  We present decompositions of the rotation curves of distant spiral galaxies
into contributions due to their bulges, disks, and putative dark haloes. In
order to set constraints on the ambiguities of the decompositions we interpret
the morphology of the spiral structures quantitatively in the framework of
density wave theory. Galaxy models constrained in such a way show that the
distant galaxies, which are much younger than nearby galaxies, are indeed also
imbedded in dark haloes as expected from contemporary theories of the cosmonogy
of galaxies.
