No. 596] EGG PRODUCTION AND SELECTION 485 



ally a homozygous race of high producers should result 

 from the continued breeding of the sons of high producers 

 to high producers. 



Since Pearl has repeatedly stated that his results apply 

 to annual production as well as winter production, it 

 might be supposed that selection during the Gowell 

 regime should have been effective. Pearl has interpreted 

 the results as due to G-owell's failure to use the progeny 

 test. Two other possibilities, however, suggest them- 

 selves. Under the Gowell regime the males came from 

 200-egg hens, but all hens laying over 150 eggs were used 

 as breeders. Possibly the latter value is too low. The an- 

 nual production corresponding to the 30-egg division- 

 point for winter production has not been stated, as far as 

 I know, but since the mean annual value of a flock of high 

 producers is stated by Pearl to be about 166 eggs, 150 

 eggs would seem sufficiently high to exclude mediocre 

 producers. The possibility, then, that this value is too 

 low may be disregarded. 



The second possibility relates to the number of males 

 used. In an actual experiment only a relatively few 

 males are used each year. The scale at which the Growell 

 experiments were carried on was hardly sufficient to equal 

 more than one or two years ' work on the scale that would 

 be required to get the males in something like the propor- 

 tions expected, and hence little or no change in egg produc- 

 tion could be expected in the period during which the mass 

 selection experiments were carried on. 



While, theoretically, mass selection should be effective 

 under the conditions stated, it would require large num- 

 bers in order to be uniformly successful. The progeny 

 test, on the other hand, produces results quickly and defi- 

 nitely. 



