AGASSIZ AND EVOLUTION. 21 



this simple contrivance, tlie dullest school-boy accomplishes intel- 

 lectual results which would defy the utmost efforts of the unaided 

 strength of the greatest genius. And this is only the simplest tool- 

 form of this method. Think of the results accomplished by the use 

 of the more complex machinery of the higher mathematics ! 



Take next the method of experiment so characteristic of physics 

 and chemistry. The phenomena of the external world are far too 

 complex and far too much affected by disturbing forces and modifying 

 conditions to be understood at once by bare, unaided intellectual in- 

 sight. They must first be simplified. The physicist, therefore, con- 

 trives artificial phenomena under ideal conditions. He removes one 

 complicating condition after another, one disturbing cause and then 

 another, watching meanwhile the result, until finally the necessary 

 condition and the true cause are discovered. On this method rests the 

 whole fabric of the physical and chemical sciences. 



But when we rise still higher, viz., into the plane of life, the phe- 

 nomena of Nature become still more complex and diflicult to under- 

 stand directly ; and yet just here, where we are the most powerless 

 without some method, our method of experiment almost wholly fails 

 zis. The phenomena of life are not only far more complex than those 

 of dead matter, but the conditions of life are so nicely adjusted, the 

 equilibrium of forces so delicately balanced, that, when we attempt to 

 introduce our clumsy hands in the way of experiment, we are in 

 danger of overthrowing the equilibrium, of destroying the conditions 

 of the experiment, viz., life ; and then the whole problem falls imme- 

 diately into the domain of chemistry. What shall we do '? In this 

 dilemma we find that Nature herself has already prepared for us, 

 ready to hand, an elaborate series of simplified condition.^ equivalent 

 to experiments. The phenomena of life are, indeed, far too complex 

 to be at once understood — the problem of life too bard to be solved — 

 in the higher animals ; but, as we go down the animal scale, compli- 

 cating conditions are removed one by one, the phenomena of life be- 

 come simpler and simpler, until in the lowest microscopic cell or 

 spherule of living protoplasm we finally reach the simplest possible 

 expression of life. The equation of life is reduced to its simplest 

 terms, and now, if ever, we begin to understand the true value of the 

 unknown quantity. This is the natural history series, or Taxonomic 

 series, already spoken of. Again, Nature has prepared, and is now 

 preparing daily before our eyes, another series of gradually simplified 

 conditions. Commencing with the mature condition of one of the 

 higher animals — for example, man — and going backward along the 

 line of individual history through the stages of infant embryo, eg^, 

 and germ — we find again the phenomena of life becoming simpler and 

 simpler, until we again reach the simplest conceivable condition in 

 the single microscopic cell or spherule of living protoplasm. This, 

 as already explained, is the embryonic or Ontogeiiic series. Again, 



