BRIEF OHNE UMSCHLAG Becker, Franz Johann Jakob Emil Author: Becker, Franz Johann Jakob Emil Recipient: Haeckel, Ernst Dating: 18.08.1916
BRIEF [O.A.] Böhtlingk, Arthur Author: Böhtlingk, Arthur Recipient: Haeckel, Ernst Dating: 20.09.1916
POSTKARTE Becker, Franz Johann Jakob Emil Author: Becker, Franz Johann Jakob Emil Recipient: Haeckel, Ernst Dating: 14.11.1916
BRIEF OHNE UMSCHLAG Becker, Franz Johann Jakob Emil Author: Becker, Franz Johann Jakob Emil Recipient: Haeckel, Ernst Dating: 18.11.1916
BRIEF OHNE UMSCHLAG Becker, Franz Johann Jakob Emil Author: Becker, Franz Johann Jakob Emil Recipient: Haeckel, Ernst Dating: 25.11.1916