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THE AMERICAN NATURALIST [Vol. XLIX 



led to suggest the existence of a second fecundity factor 

 which was not sex-linked. He assumes that this second 

 factor, like the first, is a Mendelizing factor, but without 

 any sufficient published evidence for either conclusion. 

 To this I called Dr. Pearl's attention soon after the pub- 

 lication of his paper and suggested that if possible the 

 data be put on record in such form as to allow of testing 

 this and other hypotheses concerning the genetic factors 

 concerned. For one-factor, two-factor, ten-factor and 

 infinity-factor Mendelian hypotheses would call for very 

 different ratios and distributions of fecundity among the 

 offspring. He replied that the data could not be so given 

 without an amount of work which he considered unprofit- 

 able. We are left, therefore, with only this information 

 concerning Pearl's pullets, whether each one laid more or 

 less than 30 eggs in its first winter. If we knew ivliat 

 number each one laid, we might form an intelligent 

 opinion as to whether Mendelian factors are involved, 

 and if so how many, in the same way that we can test 

 Mendel's conclusions concerning the independent inheri- 

 tance of yellow cotyledon color and round seed form in 

 peas because he tells us the actual proportions of the 

 various sorts of peas reported for each plant. Being 

 denied such information by Pearl, it is useless to dis- 

 cuss his two-factor hypothesis, for its correctness can be 

 neither proved nor disproved. 



Leaving aside the question whether any inherited factor 

 has changed as a result of selection in Pearl's experi- 

 ments, which we have no means of investigating, we can 

 consider only the question whether the gross winter egg 

 production has changed. As a basis for judgment he 

 gives us the averages of winter egg production year by 

 year for sixteen years. Pearl's graphic presentation of 

 the data (assuming that the considerable fluctuation re- 

 corded is not significant) indicates a steady decline of 

 the general flock average during the first nine years of 

 the experiment and a steady recovery and further in- 

 crease during the next seven years, which he ascribes to 



