THE MECHANISM OF THE SHADOW REFLEX IN CIRRIPEDIA. II. PHOTORECEPTOR CELL RESPONSE, SECOND-ORDER RESPONSES, AND MOTOR CELL OUTPUT

Abstract

Examination of the gross structure of the central nervous system and some of the peripheral structures involved in the shadow reflex of certain balanid Cirripedia (Balanus eburneus, B. cariosus, and B. tintinnabulum) establishes that these animals possess both paired lateral and unpaired median photoreceptors and it is suggested that this is true of all balanid Cirripedia. Intracellularly recorded sensory potentials from the lateral ocelli of B. eburneus indicate that spiking does not occur in these retinula cells, and that the response to a light flash is very similar to comparable records from other arthropod retinula cells. The primary sensory event is non-adapting, the presumed second-order cells adapt very slowly as does the cirral motor output in B. tintinnabulum. The cirral output in B. cariosus adapts rapidly as the adductor muscle motor output in both species. No significant difference in function between the lateral and the median ocelli has been shown with the procedures used in this study.