BRIEFABSCHRIFT Ritter, Paul von Author: Ritter, Paul von Recipient: Haeckel, Ernst Dating: 07.01.1886
BRIEF OHNE UMSCHLAG Harnier, Eduard von Author: Harnier, Eduard von Recipient: Haeckel, Ernst Dating: 30.05.1886
BRIEF [O.A.] Franken, Alexander Author: Franken, Alexander Recipient: Haeckel, Ernst Dating: 19.06.1886
BRIEF [O.A.] Tyrrell Leith, E... Author: Tyrrell Leith, E... Recipient: Haeckel, Ernst Dating: 12.05.1886