Vintage wall chart of the anatomy of the "Unio pictorum," (painters mussel). Lithograph on two sheets of paper, mounted on canvas. Author and illustrator was Prof. Dr. Paul Pfurtscheller. Pfurtscheller (1855-1927) produced a series of 39 "Zoologische Wandtafeln" (zoological wall plates) to be used for higher educational purposes. Although he was a modest high school teacher by training he gained recognition by the scientific community worldwide for this outstanding work. The mussel is "Plate 2" in the series. The Pfurtscheller wall charts were first published in Vienna, Austria, in 1902, by 'A. Pichler's Witwe & Sohn'. Later editions were also published by Dutch company 'Martinus Nijhoff' until 1953. This item was pubished by 'Martinus Nijhoff' presumably in the late 1920s Still one of the lithographed editions, whereas later editions used offset-printing. Lithography of course is an enormously demanding technique - especially at this large scale - which required up to 20 manual print-cycles for a single piece, since each color had to be applied separately. These colors of course were not supposed to overlap in the end. This process is what gives lithographs their extraordinary depth and unusual longevity to their colors.