place, and kindliness was rare between colleagues. After staying some time in Munich, Elie returned to Naples, war having broken out between Northern and Southern Germany. This time, in order to spend less on the journey, he took a steamer at Genoa, but with fatal results, for a storm was raging; he suffered a great deal, and, when he reached Naples, violent fits of giddiness made him incapable of doing any work at all for some time. Cholera reappeared, and the landlady of the rooms he shared with Kovalevsky died of it. Much depressed, the two started for Ischia, but Elie soon realised with terror that he was not yet well enough to work; in order to recover quickly, he went to Cava, a pretty little place, renowned for its salubrious climate. There he met Bakounine again, and they saw a good deal of each other in a friendly way. Bakounine nicknamed him "Mamma" because of his almost maternal attentions, a nickname which, for the same reason, was given him later, quite independently, by other intimates. Yet, though their relations were cordial and even affectionate, there was not really much in common between the two. Elie thought Bakounine's ideas superficial, and disliked his sectarian mentality; they ultimately drifted apart. His health having gradually recovered owing to the rest, he returned to Naples in the autumn, after the epidemic had abated, and at last resumed his work. Whilst studying the history of the development of Cephalopoda he found that they had embryonic layers similar to those of Vertebrates; this was the first time that the fact was established. It was extremely important, for it constituted a concrete and indisputable proof of the existence of a genetic connection between inferior and superior animals. Metchnikoff chose this subject for his thesis, and, having completed his researches, he returned to Russia in 1867. By this time he had made great use of his three years' stay abroad. Though he had not showed himself a docile pupil, yet he had become initiated into the organisation of scientific work in Germany; he had carried out independent researches and had been able to choose with full knowledge the future path of investigations which he was to pursue for many years in the field of Comparative Embryology. Already the observations he had made had in themselves a real importance. For instance, his studies in divers specimens of the worm type, a type which offers very heterogeneous forms, had permitted him to establish links of continuity between certain groups among them. Whilst studying those animals at Giessen in 1865, he had discovered the capital fact which proved to be the starting-point of all his future work--the _intercellular digestion_ of an inferior worm, a land planarian, the _Geodesmus bilineatus_. He had compared this digestion with that of the superior Infusoria and had seen in it one more proof of the genetic connection between the type of the Protozoa and that of worms.