1. the ontogeny of some animals encompassing the series of changes in shape, structure, and habits undergone from egg or embryonic stage into adult stage —note 1. entomology four kinds of metamorphosis are generally recognized: (a) no metamorphosis (ametabolous), in which the form emerging from the egg has the same morphology as the adult (e.g., springtails, proturans), (b) incomplete metamorphosis (hemimetabolous), in which there is no pupal stage but there is a distinct change in body form between the immature and adult stages; generally, immatures are aquatic nymphs with gills (naiads) and adults are aerial and without gills (e.g., dragonflies), (c) gradual metamorphosis, where immature nymphs and adults occupy the same habitats and feed on the same food, with a gradual change in size and body proportions and a gradual development of wings and sexual organs from one molt to the next (e.g., grasshoppers, aphids, bugs), and (d) complete metamorphosis (holometabolous), in which insects develop from egg to larva to pupa to adult —note 2. some entomologists recognize only two types of metamorphosis: complete, as defined above; and simple, consisting of no, incomplete, and gradual, as defined above 2. the change in form during the development of an insect —see life cycle, stadiumThis definition last updated 07/17/2008