22 THE POPULAR SCIENCE MONTHLY. 



that there be no excuse for man's ignorance of the laws of life, Nature 

 has prepared still another series ; and this the grandest of all, for it is 

 the cause of both the others. Commencing with the plants and ani- 

 mals of the present epoch, and going back along the track of geologi- 

 cal times, through Cenozoic, Mesozoic, Palaeozoic, Eozoic, to the very 

 dawn of life — the first syllable of recorded time — and we find again a 

 series of organic forms growing simpler and simpler, until, if we could 

 find the very first, we would undoubtedly again reach the simplest 

 condition in the lowest conceivable forms of life. This, as we have 

 already seen, is the geologic or evolution, or Pliylogenic series. "We 

 have already ex2)lained these three series, only in this connection it 

 suits our purpose to take the terms backward. 



Now, it is by comparison of the terms of each of these series going 

 up and down, and watching the first appearance, the growth, and the 

 perfecting of tissues, organs, functions, and by the comparison of the 

 three sci'ies with one another, term by term — I say it is wholly by 

 comparison of this kind that biology has in recent times become a true 

 inductive science. This is the '■'• metliod of comparison.''^ It is the 

 great method of research in all those departments which can not be 

 readily managed by the method of experiment. It has already re- 

 generated biology, and is now applied with like success in sociology 

 under the name of historic method. Yes ; anatomy became scientific 

 only through comparative anatomy, physiology through comparative 

 physiology, and embryology through compai-ative embryology. May 

 we not add, sociology will become truly scientific only through com- 

 parative sociology, and psychology through comparative psychology ? 



Now, while it is true that this method, like all other methods, has 

 been used, from the earliest dawn of thought, in a loose and imperfect 

 way, yet it is only in very recent times that it has been organized, 

 systematized, perfected, as a true scientific method, as a great instru- 

 ment of research ; and the prodigious recent advance of biology is due 

 wholly to this cause. Now, among the great leaders of this modern 

 movement, Agassiz undoubtedly stands in the very first rank. I must 

 try to make this point plain, for it is by no means generally under- 

 stood. 



Cuvicr is acknowledged to be the great founder of comparative 

 anatomy. lie it was that first perfected the method of comparison, 

 but comparison only in one series — the Taxonomic. Yon Baer and 

 Agassiz added to this, comparison in the ontogenic series also, and 

 comparison of these two series with each other, and therefore the ap- 

 plication of embryology to the classification of animals. If Yon Baer 

 was the first announcer, Agassiz was the first great practical worker 

 by this method. Last and most important of all, in its relation to 

 evolution, Agassiz added comparison in the geologic or p)hylogenic 

 series. The one grand idea underlying Agassiz's whole life-work was 

 the essential identity of the three series, and therefore the light which 



