Abstract1Urotensin II (bladder‐contracting activity) is present in the caudal spinal cords of teleosts, elasmobranchs, holosteans, and chondrosteans, in order of decreasing activity. It is questionably present in holocephalans and probably absent from lungfishes.2Cyclostomes and tailed amphibians show no evidence for any specific caudal urotensin II.3The pharmacological evidence parallels the cytological evidence for the occurrence of a caudal neurosecretory syste