BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Focke, Wilhelm Olbers Dating: 28.04.1866
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Weismann, August Dating: 04.06.1866
BRIEF [O.A.] Kauffmann, Julius Author: Kauffmann, Julius Recipient: Haeckel, Ernst Dating: 18.09.1866
BRIEF OHNE UMSCHLAG Keferstein, Wilhelm Author: Keferstein, Wilhelm Recipient: Haeckel, Ernst Dating: 17.01.1866