mistry." But why and how does this nuclear
material determine sex? In other words, what is the nature of the
process of differentiation into male and female which it sets in motion?

To begin with, we must give some account of the difference between the
cells of male and female origin, an unlikeness capable of producing the
two distinct types of gametes, not only in external appearance, but in
chromosome makeup as well. It is due to the presence in the bodies of
higher animals of a considerable number of glands, such as the thyroid
in the throat and the suprarenals just over the kidneys. These pour
secretions into the blood stream, determining its chemical quality and
hence how it will influence the growth or, when grown, the stable
structure of other organs and cells. They are called endocrine glands or
organs, and their chemical contributions to the blood are known as
_hormones_.

Sometimes those which do nothing but furnish these secretions are spoken
of as "ductless glands," from their structure. The hormones (endocrine
or internal secretions) do not come from the ductless glands alone--but
the liver and other glands contribute hormones to the blood stream, in
addition to their other functions. Some authorities think that "every
cell in the body is an organ of internal secretion",[2] and that thus
each influences all the others. The sex glands are especially important
as endocrine organs; in fact the somatic cells are organized around the
germ cells, as pointed out above. Hence the sex glands may be considered
as the keys or central factors in the two chemical systems, the male and
the female type.

These various hormones or chemical controllers in the blood interact in
a nicely balanced chemical system. Taken as a whole this is often
called the "secretory balance" or "internal secretory balance." This
balance is literally the key to the sex differences we see, because it
lies back of them; i.e., there are two general types of secretory
balance, one for males and one for females. Not only are the secretions
from the male and the female sex glands themselves quite unlike, but the
whole chemical system, balance or "complex" involved is different.
Because of this dual basis for metabolism or body chemistry, centering in
the sex glands, no organ or cell in a male body can be exactly like the
corresponding one in a female body.

In highly organized forms like the mammals (including man), sex is
linked up with _all_ t