358 



TROPICAL AMERICA AND IIS ANIMALS 



v 



/ 



being the black howler (A. nigra). Nothing, it is said, sounds more terrible than 

 the howling of these monkeys, which, w r ith short intervals, lasts from eleven o'clock 



at night until 

 daybreak. The 

 skulls of howl in cr 

 monkeys under- 

 go a kind of re- 

 trograde develop- 

 ment, in conse- 

 quence of which 

 . they assume a 



form assimilat- 

 ing to that of 

 lower mammals, 

 such as Carniv- 

 ora, rather than 

 the type distinc- 

 tive of othermon- 

 keys. The em- 

 bryonic skull, on 

 the other hand, is 

 essentially of the 

 monkey type. 

 The degeneration 

 displays itself in 

 the leno-thenini'- 

 of the facial 

 region, so that 

 the skull gradu- 

 ally passes from 

 a short to a 

 medium, or even 

 long type ; thus 

 most of the ce- 

 phalic indices be- 

 come much lower 

 than in any other 

 monkeys, while 

 the hemispheres 

 extend to a smal- 

 ler degree over 

 the cerebellum in 

 the adult than 

 in the young. 

 Although the thry marmosets, which form a family {Hapalidce) 

 by themselves, resemble the other New World monkeys in their broad 



RED HOWLEK. 



