\An`i*mal"cule\, n. [As if fr. a L. animalculum, dim.
of animal.]
1. A small animal, as a fly, spider, etc. [Obs.] --Ray.
2. (Zo["o]l.) An animal, invisible, or nearly so, to the
   naked eye. See {Infusoria}.
Note: Many of the so-called animalcules have been shown to be
      plants, having locomotive powers something like those
      of animals. Among these are {Volvox}, the
      {Desmidiac[ae]}, and the siliceous {Diatomace[ae]}.
{Spermatic animalcules}. See {Spermatozoa}.