BRIEF [O.A.] Wildpret, Hermann Author: Wildpret, Hermann Recipient: Haeckel, Ernst Dating: 08.10.1901
BRIEF [O.A.] Wildpret, Hermann Author: Wildpret, Hermann Recipient: Haeckel, Ernst Dating: 01.03.1902
BRIEF [O.A.] Wildpret, Hermann Author: Wildpret, Hermann Recipient: Haeckel, Ernst Dating: 16.06.1902
BRIEF OHNE UMSCHLAG Hertwig, Richard Author: Hertwig, Richard Recipient: Haeckel, Ernst Dating: 26.12.1912
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: An die Freunde in Jena Dating: 27.11.1866
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Carl & Charlotte [Eltern] Dating: 27.11.1866