2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/15485Recent observations have revealed the presence of a variety of small-scale ``micro-structures'' in Planetary Nebulae images. I discuss numerical hydrodynamics models of planetaries and outline the formation and growth of instabilities that may be seen in these models. It is possible that these may be the forerunners of some of the observed small-scale structures.4 pages, including 3 embedded figures. To appear in ``Asymmetrical Planetary Nebulae II: from Origins to Microstructures,'' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N. Soker, & S.A. Rappaport, edsAstrophysicstext