A Princess of Mars, although Burroughs's first published work, took six years to reach hardcovers. Readers clearly responded to the Tarzan stories more than to fantasies set on other worlds, and publishers' letters constantly requested new stories about the ape-man, which Burroughs provided, although not always graciously, for he clearly grew tired of the character and even tried at one point to kill Jane. The non-Tarzan tales undoubtedly provided a relief for their author as well as a chance to exercise his gift for creating new worlds. The Mars stories still seem somehow fresher and often more exciting than the Tarzan books which suffer increasingly from mechanical repetition; as early as 1918 Burroughs wrote, "I feel that I have said and resaid a dozen times everything that there is to say about Tarzan."

The Mars novels reiterate most of the themes of the Tarzan novels, despite the...