574 The American Naturalist. [July, 
koidal-deciduate, whereas in the Lemurs it is diffuse and nearly 
the whole surface of the chorion is villous. It appears then 
that we are dealing with two types of placentation fundament- 
ally different in structure and origin; however, the early de- 
velopment of the placenta in the Lemurs is totally unknown 
so far as I have been able to learn. Turner has described the 
placentation in the genus Lemur, and Alphonse Milne-Ed- 
wards in the Indrisine Lemurs. In all known forms of 
Lemurs the allantois is a huge sac enveloping the embryos, 
and often having numerous diverticule. Milne-Edwards calls 
attention particularly to one point, that the external layer of 
the allantois has no intimate connection with the chorion, 
and moreover it is not vascular. The question then arises, if 
the allantois takes no share in the formation of the placenta 
in the Lemurs, the latter organ probably originates from the 
chorion as in the Apes. This point is not yet proven, and it 
remains for further research to find out how the connection 
between fœtus and chorion is brought about in the Lemurs. 
Dr. Charles Sedgwick Minot, to whom I am greatly indebted 
for an important letter on the question of the placentation of 
the Primates, in his great work on “ Human Embryology,” 
divides the placentation of the Mammalia into two types, in 
the first group the allantois is large and supplies the chorion 
with its blood-vessels; this is the condition occurring in the 
majority of the Mammalia, excepting some of the Primates. 
In the more highly differentiated Anthropoidea, the allantois 
takes no part in the formation of the placenta, and the blood- 
vessels arise in the chorion and bauchstiel in situ. Dr. Minot 
designates this type as chorionic placentation. I quote two 
passages from his letter which have an important bearing on 
the question of the relations of the placentation of the Apes to 
that of the Lemurs: “ Unfortunately, nothing satisfactory is 
known of the early stages of Lemurs, which are the critical 
ones for placental homologies, but as far as our fragmentary 
knowledge goes, I fail to recognize any impossibility of regard- 
ing the placentas of Monkeys and of Lemurs as of one funda- 
mental type.” Again Dr. Minot says: “ Whether a placenta 
is diffuse or not cannot decide as to its homologies, for the 
