THE EARLY DEVELOPMENT OF THE MAMMAL 425 



h ta 



N 



ex 



pa 



vb 



FIG. 176. Diagrams of the formation of the embryonic membranes and 

 appendages in the rabbit. 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 

 gray, al, Allantois; as, allantoic stalk; b, tail bud; c, heart; d, trophoderm; 

 e, endoderm; ex, exocoelom; /, fore-gut; h, hind-gut; m, mesoderm; N, central 

 nervous system; p, pericardial cavity; pa, proamnion; s, marginal sinus (sinua 

 terminalis); /, trophoblast; ta, tail-fold of amnion; v, trophodermal villi; vb, 

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



