PLACENTA IN PERAMELES 138 



nuclei of the origin of which nc^thing is said by Hill. Apparently 

 he leaves it to be inferred that they are of the nature of syncytial 

 nuclei which have not yet reached the lobules. 



In my opinion it is quite definitely indicated that these nuclei 

 <:»riginate from the foetal ectoderm through its active prolifera- 

 tion, and such centres of proliferation are to be seen in this 

 figure. It needs, I think, no other evidence than that of Hill's 

 fig. 7 to show conclusively that such a process of proliferation 

 is in progress. 



Any possil)le doubt, however, must be dispelled by an 

 examination of figs. 8 and 9 of PI. xxx of the central portion 

 of the placental area. These are drawn at a greater magnifica- 

 tion than fig. 7, and show the features I have indicated above 

 with more certainty. I cannot see that any other conception 

 than the one I have suggested can be possible. Particularly 

 is this evident in the case of fig. 9. Here a most active prolifera- 

 tion and migration of the chromatically rich trophoblastic 

 nuclei is quite apparent, lliey have so far advanced as to 

 invade the syncytial lobules. In the latter position the original 

 maternal epithelial nuclei are being overwhelmed by the ad- 

 vancing ranks of foetal nuclei. In some cases but one or 

 two trophoblastic nuclei liave entered the syncytial nests ; in 

 extreme cases maternal syncytial nuclei appear to be entirely 

 absent, their place being taken by the newly-arrived, evidently 

 phagocytic, foetal nuclei. One result of this is that the original 

 chorionic ectoderm is now no longer a perfectly discrete layer. 

 Another is the inclusion of the maternal capillaries by the cyto- 

 plasm of the advancing trophoblast and their consequent 

 approach towards the stratum of allantoic capillaries. 



The above statements being granted, it will be easy enough 

 to apply the new interpretation to the remainder of Plill's 

 stages and figures. To the further consideration of this I will 

 ivturn in the descriptive portion of the present paper. 



Gland Alteration. — There is still, however, one point to 

 which I Avould like to draw attention at this stage. It concerns 

 a drawing of a gland in PI. xxxi, fig. 18, one of Hill's many 

 figures in which a gland is depicted. In the whole of the paper, 



