The two membranes pull apart a little and create a small pocket or sack of air. As the developing bird grows, it breathes in oxygen from the air sack and exhales carbon dioxide. Several thousand microscopic pores all over the surface of the egg allow the CO2 to escape and fresh air to get in.
This says that a very long time ago South Africa could have had glaciers and had a cold climate were as now South Africa has a very hot and humid climate.
