BRIEF [O.A.] Dieckmann, Gertha Author: Dieckmann, Gertha Recipient: Haeckel, Ernst Dating: 25.01.1900
BRIEF [O.A.] Dieckmann, Gertha Author: Dieckmann, Gertha Recipient: Haeckel, Ernst Dating: 11.05.1900
BRIEF OHNE UMSCHLAG Schleiden, Eleonore Author: Schleiden, Eleonore Recipient: Haeckel, Ernst Dating: 29.04.1900