BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Karl Dating: 17.09.1890
BRIEF [O.A.] Cherno-Wyden, M... Author: Cherno-Wyden, M... Recipient: Haeckel, Ernst Dating: 30.08.1890
BRIEF [O.A.] Bührer, Karl Wilhelm Author: Bührer, Karl Wilhelm Recipient: Haeckel, Ernst Corporation: Mittelschweizerische Geographisch-Commercielle Gesellschaft in Aarau Dating: 27.10.1890