1. Body and fin reflexes in the spinal dogfish, Scyllium canicula and Acanthias vulgaris, are described.
2. A reflex posture can be induced in inactive spinal preparations through localized exteroceptive stimuli. The location of the primary and secondary contraction areas is determined by the site of stimulation.
3. Spinal preparations of Scyllium canicula and Acanthias vulgaris display a persistent locomotory rhythm as long as they are free from contact.
4. Diffuse touch to the ventral surface of a spinal preparation has an inhibitory effect on the swimming movements. Some dogfish remain immobile after the ventral contact has been discontinued, but resume their persistent swimming after application of a gentle exteroceptive stimulus of short duration.
5. Through feeble transitory stimuli any individual swimming stroke can be retarded, temporarily arrested, reversed, accelerated and augmented. The reaction depends on the site of the stimulation and on the momentary phase of the swimming movement at which it is applied.
6. The rhythm emerging after the application of a transitory stimulus is, as a rule, out of phase with the rhythm as recorded prior to the application of the stimulus. Therefore the response cannot be interpreted as resulting from a super-position of an independent automatic rhythm integrating with a reflex, but must be considered as an interaction of two equal and mutually dependent processes.