ANSICHTSKARTE Haeckel, Walther; Haeckel, Josefa Author: Haeckel, Walther; Haeckel, Josefa Recipient: Haeckel, Ernst Dating: 22.04.1909
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Rottenburg, Paul von Dating: 10.11.1903
BRIEF MIT UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Schmidt, Heinrich Dating: 30.10.1903
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Schmidt, Heinrich Dating: 07.11.1903