STUDIES IN MAMMALIAN EMBRYOLOGY. 863 
uterine glandular epithelium (in retrograde metamorphosis) plays 
in the rabbit’s trophodisc, can partly account for this. Also the 
phenomenon, so fully described and figured by Masius, of a 
very considerable proliferation of perivascular cell-tissue in the 
rabbit’s trophodise (as distinct from the endothelial prolifera- 
: tion above noticed, but comparable to perivascular proliferations 
that also occur in the hedgehog outside the trophospongia; cf. 
pp. 830—332), points to a greater divergence of this rodent’s 
placentation from what obtains in the bat and the hedgehog, 
whose more intimate agreement has just been pointed out. With 
our scanty knowledge of the exact course of the phenomena in 
other Rodents (for which Duval’s forthcoming memoir may 
contain valuable information) it seems to be inadvisable, at 
present more especially, to insist upon any detailed comparison. 
Also the question whether very large cells, with gigantic nuclei, 
that can be observed in the mouse’s placenta, and that are 
already figured (though not further noticed) by Selenka, might 
be compared either morphologically or physiologically, or both, 
to the hedgehog’s deciduofracts. 
It was not my object in giving a more detailed account of 
the latest literature on the subject to enter into an exhaustive 
and definite comparison of the phenomena, such as they are 
described by different authors. A similar attempt would 
for the present be premature. What I specially wanted to 
point out was that in three different orders of Mammalia a 
series of placentation phenomena are being brought to light, 
which deal a serious blow to such views about the phylogeny 
of the mammalian placenta as are embodied in the well-known 
woodcuts, which have found their way into all text-books 
(Balfour, Hertwig, and others), and which we owe to that grand- 
master of placental research, Sir W. Turner. In Turner’s 
scale of comparison the lowest place is allotted to such forms 
as the pig; then come the ruminants; next, passing from the 
adeciduate to the deciduate forms, the Carnivora; and finally 
the Primates and Man. In another section of this article I 
will explain why this distinction of the placental mammals 
into Deciduata and Adeciduata should he henceforth 
