Electrical Activity in the Hydroid Cordylophora

Abstract

1. Cordylophora has two major hydranth pacemaker systems, one producing slow,, biphasic pulses at 2.0-4.0 sec. intervals (slow pulse or SP system) and one exhibiting sharp, predominantly negative potentials singly or in bursts with a normal interval of 1.5-2.0 sec. between pulses (fast pulses, FPs). 2. Both SPs and FPs are recorded throughout the hydranth, but do not spread to and are not co-ordinated in adjacent hydranths. 3. SPs could not consistently be evoked artificially and showed no clear behavioural correlates. FPs occur during feeding and following electrical stimulation, where they may accompany a muscle response. 4. FPs appear superimposed on SPs when both systems are active. Such a composite event advances the SP rhythm by an amount close to the normal FP inter-pulse time, but compensatory adjustment of the SP rhythm then occurs. 5. Treatment with 10^-5 g./ml. tetrodotoxin has no apparent effect on Cordylophora.