BRIEF OHNE UMSCHLAG Michaelis, Curt Author: Michaelis, Curt Recipient: Haeckel, Ernst Dating: 19.03.1900
BRIEF OHNE UMSCHLAG Michaelis, Curt Author: Michaelis, Curt Recipient: Haeckel, Ernst Dating: 09.03.1900
BRIEF OHNE UMSCHLAG Rüdt, Philipp August Author: Rüdt, Philipp August Recipient: Haeckel, Ernst Dating: 26.05.1900
BRIEF [O.A.] Zittel, Karl Alfred von Author: Zittel, Karl Alfred von Recipient: Haeckel, Ernst Dating: 13.05.1900