254 RAYMOND PEARL 



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 organ 

 of the female sex. The letter F is used throughout to denote the 

 presence of this factor. 



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

 (denoted by Li) 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 (denoted by Lo) when 

 present in a zygote together with F and Li leads to a high degree 

 of fecundity (winter record over 30 eggs). When Li is absent, 

 however, and Ln 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 La must be present 

 together to cause high fecundity, either of them alone, whether 

 present in one or two 'doses,' causing the same degree of low 

 fecundity. 



5. The second physiological factor Lo behaves as a sex-limited 

 (sex-correlated or sex-linked) character, in gametogenesis, accord- 

 ing to the following rule: the factor Li is never borne in any 

 gamete which also carries F. That is to say, all females which 

 bear L2 are heterozygous with reference to it. Any female may 

 be either homozygous or heterozygous with respect to Lj. Any 

 male may be either homozygous or heteroz}; gous with reference 

 to either Li, Lo or both. 



How well this hypothesis agrees with the facts has been shown 

 in detail in the preceding sections. By way of summary the 

 following table shows the accord between observation and expec- 

 tation for all matings of each general type taken together. For 

 reasons set forth below, the lumped figures do not give an alto- 



