= Metamorphosis
<Metamorphosis> is a developmental transformation between substantially different life stages, such as a tadpole becoming a <frog> or a caterpillar becoming an adult <butterfly>. It can reorganize feeding structures, movement, habitat use and internal <tissues>, rather than merely increasing size. Regulated <cell differentiation>, <tissue> remodelling and <cell death> contribute to the transition.
An early experiment showed that feeding tadpoles thyroid <tissue> accelerated differentiation relative to comparison diets. <Feeding experiments on tadpoles: the influence of specific organs given as food on growth and differentiation by J. F. Gudernatsch>[1912, feeding comparisons and accelerated metamorphic changes after thyroid diet]{ref} The intervention connected a secretory <organ> to the timing of a whole-body transformation. It did not isolate a pure hormone or establish that growth and differentiation are the same process. Modern <thyroid hormone> biology explains this amphibian example; insect <metamorphosis> uses a different hormonal system.
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