COOPERATIVE EVIDENCES OF EVOLUTION. That the general theory of evolution represents the truth of history and existing facts is supported by evidence from all departments of biology. The basis of morphology is anatomy and embryology. As soon as anatomists studied the mode of de velopment of organs and traced their history from the germ, it was found that organs of the most diverse shape and use had had a common origin. Thus the arm of man, the fore leg of the lion, the flipper of the seal, the paddle of the whale, and a fish's fin were found to be morphologically identical—the same in origin and fundamental structure—while the wings of a bird and an in sect were perceived to be simply analogous. Thus, what seemed the most diverse organs were found to have a common origin. Also cell studies proved that the cell is the unit of organic life.
Classification also yields evidence. It is now recognized that the plant and animal kingdoms may each be represented by a genealogical tree; that the members of different classes, orders, fam ilies, genera, species, and varieties are blood rela tions which have had a common descent from some primitive form, and that ultimately the vege table and animal kingdoms have descended from a common ancestor. Taxonomy is an attempt to unravel these lines of descent, In classifying animals of any group (see CLASSIFICATION), we are constructing a phylogeny or genealogical tree.
Embryology furnishes an argument. The mode of development of an animal throws light on its affinities. Thus, the barnacle (q.v.) was sup posed to he a mollusk until its development from a nauplius young, very similar to that of certain erustacea, proved that it is a member of that class. Mere resemblance between the young of members of different classes points unerringly to their common origin. Embryology (q.v.) teaches that
all plants and animals have originated from a one-celled form. At one stage the fish, amphibian, reptile, bird, mammal, and even man are indis tinguishable from each other. and the resem blanee of the early embryo points to the origin of all vertebrates from some worm-like form. From his studies on the embryology of vertebrates, Von Baer first indicated the `recapitulation the ory'—i.e. that the different stages of develop ment of a highly specialized animal constitute an epitome or recapitulation of that of the class or type to which it belongs.
As stated by Von Baer, and afterwards more fully by Agassiz, the law expresses a general filet. It was Fritz Milner who, in 186-1, explicit ly pointed out its evolutional or phylogenetic bearings, and in 1866 Haeekel restated the doc trim- in the following words: "fide developmental history (ontogeny) of an individual animal brief l• recapitulates the history of the race (phy logeny)—i.e. the most important stages of organi zation which its ancestors have passed through appeal' again, 0111 if somewhat modified in the development of individual animals." Thanks to recent advances in morphology and embryology, and pa rtienlarly to the study of vestigdial structures, we are in a position to work out the phylogeny of the animal kingdom, or any group of it, with some approximation to exacti tude. Even within the limits of a genus it is in some cases possible to detect vestiges of what were primitive characters, and thus to arrange in genealogical order the different species. It is this sort of work which gives new life, dignity, and importance to classification.