LATER DEVELOPMENT OF CHICK AND RABBIT 435 



the proamniotic area, and the folds pass in under the embryo until 



h ta 



pa 



vb 



FIG. 152. Diagrams of the formation of the embryonic membranes 

 and appendages in the rabbit. From Kellicott, after Van 

 Beneden and Julin (partly after Marshall). 



Sagittal sections. A, at the end of the ninth day ; B, early the tenth day ; C, at the end of 

 the tenth day. Ectoderm black ; endoderm dotted ; mesoderm grey, al., allantois ; as., allan- 

 toic stalk ; b., tail bud ; c.; heart ; d^ trophoderm ; e., entoderm ; ex., exoccelom ; /., fore-gut ; 

 h., hind-gut ; m., mesoderm ; n., central nervous system ; p., pericardia! cavity ; pa., proamnion ; 

 s., marginal sinus (sinus terminalis) ; t., trophoblast ; ta., tail-fold of amnion ; ., trophodermal 

 villi ; vb., trophoblastic villi ; y., cavity of yolk sac ; ys., yolk stalk. 



they completely surround it, save at the places where the allantoic 

 and yolk sac stalks leave it. In the rabbit the amniotic cavity never 



