Fig. 8. Flow field behind the eel, averaged over 14 complete tail beats, centered on the tip of the eel's tail, shown as a black circle. Arrow heads are retained for velocities lower than 6.5 mm s^-1 to indicate flow direction. Axial flow is shown in color: red is downstream and blue is upstream. Two profiles of velocity are shown in black above and below the flow field, with standard error in gray and total momentum flux represented by the trace printed beside it. Black lines across the field indicate where the velocity traces were measured (25 mm and 95 mm behind the tail). The vertical scale is the same for both traces.