IDS 



THE AMERICAN NATURALIST 



[Vol. L 



of the chromatin-particles there is no cell-constituent that 

 can be claimed to persist throughout the life-cycles of or- 

 ganisms universally. To take some concrete examples; 

 the cytoplasmic grains known as mitochondria or chron- 

 driosomes have been asserted to be persistent elements 

 throughout the germ-cycle of Metazoa, and the function 

 of being the bearers of hereditary tendencies has been as- 

 scribed to them. But Vejdovsky 22 flatly denies the al- 

 leged continuity in cases investigated by him, and though 

 chrondriosomes have been described in some Protozoa, 

 there is no evidence whatever that they are of universal 

 occurrence in Protista. Centrosomes, intranuclear or ex- 

 tranuclear, have been stated to be constant cell-compo- 

 nents in some organisms ; whether that is true or not it 

 seems quite certain that in many organisms the'cells are 

 entirely without centrosomic bodies of any kind, as for 

 example in the whole group of Phanerogams. So it is 

 with any other cell-constituent that can be named. It may 

 be that this is only the result of our incomplete knowledge 

 at the present time. I am prepared, however, to chal- 

 lenge anyone to name or to discover any cell-constituent, 

 other than the chromatinic particles, which are present 

 throughout the life-cycle, not merely of some particular 

 organism, but of organisms universally. 



In this feature of continuity the chromatin-constituents 

 of the cell present a remarkable analogy with the germ- 

 plasm of Metazoa. Just as the germ-cells of Metazoa go 

 on in an uninterrupted, potentially everlasting series of 

 cell-generations, throwing off, as it were, at each sexual 

 crisis a soma which is doomed to but a limited lease of 

 life, during which it furnishes a nutritive environment for 

 further generations of germ-cells; so in the series of cell- 

 generations themselves, whether in the germ-cell-cycles 

 of Metazoa or in the life-cycles of Protista the chromatin- 

 ] articles maintain an uninterrupted propagative series 

 within a cell-body of which the various parts have a limited 

 duration of existence, making their appearance, flourish- 



