286 



The Descent of Man. 



Paet iJ. 



on the principle of the division of labour, the one to act ex- 

 clusively as the bow, and the other as the iiddle. Dr. Gruber 

 takes the same view, and has shewn that rudimentary teeth are 

 commonly found on the inferior surface of the right wing. By 

 what steps the more simple apparatus in the Achetidee originated, 

 we do not know, but it is probable that the basal portions of 

 the wing-covers originally 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 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 variations in the roughness of the nervures 

 having been continually preserved. 



In the last and third Family, namely the Acridiidse or 

 grasshoppers, the stridulation is produced in a very different 

 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 hingitudinal row of minute, elegant, lancet- 

 shaped, elastic teeth, from 85 to 93 in number ;" and these are 

 scraped across the sharp, pngecting 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 lodged in a furrow de- 

 " signed to receive it, and 

 " then draws the leg briskly 

 " up and down. He does not 

 " play both fidiiles together, 

 " but alternately, first upon 

 " one and then on the other." 

 In many species, the base 

 of the abdomen is hollowed 

 out into a great cavity which 

 is believed to act as a re- 

 sounding board. In Pneu- 

 mora (fig. 15), a S. African 

 genus belonging to the same family, we meet with a new 



I'lg. 14. Hinri-legof Rtenobothruspratorum: 

 ?•, tlie stridulating ridge ; lower figure, the 

 teeth forming the ridge, much magnified 

 (from Landois). 



'^ Mr. Walsh also informs me 

 that he has noticed that the female 

 of the Platfiphjllum concavuin-, 

 ^' when captured makes a feeble 

 "grating noise by shuffling her 



*' wing-covers together." 

 *'' Landois, ibid. s. 113. 

 '' ' Insects of New England 



i?42, p. las. 



