346 THE DESCENT OF MAN. 



have not acquired more atrongly-marked sexual characters; for 

 though cold-blooded their passions are strong. Dr. Giinther in- 

 forms me that he has several times found an unfortunate female 

 toad dead and smothered 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 breeding- 

 season, and with so much violence, that one had its body ripped 

 open. 



Frogs 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, ac- 

 cording to our taste, a singularly inappropriate expression. 

 Nevertheless, certain frogs sing in a decidedly pleasing manner. 

 Near Rio 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 wa- 

 ter, which sent forth sweet chirping notes in harmony. The va- 

 rious 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 the males are more 

 highly-developed than those of the females. In some genera the 

 males alone are provided with sacs which open into the larnyx.'^' 

 For instance, in the edible frog (Rana esculenta) "the sacs are 

 "peculiar to the males, and become, when filled with air in 

 "the act of croaking, large globular bladders, standing 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.=° In the 

 several genera of the family the vocal organs differ considerably 

 in structure, and their development in all cases may be attributed 

 to sexual selection. 



REPTILES. 



Chelonia. — Tortoises and turtles do not offer well-marued 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 in relation tq the back of the 

 female. The male of the mud-turtle of the United States (Chrys- 

 emys picta) has claws on its front-feet twice as long as those of 

 the female; and these are used when the sexes unite.'' With the 

 huge tortoise of the Galapagos Islands (Testudo nigra) the males 

 are said to grow to a larger size than the females: during the 

 pairing season, and at no other time, the male utters a hoarse bel- 



" Bell, 'History of British Reptiles," 1849, p. 93. 



« J. Bishop, in 'Todd's Cyclop, of Anat. and Phys.' vol. iv. p. 1503. 



=»Ben, ibid. p. 112-114. 



» 'Mr. C. J. Maynard, 'The American Naturalist,' Dec. 1869, p. 555. 



