A NEW THEORY ON THE MECHANICS OF CILIARY AND FLAGELLAR MOTILITY. II. THEORETICAL CONSIDERATIONS

¹ Department of Zoology, University of North Carolina, Chapel Hill, North Carolina 27514

1. A simple basic theory to account for the mechanics of ciliary and flagellar motility is proposed. It is based in large part on the conclusions resulting from observations made on axonemes of surface body cilia and of sperm flagella of a number of lower invertebrates after maceration and negative staining with phosphotungstate.

2. Ciliary motility consists of an effective stroke brought about by the successive bending of the three doublet microtubules of one lateral half of the axoneme while the central singlet microtubules are stiffened, and a recovery stroke, similarly brought about by the three doublets of the other lateral half, while the central singlets are relaxed. Bending of each doublet is in the direction away from its dynein arms. Doublet #1, and attached doublets #5 and #6, are rendered essentially ineffective by the stiffened singlets. The length of the axoneme in relation to wavelength determines when the singlets are stiff and when relaxed, and when each lateral half doublet group is involved.

3. Planar motility (of 9 + 2 flagella) consists of movement in one direction, brought about by successive bending of the three doublets of one lateral half of the axoneme, followed by movement in the other direction due to bending of the three doublets of the other lateral half, while the central singlets remain stiffened for the active period of the entire wavelength. Movement of doublets #1, #5, #6 is inhibited by the stiffened singlets. It is the greater length of the flagellum that is chiefly responsible for the difference between flagellar and ciliary motility.

4. The helical motility of 9 + 0 and "9 + 1" axonemes is brought about by successive bending waves moving out all nine doublet microtubules, in sequential order, with no directional inhibition of any of them. The stiffened core of the "9 + 1" axoneme would be expected to decrease the amplitude of the helical beating in the latter type.