THE CHICK 



17:5 

 17s 



187 



189 

 190 



xvi LIST OF ILLUSTRATIONS. 



no. . ''"''■ 



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 17 ° 



79. Diagrammatic) transverse section across the bead 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 . 



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



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



hatching, showing the nephrostomes of the head-kidney . 



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 .... 



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



middle of the head-kidney 



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



heart, the branchial vessels, and the urinary and reproductive 

 organs 



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 194 



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



frog during the metamorphosis 195 



89. Sagittal section of a tailed frog during the metamorphosis . . 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 



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



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



193 



221 



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



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



ment of incubation 



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



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



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



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



egg. (After Coste and Duval) 



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) 231 



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



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



223 

 224 



225 



227 



233 



