INHERITANCE 317 



together albino three-quarter lops may be obtained in the 

 next generation. By continuing this process of back-cross- 

 ing with the lop-eared stock, and selecting the albino off- 

 spring obtained, the lop-eared character may be steadily 

 improved in the albinos until it is practically as good as in 

 the original lop-eared stock. The rate of improvement pos- 

 sible can be readily calculated. The albino young will be: 



After 2 generations, one half lops, 



After 4 generations, three fourths lops, 



After 6 generations, seven eighths lops, 



After 8 generations, fifteen sixteenths lops, 



After 10 generations, thirty-one thirty-seconds lops, etc. 



This will be the result on the hypothesis that no secondary 

 variation occurs in the lop-eared character. If, however, 

 variation is induced by the cross-breeding, then it is possible 

 that the desired end may be reached sooner, or that an even 

 better lop may be obtained in the albino cross-breds, than 

 that of the original pigmented stock. 



"Latent characters are an important element in practical 

 breeding. Sometimes they greatly aid the breeder's work; 

 sometimes they impede it. If a stock contains undesirable 

 latent characters which are brought into activity by cross- 

 breeding, these latent characters will have to be eliminated, 

 or a new stoc k tried ." 



Obviously, without variation no new characters are 

 obtained by such intercrossing, but merely new combina- 

 tions of characters that previously existed apart. But, 

 when new characters appear among the variants of a species, 

 and especially when a number of new characters appear 

 simultaneously as in typical cases of mutation, then inter- 

 crossing may be the means of bringing these characters 

 together in all sorts of combinations, some of which may be 

 of value to man, and some of which may be fit, and may, 

 therefore, furnish a basis for further natural evolution. 



