X 



498 THE PHYSIOLOGY OF REPRODUCTION 



that some of the vacuoles were not yet filled with maternal blood, 

 but contained a granular coagulum which might, when liberated, 

 have a digestive activity. In either case, the extensive proliferation 

 of the trophoblast appears to provide for the absorption of the 

 necrosed tissue around it, as well as for the flow of maternal blood 

 into its lacuna^ by the erosion of superficial capillaries. These two 

 objects accomplished, the greater part of the trophoblastic prolifera- 

 tion disappears. 



Sp.- 



FIG. 152. Section through embryonic region of ovum (after Peters). 

 (From C. Webster's Human Placentation.) 



E.Sch., Embryonic epiblast ; Ent., embryonic hypoblast ; Mes., niesoblast ; 

 D.S.j umbilical vesicle ; A.H., amniotic cavity ; Ekt., chorionic epiblast ; 

 #/>., space. 



Immediately after the excavation of the cavity the decidual 

 formation begins. Before this stage, the changes resemble those 

 that take place during the menstrual period. The vessels are dilated, 

 and blood extravasations occur between the cells and into the lumen. 

 The tissue is cedematous and spongy, and the swollen cells often 

 appear to be floating free in a fluid (v. Heukelom). These changes 

 are especially marked near the ovum, and they give rise to an 

 elevation which marks the resting-place of an early blastocyst. The 

 mucosa is differentiated into a superficial layer, the compacfa, and a 

 deeper layer, the spongiosa, in which are the enlarged middle portions 

 of the glands, arterioles, venules, and lymphatics. In the compacta 



