the flagellum emerges from the bacterial surface or wall (or cell envelope)` which consists of
three main layers: the outer membrane (OM), the periplasm (P) which contains a mesh of very strong
fibrous material called peptidoglycan (or murein) and an inner cytoplasmic membrane (CM). (Click
here to learn about cell membranes). Note how different this arrangement is from an animal cell which
has a single cell membrane rather than this double membrane structure. Beneath these layers is the cell
interior (the intracellular compartment) or protoplast (consisting of cytoplasm and nucleoid) and external
to these layers is the extracellular (external) environment, such as the water the bacterium is swimming
in. (Additional layers may exist outside the OM, including a slime capsule, but we shall look at these
possibilities later). This type of wall structure is particular to some types of bacteria called Gram
negative bacteria, but other wall structures occur, as we shall see later. The root of the flagellum
consists of a series of rings (made of proteins) that anchor the structure in the cell envelope.