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The basic hormonal regulation of amphibian metamorphosis was established by Gudernatch (1914). It has been well established that development and metamorphosis of amphibians are under the control of several hormones. Of these, thyroid hormone has long been known as the key hormone inducing metamorphic changes in amphibians [Frieden and Just, 1970). Although T4 is normally more abundant than T3 , it is generally accepted that the latter is responsible for most of the physiological actions of the thyroid hormones in mammals. According to Galton (1983) conversion of T4 to T3 is accelerated as metamorphosis proceeds, the latter being biologically more active than T4 . T3 binding sites in the target tissue are increased during metamorphosis. Leloup and Buscaglia (1977) recorded the importance of T3 during metamorphic climax.