[Illustration: _Cocoon of Emperor Moth._]
Upon the pear or willow tree may sometimes be found an illustration of escape from the pupa, altogether well deserving our notice. In such situations the brown flask-shaped cocoon of the emperor moth may occasionally be discovered. In structure it is composed of a solid tissue of layers of silk, almost of the texture of parchment; but at the narrow end, or that which may be compared to the neck of the flask, it is composed of a series of loosely attached longitudinal threads, converging like so many bristles to a blunt point, in the middle of which is a circular opening, through which the moth makes its escape, the threads readily yielding to pressure from within, and acting somewhat on the principle of the wires of the opening to a rat-trap, or the willow cricks of an eel-trap. The silk of its cocoon is of so strong a texture, and so closely gummed, that had both ends been similarly closed, the egress of the insect would have been impracticable. But, it may be thought, such a cocoon is exposed to the attacks of a number of insect enemies, who might easily find entrance to it at the opening thus left at one of its ends. This source of peril has been foreseen. Within the exterior funnel-shaped end, at some little distance down, the insect has constructed a second funnel composed of a similar circle of needle-pointed threads, which, proceeding from the sides of the cocoon, converge to a point, and form a cone through which not the smallest aperture is left. From the arched structure of this singular dome, and from the fact just mentioned, that no visible opening can be discerned in it from without, it is rendered quite impenetrable to the most violent attacks of besiegers, while it yields to the slightest pressure from within, and allows the insect to emerge from its cocoon with the utmost facility. When it has passed through it, the elastic threads resume their former position, and the empty cocoon presents just the same appearance that it did before. A celebrated naturalist (Rösel), was sorely perplexed at this, the first time he had the gratification of watching the insect escape. He states that he could scarcely help thinking that there was something supernatural in the appearance of one of these fine emperor moths in a box in which he had put a cocoon of this kind; but in which he could not discover the slightest appearance of any insect having escaped from it, until he slit it longitudinally, and then found it to be empty!