Cover legend: Coronal view of one hemisphere of a reeler mutant mouse brain produced by merging four pseudocolored micrographs taken at the level of the primary somatosensory “barrel” cortex. Cells are labeled with markers that in wild-type mice identify distinct cortical layers: yellow, layer II/III; green layer IV; blue, layer V. In situ hybridization for these markers in the reeler brain reveals a more-or-less random expression pattern, rather than distinct layers. This challenges the hypothesis that reeler cortex develops in an “outside-in” pattern, according to which the cortical layers should be present, but inverted. The immediate early gene c-Fos (red) identifies cells activated after exploration of a novel environment. For more information, see the article by Wagener et al. in this issue (pages 15700–15709).