The larva of the order Lepidoptera are familiar to us all, under the name of caterpillars. The insects of this order in their larval condition are almost all phytophagous, and are very uniform both in structure and in habits. The body is long and cylindrical, consisting of thirteen segments; the head is armed with powerful jaws; the three following segments, the future prothorax, mesothorax, and meta-thorax, each bears a pair of simple articulated legs. Of the posterior segments, five also bear false or pro-legs, which are short, unjointed, and provided with a number of hooklets. A caterpillar leads a dull and uneventful life; it eats ravenously, and grows rapidly, casting its skin several times during the process, which generally lasts only a few weeks; though in some cases, as for instance that of the goat-moth, it extends over a period of two or three years, after which the larva changes into a quiescent pupa or chrysalis. CHAPTER II. _THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE OF LARVÆ._ The facts recapitulated briefly in the preceding chapter show, that the forms of insect larvæ depend greatly on the group to which they belong. Thus the same tree may harbour larvæ of Diptera, Hymenoptera, Coleoptera, and Lepidoptera; each presenting the form typical of the family to which it belongs. If, again, we take a group, such, for instance, as the Lamellicorn beetles, we shall find larvæ extremely similar in form, yet very different in habits. Those, for instance, of the common cockchafer (Fig. 1) feed on the roots of grass; those of _Cetonia aurata_ (Fig. 2) inhabit ants’ nests; the larvæ of the genus _Trox_ (Fig. 3) are found on dry animal substances; of _Oryctes_ (Fig. 4) in tan-pits; of _Aphodius_ (Fig. 5) in dung; of _Lucanus_ (the stag-beetle, Fig. 6) in wood. [Illustration: FIG. 1, Larva of the Cockchafer (_Melolontha_). (Westwood, Int. to the Modern Classification of Insects, vol. i. p. 194.). 2, Larva of _Cetonia_. 3, Larva of _Trox_. 4, Larva of _Oryctes_. 5, Larva of _Aphodius_ (Chapuis and Candèze, Mém. Soc. Roy. Liège, 1853). 6, Larva of _Lucanus_. (Packard, Guide to the Study of Insects, Fig. 403).]