  We address the deviations of the scaling relations of elliptical galaxies
from the expectations based on the virial theorem and homology, including the
"tilt" of the "fundamental plane" and the steep decline of density with mass.
We show that such tilts result from dissipative major mergers once the gas
fraction available for dissipation declines with progenitor mass, and derive
the scaling properties of the progenitors. We use hydrodynamical simulations to
quantify the effects of major mergers with different gas fractions on the
structural properties of galaxies. The tilts are driven by the differential
shrinkage of the effective stellar radius as a function of dissipation in the
merger, while the correlated smaller enhancements in internal velocity and
stellar mass keep the slope of the velocity-stellar mass relation near V \pr
M_*^{1/4}. The progenitors match a straightforward model of disc formation in
LCDM haloes. Their total to stellar mass ratio within the effective radius
varies as M/M_* \pr M_*^-0.25, consistent with supernova feedback. They are
nearly homologous in the sense that the dark-matter fractions within the
effective and virial radii scale with mass in a similar way, with only a weak
decline of density with mass. The progenitor radius is roughly R \pr M_*^0.3,
compatible with today's intermediate late-type galaxies. This indicates that
the latest wet mergers involved relatively big discs. The dissipative gas to
stellar mass ratio is predicted to decline \pr M_*^-0.5, similar to the
observed trend in today's blue sequence galaxies. Such a trend should be
observed in relatively massive gaseous galaxies at z~1-4. The corresponding
"baryonic" relations are consistent with homology and spherical virial
equilibrium, V \pr R \pr M_b^1/3.
