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.
He did not then realise the full bearing of this observation, which really constituted the basis of his future phagocyte theory; this was only to appear eighteen years later.
He had also made researches on numerous specimens of insects and on the scorpion, establishing the fact that they all had embryonic layers; he concluded that he was “entitled to extend the theory of embryonic layers to Arthropoda.”
Finally, he had discovered embryonic layers similar to those of the Vertebrates in inferior Invertebrates, the Cephalopoda (Sepiola). This established a link of continuity between the higher and lower animals.
[CHAPTER XII]
Petersburg — Baer prize — Return home — Friendship with Cienkovsky — Odessa — Naturalists’ Congress at Petersburg — Departure from Odessa — Zoological Lecturer’s Chair at Petersburg — Messina — Enforced rest — Reggio — Naples — Controversy with Kovalevsky — Visit to the B. family — Mlle. Fédorovitch — Educational questions — Difficulties of life in Petersburg.
During his stay abroad, Metchnikoff had successfully carried out several researches, and this allowed him to apply for a post of docent at the new University of Odessa, which he had chosen on account of its proximity with the sea and its marine fauna. Whilst awaiting the result he went to Petersburg in order to pass his thesis and to prepare himself to become a professor. He received a pleasant welcome, for his lively and sociable disposition had made him many friends. The brothers Kovalevsky, with whom he was already on friendly terms, offered him hospitality; he also made the acquaintance of Professor Békétoff, and soon became a member of his family circle.