Cilia are tiny, hairlike structures found on surfaces of many animal and protozoan cells as well as in some lower plants. They are very similar in both structure and function to flagella. Typically about 0.82 ft (0.25 m) in diameter and 33 ft (10 m) long, cilia are enclosed within the cellular (plasma) membrane and have an interesting and complex interior structure called the axoneme made of microtubules and a large number of associated macromolecular proteins. The basic function of cilia is to move in a whip-like motion that provides motile force to allow single cells to swim through a fluid medium or to move liquids or particles across the cell surface. Protozoans, for instance, use cilia to swim, as well as to capture food and move it into their gullet. Many epithelial tissues in higher animals have a carpet of cilia that moves mucus or particulate material across cell surfaces. For...