pigment whatever in its fur, while the other 

 develops very little, nevertheless the offspring 

 are as dark as the darkest wild mice, eyes, 

 fur, and all. They look just like common house- 

 mice. This result shows that the albino varia- 

 tion is something very different in nature from 

 the modifications found in the pink-eyed brown 

 parent, since each parent contains those con- 

 stituents of the wild gray coat which the other 

 parent lacks. 



I can think of no more instructive labora- 

 tory experiment illustrative of Mendelian in- 

 heritance than to follow through two genera- 

 tions the cross just described, and to analyze 

 critically the results obtained. One who does 

 this can never be sceptical about the value of 

 crossing as an agency in the production of new 

 varieties. For in the second generation from 

 the cross he will obtain (1) ordinary gray, 

 black, cinnamon, and brown varieties; (2) pale 

 gray, black, cinnamon, and brown varieties; 

 (3) pink-eyed gray, black, cinnamon, and brown 

 varieties; (4) pink-eyed and pale gray, black, 

 cinnamon, and brown varieties; and lastly, 

 albinos, which, if he has the patience to test 



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