Hubl (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 b-cells, showed intense secretory activity as soon as the worm was injured and the ventral nerve-cord damaged.