Page:Jardine Naturalist's library Entomology.djvu/108

102 to the insect's economy, or the uses that have been made of them by naturalists in their systematic arrangements of the class.

When a mouth organised for mastication is viewed from above, the first part that meets the eye is the labrum or upper lip. It is a corneous plate, of very variable form, united posteriorly by a membranous hinge to the clypeus, with which many authors, and among others Fabricius, have confounded it. It covers the mouth above, and assists in retaining the food while undergoing the process of mastication by the mandibles. The last named organs, otherwise called the upper-jaws, are two strong, triangular, wedge-shaped, or elongated pieces, placed immediately below the labrum, articulating with the head by means of apophyses or processes, and moving horizontally in opposition to each other like the blades of scissors. When of a horny substance, which is usually the case, they are commonly dentate on their inner edge, but the denticulations are seldom or never alike in both blades, but so arranged that the projections of the one enter the notches of the other, thus admitting of a close union. The maxillæ, or feeler-jaws, as they have not inappropriately been called, are placed below the mandibles, and correspond to them in being two triangular hooks, moving horizontally in opposition to each other. They are always smaller than the mandibles, usually of a more delicate texture, and instead of being toothed on their internal edge, are for the most part fringed with hairs or bristles. They may