136 A. A. W. HUBRECHT. 
which the primarily adhesive trophoblast began to combine 
phagocytosis with mere adhesiveness. As the total surface 
of the blastocyst increased, and as the adhesion became 
localised in the maternal carunculi and embryonic cotyledons, 
the remaining surface of the blastocyst developed such 
properties that the uterine milk was easily absorbed by its 
trophoblastic outer layer. Such a process seems to have 
been further again specialised in the pig and the Lemurs, 
in which certain sac-like receptacles (Figs. 152 and 153) serve 
for the reception of foodstuffs prepared by the maternal 
mucosa, and hoarded by the embryo in these pouches. But 
I continue to maintain that these were not primitive arrange- 
ments, but derived from those where, as in Carnivores, the 
foodstuffs were sought for yet inside the uterme mucosa 
(and not in the uterine lumen) by the proliferating phagocytic 
trophoblast. 
Besides by the direct phagocytic process, nourishment and 
then especially oxygen is yet furnished to the embryonic 
blood-vessels by the osmotic processes which take place 
between the maternal blood and the embryonic ; and we may 
perhaps say that there has been a certain amount of compe- 
tition between the two systems as to which of them should be 
foremost in providing for the requirements of the internal 
parasite, the embryo. So differentiation and adaptation has 
run along very different lines, now specialising in one, now 
in the other of these two directions, but in some combining 
the effects of both. It is probable that in these latter the 
beneficial effect obtained was the maximum, and that this has 
at the same time revealed itself by higher development of 
the embryo in general. And if we try to class the mammals 
according to this principle I think we may arrive at making 
a very fair bid for a natural arrangement both as far as 
placental and other anatomical characters are concerned. 
The early Carnivores have been united by paleontologists 
in the fossil order of Creodonts, relationships between these 
and the early Ungulates being recognised. Many recent 
Insectiyores also reveal by different points their more primi- 
