104 A. A. W. HUBRECHT. 
network (area vasculosa) of the umbilical vesicle will come 
to develop on this very surface. Conditions will thus arise 
that are yet more favourable for an interchange between the 
maternal blood, slowly circulating in the trophoblastic lacunz 
and the embryonic blood-corpuscles winding their way along 
the paths of this area vasculosa of the hedgehog (Fig. 38). 
And later yet at another spot of this massive trophoblastic 
spongework, soaked with circulating maternal blood, the 
allantois of the hedgehog will find occasion to attach itself 
and to lay the foundation of the allantoidean placentation by 
which the earlier but provisional omphaloidean placentation 
(as the region of osmotic interchange above noticed is some- 
times called) is succeeded. This will be further discussed in 
Chapter VI. 
During the very considerable proliferation of the tropho- 
blast in the hedgehog here alluded to,! a further specialisa- 
tion of the different parts of it becomes apparent very soon. 
The outer layer comes to produce very large cells with big 
nuclei which in a former publication (89, p. 325) I have 
termed deciduofracts, and which seem to have a further 
phagocytic effect on the surrounding maternal tissues. Up 
to now the hedgehog’s trophoblast has retained the character 
of a massive spherical outer layer of the blastocyst, which is 
surrounded on all sides by maternal tissue (decidua capsu- 
laris), thanks to the closure of the mouth of the deep pit into 
which it has found its way in the earlier stages (p. 102). 
As development proceeds this capsularis thins out consider- 
1 I must here call attention to the fact that the trophoblast—considered by 
me in its earliest one layered stage as a larval envelope, inherited from inver- 
tebrate ancestors—remains morphologically perfectly equivalent to itself in 
later stages, however considerable may be the proliferation (and thus the 
increase in thickness combined with specialisation) which it exhibits at one or 
more spots, or even (as in the hedgehog and in man) over the whole of its 
surface. This should withhold us from applying the name of trophoderm to 
those proliferating portions of it, as Sedgwick Minot (’08) invites us to do. 
The name suggests a morphological difference which does not exist. For the 
purpose which Minot has in view, the older name of ectoplacenta proposed by 
Duval seems quite suitable (see p. 15). 
