He continued dissecting until twelve, with his hat removed lest it should impede the light, and in the full blaze of the sun, the heat of which caused his head to be constantly covered with profuse perspiration. His eyes being constantly exposed to a strong light, the effect of which was increased by the microscope, they were so affected by it, that after midday he could no longer trace the minute bodies which he examined, although he had then as bright a light as in the forenoon.” Swammerdam investigated the nature of the changes of outside form and internal structure which accompany insect life. Some of his drawings of the escape of the ephemera fly from its sheath of delicate skin on the surface of the water, and out of the wingless or nymph condition, are very beautiful. But his accuracy regarding the minute internal changes of the tissues and organs in the larva, pupa, and perfect insect is being more and more acknowledged. He taught that these changes were not sudden, but that a continuous growth of organs and tissues culminated at certain times of the life of the insect. The larva, or caterpillar, admirably adapted for its course of life, was a stage of the life cycle of a more perfect form, the imago or flying insect. Swammerdam stated that all the organs of the perfect insect—a butterfly, for instance—were in a visible yet only slightly developed condition in the caterpillar. And late researches are leading to prove that he was right, for the wings of the future fly are to be detected in the body of the tiny crawling thing that escapes from the egg.