BRIEF [O.A.] Nippold, W... K... A... Author: Nippold, W... K... A... Recipient: Haeckel, Ernst Dating: 08.02.1904
BRIEF OHNE UMSCHLAG Studer, Theophil Author: Studer, Theophil Recipient: Haeckel, Ernst Corporation: Internationaler Zoologen-Kongress Dating: 13.04.1904
BRIEF [O.A.] Brunnhofer, Hermann Author: Brunnhofer, Hermann Recipient: Haeckel, Ernst Dating: 18.06.1904