40. END GAME
WRITER: FRANK SPOTNITZ
DIR.: BOWMAN
All is explained (sorta) in this head-spinning conclusion to ''Colony.'' Scully is held captive by the nameless alien Bounty Hunter but is soon returned in a trade for Mulder's ''sister.'' Going full circle, we then follow Mulder to the Arctic in search of the alien Bounty Hunter, who ultimately escapes — for now. Historic moment: Skinner and X have it out. Critique: An exhausting, essential chapter, boasting the series' most visually stunning finale. A-

41. FEARFUL SYMMETRY
WRITER: STEVE DE JARNATT
DIR.: JAMES WHITMORE JR.
An Idaho zoo is the setting for this rather heavy-handed episode concerning man's destruction of the planet. Seems aliens are creating a kind of extraterrestrial Noah's Ark — abducting and impregnating mammals and harvesting their embryos in order to ensure the survival of the animals' species. Critique: Aside from a well-executed invisible-elephant rampage, this one's pretty much on automatic pilot. C

42. DØD KALM
WRITERS: GORDON/GANSA
STORY: GORDON
DIR.: BOWMAN
The crew of a Navy destroyer escort is decimated by a strange malady that super-accelerates the aging process. Mulder and Scully speculatively invoke meteors, free radicals, ''wrinkles in time,'' the Philadelphia Experiment, the Manhattan Project, and Roswell as they investigate and nearly perish. Creative casting: John Savage, as the freelance seaman who taxis them to the afflicted vessel. Critique: Despite clumsy makeup, isolation pays off again, and Mulder and Scully get to try a little tenderness. B

43. HUMBUG
WRITER: DARIN MORGAN
DIR.: MANNERS
Man's intolerance of abnormality is the subtext for this comic murder mystery set at a trailer park populated by gaffes, geeks, a Conundrum (wrapped in an Enigma), and other sideshow habitués. Creative casting: Everybody. Critique: Snarkily showcases the series' increasing confidence with dark humor, much of it directed at Mulder. The first of four peerless Darin Morgan scripts. A-

44. THE CALUSARI
WRITER: CHARNO
DIR.: MICHAEL VEJAR
After ''the howling heart of evil'' takes residence in a young boy, his old-country Romanian grandmother takes a stab at soul saving. Critique: An Exorcist/Omen rip-off, but a classy one. And that opener: You'll never look at kiddie railroad rides the same way again. B-

45. F. EMASCULATA
WRITERS: CARTER/GORDON
DIR.: BOWMAN
A deadly tropical parasite is introduced into a Virginia prison population. When two infected cons make a break, Mulder and Scully must beat the clock to prevent an outbreak. Critique: A good idea is tainted by plot holes as gaping and disturbing as the pustular boils you'll be treated to in this hour. C

46. SOFT LIGHT
WRITER: VINCE GILLIGAN
DIR.: JAMES CONTNER
A physicist's botched experiments into dark matter leave him with a lethal shadow that attracts the interest of Mulder, Scully — and a curiously malevolent X. Creative casting: Tony Shalhoub (Wings, Big Night) as the frazzled, hunted researcher. Critique: Gains points for the obscure subject matter; loses them for the strained conspiratorial element. B-

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