  To investigate the relationship between the pseudogap and superconductivity,
we measured both the in-plane ($\rho_{ab}$) and out-of-plane ($\rho_c$)
resistivity for oxygen-controlled Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$
single crystals subject to magnetic fields (parallel to the $c$ axis) of up to
17.5 T. The onset temperature for the superconductive fluctuation, $T_{scf}$,
is determined by the large positive in-plane magnetoresistance (MR) and
negative out-of-plane MR observed near $T_c$, whereas the pseudogap opening
temperature $T^*$ is determined by the semiconductive upturn of the zero-field
$\rho_c$. $T_{scf}$ was found to scale roughly as $T_c$, with a decreasing
temperature interval between them upon doping. On the other hand, $T^*$ starts
out much higher than $T_{scf}$ but decreases monotonically upon doping;
finally, at a heavily overdoped state, it is not observed above $T_{scf}$.
These results imply that the pseudogap is not a simple precursor of
superconductivity, but that further study is needed to determine whether or not
$T^*$ exists below $T_{scf}$ in the heavily overdoped state.
