Several species of insects produce distinctive sounds, often by a process of stridulation, in which the edges of the wings are rubbed together, or the legs are scraped over special surfaces on the wings o r body. The observation of such sound production led to the problem of hearing in these forms, for it was readily inferred that the sounds were made for purposes of communication, and hence that the insects must possess the ability to hear. This inference was made early for such familiar sound-makers as the cicada, katydid, grasshopper, and cricket, and more recently for the water-boatman (Corixa) and certain moths, which also have been observed to produce sounds.
The problem of hearing in these insects received particular emphasis from the discovery, in t2ie same species, of organs which structurally seemed suited to the reception of sound vibrations. These, the tympana1 organs, are found in various bodily regions: in the forelegs of katydids and crickets, in the abdomen in grasshoppers, cicadas and some moths, and in the metathorax in the water-boatman. I n spite of the differences in bodily position, the organs are fundamentally alike, consisting of sensory cells (scolophores) in connection 1111 this article the term 'hearing' is used broadly for a response t o vibratory stimuli by means of a specialized receptor, with no assumption that this seme in insects bears any strict relation to that known in higher forms.