DIC light micrograph of Paramecium. (Paramecium multimicronuleatum), a ciliate protozoan, with oral groove, food vacuoles, nucleus (left edge) and cilia. Paramecium are found mainly in stagnant ponds, feeding on bacteria and plant particles. They have a permanent mouth called an oral grove. Food taken in through the oral groove is digested within temporary digestive vacuoles in the cell cytoplasm. The two contractile vacuoles act as osmotic regulators, controlling the flow of water across the ciliate's membrane. The contractile vacuoles are surrounded by a halo of radiating channels. Excess water collects in the channels, drains into the vacuole and is then discharged through a pore at the surface. Magnification: x110 when shortest axis printed at 25 millimetres.