By John Beddoes. I'm sure I read this book in-game, and other books reference it, but I can't find it anywhere. Well, not in either obvious library. I'm using WIP 6.0, so maybe it was shuffled elsewhere. Does anyone know where it can be found? WIP is, by the way, an awesome expansion. 5 stars.
The Arcanum Wikia also has information regarding the races, derived from this particular work. Just in case you'd be too lazy to search the manual, or something. I don't know.