  The distribution of galaxy morphological types is a key test for models of
galaxy formation and evolution, providing strong constraints on the relative
contribution of different physical processes responsible for the growth of the
spheroidal components. In this paper, we make use of a suite of semi-analytic
models to study the efficiency of galaxy mergers in disrupting galaxy discs and
building galaxy bulges. In particular, we compare standard prescriptions
usually adopted in semi-analytic models, with new prescriptions proposed by
Kannan et al., based on results from high-resolution hydrodynamical
simulations, and we show that these new implementations reduce the efficiency
of bulge formation through mergers. In addition, we compare our model results
with a variety of observational measurements of the fraction of
spheroid-dominated galaxies as a function of stellar and halo mass, showing
that the present uncertainties in the data represent an important limitation to
our understanding of spheroid formation. Our results indicate that the main
tension between theoretical models and observations does not stem from the
survival of purely disc structures (i.e. bulgeless galaxies), rather from the
distribution of galaxies of different morphological types, as a function of
their stellar mass.
