Thyroid glands play a key role in metamorphosis of frog’s tadpole. Metamorphosis is profound changes of form during development from larva to adult animal. The process of metamorphosis is essentially under hormonal control. Hormones from the hypothalamus (e.g. TSH or thyroid stimulating hormone) and the thyroid gland regulate the process of metamorphosis. Thyroxine hormone secreted by thyroid gland affects the tissues directly, causing the degeneration and necrosis of some cells and stimulating the growth and differentiation of others.