154 THE STORY OF LIFE'S MECHANISM. 



nature has constructed the complex machines 

 which we find filling the world to-day in the 

 form of animals and plants. 



HISTORY OF THE LIVING MACHINE. 



In the first place, we must notice that these 

 machines have not been fashioned suddenly or 

 rapidly, but have been the result of a very slow 

 growth. They have had a history extending 

 very far back into the past for a period of years 

 which we can only indefinitely estimate, but 

 certainly reaching into the millions. As we look 

 over this past history in the light of our present 

 knowledge we see that whatever have been the 

 forces which have been concerned in the construc- 

 tion of these machines they have acted very 

 slowly. It has taken centuries, and, indeed, 

 thousands of years, to take the successive steps 

 which have been necessary in this construction. 

 Secondly, we notice that the machines have been 

 built up step by step, one feature being added 

 to another with the slowly progressing ages. 

 Thirdly, we notice that in one respect this con- 

 struction of the living machine by nature's pro- 

 cesses has been different from our ordinary 

 method of building machines. Our method of 

 building puts the parts gradually into place in 

 such a way that until the machine is finished it is 

 incapable of performing its functions. The half- 

 built engine is as useless and as powerless as 

 so much crude iron. Its power of action only 

 appears after the last part is fitted into place and 

 the machine finished. But nature's process in 



