Planarian regeneration in the absence of a blastema

During planarian regeneration, a new tissue called the blastema is formed after amputation and is thought to play an important role in pattern formation. To investigate its role, posterior fragments with irradiated stumps were generated by regional X-irradiation, followed by amputation. No blastema formation occurred in the irradiated fragments until 3 days after amputation, because all the neoblasts had been depleted from the stump area by irradiation. However, regeneration of the pharynx occurred in the predicted region of the fragment, even in the absence of a blastema. These results suggest that the blastema is not essential for pattern formation during planarian regeneration.