MELANIN COLOR FORMATION. 343 



representative, but all together have one basis in the germ 

 a power to oxidize tyrosin compounds, and this capable of close 

 and continuous gradations. Many other characters, moreover, 

 may also be closely connected genetically with the tyrosin oxi- 

 dizing power of the organism. This being true, it is easily seen 

 that what has been quite generally taken to be a " unit char- 

 acter " among colors cannot be in fact a " unit " of modification. 

 All tyrosin oxidations, and some others as well, may be, and 

 probably are, modified simultaneously and in corresponding 

 manner. 



The conception of " units of modification," then, which we 

 adopt as an apparent logical necessity cannot regard as " units " 

 the things that have been called unit characters in the past ; quite 

 certainly some unsound criteria, a false interpretation, a mis- 

 leading nomenclature, and some observed facts are all back of 

 the old conception as it has been applied to color behavior. , We 

 need not be surprised if it be found to embrace very little truth. 

 To determine what a real " unit of modification " is, would seem 

 to be no easy matter. Present Mendelian methods will doubtless 

 contribute something, though not nearly all, to the complete 

 story. For if and there is little doubt other definitive char- 

 acters of the soma are likewise present in the germ only as vary- 

 ing "strengths" of rather general powers or processes, these 

 same powers will exercise influence directly and indirectly, and 

 to greater or less extent, in many and diverging directions during 

 development ; so that a " unit of modification " in inheritance 

 would, in the broadest sense, include all such effects (there would 

 probably be found all gradations of such effects). Obviously, there- 

 fore, individual characters arc by no means units of inheritance or 

 modification. And in any exhaustive search for such influence 

 or modification it is quite possible that vision will sometimes be 

 forced to cover the whole field from antibodies and immunity to 

 size and color ; from the grossest structural modification to the 

 most delicate functional idiosyncrasy. 



The question will be asked how may those who reject the 

 Mendelian interpretation based on representative particles, account 

 for the segregation and proportions observed in Mendelian 

 behavior? To undertake a discussion of this point is obviously 



