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 viridisdma. Hence we may with 
confidence infer that the Locustidse are descended from 
a form, in which, as in the existing Achetidse, both 
wing-covers had serrated nervures on the under surface, 
and could be indifferently used as the bow ; but that 
in the Locustidm 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 r and 
the other as the fiddle. By what steps the more simple 
apparatus in the Achetidse originated, w r e 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 slridulation is produced in a very 
different 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 Platyphyllum concavum , “ when captured makes a feeble grating; 
u noise by shuffling her Yving-covers together.” 
3 ' Landois, ibid. s. 113. 
