Fig. 11.

Mechanism of hydrodynamic enhancement of axial roll rotation. A shows a side view and B and C a front view of nematode trajectories in a roll maneuver. The labeling convention follows that of Fig. 10. In B and C the axis of motion (toward the viewer) is indicated by the symbol $\odot$. In forward locomotion (A) the longitudinal hydrodynamic resistance ${𝐅}_H$ (red arrows) slows the nematode down. During the torsional roll (B and C), the net torque $T_H$ (magenta arrows in C) associated with ${𝐅}_H$ (red arrows) produces hydrodynamic rotation (blue arrow in B) in the same direction as the geometrical rotation of the undulation plane (progression $0\to 1\to 2$).