Chromatin as "Hereditary Substance" 339 



ni/c Hie same tendency that prevailed then to force the 

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

 anticipate that out of the chromosome theory of heredity 

 will emerge proof that these bodies are of great importance 

 in actual development, but that their importance 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 complete that the nucleus plays an 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 problem of 

 pigment formation was taken by K. Meirowsky. Besides 

 producing important evidence hearing on the old and much 

 discussed question of whether pigment 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 pyrcnoid nuclear substance. It is said 

 to pass through the nuclear membrane into the cytoplasm. 

 The particles gradually turn brown, this color appearing 

 first on their surfaces. The transformation of color is said 

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

 It is not contended that the pyrenoid substance is derived 

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

 in and is extruded from the nucleus. 



The latest contribution to this subject which has come to 

 my notice is bv Davenport Hooker. Studying the develop- 

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

 Uanti pipiens, this observer has shown conclusively that the 

 melanin granules all arise in the cytoplasm at its line of 



