The effect of vitamin A on development and differentiation of thyroid gland with particular reference of Bufo melanostictus (schneider) tadpoles of stage 34 and 36 of this toad species. Vitamin A has been found to affect differentiation of thyroid gland in the toad tadpoles and the effect is more severe on younger tadpoles as compared to the older ones. In stage 34 and 36 untreated group shows well developed thyroid gland. Vitamin A treatment of stage 34 and 36 caused reduction in the size of thyroid gland as well as decrease in the size of colloid in such cases. These tadpoles show disorganization of epithelial cells of follicles. Tadpoles of discontinuous treated group shows quite normal thyroid gland similar to control. The colloid is thin, similar, and non-condensed
Keywords: - colloid, follicles, vacuoles, thyroxine, vitamin A