The chronomorphological events during the development of the egg of the freshwater caridean prawn,Macrobrachium nobilii, were followed from spawning to hatching. The female is receptive only for a 30-minute period after the premating moult. After mating, spawning ensued within 9 ± 3 hours and was completed within 15–20 seconds. Unmated females also spawned but the eggs did not survive. The rate of egg development increased 2·5x for a temperature rise of 10°C. Hatching was synchronised underin vitro conditions indicating uniform development of a clutch.