No. 589] THE EVOLUTION OF THE CELL 



9 



as highly organized as those of Metazoa or even, in some 

 cases, much more so, back to types of structure to which 

 the term cell can only be applied by stretching its mean- 

 ing to the breaking-point. Already one generalization of 

 cytologists has been torpedoed by the study of the Pro- 

 tista. The dictum "Omnis nucleus e nucleo" is perfectly 

 valid as long as it is restricted to the cells of Metazoa and 

 Metaphyta, to the material, that is to say, to which the 

 professed cytologist usually confines his observations. 5 

 But in the Protista it is now well established that nuclei 

 can arise de novo, not from preexisting nuclei but from 

 the extranuclear chromatin for which Hertwig first coined 

 the term "chromidia." 



It is clear, therefore, that the results already gained 

 from the study of the Protista have brought about a new 

 situation which must be faced frankly and boldly. It is 

 impossible any longer to regard the cell as seen in the 

 Metazoa and as defined in the text-books as the starting- 

 point of organic evolution. It must be recognized that 

 this type of cell has a long history of evolution behind it, 

 which must be traced out, so far as the data permit. The 

 construction of phylogenies and evolutionary series is of 

 course purely speculative, since these theories relate to 

 events which have taken place in a remote past, and which 

 can only be inferred dimly and vaguely from such frag- 

 ments of wreckage as are to be found stranded on the 

 sands of the time in which we live. Many important 

 stages of evolution may be totally submerged and no 

 longer available for study and consideration. The ex- 

 tent to which such speculations will carry conviction to 

 a reasonable mind will depend entirely on the stores of 



s Vejdovsky ("Zum Problem der Vererbungstrager, " Prag, 1911-1912, p. 

 120) has already maintained, for the cells of Metazoa, that Fleming's 

 aphorism "Omnis nucleus e nucleo" should be changed to "Omnis nucleus 



of the mother-cell." If this isuia-. th.-re is but little difference in detail, 



