The material of which the case or cocoon is composed is a beautiful silken fibre, which is furnished by a spinning apparatus placed either at the extremity of the body, or more frequently at the mouth of the insect, whence it proceeds in a filament of the utmost delicacy and transparency, but at the same time of considerable tenacity. By its means alone cocoons, of a number of different kinds, some of extraordinary beauty and ingenuity, are constructed; but in other cases the insect has recourse to various materials to assist in giving strength to the walls of its cell.
The best example, and the most familiar one we can select of a purely silken cocoon, is that of those
"----spinning worms That in their green shops weave the smooth-haired silk."
This beautiful and valuable cocoon, when examined externally, appears to be formed in two different ways; for the outer covering is loose and open, while the inner one is compact and close, and so in truth it is, although both coverings are formed of a single thread. The outer has been called the _scaffolding_, by means of which the inner and more solid covering is constructed. The larva stationing itself between two leaves, or in any other suitable spot, fastens its thread to one of the adjoining surfaces, and then proceeds to draw out the fibre and fasten it in various positions until it has woven around itself an envelope, as it were, of loose gauze. After this has been done it begins to form the closer and more compact structure of the inner envelope, laying on the silk backwards and forwards in a series of zig-zags, until it has laid on several layers, and thus completely shut itself in. The loose outer portion forms what ladies so well know under the title of flos-silk; the inner fibres are the most continuous, admitting of being wound off without breaking, and they form the ordinary silk of commerce.
[Illustration: _The Larva surrounded by its Palisade._]
M. Lyonnet has given a most interesting account of the proceedings of another larva which far surpasses the silk-worm in the ingenuity of its manner of forming the cocoon. This larva is very small; in fact, not more than the sixth of an inch in length, and is found on the under side of oak-leaves. M. Lyonnet observes, that beyond all the larvæ he had ever watched, he considered this creature the most inconceivably ingenious workman. Its little cocoon is of a white colour, and of a long oval form, having its upper surface ornamented with seven upright ridges. The first thing the creature begins by doing, is to erect, in the most curious manner, a series of little upright palisades of silk at a certain distance from each other, all round its body, so as to form a sort of oval fence, and probably the larva intends them to serve as a sort of hedge to keep off intruders while it is busy at work! After spinning half its case, it turns round, and begins at the opposite end, and thus forms the other half; it then unites it in the middle, and by so doing incloses itself in a very pretty cage of silken net-work, which it subsequently strengthens by adding a firm layer on the inside. The time taken in the construction of this ingenious cocoon is not more than half-an-hour. It is quite impossible to understand how the little being contrives to form the upright ridges on the surface of its cocoon; and as the larva is so minute it is almost hopeless to expect to discover it. Attempts have been made to unravel the difficulty, but not with complete success. When, looking at some magnificent works of man, we are tempted to become inflated with pride, let the remembrance of what this tiny insect can do keep us humble, and direct our admiration rather to Him who is the Author of all wisdom, the Giver of every good and perfect gift.