162 THE BREEDING OF ANIMALS 



germ-plasm of the preceding generation. If this dis- 

 tinction and differentiation is kept clearly in mind, it 

 will help materially in the discussion of the inheritance 

 of acquired characters. If we accept Weismann's def- 

 inition of acquired characters, that they are somatic 

 modifications which do not have their origin in the germ- 

 plasm, we have to discuss only such somatic modifications 

 as may be acquired by the animal during its lifetime. 



152. Examples of acquired characters. Among the 

 common causes of the changes in the soma must be 

 grouped environment, including food and climate; use 

 and disuse of parts; disease and accidents. Each of 

 these acting separately or all of them acting together may 

 cause profound changes in the external form and develop- 

 ment of plants and animals. 



153. Food supply. Perhaps no other single environ- 

 mental influence is responsible for such profound changes 

 in the external form of plants and animals as the food 

 supply. The Kerry cattle of Ireland are a diminutive 

 race of cattle which have been long subjected to condi- 

 tions of scant supply of innutritious food. Their size 

 and hardy character must be regarded as a more or less 

 successful adaptation to their environment. When young 

 calves of the Kerry breed are surrounded with conditions 

 in which they are supplied with a generous and nutri- 

 tious food, they increase in size and come to maturity 

 at an earlier age. 1 



The Shetland pony in the barren islands of Shetland, 

 gathering a scant subsistence from the inferior grasses 

 and forage plants, develops into one of the most diminu- 

 tive races of horses known to man. The same race of 

 horses transplanted to the fertile regions of Great Britain 

 1 Miles, "Principles of Stock Breeding," p. 100. 



