Fig. (5) Change of the activity phase (open bars) and inactive phase (solid bars) of chick motility during acute hypoxia 10%O₂ (A) and 5%O₂ (B) for 20 min or 40 min. Values are expressed as percentage of the values obtained in normoxia prior to hypoxia (control) on days 10, 12, 14 and 15 of incubation. In brackets, number of embryos studied at each age.