COUPLING 97 



are demonstrated, together with three pairs of untied 

 factors operating alongside them ; and the possible 

 constitutions in a population of hens in which all three 

 sets of factors are operating are : 



At this stage the question might be asked : Are these 

 tied and free factors for plainness, gold colouring, and 

 complete barring the same in each case, or are they 

 different factors having similar effects ? If it be 

 answered that they are the same, then further questions 

 are suggested, as : At what stage in ornithic history 

 did they take different courses ? When did the tied 

 factor become tied or the free factor become free ? 

 But although the thoughts raised by these questions 

 are of great interest, their relevance to the matters now 

 in hand is not immediate and they can be little else 

 than interesting speculations. 



But Dr. Raymond Pearl found still another factor 

 coupled with femaleness and, at the same time, made 

 a discovery of great economic importance. From 1898 

 to 1908 the Agricultural Experiment Station at Orono 

 in Maine was engaged in the attempt to improve the 

 laying capacity of its Barred Rock breed of poultry. 

 Relying on the theory that this could be done by breed- 

 ing from the best laying hens and their progeny, the 

 hens were divided in two sections : the good layers 

 in one and the poor layers in the other. Sons of 

 best laying hens only were used in both sections, and 

 pullets hatched in either section were moved from that 



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