Three Parallel Conducting Systems in the Stalk of A Hydroid

Abstract

1. There are three, non-polarized conducting systems in the stalk of Tubularia. These are termed the distal opener system (DOS), the triggering system (TS), and the slow system (SS). 2. The DOS controls opening of the distal tentacles of the hydranth. Activation of the DOS produces a small electric pulse in the stalk which is conducted at about 15 cm./sec. At the base of the distal tentacles this pulse is followed by a slow potential. The slow potential but not the pulse shows antifacilitation and is quickly blocked by excess Mg²⁺, as are distal tentacle movements. This is taken to indicate that the pulse and slow potential are a result of nerve and muscle activity respectively. 3. The TS can trigger the potentials which normally appear spontaneously in the neck region of the hydranth. The TS conducts at about 17 cm./sec and has a lower threshold than the DOS. No electrical correlate of TS activity has been found. 4. Activation of the SS produces large (up to 1 mV.), slowly propagated (about 6 cm./sec.) potentials in the stalk. The SS is very labile. In a fresh animal the SS threshold is two to three times that of the DOS and the SS often fires repetitively to stimuli above its threshold. SS activity has apparently no effect on polyp behaviour or on spontaneous electrical activity in the hydranth.