With these eyes insects can only see such objects as are at a short distance. Of what use then can stemmata be to insects also provided with compound eyes? It has been remarked that most insects having this arrangement of eyes feed on the pollen of plants, and it has been surmised that the stemmata enable them to distinguish the parts of the flowers. The antennæ, commonly called horns, are two flexible appendages, of very variable form, which are joined to different parts of the head, and are always two in number. The joints of which they are made up have the power of motion, which enables the insect to move them in any direction. The antennæ consist of three parts: the basal joint, commonly distinguished by its form, length, and colour; the club, formed by a gradual or sudden thickening of the terminal joints, of which the number, form, and size present great variations; lastly, the stalk, formed by all the joints of the antennæ, except the basal, when no club exists, and in case of the existence of a club, of all those between it and the basal one. We give as examples the antennæ of two beetles, one of the genus _Asida_, the other of the genus _Zygia_ (Figs. 3 and 4). [Illustration: Fig. 3.--Antenna of a species of Asida.] [Illustration: Fig. 4.--Antenna of Zygia oblonga.] Insects, for the most part, while in repose, place their antennæ on their backs, or along the sides of the head, or even on the thorax. Others are provided with cavities in which the antennæ repose either wholly or in part. During their different movements, insects move their antennæ more or less, sometimes slowly and with regularity, at other times in all directions. Some insects impart to their antennæ a perpetual vibration. During flight they are directed in front, perpendicular to the axis of the body, or else they repose on the back. What is the use of the antennæ, resembling as they do, feathers, saws, clubs, &c.? Everything indicates that these organs play a very important part in the life of insects, but their functions are imperfectly understood. Experience has shown that they only play a subordinate part as feelers, and have nothing to do with the senses of taste or smell. There is no other function for them to fulfil, except that of hearing. On this hypothesis the antennæ will be the principal instruments for the transmission of sound-waves. The membrane at their base represents a trace of the tympanum which exists among the higher animals. This membrane then will have some connection with an auditory nerve. The mouth of insects is formed after two general types, which correspond to two kinds of requirements. It is suited in the one case to break solid substances, in the other to imbibe liquids.