INBREEDING AND SELECTION IN DROSOPHILA AMPELOPHILA 149 
for the female strain. (3) Females from the male strain mated 
with males from the male strain, and (4) the reciprocal of ‘(3)’. 
In crossing two strains as in the above experiment three possi- 
bilities might obtain. First, that the two sexes have an equal 
influence in determining the sex-ratio; second, that either sex 
have a predominant influence and third, that a ratio result unlike 
that obtaining in either of the parental strains. While the first 
is probably the expected result, the experiments show in a 
most decided way that the male has little or no influence in deter- 
mining the sex-ratio in this species (tables 10, 11 and 12). In 
most of the cases the ratio of the offspring falls pretty closely 
around that of the strain from which the females were taken. In 
two instances the ratios exceeded 100 per cent influence. The re- 
maining ones, with the exception of strain 244 in which the male in- 
fluence amounted to 35 per cent show the female influence almost 
near enough to 100 per cent to justify one in regarding the differences 
merely as fluctuations incident to the small number of individuals 
involved. The unusually great influence of the male in strain 
244 might be accounted for in two ways. First the number of 
individuals involved in this experiment are relatively small so 
that the ratios of both the control and the crossed broods are not 
as reliable as in the other experiments. Secondly, the flies used 
for this experiment were taken from the earlier generations of 
the two strains, before, we may believe, any considerable selec- 
tion had been applied to fix the character of the respective strains. 
Indeed, this seems to be borne out in the other experiments. 
The materials of the three experiments were not all taken from 
the same generation but were taken from different generations in 
the development of the strain. Thus, in experiment 1 the broods 
were taken from the first generation of strain 206 and 207. In 
experiment 2 the broods came from the second generation of 
strain 206 and the third of 207. The third experiment was made 
from the fourth and fifth generations of strains 206 and 207 
respectively. Arranging these experiments in a series, based on 
the length of time that selection had been practiced on the broods 
used, we see that the male influence decreases as the selective time 
increases. 
