Chapter VIII 

 FURTHER EXAMINATION OF THE CELL-THEORY 



OO pervasive have been the efforts to interpret organic 

 ^^ development in accordance with the cell-theory that to 

 examine them exliaustively is impossible. All one can do 

 is to choose some of the most prominent and assume that 

 if the criticism succeeds with these major efforts it could 

 succeed witli the minor ones. 



The Mosaic Theory 



Two diametrically opposed interpretations of the early 

 developmental states of the organism have figured largely 

 in later biological theorizing. According to the first, the 

 constituent cells of the earliest cleavage stages hold the re- 

 lation to one another of the stones in a mosaic work ; ac- 

 cording to the second, each cell is "totipotent," that is, sup- 

 posedly capable of producing the entire organism. 



What the Mosaic Theory Is 



What tlie phrase "mosaic work" means when applied to 

 an embryo may be stated in the words of Roux himself, the 

 discoverer of the phenomena on whicli the conception rests. 



"Mosaic work" designates those "developmental phenom- 

 ena tlu'ough wliicli in man}^ ^^S^^ those of the frog for in- 

 stance, each of the two or four first cleavage cells (or the 

 complex of descendants of these) develop btj themselves 

 alone into the corresponding body part, for example into 



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