LECTURE XXXIV. 

 CLASSIFICATION. 



Homology the basis of classification. 



Artificial Classifications. Linnaeus ; classes of plants 

 on number of stamens ; orders of plants on number of 

 pistils. 



Fishes whose tails move vertically, and those which 

 flap horizontally. 



Natural Classifications. Cuvier, Jussieu. Possibility 

 of natural classification one of the strongest argu- 

 ments for unity of life. All forms known arrange 

 themselves in a way analogous to the branches of a 

 tree. All diverge forward ; traced backward they con- 

 verge. 



Homologies of words similar to those of animals 

 and plants. Non-homologous languages. Chinese and 

 English. But all languages subject to Evolution and 

 divergence. So with all organisms. 



Missing links in classification. Horse and cow not 

 a horse-cow, but the unspecialized coryphodon. Link 

 between whale and fishes not a whale-fish, but rather 

 a reptile. Cats, or even man, are nearer fishes than 

 the degenerate whales, which are degenerations from a 

 type rudely described as bear-like or dog-like. 



How change a fish into a whale ? A whale into a 

 fish ? Impossible now. In any transformation we 

 must go back to unspecialized forms, which still retain 

 the potentialities of some other type. 



