Longitudinal section of cilia. Cilia (and flagella) are projections from the body of the cell. Motile cilia beat constantly in one direction and move substances over or around the cell. The primary purpose of cilia in mammalian cells is to move fluid, mucous or dirt over their surface. Cilia and flagella have the same internal structure; the major difference is in their length. Magnification 75,000x. Color enhancement of 9B4095.