  The stability of the shell of wrapped D6-branes on K3 is investigated from
the point of view of supergravity. We first construct an effective
energy-momentum tensor for the shell under the reasonable conditions and show
that supersymmetric solutions satisfy Israel's junction conditions at arbitrary
radius of the shell. Next we study the perturbation of the whole system
including the self-gravity of the shell. It is found that in spite of the
existence of wrapped D6-branes with negative tension, there is no eigenmode
whose frequencies of the shell and the fields are imaginary numbers, at any
radius of the shell. Furthermore, when the radius of the shell is less than the
enhan\c{c}on radius, resonances are produced, and this indicates a kind of
``instability'' of the system. This can even classically explain why the shell
is constructed at the enhan\c{c}on radius.
