Electron micrographs of axons in the P0 and adult ONL. (A,C) Axons within the P0 ONLo are of roughly uniform diameter. (B,D) Axons within the P0 ONLi are larger than those seen in the P0 ONLo. (E) Axons within the adult ONLo are approximately the same size seen in the P0 ONLo. (F) Axons within the adult ONLi are larger than those in the adult ONLo, but smaller than those in the P0 ONLi. Scale bar = 500 nm in A,B,E,F; 1 μm in C,D. Abbreviations: ONLo, outer olfactory nerve layer; ONLi, inner olfactory nerve layer.