Front Page Titles (by Subject) CHAPTER VII.: THE CORRESPONDENCE AS DIRECT BUT HETEROGENEOUS. - The Principles of Psychology
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CHAPTER VII.: THE CORRESPONDENCE AS DIRECT BUT HETEROGENEOUS. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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THE CORRESPONDENCE AS DIRECT BUT HETEROGENEOUS.
§ 129. The advance, of which we have just marked the first steps, from a correspondence that is uniform to one that is varied, begins to show itself distinctly, under either an absolute or a relative change in the environment. In the case of plants, it is seen when, from a habitat in which the elements are not only ever-present in immediate contact with the organism, but ever in a fit condition for absorption by it, we pass to a habitat in which the needful elements, though ever present, are not always in a fit condition for absorption. And in the case of animals, it is seen both on passing from the protozoa to the larger aquatic creatures, which by their increased size and consequent necessity for larger prey are in the condition of having their nutriment less uniformly diffused, and on passing from aquatic creatures to terrestrial ones, to which the less uniform diffusion of nutriment is not relative only, but absolute. In all these instances the result is, that in addition to a correspondence with ever-present coexistences in the environment, we have now a correspondence to certain sequences in it. Let us glance at each class of cases.
§ 130. In the higher plants, which require not only carbonic acid and oxygen, but light, a certain temperature, a certain soil, and a certain quantity of moisture, we find variations in the vital actions corresponding with the variations which the environment undergoes in respect to these conditions—variations corresponding with those of the hour, the weather, and the seasons. As we lately saw, the lowest life continues only so long as its environment remains practically homogeneous, both in Space and Time. The next highest order of life must be looked for in organisms displaying correspondence with the most general changes to which the environment is liable: and this is the kind of life which the vegetable kingdom at large exhibits. These changes in quantity of light and heat, are not only most general as occurring with greater regularity in time and degree than any others, but also as affecting the whole mass of the medium by which the organism is surrounded. And thus, in virtue both of their periodicity and universality, as well as by their comparative slowness, they produce only that small degree of heterogeneity in the environment, to which the small degree of heterogeneity in the visible changes of plant-life corresponds.
It should be further remarked, that the greater complexity of correspondences, and therefore greater length in the series of correspondences, which these higher plants display, involves an additional group of vital processes necessitated by increase of size. The long-continued growth rendered possible by this completer adjustment of internal relations to external relations, implying, as it does, a greater and greater remoteness in the parts of the organism from each other, supposes some means whereby these remote parts shall be put in communication; and hence a circulatory system. Or perhaps it may more strictly be said, that a circulatory system is necessitated by increase of size, joined with the division of the environment into the two halves, soil and air; and if so, the only respect in which the plant displays mechanical action, must be regarded as in correspondence with the only respect in which the elements in its environment are not coextensive in Space.
§ 131. Turning from plants to plant-animals (zoophytes), we see that while in them, there are certain general successive changes corresponding like those of plants with general successive changes in their environment, they more manifestly exhibit certain special changes, corresponding with special changes in it. While to the chemical, thermal, and hygrometric actions affecting the whole mass of its surrounding medium, the actions going on in the plant slowly respond; there is no response in it to the surrounding mechanical actions: as those of a wire-worm gnawing its roots; or a herbivore browsing on its leaves. On the other hand, the most conspicuous of the actions seen in a zoophyte, are those that result when its expanded tentacles are touched. To a relation of coexistence between tangible and other properties, presented in a particular part of the environment, there corresponds, in the organism, a relation of sequence between certain tactual impressions and certain contractions. Here there are several facts to be noticed. First, that being a stationary creature, whose medium does not supply matter to be integrated so uniformly as it supplies disintegrating matter, there arises the necessity, that the creature must obtain matter to be integrated, either by filtering out of its medium the minute portions it contains (as do those zoophytes and molluscs that absorb and expel currents), or by arresting those larger portions here and there moving through its medium; and to do this last, presupposes sensitiveness and contractility connected in the manner seen. Second, that the ability to respond, not simply to the coexistences and sequences presented by the whole mass of the environment, but to the coexistences and sequences presented by particular bodies in it, is an advance in the degree of correspondence. And third, that as these particular bodies, exhibit in virtue of their motions much more various changes than those which the environment in general undergoes, an increased heterogeneity in the correspondence is at the same time involved.
§ 132. Of all these cases however, it is to be remarked, as of those in the last chapter, that the correspondence between internal and external relations, extends only to those external relations which occur in absolute contact with the organism. Not only is it that the processes going on in the yeast-plant, cease, unless its cell-wall is bathed by the saccharine and other matters on whose affinities they depend; not only is it that the tree must have its carbonic acid, water, earthy salts, ammonia, and the rest, applied directly to its surface in the presence of light and heat, and that until they are thus applied it remains inert; but it is, that in the lowest division of the animal kingdom also, the substances to be assimilated must come in collision with the organism before any correspondence between inner and outer changes is shown. Alike in those forms of life whose environment perpetually presents the disintegrating and integrable matters under the requisite conditions; those whose environment perpetually presents them, but under variable conditions; those whose environment, though not full of integrable matter, yet contains it in such abundance that mere random locomotion brings them in contact with a sufficiency; and those whose environment contains it in moving masses of such number, that though themselves stationary, chance brings them as many as they want—alike in all these forms of life, there is an absence of that correspondence between internal relations and distant external relations, which characterizes more highly-endowed organisms.