AN ANALYSIS OF THE EFFECT OF SELECTION. 35 
There is no evidence for contamination. With the one exception 
noted above, all the variations are in the direction for which the 
Dichets were being selected. On the multiple-factor view one would 
expect this result, since it would seem likely that any modifier would 
usually affect Dichets and not-Dichets in the same direction. The 
one exception, a 7 from 1190 of the crossbred plus series, is scarcely 
surprising on this hypothesis, in view of the facts that unselected not- 
Dichet races may produce sevens (see table 2), and that 1190 was prob- 
ably not homozygous for a large number of plus modifiers. Since 
this individual was not tested, it would perhaps be futile to argue the 
ease further. 
TABLE 24. 
Bristle Nos. 
Culture. Series. Genera- 
tion 
6 7 8 9 | 10 
1277 SOA pHs se swe. 7 57 
1285 Crossbred plus. ... . a 35 i! 
1357 Crossbred plus. .... 8 et) Pome frees 4 
1810 S64epluge. Sie oes was 10 ae ay [ood 
1811 1O02 plus ysc.< ttt 7 16 
1268 Crossbred minus... . 6 seul vito ale 
1273 Crossbred minus... . uf anal lice ee: 
1878 Crossbred minus... . 10 on, Ih eee ALD: 
1879 Crossbred minus... . 10 SEL Ga | caw) 
1881 Crossbred minus... . 10 sere [teetee eae, 
1882 Crossbred minus... . 10 on 1} 31 
1892 Crossbred minus... . 10 LPN sats, Pk O 
1986 1331 (speck) minus. 5 Ai 8| | onl (4 
1996 1331 (speck) minus. 5 A ese nek 
2015 Crossbred minus... . 1l Set ida || tote) 
ae | ee 
It may be noted here that in the Star Dichzt stock referred to above 
(p. 31) there were found to be numerous not-Dichets with 9 and 10 
bristles. Unfortunately, no counts were made on these flies, and the 
nature of the extra bristles was not determined. The stock has since 
been ‘‘purified,” to rid it of certain other mutations, and the extra- 
bristled flies, formerly plentiful, have now disappeared. This stock, 
as stated above, was continued by mating together (Star) Dichet 
flies, without regard to bristle number. These extra-bristled not- 
Dichets therefore furnish evidence of the same type as that just dis- 
cussed, except that the race was not selected for bristle number. 
