POSTKARTE Recipient: Haeckel, Ernst Corporation: Administration der neuen Zürcher Zeitung Dating: 09.09.1886
BRIEF OHNE UMSCHLAG Keller, Conrad Author: Keller, Conrad Recipient: Haeckel, Ernst Dating: 24.02.1886
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Charlotte [Mutter] Dating: 24.08.1886