Chap. X. 



Orthoptera. 



285 



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

 " effect of increasing the sound." " 



Kg. 13. Chlorocoelufi Xanana (from Bates), a, b. Lobes 01 opposite wing-covers. 



We thus see that the musical apparatus is more differentiated 

 or specialised in the Looustidse (which include, I 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, detected 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, which 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 Pliasyonura viridissima. Hence we may 

 infer with confidence that the I;Ocustidse 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 differentiated and perfected, 



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



=« Landois, 'Zeitsch. f. wiss. Zoolog.' B. xvii. 1867, b. 121, 122. 



