Although not organs of sufficient size to give their colouring the requisite distinctness and amount of surface which would render it very conspicuous in our estimation, the eyes of insects are often exquisitely beautiful, and vie almost with precious stones in lustre. Their most common colour is black, or brown; but the eyes of many flies glow with fiery colours, some banded with green and purple, some variously figured black and red. Some again glitter like burnished gold shaded with the softest green; and some blaze with a play of colours, like the diamond set in jet. The eye of the dragon-fly, in particular, is a lustrous crystalline object of extreme beauty.
We have dwelt as long as our limits will permit on this wonderful apparatus of vision in insects: let us now turn our thoughts for a little space to a pair of organs which are, perhaps, of all others the most characteristic of the insect tribes: these are the _Antennæ_. We need scarcely explain what these are, or point them out to the reader, since they are so familiar to most persons, but under the erroneous, or, at any rate, the questionable expression--"the feelers." We have an excellent specimen of _antennæ_ in those of the butterflies, in which insects they are very long and elegant organs. They are attached to the head by means of a beautiful joint, called a ball and socket, the same as is often adapted to garden watering engine-pipes, so as to enable them to be moved about in all directions. They are never found absent in the perfect insect, and are manifestly organs of considerable importance in the insect economy. As to their structure,--when examined under a microscope, antennæ are found to be composed of a variable number of small round pieces, covered with a horny or leathery skin, but within being softer and hollow, so as to form a series of tubes placed end to end, all connected together in such a manner as to admit of free movement between each joint, so that the insect can bend them into any shape it may find expedient for its purposes. But it must not be supposed that all antennæ are similar in form, or there would be a risk of their being continually mistaken by the reader for some other organ. The cut on the next page will, at a glance, exhibit the astonishing variety of form assumed by these organs. The common cockchafer is possessed of antennæ as strikingly different in form from those of the butterfly, as if they were really distinct organs intended and adapted to serve different purposes. Some are long and thread-like, some resemble a necklace of pearls, some are notched like a saw, some have a resemblance to a fan, some are like a club, some resemble a fork, and some a feather; in short, their variety of form is almost endless: and they differ as much in length and in thickness; for while the antennæ of some insects are as long as, or even longer than, their bodies, those of others are very short, and little prominent; and while some are as thin and fine as the finest hair, others are nearly as thick as the true body of the insect. Let us now ask what is the use of these singular organs of the insect?