The ventral nerve cord of holometabolous insects is reorganized during metamorphosis. Certain elements, however, persist from the larval to the adult stage. A group of dorsal unpaired median neurons and a set of thoracic serotonin-immunoreactive interneurons are shown to be persistent elements in the ventral nerve cord of Tenebrio molitor. These persistent neurons retain their "bauplan" even after deprivation of the sensory neurons projecting onto them. These persistent neurons might provide a network into which newly developing sensory neurons fit during reorganization of the nervous tissue.