[a]Fig. 23.]—Caterpillar of Anosia plexippus, undergoing change into chrysalis: a, caterpillar just before rending of the skin; b, chrysalis just before the cremaster, or hook, at its end is withdrawn; c, chrysalis holding itself in place by the folds of the shed skin caught between the edges of the abdominal segments, while with the cremaster, armed with microscopic hooks, it searches for the button of silk from which it is to hang (Riley). (Compare Fig. 24, showing final form of the chrysalis.)
The Form of Chrysalids.—The forms assumed by the insect in this stage of its being vary very greatly, though there is a general resemblance among the different families and subfamilies, so that it is easy for one who has studied the matter to tell approximately to what family the form belongs, even when it is not specifically known. Chrysalids are in most cases obscure in coloring, though a few are quite brilliant, and, as in the case of the common milkweed butterfly (Anosia plexippus), ornamented with golden-hued spots. The chrysalids of the Nymphalidæ, one of the largest groups of butterflies, are all suspended. The chrysalids of the Papilionidæ, or swallowtail butterflies, are held in place by girdles, and generally are bifurcate or cleft at the upper end (Fig. 25), and are greenish or wood-brown in color.
[a]Fig. 24.]—Chrysalis of Anosia plexippus, final form (Riley).
[a]Fig. 25.]—Chrysalis of Papilio philenor: a, front view; b, side view, showing manner in which it is held in place by the girdle of silk (Riley).
[a]Fig. 26.]—Pieris protodice: a, caterpillar; b, chrysalis (Riley).
A study of the structure of all chrysalids shows that within them there is contained the immature butterfly. The segments of the body are ensheathed in the corresponding segments of the chrysalis, and soldered over these segments are ensheathing plates of chitinous matter under which are the wings of the butterfly, as well as all the other organs necessary to its existence in the airy realm upon which it enters after emergence from the chrysalis. The practised eye of the observer is soon able to distinguish the location of the various parts of the butterfly in the chrysalis, and when the time for escape draws near, it is in many cases possible to discern through the thin, yet tough and hard, outer walls of the chrysalis the spots and colors on the wings of the insect.