THE INHERITANCE OF FECUNDITY 369 



The data now in hand, however, indicate clearly, it seems to me, that 

 there must be some other factor than the anatomical one involved in 

 the existence of different degrees of actual fecundity in the domestic 

 fowl. It evidently is the case that when one bird has a winter record of 

 twice what another bird has it is not because the first has twice as many 

 oocytes in the ovary. On the contrary, it appears that all birds have an 

 anatomical endowment entirely sufficient for a very high degree of 

 fecundity, and in point of fact quite equal to that possessed by birds 

 which actually accomplish a high degree of fecundity. Whether or not 

 such high fecundity is actually realized evidently depends then upon 

 the influence of additional factors beyond the anatomical basis. As has 

 already been indicated in the preceding section, it is reasonable to sup- 

 pose that these factors are physiological in nature. 



The Mechanism of the Inheritance of Fecundity as Measured 



by Winter Egg Production 



A study of numerous statistics shows that hens fall into three well 

 defined classes in respect to winter production. These classes include 

 (a) those birds which lay no eggs whatever in the winter period (up to 

 March of the laying year) ; (b) those that lay but have a production 

 during the period of something under about 30 eggs; and finally (c) 

 those whose production exceeds 30 eggs in the winter period. The 

 division point between the two latter classes is not sharply defined in 

 every case, but it is plainly at about 30 eggs in the case of the breeds 

 and strains used in these experiments. Since in the analysis some fixed 

 point must be taken for this boundary, a production of 30 has been 

 chosen for this purpose and will be used throughout. This is an 

 arbitrary choice only in the sense that it is a convenient round number 

 lying very near where the biological division point falls, at least in the 

 strains of domestic fowls used in these experiments. The analysis could 

 doubtless be carried through nearly or quite as well by taking the 

 division point at a production of 29 or 31, but 30 is a more convenient 

 figure. 



In making the division of winter egg production into three groups 

 it must be remembered that this is a character subject to purely somatic 

 fluctuations and environmental influence. Allowance for these factors 

 must be made in interpreting and classifying results. 



Turning now to the symbolic analysis, we have to deal with three 

 factors. These are : 



1. An anatomical factor. This is basic. It consists in the presence 

 of a normal ovary, the primary organ of the female sex. In the genetic 

 analysis a separate letter need not be used for the designation of this 

 factor, but instead it will be understood to be included in the letter 

 denoting the presence of the female sex or its determiner. That is, F 



