214 THE BREEDING OF ANIMALS 



terity. The breeder of beef cattle believes that the off- 

 spring of parents which are kept in good or even in fat 

 condition are more apt to possess a tendency to fatten 

 readily than the offspring of parents kept in very thin 

 condition. The breeder of trotting horses prefers to use 

 in his stud a stallion that has a record and mares that 

 have benefited from severe training. 



In this case the biologist is probably in the main cor- 

 rect in his conclusions from the standpoint of inheritance. 

 But it is also true that the breeder of beef cattle is right 

 in maintaining his beef animals on a high plane of nutri- 

 tion, not because this will materially affect the germ-plasm, 

 but because such treatment gives the breeder an accurate 

 measure of the beef-producing characters of his breeding 

 animals. How can the breeder know that a particular 

 bull or cow possesses the ability to lay on fat rapidly 

 unless he actually tests the animal ? The breeder of 

 trotting horses likewise cannot judge accurately from an 

 external examination of a horse how fast he can trot. He 

 must be trained and his full speed developed. 



Such treatment on the part of the breeder is not for 

 the purpose of changing the hereditary capacities of an 

 animal, but for the purpose of aiding selection. Animals 

 so treated that do not come up to the standard set by the 

 breeder are eliminated. The desirable animals are pre- 

 served and encouraged to reproduce. 



202. Germinal variations. The term variation has 

 suffered from careless use, and such use has led to some 

 confusion of ideas. Differences appearing in the offspring 

 may be due to variations in the germ, or they may be due 

 to the influence of environment. What the animal 

 actually is depends upon the constitution of the germ. 

 The offspring may be exactly like the parent in the con- 



