Page:The fairy tales of science.djvu/178

146 outer skin of the caterpillar, being separated, may be easily drawn off from the butterfly which is contained and folded up in it. This done, it is clearly and distinctly seen that, within this skin of the caterpillar, a perfect and real butterfly was hidden, and therefore the skin of the caterpillar must be considered only as an outer garment, containing in it parts belonging to the nature of a butterfly, which have grown under its defence by slow degrees, in like manner as other sensitive bodies increase by accretion.

"But as these limbs of the butterfly which lie under the skin of a caterpillar cannot without great difficulty be discovered, unless by a person accustomed to such experiments—because they are then very soft, tender, and small, and are, moreover, complicated or folded together, and enclosed in some membranous covering—it is therefore necessary to defer the operation just now proposed until the several parts of the butterfly become somewhat more conspicuous than at first, and are more increased and swelled under the skin by the force of the intruded blood and aqueous humour. This is known to be the case when the caterpillar ceases to eat, and its skin on each side of the thorax, near under the head, is then observed to be more and more elevated by the increasing and swelling limbs, and shows the appearance of two pairs of prominent tubercles." Before this beautiful discovery was made the wildest theories were propounded to explain insect metamorphoses.