142 A. A. W. HUBRECHT. 
decidua reflexa quite removed out of the uterine lumen 
(Fig. 1483). This phenomenon of encapsulisation inside the 
mucosa has appeared independently in more than one order 
of mammals, and can be observed in all its transition stages 
in different genera (Vespertilio [ Fig. 159], Rodents, etc.). 
The question may be raised—but cannot yet be solved for 
the present—whether perhaps the placentation of the catar- 
rhine monkeys has not arisen by secondary modification out 
of one in which a distinct decidua reflexa existed. Different 
details seem to point in this direction; the investigation of 
the placentation of more genera of monkeys than have up to 
the present been subjected to research on this point is very 
desirable. 
The removal of the developing blastocyst out of the 
uterine lumen and its total enclosure by a decidua capsularis 
is a phenomenon of all the more primary importance, as by 
it the phenomena of osmotic and of phagocytotic nutrition 
can be eyer so much more intensified. It is clear that the 
removal out of the uterine lumen may mean a most profuse 
extravasation of blood all round the blastocyst, combined 
with constant renewal and circulation of this maternal blood, 
which is absolutely impossible as long as the blastocyst 
remains situated in the Jumen of the uterus. Man and the 
man-apes, different genera of Rodents, as well as the hedge- 
hog (Hrinaceus) and Gymuura have realised this arrangement, 
of which later investigations may yet bring to light new 
examples. We are certainly justified to say that this pheno- 
menon of the formation of a decidua capsularis must have 
made its first appearance already in a very early moment of 
the phylogeny of the placentary arrangements. 
Diametrically opposed to the intensification of both phage- 
cytotic and osmotic processes, as it 1s presented to us wherever 
a decidua capsularis has come to be developed, is another 
phenomenon which, by the very nature of it, excludes the 
combination of it with encapsulisation, viz. the early increase 
in size of the blastocyst, by which its total surface, in com- 
parison to that of the actual embryonic surface, becomes ever 
