Hypothesis of the mechanism of planar asymmetrical bending motion of flagella. (a) Doublet order of flagella at the basal body of C. reinhardtii (Hoops and Witman, 1983), showing that doublets 1 of the two flagella are facing each other. Arrows indicate the plane of bend. (b) Illustration of the generation of planar asymmetric waveform by strong and weak sides is shown.