Experimental Hybridizing 93 



albino, descended (extracted) from an animal with a uniform 

 coat, one might be led to suppose that the white of the albino 

 might go to augment the white of the spotted parent, but on the 

 contrary these hybrids are uniformly colored. In the next gen- 

 eration the two characters, U and S, separate, i.e. disjunct, 

 and the offspring give the Mendelian proportions U+2US 

 + S, i.e. one spotted to three uniform. 



II. Cross between Two Forms unequally spotted with White. 

 If a much- spotted individual is bred to one very little marked 

 with white, having for example only a little white at the end 

 of its tail, the offspring shows that the maximal dark mark- 

 ing is the dominating character. All the young have the tail par- 

 tially white, but no other white marks on the body. Yet these 

 young are not all exactly like the darker parent, since the degree 

 of tail marking, for example, may be quite variable. In the 

 next generation, when the young are inbred, the phenomenon 

 of disjunction appears. Two groups of offspring arise, one 

 oscillating around the least amount of white (one grandparent 

 type), the other around the most white-spotted type (the other 

 grandparent type). 



III. Cross between Two Much-spotted Forms. Without ex- 

 ception the young are spotted, but in variable degrees. The 

 cross may even produce albinos if the two parents are hybrids, 

 including the character A. These albinos, in turn, possess la- 

 tent the spotted character. 



Progression of the Spotted Condition by Selection. Beginning 

 with mice little marked with white and excluding in each gen- 

 eration the less-marked individuals, Cuenot found that the white 

 areas could be increased slowly but regularly, so that in two 

 and a half years mice were obtained that contained much white, 

 and differed to a large extent from the first forms used. The 

 details of the spotted type seem not to be represented in the 

 germ-plasm, because the young and the parents are not identi- 

 cal. Local factors appear to determine the limits of variation. 



In regard to the characters of albinos, it has been pointed out 

 that they carry in a latent form the characters of the race from 



