Summary

1. Sensory neural units responding to sinusoidal stretching of the body wall were studied in the earthworm, Lumbricus terrestris L. 2. A phasic stretch-sensitive unit found in segmental nerve I responded optimally to stretching at frequencies of 4-6/min. 3. The number of spikes per stretch and the spike frequency in the unit were directly related to the amplitude of the applied stretch within a range of 0-2-0-7 mm stretch/segment. 4. The ranges of amplitude and frequency sensitivity for the unit in isolated preparations corresponded closely to stretch parameters seen during peristaltic locomotion in intact animals. 5. Stretch-sensitive responses in segmental nerve II-III were more variable; some units responded to longitudinal stretch while others responded to relaxation.