HISTORY OF THE PRIMATES 585 



their limbs; the tail is very long and perfectly prehensile, 

 naked on the lower side near the end, which improves its grasp- 

 ing power. The hand has lost the thumb, but is used very 

 effectively as a hook. The species, ten or more in number, have 

 a wider range than those of Cebus and extend from Uruguay 

 to Mexico. 



The hov/ling monkeys {Alouatta, more commonly, but im- 

 properly, called Mycetes) are gifted with most unusual vocal 

 powers. Mr. Bates says of them : ''Morning and evening the 

 howling monkeys make a most fearful and harrowing roar." 

 ''The brief evening chorus of animals then began, the chief 

 performers being the howling monkeys, whose frightful un- 

 earthly roar deepened the feeling of sohtude which crept on 

 as darkness closed around us." ^ The tremendous volume of 

 sound which these small creatures are able to produce is due 

 to a resonating apparatus, formed by the great inflation of one 

 of the hyoid bones (see p. 67), normally the bony support of the 

 tongue. The tail is long and prehensile, with the end naked 

 beneath ; the thumb is well developed. 



The sakis (Pithecia) have long and non-prehensile tail 

 and complete thumb. The species of this genus have a re- 

 markable kind of distribution, which is rare among mammals, 

 though not infrequent for insects and birds. Each species 

 is limited to a definite area of forest along the Amazon and 

 its tributaries, which it occupies to the exclusion of the others. 

 The uakaris (Cacajao) are distinguished by the tail, which is 

 much shorter than in any other of the Cebidse. 



Finally, may be mentioned the nocturnal douroucoulis 

 {Nyctipithecus) , which have long, non-prehensile tail and well- 

 developed thumb. Mr. Bates describes them thus: "A third 

 interesting genus of monkeys, found near Ega, are the Nycti- 

 pitheci, or night apes, called Ei-a by the Indians. . . . They 

 sleep all day long in hollow trees and come forth to prey on 

 insects and eat fruits only at night. They are of small size, 



1 Bates, Naturalist on the Amazons, London, 1875, pp. 32, 140. 



