BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Krauseneck, Heinrich Dating: 21.04.1878
BRIEF [O.A.] Lichtenberg, Friedrich Author: Lichtenberg, Friedrich Recipient: Haeckel, Ernst Dating: 10.06.1871
BRIEF [O.A.] Littrow, Leontine von Author: Littrow, Leontine von Recipient: Haeckel, Ernst Dating: 24.04.1895
BRIEF [O.A.] Littrow, Heinrich von Author: Littrow, Heinrich von Recipient: Haeckel, Ernst Dating: 14.04.1878