404 JAS. P. HILL. 



of a very varyinof size and shape, and in places, through the 

 disappearance of the outlines between adjacent cells, large 

 multinucleate cells have been formed. The protoplasm of 

 these degenerating cells often stains just as deeply as that of 

 the syncytium, rendering it difficult to determine accurately 

 the limit between the two. In many of the ectoderm cells, 

 shown in fig. 9, the nuclei are also seen to be in various stages 

 of disintegration. Many of them stain only slightly; the 

 nuclear membrane is becoming indistinct, while the chromatin 

 is found broken up, and diffused in the form of small granules 

 throughout the delicate nuclear reticulum. Eventually the 

 position of the nucleus is only marked by a few straggling 

 irregularly thickened remnants, which finally become diffused 

 throughout the protoplasm, and lost to view. 



It may be noted that degeneration does not take place in a 

 uniform manner over any given area, but quite irregularly in 

 patches, so that in a small portion of the allantoic placental 

 area (as in fig. 9) various stages in the degenerative process 

 are met with. In certain portions of the chorionic ectoderm 

 where it still forms a continuous layer of fairly regular cells, 

 and shows no signs of the degenerative process just described, 

 I have found that the inner ends of the cells are greatly va- 

 cuolated, a fact which suggests that a process of vacuolation 

 may also play a role in the retrogression of the chorionic 

 ectoderm. 



That the chorionic ectoderm is destined to disappear is 

 abundantly evident from this stage alone, and I am inclined 

 to believe that the allantoic capillaries, so closely related to its 

 inner surface, are by no means the least active agents in 

 effecting its removal. Of direct fusion of the degenerate ecto- 

 derm with the syncytium there can be no question. All the 

 facts negative such a view. 



The role of the ectoderm is apparently merely that of 

 attaching the embryo to the previously prepared maternal 

 syncytium. Once the allantoic capillaries have spread out on 

 its inner surface, it degenerates and disappears in order to 

 allow of closer proximity between the foetal and maternal 



