J. B. Smith has clearly shown that the mandibles are compound in certain of the lamellicorns. In _Copris carolina_ (Fig. 50), he says, the small membranous mandibles are divided into a basal piece (basalis), the homologue of the stipes in the maxilla; another of the basal pieces he calls the molar, and this is the equivalent of the subgalea, while a third sclerite, only observed in Copris, is the _conjunctivus_, the lacinia (prostheca) being well developed. Smith therefore concludes “that the structure of the mandible is fundamentally the same as that of the labium and maxilla, and that we have an equally complex organ in point of origin. Its usual function, however, demands a powerful and solid structure, and the sclerites are in most instances as thoroughly chitinized and so closely united to the others that practically there is only a single piece, in which the homology is obscured.” (Trans. Amer. Ent. Soc., xix, pp. 84, 85. 1892.) From the studies of Smith and our observations on Staphylinus, Passalus, Phanæus, etc. (Fig. 50, _A_, _B_) we fully agree with the view that the mandibles are primarily 3–lobed appendages like the maxillæ. Nymphal Ephemerids have a lacinia-like process. (Heymons.) [Illustration: FIG. 50.—Mandible of _Copris carolina_.—After Smith. _A_′_C. anaglypticus_. _A_ (figure to right), do. of _Leistotrophus cingulatus_; _B_, of _Phanæus carnifex_; _g′_, end of galea,—_g_, enlarged; _c_, conjunctivus. _C_, of _Meloë angusticollis_: _l_, lacinia; _a_, lacinia enlarged. ] Mandibles are wanting in the adults of the more specialized Lepidoptera, being vestigial in the most generalized forms (certain Tineina and Crambus), but well developed in that very primitive moth, Eriocephala (Fig. 51). They are also completely atrophied in the adult Trichoptera, though very large and functional in the pupa of these insects (Fig. 52), as also in the pupa of Micropteryx (Fig. 53). They are also wanting in the imago of male Diptera and in the females of all flies except Culicidæ and Tabanidæ. They are said by Dr. Horn to be absent in the adult _Platypsyllus castoris_, though well developed in the larva; and functional mandibles are lacking in the Hemiptera. =The first maxillæ.=—These highly differentiated appendages are inserted on the sides of the head just behind the mandibles and the mouth, and are divided into three lobes, or divisions, which are supported upon two, and sometimes three basal pieces, _i.e._ the basal joint or _cardo_, the second joint or _stipes_, with the _palpifer_, the latter present in Termitidæ (Fig. 54, _plpgr_), but not always separately developed (Fig. 55). The cardo varies in shape, but is more or less triangular and is usually wedged in between the submentum and mandible. It is succeeded by the stipes, which usually forms the support for the three lobes of the maxilla, and is more or less square in shape. [Illustration: