128 A. A. W. HUBRECHT. 
of man and the hedgehog consists in the greater freedom and 
greater extension of those villi in which the embryonic blood 
circulates, bathed by the maternal blood in the trophoblastic 
lacune. These villi are in no way to be looked upon, as 
many of the text-books yet have it, as so many ingrowths 
which the chorion has sent out to penetrate into the maternal 
tissue. They are in man, and also in monkeys and Tarsius, 
erowths not of a centrifugal but of a centripetal nature, as 
we have also had occasion to describe the corresponding 
structures in the hedgehog, in Sorex, Tupaja, ete. The 
freedom with which they float about in the maternal blood is 
another characteristic of man and the monkeys (Figs. 141, 142). 
In Tarsius and in the hedgehog their arrangement is more that 
of a suspension in a very delicate and at the same time most 
intricate trellis-work formed by the trophoblast cells that have 
become spun out into this. When the connecting trabeculee of 
this trellis-work are suppressed, as we see it in the higher 
Primates, the surface available for osmotic interchange is 
naturally increased, and the free movements of the villi may 
also be considered as an advantageous circumstance 
(Fig. 144). 
About the histological details of the placenta of man and 
monkeys certain points are yet in dispute, and such investi- 
gators as Selenka (00a) and Strahl (’02, 704) seem to be 
willing to put to the account of maternal proliferation more 
than they are justified to. An agreement will, I expect, 
soon be reached, and the latest researches on these and other 
orders of mammals (Bryce, 708) seem to point in the direction, 
which Duval (’88) and myself (’88) have been indicating for 
the last twenty years, viz. final destruction of the maternal 
epithelium and circulation of the maternal blood in tropho- 
blastic lacunee. 
The histological details of the placenta of the catarrhine 
monkeys resemble very closely those of man and the Anthro- 
pomorphe. Whether their double placenta (Fig. 132) is a 
primitive or—as I hold it to be—a secondary arrangement 
(derived from an ancestral decidua capsularis) must be solved 
