  In this Comment on the paper by W. Apel and Yu. A. Bychkov, cond-mat/9610040
and Phys. Rev. Lett. 78, 2188 (1997), we draw attention to our prior
microscopic derivations of the Hopf term for various systems and to
shortcomings of the Apel-Bychkov derivation. We explain how the value of the
Hopt term prefactor $\Theta$ is expressed in terms of a topological invariant
in the momentum space and the quantized Hall conductivity of the system. (See
also related paper cond-mat/9703195)
