390 THE ORIGIN OF SPECIES 



classes; and how the several members of each class are connected 

 together by the most complex and radiating lines of affinities. We 

 shall never, probably, disentangle the inextricable web of the 

 affinities between the members 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 receives 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 formations. 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, independently 

 of their habits of life, resemble each other in the general plan of 

 their organization. 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 interesting 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 a horse, the paddle of the porpoise, 

 and the wing of the bat, should all be constructed on the same pat- 

 tern, and should include similar bones, in the same relative posi- 

 tions? 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, bandi- 

 coots — and those of some other Australian marsupials — should 

 all be constructed on the same extraordinary type, namely with 

 the bones of the second and third digits extremely slender and 

 enveloped within the same skin, so that they appear like a single 

 toe furnished with two claws. Notwithstanding the similarity of 

 pattern, it is obvious that the hind feet of these several animals 

 are used for as widely different purposes as it is possible to con- 

 ceive. The case is rendered all the more striking by the American 



