370 



cytoplasmic and nuclear portions of which do not stain well. Scattered 

 among these are smaller cells, which are found much more abundantly 

 in that part of the mass lying towards the cavity of the vesicle. The 

 smaller cells are characterized by their sharply defined outlines and 

 by the ease wäth which they take the stain. There is considerable 

 evidence to indicate that the smaller cells are gradually undergoing 

 a process of segregation from their larger fellows to form the hypo- 

 blastic layer of the vesicle. At any rate the hypoblast upon its 

 completion possesses cellular elements that very closely simulate the 

 smaller cells of earlier stages. 



». 



Fig. 1. Photograph of a median section of a young vesicle which was on the 

 point of passing from the fallopian tube into the cavity of the uterus. It measurtd 

 .263 mm. in the fixed condition. 



After the vesicle has been discharged from the fallopian tube 

 into the uterus, it migrates along a groove-like depi'ession in the 

 mucosa that leads from the tnbe to the center of the fundus, or 

 placental zone. In the course of migration the hypoblastic and epi- 

 blastic layers of the vesicle become clearly defined, while the tropho- 



