The planarian flatworm shown here possesses a remarkable ability to regenerate complex tissue structures lost to injury, including a brain and eyes. Each color represents a different layer of neurons in the head, revealed by expression of the choline acetyltransferase (ChAT) gene. Not shown in this image are the abundant stem cells that give rise to a new central nervous system as the flatworm regenerates. The Reddien Lab studies planarians to illuminate the cellular and molecular basis of regeneration.