THE AMERICAN NATURALIST [Vol. XLIX 



The Wyandottes alone give a distinctly higher mean, 

 and this the writer has also found to be true of Irish egg 

 records. The Barred Eocks in the competition this year 

 give a somewhat abnormally low winter mean. Irish 

 records give a winter mean for 48 Barred Rocks, in flocks 

 of 6 each, of 36.54 eggs per bird which is more nearly 

 normal. 



Ill 



Let us now turn to the question of the interpretation of 

 the data set forth in the preceding- section. Broadly 

 speaking what the facts gleaned from this seventeen-year 

 experiment show is that mass selection for egg produc- 

 tion was not effective, while selection which was based 

 upon the performance of the progeny was extremely and 

 quickly effective. What is the explanation of the differ- 

 ence? The facts are purely objective realities, about 

 which dispute or question is idle. They are real and 

 obvious matters. Regarding the interpretation of such 

 facts as these there have been, and no doubt will continue 

 to be for some time to come, differences of opinion 

 amongst biologists. Under these circumstances, the 

 writer will, then, with all respect and consideration for 

 the differing opinions of others endeavor to make clear 

 the view of the meaning of these results which he has 

 come to hold. 



In the first place we may definitely put aside any inter- 

 pretation which bases its explanation of the results on 

 environmental action. In an earlier paper the writer 7 

 has shown in detail the impossibility of this explanation 

 for the results during the period of mass selection (the 

 descending limb of the curve). The totality of the results 

 here presented make it still more apparent that such an 

 explanation can have no place here. We should have to 

 suppose that the environmental influences were adverse 

 throughout the period of mass selection, but suddenly 

 became favorable when the method of breeding was 

 changed, and have ameliorated at an ever increasing rate 



