The most obvious similarities are now exhausted. The parts of the machine are actuated by external, but the organs by internal, forces. The organism is a living machine. No organism, whether organic or mechanic, labors for its own sake. Every such apparatus exists for somebody’s use. But while those that employ a machine stand in outer relation to the same, those who utilize an organism are beings that themselves constitute the organic machine-parts. These are not composed of dead atoms, but of living individuals. The organism is a society which puts the organic machinery into service. It is the social tie that connects the individuals which otherwise would be a multitude of isolated beings. In all organisms there are as many organs as actual wants among the individuals that compose it. Because these individuals are kindred, they have common needs and are therefore able to use the same organ. Every particular individual requires the assistance of all the organs and must therefore stand in such relation to them all that he can utilize the work of any one. But he himself enters as a working member only in one organ, whose work is the only one he can immediately press into his service, and even this only in certain cases. All other organs stand in more or less distant relation to him. How, then, will he be able to utilize them? Only so that the organs make themselves present in his own organ, and, so to speak, reach him their different products. Like every citizen in a community, each organ ought to have a system of circulation throughout all the other organs to transfer the results of its work where it is needed. If, however, each organ were provided with such a distribution agency this would be an extravagance inconsistent with the concentration of forces that the very idea of an organism implies. Instead of many such systems we find therefore in every organism but one, whose sole purpose is to circulate the products of the various organs, and thus, so to speak, make each organ represented in every part of the whole community. We find that every organic building is constructed in this way to suit the individuals that form its building-material, and so of course it must be, since it was built for that purpose by the same individuals. The consequence is that the degree of development an organism possesses is closely related to the state of evolution reached by the individuals which constitute it. The more perfected the organism, the higher and more developed also are the necessities it is able to satisfy.