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Journal of Experimental Biology 45,357-368 (1966)
Published by Company of Biologists 1966

Neuromuscular Mechanisms of Burrow Irrigation in the Echiuroid Worm Urechis Caupo Fisher & Macginitie : II. Neuromuscular Activity of Dissected Preparations

JAMES V. LAWRY JR. ¹

¹ Department of Biological Sciences, Stanford University, Stanford, California; Gatty Marine Laboratory, St Andrews, Scotland

1. This paper describes a neurophysiological investigation of the initiation and co-ordination of the peristaltic waves in Urechis.

2. Peristaltic waves are (a) initiated in the proboscis and propagated posteriorly, and (b) initiated in the hind gut and propagated anteriorly, provided that nerve cord, body-wall and peripheral nerves are intact.

3. There is a hierarchy of pacemaker regions in the nerve cord, effective over lengths as small as 30 mm. This hierarchy is normally dominated by the pacemaker in the proboscis.

4. The pacemakers respond with increased frequency to oxygen, epinephrine and acetylcholine in concentrations of 10^-6M. Eserine potentiates the acetylcholine response. The system is insensitive to 5-hydroxytryptamine.

5. The giant fibres conduct at 1.5 m./sec. and mediate a startle response; they are not involved in the conduction of the peristaltic wave.