  We summarize results of our {\it HST} imaging survey of proto-planetary
nebula (PPN) candidates, in which we discovered two types of axisymmetric
reflection nebulosities. The Star-Obvious Low-level-Elongated (SOLE) nebulae
show a bright central star embedded in a smooth, faint extended nebulosity,
whereas the DUst-Prominent Longitudinally-EXtended (DUPLEX) nebulae have
remarkable bipolar structure with a completely or partially obscured central
star. The intrinsic axisymmetry of the PPN reflection nebulosities demonstrates
that the axisymmetry often found in planetary nebulae predates the PPN phase.
We suggest that the major cause for the apparent dual morphology is the optical
depth difference in the circumstellar dust shell rather than the inclination
angle effect.
