[Illustration: Diagram of the mouth.--_a._ The _Labrum_, or upper lip; _b._ The _Mandibles_, or upper jaws _c._ The _Maxillæ_, or lower jaws; _d._ The _Labium_, or lower lip.]
In all cases, the various parts of the mouth may be reduced to six, the names of which deserve remembering, and this will be rendered easier by the accompanying diagram, in which they are all separated and lettered, so as to distinguish each part; these six parts consist of four side-pieces, and two other organs, one above, the other below. The name of the upper organ is the _upper lip_, or in Latin, _labrum_; that of the opposite lower one, is the _lower lip_, or _labium_. The upper pair, of side-pieces, are called the _mandibles_, or upper jaws; the pair below are the lower jaws, or _maxillæ_.
Let us now briefly mention the use of these various parts of the insect's mouth; beginning with the upper lip, (_a_) or _labrum_. Unlike that organ in ourselves, the insect's upper lip is generally, in such insects as bite their food, a plate of horny substance, which serves the purpose of an upper covering to the rest of the mouth. Like our own upper lips, however, that is to say, like those of men, at least, it is fringed with a sort of _moustache_ in most cases.
The _mandibles_, (_b_) or upper jaws, in the biting insects, are instruments for cutting the food in pieces. When we bite our food, the movement of our jaw is upwards and downwards; but in the insect it is like that of a pair of scissors, or from side to side! These jaws are sometimes frightful-looking instruments, resembling, in the stag-beetle, _horns_; and their power is proportionally great. Although their general use is to masticate or crush the food for the insect, this apparatus is often employed as a formidable weapon of defence, or offence; and very frequently in the excavation of a nest or retreat for the insect. They are sometimes so constructed, as to look as if they were furnished with several teeth.
[Illustration: _The Stag-Beetle, representing its enlarged Mandibles, like horns._]
The _maxillæ_, or _lower jaws_, are less firm and strong than the preceding; but they are more complicated in their structure, and have attached to their sides remarkably delicate little processes like the antennæ, which are called the _palpi_, or, less properly, _feelers_. The lower jaws are much varied in structure in different insects; as may well be imagined, when it is mentioned that the long and beautiful spiral tube of the butterfly, by which it drains the juices of the flower, is, in reality, composed of the maxillæ, or lower jaws. In ordinary cases, the principal use of the lower jaws appears to be to hold the food, while the upper jaws bruise and crush it; but their use, of course, varies with their structure and modifications.