Experimental Hybridization 85 



of the colored types to each other as regards their inheri- 

 tance is too obscure to make it profitable to discuss the result 

 here. 



Darbishire has carried out experiments with pink- eyed, 

 spotted, waltzing mice crossed with albinos. In respect 

 to their coat color, he recognizes six groups forming a continu- 

 ous series, depending on the extent to which the pigment spots 

 cover the surface of the mice. The colors of the spots were 

 yellow, gray, black, lilac, or chocolate. When these mice were 

 crossed with albinos, supposed to be pure, spotted mice were 

 produced with dark eyes. None of the mice of this generation 

 exhibited the waltzing habit. These hybrid mice (F-^ when bred 

 inter se gave the following kinds of mice (F z ) : 



Albino 137 



Colored or piebald with dark eyes . . . 287 

 Colored or piebald with pink eyes . . . 131 



Of these mice 97 showed the waltzing habit and 458 did not. 

 The Mend elian expectation for waltzers is 138.75. The actual 

 results fall considerably below the expectation, nevertheless it 

 may be that some of the mice that did not waltz were poten- 

 tially waltzers and might have transmitted this habit as do 

 "pure" recessives. It is interesting to note that, whether the 

 Mendelian proportion is or is not given, the waltzing habit dis- 

 appears in the first generation of hybrids (FJ and reappears in 

 the second generation (F 2 ) as do other Mendelian characters. 



The expectation for albinos is approximately realized as well 

 as the expectation for the other two types. Since neither grand- 

 parent had dark eyes, this character must have been latent in 

 one of them, because it appears in all of the offspring (Fj). Dar- 

 bishire points out that his results do not conform in all respects 

 to the Mendelian rule ; but some, at least, of these difficulties are 

 not insuperable, I think, if it be granted that the so-called "pure" 

 recessives and "pure" dominants are really impure with latent 

 characters that come out on crossing. Darbishire contends, 

 and I think justly, that the behavior in inheritance of extracted 



