  Let U be a simply connected domain on the Riemann sphere whose complement K
contains more than one point. We establish a characterization of local
connectivity of K at a point in terms of the prime ends whose impressions
contain this point. Invoking a result of Ursell and Young, we obtain an
alternative proof of a theorem of Torhorst, which states that the impression of
a prime end of $U$ contains at most two points at which $K$ is locally
connected.
