animalcules

Noun

animalcule (plural animalcules)

1. (historical) A sperm cell or spermatozoon; also, the embryo that was formerly thought to be contained inside a spermatozoon in a fully developed state.
   • [Antonie van] Leeuwenhoek's most mysterious finding was yet to come, however. Inside the animalcules in the thickest part of the semen he saw / all manner of great and small vessels, so various and so numerous that I do not doubt that they be nerves, arteries and veins. …2001, David M. Friedman, “The Gear Shift”, in A Mind of Its Own: A Cultural History of the Penis, New York, N.Y.: The Free Press, →ISBN, page 76
2. (archaic) A microscopic aquatic animal, including protozoa and rotifers.
   • If we are part of nature, then we are synonymous with it at the metaphysical level, every bit as much as the first all-but-inorganic animalcules that ever formed a chain of themselves in the blow hole of a primordial sea vent.2011, John Jeremiah Sullivan, “La·hwi·ne·ski: Career of an Eccentric Naturalist”, in Pulphead, New York, N.Y.: Farrar, Straus and Giroux, →OCLC, pages 212–213
3. (obsolete) A small animal.
   • Why, there is not a Man, or a Thing, now alive but has tools. The basest of created animalcules, the Spider itself, has a spinning-jenny, and warping-mill, and power-loom within its head: […]1831, Thomas Carlyle, “Pause”, in Sartor Resartus: The Life and Opinions of Herr Teufelsdröckh. […], London: Chapman and Hall, […], →OCLC, 2nd book, page 137