AN ANALYSIS OF THE EFFECT OF SELECTION. 9 
longer. Moreover, there is a chance of combining more of the desired 
modifiers in the same individual when crossing is done, so that this 
method might produce more extreme results than the inbreeding 
method. However, each time a cross is made some of what has been 
gained may be hidden by dominants in the other stock; therefore 
progress might sometimes be slower. 
Accordingly, in these experiments parallel series have been carried 
on. In one set selection has been accompanied by continuous brother- 
sister matings; in the other, frequent crosses have been made between 
individuals more or less closely related. 'The same method has been 
followed in both the plus and the minus selected lines. The four 
series will be considered in order: (1) inbred plus; (2) crossbred plus; 
(3) inbred minus; (4) crossbred minus. 
INBRED PLUS SERIES. 
Two main lines of this series have been carried on. A few cultures 
have been made from other sources, but none of these are sufficiently 
extensive so that we need follow their histories here. 
864 Line. 
Culture 864, from which this line arose, was produced by a female 
{/ 
To 
p’s.ke'r, 
the sepia, spineless, kidney, sooty, rough stock; 847 was the result of 
mating four peach, spineless, kidney, sooty, rough males from stock to a 
/ 
of the constitution from culture 847, and two males from 
. . r . 
female of the constitution mee F This female ane 
3 Dorso- A 
was descended from the Dichet, ebony, peach, centrals, | Oflspring. 
spineless, kidney, sooty, rough, and other stocks. 
Her pedigree is not now traceable in detail. 
At the time culture 864 was counted, the scu- 
tellar bristles were not observed. The dorso- 
central bristles were recorded on 30 flies, as 
shown in table 7. 
The 3 (almost certainly a 7, according to the system later adopted), 
a male, was mated to a 2 (6) female to produce culture 893. For the 
details of the remainder of the pedigree see Appendix. 
In the accompanying tables and curves the offspring of culture 
893, above, are considered F;. Table 8 gives the data for this line 
summarized by generations. In this and the following tables, n is 
the number of individuals in the generation, M is the mean bristle- 
number of the generation, ¢ is the standard deviation, r is the parent- 
offspring correlation, and is recorded in the generation to which the 
offspring belong. Diff. M. is the mean bristle-number of the off- 
spring minus the mean bristle-number of their parents, weighted 
12 
8 
9 
1 
30 
