THE LIGHT RESPONSE AND THE RHYTHMIC POTENTIALS OF HYDRA

Abstract

Rhythmically reoccurring potentials can be reported electrophysiologically from intact hydras. Their frequency varies from about 1 per min to 12 per min. Sensory stimuli, notably the blue light, can modify their frequency and change their point of origin. Each pulse is compound and of a distinctive shape, originates from any one of several pacemakers within its through-conducting network, is seemingly independent of polyp movement, and is indirectly correlated with the animal''s behavior. Other much larger compound potentials, separately conducted, precede coordinated epidermal muscle contractions. The rhythmic potential system fulfills many criteria for a "central nervous system" for these animals. Its light sensitivity provides a mechanism for the hydra phototropic response.