n. the biological theory, now discredited, that development consists of the emerging into mature form of the traits and capacities that exist in prototypical form in the germ cell. An early example of preformism was the 16th- and 17th-century notion of the homunculus, a minute but completely formed human body believed to exist in the spermatozoon. Preformism contrasts with the epigenetic principle of successive differentiation in complex and cumulative stages of development (see epigenesis).