A polarity field is established early in the development of the Drosophila compound eye

The photoreceptors within the ommatidia of the Drosophila compound eye form a trapezoid. This occurs in two chiral forms in the dorsal and ventral half of the eye. We have used two manipulations to induce ectopic ommatidia, in combination with molecular markers for specific positions in the retinal field. We find that ectopic morphogenetic furrows induced on the eye field margin (or midline) and those induced in the body of the field have different consequences for the establishment of retinal polarity. Furthermore, the dorsal/ventral vector field is established early in development, prior to and independent of the initiation of the morphogenetic furrow. An 'early equator' model is presented to account for these and previously published data.