Experimental Hybridizing 87 



extracted albinos give always albinos. Only 2 out of 94 

 waltzed. (2) The dark-eyed mice with colored coats belonging 

 to the middle term of the Mendelian series should also give, if 

 inbred, the three types again in the proportion of 1:2:1. In 

 this connection Darbishire points out that on Galton's law of 

 inheritance the farther the individuals of this middle class are 

 removed from the first class, the fewer the albinos that should 

 appear, since they are farther removed from the original ances- 

 tor that was white. On the Mendelian law the members of 

 this middle term should always continue to give the same pro- 

 portion, 1:2:1. Experiments that Darbishire made to test this 

 point seemed to show that the results follow more nearly the 

 expectation of Galton's law; but the purity of the types used 

 may have seriously affected his results. 



Especially interesting, it seems to me, are Darbishire's experi- 

 ments with the extracted mice of the second generation having 

 pink eyes and colored coats. If these are really pure, they should, 

 if paired with pure albinos, produce animals similar to those of 

 the parent cross between colored mice with pink eyes and 

 albinos, i.e. there should be produced only spotted mice with 

 dark eyes. This, however, was not the result obtained. Of 

 98 young, 12 were albinos, while one pink-eyed (colored) indi- 

 vidual also appeared. These results are complicated by the 

 fact that the albinos used were also the extracted offspring 

 of hybrids paired with albinos. Nevertheless, even granting 

 this, it offers no explanation of why albinos should appear, and 

 the only explanation that seems reasonable is that the albino, 

 latent in the pink- eyed mice, has affected the result, pre- 

 sumably being brought out again by crossing. Sixty- three of 

 the 98 young were obtained from such contaminated albinos 

 (extracted recessives). Only seven of the unions were between 

 such pink- eyed mice and albinos which did not contain pink- 

 eyed, spotted waltzers in their immediate ancestry. From these 

 pairs 35 young were obtained, of which 10 were albinos a 

 relatively higher number of albinos, and approximately one 

 . fourth of the whole. The results seem to show that the extracted 



