STUDIES IN MAMMALIAN EMBRYOLOGY. 399 
PLATE XXI. 
Fie. 38.—The bottom of the central depression (/.) in the decidual neo- 
formation, with an early embryo in situ. (The embryo is the same as that 
represented in three consecutive sections on Pl. XVII, Figs. 22—24). The 
uterine epithelium (e.) is in evident proliferating degenerescence ; the embryo 
is immediately applied against the subepithelial stroma, in which blood-vessels 
(e a) are still very sparse, though already more conspicuous than in Pl. XX. 
Several of these small vessels have a thickened proliferating endothelium, 
Remnants of uterine glands (g/.), longitudinally cut, are seen in the lower 
half of the figure, In the lumen of the uterine depression the blood-clot 
(coa.) noticed in Pl, XX is present, and coalesces with the remnants of the 
disintegrating epithelium. This preparation and that figured on P]. XXII is 
magnified about twice as much as that of Pl. XX and XXIJI—XXVI. The 
nuclei in the embryo when judged from this figure would appear to be more 
numerous than they are in reality. This is owing to the extreme brilliancy 
of the chromatic elements taking part in the constitution both of the nuclei 
and of the protoplasm, and at the same time from more nuclei having been 
here figured than are visible in one optic section. For a more correct, but at 
the same time somewhat more schematic representation of the nuclei of this 
section of the embryo, see Fig. 24 (turned upside down). (Mus. Utr. Cat. n® 
Erin. 48 a, 27. 2s.) 
PLATE XXII. 
Fic. 39.—The same region as Fig. 38 in a more advanced stage of develop- 
ment. Here the embryo is wholly embedded in the subepithelial stroma. 
The maternal blocd-spaces (ca.) in the proliferating decidual tissue have in- 
creased and widened out, especially those that are in the immediate vicinity 
of the embryo. There is no perivascular increase of the decidual stroma, 
but a marked increase in the size of the endothelium cells of these spaces, 
which will be noticed still more clearly in the following stage figured on the 
next Plate. This stage of development of the embryo corresponds with that 
of Fig. 14. Remnants are visible of the reduced uterine glands (yi.), one of 
which is being surrounded (and perhaps directly absorbed ?) by embryonic cells. 
The trophoblast (Z7.) encloses irregular lacunar spaces (sp.) ; opposite to the 
mesometrium it is more compact, and grows out into a polar knob (ep.) that 
is directed inwards and will become the epiblast of the germinal area. hy. 
The hypoblastic vesicle, in which the embryonic and the peripheral portion 
have become histologically distinet from each other. There is a coagulum 
inside the hypoblastic vesicle. The coagulum (coa.) that fills the decidual 
depression (/.) of the preceding figures has increased in dimensions; more 
blood accumulates between it and the lower sides of the depression of which 
the degenerating epithelium is marked e. in this figure. Of this blood 
