Immunity and the Invertebrates The fabulously complex immune systems of humans and other mammals evolved over hundreds of millions of years—in sometimes surprising ways

n December 1882 a 37-year-oldRussian zoologist named ElieMetchnikoff took a fateful strollalong the beach in Messina, a town onSicily’s northeastern coast. Returning tohis cottage with the tiny, transparentlarva of a common starfish, he piercedthe creature with a rose thorn. When heexamined it the next morning, he sawminute cells covering the thorn and at-tempting to engulf it.He immediately recognized the sig-nificance of this observation