Chap. XII.J REPTILES. 37 



tlie male is longer than that of the female. In some, the 

 plastron or lower surface of the shell of the male is slight- 

 ly concave in relation to the back of the female. The 

 male of the mud-turtle of the United States ( Chrysemys 

 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, bellowing noise, which can 

 be heard at the distance of more than a hundred yards ; 

 the female, on the other hand, never uses her voice.^° 



Crocodilia. — The sexes apparently do not differ in 

 color; nor do I know that the males fight together, 

 though this is probable, for some kinds make a prodi 

 gious display before the females. Bartram*^ describes the 

 male alligator as striving to win the female by splashing 

 and roaring in the midst of a lagoon, " swollen to an ex- 

 tent ready to burst, with his head and tail lifted up, he 

 spins or twirls round on the surface of the water, like an 

 Indian chief rehearsing his feats of war." During the sea- 

 son of love, a musky odor is emitted by the submaxillary 

 glands of the crocodile, and pervades their haunts." 



Ophidia. — I have little to say about Snakes. Dr. 

 Gtinther informs me that the males are always smaller 

 than the females, and generally have longer and slenderer 

 tails ; but he knows of no other difference in external 

 structure. In regard to color, Di-. Gilnther can almost al- 

 ways distinguish the male from the female \)j his more 



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

 *^ See my ' Journal of Researches during the Yoyage of the " Bea- 

 gle," ' 1845, p. 384. 



« 'Travels through Carolina,' etc., 1Y91, p. 128. 



*^ Owen, ' Anatomy of Vertebrates,' vol. i. 1866, p. 615. 



