Chap. XVIII. VOCAL OKGANS. 277 



does not believe that the male is more noisy than the 

 female. Hence, these latter monkeys probably use their 

 voices as a mntual call ; and this is certainly the case 

 with some qnadrupeds, for instance with the beaver.^ 

 Another gibbon, the E. agilis, is highly remarkable, 

 from having the power of emitting a complete and 

 correct octave of musical notes,^ 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 Mycetes caraya are one-third 

 larger in the male than in the female, and are wonder- 

 fully powerful. These monkeys, when the weather is 

 warm, make the forests resound durins: the mornino: and 

 evening with their overwhelming voices. The males 

 begin the dreadful concert, in which the females, with 

 their less powerful voices, sometimes join, and which 

 is often continued during many hours. An excellent 

 observer, Rengger,^ could not perceive that they were 

 excited to begin their concert 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 to charm the females — 

 or whether the vocal organs have been strengthened 

 and enlarged through the inherited effects of long-con- 

 tinued use without any particular good being 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 pecu- 

 liarities occurring in seals, because they have been sup- 



5 Mr. Green, in * Journal of Linn. Soc' vol. x. Zoology, 18G9, p. 3G2. 

 c C. L. Martin, ' General Introduction to the Nat. Hist, of Mamm. 

 Animals,' 1841, p. 431. 



• ' Naturgescliichte der Sdugethiere von Paraguay,' 1830, s. 15, 21. 



