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 



FIG. 87. The arm of Hapalemur gtistus, showing its 

 brachial mammae. 



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 



