BILDPOSTKARTE Recipient: Haeckel, Ernst Corporation: Verlagsbuchhandlung Georg Reimer in Berlin Dating: 18.04.1908
BRIEF [O.A.] Hilbert, A. Author: Hilbert, A. Recipient: Haeckel, Ernst Corporation: Verlagsbuchhandlung Georg Reimer in Berlin Dating: 02.11.1908
BRIEF OHNE UMSCHLAG Hilbert, August Author: Hilbert, August Recipient: Haeckel, Ernst Corporation: Verlagsbuchhandlung Georg Reimer in Berlin Dating: 16.01.1908
BRIEF OHNE UMSCHLAG Hilbert, August Author: Hilbert, August Recipient: Haeckel, Ernst Corporation: Verlagsbuchhandlung Georg Reimer in Berlin Dating: 10.01.1908