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 exhaustively 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 with 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 the phrase "mosaic work" means when applied to 

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

 discoverer of the phenomena on which the conception rests. 



"Mosaic work" designates those "developmental phenom- 

 ena through which in many eggs, those of the frog for in- 

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

 complex of descendants of these) develop hy thevuehyes 

 alone into the corresponding body j^art, for example into 



198 



