526 A. A. W. HUBRECHT. 



lium and uterine glands, gl. (flattened against tlie outer circumference), are cut, 

 the former being indicated by dotted lines. In Fig. 11 ^ trophoblastic pro- 

 tuberances, which have already penetrated into the more centrally situated 

 crypts, are indicated by thin black lines. Other dotted lines inside of these 

 refer to allantoidean villi filling up the cavity of the hollow trophoblastic 

 protuberances. 



Fig. 11 a.— Utr. Mus. Cat. n°- Sorex 3 a, 2, 5 r. 19 *. 



Fig. 11 J.— „ „ 3 a, 2, 6 r. 17 s. 



Tig. 13. — The visible contrast between the maternal secondary crypts and 

 the trophoblastic ingrowth, ensheathing allantoidean villi, has considerably 

 diminished, making it more and more difficult to distinguish the maternal 

 from the embryonic histological elements in the placentary region. Of the 

 crypts, however, the peripheral blind ends are yet preserved and sufficiently 

 distinct. In the trophoblast we notice a region of special activity on the 

 concave placental surface where the cytoblastic thickening is particularly con- 

 siderable, secondary allantoidean villi that are rapidly forming being ensheathed 

 by it. The increase in size of the placenta is accompanied by the total dis- 

 appearance of the lateral maternal tissue against which the area vasculosa has 

 been applied. The whole of the area vasculosa (which has not stopped 

 growing, but, on the contrary, remains on the increase) is henceforth situated 

 below instead of above the trophoblastic annulus. The attachment between 

 the latter and the border of the placenta has become a circular membrane. 

 The head of the embryo is still enclosed in a proamnion, the cavity of the yolk- 

 sac is being considerably encroached upon by the embryo, and the inverted 

 area vasculosa is sinking down into it. 



Fig. 13.— Utr. Mus. Cat. n°- Sorex 130 a, 3 r. 1 s. 

 Fig. 14. — There is a considerable increase in the size of the placenta, but 

 the relation of the parts has remained very much the same to what it was in 

 Fig. 13. The layer of proliferating trophoblast is no longer so exceptionally 

 thick on the concave placental surface. The trophoblast (aud the allantoic 

 villi embedded in it) occupies seven eighths of the thickness of the uterine 

 wall in the placental region. The remnants of the cryptal region have been 

 still more considerably reduced. The trophoblastic annulus has undergone 

 no further modification. The area vasculosa has extended considerably. 



Fig. 14.— Utr. Mus, Cat. n°- Sorex 61 a, 2 r. 17 s. 

 Figs. 15 and 15 a. — The border region of the placenta just before birth. 

 The actual thickness has hardly increased when compared to Fig. 14, but the 

 ramification of the allantoic villi and the intervening strands of trophoblastic 

 tissue is ever so much more complicated. The maternal epithelial prolifera- 

 tion has now finally become reduced to mere nuclear remnants, staining more 

 deeply with carmine. The thickness of the maternal tissue outside these 

 nuclear elements has somewhat increased when compared to Fig. 14. In 

 Fig. 15 a peculiar foldings of the wall of the yolk-sac are indicated. 



Fig. 15.— Utr, Mus. Cat. n""- Sorex 100, 3 r. 10 s. 



Fig. 15 a.— „ „ 100, Ir.S s. 



