BRIEF [O.A.] Kemna, Adolf Author: Kemna, Adolf Recipient: Haeckel, Ernst Corporation: Antwerp Waterworks Company Limited Dating: 16.03.1894
BRIEF [O.A.] Cornette, Arthur Author: Cornette, Arthur Recipient: Haeckel, Ernst Corporation: De Vrije Gedachte, La Libre Pensée Dating: 07.06.1880
BRIEF OHNE UMSCHLAG Kemna, Adolf; Vyve, B. van Author: Kemna, Adolf; Vyve, B. van Recipient: Haeckel, Ernst Corporation: Réunion Scientifique d'Anvers Dating: 14.02.1894