DEVELOPMENT OF THE CHICK 125 



coelome, and the opening in the body-wall 

 of the embryo is the umbilicus. 



Formation of Embryonic Membranes (Figs. 66, 

 67, and 68). — The fully formed membranous in- 



y.s 



Fig. 67.— Diagram showing the Mode of Development of the 

 Embryonic Membranes. About fourth day. 



ch., chorion ; amn., amnion ; al., allantois ; y.s., yolk-sac ; 

 s.a., sero-arauiotic connection. 



vestments of the embryo are three in number — 

 chorion, amnion, and allantois — to which may be 

 added the yolk-sac. The chorion and amnion 

 are formed by the extra-embryonic somatopleure 

 in the following manner. A fold of the somato- 

 pleure rises up in front of and folds over the 



