ii6 



COMPARATIVE ANATOMY 



therefore a product of the splanchnopleure and is lined by endoderm. It 

 grows rapidly, swelling out into the space between the yolk-sac and the 

 chorion and eventually acquires more or less extensive and intimate fusion 



allantois 



allantoic cavity 



extra-embryonic 

 coelom 



somatopleure 



yolk sac 

 (splanchno- 

 pleure] 



albumen 



allantoic cavity 



allantois 

 serosa 



shell 



sero-amniotic 

 cavity 



yolk-sac 



albumen 



vitelline 

 membrane 



belly stalk 



Fig. 86. — Diagrams showing the extra-embryonic membranes of the chick. The 

 diagrams represent longitudinal sections of the entire egg, the body of the embryo being 

 cut transversely. C, embryo of about five days incubation; D, embryo of about fourteen 

 days incubation. (From Patten, Embryology of the Chick; after Duval.) 



with the chorion. In the apposed mesodermal layers of the allantois and 

 chorion is developed a rich network of fine blood vessels which are con- 

 nected by the allantoic arteries and veins to the main blood vessels of the 

 definitive body of the embryo. In this way an extensive circulation is 



