BRISTLE INHERITANCE IN DROSOPHILA 77 



the children having either parent below certain grades were 

 omitted. Along with these were excluded all flies whose grand- 

 parents or more remote ancestors had been excluded. This 

 reduced the numbers in the total generations very considerably, 

 and this is especially so in the latest generations. In these 

 resulting curves the parents of each generation are included in 

 the curve of the preceding generation. In figure 5 the curves 

 have been' plotted in such a way as to include similar areas, al- 

 though representing different numbers of individuals. For 

 this reason the numbers of males and females included are put 

 down beside the curves. The soUd line represents females; 

 the broken line, males. The small curves between the larger 

 ones in each case represent the parents selected from the gener- 

 ation above, to produce the generation below. 



Discussion of the curves for total generations. The original 

 parents selected from wild stock were a male with one extra 

 bristle ( + 1) and a female with two extra bristles (+2). Their 

 children are represented in the first pair of curves. The large 

 number of normal flies in this generation 44.90 per cent is due 

 to the fact that the mother was not virgin. Disregarding these, 

 the male and female modes are at +2. In the following 

 generation the modes remain at -(-2 but the upper Hmit of the 

 range goes up from -[-4 to +7. The flies chosen as parents 

 from this generation, range from +2 to +7. In the third 

 generation the modes are still at +2 but the male curve has 

 moved a little higher and the female curve is markedly above 

 the male. This is clearly seen by comparing the areas of the 

 polygons above the vertical fine drawn at +2. The flies chosen 

 from this generation range from +4 to +7. In the fourth 

 generation the female mode is raised to +3 and a clear advance 

 is shown by the whole curve. Although the male mode is still 

 at +2, the proportion of +1 males has decreased and the pro- 

 portions of -F3 and +4 have strongly increased. In the fifth 

 generation the male curve has increased its range over the pre- 

 ceding generation but as a whole has fallen back a very little. 

 The female curve has a much increased range, and a sUght sag 

 above the mode, otherwise no change. In the sixth generation 



