Central Nervous Activity in the Earthworm

Abstract

1. Regular rhythmic peristaltic movements of a preparation consisting of 20-40 complete segments of the earthworm may be initiated by longitudinal tension and by certain types of tactile stimulation. 2. Peristaltic movements do not occur in such a preparation in the absence of stimulation, and cease within a finite period after the cessation of a stimulus. 3. Peristaltic movements do not occur after excision of the nerve cord. The rhythmic responses to tension and touch are therefore together described as the peristaltic reflexes, and the response to tension is individually described as the tension reflex. 4. The preparation shows a variety of responses to touch. Tactile stimuli may evoke peristalsis; they may also elicit arhythmic contractions accompanied by immobilization of peristalsis. 5. The peristaltic reflexes can be immobilized both by heavy vibration of the apparatus, and by certain tactile stimuli. The immobilization can occur without the accompaniment of any arhythmic contraction of the preparation. The immobilization can be referred to as an inhibitory process, since it exhibits features characteristic of inhibition: (i) lessening in the amplitude of beat in recovery from complete immobilization; (ii) reduction of the frequency of beat in the same circumstance. 6. The inhibition of peristalsis is conducted through the central nervous system. 7. The inhibitory effect persists for a considerable period after cessation of the stimulus. 8. Inhibition may be followed by "rebound". "Rebound" may be caused by the subsidiary exciting effect of the inhibitory stimulus.