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.] Patschkowski, M... Author: Patschkowski, M... Recipient: Haeckel, Ernst Dating: 07.07.1886