BRIEF OHNE UMSCHLAG Fischer, Gustav Author: Fischer, Gustav Recipient: Haeckel, Ernst Dating: 25.11.1883
BRIEF [O.A.] Eber, Almi Author: Eber, Almi Recipient: Haeckel, Ernst Corporation: Verein Merkur Dating: 05.06.1883
BRIEF OHNE UMSCHLAG Geddes, Patrick Author: Geddes, Patrick Recipient: Haeckel, Ernst Dating: 11.11.1883
BRIEF OHNE UMSCHLAG Erdmann, Gustav Adolf Author: Erdmann, Gustav Adolf Recipient: Haeckel, Ernst Dating: 15.02.1883