Six or eight days after beginning the cocoon, the larval skin is moulted and the real chrysalic or pupal stage begins. This stage normally lasts till the following spring or summer. A few days before the time of emergence a pair of glands which open into the mouth become very active and secrete an acidulated fluid which escapes and wets the fore end of the cocoon, causing the resinous material binding together the fibres to become soft. Even cocoons sealed up in shellac and starch have been dissolved by this fluid, and thus the moths have been able to escape. When the cocoon has become sufficiently soft, the moth pushes its way between the fibres, but in doing so often breaks some of the threads, thus making the silk of such cocoons useless, for commercial purposes. The moth at the time of emergence, with its folded and crumpled wings, is quite a forlong-looking object. These wilted wings soon begin to fill up with fluids from the body, which is very large at this time. In some cases, the fluid is driven into the wings with so much force that they swell up, and if such a wing is punctured, thus allowing some of the fluid to escape, the mature wing will be of a smaller size than one from which no fluid has been lost. It must be remembered that it is possible to inflate a butterfly or moths wing, because the wings of insects are not composed of a single layer, but are sacs of two layers which are closely applied. It is thus possible to split the wing into upper and lower halves, but this can only be done at the time of emergence, when these two layers are not so firmly cemented together as they are in a few hours after emergence.

The enemies of Polyphemus are numerous. Birds prey upon the larvae, in addition to numerous parasitic insects which are very similar to those which destroy Cecropia.

The cocoon itself is not a complete protection because rats, and squirrels plunder them. We thus see that the life of even an insect is full of dangers, and that it is really a wonder that so many are able to become mature and reproduce.

The silk-worm moths are excellent illustrations of what is called complete metamorphosis in insects. An insect like the grasshopper, when it hatches from the egg, is very much like the adult insect in its general form and appearance; the most evident difference being the lack of wings. An insect which shows such slight changes in its growth to maturity is said to have an incomplete metamorphosis. It is incomplete in the sense that the change is not of a very radical nature. But in the case of the silk worm moths, and moths and butterflies in general, the larva which hatches from the eggs has not even the most superficial resemblance to the adult insect, the fully developed moth. This necessitates a complete change or metamorphosis in the form and structure of the insect before it can become mature. This great change is accomplished during the quiet pupal stage in the cocoon. Because the pupa is apparently passive when viewed from the exterior, one must not conclude that it is so internally; far from it; the digestive organs of the larva must be completely made over from those of a chewing leaf eater to those of a moth which can only take liquid food.

Description of Plate (from left to right): Adult Luna Male; Adult Luna Female; Luna Larva; Luna Pupa; Luna Cocoon; Adult Polyphemus Male; Adult Polyphemus Female; Polyphemus Larva; Polyphemus Pupa; Polyphemus Cocoon; Eggs on Maple Leaf.