328 A. A. W. HUBRECHT. 
however, to occur in the rabbit (Masius, a. 0.). Perivascular 
proliferation is not absent in the hedgehog, but, as we shall 
presently see, it occurs in other regions and in other stages, 
and would at the utmost only play a very secondary part. 
(2) That by the mode of formation here described there 
would be reason to suppose that between the blastocyst and the 
coagulum (coa. of figs. 7 and 39), which co-operates towards 
the closure of the lips of the reflexa, no trophospongian tissue 
is developed. Asa matter of fact there is at the outset no 
maternal tissue between the blastocyst and this coagulum (of 
figs. 7 and 39), and no maternal blood-spaces can thus in loco 
originate a trophospongia. Still in later phases the tropho- 
spongia is seen distinctly to be present in that region and to 
develop an outer layer of deciduofracts. I explain this fact by 
an ingrowth of proliferating maternal tissue in the region indi- 
cated at a period about corresponding with that of figs. 40, 41. 
In the preparations corresponding to the first-named figure 
cells are noticed occupying this space. They are evidently 
of the same nature as those of the rest of the newly developing 
trophospongia, and they certainly do not belong to the tropho- 
blastic (embryonic) tissues, nor can they be derived from the 
uterine epithelium which has disappeared and become disinte- 
grated prior to their appearance. 
The free spaces in the trophospongian cell-mass, as a matter 
of course, increase in number as the trophospongia increases 
in size. Their free communication with the trophoblastic 
spaces, of which we have traced the origin in preceding pages, 
is somuch more general, and the fusion of the maternal tropho- 
spongian with the embryonic trophoblastic tissue so much 
more complete, that the evidence of the early genetic stages is 
emphatically required to bring the conviction that, in the tro- 
phosphere of stages 29—82 (diagrams), two elements of 
different origin ought actually to be distinguished. Later on, 
the double nature of the trophosphere is again much more 
easily demonstrated by the different developmental phases 
which the trophoblast undergoes, and which were fully 
described in the preceding chapter. When once that phase 
