Together with the class of the Schizomycetes (bacteria) the Cyanophyceae belong to the division of the Schizophyta which division differs from all other plant divisions by lacking a nucleus. However, the central part of their cells is a nuclear equivalent (Procaryota). This nucleoplasm or centroplasm or central body in the Cyanophycean cell has been studied profoundly these last fifteen years (Beck, Bowen, Cassel, Fuhs, Giesy, Herbst, Hutchinson, Jensen, Jost, Pankratz, Rabinovich, Sun and others) by means of the electron microscope. The resulting papers are mostly beautifully illustrated by electron micrographs. Pure cultures of Chroococcales (Gloeocapsa, Gloeothece, Pleurocapsa) as well as Hormogonales (Anabaena, Nostoc, Microcoleus, Oscillatoria, Phormidium, Symploca) have served for these investigations. The general results of these studies have provided us with a detailed picture of the nucleoplasm. The uncoloured nucleoplasm often has a fine reticulate-fibrillar texture, the anastomosing fibrils are intertwined by cytoplasm. In the nucleoplasm have been found to occur: vacuoles, opaque globular granules and polygonous bodies, which have a connection with the reticulate structure. Though the nucleoplasm contains nuclear material, the general conclusion is that there are no chromosomes and that no mitosis occurs. Only Fuhs (1958), who discovered Feulgen-positive linear filiform or bar-shaped structures in the centroplasm, about 0.2 μ in diameter, compared these with chromosomes, for their length is more or less constant and they split longitudinally into two diverging parts. He did not see any spindle-shape, however, inherent to mitosis. Cassel and Hutchinson (1954) doubt the possibility of a comparison with chromosomes since the resembling structures vary in shape and size in various cells. Several former investigators were positive about the existence of a true nucleus and chromosomes in the cell of Cyanophyceae. Kohl (1903) wrote a book about: “Organisation und Physiologie der Cyanophyceenzelle und die mitotische Teilung ihres Kernes”, in which numerous coloured figures show the mitosis and the chromosomes, observed with a light microscope. Tolypothrix lanata was used for these studies. Kohl did not see a nuclear membrane. To-day, investigators who have made electron-microscopic studies are convinced that no such a membrane between nucleoplasm and chromoplasm exists. They, however, do not at all confirm those bold conclusions concerning chromosomes and mitosis. Cell-division starts with an annular constriction of the protoplast.