xviii Illustrations 



FIGURE PAGE 



69. Transverse Section just Posterior to the Pre- 



ceding. (After Duval) . . . .213 



70. Transverse Section through the Dorsal Region 



of an Embryo of Sixty-eight Hours. (After 

 Duval) 215 



71. Transverse Section Anterior to the Preceding. 



(After Duval) . . . . . .219 



72. Two Stages in the Development of the Chick 



Embryo: A at about the Fifth Day; fi- 

 at about the Ninth Day. (After Parker 

 and Haswell from Duval) . . . .225 



73. Transverse Section through the Dorsal Region 



of a Chick Embryo of Ninety-six Hours. 

 (After Duval) 231 



74. Transverse Section through the Wolffian 



Body. (After Duval) .... 239 



75. Heart of a Chick on the Fourth Day, Ventral 



View. (After Foster and Balfour) . . 242 



76. Diagrammatic Figure Showing the Arrange- 



ment of the Blood Vessels in a Chick Em- 

 bryo at the End of the Fifth Day. (After 

 Marshall) 247 



77. Diagram of the Venous Circulation at the Com- 



mencement of the Fifth Day. (After Foster 



and Balfour) . . . . . .252 



78. Diagram of the Venous Circulation during the 



Later Days of Incubation. (After Foster 



and Balfour) ...... 256 



