How do hormones influence regeneration in earthworms and other annelids?

In annelids, including earthworms and polychaetes, the brain serves as a critical center for hormonal control of regeneration.

Specific hormones secreted by neurosecretory cells in the brain are essential for the process, particularly for posterior regeneration. In certain polychaetes, such as Nereis, regeneration cannot occur unless the brain is present; experiments have shown that mature worms require the implantation of brains from younger individuals to successfully regenerate lost parts.12

While the brain's influence on regeneration is well-documented, researchers suggest the effect may sometimes be indirect, potentially involving other hormonal pathways such as genital inhibiting hormones. Additionally, the brain's role in these organisms is multifaceted, as it also regulates other vital life cycle processes, including reproduction, growth, and osmoregulation. The hormonal regulation of these systems highlights the complex integration of the central nervous system in managing the physiological demands of tissue replacement.21