Studies on the Myoneural Physiology of Echinodermata

Abstract

1. A myoneural preparation of Cucumaria sykion (Lampert) comprising a pharyngeal muscle and the corresponding radial nerve is described. A brief account is given of the histology of the preparation. 2. Direct stimulation of the muscle gives a single response. Above fusion frequency the tension developed by the muscle increases with increasing intensity of stimulation, but it is unaffected by the frequency of stimulation. 3. Stimulation of the radial nerve elicits a double response from the muscle. There is a ‘quick’ response which shows no myoneural facilitation and a ‘delayed’ response which shows a well-marked and prolonged facilitation. 4. The tensions developed by both quick and delayed responses depend upon the intensity of stimulation applied to the radial nerve. Both responses show well- marked refractoriness at stimulation frequencies above about 10 stim./sec. 5. It is suggested that the delayed response arises from the activity of the internmcial neurones in the motor complex, and that this is also the locus of the prolonged facilitation shown by the delayed response. 6. The similarity of the properties of this system with certain features of the chordate nervous system are pointed out, but it is considered that any simple phylogenetic conclusions are unwarranted.