Fig. 4. Alvinella pompejana embryos cultured at 2–27°C and 1 atm. Histograms show the frequency distribution of developmental stages achieved by at least 20 embryos sampled in the main culture. Embryos were observed 12 h, 24 h, 48 h and 72 h after fertilisation except in two cases: * observation 16 h after fertilisation, and ** observation 63 h after fertilisation. U, uncleaved embryos; 2c, 2-cell stage; 4c, 4-cell stage; 8c, 8-cell stage; 16c, 16-cell stage and more; D, degrading embryos.