The influence of mutations in seven neurological genes on the number of fibers in the anterior optic tract (AOT) ofDrosophila melanogasterhas been investigated. It is shown that the number of fibers in the AOT can be drastically reduced in single and especially in multiple mutants. However, no evidence for synergistic interactions between the sample of mutations used in thesine oculis(so),reduced optic lobes(rol),minibrain(mnb), andsmall optic lobes(sol) genes was obtained at the level of the AOT. TherolKS222andsomutations eliminate similar fiber sets in the AOT, which are distinctly different from those eliminated bysolKS58andmnb1.