ABSTRACT
Of the large number of published studies on the ion relations of invertebrate rhythmic muscles, the great majority concern preparations from Crustacea and molluscs—largely because the animals of these groups are provided with vigorous and experimentally convenient hearts. Data on members of other phyla are relatively few and, from the comparative point of view, their multiplication is evidently desirable. Recently, one of us published a description of the so-called “isolated extrovert” of the lugworm, Arenicola marina L., a preparation consisting of the proboscis and part of the oesophagus (Wells, 1937). Suspended in sea water, the isolated extrovert maintains for many hours a very regular and characteristic activity pattern, consisting of a series of outbursts of vigorous rhythmical contraction separated by periods of relative rest. That this is the normal activity pattern was shown in the paper already mentioned. Because of its vigour, its regularity, its long survival after excision and the ease with which that operation is performed, it is an excellent object for experiments on the action of chemical factors. The writers have undertaken a study of ion actions on this preparation. The results obtained by varying the Mg concentration form the subject of the present communication. Experiments with K and Ca have been begun and it is hoped to complete them shortly.
