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]
II. _Histionic presentation._--In the coenobia or cell-colonies of the social protists, and still better in the tissues of plants and lower, nerveless animals (sponges, polyps, etc.), we find the second stage of unconscious presentation, which consists of the common psychic activity of a number of closely connected cells. If a single stimulus may, instead of simply spending itself in the reflex movement of an organ (the leaf of a plant, for instance, or the arm of a polyp), leave a permanent impression, which can be spontaneously reproduced later on, we are bound to assume, in explaining the phenomenon, a histionic presentation, dependent on the psychoplasm of the associated tissue-cells.