Bacteria (and other prokaryotes) have the ability to move by means of flagella. Flagella are composed of the globular protein flagellin. They are extremely long and thin and cannot be seen by the light microscope unless specially stained. They are, however, readily visible under the electron microscope. Bacterial flagella propel the organism by a rotary motion. Each flagellum has three basic parts: the filament, which is the long, outermost region containing the flagellin; the hook, which is composed of a different protein and lies at the proximal end of the filament; and the basal body, which anchors the filament to the cell membrane and cell wall and is composed of a series of rings encircling a central, small rod (Gram- positive bacteria have only an inner pair of rings, while Gram- negative bacteria have both inner and outer pairs of rings).