  This work is an attempt to tie together some of the, seemingly disparate,
loose ends from the preceding papers in this series into the global view of
dust evolution in the interstellar medium. In particular, the nature of the
hydro-carbonaceous, infrared absorption and emission band carriers is discussed
within the context of a simple poly- hexa-cyclic molecular view. The sequence
of interstellar dust mantle accretion and grain- grain coagulation into
aggregates, and their consequences for the interstellar dust size distribution,
extinction and dust thermal emission, is explored. The effects of accretion and
coagulation on the interstellar gas-to-dust ratio in the Milky Way and in
distant galaxies are estimated. The importance of interstellar grain-surface
epoxide species is re-visited and the likely and consequent connection between
dense interstellar cloud dust and cometary dust explored. A possible connection
between and the origin of the suite of interstellar OCN-containing molecules,
and their interesting chemistry, is discussed. Finally, pathways to amino acid
formation and their likelihood as a universal basis for life everywhere in the
universe is speculated upon.
