BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 22.11.1898
BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 10.12.1898
BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 23.12.1898
BRIEF [O.A.] Lendenfeld, Robert von Author: Lendenfeld, Robert von Recipient: Haeckel, Ernst Dating: 06.02.1898