are subject, such parts will tend toward likeness; and this is what happens with their nervous and vascular systems. Duly to coördinate the actions of all parts of an active organism, there requires a controlling apparatus; and the conditions to be fulfilled for perfect coordination are conditions common to all active organisms. Hence, in proportion as fulfillment approaches completeness in the highest organisms, however otherwise unlike their types are, this apparatus acquires in all of them certain common characters—especially extreme centralization. Similarly with the apparatus for distributing nutriment. The relatively high activity accompanying superior organization implies great waste; great waste implies active circulation of blood; active circulation of blood implies efficient propulsion; so that a heart becomes a common need for highly evolved creatures, however otherwise unlike their structures may be. Thus is it, too, with societies. As they evolve, there arise certain conditions to be fulfilled for the maintenance of social life; and, in proportion as the social life becomes high, these conditions need to be more effectually fulfilled. A legal code expresses one set of these conditions. It formulates certain regulative principles to which the conduct of citizens must conform that social activities may be harmoniously carried on. And, these regulative principles being in essentials the same everywhere, it results that systems of law acquire certain general similarities as the most developed social life is approached.
These special replies to Mr. Leslie's objections are, however, but introductory to the general reply; which would be, I think, adequate even in their absence. Mr. Leslie's method is that of taking detached groups of social phenomena, as those of language, of fashion, of trade, and arguing (though, as I have sought to show, not effectually) that their later transformations do not harmonize with the alleged general law of evolution. But the real question is, not whether we find advance to a more definite coherent heterogeneity in these taken separately, but whether we find this advance in the structures and actions of the entire society. Even were it true that the law does not hold in certain orders of social processes and products, it would not follow that it does not hold of social processes and products in their totality. The law is a law of the transformation of aggregates; and must be tested by the entire assemblages of phenomena which the aggregates present. Omitting societies in states of decay and dissolution, which exhibit the converse change, and contemplating only societies which are growing, Mr. Leslie will, I think, scarcely allege of any one of them that its structures and functions do not, taken altogether, exhibit increasing heterogeneity. And, if, instead of taking each society as an aggregate, he takes the entire aggregate of societies which the earth supports, from primitive hordes up to highly civilized nations, he will scarcely deny that this entire aggregate has been becoming more various in the forms of societies it includes, and is still becoming more various.