TELEGRAMM Clason, Oscar (und Familie) Author: Clason, Oscar (und Familie) Recipient: Haeckel, Ernst Dating: 16.02.1894
ANSICHTSKARTE Haeckel, Ernst Author: Haeckel, Ernst Recipient: Besser, Käthe; Besser, Leopold Dating: 03.01.1903
BRIEF OHNE UMSCHLAG Besser, Leopold Author: Besser, Leopold Recipient: Haeckel, Ernst Dating: 05.07.1893
BRIEF OHNE UMSCHLAG Besser, Leopold Author: Besser, Leopold Recipient: Haeckel, Ernst Dating: 12.07.1893