3. ARBOREAL CŒNOBIA.--The cell-community takes the form of a small tree or shrub, the fixed cells secreting jelly-like stalks at their base and these forming branches. At the top of each stalk or branch is an independent cell; so in the case of the _gomphonema_ and many other diatomes, the _codonocladium_ among the flagellata, and the _carchesium_ among the ciliata. 4. CATENAL CŒNOBIA.--The cell-community forms a chain, the links of which (the individual cells) are joined in a row. We find chainlike cell-communities of this sort, or "articulated threads," even among the monera (_oscillaria_ and _nostic_ among the chromacea, _leptothrix_ among the bacteria). Among the diatomes we have the _bacillaria_, among the thalamophora _nodosaria_, as examples. Many of the lower protophyta (algaria and algetta) form the direct transition to the true algæ among the metaphyta, as the threadlike layer of the latter (for instance, _cladophora_) is only a higher development of the catenal cœnobium, with polymorphism of the co-ordinated cells. We may also regard these articulated multicellular threads as the first sketch for the formation of tissues in the metaphyta. The stable communities of cells which make up the body of the histona, or multicellular plants and animals, are called tissues (_tela_ or _hista_). They differ from the cœnobia of the protists in that the social cells give up their independence, assume different forms in the division of labor, and subordinate themselves to the higher unity of the organ. However, it would be just as difficult to lay down a sharp limit between the cœnobia and the tissues as between the protists and the histona which possess them; the latter have been developed phylogenetically from the former. The original physiological independence of the cells which have combined to form tissues is more completely lost in proportion to the closeness of their combination, the complexity of their division of labor, and the differentiation and centralization of the tissue-organism. Hence the various kinds of tissue in the body of the histona behave like the various classes and professions in a state. The higher the civilization and the more varied the classes of workers, the more they are dependent on each other, and the state is centralized.