Eli5 How do reptiles and birds get nutrients for their development when still in the egg?

Question

They’d also need oxygen for living outside of the egg so how do they live in the eggs for as long as they do without it?

In: Biology

Answer 1

The shell can actually let oxygen pass into it.

Nutrients are all stored in the yolk. It’s enough because the “pregnancy time” for egg paying species is usually rather short. 21 days for chicken for example.