We propose an alternative interpretation of the arcs in the nebular X-radiation observed by Pavlov et al (2000) & Helfand et al (2001) with the Chandra Observatory, and interpreted by the latter as an equatorial wind. We find that the bright arcs, the jet-like feature and the diffuse components in the Vela X-ray nebula can be explained together in detail by our model in which the arcs are understood as traces of the particle beams from the two magnetic poles at the shock front. We consider this as an important evidence for collimated particle beams for pulsars. We discuss the observed variability in features in the Vela X-ray nebula, and assess the relevance and implication of our model to the observations on the Crab and other remnants.