No. 552] INHERITANCE OF FECUNDITY 



703 



true for Barred Plymouth Rocks, Cornish Indian Games, 

 and all cross-bred combinations of these breeds in F t 

 and F 2 . 8 



The above statements are of definite facts, supported 

 by a mass of evidence. Their truth is objective and de- 

 pends in no way upon any theory of inheritance whatso- 

 ever. 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 a simple Men- 

 delian hypothesis respecting the inheritance of fecund- 

 ity in the fowl. This hypothesis involves the following 

 points, each of which is supported by direct and perti- 

 nent 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 

 anatomical) 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 L x ) 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 L 2 ) 

 when present in a zygote together with F and L t , leads to 

 a high degree of fecundity (winter record over 30 eggs). 



8 And F 3 . It was thought wise to delay publication any longer in order 

 to include the data for F 3 . It may be said, however, that they are in full 



