396 NOJSES OF INSECTS. 



right and left legs, which causes the regular breaks in 

 the sound. But this is not their whole apparatus of 

 song since, like the Tettigonise, they have also a tym- 

 panum or drum. De Geer, who examined the insects 

 he describes with the eye of an anatomist, seems to be 

 the only entomologist that has noticed this organ. " On 

 each side of the first segment of the abdomen," says he, 

 " immediately above the origin of the posterior thighs, 

 there is a considerable and deep aperture of rather an 

 oval form, which is partly closed by an irregular flat 

 plate or operculum of a hard substance, but covered 

 by a wrinkled flexible membrane. The opening left by 

 this operculum is semi-lunar, and at the bottom of the 

 cavity is a white pellicle of considerable tension, and shin- 

 ing like a little mirror. On that side of the aperture 

 which is towards the head, there is a little oval hole, 

 into which the point of a pin may be introduced without 

 resistance. When the pellicle is removed, a large 

 cavity appears. In my opinion this aperture, cavity, and 

 above all the membrane in tension, contribute much to 

 produce and augment the sound emitted by the grass- 

 hopper a ." This description, which was taken from the 

 migratory locust (L. migratorid], answers tolerably 

 well to the tympanum of our common grasshoppers, 

 only in them the aperture seems to be rather semicircular, 

 and the wrinkled plate which has no marginal hairs 

 is clearly a continuation of the substance of the segment. 

 This apparatus so much resembles the drum of the 

 Cicadae, that there can be little doubt as to its use. The 

 vibrations caused by the friction of the thighs and elytra 



a De Geer, Hi. 471. t. xxiii./. 2. 3. 



