Here's why:
* Fetal lungs are not functional: Fetal pigs, like human fetuses, receive oxygen and nutrients through the placenta, not their lungs. Their lungs are underdeveloped and don't have air inside.
* Density: The lung tissue itself is made of cells and other biological materials. Without air, the lung tissue is denser than water, causing it to sink.
* Air increases buoyancy: Once a baby pig takes its first breath, air fills the alveoli in the lungs. This air increases the buoyancy of the lung tissue, making it less dense than water and causing it to float.
In summary, the lung tissue of a fetal pig sinks because it lacks the air that would make it buoyant.