. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 302 DONALD P. COSTELLO. FIGURE 8. Diagram of a cross-section of a "9 + 1" flagellum to show central core and to indicate directions of successive bending of doublets to produce a wavelength of helical movement of reduced amplitude. "9 + 1" axoneme, with the number present at any time depending upon axonemal length. Considerable resistance would be provided by the complex core because of its straightening tendencies (Henley, Costello, Thomas and Newton, 1969). However, since this resistance is nondirection
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 302 DONALD P. COSTELLO. FIGURE 8. Diagram of a cross-section of a "9 + 1" flagellum to show central core and to indicate directions of successive bending of doublets to produce a wavelength of helical movement of reduced amplitude. "9 + 1" axoneme, with the number present at any time depending upon axonemal length. Considerable resistance would be provided by the complex core because of its straightening tendencies (Henley, Costello, Thomas and Newton, 1969). However, since this resistance is nondirectional, as compared with that provided by a pair of central singlets, it may serve only to reduce the amplitude of beat, and perhaps contribute to unbending. It is of interest that some spermatozoa of triclad and polyclad flatworms have very long free flagella with "9 +1" axonemes exceed- ing 200 microns in length, which are clearly observed to move with a helical beat. DISCUSSION Bradfield (1955) discussed possible mechanisms of flagellar and ciliary motility. He numbered the peripheral fibers 1 to 9, with #1 in the plane of symmetry. The direction of ciliary beat was assumed to be in the direction radially outward from fiber #1. For cilia, he assumed also that the impulse spreads around the ring in both directions, as well as to the central pair, which he considered to be more rapid conductors (Fig. 9a). For further details, see Bradfield's paper. For flagella, Bradfield hypothesized that two-dimensional waves might be produced if the impulse spreads both directions around the base from # 1 and dying out between #5 and #6 (or being reflected back) but not picked up and conducted rapidly along the flagellum by the central fibers in the manner postulated for the cilium. Bradfield suggested, also, that three-dimensional, corkscrew-like waves. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorat
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