The period of pupal sleep in the life of insects is a period of great and complex organizational changes, resulting in a new and radically different insect. The larvæ of insects devote their whole attention to growing and molting. They eat enormous quantities of food and grow large and fat. The silk worm, for example, during its thirty-day period of growth, increases its weight fifteen thousand times. At the end of its larval stage the silkworm spins for itself a cocoon by which it protects itself in the pupa stage. There emerges from the cocoon, not a worm but a silkfly. The caterpillar of the butterfly changes to a chrysalis. The outer covering of the chrysalis is a hardened shell, usually brown in color. There emerges from this, not a worm, but a butterfly. Whereas, the worm-like larva enters the cocoon or chrysalis, it emerges an adult butterfly or moth, totally changed, both in internal and external structures, with different functions to perform and a different life to lead.

It is during the stage of pupal sleep that the entire organism of the insect undergoes a complete and radical metamorphosis, there is a tearing down of old structures, a re-shuffling of materials, the creation and re-aggregation of parts, so that what emerges from the pupa, when the transformation is complete, is an organism so unlike either the pupa or the larva that it may easily be mistaken for a totally new and distinct species.

It is interesting to note that during the pupal stage of insect life no food is taken. During this period of outward quiescence, all of the material stored up by the gluttonous larva is used out of which to construct a totally new and different organism. By autolysis old structures are torn down, stored materials are digested and prepared for new use, the materials are shifted from one part of the organism to another. All of this marvellous process of metamorphosis takes place while the animal is fasting. Here is a striking example of the constructive work that the organism may carry on while abstaining from food. But it should be understood that materials could not be shifted from one part of the body to another and no-longer-needed structures could not be torn down and the materials of which they are composed could not be used out of which to construct new structures, except they they are first digested. Autolysis is as essential at this stage of the