206 BIOLOGY AND ITS MAKERS 
As we have already scen, Harvey, more than a century before 
the publications of Wolff, had clearly taught that devclop- 
ment isa process of gradual becoming. Nevertheless, Wolff’s 
work, as opposed to the new theory, was very important. 
While the facts fail to support the contention that he was 
the founder of epigenesis, it is to be remembered that he has 
claims in other directions to rank as the foremost student of 
embryology prior to Von Baer. 
Asa preliminary to discussing Wolff’s position, we should 
bring under consideration the doctrine of pre-formation and 
encasement. 
Rise of the Theory of Pre-delineation.—The idea of pre- 
formation in its first form is easily set forth. Just as when 
we examine a seed we find within an embryo plantlet, so it 
was supposed that the various forms of animal life existed 
in miniature within the egg. The process of development 
was supposed to consist of the expansion or unfolding of this 
pre-formed embryo. The process was commonly illustrated 
by reference to flower-buds. “Just as already in asmall bud 
all the parts of the flower, such as stamens and colored petals, 
are enveloped by the green and still undeveloped sepals; 
just as the parts grow in concealment and then suddenly 
expand into a blossom, so also in the development of animals, 
it was thought that the already present, small but transparent 
parts grow, gradually expand, and become discernible.” 
(Hertwig.) From the feature of unfolding this was called 
in the eighteenth century the theory of cvolution, giving to 
that term quite a different meaning from that attached to it 
at the present time. 
This theory, strange as it may seem to us now, was 
founded on a basis of actual observation—not entirely on 
speculation. Although it was a product of the seventeenth 
century, from several printed accounts one is likely to gather 
the impression that it arose in the eighteenth century, and that 
