In the previous papers (1958, 1959) the present author has described the fine structure of the metaphase spindle and the phragmoplast, and the de velopmental process of the phragmoplast and the cell plate with the help of the electron microscope.Concerning his thesis on "Electron microscope studies on the mitotic figure", there remain, however, the most basic and important problems: the one is the origin and the developmental process of the spindle body and the other that of the spindle fibers.A few theories with regard to the spindle formation in the mitosis have been offered by cytologists using various kinds of materials. Their conclusions obtained, however, showed little coincidence, viz. it is generally accepted, that there exist some differences between animal and plant, algae or fungi and the cormophyte plants, moreover, between somatic division and reduction division. With the appearance of the electron microscope the solution of these discrepancies seem to have been settled at the submicroscopic level, but practically only few results have been obtained. This failure is clearly based on the incompleteness in the fixation technique but not on the ability of the electron microscope.The biological specimens studied by the electron microscope are usually fixed with osmium tetroxide.The present author has also tried to observe the fine structure of the spindle fixed with osmium tetroxide in the ordinary way, but could not succeed to find any fine structure of the spindle which should be responsible for its anisotropic nature shown under the polarization microscope.Osmium tetroxide reveals, that it is no satisfiable fixative for fixing the fibrillar structure of the spindle. As we have already reported, the fine fibrillar structure of the spindle could be observed in the preparations fixed with cadmium chloride solution, and it becomes clear, that osmium tetroxide is by no means a fixative almighty for all the elements of the mitotic figures.Without the help of osmium tetroxide, the fibrillar structure of the spindle and the phragmoplast could be demonstrated clearly under the electron mi croscope (1958, 1959). The present study deals mainly with the develop

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