98. In the tetrahedron $ABCD$, edge $AB$ is perpendicular to edge $CD$, $\widehat{ACB} = \widehat{ADB}$, the area of the section passing through edge $AB$ and the midpoint of edge $DC$ is $S$, $|DC| = a$. Find the volume of the tetrahedron $ABCD$.
98. From the equality $\widehat{A C B}=\widehat{A D} B$ and the perpendicularity of $A B$ and $D C$, it can be derived that points $C$ and $D$ are symmetric with respect to the plane passing through $A B$ and perpendicular to $C D$.

Answer: $\frac{a S}{3}$.