140 



The cytoplasra of the trophoblastic syncytiurn, as has just been 

 pointed out, does not itself stain brilliantly, reserubling in this 

 respect the cells of the remainder of the embryo, as indeed ein- 

 bryonic cells in general. With the continued and rapid growth 

 of this central trophoblastic mass (mitoses are frequently met with) 

 the sides of the uterine lumen into which it has forced its way 

 are pushed more and more outwards, (Figs. 3, 4) so that instead 

 of being, as at first, parallel to one another, they become inclined 

 at an ever increasing angle; consequently at the end of this 

 period the trophoblast has here the form of an obtuse cone (Fig. 

 4) (ectoplacental cone of Duval) recognisable as such (and it is 

 of great importance to note this) even in later stages when the 

 flattened cells, which had previously formed so definite a line of 

 demarcation between the trophoblast and the subepithelial tissues, 

 have been disintegrated. 



At the saine time the blood lacunae become much enlarged, 

 and many of them fiow together to form large sinuses, lined by 

 a layer of flattened trophoblastic cells forming a sort of pseudo- 

 endothelium, and situated principally midway between the cyto- 

 trophoblast and that portion of the trophoblast immediately ad- 

 jacent to the maternal tissues. 



Lastly, in the very latest stages of this first period, the first 

 sigus may be detected of a process by which the layer of tro- 

 phoblast just mentioned will be converted into a tissue destined 

 to play a part of enortnous importance not only in the nutrition 

 of the embryo but also in the structural transformation of the 

 placenta itself. The process to which I refer is a vacuolation of 

 the cells (Fig. 28) (for cell boundaries have now reappeared in 

 this region). The vacuoles, at first small soon become confluent, 

 forming large irregular spaces contaiuing glycogen. These tro- 

 phoblastic glycogen cells are oblong and their nuclei agree pre- 

 cisely with respect to their uucleoli, chromatin, and the remaiuder 

 of their structure with those of the ordinary trophoblastic cells. 



The degeueration of the uterine epithelium which originally 

 adjoined the trophoblast has already been detailed; it is here 



