PEOF. W. TTTENEE ON THE PLACENTATION OF THE LEMUES. 
583 
new structural element into the consideration of the position they ought to occupy in 
the class Mammalia. If, as has been done by several eminent zoologists, the form and 
structure of the placenta are to be taken as the chief guides in the classification of the 
Mammalia, then the Lemurs can no longer be associated with those orders in which a 
discoid, deciduate placenta occurs. Not only in the form and structure of the placenta, 
but in the large size of the sac of the allantois, the Lemurs approach more closely to the 
Perissodactyla, Suina, and Cetacea than to any of the other orders of mammals, and 
ought, therefore, to be grouped along with them, if the placenta is to be taken as the 
dominant character for purposes of classification. The question, therefore, naturally 
arises whether the placental characters are of such primary importance as to outweigh, 
in framing a system of classification, those furnished by the other organic systems. The 
same question also arose in the course of an investigation into the placentation of the 
Sloths*, when I demonstrated that in Cholopus the placenta was multilobate, discoid, 
and deciduate, whilst Dr. Sharpey had previously shown that in Manis the placenta was 
diffused and non-deciduate ; so that if the placenta be taken as the basis of classification 
Manis and Cholopus could no longer be regarded as members of the same order Edentata . 
In the case of the Lemurs it will, I think, be considered by most zoologists that the 
characters of the teeth, the general configuration of the skeleton, the unguiculate digits, 
the hand-like form of the distal part of the extremities, the presence of a calcarine 
fissure in the cerebrum, and the pectoral position of at least two of the mammae are 
characters which indicate that the Lemurs have much closer affinities with those mam- 
malian orders with which it has been customary to associate them, than with the Perisso- 
dactyla, Suina, and Cetacea. Collectively these characters ought, I think, to be regarded 
as more valuable indications of structural affinity, than should the presence in the 
Lemurs of a non-deciduate, diffused placenta with a large allantois be regarded as 
indicative of structural dissimilarity from the Apes and Insectivora, though the placenta 
in the latter is deciduate and discoid and the allantois aborted. 
But though I am of opinion that the general affinities of the Lemurs are such as to 
lead one to retain them in association with the Apes and Insectivora, there can, I think, 
be no question that the diffused and non-deciduate nature of their placenta, with the 
large allantoic sac, are distinctive characters of so much importance that they cannot be 
classed in either of those orders, but have themselves an ordinal value. Hence I agree 
with those zoologists who separate the Lemurs from the Apes ; and to the distinctive 
characters derived from the teeth, skeleton, &c., advanced by previous writers, I would 
add those to be drawn from the placenta and the foetal membranes. 
In conclusion, it may not be without interest to consider how far the determination 
of the non-deciduate, diffused character of the placentation in the Lemurs affects the 
theory advanced by Professor Haeckel f, that the Half-Apes (Prosimice) were the primary 
form out of which the several orders of deciduous placental mammals had originated. 
* Transactions of the Eoyal Society of Edinburgh, 1873. 
t ‘ Natiirliche Schopfungsgeschichte.’ 
