BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 15.12.1916
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 08.08.1916
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 12.06.1916