INSECTS: WINGS AND THEIB APPENDAGES. 87 



behind which is a transparent membrane, which appears 

 tightly stretched over a semicircular rim, like the parch- 

 ment of a drum, answering in structure and in function to 

 the part so compared in the Cricket. 



This Gryllus I found would chirp freely, when held in 

 my fingers, provided I held it by the head or thorax, so 

 as not to interfere with the freedom of the wing-cases : 

 though these needed only to be partially opened, the bases 

 being merely slightly separated without affecting the general 

 contiguity. The two glassy ridges were rubbed across 

 each other, making the sharp crick. Ordinarily this was 

 done thrice, three distinct but rapid crossings making the 

 sound represented by the word " Katedid ;" but occasion- 

 ally the insect gave but a single impulse, uttering as it 

 were but one syllable of the word. 



The Locusts and Grasshoppers, however, do, it appears, 

 make use of their hind legs in producing their chirp. If 

 you look at this Grasshopper's leg, you will see that the 

 thigh is marked with a number of transverse overlapping 

 angular plates, and that the shank carries a series of short 

 horny points along each side. The insect, when it chirps, 

 brings the shank up to its thigh, and rubs both to and fro 

 against the wing-sheaths, doing this by turns with the 

 right and left legs, which causes the regular breaks in the 

 sound. The drum, on which this rubbing vibrates, has 

 been described by the anatomist, De Geer : "On each 

 side of the first segment of the abdomen," says he, "im- 

 mediately 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 oper- 

 culum of a hard substance, but covered by a wrinkled 

 flexible membrane. The opening left by this operculum is 

 semilunar, and at the bottom of the cavity is a white 

 pellicle of considerable tension, and shining 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 



