NON-BROODY AND INTENSE BROODY LINES 3 



at first egg throughout the period than did the broody line. The diflferences in mean 

 age at sexual maturity for the two lines are not significant, however, according to 

 Fisher's (1930, p. 106) method for measuring the differences in means. 



The coefficient of variation decreased slightly in both lines as the experiment 

 progressed. For the entire period the variation amounted to 12.3 per cent in the 

 non-broody line and 11.12 per cent in the broody line. These are insignificant 

 differences and the variability in both lines was probably due largely to environ- 

 mental factors as Hays (1932) points out. 



Table 1. Mean Age at First Egg in Non-Broody and Broody Lines. 



2. Winter Clutch Size 



Mean winter clutch size has been shown to be an inherited trait and is a satis- 

 factory measure of intensity. Intensity has also been shown to be one of the most 

 variable characters in the flock studied (Hays, 1932, loc. cit.). Goodale et al. 

 (1920, loc. cit.) reported lower initial egg pro'iuction in a flock of broody birds 

 where the degree of broodiness was low (1.90 periods) than in a flock of broody 

 birds with a high degree of broodiness (5.39 periods). In the Massachusetts 

 Agricultural Experiment Station flock from 1916 to 1925, a total of 1188 birds 

 showing broodiness had a mean winter clutch size of 2.96 while 2679 individuals 

 not showing broodiness in their pullet year had a mean winter clutch size of 2.50. 

 These facts indicate an association between broodiness and winter intensity. 

 The correlation between degree of broodiness and winter intensity amounts to 

 +.2548+.0186 according to Hays and Sanborn (1932 a). 



Table 2 presents the mean winter clutch size by years in the non-broody and 

 broody lines, together with their coefficients of variation and the grand means of 

 the two lines. 



There was a significant increase in intensity in both lines throughout the period. 

 There was not, however, a change of any consequence in the variability as meas- 

 ured by the coefficient of variation. The high variability in winter clutch size may 

 probably be due largely to its complex mode of inheritance, as the writer has 

 pointetl out elsewhere. 



Contrary to earlier observations, mean clutch size was slightly greater in the 

 non-broody line. The flocks hatched in 1924 and 1925 were the only exceptions. 

 The differences in clutch size for the two lines were checked by Fisher's method, 

 and it was found that the two lines are not significantly different in intensity. 



The fact that the two lines showed about the same clutch size throughout the 



