No. 580] INFERTILITY OF DROSOPHILA 241 



days after hatching, and then each was mated to a rudi- 

 mentary winged male that had similarly been isolated. 

 In about twenty minutes, on an average, mating occurred 

 in an entirely normal manner. The females that had 

 mated were kept each in a separate bottle and given the 

 best food. Kxamination showed that hardly one of the 

 females had laid eggs; but in the rare cases where a 

 few eggs were observed, some flies developed. In the first 

 experiment seventeen females were seen to mate, and were 

 then kept alone, or with their mates. One female pro- 

 duced one rudimentary winged son; another gave one 

 rudimentary winged daughter and one such son. These 

 three flies were the total output of seventeen females. 



The next point was to determine whether these seven- 

 teen females were infertile only with their own kind of 

 males. Each was again paired, this time to a male with 

 bar eyes. The character bar eye is dominant. If sperm 

 of these males should be successful, the female offspring 

 from this cross would have bar eyes, and could he distin- 

 guished from anv others that might come from the first 

 •mating. One female gave one bar daughter; another fe- 

 male also had one bar daughter. These results show that 

 the rudimentary females were no more successful with bar 

 males than with their own kind. 



In a second experiment eleven rudimentary-winged fe- 

 males were tested with rudimentary males. One gave one 

 rudimentary daughter and one rudimentary son, but also 

 two long-winged daughters. Since I had not taken the 

 same care here (using twenty-four-hour flies) as before to 

 be certain that the females were virgin, these two long- 

 winged daughters are supposedly due to fertilization be- 

 fore isolation, since long-winged males were hatching at 

 the time in the parent stock. I tested this supposition by 

 mating the two females to a rudimentary male, and ob- 

 tained the following kinds of offspring: 



