350 The Descent of Man. Paat 11 



these animals have not acquired more strongly-marked sexual 

 characters ; for though cold-blooded their passions are strong. 

 Dr. GUnther informs me that he has several times found an 

 unfortunate female toad dead and snaothered from having been 

 so closely embraced by three or four males. Frogs have been 

 observed by Professor Hoffman in Giessen fighting all day long 

 during the oreeding-season, and with so much violence, that one 

 had its body ripped open. 



Progs and toads offer one interesting sexual difference, namely, 

 in the musical powers possessed by the males ; but to speak 

 of music, when applied to the discordant and overwhelming 

 sounds emitted by male bull-frogs and some other species, seems, 

 according to our taste, a singularly inappropriate expression. 

 Nevertheless, certain frogs sing in a decidedly pleasing manner. 

 Near Eio Janeiro I used often to sit in the evening to listen to a 

 number of little Hylse, perched on blades of grass close to the 

 water, which sent forth sweet chirping notes in hai'mony. The 

 various sounds are emitted chiefly by the males during the 

 breeding-season, as in the case of the croaking of our common 

 frog.*' In accordance with this fact the vocal organs of tlie 

 males are more highly-developed than those of the females. In 

 some genera the males alone are provided v/ith sacs which open 

 into the larynx.*" For instance, in the edible frog {Liana escuh nta) 

 " the sacs are peculiar to the males, and become, when filled 

 " with air in the act of croaking, large globular bladders, stand- 

 " ing out one on each side of the head, near the corners of the 

 " mouth." The croak of the male is thus rendered exceedingly 

 powerful ; whilst that of the female is only a slight groaning 

 noise.*" lu the several genera of the family the vocal organs 

 differ considerably in structure, and their development in all 

 cases may be altributed to sexual selection. 



Ebptiles. 



Cheloiiia. — Tortoises and turtles do not offer well-marked 

 sexual differences. In some species, the tail of the male is 

 longer than that of the female. In some, the plastron or lower 

 surface of the shell of the male is slightly concave m relatioi. to 

 the back of the female. The male of the mud-turtle of the 

 United States (Ohrysemys picta) has claws on its front-fett 

 twice as long as those of the female ; and these are used when 



" Bell, 'History of Bi-itish " J. Bishop, in 'Todd's Cyclop 



K(>ntiles,' 1849, p. 93. of Anat. ,-ind Piivs.' vol. iv. f Xhdi 



»» Bell, ibid, p, 112-lU. 



