  The representation of quark distribution and fragmentation functions in terms
of non-local operators is combined with a simple spectator model. This allows
us to estimate these functions for the nucleon and the pion ensuring correct
crossing and support properties. We give estimates for the unpolarized
functions as well as for the polarized ones and for subleading (higher twist)
functions. Furthermore we can study several relations that are consequences of
Lorentz invariance and of C, P, and T invariance of the strong interactions.
