_Jaws._--The mandibles of the Hexapoda are usually strong jaws with one or more teeth at the apex (fig. 1, A, B, mn), articulating at their bases with the head-capsule by sub-globular condyles, and provided with abductor and adductor muscles by means of which they can be separated or drawn together so as to bite solid food, or seize objects which have to be carried about. They never bear segmented limbs (palps) and only exceptionally (as in the chafers) is the skeleton composed of more than one sclerite. The mandibles often furnish a good example of "secondary sexual characters," being more strongly developed in the male than in the female of the same species. In most insects that feed by suction the mandibles are modified. In bugs (Heteroptera) and many flies, for example, they are changed into needle-like piercers (fig. 2, II), while in moths and caddis-flies they are reduced to mere vestiges or altogether suppressed. As previously mentioned, a pair of minute jaws--the _maxillulae_--are present in the lowest order of insects, between the mandibles and the first maxillae. They usually consist of an inner and an outer lobe arising from a basal piece, which bears also in some genera a small palp (see APTERA). In their typical state of development, the _first maxillae_ offer a striking contrast to the mandibles, being composed of a two-segmented basal piece (_cardo_ and _stipes_, fig. 1, C, ca, st) bearing a distinct inner and outer lobe (_lacinia_ and _galea_, fig. 1, C, la, ga) and externally a jointed limb or palp (fig. 1, C, pa). Such maxillae are found in most biting insects. In insects whose mouths are adapted for sucking and piercing, remarkable modifications may occur. In many blood-sucking flies, for example, the galea is absent, while the lacinia becomes a strong knife-like piercer and the palp is well developed. In bugs and aphids the lacinia is a slender needle-like piercer (fig. 2, III), while the palp is wanting. In butterflies and moths the lacinia is absent while the galea becomes a flexible process, grooved on its inner face, so as to make with its fellow a hollow sucking-trunk, and the palp is usually very small.