EVOLUTION BY LOSS 



them one by one, will prove to be of sixteen 

 different homozygous kinds, to say nothing of 

 the much more numerous heterozygous sorts. 



No mention has thus far been made of spotted 

 races, in which a unit-character modification has 

 occurred which results in a distribution of pig- 

 ment to part of the coat only, the remainder 

 being unpigmented. Although this modifica- 

 tion apparently regulates the distribution of 

 pigment over the body, it is independent of the 

 general color factor C, since it is transmitted 

 through albinos, which by hypothesis lack C. 



Spotting is also independent of all the other 

 unit-character modifications which have been 

 described. Consequently we have in mice four 

 different series of spotted varieties, the in- 

 tense spotted, the dilute spotted, the intense 

 pink-eyed spotted, and the dilute pink-eyed 

 spotted. In each of these series are gray, 

 black, cinnamon, brown, and yellow individuals, 

 making a total of twenty spotted sorts, all of 

 which may be obtained from crossing a single 

 pair of properly selected parents, such, for 

 example, as an albino and a wild house-mouse 

 of the kind every barn contains. 



83 



