BRIEF [O.A.] Miklucho-Maclay, Nikolaj N... Author: Miklucho-Maclay, Nikolaj N... Recipient: Haeckel, Ernst Dating: 18.10.1866
BRIEF [O.A.] Schmid, Ernst Erhard Author: Schmid, Ernst Erhard Recipient: Haeckel, Ernst Dating: 16.02.1866
BRIEF [O.A.] Hildebrand, Bruno Author: Hildebrand, Bruno Recipient: Haeckel, Ernst Dating: 21.03.1866