What nutrient rich fluid feeds an unhatched chick?

An unhatched chick is nourished by the yolk sac, which contains nutrient-rich fluid derived from the egg yolk. This fluid provides essential proteins, fats, vitamins, and minerals necessary for the chick's growth and development during incubation. The yolk sac is absorbed by the chick shortly before hatching, supplying energy and nutrients until it can feed independently.