Tail regeneration in Phenylthiourea (PTU) treated tadpoles. (A) Untreated 4 day tail regenerate. (B) Tail regenerate of a tadpole treated with PTU for 4 days, starting immediately after tail amputation. (C) same tadpole as in (B), 2 days after PTU withdrawal. (D) same tadpole as in (B), 8 days after PTU withdrawal. White arrowheads mark the amputation level.