320 CHARLES ZELENY 



Among the F2 males of both the reciprocal crosses there are 

 1235 males within the range of ultra-bar, three of which come 

 just above this range having respectively 42, 42, and 44 facets, 

 and three w^hich are considerably higher having 51, 60, and 88 

 facets. Of the first three, one of the 42-facet males was tested 

 by crossing to full and shown by its dominance to be an ultra- 

 bar. It is probable from this and other evidence that this slight 

 extension of the range of ultra-bar is due to accessory factors 

 introduced by the full stock. The other three males are of a 

 different character. The 60-facet male died without a test. The 

 51- and 88-facet males when mated to full gave heterozygotes 

 which were higher than those of ultra-bar X full, but on the 

 other hand lower than those of bar X full. These heterozygotes 

 agree in character with those of the mutant in the pure ultra- 

 bar stock which was described above on p. 308. The high ex- 

 ceptional males cannot therefore be considered as bar males 

 produced by the separation of the U factor from B' by crossing 

 over. 



Among the F2 females of the cross between full females aiid 

 ultra-bar males there are 553 with the characteristics of typical 

 low heterozygotes of the Fi generation and four with higher facet 

 numbers. One of the latter has 154 facets and is considerably 

 below the range of heterozygotes between full and bar as given 

 in table 9. The other three females come within this range. The 

 one which was tested by crossing to full, however, gave only ultra- 

 bar and full males instead of bar and full as its facet number 

 seemed to indicate that it should give. It is therefore an instance 

 of failure of the ultra-bar factor to doniinate full' in the ordinary 

 manner. As in the case of the males, crossing over cannot be 

 given as an explanation of these exceptional females, though it 

 is unfortunate that some of them died before a test could be 

 made. However, even if all the exceptional untested males and 

 females were classed as bars produced by crossing over of an 

 assumed accessory ultra-bar factor, the locus of this factor would 

 have to be placed very close to bar. Absolute proof is impossible 

 because it can always be held that the new gene is so close to 

 the old one that crossing over cannot certainly be expected in any 



