S76 



THE DESCENT OF MAN 



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 longitudinal 

 row of minute, elegant, lancet- 

 shaped, elastic teeth, from 85 to 

 93 in number;" and these are 

 scraped across the sharp, pro- 



Fia. 14.— Hind-leg of Stenobothrus . , .*■ , i ■ 



pratorum; r, the stridulating ridge; lecting nerVUreS OU the WlUg- 



lower figure, the teeth forming the i • i , , i 



ridge, much magnified (from Landois). COVerS, whlCh 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 fiddles together, but alter- 

 nately, 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 resounding board. 

 In Pneumora (Fig. 15), a South African genus belonging 



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

 Platyphyllum concavum, "when captured, makes a feeble grating noise by 

 sliuffling her wing-covers together." 



™ Landois, ibid., s. 113. 



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



