Most of us have a vague idea that what we call the 'ear' is only partly concerned with the work of hearing; but only a few know exactly what a complicated organ the ear, as a whole, really is. The external 'ear' only serves as an aid to the collection of sounds, and the real work of hearing is performed by a delicate organ inside the head. Seals, moles, whales, and porpoises, birds, reptiles, and fishes have no visible ear; yet we know that they are not deaf, though in many the hearing must be dull. In all these creatures the sense of hearing lies inside the head.

But the ears of insects must be looked for in strange places indeed, and, when found, they seem to bear no sort of likeness to what most of us call ears. They may be on the antennÆ, on the trunk, or on the legs! In the grasshopper, for example (fig. 1), the ear is placed on the abdomen, just above the base of the great hind-leg, so that this leg must be pulled down before the ear can be seen. When this has been done, there will be found an oval drumhead-like spot (figs. 2 and 3); this is the outer surface of the ear. If you had sufficient skill to take away this part of the body, so as to show the inside of this drum, you would find two horn-like stalks, to each of which is fastened a small and very delicate flask, with a long neck. This is filled with a clear fluid, and corresponds to a similar structure within our own ears.

In the green grasshoppers—those delightful sprites of hot summer days—'ears' of a precisely similar structure are found on the fore-leg instead of on the body.

In a little gnat-like insect known as Corethra, common in England during the summer months, the 'ear' takes the form of delicate hairs growing out from the body on a stem, like the teeth of a comb; the base of what corresponds to the back of the comb is connected with a delicate nerve, and this, as in the case of the similar nerve in the grasshopper and locust, makes hearing possible.

Only in some ants and bees, and in some mosquitoes, is the organ of hearing placed on the head. We say on, rather than in, the head, because it is formed by a modification of part of the antennÆ. A German naturalist, named Mayer, performed an experiment to prove that the hairs on these antennÆ can be made to vibrate by means of a tuning-fork. Only those hairs which have to do with the production of sound answered to the notes of the tuning-fork, and these vibrated at the rate of five hundred and twelve vibrations per second. Other hairs vibrated to other notes, which were those of the middle octave of the piano and the next above it. Mayer also found that certain of these vibrations corresponded with the notes produced by the 'song' of the female mosquito. Consequently, when she begins to 'sing,' her tune, like the tuning-fork, sets in motion those hairs on the antennÆ of the male which are tuned to these vibrations. Having once found, by the movement of his antennÆ, much as a horse moves his ears, from which direction the sound is coming, the male is able to fly at once to his mate. From the accuracy of this flight, Professor Mayer believes that the perception of sound in these little creatures is more highly developed than in any other class of animals.

In our illustration some of these curious 'ears' are shown. Fig. 2 shows the ear of the grasshopper magnified. In fig. 3 this is further magnified to show the V-shaped mark which represents the horny stalks to which we referred, seen through the clear membrane of the drum. The dark border (b) around the drum represents a raised ridge. In fig. 4 we have the antennÆ of a gnat, some of the hairs of which serve as sound-conductors to delicate nerves lying at their base.

The sense of smell in insects lies mainly in those wonderful organs, the antennÆ or 'horns.' Scents of various kinds are perceived either through pits, or through peg-or spike-like teeth filled with fluid. The leaf-like plates of the antennÆ of the cockchafer (fig. 5) have these pits very highly developed. On the outer surface of the first 'antennal' leaf, as also on the edges of the other leaves, only scattered bristles are seen; but on the inner surface of the first and seventh leaves, and on both surfaces of all the other leaves, there are close rows of shallow, irregularly shaped hollows. Their number is enormous—in the males as many as thirty-nine thousand, and, in the female, thirty-five thousand on each antenna. As some of the scent-laden air reaches the surface of these pits, it causes the nerves of smell to be roused, and so guides the beetle to its mate, or to its food, according to the nature of the smell. These pits are so tiny that they cannot be shown on the antennal leaves of the cockchafer shown in fig. 5, but they are there. On fig. 6 a highly magnified section of one of these 'leaves' of the antenna is shown: 'p' is the pit, 'n' is the nerve, and 'S. C.' the sense-bulb of the nerve in which it terminates—the point at which the smell is perceived.

It has been proved that insects which have lost their antennÆ have no sense of smell.

W. P. Pycraft, F.Z.S., A.L.S.