SPOLIA NEMORIS. 117 
gives a long vitality to views which would most probably be 
soon abandoned if the problem were now-a-days brought for- 
ward for the very first time. Similarly, generalisations that 
were based on incomplete data, although fully justified at the 
time when they were made, are now found to obstruct the way 
to a certain extent. 
One of the mammals that will facilitate the real under- 
standing of the method according to which the very simple 
manner of foetal interchanges above alluded to has been 
converted into the more complicated placentary structures, 
is the mole. Some years ago I called attention to the fact 
(Quart. Journ. Microsc. Science,’ vol. xxx, pp. 346 and 388) 
that here, too, embryonic villi that cover the foetal envelopes 
are easily drawn out of their sheaths at birth, and that no 
afterbirth is shed, although the animal has a discoid placenta, 
which up to lately was held to mean that it was also deciduate. 
I then expressed the opinion that not only the mole is not 
deciduate, but that even embryonic tissue is left behind against 
the uterine surface, and is gradually resorbed in situ. 
According to the patient investigations made by Mr. Vern- 
hout, a pupil of the Utrecht Zoological Laboratory, which are 
at present in the press, this is actually the case. Mr. Vern- 
hout has cleared up the early details of the mole’s placentation, 
and comes to very different conclusions from those of Strahl. 
We may say that in the mole the epithelial connection, as 
it was described above for Nycticebus and others, is a phase 
that is very rapidly passed over, and that it is followed by the 
application of a trophoblastic cell-layer against the maternal 
epithelial layer. According to Mr. Vernhout’s investigations, 
based upon preparations which I have myself repeatedly had 
occasion to compare with the drawings which he is about to 
publish, the maternal epithelium is very rapidly destroyed, the 
trophoblast now becoming a pseudo-epithelium by which the 
denudated mucosa and its deepening crypts are covered. Into 
these crypts, which are in fact of embryonic origin, the allantoic 
villi penetrate and are withdrawn out of them at birth, the 
trophoblastic pseudo-epithelium, and the further derivates it 
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