An important and universal feature of all reflex phenomena is the absence of consciousness. For reasons which we shall give in the tenth chapter we only admit the presence of consciousness in man and the higher animals, not in plants, the lower animals, and the protists; consequently all stimulated movements in the latter must be regarded as reflex--that is, all movements which are not _spontaneous_, not the outcome of internal causes (impulsive and automatic movements).[14] It is different with the higher animals which have developed a centralized nervous system and elaborate sense-organs. In these cases consciousness has been gradually evolved from the psychic reflex activity, and now conscious, voluntary action appears, in opposition to the still continuing reflex action below. However, we must distinguish two different processes, as we did in the question of instinct--primary and secondary reflex action. Primary reflex actions are those which have never reached the stage of consciousness in phyletic development, and thus preserve the primitive character (by heredity from lower animal forms). Secondary reflex actions are those which were conscious, voluntary actions in our ancestors, but which afterwards became unconscious from habit or the lapse of consciousness. It is impossible to draw a hard and fast line in such cases between conscious and unconscious psychic function. Older psychologists (Herbart, for instance) considered "presentation" to be the fundamental psychic phenomenon, from which all the others are derived. Modern comparative psychology endorses this view in so far as it relates to the idea of _unconscious_ presentation; but it considers _conscious_ presentation to be a secondary phenomenon of mental life, which is entirely wanting in plants and the lower animals, and is only developed in the higher animals. Among the many contradictory definitions which psychologists have given of "presentation," we think the best is that which makes it consist in an internal picture of the external object which is given us in sensation--an "idea," in the broader sense. We may distinguish the following four stages in the rising scale of presentative function: I. _Cellular presentation._--At the lowest stages we find presentation to be a general physiological property of psychoplasm; even in the simplest unicellular protist sensations may leave a permanent trace in the psychoplasm, and these may be reproduced by memory. In more than four thousand kinds of radiolaria, which I have described, every single species is distinguished by special, hereditary skeletal structure. The construction of this specific, and often highly elaborate, skeleton by a cell of the simplest description (generally globular) is only intelligible when we attribute the faculty of presentation, and, indeed, of a special reproduction of the plastic "feeling of distance," to the constructive protoplasm--as I have pointed out in my _Psychology of the Radiolaria_.[15]