REPTILES AND AMPHIBIA 



175 



twisting its tail round her. The male in this amplexus is 

 below the female, and his tail is passed over her loins from 

 the left side to the right. The sexual difference is thus a 

 functionally produced hypertrophy of the tail and hind limbs. 

 The tail of the male has grown shorter because it is the 

 proximal part which is most used. 



In many species the males are more vividly coloured than 

 the females, and there is probably no other reason for this 

 than the greater sexual excitement of the males, which, as I 

 have suggested in many other cases, causes through nervous 

 stimulation more active production of pigment in the skin. 



The above remarks all refer to the family Salamandridse. 

 I have not seen descriptions of any sexual differences in the 

 other families of the Urodela. 



Anura. In frogs and toads generally, prominences 

 become developed on the front legs of the males during 

 the breeding season. There can be little doubt that these 

 are hereditary, but there can be equally little doubt that 

 they are the direct result of the pressure to which the 

 parts affected are subjected in the process of copulation. 

 There is no penis or intromittent organ in the frogs and 

 toads, but in the case of the Common Frog, the male seeks 

 the female in spring, and clasps her body tightly with his 

 fore limbs, remaining in this position for days or even 

 weeks till the ova of the female are discharged, when they 

 are fertilised by the simultaneous emission on the part of 

 the male. The cushion or tubercle in the Common Frog is 

 situated on the palmar surface of the innermost of the four 

 fingers, and this is the surface which is pressed by muscular 

 action against the body of the female. 



Another male peculiarity in frogs is the possession of 

 vocal sacs. These are not present in the Common Frog of 

 England, Rana temporaria, but are well developed in the 

 Edible Frog of the continent, Rana esculenta. The vocal sacs 



