1916] Reeves: Inheritance of Extra Bristles in Drosophila 501 



No record Avas kept of the size of the fiies as there was very little 

 difference. However, the extra bristles continued to appear in the 

 smaller flies with seemingly the same regularity as in the larger ones. 

 Except in large mass cultures, there was no diminishing in size at the 

 end of the hatchings. 



2. The Influence of Temperature. — Unlike the results from Miss 

 Hoge's (1915) experiments, temperature did not in our cultures in- 

 fluence the extra bristles. Eggs put under low temperature and kept 

 there until hatched produced relatively as many extra-bristled flies, 

 but hatchings took a little longer. When the temperature was in- 

 creased no appreciable difference was found in the bristle count. Thus, 

 while temperature might have a slight influence, yet it can not be 

 said to be a chief factor. 



Inheritance 



1. Mendelian Standpoint. — Table IX shows the ratios obtained in 

 crosses between normals and extras. Two P^ families were obtained 

 from such matings, containing respectively 158 normals : 9 extras 

 and 90 normals : 1 extra. These results are in accord respectively 

 with ratios 15 :1 and 63 :1, which would indicate the presence 

 of two or three equivalent factors. In the crosses made in the other 

 three Fj families the numbers obtained were too small for consider- 

 ation here. In one case all were normals, nineteen in number. In the 

 other two families only one or two flies hatched. 



The later generations shown in table IX were obtained in every 

 case by mating normal and extra sibs of the previous generation, 

 except in the P^ and Pg. Unfortunately, owing to sterility and death 

 of the extras, the only P4 and P5. cultures surviving are from collateral 

 families. The results thej^ give are, however, in general accord with 

 those of the previous generations. As shown by table IX, the various 

 ratios approximate closely in some cases to 63 :1, in others to 15 :1, 

 Mdiile still other families depart widely from either of these ratios. 



In comparing table X, in which in each generation extra sibs 

 are mated together, with table IX, in which the corresponding matings 

 were always between normal and extra, significantly different results 

 were obtained. While in matings between normal and extra ratios 

 chiefly 63 :1 and 15 :1, but never closely approaching 3 :1, were 

 obtained, in matings between extras (table X) the ratios were all 



