LIST OF ILLUSTRATIONS. XVll 



FIG. PAGE 



106. Vertical section of the blastoderm and adjacent part of the yolk of 



a hen's egg at the time of laying, but before the commencement 



of incubation. (After Duval) 235 



107. A diagrammatic figure of the blastoderm of a hen's egg about the 



twentieth hour of incubation. (In part after Duval) . . 238 



108. Transverse section across the blastoderm of a hen's egg about the 



twentieth hour of incubation 239 



109. A diagrammatic figure of the blastoderm of a hen's egg about the 



twenty-fourth hour of incubation. (In part after Duval) . . 241 



110. A chick embryo at the twenty-fourth hour of incubation ; seen from 



the dorsal surface 248 



111. A chick embryo at the thirty-sixth hour of incubation; seen from 



the dorsal surface 251 



112. A median longitudinal, or sagittal, section of a chick embryo at the 



thirty-sixth hour of incubation .251 



113. A chick embryo at the end of the third day of incubation . . 253 



114. A median longitudinal, or sagittal, section through a chick embryo 



at the end of the third day of incubation ..... 255 



115. A chick embryo at the end of the fifth day of incubation . . 257 

 lit). A median longitudinal, or sagittal, section of the head and anterior 



part of the neck of a chick embryo at the end of the eighth day 



of incubation 258 



117. Transverse section across the body of a chick embryo at the twenty- 



fourth hour of incubation 2G1 



118. Transverse section across the head of a chick embryo at the twenty- 



fourth hour of incubation 263 



119. Transverse section across the head of a chick embryo at the forty- 



third hour of incubation 264 



120. Transverse section across the head of a chick embryo at the forty- 



third hour of incubation, the section passing through the com- 

 mencing auditory pits and the heart 265 



121. Transverse section across the head of a chick embryo at the forty- 



eighth hour of incubation 276 



122. Transverse section across the fore-brain and eye of a chick embryo 



at the sixtieth hour of incubation 277 



123. A median longitudinal, or sagittal, section through a chick embryo 



at the end of the fifth day of incubation 282 



1 24. A section through the head of a chick embryo at the end of the third 



day of incubation 284 



125. The head of an embryo chick at the end of the fifth day of incuba- 



tion 287 



126. The head of an embryo chick at the end of the seventh day of in- 



cubation 288 



127. The anterior end of a chick embryo at the thirty-sixth hour of incu- 



bation 299 



128. A diagrammatic figure showing the arrangement of the blood- 



vessels in a chick embryo at the end of the fifth day of incu- 

 bation 304 



129. A transverse section across the body of a chick embryo at the forty- 



eighth hour of incubation 317 



a 



