142 W. J. MOENKHAUS 
summary of four determinations on a large scale to obtain the 
normal sex-ratio. The flies were reared in the following manner. 
Mason jars containing a large quantity of food were exposed to 
flies in nature. The jars were left open until the larvae began to 
pupate when all flies were excluded by tying a guaze over the top. 
As the imagos emerged from time to time they were preserved 
and the sex-ratios determined. For 26933 individuals, the ratio 
was one male to 1.126 females. 
In regard to these determinations only one question, so far as I 
can see, can be raised. This is the academic one of the greater 
mortality of the males during development or, to push the matter 
back a little further and to make it applicable to recent develop- 
ments in our idea of sex, the greater mortality of the male deter- 
mining sex cells. In reference to this it may be pointed out that 
the developmental conditions were as nearly normal as one can 
imagine. There was an abundance of food, air, hght and mois- 
ture, and the larvae pupated in the remnants of the food in much 
the same manner as one finds them doing in nature. In this con- 
nection the experiments of Miss King (’07) on the influence of 
food on the sex ratio of Bufo are of importance. In this she finds 
that the mortality among the males is not greater than among the 
females. From these facts and from the knowledge that has come 
to me from the extensive rearing of Drosophilas for six years I am 
convinced that the sex-ratio in this species is not one of equality. 
3. Control of sex-ratio by selection 
If the sex-ratio of this species, then, is that of 1 male to every 
1.126 females, this should be regarded as specific Just as any other 
of the specific characters of the species. It should, therefore, be 
subject to fluctuations and to control like other specific characters. 
Starting with this conception of sex-ratio, I wished to see 
whether it were possible to control this, within limits, of course, 
by the process of selection. The results of these experiments 
I propose to detail below. 
To apply the selective process on the sex-ratio, the following 
simple method was employed. Two pairs were selected from 
