EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 123 
out more and more, the trophoblast applied against it under- 
going a series of modifications, fully described by me else- 
where (’89, Pl. 26), and thus forming the bulk of the 
placenta, in which allantoic villi form an intricate network 
supporting embryonic vessels. The blood contained in the 
latter is thus bathed by the maternal blood circulating ever 
since the beginning in the intervenient meshes of the tropho- 
blastic meshwork. 
The full-grown discoid placenta of the hedgehog is thus 
nearly exclusively a product of embryonic (trophoblastic) 
activity, and has gradually become evolved out of what was 
originally a thick spherical coating of trophoblast, closely 
comparable to what we notice in man (Fig, 143). When at 
birth it comes to be severed from the maternal mucosa and 
to be expelled as “afterbirth,” a certain, though in no way 
considerable quantity of maternal tissue comes with it, the 
puerperium being accompanied by phenomena which have 
been more fully described by Strahl (07). 
After the hedgehog we will yet successively discuss of 
Insectivores, Sorex and Tupaja; of Chiroptera, Vespertilio ; 
of Carnivores, the dog; of Rodents, Lepus and Cavia; of 
Primates, T'arsius and man, 
In Sorex the maternal trophospongian proliferation is ex- 
ceptionally not in the first place subepithelial but epithelial. 
As I have described elsewhere (’94A), a considerable cushion 
of mucosal proliferation brings about the nearly cylindrical 
swelling against which (l.c., Figs. 8—11) the omphaloidean 
circulation of the embryo fits, whereas at the spot, diametrically 
opposite to the mesometrium, where the allantoidean placenta 
will later be situated, a very marked epithelial proliferation 
sets in. This proliferation soon becomes provided with 
crypts, which may on no account be confounded with the 
original glands, of which traces are co-existent with them. 
Into these crypts trophoblastic proliferations become en- 
sheathed (Hubr., ’94a, Figs. 74—81), and for a time 
maternal and embryonic proliferation are equally repre- 
sented in this region until the embryonic becomes dominant, 
