INFLUENCE OF ENVIRONMENT ON EXPECTED CLASSES. 217 



BACK-CROSS EN MASSE. 



Since rudimentary females are sterile with rudimentary males 

 the stock of rudimentary wings is maintained by breeding rudi- 

 mentary males to heterozygous, long-winged females. 



THE VIABILITY OF THE STRAP-WING RACE. 



The peculiarities of structure and inheritance of this mutant will 

 be described in another place. The stock contained "beading" 

 and overlaps in appearance the vestigial wing. The " beaded ' 

 flies that appear in F 2 are classified with "normal" or long wing, 

 those with vestigial-like wings are counted in with "strap." 

 Strap bred to wild stock gives sons and daughters with long wings. 

 These bred en masse during August gave the following results 

 in eleven cultures. About six to ten FI flies were used in each 

 culture in a medium sized bottle, and the food conditions were 

 made as favorable as possible. 



Normal. 



Strap. 



Ratio. 



The ratios range from I : 3.7, to I : 20.1. In order to compare 

 these results with matings in pairs, fifteen pairs were mated. 

 After ten days the parents were placed in a new bottle with 

 fresh food and in some cases they were carried to a third bottle. 

 The results are given in the next table (III.). 



The results from pairs approximate more nearly to expectation 

 (i : 3); the totals give a ratio of I : 3.57. The individual lots 



