BRIEF OHNE UMSCHLAG Kilpper, Gustav Author: Kilpper, Gustav Recipient: Haeckel, Ernst Corporation: Deutsche Verlags-Anstalt Stuttgart Dating: 23.10.1910
BILDPOSTKARTE Fraas, Eberhard Author: Fraas, Eberhard Recipient: Haeckel, Ernst Corporation: Königl. Naturalien-Cabinet in Stuttgart Dating: 09.08.1910
BRIEF [O.A.] Lehmann, Fritz Author: Lehmann, Fritz Recipient: Haeckel, Ernst Corporation: Fritz Lehmann Verlag Dating: 18.01.1910