Fig. 12. Vortex production at the start of swimming in the final-stage larva. (A) The initially extended body contracts rapidly to one side, producing a vortex that propagates along an axis lying at right angles to the extended body and intersecting it approximately half-way along its length. The straight open-headed arrows indicate the direction of motion of the vortex and the centre of gravity (filled circle) of the body. (B) The outer diameters (2R_e) of vortices measured at various times during the propagation of the vortex in 33 separate experiments.