282 THE DESCENT OF MAN. 



on the unrfRr side of the nervure of another species of Gryllus, 

 viz., G. domeBtjcus. With respect to the formation of these teeth. 

 Dr. Gruber has ehown^" that they have been developed by the 

 aid of selection, n-om the minute scales and hairs with which the 

 wings and body ai e covered, and I came to the same conclusion 



Fig. 13. Chlorocoelus Tanana (from Bates), a, b. Lobes of opposite 

 wing-covers. 



with respect to those of the Coleoptera. But Dr. Gruber further 

 shows that their development is in part directly due to the stim- 

 ulus from the friction of one wing over the other. 



In the Locustidse the opposite wing-covers differ from each 

 other in structure (fig. 13), and the action cannot, as in the last 

 family, be reversed. The left wing, which acts as the bow, lies 

 over the right wing which serves as the fiddle. One of the ner- 

 vures (a) on the under surface of the former is finely serrated, 

 and is scraped across the prominent nervures on the upper sur- 

 face of the opposite or right wing. In our British Phasgonura 

 viridissima it appeared to me that the serrated nervure is rubbed 



™ 'Ueber der Tonapparat der Locustiden, ein Beitrag' zum Darwin- 

 ismus,' 'Zeltscli. fur wissensch, Zcnlog.' B. xxii. 1S72, p. 100. 



