Fig. 2. Egg progression through meiosis II. By inseminating eggs with low numbers of sperm we were able to monitor accurately both second polar body formation (pb2), which occurred within 3 hours of insemination, and pronucleus (pn) formation, at about 4-6 hours. Sperm were added at time 00:00 (hours:minutes). Sample images at 20-minute intervals are shown but images were captured every 15 seconds. Scale bar: 20 µm.