Bye A. A. W. HUBRECHT. 
where the decidual tissue passes into the trophosphere the same 
distinction of the two sorts of blood-spaces is of course noticed, 
and the sheath of perivascular cells is seen to stand out boldly 
against the rest of the decidua, which shows more marked de- 
generative phenomena. There is, indeed, room for the sugges- 
tion that the perivascular cells join the trophospongia, which the 
rest of the decidual stroma can undoubtedly be said not to do, 
so that in these later phases, the material of which the tropho- 
spongia is built up would then not wholly be derived from 
endothelial proliferation, but would in part owe its origin to 
the cells that properly belong to the intervascular stroma. On 
p. 321 I have given the reasons why in the earlier stages I was 
not inclined to believe in any such participation; here in these 
later stages I will be somewhat more reserved in my opinion, 
and even acknowledge that certain preparations do encourage 
the interpretation, according to which the perivascular sheath- 
cells go and join the trophospongian cell groups. In other 
cases, however, a breaking up of the nuclei of the perivascular 
sheaths was also noticed, and this prevents me from generalis- 
ing the first observation. Here, as in so many points referred 
to in this memoir, we have as yet only the preserved prepara- 
tions from which to draw our conclusions, which for the active 
processes of growth and change we are studying 1s of course 
only an insufficient guide. 
Besides their possible contributions to the increase of the 
trophospongia, it must yet be asked if any other significance 
ought yet to be attached to these proliferative sheaths. I 
would suggest the possibility that they could act as regulators 
or even as obstructors of the blood-flow in the decidual, re- 
spectively in the placentary region. If that should be the 
case, it would be easy to understand why the phenomenon is 
noticed, both in the afferent and in the efferent vessels. I can 
do no more than indicate the problem, not offer any further 
points towards its solution. Neither towards that of the 
question, whether these vessels and their proliferation sheaths 
(fig. 50) are in any way comparable to what was noticed by 
Waldeyer and by Leopold (‘Studien tiber die Uterus Schleim- 
