INSECTS
caterpillar, for example, certainly is not a form headed toward a butterfly in its growth, and yet we know it is a young butterfly, because it hatches out of the butterfly's egg. And, as the caterpillar grows from a small caterpillar to a large caterpillar, it becomes no more like a butterfly than it was at first. It is only after it has reached maturity as a caterpillar that it undergoes a process of transformation by which it attains at last the form of the insect that produced it.
The question now arises as to whether the butterfly is a form superadded to the caterpillar, or the caterpillar a form that has deviated from the developmental line of its ancestors. This question is easily answered: the butterfly represents the true adult form of its species, for it has the essential structure of all other insects, and it alone matures the sexual organs and acquires the power of reproduction. The caterpillar is an aberrant form that somehow has been interpolated between the egg and the adult of its kind. The real metamorphosis in the lire of the butterfly, therefore, is not the change of the caterpillar into the adult, but the change of the butterfly embryo in the egg into a caterpillar. Yet the term is usually applied to the reverse process by which the caterpillar is turned back into the normal form of its species.
The caterpillar and the butterfly (Fig. 128) furnish the classical example of insect metamorphosis. Many other insects, however, undergo the same kind of transformation. All the moths as well as the butterflies are caterpillars when they are young: the famous giant moths (Plate 10), including the Cecropia, the Promethea, and the beautiful Luna (Fig. 129), as every nature student knows, come from huge fat caterpillars; the humble cutworms (Fig. 130), when their work of destruction is completed, change into those familiar brown or gray furry moths of moderate size (A) often round hidden away in the daytime and attracted to lights at night. In the spring, the
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