86 



E. CARLETON MACDOWELL 



amples from the 50 families so arranged. In mating No. 78, 

 there was no falhng off at the end of first bottle, but the second 

 bottle shows very clear falling off. There is found, then, a 

 certain relation between the time of hatching and the number of 

 extra bristles, due to conditions external to the germplasm, 

 namely, that the last flies from a bottle may be of lower grade 



TABLE 12 



Daily counts of progeny from the same parents in successive bottles, showing that when the 

 bristle numbers are lower at the end of a bottle, the high grades are regained at the begin- 

 ning of the next bottle. 



than the first ones, and when this is true, the higher grades 

 reappear in the next bottle 



It is common knowledge that the last flies from a bottle are 

 apt to be smaller than the first ones hatched. This decrease 

 in the sizes of the flies depends probably entirely upon the amount 

 of food the flies eat while larvae; this amount in turn depends 



