284 The Descent of Man. Part II. 



In the three Families the sounds are differently produced. In 

 the males of the Achetidee both wing-covers have the same 

 apparatus ; and this in the field-cricket {Gryllus camjiestris, 

 fig. 11) consists, as described by Landois,^* of from 181 to 138 

 sharp, transverse ridges or teeth (st) on the under side of one of 

 the nervures of the wing-cover. This toothed nervure is rapidly 

 scraped across a projecting, smooth, hard ner- 

 vure (r) on the upper surface of the opposite 

 wing. First one wing is rubbed over the 

 other, and then the movement is reversed. 

 Both wings are raised a little at the same 

 time, so as to increase the resonance, in 

 some species the wing-covers of the males are 

 furnished at the base with a talc-like plate.^^ 

 I here give a drawing (fig. I'i) of the teeth on 

 the under side of the nervure of another 

 Fig. 12. Teeth of Nor- species of Gryllus, viz , <7. domesticus. -With 

 ticusffiijm il'nd°oT)!" respect to the formation of these teeth. Dr. 

 Gruber lias shewn '° that they have been de- 

 veloped 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 shews that their development is in part 

 directly due to the stimulus from the friction of one wing over 

 the other. 



In the Locustidffi the opposite wing-covers differ from ear-h 

 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 nervures («) on the under surface of the former is 

 finely serrated, and is scraped across the prominent nervures 

 on the uijper surface of the opposite or right wing. In our 

 British Fhasgonura viridissima it appeared to me that the 

 serrated nervure is rubbed against the rounded hind-corner 

 of the opposite wing, the edge of which is thickened, coloured 

 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 vitivw, 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 



^* ' Zeitschvift fiir wissenschaft, ^° ' tJeber der Tonapparat der 



ZooloEC.' B. xvH. 1S67, s. 117. Locustiden, ein Beitvag zum Dur- 



^* Westwood, 'Modern C'la.s. of winisraus,' ' Zeitsch. fiir wisseusch 



Insects,' vol. i. p. 440. Zoolog." B. x.^ii. 1872, p. 100. 



