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 
case further. 
TaBLe 24, 
Bristle Nos. 
‘ Genera- 
Culture. Series. tion. 
6!|7]8]9 110 
1277 864 plus........... 7 57 
1285 Crossbred plus. ..., 7 .. | ee | 85 1 
1357 Crossbred plus..... 8 par! | nd 8d} 4 
1810 864 plus........... 10 se | -ws | EL | as 
1811 1002 plus.......... 7 16 
1268 Crossbred minus... . 6 wae | cae dS 
1273 Crossbred minus... . 7 ice |) eee 1 38) 
1878 Crossbred minus... . 10 we | ee 16 
1879 Crossbred minus... . 10 ss | «a | 20 
1881 Crossbred minus... . 10 ae | ae | 28 
1882 Crossbred minus... . 10 ee 1 | 31 
1892 Crossbred minus... . 10 ee | se. |) AO, 
1986 1331 (speck) minus. 5 sees) ust |S 
1996 1331 (speck) minus. 5 Li aw | & 
2015 Crossbred minus... . 11 -. | oe | 88 
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. 
