3826 A. A. W. HUBRECHT. 
abundantly found in the neighbourhood can easily be com- 
pared, as far as size and shape are concerned. Also in a 
following chapter I shall have to return to this feature, similar 
preparations in other mammals (rabbit, &c.) having induced 
other authors (Masquelin and Swaen, Frommel, &c.) to discuss 
the possible significance of certain decidual layers as seats of 
formation of red blood-corpuscles. 
It must finally be noticed that the thickness of the layer of 
the deciduofracts as the outer peripheral layer of the tropho- 
spongia varies very much ; sometimes ouly very few, sometimes 
numerous deciduofracts separating the more compact tropho- 
spongian tissue from the external decidua (fig. 44). And 
whereas in every preparation it is possible to find transition 
stages between the smaller trophospongia-cells and the large 
deciduofracts, there is never any transition stage which would 
allow of the conclusion that the decidual tissue outside the 
trophosphere gradually changes into this, its cells first assum- 
ing the shape of the peripheral deciduofracts and then of the 
deeper trophospongian layers. As the series of sections 
through all the successive stages all point in the same direc- 
tion, this excludes the possibility of constant new additions 
being made from the outer decidual tissue to that of the 
trophosphere, and we will have to place the increase of the 
latter to the account of its own elements, increasing at the 
first instance by self-division and proliferation. Still we have 
seen that (in the stage of figs. 40 to 42) the elements of the 
trophospongia do in the first instance arise out of those of the 
decidual swelling. 
Another detail which belongs to the ines of the 
trophospongian region deserves special notice. Among the 
true trophospongian polygonal cellular elements, but more 
often among the deciduofracts, patches of tissue are encoun- 
tered, which to all appearance do not belong to the tropho- 
spongia, but which have, on the contrary, the aspect of 
isolated patches of the tissue that composes the outer decidual 
layers. Even remnants of the epithelium-cells of the uterine 
glands (cf. fig. 89) still adhering together as rings (the 
