BRIEF [O.A.] Friedrich, Gustav Author: Friedrich, Gustav Recipient: Haeckel, Ernst Dating: 16.02.1915
BRIEF [O.A.] Schlesinger, Louis Author: Schlesinger, Louis Recipient: Haeckel, Ernst Dating: 11.08.1915
BRIEF [O.A.] Weißenborn, Adolf Author: Weißenborn, Adolf Recipient: Haeckel, Ernst Dating: 24.06.1915
BRIEF [O.A.] Hedemann, Justus Wilhelm Author: Hedemann, Justus Wilhelm Recipient: Haeckel, Ernst Dating: 29.01.1915
BRIEF [O.A.] Hedemann, Justus Wilhelm Author: Hedemann, Justus Wilhelm Recipient: Haeckel, Ernst Dating: 13.03.1915