THE LIVING MACHINE BUILDING FACTORS. 159 



the history of these machines began as a simple 

 mass of cells, there was a possibility of an almost 

 endless variety of methods of organization. But 

 as a distinct type of organization was adopted by 

 one and another line of descendants all subse- 

 quent productions were limited through the law 

 of heredity to the general line of organization 

 adopted by their ancestors. With each age th , 

 further growth of such machines must consist in 

 the further development in the perfection of its 

 parts, and not in the adoption of any new system 

 of organization. Hence it is that the history of 

 the living machine has shown a tendency toward 

 development along a few well-marked lines, and 

 although this complication becomes greater, we 

 still see the same fundamental scheme of organi- 

 zation running through the whole. As the ages 

 have progressed the machines have become more 

 perfect in the adjustment of their parts, i.e. they 

 have become more perfect machines, but the his- 

 tory has been simply that of perfecting the early 

 machines rather than the production of new 

 types. 



EVIDENCE FOR THIS HISTORY. 



As just outlined, we see that the living 

 machines have been gradually brought into 

 their present condition by a process which has 

 been called organic evolution. But we must 

 pause for a moment to ask what is our evidence 

 that such has been the history of the living 

 machine. The whole possibility of understand- 

 ing living nature depends upon our accepting 

 this history and finding an explanation of it. 



