The mouth-parts of the myriopods are so different in shape and general function from those of insects, that this character, together with the equally segmented nature of the portion of the body behind the head (the trunk), forbids our merging them, as some have been inclined to do, with the insects. There are two sub-classes of myriopods, differing in such important respects that by Pocock[1] and by Kingsley they are regarded as independent classes, each equivalent to the insects. Of these the most primitive are the Diplopoda (Chilognatha), represented by the galley-worms (Julus, etc.). [Illustration: FIG. 5.—Mandible of Julus: _l_, lacinia; _g_, galea; _p_, dens mandibularis; _ma_, “mala”; _lt_, lamina tritoria; _st_, stipes; _c_, cardo; _m_, muscle.—After Latzel. ] In the typical Diplopoda the head consists of three segments, a preoral or antennal, and two postoral, there being two pairs of jaw-like appendages, which, though in a broad morphological sense homologues of the mandibles and first maxillæ of insects, are quite unlike them in details. [Illustration: FIG. 6.—Under lip or deutomala of _Scoterpes copei_: _hyp_, hypostoma or mentum; _lam. lab_, lamina labialis; _stip. e_, stipes exterior; with the malella exterior (_mal. e_) and malella interior (_mal. i_); the stipes interior, with the malulella; and the labiella (hypopharynx of Vom Rath) with its stilus (_stil._). ] As we have previously stated,[2] the so-called “mandibles” of diplopods are entirely different from those of insects, since they appear to be 2– or 3–jointed, the terminal joint being 2–lobed, thus resembling the maxillæ rather than the mandibles of insects, which consist of but a single piece or joint, probably the homologue of the galea or molar joint of the diplopod protomala. The mandible of the Julidæ (Fig. 5, _Julus molybdinus_), Lysiopetalidæ, and Polydesmidæ consists of three joints; viz. a basal piece or cardo, a stipes, and the _mala mandibularis_, which supports two lobes analogous to the galea and lacinia of the maxilla of an insect. There is an approach, as we shall see, in the mandible of Copris, to that of the Julidæ, but in insects in general the lacinia is wanting, and the jaw consists of but a single piece.