A change in the form or function of a living
organism, by a natural process of growth or development; as, the
metamorphosis of the yolk into the embryo, of a tadpole into a frog, or
of a bud into a blossom. Especially, that form of sexual reproduction
in which an embryo undergoes a series of marked changes of external
form, as the chrysalis stage, pupa stage, etc., in insects. In these
intermediate stages sexual reproduction is usually impossible, but they
ultimately pass into final and sexually developed forms, from the union
of which organisms are produced which pass through the same cycle of
changes. See Transformation.