BRIEF [O.A.] Daumann, Friedrich Author: Daumann, Friedrich Recipient: Haeckel, Ernst Dating: 09.02.1906
BRIEF [O.A.] Jackman, Wilbur S... Author: Jackman, Wilbur S... Recipient: Haeckel, Ernst Corporation: The University of Chicago Dating: 22.10.1905
BRIEF [O.A.] Schroeder, Henry L... Author: Schroeder, Henry L... Recipient: Haeckel, Ernst Dating: 14.11.1893
BRIEF [O.A.] Dodge, Paul H... Author: Dodge, Paul H... Recipient: Haeckel, Ernst Corporation: University of Chicago