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Webster 1913 Edition

Noun.

(Biol.)

An old theory of the preëxistence of germs. Cf.

preformation ‎(plural preformations)

Prior formation.
(biology, historical) The theory that organisms are fully developed in the form of an egg or seed, and just increase in size (as opposed to epigenesis).
- 1999, Matt Ridley, Genome, Harper Perennial 2004, p. 174:
  Preformation, as even Aristotle spotted, merely postpones the problem, for how did the homunculus get its shape?