it more than others; yet many of the cells of all portions of the whole organism are capable of performing it, for almost any fragment of a sponge, if separated from the parent mass and bedded out, is capable of growing into an "individual" and of continuing the race. If we pass in succession to higher species, we find cell-specialization becoming more and more marked; we find cells becoming more and more capable of performing efficiently some one function and less and less capable of performing all other functions. A division of labour thus occurs in the cell-community similar to that which distinguishes communities of civilized men from savage communities. Every savage does everything for himself, receiving small help from the rest of the community and giving little in return; and the more utterly savage the community is, the more complete in general is the independence of the individual. But while the savage performs all the labours necessary for supporting life, he performs each one less efficiently than he would did he devote himself entirely to it. In civilized communities each man devotes himself to some special work which he performs specially well, but which would not enable him to live unless it were supplemented by the labours of other men, who in like manner perform other special duties equally well. Thus a bricklayer performs a special duty better than he could do were he also a carpenter, a farmer, and a miner; but except he receive help from the labours of others his work does not produce all that he requires to maintain life. It is not, for instance, directly productive of food and clothing. For these he depends on the labours of other specialists; and therefore the higher the state of civilization the more complete is the state of interdependence of the members of the community.
So in higher animal organisms we find that all cells have taken up special duties—have all become specialists.
