Definition of "animalcule"

[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, page 76

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, pages 212–213

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, […], book second, page 137

Is it not evident that if a parasitic animalcule desired to call its attention it would sink a hole in its shell and so stimulate its sensory apparatus?

1928 February 25 – March 3, Arthur Conan Doyle, “When the World Screamed”, in The Professor Challenger Stories […], London: John Murray, […], published , page 555