EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 137 
tive character. And, as was hinted at above (pp. 108, 126), 
it is among Carnivores that we find, both as to fixation of 
the blastocyst and histological details of the placenta, what 
may be looked upon as yet undifferentiated arrangements. 
The phagocytic phenomena are in full swing. Osmotic 
exchanges between maternal and embryonic blood are possible 
on an extensive scale, both on the omphaloidean and on the 
allantoidean plan. 
Now among Insectivores many placentas, which, as we 
know (see p. 132), are here so very varied, also come under 
this definition. The omphaloidean placentation of Erinaceus 
follows its course, and plays for some time an important part 
in bringing about osmotic exchanges. After some time it is 
stopped by removal of the area vasculosa that becomes folded 
up, and it is replaced by the allantoidean placenta. In the 
very earliest stages of the blastocyst phagocytosis has taken 
place on a most extensive scale and with undeniable intensity, 
eroding the maternal capillaria and digesting glandular and 
uterine epithelium in a manner which only finds its parallel 
among monkeys and man. 
Still it remains an open question whether the hedgehog’s 
placentation should be cited amongst the more primitive 
types. In the mole we find certain characteristics which in 
another direction seems to be primitive. Vernhout’s investi- 
gation (’94) has brought to light a very extensive phagocy- 
tosis in the early stages of placentation. At the same time we 
notice in the mole what I have termed the contra-deciduate type 
(vide Hill, 97, p. 424) of placentation. In the mole the act 
of parturition has a very peculiar character by itself through 
the fact that the embryo is expelled out of the mother’s womb 
only enveloped in the allantois with the fully extracted villi 
forming a woolly covering to that foetal involucrum. The 
trophoblast and all its proliferations, which have carried on 
such active phagocytosis, remains adherent to the uterine 
mucosa, and is neither wholly nor partially shed but gradually 
resorbed in sitt by the mother’s tissues, causing the external 
aspect of the uterus during the puerperium to have a similar 
