DEVELOPMENT OF THE CHICK 125 



coelome, and the opening in the body-wall 

 of the embryo is the urnbilicus. 



Formation of Embryonic Membranes (Figs. 66, 

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



s.a. 



ch. 



ys 



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-amuiotic 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 



