Development af the Mammal 297 



of the vesicle and the formation of the amnion 

 are also so similar to the corresponding pro- 

 cesses in the bird that they will be easily under- 

 stood by reference to Figures 93-96. 



After the mammalian ovum has reached the 

 stage of the primitive axis, above described, 



Emb 



Yk 



Yk 



FIG. 93. DIAGRAMS ILLUSTRATING THE RELATIONS OF THE 



ALLANTOIS, ETC., IN UNGUICULATE MAMMALS. (From Minot.) 



A y before, B, after, the formation of the amnion. All, entodermal allantois. 

 Am, amnion. s, body stalk. Cho, chorion. Coe^ extra-embryonic coelom. 

 Emit, anterior end of the embryo. F, yolk-sac. 



