LIST OF ILLUSTRATIONS xxi 



FIG. >'AGE 



55. Diagrams illustrating derivation of Medusa and Hydrant h . 241 



56. Eucopelia campanularia, muscle fibres and cells 243 



57. Laomedeaflexuosa and Endendrhun ramosum, development. 247 



58. Diphyes campanulata 250 



59. Porpita pacifica and P. mediterranean 251 



60. Spermatogenesis in the Mole-cricket 254 



61. Ovum of Toxopneustes lividus . . 257 



62. Maturation and impregnation of the animal ovum .... 258 



63. Pandorina moruin 263 



64. Volvox globator 265 



65. Volvox globator 266 



66. Polygordius neapolitanus, external form . 269 



67. Polygordius neapolita)nis, anatomy 271 



68. Polygordius neapolitanus, nephridium 282 



69. Polygordius^ diagram illustrating the relations of the nervous- 



system 284 



70. Polygordius neapolitanus, reproductive organs 291 



71. Polygordius neapolitanus, larva in the trochosphere stage . 293 



72. Diagram illustrating the origin of the trochosphere from the 



gastrula 295 



73. Polygordius neapolitamis, advanced trochosphere ...... 297 



74. Polygordius neapolitanus ', larva in a stage intermediate be- 



tween the trochosphere and the adult 300 



75 Starfish, ventral aspect 307 



76. Starfish, diagrammatic sections 309 



77. Starfish, digestive organs 311 



78. Starfish, water vascular system 3 J 3 



79. Starfish, early stages in development ... 316 



80. Starfish, development of bipinnaria larva 317 



81. Crayfish, side view 319 



82. Crayfish, principal appendages 322 



83 Crayfish, diagrammatic sections 328 



84. Crayfish, action of abdominal muscles 330 



85. Crayfish, leg, with muscles 331 



86. Crayfish, dissection 333 



