146 



maternal tissues (Figs. 35, 39); they frequently project boldly 

 into the lumeu of the sinus and in fact may become almost large 

 enough to deserve the name of megalokaryocytes. From what has 

 been seen of them in earlier stages there can, I think, be no 

 question whatever of their trophoblastic origin. 



The sinuses receive their blood directly from the maternal blood 

 vessels which, as may easily be demonstrated by injection, spring 

 from the uterine arteries, and pass through the middle region of 

 the allantoidean subepithelial tissue (Fig. 9, 10, 11). Peripher- 

 ally, the glycogenic layer, which is here not so thick, is bounded 

 on the upper side by a sheet of megalokaryocytes, which again 

 peripherally passes into the similarly modified trophoblast of the 

 omphaloidean region; centrally on the other hand it is only here 

 and there that a trophoblastic cell undergoes this transformation, 

 and consequently the glycogen cells here abut directly on the 

 maternal tissues. At the beginning of this period it is possible 

 still to find the layer of flattened cells separating the two, (Fig. 

 28) but this soon completely disintegrates and a little later it is 

 only possible to find cellular and nuclear débris, showing unmis- 

 takeable signs of fatty degeneration ; the nuclei exhibit the changes 

 which we have already observed ; they contain irregular chromatin 

 masses, and intensely staining nucleoplasm, while the cytoplasm 

 stains strongly with acid stains, and contains small fat granules 

 (Fig. 40); the cells in fact are dead. Above this débris, and now 

 practically in direct contact with the trophoblastic glycogenic cells 

 is the main bulk of subepithelial tissue, the differentiation of which 

 into supporting and glycogenic cells has already been traced. 



During the period with which we are at present concerned the 

 first signs of the complete disintegration of this tissue which is 

 afterwards accomplished appear. Mitotic divisions are no longer 

 found, and the tissue begins to break up into its constituent 

 elements, the rounded glycogen cells separate from one another, 

 and lie loosely about in a space crossed by the maternal arteries 

 and traversed also by the much elongated fusiform, or sometimes 

 branched supporting cells; many of them also become embedded 



