602 THE DESCENT OF MAN. 



have produced an inherited effect on the vocal or -n<? of 

 the stag as well as of other male animals ? This appears to 

 me, in our present state of knowledge, the most probable 

 view. 



The voice of the adult male gorilla is tremendous, and 

 he is furnished with a laryngeal sack, as is the adult malo 

 orang.* The gibbons rank among the noisiest of monkeys, 

 and the Sumatra species (Hylobate* syudactylus) are also 

 furnished with an air sack; but Mr/Blyth, who has had 

 opportunities for observation, does not believe that the male 

 is noiser than the female. Hence, these latter monkeys 

 probably use their voices as a mutual call ; and this is cer- 

 tainly the case with somu quadrupeds, for instance the 

 beaver, f Another gibbon, the H. agilis, is remarkable, 

 from having the power of giving a complete and correct 

 octave of musical notes, J which we may reasonably suspect 

 serves as a sexual charm; but I shall have to recur to this 

 subject in the next chapter. The vocal organs of the 

 American Mt/cetes caraya are one-third larger in the malo 

 than in the female, and are wonderfully powerful. These 

 monkeys in warm weather make the forests resound at 

 morning -and evening Avith their overwhelming voices. 

 The males begin the dreadful concert and often continue 

 it during many hours, the females sometimes joining in 

 with their less-powerful voices. An excellent observer 

 Rengger 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 particular good 

 being thus gained I will not pretend to say; but the 

 former view, at least in the case of the Hylobatcs agilis, 

 seems the most probable. 



*O\ven, " Anatomy of Vertebrates," vol. iii, p. 600. 



\ Mr. Green, in " Journal of Linn. Soc. " vol. x, Zoology, 1869, p. 

 363. 



t C. L. Martin, " General Introduction to the Nat. Hist, of Mamm. 

 Animals," 1841, p. 431. 

 "Naturgescuickte der Saugetliiere von Paraguay," 1830, ss. 



