BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Illustrirte Zeitung, Redaktion Dating: 28.01.1875
BRIEF [O.A.] Zacharias, Otto Author: Zacharias, Otto Recipient: Haeckel, Ernst Corporation: Görlitzer Anzeiger, Redaction und Expedition Dating: 19.06.1875
BRIEF [O.A.] Syrski, Simeone Adamo de Author: Syrski, Simeone Adamo de Recipient: Haeckel, Ernst Dating: 19.07.1875