National Geographic : 1949 Jul
some types of clams may disappear into the sand before you can stoop and pick them up. Most clams are diggers. All mollusks bear a remarkable organ called a mantle. This may be a mere pad or fold, or it may cover the animal more completely. You may think of it as a bit of animated skin. This mantle secretes the shell. As a result of its wonderful property we have shell collections and the colorful beauty of the illustrations in this NATIONAL GEOGRAPHIC. It may seem unique that the skin of a squashy animal can create such wonderful porcelain, but the phenomenon is no more remarkable than other accomplishments of Nature. The rocky mountain goat has su perbly curved horns; we have teeth. Shell material is secreted as a limestone substance, shaped by the instincts of the animal into the forms characteristic of its kind, and painted with pigments synthesized by this lowly creature from chemicals in its environment. Momentarily this material is soft, but it quickly hardens, whether under the water or in the air, to become one of the most time-resistant materials in our world, as witness the fossil shells that predate man's presence on earth. In museums the walls of some of the largest display halls are lined and their floors crowded with cabinets loaded with multitudes of these animal porcelains. The American Museum of Natural History in New York City has an enormous central hall with panoramas of shells, and countless more in storage. The National Museum in Washington, D. C., has tiers of cabinets with five million shells classi fied and in order. Yet, even after the museums have taken their great collections, and the private collec tors have accumulated their treasures, whose total staggers the imagination, the supply is practically inexhaustible. If we go to the beaches of Maine, Florida, or California, or wherever else tides deliver shells, we can pick up equally beautiful and startling specimens newly arrived after the last storm (pages 34 and 58). The Shell Is a Work of Art The scene is a curving beach set between a sweep of Uniola, "sea oats," shimmering with high lights, and the smooth aqua marine of the sea. Is it mere fantasy to say that this beach line, with its band of dune grass impinging on one edge and the curves of white foam from broken waves following its other edge, forms the same curve that you find in the cockle, coquina, clam, nautilus, and abalone? Look at a wave as it advances into shallow water. It is pushed up, growing higher and steeper from the opposition of a spent wave © Merl La Voy Through Shell Eyes the War Canoe "Sees" New Georgia, Solomon Islands, natives decorate the prows of their seagoing craft with handsome speci mens of Egg Shells. Ovula ovum, to help them find their way. Related to the cowries, which are used as money, these are cherished as potent charms. They are gastropods, and, when alive, move by means of a muscular foot protruding from the shell.