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 forlorn-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 moth's 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.