BRIEF [O.A.] Klaucke-Blaurock, Else Author: Klaucke-Blaurock, Else Recipient: Haeckel, Ernst Dating: 21.03.1911
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Walter Dating: 10.11.1919
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Walter Dating: 14.12.1919