Some curiosity may be felt to know in what way the silk-worm moth escapes from the double prison,--the pupa case, and the cocoon,--in which she is concealed. How is the moth to make its way through the dense mass of fibres all glued together, which walls her in on every side? Her delicate wings and body would never endure anything like the severity of the struggle necessary to enable her to force her way through this, to her, solid and resisting mass. Though much attention has been paid to the transformations of this particular insect, it is somewhat curious that it is still a matter on which opinions are divided, as to how the insect succeeds in making its egress. Some suppose that the eyes, which are the only hard organs of the head, are the instruments by which the threads are divided, their numerous minute facets serving the purpose of a file. Others hold the belief that the insect pours out a fluid which acts upon the gum and silken fibres of one end of the cocoon, and so softens them that they easily give way to the slightest pressure from within. "Perhaps the two opinions," observe Messrs. Kirby and Spence, "may be reconciled by supposing the silk-worm first to moisten, and then to break, the threads of the cocoon. In those that are of a slighter texture, a mere push against the moistened end is probably sufficient; and hence we find in so many newly-disclosed moths the hair in that part wet and closely pressed down." It has been supposed, in cases where the cocoon is a hard, almost wooden cell, that the feeble insect prisoner within is provided with a peculiar chemical fluid, of greater powers of solution than are requisite in the last instance. The cocoon of the "pussmoth," in particular, is so hard and dense, as to resist even the point of a penknife; and the insect it holds confined within it is a weak creature, totally unprovided with any apparatus fit for penetrating walls so hard and dense as these. What is it to do? "Here," observe the writers last quoted, "the eyes are clearly incompetent; nor could any ordinary fluid assist their operations, for the gum which unites the woody particles of the cocoon is indissoluble in _aqueous_ menstrua. What an aqueous solvent cannot effect, an _acid_ is competent to; and with a bag of such acid our moth is furnished. The contents of this she pours out as soon as she has forced her head through the skin of the pupa, and upon the opposite end of the cocoon. The acid instantly acts upon the gum, loosens the cohesion of the grains of wood, and a very gentle effort suffices to break down what was, a minute ago, a strong barrier. How admirable and effectual a provision! But there is yet another marvel connected with it. Ask a chemist of what materials a vessel ought to be to contain so potent an acid; he will reply,--Of _glass_.[O] Yet our moth has no glass recipient; her bottle is a membranous bag; but of so wonderful a fabric as not to be acted upon by