Élie Metchnikoff was a Russian zoologist best known for his pioneering research in immunology. In particular, he is credited with the discovery of phagocytes. In 1882 he studied strange freely moving cells in the larvae of starfishes. He started to believe that they were important to the animals' immune defenses. To test his idea, Metchnikoff inserted small thorns from a tangerine tree into the larvae. After a few hours he noticed that the motile cells had surrounded the thorns.