THE LIVING MACHINE BUILDING FACTORS. 155 



machine building is different. Every step in the 

 process, so far as we can trace it at least, has 

 produced a complete machine. So far back as 

 we can follow this history we find that at every 

 point the machine was so complete as to be 

 always endowed with motion and life activity. 

 Nature's method has been to take simpler types 

 of machines and slowly change them into more 

 complicated ones without at any moment impair- 

 ing their vigour. It is something as if the steam 

 engine of Watt should be slowly changed by add- 

 ing piece after piece until there was finally pro- 

 duced the modern quadruple expansion engine, 

 but all this change being made upon the original 

 engine without once stopping its motion. 



This gradual construction of the living ma- 

 chines has been called Organic Evolution, or the 

 Theory of Descent. It will be necessary for us, 

 in order to comprehend the problem which we 

 have before us, to briefly outline the course of this 

 evolution. Our starting point in this history 

 must be the cell, for such is the earliest and 

 simplest form of living thing of which we have 

 any trace. This cell is, of course, already a 

 machine, and we must presently return to the 

 problem of its origin. At present we will assume 

 this cell as a starting point endowed with its 

 fundamental vital powers. It was sensitive, it 

 could feel, grow, and reproduce itself. From 

 such a simple machine, thus endowed, the his- 

 tory has been something as follows : In repro- 

 ducing itself this machine, as we have already 

 seen, simply divided itself into two halves, each 

 like the other. At first all the parts thus arising 



