434 MORPHOLOGY. Chap. XIII. 



lines of affinities. We shall never, probably, disen- 

 tangle the inextricable web of affinities between the 

 members of any one class ; but when we have a dis- 

 tinct object in view, and do not look to some unknown 

 plan of creation, we may hope to make sure but slow 

 progress. 



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 organ- 

 isation. 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 name of Morphology. This is the most 

 interesting department of natural history, and may 

 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 the same bones, in the same relative positions? 

 Geoffroy St. Hilaire has insisted strongly on the high 

 importance of relative connexion in homologous organs : 

 the parts may change to almost any extent in form and 

 size, and yet they always remain connected together 

 in the same order. We never find, for instance, the 

 bones of the arm and forearm, or of the thigh and leg, 

 transposed. Hence the same names can be given to 

 the homologous bones in widely different animals. We 

 see the same great law in the construction of the mouths 

 of insects: what can be more different than the im- 

 mensely long spiral proboscis of a sphinx-moth, the 

 curious folded one of a bee or bug, and the great jaws 

 of a beetle ? — yet all these organs, serving for such dif- 



