  We propose to use Fermi-Dirac distributions for quark and antiquark partons.
It allows a fair description of the $x$-dependence of the very recent NMC data
on the proton and neutron structure functions $F_2^p(x)$ and $F_2^n(x)$ at
$Q^2=4$ GeV$^2$, as well as the CCFR antiquark distribution $x\overline q(x)$.
We show that one can also use a corresponding Bose-Einstein expression to
describe consistently the gluon distribution. The Pauli exclusion principle,
which has been identified to explain the flavor asymmetry of the light-quark
sea of the proton, is advocated to guide us for making a simple construction of
the polarized parton distributions. We predict the spin dependent structure
functions $g_1^p(x)$ and $g_1^n(x)$ in good agreement with EMC and SLAC data.
The quark distributions involve some parameters whose values support well the
hypothesis that the violation of the quark parton model sum rules is a
consequence of the Pauli principle.
