Several authors have suggested that radio jet morphologies resolved in extragalactic sources are the effects of large-scale Kelvin-Helmholtz instabilities in high-speed, pressure-confined fluid beams ejected from parent active galactic nuclei (Ferrari et al. 1978, 1979, 1981; Hardee 1979;Benford et al. 1980). In particular results from studies for cylindrical geometries indicate how to connect the “wiggles” (observed in 3C449, NGC 6251, M87 and Cen A) with helical perturbations and the “knots” (observed in NGC 315, M87, Cen Aetc.) with pinching modes. Correspondingly small scale MHD perturbations, generated by the same instability or nonlinear cascade processes, are efficient in accelerating relativistic electrons via stochastic scatterings (Lacombe 1977; Ferrari et al. 1979). This picture may satisfy both the requirements for in situ re-acceleration and the intrinsic correlation between morphology and emission.