200 THE BREEDING OF ANIMALS 



191. Examples of functional variation. In most cases 

 the functional variations in the domestic animals which 

 have become valuable to man are modifications of natural 

 functions possessed by all Wild animals living under nat- 

 ural conditions. The present stage of development in 

 domestic forms is due to artificial selection practiced by 

 man. The variations which have been desirable have 

 been preserved through selection and a gradual improve- 

 ment in functional efficiency has resulted. These varia- 

 tions may arise through sudden mutations, but such 

 marked changes in function are probably less common 

 than similar mutations in form. Variations in the func- 

 tional activities of animals are of great economic impor- 

 tance to the breeder of domestic animals. It is important 

 to know with some degree of definiteness the extent of 

 variation in function, as such knowledge will give some 

 idea of the probable limits of improvement. The follow- 

 ing examples of functional variation will be useful in 

 helping to determine the limitations of improvement. 

 Such examples may be greatly multiplied by search of 

 the literature of the subject. 



192. Variation in fertility of animals. It is well 

 known that there are wide differences among individual 

 animals and among races or breeds in their ability to 

 produce large numbers of offspring. The quality of 

 fertility is one of great practical importance and is readily 

 transmitted by heredity. Miles 1 has recorded the case 

 of a cow belonging to a French farmer which produced 

 nine calves at three births, four at the first, three at the 

 second, and two at the third. 2 A Teeswater ewe belonging 

 to Edward Eddison produced four lambs in 1772 when 



1 Miles, "Stock Breeding," p. 131. 



2 "British Husbandry," vol. II, p. 438. 



