Page:Insects - Their Ways and Means of Living.djvu/359

 CATERPILLAR AND THE MOTH

their purpose has been accomplished go into a state of dis- solution during the pupal period. The débris of their tissues is thrown into the blood, from which it is later ab- sorbed as nutriment by the newly forming organs. The caterpillar has a very elaborate system of muscles forming a complicated network of fibers against the inner surface of the body wall, some running longitudinally, others transversely, and still others obliquely. Most of the transverse and oblique fibers are hOt retained in the moth, and if specimens of those muscles are examined during the early part of the pupal period they are seen to have a weak and abnormal appearance; the structure typical of healthy muscle tissue is obscure or indistinctly evident in them, and in places they are covered with groups of free oral cells. These cells are probably p/mgocytes. A phagocyte is a blood corpuscle that destroys foreign proteid bodies in the blood, or any unhealthy tissue of the body. It is hot probable that the insect phagocytes are the active cause of the destruction of the larval tissues, but they do engulf and digest particles of the degenerating tissues. They are present in large numbers in some insects during metamorphosis, and are scarce or lacking in others. The decadent state of the larval tissues that have passed their period of activity lays them open to the attack of the phagocytes, but these tissues will go into dissolution by the solvent powers of the blood alone. Active, healthy tissues are always immune from phagocytes. Some of the larval muscles may go over intact to the adult stage, and others may require only a remodeling or an addition of fibers to make them serviceable for the purposes of the adult. The adult muscles that are com- pletely suppressed during the larval stage appear to be generated anew during the pupal stage. There is a dif- ference of opinion among investigators as to how the new muscles are developed, but it is probable that they take their origin from the same tissues that built up the larval muscles.

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INSECTS