BRIEF [O.A.] Haeckel, Siegfried Author: Haeckel, Siegfried Recipient: Haeckel, Ernst Dating: ??.??.1904
BRIEF [O.A.] Haeckel, Siegfried Author: Haeckel, Siegfried Recipient: Haeckel, Ernst Dating: 08.01.1904
BRIEF [O.A.] Haeckel, Siegfried Author: Haeckel, Siegfried Recipient: Haeckel, Ernst Dating: 03.11.1904
BRIEF [O.A.] Haeckel, Siegfried Author: Haeckel, Siegfried Recipient: Haeckel, Ernst Dating: 25.10.1904