Seite - 472 - in The Origin of Species

472 ORIGIN OF SPECIES all living and extinct forms can be grouped together within a few great classes; and how the several members of each class are connected together by the most complex and radi- ating lines of affinities. We shall never, probably, disen- tangle the inextricable web of the affinities between the mem- bers of any one class; but when we have a distinct object in view, and do not look to some unknown plan of creation, we may hope to make sure but slow progress. Professor Hackel in his 'Generelle Morphologic' and in other works, has recently brought his great knowledge and abilities to bear on what he calls phylogeny, or the lines of descent of all organic beings. In drawing up the several series he trusts chiefly to embryological characters, but re- ceives aid from homologous and rudimentary organs, as well as from the successive periods at which the various forms of life are believed to have first appeared in our geological for- mations. He has thus boldly made a great beginning, and shows us how classification will in the future be treated. MORPHOLOGY We have seen that the members of the same class, inde- pendently of their habits of life, resemble each other in the general plan of their organisation. This resemblance is often expressed by the term "unity of type ;" or by saying that the several parts and organs in the different species of the class are homologous. The whole subject is included under the general term of Morphology. This is one of the most inter- esting departments of natural history, and may almost be said to be its very soul. What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include similar bones, in the same relative positions? How curious it is, to give a subordinate though striking instance, that the hind-feet of the kangaroo, which are so well fitted for bounding over the open plains, —those of the climbing, leaf-eating koala, equally well fitted for grasping the branches of trees,—those of the ground- dwelling, insect or root-eating, bandicoots,—and those of