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TIT. Placentary stages (After the beginning of the for- 

 mation of the alluntoid placenta). In the om[)haloid part of the foetal 

 cavity the wall is more and more attenuated by extension and re- 

 sorption of tissue, although the layers may be recognised as before. 

 The increase in size of the trophoblast cells of the umbilical vesicle, 

 which had set in formerly, now leads to the formation of true 

 "monster cells", the cellular body of which often shows concentric 

 rings and other peculiarities, while the big nucleus often lies like a 

 crescent round a vacuole. This process comes nearer and nearer the 

 mesometrall}' situated formations. The entoderm, covering these monster 

 cells, is very narrow and small-celled ; where it covers the area 

 vasculosa, it consists on the other hand of cubical, strong cells. In 

 the umbilical vesicle a coagulated mass is always present. The large 

 embryo more and more invaginates the upper part of the umbilical 

 vesicle. Between the monstercells and the entoderm a sort of cuticle 

 develops. 



The processes, extending in equatorial bands, continally advance 

 tow^ards the mesometral pole of the foetal chamber, also in the 

 partitions of the foetal chambers, so that they are more and more 

 incorporated by these latter. In this manner extremely complicated 

 pictures are formed, especially in cross-sections. 



The dilatation now affects very strongly as well the placentary 

 part of the foetal chambers as their mutual connecting pieces, so that 

 the omphaloid part becomes smaller and smaller, while the formerly 

 existing comb-shaped division between them disappears. 



The progressive process finally reaches the mesometral pole of the 

 placentary space and continually advances further into the connecting 

 pieces of the foetal chambers: the still intact part of the wall, which 

 at first had the shape of a cupola, later assumes the form of an 8, 

 finally reduced to two round planes, which by the proliferation are 

 more and more limited to the connecting pieces. The progressive 

 process now forms crypts, which in other places are narrow and 

 deep, but in the place of the placenta are broad and wide by 

 dilatation and excessive proliferation of the stroma. The epithelium 

 has many layers, its surface still rises everywhere in papillae. In 

 the stroma not all the cells reach their full development as decidua 

 cells simultaneously, so that a peculiar reticulated aspect is produced. 

 Also the vessels increase. 



In this soil now the degenerative process occurs, again advancing 

 centripetally towards the mesometral pole. The epithelium becomes 

 a symplasm, exactly like that described above, but this time more 

 abundant and, everywhere covering the trophoblast. In the stroma 



