BRIEF [O.A.] Regensburger, Norbert Author: Regensburger, Norbert Recipient: Haeckel, Ernst Dating: 12.01.1908
BRIEF [O.A.] Riesterer, Wilhelm Author: Riesterer, Wilhelm Recipient: Haeckel, Ernst Dating: ??.??.1908
BRIEF [O.A.] Tannenbaum, Herbert Author: Tannenbaum, Herbert Recipient: Haeckel, Ernst Dating: 13.12.1907