ABSTRACT
The advance, of which 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.
