A change in form during the development. After hatching from the egg, an insect grows by a series of molts. After shedding the old skin they expand into a new larger one. This molting continues until the adult stage is reached. At each molt, some externally visible changes occur. This type of growing is called metamorphosis. The division of insects into apterygota, exopterygota and endopterygota is mainly based on differences in the type of metamorphosis. (See also Complete metamorphosis, Incomplete metamorphosis).