From a hint which has before been dropped, it is probable that the answer to this question will be readily anticipated. Various facts appear to show that they may be the insect's _ears_! "Can it be that such is their function?" some may exclaim, calling to mind that ears in other creatures are so different in appearance and structure from these organs. There have been many opinions on the subject, and some have maintained views completely opposed to this idea. But the greater number of entomologists seem to consider this as their most probable function. If they are not ears, we are not able to point to any other organs in the head which are. From a number of facts it is certain, that insects can hear; from which it is equally certain, that they must possess special organs. We may, therefore, until the contrary is shown with respect to them, fairly be allowed to consider the antennæ as these organs. The opinions of Messrs. Kirby and Spence on this point are conveyed in the following words:--"They conceive that antennæ by a peculiar structure may collect notices from the atmosphere, receive touches or vibrations, and communicate them to the sensorium (or brain), which, though not precisely to be called hearing, may answer the same purpose." The late celebrated Dr. W. F. Erichson of Berlin, by means of the microscope, has discovered in all insects, and especially in those most remarkable for their powers of smelling, that these organs are furnished with a number of fine pores, clothed with membrane, which he regards as organs of smell.[U]
Every one has heard of M. Pelisson, the prisoner at the Bastile, and his spider companions of the cell. This gentleman had, by patient training, engaged the attention of a spider, which used every day to come and listen to a solo on his violin, after which it would make its retreat again to its home. Now it is clear, that this little insect not only heard, but even enjoyed, the notes of his instrument; which would have been impossible, had it possessed no ears. Then again, every one must have noticed the start which a fly will make if some sharp noise be made near it, and how actively it will move its legs, and seem to be put all on the _qui vive_. A little every-day observation will furnish us with many similar instances. "A little moth," writes one of the last-mentioned authors, "was reposing on my window; I made a quiet, not loud, but distinct noise; the antenna nearest to me immediately moved towards me. I repeated the noise at least a dozen times, and it was followed every time by the same motion of that organ; till at length the insect, being alarmed, became more agitated and violent in its motions. In this instance it could not be _touch_; since the antenna was not applied to a surface, but directed towards the quarter from which the sound came, as if to listen." Can we question that the merry grasshopper, chirping all day in the field, is heard by its mate? or that the cricket on the hearth sings for its fellows, or only to please _our_ ears? or does the tap of the death-tick beetle, formerly commemorated, draw forth no answering tap from its companion on the other side of the post? All these instances, and countless more that might be mentioned, indicate, beyond a question, that insects have the faculty of hearing, and render it extremely probable that the antennæ are the organs by which this function is performed.