A bacterial cell consists of a tiny mass of cytoplasm surrounded by three distinct layers: the cytoplasmic membrane, the cell wall, and the capsule. Within the cytoplasm is DNA, material containing genetic information. Unlike that of higher organisms, the DNA of bacteria is not enclosed in a membrane-bound structure, or nucleus. Some strains of bacteria have whiplike appendages, called flagella, that enable them to move with a swimming motion. Some bacteria also have pili, short, hairlike appendages that help them adhere to certain surfaces. Some bacteria contain a special substance that allows them to emit light by a process called bioluminescence. )