324 



THE CAT. 



[chap. X. 



3 , 





Fig. 148.— Five Diagkammatic Veutral Sections through the Long ^Vxis ok a Maturing 

 Mammalian Ovum, to show the formation of its eog-membrane!j. 



In Figs. 1 — 4 the Rcctioii jiasscs tlirnu};]i tlie 

 iniclcllc of tho cniliiyo. In Fig. 5, it ]>iis.si's 

 a little oil one side, so tlmt tho left side of 

 tlie eiiibryo can be seen. 



1. Ovum in which the cliorinn has begun to he 



formed, with the lilastodcrm (and rudiment 

 oftthe embryo) williin it. The whole' gcrm- 

 A'esicle consists of ciiiblast and hyiioblast, 

 in the germ area, mesoblast (»i) has also 

 appeared. 



2. Ovum in wliieh the Iiend and tail-folds have 



contraeted the umbilical ajierturo towards 

 the yelk-sac; wliile the ascending circum- 

 vallation is seen ri.sing at either eml to form 

 the amnion. Here, then, the embryo is 

 beginning to separate J'rom the germ- 

 vesicle ((/*■). 



3. The amniotic folds being completed, have 



met in the dorsal region ; the umbilical 

 opening is more contracted, and the allan- 

 tois (ill) has begun to sjirout. Here we see 

 the double sac forming above the embryo, 

 the inner ]>art of which alone becomes the 

 amnion. The intestinal canal (tid) is begin- 

 ning to be distinctly formed. 

 Here the inner amniotic ,sae or trvie amnion 

 is detJiched from the outer or false amnion, 

 which has disappeared by coalescence with 

 the inner surface of the chorion. Tlie 

 cavity of the amnion is more disttinded, and 

 the yelk-sac (iJ^) has become smaller and 

 pedunculated. The allantois (at) ])rojeets 

 into the space Iwtween the amnion, chorion 

 and yelk-sac ; and the villi are larger, and 

 have begun to ramifj-. 



