IMPROVING EGG PRODUCTION BY BREEDING. 223 



breeding standpoint. The intelligent breeder trap-nesting his 

 flock not over three months in the year, can make practically 

 just as rapid progress in breeding for increased egg production 

 as his neighbor who trap-nests twelve months in the year. 



To return from this digression to the main line of discussion, 

 it will be remembered, then, that in what follows reference will 

 be to zvinter egg production unless the contrary is specifically 

 stated. 



5. It is found to be the case that birds fall into three rather 

 well-defined classes in respect to winter egg production. These 

 include (a) birds with high winter records, (b) birds with low 

 winter records, and (c) birds which do not lay at all in the 

 winter period. The division point between a and b for the 

 Barred Plymouth Rock used in these experiments falls at a 

 production of about thirty eggs. 



The next step is to inquire for each of these classes sepa- 

 rately how egg producing ability is inherited within the class. 

 We may first deal with high production. 



6. High productiveness may be inherited by daughters from 

 their sire, independent of the dam. This is proved by a mass 

 of detailed evidence, presented in the complete paper. This evi- 

 dence consists of the results of mating after mating, in which 

 the same proportions of daughters of high laying ability are 

 produced by the same sire, whether he is mated with dams 

 which are poor layers or with dams which are high layers. 



7. High laying ability is not directly inherited by daughters 

 from their dam. This is proved by a number of distinct and 

 independent lines of evidence, of which the most important are : 

 (a) that continued selection of high producing dams does not 

 alone alter in any way the mean egg production of the daugh- 

 ters. If an alteration does appear in any case following such 

 selection, further analysis shows that some additional element 

 other than the dam's egg record came into account in making 

 the selections of breeders, (b) The proportion of high pro- 

 ducing daughters is the same whether the dam is of high or of 

 low fecundity, provided both are mated to the same male ; 

 (c) the daughters of a high producing dam may be either high 

 layers or poor layers, depending upon their sire; (d) the pro- 

 portion of daughters which are medium or poor layers is the 

 same whether the dam is a high or a poor producer, provided 

 both are mated to the same male. 



