Experimental Hybridizing 83 



white background ; spotted or pied or piebald mice are those 

 in which these various colors appear in splotches or marks. 

 In addition to these kinds, a white mouse with dark eyes is 

 known, which is probably to judge from other white animals 

 with black eyes not derived from an albino, but from a 

 spotted animal in which the spots of dark pigment have disap- 

 peared except in the eyes. The so-called dancing mice that 

 whirl around at times are said to be of Japanese origin, and may 

 have originated from a different wild variety. 



Experiments on mice have been carried out by a number of 

 investigators, the principal results being those of von Guaita, 

 Cuenot, Parsons, Darbishire, Castle, Allen, Davenport, Schuster, 

 Haacke, and others. Von Guaita's results were not consid- 

 ered by him in the light of the Mendelian ratio, but Bateson and 

 Davenport have more recently examined them and have pointed 

 out that many of them appear to follow Mendel's law. 



Cuenot's results conform closely to the Mendelian law. He 

 found that when a gray mouse is paired with an albino, the off- 

 spring in the first generation (F^ are always gray mice the 

 gray dominating over albinism. The next generation (F 2 ) from 

 the inbred dominant gray mice gave 198 gray and 72 albino 

 mice, i.e. in the ratio of 2.75 : i, a near approach to the expecta- 

 tion of 3 : i. Later Cuenot reported that his "pure " gray x mice 

 of the third filial generation (F%) when crossed with albinos gave 

 several black mice. These black mice when bred with certain 

 albinos gave black mice, which appeared to be B(W), i.e. black 

 dominant, white recessive, for, when bred inter se, the offspring 

 were three blacks to one albino. Some of these blacks were 

 shown to be "pure " and produced a race of pure blacks. When 

 individuals of this black strain were bred to ordinary gray mice, 

 the black was recessive, giving in the second generation three 

 grays to one black. 



Cuenot made a further discovery of great interest. He found 

 when he bred the black mice to albinos that the results were 



1 These were the offspring of the second generation that had bred true and 

 shown themselves to be pure G's. 



