1 66 



H. E. EWING. 



If we now plot these results by using a scheme similar to that 

 employed to illustrate Galton's law of regression we shall have 

 the following graphical representation (Fig. i) of the regression 

 as found up to the fifteenth generation in this pure line of plant 

 lice. 



Here the heavy line represents the mean-of-the-strain base 

 line, and is placed at 1.80. The lighter parallel lines above and 



v, 



o 3 



o o 



2.15 



2.10 



2.05 



2.00 



1.95 



1.90 



1.75 



1.70 



1.65 



1.60 



1.55 



1.50 



FIG. i. Diagram showing legression within a pure line of Aphis avetKZ Fab. 

 The heavy base line at 1.80 represents the position of the mean of the line, or strain. 

 The small circles represent the positions of the parents according to the index of 

 their third and fourth antennal segments; the small number placed by each circle 

 shows the number of parents with the antennal index indicated by the circle; the 

 arrow-heads represent the positions of the mean of the fraternities obtained from 

 these various parents. The arrows show the amount of regression. 



below this base line each represent an increase or decrease in the 

 index ratio for the third and fourth antennal segments of five 

 one-hundredths. Similarly one of the vertical lines represents 

 the mean-of-the-strain base line, and is marked 1.80; and on 



