STUDIES IN MAMMALIAN EMBRYOLOGY. 503 



brought into communication with the maternal capillaries 

 during the histolytic processes there described (cf. fig. 83). 



As pregnancy advances, and as spaces that have originated 

 in these lateral proliferations by dehiscence (fig. 83) increase 

 in number and in size, the communication between the capil- 

 lary lacunae in the syncytium and the afi'erent uterine blood- 

 vessels is brought about by vessels that take their course 

 through persisting strands of proliferated epithelial tissue that 

 keep up the connection between the deeper permanent and 

 the superficial epithelial tissue {s,s, figs. 9, 10, 50, 84). 



The latter is, so to say, scaled ofi" from the rest of the 

 mucosa. Even the connecting strands just noticed disappear 

 one by one, and in the stage of figs. 11 and 12 the maternal 

 blood-flow through this region, which reached its maximum in 

 the stage of fig. 10, has again become diminished, histological 

 and degenerative phenomena of the cells and the nuclei at the 

 same time increasing. There is a very marked difi'erence 

 between the cells of this and the placental region. The com- 

 ponent cells of the latter are seen by the number of karyoki- 

 netic figures to be in rapid cell division ; those of the lateral 

 omphaloidean region show no signs of such activity ; growth 

 has here come to a standstill after the phase of fig. 10. In 

 many sections a sort of pseudo-karyokinesis was observed in 

 some of the component cells. I have figured this phenomenon 

 in fig. 84 a. It may be gathered from these figures that the 

 nuclei rather testify towards a degenerative than towards a 

 reproductive process. 



There is every reason to believe that in the process of final 

 resorption of the omphaloidean region of the mucosa an active 

 part is played by a special modification of the trophoblast, to 

 which we shall henceforth give the name of the tropho- 

 blastic annulus, and which is seen in what is evidently its 

 most active phase in figs. 10 and 84, i. e, simultaneously with 

 the maximum development of the omphaloidean circulation 

 and congestion. It is then seen to be a ring of trophoblastic 

 tissue of increased thickness as compared with the other por- 

 tions of the trophoblast. The component trophoblast cells are 



