ng of organic structures, of their internal and
external proportions of form. Physiology, the science of functions, on
the other hand, aims at a knowledge of the functions of the organs, or,
in other words, of the manifestations of life."[1]

[1] Haeckel, _Evolution of Man_, Vol. I. p. 20.

Indeed, physiology has so diverged from its sister science, morphology,
that it completely and entirely ignores two of the most important
functions of evolution, heredity and adaptation. This has been clearly
shown by Haeckel, who has done much towards bringing about a change of
opinion in these matters.[2]

[2] _Ibid._, p. 21 _et seq._

Morphology and physiology are interdependent, correlated, and connected
one with the other; and, as I will endeavor to point out as my argument
develops itself, psychology is, likewise, intimately associated with
these two manifestations of life.

It will be noticed that as forms take on more complexity, and as organs
develop new and more complex functions, _psychos_ becomes less simple
in its manifestations, and more complex in its relations to the internal
and external operations of life.

Keeping in view the definition of mind as advanced in the opening
paragraph of this chapter, it at once becomes evident that even the very
lowest forms of life possess mind in some degree. It is true that in the
_monera_, or one-celled organisms, the nerve-cell is not differentiated;
consequently, if I were to be held to a close and strict accountability,
my definition of mind would not embrace these organisms. Yet, some small
latitude must be allowed in all definitions of psychological phenomena,
especially in those phenomena occurring in organisms which typify the
very beginnings of life.

I am confident that, notwithstanding the fact that the nerve-_cell_ is
not differentiated in these primal forms, nerve-elements are,
nevertheless, present in them, and serve to direct and control life.

Mind makes itself evident in two ways--consciously and unconsciously.
The conscious manifestations of mind are volitional, while the
unconscious, "vegetative," reflex operations of mind are wholly
involuntary.

Although the unconscious mind plays fully as prominent a role in the
economy of life as does the conscious mind, this treatise will not
discuss the former, except indirectly. Yet, an outline sketch as to what
is meant by the _unconscious_ mind will be necessary, in order that the
reader may more fully com