SEXUAL SELECTION 375 



prominent nervures on the upper surface of the opposite 

 or right wing. In our British Phasgonura viridissima it 

 appeared to me that the serrated nervure is rubbed against 

 the rounded hind-corner of the opposite wing, tbe edge of 

 which is thickened, colored brown, and very sharp. In the 

 right wing, but not in the left, there is a little plate, as 

 transparent as talc, surrounded by nervures, and called 

 the speculum. In Ephippiger vilium, a member of this 

 same family, we have a curious subordinate modification; 

 for the wing-covers are greatly reduced in size, but "the 

 posterior part of the pro-thorax is elevated into a kind 

 of dome over the wing-covers, and which has probably 

 the effect of increasing the sound."" 



We thus see that the musical apparatus is more differen- 

 tiated or specialized in the Locustidse (which include, 1 

 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. '° Landois, however, de- 

 tected 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, whicb underlies 

 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 Phasgonura- viridissima. Hence we may infer 

 with confidence 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 

 Locustidse the two wing-covers gradually became differen- 

 tiated 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. Grruber takes the same view, and has 

 shown that rudimentary teeth are commonly found on the 

 inferior surface of the right wing. By what steps the more 

 simple apparatus in the Achetidse originated, we do not 



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



3s Landois, "Zeitsch. f. Wfsa. Zoolog.," B. zvii., IBS'?, 8. 121, 122. 



