The primitive organ of audition as it is to be observed in creatures of simple, comparatively speaking, organization is as simple as is the anatomy of the animals in which it is found. Commonly, it is a hollow hair, which is connected by a minute nerve-filament with the sensorium. Sound vibrations set the hair to vibrating, which in turn conveys the vibrations to the nerve-filament, and so on to the auditory centre. Sometimes the hair is not hollow; in this case, the root of the hair is intimately associated with nerve-filaments which take up vibrations. It is highly probable that the majority of the lower animals, especially those which are sound-producers, can hear just as we hear. It is also highly probable that the so-called deaf animals can hear, just as we hear when we have either been born deaf, or through disease have lost the power of hearing--by _feeling_ the sound waves. Owing to our own lack of acuteness, all of the problems involved in this question of audition in the lower animals will, probably, never be definitely settled; yet, reasoning by analogy, we can, approximately, solve some of them. By far the larger number of entomologists locate the auditory organs of insects in their antennæ. I have only to mention the names of such men as Kirby, Spence, Burmeister, Hicks, Wolff, Newport, Oken, Strauss, Durkheim, and Carus, who advance this opinion, to show what a formidable array of talent maintains it. Yet my observations lead me to believe otherwise, though these authorities are in part correct. As far as Lepidoptera are concerned, and certain of Hemiptera, they are right--the antennæ in these creatures are the seat of the organs of audition. But in Orthoptera, in most of Coleoptera, Hymenoptera, and Diptera, and in certain bugs (Hemiptera), they are located elsewhere. The habit that almost all insects have of retracting their antennæ when alarmed by noise, or otherwise, has done much to advance and strengthen the opinion that these appendages are the seat of insect ears; yet I am confident that in nine cases out of ten the antennæ are retracted through fear of injury to them, and not through any impression made on them by sound. The antennæ are the most exposed and least protected of any of the appendages or members of the insect body; hence their retraction by insects when alarmed is an instinctively protective action. They shelter them as much as possible in order to keep them from being injured. Again, although the antennæ of most insects are provided with numerous sensitive hairs, or setæ, we have no right to assume that these hairs are auditory; no "auditory rods," otoliths, etc., are to be found generally in antennæ, yet there are exceptional instances. Leydig found auditory rods in the antennæ of _Dyticus marginalis_ (Furneaux[17]), the giant water-beetle, and I myself have observed them in _Corydalis cornuta_ and other neuropterous insects. I am inclined to believe that