An Alteration of the Sex-ratio. 
83 
The reciprocal cross, namely, short proportionate males and 
rudimentary winged females gave, in the first generation, long- 
winged males and females. These inbred produced in the second 
generation : 
Long 9 Long d 1 Propt 9 Propt a* Rudim 9 Rudim cf 
265 80 36 90 0 14 
Again, the sex disproportion is observed for the long- winged 
flies, while the reverse order holds now for the proportionate wings. 
The F 2 flies from both of the above sets have been bred again in 
all possible combinations within the same set, and the dispro- 
portion of males to females was found to be transmitted to the 
next generation, although not in the same ratios. Some of the 
proportionate winged males (F 2 ) were also bred to wild flies, and 
gave 301 females and ill males. 
The most probable explanation of these results would seem to be 
either in the partial degeneration of the male producing sperma- 
tozoa as a result of crossing with the race with rudimentary wings 
or in some quantitative change in the sex determining factor. 
The effects are transmitted also to a third generation. Whether 
they are permanent or not remains to be tested. 
