6 MASS. EXPERIMENT STATION BULLETIN No. 289 



gene M. This being the case, no consistent lowering of variabihty in succeeding 

 generations might be anticipated as long as controllable environmental in- 

 fluences remain constant. 



Table 1 shows that both lines A and C were highly variable in pause duration 

 in the first generation. The number of pause birds in line C is too small to give 

 a value for this line. 



Line A had a consistent decrease in variability for length of pause in genera- 

 tions two, three and four. Line B did not decrease in variability in successive 

 generations and showed greater variability than the checks in the fourth genera- 

 tion. A sufficient number of birds with pause in line C occur only in the first 

 two generations. There is no significant change of variability in these two gen- 

 erations. 



The records on variability in pause duration in line C suggest that there may 

 be minor hereditary factors modifying pause duration. More data are necessary 

 before definite conclusions may be drawn. 



[ Days Broody 



The sum of the non-productive days associated with broody periods during 

 the pullet laying year may be used as a measure of degree of broodiness. In this 

 report only birds exhibiting broodiness in the first laying year are considered. 

 Goodale, Sanborn and White (1920) off'er a two-factor hypothesis to explain the 

 presence or absence of the broody instinct, but the causes of variation in degree 

 of broodiness have not been reported. 



Table 1 shows a large coefficient of variation for degree of broodiness in the 

 first generation for lines A and C. Line B included so few broody birds in the 

 first and second generations that the variation could not be determined. 



In general, there appears to be a decline in variability in degree of broodiness 

 in two of the lines. Since breeding females were selected in each line for freedom 

 from broodiness, it seems probable also that there may be heritable modifiers 

 affecting degree of broodiness. Further data are being secured on this particular 

 point. 



Persistency of Laying 



Persistency is a character which, like age at sexual maturity, has a relatively 

 low variability. Generation one in lines A and B had very little variability. 

 Line C, however, gave a coefficient of variation in the first generation amounting 

 to 15.82 per cent, while the normal for the flock is 14.41 per cent. 



In succeeding generations line A continued to increase in variability, strongly 

 suggesting that environmental influences were operating because selection of 

 breeders was based upon uniformity in the familj-. 



Line B changed but little in variability of persistency in the last three gener- 

 ations, but there was a marked increase from the first to succeeding generations. 



Line C began with high variability and there was a decrease with each gen- 

 eration to the very low constants of 3.98 and 4.58 per cent, respectively, in 

 generations three and fcjur. The probable explanation of this improved uniform- 

 ity lies in the fact that very high production is not possible without high per- 

 si.4ency, and in the selection of breeders on high annual egg records, the line 

 approached genetic purity for persistency. 



