Note: They are found in all seas, lakes, ponds, and streams,
as well as in infusions of organic matter exposed to
the air. They are distinguished by having vibrating
lashes or cilia, with which they obtain their food and
swim about.They are devided into the orders Flagellata,
Ciliata, and Tentaculifera. See these words in the
Vocabulary. Formely the term Infusoria was applied to
all microscopic organisms found in water, including
many minute plants, belonging to the diatoms, as well
as minute animals belonging to various classes, as the
Rotifera, which are worms; and the Rhizopoda, which
constitute a distinct class of Protozoa. Fossil
Infusoria are mostly the siliceous shells of diatoms;
sometimes they are siliceous skeletons of Radiolaria,
or the calcareous shells of Foraminifera.