BRIEF [O.A.] Leuchtenberg, Anna Author: Leuchtenberg, Anna Recipient: Haeckel, Ernst Dating: 14.02.1911
BRIEF [O.A.] Neuenborn, Hermine Author: Neuenborn, Hermine Recipient: Haeckel, Ernst Dating: 10.03.1914
BRIEF [O.A.] Neuenborn, Hermine Author: Neuenborn, Hermine Recipient: Haeckel, Ernst Dating: 02.04.1914