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: 05.09.1910
BRIEF [O.A.] Grimaldi, Vincento Author: Grimaldi, Vincento Recipient: Haeckel, Ernst Corporation: Associazione di Publica Assistenza Dating: 13.04.1911
BRIEF OHNE UMSCHLAG Groener, Maria Author: Groener, Maria Recipient: Haeckel, Ernst Dating: 06.01.1916
