BRIEF [O.A.] Böhtlingk, Arthur Author: Böhtlingk, Arthur Recipient: Haeckel, Ernst Dating: 17.09.1891
BRIEF [O.A.] Bibits, Sofie von ... Author: Bibits, Sofie von ... Recipient: Haeckel, Ernst Dating: 26.03.1912
BRIEF [O.A.] Beulwitz, Rudolf von Author: Beulwitz, Rudolf von Recipient: Haeckel, Ernst Dating: 30.12.1904