512 A. A. W. HUBREOHT. 



trophoblast which forms a hemispherical overcapping of the 

 embryo^ which is situated opposite the non-placental (equally 

 hemispherical) trophoblast, and which is separated from the 

 latter by two ring-shaped zones — the omphaloidean trophoblast 

 and the trophoblastic annulus. 



The allantoidean trophoblast is a massive layer, and though 

 the cells may be less high individually than those of the tropho- 

 blastic annulus, still they seem to be yet more active physio- 

 logically speaking, and stain more deeply with picro-carmine. 

 Another peculiarity to be noticed on the allantoidean tropho- 

 blast even before the completion of the amnion (cf. figs. 8 

 and 9) is the presence of warts or projections of proliferating 

 cells. They arise in the first instance independently of corre- 

 sponding cavities on the maternal surface against which the 

 allantoidean trophoblast is going to be applied. But when this 

 application has come about, a trophoblastic projection is present 

 at whatever point we find the maternal surface indented, i. e. at 

 the mouth of every epithelial crypt. 



The numerous crypt openings are thus in the stages of uteri 

 51 and 106 (figs. 8 — 10 and 75) already partially blocked by 

 trophoblastic cell material, and the trophoblast cells continue 

 to proliferate in the first instance there where they have pene- 

 trated into the crypts. The trophoblast applied against the 

 concave surface between the crypt openings is also in prolife- 

 ration ; later on (figs. 13 and 94-) this becomes yet more marked. 



When once the crypt openings are filled by massive knobs of 

 proliferated trophoblast, the latter are seen to become hollowed 

 put very rapidly, a phenomenon which goes apace with the 

 further development of the allantois. The latter makes its first 

 appearance while the amnion is being completed (fig. 8). After 

 this has come about, and while the omphaloidean circulation 

 reigns as yet supreme (fig. 10), the allantois rapidly extends 

 against the concave surface when the trophoblast has just be- 

 come adherent against the mouths of the epithelial crypts that 

 have arisen in this region in preparation of the processes which 

 are now going to follow. In these processes both this region 

 of the trophoblast and the allantois play the principal parts. 



