BRIEF [O.A.] Hartmann, Hans und Lotte Author: Hartmann, Hans und Lotte Recipient: Haeckel, Ernst Dating: 21.04.1918
BRIEF [O.A.] Budie-Klauke, Else Author: Budie-Klauke, Else Recipient: Haeckel, Ernst Dating: 15.02.1918
BRIEF [O.A.] Juliusburger, Otto Author: Juliusburger, Otto Recipient: Haeckel, Ernst Dating: 03.11.1918