OUR KNOWLEDGE OF MELANIN COLOR FORMA- 

 TION AND ITS BEARING ON THE MENDE- 

 LIAN DESCRIPTION OF HEREDITY. 1 



OSCAR RIDDLE. 



Hardly a year has passed since the rediscovery of Mendel's 

 Law without several additions to its descriptive terminology. 

 This may signify either one of two things : a very healthy and 

 vigorous growth, or the onset of senescence. Some of these 

 newly introduced features are plainly justifiable; but there is 

 reason to believe that the rather long series of extensions which 

 has been made in recent times carries as its result not so much 

 description of fact, as of deduction and far-reaching theory. 



The facts and phenomena discovered by Mendel, and the array 

 of facts of high importance which later workers in this field have 

 brought before biologists, have already proved their value. The 

 proved value of these facts is, however, no proof of the correct- 

 ness of Mendelian interpretations of the processes of inheritance. 

 I shall here present some facts which seem to indicate that these 

 Mendelian interpretations are not sound ; and further, that these 

 unsound interpretations now stand as a formidable block in the 

 path of progress to a better knowledge of the mechanism of 

 inheritance and development. 



Mendelian workers think that they have discovered, and cer- 

 tainly they have named and labelled, many " factors " 2 as neces- 

 sary for the production of some single characters. These 

 workers tie all of these factors together, and for them to- 

 gether they go into the germ cells, and whatever appears or 

 fails to appear in the zygote is interpreted in terms of the 



1 Read January 19 before the Biological Club of the University of Chicago. 



2 The word factor as used here in a purely Mendelian sense represents quite a 

 different thing from the physiological sense of the same word. The whole series of 

 ordinary environmental factors temperature, light, reaction of medium, concentra- 

 tion, moisture, etc., all these would not constitute even one Mendelian "factor." 

 The Mendelian " factor " is often a rather unidentifiable thing, but it is conceived of 

 as something capable of residence in, and of segregation by, the germ cells. 



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