No. 576] 



VMUMIOX IX DIWSOl'lIILA 



717 



average is 25.5 per cent. That there is a bimodal curve 

 produced may perhaps not be significant, as will appear 



TABLE I 



Crosses of Beaded to Wild Flies, showing Pkrckntages of Beaded- 



AvTragTsiz'e of brood. '. '. '. '. '. '. '. '. '. '. '. '. 203 172 148 120 180 113 101 95 130 50 73 



from the following facts, although later evidence will 

 show that it very possibly is significant. 



The per cent, of Beaded-winged offspring given by one 

 pair (Beaded X Wild) may vary at different times and 



Chart I 



Numbers of broods giving certain percentages of Beaded-winged off- 

 spring in F, generation of Beaded X Wild. (See Table I). 



under different conditions. For instance, if a pair are 

 put into a bottle with food and are left there for ten days, 

 and are then put into another bottle with fresh food and 

 left another ten days, the percentage of Beaded-winged 

 offspring will be different in the two broods. Table II 

 gives the records of such tests. The first two were made 



