THE PRINCIPLE OF ECONOMY IN EVOLUTION. 337 



associated, we should be compelled to say that, acting in accord- 

 ance with the law of least resistance, they would find it easier to 

 divide that work among their own number than for each to main- 

 tain itself apart from the rest. Yet the reality is even stronger 

 than this : since the parts are interdependent, must each act in the 

 interest of the whole of them, and are each by that whole domi- 

 nated, so to speak, into co-operation with one another for the ends 

 of maintenance. Just in proportion, moreover, as special activi- 

 ties are imposed upon special parts, in that degree are such parts 

 differentiated for the tasks they must perform ; special centers 

 and organs arise connecting the various processes with one an- 

 other, until finally the whole unified system is an aggregate of 

 co-operating but subordinated individualities, of which each is in 

 the service of all, and all act in the interest of each an aggre- 

 gate, that is to say, in which each of the parts, instead of having 

 to carry on itself all the activities of maintenance, obtains in 

 exchange for its own small contribution to the general labor the 

 services and power of the whole society. In other words, the 

 parts of such a system, impelled to the activities of maintenance, 

 move into those configurations in which self -maintenance is the 

 easiest and completest for all of them, and do so by a process of 

 gradual adaptation and interadaptation, every stage of which is a 

 stage of increasing efficiency of end and of greater economy of 

 energy in the reaching of that end. 



The progressive unification of men in the human society also 

 has its analogy in the progressive unification of the organic sys- 

 tem. In the lower planes of life lack of complete solidarity be- 

 tween all the parts and processes of an organism often manifests 

 itself in the well-known phenomenon of iterated organs. The 

 system in this stage consists, so to speak, of groups or segments, 

 and every segment has its special set of organs such, for example, 

 as the legs of the centiped and the lobster, the multiple breath- 

 ing holes of insects, and in a variety of organisms the iterated 

 eyes or ocelli, as well as the repeated nerve centers of many of the 

 lower forms. As the organism becomes unified this phenomenon 

 of iteration tends to pass away, and the change is wrought through 

 what may be called the discovery by the organism that it is easier 

 to produce and maintain a single set of organs of each kind for 

 the body as a whole than to produce and maintain and use a sepa- 

 rate set of such organs for each segment or group. Hence the 

 ascent of the organism from the stage of iterated organs to the 

 stage of single sets of organs, from the condition of imperfect to 

 the condition of perfect unification, is ascent by diminution of 

 resistance, by perfection of end, by greater economy of energy. 



As, moreover, the improvement of tools is a saving of energy 

 to the individual wielding them, so is the improvement of an 



TOL. LI. 26 



