1. Methods are described for continuous laboratory cultivation of the pelagic freshwater copepod Cyclops vicinus. 2. The embryonic development is temperature dependent in a manner typical of cyclopids. Isolated egg-sacs show a slight tendency to accelerated development. 3. Increasing day length, increasing light intensity and decreasing temperature delay the process of molting throughout the whole development, in both sexes. In the copepodid-phase development is faster in males than in females. 4. Molting activity shows a maximum in the middle of the light phase and a second maximum at the beginning of the dark phase.