Protozoa  (prō´tō-zō´ȧ).—The lowest forms of animal life.
Animalcules  (Protozoa )

In botany we find that the lowest plants are mostly of a microscopic size, and unicellular—that is, consisting of a single cell or structural unit, essentially a fragment of living matter (protoplasm), part of which is specialized into a nucleus. The lowest animals are also unicellular, and the popular term “animalcule”—a little animal—has reference to their diminutive size. One of the simplest known cases is afforded by the