Influence of the supra-oesophageal ganglion on posterior regeneration in Nereis diversicolor.

H U B L (1956) demonstrated that if the supra-oesophageal ganglion of lumbricid oligochaetes is removed at the time of amputation of a number of posterior segments, caudal regeneration is totally inhibited, but if the ganglion is not removed until 24-48 hours after amputation of the posterior segments, regeneration proceeds at the normal rate. A comparable phenomenon may occur in nereid polychaetes. Removal of the prostomium (Casanova, 1955) or, more precisely, of the supra-oesophageal ganglion (Durchon, 1956), retards regeneration but does not prevent it, but as these experiments were performed. On the day following amputation of the posterior segments it is still not certain whether the brain of Nereis is, at any stage, essential for posterior regeneration as it clearly is in lumbricids. In his investigation of Lumbricus and Allolobophora, Hubl (1956) found that neurosecretory cells in the supra-oesophageal ganglion, the &-cells, showed intense secretory activity as soon as the worm was injured and the ventral nerve-cord damaged. In the polychaete Nephtys, too, certain neurosecretory cells in the supra-oesophageal ganglion show signs of secretory activity within 6 hours of the loss of posterior segments (Clark & Clark, 1959). There is thus a very prompt response in the supra-oesophageal ganglion of lumbricid oligochaetes and nephtyid polychaetes to the loss of segments, and it is possible that this is true of nereids also. In the experiments performed on nereids by Casanova and Durchon, the supra-oesophageal ganglion remained intact for 24 hours after the segments had been removed, i.e. during the period when the initial response in the ganglion might be expected to occur. The experiment described below has been designed to complement those of Casanova and Durchon and to investigate the role of the supra-oesophageal ganglion of Nereis during the initial stages of regeneration.