BRIEF [O.A.] Kämmerer, G... Author: Kämmerer, G... Recipient: Haeckel, Ernst Corporation: Freie religiöse Gemeinde Nürnberg Dating: 20.12.1905
BRIEF [O.A.] Beisswanger, Konrad Author: Beisswanger, Konrad Recipient: Haeckel, Ernst Corporation: Konrad Beisswanger's Buchdruckerei und Verlag Dating: 19.03.1908