xvi LIST OF ILLUSTRATIONS. 



7 mm. tadpole shortly after hatching ; showing the branchial 

 blood-vessels from the ventral surface ..... 170 



78. Diagrammatic figure of the same embryo as in fig. 77, seen from the 



right side ........... 170 



7!. Diagrammatic transverse section across the head of a 7 mm. tadpole 171 



80. Diagrammatic figure of the head of a 12 mm. tadpole from the right 



side, showing the heart and branchial blood-vessels . . .173 



81. Diagrammatic figure of the arterial system of an adult frog . . 17s 



82. Transverse section through the body of a tadpole at the time of 



hatching, showing the nephrostomes of the head-kidney . . 187 

 S:>. Diagrammatic figure of a 12 mm. tadpole dissected from the ventral 

 surface, to show the heart and branchial vessels, and the head- 

 kidneys and commencing Wolffian bodies ..... 189 



84. Transverse section across a 12 mm. tadpole, passing through the 



middle of the head-kidney ........ 1 00 



85. A 40 mm. tadpole dissected from the ventral surface, to show the 



heart, the branchial vessels, and the urinary and reproductive 

 organs ............ 193 



86. A tailed frog, during the metamorphosis, dissected from the ventral 



surface to show the urinary and reproductive organs . . .193 



87. Transverse section through the hinder part of the body of a tailed 



frog during the metamorphosis ....... 1 94 



88. Transverse section through the anterior part of the body of a tailed 



frog during the metamorphosis ....... ] 95 



89. Sagittal section of a tailed frog during the metamorphosi3 . . 200 



90. The skull of a 12 mm. tadpole, seen from the right side . . . 202 

 1)1. The skull of a 12 mm. tadpole, from the dorsal surface . . . 202 



92. The skull of a 12 mm. tadpole, from the ventral surface . . . 202 



93. The skull of a tailed frog, towards the close of the metamorphosis, 



seen from the right side . . . ..... 208 



94. The skull of an adult frog, seen from the right side .... 209 

 93. The skull of an adult frog, seen from the ventral surface . . .210 



96. The skeleton of the frog, seen from the dorsal surface . . . 214 



THE CHICK 



97. The hen's egg at the time of laying ....... 221 



98. The yolk of a hen's egg at the thirty-sixth hour from the commence- 



ment of incubation ......... 223 



99. The yolk of a hen's egg at the end of the third day of incubation . 224 



100. The hen's egg at the end of the fifth day of incubation . . . 225 



101. The hen's egg at the end of the ninth day of incubation . . . 227 



102. An early stage in the segmentation of the germinal disc of the hen's 



egg. (After Coste and Duval) ....... 233 



103. A later stage in the segmentation of the germinal disc of the hen's 



egg. (After Coste and Duval) ....... 233 



104. Section through the germinal disc and adjacent parts of the yolk of 



a hen's egg about the middle of its stay in the uterus. (After 

 Duval) ............ 234 



105. Vertical section of the blastoderm and adjacent part of a hen's egg 



towards the close of segmentation. (After Duval) . . . 234 



