nervous system, or the internal texture of the brain and spinal cord.
In these we find the elaborate cell-machinery, of which the psychic or
soul-life is the physiological function. It is so intricate that most
men still look upon the mind as something supernatural that cannot be
explained on mechanical principles.

But embryological research into the gradual appearance and the
formation of this important system of organs yields the most
astounding and significant results. The first sketch of a central
nervous system in the human embryo presents the same very simple type
as in the other vertebrates. A spinal tube is formed in the external
skin of the back, and from this first comes a simple spinal cord
without brain, such as we find to be the permanent psychic organ in
the lowest type of vertebrate, the amphioxus. Not until a later stage
is a brain formed at the anterior end of this cord, and then it is a
brain of the most rudimentary kind, such as we find permanently among
the lower fishes. This simple brain develops step by step,
successively assuming forms which correspond to those of the amphibia,
the reptiles, the duck-bills, and the lemurs. Only in the last stage
does it reach the highly organised form which distinguishes the apes
from the other vertebrates, and which attains its full development in
man.

Comparative physiology discovers a precisely similar growth. The
function of the brain, the psychic activity, rises step by step with
the advancing development of its structure.

Thus we are enabled, by this story of the evolution of the nervous
system, to understand at length THE NATURAL DEVELOPMENT OF THE HUMAN
MIND and its gradual unfolding. It is only with the aid of embryology