356 SEXUAL SELECTION. Part II. 



teeth, mere rudiments, on the inferior surface of the 

 right wing-cover, which underlies the other and is 

 never used as the bow. I observed the same rudi- 

 mentary structure on the under side of the right wing- 

 cover in Phasgonura viridissima. Hence we may with 

 confidence infer that the Locustidaa are descended from 

 a form, in which, as in the existing Achetidas, both 

 wing-covers had serrated nervures on the under surface, 

 and could be indifferently used as the bow ; but that 

 in the Locustidae the two wing-covers gradually became 

 differentiated and perfected, on the principle of the divi- 

 sion of labour, the one to act exclusively as the bow and 

 the other as the fiddle. By what steps the more simple 

 apparatus in the Achetidae originated, we do not know, 

 but it is probable that the basal portions of the wing- 

 covers overlapped each other formerly as at present, and 

 that the friction of the nervures produced a grating 

 sound, as I find is now the case with the wing-covers 

 of the females. 36 A grating sound thus occasionally 

 and accidentally made by the males, if it served them 

 ever so little as a love-call to the females, might readily 

 have been intensified through sexual selection by fitting 

 variations in the roughness of the nervures having been 

 continually preserved. 



In the last and third Family, namely the Acridiidae 

 or grasshoppers, the stridulation is produced in a very 

 difYerent manner, and is not so shrill, according to Dr. 

 Scudder, as in the preceding Families. The inner sur- 

 face of the femur (fig. 13, r) is furnished with a longi- 

 tudinal row of minute, elegant, lancet-shaped, elastic 

 teeth, from 85 to 93 in number ; 37 and these are scraped 



36 Mr. Walsh also informs me that he has noticed that the female of 

 the Platyphyttum concavu.m, "when captured makes a feeble grating 

 " noise by shuffling her wing-covers together." 



3 7 Landois, ibid. s. 113. 



