448 EDWIN CARLETON MacDOWELL 



From all this it is evident that high-grade grandparents are 

 not more likely to produce high-grade grandchildren than are 

 low-grade grandparents. 



Conclusion 



When the germ plasm of a large number of long inbred flies 

 with the same pedigree and the same environment is tested by- 

 breeding, it has been found that the different bristle grades are 

 not associated with different germ plasm. This final test fully 

 substantiates the conclusions that selection could not make 

 further progress in this race and that the germ plasm was not 

 changing during the time of observation. 



MALES AND FEMALES 



All through these experiments the males and females have 

 been tabulated separately. The means and standard deviations 

 of the females are regularly greater than those of the males. 

 There is a close similarity between the direction of the fluctua- 

 tions of the means of the two sexes (MacDowell, '17, p. 114, 

 fig. 3), but there is a greater difference when the means are 

 higher. This is so true that the graph of the differences be- 

 tween the means of the sexes follows closely the fluctuations of 

 the means themselves. The correlation coefficients for the males 

 are usually lower and less often significant than those of the 

 females. Both sexes show the same general relationships to 

 the parents, yet in individual generations there are differences in 

 significance and even in sign. Such differences, as in generations 

 9, 17, 32, and 35, are clearly exceptions, yet they show the 

 amounts of difference possible between random samples of flies 

 from the same environment and the same parents. 



That linkage is not a probable explanation of this sexual 

 difference has been shown by reciprocal crosses (MacDowell, 

 '15, p. 76, table 9, fig. 4). To make a further test for sex Hnk- 

 age, correlation coefficients have been calculated for sons by 

 their mothers and by their fathers, and for daughters by their 

 mothers and by their fathers. Since most pairs of parents were 



