  We present results of numerical N-body simulations of a galactic stellar disk
embedded into a spherical dark halo. The non-linear dynamics of bending
instabilities developing in the disk is studied. The bending modes,
axisymmetric and not, are considered as main factors increasing the disk
thickness. The relation between the disk vertical scale height and the
halo+bulge-to-disk mass ratio is inferred. The method of estimation of the
spherical-to-disk mass ratio for edge-on spiral galaxies based on this relation
is studied and applied to constrain the spherical subsystem mass and the mass
of dark halos (M_h/M_d) in seven edge-on galaxies. The values of M_h/M_d are of
order 1 for our galaxies.
