  The spherical gravitational collapse and virialization of arbitrary density
fluctuations in an expanding universe is studied. In the context of the
standard cosmological model and the peak $ansatz$, disk galaxies are supposed
to be the product of "extended" gravitational collapses of regions surrounding
local-maxima of the density fluctuation field. The substructure over the main
profile (merging) is considered as a second-order phenomenon. The range and
distribution of possible mass growth histories or accretion regimes for a given
present-day mass are estimated and used as the initial condition for galaxy
formation. Considering the effect of dark halo contraction due to disk
formation, the final rotation curves are calculated. If the structural
properties of dark halos are important in establishing the Hubble sequence's
properties of visible galaxies, then this sequence is defined not only by the
mass, but among other possible parameters, by the accretion regime.
