Sitcoms It started as a one-time joke on Friends (NBC, March 9, 9:30-10 p.m.): On-the- rebound Ross (David Schwimmer) adopted a monkey, Marcel, thinking the adorable animal would help him meet women. The pet reappeared during the show's recent two-parter (Marcel swallowed Scrabble tiles and Ross had to rush him to the hospital). Now Friends is building an entire episode around Marcel: He runs away from babysitter Rachel (Jennifer Aniston), and the gang organizes a search party. At this rate, Marcel may surpass Frasier's Eddie as TV's premier nonhuman character. We just hope the little ape doesn't expect an EW cover too. Dramas The breakneck pace of ER (NBC, March 9, 10-11 p.m.) may be the secret of the series' success but it could prove to be the show's downfall. The adrenaline- fueled storytelling style is intoxicating (and no doubt realistic), but the endless stream of cases can grow numbing; it's hard to care too much about any one patient when you know another will crash through the doors in two minutes. Perhaps wary of exhausting its gimmick, ER slows down this week, concentrating mostly on a single plot: Dr. Greene (Anthony Edwards) toils to save the life of a pregnant woman (Colleen Flynn) and her fetus. Wonder if the other cast members will demand episodes of their own now?

Serials Fox's youth-oriented opuses Melrose Place (March 13, 8-9 p.m.) and Beverly Hills, 90210 (March 15, 8-9 p.m.) have always seemed like soap operas crossed with MTV, and never more so than right now. Consider: MTV Sports dude Dan Cortese starts a guest gig on Melrose as Jess, the long-lost brother of Jake (Grant Show). The siblings reunite at their mom's funeral. (This is Cortese's third series stab in as many seasons-remember the Route 66 remake and Traps with George C. Scott?) On 90210, David (Brian Austin Green) and Clare (Kathleen Robertson) enlist their pals for a video-verite project similar to MTV's Real World. Hey, if Luke Perry leaves the show next season, maybe they can replace him with Puck.

New Shows The time-slot roulette wheel keeps on spinning, and Hope & Gloria (NBC, March 9, 8:30-9 p.m.) comes up a winner. The sitcom, costarring Bob's Cynthia Stevenson and The Second Half's Jessica Lundy as Pittsburgh pals, joins NBC's unbeatable Thursday lineup. On the other hand, the legal series The Great Defender (Fox, March 12, 7-8 p.m.) craps out, landing one of TV's least- desirable berths, opposite 60 Minutes. Starring justifiably unknown Michael Rispoli, this My Cousin Vinny wannabe will be lucky to survive for 60 minutes.

Proving that powerful TV nights don't last forever, Valerie Harper tries to shore up CBS' sagging Saturday slate-where she once ruled as Rhoda on The Mary Tyler Moore Show-with the secretarial sitcom The Office (CBS, March 11, 9-9:30 p.m.). Harper has a tough job-The Boys Are Back, featuring another veteran of CBS' Saturday-night glory years, Suzanne Pleshette (The Bob Newhart Show), bombed in the same slot.