 If the parts [of an organism] were homogeneous then we should be able to call them units and there would only be one level of organization. But if each part were itself composed of parts forming in each an organized system, then clearly we should have two levels of organization and if the composing sub-parts of the first organization were intrinsically only numerically different we could speak of two homogeneous levels of organization. If, however, the sub-parts were intrinsically different then the first-order parts would be different and we should have a heterogeneous type of organization. By carrying out this process of subdivision further we could obtain very complex types of organization exhibiting a hierarchy of successive levels. And if now we consider one of the higher living organisms it is evident at once that its organization will belong to one of these heterogeneous hierarchical types. (Woodger 1929: 298)