BRIEF [O.A.] Tecklenburg, Arthur Author: Tecklenburg, Arthur Recipient: Haeckel, Ernst Dating: 14.02.1904
BRIEF [O.A.] Tecklenburg, Arthur Author: Tecklenburg, Arthur Recipient: Haeckel, Ernst Dating: 13.03.1904
POSTKARTE Tecklenburg, Arthur Author: Tecklenburg, Arthur Recipient: Haeckel, Ernst Dating: 13.07.1904