ABSTRACT
In a previous paper (Gray and Sand, 1936) the persistent swimming rhythm of the spinal dogfish was described, and an account was given of experiments which demonstrate that the locomotory rhythm is determined by the intrinsic activity of the spinal cord without the participation of proprioceptor arcs. In the course of this work it became evident that the rhythmic activity of the spinal dogfish can be modified in various ways by external mechanical stimulation. These responses present a relatively simple pattern of reflex behaviour, their number is strictly limited, and they are uniformly reproducible. For these reasons, although our experiments raise a number of physiological questions which our data cannot answer, we have thought it worth while to record these phenomena in the present communication.
