206 BIOLOGY AND ITS MAKERS 



As we have already seen, Harvey, more than a century before 

 the publications of Wolff, had clearly taught that develop- 

 ment is a 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. 



As a 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 thi 

 pre-formed embryo. The process was commonly illustrated 

 by reference to flower-buds. " Just as already in a small 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 evolution, 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 



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