EARLY. ONTOGENETIG PHENOMENA IN MAMMALS. 109 
in which, as was hinted at above, we might be tempted 
to deny the presence of any placenta, and which yet, for 
several reasons, I do not consider as primitive in respect 
to placentation. The so-called diffuse placenta has been 
looked upon by Strahl and the older anthors as_ the 
necessary starting-point from which more complicated and 
more specialised systems of placentation should be derived. 
In this they were wrong. The presence of this diffuse 
placentation in such orders as Lemures, Cetacea, Edentata, 
and Ungulates, which anatomically are widely separated, as 
well as its absence in the placentiferous Didelphia are facts 
that should render us diffident in pronouncing the diffuse 
arrangement to be archaic, and that should encourage us to 
consider whether perhaps it might not be degenerative or 
secondary simplified, similarly as the omphaloidean placen- 
tation of the opossum is most probably a secondary simplifica- 
tion of arrangements such as we find them in Perameles. 
In order to develop this more fully I will go back to 
Schoenfeld’s latest contribution to the subject. In his com- 
parative resumption of the facts established for the rabbit 
and the dog he says (03, p. 813) : 
“ In comparing the results obtained in these two mammals 
considerable analogies can be detected in the genesis of their 
placenta. I wish to throw fuli light onthe absolutely passive 
part that is played by the epithelium of the uterus and by the 
uterine glands. Those elements are destroyed in the rabbit 
and the dog;! they give rise to débris which in the rabbit 
are resorbed by the plasmodium, but especially by maternal 
leucocytes and by decidual elements (glycogen cells), which 
in their turn degenerate and are resorbed by the fcetal 
plasmodium ; in the dog the débris of the glandular cells are 
resorbed either by the foetal plasmodium or by the tropho- 
blast cells of the terminal plates. 
1 So they are, according to my own experience, in Erinaceus, Tarsius, 
Tupaja, Sciurus, Sorex (after a temporary proliferation of the maternal 
epithelium, which thus offers a more extensive pabulum to the destructive 
trophoblast cells; cf. Hubrecht, 944), Talpa, Galeopithecus, Vespertilio, 
monkeys and man. 
