86 EVENINGS AT THE MICROSCOPE. 



cases, causing the two files to rub across each other ; and 

 this gives rise to the peculiar ringing vibration, the inten- 

 sity of which is heightened by the tense " drum " acting as 

 a sounding-board. 



So at least some say ; but M. Goureau, who has pub- 

 lished some elaborate observations on the chirping of 

 insects,* asserts that the sound is chiefly owing to the 

 action of the " file " (which he calls the "bow") on the 

 longitudinally -ridged nervure, which he calls the " treble- 

 string." 



We see in this individual that is so obliging as to pro- 

 duce its chirping before us, that he elevates the wing- 

 sheaths so as to form an acute angle with the body, and 

 then rubs them together with a very brisk horizontal 

 motion ; but which of the nervures it is that actually pro- 

 duces the sounds, it would require a very careful and 

 elaborate series of experimental researches to determine. 

 It has been asserted that the legs- play a part in the music 

 by being rubbed against the bows ; this, however, seems 

 improbable from their relative position. 



In the Southern United States, I have had opportunities 

 of seeing and of hearing a very noisy performer of the 

 Gryllus tribe, called the Katedid (Pterophylla concava), 

 which sings throughout the night in the foliage of the 

 trees. The sounds, reiterated on every side, resemble a 

 score or two of quarrelsome people with shrill voices, di- 

 vided into pairs, the individuals of each pair squabbling 

 with each other ; " I did ! " " You didn't I " " I did ! " 

 " You didn't ! " the objurgation maintained with the most 

 amusing pertinacity, and without a moment's intermission. 

 Here the wing-sheaths, which are large and as it were in- 

 flated, are certainly the organs of sound. A portion of 

 each is turned, at right angles to the remainder, over the 

 back, so that the one partly overlaps the other. The 

 musical organ consists of a hard glassy ridge in front, 

 * "Ann. Soc. Ent. de France." 



