  After a brief review of the experimental results obtained in deep inelastic
lepton-nucleon scatterings and the Drell-Yan processes and their implications
for the spin and flavor contents of the nucleon, we suggest that those
features, that are contrary to the expectations of the naive quark model, can
all be accounted for in the chiral quark model of Georgi and Manohar. In our
formulation of the chiral quark model, the $\eta ^{\prime }$ meson is seen to
play an important role.
