a glutinous secretion without the assistance of threads. Saw-flies, and some other Hymenopterous tribes, construct a double cocoon, the outer one not united to the interior, but inclosing it as the shell of a nut does its kernel. Many larvæ dwell in habitations which they form with much skill and labour, to defend their tender bodies, and these likewise serve as a ready and efficient protection for the pupa. Such are the cases of the May-flies (Phryganeæ) which are common in slow flowing streams, and curious on account of the materials with which they are covered; the mantles of many leaf-rolling caterpillars, and the portable tents constructed by others. Dipterous larvæ are frequently converted into pupæ within their own skin, which changes its form and becomes of a more rigid texture for the purpose of affording it more effectual protection. The change to a pupa does not always take place immediately after the preliminary arrangements are completed, although the contrary is the general rule; a period of inactivity often ensues; and some caterpillars remain unaltered within their cocoons for months together.
Pupa. This is the most general term applied to insects in the third stage of their existence, that, namely, which intervenes between the larva and imago. It was suggested by their appearance, which resembles that of a child wrapped up in swaddling clothes, all the parts being closely folded down, and enclosed in a general envelope. It is, therefore, very applicable to the majority of them, as they are completely dormant and inert, incapable either of moving
