The musical organs of the Locustidae are different from those of the Acridiidae, and are invariably situate on the basal part of the tegmina. They are found, in the great majority of cases, only in the male; in the tribes Ephippigerides and Callimenides they exist in each sex. One of the wings bears a file on its inner surface, while the other—on the right side of the body—is provided with a sharp edge placed on a prominent part of its inner margin. By slightly tilting the tegmina and vibrating them rapidly, the edge passes under the file, and a musical sound is produced. These structures are limited to the small anal area of the wing, and when the tegmina are very greatly reduced in size, it is this part that still remains. There is much variety in the details of the structure. The nervures of this part of the tegmina are different in the male from what they are in the female, and, moreover, the two wing-covers of the male differ from one another. It is apparently the vibrations of the right tegmen that produce the sound, and this part usually bears a space of a glassy nature, which probably improves the character of the sound produced. Our chief British songster of this group, _Locusta viridissima_, is only provided with phonetic organs (Fig. 195) of a somewhat imperfect character, but in the genus _Mecopoda_ there is great perfection of the structures. The anal areas of the two tegmina are in this case {319}very different; that of the left one, which bears the file, being similar in texture to the rest of the wing-cover, while the corresponding part of the other tegmen is rigid and transparent, and greatly distorted, so as to create a cavity which, no doubt, improves the sound; the scraper too is very perfectly formed. The difference between this form of musical organ and that of _L. viridissima_ is curious, inasmuch as in the better instrument the important modifications are confined to one tegmen, while in the other form both tegmina are largely changed. The difference appears to be that in _Locusta_ the left tegmen, as well as the right one, acts as a sounding-board, while in _Mecopoda_ it does not do so, but when the wings are closed quite covers and conceals the musical instrument.