Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] bristles called sdce may be found. Determine if these rows are single or double. How many setse to a segment? Every segment except the first three and the last is provided with set«. Each seta has attached to it small muscles, which turn the seta so it may point in the opposite direction from which the worm is moving. If you watch your specimen carefully, you will see that locomotion is accomplished by the thrusting forward of the a
Elements of biology; a practical Elements of biology; a practical text-book correlating botany, zoology, and human physiology elementsofbiolog00hunt Year: [c1907] bristles called sdce may be found. Determine if these rows are single or double. How many setse to a segment? Every segment except the first three and the last is provided with set«. Each seta has attached to it small muscles, which turn the seta so it may point in the opposite direction from which the worm is moving. If you watch your specimen carefully, you will see that locomotion is accomplished by the thrusting forward of the anterior end; then a wave of muscular contraction passes dov\'n the body, thus shortening the body by drawing up the posterior end. The seta? at the anterior end serve as anchors which prevent the body from slipping backward as the posterior end is drawn up. Make a drawing of several segments to show the ar- rangement of setse. Notice that living earthworms tend to collect along the sides of a dish or in the corners. This seems to be due to an instinct which leads them to inhabit holes in the ground. Test a worm by placing half in and half out of a darkened box. Which does it seem to prefer, light or darkness? There are no eyes visible. A careful study of the worm with the microscope, however, has revealed the fact that scattered through the skin of the anterior segments are many little structures which not only distinguish between light and darkness, but also light of low and high intensity, as well as the direction from which it comes. A worm has no ears or special organs of feeling. We know that although a worm responds only to vibration's of low pitch, the sense of touch is well developed in all parts of the bod,y. Notice especially how the worm uses the whole anterior end to feel with. Jar the dish in which the worm rests hghtly, and note the reaction that takes place. Feeding Habits. — Worms may be kept in the laboratory for some time in a glass dish or box filled with
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