BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Linck, Gottlob Dating: 31.01.1913
POSTKARTE Friedrichs, Elsbeth Author: Friedrichs, Elsbeth Recipient: Haeckel, Ernst Dating: 09.06.1913
ANSICHTSKARTE Haeckel, Ernst Franz Max Author: Haeckel, Ernst Franz Max Recipient: Haeckel, Ernst Dating: 15.02.1913