Adult neurogenesis in the olfactory bulb of rodents is provided by cells which migrate tangentially from their site of genesis into the forebrain subependymal layer (SEL). This migration involves 'chains' of neuroblasts sliding into a meshwork of astrocytic cells and processes (glial tubes). The analysis of this process in postnatal rodents and in adult rabbits reveals different types of relationships occurring both among the migrating cells and between these cells and the glial structures of the SEL.