496 THE PHYSIOLOGY OF REPRODUCTION 



strands of trophoblast as into the spaces between them. Later still, 

 mesoblastic processes penetrate into the cellular buds and complete 

 the vascular chorionic villi. 



Round the blastodermic vesicle is a zone of degenerated tissue, 

 the " Detrituszone " (Fig. 151). It is uncertain whether it is formed 



Cll 



dfc 



FIG. 150. Section of a portion of the wall of the human blastocyst. 

 (Bryce and Teacher.) 



ci/t., Cyto-trophoblast ; </>'<:, decidua ; ei><i., endotheliuiu of maternal capillary ; 

 pi., plasmodium ; nz., necrotic zone of decidua. 



by the influence of the trophoblast or maternal elements. At its 

 inner edge, and within its spaces, are numerous large mononuclear 

 cells which are " more likely maternal " (Bryce and Teacher). Peters 

 also mentioned the presence of many large cells, and compared them 

 to the deciduofracts of the hedgehog. Y. Heukelom described the 

 cellular layer outside the syncytium as foetal, and derived from 

 Langhans' layer. 1 Whatever their origin, the mononuclear cells in 



1 Much uncertainty still exists regarding the origin of these large cells in 

 man and other animals. In the mouse, Duval and Sobotta consider them foetal, 



