BRIEF [O.A.] Ortmann, Arnold E... Author: Ortmann, Arnold E... Recipient: Haeckel, Ernst Dating: 16.02.1891
BRIEF OHNE UMSCHLAG Soden, Julius Freiherr von Author: Soden, Julius Freiherr von Recipient: Haeckel, Ernst Dating: 26.12.1892
BRIEF OHNE UMSCHLAG Tafel, Theodor Author: Tafel, Theodor Recipient: Haeckel, Ernst Dating: 14.07.1912