BRIEF OHNE UMSCHLAG Strasburger, Eduard Author: Strasburger, Eduard Recipient: Haeckel, Ernst Dating: 25.03.1880
BRIEF [O.A.] Alglave, Emile Author: Alglave, Emile Recipient: Haeckel, Ernst Corporation: Bibliothèque Scientifique Internationale Dating: 09.07.1880
BRIEF [O.A.] Sabatier Author: Sabatier Recipient: Haeckel, Ernst Corporation: Faculté des Sciences Dating: 21.05.1880
BRIEF [O.A.] Letourneau, Charles Author: Letourneau, Charles Recipient: Haeckel, Ernst Dating: 27.05.1880