Just as we see in an advanced community, that while the magisterial, the clerical, the medical, the legal, the manufacturing, and the commercial activities, have grown distinct, they have yet their agencies mingled together in every locality; so in a developed organism, we see that while the general functions of circulation, secretion, absorption, excretion, contraction, excitation, &c., have become differentiated, yet through the ramifications of the systems apportioned to them, they are closely combined with one another in every organ. § 60. The physiological division of labour is usually not carried so far as wholly to destroy the primary physiological community of labour. As in societies the adaptation of special classes to special duties, does not entirely disable these classes from performing one another's duties on an emergency; so in organisms, tissues and structures that have become fitted to the particular offices they have ordinarily to discharge, often remain partially able to discharge other offices. It has been pointed out by Dr. Carpenter, that "in cases where the different functions are highly specialized, the general structure retains, more or less, the primitive community of function which originally characterized it." A few instances will bring home this generalization. The roots and leaves of plants are widely differentiated in their functions: by the roots, water and mineral substances are absorbed; while the leaves take in, and decompose, carbonic acid. Nevertheless, by many botanists it is held that some leaves, or parts of them, can absorb water; and in what are popularly called "air-plants," or at any rate in some kinds of them, the absorption of water is mainly and in some cases wholly carried on by them and by the stems. Conversely, the underground parts can partially assume the functions of leaves. The exposed tuber of a potato develops chlorophyll on its surface, and in other cases, as in that of the turnip, roots, properly so called, do the like. In trees the trunks, which have in great measure ceased to produce buds, recommence producing them if the branches are cut off; sometimes aerial branches send down roots to the earth; and under some circumstances the roots, though not in the habit of developing leaf-bearing organs, send up numerous suckers. When the excretion of bile is arrested, part goes to the skin and some to the kidneys, which presently suffer under their new task. Various examples of vicarious functions may be found among animals. The excretion of carbonic acid and absorption of oxygen are mainly performed by the lungs, in creatures which have lungs; but in such creatures there continues a certain amount of cutaneous respiration, and in soft-skinned batrachians like the frog, this cutaneous respiration is important. Again, when the kidneys are not discharging their duties a notable quantity of urea is got rid of by perspiration. Other instances are supplied by the higher functions. In man