Fig. 216. — Diagram illustrating the evolution of amnion, etc. 



a./, amniotic fold ; all, cavity of allantois ; am, amnion ; cod, coelome ; emb, body of embryo ; 

 eiit, cavity of enteron ; /.a, serous membrane ; set, sero -amniotic isthmus ; y, cavity of yolk-sac. 



476 



