Source : Webster's Revised Unabridged Dictionary (1913)

Preformation \Pre`for*ma"tion\, n. (Biol.)
   An old theory of the pre["e]xistence of germs. Cf.
   {Embo[^i]tement}.

Source : WordNet®

preformation
     n : a theory (popular in the 18th century and now discredited)
         that an individual develops by simple enlargement of a
         tiny fully formed organism (a homunculus) that exists in
         the germ cell [syn: {theory of preformation}]