568* POPULAR SCIENCE MONTHLY. 



sarily implied by the evolutionary process of divergence and redi- 

 vergence 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 their 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, igno- 

 rant of trees, taking one of these protruding tips for a separate 

 plant, attempted to uproot it. He would find that below the sur- 

 face 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 dimin- 

 ishing 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 demon- 

 strated by Prof. Owen between the existing South American forms 

 and the buried forms of extinct species. The fact that in Aus- 

 tralia, long cut off from the other continents, all the indigenous 

 mammals are of the implacental type, and that the fossil mam- 

 mals 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 



