formed in the same way as are the antennae and the mouth parts, that is, they are developed from the epidermis of the corresponding larval legs; but, by reason of their creased size, they are forced to bend upward against the sides of the body of the pupa, and, when fully formed, each is round to have only its terminal part within the cuticular sheath of the leg of the caterpillar. From the thorax, the loosening of the cuticula spreads backward over the abdomen, until at last the entire insect lies ffee within the cuticular skin of the caterpillar. The so-called prepupal period of the caterpillar, therefore, is scarcely to be regarded as a truly larval stage of the in- sect. it is still clothed in the larval cuticula, and retains externally all the structural characters of the larva; but the creature itself is ira a first growth period of the pupal stage, and may appropriately be designated a propupa. When the cuticula is separated flore the epidermis all over the body, it may be cut open and taken off without injury to the wearer. The latter, now a propupa (Fig. ?59 C), is then discovered to be a thing entirely different in appearance flore the caterpillar. It bas a small head bent downward, a thoracic region of three segments, and a large abdomen. The head bears the mouth parts and a pair of large antennae (?4nt) ; the thorax carries the wings (IFs, II.'?) and the legs (L), which latter are much longer than those of the caterpillar, but, being folded beneath the wings, only their ends are visible in side view. The abdomen consists of ten segments and bas lost all ves- tiges of the abdominal legs of the caterpillar (A, .4L). Many important changes have taken place ira the form and structure of the head and in the appendages about the mouth during the change from the caterpillar to the propupa, as may be seen by comparing Figure ?59 H, with Figure I5?'. Most of the lateral areas of the caterpillar's head (Fig. ?5?), including the region of the six small eyes on each side, have been converted into the two huge eye areas of the pupa (Fig. I59 H, E), which cover the develop-
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