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In the uterus the tissues (distal wall of the yolk-sac, omphaloidean 

 trophoblast, and subjacent subepithelial tissue) which together 

 constitute the capsularis are considerably thinner than before. 

 On the mesometric side the trophoblast is seen to be penetrated 

 by the capillaries of the allantois; above this is the subepithelial 

 tissue (now transformed into maternal glycogen cells) of the allan- 

 toidean region; it is traversed by arterial blood vessels. To the 

 right and left of this are the greatly dilated venous sinuses; and 

 above is the thickening of connective tissue at the root of the 

 mesometrium. 



Fig. 11. Transverse section of a placenta on about the eighteenth day. 



On the lower surface it may be seen that parts of the yolk-sac 

 have been gathered up into the substance of the allantois; and 

 further that the edges of the placenta project downwards into the 

 yolk-sac sinus; here also the remains of the capsularis may beseen. 

 The allantoic portion of the placenta has grown considerably both 

 in height and breadth. Above it is an enormous mess of glyco- 

 genic cells, traversed by sinuses, and containing in its upper por- 

 tion the maternal blood vessels which have been engulfed. 

 Between this and the layer of flattened connective tissue is all 

 that is left of the maternal glycogenic tissue; and above this the 

 thickening at the root of the mesometrium. 



Fig. 12. A blastocyst in its pit in the uterus immediately before fixation. 

 The uterine epithelium has partly disappeared (Cf. Selenka, Fig. 6, 7) 

 (Perenyi). 



Fig. 13. An embryo in its pit at the time of fixation (the stage shown in 

 Fig. 8 compare Selenka Figs. 11, 12, 14, 15). 

 The allantoidean trophoblast has begun to proliferate invaginating 

 the embryonic knob into the yolk-sac; mitoses may be seen. 

 Some of the cells of the omphaloidean trophoblast are absorbing fat. 

 A little of the uterine epithelium, in a degenerating condition, is 

 shown above, and below the embryo ; the cells contain large fat 

 globules (compare Figs. 14 and 15). 



Elsewhere the trophoblast abuts directly on a fine fibrillar raera- 

 brane continuous with that which separates the epithelium from 

 the subepithelial tissue; the latter is vacuolated and in some places 

 contains fat (to the right of the figure). 



To the left a trophoblast cell is seen enlarging into a megalokaryo- 

 cyte, and making its way into the subepithelial tissue, pushing the 

 membrane in front of it. 

 (Aceto-corrosive-osmic). 



Fig. 13a. A trophoblast cell (from the omphaloidean region) with fat gran- 

 ules; the nucleus is dividing. 



Fig. 14. (From another section through the same embryo), 



Degeneration of the uterine epithelium. Above it is normal, below 

 cubical, and lower down completely degenerate. The dóbris has 

 become detached and fallen into the lumen, where leucocytes are 



