private void listaDeRazasToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (listaraza == null)
     {
         listaraza             = new frmListaRazas();
         listaraza.MdiParent   = this;
         listaraza.FormClosed += new FormClosedEventHandler(listaRaza_FormClosed);
         listaraza.Show();
     }
 }
 void listaRaza_FormClosed(object sender, EventArgs e)
 {
     listaraza = null;
 }