Adaptations of ciliary systems for the propulsion of water and mucus.

1. The characteristics of ciliary systems are determined by the dominance of viscous effects over inertial effects. 2. The velocity of water propulsion depends on ciliary length, beat frequency, pattern of beating, the arrangement of the cilia and their co-ordination. Beating cilia influence a layer of water only two or three cilium lengths deep, with maximal velocity near the ciliary tip. 3. Mucus is propelled by the tips of short cilia that penetrate the mucus; these cilia are closely spaced on epithelia, and achieve slow propulsion that is relatively independent of load and does not require strong ciliary co-ordination.