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THE AMERICAN NATURALIST [Vol. XLV 



breeding season only one pullet worth putting into the 

 laying house. This pullet (F163) made a winter record of 

 but 11 eggs. F163 was bred in 1910, but produced only 

 one daughter worth saving. This daughter, G429, has 

 made a winter record of 18 eggs. It would be hard to 

 get clearer evidence than that afforded by this breeding 

 history that D352 belonged to a low fecundity genotype, 

 in spite of her individual high laying record. 



The Effect of the Selection of Fecundity Genotypes 

 Let us now consider the bearing of the results so far 

 set forth on the problem of selection. Taking first the 

 question of the effect of selection for fecundity within 

 a population it is plain that if different degrees of 

 fecundity have a genotypic basis, as the facts above 

 presented and a considerable mass of data of a sim- 

 ilar kind, which owing to lack of space can not be 

 given here would appear to indicate, then the results fol- 

 lowing selection will depend entirely upon the genotypic 

 constitution of the population. If high fecundity geno- 

 types are present they can be isolated by selection. If 

 they are not present selection of high laying hens will 

 not change the average production of the flock. 



The aim of the selection experiments since 1907 has 

 been to discover and propagate separately genotypes of 

 high fecundity and genotypes of low fecundity, all the 

 birds being taken from the same general flock. The re- 

 sults of this work are shown in the following table and 

 in Fig. 5. This table is to be regarded as a continuation 

 of that given on p. 327, supra, which shows the results of 

 mass selection for high fecundity in the same stock. 



Effect of Selection for Fecundity within the Population 

 1907-08. Mean winter production of general population 15-92 



