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Continuous intra vitam observations in Nitzschia palea and supplementary ones in two other N.-species show that the division of the platelike chromatophore is intimately connected with mitosis and cytokinesis. It starts and goes on in a strictly regular course. When the ingrowing plasmatic zone of cytokinetic separation reaches the distal edge of each chromatophore, a narrow split originates and deepens until it has reached the middle of the chromatophore or a little more. Only then a second split arises at the proximal edge of the chromatophore; from there it grows in inverse direction, until it meets the first formed split in a distance of about one third from the proximal end of the chromatophore. Under normal circumstances the position of the meeting point is nearly invariable, the speed of the two progressing splits is the same, and the splitting of the two chromatophores of one cell is nearly exactly synchronized. There is only little variation in the beginning, as the split can form in somewhat different ways. Thereby a striking plasticity of the chromatophore is apparent. The cytokinesis including chromatophore division lasts about 4 1/2-5 minutes. Until now the mode of chromatophore division in Nitzschia remains without analogy. [ABSTRACT FROM AUTHOR]