BRIEF [O.A.] Awramoff, Stephan Author: Awramoff, Stephan Recipient: Haeckel, Ernst Dating: 03.07.1909
BRIEF OHNE UMSCHLAG Fürbringer, Bruno Author: Fürbringer, Bruno Recipient: Haeckel, Ernst Dating: o. D.
BRIEF OHNE UMSCHLAG Stobbe, August Author: Stobbe, August Recipient: Haeckel, Ernst Dating: 15.06.1880
BRIEF [O.A.] Aschen, Fr... von Author: Aschen, Fr... von Recipient: Haeckel, Ernst Dating: 07.10.1914