Stridulating organs, wherever they are met with, are fashioned on the same principle. The mechanism for sound-production differs conspicuously from that which produces the voice in the vertebrates. For where there are no lungs or breathing apparatus, comparable to that of birds and beasts, there can be no internal voice-mechanism. Instead, the skeleton which in these creatures forms the external surface of the body—that is to say, it encloses the muscles, whereas in the vertebrates it is internal and overlain by the muscles—produces the necessary sounds. And this by means of rubbing two opposed surfaces against one another, one of which is ridged, the other toothed. In the details both of position and structure a wonderful variety will be discovered when all the known types are surveyed, and it is possible that they perform different functions in different groups. The Locusts and Grasshoppers are among the finest performers of these “harpists,” and it would seem that in this group, at any rate, the music they make is of an erotic character. In one of our native Grasshoppers (_Stenobothrus melanopterus_) these high-pitched and somewhat strident notes are produced by rubbing the roughened inner surface of the hindmost thigh, which forms the base of the great leaping leg, against one of the libs of the wing-case which is specially enlarged and has a sharp edge. Thereby the wing is thrown into a state of vibration and the musical sound produced. The roughening of the inner surface of the thigh just referred to is produced by a row of bead-like projections whose appearance under the microscope is depicted in the adjoining illustration. This apparatus is well developed in the males, and but feebly, or not at all, in the females. That the music it produces is appreciated by the performers and their mates there can be no doubt, for they are provided with a special apparatus which fulfils the purpose of an ear. In the short-horned Grasshoppers (_Acridiidæ_) this is placed in the middle of the body just above the base of the great thigh. It differs in the details of its construction. In some cases it is formed by a delicate sheet of membrane surrounded by a rim, in others the membrane may be slightly depressed, and in some very much so, the rim closing up to form a broad slit. Such ears, it is to be noted, exist in both sexes, while the stridulating organs do not. That such sound-producing organs serve as stimulants to the sexual passions of the females is but a natural inference. Some authorities, however, regard this as doubtful, since there are species which appear to lack these stridulating instruments, though possessing ears. But closer observation will probably show that these apparently dumb species are not really so, as Dr. David Sharp, commenting on this fact remarks: “It is well known that sounds inaudible to some human ears are perfectly distinct to others. Tyndall, in his work on Sound, has illustrated this by a fact