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(biology, now historical) The outdated hypothesis that all living things proceed from pre-existing germs, and that these encase the germs of all future living things, enclosed one within another. quotations
[R]ivals professed to see an equivalent in the semen, giving rise to the ‘preformation’ or emboîtement theories which contended that the new individual was completely developed as a tiny homunculus from the moment of conception.
1997, Roy Porter, The Greatest Benefit to Mankind, Folio Society, published 2016, page 217