BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Charlotte [Mutter] Dating: 24.04.1871
BRIEF [O.A.] Zittel, Karl Alfred von Author: Zittel, Karl Alfred von Recipient: Haeckel, Ernst Dating: 13.02.1871
BRIEF [O.A.] Siebold, Carl Theodor Ernst von Author: Siebold, Carl Theodor Ernst von Recipient: Haeckel, Ernst Dating: ??.01.1871