FACTS AND FACTORS OF DEVELOPMENT 81 



by supernatural creation. If every individual 

 of the race existed within the germ cells of the 

 first parents, then in the creation of the first 

 parents the entire race with its millions of in- 

 dividuals was created at once. Thus arose the 

 theory of "emboitement,'' or infinite encase- 

 ment, the absurdities of which contributed to 

 the downfall of the entire doctrine of prefor- 

 mation, which, in the form given it by many 

 naturalists of the eighteenth century, is now 

 only a curiosity of biological literature. 



2. Epigenesis. — As opposed to this doctrine 

 of preformation, which was founded largely 

 on speculation, arose the theory of epigenesis, 

 which was in its main features founded upon 

 the direct observation of development, and 

 which maintained that the germ contains none 

 of the adult parts, but that it is absolutely 

 simple and undifferentiated, and that from 

 these simple beginnings the individual grad- 

 ually becomes complex by a process of differ- 

 entiation. We owe the theory of epigenesis, 

 at least so far as its main features are con- 

 cerned, to William Harvey, the discoverer of 

 the circulation of the blood, and to Caspar 



