OF SOUNDS. 471 



wings. The shrill tones of the grasshoppers, locusts, and field crickets 

 are therefore tolerably alike, varying merely in intensity. The tone 

 of the cricket is probably the weakest, and that of the grasshopper 

 perhaps the strongest. According to Kirby and Spence * the mole 

 cricket is said to produce a dull tone resembling that of the goat-sucker, 

 but I never heard it ; and in the insect itself I have not been able to 

 find anything analogous to a vocal organ. 



In the remaining Orthoptera which possess a voice, namely, in the 

 genus Gryllus, Fab. (Acrydium, Lat.), it is equally found in both sexes. 

 The organs which produce it lie at the base of the abdomen, upon its 

 first segment, one on each side, immediately behind the first abdominal 

 spiracle. Each presents itself as a half moon-shaped cavity, closed at 

 its base by a very delicate membrane, which is sometimes wholly free 

 (Gryllus stridulus), and at others half covered by a triangular plate, 

 projecting from the anterior margin. Close to the anterior margin of 

 this fine membrane there is a small, brown, horny spot, upon which 

 internally a delicate muscle is inserted, that runs over to a projection 

 of the external horny plate which lies over and in front of the margins 

 of the spiracle. By means of this small muscle it is made to vibrate, 

 and consequently sound, when the whole body is agitated by the 

 volatile motions. The sound thus produced is increased by a large air 

 bladder, resembling a distended trachea, lying beneath the fine mem- 

 brane, which re-echoes the sound like a sounding-board. But the tone 

 thus produced is, however, weak, but it is loudest in the thence named 

 Gryllus stridulus, and possesses no other differences than in intensity 

 and weakness. Formerly it was thought that the friction of the pos- 

 terior thighs against the wings was the sole cause of the chirping of 

 these creatures, an opinion founded upon the contemporaneous motion 

 of the wings and hind legs. Indeed, such a friction of the hinder 

 femur against the inflected margin of the superior wing appears to 

 participate in the mechanism of the sound, for even after the death of 

 the creature I could produce a similar but much weaker sound by 

 rubbing those parts together. Thus the allied genus Acrydium, F., 

 (Tetter, Lat.) appears to produce the weak tone which it emits, for it 

 has no vocal organ like Gryllus. The African genus Pneumora, Lat., 

 also is said to produce a sharp chirping noise by the friction of the 

 femur against the abdomen, or small ridges seated upon it. De Geer 

 even detected the vocal organ of Gryllus, and considered it as such, 



* lutrod. vol. ii. 



