THE LIVING MACHINE BUILDING FACTORS. 137 



show a fundamental likeness with each other 

 since they retain the fundamental characters of 

 their common ancestor, but they show also the 

 differences which they have themselves acquired. 

 And thus the process is repeated over and over 

 again. This history of the growth of these dif- 

 ferent machines has thus been one of divergence 

 from common centres, and is to be diagrammati- 

 cally expressed after the fashion of a branching 

 tree. The end of each branch represents the 

 highest state of perfection to which each line has 

 been carried. 



One other point in this history must be noted. 

 As the development of the complication of the 

 machine progressed the possibility of further 

 progress has been constantly narrowed. When 

 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 the 

 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- 



