BRIEF [O.A.] Habellock, Herbert Author: Habellock, Herbert Recipient: Haeckel, Ernst Dating: 16.02.1914
BRIEF [O.A.] Habellock, Herbert Author: Habellock, Herbert Recipient: Haeckel, Ernst Dating: 17.02.1915
BRIEF [O.A.] Habellock, Herbert Author: Habellock, Herbert Recipient: Haeckel, Ernst Dating: 17.02.1918
POSTKARTE Morawetz-Dierkes, Leopoldine von Author: Morawetz-Dierkes, Leopoldine von Recipient: Haeckel, Ernst Dating: 06.03.1904