730 THE DESCENT OF MAN 



almost certainly have been produced; and these, if they 

 proved in any way serviceable, might readily have been 

 modified or intensified by the preservation of properly 

 adapted variations. The lowest Vertebrates which breathe 

 air are Amphibians; and of these, frogs and toads possess 

 vocal organs, which are incessantly used during the breed- 

 ing season, and which are often more highly developed in 

 the male than in the female. The male alone of the tortoise 

 utters a noise, and this only during the season of love. 

 Male alligators roar or bellow during the same season. 

 Every one knows how much birds use their vocal organs 

 as a means of courtship; and some species likewise perform 

 what may be called instrumental music. 



In the class of Mammals with which we are here more 

 particularly concerned, the males of almost all the species use 

 their voices during the breeding season much more than at 

 any other time; and some are absolutely mute excepting 

 at this season. With other species both sexes, or only the 

 females, use their voices as a love-call. Considering these 

 facts, and that the vocal organs of some quadrupeds are 

 much more largely developed in the male than in the fe- 

 male, either permanently or temporarily, during the breed 

 ing season; and considering that in most of the lower classes 

 the sounds produced by the males serve not only to call but 

 to excite or allure the female, it is a surprising fact that 

 we have not as yet any good evidence that these organs are 

 used by male mammals to charm the females. The Ameri- 

 can Mycetes caraya perhaps forms an exception, as does the 

 Hylobates agilis, an ape allied to man. This gibbon has an 

 extremely loud but musical voice. Mr. Waterhouse states:" 

 "It appeared to me that in ascending and descending the 

 scale, the intervals were always exactly half tones; and I 

 am sure that the highest note was the exact octave to the 

 lowest. The quality of the notes is very musical ; and I do 



5" Given in W. 0. L. Martin's "General Introduct. to Nat. History of Mamm. 

 Animals," 1841, p. 432; Owen, "Anatomy of Vertebrates," vol. lil. p. 600. 



