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Louis Agassiz. 



periments. Commencing with the mature condition 

 of the higher animals, and going backwards along 

 the line of individual history through the stages of 

 embryo, egg, and germ, we find again the phenomena 

 of life become simpler and simpler, until we again 

 reach the simplest condition in the microscopic cell. 

 This, I will call the embryonic series. Again, that 

 there might be no excuse for man's ignorance of the 

 laws of life, nature prepares still another series of 

 experiments. Commencing with the fauna and flora 

 of the present time, and going back along the track 

 of geological history, through Tertiary, Secondary, 

 Palaeozoic and Eozoic, to the very dawn of life, we 

 find a series of organic forms becoming simpler and 

 simpler, until we again reach the simplest term in 

 the lowest conceivable forms of life. This I will 

 call the geological or palseontological, or evolution 

 series. 



Now it has been by extensive comparison in each 

 of these series up and down, and by extensive 

 comparison of the three series with each other, that 

 our knowledge of organisms has gradually become 

 scientific ; that mere accumulation of facts and phe- 

 nomena has grown with science ; that a mere heap 

 of useless rubbish has been changed into a beautiful 

 edifice. This is what is called the method of com- 

 parison — the great method used in the science of 

 life. Yes, anatomy only becomes scientific through 

 comparative anatomy. Physiology only becomes 

 scientific through comparative physiology ; and I 

 may add, psychology will never become scientific 

 except through comparative psychology. 



