production of sound, they depend upon rasping and vibrating surfaces. The rasping surfaces are usually, as in the instruments of the grasshoppers (Figs. 15, 16), parts of the legs and the wings. The sound may be intensified, as in the body of a stringed instrument, by special resonating
Fig. 18. The front wings, or tegmina, of a meadow grasshopper, Orchelimum laticauda, illustrating the sound-making organs typical of the katydid family
A, left front wing and basal part of right wing of male, showing the four main veins: subcosta (Sc), radius (R), media (M), and cubitus (Cu); also the enlarged basal vibrating area, or tympanum (Tm), of each wing, the thick file vein (fv) on the left, and the scraper (s) on the right
B, lower surface of base of left wing of male, showing the file (f) on under side of the file vein (A, fv)
C, right front wing of female, which has no sound-making organs, showing simple normal venation
areas, sometimes on the wings, sometimes on the body. The cicadas, a group of musical insects to be described in a special chapter, have large drumheads in the wall of the body with which they produce their shrill music. They do not beat these drums, but cause them to vibrate by muscles in the body. The musical members of the insect families are in nearly all cases the males, and it is usually supposed that they give their concerts for the purpose of engaging the females, but that this is so in all cases we can not be certain.
The musical instruments of the katydids are quite different from those of the grasshoppers, being situated on the over-
