324 



THE DESCENT OF MAN. 



covers had serrated nerviires 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 division of labor, the one 

 to act exclusively as the bow and the other as the fiddle. 

 Dr. Gruber takes the same view, and has shown that rudi- 

 mentary teeth are commonly found on the inferior surface 

 of the right wing. By what steps the more simple appa- 

 ratus in the Achetidae originated we do not know, but it is 

 probable that the basal portions of the wing-covers origi- 

 nally overlapped each other as they do at present; and that 



the friction of the nervures 

 produced a grating sound as 

 is now the case with the wing- 

 covers of the females.* A 

 grating sound thus occasion- 

 ally and accidentally made by 

 the males,if it served them ever 

 so little as a love-call to the fe- 

 males, might readily have been 

 intensified through sexual se- 

 lection by variations in the 

 roughness of the nervures hav- 

 ing been continuallypreserved . 

 leg of stenobothrus pra- ^^ ^^e last and third family, 

 the striduiating ridge ; namely, the Acridiidae or 



iwTemSmSn^a'fr?^^^^^ the stridulation 



is produced in a very differ- 

 ent manner, and according to Dr. Scudder, is not so shrill 

 as in the preceding families. The inner surface of the 

 femur (fig. 14, r) is furnished with a longitudinal row of 

 minute, elegant, lancet-shaped, elastic teeth from eighty- 

 five to ninety-three in number;! and these are scraped 

 across the sharp, projecting nervures on the wing-covers 

 which are thus made to vibrate and resound. Harris^ says 

 that when one of the males begins to play he first ^'^ bends 

 the shank of the hind-leg beneath the thigh, where it is 



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

 of the Platyphyllum concavum, " when captured, makes a feeble 

 grating noise by shuffling her wing-covers together." 



f Landois, ibid., s. 113. 



\ " Insects of New England," 1842, p. 133. 



Fig. 14, Hind-leg of Stenobothrus pra 

 torum. r 



