After the discovery of spermatozoa in 1677 by Dutch microscopist Antonie van Leeuwenhoek, the epigenist theory proved more difficult to defend: How could complex organisms such as human beings develop from such simple organisms? Thereafter, Joseph de Aromatari and then Marcello Malpighi and Jan Swammerdam made observations using microscopes in the late 17th century, and interpreted their findings to develop the preformationist theory. For two centuries, until the development of cell theory, preformationists would oppose epigenicists, and, inside the preformationist camp, spermists (who claimed the homunculus must come from the man) to ovists, who located the homunculus in the ova.