No. 589] THE EVOLUTION OF THE CELL 



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complex albuminoid substance rich in phosphorus. It is 

 the phosphorus-content of chromatin that is its most 

 characteristic chemical peculiarity as contrasted with the 

 cytoplasm. How far these features are common, how- 

 ever, to all samples of chromatin in all types of living 

 organisms universally, can not, I think, be stated definitely 

 at present; at any rate, it is not feasible for a cytologist 

 of these days to identify a granule in a living organism 

 or cell as chromatin solely by its chemical reactions, 

 although it is quite possible that at some future time 

 purely chemical tests will be decisive upon this point— a 

 consummation devoutly to be wished. 



The only criterion of chromatin that is convincing to 

 the present-day biologist is the test of its behavior, that 

 is to say, its relations to the life, activity and develop- 

 ment of the organism. I may best express my meaning 

 by objective examples. If I make a preparation of Arcella 

 vulgaris by suitable methods, I see the two conspicuous 

 nuclei and also a ring of granules lying in the cytoplasm, 

 stained in the same manner as the chromatin of the 

 nuclei. Are these extranuclear granules to be regarded 

 also as chromatin? Yes, most decidedly, because many 

 laborious and detailed investigations have shown that from 

 this ring of granules in A rcella nuclei can arise, usually 

 termed "secondary" nuclei for no other reason than that 

 they arise de novo from the extranuclear chromatin and 

 quite independently of the "primary" nuclei. The sec- 

 ondary nuclei are, however, true nuclei in every respect, 

 as shown by their structure, behavior and relations to 

 the life-history of the organism ; they may fuse as nuclei 

 of gametes (pronuclei) in the sexual act and they become, 

 with or without such fusion, the primary nuclei of future 

 generations of Arcella; they then divide by karyokinesis 

 when the organism reproduces itself in the ordinary way 

 by fission, and are replaced in their turn by new secondary 

 nuclei at certain crises in the life-history. In view of 

 these facts it can be asserted without hesitation that the 

 ring of staining granules in Arcella is composed of, or at 



