Observations On the Myo-Neural Physiology of the Polyclad, Planocera Gilchristi

Abstract

1. The behaviour of decerebrate specimens of Planocera gilchristi is compared with that of normal individuals in respect of locomotion, righting reactions, responses to mechanical stimulation, feeding and oviposition. It is found that the brain acts as a centre for co-ordination of locomotor activity but many other activities such as swallowing and egg laying can occur in the absence of the brain. 2. The responses to electrical stimulation of the longitudinal muscles of decerebrate individuals are described. The magnitude of the response is determined by the intensity of stimulation. No evidence for facilitation was found. 3. The major nerve trunks carry both sensory nerves to the brain and motor nerves to the longitudinal musculature. Neither motor nor sensory information leading to a contraction of the longitudinal muscles could be transmitted through the nerve network. 4. The effects of changes in the ionic composition of sea water upon spontaneous contractions of the longitudinal muscles are described. Calcium ions have an excitatory effect and in their absence the activity of the preparations is depressed. 5. The effects of various drugs upon the spontaneous activity of the longitudinal musculature are described. There is no evidence for any cholinergic mechanism, but the preparations respond to adrenaline and noradrenaline as well as to 5-hydroxytryptamine and LSD-25.