BRIEF OHNE UMSCHLAG Gelzer, Heinrich Author: Gelzer, Heinrich Recipient: Haeckel, Ernst Dating: 04.08.1892
BRIEF [O.A.] Freyer, Clemens Author: Freyer, Clemens Recipient: Haeckel, Ernst Corporation: Berliner Literarisches Auskunfts-Bureau Dating: 10.08.1892
BRIEF [O.A.] Freyer, Clemens Author: Freyer, Clemens Recipient: Haeckel, Ernst Corporation: Berliner Literarisches Auskunfts-Bureau Dating: 12.09.1892