No. 560] SHORTER ARTICLES AND DISCUSSION 509 



It is evident upon inspection of these formulae that although the 

 red females have gained over the whites, this is due solely to the 

 formation of two heterozygotes where at first we had a pure red 

 and a pure white. Since the ratio of the three types of gametes 

 does not change, we may expect the above recorded ratios of red 

 and white flies to persist indefinitely. 



Let us now observe the results of counts and compare these 

 with the theoretical ratio. The count of February 12 gave 129 

 red males, 202 red females, 21 white males and 3 white females. 

 Instead of equality in the males, we have 6 reds to 1 white, and 

 instead of 3 to 1 in the females, we have 67 reds to 1 white. 



On March 13 flies were again drawn off from the jar and 

 counted, giving 303 red males, 514 red females, 36 white males 

 and 2 white females. The males are now 8.42 reds to 1 white and 

 the females 257 reds to 1 white. 



On April 12 a count showed 1,341 red males, 1,363 red fe- 

 males, 95 white males and 24 white females, or 14.1 reds to 1 

 white among the males, and 56.8 reds to 1 white anions: the fe- 

 males. 



In general these results show that the reds are outrunning the 

 whites. Disregarding sex we expect a ratio of 5 reds to 3 whites 

 to persist in the population. On February 12 we get 14 to 1 ; on 

 March 13, 21.5 to 1 and on April 12, 22.7 to 1. On April 12 there 

 are more white females than would be expected, an irregularity 

 which can apparently be explained only by chance. The great 

 excess of females in the first two counts probably denotes that the 

 lethal factor clearly demonstrated by Morgan 2 was present in the 

 stock and the equality of the sexes in the last count denotes that 

 the lethal factor has been bred out. 



Among the flies examined in the last count were a few reds in 

 which the eyes were reduced to about one fourth the normal diam- 

 eter, and also a spotted-eyed fly which was not counted in the 

 numbers recorded. The latter had the right eye red with a white 

 patch four ommatidia in diameter near the vertex, and the left 

 eye white with a red spot eight to twelve ommatidia in diameter 

 with a few smaller red spots below it near the posterior margin. 

 Later examinations of the culture were made in the hope of ob- 

 taining a spotted-eye fly alive, but these were without success. 



s "The Explanation of a New Sex Eatio in Drcsophila," Science, N. S.. 

 XXXVI, 934, November, 1912. 



