One of Harvey's prime objects is to defend and establish, on the basis of direct observation, the opinion already held by Aristotle, that, in the higher animals at any rate, the formation of the new organism by the process of generation takes place, not suddenly, by simultaneous accretion of rudiments of all or the most important of the organs of the adult, nor by sudden metamorphosis of a formative substance into a miniature of the whole, which subsequently grows, but by epigenesis, or successive differentiation of a relatively homogeneous rudiment into the parts and structures which are characteristic of the adult.   anvd [Please select]

Preformation: the doctrine of growth or development from already existing rudiments; opposed to epigenesis: q.   anvd [Please select]

Epigenesis: the doctrine of growth from an undifferentiated germ, as opposed to preformation, which implies development from already existing rudiments.   anvd [Please select]