How do chicks breathe inside an egg?
That solid-looking eggshell has about 10,000 pores that let oxygen in and carbon dioxide and water out. When you last made an omelet, you probably noticed a paper-thin membrane separating the rest of the egg from a pocket of air on the large end of the egg. The head of a chick develops at the large end. About three days before her hatching, a baby chick punctures the air cell at the base of the egg with her sharp egg tooth (a tiny, horny point on top of her beak) and breathes her first gulp of air: still inside the egg. As soon as she can breathe, she can peep. We can hear her peeping and tapping as she methodically chips a hole in the egg. It may take thousands of taps but at last she breaks through and breathes air directly from the outside world.
