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 



