BRIEF [O.A.] Haeckel, Ingeborg Author: Haeckel, Ingeborg Recipient: Haeckel, Ernst Dating: 25.03.1918
BRIEF [O.A.] Haeckel, Ingeborg Author: Haeckel, Ingeborg Recipient: Haeckel, Ernst Dating: 09.11.1913
BRIEF [O.A.] Haeckel, Ingeborg Author: Haeckel, Ingeborg Recipient: Haeckel, Ernst Dating: 15.02.1916
BRIEF [O.A.] Haeckel, Ingeborg Author: Haeckel, Ingeborg Recipient: Haeckel, Ernst Dating: 1915.02.?? [oder 1918]
BRIEF [O.A.] Haeckel, Ingeborg Author: Haeckel, Ingeborg Recipient: Meyer, Elisabeth Charlotte Emma Dating: 14.02.1914
BRIEF [O.A.] Haeckel, Ingeborg Author: Haeckel, Ingeborg Recipient: Haeckel, Ernst Dating: 1915.??.?? - 1918.??.??