They have more air sacks than just the lungs.

他们有比肺更多的气囊。

Their vertebrae are complex and many of them have cavities inside for air sacks.

它们的椎骨很复杂，其中许多内部有空腔供气囊使用。

Now this doesn't have enough water for it to float, but if the egg sinks, that means the air sack is not yet developed in the egg.

现在没有足够的水让它漂浮，但是如果鸡蛋下沉，这意味着气囊还没有在鸡蛋里形成。