Page:Jardine Naturalist's library Entomology.djvu/107

Rh moveable parts, namely, the antennæ and the organs of the mouth. The former are the conspicuous and well known jointed organs, placed one upon each side of the head between the angle of the mouth and the eyes. They are never wholly absent, and never exceed or fall short of the number mentioned. They are planted in a cavity or socket, (Torulus) and the base is usually subglobose, forming the pivot upon which the antenna turns. Each of the joints of which they are composed has a separate motion, and they are therefore susceptible of every flexure the insect may require to give them. In regard to situation, general form and construction, number of joints, clothing, &c., antennæ vary greatly in different tribes, and their peculiarities in these respects will be specified when treating of these tribes separately. The mouth of insects differs in its external appearance according as it is designed to act upon solid or liquid food; in other words, according as it belongs to a masticating or suctorial species. But although so dissimilar in external aspect, the component parts are essentially the same in both. In masticating insects, (mandibulata) the parts are free and highly developed; in suctorial species, (haustellata) they are more or less united, forming a kind of tube for the transmission of fluids. Although we have already described both these modifications of form, some recapitulation may be useful in this place, both for the purpose of presenting a continuous view of insect structure, and conveying as accurate a notion as possible of parts so essential, whether viewed in