Twenty variations, 1971-90, assembled by Omni editor Datlow and running the entire gamut from sf through fantasy to horror and outright titillation. Aliens don't really take center stage here. Instead, we're dealing with relationships between the human sexes and how one sex often views the other as alien. The best of an otherwise disturbingly manipulative bunch: Connie Willis' devastating feminist piece, ""All My Darling Daughters,"" describing a future-Victorian society that brutally exploits women before they're even born; and James Tiptree, Jr.'s stunning psychological study, ""And I Awoke and Found Me Here on the Cold Hill's Side,"" cast as humans lusting for uncomprehending and indifferent aliens. Elsewhere, the artifice is greater, the intent murkier, the ideas thinner and less lofty: weird alien sexual habits, horrid or incomprehensible alien lusts, humorous or angry aliens; human-animal pairings; comic-book characters; poetry; sex and lies; daft post-nuclear reproduction; vampires, incubi, and lamias. With the exceptions noted above: nasty notions, cheap thrills, superficial shocks, and sometimes blatant sexploitation. Given the enormous potential; a severe disappointment.