Figure 6

Fluid streamlines around a V. rousseletii spheroid before and after light stimulation. The fluid streamlines using polystyrene beads were visualized and taken with long exposure times. (a) An exposure time of 0.3 s at 1 to 0.7 s before the light was turned on. (b) An exposure time of 0.3 s at 1 to 1.3 s after the light was turned on. (c) Time scale. (d) Closeup of a region near the anterior pole (see blue frame in a). An exposure time of 1.4 s at 1.4 to 0 s before the light was turned on. (e) Closeup of a region near the anterior pole (see blue frame in b). An exposure time of 1.4 s at 0 to 1.4 s after the light was turned on. Red arrows highlight the main streamlines, and green arrows in (a) and (b) indicate the inherent moving direction of the spheroid along the posterior-anterior axis. Light stimulation was performed with green light (2.1 μmol m^-2 s^-1). The infrared light used for dark-field micrography was inactive for phototaxis. (a), (b), (d) and (e) show the same spheroid.