HEREDITY 



varieties. The pink-eyed condition is there- 

 fore in mice a unit-character modification of 

 the pigmentation, independent of any of the 

 pigment factors previously mentioned, since 

 it can be transferred by crosses from asso- 

 ciation with one of these to association with 

 another. It may also be transmitted equally 

 well through colored and through albino in- 

 dividuals, though it produces a visible effect 

 only in colored individuals. 



Another unit-character modification of the 

 pigmentation seen in mice produces a series 

 of dilute or pale pigmented varieties, but dif- 

 ferent in character from the pink-eyed series, 

 since their eyes may be dark, not pink. The 

 pale modification of gray is known to fan- 

 ciers as " blue-gray, " that of black is known 

 as " blue," and that of brown is known as 

 " silver fawn." The pale quality is inter- 

 changeable between black, brown, and yellow 

 pigmentation, so that if one has a pale gray 

 variety he may by crosses obtain also pale 

 black, pale cinnamon, pale brown, and pale 

 yellow varieties. Or if one starts with pale 

 yellow, he may by crosses with a perfectly 



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