Page:Popular Science Monthly Volume 48.djvu/610

568* implied by the evolutionary process of divergence and redivergence with accompanying modifications.

The truths of classification, again, have a kindred meaning. Ordinary people, and even naturalists of the old school, pass by as of no significance the remarkable relations which, in both plant and animal kingdoms, exist among their divisions, subdivisions, and sub-subdivisions—classes, subclasses, cohorts, orders, genera, species, varieties. The fact that these fall into groups within groups, successively decreasing in size, consists perfectly with the supposition of common origin. Suppose an arm of a large tree to have been buried in such wise as to leave only the tips of its twigs visible; and suppose a man from the Faroe Isles, ignorant of trees, taking one of these protruding tips for a separate plant, attempted to uproot it. He would find that below the surface the twig he uncovered joined with others like itself to form a small branch; and explorations all around would prove that everywhere the local clusters of twigs thus converged. Further excavations would show that the adjacent branchlets, composed of clusters of twigs, themselves united a little deeper down, and were subdivisions of a medium-sized branch. Again digging he would discover that several such branches formed parts of a still larger branch; and so on continually, until complete clearance made it manifest that all these great branches, small branches, branchlets, and twigs, in their respective groups, had diverged from the one original arm of the tree, which itself had diverged from the stem; and that they formed groups within groups diminishing in size as they became more remote from their common parent. And now observe that while there are thus symbolized the relationships of species, genera, orders, etc., as they now exist, there are also symbolized the relationships which, so far as we know them, exist among remains contained in the Earth's crust: the two sets of phenomena correspond.

The lesson taught by the facts of distribution in Time, is also taught by the facts of distribution in Space. In various regions there are alliances between the present fauna and the past fauna found fossil: though different, they are near akin. It was "this wonderful relationship in the same continent between the dead and the living" which especially forced on Mr. Darwin the belief in descent and modification: this relationship having been demonstrated by Prof. Owen between the existing South American forms and the buried forms of extinct species. The fact that in Australia, long cut off from the other continents, all the indigenous mammals are of the implacental type, and that the fossil mammals found there are also exclusively implacental, illustrates these connections very clearly. And these likenesses of nature between present faunas and past faunas in the same localities are