FARM ANIMALS. 51 



Without dominant or stable characters, in at least one par- 

 ent, no stability in transmission can be looked for, and 

 without purity of breeding for generations dominant char- 

 acters cannot be secured. Hence the great importance of 

 purity of blood in effecting improvement in domestic ani- 

 mals. Since some inferior animals will occasionally ap- 

 pear, even where the breeding is the most skilful, the 

 necessity will always exist for the exercise of a most rigor- 

 ous selection on the part of every breeder who is to stand 

 on the upland of success. When aided by judicious selec- 

 tion, the law that like produces like enables us to effect 

 irnprovernent until a certain standard of excellence is 

 reached, to maintain improvement when it has been 

 secured, and to mould new types and form new breeds. 



By the larv or principle of variation is meant the ten- 

 dency sometimes found in animals to produce characters 

 in the progeny which differ from those of the parental 

 type. These changes relate to both form and function; 

 in time they may become modifications of the systems of 

 animals. They may be classed as gradual, or general and 

 ordinary; and as sudden, or spontaneous and extraordinary. 

 General variatiott is that tendency to change from the 

 original type which characterizes in a greater or a less de- 

 gree all the individuals of a breed. Illustrations of the 

 principle of general variation may be found, first, in the 

 tendency of grain to deteriorate which has fallen upon an 

 unkindly soil ; and second, in the quick deterioration of 

 the heavy breeds of sheep when confined to unproductive 

 and rugged pastures. Chief among the numerous causes 

 leading to general variation are changed conditions of life 

 in animals, as climate, food, habit, and environment. Some- 

 times these influences act independently and sometimes in 

 conjunction. The principle of spontaneous variation may 

 be defined as that tendency sometimes found in animals to 

 produce progeny more or less unlike either of the parents 

 or the ancestry of these. Illustrations of the operation of 

 this principle may be found in the occasional production of 

 progeny very unlike the parents or the ancestry in color, 

 form, and other characteristics, and in the existence of horn- 

 less breeds of cattle. 



