KARTE About, Edmond [et al.] Author: About, Edmond [et al.] Recipient: Haeckel, Ernst Dating: vor Juni 1879
POSTKARTE Rottenburg, Paul von Author: Rottenburg, Paul von Recipient: Haeckel, Ernst Dating: 21.10.1900
BRIEF OHNE UMSCHLAG Barbier (Witwe von Edmond Barbier) Author: Barbier (Witwe von Edmond Barbier) Recipient: Haeckel, Ernst Dating: 16.05.1886