APPLICATION OF PRINCIPLES OF BREEDING 



493 



even in selected specimens, for more than a very short term of years. More 

 careful experiments on an extensive scale have been carried on for many years 

 at the Maine Experiment Station, with similar results. 1 The present line of 

 experiment at this station seeks to determine how far egg production may be 

 improved by breeding from prepotent heavy layers. As far as increase in possi- 

 bilities of egg production in the individual is concerned, the whole question 

 seems to depend on whether or not the number of ovules produced by a bird 

 is congenitally fixed in the individual, variable in individuals, and generally so 

 small that the supply might 

 be exhausted within the aver- 

 age productive life of a hen, 

 that is, within three or four 

 years. It has been commonly 

 assumed that the possibilities 

 of production in the ordinary 

 .unimproved hen were small 

 and were increased by selec- 

 tion. It has been supposed 

 that ordinarily a hen having 

 laid a few hundred eggs would 

 permanently cease because of 

 the exhaustion of the supply 

 of ovules. The observations of 

 Raymond Pearl and Frank M. 

 Surface on the numbers of 

 visible ovules indicate that 

 there is always present a 

 greater supply of elementary 

 eggs than any hen is capable 

 of developing. Here, as every- 

 where, nature is prodigal with 

 the elements of life. With FIG. 482. Dark Brahma cockerel with extraor- 

 the number of elementary dinary breast development. (Photograph from 

 eggs in an ordinary hen five owner > F - w - Rogers, Brockton, Mass.) 



or six times as great as the 



total of eggs laid by the average hen kept until three years old, it is plain that 

 the practical problem in breeding for increase in egg production is to produce 

 stock with the substance, constitution, and functional vigor required for the com- 

 bined strains of heavy egg production and reproduction. As a rule, it is found that 



1 Actually the first line of experiment at this station showed a decrease in 

 egg production, but the results are not strictly comparable to the results of 

 experiments of individuals, because the individual breeder discards all apparently 

 inferior specimens, while at this station close selection of breeders was not fol- 

 lowed by close selection of pullets for layers, except in one or two instances 

 for special observation. 



