nates from the generalization previously reached in Political Economy. Recognition of the advantages gained by a society when different groups of its members devote themselves to different industries, for which they acquire special aptitudes and surround themselves with special facilities, led to recognition of the advantages which an individual organism gains when parts of it, originally alike and having like activities, divide these activities among them; so that each, taking a special kind of activity, acquires a special fitness for it. But now note that, when carried from Sociology to Biology, this conception was forth-with greatly expanded. Instead of being limited to the functions included in nutrition, it was found applicable to all functions whatever. It turned out that the arrangements of the entire organism, and not of the viscera alone, conform to this fundamental principle—even the differences arising among the limbs, originally alike, were soon to be interpretable by it. And then mark that the idea, thus developed into an all-embracing truth in Biology, comes back to Sociology ready to be for it, too, an all-embracing truth. For it now becomes manifest that not to industrial arrangements only does the principle of the division of labor apply, but to social arrangements in general. The progress of organization, from that first step by which there arose a controlling chief, partially distinguished by his actions from those controlled, has been everywhere the same. Be it in the growth of a regulative class more or less marked off from classes regulated—be it in the partings of this regulative class into political, ecclesiastical, etc.—be it in those distinctions of duties within each class which are signified by gradations of rank—we may trace everywhere that fundamental law shown us by industrial organization. And, when we have once adequately grasped this truth which Biology borrows from Sociology and returns with vast interest, the aggregate of phenomena which a society at any moment presents, as well as the series of developmental changes through which it has risen to them, become suddenly illuminated, and the rationale comparatively clear.
After a recognition of this fundamental kinship there can be no difficulty in seeing how important, as an introduction to the study of social life, is a familiarization with the truths of individual life. For individual life, while showing us this division of labor, this exchange of services, in many and varied ways, shows it in ways easily traced; because the structures and functions are presented in directly-perceivable forms. And only when multitudinous biological examples have stamped on the mind the conception of a growing interdependence that goes along with a growing specialization, and have thus induced a habit of thought, will its sociological applications be duly appreciated.
Turn we now from the indirect influence which Biology exerts on Sociology, by supplying it with rational conceptions of social develop-