BRIEF OHNE UMSCHLAG Krabbe, Harald Author: Krabbe, Harald Recipient: Haeckel, Ernst Dating: 28.10.1900
BRIEF OHNE UMSCHLAG Ihering, Hermann von Author: Ihering, Hermann von Recipient: Haeckel, Ernst Dating: 12.06.1878
BRIEF [O.A.] Jensen, P... L... Author: Jensen, P... L... Recipient: Haeckel, Ernst Dating: 18.11.1877
BRIEF [O.A.] Jensen, P... L... Author: Jensen, P... L... Recipient: Haeckel, Ernst Dating: 02.12.1877