532 A. A. W. HUBBECHT. 



and there flattened remnants of the endotlielium of the vessels of the allan- 

 toidean villi. In Fig. 52 the embryonic blood-spaces are wider than in Fig. 

 53, In Fig, 54 no blood-corpuscles are indicated, whereas the remnants of the 

 secondary epithelial crypts are visible as nuclear conglomerates, C, peculiar 

 corpuscles in the deeper maternal layers. 

 Utr. Mus, Cat. n°' Sorex 100, 2 r. 12 s. 



Figs. 55 — 57. — Three figures of different phases of development of the non- 



placental trophoblast and of the extenuated uterine wall. Fig, 55 taken 



from the phase of Figs. 8 and 9, The lower wall of the blastocyst is in this 



phase comparatively thick, the hypoblast even much more so than the non- 



placental trophoblast. In Fig. 56 (corresponding to Fig. 11) the same layers 



have become more considerably attenuated, and so has the uterine wall, the 



epithelium of which is consequently no longer thrown into any folds. In 



Fig. 56 a thin layer of a greenish granular coagulum is applied against the 



inner surface of the yolk hypoblast. In Fig. 57 this has considerably increased 



in thickness, and can be traced in the lower half of the yolk-sac all round. 



The greenish coagulum has parallel surfaces. To the left of g c. in Fig. 57 a 



further granular precipitate is indicated, which in this preparation fills part of 



the cre.scentic yolk-sac. In comparing Fig, 57 with 56 we see that the 



further extenuation of the muscular layers of the uterus is especially marked. 



Fig, 55,— Utr. Mus. Cat, n°- Sorex 51 e, 4 r. 13 s. 

 Fig. 56.— „ „ 3 S, 4 r, 4 s. 



Fig, 57.— „ „ 26 a, 3 r. 10 s. 



Figs, 58 — 65, — Eight different regions and different stages of development 

 of that surface of the yolk-sac, which becomes inverted from the stage of 

 Fig, 12 onward. This is the surface, stretching between the trophoblastic 

 anuulus and the embryo, on jvhich the area vasculosa develops. After the 

 inversion the vascular region increases in surface, and so does the number of 

 the vessels. The hypoblast cells increase in size, proliferate freely, and 

 acquire a deep green tinge, Neoformation of blood-corpuscles is very actively 

 going on in this region. 



Fig. 58.— Utr. Mus, Cat. n°- Sorex G\a,2r. 10 *. 



