SPIDER-MONKEYS. 



159 



tail, with the naked parts of the face flesh-coloured ; the females being of a paler 

 hue. The thumb is totally wanting. Another variety, with a distinct rudiment 

 of a thumb, is of a dark brown colour, with white on the sides of the face. 



THE WOOLLY SPIDER-MONKEY (J nat. size). 



THE SPIDER-MONKEYS. 



Genus Aides. 



The spider-monkeys may be regarded as those members of the group most 

 admirably adapted for a purely arboreal life, as is especially shown by their slight 

 bodies, the long prehensile tail, naked below at the end, and the long spider-like 

 limbs from which they derive their popular title. In the rudimentary condition, or 

 total absence, of their thumbs, the spider-monkeys may be regarded as holding the 

 same relationship to the sapajous as is presented by the thum bless monkeys (Colobus) 

 of Africa, to the langurs (Semnopithecus) of India ; and it is probable that in both 

 instances the abortion of the thumb is due to the uselessness of this digit in a 

 hand adapted to act merely as a kind of hook in swinging from branch to branch. 



