The behavior of the higher animals, especially man, was thought to be a product of impulses and ideas which got into the mind in various ways and had power to arouse certain acts and other ideas more or less mysteriously, in the manner described by the laws of ideo-motor action, attention, association by contiguity, association by similarity, suggestion, imitation, dynamo-genesis and the like, with possibly a surplus of acts and ideas due to ‘free will.’ The mind was treated as a crucible in which a multifarious solution of ideas, impulses and automatisms boiled away, giving off, as a consequence of a subtle chemistry, an abundance of thoughts and movements. Human behavior was rarely viewed from without as a series of responses bound in various ways to a series of situations. The student of animal behavior passed as quickly as might be from such mere externals to the inner life of the creature, making it his chief interest to decide whether it had percepts, memories, concepts, abstractions, ideas of right and wrong, choices, a self, a conscience, a sense of beauty. The facts in intellect and character that are due to learning, that are not the inherited property of the species and that consequently are beyond the scope of evolution in the race, were not separated off from the facts of original nature. The comparative psychologist misspent his energy on such problems as the phylogenesis of the idea of self, moral judgments, or the sentiment of filial affection. At the other extreme, the behavior of the protozoa was either contemplated in the light of futile analogies,—for instance, between discriminative reactions and conscious choice, and between inherited instincts and memory,—or studied crudely in its results without observation of what the animals really did. The protozoa were regarded either as potential ‘conscious selves’ or as drifting lumps turned hither and thither by the direct effects of light, heat, gravity and chemical forces upon their tissues. The evolution of the intellectual and moral nature which a higher animal really possesses from the sort of a nature which the real activities of the protozoa manifest, is far less difficult to explain. In so far as the higher animal is a collection of original tendencies to respond to physical events without and within the body, subject to modification by the laws of exercise and effect and by these alone, and in so far as the protozoan is already possessed of a well-defined repertory of responses connected with physical events without and within the body in substantially the manner of the higher animal’s original tendencies, the problems of the evolution of behavior are definite and in the way of solution.