Figure 4.

Schematic of the stresslet exerted on the fluid for two types of cells, and the far-field velocity field relative to the swimming velocities of the cells. The arrows within the cells' bodies show the bodies' direction of ‘forward’ locomotion and also the force by the cell bodies on the fluid. The external arrows show the associated forces by the flagella on the fluid. (a) Thrust generated in front of the body (puller). Typical of the algae Chlamydomonas, the return stroke, with somewhat folded flagella, reverses the arrows. The cell body then moves backward. The return stroke results in less motion than the forward stroke; the net motion over one complete cycle is forward. (b) Thrust generated behind the body (pusher).