BRIEF [O.A.] Mitsching, Leopold Author: Mitsching, Leopold Recipient: Haeckel, Ernst Dating: 16.11.1917
BRIEF [O.A.] Duisberg, Carl Author: Duisberg, Carl Recipient: Haeckel, Ernst Corporation: Farbenfabriken vormals Friedrich Bayer & Co. Dating: 28.03.1892