POSTKARTE Gabriel, Gábor Raimund Author: Gabriel, Gábor Raimund Recipient: Haeckel, Ernst Dating: 12.04.1911
TELEGRAMM Gabriel, Gábor Raimund Author: Gabriel, Gábor Raimund Recipient: Haeckel, Ernst Dating: 17.05.1911
BRIEF [O.A.] Gabriel, Gábor Raimund Author: Gabriel, Gábor Raimund Recipient: Haeckel, Ernst Dating: ??.??.1911
BRIEF [O.A.] Schott, Josef Johann Author: Schott, Josef Johann Recipient: Haeckel, Ernst Dating: 26.10.1911