雏鸟胚胎在蛋内如何呼吸？

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Hard-shelled bird eggs contain albumen，or“egg white"，and a yolk. The fertilized egg cell， or embryo，develops within the yolk and feeds off it， as well as the albumen. The baby bird has shelter， food， almost everything it needs inside the egg; except， it seems， a little fresh air.

硬壳鸟蛋含有蛋白（即“蛋清”），以及一个蛋黄。（剩余2377字）