[en] In this paper we reconsider a problem treated originally by Goldreich and Lynden-Bell: that of the development of localized structure in media possessing velocity shear. The paper has two broad divisions. In the first portion, we examine a Cartesian version of Jeans's classical problem of the gravitational stability of a uniform medium with a constant velocity shear in which the waves modes and the vorticity mode are treated on an equal footing. Employing a Lagrangian formalism, we show that short-wavelength vorticity perturbations would experience transient growth followed by decay. However, under favorable circumstances, disturbances of longer wavelength could undergo spectacular growth. The initial development of these interesting perturbations is due to shearing effects, but their subsequent growth is controlled by self-gravitation. There exists a striking similarity between the evolution of the wave modes and the vorticity mode. Indeed, the modes become indistiguishable when self-gravitation becomes dominant