The corresponding changes in˙VO2 were minuscule (0.116 l O2/mmHg) or, for all age groups combined, only 2.3% of the mean ˙VO2 ,ranging from ∼8% (day 10) to ∼0.5% (day 16). At E18, hypercapnia and cold respectively increased and decreased motility. Differently, the effects of hypoxia on motility were variable among embryos.