264 SEXUAL SELECTION: MAMMALS. [Part II. 



bon, the H. agilis, is highly remarkable, from having the 

 power of emitting a complete and correct octave of musi- 

 cal notes, 6 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 wonderfully powerful. These mon- 

 keys, when the weather is warm, make the forests resound 

 during the morning 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, Kengger, 7 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 power- 

 ful voices in order to beat their rivals and to charm the 

 females — or whether the vocal organs have been strength- 

 ened and enlarged through the inherited effects of long- 

 continued use without any particular good being gained 

 — I will not pretend to say ; but the former view, at least 

 in the case of the Hylobates agilis, seems the most prob- 

 able. 



I may here mention two very curious sexual pecu- 

 liarities occurring in seals, because they have been sup- 

 posed by some writers to affect the voice. The nose of 

 the male sea-elephant (3Iacrorhinus proboscideus), when 

 about three years old, is greatly elongated during the 

 breeding-season, and can then be erected. In this state it 

 is sometimes a foot in length. The female at no period 

 of life is thus provided, and her voice is different. That 



6 C. L. Martin, ' General Introduction to the Nat. Hist, of Maram. 

 Animals,' 1841, p. 431. 



1 ' Naturgeschichte der Saugethiere von Paraguay,' 1830, s. 15, 21 



