AND CLASSIFICATION. 23 



This is but the simplest illustration, taken 

 from the most familiar objects, of this compar- 

 ative method ; but the same process is equally 

 applicable to the most intricate problems in an- 

 imal structures, and will give us the clew to all 

 true affinities between animals. The education 

 of a naturalist now consists chiefly in learning 

 how to compare. If he have- any power of 

 generalization when he has collected his facts, 

 this habit of mental comparison will lead him 

 up to principles, and to the great laws of combi- 

 nation. It must not discourage us, that the pro- 

 cess is a slow and laborious one, and the results 

 of one lifetime after all very small. It might 

 seem invidious, were I to show here how small 

 is the sum total of the work accomplished even 

 by the great exceptional men, whose names are 

 known throughout the civilized world. But I 

 may at least be permitted to speak disparagingly 

 of my own efforts, and to sum up in the fewest 

 words the result of my life's work. I have de- 

 voted my whole life to the study of Nature, and 

 yet a single sentence may express all that I have 

 done. I have shown that there is a correspond- 

 ence between the succession of Fishes in geologi- 

 cal times and the different stages of their growth 

 in the egg, this is all. It chanced to be a 

 result that was found to apply to other groups 

 and has led to other conclusions of a like nature. 



