This is the second in a series of seven volumes presenting the classic works of J.-H. Rosny Aîné, the second most important figure in French science fiction after Jules Verne. Until now, Rosny, a member of the Goncourt literary academy, has best been known to the English-speaking public for his prehistoric thriller, Quest for Fire.

Predating Sir Arthur Conan Doyle, Rosny creates Lost Worlds of a different kind, where variant species are the dominant races. The Siberian valley of Nymphaeum (1893) is home to purple-skinned, water-breathing men. The Depths Of Kyamo and The Wonderful Cave Country (1896) are underground journeys featuring giant, intelligent bats. The Boar Men (1929) inhabit a mysterious island. The World of the Variants (1939) feature a parallel world which only some privileged humans can visit.