X List of Illustrations. 



Fie. PAQE 



45 

 46 



47 



34. Formation of the gastrula in Amphibia 



35. Diagram of gastrula-formation in Vertebrata with partial segmentation 



36. Development of the ovum of a Crustacean 



37. Diagrammatic sections explaining the formation of the gastrula in certain 



Hydrozoa . . 47 



38. Diagrammatic figures of the formation of the mesoblast in the Vertebrata . 48 



39. Diagrammatic transverse section showing the formation of the notoohord 



and of the nervous system in the Vertebrata . ... 49 



40. Embryo of the Dog-fish with yolk sac . . .49 



41. Diagram of a young embryo with yolk sac . . 49 



42. Dimorphism of a Heteropteran . , 54 



43. Two specimens of a Kallima ... 71 



44. Two Looper Caterpillars . ... .71 



45. An Infusorian in the free state and encysted . . . . 86 



46. An encysted Infusorian which has broken up into a number of spores 86 



47. Difflugia, Euglypha, and Rotalia , 87 



48. Nummulites distans . . . 89 



49. Eadiolarian and skeleton . . 89 



50. ActinosphsBrium Eichomii . . . 91 



51. Two Infusoria in various stages of conjugation . 93 



52. Paramcedum . . . .94 



53. Vorticella . . .94 



54. Various Monadidse ... . ' 95 



55. Diagrammatic figure of a Gregarine . 95 



56. Ooccidium oviforme . . . . . , . 97 



57. Baineyan sac in a muscle fibre . . 97 



58. Diagrammatic figures of the chief types of Coelentera 98 



59. Cells of a Ccslenterate . . . 100 



60. Hydroid colonies and polyps ... . . 104 



61. Various forms of the sexual generation of Hydromedusoids . 105 



62. Diagram of Physophora ... . 108 



63. Diagram of Porpita . , 108 



64. Section through a Soyphomedusan . . 109 



65. Development of Aurelia ... . no 



66. Longitudinal section through a solitary Anthozoon 111 



67. Transverse section of an Alcyonarian , . . 112 



68. Sections through various young Alcyonaria . 114 



69. Longitudinal and transverse sections of a Madreporarian 116 



70. Portion of a massive Madreporarian 116 



71. Portion of an arborescent Madreporarian . . . 117 



72. Small portion of Heliastrssa ... . 117 



73. Collar cells of a Sponge . .... 119 



74. Various forms of Sponges . .119 



75. Diagrammatic figures explaining the radial structure of the Echinoderma . 122 



76. Pedioellarise of a Sea-urchin . . . . 124 



77. Diagrammatic sketch of the water-vascular system of a Star-fish . 124 

 78 and 79. Diagrammatic longitudinal sections of a Star-fish and of a Sea- 

 urchin . . . . 125 



80. Diagrammatic figures of Bchinoderm larvae 126 



