As the bacteria are still often described as "cleavage-fungi" and classified along with the real fungi, we must particularly point out the wide gulf that separates the two groups. The real fungi (or _mycetes_) are metaphyta, their multicellular body (_thallus_) forming a very characteristic sort of tissue, the mycelium; this is composed of a number of interlaced and interwoven threads (or hyphens). Each fungus-thread consists of a row of lengthened cells, which have a thin membrane and enclose a number of small nuclei in the colorless plasm. Moreover, the two sub-classes of the real fungi, the ascomycetes and basimycetes, form peculiar fruit-bodies which generate spores (ascodia and basidia). There is no trace whatever of these real characteristics of the true fungus in the bacteria. Nor is it less incorrect to class them with the fungilli, the so-called unicellular fungi or phycomycetes (ovomycetes and zygomycetes); these form a special class of protists which has the closest affinity to the gregarinæ. Like the closely related chromacea, many of the bacteria show a marked tendency to form communities or cell-colonies. These cell-communities arise, as elsewhere, from the fact that the individuals, which multiply rapidly by continuous cleavage, remain joined together. This may happen in two ways. When the social bacteria secrete large quantities of gelatine, and remain distributed in this, we have the _zooglœa_ (as in the case of the _aphanocapsa_ and _glœocapsa_ among the chromacea). If, on the other hand, the long-bodied bacilli remain fastened together in rows, we get the knotted threads of _leptothrix_ and _beggiatoa_ (which may be compared with the oscillaria). And, if these threads go into branches, we have _cladothrix_. Other cœnobia of bacteria have the appearance of disks, the cytodes dividing in a plane, usually in groups of four (as in _merismopedia_), or of cube-shaped packets when they are in all three directions of space (_sarcina_).