vi PREFACE 



accepted form may be defined as consisting of Virchow's 

 " Omnis cellula a cellula" (1855) -plus Flemming's " Omnis 

 nucleus a nucleo " (1882). 



The original theory comprised two propositions; firstly, 

 that the nucleus is the unit of structure and function in 

 both plants and animals; and, secondly, that new nuclei 

 and new cells arise in an amorphous basis. The first part 

 was at once recognized by Virchow as a great advance in 

 science, but he did not attach importance to the second 

 part, which indeed was later found to be untrue for the 

 forms of life to which it was applied. In its present state 

 as defined above the theory has proved to apply to nearly 

 all known living things, and it has been the instrument by 

 which so much imperishable biology has been built up that 

 the fact that it is contradictory of dominant phases of 

 well-known groups of organisms has not yet received due 

 attention. 



It applies as far as is known to all Metazoa, and to all 

 plants above the Thallophyta, and to most of these, and to 

 many Protozoa ; but it is patently at fault when it is applied 

 to dominant phases of certain protists, some thallophytic 

 and others protozoan. 



That no qualifying clause has been added to the cell- 

 theory to meet this position is strange seeing that game- 

 togenetic chromidia are now commonplaces in biology, and 

 that these vital processes translate terms such as "free 

 nucleus-formation' 5 into prophecies fulfilled. 



