[On the formation of eye pigment granules after feeding ommochrome precursors toDrosophila v andcn].

In the mutantsv andcn ofDrosophila, which contain neither ommochrome pigment nor "empty" pigment granules, feeding of kynurenine or 3-hydroxy-kynurenine causes the formation of pigment granules which cannot be distinguished from wild type granules. Their larger diameter is about 0.4 μ, they are surrounded by a membrane, and their growth rate is identical.Measurement of growing pigment granules in proximal and more distal regions of the ommatidia has revealed a significant difference in size which can be recognized as early as 48 hours after pupation.