criticism of the idea of preformation and shows how the 

 principle of epigenesis, the "law of intercourse of the 

 animal with the world," (p. 16) is realized in the historical 

 development of organisms. 



Later on, Wolff's observations that the embryo in the 

 early stages is composed from layers, later called embryonic 

 layers, gained great importance. The study of the embryonic 

 layers, as the common form of development of all multicellular 

 animals, in the second half of the nineteenth century became 

 the base of comparative embryology. Creation and detailed 

 elaboration of this progressive direction in the study of 

 ontogenesis constitute the glory of Russian science. 



In order to evaluate to the necessary extent the 

 greatness of Wolff's scientific exploits, especially his 

 development of the theory of epigenesis, it is necessary 

 to give a brief essay of the history of the struggle between 

 supporters of preformation (preexistence) and epigenesis 

 (new formation), which represented a struggle of two outlooks, 

 two metaphysical and historical opinions of the world of 

 living creatures. 



33 



