GENERAL PRINCIPLES OF BREEDING. 43 



a view to the perpetuation of any variation 

 from an established type we must always be- 

 gin with such individuals as have manifested 

 a tendency to assume the desired form and 

 transmit it to their offspring. With a mixed 

 and heterogeneous ancestry, representing vari- 

 ous shades of divergence from the original type 

 of the species, progress in any given direction 

 by selection will, under the most favorable cir- 

 cumstances, be slow, and the results will fre- 

 quently be anything but satisfactory. There is 

 always a tendency in the offspring of a mixed 

 or improved race to revert to the original 

 form of the species from which it is deriveji. 

 This tendency, as I have shown, is most fre- 

 quently manifested where animals of a widely 

 different character are coupled, as in the case 

 of cross-breeding with distinct varieties or 

 breeds; and this, although not without its com- 

 pensating advantages in many cases, introduces 

 new elements of divergence. Hence the breeder 

 will of ben find failure where he had most ex- 

 pected success. The force of heredity is usually 

 exerted to compel the progeny to adhere to the 

 character which has become fixed in the species, 

 rather than to follow a variation from the estab- 

 lished type that was accidental or spontaneous 

 in the immediate ancestry; but when, through 

 selection of both parents with reference to this 

 particular for several generations, the influence 



