Chromatin as ''Ilcreditarf/ Substance'' 3J39 



nize the same tciidciicy tluit ])rc'vaik(l tlicii to U)i\-(i tlic 

 evidence. Forecasting in the light of history alone, we may 

 anticipate that out of the chromosome theory of hcnthty 

 Avill emerge proof that these bodies arc of great importance 

 in actual development, but that their im])ortance consists in 

 their being indispensable tools or agents of the organism 

 rather than entities, ultimate and supreme in their power 

 over the organism. Thus already the demonstration is al- 

 most if not quite com})lete that the nucleus plays a!i im- 

 portant part in the production of melanin and other organic 

 pigments, and so is a mechanism of heredity to some extent, 

 so far as colors are characteristic in genetically related or- 

 ganisms. 



A notable forward step toward solving the ])ro])l('m of 

 pigment formation was taken by K. INIeirowsky. Jiesides 

 producing important evitlence bearing on the old and nmch 

 discussed question of whether ])igment arises in the epi- 

 dermis or cutis or in both, Meirowsky turns his attention 

 to how the melanin arises within the cells. He concludes that 

 it is the result of the transformation of a colorless substance 

 originating in the nucleus. From the intense red it assumes 

 when treated with the basic stain pyronin, this substance is 

 called by the author pyrenoid nuclear substance. It is said 

 to pass through the luiclear membrane into the cytoplasm. 

 The particles gradually turn ])rown, this color appearing 

 first on their surfaces. The transformation of color is said 

 to begin in some of the substance before it leaves the luicleus. 

 It is not contended that the pyrenoid substance is derived 

 from the chromatin of the nucleus, but merely that it arises 

 in and is extruded from the nucleus. 



The latest contribution to this subject which has conic to 

 my notice is by Davenport Hooker. Studying the develop- 

 ment of pigment in various tissues of the embryo of a frog, 

 Rana pipiens, this observer has shown conclusively that the 

 melanin granules all arise in the cytoplasm at its line of 



