Electrical Responses to Light Stimuli in the Isolated Radial Nerve of the Sea Urchin, Diadema setosum (Leske)

Abstract

THE echinoid Diadema responds to changes in illumination by moving its spines. This reaction has long been known to be a reflex mediated by the radial nerves^1,2 and, though morphologically differentiated photoreceptors have not yet been found, good evidence exists that the nervous elements themselves are sensitive to light. This was first suggested by finding that the distribution of sensitivity over the body surface coincided with that of the superficial nervous system². Later, more direct evidence came from experiments in which spine movements were brought about by stimulating directly the radial nerve with a minute spot of light³.