Fig. 4. Vortex production during a mini-dive by the pupa. (A) The pupa is floating towards the surface following its initial dive into a layer of dyed water on the bottom of the container. To the right can be seen a number of vortices associated with previous dives. (B) 1.4s later, the pupa has dived out of sight, leaving behind two ring vortices produced by the first upstroke (V1) and first downstroke (V2). The arrows show the convection axes of the vortices.