( 386 ) 



concave to these sides, corresponding to the shape of the surface, 

 here occupied by the progressive and regressive processes. 



Gradually all the maternal tissue is replaced by foetal, so that 

 finally the papillae which at first were entirely maternal, have become 

 entirely foetal. Now the "vacuoles", surrounded by foetal syncytium 

 dilate further (also grow at the expense of a foetal symplasm which 

 now forms everywhere) and subdivide, a process, accompanied by 

 constantly increasing separation of the allantoic villi by these 

 cavities, containing maternal blood ; the final result is that papilla- 

 shaped lobes with secondary lateral lobules are formed, all separated 

 by allantois-strands with foetal vessels; these are surrounded by the 

 cytotrophobJast, which in its turn surrounds the "vacuoles" (now 

 identical with cavities, containing maternal blood), enclosed by a 

 layer of syncytium which at first is broad, later becomes gradually 

 narrower. The placenta, originated in this way rests on a substructure 

 of maternal tissue, composed of the same elements as formerly 

 (decidua, etc.) ; the decidua-cells often grow out strongly, while the 

 border between foetal and maternal tissue is in many places marked 

 by a narrow streak of symplasm. The formation of trophoblastic 

 giant cells gradually reaches also the supra-placentary parts, so that 

 here also the enormous cells (later often free) lie in the maternal 

 tissue. 



Outside the placenta a stage soon is reached in which the progressive 

 and regressive processes, described above, have attained their extreme 

 limit. Superficially all has been changed into symplasm, only in the 

 depth .decidua-cells still exist, which meanwhile, since the degene- 

 ration does not reach to this depth, have become pretty large. The 

 parts of the mucosa spared by these processes, are only the mucous 

 membrane of tlie dilated connecting pieces, now entirely incorporated 

 in the foetal chambers and whose mucosa, attenuated by extension, 

 only possesses crypts still, that are squeezed fiat, and a rather tliick 

 epithelium which for a part turns into symplasm. Against all these 

 extra-placentary parts lies the extra-placentary trophoblast, now con- 

 sisting entirely of giant cells which at present often get loose and 

 then lie freely amid the decidua. 



The embryo has, during its further growth, found place in the 

 umbilical vesicle which gradually has become entirely invaginated 

 and whose walls almost touch each other. The edges of the bowl, 

 thus originated and containing the embryo, are not formed by the 

 sinus terminalis; this latter lies further down in the inner wall. The 

 small space in the umbilical vesicle is still filled with coagulating 

 masses, while the entoderm, covering the area vasculosa, which now 



