Fig. 4. (A) Configuration of the caudal fin during the stroke cycle. The end of the abdomen is viewed from above, and the open and filled circles trace the paths of the base and tip of the fin respectively. Note how the fin bends specifically along the flexion line dividing the basal and apical segments of the tracheal plates. (B) Consecutive stages in the production of a ring vortex during a single right-to-left half-stroke of a larva viewed from above. These profiles are taken from Fig. 8, but also plot the path of the fin tip during the right-to-left and the following left-to-right half-strokes (160 ms position, far left). Arrows in the flow field indicate the axis of the vortex jet and the body flow contributing to the proximal vortex (20 ms position). (C) Whole-body profiles of a swimming larva at 20 ms intervals. Open and filled circles plot the path of the head and fin tip respectively. The stars plot the motion of a portion of dye streamer carried progressively to the right by the movements of the body as the undulatory wave travels caudally. By the time the larva has moved to the 80 ms position, the body-induced motion of particles in the dye stream joins the vortex jet released from the tail, which travels laterally in the direction of the arrow.
