  Adapting ideas of Daubechies and Klauder we derive a continuum path-integral
formula for the time evolution generated by a spin Hamiltonian. For this
purpose we identify the finite-dimensional spin Hilbert space with the
ground-state eigenspace of a suitable Sch\"odinger operator on
$L^2({\mathbb{R}}^2)$, the Hilbert space of square-integrable functions on the
Euclidean plane ${\mathbb{R}}^2$, and employ the Feynman-Kac-It\^o formula.
