EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 117 
has fully accepted this—that at the spot where in Perameles 
the allantois gives rise to the placentary attachment the tropho- 
blast—which in an early stage can be most sharply (Fig. 138) 
distinguished from the maternal trophospongian syncytium 
(into which the maternal epithelium has been converted)—dis- 
appears entirely in a later stage, presumably phagocytically 
destroyed by the maternal syncytium, thanks to which (Fig, 
139) the maternal blood is now brought into very close con- 
tact with the embryonic blood circulating in the allantoidean 
vessels. 
Now a phenomenon of this nature which, as even Strahl 
acknowledges, would be unique among the Mammalia, is far 
from being firmly established in Hill’s paper. In many of 
his figures, which have not been copied by Strahl, and which 
may be said to represent transitory stages between his 
figs. 149 and 150, we see the trophoblast cells of fig. 149 
becoming converted into much larger cellular elements (our 
Fig. 158), which, instead of being attacked and resorbed by 
the maternal syncytium, penetrate into this and very freely 
mix with it in a way which corresponds most closely with 
what Schoenfeld has so well described for the dog. I have 
no doubt that also Perameles offers a very good example of a 
syncytium with a double, mixed character, in which both 
maternal and foetal (trophoblastic) elements exist side by side 
of each other, and by which the endothelium of the maternal 
vessels is not attacked or eroded. Thus in the height of 
development of the Perameles’ placenta (Fig. 139) we clearly 
recognise the presence of the trophoblastic elements yet in 
full activity, which at other spots are so mixed up with the 
maternal syncytial cells as to have given rise to the erroneous 
conclusion accepted by Strahl of the trophoblast’s disappear- 
ance.' The name of semiplacenta avillosa by which Strahl 
designates it will have to be dropped. The-Perameles’ 
placenta may be said to be a somewhat simpler—because 
1 [ have to thank Mr. Hill for sending me some of his original preparations 
of the placenta of Perameles in different stages, by which I have been enabled 
to confirm the contradictory opinion here formulated. 
