Like many other first-order olfactory centers, the olfactory lobe of the moth brain is organized into histologically conspicuous synaptic glomeruli delimited by glial cells. These glomeruli in the moth offer an advantageous system in which to study the parcellation of central neuropils during development. In this article, we review the evidence that glial cells play an essential role in the induction of glomeruli by olfactory sensory axons, and we present new evidence that leads us to propose that a major role for glia in the development of glomeruli is to define for ingrowing dendrites of second-order olfactory neurons edges that lead to the formation of these cells' characteristic morphology.