The eyes of some Crustacea are carried upon jointed appendages, but this is never the case in Insects, though the eye-bearing surface may project from the head, as in _Diopsis_ and _Stylops_. Professor Huxley[48] supposes that the head of an Insect may contain six somites, the eyes representing one pair of appendages. The various positions in which the eyes of Arthropoda may be developed weakens the argument drawn from the stalk-eyed Crustacea. Claus and Fritz Müller go so far on the other side as to deny the existence of an eye-segment even in Crustacea. [48] Anat. Invert. Animals, p. 398. _Mouth-parts of the Cockroach._ Before entering upon a full description of the mouth-parts of the Cockroach, which present some technical difficulties, the beginner in Insect anatomy will find it useful to get a few points of nomenclature fixed in his memory. Unfortunately, the terms employed by entomologists are at times neither convenient nor philosophical. There are three pairs of jaws, disposed behind the labrum, as in the diagram:-- LABRUM. 1st pair of Jaws (MANDIBLES). 2nd " (MAXILLÆ). 3rd " (LABIUM, or 2nd pair of Maxillæ). [Illustration: Fig. 19.--Diagram of Cockroach Jaws, in horizontal section.] The mandible is undivided in all, or nearly all, Insects. Each maxilla may consist of A _palp_ on the outer side, A _galea_ (hood), A _lacinia_ (blade), on the inner side. The galea (hood) of the 3rd pair of jaws is sometimes called the _paraglossa_. A tongue-like process may be developed from the front wall of the mouth (_epipharynx_), or from the back wall (_hypopharynx_ or _lingua_).[49] Both epipharynx and hypopharynx project into the mouth, and, in some Diptera, far beyond it. [49] Professor Huxley has proposed to call the attached base _hypopharynx_, and the free tip _lingua_. The tip of the labium is sometimes produced into a long tongue, called the _ligula_ (strap). The mouths of Insects may be classed as:-- BITING.--Orthoptera, Neuroptera, Coleoptera (in some Coleoptera a licking tongue is developed), most Hymenoptera. LICKING AND SUCKING.--Some Hymenoptera--_e.g._, Honey Bee. SUCKING.--(_a_) With lancets--Diptera, Hemiptera. (_b_) Without lancets--Lepidoptera. The reference of these to a common plan, and the determination of the constituent parts, is mainly the work of Savigny. Mouth-parts were made the basis of the classification of Insects by Fabricius (1745–1808). [Illustration: Fig. 20.--The Jaws, separated. _Mn_, mandible, seen from behind (to left) and front (to right); _Mx_' maxilla (first pair); _Mx_" labium, or second pair of maxillæ. The other letters as before. × 20.]