  We combine deep optical and IR photometry for 326 spiral galaxies from two
recent galaxy samples and report that the surface brightness profiles of
late-type spirals are best fit by two exponentials. Moreover, the ratio of
bulge and disk scale lengths takes on a restricted range of values and is
uncorrelated with Hubble type. This suggests a scale-free Hubble sequence for
late-type spirals. Careful numerical simulations ensure that our results are
not affected by seeing or resolution effects. Many of these galaxies show
spiral structure continuing into the central regions with a previously
undetected small bar and slowly changing colors between the inner disk and the
bulge. We invoke secular dynamical evolution and interpret the nature of disk
central regions in the context of gas inflow via angular-momentum transfer and
viscous transport. In this scenario, galaxy morphologies in late-type spirals
are not imprinted at birth but are the result of evolution.
