OX

Of Man and Manta is an sf trilogy written by Piers Anthony. It consists of Omnivore (1968), Orn (1970), and 0x (1975). Omnivore has as its frame the investigation of the deaths of eighteen travelers from Earth to the planet Nacre. We see Nacre through the eyes of three surviving scientist-explorers: Cal, a blood-drinker, Veg, a vegetarian, & Aquilon, an omnivore. Orn involves travel by the scientists & mantas into a parallel dimension they dub Paleo, resembling the distant past of Earth, where they encounter dinosaurs & an intelligent flightless bird called Orn. 0X involves the three scientists attempting to return to Earth from another dimension inhabited by hostile machines. Interlopers from other realities (using technology similar to that of the scientists' government) guide & hamper the explorers. A secondary story tells of a multidimensional cellular automaton energy being named 0X & its attempts to share living space with an infant human male, a fledgling creature of Orn's species, & one of the manta-carnivores; their developing relationship leads to attempts to learn the reasons for their strange isolation from others of their kind, which eventually ties in to the story of Cal, Veg & Aquilon.