BRIEF [O.A.] Putzhardt, Johannes Author: Putzhardt, Johannes Recipient: Haeckel, Ernst Dating: 02.04.1908
BRIEF OHNE UMSCHLAG Fürbringer, Max Author: Fürbringer, Max Recipient: Haeckel, Ernst Dating: 23.07.1908
BRIEF OHNE UMSCHLAG Bergfeld, Ludwig Author: Bergfeld, Ludwig Recipient: Haeckel, Ernst Dating: 05.12.1908
BRIEF OHNE UMSCHLAG Bergfeld, Ludwig Author: Bergfeld, Ludwig Recipient: Haeckel, Ernst Dating: 15.12.1908