The notion of _will_ has as many different meanings and definitions as most other psychological notions--presentation, soul, mind, and so forth. Sometimes will is taken in the widest sense as a _cosmic attribute_, as in the "World as will and presentation" of Schopenhauer; sometimes it is taken in its narrowest sense as an _anthropological attribute_, the exclusive prerogative of man--as Descartes taught, for instance, who considered the brute to be a mere machine, without will or sensation. In the ordinary use of the term, _will_ is derived from the phenomenon of voluntary movement, and is thus regarded as a psychic attribute of most animals. But when we examine the will in the light of comparative physiology and evolution, we find--as we do in the case of sensation--that it is a universal property of living psychoplasm. The automatic and the reflex movements which we observe everywhere, even in the unicellular protists, seem to be the outcome of inclinations which are inseparably connected with the very idea of life. Even in the plants and lowest animals these inclinations, or tropisms, seem to be the joint outcome of the inclinations of all the combined individual cells. But when the "tricellular reflex organ" arises (page 115), and a third independent cell--the "psychic," or "ganglionic," cell--is interposed between the sense-cell and the motor cell, we have an independent elementary organ of will. In the lower animals, however, this will remains _unconscious_. It is only when consciousness arises in the higher animals, as the subjective mirror of the objective, though internal, processes in the neuroplasm of the psychic cells, that the will reaches that highest stage which likens it in character to the human will, and which, in the case of man, assumes in common parlance the predicate of "liberty." Its free dominion and action become more and more deceptive as the muscular system and the sense-organs develop with a free and rapid locomotion, entailing a correlative evolution of the brain and the organs of thought.