34O OSCAR RIDDLE. 



the zygote without being very appreciably increased or diminished. 



It may be, however, that more than one (almost certainly several 

 for yellow) oxidation stage- of a tyrosin compound presents only 

 the one color black. It could conceivably (see scale of colors, 

 p. 326) happen, therefore, that a certain black (low stage of oxi- 

 dation) x light yellow = yellow (dominant ?) ; but another black 

 (highly oxidized) x yellow = black (dominant ?) ; and yet each 

 of these ntigJit be true blends, i. c., attain to an exact intermediate 

 stage of oxidation to the two forms crossed. Some cases of 

 supposed dominance of color may be therefore in reality true 

 examples of blended inheritance. 



In describing color inheritance I believe that less violence is 

 done to the known facts of color formation, and at the same time 

 a sounder view of developmental and hereditary processes is main- 

 tained, if it be said - -without delimiting terminology, and with- 

 out putting a single thing into the germ except what every one 

 knows is there, and there in the form which is stated for it that 

 in the union of germ cells derived from two pure color varieties, 

 each cell brings with it a power of oxidizing tyrosin compounds, 

 and that the union of the pair of cells may give one or more of 

 the following results : 



1. The tyrosin oxidizing power of the male cell is established 

 (a) at once, or (b] in the next generation or later, throughout the 

 fertilized ovum and its derivatives. 



2. The tyrosin oxidizing power of the female cell is so estab- 

 lished. (In neither of these cases do we need to postulate the 

 continued existence of a subdued recessive factor or repre- 

 sentative.) These would be so-called dominants. 



3. The oxidizing power resulting from the union is somewhat 

 more, or somewhat less, than that of either of the gametes. 



in the egg as an index, measure, or determiner of the tyrosin oxidation powers of the 

 adult. Secrets of protoplasmic differentiation, zymogenesis, stereochemistry, and 

 catalytic action, all block for the present the tracing or predication of any such 

 relations. 



Undoubtedly enzymes have a very considerable importance in development. By 

 focusing attention too closely upon them it is possible, however, to underestimate 

 the importance of other, and even of related phenomena in which the possibility of 

 "inherited specificity" is entirely eliminated. I refer particularly to the "auto- 

 catalysis" of such substances as oils studied by Guenthe ('07), Mathews, Walker and 

 the writer ('o8<$), and others. 



