1 (p. 6) European power: King Leopold II of Belgium established the Congo Free State in 1885 as his personal possession; his systematic exploitation of the Congolese population was secured by an army—the Force Publique, led by European officers. Reports of Africans from the British colonies in Sierra Leone and Lagos (in present-day Nigeria) being “employed without their consent,” flogged, and shot in the Congo Free State became public in 1896.

2 (p. 64) Numa the lion: In the original magazine version of the novel, Burroughs had Tarzan encounter tigers, but then changed the animals to lions when he learned that tigers do not live in Africa.

3 (p. 121) “Oh, Gaberelle!”: This is presumably a mispronunciation of Gabriel, the name of one of the archangels. Later (p. 137) Esmeralda becomes convinced that Tarzan is an angel.

4 (p. 138) “higher white races”: Here is an example of the theories about race and evolution that inform the novel. For a discussion of Burroughs’s reliance on pseudo-scientific theory see the introduction.

5 (p. 149) the remains of which lay buried somewhere in the Congo valley: Burroughs alludes to legends of a lost white civilization in Africa that were popular in fiction of the period; he employed such legends in some of the Tarzan sequels.

6 (p. 174) hereditary instinct of graciousness which a lifetime of uncouth and savage training and environment could not eradicate: The theory that learned traits, such as aristocratic manners, could be inherited was developed by French naturalist Jean-Baptiste Lamarck in the early nineteenth century.

7 (p. 181) Leopold II of Belgium: The atrocities committed in the Congo Free Sate became the subject of an international humanitarian campaign. Mark Twain’s King Leopold’s Soliloquy (1905) and Arthur Conan Doyle’s The Crime of the Congo (1909) are examples of writings from the period that denounced Leopold’s rule.

8 (p. 199) “... I regret that I am not a man, that I might make it”: It appears that Jane’s gender precludes her from calling Clayton a liar because, as a matter of honor, a gentleman could not strike a woman as he would a man who accused him of being a liar.

9 (p. 205) “this superman of yours”: The first usage in English of this term, a translation of Nietzsche’s Übermensch, was by George Bernard Shaw in 1903, referring to a man of genius or a great leader. The flying superhero and champion of the underdog who went by this name did not come into existence until 1938.

10 (p. 228) the part played by fingerprints in this fascinating science: Fingerprints were used in ancient Assyria and in China for signing legal documents. In Europe and America, their use by police for identifying individuals began in the 1890s.

11 (p. 229) Negro or Caucasian: In 1892 British scientist Francis Galton, the founder of the eugenics movement, developed the system for classifying fingerprints that is still commonly used by police. Galton’s primary interest, however, was not in criminology but in advancing his “racial taxonomy.” Although he claimed to be able to identify criminals and mental and racial “inferiors” by specific facial features, he was unable to establish any racial or other classifications through fingerprints.