330 A. A. W. HUBRECHT. 
this to the fact that the part of the deciduofracts may be said 
to be played out in this stage, of which their partial disintegra- 
tion would be the outwardly visible sign. At all events, both 
the nuclei and the cell-contours are much less distinct in the 
ripe placenta, and in several specimens they can even not be 
made out at all. Still a distinct trophospongia is a normal 
constituent even of the shed after-birth. It gradually thins 
out towards the borders of the placenta, where it merges into the 
membranaceous remains of decidua reflexa and omphaloidean 
trophosphere. 
Finally, we must give our attention to that portion of the 
swollen decidual mucosa which is not converted into tropho- 
spongian tissue, and to the non-swollen mucosa opposite, 
against which the foetal membranes are applied without fusing 
with it, as they do in the Primates, where the decidua reflexa 
and the decidua vera are fused at an early stage. We have 
left it (see p. 823) when the vasifactive tissue which ab 
origine took part in its constitution, beeame more and more 
visible as blood-spaces characterised by a protruding endothe- 
lium. ‘These spaces, communicating peripherally with the 
normal arteries and veins that encircle the uterus, and that are 
brought thither along the mesometrium, do not reveal by any 
distinct anatomical detail whether they are centripetal or cen- 
trifugal, whether they carry blood towards or away from the 
trophospongia. ‘Thus it may be said in general that in the 
actual decidual tissue, arterial and venous cavities are not his- 
tologically distinct. This character of the decidual swelling is 
retained in the stages of diagrams 30 and 31. Between the 
latter stage and that of 32 a noticeable change has. set in in 
the vessels of these peripheral decidual layers. Around many 
of them there is a distinct proliferation of the cells that con- 
stitute the stroma of the decidual swelling. ‘This perivascular 
proliferation gives to some of these blood-lacunz an aspect 
that is wholly distinct from that of the other vessels, which do 
not in the least participate in the phenomenon. In every 
section they may be noticed side by side, both close to and far 
from the trophospongia. In transverse sections the nuclei of 
