egg sac

例句：

1. 1. The chicken was laying an egg in the nest.
   那只鸡正在巢里下蛋。
2. 2. The egg sac is a protective covering for the developing embryo inside the egg.
   蛋壳是胚胎在蛋内发育的保护层。
3. 3. The bird carefully removed its egg sac to inspect the contents.
   这只鸟小心翼翼地取出蛋壳，检查里面的内容物。