BRIEF [O.A.] Unna, P...(aul) G...(erson) Author: Unna, P...(aul) G...(erson) Recipient: Haeckel, Ernst Dating: 09.10.1916
BRIEF [O.A.] Unna, P...(aul) G...(erson) Author: Unna, P...(aul) G...(erson) Recipient: Haeckel, Ernst Dating: 01.11.1916
BRIEF OHNE UMSCHLAG Sokolowsky, Alexander Author: Sokolowsky, Alexander Recipient: Haeckel, Ernst Dating: 25.01.1916
BRIEF OHNE UMSCHLAG Sokolowsky, Alexander Author: Sokolowsky, Alexander Recipient: Haeckel, Ernst Dating: 01.12.1916
BRIEF [O.A.] Riess, Carl Author: Riess, Carl Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Dating: 04.12.1916