Time stamp in the movie represents hh:mm. tracked in sequential video-recorded images obtained by automatic cell tracking and focusing. We examined 12 SM-ZK and 10 WT cells and deduced that the eyespot diminished in size and disappeared at an early stage of cell division and remained undetected for 26C97 min (62 min on average, 22 min in deviation). Subsequently, two small eyespots appeared and were distributed into the two daughter cells. Additionally, the emergent flagellum gradually shortened to zero-length, and two flagella emerged from the anterior ends of the daughter cells. Our observation revealed that the eyespot and flagellum of are degraded once in the cell division, and the carotenoids in the eyespot are also decomposed. Subsequently, the two eyespots/flagella are regenerated for distribution into daughter cells. As a logical conclusion, the two daughter cells generated from a single cell division possess the equivalent organelles and each cell has eternal or non-finite life span. The two newly regenerated eyespot and flagellum grow at different rates and mature at different timings in the two daughter cells, resulting in diverse cell characteristics in has an emergent flagellum [1,2] and eyespot (or stigma) [1,3] in each cell, which constitutes single organelle. A simple but essential question arises as to how a single organelle is distributed DMAT into two daughter cells during cell division. Two simple possibilities can be conceived: one is that the single organelle is divided into two, and the other is that the original organelle is retained in one daughter cell and a new one is produced for the other daughter cell. It is essential to determine whether one of the two daughter cells receives the organelle from the parental cell as it would affect the life span of the cell. The life span of the cells may be considered eternal if both the daughter cells receive newly generated organelles and may be considered finite if one of the daughter cells contained the parental organelle and exhibits a shorter life span. The limitation of replicative life span has been reported for individual yeast cells , where the mother cell produces daughter cells through bud formation. In this case, only one daughter cell is generated at a time, and the process is relatively easy to track . In contrast, tracking the cell division of is challenging. Live imaging at a high magnification is required to track organelles within the cell during cell division because the cells swim as fast as 200 m/s or more, frequently change their shape, and exhibit euglenoid movements [1,6]. Confinement and fixation of a live cell in between two cover glasses is cumbersome as the cells escape from the observation area with euglenoid movements or are damaged severely by sandwiching pressure from the two glasses. Non live cell imaging at a high magnification is relatively easier than dynamic live cell imaging and has been extensively carried out using electron microscopy. Walne and Arnott reported the comparative ultrastructure and possible function of eyespots in and . The authors stated that the eyespot granules develop by fusion of smaller granules. Their DMAT observations, however, provided only preliminary hints as to how the eyespot develops, to say nothing of the problem of how it replicates during cell division. Osafune and DMAT Schiff analyzed the stigma and flagellar swelling in relation to light and carotenoids using transmission electron microscopy . The embedded cells were embedded in resin, sectioned, and stained before visualization. They observed that light is required to organize colored carotenoids into the spheres of stigma. Morel-Laurens et al. reported the effects CCNB1 of cell division on the stigma of and concluded that every daughter cell inherits a portion of the stigma of the maternal cell . However, the mechanisms of stigma division/generation during cell division have not been clarified. Moreover, the mode of cell division differs considerably between  and . In the present study, we performed dynamic live cell imaging of cell division using optical microscopy. Long-term tracking of a single moving cell was achieved by employing automatic XY-stage control, auto focusing of the microscope, and microfluidic devices for cell confinement. Cell division was recorded on video, and the appearance of the eyespot and the emergent flagellum (extended part out of the anterior of the cell body) was tracked in sequential images extracted from the video. We observed that the eyespot shrank and disappeared at the early stages of cell division. DMAT The emergent flagellum was retracted and disappeared before the start of nucleus segmentation. The eyespot remained undetected for approximately 30 min or more, and subsequently two small eyespots appeared and were distributed into two daughter cells. The flagellum was gradually protruded from the.