Thin sections through a single ommatidium from a wild-type or mutant Drosophila eye, immunolabeled for rhodopsin. The eyes were fixed in 3% glutaraldehyde, osmicated, and embedded in Spurr’s resin (a,b; wild-type) or fixed in 4% formaldehyde and embedded in LR White (c,d; mutant). (a) Each ommatidium contains seven rhabdomeres. (b) Rhabdomeres 1-6 express rhodopsin, while rhabdomere 7 does not. (c) In the mutant eye, ommatidia are deleted or altered. (d) The rhabdomeres are also structurally altered, but their staining pattern for rhodopsin remains unchanged, with no expression of rhodopsin in rhabdomere 7. Bars, 200 nm. (Reprinted with permission from Scion Publishing Ltd. © 2006.)