1. An optical arrangement for high-speed microcinematography has been designed so as to record ciliary movement, and the movements of single large abfrontal cilia of Mytilus gill have been photographed at 400-500 frames/sec, with brief exposures of 1/20,000 sec.
2. A quantitative description of the movement of the cilium is presented in terms of the changes of the curvature at various regions of the ciliary shaft and of the change of the basal angle.
3. The principle of the description mentioned above is also applied to the movement of the cilium in media of high viscosities, and some parameters of the movement (duration, amplitude of the basal angle, maximum curvature and propagation velocity of the bending wave) are presented.
4. The resistance experienced by the cilium during its beating has been evaluated under some hydrodynamic assumptions, and the flow induced by the cilium and the bending moment of the ciliary shaft due to the viscous resistance have been calculated over a single beat.
5. The change of the degree of bending of the ciliary shaft (curvature) takes place in advance of the change of the bending moment at the same region in the distal as well as in the proximal regions of the ciliary shaft. This fact indicates that active processes are involved in bending and unbending of the ciliary shaft during its beat.