Book Lung - Book Gills

Book Gills

Scientists think book lungs evolved from book gills. Although they have a similar book-like structure, they are found in different locations. Book gills are found externally while book lungs are found internally. Book gills are still found in horseshoe crabs which have five pairs of them, the flap in front of them being the genital operculum which lacks gills. Book gills are flap-like appendages that effect gas exchange within water and seem to have their origin as modified legs. On the inside of each appendage, there are attached over 100 thin leaf-like membranes called lamellae which appear as pages in a book, and are the areas of the gill where gas exchange takes place. These appendages move with rhythmic movements to drive blood in and out of the lamellae and to circulate water over them. Respiration being their main purpose, they can also be used for swimming in young individuals. If they are kept moist, the horseshoe crab can live on land for many hours.

Read more about this topic:  Book Lung

Famous quotes containing the words book and/or gills:

    The demonstrations are always early in the morning, at six o’clock. It’s wonderful, because I’m not doing anything at six anyway, so why not demonstrate?... When you’ve written to your president, to your congressman, to your senator and nothing, nothing has come of it, you take to the streets.
    Erica Bouza, U.S. jewelry designer and social activist. As quoted in The Great Divide, book 2, section 7, by Studs Terkel (1988)

    his gills were breathing in
    the terrible oxygen
    Elizabeth Bishop (1911–1979)