Fig. 2. Video sequence of vortex ring formation during two swimming cycles of Aurelia aurita. At 0 and 2.47 s the bell is relaxed and fully expanded. Frames at 0.63 and 3.73 s show the contraction phase and the formation of the starting vortex. Frames at 1.47 and 4.40 s show the relaxation phase, the trailing starting vortex and the formation of the stopping vortex. The frame at 2.47 shows a fully developed stopping vortex in the subumbrellar cavity.