302 MAINE AGRICUI^TURAI, EXPERIMENT STATION. I912. 



The M echanism of the Inheritance of Fecundity 



With so much by way of introduction we may proceed to the 

 subject in hand, namely a detailed account of the manner in 

 which fecundity is inherited. In this account for reasons which 

 have been stated above, and in earlier papers on this subject, 

 attention will be confined to winter tgg production. 



A. Observed types of 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 

 (fl) those birds which lay no eggs whatever in the winter period 

 (up to March i of the laying year) ; (b) those tliat 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 classes 

 (b) and (c) is not sharply defined in every case, but it is plainly 

 (as will appear later) at about 30 eggs. 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 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. Al- 

 lowance for these factors must be made in interpreting and clas-. 

 sifying results. In particular the following points must be kept 

 in mind throughout. 



( I ) A zero winter production ma)?- be due to genetic causes 

 or to purely somatic (physiological) ones, and there is nothing 

 in a single record of this sort, taken by itself, to indicate to 

 which category it belongs. A bird may carry the factor or fac- 

 tors for winter production, yet owing to purely physiological 

 causes, such as a disturbance of metabolism, or of the ovary in 

 respect to its physiology, or to disease, patent or obscure, it may 

 never actually lay during the winter period. Usually it will be 

 possible to tell from other considerations than the record itself, 

 whether a ffiven zero record is 'somatic' or 'genetic' 



