BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Ullstein & Co. Verlagsbuchhandlung Dating: 13.07.1908
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Ullstein & Co. Verlagsbuchhandlung Dating: 08.08.1908
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Ullstein & Co. Verlagsbuchhandlung Dating: 20.10.1908