Some short-fibered non-striated muscles show propagated action potentials, as the Phascolosoma probiscis retractors and the Thyone lantern retractors; others fail to propagate, as the long body wall retractors of Thyone (Prosser, Curtis and Travis, '51). I n the non-propagating muscles, contraction occurs only in the region of stimulation. Propagation in the Phascolosoina proboscis retractors is by intrinsic nerve fibers which appear to activate many muscle fibers successively (Prosser arid Melton, '54). The present paper deals with the innervation of a non-propagating smooth muscle, the long body wall retractors of T h y o n e briareiis (Lesuenr).
MATERIALS AND METHODSFreshly collected sea cucumbers were used, and the muscles were dissected in either natural or artificial sea water. Stimulation and recording was by chlorided silver electrodes making contact by means of wicks under light mineral oil. Action potentials were obtained by a direct-coupled amplifier, contractions by an RCA 5734 transducer; both were recorded on a Grass inkwriter. Artificial sea ~rrater was made by the formula of Hodgkin and Katz, '49.