Carrie Page, age 9, of Pocatello, Ida., for her question:
IS THE SPONGE REALLY AN ANIMAL?
For a long time most people believed that sponges were plants. Then in 1825 an English scientist named Robert Grant proved that sponges were animals, not plants. He watched sponges in water through a microscope and saw streams of water enter certain openings and come out through others.
Grant decided that sponges were animals, although he didn't know just what kind of animals they were. Certain cells, lining the water channels leading from the outside pores of the sponge, looked like one celled animals called protozoa, and for this reason Grant thought that perhaps the sponges were great colonies of these tiny animals.
Sponges, however, are not one celled animals.
The sponges that you use in your home are the dried out skeletons of marine animals that belong to the Porifera, a phylum or major group in the animal kingdom. Sponges have an ability to absorb water without losing their toughness.
Even though the sponge is one of the lowest forms of animal life, its structure is rather complicated. The outer layer of living tissue that surrounds it is made up of flat, scale like cells. The cells lining the canals are unlike hose found in any other animal. They are column shaped and each ends in a long lasher.
At the bases of the canals are collar like outgrowths resembling those of protozoa called collared monads. The ashers of these collar cells beat the water in and out of the ponges. In this way it receives oxygen and millions of tiny organi ms for food.
The outgoing currents contain waste product , which give fresh sponges their bad odor. For this reason, spong s are seldom eaten by other animals.
A sponge's middle layer is made up of tissue that is a clear, jellylike mass in which are located wandering cells. They digest the food and take part in breathing and in giving off the waste materials.
Sponges multiply in two ways: from buds which break off from the parent or from its own fertilized eggs. Each sponge is both male and female.
After fertilization, the eggs develop within the body of the sponge until they are large enough to escape. Then the eggs become free swimming forms that move about by means o lashers, or cilia.
Soon the eggs attach themselves to the ocean bottom or to a rock. Some do this by means of cells that give out a sticky substance while others attach themselves by root tufts, or living projections from the skeleton.
Only one family of sponges is found in fresh water. All of the others are found in salt water.
Sponges come in all shapes and in all colors.
Commercial sponges are called horny sponges They are found most often in the shallow waters of the Bahama Islands and the Mediterranean Sea. The coast of Florida is also one of the biggest sponge growing centers in the world.