by paired ecto-ethmoids (E, EC. ETH.).
So far, it will be seen, the cranial cavity has its hinder region
alone roofed over by bone, viz. by the supra-occipital : for the rest
of it the replacing bones furnish floor and side-walls only. This
deficiency is made good by two pairs of investing bones, the
parietals (PA), formed immediately in front of the supra-occipital
and usually articulating below with the ali-sphenoids, and the
f rentals (FR), placed in front of the parietals, and often connected
below with the orbito-sphenoids. A pair of nasals (NA) are
developed above the olfactory capsules and immediately in advance
of the frontals ; and below the base of the skull two important
investing bones make their appearance, the vomer (vo) — which
may be double — in front, and the para-sphenoid (PA. SPH)
behind.
The result of the peculiar arrangement of replacing and invest-
ing bones just described is that the brain-case, in becoming
ossified, acquires a kind of secondary segmentation, being clearly
divisible in the higher groups, and especially in the Mammalia,
into three quasi-segments. These are the occipital segment (B)
formed by the basi-occipital below, the ex-occipitals at the sides,
and the supra-occipital above1 ; the parietal segment (C), formed by
the basi-sphenoid below, the ali-sphenoids laterally, and the parietals
above ; and the frontal segment (D) constituted by the pre-sphenoid
below, the orbito-sphenoids on either side, and the frontals above.
It must be observed that this segmentation of the cranium is quite
independent of the primary segmentation of the head, which is
determined by the presence of myomeres and by the relations of
the cerebral nerves.
The cranial bones have constant relations to the cerebral nerves.
The olfactory nerves (A, Nv. 1) pass out one on either side of the
mesethmoid, the optic nerves (Nv. 2) through or immediately
behind the orbito-sphenoids, the fifth nerves (Nv. 5) through or
immediately behind the ali-sphenoids, and the tenth nerves (Nv. 10}
through or immediately in front of the ex-occipitals.
It will be seen that a clear distinction can be drawn between
the primary cranium or chondrocranium, formed by the fusion of the
parachordals, auditory capsules, and trabeculse, and consisting of an
undivided mass of cartilage more or less replaced by bones, and
the secondary cranium or osteocranium, modified by the super-
addition of investing bones.
1 With the occipital segment in many Fishes are amalgamated one or
several of the most anterior vertebra\
xm
PHYLUM CHORDATA
79
A similar distinction may be drawn between the primary and
secondary jaws. The primary upper jaw, or palato-quadrate,
becomes ossified by three chief replacing bones on each side, the
palatine (A, PAL.) in front, then the pterygoid (PTG.), and the
quadrate (QU.) behind, the latter furnishing the articulation for the
lower jaw or mandible. In the higher classes the primary upper
jaw does not appear as a distinct cartilaginous structure, and the
palatine and pterygoid are developed as investing bones. The
Bas
f
FlQ. 775. — Diagram of three stages in the development of the pelvic fins. In A, the anterior
pterygiophores on the right side (Ttad) have united to form a basal cartilage (Bas.) ; in B the
basalia (Bas) are fully formed and are uniting at * to form the pelvic girdle ; in C the pelvic
girdle (G) is fully constituted, and at t has segmented from the basale on the right sii'e.
Cl. cloacal aperture. (From Wiedersheim's Comparative Anatomy.)
secondary upper jaw is constituted by two pairs of investing bones,
the pre-maxilla (P.MX) and the maxilla (MX), which in bony skulls
furnish the actual anterior boundary of the mouth, the primary jaw
becoming altogether shut out of the gape. The proximal end of
the primary lower jaw ossifies to form a replacing bone, the articular
(ART.), by which the mandible is hinged : the rest of it remains as
a slender, unossified Meckel's cartilage (Mck. C), which may dis-
appear entirely in the adult. The secondary lower jaw is formed by
a variable number of investing bones, the most important of
80
ZOOLOGY
SECT
which is the dentary (DNT). In Mammalia the dentary forms the
entire mandible, and articulates, not with the quadrate, but with
a large investing bone formed external to the latter, and known
as the squamosal (SQ).
\£ In the hyoid arch a replacing bone, the hyo-mindibular (HY. M),
appears in the cartilage of the same name, and ossifications are
also formed in the various segments of the hyoid cornua (EP. HY,
C. HY, H. HY, B. HY) and of the branchial parches (PH. BR,
EP. BR, C. BR, H. BR, B. BR). In the air-breathing forms
both hyoid and branchial arches undergo more^or less complete
atrophy, the whole gill-bearing apparatus becoming reduced mainly
to a small hyoid bone serving for the support of the tongue.
SCP
CL
PU
Flos. 776 and 777. — Diagrams of the fore- and hind-limbs with the limb-girdles, actb. aceta-
bulum ; gl. gleiioid cavity ; p. cor. procoracoid ; I — -V, digits. Replacing bones — en. 1 , en. 2 ,
centralia; COR. coracoid ; dst. 1—5 distalia ; FE. femur ; PI. fibula ; fi. fibulare ; HIT.
humerus ; It. ilium ; int. intermedium ; IS. ischium ; mtcp. 1 5 metacarpals ; mtts.
1 — 5, metatarsals ; ph. phalanges : PU. pubis ; RA- radim : ra. radiate ; SCP. scapula;
TI. tibia ; ti. tibiale ; UL. ulna; ul. ulnare. Investing b:>'i3 — CL. clavicle.
The skeleton of the msdian fins is formed of a single row of
cartilaginous rays or pterygiophores (Fig. 769, G and D.f.r.), lying in
the median plane, and more numerous than the vertebrae. They
may ossify, and may be supplemented by dermil fin-rays, of
varying composition, developed in the derm towards the free
margin of the fin. The latter are clearly exoskeletal structures.
Both pectoral and pelvic fins are supported by pterygiophores
or radialia (Fig. 775, Rid.}, the basal or proximal ends of which are
articulated with stout cartilages, the basalia (Bus), often replaced
by bones, which serve to strengthen the fin at its point of union
with the trunk.
xm PHYLUM CHORDATA 81
In all classes above Fishes the paired fins are, as we have seen,
replaced by five-toed or pentadactyle limbs. These are supported by
bones, probably to be looked upon as greatly modified pterygio-
phores, and obviously serially homologous in the fore- and hind-limbs,
in the proximal division of each limb there is a single rod-like bone,
the humcrus (Fig. 776, HU), or upper-arm-bone, in the fore-limb,
the femur (Fig. 777, FE), or thigh-bone, in the hind-limb. In the
middle division there are two elongated bones, an anterior, the
radius (RA), and a posterior, the ulna (UL), in the fore-limb ; an
anterior, the tibia (TI), and a posterior, the fibula (FI), in the hind-
limb. Next follow the bones of the hand and foot, which are again
divisible into three sets : carpals or wrist-bones, metacarpals (mtcp)
or hand-bones, the phalanges (ph) or finger-bones, in the fore-
limb ; tarsals or ankle-bones, metatarsals (mtts) or foot-bones, and
phalanges (ph) or toe-bones, in the hind-limb. The carpals and
tarsals consist typically of three rows of small nodules of bone or
cartilage, the proximal row containing three, the middle two, and
the distal five elements. The three proximal carpals are called
respectively radiale (ra), intermedium (int), and ulnare (ul), those
of the middle row the first and second centralia (en. 1, en. 2), those
of the third row the five distalia (dst. 1-5), the separate elements
being distinguished by numbers, counting from the anterior or
radial edge of the limb. In the tarsus the bones of the first row
are known respectively as tibiale (ti), intermedium (int), and
f bul ire (fi), those of the second row as centralia (en. 1, en. 2), and
those of the third as distalia (dst. 1-5). The metacarpals
(mtcp. 1-5) and metatarsals (mtts. 1-5) are five rod-like bones,
one articulating with each distale : they are followed by the
phalanges (ph), of which each digit may have from one to five.
The first digit of the fore-limb (Fig. 776, 7) is distinguished as the
pollex or thumb, that of the hind-limb (Fig. 777, I) as the hallux
or great toe ; the fifth digit of each limb ( V) is the minimus.
In connection with the paired appendages are formed supporting
structures called the limb-girdles ; they occur in the portions of the
trunk adjacent to the appendages and serve for the articulation of
the latter. In the embryonic condition they are continuous with
the basalia and are probably to be looked upon as ingrowths of
the primitive fin-skeleton (Fig. 775). The shoulder-girdle or pectoral
arch has primarily the form of paired bars, which may unite in
the middle ventral line so as to form an inverted arch. Each bar—
i.e., each half of the arch — furnishes a concave or convex glenoid
surface (Fig. 776, gl.) for the articulation of the pectoral fin or fore-
limb, and is thereby divided into two portions — a dorsal or
scapular region, above the glenoid surface, and a ventral or coracoid
region below it. The coracoid region is again divisible, in all classes
above Fishes, into two portions : an anterior, the pro-coracoid
(p. cor.), and a posterior, the coracoid proper. Each of these regions
82 ZOOLOGY snot.
commonly ossifies — a replacing bone, the scapula (SCP), appearing
in the scapular region, another, the coracoid (COR), in the coracoid
region, while in relation with the pro-coracoid is formed a bone,
the clavicle (CL), largely or entirely developed independently of
pre-existing cartilage.
The constitution of the hip-girdle, or pelvic arch, is very similar.
It consists originally of paired bars, which may unite in the middle
ventral line, and are divided by the acetabulum (Fig. 777, actb.),
the articular surface for the pelvic fin or hind-limb, into a dorsal
or iliac region, and a ventral or pubo-ischial region, the latter being
again divisible, in all classes above Fishes, into an anterior portion,
or pubis, and a posterior portion, or ischium. Each region is
replaced in the higher forms by a bone, the pelvic girdle thus
consisting of a dorsal ilium (IL) serially homologous with the
scapula, an antero-ventral pubis (PU) with the pro-coracoid and
clavicle, and a postero-ventral ischium (IS) with the coracoid.
The long bones of the limbs are divisible each into a shaft, and
proximal and distal extremities. When ossification takes place the
shaft is converted into a tubular bone, the cartilaginous axis of
which is absorbed and replaced by a vascular fatty tissue called
marrow. The extremities become simply calcified in the lower
forms, but in the higher a distinct centre of ossification may appear
in each, forming the epiphysis, which finally becomes ankylosed to
the shaft.
Digestive Organs. — The enteric canal is divisible into buccal
cavity (Fig. 769, A, buc. c.), pharynx (ph.), gullet, stomach (st.),
and intestine (int.), the latter often communicating with the
exterior by a cloaca (cl.), which receives the urinary and genital
ducts. The buccal cavity is developed from the stomodseum of
the embryo : the proctodeeum gives rise to a very small area in
the neighbourhood of the anus, or, when a cloaca is present, to the
external portion of the latter ; all the rest of the canal is formed
from the mesenteron, and is therefore lined by an epithelium of
endodermal origin. The pharynx communicates with the exterior,
in Fishes and in the embryos of the higher forms, by the gill-slits
(i. br. a, 1-7} ; it communicates with the stomach by the gullet.
The stomach (st.) is usually bent upon itself in the form of a U ; the
intestine (int.) is generally more or less convoluted ; hence the
stomach and intestine are together considerably longer than the
enclosing abdominal cavity. In the embryo the intestine is some-
times continued backwards into the hsemal canal by an extension
called the post-anal gut (p. a. g.), which may perhaps indicate that
the anus has shifted forwards in the course of evolution.
The epithelium of the buccal cavity is usually many-layered,
like that of the skin, of which it is developmentally an in-turned
portion ; the pharynx and gullet have also a laminated epithelium,
xm
PHYLUM CHORDATA
but the rest of the canal is lined by a single layer of cells
underlaid by a layer of connective-tissue, the deeper part of which
is called the sub-mucosa ; epithelium and connective-tissue together
constitute the mucous membrane. The mucous membrane of
the stomach and sometimes of the intestine usually contains
close-set tubular glands ; those of the stomach, the gastric
glands, secrete gastric juice, which acts upon the proteid portions
of the food only ; the secretion of the intestinal glands digests
proteids, starch, and fats. Outside the mucous membrane are
layers of unstriped muscle, usually an internal circular and an
external longitudinal layer. Externally the intra-coalomic portion
of the canal is invested by peritoneum formed of a layer of connective-
B
A
gJT-%
FIG. 778. — A, longitudinal section of a tooth, semi-diagrammatic. PR, pulp-cavity ; PH',
opening of same ; ZB, dentine ; ZC, cement ; ZS, enamel. B, longitudinal section of
developing tooth. Eg, suhmucosa ; DS, dentine ; Ma, invaginated layer of enamel-organ ;
ME, epithelium of mouth ; O, odoutoblasts ; SK, stalk of enamel-organ ; ZK, tooth-papilla.
(From Wiedersheim's Vertebrata.)
tissue next the gut and a single-layered ccelomic epithelium facing
the body-cavity.
In connection with the enteric canal certain very characteristic
structures are developed. In the mucous membrane of the mouth
calcifications in most cases appear and form the teeth, which usually
occur in a row along the ridge of each jaw, but may be developed
on the roof of the mouth, on the tongue, and even in the pharynx.
A tooth is usually formed of three tissues — dentine, enamel, and
cement. The main bulk of the tooth is made up of dentine (Fig. 778,
A, ZB), which occurs under three forms,. Hard dentine consists of
a matrix of animal matter strongly impregnated with lime-salts
and permeated by delicate, more or less parallel, tubules containing
84 ZOOLOGY SEC*.
organic fibrils. Vaso-dentine is permeated with blood-vessels, and
consequently appears red and moist in the fresh condition. Osteo-
dentine approaches bone in its structure and mode of development.
The free surface of the tooth is usually capped by a layer of enamel
(ZS), a dense substance, either structureless or presenting a delicate
fibrillation, containing not more than 3 to 5 per cent, of animal
matter, and being, therefore, the hardest tissue in the body. The
cement (ZC) coats that" portion of the tooth which is embedded in
the tissues of the jaw, and sometimes forms a thin layer over the
enamel ; it has practically the structure of bone. At the inner end
of the tooth there is frequently an aperture (PH') leading into a
cavity (PH) filled in the fresh condition by the tooth-pulp, a sort
of connective-tissue plug abundantly supplied with nerves and blood-
vessels.
In the development of a tooth (Fig. 778, B) the deep layer of the
buccal epithelium becomes invagiiiated and grows inwards into
the sub-mucosa in the form of a narrow cord, the enamel-organ
(SK). The distal end of this enlarges into a flask-like form, and
the bottom of the flask becomes invaginated (Ma) by the growth
of a conical process of the sub-mucosa, the dental papilla (ZK).
Mesoderm cells accumulate on the free surface of the papilla and
form a distinct layer of cells called odontoblasts (0). From these
the dentine is formed in successive layers, which gradually accumu-
late between the layer of odontoblasts and the inner or invaginated
layer of the enamel-organ. The lower, or proximal, part of the
papilla remains uncalcified and forms the tooth-pulp. The enamel
is formed by the deposition of successive layers of calcific matter
from the inner or invaginated layer of the enamel-organ, the cement
by the ossification of the tissue immediately surrounding the papilla.
Thus the tooth is partly of ectodermal, partly of mesodermal origin.
In some Fishes the scales or elements of the dermal exo-
skeleton pass insensibly into the teeth over the ridges of the jaws,
and agree with them in structure, so that there can be no doubt
as to the homology of the two. Teeth are, in fact, to be looked
upon as portions of the exoskeleton which have migrated from
the skin into the buccal cavity, and even into the pharynx, and
have there increased in size and assumed special functions.
The tongue is a muscular elevation of the floor of the mouth,
supported by the basi-hyal, and usually more or less protrusible.
The roof of the buccal cavity in the embryo sends off a pouch, the
pituitary diverticulum (Fig. 769, A, pty. s.), which grows upwards,
and, losing its connection with the mouth, becomes attached to
the ventral surface of the brain as the pituitary body (pty. b.). It
may correspond with the neural gland of Urochorda.
In terrestrial Craniata buccal glands are present, opening by
ducts into the mouth : the most important of these are the racemose
salivary glands which secrete a digestive fluid — saliva, capable of
XIII
PHYLUM CHORDATA
85
converting starch into sugar. There are also two large and highly
characteristic digestive glands in the abdominal cavity, both
developed as outpushings of the intestine, but differing greatly
from one another in their fully developed state, both in outward
appearance and in histological structure : these are the liver and
the pancreas.
The liver (Fig. 769, A, Ir.) is a dark-red organ of relatively
immense size : it not only secretes a digestive juice, the bile, which
has the function of emulsifying fats, but also forms an amyloid
substance caUed glycogen or animal starch, which, after being stored
up in the liver-cells, is restored to the blood in the form of sugar.
The liver is formed of a mass of polyhedral cells (Fig. 779, I.) with
•minute intercellular spaces which receive the bile secreted from
the cells and from which it passes to the ducts (b). The pancreas
(Fig. 769, A, pn.) is a racemose gland, and secretes pancreatic juice
which acts upon pro-
teids, starch, and
fats. The ducts of
both glands usually
open into the anterior
end of the intestine :
that of the liver (b. d.)
generally gives off a
blind offshoot ending
in a capacious dilata-
tion, the gall-bladder
(g. b.) in which the
bile is stored. We
thus have one or
more hepatic ducts
conveying the bile
from the liver and
meeting with a cystic duct from the gall-bladder, while from the
junction a common bile-duct leads into the intestine.
Another . important and characteristic organ in the abdomen of
Craniata is the spleen (spl.), a gland-like organ of variable size
and shape, attached to the stomach by a fold of peritoneum, but
having no duct. It is formed of a pulpy substance containing
numerous red blood-corpuscles, many of them in process of dis-
integration : dispersed through the pulp are masses of leucocytes
which multiply and pass into the veins.
Two other ductless glands are formed in connection with the
enteric canal. The thyroid (thd.) is developed as an outpushing
of the floor of the pharynx which becomes shut off, and forms, in
the adult, a gland-like organ of considerable size. Its final posi-
tion varies considerably in the different classes. It has been com-
pared with the endostyle of Tunicata and of Amphioxus, which, as
VOL. 11 G
779. — Diagram of structure of liver, b. a small branch of
hepatic duct ; b'. its ultimate termination in the intercellular
spaces ; c. blood-capillaries ; I. liver-cells. (From Huxley's
86
ZOOLOGY
SECT.
will be remembered, is an open groove on the ventral side of the
pharynx. This view is supported by the condition of the parts in
the larval Lamprey (see Cyclostomata).
The ihymus is developed from the epithelium of the dorsal ends
of the gill-clefts : in the adult it may take the form of a number
of separate gland-like bodies lying above the gills, or may be
situated in the neck or even in the thorax. The thymus and
thyroid, by virtue of internal secretions which they produce,
and which mingle with the blood, control and modify the
physiological condition of various organs and tissues with which
they have no immediate anatomical connection.
The whole intra-abdominal portion of the enteric canal, as well
as the liver, pancreas, spleen, and, indeed, all the abdominal viscera,
are supported by folds of peritoneum, called by the general name
of mesentery (Fig. 769, C,
mes.) and having the usual
relation to the parietal and
visceral layers of the peri-
toneum.
i.br.n
1'IU. 780. — Diagrammatic horizontal section of the
pharyngeal region of a Craniate : on the left are
shown three gill-pouches (y.p.) with fixed branchial
filaments (br. /.) and separated by inter-branchial
septa (i. br. s.) ; on the right one hemibranch (hm.
br.) and two holobranchs (hi. br.) with free ilia-
ments, covered by an operculum (op). Ectoderm
dotted, endoderm striated, mesoderm evenly
shaded, visceral bars («. b.) black; pfc, pharynx. '
Two kinds of respira-
tory organs are found
in Craniata : water-breath-
ing organs or gills, and air-
breathing organs or lungs.
Gills arise as a series
r • i i r i
OI paired pouches of the
i i • i j
pHarynX WHICH extend
mifwarrlc nr fn wa rrl c +Vm
LtWardS, Or OWarClS W16
surface of the bodv, and
r> n ,1
finally Open On the 6X-
terior by the gill-slits
already noticed. Each gill-pouch thus communicates with the
pharynx by an internal (Fig. 769, B, i. br. a), with the outside
water by an external branchial aperture (e. br. a), and is
separated from its predecessor and from its successor in the
series by stout fibrous partitions, the interbranchial septa
(Fig. 780, i. br. s). The mucous membrane forming the anterior
and posterior walls of the pouches is raised up into a
number of horizontal ridges, the branchial filaments (br.f.), which
are abundantly supplied with blood. A current of water entering
at the mouth passes into the pharynx, thence by the internal
gill-slits into the gill-pouches, and finally makes its way out by the
external gill-slits, bathing the branchial filaments as it goes. The
exchange of carbonic acid for oxygen takes place in the blood-
vessels of the branchial filaments, which are, therefore, the actual
organs of respiration. It will be noticed that the respiratory
xin PHYLUM CHORDATA 87
epithelium is endodermal, being derived from that of the pharynx,
which, as we have seen, is a portion of the mesenteron.
As already mentioned, the walls of the pharynx are supported
by the visceral arches, which surround it like a series of incomplete
hoops, each half-arch or visceral bar being embedded in the inner
or pharyngeal side of an interbranchial septum. Thus the visceral
arches (v. b.) alternate with the gill-pouches, each being related
to the posterior set of filaments of one pouch and the anterior set
of the next. In the higher Fishes, such as the Trout or Cod, the
interbranchial septa become reduced to narrow bars enclosing the
visceral arches (right side of Fig. 780), with the result that a double
set of free branchial filaments springs from each visceral bar and
constitutes what is called a single gill. Thus an entire gill or holo-
branch (hi. br.) is the morphological equivalent of two half -gills—
hemibranchs (hm. br.), or sets of branchial filaments belonging to
the adjacent sides of two consecutive gill-pouches. On the other
hand, a gill-pouch is equivalent to the posterior hemibranch of one
gill and the anterior hemibranch of its immediate successor.
In some Amphibia water-breathing organs of a different kind
are found. These are the external gills : they are developed
as branched outgrowths of the body- wall in immediate relation with
the gill-slits, and differ from the internal gills just described in having
an ectodermal epithelium. They are probably, however, of the same
essential character as the endoderrnal gills (cf. also under Pisces).
Lungs (Fig. 769, A, Ig) are found in all Craniata from the Dipnoi
upwards. They are developed as a hollow outpushing from the
ventral wall of the embryonic fore-gut or anterior part of the
enteric canal ; this passes backwards and upwards, usually
dividing into right and left divisions, and finally coming to lie
in the dorsal region of the ccelome. The inner surface of the single
or double lung thus formed is raised into a more or less complex
network of ridges so as to increase the surface of blood exposed
to the action of the air ; and, in the higher forms, the ridges,
increasing in number and complexity, and uniting with one another
across the lumen of the lung, convert it into a sponge-like structure.
The respiratory epithelium is, of course, endoderrnal. Since the
lungs are blind sacs, some contrivance is necessary for renewing
the air contained in them : this is done either by a process analogous
to swallowing, or by the contraction and relaxation of the muscles
of the trunk.
In some Fishes there occurs, in the position occupied in air-
breathers by the lungs, a structure called the air-bladder, which
contains gas, and serves as an organ of flotation. Like the lungs,
it is developed as an outgrowth of the fore-gut, but, except in
four instances, from its dorsal instead of its ventral side. In
many cases the air-bladder loses its connection with the pharynx
and becomes a closed sac.
VOL n G*
88
ZQOLOGY
SECT.
.
> °
.
~ •«: '3
The blood-vascular system attains a far higher degree
o f complexity
than in any of
the groups pre-
viously studied :
its essential fea-
tures will be best
understood by a
general descrip-
tion of the circu-
latory organs of
Fishes.
The heart ( Figs.
769 and 781) is
a muscular organ
contained in the
pericardial cavity
and composed of
three chambers,
the sinus venosus
(s. v.), the auricle
• . .
a o e
JCJ • " " •
-s. v
te « ft •
•- >_ 'S
">'££'
„• CJ -°
"
fi 3 o _ _.• t-
V '? 8 H . . p,
I M »>^ . ^^
I ° . ^8 «S b ^
tricle (v.), which
form a single
longitudinal
series, the hind-
most, the sinus
venosus, opening
into the auricle,
and the auricle
into the ventricle.
They do not,
however, lie in a
straight line, but
in a zigzag fash-
ion, so that the
sinus and auricle
are dorsal in posi-
tion, the ventricle
ventral. Usually
a fourth chamber,
the conus arterio-
sus (c. art.}, is
added in front of
the ventricle. The
various chambers
are separated
xin
PHYLUM CHORDATA
89
from one another by valvular apertures (Fig. 782) which allow of
the flow of blood in one direction only, viz. from behind forwards—
that is, from sinus to auricle, auricle to ventricle, and ventricle to
conus. The heart is made of striped muscle of a special kind — the
only involuntary muscle in the body having this histological
character — which is particularly thick and strong in the ventricle.
It is lined internally by epithelium and covered externally by
the visceral layer of the pericardium.
Springing from the ventricle, or from the conus when that
chamber is present, and passing directly forwards in the middle line
below the gills, is a large, thick-walled, elastic blood-vessel, the
ventral aorta (Figs. 769, B, and 781. v. ao.}. At its origin,
which may be dilated to form a bulbus aortce, are valves so
lira
hra
FIG. 782. — Diagram illustrating the course of the circulation Li a Fish. Vessels containing
aerated blood red, those containing non-aerated blood blue, lymphatics black. B, capil-
laries of the body generally ; E, of the enteric canal ; G, of the gills ; K, of the kidneys ; L,
of the liver ; T, of the tail. a. br. a. afferent branchial arteries ; au. auricle ; c. a. conns
arteriosus : d. ao. dorsal aorta ; e. br. a. efferent branchial arteries ; h. p. v. hepatic portal
vein ; h. v. hepatic vein ; Ic. lacteals ; ly. lymphatics : pr. cr. v. precaval veins ; r. p. v. renal
portal veins ; s. v. sinus venosus ; v. ventricle ; v. ao. ventral aorta. The arrows sho\v the
direction of the current. (From Parker's Elementary Biology.)
disposed as to allow of the flow of blood in one direction only,
viz. from the ventricle into the aorta. It gives off on each side
a series of half-hoop-like vessels, the afferent branchial arteries
(a. br. a.), one to each gill. These vessels ramify extensively,
and their ultimate branches open into a network of microscopic
tubes or capillaries (Fig. 782, G), having walls formed of a single
layer of epithelial cells, which permeate the connective-tissue layer
of the branchial filaments, and have therefore nothing between
them and the surrounding water but the epithelium of the
filaments. The blood, driven by the contractions of the heart into
the ventral aorta, is pumped into these respiratory capillaries, and
there exchanges its superfluous carbonic acid for oxygen. It then
passes from the capillaries into another set of vessels which join
with one another, like the tributaries of a river, into larger and
larger trunks; finally uniting in each gill, into an efferent branchial
artery (e. br. a.). The efferent arteries of both sides pass upwards
and discharge into a median longitudinal vessel, the dorsal aorta
90 ZOOLOGY SECT.
(d. ao.), situated immediately beneath the notochord or vertebral
column. From this trunk, or from the efferent branchial arteries,
numerous vessels, the systemic arteries, are given off to all parts of
the body, the most important being the carotid arteries (Fig. 781,
c. a.) to the head, the subclavian (scl. a.) to the pectoral fins, the
cceliac (cl. a.) and mesenteric (ms. a.) to the stomach, intestine, liver,
spleen, and pancreas, the renal (r. a.) to the kidneys, the spermatic
(sp. a.) or ovarian to the gonads, and the iliac (il. a.) to the pelvic
fins. After giving off the last the aorta is continued as the caudal
artery (cd. a.) to the end of the tail.
With the exception of the capillaries, all the vessels described
in the preceding paragraph, including the dorsal and ventral
aorta3, are arteries. They are firm, elastic tubes, do not collapse
when empty, usually contain but little blood in the dead animal,
and serve to carry the blood from the heart to the body generally.
The systemic arteries branch and branch again into smaller and
smaller trunks, and finally pour their blood into a capillary network
(Fig. 782, B, K, and T) with which all the tissues of the body,
except epithelium and cartilage, are permeated. In these systemic
capillaries the blood parts with its oxygen and nutrient constituents
to the tissues, and receives from them the various products of
destructive metabolism — carbonic acid, water, and nitrogenous
waste. The systemic, like the respiratory, capillaries are micro-
scopic, and their walls are formed of a single layer of epithelial
cells.
We saw that the respiratory capillaries are in connection with
two sets of vessels, afferent and efferent. The same applies to the
systemic capillaries, with the important difference that their
efferent vessels are not arteries, but thin- walled, non-elastic,
collapsible tubes called veins. They receive the impure blood
from the capillaries, and unite into larger and larger trunks,
finally opening into one or other of the great veins, presently to be
described, by which the blood is returned to the heart. As a
general rule the vein of any part of the body runs parallel to its
artery, from which it is at once distinguished by its wider calibre,
by its dark colour— due to the contained bluish-purple blood seen
through its thin walls, by being gorged with blood after death, by
the complete collapse of its walls when empty, and by its usually
containing valves. In some cases the veins become dilated into
spacious cavities called sinuses ; but sinuses without proper walls,
such as occur in many Invertebrates, are never found in the
Craniata.
The veins from the head join to form large, paired jugular veins
(Fig. 781, j. v.) which pass backwards, one on each side of the head,
and are joined by the cardinal veins (crd. v.) coming from the trunk,
each jugular uniting with the corresponding cardinal to form a large
precavalvein (pr. cv. v.) which passes directly downwards and enters
xra PHYLUM CHORDATA 91
the sinus venosus. The blood from the tail returns by a caudal
vein (cd. v.), lying immediately below the caudal artery in the
hsemal canal of the caudal vertebrae (Fig. 769, Z>). *0n reaching
the ccelome the caudal vein forks horizontally, and the two
branches either become directly continuous with the cardinals
or pass one to each kidney under the name of the renal portal
veins (Fig. 781, r. p. v.). In the kidneys they break up into
capillaries (Fig. 782, K), their blood mingling with that brought
by the renal arteries and being finally discharged into the
cardinals by the renal veins (Fig. 781, r.v. ). Thus the blood from
the tail may either return directly to the heart in the normal
manner or may go by way of the capillaries of the kidneys.
In the latter case there is said to be a renal portal system, the
essential characteristic of which is that the kidney has a double
blood-supply, one of pure blood from the renal artery, and one of
impure blood from the renal portal vein ; in other words, it has
two afferent vessels, an artery and a vein, and the latter is further
distinguished by the fact that it both begins and ends in
capillaries instead of beginning in capillaries and ending in a vein
of higher order.
The blood from the gonads is returned to the cardinals by
veins called spermatic (sp. v.) in the male, ovarian in the female.
That from the paired fins takes, in what appears to be the most
typical case, a somewhat curious course. On each side of the
body there is a lateral vein (lat. v.), running in the body- wall and
following the course of the embryonic ridge between the pectoral
and pelvic fins. It receives, anteriorly, a subclavian vein (scl. v.)
from the pectoral fin, and posteriorly an iliac vein (il. v.) from the
pelvic fin, and in front pours its blood into the precaval.
The veins from the stomach, intestine, spleen, and pancreas join
to form a large hepatic portal vein (h. p. v.), which passes to the
liver and there breaks up into capillaries, its blood mingling with
that brought to the liver by the hepatic artery (h. a.), a branch of
the cceliac. Thus the liver has a double blood-supply, receiving
oxygenated blood by the hepatic artery, and non-oxygenated but
food-laden blood by the hepatic portal vein (Fig. 782, L). In
this way wre have a hepatic portal system resembling the renal
portal system both in the double blood-supply, and in the fact
that the afferent vein terminates, as it originates, in capillaries.
After circulating through the liver the blood is poured, by hepatic
veins (h. v.), into the sinus venosus. The hepatic, unlike the renal
portal system, is of universal occurrence in the Craniata.
In the embryo there is a sub-intestinal vein, corresponding with
that of Amphioxus, and lying beneath the intestine and the post-
anal gut. Its posterior portion becomes the caudal vein of the
adult, its anterior portion one of the factors of the hepatic portal
vein.
92
ZOOLOGY
SECT.
^
To sum up : — The circulatory organs of the branchiate Craniata
consist of (a) a muscular organ of propulsion, the heart, provided
with valves and driving the blood into (6) a set of thick-walled,
elastic, afferent vessels, the arteries, from which it passes into (c) a
network of microscopic vessels
or capillaries which permeate
the tissues, supplying them with
oxygen and nutrient matters and
receiving from them carbonic
acid and other waste products :
from the capillary network the
blood is carried off by (d) the
veins, thin-walled, non-elastic
tubes by which it is returned
to the heart. Thus the general
scheme of the circulation is
simple: the arteries spring from
the heart, or from arteries of a
higher order, and end in capil-
laries ; the veins begin in capil-
laries and end in vessels of a
higher order or in the heart.
Actually, however, the system
is complicated (a) by the inter-
position of the gills in the course
of the outgoing current, as a
result of which we have arteries
serving as both afferent and
efferent vessels of the respira-
tory capillaries, the efferent
arteries taking their origin in
those capillaries after the manner
of veins ; and (6) by the inter-
position of two important blood-
purifying organs, the liver and
the kidney, in the course of the
returning current, as a result of
which we have veins acting as
both afferent and efferent vessels
of the hepatic and renal
capillaries, the afferent vessels
ciefts ; RA, S, S1. roots of dorsal aorta ; Sb. of both Organs ending in
subclavian arteries ; Sb1. subclavian veins ; .,, . j..0 , 1 F i • r
V. ventricle ; VC. jugular vein ; Vm. vitelline Capillaries alter the lasmon OI
veins. (From Wiedersheiin's Vertebrata.)
-All
-Acd
FIG. 783. — Diagram of the vascular system in
the embryo°of an air-breathing Craniate.
A. dorsal aorta and auricle ; Ab. aortic arches ;
Acd. caudal artery ; All. allautoic arteries ;
Am. vitelline arteries ; B. ventral aorta ; c, c1.
carotid arteries ; D. precaval veins ; Ic, E.
iliac arteries ; HC. cardinal veins ; KL. gill-
RA, S, S1. roots of dorsal aorta ; Sb.
In the embryos of the higher, or air-breathing, Craniata, the
circulatory organs agree in essentials with the above description, the
most important difference being that, as no gills are present, the
xra PHYLUM CHORDATA 93
branches of the ventral aorta do not break up into capillaries, but
pass directly into the dorsal aorta, forming the aortic arches (Fig. 783,
Ab.). With the appearance of the lungs, however, a very funda-
mental change occurs in the blood-system. The last aortic arch of
each side gives off a pulmonary artery (Fig. 784, Ap.) to the corres-
ponding lung, and the blood, after circulating through the capil-
laries of that organ, is returned by a pulmonary vein (lr.), not
into an ordinary systemic vein of higher order, but into the heart
directly : there it enters the left side of the auricle, in which
a vertical partition is developed, separating a left auricle (A1),
which receives the aerated blood from the lungs, from a right
auricle (A), into which is poured the impure blood of the sinus
venosus. Lastly, in Crocodiles, Birds, and Mammals (B) the
ventricle also becomes divided into right and left chambers, and we
get a four-chambered heart, having right and left auricles and right
and left ventricles : at the same time the conus arteriosus and sinus
FIG. 781.—
venosus cease to exist as distinct chambers. The left auricle receives
aerated blood from the lungs and passes it into the left ventricle,
whence it is propelled through the system : the right auricle receives
impure blood from the system, and passes it into the right ventricle
to be pumped into the lungs for aeration. Thus the four-chambered
heart of the higher Vertebrata is quite a different thing from that
of a Fish : in the latter the four chambers — sinus venosus, auricle,
ventricle, and conus arteriosus — form a single longitudinal series,
whereas in a Mammal, for instance, the four chambers constitute
practically a double heart, there being no direct communication
between the auricle and ventricle of the right side, or respiratory
heart, and those of the left side, or systemic heart. The modifications
undergone by the arteries and veins in the higher Vertebrata will be
best considered under the various classes.
It will be noticed that there is a sort of rough correspondence
VOL. IT G**
94
ZOOLOGY
SECT.
between the blood-vessels of Craniata and those of the higher
Worms. The sub-intestinal vein, heart, and ventral aorta together
form a ventral vessel, the dorsal aorta a dorsal vessel, and the aortic
arches transverse or commissural vessels. The heart might thus be
looked upon as a portion of an original ventral vessel, which has
acquired strongly muscular walls, and performs the whole function
of propelling the blood. But in making such a comparison it
has to be borne in mind that the direction of the current of the
blood in the Craniata is exactly the opposite of that in the
Annulata.
The blood of Craniata is always red, and is specially distinguished
by the fact that the haemoglobin to which it owes its colour is not
dissolved in the plasma as in most red-blooded Invertebrates, but
is confined to certain cells called red blood-corpuscles (Fig. 785),
which occur floating in the plasma in addition to, and in far greater
numbers than, the leucocytes. They usually have the form of
flat oval discs (A), the centre bulged out by a large nucleus (nu.),
but in Mammals (B) they are bi-concave, non-nucleated, and
usually circular. The fed corpuscles do not perform amoeboid
movements.
The colour of the blood varies
I with the amount of oxygen taken
Ij up by the haemoglobin. When
thoroughly aerated it is of a bright
FIG. 785.-Surface and edge views of red scarletcolour, butassumesabluish-
blood-corpuscles of Fro£ (A) and Man purple llUC after giving Up its
(From Parkers
B
(B). nu. nucleus.
Biology.)
Owing to
oxygen to the tissues.
the fact that oxygenated blood is
usually found in arteries, it is often spoken of as arterial blood,
while the non-oxygenated, purple blood, being usually found in
veins, is called venous. But it must not be forgotten that an
artery, e.g., the ventral aorta or the pulmonary artery, may contain
venous blood, and a vein, e.g., the pulmonary vein, arterial blood.
The distinction between the two classes of vessels does not depend
upon their contents, but upon their relations to the heart and the
capillaries.
In addition to the blood-vessels the circulatory system of
Craniata contains lymph-vessels or lymphatics (Fig. 782, ly.}. In
most of the tissues there is a network of lymph-capillaries, inter-
woven with, but quite independent of, the blood-capillaries. From
this network lymphatic vessels pass off, and finally discharge
their contents into one or other of the veins. Many of the
lower Craniata possess spacious lymph-sinuses surrounding the
blood-vessels ; and there are communications between the lym-
phatics and the coalome by means of minute apertures or stomata.
The lymphatics contain a fluid called lymph, which is to all intents
and purposes blood minus its red corpuscles. The lymph-plasma
PHYTATM CHORDATA
consists of the drainage from the tissues : it makes its way into
the lymph capillaries, and thence into the lymphatics, which are
all efferent vessels, conveying the fluid from the capillaries to the
veins. Leucocytes are added to the plasma in bodies called
lymphatic glands, which occur in the course of the vessels. Valves
may be present to prevent any flow of lymph towards the
capillaries, and in some cases the flow of the fluid is assisted by
lymph-hearts, muscular dilatations in the course of certain of the
vessels. The lymphatics of the intestine have an important
function in the absorption of fats, and are known as lacteals (lc.).
The nervous
system attains a
complexity, both
anatomical and his-
tological, unknown
in the rest of the
animal kingdom. It
arises, as in other
Chordata, from a
dorsal medullary
groove the edges of
which unite and en-
close a tube. From
the ectoderm lining
the tube the whole
central nervous
system, or neuron,
is formed ; its lumen
forms the neurocoele
or characteristic
axial cavity of the
neuron. So far the
agreement with the
lower Chordata is
complete, but a fun-
damental advance is
seen in the fact that
at an early period—
before the closure of the medullary groove— the anterior end of
the neuron undergoes a marked dilatation and forms the rudiment
of the brain, the rest becoming the spinal cord. Moreover, as growth
goes on, a space appears in the mesoderm immediately surrounding
the nervous system, and forms the neural or cerebro-spinal cavity
already referred to (Fig. 769, c.s.c.), so that the neuron, instead of
being solidly imbedded in mesoderm, lies in a well-marked and
often spacious tube enclosed by the neural arches of the vertebrae,
and in front by the cranium (Fig. 769, B-D).
78G. — Transverse section of spinal cord. J, ventral
fissure ; 2, dorsal fissure ; 3, central canal ; 4, 5, bridges
connecting grey matter of right and left sides ; 6, 7, 8,
white matter ; 9, dorsal root of spinal nerve ; 10 ventral
root, a, b. dorsal horn of grey matter ; c. Clarke's column ;
e. ventral horn. (From Huxley's
96 ZOOLOGY SECT.
The spinal cord (Fig. 786) is a thick-walled cylinder, con-
tinuous in front with the brain. It is traversed from end
to end by a narrow central canal (3), lined by ciliated epithelium
derived from the superficial layer of in-turned ectoderm cells.
The dorsal surface of the cord is marked by a deep, narrow, longi-
tudinal cleft, the dorsal fissure (2), the ventral surface is similarly
scored by a groove, the ventral fissure (1) ; owing to the presence of
these fissures a transverse section presents two almost semi-
circular halves with their straight edges applied to one another
and joined in the middle by a narrow bridge (4, 5} in which the
central canal lies.
The cord is made up of two kinds of tissue. Surrounding the
central canal and having a somewhat butterfly-shaped transverse
section, is the grey matter (a. e) consisting of delicate, inter-twined,
non-medullated nerve-fibres, amongst which are numerous nerve-
cells. The superficial portion is composed of medullated nerve-fibres
running longitudinally, and is called the white matter (6, 7, 8). In
both grey and white matter the nervous elements are supported
by a non-nervous tissue called neuroglia, formed of branched cells.
From the cord the spinal nerves are given off. They arise in
pairs from the sides of the cord, and agree in number with the
myomeres. Each nerve arises from the cord by two roots, a
dorsal and a ventral. The dorsal root (Fig. 788, d. r.) is distin-
guished by the presence of a ganglion (gn. d.r.) containing nerve-cells,
and its fibres are almost exclusively afferent, conveying impulses
from the various parts and organs of the body to the central
nervous system ; the ventral root (v. r.) is not ganglionated, and
its fibres are efferent, conveying impulses from the neuron outwards.
Each root arises from one of the horns of the grey matter, and
the two mingle to form the trunk (sp. 1-3) of the nerve, which
emerges from the spinal canal usually between the arches of
adjacent vertebrae. Soon after its emergence it divides into two
chief divisions, dorsal (d.) and ventral (sp. 1, &c.). The spinal
nerves supply the muscles and skin of the trunk and limbs, and
are therefore spoken of &s somatic nerves. Frequently groups of
nerves unite with one another to form more or less complex net-
works called plexuses.
Closely associated with the spinal are the sympathetic nerves
(Fig. 788, sym.}. They take the form of paired longitudinal cords
with ganglia (sym. gn.} at intervals, lying one on each side of the
aorta in the dorsal wall of the ccelome. They contain both
afferent and efferent fibres, the afferent derived from the dorsal,
the efferent from the ventral roots of the spinal nerves, and both
traceable, through those roots, into the grey matter of the cord.
The sympathetic nerves supply the enteric canal and its glands,
the heart, blood-vessels, &c., and are therefore denominated
splanchnic nerves.
xra PHYLUM CHORDATA 97
As already mentioned, the anterior end of the nervous system
undergoes, at a very early period, a marked dilatation, and is
distinguished as the brain (Fig. 787). Constrictions appear in the
dilated part and divide it into three bulb-like swellings or vesicles,
the fore-brain (A, f. b.), mid-brain (m. b.) and hind-brain (h. b.).
Soon a hollow outpushing grows forwards from the first vesicle
(B, prs. en), and the third gives off a similar hollow outgrowth
(cblm.) from its dorsal surface. The brain now consists of five
divisions : the prosencephalon (prs. en.) and the diencephalon (dien.),
derived from the fore-brain : the mid-brain or mesencephalon
(m. b.) which remains unaltered : the epencephalon or cerebellum
(cblm.), and the metencephalon or medulla oblongata (med. obi.),
derived from the hind-brain.1 Additional constrictions appear in
the medulla oblongata giving it a segmented appearance, but they
disappear as development proceeds, and, whatever may be their
significance, have nothing to do with the main divisions of the
adult organ. The original cavity of the brain becomes corre-
spondingly divided into a series of chambers or ventricles, all
communicating with one another and called respectively the
fore-ventricle or prosoccele, third ventricle or diaccele, mid-ventricle or
mesoco3le, cerebellar ventricle or epicosle, and fourth ventricle or
metaccele.
In some Fishes the brain consists throughout life of these five
divisions only, but in most cases the prosencephalon grows out
into paired lobes, the right and left cerebral hemispheres or
parencephala (I-L, c.h.), each containing a cavity, the lateral
ventricle or paraccele (pa. cce.) which communicates with the diaccele
(di. cce.) by a narrow passage, the foramen of Monro (f. m.).
Moreover, each hemisphere gives off a forward prolongation, the
olfactory bulb or rhinencephalon (olf. I.), containing an olfactory
ventricle or rhinoccele (rh. cos.) : when there is an undivided prosen-
cephalon, the olfactory bulbs (C, D, olf. I.) spring from it. In the
embryo of some forms there is a median unpaired olfactory bulb,
like that of Amphioxus. The part of the cerebral hemisphere
with which the olfactory bulb is immediately related is the olfactory
lobe.
The brain undergoes further complications by the unequal
thickening of its walls. In the medulla oblongata the floor becomes
greatly thickened (D, H, K), while the roof remains thin, con-
sisting of a single layer of epithelial cells, assuming the character
therefore of a purely non-nervous epithelial layer (ependyme). In
the cerebellum the thickening takes place to such an extent that
the epiccele is usually obliterated altogether. In the mid-brain
the ventral wall is thickened in the form of two longitudinal
bands, the crura cerebri (cr. crb.), the dorsal wall in the form of
1 The prosencephalon is sometimes called the telencephalon, the epen-
cephalon the. metencephalon, and the metencephalon the myelencephalon.
98
ZOOLOGY
SECT.
xm PHYLUM CHORDATA 99
paired oval swellings, the optic lobes (opt. I.) : extensions of the
mesocoele into the latter form the optic ventricles or optocceles
(G. opt. cos.) : the median portion of the mesocoele is then called
the iter (I) or aqueduct of Sylvius. In the diencephalon the sides
become thickened, forming paired masses, the optic thalami (D,
F, L, o. th.), the roof remains for the most part in the condition
of a thin membrane (ependyme) composed of a single layer of cells,
but part of it gives rise to a very peculiar adjunct of the brain, the
pineal apparatus. This originates as an outgrowth which consists
typically of two narrow diverticula, one in front of the other, the
anterior being the parietal organ, the posterior the pineal organ or
epipliysis : these two parts may be developed independently, or
the latter may originate by outgrowth from the former. The
parietal organ in the Lampreys and some Reptiles develops an
eye-like organ, the pineal eye (pn. e.) at its extremity, but is vestigial
or absent in most other Vertebrates. The epiphysis is eye-like
(parapineal eye) only in the Lampreys ; in other Vertebrates it is
represented by a gland-like structure, the pineal body (pn, b.),
connected by a hollow or solid stalk with the roof of the diencephalon.
The term parapliysis is applied to a non-nervous outgrowth of
the roof of the fore-brain developed in front of the epiphysis in
the hinder region of the prosencephalon.1 The floor of the dien-
cephalon grows downwards into a funnel-like prolongation, the
infundibulum (inf.) : with this the pituitary diverticulum of the
pharynx (p. 84) comes into relation, and there is formed, partly
from the dilated end of the diverticulum, partly from the extremity
of the infundibulum, a gland-like structure, the pituitary body or
hypophysis (pt.), always situated immediately in front of the
anterior extremity of the notochord and between the diverging
posterior ends of the trabeculae. The hypophysis in higher Craniates
appears to be of the nature of a ductless, internally secreting gland.
In lower Craniata it consists of two distinct glandular parts, the
one (saccus vasculosus) situated more dorsally and formed as an
outgrowth of the infundibulum, the other (hypophysis proper)
ventral and arising from the pharyngeal diverticulum. In cases
where cerebral hemispheres are not developed, the roof or pallium
of the undivided fore-brain is reduced to a layer of epithelium
(D and E. pal.), its floor is thickened so as to form large paired
masses, the corpora striata (c. s.). When hemispheres are developed
the corpora striata form the floors of the two lateral ventricles
(L, c. s.), and the roof (pallium) of each is formed of nervous tissue.
In such cases the front wall of the diencephalon remains very thin,
and is distinguished as the lamina terminalis (I. t.) : this is the
actual anterior extremity of the central nervous system, the cerebral
hemispheres being lateral outgrowths.
In the preceding description the brain has been described as if its
1 The so-called " parapliysis " of Mammals is not homologous with this.
100 ZOOLOGY SECT.
parts were in one horizontal plane ; but, as a matter of fact, at a
very early period of development the anterior part becomes bent
down over the end of the notochord, so that the whole organ
assumes a retort-shape, the axis of the fore-brain being strongly
inclined to that of the hind-brain. The bend is known as the
cerebral flexure : it is really permanent, but, as the hemispheres
grow forward parallel to the hind-brain and the floor of the mid-
and hind-brain thickens, it becomes obscure, and is not noticeable
in the adult.
The brain, like the spinal cord, is composed of grey and white
matter, but the grey matter either forms a thin superficial layer
or cortex, as in the hemispheres and cerebellum, or occurs as gang-
lionic masses surrounded by white matter.
The whole cerebro-spinal cavity is lined with a tough membrane,
the dura mater, and both brain and spinal cord are covered by a
more delicate investment, the pia mater : the space between the
two contains a serous fluid. In the higher forms there is a delicate
arachnoid membrane outside the pia, and in many cases the regions
of the pia in immediate contact with the thin epithelial roofs of
the diencephalon and medulla become greatly thickened and very
vascular, forming in each case what is known as a choroid plexus.
From the brain are given off cerebral or cranial nerves : these,
like the spinal nerves, are paired, but unlike them, are strictly
limited in number, the number being constant, at least within
very narrow limits : there are typically ten pairs in Fishes and
Amphibians, twelve in Reptiles, Birds, and Mammals.1
The first or olfactory nerve (Fig. 788, I.) is rather a large number of
fibres than a single nerve ; it arises from the olfactory bulb, and
supplies the organ of smell, i.e., the epithelium of the olfactory sac
(see below). It is therefore a purely sensory nerve.
The second or optic nerve (II.) arises from the ventral region of
the diencephalon, just in front of the infundibulum. It differs
from all the other nerves in being originally a hollow outpushing
of the brain, containing a prolongation of the diaccele (see Fig. 795).
It supplies the retina or actual organ of light, and is therefore a
purely sensory nerve.
The third or oculomotor nerve (III.) arises from the crus cerebri
or ventral region of the mid-brain. In its course is a ganglion, the
oculomotor or ciliary ganglion (c. gn.}. It supplies four out of the
six muscles -of the eye-ball (see below, Fig. 796), viz., the superior,
inferior, and internal recti, and the inferior oblique, as well as the
ciliary muscles and muscles of the iris in the interior of the eye.
It is therefore a purely motor nerve.
1 In ma:iy Fishes a pair of very small nerves — the nervi terminales — are
given off from the cerebral hemispheres and run forward to the olfactory sacs :
they seem to be the nerves of ordinary sensatinn for these organs. Repre-
sentatives of these nerves have also been described in higher forms.
xm
PHYLUM CHORDATA
101
The fourth or trochlear nerve (Figs. 788, IV, and 796, IV.) arises from
the dorsal surface of the brain at the junction of the mid-brain
with the medulla oblongata. It is a very small and purely motor
nerve, supplying only the superior oblique muscle of the eye.
The fifth or trigeminal nerve (Fig. 788, V.) is of great size and
wide distribution. It arises from the side of the medulla, fre-
quently by two roots, a dorsal and a ventral, thus resembling in
its origin a spinal nerve. Near its origin it enters a ganglion, the
trigeminal or Gasserian ganglion (g. gn.), which maybe incompletely
divided into two parts, an antero-dorsal and a postero-ventral.
The trunk of the nerve early divides into two principal branches,
the ophthalmic and the mandibular (V. md.) : the latter sends off a
maxillary nerve (V. mx.), and we thus get the three divisions to
which the name trigeminal is due. The ophthalmic nerve frequently
. the right, a — d, fibrous supporting structures ; gr. gr' . granular layers ; n.c., n c'
n.c ., n.c . nerve-cells ; nu. nuclear layer of rods and cones ; o. n. fibres of optic nerve •'
r. rods and cones. (From Wiedersheim's Vertebrata, after Stohr.)
by a circular or slit-like aperture, the pupil, which, in the entire
eye, appears like a black spot in the middle of the coloured portion.
Except in Fishes, the pupil can be enlarged by the action of a set
of radiating unstriped muscle-fibres contained in the iris, and con-
tracted by a set of circular fibres ; and the anterior or outer portion
of the choroid, where it joins the iris, is thrown into radiating folds,
the ciliary processes (C. P.), containing unstriped muscular fibres,'
the ciliary muscle.
Lining the choroid and forming the innermost coat of the eye is
a delicate semi-transparent membrane, the retina (R.), covered on
108 ZOOLOGY SECT.
its outer or choroidal surface with a layer of black pigment (P. E.).
It extends as far as the outer ends of the ciliary processes, where
it appears to end in a wavy line, the ora serrata (o. s.) : actually,
however, it is continued as a very delicate membrane (p. c. R.) over
the ciliary processes and the posterior face of the iris. The optic
nerve (O.N.) pierces the sclerotic and choroid and becomes con-
tinuous with the retina, its fibres spreading over the inner surface
of the latter. Microscopic examination shows that these fibres,
which form the innermost layer of the retina (Fig. 794, o. n.), turn
outwards and become connected with a layer of nerve-cells (n. c.).
External to these come other layers of nerve-cells and granules,
supported by a framework of delicate fibres, and finally, forming
the outer surface of the retina proper, a layer of bodies which
correspond to modified sensory cells and are called, from their
shape, the rods and cones (r.). These are placed perpendicularly
to the surface of the retina, and their outer ends are imbedded in
a single layer of hexagonal pigment-cells, loaded with granules of
the black pigment already referred to.
Immediately behind and in close contact with the iris is the
transparent biconvex lens (Fig. 793, L.), formed of concentric layers
of fibres, each derived from a single cell. The lens is enclosed in
a delicate capsule, attached by a suspensory ligament (sp. I.) to the
ciliary processes. The suspensory ligament exerts a pull upon the
elastic lens so as to render it less convex than when left to itself ;
when the ciliary muscles contract they draw the suspensory ligament
towards the iris, relaxing the ligament and allowing the lens to
assume, more or less completely, its normal curvature. It is in
this way that the accommodation of the eye to near and distant
objects is effected.
The space between the cornea in front and the iris and lens
behind is called the aqueous cJiamber of the eye, and is filled by a
watery fluid — the aqueous humour. The main cavity of the eye,
bounded in front by the lens and the ciliary processes and for the
rest of its extent by the retina, is called the vitreous chamber, and
is filled by a gelatinous substance, the vitreous humour (V. H.).
The cornea, aqueous humour, lens, and vitreous humour together
constitute the dioptric apparatus of the eye, and serve to focus the
rays of light from external objects on the retina. The iris is the
diaphragm by which the amount of light entering the eye is regu-
lated. The percipient portion or actual organ of sight is the retina,
or, more strictly, the layer of rods and cones. The great peculiarity
of the vertebrate eye, as compared with that of a Cephalopod
(Vol. I, p. 750), to which it bears a close superficial resemblance,
is that the sensory cells form the outer instead of the inner layer
of the retina, so that the rays of light have to penetrate the remaining
layers before affecting them.
The mode of development of the eye is as characteristic as its
xin
PHYLUM CHORDATA
109
trtvl, —
structure. At an early stage of development a hollow outgrowth -
the optic vesicle (Fig. 795, A, opt. v.) — is given off from each side of
the fore-brain (dien.). It extends towards the side of the head,
where it meets with an inpushing of the ectoderm (inv. I.} which
deepens and forms a pouch, and finally, separating from the ecto-
derm, a closed sac (B, I.) with a very small cavity and thick walls.
This sac is the rudiment of the lens : as it enlarges it pushes against
the optic vesicle, and causes it to become invaginated (B) ; the
single-layered optic vesicle thus becomes converted into a two-
layered optic cup (opt. c., opt. c'.), its cavity, originally continuous
with the diacoele, becoming obliterated. The invagination of the
vesicle to form the cup does not take place symmetrically, but
obliquely from the external (posterior) and ventral aspect of the
vesicle, so that the optic cup is incomplete along one side where
there is a cleft — the choroid fissure — afterwards more or less com-
pletely closed by
the union of its - °P?-C'
edges. The outer
layer of the optic
cup becomes the
pigmentary layer
of the retina : from
its inner layer the
rest of that mem-
brane, including the
rods and cones, is
formed. The stalk
of the optic cup
occupies, in the
embryonic eye, the
place of the optic
nerve, but the actual fibres of the nerve are formed as backward
growths from the nerve-cells of the retina to the brain.
During the formation of the lens, mesoderm grows in between
the pouch from which it arises and the external ectoderm ; from
this the main substance of the cornea and its inner or posterior
epithelium are formed, the adjacent ectoderm becoming the external
epithelium. Mesoderm also makes its way into the optic cup,
through the choroid fissure, and becomes the vitreous humour.
Lastly, the mesoderm immediately surrounding the optic cup is
differentiated to form the choroid, the iris, and the sclerotic.
Thus the paired eye of Vertebrates has a threefold origin : the
sclerotic, choroid, iris, vitreous, and the greater part of the cornea
are mesodermal : the lens and external epithelium of the cornea
are derived from the ectoderm of the head : the retina and optic
nerve are developed from a hollow pouch of the brain, and are
therefore, in their ultimate origin, ectoderrnal. The sensory cells
Oflt.1l
FIG. 795. — Early (A) and later (B) stages in the development
of the eye of a Craniate, dien. diencephalon ; inv. I.
invagination of ectoderm to form lens ; I. lens ; opt. c. outer,
and opt. c'. inner layer of optic cup ; opt. st. optic stalk ;
opt. v. optic vesicle ; ph. pharynx ; pty. pituitary body .
(Altered from Marshall.)
110
ZOOLOGY
SECT.
or*
of the retina — the rods and cones, although not directly formed from
the external ectoderm, as in Invertebrates, aie ultimately traceable
into the superficial layer of ectoderm, since they are developed from
the inner layer of the optic vesicle, which is a prolongation of the
inner layer of the brain, and the latter is continuous before the
closure of the medullary groove with the ectoderm covering the
general surface of the body.
The eye-ball is moved by six muscles (Fig. 796). Four of these
arise from the inner wall of the orbit, and pass, diverging as they
go, to their insertion round the equator of the eye. One of them
is dorsal in position, and is called the superior rectus (s. r.), a second
ventral, the inferior rectus (in. r.), a third anterior, the anterior
or internal rectus (i. r.), and a fourth posterior, the posterior or
external rectus (e. r.}. The usual names (internal and external) of
the two last-named muscles originate from their position in Man,
where, owing to the eye looking forwards instead of outwards, its
anterior surface becomes in-
ternal, its posterior surface ex-
ternal. The two remaining
muscles usually arise from the
anterior region of the orbit,
and are inserted respectively
into the dorsal and ventral
surface of the eye-ball. They
are the. superior (s. o.) and
inferior oblique (i. o.) muscles.
The median or pineal eye (Fig.
797) is formed, in certain
cases, from the distal end of
FIG. TOG.— Muscles and nerves of the eye of the parietal organ already men-
a Skate (semi-diagrammatic). 111. oculo- finnpr) Tf V,oq fUp fnrrn nf a
motor nerve; IV. trochlear ; VI. abducent. ™OHea-
e. r. posterior rectus ; i. o. inferior oblique ; rounded Capsule, the Outer Or
in. r. inferior rectus; t. r. anterior rectus; Jr. . , ,, ,
or. wall of orbit ; s. o. superior oblique ; s. r. anterior portion Ot the Wall OI
which is a lens (I) formed of
elongated cells, while its posterior portion has the character of a
retina (M, r). The latter has a layer of nerve-fibres on its outer
and one of rod-like visual elements (r.) on its inner surface : it
thus agrees with the usual types of Invertebrate retina, and not
with that of the paired eye.
The organ of hearing, like that of sight, presents quite peculiar
features. It arises in the embryo as a paired invagination of the
ectoderm in the region of the hind-brain, a shallow depression being
formed which deepens and becomes flask-shaped, and finally, as
a rule, loses its connection with the external ectoderm, forming a
closed sac surrounded by mesoderm. At first simple, it soon
becomes divided by a constriction into dorsal and ventral compart-
ments. The dorsal compartment is differentiated into an irregular
e..r
XIII
PHYLUM CHORDATA
111
I
h
r
M
chamber, the utriculus (Fig. 798, u.), and, usually, three tubes,
the semicircular canals. Of these two, the anterior (ca.) and
posterior (cp.) canals, are vertical in position and have their adjacent
limbs united, so that the two canals have only three openings
between them into the utriculus : the third or external canal (ce.)
is horizontal, and opens into the utriculus at either end. Each
canal is dilated at one of its ends into an ampulla (aa., ae, ap.),
placed anteriorly in the anterior and external canals, posteriorly
in the posterior
canal. . . ' ' , ''/,,'.
The ventral
compartment o f
the auditory sac is
called the sacculus
(s.) : it gives off
posteriorly a blind
pouch, the cochlea
(I.), which attains
considerable di-
mensions in the
higher classes ;
while from its inner
face is given off a
narrow tube, the
endolympliatic duct
(de.), which either
ends blindly or
opens on the dor-
sal surface of the
head. The utricle
and saccule are
sometimes im-
perfectly differen-
tiated, and are
then spoken of
together as the
membranous vesti-
bule.
Patches of sensory cells (Fig. 799, ae.) — elongated cells produced
into hair-like processes (a. h.) — occur in the ampulla and in the
utricle and saccule : they are known as maculce acusticce and cristce
acusticce (c. r.), and to them the fibres of the auditory nerve (n.)
are distributed. A fluid, the endolymph, fills the whole of the
auditory organ or membranous labyrinth, and in it are formed otoliths
of varying size and number. There is every reason for thinking
that the labyrinth, like the otocysts or statocysts in the lower
animals, functions as an organ of equilibration as well as of hearing.
x
FIG. 797. — Section Hi the i>i,ica! eye of Sphenodon. g. blond-
vessel ; k. cavity of eye, tilled with fluid ; k. connective-tissue
capsule ; /. lens ; M. molecular layer of retina ; r. layer of rods
and cones ; st. nerve ; x. cells in nerve. (From Wiedersheim's
Vertebrata, after Baldwin Spencer.)
112
ZOOLOGY
SECT.
se
ca
ass
As the membranous labyrinth develops in the embryo, it becomes
surroundecTand enclosed by the auditory capsule, the cartilage of
which adapts itself to the form
of the labyrinth, presenting a
large excavation for the utricle
and saccule and tunnel-like pas-
sages for the canals. The audi-
tory organ does not, however, fit
tightly into this system of cavi-
ties, but between it and the
cartilage is a space, filled by a
fluid called peritymph, which acts
as a buffer to the delicate organ
floating in it.
The early history of the audi-
tory apparatus in the embryo
shows that it belongs to the
same series of structures as the
lateral-line system, of which it
may be regarded as a highly
specialised part.
Nerve - components. - - The
nerve-fibres of which the nerves-
cerebral, spinal, and sympathetic
—are made up, the nerve-com-
ponents as they are termed, are
capable of being classified in ac-
cordance with the nature of the
functions which they perform. A broad division into motor
and sensory fibres has already been referred to. A more
detailed classi-
fication is the
following :—
Division I.—
Somatic sensory,
comprising (a) the
fibres which have
to do with general
cutaneous or tac-
tile sensations ; (b)
th o s e connected
with the neuro-
mast organs and
with the auditory
orffailS • (c\ the Jl'la- 799.— Longitudinal section through an ampulla. a. c.
' ,v ' auditory epithelium ; a. h. auditory hairs ; P. part of seini-
fibres Ol the OptlC circular canal; cr. crista acustica ; ct. connective-tissue; e,i.
epithelium ; n. nerve ; v. junction with utriculus. (From
nerves. Foster and Shore's Physiology.)
FIG. 708. — External view of organ of hear-
ing of Craniata (semi-diagrammatic).
an. ampulla of anterior canal ; ae. of hori-
zontal canal ; ap. of posterior canal ; ass.
apex of superior utricular sinus ; ca. an-
terior, ce. horizontal, cp. posterior semi-
circular canal ; CMS. canal uniting sacculus
with utriculus ; de. endolymphatic duct :
7. cochlea ; rec. utricular recess ; s. saccu-
lus ; se. endolymphatic sac ; sp. posterior
utricular sinus ; s,s. superior utricular
sinus ; u. utriculus. (From Wieders-
heim's Vertebra ta.)
xra PHYLUM CHORDATA 113
Division II. — Visceral sensory, comprising (a) the fibres which
end in visceral mucosae and have to do with visceral sensations ;
(6) the fibres ending in taste-buds ; (c) those which terminate in
the olfactory epithelium.
Division III. — Somatic motor, consisting of components which
terminate in somatic musculature.
Division IV. — Visceral motor, comprising all fibres which terminate
in visceral musculature and have to do with visceral movements.
Urinogenital Organs. — In all Craniata there is so close a
connection between the organs of renal excretion and those of
reproduction that the two systems are conveniently considered
together as the urinogenital organs.
Speaking generally, the excretory organ consists of three parts,
all paired and situated along the dorsal wall of the ccelome ; the
fore-kidney or pronephros (Fig. 801, A, p. nph.), the mid-kidney or
mesonephros (ms. nph.), and the hind-kidney or metanephros (mt. nph.}.
Each of these is provided with a duct, the pro- (pn. d.), meso-
(msn. d.), or meta-nephric (mt. n. d.) duct, which opens into the
cloaca. The gonads (gon.) lie in the crelome suspended to its dorsal
wall by a fold of peritoneum : in some cases their products are
discharged into the coelome and make their exit by genital pores,
but more usually the pronephric duct in the female assumes the
functions of an oviduct and the mesonephric duct in the male those
of a spermiduct (cf. p. 116). The pronephros is almost always
functionless in the adult, and usually disappears altogether. The
mesonephros is generally the functional kidney in the lower Crauiata,
in which, as a rule, no metanephros is developed, and the meso-
nephric duct, in addition to carrying the seminal fluid of the male,
acts as a ureter. In the higher forms the mesonephros atrophies,
and the metanephros is the functional kidney, the metanephric
duct becoming the ureter.
The kidney — meso- or meta-nephros — of the adult is a massive
gland of a deep red colour made up of convoluted urinary tubules
(Fig. 800), separated from one another by connective-tissue con-
taining an abundant supply of blood-vessels. The tubules are
lined by a single layer of glandular epithelial cells (B, C), and each
ends blindly in a globular dilatation, the Malpighian capsule (A, gl.),
lined with squamous epithelium. In many of the lower Craniata,
a branch goes off from the tubule, near the Malpighian capsule,
and, passing to the ventral surface of the kidney, ends in a ciliated
funnel-like body (Fig. 801, nst.), resembling the nephrostome of a
worm, and, like it, opening into the coalome. At their opposite
ends the tubules join with one another, and finally discharge into
the ureter.
The renal arteries branch extensively in the kidney, and give off
to each Malpighian capsule a minute afferent artery (Fig. 800, A, va.) :
this pushes the wall of the capsule before it, and breaks up into a
VOL. II H
114
ZOOLOGY
SECT.
bunch of looped capillaries, called the glomerulus, suspended in the
interior of the capsule. The blood is carried off from the glomerulus
by an efferent vessel (ve.), which joins the general capillary system
of the kidneys, forming a network over the urinary tubules : finally,
the blood is returned from this network to the renal vein. The
watery constituents of the urine are separated from the blood in
traversing the glomerulus, and, flowing down the tubule, take up
and dissolve the remaining constituents — urea, uric acid, &c.—
which are secreted by the cells of the tubules.
The development of the kidney reveals a resemblance to the
ccelomoducts of Annulata which would hardly be suspected from its
adult structure. The pronephros (Fig. 801, A, p. nph.) originates
as a small number of coiled tubes formed from mesoderm in the
body-wall at the anterior end of the coelome ; they are arranged
FIG. 800. — A, part of a urinary tubule with blood-vessels, at. artery ; gL Malpighian capsule
containing glomerulus ; v. veinlet returning blood from capillary network (to the right) to
vein j)i. ; va. afferent vessel of glomerulus ; ve. efferent vessel. B, longitudinal, and C,
transverse sections of urinary tubules, a. secreting part of tubules ; b. conducting part of
tubules ; c. capillaries ; n. nuclei. (From Foster and Shore's Physiology.)
metamerically, and each opens into the ccelome by a ciliated funnel
(nst.). Obviously such tubes are coelomoducts : their chief
peculiarity is that their outer ends do not open directly on the
exterior, but into a longitudinal tube, the pronephric or segment al
duct (sg. d.), which passes backwards and discharges into the cloaca.
It seems probable that this arrangement is to be explained by
supposing that the coelomoducts originally opened externally into
a longitudinal groove, which, by the apposition of its edges, was
converted into a tube. All the tubules of the pronephros open,
by their ciliated funnels, into the narrow anterior end of the ccelome,
into which projects a branch of the aorta ending in a single large
glomerulus.
The pronephros soon degenerates, its tubules losing their connec-
tion with the pronephric duct (B), but in the meantime fresh tubules
xm
PHYLUM CHORDATA
115
appear in the segments posterior to the pronephros, and together
constitute the mesonephros or Wolffian body (B, ms. nph.}, from
which the permanent kidney is formed in most of the lower Craniata.
FIG. 801. — Diagrams illustrating the development of the urinogenital organs of Craniata.
A, development of pronephros and pronephric duct ; B, atrophy of pronephros, develop-
ment of mesonephros ; C, differentiation of pro- and mesonephric ducts ; D, development
of metanephros, male type ; E, female type. al. bl. allantoic bladder ; an. anus ; cl. cloaca ;
gon. gonad ; int. intestine ; m. c. Malpighian capsule ; ms. n. d. mesonephric duct ; ms. nph.
mesonephros ; mt. n. d. metanephric duct ; mt. nph. metanephros ; nst. nephrostome ; ov.
ovary ; p. n. d. and sg. d. pronephric duct ; p. nph. pronephros ; t. testis ; v. e. vasa efferentia.
The mesonephric tubules open at one end into the pronephric duct
(sg. d.), at the other by ciliated funnels (nst.), into the ccelome ; a
H 2
116 ZOOLOGY SECT.
short distance from the funnel each gives off a blind pouch, which
dilates at the end and forms a Malpighian capsule (m. c.), and a
branch from the aorta entering it gives rise to a glomerulus.
In some forms the pronephric duct now becomes divided by a
longitudinal partition into two tubes : one retains its connection
with the mesonephros and is known as the mesonephric or Wolffian
duct (C, ms. n. d.) : the other has no connection with the tubules, but
opens into the coelome in the region of the vanishing pronephros,
and is called the Mullerian duct (p. n. d.). In some Craniata the
Mullerian appears quite independently of the Wolffian duct :
the latter is then simply the pronephric duct after the union with
it of the mesonephric tubules.
In the higher Vertebrata, from Reptiles to Mammals, a diverti-
culum (D, E, mt. n. d.) is given off from the posterior end of the
Wolffian duct, which grows forwards and becomes connected with
the hindmost tubules. In this way is formed a metanephros
(mt. nph.), which forms the permanent kidney, and a metanephric
duct (mt. n. d.), which gives rise to the ureter. The Wolffian
body ceases to discharge a renal function, and becomes a purely
vestigial organ.
In many Fishes there is a dilatation of the ureter, the urinary
bladder, which serves as a receptacle for the urine. In the higher
Craniata the ventral wall of the cloaca sends off a pouch, the
allantoic bladder (al. bl.), which serves the same purpose, although
morphologically an entirely different structure.
The gonads (gon.) are developed as ridges growing from the
dorsal wall of the ccelome and covered by coelomic epithelium,
from the cells of which, as in so many of the lower animals, the
ova and sperms are derived. The testis consists of crypts or
tubules, lined with epithelium, and usually discharging their pro-
ducts through delicate vasa efferentia (D, v. e.) into the Wolffian
duct, but in some groups into the ccelome. The sperms are
always motile. The ovary is formed of a basis of connective-
tissue or stroma, covered by epithelium, certain of the cells of
which become enlarged to form ova. In the majority of cases the
ova are discharged from the surface of the ovary into the ccelome
and thus into the open ends of the Mullerian ducts (E, p. n. d.),
which thus function simply as oviducts, having no connection in
the .adult with the urinary system. In some groups the ova,
like the sperms, are shed into the coslome and escape by the genital
pores, and in many bony Fishes the ovary is a hollow organ, as in
Arthropoda, discharging its ova into an internal cavity, whence
they are carried off by a duct continuous with the gonad.
A few Craniata are normally hermaphrodite, but the vast
majority are dioecious, hermaphroditism occurring, however,
occasionally as an abnormality.
In close topographical relation with the urinogenital organs are
xm
PHYLUM CHORDATA
117
found certain "ductless glands," the adrenals or inter- and .v///>/v/-
renal bodies. They are developed partly from ridges of the dorsal
wall of the coelome — i.e., from mesoderm, partly from the sym-
pathetic ganglia. There may be numerous adrenals segmentally
arranged, or a single pair. Like other ductless glands the adrenals
produce an internal secretion, which mingles with the blood and
produces physiological effects on other parts.
Development.- — The ova of Craniata are usually telolecithal,
but the amount of food-yolk varies within wide limits. When it is
small in quantity, segmentation is complete but usually unequal,
when abundant, incomplete and discoidal. In the latter case the
embryo proper is formed, as in Cephalopods, from a comparatively
small portion of the oosperm, the rest giving rise to a large yolk-sac.
e-nt
Sfl.C
insd-
msd
FIG. 802. — Transverse section of earlier (A) and later (B) embryos of Frog, cce.1. coelome" ;>«/'.
prolongation of crelome into protovertebra ; ent. mesenteron ; med. gr. medullary groove;
msd. mesoderm ; nch. notoohord ; pr. v. protovertebra ; sg. d. segmental duct ; som. somatic
layer of mesoderm ; sp. c. spinal cord ; spl. splanchnic layer of mesoderm ; yk. yolk-cells.
(After Marshall.)
There is never a typical invaginate gastrula, as in Amphioxus,
but in some of the lower Craniata a gastrula stage is formed by a
combination of inpushing and overgrowth : details will be given
in the sections on the various groups. In the higher forms a
gastrula cannot be recognised with absolute certainty.
The mode of development of the mesoderm and of the ccelomr
differs strikingly from the process we are familiar with in Amphi-
oxus. At an early stage the mesoderm is found in the form of
paired longitudinal bands (Fig. 802, A, msd.) lying one on each side
of the middle line, where they are separated from one another by
the medullary groove (md. gr.} and the notochord (nch.), and com-
pletely filling the space between the ectoderm and the endoderm.
In all probability the mesoderm is derived from both of the primi-
tive germ-layers. Each mesoderm-band becomes differentiated
into a dorsal portion, the vertebral plate, bounding the nervous
118 ZOOLOGY SECT.
system and notochord, and a ventral portion, the lateral plate,
bounding the mesenteron. The vertebral plate undergoes meta-
meric segmentation, becoming divided into a row of squarish
masses, the protovertebrce or mesodermal segments (B, pr. v.) : the
lateral plate splits into two layers, a somatic (som.), adherent to the
ectoderm, a splanchnic (spl), to the endoderm. The space between
the two is the coelome (coel), which is thus a schizocoele, or cavity
hollowed out of the mesoderm, and is, except in the head-region
in the Lampreys (p. 132), at no stage in communication with
the mesenteron, like the coelomic pouches of Amphioxus. The
dorsal portion of the coelome assumes the character of a series of
paired diverticula of the main ventral part, each situated in the
interior of a protovertebra ; but such an arrangement is temporary,
and these protovertebral cavities early disappear. From the dorsal
portions of the protovertebrse the myomeres are formed, from
their ventral portions the vertebrae.
The development of the principal organs has been described, in
general terms, in the preceding account of the organs themselves :
it will be convenient to defer further consideration of this subject
until we come to deal with the development of the various types
of Craniata, and with the embryological characteristics of the classes
and sub-classes.
Metamerism. — A tendency, more or less strongly marked, to
a serial repetition of parts is to be observed in a number of different
systems of organs. Instances of this have already been pointed
out in the skeleton, and the muscular, nervous, and excretory
systems. This phenomenon seems to lead to the conclusion that
the structure of the Craniata can be understood only when they
are regarded as metamerically-segmented animals. The phase
of metamerism presented by the Craniata is, however, widely
different from that which prevails in the segmented Invertebrates.
In the latter the segmentation is usually quite distinctly pro-
nounced externally, and it may involve a metameric division
extending to the ccelome as well as to the various systems of internal
organs. In the Craniata, on the other hand, segmentation is
never visible on the exterior, and in the adult condition the ccelome
never shares in the division. Even in the case of the organs which
present metameric characters, the metamerism often appears
indefinite and uncertain : thus, as already pointed out, the
segmentation of the spinal column, which in the adult is the most
pronounced of all, does not coincide with the segmentation of the
muscular and nervous systems. Yet when we take the phenomena
of embryonic development into account, it becomes sufficiently
clear that in the Craniata we have to do with animals possessing
a metameric segmentation of the same general type as that
possessed by Amphioxus, and that the apparent anomalies are due
to processes of secondary modification.
xin PHYLUM CHORDATA 119
It is in the trunk region that the metamerism is most strongly
pronounced, and that more particularly in the lower groups. In
the head there is great specialisation in cc -ordination with the
presence in this region of the brain, the chief organs of special sense,
and the mouth and jaws ; so that, though there are indications
of metamerism of various parts, it is only by the study of
development that it is possible to interpret the structure of the
head in terms of a metameric segmentation which becomes much
modified and disguised in the adult animal. When the development
is followed out, it becomes evident that, as in the Arthropoda, the
head in Craniata is formed as a result of a process of fusion between
a number of metameres, the individuality of which is quite evident
in early stages, more particularly among lower forms, being most
pronounced in the region behind the auditory capsules.
Distinctive Characters. — The Craniata may be defined a
Euchorda in which the notochord is not continued to the end of
the snout, but stops short beneath the fore-brain, some distance
from its anterior end. A skull is always present, and there are
usually paired limbs. The ectoderm is many-layered and is never
ciliated in the adult, and only rarely in the larva. The pharynx is
of moderate dimensions, and is perforated by net more than seven
pairs of gill-slits (except in some Cyclostomes). The gill-pouches
do not open into an atrium. The liver is large, massive, and not
obviously tubular. There is a muscular, chambered heart, and the
blood contains red corpuscles. The renal tubules unite to form
large paired kidneys and open into ducts which discharge into or
near the posterior end of the intestine. The brain is complex, and
there are at least ten pairs of cerebral nerves : the spinal nerves
are, except in Cyclostomes, formed by the union of dorsal and
ventral roots. Paired eyes of great complexity, derived in part
from the brain, are present ; and there is a pair of auditory organs.
There is typically a single pair of gonads, and the reproductive
products are usually discharged by ducts derived from the renal
system. There is never a typical invaginate gastrula, and the
mesoderm arises in the form of paired longitudinal bands which
subsequently become segmented. The ccelome is nearly always
developed as a schizocoele.
CLASS I-CYCLOSTOMATA.
The Cyclostomata, or Lampreys and Hags, are eel-like animals,
distinguished from all other Craniata by the possession of a suctorial
mouth devoid of functional jaws, by the single olfactory organ, and
by the absence of lateral appendages, or paired fins.
1. EXAMPLE OF THE CLASS. — THE LAMPREY (Petromyzori).
Three species of Lamprey are common in the Northern Hemi-
sphere : the Sea-lamprey (P. marinus), which attains a length of a
120
ZOOLOGY
SECT
metre ; the Lampern, or common fresh-water Lamprey (P. fluvia-
//7/,s-), which may reach a length of about 90 cm. ; and the Sand-
pride, or lesser fresh-water Lamprey (P. planeri), not exceeding
45 cm. in length. In the Southern Hemisphere the Lampreys
belong to two genera : Mordacia, found on the coasts of Chili and
Tasmania, and Geotria, in the rivers of Chili, Australia, and New
Zealand. Both genera differ from Petromyzon in minor details
only.
External Characters. — The head and trunk (Fig. 803) are
nearly cylindrical, the tail-region compressed or flattened from
side to side. At the anterior end, and directed downwards, is a
large basin-like depression, the buccal funnel (buc.f.), surrounded with
br.cl.t
FIG. 803. — Petromyzon fluviatilis. Ventral (A), lateral (B), and dorsal (C) views of the head.
br. cl. 1, first gill-cleft ; buc.f. bncc.il funnel ; eye, eye ; mth. mouth ; na. ap. nasal aperture ;
p. papillse ; pn. pineal area ; tl.t2.t3. teeth of bucral funnel ; t 4. teeth of tongue. (After
W. K. Parker.)
papillae (p) and beset internally with yellow, horny teeth (t 1 — / 3}.
At the bottom of the funnel projects a prominence, the so-called
' tongue " (t4), also bearing horny teeth, and having immediately
above it the narrow mouth (mth.). On the dorsal surface of the
head is the single median nostril (na. ap.), and immediately behind
i£a transparent area of skin (pn.) indicates the position of the pineal
organ. The paired eyes have no eyelids, but are covered by a
transparent area of skin. The gill-slits (br. cl. 1) are seven pairs of
small apertures on the sides of the head, the first a little behind the
eyes. On the ventral surface, marking the junction between trunk
and tail, is the very small anus (Fig. 812, a.), lying in a slight depres-
sion, and having immediately behind it a small papilla pierced at
its extremity by the urinogenital aperture (z.). There is no trace
XIII
PHYLUM CHORDATA
121
of paired appendages, and the only organs of locomotion are the
unpaired fins. Two dorsal fins of approximately equal dimensions,
separated by a notch, and a caudal fin are present, the second dorsal
being continuous with the caudal.
Lampreys prey upon Fishes, attaching themselves to the bodies
of the latter by the sucker-like mouth, and rasping off their flesh
with the armed tongue. They are often found holding on to stones
by the buccal funnel, and under these circumstances perform regular
respiratory movements, the branchial region expanding and con-
tracting like the thorax of a Mammal. The reason of this is that
when the animal is adhering by the mouth the respiratory current
cannot take its usual course — entering at the mouth and leaving
by the gill-slits — but is pumped by muscular action both into and
out of the branchial apertures.
The skin is soft and slimy, mottled greenish-brown in P. marinus,
bluish above and silvery on the sides in the fresh- water species.
Ay
""•<" ' sb.oc.a
l.C.3
FIG. 804. — Pctromyzon marinus. Skull, with branchial basket and anterior part of verte-
bral column. The cartilaginous parts are dotted, a.d.c. anterior dorsal cartilage ; a. lot. c.
anterior lateral cartilage ; an. c. annular cartilage ; an. c. auditory capsule ; br. b. 1 — 7,
vertical bars of branchial basket ; br. cl. 1 — 7, external branchial clefts ; en. c. cornual
cartilage ; cr. r. cranial roof ; 1. c. 1 — 4, longitudinal bars of branchial basket ; lg. c. lingual
cartilage ; m. v. c. median ventral cartilage ; n, a. neural arch ; na. ap. nasal aperture ; nch.
notqchord ; No. 2, foramen for optic nerve ; olf. c. olfactory capsule ; pc. c. pericardia!
cartilage ; p. d. c. posterior dorsal cartilage ; p. lat. c. posterior lateral cartilage ; sb. oc. a.
subocular arch ; st. p. styloid process ; sty. c. stylifonn cartilage ; t. teeth. (After W. K.
Parker.)
The epiderm contains unicellular glands, the secretion of which
gives its slimy character to the skin. The segmental sense-organs
take the form of a lateral line which is superficial, not enclosed in a
canal, and of minute pits on the head. There is no trace of exo-
skeleton.
Skeleton.— The axial skeleton of the trunk is very simple.
There is a persistent notochord (Fig. 804, nch.) with a tough sheath
composed of an inner fibrous and an outer elastic layer. Attached
to the sides of the notochord are little vertical rods of cartilage (n.a.),
arranged segmentally, bounding the spinal canal on each side, and
corresponding to rudimentary neural and interneural arches : in
the caudal region these fuse into a single plate perforated by
foramina for the spinal nerves and sending off processes to the base
122
ZOOLOGY
SECT.
of the fin. For the rest of its extent the spinal canal is enclosed
only by tough, pigmented connective-tissue. Slender rods of
cartilage support the median fins.
ci.d.c
B
nc/t
fJ.lcil
cn.c
Fid. 805. — Fetromyzon marinus. Dorsal (A), ventral (B), and sectional (C) views of skull.
The cartilaginous parts are dotted, a. d. c. anterior dorsal cartilage ; an. c. annular cartilage ;
au. c. auditory capsule ; b. cr. f. basicranial fontanelle ; b. pi. basal plate ; en. c. cornual
cartilage ; cr. r. cranial roof ; n. a. neural arch ; na. ap. nasal aperture ; nch. notochord ;
Nv. 1, olfactory nerve ; Nv. 2, 5, and S, foramina for the optic, trigeminal, and auditory
nerves ; Nv. 5', fifth nerve ; olf. c. olfactory capsule ; p. d. c. posterior dorsal cartilage ;
p. lat. c. posterior lateral cartilage ; sb. oc. a. sub-ocular arch ; st. p. styloid process. (After
W. K. Parker.)
The cranium also exhibits a very primitive type of structure.
Its floor is formed by a basal plate (Fig. 805, b. pi.), made by the
xra PHYLUM CHORDATA 123
union of the parachordals and trabeculse, and surrounding pos-
teriorly the fore-end of the notochord. Immediately in front of
the termination of the notochord is a large aperture, the basi-cranial
fontanelle (b. cr. /.), due to the non-union of the posterior ends of
the trabeculae ; through it passes the pituitary pouch,, presently
to be referred to (Fig. 808), on its way from the olfactory sac to
the ventral surface of the notochord. Lateral walls extend upwards
from each side of the basal plate, but the roof of the cranium is
formed by membrane except at one point, where a narrow transverse
bar (cr. r.) extends across between the side- walls and furnishes a
rudimentary roof. United with the posterior end of the basal
plate are the auditory capsules (au. c.}, and the side- walls are pierced
with apertures for the cerebral nerves (Nv. 2, Nv. 5, Nv. 8.)
So far the skull is thoroughly typical, though in an extremely
simple or embryonic condition ; the remaining parts of it differ a
good deal from the ordinary structure as described in the preceding
section, and are in many cases very difficult of interpretation.
The olfactory capsule (olf. c.) is an unpaired concavo-convex plate
which supports the posterior wall of the olfactory sac and is pierced
by paired apertures for the olfactory nerves. It is unique in being
united to the cranium by fibrous tissue only.
Extending outwards and downwards from each side of the basal
plate is an inverted arch of cartilage, called the sub-ocular arch
(Figs. 804 and 805, sb. oc. a.) from the fact that it affords a support
to the eye. From its posterior end a slender styloid process (st. p.]
passes directly downwards and is connected at its lower end with
a small cornual cartilage (en. c.). Perhaps the sub-ocular arch
answers to the palato-quadrate or primary upper jaw, the styloid
and cornual cartilages to the main part of the hyoid arch. In
close relation with the angle of the sub -ocular arch is an upwardly
directed plate, the posterior lateral cartilage (p. lat. c.).
Connected with the anterior end of the basal plate is the large
bilobed posterior dorsal cartilage (p. d. c.) ; it appears to be formed
from the united anterior ends of the trabeculae. Below and pro-
jecting in front of it is the anterior dorsal cartilage (a. d. c.), which
is probably homologous with the upper labial cartilage of some
Fishes and Amphibians (see below). Also belonging to the series
of labial cartilages are the paired anterior lateral cartilages (a. I. c.)
and the great ring-shaped annular cartilage (an. c.) which supports
the edge of the buccal funnel.
The " tongue " is supported by a long unpaired lingual cartilage
(Fig. 804, Ig. c.}, which may answer to the united Meckel's cartilages
or ventral portion of the mandibular arch of other Craniata (see
p. 75) ; it is tipped in front by a small median and a pair of still
smaller lateral cartilages. Below it is a slender T-shaped median
ventral cartilage (m. v. c.), which may possibly be the median ventral
element of the mandibular arch. Lastly, attached to each side of
124 ZOOLOGY SECT.
the annular cartilage and passing backwards and downwards are
a pair of tapering, rod-like styliform cartilages (sty. c.}.
The visceral skeleton also differs in a remarkable manner from
the ordinary Craniate type, and is only doubtfully related to it.
It consists of a branchial basket, formed, on each side, of nine
irregularly curved vertical bars of cartilage (Fig. 804, br. b. 1 — 9),
the first placed almost immediately posterior to the styloid cartilage,
the second immediately in front of the first gill-cleft, the remaining
seven just behind the seven gill-clefts. These bars are united
together by four longitudinal rods (Ic. 1 — 4), of which one lies along-
side the notochord and is connected in front with the cranium, two
others are placed respectively above and below the gill-clefts, while
the fourth is situated close to the middle ventral line and is partly
fused with its fellow of the opposite side. The posterior vertical
bar is connected with a cup-like cartilage (pc. c.), which supports
the posterior and lateral walls of the pericardium. The whole
branchial basket lies external to the gill-pouches and branchial
arteries, not, like typical visceral arches, in the walls of the pharynx.
The median fins are supported by the delicate cartilaginous rods
already referred to, which are more numerous than the myomeres,
and lie parallel to one another in the substance of the fin, extending
downwards to the fibrous neural tube.
The structure of the cartilage is peculiar and varies in different
parts ; it has very little matrix.
The muscles of the trunk and tail are arranged in myomeres
which take a zig-zag course. In the branchial region they are
divided into dorsal and ventral bands, which pass respectively
above and below the gill-slits ; but in the trunk there is no division
into dorsal and ventral parts. A great mass of radiating muscle
is inserted into the buccal funnel, and the ' tongue " has an
extremely complex musculature which derives its nerve-supply
from the trigeminal.
Digestive Organs. — The teeth are laminated horny cones :
beneath them lie mesodermal papillae covered with ectoderm which
bear a superficial resemblance to the germs of true calcified teeth.
When worn out they are succeeded by others developed at their
bases. The mouth leads into a buccal cavity (Fig. 806, m.) formed
from the stomodseum of the embryo, and communicating behind
with two tubes placed one above the other : the dorsal of these is
the gullet (ces.), the ventral the respiratory tube (r. t., see below) :
guarding the entrance to the latter is a curtain-like fold, the
velum (vl.). The gullet bends over the pericardium and enters
the intestine (int.) by a valvular aperture. The intestine passes
without convolutions to the anus ; its anterior end is slightly
dilated, and is the only representative of a stomach : its posterior
end is widened to form the rectum (Fig. 812, r.). The whole of the
intestine is formed from the mesenteron of the embryo, and the
xm PHYLUM CHORDATA 125
blastopore becomes the anus, there being no proctodaeum. The
Ml*
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lumen of the intestine is semilunar, owing to the presence of a
typhlosole (Fig. 811, int.), which takes a somewhat spiral course
126 ZOOLOGY SECT.
and is hence known as the spiral valve. There is no continuous
mesentery, but a number of narrow supporting bands.
The liver (Fig. 806, Ir.) is a large bilobed organ, and is peculiar
from the fact that there is neither gall-bladder nor bile-duct in the
adult, except as an individual variation, although both are present
in the larva. There are a few follicles on the surface of the liver,
which may represent a pancreas : the spleen is absent. Paired
glands imbedded in the muscles of the head, and opening into the
mouth, are known as " salivary glands."
Respiratory Organs. — The Lampreys differ from all other
Vertebrata in the fact that the gills do not open directly into the
enteric canal in the adult, but into a respiratory tube (Fig. 806, r. t.)
lying below the gullet. This is a wide tube opening in front into
the buccal cavity, and ending blindly a short distance in front of
the heart : in the larva it communicates behind with the intestine,
and is, in fact, the pharynx, the gullet of the adult being not yet
developed ; but at the time of metamorphosis it loses its connec-
tion with the intestine, and the gullet is developed as a forward
extension of the latter — an entirely new formation. The respiratory
organs are typical gill-pouches (br. 5) : they have the form of
biconvex lenses, with numerous gill-lamella3 developed on the inner
surfaces, and are separated from one another by wide interbranchial
septa. In the larva an additional cleft has been found in front of
the first of the adult series.
Circulatory System. — The auricle (au.) lies to the left of the
ventricle (v.) and receives blood from a small sinus venosus (s.v.).
There is no conus arteriosus, but the proximal end of the ventral
aorta presents a slight dilatation or bulbus aortce. Both afferent
and efferent branchial arteries supply each the posterior hemi-
branch of one gill-pouch and the anterior hemibranch of the next :
they are thus related to the gills, not to the gill-pouches. In
addition to the paired jugulars (ju.) there is a median ventral
inferior jugular vein (i. ju.) returning the blood from the lower
parts of the head. There is no renal-portal system, the two
branches of the caudal vein being continued directly into the
cardinals (cd.). The left precaval disappears in the adult, so that
the jugulars and cardinals of both sides open into the right precaval.
The red blood-corpuscles are circular, nucleated discs. There is
a large system of lymphatic sinuses.
Nervous System. — In the brain the small size of the cerebellum
(Fig. 807, crb.) is remarkable : it is a mere transverse band roofing
over the anterior end of the metacoale. The optic lobes (opt. I.)
are very imperfectly differentiated, and the central region of the
roof of the mid-brain is formed merely of a layer of epithelium,
so that when the membranes of the brain are removed, an aperture
is left which is covered in the entire organ by a vascular thickening
of the pia, or choroid plexus (ch. pi. ^). On the dorsal border of
xm
PHYLUM CHORDATA
127
the lateral wall of the diencephalon are the two ganglia habenulce,
the right (r. gn. hb.) much larger than the left (I. gn. Tib.} : they are
connected with the pineal apparatus. Below the diencephalon is
a small flattened pituitary body (Fig. 808, pty. &.). In front of the
diencephalon are paired bean-like masses, each consisting of a small
posterior portion, the olfactory lobe (crb. h.), and a larger anterior
A'v I
FIG. 807.— Petromyzon marinus. Dorsal (A) and ventral (£) views of brain, ch. pi. 1, an-
terior choroid plexus forming roof of prosencephalon and diencephalon ; ch. pi. 2, aperture
in roof of mid-brain exposed by removal of middle choroid plexus ; ch. pi. 3, metacosle
exposed by removal of posterior choroid plexus ; crb. cerebellum ; crb. h. olfactory lobes ;
cr. crb. crura cerebri ; dien. diencephalon ; inf. infundibulum ; I. gn. hb. left ganglion"
habenulae ; med. obi. medulla oblongata ; Nv. 1, olfactory, Nv. 2, optic, Nv. 3, oculo-motor
Nv. 5, trigeminal, and Nv. S, auditory nerves ; olf. I. olfactory bulbs ; opt. I. optic lobes •
pn. pineal eye ; r. gn. hb. right ganglion habenulse. (After Ahlborn.)
portion, the olfactory bulb (olf. I.). The diacoele communicates
in front with a small prosocoele or common fore-ventricle, which is
roofed over by a choroid plexus (ch. pi. 1), and from which a trans-
verse passage goes off on each side and divides into two branches,
128
ZOOLOGY
SECT.
a rhinoccele going directly forwards into the olfactory bulb, and
a paracoela backwards into the olfactory lobe.
The pineal apparatus consists of two vesicles placed in a vertical
series : the dorsal-most of these is the vestigial pineal eye (Fig. 808,
pn. e.) : it has a pigmented retina, a flat and imperfectly formed
lens, and is connected with the right ganglion habenulae. The
lower vesicle (parapineal organ, pn.), of the same nature as the upper
but more imperfectly developed, is in connection with the small left
ganglion habenulse. The pineal eye is not an organ capable, like
the paired eyes, of forming definite images of objects, but probably
is capable of distinguishing differences in the intensity of the light.
The optic nerves differ from those of most of the higher classes in
the fact that the chiasma is not visible externally — the intercrossing
of the fibres taking place beneath the surface.
The spinal cord (Figs. 806 and 811, my.} is' flattened and band-like.
na.np.
l.(fn.hb
y<
Fia. 808. — Petromyzon. Side view of brain with olfactory and pituitary sacs, in section.
Mm. cerebellum ; crb. h. olfactory lobe ; dien. diencephalon ; /. fold, in nasal tube ; ?//.
nasal glands ; inf. infundibulum ; I. gn. hb. left ganglion habenulse ; rued. obi. medulla
oblongata ; na. ap. nostril ; nch. notochord ; Nv. 1, olfactory nerve ; Nv. 2, optic ; Nv. ,'i,
oculomotor ; Nv. 4, trochlear ; Nv. 5, trigeminal ; Nv. 6, abducent ; Nv. 7, facial ; Nv. A',
auditory ; Nv. 10, vagus ; No. 12, hypoglossal ; olf. cp. olfactory capsule ; olf. I. olfactory
bulb ; olf. m. m. olfactory mucous membrane ; opt. I. optic lobe ; pn. parapineal organ ;
pn. e. pineal eye ; pti;. b. pituitary body ; pty. p. pituitary pouch ; sp. median septum of
olfactory sac ; sp. 1, dorsal root of first spinal nerve. (Combined from figures by Ahlborn
and Kaenische.)
The dorsal roots of the spinal nerves alternate with the ventral
roots, and do not unite with them to form a trunk : the dorsal
roots are opposite the myocommas, the ventral opposite the
myomeres. A sympathetic is represented. The hypoglossal is
the first spinal nerve.
Sensory Organs.— The external nostril (Fig. 806, na", Fig. 808,
na. ap.) leads by a short passage into a rounded olfactory sac
(Fig. 806, na, Fig. 808) placed just in front of the brain and having
its posterior wall raised into ridges covered by the olfactory mucous
membrane (Fig. 808, olf. m. m.). From the bottom of the sac is
given off a large pituitary pouch (Fig. 806, na', Fig. 808, pty. p.)
xni
PHYLUM CHORDATA
129
which extends downwards and backwards, between the brain and
the skull-floor, passes through the basicranial fontanelle, and ends
blindly below the anterior end of the notochord.
The relations between the olfactory sac, the pituitary pouch, and
the pituitary body are very remarkable. In the embryo, before
the stomodseum (Fig. 809, A, stdm.) communicates with the mesen-
nch
nch
FiQ. 809. — Petromyzon. Diagrams of four stages in the development of the olfactory and
pituitary sacs. br. brain ; ent. mesenteron ; inf. iufundibulum ; I. Ip. lower lip ; nch. noto-
chord ; olf. s. olfactory sac ; pn. pineal body ; j>ty. s. pituitary sac ; stdm. stomodteum
M. Ip. upper lip. (Altered from Dohrn.)
teron, two unpaired ectodermal imaginations appear in front of
the mouth. The foremost of these is the rudiment of the olfactory
sac (olf. s.). The other, which is situated between the olfactory
sac and the mouth, is the pituitary sac (pty. s.), which in this case
opens just outside the stomodseum instead of within it as in other
Craniata : its inner or blind end extends to the ventral surface of
the fore-brain and terminates just below the infundibulum (inf.}.
As development goes on, the olfactory and pituitary imaginations
become sunk in a common pit (B), which, by the growth of the
immense upper lip (up. I.), is gradually shifted to the top of
the head (C, D), the process being accompanied by elongation of the
pituitary sac, into which the olfactory sac opens posteriorly. Where
the pituitary sac comes in contact with the infundibulum it gives
off numerous small follicles which become separated ofE and give
rise to the pituitary body (Fig. 808, pty. &.). Thus the entire nasal
VOL. II I
130
ZOOLOGY
SECT.
e-nd.a
passage of the Lamprey, including its blind pouch, is a persistent
pituitary sac into which the single olfactory organ opens. More-
over, owing to the extraordinary displacement undergone during
development, the pituitary sac perforates the skull-floor from above
instead of from below, as in all
other Craniata.
The auditory organ (Fig. 810)
is remarkable for having only
two semicircular canals, corre-
sponding to the anterior (a.s.c.)
and posterior (p.s.c.) of the typical
organ.
Organs of taste are present on
O..S.C
.s.e
sac
CLU.cl.7l
n.ca
FIG. sio.— Auditory sac of Petromyzon. the wall of the pharynx between
a. s. c. anterior semicircular canal ; aiul.n. ,1 -n j
auditory nerve : end. s. endolymphatic the glll-SaCS, and neuromast- Or
sac ; p.s.c. posterior canal ; sac. sacculus ; lptpral linp nro-an« arp nrp«pnf nn
vtr. utriculus. (After Retains.)
the head and trunk.
Urinogenitai Organs. — The kidneys (Figs. 811 and 812, k) are
long strap-shaped bodies developed from the mesonephros of the
embryo. The tubules have no nephrostomes. Each kidney is
attached along one edge to the dorsal wall of the body-cavity by a
sheet of peritoneum ; along the other
or free edge runs the ureter (ur.),
which is the undivided pronephric
duct. The ureters open posteriorly
into a small urinogenital sinus (Fig.
812, u.g.s.), placed just behind the
rectum, and opening, by a urinogenital
papilla (u.g.p.}, into a pit in which
the anus (a.) also lies. The side-walls
of the sinus are pierced by a pair of
small apertures, the genital pores (y),
which place its cavity in communica-
tion with the ccelome.
The gonad (Fig. 806, ov, Fig. 811
ts) is a large unpaired organ occupy-
ing the greater part of the abdominal
cavity and suspended by a sheet of
peritoneum. The sexes are separate,
but ova have been found in the testis
of the male* The reproductive pro-
ducts are shed into the ccelome and
make their way by the genital pores
into the urinogenital sinus, and so to the surrounding water, where
impregnation takes place.
Development. — The oosperm is telolecithal, having a con-
siderable accumulation of yolk in one hemisphere ; in correspon-
int
FIG. 811. — Petromyzon marinus.
Transverse section of trunk, cd.
cardinal veins; d. ao. dorsal aorta;
/. r. fin-rays ; /. t. fibrous tissue
of spinal canal ; int. intes-
tine, the line pointing to the
spiral valve ; k, kidneys ; lit. sub-
vertebral lymph-sinus ; m. body-
muscles ; my. spinal cord ; we. noto-
chord ; n. ca. spinal canal ; ts. testis ;
ur. ureter. (From Parker's Zootomy.)
XIII
PHYLUM CHORDATA
131
deuce with this, segmentation is complete but unequal, the morula
consisting of an upper hemisphere of small cells or micromeres
(Fig. 813, mi. m.), free from yolk, and of a lower hemisphere of
large cells or megameres (mg.m.), containing much yolk. In the
blastula stage (D) the
segmentation-cavity or
blastocoale (bid.) is
situated nearer to the
upper than to the
lower pole. A trans-
verse semilunar groove
appears which is
bounded by a promi-
nent rim towards the
future dorsal and
anterior side : this
is the blastopore
(blp.). The megameres become gradually enclosed by the micro-
meres as a result of a process which is partly invagination,
partly epiboly. During this process the segmentation-cavity
becomes displaced by the archenteron. The dorsal and ventral
. si± Petromyzon marinus. The urinogenital sinus
with posterior end of intestine and part of left kidney.
a. anus ; int. intestine ; k. left kidney ; r. rectum
ti.g.p. urinogenital papilla ; u.g.s. urinogenital sinus ;
itr. left ureter ; x, x', apertures of ureters into urinogeni-
tal sinus ; y, bristle passed into right genital pore ;
z, bristle passed from urinogenital aperture into sinus.
(From Parker's Zootomy.)
rni.m
FIG. 813. — Petromyzon. A and B, two stages in segmentation ; f , early embryo from the
posterior aspect ; D, section of blastula stage ; E, section of gastruhi stage, blp. blastopore ;
bid. blastocoele or segmentation-cavity ; k. keel ; mg. m. megameres ; mi. in. micromeres.
(After Shipley and Kupffer.)
walls of the latter, unlike those of the archenteron of Amphioxus,
differ widely from one another, the ventral wall being composed
of a thick mass of yolk-cells (megameres), while the roof is com-
paratively thin and consists of two or three layers of rounded
i 2
132
ZOOLOGY
SECT.
cells. The lumen is a narrow, dorso-ventrally compressed cleft.
When the process of gastrulation is completed, the blastopore
takes up a position at the postero-dorsal end. The development
of the central nervous system differs widely from the corres-
ponding process in Amphioxus, and is only approached among
the Craniata by the Teleostomi or Bony Fishes. The dorsal surface
becomes flattened along a narrow longitudinal area, and along this a
groove appears, which stops short just in front of the blastopore.
The area along which the groove runs soon becomes raised up above
the general surface so as to form a narrow longitudinal elevation.
Sections of this stage show that the ectoderm has developed a
thickening along the course of the longitudinal groove, and this
comes to grow downwards towards the archenteron as a solid
longitudinal medullary keel (Fig. 813, C, k ; Fig. 814, A, mk). This
is the rudiment of the central nervous system. Subsequently the
keel becomes separated off from the surface ectoderm, and lies below
A B
tic
ent
end.
FIG. 814. — Fetromyzon. Sections of embryos. A, transverse section of the trunk-region.
B, transverse section of the head-region, eve. coelomic sacs ; ect. ectoderm ; end. endoderm ;
ent. enteric cavity ; so. mesoderm-strand ; m.c., mk. medullary cord and medullary keel ; nc.
notochord. (From O. Hertwig ; A, after Goette, B, after Kupffer.)
it as a solid cord. It is only at a considerably later period that a
lumen appears in this cord, and gives rise to the ventricles of the
brain and the central canal of the spinal cord. During the formation
of the medullary keel the rudiment of the notochord is developed
from the underlying endoderm very much as in Amphioxus (p. 57).
On each side of the medullary cord and notochord is a group of
cells arranged as a longitudinal strand — the mesoderrn plates.
In the head-region (Fig. 814, B) a number of diverticula from the
archenteron — ccelomic diverticula — are given off into these strands :
in the trunk region (A) these are absent. The inner portion of the
mesoderm on each side becomes divided up into a series of meso-
dermal somites or protovertebra3, the lateral part remaining
undivided and forming the lateral plate. In this restriction of
somite-formation to the part of the mesoderm immediately adjacent
xni
PHYLUM CHORDATA
133
to the middle line, the Lamprey differs from Amphioxus and
resembles all the rest of the Craniata. The blastopore does not
close up, but is converted into the anus, so that there is no procto-
dseum. The dorsal lip of the blastopore, very prominent from the
first, becomes produced to give rise to the rudiment of the tail
region. The mouth is developed later than the anus by the
formation of a stomodseal invagination.
The young is hatched as a peculiar larval form called Ammoccetes
(Fig. 815), which differs from the adult in several respects. The
median fin is continuous. There is a semicircular, hood-shaped
upper lip (u. I.) instead of the suctorial buccal funnel of the adult,
and teeth are absent. The
buccal cavity is separated A , f' *jf\ ul^^~*&
from the pharynx by a I Yy *
velum. A ciliated peri-
pharyngeal groove encircles
the pharynx in front and
is continued backwards on
the ventral side as a median
groove opening behind into
the thyroid gland, which
thus proved to be a
s
special development of a
structure corresponding to
the endostyle of Amphioxus
(p. 46) and the Tunicata.
The eyes are rudimentary
and hidden beneath the
skin ; the brain is of far
greater proportional size
than in the adult ; and,
as already mentioned, the
gill-pouches open into the pharynx in the normal manner.
br.J
Fio. 815. — Petromyzon fluviatilis. Head of larva.
A, from beneath ; B, from the side. br. 1, first
branchial aperture ; eye, eye ; 1. I. lower lip ; na. ap.
nostril; u. 1. upper lip. £.( After W. K. Parker.); _<
2. DISTINCTIVE CHARACTERS AND CLASSIFICATION.
The Cyclostomata are Craniata in which the mouth lies at the
bottom of a sucker-like buccal funnel, or in a depression edged with
tentacles, and there are no jaws. Horny teeth are borne on the
interior of the buccal funnel and on the large " tongue." Paired fins
are absent. There is no exoskeleton ; the skin is glandular. The
vertebral column consists of a persistent notochord with a fibrous
neural tube, in which rudimentary neural arches may be developed.
The skull is largely or wholly roofed by membrane, and there is
an extensive development of labial cartilages. The segments of
the post-auditory region of the head are more distinct than in the
rest of the Craniata. The enteric canal is straight, and there is no
134 ZOOLOGY SECT.
cloaca. The respiratory organs are six to fourteen pairs of gill-
pouches. There is no conus arteriosus and no renal portal system.
There are large olfactory lobes, which may be either hollow or
solid ; the cerebellum is very small. The olfactory organ is single
and median, but is supplied by paired olfactory nerves ; it opens
into a large persistent pituitary sac which perforates the basis
cranii from above. The auditory organ has one or two semicircular
canals. The kidney is a mesonephros, the ureter a pronephric
duct. The gonad is unpaired, and there are no gonoducts, the
genital products making their exit by genital pores.
The Class is divided into two Orders.
ORDER 1. — PETROMYZONTES.
Cyclostomata in which there is a well-developed dorsal fin and
a complete branchial basket ; the pituitary sac terminates
posteriorly in a blind pouch ; the gills open into a respiratory
tube below the gullet. This order includes the Lampreys,
which belong to the genera Petromyzon, Mordacia, Geotria, and
Ichthyomyzon.
ORDER 2. — MYXINOIDEI.
Cyclostomata in which the dorsal fin is absent or feebly
developed ; the branchial basket is reduced ; the pituitary sac
opens posteriorly into the mouth ; the gills open into the pharynx
in the normal manner.
This order includes the Hags or Slime-eels, belonging to the
genera Myxine, Paramyxine, and Bdellostoma.
3. — COMPARISON OF THE MYXINOIDS WITH THE LAMPREY.
The organisation of the Lampreys is so uniform that all that
will be necessary in the present section is to indicate the principal
points in which the Hags differ from them.
Myxine is about the size of a fresh-water Lamprey— i.e. some
forty-five cm. long : Bdellostoma is fully a metre in length. Both
are remarkable for the immense quantities of slime they are
capable of exuding from the general surface and from the seg-
mentally arranged mucus-glands of the skin. It is said that two
specimens of Myxine thrown into a bucket of water are capable
of gelatinising the whole with their secretion. The slime-glands
of Myxine contain peculiar " thread-cells " containing a much-
coiled thread which unwinds either before or after the discharge
of the cell from the gland.
Myxine approaches most nearly to the condition of an internal
parasite of any Vertebrate ; it is said to attach itself to living
Fishes and gradually to bore its way into the coelome, devouring
the flesh as it goes.
XIII
PHYLUM CHORD ATA
135
There is no true buccal funnel : the space on which the mouth
opens is edged with tentacles (Fig. 816) supported by cartilages ;
there is a single median tooth above the oral aperture, and two rows
of smaller teeth on the tongue. The papillae beneath the cone-like
horny teeth bear a still closer superficial resemblance to rudiments
(or vestiges) of true calcified teeth than is the case in the Lamprey ;
but it appears that no odontoblasts and no calcified substance of
any kind are formed in connection with them. A velum separates
the buccal cavity from the
pharynx. ^ he nostril (na. na.ap
ap.) is a large unpaired A
aperture situated in the
dorsal margin of the buccal
space, and is continued
into a passage, the pitui-
tary sac, which opens into
the pharynx by an aper-
ture which appears in late
embryonic life. Myxine
commonly lives nearly
buried in mud, and the
respiratory current passes
through this passage to
the gill*.
The only fin is a narrow
caudal surrounding the end
of the tail. The respira-
tory organs present strik-
ing differences in the two
•genera. In Bdellostoma
there are in different species
six to fourteen very small
external branchial aper-
tures (br. d. 1) on each side,
each of which communi-
cates by a short tube with
one of the gill-pouches,
which is again connected
with the pharnyx by
another tube. Behind and close to the last gill-slit, oa the left
side, is an aperture leading into a tube, the cesophageo-cutaneous
rt B o
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rf-2
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gfa-3
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communicate directly with the
pharynx ; there is no respiratory
tube.
The neural canal is over-arched
merely by fibrous tissue (Fig. 817,
n.t.) ; there is no trace of neural
arches in the trunk, but in the
posterior part of the caudal region
both neural canal and notochord
are enclosed in a continuous
cartilaginous plate. Similarly the
roof of the skull is entirely mem-
branous. The nasal passage
(na. t.) is strengthened by rings
of cartilage, and the buccal
tentacles are supported by rods
of the same tissue. Behind the
styloid cartilage or hyoid bar
(st.p.) is a rod connected below
with the subocular arch ; it pro-
bably represents the first branchial
bar. The " tongue " is supported
by an immense cartilage (m. v.c.),
in part corresponding to the lin-
gual cartilage of the Lamprey.
The branchial basket is rudimen-
tary, being represented only by
certain small irregular cartilages,
such as one in the walls of the
cesophageo-cutaneous duct, and,
in Myxine (Fig. 817, br. &.), one
on the right side supporting the
common external gill-tube.
The myotomes of one side
alternate with those of the other.
The intestine is very wide.
The liver consists of two separate
portions, the ducts of which
open separately into the gall-
bladder. A pancreas-like gland
is present in both Myxine and
Bdellostoma. The brain differs
considerably from that of the
Lamprey, especially in the larger
olfactory lobes and the reduced
ventricles, and smaller mid-brain.
The dorsal and ventral roots of
XIII
PHYLUM CHORDATA
137
.i.c
the spinal nerves unite instead of remaining separate. The eyes
are vestigial and sunk beneath the skin, and the auditory organ
(Fig. 818) has only a single semi-
circular canal, which, having an
ampulla at each end, probably
represents both anterior and pos-
terior canals.
Bdellostoma has a persistent
pronephros in the form of a
paired irregularly ovoidal body
situated just above the heart and
consisting of a large number of
tubules richly branched peripher-
ally : the nephrostomes open into
the pericardium. The tubules
FIG. X18. — Auditory organ of Myxine.
amp., amp', ampullae ; end. s. endolym-
phatic sac ; s. c. semicircular canal ; utr.
sac. utriculo-sacculus. (After Retzius.)
FIG. 819. — A, portion of kidney
ureter ; 6, urinary tubule ; c,
Malpighian capsule ; d, afferent
artery ; f, efferent artery.
Compara-
do not communicate with the
pronephric duct in Myxine, but end blindly :
in Bdellostoma they open into an incom-
plete longitudinal duct, which does not
communicate with the permanent kidney-
duct. The functional kidney is the mesone-
phros, and is specially interesting from the
fact that in Myxinoids it retains in the adult
its primitive segmental arrangement. The
ureter (pronephric duct, Fig. 819, a) sends
off in each segment a coiled tubule (6) with
a single Malpighian capsule (c), into which
a branch from the aorta (d) enters and
forms a glomerulus.
Myxine is hermaphrodite, the anterior
part of the gonad being ovary, the posterior
testis : in some the ovary is mature and
the testis rudimentary, in others the oppo-
site condition holds good, so that, while
hermaphrodite, each individual is either
predominantly female or predominantly
male. The eggs of both genera are of
great proportional size, and those of Myxine
are enclosed when laid in a horny shell
bearing numerous hooked processes at each
pole; by means of these the eggs are en-
tangled together, and probably also attached
to seaweed.
In Bdellostoma stouti, the only Myxinoid
of ^^ &* development is known, the
eggs are elongated and cylindrical, and
^^ & ^ quantity Qf food.volk.
The segmentation is meroblastic, being
138
ZOOLOGY
SECT.
confined to a germinal disc situated at one end of the elongated
egg. The blastoderm thus formed extends gradually over the
surface of the yolk, which it only completely encloses at a late
stage, when the gill-clefts are all formed.
Bdellostoma differs from Petromyzon and
resembles the majority of the Craniata
in the mode of development of the central
nervous system, which is formed, not
from a solid ectodermal keel, but from an
open medullary groove the lips of
which bend inwards and unite to form a
medullary canal.
fL
HI
4. — GENERAL REMARKS.
The Lampreys and Hags are undoubtedly
the lowest of craniate Vertebrata, but are
in many respects so highly specialised that
it is a matter of great difficulty to deter-
mine their affinities with the remaining
classes. The structure of the vertebral
column and of the cranium are undoubtedly
primitive in the extreme ; but in the deve-
lopment of what may be called the accessory
portions of the skull, such as labial carti-
lages, they show a singularly high degree
of specialisation. The branchial basket is
quite sui generis, the theory that its ver-
tical bars are true branchial arches, dis-
placed outwards during development, being
quite unproved. The absence of functional
jaws is very remarkable, seeing that in the
remaining Craniata these structures always
bound the mouth at a period when the
skull is in the stage of development in
which it remains permanently in Cyclo-
stomes : it is quite possible that their func-
tionless condition may be due to degenera-
tion accompanying the Devolution of a FIG 82p._Paiaospondyiu.
suctorial mouth. The brain, in spite of its gunni (magnified), c. cirri ;
,, *-. p.a. parachordal and auditory
Small Size, IS in Some respects Of a more region; t.p. trabecular re-
advanced type than that of some of the
true Fishes. The circumstance that the
pituitary pouch perforates the skull-floor from above and be-
comes early associated with the olfactory sac is unique among
the Vertebrata. The kidney of Bdellostoma is of the most
primitive type, and the presence of a large pronephros is a
xni PHYLUM CHORDATA 139
significant archaic character. The total absence of limbs may be
a result of degeneration.
The geographical distribution of the class is interesting from
the fact that each order contains some genera which are mainly
northern, others which are exclusively southern. Petromyzon is
found on the coasts and in the rivers of Europe, North America,
Japan, and West Africa ; it is therefore mainly Holarctic. Ichthyo-
mvzon is found on the western coasts of North America, Mordacia in
Tasmania and Chili, Geotria in the rivers of Chili, Australia, and
New Zealand. Myxine occurs in the North Atlantic and on the
Pacific Coast of South America ; Paramyxine in the Pacific ;
Bdellostoma on the coasts of South Africa, New Zealand, and Chili.
No undoubted fossil remains of Cyclostomes are known, but
there is some reason to believe that a little fossil, Palceospondylus
gunni (Fig. 820), discovered in the Devonian rocks of Scotland,
may be referable to this class. It is about an inch long, and shows
two regions, the cranium and the vertebral column ; there is no
trace of exoskeleton or teeth. The vertebral column is composed
of calcified centra with neural arches ; haemal arches are present in
the caudal region ; the structure of this part of the skeleton is thus
of a distinctly higher type than in recent Cyclostomes, and this
perhaps lends support to the view that the latter are degenerate.
There is a caudal fin supported by slender, sometimes forked, rays.
The cranium consists of an anterior, probably trabecular, region
(t.p.), and of a posterior region (p.a.), which seems to answer to
the parachordals and auditory capsules. Just in advance of the
anterior region is a ring-shaped opening surrounded by cirri (c.) :
this may be either the nasal aperture or the mouth. There are
vestiges of upper and lower jaws, and about four branchial arches.
The posterior region of the skull gives off paired plates (x) which
may perhaps represent pectoral fins.
CLASS II.-PISCES.
The Pisces, including the cartilaginous Fishes, the bony Fishes,
and the Dipnoi, are Craniata which have the organs both of respira-
tion and of locomotion adapted for an aquatic mode of life. The
chief, and in the majority the only, organs of respiration are the
gills, which are in the form of series of vascular processes attached
to the branchial arches and persisting throughout life. The organs
of locomotion are the paired pectoral and pelvic fins, and the
unpaired dorsal, ventral, and caudal ; these are all supported
by fin-rays of dermal origin. A dermal exoskeleton is usually
present. In the endoskeleton the notochord is usually more or
less completely replaced by vertebra ; there is a well-developed
skull, and a system of well-formed visceral arches, of which the first
forms upper and lower jaws, the latter movably articulating with
the skull, and both nearly always bearing teeth. There is frequently
140 ZOOLOGY SECT.
an air-bladder, which in certain exceptional cases acquires the
function of a lung or chamber for breathing air. The hypophysis
is not in any way connected with the nasal chambers and lies
within the cranial cavity. There is a pair of nasal chambers which
only exceptionally communicate internally with the mouth cavity.
The auditory labyrinth contains the three typical semicircular
canals. The kidney is a persistent mesonephros.
The first two sub-classes are nearly related to one another and
are frequently regarded as sections of a single sub-class — the
Chondricliitiyes or Cartilaginous Fishes.
Sub-Class I.— Elasmobranchh.
The sub-class Elasmobranchii comprises the Sharks, Dog-fishes,
and Rays. The skeleton of these fishes, like that of the Cyclo-
stomes, is composed essentially of cartilage, and, though there
may be calcification of the substance of the cartilage, true bony
tissue, such as is found in all higher groups, is not present. The
dermal fin-rays, supported on the cartilaginous skeleton of the fin,
are of horn-like constitution. There is never (in recent forms) an
operculum or gill-cover. A cloaca is present, the external opening
of which serves as a common outlet for the rectum and the renal
and reproductive ducts. Among some of the fossil representatives
of this group are to be found the most primitive of all known Fishes.
1. — EXAMPLE OF THE SUB-CLASS : THE DOG-FISH (Scyllium
canicula or Hemiscyllium modestum).
General External Features. — The general shape of the body
(Fig. 821) may be roughly described as fusiform ; at the anterior,
or head- end it is broader and depressed ; posteriorly it tapers
gradually and is compressed from side to side. The head termi-
nates anteriorly in a short, blunt snout. The tail is narrow and
bent upwards towards the extremity. The colour is grey with
brown markings, or dark-brown above, lighter underneath. The
entire surface is covered closely with very minute hard placoid
scales or dermal teeth, rather larger on the upper surface than
on the lower. These are pointed, with the points directed some-
what backwards, so that the surface appears rougher when the
hand is passed over it forwards than when it is passed in the opposite
direction. When examined closely each scale is found to be a
minute spine situated on a broader base. The spine consists
of dentine covered with a layer of enamel ; the base is composed
of bone-like substance, and the whole scale has thus the same
essential structure as a tooth. Along each side of the head and
body runs a faint depressed longitudinal line or slight narrow
groove — the lateral line, marking the position of the lateral line
canal, which contains integumentary sense-organs.
xm PHYLUM CHORDATA 141
As ill Fishes in general, two sets of fins are to be recognised — the
unpaired or median fins, and the paired or lateral. These are all
flap-like outgrowths, running vertically and longitudinally in the
case of the median fins, nearly horizontally in the case of the lateral :
they are flexible, but stifnsh, particularly towards the base, owing
to the presence of a supporting framework of cartilage. Of the
median fins two — the dorsal— are situated, as the name indicates,
on the dorsal surface : they are of triangular shape ; the anterior,
which is the larger, is situated at about the middle of the length of
the body, the other a little further back. The caudal fin fringes the
tail : it consists of a narrower dorsal portion and a broader ventral,
continuous with one another round the extremity of the tail, the
latter divided by a notch into a larger, anterior, and a smaller,
posterior lobe. The tail is heterocercal, i.e., the posterior extremity
of the spinal column is bent upwards and lies in the dorsal portion
of the caudal fin. The ventral or so-called anal fin is situated on
the ventral surface, in Scyllium opposite the interval between' the
anterior and posterior dorsals, in Hemiscyllium behind the latter ;
it resembles the latter in size and shape.
Fio. 821. — Dog-Fish (Hemiscyllium modestum). Lateral view. (After Waite.)
Of the lateral fins there are two pairs, the pectoral and the pelvic.
The pectoral are situated at the sides of the body, just behind
the head. The pelvic, which are the smaller, are placed on the
ventral surface, close together, about the middle of the body.
In the males the bases of the pelvic fins are united together in the
middle line, and each has connected with it a clasper or copulatori/
organ. The latter is a stiff rod, on the inner and dorsal aspect
of which is a groove leading forwards into a pouch-like depression
in the base of the fin.
The mouth — a transverse, somewhat crescentic opening — is
situated on the ventral surface of the head, near its anterior end.
In front and behind it is bounded by the upper and lower jaws,
each bearing several rows of teeth with sharp points directed back-
wards. The nostrils are situated one in front of each angle of the
mouth, with which each is connected by a wide groove — the naso-
buccal groove. In Hemiscyllium the outer edge of the groove is
prolonged into a narrow sub cylindrical appendage — the barbel. A
small rounded aperture, the spiracle, — placed just behind the eye—
142
ZOOLOGY
SECT.
leads into the large pharynx. Five pairs of slits running vertically
on each side of the neck — the branchial slits — also lead internally
into the pharynx. A large median opening on the ventral surface
at the root of the tail, between the pelvic fins, is the opening leading
into the cloaca, or chamber forming the common outlet for the
intestine and the renal and reproductive organs. A pair of small
depressions, the abdominal pores, situated behind the cloacal open-
ing, lead into narrow passages opening into the abdominal cavity.
The skeleton is composed entirely of cartilage, with, in certain
places, depositions of calcareous salts. As in Vertebrates in general,
we distinguish two sets of elements in the skeleton — the axial set
and the appendicular, the former comprising the skull and spinal
column, the latter the^limbs and their arches.
n.a
n.c
n.a,
n.a
h.a
FIG. 822. — Portions of the vertebral column of Scyllium canicula. A and B, from the
trunk ; C' and D, from the middle of the tail ; A and C, two vertebrae in longitudinal section ;
7? and D, single vertebra1 viewed from one end. It, calcified portion of centrum ; c. centrum ;
for. foramen for dorsal, and for', for ventral root of spinal nerve ; h. a. hnemal arch (basi-
ventral) ; h.c. haemal ca.nal ; h.xp. haemal spine ; i.it./i. intercalary piece (interdorsal,
or interneural plate) ; n.a. neural arch ; n.c. neural canal ; n.p. neural plate (basi-dorsal) ;
n.sp. neural spine ; ntc. intervertebral substance (remains of notochord) ; r. proximal portion
of rib ; tr.pr. transverse process (bas-il stump). (From Parker's I'mclical Zooloijij.)
The spinal column is distinguishable into two regions — the
region of the trunk and the region of the tail. In the trunk-region
each vertebra (Fig. 822, A and B) consists of a centrum (c.), neural
arch (n.a.), and transverse processes (tr.pr). In the caudal region
there are no transverse processes, but inferior or hamial arches
(C, D, h.a.) take their place. The centra of all the vertebras are
deeply biconcave or ampliicodous, having deep conical concavities
on their anterior and posterior surfaces. Through the series of
centra runs the notochord (ntc.}, greatly constricted in the centrum
itself, and dilated in the large spaces formed by the apposition
of the amphiccelous centra of adjoining vertebrae, where it forms a
XIII
PHYLUM CHORDATA
143
pulpy mass. The concave anterior and posterior surfaces of the
centra are covered by a dense calcined layer, and in Heiniscyllium
eight radiating lamellse of calcined tissue run longitudinally through
the substance of the centrum itself. The centra, unlike those
of the higher forms, are developed as chondrifications of the sheath
of the notochord into which cells of the skeletogenous layer have
migrated (p. 71). On the dorsal side of the row of centra the
spinal column is represented by the series of neural arches which
support the walls of the spinal canal. Owing to the presence of a
series of intercalary cartilages the neural arches appear to be twice
as numerous as the centra. Each neural arch consists on each side
of a process, the neural process, given off from the centrum, and
trL
ip.br.5
FIG. 823. — Hemiscy Ilium, lateral view of skull with visceral arches and anterior part of spinal
column ; the branchial rays are not represented. The skull and hyoid arch are somewhat
drawn downwards, so that the hyoid and first branchial arch are not exactly in their natural
relations ; cer. hy. ceratohyal ; ep. br. 1, ep. br. 5, first and fifth epibranchials ; ql. aperture
for glossopharyngeal nerve ; b. hy. basihyal ; hy. run. hyomandibular ; interc. intercalary
(interdorsal) plates ; mrk. Meckel's cartilage ; neur. neural processes ; olf. olfactory capsule ;
oc. foramen for oculomotor ; oph. 1, foramen for ophthalmic division of facial nerve ;
opk. 2, foramen for ophthalmic division of trigeminal ; opt. optic foramen ; pal. -
liranchial ; sp. neural spines; tr. transverse processes and ribs; tri. foramen for
trigeminal nerve.
of a small cartilage, the neural plate (basi-dorsal), which becomes
completely fused with the neural process in the adult. Between
successive neural plates, the width of each of which is only about
half the length of the centrum, are interposed a series of plates
of very similar shape, the interdorsal or interneural plates. Small
median cartilages, the neural spines, fit in between both neural
and interneural plates of opposite sides and form keystones com-
pleting the arches.
The transverse processes are very short : connected with each of
them is a rudimentary cartilaginous rib (r.) about half an inch in
length.
The cranium (Fig. 823) is a cartilaginous case, the wall of which
144 ZOOLOGY SECT.
is continuous throughout, and not composed, like the skulls of
higher Vertebrates, of a number of distinct bony elements fitting
in together. At the anterior end is a rostrum, consisting in Scyllium
of three cartilaginous rods converging as they extend forwards and
the lateral ones meeting anteriorly. At the sides of the base of this
are the olfactory capsules (olf.) — thin rounded cartilaginous sacs open-
ing widely below, the cavities of the two capsules being separated
from one another by a thin septum. The part of the roof of the
cranial cavity behind and between the olfactory capsules is formed
not of cartilage, but of a tough fibrous membrane, and the space
thus filled in is termed the anterior fontanelle : in contact with the
lower surface of the membrane is the pineal body, to be afterwards
mentioned in the account of the brain. Each side-wall of this
part of the skull presents a deep concavity — the orbit — over which
is a ridge-like prominence, the supra-orbital crest, terminating
anteriorly and posteriorly in obscure processes termed respectively
the pre-orbital and post-orbital processes. Below the orbit is a
longitudinal infra-orbital ridge.
Behind the orbit is the auditory region of the skull — a mass of
cartilage in which the parts of the membranous labyrinth of the
internal ear are embedded. On the upper surface of this posterior
portion of the skull are two small apertures situated in a mesial
depression. These are the openings of the aqueductus vestibuli
(endolymphatic ducts), leading into the vestibule of the membranous
labyrinth. Behind this again is the occipital region, forming the
posterior boundary of the cranial cavity, and having in the middle
a large rounded aperture — the foramen magnum — through which
the spinal cord, contained in the neural canal and protected by the
neural arches of the vertebra, becomes continuous with the brain,
lodged in the cranial cavity. Below this, on either side is an
articular surface — the occipital condyle — for articulation with the
spinal column, and between the two condyles is a concavity, like
that of the vertebral centra, containing notochordal tissue.
A number of smaller apertures, or foramina, chiefly for the
passage of nerves, perforate the wall of the skull. Behind and to the
outer side of the anterior fontanelle are apertures (oph.2,1) through
which the ophthalmic branches of the fifth and seventh ' nerves
leave the skull. Piercing the inner wall of the orbit are foramina
through which the optic or second pair of cerebral nerves (opt.), the
oculomotor (oc.), or third, the pathetic, or fourth (path.), the tri-
geminal, or fifth (tri.), the abducent, or sixth, and the facial, or
seventh, gain an exit from the interior of the cranial cavity. Just
behind the auditory region is the foramen for the glosso-
pharyngeal (gl.), and in the posterior wall of the skull, near the
foramen magnum, is the foramen for the vagus.
In close connection with the cranium are a number of cartilages
composing the visceral arches (Figs. 823 and 824). These are in-
XIII
PHYLUM CHORDATA 145
complete hoops of cartilage, mostly segmented, which lie in the
sides and floor of the mouth-cavity or pharynx. The first of these
forms the upper and lower jaws. The upper jaw, or palatoquadrate
(pal. q.), consists of two stout rods of cartilage firmly bound to-
gether in the middle line and bearing the upper series of teeth.
The lower jaw, or Meckel's cartilage (mck.), likewise consists of two
stout tooth-bearing cartilaginous rods firmly united together in the
middle line, the union being termed the syrnphysis. At their outer
ends the upper and lower jaws articulate with one another by a
movable joint. In front the upper jaw is connected by a ligament
with the base of the skull.
Immediately behind the lower jaw is the Jiyoid arch. This
consists of two cartilages on each side, and a mesial one below.
The uppermost cartilage is the hyomandibular (hy. mn) : this
articulates by its proximal end with a distinct articular facet
on the auditory region of the skull : distally it is connected by
ligamentous fibres with the outer ends of the palatoquadrate
and Meckel's cartilage. The lower lateral cartilage is the cerato-
hyal (cer. hy.}. Both the hyomandibular and ceratohyal bear a
number of slender cartilaginous rods — the branchial rays of the
hyoid arch. The mesial element, or basihyal (b.hy.), lies in the
floor of the pharynx. Behind the hyoid arch follow the branchial
arches, which are five in number. Each branchial arch, with
exceptions to be presently noted, consists of four cartilages.
The uppermost of these — pharyngobranchial (ph. br.l-ph. br.ij] — lie
in the dorsal wall of the pharynx, not far from the spinal column ;
the pharyngobranchials of the last two arches are fused together.
The next in order — the epibranchials (ep. br.) — with the exception
of those of the last arch, bear a number of slender cartilaginous
rods — the branchial rays — which support the walls of the gill-sacs ;
and the next — the ceratobranchials (cer. br.) — are, with the same
exception, similarly provided. The hypobranchials (hyp. br.), which
succeed these, are absent in the case of the first and fifth arches.
In the middle line on the floor of the pharyngeal cavity is a mesial
cartilage — the basibranchial (Fig. 824, b. br.) — which is connected
with the ventral ends of the third, fourth, and fifth arches. A
series of slender curved rods — the extrabranchials — lie superficial
to the branchial arches, along the borders of the corresponding
external branchial clefts.
Two pairs of delicate labial cartilages are present at the sides
of the mouth, and a couple at the margins of the openings of the
olfactory capsules.
The skeleton of all the fins — paired and unpaired — presents a
considerable degree of uniformity. The main part of the expanse
of the fin is supported by a series of flattened segmented rods, the
pterygiophores or cartilaginous fin-rays, which lie in close apposition :
in the case of the dorsal fins these may be partly calcified. At
VOL. IT K
146
ZOOLOGY
SECT.
the outer ends of these are one or more rows of polygonal plates of
cartilage. On each side of the rays and polygonal cartilages are a
number of slender " horny " rays or ceratotrichia of dermal origin.1
In the smaller median fins there may be an elongated rod of
cartilage constituting the skeleton, or cartilage may be entirely
absent. In the pectoral fin (Fig. 825) the fin-rays are supported
on three basal cartilages articulating with the pectoral arch. The
latter (pect.) is a strong hoop of cartilage incomplete dorsally,
situated immediately behind the last of the branchial arches.
mck
hi/p.brt
cer.br.3
cer.br. t
c&r.br.s
-ph.br..
FlQ. 82 1. — Hemiscyllium, ventral view of the visceral arches. Letters as in preceding figure.
In addition — b. br. basibranchial plate ; cer. br. ceratobranchials ; hyp. br. hypobranchials.
It consists of a dorsal, or scapular, and a ventral, or coracoid portion,
the coracoid portions of opposite sides being completely continuous
across the middle line, while the scapular are separated by a wide
gap in which the spinal column lies. Between the two portions are
the three articular surfaces for the three basal cartilages. The
1 Though, on account of their appearance and horn -like consistency, these
structures are commonly referred to as horny, they do not consist of true horn
(which is always epidermal in origin), but of a substance called elastin,
characteristic of elastic connective -tissue fibres.
xm
PHYLUM CHORDATA
147
coracoid portions are produced forwards in the middle line into a
flattened process supporting the floor of the pericardial cavity in
which the heart is
lodged. The three
basal cartilages of
the fin are named,
respectively, the
anterior, proptery-
gium (pro.), the
middle, mesoptery-
gium (meso.), and
the posterior, me •
tapterygium (meta . ) .
Of these the first is
the smallest and the
last the largest : the
first bears only one
large ray ; the other
two bear twelve or
rays, differ-
more
ently arranged in
the two genera.
The pelvic fin
(rig. 8wO) has Only FlG . 82.-,.— Hemiscyllium, pectoral arch and fin. d. r. derma!
a single basal Car- horny rays ; meso. mesopterygium ; meta. inetapterygium ; feet.
, -i / , • pectoral arch : pro. propterygium.
tilage (meta.) articu-
lating with the pelvic arch, with which also one or two of the
fin-rays articulate directly. The
pelvic arch (pelv.) is a nearly
straight bar of cartilage which
transversely across the
d.r
surface of the body,
front of the cloacal
runs
ventral
just in
opening.
Enteric Canal (Fig. 827).-
The mouth leads into a very
wide cavity, the pharynx, into
which open at the sides the in-
ternal apertures of the branchial
clefts and of the spiracle. From
this runs backwards a short wide
tube — the oesophagus (ces.)—
which passes behind into the
stomach. The stomach is a (J-
shaped organ, with a long left
limb continuous with the oesophagus, and a short right one
passing into the intestine. At the pylorus (pyl.} — the point where
K 2
Flo. 826. — Hemiscyllium, pelvic arch ami
pelvic tin. meta. inetapterygium ; prli\
pelvic arch.
148
ZOOLOGY
SECT.
fi.
bills
.s
,
~.2S
+s
no S e'S.S gTs sfl-3
fi2f35>&T=£J
CNfl^J .
GOcS CO-OP* bO^t O C ^
XIII
PHYLUM CHORDATA
149
the stomach passes into the intestine — is a slight constriction,
followed by a thickening. The intestine consists of two parts — small
intestine or duodenum, and large intestine. The former is very short,
only an inch or two in length. The latter is longer and very wide ;
it is divisible into two portions — the colon (col.) in front and the
rectum (rect.) behind. The former is very wide and is characterised
by the presence in its interior of a spiral valve, a fold of the mucous
membrane which runs spirally round its interior, and both retards
the too rapid passage of the food and affords a more extensive
surface for absorption. The rectum differs from the colon in being
narrower and in the absence of the spiral valve ; it opens behind into
the cloaca.
There is a large liver (liv.) consisting of two elongated lobes. A
rounded sac — the gall-bladder (g. bl.) — lies embedded in the left
lobe at its anterior end. The duct of the liver — the bile-duct (b.dct.)
—runs from the liver to the intestine. Proxinially it is connected
with the gall-bladder, and by branch-ducts
with the right and left lobes of the liver. It
opens near the commencement of the colon.
The pancreas (pancr.) is a light-coloured
compressed gland consisting of two main
lobes with a broad connecting isthmus, lying
in the angle between the right-hand limb of
the stomach and the small intestine. Its
duct enters the wall of the small intestine
and runs in it for about half an inch, open-
ing eventually at the point where the small
intestine passes into the colon.
Connected with the rectum on its dorsal
aspect is an oval gland — the rectal gland
(rect. gl.) — about three-quarters of an inch in length.
The spleen (spl.) is a dark-red or purple body attached to the con-
vexity of the (J -shaped stomach and sending a narrow lobe along
the right-hand limb.
The organs of respiration in the Dog-fish are the gills, situated
in the five gill-pouches. Each gill-pouch (Fig. 828) is an antero-
posteriorly compressed cavity opening internally into the pharynx
and externally by the corresponding gill-slit. The walls of the
pouches are supported by the branchial and hyoid arches with their
rays, the first pouch being situated between the hyoid and first
branchial arches, the last between the fourth and fifth branchial
arches. On the anterior and posterior walls of the pouches are the
gills, each hemibranch consisting of a series of close-set parallel
folds or plaits of highly vascular mucous membrane. Separating
adjoining gill-pouches, and supporting the gills, are a series of broad
interbranchial septa, each containing the corresponding branchial
arch with its connected branchial rays. The most anterior hemi-
FIG. 828.— Hemiscyllium.
Branchial sac exposed from
the outside.
150
ZOOLOGY
SECT.
branch is borne on the posterior surface of the hyoid arch. The
last gill-pouch differs from the rest in having gill-plaits on its
anterior wall only. On the anterior wall of the spiracle is a vestigial
gill — the pseudobranch or spiracular gill — in the form of a few slight
ridges.
Blood-system. — The heart is situated in the pericardial
cavity, on the ventral aspect of the body, in front of the
pectoral arch, and between the two series of branchial pouches.
The dorsal wall of the pericardial cavity is supported by the
basibranchial cartilage. Placing it in communication with the
abdominal cavity is a canal — the pericardio-peritoneal canal.
The heart (Fig. 827) consists of four chambers — sinus venosus
(sin.), auricle (aur.}, ventricle (vent.}, and conus arteriosus (con.),
through which the blood passes in the order given. The sinus
7.CU1
3. 1/
ttfbr2 ucu) nfbr3a
FIG. 820. — The heart and branchial arteries of Scyllium, from the side. a/, frr.i — », afferent
branchial arteries ; an. auricle ; c. a. conns arteriosus ; cl. ' — 5, branchial clefts ; cor. coronary
artery ; d. ao. dorsal aorta : d. c. dorsal carotid artery ; ?/. frr.i — '•*, efferent branchial
arteries ; ep. br.1 — 4, epibranehial arteries ; mn. mandilmlar artery ; sp. spiracle ; s. cl. sub-
clavian artery ; s. t>. sinus venosus ; v. ventricle ; v. ao. ventral aorta ; i\ c. ventral carotid
artery. (From Parker's Practical Zoo/oiji/.)
venosus is a thin-walled, transverse, tubular chamber, into the ends
of which the great veins open. It communicates with the auricle
by an aperture, the sinu-auricular aperture. The auricle is a large,
three-cornered, thin-walled chamber, situated in front of the sinus
venosus and dorsal to the ventricle. Its apex is directed forwards,
and its lateral angles project at the sides of the ventricle : it commu-
nicates with the ventricle by a slit-like aperture guarded by a two-
lipped valve. The ventricle is a thick- walled, globular chamber,
forming the most conspicuous part of the heart when looked at
from the ventral surface. From it the conus arteriosus runs
forwards as a median stout tube to the anterior end of the peri-
cardial cavity, where it gives off the ventral aorta. It contains
two transverse rows of valves, anterior and posterior, the former
xni PHYLUM CHORD ATA 151
consisting of three, the latter of three or four. The ventral aorta
(Fig. 829) gives origin to a series of paired afferent branchial
arteries (af. br.), one for each branchial pouch. In Scy Ilium the
two most posterior arise close together near the beginning of the
ventral aorta, the third pair a little further forwards. The ventral
aorta then runs forwards a little distance and bifurcates to form
the two innominate arteries, right and left, each of which in turn
bifurcates to form the first and second afferent vessels (af. br1.,
af. br.z) of its side. In Hemiscyllium (Fig. 830) the arrangement
is somewhat different.
From the gills the blood passes by means of the efferent branchial
arteries. These efferent vessels (Fig. 829, ef. br.} form a series of
loops, one running around the margin of each of the first four
internal branchial clefts : a single vessel runs along the anterior
border of the fifth branchial cleft and opens into the fourth loop.
The four main efferent branchial vessels (epibranchials, ep. br.) run
inwards and backwards from the loops under cover of the mucous
membrane of the roof of the pharynx to unite in a large median
trunk — the dorsal aorta (d. ao.). A dorsal carotid artery (d. c.) is
given off from the first efferent branchial. A branch (hyoidcan)
given off from the same efferent vessel supplies the pseudobranch,
and the blood from the latter is taken up by the ventral carotid
(v. c.). Both carotids run forwards to supply the head.
The dorsal aorta (Fig. 829, d. ao.) runs backwards throughout
the length of the body-cavity, giving off numerous branches, and
is continued as the caudal artery, which runs in the canal enclosed
by the inferior arches of the caudal vertebrae. The first pair of
branches are the subclavians (s. cl.), for the supply of the pectoral
fins ; these are given off between the third and fourth pairs of
epibranchial arteries. The next large branch is the unpaired cosliac
(Fig. 827, ccel.) : this runs in the mesentery and divides into
branches for the supply of the stomach and liver, the first part of
the intestine, and the pancreas. The anterior mesenteric artery,
also median, supplies the rest of the intestine and gives off branches
to the reproductive organs. The lienogastric supplies part of the
stomach, the spleen, and part of the pancreas. The posterior
mesenteric is a small vessel mainly supplying the rectal gland.
Small renal arteries carry a small quantity of arterial blood to the
kidneys, and a pair of iliac arteries, likewise of small size, pass to
the pelvic fins. In addition to these a number of small arteries,
the parietal, supplying the wall of the body, are given off throughout
the length of the aorta.
The veins are very thin- walled, and the larger trunks are remark-
able for their dilated character, from which they have obtained
the name of sinuses, though they are true vessels and not sinuses
in the sense in which the word is used in dealing with the Inverte-
brates (cf. p. 90).
152
ZOOLOGY
SECT.
The venous blood is brought back from the head by a pair of
jugular or anterior cardinal sinuses (Fig. 830, jug. v.), and from the
trunk by a pair of posterior cardinal sinuses (r. and l.card.s.). At
the level of the
sinus venosus the an-
terior and posterior
cardinals of each side
unite to form a short,
b?-v4 nearly transverse sinus,
•br.t'f the precaval sinus or
ductus Cuvieri (Fig.
830, dct. c.), which is
continued into the
lateral extremity of
the sinus venosus. In-
to the precaval sinus,
about its middle, opens
an inferior jugular
sinus (inf. jug. v.}
which brings back the
blood from the floor of
the mouth and about
the branchial region of
the ventral surface.
The two posterior car-
dinal sinuses extend
backwards throughout
the length of the body-
cavity ; in front they
are enormously dilated,
behind they lie be-
tween the kidneys.
Anteriorly each re-
ceives the correspond-
ing subclavian vein
bringing the blood
from the pectoral fin
and adjacent parts of
the body-wall. The
lateral vein (I. v.), in-
stead of joining with
the subclavian
(p. 91), opens separ-
ately into the precaval.
The genital sinus discharges into the posterior cardinal sinus.
There are two portal systems of veins, the renal (r. and l.port.v.)
and the hepatic portal (hep. port, v.), by which the kidneys and liver,
r.bort.v
l.Jborb. v
ccutd.v
FIG. 830. — Hemiscyllium. Diagrammatic representation of
the ventral aorta and afferent branchial arteries, and of the
chief veins. aZi. alimentary canal; br.v.i-br.v? afferent
branchial arteries ; cau/1. v. caudal vein ; dct. c. precaval
sinns ; hi. heart ; h.port. v. hepatic portal vein ; hep. s.
hepatic sinus ; inf. jug. v. inferior jugular vein .or sinus ;
jug. a. jugular vein or sinus ; Int. v. lateral vein ; liv. liver ;
1. card. s. left cardinal sinus ; /. port. v. left renal portal vein ;
neph. kidney ; r. card. s. right cardinal sinus ; r. port. v.
right renal portal vein.
xra PHYLUM CHORDATA 153
respectively, are supplied with venous blood. The caudal vein,
which brings back the blood from the tail, running, along with the
caudal artery through the inferior arches of the vertebrae, divides on
entering the abdominal cavity into right and left renal portal veins,
which end in a number of afferent renal veins supplying the kidneys.
The hepatic portal vein (h. port, v.) is formed by the confluence of
veins derived from the intestine, stomach, pancreas, and spleen,
and runs forwards to enter the liver a little to the right of the
middle line. In Hemiscyllium a large branch connects the genital
sinus with the intestinal tributaries of the hepatic portal system :
the blood from the liver enters the sinus venosus by two hepatic
sinuses placed close together.
Nervous System. — The fore-brain consists of a rounded
smooth prosencephalon (Fig. 831, V.H.) divided into two lateral
parts by a very shallow median longitudinal groove. From its
antero-lateral region each half gives off a thick cord, which dilates
into a large mass of nerve-matter, the olfactory bulb (L. ol.), closely
applied to the posterior surface of the corresponding olfactory
capsule. The diencephalon (ZH) is comparatively small ; its roof
is very thin, while the lateral walls are composed of two thickish
masses — the optic thalami. Attached to the roof is a slender tube,
the epiphysis cerebri or pineal organ (Gp.), which runs forwards and
terminates in a slightly dilated extremity fixed to the membranous
part of the roof of the skull. Projecting downwards from its
floor are two rounded bodies, the lobi inferiores (UL), which are
dilated portions of the infundibulum. Behind these give off a
thin- walled vascular outgrowth — the saccus vasculosus (Sv.}.
Attached to the infundibulum and extending backwards from it
is a thin- walled sac — the pituitary body or hypophysis cerebri (HS),
having on its ventral surface a median tubular body attached at
its posterior end to the floor of the skull. In front of the infundi-
bulum, and also on the lower surface of the diencephalon, is the
optic chiasma, formed by the decussation of the fibres of the two
optic nerves. The mid-brain (MH) consists of a pair of oval optic
lobes dorsally, and ventrally of a band of longitudinal nerve-fibres
corresponding to the crura cerebri of the higher vertebrate brain.
The cerebellum (HH) is elongated in the antero-posterior direction,
its anterior portion overlapping the optic lobes, and its posterior
the medulla oblongata. Its surface is marked with a few fine
grooves. The medulla oblongata (NH), broad in front, narrows
posteriorly to pass into the spinal cord. The fourth ventricle or
fossa rhomboidalis (F. rho.) is a shallow space on the dorsal aspect
of the medulla oblongata covered over only by a thin vascular
membrane, the choroid plexus : it is wide in front and gradually
narrows posteriorly. At the sides of the anterior part of the
fourth ventricle are a pair of folded ear-shaped lobes, the corpora
restiformia.
154
ZOOLOGY
SECT.
The fourth ventricle or metacoele (Fig. 832, meta.) is continuous
behind with the central canal of the spinal cord. It gives off an
epicoele above, and in front is continuous with a narrow passage,
X
FIG. 831. — Brain of Scyllium canicula. A, dorsal view ; B, ventral view ; C, lateral view.
F. rho. fossa rhombohlalis (fourth ventricle) ; Gp, epiphysis ; HH, cerebellum ; HS. H, hypo-
physis ; L. ol. olfactory bulb ; MH, mid-brain ; NH, medulla oblongata ; Si', saccus vascu-
losus ; Tro, olfactory peduncle ; UL, lobi iuferiores ; VH, prosencephalon ; ZH, dien-
cephalon ; II, optic nerves ; ///, oculomotor ; IV, pathetic ; V, trigeminal ; VI, abducent ;
VII, facial ; VIII, auditory ; IX, glossopharyngeal ; X, vagus. (From Wiedersheim's
Comp. Anatomy.)
the iler or mesocoele (iter.), which opens anteriorly into a wider
space, the diaccele or third ventricle (dia.), occupying the interior of
xm
PHYLUM CHORDATA
155
the diencephalon. From this opens in front a median prosoccele,
which gives off a pair of paracodes (para.} extending into the two
lateral portions of the prosencephalon.
From the anterior enlargements of the olfactory bulbs already
mentioned spring numerous fibres which constitute the first pair
of cerebral nerves and enter the olfactory capsules. Between the
two olfactory lobes two small nerves, the terminal or pre-olfactory ,
arise from the prosencephalon : they are the nerves of ordinary
sensation for the interior of the olfactory sacs. From the optic
chiasma the two optic nerves (Figs. 831, 833, 834, 77) run outwards
through the optic foramina into the orbits, each perforating the
sclerotic of the corresponding eye and terminating in the retina.
The third, fourth, and sixth pairs of
nerves have the general origin and
distribution which have already been
described as universal in the Craniata
(p. 100).
The trigeminal (Figs. 831. 833, 834, 7)
arises in close relation to the facial.
As it passes into the orbit it swells
into a ganglion — the Gasserian. Its
chief . branches are three in number.
The first given off is the superficial
ophthalmic (Fig. 833, oph. V ; Fig. 834,
V op.), which runs forwards through
the orbit above the origin of the recti
muscles, and in very close relation
with the ophthalmic branch of the
facial. Anteriorly it breaks up into
branches distributed to the integument
of the dorsal surface of the snout.1
The main trunk of the nerve then runs
forwards and outwards across the
floor of the orbit, and divides into
two branches, the maxillary and mandi-
bular, or second and third divisions of
the trigeminal. The former (mx. V)
supplies the skin of the ventral surface of the snout, the latter
(mnd. V) the skin and muscles of the lower jaw.
Of the branches of the facial, the ophthalmic runs through the
1 In most Elasmobranchs a nerve of considerable size — the ophthalmicus
projundus (Fig. 788) — arises from the dorsal and anterior part of the Gasserian
ganglion, and is usually regarded as a branch of the trigeminal. It runs
forwards over the posterior rectus muscle and under the superior rectus, and
perforates the pre-orbital process to end in the integument of the snout.
Among other branches it gives off ciliary branches to the iris : these are
joined by the ciliary branches of the oculomotor. An ophthalmicus profundus
is not present in Scyllium in the adult condition.
metct
f
FlQ. 832. — Hemiscyllium. The
brain viewed from the dorsal side,
the roofs of the vanous ventricles
removed so as to show the rela-
tions of the cavities (semi-dia-
grammatic), cer, dilatation from
which the epicoale is given off ; dia,
diacosle, pointing to the opening
leading into the inf untlibulum ; iter.
iter or mesoco3le ; meta. metacoele ;
opt. optocoele ; para, paracoele ;
pros, prosoooele ; rh. rhinoccele.
156
ZOOLOGY
SECT.
orbit in close relation to the superficial ophthalmic branch of the
trigeminal, and is distributed to the lateral line and ampullary
canals of the snout region ; the buccal runs forwards in intimate
relation with the maxillary division of the trigeminal, and breaks
up into branches which are distributed to the sensory canals and
ampullae of the region of the snout ; the palatine (pi. VII, VIIp.)
passes to the roof of the mouth ; the main body of the nerve—
hyomandibular nerve (hy. mnd. VII, Vllhy.) — then runs outwards
close to the edge of the hyomandibular cartilage and behind the
spiracle, eventually becoming distributed to the muscles between
sp.co
FIG. 833. — Scyllium catulus. Dissection of the brain and spinal nerves from the dorsal
surface. The right eye has been removed. The cut surfaces of the cartilaginous skull and
spinal column are dotted. The buccal branch of the facial is not represented, cl.l — cl.5,
branchial clefts ; ep. epiphysis ; ex. reel, posterior rectus muscle of the eye-ball ; gl. ph.
glossopharyngeal ; hor. can. horizontal semicircular canal ; hy. mnd. VII. hyomandibular
portion of the facial ; inf. obi. inferior oblique muscle ; int. red. anterior rectus muscle ;
lat. vag. lateral branch of vagus ; mx. V. maxillary division of the trigeminal ; olf. cps.
olfactory capsule ; olf. s. olfactory sac ; oph. V. VII. superficial ophthalmic branches of
trigeminal and facial ; path, fourth nerve ; pi. VII. palatine branch of facial ; sp. co. spinal
cord ; sp, spir. spiracle ; s. reel, superior rectus muscle ; s. olb. superior oblique ; vag.
vagus ; vest, vestibule. (From Marshall and Hurst.)
the spiracle and the first branchial cleft ; a small external mandi-
bular branch (VII e.m.) comes off from it and goes to the lateral
line and ampullary canals of the lower jaw.
The eighth or auditory nerve passes directly into the internal
ear, and breaks up into branches for the supply of its various
parts. The glossopharyngeal (gl. ph., IX) perforates the posterior
part of the auditory region of the skull, and, after it reaches the
xni
PHYLUM CHORDATA
157
exterior, passes to the first branchial cleft, where it bifurcates, one
branch going to the anterior, and the other to the posterior
wall of the cleft. The last nerve of the series — the pneumogastric or
vagus (vag., X) — is a large nerve which emerges from the skull by
an aperture
situated be-
tween the audi-
tory region and
the foramen
magnum. It
first gives off a
series of four
branchial
branches, each
of which bifur-
cates to supply
the anterior and
posterior bor-
ders of the last
four branchial
clefts. The
lateralis nerve
(lat. vag., X.I.)
is frequently re-
ferred to as a
branch of the
vagus since it
runs in intimate
connection with
the trunk of
that nerve for
some distance,
but it has a
distinct origin
in the medulla :
after becoming
separated from
the vagus trunk
it runs along be-
neath the peri-
toneum opposite
the
,rr lateral line, which it supplies, to
posterior end of the body. The rest of the vagus runs backwards
to divide into cardiac branches for the heart and gastric branches
for the stomach.
It will be observed that the system of neuromast organs (lateral
line and ampullary organs) are supplied by nerve-fibres which pass
out in various branches of the facial and in the lateralis :
158 ZOOLOGY SECT.
all these fibres originate in a centre in the medulla, the acustico-
lateral centre, common to them and the fibres of the auditory nerve.
The spinal cord is a cylindrical cord which extends from the
foramen magnum, where it is continuous with the hind-brain,
backwards throughout the length of the neural canal, enclosed by
the neural arches of the vertebrae. As in the Craniata in general
(see p. 96), it has dorsal and ventral longitudinal fissures and a
narrow central canal, and gives origin to a large number of paired
spinal nerves, each arising from it by two roots.
Organs of Special Sense. — The olfactory organs are rounded
chambers enclosed by the cartilage of the olfactory capsules of
the skull, and opening on the exterior by the nostrils on the
ventral surface of the head. The interior has its lining membrane
raised up into a number of close-set ridges running out from a
median septum. The fibres of the olfactory nerves terminate in
cells of the epithelium covering the surface of these ridges.
The eye has the general structure already described as character-
ising the Craniata in general (p. 106). The sclerotic is cartilaginous,
the choroid has a shining metallic internal layer or tapetum cellu-
losum, and the lens is spherical. There are the usual eye-muscles,
the two obliques situated anteriorly, the four recti posteriorly, not em-
bracing the optic nerve. The eyelids are represented by stiff folds.
The ear consists only of the membranous labyrinth (Fig. 798),
equivalent to the internal ear of higher Craniata, the middle and
outer ear being absent. The membranous labyrinth consists of
the vestibule and three semicircular canals. The former, which is
divided into two parts by a constriction, communicates by a narrow
passage — the endolym.phatic duct or aqueductus vestibuli — with the
exterior, in the position already mentioned. Of the three semi-
circular canals, the anterior and posterior are vertical and the
external horizontal, as in Craniata in general. Each has an ampulla,
that of the anterior and external canals situated at their anterior
ends, and that of the posterior canal, which is the largest of the three
and forms an almost complete circle, at its posterior end. In
the fluid (endolymph) in the interior of the vestibule are suspended,
in a mass of gelatinous connective-tissue, numerous minute
calcareous particles or otoliths, giving it a milky character.
The sensory canals of the integument running along the lateral
line and over the head contain special nerve-endings (neuromasts),
and doubtless function as organs of some special sense (see p. 105).
The same probably holds good of a number of unbranched canals
(ampullary canals) arranged in groups situated on the anterior por-
tion of the trunk and on the head, and being particularly numerous
in the neighbourhood of the snout. These are dilated internally
into vesicles, the ampullce, provided with special nerve-endings.
Urinogenital Organs. — In the female there is a single ovary (Figs.
827, 835' ov.), an elongated soft, lobulated body, lying a little to
xiii PHYLUM CHORD ATA 159
the right of the middle line of the abdominal cavity, attached by a
fold of peritoneum, the mesoarium. On its surface are rounded
elevations or follicles of various sizes, each containing an ovum
of a bright yellow colour. There are two oviducts (Miillerian
ducts) entirely unconnected with the ovaries. Each oviduct
(Figs. 827 and 835, ovd.) is a greatly elongated tube extending
throughout the entire length of the abdominal cavity. In front
the two unite behind the pericardium to open into the abdominal
cavity by a wide median aperture (ovd'.). At about the point of
junction of the middle and anterior thirds is a swelling marking the
position of the shell-gland (sh. gl.}. The posterior part dilates to
form a wide uterine chamber, and in Scyllium the two unite to
open into the cloaca by a common aperture situated just behind the
opening of the rectum, while in Hemiscyllium they remain distinct
and have separate cloacal openings. Each kidney consists of two
parts, anterior and posterior. The former (Fig. 827, r. meson,
Fig. 835, k') is a long narrow ribbon of soft reddish substance,
which runs along throughout a great part of the body-cavity at
the side of the vertebral column, covered by the peritoneum. The
posterior portion (r. metan, k) is a compact, lobulated, dark-red
body, lying at the side of the cloaca, continuous with the anterior
portion ; like the latter, it is covered over by the peritoneum.
Both portions have their ducts. Those of the anterior are narrow
tubes, which run over its ventral surface and become dilated behind
to form a pair of elongated chambers, the urinary sinuses (Fig. 836,
ur. sin.), uniting behind into a median sinus (med. ur. sin.), opening
into the cloaca by a median aperture situated on a papilla, the
urinary papilla. The ducts of the posterior portion, the ureters,
which are usually from four to six in number, open into the urinary
sinuses.
In the male (Fig. 835, A) there are two elongated, soft, lobulated
testes, each attached to the wall of the abdominal cavity by a fold
of peritoneum — the mesorchium. From each testis anteriorly, a small
number of efferent ducts (ef.d) pass to the anterior end of a long,
narrow, strap-shaped body, which corresponds to the vestigial
anterior portion of the kidney in the female. This is the epididymis ;
the duct, spermiduct or vas deferens, runs along the entire length of
the non-renal part of the kidney, or " Ley dig's gland" and, where
it leaves the latter posteriorly, becomes a wide tube, which opens
into the urinogenital sinus (u. g. s.), a median chamber projecting
into the cloaca. Posteriorly the spermiduct dilates to form a wide
thin-walled sac, the vesicula seminalis. Closely applied to the
latter is a thin-walled elongated sac, the sperm-sac. Anteriorly
the sperm-sac narrows to a blind extremity ; posteriorly the right
and left sperm-sacs combine to form the urinogenital sinus. The
posterior part of the kidney has the same character as in the
female ; its ducts, usually five in number on each side, open into
160
ZOOLOGY
SECT
A
S.V,
cud"
Cl9
FIG. 835. — The urinogenital organs of Scyllium canicula from the ventral side. A, male,
and B, female. Only the anterior end of the gouad is represented in each figure, and except
that in B both kidneys are shown, the organs of the right side only are drawn. In A the
seminal vesicle and sperm-sac are dissected away from the kidneys and displaced outwards,
and the ureters inwards, ab. p. depression into which the abdominal pore opens ; cl. cloaca ;
els. clasper ; ef. d. efferent ducts of spermary ; k. kidney ; k'., k". anterior non-renal portion
of the kidney, forming in the male the so-called " Leydig's gland," which, together with the
coiled spermiduct, constitutes the epididymis ; Ir. anterior portion of liver ; m. d. vestigial
Miillerian duct in the male ; ces. gullet ; ov. ovary ; ovd. oviduct ; ovd'. its ccelomic aperture ;
oi'd". the common aperture of the oviducts into the qloaca : r. rectum ; sh. tjl. shell-gland ;
spd. spermiduct ; sp. s. sperm-sac ; s. v. seminal vesicle ; s. v'. its aperture into the urino-
genital sinus ; is. spermary (testis) ; u. g. s. urinogenital sinus ; ur. ureters ; ur' '. their
apertures into the urinogenital sinus ; M.S. urinary sinus. (From Parker's Practical
Zoology.)
xm
PHYLUM CHORDATA
161
the urinogenital sinus, some of the most anterior first uniting to
form a common tube. The sinus has a median aperture into the
general cavity of the cloaca situated on the summit of a prominent
urinogenital papilla. The oviducts (Miillerian ducts) of the female
are represented in the male by vestiges of their anterior portions
(m.d.). The entire kidney is sometimes regarded as a mesonephros,
but the posterior portion, developed entirely behind the portion
which, in the male, takes part in forming the epididymis, and having
FIG. 836. — Hemiscyllium. Right kidney
and urinary sinus of female, med. ur. sinus,
median urinary sinus ; neph. kidney;
ur. sinus, right urinary sinus.
FIG. 837. — Dog-fish, egg-case. (After
Dean.)
its own ducts, is sometimes looked upon as foreshadowing the
metanephros of the higher Vertebrates.
The ripe ovum, rupturing the wall of its follicle, escapes
into the abdominal cavity, whence it reaches the interior of one
of the oviducts ; there it is fertilised by sperms received from the
male in the act of copulation, and then becomes enclosed in a
chitinoid case or shell (Fig. 837) secreted by the shell-gland.
2. — DISTINCTIVE CHARACTERS AND CLASSIFICATION.
The Elasmobranchii are Pisces in which the cartilaginous cranium
is never ossified by replacing-bones, and in which investing-bones
VOL. II L
162
ZOOLOGY
SECT.
are not developed in connection either with the cranium or the
pectoral arch. The skull is hyostylic, except in some of the
Protoselachii, in which it is amphistylic (p. 76). The dermal
fin-rays are " horny " ; at their bases the fins are supported by
cartilaginous pterygiophores which are never very numerous. The
pelvic arch is a distinct cartilage. There is nearly always an
exoskeleton which is of the placoid type. The intestine has a
spiral or a scroll-like valve. A cloaca is present into which both
the rectum and the ducts of the urinary and reproductive systems
open. There is never an operculum in recent Elasmobranchs, and
only rarely in fossil forms. The inter-branchial septa are of con-
siderable breadth, and the gill-filaments are attached to them
throughout their entire extent. A mandibular spiracular gill is
only exceptionally present as a fully developed organ ; it is repre-
sented usually by a vestige (pseudobranch). A conus arteriosus is
FIG. 838.— Restoration of Cladoselache fyleri, lateral and ventral views. (After Dean.)
always developed ; it is rhythmically contractile, and in its interior
are several transverse rows of valves. The optic nerves form a
chiasma. The ova are very large ; with one possible exception
they are always fertilised internally. The oviducts are not con-
tinuous with the ovaries, but open by wide mouths into the body-
cavity.
ORDER 1. — CLADOSELACHII (PLEUROPTERYGII).
Extinct Shark-like Elasmobranchs in which both pectoral and
pelvic fins had much wider bases of attachment than in existing
forms. There is an exoskeleton of small denticles. The notochord
was persistent : there are calcified neural and hsemal arches, but
no intercalary cartilages. The caudal fin is heterocercal. Claspers
are absent. The gill-openings were apparently protected by a
XIII
PHYLUM CHORDATA
163
fold of skin. The teeth are of the nature of placoid denticles,
lateral line was represented by an open groove.
This order comprises only one
known representative — Cladoselache
(Fig. 838)— from the lower Car-
boniferous rocks of America.
ORDER 2. — PLEURACANTHEI
(ICHTHYOTOMl).
Extinct Shark-like Elasmobranchs
in which the skeleton of the pectoral
fin was constructed on the type of
the so-called archipterygium, i.e.,
consisted of an elongated, segmented
central axis bearing two rows of
jointed rays. The notochord was
persistent ; intercalary cartilages
were present in addition to neural
and haemal arches. The caudal fin
is diphycercal. Claspers were pre-
sent. There was no opercular fold,
and the teeth resemble those of
other Elasmobranchs. Placoid scales
are not known to have been present,
but the skull is protected by roofing
dermal ossifications.
This order, like the last, includes
only one satisfactorily known genus
—Pleuracanthus (Fig. 839) — of Car-
boniferous and Permian age.
The
ORDER 3. — ACANTHODEI.
Extinct Elasmobranchs (Fig. 840)
having the anterior margin of each
fin supported by a stout spine. The
tail is heterocercal. There were no
claspers. There is a placoid exo-
skeleton of small denticles. An
operculum was not present. The
notochord was persistent, with neural
and hsemal arches. Calcified plates
are present in relation to the jaws
and to the roof of the skull. The teeth
and minute, or altogether absent. The
of an open groove.
are few and large, numerous
lateral line was in the form
L 2
164
ZOOLOGY
ORDER 4. — SELACHII.
SECT.
Living and extinct Elasmobranchs in which the skeleton of the
paired fins is never of the nature of an " archipterygium." The
notochord is more or less completely replaced by vertebrae, and there
is a series of intercalary cartilages. The caudal fin is nearly always
heterocercal. Claspers are always developed. A distinct opercular
fold is never present.
FIG. 840. — Acanthodes wardi. (Restored, after Dean.)
Sub-Order a. — Protoselachii.
Selachii in which the spinal column is uncalcified, and the centra
are very imperfectly developed ; there are more than five branchial
arches. Except in Chlamydoselachus, the palatoquadrate develops
a process by which it articulates with the post-orbital region of the
skull.
This sub-order includes the Notidanidce (Hexanchus and Heptan-
chus), and Chlamydoselachus (Fig. 841), as well as, probably, many
fossil forms.
FIG. 841. — Chlamydoselachus anguineus. (From the Cambridge Katura i History, after
Giinther.)
Sub-Order b. — Euselachii.
Selachii in which the spinal column is partly or completel
calcified. There are only five branchial arches. The palatoquad
rate has no post-orbital articulation with the skull.
Section a. — Squalida.
Euselachii with fusiform body and well-developed caudal fin.
The pectorals are of moderate size. A ventral fin is present. The
vertebrae of the anterior part of the spinal column are not fused
xm PHYLUM CHORDATA 165
together. The branchial apertures and the spiracle are situated
laterally.
This section comprises all the recent Sharks and Dog-fishes, with
the exception of the Protoselachii.
Section ft. — Rajida.
Euselachii with dorso-ventrally compressed body, and, usually-,
feebly developed caudal fin. The pectorals are of great size, the
pelvics generally small. A ventral fin is usually absent. The
vertebrae of the anterior region are fused together. The branchial
apertures are ventral, the spiracles dorsal.
This section comprises all the recent and extinct Rays (Skates,
Thorn-backs, Sting-Rays, Electric Rays, Saw-fish Rays).
3. — GENERAL ORGANISATION.
External characters. — In general shape most Sharks (Fig.
842) are somewhat fusiform and slightly compressed laterally.
In the Rays (Fig. 843), on the other hand, there is great dorso-
ventral compression. The head is in many cases produced forwards
FIG. 842. — Porbeagle Shark (Lamna cornubica). (From Dean's Fishes.)
into a long rostrum, which is of immense length and bordered with
triangular teeth in the Saw-fish Shark (Pristiophorus) and Saw-fish
Ray (Pristis). In the Hammerhead Shark (Spliijrna or Zygcena) the
anterior part of the head is elongated transversely.
There are well-developed median and paired fins. The caudal
fin is large, and, as a rule, strongly heterocercal in the Sharks and
shark-like Rays, reduced in most of the latter group. The dorsal
and ventral fins are large in the Sharks, the former completely divided
into two : in the Rays the dorsal fin is usually small, and the ventral
absent. The paired fins differ widely in the two groups. In the
Sharks both pairs are well developed, the pectoral being the larger.
In the Rays the pectoral fins are extremely large, very much larger
than the pelvic, fringing the greater part of the length of the flattened
body, and becoming prolonged forwards on either side and even in
front of the head, so that the animal presents the appearance of a
broad fleshy leaf.
166
ZOOLOGY
SECT.
In all recent Elasmobranchs the male has, connected with the
pelvic fins, a pair of grooved appendages — the claspers or pterygo-
podia — -which subserve copulation.
The mouth is situated on the ventral surface of the head, usually
a considerable distance from the anterior extremity. In front of
each angle of the mouth on the ventral surface is the opening of
one of the olfactory sacs, each of which is frequently connected
by a groove — the naso-buccal groove — with the mouth-cavity.
Behind the mouth, on the dorsal surface in the Rays, and at the
side in the Sharks, is the spiracle. Along the sides of the neck
in the Sharks, and on the ventral surface in the Rays, there is on
either side a row of slit-like apertures — the branchial slits or branchial
clefts. These are usually five
in number on each side ; but
in Hexanchus and Chlamydose-
lachus there are six, and in
Heptanchus seven. In Chlamy-
doselachus (Fig. 841) a fold
comparable to a rudimentary
operculum extends back over
the first branchial cleft, and is
continuous across the middle
line ventrally ; in the re-
mainder of the sub-class no
such structure is represented.
A large cloacal opening is
situated just in front of the
root of the tail, and in most
members of the sub-class a
pair of small openings placed
close to it — the abdominal pores
—lead into the abdominal
cavity.
When the integument de-
velops any hard parts, as is the
case in the majority of the Elasmobranchs, they take the form, not of
regular scales, as in most other fishes, but of numerous hard bodies
(Fig. 844) which vary greatly in shape, are usually extremely minute,
but are in some cases developed, in certain parts of the surface, into
prominent tubercles or spines. When these hard bodies are, as is
commonly the case, small and set closely together in the skin, they
give the surface very much the character of a fine file ; and the skin
so beset, known as " shagreen," was formerly used for various
polishing purposes in the arts. This is the placoid form of exoskele-
ton, to which reference has been already made. Each of the hard
bodies has the same structure as a tooth, being composed of dentine,
capped with an enamel-like layer, and supported on a base of a sub-
FIG. 843. — Sting-Ray (Urolophus cruciatus).
(After Giinther.)
xm
PHYLUM CHORDATA
167
stance somewhat resembling the bony cement or crusta petrosa
of the tooth.
The skeleton is composed of cartilage, with, in many cases,
deposition of calcareous matter in special places — notably in the
jaws and the vertebral column. The
entire spinal column may be nearly
completely cartilaginous (Hexanchus
and Heptanchus), but usually the
centra are strengthened by radiating
or concentric lamellae of calcined
tissue ; or they may be completely
calcined. They are deeply amphi-
ccelous, the remains of the notochord
persisting in the large inter-central
spaces. Intercalary pieces (Fig. 845,
Ic.) are interposed between both
superior and inferior arches. In the
Kays (Fig. 846) the anterior part of
the spinal column becomes, converted
into a continuous solid cartilaginous
and calcified mass — the anterior verte-
bral plate (a. v. p.). As in Fishes in
general, two regions are distinguish-
able in the spinal column— the pre-
nniiflnl anrl flip rniirlril flip laftpr Vipincr FiG.844. — Dermal denticles-of Centro-
cauaai ana tne cauaai, t. ng phorus Caiceus, slightly magni-
characterised by the possession of tied. (From Gegenbaur's Comparative
. f i 11 T ,1 Anatomy.)
interior or haemal arches. In the pre-
caudal region short ribs may be developed, but these are sometimes
rudimentary or entirely absent. In the Sharks pterygiophores,
sometimes jointed, fused at their bases with the haemal spines,
support the ventral
lobe of the caudal
fin, and the dorsal
lobe of the same fin
is supported by a
series of pterygio-
phores resembling
produced neural
spines, but only
secondarily related to
Ob Jc
o o
J/7T
the
FlQ. 845. — Portion of the spinal column of Scymnus. Ic.
intercalary cartilages ; Ob, neural arches ; WE, centra. ar\r\
(From Wiedersheim's Vertebrata.) ->••-,
divided
spinal column,
sometimes also
by joints.
The dorsal and ventral fins are sometimes supported by similar
pterygiophores ; but in many cases the cartilaginous supports
of these fins consist, in whole or in part, of expanded plates of carti-
lage. The marginal portions of the unpaired fins beyond the limits
168 ZOOLOGY SECT.
of the endoskeleton are supported by dermal fibre-like structures
(ceratotrichia) composed of elastin.
The skull is an undivided mass of cartilage, hardened, in many
cases, by deposition of calcareous matter, but not containing any
true bony tissue. It consists of a cartilaginous case for the pro-
tection of the brain and the organs of special sense. The structure
of this cartilaginous brain-case as it occurs in the Dog-fish has
already been described. The main differences observable in the
different families are connected with the size and form of the rostrum.
In the Kays the lower lip of the foramen magnum is deeply excavated
for the reception of a short process, the so-called odontoid process,
which projects forwards from the anterior vertebral plate, and on
either side of this is an articular surface — the occipital condyle—
for articulation with corresponding surfaces on that plate. In the
Sharks the skull is not so definitely marked off from the spinal
column. The apertures of the aqueductus vestibuli in the Rays are
not situated in a median depression such as is observable in the
Dog-fish and in all the Sharks. The articular surface in the auditory
region for the hyomandibular is sometimes borne on a projecting
process, sometimes on the general level of the lateral surface. Some-
times in the Rays there is a smaller articulation behind for the first
branchial arch.
The upper and lower jaws — the palatoquadrate and MeckeVs car-
tilage— are connected with the skull through the intermediation
of a hyomandibular cartilage (Fig. 823, hy. mn. ; Fig. 846, h. m.).
The skull is thus of the hyostylic type as regards the mode of
suspension of the jaws. In the Sharks the palatoquadrate has
a process (absent in the Rays) for articulation with the base of
the skull in the pre-orbital region. In Hexanchus and Heptan-
chus (Fig. 847) there is in addition to this a prominent post-
orbital process of the palatoquadrate for articulation with the
post-orbital region of the skull (amphistylic arrangement). Ces-
tracion is also in a sense amphistylic ; the palatoquadrate is
firmly united with the skull, articulating with a groove on the
base, and the hyomandibular takes only a small share in the
suspension of the jaws. At the sides of the mouth in all Elasmo-
branchs are a series of labial cartilages, usually two pairs above
and one pair below. Attached to the hyomandibular is a thin
plate of cartilage — the spiracular (Fig. 846, sp.) — which supports
the anterior wall of the spiracle.
The hyoid arch proper is in most of the Elasmobranchs con-
nected at its dorsal end with the hyomandibular — sometimes
at its distal extremity, sometimes near its articulation with the
skull ; but in some Rays it is not so related, but articulates
separately and independently with the skull behind the hyo-
mandibular, and in the genera Hypnos and Trygonorliina it articu-
lates with the dorsal portion of the first branchial arch. In the
xm
PHYLUM CHORDATA
169
Sharks the hyoid is usually relatively massive ; in the Rays it is
smaller, and in most cases closely resembles the branchial arches,
and bears similar cartilaginous rays ; a larger or smaller median
element, or basihyal, is present in all cases.
There are always five pairs of branchial arches except in Hexan-
chus and Chlamydoselachus, which have six, and Heptanchus,
in which there are seven. Their dorsal ends are free in the Sharks,
bcis.br-
FIG. 846. — Skeleton of Sting-Ray (I'mlo/ilnts), ventral view. a. v. p. anterior vertebral
plate ; has. br. basi branchial plate ; br.l — br.5 branchial arches. (The branchial
rays are not represented, "the round dots indicating their articulations with the arches.)
cl. skeleton of clasper ; fi. m. hyomandibular ; hij. hyoid arch ; lab. labial cartilage ; lig.
ligament connecting the hyomandibular with the palatoquadrate and Meckel's cartilage ;
mck. Meckel's cartilage ; ms. pt. mesopterygium, and mt. fit. metapterygium of pectoral tin ;
mt. pt'. metapterygium of pelvic fin ; nas. nasal cartilage ; pal. palatoquadrate ; pect.
pectoral arch ; pi. pelvic arch ; pro. pt. propterygium ; sp. spiracular cartilage.
articulated with the anterior vertebral plate of the spinal column
in most Rays. Externally they bear a series of slender cartilaginous
branchial rays. The median ventral elements of the branchial arches
are usually more or less reduced, and in some cases are represented
by a single basi-branchial plate (Fig. 846 bas. br.). In the Rays
the fifth branchial arch articulates with the pectoral arch, a connec-
170 ZOOLOGY SECT.
tion which is absent in the Sharks. A series of slender cartilages,
probably modified branchial rays — the extra-branchial cartilages —
absent as such in some Dog-fishes and Rays, support the branchial
apertures.
The pectoral arch (Figs. 825, 846, pect.) consists of a single
cartilage, with, however, in most of the Sharks, a mesial flexible
portion by which it is divided into right and left halves. Each
lateral half consists of a dorsal scapular and a ventral cora-
coid part, the two being separated by the articular surfaces for the
basal cartilages of the fin. In the Rays, but not in the Sharks,
the dorsal ends of the pectoral arch are connected with the spinal
column (anterior vertebral plate) by a distinct articulation, the por-
tion of the arch on which ''.the articular surface is situated some-
times forming an independent cartilage (supra- scapula}. In Hep-
>"%
y
j . :» .,'»
p
fjal.tru
jtck
'
'Vwv..
FIG. 847. — Lateral view of the skull of Heptanchus. mck. Meckel's cartilage ; pal. qu. palato-
quadrate ; j>t. orb. post-orbital process of the cranium, with which the palatoquadrate
articulates. (After Gegenbaur.)
tanchus a small median ventral element may represent the sternal
apparatus of the Amphibia.
The basal pterygiophores of the pectoral fin are typically three, pro-,
meso-, and meta-pterygium (Figs. 825 and 846), but there are some-
times four, and the number may be reduced to two. The pro- and
meta-pterygia are divided in the Rays (Fig. 846) into several seg-
ments, and the former articulates, through the intermediation of
a cartilage termed the antorbital, with the olfactory region of the
skull.
The pelvic arch (pi.) is usually, like the pectoral, a single cartilage,
but in some exceptional cases it consists of two lateral portions.
In some cases a median epipubic process projects forwards from
the pelvic arch, and frequently there is on each side a prepubic
xni PHYLUM CHORDATA 171
process. A lateral iliac process, which becomes highly developed
in the Holocephali, is sometimes represented, and may attain
considerable dimensions. The pelvic fin has usually two basal
cartilages, representing the pro- and meta-pterygia, but the former
is often absent. In the male special cartilages attached to the
metapterygia support the claspers. With the basal cartilages
of both pectoral and pelvic fins are connected a number of jointed
cartilaginous fin-rays supporting the expanse of the fin.
The arrangement of the muscles is simple. The trunk-muscles
are divided into a pair of dorsal and a pair of ventral divisions,
each composed of many myomeres with intercalated myocommata
(Fig. 768, p. 68), following a metameric arrangement. The ventral
part, where it forms the muscles of the wall of the abdominal cavity,
is composed externally of obliquely running fibres, and represents
one of the two oblique muscles of the abdomen of higher forms.
Mesially this passes into a median band of longitudinally running
fibres corresponding to a primitive rectus. The muscles of the limbs
are distinguishable into two main sets — those inserted into the
limb-arch and those inserted into the free part of the appendage.
The latter, according to their insertion, act as elevators, depressors,
or adductors. A series of circular muscles pass between the carti-
lages of the visceral arches and, when they contract, have the
effect of contracting the pharynx and constricting the apertures.
A set of muscles pass between the various arches and act so as to
approximate them ; and a broad sheet of longitudinal fibres divided
into myomeres extends forwards from the shoulder-girdle to the
visceral arches.
Electric organs — organs in which electricity is formed and
stored up, to be discharged at the will of the Fish — occur in several
Elasmobranchs. They are best developed in the Electric Rays
(Torpedo and Hypnos, Fig. 848), in which they form a pair of large
masses running through the entire thickness of the body, between
the head and the margin of the pectoral fin. A network of strands
of fibrous tissue forms the support for a number of vertical prisms,
each divided by transverse partitions into a large number of com-
partments or cells. Numerous nerve-fibres pass to the various
parts of the organ. These are derived mainly from four nerves,
which originate from an electric lobe of the medulla oblongata, with
a branch from the trigeminal. By means of the electric shocks
which they are able to administer at will to animals in their
immediate neighbourhood, the Torpedo-Rays are able to ward off
the attacks of enemies and to kill or paralyse their prey. In the
other Rays in which the electric organs are developed they are
comparatively small organs situated at the sides of the root of the
tail. In all cases the cells are formed from metamorphosed muscular
fibres. *••
Luminous organs by the agency of which a phosphorescent
172
ZOOLOGY
SECT.
at..
:F
II
light is produced occur on the surface of a few pelagic Elasmo-
branchs.
Digestive System. — Teeth are developed on the palatoquadrate
and on Meckel's cartilage. They are arranged in several parallel
rows, and are developed from a groove within the margin of the
jaw, successive rows coming to the front, and, as they are worn
out, falling off and being replaced by others. In the Sharks the
teeth are usually large,
and may be long, nar-
row, and pointed, or
triangular with ser-
rated edges, or made
up of several sharp
cusps ; in the Rays,
(" however, the teeth are
more or less obtuse,
sometimes, as in the
Eagle-Rays, forming a
continuous pavement
of smooth plates
covered with enamel,
adapted to crushing
'?. food consisting of such
objects as Shell-fish
and the like. The
Sharks have a promi-
nent tongue supported
by the median basi-
hyal ; this is entirely
or almost entirely ab-
sent in the Rays. The
various divisions of the
enteric canal are simi-
lar in all the members
of the class to what
has already been de-
scribed in the case of
the Dog-fish. A spiral
valve is always pre-
sent in the large intes-
tine, though its arrangement varies considerably in the different
families. In some cases (e.g. Carcharias), the fold is not a spiral
one, but, attached by one edge in a nearly longitudinal line to the
intestinal wall, is rolled up in the shape of a scroll. A pair of
pyloric caeca occur in Lcemargus. Appended dorsally to the
rectum is a median glandular caecum, the rectal gland. The rectum
always terminates in a cloaca, into which the urinary and genital
FIG. 84S. — A Torpedo-Ray with the electric: organs dis-
sected out. On the right the surface only of the electric
organ (O.E.) is shown, on the left the nerves passing
to the organ are shown. The roof of the skull is removed
to bring the brain into view. br. gills ; /. spiracle ;
o. eyes ; tr. trigeminal ; tr'. its electric branch ; v. vagus ;
/, fore-brain ; //, mid brain ; ///, cerebellum ; IV,
electric lobe. (FromGegenbaur.)
20H PHYLUM CHORDATA 173
ducts also lead. There is always a voluminous liver and a well-
developed pancreas.
A thyroid lies in the middle line behind the lower jaw. A repre-
sentative of the thymus lies on either side, a little below the upper
angles of the branchial clefts.
The respiratory organs of the Elasmobranchii always have
the general structure and arrangement already described in the
case of the Dog-fish. In the Rays the water of respiration is taken
in mainly through the spiracles ; in the Sharks through the mouth.
In addition to the gills supported on the hyoid and branchial
arches there is also in the Notidanidee a gill on the anterior side
of the spiracular cleft — the spiracular gill — represented in many
others by a rete mirabile or network of blood-vessels (pseudobranch).
In Selache (the Basking Shark) there are a series of slender rods,
the gill-rakers, which impede the passage outwards through the
branchial clefts of the small animals on which those Sharks feed.
Blood-system. — The heart has, in all essential respects, the
same structure throughout the group. The conus arteriosus is
always contractile, and contains several rows of valves. The
general course of the circulation is the same in all (see p. 88), with
some variation in the precise arrangement of the vessels. In some
of the Rays the ventral aorta and the roots of the afferent vessels
are partly enclosed in the cartilage of the basi-branchial plate.
The brain attains a much higher stage of development than in
the Cyclostomata. The fore-brain greatly exceeds the other divisions
in size. In Scymnus there are two widely-separated parencephalic
lobes or cerebral hemispheres containing large lateral ventricles.
In other genera there is at most, as in the Dog-fish, a median depres-
sion of greater or less depth, indicating a division into two lateral
portions. In Scy Ilium, as already pointed out, there is a median
prosoccele which gives rise anteriorly to two lateral ventricles, or
paracceles, and the same holds good of Rhina and Acanthias. In
most Rays there is only a very small prosoccele without anterior
prolongations ; in Myliobatis this is absent. The olfactory bulbs
are of great size, in some cases with short and thick, in others longer
and narrower, stalks. In Scyllium, Rhina, and Acanthias, as well
as in Scymnus, they contain ventricles (rhinocceles) continuous with
the paracceles ; in the Rays they are solid.
The diencephalon is of moderate extent. On its lower aspect
are a pair of rounded lobi inferiores, which are of the nature of
dilatations of the infundibulum, and a saccus vasculosus, which is
a diverticulum of the infundibulum ; directly below the saccus
vasculosus lies the hypophysis. The epiphysis is long and narrow.
In the hind-brain the cerebellum is relatively greatly elongated
and overlaps the optic lobes and sometimes also the diencephalon
in front, while behind it extends over the anterior part of the
medulla oblongata. It usually contains a cerebellar ventricle or
174 ZOOLOGY SECT.
epicosle. The medulla is elongated in the Sharks, shorter and more
triangular in the Rays. The Electric Rays are characterised by
the presence of the electric lobes, rounded elevations of the floor
of the fourth ventricle.
Organs of Sense. — Integumentary sense-organs (neuromasts,
p. 105) are highly developed in the Elasmobranchs. They are
supplied, as already mentioned, by branches of the nerves of what
is known as the lateral system, comprising, in addition to the lateralis,
nerves in relation with the facial and sometimes the glossopharyngeal.
These integumentary sense-organs occur in the interior of a con-
tinuous system of closed tubes, the sensory tubes, more rarely of open
grooves. The chief canals of this system are a lateral-line canal,
running along the middle of each side of the body, which is con-
tinuous with certain canals in the head : these communicate with
the exterior at intervals by small pores. In addition to the canals
of the lateral-line system there are a number of isolated canals, the
ampullary canals, with neuromasts contained in terminal enlarge-
ments or ampullce ; these, which are peculiar to the Elasmobranchs,
are most numerous about the snout region. Of similar essential
character are the vesicles of Sam which occur in the Electric Rays.
The olfactory organs are a pair of cavities opening on the lower
surface of the head, a little distance in front of the mouth, and
enclosed by the cartilaginous olfactory capsules of the skull. Their
inner surface is raised up into a number of ridges on which the
fibres of the olfactory nerves are distributed. The eye has a
cartilaginous sclerotic, and is in most cases attached to the inner
wall of the orbit by means of a cartilaginous stalk. There appears
to be no mechanism providing for accommodation. A fold of the
conjunctiva resembling the nictitating membrane, or third eyelid
of higher Vertebrates, occurs in some Sharks. The ear consists
of the membranous vestibule, which is partly divided into two
(utriculus and sacculus), from which arise the three semicircular
canals with their ampullae, and also the aqueductus vestibuli or
endolymphatic duct — which opens to the exterior on the dorsal
surface of the head. In the Rays the semicircular canals form
almost complete circles and open separately into the vestibule by
narrow ducts.
Urinogenital Organs. — The kidneys, as already noticed in
the account given of the Dog-fish, differ somewhat in their relations
in the two sexes. In the male the anterior portion persists in the
epididymis, and its duct becomes the spermiduct, while the posterior
portion, which is the functional kidney, has a duct or ducts — the
ureter or ureters — of its own. In the female there is no direct
connection between the reproductive and renal organs ; the anterior
portion of the kidney may be functional, and its duct persists,
opening along with those of the posterior portion. In the male
the ureters open into a median chamber — the urinogenital sinus —
xm PHYLUM CHORD ATA 175
which extends into the cloaca, and receives also the spermiducts :
it communicates with the general cavity of the cloaca by a median
opening situated on a papilla — the urinogenital papilla. In the
female there is a median urinary sinus, into which the ureters open,
or the latter may open separately into the cloaca.
Save in certain exceptional cases (e.g. Scy Ilium), there are two
ovaries, varying considerably in form, but always characterised
towards the breeding season by the great size of the follicles enclosing
the mature ova. The oviducts (Miillerian ducts) are quite separate
from the ovaries. The right and left oviducts come into close
relationship anteriorly, being united in the middle on the ventral
surface of the oesophagus, where each opens by a wide orifice into
the abdominal cavity, or both open by a single median aperture.
The following part of the oviduct is very narrow ; at one point it
exhibits a thickening, due to the presence in its walls of the follicles
of the shell-gland. Behind this is a dilated portion which acts as
a uterus, and this communicates with the cloaca through a wide
vagina. A considerable number of the Elasmobranchii are vivi-
parous, and in these the inner surface of the uterus is beset with
numerous vascular villi, while the shell-gland is small or vestigial.
The testes are oval or elongate : the convoluted epididymis is
connected with the anterior end by efferent ducts, and from it
arises the vas deferens. The latter is dilated near its opening into
the urinogenital sinus to form an ovoid sac — the vesicula seminalis.
A sperm-sac is sometimes present, opening close to the aperture of
the vas deferens. The Miillerian ducts are vestigial in the male.
Impregnation is internal in all the Elasmobranchs with the
possible exception of Lsemargus (the Greenland Shark), the claspers
acting as intromittent organs by whose agency the semen is trans-
mitted into the interior of the oviducts.
In all the Elasmobranchs the ova are very large, consisting of a
large mass of yolk-spherules held together by means of a network
of protoplasmic threads, with, on one side, a disc of protoplasm—
the germinal disc. The process of maturation is similar to that
observable in holoblastic ova ; one polar body is thrown off in
the ovary, the other apparently at impregnation. The ripe ovum
ruptures the wall of the enclosing follicle and so passes into the
abdominal cavity to enter one of the oviducts through the wide
abdominal opening. Impregnation takes place in the oviduct, and
the impregnated ovum in the oviparous forms becomes surrounded
by a layer of semi-fluid albumen and enclosed in a shell of keratin
secreted by the shell-gland. The shell varies in shape somewhat
in the different groups : most commonly, as in many Dog-fishes
(Fig. 837), it is four-cornered, with twisted filamentous appendages
at the angles, by means of which it becomes attached to sea-weeds
and the like. In the Skates the filaments are absent. In the Port
Jackson Sharks (Cestracion, Fig. 849) it is an ovoid body, the wall
176
ZOOLOGY
SECT.
of which presents a broad, spiral flange. The young Elasmobranch
goes through its development enclosed in the shell, until it is fully
formed, when it escapes by rupturing the latter. In the viviparous
forms the ovum undergoes its development in the uterus, in which
in most cases it lies free — except in some Mustelidae and
Carchariidae, in which there is a close connection between the yolk-
sac of the embryo and the wall of the uterus, folds of the former
interdigitating with folds of the latter, and nourishment being thus
conveyed from the vascular system of the mother to that of the
foetus by diffusion. In some of the viviparous forms a distinct
though very delicate shell, some-
times having rudiments of the fila-
ments, is formed, and is thrown off
in the uterus. In the genera Rhino-
batus and Trygonorliina, which are
both viviparous, each shell encloses
not one egg, but three or four.
Lsemargus is said to differ from all
the rest of the Elasmobranchii in
having the ova fertilised after they
have been deposited, as well as in
the small size of the ova.
Development. — Segmentation is
meroblastic,1 being confined to the
germinal disc, which, before divid-
ing, exhibits amoeboid movements.
While segmentation is going on in
the germinal disc there appear a
number of nuclei, the source of
which is not certain, in the substance
of the yolk. When segmentation is
complete, the blastoderm appears as
a lens-shaped disc, thicker at one
end — the embryonic end. It is found
to consist of two layers of cells
—an upper layer in a single stratum, and a lower layer several
cells deep. A segmentation-cavity appears early among the cells
of the lower layer ; the lower-layer cells afterwards disappear
from the floor of this, the cavity then coming to rest directly on the
yolk.
An in-folding (Fig. 850) now begins at the thickened embryonic
edge of the blastoderm, which here becomes continuous with the
cells of the lower layer. The cavity (al), at first very small,
formed below this in-folding is the rudiment of the archenteron,
and the cells lining this cavity above, which form a definite layer,
partly derived from the in-folded ectoderm, partly from the cells
1 Except in one species of Cestracion.
FIG. 849. — Egg-case of Cestracion
galeatus. (After Waite.)
XIII
PHYLUM CHORDATA
177
of the lower layer, are the beginning of the definite endoderm.
The edge of the in-folding, entitled the embryonic rim, is obviously
the equivalent of the dorsal lip of the blastopore in Amphioxus.
The endoderm and its underlying cavity soon grow forwards
towards the segmentation-cavity. Under the latter appears
floor of lower-layer cells, but the cavity soon becomes obliterated
as the archenteron develops.
a
FIG. 850. — Longitudinal section through the blastoderm of a Fristiurus embryo before the
medullary groove has become formed, showing the beginning of the process of in-folding or
imagination, al. archenteron ; ep. ectoderm ; cr. embryonic rim ; in. mesoderm. (After
Balfour.)
After the formation of the embryonic rim a shield-like embryonic
area is distinguishable in front of it, with two folds bounding a
groove — the medullary groove. The mesoderm becomes estab-
lished at about the same time. It is formed from two separate
and distinct sources (Fig. 851). Along the edge of the embryonic
rim appears a horizontal groove-like depression : this — the external
FIG. 851. — Fristiurus, transverse section of blastoderm, showing the formation of the meso-
derm. bp. 1. dorsal lip of blastopore ; e. b.'- external coelomic bay ; c. b.2 internal cuulomic
bay ; ec. ectoderm ; en. endoderm ; m. f. medullary fold ; m. gr. medullary groove ; ws.1
external rudiment of mesoderm ; wzs.2 internal rudiment of mesoderm ; nc. uotochord ;
yk. yolk ; yk. n. yolk nuclei. (From O. Hertwig, after Rabl.)
coelomic bay (c.6.1) — marks the line of origin of the peripheral part
of the mesoderm (m.s.1), which grows inwards from it as a plate
of cells between the ectoderm and the endoderm. The central
part' of the embryonal mesoderm (m.s.2) is developed from the
endoderm at a point immediately external to the rudiment of the
notochord : here also a slight groove — -the internal coelomic bay
VOL. II M
178
ZOOLOGY
SECT.
(c.b.2) — is distinguishable, and from this a plate of mesoderm
cells grows outwards. Eventually the peripheral and central
plates of mesoderm come into contact and coalesce to form a
continuous sheet on each side of the middle line. Though the
mesodermal rudiments, peripheral and central, contain no cavities,
the grooves (ccelomic bays) from which their development takes its
origin may represent the cavities of the ccelomic sacs of Amphioxus.
As the blastoderm extends over the yolk, the edge forms a ridge
continuous with
the embryonic
rim. The latter
assumes the form
of twro prominent
caudal swellings
(Fig. 853, cd.).
The medullary
groove mean-
while deepens,
and its edges
grow over so as
to form a canal
(Fig. 852, C ; Fig.
854). The union
takes place first
in the middle,
the anterior and
posterior parts
(Fig. 854, neur.)
remaining open
for a while.
When the pos-
mastouerm wun emoryo in wnicii enuocierm ana mesouerm are , • , i
distinctly formed, and in which the alimentary slit has appeared. tenor part C1OS6S,
The segmentation-cavity is still represented as being present,
though by this stage it has in reality disappeared. C, older
blastoderm with embryo in which the neural canal has become
formed and is continuous posteriorly with the alimentary canal.
Ectoderm without shading ; mesoderm and also notochord black
with clear outlines to the cells ; endoderm and lower layer cells
with simple shading, al. alimentary cavity ; ch. notochord ;
ep. ectoderm ; m. mesoderm ; n. nuclei of yolk ; nc. neuroccele;
sg. segmentation-cavity ; x, point where ectoderm and endoderm
become continuous at the posterior end of the embryo.
Balfour.)
FIG. 852. — Diagrammatic longitudinal sections of an Elasmo-
branch embryo. A, section of the young blastoderm with
segmentation-cavity enclosed in the lower layer cells ; B, older
blastoderm with embryo in which endoderm and mesoderm are
so in
a way that it
encloses the blas-
topore, and there
is thus formed,
(From as in Amphioxus
and Ascidians, a
temporary passage of communication between the medullary canal
and the archenteron — the neurenteric passage.
The ectoderm gives rise, as in Vertebrates in general, not only
to the epidermis and the central nervous system, but also to the
peripheral nervous system, the lining membrane of the olfactory
sacs, the lens of the eye, and the lining membrane of the auditory
labyrinth of the mouth, and of the outer portions of the cloaca and
gill-clefts.
xm
PHYLUM CHORDATA
179
bl.e,
FIG. 853. — Embryo of Scyllium canicula with the tail-
swellings well marked and the medullary groove just
beginning, bl. f. edge of blastoderm ; bl. p. blastopore ;
cil. caudal swellings ; M. head. (After Sedgwick.)
The notochord (Fig. 852, cli.) is developed as a cord of cells
derived from the lower layer.
Each lateral sheet of mesoderm, soon after its formation by the
coalescence of the peripheral and central rudiments, becomes divided
by the development of
a horizontally directed
cleft-like space in its
interior. The inner part
of each sheet then sepa-
rates from the outer by
the formation of a longi-
tudinal fissure. The
former, which is known
as the vertebral plate,
becomes divided by
transverse fissures into
a number of squarish
masses, the protovertebrcB
or mesodermal somites.
The outer part forms a
broad plate, the lateral
plate. The lateral plate consists of two layers, a dorsal or somatic,
and a ventral or splanchnic, and the cavity between them is the
beginning of the ccelome. The protovertebrae send off cells round
the notochord to form the bodies of the vertebrae, the remainder
giving rise to the muscles
of the voluntary system.
An isthmus of mesoderm
cells (neplirotome), which
still connects each proto-
vertebra with the lateral
plate and contains a pro-
longation of the cavity,
gives rise to the pronephric
duct and tubules. The
— lateral plates eventually
bl.e unite ventrally, and their
cavities coalesce to form
the body - cavity. The
parts derived from the
FIG. 854. — Embryoof a Ray with the medullary groove _ ,
closed except at the hind end. The notched em- mesoderm are tne System
bryonic part of the blastoderm has grown faster than f ™l11Tif QT-V rvmcplpc
the rest and come to project over the surface of the ' Hdiy ^»,
yolk. bl. e. edge of blastoderm ; M. head ; neur. un- r]r>r,Yiia flip i
enclosed part of the neuroccele. (After Sedgwick.) lfe' L
connective-tissue, the
endoskeleton, the muscular and connective-tissue layers of the
alimentary canal, the vascular system, and the generative organs.
The segmentation of the mesoderm does not at first extend into
M 2
ISO
ZOOLOGY
SECT.
the head, but, on the formation of the gill-clefts, a series of meso-
dermal segments appear, the cells of which give rise to the cartilages
and muscles of the branchial, hyoid, and mandibular arches, and
probably also of the palatoquadrate and the eye.
By degrees the body of
the young Fish becomes
moulded on the blasto-
derm. This is effected by
the formation of a system
of folds, anterior, posterior,
and lateral, which grow in-
wards in such a way as to
separate off the body of
the embryo from the rest
of the blastoderm enclosing
the yolk. As the folds ap-
proach one another in the
middle, underneath the
embryo, they come to form
a constriction connecting
the body of the embryo
with the yolk enclosed in
the extra-embryonic part
of the blastoderm. The
process may be imitated if
we pinch off a portion of a
ball of clay, leaving only a
narrow neck connecting
the pinched-off portion
with the rest. The body
of the embryo is thus
gradually folded off from
the yolk-sac and comes to be
connected with it only by
a narrow neck or yolk-
FiG. 855.— Three views of the developing egg of an stalV (~R\a 8551 The head
Elasmobranch, showing the embryo, the blasto- *K ^ »',
derm, and the vessels of the yolk-sac. The shaded and tail OI the young r ish
part (bl.) is the blastoderm, the white part the un- j j-.ce
covered yolk. A, young stage with the embryo still SOO11 UlldergO aitierentia-
attached at the edge of the blastoderm ; B, older j.- J opripc r,f invnlii
stage with the yolk not quite enclosed by the blasto- uvo
derm ; C, stage after the complete closure of the yolk, tions at the sides of the neck
a. arterial trunks ot yolk-sac; bl. blastoderm; v. _. r,rr>\ r -\ i
venous trunks of yolk-sac ; y. point of closure of the (.b Ig. 855) form the bran-
yolk-blastopore ; y, portion of the blastoderm out- i • i i e, j i
side the arterial sinus terminalis. (From Balf our.) chial CleitS and Spiracle.
A number of very delicate
filaments (Figs. 850, 857) grow out from these apertures and
become greatly elongated ; these are the provisional gills, which
atrophy as the development approaches completion, their bases
alone persisting to give rise to the permanent gills. The great
x
xm
PHYLUM CHORDATA
181
development of these gill-filaments in the embryos of some vivi-
parous forms suggests that, in addition to their respiratory functions,
they may also serve as organs for the absorption of nutrient fluids
secreted by the villi of the uterine wall.1 The fins, both paired and
m.brn
m.brn
FlG. 856. — Side view of head of embryo
of ScyUium canicula, with the
rudiments of the gills on the first and
second branchial arches, eye, eye ;
m. brn. mid-brain ; mnd. mandible ;
mix. nasal sac. (After Sedgwick.)
FlG. 807. — Side view of the head of Seyllium
canicula at a somewhat later stage. The
gill-filaments have increased in number and
are present on the mandibular arch. ami.
angle of the jaw ; hy. hyoid : m. brn. mid-
brain : nas. nasal sac ; spir. spiracle. (After
Sedgwick.)
unpaired, appear as longitudinal ridges of the ectoderm enclosing
mesoderm. In some Elasmobranchs the paired fins are at first
represented on each side by a continuous ridge or fold, which only
subsequently becomes divided into anterior and posterior portions
—the rudiments respectively of the pectoral and pelvic fins. Into
these folds penetrate a series of buds from the protovertebras :
these, the muscle-buds, give rise to the fin-muscles ; at first, from
their mode of origin, they present a metameric arrangement, but
this is in great measure lost during development.
Ethology and Distribution. — The habits of the active,
fierce, and voracious Sharks, which live in the surface-waters of the
sea, waging war on all and sundry, contrast strongly with those of
the more sluggish Rays, which live habitually on the bottom,
usually in shallow water, and feed chiefly on Crustaceans and
Molluscs, with the addition of such small Fishes as they can
capture. As a group, the Elasmobranchs, more particularly the
Sharks, are distinguished by their muscular strength, the activity
of their movements, and also by the acuteness of their senses of
sight and smell.
Nearly all are marine : some ascend rivers : a very few live
habitually in fresh water. The only deep-water Elasmobranch
1 In a species of Trygon a number of the villi of the uterus project into
the pharynx of the fnetus through the spiracles, and nourishment is probably-
received by this means.
VOL. II M*
182 ZOOLOGY SECT.
known is a species of Ray, which extends to a depth of over 600
fathoms.
None of the Elasmobranchs are of very small size, and comprised
among them are the largest of living Fishes : the harmless Basking
Sharks (Selache) sometimes attain a length of 35 feet or more,
the formidable Great Blue Shark (Carcharodon) sometimes reaches
40 feet, and some of the Rays also attain colossal dimensions. In
this respect, however, recent Sharks and Rays are far behind
some of the fossil forms, certain of which, if their general dimensions
were in proportion to the size of their teeth, must have reached a
length of as much as 60 feet.
The earliest fossil remains of Elasmobranch Fishes that have
been found occur in rocks belonging to the Upper Silurian period.
Throughout the Paleozoic epoch the Elasmobranchs constituted a
very important section of the fauna — a large proportion of the fish-
remains, that have been found in Palaeozoic formations being the
remains of Elasmobranchs, mainly in the form of spines and teeth.
Most of the Pateozoic Elasmobranchs were characterised by a
great development of the exoskeleton. The teeth differ from
those of existing forms in being provided with broad bases by means
of which they articulated together, and in various groups there is
a union of the teeth by the coalescence of their bases so as to form
broad crushing plates. A similar union is not uncommon between
the parts of the general exoskeleton, a good many Palaeozoic Sharks
having been encased in an armour of solid plates formed by such a
coalescence. In the endoskeleton there is to be observed among
the fossil Elasmobranchs a gradual advance in the degree of calci-
fication of the spinal column from the Palaeozoic forms onwards,
the Protoselachii alone among existing forms representing in this
respect the condition which seems to have prevailed in the most
ancient members of the class.
The group (Cestracionts) now represented by two or three
species of Port Jackson Sharks seems to have been very abundant
in Palaeozoic times. Mitsukurina with long rostrum, occurring off
the coasts of Japan and Australia, dates from the Cretaceous
(Scapanorhynchus) .
The extinct Pleuracanthea, together with Cladoselachus, which,
as briefly stated in the sketch of the classification, differ from the
other known members of the class in the structure of the fins and
other points, range from the Devonian to the Permian, and are
perhaps also represented in the Trias.
Sub-Class II. — Holocephali.
The existing representatives of the Holocephali are included
under the single family Chimaridce, containing three genera—
Chimcera, Callorhynchus, and Harriotta. Even taking in fossil
forms, the group is a very small one ; it agrees in many funda-
XTTT
PHYLUM CHORDATA
183
mental characteristics with the Elasmobranchii, and is sometimes
included in that sub-class. Of the recent genera, Chimaara, the
so-called " King of the Herrings " (Fig. 858, A), is found on the
coasts of Europe, Japan, and Australia, the west coast of North
America, and at the Cape of Good Hope ; Callorhynchus (B) is
tolerably abundant in the South Temperate seas ; Harriotta is
a deep-sea form.
External Characters. — The general form of the body is
Shark-like, but the large, compressed head and small mouth are
frcL
FIG. 858. — A, Chimaera monstrosa ; B, Callorhynchus antarcticus. a. cl. anterior
clasper ; a. cl.' pouch for its reception ; br. ap. branchial aperture ; c.f. caudal fin ; c.f.' its
whip-like prolongation ; d. /. 1, d.f. 2, dorsal fins ;fr. cl. frontal clasper ; I. /., /. /.' labial
folds ; 1. I. lateral line ; na. ap. nasal aperture ; op. operculum ; pet. /. pectoral fin ; ptg.
pterygopodia ; pv.f. pelvic fin ; t. teeth ; tc. tactile tlap ; ii.f. ventral fin. (A after Cuvier.)
strikingly different from the depressed, shovel-shaped head and
wide mouth of most Selachians. The mouth is bounded by lip-like
folds, two. of which (B, l.f., l.f.'), placed laterally and supported by
labial cartilages, resemble the folds in which the premaxillae and
maxillae of many Bony Fishes are enclosed : a third fold, external
to and concentric with the mandible, is also supported by labial
cartilages and has the appearance of a second or external lower jaw.
In Chimera the snout is blunt, in Harriotta long and pointed ; in
Callorhynchus it is produced into a rostrum, from the end of which
184 ZOOLOGY SECT.
depends a large cutaneous flap (B, tc) abundantly supplied with
nerves and evidently serving as an important tactile organ.
A still more important difference from Elasmobranchs is the
possession of only a single external branchial aperture (br. ap.),
owing to the fact that a fold of skin, the operculum (op.), extends
backwards from the region of the hyoid arch and covers the true
gill-slits, which thus come to open into a common chamber situated
beneath the operculum and communicating with the exterior by
a single secondary branchial aperture placed just anterior to the
shoulder-girdle : there is no spiracle. Equally characteristic is
the circumstance that the urinogenital aperture is distinct from and
behind the anus, there being no cloaca.
There are two large dorsal fins (d.f. 1, d.f. 2} and a small ventral
(v. /.) ; the caudal fin (c. /.) is of the ordinary heterocercal type
in the adult Callorhynchus, but in the young (Fig. 864) the
extremity of the tail proper is not upturned, and the fin-rays are
arranged symmetrically above and below it, producing the form
of tail-fin called diphycercal. In Chimsera the tail may be produced
into a long whip-like filament (c.f.). The pectoral (pct.f.) and
pelvic (pv.f.) fins are both large, especially the former.
In the male there is a horizontal slit (B, a. cl'.) situated a little
in front of the pelvic fins ; it leads into a shallow glandular pouch,
from which can be protruded a peculiar and indeed unique
apparatus, the anterior clasper (A, a. cl.), consisting of a plate
covered with recurved dermal teeth, to which is added, in Callo-
rhynchus, a plate rolled upon itself to form an incomplete tube.
The use of this apparatus is not known. A rudiment of the pouch
occurs in the female, although the clasper itself is absent. The
male possesses, in addition, a pair of the ordinary ptenjgopodia or
posterior claspers (ptg.}, and is further distinguished by the
presence of a little knocker-like structure, the frontal clasper (fr. cl.),
on the dorsal surface of the head. In Harriotta the paired claspers
are poorly developed, and the frontal clasper is absent.
The lateral line (I. I.) is an open groove in Chimsera, a closed
tube in Callorhynchus, and there are numerous sensory pits, arranged
in curved lines, on the head. The skin is smooth and silvery, and
bears for the most part no exoskeletal structures. There are,
however, delicate, recurved dermal teeth on the anterior and frontal
claspers, and the first dorsal fin is supported by an immense bony
spine or dermal defence (sp.). In the young, moreover, there is
a double row of small dermal teeth along the back.
Endoskeleton. — The vertebral column consists of a persistent
notochord with cartilaginous arches. In Chimeera, but not in
Callorhynchus, there are calcified rings (Fig. 859, c. r.) embedded
in the sheath of the notochord. The anterior neural arches are
fused to form a high, compressed, vertical plate, to which the first
dorsal fin is articulated. The cranium (Figs. 860 and 861) has a
XIII
PHYLUM CHOEDATA
185
n.sp
Tt.a,
c.r
rich
nc7i.sh
J
very characteristic form, largely owing to the compression of the
region between and in front of the large orbits, which are separated
from the cranial cavity only by membrane in Callorhynchus (Fig.
861, or.) ; in Chimsera they lie above the level of the cranial cavity
and are separated from one 'another by a median vertical partition
of fibrous tissue (Fig. 860, i. o. s). At first sight the palatoquadrate,
or primary upper jaw, appears to be absent, but a little consideration
shows it to be represented by a triangular plate (pal. qu.) which
extends downwards and outwards from each side of the cranium
and presents at its apex a
facet for the articulation of
the mandible. The palato-
quadrate is therefore fused
with the cranium and fur-
nishes the sole support for
the lower jaw ; in a word
the skull is autostyUc. The
pituitary fossa (Fig. 861,5. t.)
is very deep and inclined
backwards ; on the ventral
surface of the basis cranii is
a pit (pt.) for the extra-cranial
portion of the pituitary body.
The posterior portion of the
cranial cavity is very high ;
the anterior part — containing
most of the fore-brain — is
low and tunnel-like, and has
above it a cavity of almost
equal size (Nv. 5 o'.) for the
ophthalmic branches of the
fifth nerves. The greater
part of the membranous laby-
rinth is lodged in a series of
pits on the side-walls of the
cranium (a.s.c., p.s.c.), and is
separated from the brain by
membrane only. The occipital region articulates with the vertebral
column by a single saddle-shaped surface or condyle (oc. en.).
There is a great development of labial cartilages, particularly
noticeable being a large plate wThich, in Callorhynchus, lies just
externally to the mandible, nearly equalling it in size and having
the appearance of a secondary or external jaw. In Callorhynchus the
snout is supported by three cartilaginous rods growing forward from
the cranium, of which one (r.) is median and dorsal and represents
the rostrum ; these, as well as the great lower labial, are represented
by comparatively small structures in Chimaera (Fig. 860, ?&.-/).
B
7Z.fl
FIG. S.")0. — Chimaeramonstrosa. .4, transverse
section of the vertebral column ; B, lateral view
of the same. c. r. calcified ring ; h. r. hrem; 1
ridge ; int. intercalary piece ; n. a. neural arch ;
nch. position of notochordal tissue ; nch. sh.
sheath of notochord ; n. sp. neural spine. (After
Hasse.)
186
ZOOLOGY
SECT.
JO
The hyoid resembles the branchial arches in form and is little
superior to them in size. Above the epihyal (Fig. 860, e. hy.}
is a small cartilage (ph.hy.), evidently serially homologous with the
pharyngobranchials, and therefore to be considered as a pharyngo-
hyal. It represents the hyomandibular of Elasmobranchs, but,
having no function to perform in the support of the jaws, it is no
larger than the corresponding segments in the succeeding arches.
Long cartilaginous rays (op. r.) for the support of the operculum
are attached to the ceratohyal.
The first dorsal fin is remarkable for having all its pterygiophores
fused into a single plate, which articulates with the coalesced
neural arches al-
ready referred to.
The remaining fins
are formed quite on
the Elasmobranch
type, as is also the
shoulder girdle.
The right and left
halves of the pelvic
arch are separate
from one another,
being united in the
middle ventral line
by ligament only ;
each presents a
narrow iliac region
and a broad flat
FIG. 860.- Chimaera monstrosa, lateral view of skull. pubo-ischial region
a. s. c. position of anterior semicircular canal ; c. hi/ nArfnrntorl V>TT- fT*rr>
ceratohyal ; e, hy. epihyal : fr. d. frontal clasper ; h. s. c. PC D-/
position of horizontal semicircular canal ; i. o. s. iriterorbital apertures O r
septum : lb. 1, lb. 2, lb. 3, labial cartilages ; Mck. C. mandible ; , ' ,
Nv. 2, optic foramen ; Nv. 10, vagus foramen; olf. cp. olfactory lenestrSB Closed by
capsule; op. r. opercular rays; pal. qu. palatoquadrate ; mpmhrinp <™P nf
ph. hy. pharyngohyal ; p. s. c. position of posterior semi- le>
circular canal ; qu. quadrate region ; r. rostrum. (After them of great size
-tLU DrCCllT . ) o
in Callorhynchus.
The skeleton of the anterior clasper articulates with the pubic
region.
Digestive Organs.— The teeth (Fig. 861) are very characteristic,
having the form of strong plates with an irregular surface and a
sharp cutting edge. In the upper jaw there is a pair of small
vomerine teeth (vo. t.) in front, immediately behind them a pair
of large palatine teeth (pal. t.), and in the lower jaw a single pair
of large mandibular teeth (mnd. t.). They are composed of vaso-
dentine, and each palatine and mandibular tooth has its surface
slightly raised into a rounded elevation of a specially hard sub-
stance, of whiter colour than the rest of the tooth, and known
as a tritor (tr.}. The stomach is almost obsolete, the enteric canal
xin
PHYLUM CHORDATA
187
passing in a straight line from gullet to anus ; there is a well-
developed spiral valve in the intestine.
Respiratory Organs.— There are three pairs of holobranchs or
complete gills borne on the first three branchial arches, and two
hemibranchs or half-gills, one on the posterior face of the hyoid,
the other on the anterior face of the fourth branchial arch. The
fifth branchial arch is, as usual, gill-less, and there is no cleft
between it and its predecessor.
The small heart resembles that of the Dog-fish in all essential
respects, being formed of sinus venosus, auricle, ventricle, and
conus arteriosus. the last with three rows of valves.
e-.l.d
•vo.l
JO.S.C
Nv.io
sac I -, ac.cn
TIC/I
FIG. 361. — Callorhynchus antarcticus, sagittal section of skull ; the labial cartilages are
removed, a.s.c. apertures through which the anterior semicircular canal passes from the
cranial cavity into the auditory capsule ; e. 1. d. aperture for endolymphatic duct ; mck. c.
Meckel's cartilage ; mnd. t. mandibular tooth ; nch. notochord ; Nv. 5, trigeminal foramen ;
Nv. 5. o. foramen for exit of ophthalmic nerves ; Nv. 5.'o', canal for ophthalmic nerves with
apertures of entrance and exit ; Nv. 10, vagus foramen ; oc. en. occipital condyle ; or.
fenestra separating cranial cavity from orbit ; pal. gn. palatoquadrate; pal. t. palatine tooth ;
pn. position of pineal body ; pt. pit for extra-cranial portion of pituitary body ; p.s.c.
apertures through which the posterior semicircular canal passes into the auditory capsule ;
qu. quadrate region of palatoquadrate ; r. rostrum ; sac. depression for sacculus ; *. t.
sella turcica ; tr. tritor ; vo. t. vomerine teeth.
The brain (Fig. 862), on the other hand, is very unlike that of
Scyllium, but presents a fairly close resemblance to that of Scymnus.
The medulla oblongata (med. obi.) is produced laterally into large
frill-like restiform bodies (cp. rst.), which bound the hinder half of
the cerebellum (cblm.). The diencephalon (dien.) is extremely
long, trough-shaped, and very thin-walled, without pronounced
optic thalami ; it is continued without change of diameter into a
188
ZOOLOGY
SECT.
distinct prosencephalon, which gives off the cerebral hemispheres
(crb. h.) right and left. The combined diaccele and prosoccele
(di. cos.) are widely open above in a brain from which the mem-
branes have been removed (A)? but in the entire organ (B) are
roofed over by a conical, tent-like choroid plexus (ch. plx. 1). The
cavities of the small, spindle-shaped hemispheres (crb. h.), some-
Q Q
meet. obi
FIG. 862. — Calloriiynchus antarcticus. A, dorsal view of brain after removal of the
membranes ; B, side view with the membranes in place, cblm. cerebellum ; ch. plx. 1,
choroid plexus of fore-brain, and ch. fix. -', of hind-brain ; cp. rst. corpus restiforme ; cp.
sir. corpus striatum ; crb. h. cerebral hemisphere ; di. coe. diaccele ; dien. diencephalon ;
for. M. foramen of Monro : Ib. inf. lobus inferior ; mcd. obi. medulla oblongata ; mt. coe.
metacocle ; No. 2, optic nerve ; Nv. 5, trigeminal ; JV>. 8, auditory ; Nv. 10, vagus ; olf. I.
olfactory bulb ; olf. p. olfactory peduncle ; opt. 1. optic lobe ; pn. b. pineal body ; pn. s.
pineal stalk ; pt/j. pituitary body.
times regarded as corresponding to olfactory lobes only, communicate
with the third ventricle by wide foramina of Monro (for. M.),
partly blocked up by hemispherical corpora striata (cp. str.).
XIII
PHYLUM CHORDATA
189
Each hemisphere is continued in
tube, the olfactory peduncle (olf.
compressed olfactory bulb (olf. I.).
The optic nerves (Nv..-) form a
chiasma. The pineal body (pn.b.)
is a small rounded vesicle borne
on a hollow stalk (pn. s.) which
runs just outside the posterior
wall of the tent-like choroid
plexus. The pituitary body (pty.}
consists of intra- and extra-cranial
portions, the former lodged in the
sella turcica, the latter in the pit
already noticed on the ventral or
external face of the skull-floor
(Fig. 861, pt.). In advanced em-
bryos the two are united by a
delicate strand of tissue.
Urinogenital Organs. — The
kidneys (Fig. 863, kd.) are lobed,
deep-red bodies, like those of the
Dog-fish, but shorter and stouter.
In the male they are much longer
than in the female ; the anterior
portion is massive, and consists
mainly of a mass of true renal
tubules ; it is indistinctly divided
into segments : the posterior
portion is narrower and also
indistinctly segmented ; from
both parts arise a number of
ducts (mesonephric ducts) the
majority of which open into the
vas deferens, while the last six
open into the urinogenital sinus.
In the female the ducts all open
into a rounded median urinary
bladder or urinary sinus, situated
between the two oviducal aper-
tures. The female reproductive
organs are also constructed on
the Elasmobranch pattern, and
are chiefly noticeable for the
immense size of the shell-glands
and of the uteri. But the male
organs present certain quite
unique characters. The testes
front into a slender thin- walled
p.), bearing at its extremity a
FIG. 86:3. — Callorhynchus antarcticus.
A, male urinogenital organs of left side-
ventral aspect ; B, anterior part of vesicula
seminalis in section, cl. cloaca ; I'/ii'l. epi-
clidymis ; kd. kidney; mill.
'^ ••
wise
r
;) al
in a symmetrical
manner. It will be obvious, however, that this homocercal tail-fin
is really quite as unsymmetrical as the heterocercal fin of the
Dog-fish, since, its morphological axis being constituted by the
notochord, nearly the whole of its rays are, in strictness, ventral.
The skull (Fig. 870) is an extremely complex structure, composed
of mingled bone and cartilage. The cartilage has no superficial
mosaic of lime-salts such as we find in many Elasmobranchs, but
certain portions of it are replaced by bones, and there are in
addition numerous investing bones developed in the surrounding
connective-tissue. As in the Dog-fish, the skull may be divided
into cranium, upper and lower jaws, with their suspensory apparatus,
and hyoid and branchial arches.
The cranium (Fig. 871) is a somewhat wedge-shaped structure,
its apex being directed forwards. At first sight the distinction
between replacing and investing bones is not obvious, but after
maceration or boiling certain flat bones (the paired parietals, PA.,
frontals, FR., and nasals, NA., and the unpaired supra-ethmoid,
xrii
PHYLUM CHORDATA
197
S. ETH.) can be easily removed from the dorsal surface ; and two
unpaired bones (the parasphenoid, PA. SPH., and vomer, VO.) from
the ventral surface. These are all investing bones : they are
simply attached to the cranium by fibrous tissue, and can readily
be prised off when the latter is sufficiently softened by maceration
or boiling. We thus get a distinction between the cranium as a
whole, or secondary cranium, complicated by the presence of invest-
ing bones, and the primary cranium or chondrocranium, left by
spnul par socc
op
dent
art
praop
FlQ. 870. — Salmo, the entire skull, from the left side. art. articular ; branch lost, branchkr
stegal rays ; dent, dentary ; epiot. epiotic ; eth. supraethmoid ; Jr. frontal ; hijom. hyo-
mandibular ; intop. interopercular ; Jug. jugal ; mpt. mesopterygoid ; mtpt. metaptery
goid ; mx. maxilla ; nas. nasal ; o. suborbitals ; op. opercular ; pal. palatine ; par. parietal :
pmr. premaxilla ; praop. preopercular ; pt. pterygoid ; pter. pterotic ; Quad, quadrate ;
socc. supraoccipital ; sphot. sphenotic ; subop. subopercular ; sympl. symplectic ; Zunge, basl-
hyal. (From Wiedersheim's Vertebrata.)
the removal of these bones and corresponding exactly with the
cranium of a Dog-fish.
The primary cranium contains the same regions as that of
Scy Ilium. Posteriorly is the occipital region, surrounding the
foramen magnum, presenting below that aperture a single concave
occipital condyle for the first vertebra, and produced above into an
occipital crest. The auditory capsules project outwards from the
occipital region, and between them on the dorsal surface of the
skull are paired oval fontanelles (fon.) closed in the entire skull by
the frontal bones. The posterior region of the cranial floor is
VOL. II N
198 ZOOLOGY SECT.
produced downwards into paired longitudinal ridges, enclosing
between them a groove which is converted into a canal by the
apposition of the parasphenoid bone and serves for the origin of the
eye-muscles. In front of the auditory region the cranium is exca-
vated on each side by a large orbit, a vertical plate or inter-orbital
septum (OR. SPH.) separating the two cavities from one another.
In front of the orbital region the cranium broadens out to form
the olfactory capsules, each excavated by a deep pit (olf. s.) for the
olfactory sac, and anterior to these is a blunt snout or rostrum.
The occipital region is formed as usual from the parachordals of
the embryonic skull, the auditory region from the auditory capsules,
and the rest of the cranium from the trabeculse.
The replacing bones, formed as ossifications in the chondro-
cranium, correspond in essentials with the typical arrangement
already described (p. 77). In the occipital region are four bones ;
the basi- occipital (B. OC.), forming the greater part of the occipital
condyle and the hinder region of the basis cranii or skull-floor :
the ex-occipitals (EX. OC.), placed one on each side of the foramen
magnum and meeting both above and below it ; and the supra-
occipital (S. OC.), forming the occipital crest already noticed.
Each auditory capsule is ossified by five bones — i.e., two more than
the typical number (p. 77) : the pro-otic (PR. OT.), in the anterior
region of the capsule, uniting with its fellow of the opposite side
in the floor of the brain-case, just in front of the basi- occipital ;
the opisthotic, in the posterior part of the capsule, external to the
ex-occipital ; the sphenotic (SPH. OT.), above the pro-otic and
forming part of the boundary of the orbit ; the pterotic (PT. OT.),
above the ex-occipital and opisthotic, forming a distinct lateral
ridge and produced behind into a prominent pterotic process ; and
the epiotic (EP. OT.), a small bone, wedged in between the supra-
and ex-occipitals and pterotic, and produced into a short epiotic
process. On the external face of the auditory capsule, at the
junction of the pro-, sphen-, and pter-otics, is an elongated facet
(h.m.) covered with cartilage and serving for the articulation of
the hyomandibular.
The trabecular region of the cranium contains six bones. Imme-
diately in front of the conjoined pro-otics, and forming the anterior
end of the basis cranii, is a small unpaired Y-shaped bone, the
basisphenoid (B. SPH.). Above it, and forming the anterior
parts of the side-walls of the brain-case, are the large paired
alisphenoids (AL. SPH.). In the inter-orbital septum is a median
vertical bone, representing fused orbitosphenoids (OR. SPH.).
Lastly, in the posterior region of each olfactory capsule, and
forming part of the boundary of the orbit, is the ecto-ethmoid
(EC. ETH.).
The investing bones already referred to are closely applied to
the roof and floor of the chondrocranium, and modify its form
xm
PHYLUM CHORDATA
199
considerably by projecting beyond the cartilaginous part, and con-
cealing apertures and cavities. The great frontals (FR.) cover the
greater part of the roof of the skull, concealing the fontanelles, and
furnishing roofs to the orbits. Immediately behind the frontals is
a pair of very small parictals (PA.) ; in front of them is an unpaired
supra-ethmoid (S. ETH.), to the sides of which are attached a pair
of small nasals (NA.). On the ventral surface is the large para-
NA.
£ 8R4
BHY
B SR 1
FIG. 871. — Salmo fario. Disarticulated skull with many of the investing bones removed.
The cartilaginous parts are dotted, fon. fontanelle ; h. m. articular facet for hyomandi-
bular ; Mck. C. Meckel's cartilage ; olf. s. hollow for olfactory sac. Replacing bones—
AL. SPH. alisphenoid; ART. articular; B. BR. 1, first basibranchial ; B. HY.
basihyal ; B. OC. basioccipital ; BR. 5, fifth branchial arch ; B. SFH. basisphenoid ;
C. BR. 1, first ceratobranchial ; C. HY. ceratohyal ; EC. ETH. ecto-ethmoid ;
E. BR. 1, first epibranchial ; E. HY. epi-hyal ; EP. OT. epiotic ; EX. OC.
ex-occipital ; H. BR. 1, first hypobranchial ; H. HY. hypohyal ; HY. M. hyomandi-
bulur ; I. HY. interhyal ; JOTS. PTG. mesopterygoid ; 1OTT. PTG. metapterygoid ;
OR. SFH. orbitosphenoid ; PAL. palatine ; BR. 1, first pharyngobranchial ;
PTG. pterygoid ; PT..OT. pterotic ; QTT. Quadrate ; S. OC. supraoccipital ; SPH. OT.
sphenotic ; SYIOT. symplectic. Investing bones — ANO. angular ; ])NT. dentary ; FR.
frontal ; JU. jugal; MX. maxilla ; XA. nasal ; PA. parietal; PA. SPH. parasphenoid ;
PMX. premaxilla ; VO. voiner.
sphenoid (PA. SPH.), which forms a kind of clamp to the whole
cartilaginous skull-floor ; and in front of and below the parasphenoid
is the toothed vomer (VO.). Encircling the orbit is a ring of scale-
like bones, the sub-orbitals (Fig. 870, o.).
In the jaws, as in the cranium, we may distinguish between
primary and secondary structures. The primary upper jaw or
palatoquadrate is homologous with the upper jaw of the Dog-fish,
but instead of remaining cartilaginous, it is ossified by five replacing
N 2
200 ZOOLOGY SECT.
bones : the toothed palatine (PAL.) in front, articulating with
the olfactory capsule ; then the pterygoid (PTG.) on the ventral,
and the mesopterygoid (MS. PTG.) on the dorsal edge of the
original cartilaginous bar ; the quadrate (QU.) at the posterior
end of the latter, furnishing a convex condyle for the articulation
of the lower jaw ; and projecting upwards from the quadrate the
metapterygoid (MT. PTG.). These bones do not, however, enter
into the gape, and do not therefore constitute the actual upper
jaw of the adult fish : external to them are two large investing
bones, the premaxilla (PMX.) and the maxilla (MX.), which
together form the actual or secondary upper jaw : they both bear
teeth. A small scale-like bone, the jugal (JU.), is attached to the
posterior end of the maxilla.
The lower jaw is similarly modified. Articulating with the
quadrate is a large bone, the articular (ART.), continued forwards
by a narrow pointed rod of cartilage : the latter is the unossified
distal end of the primary lower jaw or Meckel's cartilage ; the
articular is its ossified proximal end, and therefore a replacing bone.
Ensheathing Meckel's cartilage and forming the main part of the
secondary lower jaw is a large toothed investing bone, the dentary
(DNT.), and a small investing bone, the angular (ANG.), is attached
to the lower and hinder end of the articular.
The connection of the upper jaw with the cranium is effected
partly by the articulation of the palatine with the olfactory region,
partly by means of a suspensorium formed of two bones separated
by a cartilaginous interval : the larger, usually called the hyoman-
dibular (HY. M.), articulates with the auditory capsule by the
facet already noticed, and the small, pointed st/mplectic (SYM.) fits
into a groove in the quadrate. Both bones are attached by fibrous
tissue to the quadrate and metapterygoid, and in this way the
suspensorium and palatoquadrate together form an inverted arch,
freely articulated in front with the olfactory and behind with the
auditory capsule, and thus giving rise to an extremely mobile
upper jaw. As its name implies, the hyomandibular (together
with the symplectic) is commonly held to be the upper end of
the hyoid arch and the homologue of the hyomandibular of Elasmo-
branchs, but there is some reason for thinking that it really belongs
to the mandibular arch, and corresponds with the dorsal and
posterior part of the triangular palatoquadrate of Holocephali :
a perforation in the latter would convert it into an inverted arch
having the same general relations as the upper jaw plus suspen-
sorium of the Trout, but fused, instead of articulated, with the
cranium at either extremity.
The hyoid cornu is articulated to the cartilaginous interval
between the hyomandibular and symplectic through the inter-
mediation of a small rod-like bone, the interhyal (I. HY.), which
perhaps represents the hyomandibular of Elasrnobranchs. It is
xni
PHYLUM OHORDATA 201
ossified by three bones : an epihyal (E. HY.) above, then a large
ceratohyal (C. HY.), and below a small double hypohijal (H. HY.).
The right and left hyoid bars are connected by a keystone-piece,
the unpaired, toothed basihyal (B. HY.), which supports the tongue.
Connected with the hyomandibular and hyoid cornu are certain
investing bones serving for the support of the operculum. The
opercular (Fig. 870, op.) is articulated with a backward process of
the hyomandibular ; the pre-opercular (praop.) lies outside the
posterior border of the hyomandibular and quadrate, and clamps
them together ; the sub-opercular (subop.) is below and internal to
the opercular ; and the inter -opercular (intop.) fits between the
lower portions of the three preceding bones, and is attached by
ligament to the angle of the mandible. The twelve sabre-shaped
branchiostegal rays (branchiost.) are attached along the posterior
border of the epi- and cerato-hyal, and below the basi-hyal is an
unpaired bone, the basibranchiostegal or urohyal.
There are five branchial arches, diminishing in size from before
backwards (Fig. 871). The first three present the same segments as in
the Dog-fish : pharyngobranchial (PH. BR.) above, then epibranchial
(E. BR.), then a large ceratobranchial (C. BR.), and a small hypo-
branchial (H. BR.) below. The right and left hypobranchials of
each arch are connected by an unpaired basibranchial (B. BR.).
All these segments are ossified by replacing bones, and the basi-
branchials are connected with one another and with the basihyal
by cartilage, so as to form a median ventral bar in the floor of the
pharynx. In the fourth arch the pharyngobranchial is unossified,
and the hypobranchial absent, and the fifth arch (BR. 5) is reduced
to a single bone on each side. Small spine-like ossifications are
attached in a single or double row along the inner aspect of each of
the first four arches : these are the gill-rakers ; they serve as a
sieve to prevent the escape of food by the gill-slits.
The comparison of this singularly complex skull with the com-
paratively simple one of the Dog-fish is much facilitated by the
examination of the skull of a young Trout or Salmon. In the
latter, at about the second week after hatching, the only ossifications
present are a few investing bones ; when these are removed we get
a purely cartilaginous skull (Fig. 872), exactly comparable with
that of an Elasmobranch. There is a cranium devoid of replacing
bones and divisible only into regions ; the upper jaw is an unossified
palatoquadrate (PI. Pt., M. Pt., Qu.) and the lower jaw (Mck.) a
large Meckel's cartilage ; the suspensorium is an undivided
hyomandibular (HM.), and the hyoid and branchial arches are
unsegmented.
The first dorsal and the ventral fins are supported each by a triple
set of pterygiophores, so that the fin-skeleton is multiserial, as in
the Dog-fish. The proximal series consists of slender bony rays — •
the interspinous bones (Fig. 876, PTG. ; Fig. 873, PTG. I), lying
202
ZOOLOGY
SECT.
S.0r
T.C>
Pa.ch,
•JIM
G.ffy JU[y M<1( Sy
FIG. 872.^-Skull of young Salmon, second week after hatch-
ing ; the investing bones removed. Au. auditory capsule ;
Br. 1, first branchial arch ; Ch. notochord ; C. Hy. hyoid
cornu ; Fo. fontanelle ; G. Hy. basihyal ; H. Hi/, hypohyal ;
H. M. hyomandibular ; 7. Hy. interhyal ; I1, V-, labial carti-
lages ; Mck. Meckel's cartilage ; M. Pt. metapterygoid
region of primary tipper jaw ; Pa. ch. parachordal ; PI. Pt.
palatopterygoid region ; Qu. quadrate region ; S. Or. supra-
orbital region of cranium ; Si/, symplectic region of sus-
pensorium ; T. Cr. cranial roof ; Tr. trabecula ; //, optic
foramen ; V, trigeminal foramen. (From Parker and
Bettany's Morphology of the Skull.)
in the median plane, between the muscles of the right and left
sides, and more
numerous than the
myomeres of the
regions in which
they occur. Their
distal ends are
broadened, and with
them are connected
the second series
(PTG. 2) in the
form of small dice-
box-shaped bones ;
to these, finally, are
attached small
nodules of cartilage
(ptg. 3) forming the
third series of
radials. The dermal
fin-rays or lepi-
dotrichia (D.F.R.),
which lie in the
substance of the fin itself, are slender bones, jointed like the antennae
of an Arthropod, and mostly branched in the sagittal plane (Fig. 876,
D.F.R.). Each is formed of distinct right
and left pieces (Fig. 873), in close contact for
the most part, but diverging below to form
a forked and dilated end, which fits over
one of the cartilaginous nodules (ptg. 3).
In the caudal fin (Fig. 869) the dermal rays
(D.F.R.) are similarly seated on the broad
haemal arches of the posterior caudal verte-
brae. The second dorsal or adipose fin has,
as already noticed , no bony support.
The shoulder-girdle (Fig. 874), like the skull,
consists of a primary shoulder-girdle, homo-
logous with that of a Dog-fish, and of several
investing bones. The primary shoulder-
girdle in the young fish is formed of distinct
right and left bars of cartilage, which do not
unite with one another ventrally. In the
adult each bar is ossified by three bones, a
7 tcirv-n \ i 'i n j-u
SCapUM (SCP.), Situated ClOrsally to the
glenoid facets, and developed partly as a
replacing, partly as an investing bone ; a
. ,°' i __ \7 . , V,
coracoid (COR.), situated ventrally to the
glenoid facet, and a meso-coracoid (MS.
I1F.R
PTG.1
FIG. 873. — Salmo fario.
A dermal fin-ray with its
pterygiophore unter-
spmous bone); PTG. 2,
middle pterygiophore;
XIII
PHYLUM CHORDATA
203
COR.), situated above the coracoid and anterior to the scapula.
Externally to these is found a very large investing bone, the clavicle
(CL.), extending downwards under the throat : its dorsal end is
connected by means of a supra-clavicle (S. CL.) to a forked bone,
the post-temporal (P.TM.}, one branch of which articulates with
the epiotic, the other with the pterotic process. To the inner
surface of the clavicle are attached two flat scales of bone
(P. CL'.}, with a slender rod-like post-clavicle (P. CL.} passing
backwards and downwards among the muscles.
The structure of the pectoral fin is very simple. Articulated to
the posterior border of the scapula and coracoid are four dice-box-
shaped bones, the proximal pterygiophores or radials (PTG. 1),
followed by a row
of small nodules of
cartilage (ptg. 2)
representing distal
pterygiophores.
The main body of
the fin is supported
by dermal fin-rays,
which resemble
those of the
median fins, and
have their forked
ends seated upon
the distal ptery-
giophores : the
first ray, however,
is larger than the
rest, and articu-
lates directly with
the scapula.
There is no pel-
vic girdle, its
place being taken by a large, flat triangular bone, the basipterygium
(Fig. 875, B. PTG.), probably representing fused proximal pterygio-
phores : to its posterior border are attached three partly ossified
nodules; the distal pterygiophores (PTG.), and with these the
dermal fin-rays are articulated. The adipose lobe of the pelvic
fin is supported by a small scale-like bone.
The muscles of the trunk and tail are arranged, as in the Dog-fish,
in zigzag myomeres : there are small muscles for the fins, and the
head has a complex musculature for the movement of the jaws,
hyoid, operculum, and branchial arches.
The ccelome is divisible into a large abdomen (Fig. 876) con-
taining the chief viscera, and a small pericardial cavity, situated
below the branchial arches, and containing the heart.
FIG
DFR.
874. — Salmo fario. Left half of shoulder-girdle and
pectoral tin, from the inner surface. CL. clavicle ; COR.
coracoid; D.V.R. dermal fin-rays; MS. COR. mesocoracoid
P.CL., P.CL\ post-clavicles; PTG.l, proximal. &n&ptg. -
distal pterygiophores ; P. TM. post-temporal ; S. CL. supra-
clavicle ; SCP. scapula.
204
ZOOLOGY
SECT.
BPTC
PTG
Digestive Organs. — The mouth (Figs. 865 and 876) is very
large and has numerous small, recurved, conical teeth, borne, as
already mentioned, on the premaxillse, maxillae,
palatines, vomer, dentaries and basihyal.
They obviously serve merely to prevent the
escape of the slippery animals used as food
and are of no use for either rending or chewing.
The pharynx (ph.) is perforated on each side
by four vertically elongated gill-slits, fringed
by the bony tooth-like gill-rakers. Each gill-
slit is V-shaped, the epihyal being bent upon
the ceratohyal so that the dorsal and ventral
moieties of the branchial arches touch one
another when the mouth is closed.
The pharynx leads by a short gullet (gul.)
into a U-shaped' stomach (st.) consisting of
a wide cardiac and a narrow pyloric division :
between the latter and the intestine is a ring-
shaped pyloric valve. The intestine passes at
first forwards as the duodenum (du.), then
becomes bent upon itself (int.) and passes
backwards, without convolution, to the anus
(an.). Its posterior portion has the mucous
membrane raised into prominent annular
ridges which simulate a spiral valve.
The liver (Ir.) is imperfectly divided into right and left lobes, and
there is a large gall-bladder (g. bl). Opening into the duodenum
are about forty blind glandular tubes, the pyloric cceca (py. c.).
There is a large spleen (spl.) attached by peritoneum to the fundus
of the stomach. The stomach, duodenum, and pyloric cseca are
surrounded by loose folds of peritoneum loaded with fat.
Lying below the kidneys and extending the whole length of the
abdominal cavity is the air-bladder (a.bl.), a thin-walled sac
serving as an organ of flotation. Anteriorly its ventral wall presents
a small aperture leading, by a short pneumatic duct (pn. d.), into the
oesophagus on the dorsal side somewhat to the right of the middle
line.
Respiratory Organs. — There are four pairs of gills each with
a double row of branchial filaments, united proximally but having
their distal ends free : interbranchial septa are practically obsolete
(see Fig. 780). The gills are borne on the first four branchial
arches, the fifth arch bearing no gill. On the inner surface of the
operculum is a comb-like body, the pseudo-branchia, formed of a
single row of branchial filaments, and representing the vestigial
gill (hemibranch) of the hyoid arch.
Circulatory Organs. — The heart (Fig. 876) consists of sinus
venosus, auricle (au.), and ventricle (v.). There is no conus arteriosus,
FIG. 875. — Salmpfario.
Skeleton of left pelvic
fin, dorsal aspect.
B. PTG. basiptery-
gium ; Z>. F. R. dermal
fin-rays ; PTG. distal
pterygiophores.
xrn
PHYLUM CHORDATA
205
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206 ZOOLOGY SECT.
but the proximal end of the ventral aorta is dilated to form a bulbus
aortce (b. a.), a structure which differs from a conus in being part
of the aorta, and not of the heart ; its walls do not contain striped
muscle, and are not rhythmically contractile.
. In accordance with the atrophy of the hyoid gill there is no
afferent branchial artery to that arch, but a hyoidean artery springs
from the ventral end of the first efferent branchial and passes to
the pseudobranch. The right branch of the caudal vein is continued
directly into the corresponding cardinal, the left breaks up in the
kidney, forming a renal-portal system. There are no lateral veins,
but the blood from the paired fins is returned to the cardinals. The
red blood-corpuscles are, as in other fishes, oval nucleated discs.
Nervous System. — The brain (Fig. 877) is very different from
that of Elasmobranchs, and is in many respects of a distinctly lower
type. The cerebellum (H.H.) is very large, and bent upon itself.
The optic lobes (M.H.) are also of great size, and on the ventral
surface are large bean-shaped lobi inferior es (U.L.}. The dien-
cephalon is much reduced, and, indeed, is indicated dorsally only as
the place of origin of the pineal body (G. p.) : ventrally it is pro-
duced into the lobi inferiores with the infundibulum between them
giving attachment to the pituitary body (Hyp.}. Hence, seen from
above, the small undivided prosencephalon (V.H.) comes imme-
diately in front of the mid-brain : it has a non-nervous roof (Pall.)
and its floor is raised into prominent corpora striata (BG., Bas. G.).
The olfactory bulbs, situated in close apposition with the prosen-
cephalon without intervening olfactory peduncles or olfactory tracts
such as are present in Scyllium (L.ol.), are nearly as large as the
corpora striata, and each contains a small cavity or rhinoccele in
communication with the undivided prosoccele. Three transverse
bands of fibres connect the right and left halves of the fore-brain,
an anterior commissure joining the corpora striata, a posterior
commissure situated just behind the origin of the pineal body, and
an inferior commissure in front of the infundibulum. The pineal
body (G.p.) is rounded and placed at the end of a hollow stalk : a
shorter offshoot of the roof of the diencephalon may perhaps
represent a rudimentary pineal eye. Behind the pituitary body
is a saccus vasculosus (s.v.). The optic nerves do not form a chiasma,
but simply cross one another, or decussate (Ch.), on leaving the
brain, the right nerve going to the left, and the left nerve to the
right eye.
Sensory Organs. — The most distinctive feature of the olf actor//
sac is the possession of two small apertures, the anterior provided
with a valve.
The eye (Fig. 878) has a very flat cornea (en.) with which the
globular lens (I.) is almost in contact, so that the aqueous chamber
of the eye is extremely small. Between the cartilaginous sclerotic
(scl.) and the vascular choroid (ch.) is a silvery layer or argentea
XIII
PHYLUM CHORDATA
207
(arg.), which owes its colour to minute crystals in the cells of which
it is composed. There are no choroid processes. In the posterior
part of the eye, between the choroid and the argentea, is a thickened
A
B
LoT,
L.ol.
Fia. 877.— Salmo fario. Dorsal (A ), ventral (B), and lateral (C) views of brain. BG., Bas.
G. corpora striata ; ch, crossing of optic nerves ; G. p, pineal body ; HH. cerebellum :
Hyp, pituitary body ; Inf. infundibulum ; L. ol. olfactory bulbs ; Med, spinal cord ; MR.
optic lobes ; NH. medulla oblongata ; Pall, non-nervous roof of prosencephalon ; Sc.
saccus vasculosus ; Tr. Opt. optic tracts ; UL. lobi inferiores ; VH, prosencephalon ;
I — -X, cerebral nerves ; XII, 1, first spinal (hypoglossal) nerve ; 2, second spinal nerve!
(From Wiedersheim's I'ertebrata.)
ring-shaped structure (ch. gld.) surrounding the optic nerve, and
called the choroid gland : it is not glandular, but is a complex network
of blood-vessels, or rete mirabile. It is supplied with blood by the
208
ZOOLOGY
SECT.
efferent artery of the pseudobranch. Close to the entrance of the
optic nerve a vascular fold of the choroid, the falciform process
(pr. fl.), pierces the retina, and is continued to the back of the lens,
where it ends in a knob, the campanula Halleri (cp. hal.), which
contains smooth muscular
fibres. The falciform pro-
cess with the campanula
Halleri takes an important
part in the process of accom-
modation by which the eye
becomes adapted to forming
and receiving images of
objects at various distances.
Accommodation in the Bony
Fish is effected, not by an
alteration in the curvature
of the lens as in higher
Vertebrates, but by changes
FIG. 878.— Salmo fario. Vertical section of eye in its position, by which it
(semi-diagrammatic), arg. argentea ; ch. choroid ; >,p(-.rvmaa rnnro armrnvimnf or!
ch. aid. choroid gland ; en. cornea ; cp. hal. cam-
panula Halleri ; ir. iris ; /. lens ; opt. nv. optic towards, Or further with-
nerve ; pa. pigmentary layer ; pr. fl. processus , . , . T
faiciformis ; sci. sclerotic (dotted). drawn from, the retina. In
bringing about these changes
of position the structures in question appear to play the principal
part.
The auditory organ (Fig. 879) is chiefly remarkable for the large
size of the otoliths (ot. 1). They are three in number ; one,
called the sagitta (ot. 1), is fully 6 mm. in length, and almost fills
the sacculus : another, the asteriscus (ot. 2), is a small granule lying
in the lagena or rudimentary cochlea : the third, the lapillus (ot. 3),
is placed in the utriculus close to the ampullae of the anterior and
horizontal canals.
Urinogenital Organs. — The kidneys (Fig. 876, kd., and Fig.
880, R) are of great size, extending the whole length of the dorsal
wall of the abdomen, above the air-bladder, and partly fused
together in the middle line. They are derived from the meso-
nephros of the embryo. Their anterior ends (Fig. 876, kd, Fig.
880, R) are much dilated and consist in the adult of lymphatic
tissue, thus ceasing to discharge a renal function. The ureters
(mesonephric ducts, ur.) unite into a single tube, which is dilated
to form a urinary bladder (Fig. 876, u. bl, Fig. 880, v.), and discharges
into the urinogenital sinus.
The gonads are of great size in the sexually mature fish. The
testes (Fig. 876, ts.) are long, smooth, pinkish paired organs, extend-
ing the whole length of the abdominal cavity ; each is continued
posteriorly into a duct (v. df.) which opens into the urinogenital
sinus, and the homology of which with the ducts of the primitive
XIII
PHYLUM CHORDATA
209
nephridial system is still uncertain. The ovaries are also of the
full length of the abdominal cavity and are much wider than the
testes : they are covered with peritoneum on their inner or mesial
faces only, and the numerous ova, which are about 4 mm. in diameter,
are discharged when ripe from their outer faces into the ccelome.
There are no oviducts, but the anterior wall of the urinogenital
sinus is pierced by a pair of genital pores through which the ova
make their way to the exterior. There is reason for thinking that
these pores are to be looked upon as
degenerate oviducts, and in no way
homologous with the abdominal pores
of Elasmobranchs.
CL.S.C
p.s.c
rr
n
FIG. 879. — Salmo fario. The right auditory
organ, from the inner side ; the otoliths are
shown separately below, a. s. c. anterior semi-
circular canal ; and. nv. auditory nerve ; h. s. c.
horizontal canal ; ot. 1 — 3, otoliths ; p. s. c.
posterior canal ; sac. sacculus ; ut. utriculus.
UT
FIG. 880.— Salmo fario. The kid-
neys and adjacent parts, d, pre-
caval vein ; R (to the right),
kidney ; R (to the left), degenerate
anterior portion of kidney ; rr,
efferent renal vein ; s. subclavian
vein ; u, ur, ureter ; v, bladder.
(From Gegenbaur's Comparative
Anatomy.)
Development. — Impregnation is external, the male shedding
his milt or seminal fluid on the newly-laid eggs. The ovum is
covered by a thick membrane, the zona radiata, perforated by an
aperture, the micropyle, through which the sperms find access : it
is formed of a superficial layer of protoplasm surrounding a mass of
transparent fluid yolk of a pale yellow colour. At one pole the
protoplasm accumulates to form an elevated area or germinal disc,
in which segmentation takes place (Fig. 881, A, B) in much the
same way as in Elasmobranchs, except that, owing to the smaller
proportion of yolk, the resulting blastoderm (bl.) and the embryo
formed therefrom are proportionally much larger, and the yolk-sac
210
ZOOLOGY
SECT.
(y.s.) correspondingly smaller, than in
A B
em.
y.s
y.s
FIG. 881. — Nine stages in the development of Salmo
fario. A — H, before hatching ; I, shortly after
hatching. W. blastoderm ; emb. embryo ; r. thickened
edge of blastoderm ; y. s. yolk-sac. (A — G after
Henneguy.)
tail become free from the yolk, and at
yolk-sac (7, y.s.) is a shoe-shaped body
surface of the transparent embryo.
the two previous classes.
Epiboly takes place as
in Elasmobranchs, the
blastoderm gradually
growing round and en-
closing the yolk (C-F).
The embryo (emb.) arises
as an elevation growing
forwards from the thick-
ened edge of the blasto-
derm, and, as it in-
creases in length, ap-
pears as a clear colour-
less band (//, emb.)
winding round the
yellow yolk, and
kept in close contact
with it by the enclosing
zona radiata. There is
no open medullary
groove, the nervous
system being formed,
as in Lampreys, from a
fold of ectoderm the
walls of which are in
apposition so as to form
a keel-like ridge. The
endoderm and meso-
derm are formed as a
result of a process of
infolding of the pos-
terior edge of the
blastoderm (Fig. 882).
Gradually the head and
the time of hatching the
sessile upon the ventral
ec
en+ma
FIG. 882.— Longitudinal section of blastoderm of Salmo, at about the stage represented in
D of Fig. 881. ec. ectoderm ; en + ms, infolding giving rise to endoderm and mesoderm.
(After O. Hertwig.)
xnr PHYLUM CHORDATA 211
2. — DISTINCTIVE CHARACTERS AND CLASSIFICATION.
The Teleostomi are Pisces in which the primary cranium is
always complicated by the addition of investing bones, of which
a pair of parietals and one of frontals above, and unpaired vomer
and parasphenoid below, are the most constant. The chondro-
cranium is always more or less ossified by replacing bones, including
a supra-occipital, and the upper and lower jaws are both bounded
by investing bones. The jaws are connected with the cranium
through the intermediation of a hyomandibular, which is probably
not homologous with the similarly named element of Elasmobranchs.
The dermal fin-rays are formed of bones, and are supported by
pterygiophores which may be either cartilaginous or bony, but
which always show a great reduction in number as compared with
the homologous structures in Elasmobranchs. The primary
shoulder-girdle is complicated by the addition of investing bones, of
which a large clavicle is the most constant. The pelvic girdle
is vestigial or absent. The pelvic fins usually undergo a forward
displacement, their position being either abdominal, i.e., between
the anus and the pectoral region, or thoracic, i.e., in the pectoral
region, or jugular, i.e., under the throat. A dermal exoskeleton
is usually present. The intestine may or may not have a spiral
valve ; the anus is distinct from, and placed in front of, the urinary
and genital apertures. The gills are covered by an operculum
supported by investing bones, and the interbranchial septa are
reduced or absent, so that the gill-filaments are partially or wrholly
free ; the hyoidean gill is reduced or absent. The conus arteriosus
is sometimes present, sometimes absent ; when it is absent there
is a large bulbus aortse formed as a dilatation of the ventral aorta.
The prosencephalon has usually a non-nervous roof ; the optic
nerves either form a chiasma or simply decussate. The ova are
small ; the gonoducts are either continuous with the gonads, or
open anteriorly into the ccelome, or are absent : in the latter
case the sexual products pass out by genital pores ; true abdominal
pores may be present in addition. Segmentation of the egg is
either entire or discoidal ; development is sometimes accompanied
by a metamorphosis.
The Teleostomi are classified as follows :—
ORDER 1. — CROSSOPTERYGII.
Teleostomi in which the pectoral fin consists of a rounded basal
lobe supported by endoskeletal structures and fringed by dermal
rays. There are no branchiostegal rays. The vertebral column is
well ossified, and the caudal fin is diphycercal. The pelvic fins,
when present, are abdominal. A spiral valve and a conus arteriosus
are present, and the optic nerves form a chiasma.
212
ZOOLOGY
SECT.
The only existing members of this order are several species of
br. m
FIG. 883. — Folypterus bichir. A, entire animal ; li,
ventral view of throat, an. anus ; br. m. branchiostegal
membrane ; c. /. caudal fin ; d. /. dorsal finlets ; jug. pi.
jugular plates ; na. nostril ; pet. /. pectoral fin ; pv. /.
pelvic fin ; v. /. ventral fin. (After Cuvier.)
B
Polypterus (Fig. 883) from the Congo and Upper Nile, and Cala-
moichthys calabaricus from Old Calabar.
ORDER 2. — CHONDROSTEI.
Teleostomi in which the paired fins have no Jbasal lobe, but their
whole free portion is supported by dermal rays. There are few
replacing bones in the skull, and the primary shoulder-girdle is
unossified. The vertebral column is represented by a persistent
notochord with cartilaginous arches, and its anterior end is fused
with the cranium. Branchiostegal rays are few or absent. The tail
FIG. 884. — Acipenser ruthenus (Sturgeon), b. barbels ; c. /. caudal fin ; d. /. dorsal fin;
pet. /. pectoral fin ; pv. /. pelvic fin ; sc. scutes ; v. /. ventral fin. (After Cuvier.)
is heterocercal. The pelvic fins are abdominal. A spiral valve,
conus arteriosus, and optic chiasma are present.
This order includes the Sturgeons (Acipenser, Fig. 884, and
Scaphirhynchus) found in the rivers of Europe, Asia, and North
America ; the curious spoon-billed Polyodon, from the Mississippi ;
and Psephurus from the rivers of China.
ORDER 3. — HOLOSTEI.
Teleostomi in which the paired fins have no basal lobe. The
chondrocranium is well ossified by replacing bones and investing
bones : branchiostegal rays are present. The vertebral column
consists of bony vertebrae, and the tail is heterocercal or nearly
xni
PHYLUM CHORDATA
213
homocercal. The pelvic fins are abdominal. A reduced spiral
valve, a conus arteriosus, and an optic chiasma are present.
FIG. 885. — Lepidosteus platystomus (Bony Pike), c./. caudal fin; d. f. dorsal fin;
fl. fulcra ; 1. I. lateral line ; pet. f. pectoral fin ; pv. f. pelvic fin ; e. /. ventral fin. (After
Cuvier.)
This order includes the Gar-pike or Bony Pike (Lepidosteus,
Fig. 885), from the fresh waters of North and Central America and
Cuba, and the Bow- B
fin or Mud-fish (Amia
calva, Fig. 886) from
the rivers of the
United States.
Orders 1 — 3 are
frequently grouped
together as the sub-
class Ganoidei, and,
although such a
group is an artificial FIG. 886.— Amia calva (Bow-fin). A, the entire animal ; B,
if \vill nffon V>o ventral view of throat, br. m. branchiostegal membrane ;
le> ] c. f. caudal fin ; d.f. dorsal fin ; jug. pi. jugular plate;
Convenient to refer fct. f. pectoral fin ; pv. /. pelvic fin ; v. f. ventral fin.
„ , (After Giintlier.)
to these fishes as
" Ganoids." They are all small and numerically insignificant
groups at the present day, but formed the whole of the Teleosto-
mian fauna in the Palaeozoic and the greater part of the Mesozoic
epoch.
ORDER 4. — TELEOSTEI.
Teleostomi in which the paired fins have no basal lobe. The
skull is well ossified both by replacing and investing bones : branchi-
ostegal rays are present. The vertebral column is well ossified :
the tail is homo- or diphy cereal. There is no spiral valve except
as a vestige in one genus. The conus arteriosus is absent except
as a vestige in a small number of genera : a large bulbus aortae
is present. The optic nerves never form a chiasma and usually
simply decussate.
The vast majority of existing Teleostomi are included in this
order, which is divided into six sub-orders as follows :—
Sub-order a. — Physostomi.
Teleostei in which the air-bladder, when present, has an open
pneumatic duct. All the fin-rays are jointed, or the dorsal and
VOL. II O
214
ZOOLOGY
SECT
the pectoral are armed each with an anterior ossified spine, and
the pelvic fins, when present, are abdominal in position.
FIG. 887. — Rita buchanani, one of the Siluroids. b. barbel ; d.f. r. 1, first dorsal fin-ray;
d. f. 2, adipose fin ; pet. f. r. 1, first pectoral fin-ray ; po. f. pelvic tin ; v. f. ventral fin.
(After Day.)
Including the Cat-fishes or Siluroids (Fig. 887), Carp, Gudgeon,
Loach, Pike, Salmon and Trout (Fig. 865), Smelt, Grayling, Herring,
Anchovy, Eel, &c.
Sub-order b. — A nacanthini.
Teleostei in which the air-bladder, when present, has, except in
one species, no pneumatic duct. The rays of the unpaired and of
the pelvic fins are all jointed, and the pelvic fins are either thoracic
d.f.3
FIG. 888. — Gadus morrhua (Cod), an. anus ; c. /. caudal fin ; d. /. 1 — 3, dorsal fins ; mx.
maxilla ; pet.}', pectoral fin ; pmx. premaxilla ; po. /. pelvic liu ; t>./. 1 and 2, ventral lins.
(After Cuvier.)
or jugular. Including the Cod (Fig. 888), Haddock, Whiting,
Hake, Ling, and the Pleuronectidse or Flat-fishes (Fig. 893), such
as the Sole, Flounder, Turbot, &c.
Sub-order c. — Acanthopteri.
Teleostei in which the air-bladder, when present, has usually no
pneumatic duct. More or fewer of the rays of the dorsal, ventral,
and pelvic fins are unjointed, and have the form of strong spines.
xra
PHYLUM CHORDATA
215
The right and left bars of the fifth branchial arch are usually not
fused.
This immense group includes the greater number of marine
FIJ. 839. — Ssbastesparcoides. br. m. branchiostegal membrane; d. f. spiny portionTui'
dorsal (in ; d. /'. soft portion ; me. maxilla ; op. opercular ; pet. f. pectoral tin ; i>.mr. pre-
maxilla ; pr. op. pre-opercular ; pa. f. pelvic fin>; v.f. spiny portion of ventral lin ; c. /'. soft
portion. (After Richardson.)
fishes (Fig. 889), as well as many fresh-water forms : the Perch,
Stickleback, Sea-bream, Mullet, Mackerel, and Gurnard may be
specially mentioned.
Sub-order d. — Pharyngognathi.
Teleostei in which the right and left bars of the fifth branchial
Fio
. 890. — Labrichthys psittacula (Wrasse), d. f. hard dorsal fin; d./'. soft dorsal, l]>.
lips ; pct.f. pectoral fin ; pv. f. pelvic lin ; v.f. ventral tin. B, inferior pharyngeal bom.1 of
Labrichthys. (A, after Richardson ; B, after Owen.)
o 2
216
ZOOLOGY
SECT.
arch are fused to form a single bone in the floor of the mouth (Fig.
890, B). The remaining characters are as in Acanthopteri.
Including the Wrasses (Fig. 890) and their allies.
Sub-order e. — Plectognathi.
Teleostei having no pneumatic duct. The exoskeleton, when
present, takes the form of bony plates or spines. The gill-opening
pcfj
FIG. 891. — Ostracion (Coffer-fish), br. ap. branchial aperture ; <-f.f. pectoral
fin; v. f. ventral fin. (After Day.)
is very narrow. The mouth is very small, and the premaxiUa and
maxilla are united. The pelvic fins are absent or represented by
spines.
This is a small sub-order, including the File-fishes, Globe-fishes,
Sun-fishes and Coffer-fishes (Fig. 891).
Sub-order f. — Lophobranchii.
Teleostei having no pneumatic duct. The gills are not comb-
like, but have their filaments arranged in tufts (Fig. 892, B). The
branchial aperture is very small. The exoskeleton consists of
bony plates arranged segmentally.
This is also a very small sub-order, including only the Sea-
horses (Fig. 892), Pipe-fishes and their allies.
Sub-orders 6— / are frequently grouped together as Physoclisti,
distinguished from Physostomi by the closed air-bladder.
Systematic Position of the Example.
Salmo fario is one of several species of the genus Salmo, belonging
to the family Salmonidce, of the sub-order Physostomi and the
order Teleostei.
The absence of a spiral valve and of a conus arteriosus, the
PHYLUM CHORDATA
217
presence of a bulbus aortse, and the decussation of the optic nerves
indicate its position among the Teleostei. It belongs to the
B
FIG. 892.— Hippocampus (Sea-horse). In B the opercuhnn is removed to show the gills.
br. a p. branchial aperture ; brd. p. brood-pouch ; d.f. dorsal fin ; g. gills ; pct.f. pectoral fin.
. (From Claus and Giinther.)
Physostomi in virtue of possessing a pneumatic duct, none but
jointed fin-rays, and abdominal ventral fins. The characters which
place it among the Salmonidse are the presence of an adipose fin
and of pseudobranchise, the absence of oviducts, and the fact that
the maxilla enters into the gape of the mouth. The genus Salmo
is distinguished by its small scales, well-developed conical teeth,
absent on the pterygoids, a short ventral fin with fewer than
fourteen rays, numerous pyloric appendages, and comparatively
large ova. The distinctive characters of the various species of
Salmo depend upon comparatively minute points, such as the-
relative proportions of various parts, and are often difficult of
determination owing to individual variations correlated with
different environments. In S. fario the posterior margin of the
operculum is evenly curved, the maxilla is longer than the snout,
and the vomerine teeth are in a double series and persist throughout
life.
3. GENERAL ORGANISATION.
External Form. — The typical form of the Teleostomi is very
fairly represented by that of the Trout (Fig. 865) — a long, com-
pressed body, nearly half of which is formed by the tail, pointed
anterior and posterior ends, a large vertical tail-fin, a head of
218 ZOOLOGY SECT.
moderate size, and a terminal mouth. Such a form is eminently
fitted for rapid progression through the water. But from this
characteristic fish-form there are many striking deviations. The
body may be greatly elongated and almost cylindrical, as in the
Eels ; or of great length and strongly flattened from side to side,
as in the Ribbon-fishes ; or the head may be of immense proportional
size and strongly depressed, as in certain shore-fishes, such as the
" Fishing-frog " ; or, as in the beautiful Reef -fishes, the whole
body may be as high as it is long. The mouth sometimes has a
ventral position, as in Elasmobranchs, with the snout prolonged
over it. This is the case, for example, in the Sturgeons (Fig. 884) ;
in the allied Polyodon the snout takes the form of a horizontally
flattened shovel-like structure, about one-fourth the length of the
body. On the other hand, in the ground-feeding " Star-gazers "
and some other Acanthopteri the lower jaw is underhung like
that of a bull -dog, and the mouth becomes dorsal in position.
A beak may be produced by the prolongation of the upper jaw,
as in the Sword-fish, or of the lower jaw, as in the Half-beak or
Gar-fish, or of both jaws, as in the Bony Pike (Fig. 885). Such a
projection is not to be confounded with the snout of the Sturgeon
or Polyodon, being formed by the elongation of the bones of the
jaws (premaxilla, maxilla, dentary, &c.), whereas in the two
Chondrostean forms referred to it is the anterior region of the
cranium which is prolonged. Still another form of " snout "
is produced in many Teleostei by the great mobility of the jaws,
allowing of their protrusion in the form of a short tube. In the
Wrasses or " lip-fishes " the mouth is bounded by fleshy lips
(Fig. 890, lp.).
Tactile processes or barbels sometimes arise from the head ; the
most familiar example is that on the chin of the Cod and Haddock
(Figs. 884 and 888, 6.). An operculum is always present, and is
supported by a variable number of investing bones ; it is con-
tinued below into a branchiostegal membrane (Fig. 866, br. m.),
which, except in Crossopterygii and the Sturgeons, is supported
by bony rays. In Polypterus a pair of bony jugular plates (Fig.
883, B, jug. pi.) are placed at the lower end of the branchiostegal
membrane, between the rami of the mandible : Amia has a single
plate (Fig. 886, B, jug. pi.) in the same position. Spiracles are
present only in Polypterus (Fig. 898) and some Sturgeons.
The commonest number of median fins is two dorsals, one caudnl,
and one ventral, but this number may be increased or diminished
(Figs. 888 and 890), or there may be a continuous median fin
extending along the back and round the end of the tail to the anus.
The dorsal fin is sometimes partly or wholly represented by a
series of small finlets (Fig. 883). The tail fin may be diphycercal,
heterocercal, or homocercal, and is usually the chief organ of
progression. But in the Sea-horse (Fig. 892) there is no caudal fin,
xm PHYLUM CHORDATA 219
and the tail is prehensile, being used in the position of rest to coil,
in the vertical plane, round sea-weeds, &c. : when swimming it
hangs downwards, having no lateral movement, and locomotion is
effected by the vibration of the dorsal fin.
The dermal-rays of the caudal fin are always jointed, as in the
Trout, but in most of the Acanthopteri and Pharyngognathi
more or fewer of the foremost rays of the dorsal, ventral, and pelvic
fins are unjointed, forming spines (Figs. 889 and 890, d. /.), some-
times large and strong enough to recall the dermal defences of
some Sharks and of Holocephali (Fig. 858, d. f. r. 1, pctf. r. /). In
Polypterus (Fig. 883) each finlet is supported along its anterior
edge by a strong spine, to which the soft rays are attached.
The anterior dorsal fin may attain an immense size, and is
subject to some curious variations. In the Fishing-frog or Angler
(Lophius) its foremost rays are elongated and bear lobes or lures
by which small fishes are attracted as to the bait on a fishing-line.
In the Sucking-fish (Echeneis) the anterior dorsal fin is modified
into an adhesive disc by means of which the fish attaches itself
to the bodies of Sharks and Turtles.
The portion of the paired fins visible externally is usually very
thin, and supported entirely by dermal rays. But in the Crosso-
pterygii (Fig. 883) the rays form a fringe round a thick basal
lobe, which is supported by endoskeletal structures (vide infra).
This condition of things forms an approach to the structure met
with in Elasmobranchii and Holocephali. The pectorals vary con-
siderably in size, and in the Flying-fishes (Exoccetus, Dactylopterus)
form large, wing-like expansions, capable of sustaining the animal in
its long flying leaps into the air. In the Butterfly-fish (Gastrochisma)
the pelvic fins are similarly modified. In many Fishes the pelvics
are reduced to filaments or scales, and in some cases a sucking-disc
is developed in connection with them. The pectorals always retain
their normal position, just behind the gill-clefts, but the pelvics
often become more or less shifted forwards from the typical position
beside the vent. The change in position is least in the three
"ganoid" orders (Figs. 883-886) and in the Physostomi (Figs.
865 and 866), in which they are usually between the middle of
the abdomen and the anus, and are said to be abdominal in position ;
but in a large proportion of the fishes in the remaining orders
of Teleostei they come to be placed almost beneath the pectorals
(Fig. 890, pv. f.), when their position is called thoracic, or on the
throat (Fig. 888), when they are said to loejugula.r in position.
A very remarkable deviation from the typical form occurs in the
Flat-fishes (Pleuronectidfe), a family of Anacanthini. The body
(Fig. 893) is very deep and strongly compressed : the fish habitually
rests on the bottom, in some species on the right, in others on the
left side, partly covering itself with sand, and occasionally swimming
with a curious undulating movement. The under side is usually
220
ZOOLOGY
SECT.
pure white, the upper side dark. The eyes (r.e, I.e.) are both on
the upper or dark-coloured side, and the skull is distorted so as
to adapt the orbits to this change of position. The abdominal
cavity is very small, the anus placed far forward, and the dorsal
and ventral fins are sometimes continuous. Young Flat-fishes
swim in the ordinary vertical position, but after a time they lie
on one side and assume the adult peculiarities, the eye on the
lower side gradually rotating until it reaches the upper surface.
Many Shore-fishes exhibit protective characters, the tints and
markings of the skin being harmonised with those of the rocks,
sea-weeds, &c., among which they live. The effect may be
heightened by fringes and lobes of skin, resembling sea-weed, and
often giving the fish a most grotesque appearance. The colours
are often adaptable : Trout, for instance, alter their colour by the
ie.
FIG. 893. — Fleuronectes cynoglossus (Craig-fluke), from the right side. d. /. dorsal flu ;
1. e. left eye ; pct.f. pectoral fin ; pv.f. pelvic fin ; r. e. right eye ; v. f. ventral fin. (After
Cuvier.)
contraction or expansion of their pigment-cells, according to
whether the streams in which they live have a muddy or a sandy
bottom. In some Shore-fishes, such as those of the coral reefs,
the colours are of the most brilliant description ; vivid reds, blues,
and yellows, spots or stripes of gold or silver, are common, and
although the combination of tints may sometimes seem to our
eye rather crude and glaring, they appear to be distinctly protec-
tive, harmonising with the brilliant hues of the Coral Polypes
and other members of the reef fauna. Pelagic fishes, such as the
Mackerel and Herring, are usually steely-blue above, white beneath.
Many deep-sea Teleostei are phosphorescent : in some of these
definite luminous organs (Fig. 894) are arranged in longitudinal
rows along the body, each provided with a lens and other accessory
parts, like those of the eye, the whole organ having the character
of a minute bull's-eye lantern. Some species of the same order,
XIII
PHYLUM CHORDATA
221
such as the Weaver (Trachinus], possess poison-glands, opening
either on one of the dorsal spines, or on a spinous process of the
operculum, or, as in the Cat-fishes (Siluridae), on the spine of the
pectoral fin.
Exoskeleton. — In many Teleostomi, such as Polyodon and
many Eels, the skin is devoid of hard parts, but in most cases a
B
FIG. 804. — Stomias boa. The white dots are the luminous organs. (From Hickson, after
Filhol.)
dermal exoskeleton is present. In Amia and in the majority of
Teleostei this takes the form, as in the Trout, of scales, rounded
plates of bone imbedded in pouches of the derm and overlapping
one another from behind forwards. When the free border of the
scales presents an even curve, as in Amia and most Physostomi
and Anacanthini, they are called cycloid scales (Fig. 867) ; when, as
in most Acanthopteri, the free edge is produced into small spines
(Fig. 895, A), they are distinguished as ctenoid scales. Usually
the integument is continued
as a thin layer over the surface
of the scales, but in a good
many cases this investment is
absent. In exceptional cases
the scales may be so large and
strong as to form a rigid
armour. In the Sturgeon
(Fig. 884) there is a strong
armour, formed of stout bony
plates, or scutes, produced into
enamelled spines and articula-
ting with one another by suture. Scutes are also found in many
Siluroids (Fig. 887) and in Lopho branchii (Fig. 892) and some
Plectognathi (Fig. 891) ; while in other Plectognathi the exo-
skeleton takes the form, as in the File-fishes, of minute spines
like the shagreen of Sharks, or, as in many Globe-fishes, of long,
outstanding, bony spines. Lastly, in Polypterus and Lepidosteus
are found rhomboid or ganoid scales (Fig. 895, B), in the form
g
222
ZOOLOGY
SECT.
of thick, close-set, rhomboidal plates formed of bone, covered
externally by a layer of enamel-like material (ganoin) and joined
together by pegs and sockets. In many Ganoids the anterior
fin-rays of both median and paired fins bear a row of spine-like
scales called fulcra (Fig. 885, /.). True dermal teeth similar to
those of the Elasmobranchs occur scattered over the scales and
lepidotrichia in some Teleostomi (e.g. Lepidosteus, Polypterus) :
these may be fixed or movable (Siluroids).
Endoskeleton. — In the Sturgeons the vertebral column (Fig. 897,
WS.) consists of a persistent notochord with cartilaginous arches,
and is fused anteriorly with the cranium. In the remaining orders
bony vertebra3 are present ; the centra are biconcave, except
in some Eels,
in which the
anterior face is
flat or even
convex, and in
Lepidosteus, in
which the an-
terior face is
distinctly con-
vex. Vertebra?
of this form, i.e.
having the cen-
trum convex in
front and con-
cave behind,
are called opis-
thoccelous. Ribs
are usually pre-
sent : in Poly-
FIG. 896.— Anterior end of vertebral column of Polypterus. PS. pterUS each V6r-
parasphenoid ; .R. /— F, dorsal ribs: WK, centra ; t, ventral (pleura!) + »>...,„ T,oa fwn
ribs. (From Wiedersheim's Comparative Anatomy.)
pairs, a dorsal
pair (Fig. 896, R, I — 7) of considerable length, running between the
dorsal and ventral muscles, and a short ventral pair (f) between the
muscles and the peritoneum : the former answer to the ribs of Elasmo-
branchs, the latter to the ribs (pleural ribs) of the remaining Teleo-
stomi, which are always placed immediately beneath the peritoneum.
There may be one or more sets of intermuscular bones, attached
either to the neural arch (epineurals), to the centrum (epicentrals),
or to the ribs (epipleurals), not preformed in cartilage, but developed
as ossifications of the intermuscular septa. The posterior end
of the vertebral column is turned up in the Sturgeons, Lepidosteus,
and Amia, resulting in a heterocercal tail-fin : in Amia, however,
the fin-rays are so disposed that the fin appears almost symmetrical.
Among Teleostei the tail-fin is very usually homocercal, as in the
xm
PHYLUM CHORDATA
223
Trout, with a more or less disguised asymmetry : in many cases
in the adult the development of the large, fan-shaped, posterior
heemal arches- completely hides the upturned end of the notochord,
and in some the spinal column ends simply in a somewhat compressed
centrum around which the fin-rays are symmetrically disposed ;
such truly symmetrical tail-fins are called dipliycercal.
In the* structure of the skull the Chondrostei make the nearest
approach to Elasmobranchs. The cranium (Fig. 897) is an
undivided mass of cartilage with a few isolated replacing bones.
The roofing investing bones lie in the dermis, so as to be practi-
cally superficial, and behind pass insensibly into the scutes covering
the trunk : the fact that these bones (parietals, frontals, &c.)
are exoskeletal structures is here perfectly obvious. The same is
car
•z» IVr/r Orb -*£ n 'V
jg, Mtf | (
j i •* '
FIG. 8'J7. — Skull of Sturgeon, with the investing bones removed, .a, pharyngo-branchials ;
AF, antorbital process ; AR .articular ; b. epibranchial ; c. ceratobranchial ; C, notochord ;
Cop. basibranchials ; d, hypobranchial ; De. dentary ; OK, auditory capsule ; HM. hyoman-
dibular ; hy. hyoid cornu ; Ih. interhyal ; MA. mandible ; Na. nasal capsule ; 06. neural
arches ; PF , post-orbital process ; PQ. palatoquadrate ; Ps. Ps'. Ps". parasphenoid ; Psp.
neural spines ; Qu. quadrate ; JR. rostrum ; Ri. ribs ; Sp. N. foramina for spinal nerves ;
Sy. symplectic ; WS, vertebral column ; x. vagus foramen ; / — V, branchial arches.
(From Wiedersheim's Comparative Anatomy.)
the case in Polypterus (Fig. 898), in, which, however the replacing
bones are better developed. In Lepidosteus and Amia, and
especially the latter, the skull resembles that of the Trout in all
essential respects, the main differences consisting in the absence
of certain bones, such as the supra-occipital, and in the presence
of additional investing bones. Among Teleostei it is only in the
Physostomi that the investing bones remain separable from the
chondrocranium in the adult ; in the remaining orders, e.g. in the
Cod, Haddock, or Perch, they become grafted on to the chondro-
cranium and so closely united with the replacing bones that they
can be removed only by pulling the whole skull to pieces ; most
of the original cartilage frequently disappears in the adult and
the cranium thus becomes a firm bony mass in which no distinction
between replacing and investing bones is discernible.
The varying size of the gape, which is so noticeable a feature in
the Teleostomi, depends upon the inclination of the suspensorium :
224
ZOOLOGY
SECT.
-PffIA
Mr.
in wide-moutlied Fishes (Fig. 888) the axis of the hyomandibular
and suspensorium is nearly vertical or even inclined backwards ;
in small-mouthed forms (Fig. 891) it is strongly inclined forwards,
and the length of the jaws is proportionately reduced. In the
branchial arches the pharyngobranchials of each side are very
commonly fused, and constitute what are called the superior
pharyngeal bones : the re-
duced fifth branchial bars,
or inferior pharyngeal bones,
bite against them. The
Pharyngognathi are dis-
tinguished by having the in-
ferior pharyngeal bones united
into a single bony mass of
characteristic form (Fig. 890,
B). The gill- rakers are often
very highly developed, and
may form a mesh capable of
retaining even microscopic
organisms.
In the shoulder-girdle, as in
the skull, the Chondrostei
approach the Elasmobranchs.
There is a primary shoulder-
girdle consisting of large
paired cartilages, not united
in the middle ventral line,
and unossified : each is
covered externally by a large
scute-like investing bone, the
clavicle. In the remaining
Ganoids and in Teleostei the
primary shoulder-girdle is re-
duced in size and is usually
ossified by two bones, a
dorsal scapula and a ventral
, . , coracoid : sometimes, as in
frontal; J\l maxilla ; .V. nasal; iVa. nostril; the TrOllt, there may be ail
O]>. opercular ; Orb. orbit ; P. parietal. There- jj-,- -i -n ,- ,1
maining letters point to less important investing additional OSSmCatlOn, the
bones. The arrow is passed into the spiracle. -j \ JJ'j.', 1
(From Wiedersheim's Comparative Anatomy.) meSOCOraCOld . Additional 111-
vesting bones — supra-davicle,
post-clavicle, &c. — are added, and one of them, the post-temporal,
serves to articulate the shoulder-girdle with the skull (Fig. 874).
In the skeleton of the pectoral fin it is the Crossopterygii which
approach most nearly to Elasmobranchs. In Polypterus (Fig.
899) the basal lobe of the fin is supported by a rod-like ossified
propterygium (Pr), a broad cartilaginous, partly ossified, meso-
;. K.j».-,skuii ..i Poiyptems, from above. F,
xm
PHYLUM CHORDATA
225
Oss
JL-.J2J'
pterygium (MS), and an ossified metapterygium (MT) ; to these,
two rows of elongated radials (Ra, ^
Ral) are articulated fanwise, and
these in their turn give attachment
to the fin-rays (FS). In all the re-
maining orders the basalia (pro-,
meso-, and meta-pterygium) are ab-
sent, and the endoskeleton of the fin
consists only of a single or double row
of radials (Fig. 874).
In Polypterus there is a vestigial
pelvic girdle (Fig. 900, BP) in the
form of a small rhomboidal cartilage
to which the anterior ends of the
basalia (Bas1) are attached : thus in
the structure of the posterior ex-
tremities also, the Crossopterygii are
the most primitive of the Teleostomi.
In all the remaining orders the pelvic
girdle appears to be atrophied. The
pelvic fin is supported by a single
bone of variable form (Fig. 875,
B. PTG) and apparently arising from
the fusion of proximal pterygio-
phores. Between its posterior end
and the dermal rays irregular
nodules, representing radials, may be interposed.
The distinction between hard or unjointed fin-rays, or spines, and
soft or jointed fin-rays has already
been referred to. The first ray of
the dorsal and pectoral fins some-
times, e.g. in Siluroids (Fig. 887), has
the form of a very strong spine
articulated by a bolt-and-shackle
joint, i.e. by the interlocking of
two rings. In some cases the
first dorsal spine springs from the
skull.
The texture of the bones is sub-
ject to wride variation : in some
Acanthopteri they are very thick
and strong, in some places almost
like ivory ; while in the Lump-
fish (Cyclopterus), the huge Sunfish
(Orthagoriscus), and in many deep-
sea forms, such as the Eibbon-
fishes (Regalecus and Trachypterus), the amount of mineral matter
FIG. 899. — Pectoral fin of Polypterus.
FS. dermal rays ; MS. mesoptery-
gium ; MT. metapterygium ; NL,
nerve-foramina ; Oss. ossification in
mesopterygium ; Pr. propterygium ;
.Ra. first radials ; Ka1. second radials.
At * the bony marginal rays meet
and shut otf the middle region from
the shoulder-girdle. (From Wieders-
heim's Comparative Anato/nii.)
BP
FIG. 900. — Pelvic fin of young Poly-
pterus. Ap. part of basale ; Baa1.
basale ; B/'. pelvic cartilages (fused
in adult) ; Rad. radials. (From
Wiedersheim.)
226
ZOOLOGY
SECT.
is so small that the bones are easily cut with a knife and weigh
astonishingly little when dry.
Electric Organs. — Three genera of Teleostomi possess electric
organs, the Electric Cat-fish (Malapterurus), one of the Siluridae,
found in the fresh waters of tropical Africa, the Electric Eel
(Gymnotus), a Physostome occurring in Brazil and the Guianas,
and an American Star-gazer of the genus Astroscopus. In Mala-
pterurus the electric organ extends over the whole body, beneath
4 the skin ; in Gymno-
tus (Fig. 901) there is
a pair of batteries in
the ventral half of the
greatly elongated tail ;
in Astroscopus the
electric organs are
situated on the upper
surface of the head
just behind the eyes.
As in the Elasmo-
branchs, the electric
organs are formed by
modification of muscu-
lar tissue.
Digestive Organs.
—Some Teleostomi are
toothless ; but in most
instances teeth are pre-
sent, and may be
developed on the pre-
maxilla, maxilla, pala-
tine, pterygoid, vorner,
parasphenoid, dentary,
basihyal, and bones of
FIG. 901. — Gymnotus electricus, A, showing the extent +!,„ kranpliial arr-Vioc
of the electric organ (E). Fl, Central fin. B, small tne
portion of tail, in section. DM. DM.' dorsal muscles ; Jt is characteristic of
E. E.' electric organ ; Fl, ventral fin ; H, skin ; LH,
caudal canal ; Sep. fibrous septum ; VM. VM.' ventral most
muscles ; WS, WS', vertebral column, with spinal j. -u _
edersheim' m
ws
nerves. (From Wiedersheim's Comparative Anatomy.)
m , . . ,
1 elCOStei, With
ovno^fir>r. /-> f
eAuepuiuu
Physostomi, that the
maxilla is edentulous and does not enter into the gape (Fig. 889).
In a large majority of species the teeth are small, conical, and
recurved, suitable for preventing the struggling prey from slipping
out of the mouth, but quite unfitted for either tearing or crushing.
In some Fishes, such as the Pike, the teeth are hinged backwards
so as to offer no resistance to the passage of the prey towards the
gullet, but effectually barring any movement in the other direction.
In many deep-sea Fishes (Fig. 894) the teeth are of immense size
and constitute a very formidable armature to the jaws. Many
xm PHYLUM CHORDATA 227
instances occur in which there is a marked differentiation of the
teeth, those in the front of the jaws (Fig. 902) being pointed or
chisel-edged, and adapted for seizing, while the back teeth have
spherical surfaces adapted for crushing. In the Wrasses (Fig. 890, B)
strong crushing teeth are developed
on the pharyngeal bones. In the
Globe-fishes the teeth are apparently
reduced to one or two in each jaw,
but each " tooth " in this case really
consists of numerous calcified plates
fused together. The teeth may be
either simply embedded in the mucous
membrane so as to be detached when
the bones are macerated or boiled, or
they may be implanted in sockets of
the bone, or ankylosed to it. They
are formed of some variety of dentine,
and are often capped with enamel. Their succession is perpetual,
i.e. injured or worn-out teeth are replaced at all ages.
In some species the enteric canal shows little differentiation into
regions, but, as a rule, gullet, stomach, duodenum, ileuin, and
rectum are more or less clearly distinguishable. The stomach is
generally V-shaped, but its cardiac region may be prolonged into
a blind pouch ; it is often very distensible, allowing some of the
deep-sea Teleostei to swallow Fishes as large as themselves. In the
Globe-fishes the animal can inflate the gullet with air, when it floats
upside down on the surface of the water. The Ganoids have a spiral
valve in the intestine, which is very well developed in Polypterus
and the Sturgeon, vestigial in Lepidosteus (Fig. 904, sp. v.) and
Amia : it is absent in all Teleostei, except possibly in Chirocenlrus,
one of the Physostomi. The liver is usually large ; a pancreas
may be present as a compact gland, as in Elasrnobranchs, or may
be widely diffused between the layers of the mesentery, or in part
surrounded by the liver. Pyloric cceca are commonly present, and
vary in number from a single one to two hundred. The anus is
alwavs distinct from, and in front of, the urinogenital aperture.
Respiratory Organs. — The gills are usually comb-like, as in
the Trout, the branchial filaments being free, owing to the atrophy
of the interbranchial septa. In the Sturgeon, however, the septa
are fairly well developed, reaching halfway up the filaments, so
that the latter are free only in their distal portions ; this arrange-
ment is obviously intermediate between the Elasmobranch and
Teleostean conditions. The most striking deviation from the
normal structure occurs in Lophobranchii, in which the gill-
filaments are replaced by curious tufted processes (Fig. 892, B, . spiral
valve ; st. stomach. (From
Wiedersheim's Comparative
Anatomy, after Balfour and
Parker.)
descends or ascends
230
ZOOLOGY
SECT.
causing greater or less compression of the gases in the air-bladder,
can be brought to approximate to that of the surrounding water
by increase or decrease in the quantity of the contained gas. This
is brought about by secretion or absorption, often by means of
vaso-ganglia or red glands (Fig. 905, vs. gri). These are elevations
of the wall of the bladder, abundantly supplied with blood, and
containing tubular glands which open into the cavity of the bladder.
In Fishes with a pneumatic duct the red glands are absent, but
If. I
opt.l
•n.
FIG. S05. — Horizontal section of posterior portion of head and anterior end of air-bladder in
Pseudophycis bachus, one of the Gadidse or Cods (semi-diagrammatic), a. thickened
portion of air-bladder fitting into fenestra in posterior wall of auditory capsule ; a. bl. air-
bladder ; au. cp. outer wall of auditory capsule ; au. cp'. inner (membranous) wall ; b.
hollow offshoots of air-bladder ; cp. sir. corpora striata ; orb. cerebellum : memb. lab. mem-
branous labyrinth ; o/f. 1. olfactory bulbs ; olf. p. olfactory peduncles (olfactory tract i>>. — I'.raiii (if
dosteus, dorsal view.
cbl. cerebellum ; c. h. olfac-
tory part of prosen-
cephalon ; i/i. diencephalon ;
m. o. medulla oblongata ;
off. 1. olfactory bulbs ; o/>t.
I. optic lobes ; prs. corpora
striata. (After Balfour and
Parker.)
232
ZOOLOGY
SECT.
undivided pronephric duct : it unites with its fellow of the opposite
side before opening either directly on to the exterior or into a
urinogenital sinus. A urinary bladder is formed as a single or
double dilatation of the ureter. The right and left kidneys undergo
more or less fusion, and their anterior ends are usually converted
into adenoid or lymphatic tissue (kd.r), so that, while resembling
the rest of the organ in external appear-
ance, they do not discharge a renal
function.
The male organs of Lepidosteus may
be taken as an example of those of
(ianoids. The testis (Fig. 907, ts.) is a
paired, lobulated organ, the secretion of
which is carried by a large number of
vasa efferentia (v. ef.) into a longitudinal
canal (l.c.) lying alongside the ureter (ur.).
From this canal tubes are given off which
communicate with the urinary tubules of
the kidney or open directly into the
ureter, so that the seminal fluid has to
traverse the latter in order to reach the
urinary bladder (bl.) and make its escape
by the common urinogenital aperture
(u.g. ap.). In Teleostei there are no vasa
efferentia, but the posterior end of the
testis is directly continued into a duct
(Fig. 876, v. d.) which unites with its
fellow of the opposite side and opens
either into a urinogenital sinus, as in the
Trout, or, as in the Cod, directly on the
exterior, between the anus and the urinary
aperture. In the Eels the seminal fluid
escapes into the ccelome and is discharged
by genital pores.
In most Ganoids the oviducts (Fig. 908,
u9.a.p --w B, ovd.) have funnel-like anterior ends
(ovd.") opening into the coelome, while
FIG. 907.— Male organs ol Lepi- V • f 7 /\ ,1 v i •
dosteus. pi. bladder; i. c. posteriorly (ova. ) they discharge into the
dilated ureters (bl.). A similar arrange-
ment occurs in the Smelt, one of the
Physostomi (Salmonidae), in which the
eggs are discharged from the outer or lateral face of the ovary into
the open end of the oviduct. But in most Teleostei and in Lepi-
dosteus (Fig. 908, A) the ovary (ovy.) is a hollow sac continued
posteriorly into the oviduct (ovd.) : the eggs are set free into its
cavity from the folds into which its inner surface is produced, and
so pass directly into the oviduct without previously entering the
61
longitudinal canal ; tft. testis ;
ti.g. ap. urinogenital aperture ;
ur. ureter ; v. ef. vasa efferentia,
(After Balfour and Parker.)
XIII
PHYLUM CHORDATA
233
coelome. An ovary of this kind reminds us of the state of things
in Arthropods, in which also the ovary is a hollow organ dis-
charging its products into its internal cavity, whence they pass
directly into the continuous oviduct. It was pointed out that the
lumen of the ovary in this case was to be looked upon as a shut-off
portion of the coelome : this is certainly the case in Lepidosteus
and the Teleostei. In
the embryo a longi-
tudinal fold grows
from the ventral edge
of the then solid ovary,
r fVmt in flip FIG. 910. — Polypterus bichir. Head of advanced larva. EG.
external gill. (From Dean, after Steindachner.)
Sturgeon and
Polypterus, as in Craniates in general, there is an open
medullary groove which becomes closed in to form a medullary
canal. There is frequently a metamorphosis : in Lepidosteus,
for instance, the newly-hatched young is provided with a
sucking-disc, and the proportions of the head are quite different
from those of the adult. In the larval Sturgeon provisional
teeth are present, and in many Teleostei the young differ from the
adult in the presence of large spines, which probably, like the spines
in the zosea-stage of some Crustacea, serve a defensive purpose.
The pelagic Iarva3 of Eels are strongly compressed, perfectly trans-
parent, and have colourless blood. They are sometimes known as
;' Glass-fish," and were formerly placed in the genus Leptocephalus,
their real nature being unknown. The young of the Crossopterygii
(or at least Polypterus, Fig. 910) have external gills, as in Dipnoi
and Amphibia (vide infra), and the same holds good of Cobitis,
Heterotis, and Gymnarckus among the Teleostei.
The Geographical Distribution of the Ganoid Teleostomi is
curiously limited : they are all essentially fresh-water forms—
although some Sturgeons are found in the sea — and are almost
236
ZOOLOGY
SECT.
exclusively inhabitants of the Northern Hemisphere, and especially
of the Holarctic Kegion. The Chondrostei occur in the rivers of
Europe, Asia, and North America : one genus of Sturgeons
(Scaphirhynchus) lives in the Mississippi and in the rivers of Central
Asia, but not in the intermediate regions : in the same way Polyodon
is found only in the Mississippi, while the closely-allied Psephurus
is found in the Yangtse-kiang and Hoangho — a striking instance
of discontinuous distribution. Amia is found in the fresh waters of
the United States ; Lepidosteus extends also into Central America
and Cuba. Polypterus lives in the Upper Nile and some other
tropical African rivers ; Calamoichthys in the Old Calabar River.
B
nch
FIG. 911.— .4, restoration of Glyptolepis (Devonian) ; B, Macropoma mantelli (Cre-
taceous), a. bl. ossified air-bladder ; d.f. 1, d.f. 2, dorsal fins ; /*. a. haemal arches ; jug. pi.
jugular plates : »». a. neural arches ; nch. position of notochord ; pet. f. pectoral fin ; pv.f.
pelvic fin ; »./. ventral fin. (From Nicholson and Lydekker.)
Among Teleostei the Physostorni are largely, though not ex-
clusively, fresh-water Fish ; the Carps, Eels, Salmonoids, and
Siluroids are important examples. The Acanthopteri, Pharyngo-
gnathi, and Anacanthini are mostly marine, some being inhabitants
of the shores, some pelagic, some abyssal, extending to a depth
of nearly 3,000 fathoms. As we have seen, many species are
practically terrestrial. All the sub-orders are universally distri-
buted, so that we have to descend to families before meeting with
any important facts in geographical distribution.
The Distribution in Time of the Teleostonii is interesting
as showing the gradual replacement of the lower or more generalised
xin
PHYLUM CHORDATA
237
members of a group by the higher or more specialised forms.
During the whole of the Palaeozoic and the greater part of the
Mesozoic era the three orders of Ganoids, to-day small and isolated
groups, formed the whole of the Teleostomian fauna, and it is not
until the Cretaceous period that the Teleostei, the present dominant
order, make their appearance. From the Cretaceous onwards the
Ganoids undergo a progressive diminution in numbers, genus after
genus and family after family becoming extinct, while a corre-
sponding increase takes place in all the sub-orders of Teleostei.
The Crossopterygii make their first appearance in the Devonian
period, and, between that period and the Cretaceous, include six
families and a large number of genera and species. They exhibit
(Fig. 911) a very considerable range of variation in external and
B
FIG. 912. — A, Palaeoniscus macropomus (Permian); />. Flatysomus striatus
(Permian). (From Nicholson and Lydekker.)
internal characters. There are usually two dorsal fins, the tail
may be diphycercal or heterocercal, the scales rhomboid or cycloid.
In some genera, also, there was a persistent notochord (B. nch.},
the fossils showing well-preserved neural and haemal arches, but
no signs of centra. In many cases the interspinous bones or
proximal pterygiophores of the dorsal fins are fused into a single
ZOOLOGY
SECT.
basal bone. All agree in the possession of lobed fins ; the basal
lobe is sometimes so long as to approach the type of structure we
shall find to characterise the Dipnoi (vide infra).
The Chrondrostei are also largely represented, from the Devonian
upwards, and include a great variety of forms, many of which,
apart from the heterocercal tail, have a strong external resemblance
to Teleostei (Fig. 912). Some have the characteristic spindle-form
of strong-swimming Fishes (A), others the high, compressed form
of such shore-fishes as the Reef -fishes (B). Scutes are present in
FIG. 913. — A, Lepidotus maximus (Jurassic), s. scale ; t. teeth. B, Caturus furcatus
(Jurassic). (From Nicholson and Lydekker.)
some species, rhomboid scales in others, and in one genus the
greater part of the body is covered by cycloid scales, while rhomboid
scales occur in the upper part of the tail.
The Holostei first make their appearance in the Triassic rocks
and are abundant in Secondary and Lower Tertiary strata. They
also (Fig. 913) show a wide diversity in form and structure. The
body may be spindle-shaped or high and compressed ; the scales
may be rhomboid or cycloid, or may exhibit every gradation from
rhomboid to cycloid in passing from the trunk to the tail of one and
the same Fish ; the teeth may be sharp and conical, or blunt;
rounded, and adapted for crushing. A persistent notochord is
present in some species, a well-ossified vertebral column in others.
We see, then, that all the orders of Ganoids, during the period
xm PHYLUM CHORDATA 239
of their prime, branched out into diverse forms, adapted to different
environments, and often resembling, in a remarkable manner, the
divergent forms of Teleostei which fill similar positions at the
present day.
The Teleostei first appear in the Cretaceous rocks, where many
existing families are represented. From this period onwards the
three Ganoid orders undergo a progressive diminution in the number
of families, genera, and species, their places being taken by the
more highly differentiated Teleostei, until, at the present day, as
we have seen, they are reduced to a few scattered forms, mostly
confined to fresh waters.
Sub-class IV. - The Dipnoi.
The Dipnoi or Lung-fishes, comprising as their living repre-
sentatives only the Queensland Ceratodus or " Burnett Salmon,"
and the Mud-fishes (Protopterus and Lepidosiren) of certain South
African and South American rivers, are fishes of such well-marked
and special features that by some zoologists they are separated
from the true Fishes and regarded as constituting a separate class
of Vertebrates. One of their peculiar features is indicated by the
name Dipnoi. Not only do these animals breathe by means of
gills, like ordinary Fishes, but they have a highly-developed
apparatus for the respiration of air — -a lung or lungs — with an
arrangement of the circulation co-ordinated with this, such as is
indicated in Polypterus and Amia only among the Teleostomi.
They have bony scales and dermal fin-rays, but the paired fins,
unlike those of any other Fishes, with the exception of certain
extinct Elasmobranchs, are constructed ^OTL the biserial type
(" archipterygium," see p. 163).
1. EXAMPLE OF THE CLASS — Ceratodus (Neoceralodus
or Epicemtodus) forsteri.
The Ceratodus or " Burnett Salmon " (Fig. 914) is the largest
of the Dipnoi, attaining a length sometimes of four or five feet.
It occurs at the present day only in the Burnett and Mary Rivers
in Queensland, but fossil teeth referred to the same or nearly related
genera have been found in abundance in Palaeozoic and Mesozoic
beds in Europe, America, the East Indies, Africa, and Australia.
Ceratodus forsteri lives in still pools in which the water in the dry
season becomes extremely stagnant and overladen with decom-
posing vegetable matter ; and at that season it is only by rising to
the surface occasionally, and taking air into its lung, that it is
enabled to obtain sufficient oxygen for purposes of respiration.
Its food consists of such small animals as live among the water-
plants and decaying leaves, and in order to obtain a sufficient amount
of such food, it swallows relatively large quantities of vegetable
240
ZOOLOGY
SECT.
matter, which passes with little or no alteration through its enteric
canal. Its movements are for the
most part very sluggish, and are
chiefly effected by the agency of the
tail-fin. The paired fins are employed
in steering and balancing and in the
ascending and descending movements :
owing to their great flexibility they
are entirely incapable of supporting
the body when the fish is removed
from the water, but the pectoral fins
2 may be employed as props when it
H lies in a resting condition at the
| bottom.
External Characters. — The body
1= is fish-like (Fig. 914) with a diphycercal
= caudal fin. The surface is covered
« with thin, bony, imbricated cycloid
| scales, very large on the head and
£ trunk, somewhat smaller towards the
^ tail end, and very much smaller over
| the fins and the posterior part of the
"2 operculum.
The limbs have a characteristic
•jj shape, being in the form of two pairs
| of elongated, leaf -like, pointed paddles.
The marginal parts of the paired fins
and the whole extent of the unpaired
or caudal fin are supported by a double
series of slender fibre-like unjointed,
partly ossified, dermal rays (campto-
trichia), which are much more numer-
ous than the endoskeletal rays and
which are covered by small surface-
scales.
The mouth is situated on the ven-
tral surface of the head, close to the
anterior extremity of the snout. The
external nares differ from those of
other Vertebrates in being situated
immediately outside the aperture of
the mouth, enclosed within the upper
lip. A pair of internal nares opens
not far behind them into the anterior
part of the mouth-cavity. At the
root of the tail is the cloacal aperture with an abdominal pore on
either side of it. There is an operculum similar to that of the
•a
o
2
E
XIII
PHYLUM CHORDATA
241
Teleostomi, with a single slit-like branchial aperture behind it.
There are no spiracles. There is a well-marked lateral line.
Endoskeleton. — The spinal column (Fig. 915) is represented by
a persistent notochord, enclosed in a thick fibrous sheath, together
with neural and haemal arches.
A series of neural or basidorsal cartilages form the bases of the
neural arches, and haemal or basiventral cartilages are similarly
related below to a series of pleural ribs in the precaudal region, and
to a series of haemal arches in the caudal. These two sets of basal
cartilages are not precisely opposite throughout, and regularly
alternate for some distance in front. They are embedded in the
sheath of the notochord, but no centra are formed, and the noto-
chord, though pressed upon above and below by the series of basal
cartilages, is not constricted in the usual annular manner. At the
posterior end it becomes surrounded by cartilage. The neural and
•••/ iitrn
B I
fupra.se I
J 7
<2ent
m nit.
FIG. 915. — Ceratodus forsteri. Lateral view of the anterior portion of the skeleton.
A, anterior median investing bone of the roof of the skull ; B, posterior median investing
bone ; C, inner lateral investing bone ; has. basal cartilage of the pectoral fin ; br. branchial
arches ; dent, tooth of lower jaw ; hy. hyoid arch ; int. interoperciilum ; lam. plate over-
hanging branchial region ; mck. Meckel's cartilage ; occ. rb. occipital rib ; op. operculum ;
pal. palatoquadrate ; pet. pectoral arch ; rbs. ribs ; sub. orb. sub-orbital bones ; sq. so-called
squamosal ; supra, sc. post-temporal.
haemal arches are ossified ; each is surmounted by a rod-like neural
or haemal spine which forms part of a continuous three- jointed
ossified rod, the proximal segment being the spine, and the two
others radials. The pleural ribs are curved bony rods extending
downwards and somewhat backwards in the body- wall immediately
outside the peritoneal membrane, like the pleural ribs of the Teleo-
stomes. The first pair — the occipital ribs — (Fig. 915, occ. rb.),
thicker and straighter than the rest, are connected with the skull in
its vertebral portion.
The skull (Figs. 915, 916, and 917) consists of an undivided mass
of cartilage, devoid of fontanelles, narrowest between the orbits, and
broadening before and behind ; posteriorly it is prolonged into a
plate (lam.} overhanging the branchial region. Embedded in the
242
ZOOLOGY
•lab
pr.orb
sb.or
Lam.
art
SECT.
cartilage of the posterior
part are a pair of small
replacing bones which
appear to represent the
most anterior of the
spinal elements fused
with the skull. On the
upper surface are two
unpaired (A and B) and
four paired (C and sq.)
investing bones, the
homologies of all of
which are undetermined.
Premaxillse, maxillae,
and nasals are absent.
On the ventral surface
is a large investing bone
(Fig. 917, P.Sph.) repre-
senting the parasphenoid
In
FIG. 916. — Ceratodus forsteri. Dorsal view of the £ ^
skull. A, anterior median investing bone ; art. articular
surface for second fin-ray ; £, posterior median investing front IS a pair of Small
bone ; C, inner lateral investing bone ; lab. labial car- , , I -.
tilages ; lam. process projecting over gills ; op. pper- upper labial Or nasal
culum ; pr. orb. pre-orbital process of chondrocranium ; irf;iQrrac A -nalaf/-.
sb. or. sub-orbital bones ; sq. outer lateral investing Cdlllldges. J\. paidl
bone. (After Huxley.) quadrate cartilage (Fig.
915, pal.), firmly fixed to the side-wall of the cranium, gives attach-
ment to the mandible, so that
the skull is autostylic ; the quad-
rate element is distinct in the larva
and independently developed.
In front the palatoquadrate
contains a palatopterygoid ossi-
fication which forms the support
for the large composite tooth of
the upper jaw. The mandible
consists of Meckel's cartilage with
an angular bone behind, and a
large splenial, which bears the
tooth, in front. The dentary is
vestigial. The hyomandibular is
only represented by a small
vestige. Opercular (op.) and in-
teropercular (int.) bones support
the operculum. The hyoid (hy.)
and branchial arches (br.) are
cartilaginous. Of the latter, four
are completely developed, and a
fifth is represented by a vestige.
FIG. 917. — Ceratodus forsteri. Ventral
view of the skull, c, occipital rib ; d,
pa'atine teeth ; d' ', vomerine teeth ; na.
anterior and posterior nares ; P. palatine
region of palatopterygoid ; P. Sph. para-
sphenoid ; Pt. pterygoid ; Qu. quadrate
region ; Vo. vomer. (From Dean, after
Uiinther.)
XIII
PHYLUM CHORDATA
243
There are no branchial rays, but the branchial arches bear a series
of gill-rakers with cartilaginous supports.
The pectoral arch (Fig. 915, pel.} is a stout cartilage with two
pairs of investing bones, the clavicles on the coracoid, and the
cleithm on the scapular regions. The latter are connected with
the skull by post-temporals. The skeleton of the pectoral fin
consists of a stout basal cartilage (has.), an elongated, tapering,
central axis made up of a number of short cartilaginous segments,
and two rows of jointed cartilaginous rays extending out on either
side of the axis so as to support the middle part of the expanse of
the fin. The pelvic arch is a single cartilage, produced forwards
into an elongated rod-like epipubic process (Fig. 918). The skeleton
of the pelvic fin is similar to that
of the pectoral.
Digestive Organs. — The teeth
(Fig. 917) are of a remarkable
and characteristic shape. There
are two pairs of large compound
FIG. 918. — Ceratodus forsteri. Pelvic arch and skeleton of pelvic fin. (After Giinther.)
teeth of similar character, one pair (the palatine, d) on the roof
of the mouth (palatopterygoid bone) and the other (splenial)
on the lower jaw. Each is a curved plate with the convex border,
which is directed inwards and somewhat backwards, entire ; while
the concave border presents a series of six or seven vertical, ridge-
like projections or cusps. In addition to these, there are, in front
of the palatine pair, a pair of much smaller, simple, somewhat
chisel-like vomerine teeth (d'} placed close together and directed
vertically. In the embryo each tooth is represented by a number
of separate denticles which subsequently coalesce.
In the enteric canal the chief feature of special interest is the
presence, throughout the length of the intestine, of a spiral valve
similar to that of the Elasmobranchs and Ganoids. The rectum
opens into a small cloaca. A pair of abdominal pores open just
behind this.
Organs of Respiration. — Ceratodus combines aquatic respira-
tion by means of gills similar to those of ordinary fishes, with
aerial respiration by means of a lung.
There are four pairs of gills, each consisting of a double row of
gill-filaments supported on the branchial arches. A rudimentary
244
ZOOLOGY
SECT.
hyoidean gill or pseudobranck is present as well. The lung (Fig.
919) is an elongated median sac connected by a pneumatic duct
with a muscular chamber or vestibule opening into the ossophagus
on its ventral side by a slit-like aper-
ture or glottis. The internal surface
of the lung is sacculated, and a
regularly-arranged series of blind
pouches opens out of the main central
cavity. This lung of Ceratodus corre-
sponds morphologically to the air-
) (ladder of Ganoids and Teleosts, but
differs from it in its blood-supply and
consequently in its function, being
supplied with blood by a special
paired pulmonary artery (as is also
the case in Polypterus) and acting as
an important organ of respiration.
Blood-Vascular System. — Co-
ordinated with the existence of a
lung and distinct pulmonary circula-
tion, is a complication in the struc-
ture of the heart. The sinus venosus
is imperfectly divided into two parts,
and the cavity of the auricle is divided
into two by an incomplete septum in
the form of a ridge. The venous
blood enters the right-hand division
of the sinus venosus and passes thence
through the right-hand division of the auricle to the ventricle ;
the pulmonary vein, by which the blood is returned from the lung,
passes through the sinus, and its blood reaches the ventricle through
the left-hand division of the auricle. There are no auriculo-
ventricular valves guarding the opening between the auricle and
the ventricle. A contractile conus arteriosus is present, and has
a remarkable spirally-twisted form ; in its interior are four longi-
tudinal rows of valves, one of which is modified to form an incom-
plete longitudinal septum. The channel on the left side of this
septum, which receives the blood of the pulmonary vein, is in
communication in front with the first two aortic arches (afferent
branchials), that on the right with the last two.
The blood-vessels (Fig. 920) present an arrangement which is
intermediate in some respects between that which has been already
described as observable in the Elasmobranchs and that which will
be found to characterise the Amphibia. The four afferent branchial
arteries (off.) take their origin close together, immediately in front
of the conus, so that a ventral aorta can hardly be said to exist.
Each branchial arch has two efferent branchial arteries. A hyoid
FIG. 919. — Ceratodus forsteri.
Posterior half of the lung with the
ventral wall slit up so as to show
the interior. (After Giinther.)
XIII
PHYLUM CHORDATA
245
artery (Tiy. art.} is connected with the most anterior of these. The
eight efferent vessels unite in pairs to form four epibranchial arteries
(epi.). The latter unite dorsally to form a main trunk, which
combines with the corresponding trunk of the opposite side to form
the median dorsal aorta (d. a.). The head is supplied by carotid
rposl.cctr
1. post. car l.ant&ar
i.i/.c
FIG. 920. — Ceratodus forsteri. Diagrammatic view of the heart and main blood-vessels,
as seen from the ventral surface, aff. 1, :', 3, 4, afferent vessels ; 7 br, 2 br, 3 br, 4 br,
position of gills ; c. a. comis arteriosus ; d. a. dorsal aorta ; d. c. precaval vein ; epi. 1,
epi. 2, epi. 3, epi. 4, epibrancliial arteries ; hi/, art. hyoidean artery; i. ». c. postcaval vein ;
1. ant. car. left anterior carotid artery ; 1. aur. left auricle ; I. br. v. left brachial vein ;
1. jug. v. left jugular vein ; I. post. car. left posterior carotid artery ; /. post. card, left cardinal
vein ; /. pul. art. left pulmonary .artery ; I. sc. v. left subscapular vein ; r. ant. car. right
anterior carotid artery ; r. aur. right auricle ; r. br. v. right brachial vein ; r. jug. right
jugular vein ; r. post. car. right posterior carotid ; r. pul. art. right pulmonary artery ;
r. sc. v. right subscapular vein ; vent, ventricle. (After Baldwin Spencer.)
branches given off from the first epibranchial (1. post. car. and
r. post, car.) and from the hyoidean arteries (1. ant. car. and r. ant.
car.), and the latter also gives off a lingual artery to the tongue.
From the last (fourth) epibranchial artery arises the pulmonary
artery (I. pul. art. and r. pul. art.), carrying blood to the lung.
There are two precavals or ductus Cuvieri (d. c.), as in the Dog-
VOL. II Q
246
ZOOLOGY
SECT.
fish (p. 152). The right is formed by the union of jugular (I. jug. v.
and r. jug. v.), brachial (I. br. v. and r. br. v.), and subscapular veins
(l.sc. v. and r. sc. v.). The left receives in addition a left cardinal
vein (I. post. card.). A. large lateral cutaneous vein, running
superficially along the side of the body, opens into the subscapular.
A large poslcaval vein (i. v. c.) brings back the greater portion of
the blood from the posterior parts of the body ; it is situated
somewhat to the right of the middle line, and opens into the sinus
venosus between the two hepatic veins. A postcaval occurs in the
Dipnoi alone amongst Fishes, but is universal in all the higher
classes. Posteriorly the cardinal and the postcaval are formed by
the bifurcation of a median caudal vein ; close to its origin each
receives the efferent renal veins bringing back the blood from the
kidney. The blood from the pelvic fin is brought back by an iliac
vein which divides into two branches —
pelvic and renal portal. The former,
running forwards and inwards, unites
mesially with the corresponding vessel
of the opposite side to form a median
abdominal vein — a vessel universal in the
Amphibia, and perhaps corresponding to
the lateral veins of the Elasrnobranchs ;
it opens into the sinus venosus. The
other branch — the renal portal vein-
after receiving tributaries from the pos-
terior region of the body passes to the
corresponding kidney.1
Brain. — The whole brain (Fig. 921) is
enclosed in a tough and thick membrane,
which becomes glandular in two positions
—on the roof of the diaccele, and on
that of the metacoele. In the former
position this glandular development of
the enclosing membrane, or choroid
plexus, passes downwards into the dia-
ccele and is developed into a spongy
mass which is prolonged forwards to
the anterior end of the prosencephalon.
The prosencephalon (pros.) presents
two elongated hemispheres, which are
completely separated except posteriorly,
where they are united by a narrow
The contained cavity is divided into two by the
prolongation of the choroid plexus already referred to. The
nervous wall of the hemisphere (pallium) is very thin and is
1 How far this arrangement combines Fish-like and Amphibian characters
will be best understood at a later stage.
- ainl
Tried
FIG. 921.— Brain of Ceratodus
lorsteri, dorsal view. aud.
auditory nerve ; ell. cerebellum ;
dia. diencephalon ; fac. facial
nerve ; gl. glossopharyngeal ;
med. medulla oblongata ; meso.
mesencephalon ; oc. oculomotor
nerve ; opt. optic nerve ; pros.
prosencephalon ; rh. rhinen-
cephalou (olfactory lobe with
olfactory tract and bulb) ; vg.
vagus nerve. (Chiefly after
Sanders.)
commissure.
xm PHYLUM CHORDATA 247
incomplete dorsally and internally : basally it forms a massive
tuberculum olfactorium from which, the olfactory nerve-fibres are
derived. There is a pair of large olfactory lobes (rh.), each with
its cavity, and each prolonged into an olfactory peduncular tract,
which ends in front in an olfactory bulb in close apposition with
the nasal capsule.
The pineal body is situated on the summit of a conical mem-
branous cap on the roof of the third ventricle. The infundibulum
develops a pair of lobi inferiores. The mesencephalon (meso.) is
bilobed, but the division is not strongly pronounced. The cere-
bellum (cbl.) is very small, being little more than a transverse
bridge of nerve-matter over the anterior end of the fourth ventricle.
The medulla (ed.) is of relatively large size.
Urinogenital Organs. — The kidneys are short, being confined
to the posterior portion of the body-cavity, and are firmly attached
to the ovaris^or testes. Each has a thick-walled ureter which
joins its fellow, the passages, however, remaining distinct to near
the opening into the urinogenital division of the cloaca, when the
right opens into the left.
There are two elongated ovaries (Fig. 922, 1. ov., r. ov.), which
remain distinct throughout. The oviducts (1. ovd. and r. ovd.) are a
pair of thick-walled, greatly convoluted tubes which extend along
the whole length of the body-cavity, into which they open in front
(ccel. ap.) ; posteriorly they coalesce immediately before opening
into the cloaca. The testes are long, compressed bodies which
remain distinct from one another throughout their length. The
efferent ducts from the testes open into certain of the tubules of
the mesonephros, and the sperms are thus enabled to pass out
through the mesonephric duct. The Miillerian ducts in the male
are remarkably well developed.
In the early stages of its development (Fig. 923) Ceratodus
exhibits resemblances, on the one hand, to Petromyzon (p. 130), and
on the other to the next class to be studied — the Amphibia. The
ova become enclosed, while passing down the oviduct, in a gela-
tinous envelope which swells up considerably when it comes in
contact with the water. At what stage fertilisation takes place
is not exactly known. Segmentation is complete and unequal,
and results in the formation of a lens-shaped blastula (A) with
smaller cells on one of the convex surfaces (the future dorsal), and
larger on the other (the future ventral). A blastopore (bl. p.)
first appears on the ventral surface as a short transverse slit,
which grows into a semicircle (B) or a horse-shoe. The free ends
of this grow in towards one another and unite to enclose an
irregularly circular or elliptical space filled in by a mass of large
cells — the yolk-plug (C, yk. pi.). Soon, however, this wide aperture
becomes narrowed to a small longitudinal slit, the lips of the
anterior part of which then unite, only the most posterior part
Q 2
248
ZOOLOGY
l.ovd
lot''
FIG. 922. — Ceratodus forsteri. Reproductive organs of female;
the inner surface of the right and the outer surface of the left
ovary shown, coel. ap. coelomic aperture of oviduct ; liv. portion
of the liver ; /. OK. left ovary ; I. ov'. its posterior termination ;
/. oed. left oviduct; r. ov. right ovary; r. ord. right oviduct;
r. ov'. its posterior termination. (After Giinther.)
SECT.
remaining open
(D) and subse-
quently giving
rise to the anus.
During its in-
crease in size the
blastopore has
been growing
over towards the
dorsal side, and
when its lips be-
come united, it
extends along
the greater part
of the dorsal
surface. A nar-
row medullary
groove (E, blp.
sut.) appears
along the dorsal
surface, and a
pair of medullary
folds are seen at
the sides of this
(E) and are coal-
escent in front
of it. From the
medullary folds
and the groove
between them
the neurocoele,
and subsequently
the entire ner-
vous system, are
developed as in
Or aniata in
general (see
p. 95). The por-
tion of the
blastoderm des-
tined to give
rise to the em-
bryo becomes to
a slight extent
folded off from
the rest, which
forms an ill-
XIII
PHYLUM CHORDATA
249
defined rounded mass, or yolk-sac, to be subsequently absorbed as
development proceeds. The most important features in the later
blpsut.
med
eye
Fid. 923.— Ceratodus forsteri. Stages in the development. A, lens-shaped blastula ; Bt
stage with semicircular blastopore (bl. p.) ; G', later stages in which the blastopore (bl. p.)
has taken the formof a ring-like groove enclosing the yolk-plug (t/lk. pi.)', D, stage in which
the narrow medullary groove (Up. sut.) has appeared with the rudiment of the medullary
folds (med.) ; E, stage in which the medullary folds (med.) have become well developed ; F,
later stage with well-formed head with two visceral arches (rise.) and rudiments of eye
(eye) and ear (and.) ; pron. mesonephros. (After Semon.)
stages (F) are the negative ones of the absence of the external gills
(to be referred to below and in the account of the Amphibia), and
the absence of horny jaws.
2. DISTINCTIVE CHARACTERS AND CLASSIFICATION.
The Dipnoi are Pisces in which the notochord is persistent,
there are no vertebral centra, and the primary cranium persists
with little ossification, but has added to it a number of investing
bones. The skull is autostylic, the lower jaw articulating with a
palatoquadrate process which is immovably fixed to each side of
the skull. There are four to six cartilaginous branchial arches.
The dermal fin-rays are slender more or less ossified fibres, and are
supported by numerous cartilaginous or ossified pterygiophores.
The caudal fin is diphycercal. The paired fins are of the character
of " archipterygia." The pectoral arch is a single cartilage with a
pair of superficial investing bones on each side. The pelvic arch is
well-developed and cartilaginous. There are gills attached to the
branchial arches, and in addition a single or double lung opening
into the oesophagus by a ventral aperture. The gills are covered
over by an operculum. There is a dermal skeleton in the form of
250 ZOOLOGY SECT-
overlapping cycloid scales. There is a distinct cloaca. The
intestine contains a spiral valve. The auricle and the sinus venosus
are each imperfectly divided into two parts. There is a contractile
conus arteriosus, which has a spirally-twisted form, and is partly or
completely divided internally by a longitudinal septum. The
afferent branchial vessels take their origin close together imme-
diately in front of the conus. A pulmonary artery is given off
from the afferent branchial system on either side ; a pulmonary
vein opens into the left division of the auricle. The optic nerves
form a chiasma. The oviducts open anteriorly into the coelome.
The ova are of moderate size ; segmentation is entire.
The Dipnoi are classified as follows : —
ORDER 1. — MONOPNEUMONA.
Dipnoi in which the lung is single, and the lateral jointed rays
of the " archipterygium " are well developed.
This order comprises only the Australian Ceratodus.
ORDER 2. — DIPNEUMONA.
Dipnoi in which the lung is double, and the lateral rays of the
" archipterygium " are vestigial or absent.
This order includes Protopterus (Fig. 924) of South Africa, and
Lepidosiren of South America.
3. GENERAL REMARKS.
The three genera of living Dipnoi are closely allied in all the
most essential features of their structure, and it will only be
necessary now to mention the principal points in which Protopterus
and Lepidosiren differ from Ceratodus.
The limbs (Fig. 924) are long and very narrow, and the limb-
skeleton is correspondingly modified, consisting of a slender, jointed
axis without, or with only vestiges of, the lateral rows of rays.
A blind dorsal diverticulum of the cloaca, derived developmentally
from the urinogenital sinus, is present, and perhaps corresponds
to the sperm-sacs of the Elasmobranchs. There are two lungs,
the anterior portions of which are united to form a median chamber,
to which the presence of numerous trabeculse gives a spongy
character. There are five (or six) reduced rod-like branchial arches,
of which the last three bear the internal gills ; in addition there is
a series of external gills in the larva, vestiges of which persist in the
adult Protopterus (Fig. 925, K). In the males of Lepidosiren,
vascular filaments, which may be accessory respiratory organs, are
developed on the paired fins during the breeding season. The conus
arteriosus is completely divided by a longitudinal septum. The
pulmonary artery is given off from the point of union of the
xin
PHYLUM CHORDATA
251
epibranchial arteries into a single lateral trunk. In Protopterus
there is usually a single abdominal pore opening on the dorsal wall
of the cloaca ; this leads into a cavity into which the true abdominal
pores, which are very minute,
lead. In Lepidosiren abdominal
pores are absent.
The brain in both Lepidosiren
and Protopterus, as well as in
Ceratodus, differs from that of
Fishes in general, and resembles
that of Amphibia (see Section
XIV) in the presence of long and
relatively narrow cerebral hemi-
spheres. In the two former
these have a pallium or nervous
roof with a stratified layer of
nerve-cells. In all the Dipnoi
the part of the hemisphere (ol-
factory lobe and tuberculum)
from which the olfactory nerve-
fibres pass to the bulbus ol-
factorius is of relatively large
size, but smaller in Protopterus
and Lepidosiren. In Protopterus
and Lepidosiren the olfactory
tract is not distinguishable,
bulbus and lobus being in im-
mediate apposition instead of
being widely separated as they
are in Ceratodus. In both these
genera the dorsal part of the
mid-brain is undivided. In
both genera the kidneys are re-
latively more elongated than in
Ceratodus ; in Protopterus the
posterior portions are fused
together ; in Lepidosiren they
remain separate throughout.
In both genera the elongated
testes are distinguishable into
two regions — an anterior longer,
sperm-producing part, and a
posterior shorter part which serves as a duct and a vesicula semi-
nalis. In Lepidosiren about six vasa efferentia arise from this
posterior region and enter the Malpighian capsules of the meso-
nephros : in Protopterus there is only a single vas eSerens. The
ducts of the two kidneys open by a single aperture (Protopterus)
252
ZOOLOGY
SECT.
or two separate apertures on the summit of a urinogenital papilla
into the cloaca at the base of the cloacal caBCurn referred to
above. Many of the cellular elements, such as the blood-corpuscles,
are of comparatively large size. There is holoblastic, but unequal,
segmentation, as in Ceratodus, followed by a true invagination. A
pair of medullary folds are developed, and between them is formed
a median solid ectodermal keel in which a neurocoele only appears
subsequently. The larva has well-developed external gills.
The Dipnoi are a very ancient race. The genus Ceratodus itself
FIG. 925. — Protopterus. Skull, shoulder-girdle, and skeleton of fore-limb. AA1, splenial : AF,
pre-orbital process ; a and b (on lower jaw), and S.L. teeth ; b, basal cartilage of pectoral
fin ; £, ligamentous band connecting the mandible with the hyoid ; co. ligamentous band
connecting the dorsal end of the pectoral arch with the skull ; I), angular ; FP, fronto-
parietal ; Ht, membranous fenestra perforated by the foramen for the optic nerve (//);
Hy. hyoid ; K, external gills ; Kn, Knl, cartilage of the pectoral arch ; KR, occipital rib ;
LK and MR, investing bones of the pectoral arch ; N K, olfactory capsule ; Ob, auditory
capsule ; Occ. supra-occipital ; Op. and Op1, rudimentary opercular bones ; PQ. palato-
quadrate ; Psp. Psp1. spinous processes of the anterior vertebrae ; SE. supra-ethmoid bone ,
SK, roofing investing bones; Tr. palatoquadrate cartilage; 1FH71, anterior vertebrae
coalescent with the skull ; I-V, branchial arches {that marked / is forked and the anterior
bar may represent the first, in which case there are six branchial arches) ; 1, 2, 3, segments
of axis of pectoral fin ; *, *, vestigial lateral rays of pectoral fin. (From Wiedersheim.)
extends back to the early Mesozoic, and the remains of allied forms
(Dipterus and other genera) are found in Devonian and Carboniferous
formations. But if, as is conjectured, the Arthrodira are to be
regarded as Dipnoi, then the group dates back as far as the Silurian.
The evidence for this conclusion is, however, by no means complete,
as our knowledge of the structure of the extinct Fishes in question
is necessarily meagre. They had the head and anterior part of
both dorsal and ventral surfaces (Fig. 926) protected by bony plates,
the system of head-plates being connected with those on the trunk
by a well-developed movable joint. The notochord was persistent,
with partly calcified neural and hsemal arches, and the cranium was
XIII
PHYLUM CHORDATA
253
apparently cartilaginous ; the mandible was probably autostylic.
There were composite cutting dental plates. The pectoral fins are
unknown ; the rays of the small pelvic ( VR) were supported on a
flattened plate (VB).
With some special features of their own the Dipnoi combine
characteristics in which they resemble now one, now another, of
the other groups of Fishes, together with a few in which they
approach the next class of Vertebrates to be dealt with, viz., the
Amphibia and even the higher Vertebrates. The brain and the
heart are quite peculiar : the former in its undivided, or almost
undivided, mid-brain ; the latter in its imperfectly divided auricle,
and spirally-twisted conus. The pallium of the cerebral hemispheres
N ~, OR
FIG. 026. — Cocccsteus decipiens. Side view, restored. A, articulation of head with
trunk DB, cartilaginous basals of dorsal fin ; DP,, cartilaginous radials of dorsal fin ;
77, hsemal arches and spines ; MC. mucous canals ; JV, neural arches and spines, and
. position of notochord ; U. median unpaired plate (?) of hinder ventral region ; VB, liasaN
of pelvic fiu ; I'/?, radials of pelvic fin. (From Dean, after Smith Woodward.)
in the Dipneumona with its layers of nerve-cells has no parallel
among the lower Vertebrates. In the Limbs the Dipnoi are only
closely approached by certain extinct Elasmobranchs (p. 163). In
the presence of a cloaca and a spiral valve they also approach that
sub-class, as well as in the contractile conus — the last two features
being also shared with the Ganoid Teleostomi. The operculum
with its supporting bones connects them with the Teleostomi. The
Amphibian features will be referred to at a later stage. On the
whole, though in some respects more primitive than the members
of the other sub-classes of Pisces, the Dipnoi tend to establish a
connection between that class and the higher Vertebrates.
APPENDIX TO PISCES.
THE OSTRACODERMI.
The Ostracodermi are a group of Palaeozoic Fishes of uncertain affinity,
characterised by the extraordinary development of the exoskeleton of the
head and trunk, and the absence, in all the fossil remains hitherto found, of
endoskeleton, including jaws. It may therefore be assumed that there was
a persistent notochord, and that the rest of the skeleton was unossified. It
is uncertain whether the group should be considered the equivalent of a Class
or of a Sub-class : it is divisible into three orders, which are best considered-
separately.
254
ZOOLOGY
SECT.
ORDER 1. — HETEEOSTRACI.
This order includes four families, the Pteraspidce, the Ccelolepidce, the
Drepanaspida:, and the Psammosteidce. Of the first Pteraspis (Fig. 927) may
FIG. 927. — Pteraspis rostrata (Devonian). (From the Brit. Mus. Cat. of Fossil Fishes.)
be taken as an example. The body is elongated, and divided into an anterior
region, representing the head and fore-part of the trunk, and covered by strong
calcified plates or scutes, and a posterior or caudal region covered by rhornboidal
scales. In the anterior region there
are seven scutes above, constituting
the dorsal shield, while below there is
a single ventral shield. The dorsal
shield is produced into a rostrum,
and is hollowed by a pair of lateral
orbits, between which is a pit, on the
inner surface of the shield, probably
marking the position of the pineal
Fia. 928. — Restored outline of Lanarkia
spinosa, in the position in which it
occurs as a fossil, the head being flat-
tened and the tail twisted round so as
to appear in profile, tin each side a
much enlarged dermal denticle is
shown. (From the Cambridge Natural
History, after Traquair.)
FIG. 929. — Restored outline of the dorsal sur-
face of Drepanaspis gemundenensis.
The tail appears in profile, m. d. median
dorsal plate ; p. I. postero-lateral plate ;
r. rostral plates. (From the Cambridge
Natural History, after Traquair.)
body. The scutes contain no lacunae or canaliculi, and have not, therefore,
the structure of bone : they are lined by a nacreous -layer, and are covered
xm
PHYLUM CHORDATA
255
externally with a layer of vaso-dentine. The tail appears to have been
heterocercal. A pair of longitudinal ridges may represent paired fins.
The Coslolepidce (Fig. 928) have the head and anterior trunk region flattened
and expanded, with postero-lateral lobes which may represent paired fins.
There is a heterocercal tail-fin. Mouth, orbits, and branchial apertures have
not been detected. The exoskeleton takes the form of numerous uniform,
hollow, pointed spines, or tubercles, composed of dentine coated with ganoin.
Two genera are known of Silurian and Devonian age.
The Drepanaspidce (Fig. 929) have a somewhat similar shape, but with the
he?,d and trunk expanded into a broad shield, which is sharply marked off
from the tail. The exoskeleton consists of scales and fulcra (see p. 222),
replaced in the middle of the dorsal surface by a large dorsal plate (m. d.)'and
or
07*
op
FIG. 930. — A, restoration of shield of Cephalaspis lyelli, dorsal aspect'; ^.-diagram of ventra
aspect of shield of Cephalaspis; C, restoration of Cephalaspis murchisoni
(Devonian), op. opercular plate or pectoral fin ; or. orbit ; s. /. p. sub-frontal plate. (From
the Brit. Mus. Cat. of Fossil Fishes.)
at the sides by postero-lateral plates (p. I.). A similar combination of large
plates and small scales occurs on the ventral surface. The sole known
representative of the family is of Lower Devonian age.
The family PsamrnosteidiP has been formed for the reception of certain
fragmentary remains in the form of dermal plates which closely resemble
those of the Drepanaspidse.
ORDER 2. — OSTEOSTRACI.
Cephalaspis (Fig. 930) may be taken as an example of the five genera
included in this order. The head is covered with a calcified shield, which has
a curious resemblance to the cephalic shield of Limulus or of a Trilobite, being
gently curved above, produced behind into spines, continued ventrally into a
sub-frontal plate (B, s. /. p.), and having a pair of orbits (A, or) for the eyes
256
ZOOLOGY
SECT.
near the middle of the dorsal surface. Behind the shield, towards the ventral
surface, is a plate which perhaps supported the operculum (C, op.}, but may
represent the pectoral fin. The scutes contain some lacume, and therefore
approach in structure
A B to bone. The posterior
portion of the body is
covered by deep, nar-
row scales ; there is a
single dorsal fin and a
heterocercal caudal.
ORDER, 3. — ANTI-
ARCHA.
This group contains
five genera, of which
PterichtJiys (Fig. 931)
may be taken as an
example. It presents
a broad and high an-
terior region, covered
by articulated plates
which have the struc-
ture of bone and are
covered by a layer of
enamel, and a caudal
region covered by
rounded or hexagonal
scales. The orbits are
placed close together
on the top of the head,
and between them is a
plate pitted on its
inner surface, ap-
parently for the pineal
body. There is a pair
of large pectoral fins
(pet. /.) of a very re-
markable character,
covered by strong
scutes and divided
into two parts by a joint towards the middle ; a single dorsal fin (d. /.) with
fulcra, but apparently no fin-rays ; and a heterocercal tail-fin (c. f.).
FIG. 931.— Pterichthys testudinarius. A, dorsal, B,
ventral, C, lateral aspect, c. f. caudal fin ; d.f. dorsal fin ;
pct.f. pectoral fin. (From the Brit. Mus. Cat. of Fossil Fishes.)
CLASS IV.— AMPHIBIA.
The Amphibia are distinguished from Fishes by the possession
of pentadactyle limbs instead of paired fins, and by the absence of
fin-rays in the median fins. They nearly all breathe by gills in
the larval condition, and many of them retain those organs through-
out life ; lungs are, however, usually present in the adult. The
class includes the Frogs, Toads, Newts and Salamanders, as well
as the peculiar snake-like Caecilians, and the extinct Stegocephala
or Labyrinthodonts.
xin
PHYLUM CHORDATA
257
1. EXAMPLE OF THE CLASS. — THE COMMON FROG (Rana
temporaria), OR THE EDIBLE FROG (Rana esculenta).
Rana temporaria is the common British species of Frog, found in
ponds and damp situations all over the country, and occurring also
in America ; R. esculenta is the large green edible Frog found on the
continent of Europe and occasionally in England ; R. pipiens is the
commonest North American species of the genus. Other species
of the same genus occur in all parts of the world except New
Zealand, the southern part of South America, and the various
oceanic islands.
External Characters. — The trunk is short and stout, and is
continued, without the intermediation of a neck, into the broad,
depressed head.
There is no trace of
a tail, the anus
being terminal.
The mouth also is
terminal, and is
characterised by its
extra ordinary
width, the gape ex-
tending consider-
ably behind the
eye. On the dorsal
surface of the snout
are the small nos-
trils ; the eyes are
large and promi-
nent, and each is
provided with an
upper eyelid in the
form of a thick fold
of skin, and a nicti-
tating membrane, a much thinner fold, which arises from the lower
margin of the eye and can be drawn up over it. Close behind
the eye is a circular area of tensely-stretched skin, the tympanic
membrane, a structure not met with in any Fish : as we shall see,
it is an accessory part of the auditory organ. There is no trace of
branchial apertures.
The back has a peculiar bend or hump, in the sitting posture,
marking the position of the sacral vertebra. The limbs are of
very unequal size. The fore-limbs are short, and each consists of
an upper arm, which, in the ordinary position, is directed back-
wards and downwards from the shoulder-joint ; a, fore-arm, directed
downwards and forwards from the elbow ; and a hand, ending in
four short, tapering digits, directed forwards. The hind-limb is of
FIG. 932. — Rana temporaria. (From Mivart.)
258 ZOOLOGY SECT-
great size ; in the usual squatting posture the thigh is directed
downwards, outwards, and forwards from the thigh- joint, the
shank inwards, backwards, and upwards from the knee. The foot
consists of two parts, a tarsal region directed downwards from the
heel- joint, and five long, slender digits united by thin folds of skin
or webs. Thus the limbs are placed in such a way that the elbow
and knee face one another, and the first digit — that of the hand
probably representing the index-finger, that of the foot, the hallux
or great toe — is turned inwards or towards the median plane of
the body.
The skin is greyish-brown in R. temporaria, greenish in R.
esculenta, and is mottled, in both species, with dark brown or black ;
in R. temporaria there is a large black patch over the tympanic
region. Sexual differences occur in both species ; in R. temporaria
there is a large, black, glandular swelling on the inner side of the
hand of the male, and in R. esculenta the male has, at each angle
of the mouth, a loose fold of skin, the vocal sac, which can be inflated
from the mouth into a globular form. The skin is soft and slimy
owing to the secretion of mucous glands ; there is no trace of
exoskeleton.
Endoskeleton. — The vertebral column (Fig. 933) is remark-
able for its extreme shortness ; it consists of only nine vertebrae
(V. 1 — V. 9), the last followed by a slender, bony rod, the urostyle
(U. ST.). The second to the seventh vertebrae have similar char-
acters. The centrum (B, en) is somewhat depressed and has a
concave anterior and a convex posterior face— a form known as
proccelous. Each half of the neural arch consists of two parts, a
pillar-like pedicle (pd) springing from the centrum and extending
vertically upwards, and a flat, nearly horizontal lamina (Im),
forming, with its fellow, the roof of the neural canal. When
the vertebra? are in position, wide gaps are left between successive
pedicles ; these are the intervertebral foramina and serve for the
transmission of the spinal nerves. The zygapophyses (a. zyg) or
yoking processes are far better developed than in any Fish ; they
spring from the junction of pedicle and lamina, the anterior
zygapophysis having a distinct articular facet on its dorsal, the
posterior on its ventral surface. Thus when the vertebrae are in
position the posterior zygapophyses of each overlap the anterior
zygapophyses of its immediate successor. Laterally the neural
arch gives off on each side a large outstanding transverse process
(tr. pr) ; its crown is produced into a very small and inconspicuous
neural spine (n. sp).
The first or cervical vertebra (V. 1) has a very small centrum and
no transverse processes. There are no anterior zygapophyses, but
at the junction of centrum and arch there occurs on each side a
large oval concave facet for articulation with one of the condyles
of the skull (vide infra). The eighth vertebra has a biconcave
xrn
PHYLUM CHORDATA
259
UST
CAL
AST
FIG. 933. — Rana temporaria. A, the skeleton from the dorsal aspect ; the left half of the
shoulder-girdle and the left fore- and hind-limbs are removed, as also are the investing bones
on the left side of the skull. Cartilaginous parts dotted. Names of replacing bones in thick,
those of investing bones in italic capitals, other references in small italics, a, c. Aj/.
anterior cornu of hyoid ; actb. acetabulum ; AST. astragalus ; b. hy. basi-hyal ; C. calcar ;
CAI>. calcaneum ; EX. OC. exoccipital ; FE. femur ; /on. fon'. fontanelles ; FR. PA.
fronto-parietal ; HIT. humerus ; IL. ilium ; MX. maxilla ; olf. cp. olfactory capsule ; ot. pr.
otic process ; p. c. hy. posterior cornu of hyoid ; PMX. premaxilla ; PR. OT. pro-otic ;
QU.JU. quadrato-jugal ; RA.UL. radio-ulna; SP.ETH. sphenethmoid ; SQ. para-
quadrate; S.SCP. supra-scapula ; sus. suspensorium ; TI.FI. tibio-tibula ; tr. pr. trans-
verse process ; UST. urostyle ; V. 1 , cervical vertebra ; V. 9, sacral vertebra ; VO. yomer ;
/ — V, digits. B, the fourth vertebra, anterior face. a. zyg. anterior zygapophysis ; en.
centrum ; Im. lamina ; n. sp. neural spine ; pd. pedicle ; tr. pr. transverse process. (After
Howes, slightly altered.)
260 ZOOLOGY SECT.
centrum ; that of the ninth or sacral vertebra (V. 9) is convex in
front and presents posteriorly a double convexity articulating with
a double concavity on the anterior end of the urostyle. The latter
(U. ST.) is formed by the ossification of the perichordal tube (see
p. 71), which, in this region of the vertebral column, does not
become segmented into vertebrae.
The skull (Figs. 933 and 934) consists of a narrow brain-case,
produced behind into great outstanding auditory capsules, and in
front into large olfactory capsules. The whole of the bones of the
upper jaw are immovably fixed to the cranium, so that the only free
parts are the lower jaw and a small plate of mingled bone and
cartilage, the liyoid apparatus, which lies in the floor of the mouth
and is the sole representative in the skull of the entire hyo-
branchial or gill-bearing skeleton of Fishes.
As in the Trout, a number of investing bones can be removed
from the skull without injury to the underlying chondrocranium.
The latter, however, is not, as in the Trout, the primary cranium
alone, but, as in Holocephali and Dipnoi, the primary cranium
plus the palatoquadrate or primary upper jaw. The cranium in
the strict sense includes the brain-case and the auditory and
olfactory capsules : the palatoquadrate (pal. qu) is not a solid mass
fused throughout its length with the cranium, as in Holocephali and
Dipnoi, but rather resembles the subocular arch of the Lamprey
(p. 123), being a slender rod attached to the cranium at either
end, but free in the middle. It is divisible into three regions,
a posterior quadrate-region or suspensorium (sus), an intermediate
pteri/goid region, and an anterior palatine region. The suspensorium
extends backwards, outwards, and downwards from the auditory
region of the cranium, to which it is immovably united by its forked
proximal end, one branch of the fork — the otic process (Fig. 934,
ot. pr) — being fused with the auditory capsule, the other — the
pedicle (ped) — -with the trabecular region immediately anterior to
the auditory capsule. Ventrally the suspensorium furnishes an
articular facet for the mandible, and is connected with the delicate
rod-like pterygoid region ; this passes forwards and joins the
palatine region, which is a transverse bar fused at its inner end with
the olfactory capsule.
The occipital region of the cranium contains only two bones,
the exoccipitals (EX. OC), which lie one on each side of the foramen
magnum (for. mag) and meet above and below it : there is no
trace of supra- or basi-occipital. Below the foramen magnum are
a pair of oval projections, the occipital condyles (oc. en), furnished by
the exoccipitals and articulating with the cervical vertebra.
Each auditory capsule is ossified by a single bone, the pro-otic
(PR. OT) ; there are no other ossifications of the auditory
region (p. 77). In the adult the pro-otic fuses with the ex-
occipital : it presents on its outer surface, behind the otic process
xni
PHYLUM CHORDATA
261
of the suspensorium, a small aperture, the fenestra ovalis, closed in
the entire animal by membrane, and, when the latter is removed,
leading into the cavity of the auditory capsule, containing the
membranous labyrinth.
In front of the auditory capsules a considerable part of the
cranial wall is formed of cartilage, and presents above a single
large and a pair of sm&llfontanelles (Fig. 933, f on., f on'), but anteriorly
it is ossified by the sphenethmoid, or girdle-bone (SP. ETH), a short
bony tube divided by a transverse partition into an anterior com-
partment which lodges the hinder ends of the olfactory sacs, and a
posterior compartment which contains the olfactory bulbs. The
Nv. 2
Nv. 5, 7
FIG. 934. — Rana temporaria. The skull. A, from beneath, with the investing bones
removed on the right side (left of figure) ; B, from the left side, with mandible and hyoicl ;
C, from behind, the investing bones removed at sus. a. c. hy. anterior coriiu of hyoid ;
aud.cp. auditory capsule ; b. hy. body of hyoid ; COL,, columella ; DXT. dentary ; EX.OC.
exoccipital ; for. mag. foramen magnum ; /. ov. fenestra ovalis ; FR.PA. fronto-parietal ;
M.MCK. mentp-meckelian : MX. maxilla ; NA. nasal ; Nv. 2, optic foramen ; Nv. 5, 7,
foramen for fifth and seventh nerves ; Nv. 9, 10, foramina for ninth and tenth nerves ; oc. en.
occipital condyle ; off. cp. olfactory capsule ; ot. pr. otic process ; PAL. palatine ; pal. qu.
palate-quadrate ; PA.SPH. parasphenoid ; p. c. hy. posterior cornu of hyoid ; peil. pedicle ;
PMX. premaxilla ; PR.OT. pro-otic ; PTG. pterygoid ; Q [7.J t/.quadrato-jugal ; SP.ETH.
sphenethmoid ; SQ, paraquadrate : sip. stapes ; sus (quad) suspensonum (quadrate) ; \'O.
vomer. (After Howes, slightly altered.) A minute investing bone, the septo-maxillary,
which is present above the maxilla, close to the nostril, is not here represented.
anterior compartment is again divided by a vertical partition
which separates the olfactory sacs from one another, and the
transverse partition is perforated for the olfactory nerves. This
very peculiar and characteristic bone may be taken to represent
meso- and ecto-ethmoids and pre- and orbito-sphenoids all united
together.
The olfactory capsules (Figs. 933, 934, olf. cp) have a delicate
cartilaginous roof and floor produced into irregular processes which
help to support the olfactory sac. They are separated from one
another by a vertical plate of cartilage, continuous behind with the
girdle-bone and representing the unossified part of the mesethmoid ;
and the anterior wall of each is produced into a little curved, rod-
VOL. n R
262 ZOOLOGY SECT.
like rliinal process. The whole of the primary palatoquadrate arch
is unossified.
To this partly ossified chondrocranium the usual investing
bones are applied above and below. Covering the roof of the
brain-case is a single pair of bones, the fronto-parietals (FR. PA),
each formed by the fusion of a frontal and a parietal, distinct
in the young Frog. Over the olfactory capsules are paired
triangular nasals (NA), and applied to their ventral surfaces small
paired vomers (VO). On the ventral surface of the skull is a large
T-shaped parasphenoid (PA. SPH), its stem underlying the basis
cranii, while its two arms extend outwards beneath the auditory
capsules.
In the Trout, it will be remembered, the palatine and pterygoid
are replacing bones, formed as ossifications of the palatoquadrate
cartilage. In the Frog this cartilage is, as we have seen, unossified,
but to its ventral face two investing bones are applied, a small
rod-like palatine (PAL), and a three-rayed pterygoid (PTG) having
an anterior arm extending forwards to the palatine, an inner arm
applied to the pedicle of the suspensorium, and an outer arm
extending along the whole inner face of the suspensorium. It will
thus be seen that bones originally preformed in cartilage may give
place to investing bones, developed in corresponding situations,
but altogether independent of the cartilage, the latter remaining
unossified.
The suspensorium, as we have seen, is strengthened on its inner
face by the outer arm of the pterygoid ; externally it is similarly
supported by a hammer-shaped investing bone, the paraquadrate,
often known as the squamosal (SQ). The upper jaw is formed by
three investing bones, the small premaxilla (PMX) in front, then
the long, narrow maxilla (MX), and finally the short quadrato-
jugal (QU. JU), which is connected posteriorly with the quad-
rate.
The mandible contains a persistent MeckeVs cartilage, as a sort
of core, outside which are formed two bones, a long angulo-splenial
on its inner face, and a short dentary (DNT) on the outer face of its
distal half. The actual distal end of Meckel's cartilage is ossified
as a small replacing bone, the mento-meckelian (M. MCK), not
represented in Fishes.
The hyoid apparatus consists of a shield-shaped plate of car-
tilage, the body of the hyoid (b. hy), produced at its anterior angles
into slender rods, the anterior cornua (a. c. hy), which curve upwards
and are fused with the auditory capsules, and at its posterior angles
into partly ossified rods, the posterior cornua (p. c. hy), which extend
backwards, embracing the glottis.
Two other cranial structures remain to be noticed. External
to the paraquadrate is a ring of cartilage, the annulus tympanicus
(Fig. 947, an. tymp.), which supports the tympanic membrane as
Xtii
PHYLUM CHORDATA
263
ft U-.l'fl
the frame of a tambourine supports the parchment. Inserted into
the fenestra ovalis is a nodule of 'cartilage, the stapes (stp.), to
which is attached the inner end of a small hammer-shaped structure,
the columella (COL), the
handle of which is ossi-
fied, while its carti-
laginous head, or extra-
columella, is fixed to the
inner surface of the tym-
panic membrane.
The comparison of the
Frog's skull with those
of Fishes is facilitated
by a study of its de-
velopment. In the tad- FIG. 935.— Skull of Tadpole, au. cp. auditory capsule
fir. 7 — 4 hrsmrhial jirrlips • r. hit. rprafnhval • rnl
pole or larval Frog there
is a cartilaginous cranium
(Fig. 935) connected on
each side with a stout
inverted arch, like the subocular arch of the Lamprey or the
palatoquadrate of Chimaera or Ceratodus, and, like them, de-
veloped from the dorsal region of the mandibular arch. The
fini
br. J — 4, branchial arches ; c. hy. ceratohyal ; col.
columella ; mck. Meckel's cartilage ; olf. cp. olfactory
capsule ; opt. for. optic foramen; or. pr. orbital pro-
cess of suspensonum ; ot. pr. otic process ; pal. ptg.
palato-pterygoid bar ; qu. quadrate ; stp. stapes.
(After Marshall, slightly altered.)
FIG. 936. — Rana esculenta. The shoulder-girdle from the ventral aspect. Cartilage dotted.
Co. coracoid ; Co1, epicoracoid ; Cl. clavicle ; Ep, omosternum ; G. glenoid cavity ; Fe.
fenestra between clavicle and coracoid ; KG. cartilage separating scapula and clavicle ;
Kn. xiphisternum ; m. junction of epicoracoids ; S. scapula ; St. sternum. (From Wieders-
heim's Comparative Anatomy.)
quadrate region (qu) of this primary upper jaw is well in front
of the eye, the axis of the suspensorium being inclined for-
R 2
264
ZOOLOGY
SECT.
•S.SC/i
sc/b
FIG. 937. — Rana. Diagrammatic transverse
section through the shoulder-girdle, cor.
coracoid
cavity
(From
wards and the mandible very short, in correspondence with the
small size of the tadpole's mouth. The quadrate is fused by its
pedicle with the trabecular region, the otic process (ot. pr) which
unites it with the auditory capsule being formed later. Behind
the suspensorium are distinct hyoid (c. hy) and branchial (br. 1 — 4)
arches supporting the gills by
which the tadpole breathes. As
development goes on, the axis
of the suspensorium is rotated
backwards, producing the wide
gape of the adult, and the stout
palatopterygoid region of the
subocular arch (pal. ptg) gradu-
ally assumes the slender propor-
tions it has in the adult. The
greater part of the hyoid arch
°. • ,1 •
gives rise to the anterior cornua
ep. cor. epicoracoid ; gl. glenoid r ,\ -\ •>, -i -j
hu humerus ; scp. scapula ;*. scp. 01 the adult hyoid-apparatus,
the body of which is formed
from the basi-hyal and basi-
branchials, and its posterior cornua probably from the fourth
branchial arch. The columella is developed independently, but
may perhaps represent a pharyngo-hyal or dorsal segment of the
hyoid arch. The stapes is a detached portion of the outer wall of
the auditory capsule. Thus, with the assumption of purely aerial
respiration, the complex branchial skeleton is reduced to a simple
structure for the support of the tongue.
The shoulder-girdle has essentially the structure already described
(p. 81) in general terms as characteristic of the pentadactyle
Craniata. The scapula (Fig. 936, S, Fig. 937, scp) is ossified, and
is connected by its dorsal edge with a suprascapula (Fig. 933, S.
SCP, Fig. 937, s. scp) formed partly of bone, partly of calcined
cartilage, and developed from the dorsal region of the embryonic
shoulder-girdle. The coracoid (Fig. 936, Co., Fig. 937, cor.) is also
ossified, but the procoracoid is represented by a bar of cartilage
having an investing bone, the clavicle (Cl), closely applied to it. The
suprascapula overlaps the anterior vertebras ; the coracoid and
procoracoid are connected ventrally by a cartilage, the epicoracoid
(Fig. 936, Co1, Fig. 937, ep. cor), which is in close contact with its
fellow of the opposite side in the middle ventral line, so that the
entire shoulder-girdle (Fig. 937), like that of the Dog-fish, forms a
single inverted arch.
Passing forwards from the anterior ends of the united epicoracoids
is a rod of bone, the omosternum (Fig. 936, Ep), tipped by a rounded
plate of cartilage, and passing backwards from their posterior ends is
a similar but larger bony rod, the sternum (St), also tipped by a
cartilaginous plate, to which the name xiphisternum (Kn) is applied.
XIII
PHYLUM CHORDATA
265
These two structures are the first indication of a .sternum we have yet
met with, with the possible exception of the median ventral element
of the shoulder-girdle of Heptanchus (p. 170). The omosternum is
developed as paired forward extensions of the epicoracoids which
undergo fusion : the sternum and xiphisternum arise as paired rods
lying posterior to the epicoracoids, and subsequently uniting with
one another. This sternal apparatus of the Frog (and of the
Amphibia in general) differs developmentally from the structures
in the higher Vertebrates to which the same name is applied — the
latter being formed from separated-ofE portions of embryonic ribs
(costal sternum).
The fore-limbs deviate from the typical structure (p. 81) chiefly
in the fusion of the radius and ulna into a single radio-ulna (Fig.
933, RA. UL), and in the presence of only four complete digits with
a vestigial one on the radial side. In all probability the last repre-
sents the pollex, and the complete digits are the second to the fifth
of the typical hand. Six carpals only are present, the third, fourth,
and fifth digits articulating with a single bone which has apparently
arisen by the fusion of the third, fourth and fifth distalia and of at
least one centrale.
The pelvic girdle (Fig. 938) is very peculiarly modified ; it resembles
in form a Bird's " merrythought," consisting of two long, curved
bars articulating in front with the transverse processes of the sacral
vertebra (Fig. 933) and uniting posteriorly in an irregular vertical
disc of mingled bone and cartilage which
bears on each side a deep, hemispherical
acetabulum (G) for the articulation of the
thigh-bone. The curved rods are the ilia
(II., P) ; they expand posteriorly and.
unite with one another in the median
plane to form the dorsal portion of the
disc and about one-half of the acetabu-
lum. The posterior portions of the disc
and acetabulum are furnished by the
ischia (Is), fused with one another in the
sagittal plane, their ventral portions by
the similarly united pubes (Kn). The
ilium and ischium are formed of true bone,
the pubis of calcified cartilage ; the union
of the elements in the median plane is
called the symphysis. In the larva the
ilium is vertical, but during development
it becomes lengthened and at the same time rotated backwards,
thus bringing the articulation of the hind-limbs as far back as,
possible.
In the hind-limb the tibia and fibula are fused to form a single
tibio-fibula (Fig. 933, TI. FI), and the two bones in the proximal
II—
FIG. 938. — Rana esculenta.
Pelvic girdle from the riaht
side. G, acetabulum ; //. /',
ilium ; 7s. ischium ; Kn,
puliis. (From Wiedersheim 's
Anatomy.)
266 ZOOLOGY SECT.
row of the tarsus — the tibiale or astragalus (AST) and the fibulare
or calcaneum (CAL) — are greatly elongated and provide the leg with
an additional segment. There are three tarsals in the distal row,
one of which appears to represent the centrale, another the first
distale, and the third the fused second and third distalia. There
are five well-developed digits, and on the tibial side of the first
is a spur-like structure or calcar (c), formed of three bones, a meta-
tarsal and two phalanges : such an additional digit is called a
pre-hallux.
All the long bones of the limbs consist of the shaft formed of true
bone and of extremities of calcified cartilage. The distinction is a
very obvious one, both in the freshly-prepared and in the dried
skeleton.
The muscular system has undergone great modifications in
correspondence with the complex movements performed by the
limbs. The dorsal muscles of the trunk are no longer divisible
into myomeres, but take the form of longitudinal or oblique bands
(extensores dor si, &c.), lying partly above the vertebrae, partly
between the transverse processes, partly between the ilia and the
urostyle. The ventral muscles are differentiated into a paired
median band, the rectus abdominis (Fig. 939, ret. abd), with longi-
tudinal fibres, and a double layer of oblique fibres — obliquus
externus (obi. ext} and internus (obi. int) — extending from the
vertebral column to the recti. Both the extensor dorsi and the
rectus abdominis are traversed at intervals by transverse bands
of fibrous tissue, the inscriptiones tendinece (ins. ten), but the
segments thus formed do not correspond with the embryonic
myomeres. The right and left recti are united by a longitudinal
band of tendon, the linea alba (I. alb).
The muscles of the limbs are numerous and complex, each
segment having its own set of muscles by which the various
movements of which it is capable are performed. There are
muscles passing from the trunk to the limb-girdles ; from the trunk
or the limb-girdles to the humerus and femur ; from the humerus
and femur to the radio-ulna and tibio-fibula ; from the fore-arm or
shank to the digits ; and from one segment of a digit to another.
For the most part the limb-muscles are elongated and more or less
spindle-shaped, presenting a muscular portion or belly which passes
at either end into a tendon of strong fibrous tissue serving to fix
the muscle to the bones upon which it acts. The relatively fixed
end of a muscle is called its origin, the relatively movable end its
insertion, e.g. in the gastrocnemius muscle of the calf of the leg
(gstr) the proximal end attached to the femur is the origin, the
distal end attached to the foot the insertion. According to their
action muscles are divided into flexors which bend, and extensors
which straighten, one part upon another ; adductors which draw
towards, and abductors which draw away from, the middle line ;
xra
PHYLUM CHORDATA
267
elevators which raise, and depressors which lower, a part, such as
the lower jaw. The names of the muscles may have reference to
their position, e.g. pectoralis (pet.), the principal muscle of the chest ;
s ; ins. ten. inscriptio tendinea
alb. linea alba
xiphisternum,
tbj||k-
/. W. UbioBbula ;
268
ZOOLOGY
SECT.
or to their form, e.g. biceps, the two-headed muscle ; or to their
action, e.g. flexor tarsi ; or to their origin and insertion, e.g. coraco-
humeralis.
Digestive Organs. — The mouth leads into a wide buccal cavity
having in its roof the internal or posterior nares (Fig. 940, p. na.),
a pair of projections due to the downward bulging of the large
eyes, and the openings of the Eustachian tubes (eus. t., vide infra).
On its floor is the large tongue (tng.), attached in front and free
behind, where it ends in a double point ; by means of its muscles
it can be suddenly projected, point foremost, from the mouth, and
is used in the capture of Insects. Immediately behind the tongue
is the glottis (gl.). Teeth are arranged in a single series round the
edge of the upper jaw, attached to the premaxillse and maxillae ;
IL
PMX
si nt
FIG. 940.— Rana temporaria. Dissection fromjthe left side ; tlie viscera somewhat displaced.
an. anus ; b. d. bile-duct ; b. hy. body of hyoid ; bl. urinary bladder ; bl'. its opening into the
cloaca ; c. art. conus arteriosus ; cblm. cerebellum ; cl. cloaca ; en. 3, centrum of third verte-
bra ; cp. ad. corpus adiposum ; c rb. h. cerebral hemisphere ; d. ly. s. dorsal lymph sinus ; du.
duodenum ; ep. cor. epicoracoid ; cus. t. Eustachian tube ; FR. PA. fronto-parietal ; gl.
glottis ; rjul. gullet ; IL. ilium ; is. ischium ; kd. kidney ; /. au. left auricle ; /. Ing. left lung ;
Ir. liver ; M. MCK. mento-meckelian ; n. a 1, neural arch of first vertebra ; olf. I. olfactory
bulb ; opt. 1. optic lobe ; q. ST. omosternum ; pcd. pericardium ; PMX. premaxilla ;
pn. pancreas ; p. na. posterior naris ; pu. pubis ; ret. rectum ; r. Ing. right lung ; s. int.
ileum ; sp. cd. spinal cord ; SPH. ETH. sphenethmoid ; spl. spleen : st. stomach ; s. v. sinus
venosus ; tng. tongue ; ts. test-is ; ur. ureter ; ur' . its aperture into the cloaca ; TJST. urostyle ;
v. ventricle ; v. ly. s. ventral lymph sinus ; ro. t. vomerine teeth ; vs. sem. vesicula seminalis.
there is also a small patch of teeth (vo. t.) on each vomer just
internal to the posterior nostril. The teeth are small conical
bodies, their bases ankylosed to the bones ; their only use is to
prevent the polished or slimy bodies of the prey — Insects and
Worms — from slipping out of the mouth.
The buccal cavity narrows towards the pharynx, which leads by
a short gullet (gul.) into a stomach (st.) consisting of a wide cardiac
and a short, narrow, pyloric division. The duodenum (du), or first
portion of the small intestine, passes forwards parallel with the
stomach ; the rest of the small intestine (iteum) is twisted into a
XIII
PHYLUM CHORDATA
269
M
coil. The large intestine or rectum (ret.} is very wide and short,
and passes without change of diameter into the cloaca (cl.).
The liver (Ir.) is two-lobed ; between the right and left lobes
lies a large gall-bladder (Fig. 941, G). The pancreas (P.) is an
irregular gland sur-
rounding the bile-
duct, into which it
pours its secretion ;
the spleen (Fig. 940,
spl.) is a small, red
globular body at-
tached near the
anterior end of the
rectum. The thyroids
are small paired
organs lying below
the floor of the
mouth in front of
the glottis. The
thymus is also
paired, and is
situated behind and
below the tympanic ?
membrane. ^c~
Respiratory
Organs. - -The
lungs (1. Ing., r. Ing.)
are elastic sacs lying
in the anterior part
of the coelome above
the heart and liver ;
their size and
appearance vary
greatly according
to their state of
distension. Each contains a spacious cavity and has its walls
raised into a complex network of ridges abundantly supplied
with blood-vessels. The two lungs open anteriorly into a small
laryngo-tracheal chamber which communicates with the mouth by
the narrow slit-like glottis. The walls of the laryngo-tracheal
chamber are supported by a cartilaginous framework, and its
mucous membrane is raised into a pair of horizontal folds, the
vocal chords, by the vibration of which the croak of the Frog is
produced.
In breathing, the Frog keeps its mouth closed, and by depressing
the floor of the mouth, draws air into the buccal cavity through
the nostrils. The floor of the mouth is then raised, the nostrils,
FIG. 941. — Rana esculenta. Stomach and duodenum with
liver and pancreas. DC., Dc.i common bile-duct; DC.- its
opening into the duodenum ; D. cy. cystic ducts ; Dh.,
Dh.i hepatic ducts ; Du. duodenum ; G. gall-bladder ;
L, Ll, Z/2, L'-'>, lobes of liver, turned forwards ; Lhp. duodeno-
hepatic omentum, a sheet of peritoneum connecting the
liver with the duodenum ; M, stomach ; P. pancreas ; I'1,
pancreatic duct; Py. pylorus. (From Wiedersheim's Com-
paratiw Anatomy.)
270
ZOOLOGY
SECT.
which are valvular, are closed, and the air is forced through the
glottis into the lungs. The skin also is an important respiratory
organ.
Circulatory Organs. — The pericardium (Fig. 940, pcd.) is not
situated in front of the general ccelome, as in Fishes, but lies in
the coelomic cavity between the gullet above and the epicoracoids
below ; it consists, as usual, of a visceral layer closely adherent to
the heart, and a loose parietal layer, the two being continuous at
the bases of the great vessels and separated by a small quantity
of pericardial fluid.
The heart consists of a sinus venosus (Figs. 940 and 944, s. v.}, right
and left auricles (r. au., I. au.), a ventricle (v., vt.), and a conus
car.cfL
cftr.a.
c.a-rt
FIG. 942. — Rana temper aria. The heart from the ventral aspect with the cavities laid open.
a, a', bristle in left carotid trunk ; au. v. v. auriculo-ventricular valves ; b. b', bristle in left
systemic trunk ; c, c', bristle in left pulmo-cutaneous trunk ; car. a. carotid artery ; ear. gl.
carotid labyrinth ; c. art. conus arteriosus ; car. tr. carotid trunk ; 1. au. left auricle ; Ig. a.
lingual artery ; 1. v. longitudinal valve ; pul. cu. tr. pulmo-cutaneous trunk ; pul. v. aperture
of pulmonary veins ; r. au. right auricle ; s. au. ap. sinu-auricular aperture ; spt. aur.
septum auricularum ; v, v', valves ; vt. ventricle.
arteriosus (c. art.). The sinus venosus opens into the right auricle,
the pulmonary veins into the left : a striking advance on the
Dipnoi is seen in the greatly increased size of the left auricle and
its separation by a complete partition, the septum auricularum
(Fig. 942, spt. aur.), from the right. The two auricles open by a
common auriculo-ventricular aperture, guarded by a pair of valves
(au. v. v.), into the single ventricle. The latter has a transversely
XIII
PHYLUM CHORD AT A 271
elongated cavity, and its dorsal and ventral walls are raised up
into muscular ridges or trabeculse with interstices between them.
The conus springs from the right side of the base of the ventricle ;
it is separated from the latter by three small semilunar valves (v.),
and is traversed obliquely along its whole length by a large flap-like
longitudinal valve (l.v .) which springs from its dorsal wall and is free
ventrally. The conus passes without change of diameter into
a bulbus aortcB, the two being separated by a semilunar valve (v')
and by the free end of the longitudinal valve. The bulbus gives
off two branches, right and left, each of theln divided by two longi-
tudinal partitions into three vessels, an inner or anterior, the
carotid trunk (car. tr.), a middle, the systemic trunk or aortic arch,
and an outer or posterior, the pulmo-cutaneous trunk (pul. cu. tr.).
The carotid and systemic trunks communicate separately with the
bulbus ; the two pulmo-cutaneous trunks communicate with the
anterior end of the conus by a single valvular aperture placed just
behind the free end of the longitudinal valve (cr).
After being bound together in the way described for a short
distance, the carotid, systemic, and pulmo-cutaneous trunks separate
from one another. The carotid trunk divides into carotid (Figs. 942
and 943, car.) and lingual (Ig.) arteries for the supply of the head, the
former having at its base a small swelling, the carotid "gland " or
labyrinth (car. gl.), with a spongy interior containing numerous
cavities. The systemic trunks curve round the gullet and unite with
one another above it to form the dorsal aorta (d. ao.), from which, or
from one of the systemic trunks themselves, the arteries to all
parts of the body, except the head, the lungs, and the skin, are
given off. The pulmo-cutaneous trunk divides into two, a pul-
monary artery (pul.) to the lung, and a cutaneous artery (cu.) to the
skin.
In the tadpole there are four aortic arches, each consisting of
an afferent and an efferent branchial artery connected by the
capillaries of the gills. As the water-breathing larva undergoes
metamorphosis into the air-breathing adult the gills disappear ;
the first aortic arch loses its connection with the dorsal aorta and
becomes the carotid trunk ; the second enlarges, retains its con-
nection with the dorsal aorta, and becomes the systemic trunk ;
the third disappears ; and the fourth sends off branches to the
lungs and skin, loses its connection with the dorsal aorta, and
becomes the pulmo-cutaneous trunk.
The blood from each side of the head is returned by internal
(Fig. 944, int. ju.) and external (ext. ju.) jugular veins into the
precaval vein (pr. v.), which also receives the brachial vein (br.) from
the fore-limb, and the musculo-cutaneous vein (ms. cu.) from the
skin and muscles of the side and back, and part of the head : the
two precavals open separately into the sinus venosus.
The course of the blood from the posterior part of the body
272
ZOOLOGY
SECT.
is very different from what we have met with in Fishes, the differences
being due partly to the absence of a tail, partly to a peculiar modifica-
tion of the lateral veins,
and partly to the replace-
ment of the cardinals by
^car.gl a postcaval vein, found
among Fishes only in the
The blood from the
front part of the hind-leg
is brought back by a
femoral vein (fm.), which,
on reaching the coelome,
divides into two branches,
a dorsal and a ventral.
The dorsal branch is the
renal portal vein (rn.pt.) :
it receives the sciatic vein
(sc.) from the back of the
leg and passes to the
kidney, in which it breaks
up into capillaries. The
ventral branch is the
pelvic vein (pv.) : it unites
with its fellow of the
opposite side to form the
abdominal vein (abd. )
which passes forwards in
the ventral body-wall,
between the linea alba
and the peritoneum, to
the level of the sternum,
where it turns inwards
and divides into two
branches, both breaking
up into capillaries in the
liver. Just as it enters
the liver it is joined by
the hepatic portal vein
(hp. pt.), bringing the
blood from the stomach,
intestine, spleen, and
pancreas. The abdominal
vein also receives vesical veins (ves.) from the urinary bladder, and
a small cardiac vein from the heart (cd.). It represents the lateral
veins of Elasmobranchs united in the middle ventral line : the
pelvic veins are their posterior free portions.
FIG. 943. — Rana temporaries The arterial system,
with the heart, lungs, kidneys, and left testis, from
the ventral aspect, car. carotid artery ; car. gl. carotid
labyrinth ; c. art conns arteriosus ; car. tr. carotid
trunk ; cod. mes. coeliaco-mesenteric artery ; CM.
cutaneous artery ; d. ao. dorsal aorta ; du. duodenal
artery ; gs. gastric artery ; hp. hepatic artery ; 77. iliac
artery ; int. intestinal arteries ; Jed. kidney ; I. an. left
auricle ; Ig. lingual artery ; Ing. lung ; ces. cesophageal
artery ; pul. pulmonary artery ; pul. cu. tr. pulmo-
cutaneous trunk ; r. an. right auricle ; rn. renal arteries ;
scl. suhclavian artery ; spl. splenic artery ; syst. tr.
systemic trunk ; spm. spermatic artery ; ts. testis ; >•.
ventricle ; vert, vertebral artery.
xm
PHYLUM CHORDATA
273
Tlie blood is collected from the kidneys by the renal veins (rn.),
which unite to form the large unpaired postcaval vein (pt. cv.).
This passes forwards through a notch in the liver, receives the
hepatic veins (h.p.) from that organ, and finally opens into the sinus
venosus. Thus the blood from the hind-limbs has to pass through
pr.cv
eaelju \
l.ctu raif\ \\
/
^
pv
Fio. 944. — Rana texnporaria. The venous system with the heart, lungs, liver, kidneys, and
right testis, from the dorsal aspect, abd. abdominal vein ; br. brachial vein ; cd. cardiac
vein ; ds. Imb. dorso-lumbar vein ; rf«. duodenal vein ; ext. ju. external jugular vein ; fm.
femoral vein ; gs. gastric vein ; hp. hepatic vein ; hp. pt. hepatic portal vein ; int. intesti
veins ; int. ju. internal jugular vein ; kd. kidney ; /. au. left auricle ; Ing. lung ; Ivr. liv
intestinal
er;
ves. vesical veins.
one of the two portal systems on its way back to the heart : part
of it goes by the renal portal veins to the kidneys, and thence by
the renal veins to the postcaval, part by the pelvic and abdominal
2?4 ZOOLOGY SECT.
veins to the liver, and thence by the hepatic veins to the postcaval.
Lastly, the blood which has been purified in the lungs is returned
by the pulmonary veins (pul.) directly to the left auricle.
It will be seen that there is no trace of cardinal veins in the
Frog. But in the larva both anterior and posterior cardinal veins
are present : during the metamorphosis the ductus Cuvieri, in
which, as in Fishes, they unite, become converted into the pre-
cavals, while the posterior portions of the posterior cardinals
contribute to the formation of the postcaval, and the anterior
portions disappear.
It will be perceived that the blood poured into the right auricle
is mostly impure or venous, that poured into the left fully aerated
or arterial. When the auricles contract, which they do simulta-
neously, each passes its blood into the corresponding part of the
ventricle, which then instantly contracts, before the venous and
arterial bloods, kept separate as they are to some extent by the
muscular trabeculse acting as incomplete partitions, have time
to mix. Since the conus arteriosus springs from the right side
of the ventricle, it will at first receive only venous blood, which,
on the contraction of the conus, might pass either into the bulbus
aortse or into the aperture of the pulmo-cutaneous trunks. But
the carotid and systemic trunks are connected with a much more
extensive capillary system than the pulmo-cutaneous, and the
pressure in them is proportionally great, so that it is easier for
the blood to enter the pulmo-cutaneous trunks than to force aside
the valves between the conus and the bulbus. A fraction of a
second is, however, enough to get up the pressure in the pulmonary
and cutaneous arteries, and in the meantime the pressure in the
arteries of the head, trunk, &c., is constantly diminishing, owing to
the continual flow of blood towards the capillaries. Very soon,
therefore, the blood forces the valves aside and makes its way into
the bulbus aortse. Here again the course taken is that of least
resistance : owing to the presence of the carotid labyrinth, the passage
of blood into the carotid trunks is less free than into the wide, elastic,
systemic trunks. These will therefore receive the next portion of
blood, which, the venous blood having been mostly driven to the
lungs, will be a mixture of venous and arterial. Finally, as the
pressure rises in the systemic trunks, the last portion of blood from
the ventricle, which, coming from the left side, is arterial, will pass
into the carotids and so supply the head.
The red blood-corpuscles are, like those of Fishes, oval, nucleated
discs. The lymphatic system (Fig. 945) is very well developed,
and is remarkable for the dilatation of many of its vessels into
immense lymph-sinuses. Between the skin and muscle are large
subcutaneous sinuses (Fig. 940, v. ly. s.), separated from one another
by fibrous partitions, and the dorsal aorta is surrounded by a
spacious subvertebral sinus. The lymph is pumped into the veins
XIII
PHYLUM CHORDATA
by two pairs of lymph-hearts, one situated beneath the supra-
scapulae, the other beside the posterior end of the urostyle.
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Nervous System. — The brain (Fig. 946) has a very small cere-
bellum, large optic lobes, a well-developed diencephalon, and large
hemispheres and olfactory bulbs, the latter fused in the median
276
ZOOLOGY
SECT.
plane. The corpora striata, or basal ganglia of the cerebral hemi-
spheres, are connected together, as in all Vertebrates, by an anterior
commissure (D, com, below, lower line), above which is another com-
A
ftin
A/cd.cbl
SfJ.cd
& *V-1 cb
J m EZZ7 Med.cbl
-Sfi.cd.
. obi
Fro. 946. — Brain of Rana. A, from above ; B, from below ; C, from the side ; D, in longitudinal
vertical section. Cb, cerebellum; Cer. H, cerebral hemispheres; ch. pl.il, anterior, and
ch. pin:2, posterior choroid plexus (removed in .4) ; com, commissures, the two in front the
anterior and hijijiocampal, the two above the superior or halicnular and the posterior ; Cr. C,
crura cerebri ; ])!, diencephalon ; for. M, foramen of Monro ; ?', iter, or aqueduct of Sylvius ;
inf, infundibulum ; Uleil. obi, medulla oblongata ; Olf. /, olfactory bulb ; opt. ch, optic
chiasma ; Opt. I, optic lobe ; o/it. c, optic ventricle ; pin, stalk of pineal body ; pit, pituitary
body ; Sp. cil, spinal cord ; v'A, third ventricle ; r4, fourth ventricle ; / — X, cerebral nerves ;
ISp. '-'Up. spinal nerves. (From Parker's Practical Zooloyy. A — C, after Gaupp ; I), from
Wiedersheim's Comparative Anatomy, after Osborn.)
Kin
PHYLUM C'HOHDATA
i>77
niissure (com, below, upper line) partly representing the hippo-
camped commissure of the brain of Reptiles and Mammals. The
metacoele is covered by a thick choroid plexus ; the mesoccele is
divisible into a median passage or iter (i.), and paired optocoeles
(opt.v.) in the optic lobes: the paracceles are large cavities each com-
municating with a rhinoccele in the corresponding olfactory bulb.
The pineal body is vestigial in the adult, a lobe of the anterior choroid
plexus, with a vestige of the stalk (pin), taking the position which
it usually occupies : in the larva it is found outside the skull and
immediately beneath the skin.
The first spinal nerve performs the function of the hypoglossal
(Fig. 946, ISp.), supplying the muscles of the tongue : it passes out
between the first and second vertebrae. The spinal cord is short
and ends in a delicate filament, the filum terminate. In corre-
Tnenib.lab
lymp.cav
:\r tump, nie mb
FlU. 947. — Transverse section of head ol' Prog to show the relations of the accessory auditory
apparatus (diagrammatic). Skeletal structures black, with the exception of the columcllu.
an. tymp. anmilus tympanicus ; b. hy. body of hyoid ; buc. cat', cavity of pharynx ; ch. ;. gills ; br. d. branchial arches ; c. eye ; ect. ectoderm : end.
endoderm ; ent. enteron ; /. br. tore-brain ; //. br. liind-hrain ; m. br. mid-brain ; mil. f.
medullary fold; md. gr. medullary groove; nn'x. inr^nderm; ma. megameres ; mi. niirro-
meres ; nch. notochord; n. c. c. neurenteric canal; pcdm. proctod;eum ; pty. pituitaiy
invagination ; ret. commencement of rectum ; sk. sucker ; sp. cd. spinal curd ; st.dm sd.niii-
dseum ; t. tail; yk. yolk-cells; yk. pi. yolk lug. (A— D, F—H, and J from Ziegler's
models ; E, 1, K, and L after Marshall.)
282
ZOOLOGY
SECT.
the central nervous system. Posteriorly they are continuous
with the lips of the blastopore, so that when the neural groove
becomes closed in behind, the archenteron, as in Amphioxus,
communicates with the neuroccele by a neurenteric canal (K, n. e. c.).
The embryo soon begins to elongate ; one end is broad, and,
becoming separated by a slight constriction, is marked out as the
head : the other end is bluntly pointed and is the rudiment of
the tail (t.). On the ventral surface of the root of the tail a procto-
dceum (pcdm.) appears and communicates with the archenteron.
The head and
tail become
more distinctly
marked off from
the trunk. A
pit— the stomo-
dceum (J — L, st.
dm.) — appears
on the antero-
ventral surface of
the head, and,
immediately be-
hind it, a semi-
lunar area with
raised edges, the
sucker (sk.). At
each side of
the head two
branched pro-
cesses appear :
they are the ex-
ternal gills (br.l.,
br.3.), and the
regions from
which they arise
mark the posi-
tions of the first
and second bran
chial arches.
The embryos are now hatched as tadpoles. They swim freely
in the water or adhere to weeds by means of their suckers (Fig.
951, 7). They are still blind and mouthless, the stomodasum
not having yet communicated with the archenteron. Soon a third
pair of external gills appears on the third branchial arch, and the
first two pairs increase greatly in size (2, 2a) : the stomodseum joins
the archenteron, gill-slits (branchial clefts) are formed between the
branchial arches, and the eyes appear. The mouth is small,
bounded by lips beset with horny papillae and provided with a
FIG. 951. — Rana temper aria. Stages in the life-history,
from the newly-hatched Tadpoles (1) to the young Frog (5).
"a is a magnified view of 2. (From Mivart.)
xni PHYLUM CHORDATA 283
pair of horny jaws. The enteric canal grows to a great length
and is coiled like a watch-spring, and the tadpole browses upon
the water-weeds which form its staple food.
Soon the external gills show signs of shrivelling, and at the
same time internal gills, like those of Fishes, are developed in the
branchial clefts. A fold of skin, the operculum, appears on each
side, in front of the gills, growing from the region of the hyoid
arch, and extending backwards until the gill-slits and external gills
are covered and there is only a single small external branchial
aperture on each side, as in Holocephali (3, 4). On the right side
the operculum soon unites with the body-wall so as to close the
branchial aperture, but on the left side the opening remains for
a considerable time as the sole means of exit of the water. At
this time the tadpole is to all intents and purposes a Fish.
The lungs now appear, and the larva is for a time truly
amphibious, rising periodically to the surface to breathe air : the
single branchial aperture, however, soon closes, and henceforth
respiration is purely aerial.
In the meantime the limbs are developed. The hind-limbs
appear as little rounded buds, one on each side of the root of the
tail (5). The fore-limbs arise beneath the operculum and are
therefore hidden at first ; soon, however, they emerge by forcing
their way through the operculum. As the limbs increase in size
the tail undergoes a progressive shrinking (6-8). The mouth
widens by the backward rotation of the suspensorium, the intestine
undergoes a relative diminution in length, and vegetable is exchanged
for animal diet. The little, tailed Frog can now leaye the water
and hop about upon land ; its tail is soon completely absorbed, and
the metamorphosis is complete.
2. DISTINCTIVE CHARACTERS AND CLASSIFICATION.
The Amphibia are Craniata which, in nearly all cases, possess
gills either in the larval state only or throughout life, and which
usually breathe by lungs in the adult condition. The skin is
glandular, and there may or may not be a bony dermal exoskeleton.
When unpaired fins are present, they are never supported by
fin-rays. The paired appendages, when present, are pentadactyle
limbs : the digits are usually devoid of claws. The skull is auto-
stylic and is articulated with the first vertebra by paired occipital
condyles borne on the exoccipitals. The basi-occipital and supra-
occipital are usually, and the basisphenoid is always, absent :
there is a large parasphenoid, and there are well-developed
paraquadrates (squamosals). In the branchiate forms large hyoid
and branchial arches persist throughout life : in the non-branchiate
species these structures undergo more or less degeneration and
give rise to the hyoid-cartilage. The heart has a sinus venosus,
284 ZOOLOGY
SECT.
right and left auricles, a single ventricle, and a conns arteriosus ;
the aortic arches arise from a bulbus aortaa or abbreviated ventral
aorta. The cardinal veins undergo more or less degeneration
and are practically replaced by an unpaired postcaval vein. There
is a renal portal system, part of the returning blood from the
posterior parts of the body going through it, the rest through the
hepatic portal system by an abdominal vein which represents
fused lateral veins. The red corpuscles are oval and nucleated
and are often of unusual size. The lymphatic system is well
developed. In the brain the small size of the cerebellum is notice-
able. The olfactory sacs open into the mouth by posterior nares.
The outer wall of the auditory capsule is pierced by a fenestra
ovalis into which is inserted a cartilaginous stapes : the stapes
may be connected by a columella with a tympanic membrane.
The efferent ducts of the testis open into the urinary tubules, and
the mesonephric duct of the male is a urinogenital duct. In the
female the mesonephric ducts become the ureters, and the oviducts
are pronephric ducts with ccelomic apertures. The pronephros is
the functional kidney in the larva, the mesonephros in the adult.
There is an allantoic bladder. Development is usually accompanied
by a metamorphosis, the young being hatched in the form of a
branchiate larva.
The Amphibia are classified as follows :—
ORDER 1. — URODELA.
Amphibia which retain the tail throughout life. There are
usually two pairs of limbs of approximately equal size.
The order is conveniently divided into
a. PerennibrancJiiata, which retain the gills throughout life :
including the American Necturus, the blind Proteus of the under-
ground caves of Carniola in Dalmatia, and the Eel-like Siren of
North America.
b. Derotremata, in which the gills are lost in the adult, but
there is usually a persistent gill-cleft : including the Newt-like
Cryptobranchus and the Eel-like Amphiuma from North America,
and the Giant Salamander, Megalobatrachus, of China and Japan.
c. Myctodera, the Salamanders and Newts, in which the gills
are lost and the gill-clefts closed in the adult : including the
common Newts or Efts (Molge), the Spotted and Black Sala-
manders (Salnmandra) of the European Continent, and the
American Amblystoma, the sexually mature larva of which is the
well-known Axolotl.
ORDER 2. — ANURA.
Amphibia having no tail in the adult condition. The trunk is
short and broad, and the hind-limbs greatly exceed the fore-limbs
in size. Gills and gill-slits are never present in the adult.
Including the Frogs and Toads.
XIH
PHYLUM CHOHDATA 285
ORDER 3. — GYMNOPHIONA (APODA).
Snake-like Amphibia having neither limbs nor tail. A dermal
exoskeleton is present. There are no gills or gill-slits in the adult.
Including the Csecilians (Ccecilia, Epicrium, &c.).
ORDER 4. — STEGOCEPHALA.
Extinct tailed Amphibia, often of great size, having usually
two pairs of limbs and a well-developed dermal exoskeleton. The
group ranges from the Permian to the Trias.
Systematic Position of the Example.
The genus Rana belongs to the family Ranidce, which with three
other families constitutes the series Firmisternia, of the sub-order
Phaneroglossa and order Anura.
The absence of a tail and the presence of two pairs of limbs, of
which the posterior are larger than the anterior, place the genus
among the Anura. The presence of a tongue and of distinct
paired Eustachian tubes separates the Phaneroglossa from the
Aylossa (Pipa and Xenopus), a small group of Toads in which the
tongue is absent and the Eustachian tubes have a common median
opening. The Firmisternia are distinguished by having the
coracoids joined by a common epicoracoid cartilage in contra-
distinction to the Arcifera (Tree-frogs, Toads, &c.), in which the
epicoracoids overlap one another. The Ranidse are distinguished
from the other families of Firmisternia by having teeth in the
upper jaw and the transverse processes of the sacral vertebrae not
dilated. R. temporaria is distinguished from R. esculenta by its
smaller size and brown colour, by the large black patch in the
tympanic region, and by the absence of external vocal sacs in the
male.
3. GENERAL ORGANISATION.
The Amphibia are specially interesting as illustrating the
transition from the water-breathing to the air-breathing type of
Craniate structure. The lower forms retain their gills throughout
life, but possess lungs in addition : in the higher the gills occur
only in the larval state, and the adult breathes exclusively by the
lungs and skin, becoming transformed from an aquatic into a
terrestrial animal. At the same time further adaptations to land-
life take place, the most important being the modification of the
blood-vessels consequent on the disappearance of the gills, the loss
of median fins, and the strengthening of the limbs to support
the weight of the body.
External Characters. — An excellent example of the lower
Urodela with persistent gills is afforded by the great North American
Water-newt, Necturus maculatus (Fig. 952). The animal attains
a length of 30 cm. (more than a foot) ; the elongated trunk is
286
ZOOLOGY
SECT.
separated by a slight constriction from the depressed head, and
passes insensibly into the compressed tail, which is bordered by a
continuous median fin unsupported by fin-rays. The limbs are
o
"3
,Q
3. A, Lateral ; B, Ventral ; C, Dorsa iview.
' .4, posterior process of the os articnlare ; ('a. carotid foramen ; Ch. choana or posterior nasal
opening ; F. frontal : J. jugal ; LO. exoccipital ; MX. maxilla ; N. nasal ; No. nostril ;
O. orbit ; P. parietal ; Pa. palatine ; Pm. premaxilla ; Pof. postfrontal ; Prf. prefrontal ;
Pt. pterygoid ; Q. quadrate ; S. paraquadrate (squamosal) ; St. stapes ; T. tentacular groove ;
Vo. vomer ; A', exit of vagus nerve. (After Sarasin.)
SECT. Xtll
PHYLUM CHOPxDATA
293
Ot
Skull of Protriton, one of the
smaller Stegocephala, magnitied. Br.
branchial arches ; F. frontal; Fp, parietal
foramen ; M. maxilla : N. nasal ; Xa. nos-
tril ; Or. sclerotic plates ; P. parietal ;
Pf. prefrontal ; 7'm.c. premaxilla ; Socc.
supra-occipital. (From Wiedersheim, alter
Fritsch.)
very large and form an extremely complete and substantial
structure, especially remarkable for the way in which the small
orbit (0) is completely surrounded by bones. In the Stegocephala
(Fig. 961) the skull is broad and flattened, the supra-occipital
($. occ.) double, and the parietals (P) and f rentals (F) are separate.
Between the parietals is an aper-
ture, the parietal foramen (Fp),
which probably lodged a pineal
eye. The eyes were sometimes
surrounded by a ring of bony
sclerotic plates (Oc). Gill-arches
have been found in many species.
The shoulder-girdle of Urodela
(Fig. 962) is chiefly remarkable
for the great size of the unossified
coracoids (A, Co., B, C.) which
overlap one another on the ven-
tral body-wall. The procoracoid
(() is also large, and there is no FIG. oei
clavicle. The sternum (St.) is
usually a more or less rhomboid
plate of cartilage between the pos-
terior ends of the coracoids, and
there is no omosternum. In Nec-
turus, however, the sternum presents a very interesting structure : it
is a narrow, irregular, median bar, sending off branches right and
left into the myocommas, a condition of things which suggests its
origin by the fusion of abdominal ribs, or supporting structures
developed between the ventral portions of the myomeres, just as
the true ribs are formed between their dorsal portions. In the
Anura the epicoracoids either simply meet one another in the middle
ventral line, as in Rana, or overlap, as in the Fire-toad (Bombinator)
and the Tree-frogs (Hyla). The overlapping of the coracoids, in
Anura as in Urodela, is sometimes correlated with the absence of
an omosternum. In the Stegocephala there is a median ventral
investing bone, the inter-clavicle, which is connected on each side
with the clavicle, and extends backwards ventral to the sternum.
There is also, on each side, a bone called the cleithrum, connected
with the corresponding clavicle : there is some reason for thinking
this to be homologous with the bone usually called clavicle in
Teleostomi.
In the pelvic girdle of the Urodela the combined pubic and
ischiatic regions (Fig. 963, P, 7s) of the right and left sides are
united to form an elongated cartilaginous plate which gives off on
each side, above the acetabulum (G), a slender vertical rod, the
ilium (II). Ossifications are formed in the iliac and ischiatic
regions, but the pubic region remains cartilaginous. The resem-
VOL. TT T
294
ZOOLOGY
SECT
blance of the pelvis of the lower Urodela, and especially of Necturus,
to that of Polypterus (p. 225) and of the Dipnoi (p. 243) is note-
worthy. In Anura the pelvic girdle resembles that of the Frog.
Attached to the anterior border of the pubic region there occurs
in many Urodela
and in Xenopus a
rod of cartilage,
forked in front,
the epipubis (Ep).
It is developed in-
dependently of the
pelvis, and its re-
lations to that
structure are very
similar to those of
the sternum to the
shoulder-girdle ; it
has, in fact, been
proposed to call it
a pelvi-sternum.
The limbs of
Urodela differ
from the typical
structure already
described only in
details : there are
usually four digits
in the fore-limb
and five in the
hind-limb. In
Anura the limbs
are modified by
the fusion of the
radius and ulna
and of the tibia
and fibula, and by
the great elonga-
tion of the two
proximal tarsals.
A pre-hallux is fre-
quently present.
Myology. — I n
the lower Urodela the muscles of the trunk and tail occur in the
form of typical myomeres like those of Fishes. In the higher forms
the myomeres become converted into longitudinal dorsal bands — the
extensors of the back, paired ventral bands — the recti abdomin/x,
and a double layer of oblique muscles, covering the flanks.
FIG. 962. — A, right side of shonlder-ginlie of Salamandra • B,
shoulder-girdle and sternum of Amblystoma (Axulotl) from
the ventral aspect, a, b, processes of scapula ; C. (in B),
coracpicl : Cl. procoracoid; Co. (in A), coracoid ; G. (in A),
glenoid cavity ; L, its cartilaginous edge ; Pf (in B), glemml
cavity ; S. scapula ; SS. supra-scapula ; st. sternum ; *, t-
nerve foramina. (From Wieclersheim's Comparatire
Anatomy.)
xin
PHYLUM CHORDATA
295
FIG. 963. — Pelvic girdle of Salamandra. a, b,
processes of epipubis ; Ep. epipubis : Fu. ob-
turator foramen ; O. acetabulum ; //. ilium ;
Is. ischium ; P. pubis ; Si/, pubo-ischiatic
symphysis ; f, processes of pubis present in
some Urodeles. (From Wiedersheim.)
Digestive Organs. — The teeth are always small and ankylosed
to the bones : they may be singly or doubly pointed. They occur
most commonly on the pre-
maxillse, maxillae, and vomers,
but may also be developed on
the dentaries, palatines, and, in
one instance, on the para-
sphenoid. In many Anura, such
as the Common Toad, teeth are
altogether absent. In some of
the Stegocephala, such as Masto-
donsaurus, the teeth are extra-
ordinarily complex in structure,
the tissues being folded in such
a way as to produce in section
a complex tree-like pattern. It
is from this circumstance that
the term Labyrinthodont, often
applied to the Stegocephala, is
derived.
The enteric canal is divisible
into buccal cavity, pharynx, gullet, stomach, small intestine, rectum
and cloaca. The stomach and duodenum together form a U-shaped
loop in which the pancreas lies. The tongue in many Urodeles is
fixed and immovable, like that of a Fish : in most Anura it is
free behind, as in the Frog ; but in Xenopus and Pipa (hence
called Aglossa) it is absent.
Respiratory Organs. — With very few exceptions Amphibia
possess external gills in the larval state, and, in the perenni-
branchiate Urodela, these organs are retained throughout life.
They are branched structures, abundantly supplied with blood,
and springing from the dorsal ends of the first three branchial
arches. The epithelium covering them is ectodermal, so that they
are cutaneous and not pharyngeal gills, and are of a totally different
nature from the so-called external gills of the embryos of Elasmo-
branchii and Holocephali, which are only the filaments of the
internal gills prolonged through the branchial apertures.
Internal gills are developed only in the larva? of Anura. They
appear as papillae on the outer borders of the branchial arches
below the external gills. They closely resemble the internal gills
of Fishes and appear to be homologous with them, although it
seems probable that their epithelium is ectodermal.
In most adult Amphibia lungs are formed as outgrowths of the
ventral wall of the oesophagus. The right and left lungs com-
municate with a common laryngo-traclieal chamber, supported by
the cartilages of the larynx and opening into the mouth by a
longitudinal slit, the glottis. In the more elongated forms, such
T 2
296
ZOOLOGY
SECT.
as Siren, Amphiuma, and the Gymnophiona, the laryngo-tracheal
chamber is prolonged into a distinct trachea or wind-pipe, supported
by cartilages. In many species of Salamanders the lungs are absent,
and respiration is exclusively cutaneous and pharyngeal.
Circulatory Organs. — The heart always consists of a sinus
venosus, right and left auricles, ventricle, and conus arteriosus.
The sinus venosus opens into the right auricle, the pulmonary
veins enter the left, and the two are separated by a septum
auricularum which forms a complete partition in Anura, but in
Urodela and Gymnophiona is more or less fenestrated, i.e. formed
of a network of muscular strands with intervening spaces. The
eacl.ca.r-
R
c art
d.a.o
FIG. 964. — Heart and chief arteries of Salamandra. A. larva ; B, adult, a/, br.a. 1 — 4,
afferent branchial arteries ; 6.00. bulbus aortse ; car.yl. carotid labyrinth ; c. art. conus
arteriosus ; (/. a,o. dorsal aorta ; rf. bot. ductus Botalli ; ex. br. 1 — , external gills ; ext. car.
external carotid ; int. car. internal carotid ; /. an. left auricle ; Ing. lung ; pi. plexus, giving
rise to carotid labyrinth ; pul. a. pulmonary artery ; r. au. right auricle ; c. ventricle.
(Altered from Boas.)
conus arteriosus has no longitudinal valve in the lower Urodela
and the Gymnophiona, but is separated both from the ventricle
and from the bulbus aortaB by transverse rows of valves.
In the perennibranchiate Urodela and in the larvae of the air-
breathing forms the circulation is essentially like that of a Fish.
The bulbus aortse (Fig. 964, A, b. ao.), which represents an abbre-
viated ventral aorta, gives off four afferent branchial arteries (af.
br. a. 1 — 4)) three to the external gills, and a fourth which curves
round the gullet and joins the dorsal aorta directly. From
each gill an efferent branchial artery brings back the purified blood,
and the efferent arteries unite, in a somewhat irregular way, to
form the dorsal aorta (d. ao.}. Each afferent with the corresponding
efferent artery constitutes an aortic arch. Short connecting branches
unite the afferent and efferent arteries of each gill, carotids (ext.
car., int. car.) arise from the first efferent artery, and, when the
NTH
PHYLUM CHORDATA
Cut. in*
\
tSulcl-
T. Cam inf
pars unler.
7.i2iaca
-Gut.m. Xier.Fft.Kr.
FlQ. '.Mir>. Salamandra maculosa. Venous system, diagrammatic, from the ventral aspect.
Alul. V. abdominal vein ; Card. post. (Az.), axygos vein ; Ca>n/. I', caiulal vein ; Cut. in,
left inusculo-cutaneous vein : Cut. ml, the same on the right side (partly removed); D,
intestine ; Duct. Guv. precaval vein ; H. heart; Jug. ext. external jugular ; Jug. int. internal
jugular; Lg. V. mesenteric vein; L. Pf. hepatic portal system; L.V. hepatic vein; N,
kidney; Nier. Pfl. Kr. renal portal system; Sin. ven. sinus venosus ; Subcl. aubclavian
vein ; V. arh\ branches of renal portal vein ; V.i.Cara inf. postcaval ; I", i/iaca. iliac vein ;
T. rev. renal veins ; *, cloacal veins ; t. branch of iliac to renal portal vein ; f t, lateral
vein. (From Wiedersheim's Comparative Anatomy.)
298 ZOOLOGY SECT.
lungs appear, a pulmonary artery (pul. a.) is given off from the
dorsal portion of the fourth aortic arch of each side. In those
Urodela which in the adult condition are devoid of gills, when the
latter atrophy (B) the first aortic arch loses its connection with the
dorsal aorta, and becomes the carotid trunk ; the second increases
in size, forming the main factor of the dorsal aorta, andjbecomes
the systemic trunk ; the third undergoes great reduction, and the
fourth becomes the pulmonary artery, its dorsal portion retaining
its connection with the systemic trunk in the form of a small con-
necting branch, the ductus Botalli (d. hot.). In the Anura, as we
have seen (p. 271), the third arch vanishes completely and there is
no ductus Botalli.
As to the venous system, the Urodela exhibit very clearly the
transition from the Fish-type to the condition already described
in the Frog. The blood from the tail is brought back by a caudal
vein (Fig. 965, Gaud. V.), which, on reaching the crelome, divides into
two renal portal veins, one going to each kidney. From the kidney
the blood is taken, in the larva, into paired cardinal veins, each of
which joins with the corresponding jugular to form a precaval vein.
In the adult the anterior portions of the cardinals undergo partial
atrophy, becoming reduced to two small azygos veins (Card, post.)
which receive the blood from the region of the back : their posterior
portions unite and are continued forwards by a new unpaired vein,
the postcaval (V. cava inf.), which, joined by the hepatic veins,
pours its blood into the sinus venosus. The iliac vein from the
hind-leg divides into two branches : one joins the renal portal,
the other, representing the lateral vein of Elasmobranchs, unites
with its fellow in' the middle ventral line to form the abdominal
vein (Abd. V.) and joins the hepatic portal, its blood, after
traversing the capillaries of the liver, being returned by the hepatic
vein into the post-caval.
The red corpuscles are oval and nucleated, and are remarkable
for their unusual size. Those of Amphiuma are the largest known,
being about t'r mm. in diameter, or eight times that of a human
red corpuscle.
Nervous System and Sense-Organs. — The brain of Urodela
differs from that of the Frog in its more elongated and slender
form, in the comparatively small size of the optic lobes, and in the
non-union of the olfactory bulbs. The olfactory sacs always open
into the mouth by posterior nares situated behind or external to
the vomers. The eye has no lids in the lower forms and is de-
generate in the cave-dwelling Proteus and in some Gymnophiona.
The Urodela, the Gymnophiona, and some Anura have no tympanic
cavity or membrane, and no columella ; there is, however, a stapes
(Figs. 959, 960) in the form of a nodule of cartilage inserted in the
fenestra ovalis. In the perennibranchiate Urodeles and in the
larvae of the air-breathing forms lateral-line sense-organs are
XI11
IMfVLLIM (iFKMlDATA
209
present. There was an extensive lateral-line system, leaving its
impress on the bones of the skull, in the Stegocephala.
Urinogenital Organs. — In the Urodela the kidneys (Fig. 966,
N) are much elongated and are divided into two portions, a broad
posterior part, the functional kidney (GN), and a narrow anterior
A B
......mi
FIG. 066. — Diagrams of urinogenital organs of male (^1) and female (B) Urodele. a. collecting
tubes ; GN, sexual portion of kidney,; Ho, testis ; Ig. (Ur.) Woman duct (ureter) ; ing, »/',
vestigial Miillerian duct of male ; my. (Od), oviduct ; N, non-sexual portion of kidney ;
Ov. ovary ; Vc, vasa efferentia ; t, longitudinal canal. (From Wiedersheim's <'o»i/>nrntiri'
Anatomy, after Spengel.)
sexual part connected in the male with the efferent ducts of
the testis. Numerous ducts leave the kidney and open into the
Wolffian (mesonephric) duct [Ig. (Ur.)], which thus acts as a ureter
in the female, as a urinogenital duct in the male. The oviduct
[mg. (Od.)] is developed from the Miillerian duct, a rudiment of
which (mg., mg'.) occurs in the male. In the Gymnophiona the
kidneys extend the whole length of the ccelome, and in the young
:;oo
ZOOLOGY
SECT.
Fin. '.HIT. — Wototrema marsupiatum.
Female, with ]>?n. Amblystoma tigrinum. L irv.il or Axol
(From Mivart.)
302 ZOOLOGY SECT.
A very interesting case of pwdogenesis is furnished by the Axolotl
(Amblystoma tigrinum). This animal frequently undergoes no
metamorphosis, but breeds in the gilled or larval state (Fig. 970).
But under certain circumstances the gills are lost, the gill-slits
close, and a terrestrial salamandrine form is assumed. It is to
the branchiate stage that the name Axolotl properly applies ;
before the metamorphosis was discovered its connection with
Amblystoma was not suspected, and it was placed in a distinct
genus, Siredon, among the Perennibranchiata.
Segmentation of the egg in the Anura and Urodela is always com-
plete but unequal. In Pipa and Alytes there is a large quantity
of food-yolk, and the developing embryo lies on the surface of
a large yolk-sac. In the Gymnophiona the eggs, which are singularly
like those of a Bird, are of large size and segmentation is partial,
the formation of segments at the pole of the egg opposite that at
which the formation of the embryo begins only taking place at
the stage of gastrulation : the embryo is coiled over the surface
of the yolk as in the Trout.
Distribution. — The Urodela are almost exclusively Palsearctic
and Nearctic forms, occurring in North America, Europe, Asia, and
North Africa : a few species extend southwards into the Neotropical
and Oriental regions. The Gymnophiona, on the other hand, are
mainly southern, occurring in the Neotropical, Ethiopian, and
Oriental regions, but are absent in Australasia and the Pacific
Islands. The Anura are almost universally distributed, and are
abundant in all the greater zoo-geographical regions : they are,
however, very meagrely represented in New Zealand and are absent
in most Oceanic islands, a fact due to the fatal effects of salt water
upon the eggs and embryos of Amphibia as well as upon the adults.
Remains of Stegocephala are found in considerable abundance
from the Carboniferous to the Trias, and one genus extends
into the Lower Jurassic, after which period the order apparently
became extinct. The Urodela and Anura are not known until
the Eocene, and no fossil remains of Gymnophiona have been
found.
Mutual Relationships. — The perennibranchiate Urodela are
undoubtedly the lowest of existing Amphibia ; they lead up, through
such forms as Amphiuma, with persistent gill-slits but deciduous
gills, to the Land Salamanders, in which a purely terrestrial form is
assumed. The Stegocephala exhibit a parallel series of modifications,
some of them being perennibranchiate, others caducibranchiate.
Their skull is more complex than that of the Urodela, but their
vertebral column never reaches the same degree of specialisation as
that of the Land Salamanders, and in some cases shows a lower
grade of organisation than in any existing Amphibia. Both in
their skeleton and in the distribution of their lateral sense-organs
they show some affinity with the Crossopterygii. The Anura
xra PHYLUM CHORDATA 303
are a very specialised group : their development indicates their
derivation from branchiate tailed forms, but there is no palaeonto-
logical evidence on this point.
CLASS IV.-REPTILIA.
Reptiles, Birds, and Mammals are associated together as having
in common certain features in which they differ from lower Verte-
brates. The most important of these is the occurrence in all
three classes of certain embryonic membranes termed the amnion
and the allantois, to be described subsequently. The term Amniota
is, accordingly, frequently used for the group formed by these
three highest classes of the Vertebrata.
The classes Reptilia and Aves are much more closely allied with
one another than either of them is with the Mammalia ; and the
first two are sometimes associated together under the title of
Sauropsida. The following are some of the most salient features
of the Sauropsida when compared with the other Vertebrates :—
The integument always gives rise to important and characteristic
exoskeletal structures in the form of scales or feathers ; the dermis
may or may not take part in the formation of an exoskeleton.
The skull is well ossified : it rarely in the adult state contains a
distinct parasphenoid. There is a single occipital condyle borne
on the basi- occipital. The basi-sphenoid is a well-developed bone.
The mandible articulates with the skull through the intermediation
of a quadrate, and consists of five or six bones on each side. The
ankle-joint is an articulation between the proximal and distal
divisions of the tarsus. As in the Amphibia, there is a cloaca into
which the rectum and the renal and reproductive ducts open. The
heart consists of two auricles and a ventricle which is sometimes
incompletely, sometimes completely, divided into two parts,
BranchiaB are never present at any stage. The mesonephros is
never the functional renal organ of the adult, but is always
replaced by a metanephros. Both an amnion and an allantois are
present in the embryo, the latter becoming highly vascular and
acting as a temporary embryonic organ of respiration.
The class Reptilia comprises four orders having living repre-
sentatives, in addition to a number of extinct groups. In the
Mesozoic period the class reached its maximum both in the number
of its representatives and the size which many of them attained ;
at that period they were very unmistakably the dominant class
of the Animal Kingdom. In the Tertiary period they underwent
a decline, while the Birds, and, in a yet higher degree, the Mammals,
were gaining a preponderance over them. The living Reptiles
are the Lizards and Chamseleons, the Tuataras, the Snakes, Tortoises
and Turtles, and the Crocodiles and Alligators. Though horny
scales are not by any means present in all the Reptiles, their occur-
304
ZOOLOGY
SECT.
rence as a complete covering is characteristic of the group and
almost peculiar to it. When scales are not present, the epidermis is
always hardened and cornified so as to form plates of horny material,
such as the horny plates of the Tortoises, which protect the under-
lying parts from injury and desiccation. Bony plates are frequently
present as well. In most respects the internal structure of the
Reptilia shows a very decided advance on that of the Amphibia.
The skull and the pectoral and pelvic arches are more com-
pletely ossified, and both vascular and nervous systems show a
higher grade of organisation.
1. EXAMPLE or THE CLASS.— A LIZARD (Lacerta).
The most striking external differences between the Lizard (Fig.
971) and the Frog are the covering of scales, the comparative
smallness of the head, and the presence of a distinct neck, the great
c-T
FIG. 971. — Lacerta vlridis. (After Brehm.)
length of the caudal region, the shortness of the limbs, and the
approximate equality in length of the anterior and posterior pairs.
The anterior limbs are situated just behind the neck, springing
from the trunk towards the ventral surface. The fore-limb, like
that of the Frog, is divided into three parts, the upper-arm or
brachium, the fore-arm or anti-branchium, and the hand or manus ;
there are five digits provided with horny cla\vs, the firet digit or
pollex being the smallest. The hind-limbs arise from the posterior
xm PHYLUM CHORDATA 305
end of the trunk towards the ventral aspect ; each, like that of the
Frog, consists of three divisions — thigh or femur, shank or cms,
and foot or pes. The pes, like the manus, terminates in five clawed
digits, of which the first or hallux is the smallest. The head is
somewhat pyramidal, slightly depressed : the openings of the
external nares are situated above the anterior extremity. The
mouth is a wide slit-like aperture running round the anterior
border of the head. At the sides are the eyes, each provided with
upper and lower opaque, movable eyelids and with a transparent
third eyelid or nictitating membrane, which, when withdrawn, lies
in the anterior angle of the orbit. Behind the eye is a circular
brown patch of skin — the tympanic membrane — corresponding
closely to that of the Frog, but somewhat sunk below the general
level of the skin. The trunk is elongated, strongly convex dorsally,
flatter at the sides and ventrally. At the root of the tail on the
ventral surface is a slit-like transverse aperture — the anus or
dixical aperture. The tail is cylindrical, thick in front, gradually
tapering to a narrow posterior extremity ; it is nearly twice as
long as the head and trunk together.
There is an exoskeleton of horny scales covering all parts.
These are formed from folds of the dermis, each covered with a thick
horny epidermal layer. In size they differ in different positions.
On the dorsal surface of the trunk they are small, hexagonal, and
indistinctly keeled. On the ventral surface they are larger and
are arranged in eight longitudinal rows. Immediately in front of
the cloacal aperture is a large pre-anal plate. A collar-like ridge
of larger scales surrounds the throat. On the tail the scales are
elongated, keeled, and arranged in regular transverse (annular) rows,
giving the tail a ringed appearance. On the surface of the limbs
the scales of the pre-axial (radial or tibial) side are larger than
those of the post-axial (ulnar or fibular). The scales on the upper
surface of the head (head-shields) are large, and have a regular and
characteristic arrangement.
Endoskeleton. — The vertebral column is of great length and
made up of a large number of vertebra?. It is distinctly marked
out into regions, a cervical of eight vertebras, a thoraco-lumbar of
twenty-two, a sacral of two, and a caudal of a considerable but
indefinite number. A vertebra from the anterior thoracic region
(Fig. 972, A, B) presents the following leading features. The
centrum (cent.) is elongated and strongly proccelous, i.e. the anterior
surface is concave, the posterior convex ; the neural arch bears a
short neural spine (sp.). There are pre- and post-zygapophyses
(pr. zy, pt. zy}, the former with their articular surfaces directed
upwards, the latter downwards. On each side at the junction of
centrum and neural arch is a facet — the capitular facet — for the
articulation of a rib. The cervical vertebra in general are similar
in essential respects to those of the trunk, but are somewhat shorter.
306
ZOOLOGY
SECT
lot
•vent
hyp.
Fio. 972. — Vertebrae of Lizard. A, anterior, S, posterior
view of a thoracic vertebra ; C, lateral, D, anterior view
of atlas vertebra ; F, lateral view of axis. cent, centrum ;
hyp. hypapophysis of axis ; hit. lateral piece of atlas ;
Hg. ligamentbus band dividing the ring of the atlas
into two ; neur. neural arch of atlas : od. odontoid pro-
cess ; pr. zy. pre-zygapophysis ; pt. zy. post-zygapophy-
sis ; rb. rib ; sp. spine ; cent, ventral piece of atlas.
The first two, however, differ greatly from the others. The first
is the atlas (C, D). It has no distinct centrum, but is in the form
of a ring ; ventrally on its anterior face it bears a smooth articular
facet for the occipital condyle of the skull. It consists of three
distinct ossifications, one ventral, the others dorso-lateral : the
latter do not quite meet
dorsally, being separated
by a space bridged over
by membrane. The
second or axis (E) has a
short conical process — the
odontoid process (od)—
projecting forwards from
its centrum. In the
natural position of the
parts the odontoid pro-
cess—which is a part of
the centrum of the atlas,
and is not actually fused
with, though firmly fixed
to, the axis — lies in the
lower or ventral part of
the opening of the atlas, separated by a ligamentous band from
the upper portion, which corresponds to the neural arch, and
lodges the anterior end of the spinal cord. On the ventral surface
of the axis and of each of the following five or six vertebrae is
a distinct bony nodule, sometimes termed the intercentrum
or Jiypapophysis (hyp). The sacral vertebrae have short centra
and strong expanded processes — the transverse processes — which
abut against the ilia ; these are separately ossified, and are to be
looked upon as sacral ribs. The anterior caudal vertebrae are like
the sacral, but have the centra longer, the transverse processes
more slender, and the neural spines longer. The posterior caudal
vertebrae become gradually smaller as we pass backwards, and the
various processes reduced in prominence, until, at the posterior
end of the tail, the whole vertebra is represented merely by a rod-
like centrum. Attached to the ventral faces of the centra of a
number of the anterior caudal vertebrae are Y-shaped bones — the
chevron bones — the upper limbs of the Y articulating with the
vertebra, while the lower limb extends downwards and backwards.
In nearly all the caudal vertebrae the centrum is crossed by a narrow
transverse unossified zone through which the vertebra readily
breaks. The ribs are slender curved rods, the vertebral ends of which
articulate only with the capitular facets of the corresponding
vertebrae, there being no direct articulation with the transverse
processes. The ribs of the five anterior thoracic vertebrae are
connected by means of cartilaginous sternal ribs with the sternum.
xm PHYLUM CHORDATA 307
The posterior thoracic ribs do not reach the sternum, the sternal
ribs being very short, and free at their ventral ends. The cervical
ribs, which are present on all the cervical vertebrae with the exception
of the first three, are all shorter than the thoracic ribs, and none of
them are connected with the sternum. Thus, as regards the
structure of the vertebrae themselves, there is nothing to distinguish
the posterior cervical from the anterior thoracic ; but, for conveni-
ence of description, the first thoracic is defined as the first vertebra
having ribs connected with the sternum.
The sternum (Fig. 974, st) is a rhomboidal plate of cartilage with
a small central space, or fontanelle, completed by membrane.
Posteriorly it is produced into two slender flattened processes.
On its antero-lateral borders are articular surfaces for the bones
of the pectoral arch, and on its postero-lateral borders and the
processes are small facets for the sternal ribs.
In the skull (Fig. 973) the chondrocraniurn, though persistent,
is replaced by bones to a much greater extent than in the Frog,
and the number of investing bones is much greater. On the dorsal
and lateral surface are a large number of dermal roofing bones.
At the posterior end the rounded aperture of the foramen magnum
(for. mag.) is surrounded by four bones — a basioccipital (has. oc.)
below, exoccipitals (ex. oc.) at the sides, and a supraoccipital (supr. oc.)
above. The basioccipital forms the floor of the most posterior
portion of the cranial cavity ; posteriorly it bears a rounded promi-
nence, the occipital condyle (oc. cond). In front of it, forming the
middle portion of the floor of the cranial cavity, is the basisphenoid
(has. sph), not represented in the Frog, in front of which again is an
investing bone, the parasphenoid (para), corresponding to the bone
of the same name in the Frog and Trout, but here much reduced in
size and importance and ankylosed with the basisphenoid.
In the wall of the auditory capsule are three ossifications—
pro-otic, epiotic, and opisthotic (op. ot). The first remains distinct,
the second becomes merged in the supraoccipital, and the third
in the exoccipital. The exoccipital and opisthotic are produced
outwards as a pair of prominent horizontal processes, the parotic
processes.
The large orbits are closely approximated, being separated
only by a thin vertical interorbital septum. The cranial cavity
is roofed over by the parietals (par) and frontals (fr). The former
are united together ; in the middle is a small rounded aperture—
the parietal foramen (par. f). The frontals remain separated from
one another by a median frontal suture : between them and the
united parietals is a transverse coronal suture. The nasal cavities are
roofed over by a pair of nasals (nas). A small pre-frontal (pr. fr.)
lies in front of the frontal, and helps to bound the orbit anteriorly,
and another small bone — the lacrymal (kr) — perforated by an aper-
ture for the lacrymal duct, lies at the anterior extremity of the orbit,
308
ZOOLOGY
SECT.
just within its border. A row of small bones — the supra-orbitals
(s. orb) — bounds the orbit above, and behind is a post-orbital or
lateral post-frontal (pt. orb.) articulating with the frontal. Just
A
eacl.nar
t reins
7
n
ba*f*ff~". 7 J~;
pig cot
f •> — --T -, .tang
vj>*fc> -"£
ar^
an
FIG. 973. — Skull of Lacerta agilis. A. from above; B, from below; C, from the side.
unii, angular; art. articular ; kas.uc. basi-occipital ; fca.s-. ply. basipterygoid processes; has.
sph. basisphenoid ; col. epipterygoid ; cor. coronary ; ilent. dentary : eth. ethmoid ; <•.*•. or.
exoeeipital ; ext. nar. external nares ; for. mag. foramen magnum ; Jr. frontal ; int. nar.
internal nares ; ju. jugal ; Icr. lacrymal ; max. maxilla : was. nasal ; oc. cond. occipital con-
dyle ; o/f. olfactory capsule ; opi. ot. opisthotic ; opt. n. optic nerve ; pal. palatine ; par.
parietal ; para, parasphenoid ; par.}', parietal foramen ; p. m*. premaxilke ; pr.fr. pre-1'rontal ;
ptg. pterygoid ; pt. orb. post-orbital or lateral post-frontal ; gu. quadrate ; s. ang. supra-
angular ; s. orb. supra-orbitals ; sq. paraquadrate ; supra t.l. supratemporal 1 ; supra t.~.
squaniosal ; trans, transverse ; supr.oc. supra-occipital; vom. vomer. Tlie unlettered bone
internal to pt. orb. in A is the post-frontal. The transverse line behind//1, is a superficial
mark, not a suture. (After W. K. Parker.)
behind the post-orbital is a supra-temporal bone (supra t.l), in close
relation to which are the paraquadrate (sq) and squamosal (,s^/>w. t.2),
xra PHYLUM CHORDATA 309
the former bending forwards and upwards to form with the post-
orbital the superior temporal arch. At the anterior extremity of
the snout is a median bone formed by the coalescence of the two
premaxillcB (p. mx) ; this bears the four anterior teeth of each
side. On each side behind the premaxilla is the maxilla (max),
consisting of two portions, an alveolar bearing all the rest of the
teeth, and a palatine extending inwards on the roof of the mouth,
together with an ascending process articulating with the nasal and
pre-frontal above. Articulating behind with each maxilla is a
jugal (ju), which forms the posterior half of the ventral boundary
of the orbit. The quadrate (qu) articulates movably with the
parotic process, and bears at its distal end the articular surface for
the mandible.
In the anterior portion of the roof of the mouth, articulating
in front with the premaxiUse and maxillae, are the vomers (vom).
Behind and embracing them posteriorly are the flat palatines
(pal). The elongated pterygoids (ptg) articulate in front with the
posterior extremities of the palatines : behind each articulates
with the corresponding basi-pterygoid process (has. ptg) of the basi-
sphenoid, and sends back a process which becomes applied to the
inner face of the quadrate. A stout bone which extends between
the maxilla externally and the pterygoid internally is termed the
transverse bone or ecto-pterygoid (trans). Extending nearly verti-
cally downwards from the pro-otic to the pterygoid is a slender
rod of bone, the epi-pterygoid (col).
The columella is a small rod partly composed of cartilage and
partly of bone, the outer end of which is fixed into the inner surface
of the tympanic membrane, while the inner is attached to a small
aperture, thefenestra ovalis, in the outer wall of the auditory capsule
between the pro-otic and the opisthotic.
Certain depressions or fossae and apertures or foramina are to be
observed in the skull. The foramen magnum, the parietal foramen,
and the orbits have been already mentioned. The posterior tem-
poral fossa is situated on either side of and above the foramen
magnum, bounded above and externally by the roofing bones, and
on the inner side by the bones of the occipital region. The inferior
temporal fossa is bounded internally by the pterygoid, and is sepa-
rated from the palatine foramen by the transverse bone. The lateral
temporal fossa is the wide space in the side wall of the skull behind
the orbit ; the bony bar which limits it above is the superior temporal
arch ; a bony inferior temporal or quadratojugal arch is here absent.
The tympano-eustachian fossa, situated in the auditory region, is
bounded by the bones of that region together with the quadrate.
The posterior or internal naves are bounded posteriorly by the
palatines. The anterior or external nasal aperture is situated at the
anterior extremity of the skull bounded by the nasals and premaxillse.
Each ramus of the mandible consists of six bony elements in
VOL. TT u
310 ZOOLOGY SECT.
addition to the slender persistent MeckeVs cartilage. The proximal
element is the articular (art] which bears the articular surface for
the quadrate, and is produced backwards into the angular process.
The angular (ang) is a splint-like bone covering the ventral edge
and the lower half of the outer surface of the articular. The supra-
angular (s. ang) overlies the dorsal edge and upper half of the
outer surface of the same bone. The dentary (dent) forms the main
part of the distal portion of the mandible, and bears all the mandi-
bular teeth. The splenial is a flat splint applied to the inner face
of the dentary. The coronary (cor), a small, somewhat conical
bone, forms the upwardly directed coronoid process immediately
behind the last tooth. All these, with the exception of the articular,
are investing bones.
The hyoid apparatus (vide Fig. 979, 6. ny) consists (1) of a median
cartilaginous rod, the basi-hyal, (2) of the anterior cornua, elongated
cartilaginous rods which, connected ventrally with the basi-hyal,
curve round the gullet and end in close relation with the ventral
surface of the auditory capsule, (3) of the middle cornua, rods of
cartilage ossified at their proximal ends, and (4) of the posterior
cornua, cartilaginous rods arising from the posterior edge of the
basi-hyal and passing backwards and outwards. The middle cornua
are vestiges of the first, the posterior of the second branchial arch.
In the pectoral arch (Fig. 974) the coracoids are flat bones articu-
lating with the antero-lateral border of the sternum, and bearing
the ventral half of the glenoid cavity (glen) for the head of the
humerus ; a cartilaginous epicoracoid (ep. cor.) element lies on
the inner side of the procoracoid and coracoid ; a large gap or
fenestra divides each coracoid into a narrow anterior portion — the
procoracoid (pr. cor), and a broader posterior portion, the coracoid
proper (cor). The scapulce (sc) articulate with the outer ends of
the coracoids, and each bears the dorsal half of the glenoid cavity.
Dorsally the scapulae become expanded, and each has connected
with it a thin plate of partly calcified cartilage — the suprascapula
(supra, sc), which extends inwards towards the spinal column on
the dorsal aspect of the body. An element not hitherto met with,
except in the Stegocephala (p. 293), is the interclavicle or episternum
(epist), a cross-shaped investing bone, the stem of which is longi-
tudinal and is in the posterior portion of its extent closely applied
to the ventral surface of the anterior part of the sternum, while the
cross-piece is situated a little in front of the scapula. The clavicles
(cl) are flat curved bones articulating with one another in the middle
line and also with the anterior end of the interclavicle. The bones
of the fore-limb consist of a proximal bone or humerus, a middle
division composed of two bones — the radius and ulna, and a distal
division or manus. In the natural position of the parts the humerus
is directed, from the glenoid cavity with which it articulates,
backwards, upwards and outwards ; the radius and ulna pass
xrn
PHYLUM CHORDATA
311
7T7
FIG. 974. — Pectoral arch and sternum of Lacerta agilis.
el. clavicle ; cor. coracoid ; ep. cor. epicoracoid ; epis,t.
episternum ; tjlen. glenoid cavity for head of humerus ;
pr. cor. procoracoid ; r.l — rA first to fourth sternal ribs ;
sc. scapula; st. sternum; nupra.se. suprascapula.
(After Hoffmann.)
from their articulation with the humerus downwards and slightly
forwards, while the manus has the digits directed forwards and
outwards. When the
limb is extended at
right angles to the
long axis of the trunk,
it presents, like that
of the Frog, dorsal
and ventral surfaces,
and pre-axial and post-
axial borders, In this
position the radius is
seen to be pre-axial,
the ulna post-axial.
In the natural posi-
tion the pre-axial
border of thejmmerus
is external, and the
distal end of the fore-
arm is rotated in such
a way that, while the
pre-axial border looks
forwards and outwards
at the proximal end,
it faces directly inwards at its distal end, the manus being rotated
so that its pre-axial border looks inwards.
The humerus is a long bone consisting of a shaft and two ex-
tremities, each of the latter being formed
of an epiphysis of calcined cartilage, the
proximal rounded, the distal (trochlea)
pulley-like, with two articular surfaces, one
for the radius and the other for the ulna.
The radius is a slender bone consisting,
like the humerus, of a shaft and two epi-
physes ; the distal extremity has a con-
cave articular surface for the carpus, and
is produced pre-axially into a radial
styloid process. The proximal end of the
ulna is produced into an upwardly directed
icranon : the distal end
bears a convex articular surface for the
carpus. The carpus (Fig. 975) is com-
fl>epmetacarpais.rin(FromFw^ posed of ten small polyhedral or rounded
S!)eim>s Comparati"e Ana~ carpal bones. These consist of a proximal
row containing three, viz., the radiale (r),
ulnare (u), and intermedium (i), of a centrale (c), and of a distal row
of five (1-5} ; with an accessory or pisiform (\) bone attached
u 2
FIG. 975.— Carpus of Lacerta -l^rnc.(,(ia flip
agilis, (left) from above. /,'.
radius ; U. ulna ; c. centrale ;
i. intermedium ; r. radiale ; u.
ulnare : 1 — 5, the five distal
312
ZOOLOGY
SECT.
to the distal epiphysis of the ulna on its post-axial side. The first
digit or pollex consists of a metacarpal and two phalanges, the
second of a metacarpal and three phalanges, the third of a meta-
carpal and four phalanges, the fourth of a metacarpal and five
phalanges, and the fifth of a metacarpal and three phalanges.
The number of phalanges in the first four digits is, therefore, one
more than the serial number of the digit.
The pelvic arch (Fig. 976) consists of two triradiate bones, the
ossa innominata, each ray being a separate bone. On the outer side
at the point from which the rays diverge is a concave articular
surface — the acetabulum (Ac) — for the head of the femur. From
the region of the acetabulum one of the rays, the ilium (I), a com-
pressed rod, passes upwards and backwards to articulate with
the sacral region of
the spinal column.
A second ray — the
pubis (p) - - passes
downwards and for-
wards to meet its
fellow in the middle
line, the' articula-
tion being termed
the pubic symphysis.
In the middle line
in front, between
the anterior ends of
the pubes, is a
small nodule of
calcified cartilage,
epipubis (Cep).
third ray or
ischium (Is) runs
downwards and
backwards, and articulates with its fellow in the ischiatic symphysis,
the ventral ends of the two bones being separated by a plate of calci-
fied cartilage (S. Is). Between the pubes and ischia is a wide space,
the obturator foramen, divided by a median ligament (Ig) into a pair
of apertures, and a smaller aperture in each pubis (Fo') transmits
the obturator nerve. A small rod of bone, the os cloacce, or hypo-
ischium (Hp. Is), passes backwards from the ischiatic symphysis
and supports the ventral wall of the cloaca.
The hind-limb consists, like the fore-limb, of three divisions ;
these are termed respectively the proximal or femur, the middle
or crus, and the distal or pes. The proximal division consists
of one bone, the femur ; the middle division of two, the tibia and
fibula ; the distal of the tarsal and metatarsal bones and the
phalanges. When the limb is extended at right angles with the
FIG. 976. — Pelvis of Lacerta vivipara, from the ventral side.
Ac. acetabulum ; Cep. epipubis. Fo'. foramen for obturator
nerve ; Hp. Is. hypoischium ; /. ilium ; 1 1, process representing
the pre-acetabular part of the ilium ; Lg. ligament ; In.
ischium ; p. pubis ; pp. prepubis ; S. Is. ischiatic symphysis.
(From Wiedersheim's Comparative Anatomy.)
PHYLUM CHORDATA 313
trunk, the tibia is pre-axial and the fibula post-axial : in the
natural position of the parts the pre-axial border is internal in all
three divisions of the limb. The femur is a stout bone consisting
of a shaft and two epiphyses. The proximal epiphysis develops a
rounded head which fits into the acetabulum ; near it on the
pre-axial side is a prominence, the lesser trochanter, and a nearly
obsolete prominence on the post-axial side represents the greater
trochanter. The distal extremity is pulley-shaped, with internal
and external prominences or condyles for articulation with the
tibia ; immediately above the external condyle is a prominence or
tuberosity for articulation with the fibula. The tibia is a stout,
curved bone, along the anterior (dorsal) edge of which runs a
longitudinal ridge, the cnemial ridge : the proximal extremity
presents two articular surfaces for the condyles of the femur. The
fibula is a slender bone, the proximal end articulating with the
external tuberosity of the femur, the distal with the tarsus.
The tarsus (Fig. 977) comprises only
three bones in the adult, one large
proximal bone, the tibio-fibulare (tb. fb),
and two smaller distal (tars. dist).
Each digit consists of a metatarsal bone
and phalanges, the number of the latter
being respectively two, three, four, five,
and three. The first and second meta-
tarsals articulate with the tibial side of
the tibio-fibulare, the rest with the
,. , , . , FIG. 977. — Tarsus otLacertaagilis.
distal tarsals. -. /&. fibula; tb. tibia; tb. fb. tibio-
•nio-oc-H-jro CSTrc-f 3 .
'•+j » 5S fl £j ^*
C! >- •— •» ^s •« f^
l"l-itlli
««J°M -o. posterior ampulla ; br. basilar
branch of nerve ; ca. anterior semicircular canal ;
ce. external semicircular canal ; cp. posterior
semicircular canal ; CMS. canal connecting utri-
rulus and sacculus ; de. ductus endolymphaticus ;
I. cochlea ; mb. basilar membrane ; raa, rae, rap. rl.
branches of auditory nerve ; s. sacculus ; ss. com-
mon canal of communication between anterior
and posterior semicircular canals and utricle ;
u. utriculus. (From Wieclersheim's Comparative
Anatomy, after Retzius.)
322
ZOOLOGY
SECT.
across the cavity from the tympanic membrane, and is fixed
internally into the membrane covering over the fenestra ovalis.
The parts of the membranous labyrinth (Fig. 985) are enclosed
by the bones of the auditory region : between the membranous
wall of the labyrinth and the surrounding bone is a small space
containing fluid, the p&rilymph. The labyrinth itself consists of
the utriculus with the three semicircular canals and the sacculus with
the cochlea (lagena). The utriculus (u.) is a cylindrical tube, bent
round at a sharp angle : the semi-
circular canals (ca., ce., cp.) are
mso
r.m
FIG. 986. — Male urinogenital organs of Lacerta
viridis. The ventral wall of the cloaca is
removed, the bladder is turned to the ani-
• mal's right, and the peritoneal covering of the
left testis and epididymis is dissected away.
bl. urinary bladder ; b. Ig. fold of peritoneum
supporting epididymis ; el1, anterior and cl2.
posterior divisions of the cloaca ; ep. epididy-
mis ; k. kidney ; mso. mesorchium ; p. copu-
latory organs, of which the right is shown
retracted (/>') and the left everted (p) ; r. m.
retractor muscle of latter ; r. ridge separating
anterior and posterior divisions of cloaca ;
ret. rectum ; ret', its opening into the cloaca ;
t. testis ; u. g. urinogenital papilla and aper-
ture ; v. d. vas deferens. (From Parker's
Zootomy.)
od
FIG. 987. — Female urinogenital organs
of Lacerta viridis. The ventral
wall of the cloaca, the urinary bladder,
the posterior end of the left oviduct,
and the peritoneal investment of the
left ovary and oviduct are removed.
b. Iff. broad ligament ; el1, anterior
and clz. posterior divisions of the
cloaca ; k. kidney ; mso. meso-
arium ; od. left oviduct ; od'. its peri-
toneal aperture ; od". aperture of
right oviduct into the cloaca ; OP.
ovary ; ur. aperture of ureter. (From
Parker's Zootomy.)
arranged as in Vertebrates in general (p. 111). A narrow tube, the
ductus endolymphaticus, leads upwards towards the roof of the skull
and ends blindly in the dura mater. The sacculus is large and
rounded. The cochlea (I.) forms a flattened, not very prominent,
lobe, and is of simple form.
XIH PHYLUM CHORDATA 323
Urinary and Reproductive Systems. — The kidneys (Figs.
986 and 987, k.) are a pair of irregularly shaped, dark red bodies,
each consisting of two lobes, anterior and posterior, situated in
close contact with the dorsal wall of the posterior portion of the
abdominal cavity, and covered with peritoneum on their ventral
faces only. Their posterior portions, which are tapering, are in close
contact with one another. Each has a delicate duct, the ureter,
opening posteriorly into the cloaca. A urinary (allantoic) bladder
(bl.), a thin-walled sac, opens into the cloaca on its ventral
side.
In the male the testes (Fig. 986, t.) are two oval white bodies,
that on the right side situated just posterior to the right lobe of
the liver, that on the left somewhat further back. Each testis is
attached to the body-wall by a fold of the peritoneum, the mes-
orchium (mso.). The epididymis (ep.) extends backwards from the
inner side of each testis, and passes behind into a narrow convoluted
tube, the vas deferens or spermiduct (v. d.}, which opens into the
terminal part of the corresponding ureter. A pair of vascular
eversible copulatory sacs (p, p'.), which when everted are seen to be
of cylindrical form with a dilated and bifid apex, open into the
posterior p^art of the cloaca.
In the female the ovaries (Fig. 987, ov.) are a pair of irregularly
oval bodies having their surfaces raised up into rounded elevations,
marking the position of the ova. They are situated a little further
back than the testes, and each is attached to the body-wall by a
fold of the peritoneum, the mesoarium (mso.). The oviducts (od.)
are thin-walled, wide, plaited tubes which open in front into the
cavity of the body (od'.), while behind they communicate with the
posterior part of the cloaca, their opening (od".) being distinct from,
and a little in front of, those of the ureters. A fold of the peritoneum,
the broad ligament (b. lg.), attaches the oviduct to the body-wall.
2. DISTINCTIVE CHARACTERS AND CLASSIFICATION.
The Reptilia are cold-blooded Sauropsida (p. 303), with a horny
epidermal skeleton of scales, and frequently with an armour of
dermal bony plates. The centra of the vertebrae have spheroidal
articular surfaces. There are usually only two vertebrae in the
sacral region. The episternum, when present, always remains
distinct from the clavicles. The floor of the acetabulum is often
completely ossified. The pubes and the ischia usually meet in
ventral symphyses. The metatarsals do not become ankylosed.
The mandible, as well as several bones of the upper jaw, very
usually bear teeth. The optic lobes are situated on the dorsal
aspect of the brain. The ventricle is rarely divided by a complete
partition. There is always a paired aortic arch in the adult.
324 ZOOLOGY SECT.
ORDER I. — SQUAMATA.
Reptilia in which the surface is covered with horny scales,
sometimes with the addition of dermal ossifications. The opening
of the cloaca is transverse in direction. There is a pair of eversible
copulatory sacs in the male. The vertebrae are nearly always
procoslous. The sacrum, absent in the Ophidia and some Pythono-
morpha, consists of two vertebrae in the Lacertilia. The ribs
have simple vertebral extremities. The quadrate is usually
movably articulated with the skull. There is no inferior temporal
arch. The nasal apertures of the skull are separate. The limbs,
when present, are sometimes adapted for terrestrial locomotion
(Lacertilia), sometimes for swimming (Pythonomorpha). The teeth
are acrodont or pleurodont (see p. 345). The lungs are simple sacs.
There is always a wide aperture of communication between the
right and left divisions of the ventricular cavity. The optic lobes
are approximated, and the cerebellum is extremely small.
Sub-Order a. — Lacertilia.
Squamata in which, as a rule, the limbs are present and are
adapted for walking. The mouth is capable of being opened to
only a moderate extent. The maxillae, palatines, and pterygoids
are incapable of free movement. The rami of the mandible are
firmly united at the symphysis. There are nearly always movable
eyelids and a tympanum. A sternum and an episternum are
present.
Including all the Lizards, such as the Skincs, Geckos, Monitors,
Iguanas, Amphisbsenians, Chamaeleons, and other groups.
Sub-Order b. — Ophidia.
Squamata with long narrow body, devoid of limbs. The mouth
is capable of being opened to form a relatively very wide gape by
divarication of the jaws. The rnaxillse, palatines, and ptery-
goids are so articulated as to permit of free movement. The
rami of the mandible are connected together only by elastic fibres
at the symphysis, so that they are capable of being widely separated.
There is no separate supra-temporal ossification. Sternum and
episternum are absent. Movable eyelids and tympanum are absent.
Including all the Snakes — Vipers, Rattlesnakes, Sea-Snakes,
Fresh-water Snakes, Tree-Snakes, Blind-Snakes, Pythons, and
Boas.
Sub-Order c. — Pythonomorpha.
Extinct Squamata with elongated Snake-like body, provided
with limbs which take the form of swimming-paddles. The
skull resembles that of the Lacertilia ; a supra-temporal helps to
xiir PHYLUM CHORDATA 325
suspend the quadrate. The union of the rami of the mandible
was ligamentous. There is, as a rule, no sacrum, the ilia not
articulating with the spinal column.
ORDER II. — RHYNCHOCEPHALIA.
Lizard-like, scaly Reptiles with well-developed pentadactyle
limbs adapted for walking. The opening of the cloaca is trans-
verse. There are no copulatory sacs. The vertebrae are amphi-
coelous, sometimes enclosing vestiges of the notochord. The
sacrum consists of two vertebrae. Numerous intercentra are present.
The ribs have simple vertebral extremities, and are provided with
uncinates (see p. 335). There is a system of abdominal ribs. The
quadrate is immovably fixed to the other bones of the skull.
There are both upper and lower temporal arches. The rami of
the mandible are united by ligament. There is a sternum. The
teeth are acrodont. The lungs, heart, and brain resemble those
of the Squarnata.
This order comprises only a single living genus, Sphenodon or
Hatteria, together with a number of fossil forms.
ORDER III. — CHELONIA.
Reptilia having the body enclosed in a shell of bony plates,
consisting of a dorsal carapace and a ventral plastron, partly of
dermal, partly of endoskeletal origin. There is usually on the
surface an epidermal exoskeleton of horny plates. The vertebrae
and ribs of the thoracic region are firmly fused with the bony
carapace, into the composition of which they enter. The quad-
rate is immovably united with the skull. The nasal apertures in
the skull coalesce into one. The limbs are sometimes terminated
by clawed digits adapted for terrestrial locomotion, sometimes
modified into the shape of flippers. There are no teeth, and the
jaws have a horny investment. The lungs are compound sacs.
In essentials the heart and brain resemble those of the Squamata.
There are no copulatory sacs, but a median penis.
This order includes the Land Tortoises, Soft Tortoises, River
and Mud Tortoises, and the Turtles, besides a number of fossil
forms.
ORDER IV. — THEROMORPHA.
Extinct Reptiles with amphicoelous vertebrae sometimes enclosing
remnants of the notochord, with a sacrum composed of from two
to six vertebrae, and with ribs having bifid vertebral extremities.
The quadrate is not movable. The limbs are adapted for walking.
The pubes and ischia are united. The teeth, which are usually,
though not always, present, are highly differentiated and lodged
in sockets.
VOL. II X
326 ZOOLOGY SECT.
This order comprises a large number of extinct Reptiles, which
are grouped in the four sub-orders Anomodontia, Placodontia,
Pareiosauria, and Theriodontia (Fig. 1022).
ORDER V. — CROCODILIA.
Reptiles in which the dorsal surface, or both dorsal and ventral
surfaces, are covered with rows of sculptured bony scutes supporting
horny scales. The vertebral centra are either amphiccelous, flat
at each end, or procoelous. The anterior thoracic vertebrae have
elongated and bifid transverse processes. The sacrum consists
of two vertebrae. The ribs are bifid at their vertebral ends. The
quadrate is immovable. A sternum is present, and there is a
series of abdominal ribs. The limbs are adapted for walking.
The teeth are lodged in sockets. The lungs are compound sacs.
The ventricle of the heart is completely divided in recent forms.
The opening of the cloaca is elongated in the direction of the long
axis of the body. There is a median penis.
This order includes among living forms the true Crocodiles, the
Gavials, the Alligators, and Caimans.
ORDER VI. — SAUROPTERYGIA.
Extinct aquatic Reptiles with elongated neck, small head, short
tail, and usually flipper-like limbs. The centra are slightly
amphiccelous or quite flat. The sacrum is composed of either one
or two vertebrae. The cervical ribs are bifid, the thoracic simple.
The quadrate bone is immovable. There is no sternum. The
teeth are situated in sockets (Fig. 1023).
ORDER VII. — ICHTHYOPTERYGIA.
Extinct aquatic Reptiles, with large head, without neck,
and with elongated tail and completely flipper-like limbs. The
centra are amphiccelous, and there is no sacrum. The ribs are
bifid at their vertebral ends. The quadrate is immovable. The
premaxillse are drawn out to form an elongated rostrum. There
is no sternum, but there is a series of abdominal ribs. The
teeth are lodged in a common groove. The integument is naked
(Fig. 1026).
ORDER VIII. — DINOSAURIA.
Extinct terrestrial Reptiles with elongated limbs, having the
surface sometimes naked, sometimes provided with a bony armour.
The centra are usually amphiccelous. The sacrum consists of
from two to six vertebrae. The ribs are bifid. A sternum is
present. The quadrate is fixed. The pelvis usually resembles
that of a Bird, the ilium being extended fore and aft, and the
pubis, as well as the ischium, directed backwards. The teeth
xm PHYLUM CHORDATA 327
are lodged in sockets, and usually have compressed crowns
(Fig. 1027).
ORDER IX. — PTEROSAURIA.
Extinct Reptiles, the structure of which is greatly modified in
adaptation to a flying mode of locomotion. The vertebrae are
proccelous, the neck elongated. The sacrum contains three to six
vertebrae. The anterior thoracic ribs are bifid. The skull resembles
that of a bird in its general shape and in the obliteration of the
sutures, but not in more essential features. There is a ring of
sclerotic bones. The quadrate is immovable. There is a sternum.
The fore-limbs are modified to act as wings by the great enlarge-
ment of the post-axial digit, for the support of a fold of skin.
The posterior limbs are weak and have four or five digits. The
teeth are implanted in sockets. In the brain the optic lobes were
widely separated by the cerebellum, and the latter bore a pair of
lateral processes or flocculi (Figs. 1029-1031).
Systematic Position of the Example.
There are twenty known species of the genus Lacerta, occurring
in Europe, Asia, Africa, and North America. Lacerta is a member
of the sub -order Lacertilia of the order Squamata. The flattened
and elongated tongue with notched apex places it in the section
Leptoglossa3 of that sub-order. Among the Leptoglossse the
family Lacertidse, which comprises Lacerta and a number of other
genera, is characterised by the presence of dermal bony supra-orbital
and supra-temporal plates, by the presence of small granular or
wedge-shaped scales, and of pleurodont conical teeth, excavated at
the base. The chief distinctive marks of the genus Lacerta are
the presence of comparatively large shields on the head and on the
ventral surface, the arrangement of the scales of the trunk in
transverse rows which become circular zones or rings on the tail,
the development of a collar-like band of larger scales round the
neck, and the laterally-compressed falciform claws, grooved on the
lower surface.
3. GENERAL ORGANISATION OF RECENT REPTILIA.
External Features. — In external form, as in some other
respects, certain of the Lacertilia exhibit the least specialised
condition to be observed among the living Reptilia. Lacerta is
such a central type, and the general account of that Lizard which
has just been given applies in all the points of cardinal importance
to a large proportion of the Lacertilia. Modifications take place,
however, in a variety of different directions. Of such the following
are a few of the chief. The tail region is usually, as in the example,
extremely long and tapering ; but in some groups of Lizards it is
x 2
328 ZOOLOGY SECT.
comparatively short and thick ; and in others it is depressed and
expanded into a leaf-like form. In the Chamseleons (Fig. 988)
the long and tapering tail is used as a prehensile organ, the coiling
of which round branches of the trees in which the animal, lives
aids in- maintaining the balance of the body in climbing from
branch to branch.
In the limbs there is likewise a considerable amount of varia-
tion in the different groups of the Lacertilia. Moderately long
pentadactyle limbs like those of Lacerta are the rule. In the
Chamseleons (Fig. 988) both fore- and hind-limbs become prehensile
FIG. 988. — Chamaeleon vulgaris, x
(From the Cambridge Natural History.)
by a special modification in the arrangement and mode of articula-
tion of the digits. In these remarkable arboreal Reptiles the three
innermost digits of the manus are joined together throughout
their length by a web of skin, and the two outer digits are
similarly united : the two sets of digits are so articulated that
they can be brought against one another with a grasping movement
analogous to the grasping movement of a Parrot's foot or of
the hand of Man. A similar arrangement prevails in the pes, the
only difference being that the two innermost and three outermost
digits are united. In some groups of Lacertilia, on the other hand,
such as the Blind- Worm (Anguis), limbs are entirely absent, or are
xm PHYLUM CHORDATA 329
represented only by mere vestiges ; and numerous intermediate
gradations exist between these and forms, such as Lacerta, with
well-developed limbs. The limbless Lizards (Fig. 989) bear a very
close resemblance to the Snakes, not only in the absence of the
limbs, but also in the general form of the body and the mode of
locomotion.
The body of a Snake is elongated, narrow and cylindrical,
usually tapering towards the posterior end, sometimes with, more
usually without, a constriction behind the head. In the absence
of limbs the beginning of the short caudal region is only indicated
by the position of the cloacal opening. The fore-limbs are never
represented even by vestiges ; in some Pythons there are in-
conspicuous vestiges of hind-limbs in the form of small claw-like
processes. The mouth of the Snake is capable of being very
widely opened by the free articulation of the lower jaw, and it is
FIG. 989.— Pygopus lepidopus, with scale-like vestiges of hind-limbs. (After Brehm.)
this mainly which distinguishes it from the snake-like Lizards.
But other, less conspicuous, points of distinction are the absence of
movable eyelids in the Snake, and also the want of a tympanum.
Sphenodon or Hatteria, the New Zealand Tuatara (Fig. 990), the
only living representative of the Rhynchocephalia, is a Lizard-like
Reptile with a well-developed laterally-compressed tail, and
pentadactyle extremities, very similar to those of a typical Lizard.
The upper surface is covered with small granular scales, and a
crest of compressed spine-like scales runs along the middle of the
dorsal surface. The lower surface is covered with transverse rows
of large squarish plates.
In the Chelonia (Fig. 991) the body is short and broad, enclosed
in a hard " shell " consisting of a dorsal part or carapace and a
ventral part or plastron. These are in most cases firmly united,
apertures being left between them for the head and neck, the
tail and the limbs. The neck is long and mobile ; the tail short.
330
ZOOLOGY
SECT.
xin
PHYLUM CHORDATA
331
The limbs are fully developed though short. In some (land and
fresh-water Tortoises) they are provided each with five free digits
terminating in curved horny claws ; in the Turtles the digits are
closely united together, and the limb assumes the character of
a " flipper " or swimming paddle. The cloacal aperture is longi-
tudinal.
The Crocodilia, the largest of living Reptiles, have the trunk
elongated and somewhat depressed, so that its breadth is much
greater than its height. The snout is prolonged, the neck short,
the tail longer than the body and compressed laterally. The
limbs are relatively short and powerful, with five digits in the
manus and four in the pes, those of the latter being partly or
completely united by webs of skin. The eyes are very small ;
Fia. 991.— Grecian Tortoise (Testttdo grceca). (After Brehm.)
the nostrils placed close to the end of the snout and capable of
being closed by a sphincter muscle. The cloacal aperture is a
longitudinal slit. The dorsal and ventral surfaces are covered
with thick, squarish horny scales, often pitted or ridged, those
of the dorsal surface of the tail developed into a longitudinal
crest.
Integument and Exoskeleton. — Characteristic of the Squa-
mata is the development of horny plates which cover the entire
surface, overlapping one another in an imbricating manner. These
differ considerably in form and arrangement in different groups ;
sometimes they are smooth, sometimes sculptured or keeled.
Sometimes they are similar in character over all parts of the
surface ; usually there are specially developed scales — the head
shields — covering the upper surface of the head. In the majority
of Snakes the ventral surface is covered with a row of large
transversely elongated scales, the ventral shields. In certain Lizards
332 ZOOLOGY SECT.
(Chamseleons and Geckos) the scales are reduced and modified into
the form of minute tubercles or granules. In some Lizards special
developments of the scales occur in the form of large tubercles
or spines. Underlying the horny epidermal scales in some Lizards
(Skincoids) are series of dermal bony plates. In the integument
of the Geckos are numerous minute hard bodies which are inter-
mediate in character between cartilage and bone.
In the Snake-like Amphisbsenians there are no true scales, with
the exception of the head shields, but the surface is marked out
into annular bands of squarish areas.
In addition to the modification of the scales, the integument of
the Chamseleons is remarkable for the changes of colour which it
undergoes, these changes being due to the presence in the dermis
of pigment-cells which contract or expand under the influence of
the nervous system, reminding one of the integument of the
Cephalopoda. Less conspicuous and rapid changes of colour take
place in Anguis and in some Snakes.
In the Chelonia scales, when developed, are confined to the
head and neck, the limbs and the tail ; but in all of them, with the
exception of the Soft Tortoises, both dorsal and ventral surfaces
are covered by a system of large horny plates. A series of horny
head-shields usually cover the dorsal surface of the head. Beneath
the horny plates of the dorsal and ventral surfaces are the bony
carapace and plastron, partly composed of dermal bones, but so
intimately united with elements derived from the endoskeleton
that the entire structure is best described in connection with the
latter (vide p. 335).
In the Crocodilia, the whole surface is covered with horny plates
or scales, each usually marked with a pit-like depression about the
centre, those on the dorsal surface ridged longitudinally. Underlying
each of these, which are of epidermal derivation, is a thick pad of
dermal connective-tissue which, in the case of the dorsal scales, is
replaced by a bony scute. In the Caimans thin scutes also occur
under the ventral scales.
A periodical ecdysis or casting and renewal of the outer layers
of the horny epidermis takes place in all the Reptilia with the
exception of the Crocodiles. Sometimes this occurs in a frag-
mentary manner ; but in Snakes and many Lizards the whole
comes away as a continuous slough.
Endoskeleton. - - The vertebrae are always fully ossified.
Among recent forms the Geckos and Sphenodon (Fig. 992) are
exceptional in having the centra amphiccelous with remnants of the
notochord in the intercentral spaces. The rest of the recent
groups for the most part have the centra procoelous. In many
extinct forms the neural arches are not directly attached to the
bodies by bone (temnospondyly) : in recent forms there is a bony
union (stereospondyly) either through a suture or by fusion.
xni
PHYLUM CHORDATA
333
Intercentra may be represented by intervertebral discs of fibro-
cartilage (Crocodilia) or by bony elements formed by ossification of
the ventral portions of the discs (Geckos, Sphenodon). In Lizards
in general and the Crocodiles there are inferior processes (hypapo-
physes], perhaps representing intercentra, situated below the centra
in the anterior cervical region. Chevron bones (inferior arches)
occur in the caudal region of many Reptiles (Sphenodon, Lacertilia,
Crocodilia).
In the Snakes and in Iguanas, in addition to the ordinary
articulating processes or zygapophyses, there are peculiar articular
surfaces termed zygosphenes and zygantra (Fig. 993). The zygo-
sphene is a wedge-like process projecting forwards from the anterior
face of the neural arch of the vertebra, and fitting, when the vertebrae
are in their natural positions, into a depression of corresponding
•II. S.
/it. 5.
FIG. 992. — Vertebra
of Sphenodon,
showing the amphi-
coelous centrum (C.).
(After Headley.)
FIG. 993. — Vertebra of Python, anterior and posterior views, n. s.
neural spine ; p. z. prezygapophyses ;] pt. z. post-zygapophysis :
t. -p. transverse processes; z. [a. zygantrum ; z.s. zygosphene.
(After Huxley.)
form — the zygantrum — on the posterior face of the neural arch
of the vertebra in front. To this arrangement, as well as to the
deeply concavo-convex centra, the extraordinary flexibility and
strength of a Snake's back-bone are due.
The various regions of the spinal column are well marked in
most of the Lizards, in the Rhynchocephalia, in the Chelonia, and
in the Crocodilia (Fig. 994). In the Snakes and many of the
snake-like Lizards only two regions are distinguishable — pre-caudal
and caudal. In the others there is a sacral region comprising
usually two vertebrae, both of which have strong processes (sacral
ribs) for articulation with the ilia. The first and second vertebrae
are always modified to form an atlas and axis : in the Lacertilia
and Chelonia the latter has a distinct odontoid process. In
Chamaeleons, Sphenodon, and the Crocodiles there is a median bone,
the pro-atlas (Fig. 996, 0), intercalated between the atlas and the
occipital region of the skull.
Ribs are developed in connection with all the vertebrae of the
pre-sacral or pre-caudal region ; in the caudal region they are
33 1
ZOOLOGY
SECT.
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PHYLUM CHORDATA
335
usually replaced by inferior arches ; but Sphenodon, the Chelonia,
and Crocodilia have caudal ribs which become fused with the
vertebrae. In the Lacertilia only a small number (three or four) of
the most anterior of the thoracic ribs are connected with the
sternum by cartilaginous sternal ribs ; the rest are free, or are
connected together into continuous hoops across the middle line.
In the so-called Flying Lizards (Draco) a number of the ribs are
greatly produced, and support a pair of wide flaps of skin at the
sides of the body, acting as wings, or rather as parachutes. In
Sphenodon (Fig. 995) and Crocodilia (Fig. 994) each rib has con-
nected with it posteriorly a flattened curved cartilage, the uncinate.
In the Chelonia (Fig. 997) the total number of vertebrae is always
smaller than in the members of the other orders. The cervical
ribs are small and fused with the vertebrae. The cervical and the
caudal are the only
regions in which the
vertebrae are movable
upon one another. The
vertebrae of the trunk,
usually ten in number,
are immovably united
with one another by
means of fibre-cartila-
ginous intervertebral
discs. Each of the
neural spines, from the
second to the ninth in-
clusively, is flattened
and fused with a flat
plate of dermal origin,
the neural plate (Fig.
998), and the row of plates thus formed constitutes the median
portion of the carapace. The ribs are likewise immovable ; a short
distance from its origin each passes into a large bony dermal costal
plate, and the series of costal plates uniting by their edges form a
large part of the carapace on either side of the row of neural plates.
The carapace is made up of the neural and costal plates supple-
mented by a row of marginal plates (Figs. 997 and 998) running
along the edge, and nuchal and pygal plates situated respectively in
front of and behind the row of neural plates. In some cases the
neural plates (Chelodina) and even the costal plates and ribs
(Testudo loveridgii) are absent.
The bony elements of the plastron of the Chelonia are an anterior
and median plate (entoplastron) and four pairs of plates which
are termed in their order from before backwards epiplastra, hyo-
plastra, hypoplastra, and xiphiplastra. The median element
probably corresponds to the interclavicle or episternum of other
Po
FIG. 996. — Anterior vertebrae of young Crocodile.
A. atlas ; Ep. axis ; h. articulation of atlas wita
axis ; IS. intervertebral discs ; o. pro-atlas ; Ob.
neural arches ; Po. odontoid bone ; Ps. neural spines ;
Pt. transverse processes ; R, R,1 R,2 ribs ; s. arch
of atlas ; u. median piece of atlas ; WK. centra.
(From Wiedersheim's Comparative Anatomy.)
336
ZOOLOGY
SECT.
Reptiles, the first pair (epiplastra) to the clavicles, the others pro-
bably being of the same character as the abdominal ribs of the
Crocodilia.
The carapace of
the Luth or
Leather- backed
Turtle (Dermato-
chelys orSphargis)
is distinguished
from that of the
rest of the order
in being composed
of numerous poly-
gonal discs of bone
firmly united to-
gether, and in not
being connected
with the endo-
skeleton ; in the
plastron the
median bone is
absent.
Carapace and
plastron are firmly
fixed together by
bony union in
FIG. 997. — Cistudo lutaria. Skeleton seen from below ; the \ • ,
plastron has been removed and is represented on one side, m O S t instances,
C. costal plate; Co. coracoid ; e. entoplastron (episternum) ; V>nf onTYiafimac! fV.o
Ep. epiplastron (clavicle ?) ; F. fibula ;Fe. femur ; H. humerus ;
Hyp. hyoplastron ; Hpp. hypoplastron ; Jl. ilium ; Js. ischium ; connection is liffa-
M. marginal plates ; Nu. nuchal plate ; Pb. pubis ; Pro. pro-
coracoid or process of scapula ; PH. pygal plates ; R. radius ; So.
; T-
mentous.
The sternum in
the Lacertilia is a
plate of cartilage with a simple or bifid posterior continuation
formed by the fusion of five or six pairs of ribs. In the Ophidia
and Chelonia it is absent. ~
In the Crocodilia it is a
broad plate bearing the
coracoids and two pairs of
ribs with a posterior con-
tinuation which bifurcates
behind.
A series of ossifications
—the abdominal ribs — lie
the wall of the ab-
n
FiG. 993. — Chelone midas. Transverse section of
skeleton. C. costal plate ; C'.1 centrum ; M. mar-
ginal plate ; P. lateral element of plastron ; R. rib
V. expanded neural plate. (After Huxley.)
domen in the Crocodilia
(Fig. 994, Sta), and similar ossifications occur also in the Moni-
Sphenodon, As already noticed, the posterior
tors and in
xm
PHYLUM OHORDATA
337
elements of the plastron of the Chelonia are probably of a similar
character.
In the skull ossification is much more complete than in the
Amphibia, the primary chondrocranium persisting to a considerable
extent only in some Lizards and in Sphenodon ; and the number
of bones is much greater. The parasphenoid is reduced, and its
place is taken by the large basioccipital, basisphenoid, and pre-
sphenoid.
A fairly typical Lacertilian skull has been described in the case
of Lacerta. Its principal characteristic features are the presence of
B
Four
FlG. 990. — Skull of C'ulubriiH' Snake (Tropidonotus natrix). A, from above ; B, from below
Ag. angular ; Art. articular ; Bp. basi-occipital ; Bs. basi-sphenoid ; Ch. internal nares ;
Coco, occipital conclyle ; Dt. dentary ; Eth. ethmoid ; F. frontal ; F'. post-orbital ; Fov.
fenestra ovalis ; J/. maxilla ; N. nasal ; 01. exoccipital ; Osp. supra-occipital ; P. parietal ;
Pe. periotic ; P. f. pre-frontal ; PI. palatine ; Pmx. premaxilla; Pt. pterygoid; Qu.
quadrate; SA. supra-angular; Sgu. squamosal: Ts. transverse; Vo. vomer ; //, optic
foramen. (From Wiedersheim's Comparative Anatomy.)
an inter-orbital septum, the presence of the epipterygoid, and the
mobility of the quadrate. The last of these features it shares with
that of the Ophidia. The epipterygoid is not universal in the
Lacertilia, being absent in the Geckos, the Amphisbsenians, and the
Chamseleons. The quadrate is not always movable. The skull of
the Chamseleons has a remarkable helmet-like appearance owing to
the development of processes of the squamosal and occipital regions,
which unite above the posterior part of the cranial roof. The skull
of the Amphisbsenians differs from that of other Lacertilia and
approaches that of Snakes in the absence of an inter-orbital septum.
In the skull of the Ophidia (Fig. 999) orbitosphenoidal and
338
ZOOLOGY
SECT.
alisphenoidal elements are absent, their places being taken by
downward prolongations of the parietals and frontals. In the
substance of the mesethmoid are two cartilaginous tracts (Fig.
1000, B, T) which are the persistent trabeculse of the embryonic skull.
The inter-orbital septum is absent, and the cranial cavity is pro-
longed forwards to the ethmoidal region. Neither upper nor
lower temporal arches are present. The palatines (PI) are movably
articulated with the base of the skull ; as in the Lizards, they are
widely separated from one another, and do not develop palatine
plates. They are movably articulated behind with the pterygoids
(Pt), and the latter,_through the intermediation of the slender
transverse bones
(Ts), with the
maxillae. The pre-
maxillse are very
small (in some
venomous Snakes
entirely absent),
and when present
usually fused to-
gether. The
maxillse (Mx), usu-
ally short, articu-
late by means of
a movable hinge-
point with the
conjoined lacry-
mal and p re-
front a 1 (La),
which, in turn, is
movably con-
nected with the
frontal. The long
and slender quad-
rate (Qu) is freely articulated with the posterior end of the elongated
squamosal. The rami of the mandible, likewise long and slender,
are not united anteriorly in a symphysis, but are connected together
merely by elastic ligamentous tissue, so that, when the mouth of
the Snake is opened to allow of the entry of the relatively large
prey, which it swallows whole, they are capable of being widely
separated from one another. The Typhlopidae differ from the
rest of the Ophidia in having the maxilla immobile, the quadrate
more closely connected with the skull, and the rami of the mandible
united by a fibro-cartilaginous symphysis.
The skull of Sphenodon (Fig. 1001) differs very considerably
from that of the Lizards. There is a large supra-temporal fossa
bounded by the parietal, post-orbital (Pt. /), and squamosal, and
FIG. 1000.— A, lateral view of skull of Rattlesnake (Crotalus)
£. O. basi-occipital ; B. S. basi-sphenoid ; E. O. exoccipital ;
F. 0. fenestra ovalis ; La. conjoined lacrymal and pre-frontal ;
L. f. articulation between lacrymal and frontal ; Mn. mandible ;
MX. maxilla ; Na. nasal ; PL palatine ; Pmp. premaxilla ;
P. Sph. presphenoid ; Pt. pterygoicl ; Qu. quadrate ; Sg. squa-
mosal ; //, V, foramina of exit of the second and fifth cranial
nerves. B, transverse section at point lettered B in Fig. A ; T.
trabeculse. (After Huxley.)
XIII
PHYLUM CHORDATA
339
separated below by a bar of bone (superior temporal arch], formed
of processes of the two last-mentioned bones and of the post-
frontal, from a still larger space — the lateral temporal fossa. The
latter is bounded below by a slender bony bar (the inferior temporal
arch), formed of the long narrow jugal (Jug), with a small quad-
Pmx
Prf
FIG. 1001.— Skull ofkSphenodon. A, dorsal ; B, ventral ; C, left-sided view of skull of
Sphenodon, x 3. Col. Columella auris ; Cond. occipital condyle ; E. P. ectopterygoid ;
F. frontal ; Jug. jugal ; Max. maxilla ; iVa. nasal ; No. anterior nasal opening ; Pal.
palatine ; Par. parietal ; Pmx. premaxilla ; Prf. pre-frontal ; Pt. f. post-frontal and post-
orbital ; Pig. pterygoid or endopterygoid ; Q. quadrate and quadrato-jugal (paraquadrate) ;
Sq. squamosal ; Vo. vomer. (From the Cambridge Natural History.)
rato- jugal or paraquadrate, by which the jugal is connected with
the quadrate (Q). The lateral temporal fossa is separated from
the orbit in front by a bar of bone formed of the jugal and post-
orbital, and is bounded behind by a posterior temporal arch formed
of the parietal and squamosal. The quadrate (Qu) is immovably
fixed, wedged in by the quadrato-jugal, squamosal and pterygoid.
The prernaxillaB (Pmx) are not fused together, but separated by
340
ZOOLOGY
SECT.
a suture. There is a broad palate formed by the plate-like vomers,
palatines, and pterygoids.
In the Chelonia (Figs. 1002, 1003) all the bones, including the
quadrate, are solidly connected together. Transverse bones
(ectopterygoids), lacrynials, orbitosphenoids and alisphenoids are
absent. The place of alisphenoids is taken to a certain extent
by vertical downward plate-like extensions of the parietals, the
lower part of the plates perhaps representing the epipterygoids of
Lizards. There may be open temporal fossae, the inferior boundary
of which (inferior temporal arch] may be incomplete owing to the
absence of the quadrato-jugal (paraquadrate), or the entire temporal
region may be covered over (Turtles, Fig. 1003) by a sort of false roof
formed of expansions of the post-f rentals (ph), parietals (par), and
.^ squamosals (sq.)
P —osp with the jugal (/)
and quadrato-jugal
(q.j). The immov-
ably fixed quad-
rates (Fig. 1003,
qu, and Fig. 1002, q)
are modified to
afford a part or the
whole of the rim for
the support of the
tympanic mem-
brane. The occi-
pital condyle is
FIG. 1002. — Lateral view of skull of Emys europaea. Coc. , -i i j
occipital condyle; F. frontal; F*. post-frontal; /.foramen Sometimes tnlODeCt.
by which the olfactory nerve enters the orbit ; lug. jugal; Tjip vompr (ifi IS lin-
37. maxilla; Md. mandible; Mt. tympanic membrane; \ >
Na. external nares ; 01. exoccipital ; Osp. supra-occipital ; paired. The pala-
P. parietal ; Pf. pre-frontal ; Pmx. pre-maxilla ; Qjg. £. ,' 7.
quadrato-jugal ; Qu. quadrate ; Si. inter-orbital septum ; tines (pal) are ap-
Squ. squamosal ; Vo. vomer. (From Wiedersheim's Com- r.T,ri,,;rnQforl „ A
parative Anatomy.)
give off palatine
plates, which for a short distance cut off a nasal passage from the
cavity of the mouth. Nasals are usually absent as separate bones.
The premaxillse are very small. The rami of the mandibles are
stout, and are firmly united together at the symphysis.
In the Crocodiles (Figs. 1004, 1005), as in the Chelonia, the
quadrate (Qu) is firmly united with the other bones of the skull.
There is a membranous and cartilaginous inter- orbital septum.
There are no distinct orbitosphenoids, but alisphenoids are well
developed. The orbit is separated from the lateral temporal
fossa by a stout bar situated somewhat below the surface, and
formed of processes from the post-frontal, jugal and ectopterygoid.
The lateral temporal fossa is bounded below, as in Sphenodon,
by an inferior temporal arch composed of jugal and quadrato-
jugal (paraquadrate). The frontals are early united into one,
xin
PHYLUM CHORDATA
341
and the same holds good of the parietals. Both palatine (PI)
and pterygoid (Pt), as well as maxillse, develop palatine plates
in the roof of the mouth, cutting off a nasal passage of great length
from the cavity of the mouth, the posterior nares (ch) being situated
far back towards the posterior end of the cranial base. The nature
Kin. 1003. — Ventral view of the skull of Chelone mydas. bs. basi-sphenoid ; Jr. frontal;
j. jugal ; m. maxilla ; ob. basi-occipital ; ol. exoccipital ; op. opisthotic ; os. supra-occipital ;
pal. palatine ; par. parietal ; ph, post-frontal ; prfr. pie-frontal ; pt. pterygoid ; prm. pre-
rnaxilla ; q. quadrate ; qj. quadrato-jugal ; sq. squamosal ; v . vomer. (After Hoffmann.)
of the articulation between the mandible and the quadrate is
such that movement is restricted to the vertical plane, and lateral
displacement is further provided against by the development of
a broad process of the pterygoid against which the inner surface
of the mandibular ramus plays, an arrangement which occurs also
in most Lacertilia.
VOL. IT Y
342
ZOOLOGY
SECT.
In accordance with their purely aerial mode of respiration, the
visceral arches are much more reduced in the Reptilia than in the
Amphibia in general. The only well-developed post-mandibular
arch is the hyoid, and even this may undergo considerable reduction
(Ophidia). The branchial arches are greatly reduced or aborted
in the adult.
There is little variation in the structure of the limb-arches
,T
FIG. 1004. — Skull of Crocodilus porosus,
dorsal view, x about \. Col. buttress
connecting the post-frontal with the jugal
and ectopterygoid ; F. frontal ; Jg. jugal ;
MX. maxilla ; N-a. nasal ; P. parietal ;
Pm. premaxilla ; Po. f. post-frontal ;
Pr. f. pre-frontal ; Q. quadrate ; Qj.
quadrato-jugal ; R. characteristic ridge
on the pre-frontal bone ; Sg. squamosal ;
T. perforation in the premaxilla caused
by a pair of lower incisor teeth. (After
Gadow.)
C&ce
FIG. 1005. — Ventral view of the skull
of young Crocodile. Ch, posterior
nares ; Coco, occipital condyle ; Jg.
jugal ; M. maxilla (palatine pro-
cess) ; Ob. basi-occipital ; Orb.
orbit ; PL palatine ; Pmx. pre-
maxillae ; Pt. pterygoid ; Qj. quad-
rato-jugal ; Qu. quadrate. (From
Wiedersheim's Comparative Ana-
tomy.)
and skeleton of the limbs in the different groups of Lacertilia.
The pelvic arch is distinguished in the Lacertilia in general by
its slender character ; and the pubes and ischia are, as in
fact is the case throughout the class, separated from one
another by wide ischio-pubic foramina — a feature which markedly
distinguishes the reptilian pelvis from that of the Amphibia. In
limbless forms the pectoral arch may be present or may be absent.
In the Ophidia all trace of limbs is, as a rule, absent ; but in some
xin
PHYLUM CHORDATA
343
.r
FIG. 1006.— Tarsus of Emys europaea
(right side) from above. F. fibula ; T.
tibia ; (£.)/. t. c. the united tarsals of the
proximal row ; Ph'. first phalanx of the
fifth digit ; 1—4, distal tarsals ; /— V,
metatarsals. (From Wiedersheim's Com-
parative Anatomy.)
There are three distal
Pythons vestiges of hind-limbs are to be detected in the form of
two or three small bones which support a small horny claw.
In Sphenodon (Fig. 995) there
is a foramen above the outer
and one above the inner condyle
of the humerus. There are eleven
carpal elements, of which there are
four, including a pisiform, in the
proximal row, two centrals, and
five in the distal row. The pubes
are united in a symphysis, in front
of which is a cartilaginous epipubis.
A large oval foramen intervenes
between the ischium and the pubis.
A cartilaginous hypo-ischium is
attached to the ischia behind. In
the tarsus the tibial and fibular
elements are distinct, though firmly
united. The intermedium and the
centrale are firmly fixed to the tibiale.
tarsal bones.
In the Chelonia (Fig. 997) the interclavicle (episternum) and
clavicles are absent, unless, as is probable, the former be represented
by the median element of the plastron and the latter by the first
lateral pair. The entire pectoral arch is a
tri-radiate structure of which the most
ventral and posterior ray, ending in a free
extremity, is the coracoid ; while the other
two are the scapula and a process, sometimes
regarded as representing the procoracoid,
given off on the inner side of the scapula
near its glenoid end. The bones of the
carpus have nearly the typical arrangement,
consisting, as in Lizards, of a proximal row
of three, a distal row of five, and a centrale
between the two. The pelvis resembles
that of Lacertilia, except that it is broader
Both pubes and ischia meet
in ventral symphyses, and epipubic and
IsVot yet hypo-ischial cartilages may be present. In
the tarsus (Fig. 1006) there is usually a
t, pisiform; i—v,' the five single proximal bone and four distalia.
metacarpals. (From Wied- mi. j_i 11
ersheim's Comparative Ana- inere are never more tnan two phalanges in
any of the digits.
In the Crocodilia also the clavicle is absent, but there is an epis-
ternum. The number of carpal elements is reduced, the largest
being two proximal bones, the radiale and the ulnare (Fig. 1007, r, u).
Y 2
R u
FIG. loo?.— Carpus of young and shorter.
Alligator. C. centrale (?) ;
-R. radius ; U. ulna ; r. ra-
344
ZOOLOGY
SECT.
On the ulnar side of the latter is a small accessory bone (pisiform,^).
The pelvic arch (Fig. 1008) differs somewhat widely from that of
other living Reptiles, and the parts have been variously interpreted.
Two bones (P), which are usually regarded as the pubes, extend
from the region of the acetabula forwards and inwards, but, though
they become closely approximated anteriorly, do not meet in a
symphysis. Between and in front of their anterior extremities,
which are tipped with cartilage, extends a membrane (M) with
which are connected in front the last pair of abdominal ribs (BR).
The posterior ends of the pubes are cut off from the acetabulum
by the interposition of a pair
of bones which may be parts of
the ilia, but are separately ossi-
7/ \!k^J fied. The ischia extend down-
wards and somewhat back-
wards from the acetabula and
are fixed together ventrally
(at Sy.), but there is no true
symphysis, as their extremities
remain cartilaginous. A hypo-
ischium is not present. In
the tarsus (Fig. 1009) there
are two proximal bones — an
JSR
FIG. 1008.— Pelvis of young Alligator, ven-
tral aspect. B, fibrous band passing be-
tween the pubic and ischiatic symphyses ;
BR. last pair of abdominal ribs ; F. obtu-
rator foramen ; O. acetabulum ; //. ilium ;
Is. ischium ; M. fibrous membrane be-
tween the anterior ends of the two innomi-
nate bones and the last pair of abdominal
ribs ; P. pubis ; Sy. ischiatic symphysis ;
/, //, first and second sacral vertebrae.
(From Wiedersheim's Comparative Ana-
tomy.)
FIG. 1009.— Tarsus of Crocodile (righ .
side) from above. F. fibula ; T. tibia ;
t. i. c. the astragalus, formed of the united
tibiale, intermedium and centrale ; /.
fibulare (calcaneum) ; 1 — 3, united first,
second and third distal tarsals ; 4, fourth
tarsal ; I — IV, first to fourth metatarsals ;
VI, fifth distal tarsal and fifth meta-
tarsal. (From Wiedersheim's Compara-
tive Anatomy.)
astragalo-scaphoid and a calcaneum — the latter having a prominent
calcaneal process, and two distal tarsal bones, together with a
thin plate of cartilage supporting the first and second meta-
tarsals. The missing fifth digit is represented by a rudimentary
metatarsal.
xin PHYLUM CHORDATA 345
Digestive Organs. — The form and arrangement of the teeth
already described in the account of Lacerta prevail in the majority
of Lizards. In some of them the palatine teeth are absent. The
teeth are sometimes fixed by their bases to the summit of the
ridge of the jaw (acrodont forms), sometimes fixed by their sides
to the lateral surface of the ridge (pleurodont) ; they are never
embedded in sockets in any recent form. A Mexican Lizard,
Heloderma, differs from all the rest in having teeth which are
grooved for the ducts of poison-glands. In the Snakes (Figs. 999,
1000) teeth are rarely developed on the premaxillee, but are present
on the maxillae, palatines and pterygoids, as well as the dentary of
the mandible. They may be of the same character throughout,
solid, elongated, sharp-pointed teeth, which are usually strongly
recurved, so that they have the character of sharp hooks, their
function being to hold the prey and prevent it slipping from
the mouth while being swallowed, — not to masticate it. Non-
venomous Snakes possess only teeth of this character. In the
venomous Snakes more or fewer of the maxillary teeth assume
the character of poison-fangs. These are usually much larger
than the ordinary teeth and either grooved or perforated by a
canal for the passage of the duct of the poison-gland. In the
Vipers (Fig. 1000) there is a single large curved poison-fang with
small reserve-fangs at its base, these being the only teeth borne
by the maxilla, which is very short ; in the venomous Colubrine
Snakes the poison-fangs are either the most anterior or the most
posterior of a considerable range of maxillary teeth. In the Vipers
the large poison-fang is capable of being rotated through a con-
siderable angle, and moved from a nearly horizontal position, in
which it lies along the roof of the mouth embedded in folds of the
mucous membrane, to a nearly vertical one, when the Snake opens
its mouth to strike its prey. The rotation of the maxilla is brought
about by the backward or forward movement of the pterygoid
with the palatine and transverse. In Sphenodon (Fig. 1001)
there are pointed, triangular, laterally-compressed teeth, arranged
in two parallel rows, one along the maxilla, the other along the
palatine. The teeth of the lower jaw, which are of similar character,
bite in between these two upper rows, all the rows becoming worn
down in the adult in such a way as to form continuous ridges.
Each premaxilla bears a prominent, chisel-shaped incisor, repre-
sented in the young animal by two pointed teeth. In the young
Hatteria a tooth has been found on each vomer — a condition
exceptional among Reptiles. In the Chelonia, teeth are entirely
absent, the jaws being invested in a horny layer in such a way
as to form a structure like a Bird's beak. The Crocodilia have
numerous teeth which are confined to the premaxillae, the maxillae,
and the dentary. They are large, conical, hollow teeth devoid
of roots, each lodged in its socket or alveolus (thecodont), and each
346
ZOOLOGY
SECT.
becoming replaced, when worn out, by a successor developed on
its inner side.
A bifid tongue like that of Lacerta occurs in several families of
Lacertilia. Others have a thick, short tongue, undivided in front
and often provided with two long appendages behind. The
Monitors (Fig. 1010, A) have forked retractile tongues like those
of Snakes. The tongue of the Chamseleons is an extremely
remarkable organ ; it is of sub-cylindrical form with an enlarged
extremity, and is so extensile that it is capable of being darted
out to a distance sometimes equalling, or even exceeding, the
length of the trunk ; this protrusion can be effected with lightning-
like rapidity ; and it is in this way that the animal catches the
Insects which constitute its food. The tongue in Snakes is slender
I
c
B
FIG. 1010.— A, tongue of Monitor indicus. B, tongue of Emys europaea. C, tongue
S£. ^"Sator. L, glottis ; M, mandible ; Z, tongue ; ZS, tongue-sheath. (From
Wiedersheim s Comparative Anatomy.)
and bifid, capable of being retracted into a basal sheath, and
highly sensitive, being used chiefly as a tactile organ. The tongue
of the Crocodilia (C) is a thick, immobile mass extending between
the rami of the mandible. In some of the Chelonia (B) the tongue
is immobile ; in others it is protrusible, sometimes bifid.
In the enteric canal of the Reptiles the principal special features
to be noticed are the muscular gizzard-like stomach of the Croco-
dilia, the presence of a rudimentary caecum at the junction of
small and large intestines in most Lacertilia and in the Ophidia,
and the presence of numerous large cornified papillee in the
oesophagus of the Turtles.
Organs of Respiration.— The Reptiles all have an elongated
trachea, the wall of which is supported by numerous cartilaginous
rings. The anterior part of this is dilated to form the larynx,
the wall of which is supported by certain special cartilages— the
xm
PHYLUM CHORDATA
347
T
cricoid and the arytenoids. The trachea bifurcates posteriorly to
form two bronchi, right and left, one passing to each lung. The
lungs of the Lacertilia and Ophidia
are of the simple sac-like character
already described in the case of the
Lizard. In some the lung is incom-
pletely divided internally into two
portions — an anterior respiratory
part with sacculated walls, and a
posterior part with smooth, not
highly vascular, walls, having mainly
the function of a reservoir. The
only additional complication to be
specially noted is the presence in the
Chamseleons (Fig. 1011) of a number
of diverticula or air-sacs which are
capable of being inflated, causing
an increase in the bulk of the
animal which doubtless has an
effect on assailants. In the snake-
like Lizards the right lung is larger
than the left, and in the Amphis-
bsenians the latter is entirely
aborted. In the Snakes a similar
reduction or abortion of the left
lung is observable. In the Cro-
codilia and Chelonia the lungs are
of a more complex character, being
divided internally by septa into a
number of chambers.
Organs of Circulation. — In the
heart (Fig. 1012) the sinus venosus
is always present, though not, except
in Sphenodon, distinguishable ex-
ternally ; its aperture of commu-
nication with the right auricle is
guarded by two valves. There are,
as in the Amphibia, always two
quite distinct auricles, the right
receiving the venous blood from
the body, the left the oxygenated
blood brought from the lungs by
the pulmonary veins. But a vital
point of difference between the
heart of the Reptile and that of
the Amphibian is that in the former the ventricle is always more
or less completely divided into right and left portions. In all
FIQ. 1011. — Lungs of Chamaeleon.
T. trachea. (From Wiedersheim's Com-
parative Anatomy.)
348
ZOOLOGY
SECT
-As
1
the Lacertilia, Ophidia, and Chelonia (Fig. 1013) the structure is
essentially what has been described in Lacerta, the ventricular
septum being well-developed, but not completely closing off the
left-hand portion of the
cavity of the ventricle
from the right (cavum pul-
monale). The left-hand
portion, which is much the
larger, is further imperfectly
divided into two parts — the
cavum arteriosum on the
left and the cavum venosum
on the right — by the two
elongated flaps of the
auriculo-ventricular valve,
which project freely into
the cavity of the ventricle.
From the cavum pulmonale
arises the pulmonary artery,
and from the cavum
venosum the right and left
aortic arches. When the
auricles contract the cavum
venosum becomes filled with
venous blood from the right
auricle, the cavum arteriosum with arterial blood from the left
auricle ; the cavum pulmonale becomes filled with venous blood
which flows into it past the edges
of the incomplete septum. When
the ventricle contracts, its walls
come in contact with the edge of
the septum, and the cavum pul-
monale is thus cut off from the
rest of the ventricle. The further
contraction consequently results in -&
the venous blood of the cavum
pulmonale being driven out through
the pulmonary artery to the lungs,
while the blood which remains in
the ventricle (arterial and mixed)
is compelled to pass out through the
aorta. But in the Crocodilia (Fig.
1014) the cavity is completely
divided, so that there we may speak
of distinct right and left ventricles.
From the right arises the pulmonary artery and the left aortic
arch : from the left the right aortic arch only. The right and left
—Ac
FIG. 1012. — Heart of Lacerta muralis, ventral
view. A, A. auricles ; Ap. pulmonary artery ;
As, As1, subclavian arteries ; Ci, post-caval ; J.
jugular vein ; Ra, aortic arches (made up on
either side of two embryonic arches, 1 and 2) ;
tr, aortic root ; V. ventricle ; Vp, pulmonary
vein ; Vs, subclavian vein. (From Wiedersheim's
Comparative Anatomy.')
J.AO
Jt.'Ao.
P.A
cavum pulmonale ; C.f. cavum veno-
sum ; L. A. left auricle ; L. Ao. left
aortic arch ; P. A. pulmonary artery ;
R. A. right auricle ; R. Ao. right aortic
arch ; s, arrow showing the course of
blood in left aorta ; t, in right aorta ;
f ., v' . auriculo-ventricular valves ; w,
arrow showing the course of blood in
left auriculo-ventricular aperture ; x, in
right ; y, between cavum venosum and
cavum pulmonale ; z, in pulmonary
artery. (After Huxley.)
xra
PHYLUM CHORDATA
349
r.cttf
I .aur.ve.nl a f>
arches cross one another, and where their walls are in contact
is an aperture — -the foramen Panizzce — placing their cavities in
communication.
The brain of Reptiles is somewhat more highly organised than
that of the Amphibia. The brain substance of the cerebral
hemispheres exhibits a distinction into superficial grey layer or
cortex containing pyramidal nerve-cells, and central white medulla,
not observable in lower groups. The cerebral hemispheres are
well developed in all, and there is a hippocampus (see below in
the description of the brain of the Rabbit, and of that of the
Mammals in general) in the shape of a specially modified region
of the dorsal and mesial walls of each hemisphere, represented
less distinctly in the Amphibia ; a commissure — the hippocampal—
connects the hippo-
campi of opposite sides,
and is dorsal to the
chief cerebral commis-
sure — the anterior com-
missure. The mid-brain
consists dorsally usually
of two closely-approxi-
mated oval optic lobes ;
rarely it is divided
superficially into four.
The cerebellum is always
of small size, except in
the Crocodilia (Fig.
1015), in which it is
Comparatively highly Fio 1014 _Heart of crocodile with the principal arteries
developed, and Consists (diagrammatic). The arrows show the direction of the
/. -i • j i
OI a median and tWO
lafpral lr>T-ip«
'"S-
SenSOrV Organs. _
J V,. ,"
111 most Lacertllia, but
not in the Ophidia, the
nasal cavity consists of two parts — an outer or vestibule, and
an inner or olfactory chamber — the latter having the sense-cells
in its walls, and containing a turbinal bone. In the Turtles each
nasal chamber is divided into two passages, an upper and a lower,
and the same holds good of the hinder part of the elongated nasal
chamber of the Crocodilia.
Jacobson's organs (Fig. 983) are present in Lizards and Snakes,
absent in Chelonia and Crocodilia in the adult condition.
The eyes are relatively large, with a cartilaginous sclerotic in
which a ring of bony plates (Fig. 984) is developed in some cases.
The muscular fibres of the iris are striated. A pecten is present
in most. Most Reptiles have both upper and lower eyelids and
arterial and venous currents. I. aort. left aortic arch ;
;. aur. left auricle ; I. am. vent. ap. left auriculo-ventri-
cular aperture ; I. car. left carotid ; /. sub. left subclavian ;
1. vent, left ventricle ; pul. art. pulmonary artery ; r. aort.
right aortic arch ; r. aur. right auricle ; r. aur. vent. ap.
right auriculo-ventricular aperture ; r. car. right carotid ;
r. sub. right subclavian ; r. vent, right ventricle. (From
350
ZOOLOGY
SECT.
—B.ot.
a nictitating membrane. The greater number of the Geckos and all
the Snakes constitute exceptions, movable eyelids being absent
in both of these groups ; in the former the integument passes
uninterruptedly over the cornea with a transparent spot for the
admission of the light ; in the Snakes there is a similar modification,
but the study of development shows
that the transparent area is derived
from the nictitating membrane
which becomes drawn over the
cornea and permanently fixed. In
the Chamaeleons there is a single
circular eyelid with a central
aperture.
The middle ear is absent in the
Snakes, though a columella auris
is present, embedded in muscular
and fibrous tissue and attached
externally, in some cases at least,
to the middle of the quadrate.
Developed in close relation to
the epiphysis there is in many
Lizards (Lacerta, Varanus, Anguis,
Amphibolurus and others), and in
Sphenodon, a remarkable eye-like
organ — the parietal organ or pineal
eye (Fig. 1016), which is situated
in the parietal foramen of the
cranial roof immediately under
the integument, and covered over
by a specially modified, transparent
scale. The pineal eye is developed
from a hollow outgrowth of the
roof of the diencephalon in front of
the epiphysis ; the distal end of
this becomes constricted off as a
hollow sphere, while the remainder
is converted into a nerve. The
wall of the hollow sphere becomes
divergently modified on opposite
sides ; the distal side gives rise to
a lens-like thickening (I), the
proximal forms a membrane several layers in thickness — the
retina (r.) : the whole is enclosed in a capsule of connective-tissue
(k). The nerve usually degenerates before the animal reaches
maturity, so that the organ would appear — though evidently, from
its structure, an organ of sight — to have now entirely or nearly
lost its function.
Met
FIG. 1015. — Brain of Alligator, from
above. B. ol. olfactory bulb ; O. p. epi-
physis ; HH, cerebellum ; Mcd, spinal
cord ; MH, optic lobes ; NH, medulla
oblougata ; VH, cerebral hemispheres ;
/ — XI, cerebral nerves ; 1, 2, first and
second spinal nerves. (From Wieders-
heim's Comparative Anatomy.)
xm
PHYLUM CHORDATA
351
Reproductive Organs. — The description already given of the
reproductive organs of the Lizard (p. 323) applies, so far as all
the leading features are concerned, to all the Lacertilia and to
the Ophidia ; in Hatteria the copulatory sacs are absent.
In the Crocodilia and Chelonia, instead of the copulatory sacs,
there is a median solid penis attached to the wall of the cloaca,
and a small process or clitoris occurs in a corresponding position
in the female. Though fertilisation is always internal, most
Reptilia are oviparous, laying eggs enclosed in a tough, parchment-
like or calcified
shell. These are
usually deposited in
holes and left to
hatch by the heat
of the sun. In
the Crocodiles they
are laid in a
rough nest and
guarded by the
mother. In all
cases development
has only progressed
to a very early stage
when the deposition
of the eggs takes
place, and it is only
after a more or less
prolonged period of
incubation that the
young, fully formed
in every respect,
emerge from the
shell and shift for
themselves.
Many Lizards,
X
'\A N
.._... V-L>
_,: ,
however and most FlG- 1016- — Section of the pineal eye of Sphenodon punc-
tatum. g, blood-vessels ; h, cavity of the eye filled with
fluid ; k, capsule of connective-tissue ; I. lens ; m. molecular
layer of the retina ; r. retina ; st. stalk of the pineal eye ;
x, cells in the stalk. (From Wiedersheim's Comparative
Anatomy, after Baldwin Spencer.)
are vivi-
Snakes
parous, the ova
undergoing develop-
ment in the interior of the oviduct, and the young reaching the
exterior in the completely-formed condition.
Development.— In all the Reptilia the segmentation is
meroblastic, being confined to a germinal disc of protoplasm
situated on one side of the yolk. This divides to form a patch
of cells which gradually extends as a two-layered sheet, the blasto-
derm, over the surface of the ovum. The upper of the two layers
is the ectoderm., the lower the yolk-endoderm ; the latter is the
352
ZOOLOGY
SECT.
equivalent of the mass of yolk-cells of the Frog, and the shallow
space between it and the yolk represents the segmentation-cavity.
As the blastoderm extends (Fig. 1017), it becomes distinguishable
into a central clearer area — area pellucida (a. pel.) — and a peripheral
FIG. 1017. — A — D, early stages in the development of the Alligator. A, stage with em-
bryonic shield, primitive knot and blastopore ; B, considerably later stage in which the
medullary groove has become formed, together with the head-fold of the embryo and the
head-fold of the amnion ; C, somewhat later stage with well-developed medullary folds and
medullary groove ; D, later stage in which the medullary groove has become partly closed
in by the medullary folds and in which six pairs of protovertebrse have become developed.
amn. amnion ; a. op. area opaca ; a. pel. area pellucida ; blp. blastopore ; emb. s. embryonic
shield ; /. br. fore-brain ; h.br. hind-brain ; hd.f. head-fold ; m.br. mid-brain ; med.f.
medullary folds ; prot. v. protovertebrse ; pr. st. primitive knot. (After S. F. Clarke.)
whitish zone — area opaca (a. op.). On the former now appears an
elliptical thickened patch — the embryonic shield (emb. s.) — which is
formed by the ectoderm cells in this region assuming a cylindrical
form while remaining flat elsewhere. Behind the embryonic
shield appears a thickening, due to a proliferation of the ectoderm
PHYLUM CHORDATA
353
cells — the so-called primitive knot or primitive plate (pr. st.), and
on this is formed an invagination opening on the surface by an
aperture — the blastopore (blp.)— which subsequently takes the
form of a narrow slit running in the direction of the long axis of
//.v»v i « :/'?/ *A^,v«;« •/.''V
K^:/v/, «•;' *v>.''?«'i^rn
jaw ; N. nasal opening ; S, fibrous poison sac ; z, tongue ; za,
opening of the poison-duct ; zf, pouch of mucous membrane duce acute pain
enclosing the poison-fangs. (From Wiedersheim's Comparative • , -i
Anatomy.) witn increasing
lethargy and
weakness, and in the case of the venom of some kinds of Snakes,
paralysis. According to the amount of the poison injected (in
Xffl PHYLUM CHORDATA 357
relation to the size of the animal) and the degree of its virulence
(which differs not only in different kinds of Snakes, but in the same
Snake under different conditions) the symptoms may result in death,
or the bitten animal may recover. The poison is a clear, slightly
straw-coloured or greenish liquid ; it preserves its venomous pro-
perties for an indefinite period, even if completely desiccated. The
poisonous principles are certain proteids not to be distinguished
chemically from other proteids which have no such poisonous
properties. Immunity against the effects of the poison, and relief
of the symptoms after a bite has been inflicted, have been found
to be conferred by injections of the serum of animals which have
been treated with injections of increasing doses of the poison.
The majority of Snakes are viviparous. Some, however, lay
eggs, which, nearly always, like those of the oviparous Lizards, are
left to be hatched by the heat of the sun, some of the Pythons
being exceptional in incubating them among the folds of the body.
Sphenodon lives in burrows in company with a Bird — the Shear-
water (Puffinus) — and feeds on Insects and small Birds. It lays
eggs enclosed in a tough, parchment-like shell.
Of the Chelonia some (Land Tortoises) are terrestrial ; others
(Fresh-water Tortoises) inhabit streams and ponds, while the Sea-
Turtles and Luths inhabit the sea. Even among Reptiles they
are remarkable for their tenacity of life, and will live for a long
time after severe mutilations, even after the removal of the brain ;
but they readily succumb to the effects of cold. Like most other
Reptiles, the Land and Fresh-water Tortoises living in colder
regions hibernate in the winter ; in warmer latitudes they some-
times pass through a similar period of quiescence in the dry season.
The food of the Green Turtle is exclusively vegetable ; some of
the Land Tortoises are also exclusively vegetable feeders ; other
Chelonia either live on plant food, together with Worms, Insects,
and the like, or are completely carnivorous. All are oviparous,
the number of eggs laid being usually very great (as many as 240
in the Sea-Turtles) ; these they lay in a burrow carefully prepared
in the earth, or, in the case of the Sea-Turtles, in the sand of the
sea-shore, and, having covered them over, leave them to hatch.
The Crocodiles and Alligators, the largest of living Reptiles, are
in the main aquatic in their habits, inhabiting rivers and, in the
case of some species, estuaries. Endowed with great muscular
power, these Reptiles are able, by the movements of the powerful
tail and the webbed hind-feet, to dart through the water with
lightning-like rapidity. By lying in wait motionless, sometimes
completely submerged with the exception of the extremity of the
snout bearing the nostrils, they are often able by the suddenness
and swiftness of their onset to seize the most watchful and timid
animals. In the majority of cases the greater part, and in some the
whole, of their food consists of Fishes ; but all the larger and more
VOL. II Z
358 ZOOLOGY SECT.
powerful kinds prey also on Birds and Mammals of all kinds, which
they seize unawares when they come down to drink or attempt to
cross the stream. On land their movements are comparatively slow
and awkward, and they are correspondingly more timid and helpless.
The Crocodilia, as already mentioned, are all oviparous, and the
eggs, as large in some species as those of a Goose, are brought
forth in great numbers (sometimes 100 or more) and either buried
in the sand, or deposited in rough nests.
Geographical Distribution. — The order Lacertilia, the most
numerous of the orders of Reptiles living at the present day, is of
very wide distribution, occurring in all parts of the earth's surface
except the circumpolar regions ; but some of its larger sections are
of limited range. The Geckos are numerous in all warm countries,
their headquarters being Australia and the Oriental region. The
snake-like Pygopidse are entirely confined to the Australian
region. The Agamidse (a family which includes the Flying
Lizards besides many others) are most abundantly represented in
the Australian region, though extending to other regions of the
Old World, except New Zealand and Madagascar. Of the Iguanas
two genera occur in Madagascar and one in the Friendly Islands ;
all the other members of this group, which is a large one, are
confined to America. Three families occur exclusively in America
—the Xenosauridse, the Tejidse, and the Helodermidse, or poisonous
Lizards. The Zonuridse or Girdle-tailed Lizards are confined to
Africa and Madagascar. The Anguidse or Blind-worm Lizards are
mostly American, but are represented in Europe and Asia. The
family of the Monitors is distributed in Africa, Southern Asia,
Oceania, and the Australian region. The Snake-like Amphis-
bsenians are most numerous in America, but are well represented
in Africa, and occur also in the Mediterranean area. The Lacer-
tidse are most abundant in Africa, but occur in Europe and Asia.
The family of the Skinks (Sclncidse) is of world-wide range, but is
most abundant in Australia, Oceania, the Oriental region and
Africa. Sphenodon is confined to the New Zealand region, and at
the present day only occurs on certain small islands off the N.E.
coast and in Cook's Straits. The Chamseleons are most abundant
in Africa and Madagascar, but there are representatives in various
other parts of the Old World ; they do not occur in the Australian,
New Zealand, or Polynesian regions, and are only represented in
Europe by one species which occurs in Andalusia.
Chelonia are widely distributed over the surface of the earth, by
far the greater number being natives of tropical and temperate
zones. The Sea-turtles, including the Hawk's-bills and the Luths,
are for the most part, but not entirely, confined to the tropical
seas. Giant Land-tortoises occur, or occurred in historic times, on
islands of the Galapagos and Mascarene groups.
Of the Crocodilia the Caimans are confined to Central and South
xm
PHYLUM CHORDATA
359
A
Pmx
America. The Alligators are represented in North America by
one species and in China by another. The true Crocodiles occur
widely distributed over Africa, Southern Asia, the northern parts
of Australia and tropical America, while the Gavial occurs only in
certain Indian and Burmese rivers.
Geological Distribution.— The Squamata are geologically the
most recent of the existing orders of Reptiles. The earliest fossil
remains of
Lizards have
been found in
beds belonging
to the Jurassic
and Cretaceous
periods; but
most of the
families are not
represented
earlier than the
Tertiary. All
the known fossil
remains of
Snakes, except
one imperfectly
known form from
the Cretaceous,
have been found
in deposits of
Tertiary age.
The Rhynchoce-
phalia are much
more ancient,
being represented
in deposits as old
as the Permian
by a genus-
Pa I CB o h alter ia—
which, though
differing in some
respects from the living Hatteria, is sufficiently near it to be looked
upon as a member of the same order : and other extinct Rhyncho-
cephalians have been found in Triassic and in Tertiary strata. The
order Chelonia was represented from the Triassic period onwards.
Of the extinct forms one group — the Athecata — differs from the living
Chelonia in having the carapace incompletely developed, entirely
composed of dermal elements, and quite separate from the vertebraa
and ribs. The Crocodilia date back as far as the Trias. The most
primitive of the fossil forms (Fig. 1021) had the internal nares
z 2
FIG. 1021. — Skull of Belodon. A, from above ; B, from below.
A, orbit ; Bo, basi-occipital ; Ch, internal nares ; D, pre-orbital
fossa ; Exo. exoccipital ; Fr. frontal ; Ju. jugal ; La. lacrymal ;
MX. maxilla ; n. external nares ; Na. nasal ; Pa. parietal ; PI.
palatine ; Pmx. premaxilla ; For. post-orbital ; Prf. pre-frontal ;
Pt. pterygoid ; Qu. quadrate ; S, lateral temporal fossa ; S't
superior temporal fossa ; Sq. squamosal ; Vo. vomer. (Prom
Zittel.)
360
ZOOLOGY
SECT.
situated in front of the palatines, while the external nares were
situated towards the middle of the snout. Later forms (post-Triassic)
had palatine plates developed from the premaxillee, the maxillse,
and the palatines ; and some resembled the living members of the
order in having such plates developed also from the pterygoids ;
all had the external nares situated towards the end of the snout.
Those in which the palatine plates of the pterygoids were absent
had usually amphiccelous vertebras. Some of the fossil Crocodiles
reached an immense size.
4. EXTINCT GROUPS OF REPTILES.
PROBEPTILIA.
The Permian genera Eryops and Cricotus, formerly assigned to the
Stegocephala (p. 285), have been proved, on the ground mainly of their verte-
bral structure, to be true Reptiles, and are regarded as the most primitive
members of the class with strong Amphibian affinities.
THEROMORPHA.
The Theroniorpha are a very extensive and varied group of fossil Reptiles
which all have limbs adapted to terrestrial locomotion. The vertebrae
are aniphicoelous, and most of the ribs have distinct capitula and tubercula.
A sternum is present, and also, in many cases at least, an episternurn. The
quadrate is firmly fixed. Palatine plates are developed comparable to those
of Chelonia. There is a parietal foramen. The temporal region is in some
covered over by flattened bones as in a Turtle, in others there is a wide lateral
temporal fossa bounded above by a superior temporal arch ; in the latter
case no quadrate- jugal is developed. An arch corresponding with the
zygoma of Mammals (see Section XV) is formed by the extension backwards
of the jugal to meet an anterior process of the squamosal, both articulating
with a downgrowth from the post-frontal. In the pectoral arch, clavicle,
coracoid, pro-coracoid, and scapula are present. The pubes and ischia are
closely united, with a common symphysis, as in Mammals ; and the obturator
foramen is usually small. The teeth (Fig. 1022) (which are not present in all)
are thecodont, and in the
higher forms bear a consider-
able resemblance to those of
Mammals in the regularity of
their arrangement in sets, often
with large canines or tusks.
Palatine teeth are sometimes
present. One order, the Pla-
codontia, have remarkable
broad crushing teeth on both
upper and lower jaws and on
the palate.
The Theromorpha mainly
occur in beds between Permian and Triassic age, and have been found in
South Africa and North America, as well as Europe and India. Among
them have recently been found many transition forms which tend to bridge
over the interval between the Reptilia and the Mammalia.
SAUROPTERYGIA.
The typical representatives of this order, such as Plesiosaurus (Fig. 1023),
were aquatic Reptiles, sometimes of large size (up to 40 feet), though many
FIG. 1022.— Left lateral aspect of the skull of Gale-
saurus planiceps. or. orbit. (After Nicholson
and Lydekker.)
xm
PHYLUM CHORDATA
361
were quite small. They had a lizard-like body, a very long neck, a
relatively small head, and a short tail which supported a vertical caudal fin ;
the limbs were modified to form swimming-paddles. In older and less special-
ised members of the group, however, the limbs were not paddle-like, but
adapted for walking.
The spinal column of the Sauropterygia is characterised by the great
length of the cervical and the short-
ness of the caudal region. The verte-
brae are usually amphicoelous. The
sacrum consists of either one or two
vertebrse. There is no sternum. In
the skull there are large premaxillse ; a
bony palate is absent ; a transverse
bone is present. One temporal arch
only is developed. There is a well-
marked parietal foramen. The ring of
bony plates (developed in the sclerotic)
sc -
FIG. 1024. — Plesiosaurus, pectoral arch.
cor. coracoid ; e. episternum ; sc. scapula.
(After Zittel.)
found in the orbit of some fossil Rep-
tiles is not developed. The quadrate
is not movable. The pectoral arch
(Fig. 1024) presents some remarkable
features. The coracoids always meet
in a ventral symphysis, and the
ventral portions (acromial processes)
of the scapulae may also meet. In
front there is, in most cases, an arch of
bone, consisting of a median and two
lateral portions, which probably repre-
sent the episternum and the clavicles :
in some forms this arch is reduced or
absent. In the pelvis the broad pubes and ischia meet in the middle line :
the two symphyses may remain separate (Fig. 1025). or they may unite so
as to divide the space into two separate obturator foramina. The teeth
are implanted in distinct sockets.
The Sauropterygia date back to the Trias, and perhaps to the Permian,
extending onwards to the Cretaceous.
362
ZOOLOGY
SECT.
ICHTHYOPTERYGIA.
The Ichthyopterygia, including Ichthyosaurus (Fig. 1026) and its allies,
were aquatic Reptiles, some of very large size (30 or 40 feet in length), with
somewhat fish-like body, large head produced into an elongated snout, no
neck, and an elongated tail, with a large vertical
caudal fin, and with limbs in the form of swimming-
paddles. The vertebrse are amphiccelous. A
sacrum is absent, so that only precaudal and caudal
regions are distinguishable. The ribs have two heads
for articulation with the vertebrse : a sternum is
absent, but there is a highly developed system of
abdominal ribs. The skull is produced into an
elongated rostrum, formed chiefly of the premaxillse,
and with small nostrils situated far back. The
orbits are large and contain a ring of bones developed
in the sclerotic. An epipterygoid is present as in
Lizards, and there is a large parietal foramen.
Both superior and inferior temporal arches are
developed. The quadrate is immovably fixed to the
Pb.
FIG. 1025. — Plesiosaurus, pelvic arch. 11. ilium ; Is.
ischium ; Pb. pubis. (After Huxley.)
skull. The pectoral arch consists of coracoid, scapula,
and clavicle, the pro-coracoid being absent or very
small. The coracoids are broad bones which meet
ventrally for a short distance without overlapping.
A T-shaped episternum is present. The bones of the
pelvis are not strongly developed ; the ilia are
not connected with the spinal column ; the pubes
and ischia of opposite sides meet in ventral symphyses,
but there is no obturator foramen. Humerus and
femur are both short, and the rest of the bones of
the limb are disc-like or polyhedral. The phalanges
are numerous, and are usually in more, sometimes in
fewer, than the usual five series. The teeth are not
in separate sockets, but set in a continuous groove.
The Ichthyopterygia are of Mesozoic age, ranging
from the Upper Trias to the Upper Cretaceous.
Geographically their remains have a very wide distribution, having been
found not only in Europe and North America, but in the Arctic Regions, in
India, Africa, Australia, and New Zealand.
DINOSAURIA.
This order comprises a vast number of terrestrial Reptiles, some of gigantic
size (up to over 100 feet in length), of lizard-like or bird-like form, some
XHI
PHYLUM CHORDATA
363
approaching Birds in certain features of their structure, others coming nearer
the earliest fossil Crocodiles. The surface was in some covered with a bony
FIG. 1027. — Xguanodon bernissartensis. One sixtieth natural size. co. coracoid ; is.
ischium ; p. pubis (pectineal process) ; pp. post-pubic process (pubis) ; se. scapula
I—V, I— IV, digits. (From Zittel, after Dollo.)
armour, sometimes armed with long spines. The fore- and hind-limbs were
in some equally developed ; in others the hind-limbs were much more
powerful than the fore-limbs, and in many their structure appears adapted
to a bipedal mode of
progression (Fig. 1027).
The centra are in
general amphicoelous,
but vary greatly. The
sacral region usually
comprises 3 to 6 verte-
brae. The thoracic ribs
have double heads. Ab-
dominal ribs are some-
times present. The
sternum was incom-
pletely ossified, and an
episternum is absent.
There is no parietal
foramen. There are
complete upper and
lower temporal arches,
and the fossa is divided
into upper and lower
parts by a bar formed from the post-frontal and squamosal. Ectopterygoids
are present. The quadrate is firmly fixed. In the pectoral arch the scapula
is very large, the coracoid small, and the pro-coracoid and clavicle absent.
B
FIG. 1028. — Teeth of Iguanodon mantelli. A, from the
inner, B, from the outer side. (From Zittel, after Mantell.)
364
ZOOLOGY
SECT.
The pubis in some Dinosauria has a remarkable slender prolongation (Fig.
1027, pp.) running downwards and backwards from the body of the bone
parallel with the ischium, an arrangement not found elsewhere except in
Birds ; a pubic symphysis does not always occur. In certain points in the
structure of the hind-limb itself some of the Dinosauria also bear a resem-
blance to Birds. The teeth, which are usually compressed and may have
serrated edges, are sometimes placed in sockets, sometimes in grooves.
Iguanodon (Fig. 1027), one of the best-known genera, attains the length
in the case of one species of over 30 feet. The limb-bones are hollow. The
ischium and pubic process are long and slender, and inclined backwards and
downwards parallel to one another. The hind-foot was digitigrade, i.e., the
weight was supported on the phalanges of the digits, and the elongated meta-
tarsals, which were immovably fixed, had a nearly vertical position as in
Birds ; the fore-limbs are relatively small, and fossil footprints that have
been found indicate that the animal supported itself habitually in a half-
erect posture like a Kangaroo, with the fore-limbs raised from the ground.
The teeth (Fig. 1028) are of a remarkable shape, flattened and with serrated
edges, sometimes with vertical ridges which may be serrated. The Dinosauria
range from the Trias to the Upper Cretaceous, and were most abundant in
the Jurassic and Wealden.
PTEROSAXTRIA.
The Pterosauria or Pterodactyles are perhaps even more remarkable
modifications of the reptilian type than any of the orders that have been
hitherto alluded to. The chief
peculiarities in the structure
of these Reptiles were asso-
ciated with a flying mode of
locomotion, the organs of
. flight being, as in the Bird
and the Bat, the fore-limbs.
In the Pterodactyles (Fig.
1029) the last digit on the
ulnar side of the manus is
enormously prolonged and
thickened, and supported a
web of skin (Fig. 1031) which
extended backwards to the
hind-limbs and the tail. Most
of the bones are hollow, and
have pneumatic foramina as
in Birds (q.v.). The vertebrae
are precocious, except the
caudals, which are amphi-
ccelous. The cervical verte-
brae are elongated and stout,
the neck being of considerable
length ; there are three to six
ankylosed sacrals. The an-
terior thoracic ribs are bifid
at their vertebral ends. The
sternum is broad, with a
longitudinal keel. The skull
(Fig. 1030), set on the neck at right angles as in a Bird, is of large size and
superficially resembles that of a Bird in general shape, 'and particularly in
the presence of an elongated, pointed rostrum ; the orbits are large, and
contain a ring of sclerotic ossifications. The sutures are largely obliterated,
FIG. 1029.— Pterodactylus spectabilis. Three-
fourths of the natural size. (From Zittel, after
H. v. Mayer.)
xm
PHYLUM CHORDATA
365
as in the skull of a Bird. The quadrate is immovably fixed to the skull.
In the pectoral arch the scapula and coracoid are long and slender, like
those of Birds : pro-coracoids and clavicles are absent. The pelvis and hind-
tmx
FIG. 1030. — Skull of Scaphognathus. D. pre-orbital aperture ; Fr. frontal ; Ju. jugal,
MX. maxilla ; N. nasal opening ; Pmx. premaxilla ; Qu. quadrate. (After Zittel.)
limbs are weak as compared with the fore-limbs, and the pelvis does not
exhibit any resemblance to that of Birds, but appears to come nearer to that
of the Crocodiles. The astragalus sometimes unites with the tibia. There
is no trace of any exoskeleton. The brain, as shown by casts of the interior
BP
of the skull, bore interesting resemblances to
that of Birds in the relations of the cerebellum
and optic lobes, the latter being separated from
one another by the approximation of the cere-
bellum to the fore -brain, instead of being in
close apposition with one another as in existing
Reptiles.
The Pterosauria are confined to formations
of the Jurassic and Cretaceous periods.
PYTHONOMORPHA.
The Pythonomorpha were large marine Rep-
tiles with extremely elongated snake-like bodies,
but with well-developed limbs, which were
modified as swimming-paddles. The vertebrae,
which are very numerous, are proccelous, some-
times with, sometimes without, zygosphenes and
zygantra. The sacrum is absent as a rule. A
sternum has been found in one genus. The
skull resembles that of a Lizard, both in form
and structure ; the quadrate is mobile ; there is
a parietal foramen ; the premaxillse are united.
There is no inferior temporal arch, the quadrato-jugal being absent. The
quadrate is movable, articulating with the squamosal and epiotic. The rami
of the mandible are united by ligament at the symphysis. The pectoral arch
(Fig. 1032) comprises discoidal coracoids (c) which meet ventrally, and a
FIG. 10:51. — Rampho-
rhynchus, restored.
(After Zittel.)
366
ZOOLOGY
SECT.
scapula (sc.) which resembles that of the Rhynchocephalia : a clavicle is
never present. In the pelvis the ilium, which usually does not articulate
with the spinal column, is a rod-shaped bone : the ischium and pubis resemble
those of the Lizards. The bones of both fore- and hind -limbs are short
mc>
FIG. 1032. — Edestosaurus (Pythonomorpha). Pectoral arch and fore-limbs, c. coracoid with
pro-coracoid ; h. humerus ; me. metacarpus ; r. radius ; sc. scapula u. ulna ; /, first
digit ; V, fifth digit. (From Zittel after Marsh.)
there are five digits in each. The teeth are conical, pointed, and ankylosed
by expanded bases to the summits of the maxillae and pterygoids. Dermal
scutes have been observed in one genus.
The remains of Pythonomorpha have been found only in certain beds
belonging to the Cretaceous period in Europe, North America, and New
Zealand.
CLASS V.-AVES.
In many respects Birds are the most highly specialised of
Craniata. As a class they are adapted for aerial life ; and almost
every part of their organisation is modified in accordance with
the unusual environment. The non-conducting covering of feathers ;
the modification of the fore-limbs as wings, of the sternum and
shoulder-girdle to serve as origins of the great wing-muscles, and
of the pelvic girdle and hind-limbs to enable them to support the
entire weight of the body on the surface of the ground ; the perfec-
tion of the respiratory system, producing a higher temperature than
in any other animals : all these peculiarities are of the nature of
adaptations to flight. Add to them the absence, in all existing
Birds, of teeth, the loss of the left aortic arch, and of the right
ovary and oviduct, the specialised character of the brain, the poorly
developed olfactory organs, and the extraordinarily large and perfect
eyes, and we have a series of strongly-marked characteristics such
as distinguish hardly any other class. Moreover, the organisation
of existing Birds is, in its essential features, singularly uniform, the
entire class presenting less diversity of structure than many single
orders of Fishes, Amphibians, and Reptiles.
xm PHYLUM CHORDATA 367
1. EXAMPLE OF THE CLASS.— THE COMMON PIGEON (Columba
lima, var. domestica) .
The Common or Domestic Pigeon is known under many varieties,
which differ from one another in size, proportions, coloration,
details in the arrangements of the feathers, and in many points of
internal anatomy. The Pouters, Carriers, Fantails, and Tumblers
may be mentioned as illustrating extreme forms. All these varieties
have, however, been produced by artificial selection, that is, by
breeders selecting, generation after generation, the Birds which
most nearly attained to some artificial standard of perfection,
breeding from them alone, and killing off the inferior strains. The
ancestral species from which the domestic breeds have in this way
been evolved is the Rock Pigeon (Columba livia), which is widely
distributed in the Palasarctic and Oriental regions. The following
description refers especially to the common Dovecot Pigeon.
External Characters. — In the entire Bird (Fig. 1033) the
plump trunk appears to be continued insensibly into the small,
mobile head, with its rounded brain-case and prominent beak,
formed of upper and lower jaws covered by horny sheaths. The
head, neck, and trunk are invested in a close covering of feathers,
all directed backwards and overlapping one another. Posteriorly
the trunk gives origin to a number of outstanding feathers which
constitute what is ordinarily called the tail. From the anterior
region of the trunk spring the wings, also covered with feathers,
and, in the position of rest, folded against the sides of the body.
The legs spring from the hinder end of the trunk, but, owing to
the thick covering of feathers, only the feet are to be seen in the
living Bird, each covered with scales and terminating in four digits
(dg. 1' — dg. 4'), three directed forwards and one backwards.
In order to make a fair comparison of the outer form with that
of other Craniate types, it is necessary to remove the feathers.
When this is done, the Bird is seen to have a long, cylindrical, and
very mobile neck, sharply separated both from head and trunk.
The true tail is a short, conical projection of the trunk, known as the
uropygium, and giving origin to the group of large feathers (ret.) to
which the word "tail" is usually applied. On the dorsal surface
of the uropygium is a papilla bearing on its summit the opening
of a large gland, the oil-gland (o.gl.), the secretion of which is used
for lubricating or " preening " the feathers.
The wings show the three typical divisions of the fore-limb,
upper arm, fore-arm, and hand, but the parts of the hand are
closely bound together by skin, and only three imperfectly-marked
digits, the second (dg. 2) much larger than the first (dg. 1) and
third (dg. 3), can be distinguished. In the position of rest the three
divisions of the wing are bent upon one another in the form of a Z ;
during flight they are straightened out and extended so that the
368
ZOOLOGY
SECT.
axis of the entire wing is at right angles to that of the trunk. On
the anterior or pre-axial border of the limb a fold of skin stretches
between the upper arm and the fore-arm ; this is the alar membrane
or pre-patagium (pr. ptgm.). A similar but much smaller fold
extends, post-axially, between the proximal portion of the upper
arm and the trunk ; this is the post-patagium (pt. ptgm.).
In the hind-limb the short thigh is closely bound to the trunk,
not standing well out as in a Reptile, but directed downwards and
Fid 1033 — Columba livia. The entire animal from the left side with most of the feathers
removed, ad.dg.rmx. ad-digital remex ; al. sp. ala spuria ; an. anus ; au. ap. auditory
aperture ; cb. rmg. cubital remiges ; cr. cere : dg. 1, 2, 3, digits of manus ; dg. 1', 2', 3 ,4 ,
digits of pes ; hu.pt. humeral pteryla ; Ig. ligament of remiges ; md.dg.rmg. mid-digital
remiges ; na. nostril ; nct.m. nictitating membrane ; o.gl. oil-gland ; pr.dg.rmg, pre-digital
remiges ; pr.ptgm. pre-patagium ; pt.ptgm. post-patagium ; ret. mesial rectrix of right side ;
ret', sacs of left rectrices ; sp. pt. spinal pteryla ; ts.mtts. tarso-metatarsus ; v.apt. ventral
apterium.
forwards ; the long shank extends from the knee downwards and
backwards ; and the foot is clearly divisible into a proximal portion,
the tarso-metatarsus (ts. mtts.), and four digits, of which one, the
hallux (dg. 1'), is directed backwards, the others, the 2nd, 3rd, and
4th of the typical foot, forwards. The entire hind-limb is in a plane
parallel with the sagittal plane of the trunk.
xm
PHYLUM CHORDATA
369
rcli
The mouth is terminal, and is guarded by the elongated upper
and lower beaks ; it has, therefore, a very wide gape. On each
side of the base of the upper beak is a swollen area of soft skin,
the cere (cr.), surrounding the nostril (na.), which has thus a remark-
ably backward position. The eyes are very large, and each is
guarded by an upper and lower eyelid and a transparent nictitating
membrane (net. m.). A short distance behind the eye is the auditory
aperture (au. ap.), concealed by feathers in the entire Bird, and
leading into a short external auditory meatus, closed below by the
tympanic membrane. The anus or cloacal aperture (an.) is a large,
transversely-elongated aperture placed on the ventral surface at
the junction of the uropygium with the trunk.
Exoskeleton. — The exoskeleton is purely epidermal, like that
of the Lizard, which
it also resembles in
consisting partly of
horny scales. These
cover the tarso-meta-
tarsus and the digits
of the foot, and are
quite reptilian in
appearance and
structure. Each digit
of the foot is termi-
nated by a claw,
which is also a horny
product of the epi-
dermis ; and the
beaks are of the same
nature. The rest of
the body, however,
is covered by feathers,
a unique type of
epidermal product
found nowhere out-
side the present class.
A feather (Fig.
1034) is an elongated
structure consisting
of a hollow stalk, the calamus or quill (cal.), and an expanded distal
portion, the vexillum or vane. At the proximal end of the quill is
a small aperture, the inferior umbilicus (inf. umb.), into which fits,
in the entire Bird, a small conical prolongation of the skin, the
feather papilla. A second, extremely minute aperture, the superior
umbilicus (sup. umb.), occurs at the junction of the quill with the
vane on the inner or ventral face of the feather, i.e., the face adjacent
to the body. A small tuft of down in the neighbourhood of the
•inf. umb
Fid. 1034.— Columba livia. A, proximal portion of a
remex. cal. calamus ; inf. umb. inferior umbilicus ; rch.
rachis ; sap. umb. superior umbilicus. B, filoplume
C, nestling-down. (C. from Bronn's Thierreich.)
370
ZOOLOGY
SECT.
superior umbilicus represents the after-shaft of many Birds-
including some Pigeons (vide infra).
The vane has a longitudinal axis or rachis (rch.) continuous
proxirnally with the quill, but differing from the latter in being
solid. To each side of the rachis is attached a kind of membrane
forming the expanded part of the feather and composed of barbs—
delicate, thread-like structures which extend obliquely outwards
from the rachis. In an uninjured feather the barbs are closely
connected so as to form a continuous sheet, but a moderate amount
of force separates them from one another, and it can readily be
made out with the aid of a magnifying glass that they are bound
FIG. 1035. — Structure of Feather. A, small portion of feather with pieces of two barbs,
each having to the left three distal barbules, and to the right a number of proximal barbules,
many of them belonging to adjacent barbs. B, booklet of distal barbule interlocking with
flange of proximal barbule. C, two adjacent proximal barbules. D, a distal barbule
(From Headley, after Pycraft.)
together by extremely delicate oblique filaments, the barbules,
having the same general relation to the barbs as the barbs themselves
to the rachis.
The precise mode of interlocking of the barbs can be made out
only by microscopic examination. Each barb (Fig. 1035, A) is a
very thin and long plate springing by a narrow base from the
rachis, and pointed distally. From its upper edge — the edge
furthest from the body of the Bird — spring two sets of barbules, a
proximal set (C) directed towards the base of the feather, and a
distal set (D) towards its tip. Owing to their oblique disposition
the distal barbules of a given barb cross the proximal barbules of
the next, each distal barbule being in contact with several proximal
xm
PHYLUM CHORDATA
371
barbules of the barb immediately distal to it (A). The lower edge
of the distal barbule is produced into minute hooldets (D) : in the
entire feather the booklets of each distal barbule hook over prominent
flanges of the proximal barbules with which it is in contact (A, B).
fl M-t3 Pi ' <£<
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In this way the parts of the feather are so bound together that the
entire structure offers great resistance to the air.
Among the contour feathers which form the main covering of the
Bird and have the structure just described are found filoplumes
(Fig. 1034, B), delicate, hair-like feathers having a long axis and a
few barbs, devoid of locking apparatus, at the distal end. Nestling
Pigeons are covered with a temporary investment of down-feathers
372
ZOOLOGY
SECT.
B
(C), in which also there is no interlocking of the barbs : when these
first appear each is covered by a horny sheath like a glove-finger.
Feathers, like scales, arise in the embryo from papillae of the
skin (Fig. 1036, A, Pap.), formed of derm with an epidermal covering.
The papilla becomes sunk in a sac, the feather -follicle (B, F), from
which it subsequently protrudes as an elongated feather-germ (FK),
its vascular dermal interior being the feather-pulp (P). The
Malpighian layer of the distal part of the feather-germ proliferates
in such a way as to form a number of vertical radiating ridges
(C, Fal (&M1)) : its proximal part becomes uniformly thickened,
and in this way is produced the rudiment of a down-feather, having
a number of barbs springing, at the same level, from the distal end
of the quill. The
horny layer of
the epidermis
(HS (Sc1)) forms
the temporary
sheath which is
thrown off as the
feather grows
and expands.
The pulp of
the permanent
feather (D, F1)
is formed from
the lower or deep
end of that of
the down-
feather, and its
development is
at first similar,
but, instead of
the ridges of the
Malpighian layer
remaining all of
one size, two adjacent ones outgrow the rest and become the
rachis ; as the latter elongates it carries up with it the remaining
ridges, which become the barbs.
The feathers do not spring uniformly from the whole surface of
the body, but from certain defined areas (Fig. 1037), the feather
tracts or pterylce (sp. pt., hu. pt., &c.), separated from one another
by featherless spaces or apteria (v. apt., &c.), from which only a few
filoplumes grow. The feathers are, however, long enough to cover
the apteria by their overlap, and the body is thus completely
covered with a thick, very light, and non-conducting investment.
In the wings and tail certain special arrangements of the feathers
are to be distinguished. When the wing is stretched out at right
FIG. 1037. — Pterylosis of Columba livia. A, ventral ; B, dorsal.
al.pt. alar pteryla or wing-tract ; c.pt. cephalic pteryla or head-
tract ; cd.pt. caudal pteryla or tail-tract ; cr.pt. crural pteryla ;
cv.apt. cervical apterium or neck-space ; fm.pt. femoral pteryla ;
ku.pt. humeral pteryla ; lat.apt. lateral apterium ; sp.pt. spinal
pteryla ; v.apt. ventral apterium ; v.pt. ventral pteryla. (After
Nitzsch.)
xni PHYLUM CHORDATA 373
angles to the trunk, twenty-three large feathers (Fig. 1033) are seen
to spring from its hinder or post-axial border : these are the remiges
or wing-quills. Twelve of them are connected with the ulna and
are called cubilals or secondaries (cb. rmg.). The rest are known as
primaries : seven of these are attached to the metacarpal region,
and are hence called metacarpals (mtcp. rmg.), the remaining four
or digitals to the phalanges of the second and third digits. These
are again distinguished into a single ad-digital (ad. dg. mix.), con-
nected with the single phalanx of the third digit (Fig. 1045, ph. 3),
two mid-digitals (md. dg. rmg.) with the proximal phalanx of the
second digit (Fig. 1045, ph. 2), and two pre-digitals (pr. dg. rmg.)
with its distal phalanx (Fig. 1045, ph. 2'). A special tuft of feathers
on the anterior border of the wing, arising from the pollex (Fig. 1045,
ph. 1), forms the ala spuria (al. sp.). The spaces which would
otherwise be left between the bases of the remiges are filled in,
both above and below, by several rows of upper and under wing-
coverts. In the tail there are twelve long rectrices (Fig. 1033, ret.)
or tail-quills, springing in a semicircle from the uropygium ; their
bases are covered, as in the wing, by upper and under tail-coverts.
The whole feather-arrangement is known as the pterylosis.
Endoskeleton. — The vertebral column is distinguished from
that of most other Craniata by the great length and extreme
mobility of the neck, the rigidity of the trunk-region, and the
shortness of the tail. As in Reptilia, the cervical passes almost
insensibly into the thoracic region, and the convention is again
adopted of counting as the first thoracic (Fig. 1038, th. v. 1), the
first vertebra having its ribs united with the sternum. There are
fourteen cervical vertebrae, the last or last two of which have double-
headed ribs (cv. r.), each having its proximal end divisible into the
head proper articulating with the centrum of the vertebra, and a
tubercle with the transverse process : their distal ends are free, not
uniting with the sternum. In the third to the twelfth there are
vestigial ribs (Fig. 1039, rb.), each having its head fused with the
centrum, and its tubercle with the transverse process. The whole
rib thus has the appearance of a short, backwardly-directed
transverse process perforated at its base ; the perforation trans-
mits the vertebral artery, and is called the vertebrarterial foramen
(vrb.f.).
The centra of the cervical vertebras differ from those of all other
Vertebrata in having saddle-shaped surfaces, the anterior face
(Fig. 1039, A) being concave from side to side and convex from
above downwards, the posterior face (B) convex from side to side
and concave from above downwards. Thus the centrum in sagittal
section appears opisthoccelous, in horizontal section proccelous.
This peculiar form of vertebra is distinguished as heteroccelous.
The centra articulate with one another by synovial capsules, each
traversed by a vertical plate of cartilage, the meniscus, with a
VOL. II A A
374
ZOOLOGY
SECT.
central perforation through which a suspensory ligament passes
from one centrum to the other.
The first two vertebrae, the atlas and axis, resemble those of the
s.scr
CL.tr
cd v
ftu,
a
3V9
n.ot
car-
FIG. 1038. — Columba livia. The bones of the trunk, acr.cor. acrocoracoid ; a.tr. anti-
trochanter ; actb. acetabulum ; car. carina sterni ; cd. r. caudal vertebra; ; cor. coracoid ;
cv.r. cervical ribs ; f.trs. probe passed into foramen triosseum ; fur. furcula ; gl.cv. glenoid
cavity ; il. ilium ; is. ischium ; is. for. ischiadic foramen ; obt.n. obturator notch ; pu. pubis ;
pyg.st. pygostyle ; scp. scapula : s.scr. syn-sacrum ; ft. sternum ; st. r. sternal ribs ; th.v. 1,
first, and th.v. 5, last thoracic vertebra ; unc. uncinates ; vr.r. vertebral ribs.
Lizard, but have the various elements of which they are composed
completely fused. The small size of the ring-like atlas is noticeable.
Between the last cervical vertebra and the pelvic region come
either four or five thoracic vertebra? (Fig.
1038) — the first three, when four only are
present, the second, third, and fourth, when
there are five, united into a single mass, the
last free. The anterior thoracic as well as
the posterior cervical vertebra have the
centrum produced below into a compressed
plate, the hypapophysis, for the origin of
the flexor muscles of the neck. They all
bear ribs, each consisting of a vertebral
(vr.r.) and a sternal (st.r.) portion, and
articulating with the vertebra by a double
head. The sternal, like the vertebral rib, is
formed of true bone, not of calcified carti-
lage as in Reptiles, and articulates with
zyg. anterior zygapophysis ; » J. ....
en. centrum; n.a. neural the vertebral rib by a synovia! joint.
crv
crv
FIG. 1039. — Columba livia.
Cervical vertebra. A, an-
terior, B, posterior face. o.
verte'brarteriai foramen.
Springing from the posterior edge of the
vertebral rib is an uncinate (unc.), resembling
that of Sphenodon and the Crocodile, but formed of bone and
ankylosed with the rib.
PHYLUM CHORDATA
375
tr.p
Following upon the fourth or fifth thoracic are about twelve
vertebrae, all fused into a single mass (Fig. 1038, s.scr), and giving
attachment laterally to the immense pelvic girdle. The whole of
this group of vertebrae has, therefore, the function of a sacrum,
differing from that of a Reptile in the large number of vertebras
composing it. The first of them bears a pair of free ribs, and is,
therefore, the fifth or sixth (last) thoracic (th.v.5). The next five
or six have no free ribs, and may be looked upon as lumbar
(Fig. 1040, I.1- — s.3) : their transverse processes arise high up on
the neural arch, and the ligament uniting
them is ossified, so that the lumbar region
presents dorsally a continuous plate of
bone. Next come two sacral vertebras (c.1)
homologous with those of the Lizard : be-
sides transverse processes springing from *'
the neural arch, one or both of them bears
a second or ventral outgrowth (c.r.) spring-
ing from each side of the centrum and
abutting against the ilium just internal to
the acetabulum. These distinctive pro-
cesses are ossified independently and repre-
sent sacral ribs. The remaining five verte-
brae of the pelvic region are caudal.
Thus the mass of vertebras supporting the
pelvic girdle in the Pigeon is a compound
sacrum, or syn-sacrum, formed by the fusion
of the posterior thoracic, all the lumbar and
sacral, and the anterior caudal vertebras.
The syn-sacrum is followed by six free
caudals, and the vertebral column ends
posteriorly in an upturned, compressed
bone, the pygostyle or ploughshare-bone
(Fig. 1038, pyg.st.}, formed by the fusion of four or more of the
hindmost caudal vertebras.
Thus the composition of the vertebral column of the Pigeon may
be expressed in a vertebral formula as follows :—
Syn-sacrum.
FIG. 1040. — Columba livia.
Sacrum of a nestling (about
fourteen days old), ventral
aspect, c1. centrum of first
sacral vertebra ; c". centrum
of fifth caudal ; c.r. first
sacral rib ; I1, centrum of first
lumbar ; I-'-, of third lumbar ;
sl, of fourth lumbar ; ss, of
sixth lumbar ; tr.p. trans-
verse process of first lum-
bar ; tr.p'. of fifth lumbar ;
tr.p". of first sacral. (From
Parker's Zootumi/.)
Cerv. 14. Thor. 4 or 5 + 1. Lumb. 5 or 6. Sacr. 2. Caucl. 5 + 6 + 4 = 43.
The sternum (Fig. 1038, st.) is one of the most characteristic parts
of the Bird's skeleton. It is a broad plate of bone produced
ventrally, in the sagittal plane, into a deep keel or carina sterni
(car.), formed, in the young Bird, from a separate centre of ossifica-
tion. The posterior border of the sternum presents two pairs of
notches, covered, in the recent state, by membrane ; its anterior
edge bears a pair of deep grooves for the articulation of the
coracoids.
A A 2
376
ZOOLOGY
SECT.
The skull (Fig. 1041) is distinguished at once by its rounded
brain-case, immense orbits, and long, pointed beak. The foramen
magnum (f.m.) looks downwards as well as backwards, so as to be
visible in a ventral view, and on its anterior margin is a single,
small, rounded occipital condyle (o.c.). Most of the bones, both of
the cranial and facial regions, are firmly ankylosed in the adult,
and can be made out
young
only in the
Bird.
The o c ci p i t a 1 s,
parietals, frontals, and
alisphenoids have the
usual relations to the
brain-case, the basi-
occipital (6.0. ), as in
the Lizard, bearing
the occipital condyle.
The basisphenoid
(Fig. 1042, B.SPH.)
is a large bone form-
ing the greater part of
the basis cranii and
continued forwards,
as in the Lizard, by a
slender rostrum (Fig.
1041,j9a.s., Fig. 1042,
RST.), which repre-
sents the anterior por-
tion of the para-
sphenoid. On the
Fiu. 1041.— Columba livia. Skull of young specimen. Ventral aspect OI ^the
A, dorsal ; B, ventral ; C, left side. al.s. alisphenoid ; an. basisphenoid paired
angular ; ar. articular ; b. o. basi-occipital ; d. dentary ; , ,
e. o. exoccipital ; eu. aperture of Eustacliiau tube ; /. m. membrane DOneS, the
foramen magnum ;fr. frontal ; i. o. s. inter-orbital septum ;
ju. jugal ; /c. lacrymal ; Ib. s. lambdoidal suture ; m. eth.
mesethmoid ; mx. maxilla ; mx.p. maxillo-palatine process ;
na. na'. no,", nasal; o.c. occipital condyle; or.fr. orbital
plate of frontal ; pa. parietal ; pa.s. parasphenoid (rostrum) ; developed, and become
pi. palatine ; p.mx. preniaxilla ; pt. pterygoid ; qu. quadrate ; ,, , ,' , ., .
». an. supra-angular ; s. o. supra-occipital ; sq. squamosal ; rirmly anKylOSCQ tO It
ty. tympanic cavity; II— XII, foramina for cerebral • -i arliilf • +!IPV
nerves. (From Parker's Zootomij.) lej
probably represent the
posterior portion of the parasphenoid. The tympanic cavity is
bounded by the squamosal (Fig. 1041, sq.), which is firmly united to
the other cranial bones. The main part of the auditory capsule is
ossified by a large pro-otic (Fig. 1042, PR.OT.) : the small opisthotic
of the embryo early unites with the exoccipital, the epiotic with
the supra-occipital. The parasphenoid and mesethmoid together
form the inter-orbital septum (Fig. 1041, i.o.s.), a vertical partition,
partly bony, partly cartilaginous, which separates the orbits from
T • fa./nmfv..f.j(f
OdSl-tempOratS
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1 g.
xm
PHYLUM CHORDATA
377
one another. It is very characteristic of the Bird's skull that
the immense size of the eyes has produced a compression of this
region of the skull. The ecto-ethmoids or turbinals are compara-
tively poorly developed, in correspondence with the small size
of the olfactory organs. There are large lacrymals (Fig. 1041,
k., Fig. 1042, LCR.), and the nasals (na, na', na", NA) are forked
bones, each furnishing both an inner and an outer boundary to
the corresponding nostril.
The premaxillae (p.mx., PMX.) are united into a large triradiate
PfyJ'0*
EPOT
OP.OT
1^5gj,EX.OC
PROT\BOC
^l.pr
BSPH
'MP
QU
con
A. JVC
AR
FIG. 1042. — Sagittal section of a Bird's skull (diagrammatic). Replacing Bones— AL.SPH.
alisphenoid ; ART. articular ; B.OC. basi-occipital ; B.SPH. basl-sphenoid ; EP.OT.
epiotic ; EX.OC. exoccipital ; M.ETH. mesethmoid ; OP.OT. opisthotlc
ORB.SFH. orbito-sphenoid ; PR.OT. pro-otic ; QU. quadrate ; S.OC. supra
occipital. Investing bones — ANG. angular ; B. TMP. basi-temporal ; COR. coronary
DNT. dentary ; FR. frontal; JU. jugal ; LCR. lacrymal ; MX. maxilla; NA. nasal .
PA. parietal; PAL. palatine ; PMX. premaxilla ; PT6. pterygoid ; QU.JU. quadrato-
jugal ; RST. rostrum; /S. ANG. supra-angular; SPL. splenial ; SQ. squamosal ; VO.
vomer ; flc. fos. tloccular fossa ; mx. pal. pr. maxillo-palatine process ; opt. for. optic
foramen ; orb. pr. orbital process ; ot. pr. otic process ; pty.fos. pituitary fossa.
bone which forms practically the whole of the upper beak. The
maxillae (mx., MX.), on the other hand, are small, and have their
anterior ends produced inwards into spongy maxillo-palatine
processes (Fig. 1041, mx.p., Fig. 1042, mx.pal.pr.). The slender
posterior end of the maxilla is continued backwards by an equally
slender jugal (ju., JU.) and quadrato-jugal (QU. JU.) to the
quadrate. The latter (qu., QU.) is a stout, three-rayed bone
articulating by two facets on its otic process (ot. pr.} with the roof
of the tympanic cavity, sending off an orbital process (orb. pr.)
from its anterior margin, and presenting below a condyle for
articulation with the mandible ; it is freely movable upon its
tympanic articulation, so that the lower jaw has a double joint
as in Lizards and Snakes.
The palatines (pi, PAL.) have their slender anterior ends anky-
losed with the maxilla, their scroll-like posterior ends articulating
378
ZOOLOGY
SECT.
with the pterygoids and the rostrum. The pterygoids (pt., PTG.)
are rod-shaped and set obliquely ; each articulates behind with the
quadrate, and, at about the middle of its length, with the basi-
pterygoid process, a small faceted projection of the base of the
rostrum. There is no vomer in the Pigeon.
The mandible of the young Bird consists of a replacing bone,
the articular (ar., ART.), and four investing bones, the angular
(an., ANG.), supra-angular (s.an., S. ANG.), dentary (d., DNT.),
and splenial (SPL.), all having the same general relations as in
the Lizard. The hyoid apparatus (Fig. 1043) is of characteristic
form, having an arrow-shaped body (b. hy.) with a short pair
of anterior cornua (c. hy.) derived from the hyoid arch, and a
long pair of posterior cornua (c.br.,
cp.br.) from the first branchial. The
b h __p, columella (Fig. 1044) is a rod-shaped
bone ankylosed to the stapes, and
c bearing at its outer end a three-rayed
cartilage, the extra-columella (e.st.,
b.bn
b.br.z
s.al
st—
c br
e/b.br-
e.st.
FIG. 1044. — Columba livia. The columella auris
(magnified). The cartilaginous parts are dotted.
e. st. extra-stapedial ; f . st. infra-stapedial ; s. st.
supra-stapedial ; ft. stapes. (From Parker's
Zootomy.)
i.st., s.st.), fixed to the tympanic
membrane.
F». io43.-coiumba livia. Hyoid The shoulder-girdle (Fig. 1038) is
apparatus. The cartilaginous parts quite unlike that oi other Cramates.
are dotted, b.br. 1, b.br. ~, basi- mi r -i, vl
branchials; b.hy. basi-hyal ; c.br. Inere IS a pair OI stout, pillar-like
c^*£te^&hv'hvoidcOTn"' coracoids (cor.) articulating with deep
facets on the anterior border of the
sternum, and directed upwards, forwards, and outwards. The dorsal
end of each is produced into an acro-coracoid process (acr. cor.), and
below this, to the posterior aspect of the bone, is attached by
ligament a sabre-shaped scapula (scp.) which extends backwards
over the ribs, and includes, with the coracoid, an acute angle, the
coraco-scapular angle. The glenoid cavity (gl. cv.) is formed in
equal proportion by the two bones ; internal to it the scapula is
produced into an acromion process.
In front of the coracoids is a slender V-shaped bone, thefurcula
(fur.) or " merrythought," the apex of which nearly reaches the
sternum, while each of its extremities is attached by ligament to
the acromion and acro-coracoid processes of the corresponding
side in such a way that a large aperture, the foramen triosseum
XIII
PHYLUM CHORDATA
379
ret
(f.trs.), is left between the three bones of the shoulder-girdle. The
furcula is an investing bone and represents fused clavicles and
interclavicle.
Equally characteristic is the skeleton of the fore-limb. The
Immerus (Fig. 1045, 7m.) is a large, strong bone, with a greatly
expanded head and a prominent ridge for the insertion of the
pectoral muscle. In it, as in
all the other long bones, the
extremities as well as the shaft
are formed of true bone. The
radius (ra.) is slender and
nearly straight, the ulna stouter
and gently curved. There are
two large free carpals, a radiale
(ra.'} and an ulnare (ul/), and
articulating with these is a
bone called the carpometacarpus
(cp.mtcp.) consisting of two
rods, that on the pre-axial side
strong and nearly straight, that
on the post-axial side slender
and curved, fused with one
another at both their proxi-
mal and distal ends ; the
proximal end is produced, pre-
axially, into an outstanding
step-like process. The study
of development shows that
this bone is formed by the
union of the distal carpals
with three metacarpals (Fig.
1046), the second and third of
which are the two rod-like
portions of the bone, the first
the step-like projection. Ar-
ticulating with the first meta-
carpal is a single pointed
phalanx (Fig. 1045, ph. 1) ; the
second metacarpal bears two
phalanges, the proximal one
(ph.2r) produced post-axially into a flange, the distal one (ph.2")
pointed; the third metacarpal bears a single pointed phalanx (ph.3).
The pelvic girdle (Fig. 1038) resembles that of no other Vertebrate
with the exception of some Dinosaurs. The ilium (il.) is an immense
bone attached by fibrous union to the whole of the syn-sacmm and
becoming ankylosed with it in the adult. It is divisible into
pre-acetabular and post-acetabular portions of approximately equal
ra'
FIG. 1045. — Columba livia. Skeleton of the
left wing, cp.mtcp. carpo-metacarpus ; hu.
humerus ; ph. 1, phalanx of first digit ; ph. 2',
ph. 2", phalanges of second digit ; ph. 3,
phalanx of third digit ; pn. for. pneumatic
foramen, ra. radius ; ra'. radiale ; ul. ulna ;
ul'. ulnare.
380
ZOOLOGY
SECT.
ra
size. As usual it furnishes the dorsal portion of the acetabulum,
and on the posterior edge of that cavity is produced into a process,
the anti-trochanter (a.tr.), which works against the trochanter, a
process of the femur. The ventral portion
of the acetabulum is furnished in about
equal proportions by the pubis and
ischium (Fig. 1047) : it is not completely
closed by bone, but is perforated by an
aperture covered by membrane in the
recent state. Both pubis and ischium are
directed sharply backwards from their
dorsal or acetabular ends. The ischium
(is.) is a broad bone, ankylosed posteriorly
with the ilium, and separated from it in
front by an ischiatic foramen (Fig. 1038,
is. for. ; Fig. 1047, i.s.f.). The pubis -(pu.)
is a slender, curved rod, parallel with the
ventral edge of the ischium, and sepa-
FIO. 1046.— coiumba livia. rated from it by an obturator notch (Fig.
1038, obt.n. ; Fig. 1047, ob.f.). Neither
ischium nor pubis unites ventrally with
i, phalanx of first digit ; ph. 2, its fellow to f orm a symphysis.
-ph. 2' phalanges of second T ,-, -i-ji- i li _/• /-nv -I^AO
digit; ph. s, phalanx of third In the hind-limb the femur (.big. 1048,
digit; ra. radius; ul. ulna. fp \ • „ r-nrrmaraf iVolv clinrf >>rma Tf«
(From Parker's Zootomy.) Je-i \S a C nparatlVely Snort I
proximal extremity bears a prominent
trochanter (tr.) and a rounded head (hd.), the axis of which is at
right angles to the shaft of the bone ; so that the femur, and
indeed the whole limb, lies in a plane parallel with the sagittal
plane of the trunk, and is not directed outwards as in Reptiles.
Its distal end is produced r-? ^-
into pulley-like condyles.
There is a small sesa-
moid bone (i.e., a bone
developed in a tendon),
the patella (pat.), on the
extensor side of the knee-
joint. Articulating with
the femur is a very long
bone, the tibio-tarsus
(ti.ts.), produced on the
anterior face of its proxi-
a.tr
,.s.f
pit
Fia. 1047. — Coiumba livia. Left innominate of a
nestling. The cartilage is dotted, ac. acetabulum ;
a. tr. anti-trochanter; il. pre-acetabular, and il'. post-
acetabular portion of ilium ; is. ischium ; i. s. /.
ischiadic foramen ; ob. f. obturator notch ; pu. pubis.
(From Parker's Zootomy.)
mal end into a large
cnemial process (cn.pr.) for
the insertion of the extensor muscle of the thigh. Its proximal
articular surface is slightly hollowed for the condyle of the femur ;
its distal end is pulley-like, not concave like the corresponding
extremity of the tibia of other Amniota. The study of develop-
Mil
PHYLUM CHORD ATA
381
ment shows that the pulley-like distal end of the bone (Fig. 1049,
tl.l) consists of the proximal tarsals — astragalus and calcaneum—
tr which at an early period unite with the
hd_s~-;& tibia and give rise to the compound
shank-bone of the adult. The fibula
(fi.) is very small, much shorter than
the tibia, and tapers to a point at its
distal end.
Following the tibio-tarsus is an
elongated bone, the tarso-metatarsus
(Fig. 1048, ts. mtts.), presenting at its
foat—^$ proximal end a concave surface for the
^ , tibio-tarsus, and at its distal end three
distinct pulleys for the articulation of
"/* the three forwardly-directed toes. In
ti.ls —
K
mtl?
g
1
1
mtlf
— lit I t- •
-mtl?
I
fth.f.
third, and mtl.4,
1, proximal tarsal
cartilage. (From
ph.*
-ts.mlls
FIG. 1049.— Columba livia. Part of left foot of an
unhatched embryo (magnified). The cartilage is
dotted. mtl. 2, second, mtl. 3,
fourth metatarsal ; ti. tibia ; U.
cartilage ; tl. 2, distal tarsal
Parker's Zootomy.)
the young Bird the proximal end of
this bone is a separate cartilage (Fig.
1049, tl.2), representing the distal
tarsals, and followed by three distinct
metatarsals, belonging respectively to
the second, third, and fourth digits.
Thus the ankle-joint of the bird is a
mesotarsal joint, occurring, as in the
Lizard, between the proximal and
distal tarsals, and not, as in Mammals
(q.v.), between the tibia and the proxi-
mal tarsals. To the inner or pre-axial
side of the tarso-metatarsus, near its
distal end, is attached by fibrous tissue a small irregular bone, the
first metatarsal (Fig. 1048, mtts.^1). The digits have the same
FIG. 1048. — Columba livia.
Bones of the left hind-limb.
cn.pr. cneinlal process ;fe. femur ;
ft. fibula ; hd. head of femur ;
mtts. J, first metatarsal ; pat.
patella ; ph.l, phalanges of first
digit ; ph.4, phalanges of fourth
digit ; ti. ts. tibio-tarsus ; ts.
mtts. tarso-metatarsus ; tr. tro-
chanter.
382 ZOOLOGY SECT.
number of phalanges as in the Lizard, the backwardly-directed
hallux two, the second or inner toe three, the third or middle
toe four, and the fourth or outer toe five. In all four digits the
distal or ungual phalanx is pointed and curved, and serves for the
support of the horny claw.
It will be observed that every part of the Bird's skeleton presents
characteristic and indeed unique features. The vertebral column,
the skull, the sternum, the ribs, the limb-girdles, and the limbs
themselves are all so highly specialised that there is hardly a bone,
except the phalanges of the toes and the free caudal vertebrae,
which could possibly be assigned to any other Vertebrate class.
A further peculiarity is the fact that the larger proportion of the
bones contain no marrow, but are filled during life with air, and
are therefore said to be pneumatic. The cavities of the various
bones open externally in the dried skeleton by apertures called
pneumatic foramina (Fig. 1045, pn.fr,}, by which, in the entire
bird, they communicate with the air-sacs (vide p. 386). In the
Pigeon the bones of the fore-arm and hand, and of the leg, are
non-pneumatic.
Muscular System. — As might naturally be expected, the
muscles of the fore-limb are greatly modified. The powerful
downstroke of the wing by which the bird rises into and propels
itself through the air is performed by the pectoralis (Fig. 1050, pet.},
an immense muscle having about one-fifth the total weight of the
body ; it arises from the whole of the keel of the sternum (car. st.),
from the posterior part of the body of that bone (cp.st.}, and from
the clavicle (cl.), filling nearly the whole of the wedge-shaped space
between the body and the keel of the sternum and forming what
is commonly called the " breast " of the Bird. Its fibres converge
to their insertion (pet.") into the ventral aspect of the humerus
(hu., hu'.) which it depresses. The elevation of the wing is per-
formed, not, as might be expected, by a dorsally-placed muscle,
but by the subclavius (sb. civ.), arising from the anterior part of
the body of the sternum, dorsal to the pectoralis, and sending its
tendon (sb. civ'.) through the foramen triosseum to be inserted
into the dorsal aspect of the humerus. In virtue of this arrange-
ment, the foramen acting like a pulley, the direction of action
of the muscle is changed, the backward pull of the tendon raising
the humerus. There are three tensores patagii (tns. lg., tns. br.,
tns. ace.}, the action of which is to keep the pre-patagium tensely
stretched when the wing is extended. A similar muscle (tns. m. p.}
acts upon the post-patagium. The muscles of the digits are
naturally much reduced.
The muscles of the neck and tail are well developed ; those of
the back are practically atrophied, in correspondence with the
immobility of that region. In the leg certain of the muscles are
modified to form the perching mechanism. The toes are flexed
xin
PHYLUM CHORDATA
383
by two sets of tendons, deep and superficial. The deep tendons
of the three forwardly-directed digits are formed by the trifurcation
of the tendon of a single muscle, the peronceus medius ; that of the
hallux is derived from a separate muscle, the flexor perforans,
which is joined by a slip from the peronseus medius. Thus a
pull upon one tendon flexes all the toes. When the leg is bent,
as the bird settles to roost, the flexion of the tarso-metatarsus
on the shank puts the flexor tendons on the stretch as they pass
over the mesotarsal joint, and by the pull thus exerted the toes
are automatically bent round the perch by the simple action of
flexing the leg. They are kept in this position while the Bird
FIG. 1050.— Columba livia. The principal muscles of the left wing ; the greater part of the
pectoralis (pet.) is removed, car. st. carina sterni : c7. furcula ; cor. coracoid ; cor. br. br.
coraco-brachialis hrevis ; cor. br. Iff. coraco-brachialis longus ; cp. st. corpus sterni ; ext.
cp. rd. extensor carpi radialis ; ext. cp. ul. extensor carpi ulnaris ; fl. cp. ul. flexor carpi
ulnaris; gl. c. glenoid cavity ; hu. head of humerus ; hu'. its distal end ; pet. pectoralis ;
pet', its cut edge ; pet", its insertion ; prn. br. pronator brevis ; prn. Irj. pronator longus ;
pr. ptgm. pre-patagium ; pt. ptgm. post-patagium ; sb. civ. subclavius ; sb. civ', its tendon
of insertion passing through the foramen triosseum, and dotted as it goes to the humerus ;
tns. ace. tensor accessorius ; tns. br. tensor brevis ; ins. Ig. tensor longus ; tns. m. p. tensor
membrante posterioris ate.
is asleep by the mere weight of the body. The action is assisted
by a small but chafacteristic muscle, the ambiens, which arises
from the pubis, passes along the inner surface of the thigh, and
is continued into a long tendon which comes round to the outer
side of the knee, enclosed in a special sheath, and, continuing
down the leg, joins the superficial flexors of the digits.
Digestive Organs. — The mouth (Fig. 1051) is bounded above
and below by the horny beak, and there is no trace of teeth.
The tongue (tng.) is large and pointed at the tip. The pharynx
leads into a wide and distensible gullet (gul.) which soon dilates
into an immense reservoir or crop (crp.) situated at the base of
the neck, between the skin and the muscles, and immediately in
384
ZOOLOGY
SECT-
cti.coe crb.h
front of the sternum. In this cavity the food, consisting of grain,
undergoes a process of maceration before being passed into the
stomach. From the crop the gullet is continued backwards into
the stomach, which consists of two parts, the proventriculus (prvn.)
and the gizzard (giz.). The pro-
ventriculus appears externally like
a slight dilatation of the gullet ;
but its mucous membrane is very
thick, and contains numerous gas-
tric glands so large as to be
visible to the naked eye. The
gizzard has the shape of a biconvex
FIG. 1051. — Columba livia. Dissection from the right side. The body-wall, with the verte-
bral column, sternum, brain, &c., are in sagittal section ; portions of the gullet and crop
are cut away and the cloaca is opened ; nearly the whole of the ileum is removed, and
the duodenum is displaced outwards, a. ao. aortic arch ; bd. 1, bd. 2, bile-ducts ; b.fabr.
bursa Fabricii ; cbl. cerebellum ; coe. right caecum ; cpdm. coprodaeum ; cr. cere ; crb.k.
left cerebral hemisphere ; crp. crop ; cr. v. 1, first cervical vertebrae ; di.cce. diacoele ; dnt.
dentary ; duo. duodenum ; eus. ai>. aperture of Eustachian tubes ; giz. gizzard (dotted
behind the liver) ; gl. glottis ; r/u!. gullet ; Urn. ileum ; i. orb. sp. inter-orbital septum ;
Jed. right kidney ; Ing. right lung ; Ir. liver (right lobe) ; na. bristle passed from nostril
into mouth ; obi. sep. oblique septum ; o.gl. oil-gland ; pcd. pericardium ; pmx. premaxilla ;
pn. pancreas ; pn. b. pineal body ; p.nd. 1 — 3, pancreatic ducts ; pr. cv. right pre-caval ;
prdrn. proctodaeum ; prrn. proventriculus (dotted behind liver) ; pt. cv. post-caval ; ply. b.
pituitary body : pug. st. pygostyle ; r. an. right auricle ; r. br. right bronchus ; ret. rectum ;
r. vnt. right ventricle ; sp. cd. spinal cord ; spl. spleen (dotted behind liver) ; s. rhb. sinus
rhomboidalis ; s. sc,r. syn-sacrum ; st. carina sterni ; syr. syrinx ; th. v. J, first, and th. v. 5,
fifth thoracic vertebra ; tug. tongue ; tr. trachea ; ts. right testis ; ur. aperture of left ureter ;
urdm. urodasum ; v. (If. aperture of left vas deferens.
lens : its walls are very thick and its lumen small. The thickening
is due mainly to the immense development of the muscles which
radiate from two tendons, one on each of the convex surfaces. The
epithelial lining of the gizzard is very thick and horny, and of a
xm PHYLUM CHORDATA 385
yellow or green colour : its cavity always contains small stones,
which are swallowed by the Bird to aid the gizzard in grinding
up the food.
The duodenum (duo.} leaves the gizzard quite close to the
entrance of the proventriculus and forms a distinct loop enclosing
the pancreas. The rest of the small intestine is called the ileum
(Urn.) : it presents first a single loop ; then follows its greater part
coiled into a sort of spiral ; and lastly conies a single loop which
passes without change of diameter into the rectum (ret.), the
junction between the two being marked only by a pair of small
blind pouches or cceca (coe.). The cloaca is a large chamber divided
into three compartments, the coprodceum (cpdm.), which receives the
rectum, the urodceum (urdm.), into which the urinary and genital
ducts open, and the proctodceum (prdm.), which opens externally by
the anus.
There are small buccal glands opening into the mouth, but none
that can be called salivary. The liver (Ir.) is large, and is divisible
into right and left lobes, each opening by its own duct (6. d. 1,
b. d. 2) into the duodenum : there is no gall-bladder. The pancreas
(pn.) is a compact reddish gland lying in the loop of the duodenum,
into which it discharges its secretion by three ducts (pn. d. 1-3).
A thick- walled glandular pouch, the bursa Fabricii (b. fabr.), lies
against the dorsal wall of the cloaca in young Birds and opens
into the proctodseum : it atrophies in the adult.
Ductless Glands. — The spleen (spl.) is an ovoid red body, of
unusually small proportional size, attached by peritoneum to the
right side of the proventriculus. There are paired thyroids at the
base of the neck ; and, in young Pigeons, there is an elongated
ihymus on each side of the neck. The adrenals (Fig. 1060, adr.)
are irregular yellow bodies placed at the anterior ends of the kidneys.
Respiratory and Vocal Organs. — The glottis (Fig. 1051, gl.)
is situated just behind the root of the tongue, and leads into the
larynx, which is supported by cartilages — a cricoid divided into four
pieces, and paired arytenoids — but does not, as in other Vertebrates,
function as the organ of voice. The anterior part of the trachea
(tr.) has the usual position, ventral to the gullet ; but further back
it is displaced to the left by the crop, becoming ventral once more
as it enters the body-cavity, where it divides into the right (r. br.)
and left bronchi. The rings supporting the trachea are not
cartilaginous but bony, as also is the first ring of each bronchus,
those of the trachea completely surrounding the tube, those of the
bronchi incomplete mesially.
At the junction of the trachea with the bronchi occurs the
characteristic vocal organ, the syrinx (syr.), found in no other class.
The last three or four rings of the trachea (Fig. 1052, tr.), and the
first or bony half-ring of each bronchus (br.), are modified to form
a slightly dilated chamber, the tympanum, the mucous membrane
386
ZOOLOGY
SECT.
of which forms a cushion-like thickening on each side. At the
junction of the bronchi a bar of cartilage, the pessulus, extends
dorso-ventrally and supports an inconspicuous fold of mucous
membrane, the membrana semilunaris. The membranous inner
walls of the bronchi form the internal tympaniform membranes.
A pair of intrinsic syringeal muscles arise from the sides of the
trachea and are inserted into the syrinx, and a pair of sterno-
tracheal muscles arise from the sternum and are inserted into the
trachea. The voice is produced by the vibration of the semilunar
membrane : its pitch is altered by changes produced by the action
of the muscles.
The lungs (Figs. 1051, Ing., and 1052) are very small in com-
parison with the size of
the Bird, and are but
slightly distensible, being
solid, spongy organs, not
mere bags with saccu-
lr>'" lated walls as in Am-
phibia and many Rep-
tiles. Their dorsal sur-
faces fit closely into the
spaces between the ribs,
and have no peritoneal
covering : their ventral
sb.l
O..TII
ji.in
F,o. 1052,-Columb, UvU. The Im with H,e
faces are covered by a
strong sheet of fibrous
tissue, the pulmonary
aponeurosis or pleura
posterior end of the trachea, ventral aspect, a. in. (Fig. 1053, B, pul. ap.},
aperture of anterior thoracic air-sac ; br. principal • i i j:
bronchus ; br', br", br'" , secondary bronchi ; p. aper- a Special development OI
ture of abdominal air-sac; p.a. pulmonary artery f V,p npritnnpiiTn Tnrn fhiq
entering lung ; p. in. aperture of posterior thoracic
air-sac: p. v. pulmonary vein leaving lung; sb. b. membrane are inserted
aperture of interclavicular air-sac; sp.b. aperture of ,, ., ,.,
cervical air-sac ; ay. syrinx; tr. trachea. (From Small tan-like COStO-
pulmonary muscles,
which arise from the junction of the vertebral and sternal ribs.
The bronchus, on entering the lung, is continued to its posterior
end (Figs. 1052 and 1053), dividing into two branches, each of
which enters a bladder-like air-sac, formed as a dilatation of the
mucous membrane of the bronchus. One of these, the abdominal
air-sac (Fig. 1053, A, abd. a. s.), lies among the coils of the intestine ;
the other, or posterior thoracic air-sac (post. th. a. s.), is closely
applied to the side-wall of the body. The bronchus also gives off,
near its entrance into the lung, three short branches, one of which
becomes connected with an anterior thoracic air-sac (ant. th. a. s.),
situated just in front of the posterior thoracic ; another with an
interclavicular air-sac (int. clav. a. s.}, which is median and unpaired,
and connected with both lungs ; the third enters a cervical air-sac
xm
PHYLUM CHORDATA
387
(eery. a. .s.) placed
at the root of the
neck. Each side of
the interclavicular
gives off an axillary
air-sac, lying in the
arm-pit. All these
sacs are paired ex-
cept the inter-
clavicular, which is
formed by the
fusion of right and
left moieties. The
sacs are in com-
munication with the
pneumatic cavities
of the bones.
The ventral or
free walls of the
thoracic^ air-sacs of
each side are
covered by a sheet
of fibrous tissue,
the oblique septum
(obi. sept.), which is
continued forwards
to the pericardium,
and is united with
its fellow of the
opposite side in the
middle dorsal line :
it divides the cce-
lome into two com-
partments — one
containing the lungs
with the interclavi-
cular and thoracic
air-sacs, the other
(abd. cav.) the heart,
liver, stomach, in-
testine, &c., with
the abdominal air-
sacs.
Besides the
branches to the
air-sacs, the main
bronchus gives
^
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°-G>X O 3 4>
rt eTi'w o a
388 ZOOLOGY SECT.
off secondary bronchi, and these branch again, sending off tubes
which give rise to a system of fine branching and anastomosing
tubules, the " lung-capillaries," which make up the main substance
of the lung.
When the Pigeon is standing, the alternate elevation and de-
pression of the sternum, produced partly by the abdominal, partly
by the intercostal muscles, causes an alternate enlargement and
diminution of the capacity of the coelome, and thus pumps air in
and out of the lungs. During flight, when the weight is supported
by the wings, and the sternum is thus rendered relatively immov-
able, the same effect seems to be produced by the elevation and
depression of the back. In either case the inspired air rushes
through the lungs into the air-sacs and thence by diffusion into
the pneumatic cavities of the bones. Thus, while in other animals
a certain amount of unchanged or residual air is always left in
the lungs after each expiration, in Birds the residual air is confined
to the air-sacs and to the smaller branches of the bronchi, every
respiratory movement drawing a current of fresh or tidal air
through the lungs. As a result of this the aeration of the blood is
very complete and its temperature correspondingly high. It is
worthy of notice that Birds agree with Insects, the only other
typically aerial class, in having the inspired air distributed all
over the body, so that the aeration of the blood is not confined
to the limited area of an ordinary respiratory organ.
Circulatory Organs. — The heart (Fig. 1051) is of great pro-
portional size, and, like that of the Crocodile, consists of four
chambers— right and left auricles, and right and left ventricles.
There is no sinus venosus, that chamber being, as it were, absorbed
into the right auricle (Fig. 1054, A, r. au.). The right ventricle
(Fig. 1054, B) partly encircles the left, the former having a crescentic,
the latter a circular cavity in transverse sections. The left
auriculo-ventricular valve has the usual membranous structure,
consisting of two flaps connected with the wall of the ventricle by
tendons, but the corresponding valve of the right side (V.) is a
large muscular fold, very characteristic of the class.
The right auricle receives the right and left precavals (r. pro.,
pc. v.) and the postcaval (ptc.) ; the left four large pulmonary veins
(p. v.). The left ventricle (Fig. 1055, I. vn.), as in the Crocodile,
gives origin to the right aortic arch (a. ao.), but the right ventricle
(r. vn.) gives off only one trunk, the pulmonary artery, which soon
divides into two (r.p.a., l.p.a.). The left aortic arch is absent in
the adult, and it is the right alone which is continued into the
dorsal aorta. The result of this is that the systemic arteries receive
pure arterial blood from the left side of the heart, and the only
mingling of aerated and non-aerated blood is in the capillaries.
This is perhaps the most important physiological advance made
by Birds over Reptiles.
XIII
PHYLUM CHORDATA
389
The aortic arch curves over the right bronchus to reach the
dorsal body-wall, and then passes directly backwards as the dorsal
aorta (d. ao.}. Owing to the immense size of the pectoral muscles,
the arteries supplying them are of corresponding dimensions,
and the right and left innominate arteries (in. a.), from which the
carotids (c. c.), subclavians (br. a.), and pectorals (pc. a.) arise,
are actually larger than the aorta itself beyond their origin. In
correspondence with the position of the legs, the femoral (f. a.)
and sciatic (sc. a.) arteries arise very far forward : the caudal
artery (c.) is naturally small.
The most characteristic feature in the disposition of the
circulatory organs is the almost complete disappearance of the
Ir.a
FIG. 1054. — A, heart ol' the Pigeon, dorsal aspect, a.ao. arch of aorta ; br. a. brachial
artery ; br. u. brachial vein ; c.c. common carotid ; ju. jugular ; /. au. left auricle ; l.p.a. left-
pulmonary artery ; l.vn. left ventricle ; pc.v. left precaval ; ptc. postcaval ; p. v. pul-
monary veins ; r.au, r.au', right auricle ; r.p.a. right pulmonary artery ; r.pr.c. right pre-
caval ; r.vn. right ventricle. B heart of a. Bird with the right ventricle opened. L. V.
septum ventriculorum ; R. V. right ventricle ; V. right auriculo-ventricular valve. (A,
from Parker's Zootomy ; B, from Headley's Birds.)
renal portal system. There are two renal portal veins (r.p.) formed
by the bifurcation of the caudal ; but each, instead of breaking
up into capillaries in the kidney, sends off only a few small
branches (a. r. v.) which apparently carry blood to that organ,
the main vein passing forwards, through the substance of the
kidney, and joining the femoral vein (/. v.) from the leg to form
the iliac vein (i. v.), which, uniting with its fellow of the opposite
side, forms the post-caval (pt. c.). Thus the main part, at any
rate, of the blood from the caudal and pelvic regions is taken
directly to the heart, and not through the renal capillaries as in
most Fishes and all Amphibians and Reptiles.
At the point of bifurcation of the caudal veins a large coccygeo-
mesenteric vein (c. m. v.) comes off, and, running parallel with the
VOL. II B B
390
/OOLOGY
SECT.
sc
p.m.f.L
FIG. 1055. — Columba livia. The heart and chief blood-vessels, ventral aspect, a.ao. arch
of aorta ; a.m.a. anterior inesenteric artery ; a.r.v. afferent renal veins ; a.r.v'. vein bringing
blood from pelvis into renal portal system ; br.a. brachial artery ; br.v. brachial vein ;
c. caudal artery and vein ; c.c. common carotid artery ; c.m.v. coccygeo-mesenteric vein,
displaced to the right ; cce.a. cwliac artery ; d.ap. dorsal aorta ; e.c. external carotid artery ;
<>}>:/. epigastric vein ; e.r.v. efferent renal vein; /.a. femoral artery; /.?'. femoral vein ;
h.v. hepatic vein ; i.e. internal carotid artery ; i.il. internal iliac artery and vein ; i.m.
internal mammary artery and vein ; in. a. innominate artery ; i.v. iliac vein ; ju. jugular
vein ; ju'. anastomosis of jugular veins ; l.au. left auricle ; l.p.a. left pulmonary artery ;
1. inc. left pre-caval vein ; l.vn. left ventricle ; pc. left pectoral arteries and veins ; pc.a.
right pectoral artery ; pe.p. right pectoral vein ; p.m.a. posterior mesenteric artery ; />/<•.
postcaval vein ; ra.1, ra.", ra.3, renal arteries ; r.au. right auricle ; r.p. renal portal vein,
on the left side of the figure, supposed to be dissected so as to show its passage through
the right kidney ; r.p. a. right pulmonary artery ; r.prc. right pre-caval vein ; r.v. renal
vein ; r.vn. right ventricle ; sc. a. sciatic artery ; s'-.a. sciatic vein ; scl. a. subclavian artery ;
vr. vertebral artery and vein. (From Parker's Zootomy.)
PHYLUM CHORDATA
391
rectum, from which it receives tributaries, joins the portal vein.
The abdominal vein of Amphibians and Reptiles appears to be
represented, in part at least, by the epigastric vein (<']):^^^%^r:^
—*--(.,- .,„'•: ''WWi-*-"., ^^..J^^^^^T^^
FIG. 1005.— Ichthyornis victor. The restored skeleton. (After Marsh.)
ORDER 2. — ODONTOLOE.
Including Hesperornis 2 (Fig. 1064), a large diving and swimming
Bird from the Cretaceous of North America, and other less known
genera.
1 Recent investigations indicate that this is not a natural group, bxit that
its various genera will have to be distributed amongst various orders both of
Ratitse and of Carinatse.
2 Hesperornis is perhaps more nearly related to the Ratitae.
ZOOLOGY
ORDER 3.— ICHTHYORNITHES.
SECT.
Including Ickthyornis (Fig. 1065) and Apatornis. Tern-like Birds
from the Cretaceous of North America.
ORDER 4.— PYGOPODES.
Including the Divers (Colymbus) and the Grebes (Podicipes).
FIG. 1066. — Eudyptes antipodum. (After Buller.)
ORDER 5. — IMPENNES.
Including the Penguins (Aptenodytes, Eudyptes, &c., Fig. 1066).
ORDER 6. — TUBINARES.
Including the Petrels, such as the Albatrosses (Diomedea), Storm-
petrels (Oceanites), Fulmars (Fulmarws), Shearwaters (Puffinus), &c.
xm PHYLUM CHORDATA 403
ORDER 7. — STEGANOPODES.
Including the Boatswain-bird (Phaethon), Gannets (Sula), Cor-
morants or Shags (Phalacrocorax), Frigate-bird (Fregata), and
Pelicans (Pelecanus).
ORDER 8. — HERODIONES.
Including the Herons (Ardea, &c.), Storks (Ciconia, &c.), Ibises
(Ibis), Spoonbills (Platalea), and Flamingoes (Phcenicopterus).
ORDER 9. — ANSERES.
Including the Ducks (Anas, &c.), Geese (Anser), Swans (Cygnus),
and Mergansers (Mergus) ; and the Screamers (Palamedea and
Chauna).
ORDER 10. — ACCIPITRES.
Including the diurnal Birds of prey, such as the Eagles (Aquila),
Falcons (Falco), Vultures (Vtdtur, &c.), and Secretary Bird
(Gypogeranus). The American Vultures or Turkey-buzzards
(Cathartes) are sometimes placed in a distinct order.
ORDER 11. — CRYPTURI.
Including only the Tinamous (Tinamus, &c.).
ORDER 12. — GALLING.
Including the Fowls (Galhis), Pheasants (Phasianus), Grouse
(Tetrao), and other Game Birds ; Curassows (Crax), Brush-turkeys
(Megapodius), Hemipodes or Button-quails (Turnix), and the
Hoatzin (Opisthocomus).
ORDER 13. — GRALL^;.
Including the Rails (Rallus, Ocydromus, &c.), the flightless Giant
Rail (Aptornis), the Cranes (Grus, &c.), the Bustards (Otis), &c.
ORDER 14. — GAvi^:.1
Including the Gulls (Larus) ^nd Terns (Sterna), and the Auks
(Alca and Fratercula).
ORDER 15. — LIMICOL.E.
Including the Plovers (Charadrius, &c.), Oyster-catchers (Hcema-
topus), Curlews (Limosa), Jacanas (Parra), etc.
1 Sometimes united with the next two orders under the designation
. Charadriiformes.
404 ZOOLOGY SECT.
ORDER 16.— PTEROCLETES.
Including the Sand-grouse (Pterocles and Syrrhaptes).
ORDER 17. — COLUMB^E.
Including the Pigeons and Doves (Columba, Turtur, &c.), Crowned
Pigeons (Goura), and the extinct flightless Dodo (Didus) and Solitaire
(Pezophaps).
ORDER 18. — PsiTTACi.1
Including the Parrots (Psittacus, &c.), Parrakeets (Platycercus),
Cockatoos (Gacatua), Lories (Lorius), and Macaws (Am).
ORDER 19. — STRIGES.
Including the Owls (Strigidce).
ORDER 20. — PICARL^E.
A somewhat heterogeneous group including the Cuckoos (Cticu-
lidce), Plantain-eaters (Musophagidoe), Rollers (Coraciidcs), Motmots
(Momotidce), Kingfishers (Alcedinidce), Bee-eaters (Meropidca),
Hoopoes (Upupidce), Goat-suckers (Caprimulgi), Swifts (Cypselidce),
Humming Birds (Trochilidce), Colies (Colii), Trogons (Trogones),
Woodpeckers and Hornbills (Pici), &c.
ORDER 21. — PASSERES.
Including the Lyre-birds (Menum), Larks (Alaudidce), Starlings
(Sturnidce), Finches (Fringillidce), Swallows (Hinmdinidce), Black-
birds and Thrushes (Turdidce), Birds of Paradise (Paradiseidce),
Crows (Corvidce), &c.
Systematic Position of the Example.
The numerous species of Columba belong to the family Columbidce,
of the order Columbce.
The -following are the chief characters of the Columbse : There
are eleven primary remiges, the first very small ; the skull is
schizognathous (see p. 415) ; the oil-gland has no tuft of feathers ;
the vomer is vestigial ; there is a large crop ; the caeca are vestigial ;
and the young are non-precocious.
Of the two families of Columbae the Columbidce, or Doves and
Pigeons, are distinguished from the Dididce, including the Dodo and
Solitaire, by the power of flight and the accompanying typical
carinate characters of the sternum and shoulder-girdle.
In Columba there are twelve retrices ; the second primary remex
1 Sometimes combined with the Cuckoos.
xm PHYLUM CHORDATA 405
is longer than the sixth, and the proximal portion of the tarso-
inetatarsus is feathered.
3. GENERAL ORGANISATION.
In respect of range of structural variations, the entire class of
Birds is hardly the equivalent of a single order of Reptiles. Among
existing Birds, the Emu and the Raven, which may be said to stand
at opposite ends of the series, present nothing like the anatomical
differences to be found between a common Lizard and a Chameleon,
or between a Turtle and a Tortoise. Hence in dividing the class
into orders we find none of those striking distinctive characters
which separate the orders of Fishes, Amphibia, and Reptiles, but
have to be content with characters which in other groups would be
considered insignificant, such as details in the structure of the
skull and sternum, in the arrangement of the muscles of the wing
and leg, in the form of the foot, and in the peculiarities of the
newly-hatched young. It is for this reason that in the preceding
classification no diagnoses of the orders are given : to define them
adequately would involve a degree of anatomical detail quite beyond
the scope of the present work.
The differences between the two avian sub-classes, the ArchsB-
ornithes and the Neomithes, are, however, of a far more fundamental
nature ; and as Archseopteryx, the sole representative of the first of
these groups, is a unique form, and perhaps the best example of
an undoubted link between two classes — Reptiles and Birds — it
will be convenient to deal with it separately.
Sub-Class I.— Archseornithes.
Only two specimens of Archceopteryx lithographica have hitherto
been found, both in the finely-grained lithographic limestone of
Solenhofen, Bavaria, belonging to the Jurassic period. The Bird
(Fig. 1067) was about the size of a Crow, and in the fossils not only
are the bones preserved, but also many of the feathers.
The most striking feature in the organisation of this Bird is the
fact that the tail is composed of about 18 — 20 free caudal vertebrae
gradually tapering to the distal end as in a Lizard. The rectrices
are arranged in two rows, one on each side of the caudal vertebrae,
forming a long tail quite unlike that of any existing Bird. The
centra probably had biconcave faces. In addition to cervical and
thoracic ribs (which were apparently devoid of uncinates) there
were abdominal ribs, like those of Sphenodon and Crocodiles.
The skull (Fig. 1068) is proportionately large, with rounded
brain-case and strong jaws, in each of which is a series of conical
teeth lodged in sockets. There is no trace of sternum in either
VOL. II 00
406
ZOOLOGY
SECT.
case there is
specimen, and the coracoids (co.) are only partially visible : the
scapulas (sc.) are slender, curved bones, and there is a U-shaped
furcula (cL).
The bones of the upper and fore-arm are of the normal avian
character : only one caipal is certainly known (Fig. 1069, c.) : it
apparently belongs to
the distal row, and
is closely applied to
the first and second
metacarpals. Three
digits (d. 1, 2, 3) are
clearly visible in one
of the specimens—
that in the Berlin
Museum — the meta-
carpals of which are
usually stated to be
all free, in which
no
as
in other Birds, and
the hand approaches
the normal reptilian
type. The number
of phalanges follows
the usual reptilian
rule, two in the first
digit, three in the
second, and four in
the third, and the
ungual phalanx of
all three digits is
v i claw - shaped and
doubtless supported
a horny claw.
The remiges, like
the rectrices, are in a
wonderful state of
preservation (Fig.
1067^ and are
FIG. 1067.— Arclioeopteryx lithographica. From the \. .' /' ,
Berlin specimen, c. carpal; <•/. fiirciila ; co. coracoid; divisible, as USlial,
h. humerus; r. radius; sc. scapula ; M.ulna; I— IV, digits. . primaries Or
metacarpo-digitals, and secondaries or cubitals. The primaries
were probably attached to the second or to the second and third
of the digits just described.
The pelvis and the hind-limb have the usual avian character.
The tibia and fibula are separate. The foot consists of a slender
rm.'
XIII
PHYLUM CHORDATA
407
tarso-metatarsus and four digits, the hallux being small and directed
backwards.
In addition to the wing and tail-quills already referred to, there
are remains of contour feathers at the base of the neck and of wing-
FIG. IOCS. — Archaeopteryx lithographica. The skull, showing teeth and sclerotic
plates. (From Headley, after Dames.)
coverts. Moreover the rectrices are continued forwards by a series
of large feathers which extend for some distance along the sides of
FIG. 1069.— Archaeopteryx lithographica. The left manus. e. carpal ; dl, first digit
2, second digit ; 3, third digit ; m, m. metacarpals ; r. radius ; u. ulna. (From Headley,
after Dames.)
the body, and a row of similar but smaller feathers is attached along
both anterior and posterior faces of the tibio-tarsus.
A second species of Archaeopteryx, which has been named
ArchcBOpt&ryx siemensi, has been found more recently in the same
locality.
Sub-Class II.— Neornithes.
External Characters.— In the general build of the body the
Neornithes differ from Archseopteryx chiefly in the shorter and
stouter trunk, and in the point of articulation of the hind-limbs
being thrown forward, so as to be almost directly below the centre
of gravity of the body : the animal is thus enabled without effort
to support itself on the legs alone. In a word Birds are essentially
bipedal, the only exception being the young of the Hoatzin
(Opisthocomus), which uses its wings in climbing.
c o 2
408
ZOOLOGY
SECT.
The neck is always well developed, and is often, as in the Swan
and Flamingo, of immense proportional length. The cranial
portion of the head is usually not large, but the beak may attain
extraordinary dimensions, and exhibits a wide range of form. It
may be extremely short and wide for catching Moths and other
flying Insects, as in Swifts and Goatsuckers ; short and conical for
eating fruit, as in Finches ; strongly hooked for tearing the bodies
of animals, as in Birds of Prey, or for rending fruits of various kinds,
as in Parrots ; long, conical, and of great strength, as in Storks ;
slender and elongated, as in Swifts, Ibises, and Curlews ; broad and
flattened for feeding in mud, as in Ducks and Geese ; expanded at
the end, as in Spoonbills ; immensely enlarged, as in Hornbills and
Toucans. It is most commonly bent downwards at the tip, but
FIG. 1070. — A, Wing of nestling of Opistbocomus ; B, Wing of adult Apteryx ; both from
the inner (ventral) aspect, cb. 1, first cubital remex : dg. 1, dg. 2, dg. 3, digits ; pr. ptijm.
pre-patagium ; pt. ptgm. post-patagium. (A, after Pycraft ; £, after T. J. Parker.)
may be straight or curved upwards, as in the Avocet, or bent to
one side, as in the New Zealand Crook-billed Plover. It is some-
times, as in the Toucans, brilliantly coloured, and there may also be
bright coloration of the cere, as in the Macaws, and of naked spaces
on the head, as in the Cassowaries. In the latter the head is pro-
duced into a great horny prominence or " casque," supported by
an elevation of the roof of the skull. The cere is frequently absent.
The nostrils are placed at the base of the beak, except in Apteryx,
in which they are at the tip.
The essential structure of the wing — apart from its feathers — is
very uniform. As a rule all three digits are devoid of claws, as
in the Pigeon, but the Ostrich has claws on all three digits ; Rhea
on the first and sometimes on the second and third ; the Cassowary,
Emu, and Kiwi (Fig. 1070, B) on the second ; the Crested Screamer
xm PHYLUM CHORDATA 409
(Chauna) and two other species, and, as a rare abnormality, the
Common Fowl and Goose, on the first. With these exceptions the
hand of the adult bird has lost all the characters of a fore-foot ;
but in the young of the Hoatzin (Opisthocomus) claws are present
on the first two digits (Fig. 1070, A), which are sufficiently mobile
to be used in climbing. Besides the true claws horny spurs are
sometimes present on the carpo-metacarpus.
There is almost every gradation in the proportional length of
the hind-limb, from Birds in which nothing but the foot projects
beyond the contour feathers, and even the toes may be feathered,
to the long-legged Storks and Cranes, in which the distal part of
the tibio-tarsus is covered with scales as well as the foot. In
aquatic forms a fold of skin or web is stretched between the toes,
sometimes including all four digits, as in the Cormorants ; some-
times leaving the hallux free, sometimes forming a separate fringe
to each digit, as in the Coots and Grebes. As to the toes them-
selves, the commonest arrangement is for the hallux to be directed
backwards, and Nos. 2, 3, and 4 forwards, but in the Owls No. 4
is reversible, i.e., can be turned in either direction, and in the
Parrots, Woodpeckers, &c., it, as well as the hallux, is permanently
turned backwards. In the Swifts, on the other hand, all four toes
turn forwards. The hallux is frequently vestigial or absent, and
in the Ostrich No. 4 has also atrophied, producing the characteristic
two-toed foot of that Bird.
Pterylosis. — With the exception of the Penguins, most
Carinatae have the feathers arranged in distinct feather-tracts or
pterylse, separated by apteria or featherless spaces. These are
commonly much more distinct than in the Pigeon, and their form
and arrangement are of importance in classification (Fig. 1071). In
the Ratitse, apteria are usually found only in the young, the adult
having a uniform covering of feathers. The Ratitae, also, have
nothing more than the merest trace of hooklets on the barbules, so
that the barbs do not interlock and the vanes of the feathers are
downy or hair-like. In the Penguins the wing-feathers are
degenerate and scale-like.
Many Birds are quite naked when hatched, but in most cases
the body is more or less completely covered by a temporary crop
of feathers, the nestling -downs, of various forms, but always having
a short axis, soft loose barbs, devoid of interlocking apparatus, and,
except in the Emu, having no after-shaft (vide p. 410). They are
succeeded, as already described, by the permanent feathers.
Many Birds, such as the Swan, possess down-feathers or plumules
throughout life, interspersed among and hidden by the contour
feathers or pennce. In the Heron and some other Carinatse are
found powder-down patches (Fig. 1071, B, p. d. p, p. d. p'), areas
of downs, the ends of which break off and make a fine dust. Semi-
plumes are downs with a well-developed axis : filoplumes, as we
410
ZOOLOGY
SECT.
have seen (Fig. 1034, B), have an elongated axis and vestigial
vexillum.
In many Birds there springs from the under side of the quill,
near the superior umbilicus, a second vane, the after-shaft (Fig. 1072),
usually smaller than the main shaft, but sometimes of equal size.
Both among Carinatse and Ratitse we find genera with double-
shafted feathers and allied forms in which the after-shaft is rudi-
mentary or absent.
The feathers are always shed or " moulted " at regular intervals,
cv.a-pt
FIG. 1071.— A, pterylosis of Gypaetus (Bearded Vulture) ; B, of Ardea (Heron), a!, pt,
wing-tract ; c. pt, head-tract ; cd. pt, caudal tract ; cr. pt, crural tract ; e!>. apt. cervical
space ; hu. pt, humeral tract ; lat. apt, lateral space ; p. d. p., p. d. p', powder-down patches ;
sp. pt, spinal tract ; y. apt, ventral space ; w. pt, ventral tract.
as a rule annually. The old feathers drop out and new ones are
formed from the same pulps.
The colours of feathers present great variety. Black, brown, red,
orange, and yellow colours are due to the presence of definite pig-
ments, i.e. are absorption-colours. White, and in some cases
yellow, is produced by the total reflection of light from the spongy
air-containing substance of the feather, there being, as in nearly
all other natural objects, no such thing as a white pigment. Blue,
violet, and in some cases green are produced by the light from a
brown pigment becoming broken up as it passes through the super-
XIII
PHYLUM CHORDATA
411
ficial layer of the feathers in its passage to the eye : no blue or
violet pigments occur in feathers, and green pigments are very
rare. The beautiful metallic tints of many birds are entirely the
result of structure, owing their existence to a
thin, transparent, superficial layer, which acts
as a prism : in such feathers the colour changes
according to the relative position of the Bird
and of the eye of the observer with regard to
the source of light.
There is also infinite variety in the general
coloration of Birds. In many the colouring
is distinctly protective, harmonising with the
environment, and even changing with the
latter — as in the Ptarmigan, which is greyish-
brown in summer, white in winter, the former
hue helping to conceal the Bird among
herbage, the latter on snow. Frequently, as
in Pheasants and Birds of Paradise, the female
alone is protectively coloured, while the male
presents the most varied and brilliant tints,
enhanced by crests, plumes or tufts of feathers
on the wings, elongated tail, &c., &c. These
have been variously explained as " courtship
colours " for attracting the female ; as due
simply to the exuberant vitality of the male
Bird ; or as helping to keep the number of
males within proper limits by rendering them
conspicuous to their enemies. Such ornaments
as the bars and spots on the wings and tail
of many gregarious birds, such as Plovers,
fully exposed only during flight, and often
widely different in closely allied species, have
been explained as " recognition marks," ser-
ving to enable stragglers to distinguish between
a flock of their own and of some other
species.
Skeleton. — The vast majority of Birds have
saddle-shaped or heterocoelous cervical and
thoracic vertebrae, but the thoracic vertebrae
are opisthocrelous in the Impennes (Penguins),
the Gavise (Gulls), and the Limicolae (Plovers,
&c.), while in the Ichthyornithes alone they are
, . ' „,, J , T
biconcave. The spaces between adjacent
centra are traversed by a meniscus with a
suspensory ligament, as in the Pigeon (p. 374). The number of
vertebrae is very variable, especially in the cervical region, where
it rises to twenty-five in the Swan and sinks to nine in some
m
wary), showing after-
sluift and disconnected
j,ar»>s. (From
412
ZOOLOGY
SECT.
Song-birds. There is very commonly more or less fusion of
the thoracic vertebrae, and the formation of a syn-sacrum by
the concrescence of the posterior thoracic, lumbar, sacral, and
anterior caudal vertebrae is universal. The posterior cervical
and anterior thoracic vertebras commonly bear strong hypa-
pophyses or inferior processes for the origin of the great flexor
muscles of the neck. The number of true sacral vertebrae varies
from one to five. A pygostyle, formed by the fusion of more or
fewer of the caudal vertebrae, is of general occurrence, but is small
and insignificant or absent in the Ratitae.
FIG. 1073. — Sterna of various Birds. A, Gallus (common Fowl, young) ; B, Turdus (Thrush) •
C, Vultur (Vulture) ; D, Frocellaria (Petrel) ; E, Casuarius (Cassowary), ant. M pr
anterior lateral process ; car. carina ; cl. clavicle ; cor. coracoid ; fan. fontanelle ; fur.
furcula ; obi. lot. pr. oblique lateral process ; os. paired ossification of sternum in E ; os. 1,
carinal ossification in A ; os. 2, os. 3, lateral ossifications ; post. med. pr. posterior median
process ; post. lat. pr. posterior lateral process ; pr. cor. pro-coracoid ; scp scapula • sn
spina sterni. (A and E, after W. K. Parker ; B, C, and D, from Bronn's Thierreich.)
The ribs are always double-headed, the sternal ribs are ossified,
not merely calcified, and are united with the vertebral ribs by
synovial joints. Ossified uncinates are nearly always present, and
usually become ankylosed to the vertebral ribs.
What may be considered as the normal type of sternum is a
broad plate, concave dorsally from side to side, and produced
ventrally into an antero-posterior keel which is ossified from a
distinct centre (Fig. 1073, A, os. 1). The posterior edge of the bone
is either entire (D), or presents on each side of the keel one or two
xm
PHYLUM CHORDATA
413
more or less deep notches (A, B) or foramina (G). In the Ratitae
(E) the keel is either absent or reduced to the merest vestige, and
there is no trace of the carinal ossification in the young. External to
the coracoid grooves the anterior edge of the sternum is produced into
larger or smaller antero-lateral processes (ant. lat. pr.) ; in the Emu
these are of great size and are closely applied to the pericardium.
It was upon the characters of the raft-like sternum that the
group Ratitae was
founded, but the
difference between
them and the
Carinata) in this
respect is not ab-
solute, the ratite
condition having
been acquired by
many Carinatse
which have lost
the power of flight.
The keel is very
small in Ocydro-
mus, Notornis, and
Aptornis, three
flightless Rails—
the last extinct—
from New Zea-
land, and is prac-
tically absent in
the Dodo (Didus)
and Solitaire
(Pezophaps), two
gigantic extinct
Pigeons from
Mauritius and
Rodriguez, in the
Kakapo or
Ground-parrot
(Stringops) of New
Zealand, in the extinct Giant-Goose (Cnemiornis) from the same
country, and in Hesperornis. The absence of the carina may
therefore be considered as an adaptive modification of no significance
as indicating affinity.
The entire order of Penguins (Impennes) and the extinct Great
Auk (Alca impennis) are also flightless, but their wings, instead of
being functionless, are modified into powerful swimming paddles
(Fig. 1074). There has therefore, in these cases, been no reduction
either of the pectoral muscles or of the carina.
FIG. 1074. — Eudyptes pachyrbynchus (Penguin). Skeleton.
(From a photograph by A. Hamilton.)
414
ZOOLOGY
SECT.
The skull of Birds is generally remarkable for its huge orbits
separated by a thin inter-orbital septum, and for the comparatively
small size of the ethmoid bone and its turbinals. The most striking
exception is afforded by the Kiwi (Apteryx), in which the orbits
(Fig. 1075) are small and indistinct, while the olfactory chambers
(Ec. Eth.} extend backwards between the eyes ; the orbits being
therefore separated from one another by the whole width of the
organ of smell. The same thing occurs, to a less degree, in the
Moas.
In its essential features the skull is remarkably uniform through-
Nvff.OT.IV
S.Orb.F
JVv.VJl
FIG. 1075. — Apteryx mantelli. Skull of a young specimen, side view. The cartilaginous
parts are dotted. AL Sph. alisphenoid ; Anij. angular ; Cn. 1, en. 2, condyle of quadrate ; Dent.
dentary ; d. pr., d. pr. descending processes of nasal and frontal ; EC. Eth. ectoethmoid
Ex. col. extra-columella ; Ex. Oc. ex-occipital ; Fr. frontal ; Ju. jugal ; Lac. lacrymal ; lac.
for. lacrymal foramen ; Na. nasal ; na. ap. nasal aperture ; Nv. II, III, IV, optic foramen,^
transmitting also the 3rd and 4th nerves ; Nv. V, foramen for orbito-nasal nerve ; Nv. VII, '
for facial ; Pa. parietal ; Pal. palatine ; pa. oc. pr. par-occipital process ; Pmx. pre-
maxilla ; Pr. ot. pro-otic ; Qu. Ju. quadrato-jugal ; Qu. (orb. pr.) orbital process of quad-
rate ; S. Orb. F. supra-orbital foramen ; Sq. squamosal. (After T. J. Parker.)
out the class. The rounded form of the brain-case, more or less
concealed externally by ridges for the attachment of muscles ; the
upper beak, composed mainly of great triradiate premaxillse ; the
single, small, rounded occipital condyle ; the slender maxillo- jugal
arch ; the large parasphenoidal rostrum ; the freely articulated
quadrate, with its otic, orbital, and articular processes ; the absence
of the reptilian post-frontals ; and the early ankylosis of the bones —
all these characters are universal among Birds. There are, however,
endless differences in detail, some of which, connected with the
bones of the palate, are of importance in classification.
In the Ratitae and the Tinamous (Crypturi) there are large basi-
pterygoid processes (Fig. 1076, B, ptg. pr) springing, as in Lizards,
from the basi-sphenoid, and articulating with the pterygoids near
their posterior ends. The vomer (Vo) is large and broad, and is
usually connected posteriorly with the palatines (Pal), which do
not articulate with the rostrum. The maxillo-palatine processes
are comparatively small, and do not unite with one another or
with the vomer. This arrangement of the bones of the palate is
called drom.cBognathous.
xin
PHYLUM CHORDATA
415
In many Carinataa, e.g. the Pigeon and the Fowl, the basi-
pterygoid processes are either absent or spring from the base of
the rostrum. The vomer is small and pointed, or may be absent,
and the palatines articulate
posteriorly with the rostrum.
The maxillo-palatines do not
unite with one another.
These peculiarities charac-
terise the schizognathous
arrangement. In the Pas-
seres a similar arrangement
obtains, but the vomer is
broad and truncated instead
of pointed in front. This
gives the cegithognathous
arrangement. Lastly in the
Storks, Birds of Prey, Ducks
and Geese, &c., the maxillo-
palatines (Fig. 1077, mx. p)
fuse with one another in the
middle line, often giving rise
to a flat, spongy palate and
producing the desmognathous
arrangement.
The most specialised form
of skull is found in the
Parrots (Fig. 1078). In many
Birds the nasals and the
ascending process of the pre-
maxilla are very thin and
elastic where they join the
skull, and there is an unossified
space in the mesethmoid, so
that the upper beak is capable
of a considerable amount of
movement in the vertical
plane. In Parrots there is a
true joint between the upper
beak and the skull, allowing
of that movement of the
former which is so striking
in the living Bird. When
the mandible is depressed,
the contraction of the digastric
muscle causes a forward movement of the lower end of the quadrate,
which pushes forwards the maxillo-jugal bar and the palatines and
pterygoids, the latter sliding upon the rostrum. Both the maxillae
Oc.Cn.
S.Oo
FIG. 1076. — Apteryx mantelli. Skull of young
specimen, from below. The cartilaginous parts
are dotted. B. Oc. basi-occipital ; B. pta. pr.
basi-pterygoid process ; B. TIH/I. basi-temporal
EC. Eth. ecto-ethmoid : Bus. T. Eustachian tube
Ex. Col. extra-columella ; Ex. Oc. ex-occipital
Int.. Car. carotid foramen ; Mr. maxilla ; A>. I1//',
foramen for facial ; .Yr. IX, X, for glossopharyn-
geal and vagus ; Nv. XII, for hypoglossal ; Oc. Cn.
occipital condyle ; Oc. For. foramen magnum ;
/'«•'. palatine ; pa. oc. pr. par-occipital process ;
7'm.r. premaxilla ; Pt>'Ut in ApteryX, r en-
Js. ischium ; pb. pubis ; pp. pectineal process. • nJ ^nrnt. ftnr,o- Lirrk
(From Wiedersheim, after Johnson.) g111118} ana OOng-C
the skull alone is pneumatic,
while in the Hornbill every bone in the body contains air.
Myology. — As might be inferred from a study of the skeleton,
the muscles of flight undergo a
great reduction, often amounting
to complete atrophy, in the Ratitae ;
and to a less degree in the flightless
Carinatse. The presence or ab-
sence of an ambiens and of cer-
tain other muscles in the leg and
in the wing furnish characters of
considerable classificatory import-
ance.
Digestive Organs. — In all
existing Neornithes the jaws are
covered by a horny beak and there
are no teeth. But that teeth
were present in the more primi-
tive Birds, and have gradually
been lost during the evolution
of the recent orders, seems cer-
tain from the fact that the cre-
taceous Birds were toothed. In
Hesperornis (Fig. 1064) there
arp Irmo- nnniVal tppth in both FIG. 1084.— Apteryx oweni. Leftlhiiid-
limb of embryo, dorsal aspect, dist.
laWS, Set in a continuous groove. djstale; Fe -femur; Fib. fibula; fib.
•{. ' , . /T,. ,^,VP> ,1 hbulare ; Mt. tsl. 1 — 5, metatarsals ;
In IclltliyorniS (Fig. 1065) the Tib. tibia; lib. tibiale. (After T. J.
teeth are thecodont, like those
of the Crocodile, each being placed in a distinct socket. In
Gastornis and in Odontopteryx, an extinct carinate form allied
xm PHYLUM CHORDATA 421
to the Anseres, the margins of the bony jaws are produced into
strong, pointed, tooth-like prominences.
In the enteric canal the chief variations have to do with the size
of the crop and of the cseca, with the gizzard, and with the coiling
of the intestine. In grain-eating Birds the gizzard has thick
muscular walls and is lined by a thickened horny epithelium,
as in the Pigeon : in flesh-eaters, such as Gulls, Petrels, Hawks,
and Owls, it is thin- walled and lined with epithelium of the ordinary
character. In the Common Fowl and many other Birds the caeca
are of great length. A gall-bladder is usually present : the spleen is
always small. The tongue may be pointed, as in the Pigeon ; very
long and protrusible, as in Woodpeckers ; short and thick, as in
Parrots ; or modified for honey-sucking by the tip being produced
either into a brush-like organ or into paired sucking tubes.
There are variously situated buccal glands, to some of which the
name salivary is often applied.
Respiratory and Vocal Organs. — The rings of the trachea
are always ossified : the tube is frequently deflected to one side by
the crop, as in the Pigeon, and may undergo such an increase
in length as to extend beneath the skin of the abdomen, or even
into the keel of the sternum. The syrinx is either tracheo-bronchial,
as in the Pigeon, i.e., formed by the distal end of the trachea and
the proximal ends of the bronchi, or is exclusively tracheal or ex-
clusively bronchial. In singing Birds it is complex, and is provided
with numerous muscles — five or seven pairs.
The lungs are always firmly fixed to the dorsal body-wall by a
pulmonary aponeurosis, and are but slightly distensible. The
general arrangement of the air-sacs has been described in the
Pigeon (p. 386) : in Apteryx the abdominal air-sacs are small, and
are completely enclosed by the oblique septum, so as not to extend
into the abdominal cavity among the viscera. The bronchi send
off branches at right angles.
The Circulatory Organs agree in all essential respects with
those of the Pigeon : their most characteristic features are the large
size of the heart, the muscular right auriculo-ventricular valve,
the atrophy of the left aortic arch, and the vestigial character
of the renal portal system. The red blood-corpuscles are always
oval and nucleated.
Nervous System and Sense Organs.— The brain is also
very uniform in structure, being characterised by its short, rounded
hemispheres, large folded cerebellum produced forwards to meet
the hemispheres, and laterally placed optic lobes. In the embryo
the optic lobes have the normal dorsal position, and the whole
brain resembles that of a Reptile. In Apteryx, in correlation
with the reduction of the eyes, the optic lobes are very small,
and are situated on the under side of the brain. Above the
anterior commissure is a small bundle of fibres which has been
VOL. II D D
422 ZOOLOGY SECT.
considered as the homologue of the hijjpocampal commissure of
Mammals.
Apteryx is also distinguished by the high development of the
olfactory chamber, which extends from the tip of the beak to the
level of the optic foramina : the turbinals are large and complex,
and there is a vestige of the cartilage of Jacobson's organ. The
small eye differs from that of all other Birds in the absence of
a pecten, although a vestige of that organ occurs in the embryo.
The structure of the auditory organ is very uniform throughout
the class.
Urinogenital Organs. — In these, also, the general agreement
with the Pigeon is very close, the most characteristic feature being
the more or less complete atrophy of the right ovary and oviduct.
The Megistanes, Rhese, Anseres, and some other Birds have a penis
in the form of a thickening of the ventral wall of the cloaca : it
has a groove on the dorsal surface acting as a sperm-channel, and
its distal end is invaginated, in the position of rest, by an elastic
ligament. In the Ostrich there is a solid penis, like that of Chelonia
and Crocodiles : it can be retracted into a pouch of the cloaca.
Development. — The process of development in Birds has been
most thoroughly worked out in the Common Fowl, but enough is
known of the embryology of other Birds to show that the differences
are comparatively unimportant.
The ovum is always large owing to the great quantity of food-yolk ;
the protoplasm forms a small germinal disc at the upper pole. Im-
pregnation is internal, and as the oosperm passes down the oviduct
it is coated by successive secretions from the oviducal glands. It
first receives a coat of thick, viscid albumen (Fig. 1085, alb.), which,
as the egg rotates during its passage, becomes coiled at either end
into a twisted cord, the chalaza (ch.). Next, more fluid albumen
(a/6') is deposited layer by layer, then a tough, parchment-like
shell-membrane (sh. m.), and finally a calcareous shell (sh.). The
shell-membrane is double, and, at the broad end of the egg, the
two layers are separate and enclose an air-cavity (a.). The shell
may be white or variously coloured by special pigments : it consists
of three layers, and is traversed by vertical pore-canals, which are
unbranched in the Carinatse and in Apteryx, branched in the other
Ratita?.
The eggs may be laid on the bare ground or on the rocks by the
sea-shore, as in Penguins and Auks, or on the ledges on inaccessible
cliffs, as in the Sooty Albatross (Diomedea fuliginosa) ; but as a rule
a nest is constructed for their reception by the parent Birds. This
may simply be a hole in the sand, as in the Ostrich ; a mere
clearing on the hill-side surrounded by a low wall of earth, as in the
Wandering Albatross (Diomedea exulans) ; or a cylinder with
excavated top, built of grass, earth, and manure, as in the Molly-
mawks (Diomedea melanophrys, &c.). It may take the form of a
XIII
PHYLUM CHORDATA
423
burrow, as in many Petrels, Kingfishers, and Sand-martins, or it
may be more or less elaborately built or woven of sticks, moss,
leaves, hair, or feathers, showing every stage of constructive skill,
from the rude contrivance of sticks of the Pigeon and Eagle to the
accurately constructed cap- or dome-shaped nests of many familiar
Passeres. In the Tailor-Bird (Orthotomus) it is formed of leaves
sewn together, the beak acting as needle : in a Malayan Swift
(Collocalia) it is largely built of the secretion of the Bird's buccal
glands.
The number of eggs laid varies from 15-18 in the Partridge to
a single one in many Sea-birds and in the Kiwi. As a rule the size
of the eggs bears some proportion to that of the Bird, the smallest
alb
alb
Fio. 1085.— Callus bankiva (domestic Fow). Semi-diagrammatic view of the egg at the
time of laying, a. air-space ; alb. dense layer of albumen ; alb', more fluid albumen ; W.
blastoderm ; eh. chalaza ; sh. shell ; sh. m. shell-membrane ; sh. m. 1, sh. m. 2, its two
layers separated to enclose air-cavity. (From Marshall's Embryology, slightly altered.)
being those of Humming-birds, the largest those of the Moas and
of ^Epyornis : but in Apteryx the egg is of disproportionate size-
as large as a Swan's or an Albatross's, the Kiwi itself being no larger
than a barndoor Fowl.
Segmentation takes place during the passage of the egg down the
oviduct, and results, as in Reptiles, in the formation of a blasto-
derm (Fig. 1085, bl.) occupying a small area on the upper pole of
the yolk. After the egg is laid, the process of development is
arrested unless the temperature is kept up to about 37° to 40° C. :
this is usually done by the heat of the body of the parent Birds,
one or both of which sit upon, or incubate, the eggs until the young
are hatched ; but in the Australian mound-makers (Mega-
podius) the eggs are buried in heaps of decaying vegetable matter,
the decomposition of which generates the necessary heat.
D D 2
424
ZOOLOGY
SECT.
In the newly-laid egg the blastoderm is divisible, as in Reptiles,
into two parts, a central, clear area pellucida (Fig. 1086, ar . pi.) and
a peripheral area opaca (ar, op.}, and is formed of a superficial
ectoderm having below it a somewhat irregular aggregation of
cells not yet forming a definite layer.
On the surface of the area pellucida, as in the Reptiles, appears
an embryonic shield, the formation of which is due to the elonga-
tion of the ectoderm cells in a ventral direction. A primitive
knot (p. 353) is absent as a distinct structure, and there is no
invagination. In the posterior part of the area pellucida behind
the embryonic shield appears a longitudinal opaque band, the
primitive streak (pr. st.), and along the middle of this is formed a
groove, the primitive groove. The latter represents the blastopore of
the Reptiles, and there is no archenteric cavity. It is by active
7 pr.sl
me.s
FlQ. 1086. — Callus bankiva. Two stages! n the development of the blastoderm : diagram-
matic, ar. op. area opaca ; ar. pi. area pellucida ; M. head ; med. gr. medullary groove ;
mes. mesoderm, indicated by dotted outline and deeper shade ; pr. am. pro-amnion ; pr. st.
primitive streak ; -pr. v. protovertebrte. (From Marshall's Embryology, in part after Duval.)
proliferation of cells along the course of the primitive streak, which
represents the coalescent lips of the blastopore, leading to the
formation of masses of new cells that grow out laterally and
forwards into the space between the ectoderm and yolk-endoderm,
that the foundations of the mesoderm are formed. In the anterior
primitive streak-region the primitive knot of the Reptiles is repre-
sented by a close union, for a short space, of all three layers. In
front the primitive streak becomes free from the ectoderm and
unites below with the endoderm : this anterior extremity of the
primitive streak is known as the head-process.
As there is no invagination in Birds in general, there is no primitive
endoderm, and the definitive endoderm is formed solely from cells
underlying the embryonic shield. The notochord is formed by an
axial modification of the endoderm cells along the anterior primitive
streak-region and the head-process. In the latter is formed the
XIII
PHYLUM CHORDATA
425
anterior or head-part of the notochord, and from it are derived also
the mesoderm of the head and the endodermal lining of the head-
part of the enteric canal.
Immediately in front of the primitive streak the medullary
groove (med. gr.) appears, and the medullary folds which bound it
on the right and left diverge posteriorly, so as to embrace the
anterior end of the primitive streak, in just the same way as they
embrace the blastoporer in Amphioxus. In some Birds there is an
invagination at the anterior end of the primitive groove, resulting
in the formation of a neurenteric canal. Both primitive streak
FIG. 1087. — Gallus bankiva. Two stages in the development of the embryo, all. allantois;
am. cut edge of amniqn ; an. anus ; au. ap. auditory aperture ; au. s. auditory sac ; /. br.
fore-brain ; /./. fore-limb ; Ti.br. hind-brain ; h.l. hind-limb ; lit. heart ; hy. hyoid arch ;
m.br. mid-brain ; mn. mandlbular arch ; na. nostril ; t. tail. (After Duval.)
and medullary groove lie at right angles to the long axis of the
egg, the broad end of the latter being to the embryo's right.
The blastoderm gradually extends peripherally so as to cover
the yolk, and thereby becomes divisible into an embryonic portion,
from which the embryo is formed, and an extra-embryonic portion
which invests the yolk-sac, and takes no direct share in the formation
of the embryo. The extension of the ectoderm and endoderm
takes place regularly and symmetrically, but the extra-embryonic
mesoderm, while extending equally in the lateral and posterior
regions, grows forwards in the form of paired extensions, which
afterwards unite, so that for a time there is an area of the blastoderm
in front of the head of the embryo, formed of ectoderm and endoderm
only : this is called the pro-amnion (pr. am).
426
ZOOLOGY
SECT, xin
At an early period the vertebral plate or dorsal portion of mesoderm
bounding the medullary groove becomes segmented into proto-
vertebrse (Fig. 1086, B, pr. v.), and the lateral plate or ventral portion
of the same layer splits into somatic and splanchnic layers with
the crelome between (Fig. 1089, B).
Gradually the embryo becomes folded ofE from the yolk-sac, as
in other large-yolked eggs ; but, owing apparently to the confined
space in which it is enclosed, it soon turns- over so as to lie with
its left side against the yolk, and its right side facing the shell
(Fig. 1088). The body (Fig. 1087, A) becomes strongly flexed so as
to bring the head and tail almost into contact, and the head soon
acquires a proportionally immense size, with very large projecting
eyes. At first the head is quite like that of one of the lower verte-
brate embryos, with protuberant^brain-swellings (/. br., m. br., h. br.),
large square mouth,
ventrally placed
nostrils connected
by grooves with the
mouth, and three or
four pairs of gill-
slits. As in Reptiles,
there is never any
trace of gills. In
the Ostrich and Ap-
teryx, as well as in
some Carinata3, an
opercular fold grows
backwards from the
hyoid arch, and
covers the second
and third branchial
clefts. Soon the margins of the mouth grow out into a beak (Fig. 1087,
B), the clefts close, with the exception of the first, which gives rise
to the tympano-eustachian passage, and the head becomes charac-
teristically avian. The limbs are at first alike in form and size
(A, f. 1., h. I.), and the hands and feet have the character of paws,
the former with three, the latter with four digits ; but gradually
the second digit of the hand outgrows the first and third, producing
the characteristic avian manus (B), while the metatarsal region
elongates and gives rise to the equally characteristic foot. At the
same time feather-papillae make their appearance, arranged in
narrow and well-defined pteryla3.
At an early period capillaries appear in the extra-embryonic
blastoderm between the opaque and pellucid areas, and give rise
to a well-defined area vasculosa (Fig. 1088, ar. vase.) : they are
supplied by vitelline arteries from the dorsal aorta, and their blood
is returned by vitelline veins which join the portal vein and take the
all
FIG. 1088. — Gallus bankiva. Egg with embryo and foetal
appendages, a. air-space ; all. allantois ; am. anmion ;
ar.vasc. area vasculosa ; emb. embryo ; yk. yolk-sac. (After
Duval.)
5r
'
all
FIG. 1089. — Diagrams illustrating the development of the foetal membranes of a Bird. A,
early stagein the formation of the amuion, sagittal section ; B, slightly later stage, trans-
verse section ; 6', stage with completed amiiion and commencing allantois ; D, stage in
which the allantois has begun to envelop the embryo and yolk-sac. The ectoderm is
represented by a blue, the endoderm by a red line ; the mesoderm is grey. all. allantois ;
all', the same growing round the embryo and yolk-sac ; am. amnion ; arn.f., am.f. amniotic
fold ; an. anus ; br. brain ; ccel. coalome ; ccel'. extra-embryonic ccelome ; ht. heart ; ms.ent.
mesenteron ; mth. mouth ; nch. notochord ; sp. cd. spinal cord ; sr.m. serous membrane ;
umb.d. umbilical duct ; vt.m. vitellme membrane : yk. yolk-sac.
428 ZOOLOGY SECT.
blood, through the liver, to the heart. The vascular area gradually
extends, until it covers the whole of the yolk-sac : its vessels take
an important share in the absorption of the yolk by the embryo.
Before the embryo has begun to be folded ofi from the yolk the
rudiment of one of the two characteristic embryonic membranes,
the amnion, has appeared. A crescentic amniotic fold arises
(Fig. 1089, A, am.f.), in front of the head-end of the embryo, from
the region of the pro-amnion : it consists at first of ectoderm only,
the mesoderm not having yet spread into the pro-amnion. The
fold is soon continued backwards along the sides of the body (B)
and round the tail (A), but in these regions (am.f.) it consists from
the first of ectoderm plus the somatic layer of mesoderm, i.e., it
is a fold of what may be called the extra-embryonic body-wall.
The cavity is a prolongation of the space between the somatic and
splanchnic layers of mesoderm, i.e., is an extension of the extra-
embryonic ccelome.
The entire amniotic fold gradually closes in above (C), forming
a double-layered dome over the embryo. Its inner layer, formed
of ectoderm internally and mesoderm externally, is the amnion
(am.), the cavity of which becomes filled with a watery amniotic
fluid, serving as a protective water-cushion to the enclosed embryo.
Its outer layer, formed of ectoderm externally and mesoderm in-
ternally, is the serous membrane (sr. m.) : it comes to lie just beneath
the vitelline membrane, with which it subsequently fuses.
The second of the embryonic membranes, the allantois, is developed
as an outpushing of the ventral wall of the mesenteron at its posterior
end (C, all.), and consists, therefore, of a layer of splanchnic meso-
derm lined by endoderm. It has at first the form of a small ovoid
sac having the precise anatomical relations of the urinary bladder
of Amphibia (Fig. 1087, A, all.). It increases rapidly in size (Fig.
1088, all.), and makes its way, backwards and to the right, into
the extra-embryonic ccelome, between the amnion and the serous
membrane (Fig. 1089, C, D). Arteries pass to it from the dorsal
aorta, and its veins, joining with those from the yolk-sac, take the
blood through the liver to the heart. Next, the distal end of the
sac spreads itself out and extends all round the embryo and yolk-
sac (D, all'.), fusing, as it does so, with the serous and vitelline
membranes, and so coming to lie immediately beneath the shell-
membrane. It finally encloses the whole embryo and yolk-sac
together with the remains of the albumen, which has by this
time been largely absorbed. The allantois serves as the
embryonic respiratory organ, gaseous exchange readily taking place
through the porous shell ; its cavity is an embryonic urinary
bladder, excretory products being discharged into it from the
kidneys.
At the end of incubation the embryo breaks the shell, usually by
means of a little horny elevation or caruncle at the end of the beak.
xm PHYLUM CHORDATA 429
By this time the remainder of the yolk-sac has been drawn into
the coelome, and the ventral body-walls have closed round it.
On the shell being broken respiratory movements begin, the
aperture is enlarged, and the young bird is hatched and begins a
free life.
In the Ratitse, Anseres, Gallinse, and some other Birds the young
when hatched are clothed with a complete covering of down or of
feathers, and are able from the first to run about and feed them-
selves ; such Birds are called Prcecoces or Nidifugce. In the higher
types, such as the Rapacious Birds, Pigeons, and Passeres, the
young are at first either quite naked, blind and helpless, or covered
with mere patches of soft down, so that they require to be fed and
kept warm by the parents ; these forms are called Altrices or
Nidicolce. In many Sea-birds, such as Petrels, Gulls, and Penguins,
the young have a complete covering of woolly down, but remain
in the nest for a prolonged period, sometimes until the full size
is attained.
Distribution. — The Ratitse furnish an interesting case of dis-
continuous distribution. Struthio occurs in Africa and South-
western Asia, Rhea in South America, Dromaeus in Australia,
Casuarius in Australia, New Guinea, and some of the other Austro-
Malayan islands, and Apteryx in New Zealand. Thus, taking
recent forms only, each of the great Southern land-masses contains
one order of Ratitse not found elsewhere ; the Struthiones are
Ethiopian, but extend also into the adjacent part of the Paleearctic
region, the Rheee Neotropical, and the Megistanes Australasian.
YEpyornis, the affinities of which appear to be with the Megis-
tanes, occurs only in Madagascar, where it has become extinct
within — geologically speaking — comparatively recent times. When
we take the scattered distribution of the above-mentioned Ratitse
into consideration, one of the most remarkable facts in distribution
is the occurrence, in the limited area of New Zealand, of no fewer
than six genera and between twenty and thirty species of Dinor-
nithidse or Moas, some of which became extinct so short a time
ago that their skin, flesh, feathers, dung, and egg-shells are pre-
served.
Among the Carinatse the Penguins are exclusively southern,
occurring only in the South Temperate and Arctic Oceans. They
may be said to be represented in the Northern Hemisphere by the
Puffins and Auks, one of which, the Great Auk or Gare-fowl (Alca
impennis), was actually impennate, its wings being converted, as in
the Penguins, into paddles. The Crypturi (Tinamous) are exclu-
sively Neo-tropical, the Humming-birds American, the Birds of
Paradise and Bower-birds Australian and Austro -Malay an. Amongst
negative facts, the Psittaci or Parrots are characteristically absent
in the Palsearctic and most of the Nearctic region, the Finches in
430 ZOOLOGY SECT.
the Australasian region, as well as in New Zealand and Polynesia,
and the Starlings in both regions of the New World.
Birds are comparatively rare in the fossil state : their powers of
flight render them less liable to be swept away and drowned by
floods and so imbedded in deposits at the mouths of rivers or in
lakes. Up to the Cretaceous period, Archseopteryx, from the
Jurassic, is the only Bird known. In the Cretaceous of North
America toothed Birds of the orders Odontolcse and Ichthyornithes
make their appearance, while in the Eocene numerous interesting
forms occur, including the Gastornith.es and the Stereornithes.
Ethology. — It is impossible here to do more than allude, in the
briefest way, to the immense and fascinating group of facts relating
to the instincts, habits, and adaptations found in the present class.
Their social instincts, their song, their courtship-customs, the
wonderful advance in the parental instinct, leading to diminished
mortality in the young, are all subjects for which the reader must
be referred to the works on general Natural History mentioned
in the appendix. The same applies to the puzzling subject of
migration, which will be referred to in the Section on Distribution.
Phylogeny. — That Birds are descended from Reptilian ancestors,
that they are, as it has been said, " glorified Reptiles," seems
as certain as anything of the bind can well be. Apart from the
direct evidence afforded by Archaeopteryx and by the numerous
avian characteristics of Dinosauria and Ornithosauria, the indirect
evidence of anatomy and embryology is very strong. The single
occipital condyle, the six bones to each mandibular ramus, the ankle-
joint between the proximal and distal tarsals, the number of
phalanges in the digits of the foot, the epidermal exoskeleton
partly taking the form of scales, the meroblastic egg with large
food-yolk, the amnion, and the respiratory allantois, are all characters
common to Birds and Reptiles and not found together — indeed
for the most part not found at all — in any other class. For this
reason Reptiles and Birds are often conveniently grouped together,
as already stated (p. 303), as Sauropsida.
It seems probable that the earliest Birds could fly, and that their
evolution from Reptilian ancestors was directly connected with the
assumption of aerial habits. It is not unlikely that these ancestors
possessed a patagium, like that of Ornithosauria, and that, as
the scales of the fore-limb developed into feathers, this organ was
gradually reduced to the small pre- and post-patagia of the existing
Bird's wing. What was the nature of the Reptilian ancestor is
a question as yet quite unsolved. It can hardly have been a
Pterodactyle, since in that order the modification of the fore-limb
has proceeded on entirely different lines from those which charac-
terise Birds ; it cannot well have been a Dinosaur, since we have
xra PHYLUM CHORDATA 431
*t
no evidence that any member of that order was arboreal, or showed
the least tendency on the part of the fore-limb to assume the
wing-form. Nevertheless the skull and brain of Ornithosauria
and the pelvis and hind-limb of many Dinosauria show such
approximation to avian characters as can hardly be without
significance.
Probably the earliest Birds were all, in the etymological sense,
Carinatse, i.e., had the sternum provided with a keel for the attach-
ment of the pectoral muscles. Probably, also, they all possessed
teeth, and had diverged into well-marked orders before those organs
were lost. The Odontolcae, for instance, have their nearest allies
in the Divers (Pygopodes), while the Ichthyornithes resemble the
Terns, members of the widely separated order Gaviae.
In several existing types of Carinatae the power of flight is want-
ing, and in all such cases it is practically certain that Sightlessness
is due to the degeneration of the wings : in other words, that the
ancestors of the Penguins, Great Auk, Dodo, Weka (Ocydromus),
Kakapo (Stringops), &c., were ordinary flying Birds. In the
Penguins and the Great Auk the wings have simply undergone
a change of function, being converted into paddles, and con-
sequently the only parts of them which have degenerated are the
feathers ; but in the other forms referred to the wing has become
more or less functionless, and hence has diminished in size, while
the partial atrophy of the muscles has resulted in a more or less
complete reduction of the carina sterni and furculum and an increase
of the coraco-scapular angle. Now it is by an exaggeration of these
peculiarities that the Ratitse are distinguished from the Carinatse,
and there is every reason for thinking that they also are the descen-
dants of flying Birds, and that their distinctive characters — absence
of locking apparatus in the feathers* flat sternum, wide coraco-
scapular angle, &c. — are all due to degeneration correlated with
disuse of the wings. From the fact that the dromaeognathous skull
is more reptilian than any other type, it would seem that the
Ratitse diverged early from the carinate stock. From the fact
that, in the structure of the skull and pelvis, the Ostrich and Rhea
are widely separated both from one another and from the Austral-
asian Ratitaa, it seems probable that the three orders of Ratitse
arose independently from primitive Carinatse, and that the entire
division is to be looked upon as a convergent or polypliylctic group,
owing its distinctive characters, not to descent from a common
ancestor, but to the independent acquisition of similar characters
under the influence of like surroundings.
The question of the phylogeny of the orders of Carinatae is far too
complex to be discussed here. Suffice it to say that the Ichthy-
ornithes, Odontolcae, Impennes, Pygopodes, and Crypturi are to be
looked upon as the lowest or most generalised orders, while the
highest or most specialised are the Psi.ttaci, the Accipitres, the
432
ZOOLOGY
SECT.
Striges, the Picarise, and especially the Passeres. Among the latter
the Corvidse (Crows) are probably to be looked upon as the most
exalted members of the class (Fig. 1090).
PASSERES
GAVIAE
COIYMBI \ICHTHVORNITHES
N!
ODONTOLCA
GALLINAE
CRYPTURI
MEGISTANES
ORNITHOSAURIA
DINOSAURIA
FIG. 1090. — Diagram illustrating the Relationships of the chief groups of Birds.
CLASS VI. -MAMMALIA.
The class Mammalia, the highest of the Vertebrata, comprises
the Monotremes and Marsupials, the Hoofed and Clawed Quadrupeds,
the Whales and Porpoises and Sea-Cows, the Rodents, Bats and
Insectivores, the Lemurs and Apes, and the Human Species. All
Mammals, though many are aquatic, are air-breathers throughout
life, lungs being, as in Reptiles and Birds, the sole organs of respira-
tion. The blood of Mammals has a high temperature, resembling
in that respect the blood of Birds and differing from that of Reptiles
and Amphibia. The scales of Reptiles and the feathers of Birds
are replaced in Mammals by peculiar epidermal structures, the
hairs, usually developed in such quantities as to form a thick, soft
covering or fur. The young are nourished after birth by the secre-
tion of mammary or milk-glands.
1. EXAMPLE OF THE CLASS — THE RABBIT (Lepus cuniculus).
External Characters. — The Rabbit (Fig. 1091) is a four-
footed or quadrupedal animal, having the whole surface of its
body covered with soft fur. The head bears below its anterior
PHYLUM CHORDATA
433
extremity the mouth, in the form of a transverse slit bounded by
soft lips. The upper lip is divided by a longitudinal cleft, running
backwards to the nostrils, and exposing the chisel-shaped incisor
teeth. Behind the incisor teeth the hairy integument projects on
each side into the cavity of the mouth. At the end of the snout,
above the mouth, are the nostrils, in the shape of two oblique slits.
The large eyes, situated at the sides of the head, have each three
eyelids, an upper and a lower hairy lid, and an anterior hairless
third eyelid or nictitating membrane, supported by a plate of cartilage.
Vibrissce — very long stiff hairs — are scattered above and below the
eyes and on the snout. Behind the eyes, and a little nearer the
summit of the head, are a pair of very long flexible and movable
external ears or pinnce. These are somewhat spout-shaped,
expanding distally, and are usually placed vertically with the
concavity directed laterally and somewhat forwards, leading to the
FIG. 1091. — Lepus cuniculus. Lateral view of skeleton with outline of body.
external auditory opening. The neck is a distinct constriction, but
relatively short as compared with the neck of the Pigeon. The
trunk is distinguishable into thorax in front and abdomen behind.
On the ventral surface of the abdomen in the female are four or five
pairs of little papillse— the teats. At its posterior end, below the
root of the tail, is the anal opening, and in front of this in the male
is the penis, with a small terminal urinogenital aperture, and with
the testes, each in a prominent scrotal sac, at the sides ; and in the
female the opening of the vulva. In the space (perinceum) between
anus and penis or vulva are two bare, depressed areas of skin into
which open the ducts of certain glands — the perinceal glands — with
a secretion having a strong and characteristic odour. The tail is
very short and covered with a tuft of fluffy fur.
The fore- and hind-limbs, both of which take part in locomotion
and in supporting the weight of the animal, differ considerably in
size — the fore-limbs being much shorter than the hind-limbs.
Both have the same general divisions as in the Lizard. The upper
434
ZOOLOGY
SECT
arm is almost completely hidden by the skin, being applied closely
against the side of the body. The manus is provided with five
digits, each terminating in a horny claw. The thigh is also almost
hidden by the skin ; the pes has four digits only, all provided with
claws.
Skeleton. — The spinal column of the Rabbit is divisible, like
that of the Pigeon and the Lizard, into five regions — the cervical,
the thoracic, the lumbar, the sacral, and the caudal. In the cervical
region there are seven vertebrae ; in the thoracic twelve, or some-
times thirteen, in the lumbar seven, or sometimes six, in the sacral
four, and in the caudal about fifteen.
The centra of the vertebrae in a young Rabbit consist of three
parts — a middle part which is the thickest, and two thin discs of
bone — the epiphyses — anterior and posterior, applied respectively
to the anterior and posterior faces of the middle part or centrum
proper. Between successive centra in an unmacerated skeleton
are thin disc-like plates of fibro-cartilage — the inter-vertebral discs.
The transverse processes of all the cervical vertebrae, except the
seventh or last, are perforated by a canal, the vertebrarterial canal,
for the passage of the vertebral artery. The first vertebra or atlas
(Fig. 1092, A) resembles the corresponding Vertebra of the Pigeon
in being of the shape of a ring without any solid centrum like that
met
cent
FIG. 1092. — Lepus cuniculus. A, atlas and axis, ventral aspect, od. odontoid process o
axis. B, lateral view of axis. art. articular facet for atlas ; od. odontoid process ; pt. zy
post-zygapophysis ; sp. neural spine. C, thoracic vertebrae, lateral view. cent, centrum
fac. facet for rib ; met. metapophysis ; pr.zy. pre-zygapophysis ; pt. zy. post-zygapophysis
rb. rib ; sp. spinous process.
of the rest. On the anterior face of its lateral portions are two
concave articular surfaces for the two condyles of the skull. The
second vertebra or axis (A and B) bears on the anterior face of its
centrum a peg-like process — the odontoid process (od.) — which fits
into the ventral part of the ring of the atlas : it has a compressed
spine (sp.), produced in the antero-posterior direction ; its transverse
processes are short and perforated by a canal for the vertebral
artery. All the cervical vertebrae except the last have their trans-
verse processes bifurcated into dorsal and ventral lamellae. The
seventh differs from the others in having a more elongated neural
spine, in having its transverse processes simple and without perfora-
xm PHYLUM CHORDATA 435
tion for the vertebral artery, and in the presence on the posterior
edge of the centrum of a little concave semi-lunar facet.
The thoracic vertebrae (C) have elongated spines which are mostly
directed backwards as well as upwards. The transverse processes
are short and stout ; each bears near its extremity a small smooth
articular surface or tubercular facet for the tubercle of a rib. On
the anterior and posterior borders of each vertebra is a little semi-
lunar facet, the capitular facet (fac.), situated at the junction of
the centrum and the neural arch. The two contiguous semi-lunar
facets of successive vertebras form between them a little cup-like
concavity into which the head or capitulum of a rib is received.
The semi-lunar facet on the last cervical vertebra forms, with that
on the anterior border of the first thoracic, the concavity for the
head of the first rib.
In the lumbar region the spines are comparatively short, and
both transverse processes and bodies are devoid of facets. From
the centrum of each of the first two (or three) projects downwards
a short flattened process — the liypapophysis. Certain accessory
processes — the metapophyses (met.} and anapophyses — are well-
developed, the former being extremely long in the posterior lumbar
region. The metapophyses are situated in front, projecting forwards
and outwards over the pre-zygapophyses ; and the anapophyses
are situated below the post-zygapophyses and project backwards.
The transverse processes are long, and are directed forwards and
outwards ; that of the last lumbar is bifurcated.
The sacral vertebrae are firmly ankylosed together to form a
single composite bone, the sacrum. The vertebrae bear a close
resemblance to those of the lumbar region, but the hypapophyses
and anapophyses are wanting, and the metapophyses are com-
paratively small. The first and second bear great expanded lateral
processes, or sacral ribs, with roughened external surfaces for
articulation with the ilia. These are the only sacral vertebrae in
the strict sense of the term, the following two being in reality
anterior caudal.
Of the caudal vertebrae the more anterior resemble those of the
sacral region, and have similar processes ; but as we pass back-
wards in the caudal region all the processes gradually diminish in
size, the most posterior vertebra being represented merely by nearly
cylindrical centra.
There are twelve pairs of ribs, of which the first seven are known
as true ribs, i.e. are connected by their cartilaginous sternal parts
with the sternum ; while the remaining five, the so-called false or
floating ribs, are not directly connected with the sternum. All,
except the last four, bear two articular facets, one on the vertebral
extremity or capitulum, and the other on a little elevation "or
tubercle situated at a little distance from this— the former for
the bodies, the latter for the transverss prosssses of the verbebraa.
436 ZOOLOGY SECT, xm
The sternum consists of six segments or sternebrce: the first,
the manubrium sterni or presternum, is larger than the rest, and
has a ventral keel. With the last is connected a rounded
cartilaginous plate, the xiphisternum.
The skull (Figs. 1093, 1094), if we leave the jaws out of account,
is not at all unlike that of the Pigeon in general shape. The
length is great as compared with either the breadth or the depth ;
the maxillary region, or region of the snout (corresponding to
the beak of the Pigeon), is long in proportion to the rest, the orbits
closely approximated, being separated only by a thin inter-orbital
partition, and the optic foramina united into one. But certain
important differences are to be recognised at once. One of these
is in the mode of union of the constituent bones. In the Pigeon,
as we have seen, long before maturity is attained, the bony
elements of the skull, originally distinct, become completely fused
together so that their limits are no longer distinguishable. In
the Rabbit, on the other hand, such fusion between elements
only takes place in a few instances, the majority of the bones re-
maining more or less distinct throughout life. The lines along
which the edges of contiguous bones are united — the sutures as they
are termed — are sometimes straight, sometimes wavy, sometimes
zig-zagged serrations of the edges of the two bones interlocking ;
in some cases the edges of the bones are bevelled off and the
bevelled edges overlap, forming what is termed a squamous suture.
Another conspicuous difference between the skull of the Rabbit
and that of the Pigeon is in the mode of connection of the lower
jaw, which in the former articulates directly with the skull — the
quadrate, through which the union is effected in the Pigeon, being
apparently absent. Certain large apertures which are distinguish-
able are readily identified with the large openings in the skull of
the Pigeon. In the posterior wall of the skull is a large rounded
opening, the foramen magnum, flanked with a pair of smooth
rounded elevations or condyles for articulation with the first
vertebra, these obviously corresponding to the single condyle
situated in the middle below the foramen in the Pigeon. A large
opening, situated at the end of the snout and looking forwards,
obviously takes the place of the external nares of the Pigeon ;
and a large opening in the roof of the mouth, leading forward to
the external nasal opening, plainly represents, though much wider
and situated further back, the internal or posterior nares of the
Pigeon ; while the rounded tubular opening (and. me.} situated at
the side of the posterior part of the skull, some distance behind
the orbit, is evidently the same as the auditory aperture of the
Pigeon.
Surrounding the large opening of the foramen magnum are the
bones of the occipital region of the skull, the supra-, ex- and basi-
occipitals. The first of these (s. oc.) is a large plate of bone whose
opl.fo
o. sph
Icr
nas
cc.c
s.oc
FIG. 1093.— Lepus cuniculus. Skull. A, lateral view; B, ventral view. ang. proc.
angular process of mandible ; a.s. alisphenoid (external pterygolcl process) ; and. me.
external auditory meatus ; b. oc. basi-occipital ; b.sph. basi-sphenoid ; cond. condyle ;
fr. frontal ; int.pa. interparietal ; i.o.f. infra-orbital foramen ; ju. jugal ; Icr. lacrymal ; m.
molars ; max. maxilla ; nas. nasal ; opt. fo. optic foramen ; o.sph. orbito-sphenoid ; pa.
parietal ; pal. palatine ; pal. max. palatine plate of maxilla ; par.oc. paroccipital process ;
pal. p. max. palatine process of pre-maxilla ; p.m. pre-molars ; p. max. pre-maxilla ; pr.sph.
pre-sphenoid ; pt. pterygoid ; p. t. sq. post-tympanic process of squamosal ; s. oc. supra-
occipital ; sph. points to position of sphenoidal fissure, not clearly visible in a lateral view ;
sq. squamosal ; st.fo. stylomastoid foramen ; ty.bul. tympanic bulla ; vo. vomer ; zyg. max.
zygomatic process of maxilla.
438 ZOOLOGY SECT.
external surface is directed backwards and upwards, and elevated
in the middle into a shield-shaped prominence. The ex-occipitals
lie at the sides of the opening, and each bears the greater part of
the somewhat oval prominence or condyle with which the corre-
sponding surface of the atlas or first vertebra articulates. Each is
produced below into a process called the par-occipital (par. oc.),
closely applied to the tympanic bulla. At the end of this,
imbedded in the tendon of a muscle, the styloglossus, is a small
bony rod, the stylo-liyal. A small aperture, the condylar foramen,
situated below the condyle, is for the passage of one of the cerebral
nerves, the hypoglossal. The basi- occipital is a median plate of
bone, almost horizontal in position, which forms the floor of the
most posterior part of the cranial cavity ; it bears the lower third
of the occipital condyles. All these four bones of the occipital
region are in the adult Rabbit united together to form the single
occipital bone. Articulating in front with the basi-occipital, but
separated from it by a plate of cartilage, is a plate of bone, also
horizontal in position, which forms the middle part of the floor
of the cranial cavity. This is the basi-sphenoid ; it is perforated
at about its middle by an oval foramen — the pituitary foramen
—and on its upper surface is a depression, the sella turcica, or
pituitary fossa (Fig. 1094, s.t.), in which the pituitary body rests.
In front of it is another median bone of laterally compressed form,
the pre-sphenoid, with which it is connected by cartilage, the removal
of which leaves a gap in the dried skull ; the pre-sphenoid forms
the lower boundary of the single large optic foramen (Fig. 1093,
opt.fo.) Connected laterally with the basi-sphenoid and pre-sphenoid
are two pairs of thin irregular plates, the ali-sphenoids (as.) behind
and the orbito- sphenoids (o. sph.) in front. The alisphenoids are
broad wing-like bones, each produced below into a bilaminate
process, the pterygoid process. A large foramen, the sphenoidal
fissure (sph.), situated between the basisphenoid and the alisphenoid
of each side, transmits from the interior of the skull the third
and fourth cerebral nerves, the first and second divisions of the
fifth, and the sixth nerves.
The boundary of the anterior part of the brain- case is com-
pleted by a narrow plate of bone, the cribriform plate of the ethmoid
(Fig. 1094, eth.), perforated by numerous small foramina for the
passage of the olfactory nerves. This cribriform plate forms a
part of a median vertical bone, the mesethmoid, the remainder of
which, or lamina perpendicularis, forms the bony part of the
partition (completed by cartilage in the unmacerated skull) between
the nasal cavities. Fused with the mesethmoid are two lateral,
thin, twisted bones, the ethmo-turbinals (e. tb), and with its inferior
edge articulates a long median bone, with a pair of delicate lateral
wings, the vomer (vo.). None of these, with the exception of the
cribriform plate, take any share in the bounding of the cavity
xm PHYLUM CHORDATA 439
of the cranium. Hoofing over the part of the cranial cavity the
walls and floor of which are formed by the sphenoid elements,
is a pair of investing bones, the parietals (Fig. 1093, pa.}, and further
forward is another pair, the f rentals (//".)• The parietals are plate-
like bones, convex externally, concave internally, which articulate
with the supra-occipital behind by a transverse serrated lamb-
doidal suture. The right and left parietals articulate together
by means of a somewhat wavy suture, the sagittal ; in front a
transverse serrated suture, the coronal, connects them with the
frontals. Between the supra-occipital and the parietals is a median
ossification or inter-parietal (int. pa.). The frontals are inti-
mately united along the middle line by means of the frontal
suture. Laterally their orbital plates form an important part
of the upper portion of the inner wall of the orbit ; above
this, over each orbit, is a curved, somewhat crescentic process, the
supra-orbital process. Between the alisphenoid below, the parietal
and frontal above, the frontal and orbito-sphenoid in front, and
the parietal behind, is a. broad bone (sq.), the superior margin of
which is bevelled off : this is the squamosal. It is produced in
front into a strong zygomatic process, which curves outwards, then
downwards, and finally forwards, to unite with the jugal in the
formation of the zygomatic arch. Below the root of the process
is a hollow, the glenoid fossa. Behind the squamosal gives off a
slender process, the post-tympanic process (p. t. sq.), which becomes
applied to the outer surface of the periotic.
Between the occipital and parietal bones, below and behind the
squamosal, are the tympanic and periotic bones. The tympanic
forms the bony part of the wall of the external auditory meatus ;
below it is dilated to form a process (ty. bul.) projecting on the
under surface of the skull — the bulla tympani. The periotic is a
bone of irregular shape, its internal (petrous) portion (Fig. 1094,
peri) enclosing the parts of the membranous labyrinth of the
internal ear, and externally presenting two small openings— the
fenestra ovalis and fenestra rotunda — visible only when the tym-
panic is removed ; internally it bears a depression, the fioccular
fossa, for the lodgment of the flocculus of the cerebellum. Part
of the periotic (mastoid portion) is seen on the exterior of the
skull between the tympanic and exoccipital. The periotic and
tympanic are not ankylosed together, and are loosely connected
with the surrounding bones, being held in position by the post-
tympanic processes of the squamosal. Between the tympanic and
periotic are two foramina of importance — the stylomastoid, which
transmits the seventh cerebral nerve, and the Eustachian aperture,
at which the Eustachian tube opens.
Roofing over the olfactory cavities are two flat bones — the nasals
(nas.) — each having on its inner surface a very thin hollow process,
the naso-turbinal. In front of the nasals are the premaxillae
440 ZOOLOGY SECT.
(p. max) — large bones which form the anterior part of the snout,
bear the upper incisor teeth, and give off three processes — a nasal,
a palatine (pal. p. max), and a maxillary. The maxillce (max.],
which form the greater part of the upper jaw, and bear the pre-
molar and molar teeth, are large, irregularly-shaped bones, the
outer surfaces of which are spongy. They give off internally
horizontal processes — the palatine processes (pal. max] — which
unite to form the anterior part of the bony palate. Between the
premaxillse and maxilla? and the palatines on the lower surface
of the skull is a large triangular opening divided into two — the
anterior palatine foramina — by the palatine processes of the pre-
maxillse. On the outer surface of each maxilla, above the first
premolar tooth, is a foramen — the infra-orbital (i.o.f.) — through
which the second division of the fifth nerve passes. A strong
process which is given off from the outer face of each maxilla,
and turns outwards and then backwards to unite with the zygomatic
process of the squamosal and thus complete the zygomatic arch,
is a separate bone in the young, the malar orjugal (ju.).
The maxilla? help to bound the nasal cavities externally, and
with each is connected on its inner aspect a pair of thin scroll-like
bones — the maxillo-turbinals (Fig. 1094, mx. tb.). The rest of the
narrow bony palate, forming the roof of the mouth and the floor of
the nasal cavities, is formed by the palatine plates of the palatine
bones (pal.). The so-called pterygoids (pt.) are small irregular
bones, each of which articulates with the palatine in front and
with the pterygoid process of the alisphenoid behind : these are
probably not the equivalents of the pterygoids of other Vertebrates,
but of part of the parasphenoid. The lacrymals (kr.) are small
bones, one situated in the anterior wall of each orbit, perforated
by a small aperture — the lacrymal foramen.
In the interior of the skull (Fig. 10£4) are three cavities, the
two olfactory or nasal cavities, right and left, in front, and the
cranial cavity behind. The former are separated from one another
by a median partition or septum, partly cartilaginous, partly bony,
formed, as above described, by the mesethmoid. Each contains the
turbinals or turbinated bones of its side ; it opens on the exterior
by the large external nasal aperture, and behind it communicates
with the cavity of the mouth by the posterior nasal aperture.
The cranial cavity has its walls moulded to a considerable extent
on the surface of the contained brain, and, in consequence, there
are to be recognised concavities in the former corresponding with
the prominent portions of the latter. These concavities are termed
the fossce, and they consist of the cerebellar fossa behind and the
cerebral fossa in front, with the inconspicuous olfactory fossa in the
frontal region.
The mandible, or lower jaw, consists of two lateral halves or rami,
which are connected with one another in front by a rough articular
Xin
PHYLUM CHORDATA
441
surface or symyihysis, while behind they diverge like the limbs of a
letter V. In each ramus is a horizontal portion (anterior), which
bears the teeth, and a vertical or ascending portion, on which is
the articular surface or condyle (cond.) for articulation with the
glenoid cavity of the squarnosal ; in front of the condyle is the
compressed coronoid process. The angle where the horizontal and
ascending processes meet gives off an inward projection or angular
process (ang. pro.).
The liyoid consists, in addition to the separate vestigial stylo-
hyals already mentioned (p. 438), of a stout thick body or basi-hyal,
a pair of small anterior cornua or cerato-hyals, and a pair of long
backwardly directed cornua or thyro-Jiyals.
The auditory ossicles, contained in the cavity of the middle ear,
mortb
p.m
tybul par.oc
-/ p,sph
FIG. 1094. — Lepus cuniculus. Skull in longitudinal vertical section. The cartilaginous
nasal septum is removed, a. sph. alisphenoid ; e. oc. exoccipital ; e. tb. ethmo-turbinal ;
tth. ethmoid ; ft. fossa for flocculus of brain ; i. incisors ; mx. tb. maxillary turbinal ; n. tb.
naso-turbinal ; pal', palatine portion of the bony palate ; peri, periotic (petrous portion) ;
p. sph. pre-sphenoid ; sph. f. sphenoidal fissure ; s.t. sella turcica, or depression in which the
pituitary body lies ; I. point at which the olfactory nerves leave the skull ; II. optic
foramen ; V. mn. foramen for mandibular division of trigeminal ; VII. for facial nerve ;
VIII. for auditory nerve ; IX, X, XI, for glossopharyngeal, vagus, and spinal accessory;
XII. for hypoglossal. Other letters as in Fig. 1093. (From Parker's Practical Zoology.)
and cut off from the exterior, in the unmacerated skull, by the
tympanic membrane, are extremely small bones, which form a
chain extending, like the columella auris of the Pigeon, from the
tympanic membrane externally to the fenestra ovalis internally.
There are three of these auditory ossicles — the stapes, which corre-
sponds to the columella of the Pigeon ; the incus, and the malleus,
the latter with a slender process (processus gracilis) : these are said
to be derived respectively from the quadrate and articular elements
(q.v.) of lower vertebrates. In addition there is a small disc-like
bone, the orbicular, which is attached to the incus.
The elements of the pectoral arch are fewer than in the Lizard.
There is a broad, thin, triangular scapula, the base or vertebral edge
of which has a thin strip of cartilage (the supra-scapular cartilage)
continuous with it. Along the outer surface runs a ridge — the
spine ; the spine ends below in a long process — the acromion process
VOL. II E E
442 ZOOLOGY
• — from which a branch process or metacromion is given off behind.
The part of the outer surface of the scapula in front of the spine
is the pre-spinous or pre-scapular fossa, the part behind is the
post-spinous or post-scapular fossa. At the narrow lower end of
the scapula is a concave surface — the glenoid cavity — into which
the head of the humerus fits, and immediately in front of this is
a small inwardly curved process — the coracoid process — which is
represented by two separate ossifications in the young Rabbit.
A slender rod — the clavicle — lies obliquely in the region between
the pre-sternurn and the scapula, but only extends a part of the
distance between the two bones, and in the adult is only connected
with them through the intermediation of fibrous tissue.
The skeleton of the fore-limb is more readily comparable with
that of the Lizard than with that of the Bird ; but there is a
difference in the position of the parts owing to the rotation baek-
wards of the distal end of the humerus, all the segments being
thus brought into a plane nearly parallel with the median vertical
plane of the body, with the pre-axial border directed outwards,
and the original dorsal surface backwards. The radius and ulna
are fixed in the position of pronation, i.e., the distal end of the radius
is rotated inwards, so that, while the proximal end is external to
the ulna, the distal end becomes internal, and the digits of the
manus are directed forwards.
At the proximal end of the humerus are to be recognised :
(1) a rounded head for articulation with the glenoid cavity of
the scapula ; (2) externally a greater and (3) internally a lesser
tuberosity for the insertion of muscles ; (4) a groove, the bicipital
groove, between the two tuberosities. On the anterior surface
of the proximal portion of the shaft is a slight ridge, the deltoid
ridge. At the distal end are two articular surfaces, one large and
pulley-like — trochlea — for the ulna ; the other smaller — capitellum
—for the radius : laterally are two prominences or condyles, an
internal and an external.
The radius and ulna are firmly fixed together so as to be in-
capable of movement, but are not actually ankylosed. The radius
articulates proximally with the humerus, distally with the scaphoid
and lunar bones of the carpus. The ulna presents on the anterior
aspect of its proximal end a deep fossa, the greater sigmoid cavity,
for the trochlea of the humerus ; the prominent process on the
proximal side of this is the olecranon process. Distally it articulates
with the cuneiform.
The carpal bones (Fig. 1095), nine in number, are all small
bones of irregular shape. Eight of these are arranged in two
rows — a proximal and a distal ; the ninth, centrale (cent.), lies
between the two rows. The bones of the proximal row are-
taken in order from the inner to the outer side — scaphoid (sc.),
lunar (or semi-lunar) (lun.), cuneiform (cun.), and pisiform. Those
PHYLUM CttORDATA
443
of the distal row are, reckoned in the same order, trapezium (trpm.),
trapezoid (trpz.), magnum (mag.), and unciform (unc.).1
The five metacarpals are all small but relatively narrow and
elongated bones, the first being smaller than the rest. Each of
the five digits has three phalanges, except the first, which has
only two. The distal (ungual) phalanges are grooved dorsally
for the attachment of the horny claw.
The pelvic arch (Fig. 1096) contains the same elements as in the
Pigeon, but the union of the ilium with the sacrum is less intimate,
the acetabulum is not perforated, and the pubes and ischia of oppo-
site sides unite ventrally in a symphysis (sy.). The three bones
of the pelvis— ilium, pubis, and ischium — are separate ossifications
rad
uln
FIG. 1095. — Lcpus cuniculus. Distal
end of fore-arm and carpus, dorsal
view, the bones bent towards the
dorsal side so as to be partly sepa-
rated, cent, centrale ; cun. cuneiform ;
lun. lunar ; mag. magnum ; rad.
radius ; sc. scaphoid ; trpz. trapezoid ;
trpm. trapezium ; uln. ulna ; unc.
unciform ; I—V, bases of metacarpals.
(After Krause.)
FIG. 1096. — Lepus cuniculus. Innomi-
nate bones and sacrum, ventral aspect.
acet. acetabulum ; il. ilium ; isch. ischium ;
obi. obturator foramen ; pub. pubis ;
sacr. sacrum ; sy. symphysis.
in the young Rabbit ; but in an adult animal complete fusion
takes place between the bones. The ilium and ischium meet in
the acetabulum or articular cavity, which they contribute to form,
for the head of the femur ; but the remainder of the cavity is
bounded, not by the pubis, but by a small intercalated ossification
—the cotyloid bone. The ilium (il.) has a rough surface for articu-
lation with the sacrum. Between the pubis (pub.) in front and
the ischium (isch.) behind is a large aperture — the obturator foramen
(obt.). The femur is rotated forwards when compared with that
• The homologies of these bones are not quite certain, but are very probably
as follows : — scaphoid = radiale, lunar = 1st centrale, cuneiform = inter-
medium, pisiform = ulnare, centrale = 2nd centrale, trapezium == 1st distale,
trapezoid = 2nd distale, magnum = 3rd distale, unciform = 4th and 6th
distalia.
E E 2
444
ZOOLOGY
SfiCT.
cal
cub-
ctst
nav
cuu
of the Lizard, so that the limb is nearly in the same plane as the
fore-limb, and the pre-axial border is internal and the originally
dorsal surface anterior. The femur has at its proximal end a
prominent head for articulation with the acetabulum, external to
this a prominent process — the great trochanter, and internally a
much smaller — the lesser trochanter, while a small process or third
trochanter is situated on the outer border a little below the great
trochanter. At its distal end are two prominences or condyles,
with a depression between them. Two small sesamoids or fabellce
are situated opposite the distal end on its posterior aspect ; and
opposite the knee-joint, or articulation
between the femur and the tibia, is a
larger bone of similar character — the
knee-cap or patella. The tibia has at its
proximal end two articular surfaces for
the condyles of the femur ; distally it
has also two articular surfaces, one, in-
ternal, for the astragalus, the other for
the calcaneum. The fibula is a slender
bone which becomes completely fused
distally with the tibia.
The tarsus (Fig. 1097) consists of six
bones of irregular shape, arranged in two
rows, one of the bones — the navicular
(nav.) — being intercalated between the
two rows. In the proximal row are two
bones — the astragalus (ast.) and the cal-
caneum (cal.) — both articulating with the
tibia ; the calcaneum presents behind a
long calcaneal process. The distal row
contains three bones, the meso-cuneiform,
ecto-cuneiform, and cuboid (cub.) ; the ento-
cuneiform, which commonly forms the
FIG. io97.-i.eius cunicuius. most internal member of this row in other
skeleton of pes. ast. astra- Mammals, is not present as a separate
galus ; cal. calcaneum ; cub. , •,
cuboid ; cun. cuneiforms ; DOne.
nav. navicular. There are four metatarsals, the hallux
or first digit being vestigial and fused with the second metatarsal in
the adult. The proximal end of the second is produced into a
process which articulates with the navicular. Each of the digits
has three phalanges, which are similar in character to those of the
manus.
The coelome of the Eabbit differs from that of the Pigeon and
1 In all probability the homologies of these bones are as follows : — astra-
galus = tibiale + intermedium, calcaneum = fibulare, navicular = centrale,
ento -cuneiform = 1st distale, meso-cuneiform = 2nd distale, ecto-cuneiform =
3rd distale, cuboid = 4th and 5th distalia.
XTTT
PHYLUM CHORDATA
445
Lizard in being divided into two parts by a transverse muscular
partition, the diaphragm. The anterior part, or thorax, contains
the heart and the roots of the great vessels, the lungs and bronchi,
and the posterior part of the oesophagus. The posterior part, or
abdomen, contains the stomach and intestine, the liver and pancreas,
the spleen, the kidneys, ureters and urinary bladder, and the organs
of reproduction.
Digestive Organs. — The teeth (Fig. 1093) are lodged in sockets
or alveoli in the pre-maxillse, the maxillae, and the mandible. In
the pre-maxillse are situated four teeth — the four upper incisors.
sepl.carl
maa:.trb/-
Icrdcl
Of these the two an-
terior are very long,
curved, chisel-shaped
teeth, which are devoid
of roots, growing
throughout life from
persistent pulps.
Enamel is present, and
forms a thick layer on
the anterior convex sur-
face, which accounts
for the bevelled-off
character of the distal
e n d — t he layer of
enamel being much
harder than the rest,
which therefore wears
more quickly away at
the cutting extremity
of the tooth. Along
the anterior surface is a
longitudinal groove.
The second Dair of in- FIQ- 1098' — LePus cuniculus. Vertical section through
cisors of the upper jaw
are small teeth which
are lodged just behind
the larger pair. In the
lower jaw are two incisors, which correspond in shape with the anterior
pair of the upper jaw, the main .difference consisting in the absence
of the longitudinal groove. The remaining teeth of the upper jaw
are lodged in the maxillse. Canines, present in most Mammals as a
single tooth on each side, above and below, are here entirely
absent, and there is a considerable space, or diastema, as it is
termed, between the incisors and the teeth next in order — the
pre-molars. Of these there are three in the upper jaw and two in
the lower. They are long, curved teeth with persistent pulps like
the incisors. The first of the upper jaw is smaller than the others
Jcb
the anterior part of the nasal region of the head. inc.
section of larger incisor tooth ; jcb. lumen of Jacobson's
organ, surrounded by cartilage ; Icr. dct. lacrymal duct ;
max. maxilla ; max. trb. maxillary turbinals ; nas. nasal
bone ; nas. pal. naso-palatine canal ; sept. cart, carti-
laginous nasal septum. (After Krause.)
446
ZOOLOGY
SECT. XIII
and of simple shape, the rest have each a longitudinal groove on
the outer side and a transverse ridge on the crown. The first
pre-molar of the lower jaw has two grooves ; the second is similar
to those of the upper jaw. Behind the pre-molars are the molars,
three on each side both in the upper and lower jaws.' These are
similar to the upper pre-molars, except the last, which is small and
of simple shape.
Opening into the cavity of the mouth, or buccal cavity, are the
ducts of four pairs of salivary glands — the parotid, the infraorbital,
the sub-maxillary (Fig. 1099, s. mx. gl.}, and the sub-lingual (s. gl.).
On the floor of the mouth is the muscular tongue, covered with
a mucous membrane which is beset with many papillae, on certain
of which the taste-buds (p. 105) are situated. The roof of the
mouth is formed by the hard palate, which is crossed by a series
of tranverse ridges of its mucous membrane. Posteriorly the hard
palate passes into the soft palate, which ends behind in a free pendu-
lous flap in front of the opening of the posterior nares. At the
anterior end of the palate is a pair of openings — the naso-palatine
or anterior palatine canals, leading into the nasal chambers, and into
them open a pair of tubular structures — the organs of Jacobson (Fig.
1098, jcb.) — enclosed in cartilage and situated on the floor of the
nasal cavities. Behind the mouth or buccal cavity proper is the
• 'i :&
Fio. 1009. — Lepus cuniculus. Lateral dissection of the head, neck, and thorax. The
head and spinal column are represented in mesial vertical section ; the left lung is removed ;
the greater part of the nasal septum is removed so as to show the right nasal cavity with its
turbinals. aort. dorsal aorta ; b. hy. basi-hyal ; cbl. cerebellum ; cer. cerebral hemispheres ;
cor. v. coronary vein ; dia. diaphragm ; ep. epiglottis ; eu. opening of Eustachian tube into
pharynx ; lar. larynx ; l.j.i\ left jugular vein ; Lub.a. left subclavian artery ; l.sb.v. left
subclavian vein; max. maxilla; med. medulla oblongata; mes.eth. mesethmoid ; mx.trb.
maxillo-turbinal ; ces. oesophagus ; olf. olfactory bulb ; pi. art. pulmonary artery ; p.max.
pre-maxilla ; pr.st. presternum ; pt.c. post-caval vein ; rt.l.lng. root of left lung with
bronchus and pulmonary veins and artery cut across ; s.gl. sub-lingual salivary glands ;
s.mx.gld. sub-maxillary salivary gland ; st. sternebrje ; Ing. tongue ; tr. trachea; trb. ethmo-
turbinals ; eel. pi. soft palate.
pharynx, which in the Rabbit is not sharply marked off from the
buccal cavity, but begins where the hard palate ends. The pharynx
II
9
.1,
a
FIG. 1100. — Lepus cuniculus. The stomach, duodenum, posterior portion of rectum and
liver (in outline) with their arteries, veins and ducts. A, the coeliac artery of another
specimen (both x f). The gullet is cut through and the stomach somewhat displaced
backwards to show the ramifications of the cceliac artery (cce.a.) ; the duodenum is spread
out to the right of the subject to show the pancreas (pn.) ; the branches of the bile-duct
(c.b.d.), portal vein (-p. v.), and hepatic artery (h. a.) are supposed to be traced some dis-
tance into the various lobes of the liver, a. m. a. anterior mesenteric artery ; cau. caudate
lobe of liver with its artery, vein and bile-duct ; c.b.d. common bile-duct ; oil. st. cardiac
portion of stomach ; c. il .a. common iliac artery ; cce.a. coeliac artery ; cy. a. cystic artery ;
ai.d. cystic duct ; d. ao. dorsal aorta ; du. proximal, and du'. distal limbs of duodenum ;
du. a. duodenal artery; du.h.a. (in A), duodeno-hepatic artery ; ff. a. gastric artery and vein ;
g.b. gall-bladder ; h. a. hepatic artery ; h.d. left hepatic duct ; I. c. left central lobe of liver,
with its artery, vein and bile-duct ; 1. g. v. lieno-gastric vein ; /. I. lateral lobe of liver with
its artery, vein and bile-duct ; ms. branch of mesenteric artery and vein to duodenum ;
ms.r. mesorectum ; m.v. chief mesenteric vein ; ces. oesophagus ; p.m.a. posterior mesenteric
artery ; p.m.v. posterior mesenteric vein ; pn. pancreas ; pn.d. pancreatic duct ; p.v. portal
vein ; pt/.st. pyloric portion of stomach ; ret. rectum ; r.c. right central lobe of liver, with
artery, vein and bile-duct ; spg. Spigelian lobe of liver with its artery, vein and bile-duct ;
spl. spleen ; sp. a. splenic artery. (From Parker's Zoolomy.)
448 ZOOLOGY SECT.
is divided into two parts, an upper or nasal division and a lower
or buccal division, by the soft palate. The passage of the posterior
nares is continuous with the nasal division, at the sides of which
are the openings of the Eustachian tubes. The nasal division is
continuous with the buccal division round the posterior free edge
of the soft palate. From the buccal division leads ventrally the
slit-like opening of the glottis 1 into the larynx and trachea ; over-
hanging the glottis is a leaf -like movable flap (Fig. 1099, ep).
formed of a plate of yellow elastic cartilage covered with mucous
membrane ; this is the epiglottis. Behind, the pharynx becomes
continuous with the oesophagus or gullet (CBS.}. The latter is a
narrow but dilatable muscular tube which runs backwards from
the pharynx through the neck and thorax to enter the cavity of the
abdomen through an aperture in the diaphragm, and opens into the
stomach.
The stomach (Fig. 1100) is a wide sac, much wider at the cardiac
end, at which the oesophagus enters, than at the opposite or pyloric
end, where it passes into the small intestine. The small intestine
is an elongated, narrow, greatly coiled tube, the first part of which,
or duodenum (du and du'), forms a U-shaped loop. The large
intestine is a wide tube, the first and greater part of which, termed
the colon, has its walls sacculated, and is continued into a narrow,
smooth-walled posterior part or rectum (ret.). At the junction of
the small with the large intestine is a very wide blind tube, the
ccecum, which is of considerable length and is marked by a spiral
constriction, indicating the presence in its interior of a narrow spiral
valve. At its extremity is a small, fleshy, finger-like vermiform
appendix.
The intestine, like that of the Pigeon, is attached throughout
its length to the dorsal wall of the abdominal cavity by a mesentery,
or fold of the lining membrane or peritoneum.
The liver is attached to the diaphragm by a fold of the peri-
toneum. Its substance is partly divided by a series of fissures
into five lobes. A thin- walled gall-bladder lies in a depression on
its posterior surface. The common bile-duct (c.b.d.), formed by the
union of the cystic duct from the gall-bladder and hepatic ducts from
the various parts of the liver, runs to open into the duodenum near
the pylorus.
The pancreas (pn.) is a diffused gland in the fold of mesentery
passing across the loop of the duodenum. Its single duct, the
pancreatic duct (pn. d.), opens into the distal limb of the loop.
Circulatory Organs. — The heart (Fig. 1101) is situated in
the cavity of the thorax, a little to the left of the middle line, and
lies between the two pleural sacs enclosing the lungs. Between the
1 The term glottis is more strictly applied not to this slit, but to the slit-
like aperture between two folds of the mucous membrane within the larynx—
the vocal cords — which constitute the chief parts of the vocal apparatus.
XIII
PHYLUM CHORDATA
449
pleural sacs is a space, the mediastinum (Fig. 110-1). This is divisible
into four parts, the anterior, the dorsal, the middle, and the ventral.
In the anterior part lie the posterior part of the trachea, the neigh-
bouring parts of the oesophagus and of the thoracic duct of the
lymphatic system, the roots of the great arteries and the veins
of the precaval system, and the phrenic, pneumogastric, "and other
nerves. In the dorsal part are situated the posterior part of the
CBsophagus, the thoracic part of the dorsal aorta, the pneumogastric
nerve, the azygos vein, and the thoracic duct. The middle part is
the widest, and lodges the heart and roots of the aorta and pulmonary
artery enclosed in the pericardium, the posterior portion of the pre-
caval veins, the phrenic nerves, the terminal part of the azygos
vein, and the roots of the lungs. The ventral part contains only
areolar tissue with the thy-
mus gland. The pericardial
membrane enclosing the
heart consists of two layers,
a parietal, forming the wall
of the pericardial cavity,
and a visceral, immediately
investing the heart. Be-
tween the two is a narrow
cavity containing a little
fluid — the pericardial fluid.
In general shape the heart
resembles the heart of the
Pigeon, with the apex
directed backwards and
slightly to the left, and the
base forwards. Like that
of the Pigeon, it contains
right and left auricles and
right and left ventricles, the
right and left sides of the heart having their cavities completely
separated off from one another by inter- auricular and inter-
ventricular partitions.
Into the right auricle open three large veins — the right and left
precaval veins and the single postcaval — the first into the anterior
part, the second into the left-hand side of the posterior portion, and
the third into the dorsal surface (Fig. 1101). Projecting forwards
from it is an ear-like auricular appendix, the inner surface of which
is raised up into numerous cords of muscular fibres, the musculi
pectinati. A membranous fold, the remnant of the foetal Eustachian
valve, extends from the opening of the postcaval forwards towards
the auricular septum. The opening of the left precaval is bounded
behind by a crescentic fold, the valve of Thebesius. On the septum
is an oval area where the partition is thinner than elsewhere ; this
FIG. 1101. — Lepus cuniculus. Heart, seen from
the right side, the walls of the right auricle and
right ventricle partly- removed so as to expose the
cavities, ao. aorta ;/. ov. fossa ovalis ; l.pr.c. open-
ing of left pre-caval ; m.pap. musculi papillares ;
pt. c. post-caval ; pt. c'. opening of post-caval,
with Eustachian valve below; r.pr.c. right pre-
caval ; r.pul. right pulmonary artery ; sem. v.
semilunar valves ; tri. v. tricuspid valve.
450 ZOOLOGY SECT, xin
is the fossa ovalis (/. ov.) : it marks the position of an aperture,
the foramen ovale, in the foetus. The crescentic anterior rim of the
aperture is known as the annulus ovalis. The cavity of the right
auricle communicates with that of the right ventricle by the wide
right auriculo-ventricular opening. This is guarded by a valve,
the tricuspid (tri. v.), composed of three membranous lobes or cusps,
so arranged and attached that while they flap back against the
walls of the ventricle to allow the passage of blood from the auricle
to the ventricle, they meet together across the aperture so as to
close the passage when the ventricle contracts. The lobes of the
valve are attached to muscular processes of the wall of the ventricle,
the musculi papillares (m. pap.), by means of tendinous threads
called the chordce tendinece. The right ventricle, much thicker
than the auricle, forms the right side of the conical apical portion,
but does not extend quite to the apex. Its walls are raised up
into muscular ridges called columnce carnece. It gives off in front,
at its left anterior angle, the pulmonary artery, the entrance to
which is guarded by three pouch-like semilunar valves (sem. v.).
The left auricle, like the right, is provided with an auricular
appendix. Into its cavity on its dorsal aspect open together the
right and left pulmonary veins. A large left auriculo-ventricular
opening leads from the cavity of the left auricle into that of the
left ventricle : this is guarded by a valve, the mitral, consisting of
two membranous lobes or cusps with chordae tendinese and musculi
papillares. In the walls of the ventricle are columnse carnaee, rather
more strongly developed than in the right. At the basal (anterior)
end of the left ventricle is the opening of the aorta, guarded by
three semilunar valves similar to those at the entrance of the
pulmonary artery. J?he coronary arteries, which supply the
muscular substance of the heart, are given off from the aorta just
beyond the semilunar valves. The corresponding vein opens into
the terminal part of the left precaval. The pulmonary artery divides
into two, a right and a left, each going to the corresponding lung.
The aorta gives origin to a system of arterial trunks by which
the arterial blood is conveyed throughout the body. It first runs
forwards from the base of the left ventricle, then bends round the
left bronchus, forming the arch of the aorta (Fig. 1102), to run
backwards through the thorax and abdomen, in close contact
with the spinal column, as the dorsal aorta (d. ao.). From the arch
of the aorta are given off two large arteries, the innominate (in.)
and the left subclavian. The innominate divides to form the right
subclavian (s. cl. a.) and the right (r. c. c.) and left (I. c. c.) common
carotid arteries. The right subclavian passes to the fore-limb as
the brachial artery, giving origin first to the vertebral artery, which,
after passing up through the vertebrarterial canal, enters the cranial
cavity, having first supplied branches to the spinal cord ; and then
to the anterior epigastric or internal mammary, which supplies the
Pf-
e..e
l.c.c
vr
br
l.pr.c
FIG. 1102. — Lepus cuniculus. The vascular system. The heart is somewhat displaced to-
wards the left of the subject ; the arteries of the right and the veins of the left side are in
great measure removed, a.epg. internal mammary or anterior epigastric artery ; a.f. anterior
facial vein ; a.m. anterior mesenteric artery ; a.ph. anterior phrenic vein ; az.v. azygos vein ;
br. brachial artery ; c.il.a. common iliac artery ; c.il.v. hinder end of postcaval ; ece.
cffiliac artery ; d.ao. dorsal aorta ; e.c. external carotid artery : e.il.a. external iliac artery :
e.il.v. external iliac vein ; e.ju. external jugular vein ;fm.a. femoral artery ;fm.v. femoral
vein ; h. v. hepatic veins ; i. c. internal carotid artery ; i. cs. intercostal vessels ; i.ju. internal
jugular vein ; i. 1. ilio-lumbar artery and vein ; in. innominate artery ; I. au. left auricle ;
l.c.c. left common carotid artery ; l.prc. left precaval vein ; /. v. left ventricle ; m.sc.
median sacral artery ; p.a. pulmonary artery ; p.epg. posterior epigastric artery and vein ;
p.f. posterior facial vein ; p.m. posterior mesenteric artery ; p. ph. posterior phrenic veins ;
ptc. postcaval vein ; p. v. pulmonary vein ; r. renal artery and vein ; r. au. right auricle ;
r.c.r. right common carotid artery ; r.prc. right precaval vein ; r.v. right ventricle ; scl. a.
right subclaviau artery ; scl. v. subclavian vein ; spm. spermatic artery and vein ; s. vs.
superior vesical artery and vein ; ut. uterine artery and vein ; vr. vertebral artery. (From
Parker's Zootomy.)
452 ZOOLOGY SECT.
side of the chest behind the root of the fore-limb. The right carotid
divides opposite the angle of the jaw into internal and external
carotids. The left carotid and left subclavian correspond in their
distribution and branching to the right carotid and right subclavian
respectively. The aorta, in passing through the thorax, gives off
a series of small paired intercostal arteries (i. cs.). In the abdomen
its first large branch is the cceliac artery (003.), which supplies the
liver, stomach, and spleen. Behind this it gives origin to the
anterior mesenteric (a. m.), which supplies the intestine and the
pancreas. Opposite the kidneys it gives off the two renal arteries (r.)
for the supply of these organs, and a good deal further back the
spermatic (spm.) or ovarian arteries for the testes or ovaries as the
case may be. Just in front of the origin of the spermatic arteries
is given off a posterior mesenteric (p.m.], which supplies the hinder
part of the rectum. A series of small lumbar arteries supply the
side-walls of the abdominal cavity. Posteriorly the dorsal aorta
divides to form the two common iliac arteries (c. il. a.) which
supply the pelvic cavity and hind-limbs, a small median sacral
(caudal) artery (ms. c.) passing backwards in the middle line to
supply the caudal region.
The system of caval veins which open into the right auricle consists
of the right and left precavals and of the single postcaval. The right
precaval is formed by the union of the right jugular (e. ju.) vein and
right subclavian (scl. v.). The azygos vein (az. v.), the right anterior
intercostal (i.cs.), and the right anterior epigastric or internal mammary
also open into it. The left precaval receives a series of veins similar
to those forming the right, except that there is no azygos on the
left side (c/. p. 298).
The postcaval vein (pt. c.) is formed in the hinder part of the
abdominal cavity by the union of the internal iliacs (i. il. v.) bringing
the blood from the back of the thighs. Shortly after its origin it
receives the two external iliacs (e. il. v.) coming from the hind-
limb. In front of this a pair of ilio-lumbar (i.l.) veins join it ;
a little farther forward a pair of spermatic (spm.) or ovarian
veins ; and opposite the kidneys a pair of renal veins (r.). From
the liver the blood is carried to the postcaval by the hepatic veins.
A pair of small posterior phrenic veins (p.ph.) bring the blood from
the diaphragm and open into the postcaval as it passes through
the substance of the latter.
The hepatic portal system consists, as in other Vertebrates, of a
system of veins conveying blood from the various parts of the
alimentary canal to the liver, the trunks of the system uniting to
form the single large portal vein (Fig. 1100, p. v.). The principal
veins of the portal system are the lieno-gastric, duodenal, anterior
mesenteric, and posterior mesenteric. There is no trace of a renal
portal system. The red blood corpuscles are circular, bi-concave,
non-nucleated discs.
Xlil
PHYLUM CHORDATA
453
Respiratory Organs. — The larynx (Fig. 1103) is a chamber
with walls supported by cartilage, lying below and somewhat
behind the pharynx, with which it communicates through a slit-
like aperture. The cartilages
of the larynx are, in addition
to the epiglottis, which has
been | already referred to
(p. 448), the large thyroid
(tli.}, which forms the ventral
and lateral walls, the ring-like
cricoid (cr.), the two small
arytenoids (ary.}, and a pair
of small nodules, the carti-
lages of Santorini (sant.), situ-
ated at the apices of the
arytenoids. The vocal cords extend across the cavity from the
thyroid below to the arytenoids above. Leading backwards from
the larynx is the trachea or wind-pipe (Fig. 1099, tr.), a long tube
the wall of which is sup-
ported by cartilaginous
rings which are incomplete
dorsally. The trachea en-
ters the cavity of the
thorax, and there divides
into the two bronchi, one
passing to the root of each
lung.
The lungs (Fig. 1104) are
FlG. 1103. — Lepus cuniculus. Laryux. A,
ventral view ; B, dorsal view. ary. arytenoid ;
cr. cricoid ; ep. epiglottis : sant. cartilage of
Sautorini ; th. thyroid ; tr. trachea. (From
Krause, after Schneider.)
cent
aort
oes
-pt.cav
I. Z/*,™^™* , enclosed in the lateral parts
of the cavity of the thorax.
Each lung lies in a cavity,
the pleural sac, lined by a
pleural membrane. The
right and left pleural sacs
are separated by a con-
siderable interval owing to
FIG. 1104. — Lepus cumculus. Diagram of a , .... . =»
transverse section of the thorax in the region of the tne development in tne
ventricles to show the relations of the pleurae, meiiia- .QT,f,>;nrl V>0f,,700rl thorn nf
stiiium, etc. The lungs are contracted, aort. dorsal Par ,VW&
aorta; az.v. azygos vein; cent, centrum of thoracic a a-nopp thp mprlinstinnm
vertebra; l.lng "left lung; l.pl. left pleural sac; ? Space, I im,
l.vent. left ventricle ; my. spinal cord ; oes. ceso- m which, aS already 6X-
phagus ; par. per. parietal layer of pericardium ; pt. i • j r ,1 i j
can. post-caval, close to its entrance into right auricle ; plained, lie tne neart and
r.lny. right lung ;r.pl, right pleural cavity ; r.vent. right nfhpr nro-{in Thp Inner i«
ventricle ; *(. sternum ; v.med. ventral mediastinum. 'J-gal u^e, -1
attached only at its root,
where the pleural membrane is reflected over it. In this respect
it differs widely from the lung of the bird. It differs also in its
minute structure. The bronchus, entering at the root, divides
and subdivides to form a ramifying system of tubes, each of the
454 ZOOLOGY stecf.
ultimate branches of which, or terminal bronchioles, opens into
a minute chamber or infundibulum, consisting of a central
passage and a number of thin-walled air-vesicles or alveoli
given off from it. A group of these infundibula, supplied by a
single bronchiole, which divides within it to form the terminal
bronchioles, is termed a lobule of the lung.
In shape the lung may be roughly described as conical, with the
apex directed forwards. The base, which is concave, lies, when
the lung is distended, in contact with the convex anterior surface
of the diaphragm. The outer or costal surface is convex in adapta-
tion to the form of the side-wall of the thorax ; the internal surface
is concave.
Ductless Glands.- — The spleen is an elongated, compressed,
dark-red body situated in the abdominal cavity in close contact
with the stomach, to which it is bound by a fold of the peritoneum.
The thymus, much larger in the young rabbit than in the adult, is
a soft mass, resembling fat in appearance, situated in the ventral
division of the mediastinal space below the base of the heart. The
thyroid is a small, brownish, bilobed, glandular body situated in
close contact with the ventral surface of the larynx.
Nervous System. — The neural cavity, as in the Pigeon, con-
tains the central organs of the cerebro-spinal nervous system—
the brain and spinal cord. The brain (Figs. 1105-1107) of the
Rabbit contains the same principal parts as that of the Pigeon,
with certain differences, of which the following are the most im-
portant.
The surface of the cerebral hemispheres or parencephala (Fig.
1105, /. 6., Fig. 1106, c.h.), which are relatively long and narrow,
presents certain depressions or sulci, which, though few and in-
distinct, yet mark out the surface into lobes or convolutions not
distinguishable in the case of the Pigeon or the Lizard. A slight
depression — the Sylvian fissure — at the side of the hemisphere
separates off a lateral portion, or temporal lobe (Fig. 1107 c. h2.),
from the rest. There are very large club-shaped olfactory bulbs at
the anterior extremities of the cerebral hemispheres, and behind
each on the ventral surface of the hemisphere is the corresponding
olfactory tract leading back to a slight rounded elevation, the
tuberculum olfactorium. Connecting together the two hemispheres
is a commissural structure — the corpus callosum (Figs. 1106, 1107,
cp. cl.)— not present in the Pigeon ; this runs transversely above
the level of the lateral ventricles. Examined in transverse section,
i.e., in a longitudinal section of the brain (Fig. 1107), the corpus
callosum is seen to bend slightly downwards, forming what is
termed the genu ; posteriorly it bends downwards and forwards,
forming the splenium, which passes forwards and is united with the
fornix. Below the corpus callosum is another characteristic struc-
ture of a commissural nature — the fornix (b.fo.) — a narrow median
xiii
PHYLtJM CEtORDATA
465
strand of longitudinal fibres, which bifurcates both anteriorly and
posteriorly to form the so-called pillars of the fornix — anterior
(Figs. 1106 and 1107, a. fo), and posterior (Fig. 1106, p. fo.).
Below the corpus callosum, between it and the fornix, the thin inner
walls of the hemispheres (septum lucidum, sp. lu.) enclose a small,
f*.
J.p. -
-ii
n
xn
FIG. 1105. — Lepus cuniculus. Brain. A, dorsal, B, ventral, C, lateral view. b.o. olfac-
tory bulb ; cb'. median lobe of cerebellum (vermis) ; cb". lateral lobe of cerebellum ; cr.
crura cerebri ; ep. epiphysis ;f.b. parencephala ;f.p. longitudinal fissure ; h. b. cerebellum ;
hp. hypophysis ; m.b. mid-brain (corpora quadrigemina) ; md. medulla oblongata ; pv.
pons Varolii, the transverse fibres of which are here not indicated ; i-xii, cerebral nerves.
(From Wiedersheim.)
laterally compressed cavity, the so -called//^ ventricle or pseudocode,
this is not a true brain-ventricle, but merely a space between the
closely-apposed hemispheres.
The lateral ventricles of the cerebral hemispheres are much more
extensively developed than in the brain of the Pigeon, and of some-
what complex shape. Each consists of a middle portion or body
456
ZOOLOGY
SfccT-
roofed over by the corpus callosum, a narrow anterior prolongation,
or anterior cornu, a posterior cornu, which runs backwards and
inwards, and a descending cornu, which passes at first almost directly
outwards, then downwards, and finally inwards and forwards. On
the floor of the body of the ventricle, and continued along the whole
extent of the descending cornu, is a prominent ridge of nearly
semicircular transverse section — the hippocampus (hp. m.) ; this
corresponds in position with a groove, the hippocampal sulcus, on the
cp.cl.
9f.l
c.rs
c.rv.
p.pn.
r.rn.
FIG. 1106. — Lepus cuniculus. Two dissections of the brain from above*(nat. size). In A
the left parencephalon is dissected down to the level of the corpus callosum : on the right
the lateral ventricle is exposed. In B the cerebral hemispheres are dissected to a little
below the level of the genu of the corpus callosum ; only the frontal lobe of the left
hemisphere is retained ; of the right a portion of the temporal lobe also is left ; the velum inter -
positum and pineal body are removed, as well as the greater part of the body of the fornix,
and the whole of the left posterior pillar ; the cerebellum is removed with the exception
of a part of its right lateral lobe. a.co. anterior commissure ; a.fo. anterior pillar of fornix ;
a.pn. anterior peduncles of cerebellum ; b.fo. body of fornix ; cbl. superior vermis of cere-
bellum ; cb". its lateral lobe ; c.gn. corpus geniculatum ; c. h. cerebral hemisphere ; ch. pi.
choroid plexus ; cp. cl. corpus callosum ; cp. s. corpus striatum ; c.rs. corpus restiforme ;
d.p. dorsal pyramid ; fl. flocculus ; hp. m. hippocampus ; m.co. middle commissure ; o./1.
anterior, and o.l~. posterior lobes of corpora quadrigemina ; olf. olfactory bulb ; o. th. optic
thalamus ; o.tr. optic tract ; p.co. posterior commissure ; p.fo. posterior pillar of fornix
(taenia hippocampi) ; pn. pineal body ; pd.pn. peduncle of pineal body ; p.pn. posterior
peduncles of cerebellum ; P.M. fibres of pons Varolii forming middle peduncles of cerebellum ;
sp.lu. septum lucidum ; st. 1. stria longitudinalis ; t. s. tocnia semicircularis (narrow band of
white matter between corpus striatum and optic thalamus) ; v.vn. valve of Vieussens ;
v3, third ventricle ; v4, fourth ventricle. (From Parker's Zootomy.)
inner surface of the temporal lobe. Internally the two hippocampi
merge in a median commissural area — the psalterium or lyra (ly.).
Running along the anterior edge of the hippocampus is a ridge
of fibres — the tcenia hippocampi oxfimbria — which passes down into
the descending cornu. The union of the two tsenise forms a median
longitudinal strand, the body of the fornix, which, as already
explained, lies below the corpus callosum, continuous with the
splenium of the latter behind, but diverging from it anteriorly by
XIII
PHYLUM CHOKDATA
457
dipping down towards the base of the brain. In the angular space
between the corpus callosum above and the fornix below is the
septum lucidum with the " fifth ventricle." The tsenias hippocampi
are the posterior pillars of the fornix (Fig. 1106, p.fo.) ; the anterior
pillars (a.fo.) are a pair of vertical bands which pass from the
anterior end of the body downwards to the corpus mammillare
(see below) at the base of the diencephalon.
Lying immediately in front of the hippocampus is a vascular
membrane, the choroid plexus (ch. pi.) ; this passes inwards to
join its fellow of the opposite side through a transverse passage,
the foramen of Monro (f. m.), which opens behind into the diacoele.
The floor of the anterior cornu is formed of an eminence of grey
matter — the corpus striatum (cp. s.). The right and left corpora
striata are connected together by a narrow transverse band of
white fibres — the
anterior commis- ty
sure (a. co.) — situ-
ated in front of
the anterior pillars
of the fornix.
The diacoele^.3)
is a laterally com- J'm'
pressed cavity, the
roof of which is
formed by a deli-
cate vascular
membrane, the
velum interpositum
(vl. ip.), in which
there is a network
of blood - vessels
(choroid plexus
of the diacoele) continuous with the- choroid plexuses of the
lateral ventricles. From the posterior part of the roof of the
diaccele rise the peduncles of the pineal body. The optic thalami
(o. th.) are large masses of mixed grey and white matter forming
the lateral portions of the diencephalon ; they are connected
together by a thick mass of grey matter, the middle or soft commis-
sure (m. co.), not represented in lower Vertebrates, passing across
the diacoele. A rounded elevation near the anterior end of the
external surface of each thalamus is the corpus geniculatum (c. gn.).
The anterior boundary of the diacoele is a thin vertical lamina—
the lamina terminal-is — of which the septum lucidum is a mesial
anterior prolongation. The floor of the diencephalon is produced
downward into a mesial rounded process, the tuber cinereum or
infundibulum (inf.), to which the pituitary body is attached. In
front of this, on the ventral aspect of the brain, is a thick transverse
VOL. II F F
olf.
O.CO
1 o.ch.\inft
a.fo.
FIG. 1107. — Lepus cuniculus.
frma^
c.c. \
m.co. pvcL.
r.vn
Longitudina Ivertical section of
the brain (nat. size). Letters as in preceding figure ; in addi-
tion— cb. cerebellum, showing arbor vite ; c. c. crus cerobri ;
c. h1. parencephalou ; c. h'2. temporal lobe ; c. ma. corpus
mammillare ; /. in. foramen of Monro ; inf. infundibulum ;
ly. psalterium or lyra ; m. o. medulla pblongata ; o. ch. optic
chiasma ; olf. olfactory bulb ; ply. pituitary body ; p. va. puns
Varolii; vl. if. velum iuterpositum ; v. vn. valve of Vieussi-ns;
//, optic nerve. (From Parker's Zootomy.)
458 ZOOLOGY SECT.
band of nerve-fibres, the united optic tracts, from the anterior border
of which the optic nerves are given off. Behind the tuber cinereum,
and formed as a thickening of its posterior wall, is a rounded eleva-
tion, the corpus mammillare (c. ma.).
In the mid-brain the dorsal part is remarkable for the fact that
each optic lobe is divided into two by a transverse furrow, so that
two pairs of lobes (o.l.1, o.l.2), the corpora quadrigemina, are produced.
Between the anterior lobes passes the delicate posterior commissure
(p.co.). On the ventral region of the mid-brain the crura cerebri are
far more prominent than in the lower groups. In the hind-brain
the cerebellum (Fig. 1105, cb', cb".) is very large ; it consists of a
central lobe or vermis and two lateral lobes, divided by very numerous
fissures or sulci into a large number of small convolutions. Each
lateral lobe bears an irregularly- shaped prominence, the flocculus.
On section (Fig. 1107, cb.) the cerebellum exhibits a tree-like pattern
(arbor vitce) brought about by the arrangement of the white and grey
matter. On the ventral aspect of the hind-brain a flat band of
transverse fibres — the pons Varolii — connects together the lateral
parts of the cerebellum. The cerebellum is attached to the other
parts of the brain by three pairs of peduncles, the anterior, connecting
it with the posterior optic lobes, the middle, passing on each side
into the pons Varolii, and the posterior, connecting it with the dorsal
portion of the medulla oblongata. Between the anterior peduncles
extends a transverse band, the valve of Vieussens (Fig. 1107, v. vn.),
connected by its anterior edge with the corpora quadrigemina.
Behind this is a short tract of transverse fibres — the corpus
trapezoideum — and behind this again is a slightly elevated area
marking the position of the olivary body. The floor of the fourth
ventricle presents a median groove which ends posteriorly in a
pointed depression— caZawws scriptorius — leading into the central
canal of the spinal cord.
The Rabbit, like most other Vertebrates, possesses a sympathetic
nervous system, consisting of a series of ganglia united together by
commissural nerves, and giving off branches to the various internal
organs. Two sympathetic ganglia are situated on each side in the
neck — the anterior and posterior cervical ganglia. From the anterior
nerve-branches pass forwards to enter the cranial cavity ; from the
posterior a nerve-cord passes backwards to the first thoracic ganglion.
Of the thoracic ganglia there are twelve on each side. From one of
the more posterior of these originates the splanchnic nerve which
passes backwards into the abdomen, ending in a ganglion — the
cosliac— connected with an extensive nerve-plexus, the cosliac
plexus. In the abdomen there are, on each side, twelve ganglia,
the chain ending behind in a single ganglion impar.
In the organs of special sense the following special features
are to be seen when a comparison is made with the Pigeon or
Lizard. In the eye, the sclerotic is composed entirely of dense
XIII
PHYLUM CHORDATA
459
fibrous tissue ; the pecten is absent. In the internal ear the
principal point of difference is in the special development of the
cochlea. This part of the membranous labyrinth, instead of
retaining the simple curved form which it presents in the Bird,
is coiled on itself in a close spiral of two-and-a-half turns. The
spiral channel in the substance of the bone, in which this cochlear
spiral runs, contains three passages ; the middle one, much the
smallest, being the membranous cochlea, the uppermost the scala
vestibuli, and the lowermost the scala tympani.
The special features of the middle ear with its auditory ossicles, and
of the external ear, have been already referred to (pp. 433 and 441).
Urinogenital Organs. — The kidneys are of somewhat com-
pressed oval shape, with a notch or hilus on the inner side. They
ur
ur
FIG. 1108. — Lepus cuniculus. The urinogenital organs ; A, of male ; B, of female ; from
the left side (half nat. size). The kidneys and proximal ends of the ureters, in A the testea,
and in B the ovaries, Fallopian tubes and uteri, are not shown, an. anus ; bl. urinary
bladder ; c. c. corpus cavernosum ; c. s. corpus spongiosum ; c. gl. Cowper's gland ; g. cl.
apex of clitoris ; g. p. apex of penis ; p. gl. perineal gland ; p. gl'. aperture of its duct on the
perineal space ; pr. anterior, pr'. posterior, and pr". lateral lobes of prostate ; ret. rectum ;
r. gl. rectal gland ; u. g. a. urinogenital aperture ; u. m. uterus masculinus ; ur. ureter ;
va. vagina ; vb. vestibule ; v. d. vas deferens. (From Parker's Zootomy.)
are in close contact with the dorsal wall of the abdominal cavity,
the right being somewhat in advance of the left. Towards the
hilus the tubules of the kidney converge to open into a wide
chamber — the pelvis — which forms the dilated commencement of
the ureter. When the kidney is cut across, its substance is seen to
be divided into a central mass or medulla and a peripheral portion
or cortex. An adrenal (suprarenal) body lies in contact with the
F F 2
460
ZOOLOGY
SECT.
anterior end of each kidney. The ureter (Fig. 1108, ur.) runs
backwards to open, not into a cloaca, but directly into the urinary
bladder (bl.). The latter is a pyriform sac with muscular walls
which vary in thickness according as the organ is dilated or con-
tracted. In the male the openings of the ureters are situated
nearer the posterior narrower end or neck than in the female.
In the male Rabbit the testes are oval bodies, which, though in
the young animal occupying a similar position to that which
they retain throughout life in the Pigeon, pass backwards and
downwards as the animal approaches maturity, until they come to
lie each in a scrotal sac situated at the side of the urinogenital
opening. The cavity of each scrotal sac is in free communication
with the cavity of the abdomen by an opening — the inguinal canal.
l.ut The sperms have
an oval compressed
"head' 0-005 mm.
in length and a
slender "tail"
0-045 mm. long. A
convoluted epi-
didymis, closely ad-
herent to the testis,
forms the proximal
part of the vas
defer ens. The vasa
dcferentia (v.d.)
terminate by opening
into a urinogenital
canal, or urethra, into
which the neck of
the urinary bladder
is continued. A pros-
tate gland (pr.) sur-
rounds the com-
mencement of the urethra, the neck of the bladder, and the terminal
part of the vasa deferentia. A diverticulum of the urethra — the
uterus masculinus (u. m.) — lies embedded in the prostate gland close
to the neck of the bladder. A small pair of ovoid glands, Cowper's
glands (c. gl.), lie just behind the prostate close to the side of the
urethra.
The terminal part of the urethra traverses a cord of vascular
tissue, the corpus spongiosum (c. s.), which forms the dorsal portion
of the penis. The greater part of the penis is formed of two closely
approximated firm cores of vascular tissue — the corpora cavernosa
(c.c.), which are attached proximally to the ischia, and terminate in
a pointed apex (g.p.). A loose fold of skin, the prepuce, encloses
the penis. A pair of glands with an odorous secretion, the perineal
Vul-
r.ut
FIG. 1109. — Lepus cuniculus. The anterior eud of the
vagina, with the right uterus, Fallopian tube and ovary (iiat.
size). Part of the ventral wall of the vagina is removed, and
the proximal end of the left uterus is shown in longitudinal
section, fl. t. Fallopian tube ; fl. t'. its peritoneal aperture ;
/. ut. left uterus ; 1. ut'. left os uteri ; ov. right ovary ; r. ut.
right uterus ; r. ut' . right os uteri ; s. vaginal septum ;
va. vagina. (From Parker's Zootomy.)
xm
PHYLUM CHORDATA
461
glands (p. gl.), open on the perineal space at the base of the penis :
two similar glands, the rectal glands (r. gl.), lie on either sidfe of the
rectum.
In the female the ovaries (Fig. 1109, ov.) are small ovoid bodies
attached to the dorsal wall of the abdomen behind the kidneys.
The Graafian follicles enclosing the ova form only very small rounded
projections on their outer surface.
The oviducts in the anterior part of their extent (Fallopian
tubes, fi.t.) are very narrow and slightly convoluted. They open
into the abdominal cavity by wide funnel-shaped openings (fi.t' '.)
with fimbriated or fringed margins. Posteriorly each passes into
a thick- walled uterus (r. ut.). The two uteri open separately into
a median tube, the vagina (va.). The vestibule (Fig. 1108, vb.), or
urinogenital canal, is a wide
median passage, into which
the vagina and the bladder
open. On its ventral wall
is a small, hard, rod-like
body, the clitoris (c. c.),
with a pointed apex (g. cl.),
corresponding to the penis
of the male, and composed
of two very short corpora
cavernosa attached ant-
eriorly to the ischia, and
invested internally by a
soft, grooved corpus
spongiosum. The vulva,
or external opening of
the vestibule, is bounded
laterally by two prominent
folds— the labia major a.
Development. The
Rabbit is viviparous. The
ovum, which is of rela-
tively small size, after
it has escaped from its
Graafian follicle, passes
into the Fallopian tube, where it becomes fertilised, and then reaches
the uterus, in which it develops into the foetus, as the intra-uterine
embryo is termed. The young animal escapes from the uterus
in a condition in which all the parts have become fully formed,
except that the eyelids are closed and the hairy covering is
not yet completed. As many as eight or ten young are produced
at a birth, and the period of gestation, i.e., the time elapsing between
the fertilisation of the ovum and the birth of the young animal, is
thirty days. Fresh broods may be born once a month throughout
FIG. 1110. — Diagrammatic longitudinal section of a
.Rabbit's embryo at an advanced stage of pregnancy.
a. ainnion ; a. stalk of allantois ; a/, allantois with
blood-vessels ; c. embryo ; c. p p. s> rn. ^ = 32. The csecum is devoid of vermiform
appendage.
This family includes the Baboons (Cynocephalus) and Macaques
(Macacus).
Family iv. — Simiidce.
Anthropoidea with the pollex opposable, without cheek-pouches,
usually without ischial callosities, with a narrow nasal septum and
a bony external auditory meatus. The pectoral limbs are much
longer than the pelvic. The caecum has a vermiform appendage.
The centrale of the carpus is sometimes absent. The dental
formula is the same as that of the preceding family.
This family includes the Gibbons (Hylobates), Orangs (Simia),
Chimpanzees (Anthropopithecus), and Gorillas (Gorilla).
Family v. — Hominidce.
Anthropoidea which differ from the Simiida) mainly in the more
perfect assumption of the erect posture, co-ordinated with alteration
of the curvature of the spine, and with the more complete adaptation
of the hind-limbs to bearing the weight of the body ; in the absence
of the power of opposition in the hallux, and its more complete
development in the pollex ; in the greater length of the hind- as
compared with the fore-limbs ; in the smaller size of the canine
teeth ; and the much greater size and complexity of the brain.
This family includes only the Human Species (Homo sapiens).
VOL. II G G
474
ZOOLOGY
SECT.
Systematic Position of the Example.
The genus Lepus, to which the common Rabbit belongs, com-
prises a number of other species, the common Hare being among
the number, distinguished from one another by slight differences
in the proportions of the parts and in other general features. Lepus
is the only genus of the family Leporidce, which is associated with
the family LagomyidcB or Picas under the designation Duplici-
dentata, owing to the presence in these two families, and in these
two alone of the entire order Rodentia to which they belong, of a
second pair of incisors in the upper jaw. The chief distinctive
features of the family Leporidse are the elongated hind-limbs, the
short recurved tail, the long ears, and the incomplete clavicles.
3. GENERAL ORGANISATION.
Integument and General External Features.— Nearly all
Mammals are covered with hairs (Fig. 1111) developed in hair-
follicles. Each hair (Fig.
1112) is a slender rod, and
is composed of two parts,
a central part or pith (M)
containing air, and an
I outer more solid part or
Se
«
SM
s/t1
cortex (R) in which air
does not occur ; its outer-
most layer may form a
definite cuticle (0). Com-
monly the cortical part
presents transverse ridges
so as to appear scaly. In
one case only, viz., Sloths,
is the hair fluted longi-
tudinally. The presence
of processes on the surface,
by which the hairs when
twisted together interlock
firmly, gives a special
quality to certain kinds
of hair (wool) used for
clothing— the felting quality as it is termed. A hair is usually,
cylindrical ; but there are many exceptions : in some it is com-
pressed at the extremity, in others it is compressed through-
out ; the latter condition is observable in the hair of negroid races
of men. The fur is usually composed entirely of one kind of hair ;
but in some cases there are two kinds, the hairs of the one sort very
numerous and forming the soft fur, and those of the other consisting
of longer and coarser hairs scattered over the surface. Examples
FIG. 1111.— Section of human skin. Co, dermis ; D,
sebaceous glands ; F, fat in dermis ; G, vessels in
dermis ; GP, vascular papillae ; H. hair ; N. nerves in
dermis ; NP. nervous papillae ; .SV, horny layer of
epidermis; SD, sweat-gland ; SD1, duct of sweat-
gland ; SM, Malpighian layer. (From Wiedersheim's
Comparative Anatomy.)
XIII
PHYLUM CHORDATA
475
Set
of a hairy covering of this kind are seen in the case of the Platypus
and the Fur-Seals.
A hair, like a feather, is formed from the epidermis. The first
rudiment of a developing
hair (Fig. 1113) usually takes
the form of a slight down-
wardly projecting out-
growth, the hair-germ (grm.),
from the lower mucous layer
of the epidermis, beneath
which there is soon dis-
cernible a condensation of
the dermal tissue to form
the rudiment of a hair papilla
(pp.). In some Mammals,
however, the dermal papilla
makes its appearance before
the hair-germ. The hair-
germ, which consists of a
solid mass of epidermal cells,
elongates, and soon its axial
portion becomes condensed
and cornified to form the
shaft of the hair, while the
more peripheral cells go to
form the fining of the hair-
follicle, becoming arranged
in two layers, the inner and
outer root-sheaths (sh.l, sh.2}.
The epidermal cells in im-
mediate contact with the
hair-papilla retain their pro-
toplasmic character and form
the hair-bulb (bib.), by the
activity of which the further
growth of the hair is effected.
boon the Upper end Of the Flo 1112.— Longitudinal section through a hair (dia-
hair-shaft grOWS OUt beyond grammatic). Ap, ..band of muscular fibres inserted
the surface of the epidermis,
and the projecting part
eventually becomes much
longer than that which lies
embedded in the follicle.
At the same time the follicle
grows downwards into the
dermis. During its growth the hair is nourished by the blood-
vessels in the dermal hair-papilla, which projects into its base.
G G 2
grammatic).
into the hair-follicle ; Co. dermis ; F. external
longitudinal, and F'. internal circular librous layer
of follicle ; Ft. fatty tissue in the dermis ; GH, hya-
ijne membrane between the root-sheath and the
follicle ; HBD, sebaceous gland ; HP. hair-papilla
with vessels in its interior ; M. medullary substance
(pith) of the hair ; O, cuticle ; R, cortical layer ;
Sc, horny layer of epidermis ; SM, Malpighian layer
of epidermis ; WS, WS', outer and inner layers of
root-sheath. (From Wiedersheim's Comparative
Anatomy.)
476
ZOOLOGY
SECT.
B
cm
tnuc
PP
Modifications of the hairs are often found in certain parts. Such
modified hairs are the elongated hairs of the tails of some Mammals,
e.g., most Ungulates ; the eye-lashes of the eye-lids, which are
stronger than the ordinary hairs ; and sensitive hairs or vibrissce
about the snout. In some Mammals the hairs in part assume the
form of spines, viz., in Echidna, the Hedgehogs, and the Porcupines.
The coating of hairs is scanty in some Mammals, and is virtually
absent in the Cetacea and Sirenia. In such cases the skin is greatly
thickened, as in the
Elephants, &c. ; or, as
in the Cetacea, an un-
derlying layer of fat
performs the function
of the hair as a heat-
preserving covering.
In Manis (Fig. 1126)
the greater part of the
surface is covered with
large, rounded, over-
lapping horny scales of
epidermal origin, simi-
lar in their mode of
development to those
of Reptiles. A similar
phenomenon is seen in
the integument of the
tail of Anomalurus — a
Flying Rodent. The
Armadillo (Fig. 1125)
is the only Mammal
in which there occurs a
FIG. 1113. — Four diagrams of stages in the development of a
hair. A, earliest stage in one of those Mammals in which
the dermal papilla appears first; S, C, D, three stages in l^rinv rlov^Yinl f>rrnlf>tnv>
the development of the hair in the human embryo. Mb. "v C
hair-bulb ; cm. horny layer of the epidermis ; foil, hair-
follicle ; arm. hair-germ ; h. extremity of hair projecting on
the surface in D ; rnuc. Malpighian layer of epidermis ; />/>.
dermal papilla ; scb. developing sebaceous glands ; sh.l, sh.2,
inner and outer root-sheaths. (After Hertwig.)
(vide infra).
Also epidermal in
their origin are the
horny structures in the
form of nails, claws, or hoofs, with which the terminations of the
digit's are provided in all the Mammalia except the Cetacea. And
the same holds good of the horny portion of the horns of Ruminants.
The horns of the Rhinoceros are also epidermal, and have the
appearance of being formed by the agglutination of a number of
hair-like horny fibres.
Cutaneous glands are very general in the Mammalia, the most
constant being the sebaceous glands (Figs. 1111, D ; 1112, HBD),
which open into the hair-follicles, and the sweat glands (Fig. 1111,
8D). In many Mammals there are, in addition, in various parts of
the body, aggregations of special glands secreting an odorous matter.
xni
PHYLUM CHORDATA
477
The mammary glands, by the secretion of which the young are
nourished, are specially developed cutaneous glands. In the
Prototheria they differ somewhat widely from those of the rest of
the Mammalia in structure, and they also differ in the absence of
teats. They consist of two groups of very large tubular follicles, the
ducts of which open on the ventral surface. In Echidna (Fig.
1114) the two areas on which the ducts open become depressed
towards the breeding season to give rise to a pair of pouches—
the mammary pouches. A large brood-pouch or marsupium is
subsequently formed, and the egg is deposited in this. When the
A B
- in.
d.
FIG. 1114. — Echidna aculeata. A, lower surface of brooding female ; B, dissection showing
a dorsal view of the marsupium and mammary glands ; t t, the two tufts of hair projecting
from the mammary pouches from which the secretion flows ; b.m. brood-pouch or marsu-
pium ; cl. cloaca ; g. m. groups of mammary glands. (From Wiedersheim's Comparative
Anatomy, after W. Haacke.)
young animal is hatched it is sheltered in the posterior deeper
part of this marsupium, while in the shallower anterior part lie
the mammary pouches. In Ornithorhynchus mammary pouches
are indicated only by extremely shallow depressions, and no
marsupium is developed.
In the higher Mammals, when the mammary glands are first
developed (Fig. 1115), a depression (mammary pouch) is formed,
from the floor of which branching cylindrical strands of epidermis
grow inwards to give rise to the glands. At a later stage there
is developed around the opening or openings of the mammary
'. HI.
478
ZOOLOGY
SECT.
ducts a prominence, the teat (Fig. 1115), the wall of which may be
formed of the mammary pouch area alone (Marsupials, Kodents,
Primates), or, with greater or less reduction of the latter, mainly
from the surrounding integument. In the latter case the teat
may have a wide central canal. The number and situation of the
teats vary in the different groups, and have been noticed in the
synopsis of the characters of the orders and sub-orders (pp. 464
to 473).
The two genera of the Prototheria, Ornithorliynchus and Echidna,
differ somewhat widely from one another in general appearance.
The former (Fig. 1116) has the surface covered with a close, soft
fur, and has the upper jaw produced into a depressed muzzle,
not unlike the beak of a duck, covered with a smooth, hairless
FIG. 1115. — Diagrams of the phylogenetic development of teats, a, primitive condition corre-
sponding to the condition in Echidna ; b, Wallaby (Ualmaturus) before lactation ; c,
Opossum (Didelphi/s) before lactation ; il, Opossum during lactation ; this diagram
stands also for the Mouse and Man ; c, embryonal, and/, full-grown cow. 1, integumentary
wall ; 2, mammary area, the broken line represents the mammary pouch ; 3, milk-ducts.
(After Max Weber.)
integument, which forms a free fold or flap at the base. The
eyes are very small, and there is no auditory pinna. The legs
are short, and the five digits end in strong claws, and are con-
nected together by a web, so that the limbs are equally adapted
for burrowing and for swimming. The tail is elongated and
depressed, and is covered with fur. The male has a sharp-pointed,
curved spur on the inner side of the foot, having the duct of a
gland opening at its apex. Echidna (Fig. 1117) has the body
covered above with strong, pointed spines, between which are coarse
hairs ; the lower surface is covered with hair only. The jaws are
produced into a rostrum, which is much narrower than that of
Ornithorhynchus. The eyes are small, and there is no auditory
pinna. The limbs are short and powerful. There are five toes on
each foot, each ending in a very strong claw, by means of which
the Echidna is able to burrow with rapidity. There is a spur on
XIII
PHYLUM CHORDATA
479
the inner side of the hind foot, larger in the male than in the
female. The tail is vestigial.
The Opossums (Diddphyidce, Fig. 1118) are arboreal rat-like
Marsupials, with elongated naked muzzle, with well-developed,
FIG. 1116. — Duck-Bill (Ornitfiorftynchus anatinus). (After Vogt and Specht.)
though nailless, opposable hallux, and elongated prehensile tail.
A marsupium is sometimes present, but is absent or incomplete
in the majority. One species — the Water Opossum — has the toes
webbed. The Dasyuridse (Australian Native Cats, Tasmanian
Devil, Thylacine, &c.) often have the pollex rudimentary, the foot
FIG. 1117. — Spiny Ant-eater (Echidna aculeata). (After Vogt and Specht.)
four-toed, the hallux, when present, small and clawless, and the tail
jon-prehensile. There is a well-developed marsupium. The Native
Cats (Fig. 1119) and their near allies are cat-like animals, the largest
equal in size to a Domestic Cat, some no larger than Bats or Mice ;
480
ZOOLOGY
SECT.
the Tasmanian Devil has a more thickset body ; the Thylacine has
a remarkable resemblance in general shape, as well as size, to a Wolf.
The Banded Ant-eater (Myrmecobius) is devoid of the marsupium.
The Bandicoots (Peramelidce) are burrowing Marsupials, the
size of which varies from
that of a large Rat to
that of a Rabbit. They
have an elongated
pointed muzzle, and, in
some cases, large audi-
tory pinnae. The tail is
usually short, sometimes
long. The first and fifth
digits of the fore-feet
are vestigial or absent,
the remaining three
nearly equally de-
veloped. In the hind-
foot the fourth toe is
much longer and stouter
than the others, while
the second and third
are small and slender,
and united together by
a web of skin, and the first is vestigial or absent. The marsupium
has its opening directed backwards.
Noton/ctes, the Marsupial Mole (Fig. 1121), is a small burrowing
Marsupial, with short and powerful limbs, each with five toes,
FIG. 1118. — Virginian OpQSSum(D:lil<>i>s). (From the Cambridge Natural History.
foot partly connected together by skin. The tail is very short. The
Kangaroos and their allies (Macropodidse, Fig. 1120) are adapted,
482
ZOOLOGY
SECT.
as regards their limbs, for swift terrestrial locomotion. They
have a relatively small head and neck, the fore-limbs small, and
each provided with five digits ; the hind-legs long and powerful ;
FIG. 1122. — Wombat (Phascolomys mitchclli). (From the Cambridge Natural History.)
•
rapid progression is effected by great springing leaps, with the
body inclined forwards and the fore-limbs clear of the ground.
The foot is narrow and provided with four toes, the hallux being
absent ; the two inner (second and third) small and united together
•u
FIG. 1123. — Koala (Phascolarctos cinereus). (After Vogt and Specht.)
by integument, while the middle toe is very long and powerful.
The tail is very long, and usually thick. There is a large marsupium.
The Tree-Kangaroos differ from the ordinary Kangaroos in their
xin
PHYLUM CHORDATA
483
shorter and thicker hind-limbs, in which the second and third toes
are nearly as large as the fourth.
The Phalangers (PTialangeridcs) are climbing Marsupials which
have both fore- and hind-feet prehensile ; the second and
third toes of the hind-foot slender and united by a web, as in the
Kangaroo, but the hallux, which is nailless, opposable to them ;
the fourth and fifth nearly equal. The tail is well developed and
prehensile. A
number of Phal-
angers (Flying
Phalangers) are
provided with
lateral folds of
skin extending X: '••' AM W
from the fore- to
the hind - limbs
and, acting as a
parachute, enab-
ling the animal,
as in the Flying
Squirrels, to per-
form flying leaps
from tree to tree.
The Koalas (Fig.
1123) differ from
the Phalaugers
mainly in the
relatively thicker
body and the
vestigial tail.
The Sloths
(Bradypodidce,
Fig. 1124) are
more completely
adapted, in the
structure of their
limbs, to an ar-
boreal life than any other group of the Mammalia. They have a
short, rounded head, with small pinnae, and long, slender limbs, the
anterior much longer than the posterior, with the digits, which are
never more than three in number, long, curved, and hook-like,
adapted for enabling the animal to hang and climb, body downwards,
among the branches of trees. In the three-toed Sloth there are three
toes in both manus and pes ; in the two-toed Sloth there are only
two in the manus, three in the pes. The tail is rudimentary.
The body is covered with long, coarse hairs, which differ from those
of other Mammals in being longitudinally fluted. On these hairs
FIG. 1124. — Unau, or Two-toed Sloth (Cholcepus didactylus).
(After Vogt and Specht.)
484
ZOOLOGY
SECT.
grows abundantly an alga, the presence of which gives a greenish
tinge to the fur.
The ordinary Ant-eaters (Myrmecophagidce) have a greatly elong-
ated snout, with the mouth as a small aperture at its extremity,
small eyes, and the auditory pinna sometimes small, sometimes well
developed. There are five digits in the fore-foot, of which the
third has always a very large curved and pointed claw, rendering
the manus an efficient digging organ. The toes of the hind-foot,
four or five in number, are sub-equal, and provided with moderate-
sized claws. In walking, the weight of the body rests on the
dorsal surfaces of the second, third, and fourth digits of the manus
and on a thick callous pad on the extremity of the fifth, and, in the
pes, on the entire plantar surface. The tail is always very long,
and is sometimes prehensile. The body is covered with long hair.
In the Two-toed Ant-eater (Cycloturus) the muzzle is short ; there
are four toes in the manus, of which the second and third only have
claws,- that of the third being the longer ; the pes has four sub-equal
clawed toes, forming a hook not unlike the foot of the Sloths ; the
tail is prehensile.
In the Armadillos (Dasypodidce, Fig. 1125) the head is com-
paratively short, broad, and depressed. The number of complete
FIG. 1125. — Tatu Armadillo (Dasypus sexcinctus). (After Vogt and Specht.)
digits of the fore-foot varies from three to five ; these are pro-
vided with powerful claws, so as to form a very efficient digging
organ. The hind-foot always has five digits with smaller claws.
The tail is usually well developed. The most striking external
feature of the Armadillos is the presence of an armour of bony
dermal plates ; this usually consists of a scapular shield of closely-
united plates covering the anterior part of the body, followed by a
series of transverse bands separated from one another by hairy
skin, and a posterior pelvic shield. In the genus Tolypeutes these
bands are movable, so that the animal is enabled to roll itself up
xm
PHYLUM CHORDATA
485
into a ball. The tail is also usually enclosed in rings of bony plates,
and a number protect the upper surface of the head.
In the Scaly Ant-eaters (Manis, Fig. 1126) the head is produced
Fia. 1126. — Scaly Ant-eater (Manis gigantea). (From the Cambridge Natural History.)
into a short, pointed muzzle. The limbs are short and strong, with
five digits in each foot. The upper surface of the head and body,
the sides of the latter, and the entire surface of the tail are covered
with an investment of rounded, horny, epidermal scales. The
lower surface is covered with hair, and there are a few coarse hairs
between the scales. In walking, the weight rests on the upper
and outer side of the fourth and fifth toes of the manus and on the
sole of the pes.
The Aard-varks (Orycteropus, Fig. 1127) have a thick-set body,
FIG. 1127. — Aard-vark (Orycteropus capensis). (After Vogt and Specht.)
the head produced into a long muzzle with a small tubular mouth,
the pinnaB of great length, the tail long and thick. The fore-limbs
are short and stout, with four toes, the palmar surfaces of which
486 ZOOLOGY SECT.
are placed on the ground in walking. The hind-limb is five-toed.
The surface is covered with thick skin with sparse hairs.
The Cetacea (Fig. 1128), among which are the largest of existing
Mammals, some reaching a length of 80 or 90 feet, are characterised
by the possession of a fusiform, fish-like body, tapering backwards
FIG. 1128.— Killer (Orca gladiator). (After True.)
to the tail, which is provided with a horizontally expanded caudal
fin divided into two lobes or " flukes," and a relatively large head,
not separated from the body by any distinct neck. A dorsal median
fin is usually present. The fore-limbs take the form of flippers,
with the digits covered over by a common integument, and devoid
of claws ; the hind-limbs are absent. The mouth is very wide ; the
nostrils are situated on the summit of the head, and the auditory
pinna is absent. Hairs are completely absent, or are represented
only by a few bristles about the mouth. In the Whalebone Whales
the nostrils have two external slit-like apertures ; in the toothed
Whales, Porpoises, and Dolphins, on the other hand, the two nostrils
unite to open by a single crescentic valvular aperture. _
In the Sirenia also the body is fish-like, with a horizontal caudal
fin, the fore-limbs flipper-like, the hind-limbs absent, and the
integument almost hairless. But the body is distinctly depressed,
and the head is by no means so large in proportion as in the Cetacea
and has a tumid truncated muzzle, not far back from the extremity
of which the nostrils are situated. There is no dorsal fin. The eyes
are small, the pinna3 of the ears absent. The digits are in some cases
provided with claws.
In the Ungulata vera the claws or nails are replaced by thick,
solid masses, the hoofs, investing the lingual phalanges and bearing
the weight of the body. The number of digits is more or less reduced,
and the limbs as a whole are usually specially modified to act as
organs of swift locomotion over the surface of the ground, their
xra PHYLUM CHORDATA 487
movements being restricted, by the nature of the articulations, to
antero-posterior movements of flexion and extension. The meta-
carpal and metatarsal regions are relatively very long. In the
Artiodactyla the third and fourth digits of each foot form a sym-
metrical pair. In the Ruminants vestiges of the second and fifth
digits are also commonly present ; but these are usually not func-
tional, never reaching the ground, though in the Reindeer they are
better developed than in the others and have the effect of preventing
the foot from so readily sinking in the snow. In the Camels the
third and fourth digits alone are present. The Giraffes are dis-
tinguished from the other Ruminants by the enormous length of the
neck. Characteristic of the Ruminants, though absent in the Camels
and some others, are the cephalic appendages known as horns and
antlers. The horns of the Hollow-horned Ruminants (Oxen, Sheep,
Goats, Antelopes), sometimes developed in both sexes, sometimes
only in the males, are horny sheaths supported by bony cores which
are outgrowths of the frontal bones. In the Giraffe the horns, which
are short and occur in both sexes, are bony structures covered with
soft skin, and not at first attached by bony union to the skull,
though subsequently becoming firmly fixed. Between them is a
short rounded median bony protuberance on the frontal region of the
skull. The antlers of the Deer, which, except in the case of the
Reindeer, are restricted to the male sex, are bony growths covered
only while immature by a layer of skin, the " velvet," provided with
very soft, short fur. Antlers are shed annually, and renewed by
the growth of fresh vascular bony tissue from the summit of a
pair of short processes of the frontal bones, the pedicles. Even-
tually, when the antlers are full grown, a ring-like thickening of the
bone, the " burr," appears round the base of the antler, and con-
stricts the blood-vessels, so that the substance of the antler becomes
converted into dry, dead bone ; the skin shrivels and is peeled off.
The antler is shed by the absorption of the bone immediately
beneath the burr. The pinnae of the ear of the Ruminants are well
developed. The tail is sometimes elongated and provided with a
terminal leash of long coarse hairs ; sometimes short and bushy.
The entire surface, with the exception of the end of the muzzle,
which is naked, is always covered with a close coat of longer or shorter
hairs.
In the Pigs the legs are relatively short, and the two lateral
toes of both manus and pes are fully developed, though scarcely
reaching the ground. The surface is covered with a scanty coat
of coarse bristles. There is a truncate, mobile snout, the anterior
end of which is disc-shaped and free from hairs. The pinnae are
large ; the tail is rather long, narrow, and cylindrical, provided
with a terminal tuft of strong hairs. A remarkable feature of the
males is the development of the canine teeth of both jaws into
large, upwardly-curved tusks. In the Peccaries, which resemble
488
ZOOLOGY
SECT.
the Pigs in most of the features mentioned, the points of the upper
tusks are directed downwards.
In the Hippopotami (Fig. 1129) the body is of great bulk,
FIG. 1129.— Hippopotamus (Hippopotamus amphibius). (From the Cambridge Natural
History.)
FIG. 1130. — Burchell's Zebra (Equus burchelli). (From the Cambridge Natural History.)
the limbs very short and thick, the head enormous, with a trans-
versely expanded snout, prominent eyes, and small pinnae. The
tail is short and laterally compressed. The toes are four in each
.\*rn
PHYLUM CHORDATA
489
manus and pes, all reaching the ground. The surface is naked,
with only a few hairs in certain positions ; the skin is of great
thickness.
In the Perissodactyles the third digit is either the only complete
one in both fore- and hind-foot (Horses), or there are only three
digits — second, third, and fourth — in each (Rhinoceroses), or there
are four in the fore-foot and three in the hind (Tapirs). The
" Horses " (Equidee, Fig. 1130) have the distal divisions of the limbs
slender, the metacarpals and metatarsals nearly vertical to the
surface of the ground ; the single hoof massive and with a broad
lower surface. Though the head is elongated, the nasal region is
not produced into a proboscis. The tail is short or moderately
long, and is either beset throughout with a large number of very
long, coarse hairs, or with a tuft of such specially developed hairs
at the extremity. A mane of similar large hairs usually runs
along the dorsal surface of the neck. There is a wart-like callosity
above the wrist, and in the true Horses a second a little below
the heel or " hock."
The Tapirs (Fig. 1131) have the body more massive than the
Horses, and the limbs, especially the distal segments, shorter and
FIG. 1131. — American Tapir (Tapirus terrestris). (From the Cambridge Natural History.)
stouter. The nasal region is produced into a short proboscis.
The surface is beset with a scanty covering of hairs. The tail is
vestigial.
In the Rhinoceroses (Fig. 1132) the body is extremely massive,
the limbs short and stout, each digit provided with a hoof-like
nail. There is a short, soft muzzle. Either one or two remarkable
median horns are borne on the nasal region, not attached directly
to the skull : these are epidermal structures which are formed of
a dense aggregation of slender fibre-like elements. The eyes are
VOL. TI H H
490 ZOOLOGY SECT.
small, the auditory pinnae well developed. The surface is devoid,
or nearly devoid, of hairs, and the skin is enormously thick and in
some species thrown into deep folds. The tail is narrow and of
moderate length.
The Hyraxes are small, somewhat Rabbit-like animals, with
slender limbs and vestigial tail. There are four functional digits
in the manus and three in the pes, all provided with short, flat
nails, except the innermost of the pes, which has a curved claw.
The body is covered with soft fur.
The Elephants, the largest of existing terrestrial Mammals, have
the limbs much more typically developed than in the true Ungu-
lates, there being five * comparatively short digits, enclosed in a
common integument in each foot, all of them in the fore- and
, -
FIG. 1132. — Indian Rhinoceros (Rhinoceros indicus). (From the Cambridge Natural History.)
three or four in the hind-foot, terminating in a broad, flat nail
or hoof. The weight of the body is borne on an integumentary
pad forming the sole of the foot. The limbs are very stout and
pillar-like, and the thigh and leg when at rest are in a straight
line instead of being, as in the Ungulata vera, placed nearly at
right angles to one another — a circumstance which gives a charac-
teristic appearance to the hind-quarters. The nasal region is
produced into a proboscis or " trunk," a mobile cylindrical appen-
dage, longer than the rest of the head, at the extremity of which
the nostrils are situated. There is in the male a pair of immense
tusks — the incisors of the upper jaw. The eyes are small, the
pinnae of the ears enormous. The tail is small, and provided with
a tuft of hairs at its extremity. The skin is very thick, and provided
with only a scanty hairy covering.
xni
PHYLUM CHORDATA 491
In the Carnivora vera the typical number of digits is sometimes
present, or, more usually, there are five- in the fore- and four in the
hind-foot, or four in each. The extremities of the digits are pro-
vided with compressed, curved claws, which may be very long and
sharp, when they are capable, when not in use, of being retracted
into a sheath of skin situated at their bases ; or relatively short
and blunt, when they are incompletely, or not at all, retractile. The
Dogs (Canidce) and Cats (Felidce) are digitigrade, the Bears (Ursidce)
and allied groups plantigrade (p. 501). The Otters (Lutra) differ
from the rest in having short limbs with the toes connected by
webs of skin.
The Pinnipedia (Fig. 1133) have the proximal segments of the
limbs short, so that the arm and thigh and nearly all the fore-arm
and leg are enclosed in the common integument of the trunk ; the
manus and pes are elongated. The Earless Seals (Phoridce) are
much more completely adapted to an aquatic life than the Eared
FIG. 1133. — Seal (Phoca ritttlina).
Seals (Otariidce) and Walruses (Trichechida;), being unable to flex the
thigh forwards under the body so that the hind-limbs may aid in
supporting the weight, and thus being only able to drag themselves
along very awkwardly when on dry land. The pinna of the ear is
absent in the Earless Seals and Walruses, well developed in the
Eared Seals. The surface in all is covered with a thick, soft fur.
In the Fur-Seals there are two kinds of hairs — those of the one
kind being longer and coarser, and scattered through the more
numerous shorter and finer hairs composing the fur proper. A
remarkable feature of the Walruses is the presence of a pair of
large tusks — the enlarged canine teeth— projecting downwards
from the upper jaw.
Some of the Rodents (Beavers, Water- Voles) are aquatic,
some (Squirrels and Tree-Porcupines) are arboreal, while others
(the majority of the order) lead a terrestrial life, and are active
burrowers. They are on the whole a very uniform group, and
exhibit few such remarkable modifications as are to be observed in
some of the other orders of Mammals. They are nearly all furry
H H 2
492
ZOOLOGY
SECT.
animals with five-toed plantigrade or semiplantigrade limbs. The
tail is usually elongated, and may be naked or covered with fur ;
but sometimes, as in the Rabbits and Hares, it is very short. A
few special modifications, however, have to be noted in certain
families of Rodents. The Flying Squirrels have on each side a
fold of skin, the patagium, which serves as a parachute. The
African Flying Squirrels (Anomalurus) are remarkable also on
account of the presence of a series of overlapping horny scales on
the lower surface of the basal part of the tail. The Jerboas (Dipns)
".
FIG. 1134. — Galeopithecus. (After Vogt and Specht.)
and their allies are characterised by the great relative length of
the hind-limbs — the mode of locomotion of these remarkable
Rodents being by a series of leaps not unlike those of the Kangaroo
—and by the reduction of the number of the toes to three in some
of them. The Porcupines (HystricidcB) have numerous elongated
spines or " quills " among the hairs of the dorsal surface, and some
of them have prehensile tails. The Agoutis (Dasyproctd) and the
Capybara (Hydrochcerus) have hoof-like claws, the latter having
webs between the digits.
The Insectivora are, in general, small, furry, burrowing Mammals
with plantigrade limbs and an elongated muzzle. But there is a
XIII
PHYLUM CHORDATA
493
considerable range of modification within the order in adaptation
to different modes of life. The Colugos (Galeopithecus, Fig. 1134)
have a fold of skin (patagium) extending along each side of the neck
and body and continued between the hind-legs, enclosing the tail ;
the fore- and hind-feet are both webbed, and the tail is prehensile.
The Hedgehog (Erinaceus) has the surface beset with pointed
spines. The Moles (Talpa) and their allies, which are active
burrowers, have the limbs very short and stout and provided with
extremely strong claws. The jumping Shrews (Macroscelidce)
have slender limbs adapted to progressing by leaps on the surface
of the ground.
The Chiroptera (Fig. 1135) are the only Mammals which are
capable of active flight. The fore-limbs have the segments greatly
elongated, especially the fore-arm and the four ulnar digits, and
these support a thin fold of the integument which stretches to the
hind-limbs and constitutes the
wing.
A fold (inter- femoral
FIG. 1135. — Bat (Synotus barbastellus). (After Vogt and Specht.)
membrane) also extends between the hind-limbs, and may or may
not involve the tail. The pollex is much shorter than the other
digits, is directed forwards, and terminates in a well-developed
curved claw ; in the Megachiroptera, but not in the Microchiroptera,
the second digit also has a claw ; the other digits are always claw-
less. -The position of the hind-limbs is peculiar, and the knee is
directed backwards instead of forwards as in other Mammals ;
the five digits of the foot are all provided with claws. So complete
is the adaptation of the limbs to the purpose of flight that Bats
are only able to shuffle along with great difficulty on the ground ;
though with the aid of their claws they are able to climb and to
suspend themselves from branches of trees by the hind-feet. In
the Megachiroptera the muzzle is nearly always elongated, and the
pinna of the ear simple, while in the Microchiroptera the muzzle
is short, the pinna usually complicated by the presence of an inner
lobe or tragus, and often produced into remarkable arborescent
appendages, and the nose also often provided with elaborate leaf-
like or arborescent lobes. The surface is usually covered with
494 ZOOLOGY SECT.
soft fur, except in one group of Microchiroptera in which the integu-
ment is practically naked. The tail is sometimes short, sometimes
well developed ; in the latter case it may or may not be involved in
the tail-membrane.
In the Lemurs and their allies (Prosimii) the body is slender,
and the limbs adapted for an arboreal existence. The hallux is
divergent from the other digits of the foot and opposable to them,
and the same holds good, in some cases, of the pollex. In some, all
the digits are provided with claws, in others all but the hallux.
More commonly all the digits have flat nails, except the second
of the pes, which always has a claw. The eyes are very large.
The muzzle is sometimes elongated, sometimes short ; the nostrils
are slit-like. The tail is sometimes absent or short ; more usually
it is greatly elongated, but it is never prehensile. The surface
is always covered with soft fur.
Of the Anthropoidea the Hapalidas or Marmosets are small
squirrel-like animals with all the digits except the hallux provided
with pointed claws, with the pollex incapable of opposition, the
tail non-prehensile, and without cheek-pouches or callous patches
over the ischia. The Cebidse resemble the Hapalidae in the negative
characters of the absence of ischial callosities and of cheek-pouches,
and of the power of opposition in the hallux. But the limbs are
much longer, the digits are all provided with flat nails, and the
tail is frequently prehensile. The Cercopithecidse all have brightly-
coloured, bare, callous patches of skin (callosities) over the ischia,
and most of them have cheek-pouches for the storage of food.
All the digits are provided with flat nails. The tail may be long,
or short, or absent ; when present it is never prehensile. The
pollex, when developed, is always opposable to the other digits.
In the SimiidaB or Man-like Apes (Fig. 1136) a tail is never developed,
and there are no cheek-pouches ; ischial callosities are present only
in the Gibbons. The Gibbons can walk in an upright position,
without the assistance of the fore-limbs ; in the others, though, in
progression on the surface of the ground, the body may be held in
a semi-erect position with the weight resting on the hind-limbs,
yet the assistance of the long fore-limbs acting as crutches is necessary
to enable the animal to swing itself along.
Endoskeleton. — The spinal column of Mammals varies in the
number of vertebras which it contains, the differences being mainly
due to differences in the length of the tail. The various regions
are very definitely marked off. In the cervical region the first two
vertebrae are modified to form the atlas and axis. Owing to the
absence of distinct cervical ribs, the posterior cervical vertebrae
are much more sharply marked off from the anterior thoracic than
is the case in Reptiles and Birds. The vertebras of the cervical
region have double transverse processes (or a transverse process
perforated at the base by a foramen) in all except the last. The
XIII
PHYLUM CHORDATA
495
lower portion of the transverse process in certain cases (e.g., seventh
and sometimes some of the others in Man) arises from a separate
ossification, and this is regarded as evidence that the lower part,
even when not independently ossified, represents a cervical rib.
Seven is the prevailing number of vertebrae in the cervical region ;
there are only three exceptions to this — the Manatee, Hoffmann's
Sloth, and the three-toed Sloth (cf. p. 509). The number of
thoracic and lumbar vertebras is not so constant ; usually there
are between nineteen and twenty-three. Hyrax has a larger
FIG. 1136. — Gorilla. (From the Cambridge Natural History.)
number of thoraco-lumbar vertebrae than any other Mammal—
from twenty-nine to thirty-one.
The thoracic vertebras have ribs which are connected, either
directly or by intermediate ribs, with the sternal ribs, and through
them with the sternum. Each rib typically articulates with the
spinal column by two articulations — one articular surface being
borne on the head and the other on the tubercle. The tubercle
articulates with the transverse process, and the head usually with
an articular surface furnished partly by the vertebra with which
the tubercle is connected, and partly by that next in front ; so
that the head of the first thoracic rib partly articulates with the
centrum of the last cervical vertebra.
In all the Mammalia in which the hind-limbs exist, that is to say,
in all with the exception of the Sirenia and the Cetacea, there is a
496 ZOOLOGY SECT.
sacrum consisting of closely united vertebrae, the number of which
varies in the different orders. The caudal region varies greatly
as regards the degree of its development. In the caudal region of
many long-tailed Mammals there are developed a series of chevron,
bones — V-shaped bones, which are situated opposite the inter-
vertebral spaces.
The centrum of each vertebra ossifies from three centres1 — a
middle one, an anterior, and a posterior. The middle centre forms
the centrum proper ; the anterior and posterior form the epiphyses.
The epiphyses are almost entirely absent in the Monotremes, and
in the Dugong (Sirenia) have not been detected. Between successive
centra are formed a series of discs of fibre-cartilage — the inter-
vertebral discs — represented in lower Vertebrates only in Crocodiles
and Birds. The anterior and posterior surfaces of the centra are
nearly always flat.
The sternum consists of a number of segments — the presternum
in front, the mesosternum, or corpus sterni, composed of a number
of segments or sternebrce, in the middle, and the xiphisternum behind.
The sternum is formed in the foetus in great part by the separating
off of the ventral ends of the ribs. Some of the Cetacea and the
Sirenia are exceptional in having a sternum composed of a single
piece of bone. The sternal ribs, by which the vertebral ribs are
connected with the sternum, are usually cartilaginous, but frequently
undergo calcification in old animals, and in some cases early become
completely converted into bone.
The skull of a Mammal (Fig. 1137) contains the same chief
elements and presents the same general regions as that of the
Sauropsida, but exhibits certain special modifications. A number
of the bones present in the skull of Sauropsida are not represented,
or, at all events, not certainly known to be represented definitely
by separate ossifications in the Mammalia. Such are the supra-
orbital, the pre-frontal, the post-orbital, the ecto-pterygoid and
the quadrato-jugal. The bones of the skull, with the exception of
the auditory ossicles, the lower jaw, and the hyoid, are all
immovably united together by means of sutures.
The palatine bones develop palatine plates separating off a
posterior nasal passage from the cavity of the mouth, a condition
found among the Sauropsida only in the Crocodilia, and, to a less
extent, in the Chelonia and some Lizards.
The zygomatic arch is a strong arch of bone formed partly of
the squamosal, partly of the jugal, and partly of the maxilla : in
position it represents the upper temporal arch of Amphibia and
Sauropsida, but is differently constituted (see p. 339). The orbit
in the skull of some Mammals is completely enclosed by bone,
constituting a well-defined cavity ; in others it is not completely
1 Usually the two centres of ossification which form the neural arches also
contribute to the formation of the bony centrum.
xm
PHYLUM CHORDATA
497
surrounded by bone behind, and so communicates freely with the
temporal fossa, which lies behind it.
The periotic bones (pro-otic, opisthotic, and epi-otic) are not
separately represented in the skull of Mammals. Part of the periotic
mass sometimes projects on the exterior at the hinder part of the
lateral region of the skull, and is the mastoid portion ; the rest is
commonly called the petrous portion of the periotic, and encloses
the parts of the internal ear — the mastoid portion containing only
air-cells. The tympanic bone, which perhaps represents the
quadrato-jugal of Sauropsida, sometimes only forms a long tube,
VOL. II
H H
498 ZOOLOGY sfcc-r.
sometimes a mere ring of bone. In other cases it not only gives
rise to a tube for the external auditory meatus, but also forms the
bulla tympani, a dilated bony process containing a cavity.
The occipital region presents two condyles for the articulation of
the atlas.
The mandible consists in the adult of one bone, the equivalent
of the dentary of Sauropsida, on each side — the two rami, as they
are called, being in most Mammals closely united at the symphysis.
The mandible articulates with an articular surface formed for it by
the squamosal bone, below the posterior root of the zygomatic arch.
The hyoid consists of a body and two pairs of cornua — anterior
and posterior ; of these the anterior pair are usually longer, and
consist of several bones, the most important and most constant of
which is the stylo-hyal, connected usually with the periotic region
of the skull. The posterior cornua or thyro-hyals are usually much
smaller.
The ratio borne by the capacity of the cranial cavity to the extent
of the facial region varies greatly in the different orders. The
greater development of the cerebral hemispheres in the higher
groups necessitates a greater development of the corresponding
cerebral fossa of the cranium. This is brought about by the
bulging upwards, forwards, and backwards of the cranial roof,
resulting in a great modification in the primitive relations of certain
of the great planes and axes of the skull (Fig. 1138). Taking as a
fixed base line the basi-cranial axis — an imaginary median line
running through the basi-occipital, basi-sphenoid, and pre-sphenoid
bones — we find that the great expansion of the cerebral fossa in the
higher Mammals leads to a marked alteration in the relations to
this axis (1) of the occipital plane or plane of the foramen magnum ;
(2) of the tentorial plane or plane of the tentorium cerebelli (a
transverse fold of the dura mater between the cerebral hemispheres
and the cerebellum) ; and (3) of the ethmoidal plane or plane of the
cribriform plate of the ethmoid. In the lower Mammals (A) these
are nearly at right angles to the basi-cranial axis. In the higher
groups, by the bulging forwards and backwards of the cranial roof,
the occipital and tentorial planes incline backwards and the
ethmoidal forwards, until all three may become approximately
horizontal. At the same time there is produced a change in the
relations of the basi-cranial axis to the basi-facial axis — a line passing
along the axis of the face between the mesethmoid and the vomer.
In the lower forms the angle at which the basi-facial axis, when
produced, meets the basi-cranial is an exceedingly open one ; in
the higher forms, owing to the downward inclination of the facial
region, this angle decreases in size, though it is never reduced to less
than a right angle.
The pectoral arch of the Theria has fewer distinct elements than
that of the Sauropsida. The coracoid, which in the latter is a large
xm
PHYLUM CHORDATA
499
bone, taking a share at its dorsal end in the bounding of the glenoid
cavity, and at its ventral end articulating with the sternum, is
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Fia. 1139. — Skeleton of male Ornithorhynchus. Ventral view. The right fore-limb has been separated ani
turned round so as to bring into view the dorsal surface of the raanus : the lower jaw is removed, ace. tan
accessory tarsal bone supporting the spur ; ant. pal. for. anterior palatine foramen ; atl. atlas ; ast. astragalus ; «a
axis ; bs. oc. basi-occipital ; bs. sph. basi-sphenoid ; calc. calcaneum ; cbd. cuboid ; cerv. rb. cervical rib ; dav. clavicle
cond.for. foramen above inner condyle of humerus ; cor. coracoid ; citn. cuneiform of carpus ; dent, position of horn;
teeth ; ect. cun. ecto-cuneiform ; ent. cun. ento-cuneiform ; ep. cor. epicoracpid ; epist. episternum ; ep. pb. epipubis
fb. fibula ; fern, femur ; for. mag. foramen magnum ; alen. glenoid cavity of shoulder-joint and glenoid cavit;
for mandible ; hum. humerus ; in. cond. inner condyle of humerus ; inf. orb. for. points to position of infra-orbits
foramen ; infr. proc. inferior processes of caudal vertebrae ; int. rbs. intermediate ribs ; isch. ischium ; mat
magnum of carpus ; max. maxilla ; max. for. maxillary foramen ; metat. I, first metatarsal ; metat. V, fifth«metatai
sal ; nas. cart, nasal cartilage ; obt. obturator foramen ; ol. olecranon ; out. cond. outer condyle of humerus
pal. palatine ; pat. patella ; post. pal. for. posterior palatine foramen ; pr. max. pre-maxilla ; pr. st. presternum
pter. pterygoid ; pub. pubis ; rad. radius ; scap. scapula ; scaph. scaphoid of tarsus ; scaph. lun. scapho-lunar ; set
sesamoid bones of wrist and ankle ; sp. tarsal horny spur ; sq. squamosal ; lib. tibia ; trd. trapezoid ; trn
trapezium ; turn. c. tympanic cavity ; uln. ulna ; unc. unciform ; vom. vomer ; x, dumb-bell-shaped bone ; zm
SECT, xtn PHYLUM CHORDATA 503
epiphyses of the vertebrae are not well developed in the Platypus,
being represented only in the caudal region, and they appear to
be absent in Echidna. In both genera there is the normal number
of vertebrae in the cervical region. The odontoid process long
remains separate from the centrum of the axis. The cervical
transverse processes are separately ossified, and only completely
unite with the vertebras at a late period, sutures being traceable
in all but very old animals. Zygapophyses are absent in the
cervical region. There are nineteen thoraco-lumbar vertebras
in both genera. The transverse processes are short, and the ribs
do not articulate with them, but only with the sides of the centra.
In the sacrum of Echidna there are three or four, in that of
Platypus two, united vertebrae. The caudal region differs con-
siderably in its development in the two genera. In Echidna the
tail is very short, the vertebras depressed, with no inferior spines,
but with about five subvertebral bones, which differ from ordinary
chevron bones in being mere flat nodules. In the Platypus the tail
is long, and the number of caudal vertebrae is twenty or twenty-
one. Each has a distinct inferior spinous process (infr. proc). The
sternum consists of a pre-sternum and three keeled sternebrae : in
Echidna but not in Platypus there is a xiphisternum. The most
remarkable feature of the sternal apparatus in the Prototheria is
the presence of a T-shaped episternum (interclavicle, epist.) corre-
sponding to that of Reptiles. The sternal ribs are ossified, and
are connected with the vertebral ribs by imperfectly ossified inter-
mediate ribs (int. rbs.).
The skull of the Monotremes differs widely from that of other
Mammals. The bones early become fused together, so that it is
difficult to trace their exact boundaries. The brain-case is larger
and more rounded in Echidna than in the Platypus, in accordance
with the larger size of the brain in the former genus. In both
genera there is a pterygoid (investing) bone not separately
represented in higher Mammals, corresponding to the pterygoid of
lower Vertebrates. The parasphenoid represents the lateral parts
of the parasphenoid of lower Vertebrates and the inner lamella of
the pterygoid process (usually regarded as the pterygoid) of higher
Mammals. Perforating the posterior root of the zygomatic arch
is a canal, comparatively wide in the full-grown Ornithorhynchus,
narrow in Echidna — the temporal canal — which is not present in
higher Mammals, and apparently represents the post-temporal
fossa of Reptiles.
In Echidna (Fig. 1140) the squamosal extends further forwards,
and the posterior root of the zygomatic arch is more anterior than
in Mammals in general. The zygoma is very narrow, and there
is no rudiment of post-orbital processes : the jugal is absent as a
separate ossification. The alveolar border of the maxilla (max.)
is narrow and devoid of teeth. The nasal and premaxillary
504
ZOOLOGY
SECT.
oc.cond
region of the skull is drawn out into a long, narrow rostrum. Near
the anterior end of this is a rounded opening, the external nasal
opening, which is entirely bounded by the premaxillae — the nasals
not extending so far forwards. An aperture in the nasal septum
corresponds to an actual perforation by which the nasal cavities
are in direct communication in the living animal. The pterygoids
(pt.) are in the
form of flat
plates continuous
with the bony
palate ; they ex-
tend back so as
to form a part of
the walls of the
tympanic cavi-
ties. The tym-
panic (ty.) is an
imperfect ring
which does not
become united
with the periotic.
The mandible
consists of very
narrow styliform
rami, which are
not firmly united
at the symphysis.
The condyle
(cond.) is narrow,
rather more
elongated antero-
posteriorly than
transversely.
There are very
slight rudiments
of the angle and
FIG. 1140. — Echidna aculeata. Ventral view of skull and right ' .
ramus of mandible, ang. angle of mandible ; and. oss. audi- prOCCSS (COT.).
tory ossicles ; cond. condyle of mandible ; cor. coronoid process ; T jr plflf vrm«
max. maxilla; oc. cond. occipital condyle; pal. palatine; p. e JTlcH/ypllS
max. pre-maxilla ; pi. pterygoid ; sq. squamosal ; ty. tympanic (]£[& 1139) the
zygoma is stouter
than in Echidna, and there is a post-orbital process which is formed
by the jugal. The maxillary root of the zygoma develops a process
which supports the horny tooth (dent.) of the upper jaw. The
nasal and premaxillary region is expanded into a rostrum which
is much broader than in Echidna. The premaxillse (pr. max.)
diverge from one another anteriorly, and then curve inwards again,
xin PHYLUM CHORDATA 505
partly enclosing a large space in which the nostrils are situated,
and which is covered over in the recent state by the tough but
sensitive hairless integument investing the cartilage of the rostrum,
the latter being continuous with the nasal septum. In this space
between the premaxillae is situated a dumb-bell-shaped bone (x)
which appears to be of the nature of an anterior vomer. The
pterygoid (pter.) is much smaller than in Echidna, and does not
extend as far back as the tympanic cavity. The mandible has its
rami stouter than in Echidna ; they meet for a short distance
anteriorly, and then again diverge slightly. The condyle is much
larger than in Echidna, and is elongated transversely. In front of
it is a broad process bearing the horny tooth.
It is in the shoulder-girdle that we find perhaps the most striking
peculiarities of the skeleton of the Prototheria. There is a
T-shaped epistemum (epist.), as already stated, similar to that
of Reptiles, the median limb articulating
behind with the presternum and the cross-
piece closely applied to the clavicles. There
are two short and broad coracoids (cor.)
articulating internally and behind with the
presternum, and, externally, uniting with
the scapula to form the glenoid cavity. In acr
front of the coracoid is a flat plate, the
epicoracoid (ep. cor.). The scapula (Fig.
1141) is very unlike that of other Mammals. FIG mi.— outer surface)
„,, ' . 11 i i • left scapula ol Ormtho-
Ihere is a well-developed acromion process rhynchus. acr. process
(acr.) with which the clavicle articulates ;
this terminates the anterior border, so that
the latter would appear to correspond to *, slight ridge which bounds
,-, • j. .n *- -, <• , ! HT i the surface of origin of the
tne spine ot the scapula 01 other Mammals : sub-scapuiaris muscle an-
this is confirmed by the arrangement of the
scapular muscles. The anterior part of the inner surface is in
reality the pre-spinous fossa ; the anterior portion of the outer
surface the post-spinous fossa ; and the part behind this, separated
from it by a slight ridge, together with the posterior portion of
the inner surface, is the sub-scapular fossa.
The humerus is of remarkable shape, with greatly expanded
extremities — especially in Echidna — and prominent tuberosities
and condyles. In the carpus the scaphoid and lunar are united ;
there is no separate centrale. There are a radial sesamoid and two
very large palmar sesamoids, which are sometimes united.
In the pelvis there is a very long symphysis in which pubes
and ischia take an almost equal share. The acetabulum is per-
forated in Echidna. With the anterior border of the pubes are
articulated a pair of large epipubic or " marsupial " bones (Fig. 1139,
ep. pb.). The femur has expanded extremities with prominent
external and internal trochanters. There is a large ossified patella
506 ZOOLOGY
SECT.
(pat.). The fibula (/&.) has at its proximal end a remarkable
compressed process which ossifies from a separate centre, and
resembles the olecranon of the ulna. In the tarsus there are the
usual bones. In the Platypus the astragalus and calcaneum are
firmly united, and an accessory ossification (ace. tars.) on the inner
side in the male bears the tarsal spur. The metatarsals are short
and broad, as are all the phalanges except the last.
Skeleton of Metatheria.— In the Marsupials the inferior arch
of the atlas (Fig. 1142) is often incompletely ossified, a gap being
left in the prepared skeleton ;
sometimes the gap becomes
closed in by the ingrowths of
the lateral parts of the arch,
sometimes a small separate ossi-
fication is developed, filling up
the opening. In the trunk there
FIG. 1142.— Atlas of Kangaroo. are always nineteen vertebrae.
The transverse processes of the
thoracic vertebrae are always well developed, and the ribs
articulate with them as well as with the bodies. Prominent
metapophyses and anapophyses are developed ; these are largest
in the lumbar region. Only one sacral vertebra is present in most
Marsupials ; in some a second is ankylosed with it. The caudal
region varies greatly in length. It is short in the Koala and the
Wombat, long in the Opossums, Dasyures, Phalangers and Kan-
garoos (Fig. 1143). Chevron bones are generally present, except in
the Koala and the Wombat.
In the skull (Figs. 1144-1146) the brain-cavity is relatively
small, with the cerebellar fossa entirely behind the cerebral. The
pituitary fossa is not distinct, and there are no clinoid processes.
The zygoma is complete, but the orbit is not completely bounded
by bone behind. The jugal extends beneath the squamosal root
of the zygoma to form part of the outer wall of the glenoid fossa.
The lacrymal foramen is usually on the anterior margin of the
orbit, sometimes on the face. The palate usually presents vacuities
in its posterior portion. The pterygoid is always small. The
alisphenoid is large, and forms the anterior boundary of the tym-
panic cavity ; in the Kangaroos (Fig. 1145, all) it extends backwards
so as to join the paroccipital process, which is greatly elongated.
When an auditory bulla is developed, it is formed by this bone,
the tympanic being always small, and never ankylosed to neigh-
bouring bones. The internal carotid artery perforates the basi-
sphenoid. The optic foramen is not separate from the sphenoidal
fissure. In all except Tarsipes the angle of the mandible sends
inwards a remarkable process (ang.), and is said to be inflected.
In the pectoral arch of the Marsupials the coracoid process is,
as usual, developed from a special bony centre, and a distinct
xtn
PHYLUM CHORDATA
507
suture is often recognisable between it and the scapula until a
comparatively late stage. In the young condition (when the foetus
is attached to the teat) the coracoid is comparatively extensive and
reaches the pre-sternum ventrally. A clavicle is always present,
except in the Bandicoots, but may be incomplete. There is never
orti
it.
IV
cbd
Fia. 1143. — Skeleton of "Wallaby (HaliHulnrus ualabatus). The scapula is represented as
raised somewhat higher than it would be in the natural relations of the parts. The head of
the femur has been separated from the acetabulum. acet. acetabulum ; acr. acromion
process ; ast. astragalus ; calc. calcaneum ; cbd. cuboid ; chev. chevron bones ; cl. clavicle ;
cun. cuneiform of carpus ; epi. epipubis ; fb. fibula ; fern, femur ; hd. head of femur ; hu.
humerus ; il. ilium ; isch. ischium ; obt. obturator foramen ; orb. orbit ; pis. pisiform ; pub.
pubis; rad. radius; rb.l, first rib ; rb.13, last rib; so. scapula; st. sternum; tb. tibia; troch.
great trochanter of femur ; uln. ulna ; unc. tinciform ; IV. fourth toe.
a distinct centrale in the carpus. In the Opossums the ilium has
the primitive form of a straight, three-sided rod. In the Kan-
garoos (Fig. 1143, il.) it is still simple and three-sided, but somewhat
curved outwards ; in the rest it is more or less compressed. In
nearly all the Marsupials there is a pair of epipubic or marsupial
508
ZOOLOGY
SECT.
bones (Fig. 1143, epi.) — elongated and compressed bones which
articulate posteriorly with the anterior edge of the pubes : in the
nas
Icr
p.mctsc
ff
s.oc
FIG. 1144. — Skull of Dasyurus (lateral view), al.sph. alisphenoid ; any. angular process o ••
mandible ;//•. frontal ; ju. jugal ; Icr. lacryiua) : max. maxilla ; nas. nasal ; oc. cond. occipital
condyle ; par. parietal ; par. oc. par-occipital process ; p. max. pre-maxilla ; s. oc. supra-
occipital ; sq. squamosal ; sq'. zygomatic process of squamosal.
Thylacine they are represented only by small unossified fibro-
cartilages. In the leg the fibula is always well developed. In the
young condition of some
Marsupials there is an ac-
cessory element situated out-
side the fibula at its proxi-
mal end : this apparently
corresponds to a bone
known as the parafibula
which occurs in some Lacer-
tilia. In the Phalangers
(Fig. 1147) and the Koala
there is always a consider-
able range of movement be-
tween the fibula and the
tibia, comparable in some
degree to the movements of
bas.spTi pronation and supination of
the radius and ulna. The
foot (Figs. 1147, 1148), as
already stated in the ac-
count of the external char-
acters, presents a much
greater range of modifica-
tion than the manus.
Skeleton of Edentata.—
In the Armadillos more or
fewer of the cervical verte-
brae are ankylosed together
•ft at
esc.oc
bas.oc
FIG. 1145. — Skull of Rock Wallaby (Peirogalf
penicillata) (ventral view). Letters as In Fig.
1144, except ali. alisphenoid. In addition,
has. oc. basi-occipital ; bas. sph. basi-sphenoid ;
ex. oc. ex-occipital ; pal. palatine ; pt. pterygoid ;
ty. tympanic.
xtli
PHYLUM CHORDATA
50$
both by their bodies and by their neural arches. In the lumbar
region the metapophyses are greatly prolonged — longer than the
transverse processes — and support the bony carapace. A re-
markable peculiarity of the spinal column in the Armadillos is
the fusion of a number of the anterior caudal vertebrae with the
true sacrals to form the long sacrum, containing as many as ten
vertebras altogether (Fig. 1158). The caudal region is of moderate
length ; there are numerous chevron bones. In Manis, Orycteropus,
and Myrmecopkaga none of the neck-vertebrae are united. In the
posterior-thoracic and the lumbar regions of Myrmecophaga there
are developed complex accessory articulations between the vertebras :
the sacrum contains, in addition to the true sacral vertebrae, a
number derived from the caudal region, a condition which occurs
also in Orycteropus.
In the Sloths none of the cervical vertebrae are ankylosed together ;
max
Icr
FIG. 1146. — Skull ofWombat (Phascolomys icombat) (lateral view). Letters as in Figs. 1144
and 1145. In addition, ext. aud. opening of bony auditory meatus ; cond. condyle of mandible
but in the three-toed Sloths there is an important divergence from
ordinary Mammals in the number of vertebrae in the cervical region,
there being nine or ten instead of seven ; while in one species of
two-toed Sloth (Cholospus hqffmanni) there are only six. The
neural spines of all the vertebrae are very short. A number of the
anterior caudal vertebrae are united firmly, though not quite fused,
with one another and with the true sacrals.
In the Armadillos the sternal ribs, which are sub-bifid at their
sternal ends, are ossified, and articulate with the sternum by means
of well-developed synovial articulations. In the American Ant-
eaters there are similar synovial joints, and the sternal ends of the
sternal ribs are completely bifid. In the Sloths the sternum is
long and narrow, and there are no synovial joints. In front the
sternal ribs are ossified and completely united with the vertebral
ribs, but behind they are separated from the latter by intermediate
ribs which are less perfectly ossified.
VOL. II I I
510
ZOOLOGY
SECT.
In the Armadillos the skull (Fig. 1149) is broad and flat, the
facial region triangular. The tympanic (ly.) is in some developed
into a bulla. The bony auditory meatus is in some cases elongated.
The zygoma is complete. The pterygoids are small, and do not
develop palatine plates. The mandible has a well-developed ramus
with a prominent coro-
noid process and a well-
marked angular process.
In the American Ant-
eaters (Figs. 1150 and
1151) the skull is ex-
tremely long and narrow
—the facial region being
drawn out into a long,
narrow rostrum, with the
external nares at its ex-
ent.cun
mes.cun
FIG. 1147. — Bones of leg and foot of Phalanger. ast.
astragalus ; calc. calcaneum ; cub. cuboid ; eel, cun.
ecto-cuneiform ; ent. cun. ento-cuneit'orm ; fb. fibula ;
mes. cun. meso-cuneiform ; nav. navicular ; lib. tibia;
I—V, digits. (After Owen.)
IV
FIG. 1148. — Bones of right foot of
Kangaroo (Macropus). a. astra-
galus ; c. calcaneum ; cb. cuboid ;
e:i. ento-cuneiform ; n. navicular ;
II— V, digits. (After Flower.)
tremity. The olfactory fossae are greatly developed. The rostrum is
composed of mesethmoid, vomer, maxilte, and nasals — the pre-
maxillse being very small. The zygoma is incomplete, and the
orbit is not closed behind by bone, the post-orbital processes of
the frontal being entirely absent. The pterygoids (pter.), in all
but Cycloturus, develop palatine plates. There is no bony auditory
meatus. The mandible is entirely devoid of ascending ramus—
XIII
PHYLUM CHORDATA
511
consisting of two long and slender horizontal rami, with a very
short symphysis.
In the Sloths (Fig. 1152) the cranial region is elevated and rounded,
the facial short ; the frontal region is elevated, owing to the develop-
ment of extensive frontal air-sinuses. The premaxillse are small,
par
nas
s.oc
'.oc
FIG. 1149. — Skull of Armadillo (Dasutnis sexcinctus). Letters as in Figs. 1144 — 1140. In
addition, -peri, periotic.
and not firmly connected with the maxillaa, so that they are com-
monly lost in the macerated skull. The jugal (ju.) develops a
strong zygomatic process which bifurcates behind into two branches,
neither of which is connected with the rudimentary zygomatic
process of the squamosal, so that the zygomatic arch remains in-
complete. There are, at most, the rudiments of post-orbital pro-
par
s.oc
ju pal aLsph '
nd
cor
FIG. 1150. — Skull of Ant-eater (Myrmecophaga), lateral view, al.sph. alisphenoid ; cond.
condyle of mandible ; cor. coronoid process of mandible ; ei.oc. ex-occipital ; ext. aud.
external auditory meatus ; /r. frontal ; ju. jugal ; lor. lacrymal : max. maxilla ; nas. nasal ;
occ. cond. occipital condyle ; pal. palatine ; par. parietal ; p.indx. pre-maxilla ; s.oc. supra-
occipital ; sq. squamosal ; ty. tympanic.
cesses of the frontals. The pterygoids develop vertical laminae
and form no palatine plates. The ascending ramus and coronoid
process of the mandible are both well developed.
In the American Ant-eaters and Armadillos the bones of the
fore-limb are short and powerful. The scapula in the Ant-eaters
i i 2
512
ZOOLOGY
SECT.
s. oc
ex.oc
FIG. 1151.— Skull of Ant-eater (Myrme-
cophaga), ventral view. Letters as in
Fig. 1150. In addition, b.oc. basi-
occipital ; glen, glenoid surface for
mandible ; pter. pterygoid.
short and powerful, with well-
Lc.f
is broad and rounded ; the anterior
border unites with the coracoid
process so as to convert the
coraco-scapular notch into a fora-
men. In the middle of the spine
there is a triangular process : a
ridge on the post-spinous fossa pre-
sents the appearance of a second
spine. The fibres of origin of the
sub-scapularis muscle extend on to
the outer surface as far forward as
this ridge, so that the part of the
outer surface behind the ridge
corresponds to a part of the sub-
scapular fossa, which in other
Theria is co-extensive with the
inner surface. Except in Cycloturus
the clavicles are rudimentary. All
the carpal bones are distinct.
In the Armadillos the scapula
(Fig. 1153) has an extremely
prolonged acromion (acr.), some-
times articulating with the humerus.
A ridge (spr.) representing a second
spine is present. The clavicle is
well developed. The humerus is
developed processes and ridges, and
S.OC
FIG. 1152.— Skull of Three-toed Sloth (Bradypus tridactyJus). Letters as in Fig. 1150.
with a foramen above the inner condyle (entepicondylar foramen).
The carpus consists of the ordinary eight bones.
XIII
PHYLUM CHORDATA
513
pr.sc
In the Sloths (Fig. 1154) the arm-bones are comparatively long
and slender. A coraco-scapular foramen is formed as in the
Ant-eaters. In the three-toed Sloths (Fig. 1155) the acromion (acr.)
is at first connected with the coracoid process, but becomes reduced
and loses the connection ; in the two-toed Sloth the connection
persists. The clavicle (cl.) is not directly connected internally with
the sternum ; externally it is directly
connected with the coracoid process
—a condition observed in no other
Mammal. The humerus is very long
and slender ; so are the radius and
ulna, which are capable of a certain
amount of movement in pronation
and supination. In the carpus (Fig.
1156) the trapezoid and magnum
are united in Bradypus, distinct in
Choloepus : in the former the tra-
pezium is usually fused with the
rudimentary first metacarpal. The
first and fifth metacarpals are re-
presented only by rudiments. The
proximal phalanges of the three
digits are early ankylosed with the
corresponding metacarpals, so that it
might readily be supposed that one
of the ordinary bones of each digit
was absent.
The pelvis of the American Ant-eaters is elongated, with, a short
symphysis pubis. The ischia unite with the spinal column. There
is no third trochanter. The tibia and fibula are nearly straight,
and parallel with one another. In Cydoturus the pes is modified
to form a climbing organ.
In the Sloths the pelvis is short and wide ; the spines of the ischia
unite with the anterior caudal vertebrae so that a sacro -sciatic
foramen is formed as in Ant-eaters. The femur is long and slender ;
it is devoid of third trochanter. The tibia and fibula are also long
and slender. At its distal end (Fig. 1157) the fibula develops a
peg-like process (x) which fits into a depression in the outer face of
the astragalus. The calcaneal process is extremely prolonged in
Bradypus, in which there is a tendency to ankylosis between the
tarsal bones, and the proximal phalanges ankylose with the meta-
tarsals.
In the Armadillos the pelvis (Fig. 1158) is extremely long, and
both ilia and ischia are firmly fused with the spinal column. The
femur has a prominent third trochanter. The bones of the pes
(Fig. 1159) are normal.
Skeleton of Cetacea.— In the Cetacea (Fig. 1160) the cervical
cor
FIG. 1153. — Shoulder-girdle of Arma-
dillo (Dasypus sexcinctus). acr.
acromion ; cor. coracoid process ;
pr.sc. pre-spinous fossa; pt. sc. post-
spinous fossa ; sp. spine ; sp'. ridge
probably marking the anterior
limit of origin of the subscapularis
muscle.
514
ZOOLOGY
SECT.
region (cerv.) is always very short, and the constituent vertebrae
are often completely fused together into a continuous bony
mass, or the atlas alone may be separated from the rest ; but
I
iS
5
I
s
a
5
02
•0
4)
o
a
o
sometimes all the vertebra? are complete and separate. In
the latter case they have small arches and long transverse processes
XIII
PHYLUM CHORDATA
515
consisting of two narrow bars with a wide space between them.
The epiphyses are very distinct discs which often remain separate
from the bodies up to a late period. The neural spines are well
developed. The zygapophyses are not well developed, and are
uln
rad
acr
FIG. 1155. — Shoulder-girdle of Three-
toed Sloth (Braaypus tridactylus).
acr. acromion ; el. clavicle ; cor.
coracoid.
7TI.C.1
FIG. 1156. — Right manus of Three-toed
Sloth, cun. cuneiform; lun. lunar; m.c.l,
first metacarpal; m.c.5, rudiment of fifth
metacarpal ; pis. pisiform ; rod. radius ; sc.
scaphoid ; trd. m. trapezoid and magnun;
united ; uln. ulna ; unc. unciform.
absent in the posterior portion of the trunk. In the absence of
hind limbs there is no sacral region. The caudal region consists
of numerous vertebrae beneath which, opposite the intervertebral
spaces, are a series of chevron bones (chev.).
In the Whalebone Whales only
one pair of ribs articulates with
the sternum, and none articulate
with the bodies of the vertebra?,
but only with the transverse
processes. In the Toothed
Whales only a small number are
connected with the sternum,
sometimes through the inter-
vention of intermediate ribs,
and a few of the anterior only,
in most cases, articulate with
the bodies of the vertebrae ; but
in some a greater number ar-
ticulate with both transverse
processes and bodies by distinct
tubercles and heads.
The sternum varies in shape.
Sometimes it consists of a pre-
sternum and a series of several sternebrse without xiphisternum ;
sometimes (Fig. 1161) it is a continuous plate of bone, occasionally
with median notches or fontanelles.
In the skull (Fig. 1162) the brain-case is rounded, the jaws
greatly elongated, often unsymmetrical, The parietals (Pa) do
Fid. 1157.— Pes of Three-toed Sloth.
ast. astragalus ; calc. calcaneum ; cbd.
cuboid ; fb. fibula ; mesoc. mesocuneiform ;
metat.l, vestige of first metatarsal; metat.H,
vestige of fifth metatarsal ; nap. navicular ;
lib. tibia ; x, peg-like process at distal end
of fibula.
516
ZOOLOGY
SECT.
not meet in the middle line above in most Cetacea, being separated
by the supra-occipital (SO.) and an inter-parietal (IP.) ; there is
thus no sagittal suture.
A large supra-orbital
plate is developed from
the frontal. There are
large and stout zygo-
vecl.l-ub
cat
FiQ. 1159. — Pes of Armadillo
(Dasypus sexcinctus). asi.astra-
FiG. 1158. — Pelvis and sacrum of Armadillo (Dasypus gains ; cat. calcaneum ; cbd,
sexcinctus). ac. acetabulum ; U. ilium ; isch. ischium ; cuboid ; ect. ecto-cuneiform ;
obt.for. obturator foramen ; feet. tub. pectineal tubercle ; ent. ento-cuneiform ; mes. meso-
•pub. pubis. cuneiform ; nav. navicular.
matic processes of the squamosal, but the jugals are extremely
small. In all the recent forms the maxilla (Mx.) is very large and
extends backwards to overlap a good deal of the frontal, and for-
wards .nearly to the extremity of the snout ; while the premaxillae
(P. MX.), which are long narrow bones, bound but a very small
part of the oral border of the upper jaw. The nasals (Na.) are
v«ry small. The tympanic bone is very large, and is some-
times fused with the periotic (Mystacoceti), sometimes not
(Odontoceti). The lower jaw is remarkable for the absence of an
ascending ramus.
The scapula in most of the Cetacea is very broad and flat, ex-
panded into the shape of an open fan. The spine is usually situated
close to the anterior border, sometimes coalescent with it. The
acromion is curved and flat, the coracoid also compressed and parallel
with the acromion. In some, both acromion and coracoid are
absent. There is never any trace of a clavicle. The humerus is
short and very stout ; the head freely movable in the glenoid cavity ;
the distal articulating surfaces are flat and oblique, meeting at an
angle. The proximal ends of the radius and ulna are so firmly
united with the humerus as to allow of very little movement ;
at the distal end there are no complete synovial membranes. The
XIII
PHYLUM CHORDATA
517
S » ft
»;~ 9
8*2
..j__-ft
CO) ,;
> S 03
O .
.o-
35 I
C ^" O
E if
§S«
03 o ••
o o »i
ftg«
o"^^
''- ^ ;••?
manus is extremely modified.
There are no synovial joints ;
the carpus is in some (Whalebone
Whales) almost entirely car-
tilaginous, as also are the
metacarpals and phalanges — the
cartilages being coalescent or
separated by intervals of fibrous
tissue : in some of the carpal
elements bone is deposited. In
the toothed Whales the carpals
are completely ossified, and
are of polygonal form : the
phalanges are also ossified, with
incomplete synovial articula-
tions. In the Cetacea there are
b£ ft >a
°~"ft
feis,
^— £ FIG. 1161. — Sternum of Rorqual (Balccnop •
£ K . tera musculus). (After Flower.)
sometimes five digits, sometimes
only four : more or fewer have
considerably more than the
normal number of phalanges —
sometimes as many as fourteen.
The second digit is usually the
longest.
Vestiges of the pelvis are
present in the form of a pair of
long narrow bones (Fig. 1160,
pelv.) which lie parallel with the
spinal column some little dis-
tance below the region where
the chevron bones begin : these
appear to represent the ischia.
A second pair of smaller bones
which lie close to these in the
".2 )*
-13
o
S
ftO
518
ZOOLOGY
SECT.
Whalebone Whales are apparently vestiges of the femora, and
there may be additional vestiges representing the tibiae.
Skeleton of Sirenia. — In the Sirenia (Fig. 1163) the cervical
vertebrae do not coalesce, with the exception of two of them in
the Manatee. In the Manatee there are only six cervical vertebrae,
and the neural arches are sometimes incomplete. In the trunk
the thoracic vertebrae are numerous ; all have well-developed facets
for the heads of the ribs, and well developed zygapophyses. The
caudal vertebrae are numerous, depressed, with wide transverse
processes. The ribs are numerous, but few of them are connected
Ih
FIG. 1162. — Skull of Dolphin (Globiocephalus), sagittal section, a. angle of mandible ; an.
external nares ; AS. alisphenoid ; bh. basi-hyal ; BO. basi-occipital ; US. basi-sphenoid ; cd.
condyle of mandible ; cp. coronoid process ; Ex.O. ex-occipital ; Fr. frontal ; IP. inter-
parietal ; ME. mesethmoid ; MX. maxilla ; Na. nasal ; Pa. parietal ; Per. periotic ; PI. pala-
tine ; P.Mx. pre-maxilla ; pn. posterior nares ; PS. presphenoid ; Pt. pterygoid ; sh. stylo-
hyal ; SO. supra-occipital ; Sg. squamosal ; th. thyro-hyal ; Vo. vomer. (After Flower.)
with the sternum. The sternum is a broad bone not composed
of distinguishable segments.
The skull (Fig. 1164) is characterised by its extreme hardness.
The cranial cavity is rather long and narrow as compared with
that of the Cetacea. Although the supra-occipital (SO.) is pro-
duced forwards on the upper surface of the skull for a considerable
distance, it does not separate the parietals (Pa.) from one another.
The frontals develop broad supra-orbital plates. The zygoma is
stout. As in the Cetacea, the external nares are very wide, but
they are relatively further forwards. The nasals are rudimentary.
The tympanic and periotic are readily separable from the other
XIII
PHYLUM CHORDATA
51'9
bones. There are enormous pre-
maxillae in the Dugongs. The
mandible has a well-developed
ascending ramus and coronoid
process (cp.).
The scapula of the Sirenia, is
much more like that of the ter-
restrial Mammals than is that of
Cetacea, but is nearer that of
the Seals ; it is narrow and
curved backwards. The spine
is situated about the middle ;
the acromion is directed down-
wards. The coracoid is fairly
well developed, and of a conical
shape. The clavicle is absent,
as in the Cetacea. The skeleton
of the arm also departs less
from the ordinary Mammalian
type than in the Cetacea. The
radius and ulna are ankylosed
at their extremities. The car-
pus has seven bones in the
Manatee : the pisiform is absent.
In the Dugong coalescence takes
place between the carpal bones,
so that the number of ossifica-
tions is reduced in the adult.
There are five digits, all of which
possess the normal number of
phalanges.
The pelvis is represented by
a pair or more of vestiges
widely separated from the spinal
column, and having a vertical
position : they probably repre-
sent the ilia.
Skeleton of the Ungulata.
-In general, the centra of the
Ungulata are more or less dis-
tinctly opisthoccelous. The
odontoid process of the axis (Fig.
1165) has a peculiar spout-like
form in the majority of the Rumi-
nants, and in a less marked
degree in the Horses and Tapirs :
in the Chevrotains, the Pigs, and
e
'3
3
o
I
«*-!
o
a
5
CO
CD
r>2o
ZOOLOGY
SECT.
the Proboscidea it is conical. In the Ruminants the cervical verte-
brae present a median keel below, produced in the posterior part of
MF.
ET
PMx
ExQ
a
FIG. 1164. — Section of skull of Manatee (Manatus seneyalensis). Letters as in Fig. 1162. In
addition, ET. ethmo-turbinal ; Ty. tympanic. (After Flower.)
od.
*P
FIG. 1165. — Axis of Bed Deer (Cervus elaphus). A, lateral view; B, dorsal view, ep .
epiphysis of centrum ; od. odontoid process ; pt. z. post-zygapophysis ; sp. neural spine ;
trans, transverse process.
the region into a process. The development of the cervical neural
spines varies : in most they are elongated and compressed ; but in
xm PHYLUM CHORDATA 521
the Horses they are almost completely absent, and in the Elephants
they are all small, with the exception of the last. The number
of thoraco-lumbar vertebrse is nearly always nineteen in the
Artiodactyles, twenty-three in the Perissodactyles and in the
Proboscidea. Hyrax has a larger number of trunk-vertebrae —
twenty-eight to thirty — than any other terrestrial Mammal. The
transverse processes of the lumbar vertebrae are nearly always
elongated, flattened, and directed outwards, or outwards and slightly
forwards. Usually there is a single wide sacral vertebra united
with the ilia, ankylosed with which behind are a varying number
of narrow caudal vertebrae. There are never chevron bones in the
caudal region of any existing Ungulate.
In all the Ungulata the sternebrae are distinct. As a general
rule the presternum is narrow, sometimes (Horses and Tapirs)
greatly compressed laterally, while the mesosternum is broad ;
but in the Rhinoceros the mesosternum is no broader than the
presternum.
Among the Perissodactyle Ungulates the skull of the Horse
(Fig. 1166) is elongated, especially in the facial region ; the axis of
the skull, or the line from the anterior margin of the pre-maxillae
FiQ. 1166. — Side view of posterior parts of skull of Horse (Equus caballus). AS. alisphenoid ;
Ex O. exoccipital ; Fr. frontal ; gf. glenoicl fossa ; Ma, jugal ; oc. occipital condyle ; Pa.
parietal ; pp. par-occipital process ; Per. periotic ; pg. post-glenoid process of squamosal ;
pt. post-tympanic process ; SO. supra-occipital ; Sq. squamosal ; th. tympano-hyal ; Ty.
tympanic. (After Flower.)
to the lower edge of the foramen magnum, is nearly straight, and
both the occipital plane and ethmoidal plane are nearly perpen-
dicular to it. The supra-occipital (SO.) has a prominent transverse
crest ; and in front of this the temporal ridges, which limit the
temporal fossa above, unite to form a median longitudinal sagittal
crest, running along the course of the sagittal suture. The ex-
occipital develops a prominent, downwardly-directed, par-occipital
process (pp). The tympanic (Ty.) is small and, with the periotic
(Per.), is only loosely connected with the neighbouring bones,
522 ZOOLOGY SECT.
being held in place mainly by a post-tympanic process developed
from the squamosal. A considerable part of the periotic
(mastoid portion) appears on the surface of the skull between this
and the exoccipital. The tympanic forms a tubular auditory
meatus, but is not expanded into a bulla. The glenoid fossa is
extended transversely, and is bounded behind by a post-glenoid
process. The orbit, which is relatively small, is completely sur-
rounded by bone. The nasals are large, and are separated from
the pre-maxillse in a great part of their extent. The mandible
has a large ascending ramus, and a coronoid process which rises
high above the level of the condyle ; the latter is elongated trans-
versely in co-ordination with the form of the glenoid cavity.
The skull of the Rhinoceros differs from that of the Horse mainly
in the presence of large air-cells in the supra-occipital and parietal
bones, and in the orbit not being separated by bone from the
temporal fossa, except in the two-horned Asiatic species. The
post-glenoid process equals or exceeds the paroccipital ; the mastoid
does not appear on the surface, owing to the post-tympanic process
of the squamosal extending backwards to articulate with the
exoccipital and concealing it from view.
The skull of the Tapirs resembles that of the Rhinoceros in
most respects. As in the latter, the orbits are not completely
bounded by bone behind. The nasal openings are very large, and
extend backwards above the orbits, separated from them only by
a thin plate. The nasals are very prominent, and the inferior
and lateral boundaries of the nasal apertures are formed entirely
by the maxillae. There are large post-glenoidal and post-tympanic
processes ; the latter is united with the paroccipital process. The
mandible differs from that of the other Perissodactyles chiefly in
the prominent incurved angle.
In the Ruminant Artiodactyles (Fig. 1167) the facial region is
more or less bent downwards on the basi-cranial axis, and while the
occipital plane is nearly perpendicular to the latter, the ethmoidal
plane is nearly horizontal. There are prominent paroccipital
processes (pp). The tympanic (Ty), which may or may not be
ankylosed with the periotic, forms a tubular auditory meatus and
sometimes a distinct bulla. The mastoid appears for a short space
on the surface, between the squamosal and the exoccipital. The
frontals usually bear a pair of processes, more or less prominent, for
the support of the horns, and between these a transverse ridge
frequently extends. The orbit is completely encircled by bone,
and has a prominent margin. The nasals are elongated and the
premaxillae slender. The condyle of the mandible is broad and
flat ; the horizontal ramus usually rather slender, and expanded in
front for the lodgment of the incisors.
In the Pigs, as in the Ruminants, the facial region is bent
downwards. There is a prominent transverse occipital crest at
XIII
PHYLUM CHORDATA
523
the junction of the supra-occipital and parietals ; but the temporal
ridges do not meet in the middle to form a sagittal crest such as
occurs in the skull of the Horse. There are prominent paroccipital
processes. There is a large, but compressed, bulla tympani ; the
auditory meatus is very long, directed upwards and outwards, and
is surrounded by the post-glenoidal and post-tympanic processes,
which are in contact with one another. The mastoid is rudi-
mentary, and does not appear on the outer surface of the skull.
The frontal develops a short post-orbital process ; but this does
Pa.
Fio. 1167. — Section of skull of Sheep (Ovis aries). AS, alisphenoid ; bh. basi-hyal ; B3.
basi-occipital ; BS. bast-sphenoid ; cd. condyle ; ch. cerato-hyal ; cp. coronoid process ; eh.
epihyal ; EO. ex-occipital ; ET. ethmo-turbiual ; Fr. frontal ; ME. mesethmoid ; MT.
maxillary turbinal ; MX. maxilla ; Na. nasal ; OS. orbito-sphenoid ; Pa. parietal ; PL
palatine ; Per. periotic ; P. MX. pre-maxilla ; P.S. pre-sphenoid ; PI. pterygoid ; s.h.
stylo-hyal ; SO. supra-occipital (with inter-parietal) ; pp. par-occipital process ; th. thyro-
hyal ; Ty. tympanic ; Vo, vomer. (After Flower.)
not meet the zygoma, so that the bony margin of the orbit is
incomplete behind. The facial region as a whole is elongated and
laterally compressed. The nasals are long and narrow, and the
premaxillse send backwards long processes on each side of them.
A peculiar bone — the pre-nasal — is developed in the nasal septum.
The condyle of the mandible is transversely elongated ; the coronoid
process very small.
The skull of the Hippopotamus differs from that of the Pig
mainly in the proportions of the various parts. The cranial cavity
is relatively small, and the face large. The orbits are almost
524
ZOOLOGY
SECT.
tubular, and are almost, or quite, encircled by bone. The face is
laterally contracted in front of the orbit and again expands
anteriorly. The mandible is extremely massive ; anteriorly the
p.oc
oc.con-d
FIG. 1168. — Skull of Hyrax. Letters as in Fig. 1144 ; in addition, int. par. inter-parietal;
ty. tympanic. The suture between the frontal and parietal has been by an error made to
run behind the post-orbital process.
•
symphysial portion is greatly expanded to support the large incisor
and canine teeth.
In the Hyracoidea (Fig. 1168) the skull shows affinities with
Rodents and also with Perissodactyles. The zygomatic arch is
FlQ. 1169. — Section of skull of African Elephant (Elephas africanus), to the left of the
middle line. an. anterior nares ; ME. mesethmoid ; pn. posterior nares : Vo. vomer.
(After Flower.)
stout : it is formed mainly by the jugal (ju), which forms part
of the glenoid fossa. The post-orbital processes meet in some to
XIII
PHYLUM CHORDATA
525
bound the orbit behind ; the upper one is formed from the parietal
(par). The facial region is comparatively short. The premaxillee
(p. max) are not greatly developed. There are distinct paroccipital
processes (p. oc.). The periotic and tympanic are ankylosed
together, but not to the squamosal. The tympanic (ty.) forms a
bulla with a spout-like prolongation.
In the Proboscidea (Fig. 1169) the bones of the skull are of
enormous thickness, the inner and outer tables being separated by
extensive air-cells. The sutures are early obliterated. Paroccipital
and postglenoidal processes are absent. The tympanic forms a
large, rounded auditory bulla ; but the external auditory meatus
is bounded chiefly by the post-tympanic process of the squamosal.
The mastoid portion of the periotic does not appear on the surface.
The orbit is not completely separated by bone from the temporal
fossa. The nasal aperture is situated far back, and looks upwards
and forwards almost as in the skull of some
of the Cetacea. The chief characteristic of
the mandible is its prolongation forwards
into a spout-like process at the symphysis.
In the Ungulata vera the scapula (Fig.
1170) is never very broad ; the spine is
usually near the middle. Neither the acro-
mion nor the coracoid process is very pro-
minent ; sometimes, as in the Horse, the
former is absent. A clavicle is never
present. In the Ruminants, as in some
other Mammals, the vertebral portion of
the scapula remains cartilaginous, forming
the so-called supra-scapular cartilage (ss).
In Pigs and some Perissodactyles, though
there is no acromion, there is a triangular
process about the middle of the spine.
The humerus is short and stout, the
radius always well developed, the ulna in
some (Pigs, Hippopotami, Tapirs, and
Rhinoceroses) well developed, in others (the
Horses and the Ruminants) incomplete.
The first digit is always absent. There
is never a centrale. The trapezoid and
magnum unite in most of the Ruminants.
In the Perissodactyla the third digit in both the fore- and hind-
foot is symmetrical in itself. In the Rhinoceroses the second and
fourth are also present, and in the Tapirs (Fig. 1171) the fifth of
the fore-foot is developed as well. The Horses (Fig. 1172) present
the greatest reduction in the number of the digits observable in
any Mammal, the third being the only functional digit in each
foot. Its elongated metacarpal or metatarsal (sometimes called
ff
FiQ. 1170. — Right scapula of
Red Deer (Cervus elaphus).
a. acromion ; a/, prescapular
fossa ; c. vestigial coracoid
process ; gc. glenoid cavity ;
t>f. post-scapular fossa ; ss.
imperfectly ossified supra-
scapular portion. (After
Flower.)
VOL. II
K K
526
ZOOLOGY
SECT.
the cannon bone) has in apposition with it laterally a pair of splint-
like vestiges which represent the metacarpals or metatarsals of
the second and fourth digits. In the Artiodactyla, on the other
hand, the third and fourth digits form a symmetrical pair. In
the Ruminant Artiodactyles (Fig. 1174) the metacarpals or meta-
tarsals of these digits unite to form a single elongated bone, the
cannon bone.
The pelvis of most Ungulata is greatly elongated. The ilia are
wide transversely ; the symphysis is very long, involving a part of
n
tr-
Fio. 1171.— Bones of
the man us of Tapir
(Tapirus indicus). c.
cuneiform ; I. lunar ;
m. magnum ; p. pisi-
form ; R. radius ; s.
scaphoid ; td. trape-
zoid ; tm. trapezium ;
U. ulna; w. unciform.
(After Flower.)
FIG. 1172. — Bones of
the manus of Horse
(Equus caballus). c.
cuneiform ; I. lunar ;
m. magnum ; p. pisi-
form ; Ji. radius ; s.
scaphoid ; td. trape-
zoid ; u. unciform ;
//, IV, vestigial
second and fourth
metacarpals. (After
Flower.)
FiG. 1173. — Bones of
manus of Pig (Sus
scrofa). c. cunei-
form ; 1. lunar ; m.
magnum ; R, ra-
dius ; s. scaphoid ;
td. trapezoid ; U.
ulna ; u. unciform.
(After Flower.)
FIG. 1174. — Bones
of manus of Red
Deer (Cervus
claphus). TO2. «i5.
vestigial second
and fifth meta-
carpals ; R. ra-
dius. (After
Flower.)
the ischia as well as the pubes. In the Perissodactyla, but not
in the Artiodactyla, there is a well-marked third trochanter.
In some Ungulates (Rhinoceroses, Tapirs, Pigs, Hippopotami)
the fibula is distinct though slender. In the Horse it is represented
by a vestige. In the Ruminants it is represented only by a small
vestige, the malleolar bone, which articulates with the distal end
of the tibia.
The structure of the foot exhibits a close parallelism to that
of the manus. The tarsal bones are closely dovetailed together,
and articulate with one another by flat surfaces. The hallux is
XIII
PHYLUM CHORDATA
527
never developed. In the Perissodactyla the third digit is sym-
metrical in itself. In the Rhinoceros and Tapirs the second and
fourth digits are also completely developed ; but in the Horses
(Fig. 1175) they are represented only by splint-like vestiges of
FIG. 1175. — Dorsal surface of
right tarsus of Horse (Equus
caballus). a. astragalus ; c.
calcaneum ; cb. cuboid ; c.
united meso- and ento-
cuneiform ; c3. ecto-cunei-
form ; n. navicular ; mil,
IV, vestigial second and
fourth metatarsals ; ///,
third ruetatarsal. (After
Flower.)
FIG. 1176. — Dorsal sur-
face of right tarsus of
Red Deer (Cervus
elaphus). a. astragalus ;
c. calcaneum ; cb. cu-
boid ; ca. conjoined
ecto- and meso-cunei-
form ; mill, mlV,
third and fourth meta-
tarsals ; n. navicular.
(After Flower.)
>nI7~
FIG. 1177. — Dorsal sur-
face of right tarsus of
Pig (Sus scrofa). a.
astragalus ; c. calcan-
eum ; cb. cuboid ; c3.
ecto-cuneiform ; c2.
meso-cuneiform ; mil
—V, metatarsals ; n.
navicular. (After
Flower.)
their metatarsals, the metatarsal of the third digit forming an
elongated " cannon bone," like the metacarpal of the third digit
of the manus. In the Rhinoceroses and Tapirs all the usual
tarsal bones are present ; in the Horses the ento-cimeiform and
meso-cuneiform are united. In the Artiodactyles the third and
fourth digits form a symmetrical pair as in the manus ; and in
the Ruminants (Fig. 1176) their metatarsals unite to form a cannon
bone. In most Ruminants there are no vestiges of the second
and fifth digits. In the Pigs (Fig. 1177) all the tarsal bones are
present. In most Ruminants the cuboid and navicular are united ;
in the Camels these bones are distinct, but the ento-cuneiform is
wanting.
In the Hyracoidea the scapular is triangular, like that of the
Ungulata vera, and the spine is moderately developed, most
prominent in the middle. There is a large supra-trochlear fora-
men. The radius and ulna are complete, but often ankylosed.
K K'2
528
ZOOLOGY
SECT.
In the carpus there is a centrale between the scaphoid and the
trapezoid. There are five digits, the first very small ; in some the
last is represented only by a vestigial metacarpal.
In the femur an indistinct ridge-like elevation is to be regarded
as representing the third trochanter. The foot resembles that of
the Rhinoceros in having three digits developed ; but there is a
small bone representing the fifth metatarsal, and the ungual
phalanx of the second is cleft.
In the Proboscidea the coracoid process is small. The acromion
presents a recurved process or metacromion, as in Rodents. The
clavicle is absent. The radius and ulna are permanently fixed
in the prone condition. The manus is short and broad ; the carpals
are squarish, with flat articular surfaces. There is no centrale ;
five digits are present. The pelvis has its long axis nearly vertical.
The iliac crest is directed transversely, and is greatly expanded ;
the iliac and gluteal surfaces look almost directly forwards and
backwards. The pubes and ischia are comparatively small. The
femur is very long as compared with that of the Ungulata vera.
There is no third trochanter. The fibula is complete. The foot
is short and broad, somewhat smaller than the manus.
Skeleton of the Carnivora. — In the Carnivora the atlas is
very large, with wing-like lateral processes. The neural spine
of the axis is elongated and compressed, the odontoid conical.
The other cervical vertebra
have small spines and large
transverse processes. There
are twenty or twenty-one
thoraco - lumbar vertebrae.
The most anterior thoracics
have long, slender, back-
wardly-sloping spines. In
the posterior thoracics large
metapophyses and anapo-
physes are developed. The
transverse processes of the
lumbar vertebrae are ex-
tremely long and the spines
short. The sternum is long
and narrow, composed usually
of eight or nine pieces. The
sternal ribs are almost un-
calcified.
In the skull of the Carnivora
vera (Figs. 1178 and 1180)
there are prominent sagittal and lambdoidal crests. The temporal
fossae are very deep ; the orbits are not separated from them by
bone. The relative development of the facial region varies in
FIG. 1178.— Skull of Tiger (Fe'is tigris).
Blainville.)
(After
XIII
PHYLUM CHORDATA
529
the different groups ; in the Bears and their allies, and' in the Dogs,
it is elongated ; in the Cats it is very short. The zygoma is strong
and greatly arched
outwards. The
noid cavity is
form of a
groove, to
gle-
in the
transverse
the shape
of which the trans-
versely elongated con-
dyle is adapted. In
the Cats there is a
large rounded tym-
panic bulla (Fig. 1179),
the cavity of which is
divided into two parts
—anterior and pos-
terior— by a septum,
the anterior containing
the auditory ossicles
and the opening of the
Eustachian tube ; the
bony auditory meatus
is short : the parocci-
pital is closely applied to the posterior surface of the tympanic
bulla. In the Dogs the septum of the bulla is incomplete, the
auditory meatus short, and the paroccipital process not applied
P
Jm
oo
FIG. 1179. — Section of the left auditory bulla of Tiger (Felis
tigris). * aperture of communication between the two
chambers into which the cavity of the bulla is divided ;
a. m. external auditory meatus ; BO. basi-occipital ; e.
Eustachian tube ; ic. the inner chamber ; oc. the outer
chamber ; Pt. periotic ; s. septum between the two
chambers; Sq. squamosal. (After Flower.)
FIQ. 1180. — Lateral view of skull of Dog (Canis familiaris). C. occ. occipital condyle ; F.
frontal ; F.inf. infra-orbital foramen ; Jg. jugal ; Jm. premaxilla ; L. lacrymal ; M. Maxilla ;
Maud, external auditory meatus ; Md. mandible ; ^V. nasal ; P. parietal ; Pal. palatine ;
Pjt. zygomatic process of squamosal ; Pt. pterygoid ; Sph. ali-sphenoid ; Sg. squamosal ;
Sg. occ. supra-occiptial ; T. tympanic. (From Wiedersheim's Comparative Anatomy.)
to the bulla. In the Bears and their allies (Fig. 1181) the bulla is
usually less dilated, and the septum is absent or only represented
by a ridge, while the bony auditory meatus is elongated.
530
ZOOLOGY
SECT-
The cranium in the Pinnipedia (Fig. 1184) is broad and rounded,
rather compressed from above downwards. The orbits are large
and approach near to one another.
In the Carnivora vera the spine of the scapula is situated at
about the middle of the outer surface of the bone. The acromion
ff
Fia. 1181.— Section of the left auditory bulla and surrounding bones of a Bear (Urmsferox).
a. m. external auditory meatus ; B.O. basi-occipital ; Car. carotid canal ; e. eustachian
canal ; Sg. squamosal ; T. tympanic ; t. tympanic ring. (After Flower.)
is usually well developed, sometimes with a metacromion. The
coracoid process is very small. The clavicle is never complete,
sometimes entirely absent. There is a supra-condyloid foramen
in the Cats and some of the other groups, not in the Dogs or Bears.
The scaphoid and lunar are united (Fig. 1182). There is no
centrale. Usually a radial sesamoid is present. There are five
7V?
FIG. 1182.— Carpus of Bear (Ursus
americanus). c. cuneiform ; m. mag-
num ; p. pisiform ; r.s. radial sesamoid ;
si. scapho-lunar ; td. trapezoid ; tm.
trapezium ; M. unciform. (After
Flower.)
FIG. 1183. — The phalanges of the inidille digit
of the manus of the Lion (Feiis leo). phl.
proximal phalanx ; phz. middle phalanx ;
phs. ungual phalanx ; a, the central portion
forming the internal support to the horny
claw ; b, the bony lamina reflected around the
base of the claw. (After Flower.)
digits, though the pollex may be reduced in size, as in the Dog,
and it is vestigial in the Hyaena.
The pelvis is long and narrow. In the tarsus all the ordinary
bones are developed. The hallux is fully formed in the Bears, etc.,
but shorter than the other digits. In the Cats and Dogs it is
represented only by a vestige of the metatarsal.
xni
PHYLUM CHORDATA
531
In the Pinnipedia (Fig.
11 84-) both acromion and
coracoid are short, and
the scapula is curved back-
wards ; there is no clavicle.
The bones of the fore-limb
are short and stout ; the
humerus has a prominent
deltoid crest ; there is no
foramen above the inner
condyle. The ulna is
greatly expanded at its
proximal, the radius at its
distal end. The manus is
broad and expanded. The
scaphoid and lunar are
united to form a scapho-
lunar. The lingual pha-
langes are nearly straight,
slender, and pointed. The
ilia are short ; the sym-
physis pubis is short and
without firm union of the
bones. The femur is short,
thick, and flattened. The
fibula and tibia are com-
monly ankylosed proxi-
mally. The calcaneum is
short and usually without
a distinct calcaneal pro-
cess ; the lateral digits are
usually the longest.
Skeleton of the
Rodentia. — Among the
Rodents the Jerboas are
exceptional in having the
cervical vertebrae anky-
losed. Generally, as in the
Rabbit, the transverse pro-
cesses of the lumbar ver-
tebrae are elongated. As in
the Ungulata, the sacrum
usually consists of one
broad anterior vert ibra
followed by several
narrower ones. The caudal
region varies in length in
532 ZOOLOGY SECT.
the different families ; in some it is very short, but it is elongated
in many (the Porcupines, Squirrels, and Beavers). The sternum
of the Rodents has a long and narrow body ; sometimes there is
a broad presternum ; the posterior end is always expanded into
a cartilaginous xiphisternum.
The skull is elongated, narrow in front, broader and depressed
behind. The nasal cavities are very large, especially in the Por-
cupines, with air sinuses in the upper part. In some the optic
foramina fuse into one. An interparietal is often present. Par-
occipital processes are developed. The orbit and the temporal
fossa are always continuous. The nasal bones are large, and the
nasal apertures are terminal or nearly so. The premaxillae are
always very large. A remarkable feature of the skull is the presence
in many of a large opening corresponding to the infra-orbital foramen.
The middle part of the zygoma is formed by the jugal ; the latter
often helps to bound the glenoid cavity, as in the Marsupials. The
palate is short, and the anterior palatine foramina large. The
periotic and tympanic may become ankylosed together, but not to
the neighbouring bones. The coronoid process of the mandible is
sometimes rudimentary or absent ; the angle is often produced
into a process.
The scapula of the Rodentia is generally long and narrow. The
spine sometimes has a metacromion process and a long acromion.
The coracoid process is small. The clavicle varies as regards its
development. Vestiges of the sternal end of the coracoid are
•sometimes distinguishable. There is considerable variation in the
bones of the arm and fore-arm. The radius and ulna are in most
instances distinct, though in close and firm apposition. The
scaphoid and lunar are usually united ; the centrale is sometimes
present, sometimes absent. The pelvis and femur vary greatly.
Sometimes there is a third trochanter. The fibula is sometimes
distinct, sometimes fused with the tibia. In the Jerboa the meta-
tarsals of the three digits are fused together.
Skeleton of the Insectivora. — The neural spine of the axis
is usually well developed, that of the remaining cervical vertebrae
small or obsolete. The number of trunk-vertebras varies in the
different families from eighteen to twenty-four, and there is also
great variation in the development of the various processes. The
caudal region varies in its length ; frequently it has chevron
bones. The presternum is expanded, the mesosternum composed
of distinct, narrow sternebrse.
The skull (Fig. 1185) varies greatly in the different families,
in the higher forms approaching that of the Lemurs, with com-
paratively large cerebral fossse, large orbits with complete or
nearly complete bony rims, well-developed zygoma, and a tympanic
bulla and tubular auditory meatus. In the others the cranial
capacity is less, and the orbits and temporal fossse are completely
XIII
PHYLUM CHORDATA 533
continuous ; the zygoma is incomplete, and the tympanic does not
usually form a bulla.
The pectoral arch also varies a good deal in the different families
of the Insectivora. In the true Moles and their allies there is a
remarkable bone of cuboid shape articulating ventrally with the
presternum and dorsally with the humerus, and only connected
by a ligamentous band with the scapula. Its mode of formation
from a mass of cartilage — to the anterior face of which the clavicle,
formed as usual in membrane, becomes applied— proves that
this bone represents a pro-coracoid as well as a clavicle. In other
Insectivora this bone is not developed, and the clavicle is a distinct,
long and slender bone, but vestiges of the inner or ventral ends of
the coracoid and pro-coracoid may be recognisable. Sometimes
Fio. 1185. — Skull of Tenrec (Centetes ecaudatus). fr. frontal ; max. maxilla; pa. parietal;
p.max. premaxilla ; sq. squamosal. (After Dobson.)
the " mesoscapular segment " (p. 500) is represented by a distinct
bone intervening between the outer end of the clavicle proper and
the acromion process.
The humerus usually has a supracondylar foramen. In the
Moles this is absent, and their humerus is remarkable in other
respects, being short, greatly expanded at the extremities, with a
prominent deltoid ridge, and with two synovial articular surfaces
at the proximal end, one for the glenoid cavity of the scapula,
the other for the coraco-clavicle. The radius and ulna are com-
pletely developed in all and are usually distinct, but sometimes
fused distally. In the carpus the scaphoid and lunar sometimes
coalesce, sometimes remain distinct ; an os centrale is usually
present. In the Moles the manus is extremely broad, the breadth
being increased by the presence of a large, curved, radial sesamoid.
In the pelvis the symphysis pubis is in some cases elongated,
in others short, and sometimes absent, the pubes remaining
separated by a wide median ventral cleft. A third trochanter is
sometimes represented by a ridge. The fibula usually, though
not always, fuses distally with the tibia.
534
ZOOLOGY
SECT.
Skeleton of the
Chiroptera (Fig.
1186).— The cervical
region of the vertebral
column is character-
ised by the absence of
any distinct neural
spines, and the same
holds good to a less
extent of the trunk-
vertebras ; the trans-
verse processes of the
lumbar region are also
rudimentary. The tail
varies in development :
when it is elongated
the component verte-
brae are long, cylin-
drical centra without
•^ processes. Sagittal
!, and occipital crests are
1 developed in the skull
~ of some species. The
~x facial region is rather
£ elongated, especially in
- the Megachiroptera
£ (Fig. 1187). Post-
'S orbital processes of the
£ frontal are present or
g absent : the zygoma is
« long and slender : the
QJ
3o malar is small and ap-
J; plied to the outer sur-
% face of the zygoma.
e The long and narrow
^ nasals are in some
cases united ; the pre-
maxillae are small. The
mandible has an angu-
lar process in the
Microchiroptera, not in
the Megachiroptera.
The segments of the
sternum are sometimes
distinct, sometimes
united ; the prester-
num has a mesial keel
xni PHYLUM CHORDATA 535
developed in co-ordination witli the great size of the pectoral
muscles. The sternal ribs are ossified.
The scapula is large and oval in shape : the spine is near the
anterior margin : the post-scapula fossa has ridges for the origin of
the muscula*- fibres : the spine has a well-developed acromion.
The coracoid is elongated and in , some cases bifurcated. The
clavicle is long. The pro-coracoid is represented by a separate
ossification ; there are rudiments of the sternal end of the coracoid
between the clavicle and the first rib. The humerus and radius are
FIG. 1187.— Skull of Pteropus fuscus. (After Blainville.)
both elongated. The ulna is reduced, and is sometimes only repre-
sented by the proximal end, ankylosed with the radius. A large
sesamoid is developed in the tendon of the triceps muscle near
the olecranon process of the ulna. In the carpus the scaphoid and
lunar are united : sometimes also the cuneiform is united with
these : the pisiform is small. There is no centrale. The ungual
phalanges are absent in the nailless digits. The pelvis is small, and
the symphysis pubis often imperfect. The fibula is sometimes
well-developed, sometimes rudimentary. The tuber calcanei is
an inwardly curved process of the calcaneum, attached to which
by means of ligamentous fibres is a slender rod of bone or cartilage,
the calcar, which supports the inter-femoral membrane.
Skeleton of the Primates. — The atlas is ring-like, the
odontoid sub-conical. The spines of the cervical vertebrae are
usually well-developed and simple : in Man they are short — with
the exception of the seventh — and bifid : in some they are trifid.
The number of thoraco-lumbar vertebra is usually nineteen, but
only seventeen in Man, the Gorilla and Chimpanzee, sixteen in
the Orang ; in some Lemurs it may be twenty-three or twenty-four.
The number of sacral vertebrae varies from two to five. The sacral
region of Man, which comprises five ankylosed vertebrae, differs
from that of other Primates in its greater relative breadth and in its
536
ZOOLOGY
SECT.
backward curvature ; it forms a well-marked angle where it joins
the lumbar region — the sacro-vertebral angle — scarcely recognisable
in other Mammals. The number of caudal vertebrae varies with
the length of the tail — from four to about thirty-three. In Man
there are only four vestigial caudal vertebras, ankylosed together
to form the coccyx. In all those forms in which the tail is well
developed chevron bones are present.
The human skull (Fig. 1188) presents a marked contrast in
certain respects to that of other Mammals, but in many points is
fa
SO
a
FIG. 1188. — Skull of Man. Letters as in Fig. 1167. In addition, a. angle of mandible;
e.g. crista galli, a process of the mesethmoid ; fm. foramen magnum ; M. mastoid;
st. sella turcica. (After Flower.)
approached by that of the other Primates, more especially by that
of the Simiidae. One of the most important characteristics of the
human skull is the large size of the brain-case, the cubic content
of the cranial cavity averaging 1500 cubic centimetres in the male
of white races. This great development is most marked in that
part of the cavity which lodges the cerebral hemispheres, in adapta-
tion to the large dimensions of which the cranium bulges out both
anteriorly and posteriorly to such an extent that the entire length
of the cavity greatly exceeds that of the basi-cranial axis. A
xin PHYLUM CHORDATA 637
result of the posterior bulging of the brain-case is that the foramen
magnum (f.m) is no longer situated at the posterior extremity of the
skull as in other Mammals, but assumes a position further forwards
towards the middle of the base. The anterior expansion, causing
a strong arching forwards of the frontal region, brings about an
alteration in the position of the ethmoidal plane, which, instead of
being perpendicular or inclined to the basi-cranial axis, becomes
horizontal, and the cribriform plate forms the middle part of the
floor of the anterior extension of the cranial cavity. The fossa for
lodgment of the cerebellum lies entirely beneath the posterior
portion of the cerebral fossa : the olfactory fossa is comparatively
small. (See Fig. 1138, D.)
The outer surface is smooth and rounded, devoid of any pro-
minent ridges or crests. The occipital crest of lower Mammals
is represented merely by a rough raised line — the superior curved
line of the occiput. The paroccipital processes are only represented
by slight eminences — the jugular eminences. There is no auditory
bulla ; the mastoid portion of the periotic projects downwards as
a prominent mastoid process. The periotic, tympanic, and squa-
mosal early fuse into one bone — the temporal bone. The post-glenoid
process is very slightly developed. The whole facial region is
relatively small. The orbits, which are of moderate size, are
directed forwards ; the bony margin is complete, and a plate of
bone, developed partly from the jugal, partly from the alisphenoid,
almost completely cuts it off from the temporal fossa, leaving only
a small aperture of communication — the spheno-maxillary fissure.
The frontal suture usually early disappears. The nasals are
rarely fused. The suture between the premaxillse and the maxillae
becomes obliterated at an early stage, so that the entire upper jaw
appears to consist of a single bone. A peculiar spine, the nasal
spine, is developed in the middle line below the nasal opening. The
most marked feature of the mandible is the presence of a prominence,
the mental prominence, in the lower part of the symphysial region
($.). The stylo-hyal nearly always becomes fused — together with
the tympano-hyal — to the periotic and tympanic, giving rise to a
slender process — the styloid process (sh.) — projecting downwards
from the base of the skull.
None of the other Primates have a cranial capacity approaching
that of Man ; and those modifications in the shape of the skull
which are the concomitants of the great development of the brain
in the human species are accordingly not recognisable, or are much
less strongly marked. The various fossae of the cranium, as a
rule, occupy, however, the same relative positions as in Man ; the
cerebellar fossa is entirely beneath the cerebral ; and the ethmoidal
plane, and that of the foramen magnum (occipital plane), are usually
both horizontal or nearly so. In all the Simiidae, with the exception
of the Orang, the frontals meet in the middle line below, over
538 ZOOLOGY SECT.
the pre-sphenoid. In many monkeys the outer surface of the
cranium is smooth and free from prominent ridges ; but in the
Baboons, the Orangs, the Gorilla, and the Chimpanzee (Fig. 1189)
FIG. 1189. — Skull of Chimpanzee (Anthropopithecus troglodytes). (After Blainville .
there are strongly developed occipital, sagittal, and supra-orbital
ridges, usually much more prominent in the male than in the female,
and increasing in size with age. The paroccipital processes are
always rudimentary, but there are well-marked post-glenoid pro-
cesses. The mastoid does not form a distinct mastoid process.
In the Cebidae and Hapalidee alone is there a tympanic bulla.
The entire facial region is relatively larger than in Man ; the pre-
maxillo-maxillary region is always more prominent, and in the
Baboons projects forwards as a distinct muzzle. The orbit is
separated from the temporal fossa as in Man. The nasals are usually
ankylosed in the adult. The nasal spine is never developed. The
suture between the premaxilla and the maxilla only becomes
obliterated, if at all, in old individuals. The mental prominence
of the mandible is never developed, the anterior surface of the
symphysial region sloping backwards and downwards from the
bases of the incisor teeth. The stylo-hyal never gives rise to an
ossified styloid process.
In the skull, as in many other respects, the Lemurs occupy an
intermediate position between the higher Primates and the lower
orders of Mammals. The occipital and ethmoidal planes are
usually vertical. The tympanic forms a large bulla. The orbits,
which are large, are usually separated from the temporal fossae
only by a narrow rim of bone. The lacrymal foramen is situated
on the face outside the margin of the orbit. The facial region
is usually elongated, and may form a prominent muzzle.
In all the Primates the clavicle is present and complete, and
XIII
PHYLUM CHORDATA
539
in the scapula the spine, acromion, and coracoid process are well
developed. In Man and the higher Apes the glenoid border of the
re
r-s-
FIG. 1190.— Skeleton of Orang (Simla satyr us). (After Blainville.)
scapula is much longer than the coracoid border. In the lower
Monkeys, on the other hand, these borders are nearly equal. The
humerus is comparatively long and slender ; the tuberosities and
ridges are not, as a rule, very strongly de-
veloped. In Man and the Simiidse the bone
is twisted around its long axis ; in the lower
forms this torsion is absent. In Man and a
the higher Apes the foramen above the
inner condyle is absent ; it is present in
many of the American Monkeys and in
most Lemurs. Characteristic of the ulna
of Man and the higher Apes is the small
upward extension of the olecranon process.
The radius and ulna are distinct in all ; in
the higher forms the shafts of the two bones
are bent outwards, so that there is a wide
interosseous space, and there is considerable
freedom of movement in pronation and
supination. In the carpus (Fig. 1191) the .scaphoid and lunar are
always distinct, and a centrale is present in all except some of the
FIG. 1191. — Carpus of Baboon
(Ci/nocephalus anitbis). ce.
centrale ; c. cuneiform ; /.
lunare ; m. magnum ; p.
pisiform ; rs. radial sesa-
moid ; s. scaphoid ; tit. trupe-
zoid ; tm. trapezium ; ti.
unciforni. (After Flowt-r.)
540
ZOOLOGY
SECT.
Lemurs, the Gorilla, Chimpanzee, and Man. A pisiform is present,
and in most a radial sesamoid. As compared with that of the
other Primates, the carpus of Man is short and broad ; the tra-
pezium has a saddle-shaped articular surface turned somewhat
inwards. In Man, the Chimpanzee, Gorilla, and Orang the
carpus articulates exclusively with the radius ; in all the others
it articulates also with the ulna. In Man the pollex has a remark-
able and characteristic freedom of movement in opposition to the
other digits.
The human pelvis is remarkable for its relative breadth, for the
expanded form of the ilia and the deep concavity of their inner
surfaces, and for the shortness of the pubic symphysis. In the
higher Apes some of these features are recognisable, though less
Cct .
Mctn
Orang
FIG. 1192. — Foot of Man, Gorilla, and Orang of the same absolute length, to show the
difference in proportions. The line a'a' indicates the boundary between tarsus and meta-
tarsus ; b'b', that between the latter and the proximal phalanges ; and c'c' bounds the ends
of the distal phalanges ; a*, astragalus; ca. calcaneum ; sc. scaphoid. (After Huxley.)
pronounced ; but in the lower the ilia are long and narrow, and
usually curved outwards ; in the Old-world Monkeys the tuberosities
of the ischia are strongly everted and roughened for the attachment
of the ischial callosities.
The tibia and fibula are well developed and distinct in all. In
nearly all the hallux, owing to the form and direction of the articu-
lation between it and the internal cuneiform, is opposable to the
other digits, converting the foot into a grasping organ. The
human foot (Fig. 1192) is distinguished from that of the other
XIII
PHYLUM CHORDATA
541
Primates by the absence of this power of opposition and by the
relative length of the tarsus, which exceeds that of the metatarsus.
Digestive Organs. — Teeth are present in nearly all Mammals,
but in some they are wanting in the adult condition (Whalebone
Whales and Platypus). In
Echidna teeth are not pre-
sent even in the young. In
some of the Ant-eaters teeth
are developed in the foetus
and are thrown off in utero
-the adult animal being
devoid of them.
Teeth, as already ex-
plained in the general ac-
count of the Craniata
(p. 84), are developed partly
from the epidermis and
partly from the underlying
dermis. In the Mammals
each tooth is lodged in a
socket or alveolus in the
jaw. The part of the tooth
developed from the epider-
mis is the enamel ; the
remainder of the tooth-
dentine, cement and pulp-
being formed from the sub-
jacent mesoderinal tissue.
Along the oral surface of
the jaw is formed a ridge-
like ingrowth of the ecto-
derm— the dental lamina
(Fig. 1194, lam.). The posi-
tion of this is indicated
externally by a groove — the
dental groove (gr.), and from
it a bud is given off in
the position to be occupied
by each of the teeth. This
becomes constricted off as
a conical cap of cells — the
enamel-organ — which re-
mains in continuity with the
dental ridge only by a narrow isthmus. This cap-like form is
brought about by the development of a papilla of condensed dermal
tissue — the dental papilla (pap.), which pushes upwards, against
the enamel-organ. On the surface of this papilla, in contact with
VOL. II L L
Pro. 119:3. — Diagrammatic sections of various forms
of teeth. I, incisor or tusk of Elephant with pulp-
cavity persistently open at base ; //, human
incisor during development, with root imperfectly
formed, and pulp-cavity widely open at base ; ///,
completely formed human incisor, with pulp-
cavity opening by a contracted aperture at base
of root ; IV, human molar with broad crown and
two roots ; V, molar of the Ox, with the enamel
covering the crown deeply folded, and the de-
pressions filled up with cement ; the surface is
worn by use, otherwise the enamel coating would
be continuous at the top of the ridges. In all the
figures the enamel is black, the pulp white, the
dentine represented by horizontal lines, and the
cement by dots. (After Flower and Lydekker.)
542
ZOOLOGY
SECT.
the enainel-organ, the cells (odontoblasts) become arranged into a
layer having the appearance of an epithelium — the dentine-forming
layer. The cells of the enamel-organ form two layers, of which
that in contact with the dental papilla assumes the character of a
n.
en,.
FIQ. 1 194. — Two stages in the development of the teeth of a Mammal (diagrammatic sections).
alv. bone of alveolus ; dent. s. dental sac ; en.m. enamel-membrane ; en. pip. enamel-pulp ;
gr. dental groove ; lam. dental lamina ; lam', part of dental lamina which grows downwards
below the tooth-germ ; pap. dental papilla. (After O. Hertwig.)
layer of long cylindrical cells — the enamel-membrane (en. m.) ; the
more superficial layer consists of cubical cells. Between the
two the remaining cells of the enamel-organ become modified to
form a kind of connective tissue — the enamel-pulp (en. pip.).
The connective tissue immediately surrounding the entire rudi-
ment of the tooth becomes
vascular and forms a dis-
tinct investment— the den-
tal sac (dent, s.) ; from
this blood-vessels extend
into the papilla.
Ossification begins by
the formation of a cap of
en'mZ dentine (Fig. 1195, dent.),
produced by the dentine-
forming cells, and of a
layer of enamel (en.) on
the surface of this, pro-
duced by the cells of the
enamel membrane. To
these additional layers are
added until the crown of
the tooth becomes fully
developed. The substance
of the dental papilla gives rise to the pulp. As the tooth elongates,
it projects on the surface and eventually breaks through the mucous
membrane of the gum, the remains of the enamel-organ becoming
thrown oft. The cement is formed by the ossification of the con-
nective-tissue of the dental sac.
FIG. 1195. — Diagrammatic section showing the develop-
ment of the milk- and permanent teeth of Mam-
mals, alv. bone of alveolus ; dent, dentine ; dent. s.
dental sac ; en. layer of enamel ; en. m. enamel-mem-
brane of milk-tooth ; en. mz. enamel-membrane of
permanent tooth ; en.plp. enamel-pulp of milk-tooth;
gr. dental groove ; lam. dental lamina ; n. neck
connecting milk-tooth with lamina ; pap. dental
papilla of milk-tooth ; pap2, dental papilla of per-
manent tooth. (After O. Hertwig.)
xm PHYLUM CHORDATA 543
In the teeth of most Mammals distinct roots are formed, each with a
minute opening leading into the pulp-cavity (Fig. 1193, /// — V) ; but
in some there are no roots, the pulp-cavity being widely open below
(/), and the tooth constantly growing from the base as it becomes worn
away at the crown ; such teeth are said to have persistent pulps.
UsuaUy Mammals have two distinct sets of teeth developed,
the milk and permanent dentitions, but sometimes there is only
one, and accordingly we distinguish diphyodont and monophyodont
Mammals : in nearly all of the latter, however, another set are
developed, though they early become absorbed or remain in the
condition of functionless vestiges ; and in a considerable number
* 1 1 ' "' A A' Q Q '
O'O 1*1 ' 44 O'O
or, in a simpler form, since the teeth of the right and left sides
are always the same,
.314 3
A ft _ /v\ VYI ^^^ ft- ft-
•3' r p' 4' " 3
Echidna has no teeth at any stage. In Ornithorhynchus teeth
are present in the young and are functional for a time, but they are
thrown off when the animal is
about a year old : vestiges of an
earlier dentition have been de-
tected. The function of teeth is
performed in the adult by broad
horny plates, one on each upper
and one on each lower jaw.
The Marsupials have the milk-
dentition in a degenerate con-
dition. Germs of milk-teeth are
developed, but with the excep-
tion of one — the last pre-molar—
these remain in an imperfect
state of development, though
they persist, as functionless
vestiges, to a comparatively late
stage.
In the adult dentition of the
,, . , . . FIG. 1199.— Front view of skull of Koala
Marsupials the number Ol mClSOrS (Phascolarctos cinereus), illustrating dipro-
in the upper and lower jaws is K™tr.)and herbi
always dissimilar, except in Phas-
colomys. With regard to the arrangement of these teeth, the order
falls into two series, termed respectively the diprotodont and the
546
ZOOLOGY
SECT.
polyprotodont. In the former (Figs. 1199, 1200) the two anterior
incisors are large and prominent, the rest of the incisors and the
canines being smaller or absent. On the other hand, in the poly-
FIG. 1200. — Teeth of Great Kangaroo (Macroims major). (After Owen.)
FIG. 1201. — Front view of the skull of Tasmanian Devil (Sarcophilus nrsinus), showing
polyprotodont and carnivorous dentition. (After Flower.)
I''IQ. 1202. — Teeth of upper jaw of Opossum (I)ldflphys marsupiaUs), in all of which there
is no succession except hi the last pre-molar, the place of which is occupied in the
young animal by a molariform tooth represented in the ligure below the line of the other
teeth. (After Flower and Lydekker.)
protodont forms (Figs. 1201, 1202), which are all more or less
carnivorous, the incisors are numerous and sub-equal and the
canines large. There are typically three pre-molars and four
XIII
PHYLUM CHORDATA
547
molars. A good example of the diprotodont arrangement is the
Kangaroo (Macropus, Fig. 1200), which has the dental formula—
• 3 l
%. -, c. -, r. 2, ..„. 4
2 4
-, m. . = 34.
The canine is very small and early lost. Of the polyprotodont
forms the Australian Dasyure or Native Cat (Fig. 1144) has the
formula —
. 4 1
i. , c. p.
2 4
, m. = 42 ;
and the American Opossum (Dtidphys) (Fig. 1202)-
.513 4
-,
7te.^p.=,m.-A =50.
The Edentata, as noticed in the outline of the classification,
though not by any means all toothless, always have some defect
in the dentition ; when teeth are present in the adult the anterior
series are absent and the teeth are imperfect, wanting roots and
devoid of enamel. The tooth-characters differ widely in the
FIG. 1203.— Section of lower jaw and teeth of Orycteropus. (After Owen.
different groups. In the Sloths there are five teeth above and
four below on each side ; no second series is known. In the
American Ant-eaters there are no teeth in the adult. In the
Armadillos, on the other hand, the teeth are numerous, though
simple and rootless, and, in one genus at least, two series occur.
In the Scaly Ant-eaters there are no teeth. In the Cape Ant-eaters
(Fig. 1203), again, there are numerous teeth which are heterodont
and diphyodont, and have a peculiar structure, being perforated
by numerous minute, parallel, vertical canals ; the pulp of each
tooth, entire at its base, is divided distally into a number of parallel
columns.
In the Ungulata the dentition is heterodont and diphyodont. and
the teeth are very rarely devoid of roots. In the Artiodactyla the
pre-molars and molars differ from one another in pattern ; the
first upper pre-molar is almost always without a milk predecessor.
548
ZOOLOGY
SECT.
The Pigs (Fig. 1204) are among the very few recent Mammalia
which possess what has been referred to as a typical dentition : the
formula of the completed dentition is—
.314 3
i. B, c. -r P. £ m. -3 = 44.
The incisors of the upper jaw are vertical, those of the lower
greatly inclined forwards. The canines are greatly developed,
especially in the
male, and grow
from persistent
pulps ; both the
upper and lower
are bent up-
wards and out-
wards and work
against one
another in such
a manner that
the upper wears
on its anterior
and external
surface, the
lower at the
extremity of the
posterior sur-
face. The pre-
FiG>1204. — Left Jateral"Viewof the dentition of the Boar (Susscrofa),
the "roots of the teeth being exposed. (After Flower ;and Lydekker.)
pressed, with
longitudinal cutting edges, and the molars are provided with
numerous tubercles or cusps arranged for the most part in
transverse rows (bunodont type). The first permanent pre-molar
has no predecessor, the formula of the milk dentition being—
.31 3
'• 3' c- r m- 3 = 28'
In the typical Ruminants there are no teeth on the premaxillse,
the incisors of the lower jaw and the canines, which resemble them
in shape, biting against a thickened callous pad on the opposed
surface of the upper jaw, and the upper canines are also usually
absent ; there are three pre-molars and three molars in both upper
and lower series, all characterised by the presence of column-like
vertical folds of enamel, the interstices between which may be
filled up with cement— the worn surface of the tooth presenting
a pattern of the selenodont type (Fig. 1193, V). In the Camels
there are a pair of upper incisors and a pair of large canines in
each jaw.
XIII
PHYLUM CHORDATA
549
In the Perissodactyla the molars and pre-molars form a con-
tinuous series of large teeth with ridged or complexly-folded
crowns, the posterior pre-molars often differing little in size and
structure from the molars. In the Horse (Fig. 1205) the formula is—
.314 3
*• 3' C- 1' p' 4' m' 3 = M'
but the first pre-molar is a small tooth which soon becomes lost,
and may belong to the milk-dentition. A fold of the enamel
dips downwards (i.e. towards the root) from the extremity of the
incisor teeth like the partly inverted finger of a glove ; the canines
are small in the female, and may not appear on the surface. There
FIG. 120f>. — Side view of skull of Horse with the bone removed so as to expose the whole of
the teeth, c. canine ; Fr. frontal ; il. i'2. i:i. incisors ; L. lacrymal ; Ma. jugal ; MX. maxilla ;
nfl.mP.m3. molars ; Na. nasal ; oc. occipital condyle ; Pa. parietal ; p. ml. situation of the
vestigial first pre-molar, which has been lost in the lower, but is present in the upper jaw ;
pm'2. pm3. pm4. remaining pre-molars ; PMx. pre-maxilla ; pp. par-occipital process ; Sq.
squamosal. (After Flower and Lydekker.)
is a wide interval in both jaws between the canines and pre-molars.
The pre-molar and molar teeth present a complicated pattern due
to folds of the enamel, which differ in their arrangement in the
upper and lower jaws ; their roots become completed only at a
late period.
In the Hyracoidea the dental formula is—
.104 3
i. x, c. -, p. -7, m. ^ = 34.
£ \J jC. O
The upper incisors are not unlike the larger pair of the Rabbit in
shape, though prismatic and pointed, instead of compressed and
chisel-like ; they grow from persistent pulps. The outer incisors
650
ZOOLOGY
SECT.
are elongated, inclined forwards, and trilobed at the extremities.
The pre-molars and molars form a continuous series, separated by
an interval from the incisors, and in pattern closely resemble those
of some of the Perissodactyla.
The Elephants (Fig. 1206} have an extremely specialised denti-
tion. There are no canines and no lower incisors. The single
Fia. 1206. — Grinding surface of a partially worn'rightjupperjmolar of the African Elephant
(Elephas africanus). (After Owen.)
pair of upper incisors are developed into the enormous tusks
(Fig. 1193, /), which grow continuously from persistent pulps
throughout the life of the animal ; they are of elongated conical
form, and usually become curved. The tusks are composed of
solid dentine, enamel occurring only on the apices, and becoming
early worn away. The molars (Fig. 1206) are very large, and
their worn surfaces are marked with prominent transverse ridges ;
there are six molars altogether on each side, but only one or two
are functional at once, the more posterior moving forward and
taking the place of the more anterior as these become worn out.
When teeth are developed in the Cetacea they are nearly always
numerous, homodont, and monophyodont : in the Sperm-whales
they are confined to the lower jaw. In the Whalebone Whales,
though teeth are developed in the fetal condition (Fig. 1207),
FIG. 1207. — Left lower jaw of foetus of Balsenoptera rostrata, inner aspect, showing teeth
natural size. (After Julin.)
they become lost either before or soon after birth, and they are
succeeded in the adult by the plates of baleen or whalebone
(Fig. 1208), which, in the form of numerous triangular plates, hang
vertically downwards from the palate.
Of the Sirenia, the Dugong and Manatee have a heterodont denti-
tion ; in Rhytina teeth were absent. In the two former Sirenians
there are incisors and molars with a wide diastema between them.
XTII
PHYLUM CHORDATA
551
In the Manatee there are two rudimentary incisors on each side,
both in the upper and the lower jaw ; these disappear before the
adult condition is reached. There are altogether eleven molars
on each side above and below, but not more than six of these are
in use at once, the more anterior when worn out being succeeded by
the more posterior. They have enamelled crowns with transvers
ridges, and are preceded by milk-
teeth. In the Dugong there are no
incisors in the mandible of the adult,
and only one tusk-like pair in the
upper jaw, large in the male — in which
they grow from persistent pulps, little
developed in the female and remaining
concealed in their sockets. In the
young there are rudimentary incisors
in the mandible, and also a rudimen-
tary second pair in the tipper jaw.
There are either five or six molars on
each side, both in the upper and
lower jaws. These are cylindrical
teeth, devoid of enamel, and with
persistent pulps.
In the Carnivora vera (Fig. 1209)
the dentition is complete, heterodont,
and diphyodont, and all the teeth are
provided with roots. The incisors are
relatively small, chisel-shaped teeth ;
there are nearly always three of them
on each side, in both upper and lower
jaws. The canines are always large
and pointed. The presence of carnas-
sials, consisting of the last pre-molar
in the upper and the first molar in
the lower jaw. is universal. In front of the carnassial the teeth
are compressed and pointed ; behind it they have broad surfaces.
In the Cat family (Felidce) the formula is—
.31 3 1
t. 3, c. p p. g, m. l
The lower carnassial is thus the last of the series.
(Canidae) the formula is usually—
.3 1" 4 2
i. y c. -r p. ^ m. ^ = 42,
and in the Bears (Ursidse) it is the same.
3
In the Pinnipedia there are always fewer than ^ incisors, and
o
caruassials are not developed. The pre-molars and molars have a
FIG. 1208. — Section of upper jaw of
Balsenoptera (a), with baleen-
plates (6, c) frayed out at their free
edges (d, e). (After Owen.)
In the Dogs
552
ZOOLOGY
SECT.
compressed, conical, pointed form. The prevailing dental formula
of the Seals is —
.31 4
*• o> c- T> P- A>
i.-.' = 34.
In the Walrus the adult formula is—
11
!'
*• 0'
3 ° i«
y m. 5 = 18.
The upper canines take the form of large, nearly straight tusks.
In the large order of the Rodents the dentition is remarkably
uniform, and, in all its general characters, resembles what has
already been described in the Rabbit. But the second, smaller
Fid. 1209.— Left lower carnassial teetli of Garni vora. /.Felis; //.Canis; ///, Herpestes ;
IV, Lutra ; V, Meles ; VI, XTrsus. 1, anterior lobe (paraconid) of blade ; 2, posterior
lobe (protoconid) of blade; 3, inner cusp (metaconid) ; 4, talon (hypoconid). (After
Flower and Lydekker.)
pair of incisors of the upper jaw is present only in the Hares and
Rabbits ; the number of pre-molars and molars varies from—
p. 5, m. 2 to p. 2, m. 3,
and they may develop roots.
In the Insectivora the dentition is heterodont, complete, and
diphyodont. All the teeth are rooted. There are never fewer than
two incisors on either side of the lower jaw. The canines are not
of large size. The crowns of the molars are beset with pointed
tubercles.
In the Chiroptera the dentition is complete, and the teeth are
xni PHYLUM CHORDATA 563
all rooted. There is a milk-series which differs entirely from the
permanent teeth. In the insectivorous Chiroptera (Bats) the
molars are provided with pointed cusps, while in the frugivorous
forms (" Flying Foxes ") they are longitudinally grooved or
excavated.
In the Primates the teeth are heterodont and diphyodont, and
always form roots. There are almost invariably two incisors on
each side in each jaw, and, in all but the Hapalidse, three molars.
The dental formulae of the various families have been given in
the synopsis of the classification. The dentition of Man differs
from that of the rest of the order in the teeth forming a continu-
ous series not interrupted by a diastema, and in the comparatively
small size of the canines.
The mouth in Mammals is bounded by fleshy lips. On the floor
of the mouth is situated the tongue, which is usually well developed,
but varies in size and shape in different orders. Its surface is
covered with papillae of different forms, in association with certain
of which are the special end-organs of the nerves of taste — the
taste-buds. The roof of the mouth is formed in front by the hard
palate, consisting of the horizontal palatine plates of the maxillary
and palatine bones covered with mucous membrane. Behind the
hard palate projects backwards the soft muscular fold of the soft
palate, also with taste-buds, which divides the cavity of the pharynx
into two chambers, an upper and a lower. In front of the opening,
leading from the lower division of the pharynx into the larynx, is
a cartilaginous plate — the epiglottis — of which rudiments only are
found in certain lower Vertebrates.
The oesophagus is always a simple straight tube. The stomach
varies greatly in different orders, being sometimes simple, as in the
majority of Mammals, sometimes divided into chambers, as in the
Cetacea and the Ruminants.
In the majority of Mammals the stomach is a simple sac, as in
the Rabbit (p. 448). But in certain groups it is complicated by
the development of internal folds, and may be divided by con-
strictions into a number of different chambers. The complication
of this organ reaches its extreme Limit in the ruminant Ungulata
and in the Cetacea. In a typical Ruminant (Fig. 1210, E, Fig.
1211), such as a sheep or an ox, the stomach is divided into four
chambers — the rumen or paunch, the reticulum, the psalterium, and
the abomasum, or rennet stomach. The first of these (Fig. 1211, 6) is
much larger than the rest ; its mucous membrane is beset with
numerous short villi. The reticulum (c), which is much smaller
than the rumen, has its mucous membrane raised up into a number
of anastomosing ridges, giving its wall the appearance of a honey-
comb with shallow cells. From the aperture by which the reticulum
communicates with the rumen to that with which it communicates
with the psalterium, runs a groove bounded by a pair of muscular
554
ZOOLOGY
SECT.
ridges, which are capable of closing together in such a way as to
convert the groove into a canal. The mucous membrane of the
psalterium (d) is raised up into numerous longitudinal leaf-like
folds. The abomasum (e), smaller than the rumen, but larger than
the reticulurn, has a smooth vascular and glandular mucous mem-
A
Oe
FIG. 1210. — Different forms of the stomach in Mammals. A, Dog ; B, Mus decumanus ;
C, Mus miisculus ; D, Weasel ; E, scheme of the ruminant stomach, the arrow
with the dotted line showing the course taken by the food ; F, human stomach, a, b, c,
muscles on inner side ; d. Camel ; H, Echidna aculeata ; /, Bradypus tridac-
tylus. A. (in E and (?) abomasum ; Ca. cardiac end ; Cma, greater curvature ; Cmi,
lesser curvature ; Du. duodenum ; MB, caecum ; O, psalterium ; Oe. oesophagus ; P.
pylorus ; R. (to the right in Fig. E), tf. rumen ; R (to the left in Fig. E), t, reticulum ;
Sc. cardiac division ; Sp, pyloric division ; WZ, water-cells ; * * duodenal pouches.
(From Wiedersheim's Comparative Anatomy.)
brane. The oesophagus opens into the rumen close to its junction
with the reticulum. The herbage on which the Ruminant feeds
is swallowed without mastication, accompanied by copious saliva,
and passes into the rumen and reticulum, where it lies until, having
finished feeding, the animal begins ruminating or chewing the
XIII
PHYLUM CHORDATA
555
cud. In this process the sodden food is returned in rounded
boluses from the rumen to the mouth, and there undergoes
mastication. When fully masticated it is swallowed again in a
FIG. 1211. — Stomach of Ruminant opened to show the internal structure, a, ossophagus;
b, rumen ; c, reticulum ; d, psalterium ; e, abomasum ; /, duodenum. (After Flower and
Lydekker.)
semi-fluid condition, and passes along the groove into the reti-
culum, or over the unmasticated food contained in the latter
chamber,5,to strain through between the leaves of the psalterium
and enter the
abomasum, where
the process of
digestion goes on.
In some Rumi-
nants the psalter-
ium is wanting.
In the Camels
(Fig. 1210, G) the
stomach is not so
complicated as in
the more typical
Ruminants, there
being also no dis-
tinct psalterium,
and the rumen
being devoid of
villi ; both the
rumen and the re-
tlCulum have COn-
4- A ~4-\* 4-1^
neCteQ Wit!! tnem
a niimliprnf nnnr-Vi
anumoeroi pOUCn-
like diverticula
(w. z.), the openings of which are capable of being closed^by
sphincter muscles ; in these water is stored. In the Cetacea the
stomach is also divided into compartments. In the Porpoise
FIG 1 212.— Diagrammatic section of the stomach of the
Porpoise, a, oesophagus ; b, left or cardiac compartment ;
c? middle compartment ; d and e, the two divisions of the
right, or pykmc compartmentl; /, pylorus ; g, duodenum,
dilated at its commencement ; h, bile-duct. (After Flower
and Lydekker.)
556
ZOOLOGY
SECT.
(Fig. 1212) the oesophagus (a) opens into a spacious paunch (b),
the cardiac compartment of the stomach, with a smooth, thick,
mucous membrane. This is followed by a second chamber (c), of
considerably smaller dimensions, with a glandular mucous mem-
brane, which is thrown into a number of complex folds. A long
and narrow third, or pyloric, compartment (d, e) follows upon
this, terminating in a constricted pyloric aperture, beyond which
the beginning of the intestine is dilated into a bulb.
A caecum, situated at the junction of the large and small intes-
tines, is usually present, but varies greatly in extent in the different
orders and families. It is much larger in vegetable-feeding than
in carnivorous forms, and among the former it is those that have
a simple stomach, such as the Rabbit, that have the largest caecum.
Hyrax differs from all the rest of the class in having a pair of
supplementary caeca
situated some distance
down the large intes-
tine. A caecum is
absent in the Sloths,
some Cetacea, and a
few Carnivora.
The Prototheria re-
semble Reptiles, Birds,
and Amphibia, and
differ from other
Mammals, in the pre-
cf J sence of a cloaca, into
which not only the
FIG. 1213.— Diagrammatic plan of the liver of a Mammal rectum but the Urinary
(posterior surface), c. caudate lobe; cf. cystic fissure; o1lrl o-pnital rlnrts nr>pn
ffe. ductus venosus ; g. gall-bladder ; fc. left central lobe ; al "lb. °Pen'
II. left lateral lobe ; llf. left lateral fissure ; p. portal vein In the Marsupials
common sphincter
muscle surrounds both
anal and urinogenital
apertures and in the female there is a definite cloaca ; in nearly all
the Eutheria the apertures are distinct, and separated from one
another by a considerable space — the perinceum.
The liver (Fig. 1213) consists of two parts or main divisions,
right and left, incompletely separated from one another by a fissure
termed the umbilical, owing to its marking the position of the foetal
umbilical vein. Typically each of these main divisions is divided
by a fissure into two parts, so that right lateral (rl.) and right central
(re.) and kft lateral (II.) and left central (k.) lobes are distinguishable.
When a gall-bladder is present, as is the case in the majority of
Mammals, it is attached to, or embedded in, the right central lobe.
A fissure, the portal, through which the portal vein and hepatic
artery pass into the substance of the liver, and the hepatic vein
llf
. .
entering transverse fissure ; re. right central lobe ; rl.
right lateral lobe ; rlf. right lateral fissure ; s. Spigelian
lobe ; u. umbilical vein ; vc. post-caval. (After Flower
and Lydekker.)
a
xin PHYLUM CHORDATA 557
passes out, crosses the right central lobe near the anterior border.
The postcaval lies in contact with, or embedded in, the right
lateral lobe near its anterior border, and given off from this lobe,
between the postcaval and the portal fissure, is a small lobe, of
varying extent — the Spigelian. The term caudate lobe is applied
to a process of the right lateral lobe, of considerable extent in most
Mammals, having the postcaval vein in intimate relation to it,
and often closely applied to the kidney. A gall-bladder is usually
present, but is absent in the Cetacea, the Perissodactyle Ungulata,
the Hyracoidea, and some Rodents.
Vascular System. — The blood of Mammals is warm, having a
temperature always of from 35° to 40° C. The red corpuscles are
non-nucleated : in form they are most usually biconcave discs,
always circular in outline, except in the Camelidse, in which most
of them are elliptical. The lymphatic system of vessels is very
highly developed, ramifying richly throughout all parts of the
body. In the course of this system occur numerous lymphatic
glands. The special part of the lymphatic system of vessels (lacteals)
which ramify in the wall of the intestine and absorb the fatty
matters of the food, combine with the lymphatic vessels from the
hind-limbs and body to form a receptacle — the receptaculum chi/li—
from which a tube, the thoracic duct, which may be double, runs
forward to open into the base of one of the great veins of the
precaval system by a valvular aperture.
The general statements which have been given with regard to
the heart of the Rabbit (p. 448) hold good for the Mammalia in
general. The sinus venosus is never distinct from the right auricle ;
of its valves, which are more completely retained in the Edentata
than in the other orders, the right gives rise to the Eustachian
valve — a membranous fold, often fenestrated in the adult, extending
from the right wTall of the postcaval to the edge of the foramen
ovale (annulus ovalis) ; while the left becomes merged in the
auricular septum, helping to complete the annulus ovalis behind.
Each auricle has an auricular appendix. The right auriculo-
ventricular aperture has a three-lobed tricuspid valve, and the left
a two-lobed bicuspid, or mitral, with chordse tendineee and musculi
papillares. In all Mammals the openings of the pulmonary artery
and aorta are provided with three-lobed semilunar valves.
The single aortic arch, situated in all Mammals on the left side,
varies greatly in the way in which it gives off the main arterial
trunks. Sometimes a single large trunk passes forward from the
arch of the aorta and gives rise to both carotids and both sub-
clavians. Sometimes there are two main trunks — right and left
innominate arteries — each giving rise to the carotid and subclavian
of its own side. Sometimes there is a right innominate giving
off right carotid and right subclavian, the left carotid and left
subclavian coming off separately from the arch of the aorta ; or,
VOL. II MM
558 ZOOLOGY SECT.
as in the Rabbit, an innominate may give origin to the right sub-
clavian and both carotids, the left subclavian coming off separately.
In Monotremes and Marsupials, in most Ungulates, and in the
Rodentia, Insectivora, and Chiroptera, both right and left pre-
cavals persist ; in the others the left aborts, its vestige giving
rise to the coronary sinus. In the Monotremes the openings of
all three cavals are provided with valves, only vestiges of which
exist in the other groups. In the Monotremes all the pulmonary
veins open by a common trunk. In the Metatheria and Eutheria
the four veins sometimes open separately, sometimes the two
veins of each side unite to form a single lateral trunk. In Echidna
there is an abdominal vein corresponding to that of the Frog and
Lizard (pp. 272 and 316).
The following are some of the principal variations in the struc-
ture of the heart which occur in the different groups of Mammals.
In the Monotremes there is a deep fossa representing the fossa
ovalis in the auricular septum. The auriculo- ventricular valves
depart from the structure typical of Mammals and approach the
corresponding valves in the heart of Birds. In the Marsupials the
fossa ovalis and annulus ovalis are absent ; in the uterine foetus of
the Kangaroo the auricles communicate by a fissure, but all trace
of this becomes lost before the adult stage is reached.
In the Cetacea, Eustachian and Thebesian valves are both
absent. In some of the Cetacea the apices of the ventricles are
separated by a slight depression. In the Sirenia there is a corre-
sponding, but much deeper and wider, cleft, so that the apex of the
heart is distinctly bifid.
In the Ungulata, Eustachian and coronary valves are both
absent ; in some there is a cartilage or a bone — the os cordis—
often double, at the base of the heart. The Eustachian valve is
absent in most of the Carnivora. In the Pinnipedia an aperture of
communication between the auricles often persists in the adult.
The organs of respiration resemble those of the Rabbit in
the general features mentioned on p. 453.
In the Cetacea, the epiglottis and arytenoids are prolonged to
form a tube, which extends into the nasal chambers and is em-
braced by the soft palate, so that a continuous passage is formed
leading from the nasal chambers to the larynx, and giving rise to
the condition of intra-narial epiglottis. In all the remaining orders
a similar condition occasionally occurs — the epiglottis being pro-
duced upwards into the respiratory division of the pharynx behind
the soft palate. In fcetal Marsupials, in which the intra-narial
condition is very complete, it is obviously associated with the
passive absorption of the milk, while breathing is being carried on
continuously through the nostrils. Some Cetacea and Artiodac-
tyla, etc., are exceptional in having a third bronchus, which passes
to the right lung anteriorly to the ordinary bronchus of that side
XULI
PHYLUM CHORDATA
.•559
and to the pulmonary artery. In connection with various parts of
the respiratory system there are cavities containing air. The
connection of the tympanic cavity with the pharynx by means of
the Eustachian tubes has been already mentioned. Air-sinuses,
connected with the nasal chambers, extend into the bones of the
FIG. 1214. — Brain of Dog. A, dorsal ; B, ventral ; C, lateral aspect. B. ol. olfactory bulb ;
Cr. ce. crura cerebri ; Fi. p. great longitudinal fissure ; HH, HH', lateral lobes of cerebellum ;
Hyp. hypophysis ; Med. spinal cord ; NH, medulla oblongata ; Po. pons Varolii ; VH.
cerebral hemisphere? ; Wu, middle lobe (vermis) of cerebellum ; / — XII. cerebral nerves.
(From Wiedersheim's Convparalive Anatomy.)
skull, especially into the maxilla? and frontals, where they may
reach large dimensions, and are known as the maxillary antra and
frontal sinuses. Air-sacs are also developed in connection with the
larynx in many of the Apes.
Nervous System. — The brain of Mammals (Fig. 1214) is
M M 2
560
ZOOLOGY
SECT.
mid.com
cbl
^ . com
V
Fio. 1215. — Brain of Echidna aculeata, sagittal
section, ant. com. anterior commissure ; cbl. cere-
bellum ; c. mam. corpus mammillare ; col. forn.
column of the fornix ; c. gw, corpora rjuadrigemina ;
I/any, hab. habenular ganglion ; hip. com. Hippo-
canipal commissure ; med. medulla oblongata ;
mid. com. middle commissure ; olf. olfactory bulb ;
opt. optic chiasma ; tub. olf. tubercuhnn olfactorium ;
vent. 3, third ventricle.
distinguished by its relatively large size, and by the large size and
complex structure of the cerebral hemispheres of the fore-brain.
The cerebral hemispheres
of opposite sides are con-
nected together across the
middle hne in all Mammals,
except the Monotremes and
Marsupials, by a band of
nerve-tissue termed the
corpus callosum — a struc-
ture not present in the
Sauropsida. The hemi-
spheres, in all but certain
of the lower and smaller
Mammals, are not smooth,
but marked by a number of
grooves or sulci separating
winding ridges or convolu-
tions. The lateral ventricles
in the interior of the hemi-
spheres are of large size and
somewhat complex form.
The optic lobes, which are relatively small, are divided into four
parts, and are hence called the corpora quadrigemina. The pineal
body is always a small gland-like structure. Connecting together
the lateral parts of
the cerebellum,
which, in the higher
Mammals, attains a
high degree of de-
velopment, is a trans-
verse flattened band
—the pons Varolii
(Po.) -- crossing the
hind-brain on its ven-
tral aspect.
In the Monotremes
and Marsupials (Figs.
1215, 1216) there is
no corpus callcsum,
while the anterior
commissure (ant.
com.) is of relatively
large size, and, unlike
the corresponding
commissure in lower Vertebrates, contains fibres connecting together
areas of the non-olfactory regions (neo-pallium) of the hemispheres.
7tip.com
idcom\
&•
man
artt.com
med
c.mam
FIG. 1216.— Sagittal section of brain of Rock Wallaby
(Petroyale penicillata). ant. com. anterior commissure; cbl.
cerebellum ; c. mam. corpus mammillare ; c. iju. corpora
quadrigemina ; r.rur. crura cerebri ; epi. epiphysis, with the
posterior commissure immediately behind ; /. man. position
of foramen of Monro ; hip. com. hippocampal commissure,
consisting here of two layers continuous behind at the
splenium, somewhat divergent in front where the septum
lucidum extends between them ; hypo, hypophysis ; wt'tl.
medulla oblongata ; mid. com. middle commissure ; olf.
olfactory bulb ; opt. optic cliiasma ; vent. 3, third ventricle.
xm
PHYLUM CHORDATA
561
The hippocampi extend along the whole length of the lateral ventricles.
The layer of nerve-cells in each hippocampus gives origin, as in
Butheria, to numerous fibres, which form a layer on the surface,
the alveus, and become arranged in a band — the tcenia hippocampi.
In the Eutheria, as we have seen in the case of the Rabbit, the
taenise unite mesially to form the body of the fornix (see p. 456).
In the Monotremes and Marsupials, on the other hand, there is
no such union ; the fibres of the tsenia run towards the foramen of
Monro, where they become divided into several sets. Of these one
set, constituting the great majority of the fibres, pass into the
hippocampus of the opposite side, giving rise to a hippocampal
commissure (kip. com., cf. Figs. 946 and 982), the great development
of which readily leads to its being mistaken for a corpus callosum.
The fibres entering into the formation of this commissure corre-
spond, however, not to the fibres
of the corpus callosum, which
cbl
Fin. 1217.— Brain of Ornithorhynchus
anatinus, dorsal view (natural size), cbl.
cerebellum ; olf. olfactory bulbs.
FIG. 1218.— Brain of Echidna aculeata,
dorsal view (natural size).
is the commissure of the neo-pallium, but, as proved by their
mode of origin, to the fibres of the fornix, and they connect together
only the hippocampi, the fascia) dentatce, or specialised lower borders
of the hippocampi, and an area of the hemisphere in front of the
anterior commissure (pre-commissiiral area) : they thus constitute
an olfactory or arcliipallial commissure, since all these parts belong
to the olfactory region or archipallium of the hemispheres. In
the Monotremes (Fig. 1215) the hippocampal commissure is only
very slightly bent downwards at its posterior extremity. In most
Marsupials (Fig. 1216) it bends sharply round posteriorly and runs
forward again, becoming thus folded into two layers, dorsal and
ventral, continuous with one another at a posterior bend or splenium,
similar to the splenium of the corpus callosum. The dorsal layer
of the hippocampal commissure becomes almost completely replaced
562
ZOOLOGY
SECT.
FiG.ji2i9. — Brain of Kangaroo
major). (After Oiven.)
in the Eutheria by the fibres of the corpus callosum, and the ventral
part persists in the shape of the psalterium or lyra.
In Ornithorhyuchus (Fig. 1217) the hemispheres are smooth ; in
Echidna (Fig. 1218) they are tolerably richly convoluted. Both
genera, but more particularly
Echidna, are characterised by the
enormous development of the
parts of the hemispheres (archi-
palliurn) connected with the
olfactory sense. In the lower Mar-
supials there are no convolutions
(Notoryctes, Koala, Phalangers),
while in the higher the convolu-
tions are numerous, though the
sulci are not very deep (Macropus,
Fig. 1219). Among the Eutheria
there is a great range in the grade
of development of the brain,
from the Rodents and lower In-
sectivores to the higher Primates.
In the lower types of Mammalian
brain the cerebral hemispheres
are relatively small, do not over-
lap the cerebellum, and have
smooth, or nearly smooth, surfaces. In the higher types the
relative development of the hemispheres is immense, and their
backward extension causes them to cover over all the rest of the
brain, while the cortex is thrown into numerous complicated
convolutions separated
by deep sulci (Fig.
1220). This develop-
ment of the cerebral
hemispheres reaches its
maximum in Man.
The organs of
special sense have the
same general structure
and arrangement as in
the Sauropsida. Jacob-
son's organs, which in
the Sauropsida consti-
tute such important
accessory parts to the
olfactory apparatus, are well developed only in the lower groups
of Mammals. The olfactory mucous membrane is of great extent,
owing to the development of the convoluted ethmo-turbinal bones
over which it extends. In the toothed Cetacea alone among
FIG. 1220. — Dorsal view of brain of Gray's Whale
(Cogia grayi). (After Haswell.)
XTII
PHYLUM CHORDATA
563
sn
Mammals do the nasal chambers lose their sensory functions — the
olfactory nerves being vestigial or absent. The organs of taste
are taste-buds in the mucous membrane covering certain of the
papillae on the surface of the tongue and in that of the soft palate.
In essential structure the eye of the Mammal resembles that of
the Vertebrates in general (see p. 106). The sclerotic is composed
of condensed fibrous tissue. The pecten of the eye of Birds and
Reptiles is absent. In most Mammals there are three movable
eyelids, two, upper and lower, opaque and usually covered with
hair, and one anterior, translucent, and hairless — the nictitating
membrane. The secretions of a lacrymal, a Harderian, and a series
of Meibomian glands moisten and lubricate the outer surface of
the eye-ball and its lids. In Moles, and certain other burrowing
Insectivores and Rodents, and
in Notoryctes among the Mar-
supials, the eyes are imper-
fectly developed and function-
less.
The ear of a Mammal is
more highly developed than
that of other Vertebrates, both
in respect of the greater
complexity of the essential
part— the membranous laby-
rinth—and in the greater
development of the accessory
parts. A large external audi-
tory pinna, supported by car-
tilage, is almost invariably
present, except in the Mono-
fr-QTviafci Pafanoa anrl Sirpnii FlQ. 1221. — Sagittal section through the nasal and
Uldtd,, ^ uacea, a buccal cavities of the human head. /, //, III,
ThlS is a widelv Open fun- the three olfactory ridges formed by the tur-
,. • JL £ ' t binals ; be, entrance to the mouth ; Iff. tongue ;
liel, OI a Variety OI Shapes os, opening of Eustachian tube ; an', frontal
A'^tf^, ^4- lir,™,-.™ sinus ; sn", sphenoidal sinus ; v. i, atlas vertebra ;
in dltlerent groups, having „.«, 'axis vertebra, (After Wicdersheim.)
the function of collecting
the waves of sound. By the action of a system of muscles
it is usually capable of being turned about in different directions.
Enclosed by its basal part is the opening of the external auditory
passage (Fig. 1222, Ex.). This, the length of which varies,
leads inwards to the tympanic membrane (M.), which separates it
from the cavity of the middle ear or tympanic cavity. The wall of
the external auditory passage is sometimes entirely membranous or
cartilaginous, sometimes in part supported by a tubular part of
the tympanic bone ; in Echidna it is strengthened by a series of
incomplete rings of cartilage. The tympanic cavity, enclosed by
the periotic and tympanic bones, communicates with the upper or
respiratory division of the pharynx by a longer or shorter tubular
584
ZOOLOGY
SECT.
passage — the Eustachian tube (E.). On its inner wall are the
fenestrcB ovalis and rotunda, and across its cavity, from the tympanic
membrane to the fenestra ovalis, runs the irregular chain of auditory
ossicles — the malleus (03), the incus (0.2) and the stapes (OJ.
These vary somewhat in form in different" Mammals. The stapes
is usually perforated by a considerable foramen, as in the Rabbit,
but, in the Monotremes, certain Marsupials, and Manis among the
Edentata, approximates more towards the rod-like shape which
the columella presents in Amphibians, Reptiles, and Birds. The
membranous labyrinth (L.) of the internal ear of a Mammal is
characterised by the special development of the cochlea (Cell.},
which (except in the Monotremes) is coiled into a spiral like the
shell of a Snail.
Urinogenital Organs. — The kidneys of Mammals are compact
organs of oval
shape. On the
inner side is a
notch or hilus,
by which vessels
and ducts enter
or leave the in-
terior of the
kidney. The
substance of the
kidney consists
of two distinctly
marked portions
—a central por-
tion or medulla,
and an outer part
or cortex ; the
latter is the
secreting part ;
the former con-
sists of a mass of
straight tubules
by which the secretion is carried to the ureter. The ureter
dilates as it enters the kidneys to form a chamber — the pelvis
—into which the straight tubules of the medulla of the kidney
open. The openings of the tubules are on the summits of papillae,
which are the apices of a series of pyramidal masses into which,
in most cases, the substance of the kidney is incompletely divided.
In many Mammals, however, there is no such division of the kidney
substance, and all the ducts open on the surface of a single papilla.
In others again (Ox, Bears, Seals, Cetacea) the division is carried
so far that the kidney is divided externally into a number of
distinctly separated lobules.
Fio. 1222. — Parts of the Human ear>( diagrammatic). Cch. cochlea ;
E. Eustachian tube ; Ex. outer opening of ear ; L. labyrinth ;
M. tympanic membrane ; N. entrance of auditory nerve ; Oi, Og,
O3, the three auditory ossicles, stapes, incus, malleus. (After
Headley.)
xiii PHYLUM CHORDATA 6«5
The ureters in all the Theria open into a large median sac — -the
urinary bladder — situated in the posterior or pelvic part of the
cavity of the abdomen. From this a median passage, the urino-
genital passage or urethra — into which in the male the vasa deferentia
open — leads to the exterior. Only in the Monotremes do the two
ureters and the bladder all have separate openings into the urino-
genital division of the cloaca.
The testes are oval bodies, which only exceptionally retain their
original position in the abdominal cavity, descending in the
majority of Mammals through a canal — -the inguinal canal — in the
posterior part of the abdominal wall to lie in the perinceum, or
space between the urinogenital and anal apertures, or to be received
into a pendulous pouch of skin, sometimes double — the scrotum.
The penis, present in the males of all Mammalia, consists of two
corpora cavernosa, firm strands of vascular tissue, attached proxi-
mately to the ischia except in the Monotremes, Marsupials, and some
Edentata, and a central strand, the corpus spongiosum, perforated
by the urethral canal and often dilated at the extremity to form
the glans. The two vasa deferentia continued from the epididymes,
which are in close relation to the testes, join the urethral canal near
the neck of the bladder, each often having connected with it, near
its distal end, a sacculated reservoir — the vesicula seminalis. A
small diverticulum of the proximal part of the urethra — the uterus
masculinus — may be a remnant of the Miillerian duct. Surrounding
this part of the urethra is a glandular mass — the prostate gland ;
and the ducts of a pair of small glands — Cowper's glands — open
into the urethra near the base of the penis.
The ovaries are compressed oval bodies which retain their primary
position in the abdomen, or pass backwards into its posterior or
pelvic part. In the Monotremes, large Graafian follicles project on
the surface of the ovary, while in other Mammals the Graafian
follicles are very small, and the surface of the ovary almost smooth.
The oviducts have dilated funnel-like abdominal openings, the
edges of which, except in the Monotremes, are fimbriated or fringed.
In the Monotremes the two oviducts are distinct throughout their
length, and open separately into a urinogenital sinus. In nearly
all the Theria more or less coalescence takes place. In the Marsupials
this coalescence is confined to the proximal part of the vagina. In
the Opossums (Fig. 1223, A) the two oviducts are merely in close
apposition at one point behind the uteri, and there is no actual
coalescence. In the rest of the Marsupials (B, C) the anterior
portions of the oviduct in the region (vagina) behind the uteri unite
to form a median chamber which may send backwards a median
diverticulum (median vagina, Vg., B), and in this way communicate
behind with the urinogenital passage. In the Eutheria there is a
single median vagina (Fig. 1224, Vg.) formed by the union of the
posterior parts of the two oviducts. In some cases the two uteri
JT-
FIG. 1223. — Female urinogenital apparatus of various Marsupials. A, Didelphys dor si -
gera (young) ; B, Trichosurus ; 0, Fhascolomys wombat. B. urinary bladder ;
Cl. cloaca ; Fim. fimbrise ; g. clitoris ; N. kidney ; Oil. Fallopian tube ; Ot. its aperture ;
Ov. ovary ; r. rectum ; r1, its opening ; Sug, urinogenital canal ; Ur. ureter ; Ut . uterus ;
Utl. opening of the uterus into the median vagina (Vff.B.) ; Vg. lateral vagina ; VgJ. its
opening into the urinogenital canal ; t*. rectal elands ; t, bend between uterus and
vagina. (From Wiedersheim's Comparative Anatomy.)
SECT. XIIT
PHYLUM CHORDATA
567
(A, ut.) remain distinct ; in others their posterior portions coalesce
(B, C), the anterior parts remaining separate, so that there is formed
a median corpus
uteri
horns
with
two
or cornua.
In Primates and
some Edentates
the coalescence
goes still further,
there being an
undivided uterus
(D) in addition to
an undivided
vagina, the only
parts of the ovi-
ducts which re-
main distinct from
one another being
the narrow ante-
rior parts or Fallo-
pian tubes. In all
Mammals there is,
in the vestibule or
urinogenital pas-
sage through
which the vagina
communicates
with the exterior
by the aperture
of the vulva, a
small body — the
cl ito ris — the
homologue of the
penis, and some-
times perforated
by the urethral
canal.
Development.
-The ova of
Mammals (Fig.
1225), like those
of Vertebrates in
general, are deve-
loped from cer-
FIG. 1224. — Various forms of uteri in Euthcria. A, B, C, D,
diagrams illustrating the different degrees of coalescence of
the oviducts. A, two distinct uteri. B, bicornuate uterus.
C, uterus with a median partition. D, complete 'coalescence.
E, female reproductive organs of one of the Mitstelina with
embryos (**) in the uterus. F, female reproductive organs of
the Hedgehog. B, urinary bladder ; C'e. cervix uteri (neck of
uterus) ; N, Nn, kidneys and adrenal bodies ; Od. Fallopian
tube ; Ot. ostinm tubae (abdominal opening of Fallopian tube ;
r. rectum ; Sin/, urinogenital canal ; Ur. ureter ; Ut. uterus ; Vg.
vagina ; ft. accessory glands. (From Wiedersheim's Compara-
tive Anatom//.)
tain cells of the
germinal epithelium, the primitive ova (pr. ov.). Each of these,
surrounded by smaller unmodified cells of the epithelium, sinks
68
ZOOLOGY
SECT.
into the stroma of the ovary, in which it becomes imbedded, the
small cells forming a Graafian follicle (foil.) which encloses it.
Soon spaces filled with fluid appear among the follicle cells (Fig.
1226, A, sp.), and these eventually coalesce to form a single cavity.
Jbrov
vrv
II. V
jell
FIG. 1225.— Part of a sagittal section of an Ovary of a new-born child, bl. v. blood-vessels ;
foil, strings and groups of cells derived from the germinal epithelium becoming developed
into follicles ; 77
In many Mammals the yolk-sac, through the medium of the
chorion, enters into a close relationship with the uterine wall, and
a connection, the so-called yolk-sac placenta,, is established through
which nourishment can be conveyed to the embryo ; but this rarely
persists after the true (allantoic) placenta has become established.
The stalk of the yolk-sac, with the corresponding narrowed part
of the allantois and the vessels which it contains, forms the umbilical
cord by which the foetus is connected at the umbilicus with the
yolk-sac and placenta. This is enclosed in a sheath formed by the
ventral portion of the amnion. The part of the allantois which
remains within the cavity of the body develops into the urinary
bladder, together with a cord — the urachus — connecting the bladder
with the umbilicus.
In the Marsupials the ovum is comparatively large. After
fertilisation it becomes enclosed in a thick shell-membrane with a
layer of albumen. The first cleavage of the
ovum (Didelphys), or the fourth (Dasyurus],
involves a separation of the embryo-forming
part of its substance from that destined to
give rise only to the trophoblastic ectoderm.
Further divisions take place in such a way as
' to give rise, not to a solid morula as in the
Eutheria, but to a hollow blastodermic vesicle
with a wall composed of a single layer, the
cells on one side of which form the embryonic
area. An allantoic placenta is not developed
except in Perameles. The intra-uterine deve-
lopment of the foetus is abbreviated, and birth
takes place when the young animal is still Fia. 1234.— Mammary foetus
relatively very small and has many of the °j Kfanf*sa,rT?°f atlf ched to
. •> iii r -i T ,1-111 tne "ea';' (JMawirai size).
parts incompletely formed. In this helpless
condition the young Marsupial is placed by the mother in the mar-
supium, where it remains for a time as a mammary fcetits (Fig. 1234),
hanging passively to the teat, to which the mouth becomes firmly
adherent. The milk is expressed from the mammary gland by the
contraction of a muscle, the cremaster, and passes down the gullet
of the foetus, which is enabled to breathe unobstructedly through
the nostrils by the establishment of a continuous passage from the
nasal cavities to the larynx, as already described (p. 558).
In all the Marsupials, so far as known, the embryo is covered
over, except in a limited area, by the compressed and expanded
yolk-sac. In the majority (Fig. 1235) the allantois (all.) is small,
and is completely enclosed with the embryo in the yolk-sac. In
the Koala, however (Fig. 1236), it stands out and becomes closely
applied to the serous membrane over the small area not covered
by the yolk-sac ; but no vascular villi are developed. In the
Native Cat (Dasyurus) there is a well-developed yolk-sac placenta.
578
ZOOLOGY
SECT.
Only in the Bandicoots (Fig. 1237), so far as known, is the out-
growth of the allantois to the chorion followed by the establishment
of an intimate relationship between the chorion and the uterine
wall, with the formation of interlocking ridges and depressions, the
r/mn
cotl
all
FIG. 12:35. — Diagram of the embryo and
foetal membranes of Hypsiprymnus
rufcscens. nil. allantoic cavity ; amn.
ainnion ; amn. c. cavity of amnion ; cael.
extra-embryonic coelome ; ser. serous
membrane (chorion); yk.s. yolk-sac.
(After Semon.)
FIG. 1236. — Diagram of the embryo
and foetal membranes of Phas-
colarctos cinereus. Letters
as in Fi'i. 12 !5. (After Semon.)
cod
all
afl.s
whole constituting a placenta of the same essential character as'
that of the Eutheria, though devoid of actual villi.
The Prototheria, unlike all the rest of the Mammalia, are ovi-
parous. In Echidna only a single egg, as a general rule, is laid in
a season. This is placed in
a temporary marsupium,
formed as already described
(p. 477) in the mammary
region of the ventral surface.
The young animal soon
emerges from the egg, and
remains enclosed in the mar-
supium till it reaches an
advanced stage of develop-
ment. Ornithorhynchus de-
velops no marsupium, and
the two7eggs which it pro-
duces are deposited in its
FIG. 1237.— Diagram of the embryo and placenta of kmTOW Tn Echidna the 622-
Perameles obesula. Letters a* in Fig. 1235. uf
In addition, all. s. alUintoie stalk ; rues, mesen- shell is Composed OI keratin J
chyme of outer surface of allantois fused with . _ . , r, -,
mesenchyme of serous membrane ; *. t. sinus in UmithomyncnUS It COn-
terminaiis ; ««. uterine wai!. ^^ carbonate of lime. The
ova of the Prototheria, (Fig. 1238) are very much larger than
those of other Mammals, their greater dimensions being due to
the presence of a large proportion of food-yolk. The segmentation,
unlike that of all the Theria, is meroblastic? and the blastoderm
sf
Xtll
PHYLUM OHORDATA
f>7D
eventually forms a complete investment, of two layers, to the yolk.
An embryonic area is differentiated at one pole, and on it appears
a primitive streak with a primitive knot and head-process.
Geographical Distribution. — The Monotremes are entirely
confined to Australia, Tasmania, and New Guinea. The Mar-
supials are most abundantly represented in the Australian
region, the greater, number of the Australian families and
genera being restricted to the Australian continent and to
Tasmania, though several genera extend to New Guinea and some
of the neighbouring islands. The family Didelphyidae, or Opos-
sums, inhabits South America and extends into the southern
part of North America ; and a single genus, Ccenolestes, of a
family at one time supposed to be
related to the Australian Diproto-
donts, but now more generally
regarded as derived from Didel-
phyid (Polyprotodont) stock, has
been comparatively recently found
in South America.
The Edentates are most numer-
B ously represented in South and
/ Central America, the true Ant-
\ eaters, the Sloths, and the Arma-
\ dillos being all inhabitants of
that region. But the Scaly Ant-
eaters and the Ard-varks (Cape
Ant-eaters) are denizens of the
Old World ; the former inhabiting
Southern Africa and South-Eastern
Asia, the latter being confined to
Africa.
FIG. 1238.-^, biastuia stage of one-of the The Cetacea are cosmopolitan
Theria. B, transition stage between m their distribution '. the great
the morula and biastuia hi a Mono- ., ,
treme. Both represented in diagram- majority are marine, but SOme
ascend rivers, and a few are ex-
clusively fluviatile, inhabiting the rivers of South America and
South-Eastern Asia.
The distribution of the Sirenia is somewhat restricted. The
recently extinct Rhytina inhabited Behring's Straits. The
Manatee is confined to the Atlantic coasts of South America and
of Africa, living chiefly in the larger rivers. The Dugong occurs
on the east coast of Africa, in the Red Sea, the Indo-Malayan
islands, and the northern coast of Australia.
The Ungulata occur in all the great regions, with the
exception of the New Zealand, Polynesian, and Australian.
Oxen are, with the exception of the American Bison, natives of
the Pala3arctic, Ethiopian, and Oriental regions. Wild sheep,
580 ZOOLOGY SECT.
with the exception of one African and one North American species,
are confined to the Nearctic and Oriental regions. Goats are also
mainly Nearctic and Oriental. Antelopes are confined to the Old
World, and are by far more numerous in the Ethiopian than in other
regions. The Prongbucks are Nearctic ; the Giraffes exclusively
Ethiopian. Deer are widely distributed in the Nearctic, Neo-
tropical, Palsearctic, and Oriental regions, but are absent from the
Ethiopian. The Camels are natives of the Old World ; the Llamas
of the Neotropical region. Wild species of Pigs are widely dis-
tributed in the Old World and are absent in the New ; while the
Peccaries are confined to the Nearctic and Neotropical regions.
Hippopotami are confined to Africa. The Horses, including the
Zebras and Asses, are restricted at the present day, as regards their
natural distribution, to the Old World, though they abounded also
in America in the Pleistocene period. Rhinoceroses are Oriental
and Ethiopian. Tapirs have a singular distribution, one species
occurring in the Malay Archipelago, and the rest in the Neotropical
region. Hyraxes are confined to Africa, Arabia, and Syria. Of the
Elephants, one species is confined to the Oriental, the other to the
Ethiopian regions, but fossil remains prove that in Pleistocene
times the range of the Elephants, and their gigantic extinct allies,
the Mammoths, was very much wider, and extended over Northern
Africa and the entire Palsearctic region. Only one fossil species has
been found in America.
Carnivora, if we leave out of account the Australian Dingo or
Native Dog, are absent in the Australian, Polynesian, and New
Zealand regions, but range over all the other geographical provinces.
The Cats and the Dogs are found in all parts of this extensive area :
the Hyenas are restricted to the Western part of the Oriental
region and the warmer parts of the Holarctic and the Ethiopian.
The Civets are most abundant in Africa, Madagascar, and South-
Eastern Asia, but occur also in the Southern parts of Europe ;
and many of the smaller groups have a yet more restricted range.
Bears have a wide distribution, but are absent from the whole of
the Ethiopian region.
The majority of the Pinnipedia are found in the Arctic and
Antarctic regions, and in the temperate zones of both hemispheres,
few ranging into the tropics. The Walruses are almost exclusively
Northern, while the Eared Seals and Earless Seals are almost equally
abundant in the Northern and Southern hemispheres.
The Rodents have a wider range than any others of the orders of
land Mammals, and occur in all parts of the globe, though they are
poorly represented in Australia and Madagascar. The Rodents
reach their greatest development, as regards the number of
families, in South America, in which region occur also the majority
of the largest members of the order.
Insectivora are absent in the Australian, Polynesian, and New
xiii PHYLUM CHORDATA 581
Zealand regions, and in South America, but occur in all the other
provinces.
The Chiroptera are world-wide in distribution, occurring in
greatest abundance in tropical and warm temperate zones. The
Flying Foxes (Pteropidse) are absent from the Nearctic and Neo-
tropical regions, and the Vampire Bats occur exclusively in the
latter.
The distribution of the Lemurs is remarkable ; they occur only
in Madagascar, a limited part of South Africa, Southern India and
Ceylon, some of the islands of the Malay Archipelago, and the
Philippines. The headquarters of the group is the island of
Madagascar, of which they constitute one half of the entire
Mammalian fauna.
Of the other groups of Primates, the Marmosets (Hapalidae) and
the Cebidae are exclusively American ; the Cercopithecidae Palso-
arctic, Oriental and Ethiopian, with a single species in Madagascar.
Of the Simiidas the Gibbons occur only in South-Eastern Asia and
the Malay Peninsula ; the Orangs only in Borneo and Sumatra ;
the Gorilla and Chimpanzee in certain parts of Western Equatorial
Africa.
Geological Distribution. - - The earliest fossil remains of
Mammals have been found in strata of Upper Triassic and of
Jurassic age in Europe and America. These remains consist
almost exclusively of jaws and teeth, and, as the latter differ
widely from those of existing Mammals, there is frequently great
difficulty, in the absence of remains of the other hard parts, in
determining the affinities of these Mesozoic forms. Some of the
Triassic and Jurassic Mammalian molar teeth are constructed on
the most primitive form of the triconodont type, which has already
been referred to (p. 544) as being the primitive form in the class,
having three cones or cusps in a longitudinal row. In Dromatherium
and its allies each molar has a single main cusp with two smaller
accessory cusps. There is no decisive evidence as to the affinities
of these primitive triconodont Mammals, but they may be pro-
visionally set down as allied to the Prototheria.
Of the remainder of the Mesozoic Mammals, some were probably
Prototheria, others Metatheria, while others again may have been
Insectivores. Most of them fall into two main groups. The type
of dentition presented by the members of one of these groups
(Fig. 1239) is more nearly allied to that of the Polyprotodont
Marsupials (p. 464) than to any other. In the other group (Multi-
tuberculata) (Fig. 1240) there is a superficial resemblance to the
Diprotodont Marsupials ; a single chisel-shaped incisor is present on
each side of the lower jaw, and one large, and sometimes one or
two smaller, on each side of the upper. A wide diastema separates
these from the pre-molars. The molars present a number of variously
arranged small tubercles. In some cases the pre-molars have a
582
ZOOLOGY
SECT.
pattern similar to that exhibited by the molars, but in others they
have a cutting edge which may be serrated or obliquely grooved.
The fact that the vestigial molar teeth of Ornithorhynchus come
nearer in pattern to those of certain of the Multituberculata than to
those of any other known group is looked upon as evidence that the
affinities of the latter are rather with the Prototheria than with the
Metatheria. In the American Cretaceous beds in which these
teeth are most abundant a number of limb-bones have also been
found, some of
which show evi-
dence of Mono-
character-
treme
istics.
Fossil remains
of Mammals be
longing to the
Cretaceous age
are known only
from certain
limited beds in
North America,
in
FIG. 1239. — Phascolotherium bucklandi. Inner view of
right ramus of mandible. (After Owen.)
But in deposits
of the succeeding Tertiary period there have been found the
remains of an extensive and varied Mammalian fauna. The
earlier Tertiary Mammals in many cases present features which
enable us without hesitation to refer them to one or other of the
existing orders ; but when this is the case there is nearly always to
be recognised an absence, or a less advanced development, of some
of the more salient characteristics ; in other words, the earlier
Tertiary Mammals, when
referable to existing
orders, are less highly
specialised than the
living representatives of
these orders. No less
significant is the fact
that these early Tertiary
representatives of exist-
ing orders had the cavity
of the brain-case nearly
always much smaller in proportion to the other dimensions than in
living forms. But many are not so readily referable to existing
orders, sometimes owing to their possessing marked special features
of their own, sometimes owing to their combining characteristic
features of two or more living orders. Through the series of
Tertiary and Post-tertiary formations it is possible to trace a gradual
development from the early generalised to the existing specialised
Fio. 1240.— Plagiaulax becklesi. Muudilile with
teeth. (After Owen.)
XIII
PHYLUM CHORDATA
r,s:j
genera, and in some instances by such gradual transitions that
the actual course of the evolution can be followed stage after stage.
There is only space here for a very brief review of this extensive
and remarkable Tertiary and Post-tertiary Mammalian fauna.
No remains of Prototheria are known from the Tertiary, and
it is only when we come to Post-tertiary (Pleistocene) that we meet
with fossil representatives of the group. These, which have been
found only in Australia, differ little from the existing Echidna and
Ornithorhynchus.
Of the Marsupials, the Opossums (Didelphyidae) of America are
represented not only in Cretaceous, Tertiary, and Pleistocene deposits
in that continent, but in beds of Tertiary age in Europe. In addition,
in certain European deposits of Eocene age, there occur teeth and
jaws which may be Marsupial in character, but the affinities of
FIG. 1241. — Diprotodon australis. (From a restoration of the skeleton by Prof. E. 0.
Stirling in the Adelaide Museum.)
which are uncertain ; and in Tertiary deposits of South America
have been found numerous remains of Marsupials belonging to a
group represented by the single surviving genus, Ccenolestes. These
South American Ca3nolestoids appear, so far as is known, to have
differed from the Australian Diprotodonts in the absence of the
characteristic syndactylism of the latter. Another group of South
American Tertiary Mammals, the Sparassodonts, are regarded as
Polyprotodonts nearly related to the Tasmanian Thylacine. The
remainder of the fossil Marsupials hitherto discovered are of Pleis-
tocene age, and have nearly all been found in Australia. The
Australian Pleistocene Marsupials are for the most part referable to
existing families and even genera, representing both the Diprotodont
and the Polyprotodont sections ; but some differ widely from
existing forms. One of these, Diprotodon (Fig. 1241), was the
584
ZOOLOGY
SECT.
largest known Marsupial, having reached the dimensions of a
Rhinoceros ; it occupies a position intermediate between the
Phalangers and the Kangaroos. Unlike the latter, Diprotodon
had the limbs of approximately equal size, and adapted for walking :
FIG. 1242. — Wototherium mitchelli. Side view of skull. (After Owen.)
both manus and pes were pentadactyle with very small sub-equal
digits. Notoih&rium (Fig. 1242), somewhat smaller than Diprotodon,
but also of large size, seems to connect together Diprotodon, the
Wombats, and the Pha-
langers. Thylacoleo (Fig.
1243) is an extinct genus
referable to the Phalanger
family, and characterised
by an extremely modified
dentition, the only func-
tional teeth being a single
pair of large incisors in
the middle in both upper
and lower jaws, with a
single elongated trenchant
nrp rnnlnr nn oaoTi cirlo
pre-moiar on eacn side
FlG- 1243.— Thylacoleo carnifex. Side view
of skull> (After Flower.)
both above and below.
Among the Edentata the majority of fossil as of existing forms
have been found in South America. But the family of the Cape
Ant-eaters, at the present day confined to. South Africa, is proved ,
xin
PHYLUM CHORDATA
585
by the discovery of remains in the Pliocene of the island of Saraos
.in the Eastern Mediterranean and in the Eocene of Southern France,
to have formerly had a wider distribution. The American fossil
Edentata, all of Pleistocene age, comprise, in addition to extinct
FIG. 1244.— Glyptodon clavipes. (After Owen.)
genera of Armadillos, some of gigantic size, and one genus of Sloths,
representatives of two extinct families, the Gtyptodontidcs and the
MegatheriidcB.1 The former (Fig. 1244) are large Edentates re-
sembling the Arma-
dillos in the presence
of a bony dermal
carapace and a bony
investment for the
tail ; but in the
Glyptodontidse the
carapace has no
movable rings, so
that the animal could
not roll itself up, and
there is usually a
ventral bony shield
or plastron, never
present in the Arma-
dillos. Glyptodonts
occur in North as
FIG. 1245. — Mylodonrobustus. (Restoration, after Owen.)
well as in South
America. The Mega-
theriida3 (Fig. 1245) are Edentates, mostly of enormous size and
massive build, which combine certain of the features now charac-
teristic of the Ant-eaters (Myrmecophagidse) and the Sloths (Brady-
1 Recent remains stated to belong to a Megatherium have been found in
South America.
58(>
ZOOLOGY
SECT.
podidse) respectively, the spinal column and limbs allying them
with the former, and the crania and the teeth with the latter.
The Cetacea are represented in the Tertiary (Eocene and
Miocene) of Europe, Egypt, and North America by an extinct
sub-order — Archceoceti or Zeuglodonta, comprising only one known
genus — Zeuglodon. Zeuglodon differs from existing Cetacea mainly
in the possession of rooted heterodont teeth, and in the position of
the narial aperture, which is situated comparatively far forwards ;
the limbs are not known ; there were irregular dermal bony plates.
The remains of both Whalebone Whales and Toothed Whales occur
abundantly in Pliocene deposits, some belonging to extinct, others
to existing genera. Toothed Whales occur also in Miocene forma-
tions, and there, as well as in the Pliocene and Pleistocene of Europe,
North America, New Zealand, and Australia, are represented by an
extinct family, the
Squalodontidce,
(Fig. 1246), with
heterodont denti-
tion.
The order Si-
renia is first met
with in the Eocene,
and was repre-
sented in that and
succeeding periods
by several extinct
genera, of which
Halitherium is the best known. These were characterised
by the possession of upper incisors, in some cases of canines, of
enamelled pre-molars and molars, of a milk-dentition, and of small
vestiges of femora. The family of the Dugongs is represented by
a form nearly allied to the existing genus in the Pliocene of France,
and probably by another genus in the Tertiary of California. The
family of the Manatees is not known to be represented by any
fossil forms. The recently extinct Rhytina (" Steller's Sea-Cow "),
which lived within historic times in Behring's Straits, was the
largest known member of the order, and sometimes attained a
length of seven or eight metres.
The Tertiary Ungulata comprise an immense number of forms,
including numerous extinct families, into an account of which
it would be going beyond the scope of the present work to enter.
In the Artiodactyle series there is to be traced a progressive union
and coalescence of the third and fourth metacarpals to form the
cannon-bone, a progressive reduction of the lateral digits, and a
progressive development of horns or of tusks — absent or rudi-
mentary in the earlier representatives of the sub-order. In the
Perissodactyle series the reduction of the lateral toes reaches its
FIG. 1246. — Squalodon. Three of the lower true molars.
(After Flower.)
XIII
PHYLUM CHORDATA
r,s:
maximum in the existing genus Equus. The history of this reduc-
tion, together with the development of other characteristic features,
can be traced from pentadactyle forms with simple molars through
a long series of gradations to the monodactyle Horses with their
complexly folded molars. Similar genealogies, though not always
so complete, can be traced for the Tapirs and Khinoceroses, and for
the Deer, Camels, and Pigs.
The order Proboscidea was represented in Tertiary and
Pleistocene times, not only by forms allied to those now living
—though sometimes, as in the Mammoths, of much greater
size — but by an extinct family, the DinotheridcB (Fig. 1247) (Mio-
cene and Plio-
cene of Europe
and India),
which possess a
pair of down-
wardly - directed
tusks in the
lower jaw. The
genus Pyrothe-
rium, from the
Patagonian Ter-
tiary deposits,
was a primitive
Ungulate, with a
pair of short
tusk-like incisors
in the lower jaw,
which may have
been related to
the Proboscidea :
and Mcerithe-
rium, from the
Eocene of Egypt,
is probably also
a primitive
member of the
same order.
The Hyracoidea were represented in the Pliocene by an extinct
genus (Pliohyrax) ; and Archceohyrax, from the Patagonian Tertiary,
is perhaps also an allied form.
A separate sub-order, the Condylarthra, has been established
for a number of Eocene Ungulates, which differ somewhat widely
from all the other members of that group, and approach the
Carnivora in some respects, though having certain resemblances to
the Hyracoidea. The pre-molars and molars are short and usually
bunodont, the pre-molars being simpler than the molars, the latter
FIG. 1247. — Dinotherium giganteum
natural size. (From Zittel's
Side view of skull.
, after Kaup.)
588 ZOOLOGY SECT.
sometimes tritubercular, like those of many of the Carnivora ; the
incisors and canines also sometimes resemble those of the Carnivora.
The humerus differs from that of the other Ungulata, and resembles
that of the Carnivora in the presence of a foramen over the inner
condyle. The arrangement of the carpals corresponds with what
is observable in the Hyracoidea, and also, as in the latter group,
the femur has a third trochanter. The limbs are usually penta-
dactyle, with pointed ungual phalanges. The astragalus has, as
in the Carnivora, a uniformly rounded distal articular surface.
The fibula does not articulate with either the astragalus or the
calcaneum.
Another extinct primitive sub-order of the Ungulata is the
Amblypoda, the members of which have been found, like the
Condylarthra, in the Eocene of North America and of Europe.
These resemble the Condylarthra and Hyracoidea in the scaphoid
being opposite the trapezoid ; both magnum and unciform articulate
with the lunar. The fibula articulates with the calcaneum ; the
cuboid articulates with both the astragalus and the calcaneum ;
the feet are short, pentadactyle, and plantigrade. Canines are
present in both upper and lower jaw ; the pre-molars and molars
are short and lophodout in type. Dinocems and Tinoceras are
characterised by the process of remarkable bony prominences on
the upper surface of the skull. In the Tertiary deposits of
Patagonia and Bolivia have been found the remains of another
group of extinct Ungulates of low organisation, the Litopterna.
These had the distal segments of the limbs elongated and con-
structed on the perissodactyle type, the number of the digits
varying from five to one, the third being always the largest. The
carpal and tarsal bones do not interlock as in the existing Ungulata
vera. There is no foramen above the inner condyle, and clavicles
are absent. A third trochanter is present. The brain-case is very
much smaller than in the existing Ungulata vera. The dentition
is complete or nearly so ; the pre-molars and molars short and
provided with roots.
The Ancylopoda are another group of primitive extinct Ungulates.
The remains of some of these have only been found in the Pata-
gonian Tertiary deposits, but others had a wide range both in the
Old and New Worlds. They all differ from other groups of
Ungulates in the form of the limbs : the weight of the body appears
to have been borne on the outer edge of the manus and pes, and the
digits were evidently provided, not with true hoofs, but with pointed
claws. The teeth resemble those of the Perissodactyla.
The Typotheria and Toxodontia are two groups of extinct
Ungulata the representatives of which have only so far been found
in the South American Tertiary formations. The former differ
from ordinary Ungulates in the possession of a clavicle and the
presence of a foramen above the inner condyle of the humerus.
xur PHYLUM CHORD ATA 589
The ulna and fibula are complete, and there are either four or five
fully formed digits in each foot. The Toxodontia approach
nearer the normal Ungulate type, the clavicle and the foramen over
the inner condyle being both absent. They have a massive skull
and short stout limbs, each with three digits.
The true Carnivora of the Tertiary period are, as compared with
those of the present time, remarkable for the absence of the well-
marked distinction into groups such as are now to be recognised ;
numerous intermediate forms connect together the Dogs, Civets,
Cats, Bears, and Weasels, which, in the existing fauna, appear
separated from one another by differences of the most strongly
marked character. Several extinct families are recognised, and
one extinct order — the Creodonta. The latter present resemblances
to the Insectivora on the one hand, and to the Polyprotodont
Fia. 1248. — Tillotherium fodiens. Left lateral view of skull. (From Flower, after
Marsh.)
Marsupials on the other, such as would appear to indicate a
relationship with both of those groups.
A group of Eocene Mammals of uncertain affinities are the
Tillodontia (Fig. 1248), which by some have been elevated to the
rank of a distinct order. The Tillodontia appear to unite in a
remarkable degree, in skull and dentition, ungulate, rodent, and
carnivorous characteristics.
The Rodents were represented in the Tertiary period by all, or
nearly all, the principal groups existing at the present day, together
with several extinct families. Some of the Tertiary Rodents
attained a much larger size than any living members of the order.
Among the Tertiary Insectivora, in addition to representatives
of existing families, are a number of extinct forms. Through these
it is possible to connect the living Insectivora with the Creodont
Carnivora on the one hand, and with the Prosimii on the other.
VOL. II O O
590 ZOOLOGY SEC7
Chiroptera, not differing widely from existing forms, occurred
as early as the Eocene.
Of the Primates, Prosimii occur from the Eocene onwards.
A single extinct family is known, comprising Lemuroids which
bear a closer resemblance to Insectivora than do the living
members of the order. Of the Anthropoidea, the Hapalidae and
Cebidee are only represented in the Miocene (Eocene ?) and
Pleistocene of South America ; the Cercopithecidae in the Miocene
and Pliocene of Europe and the Pliocene and Pleistocene of
India by extinct genera (Mesopithecus, &c.) and by species of the
existing genera Macacus, Semnopithecus, and Cynocephalus, and
in the Pliocene of India, France, and Italy by species of extinct
genera. Among the Simiida3 the Gibbons occur in the Miocene of
France, the Pliocene of Germany, and the Pleistocene of Borneo.
An extinct genus, Dryojnthecus, found in the Miocene of
Europe, is perhaps related to the Gorilla ; and a species of
Orang (Simia), together with a form allied to the Chimpanzee,
occurs in the Indian Pliocene.
In deposits of late Pliocene or early Pleistocene age in Java have
been found the remains of an Anthropoid (Pithecanthropus) which
has been supposed to be an intermediate form between the man-like
Apes and Man. Traces of the existence of Man in the form of
flints of undoubted human manufacture have been found in the
Pliocene ; but any such evidences are extremely rare until we
reach the Pleistocene.
THE MUTUAL RELATIONSHIPS OF THE CHORDATA.
In discussing the relationships of the various groups of Chordata,
it will be convenient to begin with Fishes, and to work from them
upwards and downwards.
The question of the inter-relationships of the various groups of
Fishes is a very puzzling one. As in other cases of the kind, there
are three lines of evidence to be kept in mind — anatomical,
embryological, and palseontological — the last being always, when
available, the final court of appeal.
With regard to anatomical evidence, it seems fairly obvious that
Fishes having neither limbs nor jaws are more primitive than
forms in which those structures are present, unless undoubted
evidence of degeneration can be produced ; that a purely
cartilaginous skeleton is more primitive than a bony one, and a
notochord than a vertebral column, however simple ; that a brain
with distinct cerebral hemispheres is • more advanced than one
having an undivided prosencephalon ; that an autostylic skull,
being due to the concrescence of originally distinct parts, is more
specialised than a hyostylic skull ; that the loss of the spiracle
and the presence of an operculum and of a highly differentiated
xm PHYLUM CHORD ATA 591
hyoid arch are evidences of specialisation, as also is the presence
of air-bladder or lung, spiral valve, conus arteriosus, or copulatory
organs.
In embryology, eggs with much food-yolk are to be looked upon
as more modified than those with little, unless there is distinct
evidence in the latter of reversion towards an alecithal condition.
Any special contrivances for the nourishment and protection of
the embryo, obviating the necessity for the production of immense
numbers of eggs, are also marks of advance.
On both these lines of evidence the lowest place may safely
be assigned to the Cyclostomes. In spite of all the attempts that
have been made to homologise various cartilages in the neighbour-
hood of the mouth in the Lamprey with the elements of the
anterior visceral arches in higher forms, there is no real evidence
that the ancestors of the class had either jaws or limbs, and the
most reasonable theory is that they are the descendants — highly
specialised in certain respects in accordance with their peculiar
mode of life — of a primitive craniate stock.
With regard to the two largest groups of Pisces — the Elasmo-
branchii and the Teleostei — the evidence from anatomy and
embryology is conflicting. The Teleostei take the highest place
in virtue of their skeleton, operculum, air-bladder, and gills, as
well as in their extraordinary adaptability to various environments ;
but the Elasmobranchs reach a distinctly higher grade of organ-
isation in their enteric canal, heart, brain, and urinogenital organs,
as well as in their large and well-protected eggs. The anatomy
of Ganoids seems to show, however, that the spiral valve, conus
arteriosus, and typical oviducts (Miillerian ducts) have been lost
in the course of the evolution of the Teleostei, and that the simpler
structure of these organs in that order is actually a concomitant
of their extreme specialisation.
The Holocephali and the Dipnoi, white agreeing with Elasmo-
branchs in many important respects, show an advance in the
presence of an autostylic skull and of an operculum, while the
Dipnoi rise above all other Fishes in possessing not only lungs
like Polypterus, but also posterior nares and a partially divided
auricle. The lung appears to have been derived from an air-
bladder with pneumatic duct opening on the ventral wall of the
oesophagus, as in Polypterus ; by the dorsal shifting of the duct
and its final atrophy the closed air-bladder of the higher Teleostei
has arisen.
Coming to the results of Paleontology, many striking and un-
expected facts have recently been brought to light. There is reason
to believe that Palseospondylus is a Cyclostome, but one with well-
developed vertebra ; from which it must be assumed either that
the vertebral column of existing members of the class is degenerate,
or that Pala3ospondylus is a highly specialised offshoot of the
o o 2
592 ZOOLOGY SECT.
primitive Cyclostome stock, in which a vertebral column had been
independently acquired. The latter conclusion seems the more
probable, and is supported by the fact that in all three orders of
Ganoids there are some species with a persistent notochord, others
with well ossified vertebrae ; the conclusion being that the vertebral
column is a polyphyletic structure — that is, has been evolved
independently in various groups in accordance with similar
conditions.
Among extinct Elasmobranchs the Acanthodea and Pleura-
canthea had bones investing the cranium, and Cladoselache
had no claspers. These facts seem to indicate as a probable
ancestor of the Teleostomi and Dipnoi — the two sub-classes with
ossified skeleton — a generalised Blasmobranch in which fusion of
dermal ossicles into investing bones had begun, but in which the
special reproductive phenomena of the existing members of the
group — internal impregnation and few, large, well-protected eggs
—had not yet been acquired. The origin of the Dipnoi from such
a source is rendered more probable by the possession of the
characteristic biserial fin or " archipterygium " by Pleuracanthus.
The Holocephali and the existing Elasmobranchs may be considered
as having arisen from the same primitive stock along diverging
lines of descent. There is, however, at present no evidence to
trace or to explain the fusion of the palatoquadrate with the
cranium to form the characteristic autostylic skull of the Holo-
cephali and Dipnoi.
The connection of the Ostracodermi with the better-known
groups of Fishes is very uncertain. It has been proposed to class
them with Cyclostomata on account of the absence — as far as our
present knowledge goes — of jaws and limbs, and attempts have
been made to show affinities with the Xiphosura and with larval
Tunicates. They seem, however, to be undoubted Fishes, but
with no clear relationship to any existing group. The Arthrodira
appear to be most closely allied to the Dipnoi.
The question of the origin of Fishes from lower forms is involved
in the greatest obscurity. Practically the only assistance in the
solution of the problem is furnished by Amphioxus, which seems to
indicate, as the ancestral stock of Vertebrates, fish-like animals
having a skeleton in the form of a notochord, fin-rays, buccal
cartilages, and branchial rods ; a barely differentiated brain ; no
heart, but a contractile ventral vessel below the pharynx and a
dorsal vessel immediately beneath the notochord ; colourless blood ;
separate nephridia of the annulate type ; a co3lome developed as
an enteroccele ; metamerically arranged gonads devoid of ducts ;
and alecithal eggs. The forward extension of the notochord, the
immense pharynx, the very numerous gill-slits, and the atrium
are very probably characters special to the Acrania ; but even
xin PHYLUM CHORDATA
putting them aside as of no phylogenetic importance, it is obvious
that this group must have sprung from a point very low down the
chordate stem. The morphological differences between Amphioxus
and a Hag are, in fact, of a more fundamental character than
those between a Hag and a Mammal.
Still lower must have been the j)oint of origin of the Urochorda,
with the notochord confined to the tail, the dorsal mouth, the
absence of myomeres and of nephridia, and with only exceptional
and ill-defined traces of segmentation. The huge pharynx with
its innumerable stigmata is undoubtedly a secondary character ;
but the atrium, endostyle, dorsal lamina, and peripharyngeal bands
seem to indicate an affinity with the Acrania. So also do the
earlier stages of development ; but the later stages, and especially
the mode of origin of the atrium, are quite different in the
two cases.
The propriety of including the Hemichorda among the Chordata
is still sub judice. Allowing that any single organ may have a
polyphyletic origin— i.e., may arise independently in different
groups in accordance with similar needs — it seems highly impro-
bable that three such peculiar and characteristic structures as
notochord, hollow dorsal nervous system, and gill-slits can have
arisen together more than once in the history of animals ; and if it
could be shown with certainty that these three characters were all
present in the Hemichorda their place in the chordate phylum
would be assured. But the cavity or cavities in the dorsal nerve-
cord of Balanoglossus are inconstant, and are very different from
the neurocosle of Urochorda and Vertebrata, which from the first
extends through the whole length of a well-defined dorsal nervous
system. In Cephalodiscus and Rhabdopleura, moreover, there is
no trace of any such cavity.
The pharyngeal diverticulum of the Hemichorda, also, is a very
different thing from the notochord of Urochorda and Vertebrata,
nothing in the structure or development of which gives the
slightest indication that it originally arose as a forward out-
growth of the anterior portion of the mid-gut. The diverti-
culum of Hemichorda is, in fact, obviously a support to the per-
sistent prostomium of a fixed or sluggish animal, while that of
Urochorda and Vertebrata forms a strengthening axis— either to
the tail alone or to the whole body — of an active, elongated,
animal swimming by lateral movements of the tail ; and there
seems to be no reason why two such different structures should
not have had an independent origin. The supposed double
" notochord " of Actinotrocha, the larva of Phoronis, is even more
problematical.
Far more significant are the gill-slits, but even their evidence is
hardly conclusive, since they are absent in Ehabdopleura and
594 ZOOLOGY SECT.
Actinotrocha, and in Cephalodiscus are a single pair of apertures
having apparently no respiratory function. In Balanoglossus,
however, they are very numerous and increase in number with the
growth of the animal, as in Amphioxus, and the division of each
by a " tongue " is very similar in the two cases. Further homologies
have been suggested by comparing the snout of Amphioxus with
the proboscis or pre-oral lobe of Hemichorda and its pre-oral pit
with the proboscis-pore.
On the whole, although it is by no means certain that the
" chordate " peculiarities of the Hemichorda may not have been
independently evolved, it is convenient to retain them in the
present phylum, pending further knowledge of their true
affinities.
Various zoologists have supported the view that the nearest
relatives of the Chordata among the Invertebrata were forms
characterised, like all but the lowest of the former phylum, by
the occurrence of metamerism, i.e., Annulata or Arthropoda ;
while others have looked upon the metamerism of the Chordata
as independently evolved. Among the non-metameric groups
which have been supposed to have been ancestral to the Chordata
are the Nemertines — the proboscis-sheath being compared with
the notochord, and the proboscis itself with the pituitary invagina-
tion. But this view has received little support. On the other
hand, the supporters of the Annulate ancestry have been more
numerous — some seeing in the Cheetopoda, others in the
Hirudinea, the nearest Chordate relatives. The metamerism of
the Annulata is regarded as supporting this theory, as well as the
structure and arrangement of their circulatory, nervous, and
excretory systems. The notochord might have been supposed
to have originated in an Annulate from a typhlosole or from an
intestinal diverticulum or siphon. But a very serious difficulty is
met with when we proceed to try to derive the Chordate nervous
system from, that of the Annulata. Not only must the ancestral
Annulate, in order to become transformed into the primitive
Chordate, have reversed its habitual position, so that its neural
surface became dorsal instead of ventral ; but its mouth, which
pierced the central part of the nervous system, must have been
abolished, while a new one was developed on the haemal side of
the head.
Elaborate comparisons have been instituted between the brain
of Cyclostomes and Fishes and those of Crustacea and Xiphosura,
and it has been sought to explain the neuroccele as the discarded
Arthropod enteric canal. But if Amphioxus and the Urochorda,
to say nothing of the Hemichorda, are branches from some low
part of the chordate stem — a fact it seems hardly possible to
doubt — it is obvious that there can be no direct connection with
xiii PHYLUM CHORDATA 595
the highly specialised classes referred to. If, for instance, the
lower Craniata sprang either from a Chaetopod-like or from a
Limulus-like ancestor, Amphioxus and the Tunicates must either
have no connection at all with Vertebrates, or must have under-
gone a quite inconceivable amount of degeneration.
There appears, in fact, to be a good deal of evidence supporting
the view that the first developed Chordates may not have had any
such pronounced metamerism as Annulates and Arthropods possess,
and it becomes possible to look for the immediate ancestral form
among less highly organised Invertebrate groups. But on this
matter, though there is abundant scope for ingenious speculation,
no finality can be said to have been reached, and the ancestry of
Vertebrates still remains an unsolved problem.
With regard to the higher classes, Amphibians may be held to
have arisen from a Fish-type allied to the Dipnoi, the resem-
blances of which to the Amphibia are so great as to lead some
authors to place them in a distinct class intermediate between
Fishes and Amphibia. The chief difficulty in this case — and it
is a serious one — is the derivation of the pentadactyle limb
from the Fish's fin, a transformation of which no satisfactory
explanation is at present offered either by anatomy, embryology,
or paleontology.
Reptiles may be considered to have arisen from a generalised
Amphibian stock, but there is no direct evidence on this point ;
and, apart from purely theoretical considerations, there is nothing
to show how or why gills vanished so completely as to leave no
trace of their existence apart from the branchial clefts, or by what
steps the allantoic bladder became precociously enlarged into an
embryonic respiratory organ. The precise mode in which the pro-
tecting amnion arose is also very doubtful, though from theoretical
considerations it has been argued that its development in the
Hedgehog (p. 574) indicates a more primitive condition than
obtains in the other Mammalia or even in Sauropsida.
Birds appear to be undoubtedly derived from true Reptiles,
although nothing is known of the actual ancestral form.' In spite
of the enormous adaptive differences between the warm-blooded,
feathered, bipedal Bird and the cold-blooded, scaly, quadrupedal
Reptile, the connection between the two is far closer than between
any other two vertebrate classes.
Mammals also appear to have had a reptilian origin : the
numerous reptilian characters of the Monotremata certainly point
in this direction, and the reproductive processes of that group help
us to understand the stages by which the large-yolked egg of the
ancestral form, with the embryo developed outside the body,
may have given place to the secondarily alecithal egg of the
typical Mammal, giving rise to a foetus developed within
596 ZOOLOGY SECT.
the uterus, and nourished by a complete placenta. Though
palaeontology does not reveal to us the actual reptilian progenitors
of the Mammalia, yet, as already pointed out, there are some of the
Anomodontia (Theriodonta) which have pronounced mammalian
resemblances in skeleton and teeth.
The following diagram may serve as a rough illustration of the
view set forth in the preceding pages :—
MAMMALIA
AVES
AMPHIBIA
TELEOSTOMI \ i
\1 DIPNOI
1/HOLOCEPHALI
V / EXISTING
I/ ELASMOBRANCHII
PRIMITIVE ELASMOBRANCHII
CYCLOSTOMATA OSTRACODERMI
\.
ACRANIA
\
- —
UROCHORDA
HEMICHORDA
FIG. 1249. — Diagram illustrating the Mutual Relationships of the Chordata.
ON THE MUTUAL RELATIONS OF THE PHYLA OF ANIMALS.
It will be advantageous in concluding our survey of the animal
kingdom to sum up with a few remarks as to the phylogeny
of the primary groups or phyla, since that of the sub-divisions
of each phylum has already, in nearly every instance, been
discussed.
It cannot be too strongly emphasised that in the majority of
cases it is useless to seek for the ancestors of any animal among
existing forms. As far as we know, most living species are culmina-
tions— terminal branches of the great tree, not leading directly to
any other form, but connected only at the fork of a branch. It is,
as a rule, only among fossils that actual ancestral forms are to
be looked for ; hence the area of strict phylogenetic investigation
is very limited, and in most instances the only evidence is to be
sought in anatomy and embryology.
Not only are most existing species culminations, and therefor-
xiii PHYLUM CHORDATA 507
off the direct line of ancestry of other species, but, as far as we can
judge, the same is true of most genera and families, of a large
majority of orders and classes, and even of most phyla. It would
certainly seem that existing Chordata, Mollusca, Arthropoda,
Annulata, Echinodermata, Nemathelminthes, and Platyhelminthes
are all independent branches of the animal tree, having no con-
nection with one another save through the trunk.
There are, however, existing groups which seem to represent
actual stages in the existence of others. For instance, it can
hardly be doubted that Amphibia are derived from Fishes and
Birds from Reptiles ; that if we could discover the unknown
ancestors of those classes they would be classed definitely among
Pisces and Reptilia respectively, though probably not belonging to
any known order.
In the same way everything seems to point to the conclusion
that all the higher phyla must have passed through some kind of
ccelenterate stage, and, before that, some kind of protozoan stage,
so that these two phyla may be said to represent actual steps
in the evolution of the higher forms. It is therefore legitimate to
assume, in the absence of direct evidence, that the ancestors of
both the Ccelenterata and the Porifera were unicellular or " non-
cellular " forms, i.e., to be classed among the Protozoa, and that the
ancestors of the nine higher or triploblastic phyla were diploblastic
forms, i.e., to be classed among the Ccelenterata.
Most, if not all, of the triploblastic phyla appear to be terminal
or culminating groups. There is no reason for thinking that either
of the three highest phyla — the Chordata, Mollusca, and Arthropoda
—ever passed through a stage which, if known, would be classed
among Platyhelminthes, Nemathelminthes, Echinodermata, or
Annulata. The wide occurrence of the trochophore, or some
similar larval form, seems, however, to indicate a certain bond of
union. The typical trochophore of Annulata and Mollusca, the
echinopeedium of Echinoderms, the ciliated larva of Molluscoida,
the tornaria of Balanoglossus, and the adult Rotifer present, amid
endless diversity in detail, common characters which, in the absence
of better evidence, may be considered as indications of remote
affinity. The Arthropoda alone among the higher phyla are devoid
of even this slender connection with lower forms : there is no
indication throughout the phylum of anything approaching to a
trochophore ; the crustacean nauplius is quite sui generis ; and the
larval forms of Insects and Arachnids simply suggest a
homonomously segmented ancestor. This suggestion is supported
by Peripatus, the cilia, hollow appendages, nephridia, and ladder-
like nervous system of which seem to point to its derivation
from a segmented " worm " not far removed from the annulate
type.
598
ZOOLOGY
SECT, xm
In accordance with these conclusions the mutual relationships
of the phyla may be expressed in a diagrammatic form as
follows : —
CHORDATA
ARTHROPODA
MOLLUSCA
MOLLUSCOIDA
TROCHELMINTHES
\
NEMATHELMINTHES
PLATYHELMINTHES\\
COELENTERATA
PORIFERA
PROTOZOA
FIG. 1250. — Diagram illustrating the Mutual Relationships of the Phyla.
SECTION XIV
DISTRIBUTION
IN discussing the various groups of animals, the subject of their
geographical and geological distribution has in every case been
referred to, and the reader will already have noticed how strikingly
the different parts of the earth's surface at the present day, and
the different periods of its geological history, differ from one
another in respect of their animal inhabitants. In order to bring
forward the facts of distribution more prominently, the present
section will be devoted to this important subject.
1. GEOGRAPHICAL DISTRIBUTION.
The facts and ideas of which the subject of Geographical Dis-
tribution takes cognisance are clearly brought out by comparing
the fauna of Great Britain with that of the most distant of her
colonies, New Zealand, including, in each case, the adjacent
islands. The two countries are not widely different in size. The
climate of each is temperate, Great Britain extending from about
50° to 60° north latitude, and having a mean annual temperature
of about 48° F., New Zealand extending from about 34° to 48°
south latitude, and having a mean annual temperature of 55°.
Both contain mountainous regions, forests, and arable land. The
climate of both is humid, the rainfall of Great Britain being from
about 25 to 30 inches in flat, 40 to 80 inches or more in mountainous
districts, while the average rainfall for the whole of New Zealand
is about 50 to 55 inches. The physical conditions of the two
countries are thus very similar, the chief differences being the far
higher summer temperature of the northern part of New Zealand,
and the far lower winter temperature of the northern part of
Great Britain.
But when we come to compare the faunae of the two countries
these similarities disappear. In Great Britain there are about
forty species of native land Mammals, including Ungulata (Wild
Cattle, Red Deer, Fallow Deer, &c.), Carnivora (Fox, Badger, Wild
Cat, Stoat, Marten, &c.), Rodentia (Squirrel, Rabbit, Hare, &c.),
599
600 ZOOLOGY SECT.
Insect! vora (Hedgehog, Shrew, and Mole), and fifteen species of
Bats. Moreover, within the historic period, the Wolf, Bear, Wild
Boar, Reindeer, and Beaver were among the wild animals of
Britain.
In New Zealand, on the other hand, the only land Mammals
found in the islands previous to the advent of Europeans were two
species of Bats (Chalinolobus morio and Mystacina tuberculata),
the Maori Dog, which was certainly introduced by the Maories
who colonised New Zealand from some of the Pacific Islands not
many centuries ago, and the Maori Eat (Mus maorum), which
perhaps owes its introduction to the same source. With the excep-
tion, then, of Seals, two Bats, and perhaps a Rat, are the only
native Mammals of New Zealand.
The Birds of the two countries also offer a marked contrast.
Great Britain has no native Ratitse ; in New Zealand there are
now living five species of Apteryx, while within the historic
period — three or four hundred years ago or less — there lived in
the two islands half-a-dozen genera, and some five-and-twenty
species of Moas (Dmornithidee). Great Britain has no Parrots ;
New Zealand has two species of Nestor, seven Parrakeets of the
genus Cyanorhamphus, and the extraordinary Ground Parrot or
Kakapo (Stringops). On the other hand the Finches (Fringillidse)
are wholly absent in New Zealand, but abundantly represented in
Great Britain. Moreover, New Zealand is remarkable for the
large number of flightless Birds included in its fauna : besides
the Kiwis and Moas, there are Stringops (Ground Parrot) ; Ocy-
dromus, Cabalus, and Notornis (Rallidse) ; Nesonetta (the flightless
Duck of the Auckland Islands) ; besides the extinct Giant Goose
(Cnemiornis) and Giant Rail (Aptornis). In Great Britain none
of the Birds are actually flightless.
As to Reptiles, the difference is less striking, but is still suffi-
ciently marked, the most important facts being the entire absence
of Snakes in New Zealand and the presence of Sphenodon, the only
existing representative of the Rhynchocephalia. Lizards occur in
both countries, and in both Crocodilia are wholly absent, and
Chelonia occur only as occasional visitants.
Great Britain possesses four species of Tailed Amphibia (Newts),
and the same number of Frogs and Toads. In New Zealand
Urodeles are entirely absent, and there are only two rare species
of Frogs.
The fresh-water Fishes of Britain are numerous and varied ; the
most important are the various species of Salmo (Salmon and
Trout), the Perch, Carp, Grayling, Pike, Eels, &c. In New Zealand
there are only Eels, a small salmonoid, Retropinna, not found else-
where, several species of Galaxias, an exclusively Australasian,
South African, and South American Physostome, and a small
indigenous genus (Neochanna) of the same family. The differences
xiv DISTRIBUTION 601
between the marine Fishes, though obvious enough, are less
fundamental, a fair proportion of the New Zealand shore-fishes
belonging to the same families, and in some cases even to the
same genera and species, as those of Britain.
Among Mollusca the fresh-water Unio (fresh-water Mussel) is
found in both countries, but New Zealand has no species of the
common genus Helix (Land-snail), abundant in Great Britain, and
its molluscan fauna generally is very peculiar.
The Insect-fauna of New Zealand is remarkable for the paucity
of Butterflies — sixteen species against about seventy in Britain—
and for the abundance of Moths, mostly belonging to the Micro -
lepidoptera and the Geometrina. The occurrence of Peripatus in
New Zealand furnishes another strong point of contrast. Amongst
fresh-water Crustacea, the British Astacus is represented by an
allied genus Paranephrops. Among marine Crustacea many genera
are common to the two countries, but there are numerous
peculiar forms, and it is worthy of mention that the New Zealand
species of Palinurus belongs to a more generalised type than the
British species, having no stridulating organ.
The British Earthworms all belong to the familiar LumbricidcB
(including Lumbricus) and CryptodrilidcB ; in New Zealand both
these families are absent, and the majority of the Earthworms
belong to the Megascolecida3, including the genera Acanthodrilus,
OctocJicetus, &c. Lastly, there are found in New Zealand nearly
forty species of Land Planarians and one terrestrial Nemertean ;
these groups are represented in the land-fauna of Britain only by
one species of the former.
That these striking differences are quite independent of climate,
food, &c.— in other words, that the environment in the one country
is in no way inimical to the fauna of the other — is shown by the
zoological history of New Zealand since its colonisation. Apart
from domestic animals, the Brown Rat (Mus decumanus) and the
House Mouse (Mus domesticus) are now as common in New
Zealand as in Britain ; the Rabbit has become a plague, barely
kept in check by constant effort stimulated by severe legislative
enactments ; Deer flourish as well in the mountains of Otago as
in those of Scotland ; the Birds first noticed by a visitor to the
settled districts of the colony will probably be the Sparrow, Black-
bird, Thrush, Starling, and Goldfinch ; and Trout have become
so thoroughly acclimatised in the streams and lakes, that in some
districts the poorer settlers, like the British apprentices of old,
decline to eat them. We thus learn to distinguish between the
native or indigenous fauna of a country and the introduced fauna
which owes its existence to human agency ; in comparing the
faunae of any two countries, the latter element must of course be
carefully eliminated.
602 ZOOLOGY SECT.
The contrast between our two selected countries is further
emphasised when we compare the fauna of each with that of the
nearest continental area — the fauna of Great Britain with that of
the Continent of Europe, the fauna of New Zealand with that of
Australia.
With the exception of the Red Grouse (Lagopus scoticus), perhaps
the Coal Tit (Parus britannicus), and the Long-tailed Tit (Parus
rosea), and some fifteen species of fresh-water Fishes, the British
Vertebrates are all found on the European continent. On the
other hand, there are many European species of Mammals, Birds,
Reptiles, Amphibians, and Fishes which do not occur in Great Britain.
The British fauna may, in fact, be described as an isolated and
somewhat impoverished section of the general European fauna.
Now contrast New Zealand with Australia. Of the two New
Zealand Bats, one (Chalinolobus mono) occurs also in Australia ; the
other (Myslacina tuberculata) is endemic, that is, found nowhere
else. Australia, instead of having a Mammalian fauna com-
prising only two Bats and a doubtful Rat, possesses a large
number of characteristic Mammals, all except the Bats, Rats, and
Mice, and the Dingo (Canis dingo), being either Monotremes or
Marsupials. Out of about 200 species of New Zealand Birds,
fully 100 are endemic ; of the rest only about 50 are found in
Australia. Conversely Australia has a large number of charac-
teristic Birds, belonging to families wholly unrepresented in
New Zealand, such as the Birds of Paradise and Bower Birds (Para-
diseidce), Cockatoos (Cacatuidce), Mound-makers (Megapodiidce),
the Lyre-Bird (Menurci), the Emu, and the Cassowary. Among Rep-
tiles, Sphenodon, i.e., the entire order Rhynchocephalia, is endemic
in New Zealand, as also is the little Gecko Naultinus, while a
small genus of Lizards, Lyyosoma, is common to the two countries.
Australia, on the other hand, besides possessing a large number of
Lizards, such as the Monitors, is remarkable for the great number
of its Snakes, a group quite unrepresented in New Zealand, and
has two species of Crocodiles and several of Chelonia. Among
Fishes, the presence of Ceratodus in Australia is specially
remarkable. The fresh-water Crayfishes of each country are
endemic, those of New Zealand belonging to the genus Paranephrops,
those of Australia to Astacopsis, Cheraps, and Engceus. The
majority of the Australian Earthworms belong to the families
Perichcetidce and Cryptodrilidce, the latter including the Giant
Earthworm of Gippsland (Megascolides) ; the Megascolecidse are
represented, but are not dominant, as in New Zealand.
Thus, while the zoological resemblances between Great Britain
and the Continent of Europe are so close as almost to amount to
identity, there is more difference, zoologically speaking, between
New Zealand and Australia than between Europe and North
America, or between England and Japan.
xrv
DISTRIBUTION
603
The reason of this remarkable contrast is not far to seek.
Geologically speaking, Great Britain is a recently detached portion
of Europe, having been united with it during the latter part of
the Glacial period (Pleistocene), and, at the present moment, an
elevation of the bed of the English Channel to the amount of
feet would bring about a re-union (Fig. 1251). Prior to this
i\o
65
50
1(0
FlQ. 1251. — Map showing the shallow bank connecting the British Isles with
the continent. The light shade indicates a depth of less than 100 fathoms ;
the figures show the depth in fathoms. (From Wallace.)
union, moreover, it was largely submerged, so as to leave no trace
of its Pliocene fauna. Thus, the British animals are all migrants
from Europe, isolated by the post-glacial separation from Europe,
and the absence of certain European forms is due to the fact that
the separation took place too early to allow of complete migration.
New Zealand, on the other hand, instead of being separated from
604
ZOOLOGY
SECT-
the nearest continent by 21 miles of shallow sea, is divided from
Australia by 1,000 miles of ocean — the Tasman Sea — varying
from 2,000 to 2,600 fathoms (12,000-15,600 feet) in depth. It is
almost certain that there was never any direct connection between
the two countries, and the only indication of even an indirect
connection is afforded by the existence of an area of comparatively
shallow sea — i.e., under 1,000 fathoms — stretching between the
North Island of New Zealand on the one hand and Northern
Australia and New Guinea on the other (Fig. 1252). It would
take, therefore, an upheaval of over 6,000 feet to join the two
countries, and it may be taken as certain that if there ever was a
120 ||30 1140 ISO |!60 |I70 180
10
ISO
FIG. 1252. — Map showing depths of sea around Australia and New Zealand. The light
shade indicates a depth of less than 1,000 fathoms ; the dark shade indicates a
depth of more than 1,000 fathoms. (From Wallace.)
direct connection, either by continuous land or by a chain of
islands, such connection could not have been later than the early
part of the Mesozoic era.
It must also be noted that while the British fauna is related
exclusively to that of Europe, the New Zealand fauna presents not
only Australian but also Polynesian and South American affinities.
Some of the Birds are represented by the same or closely allied
species in New Caledonia, while the land Molluscs and Insects,
the Fresh-water Lamprey (Geolria), and the Earthworms, show
South American affinities. In this connection it is interesting
to find that there is a submerged bank of less depth than
the surrounding ocean — under 2,000 fathoms— passing west-
xiv DISTRIBUTION 605
wards from South America, and including many of the Pacific
Islands ; and an area, also of less than 2,000 fathoms,
in the Antarctic Ocean, sending offshoots northwards. The first
of these may possibly indicate a former westward extension of
South America, the second a former Antarctic land-area, perhaps
more or less directly connected with the existing southern conti-
nents. The whole question is quite unsettled and extremely
obscure, and is complicated by the fact that in one respect the
New Zealand fauna shows Ethiopian affinities. There have been
discovered in the Chatham Islands, a small group about 400
miles to the east of New Zealand, the remains of a long-beaked
Rail (Diaphorapteryx), evidently not long extinct, the nearest ally
of which is the Red Bird (ApJianapteryx) of Mauritius, known to
have been exterminated by human agency. Moreover, the great
Ratite Birds, the ^pyomithidae, of Madagascar show undoubted
affinities with the Dinornithidse.
The foregoing comparison of the faunse of Great Britain and
New Zealand leads us to the consideration of certain fundamental
conceptions of zoo-geography.
Insular Faunae. — We notice, in the first place, the striking
contrast between the fauna of an island which has been recently
detached from a great continental area and that of an island
which has remained isolated for an immense and unknown period.
In the one case the fauna has a strictly continental character,
there having been insufficient time for modification since the
separation took place. In the other case immigration has taken
place from various sources over a vast period of time, during which
modification has taken place to a sufficient extent to give rise to
new or endemic species.
Habitat, Range, and Station. — Each kind of animal has, as
a rule, its own habitat, fresh-water in one case, the sea between
tide-marks in another, marsh, forest, snow-clad peaks, and so on.
A similar habitat may characterise whole genera and even orders.
Keeping always to its own habitat, the range of an animal may
extend over a vast area. The marsh-loving Curlew, for instance,
is found all over the world ; the Cormorants (Phalacrocorax), Gulls
(Larus), some Ducks (Anas), &c., are also cosmopolitan or world-
wide in distribution. On the other hand, the range of a species,
genus, or order may be restricted to a single limited district. The
genus Liopelma (New Zealand Frog) is found only in certain
very limited areas ; the species Salmo killinensis (Loch
Killin Char) occurs only in Loch Killin in Inverness-shire ; the
Order Rhynchocephalia is confined to New Zealand. The entire
range may be broken up, as it were, into a number of stations,
depending sometimes on habitat, sometimes on unknown causes ;
the Tuatara, for instance, is found at present only in some half-
VOL. II P P
606 ZOOLOGY SECT.
dozen small islets, each of which is a station, while the whole of
them constitute the range of the species.
Barriers. — A barrier in zoo-geography implies any permanent
obstacle to the dispersal of a species. For instance, the Tasman
Sea is an impassable barrier to the passage of most animals be-
tween Australia and New Zealand, strong-flying birds being the
only species able to cross it. On the other hand, the number of
Birds able to pass so narrow a strait as the British Channel is very
considerable, while still narrower arms of the sea may be crossed
by a large proportion of Mammals, Insects, &c. Thus barriers are
of unequal importance according to the particular animals under
discussion ; wide deserts and lofty snow-covered mountain ranges
are impassable to most species ; to some even a narrow river or arm
of the sea is insuperable.
Means of Dispersal. — Most Mammals and many Reptiles can
swim across rivers and arms of the sea if not too broad ; thus
narrow straits and rivers are of no significance as barriers to the
dispersal of many animals. On the other hand, rivers of even
moderate breadth are insuperable barriers to Monkeys, which are
unable to swim.
Aerial animals can overcome many of the barriers impassable to
flightless forms. Birds of strong flight often pass over immense
stretches of ocean. For instance, a Cuckoo (Eu&ynamis taitensis)
habitually winters in Fiji and other Pacific islands, and spends
its summer in New Zealand, traversing the enormous distance
of 1,500 miles twice a year. Many Insects also are able to fly
great distances, especially when carried by gales.
Mechanical dispersal is an important factor in the case of many
animals. Small Crustacea and Molluscs may be carried great
distances in the mud adhering to the feet of Birds. Infusoria, the
eggs of Rotifers, and other microscopic forms may be transported
in the dried condition by wind. Birds and Insects are frequently
blown out to sea and carried for immense distances, and Mammals,
Reptiles, &c., may be widely distributed by being carried on drift-
wood, or on floating islands or " rafts " formed of large masses of
matted vegetation, such as are often detached by storms in the
tropics. Finally, the dispersal of many fixed or shore-haunting
animals is ensured by their free-swimming larvae.
Importance of the various Groups of Animals in Zoo-
Geography. — In close dependence on the means of dispersal we
have the fact that the various groups of animals are of very
unequal value in the study of distribution. The greater the
facilities for the transport of any species across a given barrier,
the less significance will attach to its occurrence on both sides of the
barrier. Conversely, when a species, having few or no facilities for
dispersal, is found on opposite sides of an important barrier, the
natural conclusion is either that the barrier is of comparatively
xiv DISTRIBUTION 607
recent formation, and that the two areas separated by it were once,
so to speak, in zoological continuity, or that the species in question
is a very ancient one, and was widely dispersed at a time when the
arrangement of the land-surface was very different from what it is
at the present day. For instance, the occurrence of strong-flying
Birds, such as Gulls and Cormorants, in widely separated countries
is a fact of no significance in determining the mutual relationships
of the faunse of those countries. But the occurrence of the same
species of Fresh-water Crayfish — to which the narrowest arm of
the sea is an insuperable barrier — in Great Britain and the
European Continent is explained only by the fact— of which
there is independent evidence — that the English Channel is of
recent formation. And when we find the various species of
Peripatus dotted over the earth's surface in an apparently casual
manner, we are forced to the conclusion that this genus must
formerly have been very widely and continuously distributed and
subsequently exterminated over the greater part of its range ;
since it is hardly possible to conceive of either the adult or the
young of this creature, living in rotten wood in the recesses of the
forest, having been transported between Australia and New
Zealand, or between Africa and the West Indies.
Speaking generally, then, it may be said that discontinuity in
the distribution of a species or other group is evidence of its
antiquity. In addition to Peripatus, the Dipnoi and the Tapirs
may be mentioned as examples.
It will be seen that terrestrial and fresh-water animals are of
more importance, from the point of view of zoo-geography, than
marine forms. Among the inhabitants of the sea, littoral species
are of greater significance than pelagic or abyssal. Amongst
land animals, those which are unable to swim, and those which
cannot survive immersion in salt water, are of more importance
than strong swimmers, or than such forms as are able to live for
a prolonged period on driftwood, or in mud attached to the feet
of Birds.
In connection with what has been said above about there being
no special significance to be attached to the distribution of certain
strong-flying Birds, it must be remarked that this is by no means
true of migratory Birds. Many British Birds, such as the Swallow,
Cuckoo, Swift, &c., spend the summer in England, the winter in
South Europe or Africa. One of the New Zealand Cuckoos winters
in Australia, the others in Fiji or some other Pacific islands. Birds
capable of such feats of flight might, one would think, soon
overspread the globe ; yet, as a matter of fact, each species is
found to keep strictly to its own definite line of migration, even
across 1,000-1,500 miles of sea.
Having now indicated the general character of the facts and
problems connected with the subject of zoo-geography, we may
p p 2
608 ZOOLOGY SECT.
proceed to give some account of the Zoo-geographical Regions
into which the land-surface of the earth is divided (see Fig. 1253).
It must be borne in mind that the determination of these
regions depends largely upon the classes of animals upon which
stress is laid, the peopling of any given portion of the earth by a
particular class depending upon the time during which it has been
in existence and its means of dispersal. Thus regions founded upon
the distribution of Mollusca will differ from those depending on
Reptiles or on Birds. The regions adopted here, are mainly
founded on the distribution of Birds and Mammals.
The whole of Europe, Africa, and Arabia north of the Tropic of
Cancer, and the whole of Asia except India, Burmah, Siam, and
South-East China, together with Japan, Iceland, the Azores, and
the Cape de Verde Islands, are so similar in their animal pro-
ductions as to form a single division of the earth's surface called
the Palaearctic Region. This region is bounded on the north,
west, and east by ocean, but its southern limits are at first sight
less obvious. It appears strange, for instance, that Northern Africa
and Arabia should be included in this region, the Mediterranean
being, as it were, ignored as a boundary. But the facts show that
the great line of sandy deserts in the region of the Tropic of
Cancer, the Sahara in Africa, and Roba el Khali in Arabia, form a
far more efficient barrier to the dispersal of species than the
Mediterranean, and it is probable that there- was direct land
connection between Europe and North Africa during the
Pleistocene period. In Asia the Himalayas form an effective
barrier, which has existed since Tertiary times, between Thibet and
India ; an ill-defined line of country following the course of the Indus
continues the boundary south-west to the shores of the Arabian
Sea ; and another ill-defined area passing south of the Yang-tse-
Kiang, and travelling northward to Shanghai, constitutes the
eastern end of the southern boundary of the region.
None of the larger groups of animals, no orders or even families,
are absolutely confined to this region, the characteristics of which
it is difficult to define without descending to genera and species.
The Moles (Talpidce), Sheep and Goats (Ovidce), and Dormice, the
Pheasants, Robins, Magpies, and many other Birds, are highly
characteristic, and many species of Deer, Oxen, and Antelopes,
Rodents, Passerines and other Birds, Reptiles, Amphibians — in-
cluding Proteus — and fresh-water Fishes, are endemic.
The Palsearctic region includes, as we have seen, nearly all the
northern portion of the eastern hemisphere ; the corresponding
part of the western hemisphere, viz., North America, with Green-
land, constitutes the Nearctic Region. It also is bounded by
the ocean on its northern, eastern, and western sides, while in the
south an ill-defined tract of country, passing between Cape San
XTV DISTRIBUTION 609
Lucas on the west and the Rio Grande del Norte on the east,
separates it" from the Neotropical region.
The Nearctic differs from the Palsearctic region in the possession
of several characteristic Mammals, such as Opossums (Diddphyidce),
the Skunk, Racoon, &c. ; many Birds, such as the Blue-jays,
and Turkey-buzzards, &c. ; Reptiles, such as Rattlesnakes and
Iguanas ; Amphibians, including the Axolotl, Necturus, Siren, and
other large Urodeles ; and numerous fresh-water Fishes, including
Amia, Lepidosteus, Polyodon, and Scaphirhynchus. Only three
entire families are endemic, two of Rodents, and one of Passerines.
On the other hand, the resemblances between the two northern
regions are very close. Both possess Wild Cats, Hyaenas, Foxes,
Weasels, Bears, Elk, Deer, Wild Oxen, Beavers, Voles, Squirrels,
Marmots, and Hares, the species of the one region being all closely
allied to, and sometimes identical with, those of the other. Thrushes,
Wrens, Tits, and Finches are also common to the two regions, and,
generally speaking, the differences between them are, as we shall see,
nothing like so striking as those between either of them and the
region or regions bounding it to the south. Hence the Palsearctic
and Nearctic regions are sometimes grouped together as a single
Holarctic Region.
In the southern regions the characteristic features are much
more striking. The Ethiopian Region is constituted by the
whole of Africa and Arabia south of the Tropic of Cancer, together
with Madagascar, Mauritius, Bourbon, Rodriguez, and the
Seychelles. The region is bounded by sea on the west, south,
and east, but on the north it is perfectly continuous with the
Palsearctic region, and it certainly seems a very remarkable fact,
until we remember what an impassable barrier is afforded by a
sandy desert of great extent, that there should be more difference
between the faunse of northern and central Africa than between
those of England and Japan, or of Alaska and Florida.
Among the animals most characteristic of the Ethiopian region
and not found elsewhere are the Gorilla, the Chimpanzee, several
Baboons, and the large majority of Lemurs, including the curious
Aye-aye (Chiromys) ; several peculiar Insectivora, such as the
Golden Moles (Chrysochloridce), and the River Shrew (Pota-
mogale) ; the African Elephant, the Hippopotamus, two or three
species of Rhinoceros, the Zebras and Quaggas, the Giraffe and
Okapi, and more than seventy species of Antelopes ; the
Aardvark (Orycteropus), one of the most singular types of
Edentata ; the Plantain-eaters (MusiphagidcB), the Secretary
Bird (Serpentarius), and many other families and genera of
Birds ; numerous snakes and other Reptiles, and several fresh-
water Fishes, including the Dipnoan Protopterus, and the Ganoid
Polypterus. The Lion, Leopard, and Ostrich are also characteristic,
610 ZOOLOGY SECT.
although not actually endemic, since the two former extend
into the Palaearctic and Oriental regions, while the Ostrich
occurs in Arabia and Syria. Almost equally remarkable are the
negative peculiarities of the region, and especially the absence
of Bears, Deer, and Oxen, and the extreme paucity of Goats,
Sheep, true Pigs (Sus), and Shrews.
The great island of Madagascar is characterised by the immense
number of Lemurs, the absence of Monkeys, and the poverty
of its carnivorous and ungulate fauna, the Lions, Antelopes, &c.,
of the African continent being all absent. Most of its Mammals
are endemic, only three t>ut of twenty-eight (including Bats) being
found in Africa. The Birds, also, are quite different from those of
the African continent. It shows affinities with America in the
presence of a peculiar family of Insectivora (Centetidce), otherwise
found only in the West Indies, and of certain Snakes ; and its
relationships with India are so marked that it has been proposed
to account for them by assuming the former existence of a
land connection, in Jurassic and Cretaceous times, extending north-
eastward across the Indian Ocean and represented at the present
day by the Seychelles and other neighbouring islands. In the
opinion of some authorities these peculiarities entitle Madagascar and
the adjacent islands to rank as a distinct zoo-geographical region.
The Oriental Region consists of India, Burmah, Siam, south-
eastern China, and certain islands of the East Indian Archipelago,
including Sumatra, Java, Borneo, and the Philippines. As we
have seen, it is separated from the Palaearctic region by the
Himalayas, continued on the west by a tract of country following
the course of the Indus, and on the east by a region curving at
first southwards and finally northwards to Shanghai. The south-
eastern boundary is an imaginary line, known as Wallace's line,
which passes between the small islands of Bali and Lombok, then
through the Straits of Macassar, between Borneo and Celebes, and
finally to the east of the Philippines. The islands to the north-
west of this line— conveniently distinguished as the Indo- Malayan
Islands — belong to the Oriental region, those to the south-east—
the Austro-Malayan Islands — to the Australian region. Curiously
enough, the zoological differences between the two groups of
islands are more marked between Bali and Lombok, separated
by a deep channel of only about twenty miles in width, than
between Borneo and Celebes, separated by the whole width of the
Straits of Macassar.
The most characteristic members of the Oriental fauna are the
Orang-utan (Simia), the Gibbons (Hylolates and Siamanga), and
numerous Lemurs ; the Tiger, which, however, extends into the
Palsearctic region, and several Bears and Civets ; the Indian
Elephant, the Indian Tapir, three species of Rhinoceros, and the
xiv DISTRIBUTION 611
Chevrotains or Mouse-deer (Tragulidce) ; and several large and
handsome Gallinaceous Birds, such as the Peacock, Argus
Pheasant, and Jungle-fowl. The resemblances to the Ethiopian
Kegion are numerous and striking, among the most important
being the presence of the Elephant, Rhinoceros, the higher Apes,
Lemurs, and Manis. On the other hand, the presence of Deer and
Bears furnishes a characteristic difference.
The Australian Region includes Australia, Tasmania, and the
Austro-Malayan Islands as defined above, from Celebes and
Lombok on the west to the Solomon Islands on the east, the
most important of them being the immense island of Papua or
New Guinea. New Zealand and Polynesia are very generally
included in this region, but it is more convenient, on the whole,
to treat them apart.
The most striking feature of the region is the almost total
absence of Eutheria, the Mammalian fauna belonging mainly to
the Marsupials and Monotremes. The last-named order is en-
tirely confined to this region, while Marsupials occur elsewhere
only in America. The only exceptions are the Dingo or Aus-
tralian Wild Dog, which is probably indigenous, the universally
distributed groups of Rats, Mice, and Bats, and, in some
of the islands bordering on the Oriental region, Deer, Civets,
and Pigs. The abundance of Marsupials is very remarkable, all
the leading groups of that sub-class, with the exception of
the Didelphyidae, or American Opossums, and Ccenolestes, being
strictly endemic.
Equally striking is the number and peculiarity of the endemic
Birds, the most important of which are the Emus and Cassowaries,
the Mound-makers or Brush Turkeys (Talegallus, &c.), the Birds
of Paradise and Bower-birds, the Lyre-bird (Menura), the Cockatoos
and Brush-tongued Lories. The great number and variety of
Parrots, Kingfishers, and Pigeons is also a marked feature, as also
is the absence of Pheasants, Woodpeckers, Finches, and other
Birds abundant in the Oriental region. Snakes, Lizards, and
Frogs are abundant, and in the rivers of Queensland occurs
Ceratodus, one of the three existing genera of Dipnoi.
The New Zealand Region comprises the three islands of
New Zealand (North, South, and Stewart's Islands), together with
Norfolk, Lord Howe, and the Kermadec Islands to the north, the
Chatham Islands to the east, and the Bounty, Antipodes, Auckland,
Campbell, and Macquarie Islands to the south.
The characteristics of the New Zealand fauna have already been
dealt with in some detail. The total absence of land Mammals,
with the exception of two Bats and a Rat, the latter probably
introduced ; the large proportion of endemic Birds, many of
612 ZOOLOGY SECT.
which are flightless ; the exclusive possession of more than half
the known genera, and of a large majority of the species of Ratitse,
and of the entire order Rhynchocephalia ; the total absence of
Ophidia, Chelonia, and Crocodilia ; the paucity of Lacertilia and
the almost total absence of Amphibia ; all these faunal characters
combine to make New Zealand one of the best marked and most
peculiar tracts on the earth's surface.
One or two facts must be mentioned with regard to the smaller
islands of the region. In Norfolk Island there existed until
recently a flightless Rail, Notornis alba, belonging to a genus the
only other species of which lives or lived in New Zealand. In
Phillip Island, close to Norfolk Island, Nestor productus formerly
occurred, a member of an endemic New Zealand family of Parrots.
In Lord Howe Island there is a species of the endemic New
Zealand flightless Rail Ocydromus. These three facts all point to
a former partial or complete land connection between New Zealand
and the islands in question. The remaining islands are closely
related to New Zealand, but with greatly impoverished faunae.
In Macquarie Island, the southernmost land outside the Antarctic
circle, there has recently been discovered an Earthworm with
distinct South American affinities.
The Polynesian Region embraces the numerous groups of
islands lying within the tropics to the east and north of the
Austro-Malayan Islands. The most important groups are New
Caledonia, the New Hebrides, Fiji, the Friendly Islands, Samoa,
the Society Islands, and the Sandwich Islands. They are all
typical oceanic islands, that is, they are of volcanic origin, have no
stratified rocks, and show no indication of former connection with
any continental area.
In correspondence with their isolated position, the faunae of
these islands, although exhibiting great variety from one group to
another, all agree in the absence of Land Mammals, except Bats,
and — with one or two exceptions — of Amphibians, in the small
total number of species, and in the very large proportion of endemic
species. The islands have evidently been peopled by waifs and
strays from other lands, at periods so remote that most of the
immigrants have assumed the character of distinct species, or even,
especially in the isolated Sandwich Islands, of distinct genera.
On the whole, the affinities of the Polynesian fauna are dis-
tinctly Australian ; they present, however, certain American char-
acteristics, especially in the occurrence of Lizards, belonging to the
American family of the Iguanidse, in Fiji. Amongst the most
notable endemic forms are the Dodo-like Pigeon, Didunculus, in
Samoa ; the Kagu (Rhinochetus), a remarkable genus of Grallae, in
New Caledonia, and the Drepanidce, a family of Passerines allied
to the American Greenlets, in the Sandwich Islands. Polynesia
xiv DISTRIBUTION 613
cannot be said to form a well-defined region, the islands composing
it being united largely on the ground of convenience.
In the Neotropical Region we have once more an immense
tract of land, presenting such well-defined fauna! characteristics as
make it one of the best-marked of all the zoo-geographical regions.
And this in spite of the fact that it is in free connection with the
Nearctic region, the two being separated by an ill-defined tran-
sition-region formed by the northern part of Mexico. The Neo-
tropical region includes, therefore, the tropical part of North
America, as well as the whole South American Continent, the
Antilles or West Indies, the Galapagos Islands, the Falkland
Islands, and Juan Fernandez. Both geological and zoological
evidence points to a complete separation of the two Americas
during the Miocene and Pliocene periods.
The endemic animals of the region are very numerous and
characteristic. They include, among Mammalia, the Prehensile-
tailed Monkeys (Cebidce) and the Marmosets (HapalidcB) ; the Chin-
chillas and Cavies, two peculiar families of Rodents ; the Jaguar ;
the Llamas and Peccaries, and a species of Tapir ; the Sloths,
Armadillos and Ant-eaters — three entire families of Edentata.
The Opossums (Didelphyidas) are also very characteristic, though
not actually endemic, since they extend into the Nearctic region.
A single additional Marsupial (Ccenolestes) of uncertain affinities
has been found in the extreme south. Among Birds the chief
endemic forms are the three species of Rhea, constituting the entire
order Rheae ; the Tinarnous, forming the order Crypturi ; the
Toucans, Screamers, Oil-bird (Steatornis), Hoatzin (Opisthocomus),
and many others. The Humming-birds, although extending into
the Nearctic Region, are a characteristic group. Boas, Rattle-
snakes, Iguanas, Crocodiles, and Caimans are abundant, and among
the fresh-water Fish are the Electric Eel (Gymnotus), and Lepido-
siren, one of the three existing genera of Dipnoi.
The negative characteristics of this region are also very remark-
able. Except in Central America and the West Indies, there are
no Insectivora ; Civets, Oxen, Sheep, Antelopes, and true Swine
(Suince) are altogether absent, and there are very few species of
Deer ; Crows and Ravens are also practically unrepresented.
In the West Indies there are no Edentata, Monkeys, or Car-
nivora, and there occurs a peculiar Insectivore, Solenodon,
belonging to the Centetidaa, otherwise found only in Madagascar.
The Galapagos Archipelago, a group of oceanic islands, about 600
miles to the west of the continent, has at the most two Mammals,
a Bat and a Mouse ; its Birds are very different from those of
the mainland, and include many endemic species ; and among the
Reptiles are the gigantic Tortoises (Testudo), of which different
species occur in the various islands.
614
ZOOLOGY
SECT.
The general relations of the zoo-geographical regions may be
expressed in a diagrammatic form as follows : — -
PALAEARCTI C
ORIENTAL
N E A R C T I C
POLYNESIAN
ETHIOPIAN
AUSTRALIAN NEW ZEALAND -NEOTROPICAL
1'IG. 1253. — Diagram showing the general relations of the zoo-geographical regions.
2. BATHYMETRICAL DISTRIBUTION.
The foregoing pages have given a brief sketch of the facts
connected with geographical or horizontal distribution. We now
turn to bathymetrical or vertical distribution — the facts concerning
the distribution of animals at various depths of the sea or of
lakes, and at various heights of the land.
The region of greatest abundance of marine life, as regards
both the number of genera and species and of individuals, is the
littoral or shore-region. The rocks left dry by the retreating
tide, the rock-pools exposed at low water, and the forests of kelp
at the limit of low tide or a few fathoms below possess an extra-
ordinarily rich and abundant fauna, including all the Calcareous
Sponges and a large proportion of the remaining groups, Hydroid
Zoophytes, Sea-anemones and Corals, Echinodermata, Turbellaria,
Nemertinea, Polychaeta, Polyzoa, Brachiopoda, decapod Crustacea,
Pelecypoda, Gastropoda, Octopoda, and Teleostei. Numerous
examples of other groups — Protozoa, the lower Crustacea, Insecta,
and Elasmobranchii — are also littoral, and Penguins, Seals, and
Sirenia may be included in the list.
Next in abundance to the littoral is the pelagic or ocean-
surface fauna, including animals which live habitually on the
surface or at slight depths of the ocean, often far from land.
Amongst them are many Foraminifera, such as Globigerina and
Hastigerina, the Radiolaria, the Siphonophora, the majority of
Medusaa, both hydrozoan and scyphozoan, nearly the whole class
of Ctenophora, many Entomostraca and Schizopoda, the hemi-
pterous Insect Halobates, the Pteropoda, Heteropoda, and some
other Gastropods, such as Glaucus, most Cephalopods, Pyrosoma
and the Salps, numerous Teleosts, such as Herrings, Flying-fish,
Mackerel, &c., the greater number of Sharks, and the majority of
Cetacea.
xiv DISTRIBUTION 615
The pelagic Invertebrates are mostly distinguished by great
transparency, and by being either colourless or of a blue or violet
hue. Pelagic Fishes are usually grey or steel-blue above, white
beneath, presenting none of the brilliant colours, varied mark-
ings, and extraordinary forms so often found among Shore-fishes.
It must be remembered that many littoral animals are pelagic
in the larval condition, or during some phase of their life-history,
e.g., many Sponges, fixed Hydrozoa and Actinozoa, Echinodermata,
Annulata, Mollusca, Crustacea, and Fishes.
The abyssal or deep-sea fauna is far more abundant than
might be supposed from the physical conditions — immense pres-
sure and absence of light and of vegetation. In most parts of the
world the bed of the ocean, at depths from 400 to 2,000-2,500
fathoms, is formed of a greyish mud called globigcrina-ooze, con-
sisting largely of the shells of Foraminifera, such as Globigerina,
Orbulina, &c., which have for the most part sunk to the bottom
after death. Below 2,500 fathoms the sea-bottom is formed of a
red clay, in which shells are absent, having apparently been
dissolved during their descent to the greater depth.
Living on the sea-bottom, and most abundant on the globigerina-
ooze, are representatives of many groups of animals : Sponges,
especially Hexactinellida ; a few Medusa3 and Corals ; examples
of all classes of Echinoderms, Stalked Crinoids and Holothurians
being especially abundant ; Crustaceans, particularly Schizopods
and Prawns ; and Teleosts. Crabs, Molluscs, and Annulates
are rare.
Many abyssal animals are blind, including several of the
Crustacea ; many others are phosphorescent, and thus supply their
own light in an otherwise dark environment. The deep-sea
Teleosts are often of very grotesque appearance, with immense
heads, wide mouths furnished with long, pointed teeth, extremely
distensible stomachs, and phosphorescent organs arranged in rows
along the body (see Fig. 894). Other forms, such as the Ribbon-
fish (Regalecus), attain a great size, and are toothless. When
brought to the surface, the expansion of the gases in the interior
of the deep-sea Teleosts often bursts the air-bladder, and produces
a general disintegration of the tissues.
Plankton, Nekton, and Benthos. — Besides being arranged
with regard to their relations to the shore, the surface of the
ocean, and its bed, marine animals are also conveniently classified
on the basis of their capacity for movement. Many forms, such
as Medusae, Siphonophora, Ctenophora, Salps, and numerous
pelagic larvae are carried along passively by oceanic currents, their
own powers of progression being of the feeblest. Such animals
together constitute the Plankton, or " drif ting-fauna." Others
swim actively by means of fins or other appendages, such as the
pelagic Teleosts and Elasmobranchs, Schizopods, Prawns, and
616 ZOOLOGY SECT.
Squids — they form the Nekton, or " swimming-fauna." Others,
again, have no natatory organs, and are either permanently fixed,
like Zoophytes and Stalked Crinoids; or move by creeping over
the sea-bottom, like Starfishes, Holothurians, Chaetopods, &c.,;
such forms constitute the Benthos, or " bottom-fauna."
The Fresh-water Fauna presents certain characteristic
features, and is divisible into fiuviatile forms, inhabiting streams
and rivers, and lacustrine forms, inhabiting lakes. It is very rich
in Lobosa, Heliozoa, Flagellata, and Infusoria, but contains very
few Foraminifera and no Radiolaria. Among Sponges there is
only a single fresh-water family, the Spongillidae : among Hydrozoa
only four genera, Hydra, Cordylophora, Limnocodium, and Limno-
cnida ; and among Actinozoa and Ctenophora not a single species.
There are also no fresh-water Echinoderms or Brachiopods, but
many Turbellaria, a few Nemertinea, and numerous Nematoda.
Among Polyzoa one genus of Endoprocta, the whole of the
Phylactolsemata, and one or two genera of Gymnolaemata are
fresh- water forms ; so also are many of the Oligocha3ta, e.g., Nais
and Tubifex, but very few Polychaeta. Fresh-water Entomostraca
are numerous and abundant, and belong to all orders except
Cirripedia ; among Malacostraca there are only some Amphipods
and Isopods, Anaspides and its allies, and Fresh-water Shrimps,
the various genera of Fresh- water Crayfishes, and a few Crabs.
The larvae of many Insects are aquatic, and there are several
aquatic Spiders. Pelecypods and Gastropods furnish abundant
fluviatile and lacustrine forms, although belonging to comparatively
few genera ; Cephalopods, on the other hand, are wholly absent
from fresh waters, as also are the Tunicata. Among Fishes there
are several species of Lampreys, and numerous Teleosts, the
Siluroids and Salmonidae being especially characteristic. There
are no fresh-water Elasmobranchs, with the exception of one or
two genera of Sting-Rays in the rivers of tropical America ; but
the Ganoids are a characteristic fresh-water group, although some
forms, such as the Sturgeons, migrate to the sea at certain seasons.
The Dipnoi are exclusively fluviatile, or live in swamps caused by
river overflow, and the perennibranchiate Amphibia, as well as the
larvae of the caducibranchiate forms, are characteristic members of
the fresh-water fauna. Many Chelonians and Crocodiles, such
Birds as Ducks and Grebes, and such Mammals as Otters, the
Hippopotamus, and Ornithorhynchus, may also be included in the
fresh-water fauna, and some Dolphins are purely fluviatile.
The animal inhabitants of large lakes, like those of the sea, are
divisible into littoral, pelagic, and deep-water forms : the pelagic
forms are, in this case also, characterised by their extreme
transparency. Mention must also be made of animals dwelling in
deep subterranean caves, shut off from sunlight, such as Proteus,
xiv DISTRIBUTION 617
the blind Urodele of the caves of Carniola, the blind Fish
(Amblyopsis spebceus) of the Mammoth caves of Kentucky, numerous
Insects, &c. These, like abyssal species, are blind, and usually
colourless, and are obviously specialised derivatives of the ordinary
fresh-water or land fauna.
In the Terrestrial Fauna, also, we find certain groups pre-
ponderant, others absent or nearly so. A terrestrial Amoeba has
been described, and the Mycetozoa are all terrestrial, but no other
Protozoa, nor any Sponges, Coelentrates, or Echinoderms. Among
Platyhelminthes we have the numerous species of Land-Planarians
and the Land-Nemertines, and among Chsetopods nearly the
whole of the Earthworms. Several Crustacea are more or less
completely adapted to terrestrial life, such as the Woodlice, Land-
crabs, Cocoa-nut Crab, and Burrowing Crayfish. The Onychophora
and Myriapoda are characteristic land-animals, so also are most
Arachnida and many Insects. Among the Mollusca the only
terrestrial forms are the majority of pulmonate Gastropoda. Among
Fishes the Climbing Perch, Periophthalmus, and some others are
imperfectly adapted to life on land, and the Caducibranch Urodeles,
the Anura, and the Gymnophiona are all terrestrial or semi-
terrestrial. The Lacertilia, Sphenodon, the majority of Snakes,
and the Tortoises are land-animals, and so also are many Birds,
including all the Ratitse, the Crypturi, Gallinse, &c., and the vast
majority of Mammals.
Among terrestrial animals, those which habitually live on the
open ground must be distinguished from arboreal forms, such
as Tree-Kangaroos, Sloths, and Monkeys, which pass their lives
among the branches of trees, and from cryptozoic forms, which
live under stones, logs of wood, &c., such as Land-Planarians,
Peripatus, Centipedes, and Woodlice.
Lastly, we have the Aerial Fauna, including animals capable
of sustaining themselves for an indefinite period in the air, such
as most Insects, the large majority of Birds, and Bats. The
Flying Fishes, Flying Dragons (Draco), Flying Phalangers, Flying
Squirrels, and Flying Lemur (Galeopithecus) are semi-aerial.
The majority of land-animals live at or near the sea-level, and
as we ascend mountains the fauna undergoes a gradual impoverish-
ment as the snow-line is approached. The higher ranges of all great
mountains have a characteristic Alpine Fauna. In the European
Alps, the Chamois (Rupicapra), Alpine Hare (Lepus variabilis),
and Marmot (Arctomys marmot] may be specially mentioned ; in
the Himalayas, Yaks (Poephagus), Musk-deer (Moschus), Goats
and Ibexes (Capra), besides abundant Birds and Insects ; in the
Andes, the Condor (SarcorJiamphus) ; in the New Zealand Alps,
the rapacious Kea or Mountain Parrot (Nexfor
618 ZOOLOGY SECT.
3. GEOLOGICAL DISTRIBUTION.
In considering the distribution of animals in past time, we are
met at the outset with the difficulty that our knowledge of the
subject is, and must always remain, very imperfect and fragmentary.
With few exceptions, only calcined, silicified, or strongly chitinised
parts are preserved in the fossil state, so that whole classes of
animals are absolutely unknown in that condition, and of the
rest our whole information depends upon the more or less imperfect
skeleton. Moreover, it is only under very favourable circumstances
that even the hard parts are preserved ; the chances are usually
in favour of the animal being devoured or disintegrated before
there is time for it to be silted over with mud or sand. And,
lastly, many rocks have been so altered by the internal heat of
the earth as to destroy any organic remains they may once have
contained. Thus, while palaeontology furnishes us with the only
sure test of phylogenetic speculation, it is a test which, more often
than not, is incapable of application, owing to the extreme imper-
fection of many parts of the geological record.
It is in the oldest of the stratified rocks that this imperfection
is most severely felt. In the Laurentian period, forming the
base of the sedimentary series (see Vol. I., p. 7), no animal or
vegetable remains are known. In certain Canadian serpentine
rocks belonging to this period there is found a remarkable structure
which, under the microscope, bears a certain resemblance to the
supplementary skeleton, with its canal-system, of an immense Fora-
minifer. On the assumption that it was the fossilised remains of
a member of this order, it was called Eozoon canadense, but later
researches seem to have shown conclusively that the supposed fossil
is of purely mineral origin. Radiolarians and Foraminifera have
been described from the Pre-Cambrian rocks of Brittany, but the
nature of the bodies in question has not yet been established
beyond dispute.
There are thus no undoubted fossil animals until the Cam-
brian period, where many existing groups appear to start
suddenly into being. We find Radiolaria, Sponges, Grapt olites,
Polyzoa, Brachiopoda, Edriasteroidea, Carpoidea, Asteroidea,
Chaetopoda (worm-tubes), Phyllocarida, Ostracoda, Trilobites, the
generalised Insects known as Palseodictyoptera, iso- and hetero-
myarian Pelecypods, Gastropods (Prosobranchs and Pteropods),
and tetrabranchiate Cephalopods (Orthoceras, &c.) — all, it will be
noticed, marine forms, with the exception of Insects.
Proceeding a stage onwards we find in the Silurian period,
in addition to the above groups, Foraminifera, Actinozoa (rugose
Corals), Ophiuroids, Echinoids, Crinoids, Cirripedes, Scorpions,
Eurypterida, Amphineura, Scaphopoda, Elasmobranchii, and
Ostracodermi.
xiv DISTRIBUTION 619
Thus, in the two earliest fossiliferous systems are found repre-
sentatives of all the skeleton-forming phyla, i.e., of all but
Platyhelminthes, Nemathelminthes, and Trochelminthes. And,
as far as our present knowledge goes, there is no indication of
any connecting link between one phylum and another, the
primary divisions of the animal kingdom having been apparently
as well characterised at that enormously distant epoch as at
the present day. Obviously all the older or more generalised
animal types, which, if we reason from analogy, we must suppose
to have preceded the present well-marked phyla, have been
destroyed by metamorphic action or otherwise, without leaving
a trace of their existence.
The Devonian period is remarkable for its abundant remains
of Fishes ; Crossopterygii, Chondrostei, and Dipnoi appear for
the first time, and all three groups of Ostracodermi are abundant.
Decapod Crustacea, of the macrurous or Shrimp type, also make
their appearance. In the Carboniferous period, notable for
its immense forest-flora, there is a great development of air-
breathing forms, such as Insects, Arachnids (Spiders), and
Myriapods, as well as Stegocephala, the earliest amphibious
Vertebrates. In the Permian rocks true air-breathing Verte-
brates first make their appearance in the form of the reptilian
orders Thermomorpha, Sauropterygia, and Rhynchocephalia. This
period is also remarkable for the occurrence of Ceratodus, the
oldest still existing genus of Vertebrates.
Thus by the end of the Palaeozoic era, every important class of
animals capable of leaving fossil remains is represented, with the
exception of Mammalia and Birds. Moreover, the Trilobites,
the Eurypterida, the Pala?odictyoptera, and the Ostracodermi come
to an end during this era, no remains of them being known in
rocks of secondary age.
In the succeeding Mesozoic era, the Triassic period intro-
duces existing orders of Insects — Orthoptera, Neuroptera, and
Coleoptera, as well as Xiphosura, siphoniate Pelecypods, opistho-
branchiate Gastropods, and dibranchiate Cephalopods (Belemnites).
The Palaeozoic types of Tetrabranchs (Orthoceras, &c.) have nearly
disappeared, and the Ammonites have become important. Among
Vertebrates are found Holostei, Chelonia, Ichthyopterygii, Croco-
dilia, and Dinosauria, the latter especially being a very prominent
group, as well as several Mammalia (Microlestes, Hypsiprym-
nopsis, &c.) of uncertain affinities.
In the Jurassic period the two highest orders of Insects,
Hymenoptera and Lepidoptera, are known for the first time, as
well as the reptilian Ornithosauria, and the earliest known Bird
(ArchcDopteryx). There are also several small Mammals (Pla-
giaulax, AmpJiitherium, Phascolotherium, &c.) belonging either to
the Prototheria or to the Metatheria, but occurring in Europe
620 ZOOLOGY SECT.
and North America, where there are at present — with the excep-
tion of the Opossums — no representatives of either order. This
seems to indicate that the lower Mammals originated in the
northern hemisphere and spread southwards.
In the Cretaceous period the Crabs — the most specialised of
the higher Crustacea — and the Teleosts — the most specialised of
Fishes — make their appearance. Of the last-named group, several
Cretaceous genera survive and nourish to the present day, e.g.,
Clupea (Herring), Esox (Pike), Osmerus (Smelt), and Beryx. Ophidia
are known for the first time, and Pythonomorpha, Dinosaurs, and
Ornithosaurs are important. Mammals are practically imknown,
but among Birds the Odontolcae and the Ichthyornithes are
characteristic. By the end of the period five entire groups of
Reptiles — the Sauropterygia, Ichthyopterygia, Pythonomorpha,
Dinosauria, and Ornithosauria — have become extinct, none of them
being known to extend into Tertiary times.
Except in California and Patagonia there is a well-marked break
between the Cretaceous and the Eocene periods, the fauna of the
latter having a comparatively modern character. The Pelecypods
and Gastropods belong to existing families and even to existing
genera, and Belemnites have almost, and Ammonites quite, dis-
appeared. The Fishes all belong to existing types ; Stegocephala
have given place to Urodela and Anura, and none of the Reptiles
belong to extinct orders. Among Birds, the Penguins, Gulls, Rails,
Owls, Picarians (Kingfishers, &c.) and Passeres have appeared, as
well as the extinct orders Stereornithes and Gastornithes, and the
goose-like Odontopteryx.
But the most noticeable feature of the period is the rise and
differentiation of the Mammalia. Among existing orders the
Marsupialia (Opossums), Cetacea (Zeuglodori), Sirenia (Prorastomus,
Eosiren), Ungulata, Carnivora, Insectivora, Chiroptera, and Primates
(Lemurs) appear for the first time, as well as the extinct orders
Creodonta, Condylarthra, Amblypoda, and Tillodontia, together
with the Dinocerata, none of which extend beyond the Eocene
period. In the lower Eocene none of the Mammals belong to exist-
ing genera, but in the upper Eocene are found Diddphys (Opossum),
Rhinoceros, Viverra (Civet), Mustela (Weasel), and possibly Canis.
The period is also remarkable for the number of annectent or
linking forms. There are, for instance, species connecting Dogs
with Bears and with Civets, Civets with Hyaenas, Hyaenas with
Cats, Pigs with Pecora, Deer with Chevrotains, Tapirs with Rhino-
ceroses and with Horses, and so on. It is perfectly clear that the
orders, sub-orders, and families of Mammalia, as we now under-
stand them, were, during the Eocene period, becoming gradually
differentiated from common ancestral forms.
In the Miocene period the Proboscidea (Elephant and Mastodon)
make their appearance, as well as Gibbon-like Anthropoid ea
XIV DISTRIBUTION 621
(Pliopithecus, Hylobates and other genera), and some other Anthro-
poidea. Many existing families have arisen, such as Hedgehogs,
Shrews, and Moles ; Mice, Eabbits, and Porcupines ; Whales and
Dolphins ; Tapirs, Hippopotami, Swine, and Antelopes ; and
species of Felis and Cam's. The Rhinoceroses of the period still
have no horns, and the antlers of the Deer are small or absent.
The Tapir-like ancestors of the Equidse found in the Eocene have
developed into more Horse-like forms, and the ancestors of the
Camels (Poebrotherium) still retain upper incisors and distinct
metacarpals. Numerous Marsupials lived in South America during
this or the preceding period : many of these were small forms
(Microbiotheridce) apparently allied to the living Ccenolesles ; others
(Sparassodonta1) were larger, carnivorous, with resemblances to the
Tasmanian Thylacinus.
The Pliocene fauna has a still more modern aspect, a large
proportion of the animals composing it belonging to existing
genera, although most of the species are extinct. Indirect evidence,
in the shape of chipped flints, of the existence of Man occurs in
deposits assigned to this period. Complex antlers have appeared
in the Deer, horns in the Rhinoceroses, and tusks in the Pigs.
The occurrence of Giant Tortoises (Testudo) in the Pliocene of both
Palsearctic and Nearctic regions, and of a Chimpanzee and a true
Ostrich (Struthio) in deposits of this age in India and the Crimea,
indicates the northern origin of these forms. Indeed it seems
probable that most of the higher Vertebrata, except Penguins and
the New-World Edentates, have originated in the Holarctic region.
In the Pleistocene period many existing species have made
their appearance, but their geographical distribution is very
different from that of the present day. For instance, the European
fauna includes many forms now confined to the Ethiopian and
Oriental regions, such as Apes, large Felidae, Hyaenas, Tapirs,
Rhinoceroses, Hippopotami, Horses, and Elephants, all of which
appear to have been driven southwards by the cold of the Glacial
epoch. In some parts of the world the Pleistocene fauna includes
remarkable and often gigantic forms now extinct — most notable
being the great Edentates (Megatherium, Mylodon, Glyptodon, &c.)
of South America, the gigantic Marsupials (Diprotodon, Nototherium)
of Australia, and the great flightless Birds (Dinornis, M-pyornis,
&c.) of Madagascar and New Zealand. Nesopithecus, which occurs
in the Pleistocene of Madagascar, is either a Monkey-like Lemur
or a true Monkey : if it be the latter, its occurrence indicates a
closer affinity between that island and Africa than their existing
faunae would indicate. Pithecanthropus, found in beds of late
Pliocene or early Pleistocene age in Java, was perhaps a connecting
link between the other Anthropoids and Man.
1 The marsupial affinities of the Sparassodonts, however, are very doubt-
ful, and the resemblances to Thylacinus may b? entirely superficial.
VOL. II Q Q
622 ZOOLOGY SECT, xiv
The Pleistocene passes insensibly into the Recent period, which
has also witnessed some important zoological changes, especially
the extinction of many interesting animal forms, for the most part
by human agency. Among these may be particularly noticed
Steller's Sea-cow (Rhytina), the Great Auk, the Dodo and Solitaire,
several flightless Rails (Aptornis, Notornis, Aphanapteryx, &c.),
the Phillip Island Parrot, and, above all, the whole great race of
Moas.
SECTION XV
THE PHILOSOPHY OF ZOOLOGY
IN dealing with the structure and development of the various
groups of animals, there has been occasion not infrequently to refer
incidentally to various subjects of a general nature, such as
evolution, heredity, and the like. Such topics, dealing, not with
the concrete facts of the science, but with abstract generalisations
deduced from the facts, may be grouped together under the
general heading of the Philosophy of Zoology. The generalisations
forming the subject-matter of the philosophy of' zoology may, in
some instances, be so clearly and directly deducible from the data
concerned that it is scarcely possible for anyone conversant
with the facts to refuse credence to the generalisation. But in
other cases the conclusion is a matter of probability only, and one
conclusion or another may be regarded as the more probable,
according to the estimate formed of the relative importance to be
attached to different sets of the facts or to different aspects of the
facts. This will become clearer as we proceed ; but at the outset
it should be distinctly understood that what follows is not to be
looked upon in the same light as the statements regarding the
known phenomena of animal life which constitute the main substance
of the preceding sections. Nearly all the subjects now to be
touched upon are, to a greater or less extent, matters in which
there may be variety of opinion among those conversant with the
phenomena ; they are all subjects which will bear discussion from
various sides ; but, as discussion is here almost out of the question,
it is possible to give little more than a brief statement of some of
the current views on these questions as an introduction to the
study of works specially dealing with them.1
The Philosophy of Zoology, or the Philosophy of Biology (for it
is here almost impossible to treat Zoology apart from its com-
panion science of Botany), aims at an explanation of the facts of
1 See Appendix II, Nos. 2, 3, 4, 14, 15, 10, 17, 19. 21, 22, 23, 36, 37, 42,
45, 55, <)2, (13, 65, 66, 67, 72, 74, 75, 77, 78, 79, 81.
Q Q 2
t-3:
624 ZOOLOGY SECT.
the science. It is observed that an animal possesses a certain
structure, develops in a certain way, has certain affinities with
other animals, has a certain geographical and geological range ;
and the attempt is made to find a satisfactory explanation of these
facts.
Evolution. — Of these facts there is, to all intents and purposes,
but one explanation requiring consideration here. The animal- and
plant-life of the globe has come to be as it now is by a process
of evolution which has been'going on continuously from an early
period in the history of the earth to the present time. The plant-
and animal-worlds, in other words, have been evolved by a gradual
process of development, in the course of which the higher forms
have originated from the lower. Evidence bearing on this doctrine
has already been encountered in abundance — in fact the theory of
evolution has to be looked upon as in many respects a guiding
principle in the study of our science ; and it has, accordingly,
been necessary in many parts of previous sections to take its truth
for granted. In discussing the relations of the various phyla to one
another, the relations of the various classes of each phylum, and
the position of the described examples within the classes ; in
referring to the homologies borne by the organs of the members
of one class to those of the members of another, it has been necessary
to assume the truth of a theory of evolution.
For the evidence, then, in favour of a doctrine of evolution the
reader is referred to the substance of previous sections, where it
will be found on almost every page. For his guidance some
landmarks may, however, be here pointed out.
Anatomical and Embryological Evidence. — A consider-
able body of the evidence in favour of the view that the higher
animals have been derived from lower forms is obtained from the
provinces of comparative anatomy and embryology. The mere
fact that we are able conveniently to express the resem-
blances and differences in structure between different groups by
the construction of such genealogical trees as have been given
in some of the previous sections tells strongly in favour of a theory
of descent ; for, though it is by assuming evolution that such
diagrams are constructed, the resemblances which they represent
point strongly to common ancestry. A theory of evolution
explains also the fact that there is running through a whole series
of forms — let us say Fishes, Amphibians, Keptiles, Birds, and
Mammals — a common type of structure, in which the same
essential parts, though perhaps differently modified in accordance
with differences in function, are to be found in the same mutual
relations. It would be difficult, on any other view of the facts,
to explain, for example, the occurrence in the wing of the Bird
and of the Bat, the flipper of the Whale, and in the fore-leg of the
Horse, of essentially the same bony elements. More difficult
xv THE PHILOSOPHY OF ZOOLOGY 625
still would it be to explain the cases in which what is a
functionally active and important part in one animal is to be found
—though only as a mere vestige, apparently quite useless — in an
allied form. Very many instances of this phenomenon will be
found in the previous chapters. The wing of the Pigeon is an
efficient organ of flight ; in the New Zealand Kiwi or Apteryx it is
a vestige, not visible externally, being covered over by the feathers
and wholly without function ; yet this vestige possesses essentially
the same bony framework and the same muscles as the complete
and functional wing of the Pigeon. Again, the teeth of the
Rabbit are parts essential to the welfare and the very existence of
the animal, and persist throughout life ; while in the Whalebone-
Whale teeth are indeed developed in the foetal condition, but are
thrown off before or shortly after birth, never being of any use for
mastication or any other purpose. The conclusion that seems to
follow from these facts is that it is at least highly probable that the
Kiwi has vestiges of wings because it is descended from birds
which, like the Pigeon, possessed functionally useful wings ; and
that the Whalebone-Whale has teeth in the foetal state because
it is descended from ancestors which possessed teeth in the adult
condition.
The fact that the embryos of animals of one great phylum or
class present a great resemblance to one another, and that the
nearer the adult forms are in structure, the closer, usually, is the
similarity in their developmental stages, tells strongly in favour of
a theory of common descent. Thus the nauplius-stage is found
in a considerable number of groups of Crustacea, but it is only
between members of families whose structure is closely similar
that there is a very near correspondence in the precise character of
the nauplius and in the stages which the larva subsequently passes
through.
Evidence of an allied character is afforded by the fact that in
the course of its development one of the higher animals sometimes
appears to exhibit in successive stages features which are per-
manent in forms lower in the scale. Thus the embryo of a Mammal
presents at an early stage visceral arches and clefts comparable
to the branchial arches and clefts of a Fish, and has a blood-
circulation in accordance with this ; while at a later stage it exhibits
in these particulars some resemblance to an Amphibian, later on to
a Reptile, and only when development is further advanced takes on
its special Mammalian characters. Again, we have seen that
such an Amphibian as the Frog is, in its early condition as a tadpole,
to all intents and purposes a Fish. Such phenomena may be
explained, according to the theory of evolution, by the supposition
that the successive stages in the development of the individual
animal tend to reproduce, though in a very abbreviated and often
greatly modified shape, the stages through which the group to
626 ZOOLOGY SECT.
which the animal belongs has passed in the course of its evolution
from lower forms. This supposition — the " biogenetic law," or
' recapitulation theory," as it is termed — though it cannot be
accepted without great modifications and reservations, yet covers
a number of facts which distinctly demand a process of evolution
for their explanation.1
The phenomenon of retrograde metamorphosis observable in
many animals, for the most part parasitic in the adult condition,
also affords evidence in favour of evolution. It would be difficult
to give any other explanation than that afforded by a theory of
descent, of the life-history of such animals as Sacculina (Vol. I.,
p. 583), the parasitic Copepoda (p. 583), or the Ascidians (Vol. II.,
p. 35). The relatively high organisation of the larva of Sacculina,
for example, with its well-marked Crustacean features, can only be
explained on the supposition that the shapeless, unsegmented
adult has been derived by a process of retrograde development from
more normally constructed ancestors.
Most Birds and Mammals, and many animals of lower groups,
exhibit a more or less strongly marked sexual dimorphism, the
males differing from the females in various other respects besides
the character of the sexual organs. Such differences can only be
explained on the supposition that they are the result of a gradual
process of modification brought about in accordance with the
more special adaptation of each sex to its special functions.
Palaeontological Evidence. — A second body of evidence in
favour of a theory of evolution comes from the side of Palaeontology.
It might, perhaps, on first considering the subject, be supposed
that, had a process of evolution taken place, we ought to be able
to find in the rocks belonging to the various geological formations
a complete series of animal- and plant-remains representing all
the stages in the evolution of the highest forms from the lowest.
Beginning with those strata in which evidence of life first appears,
we ought, it might be supposed, to be able to trace upwards,
through all the series of fossil-bearing strata, continuous, unbroken
lines of descent showing the gradual evolution of all the various
forms of plant- and animal-life. But such a supposition would
leave out of account the extreme incompleteness of the record of
1 As an instance of the difficulties in the way of the acceptance of the
biogenetic law as such, it may be pointed out here that the ovum is by no
means equivalent to the simple cell with which the phylogenetic series must
be supposed to have begun. On the contrary, the ovum of one of the higher
animals must be an extremely complex structure, and in reality widely
different from the Protozoan which, according to the biogenetic law, should
be its prototype. The ovum of the higher animal is, it is true, a single cell ;
but it is a cell which comprises potentially within itself the entire complex
adult organism, and is thus essentially an entirely different thing from the
unicellular Protozoan. The same holds good of later developmental stages :
they may resemble the adult condition of lower groups ; but they differ from
the latter in the same way as the ovum differs from the Protozoan.
xv THE PHILOSOPHY OF ZOOLOGY 627
the history of life on the globe which is preserved to us in the
rocks. In the first place, there are many groups of animals and
plants which, owing to the absence of any hard supporting parts,
are incapable of leaving any recognisable trace of their former
existence in the form of fossils. Again, even in the case of such
as have such hard parts, the conditions necessary for their pre-
servation in deposits destined to be converted into rock cannot be
of very frequent occurrence ; and many forms might fail to be
preserved simply owing to the non-occurrence of such conditions.
In the case of land-animals, such as Mammals or Reptiles, for
example, when one of them dies, it is for the most part torn to
pieces, and even the bones destroyed by various carnivorous and
carrion- feeding creatures. Only now and again would it happen
that, by becoming buried in a morass, or swept away by a flood and
buried under alluvial deposits, such forms might be preserved.
Again, great thicknesses of sedimentary strata, sometimes con-
taining fossils, can be shown to have become removed by the
agencies of denudation, or the various forces — such as the action
of waves, tides, and currents in the sea, of rain and fresh-water
streams on the land — -by which rock-masses are constantly, where
exposed, being worn away ; while other rocks, subjected to the
pressure of enormous superincumbent masses, and perhaps acted
upon by intense heat and other agents of change, have been com-
pletely metamorphosed — their mineral constituents having become
re-arranged and what organic remains they may have contained
completely destroyed. Moreover, of the fossil-bearing rocks that
remain unaltered, only a small part can be said to have been
thoroughly explored for fossil-remains.
Yet, notwithstanding these causes of imperfection in the record
of the succession of life on the earth preserved to us in the rocks,
there is sufficient evidence to enable us to judge of the general
character of the faunas (and florae) of the various geological periods.
It is manifest, from what has already been stated throughout the
earlier sections with regard to the geological history of each
phylum and class, that there has been a general progress in suc-
cessive eras from the simple to the more complex ; the higher
forms have, so far as the recorded facts enable us to judge, come
into existence later than the lower. The Vertebrata may be
taken as an example. There is no evidence of the existence of
the highest class — the Mammalia — earlier than the Triassic period
of the Mesozoic era. The case of the Birds appears at first sight
anomalous : Birds appear for the first time in deposits of Jurassic
age, and are therefore more recent than the oldest Mammals.
Birds are, however, very higly specialised Vertebrates, and should
it be proved that they appeared at a time when primitive Mammals
already existed, the separate evolution of the two classes from
lower forms would afford a sufficient explanation. Reptiles extend
628 ZOOLOGY SECT.
as far back as the Permian. Amphibians, in the shape of the
Stegocephala, first appeared in the Devonian ; while all the earliest
vertebrate remains in the Cambrian and Silurian formations
appear to belong to the class of the Fishes. Within each of these
classes a progress is usually traceable from older, more generalised
types, along diverging lines, to the various specialised forms
existing at the present day. In some cases, however, — notably in
the Amphibia, Reptilia, and Aves — the orders first represented have
become entirely extinct, and have been succeeded by others that
made their appearance on the scene at a comparatively late period.
In certain cases among the Mammalia a number of closely-related
stages have been discovered, showing, taken in their chronological
order, a gradually increasing specialisation of structure. One
of the best-known examples of this is that of the Horse, to which
attention is directed in the section on the Mammalia (p. 586). No
fewer than five parallel series of horselike Perissodactyles are
traceable, which developed and culminated separately, the cul-
minating member — viz., the genus Equus — of one only of these
series surviving to the present day. And there are other families
of Mammals, chiefly among the Ungulates (the family of the Pigs
and various families of Ruminants), in which an equally complete
history has been made out.
The direct evidence of the evolution of the Invertebrates is, in
general, very imperfect. Some existing types of a comparatively
highly organised character are to be recognised among the fossil
remains in the oldest formations — the Cambrian— in which definite
organic structures, if we except a few Radiolaria and Foraminifera,
are traceable. There is no trace of primitive fossil members of
the various invertebrate phyla, and the highly organised air-
breathing Arthropods are represented both by Scorpions and by
Insects as far back as the Silurian. Such remarkably complete
geological histories as have been traced in some of the Mammalia
are extremely rare in the Invertebrates. Such direct evidence,
however, as is obtainable points to the probability of evolution,
and it may be inferred that the absence of primitive generalised
representatives of the invertebrate phyla is most probably due
to the imperfect character of the geological record.
The Lamarckian Theory. — Supposing it to be regarded as
proved that the organic world has come to be as we find it by a
process of gradual evolution, we have next to inquire by what
agencies this process of development has been brought about. A
sketch of the history of thought on this subject will be given in
the section on the history of Zoology, and it will not be necessary
here to refer to more than the most important points.
The first noteworthy attempt to solve the problem regarding the
nature of the forces by means of which evolution has taken place
was made, long before evolution was generally accepted among
xv THE PHILOSOPHY OF ZOOLOGY 629
men of science, by Lamarck in his Philosophic Zoologique, published
in 1809. Lamarck's view was that evolution of new forms has
taken — and is taking — place, in great measure owing to the direct
action of the conditions of life on the organism, but still more
owing to the use and disuse of organs. The surroundings or
environment of the animal or plant produce a direct effect on the
individual — bring about slight modifications in one direction or
another, and these slight differences are transmitted by inheritance
to the next generation — such slight modifications going on, genera-
tion after generation, producing eventually a marked effect on the
characters of the organism. The chief agencies that might be
supposed to act in this way are climate, the nature of the country,
and food. But, in addition to these, Lamarck attributes con-
siderable influence to the use and disuse of organs. The exercise
of a part tends to increase its size and efficiency, and such increase
may be and frequently is, according to Lamarck, transmitted
to the succeeding generation. In this way, in the course of a
number of generations, very great changes might be brought about.
To take an example which is often quoted, Lamarck accounts for
the great length of the neck of the Giraffe as compared with other
Ruminants by the supposition that it has been brought about by
continuous efforts made by the animals through a long series of
generations to reach higher and higher among the foliage of the
trees from which they derive their main subsistence. (Similarly,
the disuse of a part, in Lamarck's view, gradually leads to its
diminution, and perhaps ultimately to its complete disappearance.
In this way he would explain the disappearance of the hind-limbs
in the Cetacea, of both pairs of limbs in the Snakes, of the olfactory
nerves in aquatic Mammals, and so on. Whether differences which
are produced in the individual organism by surrounding conditions
or by its own efforts may be transmitted by inheritance to suc-
ceeding generations is not yet a settled point : we shall have again
to refer to this question — the question of the inheritance of acquired
characters — at a later stage. That such inheritance, if it takes place,
could account for the development of all the various groups of animals
and plants is not held by many biologists at the present time.
Darwinian Theory. — It is to Charles Darwin that we owe
the most thorough and consistent explanation of evolution that
has hitherto been put forward — the explanation known as the
theory of Natural Selection. The development of this theory and
the share taken in it by Wallace will be sketched in the historical
section. The two main supports of Darwin's theory are two sets of
biological phenomena known respectively as the struggle for existence
and variation, both of which have to be understood before it is
possible to grasp the theory of natural selection.
Struggle for Existence. — In order that it may flourish, there
are necessary for every species of plant and animal certain conditions.
630 ZOOLOGY SECT
The plant must find a place with soil containing certain constituents,
and with a certain degree of moisture and of sunlight. For spots
presenting the necessary favourable conditions there is constantly
going on a competition between individual plants of one species
and between the members of different species. The nature of
this struggle is well seen when a piece of garden-ground is allowed
to run to waste. Its surface is soon overgrown by weeds of a
variety of kinds, which kill out some of the original garden-plants.
By and by the more hardy weeds kill out and replace such weaker
forms as may first have obtained a footing, till an entirely new set
of weeds may take the place of those that first appeared. Again,
it was shown by Darwin that in turf which is kept cut close a much
greater number of plants are enabled to grow than is the case if
the turf is allowed to grow freely. If the turf is not kept cut some
of the stronger plants gain predominance and kill out weaker forms.
In a space of turf on which Darwin experimented, no less than
half of the species present in the turf when kept pretty closely
shaven perished when it was allowed to grow freely.
Plants, however, have not only to compete with one another for
space and light and nourishment. They have also numerous
animal foes to contend with. A large proportion of young seedling
plants are destroyed by various Insects and by Snails and Slugs.
One of Darwin's experiments bearing on this point was to clear
and dig up a small plot of ground and watch the fate of the seedling
plants that sprang up on it ; he found as a result that some four-
fifths were destroyed by Insects, Snails, and Slugs. But it is
not the lower forms of animals alone that are thus destructive
to plants. Many of the Mammalia, particularly, as we should
expect, the herbivorous Ungulata, exercise a strong influence in
this way. Cattle, and Goats especially, sometimes produce a
marked effect on the flora of a country. The introduction of Goats
has been observed gradually to destroy the forests of certain
districts — the seedling plants being eaten as they appear, and
thus no young trees being developed to take the place of those
dying from old age or other causes. The mere enclosing of a piece
of moorland by means of a fence was observed by Darwin to have
resulted in the growth of a number of trees. In the unenclosed
parts the young trees were never able to make any headway against
the cattle by which they were constantly being browsed down.
Among animals, with which we are here more particularly
concerned, as well as among plants, a struggle for existence goes
on on all sides. To begin with, before there is any struggle for
existence in the strict ssnse, there is— particularly in lower groups—
a very great indiscriminate destruction of ova and young embryos.
Most lower animals produce ova in great number — hundreds, more
often thousands and tens of thousands, annually. Only a few of
these reach maturity ; a large proportion are destroyed indiscrimi-
xv THE PHILOSOPHY OF ZOOLOGY 631
nately at one stage or another of their development, some failing to
reach a spot favourable for their development, others becoming
the food of other animals. But such of the young as are less
adapted to escape the various dangers to be encountered, and less
fitted to procure the necessary food, are more likely to be destroyed.
This is one phase — and the most important, perhaps, of all — of the
struggle for existence among animals. But there is also a struggle
for existence not only between individual animals of the same
kii'd, but between animals of different kinds. This struggle, in so
far as it relates to the competition for food and shelter, is more
severe between nearly-related species ; for in such a case the food
and the favourable conditions required are the same, or nearly so,
in the two competitors. But there is also a struggle for existence
of a constant and severe kind which goes on between carnivorous
animals and the animals on which they prey — a struggle in which
the defensive qualities of the latter, such as swiftness, power of
eluding observation, power of resisting attack and the like, are
opposed to the predatory powers of the former.
Variation. — It was by observing this struggle for existence
constantly going on in nature, taken in connection with the
phenomenon of variation, that Darwin was led to his principle of
Natural Selection as accounting for evolution. Variations in
domestic animals and cultivated plants are observed to take place
in various directions. Taking advantage of this, man has been able
to select, in the animals which he has domesticated and the plants
which he has cultivated, those qualities which seemed most likely
to be useful to him ; he has thus been able to produce, from one
and the same original wild stock, widely different varieties specially
adapted for different purposes. Thus from one wild species of plant
of the order Cruciferce — viz., Brassica oleracea — have apparently
been produced all the varieties of cabbage, cauliflower, broccoli,
Brussels sprouts, and other forms, each with a peculiar and strongly
marked growth of its own. All the domestic vegetables afford us
instances of the same thing, and so do all the cultivated fruits.
The crab-apple or wild apple, for example, was the original of all
the varieties of apple, amounting to about a thousand, cultivated
at the present day — varieties presenting in many cases very great
differences in size, colour, texture, flavour, time of ripening, and
other qualities. In cultivated flowers the same holds good in an
even higher degree.
The instances of variation observable among domestic animals
are still more striking. The domestic Dog, for example, exhibits a
large number of very marked varieties. Though all these seem to
be fertile with one another, and to produce fertile offspring, it is
generally supposed that they have been derived from several wild
species with more or less hybridisation. But the enormous
differences which are to be observed between some of the varieties
632 ZOOLOGY SECT.
have been produced to a great extent under domestication. These
are not all mere superficial differences, but involve also the pro-
portions and shape of the parts of the skeleton. The difference
in the form of the skull and in the proportions of the bones of the
limbs between a Greyhound and a Bulldog, for example, are very
remarkable — so great, in fact, that if they were found to occur
between two wild forms they would justify a zoologist in referring
the two to distinct genera. Sheep and Cattle, Pigs and Horses,
present similar, though not perhaps quite so strongly marked,
varieties. One of the most remarkable cases of variation under
domestication, and one to which Darwin paid a good deal of
attention, is that of the domestic Pigeon. Of this there are a
considerable number of varieties, known to fanciers as pouters,
fantails, carriers, tumblers, and so on ; and it appears to be almost
certain that these are descended from one wild species — the blue
Rock-pigeon.
These varieties, and many more that might be mentioned, have
been produced by man selecting those forms that tended to vary
in a desired direction — have been produced, that is to say, by
artificial selection, sometimes consciously exercised, sometimes, no
doubt, unconsciously. This process has had a long period of time
for its operation, many of our domestic animals and plants having
been the objects of care and cultivation in Egypt and Western
Asia certainly several thousand years ago ; in many cases the wild
forms from which they were developed appear to have become
totally extinct.
But variation occurs among animals and plants not only under
domestication ; it occurs also in a state of nature. Evidence of
this has already been adduced in the account of certain of the
examples of the various phyla ; and in the examination of specimens
of these in the laboratory the student can hardly have failed to
notice the occurrence of individual differences not due to differences
in sex or age in animals of all classes. In this respect, in the
strength of the tendency to individual variation, there is a very
great inequality between different species of animals, some being
extremely variable, some comparatively stable. Variations of
external parts have naturally, from the greater ease with which
they may be observed, attracted most attention, but the examina-
tion of the internal parts in large numbers of individuals of the
same species, when it has been carried out, has shown that variations
in internal organs are also of great frequency.
Among the Protozoa, the Foraminifera are characterised by
numerous and marked variations — so marked as "to include, not
merely those differential characters which have usually been
accounted specific, but also those upon which the greater part of
the genera of this group have been founded, and even, in some
instances, those of its orders." The Mollusca vary also very
xv THE PHILOSOPHY OF ZOOLOGY 633
frequently and extensively, especially in the form and markings of
the shell ; and of some of the species which have been most com-
pletely studied in this respect a very large number of more or less
strongly marked varieties have been recorded. Many of the
Crustacea are also extremely variable in coloration and in the
length and proportions of the various appendages. But, among
the Arthropoda, it is in the Insecta, and more especially the
Lepidoptera, that we find the most striking instances of variation.
In the Vertebrata, also, variations in colour and proportions, as
well as in internal organs, occur frequently in all classes.
Mutations. —It has been shown by de Vries that variations are
not always of a comparatively minute character. According to
de Vries, in addition to the small fluctuations on which Darwin
mainly relied for the phylogenetic development of organisms, there
are others which occur comparatively rarely, and are of a much
more striking character. These larger variations, which de Vries
distinguishes by the name of mutations, take the form of the
sudden appearance of differences equivalent to the formation per
saltum of new species ; and it is by the successive appearance of
such steps or leaps, and not by the more gradual process of Dar-
winian variation, that, according to de Vries, progress from the
lower towards the higher is effected. The new forms developed
in this sudden way may live side by side with the old, and thus
isolation is not necessary for their perpetuation.
Natural Selection. — According to Darwin's theory of Natural
Selection, nature, i.e., the conditions under which the organism
exists, selects certain variations as they arise, very much as the
breeder or the gardener selects variations in domestic animals or
cultivated plants. Let us see how this selection is carried on.
We have seen that there is going on, on all sides, a struggle for
existence. It is at first difficult to realise the intensity of this
struggle, for there is little appearance of it on the surface. If we
consider, however, that a large proportion of living things prey on
living things of other groups, and when we bear in mind the
extremely small proportion which, in most cases, the surviving
individuals of any group bear to the number of young produced,
we come to understand that this struggle for existence must be
general and intense.
Now in the case of a species living under tolerably uniform and
stable conditions as regards climate, food-supply, and the like, the
effects of this struggle will be the survival of the fittest. Of the
young produced, only a small proportion (in most cases) reach
maturity ; some of these surviving forms have survived, perhaps,
because they have happened to escape being preyed upon by
enemies, while others have succumbed ; but there can be little
doubt that, in the long run, such individuals will survive as are
best fitted to cope with the conditions to which they are subjected
634 ZOOLOGY SECT.
—such as are swiftest, let us say, in escaping pursuit ; or such as,
by their special shade of colour or the nature of their markings,
elude the observation of an enemy ; or such as, by reason of their
thicker covering, can better endure extremes of cold. Such
surviving individuals would, it is assumed, transmit their special
properties to their progeny, and there would thus be a gradual
approximation towards a better adaptation of the species to its
surrounding conditions by virtue of this " survival of the fittest."
Let us suppose the conditions to change. Gradual changes in
climate and other conditions are known to take place owing to
subsidence or elevation of the land. But conditions might be
changed in many other ways : some animal or plant previously
used as food might become exterminated ; or a new enemy might
find its way into the district inhabited by the species. Then such
individuals as presented variations which enabled them better to
cope with the new surroundings would have the advantage over
the others, and would have a much better chance of surviving and
leaving progeny. The useful variations thus produced and trans-
mitted to the progeny would tend to increase, generation after
generation, until a form sufficiently distinct to be regarded as a new
species had become developed from the original one.
The process of survival of the fittest has a reverse side, which
has been termed the elimination of the unfit. Of the varieties
that appear some are less completely adapted to their surroundings
than the majority, and these (the conditions remaining the same)
tend to become destroyed owing to their unfitness to cope with
their environment. The result of this process of elimination
(apart altogether from the selection of progressive variations by
which evolution, according to the theory, proceeds) is to keep up
a certain standard of efficiency in the organs of the members of the
species. Under certain conditions this sustaining influence, as we
may term it, of natural selection may be suspended ; the organism
may be placed under conditions in which natural selection acts with
reduced effect or does not act at all. There is, under such circum-
stances, no " elimination of the unfit " ; and, as a result, fit and
unfit survive indiscriminately, interbreed and produce offspring,
the ultimate outcome in the course of generations being a gradual
deterioration in the whole race.
This suspension of the influence of natural selection, with its
results, has been termed cessation of selection, or panmixia. Panmixia
acts more commonly on single organs than on the entire organism.
Thus, if, owing to some change in surrounding conditions, an organ
is no longer useful, it is no longer kept up to the previous degree of
efficiency by the elimination of the individuals in which the organ
in question is imperfectly developed, and, as these cross with one
another, offspring is produced in which the organ is below the
efficient standard ; by a continuance of this process through a
xv THE PHILOSOPHY OF ZOOLOGY 635
series of generations, it is supposed that the organ gradually
dwindles in size, and may altogether disappear. Thus at that
stage in the ancestral history of the Cetacea in which they had
come to adopt a purely aquatic mode of life and no longer visited
the shore, the hind-limbs, being no longer of service, would no
longer be maintained by natural selection, and would gradually
decrease in size until, finally, they entirely disappeared. In the
case of these, as of many other rudimentary organs, however, it is
probable that natural selection played a positive part in bringing
about their diminution. Under the conditions supposed, the
possession of hind-limbs would probably be an actual disadvantage
to the animal, acting as an impediment to the swift progression
through the water, and interfering with the free movements of the
tail ; and varieties with diminished hind-limbs would, therefore,
possess an advantage over their fellows in the struggle for existence.
There would then be, in a sense, a positive reversal of selection.
Darwin's theory of selection is concerned mainly with the small
individual variations which are observed to occur, more frequently
in some species, more rarely in others. Such variations are so
slight and unimportant that it is difficult to understand how they
could be of sufficient life-and-death value to give the individuals
in which they occur sufficient advantage in the struggle for existence
to enable them to survive, wrhen others in which they are absent
perish. Failing the extermination of the unmodified individuals,
unless the appearance of the variation should happen to be coincident
with the occurrence of other factors leading to the isolation of the
individuals possessing the new variation from the stock in which
they originated, the new variety would tend to become swamped by
intercrossing with the latter and would fail to be perpetuated. If,
however, the individuals in which the new modification occurs
should by some means — such as migration beyond a geographical
barrier of some kind, or by the nature of the variation itself — be
preserved from intercrossing with the stock, then, without the
extermination of the latter being a necessary condition — without,
that is to say, a life-and-death struggle— the new form might be
preserved unaltered and perpetuated as a new and distinct variety,
which further changes similarly brought about might raise to the
rank of a species.
Detailed study of the geographical distribution of species and
varieties in certain regions, more especially in the United States of
America, has afforded much support to the view that the develop-
ment of new forms takes place as a result of the appearance of
varieties differing slightly from the parent stock and their isolation
from the latter by geographical barriers ; and by some writers
evolution is even supposed to have proceeded solely, or almost
solely, in this way with little, or entirely without, aid from natural
selection. Another kind of isolation might be supposed to take
636 ZOOLOGY SECT.
the place of geographical in preventing the intercrossing of new
varieties with the original stock. By means of sexual or physio-
logical isolation, i.e., by the form in question becoming varied
in such a way that it does not readily interbreed with the main
stock, the new variety may be as effectively isolated as if separated
from it by a geographical barrier.
That allied species and sub-species differ in their geographical
range, and are often separated by geographical barriers, and that
a physiological barrier may be set up between allied forms owing
to union between them being impossible or sterile, are facts of
great importance in the study of evolution, and the details of sucli
cases are necessary data of the science. But that the whole of
organic nature should have been evolved by variation and isolation
alone seems to be highly improbable : such a view takes no account
of progressive adaptation and orthogenetic development, and it
would seem to call for the formation of an impossible succession of
barriers.
A special phase of Natural Selection is distinguished under the
title of Sexual Selection. By means of Sexual Selection it is
attempted to explain the greater part of the secondary differences
between the sexes which are so striking in many groups of animals.
The special part which each sex has to play in the fertilising and
deposition of the ova, in protecting and procuring food for the
young, requires qualities, both anatomical and psychical, of a more
or less widely divergent character in the male and female.
Between the males of animals of many groups contests frequently
take place, and this affords us an explanation of the presence or
special development in many cases in that sex of various offensive
and defensive weapons — horns, tusks, and the like. Similarly, we
are able to understand the greater vigour, in the majority of cases,
of the male, with concomitant greater intensity of coloration, and
the development of various ornaments and excrescences not present
in the female. In many groups of Insects, and in a large proportion
of Birds, sexual differences in coloration are very marked. These
are, in some instances, to be traced to the necessity for different
protective resemblances required in the two sexes owing to different
habits, or to the necessity for protective colorations and markings
in the female and not in the male. In the case of Birds, when the
sexes differ, as they do in a large proportion of the species, the
male has always more brilliant coloration, and often possesses
also special crests or frills, wattles and the like, not present or less
developed in the female. The greater obscurity of the colouring
of the female Bird appears to be adapted to rendering her less
conspicuous to enemies, such as Birds of Prey, while sitting on the
nest ; and, in cases where the females are brightly coloured, the
nest is covered over above, or is constructed in a hole in the ground.
The brilliant colouring and other features distinguishing the males
xv THE PHILOSOPHY OF ZOOLOGY 637
of many Birds may be in great part the by-product of higher
vitality, and may thus be the indirect outcome of natural selection
leading to the more vigorous males obtaining an advantage in
contest with rivals. It is possible, also, that the choice of the
female in selecting a mate may have been a factor in bringing about
the special modifications in question. But the evidence which has
been adduced for any such selection on the part of the female of a
mate with some slight superiority in brilliancy of colouring, or in
the development of crests and the like, over his rivals, is insufficient,
and many observations tend to show that selection of this kind,
though it may occur, is exceptional. In any case, as a general
explanation of secondary sexual characters, sexual selection is not
at the present time very widely accepted as adequate.
Protective and Aggressive Resemblance and Mimicry.—
One of the most important of the phenomena which are well ex-
plained by the theory of natural selection, and which may, therefore,
well be taken as affording evidence in favour of that theory, are the
phenomena of 'protective resemblance, warning characters, and of
mimicry. In innumerable cases among all classes of animals there
are found instances of a resemblance between the animal and its
ordinary natural surroundings, which has the effect of rendering it
inconspicuous and unlikely to attract the observation of an enemy,
or of its prey. Such a resemblance is brought about sometimes
merely by colour, very often by the arrangement of the colour in a
pattern, this being frequently accompanied by modifications of
shape, including sometimes the development of special excrescences
or appendages. In some cases of protective resemblance the colour
and even the markings change with a change of the surroundings.
For details of such cases reference must be made to special works.
Many Insects present elaborate markings which give them a close
resemblance to a tuft of lichen or moss, a twig, a leaf, or other
object, and resemblances of an equally striking character occur in
other classes.
Some animals, more especially certain Insects, are protected by
their nauseous character against being devoured by animals that
would otherwise prey upon them ; but often, no doubt, such
nauseous Insects are attacked and killed before their unpalatable
character is detected. It is thus manifestly of advantage to such
animals that they should be readily recognisable, and should thus
be passed over ; and in many such cases the coloration is bright
and conspicuous, or the animal is rendered conspicuous by other
means (warning characters}.
By mimicry is meant a superficial resemblance borne by one
animal to a member of a different group. The best-known
examples of mimicry occur among the Insects. It is manifestly
of advantage to a Butterfly belonging to a group which is not
nauseous to be readily mistaken for a nauseous form with con-
VOL. II R R
638 ZOOLOGY SECT.
spicuous warning colours and markings, and this appears to be the
explanation of many cases of mimicry. Similarly, a variety of
flower-frequenting Dipterous Insects which have no sting or other
weapon bear a remarkable resemblance to Bees or Wasps, belonging
to a distinct order (the Hymenoptera) — the resemblances embracing
not only shape, colour, markings, and development of " hairs "
on certain parts, but the movements of the wings and other parts
and the humming sounds emitted, so that, on a superficial in-
spection, the mimicry appears complete.
Heredity. — The various characteristics of a plant or animal
are transmitted to the succeeding generation. In the highest
groups of animals this transmission is effected only through the
intermediation of the sexual cells — ova and sperms — since they
alone are capable of giving rise to a new generation. But in lower
organisms the faculty of reproduction is more widely diffused
among the component parts ; in some lower multicellular plants
each and every cell is capable of taking on the function of repro-
duction and giving rise to progeny similar in all respects to the
parent ; in other words, every cell in such cases must contain
germinal substance. In other, somewhat higher, forms the germinal
substance, though still widely diffused, may not be present, or
capable of becoming active, in all parts, and may be confined to the
cells of one or other of the layers. In the vegetable kingdom, even
amongst the highest forms, the germinal substance can be shown
to be widely diffused throughout the plant. Thus in many flowering
plants, if we cut a shoot into lengths, the pieces are all capable of
giving rise under suitable treatment to complete plants with flowers
containing reproductive cells ; and in many cases a leaf, or a portion
of one, is capable of a similar development. In many animals
a similar wide distribution of the germinal material may be shown to
prevail. This appears most strikingly in forms that multiply by
budding. In Hydra, for example, any part of the body seems
capable of giving off buds, and in the buds, after they have become
separate, ova and sperms are developed from the cells of the ecto-
derm. A similar phenomenon is to be observed in other Ccslen-
terates and in the Polyzoa and the Composite Ascidians, and also
in certain cases among the Platyhelminthes and Annulata. In all
these, and in other cases that might be mentioned, the germinal
substance is not confined to the reproductive cells — new repro-
ductive cells being capable of being formed from the substance of
the cells of various tissue-layers.
The phenomena of regeneration are important in connection
with this question of the site of the germinal substance. Many
members, not only of the lowest phyla, but of the Echinodermata,
the Annulata, the Arthropoda, the Mollusca and the Chordata,
are able, as has been repeatedly mentioned, to replace, by a process
resembling budding, parts that have been broken off : some of
xv THE PHILOSOPHY OF ZOOLOGY
the cells of the adult body must, therefore, in these cases retain
in a certain degree the faculty of reproduction, and must contain
germinal substance. The germinal substance concerned in re-
generation must, it is of importance to note, be capable of being
stimulated into activity in a certain definite direction by an influence
brought to bear upon it from without.
In the Vertebrata the power of regeneration, if we leave out
of account the various epidermal structures, is exceptional ; and
where it occurs (most Amphibia, some Reptiles) it is confined
to the limbs, jaws, lens of the eye, or the tail. In the highest
Vertebrates there is no power of regenerating such parts when lost,
and the capacity for reproduction is confined to the sexual cells.
A remarkable persistency characterises these reproductive cells.
By their means there are handed down from one generation to
another, with little alteration, all the characteristics of the species
of plant or animal. This special faculty of the reproductive cells
is the faculty of heredity.
Heredity does not imply absolute fixedness of all the character-
istics inherited by one generation from its predecessor. On the
contrary, as already pointed out, variations are constantly pre-
senting themselves. Some of the variations which animals exhibit
are a direct result of the action of surrounding conditions, or of
the use or disuse of parts, on the fully developed animal ; we can
in some cases actually cause the animal to change to a more or
less marked extent by placing it under different conditions.
Another set of variations produced by the action of external
influences on the organism only appears if the action takes place
in the course of development at one stage or another between the
oosperm and the adult. Of the occurrence of both these forms of
variation we have direct and positive evidence. It is a familiar
fact that increased exercise of a part tends to an increase in the
bulk of its muscles. The colours and markings of certain Fishes
can be altered at will (of course within certain limits) by changing
the material on the bottom of the aquarium in which they are
confined ; the colours of many Caterpillars may be altered by
changing the colour of their surroundings. A third set of variations
probably also occurs, though direct evidence is wanting — -namely,
variations which may arise within the sexual cells before the union
of ovum and sperm, or which may result from that union. The
former two sets of variations are generally spoken of as " acquired
characters " —new characters acquired during the lifetime of the
individual — but their nature would be more clearly indicated by
terming them extrinsic variations, as contrasted with the intrinsic
variations forming the last group.
The extrinsic variations being brought about by the action of
external conditions, their causes are very various. In every such
case the organism responds to some persistent external influence
R R 2
640 ZOOLOGY SEC*.
by undergoing some more or less persistent change. Mutilations,
the rapid mechanical removal or destruction of parts, are here,
by the terms of the above definition, excluded from the class of
variations altogether, since, though the change involved is frequently
permanent, it is effected by an influence which is temporary in its
character. This, as will be seen, is of importance in connection
with the next question we have to deal with — the inheritance of
acquired characters.
Can acquired characters or extrinsic variations be transmitted
by inheritance ? That they can be is of the essence of Lamarck's
doctrine of development, which, in fact, may be described as a
theory of development by means of the inheritance of extrinsic
variations, or, as it is sometimes called, use-inheritance. But
the maintenance of the view that extrinsic variations may be
transmitted is not inconsistent with the acceptance of natural
selection as a true cause of evolution. Evolution might be sup-
posed to be due to the selection and inheritance of both intrinsic
and extrinsic variations. From the nature of the case, evidence
in favour of the inheritance of extrinsic variations on the one hand,
and the occurrence of intrinsic on the other, is extremely difficult
to obtain. One or the other must occur, or there would be no
evolution. But to prove in any given case that a change is due
to the one factor rather than to the other is extremely difficult.
When a character not present in the parents appears in the offspring,
there is, to begin with, great difficulty in proving that it is really
new : characters not present in the parents are known to be
frequently inherited from a more or less remote ancestor. But,
if we suppose it to be established that the character is a new one
(and absolutely new characters must appear, or we should have no
evolution), then it would require a very accurate knowledge of all
the circumstances to enable us to be certain whether the appearance
of the character is not due to the action of some external influence
on the parent, either during development or in the adult state,
rather than to a change arising within the reproductive cells.
Instances are frequently brought forward which have been supposed
to afford evidence of the transmission of mutilations from parent
to offspring ; but such a transmission must, from the nature of the
case, always be extremely difficult to prove, and the majority, at
least, of such cases are found, on a careful analysis, to be capable
of other interpretations. On the other hand, though well-estab-
lished cases of the inheritance of mutilations would greatly support
the doctrine that acquired characters are transmissible, the negative
results that have attended certain experiments on mutilations
are of little value in the direction of proving that extrinsic variations
cannot be transmitted, since, as has already been pointed out, such
experiments in mutilation cannot be said to reproduce the con-
ditions under which an extrinsic variation might be supposed to
xv THE PHILOSOPHY OF ZOOLOGY 641
be transmitted ; the mutilation is instantaneous ; the variation
must be supposed to be the result of long-continued action, which,
it might be expected, would have a sufficiently profound effect to
engraft it permanently on the organism.
It should be pointed out here that there is no absolutely hard
and fast line to be drawn between the intrinsic and extrinsic
variations, since changes in the sexual cells may very well be due,
directly or indirectly, to influences exerted from without. The
material from which reproductive cells may subsequently be
fashioned is, in plants and in many animals, in such close and
intimate union — -so far as can be seen — with the other proto-
plasmic elements of the organism, that it seems highly probable
that influences affecting the latter may in many cases affect also
the former.
Another question that presents itself in connection with heredity
is : Can any special part of the germ-cell be fixed upon as the
part specially concerned in hereditary transmission ? Is it by
means of the nucleus alone that transmission takes place, or does
the cytoplasm take a share in the process ? The complicated
changes which the nucleus undergoes during mitotic division (Vol. I.,
p. 18), with the definite form and (for each species) constant number
of the chromosomes, and their precise halving during the process,
tell strongly in favour of the view that the nucleus is the vehicle
of transmission rather than the, apparently, less highly differentiated
cytoplasm. But such evidence is far from amounting to positive
proof.
To determine this point many series of embryological experiments
have been carried out. Should it prove possible to fertilise by
means of a sperm an ovum from which the nucleus had previously
been removed, and as a result to obtain an embryo, it might be
possible, by a process of exclusion, to get some light on the influence
exerted on normal development by the nucleus of the ovum. For
such experiments sperms and ova of the same species are not well
adapted, since the differences between the individuals of a species,
especially in the early stages, are not of a sufficiently strongly
marked character to permit of any definite conclusions being
arrived at regarding inheritance from one parent as against the
other. Recourse has, therefore, been had to crossing between
distinct species or distinct genera, or even between the members of
distinct classes. In such experiments the Echinoderms have
proved capable of affording the most convenient material, and have
been very largely employed. It has been found to facilitate suc-
cessful crossing between distinct kinds of Echinoderms if the ova
experimented with are first treated by certain methods which
have been found to prepare the way for the process of artificial
parthenogenesis briefly referred to in the Introduction (Vol. I.,
p. 22). The ova so treated are then shaken violently in a tube.
642 ZOOLOGY SECT.
with sea-water, until they become to some extent broken up.
From the fragments such large pieces as are found not to contain
nuclei are picked out, and the sperms of the second kind of Echino-
derm are added to the water in which these non-nucleated fragments
are contained. In many cases it is found as a result that a sperm
enters a non-nucleated fragment and an embryo becomes formed.
It now has to be determined how far this embryo resembles and
differs from the embryos of the two species from which the ovum
and the sperm respectively have been derived. This is always a
matter attended with a considerable amount of difficulty, since
such embryos can rarely be reared beyond the gastrula stage. But
evidence seems to have been obtained by means of this method that
the nucleus has not a monopoly in the transmission of the parental
characters, since in such experiments maternal features do appear
in the embryo, and these, in the absence of a female nucleus, must
have been transmitted by the agency of the cytoplasm.
Evidence tending in the same direction has been obtained as a
result of experiments on the ova of Ctenophora (Vol. I., p. 214).
If, before these are fertilised, a definite area of the cytoplasm be
removed without the nucleus being interfered with in any way,
the embryo which develops after fertilisation presents deficiencies
in the organs of definite areas corresponding to the parts which
have been removed.
It has been urged in connection with the question of heredity
that what is transmitted from generation to generation is not so
much matter as energy. The quantity of matter is always rela-
tively small ; the important fact appears to be that this relatively
small particle carries with it potential energy sufficient to effect
the structural changes which precede the beginning of the process
of assimilation, and to at least initiate that process. But we can
hardly imagine a succession of complicated and very definite changes
of structure, such as are involved in the development jaf an animal,
taking place unless the germinal matter or germ-plasm in which they
originate has a correspondingly complicated and definite structure.
The oosperm, having the faculty of reproducing the entire animal
without (in many cases) any further influence emanating from the
parent, must contain within itself something to represent each of
the parts — even each group of cells — of the adult body. The
oosperm of a Frog, for example (p. 280), simple though its structure
appears to be, must contain potentially within itself all the char-
acteristics of the adult animal, and not only these, but the char-
acteristics of each successive stage in the formation of the tadpole
and its metamorphosis into the adult Frog. Attempts have been
made to explain how it is that the reproductive cells acquire this
reproductive capacity. One of the most interesting of these is a
theory which is termed pangenesis, the origination of which is due
to Darwin, According to this theory, the cells of the various parts
xv THE PHILOSOPHY OF ZOOLOGY 643
of the body throw off minute ultra-microscopic particles or " gem-
mules," and these find their way by various channels to the
developing reproductive cells, in which they accumulate until each
reproductive cell contains gemmules representing all parts of the
body. When development takes place each gemmule develops into
the part corresponding to that from which it has been derived.
If this theory afforded a true explanation of the facts of repro-
duction, there would necessarily be accumulated in the ovum
gemmules representing not only every part of the body of the
adult, but also every stage in the development of the embryo,
and (since we see ancient ancestral characters occasionally reverted
to) something to represent the special peculiarities of former
generations. Now, it is a question if such an accumulation of
gemmules, each necessarily several times the size of a chemical
molecule, would not form a mass very much larger than an ovum.
Such a doctrine would, moreover, hardly appear to be necessary
in order to explain the facts. The accumulation in the ovum of
the hereditary tendencies (as we may call them) may only in part
take place during the lifetime of the individual : a good part of
them — all, perhaps, except such as have been more recently
acquired — might be contained in the ready-formed germinal
material handed down from previous generations.
Against a hypothesis of pangenesis such as was formulated by
Darwin, the mode of reproduction of many plants tells more
strongly perhaps than any of the facts derived from the animal
kingdom. Many of the higher flowering plants, for example, are
capable of being propagated by means of a cutting of the stem or
root, or even by a leaf. As the new plant developed from the
cutting gives rise to flower and fruit, the cutting must contain
germinal matter ; and germinal matter must, therefore, be diffused
throughout the cells of such a plant. Pangenesis, unmodified,
would require that in such a case a large proportion of the ordinary
cells of the plant should receive gemmules derived from all parts.
It is a moot point whether it is possible that any influence (such
as is presupposed in pangenesis) can pass from the cells of the
various parts of the body to the ova — whether there can be any
communication of substance carrying with it tendencies to be
transmitted to the next generation. It is certain, however, that
an influence of a centrifugal character is exerted by the sexual
cells. The absence of ovaries or testes has, in many cases, a
marked effect on certain of the characters — an effect on the
development and form of certain of the parts. This is seen not
only in higher animals (Mammals and Birds), but also among
some lower forms. In certain Crabs, for example, the presence of
Sacculina, a parasitic Rhizocephalan nourished at the expense of
the testes, which become destroyed, produces a very marked
alteration in some of the external features. But, while this is the
644 ZOOLOGY SECT.
case, an influence exerted in the opposite direction — an influence
transmitted from the other parts to the germ-cells — has not been
proved, and from the nature of the case perhaps cannot be directly
proved. Such an influence, it is hardly necessary to add, must
be presupposed if we assent to the doctrine of the inheritance of
acquired characters.
Rules or Laws of Heredity. — As in the case of the experi-
ments referred to on p. 641, by which it has been sought to deter-
mine the respective values of nucleus and cytoplasm as bearers
of the hereditary qualities, so also in the majority of the experi-
ments designed to determine the laws by which the inheritance of
paternal and maternal characters is regulated, it has been necessary
to have recourse, not to fertilisation between individuals of the
same variety, but to crossing between distinct varieties or between
distinct species with the production of bastards or mongrels (variety-
or species-crosses), since it is only in cases in which the differences
between the maternal and paternal characters are strongly marked
that it is possible to trace these characters in the descendants.
It is found that in such experiments in crossing between varieties
the result may take one or other of the three following courses.
In the first place the progeny may be intermediate in character
between the two parents : the paternal and maternal characters,
that is to say, may be mixed or blended without any tendency to
the predominance of either : a cross between a black and a white
variety, for example, in such a form of hybridisation becomes a
grey. In a second set of cases, which are the rarest of all, the
offspring exhibit paternal characters in one part or set of parts and
maternal in another : thus a cross between a black variety and a
white yields a piebald or a mottled black-and-white. This is
the so-called mosaic form of bastard-inheritance. Lastly there are
certain cases in which there is no blending and no mosaic formation,
but the paternal and maternal characters remain separate, and
appear, or fail to appear, in the progeny in a certain regular order.
This is the alternating or Mendelian form of bastard-inheritance.
It is with this last form of bastard-inheritance that the theory
of Mendel, a product of the middle of the last century, but only
comparatively recently re-discovered and given due recognition,
is concerned. Mendel's original experiments were mainly with
varieties of garden-peas. When he crossed two varieties he found
that the offspring all presented the characters of one of the parent
forms. Thus in the case of a cross between a tall and a short
variety — whether the short was fertilised by the pollen of the tall
or the tall fertilised by the pollen of the short— the progeny were
tall : in a cross between yellow-seeded and green-seeded varieties
the products were all yellow-seeded. Of the two opposed
characters, that which reappears in the offspring is known as the
dominant, that which does not appear as the recessive character ;
XV THE PHILOSOPHY OF ZOOLOGY 645
the varieties presenting these characters are accordingly spoken of
respectively as either dominant or recessive. When the hybrids, all
showing the dominant character, produce a second generation by
self-fertilisation, or fertilisation among themselves, there is a re-
appearance of the recessive character in a certain fixed proportion
of the progeny. In this second generation one quarter are pure
recessives, one quarter pure dominants, and the rest of mixed char-
acter. The pure recessives in following (inbred) generations always
remain true to the recessive character — the dominant having
evidently become eliminated from their constitution ; and the
same holds good, mutatis mutandis, for the dominants. The
intermediate forms present the dominant character, but when
inbred they behave exactly like the original hybrid, that is to say,
the progeny consist of pure dominants (a quarter), pure recessives
(a quarter), and mixed or intermediates (a half). In future genera-
tions these proportions are regularly maintained.
It is inferred from their behaviour in inheritance that the
Mendelian characters occur in pairs, the members of which have a
fixed reciprocal relationship to one another, one of them being
usually dominant, as in the case of tallness and shortness in the first
example referred to : two such characters are said to be allelo-
morphic, or reciprocating, with regard to one another. The term
segregation is applied to the process by which each becomes separated
out in the pure dominants and pure recessives of the second and
succeeding generations.
An important point in connection with the bearing of Mendelian
inheritance in plants and animals on the problems of evolution is
that the former provides a means by which new variations or
mutations when they arise may be at once fixed and become
perpetuated.
Orthogenesis. — The fact that, as shown by the evidence afforded
by both existing and extinct forms, organisms vary in such a way
as to follow definite lines leading to special adaptations (and
sometimes to excessive development of parts) is held not to be
explainable by a theory of selection of slight variations the direction
of which is under no known guidance. This definiteness in the
direction of evolution — orthogenesis — is a fact in nature of which
there is evidence on all sides. In nearly all groups and nearly
all systems of organs there is evidence of progressive development
such as cannot be supposed to be due simply to the fortuitous appear-
ance and selection of the Darwinian variations. A nervous system,
simple, diffused, and superficial in the lower members of a group,
becomes more highly elaborated, more complex, more deeply placed,
in the higher. Light-perceiving organs, mere groups of pigmented
elements, and nerve-cells with refractive bodies, in the lower forms,
become represented in the higher by complex eyes with elaborate
mechanism for the reception of images of external objects. Appen-
646 ZOOLOGY
SECT. XV
dages undergo progressive modification, so that each pair becomes
specially adapted for the performance of particular functions.
Moreover, parallel and evidently independent lines of orthogenetic
development are in many cases traceable in separate groups. As
examples may be mentioned the series of stages in the development
of complex eyes from simple rudiments, which are observable in
the Annulata, the Arthropoda, and the Chordata : the parallel and
quite unconnected stages in the reduction of the digits, leading
to the greater perfection of the limbs as running organs, to be
traced in the Perissodactyle and Artiodactyle series of the Ungulata.
In many cases such orthogenetic development has led to excessive
growth of parts — growth beyond the requirements of the organism—
an excess which has sometimes, apparently, led to extinction.
Since natural selection has been judged by many to be inadequate
to account for such straightforward progress in organisms and
organs, various other theories of orthogenesis have been put forward.
Such of these as merely postulate the existence in organisms of a
principle or tendency to develop towards a more perfect condition
fail to reach the standard of admissible scientific theories. Such
a supposed tendency is not merely analogous to the tendency of
the young organism to grow into the adult form — a phenomenon
sufficiently difficult to account for by any nexus of causes and
effects known to us : it must be something much more, since it
must be not merely a tendency to repeat what has been received
in inheritance, but must be in a highly important degree prophetic
—must, in fact, be a tendency to develop to a point beyond that
to which the hereditary impulse reaches. Other theories of ortho-
genesis rely upon the action of the environment for bringing about
the results observed : these have to encounter the same funda-
mental difficulty as the Lamarckian theory itself — the difficulty
of explaining how changes in the parents due to the effects of the
environment can be impressed on the germ-cells in such a way as
to become transmitted to the next generation. But experimental
evidence in favour of the heritable character of various changes
caused by external factors has been recently accumulating. And
many of those who concern themselves with the study of evolution
at the present day, while admitting the 'absence of any satisfactory
theory of the mode of transmission to the germ-cells of changes
of organisation in the adult of the nature of acquired characters,
are yet inclined to the view that such a transmission does occur,
and that without it it is quite impossible to account for the definite
adaptive developments that have taken place, especially since there
seems to be no convincing explanation, apart from such trans-
mission, of the mode of origin of the first beginnings of structures
destined, when further developed, to be of vital importance to the
organism, but in their early stages not of sufficient value to be
capable of determining its survival or extinction.
SECTION XVI
THE HISTORY OF ZOOLOGY
ZOOLOGY, like other branches of Natural Science, has had two
lines of progress, observation and generalisation. Without accurate
and detailed knowledge of the facts and phenomena of animal
life and structure, all theories of classification or of origin are so
much idle speculation : in the absence of philosophic spirit sug-
gesting hypotheses of greater or less magnitude, the mere accumu-
lation of facts is an empirical and barren study.
Zoology as a science, therefore, can hardly be said to have existed
until a sufficient proportion of the facts relating to animals had been
observed and recorded accurately and systematically, and until
some attempt had been made to classify these facts and to arrange
animals into larger and smaller groups according to some definite
plan.
This being the case, it may be said that the common knowledge
of animals possessed by mankind in all ages, and constantly being
developed and extended by lovers of external nature and by
anatomists working from the medical standpoint, first became
scientific and evolved itself into a system over 200 years ago, when
John Ray, an English clergyman, first grasped the idea of species
and published the earliest classification of animals founded upon
anatomical characters. Although soon overshadowed by the
greater genius of Linnaeus, Ray may safely be called the father of
modern zoological science, the only serious precursor of his Synopsis
methodica animalium, published in 1693, being the voluminous
De differentiis animalium of Edward Wotton, printed nearly
150 years earlier.
But although Zoology, as a science, was practically non-existent
up to the period referred to, much valuable knowledge of animals
had been accumulated, and was, as it were, merely waiting to be
systematised. As in other branches of knowledge, the first steps
were taken by the Greeks, and, in philosophical grasp, the zoological
writings of Aristotle (384-322 B.C.) are far in advance of those
of all other students of the subjects up to the times of Wotton and
647
648 ZOOLOGY SECT.
Ray. His treatises, especially The History of Animals, The
Generation of Animal , and The Parts of Animals, contain an
immense body of facts, many of them singularly accurate, others
as curiously incorrect, a circumstance which no one will wonder
at who, with all modern resources at his elbow, has tried to break
fresh ground in any department of Zoology. Although he pro-
pounds no definite system of classification, he clearly recognises
many of the more important animal groups, or, as he calls them,
" genera." Vertebrata, for instance, are spoken of as animals with
blood (evaifjLa) and Invertebrates as animals without blood
(ai'ai^a), colourless blood not being recognised as such. Among
animals with blood are included Viviparous Quadrupeds (Mam-
mals), Birds, Oviparous Quadrupeds (Reptiles and Amphibians),
Cetaceans, and Fishes : among bloodless forms, Malakia or soft
animals (Cephalopods), Malacostraca or soft animals with shells
(the higher Crustaceans), Entoma (Insects, Arachnids, Myriapods,
and the higher Worms), and Ostracodermata or shelled animals
(Echinoderms, Cirripedes, Pelecypods, Gastropods, and Tunicates).
Starfishes, Medusae, and Sponges are also referred to.
In the then existing state of knowledge it was impossible that
even so profound a philosopher as Aristotle could erect a science
of Zoology. No standard of nomenclature was established ; there
was no clear idea of what constitutes a species : in matters of
structure, no distinction was drawn between nerves and tendons :
in physiology the vessels and tendons were looked upon as the
organs of movement, the muscles being considered as mere packing.
Obviously, anything like real progress was barred by ignorance of
animal structure and function, and it was absolutely necessary
that exact anatomical knowledge should precede anything approach-
ing to successful generalisation.
It is, therefore, hardly to be wondered at that, up to the time
of Ray, scientific Zoology owes more to those anatomists and
physiologists whose main object was to advance the study of
Medicine, than to the naturalists in the ordinary sense of the word.
With the exception of the works of Galen (born A.D. 130), which
contain numerous observations on the Anatomy of Mammals,
anatomy, as well as Zoology in the broad sense, was practically
at a standstill from the time of Aristotle to the sixteenth century,
when Vesalius, by his observations, chiefly on the human subject,
raised anatomy to a degree of accuracy hitherto undreamt of ; and
Goiter, Bellonius, and Fabricius ab Aquapendente resumed
the study of comparative anatomy, dormant since Aristotle.
Somewhat later — -in 1645 — Severino published his Zootomia
democretcBa, the first book devoted exclusively to the general
subject of comparative anatomy.
During the same period the general knowledge of animals was
increasing, and a distinct epoch is marked by the learned and, fo
xvi THE HISTORY OF ZOOLOGY 649
the time, exhaustive Historia animalium of Conrad Gesner,
published in 1551-58, and consisting of 4,500 folio pages, with
numerous illustrations, some of them of considerable merit, some
wonderfully inaccurate ; some depicting various fabulous monsters,
such as Winged Dragons, many-headed Hydras, and crowned
Basilisks, the existence of which was not yet thoroughly discredited.
The work is, however, rather an encyclopedia than the exposition
of a science : it contains no general ideas ; there is still no con-
ception of the subordination of groups, and no exact naming either
of animals as a whole or of their various parts. Five chief groups
of animals are recognised : Viviparous Quadrupeds, Oviparous
Quadrupeds, Birds, Aquatic Animals, and Serpents. Within these
divisions the various animals are described without any attempt
at grouping. Among Aquatic Animals, for instance, Fishes,
Amphibia, Cetacea, Molluscs, Crustacea, Echinodermata, and Sea-
serpents are included.
In the seventeenth century great strides were made both in
knowledge of structure and function, in generalisation, and in
methods of investigation. Especially famous and fruitful — indeed
one of the greatest scientific events of all time — was the discovery
of the circulation of the blood, made by William Harvey in 1616,
and announced in 1628 in a small pamphlet Exercitatio anatomica
de Motu Cordis et Sanguinis. He demonstrated fully, partly by
dissections, partly by experiments on living animals, the action
of the heart as a pumping mechanism, the nature of its valves and
of those of the veins, the presence of blood — not air, as was then
supposed— in the arteries, the cause of the pulse, and the whole
course of the circulation so far as it could be known previous to
the discovery of the microscopic capillaries. Of hardly less
importance is Harvey's embryological work : he made extended
observations on the development of the Chick, and in his Exercita-
tiones de Generatione Animalium (1657) declared that all living
things arise from a primordium, or ovum, and propounded the
doctrine of epigenesis, according to which development is a process
of gradual differentiation of the primordium, whereby " out of the
inorganic arises the organic, out of the similar the dissimilar."
The primordium itself he considered might " proceed from parents,
or arise spontaneously, or out of putrefaction."
Harvey worked with no optical aid beyond a simple lens, and it
is not surprising that his results are incomplete and often
inaccurate. His successors had the advantage of the compound
microscope, invented by Hans and Zacharias Janssen about
1590-1600, and sufficiently improved during the course of the
seventeenth century to be an important engine of research in the
hands of the earliest microscopists, Malpighi in Italy, Leeuwen-
hoek and Swammerdam in Holland, Robert Hook and Nehe-
miah Grew in England. Malpighi made numerous histological
650 ZOOLOGY SECT.
discoveries, with some of which — such as the Malpighian capsules
of the kidneys and the Malpighian vessels of Insects — his name is
still associated. He was also the first to study the development
of the Chick under the microscope, and was one of the earliest
supporters of the theory of ^reformation^ according to which all
the parts and organs of the adult are present in the germ, so that
there is no differentiation, but only an unfolding. Leeuwenhoek
discovered blood-corpuscles, striated muscle-fibres, dentinal canals,
and epiderm-cells, observed the circulation of the blood in the
tadpole's tail, and described many of the lesser forms of life, such
as Infusoria, Rotifers, and Hydra. Swammerdam investigated the
anatomy of Insects and Molluscs, and the metamorphosis of
Insects, and described the three " sexes " of Bees. The researches
of Hook and Grew were mainly botanical ; both they and Malpighi
discovered in the tissues of plants little spaces with firm walls and
full of fluid ; these they called cells, thus taking the first step in
the structural analysis of the higher organisms.
Another discovery of fundamental importance was made in 1677
when Louis de Hamen observed and described the sperms of
animals. These were at first thought to be the young, which only
required to be nourished in the egg to grow into the embryo or
foetus, and were therefore considered to disprove the theory of
the ovulists—suck. as Harvey, who made the egg the origin of the
new generation — in favour of that of the spermatists, who believed
the whole material to be furnished by the male parent.
Belonging also to this period are Redi's experiments on genera-
tion, in which he began the work of establishing the doctrine of
biogenesis, according to which organisms originate only from pre-
existing organisms, and of demolishing that of abiogenesis, or
" spontaneous generation," which, maintained from the time of
Aristotle onwards, held that Flies, Lice, Worms, and other animals
were directly generated in mud, putrefying flesh, dung, &c., having,
therefore, no living progenitors. Redi's contribution to this
question lay in proving, for the first time, that the maggots, " bred
in putrefying meat, were the products of eggs laid thereon by
Flies.
Thus the seventeenth century saw a great advance in the
knowledge of animal structure and function, and the way was
paved towards a rational classification. As we have already seen,
Ray, towards the end of the century, gave Zoology as a whole a
scientific form ; he first grasped the ideas of species and of specific
characters, acknowledged anatomy as the basis of classification,
and introduced a greatly increased precision in the definition of
species and other groups, and in terminology. He had, however,
1 Often known as the theory of evolution. As, however, the latter word is
now universally used in a different sense, it is advisable to drop it in this
connection, and to employ the synonym preformation.
xvi THE HISTORY OF ZOOLOGY 651
no clear idea of genera, his genera being rather what we now
call orders or families, and he showed an undue conservatism in
retaining, as far as possible, the groups of Aristotle. His general
classification of animals is as follows :
I. Animals with (red) blood [Vertebrata].
1. Respiration pulmonary.
A. Heart with two ventricles.
(a) Viviparous.
i. Aquatic (Cetacea].
ii. Terrestrial [other Mammalia].
(b) Oviparous [Birds].
B. Heart with one ventricle.
Viviparous Quadrupeds and Serpents [i.e., Reptilia
and Amphibia].
2. Respiration branchial [Fishes].
II. Animals without (red) blood [Inverlebrata].
1. Majora.
A. Mollia [Cephalopoda].
B. Crustacea.
C. Testacea [Gastropoda and Pelecypoda],
2. Minora.
Insecta [Insecta, Arachnida, Myriapoda, and Vermes].
It will be noticed that, while the classification of Vertebrates is
fairly natural, being founded upon the rock of anatomy, the arrange-
ment of Invertebrates is no advance upon that of Aristotle : the
two main divisions depend upon mere size ; and Crustacea,
separated from the rest of the Arthropoda, are interposed between
Cephalopods and the remaining Mollusca. In association with
Ray must be mentioned his friend and fellow-worker Francis
Willughby, who made extensive contributions to Zoology.
The eighteenth century saw the imperfect efforts of Ray developed,
and in some respects perfected, by Carl Linne, or Linnaeus,
universally recognised as the founder of modern systematic
Zoology — or more accurately Biology, since his reforms equally
affected Botany. Born in Sweden in 1707, two years after Ray's
death, he published the first edition of his Sy sterna Naturce, in
1735, as a small pamphlet. The twelfth edition (1766-68) was in
three volumes, and was the last to receive the author's corrections,
but from materials left at his death in 1778 an authoritative
(thirteenth) edition in ten volumes was prepared by J. F. Gmelin.
It was Linneeus who first recognised the value of groups higher
than species — genera, orders, classes, &c., and employed them
in a definite and uniform way, with due subordination of one to
the other ; it was he who invented binomial nomenclature, the
advantage of which in promoting precision in systematic work
652 ZOOLOGY SECT.
it is impossible to overestimate. He gave each species a brief
diagnosis in Latin, so that any naturalist versed in his system could
recognise whether an animal or plant which came under his notice
was already described or not. In this way he, as it were, pigeon-
holed the facts of Biology, and so made the determination of the
proper place of any new fact a comparatively simple matter. By
universal consent, the Syslema Natures is taken as a starting-point
by systematists. It is customary to place after the name of a
species the initial or abbreviated name of the writer by whom the
species was first distinguished and named. For instance, the
Bass, a common British Teleost, was named Perca labrax by Linnaeus.
In 1828, Cuvier and Valenciennes, in their great work on Fishes,
recognised that it was generically distinct from the Perch, and,
retaining the generic name Perca for the latter, called the Bass
Labrax lupus. In 1860, further investigations into the Perch family
necessitated placing it in the genus Morone, and, according to the
law of priority, the specific name lupus gives place to labrax, the
latter having been applied by Linnaeus. The Bass is therefore
correctly called Morone labrax, Linn., the more usual name,
Labrax lupus, Cuv. and Val., becoming a synonym. In deciding
all such questions of priority, the tenth edition (1758) of the Sy sterna
NaturcB is taken as a starting-point : all species distinguished by
Linnaeus, and not subsequently split up into two or more species,
are distinguished by the abbreviation L. or Linn. For instance,
Canisfamiliaris, Linn, is the Domestic Dog, Passer domesticus, Linn.
the House Sparrow ; and names given by the older naturalists are
neglected unless endorsed by Linnaeus.
In many respects the system of Linnaeus was eminently artificial ;
he relied too much on single characters in classification, and did
not take the totality of structure into sufficient consideration. He
divided the animal kingdom into the following six classes : —
1. Mammalia.
2. Aves.
3. Amphibia [including Rcptilia and Amphibia].
4. Pisces.
5. Insecta [including all the Arthropoda].
6. Vermes [including Molluscs, Worms, Echinoderms, Ccelen-
terates, and Protozoa].
It will be seen that all the classes are of natural groups, with
the exception of the last, but that they are far from being of even
approximately equal value. The first four are what we still call
classes, but there is no attempt to unite them into a single group
of higher order ; and in this respect the classification of Linnaeus
falls behind that of Ray, who recognised the phylum Vertebrata
under the name of animals with blood. The fifth class, on the other
hand — that of Insecta— is the equivalent of an entire phylum,
Xvi THE HISTORY OF ZOOLOGY
while under the head of Vermes are included all the phyla recognised
at the present day, except Chordata and Arthropoda.
Other naturalists of the eighteenth century must be briefly
referred to. Bonnet introduced the idea of a " scale of beings ;
(echelle des etres), conceiving the true classification to be a linear
one, passing in a single series from the lowest to the highest forms.
This conception was opposed by Pallas, who introduced the true
conception of representing the relationships of the various groups
under the form of a much-branched tree. Spallanzani made
numerous investigations on reproduction, and, together with
Bonnet, Buff on, and Haller, strongly supported the doctrine of
preformation already referred to. Haller summed up the
position by stating emphatically that there was no such thing as
development or differentiation, no part of the body being made
before another, but all parts simultaneously created. It followed,
as a natural corollary from this view, that the germ destined to give
rise to an animal — i.e., the ovum according to the ovulists, the
sperm according to the spermatists — contained within itself the
germ of the next generation, this of the next, and so on, ad
infinitum, so that the first created male or female of each species
contained within its sperms or ova the germs of all future genera-
tions, enclosed one within the other, like a nest of Chinese boxes.
Buffon, as the result of numerous experiments, came to the
conclusion that the ovary secretes a seminal fluid containing moving
particles analogous to sperms, and, from this erroneous observation,
framed a theory which is an interesting anticipation of Darwin's
Pangenesis (p. 642) — namely, that organic particles, derived from
all parts of the body, occur in the seminal fluids of the two sexes,
and that the union of these in the uterus "determines them to arrange
themselves as they were in the individuals which furnished them."
The theory of preformation (as then understood) was practically
demolished, and that of epigenesis, or new formation, established
on a firm basis, by Caspar Friedreich Wolff, who at the age
of twenty-six — in 1759 — gave the most accurate account of the
development of the Chick hitherto known, and showed clearly
that there was no preformation of the various parts, but a gradual
differentiation from a layer of organised particles, or, as we should
now say, from a cellular blastoderm.
Another great eighteenth century name is that of John Hunter,
the most profound comparative anatomist and physiologist of his
time. He was not a zoologist in the narrow sense of classifier,
but his exquisite investigations on the various systems of organs
and their functions throughout the animal kingdom furnished the
science with a foundation of wide and exact knowledge which was
of far more importance than the most cunningly devised system of
classification. Important anatomical investigations were also
made during this period by Vicq d'Azyr, who enunciated the
VOL. II S S
654 ZOOLOGY SECT.
principle of serial homology ; by Peter Camper, who investigated
the pneumaticity of the bones of Birds, and was the first to apply
exact methods of measurement to the human skull ; by Alexander
Monro, who greatly advanced our knowledge of the anatomy
of fishes ; and by Poll, whose Testacea utriusque Sicilice is the
most famous of the older works on Mollusca. And in the domain
of out-door zoology — the study of the actual life of animals with
but little regard to their structure or classification, or to the broader
scientific questions connected with them — special mention must
be made of Gilbert White, whose Natural History and Antiquities
of Selborne is a classic both in science and letters.
The latter part of the eighteenth century is also specially re-
markable for the publication of the earliest scientific speculations
on the origin of species. The idea of evolution is to be found in
the works of more than one of the great Greek and Roman philo-
sophers, such as Empedocles (495-415 B.C.) and Lucretius
(99-55 B.C.) ; and the writings of some of the Fathers of the
Church, such as Augustine (A.D. 353-430) and Thomas Aquinas
(1225-1274), seem to show that they had no objection to " deriva-
tive creation," or evolution under direct Divine superintendence.
But by about the middle of the sixteenth century the idea of
the immutability of specially created species had hardened into a
dogma which it was unsafe to question ; and, this state of things
continuing, the earliest of the great evolutionists, Buff on, felt
himself obliged to qualify all his speculations with a declaration,
sincere or ironical, of his belief that species were immutable.
Linnaeus, reckoning all higher groups as subjective, contended for
the real existence of species, saying " we recognise as many species
as were originally created," and this opinion was held by the vast
majority of naturalists, not only of his own time, but up to within
forty or fifty years of the present day.
Buffon, born in the same year (1707) as Linnaeus, was, in his
methods and ideas, the exact opposite of his great systematising
contemporary. He wrote charming accounts of the external
characters and habits of animals, but declined to classify them,
on the ground that all arrangements of the kind were arbitrary,
and that it was easier, more useful, and more agreeable to consider
the lower animals in relation to ourselves. On this principle,
he begins his Histoire naturelle with Man, then takes up the various
domestic Mammals, and afterwards proceeds to consider the less
familiar forms. But he was essentially a philosophical zoologist ;
besides enunciating a theory of heredity, he grasped the idea of
homology, endeavoured to explain the facts of geographical
distribution, and, in a tentative and guarded way, admitted the
mutability of species, and advanced a hypothesis of their origin.
His speculations refer mainly to the modification, or, as he calls
it, degeneration, of domestic animals, and he sums up his position
THE HISTORY OP ZOOLOGY 655
as to the factors of the process by saying " the temperature of the
climate, the quality of nutriment, and the ills of slavery, these are
the three causes of change, of alteration, and of degeneration in
animals." In other words, he supports the theory of the direct
action of the environment.
A bolder and more consistent evolutionist than Buffo n was his
contemporary, Erasmus Darwin (1731-1802), grandfather of
the author of the Origin of Species. As a competent critic has
said, " he was the first who proposed and consistently carried out
a well-rounded theory with regard to the development of the
living world." In his Zoonomia, published in 1794-6, after
summarising the extraordinary adaptations to be seen in the
animal kingdom, he asks, " Would it be too bold to imagine that
all warm-blooded animals have arisen from one living filament
[he was a spermatist] which the great First Cause endued with
animality, with the power of acquiring new parts, attended with
new propensities, directed by irritations, sensations, volitions, and
associations ; and thus possessing the faculty of continuing to
improve by its own inherent activity, and of delivering down those
improvements by generation to its posterity, w^orld without end ? '
And a little later he inquires : " Shall we conjecture that one and
the same kind of living filament is and has been the cause of all
organic life ? ' He anticipated Lamarck in the importance he
attached to the principle of use and disuse, expressed his belief in
the inheritance of acquired characters, and recognised the im-
portance of sexual selection.
The study of Zoology was also greatly advanced during the
eighteenth century by the voyages of Cook, Bougainville, and
others. New countries were explored, the peculiarities of their
fauna3 recorded, and valuable data accumulated for the study of
distribution. In this connection the names of Sir Joseph Banks,
Solander, and the two Forsters — all attached to Cook's expedi-
tions, of Sparrmann,. and of Sir Hans Sloane, may be specially
mentioned. The last-named was one of the greatest of collectors,
and the founder of the British Museum.
The beginning of the nineteenth century was a period of great
zoological activity, distinguished by the work of some of the most
prominent leaders of the science.
J. B. P. A. de Lamarck (1744-1829) was not only a distin-
guished general zoologist and palaeontologist, but may also be looked
upon as the chief of the pre-Darwinian evolutionists. In his
Philosophic Zoologique, published in 1809, he completely rejected the
idea of the fixity of species, and endeavoured to explain the trans-
formation of one form into another by the operation of known
causes ; of these he attached most importance to the principle of
use and disuse, and he was a firm believer in use-inheritance.
He was a uniformitarian in Geology, believing that the history
s s 2
656
ZOOLOGY
SECT.
of the earth and of its past inhabitants is to be explained by the
action of the causes seen in operation to-day, and not by invoking
great catastrophes or cataclysms by which changes of vast magnitude
were suddenly produced. He considered, also, that the trans-
formation of species took place by slow, orderly changes, Nature
requiring only matter, space, and time in order to effect her various
changes. He introduced the terms Vertebrata and Invertebrata,
and, in the same year as Treviranus (1802), proposed the term
Biology for the whole science of living things.
Lamarck at first believed in a linear classification of animals, but
afterwards adopted the earliest known branching or phylogenetic
classification — a crude attempt, but interesting as being the first
of its kind. It is as follows : —
Worms [flat and round Worms]
Infusoria
Polypes [including Rotifers, Polyzoa,
Actinozoa, Crinoids, and some In
fusoria]
Radiaria [including Echinodermsam!
some Worms and Ccelenterates]
Annelids [Annulata, ftc. ]
Cirripedea
Mollusca
Fishes
Reptiles
Birds-
Monotremes
Insects
Arachnids
Crustacea
Amphibious Mammals [Sirenia and
.. Pinnipedia]
\ Cetacea
\
Ungulate Mammals
Unguiculate Mammals [Edentata, Rodentia, Marsupialia, Inseotivora,
Carnivora, Chiroptera, and Primates].
xvi THE HISTORY OF ZOOLOGY 657
The hypothesis of evolution was also supported by Lamarck's
contemporary, Etienne Geoffrey St. Hilaire, who denied
use-inheritance and considered the direct action of the environ-
ment as the sole cause of transformation. He also differed from
Lamarck in believing in the occurrence of sudden changes, e.g., in
the possibility of the emergence of a fully formed Bird from a
Reptile's egg. In systematic zoology he established the orders
Monotremata and Marsupialia : the members of the latter group
had hitherto been distributed among Rodents and Primates.
Another keen supporter of evolution was the great poet Goethe
(1739-1832), who also introduced the word Morphology, and made
important contributions to the department of science thus named.
He propounded the vertebral theory of the skull, presently to be
referred to (p. 659), recognised the importance of vestigial organs,
and predicted the presence of a premaxilla in Man — the absence of
that bone in the adult human skull being hitherto considered as
distinctively separating the genus Homo from the other Primates.
That the views of Lamarck and the other evolutionists produced
so little effect upon contemporary science is largely due to the
great and far-reaching influence of Georges Cuvier (1769-1832),
one of the greatest of comparative anatomists, whose views
dominated zoological science for half a century. He propounded
the fruitful principle of correlation, according to which peculiarities
in one part of the body are always associated with equally char-
acteristic features in other parts — e.g., the ruminating stomach
with cloven hoofs. He rejected the idea of a scale of being or unity
of type, and, in his great work, the Regne Animal, abandoning
the linear classification, divided animals into four Branches (em-
branchements), each with its own plan of organisation and in-
dependent of the rest. This conception, though not absolutely
correct, marked a great advance in classification, as the following
table shows.
Branch 1. VEETEBRATA.
,, 2. MOLLUSC A [including Tunicata, Brachiopoda, and
Cirripedia, as well as the true Mollusca].
,, 3. ARTICULATA [including Arthropoda and Annulata].
,, 4. RADIATA [including Echinodermata, Polyzoa, Nemat-
helminthes, Platyhelminthes, Ccelenterata, Sponges,
and Protozoa. The Rotifera are placed among the
Protozoa, and Bacteria and the pedicellarise of
Echinoderms are also included].
Here, it will be seen, the Vertebrata as a whole, and not the
separate classes of that phylum, are considered as the equivalent
of one of the great invertebrate sub-divisions : the Linnsean
Vermes are broken up, Mollusca being elevated to the rank of a
658 ZOOLOGY
SECT.
primary sub-division, and the articulated worms associated with
Arthropods ; while Echinoderms are grouped with Ccelenterata on
account of their radial symmetry, and the imperfectly understood
lower Worms, Sponges, and Protozoa are included in the same
branch.
Cuvier may also be said to have created the science of Palae-
ontology by his investigations of the Tertiary Mammalia of France.
As long ago as the sixth century B.C., Xenophanes had recognised
fossils as the actual remains of animals, but the usual view was
that they were merely mineral productions ; and one of the earliest
observers in modern times to perceive their true nature was
Scheuchzer, at the beginning of the eighteenth century, who
considered them as evidences of a universal deluge. Cuvier, as
well as the English geologist William Smith (1769-1839), showed
that the older fossils belonged to entirely different species, genera,
and even families, from the animals existing at the present day,
the differences being greater in the deeper than in the more
superficial formations. In this way the idea of a definite succession
of life in time was introduced. Cuvier and his followers rejected,
however, the notion of any genetic connection between the in-
habitants of successive geological periods, and considered that the
fauna of each epoch was exterminated by some cataclysm or
convulsion of nature, and the earth subsequently re-peopled by a
fresh creative act. This catastrophic view of the history of the
earth received its death-blow in 1830-33, when Sir Charles
Lyell (1797-1875) published his Principles of Geology — next
to the Origin of Species the most famous contribution to natural
science in modern times. By insisting on the evidences for con-
tinuity in the history of the earth, he prepared men's minds for the
idea of continuity in the history of its living inhabitants, and thus,
more than any of the older evolutionists, paved the way for the
reception of Darwin's views.
Apart from the work of Cuvier, the most important contri-
butions to Zoology during the first half of the nineteenth century
are in the domains of histology and embryology. In 1838 the
cell-theory, according to which all parts of the body are built up
either of cells or of tissues derived from cells, was propounded
first for plants by Schleiden and shortly afterwards for animals
by Schwann. Both, however, had an erroneous conception of
the cell, considering the cell-wall as its essential part — whence
the name cellula, a small chamber. But in 1846 the " plant-
slime," observed by Schleiden in the interior of the cell, was in-
vestigated with great thoroughness by von Mohl, and was called
by him protoplasm, a name originally used by Purkinje in 1840
for the substance of which the youngest embryos of animaJs are
composed. Albert Kolliker and others proved that animal-cells
existed in which no cell- wall was present, and Dujardin showed
xvi THE HISTORY OF ZOOLOGY 659
that Amoebae and other lowly organisms were formed entirely of
protoplasm, or, as he called it, sarcode. These discoveries paved
the way for the generalisations of Max Schultze and De Bary,
that the essential constituent of the cell is protoplasm, and that
the protoplasm of animals and plants is identical.
In embryology, the most important work of this time was that of
K. E. von Baer, who, in 1827, discovered the ovum of Mammals.
He also described three primary germ-layers — ectoderm, mesoderm,
and endoderm — in the Vertebrate embryo, and showed that histo-
logical differentiation, or the formation of the permanent tissues
from embryonic cells, proceeds hand in hand with morphological
differentiation or the evolution of organs. He was thus led to
enunciate what is known as von Baer's law, that development is
a progress from the general to the special, and to frame the general-
isation that embryos of animals belonging to various classes closely
resemble one another in their earlier stages, but diverge more and
more as development proceeds. His investigations led him to
support Cuvier's view of the division of the animal kingdom into
distinct and clearly separated types or branches.
It was during this period also that the real meaning of fertilisation
was discovered, and the controversy between ovulists and sperma-
tists finally set at rest. Artificial fertilisation had been tried in
the last century, but up to 1842 the greatest physiologist and most
accurate anatomist of his time, Johannes Muller, was unable
to state positively whether or not the sperms were parasitic animal-
cules. But in 1843 Martin Barry observed the union of ovum and
sperm in the Rabbit, and three years later Kolliker proved that
the sperms were developed from the cells of the testis.
The period under consideration also saw the development of a
school of speculative or deductive zoology. In 1790 Goethe
conceived the idea that the skull of Vertebrates is made of modified
vertebrae — in other words, that the skull is the highly differentiated
anterior end of the backbone. This theory, which may be taken
as a type of morphological speculation in the pre-evolutionary
period, was re-enunciated and greatly elaborated in 1807 by
Lorenz Oken, whose conclusions are worthy of mention, if only
to show the dangers of the deductive method in natural science,
and the lengths to which unbridled speculation may carry a pre-
sumably sane man. He did real service by demonstrating the
secondary segmentations of the bony skull ; the occipital segment
being his " ear vertebrae," the parietal his " jaw vertebrae," and the
frontal his " eye vertebrae." But he clearly went beyond the limits
of legitimate speculation when he contended that the nasal cavity
is a cephalic thorax and the mouth a cephalic abdomen ; that the
bones of the upper jaw are homologues of the fore-limbs, the lower
jaw of the hind-limbs, and the teeth of the digits.
About the middle of the century the vertebral theory, freed
660 ZOOLOUY SECT.
from the most obvious absurdities of Oken, was resuscitated and
developed by Sir Richard Owen (1803-93) in his Report on the
Archetype and Homologies of the Vertebrate Skeleton, published
in 1846. He also founded his generalisations on the structure of
the adult or late embryonic skeleton in the higher groups,
neglecting the unsegmented crania of Cyclostomes and Elasmo-
branchs and of the higher Vertebrate embryo. In his view,
the limb-girdles are modified ribs, the shoulder-girdle belonging
to the " occipital vertebra," while the limbs themselves are
" diverging appendages," or uncinates.
Owen's chief services to Zoology were, however, his numerous
and brilliant anatomical researches, such as those on Nautilus,
on Apteryx, and on the structure and homologies of the teeth in
the entire vertebrate series ; and his palaeontological investigations,
especially those on Archaeopteryx, on the fossil Mammals of
Australia, and on the Dinornithidae and other flightless Birds.
His conclusion, from the examination of a single fragmentary
femur, that there had existed in New Zealand a Bird larger and
heavier than the Ostrich — a fact then practically unknown — forms
one of the most famous stories in natural history. His contri-
butions to classification were not happy ; he took the nervous
system as the basis of his larger divisions, classifying Mammals, for
instance, according to the presence or absence of a corpus callosum
and of convolutions, and placing Man in a separate sub-class as the
supposed sole possessor of a posterior cornu and hippocampus minor.
He rendered great service to philosophical Zoology by pointing out
the distinction between homology and analogy, and by the pub-
lication of his great text-book on the Anatomy and Physiology of
Vertebrates.
The chief successor of Cuvier in France was Henri Milne-
Edwards (1800-85), who enunciated the principle of the
division of physiological labour, and modified the classification
of Cuvier in several particulars. He separated Tunicates from
Mollusca proper and united them with Polyzoa under the name of
Molluscoida, and he divided Vertebrates into Allantoidea and
Anallantoidea, according to the presence or absence of an allantois ;
in so doing he took the important step of separating Amphibia
from Reptiles, a step in which De Blainville had been his only
precursor. His learned Lemons de VAnatomie et de la Physiologie
comparees is a storehouse of information on the structure and
functions of animals.
It was not until about the middle of the century that further
increase in the knowledge of the lower animals resulted in the
gradual dismemberment of Cuvier's unnatural Branch Radiata.
Frey and Leuckart established the group Ccelenterata, and
placed Echinoderms apart ; Wiegmann removed Rotifera from
Protozoa to Vermes ; Vaughan Thomson defined the Polyzoa,
xvi THE HISTORY OF ZOOLOGY 661
and Rudolphi, Leuckart, and von Siebold showed that the
Flat-worms were in no sense Zoophytes. Sponges were considered
by some as polypes, by others as plants ; the current of water
flowing in at the pores and out at the oscula was discovered by
Robert Grant about 1820 : later Bowerbank demonstrated
the presence of cilia, and the full proof of their animal nature was
made by the researches of Lieberkiihn and Carter. The Fora-
minifera were classed as Cephalopoda until the 'thirties, when
Dujardin determined their proper place by the discovery of the
living protoplasmic body. Other important advances in classi-
fication were the separation of Cirripedia from Mollusca by
Vaughan Thomson, and the withdrawal from intestinal worms of
the parasitic Copepoda and of the Pentastomida. The Infusoria
have also had a chequered history. Ehrenberg, in his magnificent
work Die Infusionsthiere, looked upon the food-vacuoles as stomachs,
and described a complex enteric canal connecting them ; it is,
therefore, not surprising that he considered them as belonging to
the same group as Rotifers. Louis Agassiz, as late as 1859,
considered Paramrecium, Opalina, &c., to be the young of Plan-
arians and Trematodes and Vorticella to be a Polyzoan, and it was
only by the researches of Stein and others that the class of Infusoria
was fully established as a natural group of unicellular organisms.
The Swiss zoologist Agassiz (1807-73), referred to in the pre-
ceding paragraph, is interesting not only as one of the foremost
naturalists of his time and the founder of the large and active
school of zoologists in the United States, where he spent the latter
part of his life, but also as the last great biologist to maintain the
fixity of species. In his Essay on Classification, published, curiously
enough, in the same year (1859) as the Origin of Species, he supports
the proposition that the various subordinate groups of animals,
from phyla to species, are not mere " devices of the human mind
to classify and arrange our knowledge in such a manner as to bring
it more readily within our grasp and facilitate further investi-
gations," but that they " have been instituted by the Divine
Intelligence as the categories of His mode of thinking." In other
words, that in our classifications we " have followed only, and re-
produced, in our imperfect expressions, the plan whose foundations
were laid in the dawn of creation."
In 1859 occurred what may fairly be called the most important
event in the history of biological science, the publication of
Charles Darwin's Origin of Species. The evolutionary theories
of Buffon, Erasmus Darwin, Lamarck, and Geoffroy St. Hilaire
had produced little effect upon contemporary zoology ; and
Robert Chambers's Vestiges of Creation (1844), although exciting
great interest, was too crude and speculative to make many con-
verts among men of science. But Darwin had the advantage of
being not only a philosopher, but also a naturalist in the broadest
662 ZOOLOGY SECT.
sense — a systematist with a sufficient knowledge of anatomy,
thoroughly conversant with the breeding of domestic animals and
cultivated plants, a keen observer of external nature, both organic
and inorganic, and with unrivalled experience as a traveller. It
is not surprising, therefore, that the wealth of illustration, the close
reasoning, and the philosophic spirit of the Origin converted the
whole scientific world to the general doctrine of transformism
within twenty years. The theory of Natural Selection, the Survival
of the Fittest, or the Preservation of Favoured Races in the Struggle
for Life, was first grasped by Darwin in 1838, but was not published
until 1858, when it was announced simultaneously by himself and
by Alfred Russel Wallace. Both these authors had, however,
been anticipated by W. C. Wells in 1813, and by Patrick Matthew
in 1831. Darwin's other works, especially The Variations of
Animals and Plants under Domestication and The Descent of Man,
rank among the most important contributions to philosophical
Biology. With them must be mentioned the luminous Principles
of Biology of Herbert Spencer, who consistently upheld the direct
action of the environment as a factor in evolution. Wallace, on
the other hand, is a pure selectionist, while Darwin held " that
natural selection has been the main but not the exclusive means of
modification."
The additions to zoological knowledge made by the voyagers
of the eighteenth century have been referred to ; even more
important are the numerous great scientific expeditions of the
nineteenth and twentieth centuries. Among the most prominent
of these are the voyages of the French ships Astrolabe, Uranie,
Bonite and Geographe, in which researches were carried on by
Peron and La Sueur, Quoy and Gaimard, Eydoux and
Souleyet, and Hombron and Jacquinot, and given to the
world in splendidly illustrated folios. Still more famous is the
voyage of H.M.S. Beagle (1831-36), in which Darwin gained his
extraordinarily wide and accurate knowledge of natural history,
and the narration of which is published in his Naturalist's
Voyage. Other celebrated voyages are those of H.M.S. Rattle-
snake (1846-50), of which T. H. Huxley was assistant-surgeon ;
of H.M.SS. Erebus and Terror, accompanied by Sir J. D. Hooker ;
of the American " Wilkes " expedition, with J. D. Dana as
naturalist, and of the Austrian frigate Novara. But the most
famous and complete of all scientific voyages was that of H.M.S.
Challenger, in 1872-76, the five years' cruise of which was
marked by discoveries of great importance by the scientific staff,
Sir Wyville Thomson, John Murray, H. N. Moseley,
and Willemoes-Suhm, while the zoological material collected
on th3 voyage was worked out by the leading zoologists in all
parts of the world, and the results published in thirty handsome
and fully-illustrated quarto volumes.
xvi THE HISTORY OF ZOOLOGY 663
On board the United States cruisers Blake and Albatross Alex.
Agassiz made several cruises in the Gulf of Mexico (1877-80 and
1891), the Tropical Pacific (1899-1900), and the Eastern Pacific
(1904—1905), the results of which have been in part published in
The Memoirs and Bulletin of the Museum of Comparative Zoology of
Harvard College. The results of the German Deep Sea Expedi-
tion of 1898, under the leadership of C. Chun, have been appear-
ing in a long series of Memoirs since 1892 ; and those of the
German Plankton Expedition (1889) since the same year, under
the editorship of V. A. C. Hensen. An important scientific
expedition to the Dutch East Indies was the cruise of the Siboga
(1899-1900) under the directorship of Max Weber.
In land-travel, numerous journeys, and especially those of
A. R. Wallace in the Malay Archipelago and Brazil, and of
H. W. Bates in Brazil, have not only added immensely to our
knowledge of the genera of the countries visited, but have enriched
the science with the ideas of protective and aggressive characters,
of mimicry, and of the relations of organism to environment
generally.
The establishment of Zoological gardens in different parts of
the world — notably in Paris and London, Stellingen, Berlin,
Hamburg, and New York — has added greatly to our knowledge
both of the habits and of the anatomy of animals, and a similar
advance in the investigation of marine animals has followed upon
the establishment of Zoological Stations or Marine Laboratories
in various countries. The earliest and most important of these
is the Naples Station, founded in 1870 by Anton Dohrn. The
results of the researches there carried on form the most elaborate
and sumptuous series of zoological monographs ever published.
Other stations with similar aims have been instituted in all parts
of the world : of these may be mentioned those of Plymouth,
Wimereux, Roscoff, Banyuls-sur-Mer, Kiel, Helder, Trieste, Woods
Hoi1, and Tokyo : to these have been added in some countries
stations for the study of the fresh-water and terrestrial faunas.
The establishment of Zoological (or Biological) Laboratories in
connection with Universities is also a work of the last forty years,
and has had an important influence both in diffusing a knowledge
of the science and in stimulating research. Even more recent is
the complete change of view as to the functions and arrangement
of a Museum. Formerly it was looked upon as a collection of
curiosities, in which everything was to be exhibited to the public.
Now, thanks in great measure to Sir W. H. Flower in England,
and Browne Goode in America, special collections are formed
for study and research, while the cases accessible to the public are
gradually becoming a series of actual illustrations of zoological
science, in which not only the principles of classification, but the
chief facts of structure, life-history, and habit are strikingly and
664 ZOOLOGY SECT.
adequately shown. Such reforms in the arrangement of museums
and the advancement of their usefulness in many directions have
been the objects aimed at by the Museums Association, an
organisation of those interested in museums in all parts of the
world, founded in 1889.
During the second half of the last century, Zoology as a whole
has been greatly influenced by the writings of Thomas Henry
Huxley and of Ernst Haeckel. Huxley (1825-1895) was
the first to point out the homology of the ectoderm and endoderm
of Coelenterates with the two primary germ-layers of the vertebrate
embryo. He also introduced the word zooid, demolished the
vertebral theory of the skull, and placed the anatomy of the fossil
Ganoids upon a satisfactory footing, as well as making many
other important contributions to animal morphology. His Elements
of Comparative Anatomy (1864) forms an important landmark in
the history of modern Zoology, as giving the views of one of the
keenest, most logical, and least speculative of biologists just
before the time when the various improved histological and
embryological methods began to revolutionise the science.
Huxley's " eight primary categories or groups " are as follows : —
VERTEBRATA.
MOLLUSCA. ANNULOSA
MOLLUSCOIDA [including Arthropoda and Annulata].
[including Brachiopoda, Polyzoa and ANNULOIDA
Tunicata]. [including Echinodermata, Rotifera,
CCELENTERATA. Platyhelminthes and Nemathelminthes].
INFUSORIA
[including Infusoria proper and
Mastigophora].
PROTOZOA
[including Rhizopoda, Sporozoa, and Porifera].
The lower ' Worms " are associated with Echinoderms, on
account of the resemblance of the adult Eotifers, as well as of
the larvae of certain Flat Worms, to the echinopsedium. Sponges
are placed among the Protozoa, in accordance with the view that
they are to be looked upon as colonies of unicellular zooids.
Infusoria are separated from the remaining Protozoa, because
the conjugation observed in them was misinterpreted, the mega-
nucleus being considered as an ovary, the micronucleus as a testis.
Haeckel, apart from his elaborate and beautiful researches on
the Radiolaria, Calcareous Sponges, and Hydrozoa, is remarkable
as the first modern zoologist to attempt the classification of
animals on a frankly evolutionary basis. We owe to him the
terms phylogeny and ontogeny, caanogenesis and palingenesis, and
the fruitful " gastraea-theory," according to which the gastrula is
the ancestral form of all the Metazoa. His classifications take the
xvi THE HISTORY OF ZOOLOGY 665
form of genealogical trees, and he was the first to employ the
method of introducing hypothetical ancestral forms, wherever
they might be wanted to complete the connection between known
groups. He may be said, in fact, to have founded a school of
deductive zoology, the phylogenetic speculations of which are
often as ingenious and suggestive as they are transient. The
student must, however, bear in mind that Archi-molluscs, Ideal
Craniates, and Pro-mammalia are mere figments of the imagina-
tion, and have no more real existence than the " Divine Arche-
types " of an earlier school of thought.
One result of the new views on species, very obvious in the
writings of both Huxley and Haeckel, was the marked alteration
in the position assigned to Man in the animal series. Linnaeus
considered Homo as a genus of his order Primates, equivalent to
Simia, Lemur, &c. ; but Cuvier took the retrograde step of erecting
a distinct order, Bimana, to contain Man alone, the Apes and
Lemurs forming the order Quadrumana. Ehrenberg went
further, and divided the Animal Kingdom into Nations, i.e.,
Mankind, and Animals. Even as late as 1857 Owen, as we have
already seen, made a distinct sub-class, Archencephala, for Man,
the remaining Primates being included with the other higher
mammalian orders in the sub-class Gijrencepliala. This view of
the isolated position of Man was connected with the theory of his
late appearance in time, and the fact of his co-existence with the
Mammoth and other extinct Mammals, first proved by Boucher
de Perthes in 1836 by the discovery of flint axes 20-30 feet
below the present surface, was for many years almost universally
denied. But Lyell's Antiquity of Man (1863) placed the
geological evidence on a sound footing, and the same was done for
the morphological evidence by Huxley, who, in his Man's Place in
Nature (1863), summed up the position by the statement, now
universally conceded, " that the structural differences which
separate Man from the Gorilla and the Chimpanzee are not so
great as those which separate the Gorilla from the lower Apes."
Finally, Darwin, in his Descent of Man (1871), discussed the
question from every point of view, and concluded that " Man still
bears in his bodily frame the indelible stamp of his lowly origin."
It was also during the third quarter of last century that the
old doctrine of Abiogenesis or Spontaneous Generation, first
assaulted by Redi, but maintained by many naturalists from
Aristotle to Haeckel, was finally disposed of. The accurate
methods of Louis Pasteur, Lord Lister, John Tyndall, and
others, proved conclusively that the Bacteria, Monads, and other
lowly organisms which occur in putrefying substances do not arise
de novo, but are the product of germs in the floating dust of the
air by the exclusion of which putrefaction may be absolutely
prevented.
666 ZOOLOGY SECT.
During the last quarter of a century the progress of Zoology
has been profoundly influenced by the improvements in micro-
scopical methods, especially by the invention and perfection of
the microtome, the method of serial section-cutting, and the
various ways of preserving, imbedding, and staining tissues. The
microtome began as a simple contrivance for holding small objects
firmly while sections of them were cut by hand with a razor or
other knife, and has developed into the various modern forms of
the instrument in which the knife is fixed in a plane parallel to
the surface of the object, and the latter is raised mechanically by
small and equal increments as the sections are cut. In this way
perfectly regular sections are obtained of an even thickness not
exceeding the diameter of a cell. The method of imbedding
began by simply holding an object, too small or too soft to be
grasped by the fingers, between two pieces of carrot or pith, and
has gradually been evolved into the present method of complete
impregnation with paraffin or celloidin, by means of which
imbedding material and object form a homogeneous mass.
Simple preservation in alcohol has given place to elaborate fixing
methods by means of chromic, picric, or osmic acids, platinum
chloride, corrosive sublimate, etc., and gradual hardening in
alcohols of increasing strength. Similarly, direct staining with
an ammoniacal solution of carmine has developed into innumerable
methods of differential staining, mostly with aniline dyes, by
which the various tissues and the constituents of the cell—
chromatin, centrosomes, etc. — are clearly brought into view. By
the serial methods successive sections of an embryo or small
animal are mounted in regular order, so that the organs, tissues,
etc., can be traced through the series. In ^ this way the
dislocation of parts produced by dissection is avoided, organs are
seen in absolutely natural relations, and parts quite undiscernible
either by dissection or by microscopic examination of the whole
animal or of dissociated parts of it are clearly brought into view :
the study of the structure upon which the sections are intended
to throw light may be further facilitated by the fashioning of
models in wax, reconstructed by putting together reproductions of
the sections enlarged to scale. Morphological inquiry has, in fact,
been brought within measurable distance of a precision limited
only by the imperfections of our eyes and optical instruments.
Similar accuracy in the topographical anatomy of the larger
Animals, including Man, has been attained by freezing the whole
subject and cutting it into sections with a saw.
These improved methods have necessitated a re-examination by
their aid of every group in the animal kingdom, and, as a result,
our knowledge of the structure of many animals, especially of
the lower forms, of complex organs such as the vertebrate brain,
of embryology, and of the minute structure of cells and tissues
xvi THE HISTORY OF ZOOLOGY 667
has been completely revolutionised. Specially remarkable is the
advance in our knowledge of the Protozoa, Sponges, Actinozoa,
Echinoderms and Amphioxus. The new light which has been
thrown on the affinities of Balanoglossus, Rhabdopleura, and
Cephalodiscus is also worthy of special mention. Probably the
greatest of comparatively recent embryological triumphs, belonging
to the earlier part of the period now under discussion, is Kowalew-
sky Ts discovery of the notochord and hollow nervous system of
the Tunicate larva, which resulted in the removal of the Urochorda
from Molluscoida to Chordata, and in breaking down the sharp
line between Vertebrates and Invertebrates.
But perhaps the most remarkable result of improved micro-
scopical technique is the rise and development of a distinct
department of histology, known as cytology, dealing with the
minute structure of the protoplasm and nuclei and the various
intra-cellular phenomena, such as mitosis. Our knowledge of this
subject is entirely a product of the last forty-five years, and is
due in great measure, in the first instance, to the researches of
W. Fleming-, E. Strasburger, and E. van Beneden. A
modification of the cell-theory has also been necessitated by the
proof that many animal tissues do not consist of distinct cells,
but of a continuous mass of protoplasm with more or less regularly
arranged nuclei, and are therefore strictly not multicellular but
non-cellular. As certain Protozoa, such as the Mycetozoa and
Opalina, are also non-cellular, containing numerous nuclei in an
undivided mass of protoplasm, the distinction between Protozoa
and Metazoa appears to be less absolute than it was at one time
considered.
The advance in palaeontology during the same period has also
been immense. In particular the researches of E. D. Cope,
O. C. Marsh, and others in America, have added whole orders to
Zoology — the Odontolcse, Ichthyornithes, Stereornithes, Ambly-
poda and Dinocerata — and have resulted in the discovery of many
new and strange forms among the Dinosauria, Elasmobranchs,
Ganoids, and other groups, and in the tracing of the pedigrees
of the Equidse, Camelidse, and other Mammalian families. Im-
portant though less striking discoveries have also been made
among the fossil faunae of Europe, India, South Africa, and
Australia ; while among Invertebrates the attempts to trace the
pedigree of the AmmQnites and Brachiopods are specially note-
worthy.
In embryology an important landmark is furnished by F. M.
Balfour's Comparative Embryology (1880-81) ; in distribution, by
A. R. Wallace's Geographical Distribution of Animals (1876),
each the first complete treatise on the subject in question. The
zoo-geographical regions adopted by Wallace were originally
proposed by P. L. Sclater in 1857. Similar landmarks for Zoology
668 ZOOLOGY sue*.
as a whole are Huxley's Anatomy of Vertebrated Animals (1871)
and Anatomy of Invertebrated Animals (1877), Carl Gegenbaur's
Elements of Comparative Anatomy (English edition, 1878), Glaus 's
Text-Book of Zoology (1st English edition, 1884-5), Ray
Lankester's Notes on Embryology and Classification (1877), and the
same author's articles in the Encyclopedia Britannica (9th edition).
Both Glaus and Gegenbaur retain Vermes as a primary division ;
Lankester was the first to split up that unnatural assemblage into
distinct phyla, and to include Balanoglossus and the Tunicata
among Vertebrates, and Xiphosura and Eurypterida among
Arachnida. He also associated Rotifers and Chsetopods with
Arthropoda, and placed Hirudinea among the Platyhelminthes.
A later development of the same author's views on morphology
and classification is embodied in his Treatise on Zoology, of which
eight volumes have now been published (see Appendix, 675). Of
inestimable value in the advancement of the embryology of Verte-
brates is the comprehensive Handbuch (1901-1906) of O. Hertwig,
with sections by various other embryologists.
The student who is interested in the permutations and combina-
tions of modern classification may be referred to the works just
quoted as well as to the numerous text-books published of late
years. The most important point to notice in this connection
is the breaking down of the sharp boundaries between the four
Cuvierian Branches and a return to something like the conception
of unity of type, expressed, however, not as a linear series, but
as a branch-work with the most complex and often puzzling inter-
relations.
Among the numerous recent contributions to philosophical
Zoology it must suffice to mention the works on heredity and
kindred subjects of August Weismann, the most prominent
member of the ultra-Darwinian school, who deny use-inheritance
and rely upon natural selection as the main, if not the sole, factor
in evolution. The opposite view, which accepts the truth of use-
inheritance, is mainly supported by the American school of Neo-
Lamarckians. Weismann has also resuscitated the theory of
preformation under a modern form. He considers that the
various parts of the adult organism are represented in the
chromatin (germ-plasm) of the sex-cells by ultra-microscopic
particles or determinants. These and allied topics are comprehen-
sively treated from a different standpoint by O. Hertwig in his
Allgemeine Biologic (1909).
In a brief sketch like the present it is impossible to do more
than refer, in general terms and without mention of names, to the
vast amount of work now being done in every department of
Zoology. The output of original research is greater than at any
former time and is increasing rapidly, and every important addition
to our knowledge necessitates a more or less thorough reconsidera-
xvi THE HISTORY OF ZOOLOGY 669
tion of the general and special problems of morphology and
classification.
In addition to the continued study of adult structure and em-
bryology of animals and plants with their classification and
phylogeny and their distribution in space and time, the workers
in Biology during the first two decades of the twentieth century
have bestowed more attention than hitherto on (1) Experimental
Biology and Embryology, (2) Genetics, and (3) Cytology. It is in
the second of these departments — the revived and intensified
study of heredity — that the impulse towards the first and third
has mainly originated. A large part of the experimental work
accomplished has had for its object the solution of genetic problems ;
and on the other hand the attempts to co-ordinate the minutiae
of structure in the germ-cells with known phenomena of heredity
or theoretical explanations of such phenomena have given interest
and importance to most recent cytological work.
VOL. II
T T
APPENDIX
ZOOLOGICAL LITERATURE.
THE following are lists of some of the publications which will be
most useful to the student of Zoology, the first comprising books
giving directions for practical work in the laboratory ; the second,
general works on the entire subject or on one or other of its main
sub-divisions ; the third, publications in which are given the titles
and in some cases abstracts of the contents, of new works as they
appear. More or less comprehensive bibliographical lists are given
in several of the works referred to in the second list (Nos. 8, 20, 32,
35, 49, 50, 70, 82, etc.).
I. Books bearing specially on Laboratory work.
1. APATHY, S. Mikrotechnik der thierischen Morphologie, 1896-1901.
2. BROOKS, W. K. Handbook of Invertebrate Zoology, 1890. [Amceba,
Paramoecium, Vorticella, Calcareous Sponge, Zoophyte, Antho-
medusa, Leptomedusa, Starfish, Sea-urchin, Embryology and
Metamorphosis of Echinoderms, Earthworm, Leech, Crab,
Crayfish or Lobster, Metamorphosis of Crab, Cyclops (including
metamorphosis), Grasshopper, Mussel, Development of Lamelli-
branchs, Squid, Development of Squid.]
3. EHRLICH, P., KRAUSE, R., Moss, M., ROSIN, H., WEIGERT, K.
Encyclopcedie der mikroskopischen Technik, 2 vols., 2nd edition,
1910.
4. FOSTER, M., and BALFOUR, F. M. Elements of Embryology,
2nd edition, by A. Sedgwick and W. Heape, 1883. [Chick
and Rabbit.]
5. FRIEDLANDER, R. Mikroskopische Technik, 6th edition, 1900.
6. HOWES, G. B. Atlas of Practical Elementary Zootomy, 1902.
[Amoeba, Stentor, Paramoecium, Spirostomum, Vorticella,
Hydra, Fresh-water Mussel, Snail, Earthworm, Crayfish, Frog.]
671 T T 2
672 APPENDIX
7. HUXLEY, T. H., and MARTIN, H. N. A Course of Practical
Instruction in Elementary Biology, 2nd edition, by G. B. Howes
and D. H. Scott, 1888. [Amoeba, Vorticella, Paramoecium,
Opalina, Hydra, Earthworm, Crayfish, Mussel, Snail, Frog.]
8. KUKENTHAL, W. Leilfdden fur das zoologische Praktikum, 4.
Aufl., Jena, 1907.
9. LEE, A. B. Microtomists' Vade Mecum, 6th edition, 1905.
[A compendium of laboratory methods.]
10. MARSHALL, A. M. The Frog : an Introduction to Anatomy,
Histology, and Embryology, 6th edition, 1896.
11. MARSHALL, A. M., and HURST, C. H. Practical Zoology, 7th edition,
1912. [Amoeba, Vorticella, Paramoecium, Hydra, Liver-Fluke,
Leech, Earthworm, Crayfish, Cockroach, Fresh-water Mussel,
Snail, Amphioxus, Dogfish, Pigeon, Rabbit, Development of
Chick.]
12. PARKER, T. J. A Course of Instruction in Zootomy, 1884.
[Lamprey, Skate, Cod, Lizard, Pigeon, Rabbit.]
13. PARKER, T. J., and PARKER, W. N. An Elementary Course of
Practical Zoology, 5th edition, 1920. [Part I — Frog ; Part II-
Amoeba, Sphserella, Paramoecium, Vorticella, Opalina, Mono-
cystis, Hydra, Obelia, Earthworm, Nereis, Crayfish, Fresh-
water Mussel, Amphioxus, Dogfish, Rabbit ; Histology, Embry-
ology, etc.]
14. SCHNEIDER, K. C. Histologisches Praktikum der Thiere, 1908.
15. VOGT, C., and JUNG, E. Traite d'Anatomie comparee pratique,
2 vols., 1883-94 (also a German edition). [Amoeba, Foraminifer
(Polystomella), Actinosphaerium, Radiolarian (Actinometra),
Paramoecium, Dicyema, Calcareous Sponge, Alcyonium, Aurelia,
Hydra, Ctenophore (Bolina), Tsenia, Distomum, Turbellarian,
Nemertean Leech, Ascaris, Sipunculus, Rotifer (Brachionus),
Earthworm, Lobworm (Arenicola), Feather-star, Starfish, Sea-
urchin, Holothurian, Polyzoan (Plumatella), Brachiopod, Mussel,
Snail, Pteropod, Cuttle-fish, Crayfish, Centipede, Cockchafer,
Spider, Salpa, Simple Ascidian, Amphioxus, Lamprey, Perch,
Frog, Lizard, Pigeon, Rabbit.]
16. WILDER, B. G., and GAGE, S. H. Anatomical Technology [Cat.].
3rd edition, 1892.
II. General Works and Text-books.
1. BALFOUR, F. M. Treatise on Comparative Embryology, 2 vols.,
1880-81. Works, Memorial Edition, 4 vols., 1885.
2. BATESON, W. Materials for the Study of Variation, 1894.
3. BATESON, W. Mendel's Principles of Heredity, 1909.
4. BEDDARD, F. Animal Coloration, 1892.
APPENDIX 673
5. BEDDARD, F. Text-book of Zoogeography, 1895.
6. BOAS, J. E. V. Lehrbuch der Zoologie, 1891. English Translation,
1894.
7. BONNET, R. Lehrbuch der Entwickelungsgeschichte, 1907.
8. BRONN, H. G. Klassen und Ordnungen des Tierreichs. Protozoa
(BiJTSCHLi), 1880-89 ; Porifera (VOSMAER), 1887 ; Turbd-
laria (GRAFF) ; Trematoda (BRAUN) ; Cestoda (BRAUN) ; Ncmer-
tina (BURGER) ; Tunicata (SEELIGER) ; Asteroidea (LuowiG
and HAMANN) ; OpMuroidea (HAMANN) ; Echinoidea (HAMANN) ;
Crinoidea (HAMANN) ; Holothuroidea (Luowic) ; Mollusca
(KEFERSTEIN), 1862-66 ; Amphineura (SIMROTH) ; Gastropoda
(SIMROTH) ; Crustacea (GERSTACKER) ; Myriapoda (VERHOEFF) ;
Amphibia (HOFFMANN), 1873-78 ; Reptilia (HOFFMANN), 1890 ;
Aves (GADOW), 1891 ; Mammalia (GIEBEL and LECHE).
9. Cambridge Natural History.
Vol. I. Protozoa (HARTOG, M.) ; Porifera (SoLLAS, I. B. J.) ;
Coelenterates and Ctenophora (HiCKSON, S. J.) ; Echinoderms
(MAcBRiDE, E. W.), 1906.
Vol. II. Flatworms and Mesozoa (GAMBLE, F. W.) ; Nemertines
(SHELDON, L.) ; Threadworms and Sagitta (SHIPLEY, A. E.) ;
Rotifers (HARTOG, M.) ; Polycliaet Worms (BENHAM, W. B.) ;
Earthworms and Leeches (BEDDARD, F. E.) ; Gephyrea and
Phoronis (SHIPLEY, A. E.) ; Polyzoa, (HARMER, S. F.), 1896.
Vol. III. Molluscs (CooKE, A. H.) ; Brachiopods (recent), (SHIPLEY,
A. E.) ; Brachiopods (fossil), (REED, F. R. C.), 1895.
Vol. IV. Crustacea (SMITH, G.) ; Trilobites (Wooos, H.) ; Intro-
duction to Arachnida and King-Crabs (SHIPLEY, A. E.) ;
Eurypterida ( WOODS, H.) ; Scorpions, Spiders, Mites, Ticks,
etc. (WARBURTON, C.) ; Tardigrada (SHIPLEY, A. E.) ; Penta-
stomida (SHIPLEY, A. E.) ; Pycnogonida (THOMPSON, D'A. W.).
Vol. V. Peripatus (SEDGWICK, A.) ; Myriapods (SINCLAIR, F. G.) ;
Insects, Part I. (SHARP, D.), 1895.
Vol. VI. Insects, Part II. (SHARP, D.), 1899.
Vol. VII. Hemichordata (HARMER, S. F.) ; Ascidians and Amphioxus
(HERDMAN, W. A.) ; Fishes (BRIDGE, T. W., and BOULENGER,
G. A.), 1904.
Vol. VIII. Reptiles and Amphibia (GADOW, H.). 1901.
Vol. IX. Birds (EVANS, A. H.), 1897.
Vol. X. Mammalia (BEDDARD, F. E.), 1902.
10. BROOKS, W. K. The Foundations of Zoology, 1899.
11. BiiTSCHLi, 0. Vorlesungenuber vergleiclienden Anatomie, 1910, 1920.
12. CARUS, V. Geschichte der Zoologie, 1872. (French Translation,
Histoire de la Zoologie, 1880.)
674 APPENDIX
13. CUVIER, G. Regne Animal. Illustrated edition, 1849.
14. Darwin and Modern Science. Essays in commemoration of the
Centenary of Charles Darwin, 1909.
15. DARWIN, C. Origin of Species, 6th edition, 1880.
16. DARWIN, C. Descent of Man, 1882.
17. DARWIN, C. Animals and Plants under Domestication, 2 vols.,
1888.
18. DEAN, B. Fishes, Living and Fossil, 1895.
19. DELAGE, Y. L'Heredite etles grands problemes de Biologie generale,
2nd edition, 1903.
20. DELAGE, Y., et HEROUARD, E. Traite de Zoologie Concrete. I. La
Cellule et les Protozoaires, 1896. II. Spongiaires et Coelenteres,
1899. III. Echinodermes, 1903. V. Vermidiens, 1897. VII.
Prochordes, 1898.
21. DENDY, A. Outlines of Evolutionary Biology, 2nd edition, 1912.
22. DONCASTER, L. Heredity in the Light of Recent Research, 1910.
23. DONCASTER, L. Cytology, 1920.
24. DUVAL, M. Atlas d'Embryologie, 1889.
25. EIMER, T. Die Entstehung der Arten, 1888. English Translation,
Organic Evolution, 1889.
26. FLOWER, W. H. Osteology of the Mammalia, 1885.
27. FLOWER, W. H., and LYDEKKER, R. Mammals, Living and
Extinct, 1891.
28. GAUDRY, J. Les enchainements du monde animal dans les temps
geologiques, 1878.
29. GEGENBAUR, C. Elements of Comparative Anatomy. English
Translation, 1878.
30. GEGENBAUR, C. Vergleichende Anatomie der Wirbelthiere, 2 vols.,
1898 and 1901.
31. HATSCHEK, B. Lehrbu^h der Zoologie.
32. HEIDENHAIN, M. Plasma u. Zelle, 1907.
33. HEILPRIN, A. The Distribution of Animals, 1887.
34. HERTWIG, 0. Die Elemente der Entwickhingslehre des Menschen
und der Wirbelthiere, 1910.
35. HERTWIG, 0. Handbuch der vergleichenden und experimentellen
Entwickelungslehre der Wirbelthiere. Sections by various writers,
3 vols., 1901-1906.
36. HERTWIG, 0. The Biological Problem of To-day, 1896.
37. HERTWIG, 0. Allgemeine Biologie, 3rd edition, 1909.
38. HERTWIG, R. Lehrbuch der Zoologie, 9th edition, 1910. English
Translation of 3rd edition.
39. HILZHEIMER, M. Handbuch der Biologie der Wirbelthiere, 1913.
40. HUXLEY, T. H. The Anatomy of Invertebrated Animals, 1877.
APPENDIX 675
41. HUXLEY, T. H. The Anatomy of Vertebrated Animals, 1871.
42. JORDAN, D. S., and KELLOGG, V. L. Evolution and Animal Life,
1907.
43. KEIBEL, F. Normentafeln zur Entwickelungsgeschichte der ]\'ir-
beltiere. [Pig, Fowl, Ceratodus, Lizard, Rabbit, Deer, Tarsius.
Nycticebus, Man, Lapwing.] 1897-1909.
44. KELLICOTT, W. E. Text-book of General Embryology, 1914.
44a. KELLICOTT, W. E. Outlines of Chordate Development, 1914.
45. KELLOGG, V. L. Darwinism To-day, 1907.
46. KERR, J. G. Text-book of Embryology : Vertebrata, 1919.
47. KINGSLEY, J. S. Text-book of Vertebrate Zoology, 1899.
48. KORSCHELT, E., and HEIDER, K. Text-book of the Embryology <>f
1 H n'rtflirates. English edition, 4 vols., 1895.
49. LANG, A. Lehrbuch der vergleichenden Anatomie d<:r wirbellosen
Thiere, 1894. English Translation, Comparative Anatomy of
Invertebrates, 1891-6. Second German edition, Protozoa, 190L
Mollusca, 1900. Third German edition (Handbuch der Morph-
ologic der wirbellosen Thiere}, 1912.
50. LANKESTER, E. R. A Treatise on Zoology. I. Protozoa (LISTER,
MINCHIN, HICKSON). II. Porifera and Coelentera (MiNCHiN,
FOWLER, BOURNE). III. Echinoderma (BATHER). IV. Platy-
helmia, Mesozoa and Nemertini (BENHAM). V. Mollusca
(PELSENEER). VII. Crustacea (CALMAN). IX. Cyclostomes and
Fishes (GOODRICH). 1900-09.
51. LILLE Y, F. The Development of the Chick, 1908.
52. LYDEKKER, R. Royal Natural History. 6 vols. 1894-96.
53. MACBRIDE, E. W. Text-book of Embryology. Invertebrata, 1914.
54. MARSHALL, A. M. Vertebrate Embryology, 1893. [Amphioxus,
Frog, Chick, Rabbit, Human Embryo.]
55. MORGAN, C. L. Animal Life and Intelligence, 1891.
55«. MORGAN, C. L. Habit and Instinct, 1896.
56. MORGAN, T. H. Experimental Zoology, 1906.
57. NICHOLSON, H. A., and LYDEKKER, R. Manual of Palaeontology,
2 vols., 1889.
58. OPPEL, A. Lehrbuch der vergleichenden mikroskopischen Anatomie
der Wirbeltiere, 1896-1904.
59. OSBORN, H. F. From the Greeks to Darwin, 1894.
60. OWEN, R. Anatomy of Vertebrates, 4th edition, 1871.
61. PARKER, T. J. Lessons in Elementary Biology, 3rd edition, re-
printed, with corrections, 1919.
61a. PARKER, T. J., arid HASWELL, W. N. A Manual of Zoology,
reprinted 1908.
62. POULTON, E. B. Essays on Evolution, 1908.
676 APPENDIX
63. PUNNETT, R. C. Mendelism, 1911.
64. ROLLESTON, G., and HATCHETT-JACKSON, W. Forms of Animal
Life, 1888.
65. RABL, C. Geschichte der biologischen Theorien, 2 vols., 1909.
66. REINKE, J. Einleitung in die theoretische Biologic, 2nd edition,
1911.
67. ROMANES, G. J. Darwin and After Darwin, 2 vols., 1892 and 1895.
68. Roux, W. Vortrdge und Aufsdtze uber Entwickelungsmechanik
der Organismen, 1904.
69. SEDGWICK, A. A Student's Text-Book of Zoology. Vol. I. Protozoa
to Chcetognatha, 1898. Vol. II. Amphioxus and Vertebrata, 1905-
Vol. III. Tunicata, Enter opneusta, Echinodermata, Arthropoda,
1909.
70. SCHIMKEWITSCH, W. Lehrbuch der vergleichenden Anatomie der
Wirbelthiere. German Translation from Russian, 1910.
71. SCHNEIDER, K. C. Lehrbuch der vergleichenden Histologie der Thiere,
1902.
72. THOMSON, J. A. Heredity, 1908.
73. VERWORN, M. Allgemeine Physiologic, 5th edition, 1909 ; English
Translation, General Physiology, 1899.
74. VRIES, H. DE. Die Mutationstheorie, 2 vols., 1901. English
Translation by Farmer and Darbishire, 1910.
75. WAGNER, M. Die Entstehung der Arten dwell rdumliche Sonderung,
1889.
76. WALLACE, A. R. Geographical Distribution of Animals, 2 vols.,
1876.
77. WALLACE, A. R. Darwinism, 1889.
78. WALLACE, A. R. An Examination of Weismannism, 1893.
79. WALTER, H. E. Genetics, an Introduction to the Study of Heredity,
1913.
80. WEBER, M. Die Sdugetiere, 1904.
81. WEISMANN, A. The Evolution Theory, 2 vols., 1904 (Trans.
Thomson). 3rd German edition, 1913.
82. WIEDERSHEIM, R. Vergleichende Anatomie der Wirbeltiere, 7th
edition, 1909.
83. WIEDERSHEIM, R., and PARKER, W. N. Comparative Anatomy of
Vertebrates, 1907.
84. WILLEY, A. Amphioxus and the Ancestry of the Vertebrates, 1894.
85. WILSON, E. B. The Cell in Development and Inheritance, 2nd edi-
tion, 1900.
86. WOODWARD, A. S. Outlines of Vertebrate Paleontology, 1898.
87. ZIEGLER, E. H. Lehrbuch der Entwickelungsgeschichte der niederen
Wirbeltiere, 1902.
APPENDIX 677
88. ZITTEL, K. VON. Handbuch der Palaontologie, 5 vols., 1876-93.
English Translation, 2 vols., 1902.
89. ZITTEL, K. VON. Grundzuge der Palaontologie, 2 Aufl., 1903.
III. Periodical Publications containing Current Bibliographies, etc.
1. American Naturalist, fortnightly. Contains original articles, usually
of a popular character, and summaries of recent researches.
2. Anatomischer Anzeiger, fortnightly. Original papers (mostly short)
and current bibliography.
3. Annee Biologique, annual. Abstracts of works and papers on
general Biology. 1895-1911.
4. Biologisches Centralblatt, fortnightly. Contains, in addition to
original articles, resumes of recent publications.
5. Ergebnisse und Fortschritte der Zoologie. Resumes of the present
state of knowledge on special subjects.
6. International Catalogue of Scientific Literature. Zoology and
General Biology. Obtainable in sections. Full classified lists
of all current writings with indication of new species and
reference to new genera.
7. Journal of the Royal Microscopical Society, bi-monthly. Abstracts
of papers on nearly all departments of Zoology.
8. Quarterly Journal of Microscopical Science.
9. Science Progress, monthly. Contains abstracts of Zoological papers.
10. Zoological Record, annual. Bibliographical lists with some synopses
of contents.
11. Zoologischer Anzeiger, fortnightly. Original papers (mostly short
preliminary notices), and current bibliography (Bibliographia
Zoologica, also to be had separately).
12. Zoologischer Jahresbericht, annual. Published by the Naples
Zoological Station. Consists (1) of bibliographical lists, (2) of
abstracts of the contents of most of the papers, 1879-1912.
13. Zoologisches Zentralblatt, fortnightly. Consists (1) of occasional
summaries and criticism of recent work on special subjects,
(2) of abstracts of individual books or papers in all departments
of Zoology.
INDEX
INDEX
All numbers refer to pages : words in italics are names of families, genera and
species : words in thick type are names of higher divisions : words in
small capitals are names of examples. Numbers in thick type are numbers
of pages on which there are figures : an asterisk after a number indicates
a definition of the term or of the group.
A Adipose fin, 194*
Adipose lobe, 194
Adrenals, of Craniata, 117 : Frog, 278 :
Pigeon, 385 : Rabbit, 459
^Egithognathous arrangement, 415*
^Epyornis, 399, 423, 429, 621
/Epyornithes, 399*
Aerial fauna, 617*
Afferent branchial arteries, 90 : of
Amphloxus, 49 — See Vascular sys-
tem
Affinities— See Relationships
After-shaft of Feather, 370, 410*, 411
Agamidce, 358
Agassiz, Alex., 663
Agassiz, Louis, 661
Aggressive resemblance, 637
Aglossa, 285*, 295
Agoutis, 492
Air-bladder, 87* : of Trout, 204*, 205 :
Teleostomi, 229
Air-sacs, of Chamaeleon, 347 : Pigeon,
386, 387 : Birds, 421
Air-space, of Bird's egg, 422, 423
Ala spuria, 368, 373*
Alar membrane, 368
Alaudidce, 404
Albatrosses, 402, 417, 422
Albula, 231
Albumen, of Bird's egg, 394, 422, 423
Alca, 403
Alca impennis, 413
Alcedinidce, 404, 423
Ali-sphenoid, 77*— See Skull
Allantoic bladder, of Craniata, 116*
Allantoic placenta, 577
Allantois, Reptiles, 303, 354 : Bird,
427, 428 : Rabbit, 462 : Mammalia,
575
,ARD-VARKS, 465, 485, 5r/9, 584—
See Orycteropus
Abdomen — Mammals, 70*, 433
Abdominal cavity, of Craniata, 70
Abdominal pore, 65, 66, 142, 243
Abdominal ribs, 293, 336, 405
Abdominal vein, 272, 273, 316, 558
Abducent nerve, of Craniata, 101, 102
Abductor muscles, 266
Abiogenesis, 650
Abomasum, 553*
Abyssal fauna, 615*
Acanthias, 173
Acanthodei, 163*
Acanthodes, 164
Acanthodrilus, 601
Acanthopteri, 214*, 218, 219, 221, 225,
236
Accessory nerve, of Craniata, 101, 103
Accessory scapula, 417
Accipitres, 403*, 431
Acetabulum, of Craniata, 80, 82*
Acipenser, 212, 234 — See Sturgeon
Acipenser ruthenus, 212
Acrauia, 43* — See Ainphioxus
Acrocoracoid process, 378
Acrodont teeth, 345*
Acromion process, of Pigeon, 378 :
Rabbit, 441 — See Pectoral arch
Acustico -lateral centre, 158
Ad-digital, 373
Adductor muscles, 266
Adelochorda, 2* : Affinities, 13
Adhesive papilla, of Ascidian larva, 34,
35
Adipose bodies, of Frog, 279 : Lizard,
316
68 1
682
INDEX
Allelomorphic characters, 645
Alligator, 326, 343, 344, 346, 349, 357,
359
Alpine fauna, 617*
Altrices, 429*
Alveoli of lung, 454
Alveus, 561*
Alytes obstetricans, 300, 302
Amarcecium, 22
Ambiens muscle, 383*
Amblyopsis spelceus, 617
Amblypoda, 588
Amblystoma, 284, 290, 294, 301, 302
American Ant-eaters, 465, 484, 509,
511, 512, 513, 547, 579
Amia, 213, 218, 221, 222, 223, 227,
229, 231, 233, 234, 235, 236
Amia calva, 213
Ammoccetes, 133*
Amnion, of Reptiles, 303, 354 : Birds,
427, 428 : Rabbit, 461, 462 : Mam-
mals, 572, 573
Amniota, 303*
Amphibia, 64*, 256 : Example, 257 :
Distinctive characters and classi-
fication, 283 : General organisation,
285 : External characters, 285 :
Exoskeleton, 289 : Endoskeleton,
289 : Myology, 294 : Digestive
organs, 295 : Respiratory organs,
295 : Circulatory organs, 296 : Ner-
vous system and sense organs, 298 :
Urinogenital organs, 299 : Repro-
duction and development, 300 :
Distribution, 302 : Mutual relation-
ships, 302
Amphibolurus, 350, 355
Amphico?lous, 142*
Amphioxides, 43, 59, 62
Amphioxididce, 43
AMPHIOXUS, 43 : External features,
43 : Body-wall, 44, 45 : Skeleton,
45, 46, 47 : Digestive and respira-
tory organs, 46, 47, 48 : Atrium,
47, 49 : Coelome, 47, 49 : Blood-
system, 49, 50 : Excretory organs,
51 : Nervous system, 51, 52, 53 :
Sensory organs, 52, 53, 54 : Repro-
ductive organs, 54 : Development,
54, 55, 56, 57, 58, 59, 60, 61, 62 :
Distribution, 62 : Distinctive char-
acters, 62, 63 : Affinities, 63
Amphipnous, 228
Amphisbsenians, 324, 332, 337, 347,
354, 358
Amphistylic skull, 76*, 168
Amphitherium, 619
Amphiuma, 284, 286, 287, 296, 298,
302
Amphiuma tridactyla, 286
Ampulla;, 111*, 112, 174*— See Ear
Ampullary canals, 158*, 174
Anabas scandens, 228
Anacanthini, 214*, 219, 221, 236
Anapophyses, of Rabbit, 435*
Anas, 403, 408, 415, 416, 605
Anas boschas, 416
Anatomical evidence of Evolution^ 624
Anchinia, 22
Anchovy, 214
Ancylopoda, 588*
Angler, 219
Anyuidce, 358
Anguis, 328, 332, 350, 358
Angular, 199, 200*
Angular process, of mandible, 441 —
See Skull
Angulo-splenial, 261, 262
Ankylosis, 195*
Annular cartilage, of Lamprey, 122,
123
Annulus ovalis, 450*
Annulus tympanicus, of Frog, 262, 278
Anomalur'nft, 476, 492
Anomodontia, 326
Anser, 403, 415
Anseres, 403*, 422, 429
Ant-eater, American, 465, 484, 509,
511, 512, 513, 547, 579 : Banded,
480 : Cape, 465, 579 — See Onjctero-
pus : Scaly — See Manis : Two -toed,
484
Ant-eaters, 465
Antelopes, 468, 487, 580
Anterior clasper, 184
Anterior commissure, 206
Anterior vertebral plate, 167*, 169
Anthropoidea, 472*
Anthropopithecus, 473 — See Chimpan-
zee
Anth.ropopithecus troglodytes, 538
Antiarcha, 256
Aiitibrachium, 304*
Antitrochariter, 380*
Antlers, 487
Ant orbital, 170*
Anura, 284*, 285, 288, 289, 291, 293,
2!»4, 295, 296, 298, 300, 301, 302
Anwiella, 37
Aortse, 89, 90 : Ampliioxus, 49, 50—
See Vascular system
Aortic arches, 92, 93 — See .Vascular
system
Apatornis, 402
Apes, 494
Aphanapteryx, 605, 622
Apical plate, of Tornaria, 7, 8
Apoda, 285*
Appendicularia, 21, 24, 28, 29, 30, 41
Ajijiciii/icii/tir/ida', 21
Appendix, vermiform, of Rabbit, 448
Aptcnodytes, 402
INDEX
083
Apteria, 372*. 409
Apteryges, 398
Apteryx, 398. 399. 408, 414, 417, 419.
4 I'd, 421, 422. 423, 426, 421), (UK),
622
Apteryx tiHNlrtil/x, 398, 399. 419
Apteryx ntnntflli. 414. 415. 417
Apteryx owcni. 420
Aptornis, 403, 413, 417, 600, 622
Aqueduct of Sylvius, 99*
Aqueductus vestibuli, 144, 158, 174
Aqueous chamber, of Eye, 108*
Aqueous humour, 108*
Aqnilft, 403, 423
Aquinas, Thomas, 654
Ara, 404, 416
Arachnoid membrane, 100
Arbor vitas, of Rabbit, 458*
Arboreal faiuia, 617*
Archseoceti, 586
Archceohyrox, 587
Archceopteryx, 397, 405, 430, 619
Archceopteryx lithographica, 405, 406.
407, 430, 619
Archceopteryx siemensii, 407
Archseornithes, 397*, 405
Archenteron, 280*. 281
Archipallium, 561*
Archipterygium, 103*, 250
Arcijera, 285*
Arctomys marmot, 617
Ardea,'4(M, 409. 410
Area opaca, 352, 424
Area pellucid a, 352, 424
Area vasculosa, 426
Argentea, 206*, 207, 208
Aristotle, 647
Armadillos, 465, 476, 484, 508, 509.
510, 511. 512, 513, 516, 547. 579, 5S5
Arteries, 89, 90 — See Vascular system
A rthrodira, 252
Articular, 77, 79*— See Skull
Artiodactyla, 4(is*, 487, 521, 522, 526,
527, 547, 558
Arvicola, 575
Arytenoids, of Lizard, 318 : Reptilia,
347 : Pigeon, 385 : Rabbit, 453
ASCIDIA, 14 : Body-wall and Atrial
cavity, 14, 15 : Pharynx, 16, 17, 18 :
Enteric canal, 18 : Blood system,
18, 19 : Nervous system, 19, 20 :
Neural gland, 19, 20 : Excretory
system, 20 : Reproductive system,
20 : Systematic position, 23 : De-
velopment, 30
Ascidia mammillata, 35
Ascidiacea, 22*, 30
Ascidiae composite, 22*, 24, 25
Ascidise simplices, 22*, 24
Ascidians, 13
Ascidiidce, 23
Aspredo, 234
Asses, 468, 580
Astacopxix. Ho;.'
Astacus, 601
Asteriscns. 208*. 209
Astragalo -scaphoid, 344
Astragalus, 259. 266, 344, 444— See
Limb -skeleton
Astroscopus, 226
A teles, 473
Athecata, 359
Atlas, 306*
Atrial aperture, 14*, 15
Atrial canals, of Larvacea, 23
Atrial cavity, of A sciilin, 14, 15, 16, 17
Atrial lobes, of Dolinlnm, 26
Atrial siphon, 15, 17
Atriopore, of Amphioxiift, 43, 44, 47, 49
Atrium, of Ascidin. 1 6, 35 : Amphioxus,
47, 49
Auditory capsules, of Craniata, 73*
Auditory foramina, 75
Auditory nerve, 101, 102 — See Brain
Auditory organ — See Ear
Auditory ossicles, 441* — See Ear
Auditory region, of Craniata, 74*
Augustine, 654
Auks, 403, 422, 429, 431
Auricle, 88 — See Heart
Auricular appendix, 449
Australian region, 611*
Autostylic skull, 76*, 185
Aves, 64, 303, 366 : Example, 367 :
Distinctive characters and classi-
fication, 395 : General organisation,
405 : Archseornithes, 405 : External
characters of Neornithes, 407 :
Pterylosis, 409: Skeleton, 411:
Myology, 420 : Digestive organs,
420 : Respiratory and vocal organs,
421 : Circulatory organs, 421 : Ner-
vous system and sense organs, 421 :
Urinogenital organs, 422 : Develop-
ment, 422 : Distribution, 429 :
Ethology, 430 : Phylogeny, 430
Avocet, 408
Axis, 306*
Axis, basi-cranial, 498*
Axolotl, 284, 301, 302
Aye-Ayes, 472
Azygos veins, of Rabbit, 452 : of
Urodela, 297, 298
B
UBOONS, 473, 499, 538, 539
Baer, K. E. von, 659
Bahena, 466
Balcenidcp, 466
Balcenoptera musculus, 51
684 INDEX
Balcenoptera rostrata, 550, 551 Biceps muscle, 268
Balanoglossus, 2, 41, 42 : External Bicipital groove, 442
characters, 3, 4 : Ccelome, 3 : Bile, 85*
Digestive organs, 5 : Notochord or Bile ducts, 85 — See Liver
cesophageal diverticulum, 3, 6 : Biogenesis, 650
Blood -vascular system, 4. 6 : Ner- Birds — See Aves
vous system, 4, 5, 6, 7: Repro- Birds of Paradise, 404, 411, 420, 602
ductive system, 7 : Development, Blackbirds, 404
7, 8, 9 : Metamorphosis, 8, 9 Bladder, urinary, of Craniata, 116 :
Baleen, 466*, 550*, 551 Trout, 208, 209 : Teleostomi, 232 :
Baleen whales, 466 Rabbit, 459, 460 : Mammals, 565
Balfour, F. M., 667 Blainville, 660
Banded ant-eater, 480 Blastoccele, 280*
Bandicoots, 464, 480, 507, 544, 578 Blastodermic vesicle, 569
Banks, Sir J., 655 Blastula, of Amphioxus, 54, 55
Barbel, 141* Blenny, 234
Barbels, in Teleostomi, 212, 214. 218 Blind-snakes, 324, 356
Barbs, of feather, 370*, 371 Blind-worm, 328, 332, 350, 358
Barbules, of feather, 370*, 371 Blood, 94 — See Vascular system
Barriers, 606 Blood corpuscles, 50, 94 — See Vascular
Bany, Martin, 659 system
Basal plate, of Craniata, 73*, 74 Blood vessels— See Vascular system
Basalia, of Craniata, 80* Boar, 548
Basi-branchial, 74, 77, 145*, 199, 201 Boas, 324, 356
Basi-branchial plate, 169 Boatswain-bird, 403
Basi-branchiostegal, 201 Body, of vertebra, 72*
Basi-cranial axis, 498* Body-cavity — See Ccelome
Basi-cranial fontanelle, 122, 123* Body-wall, of Amphioxus, 44, 45 : of
Basi-dorsal, 143 Craniata, 67
Basi-facial axis, 498* Boltenia, 24
Basi-hyal, 74, 76* — See Skull Bombinator, 293
Basi-occipital, 77*- — See Skull Bones, of Craniata, 76
Basi-pterygium, 203, 204 Bonnet, 653
Basi-pterygoid processes, of Birds, Bony labyrinth, 394*
378*, 414, 415 : of Lizard, 308, 309 Bony Pike, 198, 213, 218
Basi-sphenoid, 77*, 376, 377— See Skull Botryllus, 22, 25
Basi-temporals, 376, 377 Bottle-nosed whales, 466, 501
Basis cranii, 74* — See Skull Boucher de Perthes, 665
Basking sharks, 173, 182 Bougainville, 655
Bastards, 644 Bovidcc, 468 — See Oxen
Bates, H. W., 663 Bowerbank, 661
Bathymetrical distribution, 614 Bower-birds, 429
Bats, 471, 493, 501, 553, 581— See Bow-fin, 190, 213
Chiroptera Brachial plexus, 277*
Bdellostoma, 134, 135, 136, 137, 138, Brachium, 67, 304
139 Brady podidce, 465 — See Sloths
Bdellostoma forsteri, 135 Bradypus tridactylus, 512, 513, 514,
Bdellostoma stouti, 137, 138 515, 554
Beak, in Teleostomi, 218 : of Pigeon, Brain, Amphioxus, 52 : of Craniata,
367 • of Neornithes, 408 95, 97 : Lamprey, 126, 127, 128.
Beaked whales, 466 153, 154, 155, 156, 157 : Elasmo-
Bears, 470, 491, 529, 530, 551, 552, branchii, 173 : Holocephah, 187,
564) 580 188 : Trout, 206, 207 : Teleos-
Beavers, 470, 491, 532 tomi, 231 : Geratodus, 246, 247 :
Bee-eaters, 404 Frog, 275, 276 : Amphibia, 298 :
Bellonius, 648 Lizard, 318, 319, 320 : Reptilia, 349,
Belly, of muscle, 266* 350 : Pigeon, 391, 392 : Aves, 421,
Belodon, 359 422 : Rabbit, 454-458 : Mammals,
Beneden, E. van, 667 577-562
Benthos, 616* Brain-case, of Craniata, 73*
Beryx, 620 Branchia, of Salpa, 27*
INDEX
685
Branchiae, of Amphioxus, 47 : Lamproy,
126 : Dog-fish, 149 : Elasmobranchii,
173 : Holocephali, 187 : Trout, 204 :
Teleostomi, 227, 228 : Ceratodus,
243, 244 : Tadpole, 282 : Amphibia,
287, 295
Branchiae, external, 250, 281, 282, 295 :
internal, 283, 295
Branchial apertures, oi Amphioxus, 46*,
47 : of Craniata, 65, 86*, 87
Branchial arches, of Craniata, 75* :
of Dog-fish, 145
Branchial basket, of Lamprey, 121,
124*
Branchial clefts, 2* — See Branchial
slits
Branchial filaments, of Craniata, 86*
Branchial junctions, of Amphioxus, 47
Branchial lamellae, of Amphioxus, 47*,
48
Branchial nerves, of Craniata, 101,
102, 103— See Brain
Branchial rays, 145*, 169
Branchial rods, of Amphioxus, 47, 48*
Branchial slits, of Balanoglossus, 3, 4 :
of Amphioxus, 46*, 47, 60, 61 : of
Cephalodiscus, 11
Branchio-cardiac vessel, 17. 19
Branchiostegal membrane, 193, 218
Branchiostegal rays, 193, 197
Branchiostoma, 43 — -See Amphioxus
Branchiostomidce, 43
Brassica oleracea, 631
Broad ligament, 323
Bronchi, of Lizard, 318 : of Pigeon,
385, 386 : of Rabbit, 453
Bronchioles, 454
Brown funnels, of Amphioxus, 47, 51
Brush-turkeys, 403
Buccal cavity, of Craniata, 82
Buccal funnel, of Lamprey, 120* :
Myxine, 135
Buccal glands, 84* : Pigeon, 385 :
Birds, 421
Budding, in Cephalodiscus, 11 : in
Ascidians, 24 : Doliolum, 37, 39 :
Salpa, 40
Buffon, 653, 654
Bufo vulgar is, 288
Bulbus aorta;, 89, 126, 205, 206, 271
Bulla tympani, 439, 498*
Bunodont, 545
Burchell's zebra, 488
Burnett Salmon, 239, 240
Burr, of antlers, 487*
Bursa Fabricii, 384, 385*
Bustards, 403
Butterfly-fish, 219
Button-quails, 403
VOL. II
C
(-SABALUS, 600
Cacatua, 404
Cacatuidce, 602
Cadophore, 38*. 39
Caducibranchiata, 287*, 291, 302
C cecilia, 285, 301
Ccecilia pachynema, 288
Csecilians. 256, 285
Csecum, 313, 317, 448, 556
Caimans, 326, 332, 358
Calamoichthys, 212, 236
Calamus, 369
Calamus scriptorius, 458*
Calcaneum, 259, 266, 444— See Limb-
skeleton
Calcar, 259, 266, 471*, 535*
Calcified cartilage, 76*
Callichthys, 229
Callithrix, 473
Callorhynchus, 183, 184, 185, 186, 187,
188, 189, 190, 191
Callosities, ischial, 494*
Cambrian, 618
Camelidce, 468 — See Camels
Camels, 468, 487, 527, 548, 554, 555,
580
Campanula Halle ri, 208*
Camper, Peter, 654
Camptotrichia, 240*
Canidce, 470, 491— See Dogs
Canines, of Rabbit, 445— See Teeth
Canis, 483, 530
Canis dingo, 602
Canisfamiliaris, 529, 530, 543, 554, 559
Cannon bone, of Horse, 526 : Rumi-
nants, 527
Cape Ant-eaters, 465, 485, 509, 547, 579,
584
Capibara, 492
Capillaries, 50, 89, 90 — See Vascular
system
Capitellum, 442
Capitular facet, 305, 435
Capitulum, 435*
Gapra, 468, 487, 617
Capri mulgidce, 404, 408
Capuchin Monkeys, 473
Capybara, 492
Carapace, of Chelonia, 329, 336
Carboniferous period, 619
Carcharias, 172*
Carchariidce, 176
Carcharodon, 182
Cardiac nerve, of Craniata, 101, 103
Cardiac sac, of Balanoglossus, 4, 6*
Cardiac vein, 272, 273
Cardinal veins, 90 — See Vascular sys-
tem
Cardio-visceral vessel, 17, 19*
U U
686
INDEX
Carina sterni, 374, 375, 412, 413
Carinatse, 400*, 410, 413, 415, 416,
417, 420, 422, 426, 429, 431
Carnivora, 469*, 528, 529, 530, 531,
556, 558, 580, 589
Carnivora vera, 469*. 491, 528, 529,
530, 551
Carotid arteries, 88, 90 — See Vascular
system
Carotid gland, 271*
Carp, 214, 230, 236
Carpals, of Craniata, 81* — See Limb-
skeleton
Carpo -metacarpus, 379
Carriers, 367
Carter, 661
Cartilage-bones, 76*
Cartilages of Santorini, 453*
Caruncle, 428*
Casque, of Cassowary, 408*
Cassowaries, 398, 408, 411, 412, 417,
419, 429
Casioridce, 470
Casuariiis — See Cassowaries
Cat-fishes, 214, 221, 225, 226, 230, 234,
236
Cathartes, 403
Cats, 470, 491, 529, 530, 551, 552, 580
Caturns Jurcatus, 238
Caudal artery, 90
Caudal ganglion, of Appendicularia,
24, 28
Caudal swellings, 178, 179
Caudal vein, 91 — See Vascular system
Caudate lobe, 557*
Cavum arteriosum, 348*
Cavxim pulmonale, 348*
Cavum venosum, 348*
CebidcK, 473*, 494, 538, 581, 613
Cebus, 473
Cell, 650
Cell-theory, 658
Cement, 83
Centetes ecniirlntits, 533
Centetida>, 610
Central canal, 95, 96*
Centrale, of Mammals, 500 — See Limb-
skeletoii
Ceiitralia, of Craniata, 80, 81*
Centrophorus calceus, 167
Centrum, of Craniata, 72*
Cephalaspis, 255, 256
Cephalaspis lyelli, 255
Cephalaspis murchisoni, 255
Cephalochorda, 43*
Cephalodiscus, 2, 9, 10, 11, 13
Ce rat o -branchial, of Craniata, 74, 76*
—See Skull
CERATODUS FORSTEBI, 239 : External
characters, 240 : Endo -skeleton, 241 :
Digestive organs, 243 : Organs of
respiration, 243,244: Blood -vascular
system, 244, 245 : Brain, 246 :
Urinogenital organs, 247, 248 :
Development, 247, 249
Cerato-hyal, 74, 76*— See Skull
Ceratotrichia, 146*, 168
Cercopithecidce, 473*, 494, 581
Cere, 368, 369*
Cerebellum, 97
Cerebral commissures, of Frog, 276,
277 : Lizard, 319— See Brain
Cerebral flexure, of Craniata, 100*
Cerebral ganglion, of Appendicularia,
24, 28
Cerebral hemispheres, 97 — See Brain
Cerebral nerves, 100 — See Brain
Cerebral vesicle, Amphioxus, 47, 52*
Cerebro -spinal cavity, of Craniata.
68*, 69, 95
Cervical ribs, 307
Cervidce, 468, 487
Cervus elaphux. 520, 525, 526, 527
Cestracion galeatus, egg-case, 175, 176
Cestracionts, 182
Cetacea, 465*, 476, 486, 495, 496, 501,
513-518, 550, 553, 555, 556, 557,
558, 563, 564, 579, 586
Chalaza, 422*. 423
Chalcides, 354
Chalinolobus morio, 600, 602
Chnmceleo viilgaris, 328
Chameleons, 324, 328, 332, 333, 337,
346, 347, 350, 354, 355, 356
Chambers, Robert, 661
Chambers, of eye. 108
Charadriiformes, 403
dlmrfidfiiifi. 403, 411
Chauna, 403, 409
Chelodina, 335
Clu'fone midas, 336, 341
Chelonia, 325*. 329, 332, 333, 335,
336, 337, 340, 341, 343, 345, 346,
347, 348, 349, 351, 357, 358, 359
Chevron-bones, 306*, 333
Chevrotains, 519
Chilobranchus, 235
Chimera, 182, 183, 184, 185, 186
Chimaeridae, 1 82
Chimpanzees, 473, 535, 538, 540, 581
Chirocentrns, 227
Chiromys, 472, 609
Chiroptera, 471*, 493. 534, 553, 558,
581, 590
Chlamydosaurus, 355
Chlamydoselachus, 164, 166, 169
Cholczpus didactylus, 483*
Cholcepns hoffmanni, 509, 513
Chondrichthyes, 140
Chondrocraiiium, 78* — See Skull
Chondrostei, 212*, 218, 221, 222, 223,
224, 227, 231, 234, 235, 236, 237, 238
INDEX
687
Chorda dorsalis — See Notochord
Chordae tendinese, 450
Chordata, 1*
Chorion, of Ascidian, 31* : Rabbit,
462 : Mammals, 572, 573
Chorionic villi, of Rabbit, 41)1'*
Choroid, 106, 107*
Choroid fissure, 109*
Choroid gland, 207*, 208
Choroid plexus, 100*, 153*
Chrysochloridce, 609
Chrysophrys, 233
Chrysothrix, 473
Chun, 663
Ciconia, 403, 408, 409, 415
Ciliary ganglion, 100, 101
Ciliary muscle, 107*
Ciliary processes. 106, 107*
Ciliated funnel, of Ascidia, 20, 29
Circulatory system — See Vascular sys-
tem
Cistudo lutaria, 336
Civets, 470, 580
Cladoselache, 162, 163
Cladoselachii, 162*
Claspers, of Dog-fish, 141 : Elas-
mobranchs, 166 : Holocephali, 183,
184
Classification — See Distinctive char-
acters and classification
Classification, of Aristotle, 648 : Gesner,
649: Ray, 651: Linnaeus, 651,052:
Lamarck, 656 : Cuvier, 657 : Hux-
ley, 664
Clans, 668
Clavellina, 32, 33
Clavicle, of Craniata, 80, 82*
Claws, 289, 369
Cleithrum, 243, 293
Climbing Perch, 228
Clitoris, of Reptilia, 351 : Rabbit,
459, 461 : Mammals, 567
Cloaca, of Craniata, 65* — See Digestive
system
Club-shaped gland, of Amphioxus, 59
Cnemial process, of Pigeon, 380*,
381
Cnemial ridge, 313
Cnemiornis, 413, 417, 600
Cobitis, 235
Coccosteus dedpiens, 253
Coccygeo-mesenteric, 389, 390
Coccyx, 536*
Cochlea, 111*, 112, 321, 322— See
Ear
Cockatoos, 404
Cod, 190, 214, 218, 223, 232, 233
Coeliac artery, 90
Cceliac plexus, 458*
Cceliaco-mesenteric artery, 315, 316
Ccelolepidce, 254, 255*
VOL. II
Ccelonii'. nf /lii/iniix/lossus, 3, 5:
Aficiilid, 21 : Am/>liii>.rtt«. 47. 48. 49,
56, 57: Craniata, o.s. 69, 119:
Trout, 203, 205: Rabbit, 444, 445
Ccelomic bays, 177, 178
Ccenolestes, 57!i. 5s3, Oil, 613, 621
Coffer-fishes, 216
Cogia, 466, 562
Coiter, 648
Colics, 404
Colii, 404
Collar, of BalanoyJosfiHfi, 3, 4
Collar-pores, 4*. 11
CollocaUa. 423
Colon, of Dogfish, 148, 149 : of Rabbit,
448
Colours, of feathers, 410
Colours, courtship, 411
Colubrine Snakes, 345
Colugos, 492, 4(13
Columba, 404
COLUMBA LIVIA, 367 : External char-
acters, 367, 368 : Exoskeleton, 369,
370, 371, 372, 373 : Endoskeleton,'
373-382 : Muscular system, 382,
383 : Digestive organs, 383, 384 :
Ductless glands, 385 : Respiratory
and vocal organs, 385, 386, 387, 388 :
Circulatory organs, 388, 389, 390.
391 ; Nervous system, 391, 392 :
Sensory organs, 393, 394 : Urino-
genital organs, 394, 395 : Systematic
position, 404
Columbse, 404*, 423, 429
Columbidce, 404
Columella amis, of Frog, 261, 263 :
Lizard, 309* : Reptilia, 350 : Pigeon,
378
Columnse earnest? , 450*
<'nl,i minis, 402, 431
Commissures, 319, 320, etc., aberrant,
319, 320
Composite Ascidian — See Ascidice Com-
positce
Cmidylar foramen, 438*
Condylarthra, 587
Condyle, of mandible, 437, 441 : of
skull, 436, 438
Cones of eye, 108
Contour feathers, 371*
Contra-deciduate |ilarrnf a, 570
('onus arteriosiis. ss
Cook, Captain, 055
Coots, 409
Cope, E. D., 067
Coprodaeum, of Pigeon, 384, 385*
Cupulatory sacs, 322, 323
( 'urnciidce, 404
Coraco-humeralis, 208
Coracoid, of Craniata, 80, 82*— See
Pectoral arch
o u 2
«88
INDEX
Co raco -scapular angle, 378
Corium — See Dermis
Cormorants, 403, 409
Cornea, 106*
Cornu, hyoid of Craniata, 76 — See
Skull
Cornual cartilage, of Lamprey, 122, 123
Corona radiata, 569*
Coronal suture, 307*, 439
Coronary, 308, 310*
Coronary arteries, 450
Coronoid process, Lizard, 310 — See
Skull of Mammals, 441
Corpora bigemina — See Optic lobes
Corpora cavernosa, 459, 460*, 461
Corpora quadrigemina, 458, 560* — See
Brain of Mammals
Corpora restiformia, of Dogfish, 153* :
Holocephali, 187 — See Brain
Corpora striata, of Craniata, 99* — See
Brain
Corpus callosum, 454, 456, 560
Corpus geniculatum, 456, 457*
Corpus luteum, 569*
Corpus mammillare, 457, 458* — See
Brain of Mammals
Corpus spongiosum, 459, 460*
Corpus sterni, 496
Corpus trapezoideum, of Rabbit, 458*
Corpus uteri, 567
Cortex, of hair, 474, 475 : of Kidney,
564
Corvidce, 404, 432
Costal plate, 335*
Costal sternum, 265*
Costo -pulmonary muscles, 386
Cotyledonary placenta, 576
Cotyledons, 467*
Cotyloid, 443, 500
Cowper's glands, 460
Craig-fluke, 220
Cranes, 403, 409
Cranial cavity, of Craniata, 68*
Cranial nerves — -See Cerebral nerves,
100 '
Craniata, 43*, 63* : Classification, 63,
64 : External characters, 65, 66,
67, 68 : Body-wall and internal
cavities, 67, 68, 69, 70 : Skeleton,
70-82 : Digestive organs, 82, 83,
84, 85, 86 : Respiratory organs, 86,
87 : Blood-vascular system, 88—94 :
Lymphatics, 89, 94, 95 : Nervous
system, 95-104 : Sensoiy organs,
104-113 : Urinogenital organs, 113-
117 : Development, 117, 118 : Meta-
merism, 118, 119 : Distinctive char-
acters, 119
Cranium of Craniata, 73* — See Skull
Crax, 403
Credontia, 589
Cremaster, 577
Cretaceous, 620
Cribriform plate, 438
Cricoid cartilage, of Lizard, 318 :
Reptilia, 347 : Pigeon, 385 : Rabbit,
453
Cristse acousticse, 111*, 112
Crocodilia, 326*, 331, 332, 333, 334,
335, 336, 340, 342, 343, 344, 345,
346, 347, 348, 349, 350, 351, 352,
357, 358, 359, 360
Crop, of Pigeon, 383*, 384
Crossopterygii, 211*, 212, 218, 219,
222, 223, 224, 225. 227, 229, 235.
236, 237, 238
Crotalus, 338
Crowned pigeons, 404
Crows, 404, 432
Crura cerebri, of Craniata, 97* — See
Brain
Crusta petrosa, 167*
Cryptobranchus, 284, 287
Cryptodrilidce, 601, 602
Cryptozoic fauna, 617*
Crypts, of uterus, 462, 576
Grypturi, 403*, 414, 417, 429, 431
Ctenoid scales, 221*
Cubitals, 373*
Cuboid, 444
Cuckoos, 404
Cuculidce, 404
Cumulus proligerus, 568*
Cuneiform, 442, 443, 500, 501
Curlews, 403, 408
Currasows, 403
Ciitaneous glands, of Mammals, 476
Cuvier, 657, 658, 665
Cyanorhamphus, 600
Cyathozooid, 37*
Cycloid scales, 221*
Cyclomyaria, 21*, 22, 25, 26, 37, 38, 39
Cycloplerufi, 225
Cyclostomata, 64, 119* : Example,
119 : Distinctive characters and
classification, 133 : Comparison of
Myxinoids with Lamprey, 134 :
General remarks, 138
Cycloturus, 484, 510, 512, 513
Cygmts, 403, 408, 409
Cynocephalus, 473, 499, 538, 539, 590
Cynocephalus anuMs, 539
Cypselidce, 404, 408, 409
Cystic duct, of Craniata, 85*
D
D
'ACTYLOPTERUS, 219
Dana, J. D., 662
Darwin, Charles, 629, 630, 661, 662
Darwin, Erasmus, 655
INDEX
689
Darwinian theory, 629
Dasypodidce, 465 — See Armadillos
Dasyprocta, 492
Dasypus sexcinctus, 484, 510, 511, 512,
5l3, 516
Dasyures, 464, 480
Dasyuridce, 464, 479, 50(5, 508, 547, 577
Dasyurus, 508, 577
Dasyurus viverrinus, 480
D'Azyr, V., 653
Decidua, 462, 576
Deciduate placenta, 462, 576
De Bary, 659
Deer, 468, 487
Deer, Red, 520, 525, 526, 527
Delphinus, 466, 486, 54:5, 544
Deltoid ridge, 442*
Demersal eggs, 235*
Dendrohyrax, 469
Dental formula, 545*
Dental groove, 541, 542
Dental lamina, 541, 542
Dental papilla, 83, 84*, 541, 542
Dental sac, 542*
Dentary, of Craniata, 77, 80*
Dentine, 83*, 84
Dentine -forming layer, 542*
Dentition — See Teeth
De Perthes, B., 665
Depressor muscles, 267*
Dermal defences, 184
Dermal fin-rays, 80*
Dermal teeth, 140, 222
Dermatochelys, 336, 357, 358
Dermis, of Amphioxus, 45 : Craniata,
67
Derotremata, 284*, 287
Desmognathous arrangement, 415*
Determinants, 668
Development, of Balanoglossus, 7, 8,
9 : Ascidian, 30, 31, 32, 33, 34, 35,
36, 37 : Pyrosoma, 37 : Doliolum,
38, 39 : Salpa, 40 : Amphioxus, 55-
62: Craniata, 117, 118: Lamprey,
130, 131, 132, 133 : Elasmobranchii,
176, 177, 178, 179, 180, 181 : Holo-
cephali, 190, 191 : Trout, 209, 210 :
Teleostomi, 234, 235 : Ceratodus,
247, 248, 249 : Frog, 279, 280, 281,
282, 283 : Amphibia, 300, 301, 302 :
Reptilia, 351, 352, 353, 354 : Aves,
422-429 : Rabbit, 461, 462 : Mam-
. mals, 567-579
Devonian period, 619
Diaccele, 97
Diaphoraptcryx, 605
Diaphragm, of Craniata, 70* : of
Rabbit, 445
Diastema, 445
Diazona, 22
Dicotyles, 468, 580
Didclphyidce, 464, 478, 479, 480, 506,
507, 546, 547, 565, 566, 577, 579,
583, 609, 613
Didelphys dorsigcra, 566
Didelphys marsupialis, 546, 547
Didelphys virginiana, 480
Dididce, 404
Didunculus, 612
Didus, 404, 417, 431
Diencephalon, of Crauiata, 97*
Diffuse placenta, 576*
Digestive system, of Balanoglossus, 4,
5, 6 : Ascidia, 18 : Appendicularia,
24, 28 : Simple Ascidians, 24, 28 :
Composite Ascidians, 28 : Salpa, 28 :
Doliolum, 28 : Craniata, 82 : Lam-
prey, 124 : Myxine, 136, 137 :
Dogfish, 147, 148, 149 : Elasmo-
branchii, 172 : Holocephali, 186 :
Trout, 204, 205 : Teleostomi, 22<>,
227 : Geratodus, 243 : Frog, 268,
269 : Amphibia, 295 : Lizard, 313,
314 : Reptilia, 345, 346 : Pigeon,
383, 384, 385 : Aves, 420, 421 :
Rabbit, 445, 446, 447 : Mammals,
541-557
Digitals, 373*
Digitigrade, 364*
Digits, 67 — See Limbs
Dingo, 580, 611
Dinoceras, 588
Dinornis robustus, 418, 621
DinornitheSi 398*, 417, 423, 429
Dinar nithidce, 398, 429
Dinosauria, 326*, 362, 363, 364
Dinotheridce, 587
Dinotherium giganteum, 587
Diomedea, 402, 417, 422
Diphycercal fin, 184*, 2:23
Diphyodont, 463*
Diploblastic forms, 597
Dipneumona, 250*
Dipnoi, 64*, 239 : Example, 239 : Dis-
tinctive characters and classification,
249, 250 : General remarks, 250
Dipodidce, 470, 531, 532
Diprotodon australis, 583, 584, 621
Diprotodont, 545
Diprotodontia, 465*, 481, 482, 483, 583
Dipterus, 252
Dipus, 492
Discoidal placenta, 576
Dispersal, 606
Distalia, of Craniata, 80, 81*
Distinctive characters and classifica-
tion, of Acrania, 62, 63 : Craniata,
64, 119 : Cyclostomata, 133 : Elas-
mobranchii, 161 : Teleostomi, 211 :
Dipnoi, 249 : Amphibia, 283 : Rep-
tilia, 323 : Aves, 395 : Mammals,
462
690
INDEX
Distribution, of Acraiiia, 62
Distribution, geographical, 598 : of
Cephalodiscus, 13 : Rhahdopleura,
13 : Urochorda, 41 : Cyclostomata,
139: Holocephali, 182 :' Teleostomi,
235 : Dipnoi, 250 : Amphibia, 302 :
Reptilia, 358, 359 : Aves, 429 :
Mammalia, 579
Distribution, geological, 618 : of Cyclo-
stomata, 139 : Elasmobranchii, 182 :
Holocephali, 1!)0 : Teleostomi, 236,
237 : Dipnoi, 252 : Amphibia, 302 :
Reptilia, 359, 360 : Aves, 430 :
Mammals, 581
Divers, 402, 431
Diverticulum, cesophageal, of Balano-
glossus, 4, 6
Dodo, 404, 413, 417, 431, 622
Dogfish, 68 — See Scyllium and Hcinl-
scyllium
Dogfishes, 165-182
Dogs, 470, 491, 499, 529, 530, 543,
551, 552, 559, 580
Dohrn, An ton, 663
Dolchinia, 22
Doliolidce, 22
Doliolum, 22, 25, 26, 28, 29, 30, 37,
38, 39, 41
Dolphins, 466, 486, 543, 544
Dominant characters, 644, 645
Dorsal aorta, 89 — See Vascular system
Dorsal fissure, 95, 96*
Dorsal lamina, 17, 18
Dorsal root, of spinal nerve, 90*, 101
Dorsal shield, Pteraspis, L'."i4
Dorsal tubercle, of Ascidia, 19, 20
Doves, 404
Down feathers, 369, 371*, 372, 409
Draco, 335, 355, 357, 617
Draco volans, 335, 355, 617
DrepanaspidcB, 254, 255*
Drepanaspis gemundenensis, 254
DrepanidcB, 612
Dromseognathous arrangement, 414*
Droni(eus, 398, 408, 409, 413, 417, 419,
429
Dromatherium, 581
Dryopithecus, 590
Dryornis, 401
Duck-Bill, 464 — See Ornithorhynchus
Ducks, 403, 408, 415, 416
Ductless glands of Craniata, 85, 117
Ductus Botalli, 296, 298*
Ductus Cuvieri, 152*
Ductus endolymphaticus, 322
Dugong, 467, 496, 501, 518, 519, 550,
551, 579, 586
Dujardin, 658
Dumb -bell -shaped bone, 502, 505*
Duodenum, 149* : of Pigeon, 384, 385 :
Rabbit, 447, 448
Duplicidentata, 474
Dura mater, 100*
E,
E
IAGLK-RAYS, 172
Eagles, 403, 415, 423
Ear, of Craniata, 110, 111, 112: of
Lamprey, 130 : Myxine, 137 : Dog-
fish, 158 : Elasmobranchii, 174 :
Trout, 208, 209 : Frog, 277, 278 :
Lizard, 321 : Reptilia, 350 : Pigeon,
369, 394 : Aves, 422 : Rabbit, 436,
459 : Mammals, 563, 564
Eared Seals, 470, 491, 580
Earless Seals, 470 — -See Phocidae
Ecdysis, 332
Echeneis, 219
Echidna, 464, 476, 477, 478, 479, 503,
504, 505, 541, 545, 554, 558, 560,
561, 562, 578
Echidna aculeata, 477, 479, 504, 554,
560, 561
Ectocuneiform, 444 — See Limb-skele-
ton
Ecto-ethmoids, of Craniata, 77, 78* —
See Skull
Ectopterygoid, 308, 309
Edentata, 465*, 508-513, 541, 557, 565,
567, 579, 584, 585
Edestosaurus, 366
Eels, 190, 214, 218, 221, 230, 232, 233,
235, 236
Efferent branchial arteries of Atnphi-
oxus, 49, 50* — See Vascular System,
89
Efts, 284, 287
Egg — See Development
Egg-shell, of Dogfish, 161 : Elasmo-
branchs, 175, 176 : Holocephali,
190 : Reptiles, 357 : Birds, 422 :
Prototheria, 569
Ehrenberg, 661, 665
Elaeoblast, 41
Elasmobranchii, 64*, 140* : Example,
140 : Distinctive characters and
classification, 161 : External char-
acters, 165 : Integument, 166 :
Skeleton, 167 : Skull, 168 : Muscles,
171 : Electric organs, 171 : Lumin-
ous organs, 171 : Digestive system,
172 : Respiratory organs, 173 :
Blood system, 173 : Brain, 173 :
Organs of sense, 174 : Urinogenital
organs, 174 : Development, 17d :
Ethology and distribution, 181
Elastin, 146*
Electric Catfish, 226
Electric Eel, 226
Electric lobe, 171, 174*
INDEX
691
Electric organs, 171, 226
Electric rays, 165, 172, 174
Elephant, African, 524, 550
Elephants, 469, 47G, 490, 541, 550, 580
Elephas, 4fi!)
ElcpJuifj iifrii-iiiiiift, 524, 550
Elevator muscles, 267*
Elimination of the unfit, 634*
Embryological evidence of evolution,
624
Embryoii ectoderm, 570*
Embryoii endoderm, 570*
Embryonal knot, 569*
Embryonic membranes, of Bird, 427,
428
Embryonic rim, 177*
Embryonic shield, 352*, 424
Empedocles, (554
Emus, 398, 408, 409, 413, 417, 419, 429
Emys eitropcea, 340, 343, 346
Enamel, 83
Enamel membrane, 542
Enamel organ, 83, 84*, 541
Enamel pulp, 542
Encephaloccele, 47, 52*
End-buds, 104*
Endemic, 602*
Endochondral ossification, 76*
Eiidolymph, 111*
Endolymphatic duct, 111*, 112
Eiidoskeleton — See Skeleton
Endostyle, of Tornaria, 9 : Asci flirt,
16, 17*, 18 : Appendicularia, 23 :
Doliolum, 26 : Ascidiaii larva, 35,
36 : of Amphioxus, 44, 46, 60, 62
Engceus, 602
Entepicondylar foramen, 512*
Enteric canal — See Digestive Organs
Enterocoele, of Amphioxus, 57
Enteropneusta, 2*, 3, 4, 5, 6, 7, 8, 9 "
Entocuneiform, 444 — See Limb-skele-
ton
Entoplastron, 335*
Eocene, 620
Eosiren, 620
Eozoon canadense, 618
Epencephalon, 97
Ependyme, 97*, 99
Epiboly, 131*, 210, 280
Epibranchial, of Craniata, 74, 76*
Epicentrals, 222*
Epicoele, 97, 174
Epicoracoid, 264 : Prototheria, 502,
505
Epicrium, 285
Epidermis, of Amphioxus, 45 : Crani-
ata, 67
Epididymis, 159, 322, 323, 460
Epigastric vein, 315, 316
Epiglottis, of Babbit, 448 : Mam-
malia, 558
Epiglottis, intra-narial, 558
EI> i //o i / ickt/i. )/#, 4 : !
Epihyal, of Craniata, 74, 76*, 199,
201
Epineurals, 222*
Epiotic, of Cranial a. 77*
Epipharyngeal groove, Ai»/i///n.rn.~i, 46
Epiphyses. of (Yanmta, 82*: Rabbit,
434 : Mammals, 4!t(i
E|ii|>hysis (wivbri), of Craniata, 99* :
of Elasmobranchii, 173
Epiplastron, 335*
Epipleurals, 222*
Epipterygoid, 308. 309, 337
Epipubic bones, 502, 505*, 507, 508
Epipubic process, 170
Epipubis, 294, 295, 312, 507 : Birds,
419
Episternum, of Lizard, 310*, 311
Rabbit, 436 : Prototheria, 503
EquidfE, 468, 488. 489
EHUUS burchelli. 488
Equus caballus, 521, 526, 527, 549
Erinaceidce, 471 — See Hedgehogs
Esox, 620
Ethiopian region, 609
Ethmoidal plane, 498*
Ethmo-turbinals, 437, 438*— See Skull
Ethology, of Elasmohranrliii, 181 :
Ceratodus, 239 : Reptiles, 354 :
Birds, 430
Euchorda, 42*
Eudynamis taitensis, 606
Eudyptes, 402
Eudyptes antipodum, 402
Eudyptes pachyrhynchus, 413
Euselachii, 164*
Eustachian aperture, 439
Eustachian tubes, of Frog, 268 : Rab-
bit, 439 : of Mammals, 563*, 564
Eustachian valve, 449, 557*
Eutheria, 465*, 558, 561, 562, 565, 567,
569, 577
Evolution, 624
Excretion, organs of, in Ascidia, 20 :
Simple Ascidians, 30 : Amphioxus,
50, 51 — See Urinogenital Organs
Ex-occipital, 77*— See Skull
Exoccrtus, 219
Exoskeleton, of Craniata, 70
Expiration, 193*
Extensor muscles, 266*
Extensores dorsi muscles, 26(5
External auditory meatus, 369
External characters, of Balanorjlossus,
1 : Ascidia, 14 : Craniata, l>.~) :
Lamprey, 120 : Dogfish, 140 :
Elasmobranchii, 165 : Holocephali,
183 : Trout, 192 : Telcostomi, 217 :
Ceratodus, 240 : Frog, 257 : Am-
phibia, 285 : Lizard, 304 : Reptilia,
692
INDEX
327 : Pigeon, 367 : Aves (Neor-
nithes), 407 : Rabbit, 432 : Mam-
malia, 474
External coelomic bay, 177*
External elastic membrane, 70, 71
External gills, 87*, 235
External rectus imiscle of eye, 110
Extra-bran chials, 170
Extra-columella, 263, 378
Extremity, of long bone, 82*
Eycloux, 662
Eye, of Salpa, 29 : of Amphioxus, 52,
53 : Craniata, 106-110 : Dogfish,
158 : Elasmobranchii, 174 : Trout,
206, 207, 208: Flat-fish, 219:
Frog, 277: Amphibia, 298: Lizard,
305, 321 : Reptilia, 349 : Pigeon,
368, 369: Aves, 421: Rabbit, 433,
458, 459 : Mammals, 563
Eye, development, 108, 109
Eyelids — Frog, 257 : Lizard, 305
Eye-muscles, 110
F
ABELLJE, 444
Fabricius ab Aquapendente, 6-4 s
Facial ganglion, of Craniata, 102
Facial nerve, of Craniata, 101, 102*
Falciform process, 208*
Falco, 403, 415
Falcons, 403, 415
Fallopian tubes, of Rabbit, 460, 461
Fan-tails, 367
Fasciae dentatse, 561*
Fat-bodies, of Frog, 278, 279
Faunas, 598
Feather-follicle, 371, 372*
Feather-germ, 371, 372*
Feather papilla, 371, 372*
Feather-pulp, 371, 372*
Feather-tracts, 372*
Feathers, of Pigeon, 367, 369, 370, 371,
372, 373 : Archseopteryx, 405, 406,
407 : Neornithes, 410
Felidce, 470, 491 — See also Felis and
Cats
Felis leo, 530
Felis tigris, 528, 529
Felting, of hair, 474
Femur, 80, 81* — See Limb -skeleton
Fenestra ovalis, 261, 277, 278, 321, 439
— See Ear
Fenestra rotunda, 321, 439
Fibula, 80, 81* — See Limb-skeleton
Fibulare, of Craniata, 80, 81*
File -fishes, 216, 221
Filo-plumes, 369, 371*, 409
Filum terminale, 277*
Fimbria, 456*
Finches, 404, 408, 429
Finlets, 218
Fin-rays, of Amphioxus, 46* : Dogfish,
145, 146 : Teleostomi, 224 : Teleostei,
219
Fins, of Amphioxus, 43, 44 : Craniata,
65, 66, 80 : Lamprey, 121 : Cyclo-
stomata, 133, 134 : Dogfish, 141 :
Elasmobranchs, 170 : Holocephali,
184, 185: Trout, 194: Teleostomi,
201, 202: Teleostei, 218, 219:
Ceratodus, 240 : Dipnoi, 250
Fins, development of, 180
Fire-toad, 293
Firmisternia, 285*
Fishing-frog, 218, 219
Flamingoes, 403, 408
Flanges, of feather, 370, 371*
Flatfishes, 214, 219
Fleming, W., 677
Flexor muscles, 266*
Flexor perforans, 383
Flexor tarsi, 268
Flippers, 486
Floccular fossa, 439
Flocculi, 458 — See Brain
Flounder, 214
Flower, W. H., 663
Fluviatile fauna, 616
Flying-fish, 219
Flying Foxes, 471, 501, 534, 553, 581
Flying Lizard, 335, 355, 358, 617
Flying Mammals, 501
Flying Phalangers, 501
Flying Squirrels, 483, 492, 501
Foetal membranes, of Mammals, 571,
572, 573
Follicle cells, of Ascidian, 30, 31 :
Salpa, 39
Fo»tanelles, of Craniata, 74* : Lam-
prey, 123 : Dogfish, 144 : Trout,
197, 199: Frog, 259, 261
Foot, 67 — See Hind-limb
Foramen, of Monro, 97 — See Brain
Foramen, ischiatic, 380
Foramen magnum, of Craniata, 74*
—See Skull
Foramen ovale, of heart, 450
Foramen Panizzae, 349*
Foramen triosseum, 379
Foramina, intervertebral, of Craniata,
71
Foramina (nerve), of Craniata, 74* — •
See Skull
Foramina, pneumatic, 379, 382
Fore-arm, 67, 304
Fore-brain, of Craniata, 97 — See Brain
Fore-kidney, 113*, 115
Fore-limb, 67
Fornix, of Rabbit, 454, 456— See
Brains of Mammals
INDEX
693
Forster, 655
FOSS.V, glcnoid, of skull, 439 : Pre-
spinous, of scapula, 442 : Post-
spinous, of scapula, 442
Fossa ovalis, 449, 450*
Fossa rhomboidalis, 153*, 154
Fossas, of cranium, 440
Fourth ventricle, 97 — -See Brain
Fowls,. 403, 409, 412. 415, 420, 421,
422, 423, 424, 425, 426
Fratercula, 403
Fregata, 403
Fresh -water fauna, 616
Fresh -water Snakes, 324, 356
Frey, 660
Frigate-bird, 403
Fringillidce, 404, 408, 430
Fritillaria, 24
Frogs, 256, 257, 284, 288, 289, 300-
See Anura
Frontal clasper, 183, 184
Frontal segment, of Craniata, 77, 78*
Frontal sinuses, 559
Frontal suture, 307*, 439
Frontals, of Craniata, 77, 78*— See
Skull
Froiito-parietals, 261, 262*
Fulcra, 213, 222
Fulmars, 402
Fulmarus, 402
Fur, 491
Fur Seals, 491
Furcula, 378*
G
rADUS MORREUA, 214
Gaimard, 662
Galaxias, 600
Galen, 648
Galeopithecus, 492, 493, 617
Galesaurus planiceps, 360
Gall-bladder, of Craniata, 69, 85* : of
Dogfish, 148, 149 : of Birds, 421 :
Rabbit, 448
Gallinse, 403*, 429, 432
Gallus, 403
Gallus bankiva, 412, 415, 420, 423, 424,
425, 426
Game birds, 403
Ganglia habenulse, 127
Ganglion, coeliac, 458
Ganglion impar, 458
Gannets, 403
Ganoidei, 213*, 219, 222, 224, 227, 229,
231, 232, 233, 235, 237, 238, 239
Ganoid scales, 221*
Ganoin, 222
Gar-fish, 218
Gar-pike, 213
Gare-fowl, 429
Gasserian ganglion, 101, 155
Gasterosteus, 234
Gastornis, 399, 420
Gastornithes, 399*, 430
Gastrsea theory, 664
Gastric glands, 83*
Gastric juice, 83*
Gastric nerve, of Craniata, 101, 103
Gastrochisma, 219
Gastrocnemius, muscle, 2(i<>, 267
Gastro -cutaneous pores, 6
Gastrula, of Amphioxus, 55 : Craniata
117
Gavice, 403, 411, 431
Gavial, 326, 359
Geckos, 324, 332, 333, 336, 350, 354,
358
Geese, 403, 408, 409, 415
Gegenbaxir, C., 668
Genital pores, of Petromyzon, 130, 131 :
of Trout,' 209
Genu, 454
Geotria, 120, 134, 139, 604
Germinal disc, 175* : of Fowl, 422
Gesner, Conrad, 649
Giant fibres, Amphioxus, 53
Giant goose, 413
Giant nerve-cells, Amphioxus, 53
Giant Rail, 403
Giant Salamander, 287
Gibbons, 473, 494, 581
Gill-pouch, of Craniata, 86*
Gill-rakers, 173, 201
Gill-rods, of Amphioxus, 46, 47, 48
Gill-slits — See Branchial slits
Gills — See Branchiae : of Craniata, 86
Giraffa, 468
Giraffes, 468, 487, 580
Girdle bone, 261
Gizzard, 384
Glands, Cowper's, 459, 460
Glass-fish, 235*
Glenoid cavity, 80, 442
Glenoid fossa (of Skull), 439— See Skull
of Mammals
Glenoid surface, of Craniata, 80, 81*
Globe-fishes, 216, 221
Globigerina-ooze, 615
Globiocephalus, 518
Glomerulus, 114* : of Balanoglossus, 6
Glossopharyngeal nerve of Craniata,
101, 102*— See Brain
Glottis, 244*, 268, 289 : Pigeon, 384,
385 : Rabbit, 453
Glycogen, 85*
Glyptodon clavipes, 585, 621
Glyptodontidce, 585
Glyptolepis, 236
Gmelin, J. F., 651
Goat-suckers, 404, 408
694
INDEX
Goats, 468. 487
Goethe, 657, 65!)
G on ads, of Craniata, 113, .115. 116 —
See Reproduction, Organs of
Goode, Brown, 663
Gorilla, 473, 494, 495, 535, 538, 540, 581
Goura, 404
Graafian follicles, 461, 568
Grallse, 4()3*
Grant, R., 661
Grayling, 214
Gray's Whale, 562
Grebes, 402, 409
Grew, Nehemiah, 649
Grey matter, 95. 96*
Groove of Hatschek, 44, 53, 54*
Ground -parrot, 413, 431, 600
Grouse. 403
Grus, 403, 409
Gudgeon, 214
Gullet — See Digestive organs
Gulls, 403, 411, 421, 429, 605
Gurnard, 215
Gustatory nerve, 101
Gymnarclms, 235
Gymnophiona, 285*, 288, 289, 291,
296, 298, 301, 302
Gymnottis, 226, 613
Gy-paetus, 410
Gypogeranns, 403, 609
H,
H
-ABITAT, 605
Haddock, 214, 218, 223, 235
Haeckel, Ernst, 664
Haemal arch, of Craniata, 69, 72
Haemal canal, of Craniata, 68*, 69, 72
Hsemal ridges, of Craniata, 71, 72
-Hcematopus, 403
Hags, 119, 134, 135, 136, 137, 138, 139
Hair-bulb, 475, 476
Hair-follicles, 474, 476
Hair-germ, 475, 476
Hair-papilla, 475, 476
Hairs, 474, 475, 476 : Development,
475, 476
Hake, 214
Half -beak, 218
Halicore, 467 — See Dugong
Halicore australis, 519
Halitherium, 586
Haller, 653
Hallux, of Craniata, 80, 81*
Halmaturus nalabatus, 478, 507
Hamen, Louis de, 650
Hammer-head Shark, 165
Hand, 67, 304
Hapale, 472, 581
Hapalidce, 472*, 494, 538, 553, 581, 613
Harderian gland, 321, 563
Hares, 470
Harriotta, 182, 183, 184
Harvey, William, 649
Hatschek, groove of, 44, 53, 54*
Hatschek's nephridium, 58*, 60
Hatteria, 325, 329, 330, 332, 333, 334,
335, 336, 337, 338, 339, 343, 345,
350, 351, 357, 358
Hawks, 421
Hawk's-bill Turtle, 358
Head, of Craniata, 65
Head-shields, of Lizard, 305, 331
Heart, of Balanor/lossus, 6 : Ascidian.
17, 18, 34 : Craniata, 88 : Lamprey,
126 : Dogfish, 150 : Elasmobranchii,
173 : Holocephali, 187 : Trout, 204,
205, 206 : Teleostomi, 231 : Cera-
todus, 244, 245 : Frog, 270, 271 :
Amphibia, 298 : Lizard, 314, 315 :
Reptilia, 347, 348, 349 : Pigeon,
388, 389 : Aves, 421 : Rabbit, 448,
449 : Mammals, 557
Hedgehogs, 471, 476, 493, 574, 575
Helix, 601
Helodemm, 345
Helodermidce, 358
Hemibranch, 86, 87*
Hemichorda, 2* : Affinities, 13
Hemimyaria, 22*
Hemipodes, 403
HEMISCYLLITTM MODESTUM, 140 :
General external features, 140, 141 :
Skeleton, 142-147 : Enteric canal,
147, 148, 149 : Organs of respiration,
149, 150 : Blood-system, 150, 151,
152, 153 : Nervous system, 153-
158 : Organs of special sense, 158 :
Urinogeiiital organs, 158, 159, 160,
161
Heiisen, V. A. C., 663
Hepatic artery, 91 — See Vascular
system
Hepatic caecum, Amphioxus, 47
Hepatic ducts, of Craniata, 85*
Hepatic portal system, 42, 49, 50, 91—
See Vascular system
Hepatic portal vein, 50, 91 — See Vas-
cular system
Hepatic vein, Amphioxus, 50
Heptanchus, 164, 166, 167, 168, 169,
170
Heredity, 638, 644
Herodiones, 403*
Herons, 403, 409, 410
Herpestes, 552
Herring, 190, 214, 220, 231, 235
Hertwig, O., 668
Hesperornis, 400, 413, 417, 420
Hesperornis regalis, 400
Heterocercal tail, 141*
INDEX
695
Heteroccelous vertebra, 373*
Heterodont teeth, 4(13*
Hi'tcrodnntiiff — Sec < 'i-x/rucion
Heterostraci, 254*, 255
Hetcmti.*, 235
Hexnnchus, 164, l(i(i, 1(57, 168, 169
Hilaire, E. G., St., (557
HihiH. 459*
Hind -brain, of Cranial a, 97 — See Brain
Hind kidney, 113 — See Metanephros
Hind-limb, 67 — See Limbs
Hip-girdle, of Craniata, 82
Hippocampal commissure, of Frog,
277 : Lizard, 319 : Reptilia, 349":
Birds, 422 : Mammals, 561
Hippocampal sulcus, 456
Hippocampus, 319, 349, 456 — See
Brain
Hippocampus (Sea-horse), 217, 234
Hippopotamus, 468. 488, 489, 501,
523, 524, 525, 520, 580
Hippopotamus amphibius, 488
HirundinidcB, 404
Hoatzin, 403, 407, 408, 409, 613
Hock, 489*
Hoffman's Sloth, 495
Holarctic region, 609
Holoblastic segmentation, 569
Holobranch, 86, 87*
Holocephali, 64*, 182 : External char-
acters, 183 : Endoskeleton, 184 :
Digestive organs, 186 : Respiratory
organs, 187 : Heart, 187 : Brain,
187, 188 : Urinogenital organs, 189 :
Development, 190, 191 : Fossil
remains, 190
Holostei, 212*, 213, 218, 221, 222, 221!,
227, 229, 231, 232, 233, 234, 235, 238
Hombrom, 662
Hominidce, 473*
Homo sapiens, 473 — -See Man
Homocercal tail-fins, 194
Homodont teeth, 463*
Hoofs, 486
Hook, Robert, 649
Hooker, J. D., 662
Hooklets, of feather, 370, 371*
Hoopoes, 404
Hombills, 404, 408, 420
Horns, of Ruminants, 487 : of Rhino-
ceros, 489
Horses, 468, 488, 489, 519, 521, 525,
526, 527, 549, 580, 587
House, of Appendicularia, 21* : of
Oikopleura, 23, 24
Howling monkeys, 473
Human species, 473
Humerus, 80, 81*
Humming-birds, 404, 423, 429
Hunter, John, 653
Huxley, T. H., 662, 664, 665, 668
Hycenn, 470, 530, 580
HycBnidtp,, 470, 530, 580
Hydrochcerus, 492
/////", 2S8, 289, 293
Hylobntes, 473, 494. 581, 610, 621
Hyoid arch, of Craniata, 75* — See
'Skull
Hyoid bone, 80*
Hyoid coniu, of Craniata, 76*, 77, 80
Hyoidcan artery, 20(5
Hyoiclean suspensoriimi, 7(1
Hyomandibular, of Craniata. 76*. 77,
80 : Dogfish, 145 : Elasmobranchii,
1(58 : Trout, 199, 200 : Teleostomi,
223
Hyomandibular nerve, of Craniata,
101, 102— See Brain
Hyoplastron, 335*
Hyostylic skull, 76*— See Skull
Hypapophysis, 306*
Hyperoodon^4:66, 501
Hypnos, 168, 171
Hypo-branchial, of Craniata, 74, 76*
Hypoglossal nerve, of Craniata, 101,
103*— See Brain
Hypo-hyal, of Craniata, 74, 76*, 199,
201
Hypo-ischium, 312. 343
Hypophysis, oiAscidia, 19, 20 : Craniata,
99 — See Brain
Hypoplastron, 335*
Hypsiprymnus rufescens, 578
Hyracidce, 469, 490, 580
Hyracoidea, 468*, 524, 527, 549, 557,
580, 587
Hyrax, 469, 495, 521, 524, 556, 580
Hystricidce, 492 — See Porcupines
1 HIS, 403, 408
Ibises, 403, 408
Ichthyomyzon, 134, 139
Icltthyophis ijl/ittitfMu, 292. 301
Ichthyopterygia, 32(5*, 362
Ichthyornis, 402, 420
Ichthyornis victor, 401
Ichthyornithes, 402*, 411, 430, 431, 432
Ichthyosaurus, 362
Ichthyotomi, 163*
Iguanas, 324, 333, 355, 358
Iguanodon, 363, 364
Iguanodon bernissartensis, 363
Iguanodon mantclli, 363
Iliac artery, 88, 90
Iliac process, 171
Iliac region, 82* : of Craniata — See
Limb-skeleton
Iliac vein, 88, 91
Ilium, 82* — See Pelvic arch
696
INDEX
Impennes, 402*, 411, 413, 422, 431,432
Incisors, of Rabbit, 445
Incubation, 395*
Incus, 441, 564
Indigenous fauna, 601*
Inferior oblique muscle of eye, 110
Inferior rectus muscle of eye, 110
Inferior temporal arch, 309
Inferior temporal fossa, 309
Inferior umbilicus, 369*
Infra-orbital glands, of Rabbit, 440
Infundibulum, of Craniata, 99 — See
Brain : of lung, 454
Inguinal canal, 460, 565
Innominate, 500 — See Pelvic arch of
Mammals
Innominate arteries, 151
Inscriptiones tendinete, of Frog, 266,
267
Insectivora, 470*, 492, 532, 533, 552,
558, 563, 580, 581, 589 *>
Inspiration, 193*.
Insular faunas, 605
Integument, of Craniata, 67 : Lam-
prey, 121 : Dogfish, 140 : Elas-
mobranchii, 166 : Holocephali, 184 :
Trout, 194 : Teleostomi, 217 : Cera-
todus, 240 : Frog, 258 : Amphibia,
288 : Lizard, 305 : Reptilia, 331,
332 : Pigeon, 369, 370, 371, 372 :
Aves, 409, 410 : Rabbit, 432 : Mam-
malia, 474
Inter-branchial septa, of Craniata, 86* :
Dogfish, 149
Intercalary pieces, 167
Intercentra, 290, 307*, 333
Interclavicle, 293 — See also Epi-
sternum
Intercostal arteries, 451, 452
Interdorsal plate, 143*
Inter-hyal, 199, 200
Intermedium, of Craniata, 80, SI* —
See Limb-skeleton
Intermuscular bones, 195
Internal coelomic bay, 177*
Internal rectus muscle of eye, 110
Inter-neural plate, 143*
Inter-opercular, 193, 197, 201
Interorbital region of skull, 74*
Interorbital septum, 198, 199, 307
Inter-parietal, 437, 439
Inter-renal bodies, 117*
Lnter-spinous bones, 199, 201*
Inter-vertebral discs, of Crocodilia , 335 :
Rabbit, 434* : Mammals, 496
Inter-vertebral foramina, 258
Intestinal glands, 83*
Intestine, of Craniata, 82
Intra-narial epiglottis, 558
Intrinsic muscles of syrinx, 386
Introduced fauna, 601*
Investing bones, 76*
Iris, 106, 107*
Ischiatic foramen, 380
Ischiatic symphysis, 312*
Ischium, of Craniata, 80, 81* — -See
Pelvic arch
Isthmus, 193*
Iter, 276, 277— See Brain
J
ACANAS, 403
Jacobson's organ, of Craniata, 106 :
of Lizard, 320, 321 : of Reptilia,
349 : of Rabbit, 445, 446 : of Mam-
mals, 562
Jacquinot, 662
Janssen, Hans and Zacharias, 649
Jaws, of Craniata, 74, 75*, 79 — See
Skull
Jerboas, 470, 492, 531, 532
Jugal, 199, 200*, 440
Jugular eminence, 537*
Jugular plate, 213, 218
Jugular veins, 90 — See Vascular sys-
tem
Jumping Shrews, 493
Jurassic period, 619
K
.AGU, 612
Kakapo, 413, 431, 600
Kangaroos, 465, 481, 482, 483, 506,
507, 510, 546, 547, 558, 577
Kea, 617
Keel, of sternum, 375
Kidney, development of, 113, 114, 115
Kidneys — -See Excretion, Organs of
Killers, 466, 486
King of the Herrings, 183
Kingfishers, 404, 423
Kiwis, 398, 417, 420, 421, 422, 423, 426,
429
Koalas, 482, 483, 499, 506, 508, 545,
562, 577, 578
Kolliker, A., 658, 659
Kowalevskia, 23, 24, 28
Kowalewsky, 667
JABIA MAJOBA, 461
Labial cartilages, of Craniata, 74, 76* :
Dogfish, 145
Labrichthys psittacula, 215
Labyrinth, carotid, 271 : membranous
— See Ear
INDEX
697
Labyrinthodonts, 256, 288, 295
LACERTA, 304, 353 : External features,
304: Exo -skeleton, 305: Endo-
skeleton, 305-313 : Digestive sys-
tem, 313, 314 : Vascular system,
314, 315, 316, 318 : Organs of
respiration, 315, 318: Brain, 318,
319, 320 : Spinal cord, 320 : Organs
of special sense, 321, 322 : Urinary
and reproductive systems, 322, 323 :
Systematic position, 327
Lacerta muralis, 348
Lacertidce, 327*, 358
Lacertilia, 324*, 327, 328, 329. 332,
333, 335, 336, 337, 338, 342, 345,
346, 347, 348, 349, 351, 353, 354,
358, 359
Lacrymal bone, 307, 308
Lacrymal gland, of Lizard, 321 :
Mammalia, 563
Lacteals, 95*
Lacustrine fauna, 616
Lcemargus, 172, 175, 176
Lagena, 208, 321, 322— See Ear
Layenorhynchus, 544
Lagomyidce, 474
Lagopus scoticus, 602
Lamarck, 629, 655, 656
Lamarckian theory, 628
Lambdoidal suture, 439
Lamina perpendicularis, 438*
Lamina terminalis, of Craniata, 99* —
See Brain
Lamna cornubica, 165
Lampern, 120
Lamprey— See Petromyzon
Lanarkia spinosa, 254
Lancelot — See Amphioxus
Land tortoises, 325, 331, 357, 358
Languets, 24*, 25, 29
Lankester, E. R., 668
Lapillus, 208*, 209
Larks, 404
Larus, 403, 411, 421, 429, 605
Larvacea, 21*, 23, 28
Laryiigeal nerves, of Craniata, 103
Laryngo-tracheal chamber, 269, 295
Larynx, of Lizard, 318 : Reptilia, 346 :
Bird, 385 : Rabbit, 453
La Sueur, 662
Lateral line, 105* : Petromyzon. 121 :
Dogfish, 140 : Holocephali, 183,
184 : Trout, 192, 194 : Ceratodus,
241 : Amphibia, 299
Lateral line canal, 140 : Elasmo-
branchs, 174
Lateral line organs, 105*, 174, 298
Lateral nerve, of Craniata, 102
Lateral plate, of Amphioxus, 59 : of
mesoderm, 118
Lateral post-frontal, 308*
Lateral temporal fossa, 309*
Lateral vein, 91
Lateral ventricle, of Craniata, 97 — See
Braii i
Laurentian period, 618
Leather-backed Turtle, 336
Leeuwenhoek, 649
Lemur, 472 — See Prosimii
Lens, 106, 108
Lens -capsule, 108
Lens involution, 109
Lepidosiren, 230. 2 .">(). i'.")l
Lepidosteus, 213, 218, 221, 222, 223,
227, 229, 231, 232, 233, 234, i':J5
Lepidosteus platystomus, 213
Lepidotrichia, 202*
Lepidotus maximus, 238
Leporidce, 470, 474
Leptocephalus, 235
Leptoglossce, 327*
LEPUS CUNICULUS, 432 : External char-
acters, 433, 434 : Skeleton, 434-444 :
Coelome, 444, 445 : Digestive organs,
445—448 : Circulatory organs. 446—
452 : Respiratory organs, 453, 454 :
Ductless glands, 454 : Nervous
system, 454, 455, 456, 457, 458:
Organs of special sense, 458 : Urino-
genital organs, 459, 460 : Develop-
ment, 461 : Systematic position,
474
Lrpiis variabilis, 617
Leuckart, 660, 661
Leucocytes, 94
Leydig's gland, 159*
Lieberkuhn, 661
Lienogastric artery, 151
Limb-girdles, of Craniata, 80, 81* — •
See Pectoral arch and Pelvic arch
Limb-skeleton, of Craniata, 79, 80 :
Dogfish, 145 : Elasmobranchii,
169 : Holocephali, 186 : Trout, 201,
202 : Teleostomi, 224 : Dipnoi,
243 : Frog, 265, 266 : Amphibia,
294: Lizard, 310, 311, 312, 313:
Reptilia, 342, 343, 344: Pigeon,
379, 380, 381 : Aves, 417, 419, 420 :
Rabbit, 442, 443, 444 : Mammalia,
500 : Prototheria, 505 : Metatheria,
508, 510 : Edentata, 511, 512, 513 :
Cetacea, 516 : Sirenia, 519 : Un-
gulata, 525 : Carnivora, 530 : Ro-
deiitia, 532 : Insectivora, 533 :
Chiroptera, 535 : Primates, 538, 539,
540,
Limbs, of Craniata, 67, 81 : Dogfish,
141 : Elasmobranchii, 165, 166 :
Holocephali, 184 : Trout, 194 :
Teleostomi, 219 : Ceratodus, 240 :
Dipnoi, 250 : Frog, 257 : Amphibia,
294 : Lizard, 304, 305 : Reptilia,
698
INDEX
328, 329, 331 : Pigeon, 307, 368 :
Aves (Neornithes), 408, 409 : Rabbit,
433 : Mammalia, 501
Limicolte, 403*, 411
Limosa, 403, 408
Linea alba, of Frog, 26G, 267
Ling, 214
Lingual cartilage, of Lamprey, 121, 123
Linnaeus, 651, 652, 654, 665
Lion, 530
I/iopelma, 605
Lip -fishes, 218
Liquor amnii, 572*
Liquor folliculi, 569*
Lister, Lord, 665
Litopterna, 588
Littoral fauna, 614*
Liver, of Asciclians, 28 : Euchorda,
42 : Amphioxiix, 47 : Craniata, 69.
85* : Petromyzon, 125. 126 : Myxinr,
136 : Dogfish, 148, 149 : Elasmo-
branchii, 173 : Trout, 205, 206 :
Teleostomi, 227 : Frog, 268, 269 :
Lizard, 313, 314 : Pigeon, 384, 385 :
Rabbit, 448 : Mammals, 556
Lizards — See Lacerta and Lacertilia
Llamas, 580
Loach, 214
Lobi inferiores, 153*, 154, 173
Lophius, 219
Lophobranchii, 216*, 221, 227
Lories, 404
Lorius, 404
Lucida, 22*
Lucretius, 654
Lumbo-sacral plexus. 277*
Luniliricidtf, 601
Lumbrictis, 601
Luminous organs, 171, 220, 221
Lump -fish, 22.~>
Lunar, 442, 443
Lung-fishes — See Dipnoi
Lungs, of Craniata, 69, 87 : Ceratodus,
244 : Frog, 268, 26!) : Tadpole, 283 :
Amphibia, 295 : Lizard. 315, 318 :
Reptilia, 347 : Pigeon. 385. 386 :
Aves, 421 : Rabbit, 453 : Mammals,
558
Luth, 336. 357, 358
Liitra, 491. 552
Lutridce., 470, 491
Lyell, Sir C., 658, 665
Lygosoma, 602
Lymph, 94*
Lymph-capillaries, 94*
Lymph-hearts, 95*, 275
Lymph-sinuses, 94*, 275
Lymph-space, 46, 50*
Lymph-vessels — See Lymphatics
Lymphatic glands, 95*
Lymphatics, 89, 94*, 274, 275, 557
Lyra, 456*, 457
Lyre-birds, 404, 602, 611
M
M
AC AC US, 473, 590
Macaques, 473
Macaws, 404, 408, 416
Mackerel, 190, 215, 220
Macropodidce, 465 — See Kangaroos
Macropoma mantelli, 236
Mncropus — See Kangaroos
Macropus bennettii, 510
Mncropus major, 546, 562
Macroscelididce, 493
Maculae acusticae, 111*
Madagascar, fauna, 610
Mceritherium, 587
Magnum, 443 — See Limb-skeleton of
Mammals
Malapterurus, 266
Malar, 440*
Malleolar bone, 526*
Malleus, 441. 564
Malpighi, 649, 650
Malpighian capsules, 113*, 114 : of
Bdellostoma., 137
Mamma? — See Teats
Mammalia, 65*, 303, 432* : Example,
432 : Distinctive characters and
classification, 462 : Integument and
general external features, 474—494 :
Endoskeletoii, 494-501 : Skeleton
of Prototheria, 501-506 : Meta-
theria, 506-508 : Edentata, 508 :
Cetacea, 513: Sirenia, 518: Un-
frulata, 519 : Carnivora, 528 : Ro-
dentia, 531 : Insectivora, 532 :
Chiroptera, 533 : Primates, 535 :
Digestive organs, 541 : Vascular
system, 557 : Organs of respiration,
558 : Nervous system, 559 : Organs
of special sense, 562 : Urinogenital
organs, 564 : Development, 567-
579 : Geographical distribution, 579 :
Geological distribution, 581
Mammary foetus, 577
Mammary glands, 477*
Mammary pouch, 477, 478
Mammoths, 580, 5S1
Man, 473, 495, 499. 536, 537, 538, 539,
540, 553, 554
Manatee, 467, 501, 519, 520, 550, 551,
579, 621
Manatus, 467, 520
Manatus senegalensis, 520
Mandible, of Craniata, 79*— See Skull
Mandibular arch, of Craniata, 75*
Mandibular nerve, of Craniata, 101
Mandibular suspensorium, 76*
INDEX
699
Manilla-., 465, 485, 509, 547, 579
Muni*. 471), 485. 500, 564
Mam'* i/ii/ini/i'ii. 485
Mantle of Ascidia, 15
Manubrium stcrni, 436*
Man us, 67, 304
Maori Uog, 600
Maori Rat, 600
Marginal plates, 335*, 336
Marmosets, 472 — See Hapalidoe
Marrow, 82*
Marsh, O. C., 667
Marsupial bones, 464, 505*, 507, 508
Marsupial Molo, 480, 481, 561, 5(53
Marsupialia, 464*. 477, 478. 479. 480.
481. 482. 483. r.oo, r.oii, 507, 508.
509. 544. 545. 546. r,r,ii. r.r.x. 560. 561.
562. 5I54. •'>(>.->. 566. r.tio, r,7<;. 577. 579,
583. 621
Marsupium, 464, 477
Mastodonsaurus, 295
Mastoid, 497, 537
Matthew, Patrick, 662
Maturation of ovum, of Ampkioxus,
54, 55
Maxilla, of Craniata, 77, 79* — See
Skull
Maxillary antra, 559
Maxillary nerve, of Craniata, 101
Maxillo-turbinals, 440*, 441
Meckel's cartilage, of Craniata, 74, 75*,
79 : of Dogfish, 145 : of Elasmo-
branchs, 168 : of Frog, 262
Mediastinum, 449*, 453
Medulla oblongata, 97* — -See Brain
Medullary canal, 32*, 33. 34
.Medullary folds, of Ascidian, 32 : of
Amphioxiis, 56
Medullary groove, of Craniata, 32, 95
Medullary keel. 131, 132*
Medullary plate, of Ascidian, 32* : of
A'lii/ili-io.vuft, 56
Megachiroptera, 471*. 493, 534, 535
Meijalobatrachnx. 2S4, 287
Megameres. 131*. 280*. 281
Megapodiidce, 602
Megapoiliitx, 403, 423, 602
, 602
--, 585, 586
Megatherium, 621
Megistanes, 398*, 422, 429, 432
Meibomian glands, 563
Meles, 552
Membrana granulosa, 568*
Membrana semilunaris, 386
Membrane bones, 76*
Membranous cochlea, 459
Membranous labyrinth, 111*, 112 — See
Ear
Membranous vestibule, 111*
Meniscus, 373*
Mental prominence, 537*
Mento-meckelian, 261. 262
Menura, 404, 602, 611
Mergansers, 403
Mergus, 403
Meroblastic segmentation, 5(59
Meropidce, 404
Merrythought, 378
Mesencephalon — See Mid-brain, 97*
Mesenteric artery, 88, 90
Mesenteries, dorsal and ventral, 4, 5
Mesentery, of Craniata, 69, 86*
Mesethmoid, 74*, 77, 78*— See Skull
Mesoarium, of Dogfish, 159 : Lizard.
322, 323*
Mrsoccele, 97 — See Brain
Meso-coracoid, 202, 203
Mesocuneiform, 444 — See Limb-skele-
ton of Mammals
Mesoderm, formation in Craniata, 117
Mesodermal segments, of Craniata, 117,
118
Mesogaster, 313*
Mesonephric ducts, of Craniata, 113*,
115
Mesonephros, of Craniata, 113*, 115:
of Cyclostomi, 134
Mesopithecus, 590
Mesoplodon, 466
Meso-pterygium, 147*, 169, 170
Meso-pterygoicl, 199, 200
Mesorchium, of Dogfish, 159* : of
Lizard, 322, 323*
Meso- rectum, 313*
Mesoscapular segment, 500*
Mesosternum, 496
Meso-tarsal joint, 381*
Metacarpals, of Craniata, 80, 81*
Metacarpals (feathers), 373
Metacoele, 97 — See Brain
Metacone, 544*
Metaconid, 545*
Metacromion, 442
Meta-discoidal placenta, 576*
Metagenesis of Thaliacea, 21
Metamerism, 118*
Metamorphosis, of Balanoylossuf!, 7,
8, 9 : of Ascidian, 22, 30 : Frog,
282
Metamorphosis, retrogressive, of Asci-
dian, 13, 36. :i7
Metanephric ducts, of Craniata, 113*,
115
Metanephros, of Craniata, 113*. 115
Metapleure, of Aniiili-iu.ru,-.-. 43. 44*. 61
Mrtupophyses, of Rabbit. 434. 435*
Metapterygium, 147*. 169, 170
Metapterygoid, 199, 200
Metatarsals, of Craniata, 80, 81*
Metatheria, 464* — See Marsupialia
Meteiicephalon, 97* — See Brain
700
INDEX
Mice, 470
Microbiotheridce, 621
Microchiroptera, 471*, 493, 534
Microlestes, 619
Micromeres, 280*, 281
Micropyle, 209
Mid-brain, of Craniata, 97*
Mid-digitals, 368, 373
Mid-kidney, 113
Milne -Ed wards, H., 660
Mimicry, 637
Minimus, of Craniata, 80, 81*
Miocene, 620
Mitral valve, 450
Mitsukiirina, 182
Moas, 398, 414, 417, 423
Mohl, von, 658
Molars, of Rabbit, 446
Mole, Marsupial, 480, 481, 561, 563
Moles, 471, 493, 533, 563, 575
Molge, 284, 287
Molgulidce, 37
Momotidce, 404
Mongrels, 644
Monitors, 324, 336, 346, 355, 358
Monkeys- — See Primates
Monophyodont Mammals, 463*
Monopneumona, 250*
Monotremata, 464*, 496, 558, 560, 561,
562, 563, 564, 565, 569, 578, 579
Monotremes — See Monotremata
Monro, Alexander, 654
Mordacia, 120, 134, 139
Morula, 577
Moschus, 617
Moseley, H. N., 662
Motmots, 404
Moulting, of feathers, 410
Mucous membrane, 83*
Mud-fishes, 213, 239
Mud tortoises, 325
Miiller, Johannes, 659
Mullerian duct, 115, 116*— See Re-
productive system
Midler ornis, 399
Mullet, 215
Multituberculata, 581, 582
Muridce, 4r/0
Murray, John, 662
Mus, 575
Mus dccumanus, 554, 601
Mus domeslicus, 601
Mus tnaorum, 600
Mus musculus, 554
Muscle buds, 181*
Muscle -plates, 45
Muscles, of Amphioxus, 45 : Lamprey,
124: Elasmobranchii, 171: Trout,
203 : Frog, 266, 267 : Amphibia,
294 : Pigeon, 382, 383 : Aves, 420
Muscular layer, of Craniata, 67, 68
Muscular system, of Amphioxus, 45
Musculi papillares, 449, 450*
Musculi pectinati, 314, 449
Musculo -cutaneous vein, 271, 273
Museums Association, 664
MusipJiagidee, 609
Musophagidce, 404
Mustela, 554, 620
Mustelidce, 176, 470, 554
Mustelus antarcticus, 68
Mutations, 633*
Mycetes, 473
Myctodera, 284*
Myelencephalon, 97*
Myliobatis, 173
Mylodon robustus, 585, 621
Myoccele, 59
Myocommas, of Amphioxus, 45* :
Craniata, 68
Myomeres, of Amphioxus, 43, 44, 45* :
Craniata, 68
Myotone, 56, 59*
Myrmecobius, 480
Myrmecophaga, 509, 511, 512
Myrinecophagid.ee, 465
Mystacina tuberculata, 600, 602
Mystacoceti, 466*, 516, 51",, 518
Myxine, 134, 135, 136, 137, 139
Myxine glutinosa, 135, 136
Myxinoidei, 134*
N,
N
ARES — See Olfactory organ
Nasal spine, 537*
Nasals, 77, 78*
Naso-buccal groove, 141
Naso -palatine canals, 446*
Naso-turbinals, 439*
Native Cats, 464 — See Dasyures
Natural selection, 629, 633*
Naultinus, 602
Navicular, 444* — See Limb-skeleton
(Mammalia)
Nearctic region, 608
Neck, of Craniata, 65
Necturus, 284, 285, 286, 291, 293, 294
Necturus maculatus, 285, 286
Nekton, 616*
Neoceratodus, 239
Neochanna, 600
Neo -pallium, 560
Neornithes, 397*, 407, 420
Neotropical region, 613
Nephridium — See Excretion, Organs of
Nephrostome — See Excretion, Organs of
Nephrotome, 179*
Nerve components, 112
Nerve -foramina, of Craniata, 74
INDEX
701
Nerves, of Amphioxus, 52, 53 : Crani-
ata, 100, 101 — See under Brain and
Spinal cord
Nervi terminates, 100*
Nervous system, of Balanoglossus, 6, 7 :
Ascidia, 19, 20 : Urochorda, 28 :
Amphioxus, 51, 52, 53 : Craniata,
95-104 — See under Brain and Spinal
cord
Nesonetta, 600
Nesopithecus, 621
Nestling-downs, 409*
Nestor, 600
Nestor notabilis, 617
Nestor productus, 612
Nests, of Birds, 422, 423 : of Stickle-
back, 234
Neural arch — See Vertebra
Neural canal, 51
Neural cavity, of Craniata, 68*, 69
Neural gland', 19, 20
Neural plate, 143*
Neural process, 143
Neural spine, 143*
Neural tube, Craniata, 70, 71*
Neurenteric canal, 33*, 56, 57, 281, 282
Neurenteric passage, 178
Neuroccele, 2*, 32, 33, 42, 47, 52, 56, 57
Neuroglia, 96*
Neuromast organs, 104, 105*
Neuromasts, 104, 105*
Neuron, 42, 47, 48, 51, 53, 56, 95
Neuroppre, 32, 52*, 53, 57, 59, 60
New Zealand, comparison of its
physical conditions and fauna with
those of Great Britain, 599
New Zealand region, 611
Newts, 256, 284, 287
Nictitating membrane, of Elasmo-
branchii, 174 : Frog, 257 : Lizard,
305 : Pigeon, 368, 369 : Rabbit,
433 : Mammalia, 563
Nidicolte, 429*
Nidifugse, 429*
Non-Ruminants, 468*
Nostril, 105
Notidanidoe, 164, 173
Notochord, 1* : Balanoglossus, 6 :
Cephalodiscus, 11 : Rhabdopleura,
12 : Appendicularia, 23, 24 : As-
cidian larva, 32, 33 : Amphioxus,
44, 45*, 47, 56, 57, 58 : Craniata,
69, 70, 71 — See Vertebral column
Notochordal sheath, 46*, 70, 71
Notochordal tissue, 46*, 70, 71
Notornis, 413, 417, 600, 622
Notornis alba, 612
Notoryctes, 480, 481, 561, 563
Notoryctes typhlops, 480, 481
Nototherium, 621
Nototherium mitchelli, 584
ZOOLOGY. VOL. II.
Nototrema marsupium, 300
Nuchal plates, 335*
Nucleus, of Salpce, 28*
Nurse, Dolioluin, 37*, 39
0,
O
'BLIQUE SEPTUM, 387*
Obliquus externus, 266, 267
Obliquus internus, 266, 287
Obstetric Toad, 300
Obturator foramen, 443*
Obturator notch, 380
Occipital condyle, 185*, 260, 436, 437,
498
Occipital plane, 498*, 499
Occipital region, 74*
Occipital ribs, 241*
Occipital segment, 77, 78*
Oceanic islands, 612*
Oceanites, 402
Octacnemus, 27, 28
Octochcetus, 601
Octopods, 614
Oculomotor ganglion, 100, 101
Oculomotor nerve, 100, 101
Ocydromus, 403, 413, 417, 431, 600,
612
Odontoblasts, 84*, 542
Odontoceti, 466*, 486, 515, 517, 562,
586
Odontoid process, of Amphibia, 290 :
Lizard, 306, 333
Odontolcse, 401*, 430, 431, 432
Odontopteryx, 420
OEsophageo-cutaneous duct, Myxinoid,
135
Oikopleura, 21, 23, 29
Oil-bird, 613
Oil-gland, 367, 368*
Okeii, Lorenz, 659
Old-world Monkeys, 540
Olecranon, 311*
Olfactory bulb, 97*, 153, 189, 206,
207, 230, 231
Olfactory capsules, 73*
Olfactory lobe, 97* — See Brain
Olfactory lobe, median : Amphioxus,
52
Olfactory nerve, 100
Olfactory organ, of Amphioxus, 52,
53 : Craniata, 105, 106 : Lamprey,
127, 128, 129, 130 : Myxinoids, 135 :
Dogfish, 158 : Elasmobranchii, 174 :
Trout, 206 : Ceratodus, 247 : Frog,
277 : Amphibia, 298 : Lizard, 321 :
Reptilia, 349 : Pigeon, 393 : Mam-
malia, 562
Olfactory peduncle, 188, 189*, 231
Olfactory region, of Skull, 74*
X X
702
INDEX
Olfactory tracts, 231
Olfactory ventricle, 97* — See Brain
Olivary body, 458*
Omentum, duodeno-hepatic, 313*
Omentum, gastro -hepatic, 313*
Omentum, great, 391
Omosternum, 263, 264*
Onychodactylus, 289
Opercular, 193*
Operculum, of Balanoglossus, 4 : Crani-
ata, 65 : Holocephali, 183, 184 :
Trout, 192, 193 : Teleostomi, 218 :
Dipnoi, 240, 241, 242 : Tadpole,
283
Ophidia, 324*, 329, 332, 333, 336, 337,
338, 342, 345, 346, 347, 348, 349,
350, 351, 356, 357, 359
Ophthalmic nerve, 101, 102, 155, 156
Ophthalmicus profundus, 155
Opisthoccelous vertebra, 222*, 289
Opisthocomus, 403, 407, 408, 613
Opistbotic, 77*— See Skull
Opossums, 464, 478, 480, 506, 507,
546, 565, 566, 579, 583
Optic capsules, 73*
Optic chiasma, 153
Optic cup, 109*
Optic foramen, 437, 438*
Optic lobes, 98, 99*- — See Brain
Optic nerve, 100, 101
Optic thalamus, 98, 99* — See Brain
Optic ventricle, 98, 99*- — -See Brain
Optic vesicle, 109*
Optoccele, 98, 99*— See Brain
Ora serrata, 106, 108*
Oral cirri of Amphioxus, 43, 44*, 47
Oral hood, 43, 44*
Oral lobes of Doliolum, 26
Oral siphon, 15*, 17
Orang, 473, 535, 537, 538, 539, 540, 581
Orbicular, of Rabbit, 441
Orbit, 73*
Orbito -sphenoid, 77*— See Skull
Oreo, 466
Orca gladiator, 486
Oriental region, 610
Ornithorhynchus, 464, 475, 477, 478,
479, 502, 503, 504, 505, 506, 541, 545,
561, 562
Ornithorhynchus anatinus, 479, 561
Ornithosauria — See Pterosauria
Orthagoriscus, 225
Orlhoceras, 619
Orthogenesis, 645
Orthotomus. 423
Orycteropodidce, 465 — See Cape Ant-
eaters
Orycteropus, 509, 547, 609
Orycteropus capensis, 485
Os cloacae, 312*
Os cordis, 558*
Osmerus, 620
Ossa innominata, 312*
Ossicula audit us, of Rabbit, 441
Ossification, centres of, 77, 542*
Osteocranium, 78*
Osteo -dentine, 84*
Osteostraci, 255, 256
Ostracion, 216
Ostracodermi, 253*, 254, 255, 256
Ostrich, 398, 399, 408, 409, 417, 419,
422, 426, 429, 431, 432
Otariidce, 470, 491, 580
Otis, 403
Otocyst, 24, 29, 34
Otoliths, 111
Otters, 470, 491
Ovarian artery, 90
Ovarian vein, 91
Ovidce, 468, 608— See Sheep
Ovis aries, 523
Ovulists, 650
Owen, R., 660, 665
Owls, 404, 409, 417, 421, 432
Oxen, 468, 487, 553, 564, 579
Oyster-catchers, 403
_L ^DOGENESIS IN AXOLOTL, 302
Pachyornis, 417
Pacinian corpuscles, 103, 105*
Palsearctic region, 608
Palceohatteria, 359
Palceoniscus macropomus, 237
Palseontological evidence of evolution,
626
Palceospondylus yunni, 138, 139
Palamedea, 403
Palate, hard and soft, 446, 553
Palatine, 77, 79*— See Skull
Palatine nerve, 101, 102*
Palatine teeth, Holocephali, 186, 187 :
Trout, 204, &c. : Ceratodus, 243
Palato-pterygoid, 243
Palato-quadrate, 74, 75*, 77— See Skull
Palinurits, 601
Pallas, 653
Pallium, 99*
Pancreas, 69, 85* — See Digestive
system
Pancreatic juice, 85*
Pangenesis, 642
Panmixia, 634
Parachordals, 73*
Paracoale, 97* — See Brain
Paracone. 544*
Paraconid, 545*
Paradiseidce, 404, 411, 429, 602
Parafibula, 508
Paramyxine, 134, 139
INDEX
703
Paranephrops, 601, 602
Paraphysis, 99*
Parapineal eye, 99*
Parapophyses, 195*
Paraquadrate, 262*, 339, 340
Parasphenoid, 77, 78*, 261, 262— See
Skull
Pareiosauria, 326
Parencephalon, 97* — See Brain
Parietal, 77, 78*— See Skull
Parietal foramen of Stegocephala,
293*
Parietal organ, 99*, 319, 320, 350,
351
Parietal segment, 77, 78*
Paroccipital, 437, 438
Parotic processes, 307
Parotid gland, 446
Parotoid glands, 288*
Parra, 403
Parrakeets, 404, 417
Parrots, 404, 408, 409, 415, 421, 429
Partridge, 423
Parus britannicus, 602
Parus rosea, 602
Passeres, 404*, 415, 423, 429, 432
Pasteur, Louis, 665
Patadum, 492*, 501
Patella, 380*, 381
Patella ulnaris, 417
Paunch — See Rumen
Peccaries, 468, 580
Pecten, of Reptilia, 321, 349 : Pigeon,
393 : Birds, 422
Pectoral arch, of Craniata, 80, 81* :
Dogfish, 146*, 147 : Elasmo-
branchii. 169, 170 : Trout, 203 :
Teleostomi, 224 : Ceratodus, 241,
243: Frog, 263, 264: Amphibia,
293, 294 : Lizard, 310, 311 : Bep-
tilia, 342, 343 : Pigeon, 374, 378,
379 : Aves, 416, 417 (Neornithes) :
Rabbit, 441 : Mammalia, 498 :
Prototheria, 505 : Metatheria, 506 :
Edentata, 512, 513, 515 : Cetacea,
516 : Sirenia, 519 : Ungulata, 525 :
Carnivora, 530 : Rodentia, 532 :
Insectivora, 533 : Chiroptera, 535 :
Primates, 539
Pectoral fin — See Fin : Skeleton of —
See Limb-skeleton
Pectoralis muscle, 267*
Pelagic eggs, 235*
Pelagic fauna, 614*
Pelagic fishes, 220
Pelagic larvae of Eel, 235
Pelecanus, 403
Pelicans, 403
Pelvic arch, of Craniata, 80, 82 * :
Dogfish, 147 : Elasmobranchii, 169,
170 : Holocephali, 186 : Trout, 203,
204 : Teleostomi, 225 : Ceratodus,
243 : Frog, 265 : Amphibia, 293,
294, 295 : Lizard, 374, 379 : Rep-
tilia, 342, 343, 344: Pigeon, 374,
379 : Aves, 417, 419 : Rabbit, 443 :
Mammalia, 500 : Prototheria, 505 :
Metatheria, 507 : Edentata, 513,
515, 516 : Cetacea, 517 : Sirenia,
521 : Ungulata, 526 : Carnivora,
530 : Rodentia, 532 : Insectivora,
533 : Primates, 540
Pelvic fin — See Fin : Skeleton of — See
Limb -skeleton
Pelvic vein, 2'/2, 273
Pelvis of kidney, 459*
Pelvi-sternum, 294*
Penguins, 402, 409, 413, 417, 419, 422,
429, 431
Penis, 351 — See Urinogenital organs
Pennse, 409*
Pentadactyle limb, 67*, 80, 81 : Skele-
ton of 80 : Origin of, 595
Perameles, 544, 577
Perameles obesula, 578
Peramelidce, 464 — See Bandicoots
Perch, 190, 215, 223, 229 : climbing,
228
Perching mechanism, 382, 383
Perennibranchiata, 284*, 285, 286,
291, 295, 296, 298, 302
Peribranchial cavity — See Atrial cavity
Pericardial cavity, 69, 70*
Pericardio-peritoneal canal, 150
Pericardium, 70*
Perichcetidce, 602
Perichondrial ossification, 76*
Perichondrium, 76*
Perichordal tube, 71*
Perilymph, 112*
Perinseal glands, of Rabbit, 433, 460
Perinaeum, 433*, 460, 556
Periophthalmus, 229
Periosteal ossification, 76*
Periotic bone, 439, 497
Peripharyngeal bands, of Appendi-
cularia, 23 : of Amphioxus, 46
Peripharyngeal groove, 17
Peripharyngeal ridge, 17
Perissodactyla, 467*, 489, 521, 525,
527, 549, 557
Peritoneum of Craniata, 69, 70*
Peri-vitelline membrane, 55
Permian period, 619
Peron, 662
Peronseus medius, 383
Persistent pulps, 543*
Pes — See Hind -limb
Pessulus, 386*
Petrels, 402, 412, 421, 423, 429
Petrogale penicillata, 508.. 560
Petrogale xanthopus, 481
x x 2
704
INDEX
PETROMYZON, 119: External char-
acters. 120, 121 : Skeleton, 121, 122.
123, 124 : Muscles, 124 : Digestive
organs, 124, 125, 126 : Respiratory
organs, 125, 126 : Circulatory sys-
tem, 126 : Nervous system, 126,
127, 128 : Sensory organs, 128, 129,
130 : Urinogenital organs, 130, 131 :
Development, 130, 131, 132, 133
Petromyzon fluviatilis, 120. 133, 501
Petromyzon marimts. 121. 122. 125.
127, 130, 131
Petromyzon planeri. 120
Petromyzontes, 134*
Pezophaps, 404, 413, 417
Phcenicopterus, 403, 408
Phaethon, 403
Phalacrocorax, 403, 409, 605
Phalangeridce, 46f>. 483, 501, 506, 510,
562
Phalangers, 465 — See Phalangeridse
Phalanges, 80, 81* — See Limb
Phaneroglossa, 285
Pharyngeal bones, superior and in-
ferior, 224*
Pharyngo-branchial, 74. 76* — See Skull
Pharyngognathi, 215*, 219, 224, 236
Pharyngo-hyal, 74, 76* — See Skull
Pharynx — See Digestive organs
Phascalarctos cinereus, 482, 545, 578
Phascolomyidce, 481, 482, 506, 509, 545
Phascolomys, 545, 566
Phascolomys mitchelli, 482
Phascolomys wombat, 509, 566
Pl.ascolotherium bucklandi, 582, 619
Pliasiamti*, 403, 411
Pheasants, 403, 411
Phoca vitulina, 491, 531
Phoccana, 466, 486, 501, 517, 543, 555,
556
Phoccena communis, 517
Phocidce, 470, 491, 531, 580
Phororhacos, 401
Phorozooid, 39*
Phrenic veins, 452
Phylogeny, of Birds, 430
Physeter, 466, 501, 550
Physoclisti, 216*
Physostomi, 213*, 214, 216, 219, 221,
223, 226, 227, 228, 231, 232, 233, 236,
238
Pia mater, 100*
Picariee, 404*, 432
Picas, 474
Pici, 404
Pigeon's milk, 395
Pigeons, 404 — See Columba
Pigment-spot, 52, 53*
Pigs, 468, 488, 519, 522, 525, 526, 527,
548, 580
Pike, 190, 214
Pineal apparatus, of Craniata, 65, 66,
99*, 110*, 111 : Petromyzon, 128
Pineal body, 99*
Pineal eye, 99, 110*, 111, 128: of
Lizards, 319, 320, 350, 351
Pineal organ, 99*, 153, 154
Pineal sense-organ, 65*, 66
Pinna, or ear, 433
Pinnipedia, 470*, 491, 501, 530, 531,
551, 552, 558, 580
Pipa americana, 285, 295, 300, 301, 302
Pipe-fish, 216, 234
Pisces, 64, 139* : Appendix, 253
Pisiform bone, 312, 442 — See Carpus
Pithecanthropus, 590, 621
Pituitary body, of Craniata, 69, 71, 84*
Pituitary body, extra-cranial portion
(Callorhynchus), 188, 189*
Pituitary diverticulum, 69, 84*
Pituitary foramen, 438*
Pituitary fossa, 438*
Pituitary pouch, Petromyzon, 128, 129,
130 : Myxinoids, 135
Placenta, Salpa, 30, 39*, 40 : Rabbit,
462 : Mammalia, 576, 577
Placodontia, 326, 360
Placoid scales, 141, 163, 166, 167
Placula, 31*
Plagiaulax becklesi, 582, 619
Plankton, 615*
Plantain-eaters, 404
Plantigrade, 501*
Plastron, 329, 335
Platalea, 403, 408
Platycercus, 404, 417
Platypus — See Ornithorhynchus
Platysomus striatus, 237
Plectognathi, 216*, 221, 231
Pleistocene period, 621
Plesiosaurus macrocephalus, 360, 361,
362
Pleura, 386*, 387
Pleuracanthei, 163*, 182
Pleuracanthus ducheni, 163
Pleura! ribs, 195
Pleurodont, 345*
Pleuronectes cynoglossus, 220
Pleuronectidce, 214, 219
Pleuropterygii, 162*
Pliocene period, 621
Pliohyrax, 587
Pliopithecus, 621
Ploughshare -bone — See Pygost yle
Plovers, 403, 411
Plumulse, 409
Pneumatic duct, of Trout, 204, 205 :
Teleostomi, 229
Pneumatic foramina, 379, 382*
Pneumaticity of bones, Pigeon, 382 :
Aves, 420
Pneumogastric, 101, 102*, 156, 157
INDEX
705
Podicipes, 402, 40 «»
Poebr other ium, 021
Poephagus, 617
Poison-glands, in Teleostei, 221 . Ophi-
dia, 345, 356
Poli, 654
Pollex, 80, 81*
Polynesian region. 0 ] 2
Polyodon, 212, 218. 221. i':jii
Polyphyletic group, 431*
Polyprotodont, 546*
Polyprotodontia, 464*, 579. 5S::
Polypterus bichir, 190. 212, 218. 210.
222, 223, 224, 225. 227. 229,235, 2:>r,.
609
Pons Varolii, 458*, 559. 560
Porcupines, 470, 47 j, 402. 532
Porpoises, 466 — See Phoccena
Port Jackson Shark, 176, 177. 1 -i-
Portal veins, 152*, 153
Post-anal gut, 69, 82*
Post-axial, 287*, 305
Postcaval vein, 272
Post -clavicle, 203*
Posterior commissure, 200
Posterior temporal fossa, 309*
Post-orbital, 308
Post-patagium, 368*
Post-temporal, 203*
Polamogale, 609
Pouters, 367
Powder-do ^11 -patches, 409*, 410
Praecoces, 429*
Pre-anal plate, 305
Pre-axial, 287*, 305
Precaval vein, 90
Precocious young, 397*
Pre-commissural area, 561*
Pre-formation, 650
Pre-f rental, 307, 308
Pre-hallux, 266, 294
Premaxilla, 77, 79*— See Skull
Premolars, 445 — See Teeth
Pre -nasal, 523*
Pre-nasal region, 74*
Pre-olfactory nerves, 155
Pre-opercular, 193
Pre-oral pit, Amphioxus, 58*, 59
Pre-patagium, 368*
Pre-pubic process, 170, 171
Prepuce, 460*
Pre -sphenoid, 77, 78*— See Skull
Presternum, 436
Primates, 471*, 478, 535-541, 567, 580,
590
Primitive groove, 280*, 424
Primitive knot, 352, 353*
Primitive streak, of Aves, 354, 424
Pristiophorus, 165
Pristis, 165
Pristiurus, 182, 183
Pro-amnion, 424. 425*
Pro -at las, 333*. 335
Proboscidea, 469*, 520, 521, 525, 528,
587
Proboscis, of Balanoglossus, 3, 4 :
Cephalodiscus, 11 : Rhabdopleura,
13
Proboscis -cavity, 3. 4, 9, 12
Proboscis-pore, 3, 4, 11, 12
Proboscis -skeleton, 4, 6*
Procellaria, 412
Processus gracilis, 441*
Proccelous vertebra, 258*
Pro-coracoid, 80, 81*, 310, 311
Proctodaeum — See Digestive system
Pronation, 442
Pronephric duct, 113*, 114, 115
Pronephros, 113*, 114, 115
Prongbuck, 580
Pro-otic, 77*— S«^ Skull
Propteiygium, 147*, 169, 170
Prosenc?phalon, 97*, 153— See Brain
Prosimii, 472*, 494, 535, 539, 540, 581
Prosoccele, 97*— See Brain
Prostate, 459, 460
Protective 'resemblance, 637
Proteus, 284, 287, 291, 298, 616
Proteus anguineus, 291
Protochorclal plate, 353, 354*
Protocone, 544*
Protoconid, 54 .V;:
Protoplasm, 658
Protopterus, 239, 250, 251, 252, 609
Protoselachii, 164*
Prototheria, 463, 464*, 477, 478, 479,
500, 501-506, 556, 578, 583
Protovertebra, 56, 59, 117, 118*, 179
Protriton, 293
Proventriculus, of Pigeon, 384*
Psalterium, of brain, 456*, 457 : of
stomach, 553*, 555
Psammosteidce, 255*
Psephurus, 212, 236
Pseudis parad-oxa, 301
Pseuclobranchia, of Dogfish, 150 :
Elasmobranchii, 173 : Trout, 204 :
Teleostomi, 227 : Ceratodus, 244
Pseudoccele, 455*
Pseudophycis backus, 230
Psittaci, 404*, 429. 431
Psittacus, 404, 408, 409, 415, 421, 429
Ptarmigans, 411
Pteraspidce, 254*
Pteraspis rostrata, 254
Pterichthys, 256
Pterobranchia, 3*, 9, 10, 11, 12, 13
Pterocles, 404
Pterocletes, 404*
Pterodactyles — See Pterosauria
Pterodactylus, 364
Pteropidce, 471 — See Flying Foxes
706
INDEX
Pteropus fuscus, 535
Pteropus jubatus, 534
Pterosauria, 327*, 364*, 365
Pterotic, 197, 198
Pterygiophores, 69, 80* — See Fins
Pterygoid, 77, 79*— See Skull
Pterygopodia, 166*
Pterylae, 372*
Pterylosis, of Pigeon, 372, 373* :
Aves, 409, 410
Ptychodera, 5
Pubic symphysis, 312*
Pubis, 80, 82*- See Pelvic arcli
Pubo-ischial region, 82*
Puffins, 429
Puffinus, 357, 402
Pulmonary aponeurosis, 386*, 387
Pulmonary artery and vein, 93
Pulmonary nerves, 103
Pupil, of eye, 107
Purkinje, 658
Pygal plates, 335*
Pygochord, 6*
Pygopidce, 358
Pygopodes, 402*, 431
Pygopus lepidopus, 329
Pygostyle, of Pigeon, 374, 375*
Pyloric caeca, of Trout, 204, 205 :
Teleostomi, 227
Pyloric valve, 204
Pylorus, 148*
Pyrosoma, 22, 27, 28, 30, 37, 41
Pyrosomidce, 22
Pyrotherium, 587
Pythonomorpha, 324*, 365, 366
Pythons, 324, 329, 333, 343, 356, 357
Q
UUADBATE, 75*, 77, 79, 337— See
Skull
Quadratojugal, 261, 262*
Quadra'tojugal arch, 309
Quadrupedal attitude, 501*
Quagga, 609
Quills, 492*
Quoy, 662
R
IABBITS, 470 — See Lepus cuniculus
Rachis, 369, 370* — See Feather
Radiale, 80, 81* — See Limb -skeleton
Radialia, radial cartilages, 79, 80* —
See Limb -skeleton
Radio-ulna 259, 265*
Radius, 80, 81* — See Limb-skeleton
Rails, 403, 413
Rajida, 165*
Rallus, 403, 413
Rana pipiens, 257
RANA TEMPOBABIA and R. ESCULENTA,
257 : External characters, 257 :
Endo -skeleton, 258, 259-266 : Mus-
cular system, 266, 267 : Digestive
organs, 268, 269 : Respiratory
organs, 268, 269 : Circulatory organs,
270-275 : Nervous system, 275,
276 : Sensory organs, 277, 278 :
Urinogenital organs, 278, 279 : De-
velopment, 279, 280, 281, 282, 283 :
Systematic position, 285
Range, 605*
Ranidce, 285*
Ranidens, 290
Rapacious Birds, 429
Ratitse, 397*, 409, 410, 412, 413, 414,
416, 417, 420, 429, 431
Rats, 470
Rattlesnakes, 324, 338, 356
Rauber's layer, 570*
Raven, 405
Ray, John, 647, 650
Rays, 165-182
Recapitulation Theory, 626
Recent period, 622
Receptaculum chyli, 557
Recessive characters, 644, 645
Recognition-marks, 411
Rectal gland, Dogfish, 148, 149
Rectrices — See Pterylosis, 368, 373
Rectus abdominis, 266, 267
Red-bodies, 230*
Red Deer, 520, 525, 526, 527
Red-glands, 230*
Redi, 650
Reef-fishes, 218, 238
Regalecus, 218, 225, 615
Regeneration, 638
Reindeer, 487
Relationships, of Hemichorda, 13, 41 :
Urochorda, 41 : Amphioxus, 63 :
Cyclostomata, 138 : Amphibia, 302 :
Aves, 430 : Chordata, 590 : Phyla
of Animals, 596
Remiges — See Pterylosis, 373*
Renal artery, 90
Renal organs — See Excretion, Organs
of, and Urinogenital organs
Renal portal system, 91*— See Vas-
cular system
Renal veins, 91
Replacing bones, 76*
Reproductive organs, of Balanoglossus,
1 : Cephalodiscus, 11 : Ascidia, 20 :
Urochorda, 30 : Amphioxus, 54, 55
— See Urinogenital organs
INDEX
707
Reptilia, 303* : Example, 304 : Dis-
tinctive characters and classification,
323 : External features, 327 : In-
tegument and exoskeleton, 331 :
Endoskeleton, 332 : Digestive or-
gans, 345 : Organs of respiration,
346 : Organs of circulation, 347 :
Brain, 349 : Sensory organs, 349 :
Reproductive organs, 351 : Develop-
ment, 351 : Ethology, 354 : Geo-
graphical distribution, 35S : Geo-
logical distribution, 359 : Extinct
groups of reptiles, 360 : Relation-
ships, 590
Respiration, organs of, Amphioxus,
47 : Craniata, 86, 87 : Petromyzon,
125, 126 : Hemiscy Ilium, 149 : Elas-
mobranchii, 173 : Holocephali, 187 :
Trout, 204 : Teleostomi, 227 : Gera-
todus, 244, 245 : Frog, 269 : Am-
phibia, 295 : Lizard, 318 : Reptilia,
346, 347 : Pigeon, 385, 386, 387,
388 : Aves, 421 : Rabbit, 453 :
Mammalia, 558
Respiratory heart, 93*
Respiratory tube of Petromyzon, 124,
125, 126*
Respiratory valves, of Trout, 193
Restiform bodies, 187, 188
Rete mirabile, 173*
Reticulum, 553*, 554
Retina, Craniata, 106, 107, 108
Retropinna, 600
Reversal of selection, 635*
Rhabdopleura, 2, 9, 12, 13, 593
RhamphorhyncJms, 365
Rhamphotheca, 395*
Rhea, 398, 408, 417, 429, 431
Rhese, 398*, 422, 429
Rhina, 173
Rhinencephaloii, 97* — -See Brain
Rhinobatus, 176
Rhinoceros, 468, 476, 489, 490, 521,
522, 525, 526, 527, 528, 580
Rhinoceros indicus, 490
Rhinochetus, 612
Rhinoccele, 97*, 173— See Brain
Rhinoderma darwini, 300
Rhomboid scales, 221*
Rhynchocephalia, 325*, 329, 330, 333,
359
Rhytina, 467, 550, 579, 586, 622
Ribbon-fishes, 218, 225, 615
Ribs, of Craniata, 69, 72 : Dogfish,
142, 143: Teleostomi, 222: Uro-
dela, 290 : Lizard, 306 : Reptilia,
333, 334, 335, 336 : Pigeon, 373 :
Aves, 412 : Rabbit, 435 : Mam-
malia, 495 : Edentata, 509 : Cetacea,
515 : Sirenia, 518 : Carnivora, 528 :
Chiroptera, 534
Rita buchanani, 214
River tortoises, 325, 331, 357
Rock-pigeon, 367
Rock Wallaby, 481, 508, 560
Rodentia, 470*, 478, 531, 532, 552,
557, 558, 563, 576, 580, 589
Rods and cones, of retina, 107, 108*
Rollers, 404
Rorqual, 517
Rostrum of skull, Craniata, 74* : Dog-
fish, 144: Trout, 198: Pteraspis,
254 : Aves, 376, 377
Rudolphi, 661
Rumen, 553*, 554
Ruminants, 468*, 476, 487, 520, 525,
526, 527, 548, 553, 554, 555
Rupicapra, 617
S
ACCULUS, 111*, 112
Saccus vasculosus, 99*, 153*, 154, 173,
206, 207
Sacral ribs, 306
Sacral vertebra, 259, 260
Sacro -vertebral angle, 536*
Sacrum, 435*
Sagitta, 208*, 209
Sagittal crest, 521*
Sagittal suture, 439
Salamanders, 256, 284, 287, 288, 289,
292, 294, 295, 296, 297, 301, 302
Salamandra, 284, 294, 295, 296
Salamandra atra, 292, 301
Salamandra maculosa, 287, 288, 297,
301
Salamandrina, 290
Saliva, 84*
Salivary glands, 84* — See Digestive
system
SALMO FARIO, 192 : External char-
acters, 192, 193, 194 : Skin and
exoskeleton, 194, 195 : Endoskele-
ton, 195-203 : Muscles, 203 : Ccelome,
203 : Digestive organs, 204, 205 :
Air-bladder, 204, 205 : Respiratory
organs, 204 : Circulatory organs,
204, 205, 206 : Nervous system,
206, 207 : Sensory organs, 206, 207,
208, 209 : Urinogenital organs, 208,
209, 210 : Development, 209, 210 :
Systematic position, 216
Salmo ferox, 192
Salmo fontinalis, 192
Salmo killinensis, 605
Salmo solar, 192
Salmon, 190, 201, 214, 235
Salmonidce, 216, 235, 236
708
INDEX
Salpa, 26, 27, 28, 29, 30, 39, 40
Salpa democratica, 26
Salpidce, 22
Sand-grouse, 404
Sand -martins, 423
Sand-pride, 120
SarcopMlus ursinus, 546
Sarcorhamphus, 617
Sargus, 227
Sauropsida, 303*, 323
Sauropterygia, 326*, 360, 361
Saw-fish rays, 165
Saw-fish shark, 165
Scala tympani, 459
Scala vestibuli, 459
Scales, 194 : of Pigeon, 369
Scaly Ant-eater, 485— See Manidse
Scapanorhyncus, 182
Scaphirhynchus, 212, 236
Scaphognathits, 365
Scaphoid, 442, 443 — See Limb-skeleton
of Mammalia
Scapula, 80, 81*, 8?— See Pectoral
arch : accessory, 417
Scapular region, 81* — See Pectoral
arch
Scheuchzer, 658
Schizoccele, 118
Schizognathous arrangement, 415*
Schleiden, 658
Schneiderian membrane, 106*, 393
Schultze, Max, 659
Schwann, 658
Scincidse — See Skinks
Sciuridce, 470, 491, 532
Sclater, P. L., 667
Sclerotic, 73*, 106, 321, 349, 393
Sclerotic plates, of Stegocephala, 293 :
Lizard, 321 : Reptilia, 349 : Pigeon,
393
Screamers, 403
Scroll-valve of Elasmobranchii, 172
Scrotal sac of Rabbit, 433, 460
Scrotum, 565
Scutes, of Teleostomi, 221 : Stego-
cephali, 289 : Reptilia, 329 : Arma-
dillos, 484
Scyllium canicula, 140— See Hemi»
scylliurn
Scymnus, 167, 173
Sea-brearn, 215
Sea-cows, 467— See Sirenia
Sea-horse, 216, 217, 218, 219, 234
Sea-snakes, 324, 356
Sea-squirts, 14
Sea-turtles, 357
Seals, 470
Sebaceous glands, 474, 475, 476
Sebastes percoides, 215
Secodont, 545*
Secondary cranium, 197
Secretary-bird, 403, 609
Segfnental duct, 114*, 115
Segregation, 645*
Selache, 173, 182
Selachii, 164*
Selenodont, 545*
Sella turcica, 74, 77*, 189
Semicircular canals, 111*, 112
Semi-lunar, 442
Semi-lunar valves, 270, 271
Semi -plumes, 409*
Semnopithecus, 590
Sense -vesicle, 34, 35, 36
Sensory organs : Amphioxus, 52, 53,
54 : Craniata, 104—See Ear, Eye,
Lateral line, Olfactory organ
Seps, 354
Septum auricularum, 270*, 296
Septum luciclum, 455, 456
Serous membrane, of Birds, 427 428 :
Mammalia, 462
Serpentarius, 609
Serramis, 233
Sesamoid bone, 380*
Severino, 648
Sexual selection, 636*
Shaft of long bone, 82*
Shagreen, 166
Shags, 403, 409
Shank, 67 — See Hind-limb
Sharks, 165-182
Shearwaters, 357, 402
Sheep, 468, 487, 523, 553, 579
Shell, of Chelonia, 329 : of Pigeon, 396
Shell-gland, Dogfish, 159, 160 : Elas-
mobranchs, 175
Shell-membrane, 396, 422, 423, 577
Shore-fishes, 220
Shoulder-girdle — See Pectoral arch
Shrews, 471, 493
Siamanga, 610
Siebold, von, 661
Silurian period, 618
Siluroids, 214, 221, 222, 225, 226, 229,
230, 234, 236
Simia, 473, 610
Simia satyrus, 539, 540
Simiidce, 473*, 494, 495, 535, 536, 537,
581
Sinus rhomboidalis, 392, 393
Sinus venosus, 88 — See Heart
Sinuses, 90, 151*
Siphons, oral and atrial, of Ascidia,
15,17
Siredon, 302
Siren, 284, 286, 287, 296
Siren lacertina, 286
Sirenia, 466*, 476, 486, 495, 496, 518,
519, 550, 558, 563, 579, 586
Skates, 165
Skeletogenous layer, 70, 71*
INDEX
709
Skeleton of Craniata — See Skull, Verte-
bral column, Ribs, Sternum, Pec-
toral arch, Pelvic arch, Limb-
skeleton
Skin, Craniata, 67
Skincs, 324, 332, 354, 358
Skull, of Craniata, 73, 74, 75, 76, 77,
78 : Petromyzon, 121, 122, 123 :
Myxinoids, 136 : Dogfish, 143, 144 :
Elasmobranchii, 168, 169 : Holo-
cephali, 184, 185, 186, 187 : Trout,
196, 197, 198, 199, 200, 201 :
Teleostomi, 223 : Ceratodus, 241,
242 : Frog, 260, 261, 262 : Amphibia,
290, 291, 292, 293 : Lizard, 307, 308,
309 : Reptilia, 337-341 : Pigeon,
376. 377, 378 : Archseopteryx, 407 :
Birds, 414-416 : Rabbit, 436-441 :
Mammalia, 496, 497, 498, 499 :
Prototheria, 502, 503, 504: Meta-
theria, 506-508 : Edentata, 510,
511, 512: Cetacea, 515, 516, 517,
518 : Sirenia, 518, 519 : Ungulata,
520-525 : Carnivora, 528, 529, 530 :
Rodentia, 532 : Insectivora, 532.
533 : Chiroptera, 534, 535 : Pri-
mates, 536-538
Slime -Eels, 134
Sloane, H., 655
Sloths, 465, 474, 483, 495, 500, 501,
509, 511, 512, 513, 514, 515, 547,
556, 579
Smelt, 214, 232, 620
Smith, William, 658
Snakes, 324 — See Ophidia : venomous,
356
Soft palate, 446*, 553
Soft tortoises, 325, 332
Solander, 655
Sole, 190, 214, 235
Solenocytes, 51
Solenodon, 613
Solitaire, 404, 413, 417, 622
Somatic motor fibres, 113*
Somatic nerves, 96*
Somatic sensory fibres, 112*
Somites, 56, 57*
Soricidce, 471, 493
Souleyet, 662
South American Ostrich — See Rhea
Spallanzani, 653
Sparassodonts, 583, 621
Sparrmann, 655
Spelerpes, 290
Spencer, Herbert, 662
Sperm-sac, of Elasmobranchii, 159,
175
Sperm Whales, 466, 501, 550
Spermatic artery, 90
Spermatic vein, 91
Spermatists, 650
Spermatophores, of Holocephali, 189,
190 : Amphibia, 300
Sphargis, 336, 357, 358
Sphenethmoid, 261*
Sphenodon punctatum, 325, 329, 330,
333, 334, 335, 336, 337, 338, 339,
343, 345, 350, 351, 357, 358
Sphenoidal fissure, 438*
Spheno -maxillary fissure, 537*
Sphenotic, 198, 199
Sphyrna, 165
Spider Monkeys, 473
Spigelian lobe, 556, 557*
Spinal accessory nerve, 321
Spinal column — -See Vertebral column
Spinal cord, of Urochorda, 34 : Amphi-
oxus, 52 : Craniata, 95, 96*
Spinal nerves, 53 : of Craniata, 96*
Spines, Spinous fin-rays of Teleostomi,
215, 219
Spiny Ant-eater, 464 — See Ecridna
Spiracle, of Dogfish, 141* : Teleostomi.
218
Spiracular cartilage, 168*, 169
Spiracular gill, 150*, 173
Spiral valve, of Petromyzon, 125, 126*,
130 : Dogfish, 148, 149 : Elasmo-
branchs, 172 : Teleostomi, 212 :
Ceratodus, 243
Splanchnic nerves, 96*
Splanchnotome, 59*
Spleen, 85*
Splenial — See Skull, 310*
Splenial teeth, 243
Splenium, 454*, 5(51*
Spontaneous generation — -See Abio
genesis
Spoonbills, 403, 408
Spurs, 409
Squalida, 164*
Squalodon, 588
Squalodontidce, 586
Squalor aj a, 190
Sguamata, 324*
Squamosal, 77, 80*— See Skull
Squamous suture, 436*
Squirrel Monkeys, 473
Squirrels, 470, 492, 532
Stapes, of Frog, 261, 263* : Urodela,
291 : Rabbit, 441
Star-gazers, 218, 226
Starlings, 404, 430
Station, 605*
Statocyst — see Otocyst
Steatornis, 613
Steganopodes, 403*
Stegocephala, 256, 285*, 288, 289, 293,
295, 299, 302
Stein, 661
Steller's Sea Cow, 586
Stereornithes, 401*, 430
710
INDEX
Stereospondyly, 332*
Sterna, 403, 419
Sternal rib- — See Rib
Sternebrae, 436*, 496
Sterno-tracheal muscles, 386
Sternum, of Craniata, 72 : Heptan-
chus, 170 : Frog, 263, 264 : Am-
phibia, 293, 294 : Lizard, 307, 311 :
Reptilia, 336 : Pigeon, 374, 375 :
Birds, 412 : Rabbit, 436 : Mam-
malia, 496 : Prototheria, 502, 503 :
Edentata, 509 : Cetacea, 515 : Sire-
nia, 518 : Ungulata, 521 : Car-
nivora, 528 : Rodentia, 532 : In-
sectivora, 532 : Chiroptera, 534
Sternum, abdominal, 336
St. Hilaire, E. G., 657
Stickleback, 215, 234
Stigmata of Ascidia, 16*, 17
Sting-rays, 165, 166, 169
Stolon, Rhabdopleura, 12 : Salpa, 27,
40 : Doliolum, 37, 38, 39
Stomach — See Digestive organs
Stomata, 94*
Stomias boa, 221
Stomodseum — See Digestive system
Storks, 403, 408, 409, 415
Storm-petrels, 402
Strasburger, E., 667
Stratum corneum — See Skin
Stratum malpighii — See Skin
Striges, 404*, 409, 417, 421, 432
Strigidce, 404
Stringops, 413, 431, 600
Stroma of ovary, 116
StrutUo, 399, 408, 409, 417, 419, 422,
426, 429, 431
Struthiones, 399*, 429
Sturgeon, 190, 212, 218, 221, 222, 223,
227, 234, 235
Sturnidce, 404, 430
Styliform cartilages, 121, 124
Stylo -glossus, 438*
Stylo -hyal, 438*, 498
Styloid process, 121, 122, 123, 311,
537
Stylomastoid foramen, 436, 439
Struggle for existence, 629*
Sub-atrial ridge, 61*. 62
Subclavian artery, 88, 90, 92, 150, 151
Subclavian vein, 92, 152
Subclavius, 382, 383
Subcutaneous sinus, 274
Sub -intestinal vein, 49, 50, 91, 94
Sub -lingual gland, 446
Sub -maxillary gland, 446
Sub-mucosa, 83*
Sub-neural gland, 19, 20, 29, 30
Sub-ocular arch, 121, 122, 123*
Sub-opercular, 193
Sub-orbitals, 197, 199
Subungulata, 468*
Subvertebral sinus, 274
Sucker of tadpole, 281, 282
Sucking-fish, 219
Suince, 613
Sula, 403
Sun-fish, 216, 225, 231
Superior curved line, 537*
Superior oblique muscle of eye, 110
Superior rectus muscle, 110
Superior temporal arch, 309*
Supra-angular, 308, 310* — See Skull
Supra -clavicle, 203
Supra-ethmoid, 197, 199
Supra-occipital, 77* — See Skull
Supra-orbitals, 308
Supra-renals, 117*
Supra-scapula : Supra-scapular carti-
lage, 170 — See Pectoral arch
Supra-temporal, 308
Surinam Toad, 300, 301, 302
Survival of the fittest, 633*
Sus, 468 — See Pigs
Sus scrofa, 526, 527, 548
Suspensorium, 76*, 260, 261
Suspensory ligament, of eye, 106, 108 :
Bird, 374
Sutures, 436*
Swallow, 404
Swammerdam, 649
Swan, 403, 408, 409
Sweat-glands, 474, 476
Swift, 403, 408, 409
Swim-bladder — See Air-bladder
Sword-fish, 218
Sylvian fissure, 454*
Sympathetic nerves : Craniata, 96* :
Rabbit, 458
Symphysis, 145*
Symplectic, 199, 200
Synapticula, of Balanoglossus, 5 :
Amphioxus, 48
Syngnathus, 434
Synotus barbastellus, 493
Syn-sacrum of Pigeon, 375*
Syrinx of Pigeon, 385, 386 : Aves, 421
Syrrhaptes, 404
Systemic heart, 93
J_ ADPOLE, 282, 283 : Skull, 263 :
Aortic arches, 271
Tsenia hippocampi, 456*, 561
Tail ; Ascidian larva, 35 : Amphioxus,
45 : Craniata, 65
Tail coverts — See Pterylosis, 373
Tailor-bird, 423
Talegallus, 611
Talpa, 493
INDEX
711
Talpidce, 471, 608 — See Moles
Tapetum, 158*
Tapirs, 468, 489, 501, 519, 521, 522,
525, 526, 527, 580
Tapirus, 468
Tapirus indicus. 526
Tapirus terrestris, 489
Tarsals, of Craniata, 80, 81*— See
Limb -skeleton
Tarsipes, 506
Tarsius, 472
Tarso -metatarsus, 368*, 381
Tasmanian Devil, 480, 546
Taste-buds, 105, 446, 553, 563
Taste, organ of, Craniata, 105*
Tatu, 484
Teats, of Rabbit, 433 : Mammalia,
478*
Tee Tees, 473
Teeth, of Craniata, 84, 85 : Petromyzon,
120, 124: Myxine, 135: Elasmo-
branchs, 172 : Holocephali, 186,
187 : Trout, 204 : Teleostomi, 226 :
Ceratodus, 242, 243 : Frog, 268 :
Amphibia, 295 : Lizard, 313 : Rep-
tilia, 345 : Archaeopteryx, 407 :
Rabbit, 437, 445 : Mammalia, 541-
553
Tejidce, 358
Telencephalon, 97*
Teleostei, 213*. 219, 220, 221, 222,
223, 224, 226, 227, 228, 229, 231,
232, 233, 234, 235, 236, 237, 239
Teleostomi, 64*, 190* : Example, 192 :
Distinctive characters and classi-
fication, 211 : External form, 217 :
Exoskeleton, 221 : Endoskeleton,
222 : Electric organs, 226 : Diges-
tive organs, 226 : Respiratory or-
gans, 227 : Air-bladder, 229 : Heart,
231 : Brain, 231 : Urinogenital
organs, 231 : Reproduction and
development, 234 : Geographical
distribution, 235 : Distribution in
time, 236
Temnospondyly, 332*
Temporal canal, 503*
Tendon, of muscle, 266*
Tenrec, 533
Tensores patagii, 382, 383
Tentacles, of Pterobranchia, 9, 10, 11,
12 : Ascidia, 15, 18 : Myxine, 135
Tentorial plane, 498*
Terns, 403, 419
Terrestrial fauna, 617
Test, of Urochorda, 14*, 15
Test-cells of ovum, 31
Testudo, 613
Testudo grceca, 333
Testudo loveridgii, 335
Tetrao, 403
Tetrazooids, 37*
Thaliacea, 21*
Thecodont teeth, 345*, 463*
Theria, 464*, 498, 500
Theriodontia, 326
Theromorpha, 325*, 360
Thigh, 67 — See Hind-limb
Thomson, Vaughan, 661
Thomson, Wyville, 662
Thoracic duct, 574
Thorax, 70*, 433
Thorn-backs, 165
Thread-cells, Myxine, 134
Three -toed Sloth — See Sloth
Thrushes, 404, 412
Thylacine, 480, 508, 583, 621
Thylacoleo carnifex, 584
Thylacus, 480, 508, 583, 621
Thymus, of Craniata, 86* : Elasmo-
branchii, 173 : Frog, 269 : Pigeon,
385 : Rabbit, 454
Thyro-hyal, 441
Thyroid, of Craniata, 85* : Elasmo-
branchii, 173 ; Frog, 269 : Lizard,
316 : Pigeon, 385 : Rabbit, 454
Thyroid cartilage — See Larynx
Tibia, 80, 81*— See Limb -skeleton
Tibiale, 80, 81* — See Limb-skeleton
Tibio-fibula, 259, 265
Tibio-fibulare, 313
Tibio-tarsus, 380, 381
Tiger, 528, 529
Tillodontia, 589
TiUotherium fodiens, 589
Tinamous, 403, 414, 417, 429, 431
Tinamus, 403, 414, 417, 429, 431
Tinoceras, 588
Toads, 256, 284, 285, 288, 295, 300
Tolypneutes, 484
Tongue, of Craniata, 84*, 192 — See
Digestive organs
Tooth-pulp, 84*
Toothed Whales, 466*
Tornaria, 7, 8, 9
Torpedo, 171, 172
Tortoises, 64
Toucans, 408
Touch-cells, 103, 104*
Touch corpuscles, 103, 104*
Toxodontia, 588
Trabeculse, 73* : heart, 271
Trabecular regions, 74*
Trachea — See Respiratory organs
Trachinus, 221
Trachypterus, 225
Tragulidce, 611
Transverse process — See Vertebra
Trapezium, 443 — See Limb-skeleton of
Mammalia
Trapezoid, 443 — See Limb-akeleton of
Mammalia
712
INDEX
Tree-frogs, 288, 289, 293
Tree Kangaroos, 482
Tree-snakes, 324, 356
Treviranus, 656
Triassic period, 619
Trichechidce, 470- — See Walruses
Trichosurus, 567
Triconodont teeth, 544*
Trigeminal ganglion, 101*
Trigeminal nerve, 101*, 154, 155, 156
Tritor, 186*, 187
Trituberculate molar, 544*
Trochanter, lesser, great, 313, 444 :
third, 444
Trochilidce, 404, 423, 429
Trochlea, 442
Trochlear nerve, 101*
Trogones, 404
Trogons, 404
Trophoblast, 570*
Tropidonotus natrix, 337
Trout, 192, 214, 220 — See Salmo fario
Trunk, of Balancglossus, 3 : Craniata,
65 : Elephant, 490*
Trunk of spinal nerve, 96*
Trunk region, 195
Trunk vertebra, 195
Trygon, 181
Trygonorhina, 168, 176
Tuatara, 329 — See Hatteria
Tuber cinereum, 457*
Tubercular facet, 435
Tuberculum olfactorium, 247*
Tumblers, 367
Tunic, of Urochorda, 14*
Tunicates — See Urochordata
Turicine, 14*
Turbinal bone, 321
Turbinals, 393
Turbinares, 402*, 412, 421, 423, 429
Turbot, 214, 235
Turdidce, 404
Turdus, 412
Turkey-buzzards, 403
Turnix, 403
Turtles, 325, 331, 346, 348, 349, 357,
358
Turtur, 404
Tusks— See Teeth
Tympanic bone, 439, 497
Tympanic bulla, 437, 438
Tympanic cavity, 277, 278
Tympanic membrane, 257, 305*
Tympano-eustachian fossa, 309
Tympanum of syrinx, 385
Tyndall, J., 665
Typhlopidce, 338
Typhlosole, of Ascidia, 15, 18* :
Petromyzon, 125, 130
Typotheria, 588
U
Ui
LNA, 80, 81* — See Limb-skeleton
Ulnare, 80, 81* — See Limb-skeleton
Umbilical cord, 577*
Umbilicus, inferior and superior, 369*
Unau, 483
Unciform, 443 — See Limb-skeleton of
Mammalia
Uncinates of Reptiles, 335* : Pigeons,
374 : Birds, 412
Ungulata, 467*, 476, 486, 519-528,
547, 553, 558, 579, 586
Ungulata vera, 467*, 486, 490, 525,
527, 528, 579
Unguligrade feet, 467*
Unio, 601
Upper arm, 67, 304
Upupidcv, 404
Urachus, 577*
Urethra, 460
Urinary bladder, 116*
Urinary tubules, 113*, 114
Uriiiogemtal organs, of Craniata, 113,
114, 115, 116, 117 : Petromyzon, 130,
131: Myxinoids, 137 : Dogfish, 158;
159, 160, 161 : Elasmobranchii, 174,
175 : Holocephali, 189. 190 : Trout,
208, 209 : Teleostomi, 231, 232, 233 :
Ceratodus, 247, 248 : Frog, 278, 279 :
Amphibia, 299, 300: Lizard, 322,
323 : Reptilia, 351 : Pigeon, 394,
395 : Aves, 422 : Rabbit, 459, 460,
461 : Mammalia, 564-567
Urinogenital organs, development of,
115, 116
Urochord-, 23*
Urochorda, 13* : Example, 14 : Dis-
tinctive characters and classifica-
tion, 20 : Systematic position of
Example, 23 : General features, 23 :
Enteric canal, 28 : Heart, 28 :
Nervous system and sense organs,
28-30 : Renal organ, 30 : Repro-
ductive system, 30 : Development
and metamorphosis, 30—40 : Dis-
tribution, &c., 40, 41 : Affinities, 41,
42
Urodeeum, 384, 385*
Urodela, 284*, 285, 287, 288, 289, 290,
291, 293, 294, 295, 296, 298, 299,
300, 302
Uro-hyal, 201
Urolophus cruciatiis, 166
Urolophus testaceus, 169
Uropygium, 367*
Urostyle, of Salmo, 196 : Frog, 258,
259 : Amphibia, 289
Ursidce, 470, 529, 530, 551— See Bears
Ursus, 552
Ursus americanus, 530
INDEX
713
Ursus Jerox, 530
Use-inheritance, 640
Uterine crypts, 462, 576*
Uterus — See Urinogenital organs
Uterus masculinus, 459, 460*
Utriculus, 111*, 112
AGINA, of Elasmobranchii, 175 :
Rabbit, 460, 461 : Mammalia, 565,
567
Vagus ganglion, 102
Vagus nerve, 102*
Valve of Thebesius, 449*
Valve of Vieussens, 457, 458*
Vampire Bats, 581
Vane, 369
Varanus, 350
Variation, 630, 631*
Vasa efferentia, 119, 120*
Vascular system, of Balanoglossus, 4,
6 : Ascidia, 17, IN, 19 : Urochorda,
28 : Amphioxus, 49, 50 : Craniata,
88-95 : Lamprey, 125, 126 : Dog-
fish, 150, 151, 152, 153: Elasmo-
branchii, 173 : Holocephali, 187 :
Trout, 204, 205 : Teleostomi, 231 :
Ceratodus, 244, 245 : Frog, 270-275 :
Amphibia, 296, 297, 298 : Lizard,
314, 315, 316 : Reptilia, 347, 348,
349 : Pigeon, 388, 389, 390, 391 :
Birds, 421 : Rabbit, 448-452 :. Mam-
malia, 557
Vaso -dentine, 84*
Vaso -ganglion, 228* — See Reel-glands
Veins, Amphioxus, 49 : Craniata, 90 —
See Vascular system
Velar tentacles, Amphioxus, 46, 47
Velum, Amphioxus, 46, 47 : Petro-
myzon, 124, 125
\Yluminterpositum, 457*
Velum transversum, 319, 320*
" Velvet," 487*
Venomous snakes, 356
Ventral aorta, Amphioxus, 49 : Crani-
ata, 88, 89 : Dogfish, 150, 151
Ventral fissure, 95, 96*
Ventral root of spinal nerve, 95, 96*
Ventral shield, of Pteraspis, 254 :
Snakes, 331
Ventricle, 88, 89 — See Heart
Ventricles — See Brain, 97
Vermiform appendix, 448
Vermis, of cerebellum, 458*
Vertebra, 72*
Vertebral column, 2* : Euchorda, 42 :
Craniata, 70, 71, 72 : Petromyzon,
121, 122 : Myxinoids, 136 : Dog-
fish, 142, 143, 144 : Elasmobranchii,
167. 169 : Holocephali, 184, 185 :
Trout, 195, 196 : Teloostomi, 222 :
Ceratodus, 241 : Frog, 258, 259 :
Amphibia, 289, 290 : Lizard, 305,
306: Reptilia, 332, 333, 334:
Pigeon, 373, 374, 375: Birds
(Neornithes), 411 : Rabbit, 434,
435 : Mammalia, 494 : Prototheria,
503 : Metatheria, 506 : Edentata,
508 : Cetacea, 514, 515 : Sirenia,
518 : Ungulata, 519, 520, 521 : Car-
nivora, 528 : Rodentia, 531 : In-
sectivora, 532 : Chiroptera, 534 :
Primates, 535
Vertebral formula, 375
Vertebral plate, 117*, 179, 426
Vertebral rib — See Rib
Vertebral theory of skull, 659, 660
Vertebrarterial canal, 434
Vertebrarterial foramen, 373*, 374
Vertebrata, 43*
Vesalius, 648
Vesicles of Savi, 174*
Vespertilio, 471
Vestibule, of Amphioxus, 44* : Rabbit,
459, 461*
Vexillum — See Feather, 369
Vibrissje, 433, 476
Vicq d'Azyr, 653
Villi, of embryo Mammals, 574, 576
Vipers, 324, 345
Virginian opossum, 480
Visceral arch, visceral bar, visceral
skeleton — Craniata, 69, 74, 75*
Visceral motor fibres, 113*
Visceral sensory fibres, 113*
Viscero -branchial vessel, 19
Vitelline membrane, 55
Vitreous chamber, 106, 108*
Vitreous humour, 106, 108*
Viverra, 620
ViverridcB, 470, 580
Viviparous Blenny, 234
Vocal chords, 269
Vocal sacs, 258, 300
Voles, 609
Vomer, 77, 78*— See Skull
Vomerine teeth— Holocephali, 186*,
187 : Trout, 204 : Urodela, 291
Vomero -palatine, 291, 292
Vultur, 403, 412
Vultures, 403, 412
Vulva of Rabbit, 433, 461
W
W
ALLABY, 478, 507
Wallace, A. R., 662, 663, 667
Wallace's line, 610
Walruses, 470, 491, 552, 580
714
INDEX
Warning characters, 283, 637*
Water-lizards, 355
Water-newt, 285
Water opossum, 479
Water-voles, 491
Weasels, 176, 470, 554
Weaver, 221
Weber, Max, 663
Weberian apparatus. 231*
Webs, 258, 409
Weismann, A., 668
Weka, 431
Wells, W. C., 662
Whalebone — See Baleen
Whalebone Whales, 446, 486, 501, 515,
517, 541, 550, 586
Whales — See Cetacea, 466
Wheel-organ of Amphioxus, 44*
White, Gilbert, 654
White matter, 95, 96*
Whiting, 214
Wiegmann, 660
Willemoes-Suhm, 662
Wfflughby, F., 651
Wing of Birds, 367, 368
Wing-coverts — See Pterylosis, 373
Wolff, C. F., 653
Wolffian body, 115
Wolffian duct, 115, 116*
Wombats, 465, 481, 482, 506, 509
Woodpeckers, 404, 409, 416, 421
Wotton, Edward, 647
Wrasse, 215, 218, 227
X
^ENOPHANES, 658
Xenopus, 285, 289, 294, 295
Xenosauridce, 358
Xiphiplastron, 335
Xiphisternum, 263, 264, 265
Y
JLAK, 617
Yolk cells, 280*
Yolk-plug, 247, 249, 280, 281
Yolk-sac, 180, 209, 210, 249, 577
Yolk-sac placenta, 577
z,
JEBRA, 468, 488, 489, 580
Zeuglodon, 586, 620
Zeuglodonta — See Archseoceti
Zoarces, 234
Zona radiata, 569*
Zonary placenta, 576*
Zonuridce, 358
Zoo -geographical regions, 608, 614
Relations of, 614
Zygcena, 165
Zygantrum, 333*
Zygapophysis, 195*
Zygomatic arch, 496*
Zygomatic process, 439
Zygosphene, 333*
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