Complex sentence: Severe health problems between 1851 and 1854 forced retirement and in 1868 he received a pension and took up the study of Diptera full-time after moving to Guben, Prussia.
Split into simpler sentences: Severe health problems between 1851 and 1854 forced retirement. In 1868 he received a pension and took up the study of Diptera full-time after moving to Guben, Prussia.