492 A. A. W. HUP.RECHT. 



epithelium disappears without any special antecedent prolifera- 

 tion) is again possible. 



This epithelial proliferation must now be described in detail. 

 When we compare fig. 4 with fig. 3 it is seen that the diameter 

 of the uterus and of its lumen have not undergone any appreci- 

 able increase. Yet the epithelial proliferation has commenced 

 in fig. 4j and is already three to five cells thick in what will after- 

 wards be the placental region ; twelve to eighteen cells on the 

 two lateral cushion-shaped surfaces, where by this time (cf. 

 fig. 4) the blastocyst has commenced to adhere to the maternal 

 tissues. The difference between this and the foregoing stage 

 is still better seen if we compare fig. 19 with fig. 17, fig. 20 

 with fig. 18, whereas figs. 67 — 69 will allow us to discuss the 

 histological detail. The preparation figured in fig. 67 leaves 

 no doubt as to the proliferation being epithelial. 



Here — and also in very many sections that were not figured 

 — the karyokinetic processes (well preserved and sharply de- 

 fined after staining with picro-carmine) leave no doubt about 

 the origin of the proliferated cell matter. It is the epithelial 

 cells lining the lumen that throw off new cells, which become 

 mixed up with connective-tissue elements that belong to the 

 layer situated between the epithelium and the muscularis. 

 However, the epithelial elements are much more numerous 

 than the connective-tissue ones. The proliferating process goes 

 on more rapidly on the lateral cushion-shaped surfaces; the 

 difi'erence between the epithelial layer and the cells that have 

 originated out of it is soon effaced; these cells are themselves 

 rapidly multiplying, and thus the first distinction is about this 

 time created between the lateral maternal tissues against which 

 the yolk-sac adheres, and the bell-shaped maternal surface, 

 against which the allantois is going to be applied. Although 

 there is no sharp boundary line, still in fig. 20 and fig. 4 it 

 is easy enough to distinguish them in a general way. 



Another distinguishing feature between these two portions 

 of the uterine surface is of great importance, viz. that in the 

 placental region the proliferated epithelial elements are very 

 soon seen to arrange themselves in a particular manner below 



