​PARAMECIUM, O. F. Müller, (often misspelt Paramaecium, Paramoecium), a genus of aspirotrochous ciliate Infusoria (q.v.), characterized by its slipper-like shape, common in infusions, especially when they contain a little animal matter. It has two dorsal contractile vacuoles, each receiving the mouths of five radiating canals from the inner layer of the ectosarc, and a large ovoid meganucleus, and one or two micronuclei. From its abundance, the ease with which it can be cultivated and observed, its relatively simple structure and adequately large size (¹⁄₁₂₅ in.), it is most frequently selected for elementary study and demonstration, as well as for purposes of research.