688 The American Naturalist. [August, 
the Primates we must first commence with the non-deciduate 
diffuse condition as found in Man, the later restriction of the 
placental area brings about complications in the relations of 
the maternal to the foetal surfaces, resulting in the formation 
of a decidua. Hubrecht himself admits that Tarsius is very 
specialized in not exhibiting in its early stages the diffuse con- 
dition of the placenta found in the Anthropoids. It seems to 
me that it is a most difficult problem to attempt to derive the 
typeof placentation of the Apes from that of Erinaceus. In 
the latter genus the placenta is derived from the allantois, 
which is a large free organ before it unites with the chorion. 
Then, again, in Erinaceus there is no early stage where the 
mesoblast lines the whole blastocyst as in Tarsius, and a por- 
tion of which membrane takes a share in the formation of the 
placental anlage. The Insectivora, however primitive they are 
in many respects, are greatly specialized in their dentition and 
placentation. 
Huxley remarks: “If Gymnura possessed a diffuse placen- 
tation, it would be an excellent representative of an undiffer- 
entiated Eutherian.” Again, he says: “ The derivation of all 
Eutheria from animals which, except for their placentation, 
would be insectiverous, is a simple deduction from the law of 
evolution.” That some Insectivora are highly degenerate in 
their cranial and dental structures, I think must be admitted. 
I refer particularly to Hemicentetes, whose supposed primitive 
type of molars is clearly a case of degeneration from the more 
normal form of tooth occurring in Centetes. 
Until it is disproved by further investigations on the early 
stages of Lemurs, I think it is most plausible to’ assume that 
the diffuse placenta of the Lemuroidea is one of the ancestral 
stages in the evolution of the Anthropoid placentation, and in 
the case of Man this diffuse non-deciduate stage is recapitulated 
in the ontogeny of Homo. , 
As far as the paleontological evidence goes it is decidedly 
in favor of the view that Apes and Lemurs are closely related. 
Beginning with the earliest known Lemur, Anaptomorphus, this 
genus shows tendencies towards the Anthropoids, and when 
we pass up into the Oligocene of the Old World, Adapis 1s 4 
