-cut boundary sharply delimits the two,
as strands and peninsulas of tissue of one portion penetrate the
other. In the history of their development in the species and the
individual, and in their chemistry and function, a sharp difference
contrasts them.

In the embryo, the cortex is derived from the same patch that gives
rise to the sex organs, the ovaries in the female, and the testes in
the male, described as the germinal epithelium. How intimately the
two sets of glands are connected is neatly pointed by this fact of a
common ancestor. All vertebrates possess adrenal glands. In the lowest
of the vertebrates, Petromyzon, the two parts are distinct, the cells
of the cortex-to-be are situated in the walls of the kidney blood
vessels, projecting as peninsulas in the blood stream, the blood
sweeping over and past them. The medulla-to-be consists of cells
accompanying the vegetative nerves. Among reptiles, the two become
adjacent for the first time, and among birds one part occupies the
meshes of the other. The size of the cortex varies directly with the
sexuality and the pugnacity of the animal. The charging buffalo, for
example, owns a strikingly wide adrenal cortex. The fleeing rabbit,
on the other hand, is conspicuous for a narrow strip of cortex in its
adrenal. Human beings possess a cortex larger than that of any other
animal.

No definite chemical substance has as yet been isolated from the
cortex. That remains a problem for the investigator of the future. But
certain observations, especially concerning the relation between
the development and behaviour of the so-called secondary sex
characteristics, those qualities of skin, hair and fat distribution,
physical configuration and mental attitudes, which distinguish the
sexes, and the condition of the gland, indicate clearly that an
internal secretion will be isolated, and that it will in its activity
furnish certain predictable features.

Three different layers of cells, arranged in strings, that
interpenetrate to form a network directly bathed by blood, that breaks
in upon them from _open_ blood vessels, compose the cortex. Most
remarkable is this method of blood supply for it is exceedingly common
among the invertebrates and rare among the vertebrates.

In certain disturbances of these glands, especially when there are
tumors, which supply a massive dose of the secretion to the blood
presumably, peculiar sex phenomena and general developmental anomalies
and i