STUDIES IN MAMMALIAN EMBRYOLOGY. 327 
glands being cut transversely) were more than once encoun- 
tered between the trophospongian cells, evidently embedded 
there temporarily and on the way of further disintegration. 
They were already noticed above (p. 322). 
This phenomenon corresponds to what we noticed in figs. 8 a 
and 39 at younger stages when not the trophospongian ele- 
ments but the trophoblast-cells had to contend with the 
evidently stronger resistance against disintegration offered by 
the cellular constituents of the uterine glands. 
But it is especially at the extreme outer border of the tro- 
phosphere that peculiar phenomena deserve our attention. 
Sometimes the boundary line between trophospongia and 
external decidua is flat and regular (fig. 47), the decidual 
elements always being in apparent retrogressive stages, which 
will be discussed further on. Generally, however, the line of de- 
marcation is far from being so regular, but is, on the contrary, 
considerably indented and ragged, patches of the decidual tissue 
projecting between the trophospongian cells, and being recog- 
nisable in their proper character: (a) by their partial adhe- 
rence to the decidual stroma; (6) by their histological 
character and their relation towards the staining reagent; (c) 
by their varied aspect in different sections, different embryos, 
and different ages. The discussion of the eventual physio- 
logical significance cf these phenomena is also better reserved 
for the following chapter. 
Recapitulating the origin of trophospongia and deciduo- 
fracts out of maternal tissue, s. stv. out of endothelium of the 
blood spaces of the decidual swelling, close to the blastocyst, 
two points should still be insisted upon : 
(1) That I cannot positively exclude the possibility that 
perhaps cells belonging to the decidual stroma may not at the 
time the trophospongia is formed take part in its formation. 
So much is certain that if they play any part at all, this is 
very much subordinate to that of the endothelial elements. I 
must at the same time repeat that it is in no way a pheno- 
menon of perivascular proliferation by which we can account 
for the origin of the hedgehog’s trophospongia. This seems, 
VOL, XXX——PART 3, NEW SER, Y 
