INHERITANCE OF FECUNDITY 185 



then a year from the time they were hatched to mate each of 

 them with a number of females, and rear to maturity and trap- 

 nest for a year a number (3 to 10 for example) of pullets grown 

 from each of the matings of each of the cockerels. Then from the 

 trap-nest records of these pullets it would be possible to conclude 

 as to what was their grandfather's gametic constitution respect- 

 ing fecundity. It is evident that relatively enormous experi- 

 mental resources would be required to carry this out on even a 

 very modest scale. Further the end would scarcely justify the 

 means from either a practical or theoretical standpoint, since the 

 theoretically expected gametic types of males can be readily 

 obtained and their pedigrees will enable one to analyze fully the 

 gametic factors and reactions involved in their production. 



Throughout the paper, then, conclusions will be drawn as to 

 gametic constitution of parents from an analysis of the female 

 progeny only. 



The reason why the other three classes of males (5, 6 and 9) 

 are not represented in the matings is to be found in the method of 

 selective breeding practised during the time in which the statis- 

 tics here analyzed were collected. The chance of using in a 

 breeding pen males of any of these types was small when the 

 selection was carried on in the way that it was. This point will 

 be more fully discussed farther on in the paper. 



Matings of Barred Plymouth Rock males of class^'^ 7 



Males of class 7, having a gametic constitution fhLi . fliL^, 

 were used more often than any other sort in the pure Barred Rock 

 matings. They are homozygous with reference to the absence of 

 the first production factor Li, and the presence of the second or 

 excess production factor L^. A reference to table 9 shows that 

 there should be no zero winter producers among their progeny. 

 The proportions of high and poor layers in the progeny depend 

 upon the nature of the female with which the male is bred. For 

 convenience the matings of each individual male will be discussed 

 separately. 



^^ The 'class' numbers throughout refer to the arbitrary designations given in 

 tables 5 to 10 inclusive. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 13, NO. 2 



