78 



Psyche 



[June 



of the primitive streak begins to invaginate (Fig. 6, a i.) and is 

 entirely invaginated about the fourtieth hour (Fig. 7) ; the anuiio- 

 tic cavity then closes. The embryo now lies on the dorsal side of 

 the amniotic ca\'ity (Figs. 7 and 8) with its caudal extremity 

 towards the anterior and its cephalic extremity towards the poste- 

 rior end of the egg; its ventral surface is turned towards the ven- 

 tral aspect of the egg. In this position the embryo develops 

 until about the fifth daj^ when the revolution of the embryo takes 

 place; a caudal flexure occurs as the embryo increases in size. 



>: — N * 



|>TtiauA cT 



Lateral view of embryo on 2d day. 



Side and front view of 'maxilla and mandible, 3d day. 



Front and side \-iew of embryo on 4th day, with detached maxilla. 



Front view of embryo of 5th day, with detached maxilla and mandible. 



Front view of head of embryo, 6th day. 



Front view of head of embryo, 10th day. 



