Effect of hydrocortisone on the axial organ of the sea star Asterias rubens.
Sea stars Asterias rubens were inoculated daily with hydrocortisone. After 3 days a plaque of lysis was formed in the center of the axial organ and increased in size if the injections were continued for 2 more days. This result is reminiscent of the effect of cortisone on the thymus of vertebrates and supports the hypothesis that the axial organ is an ancestral lymphoid tissue.