BRIEF [O.A.] Abbott, Leonard Dalt Author: Abbott, Leonard Dalt Recipient: Haeckel, Ernst Corporation: Francisco Ferrer Association Dating: 22.06.1911
BRIEF OHNE UMSCHLAG Singer, Isidore Author: Singer, Isidore Recipient: Haeckel, Ernst Corporation: The German Classics of the XIXth and XXth Centuries Dating: 14.08.1911
BRIEF [O.A.] Lotka, Alfred J... Author: Lotka, Alfred J... Recipient: Haeckel, Ernst Corporation: Scientific American Dating: 24.02.1911
BRIEF OHNE UMSCHLAG Loeb, Jacques Author: Loeb, Jacques Recipient: Haeckel, Ernst Corporation: The Rockefeller Institute for Medical Research Dating: 15.12.1911