E14 to E15 and survival to postnatal day (P)5 (anterior)
Figure 13 is a slice through the main olfactory bulb on P5 showing the adult layering pattern. On the morning of E14, most main bulb mitral cells are labeled; an occasional cell is unlabeled. Note the lack of heavily labeled cells in the internal plexiform layer compared to the E21 specimen in Figure 12; that indicates that few to no mitral cells are still migrating on P5. The granule cells themselves are mostly unlabeled because of extensive label dilution; they will be generated much later. The immature cells in the core of the olfactory bulb and in the presumptive rostral migratory stream all appear to be unlabeled, but that is because of extensive label dilution. Thus, on the morning of E14, most main bulb neuronal populations are still proliferating in their respective germinal matrices.