associated, we should be compelled to say that, acting in accordance with the law of least resistance, they would find it easier to divide that work among their own number than for each to maintain 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 dominated, so to speak, into co-operation with one another for the ends of maintenance. Just in proportion, moreover, as special activities 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 another, 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 aggregate, 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 system. In the lower planes of life lack of complete solidarity between 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 breathing 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 separate 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
