The parthenogenetic eggs of Daphnia magna may be reared in sterile pond water on tissue culture slides, completing their embryonic history from egg to free-swimming independent organisms in about 46 hours. The eggs of this animal are self-sufficient with regard to the nutritive materials already stored in them at the time of their deposition. Such eggs are transformed into fully developed young in vitro in about the same period of time as that required for the development of eggs in the brood-chamber of the mother. Fully developed young reared in vitro, when transferred to bottles containing the standard amount of culture medium, become in time sexually mature and produce young. A brief description is given of the sequence of events in the course of the development of the embryos reared on tissue culture slides, as observed by gross microscopical examination.