116 A. A. W. HUBRECHT. 
researches of Turner, Ercolani, &c., have already years ago 
thrown a flood of light. 
We find there what we find repeated in two of the genera 
which are treated of in this paper, viz. Manis and Nyc- 
ticebus. The outer layer of the blastocyst acquires numerous 
villiferous processes that are vascularized and fit into vascular 
crypts of the maternal wall, out of which they are retracted at 
birth with the greatest facility. In Nycticebus the two epithelia, 
both the embryonic and the maternal, remain intact, and the 
osmotic interchange takes place through two cell-layers of 
different origin and of different physiological significance (phy- 
logenetically). 
As soon as the complications in this arrangement commence 
to make themselves felt, which are so varied and so charac- 
teristic in the different and so-called “deciduate” orders of 
mammals, a clear insight is much less easily obtained. 
Partly because as yet only a restricted number of genera has 
been examined sufficiently in detail; partly because when such 
investigation has taken place the different observers do not 
always concur in the interpretation of the phenomena which 
present themselves on examining the microscopical prepara- 
tions of the same species. 
A significant cell-layer is by the one declared to be maternal, 
by the other to be of embryonic origin, Maternal blood is by 
the one said to be enclosed in vascular spaces, that never lose 
their real character of further extensions of capillary vessels, 
whereas the other pretends that the maternal blood penetrates 
sometimes at a very early, sometimes at a later stage of the 
ontogenesis into lacunar spaces that are wholly surrounded by 
tissue that is exclusively of embryonic origin, 
Duval very tersely expresses the latter view, of which he is 
himself one of the staunchest advocates, as follows :—** Le 
placenta représente a son origine, une hémorragie maternelle, 
circonscrite ou enkystée par des éléments fcetaux ecto- 
dermiques.” The fact that certain interpretations based on 
older researches, that could not yet profit by the modern 
technical improvements, have been adopted in the text-books, 
