874 



THE DESCENT OF MAN 



of the nervure of another species of Grryllus, viz., G. domes- 

 ticus. With respect to the formation of these teeth, Dr. 

 Gruber has shown" that they have been developed by the 

 aid of selection, from the minute scales and hairs with which 

 the wings and body are covered, and I came to the same 

 conclusion with respect to those of the Coleoptera, But 

 Dr. Gruber further shows that their development is in part 





Fig. 13. — Chlorocoelus Tanana <from Bates), o, 6. Lobes of opposite wing-oovers, 



directly due to the stimulus from the friction of one wing 

 over the other. 



In the Locustidae 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, whicii 

 nets as the bow, lies over the right wing, which serves as 

 the fiddle. One of the nervures (a) on the under surface 

 of the former is finely serrated, and is scraped across the 



•• "Ueber den Tonspparat der Loeust.iden, ein Beitrag zum Darwinismna," 

 **Zeitsct). tax Wissensch. Zoolog.," B. xxii., 1872. p. 100. 



