Thus it was in Messina that the great event of my scientific life took place. A zoologist until then, I suddenly became a pathologist. I entered into a new road in which my later activity was to be exerted. It is with warm feeling that I evoke that distant past and with tenderness that I think of Messina, of which the terrible fate has deeply moved my heart. They say that Messina will be rebuilt in the same place but in a different way. Houses will be constructed of light materials, they will be low, and the streets broad.... The town will be a new Messina, not "my Messina," not that with which so many dear memories are associated in my mind.... Metchnikoff continued to study intracellular digestion and the origin of the intestine. He foresaw that the solution of those problems would lead to general results of great importance. The study of medusæ and of their mesodermic digestion confirmed him more and more in the conviction that the mesoderm was a vestige of elements with a primitive _digestive_ function. In lower beings, such as sponges, this function takes place without being differentiated, whilst with other Coelentera and with some Echinoderma the _endoderm_ gives birth to a digestive cavity; yet, the mobile cells of the _mesoderm_ preserve their faculty of intracellular digestion. As he studied these phenomena more closely, he ascertained that mesodermic cells accumulated around grains of carmine introduced into the organism. All this prepared the ground for the phagocyte theory, of which he himself described the inception in the following words: I was resting from the shock of the events which provoked my resignation from the University and indulging enthusiastically in researches in the splendid setting of the Straits of Messina. One day when the whole family had gone to a circus to see some extraordinary performing apes, I remained alone with my microscope, observing the life in the mobile cells of a transparent star-fish larva, when a new thought suddenly flashed across my brain. It struck me that similar cells might serve in the defence of the organism against intruders. Feeling that there was in this something of surpassing interest, I felt so excited that I began striding up and down the room and even went to the seashore in order to collect my thoughts. I said to myself that, if my supposition was true, a splinter introduced into the body of a star-fish larva, devoid of blood-vessels or of a nervous system, should soon be surrounded by mobile cells as is to be observed in a man who runs a splinter into his finger. This was no sooner said than done. There was a small garden to our dwelling, in which we had a few days previously organised a "Christmas tree" for the children on a little tangerine tree; I fetched from it a few rose thorns and introduced them at once under the skin of some beautiful star-fish larvæ as transparent as water.