BRIEF [O.A.] Köppern, O... C... Author: Köppern, O... C... Recipient: Haeckel, Ernst Dating: 07.01.1906
BRIEF [O.A.] Köppern, O... C... Author: Köppern, O... C... Recipient: Haeckel, Ernst Dating: 03.03.1906
BRIEF [O.A.] Köppern, O... C... Author: Köppern, O... C... Recipient: Haeckel, Ernst Dating: 08.07.1906
BRIEF [O.A.] Köppern, O... C... Author: Köppern, O... C... Recipient: Haeckel, Ernst Dating: 29.10.1906
BRIEF [O.A.] Köppern, O... C... Author: Köppern, O... C... Recipient: Haeckel, Ernst Dating: 26.11.1906
BRIEF [O.A.] Köppern, O... C... Author: Köppern, O... C... Recipient: Haeckel, Ernst Dating: 26.12.1906