Inherent Activity in the Sea-Anemone, Metridium Senile (L.)

Abstract

1. The sea-anemone Metridium senile shows continual muscular activity. The activity is so slow that it is rarely appreciated by the eye as movement. Methods of observing and analysing such activity are discussed. 2. The activity of the column of the anemone has been analysed. It consists of a sequence of reciprocal contractions of the parietal muscles and the circular muscle coat. A sequence of activity commonly begins with a contraction of the parietals, followed by contraction of the marginal sphincter, which in turn initiates a peristaltic wave. The whole sequence lasts several minutes. The size and duration of its components may vary greatly. Activity may show a more or less regular rhythm with a period of the order of 10 min. between each major contraction. It may, however, show no trace of rhythm. 3. The activity of different parts of the body wall may show striking co-ordination. A contraction of one part of the parietal musculature is usually followed by contraction of the others. In other cases there may be no trace of co-ordination. The parietal muscles of one side may contract without contraction of those opposite, so that the animal bends over. 4. Co-ordination takes place through one part of the body wall acting as ‘leader’. The other parts of the body wall follow this contraction with long delays (up to 30 sec. or more). The delay is far greater than the through-conduction time in the nerve-net (50-80 msec. in Metridium). There is evidence that it is of local origin. One sector usually maintains leadership for long periods; but from time to time the site of leadership changes. 5. Evidence is given that the activity continues unaltered in the absence of external stimulation. It is inherent. The evidence does not suggest that it is maintained through self-stimulation by preceding contractions after the manner of a chain reflex. 6. The activity varies greatly in character and extent in different animals and in the same animal at different times. This remains true even under apparently constant environmental conditions.