. Essentials of biology presented in problems. Biology. THE WORMS 215. Diagrammatic cross section of the body of a cc&- lenterate, and that of a worm. get this food. The earth is mixed with fluids poured out from glands in the food tube, and is passed out of the body and deposited on the surface of the ground, in the form of little piles of moist earth. These are familiar sights on all lawns; they are called worm casts. Charles Darwin cal- culated that fifty-three thousand worms may be found in an acre of ground, that ten tons of soil might pass through their bodies in a single year and th
. Essentials of biology presented in problems. Biology. THE WORMS 215. Diagrammatic cross section of the body of a cc&- lenterate, and that of a worm. get this food. The earth is mixed with fluids poured out from glands in the food tube, and is passed out of the body and deposited on the surface of the ground, in the form of little piles of moist earth. These are familiar sights on all lawns; they are called worm casts. Charles Darwin cal- culated that fifty-three thousand worms may be found in an acre of ground, that ten tons of soil might pass through their bodies in a single year and thus be brought to the surface, and that they plow more soil than all the farmers put together. Earthworms, in spite of their fondness for some garden vegetables and young roots, do much good by breaking up the soU, thus allowing water and oxygen to penetrate to the roots of plants. Comparison between Hydra and Worm. — The digesti\e tract of the worm is an almost straight tube inside of another tube. The latter is divided by partitions which mark the boundary of each segment. The outer ca^•ity is known as the body cavity. In the hydra no body cavity exists, there being only a digestive cavity. In the animals higher than the coelenterates the digestive tract and body cavity are distinct. Food is digested within the food tube, is passed through the walls of this tube into the body eavit>', and is in part carried by the blood to various parts of the body. No gills or lungs are present, the thin skin acting as an organ of respiration. But the worm is unable to take in oxygen unless the membranelike skin is kept moist. Development. — Notice in some worms the swollen area called the girdle (about one third the distance from the anterior end). This area periodically forms a little sar' in which the eggs of the worm are laid. As it passes toward the anterior end of the worm, it receives from the body openings the sperms and a nutritive fluid in whifh the eggs Ii\e. The fertilize
Size: 2309px × 1082px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
