12 AN ANALYSIS OF THE EFFECT OF SELECTION. 
The female was from culture 916, which contained a sepia, spineless, 
/ 
This female was the 
offspring of a Dichet from stock and of a fly from culture 869 (q. v. 
below, in the pedigrees of 900 and crossbred minus lines). No bristle 
counts are available from culture 1002, except those of the pair (6X6) 
selected to produce culture 1072, the F, of this line. 
After this line had been inbred and selected for 11 generations, a 
pair of 7-bristled flies were taken from 2389, and their descendants were 
bred in mass cultures, unselected Dichets being mated together, for 
about 2 generations. The line was then re-established by selecting 
pairs from this stock and was inbred for 8 generations more. 
The data and curves for this line are given in table 9 and figure 4. 
kidney, sooty, rough male, and a female 
) any ras Tike | 5 Gi tars ao pO LT I? (Oe Spree 0 enO ee 
Fic. 4.—Means and standard deviations for 1002 inbred plus line. 
Here selection was perhaps effective for a few generations. Ref- 
erence to the Appendix will indicate that this effectiveness was prob- 
ably due in large part to the gradual elimination of the descendants 
of one of the F, pairs (1158), which were on the average of slightly 
lower grade than those of the other F, pair (1150). It is to be observed 
that both of the apparently successful reversed-selection series were 
made with descendants of the former branch of the family. 
The eighth to eleventh generations of this line and the contempo- 
rary eleventh to fourteenth of the 864 line gave very similar results 
as to the means and standard deviations. We shall see below (p. 19) 
reason for believing that the two lines were of very similar constitution 
at this period. The gradual rise of the means and fall of the standard 
deviations is probably of environmental rather than genetic origin. 
