  We discuss the similarities and differences for the theories of Rapp, Wambach
and collaborators (called R/W in short) and those based on Brown-Rho scaling
(called B/R), as applied to reproduce the dileptons measured by the CERES
collaboration in the CERN experiments. In both theories the large number of
dileptons at invariant masses $\sim$~$m_\rho/2$ are shown to be chiefly
produced by a density-dependent $\rho$-meson mass. In R/W the medium dependence
is dynamically calculated using hadronic variables defined in the matter-free
vacuum. In B/R scaling it follows from movement towards chiral symmetry
restoration due to medium-induced vacuum change, and is described in terms of
constituent (or quasiparticle) quarks. We argue that the R/W description should
be reliable up to densities somewhat beyond nuclear density, where hadrons are
the effective variables. At higher density there should be a crossover to
constituent quarks as effective variables scaling according to B/R. In the
crossover region, the two descriptions must be ``dual''.
