Studies in Animal Locomotion

ABSTRACT During the normal progression of a fish through water each segment of the body executes a series of transverse movements whose phase is slightly behind that of the segment lying anteriorly to itself, whilst the muscles on the two sides of each segment differ in phase from each other by one-half of a complete muscular cycle. So long as these conditions are fulfilled, regular waves of contraction pass alternately down each side of the body and tail of the fish. On the form, velocity and frequency of these waves depends the rate of progression of the animal through still water (Gray, 1933a). It is obvious that the form of the waves depends, in turn, on the degree of contraction taking place in each segment and on the phase difference which exists between successive segments. The present paper deals with the locomotory rhythm of the eel (Anguilla vulgaris), a form well suited to the purpose in view of its clearly defined muscular movements and of the remarkable viability of the fish. So far as is known, the mechanism controlling the co-ordination of fish movement has not been subjected to extensive experimental analysis, but, during the progress of the present work, important contributions have been made by von Holst (1934, 1935), to whose results reference is made in the text.