316 A. A. W. HUBRECHT. 
ing lips of the folds between which the blastocyst has disap- 
peared—becomes distended at the same time. Gradually it is 
more and more flattened out, and what was, in the stage of 
figs. 8, 37—39, still a compact mass of cellular tissue separat- 
ing the blastocyst from the uterus lumen, is in the later stages 
of development a gradually attenuating layer, which at the 
end becomes membranaceous (cf. diagrams 28—36). Its origin, 
above described, its further developmental phases (here rapidly 
sketched), and the fact that uterine glands open out both on 
the outer and on the inner surfaces of these coalescing folds, 
are so many points that demonstrate its direct homo- 
logy with what is known in the development of the 
human subject as the decidua reflexa. That it capsules 
off from the uterus-lumen a cavity in which the blastocyst is 
attached by means of villi that originally cover the whole sur- 
face (Pl. XVI, figs. 16—20), but that finally disappear, except 
in the discoidal placental area (see preceding paragraph, pp. 288 
and 295), is, of course, another point in which this fold reminds 
us of the decidua reflexa as it is known in the human subject. 
Comparison of figs. 2, 28, 29, and 37, with Kundrat and Engel- 
mann’s figure of the human reflexa (copied in Hertwig’s ‘Lehr- 
buch der Entwickelungsgeschichte,’ 1 Aufl., fig. 128), will 
further convince any impartial observer of the great similarity. 
In the hedgehog, as in the human subject, the blastocyst is 
thus in very early stages encapsuled within a projecting fold of 
the mucosa, and hidden from view when the pregnant uterus 
is slit open. This is also the case in Cavia and other rodents. 
Here, however, the process of occlusion within maternal tissue 
is very different from the one just described and from what 
obtains in man, as will be seen when comparing this account 
with Selenka’s (I. c. Pl. XIII) clear description. The rodent’s 
capsule which shuts off the embryo from the uterus lumen is 
analogous, that of Erinaceus homologous with the decidua 
reflexa of man. 
The phenomenon of hemorrhagic swelling along the lips of 
the incipient decidua reflexa is of a different nature from 
another phenomenon in which vascular tissue takes a promi- 
