prepares, elaborates, and makes use
of the material, all at the same time; the processes of formation
and growth are simultaneous ... all its parts are not fashioned
simultaneously, but emerge in their due succession and order ...
Those parts, I say, are not made similar by any successive union of
dissimilar and heterogeneous elements, but spring out of a similar
material through the process of generation, have their different
elements assigned to them by the same process, and are made
dissimilar ... all its parts are formed, nourished, and augmented
out of the same material.[21]

Actually, Harvey's exposition of epigenesis, albeit clear, is not
totally impressive, since it is largely a reflection of Aristotle's
influence. The main importance of Harvey's vigorous and cogent defense
of epigenesis is that it provided some kind of counterbalance to the
increasingly dominant preformationist interpretations of embryonic
development.

Harvey did not break with Aristotelianism; on the contrary, he lent
considerable authority to it. Unable to escape the past, he was not
completely objective in his study of generation. Everywhere the pages of
his book reveal his indebtedness to past authorities. Robert Willis, who
provided the 1847 translation of _De Generatione_, expresses this well:

[Harvey] ... begins by putting himself in some sort of harness of
Aristotle, and taking the bit of Fabricius between his teeth; and
then, either assuming the ideas of the former as premises, or those
of the latter as topics of discussion or dissent, he labours on
endeavouring to find Nature in harmony with the Stagyrite, or at
variance with the professor of Padua--for, in spite of many
expressions of respect and deference for his old master, Harvey
evidently delights to find Fabricius in the wrong. Finally, so
possessed is he by scholastic ideas, that he winds up some of his
opinions upon animal reproduction by presenting them in the shape
of logical syllogisms.[22]

Even Harvey's concept of the egg reveals a strong Aristotelian bias.
Actually, Harvey attained to his conclusion that all animals derive from
eggs by assuming that

on the same grounds, and in the same manner and order in which a
chick is engendered and developed from an egg, is the embryo of
viviparous animals engendered from a pre-existing conception.
Gener