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Metamorphosis (Greek, ‘process of change of shape’) is the term, in the life sciences, for the dramatic reorganization of structure which occurs during the life cycle of animals which transform from a larval stage to a morphologically different adult stage. It was first studied in insects by Jan Swammerdam, in the 17th century. Subsequently, morphologists used the term metamorphosis to refer to the changes which they proposed occurred when the archetype of a group of organisms changed into a particular form; it was, for example, thought by some that the vertebrate skull was a metamorphosis of several vertebrae.
In the modern sense, metamorphosis is restricted to the description of changes which occur in larvae; such changes are triggered by environmental stimuli and are controlled by hormones. The eggs laid by a frog, for example, hatch as tadpoles and feed and grow as an entirely aquatic stage, complete with gills for extracting oxygen from the water. As it grows the tadpole undergoes a metamorphosis, developing legs and losing its tail until a small frog, complete with lungs, is able to emerge from the water as an amphibian. A more dramatic metamorphosis is seen in the change from caterpillar to butterfly, via the pupal stage during which the radical changes in morphology occur. RB
See also endocrinology; phenology. |
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