ANSICHTSKARTE Bockelmann, Friedrich Author: Bockelmann, Friedrich Recipient: Haeckel, Ernst Dating: 03.03.1911
BRIEF OHNE UMSCHLAG Bauer, Klotilde Author: Bauer, Klotilde Recipient: Haeckel, Ernst Dating: 03.05.1911
POSTKARTE Bauer, Karl; Bauer, Klotilde Author: Bauer, Karl; Bauer, Klotilde Recipient: Haeckel, Ernst Dating: 29.12.1911
BRIEF OHNE UMSCHLAG Bergmann, Anton Author: Bergmann, Anton Recipient: Haeckel, Ernst Dating: 21.06.1911