(n.) A genus of minute, pale-green, globular, organisms, about one fiftieth of an inch in diameter, found rolling through water, the motion being produced by minute colorless cilia. It has been considered as belonging to the flagellate Infusoria, but is now referred to the vegetable kingdom, and each globule is considered a colony of many individuals. The commonest species is Volvox globator, often called globe animalcule.

Euglena adenovirus aerobe aerobic bacteria amoeba anaerobe anaerobic bacteria animalcule bacillus bacteria bacterium bug coccus colon bacillus diatom disease-producing microorganism dyad echovirus enterovirus filterable virus flagellate fungus germ gram-negative bacteria gram-positive bacteria microbe microorganism microspore microzoa mold monad nematode nonfilterable virus paramecium pathogen picornavirus protozoa protozoon reovirus rhinovirus rickettsia salmonella saprophyte spirillum spirochete spore sporozoon staphylococcus streptococcus tetrad triad trypanosome vibrio virus volvox vorticellum zoospore