NEUROSECRETION AND SHELL REGENERATION IN HELISOMA-DURYI (MOLLUSCA-PULMONATA)

The distribution of cells that stain positively with paraldehyde fuchsin (PAF) in the brain of H. duryi was mapped. Two cell groups occurred in the the visceral ganglion, 1 of which (group 1) contained electron-dense secretory granules resembling neurosecretory material. Backfilling experiments and serial sectioning showed that group 1 cells sent axons into the intestinal and left pallial nerves. PAF-positive material was depleted from group 1 cells between 24-48 h after shell removal and reappeared by 72 h. PAF-positive material accumlated in the axons by 24 h and disappeared by 48 h; shell regeneration was apparently completed within 15 days. Tissue injury alone or shell removal from a non-regenerating area did not cause depletion of stainable material in these cells. No change in stainability occurred in other PAF-positive cells in the brain during shell regeneration. This cycle of activity may indicate involvement of the group 1 neurosecretory cells in the control of shell regeneration.