There is another part of the mouth to which we may call special attention, as it has recently attracted more attention than it formerly did; it is a membranous lobe in the interior of the mouth, very conspicuous in Orthoptera, and called the tongue, lingua, or hypopharynx; it reposes, in the interior of the mouth (Fig. 51, _o_), on the middle parts of the front of the labium; it is probably not entirely lost in Coleoptera, but enters into the composition of the {97}complex middle part of the lip by amalgamation with the paraglossae. It has recently been proposed to treat this lingua as the morphological equivalent of the labium or of the maxillae, giving it the name of the endolabium, but the propriety of this course remains to be proved;[20] the view is apparently suggested chiefly by the structure of the mouth of _Hemimerus_, a very rare and most peculiar Insect that has not as yet been sufficiently studied. As the maxillae and labium are largely used by taxonomists in the systematic arrangement of the mandibulate Insects, we give a figure of them as seen in Coleoptera, where the parts, though closely amalgamated, can nevertheless be distinguished. This Fig. 52 should be compared with Fig. 51. In speaking of the segments of the body we pointed out that they were not separate parts but constituted an uninterrupted whole, and it is well to remark here that this is also true of the gnathites. Although the mouth parts are spoken of as separate pieces, they really form only projections from the great body wall. Fig. 51, B, shows the intimate connexion that exists between the maxillae and labium; the continuity of the mandibles with the membrane of the buccal cavity is capable of very easy demonstration. The head bears, besides the pieces we have considered, a pair of antennae. These organs, though varying excessively in form, are always present in the adult Insect, and exist even in the majority of young Insects. They are very mobile, highly sensitive organs, situate on or near the front part of the head. The antennae arise in the embryo from the procephalic lobes, the morphological import of which parts is one of the most difficult points connected with Insect embryology. The eyes of Insects are of two sorts, simple and compound. The simple eyes, or ocelli, vary in number from one to as many as eighteen or twenty; when thus numerous they are situated in groups on each side of the head. In their most perfect form, as found in adult aculeate Hymenoptera, in Orthoptera and Diptera, ocelli are usually two or three in number, and present the appearance of small, perfectly transparent lenses inserted in the integument. In their simplest form they are said to consist of some masses of pigment in connexion with a nerve.