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 



79. 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 . . 178 



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



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



83. 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 ........ ] 90 



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



heart, the branchial vessels, and the urinary and reproductive 

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



8G. 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 . . . . . . .194 



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



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



91. 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 

 9.3. 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) ........... 934 



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



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



