Microtubules and the propagation of bending waves by the archigregarine, Selenidium fallax.

1. The trophozoites of Selenidium fallax propagate bending waves at rates of up to 35 microns s-1, of a similar character to those manifested by eukaryotic cilia and flagella. A beat frequency of 0.12-0.15 Hz appears average, though rates outside this range have been recorded. Translatory locomotion at up to 6 microns s-1 has been observed. The protozoan demonstrates the presence of an active bending mechanism, probably along its entire length, and a means of coordinating adjacent bends. 2. The Reynolds number for the motion in 10(-5)-10(-4), suggesting that the hydrodynamic aspects of the trophozoite movement are amenable to analysis by similar means to those already employed for cilia and flagella. 3. It is possible that the protozoans exhibit a sliding microtubule mechanism, which could be very usefully compared with that occurring in the ciliary axoneme.