  We construct doubly periodic Stokes flows in two dimensions using elliptic
functions. This method has advantages when the doubly periodic lattice of
obstacles has less than maximal symmetry. We find the mean flow through an
arbitrary lattice in response to a pressure gradient in an arbitrary direction,
and show in a typical example that the shorter of the two period lattice
vectors is an "easy direction" for the flow, an eigenvector of the conductance
tensor corresponding to maximal conductance.
