At the extreme southern end of the park, and between the Fifth and Sixth avenue gates, is a small, irregular sheet of water, lying in a deep hollow. The surrounding hills have been improved with great taste, and the pond and its surroundings constitute one of the prettiest features of the park. The water consists mainly of the natural drainage of the ground. Along the Fifth avenue side of the park, near Sixty-fourth street, is a large and peculiar-looking building, not unlike the cadet barracks at West Point. This was formerly used by the State as an arsenal, but was purchased by the city, in 1856, for the sum of $275,000. It has been recently fitted up as a Museum of Natural History, and the first, second, and third floors contain the magnificent collection of the American Museum Association. This collection is in charge of Professor Bickmore, and includes 12,000 birds, 1000 mammals, 3000 reptiles and fishes, and a large number of insects and corals. It is the largest and most perfect collection in the country. The famous collection of the Archduke Maximilian forms the nucleus of this one. In the top floor of the Museum building is the Meteorological Observatory of the Central Park, under charge of Professor Daniel Draper. Here are ingenious and interesting instruments for measuring the velocity and direction of the wind, the fall of rain and snow, and for ascertaining the variation of the temperature, etc. The establishment is very complete, and a portion of it is open to visitors. The basement floors of the building are occupied by the offices of the Central Park authorities, and a police station. [Picture: THE MARBLE ARCH.] The open space surrounding the Museum edifice is taken up with buildings and cages containing the living animals, birds, and reptiles of the collection. They are admirably arranged, and the occupants are all fine specimens of their species. These accommodations are only temporary, as the Commissioners are now engaged in the construction of a Zoological Garden, on Eighth avenue, between Seventy-seventh and Eighty-first streets, immediately opposite the park, with which it will be connected by means of a tunnel under the Eighth avenue. Just north of the pond, and on the high ground above it, is a pretty gothic structure of stone, known as _The Dairy_. It is contiguous to the South Transverse Road, and supplies may be taken to it without using the park thoroughfares. Pure milk and refreshments, especially such as are suited to children, may be obtained at a moderate cost.