The marginal sphincter of the sea anemoneCalliactis parasitica

Abstract

1. The properties of the inhibitory response acting on the marginal sphincter ofCalliactis parasitica have been examined using partially-isolated sphincter preparations. 2. The response is active during stimulation of the preparation at frequencies ranging from 1 pulse every 4 sec to 1 every 16 sec (Fig. 1) and has a maximum effect at an inter-pulse interval of 9–10 sec (Fig. 2). 3. Fast, facilitated contractions of the sphincter can be elicited during the inhibitory period (Fig. 3) and appear to be totally independent of this effect. 4. Slow contraction of the sphincter may be delayed for periods of upto 30 min or more, provided appropriate stimulation is maintained. 5. The inhibitory effect is mediated by the through-conducting nerve-net. No other conduction system seems to be directly involved (Fig. 4). 6. A new model (Fig. 5) for the innervation of the sphincter is proposed to account for the facilitatory, excitatory and inhibitory effects encountered in this muscle.