. Biological structure and function; proceedings. Biochemistry; Cytology. Some Problems of Ciliary Structure and Ciliary Function BjORX A. Afzelius The \Veuney-(jyeu Institute for Expeiiuiental Biology, Stockholm, Su-eden The purpose of this paper is to review some of the problems of cihary movement in the hope that new findings on cihary and flagellar fine struc- ture mav shed light on the mechanisms responsible for the movement. Several questions are still to be answered: 1. Bv what mechanism do cilia and flagella work ? 2. In what respects does the fine structure of a flagellum differ from
. Biological structure and function; proceedings. Biochemistry; Cytology. Some Problems of Ciliary Structure and Ciliary Function BjORX A. Afzelius The \Veuney-(jyeu Institute for Expeiiuiental Biology, Stockholm, Su-eden The purpose of this paper is to review some of the problems of cihary movement in the hope that new findings on cihary and flagellar fine struc- ture mav shed light on the mechanisms responsible for the movement. Several questions are still to be answered: 1. Bv what mechanism do cilia and flagella work ? 2. In what respects does the fine structure of a flagellum differ from that of a cilium ? Is it possible to correlate such differences with their different modes of movement ? 3. What is the significance of the " magical 9 + 2 filament arrangement" in cilia and flagella ? Are there meaningful variations in their arrangements ? 4. Is the ciliary beat (or the flagellar beat) to be regarded as a con- traction process ? Are there significant similarities between these movements and the contraction of, for instance, a striated muscle ? The observations that are presented here have been made with the electron microscope. The different tvpes of cilia and flagella that have been chosen for study have only this in common: they have been subjected previously to a careful analysis with regard to their mo^â ements. The study has thus been intended to be an attack on the second question above. It was hoped that some definite conclusions could be made and that an answer to the second question would at the same time answer the others. Before proceeding further it is necessarv to define the words "cilium" and "flagellum". A cilium is a fine vibratile thread projecting with many others from the surface of a cell. Cilia lash in an orderlv beat in a constant direction. The beat consists of an efl'ective stroke and a recovery stroke. In the effective stroke the cilium is stiff and it dri\"es the water ahead of it; in the recovery s
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