  The problem of the gas-liquid heterophase fluctuations of a fluid within the
critical and supercritical regions is revisited. To describe the thermodynamics
and structure of the heterophase fluid, the mesoscopic equation of state is
deduced. The mesoscopic scale is connected with the sizes of the mixed bubbles
and droplets (g-fluctuons and l-fluctuons). The two-component order parameter
of the heterophase fluid describes the gas-like and liquid-like fractions. Its
interconnection with the van der Waals order parameter is ascertained. The
non-symmetric Ising-type equation of state of the heterophase fluid is analyzed
using the standard methods. The manifestations of the mesoscopic effects in the
structural and thermodynamic properties of the fluid are investigated. The
domain of applicability of a classical model is found using the mesoscopic
Ornstein-Zernike equation. The asymmetry and non-analyticity of the diameter of
the phase coexistence curve is researched. It is shown that that the critical
non-analyticity of the diameter is induced by the mesoscopic heterophase
fluctuations. The percolation thresholds of the droplets and bubbles in the
critical and supercritical fluid are determined. On the phase diagrams they
bound the domains of applicability of the droplet model.
