572 The American Naturalist. [July, 
A very important point in the early development of Tarsius 
is that the surface of the chorion never becomes entirely vil- 
lous asin man. In Cercocebus the villosities of the chorion are 
limited to dorsal and ventral areas. The fact that Tarsius has 
omitted this diffuse stage of the placenta found in the true 
Anthropoids, clearly shows that this is a specialization in the 
development of this genus. Hubrecht remarks in referring to 
this completely villous stage of the chorion of the Anthropoids: 
“Ich halte den Zustand welcher beim Menschen und Anthro- 
poiden sich erhalten hat, tur sehr primitive.” Again, he says: 
“Somit neige Ich zu der Ansicht hin, dass in diesem ununter- 
brochenen Zottenpelz ein primitiver charakter erhalten, und 
dass die partielle Zottenbildung von Niederen Affen, wie der 
Fig. K giebt; eher als ein abgeleiterer Zustand zu betrachten 
sei”! The reference he gives to Fig. K is the condition found 
in Cercocebus, where the villous areas of the chorion are re- 
stricted to patches above and below the fetus. In Erinaceus 
the amniotic cavity is formed by a splitting of the epiblast, so 
that the portion of this membrane below the amnion is the 
only part directly concerned in the growth of the embryo; 
accordingly Hubrecht designates this as the epiblast proper, © 
whereas the remainder of the epiblast not used in the forma- 
tion of the embryo he calls the trophoblast. Prof. Hubrecht 
considers the development of the amnion as occuring in Eri- 
naceus the primitive one, whereas the more ordinary way by 
folds growing over the embryo and uniting, as a secondary 
process. Tarsius follows the more normal formation of the 
amnion by the folding off of the embryo. 
In an early stage in the development of Tarsius, there occurs 
a thickening in the external epiblast or trophoblast, and on 
the opposite side from the embryonic area, this is the placental 
“anlage” or rudiment. It is important to notice that the first 
indication of the placenta is situated ventrally in relation to 
the embryo, as in the Apes it is dorsal. Again, the origin of 
the placenta in Tarsius has no connection whatever with the 
allantois, and the latter organ never becomes directly con- 
nected with the placenta as will be shown later. At the time 
1 Die Keimblase von Tarsius, Leipzig, 1896, pp. 171 and 172. 
