What does animalcule mean?
The definition of animalcule
An`i*mal”cule, n.
Etym: [As if fr. a L. animalculum, dim. of animal.]

1 A small animal, as a fly, spider, etc. [Obs.] Ray.
2 (Zoöl.)
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 Desmidiacæ, and the siliceous Diatomaceæ. Spermatic animalcules. See Spermatozoa.