It has become increasingly clear that the central nervous system is not a passive entity determined by either environment or heredity. Rather, the brain appears to interact with its environment throughout early and late development and thereby contributes to its own structural and functional systems. This study focuses on the role played by neuropeptides in the ontogeny of nervous systems from conception through death. The authors begin with a review of the role of neuropeptides in the pathology of aging. They then examine the family of insect neuropeptides which controls development, with special attention to the gypsy moth. Other topics include the biosynthesis and processing of neuropeptides during development; the regulation of mitogenesis, cell survival, and embryonic growth; the role of target issues; and the role of neuropeptides in the ontogeny of the brain systems involved in the stress response. The authors' findings have important implications for understanding the biological underlay of adaptation and coping mechanisms as well as for model development and treatment.