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Abstract:
Polarization orientation in the bee is limited to short wavelengths (Frisch, 1967; Heiversen and Edrich, 1974). Although each ommatidium contains three UV-receptors (two long and a short retinula cell) only the short and proximally located ninth retinula cell has a high sensitivity to the plane of polarized light (Menzel and Snyder, 1974).
A map over the dorsal eye of the microvillar orientations of the ninth cells was constructed using special fixation techniques that results in minimum distortion of rhabdomeric structures (Ribi, 1979).
In a region between the 5th and the 45th horizontal ommatidial row (counted from the top) three ninth cell types (X, V, Y) according to their microvilli directions, were found. One third of 119 observed ninth cells (type X cells) have their microvilli arranged 52°±7° S.D. to the z-axis. A second third of ninth cells (type V cells) have their microvilli 89°±7° S.D. to the z-axis whereas the remaining third of ninth cells (type Y cells) have their microvilli 127°±7° S.D. to the z-axis.
The analysis of polarization information based on simultaneous measurements requires at least three inputs for an unambiguous e-vector detection (Kirschfeld, 1972). The pattern of ommatidia as described here is such that three adjacent ommatidia always have ninth cells with three different microvilli directions. It is suggested that such a triplet of ommatidia represents a unit capable of unambiguous e-vector detection.
