Houseflies ( Musca domestica) at 12 to 32 hr postoviposition showed a 19% decrease in the amount of stainable material in the median neurosecretory cells (MNC), but insects ovariectomized after oviposition had a 48% decrease in stained material by 2 hr postoviposition, which persisted. This decrease in neurosecretory material (NSM) from the neurosecretory cells after oviposition and ovariectomy was followed by a 45% increase in the synthesis of NSM. Implanting ovaries into flies after oviposition and ovariectomy lessened the decrease in the amount of stained NSM from the MNC by 20 to 40%. Insects that had their ring glands removed (-RG) during the late vitellogenic phase in the first gonotrophic cycle developed mature eggs in the first cycle, but when these eggs were oviposited, the second cycle of eggs was not activated and did not develop past stage 4 or 5, and the amount of stained material in the MNC decreased 45%. However, the -RG flies allowed to retain mature eggs in the first cycle did not show a decrease in stained NSM. Thus, storage and release of NSM is independent of the ring gland but dependent upon activated ovaries. The data suggest that the oöstatic hormone is produced by NSM-activated ovaries which prevent the further release of NSM. Thus, when oviposition removes the source of oöstatic hormone, NSM is released, which activates the next gonotrophic cycle to develop and to produce oöstatic hormone. This interaction of NSM release with oöstatic hormone production maintains the cyclicity of egg development in houseflies.