Thyroid gland secretes three hormones :
(i) Thyroxine,
(ii) Tri-iodothyronine
(iii) Calcitonin.
Thyroid gland is stimulated to secrete its hormone by a pituitary gland hormone TSH (Thyroid Stimulating Hormone). Thyroxine increases BMR (Basal Metabolic Rate) and stimulates growth, tissue differentiation and metamorphosis of tadpoles into adult frog.