BRIEF [O.A.] Keller, Walther Author: Keller, Walther Recipient: Haeckel, Ernst Corporation: Franckh'sche Verlagshandlung Dating: 08.07.1913
BRIEF [O.A.] Keller, Walther Author: Keller, Walther Recipient: Haeckel, Ernst Corporation: Franckh`sche Verlagsbuchhandlung Dating: 14.01.1906
BRIEF [O.A.] Keller, Walther Author: Keller, Walther Recipient: Haeckel, Ernst Corporation: Franck`sche Verlagsbuchhandlung Dating: 08.11.1907
BRIEF [O.A.] Keller, Walther Author: Keller, Walther Recipient: Haeckel, Ernst Corporation: Franckh`sche Verlagsbuchhandlung Dating: 14.12.1905