Phases of activity in the sea-anemone, Metridium senile (L.), and their relation to external stimuli.

We have shown in a previous paper (Batham & Pantin, 19506) that the sea-anemone Metridium senile exhibits continual very slow muscular activity. It is most evident in the changes of shape of the column caused by the reciprocal contractions of the circular muscle sheet, and of the longitudinal parietal musculature which runs at the junction of each mesentery with the body wall. This inherent activity varies, so that in the same individual it presents a different pattern on different occasions. The pattern may remain constant for hours on end, and may then change over a comparatively short period. Thus a moderately filled anemone giving fairly regular and substantial contractions may pass into a condition with a larger volume and much less apparent activity, or it may pass into a condition of prolonged and almost complete contraction. These patterns of activity often endure for long periods—hours or even days. It is convenient to refer to such patterns as 'phases', and these phases form the subject of this paper.