BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: de Gruyter, Walter Dating: 16.02.1904
PORTRÄTPOSTKARTE Haeckel, Ernst Author: Haeckel, Ernst Recipient: de Gruyter, Walter Dating: 22.11.1904
POSTKARTE Haeckel, Walther Author: Haeckel, Walther Recipient: Haeckel, Ernst Dating: 1904.??.?? - 1905.??.??
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Engelmann, Wilhelm Dating: 16.02.1904
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Uslar-Gleichen, Bernhard von Dating: 13.05.1904
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Uslar-Gleichen, Bernhard von Dating: 22.05.1904
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Uslar-Gleichen, Bernhard von Dating: 03.06.1904