380 Maine: agriculturaIv experiment station. 1912. 



Barred Plymouth Rocks, Cornish Indian Games, and all cross- 

 bred combinations of these breeds in Fi and F2" 



The above statements are of definite facts, supported b)'- a 

 mass of evidence. Their truth is objective and depends in no 

 way upon any theory of inheritance whatsoever. With this 

 clearly in mind we may undertake their interpretation. 



It is believed that these general facts, and the detailed results 

 on which they are based, are completely accounted for and find 

 their correct interpretation in the simple Mendelian hypothesis 

 respecting the inheritance of fecundity in the fowl, which was 

 outlined at the beginning of this paper and has been checked 

 against the detailed data from each mating. This hypothesis 

 involves the following points, each of which is supported by 

 direct and pertinent evidence derived either from physiological 

 and statistical studies of fecundity, or from the detailed data 

 respecting the mode of inheritance of this character. 



It is assumed in this hypothesis that : 



1. There are three distinct and separately inherited factors 

 upon which fecundity in the female fowl depends. 



2. The first of these factors (which may be called the ana- 

 tomical) determines the presence of an ovary, the primary or- 

 gan of the female sex. The letter F is used throughout to de- 

 note the presence of this factor. 



3. There are two physiological factors. The first of these 

 (denoted by 7yi) is the basic physiological factor, which when 

 present alone in a zygote with F brings about a low degree of 

 fecundity (winter record under 30 eggs). This factor is under 

 no limitations in gametogenesis but may be carried in any 

 gamete, regardless of what other factors may be also present. 



4. The second, physiological factor T denoted by Lz) when 

 present in a zygote together with F and I,i leads to a high de- 

 gree of fecundity (winter record over 30 eggs). When £1 is 

 absent, however, and Li is present the zygote exhibits the same 

 general degree of fecundity (under 30) which it would if Li 

 were present alone. These two independent factors Li and Ls 



" And Fa. It has not been thougiht wise to delay publication of this 

 paper any longer in order to include the data for F3. It may be said 

 however that they are in full accord with those which have been obtained 

 from earlier cross-bird generations and the parent forms. 



