CATERPILLAR AND THE MOTH
prepupal stage of the larva. The insect in the prepupal stage bas suffered no change in external structure, it still wears the larval skin, and its visible difference f?om the active larva is a mere alteration in form. Internally, how- ever, important reconstructive processes are now taking place. The internal activities of reconstruction, which bring about the pupal metamorphosis of the larva to the adult, begin at the head end of the insect and progress poste- riorly. They are preceded by a loosening and subsequent detachment of the larval cuticula from rhe cellular layer of the skin, or epidermis, beneath it. The latter, known also as the h)'podermis, freed now from restraint, enters a period of rapid growth. On the head, the head walls are remodeled and take on a new form, and new antennae and new mouth parts are produced. The new structures have no regard for the forms of the old, though each is pro- duced from a part of the corresponding larval organ. The new antennae, for example, are formed from the larval antennae, but the antennae of the moth are to be much larger than those of the caterpillar. Only the tip, there- fore, of each new organ can be formed within the cuticular sheath of the old; the base pushes inward, and rhe don- gating shaft folds against the face of the newly forming head. The same thing is true of the maxillae and labium, but in the case of the mandibles the procedure is simpler, for the jaws are to be reduced in the moth. The epi- dermal core of each mandible, therefore, simply shrinks within the cuticular sheath of the larval organ, leaving the cavity of the latter almost empty. As the separation of the cuticula from the epidermis progresses over the region of the thorax and a free space is created between the two layers, the wing buds, which heretofore have been turned inside the caterpillar's body, now evert and come to be external appendages of the pupal body though still covered by the curicula of the larva (Fig. ?59 C, I/es, I¢"a). The legs of the moth pupa are
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INSECTS
