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

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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

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.

The yolk, the yellow part of the egg, is what feeds the animal via the umbilical cord. Then, the animal has enough strength to break and get out of the egg and consume solid food.