BRIEF [O.A.] Unna, Paul Gerson Author: Unna, Paul Gerson Recipient: Haeckel, Ernst Dating: 30.05.1915
BRIEF OHNE UMSCHLAG Sokolowsky, Alexander Author: Sokolowsky, Alexander Recipient: Haeckel, Ernst Dating: 23.12.1915
ANSICHTSKARTE Gutmann, Hermann A. Author: Gutmann, Hermann A. Recipient: Haeckel, Ernst Dating: 16.02.1915