ABSTRACT
In an earlier paper (Wells, 1937), the writer studied experimentally the movements of the proboscis in Arenicola marina, a worm which lives in a burrow and feeds by taking in the surrounding mud, and in which the brain and sense organs are very much reduced. It was shown that the intact worm, observed in a glass tube, generally exhibits periodic outbursts, either of rhythmic extrusion and withdrawal of the proboscis or, in less vigorous worms, of movements of similar type which do not result in actual extrusion, the activity outbursts alternating in either case with periods of rest. This probably means that the worms, under natural conditions, have a “feeding rhythm”, ingesting mud for a few minutes, then resting, and so on. Moreover, by considering a series of dissected preparations, it was shown that the pacemaker determining this rhythm was situated in the oesophageal wall. Periodic outbursts of excitation originate in the oesophagus and are transmitted forwards along the wall of the proboscis to the central nervous system, calling forth correlated movements of the musculatures of the proboscis itself and of the body wall.
