64 REPTILES 



horny tubercles on the hind legs, which afford good specific 

 characters. As in crickets, there is an active and a passive set 

 of these tubercles, the lower patch being rubbed against the 

 upper one, and thereby producing a musical note, as does the 

 bow of a violin. The note is clear and distinct, audible at a 

 considerable distance. As the tubercles are developed only in 

 the males, they are probably used to produce musical notes 

 solely during the breeding season, thereby informing the 

 females of the proximity of members of the opposite sex. 

 These musical instruments of the Cinostemidce are almost 

 unique among vertebrates ; the only other instances of the de- 

 velopment of a somewhat analogous apparatus in that group 

 occurring among the "geckos of the genera Teratoscincus and 

 Ptenopus, which are enabled to produce musical notes by 

 means of friction between the horny rings of their tails. This 

 sound, which is like the chirping of grasshoppers, is, however, 

 emitted by both sexes, and may be for the purpose of attract- 

 ing those insects within reach. Very probably, the clicking cry 

 of other geckos is, at least in part, of a sexual nature, and like- 

 wise the chirp of lizards. Chamaeleons both hiss faintly and 

 grunt ; but these sounds are probably uttered for the purpose of 

 frightening enemies, as is certainly the case with the hissing of 

 serpents and monitors. 



It is by no means easy, as in the case of cries, to determine 

 in all instances whether scents (or their opposite) are for the 

 purpose of attracting the individuals of a species or for repelling 

 enemies. If, however, the sense of smell in reptiles is akin to 

 that in ourselves, it may be presumed that agreeable scents are 

 connected with the sexual function, while disagreeable ones 

 are for the purpose of repelling enemies. Under the former 

 category probably comes the musky odour exhaled by croco- 

 diles from two pairs of glands, one of which is situated on the 

 throat and the other near the vent. The scent, it has been 

 suggested, leaves a musky aroma along the line of water 

 traversed by the animal, by means of which another individual 

 is enabled to ascertain its whereabouts. 



On the other hand, the exceeding ill-smelling odour exhaled 

 by Ckmmys leprosa and certain other terrapins and tortoises 

 can scarcely be regarded in any other light than as a defence 

 against enemies. In this instance the secretion, which is de- 



