A-trect. 



i.c.TW.(fo.) 



tr.ect. 



pr. amrvc. 

 embect. 



ervb. 



tr.ect. 



Diagrams illustrating the mode of formation of the blastocyst 

 in Metatheria (a-d) and Eutheria (1-3). h.c. Blastocyst cavity. 

 i.c.m. Inner cell-mass. pr.a))in.c. Primitive amniotic cavity. 

 r.l. Rauber's layer. sx. Segmentation cavity. For other 

 reference letters see explanation of plates (p. 125). 



