. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. XVII. WORMS The Earthworm. — The earthworm belongs to a group of animals called the annelids. They are so called because the body is made up of a large number of rings or segments. (Lat. annulus, a ring.) Study a living worm in order to answer the following questions. Careful study of several worms will show that the number of segments varies, the larger worms having more segments. Do the segments vary greatly in width? In shape? Notice the color of the worm; is it like that of the ground i
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. XVII. WORMS The Earthworm. — The earthworm belongs to a group of animals called the annelids. They are so called because the body is made up of a large number of rings or segments. (Lat. annulus, a ring.) Study a living worm in order to answer the following questions. Careful study of several worms will show that the number of segments varies, the larger worms having more segments. Do the segments vary greatly in width? In shape? Notice the color of the worm; is it like that of the ground in which it hves? Do the dorsal and ventral surfaces differ in color? Can you ac-. The earthworm. Note the swollen area, the clitellum. Photographed Viy Overton. count for this? The earthworm is an example of a bilaterally symmetrical animal, that is, one in which the right side is a counterpart of the left side. Compare with the starfish or sea anemone. Are the latter animals also bilaterally as well as radially symmetrical ? The two ends of the worm differ somewhat in appearance, the anterior end being pointed and the posterior rather flattened. Tests made with a pencil or other pointed object will show which end is more sensitive to touch. Which end usually goes first in crawling? Measure an earthworm when it is extended and compare with the same worm contracted. Note the difference in length. This is accounted for when we understand the method of locomotion. Under the skin are two sets of muscles, an outer set which passes in a circular direction around the body, and an inner set which runs the length of the body. The body is lengthened by the contraction of the circular muscles. How might the body of an earthworm be shortened ? Put your finger over the under surface of the worm. Notice the rough- ness. Examine the surface with a hand lens. Four rows of very minute ^ See Hunter and Valentine, Manual, page 131. 208. Please note that these images are extracted from scanned p
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