Hypophysectomy would lead to lowered thyroxine levels at either stage of development, but it would have a much more dramatic effect on an early stage tadpole, perhaps completely stopping metamorphosis. Later on, some juvenile features might be retained, but much of metamorphosis would have already occurred.
Work Step by Step
Look at Fig. 45.12 and see that the role of thyroxine is much greater at early stages of metamorphosis and extrapolate from that to the different effects of hypophysectomy at different stages of metamorphosis.