514 A. A. W. nUBRECHT. 



able extravasates. The trophoblastic knobs may yet penetrate 

 somewhat further into the crypts, but it is not in this penetra- 

 tion that the chief feature of the placental development is 

 found. That chief feature is the increase in thickness of the 

 trophoblast, and the decrease in thickness of the maternal 

 crypt region. From this latter blood passes into the 

 former ; no further maternal contribution, nor indeed any 

 penetration of maternal growths between the trophoblast (or 

 the allantois villi that are enclosed therein), can anywhere be 

 noticed. 



The trophoblast is spun out against a maternal surface spe- 

 cially prepared for its firm adhesion. A glance at figs. 10 — 15 

 will further explain this. In these figures the maternal crypts 

 represented by the red dotted lines are not represented in 

 their real number. The fact is, they are very closely pressed 

 together in the early stages (cf. figs. 24 and 74), and only those 

 crypts were inserted in the drawings with the camera (figs. 6 

 — 13) which happened to possess a more or less distended 

 lumen. 



The depth of the zone occupied by the crypts is seen to re- 

 main about stationary between the stages of the figs. 11 — 13. 

 On the contrary, the depth of the zone in which the tropho- 

 blastic protuberances are situated has very considerably in- 

 creased. 



It follows from this that when once the firm adhesion is 

 brought about there is no very active further penetration of 

 the trophoblast into the crypts, nor any extension of the 

 cryptal and intercryptal proliferation downwards between the 

 trophoblastic tissue. Great activity is, however, displayed; 

 first, in the trophoblast between the villi, where intercommuni- 

 cating spaces are being evolved, that enter into communication 

 with the maternal circulation ; second, in the trophoblastic 

 layer that covers the inner concavity of the developing placenta. 



The latter layer attains to a most considerable thickness 

 (cf. figs. 13, 30, and 94), preparing new points of insertion 

 for secondary and tertiary allantoic villi (figs. 13, 29, 30, 31, 

 91, 94), which in their turn [grow out to the length of the 



