1. The spontaneous activity and also the response mechanisms to externally applied electric shocks have been studied in the swimming sea anemone Stomphia coccinea obtained from Puget Sound, Washington.

2. Slow rhythmical activity with a repetition interval of the order of 30 min. is evident in kymograph records of whole-animal movements and also in rings of body wall isolated from the oral or basal regions.

3. By suitably placing the stimulating electrodes different parts of the musculature can be brought into contraction. Those studied were principally the parietobasilar muscles and also the longitudinal retractors, the circular muscles of the column and the isolated oral sphincter.

4. The magnitude of the response of the parieto-basilar muscles to constant-strength stimuli was very variable. Responses occur to single shocks and these increase in magnitude with increasing strength of stimulus.

5. The parietal muscles give delayed, slow contractions in response to trains of about ten stimuli at one per sec.

6. The isolated sphincter muscle shows two kinds of contraction, a quick one which occurs to single shocks and a slow one which occurs following a brief train of fairly widely separated shocks.

7. The ordinary circular muscles respond with a slow contraction to a few widely spaced shocks. They do not give quick contractions.

8. Although in many cases animals responded to eight quick shocks by giving swimming reactions this number was not found to be a precise requirement, and it varied for the same animal at different times in an unpredictable manner as well as varying from one animal to another. On one occasion a swimming response occurred after a single shock and on another after twenty-eight shocks.

9. It was found that the state of ‘facilitation’ (occurring in the response to electric shocks) of the muscles used in swimming varied a great deal but did not show any marked long-term change following a single shock or the elicitation of a swimming response.

Aided by contract (NR 104-142) between the Office of Naval Research, Department of the Navy and the University of Washington.