The Rapid Escape Response of the Earthworm Lumbricus Terrestris L.: Overlapping Sensory Fields of the Median And Lateral Giant Fibres

1. In undissected, freely mobile earthworms the sensory input for tactile stimulation to the MGF and LGF shows a region of overlap occupying a number of segments behind the clitellum. The average number of overlapping segments from a sample of 14 worms was 13 (range 0–28). 2. The overlap zone consists of segments from which both LGF and MGF spikes can be elicited. 3. Increasing stimulus intensity in the LGF field reduces the latency of the first spike until it reaches a minimum of 6 ms. This value is used to calculate conduction velocity of afferent impulses along the sensory pathway. 4. It is suggested, on the basis of conduction velocity, that the large sensory neurones in the segmental nerves are those mediating afferent events in the rapid escape response.