  Semiclassical periodic-orbit theory (POT) is applied to the physics of
nuclear structures, with the use of a realistic nuclear mean-field model given
by the radial power-law potential. Evolution of deformed shell structures,
which are responsible for various nuclear deformations, are clearly understood
from the contribution of short classical periodic orbits (POs). Bifurcations of
short POs, which imply underlying local dynamical symmetry, play significant
role there. The effect of the spin degree of freedom is also investigated in
relevance to the pseudospin symmetry in spherical nuclei and the prolate-oblate
asymmetry in shell structures of nuclei with quadrupole-type deformations.
