BRIEF [O.A.] Koldehofe, Hermann Author: Koldehofe, Hermann Recipient: Haeckel, Ernst Dating: 06.12.1916
BRIEF [O.A.] Koehlich, Richard Author: Koehlich, Richard Recipient: Haeckel, Ernst Dating: 22.09.1917
BRIEF [O.A.] Lilienstern, Edmund Author: Lilienstern, Edmund Recipient: Haeckel, Ernst Dating: 27.11.1910
BRIEF [O.A.] Rethmeyer, Fr... Author: Rethmeyer, Fr... Recipient: Haeckel, Ernst Corporation: Verlagsbuchhandlung Dating: 29.04.1905