744 



THE AMERICAN NATURALIST [Vol. XL VIII 



generation, one of which (B'lb'L) should have a consider- 

 ably higher percentage of Beaded offspring than the 

 other (B'Lb'L). If it is possible, however, that B' should 

 be dominant in the heterozygous condition and in the 

 absence of 1, then it should also be possible theoretically 

 to produce ah F 1 generation every individual of which 

 should have Beaded wings, while those with 1 as well as 

 B' (constituting one half the progeny) should have a 

 more extreme form of Beading. In practice it is not 

 usual even under the best of conditions to get more than 

 40 per cent, of Beaded-winged flies, while, as has been 

 seen, the average amount is about 25 per cent. 



B. The Effect of Belative Moisture 

 Table XXX and Charts 5 and 6 present the data for 



TABLE XXX 



Total 281 | 17.8 252 



Total Dry 533 | % Bd, 20 



Counts not made every day. 

 Bottle No. 2 was very dry and 



tal Wet, 657 | % Bd. 

 <ry small during time 0: 



this test. The parents were put into bottles of similar 

 size with plenty of food. In three of these bottles the 

 food was very wet and from time to time juice was added 

 in sufficient amount to keep the food saturated. The 

 other two bottles were made relatively dry by putting a 



