Destructor not called with forward declaration instead of include

Say you have these files:

BigClazz.h

     class Clazz; // Note the forward declaration only , no include
"Clazz.h"
     class BigClazz
     {
         public:
             BigClazz();
             ~BigClazz();
             Clazz* pclazz;
     };

BigClazz.cpp

     #include "BigClazz.h"
     BigClazz::BigClazz(){}
     BigClazz::~BigClazz()
     {
         delete pclazz; // Here the destructor of of the Clazz object
will not be called
     }

Clazz.h

     class Clazz
     {
         public:
             Clazz();
             ~Clazz();
     };

Clazz.cpp

     #include "Clazz.h"
     Clazz::Clazz(){};
     Clazz::~Clazz(){};

main.cpp

     int main(int argc, char *argv[])
     {
         BigClazz* pVM = new BigClazz();
         pVM->pclazz = new Clazz();
         delete pVM;
     }

If you run this you'll see that the Clazz destructor will not be
called when BigClazz does "delete pclazz;" in it's own destructor. But
if you replace the forward declaration in BigClazz (class Clazz;) with
an include
(#include "Clazz.h") then it works.

Any idea why?

Thanks
Eric

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