PREPOTENCY 575 



sires and dams they are able to get. The line of descent runs 

 only through the few that can produce breeders of breeders, not 

 simply performers. 



Individual excellence is not a certain guide to breeding powers, 

 and many ordinary individuals are among the greatest breeders. 

 This is neither a mystery nor a fault in heredity ; it arises from 

 the fact that individual excellence is partly a matter of individual 

 development and not a sure index of real ancestral possessions. 

 The specimen may be only fairly well born, though faultlessly 

 developed, in which case he will probably be a disappointment 

 as a breeder ; or he may be excellently born, but only fairly well 

 developed, in which case he will breed " better than he is him- 

 self " ; still again, he may be well born and perfectly developed, 

 which is best of all. 



All studies yet made show that, on the average, performers 

 (those individuals possessing high individual merit) are better 

 breeders than non-performers ; that is, than those which do not 

 show in their personal development a high degree of excellence, 

 though, as we should at once surmise, there are numerous ex- 

 ceptions, largely arising from our inability to accurately judge 

 individuals by external appearances. 



SPECIAL EXERCISES 



Work out special cases of prepotency in the breeding and speed records 

 of trotting and running horses, in the advanced registry of cows, and in the 

 famous families of beef cattle and of swine. Pay special attention to rela- 

 tive prepotency of own brothers and to the correlation between individual 

 performance and breeding powers. 



ADDITIONAL REFERENCES 



A MEASURE OF INTENSITY OF TRANSMISSION. By Francis Galton, 1899. 



Nature, LX, 29. 

 DISTRIBUTION OF PREPOTENCY. (Trotting-horse records.) By Francis 



Galton. Nature, LVIII, 246-247. 

 INFLUENCE OF SEX ON SIZE OF OFFSPRING. By F. B. Mumford. 



Experiment Station Record, XV, 542. 

 PREPOTENCY AND XENIA. By C. Correns. Experiment Station Record, 



XI, 1016. 

 PREPOTENCY OF DIFFERENT PLANTS. By W. W. Tracy. Experiment 



Station Record, XIII, 324. 



