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THE DESCENT OF MAN 



females sometimes joining in -with, their less powerful voices. 

 An excellent observer, Eengger,' could not perceive that 

 they were excited to begin by any special cause ; he thinks 

 that, like many birds, they delight in their own music, and 

 try to excel each other. "Whether most of the foregoing 

 monkeys have acquired their powerful voices in order to 

 beat their rivals and charm the females, or whether the 

 vocal organs have been strengthened and enlarged through 

 the inherited effects of long-continued use without any par- 

 ticular good being thus gained, I will not pretend to say; 

 but the former view, at least in the case of the Hylohates 

 agilis, seems the most probable. 



I may here mention two very curious sexual peculiari- 

 ties occurring in seals, because they have been supposed by 

 some writers to affect the voice. The nose of the male sea- 

 elephant {Macrorhinus prohoscideus) becomes greatly elong- 

 ated during the breeding season, and can then be erected. 

 In this state it is sometimes a foot in length. The female is 

 not thus provided at any period of life. The male makes a 

 wild, hoarse, gurgling noise, which is audible at a,great dis- 

 tance and is believed to be strengthened by the proboscis, 

 the voice of the female being different. Lesson compares 

 the erection of the proboscis with the swelling of the wat- 

 tles of male gallinaceous birds while courting the females. 

 In another allied kind of seal, the bladder-nose (^Gystophora 

 eristata), the head is covered by a great hood or bladder. 

 This is supported by the septum of the nose, which is pro- 

 duced far backward and rises into an internar crest seven 

 inches in height. The hood is clothed with short hair, and 

 is muscular; it can be inflated until it more than equals the 

 whole head in size ! The males when rutting fight furiously 

 on the ice, and their roaring "is said to be sometimes so loud 

 as to be heard four miles off. ' ' When attacked they like- 

 wise roar or bellow; and whenever irritated the bladder is 

 inflated and quivers. Some naturalists believe that the 



' "Naturgesohiohle der SSugethiere von Paraguay," 1830, s. 15, 21 



