BRIEF OHNE UMSCHLAG Krukenberg, Gustav Author: Krukenberg, Gustav Recipient: Haeckel, Ernst Dating: 30.11.1892
BRIEF OHNE UMSCHLAG Krukenberg, Gustav Author: Krukenberg, Gustav Recipient: Haeckel, Ernst Dating: 28.03.1892
BRIEF OHNE UMSCHLAG Besser, Leopold Author: Besser, Leopold Recipient: Haeckel, Ernst Dating: 23.06.1892