Thus the link between the unicellular and the multicellular beings could be constituted through the intermediary of flagellated colonies on the one hand and, on the other hand, of beings similar to a _phagocytella_. The _indivisible colony_ became the _multicellular individual_. While studying the genealogy of beings, Metchnikoff continued his researches on intracellular digestion. In 1879, at Naples and at Messina, he was able to establish the fact that the mesodermic cells of many larvæ of Echinodermata and Coelenterata, endowed with a digestive tube, nevertheless contained strange bodies. Therefore, even complicated organisms with a differentiated digestive system could still contain at the same time some primitive cells with an autonomous digestion. All these researches on the unity of the origin of multicellular beings and their morphological elements, and also those concerning intracellular digestion, were gradually preparing Metchnikoff's mind for the conception of the phagocyte theory. * * * * * We spent the summer of 1880 with my family in the country. The cereals were invaded by a harmful beetle, the _Anisoplia austriaca_, which was devastating the country. Metchnikoff took the study of this scourge to heart and tried to find a remedy. He had, the preceding year, observed a dead fly enveloped with a sort of fungus which had evidently been the cause of its death. Hence he conceived the idea that it might be possible to combat harmful insects by provoking epidemics among them. He now returned to this idea; on dead bodies of _Anisoplia_ he found a small fungus, the _muscardine_, which was invading the insects by means of filaments, and he succeeded in infecting healthy beetles. At first he confined himself to laboratory experiments; then a great landowner, Count Bobrinsky, placed experimental fields at his disposal. As the acquired results were very encouraging, Metchnikoff, forced to leave the neighbourhood, left a young entomologist in charge of the application of his method. So far as he himself was concerned, this study proved the starting-point of his researches on infectious diseases. CHAPTER XVII Death of his father- and mother-in-law--Management of country estates--Agitation and difficulties--Departure for Messina with young brothers- and sisters-in-law. In the spring of 1881, Metchnikoff having recovered from relapsing fever, we went to stay with my parents at Kieff and found my father dying. He entrusted Elie with the care of the family, and they came to live with us at Odessa. But, the following year, we had the misfortune to lose my mother also. From that moment my husband took upon himself the responsibility of the whole family.