The legendary book referred to in the crossword solution is 'ATLAS', a book written by the Greek philosopher and scientist, Aristotle. It is considered one of the most influential works of all time, as it was the first comprehensive treatise on zoology. The book contains detailed descriptions of animals, their anatomy, behavior, and habitats. It is also credited with being the first to classify animals into species and genera. Its influence can still be seen today in modern scientific classification systems.