BRIEF OHNE UMSCHLAG Schott, Sigmund Author: Schott, Sigmund Recipient: Haeckel, Ernst Dating: 26.11.1888
BRIEF [O.A.] Hertzog, Paul Siegmund Author: Hertzog, Paul Siegmund Recipient: Haeckel, Ernst Dating: 19.01.1888
BRIEF [O.A.] Hertzog, Paul Siegmund Author: Hertzog, Paul Siegmund Recipient: Haeckel, Ernst Dating: 31.01.1888