Cryptoterrestrial lore is replete with allusions to underground habitats, subterranean labyrinths navigable only to an enlightened few, and even modern-day below-ground facilities staffed, in part, by government operatives. From Richard Shaver's fancifully paranoid tales of the "Deros" to Bob Lazar's depiction of S-4 (allegedly a supersecret base a stone's throw away from Area 51), the "alien" meme challenges us with the prospect that our world is separated from the other by the merest of partitions . . . and that the CTs are almost as comfortable in our bedrooms and on our roadsides as they are in their own realm.

The image of a "Hollow Earth" populated by beings remarkably like ourselves is by no means new, yet the modern UFO phenomenon has infused it with a newly conspiratorial vigor. Stories of alien bases below the unassumingly bleak surface of the American Southwest surfaced in the wake of the MJ-12 controversy, carving the mythos into irresistible new shapes. In "Revelations," Jacques Vallee recounts a memorable exchange with the late Bill Cooper and fringe journalist Linda Moulton Howe. Told matter-of-factly about the existence of a sprawling subterranean base near Dulce, New Mexico, Vallee asked his hosts where the presumed aliens disposed of their garbage -- a sensible question if one assumes that the "Grays" in question are physical beings burdened with corresponding physical requirements.

Vallee's question is of obvious importance to the cryptoterrestrial inquiry. If we really are sharing the planet with a "parallel" species, searching for underground installations becomes imperative for any objective investigation. Our failure to find any blatant "cities" beneath the planet's surface invites many questions. Could the CTs have colonized our oceans, potentially explaining centuries of bizarre aquatic sightings? Have they intermingled to the point where they're effectively indistinguishable from us? (And, if so, how might such a scattered population summon the resources to stage UFO events?)

Finally, we're forced to consider that at least some CTs have achieved genuine space travel, throwing our definitional framework into havoc. Space-based CTs wouldn't be extraterrestrials in the sense argued by ufological pundits, but they would be something engagingly "other," even if the difference separating them from their Earth-bound peers is as substantial as that distinguishing astronauts from humans of more mundane professions.

Still, the prospect of an underground origin beckons with the inexorable logic that colors our most treasured contemporary myths. Given our yawning ignorance of our own planet -- especially its oceans, which remain stubbornly mysterious -- it remains worthy of consideration. From the lusty politics of Mount Olympus to Shaver's pulp cosmology (complete with telepathic harassment and other ingredients later found in "serious" UFO abduction literature), even a cursory assessment of subterranean mythology indicates a nonhuman presence of surprisingly human dimensions.

This striking familiarity -- so unlikely in the case of genuine extraterrestrial contact -- meshes with modern occupant reports, which typically depict humanoid beings seen in the context of extraordinary technology. Villas-Boas had sex with a diminutive female who, while strangely mannered, can hardly be termed "alien." The alarming fact that intercourse was possible at all smacks of an encounter between two human beings -- an observation routinely dismissed by proponents of the Extraterrestrial Hypothesis, who seem inordinately enamored of Villas-Boas' own conviction that he had been used as breeding stock for a race of apparent space people.

The beings encountered by Betty and Barney Hill seem at least as human when addressed safely outside the confines of ETH dogma; even Betty's dialogue with the "leader" has the nuanced, bantering quality of two strangers attempting to come to grips with a mutual predicament. Indeed, the beings' puzzlement when confronted with dentures tends to argue in favor of the Indigenous Hypothesis. We might reasonably expect bona fide ET anthropologists to set aside the minor mystery of artificial teeth with clinical detachment; instead, Betty's ability to note her abductors' astonishment (feigned or genuine) detracts from the ETH by indicating a suspiciously human rapport.