In the present chapter I propose to give a brief sketch of the general principles of Entomology, including a rudimentary glance at the anatomy and classification of insects; after which I think the reader will be in a better position to study the habits and life-histories of the individual species which follow. The first requisite is a definition of what constitutes an INSECT. _An Insect is an articulate animal having the body divided into three distinct divisions_, viz., _the_ HEAD (Fig. I. A), _the_ THORAX (B), _and the_ ABDOMEN (C). _It is furnished with three pairs of legs, and generally has two pairs of wings, and to acquire this structure the creature passes through several changes, termed its metamorphoses._ {2}The head exhibits no distinct divisions, but bears the following appendages: the eyes, antennæ, and organs of the mouth, or trophi. The eyes are of two kinds, compound and simple. The former (Fig. I. c c) are situated on the sides of the head above the mouth, and consist of two large hemispheres, composed of a great number of hexagonal divisions, each of which is a complete eye in itself. The latter (s s) are usually three in number, and are situated on the top of the head between the compound ones. They are, however, frequently wanting. The antennæ (a) are two jointed organs, one of which is placed on each side of the head, between the eyes; their functions are at present extremely doubtful, but they are invariably found in all insects. The organs of the mouth consist of the following: the labrum (Fig. II. 3), or upper lip, a horny plate, closing the mouth from above; the mandibles (1 1), or upper jaws, two strong bent hooks, articulated to the head on each side of the mouth, and opposed to one another like scissor blades; the maxillæ (2 2), or under jaws, resembling the mandibles, but more delicately constructed, and furnished with a pair of jointed appendages termed maxillary palpi (5 5); and the labium (4), or lower lip, consisting of a horny plate somewhat resembling the labrum, but provided with two jointed appendages termed the labial palpi (6 6). All these organs are subject to great modification in suctorial insects, which I shall notice further on, when dealing with the differences between the various orders. The thorax consists of three primary divisions, viz., the prothorax (Fig. I. b), mesothorax (d), and metathorax (k). The upper surfaces of these are termed the pronotum, mesonotum, and metanotum respectively, and the under the prosternum, mesosternum, and metasternum; other divisions exist in some insects, but they are not of a sufficiently {3}general character to be noticed here. The six legs are attached to the under surface of the thorax, a single pair to each division; they are composed of the following joints: coxa (Fig. I. n), trochanter (o), femur (p), tibia (r), and tarsus (s). [Illustration]