Fig. 5. (A) Path traced out by the caudal fin tip (dashed line) during a cycle of slow swimming movements. The bars on the swimming path indicate the orientation of the fin. U, instantaneous forward velocity; t, time. (B) Instantaneous force produced by the body wave (stars and dashed line), pressure force (filled circles and broken line) produced by the wake and resultant thrust force (open circles and solid line) calculated for the swimming path shown in A using the hydromechanical model. m, virtual mass per unit length of the body; W, lateral velocity of the tail tip; , the angle of inclination of tail fin to mean swimming line; , the perpendicular velocity of the tail tip.