1. The locomotory rhythm of an intact or spinal dogfish resembles that of other fish in that it is determined by the intrinsic activity of the spinal cord without the participation of proprioceptor arcs.

2. The persistent rhythm characteristic of the spinal dogfish can be accelerated or inhibited by peripheral stimuli. So long as the spinal cord is intact, localised stimuli elicit co-ordinated responses from all intact segments of the body although at least twelve intermediate segments may have been deprived of their spinal innervation. Co-ordinated responses no longer occur if two regions of the body are isolated from each other by a second spinal transection; if both such regions are of adequate length, each exhibits an independent spontaneous rhythm and responds independently to peripheral stimulation.

3. In order that a spinal preparation should exhibit spontaneous and persistent rhythmical activity, in the absence of extraneous stimuli, approximately twenty-five segments of the nerve cord are necessary.

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