BRIEF [O.A.] Theszóll, Charles Author: Theszóll, Charles Recipient: Haeckel, Ernst Dating: 23-02-1900
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Charlotte Dating: 05.05.1873
BRIEF [O.A.] Feichtinger, Alexius Baron Author: Feichtinger, Alexius Baron Recipient: Haeckel, Ernst Dating: 09.02.1914