Fig. 7. Hypothetical three-dimensional wakes of an eel. (A) In a cross-sectional view above or below the medio-frontal plane, a single vortex chain would appear as pairs of same-sense vortex pairs to either side of the mean path of motion. A strong jet flow meandering around the mean path of motion would be visible between consecutive contralateral vortices. (B) A double vortex ring wake viewed in the mediofrontal plane would appear as pairs of counter-rotating vortices to either side of the mean path of motion. A jet flow would form between the vortices of a pair. Our two-dimensional flow fields are consistent with scenario B rather than A.