US 



THE AMERICAN NATURALIST [Vol. XLIX 



Total. .37 



To these should be added : 



1 pair which gave 9.7: 1, Table V. 

 1 pair which gave 6.5: 1, Table VI 

 1 pair which gave 7.5 : 1, Table VII 

 1 pair which gave 7.5 : 1, Table X 

 1 pair which gave 59.0 : 1, Table XI 



Except for the several detached pairs at the extreme 

 limits, Fig. 1 shows a normal curve. A disturbance of 

 0.5 in either direction (less than 10 per cent.) is quite 

 within the limits of experimental accuracy. The larger 

 disturbances, ratios of 6 or 7 : 1, and also the first results 

 reported by Morgan ( '11 and '12) are yet to be explained. 

 These are too large to be attributed to experimental error. 



The data presented in the foregoing pages show that 

 there has been a marked improvement in the ratio of pink 

 to red since 1911. In one case only (1913) was the dis- 

 turbance greater than those of Morgan (59:1). The 

 remaining very marked disturbances were between 6 and 

 10 : 1. And these appeared so infrequently that in mass- 

 cultures their presence would hardly have been felt. 



A corresponding improvement has also been observed 

 in the fertility of the pink-eyed race between 1912 and 

 1913. This is seen on comparing Tables V and XII. In 

 the first, the fertility of the pink was much lower than 

 that of the red; in the second (about one year later), it 

 was as high. 



Hyde ( '14) showed that in some races of Drosophila 



