LIST OF ILLUSTRATIONS. xvii 



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 



116. 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 ..... ... 261 



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 

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



day of incubation ......... 284 



125. The he.ad 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 



