雛鳥胚胎在蛋內如何呼吸？

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.

硬殼鳥蛋含有蛋白（即“蛋清”），以及一個蛋黃。受精的卵細胞，或者說胚胎，在蛋黃中發育，并以蛋黃和蛋白為食。幼鳥在蛋內擁有庇護所、食物，幾乎一切所需；唯獨似乎缺少一點新鮮空氣。

Animals that develop inside their mothers， like mammals， get their oxygen from mom through the umbilical cord. A bird egg doesn't have as obvious a way to take in oxygen and get rid of carbon dioxide， but the egg，again， takes care of things.

在母體內發育的動物，如哺乳動物，通過臍帶從母體獲取氧氣。鳥蛋雖沒有那么明顯的方式來吸收氧氣和排出二氧化碳，但它仍能巧妙地解決這個問題。

Directly under the egg's shell are two membranes. When the eggs are laid by the mother， they're very warm，and as they cool， the material inside the egg shrinks a little bit.The two membranes pull apart a little and create a small pocket or sack of air. As the baby bird grows， it develops an allantois， which is a hollow pouch that grows out of the bottom part of the chick's gut

緊貼蛋殼下方的是兩層膜。當鳥媽媽產下蛋時，蛋的溫度很高，隨著鳥蛋冷卻，蛋內物質會略微收縮。這兩層膜會稍微分離，形成一個小氣囊或氣室。隨著幼鳥的成長，它會發育出一個尿囊，這是一個從雛鳥腸道底部生長出來的空心囊。

From there， the pouch fuses to the second membrane （the chorion） that's around the yolk， forming a chorioallantoic membrane. Working similarly to lung tissue， it connects the baby bird's circulatory system to the air outside the egg.As the embryo develops， it breathes in oxygen via that membrane and exhales carbon dioxide （CO2）. The hollow part of the allantois can also be used to store waste containing nitrogen.

隨后，這個囊與包裹蛋黃的第二層膜（絨毛膜）融合，形成絨毛尿囊膜。它的功能類似于肺組織，將幼鳥的循環系統與蛋外的空氣連接起來。隨著胚胎的發育，它通過該膜吸入氧氣并排出二氧化碳。尿囊的空心部分還可用于儲存含氮廢物。

Several thousand microscopic pores all over the surface of the bird egg allow the CO₂ to escape and fresh air to get in.These pores also allow moisture to get into the egg to keep developing bird and the egg parts from drying out， which is why hard-boiled eggs always feel a little heavier than rawones.

鳥蛋表面遍布數千個微小的氣孔，使二氧化碳得以排出，新鮮空氣得以進入。這些氣孔還能讓水分進入蛋內，防止發育中的幼鳥和蛋內部分變干，這也是為什么煮熟的雞蛋總比生雞蛋感覺稍重一些。

What becomes of that chorioallantoic membrane after the baby bird hatches？ It stays attached to the eggshell. Your chances of seeing it in an unfertilized egg-like the one you're scrambling for breakfast—are pretty low， since it exists only when a fertilized embryo begins developing. If there's no baby bird inside the egg，you won't be getting it as a morning side dish.

幼鳥孵化后，絨毛尿囊膜會怎樣呢？它會附著在蛋殼上。你在未受精的蛋（如早餐煎蛋）中看到它的概率相當低，因為它只在受精胚胎開始發育時存在。如果蛋內沒有幼鳥，你也不會在早餐時吃到它。

WordBank

shrink /frink/ v. 收縮，縮小 pore 氣孔 hatch /haetf/ v. 孵出；孵化 beattachedto依附于，附屬于