476 THE AMERICAN NATURALIST [Vol. XLIV 



from wanting to urge that it is the only possible inter- 

 pretation. The absence of a character, color in the pres- 

 ent instance must be due to local conditions; certain 

 regions are like the hornless female hybrid sheep. It 

 is well known that injuries to the skin may cause the ces- 

 sation of formation of colored hair and the production 

 of white hair. Similarly in colored animals, certain 

 regions are more prone to lack pigment than other re- 

 gions. In rodents for example, the belly, the tip of 

 the tail and the forehead seem to be such regions even 

 in animals that would be classed as uniformly colored. 

 It follows that if in certain races these regions are par- 

 ticularly deficient in their power to produce pigment a 

 spotted race will arise. Crossing with an albino race 

 does not increase the extent of the spotted area in the hy- 

 brid. On the contrary, if the white animal has been de- 

 rived from a race uniform in pigment production in these 

 regions the hybrid will be uniform, i. e., not spotted at 

 all, although one parent was spotted. 



It may appear that this view lias simply introduced the 

 spotting factor in a new guise. In a sense this is true, 

 but it recognizes a condition that is ignored by those 

 who make use of a spotted factor, for it rests on the 

 assumption that whether pigment develops in certain re- 

 gions depends not only on whether pigment producing 

 factors are present or absent in the germ cells, but on 

 the modifications of such inheritance by local conditions. 

 My conclusion is, moreover, of a piece with our general 

 knowledge of development of different organs of the 

 same embryos. 



Why, it may be asked, can not the spotted character be 

 explained on the assumption of weakened power in these 

 spotted races to produce color; or why is it not due to 

 loss of chromosomes in the early blastomeres of the germ 



The first alternative must be rejected, I believe, for 

 were the power of color product ion weakening in spotted 

 animals, the ratio being lower than 50 per cent., we should 

 still have to invoke local action to account for the results. 



