BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Zirkel, Ferdinand Dating: 27.05.1872
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Peters, Wilhelm Dating: 12.05.1872
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Ehlers, Ernst Dating: 28.12.1872