[Illustration: Figs. 102, 103.--Caterpillars of the small Tortoise-shell Butterfly (_Vanessa urticæ_) undergoing their metamorphoses.] [Illustration: Figs. 104, 105.--Chrysalides of the small Tortoise-shell Butterfly freeing themselves from the Caterpillar skin.] It remains hanging thus, often for twenty-four hours, during which time it is occupied in a difficult task, that of splitting its skin. In order to effect this, it incessantly curves and recurves its body (Fig. 102), until at last a split appears on the skin of the back, and through this split emerges a part of the body of the chrysalis. This acts as a wedge, and little by little the split widens from the head to the last of the true legs, and beyond them. Then the opening is sufficient to allow of the chrysalis drawing out its anterior portion from the envelope, which it immediately does. To set itself entirely free, the chrysalis lengthens and shortens itself alternately (Fig. 105). Each time that it shortens itself, and when it consequently distends the part of its body which is outside the old skin, that part acts against the edges of the slit, and gradually pushes the old skin upwards. Thus the caterpillar skin ascends, its plaits are pushed nearer and nearer together, and it is soon reduced to a packet so small that it covers only the end of the tail of the chrysalis (Fig. 106). But here comes the culminating point, the most difficult part of the operation. The chrysalis, which is shorter than the caterpillar, is at some distance from the silky network to which it must fix itself; it is only supported by that extremity of the caterpillar's skin which had not been split open. It has neither legs nor arms, and yet it must free itself from this remaining part of the skin, and reach the threads to which it is to suspend itself. [Illustration: Fig. 106.--Chrysalis of the small Tortoise-shell Butterfly completing the operation of casting its larval skin.] [Illustration: Fig. 107.--Chrysalis divested of the larva skin.] The supple and contractile segments of the chrysalis serve for the limbs which are wanting to it. Between two of these segments, as with a pair of pincers, the insect seizes a portion of the folded skin, and with such a firm hold that it is able to support the whole of its body on it. It now curves its hinder parts slightly, and draws its tail entirely out of the sheath in which it was enclosed. It then reposes for an instant only, for it has not yet finished the laborious operation of its deliverance. It must free itself entirely from the dry skin which surrounds the extremity of its body.