—— Notes on the epipharynx, and the epipharyngeal organs of taste in mandibulate insects. (Psyche, 1889, v, pp. 193–199, 222–228.)
Also Lubbock’s Senses, etc., of animals, and the writings of Briant, Breithaupt (titles on p. 85).
d. The organs of hearing
Although it has been denied by Forel that insects have the sense of hearing, yet the majority of writers and experimenters agree that insects are not deaf. On general grounds if, as we know, many insects produce sounds, it must follow that they have ears to hear, for there is every reason to suppose that the sounds thus made are, as in other animals, either for attracting the sexes, for a means of communication, or to express the emotions. We will begin by briefly describing the structures now generally supposed to be auditory in function, and about which there can be no reasonable doubt, and then consider the more problematical organs, closing with an account of the extremely various means of producing sounds and cries.
The ears or tympanal and chordotonal sense-organs of Orthoptera and other insects.—The ears or tympana of locusts (Acrydiidæ) are situated one on each side, on the basal joint of the abdomen, just behind the first abdominal spiracle. That this is a true ear was first suggested by J. Müller, and his opinion was confirmed by Siebold, Leydig, Hensen, Graber, Schmidt, Lubbock, etc.[[49]]
Fig. 290.—Ear of a locust (Caloptenus italicus), seen from the inner side: T, tympanum; TR, its border; o, u, two horn-like processes; bi, pear-shaped vesicle; n, auditory nerve; ga, terminal ganglion; st, stigma; m, opening, and m′, closing, muscle of the same; M, tensor muscle of the tympanum membrane.—After Graber.
The apparatus consists of a tense membrane, the tympanum, surrounded by a horny ring (Fig. 290). “On the internal surface of this membrane are two horn-like processes (o, u), to which is attached an extremely delicate vesicle (bi) filled with a transparent fluid, and representing a membranous labyrinth. This vesicle is in connection with an auditory nerve (n) which arises from the third thoracic ganglion, forms a ganglion (ga) upon the tympanum, and terminates in the immediate neighborhood of the labyrinth by a collection of cuneiform, staff-like bodies, with very finely pointed extremities (primitive nerve-fibres?), which are surrounded by loosely aggregated ganglionic globules” (Siebold’s Anatomy of the Invertebrates).
Fig. 291.—Fore tibia of Locusta viridissima. td, cover of the drum; tr, fissure between the drum and its cover.—After Graber, from Lang.