BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Siebold, Carl Theodor Ernst von Dating: 20.04.1878
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Krauseneck, Heinrich Dating: 21.04.1878
BRIEF [O.A.] Littrow, Leontine von Author: Littrow, Leontine von Recipient: Haeckel, Ernst Dating: 24.04.1895