No. 576] VARIATION IN DROSOPHILA 



747 



that this point is so low that the flies are poorly nourished 

 for lack of water, though they can survive an even 

 greater water reduction. 



It is, perhaps, needless to say that an effort has been 

 made after these experiments to keep the moisture con- 

 tent high and fairly uniform in cases where other envi- 

 ronments were being tested. 



C. The Effects of Covering with Paraffine the Mouth 

 of the Bottle in which the Flies are Developing 

 On observing that the proportion of Beaded to Normal 

 offspring was lowered as a hatch continued, it seemed 

 possible that this might be due to one or to both of two 

 causes: (1) The diminishing water content. This matter 

 has already been considered. (2) To a changing carbon- 

 dioxide content. When a brood is first counted the cotton 

 plug that has been for several days in the mouth of the 

 bottle is removed, and in removing the flies the air within 

 the bottle is very apt to be much changed. With this pos- 

 sibility in mind a number of bottles were supplied with 

 food and flies, and after ten days (when the larvae were 

 beginning to pupate) the parent flies were removed, a 

 little new food put into the bottle and a paraffine cap 

 melted over the cotton so that the bottles were tightly 



table xxxn 



Counts of Seven Broods which Hatched During Two Periods, the First 

 of Which was Spent in a Bottle Sealed with Paraffine, 



Cloth. Bottle No. 7 was not Sealed with 



