BRIEF [O.A.] Zürn, Friedrich Anton Author: Zürn, Friedrich Anton Recipient: Haeckel, Ernst Dating: 10.??.1872
BRIEF [O.A.] Hermann, Bernhard Author: Hermann, Bernhard Recipient: Haeckel, Ernst Dating: 22.07.1872
BRIEF OHNE UMSCHLAG Zechlin, Arthur Author: Zechlin, Arthur Recipient: Haeckel, Ernst Dating: 06.01.1872
BRIEF OHNE UMSCHLAG Schmitt, August Author: Schmitt, August Recipient: Haeckel, Ernst Corporation: B. G. Teubner Buchhandlung Dating: 22.03.1872