There's no sign that says "Stop and look up." Nor do you see a sign on the door as you leave the Great Ape House at the National Zoo that warns you to close the door quickly so the world's smallest monkeys don't escape. The net result of all this subtlety: Many people walk right by one of my favorite exhibits at the zoo.

Two pygmy marmosets--a monogamous pair--live in the ficus tree in the Great Ape House, running free. You will be amazed when you see these Beanie-Baby-size monkeys--the full-grown pygmy marmoset is only six inches tall, the smallest monkey species in the world. Adults weigh just four ounces, as much as an apple. And newborns weigh just half an ounce and are only two inches long.

Native to the tropical forests of Brazil, Ecuador and Peru, in the wild these little guys live in tree holes. They know how to be inconspicuous. Finding them in the Great Ape House's central indoor garden takes a little time, but that's half the fun. At first, you will see only the trees. But after a while, you may see leaves in the top of the tree moving a little, followed by a chirping. Vigilance pays off in a sighting of the pair, scratching, jumping, running, eating or grooming one another. Hint: The pygmy marmosets are rarely seen at the bases of the trees or on the floor.

Why don't they escape? Hey, have you checked the District rental market recently?

If you can't get to the zoo right away, you can check out the photos of a pygmy marmoset online at www.si.edu /organiza/museums/zoo/ zooview/exhibits/smmam /tour/pygmarm.htm. But there's nothing to compare to the thrill of the search.--Ellen K. Schwab, Bethesda

The Roof of Maryland

Marked on most state road maps is the location of its highest point. Backbone Mountain--3,360 feet on the Maryland map--has intrigued me for years. Not very high (32nd out of the 50 states) and not easy to find either, unless you know about the Highpointers, an organization that wants to help you conquer the zeniths.

The Highpointers Club (highpointers.com) offers a book listing the highest points in all 50 states (Virginia's Mount Rogers is a comparatively robust 5,729 feet and ranks 19th out of 50), complete with directions, difficulty ratings and information on how to get patches, pins and plaques indicating how many high points you have reached. Armed with the proper data for Maryland, you will know to head south on Route 219, past Silver Lake, W.Va., and start looking on your left for "HP MD" spray-painted on the back of a road sign. Park at the gated dirt road and follow the road/trail (with the HP code painted on trees), crossing from West Virginia into Maryland. Twenty minutes later you're there, at the top of Maryland. You will find a mailbox containing certificates of your achievement.

So far, I have been to 10 high points. I'd better get climbing if I want to merit the handsome 50-state plaque in this lifetime.

--Ralph Bucca, Huntingtown, Md.

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