The wing blade of Drosophila melanogaster is composed of dorsal and ventral surfaces covered with hairs and rows of morphologically distinct bristles round the margin. The mutant shaggy causes a complete transformation of hairs into bristles over the entire wing surfaces. Clones of mutant bristles have a tendency to line up into straight bristle rows. Clones are straight and orderly near the wing margin but form bundles and vesicles when a long distance from the margin. Furthermore the bristle cells move distally along the future wing blade in the general direction of the margin. From these studies, we postulate the existence of a gradient of cell affinities for bristle cells that is maximal at the dorsoventral wing margin and decreases with distance away from it. The bristle clones also move onto the wing veins and often induce the formation of new veins in the surrounding shaggy+ cells. These new veins run from the clone and join up to existing veins. We conclude that there is a close relationship between bristles and veins.

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