Origin of Species
The origin of species, first edition, by charles darwin
http://www.talkorigins.org/faqs/origin.html
The Variation of Animals and Plants Under Domestication
The Variation of Animals and Plants Under Domestication
http://www.esp.org/books/darwin/variation/facsimile/title3.html
Voyage of the Beagle
Voyage of the Beagle
http://www.literature.org/authors/darwin-charles/the-voyage-of-the-beagle/