This chapter presents an overview of cell division and growth studies on synchronized flagellates. The synchronization of the flagellate A. longa on a diurnal temperature cycle of 6.5 h at 28.5°C and 17.5 h at 14.5°C yields cultures in which all the cells divide in a burst of 2.8 h duration. The dilution of the culture with new medium once each cycle at the beginning of the cold period gives a type of continuous culture in which there appears to be a selection for cells dividing on schedule. A 100% change of O2 consumption occurs at the time of division burst, while at the same time, there is only a 66% change in the dry weight.