272 T. H. Morgan 
There can be no doubt that the two kinds of eggs are not simply 
the result of the accidental amount of material contained in them. 
If this were the case, there would be no sharp line of demarcation 
but a gradual series of sizes, and if the result were purely chance, 
there would be more eggs of intermediate sizes than of large and 
small. The facts are the reverse. ‘There are two sharply sepa- 
rated groups of eggs and while, of course, there are fluctuating size 
differences, these center around two widely separated modes. 
Two alternative views offer themselves at this point. Either 
there is a sex-determining factor in the eggs of the stem-mother 
that separates female-producing from male-producing individuals, 
or in the life of the winged individuals some factor external or 
internal turns the scale in one or in the other direction. Let us 
dwell for a moment on these possibilities. 
If a sex-determining factor is present we have found no clue 
to such in our study of the chromosomes. ‘The eggs of the stem- 
mother are all of asize. If events subsequent to the egg formation 
of the stem-mother determine whether the individual produces male 
or female eggs, the following considerations should receive attention. 
Foremost is the observed fact that the male producers contain 
small eggs, but more of them, and the sum total of egg-material 
may be actually greater in some male producers than in other 
female producers. If then some condition should bring about 
the setting free of a larger number of eggs from the ovary the pres- 
ence of so many developing at once might turn the scale so that 
the alternative of the smaller egg is followed. If this view seems 
too improbable it might be imagined that the food conditions are 
less favorable at first than later on, or vice versa, and in conse- 
quence the first individuals that mature would be male producers, 
the later ones female producers. [ find no facts to support this 
view. One argument far outweighs these possibilities. The male 
egg shows from its very earliest embryonic development that it is 
characteristically* a male and I do not think, in the light of 
other facts regarding the influence of the chromosomes on the 
early development of the egg, that the results here can be safely 
4T refer to the early differences in the cytoplasmic relations of male and female embryos. 
