STUDIES IN MAMMALIAN EMBRYOLOGY. 367 
are in apposition. I do not doubt but that Strahl will 
reconsider his opinion after a renewed comparison of his 
preparations with Masius’ figures, and after perusal of the 
description of the phenomena in the hedgehog and in the bat 
as given by myself and by van Beneden. 
Strahl’s figure of a section through the mole’s uterus at an 
early stage of fixation of the blastocyst is valuable to me, as I 
have not as yet been able to obtain material in that stage, and 
as Heape does not furnish us with any data on this head. I 
conclude from Strahl’s fig. 5, when I connect it with Heape’s 
remark that he could obtain early stages of the mole’s blasto- 
cyst by opening the uterus longitudinally and by lifting out 
the blastocyst (size 0°9 mm.) with the tip of a scalpel, that the 
blastocyst of this Insectivore is considerably larger than that 
of the hedgehog, and never becomes enclosed in folds of the 
uterine mucosa, that are comparable to the decidua reflexa of 
the hedgehog and of the Primates. The considerable difference 
in size of the blastocyst in comparison to the diameter of the 
uterus can be very keenly evaluated by comparing Strahl’s 
fig. 5 with my fig. 29. The two blastocysts are about in 
the same stage of development. I will for the present not 
attempt to answer the question whether it is the large size of 
the mole’s blastocyst that is in the way of the closing of the 
folds that might form a reflexa in the same way as in the hedge- 
hog. Or whether the formation of the reflexa has contributed 
considerably to diminish the size of the blastocyst in the 
hedgehog, highly important though this question may be, 
both for the phylogeny of the placenta and of the embryonic 
membranes. To arrive at a reasonable answer the knowledge 
of the early stages of more Insectivora, Didelphia, and Lemur- 
oidea, is required. 
I will here point out that the subepithelial proliferation 
which Strahl describes for the mole is of course homologous to 
the more spherical decidual swelling of the hedgehog, figured 
on Pl. XV, fig. 2, and is similarly situated diametrically oppo- 
site to the mesometrium. If the mole can afterwards be shown 
to undergo similar processes of trophoblastic proliferation pre- 
