Bonnet seems to think the antenna the organ of smell. Different insects, he observes, have an exquisite sense of smelling ; the organ of which is yet undiscovered. May it not reside in the antennae ? Insects are unques tionably affected by the emanation of odours ; the wasp is attracted by honey, the bee by flowers, and the fly by carrion. Nay, a plant which exhales the smell of carrion, deceives the fly, which alights on it to deposit its eggs. Yet we'should reflect, that the means of per ception are not indispensibly the same in animals pro vided with antenme, as in those of larger size, or those without them, provided with an organ exclusively adap ted to receive such impressions. Lehmann, from the result of experiments on this subject, denies that the antenna are the olfactory organ. He made an opening, an inch wide, in the side of a glass vessel, and sur rounded the edge with wax, so that a proper covering could easily be applied. An aperture was made in this covering, through which either the whole head, or the antennae only of an insect could be introduced. By means of a tube, the glass was filled with penetrating odours, vapours, or heated air ; but neither the fumes of sulphur, nor burnt feathers, produced the smallest effect on butterflies, bees, or beetles, whose antennx were exposed to them. He judges that the olfactory organ must be sought in the spiracula ; " for what else," says he, " is the sense of the particles inspired than smelling ?" Bonsdorf, in discussing whether the antenna may be the seat of hearing, mentions an experiment, where a species of beetle, whose peculiar property is folding in the antenna, when alarmed, did so on a loud noise be ing suddenly made, and fell to the ground, according to the nature of the species. But, notwithstanding that the animal previously reposed in a tranquil state, we do not consider his experiment altogether conclusive. But terflies are seen to erect their antenna on any sudden noise, and certain cole-optera to depress them, which, in our opinion, may equally arise from the sudden shock or vibration of the air. Spiders also, which want an tenna, are extremely sensible of sound. Lehmann re lates, that, on observing one descend from the roof by its thread, in quest of a female, while he was reading, he began to read aloud ; the animal, alarmed at the noise, retreated upwards ; he was silent and it returned ; on again reading aloud, it testified alarm, and ascended its thread ; nor was its apprehension of danger dispel led, until it was familiarized with the sound, or con quered by the object of pursuit. The same author deprived crickets, which are animals noted for acute ness of hearing, of the antenna, yet they were equally sensible of sound as before.
Lehmann also denies, that the antenna are at all con nected with the sense of taste. But it is evident, that they are adapted for feeling in an eminent degree. On attending to the motions of the curculio, an animal which advances with slow and cautious steps, the antenna are always seen extended before it, as if feeling the way. When the cerambya is at rest, no use is made of them ; when it begins to move, they are stretched out, and employed in examining what is fit for each progressive step. The aphides rarely move ; but no step is ever made, until the ground is ascertained by the antenna. Those of the ichneumon flies are in unremitting action, exploring all the surrounding objects, and leaving no thing untouched. Marsham has observed the ichneumon investigator, in searching out a proper place for depo siting its eggs, approach a hole in a wooden post, and thrust in its long antenna up to the head ; then retire and try other holes and crevices, until a suitable one was found. If the oniscus is withdrawn from its dark
retreats, it refuses to advance a single step, until the safety of its march has been ascertained by means of its antenna. On touching the silpha germanica, it im mediately closes up, counterfeiting death ; and all the limbs, along with the antenna, are closely contracted. But when its apprehensions of danger diminish, the antennae are cautiously unfolded ; if nothing threatens, the whole members gradually expand, and the animal makes its escape. But if still uncertain of security, the antenna are replaced down the thorax. The utility of such a sense, residing to an exquisite degree in the antenna, may readily be appreciated, on attending to the natural abode of numerous animals provided with them. Many dwell in dark, irregular chasms, clefts, or crevices, which requires an organ of extreme sensi bility to explore their way.
Although feeling may thus be the principal office of the antenna, those of some insects are so small, and placed in such a situation, that for this office only they can apparently be of very little use. Lehmann thence supposes, that they may be adapted for conveying hn pressions of the state of the air. The opinions of those, he observes, who maintain the possibility of other senses existing, than what are already known to us, are not to be despised. And he shews, that insects are, in -various cases, sensible of the peculiar state of the atmosphere. The bee, for example, suddenly retreats to its dwelling on the approach of rain ; ants, on a threatening storm, withdraw their young from the surface of the earth ; during a humid sky, musquitocs seek to harbour in our houses ; and the nocturnal flight of beetles indicates the serenity of the weather. It is necessary that some organ should be susceptible of such impressions, when we reflect, that a drop of rain will extinguish life, that unusual moisture will unfit the wings for use, and unu sual heat endanger the fracture of the elytra ; not for. getting either, that only a slight degree of cold stiffens the limbs of insects, and reduces them to a state resem bling death. But the whole surface of their bodies being covered with a strong and hard involucrum, ren ders it less sensible of the different transitions continu ally occurring in the atmosphere ; while the softer sub stance, of which the antenna are composed, is better adapted to warn them of those conditions on which their safety depends. Therefore they are surely the organ best calculated to receive the impressions_ of the air, if any one is susceptible of external effects. The feathers. branches, hairs, and spines, so numerously proceeding from the antenna, may all be devised to expose a great er surface, or some portion more acute in receiving im pressions, according to the nature of the animal, as in phalence, entices, tipula, or teuthredines. Even the antenna of dead insects are injured by the humidity of the atmosphere. The melolontha, or cock-chafer, gra dually unfolds its lamellated antenna, to try the state of the air, and never previously attempts to take flight. On removing a butterfly sitting in the sun, with its antenna erect to the shade, it immediately begins stretching them out, as if to ascertain the change that has taken place. It is necessary that those of males and of neuters should be larger than those of females, because the former roving about more in quest of females, and the latter in executing their work, should sooner become aware of the approaching changes of the atmosphere.