  The production at central rapidity of K0s, Lambda, Xi and Omega particles in
Pb-Pb collisions at 158 A GeV/c has been measured by the NA57 experiment over a
centrality range corresponding to the most central 53% of the inelastic Pb-Pb
cross section. We present the rapidity distribution of each particle in the
central rapidity unit. The distributions are analysed based on hydrodynamical
models of the collisions.
