Previous workers have found that a resting period of 6 weeks or longer (including drying) was necessary for sexual eggs of Cladocera (Daphnia and Simocephalus) to hatch. Many of these eggs of Moina macrocopa developed promptly (2 to 24 days), and without drying, after the egg-cases in which they were contained had been cast. This anomaly was found to be the general rule for eggs obtained from 3 entirely unrelated stocks of the species from widely separated localities,[long dash]New York, Rhode Island, and central Indiana, as well as for eggs obtained by crossing the N. Y. and R. I. strains. This is not known to be true for other Cladocera sexual eggs. Some theoretical implications are discussed.