The right testis lobe (50g in weight)，removed at the time of death (12 June，2000) from a senile，23 year-old Californian sea lion, Zalophus californianus, reared in the Niigata City Aquarium，was examined histologically．The epithelium of the seminiferous tubules in the testicular part comprised primary spermatocytes and a few Sertoli (sustentacular) cells．However，relict sperm and spermatids were occasionally detected in the wide lumen of the seminiferous tubules and also in the epididymal duct．These confirmed the senile, quiescent state of the animal，the testis lacking active spermatogenic and spermiogenic cells.