BRIEF [O.A.] Gümbel, Wilhelm von Author: Gümbel, Wilhelm von Recipient: Haeckel, Ernst Dating: 29.11.1873
BRIEF [O.A.] Zittel, Karl Alfred von Author: Zittel, Karl Alfred von Recipient: Haeckel, Ernst Dating: 28.10.1873
BRIEF [O.A.] Siebold, Antonie von Author: Siebold, Antonie von Recipient: Haeckel, Ernst Dating: 04.12.1873