BRISTLE INHERITANCE IN DROSOPHILA 123 



grades of the parents. The wide differences in the parents in 

 different generations is due to the fact that only one pair of 

 parents is included in each mean. The same story of inde- 

 pendence is told by these curves as by those including total gen- 

 erations (Fig. 3). As the curves demonstrate this point very 

 clearly, it will not be necessary to cite them in detail. 



Considering again the comparison between the means of 

 single families and of the total generations, one finds further 

 evidence of this independence of the grades of the parents and 

 their offspring. Single pairs of parents produce offspring whose 

 averages are close to the averages of offspring from parents 

 of various grades in the same generation. The distribution of 

 the parents selected in the whole race, given in table 1, should 

 be studied in comparison with the parents in the single line. 



So, besides finding that in successive generations high parental 

 averages are not accompanied by high filial averages, it is 

 found that in the same generation a single pair of parents pro- 

 duces offspring with an average similar to that of the offspring 

 from parents of different grades. The significance of this point 

 will be discussed in a later section. 



Conclusions from the high selected race 



From the above presentation of the facts concerning the h^'gh 

 selected race, the following conclusions are drawn: Through the 

 breeding of flies with the highest numbers of extra bristles, the 

 means of the race were raised for a series of generations; after 

 this no evidence was found of any further influence of selection 

 upon the means of the race. Since the lower limit of bristle 

 variation remains practically fixed, and the variations in the 

 upper limit are slight with no relation to the selected parents, 

 the changes in the variation of the race, as measured by the 

 standard deviations, have no genetic significance; the standard 

 deviations rise and fall with the means. The initial success 

 and subsequent failure of selection, as indicated by the means, 

 is also shown by the relationship between the grades of the 

 parents and their offspring. In the early generations an in- 



