A transformation, as by magic or sorcery. A marked change in appearance, character, condition, or function. Biology A change in the form and often habits of an animal during normal development after the embryonic stage. Metamorphosis includes, in insects, the transformation of a maggot into an adult fly and a caterpillar into a butterfly and, in amphibians, the changing of a tadpole into a frog. Pathology A usually degenerative change in the structure of a particular body tissue.