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. Ihave 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. 
