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The changes have been found to be made up of two sets of processes: histolysis, by which the whole or part of a structure disappears: and histogenesis, or the formation of the new structure.

By histolysis certain parts of the hypodermis are destroyed, while other portions of it develop into the new structures.

Hence the opinion arose that histolysis is a process of phagocytosis.

Histolysis and Histogenesis.—The process of destruction of the larval tissues was first studied in the forms where metamorphosis is greatest and most abrupt, viz. in the Muscid Diptera.

Histolysis: the degeneration and dissolution of organic tissue.