STUDIES IN MAMMALIAN EMBRYOLOGY. 535 



between the tops of the villi. With Fig. 81, Figs. 29, 89, and 93 should be 

 directly compared, as they are all preparations from the same uterus. 

 Ufcr. Mus. Cat. n°' Sorex 85/, 3 r. 13 *. 



Fig. 82.— a section through a corresponding region in a later stage (cf. 

 Fig. 13). The plasmodiblast between the villi is being attenuated as the 

 number and the length of the villi increase. The more deeply staining layer 

 of cytoblast surrounding the villi is no longer distinct ; its elements have 

 assimilated with the intervening plasmodiblast. The passage of blood from 

 a maternal vessel, with distinct endothelium, into the trophoblastic blood- 

 spaces can be distinctly traced in this and the neighbouring sections. The 

 cytoblastic layer of the trophoblast, if it is no longer distinct round the 

 villi, is all the more massive on the free concave surface of the placenta, 

 which is, however, not represented in this figure (cf. Figs. 30 and 94, taken 

 from the same uterus). 



Utr. Mus. Cat. n°- Sorex 130 a, 2 r. 18 s. 



PLATE 38. 

 Figures 83—85 X 260. Fig. 84 « X 60. Fig. 86 x 480. 



Fig, 83. — Fragment of a section through the region of the omphaloidean 

 trophoblast and the adjoining maternal tissue, in an early stage (cf. Fig. 6). 

 One of the first phenomena of dehiscence in the deeper proliferated maternal 

 layers is visible as a solution of continuity in the middle of the lower half 

 of the figure. The omphaloidean trophoblast is considerably thickened — 

 without as yet being adherent to maternal tissue — in the upper half of the 

 figure ; in the lower half adhesion has come about, and at the same time 

 considerable histolytical transformations have commenced. Maternal uterine 

 epithelium is only intact in the very topmost portion of the figure. Maternal 

 blood is seen to pass from the blood-spaces of the maternal proliferation 

 into the syncytial tissue, in the region where maternal and trophoblastic 

 elements have fused together. Remnants of compressed uterine glands are 

 seen between the muscularis and the epithelial proliferation. 

 Utr. Mus. Cat. n°' Sorex 45 e, 5 r. 6 s. 



Fig. 84. — Section through the uterine wall in the region of the tropho- 

 blastic annulus (cf. Fig. 10). There is a considerable blood-extravasate 

 between the annulus and the tissues that are in process of resorption. 

 Blood-corpuscles are being actively absorbed into the protoplasm of the cells 

 of the trophoblastic annulus. In the region of the omphaloidean trophoblast 

 there is a very intimate fusion between embryonic and maternal tissue. In 

 the deeper layers of the proliferated maternal epithelium dehiscence is 

 actively going on, and a fresh layer of uterine epithelium is developing below 

 the tissues that are being resorbed. From the upper rim of the trophoblastic 



