PLAN AHEAD: Visitors to the Galapagos National Park are limited to 12,000 a year as part of Ecuador's efforts to minimize ecological damage to the islands. Park tax is $30 (U.S.) as you enter. Most travel agencies can book you on the larger vessels. Specialized agencies also organize groups with a university biology professor or other expert for the smaller yachts.

GETTING THERE: Regular flights leave Miami, New York or Los Angeles via Ecuatoriana and Eastern Airlines to mainland Ecuador. Tame Airline flies you to a landing strip on the small island of Baltra, where a bus takes you to the harbor to board your boat.

GETTING AROUND: Expeditions may be made on a variety of boats, including the Santa Cruz and the Buccaneer (each carrying 90 passengers); the Neptune, carrying 80; the Iguana, 68; the Delfin, 38; and the Isabela, 16. Cruises are four, five, eight or 15 days. You should be a good walker and moderately agile.

WHAT TO TAKE: For hikes around the islands and for nights on ship, casual clothing for a temperate climate is needed. No ties or "dressy" clothes are worn on board. Take plenty of film, as well as sun-screen lotion, a hat and a long-sleeved cotton shirt for protection from the strong sun, and running or walking shoes.

READING: For a clear picture of the importance of the Galapagos in Darwin's life and theory, read "The Essential Darwin" (Little, Brown) or "Evolution" by Ruth Moore and the editors of Life (Time-Life Books).