Ciliary and Flagellar Movements

Cilia and flagella or their derivatives occur in all animal phyla. They constitute the primary locomotor y structures of many protozoa and of several kinds of metazoan cells, for example, sperm, ciliated epithelia of invertebrates and vertebrates. Derivatives of cilia occur in a wide variety of photoreceptor, mechanoreceptor and chemoreceptor cells.

Figure: Ciliary and Flagellar Movements

Cilia and flagella have a similar internal structure; the difference lies in their beating patterns which are illustrated in Figure. A flagellum like a tail of sperm, beats with a symmetrical undulation that is propagated as a wave along the flagellum.  A cilium, in contrast beats asymmetrically with a fast or dash-like stroke in one direction, followed by a slower recovery motion in which the bending cilium returns to the original position. In flagellar motion, water is propelled parallel to the long axis of the flagellum; in ciliary motion water is propelled parallel to the surface that bears the cilia.