151 



liniug, and irregularly crossiug these cavities undergo glycogenic 

 vacuolation. Around the periphery of the placenta the glycogeuic 

 layer is bouuded above by the megalokaryocytes, in the centre 

 it abuts directly on the maternal tissues. The disintegration of 

 the latter is during this last period completed (Figs. 31, 32c/); 

 the rouuded glycogen cells become more widely separated from 

 one another and may be seen to be breaking up, the sole relic 

 of the once compact allautoidean subepithelial tissue. Upon the 

 space thus denuded of its glycogen cells the trophoblastic glyco- 

 genic tissue encroaches, first creeping up the sides of the blood 

 vessels, which become thus completely engulfed, and afterwards 

 filling up the intervening spaces. 



If during this process the advanciug edge of the trophoblast 

 be carefully examined (Fig. 29) there will be found embedded in 

 it the debris of maternal cells of all kinds; and all may be 

 distinguished from the more active, living tissue of the tropho- 

 blast, the fatty cells by their fat and their distorted nuclei (Fig. 

 40) the glycogen cells by their peculiar characters, the supportiug 

 cells by their shape and in some cases by their staining reaction 

 of their nuclei. I have found that with methyl-blue-eosin it is 

 possible to stain these nuclei purple, while the nuclei both of the 

 trophoblastic and of the maternal glycogen cells, stain blue. 



The encroachment of the trophoblast continues until the rnus- 

 cularis is reached, the layer of fiattened connective tissue cells 

 disappearing in the midclle region of the placenta. At the end of 

 placentation therefore we may distinguish two regions in the non- 

 allantoic portion of the trophoblast; firstly a region nearest the 

 embryo, traversed by sinuses, and contaiuing tracts of cells in 

 which vacuolation is yet incomplete, and secondly a mass of cells 

 nearest the mother in which are embedded the maternal arteries, 

 the supporting cells and the granules which are the only remains 

 of the original subepithelial tissue (Fig. 39). The presence of 

 glycogen in the cells is demonstrable in both regions, the cells 

 in fact are so distended with in that only a thin protoplasmic 

 envelope remains, which when the glycogen is used up collapses; 



