Abstract
1. The physiological effects of egg turning during incubation are described. 2. There was a critical period for turning, from days 3 to 7 of incubation, which affected hatchability, embryo growth and utilisation of extra‐embryonic fluids. 3. Failure to turn eggs retarded formation of allantoic and amniotic fluids, restricted alumen uptake and retarded growth of the embryo, but only after day 12 of incubation.