1. Isolated marginal sphincters of Calliactis and Metridium show little spontaneous activity, but over a limited frequency range give quick facilitated contractions to not less than two stimuli, and slow contractions having latencies of many seconds to multiple stimuli over a wider frequency range.
2. Earlier observations on the effects of ions on whole animals are confirmed and extended. Excess K+ causes spontaneous quick contractions and responses to single stimuli; excess Ca2+ has no direct excitatory effects, but causes an immense enhancement of the quick response without affecting the slow response to stimulation; excess Mg2+ abolishes both quick and slow contractions.
3. Most drugs, including acetylcholine and its associates, histamine, and 5-hydroxytryptamine, have no effects on either quick or slow contractions. Important effects occur only with tyramine, tryptamine and adrenaline at concentrations of 1 x 10-5 and 1 x 10 -4. No inhibitory drug was discovered.
4. Tyramine has no direct excitatory effects but it greatly enhances the quick facilitated responses without enhancing (and in some circumstances depressing) the slow responses to stimuli. It also causes small responses to single stimuli.
5. Tryptamine causes direct quick contractions of the sphincter, gives quick responses to single stimuli and somewhat enhances both quick and slow responses to stimuli.
6. Adrenaline has no effect on quick facilitated responses but causes direct slow responses and some enhancement of slow responses to stimuli.
7. The effects of ions and drugs are obtained only when they are applied directly to the sphincter region. They do not occur when they are applied only to an attached strip of column.
8. It is noted that the effects of excess K+ and tryptamine are identical, and that the effects of excess Ca2+ and tyramine are also identical; adrenaline stands alone as a ‘slow-excitor’.
9. The physiological significance of the results is discussed in relation to different components of the responding system and to the mechanisms of quick and slow contraction in the sphincters.