Complex sentence: In 1837 he defended his thesis in Königsberg, then in Prussia later he became Professor of Zoology in and at the Universität Dorpat (1843-1856) then at Breslau.
Split into simpler sentences: In 1837 he defended his thesis in Königsberg, then in Prussia. Later he became Professor of Zoology in the Universität Dorpat (1843-1856) then at Breslau.