Chap. X.] ORTHOPTERA. 345 



wing-covers, and which has probably the effect of increas- 

 ing the sound." 34 



We thus see that the musical apparatus is more differ- 

 entiated or specialized in the Locustidse, which includes, 

 I believe, the most powerful performers in the Order, than 

 in the Achetidse, in which both wing-covers have the 

 same structure and the same function. 35 Landois, however, 

 detected in one of the Locustidse, namely, in Decticus, 

 a short and narrow row of small teeth, mere rudiments, on 

 the inferior surface of the right wing-cover, which under- 

 lies the other and is never used as the bow. I observed 

 the same rudimentary structure on the under side of the 

 right wing-cover in Phasgonara viridissima. Hence we 

 may with confidence infer that the Locustidse are de- 

 scended from a form, in which, as in the existing Ache- 

 tidse, 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 be- 

 came differentiated and perfected, on the principle of the 

 division of labor, the one to act exclusively as the bow 

 and the other as the fiddle. By" what steps the more 

 simple apparatus in the Achetidse 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 ac- 

 cidentally 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. 



34 "Westwood, ' Modern Class, of Insects,' vol. i. p. 453. 



» Landois, ibid. s. 121, 122. 



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



