_Head._--The head-capsule of an insect (figs. 1, 2) is composed of a number of sclerites firmly sutured together, so that the primitive segmentation is masked. Above is the crown (_vertex_ or _epicranium_), on which or on the "front" may be seated three simple eyes (ocelli). Below this comes the front, and then the face or clypeus, to which a very distinct upper lip (_labrum_) is usually jointed. Behind the labrum arises a process--the _epipharynx_--which in some blood-sucking insects becomes a formidable piercing-organ. On either side a variable amount of convex area is occupied by the compound eye; in many insects of acute sense and accurate flight these eyes are very large and sub-globular, almost meeting on the middle line of the head. Below each eye is a cheek area (_gena_), often divided into an anterior and a posterior part, while a distinct chin-sclerite (_gula_) is often developed behind the mouth. [Illustration: From Miall and Denny, _The Cockroach_, Lovell Reeve & Co. FIG. 1.--Head and Jaws of Cockroach (_Blatta_). Magnified 10 times. A, Front; B, side; C, back; v, vertex; f, frons; cl, clypeus; lbr, labrum; oc, compound eye; ge, gena; mn, mandible; ca, st, pa, ga, la, cardo, stipes, palp, galea, lacinia of first maxilla; sm, m, pa', pg, sub-mentum, mentum, palp, galea of 2nd maxilla.] _Feelers._--Most conspicuous among the appendages of the head are the feelers or antennae, which correspond to the anterior feelers (antennules) of Crustacea. In their simpler condition they are long and many-jointed, the segments bearing numerous olfactory and tactile nerve-endings. Elaboration in the form of the feelers, often a secondary sexual character in male insects, may result from a distal broadening of the segments, so that the appendage becomes serrate, or from the development of processes bearing sensory organs, so that the structure is pinnate or feather-like. On the other hand, the number of segments may be reduced, certain of them often becoming highly modified in form. [Illustration: After Marlatt, _Entom. Bull._ 14, n. s. (U.S. Dept. Agric.). FIG. 2.--Head of Cicad, front view. Ia, frons; b, clypeus (the pointed labrum beneath it); II, mandible; III, first maxilla; (a, base; b, sheath; c, piercer), III', inner view of sheath; IV, second maxillae forming rostrum (b, mentum; c, ligula).]