A mutant MT of Micrococcus lysodeikticus (luteus) IFO 3333, whose minimum growing unit is not a single cell, but a tetrad unlike the wild-type divides by binary fission of each monococcus, and then separates first into two daughter tetrads, second into four tetrads and third into eight tetrads. The three planes of either the cell division or the cell separation are equivalent to one another and oriented at right angles in three dimensions, respectively. The process of consecutive cell divisions and separations of the mutant tetrads was schematically illustrated.