BRIEF [O.A.] Theszóll, Charles Author: Theszóll, Charles Recipient: Haeckel, Ernst Dating: 23-02-1900
BRIEF [O.A.] Hartmann, S... E... Author: Hartmann, S... E... Recipient: Haeckel, Ernst Dating: 19.12.1913
BRIEF [O.A.] Lambrecht, Koloman Author: Lambrecht, Koloman Recipient: Haeckel, Ernst Dating: 07.04.1914