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,): — 
AlbInG ve ee ee ee ee we ee 1B7 
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 Mendelian 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 (F) and reappears in 
the second generation (/,) 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 (F,).  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 
