Or rather, do the chicks inside eggs breathe? Does oxygen diffuse into the egg through the shell, or is the egg an entirely self-contained little life-support unit? If you put an egg in an air-tight incubator filled entirely with nitrogen, would the chick inside die?
Yes, they do – the chicks have to respirate, and so carbon dioxide has to go out and fresjh air in. The egg shells are composed of granukles that are tightly-packed, but which leave microscopic fractal paths through to the inside.
All eggs have to do this – bird and reptile and other. the problem becomes an interesting one with insect eggs, because they’re so small. The embryos have to be able to breathe, yet they can’t lose their precious interior water to evaporation. There’s an article on it in Scientific American back in, I think, the 1980s.