simple
chemical agent in the secretion might account for the whole
difference--merely causing a genetic basis already present to express
itself in the one or the other manner.

This may be illustrated by the familiar case of the crustacea _Artemia
salina_ and _Artemia Milhausenii_. These are so unlike that they were
long supposed to be different species; but it was later discovered that
the genetic basis is exactly the same. One lives in 4 to 8% salt water,
the other in 25% or over. If, however, the fresh-water variety is put in
the saltier water with the salt-water variety, all develop exactly
alike, into the salt-water kind. Likewise, if the salt-water variety is
developed in fresh water, it assumes all the characteristics of the
fresh-water kind. Thus the addition or subtraction of a single chemical
agent--common salt--makes all the difference.

If this basis for sex is single, it is represented by the male plumage
in domestic birds, the secretions from the sex-glands acting as
modifiers. But a great deal of evidence has been produced to show that
the genetic basis, in man and some other forms at least, is double. That
is, we must think of two genetic bases existing in each individual--each
representing one of the two types of secondary sex characters. The
primary sex (i.e., the sex glands) would then determine which is to
express itself. In the domestic birds described above, the male type of
body appears in the absence of the ovarian secretion, and the female
type in its presence. In man and the more highly organized mammals, we
must use "secretions" in the plural, since a number of them, from
different glands, act together in a "complex." Goodale, experimenting
with birds, was unable to definitely decide whether the basis for sex
was single or double in that material, though he favoured the latter
explanation.

Dr Bell, the English gynecologist, using human surgical cases as a
basis, commits himself strongly to the dual basis.[2, p.13.] "Every
fertilized ovum," he says, "is potentially bisexual," but has "a
predominating tendency ... toward masculinity or femininity." But "at
the same time," he remarks, "it is equally obvious that latent traits of
the opposite sex are always present." After discussing mental traits
observed in each sex which normally belong to the other, he concludes as
follows: "If further evidence of this bisexuality, which exists in
everyone, were required, it is to be found in the embryolo