together, while hairy caterpillars, such as those of the Tiger-moths, work some of their hairs in with the silk to make a firm cocoon (fig. 17 b).  On the other hand, those caterpillars known as ‘silkworms’ make a dense cocoon of pure silk, consisting of two layers, the outer of coarse and the inner of fine threads.  Silken cocoons very similar in appearance are spun by the larvae of small Ichneumon-flies.  Many pupae lie in a loose cocoon formed of a few interlacing threads, as for example the conspicuous black and yellow banded pupa of the Magpie-moth (Abraxas grossulariata) and the pupae of various leaf-beetles.  Others again spin together the edges of leaves with connecting silken threads.  The grubs of bees and wasps which are reared in the comb-chambers of their nests seal up the opening of the chamber with a lid, partly silk (fig. 18 co) and partly excretion, when ready to pass into the pupal state.  An additional external ‘capping’ may be also supplied by the workers.

The pupae of butterflies are especially interesting, as illustrating the extreme reduction of the silken cocoon.  The pupa of a ‘swallowtail’ (Papilionid) or a ‘white’ (Pierid) butterfly (fig. 23) may be found attached to a twig of its food-plant or to a wall, in an upright position, its tail fastened to a pad of silk and a slender silken girdle encircling its thorax.  The pupa of a ‘Tortoiseshell’ or ‘Admiral’ (Nymphalid) butterfly hangs head downwards from a twig, supported only by the tail-pad of silk, which, useless as a shelter, serves only for attachment.  The pupa is fastened to this pad by a spiny hook or process, the cremaster (fig. 23 cr), on the last abdominal segment.  The cremaster is a characteristic structure in the pupa of a moth or butterfly.  C.V.  Riley (1880) and W. Hatchett-Jackson (1890) have shown that it corresponds with a spiny area, the suranal plate, which lies above the opening of the caterpillar’s intestine.  The means by which the suspended pupa of a nymphalid butterfly attaches its cremaster to the silken pad which the larva has spun in preparation for pupation, is worthy of brief attention.  The caterpillar, hanging head downwards, is attached to the silken pad by its hindmost pair of pro-legs or claspers and by the suranal plate, and the cuticle is slowly worked off from before backwards, so as to expose the pupa.  Were the process of moulting to be simply completed while the insect hangs by the claspers, the pupa would of course fall to the ground.  But there is enough adhesion between the pupal and larval cuticles at the hinder end of the body, especially by means of the everted lining of the hind-gut, for the pupa to be supported while it jerks its cremaster out of the larval cuticle and works it into the meshes of the silken pad.  The moult is thus completed and the pupa hangs securely all the time.  In the numerous cases where the pupa is enclosed in a cocoon, the cremaster serves to fix the pupa to the surrounding