Two long sets of scientific notes were made by Charles Darwin during the voyage of the Beagle. Those transcribed here are concerned with natural history, and although in 1839 he drew on them quite extensively in writing his famous " Journal of Researches ", neither they nor his geology notes have previously been published. He was a superb observer, and recorded vividly and accurately his first impressions of the appearance and behaviour of the wide range of animals, from ants to ostriches, encountered during his travels. Often he performed little experiments on the creatures that he captured, and he was never happy until he had exhaustively explored the why and wherefore of every one of his observations. During the long periods on board ship, he carried out a thorough analysis of hitherto unrecognised features of the internal anatomy of a variety of marine invertebrates, and made elegant pencil drawings of them under his dissecting microscope. The volume also includes his lists of 1 500 specimens preserved in Spirits of Wine, and some 3 500 not in Spirits, with impeccably accurate cross references to the main notes. Although his notes were made strictly for his own use, and were often highly technical, they were well written throughout, and contain many highly readable passages. Only towards the very end of the voyage were his first doubts about the immutability of species consciously pressed, but here are to be found the first seeds of his theory of evolution, and of the important new fields of behavioural and ecological study of which he was one of the principal founders.