  A gas of electrons confined to a plane is examined in both the relativistic
and nonrelativistic case. Using a (0+1)-dimensional effective theory, a
remarkably simple method is proposed to calculate the spin density induced by
an uniform magnetic background field. The physical properties of possible
fluxon excitations are determined. It is found that while in the relativistic
case they can be considered as half-fermions (semions) in that they carry half
a fermion charge and half the spin of a fermion, in the nonrelativistic case
they should be thought of as fermions, having the charge and spin of a fermion.
