BRIEF OHNE UMSCHLAG Anonym (P. B.) Author: Anonym (P. B.) Recipient: Haeckel, Ernst Dating: ??.06.1907
BRIEF [O.A.] Schreyer Author: Schreyer Recipient: Haeckel, Ernst Corporation: Reichsbund für Deutsches Staatsbürgertum Dating: 28.06.1919
BRIEF [O.A.] Vatteroth, Wilh... Author: Vatteroth, Wilh... Recipient: Haeckel, Ernst Dating: 22.09.1908
BRIEF OHNE UMSCHLAG Grober, Julius Author: Grober, Julius Recipient: Haeckel, Ernst Dating: 03.04.1909
BRIEF OHNE UMSCHLAG Grober, Julius Author: Grober, Julius Recipient: Haeckel, Ernst Dating: 26.07.1909