BRIEF [O.A.] Franco, Isidoro de Author: Franco, Isidoro de Recipient: Haeckel, Ernst Dating: 08.12.1906
BRIEF [O.A.] N.N. Author: N.N. Recipient: Haeckel, Ernst Corporation: Freidenker Vereinigung Dating: 29.07.1906
BRIEF [O.A.] Tschirn, G. Author: Tschirn, G. Recipient: Haeckel, Ernst Corporation: Vorstand des deutschen Freidenkerbundes Dating: 30.06.1906
BRIEF OHNE UMSCHLAG Eggeling, Heinrich von Author: Eggeling, Heinrich von Recipient: Haeckel, Ernst Dating: 28.08.1906
