PRE FORM A TIONIST THE ORIES 



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generation and development, and ended by almost denying 

 them both. He assumed "as a fundamental principle, that 

 nothing is generated, and that what we call generation is but the 

 simple development of what pre-existed under an invisible form, 

 and more or less different from that which becomes manifest 

 to our senses." In the same way, the renowned physiologist, 

 Albrecht von Haller, said " Esgibt kein Werden " (" There is no 

 becoming ") ; and it became the fashion to declare that all 

 development was an illusion — only an unfolding or evolutio. In 

 contrast to Harvey's conclusion, " The first concrement of the 

 future body grows, gradually divides, and is distinguished into 

 parts ; not all at once, but some produced after the others, each 

 emerging in its order," Haller wrote, " No part of the body is 

 made from another ; all are created at once." 



To the main conception of preformation and unfolding, two 

 subsidiary hypotheses were added : (i) that of emboitement, 

 according to which the germ contains the preformation not of 

 one organism only, but of successive generations ; and (ii), that 

 germs occurred scattered throughout the organism, capable 

 of developing into buds, of replacing lost parts, and so forth — 

 neither of them ideas to be laughed at, though their particular 

 expression was necessarily erroneous. 



The long-lived theory, variously termed the " preformation 

 theory," the " theory of evolutio," the " mystical hypothesis," 

 the theory of "emboitement" or " Einschachtelung," or "die 

 Skatulationstheorie," seemed to get its deathblow from Wolff's 

 demonstration (1759) of " epigenesis," or the gradual develop- 

 ment of obvious complexity from an apparently simple rudiment. 

 We say " seemed," because the theory, as theories will, persisted 

 long after the deathblow was given. Moreover, though Wolff 

 demonstrated in the chick that gradual becoming which we call 

 development, he had no way of accounting for the uniqueness 

 of the germ-cells, and had to fall back on the postulate of a 

 vis corporis essentialis. 





