THE ELIMINATION OF THE SEX CHROMOSOMES 
FROM THE MALE-PRODUCING EGGS 
OF PHYLLOXERANS 
fH MORGAN 
From the Zoélogical Laboratory, Columbia University 
TWENTY-NINE FIGURES 
My studies of the life cycle of the phylloxerans of the hickories 
have shown first (08) why the fertilized eggs produce only 
females,! and second (’09) that the production of the males is 
caused by the elimination of a chromosome from the male-pro- 
ducing egg.? One essential point in the life cycle still remained 
unexplained; namely, the cause of the production of small male- 
and large female-producing eggs. The differentiation of these 
two kinds of eggs precedes, in the life cycle, the formation of 
the true males and sexual females. Jt may appear therefore 
that the question of the sex determination antedates those changes 
that lead to the elumination of a chromosome from the male-produc- 
ing egg, and, wf so, the real question of sex determination might 
seem to lie deeper than the maneuvres of the sex chromosomes. 
Until this point is cleared up the value of the chromosome 
hypothesis in sex determination may seem to hang in the balance. 
I am now able to bring forward certain evidence which I believe 
throws light on this important topic and I am prepared to offer 
an hypothesis based on the new evidence, which, if true, substan- 
tiates the view that one of the essential changes in the formation 
of the large and the small eggs is connected with changes in the 
sex chromosomes. 
1 Proc. Soc. Exp. Biology and Medicine, vol. 5, 1908, and Science, vol. 29, 1909. 
2 Proc. Soc. Exp. Biology and Medicine, vol. 7, 1910. 
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THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, NO. 4 
