BILDPOSTKARTE Haeckel, Walter Author: Haeckel, Walter Recipient: Mentz, Georg; Mentz, Frida Dating: 16.06.1912
BILDPOSTKARTE Haeckel, Walter Author: Haeckel, Walter Recipient: Seegy (Segi), Hermann Dating: 02.07.1912
BRIEF OHNE UMSCHLAG Haeckel, Walter Author: Haeckel, Walter Recipient: Plate, Ludwig Dating: 20.10.1912