THE BAR EYE MUTANT OF DROSOPHILA 529 



SUMMARY 



1. Three successive selections for high number of facets in 

 the 'bar eye' race of Drosophila increased the mean number of 

 facets from 98.0 to 139.5. 



2. Three smiilar selections for low number decreased the mean 

 from 98.0 to 83.7. 



3. The lowest individual, 89.0, in the 'high' lines after three 

 selections is higher than the mean of the 'low' strains, 83.7, 

 and the highest individual of the 'low' lines, 137.0, is lower than 

 the mean of the 'high' strains, 139.5. 



4. Significant progress was noted in each of the three selections 

 in both 'high' and 'low' lines. 



5. There are some differences in variability in the different 

 generations but no significant change is proven. 



6. Regression toward the mean of the general unselected popu- 

 lation decreases with successive selections. 



7. Regression toward the mean of the parental populations 

 increases with successive selections. This increase makes it im- 

 probable that 'bar eye' stock can be raised to the original level 

 by continued selection. 



8. It is apparent from these data that individuals in anj^ 

 generation differ as regards germinal constitution. 



9. If this difference in gemiinal constitution is solely in the 

 unit factor concerned in 'barring,' variability in this unit factor 

 must be assumed. 



10. It is however more probable that there are other factors 

 concerned in facet number. In that case the selection effect 

 may be due either to variability of single unit factors or to 

 presence of original differences in factorial composition. That 

 it is due in part at least to the latter is indicated by the increase 

 in regression toward the mean of the parental generation with 

 successive selections. 



