BRIEF [O.A.] Thoden van Velzen, S... K... Author: Thoden van Velzen, S... K... Recipient: Haeckel, Ernst Dating: 05.05.1916
POSTKARTE Thoden van Velzen, S... K... Author: Thoden van Velzen, S... K... Recipient: Haeckel, Ernst Dating: 14.05.1916
BRIEF [O.A.] Thoden van Velzen, S... K... Author: Thoden van Velzen, S... K... Recipient: Haeckel, Ernst Dating: 30.06.1916