141 



only necessary to add that the disruption which coraraenced iii 

 the embryonic pit or crypt, gradually proceeds upwards, affecting 

 the epitheliuni lining the origiual lunien, so that by the begiuning 

 of the next period little or no tracé is left here of any epithe- 

 liuni at all, except the débris which has been devoured by the 

 trophoblast. Beneath the epitheliuni at first, but by the degene- 

 ration of the latter brought into closest approximation with the 

 trophoblast, is the layer of now flattened, but once vacuolated 

 cells already referred to; with the growth of the trophoblast, and 

 consequent outward displacement of the sides of the lumen this 

 layer becomes broken and interrupted, but the cells of which it 

 consists still reniain recognisable at the end of this period, and 

 may even be detected in the beginning of the next (Fig. 28). 



Beneath this again is the remainder of the subepithelial tissue 

 of the uterus, a tissue which first undergoes peculiar raodifications, 

 of the greatest physiological significance, and finally, when it has 

 degenerated, is replaced by the above nientioned glycogenic cells 

 of trophoblastic origin. This however is anticipating. The tissue 

 in question arises, as does the subepithelial tissue of' the capsu- 

 laris, by a proliferation of cells between the muscularis and the 

 epitheliuni; but whereas in the latter case the cells are large 

 and often contain nuraerous nuclei of considerable size, in the 

 former the cells are small, and uninucleate. They form a compact 

 mass, penetrated in the centre by small blood vessels derived from 

 the uterine arteries. Laterally, they exteud between the venous 

 sinuses which we have seen to emerge, radiating outwards and 

 upwards, from the lacunae of the trophoblast. Mitoses are of 

 frequent occurrence in the cells at first, but gradually cease 

 towards the end of this period; in other words the proliferation 

 of cells in this region ceases just about the time when glycogenesis 

 is commencing in the trophoblast. In the last mentioned layer on 

 the other hand nuclear divisions may be observed till the close 

 of placentation. 



Among the cells two kinds may be distinguished at a compa- 

 ratively early stage, firstly rounded cells, and secondly, elongated, 



