Do Monarch butterflies have a polarization compass?

Fig. 2:

Light micrograph (left) and electron micrographs (right) of histological cross-sections of ommatidia in the dorsalmost part of the compound eye. The ommatidia of the dorsal rim area (upper half) have rectangular rhabdoms with straight microvilli of only two, mutually othogonal directions whereas the rounded rhabdoms of the regular ommatidia (lower half) contain partly curved microvilli.