urture.
He simply cannot but believe that the sex of the individual is as inborn
as his backbone, and as incapable of being created by varying conditions
of nurture. The causation of sex is therefore really a problem in
heredity; and we may most confidently assert, in the first place, that
the sex of every human being is already determined at the moment of
conception when, indeed, the new individual is created: determined then
by the nature and constitution of the living cells--or of one of
them--which combine to form the new being. Subsequent attempts to affect
the sex, as by means of the mother's diet and the like, are palpably
hopeless from the outset and always will be. This is by no means to say
that conditions affecting the mother--as, for instance, the
semi-starvation of a prolonged siege--may not affect the construction of
the germ-cells which she houses, and which are constantly being formed
within her from the mother germ-cells, as they are called. But any given
final germ-cell, such as will combine with another from an individual of
the opposite sex to form a new being, is already determined, once for
all, to be of one sex or the other. We naturally ask, then, how the two
parents are concerned in this matter; and the first remarkable answer
returned by the Mendelian workers during the last three or four years is
that it is the mother who determines the sex of her children in the case
of all the higher animals. Her contribution to the new being is called
the ovum, and it is believed that ova are of two kinds, or, we are quite
right in saying, of two sexes.

Those who are now working at these problems experimentally, actually
seeing what happens in given cases, and whom we may for convenience call
Mendelians after the master who gave them their method and their key,
have latterly obtained results the main tenour of which must be stated
here, as they indicate the lines of a portion of the succeeding
argument. The task was to attack experimentally the determination of
sex--a fascinating problem for which so many solutions that failed to
hold water have been found, but hitherto no others. In finding the
answer to it, as they appear certainly to have done so far as the higher
animals are concerned, the Mendelians are also beginning to ascertain,
as we shall see, certain basal facts as to the composition or
constitution of the individual; and to us, who wish to know exactly
what a woman is, and what she is as distin