POSTKARTE Schuster, Adolf Niklaus Author: Schuster, Adolf Niklaus Recipient: Haeckel, Ernst Dating: 03.10.1916
BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 22.01.1906
BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 27.05.1908
BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 15.08.1912
BRIEF [O.A.] Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 18.08.1912
POSTKARTE Kühnel-Engelsberg, Rudolf Author: Kühnel-Engelsberg, Rudolf Recipient: Haeckel, Ernst Dating: 21.08.1912
BRIEF [O.A.] Kühnel-Engelsberg, Betty Author: Kühnel-Engelsberg, Betty Recipient: Haeckel, Ernst Dating: 16.12.1917