14. From an arbitrary tetrahedron, four smaller tetrahedra are separated by four planes passing through the midpoints of the edges emanating from each vertex. Calculate the ratio of the volume of the remaining body to the volume of the original tetrahedron.
14. Each of the separated tetrahedra is homothetic to the original with a coefficient of $\frac{1}{2}$, so its volume is $\frac{1}{8}$ of the volume of the tetrahedron. Since a total of 4 tetrahedra are removed, each pair of which does not share any internal points, it means that half of the volume has been removed. Therefore, the volume of the remaining body is half of the volume of the given tetrahedron.