THE MECHANISM OF THE SHADOW REFLEX IN CIRRIPEDIA. I. ELECTRICAL ACTIVITY IN THE SUPRAESOPHAGEAL GANGLION AND OCELLAR NERVE

Abstract

Electrical activity of various parts of the nervous system in Mitella polymerus, Lepas anatifera, Balanus cariosus, and Balanus eburneus indicates that the primary event at the photoreceptor is an "on" response that takes the form of a simple electroretinogram similar to that found in other arthropods. Evidence is presented that this information is transmitted via electrotonic spread to second order neurons in the supraesophageal ganglion which are released from inhibition at "off" and respond in a pure "off" fashion, thus initiating motor activity that results in the withdrawal-closure protective "shadow reflex". Adaptation to multiple shadows occurs just prior to or at the motor output stage thus preventing the animal from responding to repeated, inconsequential shadows in nature.