The eggs of birds have shells that allow gas exchange but restrict the passage of water. Nitrogenous waste produced by the embryo must be contained within the egg until hatching. This waste is stored in a sac, called the allantois, in the form of

Question

Quizplus · Accepted Answer

The allantois in bird eggs stores nitrogenous waste primarily in the form of uric acid. Uric acid is less toxic and more water-soluble than ammonia, making it suitable for storage in the egg without harming the embryo.

The Eggs of Birds Have Shells That Allow Gas Exchange