BRIEF [O.A.] Kantorowicz, Eugen Author: Kantorowicz, Eugen Recipient: Haeckel, Ernst Dating: 25.04.1904
BRIEF [O.A.] Lippmann, Johanna Author: Lippmann, Johanna Recipient: Haeckel, Ernst Dating: 19.05.1911
BRIEF [O.A.] Lippmann, Johanna Author: Lippmann, Johanna Recipient: Haeckel, Ernst Dating: 13.06.1911