48 



EDWARD MCCRADY, JR. 



albumen at the animal pole than at the vegetal. This differ- 

 ence in rate of absorption is so decided that it causes the 

 vesicle to migrate across the albumen layer until the medul- 

 lary plate comes into contact with the shell membrane. This 



16 



Fig. 15 Stage 13 ellipsoid blastocyst showing medullary plate in contact with 

 shell membrane (Hartman, '19). 



Fig. 16 Stage 14 bilaminar blastocyst (Hartman, '19). 



contact is not attained until the end of the sixth day; and 

 by this time the endoderm has extended itself completely 

 around the inside of the vesicle. 



