§ 54d. But in the _Metazoa_ and _Metaphyta_ at large, the associated units are, with the exceptions just indicated, completely subordinated. The unit-life is so far lost in the aggregate life that neither locomotion nor the relative motion of parts remains; and neither in shape nor composition is there resemblance to protozoa. Though in many cases the internal protoplasm continues to carry on vital processes subserving the needs of the aggregate, in others vital processes of an independent kind appear to cease. It will naturally be supposed that after recognizing this fundamental trait common to all types of organisms above the _Protozoa_ and _Protophyta_, the next step in an account of structure must be a description of their organs, variously formed and combined--if not in detail yet in their general characters. This, however, is an error. There are certain truths of structure higher in generality than any which can be alleged of organs. We shall see this if we compare organs with one another. Here is a finger stiffened by its small bones and yet made flexible by the uniting joints. There is a femur which helps its fellow to support the weight of the body; and there again is a rib which, along with others, forms a protective box for certain of the viscera. Dissection reveals a set of muscles serving to straighten and bend the fingers, certain other muscles that move the legs, and some inconspicuous muscles which, contracting every two or three seconds, slightly raise the ribs and aid in inflating the lungs. That is to say, fingers, legs, and chest possess certain structures in common. There is in each case a dense substance capable of resisting stress and a contractile substance capable of moving the dense substance to which it is attached. Hence, then, we have first to give an account of these and other chief elements which, variously joined together, form the different organs: we have to observe the general characters of _tissues_.