334 OSCAR RIDDLE. 



gests that such may be a true, and, indeed, the truest conception 

 of a color blend ; and an examination of the experimental results 

 gives considerable support to this view. Castle ('06) reports 

 that he secured yellow mice from three sources, viz. : Y<^ x Ch $, 

 A x B, A x Ch. It will be observed that each of these crosses 

 has one color (yellow, chocolate, black, albino) more oxidized 

 than yellow, and one less oxidized than yellow (see Table II.) ; 

 that is, the yellow produced in these cases is apparently a blend. 1 

 The general fact of the unstable (heterozygous) character of all 

 yellow mice is, quite possibly, evidence of the same kind. 



Heretofore a blend, say between white and black, has been 

 considered a mixture of these two colors, a spotted animal, a 

 form in which black was diminished, etc., but a little reflection 

 upon facts already stated concerning the nature of these color 

 characters reveals very distinct colors as none the less very distinct 

 blends ! 



At present the biological data are wanting to quantitatively 

 seriate all of the several colors ; but there is apparently enough 

 data to warrant the definite statement that yellow mice are forms 

 with the power to oxidize tyrosin compounds to an intermediate 

 point. Thus the biological data again parallel chemical experience. 



Cuenot, Bateson and others " explain " color inheritance on the 

 assumption that "recessives " lack altogether the factors of color 

 production ; but Castle has convincingly argued that this cannot 

 be true, because in such forms small amounts of pigment actually 

 form, etc. Castle tried to explain these phenomena upon the 

 supposition that all of the factors may be present, but that " the 

 presence of one character often inhibits the activity of another," 

 i. e., upon grounds of activity and latency. I would urge that 

 we are now quite ready to take the next step, which seems to lie 

 in the opposite direction, and say that we have to do neither with 

 absent factors nor with the inhibition of present factors ; that in 

 gametic unions we deal not at all with " factor " particles, but 

 merely mix, and amalgamate to various degrees, powers of tyrosin 

 oxidation ; and the conditions supplied by the differentiation of 



1 Cuenot says of his yellow mice that they contain numerous unfixable variations, 

 not hereditary, ranging from a clear orange yellow to a sooty or grayish yellow, not 

 very different from the color of gray mice. Does this look like purity of gametes, or 

 a wide range of blending, which? 



