HMS Beagle

H. M. S. Beagle by R. O. Wagner, 1964
Source: Rose-Hulman College 
[Click picture for a larger view]

Here is some information from Ships of the World; An Historical Encyclopedia:

HMS Beagle
Bark (3m). L/B/D: 90.3 × 24.5 × 12.5 (27.5m × 7.5m × 3.8m). Tons: 235 bm. Hull: wood. Comp.: 75. Arm.: 5 × 6pdr, 2 × 9pdr. Des.: Sir Henry Peake. Built: Woolwich Dockyard; 1820.

HMS Beagle was originally launched as one of 115 Cherokee-class 10-gun brigs built by the Royal Navy between 1807 and 1830 and used in a variety of roles including surveying and antislaver patrols. By the time of her first voyage Beagle had been converted to a bark rig.

HMS Beagle was a three-masted bark (also spelled barque). Here is a simple diagram of a bark:
HMS Beagle rigged as a bark. The foremast and the main mast (the first two masts) have square sails. The mizzenmast has fore-and-aft sails.
Here is a model of the HMS Beagle:

Source: VICTORY ADVENTURE'S SOUTHERN OCEANS EXPEDITIONS

Here is a cross-section view of the HMS Beagle, attributed to Darwin's former shipmate, Philip King:
Source: The C. Warren Irvin, Jr., Collection of Charles Darwin and Darwiniana, University of South Carolina
[Click picture for a larger, although not very clear, view.]
This paragraph from Ships of the World: An Historical Encyclopedia describes the purpose of Beagle's second voyage, and tells about what Charles Darwin was doing on the voyage:

FitzRoy commanded Beagle on her subsequent circumnavigation during which she was to complete the survey of Tierra del Fuego, the Chilean coast, and a number of Pacific islands, and to carry out chronometric observations—she carried 22 chronometers. Among the 74 crew and passengers were three Fuegians who had been taken to England and were returning home. Also assigned to the ship was a twenty-one-year-old botany student, Charles Darwin, whose professor, J. S. Henslow, considered him not a "finished naturalist, but ... amply qualified for collecting, observing, and noting, anything new to be noted in Natural History." Beagle departed Devonport on December 27, 1831, and after stops in the Cape Verde Islands and Bahía arrived at Rio de Janeiro on April 4. After three months of hydrographic surveys of the Brazilian coast (Darwin was occupied in researching the rain forest), Beagle proceeded to Bahía Blanca, Argentina. It was there that Darwin first uncovered fossils that led him to question the relationship of living and extinct species.

And our last picture is of a watercolor painted in 1841 by Owen Stanley. It depicts HMS Beagle at Sydney harbor in New South Wales.

HMS Beagle at Sydney from an 1841 watercolour by Owen Stanley.
Source: The C. Warren Irvin, Jr., Collection of Charles Darwin and Darwiniana, University of South Carolina
[Click picture for a larger view]