WAVE-FORM GENERATION IN RHAMPHICHTHYS-ROSTRATUS (L) (TELEOSTEI, GYMNOTIFORMES)

Rhamphichthys rostratus (L.) emits brief pulses (2 ms) repeated very r egularly at 50 Hz. The electric organ shows a heterogeneous distributi on of the electrocyte tubes and the occurrence of three electrocyte ty pes (caudally innervated, rostrally innervated and marginally-caudally innervated). In the sub-opercular region the electric organ consists of a pair of tubes containing only caudally innervated electrocytes. A t the abdominal region the EO consists of three pairs of tubes. Each p air contains one of the described electrocyte types. The number of ele ctrocyte tubes increases toward the tail to reach nine or ten pairs in the most caudal segments. In the intermediate region most tubes conta in doubly innervated electrocytes except the ventral pair that contain s caudally innervated electrocytes. The caudal 25% contains exclusivel y caudally innervated electrocytes. The electric organ discharge consi sts of five wave components (V1 to V5). Electrophysiological data are consistent with the hypothesis that V1 results from the activity of th e rostral faces of rostrally innervated electrocytes. V2 results from the activities of rostral faces of marginally-caudally innervated elec trocytes while V3 results from the activities of caudal faces of most electrocytes. Curarization experiments demonstrated that V4 and V5 res ult from action potential invasion and are not directly elicited by ne ural activity.