Stimulation of Egg Laying: Possible Neuroendocrine Function of Bag Cells of Abdominal Ganglion of Aplysia californica

Two groups of identified cells in the abdominal ganglion of Aplysia californica have been classified as neurosecretory on the basis of several morphological features1,2. These are the two clusters of bag cells and the white cells R3–R14 (Fig. 1). To investigate the possible neurosecretory function of this ganglion I homogenized four ganglia, and injected the material into the haemocoel of a small animal. Twelve hours later I found a string of gelatinous material resembling the eggs which are occasionally laid by larger animals. This suggested that the ganglion contains a substance which stimulates egg laying. To examine this possibility further four ganglia from large animals (500–700 g) were homogenized in 0.25 ml. of sea water in a small glass tissue grinder fitted with a glass pestle. The resulting suspension was injected into the haemocoel of a large animal (500 g) which had been isolated for a week, during which time it laid no eggs. Within 1.5 h of the injection the animal laid a string of eggs weighing approximately 2 g. In two other experiments, this animal again laid eggs after similar injections.