110 A. A. W. HUBRECHT. 
A second point which they have in common concerns the 
important part that is played in both cases by the foetal 
plasmodium. By its presence it brings about the destruction 
of the epithelium and of the glands; both in the rabbit and 
the dog it penetrates in the connectivo-vascular decidual 
tissue and reaches the maternal vessels, which it separates 
from their adventitial (decidual) cells. 
If, however, in these two animals, the presence of the egg 
in the uterine cavity can somehow provoke a reaction on the 
part of the connective tissue that has become decidual, which 
is characterised by an active proliferation of its elements, 
then—at the same time there exists a considerable difference 
between the two species with respect to the evolution of the 
decidual cells. In the rabbit these last named are destroyed 
wherever they come in contact with the foetal tissue, particu- 
larly with the plasmodium: m the dog, on the contrary, the 
connective tissue-cells are not destroyed; they take part in 
the constitution of the plasmodium, they fuse with it, and 
give rise to a mixed plasmodium. ‘The connective tissue-cells 
of the rabbit succumb in the struggle with the invading 
foetal elements, whereas in the dog they resist and associate 
themselves with the latter. The same is the case for the 
endothelium of the blood-vessels; it disappears in the rabbit, 
it persists in the dog. . . . The placentary ectoblast 
(Hubrecht’s trophoblast) is thus differentiated into a cyto- 
trophoblast (inner) and a plasmoditrophoblast (outer layer). 
The plasmoditrophoblast adheres at a given moment against 
the uterine epithelial symplasma and brings about the dis- 
appearance, the destruction of the latter. The plasmodi- 
trophoblast then penetrates into the modified uterine con- 
nective (decidual) tissue, which in Hubrecht’s terminology is 
known as the trophospongia. 
In invading the trophospongia the plasmoditrophoblast 
brings about the destruction of the latter in the rabbit, 
whereas in the dog it associates itself with it into a mixed 
plasmodium.”’ 
I have given this long citation because it is such a clear 
