ATAVISM. 165 
have disappeared, whilst in the ring-tailed, black, and 
mongoose lemurs the pectoral pair alone persist. 
The persistence of the pectoral pair in these lemurs 
may possibly be explained by the curious manner in 
which they carry the young. Lemur macaco has usually 
one at a birth, and this is carried about entwined around 
its mother in the manner represented in fig. 88. I have 
watched the young lemur, and find that it rarely leaves 
its mother, and it is clear that whilst holding on in this 
Fic. 87.—The arm of Hafalemur guseus, showing its 
brachial mammee. 
way it would be difficult for it to use the inguinal teats, 
if any existed, whilst it is within easy access of the 
pectoral pair. It seems to me reasonable to suppose 
that this habit of carrying the young has led to the 
pectoral teats being most used, and their gradual 
enlargement from increased use would slowly bring 
about the suppression of the little used inguinal set. 
Usually the nipples are present in the male, and have 
a disposition corresponding to that of the female. 
A review of the arrangement of the milk glands in 
mammals generally indicates that primitively they were 
