BRIEF OHNE UMSCHLAG N.N. Author: N.N. Recipient: Haeckel, Ernst Corporation: Münchner Kind'l, Deutsche Bier-Halle und Wein-Stube Dating: 16.02.1904
TELEGRAMM Mentz, Frida, geb. Kessel Author: Mentz, Frida, geb. Kessel Recipient: Haeckel, Ernst Dating: 16.02.1904
POSTKARTE Klinghammer, Waldemar Author: Klinghammer, Waldemar Recipient: Haeckel, Ernst Dating: 09.03.1911
BRIEF [O.A.] Semon, Richard W... Author: Semon, Richard W... Recipient: Haeckel, Ernst Dating: 26.11.1905
BRIEF [O.A.] Semon, Richard W... Author: Semon, Richard W... Recipient: Haeckel, Ernst Dating: 23.12.1905