HEARING IN INSECTS. 



79 



which the insect rubs these nervures against each 

 other, produces a vibration in the membrane, whence 

 the sound is augmented. ^^ By alternating the motion 

 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 ;| 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 {Grtjllidce) 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 flat plate or lid, of a 

 hard substance, but covered by a flexible, wrinkled 



Drum of the grasshopper. 



A, part of the first ring 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 b is re- 

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

 d, Oval hole. 



De Geer, Memoires, iii, 429. 



t J. R. 



