Fig. 6. Visualisation of a train of consecutive ring vortices shed to the dorsal side of the swimming line. The larva is swimming obliquely upwards, as indicated by the broken arrow in a, and is viewed from its right side (dorsal side is to the left of the profile). On the far left in a is a vertical dye streamer. b and c show stages in the penetration of the streamer by ring vortices released from the larva during consecutive dorsal half-strokes. The arrows in b and c indicate the direction of propagation of the ring vortices.