HEARING IN INSECTS. 



19 



which the insect rubs these nervures ai^ainst each 

 other, produces a vibration in the membrane, whence 

 the sound is augmented*." By alternating- the mo- 

 tion rapidly from right to left, the sound is produced 

 in an almost continued strain, as we have remarked 

 in those we have kept in our study t; while in the 

 crickets, who alternate the motion more slowly, the 

 sound is emitted at interrupted intervals, — a remark 

 which any person may readily verify. 



The grasshoppers and locusts (Locustidce) pro- 

 duce their chirp by applying the hind shank to the 

 thigh, rubbing it smartly against the wing-case, and 

 alternating the right and left legs. They have also 

 a drum like the preceding family {Gryllidee) for 

 augmenting the sound. " On each side," says De 

 Geer, '' of the first segment of the abdomen, imme- 

 diately above the origin of the hind thighs, there is 

 a large deep opening, somewhat oval in form, and 

 partly closed by an irregular ilat plate or lid, of a 

 hard substance, but covered by a flexible, wrinkled 



A B 



Drum of the grasshopper. 



A, Part of the first rine; of the abdomen, greatly magnified, a, Deep 

 cavity, partially covered by the plate b. 



B, The cavity with the parts as they appear when the plate h is re- 

 moved, c. White membrane, stretched across the bottom of the cavity. 

 d. Oval hole. 



* De Geer, Memoires, iii. 429. 



t J. R. 



