Chap, xi.] VOCAL ORGANS OF INSECTS. 389 



therefore, be reversed. In the grasshoppers the sound- 

 producing organs are developed not on the wings but 

 on the legs, the upper joints of which are provided 

 with rather less than one hundred minute denticles 

 which scrape on the wings ; in the males of an allied 

 form (Pneumora), the legs are rubbed against a notched 

 ridge which is developed on either side of the abdo- 

 men, and the resonance is greatly increased by the 

 whole body being distended with air. In most cases 

 among the Orthoptera the males are alone vocal, and 

 the object of the use of these organs is, no doubt, that 

 of attracting the female. 



In the hemipterous Homoptera, of which the Cicadas 

 are members, and of which the males are alone vocal, 

 the sound seems to be produced by the vibration of 

 membranes, placed on either side of the stigmata of 

 the metathorax, and set in motion by the respiratory 

 air. 



The Hymenoptera, among which are the bees that 

 hum, would appear to produce sounds by the move- 

 ment of the abdominal segments on one another ; 

 these, as Mr. Darwin has observed, are marked with 

 very fine concentric ridges, such as are found also on 

 the thoracic collar, with which the head articulates. 

 Among the Coleoptera (beetles), there are forms such 

 as the carrion beetles (Necrophorus), and others 

 which make very distinct sounds ; these are ordinarily 

 produced by rasped ridges, which are placed on various 

 parts of the body and worked against the edges of the 

 elytra or wing-covers ; or parts of the leg work against 

 ridges on the abdomen ; or the elytra are ridged, as in 

 some of the water beetles ; or, lastly, two of the seg- 

 ments of the thorax may work on one another ; in the 

 latter case the ridges may be developed either on the 

 upper or on the lower surface. The vocal or stridu- 

 lating organs of Coleoptera appear to be equally or 

 nearly equally developed in both sexes, and it is rare 



