BRISTLE INHERITANCE IN DROSOPHILA 89 



than the inbred flies mated in pairs. It is also found that the 

 first flies that hatch from a new culture bottle are larger and have 

 increased bristle numbers and low grade pairs separated from 

 mass cultures give children of as high grades as are found in the 

 inbred lines raised at the same time (table 16). The mass cul- 

 tures, from whic*h the parents in this table were taken, were 

 started from the 5th and 6th selected generations and had been 

 running eight months. The three inbred faixiilies shown from 

 the 16th generation are the only ones mated very nearly at the 

 same time as the three pairs taken from the mass cultures. This 

 table has a deep significance in relation to the accomplishments 

 of selection in the ten generations between the 6th to 16th. 



2. DISCUSSION 



Thus there is evidence to show that flies bqlow a certain size 

 are apt to have fewer extra bristles than larger flies and that 

 the size is largely dependent upon the condition and amount of 

 food, or, more generally, on the environment; further, that 

 males are shorter and have fewer extra bristles than females, 

 and that the differences between mass cultures and the inbred 

 lines disappear when the flies from the mass cultures are bred in 

 pairs. It seems as though the small underfed flies do not have 

 enough material to develop as many extra bristles as the larger 

 flies can. 



The measurements used in the correlation tables do not make 

 very satisfactory data, as the distention of the abdomen and 

 so, the length of the fly, varies with the amount of food con- 

 tained, but, however little light the tables may give as to the 

 actual amount of correlation and influence of the environment, 

 it is believed that the errors in measurement due to the varying 

 abdominal contents are not great enough to prevent the con- 

 clusion that such an influence of environment does exist. The 

 fact of most importance at present, whatever its explanation 

 may be, is that the numbers of extra bristles are influenced in 

 some direct or indirect way by the conditions in the bottles. 



